JP2017218701A - Heat resistant wet nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant nonwoven fabric that has a low basis weight, is dense and has sufficient heat-resistance, in a heat-resistant wet type nonwoven fabric containing PPS fibers.SOLUTION: A heat-resistant wet type nonwoven fabric containing polyphenylene sulfide fibers includes a fiber layer containing stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers and an inorganic fine particle-containing layer provided on at least one surface of the fiber layer, in which, preferably, the inorganic fine particles are particles of at least one kind selected from the group consisting of magnesium hydroxide, mica and clay.SELECTED DRAWING: None

Description

  The present invention relates to a heat-resistant wet nonwoven fabric containing polyphenylene sulfide fibers.

  Polyphenylene sulfide (PPS) fiber is a high-performance fiber with excellent heat resistance, chemical resistance, hydrolysis resistance, dimensional stability during moisture absorption, insulation, flame retardancy, and heat retention, so its use is expanding doing. For example, filters for collecting high-temperature gas dust, canvas for dryers used in the drying process of industrial products, roll wiping materials for office copiers, insulating materials for electrical equipment, cushioning materials (cushion materials), heat insulation cloths, batteries Uses such as a separator can be mentioned.

  As a heat resistant nonwoven fabric containing PPS fibers, a heat resistant wet nonwoven fabric manufactured by a wet papermaking method is known. For example, a heat-resistant wet nonwoven fabric using a stretched PPS fiber and an unstretched PPS fiber is known (see, for example, Patent Documents 1 and 2). In general, wet nonwoven fabrics are characterized by being denser than dry nonwoven fabrics when they have the same basis weight. However, the heat-resistant wet nonwoven fabric containing PPS fibers is less likely to have a low density and tends to be bulky. Therefore, in order to cope with the downsizing of electrical equipment and batteries, in applications such as insulating materials for electrical equipment and battery separators, etc., a wet type containing PPS fibers that are low in weight and dense and have sufficient heat resistance. There is a need for nonwoven fabrics.

JP 2010-24574 A JP 2011-106043 A

  An object of the present invention is to provide a heat-resistant nonwoven fabric that has a low basis weight and is dense and has sufficient heat resistance in a heat-resistant wet nonwoven fabric containing PPS fibers.

  The above problems can be solved by the following invention.

(1) In a heat-resistant wet nonwoven fabric containing polyphenylene sulfide fibers, a fiber layer containing stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers, and inorganic fine particles formed on at least one surface of the fiber layer A heat-resistant wet nonwoven fabric characterized by having a layer.

(2) The heat-resistant wet nonwoven fabric according to (1), wherein the inorganic fine particles have a particle size of 0.5 to 20 μm.
(3) The heat resistant wet nonwoven fabric according to (1) or (2), wherein the inorganic fine particles are at least one selected from the group consisting of magnesium hydroxide, mica and clay.

  ADVANTAGE OF THE INVENTION According to this invention, in the heat resistant wet nonwoven fabric containing a PPS fiber, it can provide the heat resistant nonwoven fabric which is low-weight and dense and has sufficient heat resistance.

  The present invention relates to a heat-resistant wet nonwoven fabric containing polyphenylene sulfide fibers, a fiber layer containing stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers, and inorganic fine particles provided on at least one surface of the fiber layer And a containing layer. This layer structure can achieve the effect of being dense and low in weight and having sufficient heat resistance.

A polyphenylene sulfide (Polyphenylene sulfide) fiber is a synthetic fiber made of a polymer (PPS polymer) having — (C ₆ H ₄ —S) — as a polymer structural unit as a main structural unit. Representative examples of the PPS polymer include polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfide ketone and the like. Moreover, these random copolymers, block copolymers, etc. are also mentioned. Furthermore, the mixture of the said polymer is mentioned. As a particularly preferred PPS polymer, polyphenylene sulfide containing preferably 90% by mass or more of a p-phenylene unit represented by — (C ₆ H ₄ —S) — is mentioned as the main structural unit of the polymer.

  In the present invention, as the PPS fiber, a stretched PPS fiber and an unstretched PPS fiber are used. Most of the unstretched PPS fibers have an amorphous structure, and can be melted by applying heat to serve as binder fibers. The drawn PPS fiber is stretched in the fiber production process, so that the single fiber strength of the fiber is strong and the dimensional stability is excellent. In the present invention, a nonwoven fabric excellent in heat resistance can be provided by using a stretched PPS fiber and an unstretched PPS fiber in combination.

