Back to EveryPatent.com
United States Patent |
5,695,691
|
McLaughlin
,   et al.
|
December 9, 1997
|
Colloidal particles of solid flame retardant and smoke suppressant
compounds and methods for making them
Abstract
The present invention concerns finely divided particles of compounds that
provide flame retardancy and/or smoke suppressant properties to fibers,
textiles, polymeric articles, paper, paint, coating and insulation. More
particularly, the present invention concerns colloidal-sized particles of
hydrated salts, organic phosphates, metal borates, polyamides, solid
halogenated flame retardants with a melting point greater than 250.degree.
C., molybdenum compounds, metallocenes, antimony compounds, zinc
compounds, bismuth compounds and other solid chemicals which act as flame
retardants or smoke suppressants. The present invention also concerns
various milling processes to reduce these materials to colloidal sizes and
to disperse them in water, organic liquids and meltable solids.
Inventors:
|
McLaughlin; John (Media, PA);
Podwirny; Philip S. (Haddonfield, NJ);
Morley; John C. (Devon, PA)
|
Assignee:
|
Anzon, Inc. (Philadelphia, PA)
|
Appl. No.:
|
483032 |
Filed:
|
June 7, 1995 |
Intern'l Class: |
C09K 021/00; C09K 003/28; B02C 019/00 |
Field of Search: |
252/2,8,601,610,611
427/191
241/16
428/546
|
References Cited
U.S. Patent Documents
2621859 | Dec., 1952 | Phillips | 241/47.
|
2678168 | May., 1954 | Phillips | 241/47.
|
3090567 | May., 1963 | Schafer | 241/22.
|
3405874 | Oct., 1968 | Brizon | 241/174.
|
3540663 | Nov., 1970 | Dietz | 241/22.
|
3624043 | Nov., 1971 | Siclari et al. | 260/75.
|
3676362 | Jul., 1972 | Yates | 252/309.
|
3677476 | Jul., 1972 | Harned | 241/21.
|
3759500 | Sep., 1973 | Nerozzi | 266/9.
|
3816080 | Jun., 1974 | Bomford et al. | 29/182.
|
3947277 | Mar., 1976 | Carnahan et al. | 106/26.
|
3951894 | Apr., 1976 | Whelan, Jr. | 106/15.
|
3969570 | Jul., 1976 | Smith | 428/336.
|
3995817 | Dec., 1976 | Brociner | 241/30.
|
4065544 | Dec., 1977 | Hamling et al. | 423/252.
|
4075032 | Feb., 1978 | Thomas | 106/303.
|
4120798 | Oct., 1978 | Mischutin | 252/8.
|
4192664 | Mar., 1980 | Joshi | 65/22.
|
4230462 | Oct., 1980 | Moskowitz | 51/307.
|
4332354 | Jun., 1982 | deMonterey et al. | 241/16.
|
4367164 | Jan., 1983 | Shiroto et al. | 252/457.
|
4367165 | Jan., 1983 | Asaoka et al. | 252/457.
|
4404023 | Sep., 1983 | Gluck | 75/0.
|
4624418 | Nov., 1986 | Szkaradek | 241/46.
|
4627959 | Dec., 1986 | Gilman et al. | 419/61.
|
4647304 | Mar., 1987 | Petovic-Luton et al. | 75/0.
|
4651935 | Mar., 1987 | Samosky et al. | 241/65.
|
4676439 | Jun., 1987 | Saito et al. | 241/172.
|
4680204 | Jul., 1987 | Das et al. | 427/407.
|
4690970 | Sep., 1987 | Feinauer et al. | 524/504.
|
4776937 | Oct., 1988 | Gupta et al. | 204/157.
|
4787561 | Nov., 1988 | Kemp, Jr. et al. | 241/30.
|
4844355 | Jul., 1989 | Kemp, Jr. et al. | 241/172.
|
4913361 | Apr., 1990 | Reynolds | 241/259.
|
4966331 | Oct., 1990 | Maier et al. | 241/172.
|
5033682 | Jul., 1991 | Braun | 241/16.
|
5065946 | Nov., 1991 | Nishida et al. | 241/16.
|
5075206 | Dec., 1991 | Noda et al. | 430/531.
|
5083712 | Jan., 1992 | Askew et al. | 241/16.
|
5112388 | May., 1992 | Schulz et al. | 75/255.
