JPH11350396A - Nonwoven fabric, separator for battery and filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonwoven fabric useful for a separator for battery, a filter, etc., by including a conjugate fiber (fiber A) splittable into plural ultrafine fibers (fiber B) and partly splitting the fiber A into the fibers B by a specific treatment. SOLUTION: A web produced by wet process and containing at least one kind of conjugate fiber (fiber A) splittable into two or more ultrafine fibers (fiber B) is subjected to heat-welding treatment and pressed with a linear pressing member having irregular surface to effect the splitting of at least a part of the fiber A into the fiber B and obtain the objective nonwoven fabric. The fiber A is preferably composed of two or more kinds of resin components having a melting point difference of >=10 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a nonwoven fabric, a battery separator and a filter.

[0002]

[Prior art]

[0003] The nonwoven fabric made of microfiber has a large specific surface area of the fiber and a small fiber diameter.
It has excellent wiping properties, concealing properties, and flexibility, and is suitably used for battery separators, filters, interlinings, masks, wipers, sanitary materials, and the like. Methods for obtaining ultrafine fibers are roughly classified into a sea-island method, a straight spinning method, and a division method.

[0004] Non-woven fabrics using sea-island type ultrafine fibers are disclosed in JP-B-45-6297 and JP-B-45-9907.
Non-woven fabrics disclosed in Japanese Patent Publication No. Sho 60-7723 and the like are known, but in order to obtain a non-woven fabric consisting of the sea-island type ultrafine fibers, a solvent for dissolving the sheath component must be used. In addition, equipment for the melting process must be installed.

[0005] In the case of obtaining a nonwoven fabric made of a direct spinning type ultrafine fiber, it is difficult to operate stably for a long time.
In order to stably obtain a nonwoven fabric having a uniform basis weight, it is necessary to use a plurality of spinning machines, which has disadvantages that the production equipment becomes large and the cost is high. Further, the spun fiber has a disadvantage that it is difficult to increase the mechanical strength of the nonwoven fabric because the fiber has a small diameter and is not oriented. For example, battery separators are required to be thinner in light of the need for lighter batteries and higher capacity.However, in the direct spinning method, the mechanical strength of the nonwoven fabric is low. Difficult to respond.

[0006] Non-woven fabrics made of ultrafine fibers of the split type are disclosed in JP-A-4-185793 and JP-A-5-21465.
No. 3 discloses an example in which a splittable conjugate fiber is divided by a hydroentanglement treatment. In this case, the mechanical strength of the nonwoven fabric can be increased by entanglement of the fibers at the same time as the division, and a nonwoven fabric with an excellent texture can be obtained. Therefore, this method is suitable as a method for obtaining a nonwoven fabric made of ultrafine fibers. However, there are disadvantages in that expensive equipment must be provided and energy cost is required to generate a high pressure in the fluid. Furthermore, in the case of a nonwoven fabric having a low basis weight, there is a problem that the hydroentanglement marks become pinholes and hinder the separability and concealability of the nonwoven fabric. In addition, the hydroentanglement process requires a drying step, and thus has a problem that the energy cost is higher.

[0007]

An object of the present invention is to provide a nonwoven fabric made of ultrafine fibers of a split system, and a battery separator and a filter using the nonwoven fabric. An object of the present invention is to provide a nonwoven fabric, a battery separator, and a filter.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following invention.

(1) A wet papermaking web containing at least one kind of splittable conjugate fiber (fiber A) which can be split into at least two or more ultrafine fibers (fiber B) is subjected to a heat fusion treatment,
Next, a non-woven fabric is characterized in that at least a part of the fiber A is divided into the fiber B by being subjected to a pressure treatment by a linear pressure member having irregularities.

(2) The nonwoven fabric according to the above (1), wherein the fiber A comprises two or more kinds of resin components.

(3) The nonwoven fabric according to the above (2), wherein the difference in melting point between the resin component having the lowest melting point and the resin component having the highest melting point in the fiber A is 10 ° C. or more.

(4) The above-mentioned (3), wherein the web contains heat-fusible fibers (fibers C) containing at least a resin component having a melting point lower than that of the fiber A having the lowest melting point. Nonwoven.

