JPH04103607A - Highly water-absorptive polymer and its production - Google Patents

Abstract

PURPOSE:To obtain the title polymer excellent in resistance to heat and light, useful for gels to be used for cold or heat storage materials, fragrances etc., by polymerization of a monomer mixture comprising an acrylic acid-based monomer and a hindered amine-contg. acrylic ester. CONSTITUTION:A polymerization is carried out for a monomer mixture comprising (A) an acrylic acid-based monomer of formula I (R<1> is H or methyl; X is H, alkali metal or ammonium) and (B) a hindered amine-contg. acrylic ester of formula (R<2> and R<3> are each H or methyl) to obtain the objective polymer made up of (1) 80-99.9mol% of structural unit of formula III and (2) 0.1-20mol% of another structural unit of formula 7 with a total of both the structural units accounting for >=90mol% of the final polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] <Industrial Application Field> The present invention relates to a superabsorbent polymer and a method for producing the same. The polymer obtained by the present invention has high water absorption performance, and the water-absorbing gel is stable with very little deterioration over time even when exposed to light or in a high-temperature atmosphere. It can be effectively used as materials that require durability (heat resistance), such as gels, water retention gels for agriculture and horticulture, gels for artificial snow, water stop agents for outdoor civil engineering work, and lubricants.

<Prior Art and Problems> In recent years, superabsorbent resins that absorb water tens to hundreds of times their own weight have been proposed. For example, starch graft polymers (Japanese Patent Publication No. 53-46199, etc.), cellulose modified materials (
JP-A No. 50-80376, etc.), crosslinked water-soluble polymers (Japanese Patent Publication No. 43-23462, etc.), self-crosslinking type acrylic acid alkali metal salt polymers (Japanese Patent Publication No. 54-30, etc.)
No. 710, etc.), and these are being developed for use in a wide range of fields, including as absorbents for sanitary products and disposable diapers, as water retention agents for agriculture and horticulture, and as other industrial materials. .

However, although these superabsorbent resins have excellent ability to absorb a large amount of water and stability over time when dry, they have extremely poor stability in a water-absorbed state.

For example, if a gel-like material that has absorbed water is exposed to sunlight, it often deteriorates and becomes fluid within just a few hours, making it impossible to maintain its gel-like shape. Additionally, if a gel-like material is filled in a sealed container or the like without physical moisture evaporation and placed in a high temperature atmosphere (80°C or higher), it may similarly deteriorate within a few to 24 hours. .

Therefore, such super-absorbent resins (water-absorbing gels) are used as water-retaining agents, especially for gardening (ornamental purposes), and cold-storage agents (such as films for keeping food cold, etc., and molded product containers filled with KEL) during storage. When used in fields that require light resistance and heat resistance, such as heat storage agents, water stop agents and lubricants for outdoor civil engineering work, and artificial snow, gel The durability is not sufficient, which is a major obstacle in practical use.

Methods of improving the light resistance and heat resistance of water-absorbing gel include a method of mixing carbon black or activated carbon with a super absorbent resin (Japanese Patent Application Laid-Open No. 51-38271), and acrylic acid-based 1j.
Sulfoalkyl (meth) as a comonomer in iffi form
T: Water-insoluble water-absorbing resin obtained by polymerizing together with a crosslinking agent in the presence of an acrylate monomer
No. 6309), etc. have been proposed.

However, these methods have small effects and are still insufficient, posing a practical problem.

[Summary of the invention]

Summary> The present inventors have conducted various studies to solve the above problems, and as a result, in the polymerization of acrylic acid monomers,
We have discovered that a superabsorbent polymer with excellent heat resistance and light resistance can be obtained by copolymerizing a hindered amine-containing acrylic ester.

That is, the superabsorbent polymer according to the present invention contains 80 to 99.9 mol% of structural units represented by the following general formula (I).
and a structural unit represented by the following general formula (n) 0. 1~
20 mol%, structural units (I) and (II)
It is characterized in that the total amount of is 90 mol% or more.

□ (However, R1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkali metal, or an ammonium group.) R2 (However, R2 and R3 each represent a hydrogen atom or a methyl group.) The method for producing a water-absorbing polymer involves polymerizing a monomer mixture comprising an acrylic acid monomer represented by the following general formula (m) and a hindered amine-containing acrylic ester represented by the following general formula (IV). It is characterized by:

(However, R1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkali metal, or an ammonium group.) (However, R2 and R3 each represent a hydrogen atom or a methyl group.) <Effects> Effects obtained by the present invention The super-absorbent polymer has high water-absorbing performance, and its water-absorbing gel is stable with very little deterioration over time even when exposed to light or in a high-temperature atmosphere. Therefore, the superabsorbent polymer according to the present invention is
In many fields where durability and heat resistance are required, for example, cold storage agents, heat storage gels, air freshener gels, water retention gels for agriculture and gardening, gels for artificial snow, water stop agents for outdoor civil engineering work, lubricants, etc. It can be used effectively as a

[Detailed description of the invention]

<Super absorbent polymer> The super absorbent polymer according to the present invention has the following general formula (I).
It consists of 80 to 9 structural units represented by 9 mol% and 0 to 1 to 20 mol% of structural units represented by the following general formula (II), and the total amount of structural units CI) and (n) is It is 90 mol% or more.

