Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
  • D04H1/558—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving in combination with mechanical or physical treatments other than embossing
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
  • D04H1/4326—Condensation or reaction polymers
  • D04H1/4334—Polyamides
  • D04H1/4342—Aromatic polyamides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H1/00—Paper; Cardboard
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
  • D21H13/10—Organic non-cellulose fibres
  • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H13/26—Polyamides; Polyimides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
  • D21H25/04—Physical treatment, e.g. heating, irradiating

Definitions

• the present invention relates to a method for producing an electrically insulating material having excellent heat resistance, particularly a method for producing aramid paper which makes it possible to produce thin aramid paper having high strength and insulating property.
• aramid paper which is a synthetic paper made of aromatic polyamide, has been used as a base for electrically insulating materials and aircraft honeycombs due to its excellent heat resistance, flame retardance, electrical insulating property, toughness, and flexibility.
• paper containing Nomex (registered trademark) fibers manufactured by DuPont (USA) is produced by mixing poly(meta-phenylene isophthalamide) short fibers and fibrids in water, then papermaking the mixed slurry, followed by calendering process. This paper is known to still have high strength and toughness as well as excellent electrical insulating property, even at high temperatures.
• Patent Literature 1 discloses a method for producing aramid paper that includes sandwiching aramid paper made of a mixture of fibrids formed from aromatic polyamides and short fibers between at least a pair of heating elements, followed by hot pressing, wherein the shrinkage rate of the aramid paper after hot pressing by the heating elements is 3% or less.
• a pair of calender rolls is used as the pair of heating elements, and the hot pressing is performed once at a calender roll surface temperature of 250°C and a roll pressure of 2500 kg/cm 2 or 1250 kg/cm 2 .
• This method has been shown to produce a thin electrical insulating sheet material with high heat resistance (Examples).
• aramid paper of the desired thinness cannot be obtained when the hot pressing is performed at 330°C, which is a temperature above the glass transition temperature of aramid paper (Comparative Examples 2 and 3).
• Patent Literature 1 Japanese Patent Application Publication No. 2016-223021
• An object of the present invention is to provide a method for producing aramid paper which, in addition to being thin, dense, and excellent in electrical properties, can further produce aramid paper having high mechanical properties, in particular, high tensile strength.
• the present inventors have made earnest studies and arrived as a result at the present invention based on the knowledge that the above object can be achieved by performing, at least twice, a hot-pressing treatment step under specific temperature conditions in which a sheet-shaped material formed from a mixture with specific ratios of aramid short fibers and aramid fibrids is sandwiched between a pair of heating elements and subjected to a high pressure.
• the present invention provides the following [1] to [10].
• the production method of the present invention by appropriately adjusting the amount of aramid short fibers and aramid fibrids used as raw materials for the production of aramid paper, as well as the pressing pressure in the hot-pressing treatment step, it is possible to easily produce aramid paper with a wide range of thicknesses, for example, up to 200 ⁇ m, and with excellent mechanical properties, electrical properties, and heat resistance.
• aramid means a linear polymer compound in which 60% or more of its amide bonds are directly bonded to an aromatic ring.
• Such an aramid includes, for example, polymetaphenylene isophthalamide and copolymers thereof, polyparaphenylene terephthalamide and copolymers thereof, copolyparaphenylene 3,4'-diphenyl ether terephthalamide, and the like.
• These aramids are industrially produced, for example, by a solution polymerization method involving a condensation reaction between an aromatic acid dichloride and an aromatic diamine, a two-step interfacial polymerization method, or the like, and are available as commercial products, but are not limited thereto.
• polymetaphenylene isophthalamide is preferably used because it has properties such as good molding processability, heat adhesion, flame retardance, and heat resistance.
• the aramid short fiber is a fiber made from aramid cut into a predetermined length, and such a fiber includes, but is not limited to, those available under the trade names "Teijinconex (registered trademark)” from Teijin Limited, "Nomex (registered trademark)” from DuPont, and the like, for example.
