JPH07122258A - Nonwoven fabric for alkaline battery separator and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a nonwoven fabric and its manufacture for an alkaline battery separator excellent in absorbability and holdability of an electrolyte. CONSTITUTION:A constitution is formed of polyethylene flap pulp of beating flash spinning high density polyethylene fiber untied until a mean fiber length is decreased to 1.20mm or less and polyolefin system fiber provided with one or two kinds or more of an ethylene vinyl alcohol copolymer component. The polyolefin system fiber is preferably specific devision type compound fiber or heat bonding compound fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkali which is interposed between the positive and negative electrodes of an alkaline battery to prevent a short circuit between them and to sufficiently hold an electrolytic solution to smoothly promote an electromotive reaction. The present invention relates to a non-woven fabric for a battery separator, and more particularly to a non-woven fabric for an alkaline battery separator which has both excellent liquid absorbing and liquid retaining properties of an electrolytic solution and other properties, and a method for producing the same.

[0002]

2. Description of the Related Art Alkaline batteries are widely used in electronic devices which are remarkably miniaturized and lightweight because they are excellent in charge / discharge characteristics and overcharge / overdischarge characteristics and can be repeatedly used with a long life. The characteristics of such an alkaline battery greatly depend on the characteristics of the battery separator.

The following performance is generally required for the alkaline battery separator. (1) The positive electrode and the negative electrode can be physically separated. (2) It must have electrical insulation to prevent short circuits. (3) Must have electrolytic solution resistance. (4) It has electrochemical oxidation resistance. (5) It exhibits low electric resistance in a state of containing an electrolytic solution. (6) The electrolytic solution is easily wetted and the amount of the electrolytic solution retained is large. (7) It must have the strength and rigidity to withstand the battery assembly process. (8) Do not emit harmful substances for batteries. (9) Be breathable.

Therefore, conventionally, a nonwoven fabric made of polyamide fiber is used as a separator for alkaline batteries, which is easily wetted by the electrolytic solution and has a large holding amount, and has low electric resistance in the state of containing the electrolytic solution. In addition, a polyolefin fiber non-woven fabric is used as a separator for batteries that require durability at relatively high temperatures.

However, the above-mentioned separator for an alkaline battery made of a nonwoven fabric of polyamide fiber has a drawback that nitrogen oxide is eluted from the fiber by repeated use and the life of the battery is shortened. Further, since the one made of the polyolefin fiber nonwoven fabric has a low water absorption, it is difficult to be wet with the electrolytic solution, and the amount thereof retained is small. Therefore, this non-woven fabric may be subjected to a surfactant treatment or the like, but the surfactant has a problem with the electrolytic solution resistance, and it has been possible to sufficiently improve the liquid absorbing property and the liquid retaining property of the electrolytic solution. Not in.

Therefore, recently, in order to improve both the electrolytic solution resistance and the electrochemical oxidation resistance, and the wettability of the electrolytic solution and the retained amount thereof, for example, for an alkaline battery disclosed in JP-A-3-257755. A separator has been proposed. This separator is composed of a non-woven fabric containing 35% or more of splittable conjugate fibers of polyolefin and ethylene vinyl alcohol copolymer. However, a separator made of a non-woven fabric containing 35% or more of the splittable conjugate fiber described above,
As the content of the splittable conjugate fiber increases, the air permeability of the nonwoven fabric becomes very poor, and oxygen generated in the positive electrode becomes less likely to permeate to the negative electrode side, resulting in an increase in battery internal pressure. In addition, the wettability of the non-woven fabric with respect to the electrolytic solution and the amount of retention thereof are insufficient.

Further, in Japanese Patent Laid-Open No. 2-181363,
A fiber comprising a polyolefin polymer having a hydroxyl group on the surface of the core fiber, a fiber comprising a polyolefin polymer having an amide group on at least the surface of the core fiber, and a composition comprising a synthetic pulp were made by a papermaking method. A separator for an alkaline secondary battery is disclosed. However, this separator has the drawback that nitrogen oxides are eluted from the fibers in which the polyolefin polymer having an amide group is present on the surface of the core fiber, which shortens the life of the battery, and the polyethylene type used as a synthetic pulp. Synthetic pulp
Since it is flat like wood pulp and has been fibrillated, it has the drawbacks of filling the voids in the sheet, impairing the permeability of the electrolyte, and increasing the electrical resistance.