(5) The nonwoven fabric according to the above (4), wherein at least a part of the resin component having the lowest melting point of the fiber C and / or the fiber A is fused by a heat fusion treatment.

(6) The nonwoven fabric according to the above (1) to (5), wherein the fineness of the fiber B is 0.5 denier or less.

(7) The nonwoven fabric according to any one of the above (1) to (6), which has been subjected to a hydrophilic treatment.

(8) The nonwoven fabric according to the above (7), wherein the hydrophilic treatment is a graft treatment.

(9) A battery separator comprising the nonwoven fabric according to any one of (1) to (8).

(10) A filter comprising the nonwoven fabric according to any one of the above (1) to (8).

The nonwoven fabric (1) of the present invention is a wet-laid paper web containing at least one kind of splittable conjugate fiber (fiber A) which can be split into at least two or more ultrafine fibers (fiber B). By performing the pressure treatment by the pressurizing body, at least a part of the fiber A is divided into the fiber B, so that energy cost is not required as in the hydroentanglement treatment, and defects such as pinholes are formed. Never be.
In addition, since the mechanical strength of the wet papermaking web is increased by performing the heat fusion treatment before the pressure treatment, the web is not broken by the pressure treatment.

As in the nonwoven fabric (2) of the present invention, when the fiber A is composed of two or more kinds of resin components, hydrophilicity,
It is possible to obtain a nonwoven fabric having various properties such as hydrophobicity, heat fusion property, heat resistance and the like. Further, for example, as in the nonwoven fabric (3) of the present invention, if the difference in melting point between the resin component having the lowest melting point and the resin component having the highest melting point in the fiber A is 10 ° C. or more, the thermal melting before the pressure treatment is performed. By the bonding treatment, only the resin of the low melting point component can be thermally fused. When the resin of the low melting point component and the resin of the high melting point component are heat-sealed together, the fiber A may not be easily divided by the pressure treatment.

Like the nonwoven fabric (4) of the present invention, the web contains heat-fusible fibers (hereinafter referred to as fibers C) containing at least a resin component having a melting point equal to or lower than the resin component having the lowest melting point of the fibers A. Thus, as in the nonwoven fabric (5) of the present invention, the fiber C and / or the fiber A
At least a part of the resin component having the lowest melting point can be fused. Therefore, the mechanical strength of the web becomes higher, and the resistance to the pressure treatment can be increased.

Further, as in the nonwoven fabric (6) of the present invention, when the fineness of the fiber B after division is 0.5 denier or less, the nonwoven fabric has good properties such as separability and concealability. .

Since the non-woven fabric (7) of the present invention has been subjected to a hydrophilic treatment, it can be suitably used for battery separators, filters and the like. As the hydrophilic treatment,
A graft treatment is preferred because hydrophilicity is maintained for a long time.

The battery separator of the present invention is made of the above-mentioned non-woven fabric, and therefore has excellent electrolytic solution retention. The filter of the present invention is also made of the above-described non-woven fabric, and thus has excellent separability.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The splittable conjugate fiber (fiber A) according to the nonwoven fabric of the present invention can be split into two or more ultrafine fibers (fiber B). As a component constituting the fiber A, an organic component such as polyester, polyolefin, polyacrylonitrile, polyvinyl alcohol, polyamide, and regenerated cellulose is used, and these components can be used in combination. Also, even with the same components, the degree of polymerization can be changed,
It can be used by mixing with other components or by performing chemical modification. For example, a combination of similar resins of polypropylene and polyethylene is also possible.

The nonwoven fabric of the present invention has a fiber A
At least a part of the resin component having the lowest melting point and / or at least a part of the fiber C among the resin components constituting the fiber A are fused. Due to the pressure treatment, it is difficult to split the fibers into fibers B. Therefore, the melting point difference between the resin component having the lowest melting point and the resin component having the highest melting point among the resin components constituting the fiber A is 10 ° C. or more so that the entire resin component constituting the fiber A is not fused. As described above, it is preferable to select the resin component of the fiber A. For example, when the fiber A is composed of two types of resin components, combinations of polyamide and polyester, polyamide and polyolefin, polyester and polyolefin, and polypropylene and polyethylene can be mentioned.

