Automobile component and method for manufacturing automobile component

Abstract

Disclosed is an automobile component having an excellent vibration damping property.　An automobile component according to the present disclosure comprises a first component, a second component, and a joining part that joins the first component and the second component to each other. The joining part is provided with one or both of a welding part and a mechanical joining part and a foam resin for adhering the first component and the second component to each other.

Description

Automobile parts and manufacturing method of automobile parts

[0001] The present application discloses an automotive part and a method for manufacturing the automotive part.

[0002] In recent years, in order to reduce the weight of automobile bodies while maintaining their strength, ultra-high tensile steels have been adopted as constituent materials for automobile parts, and the thickness of automobile parts has been reduced. However, the reduction in thickness of automobile parts poses a problem in that noise caused by vibrations, such as road noise, becomes more pronounced. For example, vibrations and noise can be transmitted from the automobile's suspension parts to the interior of the vehicle via the frame and panels. In this regard, automobile parts with excellent vibration-damping properties that can reduce vibrations and the like are desired. For example, various vibration-damping steel sheets that can be used as automobile parts have been disclosed (Patent Document 1, etc.).

[0003] Japanese Patent Application Publication No. 4-319433

[0004] Conventional automobile parts have room for improvement in terms of vibration damping.

[0005] The present application discloses the following aspects as one means for solving the above-mentioned problems. <Aspect 1> An automobile part comprising: a first part; a second part; and a joint joining the first part and the second part, wherein the joint comprises one or both of a weld and a mechanical joint, and a foamed resin bonding the first part and the second part. <Aspect 2> The automobile part according to Aspect 1, wherein a portion of the first part and a portion of the second part overlap at the joint, and the foamed resin accounts for 50% or more of the entire overlapping portion of the first part and the second part. <Aspect 3> The automobile part according to Aspect 1 or 2, wherein the foamed resin has a foam content of 1% or more and 70% or less. <Aspect 4> The automobile part according to any of Aspects 1 to 3, wherein the size of the bubbles contained in the foamed resin is 10 μm or more and 3000 μm or less. <Aspect 5> The automotive part of any one of aspects 1 to 4, wherein the loss factor η is 0.02 or more and 0.25 or less. １where the loss factor η １ is the loss factor measured by dynamic viscoelastic measurement in a three-point bending mode at a measurement frequency of 10 Hz, and is the largest loss factor among those at temperatures between 0°C and 30°C. <Aspect 6> The automotive part of any of Aspects 1 to 5, wherein one or both of the first part and the second part comprise a steel plate, and the steel plate has a plate thickness of 0.3 mm or more and 5.0 mm or less. <Aspect 7> The automotive part of any of Aspects 1 to 6, wherein the first part is a frame, and the second part is a panel. <Aspect 8> A method for manufacturing an automotive part comprising a first part and a second part, the method comprising: applying a resin composition to one or both of a portion of the first part and a portion of the second part; bonding the first part and the second part via the resin composition; foaming the resin composition; and performing one or both of welding and mechanical joining on the bonded portion of the first part and the second part.

[0006] The automotive component of the present disclosure has excellent vibration damping properties.

[0007]

[0023] FIG. 1 is a schematic diagram showing an example of the configuration of an automobile part.

[0024] FIG. 2 is a schematic diagram showing an example of the configuration of a joint between a first part and a second part in an automobile part, in a plan view.

[0025] FIG. 3 is a schematic diagram showing a cross section taken along arrows IV-IV in FIG. 3.

[0026] FIG. 4 is a schematic diagram showing an example of a cross section at a joint between a first part and a second part in an automobile part, in which a foamed resin is present around a welded part.

[0027] FIG. 5 is a schematic diagram showing a cross section taken along arrows IV-IV in FIG. 3.

[0028] FIG. 6 is a schematic diagram showing an example of a cross section at a joint between a first part and a second part in an automobile part, in which a foamed resin is not present around a welded part.

[0029] FIG. 7 is a schematic diagram showing an example of a cross section at arrows V-V in FIG. 2.

[0029] FIG. 8 is a schematic diagram showing an example of a cross section at a portion of a joint between a first part and a second part in an automobile part that is not welded or mechanically joined (a portion away from a welded part or a mechanically joined part).

[0029] FIG. 9 is a schematic diagram showing an example of a flow of a manufacturing method for an automobile part. 1 shows an example of the flow of a manufacturing method for an automotive part. 2 shows a schematic diagram of the configuration of a sandwich steel plate used to evaluate the loss factor. 3 shows the relationship between the air bubble ratio and the loss factor. 4 shows a schematic diagram of the configuration of a part used to evaluate the volume of sound radiation from a panel. 5 shows the relationship between the area ratio of adhesive containing bubbles and adhesive without bubbles, and the maximum panel sound radiation ratio (relativized to 100% the maximum panel sound radiation when 100% adhesive without bubbles is applied). 6 shows the relationship between the area ratio of adhesive containing bubbles and adhesive without bubbles, and the average panel sound radiation ratio (relativized to 100% the average panel sound radiation when 100% adhesive without bubbles is applied).

[0008] 1. Automobile Part Hereinafter, an embodiment of an automobile part according to the present disclosure will be described with reference to the drawings. However, the automobile part according to the present disclosure is not limited to the following embodiment.

[0009] 1 to 5, an automobile component 100 according to one embodiment includes a first component 10, a second component 20, and a joint 30 that joins the first component 10 and the second component 20. Here, the joint 30 includes one or both of a welded portion 31 and a mechanical joint (not shown), as well as a foamed resin 32 that bonds the first component 10 and the second component 20 together.

[0010] 1.1 First Component and Second Component As shown in FIG. 1 , the automotive component 100 includes a first component 10 and a second component 20. The first component 10 and the second component 20 may be different components. The first component 10 may be, for example, a frame, a panel, or another component. The second component may be, for example, a frame, a panel, or another component.

[0011] In one embodiment, the first component 10 may be a skeleton, and the second component 20 may be a panel. In this case, the skeleton and the panel can be firmly joined via a joint 30 (described later), and the presence of the foamed resin 32 can enhance vibration damping between the skeleton and the panel. In other words, it is possible to suppress the propagation of vibration from the skeleton to the panel and from the panel to the skeleton.

[0012] Alternatively, in one embodiment, the first component 10 may be a skeleton, and the second component 20 may be a skeleton different from the first component 10. In this case, one skeleton and another skeleton can be firmly joined via a joint 30 described below, and the presence of the foamed resin 32 can enhance vibration damping between the one skeleton and another skeleton. In other words, the propagation of vibration from the one skeleton to the other skeleton can be suppressed.

[0013] Alternatively, in one embodiment, the first component 10 may be a panel, and the second component 20 may be a panel different from the first component 10. In this case, the first panel and the second panel can be firmly joined via a joint 30 (described later), and the presence of the foamed resin 32 can enhance vibration damping between the first panel and the second panel. In other words, the propagation of vibration from the first panel to the second panel can be suppressed.

