Hemmed portion structure of vehicle body

Abstract

To provide a hemmed portion structure of a vehicle body capable of suppressing corrosion of an outer panel and an inner panel even when water enters a region on the open side of the hemmed portion.SOLUTION: The hemmed portion structure of a vehicle body includes an outer panel 10, an inner panel 20, and an adhesive 30 that joins the outer panel and the inner panel. An edge portion of the outer panel is folded back so as to wrap around an edge portion of the inner panel, thereby forming a hemmed portion. The adhesive 30 contains thermally responsive microcapsules 31M enclosing an anti-corrosion wax, and a surface of the adhesive that is exposed from the outer panel 10 and the inner panel 20 is covered with a coating film 33 of the anti-corrosion wax.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a hemming structure for an automobile body. [Background technology]

[0002] An automobile body is equipped with many body components, such as a hood, doors, fenders, and tailgate. Each of these components is provided with an inner panel and an outer panel, respectively, inside and outside the vehicle. As shown in FIG. 7 , hemming is used to join an outer panel 10 and an inner panel 20. Furthermore, a widely adopted construction method involves applying an adhesive 60 to the hemmed portion to prevent misalignment between the panels. More specifically, after press-molding each panel, an adhesive is applied, hemming is performed, and the adhesive is then cured during paint baking. Therefore, a thermosetting adhesive 60 that cures upon heating (approximately 120 to 200°C) is used. Both conductive and non-conductive adhesives are used. The conductive adhesive used in the hemmed portion ensures conductivity by having a carbon-based conductive filler that is connected in a network-like manner within the adhesive.

[0003] As an example of such hemming bending using an adhesive, Patent Document 1 describes a method for forming a hemming portion of an automobile body, which is characterized by filling an adhesive containing a thermally expandable filler into the gap in the hemming portion of an automobile body consisting of an interior panel and an exterior panel having a bent portion that covers the edge of the interior panel, and then expanding the adhesive by a heat treatment performed to harden the paint, thereby covering the edge of the paint. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2582780 Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in Figure 8, the hemmed portion has a structure in which the hemmed interior 18, where the outer panel 10 is folded back, forms a closed, bag-like space formed by the inner panel 20 and adhesive 60. This hemmed interior 18 is a region where electrodeposition coating is difficult to apply because air cannot escape during the electrodeposition coating process, preventing the entry of electrodeposition liquid. On the other hand, the opposite side of the adhesive 60 from the hemmed interior 18 (the upper side in Figure 8) is open, allowing the electrodeposition liquid to enter and electrodeposition coating to be applied.

[0006] 8, if the adhesive 60 is non-conductive, an electrodeposition coating 70 is formed on the surfaces of the outer panel 10 and the inner panel 20, but the electrodeposition coating does not adhere to the surface of the non-conductive adhesive 60, not only inside the hemming bend 18 but also on the open side, and therefore no electrodeposition coating 70 is formed. As a result, gaps are created at the boundaries between the exposed surface of the non-conductive adhesive 60 on the open side and the electrodeposition coating 70 on the surfaces of the outer panel 10 and the inner panel 20, forming weak points. If water seeps into these gaps, corrosion 12, 22 occurs in the outer panel 10 and the inner panel 20, which is a problem.

[0007] 9, when a conductive adhesive 61 is used, the electrodeposition paint also adheres to the surface of the adhesive 61 during the electrodeposition coating process, making it possible to form the electrodeposition coating 70 without gaps on the exposed surfaces of the outer panel 10, the inner panel 20, and the adhesive 60. However, the conductive adhesive 61 has a higher electrical resistance than the metal outer panel 10 and inner panel 20, so the amount of electrodeposition paint that adheres is small. Therefore, the electrodeposition coating 70a on the exposed surface of the conductive adhesive 61 is not formed to a sufficient thickness, which causes the same problem of corrosion as when the non-conductive adhesive 60 shown in FIG.

