JPH02153907A - Production of highly hygroscopic polymer - Google Patents

Abstract

PURPOSE:To obtain the subject polymer useful for hygienic material, etc., having excellent water-absorptivity, fluidity and transportability by using mixed surfactant comprising sorbitan fatty acid ester and saccharose fatty acid ester having respectively specific HLB values. CONSTITUTION:Acrylic acid-based monomer selected from a group of acrylic acid and/or methacrylic acid and alkali metallic salt of said acid is subjected to opposite phase suspension polymerization in a hydrocarbon solvent using initiator of radical polymerization in the presence of crosslinking agent. In said process, a mixture of sorbitan fatty acid ester having at least appearance of solid state at normal temperature and 1-8 HLB value and saccharose fatty acid ester having 1-6 HLB is used as a surfactant applying to opposite phase suspension polymerization to afford the aimed polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] Industrial Field of Application The present invention relates to a method for producing superabsorbent polymers.

The superabsorbent polymer obtained by the present invention is highly safe,
It has excellent water absorption performance and has a large average particle size. Furthermore, since the product has good fluidity and transportability, it can be advantageously used for various water-absorbing materials.

Conventional technology In recent years, superabsorbent polymers have been used not only in the field of sanitary materials such as sanitary products and disposable diapers, but also in industrial applications such as water-stopping materials, anti-condensation materials, freshness preservation materials, solvent dehydration materials, greening, agricultural and horticultural applications, etc. It is a synthetic polymer that is now being put into practical use in the field, and its range of applications is expected to further expand in the future.

Examples of this type of superabsorbent polymer include starch-acrylonitrile graft copolymer hydrolyzate, carboxymethyl cellulose crosslinked product, polyacrylic acid (salt) crosslinked product, acrylic acid (salt)-vinyl alcohol copolymer, and polyethylene oxide. Crosslinked products and the like are known.

However, although all of these highly water-absorbent polymers have almost satisfactory water absorption capacity, it is difficult to say that they simultaneously satisfy various water absorption properties such as water absorption rate and water retention capacity. That is, polymers with high water absorption ability have a slow water absorption rate and poor water retention ability into the membrane.

Methods for improving the water absorption rate of the superabsorbent polymer include a method of mixing a so-called lubricant such as a lipophilic surfactant, a non-volatile hydrocarbon, or calcium stearate;
A method has been proposed in which the hydrophilicity of the polymer is reduced by increasing the crosslinking density of the polymer itself. However, the former method involves mere physical mixing and the lubricant is not chemically immobilized on the polymer, so although an improvement can be seen in the very early stages, the problem is that the effect is not permanent. .

Furthermore, the latter method has the problem of reducing the water absorbing ability of the polymer itself.

Next, regarding the average particle size, particularly superabsorbent polymers synthesized by reverse-phase suspension polymerization have many fine particles and are often difficult to handle.

Common methods for increasing the average particle size of superabsorbent polymers include a method in which a thickener is added to the monomer phase and polymerized, a method in which the produced fine particles are granulated using a binder, and the like. However, the former method is not a good method because it increases the viscosity of the monomer phase, which causes the polymer particles to become viscous with each other, resulting in all or part of the polymer particles becoming agglomerated. Furthermore, since the latter uses a binder, it is disadvantageous in terms of safety and cost.

In addition, the use of various surfactants has been proposed for the purpose of improving water absorption performance or increasing the average particle size.

As such, for example, ■ HLB8~ described in JP-A-56-131608;
Method using 12 surfactants■ JP-A-57-1.5
8209 and JP-A No. 57-158210, a method using a cellulose-based protective colloid; ■ A method using a sucrose fatty acid ester, described in JP-A No. 61-43606; and JP-A No. 62-172,006. HLB2~
Examples include methods using 16 polyglycerin fatty acid esters.

However, although method (2) improves the average particle diameter of the resulting polymer and reduces the number of fine particles, it is not always satisfactory in terms of stable operation because the polymer adheres to the walls of the polymerization tank during polymerization. I can't say it's possible.

