JP7211791B2 - Short carbon fiber wet-laid nonwoven fabric and carbon fiber reinforced resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to short carbon fiber wet-laid nonwoven fabrics and carbon fiber reinforced resins.

Carbon fiber is lighter than iron and has excellent mechanical properties such as high strength. Therefore, carbon fiber composite materials are used in a wide range of fields, such as aircraft, automobiles, tennis rackets, fishing rods, and blades for wind power generation, and their applications are expected to expand in the future.

Currently, the main carbon fibers are PAN-based carbon fibers obtained by carbonizing and graphitizing polyacrylonitrile, and pitch-based carbon fibers obtained by melt-spinning tar pitch liquefied coal and then carbonizing and graphitizing it. Carbon fiber is used. The carbon fibers produced in this way are either processed as a fabric, or after being arranged in one direction, a material called carbon fiber prepreg impregnated with uncured resin is cut to fit the mold of the target molding. It is often used as a carbon fiber reinforced resin (hereinafter, "carbon fiber reinforced resin" may be abbreviated as "CFRP") that is obtained by curing the resin later. Alternatively, when using carbon fibers obtained by recycling CFRP waste materials, the carbon fibers become short fibers in the recycling process and become short carbon fibers, so it cannot be processed as a woven fabric, so it is processed as a nonwoven fabric. It is common to

As a method for forming a short carbon fiber into a sheet to form a short carbon fiber wet-laid nonwoven fabric, the short carbon fiber and the water-swollen fibrillated fiber are dispersed in water to prepare a slurry for papermaking, the fibers are entangled, and the short carbon fiber is prepared. A method of making a wet-laid nonwoven is disclosed. Examples of water-swollen fibrillated fibers include fibrillated para-aromatic polyamide fibers and fibrillated acrylic fibers (see Patent Document 1). However, Patent Document 1 does not consider the molding flowability of fibers and resins and the uniformity of carbon short fibers in the nonwoven fabric when CFRP processing the carbon short fiber wet-laid nonwoven fabric. may cause trouble. If the molding fluidity of the fiber/resin is low during CFRP processing, the fiber/resin may not spread to fine parts when processing CFRP with a complex shape, and processing into a complex shape may not be possible. In addition, if the short carbon fibers in the nonwoven fabric are not uniform, the strength after CFRP processing will also be uneven, which may not be suitable for CFRP.

In addition, as another method for producing a carbon short fiber wet-laid nonwoven fabric, in a method for producing a carbon short fiber wet-laid nonwoven fabric composed of 75% to 97% by mass of carbon short fibers and 25% to 3% by mass of cellulose, a nitrogen-containing organic An aqueous dispersing aid containing a solvent is added to 10% by mass or less of the short carbon fibers and the short carbon fibers are added to a predetermined amount of water and stirred, and the solid content concentration of the slurry is reduced to 0.05% by mass or less with water. A wet papermaking method is disclosed after passing through the step of diluting and circulating (see Patent Document 2). However, the carbon short fiber wet-laid nonwoven fabric of Patent Document 2 is a nonwoven fabric having gas permeability and conductivity, and is not a nonwoven fabric used for CFRP. Molding fluidity and uniformity of short carbon fibers in the nonwoven fabric are not considered, and problems may occur during or after CFRP processing.

WO 2014/021366 pamphlet JP 2004-353124 A

An object of the present invention is to obtain a short carbon fiber wet-laid nonwoven fabric that exhibits excellent molding fluidity when processed into CFRP, and that has excellent strength and uniformity after CFRP processing.

The present inventors have found the following means as a result of conducting research to solve this problem.

