JP2020051000A - Manufacturing method of carbon fiber unwoven fabric - Google Patents

Abstract

To provide a manufacturing method of a carbon fiber unwoven fabric reducing generation of defects such as wrinkle or nick, suppressing cut of a sheet and good in a tone.SOLUTION: There is provided a manufacturing method for forming a carbon fiber unwoven fabric containing a carbon fiber and a thermoplastic resin fiber by a wet type papermaking method, in which a water drop is sprayed to wet paper before passing through a suction device arranged before a press roll of press part after passage through a couch roll 5 of the foamer part 2 with water amount of 0.2 L to 2.5 L per 1 square meter of the wet paper in a former part 1 in a papermaking process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a carbon fiber nonwoven fabric, which comprises forming a carbon fiber nonwoven fabric containing carbon fibers and thermoplastic resin fibers by a wet papermaking method.

  A carbon fiber reinforced resin composite formed by combining carbon fiber and a resin has a strength and an elastic modulus comparable to a metal material, but has a smaller specific gravity than a metal material. It has no rusting and is resistant to acids and alkalis, so 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 of a carbon fiber cloth such as a long fiber woven fabric, an open fiber woven fabric, a unidirectional web, a long fiber nonwoven fabric, and a short fiber nonwoven fabric, and a resin such as a thermosetting resin or a thermoplastic resin. This is the composite. The most common carbon fiber reinforced resin composite is a composite of carbon long fiber cloth and thermosetting resin, but it is difficult to design, it is not a homogeneous material, molding time is long, expensive, etc. There were challenges.

  As a method of solving these problems, a carbon fiber reinforced thermoplastic resin composite in which a nonwoven fabric containing carbon fibers (carbon fiber nonwoven fabric) is combined with a thermoplastic resin has been proposed (for example, see Patent Documents 1 to 4). ). By using the carbon fiber nonwoven fabric and the thermoplastic resin, easy design and workability can be obtained, and the molding process time can be shortened.

  As a method for forming a carbon fiber nonwoven fabric, a card method (for example, see Patent Documents 1 and 5) in which fibers are mechanically defibrated and entangled to form a sheet by passing fibers between needles and rolls having irregularities (for example, see Patent Documents 1 and 5), Dry method, such as air-lay method, which floats, defibrate, and sucks into a screen to form a sheet, disperses fibers in a liquid such as water, defibrate with a pulper, etc. And the like, for example, a wet papermaking method in which the liquid is dried to form a sheet (for example, see Patent Documents 2 and 4). In order to obtain a carbon fiber nonwoven fabric having good formation and a relatively low basis weight, a wet papermaking method is preferable.However, when the content of carbon fibers in the carbon fiber nonwoven fabric is high, wrinkles during papermaking are affected by the rigidity of the carbon fibers. There is a problem that defects such as cuts and cuts and sheet cutting may occur.

JP 2004-43985 A JP 2011-21303 A JP 2013-202891 A JP 2014-224333 A JP-A-2006-151081

  An object of the present invention is to provide a method for producing a carbon fiber nonwoven fabric that reduces the occurrence of defects such as wrinkles and cuts, suppresses sheet cutting, and has a good formation.

  The above problem can be solved by the following invention.

(1) A manufacturing method for forming a carbon fiber nonwoven fabric containing carbon fibers and thermoplastic resin fibers by a wet papermaking method, in a wet part of a papermaking process, after passing through a couch roll in a former part and before a press roll in a press part. A method for producing a carbon fiber nonwoven fabric, comprising spraying water droplets per square meter of wet paper with a water amount of 0.2 L or more and 2.5 L or less on the wet paper before passing through the suction device installed in the apparatus.

(2) The method for producing a carbon fiber nonwoven fabric according to the above (1), wherein the average particle size of the water droplets is 400 μm or less.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a defect, such as a wrinkle and a cut, is reduced, cutting of a sheet | seat can be suppressed, and the carbon fiber nonwoven fabric of favorable formation can be manufactured.