In addition, in method (2), if even a small amount of cellulose-based protective colloid remains on the polymer surface, it will melt during drying, causing part of the polymer to form into lumps and causing problems with fluidity and transportability. It is difficult to say that it is a good method because of the following.

Method (2) is highly safe and yields polymers with relatively large particle sizes, but it tends to be inferior in water absorption performance, especially in water absorption speed and water holding capacity, compared to when other surfactants are used. .

Method (2) has a very narrow tolerance range for manufacturing conditions to obtain polymers with large particle diameters, and if these conditions are exceeded, bulk polymerization occurs, so it is not advantageous when considering stable industrial production. It's hard.

Therefore, there is still no superabsorbent polymer that has a large average particle diameter and fully satisfies the various water absorption properties required of a superabsorbent polymer. When considering the diameter and production stability, there is still room for improvement.

[Summary of the invention]

Summary The present invention aims to provide a method for easily producing a superabsorbent polymer that is highly safe, has excellent water absorption performance, has a large average particle size, and has good fluidity and transportability as a product. It is something to do.

As a result of various studies aimed at solving the above-mentioned problems, the present inventors have found that, in the above-mentioned reverse phase suspension polymerization method, as a surfactant, (a) (i) has a solid appearance at least at room temperature; , ■ By using a mixed surfactant of sorbitan fatty acid ester with an HLB value in the range of 1 to 8 and (b) sucrose fatty acid ester with an HLB value in the range of 1 to 6, it is highly safe. The present invention was completed based on the discovery that a superabsorbent polymer having excellent water absorption performance, a large average particle diameter, and good fluidity and transportability as a product can be obtained.

That is, the method for producing a superabsorbent polymer according to the present invention involves adding a radical polymerization initiator to an acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof in the presence of a crosslinking agent. In the method of reverse-phase suspension polymerization in a hydrocarbon solvent, the surfactant used in the reverse-phase suspension polymerization (a) has the appearance of a solid state at least at room temperature and has an HLB value of 1 to 1. Sorbitan fatty acid ester in the range of 8 and (b) HLB value of 1 to 6
It is characterized by being a mixed surfactant with a sucrose fatty acid ester within the range of .

Effects The superabsorbent polymer produced by the present invention has excellent water absorption properties such as water absorption capacity, water absorption rate, and water retention capacity. In addition, it has a large average particle diameter and has good fluidity and transportability as a product.

[Detailed description of the invention]

Monomer As the monomer to be polymerized in the present invention, an acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof is used. The alkali metal salt referred to here is a salt obtained by neutralizing the carboxyl group of acrylic acid and/or methacrylic acid with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. It's about salt. In terms of performance, price, etc. of the produced polymer,
Salts obtained by neutralizing acrylic acid and/or methacrylic acid with sodium hydroxide are particularly preferably used. The degree of neutralization of acrylic acid and/or methacrylic acid is one of the very important factors when considering the performance of the superabsorbent polymer in the present invention, and it When considering balance, it is desirable that 50 to 95 mol% of all carboxyl groups in the acrylic acid monomer be neutralized. If the degree of neutralization is less than 50 mol%, water absorption capacity tends to be poor, making it difficult to maintain well-balanced performance. Conversely, if more than 95 mol% is neutralized,
Since the polymerization rate becomes extremely slow, neutralization has little merit.

The concentration of these acrylic acid monomers in solution is 2
It is preferably 0% or more, particularly 30% to 60%.

In addition, in the present invention, in addition to the above-mentioned acrylic acid monomers, 7mers copolymerizable with these monomers, such as maleic acid (
Salt), itaconic acid (salt), acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-hydroxyethyl (meth)acrylate, etc. also substantially improve the water absorption performance of water-absorbing polymers. It is also possible to use them together as long as they do not damage the product.

Crosslinking agent The above acrylic acid monomer undergoes self-crosslinking to some extent and becomes a highly water-absorbing polymer even without the use of any crosslinking agent. It is necessary to add a crosslinker component. As the crosslinking agent component, a water-soluble compound having two or more polymerizable unsaturated groups in the molecule and exhibiting copolymerizability with the acrylic acid monomer, such as N,N'-methylenebisacrylamide, N, Bisacrylamides such as N'-methylenebismethacrylamide are common and preferred.

