JP3330689B2 - Method for producing superabsorbent polymer with improved gel strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a superabsorbent polymer. More specifically, the present invention relates to a method for producing a superabsorbent polymer having simultaneously improved gel strength after water absorption, stability over time of the gel, and "stickiness" of the gel surface.

[0002]

2. Description of the Related Art In recent years, superabsorbent polymers have been widely used in the field of sanitary products such as sanitary products and disposable disposable diapers, as well as water-stopping materials, anti-condensation materials, freshness preserving materials, solvent dehydrating materials and the like. It is a synthetic polymer that is being put to practical use in various industrial products, and also in the fields of greening, agricultural and horticultural fields, and the like, and its application range is expected to further expand in the future. In recent years, sanitary articles such as sanitary articles, disposable paper diapers and incontinence pads have been improved in wearing feeling due to improvements in materials used, draping, various gatherings, and the like, and the wearing time has been increasing. In addition, industrial products and agricultural and horticultural products are sometimes used under extremely severe conditions.

On the other hand, the superabsorbent polymer swells due to water absorption to form a gel. In particular, when a body fluid such as urine is absorbed, the gel loses its strength with the passage of time, and at the same time, the surface becomes "sticky". Tend to be. This has been a particular problem for sanitary products where the equipment time is increasing. It is considered that such time-dependent deterioration of the gel is caused by various oxidation-reduction compounds, enzymatically active substances, and the like contained in body fluids such as urine, which break chemical bonds of the superabsorbent polymer. Further, it is considered that the decomposition of the gel does not proceed by a single mechanism but by a plurality of mechanisms. Therefore, in reality, the degree of decomposition of the superabsorbent polymer varies greatly depending on the state at the time of liquid absorption, individual differences in body fluids, and the like. Therefore, a highly water-absorbing polymer having excellent gel strength and gel stability for all body fluids such as urine is desired.

As a method of improving the gel strength and the gel stability, for example, a method of increasing the crosslink density of the superabsorbent polymer can be considered. In this case, however, there is a problem that the water absorption ability decreases as the crosslink density increases. . In addition, by adding oxygen-containing inorganic salts, radical scavengers, antioxidants, oxidizing agents, sulfur-containing reducing agents, metal chelating agents, radical chain inhibitors, phosphinic acid-containing amines, etc. to the superabsorbent polymer, the gel is stabilized. Various proposals have been made to improve the properties, but the use of these drugs is not always effective for body fluids with large individual differences, and when there is a safety problem depending on the amount added. There is also.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has been described as being capable of absorbing body fluids such as human urine having a large individual difference without impairing the original water absorption performance of the superabsorbent polymer. It is an object of the present invention to provide a method for producing a superabsorbent polymer in which the strength of the gel, the stability of the gel over a long period of time, and the "stickiness" of the gel surface are simultaneously improved.

[0006]

[Summary of the Invention] The present inventors have found that the above object can be achieved by treating a superabsorbent polymer with alkoxytitanium. That is, the method for producing a superabsorbent polymer having improved gel strength according to the present invention comprises a superabsorbent polymer having a crosslinked structure and containing a carboxyl group and / or a carboxylate group as a component of the polymer . Carboxyl
Two or more groups capable of reacting with a group and / or a carboxylate group
Surface cross-linking with a cross-linking agent having a functional group of
Formula: X (R) _m Si (Y) _3-m (where X is a carboxyl group in the superabsorbent polymer and
And / or R is a functional group capable of reacting with a carboxylate group.
Y represents a hydrolyzable group, m represents 0, 1 or
2) surface modification with a silane compound represented by
And then treating with alkoxytitanium .

[Specific description of the invention] <Superabsorbent polymer> The superabsorbent polymer used in the method of the present invention has a crosslinked structure and has a carboxyl group and / or a carboxylate group. It is contained as a constituent component, specifically, a crosslinked product of polyacrylate, a crosslinked product of starch-acrylate graft copolymer, a hydrolyzate of a crosslinked product of starch-acrylonitrile graft copolymer, acrylic ester A hydrolyzate of a crosslinked product of a vinyl acetate copolymer, a crosslinked product of an acrylate-acrylamide copolymer, a hydrolyzed product of a crosslinked polyacrylonitrile, and the like. The average particle size of the superabsorbent polymer powder is 10 to 2,000 μm, particularly 50 to 1,0 μm.
00 μm is preferred. These superabsorbent polymers can be produced by a known method, and commercially available ones can also be used.

