JPH0694625B2 - Method for producing water-absorbent nonwoven fabric - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a water-absorbent nonwoven fabric. More specifically, water absorption properties that can be suitably used in fields requiring water retention and water retention such as paper diapers, sanitary napkins, bandages and other hygiene / medical materials, food fields, industrial fields, agricultural and forestry fields, civil engineering fields, etc. And a method for producing a water-absorbent nonwoven fabric having excellent flexibility.

(Prior Art) In recent years, as a method for obtaining a water-absorbent nonwoven fabric having a water-absorbent polymer fixed on the nonwoven fabric, after a monomer capable of forming a water-absorbent polymer by polymerization is attached onto the nonwoven fabric by a method such as spraying or coating, Various methods for polymerizing the monomer have been proposed (Japanese Patent Publication No. 57-500546 and Japanese Patent Application Laid-Open No. 61-275355).

However, according to these known methods, although the falling of the water-absorbent polymer from the nonwoven fabric can be prevented to some extent, the water-absorption characteristics and flexibility such as the water-absorption rate and the moisture-absorption rate of the obtained water-absorption nonwoven fabric are insufficient. In addition, it is difficult to industrially stably manufacture a water-absorbent nonwoven fabric that is satisfactory in terms of performance due to scattering of a monomer and uneven distribution during manufacturing.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned problems in industrially producing a water-absorbent nonwoven fabric having remarkably improved water-absorption characteristics and flexibility.

Therefore, an object of the present invention is to provide a method for industrially easily producing a water-absorbent nonwoven fabric in which a water-absorbent polymer is firmly fixed to the nonwoven fabric and the water-absorbent property is remarkably improved while maintaining the flexibility of the nonwoven fabric. To do.

(Means and Actions for Solving the Problem) The present inventors can solve the above-mentioned problems by adhering an aqueous monomer solution thickened to a specific viscosity to a specific nonwoven fabric by a specific method and then performing polymerization. They have found the present invention and reached the present invention.

That is, the present invention is to impregnate a nonwoven fabric (II) having a compression elastic modulus of 60% or more with an aqueous solution (I) containing a monomer capable of forming a water-absorbing polymer by polymerization and hydroxyethyl cellulose and having a viscosity increased to 100 cps or more. The resulting impregnated non-woven fabric is applied to the non-woven fabric (II) having a normal thickness of 15
The present invention relates to a method for producing a water-absorbent non-woven fabric, which comprises introducing the monomer into at least one pair of rolls having a gap of not more than%, passing the rolls through the rolls, and then polymerizing the monomer.

The monomer used in the present invention is one capable of forming a water-absorbing polymer which absorbs an aqueous liquid and swells by polymerizing, for example, a carboxyl group such as (meth) acrylic acid, maleic acid or salts thereof. Monomers included; sulfonic acid-containing monomers such as 2-acrylamido-2-methylpropane sulfonic acid, vinyl sulfonic acid, or salts thereof; amide group-containing monomers such as acrylamide; and one selected from these Alternatively, two or more kinds can be used as a main component. Particularly, acrylic acid or a salt thereof is preferably used, and the neutralization rate of acrylic acid is preferably 30 mol% or more from the viewpoint of water absorption performance.

A cross-linking agent may be included in the aqueous solution (I) in order to improve the water absorbing performance of the water absorbing polymer obtained by polymerizing the above-mentioned monomer. Examples of such a cross-linking agent include polyfunctional ethylenically unsaturated compounds such as methylenebis (meth) acrylamide, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, triallylamine, and trimethylolpropane tri (meth) acrylate. Monomers, polyglycidyl ethers such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether; polyols such as glycerin and pentaerythritol; polyamines such as ethylenediamine and polyethyleneimine; carboxyls such as polyvalent metal salts such as calcium chloride and aluminum sulfate. A compound having two or more functional groups capable of reacting with a functional group such as a group or a sulfone group can be preferably used. The addition amount of the crosslinking agent is preferably in the range of 0.01 to 10% by weight with respect to the monomer.

