WO2024106508A1 - Metal-coated fiber-reinforced plastic and method for producing same - Google Patents

Abstract

This method for producing a metal-coated FRP comprises: a first step in which metal particles are sprayed onto one surface of an FRP with a compressed gas by a cold spraying method, the temperature of the compressed gas is set to at least one of a temperature that is higher than the melting point of the metal particles and a temperature that is higher than the decomposition temperature of the FRP, and the temperature of the one surface of the FRP is set to a temperature which is not less than at least one of a temperature that is higher than the melting point of the metal particles and a temperature that is higher than the decomposition temperature of the FRP, so that some of reinforcing fibers are exposed in the one surface of the FRP; and a second step in which metal particles are sprayed onto the one surface of the FRP, where the reinforcing fibers are exposed, with a compressed gas by a cold spraying method, the temperature of the compressed gas is set to a temperature that is lower than the melting point of the metal particles, while being lower than the decomposition temperature of the FRP, and the temperature of the one surface of the FRP is set to a temperature that is lower than the melting point of the metal particles, while being lower than the decomposition temperature of the FRP, so that a metal coating film that is composed of the metal particles is formed on the one surface of the FRP.

Description

Metal-coated fiber-reinforced plastic and its manufacturing method

The present invention relates to a metal-coated fiber-reinforced plastic and a method for producing the same.
This application claims priority based on Japanese Patent Application No. 2022-183535, filed in Japan on November 16, 2022, the contents of which are incorporated herein by reference.

Carbon fiber reinforced plastics (CFRP) are widely used in various industrial applications, such as in the aerospace and automotive fields, due to their high strength, excellent corrosion resistance, and light weight. However, CFRP has issues with low electrical conductivity and thermal resistance. For example, low electrical conductivity in aircraft components and fuselages can cause damage from lightning strikes, posing a threat to passengers and crew during flight. Similar cases have also been reported in automobiles, etc. Therefore, "metallization," in which the surface of CFRP is coated with metal, has been considered as a method to improve the lightning resistance of CFRP.

The cold spray method, which allows for the formation of a metal coating in a solid state, is a promising method for improving the lightning resistance of CFRP because it causes minimal thermal damage to the plastic that constitutes the CFRP. To date, metallization of CFRP with metals such as tin, zinc, copper, and aluminum has been considered. Among these, tin has excellent film-forming properties due to its low melting point and softness.

When forming a metal coating made of tin by cold spraying on a CFRP substrate with a matrix of epoxy resin, a thermosetting resin, it is known that increasing the temperature of the compressed gas used to spray the tin particles from 473 K to 523 K increases the adhesive strength of the tin/CFRP interface (see, for example, Non-Patent Documents 1 and 2). However, the adhesive strength of the tin/CFRP interface evaluated by the pull-off method was a low 2.5 MPa, which was an issue.

The adhesive strength between tin and thermosetting CFRP is known to be 2.8 MPa (see, for example, Non-Patent Document 3). In other words, the challenge in CFRP metallization has been to improve the adhesive strength between metal and CFRP.

Methods have been proposed to increase the adhesive strength of a metal/CFRP interface produced by cold spraying.
For example, it is known that carbon nanotubes are added to CFRP to improve the strength of the interface between the CFRP and steel. It is known that carbon nanotubes present at the interface between the CFRP and steel improve the load transfer between the CFRP and steel, and increase the shear bond stress from 21.8 MPa to 23.8 MPa (see, for example, Non-Patent Document 4).

It is known that adding multi-walled carbon nanotubes to resin improves the adhesion strength of the Ti/CFRP interface (see, for example, Non-Patent Document 5).

It is known that silane coupling treatment of the Ti surface improves the adhesion of the Ti/CFRP interface in friction stir welding through the formation of chemical bonds with hydroxyl groups in a condensation reaction (see, for example, Non-Patent Document 6). However, the use of additives and surface treatments incurs additional costs, making them undesirable from an industrial perspective.

Sun J, Zhou S, Yamanaka K, Ichikawa Y, Saito H, Ogawa K, et al. Thermal Effects in Sn Coating on a Carbon Fiber Reinforced Plastic by Cold Spraying. Journal of Thermal Spray Technology 2021;30:1254-1261. Sun J, Yamanaka K, Zhou S, Saito H, Ichikawa Y, Ogawa K, et al. Adhesion mechanism of Sn coatings on the carbon fiber reinforced plastics using cold spray technique. Applied Surface Science 2022;579:151873. Che H, Vo P, Yue S. Metallization of carbon fiber reinforced polymers by cold spray. Surface and Coatings Technology 2017;313:236-47. Korayem AH, Li CY, Zhang QH, Zhao XL, Duan WH. Effect of carbon nanotube modified epoxy adhesive on CFRP-to-steel interface. Composites Part B: Engineering 2015;79:95-104. Jin K, Wang H, Tao J, Zhang X. Interface strengthening mechanisms of Ti/CFRP fiber metal laminate after adding MWCNTs to resin matrix. Composites Part B: Engineering 2019;171:254-63. Choi JW, Morisada Y, Liu H, Ushioda K, Fujii H, Nagatsuka K, et al. Dissimilar friction stir welding of pure Ti and carbon fiber reinforced plastic. Science and Technology of Welding and Joining 2020;25:600-608.

The present invention was made in consideration of the above circumstances, and aims to provide a metal-coated fiber-reinforced plastic that has excellent adhesion between the fiber-reinforced plastic and the metal coating, and a method for producing the same.

The present invention has the following aspects.
[1] A first step of spraying metal particles onto one side of a fiber-reinforced plastic with compressed gas by a cold spray method, in which the temperature of the compressed gas is set to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber-reinforced plastic, thereby raising the temperature of one side of the fiber-reinforced plastic to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber-reinforced plastic, thereby exposing a portion of the reinforcing fibers contained in the fiber-reinforced plastic to one side of the fiber-reinforced plastic;
a second step of spraying metal particles using a compressed gas by a cold spray method onto one side of the fiber-reinforced plastic where the reinforcing fibers are exposed, wherein the temperature of the compressed gas is set to a temperature lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber-reinforced plastic, thereby setting the temperature of one side of the fiber-reinforced plastic to a temperature lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber-reinforced plastic, thereby forming a metal coating made of the metal particles on one side of the fiber-reinforced plastic.
[2] The method for producing a metal-coated fiber-reinforced plastic according to [1], wherein in the first step, the arithmetic mean height (Sa) of one surface of the fiber-reinforced plastic is set to 20 μm or more and 40 μm or less.
[3] A metal-coated fiber-reinforced plastic comprising a fiber-reinforced plastic containing reinforcing fibers and a metal coating formed on one surface of the fiber-reinforced plastic,
A metal-coated fiber-reinforced plastic, wherein the reinforcing fibers protrude toward the metal coating at the interface between the fiber-reinforced plastic and the metal coating.
[4] The metal-coated fiber-reinforced plastic according to [3], wherein the arithmetic mean height (Sa) of one surface of the fiber-reinforced plastic is 20 μm or more and 40 μm or less.

