JP2984561B2 - Battery separator and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator suitable for an alkaline storage battery such as a nickel-cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery.

[0002]

2. Description of the Related Art Generally, non-woven fabrics made of nylon or polypropylene fibers by a dry method (hereinafter referred to as dry non-woven fabrics) and non-woven fabrics manufactured by a wet papermaking method (hereinafter referred to as wet non-woven fabrics) are used as battery separators. in use.

[0003] In recent years, as the size and weight of electronic devices have been reduced, and the capacity of batteries has been required to be higher, the amount of the positive electrode active material and the negative electrode active material has been increased by reducing the thickness of the separator. Attempts have been made to achieve higher capacity.

[0004]

However, in general, when the thickness of the separator is reduced, the liquid retention ability is reduced. Therefore, when the charge and discharge are repeated, the problem arises that the life of the separator is shortened due to the liquid dying of the separator. Also, especially in the case of dry nonwoven fabric,
If the thickness is reduced, the uniformity of the nonwoven fabric is significantly impaired. However, if the uniformity of the separator is reduced, there is a problem that a short circuit is likely to occur between the positive electrode and the negative electrode.
On the other hand, when trying to reduce the thickness of the wet nonwoven fabric, the tensile strength is significantly reduced, and when this is used as a separator,
There is a problem that winding cannot be performed. For these reasons, the thickness of the nonwoven fabric used as a battery separator is limited to 0.15 to 0.20 mm, and the battery capacity cannot be significantly improved.

In view of the above circumstances, the present invention provides a battery separator having excellent liquid retention and uniformity, having a small thickness, and capable of contributing to an improvement in battery capacity without reducing battery life. It was made for the purpose.

[0006]

That is, the battery separator of the present invention comprises 20 to 30% by weight of a thermoadhesive fiber having a length of 5 to 15 mm, and a polyolefin polymer (component A) and ethylene vinyl alcohol in a fiber cross section. 50 to 80% by weight of a splittable conjugate fiber having a length of 5 to 15 mm in which polymers (component B) are alternately arranged adjacent to each other, and a finer size than the ultrafine fiber formed by splitting the splittable conjugate fiber Is mixed with 10 to 30% by weight of synthetic fibers having a length of 5 to 15 mm, and the fine fibers are formed by splitting the splittable conjugate fibers, and the fibers are entangled with each other, and some of the fibers are mutually A nonwoven fabric characterized by being adhered, having a thickness of 0.08 mm or more and less than 0.15 mm, and a liquid retention rate of 380% or more. Hereinafter, the contents will be described.

The above-mentioned heat-adhesive fiber refers to a fiber which is softened and melted by heat and functions to bond the fibers.
As such a fiber, for example, it is preferable to use a polyolefin-based thermo-adhesive fiber such as polyethylene or polypropylene.

In particular, in the present invention, in order to improve the strength of the separator, it is preferable to use a core-sheath type composite fiber whose sheath is composed of a low melting point component and whose core is composed of a high melting point component.
Among them, the core-in-sheath type composite fiber in which the core component is composed of polypropylene and the sheath component is composed of polyethylene is excellent in alkali resistance because it is composed of a polyolefin-based component,
It is most preferably used, since it has good bonding property with the splittable conjugate fiber composed of polypropylene and ethylene vinyl alcohol copolymer described later.

Preferably, the proportion of the heat-adhesive fibers is 20 to 30% by weight. If the amount is less than 20% by weight, the bonding between the fibers is insufficient and the form of the wet nonwoven fabric cannot be stabilized. If the amount exceeds 30% by weight, the proportion of the splittable conjugate fibers and fibers having a large fineness described below is small. It is because it becomes.

