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United States Patent |
5,219,984
|
Shiraki
,   et al.
|
June 15, 1993
|
Process for treatment of polyethylene terephthalate, polyethylene
terephthalate for molding purposes and process for preparation thereof
Abstract
According to the present invention, a process which comprises bringing
polyethylene terephthalate having an intrinsic viscosity of at least 0.50
dl/g and a density of 1.38 g/cm.sup.3 or more into contact with water is
provided.
In the water-treated polyethylene terephthalate obtained in the present
invention, amounts of oligomers and acetaldehyde formed at the time of
molding said polyethylene terephthalate into molded articles are small,
and the contamination of the mold therewith is difficult to occur and
further the contents of said molded articles does not change in flavor and
fragrance.
Inventors:
|
Shiraki; Shigemi (Kuga, JP);
Tanaka; Yasuhiro (Kuga, JP);
Sakai; Masayuki (Kuga, JP)
|
Assignee:
|
Mitsui Petrochemical Industries, Ltd. (Tokyo, JP)
|
Appl. No.:
|
835077 |
Filed:
|
February 18, 1992 |
Foreign Application Priority Data
| Mar 31, 1989[JP] | 1-83353 |
| Mar 31, 1989[JP] | 1-83354 |
| Mar 31, 1989[JP] | 1-83355 |
| Mar 31, 1989[JP] | 1-83356 |
| Apr 14, 1989[JP] | 1-94596 |
| Apr 14, 1989[JP] | 1-94597 |
| May 31, 1989[JP] | 1-138179 |
| May 31, 1989[JP] | 1-138180 |
Intern'l Class: |
C08F 006/00 |
Field of Search: |
528/308.2,308.4,308.5,499,502,503
|
References Cited
U.S. Patent Documents
4154920 | May., 1979 | Jabarin | 528/272.
|
4289874 | Sep., 1981 | Bockrath | 528/487.
|
4591629 | May., 1986 | El-Ghatta et al. | 528/308.
|
4609721 | Sep., 1986 | Kirshenbaum et al. | 528/285.
|
Foreign Patent Documents |
0300981 | Jan., 1989 | EP.
| |
3503330 | Aug., 1986 | DE.
| |
Other References
Patent Abstracts of Japan, vol. 9, No. 88, (C-276)(1311), Dec. 12, 1984.
Patent Abstracts of Japan, vol. 8, No. 110, (C-224), May 23, 1984.
Patent Abstracts of Japan, vol. 4, No. 42, (C-5)(524), Apr. 3, 1980.
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Sherman and Shalloway
Parent Case Text
This application is a continuation of application Ser. No. 07/500,004,
filed Mar. 27, 1990, now abandoned.
Claims
What is claimed is:
1. In a process for treatment of polyethylene terephthalate, the
improvement which comprises bringing polyethylene terephthalate obtained
through a solid phase polycondensation step having an intrinsic viscosity
of at least 0.05 dl/g, an oligomer content of less than 0.50% by weight
and a density of more than 1.38 g/cm.sup.3 into contact with water.
2. The process as claimed in claim 1 wherein the contact of the
polyethylene terephthalate with water is carried out by immersing said
polyethylene terephthalate for a period of from 1 minute to 100 hours or
more in water kept at a temperature of from 1.degree. C. to 150.degree. C.
3. The process as claimed in claim 1 wherein the contact of the
polyethylene terephthalate with water is carried out by bringing said
polyethylene terephthalate into contact with water vapor or water
vapor-containing gas kept at a temperature of from 1.degree. C. to
150.degree. C. for a period of from 1 minute to 1 year.
4. In a process for preparing polyethylene terephthalate, the improvement
which comprises involving
an esterification step of esterifying terephthalic acid or its
ester-forming derivative with ethylene glycol or its ester-forming
derivative,
a liquid phase polycondensation step of melting by heating the
esterification product obtained in the above-mentioned esterification step
in a polycondensation catalyst,
a solid phase polycondensation step of heating in an inert atmosphere the
polycondensation reaction product obtained in the above-mentioned liquid
phase polycondensation step at a temperature of below the melting point of
said polycondensation reaction product, and
a water treatment step of bringing the polycondensation reaction product
obtained in the above-mentioned solid phase polycondensation step into
contact with water.
5. The process as claimed in claim 4 wherein the water treatment is carried
out by immersing the polyethylene terephthalate for a period of from 1
minute to 100 hours or more in water kept at a temperature of from
1.degree. C. to 150.degree. C.
6. The process as claimed in claim 4 wherein the water treatment is carried
out by bringing the polyethylene terephthalate into contact with water
vapor or water vapor-containing gas kept at a temperature of from
1.degree. C. to 150.degree. C. for a period of from 1 minute to 1 year.
Description
FIELD OF THE INVENTION
This invention relates to processes for treatment of polyethylene
terephthalate used in molding therefrom bottles, sheets, films or the like
molded articles, and more particularly to the processes for the treatment
of polyethylene terephthalate to obtain such polyethylene terephthalate as
may be useful for molding purposes, by the use of which the contamination
of the mold therewith is difficult to occur.
In another aspect, the invention relates to polyethylene terephthalate used
in molding therefrom bottles, sheets, films or the like molded articles,
the more particularly to polyethylene terephthalate, by the use of which
the contamination of the mold therewith is difficult to occur, and also to
processes for preparing the same.
Further, the invention relates to polyethylene terephthalate used in
molding therefrom bottles, sheets, films, or the like molded articles, by
the use of which acetaldehyde is difficult to form.
BACKGROUND OF THE INVENTION
Various resins have heretofore been used as materials for containers of
seasonings, oils, beverages, cosmetics and detergents according to the
kind of contents with which the containers are filled and to the purpose
which the containers are used.
Because of its excellent mechanical strength, heat resistance, transparency
and gas barrier properties, polyethylene terephthalate is a useful
material for forming containers to be filled particularly beverages such
as fruit juices, cooling drinks and carbonated drinks.
Such polyethylene terephthalate as referred to above may, for example be
prepared by esterifying terephthalic acid or its ester-forming derivative
with ethylene glycol or its ester forming derivative in the presence of an
esterification catalyst, and polymerizing the esterified product in liquid
phase in the presence of a polymerization catalyst, followed by solid
phase polycondensation. In general, polyethylene terephthalate thus
prepared is fed to a molding machine such as an injection molding machine
and molded into a blow-molding preform, and thereafter the preform is
inserted into a mold of a predetermined shape and stretch blow-molded into
a blown container, and if necessary followed by heat setting.
However, known polyethylene terephthalate obtained by the conventional
procedure as mentioned above contains oligomers such as cyclic trimer,
with the result that the oligomers attach to the inner surface of
blow-molding mold and contaminate the mold therewith or attach to the vent
portion of mold of the injection machine as mentioned above and
contaminate the mold therewith.
Such contamination of the mold as mentioned above forms the determining
cause for surface roughness or chalking of the resulting bottle. If the
bottle obtained is chalked, either partly or wholly, it has to be
discarded. Owing to such circumstances, in molding bottles out of the
known polyethylene terephthalate, there was such a serious problem that
contaminants attached to the mold must be removed therefrom at frequent
intervals and hence productivity of the bottle markedly decreases.
In light of such existing circumstances as mentioned above, the present
inventors extensively studied with the view of obtaining polyethylene
terephthalate, by the use of which the contamination of the mold therewith
is difficult to occur, and have found that the contamination of the mold
at the time of molding polyethylene terephthalate is mainly attributable
to an increased amount of oligomers such as cyclic trimers contained in
the polyethylene terephthalate, said oligomers being formed in large
amounts at the time when said polyethylene terephthalate is molded.
The present inventors further studied on the basis of the above-mentioned
finding, and eventually have found that the increase in amount of the
oligomers in polyethylene terephthalate at the time of molding may be
inhibited by bringing the polyethylene terephthalate into contact with
water, and they have accomplished the present invention.
Furthermore, the present inventors have found that there is an intimate
relationship between a rate of polycondensation at the time when
polyethylene terephthalate used for molding is subjected under specific
conditions to solid phase polycondensation treatment and an increasing
amount of oligomers formed at the time of molding, and that if the rate of
polycondensation treatment of the polyethylene terephthalate is less than
a specific value, the contamination of the mold at the time of molding is
difficult to occur, on the basis of which finding the present invention
has been accomplished.
In this connection, Japanese Patent L-O-P Publn. No. 25815/1984 discloses a
process which comprises treating particulate polyethylene terephthalate,
prior to solid phase polycondensation thereof, with water vapor heated to
above 110.degree. C. so as to crystallize the polyethylene terephthalate.
Further, Japanese Patent L-O-P Publn. No. 219328/1984 discloses a process
for preparing polyesters of high polymerization degree, which comprises a
step of moisture conditioning a polyester having ethylene terephthalate
units as the main repeating units and having an intrinsic viscosity of at
least 0.4 dl/g and a density of less than 1.35 g/cm.sup.3 so as to have
the moisture content of at least 0.2% by weight, a step of
precrystallizing the polyester thus treated, and a step of solid phase
polymerizing the precrystallized polyester at a temperature of above
180.degree. C. and below 240.degree. C. in an inert gas atmosphere or
under reduced pressure.
OBJECT OF THE INVENTION
The present invention is intended to solve such problems associated with
the prior art as mentioned above, and an object of the invention is to
provide processes for treatment of polyethylene terephthalate to obtain
such polyethylene terephthalate as may be useful for molding purposes, by
the use of which an increasing amount of oligomers such as cyclic trimer
formed at the time of molding is small and the contamination of mold
therewith is difficult to occur.