[0008] The superabsorbent polymer used in the present invention may have a crosslinked surface. As a crosslinking agent used for surface crosslinking, any crosslinking agent having two or more functional groups capable of reacting with a carboxyl group and / or a carboxylate group can be used.
For example, a polydiglycidyl ether compound, a haloepoxy compound, an aldehyde compound, an isocyanate compound and the like can be used, and a polydiglycidyl ether compound is generally used. The use amount of these crosslinking agents is not particularly limited, but is usually 0.005 to 5.0% by weight based on the polymer.
Used in the range.

Further, the superabsorbent polymer used in the present invention may have a modified polymer surface.
Examples of the compound used as the surface modifier include a polyvalent metal compound such as aluminum hydroxide and a silane compound represented by the following general formula. X (R) _m Si (Y) _3-m (where X is a functional group capable of reacting with a carboxyl group and / or carboxylate group in the superabsorbent polymer, R is a hydrocarbon group, and Y is Represents a decomposable group, and m is 0, 1 or 2). Specific examples of the silane compound represented by the above formula include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl)
Aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride and the like. The amount of the surface modifier used is not particularly limited, but is usually 0.001 to 10.0% by weight based on the polymer.

<Alkoxytitanium> As the alkoxytitanium used in the present invention, any organic titanium compound containing a reactive alkoxy group in the molecule can be used. Specifically, tetramethoxytitanium,
Titanium tetraethoxy, titanium tetraisopropoxy,
Titanium tetrabutoxy, tetrakis (2-ethylhexyloxy) titanium, tetrastearyloxy titanium, tetraisopropoxy titanium polymer, tetrabutoxy titanium polymer, diisopropoxy bis (acetylacetonato) titanium, dibutoxy bis (triethanol aminato) titanium, tri Butoxytitanium stearate, dihydroxybis (lactato) titanium, diisopropoxytitanium distearate and the like can be mentioned, and one or more of these can be used. Among these compounds, tetraisopropoxytitanium and dibutoxybis (triethanolaminato) titanium are preferred. The amount of the alkoxytitanium used in the present invention varies depending on the type of the polymer to be used, and cannot be specified unconditionally, but is generally 0.001 to 10% by weight, preferably 0.05 to 3% by weight based on the polymer. is there. If the amount is less than 0.001%, the gel stability of the superabsorbent polymer with respect to body fluids is insufficiently improved, and if it exceeds 10% by weight, the water absorbing ability of the superabsorbent polymer decreases.

<Treatment method> The treatment of the superabsorbent polymer of the present invention with alkoxytitanium can be carried out in various modes. For example, a wet method of adding alkoxytitanium in a slurry state in which a superabsorbent polymer is dispersed in a solvent, a dry method of spraying alkoxytitanium with dry air or nitrogen gas while forcibly stirring the superabsorbent polymer, or the like can be used. it can. As the solvent used in the wet method, any inert solvent such as hydrocarbons, alcohols, and ethers can be used. The alkoxytitanium treatment according to the present invention is usually performed on a polymer in a water-containing state, but can also be performed on a dry polymer.
The processing temperature is generally 10 to 180 ° C, preferably 80 to 180 ° C.
120 ° C.

[0012]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. The following characteristic values of the superabsorbent polymer obtained in the examples were measured by the following methods.

<Water absorption capacity>
Mesh nylon bag (size of 10cm x 20cm)
And immersed in 1 liter of artificial urine for 30 minutes. Thirty minutes later, the nylon bag was lifted up, drained for 15 minutes, weighed, blank corrected, and the weight of the artificial urine absorbed by 1 g of the superabsorbent polymer was defined as the water absorbing capacity. The composition of the artificial urine is shown below. Artificial urine composition urine 1.94% sodium chloride 0.80% calcium chloride 0.06% magnesium sulfate 0.10% pure water 97.10%

<Gel Strength> 1 g of the superabsorbent polymer was mixed with 25 g of adult human urine (mixed with urine of 5 adults) to absorb 25 g of water.
After leaving the gel at 30 ° C. for 30 minutes, the gel was subjected to a rheometer (Model NRM-2002J manufactured by Fudo Kogyo Co., Ltd.), and the force at the time when the cell entered the gel was defined as the gel strength.

<Gel Stability> A sample similar to the gel strength described above was prepared and left in a thermostat at a set temperature of 40 ° C. for 16 hours. The gel strength after standing was measured by the above method, and the stability of the gel was evaluated. In addition, this test
The measurement was performed five times on different measurement days in consideration of individual differences in human urine.

<"Glutiness" on Gel Surface> The "stickiness" of the swollen gel after measuring the stability of the gel was evaluated by touch according to the following evaluation criteria. : The swollen gel is quite “crisp” and has a dry feeling. Δ: The swollen gel was partially sticky. ×: The swollen gel is sticky and the hands are sticky.

In the following Examples and Comparative Examples, the following superabsorbent polymers were used. Superabsorbent polymer (A) In a 5,000 ml four-necked round bottom flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube, 1210 g of cyclohexane was added, and 9 g of sorbitan monostearate was added. After dissolving, blow in nitrogen gas,
Dissolved oxygen was expelled. Separately, 350 g of acrylic acid was externally cooled with ice in a beaker having a capacity of 2,000 ml, and 143.1 g of 95% pure sodium hydroxide dissolved in 727.7 g of water was added thereto.
0% was neutralized. In this case, the monomer concentration in the aqueous solution corresponds to 35% by weight as the monomer concentration after neutralization. Next, 0.37 g of N, N'-methylenebisacrylamide and 0.94 g of potassium persulfate were added and dissolved, and nitrogen gas was blown out to expel residual oxygen.
The contents of the four-necked round bottom flask were added
The contents of the 0 ml beaker were added, dispersed by stirring, and the inside temperature of the flask was raised with a hot water bath while bubbling nitrogen gas. After several tens of minutes, the temperature reached 75 ° C. Then, the internal temperature was maintained at 60 to 65 ° C., and the reaction was carried out for 3 hours while stirring. The stirring was performed at 145 rpm. After the reaction for 3 hours, when the stirring was stopped, the wet polymer particles settled at the bottom of the round-bottom flask, so that they could be easily separated into the cyclohexane phase by decantation. The separated wet polymer was transferred to a reduced-pressure drier and heated to 90 ° C. to remove attached cyclohexane and water. As a result, 400 g of a smooth superabsorbent polymer was obtained. 100 g of the dry polymer thus obtained is 500 m
l of an eggplant-shaped flask and then cyclohexane 1
22.5 g was added to form a slurry. While stirring this slurry, a liquid in which 0.44 g of γ-glycidoxypropyltrimethoxysilane was dispersed in 22.5 g of water was added,
Stirred at room temperature for 30 minutes. Then, in a 105 ° C. oil bath,
After immersion for 0 minutes, the mixture was evaporated to dryness under reduced pressure while maintaining the same oil bath temperature to obtain 95 g of a dry polymer.

Superabsorbent polymer (B) Except that 0.8 g of ethylene glycol diglycidyl ether was used instead of γ-glycidoxypropyltrimethoxysilane in the synthesis of superabsorbent polymer (A ) described above. To obtain 95 g of a dry polymer.

[0019]

[0020]

Example 1 100 g of superabsorbent polymer (A) and 10 parts of cyclohexane
9 g of water was added to the slurry consisting of 0 g under stirring.
At 50 ° C., 1 g of di-n-butoxybis (triethanolaminato) titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 2 100 g of superabsorbent polymer (A) and cyclohexane 10
To a slurry consisting of 0 g, 10 g of water was added with stirring, 2 g of di-i-propoxybis (acetylacetonato) titanium was added at 10 ° C., and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 3 100 g of superabsorbent polymer (A) and cyclohexane 10
6 g of water was added to the slurry consisting of 0 g under stirring.
At 10 ° C., 0.2 g of tetraisopropoxy titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 4 100 g of superabsorbent polymer (A) and cyclohexane 10
6 g of water was added to the slurry consisting of 0 g under stirring.
At 10 ° C., 0.5 g of tetraisopropoxy titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 5 100 g of superabsorbent polymer (A) and 10 parts of cyclohexane
0.5 g of tetraisopropoxytitanium was added to the slurry consisting of 0 g at 10 ° C. with stirring and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 6 100 g of superabsorbent polymer (A) and 10 parts of cyclohexane
6 g of water was added to the slurry consisting of 0 g under stirring.
At 10 ° C., 1.0 g of tetraisopropoxy titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 7 100 g of superabsorbent polymer (A) and cyclohexane 10
To the slurry consisting of 0 g, 1.0 g of tetraisopropoxytitanium was added at 10 ° C. with stirring and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 8 100 g of superabsorbent polymer (A) and 10 cyclohexane
25 g of water was added to the slurry composed of 0 g with stirring, 1 g of tetra-n-butoxytitanium polymer (Nippon Soda Co., Ltd., B-4) was added at 50 ° C., and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 9 100 g of superabsorbent polymer (A) and cyclohexane 10
20 g of water was added to the slurry consisting of 0 g with stirring, 3 g of tetrastearyloxytitanium was added at 50 ° C., and the mixture was mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 10 100 g of superabsorbent polymer (B) and cyclohexane 10
9 g of water was added to the slurry consisting of 0 g under stirring.
At 50 ° C., 1 g of di-n-butoxybis (triethanolaminato) titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 11 100 g of superabsorbent polymer (B) and cyclohexane 10
6 g of water was added to the slurry consisting of 0 g under stirring.
At 10 ° C., 0.5 g of tetraisopropoxy titanium was added and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 12 100 g of superabsorbent polymer (B) and cyclohexane 10
0.5 g of tetraisopropoxytitanium was added to the slurry consisting of 0 g at 10 ° C. with stirring and mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