[0008] Therefore, whether non-conductive or conductive adhesives 60, 61 are used after the electrodeposition coating 70 is formed, by applying a waterproof anti-rust wax to the exposed surfaces of the adhesives 60, 61, it is possible to prevent water from penetrating into the gap at the boundary between the adhesives 60, 61 and the electrodeposition coating 70. However, in order to apply the anti-rust wax to the exposed surfaces of the adhesives 60, 61, because the exposed surfaces of the adhesives 60, 61 are inside the door or hood, a hole must be made in the inner panel 20, a dedicated spray gun nozzle (not shown) must be inserted, and the anti-rust wax must be sprayed onto the exposed surfaces of the adhesives 60, 61 to apply it.

[0009] Because holes large enough to accommodate a nozzle must be located on the flat portion of the inner panel 20, they cannot be located near hemmed areas, such as vertical walls or corners, which means the rust-preventive wax must be sprayed from a distance using a spray gun. Because the rust-preventive wax is far from the target exposed surfaces of the adhesives 60 and 61, it spreads due to air resistance and adheres to the surfaces of the outer panel 10 and inner panel 20 around the hemmed areas. If exposed to high temperatures during the wax application process or during product use, the rust-preventive wax adhering to the areas around the hemmed areas can leak out through small holes (not shown), such as drainage holes, in the inner panel 20, resulting in cosmetic defects. Furthermore, because the target exposed surfaces of the adhesives 60 and 61 are located inside the door or hood in narrow areas and difficult to see from the outside, the rust-preventive wax tends to deviate from its target and is difficult to inspect after application.

[0010] Patent Document 1 shows a method in which a thermally expandable filler is contained in the adhesive, and the adhesive expands when the paint is baked to cover weak spots. However, there is a concern that the thermal expansion of the adhesive will cause deformation of the panel, which will impair the aesthetic appearance or reduce the bonding strength of the hemmed area.

[0011] In view of the above problems, the present invention aims to provide a hemming structure for an automobile body that can suppress corrosion of the outer panel and inner panel even if water penetrates into the open area of ​​the hemming. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the present invention provides a hemming structure for an automobile body comprising an outer panel, an inner panel, and an adhesive that joins the outer panel and the inner panel, wherein the edge of the outer panel is folded back to wrap around the edge of the inner panel to form the hemming, the adhesive contains heat-responsive microcapsules that encapsulate anti-rust wax, and at least a portion of the exposed area of ​​the adhesive is covered with a coating of the anti-rust wax. [Effects of the Invention]

[0013] Thus, according to the present invention, the adhesive that joins the outer panel and the inner panel contains heat-responsive microcapsules that encapsulate anti-rust wax, so that the portions of the adhesive exposed from the outer panel and the inner panel can be covered with a coating of anti-rust wax, thereby suppressing corrosion. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a flow chart showing an example of a method for forming a hemming portion structure of an automobile body according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing one embodiment of the hemming portion structure after electrodeposition coating shown in FIG. 1. [Figure 3] 2 is a cross-sectional view schematically showing an embodiment of the hemming portion structure shown in FIG. 1 immediately after paint baking. [Figure 4] FIG. 4 is a cross-sectional view schematically showing the formation of a coating of rust-preventive wax in the hemming structure shown in FIG. 3. [Figure 5] FIG. 10 is a cross-sectional view schematically showing another embodiment of a hemming portion structure for an automobile body according to the present invention. [Figure 6] FIG. 10 is a cross-sectional view schematically showing yet another embodiment of a hemming portion structure for an automobile body according to the present invention. [Figure 7] 1 is a schematic diagram showing an example of a hemming portion structure of an automobile body. [Figure 8] FIG. 10 is a cross-sectional view schematically showing an example of a conventional hemming portion structure. [Figure 9] FIG. 10 is a cross-sectional view schematically showing another example of a conventional hemming portion structure. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a hemming structure for an automobile body according to the present invention will now be described with reference to the accompanying drawings. Note that the drawings are illustrated for simplicity and clarity of the configuration, and are not necessarily drawn to scale.

