JPH0729561A - Battery separator and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a separator suitable for use in a nickel-hydrogen battery, by mixing specified divided-type composite fibers, thermally adherable fibers, and specified synthetic fibers in a specified ratio and performing wet paper making with respect to the resulting mass, and, after performing high-pressure water treatment, performing thermal calender treatment and thereby making each of the tensile strength and liquid- retaining percentage greater than specified. CONSTITUTION:A 5-15mm length divided type composite fiber (D fiber) which has section in which a polyolefin polymer (A component) and an ethylene vinyl alcohol copolymer (B component) are alternately disposed in an adjacent manner to each other is prepared. A 60 to 80wt.% of this D fiber, 20 to 30wt.% of thermally adherable composite fiber (T fiber), and 10 to 20wt.% of 5-15mm length synthetic fiber having a greater deniel than that of post-division ultra-fine fiber of the D fiber as well as the T fiber are mixed together, whereupon wet paper making is performed. After desiccation of the resulting mass, high-pressure water treatment is carried out, and after the D fibers have been divided and the relevant fibers have been thus entangled with one another, thermal calender treatment is performed. As a result, a separator with a finished thickness of 0.15 to 0.21mm which has a longitudinal tensile strength of 6.0kg/15mm or more and a liquid-retaining percentage of 380% or more is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator, and more particularly to a battery separator suitable for a nickel-hydrogen alkaline storage battery having a negative electrode having an electrode capable of absorbing and releasing hydrogen.

[0002]

2. Description of the Related Art In particular, a separator for a nickel-hydrogen battery is required to have alkali resistance, a uniform thickness and a sufficient liquid retaining property, and therefore it has been conventionally produced by a wet papermaking method using a polyolefin fiber as a raw material. A wet non-woven fabric having a predetermined thickness is widely used. However, the conventional battery separator made of a wet non-woven fabric is poor in tear resistance and flexibility, and it is difficult to obtain a uniform bendability at the time of winding.

For the purpose of improving this difficulty, for example, as disclosed in Japanese Patent Laid-Open No. 3-230473,
A battery separator has been proposed in which a wet fiber web made of short fibers is laminated on at least one surface of a coarse base fabric to make a paper, and the resulting wet-laid nonwoven fabric is subjected to a water treatment to entangle short fibers with the base fabric.

[0004]

However, the above-mentioned battery separator obtained by entanglement of short fibers with the base fabric has the advantages that it is excellent in tensile strength, has a good winding property, and has a small variation in thickness. However, since the base cloth occupies a large proportion of the thickness of the separator, the liquid retention rate and the liquid absorption speed are inferior to a wet non-woven fabric having the same thickness without the base cloth.

From the above, in the industry, it has excellent alkali resistance, can withstand tension at the time of winding without interposing a base cloth, has a large liquid retention rate, and has a suitable hydrogen gas generated from the negative electrode. There has been a strong demand for a separator for nickel-hydrogen batteries having a permeability (air permeability). The present invention has been made in order to meet such a demand and particularly to provide a separator suitable for a nickel-hydrogen battery.

[0006]

According to the present invention, a heat-adhesive conjugate fiber is mixed with a short fiber of a splittable conjugate fiber composed of a polyolefin polymer and an ethylene vinyl alcohol copolymer, and the splittable conjugate fiber of the splittable conjugate fiber is further mixed. The above-mentioned object is obtained by mixing the ultrafine fibers after the splitting and the short fibers of the synthetic fibers having a larger denier than the mixed thermoadhesive conjugate fibers for wet papermaking, and subjecting the obtained wet-laid nonwoven fabric to a high-pressure water stream thermal calendering. The battery separator is compatible with.

That is, in the battery separator of the present invention, the heat-adhesive composite fiber is 20 to 30% by weight, and the polyolefin polymer (component A) and the ethylene vinyl alcohol copolymer (component B) are alternately adjacent to each other in the fiber cross section. 60 to 80% by weight of the splittable conjugate fiber having a length of 5 to 15 mm, which is arranged so as to have a denier larger than that of the ultrafine fiber after splitting of the splittable conjugate fiber and the heat-bondable conjugate fiber. ~ 1
20 to 10% by weight of 5 mm synthetic fiber is mixed and wet papermaking, and after papermaking drying, high pressure water stream treatment is performed to divide the above-mentioned splittable conjugate fiber into interfiber entanglement and then heat calendering treatment. It is finished to a predetermined thickness, the finished thickness is 0.15 to 0.21 mm, the longitudinal tensile strength is 6.0 kg / 15 mm or more, and the liquid retention rate is 380.
% Or more.

