Process for Preparing an Alkali Acrylate Polymer Having High Salt

Patentamt

JEuropâischesà European Patent Office Qj) Publication number: O 036 463

Office européen des brevets B1

CÎ2) EUROPEAN PATENT SPECIFICATION

@ Dateof filing: 14.11.80

@ Process for preparing an alkali acrylate polymer having high sait solution-absorbency and polymer produced thereby.

(30) Priority: 19.03.80 JP 34967/80 @ Proprietor: SEITETSU KAGAKU CO., LTD. 346-1, Miyanishi Harimacho, Kako-gun Hyogo-ken 673-01 (JP) (43) Date of publication of application: 30.09.81 Bulletin 81/39 @ Inventor: Obayashi, Shigeji 31-2, Matsugaoka-3-chome @ Publication of the grant of the patent: Akashi-shi (JP) 1 4.03.84 Bulletin 84/1 1 Inventor: Nakamura, Morio 790-5, Kuchiri Onoecho, Kakogawa-shi (JP) @ Designated Contracting States: Inventor: Fujiki, Koichi AT BE CH DE FR GB IT LI NL SE. 790-6, Kuchiri Onoecho, Kakogawa-shi (JP) Inventor: Yamamoto, Takushi (56) References cited: 2-1 -302, Shinryodai-3-chome FR-A-2 140116 Tarumi-ku. Kobe (JP) FR- A -2 360 612

@ Representative: Marshall, Monica Anne et al, GALLAFENT & CO. 8 Staple Inn London WC1V7QH (GB)

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. This invention relates to a process for pro- merisation, inverse emulsion polymerisation ducing an acrylate polymer having high water- and inverse suspension polymerisation. In the absorbency and particularly salt solution- processes other than the inverse emulsion poly- absorbency and to the water-absorbent resin. merisation and inverse suspension poly- Water-absorbent resins are used in the field merisation, however, the heat of poly- of sanitation as for example menstrual articles, merisation is difficult to remove and the vis- diapers and disposable house-cloths and in the cosity of the polymerisation mixture becomes field of agriculture and horticulture as water too high for the production to be carried out in a retentive materials. Further, they are useful in conventional polymerisation vessel. Further, a other various fields such as the coagulation of powdery product is difficult to obtain by these sludges, the prevention of dew condensation on processes. construction materials, dehydration of oils. As An example of the inverse emulsion poly- such water-absorbent resins, there are known merisation process is mentioned in Japanese for example carboxymethyl celluloses, partially Patent Publication No. 10,644/59 (U.S.P. crosslinked polyethylene oxides, hydrolysates of 3,284,393). When, for example, acrylic acid is starch-acrylonitrile graft copolymers, and par- used as the starting material, the polymer tially crosslinked polyacrylic acid salts. obtained is insoluble in water and does not However, carboxymethyl celluloses and par- exhibit sufficient absorbency for the polymer to tially crosslinked polyethylene oxides have so be called a water-absorbent resin even if it is low an absorbency that deionized water can be neutralised with an alkali such as sodium absorbed in an amount of at most 30 times the hydroxide. As a process for producing an acrylic weight of polymers themselves. acid-alkali metal acrylate polymer having water- Although hydrolyzates of starch-acrylonitrile absorbability, the inverse suspension poly- graft copolymers have a relatively high merisation process mentioned in Japanese deionized water-absorbency corresponding to Patent Publication No. 30,710/79 can be 300-500 times their own weight, the saline referred to, according to which a water-absor- solution-absorbency of the hydrolysates is only bent resin capable of absorbing 400-500 about 30-40 times their own weight and times its own weight of deionized water is products cannot be stored for long periods of obtained by polymerising an aqueous solution time because the starch, the main component, of acrylic acid and an alkali metal acrylate rots. The partially crosslinked polyacrylic acid having a monomer concentration of 40% by salts are not greatly different from the above- weight or more and containing a water-soluble mentioned hydrolyzates of starch-acrylonitrile radical polymerization initiator in a petroleum graft copolymers in absorbency. That is, none of type aliphatic hydrocarbon solvent in the these resins can be said to have a sufficiently presence of a sorbitan fatty acid ester having an high absorbency. Practically speaking, in the HLB value of 3-6. According to the measure- usages concerned with sanitation, for example, ment of the present inventors, however, the the fluids to be absorbed such as urine