JPH08311765A - Polyolefin nonwoven fabric - Google Patents

Abstract

PURPOSE: To produce a nonwoven fabric which is excellent in air permeability, hydrophilic properties, chemical resistance and tensile strength at breakage and suitably useful as a battery separator by surface-modifying a polyolefin nonwoven fabric by treatment with atmospheric pressure plasma. CONSTITUTION: A nonwoven fabric comprising a polyolefin sheath-core type conjugated fiber in which the core component is polypropylene and the sheath component is polyethylene is surface-modified with atmospheric pressure plasma in an argon/acetone mixed gas to give the objective nonwoven fabric of 0.1-0.5 O/C elementary ratio according to the ESCA measurement, <=0.01 O/C ratio according to the organic elementary analysis, with a thickness of 50-300μm, preferably 100-300μm, a unit weight of 20-120g/m<2> , preferably 30-100g/m<2> , a tensile strength at break of 20kgf/2cm and air permeability of 5-150cm<3> /cm<2> /see, preferably 10-150cm<3> /cm<2> /sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin-based non-woven fabric having excellent breathability, hydrophilicity, chemical resistance and tensile breaking strength. Specifically, it relates to a nonwoven fabric mainly used for battery separators.

[0002]

2. Description of the Related Art Nylon nonwoven fabric has been widely used as a separator for nickel-cadmium storage batteries. This is because nylon nonwoven fabric has appropriate strength, gas permeability and hydrophilicity.

However, it is difficult to say that nylon has sufficient alkali resistance and oxidation resistance, and it is known that it decomposes relatively easily at a temperature of 45 ° C. or higher. That is, when the battery is charged at a high temperature, the oxygen gas generated in the battery decomposes nylon into carbon dioxide gas, water, ammonia and the like, and the carbon dioxide gas and ammonia adversely affect the battery characteristics. Further, when the decomposition is further advanced, the insulating ability as a separator is lowered, and finally an internal short circuit of the battery is caused.

In order to solve this problem, attempts are being made to change the material of the separator to a polyolefin resin. In particular, polyolefin-based nonwoven fabrics have come to be used mainly in batteries used at high temperatures.

[0005]

However, although the polyolefin-based non-woven fabric has good chemical resistance such as alkali resistance and oxidation resistance, it has a drawback that it has poor affinity with the electrolytic solution and poor retention. are doing. A method of applying a surfactant in order to solve the problems of the polyolefin-based non-woven fabric and to improve the electrolyte retaining ability (JP-A-60-
255107), but in this case, the outflow of the surfactant becomes a problem. Moreover, once dried, it no longer exhibits hydrophilicity and is not a fundamental solution.

Various methods for grafting a hydrophilic monomer onto the surface of a hydrophobic polymer have been proposed (Japanese Patent Publication No. 56-44098). However, the reaction is complicated, it is difficult to cut the main chain, crosslink, it is difficult to adjust the mutual entanglement such as grafting efficiency, and there is a problem that it is difficult to uniformly carry out the graft polymerization even inside the space of the polymer porous body. is there.

Further, there is a method of performing low temperature plasma treatment under a pressure condition of several Torr or less (Japanese Patent Laid-Open No. 58-94).
752, JP-A-6-79832, etc.). However, this method requires high vacuum conditions, continuous treatment of large-sized materials is difficult, the apparatus cost is high, and it is unsuitable for treating a large area in a large amount like a nonwoven fabric for battery separators.

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, when a polyolefin-based nonwoven fabric is subjected to atmospheric pressure plasma treatment so as to have a specific element composition ratio,
The inventors have found that the liquid absorbing property, the hydrophilic property, and the liquid retaining property are improved without impairing the strength of the polyolefin-based nonwoven fabric, and thus the present invention has been accomplished. That is, the gist of the present invention is a polyolefin nonwoven fabric surface-modified by atmospheric pressure plasma treatment, and the elemental composition ratio (O / C) of oxygen to carbon by ESCA measurement of the nonwoven fabric is 0.1 to 0. 5, and
O / C by organic element analysis is 0.01 or less, and it exists in the polyolefin nonwoven fabric characterized by the above-mentioned.

