JP2000110059A - Binder for producing nonwoven cloth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for nonwoven cloth suitable for producing cellulosic nonwoven cloth having a large water absorbability and excellent wet strength. SOLUTION: This binder for producing nonwoven cloth is an aqueous resin dispersion in which fine particles of a copolymer resin obtained by copolymerizing a monomer mixture containing alkyl (meth)acrylate, styrene (meth)acrylate and N-methylol (meth)acrylamide or N-alkoxymethyl (meth) acrylamide as essential components, and has pH <=6.5, and contains 0.3-5 pts.wt. of dialkylsulfosuccinic acid-based surfactant based on 100 pts.wt. of the copolymer resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for producing a nonwoven fabric, and more particularly, to a binder suitable for producing a nonwoven fabric made of cellulosic fibers such as cotton, pulp, hemp and rayon. The cellulosic nonwoven fabric obtained by using the binder of the present invention is excellent in water absorbency and is suitably used for a wide range of uses including wipes and water absorbent sheets.

[0002]

2. Description of the Related Art Today, nonwoven fabrics are widely used as clothes, building materials, civil engineering materials, and living-related materials. Above all, a cellulosic nonwoven fabric using a cellulosic fiber having hydrophilicity as a raw material fiber has been used as a domestic or industrial wipe or a water-absorbing sheet since it exhibits excellent water absorption to an aqueous liquid. Although the above-mentioned cellulosic nonwoven fabric is excellent in hydrophilicity, there is a problem that water easily penetrates between the fibers and between the fibers and the binder, and as a result, the strength is reduced in a wet state. Conventionally, styrene-butadiene copolymers, ethylene-vinyl acetate copolymers and the like have been used as fiber binders that can increase the strength in the wet state (hereinafter referred to as wet strength) while maintaining the hydrophilicity of the cellulosic nonwoven fabric. Aqueous resin dispersions containing an acrylic copolymer or the like as a main component are known.

[0003] However, even if the above aqueous resin dispersion is used as a fiber binder, sufficient wet strength cannot be obtained yet, so that it has been proposed to use another resin together with the above aqueous resin dispersion. That is,
JP-A-3-74416 proposes to use a partially methylated methylolmelamine resin in combination with such a resin dispersion. However, there is a problem that formaldehyde is generated from the nonwoven fabric obtained by this method,
Its use was limited. Japanese Patent Application Laid-Open No. 61-289161 proposes to use a nitrogen-containing glyoxal resin which does not generate formaldehyde, but this method has a problem that the nonwoven fabric turns yellow. In addition, it is known to use a water-soluble polymer having a carboxyl group or a sulfonic acid group in combination, but it is difficult to achieve both water absorption and wet strength to the nonwoven fabric, and the resulting nonwoven fabric has Performance was just a step away.

[0004]

DISCLOSURE OF THE INVENTION The present invention relates to a hygienic nonwoven fabric which is excellent in both wet strength and water absorption, which have been difficult to achieve in a nonwoven fabric, and in which the generation of formaldehyde and the elution of water-soluble components are extremely small. The purpose was to provide a binder suitable for production.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, the present invention provides a copolymer resin obtained by copolymerizing a monomer mixture containing alkyl (meth) acrylate, styrene and N-methylol (meth) acrylamide or N-alkoxymethyl (meth) acrylamide as essential components. Is an aqueous resin dispersion having fine particles dispersed in an aqueous medium and having a pH of 6.5 or less, wherein a dialkyl sulfosuccinic acid-based surfactant is used in an amount of 0.3 per 100 parts by weight of the copolymer resin. It is a binder for nonwoven fabric production consisting of an aqueous resin dispersion containing up to 5 parts by weight. Hereinafter, the present invention will be described in more detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the aqueous resin dispersion of the present invention, a monomer containing alkyl (meth) acrylate, styrene and N-methylol (meth) acrylamide or N-alkoxymethyl (meth) acrylamide as essential components A copolymer resin obtained by copolymerizing the mixture is dispersed in an aqueous medium. Preferred alkyl (meth) acrylates in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate. Is mentioned. In the present invention, a copolymer resin having a wide range of glass transition temperature (hereinafter, referred to as Tg) such as −50 to 100 ° C. can be obtained by appropriately selecting the type of the alkyl (meth) acrylate to be used. A soft nonwoven fabric is obtained from a copolymer resin having a low Tg, while a soft nonwoven fabric is obtained from a copolymer resin having a high Tg.