It is a papermaking process drawing regarding the manufacturing method of the present invention.

  The production method of the carbon fiber nonwoven fabric of the present invention is a production method of forming a carbon fiber nonwoven fabric containing carbon fibers and thermoplastic resin fibers by a wet papermaking method, and in a wet part of a papermaking process, after passing through a coach roll of a former part. Water droplets are sprayed on a wet paper web before passing through a suction device installed in front of a press roll of a press unit with a water amount of 0.2 L or more and 2.5 L or less per square meter of wet paper.

The carbon fiber nonwoven fabric produced by the production method according to the present invention contains at least carbon fibers and thermoplastic resin fibers. Basis weight of the carbon fiber nonwoven fabric is preferably 10 to 200 g / ^{m 2,} and more preferably 20 to 150 g / ^{m 2.}

  As the carbon fibers, PAN-based carbon fibers made from polyacrylonitrile (PAN), pitch-based carbon fibers made from pitches, PAN-based regenerated carbon fibers made from polyacrylonitrile, and pitch-based carbon fibers are used as raw materials. Pitch-based recycled carbon fibers can be used. The fiber diameter of the carbon fiber is preferably from 3 to 20 μm, more preferably from 5 to 15 μm. Further, the fiber length of the carbon fiber is preferably 1 to 50 mm, and more preferably 3 to 20 mm. The content of carbon fibers is preferably 50 to 96% by mass, and more preferably 70 to 93% by mass, based on all fibers in the nonwoven fabric.

  The recycled carbon fiber is a recycled product obtained from a carbon fiber reinforced resin composite obtained by compounding a carbon fiber and a resin. The carbon fiber reinforced resin composite is a composite of a carbon fiber cloth such as a long fiber woven fabric, an open fiber woven fabric, a unidirectional web, a long fiber nonwoven fabric, and a short fiber nonwoven fabric, and a resin such as a thermosetting resin or a thermoplastic resin. This is the composite. The most common carbon fiber reinforced resin composite is a composite of a carbon long fiber fabric and a thermosetting resin. Examples of the carbon fiber include PAN-based carbon fiber made of polyacrylonitrile as a raw material and pitch-based carbon fiber made of pitches as a raw material. The carbon fiber obtained by removing the resin from the carbon fiber reinforced resin composite by a regeneration treatment method such as a heat treatment method, a sintering method, a superheating method, and a superheated steam method is a recycled carbon fiber.

  The thermoplastic resin fiber is added to prevent the carbon fiber from detaching from the nonwoven fabric and to add strength to the carbon fiber nonwoven fabric. Examples of the thermoplastic resin fiber include polyvinyl alcohol (vinylon) fiber, polyester core-sheath fiber whose surface has a low melting point, undrawn polyester fiber, polycarbonate (PC) fiber, polyolefin fiber, and polyolefin whose surface has a low melting point. Core-sheath fibers, polyolefin fibers having a surface made of an acid-modified polyolefin, aliphatic polyamide fibers, undrawn polyphenylene sulfide fibers, polyether ketone ketone fibers, and the like.

  When the thermoplastic resin fiber has a melting point, the melting point is preferably from 60 to 260 ° C, more preferably from 60 to 230 ° C, and still more preferably from 60 to 180 ° C. When the melting point of the thermoplastic resin fiber is within this temperature range, the heat treatment in the nonwoven fabric manufacturing process imparts binding properties and imparts strength to the carbon fiber nonwoven fabric.

  Polyvinyl alcohol (vinylon) fiber, which is a thermoplastic resin fiber, does not show a clear melting point, but is melted at 60 to 100 ° C. in the presence of water. Thus, the binding property is given, and the strength is given to the carbon fiber nonwoven fabric.

  The fiber diameter of the thermoplastic resin fiber is preferably from 3 to 40 μm, more preferably from 5 to 20 μm. Further, the fiber length of the thermoplastic resin fiber is preferably 1 to 20 mm, more preferably 3 to 12 mm.

