JP2002054085A - Nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonwoven fabric having excellent shielding tendency and filter property and also deformation resistance or form retainability. SOLUTION: This nonwoven fabric is characterized by containing >=70 wt.% of high-modulus polyolefin fibers 0.06-1.1 dtex in single fiber fineness, 1-80 mm in fiber length and 400-2,700 cN/dtex in modulus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonwoven fabric particularly suitable for use as a separating material such as a filter and a battery separator.

[0002]

2. Description of the Related Art Conventionally, nonwoven fabrics made of ultrafine fibers such as polyolefin and synthetic cellulose have been used as battery separators and gas-liquid filters because of their excellent shielding properties and small pore size. On the other hand, high-modulus fibers have been used as impact-resistant materials, tension materials, ropes, nets, composite reinforcing materials, and the like, utilizing their properties. In order to respond to recent demands for miniaturization of batteries and improvement in filter accuracy, it is advantageous to use ultra-fine fibers. However, there is a problem in that the nonwoven fabric has low deformation resistance to external force and low shape retention. In the battery separator, there is a problem that a break occurs due to a tension in a battery manufacturing process, a burr of an electrode plate penetrates through the separator, a short circuit occurs, or a separator is torn by an edge of the electrode plate or the like. In order to solve such a problem, it is preferable to use a very fine elastic fiber as a reinforcing material. However, the high elasticity fiber generally has a fiber denier larger than 1.1 dtex and may be used alone or in combination to form a nonwoven fabric. Properties and filter characteristics could not be obtained. It is also possible to use submicron fibers obtained by splitting and fibrillating liquid crystal fibers such as para-aramid, but there is a problem that the acid resistance is poor.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nonwoven fabric having excellent shielding properties and filter properties, and having excellent deformation resistance and shape retention.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a nonwoven fabric particularly suitable as a filter or a battery separator has the following constitution.

That is, the present invention provides a single fiber fineness of 0.06 to
1.1 dtex, fiber length 1-80 mm, elastic modulus 40
A nonwoven fabric comprising 70% by mass of a high elasticity polyolefin fiber having a mass fraction of 0 to 2700 cN / dtex. Further, the fiber length of the high-modulus polyolefin fiber is 1 to 20 mm, and the fibril-like fiber is manufactured by a papermaking method.
A nonwoven fabric characterized by containing 30% by mass, and the fibril-like fiber is a synthetic pulp.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
Examples of the high elastic modulus polyolefin fibers that can be suitably used in the nonwoven fabric of the present invention include ultrahigh molecular weight polyolefin fibers. As a means for producing fibers, a gel spinning method is generally used, but another method can be employed. As a method for producing a nonwoven fabric suitable for the present invention, there are a dry card method and a wet papermaking method, and a hydroentangling treatment may be performed. Polyolefins and polypropylenes are generally used as the polyolefin, but are not particularly limited thereto.

The nonwoven fabric of the present invention, which is preferably used as a separating material for filters and battery separators, has a single fiber fineness of 0.06 to 1.1 dtex and a fiber length of 1 to 8 dtex.
It contains high-modulus polyolefin fibers having a modulus of elasticity of 0 to 0 mm and a modulus of 400 to 2700 cN / dtex in a mass fraction of 70% by mass or more.

[0008] In order to improve the shielding property or the filter property, the fiber denier needs to be 0.06 to 1.1 dtex. When the thickness exceeds 1.1 dtex, the shielding property and the like decrease. On the other hand, denier is 0.06 dt
If it is smaller than ex, problems such as increased spinning instability such as yarn breakage during the fiber production process and reduced operability and reduced productivity arise. Preferably 0.06-0.0.
66 dtex, more preferably 0.07 to 0.33 dt
ex. On the other hand, if the fiber diameter is too small, in the production of a dry nonwoven fabric, there is a problem that the fiber opening property in card processing or the like is reduced. If the fiber length is less than 1 mm, the effect of improving shape retention and dimensional stability due to the use of the high elasticity fiber is not seen. If the fiber length exceeds 80 mm, there is a problem in the fiber opening properties in both dry and wet nonwoven fabric manufacturing processes.

