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| United States Patent |
5,196,474
|
|
Wilson
, et al.
|
March 23, 1993
|
Polymer composition for use as flexible, dimensionally stable coating;
and method
Abstract
A curable polymer composition for use in providing a dimensionally stable
coating comprises a semi-interpenetrating polymer network. The
semi-interpenetrating polymer network includes a reactive polymer
component, cross-linking agent, and non-reactive polymer component. The
non-reactive polymer component has a molecular weight of about
7,000-30,000, and preferably about 15,000. In preferred embodiments, the
reactive polymer has a molecular weight of about 30,000-200,000, and
preferably about 40,000-60,000. Spacecoat compositions made with
formulations described, exhibit good long-term stability, and resistance
to failure upon embossing of a substrate to which the retroreflective
sheeting is applied.
| Inventors:
|
Wilson; Bruce B. (St. Paul, MN);
Grunzinger; Raymond E. (St. Paul, MN)
|
| Assignee:
|
Minnesota Mining and Manufacturing Company (Saint Paul, MN)
|
| Appl. No.:
|
640231 |
| Filed:
|
January 11, 1991 |
| Intern'l Class: |
C08J 003/18; C08K 005/12; C08L 031/00 |
| Field of Search: |
524/502,507,513,538,539
|
References Cited
U.S. Patent Documents
| 2407680 | Sep., 1946 | Palmquist et al. | 88/32.
|
| 3795435 | Mar., 1974 | Schwab | 350/105.
|
| 4569857 | Feb., 1986 | Tung et al. | 427/163.
|
| 4648932 | Mar., 1987 | Bailey | 156/276.
|
| 4664966 | May., 1987 | Bailey et al. | 428/203.
|
| 4725494 | Feb., 1988 | Belisle et al. | 428/325.
|
| 4983436 | Jan., 1991 | Bailey et al. | 428/40.
|
| Foreign Patent Documents |
| 454227 | Feb., 1971 | AU.
| |
Other References
J. W. Barlow and D. R. Paul, "Polymer Blends and Alloys-A Review of
Selected Considerations", Polymer Engineering and Science, Oct. 1981, vol.
21, No. 15.
L. H. Sperling, "Interpenetrating Polymer Networks and Related Materials",
Plenum Press, New York and London, 1981, pp. 1-10.
D. A. Thomas and L. H. Sperling, "Interpenetrating Polymer Networks",
Polymer Blends, Paul, D. R. and Newman, S. (ed), Ch. 11, vol. 2, 1978, pp.
2-33.
H. I. Frisch, "Tangled Polymers," Chemtech, Mar. 1977, pp. 188-191.
|
Primary Examiner: Michl; Paul R.
Assistant Examiner: Rajguru; U. K.
Attorney, Agent or Firm: Little; Douglas B., Kirn; Walter N., Griswold; Gary L.
Parent Case Text
This is a division of application Ser. No. 07/239,950 filed Sep. 2, 1988
now U.S. Pat. No. 5,008,142.
Claims
What is claimed and desired to be secured by Letters Patent is as follows:
1. A curable composition useful in preparing a semi-interpenetrating
polymer network; said composition comprising a mixture of:
(a) a reactive polymer component selected from the group consisting of
polyesters, polyethers, polyamides, and polyurethanes and having a weight
amperage molecular weight of about 30,000 to 200,000 and a hydroxyl number
of 100-200; and
(b) a non-reactive polymer component having a weight average molecular
weight of between about 7,000 and about 30,000; said non-reactive polymer
component being at least 40% extractable upon cure of said composition.
2. A composition according to claim 1 wherein said non-reactive polymer
component is a plasticizer.
3. A composition according to claim 1 including a cross-linking agent which
is at least di-functional and comprises an aminoplast resin.
4. A composition according to claim 3 wherein the cross-linking agent is a
methoxymethylated melamine.
5. A composition according to claim 1 wherein said reactive polymer
component is selected from the group consisting of: polyvinyl acetals;
acrylic copolymers, polyurethanes; polyesters; polyamides;
polyester-amides and mixtures thereof.
6. A composition according to claim 5 wherein said reactive polymer is a
polyvinyl butyral material.
7. A composition according to claim 1 wherein said non-reactive polymer
component includes no more than about 10 sites of cross-linkable
functionality per 15,000 weight average molecular weight of non-reactive
polymer component.
8. A composition according to claim 7 wherein said non-reactive polymer
component is a polycaprolactone material.
9. A composition according to claim 1 including:
(a) about 55-95%, by weight, reactive polymer component; and
(b) about 5-25%, by weight, non-reactive polymer component.
10. A composition according to claim 9 including about 5-15%, by weight,
cross-linking agent which is at least di-functional with respect to
reaction with said cross-linkable polymer.
11. A composition according to claim 10 wherein said cross-linking agent is
selected from the group consisting of: aminoplast resins; aziridines;
epoxy resins; isocyanates; aldehydes; azlactones and mixtures thereof.
12. A flexible, cured resin; said resin comprising a semi-interpenetrating
polymer network which is a heat-cured reaction product of:
(a) a reactive polymer component selected from the group consisting of
polyesters, polyethers, polyamides and polyurethanes and having a weight
average molecular weight of about 30,000 to 200,000;
(b) a cross-linking agent which is at least di-functional with respect to
reaction with said reactive polymer component; and
(c) a non-reactive polymer component, at least 40% of which is extractable
from the resin, having a weight average molecular weight of between about
7,000 and 30,000.
13. A resin according to claim 12 wherein said reactive polymer component
is a polymer material having a hydroxyl number of 100-200.
14. A resin according to claim 13 wherein said reacive polymer component is
polyvinyl butyral polymer.
15. A resin according to claim 12 wherein said non-reactive polymer
includes no more than about 10 sites of cross-linkable functionality per
15,000 weight average molecular weight of non-reactive polymer.
16. A resin according to claim 15 wherein said non-reactive polymer
component is polycaproplactone polymer.
17. A resin according to claim 12 wherein said cross-linking agent si
selected from the group consisting of: aminoplast resin; aziridines; epoxy
resins; isocyanates, aldehydes; azlactones and mixtures thereof.
Description
Field of the Invention
The present invention concern polymer compositions, and in particular,
polymer compositions usable in applications wherein dimensional stability
is important. The compositions of the present invention are particularly
well-suited for use as spacecoat material in retroreflective sheeting or
the like. More specifically the invention concerns polymer coatings usable
as a spacecoat between reflector and lens in an enclosed lenses
retroreflective sheeting application.
BACKGROUND OF THE INVENTION
Enclosed lens retroreflective sheeting generally comprises reflective
sheeting having a polymer matrix thereon, with glass beads embedded in the
matrix. A mirror or reflective surface, generally formed from a metallic
vapor coat or the like, is formed on a back side of the polymer/bead
composite. In typical operation, light passes through the beads, which
individually act as lenses focusing the light and directing same against
the mirror surface. The light is then reflected back through the beads,
and toward the source. Typically, the mirror surface is separated from the
glass beads by a spacing layer coat or spacecoat, which provides for s
preferred focal length between the beads and the reflective surface. It is
noted that one reason such embedded lens arrangement are useful, is that
incident light rays are focused onto the reflective layer irrespective of
whether the front of the sheeting is wet or dry.
The elements of the typical enclosed or embedded lens retroreflective
sheeting are: lens arrangement (beads imbedded in polymer), spacing layer
(spacecoat), and reflector surface (vapor coat); The sheeting may include
other elements such as an outer protective layer, and/or an adhesive layer
for mounting. Herein the term "spacecoat" is means to generally refer to
the resin which provides for a separation between the embedded lenses and
the reflective coat, regardless of the process of formation. The end
product will generally be referred to as an enclosed (or embedded) lens
retroreflective sheeting, again regardless of the process of its
formation.
In a typical application, the reflective surface is formed as a layer
having a plurality of cupped or concentrically coated portions or concave
portions, one each of which is in association with each bead or embedded
lens. The concentrically coated portions facilitate a desired reflection
of light which has passed through the lenses, regardless of the direction
from which the light initially impinges onto the sheeting. In part, the
cupped construction of the mirrored surface ensures that much of the light
reflected by the retroreflective surface is directed back toward the
source.
Enclosed lens retroreflective sheeting and the use of glass beads to
provide for reflex light reflectors are described in Palmquist et al., No.
2,407,680; May, No. 4,626,127; Tung et al., No. 4,367,920; Tung et al.,
No. 4,511,210; and, Tung et al., No. 4,569,857; these references being
incorporated herein by reference.
From the above, it will be apparent that the nature of the spacecoat is
very important. In particular, the spacecoat must be of a material than
can be precisely applied, and which will be dimensionally stable in use.
By "precisely applied" it is meant that application with precise control
of thickness and conformation to the beads is obtainable. By
"dimensionally stable" it is meant that the spacecoat should be
sufficiently strong and durable (i.e. stable) over time, to maintain
proper spacing and relative orientation between the individual glass
beads, and the cup-shaped reflective surface. Any substantial deformation
of the spacecoat, will lead to significant reduction in reflective ability
(or power) of the retroreflective material.
In a typical application, enclosed lens retroreflective sheeting is applied
to a substrate, such as wood, plastic, or metal, typically used to form a
highway sign, license plate, or safety sign. Retroreflective material,
when so applied, makes the objects formed from the substrate more
conspicuous at night.
In some instances, it is desired to emboss a substrate having a
retroreflective surface thereon. For example, a sheet of metal license
plate material having a reflective surface thereon may be embossed to
provide for conspicuity. Typically, the embossed letters or numbers are
painted or otherwise colored to provide for greater contrast with
reflective background. In some instances the colored symbols may be
covered by an outer layer of a transparent thermosetting polymeric resin.
If the spacecoat is not substantially dimensionally stable, significant
loss of reflective ability will occur as a result of the embossing. Also,
exterior durability will diminish. That is, the spacecoat will tend to
crack, wrinkle, split, fracture or peel, along points of a stress
associated with the embossing. It is noted that the same would be likely
for any substantial bending of the substrate, not merely for embossing.
Past polymeric compositions used for spacecoats have been less than
completely acceptable with respect to this dimensional stability. That is,
substantial distortion of the reflective surface readily occurs,
especially if embossing or the like is conducted on the coated substrate.
This has led to substantial loss of reflective power for the
retroreflective surface. Further, cracks or splits associated with the
embossing have formed sites at which deterioration of the retroreflective
surface can begin to occur, leading to a shorter product lifetime than
desirable. What has been needed has been a polymer composition which
provides for relatively high dimensional stability of the spacecoat.
It will be readily understood that a polymer composition which provides for
the above related characteristics when used as a cured spacecoat would
probably have utility in other, non-embedded lens, applications wherein
dimensional stability is important.
SUMMARY OF THE INVENTION
According to the present invention, a preferred polymer composition is
provided for use in applications wherein long term dimensional stability
and ability to withstand lateral stress are important. In particular, the
composition is well suited for use as a spacecoat, in an enclosed lens
retroreflective sheeting application.
Polymer compositions according to the present invention are generally
semi-interpenetrating polymer network (semi-IPN) systems, when cured. A
semi-IPN composition enables the coating to endure non-linear stress
without substantial fracture, while also providing appropriate dimensional
stability for long term brightness retention.
As previously suggested, spacecoats should exhibit sufficient optical
clarity (transmission) for operation. The specific level of acceptable
transmission will depend in part upon application. Typically at least
about 80% transmission, as measured by the method of ASTM D-1003, is
preferred for application in license plate and highway sign coatings. Some
typical components for use in semi-IPN's usable to obtain such a level of
transmission are described in the experiments below.
Preferred compositions according to the invention include a reactive
component in association with a cross-linking agent. Preferably the
combination is one that can be readily, selectively, and substantially
(e.g. >90%) cured, in relatively little time. In this manner, dimensional
stability of the "spacecoat" is facilitated.
Inter-penetrating polymer networks (IPN's) are mixtures of two or more
distinct polymer phases that cannot be completely physically separated.
Semi-IPN's are polymer blends in which only one of the polymer components
is substantially reacted or cross-linked. See, for example, Barlow, J.W.,
et al., "Polymer Blends and Alloys - A Review of Selected Considerations",
Polymer Eng. and Science, Vol. 21, No. 15 p. 985-996 Oct. 1981); "Tangled
Polymers", CHEMTECH, Mar. 1977 (p. 188-191); anc, Polymer Blends Vol. 2,
E. by D.R. Paul and S. Newman, Academic Press, Inc. (1978); these
references being incorporated herein by reference.
Semi-IPN's usable according to the present invention, include: the
substantially cross-linked or reactive polymer (cross-linked by the
cross-linking agent); and, substantially non-cross-linked or non-reactive
polymer, wherein the molecular weight of the reactive polymer is
preferably within the range of 30,000 to 200,000 (weight average molecular
weight), and wherein the non-reactive polymer is substantially
extractable, i.e. is at least 40% extractable, from the cured composition.
For such compositions, the non-reactive polymer is preferably of a
structure allowing it to effectively plasticize the cured, reactive
polymer. That is, the presence of the non-reactive, extractable,
plasticizing polymer leads to a blend which, although dimensionally
stable, can sufficiently deform so as to accommodate embossing or similar
stresses to the substrate on which the retroreflective sheeting is
applied. Preferably, the reactive polymer provides for a substantial
cross-link density, in order to facilitate dimensional stability.
Herein the term "non-reactive polymer" and variants thereof is meant to
refer to material which, when the semi-IPN is formed, is still
substantially (>40%) extractable therefrom. That is, the non-reactive
polymer does not substantially react with the cross-linking agent. The
term "reactive polymer" and variants thereof is meant to refer to the
cross-linked component, not substantially extractable upon cure.
It is important to obtain relatively rapid, substantially complete, cure of
the reactive polymer, during initial stages of construction of a
retroreflective sheeting surface in accordance with the present invention.
A reason for this is that if cure is not substantially complete before the
reflective layer is applied, but rather cure continues to run after the
reflective layer is applied, distortion of the spacecoat, resulting from
the cross-linking reaction and leading to loss of reflective ability, may
occur. Also, slow cure leads to inefficiencies during production.
In preferred applications, the non-reactive polymer is a polymer component
having a weight average molecular weight of about 7,000-30,000, and
preferably about 15,000. Most preferably, the non-reactive polymer
component has relatively little functionality associated therewith, that
can be involved in the cross-linking reactions. Typically, this requires a
cross-linkable functionality for the non-reacting polymer of no greater
than about 2-10 per 15,000 weight average molecular weight of polymer.
Typical non-reacting polymers for use in compositions according to the
present invention include: polyesters, polyethers, polyamides,
polyurethanes and some polymers of ethylenically unsaturated monomers.
Preferred polymers are polyesters, and preferred polyesters include
polycarolactones (typically hydroxy terminated), and polymers derived from
2,9- and 3,10-bis(hydroxymethyl)tricyclo[5.3.2.sup.6,8 . 0.sup.1,8
]-decane (such as available under the tradename Huls LTW, from Huls
America, Piscataway, N.J. 08855). Mixtures of materials may be used as the
non-reactive polymer or polymer component.
As used herein, the term "weight average molecular weight" shall be
understood as referring to molecular weight as determined by conventional
gel pretreating chromatography (gpc) methods. Further, when referring to
polymer material, the term "molecular weight" as used herein shall be
understood as referring to weight average molecular weight.
Preferably the reacting or reactive polymer is a cross-linkable polymer
component capable of substantial, relatively rapid cross-linking. Typical
reactive polymers usable in compositions according to the present
invention include: polyvinylacetals such as polyvinyl formal and
polyvinylbutyral; acrylic copolymers; polyurethanes; polyesters;
polyamides, polyester-amides and acrylic block and graft copolymers.
Mixtures of materials may be used as the reactive polymer or polymer
component. A preferred reactive polymer material is a polyvinylbutyral
resin having a molecular weight (weight average) of about 45,000-55,000.
Two such materials are available under the tradename Butvar.RTM., from
Monsanto Polymer Products Co., St. Louis, MO, 63167, as Butvar.RTM. B-76
and Butvar.RTM. B-90. It is noted that while the preferred materials
listed are hydroxyfunctional, other functional groups for cross-linking
may be used.
A variety of cross-linkers, or cross-linking polymers, may be utilized in
association with polymer compositions according to the present invention.
In general, what is required is at least a di-functional material,
exhibiting useful properties for relatively low temperature curing
applications. Mixtures of materials may be used as the cross-linker.
Preferably, the cross-linker is one which reacts relatively rapidly, to
lead to substantially complete cure in relatively little time. It is
preferred, though not required, that the cross-linker be one which can
react at an appreciable rate in the presence of little or no catalyst.
Typical cross-linkers usable in compositions according to the present
invention include: aminoplast resins such as: urea-formaldehyde resins;
melamine-formaldehyde resins; glycouril-formaldehyde adducts; and, acrylic
copolymers containing etherified adducts of the reaction product of
acrylamide and formaldehyde. Cross-linkers could also include:
polyfunctional aziridines; epoxy resins; isocyanates; aldehydes;
azlactones and/or any other polyfunctional material whose functional
groups are reactive with the functional groups of the reactive polymer.
Preferred cross-linkers are methoxymelamine resins, such as for example,
Resimene.RTM. 717 and 730, Monsanto Co., St. Louis, MO, 63167.
The drawings constitute a part of the specification, and include exemplary
embodiments of the invention. In some instances, relative material
thicknesses and component sizes may be shown exaggerated, to facilitate an
understanding of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a license plate having an enclosed lens
retroreflective coating thereon, according to the present invention.
FIG. 2 is a side elevational view of the license plate shown in FIG. 1.
FIG. 3 is an enlarged fragmentary side cross-sectional view taken generally
along line 3--3, FIG. 1.
FIG. 4 is an enlarged, fragmentary, cross-sectional view of a portion of
substrate having an embedded lens retroreflective coating thereon.
DETAILED DESCRIPTION OF THE INVENTION
The present invention concerns a polymer blend usable for example as a
preferred spacecoat to form an embedded or enclosed lens retroreflective
sheet for a substrate. Such coated substrates, for example, can be
fabricated into license plates or the like. In the embodiment described,
the substrate comprises a metal sheet, for example, a metal license plate
blank. However, polymer blends according to the present invention may be
utilized in any of a variety of applications, especially including those
wherein good dimensional stability of the cured polymer and capability of
accommodating bending or embossing of the substrate, are required. While
the invention broadly concerns a preferred polymer blend, usable in many
applications, a particular application with respect to a license plate
will be described in detail, in order to facilitate an understanding of
the need for a composition having the physical and chemical
characteristics of preferred compositions according to the present
invention.
Application of the Invention to a License Plate
The reference numeral 1, FIG. 1, generally designates a license plate
having a retroreflective coating, including a spacecoat according to the
present invention thereon. The license plate 1 generally comprises a metal
substrate 3, formed from aluminum or the like, having characters 4
embossed therein. The characters 4 are generally embossed such that they
are raised, i.e. project outwardly, from surface 5 of license plate 1;
that is, they project toward the viewer. This will be better understood by
reference to FIG. 2. Typical, conventional, embossed license plates carry
characters thereon which are embossed, relative to the remainder of
substrate 3, a total of at least about 60-80 mils (0.15-0.20 cm). It is
noted that license plate 1 includes an outer border 6 debossed away from
the viewer, FIG. 1. Although the present invention is primarily described
with respect to applications concerned with embossed letters, it will be
understood that similar concerns and problems are involved with debossed
symbols are involved.
In general, it is desirable that at least portions of surface 5 be
substantially reflective, so that the license plate 1 will be very
conspicuous, even at night and when viewed from a considerable distance.
In general it is desirable to provide a license plate 1 which is very
strongly retroreflective, so that it can be seen from a considerable
distance, with only a small amount of light directed thereon. Further, an
embedded lens arrangement is useful at least in part because good
reflection is obtained under both wet and dry conditions.
In general, what is needed is a retroreflective sheeting at surface 5 of
license plate 1. A commonly used type of such a sheeting is an enclosed
lens retroreflective sheeting, which can be readily applied to, or
laminated on, surface 5. Such sheeting is well-known, and one is generally
represented, schematically, in cross-section in FIG. 4.
Referring to FIG. 4, substrate 3 is depicted as having sheeting 10 applied
thereto. The sheeting 10 comprises a plurality of materials. In
particular, sheeting 10 includes an outer protective coating (top layer)
14, a resin layer 15 including a monolayer of beads (lenses) 16 therein,
spacecoat 10, reflective surface 19 and an adhesive layer 20.
Still referring to FIG. 4, typical operation of enclosed lens sheeting 10
will be understood. Light, for example, may enter sheeting 10 along the
direction indicated by paths 25. As the light passes through any given
lens 16, it is focused thereby, onto reflective surface 19. The light is
then reflected off of surface 19, back through beads 16, and outwardly
from sheeting 10. Thus, beads 16 generally act as lenses. While the beads
16 in FIG. 4 are all shown of about the same size, there is no requirement
that they be so.
The reflective surface 19 includes a plurality of recesses, cavities or
cups 30 therein, each cup 30 being centered with respect to an associated
bead 16. The cups 30 are preferably spherical in curvature, so that a
relatively constant distance between reflective surface 19, and any
associated bead 16, is maintained. That is, the cups 30 collectively
define a "concentric" or "concentrically applied" coating. With such a
preferred curvature, and a selected distance of separation between each
bead 16 and its associated cup 30, a high degree or power of reflection
can be obtained. In general, a preferred, constant, distance is maintained
between the center of each bead 16 and its associated cup 30 in the
reflective surface 19. For preferred applications, the distance between
the outer surface of each bead 16 and its associated cup 30 is between
about 0.2 and 0.6, and preferably about 0.4, times the radius of the beads
16. Typically the beads 16 have a radius of about 20-100 micrometers.
Beads or lenses having a refractive index of about 2.2-2.3 are typically
used in embedded lens arrangements.
Maintenance of a selected distance for any given application is important,
as the distance provides for appropriate focusing between the lenses (i.e.
The beads or spheres 16) and the reflective surface 19. Thus, the light is
readily focused, and a high degree or power of reflection of that light
occurs.
The spacecoat 18, then, provides for numerous important characteristics.
First, the spacecoat 18 generally comprises a resin surface providing for
and maintaining selected orientation between spheres 16 and associated
cups 30. That is, spacecoat 18 maintains the selected necessary, and
constant, spacing. Further, reflective surface 19 is typically a
reflective metal surface prepared by vapor deposition of metal onto a
plurality of convex bumps formed in spacecoat 18 during a process of
manufacture of sheeting 10.
The dimensional stability of cured spacecoat 18 is very important. If the
spacecoat 18 changes conformation, after manufacture, the reflective power
of sheeting 10 will decrease. For example, if spacecoat 18 is not
sufficiently stable, the cupping may change, and the reflective surface 19
may wrinkle or buckle. Any of these deformations can damage sheeting 10
such that its reflective power is lessened.
It is also important that spacecoat 18 be stable with respect to further
chemical reaction. Generally, spacecoat 18 is formed from cured polymeric
resin. If cure is not substantially complete during early stages
manufacture, i.e. before application of the reflective coat or surface 19
and cure is not readily controllable, a continued, slow, curing may take
place after reflective surface 19 is applied. Should cure continue even
after the reflective surface 19 is applied to the spacecoat 18, the result
may be a substantial loss of reflective power due to cnange in
conformation of the spacecoat during the further cure. In particular, as
the resin material cures, it often changes in volume. Once the reflective
surface 19 is applied to spacecoat 18, should the spacecoat 18 continue to
change volume (i.e. continue to cure), the reflective surface 19 may
contract and crack, again with the result being a loss in reflective power
of sheeting 10. From this, it will be understood that generally it is
preferred to provide a resin for spacecoat 18 which is not only
dimensionally stable, but which is substantially completely cured within a
relatively short period of time during manufacture, so that the likelihood
of substantial continued curing taking place after the reflective surface
19 is applied is minimal, and/or production is not delayed. From these
stated requirements, it will be apparent that in many ways it is desirable
to have a spacecoat which is heavily cross-linked (has a high cross-link
density) and is relatively rigid and inflexible, once cured. Indeed, in
some applications, such spacecoats function well. However, in applications
such as for license plates, deformation of the substrate 3, from the
planar, after application of sheeting 10, is commonly required. For
example, when characters 4 are embossed into substrate 3, the sheeting 10
in the area of the embossed characters 4, is deformed, or bent,
considerably. If the spacecoat 18 is of relatively rigid, highly
cross-linked material, it will fracture, crack or split under stress, and
will not deform with the substrate bends used in forming the embossed
characters 4. This will lead to loss of reflective power. Also, such
splitting or cracking may lead to weak portions of sheeting 10, and
eventual premature peeling of portions of sheeting 10 from license plate
1. It is noted that such fracturing, cracking or splitting is most likely
to occur where bends are the greatest, and stress on spacecoat 18 is
maximal.
In order to accommodate a substrate 3 which is deformed during use, it is
desirable that the spacecoat 18 be formed from a resin capable of
substantial dimensional stability, but which at the same time has an
appropriate tensile strength and elongation, low glass transition
temperature, and similar physical characteristics so that it can be
readily applied and deformed without fracture, shear, crack, peel or
similar problems. It would be most desirable to have a spacecoat usable
such that when sheeting 10 is deformed, substantial loss of reflective
power, at most, only occurs in the reflective surface 19 at the most
extreme bends or deformations. That is, very little reflective power is
lost, even in the vicinity of the sheeting adjacent the deformation, bend,
embossed character, etc.
To achieve the above characteristics in a spacecoat, according to the
present invention a polymer blend is used as the spacecoat 18. More
specifically, a semi-inter-penetrating polymer network (semi-IPN) is
provided. Such a network includes a highly cross-linked or reactive
polymer component, which provides much of the dimensional stability of the
resin or network. The reactive component is generally linked, by means of
a conventional cross-linking agent or cross-linker. Preferably a
relatively reactive cross-linker is used, so that nearly complete cure
rapidly occurs. Herein the highly cross-linked component will be referred
to as formed from a "reactive" or "reacting" polymer or resin component.