and saline solution-absorbency of said water-absor- catamenial blood contain electrolytes such as bent resin is as low as 35-50 times its own sodium chloride and calcium chloride. Further, weight. in the case of agricultural and horticultural In general, the polymer obtained by the usages, the soil contains electrolytes including inverse suspension polymerization of acrylic fertilizer components. Therefore, a water-absor- acid and an alkali metal acrylate is considered bing material having a high absorbency not only to exhibit water-absorbency owing to the of deionized water but also of aqueous elec- hydrophilic group contained in its structural unit trolyte solutions is needed. The field of appli- and the complicated entanglement of the high cation of water-absorbent resins will accord- polymer molecular chains as well as to the ingly be broadened by developing a polymer pseudo-crosslinked structure which the polymer having high salt solution-absorbency. contains in a very small amount. As mentioned above, a variety of polymers In order to obtain a high polymer with an are known as water-absorbent resins. The emulsion or suspension polymerization system present inventors have considered that it is including an inverse emulsion or suspension advantageous to produce a water-absorbent system, it is conventional to increase the resin by using acrylic acid as a starting material monomer concentration, to decrease the because it has a constant quality and is readily concentration of polymerization initiator, to available commercially. Based on this con- lower the polymerization temperature, and to sideration, detailed studies have been carried keep the monomer droplets as fine as possible. out. Although the same conditions as above are For the polymerisation of acrylic acid and an considered also applicable to the production of acrylate, there have hitherto been known a high polymer by the inverse suspension poly- various processes such as bulk polymerisation, merization of acrylic acid and an alkali metal aqueous solution polymerisation, spray poly- acrylate, it is indispensable to keep the degree of polymerization high and, at the same time, to their attention to the point that, if the quan- give the polymer an appropriate amount of tities of polymerization heat generated in unit pseudo-crosslinked structure in order to impart period of time are the same, the droplet an excellent absorbency to the polymer pro- diameter of the aqueous monomer solution is in duced by the inverse suspension poly- a contradictory relation to the amount of polymerization of acrylic acid and an alkali metal merization heat released into the solvent layer. acrylate. One of the methods of forming a slight Thus the degree of polymerization of the amount of pseudo-crosslinked structure is to resulting polymer would become higher and the increase the monomer concentration of the pseudo-crosslinking reaction would take place aqueous monomer solution to more than 40% more easily by developing the Trommsdorff by weight in the inverse suspension system. In effect more conspicuously, which is caused by this case, however, the polymer obtained increasing the monomer droplet diameter cannot be said to have a sufficient absorbency within the range in which the emulsion stability because it can absorb about 400-500 times is not adversely affected thereby and reducing its own weight of deionized water but only the quantity of the heat released per unit weight 35-50 times its own weight of saline solution. of the monomer droplet, and have conse- The present inventors have conducted exten- quently accomplished a process for producing a sive studies about a process for producing a high absorbency polymer by using a surfactant polymer much superior in absorbency to the having an HLB value of 8-12 which is existing water-absorbent resins. As a result, the generally considered to be unsuitable for inventors have paid their attention to the point inverse suspension polymerization systems and that acrylic acid and an alkali metal acrylate or inverse emulsion polymerization systems. ammonium acrylate form a high polymer in a It is an object of this invention to provide a short period of time while forming pseudo- polymer having high-water absorbency and in crosslinkages and entanglements of molecular particular having high salt solution-absorbency. chains in the process of polymerization and the It is another object of this invention to point that an aqueous solution of acrylic acid provide a process for