Structural material for automobile and method for producing same

Abstract

Provided are: an automotive structural material that makes it possible to prevent chipping and electrolytic corrosion without using protection tape, obviates having to adjust unevenness for the purpose of painting, and moreover can be manufactured in a short time; and a method for manufacturing the automotive structural material. The present invention pertains to an automotive structural material that contains carbon-fiber-reinforced plastic, the automotive structural material having a base layer 3 composed of a cured sheet-molding compound 1 containing staple carbon fiber and a thermosetting resin, and a protective layer 4 that is laminated on the base layer 3 and is composed of a cured glass paper prepreg 2 or a glass cloth prepreg containing glass fiber and a thermosetting resin, the base layer 3 and the protective layer 4 being integrally cured.

Description

Automotive structural material and its manufacturing method

[0001] The present invention relates to a structural material for automobiles and a method for manufacturing the same.

[0002] BACKGROUND ART CFRP (Carbon Fiber Reinforced Plastic) made of SMC (Sheet Molding Compound) containing carbon fiber is sometimes used as a structural material (interior material) of an automobile.

[0003] In this case, two measures are required: A) to deal with chipping of the CFRP or micro-fractures in the carbon fibers that occur when a stone hits the CFRP component while driving (chipping prevention), and B) to deal with galvanic currents that occur when the joints between the CFRP and steel or aluminum become wet with rain or dew (electrolytic corrosion prevention).

[0004] Therefore, as disclosed in Patent Document 1, for example, a protective film (protection tape) made of a base material made of polyurethane or polyester with an acrylic adhesive applied to one side thereof may be attached to the surface of the CFRP component to achieve the above-mentioned A (countermeasures against chipping) and B (countermeasures against electrolytic corrosion).

[0005] JP 2023-80853 A

[0006] The above-mentioned protection tape is applied to the surface of a CFRP member after removing any irregularities on the surface of the CFRP member that has been heat-molded and then removing the inactive layer on the surface of the CFRP molded product by sanding or cutting.

[0007] However, applying this protection tape is troublesome, prone to wrinkling and lifting, and improper application can cause the protection tape to peel off while the vehicle is in motion. If the tape peels off, not only will it no longer function as a chipping or electrolytic corrosion protection measure, but if the tape peels off midway at the joint between the CFRP and steel or aluminum, rain and dew droplets or condensation can accumulate between the CFRP component and the tape. These droplets (liquid) act as an aqueous electrolyte solution, with the CFRP acting as the positive electrode and the steel or aluminum acting as the negative electrode, causing a galvanic current to flow and the progression of electrolytic corrosion. When electrolytic corrosion occurs, the steel or aluminum corrodes, eventually failing to function as a structural member.

[0008] As a method for implementing the above-mentioned A (countermeasures against chipping) and B (countermeasures against electrolytic corrosion) without using the above-mentioned protection tape, there is a method of forming an anti-chipping layer or an anti-electrolytic corrosion layer by painting. In this case, as with the treatment before applying the protection tape, it is necessary to eliminate unevenness on the surface of the CFRP member, remove the inactive layer on the surface of the CFRP molded product by sanding or cutting, and then fill any remaining depressions with putty to create a flat base (this is called the unevenness adjustment process), and then form the paint layers on top of that base by applying an undercoat, an intermediate coat, and a top coat.

[0009] The specific processes for applying primer, intermediate coat, and top coat are as follows: Primer: This process forms a primer layer to ensure adhesion between the CFRP surface and the substrate after unevenness adjustment, to improve corrosion resistance to alkalis and acids on the CFRP surface, and to enhance adhesion to the intermediate coat. The primer layer is 25 μm to 30 μm thick. Intermediate coat: This process forms an intermediate coat to maintain the smoothness of the primer layer, to improve impact resistance for the entire coating, and to enhance adhesion to the top coat. The intermediate coat is 40 μm to 45 μm thick (this intermediate coat mainly functions to prevent chipping). When painting or printing a color or design, this is done on top of the intermediate coat. The intermediate coat also serves the purpose of forming a smooth base for painting or printing a color or design. Top coat: This process forms a top coat to maintain gloss, provide aesthetic appeal, scratch resistance, weather resistance, and stain resistance. The thickness of the top coat layer is 40 μm to 90 μm (the undercoat layer, intermediate coat layer and top coat layer function as a countermeasure against electrolytic corrosion).

[0010] Each of the primer, intermediate, and topcoat processes involves drying and curing before proceeding to the next step. For the intermediate coat, the primer layer is sprayed with a spray gun to form a coating, which is then dried and cured. The primer layer is then sanded with #400 sandpaper to create a smooth base for the intermediate coat. Similarly, the intermediate coat is dried and cured after formation of the coating, and then sanded with #600 sandpaper to create a smooth base for the top coat. The final top coat is sanded with #1000 sandpaper to develop gloss and aesthetic appeal.

[0011] In addition, during the primer, intermediate coat, and top coat processes, the thickness of each layer of paint may be reduced and two coats applied to avoid microcracks and peeling from the lower layer due to shrinkage during drying and hardening (as cracks may occur if the paint is applied too thickly all at once).

[0012] Therefore, although it is possible to carry out the above-mentioned A (countermeasures against chipping) and B (countermeasures against electrolytic corrosion) by painting, many steps and man-hours are required before the painting is completed.

[0013] The present invention has been made in consideration of the current situation as described above, and aims to provide an unprecedented automotive structural material and a manufacturing method thereof that can prevent chipping and electrolytic corrosion without using protection tape, does not require unevenness adjustment for painting, and can be manufactured in a short time.

[0014] The gist of the present invention will be explained with reference to the accompanying drawings.

[0015] A first aspect of the present invention relates to an automotive structural material containing carbon fiber reinforced plastic, comprising: a base layer 3 made of a cured product of a sheet molding compound 1 containing short carbon fibers and a thermosetting resin; and a protective layer 4 laminated on the base layer 3 and made of a cured product of a glass paper prepreg 2 or a glass cloth prepreg containing glass fibers and a thermosetting resin, wherein the base layer 3 and the protective layer 4 are cured integrally.

[0016] A second aspect of the present invention relates to the automotive structural material of the first aspect, characterized in that the thickness of the protective layer 4 is 0.15 mm or more and 0.50 mm or less.

[0017] A third aspect of the present invention relates to the automotive structural material of the second aspect, characterized in that the breakdown voltage is 3 kV or more.

[0018] A fourth aspect of the present invention relates to the automotive structural material of the second aspect, characterized in that the breakdown voltage is 5 kV or more.

[0019] In addition, a fifth aspect of the present invention is a fabric according to any one of the first to fourth aspects, wherein the protective layer 4 has a basis weight of 50 g / m ２ The present invention relates to a structural material for automobiles, characterized by containing the above glass paper.

[0020] In a sixth aspect of the present invention, in any one of the first to fourth aspects, the protective layer 4 has a basis weight of 100 g / m ２ The present invention relates to an automobile structural material characterized by including the above glass cloth.

[0021] A seventh aspect of the present invention relates to a method for manufacturing an automotive structural material containing carbon fiber reinforced plastic, comprising: a laminating step of laminating a semi-cured sheet molding compound 1 containing short carbon fiber and a thermosetting resin with a semi-cured glass paper prepreg 2 or glass cloth prepreg containing glass fiber and a thermosetting resin; and a curing step of applying pressure and heat to the laminated sheet molding compound 1 and the glass paper prepreg 2 or the glass cloth prepreg to integrally cure them.

[0022] An eighth aspect of the present invention relates to the method for manufacturing an automotive structural material according to the seventh aspect, characterized in that the resin content of the glass paper prepreg 2 or the glass cloth prepreg is 80 wt % or more and 95 wt % or less.

[0023] The ninth aspect of the present invention relates to the method for producing an automotive structural material according to the seventh aspect, characterized in that the resin flow of the glass paper prepreg 2 or the glass cloth prepreg, as expressed by the following formula, is 50% or more and 80% or less: Resin flow (%) = Amount (g) of resin that flows out when press-molded under conditions of 150°C and 0.3 MPa / Weight (g) of the prepreg before resin flows out during press-molding

[0024] A tenth aspect of the present invention relates to the eighth aspect of the method for producing an automotive structural material, characterized in that the resin flow of the glass paper prepreg 2 or the glass cloth prepreg, as expressed by the following formula, is 50% or more and 80% or less: Resin flow (%) = Amount (g) of resin that flows out when press-molded under conditions of 150°C and 0.3 MPa / Weight (g) of the prepreg before resin flows out during press-molding

[0025] In addition, an eleventh aspect of the present invention is the glass paper prepreg 2 according to any one of the seventh to tenth aspects, wherein the glass paper prepreg 2 has a basis weight of 50 g / m ２ The present invention relates to a method for manufacturing an automobile structural material, which is characterized by including the above glass paper.

