JPH0441532A - Reclamation of fine powder of super-absorptive polymer - Google Patents

Abstract

PURPOSE: To lower cost and dust by grinding an amorphous gel obtain by wetting a specific super-absorbing polymer fine powder before drying the same.

CONSTITUTION: A super-absorbing polymer fine powder selected from a grafted starch super-absorbing polymer a synthetic super-absorbing polymer and a crosslinked super-absorbing polymer is wetted with deionized water having a temp. range from temp. slightly higher than freezing temp. to a b.p. (65-160°F) to obain an amorphous gel with solid content of 5-70%. Next, this gel is subjected to wet grinding and subsequently supplied to a belt dryer, a tray dryer or a fluidized bed dryer to be dried until moisture content becomes 1-15% and the dried ground gel is subjected to dry grinding if necessary.

COPYRIGHT: (C)1992,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Field of Industrial Application The present invention provides a novel method for recovering and regenerating superabsorbent polymer fines. This method reconstitutes the fine powder into superabsorbent polymers used in applications such as diapers, sanitary napkins, soil additives, fuel filters, desiccants, cement, and sludge dewatering agents.

BACKGROUND OF THE INVENTION Hydrogel-forming polymer compositions (hereinafter referred to as superabsorbent polymers) are used as absorbents in absorbent structures and articles. Synthetic superabsorbent polymers are
It is typically produced by one of the methods such as gel, inverted suspension or modified bulk polymerization. Typical gel processes for making superabsorbent polymers are described in U.S. Pat. No. 4,654,039 (Brandt et al.) issued March 31, 1987 and No. 4,288,082 (Tsubakimoto et al.). A typical inverted suspension process for making superabsorbent polymers is described in U.S. Pat. No. 4,698, issued October 6, 1987.
No. 404 (Cramm et al.), 198
U.S. Patent No. 4,4411i, 261, issued May 1, 2013
Specification (Yamasaki et al.) and 1
It is disclosed in specification No. 4,340,708 issued on July 20, 1982. The modified bulk method was introduced on October 2, 1987.
It is described in US Pat. No. 4,703,067 (Mikita et al.), issued on the 7th.

The Plant et al. patent describes the preparation of a reaction mixture consisting essentially of a specified amount of unsaturated polymerizable acid foundation (1 monomer) in an aqueous medium, a crosslinking agent, and optionally a free radical initiator; subjecting the mixture to polymerization conditions to produce and produce a substantially water-insoluble, slightly crosslinked polymeric material having specific gel volume, gel strength, and extractable polymer content characteristics under certain conditions; neutralizing at least a portion of the acid functional groups of the polymeric material with salt cations to form a partially neutralized polymeric material having a degree of neutralization of at least 25%. The hydrogel material formed by the method described in the patent specifies an optionally dry and absorbable hydrogel-forming polymeric material that subsequently regenerates the hydrogel upon contact with water or body fluids. I can do it.

A typical inverted suspension process for making superabsorbent polymers is disclosed in the Kram et al. patent. In this method, an aqueous solution of acrylic acid and alkali metal acrylate or ammonium acrylate in which the molar ratio of acrylic acid to alkali metal acrylate-1 or ammonium acrylate is from 50,150 to 2/98, is prepared with an HLB value of 8 to 2/98. 12 in a cycloaliphatic or aliphatic hydrocarbon solvent containing a surfactant, and the resulting suspension is subjected to inversion suspension polymerization in the presence of a water-soluble radical polymerization initiator, and if necessary, Polymerization is carried out in the presence of a water-soluble chain transfer agent by crosslinking the resulting polymer with a crosslinking agent. This water-soluble chain transfer agent is formic acid.

Mikita et. A method is disclosed comprising combining monomers in an amount of 55 to 80 percent by combined weight to form a monomer mixture, and adding a polymerization initiator to the monomer mixture to initiate polymerization of the monomer mixture. The monomer mixture is polymerized by utilizing the exothermic heat of reaction as essentially the only non-ambient energy source without external heating, removing water from the polyacrylate resin and creating a crosslinked polyacrylate resin. The water content is sufficiently low, i.e. below 15%, to form a product which can be ground, for example by milling, without intermediate drying steps.

Each of the methods described above used to produce superabsorbent polymers can produce superabsorbent polymer fines. Superabsorbent polymer fines are defined as particles whose particle size is too small for those currently available on the market, such as diapers, sanitary napkins, etc. The fine powder can be produced either during the polymerization step of the above process or during the subsequent step of grinding and sizing the superabsorbent polymer to meet the desired particle size specifications.