<1> The number of bundled short carbon fibers is 5 or more The number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the wet heat adhesive binder resin fiber A short carbon fiber wet-laid nonwoven fabric having a blending amount of less than 15% by mass, a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m, and containing cellulose fibers .
<2> The short carbon fiber wet-laid nonwoven fabric according to <1>, wherein the blending amount of the short carbon fibers is 10% by mass or more and 98% by mass or less.
<3> The short carbon fiber wet-laid nonwoven fabric according to <1> or <2>, which has a basis weight of 20 g/m ² or more and less than 500 g/m ² .
<4> A carbon fiber reinforced resin comprising the short carbon fiber wet-laid nonwoven fabric according to any one of <1> to <3> and a resin compounded with the short carbon fiber wet-laid nonwoven fabric.

According to the present invention, it is possible to obtain a short carbon fiber wet-laid nonwoven fabric that exhibits excellent molding fluidity when processed into CFRP and has excellent strength and uniformity after CFRP processing.

FIG. 2 is a diagram showing a method of rib molding during <CFRP molding fluidity evaluation> in Examples.

The present invention is an invention for obtaining a short carbon fiber wet-laid nonwoven fabric having excellent molding fluidity when processed into CFRP. When processing the short carbon fiber wet-laid nonwoven fabric into CFRP, if the short carbon fiber wet-laid nonwoven fabric has low molding fluidity, a problem may occur in that it cannot be processed into a complicated shape. That is, the short carbon fibers do not flow together with the resin, and only the resin forms a complicated shape, but the strength of the portion where only the resin is present becomes extremely weak, which may cause a problem that it is not suitable for CFRP. In addition, even if the short carbon fiber wet-laid nonwoven fabric has molding fluidity, when the short carbon fibers flow, the short carbon fibers gather together and create areas with high density. Since the strength of the density portion becomes uneven, the quality of the CFRP becomes uneven, which sometimes causes a problem that it is not suitable as a short carbon fiber wet-laid nonwoven fabric for CFRP processing.

In order to solve these problems, as a result of intensive research, the number of carbon short fiber bundles in which the number of bundled carbon short fibers is 5 or more is 3 or more per 1 cm ² and the average fiber length of the carbon short fibers is 1 mm or more. A short carbon fiber wet-laid nonwoven fabric having a length of less than 50 mm, a wet heat adhesive binder resin fiber content of less than 15% by mass, and a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m, It was found that the short carbon fiber wet-laid nonwoven fabric has high molding fluidity and high strength and uniformity after CFRP processing.

A short carbon fiber wet-laid nonwoven fabric in which the number of bundled short carbon fibers is 5 or more and less than 3 short carbon fiber bundles per 1 cm ² has low molding fluidity due to the intricate interlacing of the dispersed short carbon fibers. Therefore, it may not be suitable as a short carbon fiber wet-laid nonwoven fabric for CFRP. When the average fiber length of the short carbon fibers is less than 1 mm, the short carbon fibers are short, so that the strength of the short carbon fiber wet-laid nonwoven fabric is not sufficiently exhibited, and the strength after CFRP processing becomes weak. In addition, when the average fiber length of the carbon short fibers is 50 mm or more, the short carbon fiber wet-laid nonwoven fabric is less suitable for CFRP because the long fibers are interlaced in a complicated manner, resulting in low molding fluidity of the short carbon fiber wet-laid nonwoven fabric. Absent. The average fiber length of the short carbon fibers is more preferably 3 mm or more and 30 mm or less.

If the tensile strength in the machine direction is less than 30 N/m, frequent paper breaks occur during papermaking, resulting in markedly inferior productivity, which is not suitable as a short carbon fiber wet-laid nonwoven fabric for CFRP. If the tensile strength in the machine direction is 5000 N/m or more, the fibers are strongly bound to each other, resulting in low molding fluidity and not suitable as a short carbon fiber wet-laid nonwoven fabric for CFRP. The tensile strength in the machine direction is more preferably 50 N/m or more and 4500 N/m or less, and still more preferably 100 N/m or more and 4000 N/m or less.

In the present invention, the amount of short carbon fibers is preferably 10 to 98% by mass, more preferably 20 to 97% by mass, more preferably 30 to 98% by mass, based on the total fibers contained in the short carbon fiber wet-laid nonwoven fabric. More preferably, it is 96% by mass. If the blending amount of the short carbon fibers is less than 10% by mass, the effects of "high strength and light weight" that the short carbon fibers have when processed may not be sufficiently exhibited. If the content of short carbon fibers is more than 98% by mass, the binding between fibers may be insufficient, and fibers may fall off.