  Considering the production efficiency in the wet papermaking method, the fiber length of the PPS fiber is preferably 1 to 30 mm, more preferably 3 to 12 mm. Further, the fiber diameter of the PPS fiber is preferably 30 μm or less, more preferably 25 μm or less, and further preferably 20 μm or less. The lower limit of the fiber diameter is preferably 0.1 μm or more.

  In this invention, it is preferable that the compounding quantity of the unstretched PPS fiber in the fiber layer of a heat resistant wet nonwoven fabric is 40-80 mass% with respect to the total fiber amount in the said fiber layer, More preferably, it is 50-70 mass%. It is. When the blending amount of unstretched PPS fibers is less than 40% by mass, the binder effect for bonding the fibers to each other is insufficient, the strength of the fiber layer is lowered, and the strength of the heat-resistant wet nonwoven fabric may be lowered. Moreover, even if the fabric weight of a fiber layer is made low, it becomes difficult to make a fiber layer thin, and a fiber layer may become bulky. On the contrary, if the blending amount of the unstretched PPS fiber exceeds 80% by mass, the heat resistance and dimensional stability of the fiber layer may be lowered.

In the present invention, in order to obtain a dense heat-resistant wet nonwoven fabric having sufficient heat resistance and strength, the basis weight of the fiber layer of the heat-resistant wet nonwoven fabric is 20 to 60 g / m ² and the thickness is 25 to 80 μm. It is preferable that the basis weight is 25 to 50 g / m ² , and it is more preferable that the thickness is 30 to 70 μm. The basis weight means the basis weight based on the method defined in JIS P 8124.

  In the present invention, the fiber layer is manufactured by a wet papermaking method. First, stretched PPS fibers and unstretched PPS fibers are uniformly dispersed in water, and then a slurry is prepared through a process such as screen (removal of foreign matters, lumps, etc.). The final fiber concentration of the slurry is preferably 0.01 to 0.50 mass%. The slurry is made up with a paper machine to obtain a wet paper. In the process, chemicals such as a dispersant, an antifoaming agent, a hydrophilic agent, an antistatic agent, a polymer viscosity agent, a release agent, an antibacterial agent, and a bactericide may be added.

  As the paper machine, for example, a paper machine that uses a paper net such as a long net, circular net, or inclined wire alone, or a combination paper machine that has two or more types of same or different types of paper nets installed online is used. can do. In addition, when the fiber layer has a multi-layer structure of two or more layers, a fiber bonding method in which wet papers made by each paper machine are laminated, or after forming one layer, fibers are put on the layer. The fiber layer can be produced by a casting method in which the dispersed slurry is cast and laminated. When casting the slurry in which the fibers are dispersed, the previously formed layer may be in a wet paper state or in a dry state. Also, two or more dry layers can be thermally fused to form a multi-layered fiber layer.

  In the wet papermaking method, a wet paper manufactured by a papermaking net is dried with a Yankee dryer, an air dryer, a cylinder dryer, a suction drum dryer, an infrared dryer, or the like to obtain a sheet-like fiber layer. When the wet paper is dried, it is brought into close contact with a hot roll such as a Yankee dryer and dried by heat and pressure to improve the smoothness of the contacted surface. Hot-pressure drying means that wet paper is pressed against a hot roll with a touch roll or the like and dried. The surface temperature of the hot roll is preferably 100 to 180 ° C, more preferably 100 to 160 ° C, and still more preferably 110 to 160 ° C. The pressure is preferably 50 to 1000 N / cm, more preferably 100 to 800 N / cm.

  In the present invention, the fiber layer can also be subjected to a thermal calendar process. Examples of the calendar unit used for the thermal calendar treatment of the fiber layer include a calendar unit of a combination of rolls such as a metal roll-metal roll, a metal roll-elastic roll, a metal roll-cotton roll, and a metal roll-silicon roll. These calendar units can be used alone or in combination of two or more.

  The surface temperature of the metal roll during the heat calendar treatment is preferably 100 to 250 ° C, more preferably 130 to 230 ° C, and further preferably 150 to 230 ° C. When the temperature of the metal roll is lower than 100 ° C., the melting of the PPS fiber does not proceed and the fiber-fiber binding may not proceed. Moreover, when the temperature of a metal roll is higher than 250 degreeC, the fiber which comprises a fiber layer may stick to a metal roll, and may impair the uniformity of the fiber layer surface.

  The nip pressure of the nip during the heat calendar process is preferably 190 to 1800 N / cm, and more preferably 390 to 1500 N / cm. The processing speed is preferably 5 to 150 m / min, and more preferably 10 to 80 m / min.