The present invention provides a metal-coated fiber-reinforced plastic that has excellent adhesion between the fiber-reinforced plastic and the metal coating, and a method for producing the same.

1 is a cross-sectional view in the thickness direction of a metal-coated fiber-reinforced plastic showing a schematic configuration of the metal-coated fiber-reinforced plastic according to one embodiment of the present invention. FIG. 1 is a digital microscope image showing the observation result of the surface of a test piece in Comparative Example 1, in which a tin coating was produced on a CFRP substrate in a single-step process with the temperature of compressed air in a gas chamber set to 473 K. 1 is a digital microscope image showing the observation result of the surface of a test piece in Comparative Example 1, in which a tin coating was produced on a CFRP substrate in a single-step process with the temperature of compressed air in a gas chamber set to 523 K. FIG. 13 is a field emission scanning electron microscope image showing the observation result of a cross section in the thickness direction of a test piece in Comparative Example 1, in which a tin coating was produced on a CFRP substrate in a single-step process with the temperature of compressed air in a gas chamber set to 473 K. FIG. 13 is a field emission scanning electron microscope image showing the observation result of a cross section in the thickness direction of a test piece in Comparative Example 1, in which a tin coating was produced on a CFRP substrate in a single-step process with the temperature of compressed air in a gas chamber set to 523 K. 1 is a digital microscope image showing the observation result of the surface of a test piece in Example 1, in which a tin coating was produced on a CFRP substrate by performing one pass in the first step of the two-step process. 1 is a digital microscope image showing the observation result of the surface of a test piece in Example 1, in which a tin coating was produced on a CFRP substrate by performing two passes in the first step of the two-step process. 1 is a digital microscope image showing the observation result of the surface of a test piece in Example 1, in which a tin coating was produced on a CFRP substrate by performing three passes in the first step of the two-step process. 1 is a digital microscope image showing the observation result of the surface of a test piece in Example 1, in which a tin coating was produced on a CFRP substrate by performing four passes in the first step of the two-stage process. 1 is a digital microscope image showing the surface morphology of a CFRP substrate after the first step of a two-step process in Example 1, where the number of passes in the first step is one. 1 is a digital microscope image showing the surface morphology of a CFRP substrate after the first step of a two-step process in Example 1, where the number of passes in the first step is three. FIG. 1 is a diagram showing the relationship between the number of passes in the first step of the two-step process and the arithmetic mean height (Sa) of the surface of the CFRP substrate in Example 1. 1 is a digital microscope image showing a tin/CFRP interface in Example 1. 1 is a scanning electron microscope image showing the surface of the tin coating after a pull-off test in Example 1. 1 is a scanning electron microscope image showing the surface of the tin coating after a pull-off test in Example 1. 1 is a scanning electron microscope image showing the surface of the tin coating after a pull-off test in Example 1. FIG. 1 is a diagram showing the evaluation results of adhesive strength by a pull-off test for the test pieces of Example 1 and Comparative Example 1. 1 is a scanning electron microscope image of the water-atomized tin powder raw material in Experimental Example 1. FIG. 1 is a graph showing the particle size distribution of water-atomized tin powder raw material in Experimental Example 2. 1 is a scanning electron microscope image of a cross section of a CFRP substrate in Experimental Example 3. 13 is a scanning electron microscope image of the surface of a CFRP substrate observed in Experimental Example 4 when the temperature of compressed air in the gas chamber was set to 473 K. FIG. 22 is an enlarged view of FIG. 21. 13 is a scanning electron microscope image of the surface of a CFRP substrate observed in Experimental Example 4 when the temperature of compressed air in the gas chamber was set to 523 K. FIG. 24 is an enlarged view of FIG. 23. 13 is a scanning electron microscope image of the surface of a CFRP substrate observed in Experimental Example 4 when the temperature of compressed air in the gas chamber was set to 573 K. FIG. 25 is an enlarged view of FIG. 13 is a scanning electron microscope image of the surface of a CFRP substrate observed in Experimental Example 4 when the temperature of compressed air in the gas chamber was set to 623 K. FIG. 27 is an enlarged view of FIG. FIG. 13 is a diagram showing the measurement results of the surface roughness of a CFRP substrate in Experimental Example 5. 13 is a scanning electron microscope image of a cross section of a CFRP substrate on which a tin coating was formed in Experimental Example 6, where the temperature of compressed air in the gas chamber was set to 473 K. 13 is a scanning electron microscope image of a cross section of a CFRP substrate on which a tin coating was formed in Experimental Example 6, where the temperature of compressed air in the gas chamber was set to 523 K. 13 is a scanning electron microscope image of a cross section of a CFRP substrate on which a tin coating was formed in Experimental Example 6, where the temperature of compressed air in the gas chamber was set to 573 K. 13 is a scanning electron microscope image of a cross section of a CFRP substrate on which a tin coating was formed in Experimental Example 6, where the temperature of compressed air in the gas chamber was set to 623 K. FIG. 13 is a diagram showing the results of measuring the thickness of a tin coating on a CFRP substrate in Experimental Example 7. FIG. 13 is a diagram showing the results of measuring the erosion depth of a CFRP substrate in Experimental Example 7. FIG. 13 is a schematic diagram showing a method for analyzing a region on the surface of a CFRP substrate that is affected by heat in Experimental Example 8. FIG. 13 is a diagram showing the results of measuring the surface temperature of a CFRP substrate when a tin coating is formed by a low-pressure cold spray method in Experimental Example 8. FIG. 13 is a diagram showing the transition of the maximum surface temperature of the CFRP substrate from the start to the end (about 80 seconds) of formation of a tin coating at each compressed air temperature in the gas chamber in Experimental Example 9. FIG. 13 is a diagram showing the transition of the maximum temperature change rate on the surface of the CFRP substrate from the start to the end (approximately 80 seconds) of formation of a tin coating at each compressed air temperature in the gas chamber in Experimental Example 9. 13 is a graph showing the film-forming efficiency of tin particles on the surface of a CFRP substrate and the adhesion strength of a tin coating on the surface of a CFRP substrate in Experimental Example 10.

Hereinafter, a metal-coated fiber-reinforced plastic and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings used in the following description show characteristic parts in an enlarged scale for convenience, and the dimensional ratios of each component may differ from the actual ones.
Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them, and can be modified as appropriate within the scope that does not change the gist of the invention.

[Metal-coated fiber-reinforced plastic]
FIG. 1 shows a schematic configuration of a metal-coated fiber-reinforced plastic according to one embodiment of the present invention, and is a cross-sectional view in the thickness direction of the metal-coated fiber-reinforced plastic.
As shown in FIG. 1 , a metal-coated fiber-reinforced plastic 1 includes a fiber-reinforced plastic 10 and a metal coating 20 formed on one surface 10 a of the fiber-reinforced plastic 10 .
The thickness of the metal-coated fiber reinforced plastic 1 may be set to an appropriate value depending on the application, etc., but is usually 30 μm or more and 200 μm or less, and preferably 50 μm or more and 100 μm or less.

Fiber reinforced plastic (hereinafter sometimes abbreviated as “FRP”) 10 includes a matrix resin 11 and reinforcing fibers 12 contained within the matrix resin 11 .
In the metal-coated fiber-reinforced plastic 1 of this embodiment, the reinforcing fibers 12 protrude toward the metal coating 20 at the interface between the fiber-reinforced plastic 10 and the metal coating 20 , in other words, at one surface 10 a of the fiber-reinforced plastic 10 .
The amount of fibers contained in the fiber reinforced plastic 10 is not particularly limited, but the fiber volume content is preferably 30 volume % or more and 70 volume % or less.

The arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is preferably 20 μm or more and 40 μm or less. If the arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is equal to or more than the lower limit, the adhesive strength at the interface between the fiber reinforced plastic 10 and the metal coating 20 is improved due to the anchor effect of the reinforcing fibers 12. If the arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is equal to or less than the upper limit, the metal coating 20 adheres to the reinforcing fibers 12 protruding toward the metal coating 20.

The arithmetic mean height (Sa) of one surface 10a of the fiber-reinforced plastic 10 can be measured using a method that complies with ISO 25178.

At the interface between the fiber-reinforced plastic 10 and the metal coating 20, the exposure rate of the reinforcing fibers 12 is preferably 90% or more, more preferably 95% or more, and particularly preferably 100%. When the exposure rate of the reinforcing fibers 12 is equal to or greater than the lower limit, the anchor effect of the reinforcing fibers 12 improves the adhesion strength at the interface between the fiber-reinforced plastic 10 and the metal coating 20.

The exposure rate of the reinforcing fibers 12 at the interface between the fiber-reinforced plastic 10 and the metal coating 20 refers to the area of the reinforcing fibers 12 that are not covered by the matrix resin 11 and are exposed relative to the total area of the surface (excluding the area of the portion not forming the metal coating 20) when the interface is viewed in a plan view from the metal coating 20 side.

"Matrix resin"
The matrix resin 11 is not particularly limited as long as it is a resin generally used in fiber-reinforced plastics, and examples thereof include epoxy resin, unsaturated polyester, vinyl ester, phenol, cyanate ester, polyimide, polyamide, polycarbonate, polyphenylene sulfide, polyether ether ketone, etc.

"Reinforced fiber"
The reinforcing fibers 12 are not particularly limited as long as they are fibers generally used in fiber-reinforced plastics, and examples thereof include carbon fibers and glass fibers.

The thickness (outer diameter) of the reinforcing fiber 12 is not particularly limited, but for example, if the reinforcing fiber 12 is carbon fiber, it is 5 μm to 10 μm, and if the reinforcing fiber 12 is glass fiber, it is 5 μm to 35 μm.

"Metal coating"
The metal constituting the metal coating 20 is not particularly limited as long as it can improve the electrical conductivity and lightning resistance of the fiber reinforced plastic 10, and examples of the metal include tin (Sn), zinc (Zn), copper (Cu), aluminum (Al), etc. Among these, tin is preferable from the viewpoint of film-forming properties and thermal effects on the fiber reinforced plastic 10.

The thickness of the metal coating 20 is not particularly limited, and can be thicker than 3 mm, but is preferably 10 μm to 3000 μm, and more preferably 10 μm to 300 μm. When the thickness of the metal coating 20 is equal to or greater than the lower limit, the metal coating 20 becomes a uniform and dense film. When the thickness of the metal coating 20 is less than the lower limit, the metal coating 20 becomes non-uniform, making it difficult to completely cover one surface 10a of the fiber reinforced plastic 10 with the metal coating 20. When the thickness of the metal coating 20 is equal to or less than the upper limit, no residual stress (internal stress) is generated in the metal coating 20, and peeling of the metal coating 20 from the fiber reinforced plastic 10 can be suppressed.

The metal coating 20 does not have to be provided continuously over the entire surface of one surface 10a of the fiber reinforced plastic 10, and may be provided intermittently.
The coverage of the metal coating 20 on the surface 10a is preferably 90% or more, and more preferably 100%.

The coverage rate of the metal coating 20 refers to the area that the metal coating 20 occupies on one surface 10a of the fiber reinforced plastic 10 relative to the total area of the outermost surface 1a of the metal coated fiber reinforced plastic 1 when the metal coated fiber reinforced plastic 1 is viewed in plan from the metal coating 20 side.

The coverage of the metal coating 20 can be measured by image analysis using a microscope.

The metal-coated fiber-reinforced plastic 1 of this embodiment has excellent adhesion between the fiber-reinforced plastic 10 and the metal coating 20. In addition, the metal-coated fiber-reinforced plastic 1 of this embodiment has excellent electrical conductivity and lightning resistance.

[Metal-coated fiber-reinforced plastic manufacturing method]
A manufacturing method of a metal-coated fiber reinforced plastic according to one embodiment of the present invention includes a first step of spraying metal particles with compressed gas by a cold spray method onto one side of a fiber reinforced plastic, wherein the temperature of the compressed gas is set to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber reinforced plastic, thereby setting the temperature of one side of the fiber reinforced plastic to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber reinforced plastic, thereby exposing a portion of the reinforcing fibers contained in the fiber reinforced plastic to one side of the fiber reinforced plastic; and a second step of spraying metal particles with compressed gas by a cold spray method onto one side of the fiber reinforced plastic from which the reinforcing fibers are exposed, wherein the temperature of the compressed gas is set to a temperature lower than the melting point of the metal particles and a temperature lower than the decomposition temperature of the fiber reinforced plastic, thereby setting the temperature of one side of the fiber reinforced plastic to a temperature lower than the melting point of the metal particles and a temperature lower than the decomposition temperature of the fiber reinforced plastic, thereby forming a metal coating composed of the metal particles on one side of the fiber reinforced plastic. However, the temperature of the compressed gas in the second step is lower than the temperature of the compressed gas in the first step. The decomposition temperature of a fiber-reinforced plastic refers to the temperature at which the molecular structure of the resin contained in the fiber-reinforced plastic is destroyed and decomposition occurs when the resin is heated to a temperature higher than this temperature.
The cold spray method is a method in which powder is sprayed in a solid state using a supersonic flow to collide with an object to be coated, forming a coating.

The manufacturing method for metal-coated fiber-reinforced plastic according to this embodiment will be explained using FIG. 1.

"First step"
In the first step, metal particles are sprayed with compressed gas by a cold spray method onto one surface 10a of the fiber-reinforced plastic 10. As a result, a part of the reinforcing fibers 12 contained in the fiber-reinforced plastic 10 is exposed on the one surface 10a of the fiber-reinforced plastic 10.