[0014] The framework may be any framework of an automobile, and the specific type thereof is not particularly limited. The framework may be, for example, a member such as a floor member, a side member, or a cross member; a pillar such as an A-pillar, a B-pillar, or a C-pillar; a sill such as a side sill; or a floor cross member.

[0015] The panel may be any panel of an automobile, and the specific type thereof is not particularly limited. The panel may be, for example, a floor panel, a roof panel, an inner panel, a back panel, a door, a hood, a wheelhouse, or a cowl portion.

[0016] 2A to 2D show specific examples of combinations of a first component 10 and a second component 20. FIG. 2A shows an automotive component having an A-pillar as the first member 10 and a roof panel as the second member 20. FIG. 2B shows an automotive component having an inner panel of a wheelhouse as the first member 10 and an outer panel of the wheelhouse as the second member 20. FIG. 2C shows an automotive component having a side sill as the first member 10 and a floor panel as the second member 20. FIG. 2D shows an automotive component having a front side member as the first member 10 and a floor cross member as the second member 20. As shown in FIGS. 2A to 2D, the technology of the present disclosure is applicable to various automotive components.

[0017] The material and shape of the first component 10 and the second component 20 may be any material that allows welding and / or mechanical joining. The material of the first component 10 and the second component 20 may be at least one material selected from, for example, a metal material, a plastic material, a rubber material, a fiber-reinforced plastic (FRP), and the like. The first component 10 and the second component 20 may be made of the same material or different materials. In particular, excellent strength is likely to be ensured when one or both of the first component 10 and the second component 20 are made of a metal material. Furthermore, excellent strength is also likely to be ensured when one or both of the first component 10 and the second component 20 are made of a fiber-reinforced plastic material.

[0018] The type of metallic material is not particularly limited and may be at least one selected from iron, titanium, aluminum, magnesium, and alloys thereof. Examples of alloys include iron-based alloys (including stainless steel), Ti-based alloys, Al-based alloys, and Mg alloys. In one embodiment, one or both of the first component 10 and the second component 20 may be made of steel. The steel is not particularly limited and may be, for example, steel standardized by the Japanese Industrial Standards (JIS). Specific examples include carbon steel, alloy steel, and high-tensile steel used for general structures and machine structures. The steel components are not particularly limited and may contain one or more of Mn, Si, P, Al, N, Cr, Mo, Ni, Cu, Ca, Mg, Ce, Hf, La, Zr, and Sb in addition to Fe and C. For example, the steel may contain C, Si, Mn, P, S, Al, and N, with the balance being Fe and impurities.

[0019] Fiber-reinforced plastic materials (FRP) are made by reinforcing a matrix resin with a fiber material. The types of resin and fiber material are not particularly limited. FRP may consist only of a matrix resin and a fiber material. Alternatively, FRP may contain various additives, such as conductive particles, inorganic fillers, rubber materials, pigments, colorants, antioxidants, and flame retardants, to impart functionality. FRP may be single-layer or multi-layer, and the number of layers may be selected depending on the application. The matrix resin contained in fiber-reinforced plastic materials (FRP) is not particularly limited and may be a thermoplastic resin, a thermosetting resin, or a combination thereof. In particular, thermoplastic resins have good flexural strength and excellent processability. For example, the thermoplastic resin may be contained in an amount of 50 parts by mass or more, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more per 100 parts by mass of the resin component. The matrix resin may be a thermoplastic resin only. The thermoplastic resin that can be used for the matrix resin is not particularly limited, and may be one or more selected from the group consisting of polyolefins and their acid-modified products; polypropylene; polystyrene; polymethyl methacrylate; AS resin; ABS resin; thermoplastic aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate; thermoplastic epoxy resin; polyimide; polyamide; polyamideimide; polyetherimide; polyethersulfone; polyphenylene ether and its modified products; polyphenylene sulfide; polyoxymethylene; polyarylate; polyether ketone; polyether ether ketone; polyether ketone ketone; and nylon. The thermosetting resin that can be used for the matrix resin is not particularly limited, and may be one or more selected from the group consisting of epoxy resins, vinyl ester resins, phenolic resins, and urethane resins. The fiber material contained in the fiber-reinforced plastic material (FRP) is not particularly limited, and may be, for example, at least one selected from carbon fiber, boron fiber, silicon carbide fiber, glass fiber, aramid fiber, etc. The fiber material may be either long or short fibers. In particular, FRP containing carbon fibers has excellent strength.The type of carbon fiber may be, for example, PAN-based or pitch-based, and can be selected depending on the purpose and application. The fiber material may be one of the above-mentioned fibers, or a combination of multiple types. Examples of reinforcing fiber substrates (prepregs) that serve as the base material for the above-mentioned fiber materials include nonwoven fabric substrates using chopped fibers, cross materials using continuous fibers, and unidirectional reinforcing fiber substrates (UD materials). From the perspective of reinforcing effect, it is preferable to use cross materials or UD materials as the reinforcing fiber substrate. The volume fraction (Vf) of the fiber material in the FRP is not particularly limited, but from the viewpoints of strength and processability, it is preferably 20% by volume or more and 70% by volume or less. The Vf of the fiber material in the FRP is more preferably 25% by volume or more or 30% by volume or more, and more preferably 65% ​​by volume or less or 60% by volume or less. Measurement of Vf can be performed using methods known to those skilled in the art.

[0020] The shapes of the first component 10 and the second component 20 may be determined depending on the application. In one embodiment, one or both of the first component 10 and the second component 20 may be steel sheets. The steel sheets may be optionally surface-treated. Here, the surface treatment may be at least one selected from, for example, various plating treatments such as zinc plating (hot-dip galvanizing, electrogalvanizing, etc.) and aluminum plating, chemical conversion treatments such as chromate treatment and non-chromate treatment, and physical surface roughening treatments such as sandblasting or chemical surface roughening treatments such as chemical etching, but is not limited to these. Furthermore, the steel sheets may be subjected to alloy plating or multiple types of surface treatments. The surface treatment of the steel sheets preferably includes at least a treatment aimed at imparting rust resistance.

[0021] In recent years, in order to reduce the weight of automobile bodies while maintaining the strength of the body, ultra-high tensile steel has been adopted as a constituent material for automobile parts, and the thickness of the automobile parts has been reduced. However, the reduction in thickness of the automobile parts makes it easier for vibrations and noises, such as road noise, to propagate. In other words, when one or both of the first component 10 and the second component 20 are thin-walled components, problems related to vibrations and noise are more likely to become apparent. In contrast, in this embodiment, as described below, high vibration damping can be ensured by combining a foamed resin 32 with one or both of the welded portion 31 and the mechanical joint at the joint 30. In other words, even when one or both of the first component 10 and the second component 20 are thin-walled components, the automobile part 100 has excellent vibration damping properties and can solve problems related to vibrations and noise.