• the length of the aramid short fibers can generally be selected from the range of 1 mm or more and less than 25 mm, and preferably 2 mm or more and less than 12 mm.
• the length of the short fibers is 1 mm or more, the mechanical properties of the sheet material are good, and meanwhile, those having a length of 25 mm or less are preferable because they can suppress the occurrence of "entanglement” and "binding" in the production of aramid paper by the wet method described later.
• the fiber diameter of the aramid short fibers can be selected from the range of, for example, 0.1 to 40 ⁇ m, preferably 0.5 to 25 ⁇ m, and more preferably 1 to 20 ⁇ m.
• the aramid fibrid is a film-shaped fine particle composed of aramid, and is sometimes referred to as aramid pulp.
• the method for producing aramid fibrid include, for example, the methods described in Japanese Examined Patent Application Publication No. Sho 35-11851 , Japanese Examined Patent Application Publication No. Sho 37-5732 , and the like.
• the aramid fibrid has papermaking properties like ordinary wood (cellulose) pulp, and can be formed into a sheet by a papermaking machine after being dispersed in water. In this case, a so-called beating process can be performed for the purpose of maintaining the quality suitable for papermaking.
• This beating process can be performed by a disc refiner, beater, or other papermaking raw material processing device that exerts a mechanical cutting action.
• the morphological change of the fibrid can be monitored at the freeness specified in JIS P8121.
• the freeness of the aramid fibrid after the beating process is preferably in the range of 10 to 300 cm 3 (Canadian standard freeness). With a fibrid having a freeness in this range, it is possible to suppress a decrease in the strength of the sheet-shaped material formed therefrom.
• the freeness is larger than 10 cm 3 , the progress of fibrid refinement can be suppressed, so that the so-called deterioration of the binder function can be suppressed.
• Aramid paper in the present invention is produced by a method for producing aramid paper, including: performing, at least twice, a hot-pressing treatment step in which aramid short fibers and aramid fibrids are mixed in a mass ratio of 60/40 to 10/90 to form a sheet-shaped material, and the resulting sheet-shaped material is sandwiched between a pair of heating elements and subjected to a pressure of 500 kg/cm 2 or more, wherein the hot-pressing treatment step performed at least twice includes a hot-pressing treatment step (a) at a temperature above a glass transition temperature of aramid and a subsequent hot-pressing treatment step (b) at a temperature below the glass transition temperature of aramid.
• the aramid short fibers and aramid fibrids are first mixed in a mass ratio of 60/40 to 10/90, preferably in a mass ratio of 55/45 to 15/85, and more preferably in a mass ratio of 50/50 to 20/80 to form a sheet-shaped material.
• aramid short fibers and aramid fibrids are dry blended and then airflow is used to form a sheet
• the wet paper making method it is a general method that a single or mixed aqueous slurry containing at least aramid fibrids and aramid short fibers is pumped into a papermaking machine, dispersed, and then dehydrated, pressed, and dried before being rolled into sheets.
• a papermaking machine a long net papermaking machine, a circular net papermaking machine, an inclined papermaking machine, and a combination papermaking machine combining these, and the like are used.
• a composite sheet composed of multiple paper layers can be obtained by forming sheets of slurries having different mixing ratios and putting them together. Additives such as dispersibility improvers, defoamers, and paper strength enhancers are used during papermaking as needed.
• aramid short fibers in addition to the above-mentioned aramid short fibers, other fibrous components (for example, organic fibers such as polyphenylene sulfide fibers, polyether ether ketone fibers, cellulosic fibers, PVA fibers, polyester fibers, polyarylate fibers, liquid crystal polyester fibers, and polyimide fibers, and inorganic fibers such as glass fibers, rock wool, asbestos, and boron fibers) can be added as long as the object of the present invention is not impaired.
• the proportion of the aramid short fibers in the total constituent fibers is 80% by mass or more, and more preferably 90% by mass or more.