Further, in the manufacturing method, 20 to 30% by weight of the heat-adhesive conjugate fiber is used, and the polyolefin polymer (component A) and the ethylene vinyl alcohol copolymer (component B) are alternately adjacent to each other in the fiber cross section. Arranged length 5
60 to 80% by weight of split type conjugate fiber having a length of -15 mm, and 10 to 20% by weight of synthetic fiber having a length of 5 to 15 mm and a denier larger than that of the heat-bondable conjugate fiber and the ultrafine fiber after splitting of the split type conjugate fiber. % And mixed by wet papermaking, the obtained wet-laid nonwoven fabric is heat-treated to melt the low-melting component of the above-mentioned thermoadhesive composite fiber to perform inter-fiber joining, and then this wet-laid nonwoven fabric is subjected to high-pressure water flow treatment. The above-mentioned splittable conjugate fiber is characterized in that it is subjected to ultrafine splitting and interfiber entanglement, followed by thermal calendering to obtain a desired thickness.

The above-mentioned heat-adhesive conjugate fiber is a core-sheath type composite fiber in which a high melting point polymer is a core component and a low melting point polymer is a sheath component, for example, polypropylene is a core component and high-density polyethylene is a sheath component (core-sheath). 50:50 volume ratio core-sheath type composite fiber (fineness 1.0 to 1.5 denier, fiber length 5 to 10 m)
m) can be mentioned.

Examples of the polyolefin polymer used as the component A of the above splittable conjugate fiber include polypropylene and polyethylene, and the ethylene vinyl alcohol copolymer as the component B has an ethylene content in view of spinnability and hydrophilicity. 20 to 45% is preferable.

In the splittable conjugate fiber composed of the A component and the B component, the A and B components are alternately adjacent to each other in the fiber cross section, and the constitutional units are continuous in the longitudinal direction, and a part of all the constitutional units. Necessarily has a cross-sectional shape exposed on the fiber surface, and the composite ratio of both components A and B may be determined in consideration of the balance between durability and hydrophilicity of the battery separator. A from the viewpoint of ease of spinning in the spinning process and affinity for the electrolyte solution
Component: B component is preferably about 30:70 to 70:30.

1 to 3 show typical sectional shapes of splittable conjugate fibers. The thickness of the fibers of the A and B components after the division is preferably about 0.2 to 0.5 denier, and when the fiber is finer than 0.2 denier, the durability is drastically reduced.
If it is thicker than 5 denier, the liquid retaining property will decrease.

As the synthetic fiber having a high fineness, which is mixed with the heat-bondable conjugate fiber and the splittable conjugate fiber, general-purpose synthetic fibers such as polypropylene, polyethylene, polyester and nylon can be applied. In order to secure the liquid voids, polypropylene having a fineness of 2 to 8 denier and slightly rigidity and high strength, for example, high strength polypropylene fiber [trade name: PNHC (manufactured by Daiwa Spinning Co., Ltd.)] is suitable.

[0014]

The heat-adhesive conjugate fiber is made into a wet non-woven fabric with the above-mentioned mixed fiber, and then the low melting point component is melted by heat treatment at a temperature higher than the melting point of the low melting point component,
The strength of the wet-laid nonwoven fabric is increased to stabilize the morphology.

The splittable conjugate fiber is incompletely split by being beaten by a pulper or a mixer at the time of papermaking, and further split by a water stream treatment after papermaking to be separated into ultrafine fibers of component A and component B and thermally bonded. Are entangled with the functional composite fiber and the mixed synthetic fiber to form fine inter-fiber voids to increase the electrolyte retention capacity by synergistic action with the hydrophilicity of the B component, and the alkali resistant A component is a non-woven fabric, that is, a battery separator. Improve the durability of.

A small amount of mixed synthetic fibers having a high fineness is
It is entangled in random directions by the above water flow treatment, suppresses the reduction of the thickness of the nonwoven fabric by the water flow treatment and has a reinforcing effect, holds sufficient voids in the nonwoven fabric to increase the liquid retention rate and improve the tensile strength. To prevent breakage during winding.

Further, by adopting the wet papermaking method for forming the non-woven fabric as the base material of the battery separator,
As compared with the dry method, the fiber density of the non-woven fabric can be balanced, and the air permeability of the obtained separator is uniform over the entire surface. Then, the strength of the non-woven fabric is increased by the dry bonding of the heat-adhesive composite fibers to stabilize the morphology, and the disturbance of the fibers during roll winding and handling is prevented, and a high-pressure water stream treatment device with a uniform fiber density maintained. Can be supplied to.