|
5145684 | Sep., 1992 | Liversidge et al. | 424/489.
|
5147449 | Sep., 1992 | Grewe et al. | 75/354.
|
5171484 | Dec., 1992 | Nishimura et al. | 252/62.
|
5246488 | Sep., 1993 | Tanaka et al. | 106/14.
|
5246504 | Sep., 1993 | Ohta et al. | 136/201.
|
5270076 | Dec., 1993 | Evers | 427/220.
|
5281128 | Jan., 1994 | Dalla Betta et al. | 431/7.
|
5281379 | Jan., 1994 | Noguchi et al. | 264/102.
|
5294584 | Mar., 1994 | Yoshida et al. | 502/242.
|
5338712 | Aug., 1994 | MacMillan et al. | 501/94.
|
5350437 | Sep., 1994 | Watanabe et al. | 75/346.
|
5409980 | Apr., 1995 | Myszak, Jr. | 524/409.
|
Foreign Patent Documents |
55-104658 | Aug., 1980 | JP.
| |
1507443 A2 | Sep., 1989 | SU.
| |
1366104 | Sep., 1974 | GB.
| |
1371588 | Oct., 1974 | GB.
| |
WO95/24359 | Sep., 1995 | WO | .
|
Primary Examiner: Wu; Shean
Attorney, Agent or Firm: Kenyon & Kenyon
Claims
What is claimed is:
1. Finely divided particles of a solid chemical compound having flame
retardant or smoke suppressant properties, said particles having a
volumetric average particle size of less than 0.1 micron, said particles
having a size distribution such that at least 99% of said particles have
sizes less than about 1 micron, and said particles being produced by
comminution.
2. The finely divided particles of claim 1, wherein at least 99.9% of said
particles have sizes less than 1 micron.
3. The finely divided particles of claim 1, wherein said solid chemical
compound is selected from the group consisting of hydrated salts, organic
phosphates, metal borates, polyamides, solid halogenated flame retardants
with a melting point greater than 250.degree. C., molybdenum compounds,
metallocenes, antimony compounds, zinc compounds, and bismuth compounds.
4. The finely divided particles of claim 1, wherein said solid chemical
compound is selected from the group consisting of aluminum trihydrate,
magnesium sulphate pentahydrate, magnesium hydroxide, hydrated magnesium
carbonate, ammonium polyphosphate, melamine pyrophosphate, barium
metaborate, melamine, brominated polymers, ethylene
bis-tetrabromophthalamide, decabromodiphenylethane,
dodecachlorododecahydrodimethanodibenzocyclooctene, molybdenum oxide,
ammonium octamolybdate, ferrocene, antimony metal, antimony pentoxide,
sodium antimonate, mixed metal oxide of zinc and magnesium, zinc sulfide
and bismuth subcarbonate.
5. The finely divided particles of claim 1, wherein said solid chemical
compound is zinc borate.
6. The finely divided particles of claim 1, wherein said solid chemical
compound is decabromodiphenyloxide.
7. The finely divided particles of claim 1, wherein said solid chemical
compound is antimony trioxide.
8. A dispersion comprising a fluid vehicle, a dispersion agent and the
particles of claim 1.
9. The dispersion of claim 8, wherein said fluid vehicle is selected from
the group consisting of organic liquids, polyvinyl chloride plasticizers
and low melting point waxes or fats.
10. The dispersion of claim 8, wherein said fluid vehicle is selected from
the group consisting of dimethylacetamide, ethylene glycol and
diisodecylphthalate.
11. The dispersion of claim 8, wherein said fluid vehicle is water.
12. The dispersion of claim 8, wherein said dispersion agent is selected
from the group consisting of cationic surfactants, amphoteric surfactants,
and non-ionic surfactants.
13. The dispersion of claim 8, wherein said dispersion agent is selected
from the group consisting of wetting agents and anionic surfactants.
14. Finely divided particles of antimony trioxide having a volumetric
average particle size of less than 0.1 micron, at least 99% of said
particles having sizes less than about 1 micron, said particles being
produced by comminution and being dispersed in a fluid vehicle containing
a dispersion agent.
