JP4916984B2 - Non-woven - Google Patents

Description

  The present invention relates to a nonwoven fabric excellent in heat resistance and chemical resistance, and having a good formation, and a method for producing the same.

  Nonwoven fabrics are widely used in various fields as various industrial materials and construction materials. However, commonly used nonwoven materials are cotton, rayon, polyethylene terephthalate, polypropylene, nylon, etc., and nonwoven fabrics produced from these materials do not exhibit satisfactory heat resistance and chemical resistance, It cannot be used for special applications that require chemical resistance.

  For example, Patent Document 1 (Japanese Patent Laid-Open No. 7-228718) discloses a microporous polyolefin film made of a polyolefin composition containing 10% by weight or more of ultrahigh molecular weight polyolefin, and has a through-hole having a micro three-dimensional network structure. A polyolefin microporous membrane characterized by the above is disclosed. This document describes that such a microporous film is suitable for a lithium secondary battery separator because a through hole having a micro three-dimensional network structure is formed. However, in the microporous membrane formed of polyolefin as described in Patent Document 1, when this microporous membrane is used as a separator, the microporous membrane is not less than 160 ° C. due to the low heat resistance of polyolefin. It shrinks.

  When the separator is damaged due to shrinkage of the microporous film or the like, the separator cannot perform the function of squeezing the positive electrode and the negative electrode of the battery, and as a result, a short circuit (internal short circuit) between the positive electrode and the negative electrode occurs. Such a short circuit leads to abnormal heat generation or ignition of the battery and greatly reduces the safety of the battery.

  As a nonwoven fabric with improved heat resistance, Patent Document 2 (Japanese Patent Laid-Open No. 5-335005) discloses a nonwoven fabric made of aramid fibers, which is a polymer of wholly aromatic polyamide. This document describes that when this non-woven fabric is used as a separator, the decomposition gas of the electrolytic solution is difficult to be ejected rapidly from the battery container even if the battery is abnormally heated from the outside in a charged state. Yes. However, since aramid resin has a hygroscopic property, its reliability is low when used for electrical equipment. Furthermore, in this document, since a nonwoven fabric is produced using a papermaking method for an aramid resin, only a thick nonwoven fabric can be produced. As a result, the separator cannot be thinned, and the internal resistance of the battery is reduced. It cannot be reduced.

  Patent Document 3 (Japanese Patent Laid-Open No. 10-64502) discloses a wet nonwoven fabric made of polyphenylene sulfide fiber, and 30% by weight potassium hydroxide when measured according to the birec method defined in JIS L-1096. A battery separator is disclosed in which the liquid absorption rate of the aqueous solution is 10 mm / 30 minutes or more and the liquid retention is 100% or more. However, it is difficult for a nonwoven fabric made of polyphenylene sulfide fibers to continue to function as a separator at a high temperature of 180 ° C. or higher when the battery abnormally generates heat.

  On the other hand, Patent Document 4 (Japanese Patent Application Laid-Open No. 2002-061064) proposes a method for producing a melted liquid crystal-forming wholly aromatic polyester nonwoven fabric obtained by a melt blown method by roll pressing. However, the nonwoven fabric obtained by this method may have a large difference in fiber density, and the coarse part of the fiber becomes a defect depending on the application.

JP-A-7-228718 JP-A-5-335005 JP-A-10-64502 JP 2002-061064 A

An object of the present invention is to provide a nonwoven fabric that not only has excellent heat resistance and chemical resistance, but also has a good texture even when it is thin.
Another object of the present invention is to provide a non-woven fabric with little difference in fiber density regardless of the basis weight.
Still another object of the present invention is to provide a method for efficiently producing a nonwoven fabric having excellent characteristics as described above.

  As a result of intensive studies in order to solve the above-described problems of the prior art, the present inventors have developed a liquid crystal-forming fully aromatic polyester polymer having a melt viscosity at 310 ° C. of 20 Pa · s or less at a high temperature and high speed. It is a liquid crystal-forming wholly aromatic polyester polymer that is difficult to handle by spraying the high-temperature high-speed fluid onto a cooled metal roll at a predetermined collection distance for cooling and solidifying and collecting. However, it is possible to process easily while improving the dispersibility of the fiber, and as a result, it is possible to obtain a non-woven fabric excellent in heat resistance and chemical resistance as well as having good formation with little difference in fiber density. The present invention was completed.