[0022] In one embodiment, one or both of the first part 10 and the second part 20 may include a steel plate, and the steel plate may have a plate thickness of 0.3 mm or more and 5.0 mm or less. The plate thickness of the steel plate may be 0.5 mm or more and 3.0 mm or less, or 1.0 mm or more and 3.0 mm or less. In this application, the term "steel plate" is a concept that includes a formed product obtained by imparting a bend, unevenness, or the like to a steel plate.

[0023] In one embodiment, one or both of the first component 10 and the second component 20 may comprise a steel plate, and the steel plate may have a tensile strength of 250 MPa or more and 2500 MPa or less and a plate thickness as described above. The tensile strength of the steel plate may be 300 MPa or more, 350 MPa or more, 400 MPa or more, 450 MPa or more, 500 MPa or more, 550 MPa or more, 600 MPa or more, 650 MPa or more, 700 MPa or more, 750 MPa or more, 780 MPa or more, 800 MPa or more, 850 MPa or more, 900 MPa or more, 950 MPa or more, 980 MPa or more, 1000 MPa or more, 1050 MPa or more, 1100 MPa or more, or 1200 MPa or more. Pa or more, 1150 MPa or more, 1180 MPa or more, 1200 MPa or more, 1250 MPa or more, 1300 MPa or more, 1350 MPa or more, 1400 MPa or more, 1450 MPa or more, or 1470 MPa or more, and may be 2200 MPa or less, 2000 MPa or less, 1800 MPa or less, 1500 MPa or less, 1300 MPa or less, or 1180 MPa or less. Note that, in the present application, "tensile strength" is in accordance with JIS Z 2241:2011.

[0024] 1.2 Joint Portion As shown in Fig. 1, in the automotive component 100, the first component 10 and the second component 20 are joined via a joint portion 30. As shown in Figs. 3, 4A, and 4B, the joint portion 30 includes one or both of a weld portion 31 that joins the first component 10 and the second component 20 by welding and a mechanical joint portion (not shown) that mechanically joins the first component 10 and the second component 20. Furthermore, as shown in Fig. 5, the joint portion 30 includes a foam resin 32 that bonds the first component 10 and the second component 20 together.

[0025] 1.2.1 Welded Joint and Mechanical Joint At the joint 30 of the automotive component 100, the first component 10 and the second component 20 are firmly joined by one or both of a welded joint 31 and a mechanical joint. While spot welds are shown as examples of welded joints 31 in FIGS. 3, 4A, and 4B, the type of welded joint 31 is not limited thereto. The welded joint 31 may be at least one type selected from, for example, spot welds, resistance welds, seam welds, laser welds, and element welds. Meanwhile, the mechanical joint may be at least one type selected from, for example, riveted joints, hemmed joints, drilled and screwed joints, bolted joints, and friction stir welds. More specifically, the joint 30 may include at least one selected from spot welds, projection welds, arc spot welds, laser welds (linear, spot, O-shaped, or C-shaped), hemmed sections, blind rivet joints, self-piercing rivet joints, resistance element welds, element arc welds, and friction stir spot welds. As shown in Figures 4A and 4B, when the first component 10 and the second component 20 are spot welded, a nugget 31a, where the metal components melt and solidify, is formed at the area pressed by the electrode, and a corona bond, where the metal components are joined without melting, may be formed around the nugget 31a. The "corona bond" refers to the area where the first component and the second component are pressed together, formed around the nugget.

[0026] The shape, size, number, and spacing of the welds 31 and mechanical joints are not particularly limited as long as they can join the first component 10 and the second component 20. Appropriate welds 31 and mechanical joints may be adopted depending on the thickness, materials, etc. of the first component 10 and the second component 20, the target joint strength, etc. Furthermore, as shown in FIG. 4A , foamed resin 32 may be present around the welds 31 and mechanical joints between the first component 10 and the second component 20. In other words, the welds 31 and mechanical joints may be formed so as to penetrate the foamed resin 32. Alternatively, as shown in FIG. 4B , foamed resin 32 may not be present around the welds 31 and mechanical joints between the first component 10 and the second component 20. In other words, foamed resin 32 may be disposed in a portion of the joint 30 away from the welds 31 and mechanical joints (e.g., between one weld 31 and another weld 31).

[0027] 1.2.2 Foamed Resin As shown in FIG. 5 , at the joint 30 of the automotive component 100, the first component 10 and the second component 20 are bonded together by a foamed resin 32. By combining the foamed resin 32 with the welded portion 31 and / or mechanical joint at the joint 30, excellent vibration damping can be achieved between the first component 10 and the second component 20. That is, vibrations in the first component 10 are attenuated by the foamed resin 32 and are less likely to propagate to the second component 20. Furthermore, vibrations in the second component 20 are attenuated by the foamed resin 32 and are less likely to propagate to the first component 10. For example, if the first component 10 is a frame and the second component 20 is a panel, even if vibrations such as road noise propagate from the vehicle's suspension components to the frame during vehicle travel, the propagation of the vibrations from the frame to the panel is suppressed, thereby suppressing vibrations and noise inside the vehicle. As such, the automotive component 100 according to this embodiment has excellent vibration damping.

[0028] 5, the foamed resin 32 has resin 32a and air bubbles (voids) 32b. There are no particular limitations on the type of resin 32a, as long as it is capable of bonding the first component 10 and the second component 20. In the automotive component 100, for example, the resin 32a exhibits vibration-damping properties through shear deformation, and the presence of air bubbles (voids) 32b together with the resin 32a is thought to induce shear deformation, further enhancing the vibration-damping effect.

[0029] That is, the foamed resin 32 contains the resin 32a and the bubbles 32b, resulting in a high loss factor. In other words, the loss factor of the foamed resin 32 containing the bubbles 32b is likely to be higher than the loss factor of the resin 32a alone. In particular, when the resin 32a (cured resin) constituting the foamed resin 32 has a loss factor above and below a certain level, the introduction of the bubbles 32b effectively increases the loss factor. For example, blending various additives into the cured resin increases the amount of components not incorporated into the crosslinked structure of the cured resin, thereby reducing the crosslink density of the cured resin and decreasing the elastic modulus. A decrease in the elastic modulus of the cured resin increases the density of strain energy concentrated at the interface between the voids created by the bubbles 32b and the resin 32a, thereby improving the loss factor and further enhancing the vibration damping effect. However, if the amount of additive is increased too much in order to further increase the loss factor of the cured resin, the elastic modulus will decrease excessively, making it difficult to maintain the shape, making it impossible to introduce air bubbles into the cured resin, and when air bubbles 32b are introduced, the amount of resin component will decrease due to the air bubbles 32b escaping to the outside of the part along with the resin component, resulting in a decrease in the loss factor. In this regard, when the loss factor of resin 32a alone is 0.02 or more and 0.25 or less, the loss factor of foamed resin 32 including air bubbles 32b is likely to be larger than the loss factor of resin 32a alone without air bubbles 32b.