15. A process for producing finely divided particles of a solid compound
having flame retardant or smoke suppressant properties comprising:
loading an agitated media mill with comminuting media, a fluid vehicle, and
starting particles of a solid compound having flame retardant or smoke
suppressant properties; and
agitating said comminuting media, fluid vehicle, and starting particles
until said starting particles are reduced in size by at least 10% and
comminuted particles are produced within said agitated media mill having a
size distribution wherein said comminuted particles have a volumetric
average particle size of less than 0.1 micron and wherein at least 99% of
said comminuted particles is sized less than 1 micron.
16. The process of claim 15, wherein said slurry further comprises a
dispersion agent.
17. The process of claim 15, wherein said agitated media mill is operated
at a tip speed ranging from 1000 to 6000 feet per minute.
18. The process of claim 15, wherein said comminuting media are provided in
an amount sufficient to fill about 80 to 92% of the bulk volume within
said mill.
19. The process of claim 15, wherein said comminuting media are selected
from the group consisting of sand, glass beads, metals, and ceramics.
20. The process of claim 19, wherein said comminuting media are selected
from the group consisting of barium titanite, leaded soda lime,
borosilicate, carbon steel, stainless steel, tungsten carbide, zirconium
silicate, and alumina.
21. The process of claim 19, wherein said media is yttrium stabilized
zirconium oxide.
22. The process of claim 15, wherein said solid chemical compound is
selected from the group consisting of hydrated salts, organic phosphates,
metal borates, polyamides, solid halogenated flame retardants with a
melting point greater than 250.degree. C., molybdenum compounds,
metallocenes, antimony compounds, zinc compounds, and bismuth compounds.
23. The process of claim 15, wherein said solid chemical compound is
selected from the group consisting of zinc borate, decabromodiphenyloxide
and antimony trioxide.
24. The process of claim 15, wherein said fluid vehicle is selected from
the group consisting of organic liquids, polyvinyl chloride plasticizers
and low melting point waxes or fats.
25. The process of claim 15, wherein said fluid vehicle is selected from
the group consisting of dimethylacetamide, ethylene glycol and
diisodecylphthalate.
26. The process of claim 15, wherein said fluid vehicle is water.
27. The process of claim 16, wherein said dispersion agent is selected from
the group consisting of cationic surfactants, amphoteric surfactants, and
non-ionic surfactants.
28. The process of claim 15, wherein said dispersion agent is selected from
the group consisting of wetting agents and anionic surfactants.
29. Finely divided particles of a solid chemical compound having flame
retardant or smoke suppressant properties, produced by the process of
claim 15.
30. The process of claim 15, wherein said comminuting media has an average
size ranging from about 0.012 to 0.2 mm.
31. The process of claim 30 wherein said comminuting media is yttrium
stabilized zirconium.
32. The method of claim 31 wherein said comminuting media has an average
diameter of about 0.2 mm.
33. A process for producing finely divided antimony trioxide comprising:
loading an agitated media mill with ceramic comminuting media, a fluid
vehicle, a dispersion agent and starting particles of antimony trioxide;
and
agitating said comminuting media, fluid vehicle, dispersion agent and
antimony trioxide starting particles until said antimony trioxide starting
particles are reduced in size by at least 10% and comminuted antimony
trioxide particles are produced within said agitated media mill having a
size distribution wherein said comminuted antimony trioxide particles have
a volumetric average particle size of less than 0.1 micron, and wherein at
least 99% of said comminuted antimony trioxide particles are sized less
than 1 micron.
34. The process of claim 33 wherein said dispersion agent is an anionic
surfactant.
35. The process of claim 33 wherein said fluid vehicle is water.
36. The process of claim 33 wherein said ceramic comminuting media is
yttrium stabilized zirconium oxide having an average diameter of about 0.2
mm.
37. The finely divided particles of claim 14 wherein said dispersion agent
is an anionic surfactant.
38. The finely divided particles of claim 14 wherein said fluid vehicle is
water.
39. A process for producing finely divided particles of a solid compound
having flame retardant or smoke suppressant properties comprising:
loading an agitated media mill with comminuting media, a fluid vehicle, and
starting particles of a solid compound having flame retardant or smoke
suppressant properties; and
agitating said comminuting media, fluid vehicle, and starting particles
until said starting particles are reduced in size by at least 10% and
comminuted particles are produced within said agitated media mill having a
size distribution wherein said comminuted particles have a volumetric
average particle size of less than 0.25 microns and wherein at least 99%
of said comminuted particles is sized less than 1 micron, wherein said
size distribution is produced in a residence time of less than 15 minutes.