In the present invention, short carbon fibers refer to fibers having a fiber length of 50 mm or less. Also, the lower limit of the fiber length is preferably 0.1 mm. If the fiber length of the short carbon fibers is less than 0.1 mm, the fibers may fall off during the production of the wet-laid nonwoven fabric. Although the upper limit of the fiber length is not particularly specified, if fibers with a fiber length exceeding 50 mm are included, the fibers may form clumps with the fibers as nuclei, making it difficult to perform uniform papermaking in some cases.

As short carbon fibers, short carbon fibers manufactured by any manufacturing method such as PAN-based and pitch-based short fibers can be used. Also, there is no problem with short carbon fibers that are new and unused, or short carbon fibers that are obtained by recycling discarded carbon fibers. Considering the cost required to obtain short carbon fibers, short carbon fibers obtained by recycling are more preferable.

In the short carbon fiber wet-laid nonwoven fabric of the present invention, a binder synthetic fiber can be used as long as the performance is not impaired. Examples of binder synthetic fibers include composite fibers such as core-sheath fibers (core-shell type), parallel fibers (side-by-side type), and radially split fibers; undrawn fibers; low melting point synthetic resin single fibers; wet heat adhesive binder resin fibers, etc. . The binder synthetic fiber has a low glass transition temperature or melting temperature (melting point) of the whole fiber or a part of the fiber, and exhibits binder ability in the drying process of the paper machine. Composite fibers are less likely to form a film, so the mechanical strength can be improved while maintaining the spaces of the short carbon fiber wet-laid nonwoven fabric. More specifically, composite fibers include a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), and a high melting point polyester (core) and low melting point polyester (sheath). and a combination of high melting point polyester (core) and polyethylene (sheath). Examples of undrawn fibers include undrawn fibers such as polyester. In addition, low-melting synthetic resin single fibers such as single fibers (full-melting type) composed only of low-melting resins such as polyethylene and polypropylene, and wet heat adhesive binder resin fibers such as polyvinyl alcohol are coated in the drying process. can be used in the present invention.

In the present invention, the blending amount of the wet heat adhesive binder resin fiber is less than 15% by mass, more preferably less than 12% by mass, and even more preferably less than 10% by mass, based on the total fibers contained in the short carbon fiber wet-laid nonwoven fabric. . If the content of the wet heat adhesive binder resin fiber is 15% by mass or more, the short carbon fibers are strongly bound to each other, impeding molding fluidity, and the short carbon fiber wet-laid nonwoven fabric for CFRP is not suitable. The lower limit of the amount of the wet heat adhesive binder resin fiber is not particularly specified, and even if it is 0% by mass, there is no problem. tend to be stable.

The short carbon fiber wet-laid nonwoven fabric of the present invention may contain semi-synthetic fibers, synthetic fibers (excluding binder synthetic fibers), inorganic fibers, cellulose fibers, etc., as long as the performance is not impaired.

Synthetic fibers (excluding binder synthetic fibers) include, for example, polyolefin-based, polyamide-based, polyacrylic-based, vinylon-based, polyvinylidene chloride-based, polyvinyl chloride-based, polyester-based, benzoate-based, polyclar-based, phenol-based, etc. Synthetic fibers may be mentioned. Examples of inorganic fibers include inorganic fibers such as glass fibers, rock fibers, slag fibers, and metal fibers. Semisynthetic fibers include acetate, triacetate, promix, and the like.