[0016] The hemming structure for an automobile body of this embodiment includes an outer panel, an inner panel, and an adhesive that joins the outer panel and the inner panel, and the edge of the outer panel is folded back to enclose the edge of the inner panel to form the hemming. The adhesive contains thermoresponsive microcapsules that encapsulate rust-preventive wax, and at least a portion of the exposed area of ​​the adhesive is covered with a coating of rust-preventive wax.

[0017] The hemming structure of this embodiment can be formed, for example, by a hemming portion forming method including a press forming step S1, a hemming step S2, and an electrodeposition coating step S3, as shown in Fig. 1. The hemming step S2 includes two sub-steps: adhesive application S2-1 and hemming bending S2-2, and the electrodeposition coating step S3 includes three sub-steps: water washing and chemical conversion treatment S3-1, electrodeposition coating S3-2, and paint baking S3-3.

[0018] The press-forming process S1 is a process in which an outer panel to be placed on the outside of the vehicle body and an inner panel to be placed inside the vehicle body are press-formed into predetermined shapes for a hood, a door, a fender, a back door, etc. The outer panel and the inner panel may be made of a steel plate or an aluminum alloy plate, for example.

[0019] Next, adhesive application S2-1 of the hemming step S2 is a sub-step of applying adhesive to the joint between the outer panel and the inner panel. The adhesive in this embodiment has microcapsules dispersed therein. The base adhesive may be an adhesive commonly used for hemming, such as an epoxy adhesive or a phenolic adhesive. The adhesive may be conductive or non-conductive. For example, if the adhesive is conductive, it may contain a conductivity-imparting agent such as a conductive carbon filler. The adhesive may be either a room-temperature curing type or a thermosetting type.

[0020] Microcapsules have a thermal responsiveness such that they melt or soften when heated, releasing their contents. Examples of such thermally responsive microcapsules include phenolic resin microcapsules disclosed in JP-A-7-51560 and JP-A-6-145421, and polyurethane resin microcapsules disclosed in JP-A-5-317694. The size of the microcapsules is not particularly limited, but for example, those with an average diameter in the range of 50 to 500 μm are used.

[0021] The response temperature (T3) of the thermoresponsive microcapsules is preferably lower than the curing temperature (T1) of the electrodeposition paint used in electrodeposition coating S3-2 in the electrodeposition coating step S3 described below, thereby allowing the encapsulated materials to be released by the paint baking S3-3 in the electrodeposition coating step S3. The response temperature (T3) of the thermoresponsive microcapsules is preferably 15°C lower than the curing temperature (T1) of the electrodeposition paint, and more preferably 30°C lower. In other words, when T1 is 200°C, T3 is preferably 185°C or lower, and more preferably 170°C or lower.

[0022] On the other hand, when the base adhesive is a thermosetting type, the response temperature (T3) of the heat-responsive microcapsules is preferably set to a temperature higher than its curing temperature (T2), thereby preventing the released contents of the microcapsules from mixing with the base adhesive. When a room temperature curing type base adhesive is used, the response temperature (T3) of the heat-responsive microcapsules is preferably set to be higher than room temperature, but in order to prevent the heat-responsive microcapsules from releasing the contents due to a thermal response before reaching the paint baking S3-3 in the electrodeposition coating step S3, for example, a temperature of 80°C or higher is more preferable, and 120°C or higher is even more preferable.

[0023] The microcapsules contain anti-rust wax. Anti-rust waxes widely used in automobiles and the like can be used. Anti-rust waxes typically contain a wax for rust prevention and film formation and a volatile organic component. When unused, such anti-rust waxes are liquid at room temperature or higher, but after use, the organic component volatilizes and solidifies, forming an anti-rust film. The wax component contained in the anti-rust wax is not particularly limited, but examples thereof include paraffin wax, microcrystalline wax, oxidized wax, and combinations thereof.