The splittable conjugate fiber used in the present invention is a conjugate fiber containing a polyolefin polymer as an A component and an ethylene vinyl alcohol copolymer as a B component. here,
Polyolefin polymers are employed to impart chemical resistance to the separator, and ethylene vinyl alcohol copolymers are employed to impart hydrophilicity to the separator. As the polyolefin polymer, polypropylene and polyethylene can be preferably used. Also, as the ethylene vinyl alcohol copolymer, those having an ethylene content of 20 to 50 mol% can be preferably used in consideration of spinnability and hydrophilicity.

In the splittable conjugate fiber, the A component and the B component are alternately adjacent to each other in the fiber cross section, and the constituent units are continuous in the length direction. Has a cross-sectional shape that is exposed to the outside.
Specifically, those in which the A and B components are arranged as shown in FIGS. 1 to 3 can be preferably used. The composite ratio of the A and B components is desirably about 30:70 to 70:30 for the A component: B component in view of the easiness of the spinning process and the affinity for the electrolytic solution.

[0012] The splittable conjugate fiber is split by a high-pressure water flow treatment or the like described later to form an ultrafine fiber.
If the ratio of the ultrafine fibers formed by the splitting of the splittable conjugate fibers to the entire nonwoven fabric is too large, or the fineness of the ultrafine fibers is too small, the nonwoven fabric is "too tight", so care must be taken. Here, "the fabric is too tight" means that the fiber gap becomes too small, and as a result, the air permeability, the liquid retaining property, and the like decrease. Therefore, the ratio of the splittable conjugate fiber is 50
It is preferably from 80 to 80% by weight, and it is desirable to use a splittable conjugate fiber having a fineness of the formed ultrafine fiber of 0.1 to 0.5 denier. The ratio of splittable conjugate fibers is 5
If the content is less than 0% by weight, the proportion of the ethylene-vinyl alcohol copolymer is small, and if the fineness of the fine fibers exceeds 0.5 denier, the surface area of the fine fibers composed of the ethylene-vinyl alcohol copolymer is small, so The liquid property is lowered, which is not preferable.

In order to prevent such “overtightening”, synthetic fibers having a finer size than the ultrafine fibers formed by splitting the splittable conjugate fibers (hereinafter referred to simply as fibers having a high fineness) are 10 to 30. It is desirable to mix by weight. The fineness of the nonwoven fabric is not particularly limited as long as it is larger than the fineness of the ultrafine fibers. Further, the material is not particularly limited, and synthetic fibers generally used such as polypropylene, polyethylene, polyester, and nylon can be used. In particular, a rather rigid and high-strength polypropylene fiber having a fineness of 0.6 to 1.0 denier is most preferably applied in order to impart alkali resistance to the separator and secure an appropriate fiber gap.

The above-mentioned heat-adhesive fiber, splittable conjugate fiber,
All fibers with large fineness have a fiber length of 5 to 15 mm
It is desirable that If it is less than 5 mm, the entanglement between the fibers due to the high-pressure water flow treatment becomes insufficient, and if it exceeds 15 mm, the dispersibility of the fibers in the slurry becomes poor, especially when producing a nonwoven fabric by a wet papermaking method, so that a uniform nonwoven fabric cannot be obtained. It is.

Next, a method for manufacturing the battery separator of the present invention will be described. As a method for producing the nonwoven fabric serving as the base material of the separator of the present invention, a wet papermaking method is desirable. This is because a uniform nonwoven fabric can be obtained by the wet papermaking method. The wet papermaking may be performed by a usual method, and first, the heat-adhesive fibers 20 to
30% by weight, 50-80% by weight of the splittable conjugate fiber, and 10-30% by weight of a fiber having a large fineness are mixed to form 0.01% by weight.
Disperse in water to a concentration of ~ 0.6% to prepare a slurry. At this time, a small amount of a dispersant may be added. JP-A-5-21 which describes a method for producing a wet nonwoven fabric
According to Japanese Patent No. 4653, it is known that the strength of the obtained nonwoven fabric is improved by preliminarily dividing the splittable conjugate fiber during slurry preparation, but in the present invention, the splitting ratio is suppressed to 30% or less. Is desirable. It is not preferable to make paper in a state where the paper is further divided, since the uniformity of the obtained nonwoven fabric is reduced.