A further object of the invention is to provide polyethylene terephthalate
for molding purposes, by the use of which the amount of oligomers such as
cyclic trimer formed at the time of molding is small and the contamination
of mold therewith is difficult to occur, and processes for preparing the
same.
SUMMARY OF THE INVENTION
The process for treatment of polyethylene terephthalate of the present
invention is characterized by bringing polyethylene terephthalate into
contact with water, said polyethylene terephthalate having an intrinsic
viscosity of at least 0.50 dl/g and a density of more than 1.38
g/cm.sup.3.
Such contact of polyethylene terephthalate with water may be effected, for
example, by bringing the polyethylene terephthalate into contact with
water at a temperature of from 1.degree. C. to 150.degree. C. for a period
of 1 minute to 100 hours.
Furthermore, the contact of polyethylene terephthalate with water may be
effected by bringing the polyethylene terephthalate into contact with
water vapor or a water vapor containing gas at a temperature of from
1.degree. to 150.degree. C. for a period of 1 minute to 1 year.
The process for preparing polyethylene terephthalate of the invention, for
example, is characterized by comprising an esterification step which
comprises esterifying terephthalic acid or its ester-forming derivative
with ethylene glycol or its ester-forming derivative, a liquid phase
polycondensation step which comprises heating and melting the
esterification product obtained in the above-mentioned esterification step
in the presence of a polycondensation catalyst, a solid phase
polycondensation step which comprises heating the polycondensation
reaction product obtained in the above-mentioned liquid phase
polycondensation step to a temperature below its melting point in an inert
atmosphere, and a water treatment step which comprises bringing the
polycondensation reaction product obtained in the above-mentioned solid
phase polycondensation step into contact with water.
The first polyethylene terephthalate of the invention is characterized in
that the polyethylene terephthalate has an intrinsic viscosity of at least
0.50 dl/g and a density of more than 1.38 g/cm.sup.3, and that the rate of
polycondensation employed at the time when said polyethylene terephthalate
is subjected to the solid phase polycondensation treatment at a
temperature of 215.degree. C. in an inert atmosphere is less than 0.0055
dl/g.hr.
The second polyethylene terephthalate of the invention is characterized in
that the polyethylene terephthalate has an intrinsic viscosity of at least
0.50 dl/g, a density of more than 1.38 g/cm.sup.3 and the oligomer (the
cyclic trimer) content of less than 0.50% by weight, and that the
increased amount y (wt %) of the oligomer contained in the polyethylene
terephthalate after said polyethylene terephthalate has been molded into a
stepped square plate by melting at 290.degree. C. is defined as
y.ltoreq.-0.20x+0.2 wherein y is an increased amount (wt %) of the
oligomer after molding, and x is the oligomer concentration (wt %) prior
to molding.
The third polyethylene terephthalate of the invention is characterized in
that the polyethylene terephthalate has an intrinsic viscosity of at least
0.50 dl/g, a density of more than 1.38 g/cm.sup.3, and that when a rate of
polycondensation in the solid phase polycondensation treatment of the
polyethylene terephthalate conducted by heating at a temperature of
215.degree. C. in an inert atmosphere is taken as V.sub.0, and when a rate
of polycondensation in the solid phase polycondensation treatment
conducted after bringing the polyethylene terephthalate into contact with
hot water kept at 95.degree. C. for 8 hours is taken as V.sub.1, the
V.sub.1 /V.sub.0 ratio is defined as 0.2-1.0.
The fourth polyethylene terephthalate of the invention is characterized in
that the polyethylene terephthalate has an intrinsic viscosity of at least
0.50 dl/g, a density of more than 1.38 g/cm.sup.3 and the oligomer content
of less than 0.5% by weight, and that when the oligomer content in a
stepped square plate obtained by injection molding the polyethylene
terephthalate, as it is, at a molding temperature of 290.degree. C. is
taken as W.sub.0 (wt %), and when the oligomer content in a stepped square
plate obtained by drying the polyethylene terephthalate after being
immersed in hot water kept at 95.degree. C. for 8 hours and injection
molding the thus treated polyethylene terephthalate into the molded
article is taken as W.sub.1 (wt %), the remainder left by subtracting
W.sub.1 from W.sub.0 is 0-0.12% by weight.
The fifth polyethylene terephthalate of the invention is characterized in
that the polyethylene terephthalate has an intrinsic viscosity of at least
0.50 dl/g, a density of more than 1.38 g/cm.sup.3 and that when the
acetaldehyde content of an article obtained by injection molding the
polyethylene terephthalate at a molding temperature of 290.degree. C. is
taken as W.sub.0 (wt %) and, on one hand, when the acetaldehyde content of
an article obtained by injection molding likewise the polyethylene
terephthalate which has been immersed in hot water kept at 95.degree. C.
for 8 hours and dried is taken as W.sub.1 (wt %), W.sub.0 -W.sub.1 is 0-5
ppm by weight.
In the polyethylene terephthalates of the invention as illustrated above,
amounts of oligomers and acetaldehyde formed at the time of molding said
polyethylene terephthalates into molded articles are small, and
accordingly the contamination of the mold therewith is difficult to occur,
and further the contents of said molded article do not change in flavor or
fragrance, since the acetaldehyde is difficult to form.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a slant view of a stepped square plate molded article.
FIG. 2 is a graph showing the relationship between the amount of oligomer
contained in particulate polyethylene terephthalate prior to molding
thereof and the oligomer concentration in a stepped square plate molded
therefrom.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the process for treatment of polyethylene terephthalate, the
process for preparing of polyethylene terephthalate, and the polyethylene
terephthalates of the present invention are illustrated in detail.
The polyethylene terephthalate used in the process for treatment of
polyethylene terephthalate of the invention preferably has specific
intrinsic viscosity and density.
Such polyethylene terephthalate as used in the invention may be prepared
from starting materials comprising of terephthalic acid or its
ester-forming derivative and ethylene glycol or its ester-forming
derivative, and this polyethylene terephthalate may also be
copolycondensed with less than 20 mol % of other dicarboxylic acids and/or
other glycols.
Dicarboxylic acids, other than terephthalic acid, which may be used in the
copolycondensation mentioned above include, for example, aromatic
dicarboxylic acids such as phthalic acid, isophthalic acid,
naphthalenedicarboxylic acid, diphenyldicarboxylic acid and
diphenoxyethanedicarboxylic acid, aliphatic dicarboxylic acids such as
adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid, and
alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.
Glycols, other than ethylene glycol, which may be used in the
above-mentioned copolycondensation include, for example, aliphatic glycols
such as trimethylene glycol; propylene glycol, tetramethylene glycol,
neopentyl glycol, hexamethylene glycol and dodecamethylene glycol;
alicyclic glycols such as cyclohexane dimethanol; bisphenols; and aromatic
diols such as hydroquinone and 2,2-bis(4-
.beta.-hydroxyethoxyphenyl)propane.
The starting materials containing terephthalic acid or its ester-forming
derivative and ethylene glycol or its ester-forming derivative as
mentioned above are esterified in the presence of an esterification
catalyst, followed by liquid phase polycondensation in the presence of a
polycondensation catalyst and then followed by solid phase
polycondensation.
An example of preferred processes for the preparation of polyethylene
terephthalate to be subjected to the water treatment in the present
invention is illustrated below, but it should be construed that the
invention is in no way limited to the process exemplified herein. In the
exemplified process, first of all a slurry containing terephthalic acid or
its ester-forming derivative and ethylene glycol or its ester-forming
derivative is prepared.
The slurry as prepared above contains 1.02-1.4 moles, preferably 1.03-1.3
moles, based on 1 mole of terephthalic acid or its ester-forming
derivative, of ethylene glycol or its ester-forming derivative. This
slurry is fed continuously to an esterification reaction process.
The esterification reaction is carried out with an apparatus having at
least two esterification reactors connected in series under the conditions
where ethylene glycol is refluxed, while removing out of the system the
water formed by the reaction by means of a rectification column. The
reaction conditions under which the esterification reaction is carried out
are such that the temperature of the first stage esterification reaction
is usually 240.degree.-270.degree. C., preferably 245.degree.-265.degree.
C., the pressure is usually 0.2-3 kg/cm.sup.2 G, preferably 0.5-2
kg/cm.sup.2 G, the temperature of the final stage esterification reaction
is usually 250.degree.-280.degree. C., preferably 255.degree.-275.degree.
C., and the pressure is usually 0-1.5 kg/cm.sup.2 G, preferably 0-1.3
kg/cm.sup.2 G.
Accordingly, when the esterification reaction is carried out in two stages,
the esterification reaction conditions for the first and second
esterification reactions are as defined above, and when said reaction is
carried out in at least three stages, the esterification reaction
conditions for the esterification reaction from the second stage to the
stage prior to the final stage are intermediate between those of the first
and final stage.
For instance, when the esterification reaction is carried out in three
stages, the reaction temperature of the second stage esterification
reaction is usually 245.degree.-275.degree. C., preferably
250.degree.-270.degree. C., and the pressure is usually 0-2 kg/cm.sup.2 G,
preferably 0.2-1.5 kg/cm.sup.2 G. Although the rate of reaction to be
attained in each stage of these esterification reactions, it is desirable
that the increase and degree of the rate of reaction in each stage are
smoothly distributed and the rate of reaction attained in the
esterification reaction product of the final stage is usually at least
90%, preferably at least 93%.
By virtue of these esterification processes mentioned above, a lower
condensate is obtained, and this lower condensate has usually a number
average molecular weight of 500-5000.
The esterification reaction as illustrated above ma be carried out without
addition of additives other than terephthalic acid and ethylene glycol,
and may also be carried out in the presence of polycondensation catalysts
as will be mentioned later. Furthermore, it is preferable that the
above-mentioned esterification reaction is carried out with a further
addition thereto of small amounts of tertiary amines such as
triethylamine, tri-n-butylamine and benzyldimethylamine; quaternary
ammonium hydroxides such as tetraethylammonium hydroxide,
tetra-n-butylammonium hydroxide and trimethylbenzylammonium hydroxide; and
basic compounds such as lithium carbonate, sodium carbonate, potassium
carbonate and sodium acetate, whereupon the proportion in the main chain
of polyethylene terephthalate of the dioxyethylene terephthalate units can
be maintained at a relatively low level.
Subsequently, the lower condensate thus obtained is fed to a liquid phase
polycondensation process wherein this lower condensate is polycondensed
under reduced pressure in the presence of a polycondensation catalyst
while heating at a temperature of above a melting point of the resulting
polyethylene terephthalate and removing out of the system the glycol
formed at that time.
The liquid phase polycondensation reaction as referred to above may be
carried out in a single stage or by dividing the process into plurality of
stages. When the polycondensation reaction is carried out in a plurality
of stages, the polycondensation reaction conditions employed are such that
the reaction temperature of the first stage polycondensation is usually
250.degree.-290.degree. C., preferably 260.degree.-280.degree. C. and the
pressure is usually 500-20 Torr, preferably 200-30 Torr, and the
temperature of the final stage polycondensation reaction is usually
265.degree.-300.degree. C., preferably 270.degree.-295.degree. C. and the
pressure is usually 10-0.1 Torr, preferably 5-0.5 Torr.
When the polycondensation reaction is carried out in two stages, the
polycondensation reaction conditions for the first and second stage are as
defined above, and when said reaction is carried out in at least three
stages, the reaction conditions for polycondensation reactions from the
second stage to the stage prior to the final stage are intermediate
between those for the first and final stages.
For instance, when the polycondensation reaction is carried out in three
stages, the reaction temperature of the second stage polycondensation
reaction is usually 260.degree.-295.degree. C., preferably
270.degree.-285.degree. C. and the pressure is usually 50-2 Torr,
preferably 40-5 Torr. Although an intrinsic viscosity (IV) of the
polycondensate formed in each of these polycondensation reaction processes
is not particularly limited, it is desirable that the degree of rise in
intrinsic viscosity is smoothly distributed, and an intrinsic viscosity
(IV) of polyethylene terephthalate obtained from the polycondensation
reactor of the final stage is usually 0.35-0.80 dl/g, preferably 0.45-0.75
dl/g.
In the present specification, the intrinsic viscosity is determined by
calculating a viscosity of a solution of polyethylene terephthalate as
measured at 25.degree. C., said solution being prepared by heating 1.2 g
of polyethylene terephthalate to dissolve in 15 cc of o-chlorophenol,
followed by cooling.
The polyethylene terephthalate thus obtained has a density of usually 1.33
g/cm.sup.3 -1.35 g/cm.sup.3.
In the present specification, the density of polyethylene terephthalate is
measured at a temperature of 23.degree. C. by means of a density gradient
tube.
The polycondensation reaction as illustrated above is desirably carried out
in the presence of catalyst and stabilizers. The catalysts used may
include germanium compounds such as germanium dioxide, germanium
tetraethoxide and germanium tetra-n-butoxide, antimony catalysts such as
antimony trioxide, and titanium catalysts such as titanium tetrabutoxide.
Of these catalysts exemplified above, preferred is germanium dioxide,
because the resulting polyethylene terephthalate is excellent in hue and
transparency. The stabilizers used may include phosphoric acid esters such
as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate,
trioctyl phosphate, triphenyl phosphate and tricresyl phosphate;
phosphorous acid esters such as triphenyl phosphite, trisdodecyl phosphite
and trisnonylphenyl phosphite; acid phosphate such as methyl acid
phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl acid
phosphate and dioctyl phosphate; and phosphoric compounds such as
phosphoric acid and polyphosphoric acid. The amount, based on the weight
of the mixture of terephthalic acid and ethylene glycol, of the catalyst
used is usually 0.0005-0.2% by weight, preferably 0.001-0 05% by weight in
terms of the weight of the metal in the catalyst, and the amount of the
stabilizer used is usually 0.001-0.05% by weight, preferably 0.002-0.02%
by weight in terms of the weight of phosphorus atom in the stabilizer.
These catalysts and stabilizers may be added at the stage of the
esterification reaction process or may be fed to the reactor of the first
stage polycondensation reaction process.
The polyethylene terephthalate used in the present invention may contain
dicarboxylic acid other than terephthalic acid or diol other than ethylene
glycol in an amount of less than 20 mol %, and particularly useful
polyethylene terephthalate are those in which the content of ethylene
terephthalate units (a) of the formula [I],
##STR1##
is 95.0-99.0 mol % and the content of dioxyethylene terephthalate units
(b) of the formula [II]
##STR2##
is 1.0-5.0 mol %.
The polyethylene terephthalate thus obtained from the final
polycondensation reactor is usually molded into the form of granule (chip)
by the melt extrusion molding method.
The particulate polyethylene terephthalate thus prepared desirably has an
average diameter of usually 2.0-5.0 mm, preferably 2.2-4.0 mm.
This particulate polyethylene terephthalate is then fed to a solid phase
polycondensation process.
The particulate polyethylene terephthalate may also be fed to the solid
phase polycondensation process after having been pre-crystallized by
heating up to a temperature lower than the temperature at which the solid
phase polycondensation is carried out.
The pre-crystallization process mentioned above may be carried out by
heating the particulate polyethylene terephthalate in a dried state at a
temperature of usually 120.degree.-200.degree. C., preferably
130.degree.-180.degree. C. for a period of from 1 minute to 4 hours, or by
heating the particulate polyethylene terephthalate in a water vapor
atmosphere or a water vapor containing inert gas atmosphere at a
temperature of usually 120.degree.-200.degree. C. for a period of at least
1 minute.
The solid phase polycondensation process to which the particulate
polyethylene terephthalate is fed comprises at least one stage, and the
solid phase polycondensation reaction is carried out in an atmosphere of
inert gas such as nitrogen gas, argon gas or carbonic gas under the
conditions such that the polycondensation temperature is usually
190.degree.-230.degree. C., preferably 195.degree.-225.degree. C., and the
pressure is usually from 1 kg/cm.sup.2 G to 10 Torr, preferably from
normal pressure to 100 Torr. Of the inert gases mentioned above, preferred
is nitrogen gas.
The polyethylene terephthalate thus obtained through the solid phase
polycondensation process desirably has an intrinsic viscosity of usually
at least 0.50 dl/g, preferably at least 0.54 dl/g.
This polyethylene terephthalate desirably has a density of usually 1.38
g/cm.sup.3 or more, preferably at least 1.39 g/cm.sup.3.
The amount of the oligomer, a cyclic trimer of the formula
##STR3##
contained in the above-mentioned polyethylene terephthalate is less than
0.9% by weight, preferably less than 0.5% by weight, further preferably
less than 0.45% by weight and especially less than 0.4% by weight.
In the present specification, the amount of oligomer contained in the
polyethylene terephthalate is measured in the following manner.
That is, a predetermined amount of polyethylene terephthalate is dissolved
in o-chlorophenol, separated again with tetrahydrofuran, and filtered to
remove linear polyethylene terephthalate from the filtrate. Subsequently,
the filtrate obtained is fed to a liquid chromatograph (LC 7 A,
manufactured by Shimadzu Seisakusho Ltd.) to obtain the amount of oligomer
contained in the polyethylene terephthalate, and the value of said amount
of oligomer is divided by the amount of the polyethylene terephthalate
used in the measurement and the result obtained is taken as the oligomer
content (wt %).
In the present invention, the particulate polyethylene terephthalate thus
obtained is subjected to water treatment, wherein this particulate
polyethylene terephthalate is brought into contact with water, water vapor
or water vapor-containing gas.
The contact of the particulate polyethylene terephthalate with water may be
accomplished by immersing said polyethylene terephthalate in water kept at
a temperature of from 1.degree. C. to 150.degree. C. for a period of from
1 minute to 100 hours or more, preferably from 5 minutes to 10 hours.
Desirably, the particulate polyethylene terephthalate is immersed in hot
water kept at 30.degree.-150.degree. C. for a period of from 1 minute to
10 hours. More desirably, the particulate polyethylene terephthalate is
immersed in hot water kept at 40.degree.-110.degree. C. for a period of
from 3 minutes to 5 hours. Most desirably, the particulate polyethylene
terephthalate is immersed in hot water kept at 50.degree.-100.degree. C.
for a period of from 5 minutes to 3 hours.
The contact of the particulate polyethylene terephthalate with water vapor
or water vapor-containing gas may be accomplished by passing through said
particulate polyethylene the water vapor, water vapor-containing gas or
water vapor-containing air kept at a temperature of usually from 1.degree.
C. to 150.degree. C., preferably 40.degree.-150.degree. C. and especially
50.degree.-110.degree. C. in an amount of at least 0.5 g in terms of water
vapor per 1 kg of said particulate polyethylene terephthalate, thereby
bringing the particulate polyethylene terephthalate into contact with the
water vapor. The contact may also be accomplished in an atomosphere of
water vapor or water vapor-containing gas.