Although the fiber length of synthetic fibers (excluding binder synthetic fibers), binder synthetic fibers, inorganic fibers and semi-synthetic fibers is not particularly limited, it is preferably 3 mm or more and less than 30 mm. As the fiber length of these fibers increases, the number of contact points between fibers increases, and the fibers tend to be less likely to fall off. Therefore, the fiber length of these fibers is preferably 3 mm or more. If the fiber length is too long, the papermaking properties and texture of the nonwoven fabric may deteriorate, so it is preferably less than 30 mm. Although the fiber diameter is not particularly limited, it is preferably 1 μm or more and less than 30 μm, and particularly preferably 2 μm or more and less than 20 μm. When fibers with a fiber diameter of less than 1 μm are blended, the inside of the short carbon fiber wet-laid nonwoven fabric becomes an excessively dense structure. It may hinder the performance of the CFRP after processing. If the fiber diameter is 30 μm or more, synthetic fibers (excluding binder synthetic fibers) or inorganic fibers may easily come off.

Types of cellulose fibers include natural cellulose fibers and regenerated cellulose fibers. Natural cellulose fibers include wood pulps such as softwood pulps and hardwood pulps; woody or herbaceous pulps such as straw pulps, bamboo pulps, linter pulps and kenaf pulps. Regenerated cellulose fibers include regenerated cellulose fibers such as rayon, cupra, and lyocell. These cellulose fibers may be fibrillated (beaten) without any problem. Furthermore, pulp fibers obtained from waste paper, waste paper, etc. may be used.

Among the cellulose fibers, it is preferable to use one or more cellulose fibers selected from the group consisting of softwood pulp, linter pulp and lyocell, and more preferably lyocell. Also, the lyocell is preferably fibrillated (beaten). By using these preferable cellulose fibers, it is possible to suppress the shedding of the fibers. In addition, the effect of stabilizing the operability when producing the short carbon fiber wet-laid nonwoven fabric by the papermaking method can also be obtained.

Fibrillated (beaten) cellulose fibers can be produced by fibrillating the above cellulose fibers. Devices for fibrillation include beaters, PFI mills, single disc refiners (SDR), double disc refiners (DDR), ball mills, dyno mills, mixers, grinders, and high-speed grinders used for dispersing and grinding pigments. A rotating blade homogenizer that applies shearing force with rotating blades, a double cylindrical high-speed homogenizer that produces shearing force between a cylindrical inner blade that rotates at high speed and a fixed outer blade, and atomization by ultrasonic impact. A high pressure ultrasonic crusher that applies a pressure difference of at least 20 MPa to the fiber suspension to pass through a small-diameter orifice to a high speed, which is then collided and rapidly decelerated to apply a shearing force and a cutting force to the fiber. A device such as a homogenizer may be used. Fibrillated cellulose fibers can be produced by using these devices alone or in combination. Then, by adjusting fibrillation conditions such as the type of equipment and processing conditions (fiber concentration, temperature, pressure, rotation speed, refiner blade shape, refiner plate gap, number of processing times), the desired fibrillation can be achieved. status can be obtained.

When cellulose fibers are blended, the blending amount is preferably 1% by mass or more and less than 30% by mass, and more preferably 2% by mass or more and less than 20% by mass. When the amount of cellulose fiber blended is less than 1% by mass, there is no difference from the case where cellulose fiber is not blended. When the content of cellulose fibers is 1% by mass or more, the number of contact points between fibers increases, paper breakage is less likely to occur during papermaking, and more stable production becomes possible. If the blending amount of cellulose fibers is 30% by mass or more, the cellulose fibers may inhibit the permeation of the resin during CFRP processing, and it may be difficult to uniformly impregnate the resin.

The short carbon fiber wet-laid nonwoven fabric of the present invention is obtained by a papermaking method in which short carbon fibers are formed into a sheet by a paper machine.

In the papermaking method, for example, a Fourdrinier method, a cylinder method, or an inclined wire method can be used. A paper machine having one of these papermaking systems alone may be used, or a combination paper machine in which two or more papermaking systems of the same or different types are installed online may be used. In order to produce a carbon short fiber wet-laid nonwoven fabric with excellent uniformity, it is preferable to use a papermaking method such as a fourdrinier method or an inclined wire method, which can gently dewater the slurry on the wire. The short carbon fiber wet-laid nonwoven fabric of the present invention may have a single layer or multiple layers.

