JPH0436304A - Preparation of highly water-absorbent polymer - Google Patents

Abstract

PURPOSE:To prepare the title polymer having excellent water absorption properties, a large mean particle diameter, and good flowability and transportability as a product by allowing (meth)acryilic acid or an alkali salt thereof to undergo reversed phase suspension polymn. in a hydrocarbon solvent in the presence of a specific phosphoric ester surfactant. CONSTITUTION:In a process wherein a monomer selected from the group consisting of (meth)acrylic acid and alkali metal salts thereof is allowed to undergo reversed phase suspension polymn. in a hydrocarbon solvent, in the presence of a crosslinker [e.g. N,N'-methylenebis(meth)acrylamide], using a radical initiator [e.g. ammonium persulfate, or an azo initiator such as azobis-(2- amidinopropane)-hydrochloride], a phosphoric ester surfactant of formula I (wherein R is 8-30C alkyl or alkylphenyl; R' is OH or a group of formula II; and (n) is 1-5) is used. The polymer product gives a highly water-absorbent polymer which, excellent in safety and having excellent water absorption properties, a large mean particle diameter, and good flowability and transportability as a product, is suitably used in many applications as a water absorbent material.

Description

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

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

<Prior art> 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, and solvent dehydration materials, greening, and agriculture and horticulture. It is a synthetic polymer that is being put into practical use for various purposes, 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, a polymer with high water absorption capacity has a slow water absorption rate and poor water retention capacity in terms of -C.

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 there is a problem in that although an improvement is seen in the very early stages, 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 diameter, 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, causing the polymer particles to stick to each other, resulting in all or part of the polymer particles becoming lumpy. Furthermore, since the latter uses a binder, it is disadvantageous in terms of safety and cost.

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

As such, for example, a method using surfactants HL and B8 to B12 is described in JP-A-56-131608.

However, although this method improves the average particle size of the obtained 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. It can not be said. Moreover, polymers whose particle size is increased by this method tend to have poor water absorption performance when used for boat fishing. Therefore, there is still no polymer that has a large average particle size and fully satisfies the various water absorption properties required for superabsorbent polymers. When considering production stability, there is still room for improvement.

[Summary of the invention]

LjL The present invention provides 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. That is.

As a result of various studies aimed at solving the above-mentioned problems, the present inventors have discovered that in the above-mentioned reverse phase suspension polymerization method, -successive (wherein R is a carbon number of 8 to 3 o) as a surfactant. an alkyl group, or
represents an alkylphenyl group, R' is -OH group or formula +
QC) represents a group of 12CH2+TOH. Further, n is an integer from 1 to 5. ) By using a phosphate ester surfactant represented by The present invention was completed based on the discovery that it is possible to obtain a synthetic polymer.

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 has the general formula (wherein R is an alkyl group having 8 to 30 carbon atoms, or
Represents an alkylphenyl group, R' is 10H group or formula +
0CHzCHz h Represents a group of OR. Further, n is an integer from 1 to 5. ) It is characterized by being a phosphate ester surfactant represented by:

Wataru-! 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 The monomer to be polymerized in the present invention is an acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof. The alkali metal salt referred to here refers to 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 is about. In terms of the performance and price 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 is important to consider the total balance of performance of the superabsorbent polymer produced. In some cases, 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, and 30 to 60%.

In addition to the above-mentioned acrylic acid monomers, the present invention also uses monomers 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.

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, but in order to maintain a well-balanced water absorption performance, it is necessary to use this 7-mer aqueous solution. It is necessary to add a crosslinking agent component to the 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 above crosslinking agent component is usually added to the monomer aqueous solution.
About 0.005-0.5% by weight, preferably about 0.01-0.01% by weight
It is appropriate to use it in a range of 0.3% by weight.

In the reverse-phase suspension polymerization method of the present invention, a water-soluble radical polymerization initiator is usually dissolved in the monomer aqueous solution in advance.The water-soluble radical polymerization initiator used here is Persulfates such as potassium persulfate and ammonium persulfate, azobis-(2-amidinopropane)
Typical examples include azo initiators such as hydrochloride. These radical polymerization initiators are usually used in an amount of about o, ooi to 5.0% by weight, preferably about 0.01 to 1% by weight, based on the monomer aqueous solution.
．． It is appropriate to use it in the range of 0% by weight.