40. A process for producing finely divided antimony trioxide comprising:
loading an agitated media mill with ceramic comminuting media, a fluid
vehicle, a dispersion agent and starting particles of antimony trioxide;
and
agitating said comminuting media, fluid vehicle, dispersion agent and
antimony trioxide starting particles until said antimony trioxide starting
particles are reduced in size by at least 10% and comminuted antimony
trioxide particles are produced within said agitated media mill having a
size distribution wherein said comminuted antimony trioxide particles have
a volumetric average particle size of less than 0.25 microns and wherein
at least 99% of said comminuted antimony trioxide particles are sized less
than 1 micron, wherein said size distribution is produced in a residence
time of less than 15 minutes.
Description
FIELD OF THE INVENTION
The present invention concerns finely divided particles of compounds that
provide flame retardancy and/or smoke suppressant properties to fibers,
textiles, polymeric articles, paper, paint, coatings and insulation. More
particularly, the present invention concerns colloidal-sized particles of
hydrated salts, organic phosphates, metal borates, polyamides, solid
halogenated flame retardants with a melting point greater than 250.degree.
C., molybdenum compounds, metallocenes, antimony compounds, zinc
compounds, bismuth compounds and other solid chemicals which act as flame
retardants or smoke suppressants. The present invention also concerns
various milling processes to reduce these materials to colloidal sizes and
to disperse them in water, organic liquids and meltable solids.
BACKGROUND OF THE INVENTION
The ability of various solids to act as flame retardants and/or smoke
suppressants is known in the art. Such solids act by various mechanisms to
provide flame retardancy including the following:
a) Release of Water and/or Carbon Dioxide--Hydrated salts (such as
magnesium sulfate pentahydrate, aluminum trihydrate, magnesium hydroxide,
hydrated magnesium carbonate and so forth) decompose at high temperatures,
and release water and or carbon dioxide in an endothermic reaction to
quench a fire.
b) Char Formation--When exposed to high temperatures, char formers, which
include organic phosphates, zinc compounds, nitrogen compounds (such as
melamine esters and polyamides) and metal borates, form char barriers
which insulate the combustible materials from the fire.
c) Free Radical Capture/Oxygen Deprivation--Halogen compounds alone or in
combination with antimony will prevent combustion. The primary mechanism
is believed to be the formation of a dense gas layer above the burning
substance that inhibits or prevents oxygen from reaching the combustible
material. There is also evidence in support of the ability of antimony
halides to scavenge free radicals in the flame, stopping the reaction.
d) Smoke Suppression--Smoke suppressants work by aiding the complete
oxidation of carbonaceous materials formed in the flame and/or the
formation of char or glasses. They are usually catalysts for oxidation
reactions and/or char or glass formers. Typical smoke suppressants are
molybdenum oxide and ferrocene or other metallocenes.
All of the above listed solids are used commercially to provide either
flame retardancy or low smoke generation to plastics, carpets, fabrics,
paper, paints, coatings, adhesives, wood composites and so forth.
Unfortunately, the use of such solids often imparts other undesirable
properties to the item to which they are added. Typical undesirable
properties that result from adding solid particles of flame retardant or
smoke suppressant compounds include: pigmentation (.e.g., addition of
unwanted colors), opacity (e.g., loss of light transmission), stiffness
(e.g., loss of hand in textiles), lowered impact strength (resulting,
e.g., an increase in crack propagation), and setting of solids (in, e.g.,
paints, coatings and adhesives). Such undesirable properties can be
reduced or eliminated by reducing average particle size and eliminating
substantially all particles above about 1 micron.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide colloidal
particles (particles having a size ranging from 10.sup.-9 to 10.sup.-6 m)
of solid flame retardant and/or smoke suppressant compounds, including
hydrated salts (such as aluminum trihydrate, magnesium sulphate
pentahydrate, magnesium hydroxide and hydrated magnesium carbonate),
ammonium polyphosphate, organic phosphates (such as melamine
pyrophosphate), metal borates (such as zinc borate and barium metaborate),
polyamides, melamine, solid halogenated flame retardants with a melting
point greater than 250.degree. C. (such as brominated polymers,
decabromodiphenyloxide, ethylene bis-tetrabromophthalamide,
decabromodiphenylethane, and
dodecachlorododecahydrodimethanodibenzocyclooctene), molybdenum compounds
(such as molybdenum oxide and ammonium octamolybdate), metallocenes (such
as ferrocene), antimony compounds (such as antimony metal, antimony
trioxide, antimony pentoxide and sodium antimonate), zinc compounds (such
as mixed metal oxide of zinc and magnesium, or zinc sulfide) and bismuth
compounds (such as bismuth subcarbonate), as well as a process for
producing them.
