JP2005146428A - Nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonwoven fabric of a PPS (polyphenylene sulfide) fiber so as to retain sufficient strength even for a thin nonwoven fabric. <P>SOLUTION: The nonwoven fabric is characterized in that the short fiber fineness is ≤0.5 dtex and the tensile strength is ≥3.0 cN/dtex. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nonwoven fabric, and more particularly to a nonwoven fabric comprising PPS fibers made of a polyphenylene sulfide (hereinafter abbreviated as PPS) polymer.

  PPS fibers are excellent in heat resistance, chemical resistance, flame retardancy, and the like, and are expected to be used in applications such as various filters, electrical insulating materials, papermaking canvases, and battery separators using this feature.

  For example, the battery separator needs to have micropores that prevent ions from being short-circuited between the electrodes and can move ions in the electrolyte, and wet nonwoven fabrics made of short fibers are used. Since the nonwoven fabric of this battery separator is used by being immersed in an electrolyte such as a strong alkaline aqueous solution or an organic solution, the short fiber material constituting this nonwoven fabric does not decompose into a strong alkaline aqueous solution or an organic solution, Chemical resistance is required.

  Polyethylene, polypropylene, etc. can be applied to battery separators as materials with high chemical resistance, but these materials have a low melting point and are difficult to use continuously at temperatures around 80 ° C. However, it cannot respond to further improvement in heat resistance that can withstand. In this respect, it is known that PPS is excellent in chemical resistance and has a high melting point (285 ° C.) and can be suitably applied to battery separators and the like (see Patent Documents 1, 2, and 3).

In recent years, for the purpose of further improving battery performance, as a nonwoven fabric for battery separator, in addition to further improving heat resistance, it is also required to make it thinner to reduce internal resistance. However, simply thinning the nonwoven fabric has a problem in that the mechanical strength of the nonwoven fabric cannot be maintained, resulting in a short circuit between the electrodes.
JP-A-1-272899 JP-A-9-67786 JP-A-10-64502

  An object of this invention is to provide the nonwoven fabric of PPS fiber which can maintain sufficient intensity even if it is a thin nonwoven fabric.

  That is, the present invention is a nonwoven fabric characterized by comprising PPS fibers having a short fiber fineness of 0.5 dtex or less and a tensile strength of 3.0 cN / dtex or more.

  According to the present invention, it is possible to provide a non-woven fabric of PPS fibers that can maintain sufficient strength even when thinned.

  Hereinafter, the nonwoven fabric of the present invention will be described in detail.

  The nonwoven fabric of the present invention comprises PPS fibers.

  In the present invention, PPS means a polymer having phenylene sulfide units such as p-phenylene sulfide units and m-phenylene sulfide units as repeating units. The PPS may be a homopolymer composed of either a p-phenylene sulfide unit or an m-phenylene sulfide unit, or may be a copolymer having both. In addition, other aromatic sulfides may be copolymerized as long as the effects of the present invention can be obtained.

  The PPS preferably has a weight average molecular weight of 30,000 to 70,000, more preferably 40,000 to 60,000. By setting the weight average molecular weight to 30,000 or more, yarn breakage can be suppressed in the spinning process, and the spinning tension can be set higher, whereby stable spinnability can be obtained. Accordingly, PPS fibers having excellent mechanical properties can also be obtained. Further, by setting the weight average molecular weight to 70,000 or less, it is possible to suppress the melt viscosity of PPS in the melt spinning process, and it is not necessary to set the spinning equipment to a special high pressure resistance specification, thereby reducing the cost of manufacturing equipment.

  Further, the PPS fibers constituting the nonwoven fabric of the present invention may be mixed with other polymers such as other aromatic sulfides within the range where the effects of the present invention can be obtained.

  The PPS fiber used in the present invention must have a single fiber fineness of 0.5 dtex or less. When the single fiber fineness exceeds 0.5 dtex, it becomes difficult to obtain the denseness of the nonwoven fabric or to thin the nonwoven fabric. The upper limit value of the single fiber fineness is preferably 0.4 dtex or less. On the other hand, in order to improve fiber dispersion in the manufacturing process of the nonwoven fabric such as a wet method, the lower limit value of the single fiber fineness is preferably 0.05 dtex or more, more preferably 0.1 dtex or more.

  In general, PPS fibers are inferior in spinning stability compared to general-purpose polyester and nylon, and it is difficult to produce ultrafine fibers. However, PPS fibers with a single fiber fineness as described above are drawn using super-drawing behavior (super draw). This can be achieved by a combination of (hereinafter referred to as super draw stretching) and stretching with a neck (hereinafter referred to as neck stretching). Superdrawing occurs, for example, in stretching in which the stretching temperature is set to a certain level or higher than that of neck stretching, and is a thinning behavior without a neck, and is not accompanied by an increase in the degree of orientation. As conditions for combining super draw stretching and neck stretching, for example, super draw stretching is first performed 4 to 10 times in a 100 to 120 ° C. liquid bath, and then neck stretching is performed in a 90 to 98 ° C. liquid bath. Among them, stretching is preferably performed 2 to 4 times.

  Moreover, the PPS fiber which comprises the nonwoven fabric of this invention must be 3.0 cN / dtex or more in tensile strength, Preferably it is 4.0 cN / dtex or more. If the tensile strength is less than 3.0 cN / dtex, the strength of the nonwoven fabric that can meet the high demands described above cannot be obtained. Although the tensile strength has never been high, even if an excessively high strength is to be obtained, increasing the degree of polymerization of PPS or increasing the draw ratio in the drawing process will make the processes unstable. In other words, the cost of manufacturing equipment is also increased, so that the upper limit of the tensile strength may be 7.0 cN / dtex or 5.0 cN / dtex. In order to obtain such strength, for example, the weight average molecular weight of the PPS polymer is 30,000 to 70,000, preferably 40,000 to 60,000, particularly around 50,000, and the necking stretch ratio is 2 to 4 times. And good.

  Moreover, it is preferable that the PPS fiber which comprises the nonwoven fabric of this invention is 15% or less in dry heat shrinkage | contraction in 180 degreeC, More preferably, it is 10% or less. By setting the dry heat shrinkage rate to 15% or less, it is possible to prevent the occurrence of defects such as wrinkles on the paper surface during heat treatment with a calender roll in the wet nonwoven fabric manufacturing process. Moreover, it is set as the nonwoven fabric excellent in dimensional stability, and the deformation | transformation etc. of a nonwoven fabric can be prevented also in the use use under the above high temperature environments. In obtaining such a dry heat shrinkage rate, the condition of the combination of the super draw stretching and the neck stretching as described above is one of the preferable achievement means.

  The PPS fiber constituting the nonwoven fabric of the present invention preferably has a fiber length of 2 to 30 mm. By setting the fiber length to 2 mm or more, the cutting resistance at the time of cutting is suppressed, the cutting becomes easy, the fibers are prevented from being tangled by the resistance at the time of cutting, and the dispersibility is also improved. On the other hand, when the fiber length is 30 mm or less, more preferably 10 mm or less, the fibers are not entangled during dispersion and the dispersibility is improved.

  From the PPS fibers as described above, the nonwoven fabric of the present invention can be obtained by a wet method, a dry method or the like. Moreover, you may mix with raw materials other than the above-mentioned PPS fiber in the range which does not deteriorate the denseness, heat resistance, and chemical resistance of a nonwoven fabric, deviating from the objective of this invention. As a standard of the mixing ratio of the PPS fibers as described above, it is preferably 50% by weight or more, more preferably 80% by weight or more with respect to the whole fibers constituting the nonwoven fabric.

The basis weight of the nonwoven fabric is preferably 10 to 100 g / m ² , more preferably 10 to 50 g / m ² in applications such as electrical insulators and battery separators.

  The nonwoven fabric of the present invention may be further processed according to its use. When the electrolyte is used in a battery separator made of an aqueous solution, the ionic conductivity can be improved by treating the nonwoven fabric with fuming sulfuric acid or chlorosulfonic acid to sulfonate it. The nonwoven fabric can be used as an electrode material by plating the surface with noble metal or the like by chemical plating such as electroless plating.

  Hereinafter, the present invention will be described in detail using examples.

(Measuring method)
(1) Fineness It measured according to the method of JIS L-1015 (1999) -8.5.

(2) Tensile strength Measured according to the method of JIS L-1015 (1999) -8.7.

(3) Dry heat shrinkage rate It measured at the processing temperature of 180 degreeC according to the method of JISL-1015 (1999) -8.15.

  In addition, about the measurement of said (1)-(3), what was cut | disconnected to length 51mm for measurement was used separately from the single fiber cut | disconnected for nonwoven fabrics in each Example and the comparative example.

(4) Fiber length It measured according to the method of JIS L-1015 (1999) -8.4.

(5) Paper Tensile Strength In each Example / Comparative Example, the sample in each of the longitudinal direction (the progress direction of the nonwoven fabric production process) and the lateral direction (the width direction of the nonwoven fabric production process) from the nonwoven fabric after hot pressing. A sample having a width of 15 mm and a sample length of 180 mm was taken and measured at a crosshead speed of 200 mm / min according to JIS P8113. The number of n was set to n = 10 in each of the vertical and horizontal directions, but the test piece slipped during the test, fractured within the gripping tool or within 10 mm from the gripping tool, or the width direction of the test piece. Retesting was performed when there was evidence of uneven loading throughout.

[Example 1]
A PPS polymer having a weight average molecular weight of 50,000 is discharged at a spinning temperature of 320 ° C. from a spinneret (number of holes 1200) having round discharge holes at a discharge rate of 350 g / min, and at a take-up speed of 1100 m / min. I took it.

  Next, the obtained unstretched yarn is converged to form a yarn bundle, stretched 6 times in 110 ° C. ethylene glycol as super draw stretching, and then continued in 98 ° C. water as neck stretching without being wound once. Stretched 2.5 times.

  The obtained bundle of PPS drawn fibers was cut into 5 mm to obtain PPS short fibers.

  Only the sample for measuring the physical properties of the fiber was cut into 51 mm and used for measurement.

Next, the obtained PPS short fibers are dispersed in water so that the fiber concentration is 0.4% by weight, and the slurry is supplied to a circular paper machine. A wet nonwoven fabric having a basis weight of 15 g / m ² is obtained. Obtained.

  This nonwoven fabric was hot-pressed through a 240 ° C. calendar.

[Comparative Example 1]
A PPS polymer having a weight average molecular weight of 50000 is discharged at a spinning temperature of 320 ° C. from a spinneret (number of holes 1200) having round discharge holes at a discharge rate of 90 g / min, and spinning at a take-up speed of 1100 m / min. I went there, but the spinnability was poor, and many yarn breaks occurred.

  Next, barely obtained undrawn yarn was converged into a bundle of yarns, and was drawn 2.5 times in 98 ° C. water as neck drawing.

The obtained bundle of PPS drawn fibers was cut into 5 mm to obtain PPS short fibers.
Only the sample for measuring the physical properties of the fiber was cut into 51 mm and used for measurement.

Next, the obtained PPS stretched fiber is dispersed in water so that the fiber concentration is 0.4% by weight, and the slurry is supplied to a circular paper machine. A wet nonwoven fabric having a basis weight of 15 g / m ² is obtained. Obtained.

  This nonwoven fabric was hot-pressed through a 240 ° C. calendar.

  Table 1 shows the results of evaluation for Example 1 and Comparative Example 1.

実施例１と比較例１とから確認できるように、繊維強度を３ｃＮ／ｄｔｅｘ以上にすることで、抄紙引っ張り強さを大幅に向上できるとともに、乾熱収縮率を１５％以下にすることで、抄紙表面のシワの発生を抑制することができた。

As can be confirmed from Example 1 and Comparative Example 1, by making the fiber strength 3 cN / dtex or more, paper tensile strength can be greatly improved, and by making the dry heat shrinkage rate 15% or less, The generation of wrinkles on the paper surface could be suppressed.

Claims (3)

A non-woven fabric comprising polyphenylene sulfide fibers having a single fiber fineness of 0.5 dtex or less and a tensile strength of 3.0 cN / dtex or more. The nonwoven fabric according to claim 1, wherein the content of polyphenylene sulfide fibers having a single fiber fineness of 0.5 dtex or less and a tensile strength of 3.0 cN / dtex or more is 50 wt% or more. The nonwoven fabric according to claim 1 or 2, wherein the polyphenylene sulfide fiber has a dry heat shrinkage of 15% or less.