In the first step, the temperature of the compressed gas is set to a temperature higher than the melting point of the metal particles to be sprayed onto the fiber reinforced plastic 10 and a temperature higher than the decomposition temperature of the fiber reinforced plastic 10. When the temperature of the compressed gas is at least one of the temperatures higher than the melting point of the metal particles and the decomposition temperature of the fiber reinforced plastic 10, when the metal particles are sprayed onto one surface 10a of the fiber reinforced plastic 10, the temperature of the one surface 10a of the fiber reinforced plastic 10 becomes equal to or lower than the temperature of the compressed gas, and the one surface 10a of the fiber reinforced plastic 10 is scraped (erosion), and the reinforcing fibers 12 can be exposed from the matrix resin 11. Note that erosion refers to the scraping and disappearance of the matrix resin 11 due to the temperature of the fiber reinforced plastic 10 becoming higher than the decomposition temperature. In addition, in the first step, the matrix resin 11 may or may not be melted. Furthermore, in the first step, the higher the temperature, the faster the processing by erosion.
The temperature of the compressed gas is either or both of a temperature higher than the melting point of the metal particles sprayed onto the fiber reinforced plastic 10 and a temperature higher than the decomposition temperature of the fiber reinforced plastic 10. Thereby, the temperature of the one surface 10a of the fiber reinforced plastic 10 is made equal to or lower than the temperature of the compressed gas.
The temperature of the compressed gas being either or both of a temperature higher than the melting point of the metal particles sprayed onto fiber reinforced plastic 10 and a temperature higher than the decomposition temperature of fiber reinforced plastic 10 specifically means that the temperature of the compressed gas is either or both of a temperature that is 10°C or more and 100°C or less higher than the melting point of the metal particles and a temperature that is 10°C or more and 200°C or less higher than the decomposition temperature of fiber reinforced plastic 10.
The temperature of one side 10a of fiber reinforced plastic 10 being equal to or higher than either one or both of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber reinforced plastic specifically means that the temperature of one side 10a of fiber reinforced plastic 10 is equal to or higher than either one or both of a temperature that is 10°C to 200°C higher than the melting point of the metal particles and a temperature that is 10°C to 150°C higher than the decomposition temperature of the fiber reinforced plastic.

The pressure of the compressed gas in the first step is not particularly limited, but is preferably 0.2 MPa or more and 1.0 MPa or less, and more preferably 0.2 MPa or more and 0.6 MPa or less. If the pressure of the compressed gas is equal to or more than the lower limit, the surface 10a of the fiber reinforced plastic 10 will be scraped when the metal particles are sprayed onto the surface 10a of the fiber reinforced plastic 10. If the pressure of the compressed gas is equal to or less than the upper limit, damage to the reinforcing fibers 12 can be suppressed when the metal particles are sprayed onto the surface 10a of the fiber reinforced plastic 10.

Compressed gases include, for example, compressed air, nitrogen, helium, etc.

The metal particles are particles of metal that make up the metal coating 20. The average particle size of the metal particles is not particularly limited, but is, for example, 1 μm or more and 100 μm or less. If the average particle size of the metal particles is within the above range, a dense metal coating 20 can be formed. Note that in the first step, a small amount of metal particles may accumulate on one surface 10a of the fiber reinforced plastic 10, but this does not result in the formation of a uniform metal coating 20.

In the first step, it is preferable that the arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is set to 20 μm or more and 40 μm or less by exposing the reinforcing fibers 12 from the matrix resin 11. When the arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is equal to or more than the lower limit, the adhesive strength at the interface between the fiber reinforced plastic 10 and the metal coating 20 is improved due to the anchor effect of the reinforcing fibers 12. When the arithmetic mean height (Sa) of one surface 10a of the fiber reinforced plastic 10 is equal to or less than the upper limit, the metal coating 20 adheres to the reinforcing fibers 12 protruding toward the metal coating 20 side.
The arithmetic mean height (Sa) can be adjusted by the conditions of the first step, for example, by adjusting the number of passes in the cold spray method. Here, the "number of passes" refers to the number of times that the fiber reinforced plastic 10 passes through a nozzle that sprays compressed gas in the cold spray method. The optimal number of passes also depends on various conditions such as the pressure of the compressed gas.

"The Second Step"
In the second step, metal particles are sprayed by a cold spray method using compressed gas onto one surface 11a of the matrix resin 11 where the reinforcing fibers 12 are exposed, in other words, onto one surface 10a of the fiber reinforced plastic 10. As a result, a metal coating 20 made of the metal particles is formed on one surface 10a of the fiber reinforced plastic 10.

In the second step, the temperature of the compressed gas is set to a temperature lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber reinforced plastic 10, so that the temperature of one side 10a of the fiber reinforced plastic 10 is lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber reinforced plastic 10, and the metal particles can be deposited on one side 10a of the fiber reinforced plastic 10 to form a uniform metal coating 20.
The temperature of the compressed gas being lower than the melting point of the metal particles and lower than the decomposition temperature of fiber reinforced plastic 10 specifically means that the temperature of the compressed gas is 10°C to 150°C lower than the melting point of the metal particles and 50°C to 400°C lower than the decomposition temperature of fiber reinforced plastic 10.
The temperature of one side 10a of fiber reinforced plastic 10 being lower than the melting point of the metal particles and lower than the decomposition temperature of fiber reinforced plastic 10 specifically means that the temperature of one side 10a of fiber reinforced plastic 10 is a temperature that is 10°C or more and 150°C or less lower than the melting point of the metal particles and a temperature that is 10°C or more and 400°C or less lower than the decomposition temperature of fiber reinforced plastic 10.

The pressure of the compressed gas in the second step is not particularly limited, but is preferably 0.2 MPa or more and 1.0 MPa or less, and more preferably 0.2 MPa or more and 0.6 MPa or less. If the pressure of the compressed gas is equal to or more than the lower limit, when the metal particles are sprayed onto one surface 10a of the fiber reinforced plastic 10, the metal particles can be deposited on the one surface 10a of the fiber reinforced plastic 10 to form a uniform metal coating 20. If the pressure of the compressed gas is equal to or less than the upper limit, damage to the reinforcing fibers 12 can be suppressed when the metal particles are sprayed onto one surface 10a of the fiber reinforced plastic 10.

In addition, the deposition efficiency (DE) of the metal particles on one surface 10a of the fiber reinforced plastic 10 is preferably 60% or more, and more preferably 80% or more. The deposition efficiency of the metal particles is the ratio of the mass of tin particles attached to one surface 10a of the fiber reinforced plastic 10 to the mass of tin particles sprayed onto one surface 10a of the fiber reinforced plastic 10. A higher deposition efficiency of the metal particles is industrially preferable, and the adhesion strength at the interface between the fiber reinforced plastic 10 and the metal coating 20 can be further improved.