In the papermaking process, a pulper is used to defiber for the purpose of dispersing the fibers. The type of pulper is not particularly limited, and a vertical pulper may be used, a horizontal pulper may be used, and other types of pulpers may be used without any problem. The pulper's disintegration ability is not particularly limited, but if the pulper's disintegration ability is too strong, the short carbon fibers may be crushed by the pulper and become milled, resulting in reduced strength after CFRP processing. If the pulper's disintegration ability is too weak, the short carbon fibers may not be disintegrated at all, resulting in poor texture, uneven carbon short fibers, and uneven strength after CFRP processing. It is desirable to control the state of disaggregation of short carbon fibers by adjusting the strength and time of the pulper.

In the papermaking process, various anionic, nonionic, cationic or amphoteric dispersants and antifoaming agents are used when dispersing fibers in water for the purpose of uniformly dispersing fibers in water or for the purpose of imparting various functions. , Hydrophilic agents, drainage agents, paper strength improvers, viscous agents, antistatic agents, polymer viscous agents, release agents, antibacterial agents, bactericides, pH adjusters, pitch control agents, slime control agents, etc. It may be added.

The short carbon fiber wet-laid nonwoven fabric of the present invention may optionally contain a sizing agent. As the sizing agent, reinforced rosin sizing agents, rosin emulsion sizing agents, petroleum resin-based sizing agents, synthetic sizing agents, neutral rosin sizing agents, alkylketene dimers (AKD ) and other sizing agents can be used.

The wet paper produced by the paper machine 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 short carbon fiber wet-laid nonwoven fabric. When the wet paper is dried, it is brought into close contact with a hot roll such as a Yankee dryer and dried under heat and pressure, thereby improving the smoothness of the contacted surface. Hot and pressure drying means drying by pressing the wet paper against a hot roll with a touch roll or the like. The surface temperature of the heat roll is preferably 100 to 180°C, more preferably 100 to 160°C, even more preferably 110 to 160°C. The pressure is preferably 50-1000 N/cm, more preferably 100-800 N/cm.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. The parts and percentages in the examples are based on mass. Examples 17 and 18 are reference examples.

Example 1
A short carbon fiber having a fiber length described in Table 1, a beaten lyocell, and a PVA binder (manufactured by Kuraray, product name: VPB107-1) were added to water at the blending ratio (mass basis) described in Table 1, and a vertical pulper was added. After mixing and dispersing the wet paper for 10 minutes, the wet paper is wet paper-made in a single layer with an inclined wire method, dried with a Yankee dryer at a surface temperature of 130 ° C., and a paper-making speed of 20 m / min and a basis weight of 50 g / m ² carbon A short fiber wet-laid nonwoven fabric was obtained.

Examples 2, 3, Comparative Examples 1 and 2
Short carbon fiber wet-laid nonwoven fabrics of Examples 2 and 3 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the dispersed state of the short carbon fibers was changed to the number of fiber bundles shown in Table 1. .

Examples 4-7, Comparative Examples 3 and 4
Short carbon fiber wet-laid nonwoven fabrics of Examples 4 to 7 and Comparative Examples 3 and 4 were obtained in the same manner as in Example 1, except that the mixing ratio and average fiber length of the short carbon fibers were changed to those described in Table 1.

Examples 8-19, Comparative Examples 5 and 6
Short carbon fiber wet-laid nonwoven fabrics of Examples 8 to 19 and Comparative Examples 5 and 6 were obtained in the same manner as in Example 1, except that the blending ratios of the short carbon fibers, cellulose fibers, and synthetic binder fibers were changed to those described in Table 1. .

Examples 20-23
Short carbon fibers of Examples 20 to 23 were wet-processed in the same manner as in Example 1, except that the blending ratios of short carbon fibers, cellulose fibers, synthetic fibers (excluding synthetic binder fibers), and synthetic binder fibers were changed to the values shown in Table 1. A non-woven fabric was obtained.