That is, the present invention made on the basis of the above examination results is mainly composed of a molten liquid crystal-forming wholly aromatic polyester having a melt viscosity at 310 ° C. or higher of 20 Pa · s or less and an average fiber diameter of 1 to 15 μm. A non-woven fabric made of a certain filament. In the non-woven fabric, image data (0.026 mm ² / pixel; 256 gradations) of a sample piece when a sample piece of 10 cm × 8 cm is irradiated with transmitted light, and a sample piece The standard deviation of the formation index obtained by binarizing the difference from the blank image data without placing the mark by the TOKS method is 5.0 or less.

  In the non-woven fabric, even if the thickness is small, the non-woven fabric has good formation and the standard deviation of the formation index is small. For example, the non-woven fabric may have a thickness of about 20 to 200 μm. About 90-900 may be sufficient as the product with the standard deviation of a formation index.

Moreover, since the said nonwoven fabric can make a formation favorable irrespective of the magnitude | size of a fabric weight, the nonwoven fabric which satisfy | fills following formula (1) may be sufficient.
8 ≦ (B × C) / A ≦ 15 (1)
[In the formula, A: basis weight of nonwoven fabric (g / m ² ), B: thickness of nonwoven fabric (μm), C: standard deviation of formation index. ]

Such a non-woven fabric is preferably produced by a melt blown method, and the non-woven fabric is made of a molten liquid crystal-forming wholly aromatic polyester having a melt viscosity at 310 ° C. of 20 Pa · s or less, a spinning temperature of 310 to 360 ° C., and a hot air temperature. It can be produced by spraying and collecting on a cooled metal roll at a collection distance of 2 to 20 cm as a high-temperature high-speed fluid of 310 to 380 ° C. and an air amount of 10 to 50 Nm ³ per 1 m width of the nozzle.

  Furthermore, in the said manufacturing method, the nonwoven fabric sprayed and collected may be further solid-phase polymerized to improve the strength of the nonwoven fabric.

  In the specification, “melted liquid crystal-forming wholly aromatic polyester” means a wholly aromatic polyester resin exhibiting optical anisotropy (liquid crystallinity) in the melt phase. The liquid crystallinity can be easily identified by heating the sample on the hot stage in a nitrogen atmosphere and observing the transmitted light.

In addition, the “geographic index” refers to non-woven fabric image data (0.026 mm ² / pixel; 256 gradations) obtained by applying transmitted illumination to the non-woven fabric in the same manner. The density value per pixel obtained by subtracting from the blank image data (0.026 mm ² / pixel; 256 gradations) obtained by normalization and then binarizing the standardized image data by the TOKS method (256 steps from 0 to 255). That is, the standard deviation of the formation index becomes lower as the formation of the nonwoven fabric becomes more uniform, and the standard deviation of the formation index becomes higher as the formation of the nonwoven fabric becomes more uneven.

In the present invention, a non-woven fabric with good formation and small difference in fiber density can be obtained by processing a molten liquid crystal-forming wholly aromatic polyester excellent in heat resistance and chemical resistance by a specific production method. .
In addition, the nonwoven fabric of the present invention is not only excellent in heat resistance and chemical resistance, but also can maintain the uniformity of formation even if the nonwoven fabric is thin and has a small basis weight.

  Moreover, in the manufacturing method of the nonwoven fabric of this invention, the nonwoven fabric which has such an outstanding characteristic can be mass-produced efficiently.

  The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. The drawings are not necessarily drawn to scale, but are exaggerated in illustrating the principles of the invention. In the accompanying drawings, the same part number in the plurality of drawings indicates the same part.

[Nonwoven fabric]
The nonwoven fabric of the present invention is composed of a filament having a melt liquid crystal-forming wholly aromatic polyester having a melt viscosity at 310 ° C. or higher of 20 Pa · s or less and an average fiber diameter of 1 to 15 μm. Moreover, since this nonwoven fabric has good formation, the uniformity of the formation index obtained by transmitting light through the nonwoven fabric is high, and the standard deviation of the formation index is small.