The other major component of the semi-IPN is a "non-cross-linked",
"non-reacting" or "non-reacted" polymer. That is, the second polymer
component, while it is somewhat trapped within the overall polymer
network, is not substantially cross-linked with the first polymer
component. Further, the second polymer is not substantially cross-linked
with itself. In general, the non-reacting polymer is substantially
extractable, i.e. is at least 40% extractable, from the cured polymer as
defined below.
It will be understood that mixtures of material can be utilized as the
reactive component, the cross-linking agent and/or the non-reactive
component. In general, all that is required is overall characteristics of
the components as described.
Preferred resin compositions for use in spacecoats according to the present
invention include the following: a first polymer component comprising a
reactive polymer; and, a second polymer component which is substantially
non-reactive, extractable from the cured resin up to at least 40%, and
which has a weight average molecular weight within the range 7,000 to
30,000. In use, compositions according to the present invention will also
include a cross-linking agent, or cross-linker, as described in further
detail below.
Referring to each of the components individually:
The Reactive Polymer
As previously suggested, desired characteristics of the reactive polymer
include that: it can be cross-linked in the presence of the non-reactive
polymer; it is capable of providing for high dimensional stability; and it
can be readily applied as a coating, with ability to control, very
precisely, the thickness of the coating and the conformation of the
coating. A mixture may be used as the cross-linkable polymer.
Preferred reactive polymers have a weight average molecular weight between
about 30,000 and 200,000, and preferably about 40,000-60,000. A relatively
high degree of cross-linkable functionality, typically hydroxy
functionality, in order to provide for substantial cross-linking, is
preferred. A hydroxyl number of 100-200 as defined by ASTM standard
D-1396, has been found for at least two useful reactive polymers,
Butvar.RTM. B-76 and Butvar.RTM. B-90, described below.
Typical polymers which include appropriately reactive hydroxy moieties
include polymers, or copolymers, which include polyvinylacetals and/or
polyesters.
A list of useful materials for the reactive polymer was provided in the
SUMMARY above. A particular, preferred, class of materials usable as the
reactive polymer, comprises polyvinyl acetal resins. Within the molecular
weight range stated above, such materials are easily handled, as they are
powders at STP (Standard Temperature and Pressure). One useful,
commercially available, class of polyvinyl acetal resins (more
specifically polyvinyl butyral resins) is sold under the mark Butvar.RTM.
(Monsanto, St. Louis, MO, 63167). A particularly useful Butvar.RTM.
material is B-76, which has a weight average molecular weight of about
45,000-55,000, and a hydroxy content, expressed as percent polyvinyl
alcohol, of about 9.0-13.0%. Butvar.RTM. B-76 is a random polymer
containing the elements of vinyl alcohol, vinyl butyral and vinyl acetate.
Another useful material is Butvar.RTM. B-90, a polymer containing the same
elements and which has a weight average molecular weight of 38,000-45,000,
and a polyvinyl alcohol content of 18-20%.
The Cross-Linking Agent
A variety of cross-linking agents may be utilized with reactive polymers,
in compositions according to the present invention. In general, what is
required is a cross-linking agent which will readily react with the
reactive moieties of the cross-linking polymer, and which will provide for
a substantial amount of cross-linking, i.e. is at least di-functional with
the desired physical characteristics of the final composition. A
cross-linking agent which can react at relatively low temperatures, on the
order of 200.degree. F. to 300.degree. F. (93.degree.-149.degree. C.) is
preferred. Further, for many applications it is preferred to use an agent
which does not substantially react at room temperature. In this manner, a
storage stable composition may be prepared with the cross-linking agent
therein.
It is further desirable that the cross-linking agent be such that reaction
with the reactive polymer can be efficiently carried to substantial
completion. By "completion" as used in this context, it is meant that
polymer cure to a stage whereat relatively little further reaction causing
change in volume or conformation will occur. That is, a hard, cured,
dimensionally stable coat is obtained. A reason for this, as suggested
above, is to ensure that after the reflective layer is applied to the
spacecoat, the spacecoat will not substantially shrink or otherwise deform
due to further cross-linking reaction therein.
Preferably, the reactive polymer is provided in substantial excess relative
to the cross-linker or cross-linking agent. Typically, at least about 10%
excess equivalents of the reactive functionality on the reactive polymer
to functional sites on the cross-linking agent should be used. This helps
ensure substantially complete reaction in relatively little time.
The cross-linking agents (or cross-linkers) which exhibit the above,
preferred, qualities include: aminoplast resins such as urea-formaldehyde
resins; melamine formaldehyde; glycouril formaldehyde adducts; and,
acrylic copolymers containing etherified adducts of the reaction product
of acrylamide and formaldehyde. Cross-linkers can also include:
polyfunctional aziridines; epoxy resins; isocyanates; aldehydes;
azlactones and/or any other polyfunctional material whose functional
groups are reactive with the functional groups of the reactive polymer.
Methoxymelamine resins perform particularly well.
Two commercially available methoxymelamine resins, usable as cross-linking
agents in compositions according to the present invention, are
Resimene.RTM. 717 and Resimene.RTM. 730 (Monsanto Co., St. Louis, MO,
63167). Resimene.RTM. 717 is a high solids methylated melamine
cross-linking resin which can exhibit uncatalyzed curing at as low as 250
degrees Fahrenheit (121.degree. C.), and catalyzed curing at as low as 200
degrees Fahrenheit (93.degree. C.). High cross-linking efficiency is
exhibited by this compound. It is compatible with a great many solvents,
including ketones, esters, alcohols, glycol ethers and aromatic
hydrocarbons, and it has some limited compatibility with aliphatic
hydrocarbon solvents. It is noted that Resimene.RTM. 717 (in its monomeric
form) is tri-functional, i.e. it includes three reactive sites for
cross-linking. Further, the relatively short ether groups in Resimene.RTM.
717 (methyl groups) help provide for a relatively rapidly acting
cross-linking agent. Mixtures of materials may be used as the
cross-linker.
The Non-Reactive Polymer
The non-reactive polymer is generally relatively low in functionality, with
respect to the cross-linking agent, so it is not substantially chemically
incorporated into the cross-linked resin. It is preferred that the
non-reactive polymer included in the final polymer composition be such
that it can be extracted from the cured polymer, at least about 40%, and
preferably above about 70%. Further, it is preferred that the non-reactive
polymer be such as will provide a plasticizing effect to the overall cured
polymer. Mixtures of materials may be used as the non-reactive polymer or
polymer component. Each material of the mixture, however, should
independently satisfy the requirements for the non-reactive polymer.
It has been observed that those compositions which were made according to
the experimentals listed below and which exhibited utility generally
appeared to show some discontinuity, i.e. The non-reactive polymer
appeared to at least partially form suspended crystal, in the reactive
polymer.
