JP2019035163A - Production method of carbon staple fiber nonwoven fabric - Google Patents

Abstract

To provide a carbon staple fiber nonwoven fabric difficult to cause fiber dropout, having excellent processability on molding processing and showing excellent strength.SOLUTION: The production method of a carbon staple fiber nonwoven fabric, containing a carbon staple fiber and a binder synthetic fiber and obtained by drying wet type fiber web produced by wet machining, is a production method of carbon staple fiber nonwoven fabric characterized by that a wet type fiber web is dried while being brought into contact with a metal heat roll having a fluororesin-processed surface, wherein the wet type fiber web is preferably dried while being sandwiched between the fluororesin-processed metal heat roll surface and a dryer canvas.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a carbon short fiber nonwoven fabric.

  Carbon fiber reinforced resin composite formed by combining carbon fiber and resin has strength and elastic modulus comparable to metal materials, but has a smaller specific gravity than metal materials, so the weight of members can be reduced, In addition, since it has no rusting problems and is resistant to acids and alkalis, it is used in electronic equipment materials, electrical equipment materials, civil engineering materials, building materials, automotive materials, aircraft materials, and various manufacturing industries. Used in manufacturing parts such as robots and rolls.

  The carbon fiber reinforced resin composite is a composite in which a carbon fiber fabric such as a long fiber woven fabric, a spread fabric, a unidirectional web, and a short fiber nonwoven fabric is combined with a resin such as a thermosetting resin or a thermoplastic resin. It is. The most common carbon fiber reinforced resin composite is a composite of a long fiber nonwoven fabric and a thermosetting resin, but it is difficult to design, is not a homogeneous material, has a long molding time, is expensive, etc. There was a problem.

  As a carbon fiber reinforced resin composite that has solved these problems, a carbon fiber reinforced thermoplastic resin composite in which a nonwoven fabric containing carbon short fibers (carbon short fiber nonwoven fabric) and a thermoplastic resin is combined has been proposed ( For example, refer to Patent Documents 1 to 6). By using a carbon short fiber nonwoven fabric, homogeneity is enhanced, and by using a thermoplastic resin, easy design and processability are obtained, it is inexpensive, and recycling is possible.

  When a carbon short fiber nonwoven fabric is used as a base material of a carbon fiber reinforced resin composite, it is desirable that the content of carbon short fibers as the carbon short fiber nonwoven fabric is high. However, when the carbon short fiber content of the carbon short fiber nonwoven fabric increases, the strength of the carbon short fiber nonwoven fabric decreases. As a result, when dealing with carbon short fiber nonwoven fabrics, there are problems that fibers fall off from the surface of carbon short fiber nonwoven fabrics, and that the uniformity of carbon short fiber nonwoven fabrics is impaired by pressure during the molding process. It was easy.

JP 2013-208791 A JP 2013-202891 A JP 2011-21303 A JP 2004-43985 A JP 2011-194852 A JP 2014-224333 A

  An object of the present invention is to provide a carbon short fiber nonwoven fabric that is less likely to cause fiber dropping, has excellent processability during molding, and has excellent strength.

  The above problems can be solved by the following invention.

(1) A metal having a surface subjected to fluororesin processing in a method for producing a carbon short fiber nonwoven fabric, which comprises carbon short fibers and a binder synthetic fiber, and dries a wet fiber web produced by a wet papermaking method. A method for producing a carbon short fiber nonwoven fabric, wherein the wet fiber web is dried while being in contact with a heat roll.

(2) The method for producing a short carbon fiber nonwoven fabric according to the above (1), wherein the wet fiber web is dried in a state sandwiched between a metal heat roll surface subjected to fluororesin processing and a dryer canvas.

  According to the present invention, when a wet fiber web is dried by contacting the wet fiber web with a metal heat roll having a surface subjected to fluororesin processing, the fibers are detached from the web surface. Thus, there can be provided a short carbon non-woven fabric excellent in strength with few defects, without any paper break due to sticking of the wet paper web to the metal heat roll surface. Furthermore, by drying the wet fiber web in a state sandwiched between a metal heat roll surface subjected to fluororesin processing and a dryer canvas, it is possible to provide a carbon short fiber nonwoven fabric having further excellent strength.