The slurry is formed using a long net or round net paper machine. The basis weight can be adjusted by the amount of the fiber, but in order to make the final thickness 0.08 mm or more and less than 0.15 mm, the basis weight is desirably ²⁰ to 50 g / m ² . If it is less than 20 g / m ² , the fiber density of the nonwoven fabric becomes small, so that a short circuit is likely to occur between the positive electrode and the negative electrode.
If the amount exceeds g / m ² , the fiber density becomes too large, and the air permeability and the liquid retention are reduced.

Next, the heat-adhesive fibers are melted to bond the fibers. The melting of the heat-adhesive fibers may be carried out simultaneously with the drying in the drying treatment in the papermaking process, or may be carried out by temporarily forming a wet nonwoven fabric and then heating.
Then, the fibers are bonded by melting the heat-adhesive fibers,
After the morphology has been stabilized, high-pressure water flow treatment is performed to divide the splittable conjugate fibers to form ultrafine fibers and entangle the fibers. After that, heat calendering and finishing to a thickness of 0.08 mm or more and less than 0.15 mm,
The battery separator of the present invention is used.

[0018]

In the present invention, the heat-adhesive fibers work to stabilize the form of the wet nonwoven fabric by bonding the fibers.

The splittable conjugate fiber composed of a polyolefin polymer and an ethylene vinyl alcohol copolymer is split by the action of high-pressure water flow to form ultrafine fibers, which are entangled to form fine interfiber voids in the nonwoven fabric. Due to the formation, the hydrophilicity of the ethylene vinyl alcohol copolymer and the phase difference contribute to an improvement in the liquid retention rate of the electrolytic solution. Furthermore, since the ethylene vinyl alcohol copolymer exhibits excellent wet heat adhesiveness, it also plays a role of a binder and contributes to improvement of the strength of the nonwoven fabric. Further, the alkali-resistant polyolefin polymer improves the durability of the nonwoven fabric, that is, the battery separator.

The fibers having a large fineness prevent the nonwoven fabric from becoming too tight due to the entanglement of the ultrafine fibers, and provide an appropriate gap to the battery separator to prevent a decrease in air permeability and liquid retention.

In the method for producing a battery separator according to the present invention, since the wet papermaking method is employed for producing the nonwoven fabric serving as the base material of the separator, the fiber density of the nonwoven fabric can be equalized as compared with the dry method, and the thickness can be reduced. Can be reduced. Furthermore, according to the production method of the present invention, since the heat-adhesive fibers are melted and the fibers are bonded in advance, the form is stabilized, and the fibers are prevented from being disturbed at the time of roll winding or handling, and the fibers are evenly distributed. The fiber can be supplied to the high-pressure water treatment apparatus while maintaining the fiber density. Further, since the splittable conjugate fiber is split after the heat bonding to form the ultrafine fibers, there is an advantage that the properties unique to the ultrafine fibers, namely, the flexibility and the drapability are not impaired.

[0022]

【Example】

[Example 1] A thermo-adhesive fiber which is a core-sheath type composite fiber having a fineness of 1.5 denier, a fiber length of 10 mm, and a core / sheath component of polypropylene / high-density polyethylene (composite ratio 50/50) was 30% by weight. , A component is polypropylene, B component is ethylene vinyl alcohol copolymer (ethylene content 38
Mol%), having a cross-sectional shape as shown in FIG.
60% by weight of a splittable conjugate fiber having a denier of 3 denier and a fiber length of 6 mm having a volume ratio of the component A / B of 50/50 and a polypropylene fiber having a denier of 0.7 denier, a fiber length of 10 mm and a strength of 9 g / d were obtained. % By weight and a slurry was prepared so as to have a concentration of 0.5%.
A wet nonwoven fabric of 5.6 g / m ² was prepared. Next, this nonwoven fabric was subjected to a heat treatment at 130 ° C. using a hot air penetration type drier to melt the high-density polyethylene of the heat-adhesive fibers and bond the fibers. Then, the high-pressure columnar water stream with a water pressure of 130 kg / cm ² is sprayed on the front and back surfaces of the heated nonwoven fabric to split the splittable conjugate fibers to form ultrafine fibers having a fineness of 0.19 to 0.20 denier. At the same time, the fibers were entangled and then calendered to a thickness of 0.13 mm to form a nonwoven fabric for a battery separator.

Example 2 The same fibers as those used in Example 1 were mixed at the same ratio to prepare a wet nonwoven fabric having a basis weight of 35.2 g / m ^{2 in} the same manner as in Example 1.
In the same manner as in Example 1, a non-woven fabric for a battery separator having a thickness of 0.10 mm was obtained by a heat treatment, a high-pressure water flow treatment, and a heat calender treatment.

[Comparative Example 1] A wet nonwoven fabric was prepared in the same manner as in Example 1 using only the splittable conjugate fiber used in Example 1 above, and water pressure 1 was applied to the front and back surfaces of the obtained wet nonwoven fabric.
By injecting a 30 kg / cm ² high-pressure columnar water stream, the splittable conjugate fiber is split to have a fineness of 0.19 to 0.20.
A denier ultrafine fiber is formed and the fibers are entangled with each other, and then heat calendered to a thickness of 0.13 mm.
To give a nonwoven fabric for a battery separator.

Comparative Example 2 A wet nonwoven fabric was prepared in the same manner as in Example 1 by mixing 30% by weight of the heat-adhesive fiber used in Example 1 and 70% by weight of the splittable conjugate fiber. Heat treatment, high-pressure water flow treatment in the same manner as in Example 1,
And heat calendering to a thickness of 0.13mm,
A non-woven fabric for a battery separator was formed.

Comparative Example 3 The same fibers as those used in Example 1 were mixed in the same ratio, and a wet nonwoven fabric having a basis weight of 45.3 g / m ² was prepared in the same manner as in Example 1; Heat treatment was performed at 130 ° C. using a penetration type drier to melt the high-density polyethylene of the heat-adhesive fibers and bond the fibers. Next, heat calender processing and thickness 0.13mm
To give a nonwoven fabric for a battery separator.

[Comparative Example 4] Fineness 2 using ethylene-vinyl alcohol copolymer as a sheath component and polypropylene as a core component
Denier, 50% by weight of core-sheath composite fiber with 51 mm fiber length
And 50% by weight of a core-sheath type composite fiber having the same composition and the same composite ratio as that of the heat-adhesive fiber used in Example 1 having a denier of 0.9 denier and a fiber length of 38 mm, and mixing with a parallel card to form a web. And heat-treated at 130 ° C. to melt the high-density polyethylene of the heat-adhesive fiber to bond the fibers together to form a nonwoven fabric for a battery separator.

Table 1 shows the physical properties of the battery separators of Examples 1 and 2 and Comparative Examples 1 to 4.

[0029]

[Table 1]

The evaluation of the physical properties in the table was performed by the following methods.

[Tensile strength, elongation] JIS P 8113
Was measured in accordance with the tensile test method for paper and paperboard.

[Tear Strength] The tear strength was measured according to the test method for tear strength of paper and paperboard according to JIS P 8116.

[Liquid absorption speed] 25 × 25 from the sample width direction
Three 0 mm test pieces are collected and brought into a water equilibrium state. Next, the test piece is pinned to a horizontal bar supported at a predetermined height on a water tank containing a potassium hydroxide aqueous solution (hereinafter abbreviated as KOH solution) having a specific gravity of 1.30 and kept at 20 ° C. Align the lower end of the test piece with the line, lower the horizontal bar, and stand vertically so that the lower end of the test piece is immersed in the liquid by 5 mm.
The height at which the OH solution rose was measured after 30 minutes.

[Liquid retention ratio] The weight (W) of the test piece in a water equilibrium state is measured up to 1 mg. Next, KOH with a specific gravity of 1.30
The test piece was immersed in the solution, allowed to absorb the KOH solution for 1 hour, pulled up from the solution, and allowed to stand for 10 minutes. Then, the weight (W ₁ ) of the test piece was measured, and the liquid retention rate (%) = (( W ₁ −
The liquid retention was calculated from the formula of W) / W) × 100.

[Woundability] The results are shown in the order of 巻, △, △, and × from the separator having the best winding property.

[Maximum pore diameter] The maximum pore diameter was measured according to the bubble point method.

[Air permeability] Using a Frazier type testing machine,
It was measured according to JIS L 1096.

[0038]

As described above, the battery separator of the present invention is
Despite having a smaller thickness than conventional separators,
Since it exhibits excellent liquid retention and liquid absorption properties, the capacity of the battery can be improved without shortening the battery life. Further, when the nonwoven fabric serving as the base material of the battery separator of the present invention is manufactured by a wet papermaking method, a uniform nonwoven fabric can be obtained even if the thickness is reduced, so that a positive electrode based on a decrease in uniformity like a dry nonwoven fabric is used. There is no short circuit between the anode and the negative electrode. Furthermore, in the battery separator of the present invention, the ultrafine fibers formed by splitting the splittable conjugate fibers are entangled with each other, and some of the fibers are mutually bonded by wet heat bonding of the ethylene vinyl alcohol copolymer. So
It shows tensile strength and tear strength enough to withstand winding even with a small thickness. In addition, since it has excellent flexibility, no fold is generated at the time of winding. Therefore, when a battery is manufactured using this, a high-capacity battery can be obtained without particularly affecting the electrode winding step and battery performance.

[Brief description of the drawings]

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

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

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

[Explanation of symbols]

 1 A component 2 B component

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 2/16

Claims (3)

(57) [Claims] 1. A heat-adhesive fiber having a length of 5 to 15 mm.
0% by weight and a length of 5 to 15 mm in which a polyolefin polymer (component A) and an ethylene vinyl alcohol copolymer (component B) are alternately arranged adjacent to each other in the fiber cross section.
50 to 80% by weight of the splittable conjugate fiber and 10 to 30% by weight of a synthetic fiber having a length of 5 to 15 mm and a fineness greater than the ultrafine fiber formed by splitting the splittable conjugate fiber, An ultra-fine fiber is formed by splitting the splittable conjugate fiber, and the fibers are entangled with each other, and a part of the fibers is bonded to each other, and has a thickness of 0.08 mm or more and less than 0.15 mm. And a liquid separator having a liquid retention of 380% or more. 2. The battery separator according to claim 1, wherein the heat-adhesive fiber is a core-sheath type composite fiber having polyethylene as a sheath and polypropylene as a core. 3. A thermoadhesive fiber having a length of 5 to 15 mm.
0% by weight and a length of 5 to 15 mm in which a polyolefin polymer (component A) and an ethylene vinyl alcohol copolymer (component B) are alternately arranged adjacent to each other in the fiber cross section.
And 50 to 80% by weight of the splittable conjugate fiber and 10 to 30% by weight of a synthetic fiber having a length of 5 to 15 mm and a fineness larger than the ultrafine fiber formed by splitting the splittable conjugate fiber. Then, the heat-bondable fiber is melted by a drying treatment in a papermaking process or by a heat treatment after the papermaking to bond the fibers, and then the wet nonwoven fabric is subjected to a high-pressure water flow treatment to split the splittable conjugate fiber. A method of manufacturing a battery separator, comprising forming ultrafine fibers and entanglement between the fibers, and then subjecting the fibers to a calendering treatment to finish the thickness to a thickness of 0.08 mm or more and less than 0.15 mm.