Preferred non-reactive polymers are polycaprolactones. It has been observed
that with such compounds, in the preferred molecular weight range, there
is relatively little chemical incorporation of the non-reactive polymer
into the polymer network, by reaction with the cross-linker, and the
non-reacting material is readily extractable from the cured polymer.
As indicated by the following examples, it has been observed that the
non-reactive polymer must, in general, have a molecular weight (weight
average) of about 7,000-30,000, in order to be effective in compositions
according to the present invention. Preferred polycaprolactones are those
having a molecular weight of about 12,000-18,000, and most preferably
about 15,000.
With respect to the molecular weight range, as the following examples
indicate, relatively low molecular weight non-reactive agent
(polycaprolactones), on the order of 3,000 molecular weight, can be used
to form spacecoats that can be embossed relatively successfully. However,
the brightness of the spacecoat in the embossed region was not found to be
acceptable. Low brightness of this type is generally due to an overly soft
spacecoat, which can deform under embossing with loss of concentricity
(cupping). Alternatively stated, a significant amount of low molecular
weight polycaprolactone results in an overall composition not having
acceptable long-term dimensional stability.
Too high a molecular weight of non-reactive material (polycaprolactone) is
also undesirable. As the experiments show, when a 40,000 molecular weight
polycaprolactone was used, good wrinkle resistance and cupping were found;
however, the sheeting did not accept embossing well. That is, the sheeting
tended to fracture, crack and/or peel under a bending stress to the
substrate.
Further, a blend of high molecular weight/low molecular weight non-reactive
polymer (polycaprolactones) was also found to be undesirable. As the
experiments show, the mixtures resulted in cured compositions which
exhibited poor brightness retention, and which did not emboss well.
In general, to achieve a desired spacecoat, the semi-IPN polymer
composition must have a non-reactive polymer of a molecular weight (weight
average) somewhere between 3,000 and 40,000 and preferably within the
range of about 7,000-30,000. Most preferably, the weight average molecular
weight of the non-reactive polymer is about 15,000. An acceptable
non-reactive polymer is Union Carbide P-300, a polycaprolactone having a
molecular weight of about 15,000.
The Overall Formulation
In general, polymer compositions according to the present invention,
uncured, include, by weight, about 55-95% reactive polymer component,
5-20% cross-linker, and 2-25% non-reactive polymer component. Two
preferred formulations comprise: a first formulation of 80-90% Butvar.RTM.
B-76, 5-15% Resimene.RTM. 730 and 3-8% P-300; and, a second formulation
comprising 85-95% Butvar.RTM. B-90; 3-8% Resimene.RTM. 717 and 3-8% Huls
LTW.
A particular preferred composition for use as a spacecoat according to the
present invention comprises, by weight: 85 parts B-76, 10 parts
Resimene.RTM. 730 and 5 parts polycaprolactone P-300.
Preparation of the Spacecoat Formulation
During preparation of the formulation, the reactive polymer is dissolved in
an appropriate solvent system. It is noted that Butvar.RTM. B-76 is a
powder at STP.
A wide variety of solvents, or solvent systems, may be utilized. In
general, mixtures of alcohols, glycol ethers, propylene glycol ethers,
propylene glycol acetates, or ethylene glycol acetates are usable. A
preferred solvent system comprises dipropylene glycol monomethyl ether.
One such material is available under the trade name DPM from Dow Chemical,
Midland, Michigan. Butvar.RTM. B-76 and B-90 are readily soluble in DPM,
if about 3 to 4 parts solvent are used per part Butvar.RTM., by weight. In
general, the cross-linker can be added directly to the solvent system.
That is, no further solvent is typically needed. The non-reactive polymer
is generally dissolved in an appropriate solvent for accumulation with the
other components of the space coat. Polycaprolactone plasticizers within
the preferred weight average molecular weight range of 7,000-30,000 are
readily soluble in DPM.RTM., Dow Chemical. For a typical application, the
solution is made with 33% solids (by weight) and solvent heated to about
150.degree. F. (66.degree. C.) to effect solution of the polycaprolactone.
The non-reactive polymer (plasticizer) solution is then added to the
reactive polymer/cross-linker agent solution, with mixing. The final
composition, in solvent, is storage stable at ambient conditions. It is
noted that the reactive polymer and non-reactive polymer should be such
that when mixed there is good miscibility and no substantial phase
separation. That is, the reactive and non-reactive polymers should be
compatible.
Enclosed Lens Retroreflective Sheeting Preparation
A wide variety of specific processes are known for preparation of enclosed
lens sheeting. In a typical process, a top film is coated onto a carrier
web. The monolayer of beads is then attached to the top film, typically
either: by coating a curable film onto the top film, and then covering
this layer with the glass beads; or, by placing the beads directly onto
the top film and heating the construction to provide adhesion. After the
layer of beads is in place, the spacecoat is typically applied to the
construction by casting and curing (coating). Preferred spacecoats
according to the present invention can generally be applied in solutions
comprising about 10-50%, and preferably about 18-40%, solids.
The construction is then heated to above 250.degree. F. (121.degree. C.) in
order to cure the spacecoat and drive off the solvent. Following cure, the
spacecoat is coated with the reflective layer. Generally, the reflective
layer is a metal reflective layer approximately 1000 .ANG. (0.0010
micrometers) thick. Typically, high vacuum deposition of a vaporized
aluminum is used.
Finally, a layer of adhesive is typically added to the metal vapor coat, to
provide for adhesion to the substrate (the license plate blank for
example). The carrier web can then be removed, to provide for the finished
sheeting. In some instances an outermost protective layer may be added.
Experimentals
General Tests for Function
In order to test dimensional stability with respect to withstanding
embossing of the substrate, otherwise conventional retroreflective
coatings, using polymer compositions described below for the spacecoat,
were prepared and applied to an aluminum license plate blank, by means of
a conventional pressure sensitive adhesive. The entire construction was
then embossed in an hydraulic press, with a series of letters, as would be
conventional for embossing a license plate. The evaluation was of the
amount of embossing which the construction could endure without visible
cracking of the spacecoat. In general, if the overall construction could
withstand 100 mils (0.254 cm) of embossing, without visible signs of
cracking, it was considered embossable. The time duration of the embossing
operation was approximately one second, and was carried out at ambient
temperatures.
More specifically, for the embossability tests, a conventional license
plate blank, 6.times.12 inches and 0.06 inches thick (15.24.times.30.48 cm
and 0.1524 cm thick) was used. After coating and cure, a sample embossment
was achieved by placement between a male./female die pair with compression
at a 3 bar for a duration of 1 second at ambient temperature. The die pair
comprised a series of 5 "O's" progressing in height, at 10 mil increments,
from 60 mil to 100 mil (0.025 cm increments from 0.1524 cm to 0.254 cm).