  In the method for producing a carbon short fiber nonwoven fabric of the present invention, a wet fiber web is formed by a wet papermaking method using a slurry containing carbon short fibers and binder synthetic fibers. Next, the wet fiber web is directly contacted with a metal heat roll having a surface subjected to fluororesin processing and dried to produce a carbon short fiber nonwoven fabric.

  Examples of the carbon short fibers include PAN-based carbon short fibers made from polyacrylonitrile (PAN) as a raw material, and pitch-based carbon short fibers made from pitches. The fiber diameter of the short carbon fibers is preferably 3 to 20 μm, and more preferably 5 to 15 μm. Moreover, it is preferable that the fiber length of a carbon short fiber is 1-30 mm, and it is more preferable that it is 3-12 mm.

  In the present invention, recycled carbon short fibers can be used as the carbon short fibers. The recycled carbon fiber is a material obtained by sintering and removing a resin component from a carbon fiber and a resin composite once formed into a molded body in an inert gas such as argon or nitrogen or in water vapor. In particular, the sintering method using superheated steam is an effective method that is inexpensive and does not pollute the environment because it returns to water when heat is removed in the atmosphere. The resin composite made of prepreg has various forms such as an angle ply laminated body. Usually, after being reduced to a certain size, it is sintered, and the thermosetting resin is removed and cut. In this case, recycled carbon short fibers having different fiber lengths are obtained. In the present invention, when a recycled carbon short fiber is used as the carbon short fiber, a preferable fiber length is 3 to 500 mm, and more preferably 6 to 150 mm.

  The carbon short fiber content in the carbon short fiber nonwoven fabric is preferably 50 to 92% by mass, more preferably 60 to 90% by mass, and still more preferably 65 to 90% by mass.

  The binder synthetic fiber is added to prevent the carbon short fibers from being detached from the nonwoven fabric and to impart strength to the carbon short fiber nonwoven fabric. Binder synthetic fibers include amorphous polyvinyl alcohol (PVA) short fibers, core-sheath polyester fibers whose surfaces have a low melting point, unstretched polyester fibers, polycarbonate (PC) fibers, polyolefin fibers, and low melting points on the surface. Examples thereof include polyolefin core-sheath fibers, polyolefin fibers whose surfaces are made of acid-modified polyolefin, aliphatic polyamide fibers, unstretched polyphenylene sulfide fibers, polyether ketone ketone fibers, and the like. The binder synthetic fibers are preferably non-fibrillated short fibers in a non-fibrillated state called “staples”. As the polyester, polyethylene terephthalate (PET) is preferable.

  The melting point of the binder synthetic fiber is preferably 60 to 260 ° C, more preferably 60 to 230 ° C, still more preferably 60 to 180 ° C, and particularly preferably 80 to 160 ° C. When the melting point of the binder synthetic fiber is within this temperature range, the heat treatment in the nonwoven fabric manufacturing process imparts binding properties and imparts strength to the carbon short fiber nonwoven fabric.

  The fiber diameter of the binder synthetic fiber is preferably 3 to 40 μm, and more preferably 5 to 20 μm. Moreover, it is preferable that the fiber length of a binder synthetic fiber is 1-20 mm, and it is more preferable that it is 3-12 mm.

  Content of the binder synthetic fiber in a carbon short fiber nonwoven fabric becomes like this. Preferably it is 5-50 mass%, More preferably, it is 7-40 mass%, More preferably, it is 7-30 mass%.

  When manufacturing the carbon short fiber nonwoven fabric of this invention, in addition to a carbon short fiber and a binder synthetic fiber, a fibrillated fiber can be used together. By using the fibrillated fibers in combination, the effect of improving the strength of the wet fiber web and preventing paper breaks in the production process is enhanced. Further, it is possible to provide a carbon short fiber nonwoven fabric that is moderately entangled with short carbon fibers and binder synthetic fibers, is excellent in strength, and has few fibers falling off.

