JPH0754255A - Nonwoven fabric having water absorption property - Google Patents

Abstract

PURPOSE:To obtain water absorbing nonwoven fabric having high water absorbing ability, excellent flexibility, handle, processing suitability and high tensile strength. CONSTITUTION:This water absorbing nonwoven fabric comprises a composite sheet wherein synthetic yarn is interlaced with cellulosic yarn and the cellulosic yarn has 0.35-1.6 substitution degree of carboxymethyl group and cross-linked.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a water absorbent nonwoven fabric. More specifically, the present invention is composed of a composite sheet in which synthetic fibers and superabsorbent cellulose-based fibers are entangled with each other, having a water absorption capacity equivalent to that of the superabsorbent resin, and having not only excellent flexibility, texture and processability. The present invention relates to a water-absorbent non-woven fabric having excellent sheet strength even after absorbing water.

[0002]

2. Description of the Related Art In recent years, a group of materials called super water absorbent resins have been known as water absorbent materials for water or aqueous solutions containing salts such as saline. Basically, these resin materials have a chemical structure in which a water-soluble polymer is slightly crosslinked to make it insoluble in water. Examples of such a highly water-absorbent material include, for example, starch obtained by graft-polymerizing acrylonitrile and then hydrolyzing it, starch obtained by graft-polymerizing an acrylic acid metal salt, and acrylic acid polymerized with a copolymerizable cross-linking agent. A large number of crosslinking resins, hydrolysates of methyl methacrylate-vinyl acetate copolymers, etc. have been proposed, and some of them have been put to practical use.

Since most of these conventional materials are fine powders or granules, they are hardly used as they are in practical use and require some kind of support material. For example, in the production of disposable paper diapers, it is widely spread between fluff pulp mats, and in the case of other products, it is sandwiched between sheet materials such as paper, non-woven fabric and synthetic resin sheet.

When manufacturing such a composite material, a predetermined amount of the water-absorbent resin must be evenly dispersed, and it is necessary to fix the dispersed water-absorbent resin so as not to fall off, which is troublesome. It is a thing. Also when using,
The water-absorbent resin gel particles that have absorbed water have a drawback that they are likely to fall out of the support material or fall off, and when using the most common fluff pulp mat or paper as the support material, the strength is greatly reduced after water absorption, It has a problem that it easily loses its shape.

As an attempt to solve these problems of conventional superabsorbent polymers, a method of producing a fibrous superabsorbent resin and using it as it is or after processing it into a sheet (Japanese Patent Laid-Open No. 57-21549). JP-A-63-159
No. 440), a method in which a water-absorbent resin powder is dispersed in a binder resin solution to form a paint, and this is applied to a support material (Japanese Patent Publication No. 55-50074), a water-soluble monomer together with a crosslinkable monomer is added to fluff pulp, After impregnating paper, non-woven fabric or the like, polymerization is performed to form a water-absorbent resin to obtain a composite water-absorbing material (JP-A-59-204975, JP-A-60-149609, JP-A-63-10638).
JP-A-63-105044 and JP-A-2-111484
And Japanese Patent Laid-Open No. 61-194300).

Further, as a similar attempt, a method of impregnating fluff pulp, paper, nonwoven fabric, etc. with a water-soluble polymer together with a cross-linking agent and then carrying out a cross-linking reaction to form a water-absorbing resin to obtain a composite water-absorbing material JP-A-59-45695, JP-A-62-275146, JP-A-1-203084), and a sheet made of a cellulose fiber,
A method in which carboxymethyl cellulose having a crosslinked structure is chlorinated to impart water absorbability while maintaining the sheet structure (JP-A-60-71797, JP-A-61-893).
No. 64) is known.