  In this invention, when a fiber layer is a multilayer structure, the multilayer structure with the same fiber mixing of each layer may be sufficient, and the multilayer structure from which the fiber mixing of each layer differs may be sufficient. In the case of a multilayer structure, the fiber concentration of the slurry can be lowered by lowering the basis weight of each layer, so that the formation of the fiber layer is improved, and as a result, the uniformity of the formation of the fiber layer is improved. Moreover, even when the formation of each layer is non-uniform | heterogenous, it can compensate by laminating | stacking. Furthermore, the papermaking speed can be increased, and the operability can be improved.

  In the present invention, the inorganic fine particles are preferably inorganic fine particles having a dehydration temperature of crystal water or structured water of 250 ° C. or higher. “Inorganic fine particles having a dehydration temperature of crystal water or structured water of 250 ° C. or higher” also includes inorganic fine particles that do not have crystal water or structured water. When inorganic fine particles having crystal water or structured water are heated, a dehydration reaction occurs and water is released. This dehydration reaction is an endothermic reaction. Therefore, when the inorganic fine particles are inorganic fine particles having a dehydration temperature of crystal water or structured water of 250 ° C. or higher, the heat resistance of the heat-resistant wet nonwoven fabric is further improved. In addition, when the inorganic fine particles are inorganic fine particles that do not have crystallization water or structural water, since the crystal structure of the inorganic fine particles hardly changes even when heated, the heat resistant wet nonwoven fabric is less likely to be deformed, and the heat resistance is improved. An excellent heat-resistant nonwoven fabric is obtained.

  A more preferable dehydration temperature of the inorganic fine particles is 300 ° C. or higher, and a more preferable dehydration temperature is 350 ° C. or higher. Examples of the inorganic fine particles include aluminum hydroxide (200 to 350 ° C.), magnesium hydroxide (330 to 430 ° C.), calcium hydroxide (400 to 500 ° C.), chromium hydroxide, zirconium hydroxide, nickel hydroxide, water Examples thereof include boron oxide, clay, boehmite (400 to 600 ° C), die spore (450 to 650 ° C), mica (550 ° C), and alumina. Particularly preferred inorganic fine particles are aluminum hydroxide, boehmite, die spore, magnesium hydroxide, clay and mica. These inorganic fine particles may be used alone or in combination of two or more. In the present invention, the dehydration temperature of the inorganic fine particles can be measured by differential scanning calorimetry (DSC). The measurement conditions are a temperature rise rate of 10 ° C./min and a temperature range of 30 to 900 ° C. in a nitrogen gas atmosphere.

  As a method for obtaining a dense heat-resistant wet nonwoven fabric, first, there is a method of adjusting the particle size and particle structure of inorganic fine particles. By reducing the particle size of the inorganic fine particles, it can be made dense. Moreover, it can be made dense by reducing the primary structure and secondary structure of the particles. In addition, the particle diameter in this invention refers to the average particle diameter (D50) measured by a laser diffraction scattering method.

  In the present invention, the particle size of the fine particles is preferably 0.5 to 20 μm, more preferably 0.5 to 10 μm. When the particle diameter is within the above range, a dense heat-resistant wet nonwoven fabric excellent in heat resistance is easily obtained. When the particle diameter of the fine particles is less than 0.5 μm, workability when providing the inorganic fine particle-containing layer may be lowered. From the viewpoint of heat resistance, the blending amount of the inorganic fine particles is preferably 20 to 80% by mass in the total solid content of the nonwoven fabric.

  Second, there is a method of calendering a fiber layer or a heat-resistant wet nonwoven fabric. The thickness can be adjusted by calendering, and a dense heat-resistant wet nonwoven fabric can be obtained. By applying heat and calendering, the adhesive in the unstretched PPS fiber and the inorganic fine particle-containing layer melts and the adhesion between the heat-resistant wet nonwoven fabrics becomes strong, thereby obtaining a dense heat-resistant wet nonwoven fabric. It is possible.

  In the present invention, the inorganic fine particle-containing layer may contain an adhesive. Specific examples of the adhesive include urethane resin, epoxy resin, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate ester, and styrene / acrylate copolymer. Styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / styrene terpolymer, and polyvinyl acetate. Of these, urethane resins and epoxy resins are preferable. In the present invention, the amount of the adhesive in the inorganic fine particle-containing layer is preferably 5 to 30% by mass in terms of the heat resistance of the heat-resistant wet nonwoven fabric and the strength of the inorganic fine particle-containing layer.