It is also an object of the present invention to provide stable dispersions
of these materials in water, organic liquids or meltable solids, and to
provide a method for producing the same.
Colloidal particles of insoluble, solid flame retardant and/or smoke
suppressant compounds are advantageous for use as external flame retardant
coatings on textiles or as internal flame retardant additives to systems
such as coatings, plastic, textiles and rubber.
Dispersions of such particles are convenient, because they allow the
particles to be transported, while simultaneously inhibiting the particles
from coalescing into larger agglomerates.
These and other objects and advantages have been achieved by the present
invention, wherein colloidal-sized particles of insoluble solid flame
retardant and/or smoke suppressant compounds are provided by means of a
high energy mill, such as a media mill, even though commercial suppliers
of such milling equipment do not suggest that such particle sizes can be
achieved.
According to an embodiment of the present invention, an agitated media mill
loaded with comminuting media is provided with a slurry comprising a fluid
vehicle and particles of a solid compound having flame retardant or smoke
suppressant properties. The slurry is processed in the agitated media mill
until the particles are reduced in size by at least 10%, more preferably
50 to 90%, and even more preferably 10 to 99%. Moreover, the particles
have a volumetric average particle size of less than 0.5 micron,
preferably 0.01 to 0.5 micron, more preferably 0.01 to 0.25 micron, and
even more preferably 0.01 to 0.1 micron. It is preferred that at least 99%
of said particles have sizes less than 1 micron. More preferably at least
99.9% of the particles should have sizes less than 1 micron. It is also
preferred that the slurry further comprise a dispersion agent.
Other objects and advantages of the invention and alternative embodiments
will readily become apparent to those skilled in the art, particularly
after reading the detailed description, and examples set forth below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Wet media milling is the preferred process for making the finely divided
particles of the present invention. In general, the ultimate
characteristics of material comminuted in a wet media mill, particularly
the particle size, is determined by several processing variables.
For example, the type of mill can affect the ultimate characteristics of
the comminuted materials. The mill type can also determine how quickly a
particular result may be achieved.
Other factors also determine the ultimate characteristics of the comminuted
material, as well as the time and energy it takes to achieve them.
Examples of such factors include the following:
(1) In wet media milling, smaller media are more efficient in producing
finer particles within times of 10 minutes and less.
(2) More dense media and higher tip speeds are desired to impart more
energy to the particles being comminuted.
(3) Lower fluid viscosities are beneficial in comminuting particles.
(4) As the particles are reduced in diameter, exposed surface areas
increase, and a dispersion agent is generally used to keep small particles
from agglomerating. In some cases dilution alone can help achieve a
particular ultimate particle size, but a dispersion agent is generally
used to achieve long-term stability against agglomeration. The above and
other factors that influence comminuting performance is discussed in the
paragraphs that follow.
As used herein "particle size" refers to a volumetric average particle size
as measured by conventional particle size measuring techniques such as
sedimentation, photon correlation spectroscopy, field flow fractionation,
disk centrifugation, transmission electron microscopy, and dynamic light
scattering. A dynamic light scattering device such as a Horiba LA-900
Laser Scattering particle size analyzer (Horiba Instruments, Irvine,
Calif.) is preferred by the present inventors, because it has advantages
of easy sample preparation and speed. The volumetric distribution of the
sample relates to the weight distribution.
Milling Equipment
The milling equipment preferred for the practice of the invention are
generally known as a wet agitated media mills, wherein comminuting media
are agitated in a milling chamber. The preferred method of agitation is by
means of an agitator comprising a rotating shaft, such as those found in
attritor mills. The shaft may be provided with disks, arms, pins, or other
attachments. The portion of the attachment that is radially the most
remote from the shaft is referred to herein as the "tip". The mills may be
batch or continuous, vertical or horizontal. A ball mill is an example of
a rudimentary agitated media mill.
