JP6991483B2 - Method for manufacturing carbon fiber reinforced thermoplastic resin composite material - Google Patents

Description

The present invention relates to a method for producing a fiber-reinforced thermoplastic resin composite material from carbon fibers.

Fiber reinforced composite materials (CFRP) such as carbon fiber are attracting attention as lightweight materials, and are widely used in aircraft, automobiles, windmill blades, robot arms, drones, sports equipment, and the like. It is expected that the market for fiber-reinforced composite materials will continue to expand, as gaining light weight will lead to improved fuel efficiency and reduced environmental impact. On the other hand, scraps in the middle of the fiber-reinforced composite material manufacturing process and waste composite materials that have reached the end of their useful life (collectively referred to as waste materials) are already reaching the scale of tens of thousands of tons per year. Therefore, the technology for recycling CFRP waste materials is extremely important, and several methods have been proposed (Patent Documents 1 and 2).

Reference 1 relates to a technique (thermal decomposition method) for recovering carbon fibers from a composite material (hereinafter referred to as CFRP) in which a thermosetting resin (mainly an epoxy resin) is reinforced with carbon fibers. This is a method in which the discarded CFRP is cut into an appropriate size and oxidized in air at about 550 ° C. to recover the remaining carbon fibers. In this case, there is a problem that the carbon fiber is oxidized due to the high temperature treatment in the oxidizing atmosphere, and the strength is lowered. In addition, since the recovered carbon fibers are entangled in the thermal decomposition process, it is difficult to process them into a composite material.

In Patent Document 2, the discarded CFRP is cut into a size of about 20 mm and heat-treated at about 450 ° C. or lower at which the oxidation reaction of carbon fibers does not occur in the air. This is a method in which the heat-treated CFRP is immersed in an electrolyte solution, and when the CFRP is used as an anode and electrolyzed, the carbonized resin residue is removed by the heat treatment and the carbon fibers are recovered. In this method, since the electrolysis treatment is performed in a stationary state, the orientation of the recovered carbon fibers is linear and wet while maintaining the CFRP state, so that it is easy to make a non-woven fabric and it is easy to process it into a composite material. be. In addition, there is almost no decrease in the strength of the carbon fiber in the recovery process.

Generally, when a structure is manufactured by reinforcing a fiber base material with a resin, the thicker the fiber base material, the better the productivity. If the resin is thermosetting, the resin may be impregnated between the single yarns constituting the fiber base material while the viscosity of the resin before curing is low, and the resin may be cured and molded.

However, when the resin is thermoplastic, it is difficult to impregnate the resin between the single yarns constituting the fiber base material because the melt viscosity is high. In order to increase molding productivity, increasing the basis weight of the non-woven fabric further reduces the resin impregnation property, making it difficult to manufacture high-performance composite materials.

Japanese Unexamined Patent Publication No. 6-298991 Japanese Patent No. 60444946

When mass-producing a composite material composed of a thermoplastic resin as a matrix resin using a thick carbon fiber non-woven fabric as a reinforcing material, there are the following problems.
(1) Since the melt viscosity of the thermoplastic resin is generally extremely high, it is difficult to impregnate the resin between the reinforcing fiber single yarns constituting the nonwoven fabric.
(2) In order to increase the productivity of the composite material, it is conceivable to use a thick non-woven fabric as a reinforcing material, but the difficulty of impregnating with the thermoplastic resin further increases.

An object of the present invention is to provide a simple method for producing a composite material having excellent mechanical properties, in which carbon fibers are made into a non-woven fabric and further used as a fiber-reinforced thermoplastic resin composite material in order to solve the above two problems. To provide.