The present invention will be described in detail below. The polyolefin non-woven fabric of the present invention is an ESCA (Electron Spect
The elemental composition ratio of oxygen to carbon (O / C) measured by roscopy for chemical analysis (O / C) is 0.1 to 0.5, and the elemental composition ratio of oxygen to carbon (O / C) determined by organic element analysis is 0.01 or less. Is characterized in that.

The polyolefin-based nonwoven fabric is subjected to atmospheric pressure plasma treatment to introduce oxygen into the surface of the fibers constituting the nonwoven fabric. As a result, the wettability of the polyolefin-based nonwoven fabric with the alkaline electrolyte is improved, and the electrolyte absorbability and liquid retention are also improved. Regarding the amount of oxygen introduced to the surface of the polyolefin nonwoven fabric, the elemental composition ratio of oxygen to carbon measured by ESCA is in the range of 0.1 to 0.5. If this ratio is less than 0.1, it means that plasma treatment sufficient to modify the surface is not performed, and the hydrophilicity is insufficient. Conversely, even if it exceeds 0.5,
The effect no longer increases, and the strength of the nonwoven fabric made of polyolefin fibers decreases.

Here, the elemental composition measured by ESCA means ESC manufactured by PERKIN ELEMERPHI.
A-5500MC is used, and the radiation source is Al, 14k
Measured under the conditions of V and 150 W (using a monochromator, take-out angle of 65 degrees). The polyolefin-based nonwoven fabric of the present invention has an elemental composition ratio of oxygen to carbon (O / C) of 0.01 or less measured by organic elemental analysis.
The increase in this ratio means that oxygen is fixed even inside the polyolefin-based nonwoven fabric.
If this ratio exceeds 0.01, the internal structure of the polyolefin changes, and the heat resistance and strength, which are the characteristics of the polyolefin, decrease, which is not preferable.

The elemental composition measured by organic elemental analysis means the PERKIN ELEMER PHI.
Using an organic elemental analyzer 240C manufactured by the same company, carbon, hydrogen and nitrogen were measured under the conditions of a combustion tube temperature of 920 ° C. and a reduction temperature of 600 ° C., and the balance was oxygen.

Examples of the polyolefin fibers used herein include homopolymers and copolymers such as polyethylene and polypropylene, and hydrocarbon-based polyolefin fibers such as ethylene-vinyl acetate copolymer containing 70% or more of ethylene. Preferably containing a fiber having a core-sheath structure,
More preferably, 30% or more of the fibers constituting the non-woven fabric are desirably fibers having a core-sheath structure.

A fiber having a core-sheath structure means a structure in which core components and sheath components are concentrically arranged in the fiber cross section (SHEATH-
(CORE) and parallel structure with eccentric core components
It is a fiber (SIDE BY SIDE) (side by side type). Any ratio of the core and the sheath can be used. Preferably, the area ratio of the cross section is core: sheath = 10: 1 to 1: 1.
Ten fibers are preferably used.

The fibers having a core-sheath structure are preferably those in which the core component is polypropylene and the sheath component is polyethylene. By using polypropylene as the core component, it is possible to maintain the structure of the separator when the battery is exposed to high temperature due to a short circuit, overcharge, or the like.
The strength at the time of assembling the battery can be obtained, and by using polyethylene as the sheath component, the fibers can be easily heat-sealed, and a non-woven fabric having excellent strength can be manufactured.

The polyolefin nonwoven fabric of the present invention can be manufactured by a known method. For example, a wet manufacturing method in which fibers are uniformly suspended in water and formed into a rake sheet with a wire mesh, an air raid method in which fibers are scattered in the air, and then collected in a wire mesh to form a card, spinning A spun bond method and a melt blow method, which form a web directly from a machine, can be used.

The polyolefin-based nonwoven fabric of the present invention can be obtained by subjecting polyolefin fibers before or after non-woven to atmospheric pressure plasma treatment. Of these, the treatment of the nonwoven fabric itself is preferable from the viewpoint of the ease of the treatment process. The atmospheric pressure plasma treatment in the present invention is a method of irradiating with plasma by performing glow discharge at around 1 atm.
Various known methods such as those disclosed in JP-A-4525 and JP-A-6-182195 can be used. For example, by introducing an inert element-containing gas such as argon or helium into the plasma generator, performing glow discharge at about 1 atm and performing plasma excitation, a non-woven fabric installed between electrodes in the plasma generator. The surface of the fibers constituting the is treated.