The cross-sectional shape of the fiber A according to the nonwoven fabric of the present invention is, for example, a chrysanthemum-shaped one in which one resin component 1 shown in FIGS. 3 (e), a resin component 1 and another resin component 2 alternately laminated in layers can be used.

The cross-sectional shape of the fiber B is a wedge shape, a substantially elliptical shape, a circular shape, an elliptical shape, a flat shape, or the like. The fineness of the fiber B is preferably 0.5 denier or less, and the average fiber diameter thereof is preferably 0.1 to 6 μm in terms of circular cross section. If the average fiber diameter is less than 0.1 μm, the mechanical strength of the nonwoven fabric decreases. When the average fiber diameter exceeds 6 μm, the specific surface area decreases,
Feeling worse.

The fineness of the fiber A itself used in the present invention is 0.1.
It is 5 to 8 denier, more preferably 0.5 to 6 denier. When the fiber A having a thickness of more than 8 deniers is used, the pressure is not large enough to prevent the web from being broken in the pressure treatment step, and the pressure does not reach the center of the fiber.

In the nonwoven fabric of the present invention, in addition to the fiber A,
For example, recycled fiber such as rayon, semi-synthetic fiber such as acetate, nylon, vinylon, vinylidene, polyvinyl chloride, polyester, acrylic, polyethylene,
Polyolefins such as polypropylene, synthetic fibers such as polyurethane, polychloral, or ethylene-vinyl alcohol copolymer, vegetable fibers such as cotton, and animal fibers such as wool can be used. In particular, in order to increase the mechanical strength of the nonwoven fabric by heat fusion processing,
It is preferable to use a heat-fusible fiber (fiber C) composed of a single resin component or a plurality of resin components such as a core-sheath type, a parallel type, and an eccentric type.

The fibers C related to the nonwoven fabric of the present invention are fibers A
It is preferable to contain at least a resin component having a melting point equal to or lower than the resin component having the lowest melting point. More preferably, the fiber A contains a resin component having a melting point lower by 10 ° C. or more than the resin component having the lowest melting point. That is,
By performing the heat-sealing treatment at a temperature lower than the melting point of the resin component having the lowest melting point of the fiber A and higher than the melting point of the resin component of the fiber C, the fiber A is not heat-sealed.
The division into the fibers B is facilitated.

In the nonwoven fabric (5) of the present invention, the wet papermaking web is subjected to a heat fusion treatment, and at least a part of the resin having the lowest melting point of the fiber C and / or the fiber A is fused. Due to this heat fusion, the mechanical strength of the nonwoven fabric is increased, and in the pressure treatment which is the process of dividing the fiber A,
It is possible to obtain ultrafine fibers (fiber B) without breaking the web.

The web of the present invention is formed by a wet papermaking method. The wet papermaking method can obtain a more uniform and dense web.

In the nonwoven fabric of the present invention, the pressure treatment for dividing the fibers A is performed using a linear pressure member having irregularities. For example, (a) a pressure treatment using a roll pair including at least one roll having irregularities (b) a pressure treatment in which a web is sandwiched between metal meshes and the like and a load is applied using a calendar roll and the like (c) the web is rolled and conveyed A buckling process for buckling the fiber A by applying stresses in the direction perpendicular to the conveying direction and in the opposite direction from the upper surface of the web while conveying the web, and applying a load in the thickness direction. Buckling form imparting processing for sandwiching and forming a buckling form (e) Processing for continuously imparting a buckling form by ironing the web with edges or the like.

As a roll pair that can be used in the pressure treatment (a), a roll pair as shown in FIG. 1 can be mentioned. At least one of the rolls forming the roll pair may have irregularities. The shape of the irregularities may be either rectangular or round.

The irregularities may be continuous or intermittent in the direction parallel to the roller axis as shown in FIGS. 2A and 2B, and the arrangement may be various such as parallel, spiral, random, and the like. Can be selected.