[0030] The foamed resin 32 may be obtained, for example, by forming a resin composition layer containing a resin component (A), a curing agent (B), and a foaming agent (C) between the first part 10 and the second part 20, and then by reacting the resin component (A) with the curing agent (B) to obtain the cured resin 32a, and by generating bubbles 32b using the foaming agent (C). That is, the foamed resin 32 may contain components derived from the resin component (A) and the curing agent (B) and components obtained after foaming of the foaming agent (C). The components contained in the foamed resin 32 can be identified using various analytical devices. For example, by analyzing the components contained in the foamed resin 32, the types and amounts of "components derived from the resin component (A) and the curing agent (B)" and "components remaining after foaming of the foaming agent (C)" can be identified. The types and amounts of the resin component (A) and the curing agent (B) can be identified from the types and amounts of the "components derived from the resin component (A) and the curing agent (B)." The type and amount of the foaming agent (C) can be identified from the types and amounts of the "components remaining after foaming of the foaming agent (C)." In this embodiment, the components contained in the foamed resin 32 can be identified using known methods. For example, and not limited to the following example, pyrolysis GC-MS (Gas Chromatography-Mass Spectrometry) measurement can be used to analyze the components contained in the foamed resin by directly and instantaneously pyrolyzing a trace amount of foamed resin at a high temperature and introducing the generated gas components into a GC-MS.

[0031] The resin component (A) may be at least one selected from, for example, vinyl chloride resin, vinyl acetate resin, polyvinyl alcohol, polycarbonate, polyvinyl butyral, polystyrene, ABS resin, polymethyl methacrylate (methacrylic resin), polyphenylene oxide, polyurethane, ionomer resin, cellulose-based plastic, polyethylene, polypropylene, polyamide (nylon), polyacetal (polyoxymethylene), polyphenylene sulfide, vinylidene chloride resin, polyethylene terephthalate, fluororesin, phenolic resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, silicon resin, alkyd resin, polyimide, polyaminobismaleimide, casein resin, furan resin, and urethane resin.

[0032] The curing agent (B) may be any agent that promotes the curing of the resin component (A). For example, when the resin component (A) is an epoxy resin, the curing agent (B) may be one or both of an amine-based curing agent and an acid anhydride curing agent. When the resin component (A) is a urethane resin, the curing agent (B) may be a polyisocyanate compound or the like.

[0033] The blowing agent (C) may be, for example, at least one selected from azodicarbonamide (ADCA), N,N'-dinitrosopentamethylenetetramine (DPT), 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH), hydrazodicarbonamide (HDCA), barium azodicarboxylate, sodium hydrocarbon, and the like. Furthermore, in order to adjust the bubble generation temperature, the blowing agent (C) may be combined with a blowing aid (D) as necessary. The blowing aid (D) may be, for example, at least one selected from a urea-based aid, a vulcanization accelerator, salicylic acid, zinc oxide, and the like.

[0034] When forming the foamed resin 32, there are no particular limitations on the blending ratio of the resin component (A), curing agent (B), and blowing agent (C). An appropriate blending ratio is adopted depending on the amount of bubbles 32b (cell content) to be generated in the foamed resin 32. According to the inventor's findings, if the amount of blowing agent (C) is too small, the effect of improving the loss factor may be reduced. On the other hand, if the amount of blowing agent (C) is too large, the foaming rate may be too high, resulting in a corresponding reduction in the amount of resin 32a in the foamed resin 32, which may reduce the effect of improving the loss factor. Furthermore, if the amount of blowing agent (C) is too large, the resin component (A) may easily escape from the gap between the first member 10 and the second member 20 during the curing of the resin component (A). As a result, bubbles may not be properly introduced, which may reduce the effect of improving the loss factor. According to the findings of the present inventors, when the foamed resin 32 is obtained by foaming 0.1 to 20 parts by mass of the foaming agent (C) relative to 100 parts by mass of the resin component (A), the effect of improving the loss factor is significantly enhanced, and excellent vibration-damping performance is likely to be ensured. In particular, when the foamed resin 32 is obtained by foaming 0.5 to 5 parts by mass of the foaming agent (C) relative to 100 parts by mass of the resin (A), even more excellent vibration-damping performance is likely to be ensured. The foam content of the foamed resin 32 may be, for example, 1% to 70%, preferably 3% to 50%, and more preferably 5% to 30%. The lower the foam content, the less effective it is in increasing the loss factor. It is believed that a higher foam content enhances the effect of increasing the loss factor. However, if the foam content is too high, the amount of resin 32a becomes relatively small, which may actually decrease the loss factor. The foam content can be measured, for example, using an ultrasonic microscope. When the first and second components are steel plate components, the foam content of the foamed resin can be measured as follows: A sample (a plate-shaped test piece consisting of two steel plates sandwiching a resin layer) is removed from the automobile part and placed in distilled water with the steel plates facing upside down. A 10 mm × 10 mm field of view is observed at a location 1 mm or more away from the edge of the sample (the portion toward the center of the sample) using a reflective scanning acoustic microscope at an ultrasonic frequency of 50 MHz, and image information is collected from 10 fields of view per sample using the scanning acoustic microscope. The image information is then binarized so that the edges of the internal bubbles can be recognized as circles or ellipses.The area of ​​the binarized circular or elliptical section is taken as the area of ​​the bubbles observed from above the sample, and the overall area ratio of the bubbles is determined by image analysis. The average value is calculated for the 10 fields of view, and this average value is taken as the "bubble ratio." Note that even when the first and second parts are parts other than steel plates, the bubble ratio of the foamed resin can be calculated in the same manner as above. The method for measuring the bubble ratio will be explained in more detail in the examples below.

[0035] The resin composition of the foamed resin 32 before curing may contain a curing accelerator (E) as an optional component. The curing accelerator (E) may be selected appropriately depending on the type of resin component (A), etc. The amount of the curing accelerator (E) to be added depends on the type of the curing accelerator (E). The foamed resin 32 may also contain other additives. The other additives may be at least one selected from components that contribute to improving vibration damping, impact modifiers, adhesion promoters, antifoaming agents, leveling agents, etc. Examples of components that contribute to improving vibration damping include rosin-based resins. Examples of impact modifiers and adhesion promoters include at least one selected from core-shell rubber particles, carboxyl-terminated butadiene nitrile rubber (CTBN), thermoplastic elastomers, and acrylic block copolymers.

[0036] As described above, the foamed resin 32 contains the air bubbles 32b. By introducing the air bubbles 32b into the foamed resin 32, the loss factor η of the automotive part 100 is increased compared to when the air bubbles 32b are not introduced. １ In particular, when the size of the bubbles 32b contained in the foamed resin 32 is 10 μm or more and 3000 μm or less, the loss factor η １ It is easy to further improve the loss factor η １ From the viewpoint of further improving the above, the size of the bubbles 32b may be 50 μm or more, 100 μm or more, 200 μm or more, or 300 μm or more, and may be 2500 μm or less, 2000 μm or less, or 1500 μm or less. These lower limit values ​​and upper limit values ​​may be any combination.