[0026] In addition, a twelfth aspect of the present invention is the glass cloth prepreg according to any one of the seventh to tenth aspects, wherein the glass cloth prepreg has a basis weight of 100 g / m ２ The present invention relates to a method for producing an automobile structural material characterized by including the above glass cloth.

[0027] Because the present invention is configured as described above, it is possible to prevent chipping and electrolytic corrosion without using protection tape, it does not require unevenness adjustment for painting, and it can be manufactured in a short time, resulting in an unprecedented automotive structural material and manufacturing method thereof.

[0028] 10 is a schematic explanatory perspective view of the present embodiment. FIG. 10 is a schematic explanatory diagram of a prepreg manufacturing apparatus (vertical coating machine). FIG. 10 is a schematic explanatory perspective view illustrating a lamination process. FIG. 10 is a schematic explanatory cross-sectional view illustrating a curing process. FIG. 10 is a graph illustrating a temperature program and a pressure program. FIG. 10 is a schematic explanatory cross-sectional view showing an example of autoclave molding. FIG. 10 is a schematic explanatory diagram of a manufacturing apparatus for SMC. FIG. 10 is a schematic explanatory perspective view of an SMC product. FIG. 10 is a schematic explanatory perspective view illustrating the fiber density of an SMC product. FIG. 10 is a schematic explanatory cross-sectional view of the main part of FIG. 9. FIG. 10 is a schematic explanatory perspective view of an SMC after molding (after curing). FIG. 10 is a schematic explanatory cross-sectional view of an SMC provided with a conventional paint layer. FIG. 10 is a schematic explanatory cross-sectional view illustrating surface cutting processing. FIG. 10 is a schematic explanatory cross-sectional view illustrating putty filling after surface cutting processing. FIG. 10 is a schematic explanatory view illustrating a cross-cut method test after impact. FIG. 10 is a schematic explanatory view illustrating a dielectric breakdown test.

[0029] A preferred embodiment of the present invention will be briefly described below, illustrating the operation of the present invention with reference to the drawings.

[0030] The protective layer 4 made of a cured product of glass paper prepreg 2 or glass cloth prepreg laminated on the base layer 3 effectively prevents the above-mentioned chipping.

[0031] Furthermore, the protective layer 4 is a glass fiber reinforced resin layer having electrical insulation properties, and the base layer 3 and the protective layer 4 are hardened integrally, so that the two adhere well to each other and the protective layer 4 is less likely to peel off or lift off (the accumulation of rain and dew drops or condensation between the base layer 3 and the protective layer 4 is suppressed), and therefore the above-mentioned electrolytic corrosion is also effectively prevented.

[0032] Furthermore, because the protective layer 4 is formed from glass paper prepreg 2 or glass cloth prepreg, which can hold a large amount of resin, any recesses in the surface of the sheet molding compound can be filled with the resin of the prepreg when it is cured integrally with the base layer 3, making the surface (the surface on the protective layer side) as flat as possible. This also makes it possible to eliminate the need for unevenness adjustment for painting (design painting that is not intended to prevent chipping or electrolytic corrosion).

[0033] Furthermore, the base layer 3 and the protective layer 4 can be molded simultaneously as a single unit by laminating the semi-cured sheet molding compound 1 with the semi-cured glass paper prepreg 2 or glass cloth prepreg, and then applying pressure and heat. This provides more efficient protection against chipping and electrolytic corrosion than applying protection tape or painting.

[0034] Furthermore, as will be described in detail later, the sheet molding compound 1 (SMC 1 containing carbon fiber) of the base layer 3 is lighter than SMC containing glass fiber, and since it can be hardened in the shortest time of all thermosetting FRPs, the molding cycle is short (close to the working time of metal press molding).Furthermore, it is the only FRP that is an isotropic material, so material design can be done in the same way as steel, making it ideal for use as an automotive structural material.The above-mentioned measures against chipping and electrolytic corrosion are achieved by the protective layer, making the present invention extremely suitable for use as an automotive structural material.

[0035] Specific embodiments of the present invention will be described with reference to the drawings.

[0036] This example is an automotive structural material containing carbon fiber reinforced plastic (CFRP), and as shown in FIG. 1, it has a base layer 3 made of a cured product of sheet molding compound 1 (carbon fiber-containing SMC1) containing short carbon fiber and thermosetting resin, and a protective layer 4 laminated on the base layer 3 and made of a cured product of glass paper prepreg 2 containing glass fiber and thermosetting resin, with the base layer 3 and protective layer 4 being cured integrally.

[0037] To effectively prevent chipping, the protective layer 4 preferably has a thickness of 0.15 mm to 0.50 mm. In this embodiment, it is set to 0.20 mm. The thickness of the base layer 3 is approximately 2 mm to 8 mm and can be set appropriately depending on the application. In this embodiment, the thickness of the base layer 3 is 2.7 mm.

[0038] In order to effectively prevent electrolytic corrosion, the breakdown voltage in this embodiment is preferably 3 kV or more. In this embodiment, it is set to 4.48 kV. The breakdown voltage is more preferably 5 kV or more.

[0039] The protective layer 4 can be impregnated with a sufficient amount of resin to fill the recesses on the surface of the sheet molding compound 1, and can be coated with resin using a vertical coating machine to form a prepreg. The tensile strength in the length direction of the glass paper is higher than the tensile strength in the width direction. The anisotropic basis weight is 50 g / m. ２ A cured product of the glass paper prepreg 2 containing the above glass paper, or a glass paper having a basis weight of 100 g / m ２ It is desirable that the protective layer is a cured product of a glass cloth prepreg containing the above glass cloth. In this example, the protective layer has a basis weight of 50 g / m ２ The glass paper prepreg 2 contains the glass paper.

[0040] That is, this example has a two-phase layer structure consisting of an anisotropic glass paper prepreg layer (a fiber substrate layer in the form of a nonwoven fabric with anisotropic fiber orientation; a protective layer) and an SMC layer (base layer) containing carbon fiber.

[0041] Prepreg is a fiber substrate impregnated with resin, but the resin is not completely cured; rather, the curing process is stopped halfway to leave it in a semi-cured state. Prepreg is a material that is given flexibility so that it can be conformed to a mold (so that it can be shaped into the desired shape) in the subsequent press molding or autoclave molding process, and the resin is completely cured by the heat and pressure of press molding or autoclave molding to obtain an FRP of the desired shape.

[0042] <Manufacturing Method> This example can be manufactured by, for example, a lamination step of laminating a semi-cured sheet molding compound 1 (SMC1 containing carbon fiber) containing short carbon fiber (continuous carbon fiber cut into short lengths) and a thermosetting resin with a semi-cured glass paper prepreg 2 or glass cloth prepreg containing glass fiber and a thermosetting resin, and a curing step of pressurizing and heating the laminated sheet molding compound 1 and the glass paper prepreg 2 or the glass cloth prepreg to integrally cure them.

[0043] A known (commercially available) composition can be appropriately adopted as the sheet molding compound 1 that becomes the base layer 3. For example, a resin compound containing 50 wt % carbon fiber and 50 wt % resin, and vinyl ester resin that hardens when heated at 150° C. for 5 minutes, can be adopted.

[0044] The glass paper prepreg 2 or glass cloth prepreg that forms the protective layer 4 may have a resin content of 80 wt % or more and 95 wt % or less.

[0045] Furthermore, the glass paper prepreg 2 or the glass cloth prepreg may have a resin flow of 50% or more and 80% or less, as described below.

[0046] The manufacturing method will now be described in more detail.

[0047] This section describes a method for manufacturing the glass paper prepreg 2 (glass cloth prepreg) used in the lamination process. Figure 2 is a schematic diagram of a vertical coating machine for prepreg coating. The vertical coating machine includes a delivery section 11 that delivers rolled glass paper 10 and a take-up section 12 that winds up the resin-impregnated glass paper prepreg 2. Between these sections are a resin impregnation tank 13 for impregnating the glass paper 10 with resin, and a heating section 14 (vertical semi-curing zone) in which the resin-impregnated glass paper 10 that has passed through the resin impregnation tank 13 passes vertically to heat and semi-cure the resin impregnated in the glass paper 10. In the figure, reference numeral 15 denotes a tension roller.

[0048] This vertical coating machine allows continuous prepreg coating (prepreg production) by setting glass paper 10 in the delivery section 11, introducing the glass paper 10 into a resin impregnation tank 13 and impregnating it with the resin in the tank, semi-curing the resin impregnated and coated on the glass paper 10 in a vertical semi-curing zone (heating section 14), and winding up the semi-cured glass paper prepreg 2 in the winding section 12.

