JPH02194010A - Production of polymetal acrylate - Google Patents

Abstract

PURPOSE:To obtain a highly water-absorptive polymetal acrylate having well balanced water absorptivity and gel strength by treating a product of the reversed phase suspension polymerization of an aqueous solution of a metal acrylate with a water-soluble organic solvent, filtering the treated product and drying the obtained filtration residue. CONSTITUTION:An aqueous solution of a metal acrylate is subjected to reversed phase suspension polymerization in the presence of an organic solvent, a surfactant, a polymerization initiator and a crosslinking agent. The product is treated with a water-soluble organic solvent and filtered, and the filtration residue is dried. Alternatively, the product of reversed phase suspension polymerization is filtered and the filtration residue is treated with a water-soluble organic solvent and dried. Examples of the water-soluble organic solvent include acetone, furfural, dimethylformamide, ethyl acetate, methyl ethyl ketone, methyl alcohol and ethyl alcohol.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing polyacrylic acid metal salt, and more specifically, to a method for producing a polyacrylic acid metal salt, which has high water absorption properties and is used as a material for disposable diapers, sanitary products, and other water-absorbent resins. The present invention relates to a method for producing a polyacrylic acid metal salt.

[Prior Art] Polyacrylic acid metal salts having water absorption properties have been known as materials for disposable diapers, sanitary products, and the like. Various studies have been made to improve the water absorption of this polyacrylic acid metal salt.

In this study, as a method to improve the water absorption rate and amount, a method was proposed in which the water content of the produced metal polyacrylic acid salt was controlled within a specific range, and a specific crosslinking agent was added to it to cause crosslinking. is known (Japanese Unexamined Patent Publication No. 59-6
Publication No. 2665).

Although the polyacrylic acid metal salt obtained by this method shows sufficient improvement in water absorption rate, the balance between water absorption and gel strength has not yet reached a satisfactory level.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing a polyacrylic acid metal salt having well-balanced water absorption and gel strength.

[Means for Solving the Problems] As a result of various studies on the post-treatment of a polymerization product obtained by reverse-phase suspension polymerization of an aqueous solution of metal acrylate, the present inventors have determined that a specific organic solvent can be used to The inventors have discovered that a polyacrylic acid metal salt having excellent water absorbency and gel strength, as well as a well-balanced property, can be obtained by processing the polyacrylic acid, and based on this knowledge, the present invention has been completed. It's arrived.

That is, the first invention of the present application is as follows: (1) An aqueous solution of acrylic acid metal salt is subjected to reverse phase suspension polymerization in the presence of an organic solvent, a surfactant, a polymerization initiator, and a crosslinking agent, and the resulting polymerization product is dissolved in water. The second invention is a method for producing a metal salt of polyacrylic acid, which comprises treating the salt with an organic solvent, filtering it, and then drying the filtration residue. In the presence of an agent and a crosslinking agent, an acrylic acid metal salt aqueous solution is subjected to reverse phase suspension polymerization,
The method for producing a polyacrylic acid metal salt is characterized in that the obtained polymerization product is filtered, the filtered residue is treated with a water-soluble organic solvent, and then dried.

The present invention will be explained in detail below.

The acrylic acid metal salts used as monomers in the present invention include sodium acrylate, potassium acrylate,
Examples include lithium acrylate, among which sodium acrylate is preferably used.

This acrylic acid metal salt can be prepared, for example, by neutralizing acrylic acid with an aqueous solution of an alkali metal hydroxide. The degree of neutralization at this time may be completely neutralized, but it is preferably 50 to 95%, more preferably 65 to 85%.

In the polymerization, the aqueous acrylic acid salt solution prepared in this manner is used.

There is no particular limit to the concentration of the aqueous solution at this time, but it is usually 3.
It is desirable that the amount is 0% by weight or more, preferably 35 to 75% by weight.

Preferred organic solvents include aliphatic hydrocarbons such as pentane, hexane, heptane, and octane, and alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclohebutane, and cyclooctane.

Although there is no particular restriction on the amount used, it is usually used in an amount of 1 to 5 times the weight of the aqueous acrylic acid metal salt solution. Further, as the surfactant used in the polymerization, an oil-soluble surfactant is used, and a nonionic surfactant having an HLB of 3 to 8 is particularly desirable.

This surfactant includes sorbitan fatty acid ester,
Examples include polyoxyethylene sorbitan fatty acid ester, among which sorbitan monostearate is preferred.

There are no particular restrictions on the amount of surfactant used, but
Usually, the amount is 1 to 10% by weight based on the acrylic acid metal salt.

As the polymerization initiator, a water-soluble radical generator is used, and examples of the radical generator include potassium persulfate, ammonium persulfate, hydrogen peroxide, and a water-soluble azo compound.

These polymerization initiators may be used as redox initiators in combination with reducing substances such as sulfites or amines.