producing said polymer. and an alkali metal acrylate or ammonium According to this invention, there is pro- acrylate forms a relatively stable suspension vided a process for producing an acrylate phase even when using a surfactant having an polymer by subjecting to inverse suspension HLB value higher than 3-6, which has hitherto polymerization an aqueous solution of acrylic been considered suitable for the case of W/O acid and an acrylate, wherein the molar ratio of type inverse suspension phase, whereby it has the acrylic acid to the acrylate is 50/50 to 2/98 surprisingly been found that there is obtained a and the monomer concentration is at least 40% polymer having so markedly excellent an absor- by weight, in the presence of a water-soluble bency as to be able to absorb at least 800 times radical polymerization initiator characterised in its own weight of deionized water and at least that there is used a suspension of an aqueous 80 times its own weight of saline solution by solution of acrylic acid and an alkali metal suspending an aqueous solution of acrylic acid acrylate or ammonium acrylate in an alicyclic or and an alkali metal acrylate or ammonium aliphatic hydrocarbon containing a surface acrylate in an alicyclic or aliphatic hydrocarbon active agent having an HLB value of 8 to 12. If solvent containing a surfactant having an HLB necessary, the resulting polymer may be cross- value of 8-12, subjecting the suspension to linked with a crosslinking agent. inverse suspension polymerization in the The process of this invention is an presence of a water-soluble radical poly- unexpected process, and the polymer obtained merization initiator and, if necessary, carrying is a novel resin having so high a water-absor- out a crosslinking reaction with a crosslinking bency as to be impossible to expect from agent. conventional water-absorbent resins. In polymerization reactions, there is generally The acrylic acid monomer used in the poly- observed the so-called Trommsdorff effect: that merization has to be neutralised partially with is the viscosity of the polymerization system an alkali such as sodium hydroxide, ammonium increases and the diffusibility of the polymer hydroxide or potassium hydroxide, and the decreases, with the progress of polymerization, appropriate degree of neutralization is 50-98 and hence, the rate and degree of poly- mole percent. If the degree of neutralization is merization increase rapidly. The same ten- less than 50 mole percent, the pseudo-cross- dency as above is also observed in the inverse linking reaction takes place to an extremely high suspension polymerization of an aqueous extent and the absorbency of the polymer solution of acrylic acid and an alkali metal obtained decreases greatly. If the degree of acrylate or ammonium acrylate, and the rate of neutralization exceeds 98 mole percent, the polymerization in said polymerization system is major part of the polymer becomes water- so high as to emit the heat of polymerization soluble. rapidly which causes a pseudo-crossiinking The solvent used in this invention is an ali- reaction. It has been thought that a water- cyclic hydrocarbon or an aliphatic hydrocarbon. absorbent polymer is obtained owing to these As said alicyclic hydrocarbon, preferred are for phenomena. The present inventors have paid example cyclopentane, methylcyclopentane, cyclohexane and methylcyclohexane. As said absorbency and particle diameter of the aliphatic hydrocarbon, there are preferable for polymer formed are substantially the same as example n-pentane, n-hexane, n-heptane and those mentioned above, even if the amount of ligroin. If an aromatic hydrocarbon such as surfactant used is reduced to the neighbour- benzene, toluene or xylene is used as the hood of its critical micelle concentration. solvent, the resulting polymer becomes a mass, Further, if the amount of the surfactant used and a step of pulverization is required for is reduced below the critical micelle concen- obtaining a granular or powdery polymer, so tration or the polymerization is carried out that they cannot be said to be practical under an insufficient stirring conditions, a lump solvents. of polymer is formed or the polymer obtained is The radical polymerization initiator must be uneven in absorbency. water-soluble, and the generally used water- On the other hand, if a surfactant having an soluble radical polymerization initiators such as HLB value exceeding 12 is used, the polymer potassium persulfate and ammonium per- formed during the