• a hot-pressing treatment step is performed at least twice in which the sheet-shaped material obtained as described above is sandwiched between a pair of heating elements and subjected to a pressure of 500 kg/cm 2 or more.
• the hot-pressing treatment step performed at least twice includes a hot-pressing treatment step (a) at a temperature above a glass transition temperature of aramid and a subsequent hot-pressing treatment step (b) at a temperature below the glass transition temperature of aramid.
• the pressure is preferably 500 to 10000 kg/cm 2 , and more preferably 1000 to 5000 kg/cm 2 .
• the hot-pressing treatment step (a) is preferably performed at a temperature higher than the glass transition temperature of aramid by 15°C or higher, preferably 20°C or higher, and below the decomposition temperature of aramid, preferably up to 380°C, while applying a pressure of 500 kg/cm 2 or more.
• the glass transition temperature of aramid is considered to be around 280°C, and the decomposition temperature is considered to be around 400°C.
• the hot-pressing treatment step (b) is preferably performed at a temperature lower than the glass transition temperature of aramid by 10°C, preferably by 20°C to 180°C, and preferably by 100°C, while applying a pressure of 500 kg/cm 2 or more. Note that it is more preferable that the heating temperature difference between the hot-pressing treatment steps (a) and (b) is 50°C or more.
• the heating temperature in the hot-pressing treatment step can be expressed as the surface temperature of the heating elements, and when calender rolls are used as the heating elements, it can be expressed as the surface temperature of the calender rolls.
• the mechanical strength can be further improved by performing hot pressing at a temperature above the glass transition temperature, and due to the high temperature of the heating elements, the sheet, once compressed in the thickness direction by the heating elements, also swells in the thickness direction immediately after being released from the heating elements, and the effect is particularly large for thinner sheets, which is a factor that makes it impossible to increase the strength of thin aramid paper and at the same time increase its density.
• by performing hot pressing more than once with the above temperature difference it has become possible to obtain aramid paper that is thin and has both mechanical properties and electrical properties.
• a pressure releasing step between the hot-pressing treatment steps (a) and (b), in which pressure on the hot-pressed sheet is released.
• the temperature of the hot-pressed aramid paper is preferably cooled below the glass transition temperature by being released from the pressure by a pair of heating elements, preferably a pair of calender rolls, and coming into contact with outside air, preferably air.
• a pressure releasing step can be provided by installing a pair of calender rolls and a subsequent pair of calender rolls at a distance from each other.
• a pressure treatment step at room temperature or the like may be combined.
• the hot-pressing treatment step (b) may include multiple hot-pressing treatment steps having different pressures and temperatures. Further, before the hot-pressing treatment step (b) is performed, multiple hot-pressing treatment steps (a) may be performed.
• the production method of the present invention by appropriately adjusting the amount of aramid short fibers and aramid fibrids used as raw materials for the production of aramid paper, as well as the pressurization pressure in the hot-pressing treatment step, it is possible to easily produce aramid paper with a wide range of thicknesses, for example, up to 200 ⁇ m (preferably 5 ⁇ m or more and 100 ⁇ m or less, with a density of 0.70 to 1.0 g/cm 3 ), and with excellent mechanical properties, electrical properties, and heat resistance.
• aramid paper which is made into a sheet by mixing aramid short fibers and aramid fibrids in a mass ratio of 60/40 to 10/90, with a thickness of 5 to 35 ⁇ m, a density of 0.70 to 1.0 g/cm 3 , preferably 0.75 to 0.95 g/cm 3 , and a tensile strength of 45 MPa or more.
• the thickness is preferably 10 to 30 ⁇ m, and more preferably 15 to 30 ⁇ m.
• aramid paper having the above properties and having a basis weight of 5 to 25 g/m 2 , and preferably 10 to 25 g/m 2 .
• the tensile strength represents the tensile strength per unit cross-sectional area, and the average value in the vertical direction and the horizontal direction is taken as the tensile strength.