  Examples of fibrillated fibers include fibers formed by fibrillating natural fibers, regenerated fibers, synthetic fibers, and the like. Examples of natural fibers include cellulose fibers derived from wood, cellulose fibers derived from non-wood such as hemp, cotton, and sugarcane, biocellulose fibers, wool, and silk. Examples of regenerated fibers include solvent-spun cellulose fibers and cupra fibers. Synthetic fibers include polypropylene, polyethylene, polymethylpentene, polyester, polyester derivatives, acrylic polymers, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, poly Ether, polyvinyl alcohol, aliphatic polyamide, aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyester, polyamideimide, polyimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly Examples thereof include fibers made of a resin such as -p-phenylenebenzobisoxazole and polytetrafluoroethylene. The degree of fibrillation is preferably 0 to 600 ml, more preferably 0 to 500 ml, and still more preferably 0 to 400 ml, according to JIS P8121.

  The content of the fibrillated fiber in the carbon short fiber nonwoven fabric is preferably 2 to 10% by mass, more preferably 3 to 8% by mass, and further preferably 3 to 7% by mass.

  The carbon short fiber nonwoven fabric produced by the method for producing a carbon short fiber nonwoven fabric of the present invention is produced by a wet papermaking method. In the wet papermaking method, first, short carbon fibers, binder synthetic fibers, and if necessary, fibrillated fibers are uniformly dispersed in water, and then passed through a process such as screen (removal of foreign matter, lumps, etc.), and the final fiber concentration Is adjusted to 0.01 to 0.50% by mass with a paper machine to obtain a wet fiber web. In order to make the dispersibility of the fibers uniform, chemicals such as dispersants, antifoaming agents, hydrophilic agents, antistatic agents, polymer thickeners, mold release agents, antibacterial agents, bactericides, etc. may be added during the process. is there.

  As the paper machine, for example, a paper machine using a paper net such as a long net, a circular net, or an inclined wire alone, or a combination paper machine in which two or more paper nets of the same type or different types are installed online is used. be able to. In addition, when the nonwoven fabric has a multilayer structure of two or more layers, a fiber bonding method in which wet fiber webs made by each paper machine are laminated, or after forming one layer, fibers are put on the layer. A nonwoven fabric can be manufactured by a casting method in which the dispersed slurry is cast to form a laminate. When the slurry in which the fibers are dispersed is cast, the previously formed layer may be either a wet fiber web state or a dry state. In addition, two or more dry layers can be heat-sealed to form a multilayered nonwoven fabric.

  In the present invention, when the carbon short fiber nonwoven fabric has a multilayer structure, it may have a multilayer structure in which the fiber blend of each layer is the same, or may have a multilayer structure in which the fiber blend of each layer is different. In the case of a multilayer structure, since the fiber concentration of the slurry can be lowered by reducing the basis weight of each layer, the texture of the nonwoven fabric is improved, and as a result, the uniformity of the texture of the nonwoven fabric is improved. Even if the texture of each layer is uneven, it can be compensated by stacking. Furthermore, the papermaking speed can be increased, and the operability can be improved.

  In the method for producing a carbon short fiber nonwoven fabric of the present invention, a wet fiber web produced by a wet papermaking papermaking mesh is dried while being brought into contact with a metal heat roll having a surface subjected to fluororesin processing. Specifically, it is dried with a Yankee dryer or a cylinder dryer incorporating a metal heat roll having a surface subjected to fluororesin processing. By applying fluororesin processing to the surface of the metal heat roll, the binder synthetic fiber contained in the wet fiber web is prevented from sticking to the metal heat roll, and as a result, the wet fiber web in contact with the metal heat roll It becomes possible to eliminate the dropping and peeling of the fibers from the surface.

  When the wet fiber web is dried, the strength of the carbon short fiber nonwoven fabric is improved by bringing the wet fiber web into close contact with a metal heat roll that has been subjected to fluororesin processing and drying it under hot pressure. Hot-pressure drying means pressing the wet fiber web against the hot roll with a touch roll or the like to dry it. 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.