The pressure treatment for the nonwoven fabric of the present invention is preferably performed at a temperature lower than the melting point of the resin component forming the fibers A and C. At temperatures above the melting point, resolution may be hindered. Further, by performing the pressure treatment a plurality of times, the fiber A can be divided more efficiently.

Fiber A is completely converted to fiber B by pressure treatment.
The fibers that are being divided into fibers B may be mixed. Examples of the fiber in the state of being divided include: (a) a fiber separated from the tip, such as pine needles; (b) a fiber with its antinode separated; (c) a fiber B from the fiber A (D) A fiber in which the fibers in the states (a) to (c) are mixed may be mentioned.

The hydrophilic treatment relating to the nonwoven fabric (7) of the present invention means a graft treatment, a sulfonation treatment, a surfactant immersion treatment, a corona treatment, a plasma treatment, a fluorine gas treatment, a resin coating treatment and the like. Among these treatments, a graft treatment in which hydrophilicity is maintained semi-permanently is particularly preferable.

Examples of the grafting method relating to the nonwoven fabric (8) of the present invention include a method in which the nonwoven fabric is immersed in a solution containing a monomer and a polymerization initiator and then heated, and a method in which the monomer is applied to the nonwoven fabric and then irradiated with radiation. There is a method of irradiating the non-woven fabric with a monomer after irradiating the non-woven fabric, a method of immersing the non-woven fabric in a solution containing a sensitizer and the monomer, and then irradiating the non-woven fabric with ultraviolet rays. In addition, it is possible to efficiently impart hydrophilicity to the nonwoven fabric.

Monomers that can be used in the grafting process for the nonwoven fabric of the present invention include (meth) acrylic acid, crotonic acid, vinyl acetic acid, maleic acid, fumaric acid,
Unsaturated carboxylic acids such as itaconic acid and derivatives thereof can be used as monomers.

Examples of sensitizers that can be used in the graft polymerization treatment with ultraviolet light include benzoin butyl ether, benzoin ethyl ether, benzyl dimethyl ketal, diethoxyacetophenone, acyloxime ester, chlorinated acetophenone, hydroxyacetophenone, and acylphosphine oxide. Sensitizers having an acetophenone structure, benzophenone, Michler's ketone,
Examples thereof include sensitizers having a thioxanson structure such as dibenzosuberone, 2-ethylanthraquinone, isobutylthioxanson, and benzyl; peroxides such as benzoyl peroxide; and metal ions.

The graft polymerization treatment with ultraviolet rays is preferably performed under deoxygenation. Under deoxygenation, ultraviolet light irradiated with nitrogen is light in the region of 200 to 400 nm, the sensitizer is excited by receiving this light, pulls out hydrogen from the polyolefin constituting the fibers of the nonwoven fabric, and generates radicals. Form. The generated radical reacts with the above monomer to initiate polymerization. It is preferable that the monomer not contributing to the graft reaction and the homopolymer not chemically bonded to the fiber be removed through a washing step after polymerization.

As a medium for the solution or dispersion in which the monomer and the sensitizer are dissolved, water can be used advantageously. If the solubility of the monomer or sensitizer in water is low,
Various organic solvents can be added.

The nonwoven fabric of the present invention has no defects such as pinholes unlike the nonwoven fabric subjected to the hydroentanglement treatment. Therefore, it is particularly suitable for a nonwoven fabric made of ultrafine fibers having a low basis weight.

Since the battery separator of the present invention comprises the nonwoven fabric of the present invention, it has excellent concealing properties. Therefore, the battery separator of the present invention is a primary battery such as an alkaline manganese battery, a mercury battery, a silver oxide battery, an air battery, a nickel-cadmium battery, a silver-zinc battery, a silver-cadmium battery, a nickel-hydrogen battery, and a nickel-hydrogen battery. -It can be suitably used for secondary batteries such as zinc batteries, rechargeable alkaline manganese batteries, and lithium batteries. In addition, the nonwoven fabric (7) of the present invention that has been subjected to the hydrophilization treatment has a good affinity for the electrolytic solution, and can be more suitably used for a battery separator.