The manufacturing method for metal-coated fiber-reinforced plastic of this embodiment produces a metal-coated fiber-reinforced plastic 1 that has excellent adhesion between the fiber-reinforced plastic 10 and the metal coating 20. Furthermore, the manufacturing method for metal-coated fiber-reinforced plastic of this embodiment produces a metal-coated fiber-reinforced plastic 1 that has excellent electrical conductivity and lightning resistance.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Example 1]
"Preparation of test specimens"
Water-atomized Sn powder (Sn-AtW-250) manufactured by Fukuda Metal Foil and Powder Co., Ltd. was used as the raw material. The average diameter (median diameter, D50) of the raw material powder measured using a laser light scattering diffraction particle size distribution analyzer (LS230, Beckman Coulter) was 24.28 μm. The CFRP substrate used was manufactured by JAMCO Corporation, and contains carbon fiber and an epoxy resin, which is a thermosetting resin, as the matrix. The CFRP substrate (30 mm x 30 mm x 2 mm) was cured and was made by stacking a total of 52 layers of CF laminates, each layer rotated 90 degrees. Each CFRP substrate was degreased with acetone before the cold spray experiment described below. The decomposition temperature of the CFRP substrate is 553 K.

Cold spray experiments were performed using a low-pressure cold spray device (Dymet 423J) manufactured by Obninsk Center for Powder Spraying. In the cold spray experiments, compressed air was heated in a chamber and water-atomized Sn powder was sprayed onto the CFRP substrate through a Laval nozzle.
In the above-mentioned method for manufacturing metal-coated fiber reinforced plastic, in the first step, the temperature of the compressed air was set to 623 K in order to modify one side of the CFRP substrate. In the second step, the temperature of the compressed air was set to 523 K to obtain a test piece having a uniform metal coating (tin coating) made of tin formed on one side of the CFRP substrate. Note that the temperature of the compressed air in this example and the following examples, comparative examples, and experimental examples is the temperature of the compressed air in the chamber.

In order to optimize the process, the number of passes in the first step was changed to evaluate the effect of the degree of erosion on the CFRP surface and the adhesion strength of the Sn/CFRP interface after the second step. The process conditions are shown in Tables 1 and 2. The processing conditions investigated are summarized in Tables 1 and 2. For comparison, test specimens were also prepared in a single step.

"Evaluation of the surface profile of tin coatings"
The surface profile of the tin coating was evaluated using a digital microscope (VHX-5000) manufactured by Keyence Corporation.

"Cross-sectional observation of test piece"
Cross-sectional observation of the test piece was carried out using a field emission scanning electron microscope (S-3400N) manufactured by Hitachi High-Tech Corp. The cross-sectional observation sample was polished with emery paper (#200-2000) and then mirror-finished with a colloidal silica suspension (OP-U) manufactured by Struers.

"Measurement of surface roughness of test piece"
The surface roughness of the CFRP substrate after the first step was evaluated using a digital microscope (VHX-5000) manufactured by Keyence Corporation, and the arithmetic mean height (Sa) of the surface of the test piece was calculated.

"Measurement of adhesion strength between tin film and CFRP substrate"
The adhesion strength between the tin coating and the CFRP substrate was evaluated by a pull-off test based on the ASTM D4541 standard. In this Example 1, a pull-off adhesion tester (Elcometer 106) manufactured by Elcometer Instruments was used. First, a dolly with a diameter of 20 mm was attached to the surface of the tin coating with an adhesive, and then the tin coating was pulled out vertically to measure the adhesion strength. For the pull-off test, a sample polished to a thickness of about 4 mm including the CFRP substrate and the tin coating was used, and polishing was performed so that the surface roughness (Sa) of the tin coating was 20±2.5 μm. The surface morphology of the tin coating and the CFRP substrate side after the pull-off test was observed using a field emission scanning electron microscope (S-3400N) manufactured by Hitachi High-Tech Corporation.

"Evaluation results"
FIG. 2 shows the observation result of the surface of a test piece when a tin coating is formed on a CFRP substrate by a single-step process with a compressed air temperature of 473K. FIG. 3 shows the observation result of the surface of a test piece when a tin coating is formed on a CFRP substrate by a single-step process with a compressed air temperature of 523K. FIG. 4 shows the observation result of a cross section in the thickness direction of a test piece when a tin coating is formed on a CFRP substrate by a single-step process with a compressed air temperature of 473K. FIG. 5 shows the observation result of a cross section in the thickness direction of a test piece when a tin coating is formed on a CFRP substrate by a single-step process with a compressed air temperature of 523K. In FIG. 4 and FIG. 5, "CF" refers to carbon fiber. The same applies to the following figures.

The results shown in Figures 2 to 5 confirm that a uniform tin coating was formed on the CFRP substrate regardless of whether the compressed air temperature was 473K or 523K. Furthermore, when the compressed air temperature was 473K, a clear tin/CFRP substrate interface was observed. On the other hand, when the compressed air temperature was 523K, the CFRP substrate was slightly eroded, resulting in a more complex tin/CFRP substrate interface morphology involving direct contact between the carbon fiber (CF) and the tin.

Figure 6 shows the observation results of the surface of a test piece when a tin coating was produced on a CFRP substrate with one pass in the first step of the two-step process. Figure 7 shows the observation results of the surface of a test piece when a tin coating was produced on a CFRP substrate with two passes in the first step of the two-step process. Figure 8 shows the observation results of the surface of a test piece when a tin coating was produced on a CFRP substrate with three passes in the first step of the two-step process. Figure 9 shows the observation results of the surface of a test piece when a tin coating was produced on a CFRP substrate with four passes in the first step of the two-step process.

The results shown in Figures 6 to 9 confirm that, in the test specimens produced by the two-step process, a uniform tin coating was formed on the CFRP substrate, similar to the test specimens produced by the single-step process. Note that the deposits on the edges of the tin coating of the test specimens produced with three and four passes of the first step were formed in the first step. These were removed by polishing before the pull-off test described below.

Figure 10 shows the surface morphology of the CFRP substrate after the first step of the two-step process when the number of passes for the first step is one. Figure 11 shows the surface morphology of the CFRP substrate after the first step of the two-step process when the number of passes for the first step is three.

In the first step, where the compressed air temperature was set to 623K, erosion occurred, removing the epoxy resin on the surface of the CFRP substrate and exposing the carbon fibers. Erosion was observed to become more pronounced as the number of passes in the first step increased, and after the first step was performed three times, the carbon fiber exposure rate increased. It was also observed that molten tin was partially attached to the exposed carbon fibers.

Figure 12 shows the arithmetic mean height (Sa) of the surface of the CFRP substrate after the first step. The results shown in Figure 12 show that compared to the arithmetic mean height (Sa = 17.9 ± 1.2 μm) of the surface of the CFRP substrate before the cold spray experiment, the arithmetic mean height (Sa) of the surface of the CFRP substrate after the first step has increased, and that the arithmetic mean height (Sa) increases with an increase in the number of passes.