The nonwoven fabric made by the papermaking method is preferable for obtaining a nonwoven fabric having a uniform formation. However, in order to manufacture the nonwoven fabric by papermaking, the length of the high modulus fiber is preferably 20 mm or less.
It is more preferably 15 mm or less. Further, when the thickness is 12 mm or less, the uniformity of the formation of the nonwoven fabric can be improved, which is particularly preferable. The elastic modulus of the fiber is 400 to
It is preferably between 2700 cN / dtex. 4
If it is less than 00 cN / dtex, the reinforcing effect is not so much recognized, and it is difficult to produce a high modulus fiber exceeding 2700 cN / dtex.

In the present invention, the high modulus fiber is contained in an amount of 70% by mass or more. If the fiber content is less than 70% by mass, the strength of the nonwoven fabric when thinned, particularly the piercing strength, is reduced. The piercing strength of the nonwoven fabric in the present invention is preferably at least 1N. In addition, even if a high-strength fiber is used to improve the shape retention and dimensional stability of the nonwoven fabric, when the fiber is a short fiber, the entanglement and adhesion of the fiber strongly contribute to the end portion of the fiber. And other fiber components are cut off, so no effect is observed. In order to obtain a nonwoven fabric having good morphological stability and dimensional stability, which is the object of the present invention, it is important that the elastic modulus, which has a correlation with the compression resistance of the fiber, be high.

In order to increase the strength and elongation characteristics of the nonwoven fabric, it is preferable to mix and disperse the fibril-like fibers in the nonwoven fabric. When the fibrils are entangled with each other, the strength and elongation characteristics of the nonwoven fabric can be improved. The method for producing fibril-like fibers is not particularly limited, but it is common to use a flash spinning method or the like for olefin materials, and to use an acid treatment for cellulose materials such as polynosic or rayon. The content of the fibrillated fibers is preferably from 10 to 30% by mass. If it is less than 10% by mass, the effect of improving the elongation property is small.

The fibril-like fibers are preferably thermoplastic, because the shape retention can be further improved by heat fusion. At present, synthetic pulp, which is a fibrillated fiber having a fiber length of about 0.3 to 3 mm, has been put on the market. It is particularly preferable because it does not cause thermal damage to the elastic modulus fiber and there is no problem of sheet shrinkage. The fiber length of the fibrillated fiber is also preferably 80 mm or less, and particularly preferably 20 mm or less when a papermaking method is used.

When the nonwoven fabric of the present invention is used as a battery separator, it is desirable that at least some of the fibers have a sulfonated fiber. It is presumed that the sulfonation improves the wettability of the liquid and improves the liquid retention and rapid chargeability of the electrolyte. Examples of the sulfonation method include a method of performing a heated concentrated sulfuric acid treatment in a liquid phase or a method of performing a sulfurous acid gasification treatment. After sulfonation, impurities are generated at the time of treatment, so that it is necessary to thoroughly wash with pure water or the like.

When the nonwoven fabric of the present invention is used as a battery separator, the thickness of the nonwoven fabric is preferably between 10 and 150 μm. If the thickness is less than 10 μm, the liquid retaining property of the electrolytic solution is reduced, and the shielding property is deteriorated. Further, the strength and piercing strength of the nonwoven fabric are undesirably reduced. Conversely, if it is larger than 150 μm, the size of the battery is undesirably increased. The basis weight of the nonwoven fabric is preferably between 5 and 100 g / m ² ,
Particularly preferred is ５０50 g / m ² . If the basis weight is less than 10 g / m ^{2, the} effect of improving shape retention is not recognized. this is,
It is presumed that it is difficult to uniformly disperse the high-modulus olefin fibers, and the fibers have become ubiquitous. Conversely 100g
/ M ² is not preferable because the thickness is large.

When the nonwoven fabric of the present invention is used as a filter, the thickness of the nonwoven fabric is preferably between 80 and 300 μm. When the thickness is smaller than 80 μm, the filter performance is deteriorated, which is not preferable, and the strength of the nonwoven fabric is also reduced. Conversely, even if it is larger than 300 μm, the filter performance is not so much improved. Also, the basis weight of the nonwoven fabric is preferably in between 20 to 100 g / m ^2, especially 20 to 50 g / m ² is preferred. If the basis weight is less than 20 g / m ^{2, the} effect of improving shape retention is not recognized. this is,
It is presumed that it is difficult to uniformly disperse the high-modulus olefin fibers, and the fibers have become ubiquitous. Conversely 100g
If it is greater than / m ^2, there is no need to improve the composition.