• the tensile strength of the aramid paper of the present invention is preferably 45 MPa or more, more preferably 47 MPa or more, and further preferably 50 MPa or more.
• the upper limit of the tensile strength is preferably 120 MPa.
• the glass transition temperature is a value obtained by raising the temperature of a test specimen from room temperature at a rate of 3°C/min and measuring the calorific value using a differential scanning calorimeter, drawing two extension lines on the endothermic curve, and then intersecting the endothermic curve with the 1/2 straight line between the extension lines, and the glass transition temperature of the aramid paper used in the Examples was 275°C.
• Fibrids of polymetaphenylene isophthalamide were produced by a method using a pulp particle production apparatus (wet precipitator) composed of a combination of a stator and a rotor described in Japanese Examined Patent Application Publication No. Sho 52-15621 . This was treated with a beating machine to adjust to a length-weighted average fiber length of 0.9 mm (freeness of aramid fibrids: 100 cm 3 (Canadian standard freeness)).
• meta-aramid fibers manufactured by DuPont Nomex (registered trademark), single yarn fineness 2 denier, fiber diameter 15 ⁇ m
• DuPont Nomex (registered trademark), single yarn fineness 2 denier, fiber diameter 15 ⁇ m
• aramid short fibers a length of 6 mm
• Aramid fibrids and aramid short fibers prepared as described above were dispersed in water to prepare slurries. These slurries were mixed so that the aramid fibrids and aramid short fibers had the blending ratios (mass ratios) shown in Table 1, and sheet-shaped materials were prepared with a TAPPI-type manual paper machine (cross-sectional area 625 cm 2 ). Subsequently, the resulting sheets were adjusted by a pair of metal calender rolls so that the peripheral length of the contact between the rolls and the aramid paper was 1 mm, and then hot pressed twice under the conditions shown in Table 1 to obtain aramid paper. Table 1 shows the main characteristic values of the aramid paper thus obtained.
• Example 1 Example 2
• Example 3 Example 4 Raw Material Composition % by Mass Aramid Fibrid 80 80 50 50 Aramid short Fiber 20 20 50 50 Hot Pressing (1st Time) Pressure kg/cm 2 2500 2500 2500 2500 Roll Surface Temperature °C 330 330 330 330 Hot Pressing (2nd Time) Pressure kg/cm 2 2500 2500 2500 2500 Roll Surface Temperature °C 200 250 200 250 Basis Weight g/m 2 20 20 20 20 20 Thickness ⁇ m 23 24 25 26 Density g/cm 3 0.86 0.83 0.78 0.76 Tensile Strength MPa 53 52 55 54 Breakdown Voltage kV/mm 31 30 30 29
• Aramid fibrids and aramid short fibers prepared as described above were dispersed in water to prepare slurries. These slurries were mixed so that the aramid fibrids and aramid short fibers had the blending ratios (mass ratios) shown in Table 2, and sheet-shaped materials were prepared with a TAPPI-type manual paper machine (cross-sectional area 625 cm 2 ). Subsequently, the resulting sheets were adjusted by a pair of metal calender rolls so that the peripheral length of the contact between the rolls and the aramid paper was 1 mm, and then hot pressed under the conditions shown in Table 2 to obtain aramid paper. Table 2 shows the main characteristic values of the aramid paper thus obtained.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)
• Nonwoven Fabrics (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 2019
  • 2019-02-22 JP JP2019030228A patent/JP7183073B2/ja active Active
• 2020
  • 2020-02-12 EP EP20759667.7A patent/EP3929354A1/fr not_active Withdrawn
  • 2020-02-12 WO PCT/JP2020/005278 patent/WO2020170902A1/fr unknown
  • 2020-02-12 KR KR1020217029821A patent/KR20210126729A/ko unknown
  • 2020-02-12 TW TW109104408A patent/TWI832969B/zh active
  • 2020-02-12 CN CN202080015829.2A patent/CN113423888A/zh active Pending

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