[0024] In addition, the present invention can also use anti-rust waxes that are solid at room temperature but melt when heated. Specifically, as long as the anti-rust wax has fluidity at the curing temperature (T1) of the electrodeposition paint, it can be used in the present invention whether it is liquid or solid at room temperature before use.

[0025] The hemming step S2-2 in the hemming step S2 may be a commonly performed hemming step, which is a sub-step in which the edge of the outer panel is folded back so as to be wrapped around the edge of the inner panel, thereby joining them together.

[0026] The washing and chemical conversion treatment S3-1 of the electrodeposition coating process S3 is a sub-process that involves washing and chemical conversion treatment, which are commonly performed as pretreatment before electrodeposition coating. Washing removes dirt and oil from the surfaces of the outer and inner panels, and chemical conversion treatment forms a chemical coating on the surfaces of the outer and inner panels. Examples of chemical conversion treatments include zinc phosphate treatment.

[0027] The electrodeposition coating S3-2 in the electrodeposition coating step S3 can be a commonly performed electrodeposition coating. This is a sub-step in which the outer panel and inner panel are immersed in an electrodeposition tank filled with an electrodeposition solution and an electric current is passed through to adhere the electrodeposition paint to the exposed surfaces of the outer panel and inner panel. For example, cationic electrodeposition paint can be used as the electrodeposition paint. The electrodeposition paint has a curing temperature (T1) of, for example, 120 to 200°C. Figure 2 shows the hemmed area after electrodeposition coating S3-2 is performed in this manner. Note that Figure 2 shows the case where a non-conductive adhesive is used as the adhesive.

[0028] As shown in Figure 2, at the hemming portion, the edge of the outer panel 10 is folded back to enclose the edge of the inner panel 20, and adhesive 30 is applied between the outer panel 10 and the inner panel 20. The hemmed interior 18 where the outer panel 10 is folded back forms a closed void with a bag structure formed by the inner panel 20 and the adhesive 30. Heat-responsive microcapsules 31M containing anti-rust wax are dispersed in the adhesive 30.

[0029] Electrodeposition paint 40 is applied to the exposed surfaces of outer panel 10 and inner panel 20. In Figure 2, because adhesive 30 is non-conductive, electrodeposition paint 40 does not adhere to the exposed surface of adhesive 30 due to electrodeposition coating S3-2. Of course, electrodeposition paint 40 does not adhere to the exposed surface of adhesive 30 on the hemmed bent interior 18 side either, because hemmed bent interior 18 has a closed bag structure and does not allow the electrodeposition liquid to penetrate. Then, paint baking S3-3 is performed to harden the electrodeposition paint 40.

[0030] The paint baking S3-3 in the electrodeposition coating process S3 may be a commonly performed paint baking, and is a sub-process in which the outer panel 10 and the inner panel 20 are heated to the curing temperature (T1) of the electrodeposition paint 40 to cure the electrodeposition paint 40 and form an electrodeposition coating film 40C. Figure 3 shows the hemmed area immediately after the paint baking S3-3 has been performed.

[0031] 3, when the hemming portion is heated by the paint baking S3-3 and reaches the response temperature (T3) of the heat-responsive microcapsules 31M, the heat-responsive microcapsules 31M release the rust-preventive wax contained therein by melting, etc. Then, the rust-preventive wax in the microcapsules close to the exposed surface of the adhesive 30 flows out onto the exposed surface of the adhesive 30, leaving behind microcapsule cavities 31E in the adhesive 30.