Rating the response to embossment involved visual inspection of the letter
edges for cracks. The resulting assigned values reflected the amount of
embossment the construction could withstand, without fracture. An
embossability of less than 100 mils (0.254 cm) was considered
unacceptable.
While in some applications, substrates, such as license plates, having
retroreflective sheeting thereon are normally embossed only to about 80
mils (0.20 cm), an embossability of less than about 100 mils (0.254 cm)
was considered unacceptable for compositions according to the present
invention. There are several reasons for this. First, some characters may,
when embossed, cause greater stress, in localized area, to the coating
than to the "O's" of the test. Secondly, it is preferred to have a "safety
margin". That is, if a coating visibly shows cracking at 100 mils (0.254
cm) but not at 80 mils (0.20 cm), it can be assumed that even at the 80
mil embossing significant stress will have occurred, and points of failure
not viewable may have occurred. Requiring the coating to test acceptable
for embossability to 100 mils (0.254 cm) addresses such concerns.
The wrinkling resistance of spacecoats made using compositions according to
the present invention was measured by microscopic analysis of the
construction, both before and after afixing to a substrate. Wrinkling was
generally initiated and accelerated, by heating the unmounted construction
at 150 degrees Fahrenheit (65.degree. C.) for a minimum of one hour.
Visual inspection, aided by a 200.times. microscope magnification and top
surface lighting, was used to examine for wrinkling.
Scale Used to Report Concentric-Coatability or Cupping
In the data reported for the following experimentals, a scale of 1 (best)
to 9 (worst) was used to rate the concentric coatability. The scale is
based upon the level of cupping observed in the applied spacecoat.
Usually, high incidence of poor cupping is accompanied by substantial
wrinkling. A value of about 6 or less is acceptable at least for some
applications. Preferred compositions are those with a value of 4 or less.
______________________________________
Scale Observation
______________________________________
1 Easy to locate beads and voids between beads,
sharp hexagonal reflection can be seen
coinciding with the spaces between the beads.
Vapor coated surface appears dark with sharp
glare off the top of each spherical surface.
2 Easy to locate beads and voids between beads,
the hexagonal pattern begins to break down and
becomes less focused. The vapor coated surface
still appears dark with sharp points of light
off the top of the spherical surfaces.
3 Location of individual beads still possible,
hexagonal pattern between beads is broken down.
Observation of considerably greater glare.
4 Bridging between beads begins to occur.
5 General bridging between beads. It is
difficult to locate some beads.
6 Bridging between beads is nearly continuous,
individual bead identification becomes
difficult.
7 Cannot locate many individual beads, bead
clusters still visible. Very little depression
between beads.
8 Very few locatable bead clusters, surface
appears flat except for a few waves.
9 Virtually flat, no beads visible.
______________________________________
Of course, with respect to compositions according to the present invention,
preferred compositions are those which show a value of 1 or about 1 on the
cupping scale.
Wrinkling Scale
In the data reported for the following experimentals, a scale of 1 to 9 was
used to describe wrinkling. A value for wrinkling was assigned, according
to the following guidelines. In general, a value on the wrinkling scale of
about 6 or less is acceptable, at least for some applications. Preferred
compositions exhibit a value of 4 or less.
______________________________________
Scale Observations
______________________________________
1 No wrinkling.
2 Very small incidence of isolated small ripples,
typically located at top or edges of the
spherical coating of polymer over glass bead.
1 wrinkle/30-50 beads, 1/4 to 1/2 bead diameter
long.
3 Isolated incidences of small wrinkles,
wrinkling between beads may be longer. 1
wrinkle/10-20 beads, 0.5 to 1 bead diameter
long.
4 General isolated wrinkling, increasing
wrinkling incidents particularly between the
beads. Begin to see multiple wrinkles. 1
wrinkle/1-5 beads, 0.5 to 2 bead diameter long.
Some brightness lost.
5 Wrinkling begins to become continuous, multiple
rippling particularly between beads. Wrinkles
begin to climb up side of bead. 1+
wrinkle/bead, wrinkle length is anywhere from
0.25 diameter to several bead diameters.
(There is significant brightness loss.)
6 General continuous wrinkles. Wrinkling is on
top of bead, multiple wrinkling with some
spherical surface left.
7 General continuous wrinkles covering the entire
spacecoat. (Much of the brightness is gone,
more than 50% reduction.)
8 General continuous wrinkling with the addition
of "microwrinkles". Microwrinkles have a very
small radius at the observed magnification of
200x. (There is little retroreflective
brightness left in the sheeting.)
9 General microwrinkles. There is no brightness
left in the sheeting.)
______________________________________
Analysis of Cross-Linking
In order to test the nature of cured semi-IPN's made with polymer
compositions according to the present invention, a soxhlet extraction test
was developed. In general, test spacecoat resin compositions were
prepared, and coated onto a silicon-coated release liner, to give a final
coating thickness of 1.5-2.0 mils (25-50 micrometers). The resultant
coatings were placed in a 200 degrees Fahrenheit (93.degree. C.) oven for
8 minutes, followed by placement for another 8 minutes in a 350 degrees
Fahrenheit (177.degree. C.) oven.
Small pieces (1-3 grams) of the film were prepared and weighed. Each piece
was placed in an extraction thimble.
A soxhlet extractor with methylene chloride (dichloromethane) as the
solvent, was used as a means to extract the soluble portion of the films.
The residence time in the extractors for each sample/thimble was 4 days.
Determination of the amount of extractable mass was achieved by weighing
the dried thimbles after extraction. The solvent, containing extractables,
was concentrated, and analyzed by fourier transform IR, using conventional
techniques. As will be apparent from the examples reported, in all
instances of acceptable polymers non-reactive components were extractable,
and therefore not involved in the cross-linking. On the other hand, most
of the vinylacetyl polymer was not extractable, and therefore is
considered to have been highly cross-linked.
The Materials
The reactive polymer used in most of the experiments was either Butvar.RTM.
B-76 or Butvar.RTM. B-90 (Monsanto Co., St. Louis, MO, 63167), as (B-76 or
B-90) indicated. In one comparative experiment Vitel PE307 was used. Vitel
PE307 is a polyester prepared from ethylene glycol, neopentylglycol,
isophthalic acid, terphthalic acid and sebacic acid. It is available from
Goodyear, Akron, OH. Vitel has a weight average molecular weight of about
50,000.
A variety of polycaprolactone "tones" or "plasticizers" were used were used
as non-reactive polymer. In particular, polycaprolactones having the
molecular weights of 3,000; 15,000; and, 40,000 were used. The commercial
products used were Union Carbide 0260, P-300 and P-700, respectively. In
one comparative experiment Huls LTW was used. This compound, previously
identified has a weight average molecular weight of about 15,000. In
another comparative example Aroplaz 1351 was used. Aroplaz 1351 is a
non-oxidizing long oil alkyd resin having a weight average molecular
weight of about 3,300, obtained from Spencer-Kellogg, Buffalo, N.Y.