The N-alkoxymethyl (meth) acrylamide includes N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide and the like. In N-methylol (meth) acrylamide or N-alkoxymethyl (meth) acrylamide (hereinafter collectively referred to as crosslinkable amide), N-methylol (meth) acrylamide is more preferable. When using the aqueous resin dispersion containing a copolymer resin in the present invention as a fiber binder, in the step of heat treatment, self-crosslinking by the crosslinkable amide constituting the copolymer resin or crosslinking reaction with hydroxyl groups of cellulose fibers. As a result, the toughness and water resistance of the nonwoven fabric are obtained, and at the same time, the wet strength is improved.

[0008] The preferred amount of the essential monomer used to obtain the copolymer resin is based on the total amount of all monomers including monomers other than the essential monomer described below. 5 to 84% by weight of alkyl (meth) acrylate, 15 to 90% by weight of styrene, and 0.2 to 5% by weight of crosslinkable amide
It is. If the amount of styrene is less than 15% by weight, the wet strength of a nonwoven fabric using a binder made of a copolymer resin obtained tends to be insufficient, while if it exceeds 90% by weight, the adhesiveness of the copolymer resin as a binder Tends to decrease. When the amount of the crosslinkable amide used is less than 0.2% by weight, the obtained coating film obtained by drying the binder made of a copolymer resin is insufficiently crosslinked, so that the wet strength tends to be insufficient.
On the other hand, if the amount of the crosslinkable amide exceeds 5% by weight, the polymerization itself tends to be unstable. The amount of the alkyl (meth) acrylate used is obtained by subtracting the amounts of styrene and the crosslinkable amide from 100% by weight.

In the present invention, in order to obtain a copolymer resin,
If desired, monomers other than the above essential monomers can be used in an amount of 0 to 50% by weight based on the total amount of all the monomers. Monomers other than the essential monomers (hereinafter referred to as other monomers) include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and hydroxypolyoxyethylene (meth) acrylate , Hydroxyl-containing acrylates such as hydroxypolyoxypropylene (meth) acrylate and hydroxypolyoxybutylene (meth) acrylate, and α, β-ethylenic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, maleic acid and fumaric acid Unsaturated carboxylic acids, vinyl esters such as vinyl acetate, nitriles such as acrylonitrile and methacrylonitrile, vinyls such as vinyl chloride, vinylidenes such as vinylidene chloride, butenes such as butadiene, chloroprene, isoprene, and biene. Nylpyridine and N-vinylpyrrolidone.

[0010] Among the other monomers described above, preferred monomers are those which improve the wet strength of the obtained nonwoven fabric.
They are hydroxyl-containing acrylates and α, β-ethylenically unsaturated carboxylic acids. The hydroxyl group-containing acrylate and the α, β-ethylenically unsaturated carboxylic acid are cross-linked to each other in the copolymer resin or cross-linked with the cross-linkable amide. The groups act as catalysts in the self-crosslinking of the crosslinkable amide and in the crosslinking between the crosslinkable amide and the hydroxyl group. Further, the α, β-ethylenically unsaturated carboxylic acid improves the dispersion stability of the copolymer resin in an aqueous medium. The preferred use amount of the hydroxyl group-containing acrylate and the α, β-ethylenically unsaturated carboxylic acid is 0.2 to 5% by weight based on the total amount of all monomers.