  When producing a carbon fiber nonwoven fabric in the present invention, fibers such as thermosetting resin fibers, glass fibers, and cellulose fibers can be used in addition to carbon fibers and thermoplastic resin fibers. The combined use of fibrillated cellulose fibers among the cellulose fibers improves the strength of the wet paper and increases the effect of preventing paper breakage in the manufacturing process. Further, it is possible to provide a carbon fiber nonwoven fabric which is moderately entangled with carbon fibers and thermoplastic resin fibers, has excellent strength, and has little fiber loss.

  The fibrillated cellulose fiber is not a film but a fiber having a very finely divided portion mainly in a direction parallel to the fiber axis, and at least a part of which has a fiber diameter of 1 μm or less. It is preferable that the aspect ratio of the length to the width is 20 to 100,000. The modified freeness is preferably from 0 to 770 ml, more preferably from 0 to 600 ml. Further, the mass average fiber length is preferably 0.1 to 2 mm. The content of the fibrillated cellulose fibers is preferably from 2 to 20% by mass, more preferably from 2 to 10% by mass, based on all the fibers in the nonwoven fabric. The modified freeness in the present invention is the same as in the present invention except that a wire mesh (manufactured by PULP AND PAPER RESEARCH INSTITUTE OF CANADA) having a wire diameter of 0.14 mm and an opening of 0.18 mm is used as a sieve plate and the sample concentration is set to 0.1%. It is the freeness measured according to JIS P8121-2: 2012.

  Cellulose materials for fibrillated cellulose fibers include vegetable pulp, solvent-spun cellulose, semi-synthetic cellulose, and the like. Examples of the plant pulp include wood pulp such as kraft pulp (KP), dissolved pulp (DP), and dissolved kraft pulp (DKP) using hardwood (L) and softwood (N). Non-wood pulp such as straw pulp, hemp pulp, cotton pulp, cotton linter pulp, and kenaf pulp may also be used. Examples of commercially available products include Selish (registered trademark, manufactured by Daicel Finechem).

  Examples of a method for obtaining fibrillated cellulose fibers include a method in which a slurry in which a cellulose material is dispersed in water is mechanically pulverized to fibrillate the fibers of the cellulose material to form microfibrils. Examples of the device for defibrating the cellulose material include a disc refiner, a stone mill type grinder, a high-pressure homogenizer, a ball mill, a device for an underwater counter collision method, and an ultrasonic crusher. These devices can be used in appropriate combination.

  In the present invention, the carbon fiber nonwoven fabric is manufactured by a wet papermaking method. In the wet papermaking method, first, carbon fibers and thermoplastic resin fibers, and optionally other combined fibers, are uniformly mixed and dispersed in water to form a slurry, and then, through a process such as a screen (removal of foreign matters, lumps, etc.). To obtain a slurry in which the final fiber concentration is adjusted to 0.01 to 0.50% by mass. The slurry is made in a paper machine to obtain wet paper (wet nonwoven fabric). Add chemicals such as dispersant, defoamer, hydrophilizing agent, antistatic agent, polymer thickener, mold release agent, antibacterial agent, bactericide, etc. in the process to make the fiber dispersibility uniform. In some cases.

  As the paper machine, for example, a paper machine using a single net such as a long net, a circular net, or an inclined wire, or a combination paper machine in which two or more nets of the same type or different types are installed online is used. be able to. Further, when the carbon fiber nonwoven fabric has a multilayer structure of two or more layers, a laminating method of laminating wet paper made by each paper machine, or forming one layer, and then forming a fiber on the layer The carbon fiber nonwoven fabric can be manufactured by a casting method or the like in which a slurry in which is dispersed is cast and laminated. When the slurry in which the fibers are dispersed is cast, the previously formed layer may be in a wet paper state or a dry state. Alternatively, two or more layers in a dry state may be thermally fused to form a carbon fiber nonwoven fabric having a multilayer structure.