The present invention is as follows.
[1]
(A) The carbon fiber is made into a non-woven fabric together with the aqueous self-emulsifying emulsion of the thermoplastic urethane resin, or (B) the aqueous self-emulsifying emulsion of the thermoplastic urethane resin is added to the wet carbon fiber non-woven fabric to make the thermoplastic urethane. Step of obtaining carbon fiber nonwoven fabric bonded and coated with resin (1),
A step (2) in which at least one non-woven fabric obtained in the step (1) and at least one thermoplastic resin sheet as a matrix member are alternately laminated and then heated to obtain a fiber-reinforced thermoplastic resin composite material (2).
A method for manufacturing a fiber-reinforced thermoplastic resin composite material, including.
[2]
The production method according to [1], wherein the thermoplastic urethane resin has a glass transition temperature of 40 ° C. or higher.
[3]
The thermoplastic urethane resin is a non-yellowing ester-based, non-yellowing ester / ether-based, non-yellowing carbonate-based, or aromatic isocyanate-based aqueous urethane resin, and the particle size of the emulsion is 0.01 to. The production method according to [1] or [2], which is in the range of 0.1 μm.
[4]
The production method according to any one of [1] to [3], wherein in the step (1), the emulsion is used in the range of 5 to 15 parts by mass in terms of solid content with respect to 100 parts by mass of carbon fiber.
[5]
For some or all of the carbon fibers used in the step (1), the carbon fiber composite material is heat-treated in an oxidizing atmosphere and then anodized to separate and recover the carbon fibers from the resin component contained in the carbon fiber composite material. The obtained wet carbon fibers are obtained. In (A), the wet carbon fibers are used as they are for making a non-woven fabric, and in (B), the wet carbon fibers are used as a non-woven fabric to obtain a moistened carbon fiber non-woven fabric [1]. ] To [4].
[6]
The production method according to any one of [1] to [5], wherein the nonwoven fabric obtained in the step (1) has a basis weight in the range of 100 g to 2000 g / m ² .

According to the present invention, even if a carbon fiber non-woven fabric is used as a base material, a composite material having excellent mechanical properties using a thermoplastic resin as a matrix can be produced, and according to this production method, high productivity is achieved. Mass production of composite materials is also possible.

For example, when the wet carbon fiber (recycled carbon fiber) recovered from the CFRP waste material is used as it is by the method described in Patent Document 2, it is easy to produce a nonwoven fabric (paper) by a wet method. The single yarn of carbon fiber in a wet state is arranged in a straight state without refraction or bending, and it is possible to obtain a pseudo-isotropic material in which the direction of the fiber is random in a plane.

The method for producing a fiber-reinforced thermoplastic resin composite material of the present invention includes the following steps (1) and (2).
Steps (1): (A) Non-woven fabric of carbon fiber together with water-based self-emulsifying emulsion of thermoplastic urethane resin, or (B) Water-based self-emulsifying emulsion of thermoplastic urethane resin is added to (B) wet carbon fiber non-woven fabric. And dried to obtain a non-woven fabric sheet bonded and coated with a thermoplastic urethane resin.
Step (2): At least one non-woven fabric sheet obtained in step (1) and at least one thermoplastic resin sheet as a matrix member are alternately laminated and then heated to obtain a fiber-reinforced thermoplastic resin composite material. ..

The carbon fibers are made into a non-woven fabric together with a water-based self-emulsifying emulsion of a thermoplastic urethane resin. Specifically, the carbon fibers are mixed with a water-based self-emulsifying emulsion of a thermoplastic urethane resin, and then made into a non-woven fabric by a conventional method. Alternatively, a water-based self-emulsifying emulsion of a thermoplastic urethane resin is applied to the wet non-woven carbon fiber and then dried to obtain a non-woven fabric sheet bonded and coated with the thermoplastic urethane resin. The wet carbon fiber nonwoven fabric preferably has a moisture content of, for example, 10% or more, more preferably 30% or more. Since the aqueous emulsion is a self-emulsifying type, it does not contain extra components such as surfactants, does not impair the physical characteristics of the composite material when used as a composite material, and has excellent strength even when recovered carbon fiber is used. It is suitable because a composite material can be obtained.

Recycling obtained by heat-treating the carbon fiber composite material (CFRP waste material, etc.) described in Patent Document 2 in an oxidizing atmosphere and then anodizing the carbon fiber composite material to separate and recover the carbon fiber from the resin component contained in the carbon fiber composite material. The carbon fibers separated and recovered after anodization are in a wet state. The water content of the recovered carbon fiber depends on the separation and recovery method, but is, for example, 30% or more. Therefore, using the wet carbon fiber as it is in the method (B) of the step (1) simplifies the manufacturing process, and since the carbon fiber is in the wet state, it becomes familiar with the water-based self-emulsifying emulsion. It is preferable because the adhesion between the carbon fibers to the thermoplastic urethane resin and the coating of the carbon fibers are good, and the strength of the finally obtained composite material is improved.