Pot-Medium The solvent for reversed-phase suspension polymerization used in the present invention is preferably an aliphatic hydrocarbon or an alicyclic hydrocarbon. Specifically, normal pentane, normal hexane, normal heptane, cyclohexane, ligroin, etc. are listed, and cyclohexane and normal hexane are particularly preferred from the viewpoint of removing polymerization heat and drying the obtained polymer.

The ratio of the solvent to the polymerizable monomer is usually in a volume ratio of 1:1 to 5:1.

The phosphate ester surfactant used in the present invention is chemically structurally and physiologically based on natural phospholipids (lecithin,
Since it is similar to other surfactants (such as cephalin), it is less toxic and less irritating than other surfactants, making it a preferred surfactant from a safety standpoint.

The amount of these surfactants added is usually 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the monomer.
is a quantity in the range of . If the amount added is less than 0.1% by weight, the desired dispersion effect cannot be obtained, and if it exceeds 10% by weight, the polymer tends to aggregate when dried after polymerization, which is not preferable. .

Examples of typical phosphoric acid esters include dioxyethylene octadodecyl ether phosphoric acid, di(dioxyethylene) octadodecyl ether phosphoric acid, polyoxyethylene(6) octadodecyl ether phosphoric acid, and di(polyoxyethylene(6) octadodecyl ether phosphoric acid). 6)) Octadodecyl ether phosphoric acid, di(polyoxyethylene (8))-p-nonylphenyl ether phosphoric acid, dioxyethylene-p-dodecylphenyl ether phosphoric acid, di(dioxyethylene)-
Examples include p-dodecyl phenyl ether phosphoric acid.

l-As mentioned above, the present invention uses an acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof, in combination with a crosslinking agent, a radical polymerization initiator, and two types of surfactants. Polymerization is carried out by reverse phase suspension polymerization in the presence of. 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 of adding a surfactant to an aqueous acrylic acid monomer solution in which a crosslinking agent and a radical polymerization initiator are dissolved, adding this to a hydrocarbon solvent to suspend it, and polymerizing by heating; (c) Examples include a method in which an aqueous acrylic acid monomer solution in which a crosslinking agent and a radical polymerization initiator are dissolved is added to a hydrocarbon solvent and suspended, and then a surfactant is added and polymerization is carried out by heating. be able to.

The polymerization temperature is 40 to 120°C, preferably 60 to 90°C.
℃ is 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, and water retention capacity, and was measured as follows. The method for measuring the average particle diameter is also described.

1 g of Kosui Ke super absorbent polymer in a 400 mesh nylon bag (
10cm x 10cm) and 1! 0.9% of
Soak in physiological saline for 30 minutes. After 30 minutes, pull up the nylon bag, drain it for 15 minutes, weigh it, make a blank correction, and find out that 0.9% of the amount absorbed by 1g of super absorbent polymer.
The weight of physiological saline was defined as water absorption capacity.

Water absorption rate was measured using the apparatus shown in Figure 1. 1.0 g of a superabsorbent polymer is placed on a nonwoven fabric on a support plate with small holes.

The amount of water absorbed by the superabsorbent polymer when brought into contact with 0.9% physiological saline was measured from the bottom surface. After the start, the amount of 0.9% saline water absorbed in 1 minute was defined as the water absorption rate.

Using the apparatus shown in FIG. 1, 25 d of 0.9% physiological saline was uniformly absorbed into the superabsorbent polymer Ig. Place this water-absorbing gel in a 400-mesh nylon bag (10cm x 1
0cm) and seal the entrance.

Cover the top and bottom of this sample with filter paper (10CIX I 0CI)
Hold 10 sheets at a time and apply a load of 45 g/aj to each of them for 3
Take a minute. The amount of 0 and 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 JIS standard sieves, 42,60°80.1
00,150,200.325 mesh sieve was used to determine the mass-based particle size distribution, and the mass-based particle size distribution was determined using a sieve stirrer, a reflux condenser,
121 g of cyclohexane was placed in a 500 d round-bottom flask equipped with a thermometer and a nitrogen gas inlet tube, and 0.0 g of a phosphate ester surfactant represented by the following formula (I) was added.
After adding and dissolving 9 g, nitrogen gas was blown in to drive out dissolved oxygen.