The contact of the particulate polyethylene terephthalate with water vapor
mentioned above is effected for a period of usually from 1 minute to 1
year, preferably from 5 minutes to 14 days.
The thus water-treated polyethylene terephthalate in the manner as
illustrated above may be prepared by carrying out a series of steps which
involve
a step of esterifying terephthalic acid or its ester-forming derivative
with ethylene glycol or its ester-forming derivative,
a step of liquid phase polycondensing the esterification product obtained
in the above-mentioned step by heating said product to melt in the
presence of a polycondensation catalyst,
a step of solid phase polycondensing the polycondensation reaction product
obtained in the above-mentioned liquid phase polycondensation step in an
inert atmosphere by heating said reaction product to a temperature below
the melting point thereof, and
a step of water-treating the polycondensation reaction product obtained in
the above-mentioned solid phase polycondensation step by bringing said
reaction product into contact with water.
By subjecting polyethylene terephthalate to water treatment in the manner
mentioned above, not only the rate of solid phase polycondensation of said
polyethylene terephthalate decreases but also an increase in amount of the
oligomer formed in a stepped square plate molded out of said polyethylene
terephthalate heated and melted at a temperature of 290.degree. C. may be
inhibited.
When such polyethylene terephthalate as treated with water, the rate of
solid phase polycondensation of which has been decreased, is solid phase
polycondensed by heating at a temperature of 215.degree. C. in an inert
gas atmosphere, the rate of polycondensation is less than 0.0055 dl/g.hr,
preferably less than 0.005 dl/g.hr, further preferably less than 0.004
dl/g.hr and especially less than 0.003 dl/g.hr.
In the present specification, the rate of polycondensation of polyethylene
terephthalate at the time when said polyethylene terephthalate is solid
phase polycondensed is measured in the following manner.
A cylindrical stainless steel container of 22 mm in inside diameter and 80
mm in height is filled with 60 g of particulate polyethylene
terephthalate, and then sealed. This container has at the bottom portion a
nozzle for breathing inert gas, and is so designed that the inert gas is
discharged out of the system through the upper portion thereof.
The solid phase polycondensation is carried out by passing nitrogen gas as
the inert gas through the sealed stainless steel container packed with the
particulate polyethylene terephthalate, said stainless steel container
having been fitted to and held in a sand bath having a heating equipment
(containing aluminum oxide, manufactured by Nippon Percalizino Co.)
The nitrogen gas used has a dew point of less than -50.degree. C. and an
oxygen content of less than 20 ppm, and is preheated, prior to feeding to
the stainless steel container, so as to have the same temperature as that
of the bath. The nitrogen gas is fed to the stainless steel container at a
rate of 200 Nl/hr.
The sand bath is brought by means of air to a fluid state so that the
temperature of the bath becomes uniform and no temperature distribution
occurs. The heater of the sand bath is so controlled that the bath
temperature coincides with the predetermined solid phase polycondensation
temperature by means of a program controller.
The rate of the solid phase polycondensation is determined by the following
manner using the above-mentioned cylindrical stainless steel container and
sand bath. The solid phase polycondensation reaction is carried out by
fitting the sealed cylindrical stainless steel container filled with
particulate polyethylene terephthalate to the sand bath, passing nitrogen
gas at a rate of 200 Nl/hr through the container, elevating the
temperature of the sand bath from room temperature up to 170.degree. C. in
30 minutes, maintaining the elevated temperature at 170.degree. C. for 1
hour, elevating said temperature from 170.degree. C. up to 215.degree. C.
in 30 minutes and maintaining the elevated temperature at 215.degree. C.
for 4 hours.
After the completion of the solid phase polycondensation reaction, the
heating is stopped, the temperature in the sand bath is lowered up to
70.degree. C. while passing the nitrogen gas through the container, and
the container is taken out from the sand bath to measure an intrinsic
viscosity g/dl (IV) of the solid phase polycondensed particulate
polyethylene terephthalate. This IV value as obtained is taken as A dl/g.
In the same manner as above, IV of the particulate polyethylene
terephthalate is measured, except that the retention time at 215.degree.
C. is changed from 4 hours to 20 hours. This IV value as obtained is taken
as B dl/g.
The rate of solid phase polycondensation is calculated from the following
equation.
##EQU1##
wherein R is a rate of solid phase polycondensation (dl/g.hr), and A and B
individually represent IV value (dl/g) as measured after the retention
time at 215.degree. C. for 4 and 20 hours, respectively.
In the polyethylene terephthalate subjected to water treatment in the
manner as mentioned above, an increase in amount of the oligomer formed in
the course of the subsequent molding of said polyethylene terephthalate is
markedly inhibited. This can be confirmed by measurement of the increased
amount of the oligomer formed in a stepped square plate molded out of the
water-treated polyethylene terephthalate heated to melt at a temperature
of 290.degree. C. The increased amount y (wt %) of the oligomer formed in
the stepped square plate molded out of the water-treated polyethylene
terephthalate of the present invention heated to melt at a temperature of
290.degree. C. is usually y.ltoreq.-0.20x+0.2, preferably
y.ltoreq.-0.20x+0.18 and further preferably y.ltoreq.-0.20x+0.16, wherein
x is the oligomer concentration (wt %) in the polyethylene terephthalate
prior to being molded into the stepped square plate.
In the present specification, the increased amount y (wt %) of the oligomer
formed in the stepped square plate molded out of the particulate
polyethylene terephthalate is measured in the following manner.
That is, 2 kg of the particulate polyethylene terephthalate, the oligomer
content of which has previously measured (measured value %), is dried for
at least 16 hours with a tray dryer at a temperature of 140.degree. C. and
a pressure of 10 Torr so that the moisture content of said polyethylene
terephthalate becomes less than 50 ppm.
Subsequently, the dried particulate polyethylene terephthalate is fed to an
injection molding machine (M-70A, manufactured by Meiki Seisakusho K. K.)
and injection molded at a cylinder temperature of 290.degree. C. and a
temperature of water cooling mold of 15.degree. C. to obtain a molded
stepped square plate.
The injection molding of the molded stepped square plate is carried out by
feeding the dried particulate polyethylene terephthalate from a hopper to
the injection molding machine while adjusting the batch weighing to 12
seconds and the injection to 60 seconds. The reaction time of molten resin
in the molding machine is adjusted to about 72 seconds. The molded stepped
square plates each have a weight of 75 g, and the specimen for measuring
the oligomer content is selected from among the molded plates obtained at
the eleventh to fifteenth molding after the injection of injection
molding.
The molded stepped square plate 1 has such a shape as shown in FIG. 1, and
a thickness of portion A of said plate is about 6.5 mm, that of portion B
is about 5 mm and that of portion C is about 4 mm. Using this portion C,
the increased amount of the oligomer formed in the polyethylene
terephthalate as molded into the stepped square plate is measured.
This molded plate having a thickness of 4 mm is then cut into chips which
are then used as specimens for measuring the oligomer content.
The oligomer content in the polyethylene terephthalate constituting the
stepped square plate is measured in the same manner as mentioned above.
In the polyethylene terephthalate treated with water as aforesaid, when the
oligomer content in a molded article obtained by injection molding said
polyethylene terephthalate at a molding temperature of 290.degree. C. is
taken as W.sub.0 (wt %) and the oligomer content in a molded article
obtained by immersing said polyethylene terephthalate in hot water kept at
95.degree. C. for 8 hours followed by drying and then injection molding
the dried polyethylene terephthalate is taken as W.sub.1 (wt %), it is
desirable that W.sub.0 -W.sub.1 is 0-0.12% by weight, preferably 0-0.11%
by weight and especially 0-0.10% by weight.
When a molded article is intended to obtain by using such polyethylene
terephthalate as having the oligomer content of 0-0.12% by weight
expressed in terms of W.sub.0 -W.sub.1 as defined above, the oligomer is
difficult to form in the resulting molded article and accordingly the
contamination of the mold therewith can be effectively inhibited.
When the polyethylene terephthalate subjected to water treatment, the rate
of solid phase polycondensation of which has been decreased as mentioned
above, is solid phase polycondensed by heating at a temperature of
215.degree. C. in an inert gas atmosphere, the rate of polycondensation as
measured at that time is taken as V.sub.0, and when said polyethylene
terephthalate is immersed in hot water kept at 95.degree. C. for 8 hours
followed by drying and solid phase polycondensed in the same manner as
above, the rate of solid phase polycondensation as measured at that time
is taken as V.sub.1, it is desirable that a ratio of polycondensation rate
V.sub.1 /V.sub.0 is 0.2-1.0, preferably 0.22-1.0 and especially 0.25-1.0
When a molded article is intended to obtain by such polyethylene
terephthalate as having the ratio of polycondensation ratio V.sub.1
/V.sub.0 of 0.2-1.0, the oligomer is difficult to form in the resulting
molded article and accordingly the contamination of the mold therewith can
be effectively inhibited.
Furthermore, when the acetaldehyde content of an article obtained by
injection molding the polyethylene terephthalate at a molding temperature
of 290.degree. C. is taken as W.sub.0 (wt %) and, on one hand, when the
acetaldehyde content of an article obtained by injection molding likewise
the polyethylene terephthalate which has been immersed in hot water kept
at 95.degree. C. for 8 hours and dried is taken as W.sub.1 (wt %), W.sub.0
-W.sub.1 is 0-5 ppm by weight.