Examples 24-30 and Comparative Example 7
Short carbon fiber wet-laid nonwoven fabrics of Examples 24 to 30 and Comparative Example 7 were obtained in the same manner as in Example 1, except that the basis weight and fiber blending ratio of the short carbon fiber wet-laid nonwoven fabric were changed to those described in Table 1.

Details of the fibers listed in Table 1 are as follows.

Beating lyocell: Lyocell fibers (fineness 1.4 decitex, fiber length 3 mm) are processed using a double disc refiner to generate branches with an average fiber diameter of 1 μm or less from a stem with an average fiber diameter of 14.0 μm. fiber.
Beat softwood pulp: Natural softwood pulp prepared to have a freeness of 500 ml CSF.
PET fiber: polyethylene terephthalate (PET) drawn fiber, fineness 1.7 decitex, fiber length 5 mm
Aramid fiber: fineness 0.9 decitex, fiber length 5 mm
PVA binder: Polyvinyl alcohol binder synthetic fiber (wet heat adhesive binder resin fiber, manufactured by Kuraray, product name: VPB107-1)
PET binder: PET unstretched binder synthetic fiber (heat-fusible binder synthetic fiber, fineness 1.2 decitex, fiber length 5 mm)

In the carbon short fiber wet-laid nonwoven fabrics produced in Examples and Comparative Examples, the number of carbon short fiber bundles having 5 or more bundled short carbon fibers (number of fiber bundles), the basis weight, and the tensile strength (strength) in the machine direction were measured. It was measured. In addition, the strength, uniformity and molding fluidity after CFRP processing were evaluated. Table 1 shows the measurement results and evaluation results.

<Number of fiber bundles>
The carbon short fiber wet-laid nonwoven fabric was cut to 1 cm×1 cm, and the number of carbon short fiber bundles containing 5 or more bundled carbon short fibers was observed with a loupe and counted.

<Basis weight>
The basis weight of the short carbon fiber wet-laid nonwoven fabric was measured according to JIS P 8124:2011.

<Strength>
The tensile strength was measured according to JIS P8113 (2006). A tensile tester (trade name: Tensilon (registered trademark) UTM-III-100 type, manufactured by Japan A&D Co., Ltd.) was used. A value of N/m was obtained from the measured tensile strength.

<Papermaking stability>
The stability of papermaking was evaluated in papermaking of short carbon fiber wet-laid nonwoven fabric. When the stability of papermaking is low, stable production may become difficult.

◯: Problems such as paper breakage do not occur, and stable papermaking is possible.
Δ: Paper can be made, although some problems such as paper breakage occurred.
x: Problems such as paper breakage occurred frequently, and stable papermaking was not possible.

<CFRP processing>
A short carbon fiber wet-laid nonwoven fabric was subjected to CFRP processing. After applying a thermosetting resin (epoxy resin) mixed with a curing agent to the short carbon fiber wet-laid nonwoven fabric in an amount twice the weight of the short carbon fiber wet-laid nonwoven fabric, it is hot-pressed (temperature: 120°C) to a thickness of 2 mm. ° C. and a pressure of 5 MPa) to obtain a CFRP plate of carbon short fiber wet-laid nonwoven fabric.

The epoxy resins used are as follows.
Epoxy resin: GM-6800 (Blenny Giken)
Viscosity after mixing curing agent: 505 cps

The epoxy resin was processed by CFRP after mixing the curing agent so that the ratio of main agent/curing agent was 10/3.

<Strength evaluation after CFRP processing>
The strength of the produced CFRP plate was evaluated by measuring N=10 times for each sample according to JIS K 7074:1988.

◯: Sufficiently high strength was obtained as CFRP.
Δ: A high strength was obtained although the CFRP was slightly low.
x: Insufficient strength as CFRP.

<Uniformity evaluation after CFRP processing>
The coefficient of variation of the strength of the produced CFRP plate was determined and evaluated.