Of course, a new cut carbon fiber alone or a mixture of recovered carbon fibers described in Patent Document 2 may be used. When a new cut carbon fiber is used, it is used in the method (A) of the step (1), or the new cut carbon fiber is moistened by a conventional method and then the method (B) of the step (1). It can also be used for.

The thermoplastic urethane resin used here preferably forms a thermoplastic film having a heat resistance of 250 ° C. or higher after being dried. The particle size of the aqueous emulsion is preferably in the range of, for example, 0.01 to 0.1 μm from the viewpoint that it can be impregnated between carbon fibers having a single yarn diameter of about 5 to 10 μm.

The glass transition temperature is, for example, from the viewpoint that the thermoplastic urethane resin melts together with the thermoplastic resin in the heating in the step (2) and can be appropriately mixed with the thermoplastic resin to contribute to the improvement of the strength of the obtained composite material. , 40 ° C. or higher is appropriate, and more preferably 80 ° C. or higher.

The material of the thermoplastic urethane resin is not particularly limited, and examples thereof include non-yellowing ester-based, non-yellowing ester / ether-based, non-yellowing carbonate-based, and aromatic isocyanate-based aqueous urethane resins. .. The water-based self-emulsifying emulsion of a thermoplastic urethane resin having the glass transition temperature and the particle size of the emulsion is available as a commercial product, for example, in the Superflex series of Dai-ichi Kogyo Seiyaku.

The amount of the emulsion used is such that the emulsion is used in the range of 5 to 15 parts by mass in terms of solid content with respect to 100 parts by mass of carbon fibers, even when recycled carbon fibers are used, adhesion between carbon fibers and surface. It is suitable from the viewpoint that the adhesiveness to the thermoplastic resin is improved by the coating of the above material and a composite material having excellent mechanical strength can be obtained. If it is less than 5 parts by mass, it is difficult to completely fill the voids between the single yarns with the resin, and it tends to be difficult to obtain a composite material having excellent mechanical properties. Even if it exceeds 15 parts by mass, there is a tendency that a composite material having more excellent mechanical properties cannot be obtained.

The nonwoven fabric obtained in the step (1) preferably has a basis weight in the range of 100 g to 2000 g / m ² . When the basis weight is 100 g / m ² or less, the productivity of the composite material is low, so that the economic effect of the present invention tends to be poor. On the contrary, at 2000 g / m ² or more, it tends to be technically difficult to make a non-woven fabric, and it takes time to dry after making a non-woven fabric, so that the economic efficiency tends to decrease.

The nonwoven fabric bonded and coated with the thermoplastic urethane resin is preferably heat-dried before being subjected to the step (2). The heat-drying can be appropriately determined in consideration of the thermal properties of the thermoplastic urethane resin and in consideration of the good adhesion and coating of the carbon fibers. For example, it can be dried in the range of 100 to 160 ° C. Examples of the drying method include hot air drying, hot plate drying, infrared drying and the like. After drying, it is preferable to pressurize and flatten the plate. The dried non-woven fabric preferably has a water content of 5% or less, preferably 1% (almost dry).

In the step (2), at least one non-woven fabric obtained in the step (1) and at least one thermoplastic resin sheet as a matrix member are alternately laminated and then heated to obtain a fiber-reinforced thermoplastic resin composite material. .. The thermoplastic resin sheet used in the step (2) constitutes a matrix member of the composite material. The thermoplastic resin used as the matrix member is not particularly limited, but a thermoplastic resin having a high adhesive force with the thermoplastic urethane resin for filling is preferable. A synthetic resin that melts at a temperature equal to or lower than the thermal decomposition temperature of the thermoplastic urethane resin is preferable. Specifically, nylon, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polyether sulfone and the like can be used.