FIG. 1 is a schematic view showing a method for measuring the formation index of the nonwoven fabric of the present invention. Light emitted from the light source 1 passes through a sample piece 3 (8 cm × 10 cm) on a transparent sample stage 2 disposed 15 cm above the light source 1. Using the CCD camera 10 (Sony Corporation, XC-75; 0.026 mm ² / pixel) disposed 20 cm above the sample piece 3, an image of the sample piece 3 through which light is transmitted is taken. This image data (A) is taken into the image processing apparatus 20 as 256-gradation image data.

  On the other hand, blank image data (B) is taken into the image processing apparatus 20 by the CCD camera 10 in the same manner except that no sample piece is arranged as a blank. In the image processing apparatus 20, after subtracting the image data (A) from the image data (B), the subtracted image data is binarized by the TOKS method, and the standard deviation of the formation index of the sample piece is calculated. Such image processing can be performed using, for example, “image analyzer V10” manufactured by Toyobo Co., Ltd.

  By this method, the degree of formation of the nonwoven fabric, which could not be identified conventionally, is quantified, and the uniformity of the formation of the nonwoven fabric can be judged from the standard deviation of the obtained formation index.

  If the standard deviation of the formation index of the nonwoven fabric is 5.0 or less, the formation is good, and the standard deviation is preferably about 1.0 to 4.9, more preferably 4.85 or less. May be.

  Although the nonwoven fabric of this invention can select arbitrary thickness according to a use, For example, from a viewpoint of weight reduction, the thickness of a nonwoven fabric becomes like this. Preferably it is about 20-200 micrometers, More preferably, it is about 30-150 micrometers.

  Moreover, since the nonwoven fabric of this invention can achieve favorable formation even if thickness is thin, the product of thickness and the standard deviation of a formation index can be made small. For example, the product of the thickness (μm) of the nonwoven fabric and the standard deviation of the formation index is preferably about 90 to 900.

Furthermore, even if the nonwoven fabric of this invention has a small fabric weight, it can achieve a favorable formation, and it is preferable that the nonwoven fabric of this invention satisfy | fills following formula (1).
8 ≦ (B × C) / A ≦ 15 (1)
[In the formula, A: basis weight of nonwoven fabric (g / m ² ), B: thickness of nonwoven fabric (μm), C: standard deviation of formation index. ]
Furthermore, it is preferable that the nonwoven fabric of this invention satisfy | fills following formula (2).
10 ≦ (B × C) / A ≦ 14 (1)
[Wherein A, B and C are the same as in formula (1)]

(Molten liquid crystal forming wholly aromatic polyester)
The melted liquid crystal-forming wholly aromatic polyester used in the nonwoven fabric of the present invention is not particularly limited as long as the melt viscosity at 310 ° C. is 20 Pa · s or less. For example, p-hydroxybenzoic acid and 1,6-hydroxynaphthoic acid are used. Examples include acid condensates and copolymers thereof, and polyesters having structural units as shown in the following chemical formula.

A wholly aromatic polyester having a melt viscosity at 310 ° C. exceeding 20 Pa · s is not preferable because it is difficult to make ultrafine fibers, oligomers are generated during polymerization, and troubles occur during polymerization and granulation. On the other hand, if the melt viscosity is too low, fiberization is difficult, and it is desirable that the melt viscosity is preferably 5 Pa · s or more at 310 ° C. When expressed in terms of intrinsic viscosity, the wholly aromatic polyester used in the present invention desirably has an intrinsic viscosity (ηinh) of 6.0 or less, and preferably 3.0 to 6.0. A melt liquid crystal-forming wholly aromatic polyester having such a melt viscosity can be produced by a conventionally known polymerization technique of wholly aromatic polyester, and “Vectra” (registered trademark) A, L type from Polyplastics Co., Ltd. Etc. are provided.

  The molten liquid crystal-forming wholly aromatic polyester may be used by adding other polymers, additives, and the like as long as the strength does not substantially decrease. For example, examples of additives include stabilizers (for example, antioxidants, ultraviolet absorbers, heat stabilizers, etc.), lubricants, flame retardants, antistatic agents, dispersants, fluidizing agents, and the like. These additives can be used alone or in combination of two or more.