Figure 13 shows a digital microscope image of the tin/CFRP interface. From the results shown in Figure 13, it was observed that the carbon fibers are present protruding from inside the tin coating. The carbon fibers thus present inside the tin coating function as anchors that suppress delamination.

Figures 14 to 16 show scanning electron microscope images of the surface of the tin coating after the pull-off test for the test piece of Example 1. The results shown in Figures 14 and 15 suggest that the tin coating on the surface was deformed when the carbon fibers present inside the tin coating were pulled out by external force. In Figure 15, "Extracted CF" refers to the carbon fibers pulled out in this manner. Furthermore, the results shown in Figure 16 show that some of the carbon fibers remain on the surface of the tin coating. In Figure 16, "Lifted Sn" refers to the tin coating being lifted and deformed when the carbon fibers present inside the tin coating were pulled out by external force.

In this carbon fiber pulling process, frictional resistance occurs at the tin/CFRP interface. Furthermore, under external force, the tin lifted by the carbon fiber exhibits plastic deformation of the tin coating. This provides resistance to the interfacial peeling that occurs during the pull-off test, demonstrating an anchor effect via the carbon fiber at the tin/CFRP interface.

Figure 17 shows the results of the evaluation of adhesion strength by pull-off test for the test pieces of Example 1 and Comparative Example 1. From the results shown in Figure 17, it can be seen that in the test pieces produced by the single-step process, the adhesion strength increased as the temperature of the compressed air increased from 473 K to 523 K, but the adhesion strength was still around 2 MPa.

On the other hand, the test pieces produced by the two-step process had significantly improved adhesion strength compared to the test pieces produced by the single-step process. As the number of passes in the first step increased, the final adhesion strength gradually increased, and the adhesion strength of the test piece with three passes in the first step was 6.25 MPa, more than twice the adhesion strength of the test piece produced by the single-step process. Furthermore, the adhesion strength of the test piece with four passes in the first step was equivalent to that of the three passes.

The surface roughness of the CFRP substrate after the first step increases with the number of passes in the first step, as erosion becomes more severe, and the arithmetic mean height (Sa) increases. However, it was determined that the optimal condition for the first step is three passes, with the threshold arithmetic mean height (Sa) being approximately 40 μm.

When the first step was performed three times, two carbon fibers with different fiber directions were exposed. Therefore, when improving adhesion using a two-step process, the first step only exposes the carbon fibers, making it possible to improve adhesion strength while minimizing damage to the CFRP substrate. The reason for this is thought to be that when the arithmetic mean height (Sa) of the surface of the CFRP substrate exceeds 40 μm, the tin sprayed together with the compressed air cannot adhere sufficiently to the complex shape of the surface of the CFRP substrate.

[Experimental Example 1]
A water atomized tin powder raw material (Sn-AtW-250, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) was prepared. The water atomized tin powder raw material was observed with a scanning electron microscope (JCM-6000, manufactured by JEOL Ltd.). The scanning electron microscope image is shown in FIG. 18. From the results shown in FIG. 18, it was found that the shape of the water atomized tin powder raw material was irregular.

[Experimental Example 2]
The particle size distribution of the water atomized tin powder raw material was measured using a laser light scattering diffraction particle size distribution analyzer (LS230, manufactured by Beckman Coulter, Inc.). The results are shown in Figure 19. From the results shown in Figure 19, it was found that the average particle size of the water atomized tin powder raw material was 24.28 μm.

[Experimental Example 3]
A CFRP substrate (manufactured by JAMCO Corporation) measuring 30 mm x 30 mm x 2 mm was prepared.
52 CFRP substrates were stacked, and the stack was surrounded by a prepreg thermosetting epoxy resin composed of carbon fiber laminate, and thermally cured. The obtained cured product was pressurized in the thickness direction at a pressure of 0.3 MPa and a temperature of 423 K for 1 hour. The cured product was then cooled to room temperature (299.15 K). The cross section of the obtained cured product (CFRP substrate) was observed with a scanning electron microscope (JCM-6000, manufactured by JEOL Ltd.). The scanning electron microscope image is shown in FIG. 20. As shown in FIG. 20, the obtained CFRP substrates were adjacent to each other, and the direction of the carbon fibers of one CFRP substrate was almost perpendicular to the direction of the carbon fibers (CF direction) of the other CFRP substrate.

[Experimental Example 4]
"Formation of tin film"
A tin coating made of tin particles was formed on a CFRP substrate by the following method.
The tin coating was formed using a low pressure cold spray system (Dymet 423J, Obninsk Centre for Powder Spraying, Russia).
Compressed air was supplied to the CFRP substrate via a De Laval nozzle.
The CFRP substrate was placed on a stage, and a tin coating was formed on the CFRP substrate while the CFRP substrate was moved from the start to the end of the formation of the tin coating.
It was positioned in one direction along the center line of the CFRP substrate.
In forming the tin coating, the temperature of the compressed air was changed to 473K, 523K, 573K, and 623K.
Table 3 shows the conditions for forming the tin coating by the low pressure cold spray method.
The formation of the tin coating was repeated three times at the same temperature.

"Measurement of surface temperature of CFRP substrate during formation of tin coating"
The surface temperature of the CFRP substrate during the formation of the tin coating by the low-pressure cold spray method was measured using an infrared thermography camera (InfReC R300, manufactured by Nippon Avionics Co., Ltd.).
Thermal images were taken at one second intervals to measure the surface temperature of the CFRP substrate.
The measurable temperature range is 273K to 773K.
The atmospheric temperature in the place where the surface temperature of the CFRP substrate was measured was set to 298 K, and the atmospheric humidity was set to 46%.
The thermal images were obtained by detecting infrared radiation emitted from the CFRP substrate.
The amount of infrared energy emitted from the CFRP substrate is displayed as a pixel-by-pixel colored image.The temperature data was analyzed using an InfReC Analyzer NS9500 Professional (manufactured by Nippon Avionics Co., Ltd.).
When a tin coating was formed on the surface of the CFRP substrate at each temperature, the surface of the CFRP substrate was observed with a scanning electron microscope (SU-70 and S-3400N, manufactured by Hitachi High-Technologies Corporation).
The results are shown in Figures 21 to 28.

FIG. 21 is a scanning electron microscope image of the surface of a CFRP substrate when the temperature of compressed air is set to 473K. "Deposition Area" in FIG. 21 indicates the tin coating formed by cold spray. FIG. 22 is an enlarged view of FIG. 21. FIG. 23 is a scanning electron microscope image of the surface of a CFRP substrate when the temperature of compressed air is set to 523K. "Spray path" in FIG. 23 indicates the center line of the nozzle position moving relatively to the CFRP substrate. FIG. 24 is an enlarged view of FIG. 23. FIG. 25 is a scanning electron microscope image of the surface of a CFRP substrate when the temperature of compressed air is set to 573K. FIG. 26 is an enlarged view of FIG. 25. FIG. 27 is a scanning electron microscope image of the surface of a CFRP substrate when the temperature of compressed air is set to 623K. FIG. 28 is an enlarged view of FIG. 27.
As shown in FIG. 26, when the temperature of the compressed air was 573K, the carbon fibers were slightly exposed on the surface of the CFRP substrate. Also, as shown in FIG. 28, when the temperature of the compressed air was 623K, the carbon fibers were exposed on the surface of the CFRP substrate. That is, when the temperature of the compressed air was 573K or more, the temperature of the surface of the CFRP substrate could be made higher than the melting point of the tin particles and higher than the decomposition temperature of the CFRP substrate, and erosion occurred, exposing the carbon fibers on the surface of the CFRP substrate. Also, from FIG. 25 and FIG. 27, it can be seen that the tin powder that bounced off the CFRP substrate was piled up on both sides of the spray position (Bumpy deposit). In FIG. 26 and FIG. 28, "Fractured CF" indicates a state in which the carbon fibers are broken as a result of the first step.

[Experimental Example 5]
"Measurement of surface roughness of CFRP substrate"
In Experimental Example 4, the surface roughness of the CFRP substrate on which the tin coating was formed was measured.
The surface roughness of the CFRP substrate was measured using a digital microscope (VHX-5000, manufactured by Keyence Corporation).
The results are shown in Figure 29.
From the results shown in Figure 29, it was found that when the compressed air temperature was 623 K, the surface roughness of the CFRP substrate increased, erosion occurred, and the amount of carbon fiber exposed on the surface of the CFRP substrate increased.

[Experimental Example 6]
"Observation of the cross section of a CFRP substrate"
In Experimental Example 4, the cross section of the CFRP substrate on which the tin coating was formed was observed with a scanning electron microscope (SU-70 and S-3400N, manufactured by Hitachi High-Technologies Corporation).
The results are shown in Figures 30 to 33.
As shown in Fig. 32, when the temperature of the compressed air was 573 K, a small amount of carbon fiber was exposed on the surface of the CFRP substrate. Also, as shown in Fig. 33, when the temperature of the compressed air was 623 K, carbon fiber was exposed on the surface of the CFRP substrate. In other words, it was found that when the temperature of the compressed air was 573 K or higher, the surface temperature of the CFRP substrate could be made higher than the melting point of the tin particles and higher than the decomposition temperature of the CFRP substrate, causing erosion and exposing carbon fiber on the surface of the CFRP substrate.

[Experimental Example 7]
"Measurement of thickness of tin coating on CFRP substrate, measurement of erosion depth on CFRP substrate"
In Experimental Example 4, the thickness of the tin coating on the CFRP substrate on which the tin coating was formed and the erosion depth of the CFRP substrate were measured. The thickness of the tin coating was measured based on the surface of the CFRP substrate. The erosion depth of the tin coating was measured based on the surface of the CFRP substrate.
The thickness of the tin coating and the erosion depth of the CFRP substrate were measured directly from FIGS. 30 to 33 obtained in Experimental Example 6.
The results are shown in Figures 34 and 35.
From the results shown in Fig. 34, it was found that the tin film disappears when the temperature of the compressed air is 573 K or higher. It was found that when the temperature of the compressed air is 623 K, the tin film almost disappears.
From the results shown in FIG. 35, it was found that when the temperature of the compressed air was 573 K or higher, the erosion depth of the CFRP substrate increased.

[Experimental Example 8]
"Measurement of surface temperature distribution"
The CFRP substrate was fixed to a stage as shown in Fig. 36. In order to clarify the area on the surface of the CFRP substrate that would be affected by heat, two areas were identified: area a (a band-shaped area located in the center of the surface of the laminate along one direction of the surface of the laminate) and area b (two band-shaped areas located on either side of area a along one direction of the surface of the laminate).
In the same manner as in Experimental Example 4, a tin coating made of tin particles was formed on a CFRP substrate.
In forming the tin coating, the temperature of the compressed air was changed to 473K, 523K, 573K, and 623K.
The surface of the CFRP substrate after the formation of the tin coating was observed with a scanning electron microscope (SU-70 and S-3400N, manufactured by Hitachi High-Technologies Corporation).
The results showed that when the temperature of the compressed air was between 473K and 573K, region a was covered with a tin film, which was then replaced by the eroded CFRP, and when the temperature of the compressed air stream was higher, molten tin clusters were attached to the surface of the CFRP substrate.
On the other hand, epoxy resin was mainly present on the surface of region b when the compressed air temperature was 473 K to 523 K. When the compressed air temperature was 473 K to 523 K, uneven deposits of tin were present on the surface of the portion of region b adjacent to region a.
In addition, similarly to Experimental Example 4, the surface temperature of the CFRP substrate was measured during the formation of the tin coating by the low-pressure cold spray method.
The results are shown in Figure 37.
Before forming the tin coating by the low pressure cold spray method, the surface temperature of the CFRP substrate was about 308 K. Here, the emissivity of the surface of the CFRP substrate was assumed to be 0.4, which is the emissivity of carbon fiber (CF).
From the results shown in Figure 37, when the temperature of the compressed air was set to 473K or higher (523, 573, 623K), the surface temperatures of region a and region b were lower than the temperature of the compressed air, except when the temperature of the compressed air was 623K. In addition, the surface temperature of region a was almost the same as or higher than the surface temperature of region b. In addition, the difference between the surface temperatures of region a and region b gradually increased with the increase in the temperature of the compressed air. When the temperature of the compressed air was 623K, the surface temperature of the CFRP substrate finally reached about 658K. These behaviors were consistent with the temperature of the tin coating being higher than the surface temperature of the CFRP substrate.

[Experimental Example 9]
"Measurement of maximum surface temperature of CFRP substrate"
In the same manner as in Experimental Example 8, a tin coating made of tin particles was formed on a CFRP substrate.
In forming the tin coating, the temperature of the compressed air was changed to 473K, 523K, 573K, and 623K.
In the same manner as in Experimental Example 4, the surface temperature of the CFRP substrate was measured during the formation of a tin coating by the low-pressure cold spray method.
The results are shown in Figures 38 and 39.
FIG. 38 is a diagram showing the transition of the maximum value of the surface temperature of the CFRP substrate from the start to the end (about 80 seconds) of the formation of the tin film at each compressed air temperature. It is considered that the fluctuation of the surface temperature of the CFRP substrate was caused by the thermal cycle during the formation of the tin film. It was found that the higher the temperature of the compressed air, the higher the maximum value of the surface temperature of the CFRP substrate. In addition, when the temperature of the compressed air was 473K, the surface temperature of the CFRP substrate did not change significantly from the start of the formation of the tin film until 50 seconds, and was about 308K, which is the surface temperature of the CFRP substrate before the formation of the tin film. From the start of the formation of the tin film until 50 seconds, the heat accumulated during the formation of the tin film was negligible, whereas after 50 seconds from the start of the formation of the tin film, the surface temperature of the CFRP substrate rose slightly to 350K. In contrast, when the temperature of the compressed air was 523K, within 10 seconds from the start of the formation of the tin film, the surface temperature of the CFRP substrate rose rapidly and remained within a substantially constant range until the formation of the tin film was completed. It was also found that when the temperature of the compressed air was 573 K or higher, the surface temperature of the CFRP substrate was equal to or higher than the melting point of tin (505 K). Therefore, it was found that erosion occurred even when the temperature of the compressed air was 573 K.