Moreover, a water-soluble azo compound can also be used as a polymerization initiator. Such azo compounds include 2.2
'-azobis(2-methylpropionamidine) dihydrochloride, 2.2'-azobis[2-(2-imidacillin-2-yl)propane] dihydrochloride, 2
．． Azoamidine compounds such as 2″-azobis(2-methyl-N-7enylpropionamidine) dihydrochloride, 2,2′-azobis[N-(4-hydroxyphenyl)-2-methylpropionamidine J dihydrochloride, 2-2-Azobis(2-methyl-N-[1,1
-bis(hydroxymethyl)-2-hydroxyethyl]
Examples include azoamide compounds such as propionamide) and 2.2°-azobis[2-methyl-N-(2-hydroxyethyl)propionamide].

The amount of this polymerization initiator used is usually 0.0000000000 based on the acrylic acid metal salt. O1 to 1.0% by weight, but the amount is not particularly limited.

Further, as a crosslinking agent, an epoxy compound, a hydroxy compound, a haloepoxy compound, a polyaldehyde, a polyamine, or the like is used.

Epoxy compounds used here include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanesiol diglycidyl ether, glycerin polyglycidyl ether, and trimethylol. Examples include propane polyglycidyl ether.

Examples of the hydroxy compound include ethylene glycol, diethylene glycol, triethylene glycol, di-, tri- or more polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, di-, tri- or more polypropylene glycol, and the like. Further, examples of the haloepoxy compound include epichlorohydrin and σ-methylchlorohydrin, examples of the polyaldehyde include geltaraldehyde and glyoxal, and examples of the polyamine include ethylenediamine.

There are no particular restrictions on the amount of crosslinking agent used, but it is usually 0.0001 to 0.000 g per 100 g of acrylic acid metal salt.
1 equivalent, preferably 0.0002 to 0.05 equivalent.

In the present invention, a polyacrylic acid metal salt is produced by using an acrylic acid metal salt in the form of an aqueous solution and performing reverse phase suspension polymerization in the presence of the above-mentioned organic solvent, surfactant, polymerization initiator, and crosslinking agent. do.

Here, reverse phase suspension polymerization means that a surfactant and a crosslinking agent are dissolved in a solvent phase (oil phase), while an acrylate and a polymerization initiator are dissolved in an aqueous phase. When left standing, a polymerization system is formed from two phases: an oil phase (0) and an aqueous phase (W). This is a polymerization method in which the polymerization system is brought into a suspended state by stirring the polymerization system, a system (Wlo) in which the water phase is dispersed in the oil phase is formed, and the polymerization reaction proceeds.

Polymerization conditions are also not particularly limited, usually 10 to 95°C.
1. Preferably, the temperature is 20 to 85° C., for 1 to 15 hours, preferably 2 to 10 hours, and is usually carried out at normal pressure.

The first invention in the present application is polymerized as described above,
The method for producing a polyacrylic acid metal salt is characterized in that the obtained polymerization product is treated with a water-soluble organic solvent, filtered, and then the filtration residue is dried.

Specifically, after the polymerization is completed, a water-soluble organic solvent is added to the obtained polymerization product, and the mixture is stirred and mixed.

There is no particular limit to the amount of water-soluble organic solvent added at this time, but it is usually 50 to 1 part by weight per 100 parts by weight of the polymerization product.
000 parts by weight, preferably 100 to 800 parts by weight.

In this treatment, examples of the aqueous organic solvent used include acetone, acetonitrile, furfural, dimethylformamide, ethyl acetate, methyl ethyl ketone, methyl alcohol, ethyl alcohol, and isopropyl alcohol.

There is no particular restriction on the furnace material used for filtering, and filters made of paper, glass, glass fiber, asbestos, etc. can be used.

Moreover, as a form of filtration, natural (gravity) filtration, vacuum filtration, or pressure filtration is appropriately used.

After the polymerization product is treated with a water-soluble organic solvent and filtered, the filtration residue is dried.

There are no particular restrictions on the drying conditions, and the drying conditions are usually 50%
Heat and dry at a temperature of -150°C for 1 to 24 hours. This drying is carried out under normal pressure or reduced pressure.

The second invention in the present application is polymerized as described above,
The method for producing a polyacrylic acid metal salt is characterized in that the obtained polymerization product is filtered, the obtained filtration residue is treated with a water-soluble organic solvent, and then dried.

Specifically, the filtration residue is washed with a water-soluble organic solvent.

There is no particular restriction on the amount of water-soluble organic solvent used in this step, as long as the filtration residue is wetted with the water-soluble organic solvent.

In addition, the type of water-soluble organic solvent, conditions for filtration and drying, etc. are the same as in the first invention.

〔Example〕

The present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 4 and Comparative Examples 1 to 4 Into a 500+lIQ four-necked round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube, the indicated amount of the indicated organic solvent was added, and then the indicated amount was added to the indicated amount. After adding and dissolving the indicated amounts of the surfactant and the indicated crosslinking agent,
Dissolved oxygen was removed by blowing nitrogen gas.

