JPS61293246A - Method for improving water retention of water-absorbing resin under pressure - Google Patents

Abstract

PURPOSE:To improve the water retention of a water-absorbing resin under pressure, by adding a cationic surfactant to said resin. CONSTITUTION:0.01-5pts.wt. cationic surfactant (e.g. alkyltrimethylammonium halide) is blended with 100pts.wt. (on a solid basis) water-absorbing resin such as partially crosslinked (meth)acrylic acid (co)polymer contg. a carboxylate group as the structural unit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modifying a water-absorbing resin, and more particularly, a method for modifying a water-absorbing resin, and more particularly, a method for modifying a water-absorbing resin containing a carboxylate group as a constituent component of a polymer. The present invention relates to a method of improving the water-absorbing resin raw material's water-absorbing ability, water-absorbing rate, and gel strength upon water absorption by adding a surfactant, especially its water-retaining property under pressure.

Sho-Beiichi-Ei-Ei Water-absorbing resin is used in sanitary products such as sanitary products, diapers, and disposable rags, as well as agricultural and gardening products such as water retention agents, as well as for coagulation of sludge, prevention of condensation on building materials, and oil-absorbing resins. It is also used for purposes such as dehydration.

Examples of this water-absorbing resin include carboxymethylcellulose crosslinked products, polyoxyethylene partially crosslinked products, starch-acrylonitrile graft copolymer hydrolysates, Fi powder-acrylic acid graft copolymers; acrylic acid or methacrylate polymers. Partially crosslinked products, partially crosslinked products of acrylic acid or methacrylate copolymers, vinyl alcohol-acrylate copolymers, and the like are known. The performance of these water-absorbing resins is largely influenced by their manufacturing method, but there is still room for improvement in the required performances such as water-absorbing capacity, water-absorbing rate, and gel strength. In addition, as a result of recent research and development, water-absorbent resins that can almost simultaneously satisfy the above-mentioned performance requirements are being developed, but even with these water-absorbent resins, the water retention properties (wet back properties) under pressure are by no means satisfactory. Currently, no water-absorbing resin has been found that has such excellent pressurized water retention properties. However, unlike absorbent substances such as pulp and sponge, water-absorbent resins have the general feature that they do not easily release water once they have been absorbed. At the bottom, there is a tendency for water to separate, albeit slightly.
In this case, when used in sanitary materials such as disposable diapers and sanitary products, there is a risk of causing discomfort due to the return of urine and menstrual blood, making it unsuitable for use as sanitary materials.

11. In view of the above-mentioned circumstances, the inventors of the present invention have improved the water-absorbing resin's water-absorbing ability, water-absorbing speed, and gel strength during water-absorbing without impairing its water-absorbing properties under pressure. We conducted extensive research with the aim of providing a method to do so.

As a result, using a conventionally known water-absorbing resin containing carboxylate groups as a component of the polymer as a raw material,
It has been found that when a cationic surfactant is added to the resin, the above-mentioned problems can be solved and a water-absorbing resin having excellent performance that meets the objective can be provided.

The present invention was completed based on this new knowledge.

The present invention is characterized in that a cationic surfactant is added to a water-absorbing resin raw material containing a carboxylate group as a constituent component of the polymer, thereby improving the pressurized water retention property of the water-absorbing resin. It concerns the method of improvement.

The water-absorbing resin with improved pressurized water retention according to the present invention hardly releases the water once absorbed by the water-absorbing resin under load or pressurized conditions, and as a result, it can be used, for example, in disposable diapers, sanitary products, etc. It has the advantage of reliably eliminating the discomfort caused by the return of urine and menstrual blood when used in sanitary materials such as, and can be used as an even better sanitary material.

In the present invention, the water-absorbing resin used as a raw material may be one containing a carboxylate group as a constituent component of the polymer, and can be appropriately selected from among the various known resins mentioned above. In the present invention, the carboxylate group is defined as a concept including a carboxyl group.

Among the above-mentioned water-absorbing resin raw materials, considering the inherent properties of water-absorbing resins, such as water-absorbing ability, water-absorbing rate, and gel strength at the time of water absorption, the starch-acrylonitrile graft copolymer hydrolyzate, starch-acrylic Acid graft copolymers, partially crosslinked products of acrylic acid or methacrylate polymers, partially crosslinked products of acrylic acid or methacrylate based copolymers (hereinafter, the latter two will simply be referred to as (meth)acrylic acid based (co)) (referred to as a partially crosslinked polymer) is preferably used. Particularly preferred partially crosslinked products of the (meth)acrylic acid-based (co)polymers are disclosed in, for example, JP-A No. 56-93711, JP-A No. 56-93711;
6-131608, JP 56-147806, JP 58-71907, JP 58-1
17222 @ Publication, Special Publication No. 54-30710, Publication No. 37994-197, Publication No. 53-46200
M publication, US Pat. No. 4,041,228, etc. Water-absorbing resins described in these documents, especially (meth)acrylic acid-based (
Partially crosslinked co)polymers have resin performance that differs to some extent based on the different manufacturing methods employed, but the C4 resin performance can be changed as desired by selecting the a-forming conditions, etc., as desired. Generally their water absorption capacity is 100-100
0. Water absorption speed is 2 to 30 seconds, gel strength at time of water absorption is 1.0
~5.0×10' dyne/Cl112, all of which can be preferably used in the present invention.

The cationic surfactant used in the present invention is not particularly limited and may be any of a variety of known surfactants, but higher alkylamine salts and quaternary ammonium salts are preferably used, and in particular, pressurized water retention. Quaternary ammonium salts are preferred from the viewpoint of properties. However, according to research conducted by the present inventors, in order to improve the pressurized water retention properties of water-absorbent resin raw materials, the use of the above-mentioned cationic surfactants, especially quaternary ammonium salts, is an essential requirement. This is the first time that the desired effect of the present invention can be achieved.

On the other hand, even if a nonionic surfactant or an anionic surfactant is used, the object of the present invention cannot be achieved basolaterally.

More specifically, examples of the quaternary ammonium salt as the cationic surfactant include alkyl quaternary ammonium salt, alkylbenzyl quaternary ammonium salt,
Examples include quaternary ammonium salts having a nitrogen ring.

The alkyl quaternary ammonium salt has 10 to 18 carbon atoms.
Examples include alkyltrimethylammonium halide, alkyldimethylethylammonium halide, and the like having an alkyl group. Alkylbenzyl quaternary ammonium salts include alkyldimethylbenzylammonium halides having an alkyl group having 10 to 18 carbon atoms, and the like. In addition, quaternary ammonium salts having a nitrogen ring include
Included are alkylpyridinium halides and alkylpicolinium halides having an alkyl group having 10 to 18 carbon atoms.

In addition, as the above-mentioned halide, chloride or bromide can be obtained suitably.

In the present invention, it is necessary to add a cationic surfactant, especially a quaternary ammonium salt, to the water-absorbing resin raw material, especially a partially crosslinked product of a (meth)acrylic acid-based (co)polymer. This makes it possible to improve pressurized water retention, which is a drawback of conventional water absorbent resins. The amount of surfactant used (solid weight) is determined by taking into consideration the pressurized water retention properties and economic efficiency of the resulting water-absorbent resin, and is usually 0.00% relative to the water-absorbent resin (solid weight). 01 to 5%, preferably 0.1 to 2.0%.

The method of adding a surfactant to the water-absorbing resin raw material may be selected depending on the manufacturing method, manufacturing stage, etc. of the water-absorbing resin raw material. For example, in the case of water absorbent resins obtained by employing the so-called reverse phase suspension polymerization method disclosed in JP-A-56-131608, JP-A-58-117222, etc., the pearls obtained When carrying out a rapid crosslinking reaction of a polymer with a crosslinking agent such as ethylene glycol diglycidyl ether, a surfactant may be mixed and added to the aqueous solution of the crosslinking agent. In addition, when using a commercially available water-absorbing resin containing carboxylate groups (usually in the form of powder) as a raw material, the surfactant may be simply stirred and mixed into the water-absorbing resin powder, or the surfactant may be added to the water-absorbing resin powder. A method can be adopted in which the agent is diluted with a small amount of water, mixed, and then dried. When implementing such a method, it is best to adopt a method that allows the cationic surfactant to be added and dispersed substantially uniformly into the water-absorbing resin powder. A homogeneous dispersion method using a conventional stirring device simultaneously with or after the addition by a one-way spray method is preferred.

According to the above procedure, the cationic surfactant quickly and selectively forms an ionic bond to the carboxylate groups contained in the water-absorbing resin (particularly those existing near the surface of the water-absorbing resin powder). Therefore, it can be relatively easily localized near the surface of the water absorbent resin.

Thus, according to the present invention, a cationic surfactant, especially a quaternary ammonium salt, can be added to a water-absorbing resin raw material, especially a partially crosslinked product of a (meth)acrylic acid-based (co)polymer. In particular, the surfactant can be localized near the surface of the raw material water-absorbing resin (powder), which solves problems that could not be solved with conventional techniques, such as the inherent water-absorbing ability of the water-absorbing resin, Its pressurized water retention properties can be improved without reducing the speed and gel strength upon water absorption.

The water-absorbing resin obtained by the method of the present invention can not only be used as it is for conventional purposes, but also particularly suitable for use in sanitary materials that are strictly required to have pressurized water retention properties.

EXAMPLES The method of the present invention will be explained in more detail below with reference to Examples, but it goes without saying that the present invention is not limited thereto.

Example 1 72.1 CJ of acrylic acid was added to 22.2 CJ of deionized water, and to this was added 49.5 g of potassium hydroxide with a purity of 85% and 0.0 CJ of N,N-methylenebisacrylamide. OIQ was sequentially added to prepare a potassium acrylate aqueous solution (neutralization degree 75%) with a mixed monomer concentration of 70% by weight.

The aqueous solution prepared above was kept at 70°C, and 2.9q of an 18% aqueous solution of ammonium persulfate (potassium acrylate, free acrylic acid, and N) was added to it.

0.0% based on the total weight of N-methylenebisacrylamide.
5% by weight) and 1.7 g (0.5% by weight) of a 30.6% aqueous solution of sodium bisulfite were mixed, and the mixed solution was spread on an endless moving belt in a layer having a thickness of about 1Q mm. The polymerization reaction started in about 30 seconds and was completed in about 1 minute. The maximum temperature during that time was about 120°C.

Thus, the water content is 11% and the residual monomer concentration is 1200 pl).
A strip-shaped dry solid of a potassium polyacrylate crosslinked product of m was obtained. Hereinafter, this will be referred to as water absorbent resin A. This was pulverized using a pulverizer, and the resulting powder had a water absorption capacity of 450. Note that this water absorption capacity is evaluated by the method described later.

Aerosil 200 is added to the water absorbent resin A100O obtained above.
(Average particle size: about 0.012 μm, fine particulate silica manufactured by Nippon Aerosil ■) ICl was added and thoroughly stirred. Further, while stirring, 2 q of a 30% aqueous solution of trimethyl lauryl ammonium chloride was added uniformly, and then heated to 70-80°C.
It was held for 5 minutes.

The water absorption capacity, water absorption rate, and pressurized water retention of the obtained water absorbent resin were each measured according to the following methods.

The results are shown in Table 1.

(Water absorption capacity) Add 150g of deionized water and 0.12CI of water-absorbent resin sample to a 2001TIQ beaker, leave it for 30 minutes, separate the two houses with a 200-mesh wire mesh, and measure the weight of the black water flowing out. Water absorption capacity was calculated using the following formula.

(Water absorption rate) In advance, put physiological saline (0.9% saline > 500) and a stirrer into a 100% desorbing beaker, stir at a speed of 600 rpm with a magnetic stirrer, and add a water-absorbing resin sample into the beaker. When 2q is added, gelation occurs due to water absorption and swelling, fluidity decreases and the water vortex at the center of stirring disappears.The time required from the addition of the water absorbent resin sample until the vortex disappears is measured, and the water absorption rate is determined. shall be.

(Gel strength) A gel (hereinafter referred to as 30x gel) was prepared by mixing 60 g of physiological saline and 2.0 g of a water-absorbing resin sample, and the surface hardness of the gel was measured using a Neocard meter manufactured by Iio Electric Co., Ltd. measure). Here, the surface hardness is expressed as a resistance force that prevents the pressure-sensitive shaft from pushing away the gel and entering the sample surface.

