JPH0778095B2 - Method for producing high expansion type water-absorbent polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a highly expansive water-absorbing polymer. The polymer produced according to the present invention is of high expansion type,
Since it has good air permeability and does not cause stickiness of gel after absorbing water, it can be used as a water retention material for agricultural and horticultural soils, sanitary materials (paper diapers, sanitary napkins) and the like.

[Prior Art] Water-absorbent polymers are used for sanitary products, sanitary materials such as disposable diapers,
It is a useful synthetic polymer used for various purposes such as coagulation of sludge and dehydration of oils as well as being used for water retention in agriculture and horticulture. These polymers are hydrolyzates of starch-acrylonitrile graft polymer (Japanese Patent Publication No. 53-46199, Japanese Patent Publication No. 55-4820), and modified cellulose (Japanese Patent Publication No. 50-80376). Sodium polyacrylate by turbidity method (Japanese Patent Publication No. 54-3
No. 0710, JP-A-56-26909) Sodium polyacrylate obtained by an aqueous solution polymerization method (adiabatic polymerization, thin film polymerization) (JP-A-55-133413) Cross-linked product of water-soluble polymer (JP-B-43- 23462) Starch-sodium acrylate graft polymer (Japanese Examined Patent Publication)
No. 53-46199) is known.

[Problems to be Solved by the Invention] However, the above method has the following problems.

It has drawbacks such as insufficient water absorption capacity, low water absorption speed even if water absorption capacity is high, and poor dispersibility in water.

After absorbing water, the gel becomes sticky, and when considering hygiene materials, there is concern about the effect on the skin.

The air permeability is poor due to the aggregation of the polymer particles in a water-swelling state, and there is a risk that the roots will rot when considering a water retaining material for soil.

[Means for Solving Problems] As a result of intensive studies conducted by the present inventors to improve the conventional drawbacks, the present invention rapidly expands when water is absorbed, the gel after water absorption is not sticky, and is breathable. The method for producing a high expansion polymer has been completed.

According to the present invention, a water-absorbing polymer containing an acrylic acid alkali salt obtained as a monomer as a constituent component of a polymer is subjected to azeotropic dehydration in the presence of a binary metal hydroxide having anion exchange ability. A method for producing a highly expansive water-absorbing polymer, which comprises crosslinking with a crosslinking agent having two or more functional groups and then drying.

In the production method of the present invention, the polymerization of the monomer is carried out by using a water-soluble radical polymerization initiator in an aliphatic hydrocarbon solvent in the presence of a dispersant containing an aqueous solution containing 40% by weight or more of a vinyl monomer having a carboxyl group. It is preferable to carry out the polymerization reaction by dispersing and suspending.

And as the water-absorbing polymer containing the alkali salt of acrylic acid as a constituent component of the polymer in the present invention, in addition to the alkali salt of a homopolymer of acrylic acid, monomers copolymerizable with acrylic acid or an alkali salt of acrylic acid It also includes an alkali salt of an acrylic acid copolymer obtained by copolymerization with.

Here, as the monomer copolymerizable with acrylic acid or an alkali salt of acrylic acid, acrylic acid esters such as methyl acrylate and ethyl acrylate; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; hydroxyethyl acrylate And hydroxyalkyl acrylates such as hydroxyethyl methacrylate; vinyl aromatic monomers such as styrene, α-methylstyrene, p-methylstyrene, and the like. In the case of copolymers,
It is preferable that the acrylic acid alkali salt component is contained in an amount of 75 mol% or more.

As a method for obtaining a high expansion polymer containing a carboxyl group, in the present invention, W / O suspension polymerization is preferable from the viewpoint of workability, etc., because after polymerization, it is dried by azeotropic dehydration. W / O suspension polymerization includes sorbitan monostearate, sorbitan distearate, sorbitan fatty acid esters such as sorbitan monolaurate, and cellulose ether maleated polyethylene such as ethyl cellulose and benzyl cellulose, and maleated polybutadiene as a surfactant. Examples of the polymer dispersant include one or two of these.
Any one or more species may be used. The hydrophobic solvent used at that time includes aliphatic hydrocarbons such as n-hexane, heptane and octane, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane and decalin, aromatic hydrocarbons such as benzene, toluene and xylene. And halogenated hydrocarbons such as chlorobenzene and dichlorobenzene.

In the method of the present invention, a particularly important requirement is that during the azeotropic dehydration, the crosslinking reaction is carried out in the presence of a binary metal hydroxide having anion exchange ability. The binary metal hydroxide used in the present invention has an effect of improving air permeability and an effect of improving water retention between the water-swelled polymer particles, and further has an effect of highly expanding the polymer particles. It is possible to use a binary metal hydroxide having an anion exchange capacity, such as the hydrotalcite described above.

It is not clear why the highly expansive water-absorbent polymer obtained in the present invention expands rapidly when it absorbs water, but 1) it does not exhibit expansiveness even if the polymerized and dried polymer and the binary metal hydroxide are simply mixed, The IR and X-ray analysis data are also different. 2) During azeotropic dehydration, it does not expand even in the absence of either a binary metal hydroxide or a cross-linking agent.

That is, since a slurry-like polymer obtained by polymerizing an acrylic acid alkali salt, a binary metal hydroxide and a cross-linking agent are different in molecular order, a completely new complex is formed. It is expansive due to the ionic repulsion between them.

In the present invention, the addition amount of the binary metal hydroxide having anion exchange ability varies depending on the kind and the kind of the polymer, but is usually 1 to 30% by weight relative to the monomer in an appropriate range. More preferably, it is 5 to 20% by weight with respect to the monomer. When the amount of the binary metal hydroxide added is less than 1% by weight, the polymer does not exhibit high expansion property,
If the amount is larger than the above, the polymer particles tend to aggregate when the binary metal hydroxide is added, resulting in blocking.

The crosslinking agent used in the present invention may be any compound as long as it is a compound having two or more functional groups capable of reacting with a carboxyl group (or a carboxylate group). As such a cross-linking agent,
For example, polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether;
Examples thereof include haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; polyaldehydes such as glutaraldehyde and glyoxal.

The amount of cross-linking agent added varies depending on the type of cross-linking agent and the type of polymer, but is usually 0.05 to 2% by weight with respect to the monomer.
Is an appropriate range. More preferably for the monomer
It is 0.2 to 1.0% by weight. The amount of the crosslinking agent used is 0.05% by weight
If the amount is less than 2, the high expansion polymer cannot be obtained, and if it exceeds 2% by weight, the crosslinking density becomes too high.
A significant decrease in water absorption capacity occurs.

The high expansion type water-absorbing polymer obtained by the present invention shows a maximum expansion of 4 times with respect to the added water, but even if only the binary metal hydroxide and the crosslinking agent are added, the high expansion type polymer is No, it is not the intention of the present invention.

[Advantages of the Invention] By using the method of the present invention, it is possible to obtain a highly expansive water-absorbing material having good water-absorption ability, high water-absorption rate, non-sticky gel after water-absorption, and breathability. It is very advantageous for use as a water absorbing agent for sanitary materials and a water retaining agent for agriculture, since there is no fear of "leakage" on the skin and fear of root rot.

[Examples] Next, the method of the present invention will be specifically described with reference to Examples.
The water absorption capacity and volume ratio in the following examples and comparative examples are values obtained by the following operations.

For absorbing water of ion-exchanged water, add 0.5 g of dry polymer
It was dispersed in ion-exchanged water, and allowed to stand for a whole day and night, then the swelling polymer weight (W) obtained by passing through a 60-mesh wire net was measured, and this value was divided by the initial dry polymer weight (Wo). It is a value. That is, water absorption capacity of ion-exchanged water (g / g) = W
/ Wo.

For saline water absorption capacity, dry polymer 0.2g to 60g
Was dispersed in 0.9% saline solution, allowed to stand for 20 minutes, and then passed through a 100-mesh wire net to measure the swollen polymer weight (W),
It is the value obtained by dividing this value by the initial dry polymer weight (Wo). That is, the physiological saline absorption capacity (g / g) = W / Wo.

The volume ratio was measured by measuring the volume (V) of the swollen polymer obtained by placing 0.2 g of dry polymer (42 mesh sieve ON, 16 mesh sieve pass) in a Nessler tube, and adding this value to the volume of water (Vo). It is the value obtained by dividing. That is, volume ratio And

The volume ratios in Example 2 and below are values of a swollen polymer obtained by taking 0.2 g of the dry polymer in a Nessler tube and adding 2.0 g of ion-exchanged water.

Example 1 A separa flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube was charged with 360.7 g of 1n-hexane and 4.32 g of sorbitan monolaurate, and the mixture was heated to 50 ° C. and dissolved at room temperature. Below, 0.24 g of potassium persulfate was added to an aqueous solution dissolved in 10 g of water.

On the other hand, in an Erlenmeyer flask, 72.0 g of acrylic acid was partially neutralized with 32.2 g of sodium hydroxide dissolved in 93.6 g of water to adjust the monomer concentration in the monomer aqueous solution to 43%. This monomer aqueous solution was added dropwise to the above-mentioned Separa flask under bubbling of a nitrogen gas stream over 1 hour, polymerized, refluxed for 1 hour, 0.1 g of 30% hydrogen peroxide solution was added, and the reflux was continued for 2 hours.

After that, 8.85 g of synthetic hydrotalcite (Kyowa Kagaku, Kyoward 500, Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O) and 0.73 g of ethylene glycol diglycidyl ether were added,
After azeotropic dehydration and drying, a white powdery granular polymer was obtained.