The aqueous resin dispersion of the present invention is an aqueous resin dispersion in which fine particles of a copolymer resin composed of the above-mentioned monomer are dispersed in an aqueous medium, preferably, the monomer is subjected to aqueous emulsion polymerization. An aqueous resin dispersion obtained by
Further, the copolymer resin contains 0.3 to 5 parts by weight of a dialkyl sulfosuccinic acid-based surfactant per 100 parts by weight of the copolymer resin. If the content of the dialkyl sulfosuccinic acid-based surfactant in the aqueous resin dispersion is less than 0.3 parts by weight, sufficient water absorption cannot be imparted to the nonwoven fabric, while the wet strength of the nonwoven fabric exceeds 5 parts by weight. Is inferior. A more preferred amount of the dialkyl sulfosuccinic acid-based surfactant is 0.5 to 3 parts by weight. In the present invention, as described above, the problem could be solved by including a specific amount of a dialkyl sulfosuccinic acid-based surfactant in the aqueous resin dispersion. In contrast, surfactants other than dialkylsulfosuccinic surfactants, hydrophilic compounds such as water-soluble polymers or urea can impart the same hydrophilicity to nonwoven fabrics as dialkylsulfosuccinic surfactants. Did not.

As a method for adding the dialkyl sulfosuccinic acid-based surfactant to the aqueous resin dispersion, it is possible to use a dialkyl sulfosuccinic acid surfactant as an emulsifier for emulsion polymerization for synthesizing the aqueous resin dispersion.
Alternatively, there may be mentioned a method of simply adding the compound after the emulsion polymerization.
Specific examples of the dialkylsulfosuccinic surfactant include dibutyl, diamyl, dihexyl, dicyclohexyl, dioctyl, didodecyl, and diisotridecyl sodium salts of sulfosuccinic acid or ammonium salts thereof. Preferred dialkyl sulfosuccinic surfactants are sodium dioctyl sulfosuccinate and sodium diisotridecyl sulfosuccinate.

Next, a method for producing an aqueous resin dispersion from the above monomers will be described. As described above, a preferred method for producing an aqueous resin dispersion is an aqueous emulsion polymerization method of a monomer. Examples of the emulsifier used in the emulsion polymerization include anionic surfactants such as sodium dialkylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium alkyldiphenylether disulfonate; and polyoxyethylene. Nonionic surfactants such as higher alcohol ethers and polyoxyethylene alkyl phenyl ethers; polycarboxylic acid-based polymer surfactants; and nonionic polymer surfactants such as polyvinyl alcohol are used alone or in combination of two or more. Can be used in combination. The preferred amount of the emulsifier varies depending on the type of the emulsifier used, but is usually 0.05 to 5 parts by weight per 100 parts by weight of the monomer.

As the polymerization initiator, persulfates such as potassium persulfate and ammonium persulfate, peroxides such as hydrogen peroxide, benzoyl peroxide and t-butyl hydroperoxide can be used. These may be used in a redox system using a reducing agent such as sodium bisulfite or ascorbic acid in combination. This amount may be about the same as that used in known emulsion polymers. The preferred monomer concentration in the aqueous emulsion reaction solution is 10 to 70% by weight.

[0015] The aqueous resin dispersion of the present invention must have a pH of an aqueous medium of 6.5 or less. When the pH of the aqueous resin dispersion exceeds 6.5, in the step of heating and drying the aqueous resin dispersion used as a fiber binder, the crosslinking reaction of the crosslinkable amide becomes incomplete, and the resulting nonwoven fabric cannot be used. Formaldehyde is generated at times. As an example of the means for controlling the pH of the aqueous resin dispersion to 6.5 or less, use of a persulfate-based initiator as a polymerization initiator in the emulsion polymerization is mentioned. By using the polymerization initiator, the pH of the obtained aqueous resin dispersion is usually 5 or less, so that if used as it is, the requirements of the present invention are satisfied. Further, even when an α, β-ethylenically unsaturated carboxylic acid is used as a monomer forming the copolymer resin, an acidic aqueous resin dispersion can be obtained. If necessary, when a basic compound is added to neutralize the acidic compound, the pH of the aqueous resin dispersion may be reduced.
Careful neutralization is required so that H does not exceed 6.5. As the basic compound, a volatile basic compound is preferable, and ammonia is particularly preferable.

The nonwoven fabric binder of the present invention comprises the above aqueous resin dispersion, but other substances may be added as desired. Specific examples of the substance that can be added include an antifoaming agent, a preservative, a catalyst for an N-methylol crosslinking reaction, and a formaldehyde scavenger. Raw fibers used with the binder of the present invention to produce a nonwoven fabric include natural celluloses such as cotton, pulp and hemp, rayon-based, polyester-based, polyamide-based, wool, and jute. Preferably, rayon and natural cellulosic fibers, for which it was conventionally difficult to achieve both high water absorption and excellent wet strength, are more preferable, and natural cellulosic fibers are more preferable. Hereinafter, by giving Examples and Comparative Examples,
The present invention will be described more specifically. Note that “parts” or “%” in each example is based on weight.