  Furthermore, the wet fiber web is dried in a state sandwiched between a metal heat roll surface subjected to fluororesin processing and a dryer canvas, thereby providing a carbon short fiber nonwoven fabric having superior strength and uniformity. be able to. By drying the wet fiber web between the metal heat roll and the dryer canvas, heat can be efficiently transferred from the metal heat roll to the wet fiber web, and the strength of the carbon short fiber nonwoven fabric is improved.

  The carbon short fiber nonwoven fabric produced by the production method of the present invention can be provided as a composite formed by laminating with a thermoplastic resin film. The composite can be produced by superposing a carbon short fiber nonwoven fabric and a thermoplastic resin film, and subjecting them to heat treatment or heat pressure treatment. A molded product can be produced by subjecting this composite to hot pressing (hot pressing).

  Examples of the thermoplastic resin of the thermoplastic resin film include polyolefin resins such as polyethylene resin, polypropylene resin and polybutylene resin; methacrylic resins such as polymethyl methacrylate resin; polystyrene resins such as polystyrene resin, ABS resin and AS resin; polyethylene Polyester resins such as terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate resin, polyethylene naphthalate (PEN) resin, poly 1,4-cyclohexyldimethylene terephthalate (PCT) resin; 6-nylon Polyamide (PA) resin such as resin, 6,6-nylon resin; polyvinyl chloride resin; polyoxymethylene (POM) resin; polycarbonate (PC) resin; polyphenylene sulfide (PP Modified polyphenylene ether (PPE) resin; polyetherimide (PEI) resin; polysulfone (PSF) resin; polyethersulfone (PES) resin; polyketone resin; polyarylate (PAR) resin; polyether nitrile (PEN) resin Polyetherketone (PEK) resin; Polyetheretherketone (PEEK) resin; Polyetherketoneketone (PEKK) resin; Polyimide (PI) resin; Polyamideimide (PAI) resin; Fluorine (F) resin; Liquid crystalline polymer resin: polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, polyisoprene, or fluorine-based thermoplastic elastomer; or a copolymer resin or modified resin thereof; ionomer Resins. Among these resins, one type or two or more types can be used. From the viewpoint of combustibility, PC, PPS, PEEK, PEI and the like are preferable.

  Examples of the ionomer resin include an ethylene ionomer resin obtained by neutralizing a part of the carboxyl group of the ethylene-unsaturated carboxylic acid copolymer resin with a metal ion. A product obtained by neutralizing 10 mol% or more, preferably 10 to 90 mol%, of a carboxyl group with a metal ion is used. Examples of the metal ion include alkali metal such as lithium and sodium; and polyvalent metal ion such as alkaline earth metal such as zinc, magnesium and calcium.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. All parts and percentages in the examples are based on mass unless otherwise specified.

The raw fiber was weighed with the “fiber blending” shown in Table 1 and dispersed in a dispersion concentration of 0.2 mass% and a dispersion time of 5 minutes. Then, the wet fiber web was formed on a circular paper machine having a 90-mesh metal wire. Formed. Thereafter, the wet fiber web was dried under the “drying process conditions” shown in Table 1, and carbon short fiber nonwoven fabrics of Examples 1 to 5 and Comparative Examples 1 to 3 having a basis weight of 50 g / m ² were obtained.

“Carbon fiber”: Carbon fiber manufactured by Zoltech, fiber diameter 7 μm, 6 mm cut product “core-sheath PET fiber”: fiber diameter 15 μm × 5 mm cut product (glass transition temperature of sheath part 72 ° C.)
“PVA fiber”: fiber diameter 11 μm × 3 mm cut product “microfibril cellulose”: “Cerish (registered trademark) KY100G” manufactured by Daicel Finechem

  The following evaluation was performed on the carbon short fiber nonwoven fabrics produced in the examples and comparative examples, and the results are shown in Table 2.