Further, a polymerization initiator for accelerating the polymerization of the monomer may be contained in the aqueous solution (I) in advance. Examples of such a polymerization initiator include persulfate in the case of thermal polymerization,
Hydrogen peroxide, a thermally decomposable water-soluble radical generator typified by 2,2-azobis (amidinopropane) dihydrochloride,
In the case of polymerization by light or ultraviolet rays, photosensitizers such as benzophenone and benzoin can be mentioned. The addition amount of these polymerization initiators is preferably in the range of 0.03 to 6% by weight with respect to the monomer.

The important point in the present invention is that the aqueous solution (1I) contains hydroxyethyl cellulose and the viscosity measured at 20 ° C. using a Brookfield rotational viscometer is increased to 100 cps or more. When the viscosity of the aqueous solution (I) is less than 100 cps, the aqueous solution (I) impregnated and adhered onto the nonwoven fabric (II) tends to be biased or dropped before the polymerization, which easily causes an increase in manufacturing cost and deterioration of working environment. In addition, the water-absorbent nonwoven fabric obtained is also not preferable because the water-absorbing property is insufficient.
That is, by using hydroxyethyl cellulose as a thickening agent, excellent effects can be obtained in terms of the thickening effect and the water absorption characteristics of the resulting water absorbent nonwoven fabric.

The concentration of the monomer in the thickened aqueous solution (I) containing the above monomer and hydroxyethyl cellulose is preferably in the range of 25 to 90% by weight, particularly 30 to 70% by weight. If it is less than 25% by weight, the water absorption capacity of the water absorbent nonwoven fabric tends to decrease, and if it is more than 90% by weight, the polymerization rate tends to decrease.

Further, the concentration of hydroxyethyl cellulose in the aqueous solution (I) may be a concentration sufficient to increase the viscosity of the aqueous solution (I) to 100 cps or more, and is appropriately determined depending on the type of hydroxyethyl cellulose. However, at a high concentration such that the viscosity of the aqueous solution (I) exceeds 50,000 cps, the impregnating property of the aqueous solution (I) into the nonwoven fabric (II) may be deteriorated and the water absorbing property of the water absorbent nonwoven fabric may be impaired.

In the present invention, selection of the non-woven fabric is important. The nonwoven fabric (II) used in the present invention must be bulky and have a high porosity, and in particular, it is essential that the compression elastic modulus is 60% or more. If the compression modulus is less than 60%, a water-absorbent nonwoven fabric having excellent water-absorbing properties and flexibility cannot be obtained.

The compressive elastic modulus in the present invention is defined according to the method described in Japanese Industrial Standard (JIS) L1096, and specifically defined by the following method. That is,
Collect 3 pieces of 5x5cm non-woven fabric test piece and stack 3 pieces with compression elasticity tester (5cm presser) to get initial load of 7g / cm
Measure the thickness (To) under ² , then set the load to 150 g / cm ² and leave it for 1 minute to measure the thickness (T ₁ ). After removing the load and leaving for 1 minute, the initial load is again measured under the same 7 g / cm ² to measure the thickness (T ₂ ), and the compression modulus (%) is calculated by the following formula. The compression elastic modulus was measured 5 times and expressed as an average value.

Here, To: Thickness when an initial load is applied (mm) T ₁ : Thickness when a load of 150 g / cm ² is applied (mm) T ₂ : When returned to the same 7 g / cm ² as the initial load Thickness (mm) Specific examples of such a non-woven fabric (II) include a fineness of 2 to 15
There is a non-woven fabric obtained by forming a web by carding with fibers containing denier (preferably 4 to 10 denier) polyethylene, polypropylene, polyester, polyamide, or a mixed fiber of these as essential constituents, and then stabilizing the shape. As the shape stabilizing method, known techniques such as heat fusion, adhesive bonding, and fiber entanglement can be adopted. The basis weight of the nonwoven fabric (II) used in the present invention, 15 to 100 / m ^2, in particular in the range of 20 to 60 g / m ² is preferred.