[0037] In this application, "bubble size" refers to the "average circle-equivalent diameter of bubbles" measured by X-ray CT. Specifically, a three-dimensional image of the resin foam is obtained by X-ray CT. From the obtained three-dimensional image, information on a cross section that crosses the half-thickness position of the foam along the surface direction is obtained. Each of the multiple bubbles contained in the cross section is converted into a circle of the same area to determine the circle-equivalent diameter. The number average value of each circle-equivalent diameter is considered to be the "bubble size." The measurement conditions for X-ray CT are as follows: X-ray CT measurement device: Xradia520Versa (manufactured by ZEISS) Tube voltage: 30 kV Tube current: 0.67 mA Magnification axial ratio: 0.4 times (lens magnification) Analysis method: Analysis using image analysis software "Avizo Inspect" manufactured by Thermo Fisher Scientific

[0038] The bubble identification method is explained in more detail below. Bubbles are identified by using two functions—Watershed (Separate Object) and Opening—of the image analysis software "Avizo Inspect" in 3D images obtained by X-ray CT. Watershed is a method for identifying two connected bubbles as two separate bubbles rather than a single bubble. Specifically, a point a certain distance from the bubble's outline is defined as the bubble's core. The area of ​​the core expanded until it touches the bubble's outline or another core is considered a bubble. Opening is a method for identifying individual bubbles when multiple connected bubbles form a dumbbell shape. Specifically, compressing a bubble causes the axis of the dumbbell shape to disappear, allowing the two separated bubbles to be identified. Then, by returning the bubble size by the amount of compression, the disappeared area can be identified as a single bubble based on the difference between the pre- and post-compression images.

[0039] In the automobile component 100, when the elastic modulus of the resin constituting the foamed resin 32 (the portion of the foamed resin 32 excluding the air bubbles 32 b) is within a predetermined range, the loss factor η １For example, the elastic modulus of the resin at 0 to 30°C may be 1200 MPa or more and 3000 MPa or less. The elastic modulus may be 1500 MPa or more, 1750 MPa or more, or 2000 MPa or more, and may be 2750 MPa or less, 2500 MPa or less, or 2250 MPa or less. In particular, when the elastic modulus is 1750 MPa or more and 2250 MPa or less and the size of the cells 31 is within the above-mentioned predetermined range, the loss factor η １ In the present application, the "elastic modulus" of a resin is measured by a tensile test.

[0040] As shown in Figures 3 and 4, the foamed resin 32 is sandwiched between the first component 10 and the second component 20. The thickness of the foamed resin 32 (thickness of the adhesive layer) is thin enough to allow the above-mentioned welding or mechanical joining (e.g., spot welding). The thickness of the foamed resin 32 may be, for example, 1.0 µm or more and 1.0 mm or less, or 10 µm or more and 0.2 mm or less. In this embodiment, even if the thickness of the foamed resin 32 is thin, the automotive component 100 has excellent vibration damping properties. For example, even if the thickness of the foamed resin 32 is 0.50 mm or less, excellent vibration damping performance can be exhibited. The thickness of the foamed resin 32 may be 0.10 mm or more and 0.50 mm or less. The thickness may be 0.15 mm or more, 0.20 mm or more, or 0.25 mm or more, or 0.45 mm or less, 0.40 mm or less, or 0.35 mm or less. These lower and upper limits may be any combination.

[0041] In the automotive component 100, it is believed that the higher the area ratio of the foamed resin 32 in the joint 30, the better the vibration damping properties will be. However, the foamed resin 32 does not have to be present throughout the entire joint 30. In this regard, for example, in the joint 30, a portion of the first component 10 and a portion of the second component 20 are overlapped, and the area ratio of the foamed resin 32 to the entire overlapping portion of the first component 10 and the second component 20 may be 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, or 80% or more. The upper limit of the area ratio of the foamed resin 32 depends on the area ratio of the spot welded portion 31. In the joint 30, a resin containing no bubbles may be used in combination with the welded portion 31, the mechanical joint, and the foamed resin 32.

[0042] 1.3 Loss factor η １ According to the new findings of the inventors, the loss factor η of the automobile part 100 １ In particular, when the loss coefficient η due to the introduction of the air bubbles 32b in the foamed resin 32 is within a certain range, １ The improvement effect of the loss factor η of the automobile part 100 is remarkable. １ In the region where the loss coefficient η of the automobile part 100 exceeds a certain value, the loss coefficient η of the automobile part 100 is smaller when the foamed resin 32 does not contain bubbles than when the foamed resin 32 contains bubbles 32b. １ That is, the loss factor η of the automotive part 100 is likely to increase. １ In the region where the loss factor η of the automotive component 100 exceeds a certain value, the advantageous effect of introducing the air bubbles 32b into the foamed resin 32 is lost, and in fact, there are cases where the performance is better without introducing the air bubbles 32b. １ If the loss factor η is less than a certain value, it is difficult to improve the loss factor even if the air bubbles 32b are introduced. １ The improvement effect is that the automotive part 100 has a loss factor η of 0.02 or more and 0.25 or less. １ This is particularly noticeable when the automotive component 100 has a loss factor η １When the loss factor η of the automobile part 100 is 0.10 or more and 0.25 or less, the introduction of bubbles exerts a more excellent effect. １ may be 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, or 0.12 or more, and may be 0.24 or less, 0.23 or less, 0.22 or less, 0.21 or less, or 0.20 or less.

[0043] Furthermore, as described above, even when the resin constituting the foamed resin 32 (the resin not including the bubbles 32b) itself has a loss coefficient that is equal to or greater than a certain value and equal to or less than a certain value, the loss coefficient η of the automotive part 100 due to the introduction of the bubbles 32b can be reduced. １ The effect of improving the loss factor is likely to be enhanced. For example, by blending the above-mentioned additives with the resin, the amount of components not incorporated into the crosslinked structure of the resin increases, reducing the crosslink density of the cured product and the elastic modulus. A decrease in the elastic modulus of the resin increases the density of strain energy concentrated at the interface between the voids created by the bubbles and the resin, thereby improving the loss factor and further enhancing the vibration-damping effect. However, increasing the amount of additives to further increase the loss factor of the foamed resin 32 further reduces the elastic modulus, making it difficult to maintain the shape and preventing the introduction of bubbles 32b into the foamed resin 32, making it difficult to contribute to increasing the loss factor. According to the inventor's findings, when the loss factor of the resin itself constituting the foamed resin 32 (the resin without bubbles 32b) is 0.02 or more and 0.25 or less, the effect of introducing bubbles on increasing the loss factor is significant. When the loss factor of the resin itself is less than 0.02, the elastic modulus is high and the density of strain energy concentrated at the interface between the voids created by the bubbles and the resin is small, so the effect of introducing bubbles on increasing the loss factor is small. Furthermore, if the loss factor of the resin itself exceeds 0.25, the elastic modulus is so low that it becomes difficult to maintain the shape, making it impossible to introduce air bubbles into the cured resin, and the effect of increasing the loss factor becomes small.

