U.S. patent application number 09/747635 was filed with the patent office on 2002-04-04 for water absorbing polymer.
Invention is credited to Freeman, Clarence S., Freeman, Jon Joseph, Freeman, Matthew Max.
Application Number | 20020039655 09/747635 |
Document ID | / |
Family ID | 27413728 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020039655 |
Kind Code |
A1 |
Freeman, Clarence S. ; et
al. |
April 4, 2002 |
Water absorbing polymer
Abstract
A process for producing a substantially dry polymer particle
powder. A mixture of polymerization reagents is formed from a
mixture of at least one monomer source and a solvent selected from
the group consisting essentially of water and organic solvents and
an initiator source. The mixture of polymerization reagents is
sprayed into a heated, controlled atmosphere, forming droplets of
the mixture which are allowed to fall through the heated,
controlled atmosphere for a sufficient period of time to obtain a
desired degree of polymerization. The solvent is continuously
evacuated from the atmosphere during the polymerization
process.
Inventors: |
Freeman, Clarence S.;
(Channelview, TX) ; Freeman, Matthew Max;
(Channelview, TX) ; Freeman, Jon Joseph;
(Channelview, TX) |
Correspondence
Address: |
Frank S. Vaden III
Bracewell & Patterson, L.L.P.
P.O. Box 61389
Houston
TX
77208-1389
US
|
Family ID: |
27413728 |
Appl. No.: |
09/747635 |
Filed: |
December 21, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09747635 |
Dec 21, 2000 |
|
|
|
08973574 |
Mar 9, 1998 |
|
|
|
6291605 |
|
|
|
|
08973574 |
Mar 9, 1998 |
|
|
|
PCT/US96/09132 |
Jun 6, 1996 |
|
|
|
PCT/US96/09132 |
Jun 6, 1996 |
|
|
|
08468079 |
Jun 6, 1995 |
|
|
|
5674903 |
|
|
|
|
08468079 |
Jun 6, 1995 |
|
|
|
07855458 |
Mar 19, 1992 |
|
|
|
07855458 |
Mar 19, 1992 |
|
|
|
07534177 |
Jun 6, 1990 |
|
|
|
Current U.S.
Class: |
428/402.24 ;
524/832; 525/242; 525/329.7; 525/330.3 |
Current CPC
Class: |
B01J 2219/00135
20130101; B01J 14/00 20130101; B01J 2219/0009 20130101; B01J 2/04
20130101; B01J 10/002 20130101; B01J 2219/00099 20130101; B01J
2219/00083 20130101; B01J 2219/0015 20130101; C02F 1/56 20130101;
B29B 9/10 20130101; B01J 2219/00157 20130101; C08F 20/06 20130101;
B01J 19/26 20130101; B01J 19/0013 20130101; Y10T 428/2989 20150115;
B01J 2219/00063 20130101; B01J 2219/00162 20130101 |
Class at
Publication: |
428/402.24 ;
524/832; 525/242; 525/329.7; 525/330.3 |
International
Class: |
C08L 031/00; C08J
003/00; C08L 033/00; C08L 035/00 |
Claims
What is claimed is:
1. A polymerization apparatus comprising: a reaction chamber; means
for heating said reaction chamber; means for controlling the
pressure within said reaction chamber; one or more nozzles
connected to a feed line for receiving a mixture of a monomer
source and an initiator source; and means for spraying the mixture
into the top section of the reaction chamber such that said
spraying results in the formation of droplets of said mixture which
experience free fall through the reaction chamber for a sufficient
period of time to obtain a desired degree of polymerization.
2. The apparatus as set forth in claim 1, further comprising a
means for removing the polymer from the bottom of said reaction
chamber while maintaining the heat and the pressure within the
chamber.
3. The apparatus as set forth in claim 2, wherein the means for
removing the polymer comprises a trough located in the bottom of
the reaction chamber, a first auger mounted in the bottom of said
trough for moving the polymer out of the chamber, a bin into which
said first auger deposits the polymer and a second auger mounted in
the bottom of said bin for moving the polymer out of said bin.
4. The apparatus as set forth in any one of the preceding claims,
further comprising a means for controlling the temperature of the
monomer and initiator mixture in said feed line.
5. The apparatus as set forth in any one of the preceding claims,
further comprising a means for mixing the monomer and initiator
before the mixture of monomer and initiator is sprayed from said
nozzles.
6. The apparatus as set forth in any one of the preceding claims,
further comprising a means for removing unpolymerized monomer from
said reaction chamber.
7. The apparatus as set forth in any one of the preceding claims,
further comprising a means for purging the mixture in said feed
line.
8. The apparatus as set forth in claim 7, wherein the feed line
purging means comprise means to purge the feed line with
nitrogen.
9. The apparatus as set forth in any one of the preceding claims,
further comprising a means for purging said reaction chamber.
10. The apparatus as set forth in claim 9, wherein reaction chamber
purging means comprise means to purge the reaction chamber with
nitrogen.
11. The apparatus as set forth in any one of the preceding claims,
wherein said reaction chamber is from about 3.65 meters in height
to about 30.48 meters in height.
12. The apparatus as set forth in any one of the preceding claims,
further comprising a separate reservoir for said monomer source and
said initiator source.
13. The apparatus as set forth in claim 12, further comprising a
reservoir for a crosslinker source.
14. The apparatus as set forth in claim 13, wherein said
crosslinker source is connected to means adapted to add crosslinker
source to said mixture of monomer source and initiator source prior
to the mixture being sprayed into said reaction chamber.
15. The apparatus as set forth in any one of the preceding claims,
wherein the mixture is sprayed into said reaction chamber at from
about 517 KPa to about 13.7 MPa of pressure.
16. The apparatus as set forth in any one of the preceding claims,
wherein means are provided to maintain the pressure in the reaction
chamber at less than ambient pressure.
17. The apparatus as set forth in claim 16, wherein said means
maintain the pressure in the reaction chamber at a pressure of from
about 338.6 to about 50,790 N/m.sup.2 below ambient pressure.
18. The apparatus as set forth in any one of the preceding claims,
wherein said reaction chamber is heated to a temperature of from
about 23.8.degree. C. to about 176.7.degree. C.
19. The apparatus according to any of the preceding claims, wherein
means are provided to increase or decrease the size of each nozzle
opening.
20. The apparatus as set forth in any one of claims 1 to 18,
wherein, in use, the monomer source is a functionalized or an
unfunctionalized olefin.
21. The apparatus as set forth in any one of claims 1 to 18,
wherein, in use the monomer source is acrylic acid.
22. The apparatus as set forth in any one of claims 1 to 18,
wherein, in use, said monomer source is selected from the group of
compounds consisting of ethylenes, dienes, styrenes, propylenes,
vinyls, acrylates, methacrylates, acrylonitrile, methacrylonitrile,
acrylamide, methacrylamide, and alkenes.
23. An apparatus for continuous production of a detergent
comprising: a reaction chamber; means for heating said reaction
chamber; means for controlling the pressure within said reaction
chamber; one or more nozzles connected to a feed line for receiving
a mixture of a detergent raw materials; and means for spraying the
mixture into the top section of the reaction chamber such that said
spraying results in the formation of droplets of said mixture which
experience free fall through the reaction chamber for a sufficient
period of time to obtain a substantially dry detergent powder.
24. A polymerization process comprising the steps of: (a) preparing
a first mixture of at least one monomer source and a solvent
selected from the group consisting of water, organic solvents and
mixtures thereof; (b) adding an initiator source to the first
mixture to form a second mixture; (c) spraying the second mixture
into a heated, pressure controlled, substantially static
atmosphere, said spraying resulting in the formation of droplets of
said second mixture; and (d) allowing said droplets of the sprayed
second mixture to fall through the heated, substantially static
atmosphere for a period of time sufficient to obtain a desired
degree of polymerization.
25. The polymerization process as set forth in claim 24, wherein
the heated, substantially static atmosphere is maintained in a
closed vessel, or reaction chamber.
26. The polymerization process as set forth in claim 25, wherein
said second mixture is sprayed in at the top section of the vessel,
or reaction chamber.
27. The polymerization process as set forth in claim 25 or 26,
wherein said vessel reaction chamber is about 3.65 to 30.48 meters
in height.
28. The polymerization process as set forth in any one of claims 24
to 27, wherein said second mixture is sprayed into the atmosphere
through one or more nozzles.
29. The polymerization process as set forth in any one of claims 24
to 28, wherein the size of the polymer particle produced is
selected by increasing or decreasing the size of the nozzle
opening.
30. The polymerization process as set forth in any one of claims 24
to 29, which further comprises adding a neutralizer to the first
mixture.
31. The polymerization process as set forth in any one of claims 24
to 30, wherein said solvent is continuously evacuated from the
atmosphere during the polymerization process.
32. The polymerization process as set forth in any one of claims 24
to 31, wherein a substantially dry polymer powder is formed as a
result of the polymerization process.
33. The polymerization process as set forth in claim 32, wherein
the dry polymer powder is recovered while maintaining a heated,
substantially static atmosphere.
34. The polymerization process as set forth in claim 32 or 33,
wherein the dry polymer powder produced comprises a water-absorbing
polymer.
35. The polymerization process as set forth in claim 32 or 33,
wherein the dry polymer powder produced comprises a polymer
suitable for use as a powder coating.
36. The polymerization process as set forth in claim 32 or 33,
wherein the dry polymer powder produced comprises an irregularly
puffed shaped polymer having relatively low density.
37. The polymerization process as set forth in any one of claims 24
to 37, wherein said atmosphere is at a temperature of from about
23.8.degree. C. and to about 176.7.degree. C.