The obtained dry polymer has a water absorption capacity of 210 (g / g) for ion-exchanged water and a water absorption capacity of 40 (g / g) for physiological saline.
g) and a volume ratio of 3.5 (cm ³ / cm ³ ) (water 2.0 g added).

Further, ion-exchanged water was added to 0.2 g of the dried polymer (passed through a 16-mesh sieve) obtained above, and the relationship between the addition amount of ion-exchanged water and the volume ratio V / Vo of the swollen polymer was investigated. As shown in the curve A in FIG. 1, the results showed a volume expansion significantly larger than the volume corresponding to the added amount of water. For comparison, the same test was carried out on a commercially available sodium acrylate-based water-absorbing polymer (Poise SA-20 manufactured by Kao Corporation), and the volume expansion was small as shown by the curve B in FIG. .

Example 2 Polymerization and drying were carried out in the same manner as in Example 1 except that sorbitan monostearate was replaced by 4.32 g instead of sorbitan monolaurate to obtain a white powdery granular polymer. The resulting dried polymer has a water absorption capacity of 145 (g / g for ion-exchanged water).
g), water absorption capacity for physiological saline is 31 (g / g), volume ratio
The polymer was 3.0 (cm ³ / cm ³ ).

Example 3 Polymerization and drying were carried out in the same manner as in Example 1 except that 4.32 g of sorbitan distearate was used instead of sorbitan monolaurate to obtain a white powdery granular polymer. The resulting dried polymer has a water absorption capacity of 120 (g /
g), water absorption capacity for physiological saline is 28 (g / g), volume ratio
The polymer was 3.0 (cm ³ / cm ³ ).

Example 4 Polymerization was carried out in the same manner as in Example 1 to give 8.85 g of the binary metal hydroxide shown in Table 1 and ethylene glycol glycidyl ether.
0.73 g was added at the time of azeotropic dehydration and dried to obtain white powdery granular polymers.

Example 5 Polymerization was carried out according to Example 1, and the amounts of the binary metal hydroxide and ethylene glycol diglycidyl ether shown in Table 2 were added during azeotropic dehydration, followed by drying to obtain white powdery granular polymers. Obtained.

Comparative Example 1 Polymerization was carried out according to Example 1, and Kyoward 500 8.85 g
Only was added at the time of azeotropic dehydration and dried to obtain a white powdery granular polymer. The obtained polymer was a polymer having a water absorption capacity of 80 (g / g) for ion-exchanged water, a water absorption capacity of 47 (g / g) for physiological saline, and a volume ratio of 1.3 (cm ³ / cm ³ ).

Comparative Example 2 Polymerization was carried out in the same manner as in Example 1, and only 0.73 g of ethylene glycol glycidyl ether was added during azeotropic dehydration, followed by drying to obtain a white powdery granular polymer. The obtained polymer has a water absorption capacity of 120 (g / g) for ion-exchanged water, a water absorption capacity of 31 (g / g) for physiological saline, and a volume ratio of 1.5 (cm ³ /
cm ³ ).

Comparative Example 3 Kyoward 500 was added to 100 parts of the polymer of Comparative Example 1 to 100 parts.
When added well and mixed well, it has a water absorption capacity of 120 (g / g) for ion-exchanged water and 35 (g / g) for physiological saline.
g) and the volume ratio was 1.5 (cm ³ / cm ³ ).

[Brief description of drawings]

Figure 1 shows the amount of ion-exchanged water added and volume ratio V / Vo of swollen polymer when ion-exchanged water was added to dry polymer (where Vo is the volume of added water and V is the volume of swollen polymer). Curve A shows the test result of the dry polymer obtained in Example 1, and curve B shows the test result of the commercial polymer.

Front page continuation (72) Inventor Chuzo Kato 2-3-4 Kamiosaki, Shinagawa-ku, Tokyo (56) References JP-A-60-147475 (JP, A)

Claims (5)

[Claims] 1. A water-absorbing polymer containing an acrylic acid alkali salt obtained by polymerization of a monomer as a constituent component of a polymer is subjected to azeotropic dehydration in the presence of a binary metal hydroxide having an anion exchange ability, A method for producing a highly expansive water-absorbing polymer, which comprises crosslinking with a crosslinking agent having two or more functional groups and then drying. 2. The method for producing a highly expansive water-absorbing polymer according to claim 1, wherein the binary metal hydroxide having anion exchange ability is hydrotalcite. 3. The method for producing a highly expansive water-absorbing polymer according to claim 1, wherein the binary metal hydroxide having anion exchange capacity is used in an amount of 1 to 30% by weight based on the monomer. 4. The method for producing a highly expansive water-absorbing polymer according to claim 1, wherein the crosslinking agent is ethylene glycol diglycidyl ether. 5. The cross-linking agent is contained in an amount of 0.05 to 2% by weight based on the monomers.
The method for producing a high expansion type water-absorbent polymer according to claim 1, which is used.