[0049] Below, we will explain in detail how to create a coating base (protective layer 4) for SMC1 containing cylindrical (curved cylindrical, semi-cylindrical) carbon fibers with a width of 1000 mm and a length of 1500 mm, which does not require unevenness adjustment for painting or printing.

[0050] The prepreg is coated using the vertical coating machine described above. ２ A roll of glass paper 10 having a width of 1,040 mm and a length of 100 m is set. The tensile strength of this glass paper 10 is 5 N / 15 mm in the length direction and 2 N / 15 mm in the width direction, and it has anisotropy, with the strength being higher in the length direction than in the width direction.

[0051] A resin containing phenoxy resin and urethane acrylate resin in a ratio of 15:85, or a resin containing 100% urethane acrylate resin, is placed in the resin impregnation tank of a vertical coating machine. The glass paper 10 is impregnated with the resin as it passes through the resin impregnation tank, and then becomes semi-cured as it passes through the semi-curing zone.

[0052] The preferred method for impregnating the glass paper 10 with resin is the dipping method, in which the entire glass paper is immersed in a resin impregnation tank, as shown in Figure 2. In addition to the dipping method, prepreg coating methods include the hot melt method, in which heated and molten resin is forced into one side of the fiber substrate using the pressure of a roll or press plate, and the fiber substrate is fully impregnated (uniformly impregnated with resin) using the temperature and pressure of the subsequent press molding or autoclave molding process for the prepreg. However, to achieve the effect of eliminating the need for unevenness adjustment for the paint base, the dipping method is preferred because it allows sufficient resin impregnation during the prepreg coating process.

[0053] In this example, the heating temperature of the prepreg semi-curing zone (heating unit 14) of the vertical coater is set to 150°C. However, the temperature of the semi-curing zone and coating speed can be appropriately determined depending on the length and heating capacity of the semi-curing zone and the gel time of the resin so that the resulting prepreg reaches the desired semi-cured level. For example, the temperature of the semi-curing zone can be increased from 150°C to 180°C, and the coating speed can be increased based on the residence time in the semi-curing zone, the gel time of the resin, and the semi-cured state of the resin impregnated into the prepreg after passing through the semi-curing zone. The resulting prepreg is wound up in the winding unit 12. In this example, a vertical coater in which the semi-curing zone extends vertically (up and down), is used for explanation. However, a horizontal coater in which the prepreg semi-curing zone extends horizontally (front-to-back or left-to-right), may also be used.

[0054] When coating the prepreg, the inventors tried glass paper with a tensile strength of less than 5 N / 15 mm in the length direction and less than 2 N / 15 mm in the width direction, but the forward tension and back tension during prepreg coating caused the glass paper to tear in the length direction and width direction, making continuous coating impossible. Therefore, it is desirable that the tensile strength of the glass paper used for coating the prepreg be 5 N / 15 mm or more in the length direction and 2 N / 15 mm or more in the width direction.

[0055] The resin impregnated into prepreg reaches a semi-cured state. However, the range of semi-cured states is quite wide, from a sticky, sticky feeling on the surface of the prepreg to a smooth, paper-like feel. This semi-cured state is determined by the resin flow of the prepreg. The obtained prepreg is cut into a set of four pieces (e.g., 200 mm x 200 mm), and these pieces are press-molded in a press molding machine at a predetermined temperature and pressure (a temperature and pressure that will cure the impregnated resin composition; in this example, a temperature of 150°C and a pressure of 0.3 MPa). The degree of semi-curing is determined by the amount of resin that flows after molding. In this determination method, the fiber substrate (here, glass paper) remains in place without flowing with the resin, so the semi-cured state can be measured by the resin flow. If the resin is sticky and sticks to your hands, the amount of resin that flows will be large, and if it is smooth enough to handle paper, the amount of resin that flows will be small. The degree of semi-cure is determined by the percentage of the weight of this flowed-out resin and the weight of the prepreg before the flow-out. In this example, the percentage calculated using the following formula is defined as the resin flow. Resin flow (%) = Amount of resin (g) that flows out when press-molded under conditions of 150°C and 0.3 MPa / Weight of prepreg before resin flows out during press-molding (g) Here, "amount of resin that flows out (g)" is "weight of prepreg before resin flows out during press-molding - weight of prepreg after resin flows out after press-molding."

[0056] Various prototypes were made by varying the prepreg coating conditions of the vertical coating machine (for example, coating speed, resin viscosity, temperature setting of the prepreg semi-curing zone, etc.) to determine the glass paper prepreg coating conditions suitable for chipping prevention, and a glass paper prepreg 2 with a resin content of 80 wt% and a resin flow of 50% was obtained. One sheet of this glass paper prepreg 2 with a resin content of 80 wt% and a resin flow of 50% was prepared, measuring 1000 mm wide and 1500 mm long (at this point, the glass paper prepreg 2 was in a semi-cured state and not yet cured).

[0057] In addition to the glass paper prepreg 2 obtained as described above, an SMC 1 containing carbon fiber is prepared. Specifically, a resin compound (vinyl ester resin that hardens when heated at 150°C for 5 minutes) is added at 1000 g / m ２ The cut carbon fibers were adjusted to 1000 g / m ２ (carbon fiber weight content 50 wt%, resin weight content 50 wt%), and the total weight of the resin compound and fiber was adjusted to 2000 g / m ２ Two sheets of SMC1 containing carbon fiber are prepared, each having a width of 1000 mm and a length of 1500 mm (at this stage, the SMC1 containing carbon fiber is in a semi-cured state and has not yet been cured).

[0058] As shown in Figures 3 and 4, the glass paper prepreg 2 and carbon fiber-containing SMC 1 were laminated together, with one sheet of the glass paper prepreg 2 laminated on top of two sheets of carbon fiber-containing SMC 1 (lamination process). The resulting mixture was then placed in a 1000 mm wide, 1500 mm long lower mold 20 with a cylindrical convex curved surface. A corresponding upper mold 21 with a cylindrical concave curved surface was then fitted over the lower mold 20. The resulting mixture was heated and pressed at 150°C and 10 MPa. The heating and pressure were maintained for 5 minutes, and then water was passed through the mold as a refrigerant to cool it to 50°C over 5 minutes. After 10 minutes of heating and pressing, the mold was released, resulting in a molded SMC-CFRP product (automotive structural material) (curing process). Reference numeral 22 in the figures denotes a mold release agent.

[0059] The surface of the obtained SMC-CFRP molded article on the glass paper prepreg side is smooth and free of the recesses typical of SMC, and the molded article is cylindrical and 2.85 mm to 2.95 mm thick (at this point, both the glass paper prepreg 2 and the SMC 1 containing carbon fiber have cured).

[0060] This cylindrical SMC-CFRP molded product can be produced not only by the press molding method described above, but also by other molding methods, such as autoclave molding. The temperature, pressure, and vacuum programs for autoclave molding are determined appropriately depending on the curing characteristics of the SMC and prepreg used in the molding. For example, a program like that shown in Figure 5 is used. The temperature program involves raising the temperature from room temperature (20°C) to 150°C at 6.5°C per minute, holding at 150°C for 5 minutes, and then lowering the temperature to room temperature at 6.5°C per minute. The pressure program involves raising the pressure inside the autoclave from 0 MPa to 0.5 MPa at 0.1 MPa per minute, holding at 0.5 MPa for 39 minutes, and then lowering the pressure to 0 MPa at 0.5 MPa per minute. The vacuum program maintains a predetermined vacuum state from 0 minutes at the start of molding until 45 minutes at the end of molding, when the temperature and pressure reduction are completed. As for the molds used in autoclave molding, both an upper mold and a lower mold may be used as in the press molding described above, but it is also possible to use only the lower mold and have the upper side of the molded product serve as the bagging film surface used for vacuum bags in autoclave molding, or to use only the upper mold and have the lower side of the molded product serve as the bagging film surface used for vacuum bags in autoclave molding. Which side comes into contact with the mold and which side serves as the bagging film surface can be determined appropriately depending on the appearance desired for the SMC-CFRP molded product.

[0061] Figure 6 is a schematic diagram illustrating an example of autoclave molding using only a lower mold 31, with the upper side of the molded product covered with a bagging film used for vacuum bags in autoclave molding. Two sheets of carbon fiber-containing SMC 1 are laminated on the lower mold 31, and one sheet of glass paper prepreg 1 is then laminated on top of them. This laminate is then placed on a cylindrically curved lower mold 31 measuring 1000 mm wide and 1500 mm long. A spacer mold 32 is then placed on top of this. Another laminate is then placed on top of this spacer mold 32, and another spacer mold 32 is then placed on top of that. Repeatedly setting the laminate and spacer mold 32, the assembly is covered with a bagging film 33 used for vacuum bags, and autoclave molding is performed. This allows multiple SMC-CFRP molded products to be obtained in a single molding run, thereby reducing molding costs. In the figure, reference numeral 34 denotes a vacuum exhaust system, and 35 denotes a sealant tape.