[0044] In this application, the loss factor η １" is the loss factor measured by dynamic mechanical analysis (DMA) in a three-point bending mode at a measurement frequency of 10 Hz, and is the largest loss factor between 0°C and 30°C. DMA is a method for measuring the mechanical properties of a sample by applying time-varying strain or stress (vibration) to the sample and measuring the resulting stress or strain. DMA can measure the temperature and frequency dependencies of the storage modulus, loss modulus, loss factor, etc. as the viscoelastic properties of the sample, and among these, the loss factor is generally used as an index of vibration damping performance. Loss factor η of automotive parts １ can be measured by cutting out a part of an automobile part and placing the obtained sample at a predetermined position in a device for measuring the loss factor. The size of the sample is not particularly limited as long as the loss factor can be measured. For example, a sample having a width of 10 mm and a length of 20 to 55 mm is cut out from the automobile part using a cutting machine, and the loss factor is measured. A desirable size is 10 mm in width and 40 mm in length. Here, the sample does not include the mechanical joint. In other words, a portion consisting of the first part, the second part, and the foamed resin arranged between them is cut out from the joint of the automobile part, and this is used as a sample to measure the loss factor η １The loss factor is measured using a DMA7100 manufactured by Hitachi High-Tech Science Corporation. The measurement conditions are a two-cycle heating cycle: heating from -100°C to 200°C at 2°C / min, cooling from 200°C to -100°C, and then heating again from -100°C to 200°C at 2°C / min. The measurement frequency is set to 10 Hz, and the loss factor is measured during the second heating cycle in three-point bending mode. The same applies to measuring the "loss factor of the resin (cured resin) itself that constitutes the foamed resin." In this case, a bubble-free cured resin can be separately prepared and the loss factor measured in the same manner. For example, a bubble-free cured resin can be formed between a first plate-like member and a second plate-like member, and then the first plate-like member and the second plate-like member can be peeled off to prepare the cured resin for measuring the loss factor. Alternatively, there may be cases where the loss factor of a composite consisting of the first plate-shaped member, the second plate-shaped member, and the cured resin sandwiched between them is substantially the same as the loss factor of the cured resin, regardless of whether the first plate-shaped member and the second plate-shaped member are present (the influence of the plates themselves on the loss factor is small). In this case, the loss factor of the composite itself may be measured without peeling off the first plate-shaped member and the second plate-shaped member, and this may be considered as the loss factor of the cured resin itself.

[0045] 2. Manufacturing Method of Automotive Component The automotive component 100 can be manufactured, for example, by the following method. As shown in Figures 6A and 6B, a manufacturing method of the automotive component 100 including a first component 10 and a second component 20 may include applying a resin composition to one or both of a portion of the first component 10 and a portion of the second component 20 (an application step), bonding the first component 10 and the second component 20 via the resin composition (an adhesion step), foaming the resin composition (a foaming step), and performing one or both of welding and mechanical bonding on the bonded portion between the first component 10 and the second component 20 (a bonding step).

[0046] 2.1 Coating Step In the coating step, a resin composition is applied to one or both of a portion of the first component 10 and a portion of the second component 20. The resin composition may contain, for example, the resin component (A), the curing agent (B), and the foaming agent (C) described above. The method for applying the resin composition is not particularly limited. For example, an applicator or the like may be used. The coating area and amount may be determined appropriately depending on the area, thickness, and the like of the foamed resin 32 to be finally obtained.

[0047] 2.2 Bonding Step In the bonding step, the first component 10 and the second component 20 are bonded together via the resin composition. For example, the first component 10 and the second component 20 can be bonded together by overlapping them with the resin composition interposed therebetween and then curing the resin composition by heating or the like. At this time, the foaming step described below may be performed. The heating means and heating temperature are not particularly limited.

[0048] 2.3 Foaming Step In the foaming step, the resin composition is foamed. Specifically, the resin composition is heated, for example, to generate bubbles due to the action of the foaming agent (C) contained in the resin composition. The foaming step may be performed simultaneously with the bonding step, or may be performed at a different time.

[0049] 2.4 Joining Process In the joining process, one or both of welding and mechanical joining are performed on the bonded portion between the first component 10 and the second component 20. The "bonded portion" refers to the portion that includes the portion to which the resin composition is applied and that will ultimately become the bonded portion 30. The joining process may be performed after the curing and foaming of the resin composition, as shown in FIG. 6A, or may be performed before that, as shown in FIG. 6B. The conditions for welding and mechanical joining are not particularly limited. The types of welding and mechanical joining are as described above.

[0050] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0051] 1. Loss Factor Evaluation To simulate the evaluation of the loss factor at the joint between the first and second parts, a rectangular sandwich steel plate as shown in FIG. 7 was fabricated and the loss factor was evaluated. Specifically, two 30 × 250 mm planar rectangular steel plates with a thickness of 0.8 mm were prepared. An adhesive (resin component (A): epoxy resin, curing agent (B): dicyandiamide (DICY), foaming agent (C): N,N'-dinitropentamethylenetetramine (DPT)) was applied to the entire surface of one of the steel plates using an applicator. After the other steel plate was placed on top of the other steel plate along with a spacer, the two steel plates were bonded together via the adhesive by heating and pressing them in a hot press. The amount of foaming agent (C) contained in the adhesive was varied to fabricate multiple sandwich steel plates with different cellular fractions in the adhesive resin layer. Specifically, sandwich steel plate A with a cellular fraction of 0%, sandwich steel plate B with a cellular fraction of 6%, and sandwich steel plate C with a cellular fraction of 20% were obtained. Here, the air void content of the adhesive resin layer in each sandwich steel plate was measured as follows. That is, a 30 mm x 250 mm plate-shaped test piece (sample) was prepared, in which a resin layer of 300 μm ± 30 μm with varying air void content was sandwiched between two 0.8 mm thick steel plates. The steel plates were placed upside down in distilled water. A 10 mm x 10 mm field of view was observed from above using a reflective scanning ultrasonic microscope at an ultrasonic frequency of 50 MHz in the center part of the sample, at a distance of 1 mm or more from the edge, and image information of the scanning ultrasonic microscope image from five fields of view was collected. If a 10 mm x 10 mm field of view could not be secured due to the size of the sample, a total of 500 mm was used. ２ Furthermore, the sample was turned over and five visual fields were observed in the same manner, obtaining image information of a total of 10 visual fields per sample (if a visual field of 10 mm x 10 mm cannot be secured due to the size of the sample, the total of all visual fields should be 1000 mm). ２ The area of ​​the bubble observed from above the sample was determined by image analysis, and the average value of the 10 fields of view was calculated. This average value was used as the "bubble ratio" (if a field of view of 10 mm x 10 mm cannot be secured due to the size of the sample, the total area of ​​the bubble was calculated to be 1000 mm). ２The "porosity" can be determined by the image analysis described above from the observation results of the area. The reason for observing both the front and back sides of the sample with an ultrasonic microscope as described above is that ultrasonic waves are difficult to transmit through the resin and are attenuated, so it is thought that images of the entire 300 μm thick resin layer could not be obtained. On the other hand, since the porosity can be considered to be uniform in the resin thickness direction, the porosity can be determined by measuring using the above observation method even if the resin thickness is 300 μm or more. Note that in the ultrasonic microscope observation described above, the effects of the chemical composition and thickness of the steel sheet can be substantially ignored, and substantially the same results are obtained at least for steel sheets up to a thickness of 2.0 mm.