[Method for producing nonwoven fabric]
The nonwoven fabric of the present invention can be produced by using the molten liquid crystal-forming wholly aromatic polyester and utilizing a flash spinning method, a melt blown method or the like. The melt blown method is preferable because it can relatively easily produce a nonwoven fabric made of ultrafine fibers, and can minimize the influence on the environment without requiring a solvent during spinning.

  FIG. 2 shows an outline of the production process of the nonwoven fabric of the present invention by the melt blown method. First, the molten liquid crystal-forming wholly aromatic polyester 4 is melted by an extruder and enters a molten state toward the nozzle 5. On the other hand, heated hot air is injected from the hot air injection grooves 6 and 6 provided on both sides of the nozzle 5, and the polyester is used as the high-temperature high-speed fluid 7. The high-temperature high-speed fluid 7 is sprayed onto a cooling metal roll 8 having a smooth surface, taken up by a take-up roll 9, and taken up by a take-up roll 10.

For example, the molten liquid crystal-forming wholly aromatic polyester has a high temperature under spinning conditions of a spinning temperature of 310 ° C. to 360 ° C., a hot air temperature (primary air temperature) of 310 ° C. to 380 ° C., and an air amount of 10 to 50 Nm ³ per 1 m width of the nozzle. The high-speed fluid 7 is sprayed from the nozzle 5 onto the cooling metal roll 8 at a collection distance of 2 to 20 cm (preferably about 2.5 to 13 cm). The surface of the metal roll is cooled by a known or conventional cooling means. Since the metal roll is disposed at a predetermined distance with respect to the nozzle and the metal roll is cooled, even the melted liquid crystal-forming wholly aromatic polyester heated at a high temperature has a very uniform fiber. Can be dispersed and cooled and solidified quickly, and the formation of the nonwoven fabric can be improved.

  Since it is formed by such a manufacturing method, the nonwoven fabric of the present invention is formed from substantially continuous filaments. Moreover, from a viewpoint of web formation of a nonwoven fabric, an average fiber diameter needs to be about 1-15 micrometers, Preferably it is about 3-10 micrometers. In addition, in this invention, an average fiber diameter refers to the average value of the value which magnified and imaged the nonwoven fabric with the scanning electron microscope, and measured the diameter of arbitrary 100 fibers.

  Furthermore, in the production method of the present invention, in order to improve the strength of the nonwoven fabric, the obtained nonwoven fabric may be further heat-treated to proceed with solid phase polymerization in a fibrous form. Since the non-woven fabric of the present invention is composed of ultrafine fibers and the specific surface area is remarkably increased, by-products generated with the progress of polymerization can be easily detached, and the polymerization reaction can be carried out very efficiently.

  In the solid phase polymerization, depending on the characteristics of the melt liquid crystal forming polyester to be used, an inert gas such as nitrogen is used, the treatment is performed in the air, or the solid phase polymerization is first performed in the inert gas. It is possible to select as appropriate, for example, to complete solid phase polymerization in air.

  In particular, molten liquid crystal forming polyester often undergoes cross-linking reactions such as dehydrogenation and oxygen cross-linking when proceeding with solid-phase polymerization in the air, and further improves the chemical resistance, water resistance and heat resistance of the nonwoven fabric. Can do. When these reactions are expected, it is preferable to proceed with solid-state polymerization in an inert gas in the initial stage to increase the molecular weight and then proceed with the reaction in air.

  If necessary, a method of managing the oxygen concentration, for example, selecting a reaction in air having an oxygen concentration of 10% can be exemplified as one of the options. It is also possible to advance the solid-phase polymerization reaction in an inert gas such as nitrogen in the initial stage, to make an aerobic atmosphere at the stage when the degree of polymerization is increased, and further proceed the reaction such as crosslinking and carbonization. .

  The nonwoven fabric of the present invention is excellent in heat resistance and chemical resistance because it contains a specific molten liquid crystal forming wholly aromatic polyester as a main component. Furthermore, since it is produced by a specific manufacturing method, the formation can be improved even if the nonwoven fabric is thin. Moreover, even if the nonwoven fabric has a small basis weight, a highly uniform texture can be imparted to the nonwoven fabric.