38. The polymerization process as set forth in any one of claims 24
to 37, wherein said substantially static atmosphere is at reduced
pressure.
39. The polymerization process as set forth in any one of claims 24
to 38, wherein said substantially static atmosphere is at positive
pressure.
40. The polymerization process as set forth in claim 38, wherein
said heated, substantially static controlled atmosphere is
maintained at a pressure of from about 388.6 to about 50,790
N/m.sup.2 below ambient pressure.
41. The polymerization process as set forth in any one of claims 24
to 40, wherein said second mixture is sprayed into the heated,
substantially static atmosphere at a pressure of between about 517
KPa and about 13.7 MPa.
42. The polymerization process as set forth in any one of claims 24
to 41, wherein the monomer source is an aqueous solution of a
monomer and the solvent is water.
43. The polymerization process as set forth in any one of claims 24
to 41, wherein the monomer source is an aqueous emulsion of a
selected monomer and the solvent is water.
44. The polymerization process as set forth in any one of claims 24
to 43, wherein said first mixture is cooled prior to adding the
initiator source.
45. The polymerization process as set forth in any one of claims 24
to 44, which further comprises adding a crosslinker to the first
mixture.
46. The polymerization process as set forth in claim 45, wherein
the crosslinker source is an aqueous solution of a selected
crosslinker and the solvent is water.
47. The polymerization process as set forth in claim 45, wherein
the crosslinker source is an aqueous emulsion of a selected
crosslinker and the solvent is water.
48. The polymerization process as set forth in one of claims 24 to
47, wherein the monomer source is a water-soluble, unsaturated
monomer.
49. The polymerization process as set forth in any one of claims 24
to 48, wherein the monomer source is an unfunctionalized
olefin.
50. The polymerization process as set forth in any one of claims 24
to 48, wherein the monomer source is a functionalized olefin.
51. The polymerization process as set forth in any one of claims 24
to 48, wherein the monomer source is acrylic acid.
52. The polymerization process as set forth in any one of claims 24
to 48, wherein said monomer source is selected from the group
consisting of ethylenes, dienes, styrenes, propylenes, vinyls,
acrylates, methacrylates, acrylonitrile, methacrylonitrile,
acrylamide, methacrylamide, and alkenes.
53. The polymerization process as set forth in any one of claims 24
to 47 wherein the first mixture is cooled prior to adding the
initiator source.
54. The polymerization process as set forth in any one of claims 24
to 53 which further comprises adding a neutralizer to the first
mixture.
55. The polymerization process as set forth in any one of claims 24
to 54 wherein the second mixture is maintained at a temperature
between about 26.6 degrees C. and about 93.3 degrees C.
56. A polymerization process for producing an acrylic acid
containing polymer comprising the steps of: (a) preparing an
aqueous mixture of partially neutralized acrylic acid; (b) adding a
polymerization initiator to the aqueous mixture to form a second
mixture; and (c) spraying said second mixture into a heated,
pressure controlled, substantially static atmosphere, said spraying
resulting in the formation of droplets of said second mixture; and
(d) allowing said droplets of the sprayed second mixture to fall
through the heated, substantially static atmosphere for a
sufficient period of time to obtain a desired degree of
polymerization and thus form a partially neutralized acrylic acid
containing polymer in particle powder form.
57. A process for the continuous preparation of a copolymer for use
as a powder coating comprising the steps of: (a) preparing a liquid
mixture of two or more monomers; (b) homogenizing a pigment with
the liquid mixture of monomers; (c) spraying the liquid mixture
into a heated, pressure controlled, substantially static
atmosphere, said spraying resulting in the formation of droplets of
the mixture; and (d) allowing said droplets of the sprayed mixture
to fall through the heated, substantially static atmosphere a
period of time sufficient to obtain a substantially dry copolymer
that may be used for powder coating applications.
58. A process for the continuous preparation of an irregularly
puffed shaped polymer comprising the steps of: (a) preparing a
liquid mixture of one or more monomers; (b) spraying the liquid
mixture into a heated, pressure controlled, substantially static
atmosphere having reduced pressure, said spraying resulting in the
formation of droplets of the mixture; (c) allowing said droplets of
the sprayed mixture to fall through the heated, substantially
static atmosphere a period of time sufficient to obtain a
substantially dry irregularly puffed shaped polymer having
relatively low density.
59. A process for the continuous preparation of a detergent
comprising the steps of: (a) preparing a liquid mixture of
detergent raw materials; (b) spraying the liquid mixture into a
heated, pressure controlled, substantially static atmosphere, said
spraying resulting in the formation of droplets of the mixture; and
(c) allowing said droplets of the sprayed mixture to fall through
the heated, substantially static atmosphere a period of time
sufficient to obtain a substantially dry detergent powder.
60. The polymer product produced by the process of any one of
claims 24 to 58.
61. An acrylic acid containing polymer produced by an aqueous
radical polymerization process comprising the steps of: (a)
preparing an aqueous mixture of partially neutralized acrylic acid;
(b) adding a polymerization initiator to the aqueous mixture to
form a second mixture of polymerization reagents; (c) spraying said
second mixture into a heated, substantially static atmosphere, said
spraying resulting in the formation of droplets of said second
mixture; and (d) allowing said droplets of the sprayed second
mixture to fall through the heated, substantially static atmosphere
for a period of time sufficient to obtain a desired degree of
polymerization and thus form a partially neutralized acrylic acid
containing polymer in particle powder form.
62. The polymer as set forth in claim 61, wherein said polymer
produced is a water-absorbing polymer.
63. The polymer as set forth in claim 61, wherein said polymer
produced is a copolymer may be used for powder coating
applications.
64. The polymer as set forth in claim 61, wherein said polymer
produced is an irregularly puffed shaped polymer having relatively
low density.
65. The polymer as set forth in any one of claims 61 through 64,
wherein said polymer is produced in particle powder form and has a
particle size of less than approximately 100 microns.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a spray polymerization
process, an apparatus for producing a dry polymer and a polymer
having novel physical characteristics. Particularly, the present
invention relates to a polymerization process for the continuous
production in a controlled atmosphere of a substantially dry
polymer particle powder comprising polymer particles of desired
size, shape and density from a liquid monomer source.
[0002] It is known in the art that polymers may be synthesized by
step polymerization and chain polymerization processes. Chain
polymerization is initiated by a reactive species produced by a
compound or compounds referred to as an initiator. Generally,
monomers show varying degrees of selectivity with regard to the
type of reactive center that will cause chain polymerization.
Monomers show high selectivity between anionic and cationic
initiators, however, most monomers will undergo polymerization with
a radical initiator, although at varying rates. Examples of the
types of monomers which will polymerize to high molecular weight
polymers in the presence of a radical initiator include: ethylene;
1,3-dienes; styrene; halogenated olefins; vinyl esters; acrylates;
methacrylates; acrylonitrile; methacrylonitrile; acrylamide;
methacrylamide; N-vinyl carbazole; N-vinyl pyrrolidone.
[0003] Essentially, radical polymerization conditions are either
homogenous or heterogeneous, depending upon whether the initial
reaction mixture is homogenous or heterogeneous. Some homogeneous
systems however, may become heterogeneous as polymerization
proceeds due to the insolubility of the polymer in the reaction
media. Generally, mass and solution polymerizations are homogeneous
processes, while suspension and emulsion polymerizations are
heterogeneous processes. All monomers can be polymerized by any of
the various processes however, it is usually found that for
commercial considerations the polymerization of a particular
monomer is best carried out by one or two of the processes.
[0004] Bulk or mass polymerization of a pure monomer offers the
simplest process with a minimum of contamination of the product.
Bulk polymerization, however, is difficult to control due to the
characteristics of radical chain polymerization. The bulk process
is highly exothermic, high activation energies are involved, and
there is a tendency toward the gel effect. Such characteristics
make the dissipation of heat difficult, therefor, careful
temperature control is required during bulk polymerization
processes. Additionally, the viscosity of the reaction system
increases rapidly at a relatively low conversion, thereby requiring
the use of elaborate stirring equipment. Localized "hot spots" may
occur which damage, degrade and discolor the polymer product, and a
broadened molecular weight distribution may result due to chain
transfer between polymer molecules. There is also the risk in
extreme cases that an uncontrolled acceleration of the
polymerization rate can lead to disastrous runaway-type
reactions.
[0005] Many of the disadvantages of bulk polymerization may be
overcome by polymerizing a monomer in a solvent (solution
polymerization). The solvent, which may be water, acts as a diluent
and aids in the transfer of the heat of polymerization. The solvent
can be easily stirred since the viscosity of the reaction mixture
is decreased. Although thermal control of a solution polymerization
process is easier than with mass or bulk polymerization, the purity
of the polymer may be affected if there are difficulties in
removing the solvent during and following polymerization.
[0006] Heterogeneous polymerization is used extensively to control
the thermal viscosity problems often associated with homogeneous
processes. Precipitation polymerization is a heterogeneous
polymerization process which begins as a homogeneous polymerization
but converts to heterogeneous polymerization. A monomer either in
bulk or in solution (usually aqueous but sometimes organic) forms
an insoluble polymer in the reaction medium. Precipitation
polymerization can be referred to as powder or granular
polymerizations because of the forms in which the final polymer
products are obtained. The initiators used in precipitation
polymerization are soluble in the initial reaction medium and
polymerization proceeds following absorption of monomer into the
polymer particles.