○: The coefficient of variation was less than 10%, and the strength was uniform. △: The coefficient of variation was 10 to 30%, and the strength was somewhat uneven.
x: The coefficient of variation was higher than 30%, and the strength was uneven.

<CFRP molding fluidity evaluation>
In order to measure the molding fluidity of the short carbon fiber wet-laid nonwoven fabric, a short carbon fiber wet-laid nonwoven fabric + epoxy resin composite obtained by coating the short carbon fiber wet-laid nonwoven fabric with a thermosetting resin in the same manner as <CFRP processing> above. A body 31 is placed between an upper plate (with slits) 11 and a lower plate (without slits) 21, and hot-pressed (at a temperature of 120° C. and a pressure of 5 MPa) to form ribs 41 having a width of 2 mm and a length of 50 mm. Then, molding fluidity was evaluated (Fig. 1).

◯: Ribs containing short carbon fibers were formed higher than 3 mm, and high molding fluidity was observed.
Δ: Ribs containing short carbon fibers were formed in the range of 0.5 to 3 mm in height, and slightly high fluidity was observed.
x: Ribs containing short carbon fibers were formed below 0.5 mm, and molding fluidity was not observed.

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is In Examples 1 to 3, which are short carbon fiber wet-laid nonwoven fabrics characterized by having a tensile strength of less than 15% by mass and a tensile strength in the machine direction of 30 N / m or more and less than 5000 N / m, excellent molding fluidity and It can be seen that the CFRP has strength and uniformity after processing. Since there are many short carbon fiber bundles, there are few carbon short fibers that are intricately entangled, and since the amount of the wet heat adhesive binder resin fiber is small, the binding between fibers is suppressed to an appropriate strength. It is presumed that excellent molding fluidity was exhibited.

In addition, in Comparative Examples 1 and 2 in which the number of bundled short carbon fibers is 5 or more and the number of short carbon fiber bundles is less than 3 per 1 cm ² , although excellent strength after CFRP processing is obtained, molding during CFRP processing It can be seen that the liquidity is low. It is presumed that this is because the short carbon fibers are intricately entangled and are in a state where it is difficult for the short carbon fibers to flow, resulting in poor molding fluidity and uniformity.

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is In Examples 4 to 7, which are short carbon fiber wet-laid nonwoven fabrics characterized by having a content of less than 15% by mass and a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m, excellent molding fluidity and CFRP It can be seen that it has strength and uniformity after processing. Even if the blending ratio of short carbon fibers was changed to adjust the average fiber length, it is presumed that excellent molding fluidity was exhibited in the range of 1 mm or more and less than 50 mm.

Further, even if the average fiber length of the short carbon fibers is 1 mm, in Comparative Example 3 in which the number of short carbon fiber bundles is less than 3 per 1 cm ² , although high molding fluidity is confirmed, papermaking stability and CFRP It can be seen that the strength after processing is inferior. It is speculated that the reason for the low papermaking stability is that the short carbon fibers have an average fiber length of 1 mm and the number of short carbon fiber bundles is small. It is speculated that the reason why the strength after CFRP processing is inferior is that the short carbon fibers have an average fiber length of 1 mm and the number of short carbon fiber bundles is small. In addition, in Comparative Example 4 in which the average fiber length of the carbon short fibers was 50 mm, the short carbon fibers were intricately entangled with each other, making it difficult for the fibers to flow, presumably resulting in poor molding fluidity. As for papermaking, long short carbon fibers are complicatedly entangled and tend to form lumps, resulting in poor stability.

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is In Examples 8 to 19, which are short carbon fiber wet-laid nonwoven fabrics characterized by having a tensile strength of less than 15% by mass and a tensile strength in the machine direction of 30 N / m or more and less than 5000 N / m, excellent molding fluidity and CFRP It can be seen that it has strength and uniformity after processing. Even when the blending amounts of cellulose fibers and wet heat adhesive binder resin fibers were adjusted, excellent molding fluidity was exhibited when the ratio of wet heat adhesive binder resin fibers was less than 15% by mass. Moreover, even when only the cellulose fiber is blended, or when only the wet heat adhesive binder synthetic fiber or the heat fusible binder resin fiber is blended, excellent molding fluidity is exhibited without any problem.