Separately, take the indicated amount of acrylic acid in an Erlenmeyer flask, add sodium hydroxide (purity 95%) to 39 g of water while cooling on ice.
) was added in the indicated amount so that the sodium acrylate in the aqueous solution had the indicated concentration to prepare an aqueous sodium acrylate solution. After adding the indicated amount of the polymerization initiator to this aqueous solution and dissolving it, nitrogen gas was blown into the solution to remove dissolved oxygen present in the aqueous solution.

The above-mentioned surfactant was dissolved in the sodium acrylate aqueous solution thus obtained.

This aqueous solution was added and dispersed in an organic solvent, and polymerization was carried out by stirring at the indicated temperature for the indicated time while introducing a slight amount of nitrogen gas.

After the polymerization was completed, the indicated water-soluble organic solvent was added to the obtained polymerization product and mixed with stirring.

This treated product was subjected to natural filtration using filter paper, and the resulting filtration residue was heated and dried under the indicated conditions to obtain sodium polyacrylate. In addition, in Comparative Examples 1 to 4, the treatment with a water-soluble organic solvent was not performed.

The water absorption and gel strength of this sodium polyacrylate were measured.

The results are shown in Table 1. Water absorption and gel strength were measured as follows.

Absorption Amount> Add 750 g of pure water and 0.5 g of water-absorbing resin to a TA wide-mouth bottle and leave it for 15 hours.

Thereafter, the resin was filtered through an 80-mesh wire mesh, the weight of the resulting swollen resin was measured, and the amount of water absorbed was calculated using the following formula.

Gel strength> Take 2 g of water absorbent resin in a beaker and add 2 g of methanol to sufficiently wet the water absorbent resin. Add this to 40g of pure water
Pour in all at once, shake thoroughly to absorb water, and use as a sample.
Gel strength was measured using the apparatus shown in the figure.

At this time, the smooth plate 2 had a thickness of 60 mm, and the thickness of the warm resin 3 was 51 mm. Gel strength was calculated based on the weight of the weight when the sample was crushed.

(The following is a blank space) -5; Examples 5 to 8 and Comparative Examples 5 to 8 The polymerization products obtained in the same manner as Examples 1 to 4 were naturally filtered using filter paper, and the obtained filtration residue was filtered into the indicated water-soluble Washed with an organic solvent, then heated and dried under the indicated conditions,
Obtain sodium polyacrylate.

Note that in Comparative Examples 5 to 8, washing with a water-soluble organic solvent was not performed.

The results are shown in Table 2.

(Space below) Comparative Example 9 230 m of cyclohexane (1, sorbitan monostearate) was added to a 5,00 ml four-day round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube.
Prepare 89 and raise the temperature to 75°C. Separately, in an Erlenmeyer flask, 30 g of acrylic acid was neutralized with 13.49 g of caustic soda dissolved in 399 g. of water. The concentration of 7mer in the aqueous monomer solution was 45% (water content 55%). Then, 0.1 g of potassium persulfate was added and dissolved. This 7mer aqueous solution was dropwise polymerized in the above-mentioned 4-hole flask under a nitrogen atmosphere over a period of 1.5 hours, and then maintained at 70 to 75° C. for 0.5 hours to complete the polymerization. Thereafter, the water content in the polymer suspended in cyclohexane was controlled to 35%, 27%, and 20% by azeotropic dehydration (cyclohexane was refluxed). After this, an aqueous solution of 3 g of ethylene glycol diglycidyl nitrate o, o dissolved in 1 mQ of water was added at 73°C, and after keeping at this temperature for 2 hours, cyclohexane was removed, and the polymer was heated at 80 to 100°C under reduced pressure. It was dried to obtain a water-absorbing polymer.

The water absorption of this polymer is 5109/9 (35% water content in the polymer), 6009/9 (27% water content) and 75
0g/g (20%) and t;.

In addition, the gel strength is 20 g/cm" (35% water content in the polymer), 2297 cm" (27% water content) 8
The weight was 21 g/cm" (20%).

〔Effect of the invention〕

According to the present invention, it is possible to obtain a polyacrylic acid metal salt which has excellent water absorbency and gel strength, and which has a good balance between the two without being biased towards one. Therefore, it is extremely useful as a method for producing superabsorbent resins used as materials for disposable diapers, sanitary products, etc.

[Brief explanation of the drawing]

The figure is a drawing explaining the outline of a measuring device for measuring gel strength, and the symbols in the figure are 1:1! 2: Smooth plate, 3:
Swelling resin sample, 4: stand.

Claims (1)

[Claims] 1. In the presence of an organic solvent, a surfactant, a polymerization initiator, and a crosslinking agent, an aqueous solution of acrylic acid metal salt is subjected to reverse phase suspension polymerization, and the resulting polymerization product is treated with a water-soluble organic solvent. A method for producing a metal salt of polyacrylic acid, the method comprising: drying the filtration residue after filtration. 2. In the presence of an organic solvent, a surfactant, a polymerization initiator, and a crosslinking agent, an aqueous acrylic acid salt solution is subjected to reverse phase suspension polymerization, the resulting polymerization product is filtered, and the filtration residue is treated with a water-soluble organic solvent. A method for producing a metal salt of polyacrylic acid, the method comprising: drying the metal salt of polyacrylate.