Among the above-mentioned methods, the method of producing a fibrous superabsorbent resin and using it as it is or by processing it into a sheet form requires complicated manufacturing steps and requires special raw materials. Therefore, the cost is high. In a method in which a water-absorbent resin powder is dispersed in a binder resin solution to form a coating material and the coating material is applied to a support material, the film of the binder resin inhibits water absorption, resulting in a marked decrease in water absorption rate. In order to avoid this, if the amount of binder resin used is suppressed, or if a water-soluble resin is used as a binder, it is inevitable that gel particles fall off from the support material during water absorption.

Many methods have been studied for impregnating fluff pulp, pulp paper, non-woven fabric and the like with a water-soluble monomer together with a cross-linking monomer, and then polymerizing them to form a water absorbent resin to obtain a composite water absorbent material. When the amount is large, the support becomes inflexible and hard and brittle, and the workability and texture are remarkably impaired. In a similar method to this, a method of impregnating fluff pulp, paper, nonwoven fabric or the like with a water-soluble resin together with a cross-linking agent and then performing a cross-linking reaction to form a water-absorbent resin to form a composite water-absorbing material is also known. In order to form a water absorbent resin with a high water absorption,
It is necessary to impregnate a high molecular weight water-soluble resin, which is difficult due to its very high viscosity.

Further, the same drawbacks as in the case of the monomer impregnation are that the obtained composite water-absorbing material becomes hard and brittle, and the workability and the texture are remarkably impaired. Further, a sheet made of a cellulosic fiber, while maintaining the structure of the sheet, in a method of chlorinated carboxymethylcellulose having a crosslinked structure to give water absorption, although flexibility, texture, and processability are excellent, after absorbing water. It has the drawback that the sheet strength is completely lost and the material is defibrated.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional superabsorbent material, has a water absorption capacity equivalent to that of the superabsorbent resin, and has flexibility, texture, processability and An object of the present invention is to provide a water-absorbent nonwoven fabric having excellent sheet strength after absorbing water.

[0011]

The water absorbent nonwoven fabric of the present invention comprises a composite sheet containing synthetic fibers and cellulosic fibers, wherein the cellulosic fibers have a carboxymethyl group and are crosslinked. The degree of substitution of the carboxymethyl group is 0.35 to 1.6. And JIS P81 of the composite sheet
The wet tensile strength of a 25 mm wide test piece measured by the method shown in No. 35 is 0.1 to 10.0 Kgf, and the pure water absorption is 25 to the composite sheet weight before water absorption.
It needs to be 160 times.

The materials constituting the water absorbent nonwoven fabric of the present invention will be described in detail below. As the synthetic fibers used in the present invention, conventionally known fibers can be used. For example, polyolefin fibers, polyester fibers, polyamide fibers, polyacrylic acid ester fibers, polyurethane fibers and the like can be used. These synthetic fibers may be used in a fiber state, or may be used in a sheet state, that is, a nonwoven fabric state.

As the non-woven fabric, a non-woven fabric produced by a conventionally known method, for example, a dry non-woven fabric, a wet non-woven fabric, a spunbonded non-woven fabric, a melt blown non-woven fabric or the like can be used. The fineness of the fiber is not particularly limited, but it is preferably 0.3 to 10 denier. When the fineness of the fiber exceeds 10 denier and becomes thicker, the flexibility of the non-woven fabric decreases, and the flexibility, texture and processability of the water absorbent non-woven fabric deteriorate. If the fiber fineness is less than 0.3, the density of the non-woven fabric tends to be high, and the non-woven fabric tends to be paper-like, making it difficult to control the properties of the non-woven fabric.

The cellulosic fibers used in the present invention include pulp fibers produced from wood, non-wood pulp fibers produced from herbs, regenerated cellulose fibers and the like. Pulp fibers produced from wood include, for example, chemical pulp fibers obtained by cooking softwood or hardwood with the Kraft method, sulfite method, soda method, polysulfide method, refiner, mechanical pulp fiber pulped by mechanical force such as grinder. Examples include semi-chemical pulp fibers that have been pulped by mechanical force after chemical pretreatment, or waste paper pulp fibers, and they can be used in unbleached or bleached states, respectively. Examples of the non-wood pulp fibers produced from herbs include fibers obtained by pulping cotton, manila hemp, flax, straw, bamboo, pagas, kenaf, mulberry, sanpei, etc. in the same manner as wood pulp.