[0052] The center of each of the prepared sandwich steel plates A to C was fixed to a vibrator and vibrated from 0 to 6000 Hz. The acceleration at the vibration point was measured for each of the first to third bendings, and the loss factor was determined using the half-width method. Figure 8 shows the relationship between the porosity of the adhesive resin layer and the loss factor. In Figure 8, the loss factor of the void-free sandwich steel plate A is set as the reference (1.0), and the loss factors of the sandwich steel plates B and C are shown relative to each other.

[0053] As shown in FIG. 8, it can be seen that the loss factor is improved by including air bubbles in the adhesive resin layer.

[0054] 2. Application to Automotive Parts As shown in Figure 9, double-hat-shaped frameworks (1.0 mm thick) were bonded to both ends of a flat panel (990 mm on each side, 1.0 mm thick) with adhesive resin layers, and spot welding (spot welding interval: 30 mm) was performed at the bonded portions. Vibration damping was evaluated for this case. Specifically, vibration was applied to one end face of each framework, while the other end faces were fixed, and the sound level radiated from the panel was evaluated by simulation. The noise level when the adhesive application area was 100% bubble-free was defined as the reference (100%). The degree of noise reduction was evaluated when some or all of the bubble-free adhesive was replaced with an adhesive containing bubbles. MSC Software's Nastran software was used for the analysis.

[0055] 10A and 10B show the relationship between the application area ratio of the adhesive resin layer containing bubbles ([application area of ​​adhesive resin layer containing bubbles] / [total application area of ​​adhesive]) and the panel radiated sound. Fig. 10A shows the relationship between the area ratio of the adhesive containing bubbles and the adhesive without bubbles and the maximum panel radiated sound ratio (relative to the maximum panel radiated sound when 100% of the adhesive without bubbles is applied as 100%), and Fig. 10B shows the relationship between the area ratio of the adhesive containing bubbles and the adhesive without bubbles and the average panel radiated sound ratio (relative to the average panel radiated sound when 100% of the adhesive without bubbles is applied as 100%). As shown in Figs. 10A and 10B, the panel radiated sound decreases as the application area of ​​the adhesive resin layer containing bubbles increases. It can be seen that, in particular, a stable effect can be obtained for the maximum panel radiated sound when the area ratio of the adhesive resin layer containing bubbles is 50% or more.

[0056] Although the above examples illustrate a configuration in which a foamed resin is combined at the joint of an automotive part having a double hat member as a framework and a panel, the technology of the present disclosure is not limited to this configuration. It is believed that the technology of the present disclosure can be used to achieve predetermined effects even when joining frameworks or panels, etc. Furthermore, while the above examples illustrate a configuration in which spot welding is used at the joint of an automotive part, the technology of the present disclosure is not limited to this configuration. Even when forming a joint by welding or mechanical joining other than spot welding, it is believed that a part with excellent vibration damping properties can be obtained by combining the welding or mechanical joining with a foamed resin. Furthermore, while the above examples illustrate a configuration in which an automotive part is constructed using steel plates, the material and shape of the automotive part are not limited to this.

[0057] From the viewpoint of suppressing vibrations and the like transmitted from the suspension parts to the panel via the frame when the vehicle is running, it is preferable to use foamed resin in conjunction with welding and / or mechanical joining at the joints between the frame and the panel, and it is particularly preferable to use foamed resin in conjunction with welding (particularly spot welding) at the joints between the steel frame and the steel panel.

[0058] 3. Summary From the above results, it can be said that an automotive part that satisfies the following requirements (1) and (2) has excellent vibration damping properties. (1) The automotive part includes a first part, a second part, and a joint that joins the first part and the second part. (2) The joint includes one or both of a welded part and a mechanical joint, and a foamed resin that bonds the first part and the second part.

[0059] 4. Additional Experiments The following additional experiments were conducted to investigate the optimal form of the joint between the foamed resin and the automobile parts.

[0060] 4.1 Preparation of Resin Composition In the following examples, an epoxy resin (YD-127 manufactured by Nippon Steel Chemical & Material Co., Ltd.) or a copolymer polyester composition (Pylon (registered trademark) UR manufactured by Toyobo MC Co., Ltd.) is used as the resin (A) to prepare a composite having a foamed resin between two steel plates, but the type of resin (A) applicable to the technology of the present disclosure is not limited to these.

[0061] 4.1.1 Introducing Bubbles into Cured Resin Among the resin compositions shown in Tables 1 to 4 below, those using DICY as the curing agent (B) were prepared as follows. First, a portion of the resin (A) was set aside, and the foaming agent (C), foaming aid (D), curing agent (B) (trade name: DICY15), and curing accelerator (E) (trade name: DCMU) were uniformly dispersed using a three-roll mill to prepare composition X. All components shown in Tables 1 to 4 below, except for those used to prepare composition X, were weighed into a glass flask and heated and mixed at 150°C to obtain a uniform masterbatch. Next, the obtained masterbatch was cooled to below 60°C, and then composition X was weighed and added. The mixture was heated and mixed at 60 to 70°C to obtain a uniform dispersion, yielding a resin composition. The compositions of the obtained resin compositions are as shown in Tables 1 to 4 below.

[0062] Of the resin compositions shown in Tables 1 to 4 below, those using TPP as the curing agent (B) were prepared as follows: All components shown in Tables 1 to 4 below were weighed into a glass flask and mixed under heating at 60 to 70°C to obtain a resin composition.

[0063] 4.1.2 Cases in which bubbles are not introduced into the cured resin Among the resin compositions shown in Tables 1 to 4 below, those using DICY as the curing agent (B) were prepared as follows. First, a portion of the resin (A) was set aside, and the curing agent (B) (trade name: DICY15) and the curing accelerator (E) (trade name: DCMU) were uniformly dispersed using a three-roll mill to prepare composition Y. All of the components shown in Tables 1 to 4 below, except for those used to prepare composition Y, were weighed into a glass flask and heated and mixed at 150°C to obtain a uniform masterbatch. Next, the obtained masterbatch was cooled to below 60°C, and then composition Y was weighed and added. The mixture was heated and mixed at 60 to 70°C to obtain a uniform dispersion, yielding a resin composition. The compositions of the obtained resin compositions are as shown in Tables 1 to 4 below.

[0064] Of the resin compositions shown in Tables 1 to 4 below, those using TPP as the curing agent (B) were prepared as follows: All components shown in Tables 1 to 4 below were weighed into a glass flask and mixed under heating at 60 to 70°C to obtain a resin composition.