Since the filter of the present invention is composed of the above-mentioned nonwoven fabric, it has excellent separability. Therefore, it can be used as a solid / solid separation filter, a solid / liquid separation filter, a solid / gas separation filter, a liquid / liquid separation filter, a liquid / gas separation filter, a gas / gas separation filter, and the like. In particular, since the nonwoven fabric (8) of the present invention has ion exchange ability, it can be suitably used as a chemical filter.

Since the nonwoven fabric of the present invention contains ultrafine fibers, it is excellent in separability, liquid retention, wiping, hiding, flexibility and the like. Therefore, battery separator,
In addition to filters, it can be suitably used for interlining, cotton filling, masks, base cloth for patches, leakproof sheets, wipers, ceiling materials for automobiles and the like, wallpaper, and the like. Various post-processing such as compounding with other materials can be performed to suit these uses.

[0049]

The present invention will be described below in detail with reference to examples.

Example 1 Production of a wet papermaking web A fineness of 2 denier composed of polypropylene and high density polyethylene (melting point 128 ° C.) having a cross-sectional shape as shown in FIG. .5μ
m), a core-sheath fiber having a denier of 2.0 denier and a fiber length of 10 mm comprising 65 parts by weight of a splittable conjugate fiber having a fiber length of 5 mm, polypropylene as a core component and low-density polyethylene as a sheath component (melting point: 110 ° C.) 30 parts by weight and 5 parts by weight of hot water-soluble polyvinyl alcohol fiber (VPW103; manufactured by Kuraray) impregnated with a 1% by weight solution of a nonionic surfactant are put into water, and stirred for 3 minutes by a high-speed mixer. After the fibers were disintegrated, the mixture was gently stirred in a chest equipped with a reciprocating rotary stirrer (Agitator, manufactured by Shimazaki Seisakusho). Then, the polyacrylamide was quickly added to 0.1.
A 1% by weight aqueous solution (viscosity agent) was appropriately added, followed by gentle stirring to prepare a uniform slurry. Using the slurry, to produce a width 50 cm, a basis weight of 50 g / ^{m 2} wet papermaking web with a round net paper machine.

[0051] The heat-sealing the wet papermaking web through the 120 ℃ of hot-air dryer,
Only the low-density polyethylene component of the core-sheath fiber was fused.
The fiber cross section of the web after the heat fusion treatment was observed with a scanning electron microscope (FIG. 4).

Pressure Treatment The wet paper web subjected to the heat fusion treatment was subjected to a pressure treatment at room temperature with a pair of rolls shown in FIG. 1 to obtain a nonwoven fabric. The fiber cross section of the nonwoven fabric was observed with a scanning electron microscope, and it was confirmed that the splittable conjugate fiber was split (FIG. 5). In addition, it was confirmed visually that there was no defect such as a pinhole. The conditions for the pressure treatment are as follows. Roll pair: metal roll / metal roll Linear pressure: 40 kg / cm ²

Example 2 Hydrophilic treatment The nonwoven fabric obtained in Example 1 was mixed with 1 part by weight of polyoxyethylene alkylpropenyl phenyl ether (NE-10: manufactured by Asahi Denka), 50 parts by weight of acrylic acid, and 0.5 parts by weight of benzophenone. Parts, 49 parts by weight of ion-exchanged water, immersed in low-pressure ultraviolet light for 1 minute using a low-pressure mercury lamp under deoxygenation, and then washed with ion-exchanged water and subjected to graft polymerization. A nonwoven fabric subjected to a hydrophilic treatment was obtained. The nonwoven fabric was used as a battery separator to produce a nickel-hydrogen secondary battery. This battery had a high capacity and a long life.