(However, R1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkali metal, or an ammonium group.) (R2 and R3 each represent a hydrogen atom or a methyl group) In the general formula (I) Position 111 of the represented structure is 80 moles 90
If it is less than 100%, the superabsorbent polymer obtained will not have sufficient water absorption capacity. Further, if the structural unit represented by the general formula (II) is less than 0.1 mol %, the superabsorbent polymer obtained will not have sufficient durability (heat resistance and durability).

and other compounds> The superabsorbent polymer according to the present invention has the above-mentioned structural unit (I
) and (It),
Structural units (I) and (II) may be used as long as the water absorption properties of the resulting polymer are not excessively impaired, that is, generally the total amount of structural units (I) and (n) is not less than 90 mol Qo.
) (ie, monomers (I) and (■)) may be reacted with other compounds. Examples of such compounds include copolymerizable heptamer 1 crosslinking agents and the like.

Examples of copolymerizable monomers include hydrophilic monomers having a copolymerizable double bond in the molecule, such as itaconic acid (salt), maleic acid (salt), and 2-acrylamido-2-methylpropanesulfonic acid (salt). ), 2-(meth)acryloylethanesulfonic acid (salt), (meth)acrylamide,
Examples include vinylsulfonic acid and hydroxyethyl (meth)acrylate. It is also possible to use one or more of these in combination.

In addition, as a crosslinking agent, (a) structural unit (I) and (
U) (i.e. monomer (I[[)
and (■)) Compounds having two or more double bonds copolymerizable with, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,
Probylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, N,N'-methylenebis(meth)acrylamide, diallyl phthalate, diallyl maleate , diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, etc. (b) Structural unit (I) or (II)
) is a compound having two or more functional groups that can react with a carboxyl group during polymerization or during drying after polymerization, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, aliphatic di- or polyglycidyl ethers of alcohols, or (c) intermediate between the former two, i.e. - with a copolymerizable double bond as shown in (a) in the molecule and as shown in (b). 1 each with a reactive functional group such as
Compounds having more than 100% acetate, such as glycidyl (meth)acrylate, etc., can be mentioned. Such crosslinking agents can be used alone or as a mixture of two or more.

The amount of these crosslinking agents used is 0.001 to 10
% by weight, preferably 0.01-2% by weight. o. 0
．． 001 weight ff 9ci or more, the water absorption capacity becomes extremely large, but the gel strength of the super absorbent polymer when water is absorbed becomes extremely weak, and when it exceeds 10 weight 2%, the water absorption gel strength is not particularly improved. However, the water absorption capacity is quite small, which poses a practical problem.

Production of Super Water Absorbent Polymer Acrylic Acid Monomer The acrylic acid monomer used in the present invention is represented by the following general formula (m).

CH-C(]II) ″ 1 oox (However, R1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkali metal, or an ammonium group) As such an acrylic acid monomer, 5 of all carboxyl groups (-COOX (X-hydrogen atom))
0 to 95 mol %, especially 60 to 90 mol %, or neutralized with an alkali metal or ammonium salt is preferred. Therefore, such a preferred acrylic acid monomer contains 5 to 50 mol% of acrylic acid (R1-hydrogen atom) and methacrylic acid (R1-methyl group),
It is a mixture consisting of ~95 mol % of their alkali metal salts (X-alkali metal) and ammonium salts (X-ammonium groups).

The degree of neutralization of (meth)acrylic acid (herein, "(meth)acrylic" refers to both acrylic and methacryl. The same applies hereinafter in this specification) is limited to the above-mentioned preferred range. Although this is not the case, if the degree of neutralization is less than 50 mol%, the water absorption capacity of the superabsorbent polymer produced will decrease.

Alkali metal hydroxides, bicarbonates, and the like can be used to neutralize (meth)acrylic acid, but alkali metal hydroxides are particularly preferred in the present invention. Specific examples include sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like. From the viewpoint of the performance, price, etc. of the produced polymer, the former two are preferable.

Hindered amine-containing acrylic ester The hindered amine-containing acrylic ester used in the present invention is represented by the following general formula (TV).

(However, R2 and R3 each represent a hydrogen atom or a methyl group.) Specifically, 2. 2. 6. 6-tetramethyl-4
-piperidyl-acrylate, 2,2.6.6-tetramethyl-4-piperidyl-methacrylate and 1.2.
There are four types: 2,6.6-bentamethyl-4-piperidyl-acrylate and 1,2,2,6.6-bentamethyl-4-piperidyl-methacrylate.

Polymerization> In the present invention, a polymerization method in which a water-soluble monomer is generally polymerized is employed. Such a method is well known as a method for producing superabsorbent polymers, and any method can be employed in the present invention as long as it does not go against the spirit of the invention. A particularly preferred polymerization method in the present invention is an aqueous solution polymerization method in which an aqueous monomer solution itself is polymerized.

Further, the total monomer concentration in the aqueous solution of the acrylic acid monomer represented by the general formula (III) and the hindered amine-containing acrylic ester represented by the general formula (IV) is 20% by weight or more and not more than the saturated concentration. That's good.

When producing a superabsorbent polymer according to the present invention,
It is common to use radical polymerization initiators. The radical polymerization initiators used in the production method of the present invention include water-soluble radical polymerization initiators, such as persulfates such as ammonium persulfate and potassium persulfate, 2.2'
-Azobis(2-amidinopropane) dihydrochloride, 4,4
Examples include azo initiators such as '-azobis(4-cyanovaleric acid). Furthermore, when the weight initiator is a peroxide such as hydrogen peroxide, ammonium persulfate, potassium persulfate, etc., it can also be used as a redox initiator in combination with a reducing compound such as sulfite, ascorbic acid, or amine. .

The amount of the radical polymerization initiator as described above is -0.001 to 10% by weight for boat fishing, based on the total amount of the acrylic acid monomer and hindered amine-containing acrylic ester.
Preferably it is 0.01 to 1 weight 06.

Experimental Example> Example 1 30 g of acrylic acid was placed in a 100 cc conical flask, and 16.8 g of pure water was added thereto and mixed.

To this was neutralized by gradually adding 15.2 g of potassium hydroxide while cooling with water. This product has a neutralization degree of acrylic acid of 65 mol%.
．． The monomer concentration of acrylic acid and potassium acrylate was 65% by weight.

Next, as a comonomer, 2. 2. After adding and dissolving 1.5 g of 6.6-tetramethyl-4-piperidyl-acrylate, N and N' were added as crosslinking agents.
-0.1 g of methylenebisacrylamide and 0.4 g of 319° hydrogen peroxide solution as a polymerization initiator were dissolved. Next, a 5% aqueous solution of ascorbic acid as a reducing agent was sprayed into the solution prepared in this manner from a spray nozzle. Polymerization occurred immediately and a gel-like hydrated polymer was obtained. This was dried in a hot air dryer at 130°C for 5 hours, and then ground in a knife-type grinder to form a powdery copolymer (I
) was obtained. The water absorption capacity of this polymer was measured (details of the polymer water absorption capacity test will be described later), and the result was 255 times.

Example 2 Example 1-2. 2.6. Instead of using 6-tetramethyl-4=piperidyl-acrylate, 2.2,6.
A copolymer (2) was obtained in the same manner as in Example 1, except that the same amount of 6-tetramethyl-4-piperidyl-methacrylate was used. The water absorption capacity of this polymer was 245 times higher.

Comparative Example 1 Example 1-2. 2. 6. 6-tetramethyl-4-
A standard polymer consisting only of polyacrylic acid and potassium polyacrylate without the addition of piperidyl-acrylate was obtained. The water absorption capacity of this polymer was 270 times higher.

Evaluation test method> Copolymer polymers (I) and (
2) The following tests were conducted on a total of four types of standard polymer obtained in Comparative Example 1 and a commercially available super absorbent polymer (Comparative Example 2).

[1 piece water absorption capacity test Weigh out 0.2g of super absorbent polymer accurately and add it to 100% of pure water.
The sample was immersed in 0 cc of water, stirred with a magnetic stirrer, and allowed to absorb water for 1 hour. After absorbing water, the gel was sieved through a 200-meter sieve and drained for 15 minutes, and then the weight of the swollen gel was measured, and the pure water absorption capacity was calculated according to the following formula.

Weight of swollen gel (g) Add 150 g of pure water to 1 g of super absorbent polymer and swell by absorbing water, then put 100 g each of the water-absorbing gel into a transparent polyethylene bag with a thickness of 0.05 mm during summer (July to August). ) exposed to sunlight. At this time, the appearance of the water-absorbing gel was observed over time. The results are shown in Table-1.

[3] Heat resistance test [2 pieces Water absorbing gel prepared in the same way as the light resistance test was
After putting each g in a glass bottle and sealing the bottle, the mixture was placed in a constant temperature bath at 90° C., and the state of the water-absorbing gel was observed. Table 2 shows the results.
It was shown to.

Claims (1)

[Claims] 1. Structural units 80 to 80 represented by the following general formula (I)
Consisting of 99.9 mol% and 0.1 to 20 mol% of the structural unit represented by the following general formula (II), the structural unit (I)
and (II) in a total amount of 90 mol% or more. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (However, R^1 represents a hydrogen atom or a methyl group, and
indicates a hydrogen atom, an alkali metal, or an ammonium group) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (II) (However, R^2 and R^3 each indicate a hydrogen atom or a methyl group) 2. The following general Claim 1, characterized in that a monomer mixture comprising an acrylic acid monomer represented by formula (III) and a hindered amine-containing acrylic ester represented by the following general formula (IV) is subjected to polymerization conditions. A method for producing a superabsorbent polymer as described in . ▲There are mathematical formulas, chemical formulas, tables, etc.▼(III) (However, R^1 represents a hydrogen atom or a methyl group, and
(represents a hydrogen atom, an alkali metal, or an ammonium group) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(IV) (However, R^2 and R^3 each represent a hydrogen atom or a methyl group)