[0008]

Therefore, it is not possible to make the separator thin while having the above-mentioned various performances, and the alkaline battery using such a separator is a recent cordless device. There is a problem that it is not possible to achieve high-level characteristics such as high capacity, long life, and high reliability, which are necessary for use.

An object of the present invention is to provide a non-woven fabric for an alkaline battery separator, which has a low basis weight and also has the above-mentioned various properties, and is particularly excellent in both the initial liquid absorbing property and liquid retaining property of an electrolytic solution, and a method for producing the same. To do.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has invented a nonwoven fabric for an alkaline battery separator and a method for producing the same.
That is, the non-woven fabric for an alkaline battery separator of the present invention is a polyethylene fluff pulp made of a pulp pulp obtained by beating pulp-spun high-density polyethylene fibers until the average fiber length becomes 1.20 mm or less, and one or two kinds.
It is characterized in that it is composed of a polyolefin fiber having at least one ethylene vinyl alcohol copolymer component.

Further, a splittable conjugate fiber in which a polyolefin fiber having one or more ethylene vinyl alcohol copolymer components is bonded to a polyolefin polymer and an ethylene vinyl alcohol copolymer, Alternatively, the heat-adhesive conjugate fiber comprises polyolefin as a core component and ethylene-vinyl alcohol copolymer as a sheath component.

The method for producing a non-woven fabric for an alkaline battery separator according to the present invention comprises a polyethylene fluff pulp comprising polyethylene pulp which is beaten from flash-spun high-density polyethylene fibers until the average fiber length becomes 1.20 mm or less, and one or A polyolefin-based fiber having two or more ethylene vinyl alcohol copolymer components is dispersed in water to form a slurry, and the slurry is made into a paper by a wet papermaking method to form a web, and then the web. Is characterized by being hot pressed.

As the polyethylene fluff pulp in the present invention, a high-density linear polyethylene resin is dissolved in trichlorofluoromethane, and a highly saturated mixed solution thereof is flash-spun to give a very fine and highly flexible continuous reticulated fibril structure. Use filament strands. This strand is formed into a sheet, the sheet is lightly solidified and cut into small pieces to produce a 2 wt% concentration aqueous slurry for refining, and further polyvinyl alcohol and a surface active agent are used. Agent 2
2% by weight dispersion enhancer prepared at 0: 1 was added,
It is possible to use one that is passed through a single disc refiner and adjusted to an appropriate fiber length.

The morphology of the polyethylene fluff pulp in the present invention has a fiber diameter of 1 to 20 μm as observed by a microscope and an average fiber length of 1.20 mm or less, preferably 0.5 according to TAPPI T232hm-85.
The range is from 1.0 mm. Furthermore, TAPPI T22
The drainage coefficient measured according to 1-OS63 is given in seconds per gram and is 2.5 seconds / g or more, preferably 3 seconds / g or more.

The above-mentioned polyethylene fluff pulp has an excellent specific surface area, a high fiber orientation, and an excellent water wettability. Therefore, when it is used as a separator for alkaline batteries, it absorbs water into an electrolytic solution. Then, the effect of improving the liquid retention property and the tensile strength was found. Further, in the conventional synthetic pulp, when the blending amount is increased, the air permeability and the permeability of the electrolytic solution are deteriorated, whereas in the polyethylene fluff pulp, the fibers are short and fluffy, and the air permeability is deteriorated. It has the characteristic of never happening.

The polyolefin fiber having the ethylene vinyl alcohol copolymer component in the present invention is a known fiber formed from an ethylene vinyl alcohol copolymer, and is a known fiber formed from an ethylene vinyl alcohol copolymer. It includes various types of bicomponent fibers formed from other polymers. You may use these individually or in mixture of 2 or more types.

The ethylene vinyl alcohol copolymer can be obtained by saponifying a copolymer of ethylene and vinyl acetate. In terms of its spinnability and liquid retention, MF
R (Melt Fluorate) 20-100 ethylene
Content of ~ 45 mol% is preferable, and saponification degree is 98%.
It is more preferable that the above is satisfied.

Polyolefins such as polyethylene and polypropylene are preferable as the above-mentioned other polymers used for forming the conjugate fiber, and polyolefins having MFR of 10 to 100 are particularly preferable.

As a preferred example of the composite fiber, one component of the ethylene vinyl alcohol copolymer and the other polymer is interposed between the other components, and each component is divided into at least two or more and each of them is divided. A splittable conjugate fiber is a constituent unit of the fiber cross section, and a part of each adjacent constituent unit is exposed on the fiber surface. In order to secure sufficient water absorption, it is preferable that the ethylene vinyl alcohol copolymer component accounts for 20% or more of the fiber surface.

Another preferred example of the conjugate fiber is a core-sheath type conjugate fiber having an ethylene vinyl alcohol copolymer and another polymer as a sheath component and a core component, respectively, or a (co) polymer thereof. Examples of the heat-bondable conjugate fiber include the bimetal-type conjugate fiber and the like.

In order to adjust the pore diameter when the nonwoven fabric is formed, the fiber diameter of the splittable conjugate fiber after splitting is 3 to 10 μm.
m, and the fiber diameter of the heat-adhesive conjugate fiber is preferably 15 to 25 μm.

In the non-woven fabric for an alkaline battery separator of the present invention, in order to secure sufficient air permeability and prevent a short circuit, the maximum pore diameter is 70 μm or less and the average pore diameter is 25 μm.
It is preferable that m or less and the maximum pore diameter / average pore diameter is 3 or less.

From the viewpoint of the air permeability when the nonwoven fabric is formed and the liquid retaining property of the electrolytic solution, a polyolefin system containing 5 to 30% by weight of polyethylene fluff pulp and an ethylene vinyl alcohol copolymer component. Of the fibers, 10 to 30% by weight of splittable conjugate fibers and 40 to 40 of heat-bondable conjugate fibers are used.
A nonwoven fabric produced by mixing 70% by weight is particularly preferable.

The non-woven fabric for an alkaline battery separator of the present invention can be formed by using the above fibers by a known method such as a wet papermaking method, a card method, a cross layer method or a random weber method. The wet papermaking method described in 1) is particularly preferable because it can easily form a nonwoven fabric having a uniform texture and having an appropriate pore diameter.

That is, first, polyethylene fluff pulp and a polyolefin fiber containing one or more ethylene vinyl alcohol copolymer components are dispersed in water together with a surfactant to form a slurry. The slurry is made into paper to produce a web having a thickness of 250 μm or less, for example. Then, the web is subjected to hot pressing such as calender roll processing to produce a non-woven fabric adjusted to an appropriate thickness. The thickness of the nonwoven fabric is preferably 180 μm or less so that it can be suitably used as an alkaline battery separator for cordless devices. It is preferable to treat the web with a wetting agent such as a surfactant before hot pressing.

[0026]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.
In the examples, all parts and% are by weight.

Example 1 5 parts of polyeretin fluff pulp having a fiber diameter of 1 to 20 μm and an average fiber length of 0.76 mm, a fineness of 3 denier composed of crystalline polypropylene and an ethylene vinyl alcohol copolymer, 30 parts of a splittable conjugate fiber having a fiber length of 5 mm (hereinafter referred to as fiber A), polypropylene as a core component,
The ethylene vinyl alcohol copolymer is a sheath component, the core-sheath volume ratio is 50:50, the fineness is 2 denier, and the fiber length is 10 m.
A heat-bonding composite fiber of m (hereinafter referred to as fiber B) was mixed at a ratio of 65 parts to prepare a web having a basis weight of 50 g / m ² by a wet papermaking method. Then, the web was impregnated with 0.10 g / m ² of a surfactant by a size press, the web was dried by a hot air dryer, and then calender roll treatment was performed at a low temperature to obtain a thick film. A nonwoven fabric for an alkaline battery separator was obtained by cutting into a nonwoven fabric having a thickness of 180 μm and cutting.

Example 2 A nonwoven fabric for an alkaline battery separator was prepared in the same manner as in Example 1 except that the ratio of polyethylene fluff pulp, fiber A and fiber B used in Example 1 was changed to 15:25:60. Obtained.

Example 3 Polyethylene fluff pulp having an average fiber length of 1.17 mm was used in place of the polyethylene fluff pulp used in Example 1, and the ratio of the polyethylene fluff pulp, fiber A and fiber B was 30: A non-woven fabric for an alkaline battery separator was obtained in the same manner as in Example 1 except that the ratio was set to 25:45.

Comparative Example 1 A non-woven fabric for an alkaline battery separator was obtained in the same manner as in Example 2 except that polyethylene fluff pulp having an average fiber length of 1.28 mm was used.

Comparative Example 2 A nonwoven fabric for an alkaline battery separator was obtained in the same manner as in Example 1 except that polyethylene fluff pulp was not used and the ratio of fiber A and fiber B was 30:70.

Comparative Example 3 The current nylon dry-type nonwoven fabric (melt spinning type) was used as an alkaline battery separator nonwoven fabric.

The nonwoven fabrics for alkaline battery separators produced in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated by the following evaluation methods, and the results are shown in Table 1.

Evaluation method: [Longitudinal tensile strength] When wound around the electrode plate, since it is wound while pulling in the flow direction, the tensile strength (kg / 2 cm width) in the longitudinal direction (flow direction) is measured to evaluate the strength of the nonwoven fabric. did. Tensile strength was measured by JIS-8113, the separator was cut into a width of 2 cm and a length of 20 cm, and a load at break was measured 10 times at a full scale of 10 kg using a Tensilon measuring machine (HTM-100 manufactured by Orientec Co., Ltd.). The average value was shown.

Frazier Air Permeability The Frazier air permeability (cc / cm ² / sec) was measured as an evaluation of the ease with which oxygen generated from the positive electrode side permeates the negative electrode side through the nonwoven fabric. Frazier air permeability is JIS-L-1096
Thus, the amount of air passing through the test piece was measured 5 times using a Frazier type air permeability tester, and the average value was shown.

[Pore Diameter] The pore diameter (μm) was measured as an evaluation of the permeability of oxygen generated from the positive electrode side to the negative electrode side and whether or not a short circuit occurs due to the large pore diameter of the nonwoven fabric.
Regarding the pore diameter, the maximum pore diameter and the average pore diameter were determined by the bubble point method and the mean flow method described in ASTM-F-316.

[Liquid-absorbing property] As an evaluation of the ease of impregnation of the non-woven fabric with the electrolytic solution (initial wettability), the electrolytic solution absorbing speed (3
The cm) after 0 minutes was measured. The electrolyte absorption rate was determined by taking three 2.5 cm x 18 cm test pieces from the length direction of each sample, predrying them at 40 ± 5 ° C, and reducing the water content to below the official moisture content. Is left in a test room under standard greenhouse conditions, then the sample is weighed at intervals of 1 hour or more, and the difference in mass before and after that is within 0.1% of the mass after that (this state is the water equilibrium state). That is). Next, test piece 2
Caustic potash (K) with a specific gravity of 1.3 (20 ° C) at 0 ± 2 ° C
OH) solution is placed in a water tank with a horizontal bar of a predetermined height, each sample is aligned with its lower end and fixed with a pin, and each sample is hung down. The lower end of the sample was soaked in the liquid by 5 cm, and after 30 minutes, the height at which the KOH solution rose due to the capillary phenomenon was measured.

[Liquid Retention] As an evaluation of the liquid retention of the electrolytic solution of the nonwoven fabric, the electrolytic solution retention rate (%) was measured. The electrolytic solution retention rate is the weight W (mg) when three equilibrium states are obtained by collecting three 10 cm × 10 cm test pieces from each sample.
To measure. Next, the test piece was spread in the above KOH solution and immersed, left for 1 hour or more, taken out of the solution, and one corner of the test piece was clipped and hung, and after 10 minutes, the weight W ₁ (mg) Was measured, and the initial electrolyte solution retention rate (%) was calculated by the following formula 1.

[0039]

[Formula 1] Electrolytic solution retention rate (%) = [(W ₁ −W) / W] × 100

[Alkali resistance] As an evaluation of the alkali resistance of the nonwoven fabric, the weight loss rate (%) after the alkali treatment was measured. The weight loss rate after alkali treatment is 10 cm x from each sample.
Three test pieces with a size of 10 cm were sampled, the weight W (mg) at the time of water equilibrium was measured, and then the test piece was dipped in a KOH solution having a concentration of 30% corresponding to an electrolytic solution to obtain 80 ± 2.
Store in an atmosphere at ℃ for 7 days. After that, the sample taken out was washed with water and dried until reaching the neutralization point, and the weight W ₂ (mg) at the time of reaching a water equilibrium state again was measured, and the weight loss rate (%) after alkali treatment was calculated by the following formula 2. It was

[0041]

[Formula 2] Weight loss rate after alkali treatment (%) = [(W-
W ₂ ) / W] × 100

[0042]

[Table 1]

From the results shown in Table 1 above, the non-woven fabrics for alkaline battery separators of Examples 1 to 3 were the same as those of Comparative Example 2 or 2.
Compared to a non-woven fabric for an alkaline battery separator consisting only of a polyolefin fiber having at least one ethylene vinyl alcohol copolymer component, in order to blend polyethylene fluff pulp in addition to those fibers, It excels in liquid absorption and electrolyte retention. In addition, in comparison with the nylon non-woven fabric for alkaline battery separator of Comparative Example 3,
Excellent tensile strength and alkali resistance.

The non-woven fabric for an alkaline battery separator of Comparative Example 1 is a case where the average fiber length of polyethylene fluff pulp exceeds 1.20 mm as compared with the non-woven fabric for an alkaline battery separator of Example 2, but it is difficult to disperse. Becomes
Tangles and deception occurred. As a result, countless small lumps of polyethylene fluff pulp were formed in the non-woven fabric for an alkaline battery separator, and the formation became poor. In addition, since small polyethylene fluff pulp lumps were generated, various performances such as tensile strength, air permeability, liquid absorption and liquid retention were inferior to those of the non-woven fabric for an alkaline battery separator of Example 2.

[0045]

The non-woven fabric for alkaline battery separators of the present invention contains a polyolefin fiber having a polyethylene fluff pulp and an ethylene vinyl alcohol copolymer component, and therefore has high strength and alkali resistance of the fiber itself. Also, it has an excellent liquid absorbing property to the electrolytic solution. for that reason,
High resistance to electrolytic solution and resistance to electrochemical oxidation, easy to wet with electrolytic solution, and large amount of liquid retention. Further, the nonwoven fabric for an alkaline battery separator of the present invention produced by using these fibers in combination has a low basis weight and has a uniform pore diameter, and therefore, has a pore diameter smaller than that of the conventional one and obtains the same air permeability as the conventional one. You can also Therefore, the thickness of the non-woven fabric can be further reduced and the weight can be reduced. As a result, in the alkaline battery separator non-woven fabric and the method for producing the same of the present invention, it has various performances required for an alkaline battery separator, and is particularly excellent in the electrolyte absorbability and liquid retention, high capacity, long life, and high reliability. It can be suitably used for an alkaline battery of a cordless device that requires high characteristics such as a property.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area D21H 15/10

Claims (3)

[Claims] 1. A polyethylene fluff pulp consisting of polyethylene pulp obtained by beating pulp-spun high-density polyethylene fibers until the average fiber length becomes 1.20 mm or less, and one or more ethylene vinyl alcohol copolymers. A non-woven fabric for an alkaline battery separator, which is composed of a polyolefin fiber having a component. 2. A split-type composite fiber in which a polyolefin fiber is formed by joining a polyolefin polymer and an ethylene vinyl alcohol copolymer, or polyolefin is used as a core component, and an ethylene vinyl alcohol copolymer is used as a sheath component. The non-woven fabric for an alkaline battery separator according to claim 1, which is a heat-bondable composite fiber. 3. A polyethylene fluff pulp composed of polyethylene pulp obtained by beating pulp-spun high-density polyethylene fibers until the average fiber length becomes 1.20 mm or less, and one or more ethylene vinyl alcohol copolymers. An alkaline battery characterized in that a polyolefin-based fiber having a component is dispersed in water to form a slurry, the slurry is made into a paper by a wet papermaking method to form a web, and then the web is hot pressed. A method for producing a nonwoven fabric for a separator.