For example, in the production of superabsorbent polymer materials used as absorbents in certain personal products, approximately +280
All particles smaller than mesh are considered fines. The fines recovered from the superabsorbent material used in this particular application can be in an amount of 5-35% of the total amount of polymer produced.

Superabsorbent fines are particles whose size is too small for certain market applications, so they are typically removed from commercial products by a particle sizing process.

The resulting fines are typically stored or disposed of until a suitable market is found for them. Superabsorbent fine powders are of limited commercial use because their small particle size typically causes them to be difficult to handle, such as forming gels or dusting.

Fines remaining in commercially used superabsorbent polymeric materials can also cause gel blocking, ie, the fines can block large particles and reduce the overall absorbent capacity of the material. Because of gel bronking effects, fine powders are usually separated from superabsorbent polymeric materials prior to commercial application.

Due to the high disposal, storage and handling costs associated with superabsorbent polymer fines, it is desirable to develop new methods of handling and utilizing these fines. The inventors have discovered a new method to recover and regenerate superabsorbent polymer fines to make them suitable for commercial use.

Other methods have attempted to convert polymeric fines into commercially acceptable polymeric materials by flocculating the fines together by heating or adding chemical binders. Such agglomeration method includes 1c170 May 2
It is disclosed in U.S. Pat. Hoffmann's patent specification states that fine polymer powder is agglomerated in a fluidized bed in which a mixture of two gases, the smaller of which is heated to a temperature above the softening point of the polymer, is maintained in a fluidized state. A method for locally causing aggregation is disclosed. Polymer powder is
The heavy agglomerates that have locally agglomerated and settled at the bottom of the fluidized bed are removed and fresh powder is added to the softened zone.

A problem with agglomerating polymer fines by heating or chemical binders is that abrasion of the agglomerated particles may occur during commercial production or use.

The fragmented fine powder is usually smaller than the allowable particle size range and may cause gel blocking or other handling problems, so it is not desirable for boat fishing.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a unique method of solving the disposal and handling problems associated with superabsorbent polymer fines and the wear problems typically associated with agglomerated particles. An advantage of the method of the present invention is that superabsorbent polymer fines are recovered and reconstituted into a commercially acceptable amorphous superabsorbent polymer material. Furthermore, the method of the invention avoids the high costs and dust handling problems associated with storage, disposal and use of fines. Further advantages of the invention will become apparent from the description below.

The main objective of the present invention is to provide a method for reconstituting superabsorbent polymer fines.

The present invention is a method for regenerating superabsorbent polymer fines, wherein the superabsorbent polymer fines is selected from the group consisting of starch grafted superabsorbent polymers, synthetic superabsorbent polymers, and crosslinked superabsorbent polymers. The steps include sufficiently moistening the superabsorbent polymer fine powder to form an amorphous gel of the fine powder, pulverizing the gel, and drying the pulverized gel to form a superabsorbent polymer. forming a material.

The present invention is a method for regenerating superabsorbent polymer fines, wherein the superabsorbent polymer fines is selected from the group consisting of starch grafted superabsorbent polymers, synthetic superabsorbent polymers, and crosslinked superabsorbent polymers. thoroughly wetting the superabsorbent polymer fines to form an amorphous gel of the fines, and combining the fines gel with a gel from an ongoing superabsorbent polymerization process. Also provided is a method comprising: The superabsorbent polymer materials formed by the present invention can be used in diapers, sanitary napkins, dish towels, soil additives, fuel filters, sludge coagulation, dew condensation prevention (desiccants)
It is suitable for commercial use as an absorbent in applications such as dehydration of oils and oils.

In a preferred embodiment, the drying step can be followed by a step of grinding the superabsorbent polymeric material to a particle size sufficient for commercial use. The drying and grinding step may optionally be followed by a step of sorting the dried and ground material to recover particles of a desired size. Undesirable particles are
It can be recovered and further ground or reconstituted.

The fine powder is preferably moistened with water, for example deionized water,
solids content of about 5-70%, preferably solids content of about 20-5%
0%, most preferably a solids content of about 35-4596. The temperature of the water used in the wetting step is preferably in the range of about 65 to 160 degrees centigrade, although temperatures outside this range, from slightly above the freezing point to the boiling point, can also be used.

Further, the wetting step is preferably carried out under stirring conditions so that the wet superabsorbent polymer fine powder is sufficiently stirred to form an amorphous gel.

The object of the present invention is to dry the superabsorbent polymer fine powder gel sufficiently so that the water content is about 1 to 15%, preferably about 1 to 4%.
% range of superabsorbent polymeric materials.

The superabsorbent polymer fines reconstituted by the method of the present invention may be any starch grafted superabsorbent polymer, synthetic superabsorbent polymer and crosslinked superabsorbent polymer. Crosslinked polymers are substantially water-insoluble, slightly crosslinked, partially neutralized hydrogel-forming polymeric materials, such as crosslinked polyacrylate superabsorbent polymers.

The invention may also include a number of additional features, as described further below.

DETAILED DESCRIPTION OF THE INVENTION Superabsorbent polymers, such as synthetic superabsorbent polymers, starch-grafted superabsorbent polymers and cross-linked polyacrylate superabsorbent polymers, can be used in diapers, sanitary napkins, soil additives, fuel filter dryers, etc. It can be used in applications such as cleaning agents, cement and sludge dewatering. During commercial production or use of such polymers, undesirable small particles called fines may be generated.

Such fines may be the result of abrasion during the polymerization process, during subsequent processing steps in which the superabsorbent polymer is ground and/or classified to meet desired particle size specifications, or during commercial production or use. It may occur as follows.

The present invention provides a novel method for recovering and reconstituting superabsorbent polymer fines. Although any superabsorbent polymer fines can be reconstituted by the present invention, starch grafted superabsorbent polymers, synthetic superabsorbent polymers and crosslinked polyacrylate superabsorbent polymers are particularly suitable.

Superabsorbent polymer fines are - for boat fishing, substantially water-insoluble, slightly cross-linked and partially neutralized hydrogel-forming polymeric materials.

Such crosslinked polymers include crosslinked polyacrylate superabsorbent polymers. Polyacrylate superabsorbent polymers contain acrylic acid and/or alkali metal salts of acrylic acid alone or with other monomers and/or
Alternatively, it can be formed by polymerization in combination with a crosslinking agent known to be useful in the production of water-absorbing polymers. Examples of these salts include nonionic monomers such as acrylamide, methyl methacrylate and N-vinylpyrrolidone; sulfonated monomers such as sodium acrylamide methanesulfonate and sodium styrene sulfonate; and diallyldimethylammonium chloride and Examples include, but are not limited to, cationic salts such as dimethylaminoethyl methacrylate-methyl chloride quaternary salt.

Other crosslinked superabsorbent polymers and methods of manufacture are described in U.S. Pat. No. 4,703,067, all of which are incorporated herein by reference.

The present invention involves sufficiently wetting superabsorbent polymer fines to form a finely divided gel, crushing the gel, and drying the crushed gel, thereby forming a superabsorbent material suitable for commercial use. The superabsorbent polymer fine powder is reconstituted by the step of Any superabsorbent polymer fines, particularly starch-grafted superabsorbent polymer fines, synthetic superabsorbent polymer fines, and crosslinked superabsorbent polymer fines, can be reconstituted by the method of the present invention.

The superabsorbent polymer fines can also be reconstituted by sufficiently wetting the superabsorbent polymer fines to form a fines gel and combining this fines gel with the gel from the ongoing gel polymerization process. .

The combination can be carried out either before or after the wet grinding of the fine powder gel.

If desired, the drying step can be followed by additional steps of dry milling and sizing or separation to obtain particles of the desired size.

The superabsorbent polymer micropowder is wetted or rewetted into a swollen state to form a continuous amorphous gel mass free of discrete particles. Preferably, wetting of the fine powder should be carried out under agitated conditions to sufficiently disperse the liquid or other wetting agent into the fine powder to provide a uniform, amorphous or homogeneous gel.

Either water or deionized water can be used to wet the fine powder. Wet the fine powder and reduce the solid content to about 5-70
%, preferably about 20-50% solids, most preferably about 35-45% solids. The temperature of the wetting agent, such as water, may range from about 65 to 160 degrees Fahrenheit, although other temperatures may be used.

The amorphous gel formed by wetting and swelling the fine powder under agitation conditions is then ground by any conventional wet grinding equipment. This amorphous gel is finely chopped or chopped by a wet milling device to a particle size that satisfies the drying process and future processing requirements. The inventors
We are also considering directly combining the shredded gel with gel from an ongoing gel polymerization process.

Preferably, the fine powder and water are mixed and rewetted sufficiently to form a solid or continuous amorphous shell.

Mixing can be carried out either batchwise or in continuous mixing equipment. The mixing time required to obtain such a gel will vary depending on the type of mixing equipment used.

The drying step is carried out either in a belt dryer, tray dryer, fluidized bed dryer or any other means known to those skilled in the art. The Kel is sufficiently dried to facilitate dry milling into superabsorbent polymeric materials. That is, the gel is sufficiently dried to have a water content of about 1 to 15%, preferably about 1 to 4%.
of the superabsorbent polymer material.

After the drying step, the superabsorbent polymeric material can optionally be dry milled. Useful types of grinding equipment include, but are not limited to, hammer mills, bottle mills, ball mills, and roll mills such as two roll grinders. The particles can be ground to any desired particle size depending on their intended use.

Particle size separation of the superabsorbent polymer material reconstituted by the method of the invention allows fines and larger particles to be recycled for further reprocessing.

SEM micrographs show that the reconstituted superabsorbent polymer fine powder is not an aggregate of fine powder, and the structure is similar to that of some conventional methods.
It shows amorphous, non-discontinuous particles similar to superabsorbent polymer particles formed, for example, by gel polymerization methods.

These reconstituted superabsorbent particles can therefore be used alone or mixed with particles formed by conventional methods for commercial applications.

[Example] Example 1 Three samples were reconstituted at 20-25% solids.

Samples 1.2 and 3 were crosslinked polyacrylate superabsorbent polymer fines. Sample 4 was a comparative sample containing a crosslinked polyacrylate superabsorbent material.

Samples 1 to 3 were reprocessed in the following manner.

The superabsorbent polymer fines were rewetted with deionized water in a 5 gallon container to 20-25% solids, and the fines and water were mixed in a portaple mixer for approximately 1 hour to remove all solids. Rewet to form a gel and the gel product is 174”
Berkel Lab Mincer with Die
Lab Mincer), collect the shredded product on a dryer pan, and dry the gel product in a 200-210 cylinder forced circulation oven for 3-4 hours to dry the superabsorbent polymer material. to 4-5% moisture, manually disintegrate large particles, and grind the dried superabsorbent polymer material in a 6” twin-roll mill (STURTEUANT MILL). The material was sized through a 20 mesh screen, the +20 mesh was returned to the mill for further reprocessing, and the product was analyzed.

The temperature of the deionized water was varied between 65-160°F. The data and results for Samples 1 to 3 and Comparative Sample 4 are shown in Table 1 below.

Screen analysis + 20 meshes + 40 meshes + 70 meshes + 140 meshes + 200 meshes - 200 meshes Table -1 Experiment 1 Experiment 2 2.8 3.0 52.8 54,9 25.4 24,8 13.0 11.8 2.45 2 .2 3.5 3.2 Experiment 3 2.3 50.1 2G, 6 13.8 2.9 4.2 Comparative sample 1.3 61.2 26.6 8.4 1.1 1.4 Experiment 1 : 20% solids, Experiment 2: 20% solids, Experiment 3: 25% solids, Comparative sample: 150-160"F, 0.28" gap 70-75
"F, 0.28" gap 65 bottom, 0.28
For the "gap 0.28" gap 20-25% solids, the fine powder was reprocessed into amorphous superabsorbent particles similar in size to Comparative Sample 4.

Evaluation of SEM micrographs of these samples indicates that the reconstituted superabsorbent polymer fines are not aggregates or that the particles are more porous than control sample 4.

Example 2 In another experiment, three types of crosslinked polyacrylate superabsorbent polymer fines were reprocessed using the method of the present invention for reconstituting the fines.

A fourth sample, a crosslinked polyacrylate superabsorbent polymer, was used as a comparison sample. Samples 1-3 were rewetted in a Nauta mixer (75 gallons) to 20.30 and 35% solids, respectively.

The stirrer was set at 90 rpm to ensure complete wetting of the fines. Finally, add superabsorbent polymer fine powder,
A scoop was used to add the powder into the Nauta mixer through the 12" intake. The fines were added gradually so that the fines mixed with the water to form a continuous amorphous gel. All of the water and Once the fines were added to the mixing device, mixing was continued for 30 minutes. The resulting gel was then transferred to a Berkel Lab Mincer equipped with a 1/4" die to grind the gel. The crushed or finely chopped gel product is then added to about 20
In a forced circulation oven from 0 to 210 degrees Fahrenheit, the moisture content is approximately 5.
% for approximately 2 to 5 hours. The dried superabsorbent material was then milled in a two-roll mill with a gap set at 0.028". The milled material was then
The particles were passed through a 0 mesh screen to be sized to a desired particle size standard, and the +20 mesh particles were returned to the mill for further pulverization.

The results for these samples are shown in Table 2 below.

Table-2 Experiment 1 Experiment 2 Experiment 3 Mixing device Nauta Nauta Nauta Solid content (%) 20.0 30.0 35
．． 0 temperature (di) 84.0 90.0
104.0 Product water particle size 2.8 3.
9 4.9+14 mesh 0.1 0
．． 2 0.8 0.0+20 mesh 0
．． 8 0.6 5.0 0.2+50 mesh 68.7 Bo, 5 B3,5
70.5+100 mesh 18.4
25.0 16.8 18.9+325 mesh 11.4 12.812.9 9.8
-325 mesh 0.6 0.9 1.
4 0.7 Comparative Sample Plant Example 3 A sample of superabsorbent polyacrylate powder was prepared from Examples 1 and 2, except that the powder and water were agitated by a 5" diameter continuous two-roll screw mixer instead of a batch mixer. Six samples were tested with solid content ranging from 30 to 3896. The results of the six experiments are shown in Table 3 below.

Table-3 Experiment 1 Experiment 2 Experiment 3 Experiment 4 Experiment 5+ 20I Go/Go 0.8 0.7 1.
2 0.2 0.1+ 50 ranoko
59,8 53.6 65,9
44.4 38.2+100♂? /, 22
．． 8 25, 8 18, 5 27, 5 25.
3+200♂fu/yu 12.7 14.4
9.9 18,1 21.6+
325 mef/yu 3.4 4.6
3.6 7,2 10.4325
6 noyu 0.4 1.1 0
．． 9 2.6 4.2 Supply solid content 3
0 36 35 35 38 Experiment 6 0.7 53.2 24.3 5.7 1.7 Several embodiments of the present invention have been shown and described, and these embodiments may be modified in many ways as will be apparent to those skilled in the art. It should be clearly understood that changes and modifications can be made. It is therefore intended that the invention not be limited to the detailed description shown and described above, but is intended to cover all changes and modifications that come within the scope of the appended claims.

Applicant's representative: Mr. Sato

Claims (1)

[Claims] 1. A method for regenerating superabsorbent polymer fine powder, wherein the superabsorbent polymer fine powder is selected from the group consisting of starch-grafted superabsorbent polymers, synthetic superabsorbent polymers, and crosslinked superabsorbent polymers. The method comprises: sufficiently wetting the superabsorbent polymer fine powder to form an amorphous gel of the fine powder; pulverizing the gel; drying the pulverized gel; forming a superabsorbent polymeric material. 2. The method of claim 1, wherein the step of drying is followed by comminution of the superabsorbent polymer material. 3. The method of claim 2, wherein particles of a desired size are captured by sorting the particle size of the ground superabsorbent polymer material after the step of grinding the superabsorbent polymer material. 4. The method according to claim 1, wherein the superabsorbent fine powder is wetted with water at a temperature ranging from around a temperature slightly above the freezing temperature to the boiling point. 5. The method according to claim 4, wherein the water is deionized water. 6. Wet the superabsorbent polymer fine powder to reduce the solid content to about 5.
6. A method according to any one of claims 1 to 5, wherein the amount is 70%. 7. Claim 1, wherein the wetting step is performed under stirring conditions.
7. The method according to any one of . 8. The gel is sufficiently dried by a belt dryer, trade dryer or fluid bed dryer to form a superabsorbent polymeric material having a moisture content in the range of about 1-15%. The method described in section. 9. Any one of claims 1 to 8, wherein the crosslinked superabsorbent polymer is a substantially water-insoluble, slightly crosslinked, partially neutralized, hydrogel-forming polymeric material. The method described in. 10. The method of claim 9, wherein the crosslinked superabsorbent polymer is a crosslinked polyacrylate superabsorbent polymer. 11. A method for regenerating superabsorbent polymer fine powder, the superabsorbent polymer fine powder comprising a starch-grafted superabsorbent polymer,
sufficiently wetting the superabsorbent polymer fine powder to form an amorphous gel of the fine powder, the superabsorbent polymer being selected from the group consisting of synthetic superabsorbent polymers and crosslinked superabsorbent polymers; combining the finely divided gel with gel from an ongoing superabsorbent polymerization process. 12. The method of claim 11, wherein the finely divided gel is milled and then combined with the gel from an ongoing superabsorbent polymerization process.