A molded article obtained from polyethylene terephthalate, in which the
acetaldehyde content is measured, is prepared by drying particulate
polyethylene terephthalate using a tray dryer for at least 16 hours at a
temperature of 140.degree. C. and a pressure of 10 Torr so that the
moisture content of said particulate polyethylene terephthalate becomes
less than 50 ppm, and then injection molding the dried particulate
polyethylene terephthalate by using an injection molding machine (M-70A,
manufactured by Meiki Seisakusho K. K.) at a cylinder temperature of
290.degree. C. and a temperature of water cooling the mold of 15.degree.
C.
In an article molded out of such polyethylene terephthalate as having
W.sub.0 -W.sub.1 of 0-5 ppm as defined above, the acetaldehyde is
difficult to form and accordingly the molded article does not emit foul
odor or foreign odor, and the contents of said molded article do not
change in flavor or fragrance.
In the present specification, the content of acetaldehyde contained in the
polyethylene terephthalate is determined by cooling and pulverizing 2 g of
a specimen, bringing the specimen back to room temperature, filling a
container with 1 g of the specimen collected and 2 cc of an internal
standard solution, and sealing the container. Thereafter, the acetaldehyde
is extracted for 1 hour in an oven at 120.degree. C., cooled with ice, and
5 .mu.l of the supernatant is measured by GC-6A of Shimadzu Seisakusho K.
K. to obtain the acetaldehyde content.
By subjecting polyethylene terephthalate to water treatment in the manner
as mentioned hereinbefore, not only the rate of polycondensation of the
polyethylene terephthalate decreases but also an increase in amount of
oligomers such as the cyclic trimer or acetaldehyde contained in the
polyethylene terephthalate at the time of molding thereof can be
inhibited, and this is considered ascribable to the fact that by
subjecting the polyethylene terephthalate to water treatment, a
polycondensation catalyst, for example, germanium catalyst undergoes
deactivation and accordingly a decomposition reaction or ester interchange
reaction scarcely proceeds and, on that account, the amount of oligomers
such as the cyclic trimer formed thereby becomes small.
As stated hereinbefore, the polyethylene terephthalate subjected to water
treatment contains small amounts of oligomer formed at the time of molding
said polyethylene terephthalate. Accordingly, when this polyethylene
terephthalate is fed to a molding machine such as an injection molding
machine and molded into a preform for blow molding, this preform is
stretch blow molded by inserting it into a mold of a predetermined shape
and then, if necessary, heat set to obtain a blow molded container, the
contamination of the mold with oligomers such as the cyclic trimer is
difficult to occur and further acetaldehyde is difficult to form.
EFFECT OF THE INVENTION
In the process for treatment of polyethylene terephthalate of the present
invention, the polyethylene terephthalate having an intrinsic viscosity of
at least 0.50 dl/g and a density of at least 1.37 g/cm.sup.3 is treated
with water by bringing said polyethylene terephthalate into contact with
the water. In the polyethylene terephthalate subjected to the water
treatment, only small amounts of oligomers such as cyclic trimer is formed
at the time when said polyethylene terephthalate is molded and, moreover,
because the total amount of oligomers such as the cyclic trimer contained
in the polyethylene terephthalate at the time of molding thereof is small,
the contamination of the mold therewith is difficult to occur.
Accordingly, when the polyethylene terephthalate treated with water in
accordance with the present invention is molded into a molded article,
there is no need for cleaning the mold frequently and thereby to improve
productivity of molded articles such as bottle. The bottle molded out of
the water-treated polyethylene terephthalate can be prevented from
chalking and, moreover, practically little acetaldehyde is formed at the
time of molding said polyethylene terephthalate.
The present invention is illustrated below with reference to examples, but
it should be construed that the invention is in no way limited to those
examples.
EXAMPLE 1
In a stainless steel container, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3, the oligomer content of 0.31% by weight and an average
particle diameter of 2.8 mm was immersed in 6.5 kg of distilled water.
Subsequently, the stainless steel container charged with the polyethylene
terephthalate and distilled water was heated externally to control the
temperature inside the container to 90.degree. C. (the temperature inside
the container was elevated to 90.degree. C. in 10 minutes), and the water
treatment of the polyethylene terephthalate was carried out for 4 hours
while maintaining at that temperature, and the water-treated polyethylene
terephthalate was dehydrated and dried in a nitrogen gas atmosphere at
140.degree. C. for 14 hours.
The rate of polycondensation was 0.0026 dl/g.hr when the dried polyethylene
terephthalate was subjected in the manner as already illustrated in the
present specification to solid phase polycondensation treatment by heating
at a temperature of 215.degree. C. in a nitrogen gas atmosphere.
A stepped square plate molded out of the above-mentioned polyethylene
terephthalate with an injection molding machine (M-70A of Meiki Seisakusho
K. K.) at 290.degree. C. according to the aforementioned procedure had the
oligomer content of 0.35% by weight, thus an increased amount of the
oligomer was 0.04% by weight.
EXAMPLE 2
In the same procedure as in Example 1, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.78 gl/g, a density of
1.40 g/cm.sup.3, the oligomer content of 0.28% by weight and an average
particle diameter of 2.6 mm was subjected to hot water treatment to
measure a rate of solid phase polycondensation, whereby the rate of
polycondensation as measured was 0.0016 dl/g.hr.
A molded article obtained by the same procedure as in Example 1 had the
oligomer content of 0.29% by weight, thus an increased amount of the
oligomer was 0.01% by weight.
EXAMPLE 3
A stainless steel container was charged 5 kg of the same polyethylene
terephthalate as used in Example 1, and water vapor was passed
therethrough at a rate of 0.5 kg/hr for 30 minutes.
A molded article obtained by the same procedure as in Example 1 had the
oligomer content of 0.40% by weight, thus an increased amount of the
oligomer was 0.09% by weight.
EXAMPLE 4
A pressure stainless steel container was charged with 5 kg of the same
polyethylene terephthalate as used in Example 1, and water vapor having a
pressure of 0.43 kg/cm.sup.2 was passed therethrough at a rate of 0.5
kg/hr for 30 minutes.
The polyethylene terephthalate thus treated was dried in the same procedure
as in Example 1 and measured for a rate of solid phase polycondensation,
whereby the rate of polycondensation as measured was 0.0048 dl/g.hr.
A molded article obtained in the same procedure as in Example 1 had the
oligomer content of 0.37% by weight, thus an increased amount of the
oligomer was 0.06% by weight.
EXAMPLE 5
In a stainless steel container, 5 kg of the same polyethylene terephthalate
as used in Example 1 was immersed in 6.5 kg of distilled water kept at
18.degree. C.
After immersing for 30 minutes, the polyethylene terephthalate was
dehydrated and dried in the same procedure as in Example 1, and the dried
polyethylene terephthalate was then measured for rate of solid phase
polycondensation, whereby the rate of polycondensation as measured was
0.0042 dl/g.hr.
A molded article obtained by the same procedure as in Example 1 had the
oligomer content of 0.39% by weight, thus an increased amount of the
oligomer was 0.08% by weight.
COMPARATIVE EXAMPLE 1
The same polyethylene terephthalate as used in Example 1 was dried in
nitrogen gas at 140.degree. C. for 14 hours, and the dried polyethylene
terephthalate was subjected to solid phase polycondensation treatment by
heating at a temperature of 215.degree. C. in a nitrogen atmosphere to
measure a rate of solid phase polycondensation, whereby the rate of
polycondensation as measured was 0.0067 dl/g.hr.
An article molded out of the thus treated polyethylene terephthalate at
290.degree. C. had the oligomer content of 0.50% by weight, thus an
increased amount of the oligomer was 0.19% by weight.
COMPARATIVE EXAMPLE 2
The same polyethylene terephthalate as used in Example 2 was measured in
the same procedure as in Comparative Example 1 for rate of solid phase
polycondensation, whereby the rate of polycondensation as measured was
0.0057 dl/g.hr, and an article molded out of said polyethylene
terephthalate had the oligomer content of 0.46% by weight, thus an
increased amount of the oligomer was 0.18% by weight.
EXAMPLE 6
Using a continuous polycondensation apparatus comprising the 1st, 2nd, 3rd,
4th and 5th reactors which are of the tank type and the 6th reactor which
is a biaxial rotary type horizontal reactor, continuous polymerization was
carried out in the following manner to prepare polyethylene terephthalate.
A slurry prepared by mixing 1473 parts by weight of high purity
terephthalic acid with 645 parts by weight of ethylene glycol was
continuously fed per hour to the first reactor in which 3750 parts by
weight of a reaction liquid had previously been retained with stirring at
255.degree. C. and 1.7 kg/cm.sup.2 G to carry out the first stage
esterification reaction. In the first stage esterification reaction, a
mixture of 203 parts by weight of water and 3 parts by weight of ethylene
glycol was distilled off. The first stage esterification reaction product
was so controlled that an average retention time becomes 2.0 hours, and
the reaction product was introduced with stirring into the second reactor
maintained at 260.degree. C. and 0.8 kg/cm.sup.2 G.
In the second reactor, a homogeneous mixture of 0.25 part by weight of
germanium dioxide and 32 parts by weight of ethylene glycol per hour was
continuously fed and, at the same time, a mixture of 84 parts by weight of
water and 7 parts by weight of ethylene glycol per hour was continuously
distilled off, and the second stage esterification reaction was continued.
The second stage esterification reaction product was so controlled that an
average retention time becomes 2.0 hours, and the reaction product was
introduced with stirring to the third reactor maintained at 265.degree. C.
and normal pressure.
