JPH0338288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water-absorbing material that does not dissolve in water, can highly absorb a large amount of aqueous liquid, and can stably retain it. More specifically, the present invention relates to a water-absorbing material made of a water-insoluble bead-like self-crosslinking water-absorbing polymer that is highly water-absorbent and has a high water absorption rate. Conventionally, paper, pulp, sponge, etc. have been used as water-absorbing or water-retaining materials in sanitary materials such as sanitary napkins and paper diapers, and in the agricultural field. However, if pressure is applied, a large portion of it will be squeezed out. As alternatives to these materials, several water-absorbing materials have been proposed in recent years, such as hydrolysates of starch-acrylonitrile graft polymers, modified cellulose ethers, and modified polyethylene oxides. However, they are not sufficient water-absorbing materials because their performance as water-absorbing agents is insufficient, and because they are made from natural materials, there is a risk of spoilage, and the manufacturing method is complicated. It's difficult. The present inventors have previously proposed a method for producing a water-absorbing material that improves these drawbacks (Japanese Patent Publication No. 30710/1983). In general, the required physical properties of a water-absorbing material include (1) water absorption amount, (2) water absorption rate, (3) gel strength after water absorption, and (4) shape, and a water-absorbing material is only good if it satisfies these physical properties. Can be done. However, the water-absorbing material produced by the method disclosed in Japanese Patent Publication No. 54-30710 also has various drawbacks. That is, because sorbitan fatty acid ester is used as a protective colloid in the w/o suspension polymerization method, the particle size of the obtained polymer is
It becomes a very fine powder of less than 100 μm, so when handling powder, dust countermeasures are required. Another drawback is that when the powder comes into contact with an aqueous liquid, it tends to cause a "sticky" phenomenon, resulting in a slow water absorption rate. The present inventors have conducted intensive research to improve these drawbacks and to develop a water-absorbing material that satisfies the above-mentioned required physical properties.As a result, we have developed a method in which an aqueous monomer solution is dispersed/suspended in a hydrophobic liquid and then polymerized. /o In the suspension polymerization method, a cellulose ester or cellulose ether that is oil-soluble at the polymerization temperature is used as a protective colloid, a halogenated aromatic hydrocarbon or hydrocarbon is used as a solvent, and a persulfate is used as a polymerization initiator. By adjusting the concentration of the monomer aqueous solution within a specific range, the particle size of the obtained polymer was 100 μm.
The inventors have discovered that it is possible to obtain a water-absorbing material that is large in size, highly absorbent, and has a high water absorption rate, and has completed the present invention. That is, the present invention involves dispersing an aqueous solution of a water-soluble ethylenically unsaturated monomer selected from acrylic acid, acrylate, acrylamide, and N-substituted acrylamide in a hydrocarbon or halogenated aromatic hydrocarbon without containing a crosslinking agent.・When suspending and polymerizing, use cellulose ester or cellulose ether that is oil-soluble at the polymerization temperature as a protective colloid, use persulfate as a polymerization initiator, and further increase the concentration of the monomer aqueous solution to 40% by weight. The present invention provides a water-absorbing material made of a water-insoluble bead-like self-crosslinking water-absorbing polymer obtained by polymerization at a temperature of 60° C. or higher at a saturation concentration. A w/o suspension polymerization method using oil-soluble cellulose ester or cellulose ether as a protective colloid is disclosed, for example, in JP-A-55-7825, focusing on water-soluble sodium polyacrylate and polyacrylamide. This technique can be applied to the present invention. Preferred water-soluble ethylenically unsaturated monomers used in the present invention are sodium acrylate, acrylamide, and 2-acrylamide-2.
-Methylpropanesulfonic acid. Moreover, two or more types of these monomers can be used. In order to obtain a water-absorbing material, the monomer concentration of the monomer aqueous solution is particularly important, and as in the present invention, in order to perform self-crosslinking in the absence of a crosslinking agent and make it water-insoluble, the monomer concentration is particularly important. The concentration is 40wt% or more up to saturation concentration. If the monomer concentration is less than 40 wt%, sufficient crosslinking reaction will not occur, resulting in the formation of a water-soluble polymer, which will not provide sufficient water absorption amount and water absorption rate. Therefore, they are excluded from the present invention.
Incidentally, the saturated concentration of sodium acrylate at room temperature at a neutralization degree of 75 mol% is approximately 45 wt%. The cellulose ester or cellulose ester that is oil-soluble at the polymerization temperature and used as a protective colloid in w/o suspension polymerization in the present invention refers to the cellulose ester or cellulose ester that is insoluble or cellulose ester in the hydrocarbon or halogenated aromatic hydrocarbon that is the dispersion medium at room temperature. Refers to substances that are poorly soluble and soluble at polymerization temperatures (50°C or higher). Examples of such cellulose esters or ethers include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, ethyl cellulose, benzyl cellulose, and ethyl hydroxyethyl cellulose. Particularly preferred are cellulose acetate butyrate, ethylcellulose, and ethylhydroxyethylcellulose. The dispersion medium used in the present invention is preferably a hydrocarbon having 6 to 10 carbon atoms or a halogenated aromatic hydrocarbon. For example, aromatic hydrocarbons such as benzene, ethylbenzene, toluene, xylene, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclooctane, decalin, aliphatic hydrocarbons such as hexane, pentane, heptane, octane, chlorobenzene, bromine, etc. These include halogenated hydrocarbons such as benzene and dichlorobenzene, preferably toluene, xylene, cyclohexane, methylcyclohexane, hexane, heptane, chlorobenzene, and dichlorobenzene. These dispersion media can be used in combination of two or more types of solvents depending on the type of cellulose ester or ether. Moreover, a single solvent can be used as a dispersion medium by selecting the cellulose ester or ether to be used. In this case, recycling of the dispersion medium becomes easy, which is extremely advantageous industrially. Suitable cellulose derivatives when toluene, xylene, ethylbenzene, chlorobenzene, dichlorobenzene, etc. are used alone as a dispersion medium include ethylcellulose with an ethoxy group content of 43 to 47 wt%, and ethyl cellulose with a butyryl group content of 20 to 50 wt%. It is cellulose acetate butyrate. Cellulose derivatives suitable for using cyclohexane, cyclopentane, methylcyclohexane, decalin, etc. as a dispersion medium have an ethoxy group content of 47
~50wt% ethylcellulose. n-
A cellulose derivative suitable for using hexane, n-heptane, n-octane, etc. alone as a dispersion medium is ethylhydroxyethylcellulose. The amount of protective colloid used is 0.05 to 10wt relative to the dispersion medium.
%, preferably in the range of 0.5 to 5 wt%. Polymerization can be carried out at any temperature from 50°C to the boiling point of the dispersion medium. The temperature is preferably 60° C. or higher, and it is particularly preferable to carry out the polymerization at an azeotropic temperature of the dispersion medium and water from the viewpoint of removing polymerization heat. The volume ratio of the dispersion medium to the aqueous monomer solution can vary over a wide range, but is generally in the range of 1:2 to 5:1 from the standpoint of removing polymerization heat and controlling the polymerization temperature. As polymerization initiators for the polymerization of aqueous monomer solutions it is necessary to use persulfates, such as potassium persulfate, ammonium persulfate, etc. When other radical polymerization initiators are used, such as hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, and azo compounds such as 2,2'-azobis-2-amidinopropane hydrochloride, the resulting polymer is water-soluble. Therefore, the purpose of the present invention cannot be achieved. In the present invention, as mentioned above, the monomer concentration is 40%, which does not contain a crosslinking agent but contains a persulfate.
A water-insoluble bead-like self-crosslinking water-absorbing polymer is produced by using an aqueous solution of a water-soluble ethylenically unsaturated monomer having a concentration of at least % by weight and using a cellulose ester or cellulose ether that is oil-soluble at the polymerization temperature as a protective colloid. Manufactured. The method disclosed in JP-A-55-7825 uses a hydrocarbon or halogenated hydrocarbon as a dispersion medium, and a protective colloid that is insoluble at room temperature in order to obtain a water-soluble polymer with a high molecular weight and uniformity. Alternatively, an oil-soluble cellulose ester or cellulose ether that is sparingly soluble and soluble at the polymerization temperature is used. On the other hand, the present invention applies the method described in JP-A No. 55-7825, and further provides an aqueous solution which does not contain a crosslinking agent but contains a persulfate and has a monomer concentration of 40% by weight or more. By using an aqueous ethylenically unsaturated monomer solution, it is possible to obtain a uniform, water-insoluble, self-crosslinking superabsorbent polymer with a high molecular weight. Therefore, the self-crosslinking bead-like polymer produced according to the present invention has a large and uniform particle size, is water-insoluble, and has high water absorption. Insoluble means that when a polymer is placed in water and stirred at room temperature, it absorbs water and swells to form a gel, but if stirring is stopped and the polymer is left standing, it loses fluidity or undergoes phase separation. This means that a homogeneous aqueous solution is formed by stirring, and this state continues even if the stirring is stopped and the solution is left at the same temperature. In the method disclosed in JP-A-55-7825, a crosslinking reaction is prevented by using an azo initiator to obtain a water-soluble polymer. The polymer produced according to the present invention is essentially insoluble in water and has the unique property of absorbing and retaining water. In order to provide this property, it is essential to cause a crosslinking reaction to insolubilize the polymer during its production. The reason is that when a water-soluble polymer is mixed with the water-insoluble polymer according to the present invention, the water absorption rate decreases, and the polymer after water absorption becomes slimy, does not have a smooth feel, and is difficult to handle. This excludes water-soluble polymers for the purposes of this invention. In the present invention, a crosslinking reaction is actively carried out to obtain a water-insoluble water-absorbing polymer.As a means for achieving this purpose, specifically, a high monomer concentration as proposed in Japanese Patent Publication No. 54-30710 is used. There is a method of insolubilization by self-crosslinking reaction. In this case, the necessary conditions for the self-crosslinking reaction to occur are that a persulfate is used as an initiator and that the concentration of the aqueous monomer solution is 40 wt% or more. In this case, the azo initiator and the water-soluble hydroperoxide initiator do not cause a self-crosslinking reaction, and even if the concentration of the monomer aqueous solution is 40 wt% or less, they do not cause a self-crosslinking reaction. The polymer produced according to the present invention has a significantly large particle size, and because of its large particle size, it has the attributes of high water absorption and high water absorption rate. Such a water-insoluble polymer with a large particle size is produced by using conditions that cause a self-crosslinking reaction in suspension polymerization as described above, and
Production becomes possible only by using oil-soluble cellulose esters or cellulose ethers as protective colloids. The combination of monomer concentration, polymerization temperature, and type of polymerization initiator is important as conditions for obtaining a water-absorbing material with a significantly large particle size of 100 μm or more, high absorbency, and a fast water absorption rate through such self-crosslinking reaction. The present invention provides excellent water absorption in the presence of an oil-soluble cellulose ester or cellulose ether as a protective colloid, at a monomer concentration of 40% by weight to saturated concentration, at a polymerization temperature of 60°C or higher, and in combination with the use of persulfate as a polymerization initiator. The combination of the present invention is novel and produces remarkable effects that could not have been predicted in the past. The advantages of the present invention are that the particle size of the produced polymer has increased, making dust countermeasures unnecessary, and that a water-absorbing material with high water absorption and a fast water absorption rate has been obtained, which expands the uses of the polymer. This is now possible. For example, in addition to conventional water retention agents, water can also be instantly removed from oil and water mixtures. In other words, it can be used not only as a dehydrating agent but also as a material for sanitary products. In other words, even in fields where a large amount of urine, etc. must be absorbed at once, such as with paper diapers, by absorbing it in an instant, there is no "leakage" or "wet feeling", and there is no discomfort left afterwards. It made it possible to say no. The water absorption amount in the present invention is a value determined by the following operation. That is, about 1 g of polymer was dispersed in a large excess of physiological saline, sufficiently swollen, and then
Spend time in mesh wire mesh. The resulting swollen polymer weight (W) was measured, and this value was divided by the initial polymer weight (W ₀ ) to obtain a value, that is, water absorption (g/g) = W/W ₀ . Also, the water absorption rate is 5ml of physiological saline and 0.5ml of polymer.
It is also expressed as the time required for absorption of g. The present invention will be specifically explained below using Examples and Comparative Examples. The contents of acetyl groups, bityryl groups, and ethoxy groups in the cellulose ester or ether used here are as follows. Cellulose acetate butyrate (manufactured by Eastman Kodak Co., Ltd., trademark CAB381-20)...acetyl group content 13 wt%, butyryl group content 37 mt% Ethyl cellulose (manufactured by Hercules Co., Ltd., trademark ethyl cellulose N-200)...ethoxy group content
47.5-49.0wt% Example 1 In a 500ml four-neck round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube, 230ml of cyclohexane and 1.86g of ethylcellulose (manufactured by Hercules, trademark ethylcellulose N-200) were added. After charging, nitrogen gas was blown in to drive out dissolved oxygen, and the temperature was raised to 75°C. Separately, in a flask, while cooling 30g of acrylic acid from the outside, add 40g of ion-exchanged water.
Neutralized with 13.4 g of 98% caustic soda dissolved in
The monomer concentration in the aqueous phase was 45 wt%. Next, 0.1 g of potassium persulfate was added and dissolved, and then nitrogen gas was blown into the aqueous solution to remove oxygen present in the aqueous solution. The contents of this flask were added all at once to the four-necked flask and polymerized. After the polymerization was completed, the temperature was maintained at 75°C and the reaction was continued for 1 hour. Cyclohexane is distilled off under reduced pressure, and the remaining swollen polymer portion is
It was dried under reduced pressure at °C to obtain spherical particles with a center particle size of 100 to 350 μm. Example 2 The procedure was carried out in the same manner as in Example 1, except that 50 g of ion-exchanged water was used in the monomer aqueous solution portion. In other words, the monomer concentration in the aqueous phase was 40 wt%. Example 1 below
Spherical particles having a center particle diameter of 100 to 420 μm were obtained in the same manner as above. Example 3 The procedure was carried out in the same manner as in Example 1, except that 1.0 g of ethyl cellulose (manufactured by Hercules) was used as a protective colloid.
Trademark ethylcellulose N-22) was used. Thereafter, spherical particles having a center particle diameter of 100 to 450 μm were obtained in the same manner as in Example 1. Example 4 In the polymerization reactor of Example 1, 230 ml of hexane,
2.21 g of ethyl hydroxyethyl cellulose (manufactured by Hercules, trademark E.H.E.C.Low) was charged, and the temperature was raised to 65°C. On the other hand, in a flask, 26 g of acrylic acid and 4 g of 2-acrylamido-2methylpropanesulfonic acid were neutralized with 12.2 g of 98% caustic soda dissolved in 44 g of ion-exchanged water. Further, 0.1 g of ammonium persulfate was added and dissolved to form a monomer aqueous solution. The monomer concentration in the aqueous phase is approximately
It was 42wt%. Thereafter, the same procedure as in Example 1 was carried out to obtain spherical particles having a center particle diameter of 100 to 350 μm. Example 5 In the polymerization recipe of Example 4, in the monomer aqueous solution portion, 24 g of acrylic acid was neutralized with 10.2 g of 98% caustic soda dissolved in 50 g of ion-exchanged water, and then 6 g of acrylamide and 0.1 g of potassium persulfate were added. was added and dissolved to form a solution. The monomer concentration in the aqueous phase is
It was 40wt%. The following operations were carried out in the same manner as in Example 4,
Spherical particles with a center particle diameter of 100 to 300 μm were obtained. Example 6 230 ml of monochlorobenzene and 2.3 g of cellulose acetate butyrate were placed in the polymerization reactor of Example 1.
(Manufactured by Eastman Kodatsu, trademark CAB381-20)
was charged and the temperature was raised to 80°C. On the other hand, an aqueous monomer solution was prepared in a flask with 50 g of acrylamide, 50 g of ion-exchanged water, and 0.1 g of ammonium persulfate.
The monomer concentration in the aqueous phase was 50 wt%. The following operation was carried out in the same manner as in Example 1, and the central particle size was 100 to 250 μm.
spherical particles were obtained. Comparative Example 1 A water-insoluble spherical polymer was obtained according to Example 1 described in Japanese Patent Publication No. 54-30710. That is, sorbitan monostearate was used as a protective colloid. The center particle size of this product was 10 to 70 μm. Comparative Example 2 Polymerization was carried out using 1.86 g of sorbitan distearate as a protective colloid in the polymerization recipe of Example 2 to obtain a spherical polymer. The center particle size of this product was 10 to 70 μm. Comparative Example 3 A spherical polymer was obtained under the polymerization conditions of Example 1 using 2,2'-azobis-2-amidinopropane hydrochloride as an initiator. The central particle size of this material is 100~
Although it had a diameter of 350 μm, it dissolved in water and became a viscous aqueous solution. Comparative Example 4 A spherical polymer was obtained using a sodium acrylate aqueous solution diluted to a concentration of 30 wt % under the polymerization conditions of Example 1 as a monomer aqueous solution. This material had a central particle size of 100 to 350 μm, but dissolved in water to form a viscous aqueous solution. Table 1 shows the water absorption amount and water absorption rate of each polymer obtained in Examples 1 to 6 and Comparative Examples 1 to 4. 【table】

Claims (1)

[Claims] 1. Dispersing and suspending an aqueous solution of a water-soluble ethylenically unsaturated monomer selected from acrylic acid, acrylate, acrylamide, and N-substituted acrylamide that does not contain a crosslinking agent in a hydrocarbon or halogenated aromatic hydrocarbon, During polymerization, a cellulose ester or cellulose ether that is oil-soluble at the polymerization temperature is used as a protective colloid, and
A water-insoluble bead-shaped self-crosslinking water-absorbing polymer obtained by polymerizing at a temperature of 60°C or higher using a persulfate as a polymerization initiator and adjusting the concentration of the monomer aqueous solution within the range of 40% by weight to saturated concentration. A water-absorbing material made of