(Pressurized water retention) A 0.50% water absorbent resin sample was placed in an aluminum saucer (diameter 5.5 cm, depth 1 cm), and then 15 g of physiological saline was added and left for 2 minutes. After that, 2 sheets of paper 1 with a diameter of 5.5 cm
One sheet was placed over the top and a load was applied for 9110 minutes. Increased weight of the remaining 10 sheets of paper excluding the bottom paper that directly contacts the water-absorbing resin sample (unit: Q)
is measured and used as a measure of pressurized water retention.

Example 2 A desired water-absorbing resin was obtained in the same manner as in Example 1, except that 2q of a 30% aqueous solution of dimethylbenzyllauryl ammonium chloride was used instead of trimethyllauryl ammonium chloride.

Table 1 shows various measurement results of the obtained water absorbent resin.

Example 3 The same procedure as in Example 1 was repeated except that 6q of a 10% aqueous solution of N-laurylpyridinium chloride was used instead of trimethyllauryl ammonium chloride, but the desired water-absorbing resin was used.

Table 1 shows various measurement results of the obtained water absorbent resin.

Example 4 39.1 g of acrylic acid with a purity of 99.8% by weight was mixed with 100-
of 22.6% by weight while cooling and stirring.
After dropping an aqueous sodium hydroxide solution 765Q to neutralize the solution to 80 mol%, 0.13 q of potassium persulfate was added and dissolved at room temperature while stirring.

213 g of cyclohexane and 1.9 g of sorbitan monolaurylate with an HLB of 8.6 were charged into a 500-liter flask equipped with a reflux condenser and the inside of the system was purged with nitrogen in advance, and after dissolving the surfactant at room temperature with stirring, the acrylic A partially neutralized acid salt aqueous solution was added dropwise and suspended. After the system was sufficiently replaced with nitrogen again, the temperature was raised to bring the bath temperature to 55-6.
The polymerization reaction was carried out at 0°C for 3 hours.

The produced polymer solution was evaporated to dryness under reduced pressure to obtain 480 liters of dry polymer in the form of fine granules. Hereinafter, this will be referred to as water absorbent resin B.

A desired water-absorbing resin was obtained in the same manner as in Example 1, except that water-absorbing resin B obtained above was used instead of water-absorbing resin A.

Table 1 shows the results of various measurements on the water-absorbing resin.

Example 5 50CJ of corn starch and 200mG of water and 1
000p of methanol was charged into a reaction vessel equipped with a stirring bar, nitrogen blowing tube, and thermometer, and heated to 55°C under a nitrogen stream.
After stirring for 1 hour, the mixture was cooled to 30°C, and added with 200 acrylic acid, 80 g of sodium acrylate, 40 q of ceric ammonium nitrate solution (1/10 mole cerium ion in INiill acid) and 1 q of N, N- Methylenebisacrylamide was added and polymerized by stirring at 40°C for 3 hours, resulting in a white suspension.

Thereafter, this suspension was filtered, and the resulting powder was washed with a water-methanol mixed solution (water to methanol ratio 2:10), dried under reduced pressure at 60°C for 3 hours, and then ground to give 138 g of powdery water absorbent powder. Resin was obtained. This is referred to as water absorbent resin C.

A desired water-absorbing resin was obtained in the same manner as in Example 1, except that the water-absorbing resin C obtained above was used instead of the water-absorbing resin.

Table 1 shows the results of various measurements of the water-absorbing resin.

Comparative Example 1 Water absorbent resin A used as a raw material in Example 1 was used as a comparative water absorbent resin. The results of evaluating various performances are shown in Table 1.

Comparative Example 2 Water absorbent resin B used as a raw material in Example 4 was used as a comparative water absorbent resin. Its various performances were evaluated. The results are shown in Table 1.

Comparative Example 3 The water absorbent resin used as a raw material in Example 5 was used as a comparative water absorbent resin. The results of evaluating its various performances are shown in the first
Shown in the table.

Chapter 1 Table (that's all)

Claims (3)

[Claims] (1) A method for improving the pressurized water retention of a water-absorbing resin, which comprises adding a cationic surfactant to a water-absorbing resin raw material containing a carboxylate group as a constituent component of the polymer. (2) The method according to claim 1, wherein the water absorbent resin raw material is a partially crosslinked product of an acrylic acid or methacrylic acid polymer or a partially crosslinked product of an acrylic acid or methacrylic acid copolymer. (3) The method according to claim 1 or 2, wherein the cationic surfactant is a quaternary ammonium salt.