The performance of the nonwoven fabric produced in each example was evaluated by measuring the following physical properties and properties. ○ Glass transition temperature of copolymer resin After drying the aqueous resin dispersion at 40 ° C for 24 hours,
For the resin that was heat-treated for 4 minutes, a differential scanning calorimeter [Seiko Electronics Corporation Disk Station SSC5
200H].

○ Performance of nonwoven fabric 1) Preparation of nonwoven fabric for evaluation In place of producing nonwoven fabric for evaluation from the aqueous resin dispersion obtained in each example and raw material fibers, a commercially available pulp nonwoven fabric was treated as follows. Was used to evaluate the performance of the aqueous resin dispersion as a binder. After impregnating so that the solid content of the aqueous resin dispersion adheres to the pulp non-woven fabric having a basis weight of about 45 g / m ^{2 in} an amount of 20% of the basis weight of the fiber, the pulp is then heated to 150 ° C
And heat-treated at 180 ° C. for 1 minute. 2) Non-woven fabric texture Touch the non-woven fabric for evaluation (hereinafter simply referred to as test cloth) with your hand, and adjust the soft, slightly soft, normal,
It was rated on a five-point scale.

3) Non-woven fabric wet strength A test cloth is cut into a 25 mm width, immersed in water at 23 ° C. for 24 hours, and immediately taken out of the water, and immediately used with a tensile tester (TENSILON / UTM-4L, manufactured by Toyo Seiki Co., Ltd.). Using the pulling speed
300 mm / min, distance between chucks 50 mm, 23 ° C, humidity 65%
A tensile test was performed under an atmosphere of. ◎ indicates that extremely good wet strength was obtained, ○ indicates that good wet strength was obtained, and x indicates that only insufficient wet strength was obtained. 4) Water absorption time Cut a test cloth into a 100 mm x 100 mm square, stack five sheets, and staple the four corners to obtain a test piece. The test pieces were gently dropped into water adjusted to 20 ° C., and the time until all five sheets were wet was measured. The shorter the water absorption time, the better the nonwoven fabric is in water absorption. When the water absorption time was much shorter than the target, ◎ was given, when the water absorption time was shorter, and x was given when the water absorption time was longer than the target.

5) Amount of Free Formaldehyde The amount of formaldehyde released from the test cloth was evaluated according to the acetylacetone method specified in Ordinance No. 34 of the Ministry of Health and Welfare in 1974. Those that satisfy A-A0 <0.5, which are specified in the Ministerial Ordinance No. 34 as the regulation values for baby clothes within 24 months of age, are marked with "O", and those with A-A0 of 0.5 or more are marked with "x". 6) Potassium permanganate consumption In accordance with the standards stipulated in the "3rd apparatus and containers and packaging" of the "Food and Additives Standards" of the Food Sanitation Law, the amount of potassium permanganate consumption for test cloths It was measured. If the product satisfies the standard reference value of 10 ppm or less, it is marked as ○ and 10
Those exceeding ppm were marked with x.

[0021]

Example 1 20 parts of styrene, 60 parts of n-butyl acrylate,
10 parts of 2-ethylhexyl acrylate, 10 parts of n-butyl methacrylate, 2 parts of acrylic acid, 2 parts of 2-hydroxyethyl methacrylate, and 2 parts of N-methylolacrylamide were added to 30 parts of water.
And 0.5 part of sodium lauryl sulfate, and a monomer emulsion is prepared using a homomixer. Water 70
A resin emulsion was obtained by a semi-batch emulsion polymerization method in which the monomer emulsion was charged into the flask charged with the parts for 4 hours. In addition, ammonium persulfate is used as a polymerization initiator.
0.4 parts was used and the polymerization temperature was 85 ° C. The obtained emulsion is adjusted to pH 5 with ammonia, and sodium dioctylsulfosuccinate is used as an active ingredient.
2 copies [Kao Corporation, Perex OTP, active ingredient 70%]
By addition, the water-dispersible resin dispersion of Example 1 was obtained. The glass transition temperature of the dried product of the water-dispersible resin dispersion was measured. Further, non-woven fabric processing is performed using the water-dispersible resin dispersion as a binder, and the obtained non-woven fabric is
The texture, wet strength, water absorption time, free formaldehyde content and potassium permanganate consumption were evaluated. Table 1 shows the composition and evaluation results. Table 1 also shows the composition and evaluation results in the following examples.