As the regenerated cellulose fiber, cellulose is made into a solution in the form of viscose, and then viscose rayon is prepared by regenerating and spinning cellulose in an acid, and cellulose is dissolved in a copper ammonia solution and then in an acid. Examples thereof include regenerated and spun copper ammonia rayon and regenerated cellulose fibers obtained by spinning after dissolving in a non-aqueous cellulose solvent such as N-methylmorpholine-N-oxide.

In the present invention, a known method can be used as a method for producing a composite sheet comprising synthetic fibers and cellulosic fibers. For example, "Research
disclosure, 17060, June 197
The composite sheet obtained by the method of hydroentangling a synthetic fiber nonwoven fabric and a paper sheet described in 8 "is excellent in texture and processability and can be effectively used in the present invention. As the synthetic fiber non-woven fabric, it is necessary to have the strength to withstand the pressure of water flow, and the long fiber non-woven fabric is preferable.

Alternatively, synthetic fiber short fibers and cellulosic fibers may be mixed in advance to form a web by a dry or wet method to form a composite sheet. In this case, it is necessary to partially bond the synthetic fibers to each other in order to maintain the wet tensile strength of the composite sheet. As a method of partially adhering the synthetic fibers to each other, any known method may be used, such as a method of spraying an adhesive and then heating and adhering it, or a method of mixing heat fusion fibers and adhering by heating. The method, the method using needle punch, the method using stitch bond, etc. can be used.

In the present invention, the compounding ratio of the synthetic fiber and the cellulosic fiber constituting the composite sheet is 1
On the other hand, it is preferable that the cellulosic fibers are 1 to 19. When the ratio of the cellulosic fibers to the synthetic fibers is less than 1, the amount of the cellulosic fibers to the synthetic fibers is relatively small, and the water absorption amount of the obtained sheet is small. On the other hand, when the ratio of the cellulosic fibers is more than 19, the entanglement between the synthetic fibers and the cellulosic fibers is less likely to occur, and the swollen cellulosic fibers easily fall off when the obtained sheet is made to absorb water. And the wet tensile strength is further reduced.

It is known that cross-linking and carboxymethyl groups are imparted to cellulosic fibers to show high water absorption, and many methods for carboxymethylation are also known. Basically, the alkali hydroxide and monochloroacetate may be reacted with the composite sheet in a solvent such as water or isopropyl alcohol. A method of reacting while maintaining the structure of the composite sheet is disclosed in JP-A-60-71797.
The methods disclosed in Japanese Patent Laid-Open No. 61-89364 and Japanese Patent Laid-Open No. 61-89364 are known. As the alkali hydroxide, an alkali metal hydroxide is generally used, and sodium hydroxide is preferable in terms of cost. As the monochloroacetate salt, an alkali metal salt or an ammonium salt is used, and generally sodium monochloroacetate and potassium monochloroacetate are used.

The method for introducing the cross-linking is not particularly limited, either, but it is also possible to react the cellulosic fiber with a cross-linking agent in advance and then carry out carboxymethylation. May be allowed to act simultaneously, or the crosslinking agent may be allowed to act after carboxymethylation. As the crosslinking agent, aldehydes such as formaldehyde and glyoxal; N-methylol compounds such as dimethylolurea, dimethylolethyleneurea, and dimethylolimidazolidone; oxalic acid, maleic acid, succinic acid, polyacrylic acid, and the like. Polyhydric carboxylic acids; polyhydric epoxy compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and diepoxy butane; divinyl sulfone and divinyl compounds such as methylenebisacrylamide, dichloroacetone, dichloropropanol, and dichloro Polyvalent halogen compounds such as acetic acid; halohydrin compounds such as epichlorohydrin and epibromohydrin; and polyvalent aziridine compounds can be used.

The amount of the cross-linking agent added varies depending on the type of the cross-linking agent or the reaction conditions, but it is 0.
It is preferably from 1 to 10% by weight. The pure water absorption of the cellulosic fiber having crosslinks and carboxymethyl groups is determined mainly by the degree of substitution of carboxymethyl groups and the crosslink density. The pure water absorption is theoretically higher as the substitution degree of the carboxymethyl group is higher, but the substitution degree of 0.35 to 1.6 is suitable for practical use. Even if the degree of substitution exceeds 1.6, the amount of water absorption is almost saturated, which is disadvantageous because the cost of the obtained sheet increases. Further, when carrying out carboxymethylation, depolymerization of cellulose molecules may occur, and conversely, a phenomenon may occur in which the amount of water absorption decreases. On the other hand, if the degree of substitution is less than 0.35, a sufficient amount of pure water absorption cannot be obtained.

The water absorption of pure water increases as the crosslink density decreases, but if it is too low, the gel strength upon absorption of water is weak and the water-soluble carboxymethylcellulose salt remains, which is not preferable because it becomes sticky. On the contrary, if the crosslink density is too high, the amount of water absorption decreases, so it is necessary to set the optimum crosslink density depending on the application. In the present invention,
By adjusting the degree of carboxymethyl group substitution and the crosslink density, the amount of pure water absorbed may be 25 to 160 times the weight of the composite sheet before water absorption.

The water absorbent nonwoven fabric of the present invention comprises a composite sheet containing synthetic fibers and cellulosic fibers, and the cellulosic fibers have carboxymethyl groups and are crosslinked. Synthetic fibers not only give the water-absorbent nonwoven fabric of the present invention flexibility, texture and processability,
Since the synthetic fiber itself has almost no water absorption, the wet tensile strength can be kept high even when water is absorbed. Cellulosic fibers are only entangled with synthetic fibers,
It hardly deteriorates the flexibility, texture and processability of the water absorbent nonwoven fabric. Further, since it has a cross-linking bond and a carboxymethyl group, it exhibits high water absorption, and even if it absorbs water, it is entangled with the synthetic fiber, so that it is difficult to detach from the synthetic fiber.

The water-absorbent nonwoven fabric obtained by the present invention not only absorbs a large amount of water, but also exhibits a high water-absorbing ability to an aqueous solution containing ions such as saline and urine. . Further, it has an excellent feature that it does not easily re-emit water even if pressure is applied in a water absorbing state. Therefore, used disposable diapers, sanitary materials such as sanitary products, soil water retention agents, agricultural material fields such as nursery sheets, food freshness retaining materials, food fields such as dehydration materials, and building materials such as dew condensation prevention sheets for buildings. It can be used as a wide range.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples. The water absorption, the wet tensile strength, and the degree of carboxymethyl group substitution in each example and comparative example were measured by the methods described below.

Pure water absorption: Four test samples of 2.5 cm × 2.5 cm square were enclosed in a bag of 250 cm nylon wire of 10 cm × 10 cm square and deionized through an ion exchange resin. Was immersed in pure water obtained by distillation for 10 minutes to absorb water, and then it was lifted and suspended, drained for 10 minutes, and then the weight of the test sample was measured. The amount of absorbed water was indicated by the weight (g) of the pure water. Wet tensile strength: 2 according to the method of JIS P8135
The value in the vertical direction was measured using a test piece having a width of 5 mm.

Carboxymethyl group substitution degree: 2.5 cm ×
Four 2.5 cm square test samples were dried in a vacuum dryer at 60 ° C. for 4 hours, then weighed, and the value obtained by subtracting the weight of the synthetic fiber nonwoven fabric from this value was taken as carboxymethyl cellulose in the composite sheet. Weight and weight. The sample after the weight measurement was transferred to a petri dish, and 50 ml of a methanol / hydrochloric acid solution (a mixed solution of 70% by weight methanol aqueous solution with hydrogen chloride dissolved therein at a concentration of 1 mol / liter) was added and left for 1 hour, and then methanol was added. Was thoroughly washed with to completely remove hydrochloric acid, and air-dried. Then, the air-dried sample was placed in a 300 ml Erlenmeyer flask, about 20 ml of 0.1N sodium hydroxide solution and 100 ml of pure water were added, and the mixture was slowly stirred for 1 hour, and then phenolphthalein was added with 0.1N hydrochloric acid. Titration was performed as an indicator, and the substitution degree was calculated by the following formula.

Y = 0.1A-0.1B (1) Substitution degree = 162Y / (1000W-80Y) (2) However, in the formula, A: Amount of 0.1N sodium hydroxide solution (ml) B: 0. Amount of 1N hydrochloric acid (ml) Y: Amount of carboxymethyl group (milliequivalent) W: Weight of carboxymethyl cellulose (g)

Example 1 A polypropylene spun-bonded non-woven fabric (fineness: 2.5 denier) having a basis weight of 12 g / m ² was bleached with softwood kraft pulp (N
BKP) is hydroentangled to an amount of 38 g / m ² ,
A composite sheet was made. 20 cm for the obtained composite sheet
Cut to a size of 30 cm (weight 3 g), sodium hydroxide 10.4% by weight, potassium monochloroacetate 34.6
Wt%, epichlorohydrin 1.0 wt%, water 54.0
After soaking in a mixed solution of 1% by weight for 1 minute, it was sandwiched between filter papers and pressed so that 2 g of the mixed solution adhered to 1 g of the composite sheet. This was placed in a polyethylene bag and placed in a dryer kept at 60 ° C. for 4 hours to carry out carboxymethylation and crosslinking of NBKP.

Then, the operation of immersing in a 70 wt% methanol aqueous solution, sandwiching it between filter papers and pressing it was repeated 4 times to thoroughly wash the composite sheet. Finally, it was dipped in 100% methanol, sandwiched between filter papers, pressed, and then air-dried to obtain a water-absorbent nonwoven fabric. In addition, the substitution degree of the carboxymethyl group of NBKP in the obtained water absorbent nonwoven fabric was 0.47. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Example 2 NBKP was added to a polyethylene terephthalate spunbonded non-woven fabric (fineness 2.3 denier) having a basis weight of 12 g / m ² with 68 NBKP.
A composite sheet produced by hydroentangling so as to have an amount of g / m ² was wound around a polypropylene cylinder having a diameter of 3 cm and a length of 30 cm for 20 m. The roll is immersed in a mixed solution of 10.4% by weight of sodium hydroxide, 34.6% by weight of potassium monochloroacetate, 1.0% by weight of epichlorohydrin, and 54.0% by weight of water to completely impregnate it. It was At this time, the mixed liquid is 6.4 g per 1 g of the composite sheet.
It was attached. This roll was placed in a polyethylene bag and left at room temperature for 24 hours to carry out carboxymethylation and crosslinking of NBKP. This was dehydrated with a centrifugal dehydrator, then immersed in a 70% by weight aqueous methanol solution, and dehydrated with a centrifugal dehydrator, which was repeated 10 times for sufficient washing. Finally, soak in 100% methanol and spin-dry with a centrifugal dehydrator,
It was dried in a dryer at 60 ° C to obtain a water-absorbent nonwoven fabric. In addition, the substitution degree of the carboxymethyl group of NBKP in the obtained water absorbent nonwoven fabric was 0.44. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Example 3 70% by weight of hardwood bleached kraft pulp (LBKP) was mixed with 30% by weight of polyester fiber (fineness: 1.5 denier), and heat embossing was applied to a base paper made to have a basis weight of 50 g / m ^2. Then, the polyester fibers were partially fused and bonded to each other to obtain a composite sheet. This composite sheet was treated in the same manner as in Example 1 to carry out carboxymethylation and crosslinking of LBKP to obtain a water absorbent nonwoven fabric. In addition,
The degree of substitution of carboxymethyl groups of LBKP in the obtained water absorbent nonwoven fabric was 0.48. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Example 4 80% by weight of rayon staple having a fineness of 3 denier and a fiber length of 51 mm was mixed with 20% by weight of heat-fusible polyester fiber having a fineness of 1.5 denier and a fiber length of 40 mm, and a basis weight of 60 g was obtained using a card. / M ² web, and then the polyester fibers were bonded through the heating rolls to form a composite sheet. This composite sheet was treated in the same manner as in Example 1 to carboxymethylate and crosslink rayon staples to obtain a water absorbent nonwoven fabric. The degree of substitution of carboxymethyl groups of rayon staple in the obtained water-absorbent nonwoven fabric is 0.4.
It was 5. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Example 5 A water absorbent nonwoven fabric was obtained in the same manner as in Example 1 except that the treatments of carboxymethylation and crosslinking of NBKP were repeated twice. The degree of substitution of carboxymethyl groups of NBKP in the resulting water absorbent nonwoven fabric was 0.81. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Example 6 A water-absorbent nonwoven fabric was obtained in the same manner as in Example 1 except that carboxymethylation and crosslinking of NBKP were carried out under the reaction conditions of 60 ° C. for 15 minutes. N in the obtained water-absorbent nonwoven fabric
The substitution degree of carboxymethyl group of BKP was 0.35. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Comparative Examples 1 to 4 In Examples 1 to 4, Comparative Examples 1 and 2, respectively, were prepared by using samples before carrying out carboxymethylation and crosslinking of pulp fibers.
Comparative example 2, comparative example 3, and comparative example 4 were used. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of each sample.