A horizontal continuous media mill equipped with an internal screen having
hole sizes that are 1/2 to 1/3 the media diameter is preferred as an
efficient media mill for the practice of the present invention. High
loadings of media are possible (e.g., loadings of 92%).
An increase in the amount of comminuting media in the chamber will increase
comminuting efficiency by decreasing the distances between individual
comminuting media particles and increasing the number of surfaces
available to shear the material to be comminuted. The volume of
comminuting media can be increased until the comminuting media constitutes
up to about 92% of the mill chamber bulk volume (dead space between
particles is excluded). At levels substantially above this point, the
media locks up.
Starting Materials
By the present invention, flame retardants or smoke suppressants can be wet
milled to levels that are currently not achievable with dry milling
techniques.
Within reason, the size of the feed material that is to be comminuted is
not critical. For example, antimony trioxide can be reduced to a 0.10
micron average particle size with an agitated media mill using the process
of the present invention, whether starting from particles that have an
average particle size of 4.3 microns, 2.0 microns, or 0.6 micron. However,
in generally, the feed material should not be more than 10% of the size of
the comminuting media. Other flame retardants such as decabromodiphenyl
oxide and zinc borate can be similarly reduced to 0.25 and 0.14 micron or
less, respectively, in short comminuting times.
Faster milling times can be achieved, if smaller starting materials are
used. Thus, it is preferable to start with particles that are as small as
is economically feasible, to reduce milling time. For example, 0.5 micron
antimony trioxide feed material (as measured by Transmission Electron
Microscopy) can be comminuted to a desired size (e.g., 0.1 micron) in a
shorter time than can a 4.3 micron material. For this reason, antimony
trioxide having a 0.5 micron average particle size is preferred to
material having a larger particle size. When such material is used, a
tight particle distribution can be achieved, as well as a short milling
time.
Comminuting Media
Acceptable comminuting media for the practice of the present invention
include sand, glass beads, metals, and ceramics. Preferred glass beads
include barium titanite (leaded), soda lime (unleaded), and borosilicate.
Preferred metals include carbon steel, stainless steel and tungsten
carbide. Preferred ceramics include yttrium stabilized zirconium oxide,
zirconium silicate, and alumina. The most preferred comminuting media for
the purpose of the invention is yttrium stabilized zirconium oxide.
Each type of media has its own advantages. For example, metals have high
specific gravities, which increase comminuting efficiency due to increased
impact. Metal costs range from low to high, and contamination may be an
issue. Glasses are advantageous from the standpoint of low cost and the
availability of small sizes as low as 0.004 mm. Such small sizes make
possible a finer ultimate particle size. The specific gravity of glasses,
however, is lower than other media and more milling time is required.
Finally, ceramics are advantageous from the standpoint of low wear, low
porosity and ease of cleaning.
The comminuting media used for particle size reduction are preferably
spherical. As noted previously, smaller comminuting media sizes result in
smaller ultimate particle sizes. The comminuting media for the practice of
the present invention preferably have an average size ranging from 0.004
to 1.2 mm, more preferably 0.012 to 0.2 mm. By using properly selected
comminuting media, the milling process of the present invention actually
comminutes particles, rather than deagglomerating clumps of particles--a
task for which media mills are normally used.
Fluid Vehicles
Fluid vehicles in which the particles may be comminuted and dispersed
include water, organic liquids (such as dimethylacetamide or ethylene
glycol), polyvinyl chloride plasticizers (such as diisodecylphthalate) and
low melting solids such as waxes or fats wherein the milling is conducted
at temperatures greater than the melting point of the waxes or fats. In
general, as long as the fluid vehicle used has a reasonable viscosity and
does not adversely affect the chemical or physical characteristics of the
particles, the choice of fluid vehicle is optional. Water is ordinarily
preferred.
Dispersion Agents
Dispersion agents preferably act to wet newly exposed surfaces that result
when particles are broken open. Dispersion agents also preferably
stabilize the resulting slurry of milled particles by providing either (1)
a positive or negative electric charge on the milled particles or (2)
steric blocking through the use of a large bulking molecule. An electric
charge is preferably introduced by means of anionic and cationic
surfactants, while steric blocking is preferably performed by absorbed
polymers with charges on the particle which repel each other. Zwitterionic
surfactants can have both anionic and cationic surfactant characteristics
on the same molecule.