In the third reactor, homogeneous mixture of 1.23 parts by weight of
trimethyl phosphate and 22 parts by weight of ethylene glycol per hour was
continuously fed and, at the same time, a mixture of 21 parts by weight of
water and 38 parts by weight of ethylene glycol per hour was continuously
distilled off, and the third stage esterification reaction was continued.
The third esterification reaction product was also so controlled that an
average retention time becomes 2.0 hours, and the reaction product was
continuously introduced with stirring into the fourth reactor maintained
at 275.degree. C. and 70 mm Hg. In the fourth reactor, a mixture of 62
parts by weight of water and 6 parts by weight of ethylene glycol per hour
was continuously distilled off, and the first stage polycondensation
reaction was carried out. The first stage polycondensation reaction
product was so controlled that an average retention time becomes 1.0 hour,
and the reaction product was continuously introduced with stirring into
the fifth reactor maintained at 280.degree. C. and 5 mm Hg.
In the fifth reactor, a mixture of 26 parts by weight of water and 3 parts
by weight of ethylene glycol per hour was continuously ditilled off, and
the second stage polycondensation reaction was continued. The second stage
polycondensation reaction product was so controlled that an average
retention time becomes 1.0 hour, and the reaction product was continuously
introduced into the sixth reactor which is a horizontal biaxial rotary
reactor maintained at 282.degree. C. and 1.8-2.5 mm Hg.
In the sixth reactor, a reaction mixture of 12 parts by weight of ethylene
glycol and 1 part by weight of water per hour was continuously distilled
off, and the third stage polycondensation reaction was continued. The
third stage polycondensation reaction product was so controlled that an
average retention time becomes 2.5 hours, and the reaction product was
continuously withdrawn out of the reactor by means of a
polyester-withdrawing equipment into the form of strand. The strand
withdrawn was cooled by immersing in water and then cut up by means of a
strand cutter into the form of chip. The polyethylene terephthalate
obtained by the above-mentioned liquid phase polymerization had an
intrinsic viscosity of 0.57 dl/g as measured in o-chlorophenol at
25.degree. C. and the content of dioxyethylene terephthalate component of
2.50 mol %.
Further, the polyethylene terephthalate obtained by the above mentioned
liquid phase polymerization was dried and crystallized in a nitrogen
atmosphere at about 140.degree. C. for about 15 hours, and then fed to a
column solid phase polymerizer to carry out solid phase polymerization in
a nitrogen atmosphere at 205.degree. C. for 15 hours. The polyethylene
terephthalate thus obtained had an intrinsic viscosity of 0.80 dl/g as
measured in o-chlorophenol at 25.degree. C., a density of 1.40 g/cm.sup.3,
the oligomer content of 0.32% by weight and the content of dioxyethylene
terephthalate component of 2.53 mol %.
In a stainless steel container, 5 kg of the polyethylene terephthalate (A)
obtained above was immersed in 6.5 kg of distilled water.
Subsequently, the stainless steel container charged with the polyethylene
terephthalate and distilled water was heated externally to control the
temperature inside the container to 90.degree. C., and maintained at that
temperature for 4 hours to carry out water treatment. The water-treated
polyethylene terephthalate was dehydrated and dried at 140.degree. C. in a
nitrogen atmosphere for 14 hours.
When the thus dried polyethylene terephthalate was subjected to solid phase
polycondensation treatment in the manner illustrated already in the
specification by heating at a temperature of 215.degree. C. in a nitrogen
gas atmosphere, the rate of polycondensation as measured was 0.0026
dl/g.hr.
An article molded out of the above-mentioned polyethylene terephthalate
using an injection molding machine (M-70A manufactured by Meiki Seisakusho
K. K.) at 290.degree. C. had the oligomer content of 0.35% by weight, thus
an increased amount of the oligomer was 0.04% by weight.
EXAMPLE 7
Example 6 was repeated except that the water treatment of polyethylene
terephthalate was conducted by passing 0.5 kg/hr of water vapor through
the stainless steel container filled with 5 kg of the polyethylene
terephthalate (A).
In the same procedure as in Example 6, the polyethylene terephthalate thus
treated was dried and then subjected to solid phase polycondensation
treatment to measure a rate of solid phase polycondensation, whereby the
rate of polycondensation as measured was 0.0052 dl/g.hr.
An article molded by the same manner as in Example 6 had the oligomer
content of 0.40% by weight, thus an increased amount of the oligomer was
0.09% by weight.
EXAMPLE 8
Example 6 was repeated except that the water treatment of polyethylene
terephthalate was conducted by charging a pressure stainless steel
container with 5 kg of the polyethylene terephthalate (A) and passing
therethrough water vapor (saturation temperature 110.degree. C.) of 0.43
kg/cm.sup.2 at a rate of 0.5 kg/hr for 30 minutes.
In the same procedure as in Example 6, the polyethylene terephthalate thus
treated was dried and then subjected to solid phase polycondensation
treatment to measure a rate of solid phase polycondensation, whereby the
rate of polycondensation as measured was 0.0048 dl/g.hr.
An article molded by the same manner as in Example 6 had the oligomer
content of 0.37% by weight, thus an increased amount of the oligomer was
0.06% by weight.
EXAMPLE 9
Example 6 was repeated except that the water treatment was conducted by
immersing the polyethylene terephthalate (A) for 30 minutes in distilled
water kept at 18.degree. C.
In the same procedure as in Example 6, the polyethylene terephthalate thus
treated was dried and then subjected to solid phase polycondensation
treatment to measure a rate of solid phase polycondensation, whereby the
rate of polycondensation as measured was 0.0042 dl/g.hr.
An article molded by the same manner as in Example 6 had the oligomer
content of 0.39% by weight, thus an increased amount of the oligomer was
0.08% by weight.
COMPARATIVE EXAMPLE 3
The polyethylene terephthalate obtained in Example 6 without subjecting to
hot water treatment was dried in a nitrogen gas at 140.degree. C. for 14
hours, and then subjected to solid phase polycondensation treatment by
heating in a nitrogen atmosphere at 215.degree. C. to measure a rate of
solid phase polycondensation, whereby the rate of polycondensation as
measured was 0.0067 dl/g.hr.
An article molded out of this polyethylene terephthalate at 290.degree. C.
had the oligomer content of 0.50% by weight, thus an increased amount of
the oligomer was 0.19% by weight.
EXAMPLE 10
In a stainless steel container, 5 kg of polyethylene terephthalate having
an intrinsic viscosity of 0.80 dl/g, a density of 1.40 g/cm.sup.3 and the
oligomer content of 0.33% by weight was immersed in 6.5 kg of distilled
water.
Subsequently, the stainless steel container charged with the polyethylene
terephthalate and distilled water was heated externally to control the
temperature inside the container to 95.degree. C., and maintained at that
temperature for 4 hours to carry out hot water treatment. The polyethylene
terephthalate thus treated was dehydrated and then dried at 140.degree. C.
in a nitrogen gas atmosphere for 14 hours.
When the thus dried polyethylene terephthalate was subjected to solid phase
polycondensation treatment in the manner illustrated already in the
specification by heating at 215.degree. C. in a nitrogen gas atmosphere,
the rate of polycondensation as measured was 0.0026 dl/g.hr.
A stepped square plate molded at 290.degree. C. out of the above-mentioned
polyethylene terephthalate using an injection molding machine (M-70A of
Meiki Seisakusho K. K.) had the oligomer content of 0.35% by weight and
the acetaldehyde content of 7.6 ppm.
EXAMPLE 11
In the same procedure as in Example 10, 5 kg of polyethylene terephthalate
having an intrinsic viscosity of 0.78 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.28% by weight was subjected to hot water
treatment to measure a rate of solid phase polycondensation, whereby the
rate of polycondensation as measured was 0.0016 dl/g.hr.
A molded article obtained by the same procedure as in Example 10 had the
oligomer content of 0.29% by weight and the acetaldehyde content of 7.5
ppm.
EXAMPLE 12
A stainless steel container was charged with 5 kg of the same polyethylene
terephthalate as used in Example 10, and water vapor was passed
therethrough at a rate of 0.5 kg/hr for 30 minutes.
The polyethylene terephthalate thus treated was dried and measured for a
rate of solid phase polycondensation in the same manner as in Example 10,
whereby the rate of polycondensation as measured was 0.0052 dl/g.hr.
A molded article obtained by the same procedure as in Example 10 had the
oligomer content of 0.40% by weight.
COMPARATIVE EXAMPLE 4
The polyethylene terephthalate used in Example 10 was dried at 140.degree.
C. in a nitrogen gas atmosphere for 14 hours, and then subjected to solid
phase polycondensation treatment by heating at a temperature of
215.degree. C. in a nitrogen atmosphere to measure a rate of solid phase
polycondensation, whereby the rate of polycondensation as measured was
0.0067 dl/g.hr.
An article molded at 290.degree. C. out of the above-mentioned polyethylene
terephthalate had the oligomer content of 0.51% by weight and the
acetaldehyde content of 15 ppm.
COMPARATIVE EXAMPLE 5
The polyethylene terephthalate used in Example 11 was measured for a rate
of solid phase polycondensation in the same procedure as in Comparative
Example 4, whereby the rate of polycondensation as measured was 0.0057
dl/g.hr.
An article molded at 290.degree. C. out of the above-mentioned polyethylene
terephthalate had the oligomer content of 0.46% by weight and the
acetaldehyde content of 14.2 ppm.
EXAMPLE 13
In a stainless steel container, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.33% by weight was immersed
in 6.5 kg of distilled water.