In addition, in Comparative Examples 5 and 6, in which the content of the wet heat adhesive binder resin fiber is 15% by mass or more, the strength of the short carbon fiber wet-laid nonwoven fabric is high, and the molding fluidity during CFRP processing is poor. It is presumed that this is because the short carbon fiber wet-laid nonwoven fabric has a high strength, and the strength of the short carbon fiber wet-laid nonwoven fabric is stronger than the force with which the resin flows, so that the short carbon fibers were difficult to flow.

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is In Examples 20 to 23, which are short carbon fiber wet-laid nonwoven fabrics characterized by having a content of less than 15% by mass and a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m, excellent molding fluidity and CFRP It can be seen that it has strength and uniformity after processing. From Example 20, it can be seen that excellent molding fluidity and strength after CFRP processing are maintained even when the cellulose fiber is changed. Also, from Example 21, it can be seen that even when the PET unstretched binder synthetic fiber is used instead of the wet heat adhesive binder resin fiber, excellent molding fluidity and strength after CFRP processing are maintained. In addition, from Examples 22 and 23, even if synthetic fibers such as PET fibers and aramid fibers (excluding binder synthetic fibers) are blended, excellent molding fluidity and strength after CFRP processing remain unchanged.

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is In Examples 24 to 30, which are short carbon fiber wet-laid nonwoven fabrics characterized by having a content of less than 15% by mass and a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m, excellent molding fluidity and CFRP It can be seen that it has strength and uniformity after processing. Even if the basis weight of the short carbon fiber wet-laid nonwoven fabric is changed, if the strength of the short carbon fiber wet-laid nonwoven fabric is 30 N/m or more and less than 5000 N/m, it has excellent molding fluidity and strength after CFRP processing without change. I understand. However, in Example 24, which had a low basis weight and a low tensile strength in the machine direction, paper breakage occurred during papermaking, resulting in a slight lack of stability in papermaking. In Example 29, which had a large basis weight, the wet paper was difficult to dry, resulting in a slight lack of stability in papermaking. In Example 30, which had the same basis weight as Example 224 but had a higher blending amount of short carbon fibers, more paper breakage occurred during papermaking, and the papermaking stability was lower than that of Example 24.

Furthermore, in Comparative Example 7, in which the content of short carbon fibers is high and the tensile strength in the machine direction is less than 30 N/m, a large number of paper cuts occur and the papermaking stability is significantly lacking. As a result, it is not suitable as

The short carbon fiber wet-laid nonwoven fabric of the present invention can be suitably used for carbon fiber reinforced resin (CFRP) processing.

11 Upper plate (with slit)
21 lower plate (no slit)
31 carbon short fiber wet-laid nonwoven fabric + epoxy resin composite 41 rib

Claims (4)

The number of bundled short carbon fibers is 5 or more, and the number of short carbon fiber bundles is 3 or more per 1 cm ² , the average fiber length of the short carbon fibers is 1 mm or more and less than 50 mm, and the blending amount of the wet heat adhesive binder resin fiber is A short carbon fiber wet-laid nonwoven fabric comprising cellulose fibers in an amount of less than 15% by mass, having a tensile strength in the machine direction of 30 N/m or more and less than 5000 N/m. The carbon short fiber wet-laid nonwoven fabric according to claim 1, wherein the carbon short fiber content is 10% by mass or more and 98% by mass or less. The short carbon fiber wet-laid nonwoven fabric according to claim 1 or 2, having a basis weight of 20 g/m ² or more and less than 500 g/m ² . A carbon fiber reinforced resin comprising the short carbon fiber wet-laid nonwoven fabric according to any one of claims 1 to 3 and a resin compounded with the short carbon fiber wet-laid nonwoven fabric.

Images