  Such non-woven fabrics are excellent in heat resistance and chemical resistance, have good formation and have few rough parts of fibers, and are useful as reinforcing materials for high-frequency circuit boards, as well as various filters, various battery separators, It is also useful as a capacitor separator.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. The physical properties of the nonwoven fabric were measured by the following measuring methods.

(Melt viscosity Pa · s)
Using a Toyo Seiki Capillograph Type 1B, measurement was performed under conditions of a temperature of 310 ° C. and a shear rate of r = 1000 sec− ¹ .

(Evaluation of chemical resistance)
It was immersed in o-chlorophenol at 30 ° C. for 24 hours, and the degree of dissolution was confirmed visually. Further, boiling treatment was performed for 1 hour in a 1N aqueous sodium hydroxide solution, and the weight reduction rate was confirmed. In the present invention, “substantially insoluble in a solvent” means that it is insoluble in o-chlorophenol, and even if the boiling treatment is carried out for 1 hour in a 1N aqueous sodium hydroxide solution, the weight reduction rate is reduced. It means 10% or less.

(Evaluation of heat resistance)
A hot air of 100 ° C. was passed through the nonwoven fabric, and the presence or absence of a shape change was confirmed visually. When the shape did not change, it was determined that the heat resistance was good, and when the shape changed, it was determined that the heat resistance was poor.

(Measurement of heat distortion temperature)
Using TMA-50 manufactured by Shimadzu Corporation, the sample length is set to 20 mm, 1 g per 1 g of the sample weight to be measured is given, and the temperature is raised from room temperature at a heating rate of 5 ° C./min. Let it be the heat distortion temperature. The temperature was defined by the intersection of tangent lines from the temperature-elongation curve.

(Thickness μm)
A 100 × 100 mm test piece was taken from the sample length direction and measured with a dial thickness gauge.

(Average fiber diameter μm)
A 100 × 100 mm test piece is taken from the sample length direction, and the obtained test piece is enlarged and photographed with a scanning electron microscope, and after measuring the diameter of an arbitrary 100 fibers, an average value thereof is calculated. did.

(Weight per unit g / m ² )
A test piece of 100 × 100 mm was taken from the sample length direction, the mass in a moisture equilibrium state was measured, and calculated per 1 m ² .

(Standard deviation of formation index)
First, the formation index of the nonwoven fabric was measured as follows. That is, as shown in FIG. 1, sample light 3 from a light source 1 (Matsushita Electric Works Co., Ltd., FCL32ECW / 30) is emitted from a sample piece 3 on a transparent sample base 2 disposed 15 cm above the light source 1. (8 cm × 10 cm) was emitted.
An image of the sample piece 3 through which light is transmitted is taken with a CCD camera 11 (Sony Corporation, XC-75; 0.026 mm ² / pixel) disposed 20 cm above the sample piece 3. As gradation image data, this image data (A) was captured in an image processing apparatus 20 (image analyzer V10 manufactured by Toyobo Co., Ltd.). On the other hand, blank image data on which no sample piece was set was also photographed by the CCD camera 11 in the same manner as described above except that no sample piece was set, and was taken into the image processing apparatus 20 as image data (B).
The image data (A) was subtracted from the obtained image data (B), the subtracted data was binarized by the TOKS method and subjected to image analysis, and then the standard deviation of the sample formation index was calculated.

Example 1
Liquid crystal-forming wholly aromatic polyester (VECTRA-A type manufactured by Polyplastics Co., Ltd .; melt viscosity at 310 ° C. 10 Pa · s, intrinsic viscosity 5.8) was sufficiently dried with a low dew point air dryer. The mixture was extruded by a shaft extruder and supplied to a melt blown nonwoven fabric manufacturing apparatus having a nozzle having a width of 1 m and a hole number of 1000. Cooled metal cooled with a water-cooled pipe at a collection distance of 3 cm with a melt blown device at a single-hole discharge rate of 0.3 g / min, a resin temperature of 320 ° C., a hot air temperature of 320 ° C., and an air amount of 30 N m ³ per 1 m of nozzle width. It was sprayed on a roll and solidified by cooling to obtain a melt blown nonwoven fabric. The obtained nonwoven fabric had the characteristics shown in Table 1.