Example 3 Production of a wet papermaking web A fineness of 3 denier composed of polypropylene and an ethylene-vinyl alcohol copolymer having a cross-sectional shape as shown in FIG. 3 (a), 0.2 denier after fiber division (3. 9μ
m), 77 parts by weight of a splittable conjugate fiber having a fiber length of 6 mm, a fineness of 0.7 denier composed of polypropylene as a core component and polyethylene as a sheath component (melting point 128 ° C.), and 19 wt. Part is impregnated with a 1% by weight solution of a nonionic surfactant, and hot water-soluble polyvinyl alcohol fiber (VPW103; manufactured by Kuraray) 3
A part obtained by impregnating a part by weight of a 1% by weight solution of a nonionic surfactant is poured into water, and the mixture is stirred with a high-speed mixer for 3 minutes to disintegrate the fibers. Then, a reciprocating rotary stirrer (Agiter, Shimazaki Seisakusho) Gently stirred in a chest fitted with the same. Next, a 0.1% by weight aqueous solution of polyacrylamide (viscosity agent) was promptly added, followed by gentle stirring to prepare a uniform slurry. Using the slurry, a wet papermaking web having a width of 50 cm and a basis weight of 50 g / m ² was produced by a round paper machine.

[0055] through a heat-sealing the wet papermaking web to 140 ℃ of hot-air dryer,
Only the polyethylene component of the core-sheath fiber was fused.

[0056] The roll pair of uneven rolls shown in wet papermaking web after pressure treatment heat-sealing at a 1 changed to 2 (2), in the pressure treatment applied at room temperature, to obtain a nonwoven fabric. The fiber cross section of the nonwoven fabric was observed with a scanning electron microscope, and it was confirmed that the splittable conjugate fiber was split. In addition, it was confirmed visually that there was no defect such as a pinhole. The conditions for the pressure treatment are as follows. Roll pair: metal roll / metal roll Linear pressure: 30 kg / cm ²

[0057]

As described above, the non-woven fabric of the present invention is a non-woven fabric composed of ultrafine fibers of the split type, and therefore has excellent properties such as separability and concealment. By splitting the splittable conjugate fiber by the pressure treatment, it is an excellent nonwoven fabric that has no defect even in a nonwoven fabric having a particularly low basis weight. The nonwoven fabric of the present invention can be suitably used for battery separators and filters by utilizing such effects.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a pair of rolls as an example of a linear pressing body according to the present invention.

FIG. 2 is a schematic view showing an example of a roll that is a linear pressure body according to the present invention.

FIG. 3 is a schematic view showing an example of a cross-sectional shape of a splittable conjugate fiber according to the present invention.

FIG. 4 is an electron micrograph showing a cross section of a fiber in a web before pressure treatment in Example 1.

FIG. 5 is an electron micrograph showing a cross section of a fiber in a nonwoven fabric after pressure treatment in Example 1.

[Explanation of symbols]

 1 One resin component 2 Other resin components

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanobu Matsuoka 3-4-2, Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Paper Mills Co., Ltd.

Claims (10)

[Claims] At least two or more ultrafine fibers (hereinafter referred to as “fine fibers”)
Splittable conjugate fiber that can be split into fibers B) (hereinafter fiber A)
Is subjected to a heat fusion treatment, and then subjected to a pressure treatment by a linear pressing body having irregularities, so that at least a part of the fiber A is divided into the fiber B. Nonwoven fabric characterized by being made. 2. The nonwoven fabric according to claim 1, wherein the fibers A are composed of two or more resin components. 3. The nonwoven fabric according to claim 2, wherein the difference in melting point between the resin component having the lowest melting point and the resin component having the highest melting point in the fiber A is 10 ° C. or more. 4. The fiber according to claim 3, wherein the web contains heat-fusible fibers (hereinafter, referred to as fibers C) containing at least a resin component having a melting point equal to or lower than the resin component having the lowest melting point of the fibers A. Nonwoven. 5. The nonwoven fabric according to claim 4, wherein at least a part of the resin component having the lowest melting point of the fiber C and / or the fiber A is fused by the heat fusion treatment. 6. The nonwoven fabric according to claim 1, wherein the fineness of the fiber B is 0.5 denier or less. 7. The nonwoven fabric according to claim 1, which has been subjected to a hydrophilic treatment. 8. The nonwoven fabric according to claim 7, wherein the hydrophilic treatment is a graft treatment. 9. A battery separator comprising the nonwoven fabric according to any one of claims 1 to 8. 10. A filter comprising the nonwoven fabric according to claim 1. Description: