JP3219819B2 - Battery separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator 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 Conventionally, as a separator for an alkaline storage battery, a dry short-fiber nonwoven fabric made of polyamide fiber such as 6-nylon and 6,6-nylon or polyolefin fiber such as polypropylene has been widely used. The separator made of this short fiber non-woven fabric has high mechanical strength and good workability, but due to the increase in the number of electrode active materials due to the recent increase in battery capacity, or the thinning of the separator,
Problems have arisen, such as the movement of the falling-off active material and insufficient holding power of the electrolytic solution.

In order to solve these problems, a separator made of a melt-blown nonwoven fabric has been proposed.
Since the melt-blown non-woven fabric is made of ultra-fine fibers, the maximum pore size of the non-woven fabric can be reduced, and a high porosity can be obtained. Can be resolved. However, the melt-blown nonwoven fabric has a low air permeability, so that when the active material is increased, a large amount of reactive gas cannot be escaped, and as a result, the internal pressure of the battery increases,
There was a drawback that quick charging became difficult.

[0004] Further, there is also known a laminate obtained by laminating a short fiber nonwoven fabric and a melt blown nonwoven fabric. For example, JP-A-61-281454 discloses that a melt-blown non-woven fabric having a single fiber diameter of 0.1 to 2 μm and a short-fiber non-woven fabric having a single fiber diameter of 5 μm or more are pressure-bonded, adhesive, or sprayed with high-pressure water. A laminated battery separator is described.

[0005] A melt blown nonwoven fabric and a short fiber nonwoven fabric are
Laminated and integrated by pressure bonding or adhesive, compared to a single melt-blown nonwoven fabric with the same basis weight, show excellent values in strength and air permeability, and show the same performance in preventing migration of active material, There is a problem that the battery has a short life due to liquid leakage due to poor liquid retention. In addition, when the melt-blown nonwoven fabric and the short-fiber nonwoven fabric are laminated and integrated by spraying high-pressure water, the through-holes are formed in the melt-blown nonwoven fabric, and the maximum pore diameter increases. There was a drawback that it was difficult to prevent it.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and provides a battery separator excellent in the function of preventing the movement of an active material, the permeability, and the retention of an electrolyte. The purpose is to provide.

[0007]

Means for Solving the Problems] To solve the above problems, the present invention is "basis weight 10 g / ^{m 2} or more, 60 g / ^{m 2}
A battery separator comprising the following melt-blown web and a hydro-entangled nonwoven fabric obtained by subjecting a melt-blown web to a hydro-entanglement process, by lamination and integration by thermocompression bonding. ”.

[0008]

As described above, the melt-blown nonwoven fabric has excellent properties in preventing the movement of the active material and in retaining the electrolyte, but also has a disadvantage in that the air permeability is poor. On the other hand, the conventional one in which the melt-blown non-woven fabric and the short-fiber non-woven fabric having a lower fiber density than the melt-blown non-woven fabric are laminated and integrated can reduce the basis weight of the melt-blown non-woven fabric layer, compared to the melt-blown non-woven fabric with the same mesh. Therefore, the air permeability can be improved as a whole. However, the short-fiber nonwoven fabric having a coarse fiber density is inferior to the meltblown nonwoven fabric having the same weight in the electrolytic solution in holding ability, so that the holding ability of the entire laminate is reduced. In the present invention, as a nonwoven fabric laminated and integrated with the meltblown web, by using a hydroentangled nonwoven fabric subjected to a hydroentanglement treatment on the meltblown web, as a whole laminate, both characteristics of air permeability and retention of electrolyte solution are obtained. They found that it could be improved. That is, in the nonwoven fabric subjected to the hydroentanglement treatment, the density of the fibers constituting the nonwoven fabric is partially increased by the action of the water current, so that the retention of the electrolytic solution is improved.

In the present invention, the melt blown web is
Has a function as a filter for preventing movement of the active material. Melt blow web is a web obtained by jetting high-speed heated airflow from both sides while melt-spinning and thinning the fiber, collecting it on a screen to form a web, and having an average fiber diameter of 0.5 to more than 10 μm. Of ultrafine fibers. For use in the present invention, the average fiber diameter is 1.
It is preferred to use a 5-8 μm meltblown web. If the average fiber diameter is less than 1.5 μm, the strength of the single fiber is insufficient, and the air permeability is undesirably low. If the average fiber diameter exceeds 8 μm, the maximum pore size becomes too large, and it becomes difficult to prevent the movement of the electrode active material.

The basis weight of the melt blown web is 10 g.
/ M ² or more, and it is 60 g / m ² or less . Basis weight of the meltblown webs, as the air permeability becomes higher small, the basis weight is less than 10 g / m ^2, variations in the maximum pore size is increased, undesirably making it difficult to obtain a desired maximum pore size. In addition, the basis weight is 60
Even if the amount exceeds g / m ² , the maximum pore size hardly changes, and only a decrease in air permeability is caused. More preferably, the basis weight is 20 to 50 g / m ² and the porosity is 90
% Is preferably used.

The synthetic resin constituting the melt blown web of the present invention includes polyamide resins such as 6-nylon and 6,6-nylon, polyolefin resins such as polypropylene and polyethylene, or polyphenylene sulfide resin, polystyrene resin and polysulfone resin. And an alkali-resistant material such as a fluororesin.

Next, a description will be given of a hydroentangled nonwoven fabric laminated and integrated with the meltblown web.

Although the melt blown web is inferior in air permeability, the water entangled nonwoven fabric subjected to the water entanglement treatment has through holes formed therein, so that the air permeability is improved, and furthermore, the action of the water flow is increased. Since the fiber density is partially increased, the retention of the electrolyte is also improved. As the melt blown web constituting the hydroentangled nonwoven fabric, those described above can be used.

The basis weight of the hydroentangled nonwoven fabric is 10 g / m ² or more, and the total basis weight with the above-mentioned melt blow web is used.
It is appropriately selected so as to be 40 to 100 g / m ² .

As the water entanglement treatment, a conventionally known method can be adopted. The support on which the water entangled material is placed may be a perforated screen-shaped one in which the water flow penetrates the support after the water flow penetrates the water entangled material, or the water flow is entangled with the water entangled material. A non-porous material that penetrates the processed object and hits the support and rebounds can be used. In addition, a water stream can be jetted from both sides of the water-entangled entangled material.

The conditions for the water entanglement treatment are as follows: the nozzle orifice diameter is 0.05 to 0.20 mm, and the orifice interval is 0.5 to 1.5 m.
m, Distance pressure 30~70kg / cm ^2, from the orifice to the hydroentanglement treated is 5 to 30 cm, but the number of penetrating is suitably 2-5 times the production rate, of the hydroentangled treated Set appropriately according to the basis weight and the like.

Next, a method for laminating and integrating a melt blown web and a hydroentangled nonwoven fabric by thermocompression bonding will be described. In thermocompression bonding, it is necessary to set the temperature and pressure so that the surface of the melt blown web and the laminated surface do not form a film.

The thermocompression bonding is preferably performed at the crystallization temperature of the fibers constituting the melt blown web. Here, the crystallization temperature refers to a temperature range in which the crystallization of the non-crystalline portion of the fibers constituting the melt-blown web proceeds when the melt-blown web is heated, and is a melt-blown obtained by a differential scanning calorimetry or the like. In the differential thermal curve of the web, it refers to a temperature range that is higher than the glass transition temperature and lower than the melting point, and that is an inflection point of the differential heat curve that is equal to or higher than the lowest temperature and is equal to or higher than the maximum and equal to or lower than the highest temperature.
For example, the fibers constituting the melt blown web are 6-
In the case of nylon, its crystallization temperature is 77-187 ° C, in the case of 6,6-nylon it is 100-238 ° C, in the case of polypropylene it is 55-140 ° C, in the case of polyphenylene sulfide it is 106-243 ° C. . The pressure is preferably 0.6 to 5 kg / cm. If the linear pressure is less than 0.6 kg / cm, a sufficient adhesive strength cannot be obtained, and if it exceeds 5 kg / cm, the porosity becomes low.

The fibers constituting the melt blown web are slightly stretched when a high-speed heated airflow is injected, but the stretching degree is low and has many amorphous portions. When hot pressing is performed under the above conditions, only the non-crystalline portion is softened and bonded, but the crystalline portion is not affected, and the original state is maintained. Lamination and integration can be performed without occurrence. Moreover, since the fibers in the non-crystalline portion adhere and adhere to the crystallization, the strength of the fibers themselves constituting the web increases.

For the thermocompression bonding, a calender roll having a preheating zone is used, and the roll surface is heated to the crystallization temperature and pressed at the same time. A method of pressing the web with a calender roll heated to the crystallization temperature can be adopted. In the latter case,
If the melt blown web is not pressed immediately after reaching the crystallization temperature, the crystallization of the non-crystalline portion proceeds, and the effect as an adhesive cannot be obtained. Therefore, it is preferable that drying by a hot air dryer or the like after the hydroentanglement treatment is also performed at a temperature at which crystallization of the non-crystalline portion is not promoted.

Before thermocompression bonding, spray impregnation etc.
The case where thermocompression bonding is performed after the binder is attached to the laminated surface is also included in the thermocompression bonding according to the present invention.

The roll in the present invention includes a belt type or a combination of a roll and a belt type in addition to a normal roll. As the surface material of the roll in the case of a normal roll, a combination of rubber and rubber is most preferable, but a combination of steel-steel, steel-rubber, cotton-steel, and cotton-cotton is also possible.

The total basis weight after lamination of the melt blown web and the hydroentangled nonwoven fabric is preferably 40 to 100 g / m ² as described above, and the porosity after lamination and integration is 60 to 75%. Is preferred.

The form of lamination and integration of the melt blown web and the hydro-entangled nonwoven fabric is not only a two-layer structure but also a three-layer structure in which the hydroentangled nonwoven fabric is on both sides of the melt blown web. It is also possible to form a three-layer structure on both sides, and to insert a coarse material such as a mesh, a thread, or a knit for the purpose of reinforcement.

In addition, the alkali-resistant synthetic fibers used in the present invention are all highly hydrophobic and have low water retention of the fibers themselves. And the content of the electrolytic solution can be increased. As the hydrophilic treatment agent, an anionic, cationic or nonionic surfactant can be used, and a nonionic surfactant having particularly good alkali resistance is suitably used.

Hereinafter, the present invention will be further described with reference to examples. In addition, the measuring method or definition of the physical property value shown in this specification is as follows.

(Maximum pore diameter) This is based on the bubble point method, and the actual measurement was carried out using a porometer (POROMETER), a pore diameter distribution measuring instrument manufactured by Coulter Electronics Limited.

(Void ratio) Here, [rho the apparent density calculated from basis weight and thickness of the nonwoven fabric, [rho ₀ is the density of the synthetic fibers constituting the nonwoven fabric.

(10% modulus) The tensile strength when the elongation reaches 10%.

(Water retention ratio) The mass (W) of the sample in a water equilibrium state was measured, immersed in a potassium hydroxide solution having a specific gravity of 1.30 (20 ° C.) at room temperature, and allowed to absorb sufficiently for 1 hour or more. The mass (W ₁ ) after processing at 3000 rpm for 1 minute using a centrifuge with a radius of 9 cm was measured and calculated by the following equation.

(Air permeability) The air permeability was measured using a Frazier tester. (JIS L 1096)

[0032]

【Example】

Step A: The entangled material is placed on a net screen moving at 10 m / min, and the nozzle orifice diameter is 0.15 mm.
A process of performing water entanglement three times from one side under the conditions of φ, orifice interval 0.8 mm, distance from the nozzle orifice to the water entangled material 30 mm, and water pressure 40 kg / cm ² . Step B: a step of thermocompression bonding at a temperature of 180 ° C. and a linear pressure of 4 kg / cm for 10 seconds using a calender roll of fluoro rubber having a preheating zone.

Base Fabric A: A melt-blown web made of 6-nylon manufactured by melt-blowing so that the average fiber diameter is about 3.5 μm and the porosity is 90%. Base fabric B: a hydroentangled nonwoven fabric obtained by subjecting step A to base fabric A. Base cloth C: 6-nylon short fibers (2d × 3
Non-woven fabric formed by forming a web of core-sheath type composite fiber (2d × 38 mm) consisting of a core of 6-nylon and a sheath of 6 / 12-nylon copolymer, and heat-bonded.

(Examples 1 to 4, Comparative Example 4) For a battery made of a nonwoven fabric having a total basis weight of 80 g / m ² , which is obtained by laminating base cloths A and B with various basis weights and laminating and integrating them by thermocompression bonding in step B. In the separator, the basis weight of the base cloth A: the basis weight of the base cloth B was 10 g / m ² : 70 g /
m ² and an example those ^{1,20g / m 2: 60g / m} 2 and the ones in Example 2,30g / m ^2: implementing what was 50 g / m ² Example 3,50g / m
^2: implementing what was 30 g / m ² Example 4,6g / m ^2: what was 74 g / m ² was Comparative Example 4.

(Comparative Example 1) A battery separator made of a nonwoven fabric obtained by subjecting the base fabric A having a basis weight of 80 g / m ² to the thermocompression bonding in Step B was used as Comparative Example 1. (Comparative Example 2) basis weight only base fabric B of 80 g / m ^2, compared battery separator consisting subjected to thermocompression bonding step B nonwoven Example 2
And (Comparative Example 3) A battery separator made of a nonwoven fabric obtained by laminating a base fabric A having a basis weight of 30 g / m ^{2 and} a base fabric C having a basis weight of 50 g / m ² by thermocompression bonding in Step B was taken as Comparative Example 3. .

Table 1 shows the physical properties of Examples 1 to 4 and Comparative Examples 1 to 4 measured by the above methods. In addition, the porosity of Examples 1-4 and Comparative Examples 1-4 is 62-
It was 63%.

[0038]

[Table 1]

Generally, in order to prevent the movement of the active material, it is necessary that the maximum pore diameter is less than 45 μm. In addition, in the present invention, in addition to this, the air permeability is 5.5 cc / cm ²
s or more, and a battery separator that satisfies a liquid retention of 100% or more.

The battery separators according to the first to fourth embodiments of the present invention satisfy all of the above-mentioned objectives. In addition, although the 10% modulus was slightly reduced, there was no problem in workability during winding. The battery separator made of a single melt-blown nonwoven fabric not subjected to the hydroentanglement treatment shown in Comparative Example 1 has an air permeability of 5.5 cc / cm.
Does not satisfy ² · s or more and liquid retention rate of 100% or more. Comparative Example 2 was only the hydroentangled nonwoven fabric layer, and did not have the melt blown web layer having a function as a filter for preventing the movement of the active material, and therefore did not satisfy the maximum pore diameter of less than 45 μm, There is a high risk of causing active material migration. The conventional one in which the melt blown web shown in Comparative Example 3 and the short-fiber nonwoven fabric not subjected to the hydroentanglement treatment are laminated and integrated is excellent in the air permeability and the 10% modulus, but the liquid retention is greatly reduced. ing. In Comparative Example 4, the melt blown web had a basis weight of less than 10 g / m ² , and thus had a large variation in the maximum pore size, making it difficult to obtain stable quality. The battery separators according to the present invention of Examples 1 to 4 are generally well-balanced.

[0041]

The battery separator of the present invention has a basis weight of 10
g / m ² or more and 60 g / m ² or less and a hydro-entangled non-woven fabric made of the melt blow web are laminated and integrated by thermocompression bonding, so that the excellent active material migration prevention function of the melt blow web is provided. In addition, the air permeability, which is a drawback thereof, can be improved without impairing the retention of the electrolytic solution.

Claims (1)

(57) [Claims] 1. A basis weight 10 g / ^{m 2} or more, 60 g / ^{m 2} or more
A battery separator, wherein a lower melt blown web and a hydroentangled nonwoven fabric obtained by subjecting the meltblown web to a hydroentanglement treatment are laminated and integrated by thermocompression bonding.