As a method of impregnating and adhering the aqueous solution (I) containing a monomer and hydroxyethyl cellulose to the nonwoven fabric (II), the aqueous solution (I) can be sufficiently impregnated so as to be substantially uniform in the thickness direction of the nonwoven fabric (II). There is no particular limitation so long as it is an aqueous solution (I), for example, using an impregnation roll coater
The method of applying and impregnating the non-woven fabric (II) to the non-woven fabric (II), the method of dipping the non-woven fabric (II) in the aqueous solution (I) and impregnating the non-woven fabric (II), and the like are thrown. If the impregnation of the aqueous solution (I) into the nonwoven fabric (II) is insufficient, a water absorbent nonwoven fabric having excellent water absorbing properties cannot be obtained.

On the other hand, in the method using spraying or spraying or the printing method using a printing roller or screen, the aqueous solution (I) adheres only to the surface portion of the nonwoven fabric (II) to which the aqueous solution (I) has been supplied. And impregnation becomes insufficient, which is not preferable.

In the present invention, the nonwoven fabric impregnated with the aqueous solution (I) is 15% or less of the normal thickness of the nonwoven fabric (II) after the aqueous solution (I) is impregnated and adhered to the nonwoven fabric (II), or at the same time when the impregnated and adhered solution is formed. It is important that the aqueous solution (I) is introduced into at least one pair of rolls having a gap of 1, the aqueous solution (I) is squeezed through the rolls, and then the polymerization is carried out. On this occasion,
When the roll gap is larger than 15% of the normal thickness of the nonwoven fabric (II), the water absorbing property and flexibility of the resulting water absorbent nonwoven fabric are remarkably inferior, which is not preferable.
The linear velocity at the time of passing between the rolls may be appropriately determined, but from the viewpoint of productivity and water absorption performance, it is preferably in the range of 0.1 to 100 m / min. In order to impregnate the aqueous solution (I) into the nonwoven fabric (II) and guide the impregnated nonwoven fabric to the rolls to pass between the rolls, the nonwoven fabric (II) should have a thickness of 15% or less of the normal state. It suffices to supply a sufficient amount of the aqueous solution (I) to the roll gap inlet side of the nonwoven fabric that passes through the gaps of the rolls having gaps.

In order to polymerize the monomer attached to the nonwoven fabric in the present invention, a known method used in producing a water-absorbent polymer is used, for example, a thermal polymerization method, an ultraviolet polymerization method, a radiation polymerization method using an electron beam, etc. Can be adopted,
They can also be used in combination. The polymerization is preferably carried out in a polymerization-inert atmosphere such as nitrogen. Further, after the polymerization, water contained in the water-absorbent nonwoven fabric may be dried and removed by a method such as hot air, microwave, infrared ray or the like, if necessary.

(Effect of the invention) According to the method of the present invention, the water-absorbent polymer is uniformly distributed and fixed in the nonwoven fabric in the state where the swelling-allowed voids are secured, and therefore the water-absorbing polymer is absorbed without impairing the original flexibility of the nonwoven fabric. It is possible to manufacture a water-absorbent non-woven fabric having significantly improved properties with good productivity and without deteriorating the working environment.

The water-absorbent nonwoven fabric thus obtained is excellent in flexibility, water absorption / desorption rate, and water absorption rate, for example, sanitary materials and medical materials such as paper diapers and sanitary napkins, and agricultural and horticultural applications.
It can be preferably used for applications requiring water retention and water absorption (wetness) such as civil engineering, food, and other industrial materials.

(Examples) Hereinafter, the present invention will be described with reference to Examples. The water absorption characteristics and flexibility of the water absorbent nonwoven fabric described in the examples were evaluated by the following methods using a sample obtained by drying the water absorbent nonwoven fabric under reduced pressure at 100 ° C. for 30 minutes. Moreover, all parts in the examples represent parts by weight.