Comparative Example 5 Example 1 was applied to a paper of NBKP having a basis weight of 50 g / m ^2.
The same treatment as above was performed to carry out carboxymethylation and crosslinking to obtain a water absorbent sheet. The degree of substitution of carboxymethyl groups of the resulting water absorbent sheet was 0.44. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent sheet.

Comparative Example 6 A non-woven fabric produced by intertwining continuous filaments of copper ammonia rayon, having a fineness of 2 denier and a basis weight of 80 g / m 2.
² and a density of 0.25 g / cm ³ were used for Example 1.
The same treatment as above was performed to obtain a water-absorbent nonwoven fabric. The degree of substitution of carboxymethyl groups of the resulting water-absorbent nonwoven fabric was 0.45. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

Comparative Example 7 A water absorbent nonwoven fabric was obtained in the same manner as in Example 1 except that NBKP was subjected to carboxymethylation and crosslinking treatment under the reaction conditions of 60 ° C. for 10 minutes. N in the obtained water-absorbent nonwoven fabric
The substitution degree of carboxymethyl group of BKP was 0.32. Table 1 shows the measurement results of the pure water absorption and the wet tensile strength of the water absorbent nonwoven fabric.

[0040]

[Table 1]

As is clear from Table 1, the water-absorbent nonwoven fabric of the present invention of each example had good pure water absorption and wet tensile strength, but each of the different constitutions from the present invention. The water-absorbent nonwoven fabric of Comparative Example was inferior in any of the properties, and the effect of the present invention was confirmed.

[0042]

The water-absorbent nonwoven fabric of the present invention has a high water-absorbing ability and can be used in the same manner as the super-absorbent resin, but it has a drawback of the super-absorbent resin, that is, fine powder or granules. Therefore, the problem that it is difficult to handle when manufacturing applied products is greatly improved. Furthermore, the water-absorbent nonwoven fabric of the present invention is not only excellent in flexibility, texture, and processability, but also maintains sheet strength after absorbing water, and can be used alone without being complexed with other materials. It can be suitably used in a wide range of fields.

Claims (1)

[Claims] 1. A composite sheet comprising synthetic fibers and cellulosic fibers, wherein the cellulosic fibers have a carboxymethyl group and are cross-linked, and the degree of substitution of the carboxymethyl group is 0.35. A water-absorbent non-woven fabric, which is 1.6.