[0007] Suspension polymerization, also referred to as bead or pearl
polymerization, is carried out by suspending the monomer
(discontinuous phase) as droplets (50 to 500 .mu.m in diameter) in
water (continuous phase). The ratio of water to monomer typically
will vary from about 1:1 to 4:1 in most polymerizations. The
monomer droplets which are subsequently converted to polymer
particles do not coalesce due to agitation and the presence of
suspension stabilizers also referred to as dispersants or
surfactants. Stabilizers may be water soluble polymers or water
insoluble inorganic powders. The suspension stabilizers are used
typically in an amount that is less than 0.1 weight percent of the
aqueous phase. The two-phase suspension system cannot be maintained
in suspension polymerization without agitation.
[0008] Suspension polymerization initiators are soluble in the
monomer droplets and are referred to as oil-soluble initiators.
Suspension polymerization in the presence of high concentrations of
water soluble stabilizers are used to produce latex-like
dispersions of particles having small particle size. Such
suspension polymerizations may be referred to as dispersion
polymerizations. Inverse microsuspension polymerization involves an
organic solvent as a continuous phase of a water soluble monomer
either neat or dissolved in water. Inverse dispersion refers to
systems involving the organic solvent as continuous phase with
dissolved monomer initiator that yield insoluble polymer.
[0009] Emulsion polymerization involves the polymerization of
monomers in the form of emulsions, i.e., colloidal dispersions.
Emulsion polymerization differs from suspension polymerization in
the type and smaller size of the particles in which polymerization
occurs, in the kind of initiator employed, and in the dependence of
polymer molecular weight on reaction parameters. For most
polymerization processes there is an inverse relationship between
the polymerization rate and the polymer molecular weight. Large
decreases in the molecular weight of a polymer can be made without
altering the polymerization rate by using chain transfer agents.
Large increases in molecular weight can be made only by decreasing
the polymerization rate, by lowering the initiator concentration,
or lowering the reaction temperature.
[0010] Emulsion polymerization allows increasing the polymer
molecular weight without decreasing the polymerization rate.
Emulsion polymerization has the advantage of being able to
simultaneously obtain both high molecular weights and high reaction
rates. The dispersing medium is usually water in which the various
components are dispersed by means of an emulsifier. Other
components include the monomer, a dispersing medium and a water
soluble initiator. Surfactants are typically used in emulsion
polymerizations at from 1 to 5% weight. The ratio of water to
monomer is generally in the range 70/30 to 40/60 by weight.
[0011] The polymerization processes discussed above involve
additional steps either to dry the polymer formed, separate the
polymer from the organic solvent used in the process, or to recover
the organic solvent. The added steps require additional energy and
time in preparing the final product, thereby increasing the cost of
the polymer produced. Moreover, the polymers produced using these
known processes typically are produced as an agglomeration which
must, following drying, be pulverized or in some way broken up to
yield a usable polymer product. Breaking up the polymer product by
grinding or pulverizing produces a substantial amount of dust which
raises environmental and health concerns to those having to work in
and around the polymer dust.
[0012] Therefore, there remains a need for a polymerization process
and an apparatus in which to carry out the process which will
enable the production of a dry polymer particle powder, thus
eliminating the need to dry and pulverize the polymer product
produced. There is also a need for a polymerization process for
producing polymers which are immediately available for use
following the completion of the polymerization process.
[0013] Finally, there is a need for a process to produce a polymer
which allows the size, shape, and density of the polymer to be
controlled easily and precisely. This is particularly important,
for example, with polymers used in situations where a smooth
surface is beneficial, such as in fiber optic cables. Fiber optic
cables, which are becoming more common in telecommunications, are
susceptible to invasive water. However, the use of super-absorbing
polymers in fiber optic cables is problematical because of the
relatively "soft" cladding around each fiber. The "softness" of the
cladding makes it prone to scratching, which alters the refractive
index of the cladding, and therefore, the ability of the fiber to
conduct light. Experimentation has shown that superabsorbers
produced by known processes cause very fine scratching of the
cladding, an effect which is attributed to the rough surfaces of
the polymer particles resulting from the pulverization, grinding,
or chopping of the solid cross-linked polymer resulting from the
above-described production methods into a fine powder as described
above. The scratches in the surface of the cladding occur whenever
the fiber optic cable is flexed, e.g., when the cable is wound on a
spool and then wound off the spool for installation.
[0014] Polymerization processes frequently require that
polymerization take rate or on a nucleating particle of some kind.
For example, U.S. Pat. No. 4,135,043 discloses a process for
manufacturing hydrophilic polymers. A previously formed polymer is
coated with similar type monomers to form a coating on the polymer
seed. Thereafter, the coated seed is heated in order to polymerize
the coating thereon. Processes of this type also require that the
additional production steps discussed above be employed.
[0015] Exemplary shortcomings of current polymerization processes
are the known methods for the production of water-absorbing
polymers. Such methods can be categorized as involving either an
aqueous system or a multi-phase process. Aqueous systems for
production of such polymers generally result in a semi-solid mass
of material from which water must be removed in an energy-intensive
drying step. For instance, in U.S. Pat. No. 4,295,987, the mixture
of polymerized monomers must be dehydrated with excess methanol to
form a firm solid that is dried in, for instance, a vacuum oven,
and then ground into particles of a desired size or into a
powder.
[0016] Also known are methods for continuous production of such
polymers in an aqueous system as illustrated by the description set
out in U.S. Pat. No. 4,525,527, hereby incorporated in its entirety
by this specific reference thereto. Briefly, that patent describes
the heating of an aqueous monomer solution to which an initiator is
added by pouring the initiator onto the mixture as the mixture
flows onto a traveling conveyer belt. The polymerization is
exothermic, helping to drive off the water, and results in a
"relatively dry, solid polymer of low water content", said to be
8-15% water. The solid polymer is then made into a powder by
pulverization.
[0017] Multi-phase processes involve polymerization of an aqueous
reaction mixture in an inert organic solvent, followed by the
removal of the solvent from the polymerized product. So far as is
known, such processes are batch processes, and a representative
example of such a process in U.S. Pat. No. 4,446,261, hereby
incorporated in its entirety by this specific reference thereto.
That patent describes the preparation of polymer beads by
suspension of an aqueous solution monomer and crosslinker in a
hydrocarbon or halogenated aromatic hydrocarbon and polymerization
of the monomer upon addition of a water soluble initiator. As
described in that patent, the hydrocarbon is removed by
distillation under reduced pressure and the residual polymer
particles dried by heating under reduced pressure.
[0018] Other examples of such processes are found in the following
U.S. patents:
1 AQUEOUS 3,661,815 3,669,103 4,071,650 4,167,464 4,286,082
4,295,987 4,342,858 4,351,922 4,389,513 4,401,795 4,525,527
4,552,938 4,612,250 4,618,631 4,654,393 4,703,067 MULTI-PHASE
4,059,552 4,093,776 4,340,706 4,446,261 4,459,396 4,666,975
AQUEOUS/MULTI-PHASE 4,062,817 4,654,039
[0019] Both types of processes are characterized by a number of
disadvantages which add to the cost of producing such polymers such
that there is a need for an improved method for producing these and
other polymers. For instance, both aqueous and multi-phase batch
processes require drying of the polymer.
[0020] Another disadvantage to producing polymers by known
polymerization methods, particularly with respect to
water-absorbing polymers, is the difficulty often experienced in
controlling the size, shape, and density of the polymers produced.
For example, water-absorbing polymer particles with a smooth
external surface are, so far as is known by Applicants, are
previously unknown. It appears that at least some multi-phase
methods for production of such polymers result in spherical (see,
for instance, column 5, lines 39, 48 and 60 of the
above-incorporated U.S. Pat. No. 4,446,261) or donut-shaped (see
column 6, line 57 of the above-incorporated U.S. Pat. No.
4,342,858) particles, but Applicants have been unable to find any
such particles which have a smooth surface. Instead, all known
particles are characterized by either a rough surface or by a
surface such as that described in the above-listed U.S. Pat. No.
4,342,8 (column 6, lines 56-58) as being "high surface area donuts
of collapsed spherical shapes with 2 to 5 micron protuberances on
their surfaces".
[0021] Some additional disadvantages are characterized at, for
instance, column 2, lines 56 et seq. of U.S. Pat. No. 4,093,776 and
column 1, lines 18-56 of U.S. Pat. No. 4,625,001, both hereby
incorporated in their entirety by this separate reference
thereto.
[0022] It is, therefore, an object of the present invention to
provide a novel polymer in which the size, shape and density of the
polymer can be easily and precisely controlled, and a process and
apparatus for doing so.
[0023] It is another object of the present invention to provide a
novel polymer in which the degree of crosslinking and the water
content of the resulting particle can be conveniently and precisely
controlled, and a process and apparatus for doing so.
[0024] It is an object of the present invention to provide a novel
polymer which is not formed on a substrate or other precursor which
acts as a seed or nucleus for the polymer formation, and a process
and apparatus for doing so.
[0025] It is an object of the present invention to provide a
process and apparatus for producing a polymer which eliminates the
difficulty inherent in the handling of the highly viscous solution,
gel, or cake resulting from the production of such polymers with
known processes.
[0026] It is another object of the present invention to eliminate
the necessary grinding, pulverization, and/or chopping of a
semi-solid mass of polymer which characterizes known processes for
making polymers.
[0027] It is another object of the present invention to eliminate
the costly step of recovering the organic solvent or medium used in
known processes for the production of polymers.
[0028] Another object of the present invention is to provide a
process and apparatus for producing a polymer which eliminates the
costly drying step of many known processes for producing
polymers.
[0029] It is an object of the present invention to provide a
polymerization process which allows the polymerization reaction,
polymer particle size, polymer particle shape, and water content of
the polymer particle powder produced to be easily controlled.
[0030] It is an object of the present invention to provide a
process and apparatus for using a fluid source of a selected
monomer to produce a substantially dry polymer particle powder.