The crosslinking agent component is usually about 0.005 to 0.5% by weight, preferably about 0.01 to 0.0% by weight, based on the monomer aqueous solution.
．． It is appropriate to use it in a range of 3% by weight.

Radical Polymerization Initiator In the reverse phase suspension polymerization method of the present invention, a water-soluble radical polymerization initiator is usually dissolved in advance in the monomer aqueous solution. Examples of water-soluble radical polymerization initiators used here include persulfates such as potassium persulfate and ammonium persulfate, and azobis-(2-amidinopropane).
Typical examples include azo initiators such as hydrochloride. These radical polymerization initiators are usually used in an amount of about 0.001 to 5.0% by weight, preferably about 0.01 to 5.0% by weight, based on the monomer aqueous solution.
It is appropriate to use it within the range of 1.0ff11%.

Solvent The solvent for reverse phase suspension polymerization used in the present invention is preferably an aliphatic hydrocarbon or an alicyclic hydrocarbon. Specific examples include normal pentane, normal hexane, normal heptane, cyclohexane, and ligroin.

Among these, cyclohegyu-san and normal hegyo-san are particularly preferred from the viewpoint of removing polymerization heat and drying the obtained polymer.

Surfactant The surfactant used in the present invention, that is, sorbitan fatty acid ester and sucrose fatty acid ester, is known as a food emulsifier and is safe, meeting the specifications of the Japanese Food Additives Standard. It is a very preferable surfactant from the viewpoint of safety.

When using a mixture of these surfactants, it is essential that the sorbitan fatty acid ester (a): ■ have a solid appearance at least at room temperature, and ■ have an HLB value in the range of 1 to 8. becomes.

If even a small amount of sorbitan fatty acid ester that does not meet the conditions (2) remains on the polymer surface, the fluidity and transportability of the product polymer will deteriorate. This is not preferable because it tends to lower the

The other sucrose fatty acid ester (b) preferably has an HLB value in the range of 1 to 6.

Sucrose fatty acid esters with an HLB value of more than 6 tend to have a fine particle size of the resulting polymer.

The amount of these surfactants added is usually 0.1 to 10% by weight, preferably 0.1 to 10% by weight, based on the monomer in a mixed state. This phylum ranges from 5 to 5% flea mass. Added amount is 0
．． If it is less than 1% by weight, the desired dispersion effect cannot be obtained, and if it exceeds 10% by weight, there is a tendency for the polymer to aggregate when it is dried after polymerization, which is not preferable.

The mixing ratio of these surfactants is a very important factor in establishing water absorption performance and particle size, and is usually 80:20 to 20:80 by weight of sorbitan fatty acid ester to sucrose fatty acid ester. , preferably 60:40-4
Mix in the range of 0:60.

Examples of representative sorbitan fatty acid esters include sorbitan monopalmitate (I (LB: 6.7)) sorbitan monostearate (HLB-4,7), sorbitan sesquistearate (HLB-4,2), and sorbitan tri. Stearate (HLB-2, 1), etc. are listed.

Polymerization As described above, the present invention is characterized in that an acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and its alkali metal salts is used in the presence of a crosslinking agent, a radical polymerization initiator, and two types of surfactants. Below, polymerization is carried out by a reversed phase suspension polymerization method. acrylic acid monomer,
The order of addition, mode of addition, and polymerization operation of the crosslinking agent, radical polymerization initiator, and surfactant are arbitrary as long as they do not contradict the purpose of the present invention. For example, (a) an aqueous acrylic acid monomer solution in which a crosslinking agent and a radical polymerization initiator are dissolved is added to a hydrocarbon solvent to which a surfactant has been added, suspended, and then heated to polymerize. how to do,
(b) A method in which a surfactant is added to an aqueous acrylic acid monomer solution in which a crosslinking agent and a radical polymerization initiator are dissolved, and this is added to a hydrocarbon solvent to suspend it and polymerize by heating. c) Adding an aqueous acrylic acid monomer solution in which a crosslinking agent and a radical polymerization initiator are dissolved to a hydrocarbon solvent to suspend it, and then adding a surfactant,
Examples include a method of polymerizing by heating.

Polymerization temperature is 40-120°C, preferably 60-90°C
, will be adopted. The polymerization time varies depending on the polymerization temperature, etc., but for boat fishing it is about 30 minutes to 6 hours, preferably 1 hour to 4 hours. After the polymerization is completed, the polymer is separated from the hydrocarbon solvent and dried to obtain the desired powdered superabsorbent polymer.

[Experiment example]

The present invention will be explained in detail below using experimental examples.

The water absorption performance of the superabsorbent polymer refers to water absorption capacity, water absorption rate (diffusion rate), and water retention capacity, and was measured as follows. The method for measuring the average particle diameter is also described.

Water absorption capacity 1g of super absorbent polymer in a 400 mesh nylon bag (
(size: 10cm x lOcm) and 1 liter of 0
．． 9% - Soak in saline for 30 minutes.

After 30 minutes, pull up the nylon bag, drain it for 15 minutes, weigh it, make a blank correction, and add super absorbent polymer 1.
The weight of 0.9% physiological saline absorbed by g was defined as the water absorption capacity.

Water absorption rate (diffusion rate) 'APE was determined using the apparatus shown in FIG. 1.0 g of a superabsorbent polymer is placed on a nonwoven fabric on a support plate with small holes. When the superabsorbent polymer was brought into contact with 0.9% physiological saline from the lower surface, the amount of water absorbed by the superabsorbent polymer was measured. Water absorbed in 10 minutes after starting 0, 9
The amount of % physiological saline was defined as the water absorption rate (diffusion rate).

Water Retention Capacity Using the apparatus shown in FIG. 1, 25 ml of 0.9% physiological saline is uniformly absorbed into 1 g of superabsorbent polymer. This water-absorbing gel is packed in a 400-mesh nylon bag (10cn+
X I Cleyn) and seal the entrance. This sample was sandwiched between 10 pieces of filter paper (10 cm x 10 cm) at the top and bottom, and a load of 45 g/cd was applied for 3 minutes. The amount of 0.9% physiological saline transferred to the filter paper was measured, and the water retention capacity was determined from the amount of water absorbed before and after pressurization.

Among the standard sieves with average particle size of JIS standard, 42.60.80.1
A particle size distribution based on mass was determined using a sieve with a mesh size of 00.150.200.325, and the 50% particle size based on mass was taken as the average particle size.

Example 1 282 g of cyclohexane was placed in a 1 liter four-eye round bottom flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, and 1.05 sr of sorbitan monostearate and sucrose fatty acid were added to this. Ester (manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK-Ester F-10J) 1
．． After adding and dissolving 05g, nitrogen gas was blown into the solution.
Dissolved oxygen was expelled.

Separately, in a 500 ml conical beaker, 70 g of acrylic acid was added to 185 g of water while cooling with ice from the outside.
28.6 g of 95% pure sodium hydroxide dissolved in 85 g was added to neutralize 70 mole % of the total carboxyl groups. In this case, the concentration of 7mer in water is 30% by weight
corresponds to Next, 0.098 g of N,N'-methylenebisacrylamide and 0.0 g of potassium persulfate were added to this.
．． After adding and dissolving 243 g, nitrogen gas was blown in to drive out dissolved oxygen.

Add this volume ff15 to the contents of the four-necked round bottom flask.
00 ml of the contents of the conical beaker was added, stirred to disperse, and the temperature inside the flask was raised in an oil bath without bubbling nitrogen gas.As it reached around 60°C, the internal temperature rose rapidly. After several tens of minutes, the temperature reached 75°C. Next, the internal temperature was maintained at 60 to 65° C. and the mixture was reacted for 3 hours with stirring. In addition, stirring is at 25 rpm.
I did it.

After reacting for 3 hours, stirring was stopped and the wet polymer particles settled to the bottom of the round bottom flask and were easily separated from the cyclohexane phase by decantation. The separated wet polymer was transferred to a vacuum dryer and heated to 80 to 90°C to remove adhering cyclohexane and water, yielding about 90 g of a smooth powdered polymer.

Example 2 In Example 1, 1.75 g of sorbitan monostearate and sucrose fatty acid ester (D
About 90 g of powdered polymer was obtained in the same manner except that 1.75 g of K-ester F-10) was used.

Example 3 In Example 1, sorbitan monostearate 1.4Of and sucrose fatty acid ester (D
About 90 g of powdered polymer was obtained in the same manner except that 0.7 g of K-ester F-10) was used.

Example 4 In Example 1, sorbitan monostearate 1.05% was used as the surfactant. and sucrose fatty acid ester (manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK-ester F-2
Approximately 90 g of powdered polymer was obtained in the same manner except that 1.05 g of OJ was used.

Example 5 In Example 1, 1.40 g of sorbitan monostearate and sucrose fatty acid ester (D
K-ester F-20) 0. Approximately 90 g of powdered polymer was obtained in the same manner except that 7 g was used.

Example 6 In Example 1, as a surfactant, sorbitan tristearate)1. Approximately 90 g of powdered polymer was obtained in the same manner except that DK-ester F-10 and 1.05 g of sucrose fatty acid ester (DK-ester F-10>1.05 g) were used.

Example 7 In Example 1, 1.05 g of sorbitan tristearate and sucrose fatty acid ester (manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK-ester F-5) were used as surfactants.
About 90 g of powdered polymer was obtained in the same manner except that 1.05 g of 0J) was used.

Comparative Example 1 About 90 g of powdered polymer was obtained in the same manner as in Example 1, except that 2.1 g of sucrose fatty acid ester (DK-ester F-10) was used as the surfactant.

Comparative Example 2 About 90 g of powdered polymer was obtained in the same manner as in Example 1, except that 2.1 g of sucrose fatty acid ester (DK-ester F-20) was used as the surfactant.

Comparative Example 3 About 90 g of powdered polymer was obtained in the same manner as in Example 1 except that 2.1 g of sorbitan monostearate was used as the surfactant.

Comparative Example 4 In Example 1, 1. As surfactants, 1.89 g of sorbitan monostearate and sucrose fatty acid ester (
About 90 g of powdered polymer was obtained in the same manner except that 0.21 g of DK-ester F-10) was used.

Comparative Example 5 In Example 1, 0.21 g of sorbitan monostearate and sucrose fatty acid ester (D
About 90 g of powdered polymer was obtained in the same manner except that 1.89 g of K-ester F-10) was used.

Comparative Example 6 In Example 1, hydroxyethylcellulose (manufactured by Fuji Chemical Co., Ltd., Fujihetsuku A-5000) was added to the monomer phase.
About 9 g of powdered polymer was added in the same manner except that 2.3 g of
Obtained 0g.

The results of the water absorption performance, average particle diameter, and fluidity of the above polymer are shown in Table 1 below.

It can be seen that the average particle diameter is as shown in the table below, and the fluidity is also good.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing an apparatus used to measure the water absorption rate and water retention capacity of superabsorbent polymers. DESCRIPTION OF SYMBOLS 1... Super absorbent polymer (Ig), 2... Support plate with small holes, 3... Nonwoven fabric, 4... 0.9% saline, 5... Buret, 6... Rubber stopper, 7, 8...
・Valve, 9...Air inlet.

Claims (1)

[Claims] An acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof is subjected to reverse phase suspension polymerization in a hydrocarbon solvent using a radical polymerization initiator in the presence of a crosslinking agent. In the method, the surfactant used in the reverse phase suspension polymerization is (a) a sorbitan fatty acid ester that has a solid appearance at least at room temperature and has an HLB value in the range of 1 to 8, and (b) an HLB value. is 1
A method for producing a superabsorbent polymer, characterized in that it is a mixed surfactant with a sucrose fatty acid ester in the range of .