(Example 2)
A melt blown nonwoven fabric was obtained in the same manner as in Example 1 except that the basis weight was 25 g / m ² . The obtained nonwoven fabric had the characteristics shown in Table 1.

(Example 3)
A melt blown nonwoven fabric was obtained in the same manner as in Example 1 except that the basis weight was 15 g / m ² . The obtained nonwoven fabric had the characteristics shown in Table 1.

(Comparative Example 1)
Instead of spraying and collecting on a cooled metal roll cooled by a water-cooled pipe, which is the collection method performed in Example 1, a method of collecting by suction on a net at a collection distance of 15 cm was adopted. Except for the above, a nonwoven fabric was obtained in the same manner as in Example 1. The obtained nonwoven fabric had the characteristics shown in Table 1.

(Comparative Example 2)
Instead of spraying onto a cooled metal roll cooled with a water-cooled pipe, which is the collection method performed in Example 2, a method of collecting by suction on a net at a collection distance of 15 cm was adopted. Except for this, a nonwoven fabric was obtained in the same manner as in Example 2. The obtained nonwoven fabric had the characteristics shown in Table 1.

  As shown in Table 1, the nonwoven fabrics obtained in Examples 1 to 3 have a small standard deviation of the formation index even if the thickness is small, and can improve the uniformity of formation, and the thickness (B) and formation The product of the index with the standard deviation (C), that is, (B) × (C) could be reduced. In addition, even if the basis weight is small, the formation uniformity is excellent, so the product of the thickness and the standard deviation of the formation index with respect to the basis weight (A), that is, (B) × (C) / (A) is also reduced. I was able to. Furthermore, the nonwoven fabric was excellent in chemical resistance and heat resistance.

  On the other hand, the nonwoven fabrics obtained in Comparative Examples 1 and 2 have the same chemical resistance, heat resistance, and dielectric properties as the examples, but the formation is not as uniform as the examples, so the standard deviation of the formation index Became larger. Also, the product [(B) × (C)] of the thickness (B) and the standard deviation (C) of the formation index and the value of [(B) × (C) / (A)] It became bigger.

  As described above, the preferred embodiments of the present invention have been described with reference to the drawings. However, various additions, modifications, or deletions can be made without departing from the spirit of the present invention, and these are also included in the present invention. It is included in the range.

It is the schematic which shows the measuring method of the formation index of the nonwoven fabric of this invention. It is the schematic which shows the process of manufacturing the nonwoven fabric of this invention by the melt blown method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Sample stand 3 ... Sample piece 4 ... Molten molten liquid crystal forming fully aromatic polyester 5 ... Nozzle 6 ... Hot-air jet groove 7 ... High-temperature high-speed fluid 8 ... Cooling metal roll 9 ... Take-up roll 10 ... Winding up Roll 11 ... CCD camera 20 ... Image processing device

Claims (4)

A nonwoven fabric comprising filaments having a melt liquid crystal-forming wholly aromatic polyester having a melt viscosity at 310 ° C. or higher of 20 Pa · s or less and an average fiber diameter of 1 to 15 μm,
The difference between the image data of the sample piece (0.026 mm ² / pixel; 256 gradations) when the transmitted light is irradiated to the 10 cm × 8 cm sample piece and the blank image data in which the sample piece is not arranged is represented by the TOKS method. The nonwoven fabric whose standard deviation of the formation index obtained by binarizing is 5.0 or less.   The nonwoven fabric according to claim 1, wherein the nonwoven fabric has a thickness of 20 to 200 µm, and the product of the nonwoven fabric thickness (µm) and the standard deviation of the formation index is 90 to 900. The nonwoven fabric satisfying the following formula (1) according to claim 1 or 2.
8 ≦ (B × C) / A ≦ 15 (1)
[In the formula, A: basis weight of nonwoven fabric (g / m ² ), B: thickness of nonwoven fabric (μm), C: standard deviation of formation index. ]   The nonwoven fabric in which the nonwoven fabric was manufactured by the melt blown method in any one of Claims 1-3.

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