(1) Water absorption characteristics A sample (1 g) cut into 5 cm x 5 cm was immersed in a sufficient amount (about 1 liter) of deionized water for a predetermined time, then drained on an 18-mesh wire net, and the sample weight after absorption was measured. The value obtained by dividing by the sample weight before water absorption was defined as the water absorption capacity (g / g). This water absorption ratio was measured for samples immersed in deionized water for 1 minute, 3 minutes and 5 minutes, and water absorption characteristics such as water absorption amount and water absorption speed were evaluated by them.

(2) Flexibility A sensory test based on the feel of the hand was conducted, and the following criteria were applied.
It was evaluated in two stages.

◯: No resistance was felt when the sample was squeezed in the hand, and the sample had a good feel.

×: Resistance was felt when the sample was squeezed in the hand,
It felt uncomfortable.

In addition, using a water-absorbent nonwoven fabric and a sample obtained by cutting each of the nonwoven fabrics used to create it into 2 cm × 15 cm, JIS JIS
Measure the 45 ° cantilever value (cm) according to L1096,
The flexibility was evaluated by the difference in the cantilever value between the water-absorbent nonwoven fabric and the nonwoven fabric. The smaller the degree of flexibility, the better the flexibility of the water absorbent nonwoven fabric.

Example 1 Aqueous solution of acrylic acid monomer consisting of 25 mol% acrylic acid and 75 mol% sodium acrylate (monomer concentration
0.5% by weight of sodium persulfate (37% by weight) (to acrylic acid type monomer) and methylenebisacrylamide
0.17 wt% (to acrylic acid type monomer) was mixed and dissolved. Next, 100 parts of this monomer aqueous solution was added to hydroxyethyl cellulose (manufactured by Daicel Chemical Industries, Ltd. EP-85
0) 0.75 parts were mixed and dissolved to prepare an aqueous solution (1). The viscosity of this aqueous solution (1) was 6900 cps when measured with a Brookfield viscometer (rotor rotation speed 3 rpm) at 20 ° (same in the following examples).

Next, a polyester nonwoven fabric having a basis weight of 30 g / cm ² , a compression elastic modulus of 85% and a thickness of 3 mm is immersed in the aqueous solution (1) to prepare the aqueous solution (1).
After impregnating the non-woven fabric with the non-woven fabric, the non-woven fabric is passed through a pair of rolls with a roll gap of 0.25 mm and a roll diameter of 50 mm at a linear velocity of 3 m / min to obtain a non-woven fabric with an adhesion amount of the aqueous solution (1) of 150 g / m ^2. It was

The non-woven fabric to which this aqueous solution (1) has adhered is treated under a nitrogen atmosphere for 100
The water-absorbent nonwoven fabric (1) was obtained by heating to ° C and polymerizing the monomer adhering to the nonwoven fabric.

Example 2 A water absorbent nonwoven fabric (2) was obtained in the same manner as in Example 1 except that the roll gap was 0.09 mm. The amount of the aqueous solution (1) deposited in this case was 60 g / m ² .

Example 3 A polyester nonwoven fabric having a basis weight of 20 g / m ² , a compressive elastic modulus of 65% and a thickness of 1 mm was immersed in the aqueous solution (1) obtained in Example 1, and then the nonwoven fabric impregnated with the aqueous solution (1) was rolled. It was guided to a pair of rolls having a roll diameter of 50 mm with a gap of 0.12 mm and passed between the rolls at a linear velocity of 3 m / min to obtain a non-woven fabric having an adhesion amount of the aqueous solution (1) of 95 g / m ² .

The non-woven fabric to which this aqueous solution (1) has adhered is treated under a nitrogen atmosphere for 100
The mixture was heated to ℃, and the monomers adhering to the nonwoven fabric were combined to obtain a water-absorbent nonwoven fabric (3).

Example 4 A water absorbent nonwoven fabric (4) was obtained in the same manner as in Example 1 except that the amount of methylenebisacrylamide added in Example 1 was 0.1% by weight (based on the acrylic acid type monomer). The viscosity of the aqueous solution containing the monomer and hydroxyethyl cellulose and the amount of the aqueous solution deposited in this case were the same as in Example 1.