At least one non-woven fabric and at least two thermoplastic resin sheets as matrix members are alternately laminated. Preferably, both sides of the nonwoven fabric are sandwiched so as to be covered with a thermoplastic resin sheet. That is, the thermoplastic resin sheets n + 1 are alternately laminated on the n non-woven fabrics. The thickness of the thermoplastic resin sheet can be appropriately determined according to the texture of the nonwoven fabric and further according to the desired mass ratio of the nonwoven fabric in the composite material and the thermoplastic resin as the matrix member. The mass ratio of the non-woven fabric to the thermoplastic resin as the matrix member is not particularly limited, but can be in the range of 10 to 1000 parts by mass of the thermoplastic resin as the matrix member with respect to 100 parts by mass of the non-woven fabric, which is preferable. Is in the range of 25 to 400 parts by mass. The ratio of the fiber to the resin is not particularly limited, but the volume content of the fiber is preferably 20 to 80%. If it is 20% or less, the mechanical properties as a composite material are low, and there is little point in applying it. If it exceeds 80%, the mechanical properties may be deteriorated.

The obtained laminate is heated to obtain a fiber-reinforced thermoplastic resin composite material. When heating, it is preferable to pressurize from both sides of the laminate. The heating temperature can be appropriately determined in consideration of the thermoplasticity (melting temperature) of the thermoplastic resin constituting the thermoplastic resin sheet. Further, the pressurizing pressure can be appropriately determined in consideration of the heating temperature and the viscosity of the thermoplastic resin at that temperature. A fiber-reinforced thermoplastic resin composite material can be produced by alternately arranging the uppermost surface of the flattened nonwoven fabric, the nonwoven fabric and the thermoplastic resin film, and heating and pressurizing them to integrate them.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are examples of the present invention, and the present invention is not intended to be limited to the examples.

Example 1-1 (in the case of recycled carbon fiber)
(1) The CFRP recovered with reference to Cited Document 2 was cut into 20 mm and then heated at an air atmosphere of 375 ° C. for 1 hour to remove most of the matrix resin. Then, it was immersed in a 0.2N sulfuric acid aqueous solution and anodized at 12 V for 3 minutes.
(2) The recovered lumpy carbon fibers were washed with water and dehydrated to obtain recovered carbon fibers having a water content of 50%. A non-woven fabric having a fiber basis weight of 360 g / m ² (moisture content 50%) was prepared according to a conventional method.
(3) An amount equivalent to a solid content of 36 g / m ² of the non-yellowing ether-based self-emulsifying polyurethane emulsion "Superflex 130" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was uniformly applied to this, and on a wire mesh. It was dried with hot air at 120 ° C. for 2 hours. After drying, it was removed from the wire mesh to obtain a plate-shaped sheet having a thickness of 0.2 mm.

(4) Seven of these sheets and eight of 0.2 mm thick polypropylene sheets P8134 manufactured by Sekisui Chemical Co., Ltd. were alternately stacked and heated to 200 ° C. with a hot press manufactured by Kawanaka Sangyo Co., Ltd. 5 After heating for 1 minute to melt the polypropylene sheet, the polypropylene sheet was held at a pressure of 6 MPa for 10 minutes. Then, the temperature was lowered to 50 ° C. while maintaining the pressure. The mold was disassembled to obtain a plate-shaped composite material having a size of 30 cm square and a thickness of 3 mm.
(5) This was cut out with a diamond cutter to prepare a test piece having the following shape, a tensile test was carried out in accordance with ^JIS7115-1986 , and the results are shown in Table 1.
<Tensile test> Described in No. 1 test piece JIS7115 ^-1986 6.1.1 (1)

Example 1-2
The lumpy carbon fibers recovered in the same manner as in (1) of Example 1-1 were washed with water and dehydrated to obtain recovered carbon fibers having a water content of 50%. To this, add an amount equivalent to the solid content of 36 g / m ² of the non-woven ether-based self-emulsifying polyurethane emulsion "Superflex 130" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Created a non-woven fabric of 360 g / m ² (moisture content 50%). Then, it was dried on a wire mesh with hot air at 120 ° C. for 2 hours. After drying, it was removed from the wire mesh to obtain a plate-shaped sheet having a thickness of 0.2 mm. A plate-like composite material was obtained from this sheet by the same procedure as in (4) of Example 1-1. A composite tensile strength almost equivalent to that of the plate-shaped composite material of Example 1-1 was obtained.

Example 2-1 (ordinary non-woven fabric manufacturing method)
(1) 360 g of continuous carbon fiber composed of 12,000 single yarns having a diameter of 7 microns was cut into a length of 20 mm and dispersed in water in which an anionic surfactant was dissolved.
(2) The dispersion liquid was filtered through a 100 cm square wire mesh to obtain a wet non-woven fabric (fiber basis weight in a dry state: 360 g / m ² ). The entire wire mesh was pressed to set the moisture content to 50%.