Example 13 100 g of superabsorbent polymer (B) and cyclohexane 10
20 g of water was added to the slurry consisting of 0 g with stirring, 3 g of tetrastearyloxytitanium was added at 50 ° C., and the mixture was mixed for 30 minutes. Subsequently, drying was performed at a bath temperature of 105 ° C. under reduced pressure for 30 minutes to obtain a superabsorbent polymer.

[0034]

[0035]

The above measurement was performed on the superabsorbent polymer obtained in the above example. The results are shown in Table 1.

Comparative Examples 1 and 2 The above measurements were carried out on the superabsorbent polymer (A) (Comparative Example 1) and the superabsorbent polymer (B) (Comparative Example 2 ) which were not treated with the alkoxytitanium according to the present invention. Was. The results are shown in Table 1.

[Table 1]

[0038]

As described above, the superabsorbent polymer produced by the method of the present invention can absorb the body fluid such as human urine having a large individual difference without impairing the original water absorbing performance of the superabsorbent polymer. The strength of the gel of (case), the stability of the gel over a long period of time, and the "stickiness" of the gel surface are simultaneously improved irrespective of individual differences in body fluids. Therefore, it can be advantageously used especially in the field of sanitary articles such as disposable diapers.

────────────────────────────────────────────────── ─── Continuation of the front page Examiner Tamotsu Fujimoto (56) References JP-A-6-306118 (JP, A) JP-A-49-122590 (JP, A) JP-A-2-150462 (JP, A) ( 58) Surveyed field (Int.Cl. ⁷ , DB name) C08L 1/00-101/16 C08K 3/00-13/08 C08F 8/42

Claims (4)

(57) [Claims] 1. A super-absorbent polymer having a cross-linked structure and containing a carboxyl group and / or a carboxylate group as a constituent of a polymer, comprises a carboxyl group and / or
Represents two or more functional groups capable of reacting with a carboxylate group.
Surface crosslinking with a crosslinking agent having the general formula: X
(R) _m Si (Y) _3-m (where X is a superabsorbent polymer)
Carboxyl group and / or carboxylate group
R is a hydrocarbon group, and Y is a hydrolyzable group.
And m is 0, 1 or 2).
After either surface modified by compounds, process for production of superabsorbent polymers with improved characteristics and to Ruge Le intensity that treatment with alkoxy titanium. 2. The superabsorbent polymer is a crosslinked polyacrylate, a crosslinked starch-acrylate graft copolymer,
From a hydrolyzate of a starch-acrylonitrile graft copolymer cross-linked product, an acrylate-vinyl acetate copolymer cross-linked product, an acrylate-acrylamide copolymer cross-linked product and a polyacrylonitrile cross-linked hydrolyzate The method according to claim 1, which is selected from the group consisting of:
A method for producing a superabsorbent polymer having improved gel strength . Wherein the crosslinking agent is poly diglycidyl ether compounds, improved gel strength according to claim 1 or 2
A method for producing a superabsorbent polymer . 4. The silane compound is γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ- (2-amino Ethyl) aminopropyltrimethoxysilane, γ- (2
-Aminoethyl) aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-chloropropyl trimethoxysilane, from γ- chloropropyl methyl dimethoxy silane and octadecyl dimethyl [3- (trimethoxysilyl) propyl] ammonium chloride
Is from one or more selected group consisting of, claim 1
Or a superabsorbent polymer having improved gel strength according to 2 above
Manufacturing method.