Example 5 An aqueous solution (2) containing a monomer and hydroxyethyl cellulose was obtained in the same manner as in Example 1 except that the amount of hydroxyethyl cellulose used in Example 1 was changed to 1.5 parts. The viscosity of this aqueous solution (2) was 25000 cps.

Next, a polyester nonwoven fabric having a basis weight of 32 g / m ² , a compression elastic modulus of 82% and a thickness of 3 mm is immersed in the aqueous solution (2) to prepare the aqueous solution (2).
After impregnating the non-woven fabric with the non-woven fabric, pass it through a pair of rolls with a roll gap of 0.07 mm and a roll diameter of 50 mm at a linear velocity of 10 m / min to obtain a non-woven fabric with an aqueous solution (2) adhesion of 27 g / m ^2. It was

The non-woven fabric to which this aqueous solution (2) is attached is put under a nitrogen atmosphere for 100
The mixture was heated to ° C to polymerize the monomer adhering to the nonwoven fabric to obtain a water absorbent nonwoven fabric (5).

Example 6 25 mol% acrylic acid and 75 mol% potassium acrylate
An aqueous solution of acrylic acid-based monomer consisting of (monomer concentration
0.5 wt% of potassium persulfate (to acrylic acid type monomer) and 0.1 wt% of diethylene glycol diacrylate (to acrymatic acid type monomer) were mixed and dissolved in 45 wt%). Next, 100 parts of this monomer aqueous solution was added to hydroxyethyl cellulose (manufactured by Daicel Chemical Industries, Ltd. EP-
850) 0.45 parts were mixed and dissolved to prepare an aqueous solution (3).
The viscosity of this aqueous solution (3) was 600 cps.

Next, a polyester-polypropylene non-woven fabric with a basis weight of 30 g / m ² , a compression elastic modulus of 90%, and a thickness of 5 mm was installed horizontally on the left and right with a roll gap of 0.1 mm and a line with a roll diameter of 100 mm. While passing the solution at a speed of 5 m / min, the aqueous solution (3) was supplied to an inlet position where the nonwoven fabric was wound between rolls to obtain a nonwoven fabric having an adhesion amount of the aqueous solution (3) of 70 g / m ² .

The non-woven fabric to which this aqueous solution (3) has adhered is treated under a nitrogen atmosphere for 100
The mixture was heated to ° C to polymerize the monomers adhering to the non-woven fabric to obtain a water-absorbent non-woven fabric (6).

Example 7 Instead of sodium persulfate in Example 1, 2,2'-
1% by weight of azobis (2-amidinopropane) dihydrochloride
(Acrylic acid-based monomer) An aqueous solution (4) containing a monomer and hydroxyethyl cellulose was obtained in the same manner as in Example 1 except that the monomer was used. The viscosity of this aqueous solution (4) was 6900 cps.

Next, a polyester-polypropylene non-woven fabric having a basis weight of 35 g / m ² , a compression elastic modulus of 75% and a thickness of 5 mm is dipped in the aqueous solution (4) to impregnate and adhere the aqueous solution (4) to a roll with a roll gap of 0.1 mm. Linear velocity between a pair of rolls with a diameter of 50 mm 1
The solution was passed through at a rate of m / min to obtain a nonwoven fabric having an amount of the aqueous solution (4) attached of 200 g / m ² .

The non-woven fabric to which this aqueous solution (4) has adhered is put under a nitrogen atmosphere for 120
The mixture was heated to ° C to polymerize the monomer adhering to the nonwoven fabric to obtain a water absorbent nonwoven fabric (7).

Comparative Example 1 A comparative water absorbent nonwoven fabric (1) was obtained in the same manner as in Example 1 except that the roll gap was 0.5 mm. In this case, the amount of the aqueous solution (1) attached was 270 g / m ² .