[0022]

Examples 2, 5, 8, 10, 11 Except that the monomers used in Example 1 were changed to the monomers shown in Table 1 to change the glass transition temperature of the resin, respectively. Performed in the same manner as in Example 1.

Examples 3, 4, and 7 The same procedures as in Example 1 were carried out except that the monomers used in Example 1 were changed to the monomers shown in Table 1, respectively.

[0023]

Example 6 The sodium dioctylsulfosuccinate added in Example 5 was replaced with sodium diisotridecylsulfosuccinate [Perex OTP, manufactured by Kao Corporation, active ingredient 70].
%] In the same manner as in Example 5.

Example 9 The same procedure as in Example 8 was carried out except that sodium dioctylsulfosuccinate, which was added in 2 parts as the active ingredient in Example 8, was changed to 0.5 part as the active ingredient.

[0024]

Comparative Example 1 From the monomers used in Example 5, N-
The procedure was performed in the same manner as in Example 5, except that methylolacrylamide was omitted.

Comparative Example 2 With respect to the monomers used in Example 5, N-methylolacrylamide alone was increased to 6 parts, and emulsion polymerization was carried out without changing other conditions. During the polymerization, the reaction liquid rapidly increased in viscosity, and it was difficult to continue the polymerization, so the reaction was stopped. Therefore, the evaluation could not be performed. Table 1 shows only the composition.

[0025]

Comparative Examples 3 and 4 Comparative Example 3 was repeated except that sodium dioctylsulfosuccinate was added in an amount of 2 parts as an active ingredient in Example 5.
Comparative Example 5 was carried out in the same manner as in Example 5, except that 6 parts of the active ingredient was added.

Comparative Example 5 The same procedure as in Example 5 was carried out except that the pH of the water-dispersible resin composition was adjusted to 7.5.

[0026]

[Table 1]

[0027]

According to the binder for producing nonwoven fabric of the present invention, nonwoven fabrics having various textures can be produced, and the nonwoven fabric has excellent wet strength and large water absorption. Such performance is not found in the cellulosic nonwoven fabric, and the value of the present invention achieving this is great. Furthermore, the nonwoven fabric is hygienic with little generation of formaldehyde or elution of other water-soluble harmful substances.

 ──────────────────────────────────────────────────続 き Continued on front page F-term (reference) 4J002 BC041 BG041 BG051 BG061 EV236 FD316 GK02 HA07 4L047 AA08 AB02 BA15 BC07 CB07 CC01 CC10 4L055 AA07 AA08 AF09 AG36 AG63 AG71 AG73 AG97 AH29 AH33 AH37 FA30 GA32

Claims (3)

[Claims] 1. A copolymer resin obtained by copolymerizing a monomer mixture containing alkyl (meth) acrylate, styrene and N-methylol (meth) acrylamide or N-alkoxymethyl (meth) acrylamide as essential components. An aqueous resin dispersion in which fine particles are dispersed in an aqueous medium and the pH is 6.5 or less, wherein the copolymer resin 100
A binder for nonwoven fabric production, comprising an aqueous resin dispersion containing 0.3 to 5 parts by weight of a dialkyl sulfosuccinic acid-based surfactant per part by weight. 2. The copolymerization ratio of N-methylol (meth) acrylamide or N-alkoxymethyl (meth) acrylamide in the copolymerization for obtaining the copolymer resin is as follows:
The binder for producing a nonwoven fabric according to claim 1, wherein the binder is 0.2 to 5% by weight based on the total amount of all monomers. 3. A nonwoven fabric comprising the binder for producing a nonwoven fabric according to claim 1 or 2 and a cellulosic fiber.