polymerization becomes a sulfate are suitably used. They may be block and has such a low absorbency that it combined with for example a sulfite to form a cannot be said to be a practical water-absor- redox type initiator. However, the use of oil- bent resin. soluble radical polymerization initiators is not The amount of the surfactant used is pre- desirable because they generally form a water- ferably in the range of 1-15% by weight based soluble polymer. The water-soluble radical poly- on the weight of the monomers. If it is less than merization initiator is used preferably in an 1% by weight, the emulsion cannot be kept in a amount of 0.005-1.0 mole percent based on stable state. If more than 15% by weight of the the total amount of the monomers. If it is less surfactant is used, no improved result corres- than 0.005 mole percent, the polymerization ponding thereto is obtained, and hence, it is not reaction takes a very long period of time. If it is economical. more than 1.0 mole percent, a polymer having a The polymerization temperature is pre- low absorbency is formed. ferably in the range of from 20° to 100°C, As the surfactant used in the inverse sus- more preferably from 40° to 80°C. If the poly- pension polymerization of this invention, any merization is carried out at a temperature surfactant may be used as long as its HLB is higher than 100°C, the amount of pseudo- 8-12, though for example a sorbitol fatty acid crosslinkage becomes extremely high and on ester, a sorbitol fatty acid ester ether, a sorbitan the contrary, the absorbency of the polymer fatty acid ester, a sorbitan fatty acid ester ether decreases. If the polymerization is carried out at give particularly good results. If acrylic acid and a temperature lower than 20°C, the poly- an alkali metal acrylate or ammonium acrylate merization rate is decreased and, in addition, a are polymerized in the inverse suspension water-soluble polymer is formed. system with said surfactants, there can be A water-absorbent resin suitable for usages obtained a high water-absorbent polymer necessitating stability in the fluid-absorbed capable of absorbing at least 800 times its own state for a long period of time or a high rate of weight of deionized water and at least 80 times absorption can be obtained by crosslinking the its own weight of saline solution in the form of polymer of this invention in the presence of a uniform granules. crosslinking agent. In general, requirements of surfactants used As the crosslinking agent for compounds in the polymerization are that the poly- containing a carboxyl group, a variety of sub- merization mixture forms a stable emulsion, the stances are known. In order to improve the surfactant does not retard the polymerization stability in the water-absorbed state and to reaction, and uniform polymer particles are improve the absorption rate without greatly formed without coagulation or separation. The decreasing the absorbency which is the charac- above-mentioned surfactants used in this teristic feature of the water-absorbent resin, a invention sufficiently fulfil these requirements. water-soluble diglycidyl ether compound, a When the polymerization is carried out by haloepoxy compound or an aldehyde compound using a surfactant having an HLB value of less may for example be used as the crosslinking than 8 such as sorbitan monostearate, a stable agent. Amongst these the water-soluble emulsion is formed but the deionized water- diglycidyl ether compounds are particularly pre- absorbency of the polymer obtained is as low as ferred. The water-soluble diglycidyl ether 400-500 times its own weight and the saline compounds include, for example, (poly)ethylene solution-absorbency thereof is as low as 35- glycol diglycidyl ether, (poly)propylene glycol 50 times its own weight. Further, the polymer diglycidyl ether, and (poly)glycerin diglycidyl formed is in the form of a powder having too ether. The haloepoxy compounds include, for small a particle diameter, so that the polymer is instance, epichlorohydrin and a-methylepi- lost as dust at the time of drying or practical chlorohydrin. The aldehyde compounds include, use. Although reducing the amount of sur- for example, glutaraldehyde, glyoxal and thio- factant used or decreasing the power of stirring diacetoaldehyde. These compounds are all the polymerization mixture may be thought of usable in this invention. By carrying out the for overcoming the above-mentioned faults, the crosslinking reaction with the above-mentioned crosslinking