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EP-3640398-B1 - WET NONWOVEN FABRIC CONTAINING META-ARAMID AND POLYPHENYLENE SULFIDE, AND MULTILAYER SHEET OF SAME

EP3640398B1EP 3640398 B1EP3640398 B1EP 3640398B1EP-3640398-B1

Inventors

  • HARADA, MASARU
  • TSUCHIKURA, HIROSHI

Dates

Publication Date
20260506
Application Date
20180605

Claims (6)

  1. A wet nonwoven fabric comprising a meta-aramid fiber and a polyphenylene sulfide short fiber, wherein a proportion of the polyphenylene sulfide short fiber at least partially fused in the wet nonwoven fabric is 40% or less, a proportion of a meta-aramid fiber fibrillated in the wet nonwoven fabric is 15% or more, wherein a freeness of the meta-aramid fiber fibrillated using the Canadian standard freeness tester in conformity with JIS P8121-2 (2012) is 10 to 900 cm 3 , and the wet nonwoven fabric has a dielectric breakdown strength of 17 kV/mm or more.
  2. A method for producing the wet nonwoven fabric according to claim 1, the method comprising subjecting a dry web obtained by fabricating a wet nonwoven fabric containing a meta-aramid fiber and a polyphenylene sulfide short fiber and then by removing moisture to a heating and pressurization treatment at a temperature equal to or higher than a glass transition point of the polyphenylene sulfide short fiber and equal to or lower than a melting point of the meta-aramid fiber.
  3. A laminated sheet comprising the wet nonwoven fabric according to claim 1 laminated on at least one surface of a thermoplastic resin sheet.
  4. The laminated sheet according to claim 3, wherein a thermoplastic resin constituting the thermoplastic resin sheet is selected from polyethylene terephthalate, polyethylene naphthalate, and polyphenylene sulfide.
  5. An electrical insulating paper comprising the wet nonwoven fabric according to claim 1.
  6. An electrical insulating sheet comprising the laminated sheet according to claim 3 or 4.

Description

TECHNICAL FIELD The present invention relates to a wet nonwoven fabric containing meta-aramid and polyphenylene sulfide and a laminate (laminated sheet) of the same, which are suitable as electrical insulating paper or an electrical insulating sheet. BACKGROUND ART Paper and laminates thereof are demanded in a wide range of fields and used in various things such as filters, separators, and electrical insulating members. The heat resistance and denseness required for paper and laminates there of vary depending on the respective applications. In recent years, the development of electric vehicles has progressed as the interest in environmental problems has increased, and particularly amelioration in efficiency and advancement of industrial motors including in-vehicle motors are desired. Under such circumstances, the performance of insulating paper or insulating sheets which are formed of paper or laminates thereof and used in industrial motors is also required to be enhanced. The heat resistance and durability required for insulating members differ depending on the use environment, but the use environment temperature of industrial motors such as in-vehicle motors exceeds 100°C in some cases, and thus the insulating members are also required to exhibit such heat resistance. Examples of the material for insulating paper used in a high temperature environment include electrical insulating paper obtained by mixing an aramid fiber as a heat resistant fiber and a polyphenylene sulfide fiber, and this electrical insulating paper is disclosed in Patent Document 1 and Patent Document 2. Moreover, in order to improve insulating properties, it is effective to improve the denseness of a wet nonwoven fabric, and a method in which a pulp-shaped fiber aggregate is mixed is conceivable. Furthermore, a method is also known in which a wet nonwoven fabric is subjected to a heating and pressurization treatment to densify the structure so as to improve the insulating properties. Moreover, for example, Patent Documents 3 and 4 disclose wet nonwoven fabrics containing fibrillated pulp-shaped aramid fibers and undrawn polyphenylene sulfide fibers. Patent Document 5 relates to a blend formed paper, containing specific amounts of polyphenylene sulfide fibers and aromatic polyamide fibers, excellent in flame retardance, heat resistance, strength and electrical characteristics and suitably useful for ultrahigh-voltage insulation. The blend formed paper containing polyphenylene sulfide fibers and aromatic polyamide fibers in amounts accounting for ≥80wt.%. Both fibers respectively account for ≥30wt.%. Patent Document 6 discloses a high-strength aramid paper and a method for preparing the same through dissolving and re-pressing self-reinforcing. The method comprises the following steps: subjecting polyphenylene sulfide fiber to pretreatment, then mixing the pretreated polyphenylene sulfide fiber, aramid fiber and aramid pulp, subjecting dried raw paper to dipping and then pressing treated sample paper; soaking the treated sample paper in a washing solution and removing an organic solvent and inorganic salt left in the paper; and pressing the treated sample paper. When the high-strength aramid paper has gram weight of 10 to 200 g/m2, the aramid paper has a thickness of 20 to 400 µm, tensile strength of 10 to 150 KN/m and dielectric strength of 30 to 70 kV/mm. The aramid paper and polyphenylene sulfide are used as raw materials. The method is environment friendly and low in cost. The prepared paper has high strength and good evenness, and industrial production can be realized through partial reconstruction of conventional paper machines. PRIOR ART DOCUMENT PATENT DOCUMENTS Patent Document 1: Japanese Patent Laid-open Publication No. 7-189169Patent Document 2: Japanese Patent Laid-open Publication No. 2-47389Patent Document 3: Japanese Patent Laid-open Publication No. 2001-40597Patent Document 4: Japanese Patent Laid-open Publication No. 2009-277653Patent Document 5: JP H02 47389 APatent Document 6: CN 106 087 529 A SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION However, an insulating member such as insulating paper is required to exhibit not only excellent insulating properties but also mechanical properties, processability, and workability when being disposed and inserted inside an electrical member for a motor and the like. Patent Document 1 and Patent Document 2 disclose electrical insulating paper obtained by mixing an aramid fiber and a polyphenylene sulfide fiber, but there are through-holes which allow the air to pass through in these mixed paper, an electric current passes through the through-hole portions, and thus the dielectric breakdown strength cannot be improved. In addition, the insulating paper is required to be pasted to a film since the tension and stiffness thereof are also weak. In addition, Patent Document 3 discloses a wet nonwoven fabric which contains a fibrillated pulp-shaped aramid fiber and an undr