[0018]

【Example】

Example 1 A core-sheath type heat-bondable composite fiber (hereinafter referred to as A fiber) having a core component of polypropylene, a sheath component of high density polyethylene (core-sheath volume ratio of 50:50), a fineness of 1.5 denier and a fiber length of 10 mm. ) Is 45% by weight, and as shown in FIG. 1, the polyolefin polymer is component A (1) and the ethylene vinyl alcohol copolymer is B in the fiber cross section.
Component (2), A component (1) and B component (2) are alternately arranged adjacent to each other in a radial pattern with a volume ratio of 50:50 and a length of 5 mm. 4)
5% by weight and 10% by weight of polypropylene fiber (hereinafter referred to as C fiber) having a fineness of 2 denier, a fiber length of 6 mm, and a strength of 9 g / denier were mixed with a pulper and wet-processed to produce a basis weight of 70.5 g. Wet non-woven fabric.

Next, this wet-laid nonwoven fabric was heat-treated with hot air at 130 ° C. to melt the polyethylene component of the A fiber to bond the fibers together.

Next, the front and back of this wet-laid nonwoven fabric are subjected to a high-pressure columnar water flow treatment (back pressure of 130 kg / cm ² ) to perform ultrafine division of the above-mentioned splittable conjugate fiber (fineness after splitting is 0.19 denier) and also between fibers. It was entangled and then heat-calendered to obtain a nonwoven fabric for battery separator having a desired thickness. The finished thickness was 0.18 mm.

"Example 2" The mixing ratio of the above A fibers, B fibers and C fibers was set to 30:60:10, and Example 1 was used.
In the same manner as in (1), a wet papermaking process, a heat treatment, a high-pressure water stream treatment, and a heat calendar treatment were performed to obtain a nonwoven fabric for a battery separator having a thickness of 0.17 mm.

Example 3 The mixing ratio of the above A fibers, B fibers and C fibers was set to 20:60:20, and Example 1 was used.
Similarly to the above, wet papermaking was performed, and heat treatment, high-pressure water stream treatment and thermal calender treatment were performed to obtain a nonwoven fabric for battery separators having a thickness of 0.19 mm.

Comparative Example 1 Only the B fiber was wet-paper-made, and the obtained wet-laid nonwoven fabric was subjected to high-pressure columnar water flow treatment (back pressure of 130 kg / cm ² ) to obtain an ultrafine split of the splittable conjugate fiber ( The fineness after division was 0.19 denier and the fibers were entangled, and then heat calendered to obtain a 0.21 mm thick nonwoven fabric for battery separators.

Comparative Example 2 20% by weight of the above A fiber,
80% by weight of B fiber was mixed, wet papermaking was performed in the same manner as in Example 1, and heat treatment, high-pressure water stream treatment and thermal calender treatment were performed to obtain a 0.21 mm-thick non-woven fabric for a battery separator.

Comparative Example 3 As shown in FIG.
In the cross section of the fiber, a polyolefin polymer (A component) and an ethylene vinyl alcohol copolymer (B component) are alternately arranged so as to have a fineness of 3 denier and a length of 51.
mm split type composite fiber (hereinafter referred to as D fiber) is prepared,
With this D fiber, the basis weight is 75 by the cross layer method.
A g / m ² web was prepared, and the ethylene vinyl alcohol copolymer was gel-pressed through a 180 ° C. hot calender roller to form a 0.21 mm thick nonwoven fabric for battery separators.

Comparative Example 4 The web of Comparative Example 3 was subjected to a fiber splitting treatment (fineness after splitting was 0.19 denier on average) and an entanglement treatment by a high-pressure water jet method, followed by drying and calender roller treatment to obtain a thickness. It was a 0.21 mm non-woven fabric for a battery separator.

Comparative Example 5 The core component is polypropylene and the sheath component is high density polyethylene (core-sheath volume ratio 50: 5).
0), a fineness of 1.5 denier, 40% by weight of the core-sheath type thermoadhesive composite fiber having a fiber length of 51 mm, and 60% by weight of the D fiber were mixed to form a web having a basis weight of 72.9 g / m ² . Done This web is treated with a hot air processor (140 ° C.) to bond the fibers by melting the high density polyethylene, and while the high density polyethylene is in a softened state, it is subjected to a calendar roller treatment and has a thickness of 0.22 mm for a battery separator non-woven fabric. I said.

The nonwoven fabrics of Examples 1 to 3 and Comparative Examples 1 to 5 were used as battery separators. Separately, conventionally used separators for alkaline batteries (papermaking products) were obtained, and the performance of each separator was obtained. And the physical properties were compared. The results are shown in Table 1.

[0029]

[Table 1]

The liquid absorption rate and the liquid retention rate were measured as follows. Absorption rate: 25 x 250 mm test piece 3 from the sample width direction
Take a sample and bring it to water equilibrium. Next, the test piece is at 20 ° C.
Pin it to a horizontal bar supported at a certain height above a water tank containing a KOH solution with a specific gravity of 1.30 kept at. Align the lower end of the test piece in a line and lower the horizontal bar so that the lower end of the test piece is 5 mm.
It was stood vertically so that it was immersed in the liquid, and the height at which the KOH solution rose due to the capillary phenomenon was measured after 30 minutes. Liquid retention rate: Three test pieces (202.5 cm ² ) having a shape as shown in Fig. X are sampled from the width direction of the sample, and the weight (W) in a water equilibrium state is measured up to 1 mg. Next, KO with a specific gravity of 1.30
The test piece was spread and dipped in the H solution, absorbed for 1 hour, then pulled out of the solution and the weight of the test piece after 10 minutes (W ₁ ).
Was measured and the liquid retention rate was calculated by the following formula. Liquid retention rate (%) = (W−W ₁ ) / W × 100

[0031]

As described above, the battery separator of the present invention is
Since the non-woven fabric substrate is formed by the wet papermaking method, the fiber density is uniform, and the inter-fiber entanglement is promoted by the water flow treatment, and the tensile strength is improved in combination with the bonding force of the heat-adhesive composite fiber. Withstands tension when wound as a separator. In addition, the component A and the component B of the splittable conjugate fiber are divided and made extremely fine, the durability by the component A and the liquid retaining property by the component B effectively act, and the nonwoven fabric is formed by mixing synthetic fibers having a large fineness. It does not become paper-like, has a remarkably good liquid retention rate, and secures appropriate air permeability, and is suitable as a separator for nickel-hydrogen batteries.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a splittable conjugate fiber used in an example of the present invention.

FIG. 2 is an enlarged view of a fiber cross section of another example of the splittable conjugate fiber applicable to the present invention.

FIG. 3 is a fiber cross-sectional enlarged view of another example of the splittable conjugate fiber applicable to the present invention.

[Explanation of symbols]

 1. A component 2. B component

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[Procedure amendment]

[Submission date] October 26, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Battery separator and method for manufacturing the same

Claims (2)

[Claims] 1. A heat-bondable composite fiber is 20 to 30% by weight.
And a polyolefin polymer (component A) in the fiber cross section
60 to 80% by weight of the splittable conjugate fiber having a length of 5 to 15 mm, which is alternately and adjacently arranged with ethylene vinyl alcohol copolymer (component B), and the heat-bondable conjugate fiber and the splittable conjugate fiber. 10 to 2 synthetic fibers with a length of 5 to 15 mm, which have a greater denier than the ultrafine fibers after splitting of the composite fibers
0% by weight is mixed and wet papermaking is performed, and after the papermaking is dried, a high-pressure water stream treatment is applied to divide the above-mentioned splittable conjugate fibers into inter-fiber entanglements, and then heat calendering is applied to obtain a predetermined thickness. The finished thickness is 0.15 to 0.
At 21 mm, the tensile strength in the longitudinal direction is 6.0 kg / 15
A battery separator having a thickness of at least mm and a liquid retention rate of at least 380%. 2. The heat-adhesive conjugate fiber is 20 to 30% by weight,
60 to 80% by weight of splittable conjugate fiber having a length of 5 to 15 mm, which is obtained by alternately arranging a polyolefin polymer (A component) and an ethylene vinyl alcohol copolymer (B component) in the fiber cross section, A wet non-woven fabric obtained by mixing 10 to 20% by weight of a synthetic fiber having a length of 5 to 15 mm, which has a greater denier than the heat-adhesive conjugate fiber and the ultrafine fiber after division of the above-mentioned splittable conjugate fiber, and wet papermaking. Is heat-treated to melt the low-melting component of the heat-adhesive conjugate fiber to perform inter-fiber joining, and then the wet-laid nonwoven fabric is subjected to high-pressure water flow treatment to perform ultrafine division of the splittable conjugate fiber and interfiber entanglement. A method of manufacturing a battery separator, which comprises: