JP3217094B2 - Manufacturing method of 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 nonwoven fabric made of polyamide fibers such as 6-nylon and 6,6-nylon or polyolefin fibers such as polypropylene has been widely used. Although the separator made of this dry nonwoven fabric has high mechanical strength and good workability, the increase in the electrode active material accompanying the recent increase in the capacity of the battery or the thinning of the separator causes the movement of the falling active material and the electrolyte solution. Has a problem of insufficient holding power.

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, since the air permeability of the melt blown nonwoven fabric is low, when the active material is increased, a large amount of the generated reaction gas cannot be escaped, and as a result, the internal pressure of the battery increases,
There was a drawback that quick charging became difficult. Furthermore, since the melt-blown nonwoven fabric has low mechanical strength, it is difficult to perform winding processing at the time of assembling a battery, and there is a problem that a hole is formed by cutting at an electrode crack edge during use.

[0004] On the other hand, attempts have been made to impart strength to the dry nonwoven fabric, prevent the active material from migrating, and retain the electrolytic solution by integrating the dry nonwoven fabric and the meltblown nonwoven fabric by lamination. I have.
For example, JP-A-61-281454 discloses that the single fiber diameter is 0.
A battery separator is described in which a polyester melt blown web having a thickness of 1 to 2 μm and a nonwoven fabric having a single fiber diameter of 5 μm or more are laminated and integrated by spraying high-pressure water.

[0005] The method of laminating and integrating by injection of high-pressure water is as follows.
Since bonding is performed only by entanglement of fibers without using any adhesive, impurities etc. are not eluted or the pore size is not covered by the adhesive, and through holes are formed by the action of high-pressure water Therefore, it is possible to obtain a gas separator having excellent gas permeability, and it can be said that this is a preferable method for stacking and integrating the battery separator.
However, the nonwoven fabric sprayed with high-pressure water has a property that its maximum pore size becomes larger, and thus has a problem that the function of preventing movement of the active material is hindered.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and provides gas permeability without impeding the function of preventing the movement of an active material.
Still another object is to provide a method for producing a battery separator that can impart mechanical strength.

[0007]

According to the first aspect of the present invention, a melt-blown nonwoven fabric made of an alkali-resistant synthetic resin is entangled with high-pressure water and then subjected to a peripheral speed reduction. A method for producing a battery separator characterized by hot pressing between different rolls,
According to the invention of claim 2, after a melt-blown nonwoven fabric made of an alkali-resistant synthetic resin and a short fiber web made of an alkali-resistant synthetic resin are entangled with high-pressure water (hereinafter referred to as “water entanglement treatment”). And hot pressing between rolls having different peripheral speeds.

[0008] The melt blow method is a method in which melt spinning is performed.
A high-speed heating air stream is jetted from both sides to thin the fibers, which are collected on a screen to form a nonwoven fabric. According to the melt-blowing method, ultrafine fibers having an average fiber diameter of 0.5 to several tens of μm can be obtained. However, it is preferable to use a melt-blown nonwoven fabric having an average fiber diameter of 1.5 to 8 μm as the material used in the present invention. 1.5 μm average fiber diameter
If the average fiber diameter is less than 8 μm, the maximum pore diameter becomes too large to prevent the movement of the electrode active material. Basis weight of the meltblown nonwoven fabric is 40 to 100 g / m ^2, thickness 360～900Myuemu, porosity 90%
A degree is suitably used.

The alkali-resistant synthetic resin constituting the melt-blown nonwoven fabric 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 resins and polystyrene resins. Etc. can be used.

As the water entanglement treatment, a conventionally known method can be employed. As the support on which the water-entangled material is placed, 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 the water-entangled material After passing through, a non-porous material can be used which rebounds against the support. In addition, a water stream can be jetted from both sides of the entangled material.

The conditions for the water entanglement treatment are as follows: the nozzle orifice diameter is 0.05 to 0.15 mm, and the orifice interval is 0.5 to 1.5 m.
m, hydraulic 30~70kg / cm ^2, the distance from the orifice to the hydroentanglement product is 5 to 30 cm, the number of times for passing is 2 to 5 times is appropriate, production rate, suitably by the basis weight, etc. of the aqueous fluid Set.

By subjecting the meltblown nonwoven fabric to the hydroentanglement treatment, a through hole is formed in the meltblown nonwoven fabric, so that gas permeability is improved. Further, the density of the fibers constituting the melt-blown nonwoven fabric can be partially increased by the hydroentanglement treatment, and the melt-blown nonwoven fabric has a minimum thickness against external force due to the portion where the fiber density is increased. Can be secured, so that the retention of the electrolytic solution is improved.

However, at the same time, the maximum pore diameter is increased to about three times, so that it is difficult to completely prevent the movement of the active material. Therefore, the present inventors have conducted intensive studies and found that a melt-blown nonwoven fabric subjected to hydroentanglement treatment is
It has been found that by treating between rolls having different peripheral speeds, the movement of the active material can be prevented without substantially lowering the retention of the electrolytic solution and the gas permeability.

That is, the maximum pore diameter can be reduced by about 50% by applying a shearing force by treating between rolls having different peripheral speeds, and furthermore, a through-hole penetrating perpendicularly to the surface of the nonwoven fabric. Can be inclined with respect to the surface of the nonwoven fabric, so that the movement of the active material can be further prevented.

The peripheral speed ratio of the roll is greater than 1: 1 and 1:
It is preferably 1.5 or less. When the peripheral speed ratio exceeds 1: 1.5, wrinkles are generated in the nonwoven fabric, and a uniform separator cannot be obtained, which is not preferable.

The hot pressing by the above-mentioned roll is performed after the melt-blown nonwoven fabric subjected to the hydroentanglement treatment is dried by a hot-air dryer or the like.

The hot pressing is preferably performed at the crystallization temperature of the fibers constituting the melt blown nonwoven fabric. Here, the crystallization temperature refers to a temperature range in which the crystallization of the non-crystalline portions of the fibers constituting the melt-blown nonwoven fabric proceeds when the meltblown nonwoven fabric is heated, and is a melt-blown material obtained by a differential scanning calorimetry or the like. In the differential heat curve of the nonwoven fabric, it refers to a temperature range higher than the glass transition temperature and lower than the melting point, and an inflection point of the differential heat curve between the lowest temperature and the maximum value and the highest temperature or lower. For example, the fibers that make up the meltblown nonwoven fabric
For 6-nylon, the crystallization temperature is 77-187 ° C, for 6,6-nylon 100-238 ° C, for polypropylene 55-140 ° C, for polyphenylene sulfide 106-243 ° C. It is. The linear pressure of the heat press is 0.6-5kg
/ cm is preferable. When the linear pressure is less than 0.6 kg / cm, sufficient strength cannot be obtained, and when it exceeds 5 kg / cm, the porosity is low.

The fibers constituting the melt-blown nonwoven fabric are slightly stretched when a high-speed heating air stream is jetted, but the stretching degree is low and has many non-crystalline portions. When hot pressed under the conditions described above, only the non-crystalline part is softened and bonded, but the crystalline part is not affected and the original state is maintained. Strength can be imparted without occurring. Moreover, since the fibers in the non-crystalline portion adhere and adhere to the crystallization, the strength of the fibers constituting the non-woven fabric also increases.

For the hot press, a calender roll having a heating zone is used, and the roll surface is heated to the crystallization temperature and pressed at the same time, or the roll surface is crystallized immediately after the melt blown nonwoven fabric is heated to the crystallization temperature in advance by a drier or the like. A method in which the nonwoven fabric is pressed with a calender roll heated to the formation temperature can be employed. In the latter case, if the melt-blown nonwoven fabric 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. Drying with a hot air dryer is also preferably performed at a temperature at which crystallization of the non-crystalline portion is not promoted.

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.

After laminating the short fiber web on the melt-blown nonwoven fabric, it is subjected to a hydroentanglement treatment so that the short fiber web and the meltblown nonwoven fabric are entangled and integrated, whereby the mechanical strength can be improved.

The staple fiber web is a staple fiber formed into a web by a conventionally known dry method, air lay method, wet method or the like. The staple fiber web preferably has a basis weight of 10 to 50 g / m ^2. Used for

As the short fibers, polyamide fibers such as 6-nylon and 6,6-nylon, polyolefin fibers such as polypropylene and polyethylene, polyphenylene sulfide fibers, aramid fibers and the like can be used. It is preferable to use a resin having an adhesiveness having a lower melting point than that of a synthetic resin, since high strength can be obtained. Also, split fibers such as 6-nylon / 6,6-nylon, polyethylene / polypropylene, polyethylene / polyethylene terephthalate, 6-nylon / polyethylene, 6-nylon / polypropylene core-sheath or side-by-side composite fibers, orange fibers, etc. Can also be suitably used. The average fiber diameter of the short fibers is not particularly limited, but the thinner and higher the strength, the more preferable. The fiber length of the short fibers is preferably 10 to 80 mm.

The weight ratio of the melt blown nonwoven fabric to the short fiber web is preferably 80% by weight: 20% by weight to 60% by weight: 40% by weight, and the basis weight after lamination is preferably 40 to 100 g / m ² . If the short fiber web is less than 20% by weight, the reinforcing effect cannot be obtained. If the short fiber web exceeds 40% by weight, the maximum pore size increases, and the liquid retention rate is undesirably reduced. As described above, when a material having an adhesiveness having a lower melting point than that of the synthetic resin constituting the meltblown nonwoven fabric is used, the short fiber web has sufficient strength at 20% by weight. Excellent in all of the rate, the function of preventing the movement of the active material, the air permeability, and the strength are obtained.

The method of laminating the melt-blown nonwoven fabric and the short fiber web is, in addition to the two-layer structure, a three-layer structure in which the short fiber web is on both sides of the melt-blown nonwoven fabric. A three-layer structure is also possible.

The hydroentanglement process and the process using a calender roll may be performed under the same conditions as those described above.

Further, 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.

(Porosity) 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%.

(Liquid retention ratio) A sample (mass W) in a water equilibrium state was immersed in a potassium hydroxide solution having a specific gravity of 1.30 (20 ° C.) at room temperature to be sufficiently absorbed (1 hour or more). And the mass (W ₁ ) after 10 minutes was measured and calculated by the following equation.

(Air permeability) Measured using a Frazier tester. (JIS L1096)

[0034]

[Example] Step 1: The entangled material is placed on a net screen moving at 10 m / min, and the nozzle orifice diameter is 0.07 mm.
Step of performing water entanglement three times from one side under the conditions of φ, orifice spacing 0.8 mm, distance from nozzle orifice to water entangled material 8 cm, water pressure 50 kg / cm ² . Step 2: A step of using a calender roll having a heating zone of 70 cm width and surface material of fluoro rubber and having a heating zone, arbitrarily setting the peripheral speed ratio of the roll, and heating and pressing at a temperature of 180 ° C. and a linear pressure of 4 kg / cm for 10 seconds.

(Examples 1 and 2, Comparative Examples 1 to 4) The average fiber diameter was about 3 μm and the basis weight was 58 g /
m ² , a melt-blown nonwoven fabric made of 6-nylon manufactured to have a thickness of 500 μm is referred to as a raw material 1, and the raw material 1 is
Comparative Example 1 was processed in Step 2 with a peripheral speed ratio of the rolls of 1: 1. The raw material 1 was treated in Step 1, dried with a hot air dryer, and then treated in Step 2 with the roll at a peripheral speed ratio of 1: 1.2 in Example 1, and treated in a ratio of 1: 1.5 with Example 2, The sample treated as 1: 1 was designated as Comparative Example 2, and the one treated at 1: 1.7 was designated as Comparative Example 3.

A melt-blown nonwoven fabric made of 6-nylon manufactured by the melt blow method to have an average fiber diameter of about 4 μm, a basis weight of 58 g / m ² , and a thickness of 470 μm is referred to as a raw material 2. In addition, a roller treated in Step 2 with a peripheral speed ratio of 1: 1 was used as Comparative Example 4, and the physical property values of each were shown in Table 1.

[0037]

[Table 1]

(Examples 3 and 4, Comparative Examples 5 and 7) A short fiber web was prepared from 6-nylon short fibers (2d × 38 mm) by a card method. Further, a melt-blown nonwoven fabric made of 6-nylon having an average fiber diameter of about 3 μm and a porosity of about 90% was produced by a melt blow method. The short fiber web and the meltblown nonwoven fabric are laminated at various weight ratios, and the total basis weight is
It was adjusted to 60 g / m ² . The obtained laminate is treated in step 1 and dried with a hot air drier, and then in step 2, the peripheral speed ratio of the rolls is 1:
The sample treated as 1 was used as Comparative Example 5 (weight ratio of short fiber web to melt blown nonwoven fabric 2: 8), and the peripheral speed ratio of the roll
Those treated as 1: 1.5 were treated in Example 3 (weight ratio 2: 8), Example 4 (weight ratio 4: 6), Comparative Example 6 (weight ratio 1: 9), and Comparative Example 7 (weight ratio 5: 5). ) And the physical properties of each are shown in Table 2.

Example 5 A short fiber web was formed from short polypropylene fibers (1.5 d × 38 mm) by a card method. This short fiber web and a melt-blown nonwoven fabric made of 6-nylon having an average fiber diameter of about 3 μm and a porosity of about 90% were laminated at a weight ratio of 2: 8 so that the total basis weight was 60 g / m ² . The obtained laminate was treated in step 1, dried with a hot air drier, and then treated in step 2 with a roll peripheral speed ratio of 1: 1.5, which was designated as Example 5, and the physical properties are shown in Table 2.

[0040]

[Table 2]

Generally, in order to completely prevent the movement of the electrode active material in the battery separator, the maximum pore size is 45 μm.
It is required to be less than μm. As is clear from Table 1, Comparative Example 2 which was subjected to the hydroentanglement treatment was:
Compared to Comparative Example 1 not subjected to the hydroentanglement treatment, the liquid retention rate and the air permeability are superior, but the maximum pore diameter is 64.
It has expanded to μm. In Examples 1 and 2 processed between rolls having different peripheral speeds, the maximum hole diameter was 45%.
μm or less, and the liquid retention rate and air permeability were slightly inferior to those of Comparative Example 2, but Comparative Example 1
Excellent enough compared to Further, in the case of Comparative Example 3, since the treatment was carried out at a peripheral speed ratio exceeding 1: 1.5, wrinkles were generated in the nonwoven fabric, the resulting sheet was not uniform, and was not practically usable. In Comparative Example 4, since the melt-blown nonwoven fabric having a larger average fiber diameter than that of the raw materials of Examples 1 and 2 was used as the raw material, Comparative Example 1 was used in terms of air permeability.
Although it is superior to the above, it is inferior in liquid retention because it is not subjected to the water entanglement treatment.

As is clear from Table 2, when the short fiber web is laminated and subjected to the hydroentanglement treatment, the 10% modulus is greatly improved, but even in this case, the treatment is performed between rolls having different peripheral speeds. Comparative Example 5, which was not prepared, did not satisfy the maximum pore diameter of 45 μm or less. In the case of Comparative Example 6, the reinforcing effect was not obtained because the weight ratio of the short fiber web was less than 20% by weight. Conversely, in the case of Comparative Example 7, the weight ratio of the short fiber web was 40% by weight. Maximum hole diameter of 45
μm or less is not satisfied, and the liquid retention is also low.

Examples 3 to 5 have a 10% modulus,
Satisfactory values are shown for the maximum pore size, liquid retention rate, and air permeability. In particular, in the case of Example 5, the synthetic resin constituting the melt-blown nonwoven fabric as the short fiber, that is, 6-
By using a polypropylene short fiber having a lower melting point than nylon, the adhesion between the meltblown nonwoven fabric and the short fiber web is improved, so even if the weight ratio of the short fiber web is small, a 10% modulus shows a high value. It shows satisfactory values for the maximum pore size, liquid retention rate, and air permeability.

[0044]

According to the manufacturing method described in claim 1,
It is possible to obtain a battery separator having excellent liquid retention, air permeability, and a function of preventing an active material. Further, according to the manufacturing method described in claim 2, a battery separator excellent in strength in addition to a liquid retention rate, air permeability, and a function of preventing an active material can be obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-114055 (JP, A) JP-A-60-75659 (JP, A) JP-A-62-299557 (JP, A) JP-A-1- 118659 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 2/14-2/18

Claims (2)

(57) [Claims] 1. A method for producing a battery separator, comprising: subjecting a melt-blown non-woven fabric made of an alkali-resistant synthetic resin to an entanglement treatment with a high-pressure water stream, followed by hot pressing between rolls having different peripheral speeds. 2. A melt-blown nonwoven fabric made of an alkali-resistant synthetic resin and a short fiber web made of an alkali-resistant synthetic resin are entangled with high-pressure water, and then hot-pressed between rolls having different peripheral speeds. Of producing a battery separator.