Formula (1) Separately, in a conical beaker with a capacity of 300 d, 79.65 g of water was added to 30 g of acrylic acid while cooling it with water from the outside.
11.65 g of 95% pure sodium hydroxide dissolved in g was added to neutralize 70 mol% of the total carboxyl groups. The monomer concentration relative to water in this case corresponds to 30% by weight as the monomer concentration after neutralization. Then,
Add to this 0.04 N,N'-methylenebisacrylamide
After adding and dissolving 2 g of potassium persulfate and 0.104 g of potassium persulfate, dissolved oxygen was expelled by blowing in nitrogen gas.

Add this volume of 300 to the contents of the four-day round bottom flask.
When the contents of the conical beaker were added and dispersed by stirring, the temperature inside the flask was raised in an oil bath without bubbling nitrogen gas, and after reaching around 60°C, the internal temperature rose to 2. The temperature rose sharply, reaching 75°C after several tens of minutes. 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 250 rpm.
This was done on n+.

After reacting for 3 hours, stirring was stopped and the wet polymer particles settled to the bottom of the round bottom flask and could be 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 35 g of a smooth powdered polymer.

Example 2 About 35 g of powdered polymer was obtained in the same manner as in Example 1, except that 1.8 g of the phosphoric acid ester represented by formula (1) was used as the surfactant.

Example 3 About 35 g of a powdered polymer was obtained in the same manner as in Example 1, except that 2.7 g of a phosphoric acid ester represented by formula CI) was used as a surfactant.

Example 4 About 35 g of powdered polymer was obtained in the same manner as in Example 1, except that 0.9 g of the phosphoric acid ester represented by formula (II) was used as the surfactant.

Formula (II) Example 5 Approximately 35 g of powdered polymer was obtained in the same manner as in Example 1, except that 0.9 g of the phosphoric acid ester represented by the formula (II[) was used as the surfactant.

Formula (1) Example 6 In Example 1, sodium hydroxide 10.0 g water 7
Approximately 35 g of powdered polymer was obtained in the same manner except that 8.3 g was used. (60 mol% of all carboxyl groups were neutralized.) Example 7 In Example 1, 2,2'-azobis-(2-amidinopropane) was used instead of potassium persulfate as the polymerization initiator. Using 0.104 g of dihydrochloride, and 0.063 g of N,N'-methylenebisacrylamide as a crosslinking agent.
About 35 g of powdered polymer was obtained in the same manner except that g was used.

Comparative Example 1 About 35 g of powdered polymer was obtained in the same manner as in Example 1, except that 0.9 g of sorbitan monolaure was used instead of the phosphate ester surfactant.

Comparative Example 2 About 35 g of powdered polymer was obtained in the same manner as in Example 1, except that 0.9 g of decaglyceryl pentastearate was used instead of the phosphate ester surfactant.

Comparative Example 3 In Comparative Example 1, hydroxyethyl cellulose (manufactured by Fuji Chemical Co., Ltd., Fujihetsuta A-5000) was used as the monomer phase.
The powder was prepared in the same manner except that 1.0 g of the powder was added as shown in Table 1 below.

As is clear from the results shown in Table 1, the superabsorbent polymer of the present invention has excellent water absorption performance such as water absorption capacity, water absorption rate, and water retention capacity, and has a large average particle diameter. I know that there is.

[Brief explanation of drawings]

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] 1) An acrylic acid monomer selected from the group consisting of acrylic acid and/or methacrylic acid and alkali metal salts thereof is treated in a hydrocarbon solvent using a radical polymerization initiator in the presence of a crosslinking agent. In the method of reverse phase suspension polymerization in
The surfactant used in reverse-phase suspension polymerization has a general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R is an alkyl group having 8 to 30 carbon atoms, or
Represents an alkylphenyl group, R' is -OH group or formula ▲
There are mathematical formulas, chemical formulas, tables, etc. Represents the group ▼. Further, n is an integer from 1 to 5. ) A method for producing a superabsorbent polymer, characterized in that it is a phosphate ester surfactant represented by: 2) The production method according to claim 1, wherein 50 to 95 mol% of the total carboxyl groups of the acrylic acid monomer are neutralized with an alkali metal salt.