Subsequently, the stainless steel container charged with the polyethylene
terephthalate and distilled water was heated externally to control the
temperature inside the container to 90.degree. C., and maintained at that
temperature for 4 hours to carry out hot water treatment. The thus treated
polyethylene terephthalate was then dehydrated and dried to obtain the
particulate polyethylene terephthalate of the present invention.
Using a tray dryer, 2 kg of the particulate polyethylene terephthalate thus
obtained was dried for at least 16 hours at a temperature of 140.degree.
C. and a pressure of 10 Torr to reduce the moisture content of said
particulate polyethylene terephthalate to less than 50 ppm.
The dried particulate polyethylene terephthalate was injection molded into
a stepped square plate having a thickness of 4 mm using an injection
molding machine (M-70A of Meiki Seisakusho K. K.) at a cylinder
temperature of 290.degree. C. and a temperature of water cooling the mold
of 15.degree. C.
The stepped square plate having a thickness of 4 mm was then cut into chips
which were used as specimen for measuring the oligomer content of the
plate. This stepped square plate had the oligomer content of 0.35% by
weight, thus an increased amount of the oligomer was 0.02% by weight.
EXAMPLE 14
In the same procedure as in Example 13, 5 kg of polyethylene terephthalate
having an intrinsic viscosity of 0.78 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.28% by weight was subjected to hot water
treatment, and then molded into a stepped square plate. The oligomer
content of this stepped square plate as measured was 0.29% by weight, thus
an increased amount of the oligomer was 0.01% by weight.
EXAMPLE 15
A stainless steel container was charged with 5 kg of the polyethylene
terephthalate used in Example 13, and water vapor was passed therethrough
for 30 minutes at a rate of 0.5 kg/hr.
In the same procedure as in Example 13, the thus treated polyethylene
terephthalate was dried and then molded into a stepped square plate to
measure the oligomer content of the stepped square plate, whereby the
oligomer content was 0.40% by weight, thus an increased amount of the
oligomer was 0.07% by weight.
COMPARATIVE EXAMPLE 6
The polyethylene terephthalate used in Example 13 was dried in a nitrogen
gas at 140.degree. C. for 14 hours, and then molded, as it was, into a
stepped square plate in the same procedure as in Example 13 to measure the
amount of oligomer contained in this plate, whereby the oligomer content
was 0.51% by weight, thus an increased amount of the oligomer was 0.18% by
weight.
COMPARATIVE EXAMPLE 7
The polyethylene terephthalate used in Example 14 was molded into a stepped
square plate in the same procedure as in Comparative Example 6 to measure
the amount of oligomer contained in this plate, whereby the oligomer
content as measured was 0.46% by weight, thus an increased amount of the
oligomer was 0.18% by weight.
Results obtained in Examples and Comparative Examples were shown in FIG. 2
wherein the abscissa indicates oligomer concentration (wt %) in the chips
prior to molding, and the ordinate indicates an increased amount of the
oligomer contained in the stepped square plate as molded.
EXAMPLE 16
In a stainless steel container, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.33% by weight was immersed
in 6.5 kg of distilled water. The stainless steel container charged with
the polyethylene terephthalate and distilled water was heated externally
to control the temperature inside the container, and maintained at that
temperature to carry out hot water treatment. The polyethylene
terephthalate thus treated was dehydrated and dried to obtain the
polyethylene terephthalate of the present invention.
In a square plate obtained by injection molding the dried particulate
polyethylene terephthalate at a cylinder temperature of 290.degree. C.,
the oligomer content as measured was 0.35% by weight, and the acetaldehyde
concentration was 7.6 ppm.
When the water-treated and dried particulate polyethylene terephthalate was
subjected to solid phase polycondensation treatment by heating at a
temperature of 215.degree. C. in a nitrogen gas atmosphere in the manner
as already illustrated in the present specification, the rate of
polycondensation was 0.0026 dl/g.hr. This rate of polycondensation is
taken as V.sub.0.
Subsequently, this water-treated and dried particulate polyethylene
terephthalate was further subjected to hot water treatment for 8 hours at
a temperature of 95.degree. C. inside the stainless steel container,
dehydrated and dried to measure a rate of solid phase polycondensation,
whereby the rate of polycondensation was 0.0012 dl/g.hr.
When this rate of solid phase condensation was taken as V.sub.1, V.sub.1
/V.sub.0 was 0.46.
EXAMPLE 17
Example 16 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.78 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.28% by weight was used.
Results obtained are shown in Table 1.
The acetaldehyde concentration as measured in Example 17 was 7.5 ppm.
EXAMPLE 18
A stainless steel container was charged with 5 kg of particulate
polyethylene terephthalate having an intrinsic viscosity of 0.80 dl/g, a
density of 1.40 g/cm.sup.3 and the oligomer content of 0.33% by weight,
and water vapor was passed therethrough for 0.5 hour at a rate of 0.5
kg/hr.
Example 16 was then repeated except that the polyethylene terephthalate
obtained above was used.
Results obtained are shown in Table 1.
EXAMPLE 19
Example 18 was repeated except that the water vapor was passed for 4 hours
instead of 0.5 hour.
Results obtained are shown in Table 1.
EXAMPLE 20
Example 18 was repeated except that the water vapor was passed for 2 hours
instead of 0.5 hour.
Results obtained are shown in Table 1.
EXAMPLE 21
Example 16 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.80 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.33% by weight was subjected to hot water
treatment in the stainless steel container by controlling the temperature
inside the container to 95.degree. C. and holding the polyethylene
terephthalate therein for 16 hours, dehydrated and dried to obtain the
polyethylene terephthalate of the present invention.
Results obtained are shown in Table 1.
EXAMPLE 22
Example 16 was repeated except that the hot water treatment time employed
was 0.5 hour instead of 4 hours.
Other results obtained are shown in Table 1.
EXAMPLE 23
Example 16 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.80 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.29% by weight was used instead.
Other results obtained are shown in Table 1.
EXAMPLE 24
Example 16 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.82 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.29% by weight was used instead.
Results obtained are shown in Table 1.
COMPARATIVE EXAMPLE 8
The particulate polyethylene terephthalate used in Example 16, which had
not been subjected to water treatment, was dried and injection molded at a
cylinder temperature of 290.degree. C. into a square plate. On
determination, the square plate had the oligomer content of 0.51% by
weight and the acetaldehyde concentration of 15 ppm.
When the particulate polyethylene terephthalate was subjected to solid
phase polycondensation treatment by heating at a temperature of
215.degree. C. in a nitrogen atmosphere, the rate of polycondensation as
determined was 0.0067 dl/g.hr. This rate of solid phase polycondensation
is taken as V.sub.0.
Subsequently, when this particulate polyethylene terephthalate was
subjected at the temperature inside a stainless steel container for 8
hours to hot water treatment, dehydrated and dried to measure a rate of
solid phase polycondensation, the rate of polycondensation as determined
was 0.0011 dl/g.hr. When this rate of solid phase polycondensation is
taken as V.sub.1, V.sub.1 /V.sub.0 was 0.16.
COMPARATIVE EXAMPLE 9
Comparative Example 8 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.78 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.28% by weight was used
instead.
Results obtained are shown in Table 1.
The square plate has the oligomer content of 14 ppm.
COMPARATIVE EXAMPLE 10
Comparative Example 8 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.29% by weight was used
instead.
Other results obtained are shown in Table 1.
COMPARATIVE EXAMPLE 11
Comparative Example 8 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.82 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.39% by weight was used
instead.
Results obtained are shown in Table 1.
The acetaldehyde concentration of the square plate was 14 ppm.
TABLE 1
______________________________________
Rate of solid phase
Rate of solid phase
polycondensation
polycondensation
V.sub.0 V.sub.1 V.sub.1 /V.sub.0
______________________________________
Example 16
0.0026 0.0012 0.46
Example 17
0.0016 0.00095 0.59
Example 18
0.0052 0.0014 0.23
Example 19
0.0038 0.0012 0.32
Example 20
0.0046 0.0014 0.30
Example 21
0.0013 0.0011 0.85
Example 22
0.0033 0.0012 0.36
Example 23
0.0020 0.0012 0.60
Example 24
0.0032 0.0014 0.44
Comparative
0.0067 0.0011 0.16
Example 8
Comparative
0.0057 0.00085 0.15
Example 9
Comparative
0.0078 0.0013 0.17
Example 10
Comparative
0.0069 0.0012 0.17
Example 11
______________________________________
EXAMPLE 25
In a stainless steel container, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.33% by weight was immersed
in 6.5 kg of distilled water. Subsequently the stainless steel container
charged with the polyethylene terephthalate and distilled water was heated
externally to control the temperature inside the container and maintained
at that temperature for 4 hours to carry out hot water treatment. The
polyethylene terephthalate thus treated was dehydrated and dried to obtain
the polyethylene terephthalate of the present invention.
A square plate obtained by injection molding this dried particulate
polyethylene terephthalate at a cylinder temperature was measured for the
amount of oligomer contained therein, whereby the oligomer content as
determined was 0.35% by weight, and the acetaldehyde concentration of this
square plate was 7.6 ppm. This oligomer content is taken as W.sub.0.
Subsequently, the dried particulate polyethylene terephthalate was further
subjected to hot water treatment at a temperature inside the stainless
steel container of 95.degree. C. for 8 hours, dehydrated and then dried.
The oligomer content of a square plate obtained by injection molding at a
cylinder temperature of 290.degree. C. the particulate polyethylene
terephthalate thus treated was 0.34% by weight. When this oligomer content
was taken as W.sub.1, W.sub.0 -W.sub.1 was 0.01% by weight.