  In the present invention, when the carbon fiber nonwoven fabric has a multi-layer structure, the multi-layer structure in which the fiber composition of each layer is the same or the multi-layer structure in which the fiber composition of each layer is different may be used. In the case of a multilayer structure, the fiber density of the slurry can be reduced by reducing the basis weight of each layer, so that the formation of the carbon fiber nonwoven fabric is improved, and as a result, the uniformity of the formation of the carbon fiber nonwoven fabric is improved. . Even if the formation of each layer is not uniform, it can be compensated by laminating. Further, the papermaking speed can be increased, and the effect that the operability is improved can be obtained.

  In the wet papermaking method, a wet paper made by a papermaking net is transferred onto a support such as a felt, dewatered with a press roll or the like, and the moisture content is controlled, and then a Yankee dryer, an air dryer, and a cylinder dryer are used. Then, by drying with a suction drum dryer, an infrared dryer, etc., a sheet-like wet-laid nonwoven fabric can be obtained. When the wet paper is dried, the wet paper is brought into close contact with a hot roll such as a Yankee dryer and dried under hot pressure, whereby the smoothness of the adhered surface is improved. Hot-press drying refers to pressing wet paper against a hot roll with a touch roll or the like to dry. The surface temperature of the heat roll is preferably from 100 to 180C, more preferably from 100 to 160C, and still more preferably from 110 to 160C. The pressure is preferably 50 to 1000 N / cm, more preferably 100 to 800 N / cm.

  The method for producing a carbon fiber nonwoven fabric of the present invention will be specifically described with reference to FIG. FIG. 1 shows a former part, a press part, and the like of a wet part which is a part of a web paper machine.

  In the method for producing a carbon fiber nonwoven fabric of the present invention, a raw material slurry is supplied to the circular net 4 from the former inlet 3 of the former part 2 of the wet part 1, and the carbon fiber and the thermoplastic resin fiber formed on the circular net Is transferred to the felt 6 in contact with the couch roll 5. The wet paper web transferred from the felt is sprayed with water droplets from the water droplet supply device 7 to the wet paper web after the paper web passes through the coach roll and before the paper web passes through the suction device 9 installed in front of the press roll 10 of the press unit 8. After the felt and the felt are brought into close contact with each other, the felt is conveyed together with the felt, dewatered by a suction device and a press roll in a press section, the moisture content of the wet paper is appropriately adjusted, and then dried by a dryer to produce a carbon fiber nonwoven fabric.

  In the manufacturing method of the present invention, the term "after passing through the couch roll" means immediately after the felt is separated from the cylindrical surface of the couch roll. In addition, the suction device installed in front of the press roll is a device that contacts the back of the felt after passing the coach roll and before the press roll, and if there are multiple suction devices, it is installed closest to the press roll. It was done. “Before passing through the suction device” means up to immediately before passing through the lowermost transport end of the suction device. In the papermaking of carbon fiber nonwoven fabric, wet paper mainly containing carbon fibers has low flexibility and rigidity, and when the felt in the process bends through a roll, the wet paper cannot follow the bending of the felt, Voids are likely to be formed between the wet paper and the felt, which may cause wrinkles and cuts, and further, may cause the sheet to be cut. According to the manufacturing method of the present invention, by spraying water droplets onto the wet paper before passing through the suction device installed in front of the press roll of the press unit after passing through the former roll of the former unit and supplying the moisture, the adhesion between the felt and the wet paper web is achieved. , And these problems can be improved. If water is supplied by spraying water droplets on the wet paper web when passing through the couch roll, swelling may occur due to air partially trapped between the wet paper web and the felt, leading to formation problems. Also, if water is supplied by spraying water droplets on a wet paper web after the suction device in front of the press roll, the moisture content of the wet paper web increases, and it tends to be insufficiently dried at the time of papermaking of a nonwoven fabric with a high basis weight, and sufficient strength is not obtained, Sheet cutting is likely to occur. The amount of water of the water droplets is 0.2 L or more and 2.5 L or less, and more preferably 0.8 L or more and 2.0 L or less per square meter of wet paper. If the amount of water droplets is less than 0.2 L per square meter of wet paper, the adhesiveness between the felt and the wet paper will be insufficient. Getting worse. As a water droplet supply device, it is desirable to provide one or more spray nozzles capable of supplying fine water droplets in accordance with the papermaking width of wet paper. As the spray nozzle, there can be used a spray nozzle in which water droplets are sprayed conically from the nozzle, and a spray nozzle in which water droplets are sprayed in a fan shape from the nozzle. As the angle for supplying the water droplet, the angle formed by the center line of the water droplet to be sprayed and the wet paper is preferably 90 degrees or less. However, this angle is an angle formed by the center line between the wet paper web before the water droplet is supplied and the sprayed water droplet. The distance between the water drop supply device and the wet paper is preferably 50 mm or more and 600 mm or less. In the production method of the present invention, it is preferable that the average particle diameter of the water droplet is 400 μm or less. The average particle diameter of the water droplet can be measured by a liquid immersion method, a laser diffraction method, or the like. In the present invention, the average particle diameter measured by the liquid immersion method is shown.

  Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the examples.

Raw material fibers were added to water according to the "fiber blending" shown in Table 1, and dispersed using a pulper at a concentration of 1.0% by mass for 5 minutes to form a slurry. Slurry. This papermaking slurry is supplied from the former inlet and is made up with a circular mesh having a 90-mesh metal wire to form a wet paper containing carbon fibers and thermoplastic resin fibers. After the transfer of the wet paper, water droplets were sprayed from the water droplet supply device on the wet paper at a position 1 m after passing through the coach roll under the “water droplet supply conditions” shown in Table 1, and then dewatered with a suction device and then a press roll to wet the wet paper. The water content of the paper was adjusted, and dried with a Yankee dryer having a surface temperature of 150 ° C., to produce carbon fiber nonwoven fabrics of Examples 1 to 6 and Comparative Examples 1 to 3 having a winding length of 100 m and an average basis weight of 55 g / m ² . In addition, the length of the felt from the couch roll to the press roll of the paper machine used in the examples and comparative examples is 10 m.

“Carbon fiber”: PAN-based carbon fiber manufactured by Zoltek, fiber diameter 9 μm, fiber length 3 mm
“PP / PE core / sheath fiber”: polypropylene / polyethylene core / sheath fiber, fiber diameter 10 μm, fiber length 5 mm (melting point of polyethylene of sheath portion 130 ° C.)
“PVA fiber”: polyvinyl alcohol (vinylon) fiber, fiber diameter 11 μm, fiber length 3 mm (dissolution temperature in water 70 ° C.)
"Fibrillated cellulose fiber": "Selish (registered trademark) KY-100G" manufactured by Daicel Finechem

  The following evaluations were performed on the carbon fiber nonwoven fabrics manufactured in Examples and Comparative Examples, and the results are shown in Table 2.

(Evaluation of papermaking properties)
The number of wrinkles and cuts in the sheet generated in 100 m of the carbon fiber nonwoven fabric was confirmed. The results are shown in Table 2. Table 2 shows the number of times the sheet was cut during paper making of 100 m.

(Evaluation of formation of non-woven fabric)
A carbon fiber nonwoven fabric having a width of 400 mm and a flow direction of 500 mm was collected, and the formation and the surface condition of the carbon fiber nonwoven fabric when the carbon fiber nonwoven fabric was observed with transmitted light were visually evaluated according to the following criteria. Here, the formation unevenness indicates that there is a portion where a density difference occurs when the nonwoven fabric is observed with transmitted light.