agents, the water absorption having an improved stability in the powdery rate and the stability in the fluid-absorbed state state and in the water-absorbed state for a long can be improved without greatly decreasing the period of time. This is an excellent effect which absorbency. Particularly, when ethylene glycol has hitherto not been known at all. diglycidyl ether is used, a good result is The term "absorbency" used herein means a obtained. Further, by carrying out the cross- value determined according to the following linking reaction, the formation of an unswollen procedure: In the case of deionized water- powder lump, which tends to be caused at the absorbency, 2 liters of deionized water and 1 g beginning stage of water absorption, can be of the dried polymer were placed in a 3-liter prevented and the rate of absorption when beaker, and water was absorbed by the polymer absorbing water can also be improved. When a for 30 minutes with stirring, after which the powdery material has absorbed moisture, polymer was collected by filtration with a 100- agglomeration of particles tends to occur to mesh metallic wire gauze, the volume of the injure the flow property of the powdery swollen polymer obtained as a filtered cake was material. According to this invention, this fault measured by means of a measuring cylinder, can also be overcome and a powdery material and the value was taken as the deionized water- having a good flow property can be obtained. absorbency. The amount of the crosslinking agent used In the case of saline solution-absorbency, may vary depending upon the kind of the cross- 200-ml of saline solution (0.9% by weight linking agent. When, for example, a water- aqueous sodium chloride solution) and 1 g of soluble diglycidyl ether compound is used, the dried polymer were placed in a 300-ml beaker amount thereof is preferably in the range of and the solution was absorbed by the polymer 0.005-5.0% by weight based on the weight of for 30 minutes with stirring, after which it was the monomers. If it is smaller than 0.005% by filtered with a 200-mesh metallic wire gauze, weight, the effect of the addition of the the volume of the swollen polymer obtained as compound cannot be obtained. If the amount is a filtered cake was measured by means of a larger than 5.0% by weight, there is obtained a measuring cylinder and the value was taken as polymer having so high a degree of cross- the saline solution-absorbency. linking that the absorbency of the polymer is This invention will be explained below markedly lowered. referring to Examples and Comparative The crosslinking agent may be added at any Examples. time after the completion of the polymerization to develop the above-mentioned performances Example 1 fully. For example, a crosslinking agent may be In a 200-ml flask was placed 39.1 g of added to the polymerization mixture and the acrylic acid having a purity of 99.8% by weight. resulting mixture heat-treated, or the poly- While cooling it, 76.5 g of 22.6% by weight merization mixture may be poured into a aqueous sodium hydroxide solution was solvent, such as a lower alcohol or acetone, dropped thereinto with stirring to neutralize the containing a crosslinking agent. The mixture acrylic acid to an extent of 80 mole percent. thus obtained may be heat-treated as such, or it Then, 0.13 g of potassium persulfate was is also possible to heat and evaporate the added and stirring was continued at room tem- mixture in the form of a slurry to dryness to perature to dissolve it. remove the solvent and simultaneously effect 213 g of cyclohexane and 1.9 g of sorbitan the crosslinking reaction. monolaurate having an HLB value of 8.6 were The characteristic feature of this invention charged into a 500-mi flask equipped with a consists in that a surfactant having an HLB reflux condenser, the inner atmosphere of value of 8-12, which has hitherto been con- which had previously been replaced with sidered unsuitable for inverse suspension nitrogen, and the surfactant was dissolved at systems or inverse emulsion systems, is used. It room temperature with stirring. Then, the also consists in that the polymer formed by the above-mentioned aqueous solution of partially polymerization is much superior in absorbency neutralized acrylic acid salt was dropped there- to the hitherto known water-absorbent resins, into and suspended therein. The inner that a uniform granular polymer can be atmosphere was again replaced with nitrogen obtained, and that a polymer having an