EXAMPLE 26
Example 25 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.78 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.28% by weight was used instead.
Results obtained are shown in Table 2.
EXAMPLE 27
A stainless steel container was charged with 5 kg of particulate
polyethylene terephthalate having an intrinsic viscosity of 0.80 dl/g, a
density of 1.40 g/cm.sup.3 and the oligomer content of 0.33% by weight,
and water vapor kept at 100.degree. C. was passed therethrough at a rate
of 0.5 kg/hr for 0.5 hour.
Thereafter, Example 25 was repeated except that the particulate
polyethylene terephthalate thus treated was used instead.
Results obtained are shown in Table 2.
EXAMPLE 28
Example 27 was repeated except that the water vapor was passed through the
stainless steel container charged with the particulate polyethylene
terephthalate for 4 hours instead of 0.5 hour.
Results obtained are shown in Table 2.
EXAMPLE 29
Example 27 was repeated except that the water vapor was passed through the
stainless steel container charged with the particulate polyethylene
terephthalate for 2 hours instead of 0.5 hour.
Results obtained are shown in Table 2.
EXAMPLE 30
Example 25 was repeated except that in the stainless steel container,
particulate polyethylene terephthalate having an intrinsic viscosity of
0.80 dl/g, a density of 1.40 g/cm.sup.3 and the oligomer content of 0.33%
by weight was subjected to hot water treatment by controlling the
temperature of water inside the container to 95.degree. C. and maintaining
the water at that temperature for 16 hours, and the particulate
polyethylene terephthalate thus treated was dehydrated and dried to obtain
the polyethylene terephthalate of the present invention.
Results obtained are shown in Table 2.
EXAMPLE 31
Example 25 was repeated except that the hot water treatment time employed
was 0.5 hour instead of 4 hours. In this example, the acetaldehyde
concentration of the square plate was 7.9 ppm.
Other results obtained are shown in Table 2.
EXAMPLE 32
Example 25 was repeated except that the particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.29% by weight was used
instead. In this example, the acetaldehyde concentration of the square
plate was 3.3 ppm.
Other results obtained are shown in Table 2.
EXAMPLE 33
Example 25 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.82 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.39% by weight was used instead.
Results obtained are shown in Table 2.
COMPARATIVE EXAMPLE 12
The particulate polyethylene terephthalate used in Example 25, which had
not been subjected to water treatment, was dried and injection molded at a
cylinder temperature of 290.degree. C. into a square plate. On
determination, the square plate had the oligomer content of 0.51% by
weight. This oligomer content is taken as W.sub.0.
The acetaldehyde concentration of this square plate was 15 ppm.
Subsequently, when a square plate was obtained by injection molding at a
cylinder temperature of 290.degree. C. the above-mentioned particulate
polyethylene terephthalate which had been subjected to hot water treatment
in a stainless steel container at a temperature of water inside the
container controlled to 95.degree. C. for 8 hours, dehydrated and dried,
the oligomer content of the square plate was 0.35% by weight. When this
oligomer content was taken as W.sub.1, W.sub.0 -W.sub.1 was 0.16% by
weight.
COMPARATIVE EXAMPLE 13
Comparative Example 12 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.78 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.28% by weight was used
instead.
Results obtained are shown in Table 2.
COMPARATIVE EXAMPLE 14
Comparative Example 12 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.29% by weight was used
instead. In this example, the acetaldehyde concentration of the square
plate was 14 ppm.
Other results obtained are shown in Table 2.
COMPARATIVE EXAMPLE 15
Comparative Example 12 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.82 dl/g, a density of
1.40 g/cm.sup.3 and the oligomer content of 0.39% by weight was used
instead.
Results obtained are shown in Table 2.
EXAMPLE 34
Example 25 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.79 dl/g, a density of 1.40 g/cm.sup.3
and the oligomer content of 0.29% by weight was used and the particulate
was kept in an atomosphere of 90% relative humidity at a temperature of
40.degree. C. for 7 days.
TABLE 2
______________________________________
Oligomer content of
starting material
Oligomer content of
after hot water
starting material
treatment W.sub.0 /W.sub.1
W.sub.0 (wt %)
W.sub.1 (wt %)
(wt %)
______________________________________
Example 25
0.35 0.34 0.01
Example 26
0.29 0.28 0.01
Example 27
0.40 0.34 0.06
Example 28
0.37 0.34 0.03
Example 29
0.40 0.33 0.07
Example 30
0.34 0.33 0.01
Example 31
0.37 0.34 0.03
Example 32
0.34 0.32 0.02
Example 33
0.41 0.39 0.02
Comparative
0.51 0.35 0.16
Example 12
Comparative
0.46 0.29 0.17
Example 13
Comparative
0.49 0.33 0.16
Example 14
Comparative
0.53 0.40 0.14
Example 15
Example 34
0.31 0.29 0.02
______________________________________
EXAMPLE 35
In a stainless steel container, 5 kg of particulate polyethylene
terephthalate having an intrinsic viscosity of 0.80 dl/g, a density of
1.40 g/cm.sup.3 and the acetaldehyde content of 0.8 ppm was immersed in
6.5 kg of distilled water. The stainless steel container charged with the
polyethylene terephthalate and distilled water was heated externally, the
temperature inside the container was controlled to 95.degree. C. and the
container was maintained at this state for 4 hours to carry out hot water
treatment of said polyethylene terephthalate. The polyethylene
terephthalate thus treated was dehydrated and dried to obtain the
polyethylene terephthalate of the present invention.
The polyethylene terephthalate thus treated was dried and then molded at a
cylinder temperature of 290.degree. C. into a square plate. The
acetaldehyde content of the square plate was 7.2 ppm. This value is taken
as W.sub.0.
Subsequently, this particulate polyethylene terephthalate was subjected at
the temperature of 95.degree. C. for 8 hours to hot water treatment,
dehydrated and dried, and then molded at a cylinder temperature of
290.degree. C. into a square plate. The acetaldehyde content of the square
plate was 6.0 ppm. This value is taken as W.sub.1.
W.sub.0 -W.sub.1 was 1.2 ppm.
EXAMPLE 36
Example 35 was repeated except that the water treatment was conducted at a
temperature of 55.degree. C. for 4 hours.
W.sub.0 was 9.0 ppm and W.sub.1 was 6.2 ppm and accordingly W.sub.0
-W.sub.1 was 2.8 ppm.
EXAMPLE 37
Example 35 was repeated except that the water treatment was conducted at a
temperature of 55.degree. C. for 2 hours.
W.sub.0 was 10.2 ppm and W.sub.1 was 6.5 ppm and accordingly W.sub.0
-W.sub.1 was 3.7 ppm.
EXAMPLE 38
Example 35 was repeated except that particulate polyethylene terephthalate
having an intrinsic viscosity of 0.78 dl/g, a density of 1.40 g/cm.sup.3
and the acetaldehyde content of 0.6 ppm was used instead.
W.sub.0 was 7.5 ppm and W.sub.1 was 6.0 ppm and accordingly W.sub.0
-W.sub.1 was 1.5 ppm.
EXAMPLE 39
A stainless steel container was charged with 5 kg of the same polyethylene
terephthalate as used in Example 35, and water vapor of 100.degree. C. was
passed therethrough at a rate of 0.5 kg/hr for 2 hours.
The polyethylene terephthalate thus treated was dried and then molded into
a square plate as in Example 35.
W.sub.0 was 10.0 ppm and W.sub.1 was 6.5 ppm and accordingly W.sub.0
-W.sub.1 was 3.5 ppm.
EXAMPLE 40
The particulate polyethylene terephthalate as used in Example 35 was kept
in an atomosphere of relative humidity of 90% at a temperature of
40.degree. C. for 7 days.
The polyethylene terephthalate thus treated was dried and molded into a
square plate as in Example 35.
W.sub.0 was 8.6 ppm and W.sub.1 and 6.0 ppm and accordingly W.sub.0
-W.sub.1 was 2.6 ppm.
COMPARATIVE EXAMPLE 16
The particulate polyethylene terephthalate used in Example 35 without
subjecting to hot water treatment was molded at a cylinder temperature of
290.degree. C. into a square plate. The acetaldehyde content of the square
plate was 15 ppm. This value is taken as W.sub.0.
The particulate polyethylene terephthalate was subjected at the temperature
of 95.degree. C. for 8 hours to hot water treatment, dehydrated and dried,
and then molded at a cylinder temperature of 290.degree. C. into a square
plate. The acetaldehyde content of the square plate was 6.5 ppm. This
value is taken as W.sub.1.
W.sub.0 -W.sub.1 was 8.5 ppm.
COMPARATIVE EXAMPLE 17
Comparative Example 16 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.78 dl/g, a density of
1.40 g/cm.sup.3 and the acetaldehyde content of 0.6 ppm was used instead.
W.sub.0 was 14.2 ppm and W.sub.1 was 6.0 ppm and accordingly W.sub.0
-W.sub.1 was 8.2 ppm.
COMPARATIVE EXAMPLE 18
Comparative Example 16 was repeated except that particulate polyethylene
terephthalate having an intrinsic viscosity of 0.82 dl/g, a density of
1.40 g/cm.sup.3 and the acetaldehyde content of 0.8 ppm was used instead.
W.sub.0 was 14.0 ppm and W.sub.1 was 7.0 ppm and accordingly W.sub.0
-W.sub.1 was 7.0 ppm.
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