  In the present invention, various additives such as a dispersant, a wetting agent, a thickener, and a water repellent can be added to the inorganic fine particle-containing layer as long as the effects of the invention are not impaired.

  In the present invention, the method for providing the inorganic fine particle-containing layer is not particularly limited. For example, inorganic fine particles using a coater such as an air doctor coater, blade coater, knife coater, rod coater, squeeze coater, impregnation coater, gravure coater, kiss roll coater, die coater, reverse roll coater, transfer roll coater, spray coater, etc. An inorganic fine particle-containing layer can be provided by applying a coating liquid containing a selenium to a fiber layer and drying it.

In the present invention, the coating amount of the inorganic fine particle-containing layer is absolutely dry, preferably 10 to 55 g / m ² , more preferably 10 to 40 g / m ² . When the coating amount is 10 g / m ² or more, the fiber layer surface is easily sufficiently covered with the inorganic fine particle-containing layer, and the heat resistance is easily improved. Moreover, by being 55 g / m < ² > or less of coating amount, the thickness increase of a heat resistant wet nonwoven fabric can be suppressed, and it becomes easy to obtain a precise heat resistant nonwoven fabric.

  In the present invention, for the heat-resistant wet nonwoven fabric having a fiber layer and an inorganic fine particle-containing layer provided on at least one surface of the fiber layer, the flatness and thickness of the surface of the heat-resistant wet nonwoven fabric are controlled. Thermal calendering can be applied for the purpose. The heat calender treatment of the heat-resistant wet nonwoven fabric can use the calender unit and conditions in the heat calender treatment of the fiber layer described above. The surface temperature of the metal roll during the heat calender treatment is the heat calender of the fiber layer. It is preferable to make it higher than the treatment, preferably 100 to 250 ° C, more preferably 130 to 250 ° C, and still more preferably 150 to 250 ° C.

Basis weight of the heat-resistant wet-laid nonwoven fabric of the present invention is not particularly limited, preferably 40 to 100 g / ^{m 2,} more preferably 40 and 80 g / ^{m 2.} When the basis weight is less than 40 g / m ² , the uniformity, denseness, and heat resistance of the heat-resistant wet nonwoven fabric may be insufficient. If the basis weight exceeds 100 g / m ² , the thickness may not be sufficiently reduced even if the thermal calendar process is performed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. In the examples, all parts and percentages are by mass unless otherwise specified.

(fiber)
PPS drawn fiber: Fineness 1.7 decitex, fiber length 5mm
PPS unstretched fiber: Fineness 2.2 decitex, fiber length 5mm

<Example 1>
(Fiber layer)
In the fiber formulation shown in Table 1, the fiber is dispersed in water at a dispersion concentration of 0.1% by mass for 10 minutes, and wet paper is formed using a circular paper machine. Then, it was hot-pressure dried, and then heat calendered at a processing temperature of 220 ° C. and a processing speed of 10 m / min by a metal roll-metal roll calendar unit to obtain a fiber layer. Table 1 shows the basis weight and thickness of the fiber layer.

(Coating liquid for inorganic fine particle content layer)
1 part of a dispersant and 26 parts by weight of water were added to 100 parts by weight of magnesium hydroxide having a particle diameter of 1.2 μm, which is an inorganic fine particle, and dispersed to prepare a magnesium hydroxide aqueous dispersion. Next, 16 parts by mass of urethane resin as an adhesive was added to 75 parts by mass of this magnesium hydroxide aqueous dispersion, and the mixture was stirred and mixed. Subsequently, 9 parts by mass of a polyvinyl alcohol (PVA) resin was added as a thickener and stirred and mixed. Finally, preparation water was added so that the solid content concentration was 34% by mass to prepare coating solution 1.

(Inorganic fine particle content layer)
On one side of the fiber layer, the coating liquid is applied so that the dry coating amount is 25 g / m ² and then dried to provide an inorganic fine particle layer. By a calendar unit of metal roll-metal roll, a processing temperature of 240 ° C. Then, a heat calender treatment was performed at a processing speed of 10 m / min to produce a heat-resistant nonwoven fabric.

<Example 2>
A heat-resistant wet nonwoven fabric was produced in the same manner as in Example 1 except that 100 parts by mass of natural mica having a particle diameter of 5.0 μm was used as the inorganic fine particles.

<Example 3>
A heat-resistant wet nonwoven fabric was produced in the same manner as in Example 1 except that 100 parts by mass of flat clay having a particle diameter of 2 to 20 μm was used as the inorganic fine particles.

<Examples 4 and 5>
As described in Table 1, a heat-resistant wet nonwoven fabric was produced in the same manner as in Example 1 except that the fiber composition was changed.