sufficiently and then the temperature was improved stability of absorbency in the fluid- raised, and polymerization reaction was carried absorbed state for a long period of time and an out for 3 hours while keeping the bath tem- improved absorption rate can be obtained by perature at 55-60°C. using for example a water-soluble diglycidyl By evaporating the polymerization mixture ether compound as a crosslinking agent. thus formed to dryness under reduced pressure, According to this invention, it has become 48.0 g of a particulate dry polymer was possible to produce a water-absorbent resin obtained. The deionized water-absorbency of having a deionized water-absorbency corres- the polymer corresponded to 1,250 times in its ponding to at least 800 times its own weight own weight and the saline solution-absorbency and a saline solution-absorbency corres- corresponded to 120 times in its own weight. ponding to at least 80 times its own weight and As measured after 5 minutes, the deionized water-absorbency was 300 times and saline In the powdery state and in the water-absorbed solution-absorbency was 25 times. In the state, no change in absorbency was observed powdery state, the polymer exhibited no change for a long period of time. in absorbency over a long period of time. Example 6 Example 2 The same procedure as in Example 5 was The same procedure as in Example 1 was repeated, except that the amount of ethylene repeated to effect partial neutralization, poly- glycol diglycidyl ether added was altered to 0.1 merization and evaporation to dryness, except g to obtain 48.0 g of a particulate dry polymer. that the surfactant was replaced by oxy- The deionized water-absorbency was 1,150 ethylenesorbitan monostearate ether (EO 3- ml/g-polymer, and the saline solution-absor- mole adduct) having an HLB value of 9.0, bency was 105 ml/g-polymer. The water whereby 47.5 g of a particulate dry polymer absorption rate was high in all the cases. In the was obtained. The deionized water-absorbency powdery state and in the water-absorbed state, was 1,050 ml/g-polymer and the saline no change in absorbency was observed for a solution-absorbency was 100 ml/g-polymer. In long period of time. the powdery state, no change in absorbency was observed for a long period of time. Example 7 The same procedure as in Example 5 was Example 3 repeated, except that the ethylene glycol The same procedure as in Example 1 was diglycidyl ether was replaced by 0.4 g of repeated to carry out partial neutralization, glycerin diglycidyl ether, to obtain 48.7 g of a polymerization, and evaporation to dryness, particulate dry polymer. The deionized water- except that the solvent for polymerization absorbency was 800 ml/g-polymer, and the (cyclohexane) was replaced by n-hexane and saline solution-absorbency was 80 ml/g- the amount of polymerization initiator was polymer. The water absorption rate was high in altered to 0.39 g, whereby 48.4 g of a par- all of the cases. In the powdery state and in the ticulate dry polymer was obtained. The water-absorbed state, no change in absor- deionized water-absorbency was 1,050 ml/g- bency was observed for a long period of time. polymer, and the saline solution absorbency was 80 ml/g-polymer. In the powdery state, no Example 8 change in absorbency was observed over a long In 300 g of methanol was dissolved 0.4 g of period of time. ethylene glycol diglycidyl ether. The resulting solution was added to the polymer solution Example 4 formed by carrying out polymerization in the The same procedure as in Example 1 was same manner as in Example 1, and the poly- repeated to carry out partial neutralization, merization mixture obtained was subjected to polymerization and evaporation to dryness, crosslinking reaction at 50°C for 3 hours. By except that acrylic acid was neutralized to an evaporating the reaction mixture to dryness 49.0 of excent of 65 mole percent with 61.0 g of 9.8% under reduced pressure, g a particulate The deionized by weight aqueous ammonia solution, whereby dry polymer was obtained. water- and the 44.5 g of a particulate dry polymer was absorbency was 1,000 ml/g-polymer, obtained. The deionized water-absorbency was saline solution-absorbency was 90 ml/g- 1,100 ml/g-polymer, and the saline solution- polymer. The water-absorption rate was high in absorbency was 105 ml/g-polymer. In the all the cases. In the powdery state, no change in powdery state, no change in absorbency was absorbency was observed for a long period of observed for a long period of time. time.