(Surface condition evaluation)
The surface conditions of the front and back surfaces of a 25 cm × 25 cm short carbon fiber nonwoven fabric were visually evaluated according to the following indices. If it was “2” or more, it was judged that it could be used practically.

“4”: The surface is smooth, and no fibers fall off even when the surface is rubbed.
"3": Surface irregularities are hardly seen. Even if the surface is rubbed, there is almost no loss of fibers.
“2”: A depression is seen on the surface. When the surface is rubbed, there is a slight loss of fibers.
“1”: Concavities and convexities in which fibers floated on the surface are observed. When the surface is rubbed, fiber dropout is observed.

(Specific strength evaluation)
A carbon short fiber nonwoven fabric having a width direction of 15 mm and a flow direction of 240 mm was collected to obtain a longitudinal strength measurement paper piece, and a carbon short fiber nonwoven fabric having a width direction of 240 mm and a flow direction of 15 mm was collected to obtain a transverse strength measurement paper piece. The tensile strength of the obtained longitudinal / lateral strength measuring paper piece was measured at a pulling speed of 20 mm / min according to JIS P8113 (1976). A value obtained by dividing an average value of longitudinal and lateral strength (unit: N / 15 mm) by basis weight was defined as “specific strength”. The “specific strength” is practically preferably 0.40 ((N / 15 mm) / (g / m ² )) or more, more preferably 0.60 ((N / 15 mm) / (g / m ^2). )) Or more, and more preferably 0.65 ((N / 15 mm) / (g / m ² )) or more.

  By comparing Example 1 with Comparative Examples 1 and 2, a short carbon fiber nonwoven fabric containing short carbon fibers and binder synthetic fibers was produced. Paper is cut off by sticking the wet fiber web to the surface of the metal heat roll by drying while making contact with a metal heat roll having a surface that has been subjected to resin processing. It can also be seen that a carbon short fiber nonwoven fabric excellent in strength with few defects can be efficiently provided.

  By comparing Example 1 with Comparative Example 3, the carbon short fiber nonwoven fabric contains binder synthetic fiber and is dried while contacting the wet fiber web with a metal heat roll having a surface subjected to fluororesin processing. Thus, it can be seen that a carbon short fiber nonwoven fabric excellent in strength with few defects can be provided.

  By comparing Example 1 and Example 2, even when the binder synthetic fiber is changed from PVA fiber to core-sheath PET fiber, the wet fiber web is brought into contact with a metal heat roll having a surface subjected to fluororesin processing. It can be seen that a carbon short fiber non-woven fabric excellent in strength with few defects can be provided by drying while making it dry.

  By comparing Example 1 and Example 3, microfibrillated cellulose is used together with binder synthetic fiber, and drying is performed while the wet fiber web is brought into contact with a metal heat roll having a surface subjected to fluororesin processing. It turns out that the carbon short fiber nonwoven fabric excellent in surface strength and the intensity | strength of the whole nonwoven fabric can be provided.

  From the comparison between Example 1 and Example 4 and the comparison between Example 3 and Example 5, the wet fiber web was dried in a state sandwiched between the surface of the metal heat roll treated with fluororesin and the dryer canvas. Thus, it can be seen that a carbon short fiber nonwoven fabric having superior surface strength and overall nonwoven fabric strength can be provided.

  The carbon short fiber nonwoven fabric and composite of the present invention can be used for manufacturing parts such as electronic equipment materials, electrical equipment materials, civil engineering materials, building materials, automobile materials, aircraft materials, robots and rolls used in various manufacturing industries, etc. It is.

Claims (2)

  In a method for producing a carbon short fiber nonwoven fabric, comprising a carbon short fiber and a binder synthetic fiber, and drying a wet fiber web produced by a wet papermaking method, a metal heat roll having a surface subjected to fluororesin processing. A method for producing a short carbon fiber nonwoven fabric, wherein the wet fiber web is dried while contacting.   The method for producing a carbon short fiber nonwoven fabric according to claim 1, wherein the wet fiber web is dried in a state sandwiched between a metal heat roll surface subjected to fluororesin processing and a dryer canvas.