The atmospheric pressure plasma treatment does not require a vacuum chamber or a vacuum pump as compared with the low pressure plasma treatment, and is industrially advantageous as compared with the vacuum plasma treatment in terms of equipment and shortening the time for treatment preparation. Further, the atmospheric pressure plasma treatment is performed at several kHz, and compared with the low pressure plasma treatment which is performed by using a high frequency radio wave of several MHz, it can be performed at a lower discharge frequency, which reduces damage to the nonwoven fabric. There is also an advantage that you can.

The polyolefin non-woven fabric thus obtained has a thickness of usually 50 to 300 μm, preferably 100 to 3 for use as a battery separator.
The range is preferably 00 μm. When the thickness is less than 50 mμ, the basis weight decreases, and problems such as difficulty in optimizing air permeability occur. On the other hand, if it is thicker than 300 mμ, it is disadvantageous in terms of downsizing of the battery.

The basis weight is usually 15 to 150 g / m ² , and preferably 30 to 100 g / m ² . If it is less than 15 g / m ² , sufficient strength cannot be obtained. On the other hand, when the amount is more than 150 g / m ² , the thickness increases and the air permeability decreases. It is desirable that the tensile strength at break is usually in the range of 2 to 20 kgf / 2 cm.
If it is less than 2 kgf / 2 cm, the film may be broken during the assembly of the battery.

The air permeability, when measured by the Frazier method, is usually 5 to 150 cm ³ / cm ² / sec, preferably 10 to 150 cm ³ / cm ² / sec. If it is less than 5 cm ³ / cm ² / sec, the internal resistance of the battery becomes large, and 150 cm ³ / cm ² / sec
If it is larger than that, strength is insufficient due to the balance of thickness and basis weight. These polyolefin-based nonwoven fabrics may be a single layer or a laminate of two or more types of nonwoven fabrics.

[0022]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples,
Each measurement was performed by the following method.

(1) ESCA measurement ESCA-5 manufactured by PERKIN ELMER PHI
The surface elemental composition analysis of the sample was performed using 500 MC. As the measurement conditions, the excitation source used was Al-Kα ray, output 14 kV, 150 W, monochromator used,
The analysis area was 0.8 mm × 3.5 mm and the take-out angle was 65 degrees.

(2) Organic element analysis Using an organic element analyzer 240C manufactured by PERKIN ELMER PHI, carbon, hydrogen and nitrogen of the entire sample were analyzed under the conditions of a combustion tube temperature of 920 ° C and a reduction temperature of 600 ° C. . The amount of oxygen contained is carbon, hydrogen,
It was calculated by subtracting the weight of nitrogen.

(3) Tensile breaking strength A sample width of 20 m was measured using an Instron type universal testing machine.
m, 50 mm between chucks, pulling speed 200 mm / m
It was pulled in and the stress at break was measured.

(4) Electrolyte absorption height The sample was cut into a strip having a width of 25 mm, the sample end was immersed in a 30 wt% potassium hydroxide aqueous solution, and the temperature was adjusted to 24
The height of absorption rise of the aqueous potassium hydroxide solution was measured when it was placed vertically in a room at 65 ° C and a humidity of 65% and left standing for 30 minutes. (5) Air permeability According to JIS L1096-1979, the air permeability was measured by a gas permeability tester manufactured by Toyo Seiki Seisakusho.

Reference Example 1 A fiber having a denier of 1.5 and a core component of polypropylene and a sheath component of polyethylene and a core-sheath ratio of 1: 1.
2%, eccentric core component is polypropylene, and sheath component is polyethylene (side-by-side type) 3% denier fiber 8%, and melting point is 132 ° C. polyethylene fiber 2
Nonwoven fabric manufactured by wet method consisting of 0% (basis weight 59 g / m
² , thickness 250 μm, air permeability 90 cm ³ / cm ² / se
Various physical properties of c) were measured. The measurement results are shown in Table-1. Both the ESCA measured value and the organic elemental analysis value had an O / C value of 0, and there was no hydrophilicity, and the electrolytic solution did not permeate.

Example 1 The nonwoven fabric of Reference Example 1 was subjected to atmospheric pressure plasma treatment under the following conditions. Plasma treatment conditions: Gas: Argon + acetone Treatment pressure: 1 atm Electricity: 5 kHz, 150 W Treatment time: 60 seconds

After completion of the reaction, ESCA measurement, organic elemental analysis, liquid absorption height of electrolyte, basis weight, tensile strength at break, and air permeability were measured. The results are shown in Table 1. As compared with the untreated product of Reference Example 1, the liquid absorption height of the electrolytic solution was improved without lowering the basis weight, air permeability, and strength.

Example 2 The nonwoven fabric described in Reference Example 1 was treated under the following plasma treatment conditions. Plasma processing conditions: Gas: Argon + acetone Processing pressure: 1 atm Electricity: 5 kHz, 150 W Processing time: 20 seconds

After completion of the reaction, ESCA measurement, organic element analysis, liquid absorption height of electrolyte, basis weight, tensile rupture strength, and air permeability were measured. The results are shown in Table 1. The basis weight, air permeability and strength did not change and the liquid absorption height was improved compared to before plasma treatment.

Reference Example 2 1.5 denier fiber 7 in which the core component is polypropylene and the sheath component is polyethylene, and the ratio of the core and the sheath is 1: 1.
Wet-produced non-woven fabric composed of 0% and 30% polyethylene fiber having a melting point of 125 ° C. (grammage 59 g / m ² , thickness 1
Various physical properties of 60 μm and air permeability of 36 cm ³ / cm ² / sec) were measured. The measurement results are shown in Table-1. Both the ESCA measured value and the organic elemental analysis value had an O / C value of 0, and there was no hydrophilicity, and the electrolytic solution did not permeate.

Example 3 The long nonwoven fabric of Reference Example 2 was continuously subjected to atmospheric pressure plasma treatment. Plasma processing conditions: Gas: Argon + CO ₂ Processing pressure: 1 atm Electricity: 5 kHz, 150 W Line speed: 2 m / min

After completion of the reaction, ESCA, organic elemental analysis, liquid absorption height of electrolyte, basis weight, tensile strength at break and air permeability were measured. The results are shown in Table 1. The basis weight, air permeability and strength did not change, indicating that oxygen was introduced. As compared with the non-woven fabric before plasma treatment (Reference Example 2), the height of electrolyte absorption was improved.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

EFFECT OF THE INVENTION The polyolefin-based nonwoven fabric of the present invention has a high degree of hydrophilicity, despite being treated by a simple method, and does not impair the properties such as strength of the polyolefin fiber nonwoven fabric itself. Its industrial value is high.

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Claims (5)

[Claims] 1. A polyolefin-based non-woven fabric surface-modified by atmospheric pressure plasma treatment, wherein the non-woven fabric ESC
Elemental composition ratio of oxygen to carbon measured by A (O / C)
Of 0.1 to 0.5 and O / C of 0.01 or less by organic element analysis. 2. The thickness of the polyolefin-based nonwoven fabric is 50 to 3
00 μm, basis weight 20 to 120 g / m ² , tensile breaking strength 2 to 20 kgf / 2 cm, air permeability 5 to 150 cm ^3.
/ Cm < ² > / sec, The polyolefin type nonwoven fabric of Claim 1 characterized by the above-mentioned. 3. The thickness of the polyolefin non-woven fabric is 100 to.
300 μm, basis weight 30 to 100 g / m ² , tensile breaking strength 2 to 20 kgf / 2 cm, air permeability 10 to 150 c
The polyolefin non-woven fabric according to claim 1, which has a m ³ / cm ² / sec. 4. The fiber constituting the polyolefin-based non-woven fabric contains a fiber having a core-sheath structure in which a core component is polypropylene and a sheath component is polyethylene. Polyolefin non-woven fabric. 5. A battery separator using the polyolefin nonwoven fabric according to any one of claims 1 to 4.