Example 5 Example 9 in 8 In 4.0 g of water was dissolved 0.4 g of The same procedure as Example was ethylene glycol diglycidyl ether (molecular repeated to carry out polymerization and cross- weight 174). The resulting solution was added linking reaction, except that the crosslinking to the polymer solution obtained by the same reaction and a drying under atmospheric procedure as in Example 1, and the resulting pressure was simultaneously carried out at mixture was subjected to crosslinking at 50°C 105°C, whereby 48.5 g of a particulate dry for 3 hours. By evaporating the resulting polymer was obtained. The deionized water- reaction mixture to dryness under reduced absorbency was 940 ml/g-polymer, and the 87 ml/g- pressure, 48.5 g of a particulate dry polymer saline solution-absorbency was was obtained. The deionized water-absorbency polymer. The water absorption rate was high in was 900 ml/g-polymer, and the saline solution- all of the cases. In the powdery state and in the absor- absorbency was 85 ml/g-polymer. As measured water-absorbed state, no change in after 5 minutes, the deionized water-absorbency was observed for a long period of time. bency became 550 ml/g-polymer and the saline solution-absorbency was 45 ml/g-polymer. The Example 10 water absorption rate was high in all the cases. The same procedure as in Example 8 was repeated, except that the ethylene glycol saline solution-absorbency was at most 10 diglycidyl ether was replaced by 0.1 g of epi- ml/g-polymer. chlorohydrin, whereby 48.0 g of a particulate dry polymer was obtained. The deionized water- Comparative Example 6 absorbency was 900 ml/g-polymer, and the The same procedure as in Example 5 was saline solution-absorbency was 85 ml/g- repeated, except that 3.9 g of ethylene glycol polymer. The water absorption rate was high in diglycidyl ether was used instead of 0.4 g, all of the cases. In the powdery state and in the whereby 51.0 g of a particulate dry polymer water-absorbed state, no change in absor- was obtained. The deionized water-absorbency bency was observed for a long period of time. was 50 ml/g-polymer and the saline solution- absorbency was 10 ml/g-polymer. Comparative Example 1 The same procedure as in Example 1 was Comparative Example 7 repeated to carry out partial neutralization, The same procedure as in Example 5 was polymerization, and evaporation to dryness, repeated, except that 0.001 g of ethylene glycol except that the surfactant was replaced by 1.9 diglycidyl ether was used instead of 0.4 g, g of sorbitan monostearate having an HLB value whereby 49.3 g of a particulate dry polymer of 4.7, whereby 48.0 g of a fine powder of a dry was obtained. The deionized water-absorbency polymer was obtained. The deionized water- was 1,150 ml/g-polymer, and the saline absorbency was 520 ml/g-polymer, and the solution-absorbency was 120 ml/g-polymer. saline solution-absorbency was 50 ml/g- The addition of a crosslinking agent brought no polymer. noticeable effect.

Comparative Example 2 The same procedure as in Example 1 was repeated to carry out partial neutralization, 1. A process for producing an acrylate polymerization and evaporation to dryness, polymer by subjecting to inverse suspension except that the surfactant was replaced by 1.9 polymerization an aqueous solution of acrylic g of polyoxyethylene sorbitan monostearate acid and an acrylate, wherein the molar ratio of ether (EO 21-mole adduct) having an HLB value the acrylic acid to the acrylate is 50/50 to 2/98 of 14.9, whereby 48.7 g of a dry polymer in the and the monomer concentration is at least 40% form of an agglomerate lump was obtained. The by weight, in the presence of a water-soluble polymer was substantially dissolved in either radical polymerization initiator characterised in deionized water or saline solution. that there is used a suspension of an aqueous solution of acrylic acid and an alkali metal Comparative Example 3 acrylate or ammonium acrylate in an alicyclic or The same procedure as in Example 1 was aliphatic hydrocarbon containing a surface repeated to carry out partial neutralization, active agent having an HLB value of 8 to 12. polymerization and evaporation to dryness, 2. A process according to claim 1 charac- except that the solvent for polymerization was terised in that, after