"A": No streaks or irregularities were observed on the surface of the carbon fiber nonwoven fabric, and when observed with transmitted light, there was no formation unevenness, and it was uniform and very good.
"O": Although slight streaks and irregularities are seen on the surface of the carbon fiber nonwoven fabric, when observed with transmitted light, there is almost no formation unevenness, and it is uniform and good.
“△”: Streaks and irregularities are observed on the surface of the carbon fiber nonwoven fabric, and when observed with transmitted light, formation unevenness is slightly observed and not very good.
“×”: Many streaks and irregularities were observed on the surface of the carbon fiber nonwoven fabric, and when observed with transmitted light, many formation irregularities were observed and poor.

  By performing the production method of the example, the generation of wrinkles and cuts during the papermaking of the carbon fiber nonwoven fabric is reduced, and continuous papermaking can be performed without cutting the sheet, which is excellent.

  Comparing Example 1 with Comparative Example 1, it was found that in Comparative Example 1 in which water droplets were not sprayed on the wet paper before passing through the suction device provided in front of the press roll in the press unit after passing through the couch roll in the former unit, Many wrinkles and cuts are generated in the nonwoven fabric, and a plurality of sheets are cut during the papermaking, and the papermaking properties are significantly poor.

  Comparing Example 1 with Comparative Example 2, both Example 1 and Comparative Example 2 spray water droplets on wet paper before passing through a suction device installed in front of the press roll in the press unit after passing through the couch roll in the former unit. However, Comparative Example 2 is less than the required amount of spray water, and therefore, although less than Comparative Example 1, a large number of wrinkles and cuts are generated in the carbon fiber nonwoven fabric, and furthermore, the sheet is cut during the papermaking. Poor sex.

  Comparing Example 4 with Comparative Example 3, in Comparative Example 3, water droplets were sprayed on wet paper web after passing through the couch roll in the former section and before passing through the suction device installed in front of the press roll in the press section. Since the amount of water is too large, wrinkles and cuts are generated more frequently than in Example 4, and cutting of the sheet can be suppressed, but formation of the obtained carbon fiber nonwoven fabric is significantly inferior.

  Comparing Example 1 and Example 2, Example 2 containing fibrillated cellulose fibers has less occurrence of wrinkles and cuts, probably because the interaction with carbon fibers and thermoplastic resin fibers is stronger. preferable.

  When Example 2 and Example 3 are compared, Example 3 in which the amount of water sprayed onto the wet paper web after passing through the couch roll in the former section and before passing through the suction device installed in front of the press roll in the press section is more preferable. Has no wrinkles or cuts, has a good formation and is excellent.

  When Example 4 and Example 5 are compared, Example 4 in which the amount of water sprayed onto the wet paper web after passing through the couch roll in the former section and before passing through the suction device installed in front of the press roll in the press section is more preferable. Has no wrinkles or cuts, has a good formation and is excellent.

  Comparing Example 5 with Example 6, the average particle diameter of water droplets sprayed on wet paper before passing through a suction device installed in front of the press roll in the press unit after passing through the former roll in the former unit is in a more preferable range. Certain Example 5 has less wrinkles and a good formation and is excellent.

  The carbon fiber non-woven fabric obtained by the method for producing a carbon fiber non-woven fabric of the present invention includes electronic device materials, electric device materials, civil engineering materials, building materials, automobile materials, aircraft materials, robots and rolls used in various manufacturing industries. It can be used for manufacturing parts.

DESCRIPTION OF SYMBOLS 1 Wet part 2 Former part 3 Former inlet 4 Circle net 5 Couch roll 6 Felt 7 Water drop supply device 8 Press part 9 Suction device 10 Press roll

Claims (2)

  A manufacturing method for forming a carbon fiber nonwoven fabric containing carbon fibers and thermoplastic resin fibers by a wet papermaking method.In a wet part of a papermaking process, the paper is placed before a press roll in a press part after passing through a couch roll in a former part. A method for producing a carbon fiber nonwoven fabric, comprising spraying water droplets on a wet paper before passing through a suction device with a water amount of 0.2 L or more and 2.5 L or less per square meter of wet paper.   The method for producing a carbon fiber nonwoven fabric according to claim 1, wherein the average particle size of the water droplets is 400 µm or less.