[0065] 4.2 Preparation of Composite Two steel plates (thickness 0.4 mm) were prepared. The resin composition obtained as described above was applied to one of the steel plates using an applicator to a uniform thickness. The other steel plate was placed on the applied surface together with a PTFE spacer to obtain a laminate consisting of steel plate / resin composition / steel plate. The laminate was pressed and held at a predetermined temperature in a hot press to obtain a composite (sandwich steel plate) consisting of steel plate / cured resin / steel plate. The thickness of the cured resin in the plate thickness direction was 400 μm. The obtained composite was cut into a length of 40 mm x width of 10 mm, and the loss factor η １ The test pieces were used for measurement.

[0066] 4.3 Loss factor η １ Measurement of the loss factor η of the obtained composite １ The loss factor η １The measurement method is as explained in the embodiment (the loss factor is measured by dynamic viscoelasticity measurement in a three-point bending mode at a measurement frequency of 10 Hz, and is the largest loss factor between 0°C and 30°C).

[0067] 4.4 Confirmation of the Presence of Air Bubbles The above test pieces were cut and the cut surfaces were visually inspected to confirm the presence of air bubbles.

[0068] 4.5 Evaluation Results Tables 1 to 4 below show the composition of each resin composition, curing temperature, curing time, presence or absence of bubbles, and loss factor η when bubbles are present. １ , and the loss coefficient η when no air bubbles are included ２ The "Kane Ace MX-154" in Tables 1 to 4 is a masterbatch in which 40% core-shell rubber is dispersed in 60% epoxy resin. In Table 4, the values ​​in parentheses shown for examples using "Kane Ace MX-154" are overall values ​​obtained by dividing Kane Ace MX-154 into epoxy resin and core-shell rubber, and assuming resin (A) to be 100 parts by mass.

[0069]

[0070]

[0071]

[0072]

[0073] From the results shown in Tables 1 to 4, the loss factor η of the composite when air bubbles are contained in the cured resin １ The loss factor η of the composite without bubbles is ２ It can be seen that in some cases the vibration damping effect is significantly improved compared to the case of the resin. It is thought that the inclusion of bubbles in the cured resin concentrates strain energy at the interface between the voids created by the bubbles and the resin when the composite vibrates, thereby enhancing the vibration damping effect. The effect of introducing bubbles is as follows: １ This problem occurs particularly remarkably when the loss factor η of the composite is in the range of 0.02 or more and 0.25 or less. １ In the region where exceeds 0.25, the loss factor η when air bubbles are contained in the cured resin １Loss factor η without bubbles ２ In other words, it can be seen that the effect of introducing air bubbles is lost. Also, as is clear from the results shown in Tables 1 to 4, the loss factor η １ In the region where is less than 0.02, the loss factor η can be reduced by including air bubbles in the cured resin. １ Although it can improve the performance, the effect is small.

[0074] Loss factor η １ In the region where the loss coefficient η exceeds 0.25, the introduction of air bubbles １ The reason why the resin does not contribute to the improvement of the properties is thought to be, for example, as follows: if the loss factor is high and the modulus of elasticity is low (soft), air bubbles escape together with the resin during foaming and curing, and the air bubbles are not introduced into the resin in an appropriate manner, and furthermore, the amount of resin is thought to be reduced.

[0075] Loss factor η １ In the region where is less than 0.02, the loss coefficient η due to the introduction of bubbles １ The reason for the decrease in the improvement effect of (1) is thought to be, for example, as follows: Even if air bubbles are introduced into a resin with a small loss factor and a high elastic modulus (hard), when the composite vibrates, it is difficult for strain energy to concentrate at the interface between the voids caused by the air bubbles and the resin, and it is possible that almost no vibration-damping effect is obtained.

[0076] Furthermore, as is clear from the results shown in Tables 1 to 4, when the amount of foaming agent added to 100 parts by mass of resin is up to 5 parts by mass, the loss factor η １ This is thought to be because an increase in the amount of foaming agent added increases the foam content in the cured resin, allowing for the introduction of a suitable number of bubbles. On the other hand, when the amount of foaming agent added is 10 parts by mass or 20 parts by mass, the loss modulus η １The loss factor tends to become smaller. When the foaming agent is excessive, the foaming rate becomes excessive, and the amount of resin decreases accordingly, which is thought to be the reason for the decrease in the loss factor. Also, when the foaming agent is excessive, in some cases, air bubbles may escape from between the plates during resin hardening, and the air bubbles may not be properly introduced.

[0077] 4.6 Investigation of Bubble Size The size (average circle equivalent diameter) of bubbles contained in the cured resin was measured for the above-mentioned Reference Examples 7, 17, and 25. The method for measuring bubble size was as described in the embodiment of this specification. The results are shown in Table 5 below.

[0078]

[0079] As is clear from the results shown in Table 5, when the size of the bubbles contained in the cured resin is 10 μm or more and 3000 μm or less, the loss factor η １ It can be said that the improvement effect is more significantly enhanced.

[0080] 100 Automobile part 10 First part 20 Second part 30 Joint 31 Mechanical joint 31a Nugget 32 ​​Foamed resin 32a Resin 32b Air bubbles

Claims

1. An automotive part, comprising: a first part, a second part, and a joint portion that joins the first part and the second part, wherein the joint portion includes one or both of a welded portion and a mechanical joint portion, and a foamed resin that adheres the first part and the second part. An automotive part.

2. The automotive part according to Claim 1, wherein at the joint portion, a part of the first part and a part of the second part are overlapped, and an area ratio of the foamed resin in the entire overlapping portion of the first part and the second part is 50% or more. An automotive part.

3. The automotive part according to Claim 1 or 2, wherein a bubble ratio of the foamed resin is 1% or more and 70% or less. An automotive part.

4. The automotive part according to Claim 1 or 2, wherein a size of bubbles included in the foamed resin is 10 μm or more and 3000 μm or less. An automotive part.

5. The automotive part according to Claim 1 or 2, An automotive part.

6. A loss coefficient η of 0.02 or more and 0.25 or less １ and the loss coefficient η １ is a loss coefficient measured in a three-point bending mode at a measurement frequency of 10 Hz by dynamic viscoelasticity measurement, and is the largest among the loss coefficients between 0°C and 30°C. The automotive part according to Claim 1 or 2, wherein one or both of the first part and the second part include a steel plate, and the steel plate has a plate thickness of 0.3 mm or more and 5.0 mm or less. An automotive part.

7. The automotive part according to Claim 1 or 2, wherein the first part is a frame, and the second part is a panel. An automotive part.

8. A method for manufacturing an automotive part including a first part and a second part, the method comprising: applying a resin composition to one or both of a part of the first part and a part of the second part; adhering the first part and the second part via the resin composition; foaming the resin composition; and performing one or both of welding and mechanical joining on an adhered portion between the first part and the second part. A manufacturing method. ​ ​