(3) To this, a solid content of 36 g of a non-yellowing ether-based self-emulsifying polyurethane emulsion "Superflex 130" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was uniformly applied, and dried with hot air at 120 ° C. for 2 hours. .. After drying, it was removed from the wire mesh and heat-pressed to obtain a plate-shaped non-woven fabric (thickness: 0.2 mm).

(4) Seven plate-shaped non-woven fabrics cut into 30 cm squares and eight polypropylene sheets manufactured by Sekisui Molding Industry Co., Ltd. with a thickness of 0.2 mm were stacked vertically in a metal frame, and in Example 1-1. By the same procedure as in (4), a plate-shaped composite material having a size of 30 cm square and a thickness of 3 mm was obtained.
(5) This was cut out with a diamond cutter to prepare a test piece having the same shape as in Example 1-1, and a tensile test was carried out in accordance with ^JIS7115-1986 .

Example 2-2
A non-woven ether manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was added to a dispersion liquid in which carbon fibers were dispersed in water in which an anionic surfactant was dissolved, which was obtained in the same manner as in (1) of Example 1-1. A solid content of 36 g of the self-emulsifying type polyurethane emulsion "Superflex 130" was added and filtered into a 100 cm square wire mesh to obtain a wet non-woven fabric (fiber texture in a dry state: 360 g / m ² ). The entire wire mesh was pressed to set the moisture content to 50%. This was dried with hot air at 120 ° C. for 2 hours. After drying, it was removed from the wire mesh and heat-pressed to obtain a plate-shaped non-woven fabric (thickness: 0.2 mm). A plate-shaped composite material was obtained from this nonwoven fabric sheet by the same procedure as in (4) of Example 1-1. A composite tensile strength almost equivalent to that of the plate-shaped composite material of Example 2-1 was obtained.

From Table 1 above, the tensile strength is improved by the polyurethane treatment. In particular, it was confirmed that the composite material produced from recycled carbon fiber was almost equivalent to the new carbon fiber.

The present invention is useful for effective utilization of carbon fibers recovered from carbon fiber composite materials.

Claims (6)

(A) The carbon fiber is made into a non-woven fabric together with the aqueous self-emulsifying emulsion of the thermoplastic urethane resin, or (B) the aqueous self-emulsifying emulsion of the thermoplastic urethane resin is added to the wet carbon fiber non-woven fabric to make the thermoplastic urethane. Step of obtaining carbon fiber nonwoven fabric bonded and coated with resin (1),
A step (2) in which at least one non-woven fabric obtained in the step (1) and at least one thermoplastic resin sheet as a matrix member are alternately laminated and then heated to obtain a fiber-reinforced thermoplastic resin composite material (2).
A method for manufacturing a fiber-reinforced thermoplastic resin composite material, including. The production method according to claim 1, wherein the thermoplastic urethane resin has a glass transition temperature of 40 ° C. or higher. The thermoplastic urethane resin is a non-yellowing ester-based, non-yellowing ester / ether-based, non-yellowing carbonate-based, or aromatic isocyanate-based aqueous urethane resin, and the particle size of the emulsion is 0.01 to. The production method according to claim 1 or 2, which is in the range of 0.1 μm. The production method according to any one of claims 1 to 3, wherein in the step (1), the emulsion is used in the range of 5 to 15 parts by mass in terms of solid content with respect to 100 parts by mass of carbon fiber. For some or all of the carbon fibers used in the step (1), the carbon fiber composite material is heat-treated in an oxidizing atmosphere and then anodized to separate and recover the carbon fibers from the resin component contained in the carbon fiber composite material. The obtained carbon fiber in a wet state. In (A), the wet carbon fiber is used as it is for making a non-woven fabric, and in (B), a moistened carbon fiber non-woven fabric is obtained by using the wet carbon fiber as a non-woven fabric. The manufacturing method according to any one of 1 to 4. The production method according to any one of claims 1 to 5, wherein the nonwoven fabric obtained in the step (1) has a basis weight in the range of 100 g to 2000 g / m ² .