<Examples 6 and 7>
As described in Table 1, a heat-resistant wet nonwoven fabric was produced in the same manner as in Example 1 except that the basis weight of the fiber layer was changed.

<Examples 8 and 9>
As described in Table 1, a heat-resistant wet nonwoven fabric was produced in the same manner as in Example 1 except that the dry coating amount of the inorganic fine particle layer was changed.

<Examples 10 and 11>
As described in Table 1, a heat-resistant nonwoven fabric was produced in the same manner as in Example 1 except that the particle diameter of magnesium hydroxide, which is an inorganic fine particle, was changed.

<Comparative Example 1>
The fiber layer obtained in Example 1 was used as the heat-resistant wet nonwoven fabric of Comparative Example 1.

  The following evaluation was performed on the heat-resistant wet nonwoven fabrics of Examples and Comparative Examples, and the results are shown in Table 1.

(Heat resistance: tensile strength)
A heat-resistant wet nonwoven fabric is cut into a width direction of 25 mm and a flow direction of 150 mm, and fixed to a chuck of a tabletop material testing machine (device name: STA-1150, manufactured by Orientec Co., Ltd.) with a chuck interval of 80 mm, 100 mm / min The maximum load when the upper chuck was pulled up until the nonwoven fabric broke at a constant speed was defined as the tensile strength. Subsequently, about the heat resistant wet nonwoven fabric after heat-processing in a 200 degreeC dryer for 72 hours, a tensile strength is measured by the method similar to the above, and the maintenance rate of the tensile strength after heat processing with respect to the tensile strength before heat processing ( Tensile strength after heat treatment / tensile strength before heat treatment × 100, unit:%) was determined and evaluated according to the following criteria.

100%: ◎
Less than 100%, 98% or more: ○
Less than 98%, 96% or more:
Less than 96%: ×

(Heat resistance: shrinkage)
The heat-resistant wet nonwoven fabric cut to 100 mm square was heat-treated in a dryer at 200 ° C. for 72 hours. The dimension in the flow direction before and after the heat treatment is measured in units of 0.1 mm, and the change rate of the dimension after the heat treatment relative to the dimension before the heat treatment (size after the heat treatment / dimension before the heat treatment × 100, unit:%). Was evaluated according to the following criteria.

99% or more: ◎
Less than 99%, 98% or more: ○
Less than 98%, 97% or more: △
Less than 97%: ×

  The heat-resistant wet nonwoven fabric of Comparative Example 1 comprising the stretched PPS fiber and the unstretched PPS fiber, and the blending amounts of the unstretched PPS fiber and the stretched PPS fiber are 60 parts by mass and 40 parts by mass, Having an inorganic fine particle-containing layer by comparing the heat-resistant wet nonwoven fabric of Examples 1 to 3 and 6 to 11 with a heat-resistant wet nonwoven fabric as a fiber layer and having an inorganic fine particle-containing layer on one side of the fiber layer It can be seen that the heat resistance of the heat-resistant wet nonwoven fabric is improved.

In Example 11 in which the particle size of the inorganic fine particles is less than 0.5 μm, the coating liquid was applied so that the absolute dry coating amount was 25 g / m ² . The absolutely dry coating amount was 20 g / m ² . In Example 1 in which the particle size of the inorganic fine particles was 0.5 μm or more, no see-through of the coating liquid was confirmed. Comparing Example 10 in which the particle size of the inorganic fine particles exceeds 20 μm and Example 3 in which the particle size of the inorganic fine particles is 20 μm or less, the heat-resistant wet nonwoven fabric of Example 3 is more dense and heat-resistant. It turns out that it is excellent in.

  The heat-resistant wet nonwoven fabric of the present invention includes a filter used for high-temperature gas dust collection, a canvas for a dryer used in a drying process for industrial products, a roll wiping material for an office copying machine, an insulating material for electrical equipment, a cushioning material (cushion material) ), Thermal insulation cloth, battery separator, and the like.

Claims (3)

  In a heat resistant wet nonwoven fabric containing polyphenylene sulfide fibers, a fiber layer containing stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers, and an inorganic fine particle-containing layer provided on at least one surface of the fiber layer A heat-resistant wet nonwoven fabric characterized by comprising:   The heat-resistant wet nonwoven fabric according to claim 1, wherein the inorganic fine particles have a particle size of 0.5 to 20 µm.   The heat-resistant wet nonwoven fabric according to claim 1 or 2, wherein the inorganic fine particles are at least one selected from the group consisting of magnesium hydroxide, mica and clay.