[0031] Other objects, and the advantages, of the present invention
will be made clear to those skilled in the art from a review of the
following detailed description of the presently preferred
embodiments thereof.
SUMMARY OF THE INVENTION
[0032] An atmospheric chain polymerization process is provided. The
process comprises preparing a first mixture of at least one monomer
source and a solvent selected from the group consisting of water,
organic solvents and mixtures thereof, and adding an initiator
source to the first mixture to form a second mixture of
polymerization reagents. A crosslinker, neutralizer, or other
reagents may also be added to the first mixture. The mixture of
polymerization reagents is sprayed into a heated, controlled
atmosphere. The heated, controlled atmosphere is maintained in a
closed vessel, such as a reaction chamber. Spraying the mixture
results in the formation of droplets which experience free fall
through the heated, controlled atmosphere for a sufficient period
of time to obtain a desired degree of polymerization. The solvent
is continuously evacuated from the atmosphere during the
polymerization process.
[0033] It is preferred that the mixture of polymerization reagents
is sprayed into the chamber at the top section of the chamber. It
is also preferred that the reaction chamber is about 3.65 to about
30.48 meters in height. Preferably, the pressure in the reaction
chamber is maintained at less than ambient atmospheric pressure.
Desired pressure levels include from about 338.6 to about 50,790
N/m.sup.2 below ambient atmospheric pressure. Further, it is
preferred that the reaction chamber is heated to a temperature of
from about 23.8.degree. C. to about 148.8.degree. C. during the
polymerization reaction.
[0034] It is further preferred that the first mixture is maintained
at a desired temperature and pressure prior to adding the initiator
source. It is also preferred that the second mixture is maintained
at a temperature of between about 26.6.degree. and about
93.3.degree. C.
[0035] In the preferred embodiment of the process, the second
mixture of reagents is sprayed into the atmosphere through one or
more nozzles. A substantially dry polymer particle powder is
produced by the polymerization reaction. Polymer particle is
defined herein as a substantially dry powder-like product.
Substantially dry means that the particles will not agglomerate or
stick together, and the powder is free flowing. The present process
enables the production of polymers from about 20 microns to about
125,000 microns in size. However, polymer size, shape, and density
in a powder will be fairly uniform when prepared under similar
pressure, temperature, and the other parameters which will be more
fully discussed in the Detailed Description of the Invention.
[0036] The size of the polymer particle produced may be varied by
increasing or decreasing the size of the nozzle opening. In the
preferred process the mixture of polymerization reagents is sprayed
into the heated, controlled atmosphere at a pressure of between
about 517 KPa and about 13.7 MPa. The dry polymer particle powder
may be recovered while maintaining a heated, controlled
atmosphere.
[0037] The monomer source may be an aqueous solution, slurry, or
emulsion of a selected monomer. The preferred solvent is water.
Similarly, the crosslinker source may be an aqueous solution,
slurry, or emulsion of a selected crosslinker and the solvent is
water.
[0038] Monomer sources which may be polymerized using the process
include unfunctionalized olefins and functionalized olefins,
including but not limited to acrylic acid, ethylenes, dienes,
styrenes, propylenes, vinyls, methacrylates, acrylonitrile,
methacrylonitrile, acrylamide, methacrylamide, and alkenes.
[0039] A polymerization process is also provided for producing an
acrylic acid containing polymer. The process comprises the steps of
preparing an aqueous mixture of partially neutralized acrylic acid,
adding a polymerization initiator to the aqueous mixture to form a
second mixture of polymerization reagents, and spraying said second
mixture into a heated, controlled atmosphere. The spraying of the
mixture results in the formation of droplets of said second mixture
which are allowed to fall through the heated, controlled atmosphere
for a sufficient period of time to obtain a desired degree of
polymerization and thus form a partially neutralized acrylic acid
containing polymer in particle powder form.
[0040] Polymers produced according to the process are also
provided.
[0041] A radical polymerization apparatus is provided. The
apparatus comprises a reaction chamber, a means for heating the
reaction chamber, preferably from about 3.65 to about 30.48 meters
in height, a means for controlling the pressure within said
reaction chamber, one or more nozzles connected to a feed line for
receiving a mixture of a monomer source and an initiator source,
and a means for spraying the mixture into the top section of the
reaction chamber. Spraying the mixture into the chamber results in
the formation of droplets which fall through the reaction chamber
for a sufficient period of time to obtain a desired degree of
polymerization. It is preferred that the mixture is sprayed into
the reaction chamber at from about 517 KPa to about 13.7 MPa of
pressure.
[0042] Preferably, the pressure in the reaction chamber is
maintained at less than ambient pressure. Desired pressure levels
include from about 338.6 to about 50,790 N/m.sup.2 below ambient
atmospheric pressure. Further, it is preferred that the reaction
chamber is heated to a temperature of from about 23.8.degree. C. to
about 148.8.degree. C. during the polymerization reaction.
[0043] The apparatus may further comprise a means for removing the
polymer from the bottom of said reaction chamber while maintaining
the heat and the pressure within the chamber. The means for
removing the polymer may comprise a trough located in the bottom of
the reaction chamber, a first auger mounted in the bottom of the
trough for moving the polymer out of the chamber, a bin into which
the first auger deposits the polymer and a second auger mounted in
the bottom of the bin for moving the polymer out of the bin.
[0044] It is preferred that the apparatus further comprises a means
for controlling the temperature of the monomer and initiator
mixture in the feed line. It is also preferred that the apparatus
includes a means for mixing the monomer and initiator before it is
sprayed into the chamber.
[0045] Means are also provided for removing unpolymerized monomer
in a vapor state from said reaction chamber by purging the reaction
chamber with nitrogen. Separate reservoirs are provided for the
monomer source and the initiator source. Reservoirs may also be
provided for a crosslinker source, and other reagents. When it is
desired that crosslinked polymer structures be produced,
crosslinker is added to the mixture of monomer source and initiator
source prior to the mixture being sprayed into the reaction
chamber.
[0046] Polymers produced using the apparatus may be polymerized
from unfunctionalized olefins and functionalized olefins, including
but not limited to acrylic acid, ethylenes, dienes, styrenes,
propylenes, vinyls, methacrylates, acrylonitrile,
methacrylonitrile, acrylamide, methacrylamide, and alkenes.
[0047] A polymer is produced by a radical polymerization process
comprising the steps of preparing a first mixture of at least one
monomer source and a solvent selected from the group consisting
essentially of water and organic solvents, adding an initiator
source to the first mixture to form a second mixture of
polymerization reagents, then spraying the second mixture of
reagents into a heated, controlled atmosphere. The heated,
controlled atmosphere is maintained in a closed vessel or reaction
chamber which is preferably about 3.65 to about 30.48 meters in
height. Preferably., the second mixture is sprayed in at the top
section of the vessel.
[0048] It is preferred that the first mixture is maintained at a
desired temperature and pressure prior to adding the initiator
source. It is also preferred that the second mixture is maintained
at a temperature of between about 26.6.degree. C. and about
93.3.degree. C. The spraying of the second mixture of reagents into
the atmosphere through one or more nozzles results in the formation
of droplets which are allowed to fall through the heated,
controlled atmosphere for a sufficient period of time to obtain a
desired degree of polymerization. The solvent and unpolymerized
monomer is continuously evacuated from the atmosphere during the
polymerization process. The polymer produced is in dry particle
powder form and is recovered from the vessel while maintaining a
heated, controlled atmosphere. The polymers may range in size from
about 2 to about 125,000 microns in size. The size of the polymer
particle produced can be varied by increasing or decreasing the
size of the nozzle opening. It is preferred that the second mixture
of polymerization reagents be sprayed into the heated, controlled
atmosphere at a pressure of between about 517 KPa and about 13.7
MPa.
[0049] In a preferred embodiment, the atmosphere is maintained at a
temperature of from about 23.8.degree. C. to about 148.8.degree. C.
It is also preferred that the controlled atmosphere is at reduced
pressure maintained at a pressure of from about 338.6 to about
50,790 N/m.sup.2 below ambient atmospheric pressure.
[0050] When desired to produce crosslinked polymer structures, a
crosslinker may be added to the first mixture. A neutralizer may
also be added to the first mixture. The monomer source may be a
water-soluble, unsaturated monomer which, when a crosslinker is
added to the polymerization mixture of reagents, results in a
water-absorbing polymer being produced.
[0051] The monomer source may be an aqueous solution, slurry, or
emulsion of a selected monomer. The preferred solvent is water.
Similarly, the crosslinker source may be an aqueous solution,
slurry, or emulsion of a selected crosslinker and the solvent is
water.
[0052] The monomer source may be unfunctionalized olefins or
functionalized olefins, including but not limited to acrylic acid,
or selected from the group of compounds consisting essentially of
ethylenes, dienes, styrenes, propylenes, vinyls, esters, acrylates,
methacrylates, acrylonitrile, methacrylonitrile, acrylamide,
methacrylamide, and alkenes.
[0053] An acrylic acid containing polymer is produced by an aqueous
radical polymerization process comprising the steps of preparing an
aqueous mixture of acrylic acid, adding a polymerization initiator
to the aqueous mixture to form a second mixture of polymerization
reagents, and spraying the second mixture into a heated, controlled
atmosphere. Spraying results in the formation of droplets of the
second mixture. The droplets of the sprayed second mixture are
allowed to fall through the heated, controlled atmosphere for a
sufficient period of time to obtain a desired degree of
polymerization and thus form an acrylic acid containing polymer in
particle powder form. The polymer produced is a water-absorbing
polymer in substantially dry powder form and has, for example, a
particle size of less than approximately 100 microns.
[0054] An unexpected advantage of producing polymers in accordance
with the present invention is the production of a particle having a
smooth external surface, making possible certain new uses for such
polymers, particularly water-absorbing polymers. For instance,
known water absorbing polymers may be used to advantage in
telecommunications cables for the purpose of protecting the
conductors from shorts caused by invasive water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] FIG. 1 is a schematic representation of an apparatus
constructed in accordance with the present invention.
[0056] FIG. 2 is a sectional view, taken along the lines 2-2 in
FIG. 1, of the apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0057] Referring first to FIG. 1, there is shown an apparatus
constructed in accordance with the present invention designated
generally at reference numeral 10. Briefly, the apparatus 10 is
comprised of a reaction chamber or other closed vessel 12, means
for heating the reaction chamber 12, shown schematically at
reference numeral 14, means for reducing the pressure in reaction
chamber 12 in the form of the vacuum pump 16, nozzle 18 connected
to a feed line 20 for receiving a mixture of a monomer and an
initiator from the respective sources 22 and 28 thereof, and means,
in the form of the bins and auger system indicated generally at
reference numeral 26, for removing the dry polymer particle powder
produced in reaction chamber 12 from the bottom thereof while
maintaining reduced pressure in the reaction chamber 12. Reaction
chamber 12 will preferably be about 3.65 to about 30.48 meters in
height.
[0058] In more detail, the apparatus 10 includes sources, or
reservoirs, of monomers 22, initiator 28, and a third reservoir 24
preferably comprising a source of a crosslinker. A crosslinker or
combination of crosslinkers will be added to the monomer and
initiator mixture when it is desirable to produce crosslinked
polymer structures, such as water-absorbing acrylic family
polymers. Other reservoirs (not shown), each preferably
individually temperature controlled, are provided for other
monomers (for co-polymerization processes), water, neutralizer,
stabilizer, transfer agent, solvent, or other reagents.
[0059] Each of the reservoirs 22, 24 and 28 may contain an aqueous
and/or organic solvent-based solution, suspension, or emulsion of
the respective reagent and therefore is preferably provided with
valves 30, 32 and 34, respectively, for controlling the flow of the
respective reagents therefrom under the influence of the pumps 36.
Alternatively, feed line 20 is pressure fed from the respective
reservoirs 22, 24 and 28. Feed line 20 is provided with means,
indicated generally at reference numeral 44, for mixing the aqueous
and/or organic solvent-based mixture of reagents to insure uniform
distribution between monomer, initiator, and other reagents of the
polymerization mixture. Mixing means 44 takes a number of forms
known in the art such as an in-line screw or auger, mill, vat with
stirring blades, or baffle system. Also provided is a hatch 38 in
the housing of mixing means for adding any other types of
reagents.
[0060] Because the polymerization of the monomer begins almost
instantaneously upon the mixing of the initiator and monomer and
proceeds rapidly in an exothermic reaction, the temperature of the
mixture in feed line 20 is used to control the degree of
polymerization of the monomer and, when crosslinkers are added, the
degree of crosslinking of the polymer structure (note that FIG. 1
is not drawn to scale). To that end, a means is provided for
controlling the temperature of the mixture in feed line 20 which is
shown schematically at reference numeral 42. Temperature control
means 42 may take the form of a water bath, refrigeration coils,
insulation, a combination of heating elements and refrigeration
coils, or any other means known for controlling temperature,
depending upon the nature of the monomer(s) being polymerized
and/or crosslinked. Means 42 is used primarily to reduce the heat
resulting from the exothermic polymerization reaction. Lowering the
temperature of the reagent mixture in line 20 prevents the
polymerization rate of the monomer source.
[0061] In a preferred embodiment, line 20 is provided with a
nitrogen pure chamber 45 fed by a line 46 having a valve 48 therein
for a flow of nitrogen to purge the mixture of reagents flowing
therethrough. A metered pump 40 in feed line 20 provides control
over the pressure and rate of flow of the mixture of reagents.
[0062] The pressure of the atmosphere in reaction chamber 12 is
controlled during the polymerization reaction. The pressure of the
atmosphere in reaction chamber 12 may be reduced relative to the
ambient pressure by vacuum pump 16, the atmosphere therein being
removed from reaction chamber 12 through line 50. A filter 52 is
provided at the intake of line 50 to prevent droplets/particles of
polymerized monomer from being pulled into vacuum pump 16. Filter
52 is preferably set in a frame accessible from the exterior of
reaction chamber 12 to facilitate periodic changing of the filter
element (not shown).
[0063] The pressure of the atmosphere in reaction chamber 12 may
also be increased above ambient atmospheric pressure in order to
produce a polymer particle of a more dense construction than is
produced at below atmospheric pressure.
[0064] An air intake or vent line 54 having a flow control valve 56
therein is provided at the top of reaction chamber 12 for allowing
ambient air into reaction chamber 12 to purge line 50 and pump 16
and/or in the event of an emergency shutdown. Instead of using air
intake line 54 as a vent, nitrogen can also be introduced into the
atmosphere in reaction chamber 12 through line 54 to purge the
atmosphere therein, in which case, a purge line 55 is provided for
recapturing the nitrogen. Again, a filter 57 prevents polymer
particles from being pulled into line 55. Reaction chamber 12 is
also provided with means 62, in the form of a clean-out hatch, for
removing unpolymerized monomer, or, in the event of a malfunction
of particle removing means 26, the dry polymerized particles, from
the bottom thereof. Heater 14 may be multiple resistive heating
elements, gas burners, or steam lines, indicated schematically at
reference numeral 58, powered from a common line 60 from a source
of electricity, steam, or gas (not shown).
[0065] Means 26 is provided for removing the polymer from the
bottom of reaction chamber 12 while maintaining the heat and
atmosphere therein. Means 26 may be any of the devices known to
those skilled in the art. For example, as shown in FIG. 1, a
V-shaped trough 64 is formed from two sloping sides 66 which form
the bottom of reaction chamber 12. A first auger, screw, or other
continuous conveyer system 68 is mounted in the bottom thereof for
moving the particles of polymer out of reaction chamber 12 for
deposit into a bin 70. Bin 70 is provided with a second auger,
screw, or other continuous conveyer system 72 mounted in the bottom
thereof for moving the polymer deposited therein by first auger 68
out of bin 70 into a hopper, bag or other storage/collection
container 74. The respective augers 68 and 72 are driven by motors
76 and 78 or by a single motor and belt pulley system (not
shown).
[0066] The accumulated dry polymer particles 80 in the bottom of
tower 12 cover the portal 82 out of the bottom reaction chamber 12
to maintain the reduced pressure therein as first auger 68 moves
the accumulated polymer particles 80 into bin 70. A shroud 84
covers first auger between reaction chamber 12 and bin 70 to
prevent the influx of ambient air into reaction chamber 12 and bin
70 is closed by a lid 86 at the top thereof. A portal 88 in the
bottom of bin 70 allows the accumulated polymer particles in bin 70
to be moved out of bin 70 into hopper 74. In the same manner that
the accumulated polymer particles 80 cover the portal 82 in the
bottom of reaction chamber 12, accumulated polymer particles 90
cover the portal 88 in the bottom of bin 70 to prevent an influx of
ambient air therethrough.
[0067] As will be explained below, the conditions under which
polymerization and crosslinking occur are such that the particles
of polymer 80 which accumulate at the bottom of reaction chamber 12
are substantially dry and have a low moisture content, and in light
of the ability of some polymers to absorb moisture, preventing
access to the accumulated polymer 80 by relatively humid ambient
air is necessary to preventing the caking of the dry, accumulated
polymer 80 as it is moved out of reaction chamber 12. Those skilled
in the art who have the benefit of the disclosure will recognize
that other means can be utilized to remove the dry accumulated
polymer 80 from the bottom of reaction chamber 12 without breaking
the vacuum therein. For instance, commercially available gravity
feed, intermittent dump, and suction devices are all used to
advantage for this purpose.
[0068] As shown in FIG. 2, feed line 20 enters reaction chamber 12
and terminates in a loop 94 having a plurality of nozzles 18 set
therein. Alternatively, a single nozzle may be used. Nozzles 18 are
preferably screwed into the threads 96 formed at intervals around
the loop 94 for ease in removing nozzles 18 for cleaning and/or
changing. In another preferred embodiment (not shown), the loop 94
in feed line 20 is positioned outside of the top of tower 12. The
latter embodiment is particularly advantageous for frequent
changing of nozzles 18 to, for instance, change the diameter of the
polymeric spheres.
[0069] If larger diameter particles are desired, the mixture in
line 20 is sprayed into reaction chamber 12 at relatively low
pressure, e.g., about 517 KPa to about 2.06 MPa through nozzles 18
having a larger diameter orifice, for instance, a number 16 nozzle.
If it is desired to produce a smaller diameter sphere, the pressure
in line 20 is increased with pump 40, e.g., from about 1.03 MPa on
up to as high as perhaps 13.7 MPa, causing the mixture to be
atomized into finer sized particles. If even smaller particles are
desired, or if it is desired to produce smaller diameter particles
at lower spray pressures, nozzles 18 are replaced with nozzles
having smaller orifices, e.g., a number 64 nozzle.
[0070] With reference to the figures, the method of continuously
producing a polymer in accordance with the present invention will
now be explained. The method comprises the mixing of the monomer
source in water or organic solvent in mixer 44 to prepare a liquid
monomer source. Alternatively, liquid monomer sources may be
obtained from sources known to those skilled in the art. It is
preferred that the monomer be an aqueous monomer source. An
initiator, crosslinker, additional water, neutralizer and/or other
reagents may be added to the monomer source in mixer 44. In the
preferred embodiment of the process, the monomer, initiator, and
other reagents used will be soluble in water or the organic solvent
used to prepare the liquid monomer source. It is preferred,
however, that the monomer, initiator and other reagents are soluble
in water. Initiator sources suitable for use with selected monomers
will be known to those skilled in the art.
[0071] It is preferred that the initiator is added downstream from
the monomer source immediately prior to the mixture being sprayed
into the reaction chamber 12 to reduce the likelihood that line 20
or nozzles 18 will become clogged by prepolymerization of the
monomers. Although it is preferred that an initiator be added to
the monomer source, some monomers may undergo self-initiated
polymerization, thus eliminating the need for an initiator.
However, the rate and extent of polymerization is facilitated by
the use of an initiator.
[0072] Note that it may be advantageous to agitate or otherwise
insure adequate mixing of initiator and aqueous mixture by use of a
second mixing means (not shown) similar to mixing means 44
downstream of the point at which the initiator is added to line
20.
[0073] Reaction chamber 12 is heated by heater 14 and the pressure
of the atmosphere is controlled according to the monomer source
being polymerized. Desired pressures at which to cause
polymerization of selected monomers will be known to those skilled
in the art. The atmosphere is maintained at a reduced pressure by
vacuum pump 16. The atmosphere may be controlled at a positive
pressure by use of a pressure release valve in conjuction with the
pressure evacuation pump. However, a positive pressure may be
established by a pressure pump or other means known to those in the
art in the chamber prior to spraying in the mixture.
[0074] The mixture of monomers and/or reagents is sprayed into the
heated, controlled atmosphere, thereby forming droplets of the
mixture. The droplets are allowed to fall through the reaction
chamber for a period of time sufficient to allow the desired degree
of polymerization of the monomers, and where a crosslinker has been
added, crosslinking of the polymerized monomer, to form particles
of polymer. The polymer particles formed may be linear, branched or
crosslinked polymers, depending upon the composition of the sprayed
mixture.
[0075] As the droplets of the mixture of monomers and/or reagents
fall from the spray nozzle through the chamber, water and/or
solvents associated with the polymerization mixture are continually
evaporated or volatilized as the polymerization reaction occurs. In
the presence of the preferred reduced pressure within chamber 12,
water and/or solvent associated with the mixture is continually
evaporated or volatilized due to both the presence of heat and the
reduced pressure. Vapors are evacuated by vacuum pump 16 during the
polymerization action. Alternatively, in the presence of positive
pressure within chamber 12, the water and/or solvent associated
with the mixture is evaporated due to the heat within the
chamber.
[0076] The polymer particles produced as a result of the
polymerization process are in the form of a substantially dry
powder 80. The polymers produced in dry particle form by this
process may have a particle size from as small as approximately 2
microns up to as large as about 125,000 microns (approximately 1/8
inch). The size of the polymer will depend upon the pressure,
temperatures, and other parameters discussed more fully below which
are present and/or utilized during the polymerization process. The
polymer size, shape, and density, however, will be relatively
uniform when produced under similar conditions. The fallen
particles of polymer 80 which collect at the bottom of reaction
chamber 12 are removed while continuing to control the pressure
within the chamber. The atmosphere will be maintained at the
pressure desired for the selected polymerization desired as the
polymer is removed.
[0077] In a particularly preferred embodiment, the method of the
present invention additionally comprises allowing sufficient fallen
particles of polymer 80 to accumulate at the bottom of reaction
chamber 12. The accumulated polymer particles form a large enough
mass of heated particles to decrease the amount of energy required
to maintain the temperature of the atmosphere within reaction
chamber 12 at a desired temperature.
[0078] It is preferred that the atmosphere in reaction chamber 12
be heated to a temperature of between about 23.8.degree. C. and
about 148.8.degree. C. Temperatures of between about 82.2.degree.
C. and about 110.degree. C. have been found to be particularly
preferred. Although it is possible to make polymers at temperatures
below 37.8.degree. C., a larger reduction of the pressure within
reaction chamber 12 must be present if low water or solvent content
and low residual monomer levels are to be maintained.
[0079] The polymerization reaction and, when crosslinker is added
to the mixture, crosslinking which occurs as the droplets fall
through reaction chamber 12 is exothermic such that relatively
little external heat is needed from heater 14 once a desired
temperature is reached and the continuous
polymerization/crosslinking is underway. Hence, temperatures of
well above, for instance, 37.8.degree. C. can be maintained without
compromising the efficiency of the method. Further adding to the
efficiency of the method of the present invention is the heat
retention of the accumulated mass of particles 80 at the bottom of
reaction chamber 12.
[0080] The pressure of the atmosphere inside reaction chamber 12
need not be reduced below or raised above ambient atmospheric
pressure to produce polymers. However, even relatively minor
reductions in the pressure below nominal ambient pressure of about
101,580 N/m.sup.2 cause disproportionate decreases in the water
content of the polymers produced and the amount of unpolymerized
residual monomer which does not participate in the polymerization
and/or cross-linking reaction. For this reason it is preferred that
the polymerization process be conducted under reduced pressure
conditions in the chamber.
[0081] Reductions in pressure of from about 338.6 up to about
50,790 N/m.sup.2 is preferred for use in connection with the method
of the present invention. For a given particle size, the water
and/or residual monomer content is directly correlated between the
temperature of the atmosphere within reaction chamber 12 and the
pressure at which the atmosphere within reaction chamber 12 is
maintained. As a general rule, as temperature is increased, the
percentage of residual monomer and/or water or solvent content can
be maintained at low levels with progressively smaller reductions
in pressure relative to ambient pressure. Likewise, as the pressure
of the atmosphere in reaction chamber 12 is decreased relative to
ambient, low percentages of residual monomer and/or water or
solvent content can be maintained with progressively lower
temperatures.
[0082] Alternatively, the polymerization reaction may be conducted
under increased pressure conditions within reaction chamber 12.
Increases in pressure within the reaction chamber of from about
ambient to about 2 psi may be used to practice the invention. As a
general rule, as temperature is increased, the percentage of
residual monomer and/or water or solvent content can be maintained
at desired low levels with progressively smaller increases in
pressure relative to below ambient pressures. Likewise, as the
pressure of the atmosphere in reaction chamber 12 is increased
relative to ambient, low percentages of residual monomer and/or
water or solvent content can be maintained with progressively
higher temperatures.
[0083] The shape of the polymer is also influenced by the below
ambient pressure in the chamber. Varying the pressure allows
production of from spherical to more irregular-shaped polymers. At
lower below ambient pressures, the polymers will be less uniform in
shape and have rougher edges or flake-like appearances. As the
reduced pressure approaches ambient, the polymers become more
spherical than is observed with polymers produced, for example, at
15 inches of Hg below atmospheric ambient pressure. Increasing the
pressure within the chamber enables the production of a smoother,
more dense polymer sphere than those produced in low atmospheric
pressure conditions.
[0084] The period of time required during which the droplets fall
through the atmosphere within reaction chamber 12, determine the
height of the reaction chamber. As a general rule, fall times of
between about 5 and about 60 seconds are required under the
preferred conditions of temperature and controlled pressure to
achieve the desired degree of polymerization, crosslinking, and
evacuation of water/solvent and residual monomer for most
monomer/crosslinker mixtures. Experimentation has shown that
reaction chamber height must be adequate to allow sufficient
reaction chamber fall times in order to achieve the desired extent
of polymerization.
[0085] The period of time the droplet is allowed to fall through
reaction chamber 12 (and hence, the height of that chamber) is also
related in part to the diameter of the droplet sprayed from nozzle
18. A nozzle 18 having a large orifice 98 therein produces a larger
diameter droplet such that either the reaction chamber fall time of
the droplet may be increased, the reduction in the pressure of the
atmosphere in reaction chamber 12 may be increased, the temperature
may be increased, or some combination of changes in these three
parameters may be effected, in order to obtain the desired degree
of polymerization, and water/solvent evaporation throughout the
resulting particle. In the case of very large diameter droplets,
pressure reductions of greater than 67,720 N/m.sup.2, temperatures
of over 101.7.degree. C., and reaction chamber fall times in the 20
second or higher range may be required to allow the desired degree
of polymerization and evaporation of liquid.
[0086] Another variable affecting the production of polymers in
accordance with the method of the present invention is the pressure
at which the mixture of monomer and initiator and/or crosslinker is
sprayed into the heated, controlled atmosphere in reaction chamber
12. In general, as the pressure at which the mixture is sprayed
increases, the size of the droplet decreases, requiring concomitant
changes in either reaction chamber fall time, temperature,
reduction in pressure in reaction chamber 12, the diameter of the
orifice 98 in nozzle 18, or some combination thereof. Satisfactory
results have been obtained at spray pressures of between about 517
KPa and about 13.7 MPa, and pressures of between about 698.3 KPa
and about 1.20 MPa represent a particularly preferred embodiment of
the method of the present invention. The pressure in the line at
which the mixture is sprayed, as well as the reduced temperature,
prevent the polymerization of monomers prior to their being sprayed
into the chamber. Therefore, the combination of decreasing
temperature in the feed line, increasing pressure in the feed line
and introducing the initiator immediately prior to spraying the
mixture into the chamber essentially eliminates any
prepolymerization of monomer in the feed line.
[0087] A final variable affecting the method of the present
invention and the various parameters of pressure, temperature and
fall time at which the method is conducted is the nature of the
monomer, initiator, crosslinker and other reagents desired to be
polymerized. By reference herein to a monomer, it is intended to
refer to any organic molecule which is capable of being polymerized
by covalent bonding to other organic molecules and/or itself to
form chains. Many of the polymers can also be crosslinked. Although
it is not intended to limit the method of the present invention to
only the following monomers, the following listing will provide an
example of certain monomers, including functionalized and/or
unfunctionalized olefins, which may be polymerized and in most
cases crosslinked in accordance with the method of the present
invention:
[0088] (a) water-soluble, ethylenically unsaturated monomers as
described in the above-incorporated Yamasaki, et al. U.S. Pat. No.
4,446,261: acrylic acid, methacrylic acid, salts of acrylic acid
and methacrylic acid, acrylamide, methacrylamide, N-substituted
acrylamides, N-substituted methacrylamide,
2-acryloylethane-sulfonic acid, 2-methacryloylethane sulfonic acid,
salts of 2-acryloylethane-sulfonic acid and
2-methacryloylethane-sulfonic acid, styrene-sulfonic acid, salts of
styrene-sulfonic acid, 2-hydroxyethyl acrylate and
2-hydroxyethylmethacrylate;
[0089] (b) the monomers described in Markus, U.S. Pat. No.
2,810,716: acrolein, allylidenediacetate, acrylonitrile, esters of
acrylic and methacrylic acid (including methyl methacrylate, ethyl
methacrylate, fumaric acid, monomethylfumarate, dimethylfumarate,
monoethylfumarte, diethylfumarte, maleic anhydride, maleic acid,
monomethylmaleate, dimethylmaleate, monoethylmaleate,
diethylmaleate, dimethylmethylenemalonate, diethylmethylene
malonate, itaconic acid, monomethylitaconate, dimethyl itaconate,
monoethyl itaconate, diethylitaconate, atrophic acid, methyl
atropate, and ethyl atropate), chloracrylic acid and esters
thereof, bromoacrylic acid and esters thereof, iodoacrylic acid and
esters thereof, ortho-, meta-, and paramethylstyrene, fluorostyrene
and chlorostyrene, a-sulfoacrylic acid, salts and esters,
a-amino-acrylic acid, salts and esters, n-monomethyl and
N,N'-dimethyl acrylamide, acrylic and methacrylic anhydride,
methylvinylketone, hydroxymethylvinylketone, ortho- and
paramethoxystyrene, ethyleneglycol monomaleate, ethylglycol
monofumarate, N-vinylmethylacetamide, vinyl acetate, vinyl
butyrate, vinyl benzoate, vinylquinoline, and vinylpyridines such
as 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine,
2-vinyl-5-ethylpyridine, N-vinylpyrrolidone, cyclopentadiene,
N-vinylphthalimide, N-vinylsuccinimide, N-vinylacetamide and
N-vinyl-diacetamide;
[0090] (c) the monomers described in Glavis, et al., U.S. Pat. No.
2,956,046: salts of unsaturated monomeric acids such as quaternary
ammonium salts and amine salts thereof and salts of ammonia, alkali
metals and alkaline earth metals, including
B-hydroxyethyltrimethylammoni- um acrylate, benzyltrimethyl
ammonium acrylate, amine salts, monomethylammonium acrylate, and
di- and tri- methylammonium acrylate;
[0091] (d) the monomers described in Wichterle, et al., U.S. Pat.
No. 3,220,960: dimethylaminoethyl methacrylate, piperidinoethyl
methacrylate, morpholinoethyl methacrylate, methacrylylglycolic
acid, methacrylic acid, monomethacrylates of glycol, glycerol and
ployhydric alcohols, dialkylene glycols and polyalkylene glycols
and the corresponding acrylates;
[0092] (e) the monomers described in Bashaw, et al., U.S. Pat. No.
3,229,769: cross-linked, substantially water-insoluble,
water-swellable sulfonated alkaryl and aromatic polymers such as
cross-linked polysodium styrene sulfonate and sulfonated
polyvinyltoluene salts, copolymers of such sulfonated alkaryl and
aromatic materials with acrylonitriles, alkyl acrylonitriles,
acrylates and methacrylates, cross-linked polyvinyl alcohol and
polyacrylamide and crosslinked copolymers of polyacrylamide, e.g.,
of acrylamide and acrylic acid or acrylamide and monovalent salts
of acrylic acid, and cross-linked heterocyclic monomers such as
polyvinyl morpholinone, poly-5-methyl-N-vinyl-2-oxazolidinone, and
polyvinyl pyrrolidene;
[0093] (f) the monomers described in Assarsson, U.S. Pat. No.
3,664,343: water-insoluble hydrophilic poly (ethylene oxide)
polymers made by subjecting water-soluble poly (ethylene oxide)
polymers to ionizing radiation (such polymers are homopolymers of
ethylene oxide and copolymers of ethylene oxide with one or more
alkylene oxides such as propylene oxide, styrene oxide, and
1,2-butylene, 2,3-butylene and isobutylene oxide, all as described
in U.S. Pat. Nos. 3,127,371, 3,214,387, 3,275,998, 3,275,199 and
3,399,149);
[0094] (g) the monomers described in Gross, et al., U.S. Pat. No.
3,926,891: alkyl acrylates and methacrylates such as methyl
acrylate, ethyl acrylate, propyl acrylate, hexyl acrylate, butyl
methacrylate, hexyl methacrylate, octyl methacrylate, decyl
methacrylate and omega hydroxy alkyl acrylates such as
2-hydroxyethyl acrylate, hydroxymethyl acrylate, 3-hydroxypropyl
acrylate and 4-hydroxybutyl acrylate;
[0095] (h) ethylene, 1,3-dienes, styrene, halogenated olefins,
vinyl esters, acrylates, methacrylates, acrylonitrile,
methacrylonitrile, acrylamide, methacrylamide, N-vinyl carbazole,
N-vinyl pyrrolidone, propylene, and
[0096] (i) alkenes, vinyl acetate.
[0097] It will be understood by those skilled in the art who have
the benefit of this disclosure that the references to a monomer
throughout this specification and claims also contemplate the
co-polymerization of monomers such as maleic acid and styrene to
form commercially useful co-polymers, graft polymers, block
polymers. Examples of such co-polymerizations can be found, for
instance, at column 2, lines 66 et. seq. of U.S. Pat. No.
4,057,521. As is the case for the selection of a particular
combination of monomer, crosslinker and initiator for
polymerization and cross-linking in accordance with the method of
the present invention, the selection of such combinations of
monomers is well known in the art and forms no part of the
invention hereof such that further description of such
co-polymerizations is unnecessary.
[0098] In the same manner that the method of the present invention
is not restricted with respect to the particular monomer or
monomers utilized, a large number of crosslinkers are utilized to
advantage. Such crosslinkers include any organic compound capable
of reacting with an organic polymer in aqueous solution and
include, generally, compounds having at least two polymerizable
double bonds, compounds having at least one polymerizable double
bond and at least one functional group reactive with an
acid-containing monomer or polymer, compounds having at least two
functional groups reactive with an acid-containing monomer or
polymer, and polyvalent metal compounds which are capable of
forming ionic cross-linkages. A non-limiting listing of a number of
such crosslinkers includes:
[0099] polyvinyls, e.g., divinylbenzene, divinyltoluene, divinyl
acid anhydrides, divinyl sulfone, divinyl benzene sulfonate, and
their alkyl or halogen-substituted products;
[0100] polyesters of unsaturated mono- or polycarboxylic acids with
polyols, e.g., ethylene glycol, trimethylol propane, glycerine, and
polyoxyethylene glycols;
[0101] bisacrylamides, e.g., N,N'-methylene-bisacrylamide and
N,N'-methylenebismethacrylamide;
[0102] carbamyl esters obtained by reacting polyisocyanates with
hydroxyl-group containing monomers;
[0103] di-, tri-, or tetraesters of acrylic or methacrylic
acid;
[0104] polyallyl esters of polycarboxylic acids, e.g., diallyl
phthalate and diallyl adipate;
[0105] esters of unsaturated mono- or polycarboxylic acids with
mono-allyl esters of polyols, e.g., the acrylic acid of
polyethylene glycol monoallyl ether, allyl acrylate, diallyl
ethylene glycol ether, and divinyl ether of ethylene tri- or
diethylene glycol;
[0106] di- or triallylamine, N,N'-diallylacrylamide,
diallylmethacrylamide;
[0107] N-methylol acrylamide, N-methyloylmethacrylamide;
[0108] glycidyl acrylate and methacrylate, polyethylene glycol
diacrylate, polyethylene glycol dimethacrylate;
[0109] substituted hexadienes such as
2,5-dimethyl-3,4-dihydroxy-1,5-hexad- iene and
2,5-dimethyl-2,4-hexadiene;
[0110] olefinically unsaturated mono- or polycarboxylic acids such
as acrylic, methacrylic, crotonic, isocrotonic, angelic, tiglic,
senecioic, maleic, fumaric, itaconic, aconitic, teraconic,
citraconic, mesaconic, and glutaconic acid;
[0111] glyoxal;
[0112] polyols, e.g., ethylene glycol and polyhaloalkanols such as
1,3-dichloroisopropanol and 1,3-dibromoisopropanol;
[0113] polyamines, e.g., alkylene diamines (ethylene diamine),
polyalkylene polyamines, triethanolaminediacrylate and
dimethacrylate, triethanolamine triacrylate and trimethacrylate,
and diacrylate and dimethacrylate of bishydroxylacetamide;
[0114] polyepoxides and haloepoxyalkanes, e.g., epichlorhydrin,
epibromohydrin, 2-methyl epichlorhydrin and epiiodohydrin;
[0115] polyglycidyl ethers and polyol polyglycidyl ethers such as
ethylene, diethylene, and propylene glycol diglycidyl ether,
glycerin triglycidyl ether, glycerin diglycidyl ether and
polyethylene glycol diglycidyl ether, tartaric acid diacrylate and
trimethacrylate, triethylene glycol diacrylate and dimethacrylate,
ethylene glycol dimethacrylate and propylene glycol diacrylate;
[0116] oxides;
[0117] hydroxides;
[0118] weak acid salts (e.g., carbonate, acetate) of alkaline earth
metals (calcium, magnesium) and zinc, strontium and barium, e.g.,
calcium oxide and zinc diacetate; and
[0119] polyvalent metal salts of acrylic acid and methacrylic
acid.
[0120] Likewise, it is not intended that the method of the present
invention be restricted with respect to the initiator utilized.
Radicals can be produced by a variety of thermal, photochemical,
and redox (oxidative-reduction) methods known to those skilled in
the art. The benefits of initiator selection are also known to
those skilled in the art. Appropriate polymerization initiators
well known in the art include:
[0121] peroxygen compounds (sodium, potassium and ammonium
persulfate), hydrogen peroxide, caprylyl and benzol peroxide,
cumene hydroperoxides, acetyl peroxide, tert-butyl diterphthlate,
tertbutylperbenzoate, sodium peracetate, tertbutylhydroperoxide,
sodium percarbonate, and conventional redox initiator systems such
as are formed by combining a peroxygen compound with a reducing
agent such as sodium or ammonium sulfite or bisulfite, L-ascorbic
acid, or ferrous salts;
[0122] peroxides in combination with a reducing agent;
[0123] tetraphenylsuccinodinitrile,
tetra-p-methoxyphenylsuccinodinitrile; and
[0124] azo initiators such as azobisisobutyronitrile (AIBN),
4-t-butylazo-4'-cyano-4,4'-azobis (4-cyanovaleric acid),
2,2'-azobis (2-amidino-propane)-hydrochloric acid salt.
[0125] It is also common to use mixtures of one or more of such
initiators.
[0126] The present invention can be better understood by reference
to the following, non-limiting examples of cross-linked,
water-absorbing polymers produced in accordance with the method
described above.
EXAMPLE 1
[0127] Aqueous solutions of the initiators sodium persulfate and
2,2'-azobis (2-amidinopropane HCl (ABAH) (Polysciences, Inc.,
Warrington, Pa.) and ascorbic acid were prepared in the following
proportions (all parts by weight):
2 initiator water sodium persulfate 0.650 12.346 ABAH 0.975 12.021
ascorbic acid 0.013 12.983
[0128] Other reagents were used in the following proportions:
3 water 29.70% acrylic acid (Catalog No. 42.61% 14723-0, Aldrich
Chemical Co., Milwaukee, WI) triallylamine (Catalog No. 0.30%
T4500-4, Aldrich Chemical Co., Milwaukee, WI) caustic soda 22.12%
ascorbic acid solution 1.05% ABAH solution 2.11% sodium persulfate
solution 2.11%
[0129] The water and acrylic acid were mixed while holding the
temperature at 10.degree. C. and the triallylamine added. Caustic
soda was added at a rate slow enough to hold the temperature under
40.degree. C., then temperature was brought down to 7.degree. C.
and held at that temperature as the ascorbic acid and ABAH
solutions were added. The resulting aqueous mixture was purged with
nitrogen for 4 to 5 minutes and the sodium persulfate added. That
mixture was mixed for 30 seconds at a temperature under
37.8.degree. C. The mixture was then sprayed into a reaction
chamber constructed in accordance with the teachings of the present
invention that was about 4.57 meters high with an atmospheric
pressure therein of about 33,860 N/m.sup.2 below ambient and which
had been heated to about 107.2.degree. C. The resulting
water-absorbing spherical particles were smooth surfaced, ranged
between about 50 to about 100 microns in diameter, and had a water
content of about 2%.
EXAMPLE 2
[0130] The method described in Example 1 was modified by using the
following proportions of reagents:
4 water 26.00% acrylic acid (see Example 1) 44.85% triallylamine
(see Example 1) 0.31% caustic soda 23.29% ascorbic acid solution
1.11% ABAH solution 2.22% sodium persulfate solution 2.22%
[0131] All process parameters were the same as in Example 1 except
that the temperature of the reaction chamber 12 was 65.6.degree. C.
and the pressure of the atmosphere in the reaction chamber 12 was
not reduced below ambient pressure. Although the resulting
spherical particles were smooth surfaced and capable of efficient
water absorption, water content was about 8%. When repeated using
potassium hydroxide in place of caustic soda, yield dropped by
about 50%.
EXAMPLE 3
[0132] The method described in Example 1 was modified by omission
of the initiator ascorbic acid. The resulting smooth-surfaced
spherical particles were obtained in approximately the same yield
and size as obtained in Example 1, but water content was about
4%.
[0133] The polymerization process of the present invention produces
a dry powder-like particle, eliminating the need for drying,
grinding, pulverizing and/or other methods to produce suitable for
immediate use in the range of from about 2 to 125,000 microns in
size. Moreover, this invention utilizes liquid monomer sources to
produce a substantially dry polymer particle which does not rely
upon a substrate on which to initiate formation.
[0134] The process and apparatus described herein may also be used
in the continuous preparation of soaps and detergents. The raw
materials of soap or detergent production are mixed and/or
homogenized, and subjected to treatments, as known to those skilled
in the art to prepare a liquid mixture of soap- or detergent-making
compounds. The liquid mixture is then sprayed into the reaction
chamber according to the above description. Standard soap and
detergent formulations known to those skilled in the art may be
used to prepare a substantially dry powdered soap or detergent.
[0135] The preparation of a soap or detergent will not require that
the temperature in the feed line of the above-described process and
apparatus be reduced. The liquid mixture will however, be subjected
to pressure in the line and to the spraying and chamber conditions
described above. Varying chamber pressure and temperature as
described above will produce similar results in detergent and soap
production as are obtained from monomer polymerization.
[0136] The process and apparatus described herein may also be used
in the preparation of several novel polymer products. Foremost, it
has been found that by altering the operational parameters of the
apparatus, not only is the size and density of the product varied,
but the shape and physical properties of the products are varied as
well. More particularly, when the apparatus is operated at lower
pressures and higher temperatures, the water or other solvent in
the mixture droplets is violently released during polymerization.
The result is a substantially dry polymer product which has a
puffed out irregular shape not unlike cooked popcorn. The novelty
of this product is believed to be in its irregular puffed shape,
its low density, and in the case of the water absorbing polymers,
an enhanced ability to absorb water or urine due to an increase in
the polymer's surface area. Further, a product with these
characteristics is obtained without spray drying or additional
processing as is required in the known processes for obtaining
similar products.
[0137] Similar known products do not have the same degree of
irregularity in their shape as they are most commonly formed
through the mechanical processes of pulverizing and chopping a mass
of polymer material. Thus, known irregularly shaped polymers have
less surface area and commonly have higher densities. Known methods
for obtaining irregularly shaped polymer products are described in
U.S. Pat. No. Re. 32,649 entitled "Hydrogel-Forming Polymer
Compositions For Use in Absorbent Structures," reissued to Brandt
et al. on Apr. 19, 1988 and U.S. Pat. No. 4,625,001 entitled
"Method for Continuous Production Of Cross-Linked Polymer" issued
to Tsubakimoto et al. on Nov. 25, 1986. These patents are
incorporated herein by reference.
[0138] An additional novel product is obtained from the process and
apparatus described herein in the form of a substantially dry
pigmented copolymer product for use in powder coating techniques.
To obtain this product the process further comprises the steps of
adding a second monomer to the first mixture and the step of adding
a pigment to the first mixture. The homogenized mixture is then
sprayed into the apparatus forming mixture droplets which
polymerize during free fall. The product obtained from this process
is a substantially dry, pigmented copolymer that is radiation
curable for use in powder coating applications; additional chemical
or mechanical processing of the copolymer product is not
required.
[0139] The production of copolymers for use as binders in powder
coatings is described in U.S. Pat. No. 5,484,850 entitled
"Copolymers Crosslinkable By A Free Radical Method" issued to
Kempter et al. on Jan. 16, 1996. This patents is incorporated
herein by reference. As described in the Kempter patent, copolymers
for use in powder coatings typically require several manufacturing
steps in their production. The monomer reagents are first
polymerized into a copolymer. The copolymer is then dispersed or
dissolved in an emulsion or solution in order to introduce
additives by various known techniques. Lastly, the copolymer
composition is dried in a conventional manner. A substantially dry,
colored copolymer is formed from a homogenized mixture of monomers
and various additives in a single step in the process and apparatus
described herein.
[0140] The term "controlled atmosphere" as used herein describes
the internal condition of the apparatus and the reaction conditions
of the polymerization process. As such, "controlled atmosphere"
refers to an atmosphere that is substantially static. Any currents
or movement of gases within the apparatus or in the vicinity of
where the polymerization process is being carried out should be
minimized; there should be no currents or turbulence present to
interfere with the free fall of the polymerizing droplets. While
the droplets are generally described as falling through the
apparatus, they are more accurately described as experiencing a
free fall, which is preferably influenced only by the force of
gravity.
[0141] Those skilled in the art who have the benefit of this
disclosure will recognize that the above examples are set out by
way of exemplification and for the purpose of complying with the
requirements of the Patent Statute, and that those examples are not
intended to limit the scope of the present invention. Likewise,
with respect to the apparatus 10, it will be recognized that
changes can be made to the individual structural elements
comprising that apparatus without changing the manner in which
those elements function to achieve the intended result thereof. All
such changes are intended to fall within the scope of the following
claims.
* * * * *