Further, the tensile strength of the nonwoven fabric is 15 to 300.
Preferably, the width is N / 5 cm. If the width is less than 15 N / 5 cm, the nonwoven fabric is likely to be cut in a calendering step or the like for improving the strength. In particular, in battery separator applications, the width is preferably 50 N / 5 cm or more, more preferably 60 N / 5 cm or more, and particularly preferably 80 N, since it is used on a tape having a narrow width.
/ Cm width or more. In the nonwoven fabric of the present invention, it is preferable to improve the strength of the nonwoven fabric by strengthening the adhesion between the fibers by means of heat fusion such as calendering. It is also preferable to composite with another nonwoven fabric by lamination or the like.

[0017]

EXAMPLES Examples of the nonwoven fabric of the present invention will be described below, but the present invention is not limited to these examples. The measurement method used in the present invention is described below. a. Weight (g / m ² ) Five sheets are cut out in a fixed area and weighed with a precision balance. The measured values were arithmetically averaged and converted to about 1 m ² to obtain the basis weight.

B. Thickness (μm) The thickness at the center of each sheet under a load of 20 g / cm ² was 5
The points were measured and the arithmetic average was taken as the thickness of the nonwoven fabric.

C. Fiber elastic modulus The fiber was set in an Instron type tensile tester, and the test length was 20.
cm and a tensile speed of 10 cm / min to determine the elastic modulus.

D. Liquid filtration accuracy Set the non-woven fabric in a 47mmφ
Viscosity 200 in which 200 ppm of IS11 particles are dispersed.
A filtration test was carried out using an aqueous solution of cp syrup (maltose). The initial concentration was measured by measuring the inlet concentration and the outlet concentration two minutes after the start of the test. The time until the pressure reached 98 kPa was defined as life. Filtration accuracy (%) = [1- (outlet concentration / inlet concentration)] × 1
00

E. A nickel metal hydride battery having a battery capacity retention of 2500 mAh was prepared, and after fully charged, the battery was allowed to stand at 40 ° C. for 7 days, and the discharge capacity was expressed as a percentage, with the discharge capacity after full charge being 100%.

F. Puncture strength The puncture strength was measured using a KES-G5 handy compression tester (Kato Tech Co., Ltd.) and the sample was 1.12 in diameter.
When the needle was fixed to a circular hole holder having an area of 8 cm and an area of 1 cm ² and a needle having a spherical tip of 0.5 R and a diameter of 1 mmφ was lowered at a speed of 2 mm / sec, the value was obtained when the stress became maximum.

Example 1 Single yarn fineness was 0.33 and 1.
1 dtex high strength polyethylene fibers were made by gel spinning. The modulus of the fiber is 1115 and 923 cN /
dtex. This polyethylene fiber is cut into 6 mm, and synthetic pulp SWP (manufactured by Mitsui Chemicals, Inc., L
-100) at a mass ratio of 80:20,
Paper was made using an APPI type paper making tester. Table 1 shows the physical property values of the obtained nonwoven fabrics A to F.

[0024]

[Table 1]

(Example 2) Nonwoven fabric A obtained in Example 1
And an average fiber diameter of 0.033 dtex and a basis weight of 20 g / m ^2.
The polypropylene melt blown nonwoven fabric is calendered at 110 ° C. to fuse and laminate the fibers, and the total weight is 7
A nonwoven fabric of 0 g / m ² and a thickness of 140 μm was obtained. Sulfonation treatment was performed in a sulfurous acid gas atmosphere to evaluate battery performance. There were no holes or other troubles during the battery installation process. The capacity retention of the battery was as high as 76%, which was very suitable.

Example 3 Short fiber fineness of Example 1 0.3
3dtex high modulus fiber and synthetic pulp SWP (L-1
00) and 1.1 dtex of fibrillated rayon (CSF200, manufactured by Toyobo Co., Ltd.) at a mass ratio of 7
After mixing at a ratio of 0:10:20, papermaking was performed. The obtained nonwoven fabric is calendered at 110 ° C. with a polypropylene meltblown nonwoven fabric having an average fiber diameter of 3 μm and a basis weight of 20 g / m ² , and the fibers are fused and laminated.
A nonwoven fabric having a thickness of m ² and a thickness of 95 μm was obtained. When the performance of the liquid filter was measured, the filtration accuracy was as high as 95% and the life was as long as 9 minutes and 50 seconds.

(Comparative Example 1) Average fiber diameter 0.033 dte
x, a polypropylene meltblown nonwoven fabric having a basis weight of 55 g / m ² was calendered at 110 ° C., and fibers were fused and laminated to obtain nonwoven fabrics having a thickness of 150 μm and 93 μm. The nonwoven fabric having a thickness of 150 μm was subjected to a sulfonation treatment in a sulfurous acid gas atmosphere to evaluate battery performance. When assembled into a battery, in two of the three batteries, the burr of the electrode punctures the nonwoven fabric and damages the nonwoven fabric, resulting in a poor yield. When the capacity retention of only one good battery was measured, it was as high as 75% and showed good characteristics. 93μ thick
The nonwoven fabric of m was evaluated for filter performance. The filtration accuracy two minutes after the start of the filtration test was as high as 97%, but the life was short, 3 minutes and 24 seconds, which was a problem. Since the permeation resistance of the liquid at the time of filtration is large, it is presumed that the cause is that the nonwoven fabric was crushed by the back pressure of the liquid and the pore diameter became small.

Comparative Example 2 A high-strength polyethylene fiber having a single yarn fineness of 2.5 dtex was prepared by gel spinning. The elastic modulus of the fiber was 860 cN / dtex. In the same manner as in Example 1, nonwoven fabrics having a basis weight of 21 g / m ² and 14 g / m ² were prepared. Table 1 shows the physical properties of the obtained nonwoven fabrics G and H.

Comparative Example 3 The fiber of Example 1 was cut into 30 mm and 100 mm. Papermaking was performed using the fibers cut to 30 mm in the same manner as in Comparative Example 1, but a large number of fiber masses (fiber balls) were generated during the dispersion of the fibers, and a uniform nonwoven fabric could not be obtained. Also, 100m
After being cut into m, crimping was applied to the card, but the card passing property was poor and the productivity was very poor.

(Comparative Example 4) Thickness 12 prepared in Comparative Example 2
When the filter performance was evaluated using a nonwoven fabric of 6 μm, the life was 32 minutes and 27 seconds, which was a good result. However, the filtration accuracy 2 minutes after the start of the filtration test was as low as 62%. It is presumed that although the fiber diameter is large, the permeation resistance of the liquid during filtration is small, but the pore size is large and the filtration accuracy is low. The nonwoven fabric having a thickness of 90 μm and a polypropylene meltblown nonwoven fabric having a fiber diameter of 0.033 dtex and a basis weight of 20 g / cm ² prepared in Comparative Example 1 were calendered at 110 ° C. to fuse the fibers into a nonwoven fabric having a thickness of 100 μm. Sulfonation treatment was performed in a sulfurous acid gas atmosphere to evaluate battery performance. When the capacity retention of the battery was measured, it was as low as 65%.

[0031]

The single fiber fineness is 0.06 to 1.1 dtex.
And a nonwoven fabric mainly composed of ultrafine fibers having a high modulus of elasticity of 400 to 2700 cN / dtex, so that it has excellent dimensional stability and shape retention, and is used for battery separators, gas-liquid filters, and medical treatment. It can be used as a nonwoven fabric suitable for use.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D019 AA01 AA03 BA13 BB03 BB05 DA01 4L047 AA14 AB01 AB02 AB06 AB08 BA21 BA22 CA19 CB01 CB10 CC12 4L055 AF10 AF15 AF16 AF44 BE14 BE20 EA04 EA16 EA19 FA11 GA31 GA39 GA50 H02 CC02 HH01 HH03

Claims (4)

[Claims] (1) a single fiber fineness of 0.06 to 1.1 dtex;
Fiber length 1-80mm, elastic modulus 400-2700cN
A nonwoven fabric characterized by containing 70% by mass or more of a high modulus polyolefin fiber having a mass fraction of / dtex. 2. The high elastic modulus polyolefin fiber having a fiber length of 1
The nonwoven fabric according to claim 1, wherein the nonwoven fabric is manufactured by a papermaking method. 3. The nonwoven fabric according to claim 2, which contains 10 to 30% by mass of fibril-like fibers. 4. The nonwoven fabric according to claim 3, wherein the fibril-like fibers are synthetic pulp made of polyolefin.