the polymerization reaction, replaced by 213 g of toluene, whereby a dry there is added a crosslinking agent and the polymer in the form of a block was obtained. resulting mixture is subjected to a crosslinking reaction. Comparative Example 4 3. A process according to claim 2 charac- The same procedure as in Example 1 was terised in that the crosslinking agent is ethylene repeated to carry out partial neutralization, glycol diglycidyl ether and it is used in an polymerization and evaporation to dryness, amount of 0.005-5.0% by weight based on except that the neutralization was effected to a the weight of the monomers. full extent of 100% with 82.3 g of 26.3% by 4. A process according to any one of claims weight aqueous sodium hydroxide solution, 1 to 3 characterised in that the surface active whereby 49.8 g of a particulate dry polymer agent having an HLB value of 8-12 is sor- was obtained. The deionized water-absorbency bitan monolaurate. was 20 ml/g-polymer, and the saline solution- 5. A process according to any one of claims absorbency was 10 ml/g-polymer. 1 to 4 characterised in that the hydrocarbon is cyclohexane. Comparative Example 5 The same procedure as in Example 1 was repeated to carry out partial neutralization, polymerization and evaporation to dryness, 1. Verfahren zum Herstellen eines Acrylat- except that the neutralization was effected to polymers, bei welchem eine wässrige Lösung an extent of 30 mole percent with 62.7 g of von Acrylsäure und eines Acylats, worin das 10.4% by weight aqueous sodium hydroxide Molverhältnis der Acrylsäure zum Acrylat 50/50 solution, whereby 43.3 g of a particulate dry bis 2/98 und die Monomerkonzentration polymer was obtained. The deionized water- zumindest 40 Gew.-% beträgt, in Anwesenheit absorbency was 120 ml/g-polymer and the eines wasserlöslichen radikalischen Poly- merisationsinitiators einer inversen Sus- d'acrylate en soumettant à la polymérisation en pensionspolymerisation unterworfen wird, suspension inverse une solution aqueuse dadurch gekennzeichnet, daß eine einen ober- d'acide acrylique et un acrylate, dans lequel le flächenaktiven Stoff mit einem HLB-Wert von 8 rapport molaire de l'acide acrylique à l'acrylate bis 12 enthaltende Suspension einer wässrigen est de 50/50 à 2/98 et la concentration du Lösung von Acrylsäure und eines Alkalimetall- monomère est au moins de 40% en poids, en acrylats oder von Ammoniumacrylat in einem présence d'un initiateur de polymérisation radi- alicyclischen oder aliphatischen Kohlenwasser- calaire soluble dans l'eau, caractérisé en ce stoff verwendet wird. qu'on utilise une suspension d'une solution 2. Verfahren nach Anspruch 1, dadurch aqueuse d'acide acrylique et d'un acrylate de gekennzeichnet, daß nach abgeschlossener métal alcalin ou d'acrylate d'ammonium dans Polymerisationsreatkion ein Quervernetzungs- un hydrocarbure aliphatique ou cycloali- mittel zugesetzt und das erhaltene Gemisch phatique contenant un agent actif en surface einer Quervernetzungsreaktion unterworfen ayant une valeur de HLB de 8 à 12. wird. 2. Un procédé selon la revendication 1, 3. Verfahren nach Anspruch 2, dadurch caractérisé en ce que, après la réaction de poly- gekennzeichnet, daß als Quervernetzungs- mérisation, on a ajouté un agent réticulant et on mittel Äthylenglykoldiglycidyläther verwendet soumet le mélange résultant à une réaction de una in einer Menge von 0,005 bis 5,0 Gew.-96, réticulation. bezogen auf das Gewicht der Momere, einge- 3. Un procédé selon la revendication 2, setzt wird. caractérisé en ce que l'agent réticulant est 4, Verfahren nach irgendeinem der An- l'éthylène glycol diglycidyl éther et qu'il est uti- sprüche 1 bis 3, dadurch gekennzeichnet, daß lisé à raison de 0,005 à 5% en poids par rapport der einen HLB-Wert von 8 bis 12 besitzende au poids des monomères. oberflächenaktive Stoff Sorbitanmonolaurat ist. 4. Un procédé selon l'une quelconque des 5. Verfahren nach irgendeinem der An- revendications 1 à 3, caractérisé en ce que sprüche 1 bis 4, dadurch gekennzeichnet, daß l'agent actif en surface ayant une valeur de HLB der Kohlenwasserstoff Cyclohexan ist. de 8 à 12 est le monolaurate de sorbitan. 5. Un procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce que 1. Un procédé pour fabriquer un polymère l'hydrocarbure est le cyclohexane.