FIG. 39 is a diagram showing the transition of the maximum value of the temperature change rate on the surface of the CFRP substrate from the start to the end (about 80 seconds) of the formation of a tin coating at each compressed air temperature.
The temperature change rate is defined as the temperature change per second and is calculated directly from FIG.
From the results shown in Fig. 39, it was found that the higher the temperature of the compressed air, the greater the temperature change rate. When the temperature of the compressed air was 573 K or higher, the temperature change rate became greater. This indicates that a significant thermal gradient was generated on the surface of the CFRP substrate due to the temperature change.

When the temperature of the compressed air was 473 K, the maximum surface temperature of the CFRP substrate was about 377 K. This temperature is lower than the glass transition temperature (Tg, about 420 K) of the epoxy resin. When the glass transition temperature is exceeded, the cured epoxy resin softens and cannot withstand the impact of the tin particles sprayed by the cold spray method.
When the temperature of the compressed air was 523 K, the maximum value of the surface temperature of the CFRP substrate was about 464 K. Therefore, the epoxy resin in the top layer of the CFRP substrate was eroded by the impact of the tin particles sprayed by the cold spray method.
When the compressed air temperature was 573K, the maximum surface temperature of the CFRP substrate was about 538K. When the compressed air temperature was 623K, the maximum surface temperature of the CFRP substrate was about 658K. When the compressed air temperature was 573K or higher, the maximum surface temperature of the CFRP substrate was much higher than the glass transition temperature of the epoxy resin. Therefore, erosion of the CFRP substrate progressed at these temperatures. In particular, when the compressed air temperature was 623K, erosion occurred continuously in multiple layers of the CFRP substrate.

[Experimental Example 10]
"Measurement of the film formation efficiency of tin particles on the surface of a CFRP substrate"
In the same manner as in Experimental Example 4, a tin coating made of tin particles was formed on a CFRP substrate.
In forming the tin coating, the temperature of the compressed air was set to 523K.
For comparison, the method described in Non-Patent Document 7 (H. Che, P. Vo, S. Yue, Metallization of carbon fiber reinforced polymers by cold spray, Surf. Coat. Technol. 313 (2017) 236-247.) and the method described in Non-Patent Document 8 (G. Archambault, B. Jodoin, S. Gaydos, M. Yandouzi, Metallization of carbon fiber reinforced polymer composite by cold spray and lay-up molding A tin coating made of tin particles was formed on a CFRP substrate by the method described in Non-Patent Document 9 (G. Archambault, B. Jodoin, S. Gaydos, M. Yandouzi, Metallization of carbon fiber reinforced polymer composite by cold spray and lay-up molding processes, Surf. Coat. Technol. 300 (2016) 78-86.).
In each example, the deposition efficiency (DE) of the tin particles on the surface of the CFRP substrate was measured. The deposition efficiency of the tin particles is the ratio of the mass of the tin particles attached to the surface of the CFRP substrate to the mass of the tin particles sprayed onto the surface of the CFRP substrate.
The adhesion strength of the tin coating to the surface of the CFRP substrate was measured by a pull-off test.
The results are shown in Figure 40. The formation of the tin coating according to the present invention was designated "Example 2", the formation of the tin coating by the method described in Non-Patent Document 7 was designated "Comparative Example 2", the formation of the tin coating by the method described in Non-Patent Document 8 was designated "Comparative Example 3", and the formation of the tin coating by the method described in Non-Patent Document 9 was designated "Comparative Example 4".
40, the deposition efficiency (DE) of the tin particles on the surface of the CFRP substrate was 80% in Example 2. The adhesion strength of the tin coating was 4.8 MPa to 6.5 MPa.
In Comparative Example 2, the efficiency of film formation of tin particles on the surface of the CFRP substrate was 10% to 20%, and the adhesion strength of the tin film was 2.5 MPa to 7.7 MPa.
In Comparative Example 3, the adhesion strength of the tin coating was 1 MPa to 1.5 MPa.
In Comparative Example 4, the adhesion strength of the tin coating was 1 MPa to 2.5 MPa.

The present invention provides a metal-coated fiber-reinforced plastic that has excellent adhesion between the fiber-reinforced plastic and the metal coating.

1 Metal-coated fiber-reinforced plastic 10 Fiber-reinforced plastic 11 Matrix resin 12 Reinforced fiber 20 Metal coating

Claims (4)

a first step of spraying metal particles onto one surface of a fiber-reinforced plastic with a compressed gas by a cold spray method, in which the temperature of the compressed gas is set to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber-reinforced plastic, thereby raising the temperature of one surface of the fiber-reinforced plastic to at least one of a temperature higher than the melting point of the metal particles and a temperature higher than the decomposition temperature of the fiber-reinforced plastic, thereby exposing a portion of the reinforcing fibers contained in the fiber-reinforced plastic to one surface of the fiber-reinforced plastic;
a second step of spraying metal particles using a compressed gas by a cold spray method onto one side of the fiber-reinforced plastic where the reinforcing fibers are exposed, wherein the temperature of the compressed gas is set to a temperature lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber-reinforced plastic, thereby setting the temperature of one side of the fiber-reinforced plastic to a temperature lower than the melting point of the metal particles and lower than the decomposition temperature of the fiber-reinforced plastic, thereby forming a metal coating made of the metal particles on one side of the fiber-reinforced plastic. The method for manufacturing metal-coated fiber-reinforced plastic according to claim 1, wherein in the first step, the arithmetic mean height (Sa) of one surface of the fiber-reinforced plastic is set to 20 μm or more and 40 μm or less. A metal-coated fiber-reinforced plastic comprising a fiber-reinforced plastic containing reinforcing fibers and a metal coating formed on one surface of the fiber-reinforced plastic,
A metal-coated fiber-reinforced plastic, wherein the reinforcing fibers protrude toward the metal coating at the interface between the fiber-reinforced plastic and the metal coating. The metal-coated fiber-reinforced plastic according to claim 3, wherein the arithmetic mean height (Sa) of one surface of the fiber-reinforced plastic is 20 μm or more and 40 μm or less.

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