The preferred cross-linking agent utilized were melamine resins, in
particular, methoxymelamine resins. Two commercial products were used.
These are Resimene.RTM. 717 (Monsanto Co., Sr. Louis, MO, 63167), and
Resimene.RTM. 730 (Monsanro Co., St. Louis, MO 63167). Two other
cross-linking agents, Cymel 301 and Cymel 1171 were used in comparative
examples. Cymel 301 is a hexamethoxy methyl melamine-formaldehyde resin
available from American Cyanamid, Wayne, NJ. Cymel 1171 is a
glycouryl-formaldehyde adduct available from American Cyanamid. In another
comparative experiment, Beckamine P138 was used. Beckamine P138 is
butylated urea-formaldehyde resin available from Reichold Chemicals, White
Plains, NY. 10603.
In one comparative example, the resin included Vitel PE200D. Vitel PE200D
is a polyester composed of ethylene glycol, neopentylglycol, isophthalic
and terphthalic acids, available from Goodyear. This material has a weight
average molecular weight of about 50,000 and was observed to be
extractable.
Experimenr 1
Use of Plasticizer of Moderate Molecular Weight
A series of compositions using non-reacting polymer of moderate
(7,000-30,000) molecular weight were made. The compositions were generally
prepared in solution (25-30%) with butyl cellosolve or Dowanol DPM to form
spacecoating in an embedded lens retroreflective sheeting, prepared
according to the above-described general process. The sheeting was tested
for embossability and wrinkling, according to the above described test
procedures. Table I below presents the results for tests for
embossability, and observations of concentric coatability and wrinkling
according to previously described procedures. The figure used under
embossability is an indication of the height, in mils, of the highest
embossed character tested which did not show cracking, fracture or peel.
Since the highest embossed character was 100 mils, where the number 100
appears in the embossability column, no indication is made whether or not
a next higher embossed character would show cracking fracture or peel.
TABLE I
______________________________________
Samp. Polymer Comp. Emboss- *Conc.-
Wrinkle
No. (% by weight) ability coat. Value
______________________________________
1 60% B76 100 mils 5 6
20% Resimene 717
(0.254 cm)
20% P300
2 60% B76 100 mils 6 6
20% Resimene 730
(0.254 cm)
20% P300
3 85% B76 100 mils 2 1-2
10% Resimene 730
(0.254 cm)
5% P300
4 90% B76 100 mils 1 1
5% Resimene 717
(0.254 cm)
5% Huls LTW
5 90% B76 100 mils 1 1
5% Resimene 717
(0.254 cm)
5% P300
6 90% B90 100 mils 1 1
5% Resimene 717
(0.254 cm)
5% Huls LTW
______________________________________
*Concentric coatability
While the composition of tests 3, 4, 5 and 6 are preferred, it is believed
that each of the defined compositions is acceptable with respect to
embossability, concentric-coatability, and wrinkle value.
Composition 1 was studied, for extractable polymer, using the described
soxhlet extraction procedure. The percent of the overall mass which could
be extracted was about 37.3% The composition of the extracted material was
evaluated by IR to be 47%/13%/40% of B76/Resimene 717/P300. It was
calculated that therefore, about 74% by weight of the non-reacting polymer
(P300) was extractable.
Experiment 2
Comparison of a Composition Made with Low Molecular Weight Reactive Polymer
For comparison to the examples reported in Experiment 1, a composition
using a low molecular weight (about 3,000) polymer as the non-reactive
polymer (Union Carbide Tone 0260) was analogously prepared. Table II below
reports the results using this composition.
TABLE II
______________________________________
Samp. Polymer Comp. Emboss- *Conc.-
Wrinkle
No. (% by weight) ability coat. Value
______________________________________
7 60% B76 100 mils 8 8
20% Resimene 717
(0.254 cm)
20% 0260
______________________________________
*Concentric coatability
It is apparent that when a low molecular weight non-reactive polymer was
used, although a high degree of embossability was obtained, the resulting
cured composition was not dimensionally stable. That is, it shows
unacceptable concentric-coatability and unacceptable wrinkle value.
Experiment 3
Comparison of a Composition Made with High Molecular Weight Non-Reactive
Polymer
For comparison to Composition Nos. 1-7, reported in experiments No. 1 and 2
above, a composition made with a relatively high molecular weight
non-reactive polymer (40,000 molecular weight) was analogously prepared.
Table III below reports the results.
TABLE III
______________________________________
Samp. Polymer Comp. Emboss- *Conc.-
Wrinkle
No. (% by weight) ability coat. Value
______________________________________
8 60% B76 80 mils 3 2
20% Resimene 717
(0.20 cm)
20% P700
______________________________________
*Concentric coatability
It is apparent that with a relatively high molecular weight non-reactive
polymer, lower embossability is obtained, although dimensional stability
otherwise results.
Experiment 4
Comparative Coating Made with a Blend of High Molecular Weight and Low
Molecular Weight Non-Reactive Materials
A composition comprising a mixture of non-reactive polymer materials, the
blend used for the mixture comprising both high molecular weight and low
molecular weight non-reactive polymers, was analogously prepared. The
results are reported in Table IV below.
TABLE IV
______________________________________
Samp. Polymer Comp. Emboss- *Conc.-
Wrinkle
No. (% by weight) ability coat. Value
______________________________________
9 60% B76 80 mils 8 7
20% Resimene 717
(0.20 cm)
10% P700
10% 0260
______________________________________
*Concentric coatability
Experiment 5
Comparative Coatings Made with Reactive Polymer other than B76 and/or
Cross-Linker other than Resimene 717 or 730
Further comparative examples are reported in Table V below. it is noted
that none of he compositions shows both acceptable embossability and
dimensional stability (as indicated by concentric-coatability or wrinkle
value).
TABLE V
______________________________________
Samp. Polymer Comp. Emboss- *Conc.-
Wrinkle
No. (% by weight) ability coat. Value
______________________________________
10 60% B76 100 mils 8 8
20% Cymel 1171
(0.254 cm)
20% 0260
11 35% Vitel PE307
90 mils 4 3
12% Cymel 301 (0.23 cm)
53% Vitel PE200D
12 63% B76 60 mils 7 5
23% Beckamine (0.15 cm)
P138
14% Aroplaz 1351
______________________________________
*Concentric coatability
It will be understood that while certain specific embodiments of the
present invention are related in the examples, these are merely exemplary,
and the invention may be embodied in various forms.
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