Preferred dispersion agents for the practice of the invention include
wetting agents (such as Triton X-100 and Triton CF-10, sold by Union
Carbide, Danbury, Conn., and Neodol 91-6, sold by Shell Chemical); anionic
surfactants (such as Tamol 731, Tamol 931 and Tamol-SN, sold by Rohm &
Haas, Philadelphia, Pa., and Colloid 226/35, sold by Rhone Poulenc);
cationic surfactants (such as Disperbyke 182 sold by Byke Chemie,
Wellingford, Conn.); amphoteric surfactants (such as Crosultain T-30 and
Incrosoft T-90, sold by Croda, Inc., Parsippany, N.J.); and non-ionic
surfactants (such as Disperse-Ayd W-22 sold by Daniel Products Co., Jersey
City, N.J.). Most preferred dispersion agents are anionic surfactants such
as Tamol-SN.
Other Milling Parameters
The relative proportions of particles to be comminuted, fluid vehicles,
comminuting media and dispersion agents may be optimized for the practice
of the present invention.
Preferably, the final slurry exiting the mill comprises the following: (1)
5 to 60 wt %, more preferably 15 to 45 wt % of the particle to be
comminuted (2) 40 to 95 wt %, more preferably 55 to 85 wt % of the fluid
vehicle; and (3) 2 to 15 wt %, more preferably 6 to 10 wt % of the
dispersion agent.
Preferably the comminuting media loading as a percent of the mill chamber
volume is 80 to 92%, more preferably 85 to 90%.
The agitator speed controls the amount of energy that is put into the mill.
The higher the agitator speed, the more kinetic energy is put into the
mill. Higher kinetic energy results in greater comminuting efficiency, due
to higher shear and impact. Thus, an increase in agitator RPM results in
an increase in comminuting efficiency. Although generally desirable, it is
understood by those skilled in the art that an increase in comminuting
efficiency will be accompanied by a concurrent increase in chamber
temperature, chamber pressure, and wear rate.
The tip speed of the agitator represents the maximum velocity (and, thus,
kinetic energy) experienced by the particles to be milled. Thus, larger
diameter mills can impart media velocities equal to those of smaller mills
at a lower RPM.
Residence time (referred to cumulatively as retention time) is the amount
of time that the material spends in the comminuting chamber while being
exposed to the comminuting media. Residence time is calculated by simply
determining the comminuting volume that is available for the mill and
dividing this figure by the rate of flow through the mill (throughput
rate). In general, a certain residence time will be required to achieve
the ultimate product characteristics desired (e.g., final product size).
If this residence time can be reduced, a higher throughput rate can be
achieved, minimizing capital costs. For the practice of the present
invention, the residence time can vary, but is preferably less than 15
minutes, and more preferably less than 10 minutes.
It is often desirable to stage two or more mills in series, particularly
when dramatic reductions in particle size are necessary to optimize
comminution efficiency. Maximum particle size reduction within a given
milling step typically ranges from about 10:1 to as high as about 40:1 and
is to some extent dependent upon media size. As a result, the number of
milling steps increases as the overall size reduction requirement
increases. Effects similar to that of staged mills can also be achieved
using a single mill by collecting the output and repeatedly feeding the
output through the mill. However, residence time may be longer to achieve
similar ultimate particle size.
EXAMPLES
The following examples, as well as the foregoing description of the
invention and its various embodiments, are not intended to be limiting of
the invention but rather are illustrative thereof. Those skilled in the
art can formulate further embodiments encompassed within the scope of the
present invention.
Example 1
A 10 liter horizontal continuous media mill (Netzsch, Inc., Exton, Pa.) was
90% filled with YTZ (yttrium stabilized zirconium oxide) media with an
average diameter of 0.2 mm and a specific gravity of 5.95 (Tosoh Corp.,
Bound Brook, N.J.). A 0.1 mm screen was installed inside the mill at the
outlet. Forty-five pounds of antimony trioxide with an average starting
particle size of 2.0 microns (Cookson Specialty Additives, Anzon Division,
Philadelphia, Pa.) were slurried in 55 pounds of water and 4.5 pounds of
Tamol-SN.
The mill was operated at a tip speed that averaged 2856 feet per minute.
After 7.5 minutes of retention time (5 passes through the mill) the
average particle size, by volume, was reduced to 0.102 micron and 99.9% of
the particles had sizes less than 0.345 micron.