Comparative Example 2 A comparative water absorbent nonwoven fabric (2) was obtained in the same manner as in Example 3 except that a polyester nonwoven fabric having a basis weight of 20 g / m ² , a compression elastic modulus of 50% and a thickness of 1 mm was used as the nonwoven fabric. . In this case, the adhesion amount of the aqueous solution (1) is 100 g / m ²
Met.

Comparative Example 3 A comparative aqueous solution (1) was obtained in the same manner as in Example 1 except that the amount of hydroxyethyl cellulose used was 0.18 part. The viscosity of this comparative aqueous solution (1) was 50.
It was cps.

Next, a comparative water absorbent nonwoven fabric (3) was obtained in the same manner as in Example 3 except that the comparative aqueous solution (1) was used instead of the aqueous solution (1) in Example 3. The amount of the comparative aqueous solution (1) attached in this case was 90 g / m ² .

Comparative Example 4 0.5% by weight of sodium persulfate (to acrylic acid type monomer) and methylenebisacrylamide were added to an aqueous solution of an acrylic acid type monomer consisting of 50% by mole acrylic acid and 50% by mole sodium acrylate (monomer concentration 50% by weight). 0.17 wt% (to acrylic acid type monomer) was mixed and dissolved. Next, 1.5 parts of polyvinyl alcohol (manufactured by Kuraray Co., Ltd.) was mixed and dissolved in 100 parts of this monomer aqueous solution to prepare a comparative aqueous solution (2). The viscosity of this comparative aqueous solution (2) was 50 cps.

Next, a comparative water absorbent nonwoven fabric (4) was obtained in the same manner as in Example 3 except that the comparative aqueous solution (2) was used instead of the aqueous solution (1) in Example 3. The amount of the comparative aqueous solution (2) attached in this case was 90 g / m ² .

Comparative Example 5 0.5% by weight of sodium persulfate (to the acrylic acid type monomer) and methylenebisacrylamide were added to an aqueous solution of an acrylic acid type monomer consisting of 25% by mole of acrylic acid and 75% by mole of sodium acrylate (monomer concentration 30% by weight). 0.17 wt% (to acrylic acid type monomer) was mixed and dissolved. Next, 7.5 parts of polyvinyl alcohol (Kuraray Co., Ltd.) was mixed and dissolved in 100 parts of this monomer aqueous solution to prepare a comparative aqueous solution (3). The viscosity of this comparative aqueous solution (3) was 740 cps.

Next, a comparative water absorbent nonwoven fabric (5) was obtained in the same manner as in Example 3 except that the comparative aqueous solution (3) was used instead of the aqueous solution (1) in Example 3. The amount of the comparative aqueous solution (3) attached in this case was 90 g / m ² .

Example 8 Water absorbent non-woven fabrics (1) to (7) and comparative water absorbent non-woven fabrics (1) to 1 obtained in Examples 1 to 7 and Comparative Examples 1 to 5
With respect to (5), the water absorption characteristics and flexibility were evaluated by the methods described above, and the results are shown in Table 1.

Front page continuation (72) Inventor Tadao Shimomura 5-8 Nishimitabicho, Suita City, Osaka Prefecture Central Research Laboratory, Nippon Shokubai Chemical Co., Ltd. (56) Reference JP-A-63-105044 (JP, A) 63-34661 (JP, Y2)

Claims (2)

[Claims] 1. A compressive modulus of elasticity of an aqueous solution (I) containing a monomer capable of forming a water-absorbing polymer by polymerization and hydroxyethyl cellulose and having a viscosity of 100 cps or more.
% Of the nonwoven fabric (II) is impregnated and adhered, and the resulting impregnated nonwoven fabric is guided to at least one pair of rolls having a gap of 15% or less of the normal thickness of the nonwoven fabric (II) and passed between the rolls. A method for producing a water-absorbent non-woven fabric, which comprises subjecting the monomer to polymerization after being swollen. 2. The method for producing a water-absorbent nonwoven fabric according to claim 1, wherein the monomer capable of forming a water-absorbent polymer by polymerization has acrylic acid or a salt thereof as a main component.