[0062] In the above-described press molding, to obtain a smooth surface without the recesses characteristic of SMC on the glass paper prepreg side of the SMC-CFRP molded product, the resin content of the glass paper prepreg 2 is preferably 80 wt% to 95 wt% and the resin flow is preferably 50% to 80%. If the resin content is less than 80 wt%, the absolute amount of resin is insufficient to cover the entire glass paper, resulting in crater-like recesses in the cured glass paper prepreg 2 layer. Furthermore, even when the resin content is high (e.g., 90 wt%), if the resin flow is 50% or less, the resin does not penetrate the entire glass paper prepreg 2 layer, resulting in slight recesses noticeable to the naked eye and touch. On the other hand, when the resin flow exceeds 80%, excessive resin from the glass paper prepreg 2 flows out during press molding, making it impossible to obtain a satisfactory surface without recesses.

[0063] When the cross section of this SMC-CFRP molded product was observed under a microscope, it was found that the layer of SMC 1 containing carbon fiber (base layer 3) and the layer of glass paper prepreg 2 (protective layer 4) were integrated and well bonded, and the unit weight was 50 g / m ２In the case of the glass paper prepreg 2 using the glass paper of the above, the base layer 3 made of SMC 1 containing carbon fiber had a thickness of 2.7 mm to 2.8 mm, and the protective layer 4 made of glass paper prepreg 2 had a thickness of 0.18 mm to 0.20 mm.

[0064] Also, the unit weight is 100 g / m ２ In the case of the glass paper prepreg 2 using the glass paper of the above, the base layer 3 made of SMC 1 containing carbon fiber had a thickness of 2.7 mm to 2.8 mm, and the protective layer 4 made of glass paper prepreg 2 had a thickness of 0.40 mm to 0.42 mm.

[0065] In this embodiment, the glass paper prepreg 2 is used as the protective layer 4, but the unit weight is 110 g / m ２ or 214 g / m ２ The glass cloth prepreg may be manufactured using the above-mentioned vertical coating machine, similar to the glass paper prepreg 2. The glass cloth prepreg is preferably impregnated with resin by the dipping method, similar to the glass paper. The tensile strength of the glass cloth is 110 g / m2. ２ However, since the resistance is 150N / 15mm or more in the length direction and 120N / 15mm or more in the width direction, it will not be torn off in the length direction or width direction due to forward tension or back tension, as is the case when applying glass paper prepreg.

[0066] <Background> The background that led to the above-described configuration and manufacturing method will be described in more detail.

[0067] - About SMC SMC is a semi-cured material made by mixing fibers and resin used in FRP molding. Unlike unidirectional prepreg and cross prepreg, which are made by semi-curing epoxy resin with a base material of continuous glass or carbon fiber or woven fabric made of continuous fiber, SMC often uses a viscous resin paste (resin compound) of unsaturated polyester resin or vinyl ester resin instead of epoxy resin.

[0068] SMC is manufactured using a manufacturing apparatus such as that shown in Fig. 7. Specifically, SMC is manufactured by applying resin compound 40 to carrier films 46 delivered from a delivery section 45 to form sheets, cutting continuous fibers 42 into lengths of 1 / 2 inch (12.5 mm) to 2 inches (50 mm) using a roving cutter 41 to form short fibers 43, which are randomly dropped onto the resin compound 40, and impregnating the fibers with resin while forcing the short fibers 43 into the resin compound 40 with the pressure of an impregnation roll 44. The semi-cured SMC 50 is then sequentially wound up on a winding section 47. The wound roll-shaped SMC product (semi-cured SMC 50) is shown in Fig. 8.

[0069] The semi-hardened SMC 50 thus produced is then heated and pressurized by press molding in the next step to obtain an FRP molded product of the desired shape.

[0070] SMC is characterized by its short curing time and minimal anisotropy (e.g., high strength and modulus in the longitudinal direction, low strength and modulus in the transverse direction) characteristic of FRP. Prepregs, which utilize the polymerization reaction of epoxy resin, are cured by heating at 130°C to 150°C for 1 to 2 hours, while SMCs, which utilize the radical reaction of unsaturated polyester resin or vinyl ester resin, are cured by heating at 130°C to 150°C for 3 to 10 minutes. Glass fiber SMC (SMC-GFRP) is used in bathtubs for residential modular baths. SMC is also beginning to be used in mobility components for automobiles (including motorcycles) and bicycles. Its cycle time (operation time) can be measured in minutes, similar to that of sheet metal press molding for automobiles, thereby reducing molding costs by increasing output per unit time.

[0071] On the other hand, SMC can shorten the molding cycle time, but because the continuous fibers are cut from 1 / 2 inch (12.5 mm) to 2 inches (50 mm), there is no fiber continuity. Therefore, it does not have the same mechanical properties as continuous fibers. Many FRPs (such as FRPs with unidirectional fibers and FRPs with woven fabric) have high strength and high elastic modulus because the fibers are continuously connected, but SMC does not have high strength or high elastic modulus.

[0072] For example, Table 1 shows the physical properties of SMC (SMC-GFRP) made of glass fibers (chopped fibers) and unidirectional GFRP made of glass fibers (continuous fibers).

[0073]

[0074] SMC-GFRP has significantly lower mechanical properties than continuous fiber unidirectional GFRP, with a tensile strength one-tenth that of unidirectional GFRP, a bending strength one-fifth, and a bending modulus one-third. This tendency is also seen in SMC-CFRP, which contains carbon fiber. When using SMC as a structural material, whether it is SMC-GFRP made with glass fiber or SMC-CFRP containing carbon fiber, if you want to increase the load-bearing capacity or rigidity, you need to take care to laminate multiple sheets of semi-cured SMC and harden them by press molding, increasing the thickness of the molded product to achieve the required rigidity and load-bearing capacity.

[0075] Increasing the thickness of a molded product increases the density difference in the fiber basis weight depending on the location on the molded product, which tends to increase the unevenness of the molded product surface. When applying protection tape, the number of steps required to eliminate the unevenness on the surface of the SMC molded product increases. Furthermore, when painting, in addition to the step to eliminate the unevenness, an additional step is required to fill in the recesses with putty to create a flat base (unevenness adjustment step), which increases the number of steps required.

[0076] SMC uses cut fibers, so the fibers are not continuous. For example, a cut fiber of 1 inch length may bend or be roughly straight, and the fibers in SMC may be 1 meter long. ２ The fiber direction is randomly distributed within a certain area (e.g., 1 m ２) Because the fibers are randomly oriented in this way, SMC is the only FRP known to be a nearly isotropic material. In other words, SMC-FRP is a nearly isotropic material similar to steel, with almost no anisotropy, such as high strength and elastic modulus in the length direction and low strength and elastic modulus in the direction perpendicular to the length, as is the case with unidirectional FRP.

[0077] Isotropy refers to the property that, for example, when the material is in plate form, the bending and tensile strength and modulus of elasticity are approximately the same in all directions, including the width direction, length direction, and diagonal directions. In FRP, quasi-isotropy refers to a laminate that uses continuous fibers and has fiber orientations of 0 degrees, 90 degrees, and ±45 degrees. SMC differs from this quasi-isotropic state, so it is described as roughly isotropic.

[0078] As mentioned above, SMC is generally isotropic, which makes it preferable for designers in the automotive industry, who have long used steel, because it allows them to design materials with the same feel as steel. Furthermore, because it can be press-formed in 3 to 10 minutes, which is close to the takt time (work time) required for press-forming metal, it has been used in recent years as interior materials for several vehicle models. For example, to reduce weight, SMC containing carbon fiber (SMC-CFRP) is used in the back door of the Prius PHV and the door inner of the Lexus LC500. Currently, SMC-CFRP is primarily used as an interior material, combined with steel and aluminum exterior materials.

[0079] Representative fibers used in SMC include glass fiber and carbon fiber. Glass fiber is electrically insulating, but carbon fiber is not, and instead conducts electricity (is conductive). SMC containing carbon fiber (SMC-CFRP) uses cut fibers, and when one cut fiber comes into contact with another cut fiber, an electrical path is created, resulting in conductivity (percolation phenomenon).

[0080] When SMC-CFRP comes into contact with steel or aluminum, care must be taken because if water droplets such as condensation accumulate in that area, the droplets will act as an electrolyte solution, with the SMC-CFRP as the positive electrode and the steel or aluminum as the negative electrode, causing a galvanic current to flow and causing electrolytic corrosion to progress.

[0081] Carbon fiber FRP (CFRP) has the property of conducting electricity, so when the area where the CFRP comes into contact (joined) with steel or aluminum gets wet with rain or dew, the potential difference caused by the ionization tendency of the carbon and the steel or aluminum causes the water droplets from the rain or condensation to act as an electrolyte solution, with the CFRP becoming the positive electrode and the steel or aluminum becoming the negative electrode, causing a minute current to flow. This is called a galvanic current.

[0082] In a voltaic cell, where copper is the positive electrode and zinc is the negative electrode, the easily ionized zinc is gradually eroded, and corrosion of the zinc progresses. Similarly, in the area where the SMC-CFRP interior comes into contact with the steel or aluminum exterior, the steel or aluminum corrodes in the same way as the zinc in a voltaic cell. This is called "galvanic corrosion." If the rainwater falling is slightly acidic, or if you park your car by the sea after it rains, the water will become an electrolyte solution containing a small amount of hydrochloric acid, which will cause iron ions to be released from the steel components and aluminum ions to be released from the aluminum components, further accelerating this corrosion (galvanic corrosion).

[0083] Therefore, electrical insulation is required at the contact surface between SMC-CFRP and steel or aluminum. Applying protection tape to the CFRP surface can provide electrical insulation, but as mentioned above, applying protection tape requires smoothing the CFRP surface. Furthermore, protection tape can peel off over time, and if it does, corrosion (galvanic corrosion) occurs on the metal side at the contact surface between the metal member and CFRP. When a peeled area and an unpeeled area become the contact surface between the metal member and CFRP, dew (water droplets) accumulate at that area, increasing the likelihood of corrosion (galvanic corrosion) on the metal side.

[0084] To prevent chipping and electrolytic corrosion, one method is to create a protective layer by painting CFRP. Using SMC-CFRP as an example, the molding process and painting process are explained below.

[0085] SMC-CFRP is manufactured in the same manner as above using the manufacturing apparatus shown in Figure 7. That is, a viscous resin paste (resin compound) of unsaturated polyester resin or vinyl ester resin is formed into a sheet, short carbon fibers, cut into 1 / 2 inch (12.5 mm) to 2 inches (50 mm) continuous fibers, are randomly dropped onto the resin compound, and the fibers are impregnated with resin while being pressed into the resin compound by a pressure roll (impregnation roll). SMC-CFRP is then painted in a separate process on the surface of the molded product after the semi-cured SMC-CFRP is placed in a mold and press-molded under heat and pressure.

[0086] In SMC, the fiber weight varies depending on the area. For example, if the resin compound is 1000 g / m ２ The cut carbon fibers were adjusted to 1000 g / m ２ The total weight of the resin compound and fiber was adjusted to 2000 g / m ２ In the case of an SMC containing carbon fiber (carbon fiber weight content 50 wt%, resin weight content 50 wt%), ２ Among them, a certain 50mm x 50mm area range has a density of 2300g / m ２ , and another 50mm x 50mm area is 1700g / m ２ Thus, the fiber distribution causes variations in the fiber weight of ±5% to ±15%.

[0087] That is, as shown in FIG. 9, the SMC product (semi-cured SMC 50) has a tensile strength of 2300 g / m ２ The area 50a has a dense fiber, 1700 g / m ２The fibers become coarse in area 50b. When such an SMC is press-molded, the molded product tends to be thicker in areas where the fibers are dense (areas where the resin content is relatively low; area 50a), and thinner in areas where the fibers are sparse (areas where the resin content is relatively high; area 50b) (see Figure 10). For example, when SMC is press-molded into a flat plate, even on the same plane of the molded product, a 100 mm x 100 mm area in one area will have the desired thickness, but another 100 mm x 100 mm area in another area will be slightly thinner than the desired thickness.

[0088] The difference in thickness caused by this variation in basis weight appears as a difference in height on the surface of the SMC press-molded product, and the difference between the high and low points on the surface of the SMC molded product is 50 μm to 60 μm, and in the deepest cases, it can be 70 μm to 80 μm. When the storage life of the SMC is advanced (for example, an SMC with a storage life of two weeks at room temperature from the date of manufacture has been stored at room temperature for more than three weeks from the date of manufacture), in addition to the factor of variation in the basis weight of the SMC, the SMC resin becomes less likely to flow, and the difference between the high and low points on the surface of the SMC press-molded product can reach 80 μm or more.

[0089] SMC, whether it's SMC-GFRP made with glass fiber or SMC-CFRP containing carbon fiber, is press-molded using a mold to obtain a molded product of the desired shape. During press molding, a viscous resin paste (resin compound) and fibers cut into 1 / 2 inch (12.5 mm) to 2 inches (50 mm) are processed into the desired shape, and the press pressure is set to 2 MPa to 10 MPa (20 kg / cm) so that the resin and fibers reach every corner of the mold. ２ ~100 kg / cm ２) is molded under extremely high pressure. The high pressure applied during press molding often causes the molded product to stick to the mold, making demolding take a long time. To improve demolding (to prevent the molding cycle time from becoming longer and reducing output), a mold release agent is applied to the upper and lower halves of the mold after each molding, and after heating at 130°C to 150°C for 3 to 10 minutes to harden, the molded product can be smoothly demolded from the mold without breaking or damaging it (see Figure 4).

[0090] Incidentally, when thermosetting resins used in the manufacture of carbon fiber CFRP and glass fiber GFRP, including the unsaturated polyester resin or vinyl ester resin used in SMC, are heated and cured, an inactive layer (a layer that repels adhesives and paints) of 10 μm to 30 μm thick is formed on the surface of the FRP molded product, making it unsuitable for bonding to other materials or for painting.

[0091] In particular, in the case of SMC, the molding method mainly used is press molding, and the release agent applied to the mold migrates to the surface of the SMC molded product, making the inactive layer on the surface of the FRP molded product even more unsuitable for adhesion to other materials or painting. Good mold releasability from the mold is due not only to the effect of the release agent itself, but also to the slight migration of the release agent to the surface of the SMC molded product, which improves mold releasability. For example, even in FRP, which does not use a release agent, such as in FW (filament wound) molded products, an inactive layer forms on the surface. In the case of SMC molding, the slight migration of the release agent to this inactive layer makes this inactive layer even more unsuitable for adhesion to other materials, adhesion, and painting.

[0092] In fact, when water is sprayed onto the surface of the molded SMC with a spray bottle, it repels in droplets. Furthermore, even cellophane tape cannot be stuck to the surface of the pressed SMC; it peels off, making it an inert surface that repels other materials.

[0093] This inactive layer becomes an obstacle when painting or applying protective tape to prevent chipping or electrolytic corrosion, when applying design (design painting or top coat painting), or when bonding the SMC to other materials with adhesives (because the paint or adhesive does not adhere well to the surface of the FRP molded product), so if the surface of the SMC (cured resin) is to be painted or if other materials are to be attached or bonded after molding, the inactive layer must be removed by surface cutting processes such as sanding or sandblasting. Figure 11 shows a schematic diagram of the SMC 51 and inactive layer 52 after molding (curing).

[0094] When painting the surface of an SMC molded product to prevent chipping, electrolytic corrosion, or to enhance its aesthetic appeal, in order to ensure good adhesion of the paint to the surface of the SMC molded product, it is necessary to perform a surface cutting process such as sanding or sandblasting on the surface of the SMC molded product, along with an inert layer on the surface, so that the convex parts of the unevenness caused by press molding are aligned with the concave parts until there is no difference in height (unevenness adjustment). This applies to both the SMC-CFRP molded product of this example and the SMC-GFRP molded product made from glass fiber. For painting or for bonding or pasting with other materials, the surface of the molded product must be surface cut to a level where the parts other than the concave parts are aligned with the low parts (concave parts).

[0095] However, if the recesses are deep (for example, about 80 μm), and the surface of the FRP molded product is subjected to surface cutting processes such as sanding or sandblasting until the recesses disappear in order to obtain a good base for painting, the fibers near the surface layer will be severed, reducing the strength and elastic modulus of the SMC-CFRP molded product. The areas where the fibers are severed will become locally weak, and if the SMC-CFRP molded product is 1 mm thick or less, any impact will cause it to break like a shoji screen being torn with a fist.

[0096] Furthermore, if surface cutting processes such as sanding and sandblasting are limited to a level that does not cut the fibers of the SMC-CFRP molded product, depressions will remain on the surface of the SMC-CFRP molded product. These depressions must be eliminated, for example, to allow for good painting of the surface of the SMC-CFRP molded product or the application of protection tape.

[0097] Therefore, conventionally, before painting the surface of this SMC-CFRP molded product or applying protection tape, the surface is degreased by surface cutting processes such as sanding or sandblasting to the extent that the surface fibers of the SMC-CFRP molded product are not cut, and then the recesses are filled with a polyester resin-based putty.The areas filled with this putty are then surface cut again to smooth out any unevenness, and a design is imparted to the surface of the SMC-CFRP molded product after this unevenness correction.

[0098] Regarding painting, we will now explain in detail the conventional painting method, which also serves as a countermeasure against chipping and electrolytic corrosion. This will involve molding SMC-CFRP into a cylindrical (semi-cylindrical) shape, like a cut-out portion of a 1000 mm wide, 1500 mm long cylinder, and the process from preparing the base (adjusting for unevenness) to finishing the painting when painting the surface of the molded product.

[0099] First, an SMC (in a semi-cured state before curing) containing carbon fibers cut into a rectangular shape having a width of 1000 mm and a length of 1500 mm is prepared.

[0100] The SMC containing this carbon fiber is made by mixing the resin compound at 1000 g / m ２ The cut carbon fibers were adjusted to 1000 g / m ２ The total weight of the resin compound and fiber is adjusted to 2000 g / m ２ The resin compound is an SMC containing carbon fiber (carbon fiber weight content: 50 wt %, resin weight content: 50 wt %), and a vinyl ester resin (or unsaturated polyester resin) that hardens when heated at 150°C for 5 minutes.

[0101] Two sheets of this carbon fiber-containing SMC are laminated and set in a cylindrical lower mold, and an upper mold is fitted over them. The laminate is then heated and compressed (heat pressed) at a temperature of 150°C and a pressure of 10 MPa. The heating and pressure application is maintained for 5 minutes, and then water is passed through the mold as a refrigerant to cool it to 50°C over 5 minutes. 10 minutes after heating and compressing, the mold is opened to obtain an SMC-CFRP molded product.

[0102] In this SMC-CFRP molded product, due to the unevenness of the basis weight of the carbon fiber, for example, the total basis weight of the resin compound and the fiber is 2000 g / m ２ In the case of SMC containing carbon fiber (carbon fiber weight content 50 wt%, resin weight content 50 wt%), ２ Among them, the area range of a certain part is 2300 g / m ２ , another part of the range is 1700 g / m ２ Due to this unevenness in the basis weight of the carbon fibers, the surface of the molded product may become uneven, with the molded product being thicker in areas where the fibers are dense and thinner in areas where the fibers are sparse.

[0103] Another example of a defect is that even if the storage life of an SMC containing carbon fiber in a semi-cured state before curing by press molding is within its effective period, the resin flow during press molding may be insufficient depending on the storage conditions. During press molding, there are areas where the surface of the upper mold is in sufficient contact with the SMC containing carbon fiber and the desired thickness is achieved, and areas where the resin flow is insufficient and the surface of the upper mold is not in sufficient contact with the SMC containing carbon fiber and the desired thickness is not achieved, resulting in the formation of depressions on the surface of the molded product.

[0104] To form a good paint layer on the surface of an SMC-CFRP molded product to prevent chipping and electrolytic corrosion, the following process is required. Figure 12 shows a cross-sectional view of an SMC with a conventional paint layer. In the figure, reference numeral 53 denotes the putty-filled area, 54 denotes the primer layer, 55 denotes the intermediate coat layer, 56 denotes the design paint layer, and 57 denotes the top coat layer. When using an SMC-CFRP molded product with an uneven surface as described above, extra man-hours are required, especially in processes 1 and 2 described below.

[0105] Step 1: As shown in Figure 13, the surface of the SMC-CFRP molded product is machined (sanded or sandblasted) to a depth D that does not cut the fibers, and then degreased. During this process, shallow recesses 59 disappear, but deep recesses 60 remain (see Figure 14).

[0106] Step 2: Any recesses (parts of the deep recesses 60) remaining on the surface of the SMC-CFRP molded product after the surface cutting process are filled with putty, such as a black polyester resin-based putty (see Figure 14; reference numeral 53 denotes the putty-filled area). This putty is cured according to the recommended curing conditions (temperature and time) for the putty used. For example, it is exposed to hot air at 40 to 60°C for 3 to 6 hours, or cured at room temperature for one day. After curing, the protrusions on the surface of the SMC-CFRP molded product are sanded with, for example, #240 sandpaper to smooth out any unevenness so that the surface to be painted is roughly flat and free of any extreme protrusions. In Step 2, when the putty is cured or the paint is dried and cured, if the temperature is set to, for example, 80° C. or higher, the drying and curing time will be shorter, but this will cause microcracks in the putty or paint and peeling from the surface of the SMC-CFRP molded product, so it is desirable to cure the putty and the paint at a low temperature, for example, 60° C. or lower. If the temperature is lowered, the drying and curing time will be longer.

[0107] Step 3: After the unevenness adjustment, a clear paint to form a primer layer is applied to the surface of the SMC-CFRP molded product with a spray gun to a thickness of 25 μm to 30 μm, and the paint is then kept at 40°C for half a day to a day, for example, to dry and harden.

[0108] This undercoat layer is formed to a thickness of 25 μm to 30 μm for the purposes of obtaining adhesion between the surface of the SMC-CFRP molded article and the substrate after unevenness adjustment, and for the purpose of providing corrosion resistance to alkalis and acids on the surface of the SMC-CFRP molded article, as well as adhesion to the intermediate coat layer described below.

[0109] Step 4: A clear coating material for forming an intermediate coating layer is applied to the surface of the undercoat layer with a spray gun to a thickness of 40 μm to 45 μm, and the coating material is then dried and hardened, for example, by holding it at 40°C for half a day to a day.

[0110] This intermediate layer is formed to a thickness of 40 μm to 45 μm in order to maintain the smoothness of the primer layer and to provide impact resistance to the entire coating. It also ensures adhesion to the topcoat layer, which will be described later. When design painting (or design printing) is performed, it is applied on top of this intermediate layer. The intermediate layer also serves the purpose of forming a smooth base for design painting or printing.

[0111] Step 5: When applying a pearlescent coating or coloring the coated surface as a design coating, a pearlescent coating or coloring layer is formed on the surface of the intermediate coating layer after the intermediate coating layer has been formed to a thickness of 15 μm to 20 μm. This design coating layer (design layer), like the other layers, is also kept, for example, at 40° C. for half a day to a day, to dry and harden.

[0112] In addition to design painting, there are also cases where a brand name or design is silk-screened or a sticker is attached to add a design.

[0113] Step 6: A clear paint to form a topcoat layer is applied to the surface of the design layer with a spray gun to a thickness of 40 μm to 45 μm, and the paint is then left to dry and harden, for example, at 40°C for half a day to a day.

[0114] If you want to make the surface of an SMC-CFRP molded product appear transparent and stand out from the molded surface (the marbled pattern caused by the variations in density of the carbon fiber as the resin flows) to enhance the design, you can simply paint the primer, intermediate coat, and top coat with transparent paint. In this case, step 5, the design painting process, can be omitted.

[0115] In addition to SMC molded products containing carbon fiber (SMC-CFRP), in the case of CFRP molded products made from carbon cloth (woven carbon fiber), if you want to make the carbon cloth weave stand out transparently on the surface to enhance the design, you can do the same by using transparent paint for the primer, intermediate coat, and top coat. In this case, too, the design painting process in step 5 can be omitted.

[0116] Step 7: If necessary, a clear coating to form a second topcoat layer is applied to the surface of the topcoat layer with a spray gun to a thickness of 40 μm to 45 μm, and the coating is then dried and cured, for example, by holding the coating at 40°C for half a day to a day.

[0117] This top coat layer is called a top coat coating and is formed to a thickness of 40 μm to 90 μm for the purposes of maintaining gloss, improving aesthetics, scratch resistance, weather resistance, and stain resistance, as well as preventing chipping and electrolytic corrosion.

[0118] The above steps 1 to 7 explain the process of surface painting with a glossy finish used on car bodies, etc. However, there is also a painting method called "chipping painting" that is specifically designed to prevent chipping. Chipping painting is formed after forming the undercoat layer in step 4 (or after forming the primer layer in step 3), and the coating thickness is 100 μm or more, making it a so-called thick coating. Chipping painting does not have the topcoat layer in steps 6 and 7, and the painted surface is dull and rough.

[0119] Chipping paint prevents chipping by dispersing the impact stress on the paint film when a pebble hits it with this rough surface. While the surface coating using steps 1 to 7 described above also prevents chipping, when a pebble hits this paint film, the cracks in the paint film spread in a spider web-like pattern, just like glass hit by a bullet. Chipping paint is a painting method that can be expected to prevent the cracks from spreading in a spider web-like pattern when a pebble hits it. This chipping paint is used on the underside of a car body (the side closest to the ground), bumpers, grilles, etc.

[0120] The disadvantage of chip-resistant paint is that the painted surface is rough and bumpy, making it prone to collecting dirt and dust. Additionally, because there is no clear coat or top coat to protect the painted surface from UV rays, UV damage and dirt accumulate directly on the chip-resistant paint surface. UV rays, in particular, have the effect of degrading the paint film, so there is a risk that the paint film will be destroyed when a pebble hits the painted surface. If the paint is destroyed, the carbon fibers in the SMC-CFRP molded product will be exposed, and the chipping and electrolytic corrosion protection will be lost.

[0121] Also, chipping paint can peel off even when washed, so when washing the car, it is necessary to wash it by hand using a lot of water rather than using a car wash machine.

[0122] SMC-CFRP molded products are subjected to the surface coating process described above through steps 1 to 7, as well as the anti-chipping coating described above, which is a specialized anti-chipping treatment. There is a demand for simplifying the above-mentioned coating process, which involves many steps and man-hours and can take several days to complete, including coating to prevent chipping and electrolytic corrosion, and even coating to add designs.

[0123] Furthermore, in mobility vehicles such as automobiles and motorcycles, chipping can occur when small pebbles strike the CFRP surface during operation, causing scratches or chipping of the CFRP component. It is necessary to prevent chipping by damaging the FRP fibers and preventing further fracture. Countermeasures against chipping include painting and applying the aforementioned protection tape (protection tape or decorative film with adhesive on one side of the SMC-CFRP surface). However, this protection tape can sometimes fail to conform to the three-dimensional shape, resulting in partial "lifting." In particular, in the case of SMC-CFRP and SMC-GFRP molded products, the surface of the molded product has an inert layer resulting from the transfer of release agents during press molding, preventing the protection tape from adhering. To achieve adhesion, similar to the painting method described above, the inert layer must be removed by surface cutting processes such as sanding or sandblasting (see Figures 13 and 14).

[0124] As described above, in the case of automobiles and other mobility products, measures such as painting and applying protective tape are taken to prevent chipping of CFRP components. However, both painting and applying protective tape require surface preparation through surface cutting processes such as sanding and sandblasting, and there is a demand for simplifying these processes.

[0125] The inventors focused on the fact that the above-mentioned surface preparation is troublesome, and as a result of extensive research, they discovered the configuration of the automotive structural material according to this embodiment and a manufacturing method thereof, which can prevent chipping and electrolytic corrosion without relying on protection tape or paint, and which also makes unevenness adjustment unnecessary.

[0126] <Effects> Since this embodiment is configured as described above, chipping and electrolytic corrosion can be prevented without using protection tape, unevenness adjustment for painting is not required, and furthermore, it is an excellent structural material for automobiles that can be manufactured in a short time, and is particularly suitable for use as an interior material.

[0127] An experimental example that supports the effects of this embodiment will be described below.

[0128] Experimental Example 1: A cross-cut test was conducted to compare the adhesion (adhesion) between the protective layer and the base layer of this example with that of a coating and a protection tape. Specifically, the comparison was performed in accordance with the cross-cut test method according to JIS K5600 for coating thicknesses of 121 μm to 250 μm (0.121 to 0.250 mm).

[0129] As shown in Figure 15, a plastic hammer H (OH Industries Soft Hammer FP Part II, total length 300 mm, weight 340 g, head diameter φ23 mm) was used with the handle of the hammer in contact with table T, and the head was allowed to fall naturally from a height of 200 mm to strike test piece X with grid-like cuts, and then a cross-cut method test was performed for comparison.

[0130] The experimental results are shown in Table 2. Each of the SMC molded products containing carbon fiber had the above-mentioned unit basis weight of 50 g / m ２The glass paper prepreg having the protective layer of this example containing the glass paper of Experimental Example 1-1 was used as the glass paper prepreg having the above-mentioned unit weight of 100 g / m. ２ The specimen provided with the protective layer of this embodiment made of glass paper prepreg containing the glass paper was designated Experimental Example 1-2, the specimen provided with paint as the protective layer was designated Comparative Example 1-1, and the specimen provided with protection tape as the protective layer was designated Comparative Example 1-2.

[0131]

[0132] The thickness of the protective layer in Experimental Example 1-1 was 0.18 mm to 0.20 mm, and it was confirmed that an anti-chipping layer equivalent to those in Comparative Examples 1-1 and 1-2 could be obtained.

[0133] Furthermore, it was confirmed that in Experimental Example 1-2, the thickness of the protective layer was 0.40 mm to 0.42 mm, which was approximately twice as thick as that of Comparative Example 1-1.

[0134] The protective layers of the cured glass paper prepreg in Experimental Examples 1-1 and 1-2 were tested by the normal cross-cut method and by the cross-cut method after hitting with a hammer, and in both cases they were classified as Class 0, meaning no peeling.

[0135] In contrast, in the case of the paint of Comparative Example 1-1, the test using the cross-cut method after hitting with a hammer showed partial paint peeling, with peeling at the intersections of the cross-cuts, resulting in a rating of Category 1. In the case of the protection tape of Comparative Example 1-2, in both the test using the normal cross-cut method and the test using the cross-cut method after hitting with a hammer, the protection tape peeled off in areas where it was not applied properly, resulting in a rating of Category 3.

[0136] In Experimental Examples 1-1 and 1-2, the surface layer of the carbon fiber-containing SMC contained a molding layer made of glass paper prepreg (a protective layer made of cured glass paper prepreg). This glass paper prepreg molding layer had a resin content of 80 wt % and a resin flow rate of 50%, resulting in a high level of resin flow. Therefore, the resin contacted the entire surface of the upper mold, as well as the surface of the lower mold, resulting in a molded product of the desired shape with a surface roughness equivalent to that of the mold. Therefore, no recesses were formed in the molded product due to the coarse fiber density characteristic of SMC. In other words, the recesses on the SMC surface were filled with the resin from the glass paper prepreg, and the resin layer came into contact with the upper and lower molds, preventing recesses from forming on the surface of the molded product (protective layer surface).

[0137] In the case of measures against chipping and electrolytic corrosion, this surface can be left as is, but when applying a design paint to the surface layer of the SMC containing carbon fiber after molding, the signing treatment or sandblasting treatment in the above-mentioned painting step 1 can be performed up to 0.15 mm (150 μm) in Experimental Example 1-1 and up to 0.35 mm (350 μm) in Experimental Example 1-2 without worrying about cutting the fibers. Furthermore, because there are no recesses on the surface of the molded product as described above, it is possible to omit the unevenness adjustment step in the above-mentioned painting step 2, which involves filling recesses with putty or signing the recesses partially.

[0138] Experimental Example 2 To compare the galvanic corrosion resistance of the protective layer of this example with a case where nothing was laminated or attached to an SMC molded article containing carbon fiber, and a case where a protection tape was attached to the surface of an SMC molded article containing carbon fiber, a dielectric breakdown test was carried out in accordance with JIS K6911 using the apparatus shown in Figure 16. In the figure, symbol P is a high-voltage power supply, E1 is an upper electrode, E2 is a lower electrode, and X is a test specimen.

[0139] The experimental results are shown in Table 3. The SMC containing carbon fiber had a basis weight of 25 g / m ２ , 50 g / m ２ , 75 g / m ２ , 100 g / m ２ , 125 g / m ２The glass paper prepreg having a protective layer containing the glass paper of Experimental Example 2-1 and a weight per unit area of ​​110 g / m ２ , 214 g / m ２ The one provided with a protective layer made of glass cloth prepreg containing the glass cloth was designated Experimental Example 2-2, the one with nothing laminated or attached was designated Comparative Example 2-1, and the one with protection tape attached was designated Comparative Example 2-2.

[0140] The glass cloth used in Experimental Example 2-2 had a fiber weight of 110 g / m ２ The glass cloth commonly known as 1031 is made of E225 yarn, 62 warp threads / 25 mm, and 58 weft threads / 25 mm. The fiber weight is 214 g / m ２ The glass cloth commonly known as 7628 is made of ECG75 yarn, 44 warp yarns / 25 mm, and 33 weft yarns / 25 mm. The resin content of the glass cloth prepreg using these yarns was 80 wt %, and the resin flow was 50%.

[0141]

[0142] When SMC containing carbon fiber is used on a surface that comes into contact with metal, the SMC side must be insulated. The dielectric breakdown voltage is an indicator of the degree of insulation, and if the dielectric breakdown voltage on the SMC side is 3 kV or higher, preferably 5 kV or higher, electrolytic corrosion between the SMC and metal becomes less likely to occur.

[0143] The breakdown voltage of Comparative Example 2-1 was 0.26 kV, and it is clear that electrolytic corrosion may occur on the metal side.

[0144] On the other hand, the breakdown voltage of Comparative Example 2-2 was 8.22 kV, exceeding 5 kV, making the possibility of electrolytic corrosion on the metal side extremely low. However, when applying a protection tape to the surface of an SMC molded product containing carbon fiber, as described above, the surface of the SMC molded product containing carbon fiber has an inactive layer due to the migration of the release agent during press molding. For application, a process for removing this inactive layer by surface cutting, such as sanding or sandblasting, is required, similar to the unevenness correction and surface preparation of paint. Furthermore, if the tape is not sufficiently adhered, it may peel off during use, or rain and dew or condensation may penetrate through gaps where the tape is not sufficiently adhered, causing electrolytic corrosion. Furthermore, even if the tape is sufficiently adhered at the time of application, if the protection tape is partially peeled off due to vibrations during movement of a vehicle such as a car, electrolytic corrosion may occur.

[0145] In contrast, in Experimental Example 2-1, the fiber basis weight was 25 g / m ２ When glass paper with a fiber basis weight of 50 g / m is used, the breakdown voltage is 1.8 kV, which is 3 kV or less, and there is a high possibility of electrolytic corrosion occurring. ２ When glass paper with a fiber weight of 50 g / m is used, the breakdown voltage is 4.48 V, which is 3 kV or more at which electrolytic corrosion does not occur, and the possibility of electrolytic corrosion is significantly reduced. Therefore, when using a cured glass paper prepreg as an insulating layer (to prevent electrolytic corrosion), ２ It is desirable to use the above glass cloth.

[0146] In addition, the fiber basis weight is 75 g / m ２ When glass paper of this type is used, the breakdown voltage is 5.46 kV, which is 5 kV or more at which electrolytic corrosion occurs very rarely, and is therefore a sufficient level as a countermeasure against electrolytic corrosion.

[0147] Furthermore, the inventors have found that the fiber basis weight is 100 g / m ２ When glass paper of this type was used, the breakdown voltage was 6.55 kV and the fiber weight was 125 g / m ２It has been confirmed that the breakdown voltage increases as the fiber weight of the glass paper prepreg increases, with the breakdown voltage being 7.28 kV when glass paper of this type is used. In other words, by using a prepreg made of glass paper with a high fiber weight (in other words, thicker), it is possible to obtain an SMC (SMC-CFRP) molded product containing carbon fiber with a surface layer that is effective in preventing electrolytic corrosion.

[0148] In addition, in Experimental Example 2-2, the fiber basis weight was 110 g / m ２ When glass cloth with a fiber weight of 214 g / m is used, the breakdown voltage is 2.15 kV, which is less than 3 kV, and there is a high possibility of electrolytic corrosion occurring. ２ When glass cloth with a fiber weight of 200 g / m is used, the breakdown voltage is 3.88 kV, which is above 3 kV at which electrolytic corrosion does not occur, and the possibility of electrolytic corrosion is significantly reduced. Therefore, when using a cured glass cloth prepreg as an insulating layer (anti-corrosion measure), ２ It is desirable to use the above glass cloth.

[0149] In this embodiment, as described above, an example of laminating glass paper prepreg onto SMC is mainly described. However, even if the object to be laminated is not SMC but a prepreg (unidirectional prepreg or cross prepreg) made of carbon fiber and epoxy resin, countermeasures against chipping and electrolytic corrosion can be taken in the same way as when laminating glass paper prepreg onto SMC.

[0150] When the laminated object is a general-purpose epoxy CF prepreg made of carbon fiber and epoxy resin that cures at 130°C, an epoxy resin containing a bifunctional epoxy resin and an amine curing agent in a ratio of, for example, 100:8 to 100:10 is introduced into the resin impregnation tank of the vertical coating machine that coats the glass paper prepreg, so that the curing characteristics are similar to those of the epoxy CF prepreg. This allows the epoxy CF prepreg and the glass paper prepreg to cure in the same manner, enabling simultaneous integral molding of the epoxy CF prepreg and the glass paper prepreg. By making the curing characteristics of the resin used in the glass paper prepreg the same or similar to those of the epoxy CF prepreg resin, the epoxy CF prepreg resin and the glass paper prepreg resin flow into each other and cure simultaneously, even when molding a three-dimensional curved surface material, resulting in a molded product with sufficient adhesive strength between the laminated epoxy CF prepreg and the glass paper prepreg.

[0151] In other words, by coating the glass paper prepreg with a resin that has curing properties that match the curing properties of the resin of the object to be laminated, such as SMC or epoxy CF prepreg, a layer of glass paper prepreg with high adhesive strength can be obtained.

[0152] The glass paper prepreg layer is a thin glass fiber substrate called glass paper, but it becomes a GFRP (glass fiber reinforced plastic) layer, which has overwhelmingly higher breaking strength (load value at the time of breaking) and breaking toughness (ability to withstand just before the breaking load) than a coating made of resin alone.

[0153] Furthermore, the glass paper prepreg layer has a high adhesive strength with the carbon fiber SMC layer or the CFRP layer made of epoxy CF prepreg, so the glass paper prepreg layer does not peel off from the underlying SMC or CFRP layer, and its resistance to chipping when hit by pebbles is extremely higher than that of paint.

[0154] Similarly, the highly adhesive glass paper prepreg layer does not expose the carbon fibers of the SMC layer or CFRP layer made of carbon fiber underneath due to peeling or destruction of the glass paper prepreg layer, so it does not come into contact with rainwater. Therefore, even if steel or aluminum is nearby, minute currents (galvanic currents) do not flow, and resistance to electrolytic corrosion is extremely high.

Claims

1. An automobile structural material containing carbon fiber reinforced plastic, comprising: a base layer made of a cured sheet molding compound containing short carbon fibers and a thermosetting resin; and a protective layer laminated on the base layer and made of a cured glass paper prepreg or a cured glass cloth prepreg containing glass fibers and a thermosetting resin, wherein the base layer and the protective layer are cured integrally.

2. An automobile structural material according to claim 1, characterized in that the thickness of said protective layer is 0.15 mm or more and 0.50 mm or less.

3. The automotive structural material according to claim 2, characterized in that the dielectric breakdown voltage is 3 kV or more.

4. The automotive structural material according to claim 2, characterized in that the dielectric breakdown voltage is 5 kV or more.

5. In the automobile structural material according to any one of claims 1 to 4, the protective layer has a basis weight of 50 g / m ２ An automobile structural material comprising the above glass paper.

6. In the automobile structural material according to any one of claims 1 to 4, the protective layer has a basis weight of 100 g / m ２ An automobile structural material comprising the above glass cloth.

7. A method for manufacturing an automobile structural material containing carbon fiber reinforced plastic, comprising: a lamination step of laminating a semi-cured sheet molding compound containing short carbon fibers and a thermosetting resin, and a semi-cured glass paper prepreg or glass cloth prepreg containing glass fibers and a thermosetting resin; and a curing step of pressurizing and heating the laminated sheet molding compound and the glass paper prepreg or the glass cloth prepreg to integrally cure them.

8. A method for manufacturing automotive structural materials as described in claim 7, characterized in that the resin content of the glass paper prepreg or the glass cloth prepreg is 80 wt % or more and 95 wt % or less.

9. A method for manufacturing a structural material for automobiles according to claim 7, characterized in that the resin flow of the glass paper prepreg or the glass cloth prepreg, expressed by the following formula, is 50% or more and 80% or less: Resin flow (%) = Amount of resin (g) that flows out when press-molded under conditions of 150°C and 0.3 MPa / Weight (g) of prepreg before resin flows out during press-molding 10. A method for manufacturing structural materials for automobiles according to claim 8, characterized in that the resin flow of the glass paper prepreg or the glass cloth prepreg, expressed by the following formula, is 50% or more and 80% or less: Resin flow (%) = Amount of resin (g) that flows out when press-molded under conditions of 150°C and 0.3 MPa / Weight of prepreg before resin flows out during press-molding (g) 11. In the method for manufacturing an automobile structural material according to any one of claims 7 to 10, the glass paper prepreg has a basis weight of 50 g / m ２ A method for producing an automobile structural material, comprising the above glass paper.

12. In the automobile structural material according to any one of claims 7 to 10, the glass cloth prepreg has a basis weight of 100 g / m ２ A method for producing an automobile structural material, comprising the above glass cloth.

Images