Example 2
The same mill, media and loading as in Example 1 were used. This time,
antimony trioxide feed having a 0.6 micron average particle size (Cookson
Specialty Additives, Anzon Division, Philadelphia, Pa.) was used. Thirty
pounds of the antimony trioxide were slurried with 70 pounds of water and
1.8 pounds of Tamol-SN and 0.9 pounds of Triton CF-10.
The tip speed during the run averaged 2878 feet per minute. After 4.8
minutes of retention time in the mill (4 passes), the volume average
particle size was 0.11 micron and 99.9% of the particles had sizes less
than 0.31 micron.
Example 3
The same mill, media, antimony trioxide and loading as in Example 1 were
used. This time no surfactants were used.
Twenty-eight pounds of the antimony trioxide were slurried with 100 pounds
of water. Tip speed was 3023 feet per minute. After 2.4 minutes of
retention time (2 passes). The average particle was 0.13 micron with 99.9%
of the particles having sizes less than 1.06 micron.
Since the viscosity of the product was high, 35 additional pounds of water
were added. After 1.8 minutes of additional retention time (2 extra
passes), the average particle size was further reduced to 0.10 micron,
with 99.9% of the particles having sizes less than 0.32 micron.
Example 4
The same mill, media, and loading as in Example 1 were used. Thirty pounds
of 4 micron antimony trioxide feed material (Cookson Specialty Additives,
Anzon Division) were slurried with 70 pounds of water and 2.8 pounds of
Tamol-SN. Tip speed was 2860 feet per minute. After 7 minutes of retention
time (5 passes), the average particle size was 0.10 micron with 99.9% of
the particles having sizes less than 1.2 micron.
Example 5
Using the same mill, media and loading of Example 1, 80 pounds of a
brominated organic flame retardant (decabromodiphenyl oxide) (Arblemarle,
Inc. Baton Rouge, La.; Great Lakes, Lafayette, Ind.; Ameribrom, Inc., New
York, N.Y.) were slurried with 55 pounds of water. The starting particle
size averaged 2.7 microns with some particles as large as 10 microns.
After 10.4 minutes of retention time (6 passes), the average particle size
was 0.25 micron, with 99.9% of the particles having a size less than 2.70
micron.
Example 6
The 10 liter horizontal media mill of Example 1 was 90% filled with 4-6 mm
electrofused zirconia/silica ceramic beads having a specific gravity of
3.85 (SEPR, Mountainside, N.J.). The same 0.1 mm screen of Example 1 was
used inside the mill.
50 pounds of 2 micron antimony trioxide feed were mixed with 11 pounds of
water and 5 pounds of Tamol-SN. After 7.8 minutes of retention time, the
average particle size was 0.20 micron, with 99.9% of the particles having
sizes below 0.46 micron.
Example 7
A 10 liter horizontal media mill of Example 1 was 90% loaded with
borosilicate glass beads having a 0.093 mm mean diameter and a specific
gravity of 2.6 sold by Potters Industries. A 0.025 mm screen was used in
the mill.
Fifty pounds of 0.6 micron antimony trioxide were slurried with 61 pounds
of water and 5 pounds of Tamol-SN. The tip speed was 3420 feet per minute.
Mill amperage was only 67% of similar runs using the 5.95 specific gravity
media. The resulting antimony trioxide product had a 0.09 micron average
particle size, with 100% of the particles having sizes less than 0.30
micron.
Example 8
The 10 liter continuous horizontal media mill Example 1 was 90% loaded with
the YTZ media of Example 1. Fifty pounds of zinc borate having an average
particle size of 9.8 microns (Cookson Specialty Additives, Anzon Division,
Philadelphia, Pa.) were slurried in 93 pounds of water and 3 pounds of
Tamol-SN.
Tip speed was 2788 feet per minute. After 8.9 minutes (4 passes) of
retention time, the average particle size was reduced to 0.14 micron, with
99.9% of the particles having sizes less than 0.41 micron.
Example 9
An attritor (Union Process, Inc., Akron, Ohio) with a 750 cc tank volume
was loaded with 250 cc of YTZ powder (Metco, Inc., Westbury, N.Y.)
screened to a size of 0.053 mm. 180 g of the slurry of Example 1 were
added to the attritor. After running the attritor at 4000 RPM (3600 ft/min
tip speed) for 60 minutes, the average particle size of the resulting
product was 0.07 microns.
Top