[0032] Because the rust-preventive wax is a low-viscosity liquid at the curing temperature (T1) of the electrodeposition paint, it is fluid when first poured out, but as shown in Figure 3, the organic components volatilize on the exposed surface of the adhesive 30, causing it to solidify and form a rust-preventive coating 33. In this way, the exposed surface of the adhesive 30 is covered with the rust-preventive coating 33, and the rust-preventive coating 33 can seal any gaps that occur at the boundaries between the adhesive 30 and the electrodeposition coating 40C on the surfaces of the outer panel 10 and the inner panel 20, so that even if water seeps into these areas, corrosion of the outer panel 10 and the inner panel 20 can be prevented.

[0033] Even though microcapsules 31M are dispersed in adhesive 30, the volume change of adhesive 30 is the same as that of conventional adhesives in which microcapsules 31M are not dispersed, and therefore there is no risk of deformation of the panel or overflow of adhesive.

[0034] Furthermore, by incorporating heat-responsive microcapsules 31M encapsulating rust-preventive wax into the adhesive 30 and then performing the paint baking step S3-3 of the electrodeposition coating process S3 to cause the rust-preventive wax to flow out of the heat-responsive microcapsules 31M and form a rust-preventive coating 33 on the exposed surface of the adhesive, excess rust-preventive wax can be prevented from adhering to the outer panel 10 or the inner panel 20 around the hemming portion, preventing poor appearance due to wax leakage. Furthermore, by eliminating the need to apply the rust-preventive wax with a spray gun after paint baking, production efficiency can be improved. Furthermore, there is no need to provide a hole in the inner panel 10 for inserting the nozzle of the spray gun, which prevents a decrease in the strength of the inner panel 10.

[0035] 2 and 3, the case where a non-conductive adhesive 30 having microcapsules 31M dispersed therein has been described, but the present invention is not limited to this. For example, even if a conductive adhesive is used instead of the non-conductive adhesive, a rust-preventive coating can be formed on the exposed surface of the adhesive, and corrosion of the panel can be prevented. This is because the response temperature (T3) of the thermo-responsive microcapsules is lower than the curing temperature (T1) of the electrodeposition paint, and therefore the rust-preventive wax can be caused to flow out of the microcapsules before the electrodeposition paint cures, forming a rust-preventive coating on the exposed surface of the adhesive.

[0036] 4, adhesive 34 without dispersed microcapsules may be applied to outer panel 10 in adhesive application S2-1 of hemming step S2, and then thermo-responsive microcapsules 35M may be projected onto the side of adhesive 34 (the portion that will become the exposed surface of the adhesive after hemming step) using air pressure or the like. Then, hemming bending S2-2 of hemming step S2 folds the edge of outer panel 10 so as to enclose it with the edge of inner panel 20, as shown in FIG. 5, and then electrodeposition paint 40 is applied to the exposed surfaces of outer panel 10 and inner panel 20 by electrodeposition coating S3-2 of electrodeposition coating step S3. Then, by heating the hemmed portion in paint baking S3-2 of electrodeposition coating step S3, electrodeposition paint 40 hardens to form electrodeposition coating film 40C, and rust-preventive wax is released from thermo-responsive microcapsules 35M and flows onto the exposed surface of adhesive 34, forming rust-preventive coating 36, as shown in FIG. Microcapsule cavities 35E remain in the adhesive 34.

[0037] This also allows the exposed surface of adhesive 34 to be covered with anti-rust coating 36, thereby achieving the same effect as the embodiment shown in Figures 2 and 3. Furthermore, while in the embodiment shown in Figures 2 and 3 microcapsules 31M are evenly dispersed in adhesive 30, in this embodiment microcapsules 35M can be unevenly distributed on the exposed surface of adhesive 34 as shown in Figures 5 and 6, so the amount of microcapsules used can be significantly reduced. [Explanation of symbols]

[0038] 10 outer panel 18 Hemming and bending inside 20 Inner Panel 30, 34 Adhesive 31M, 35M Thermoresponsive microcapsules 33, 36 Anti-rust coating 40 Electrodeposition paint

Claims

1. A hemming portion structure for an automobile body, comprising an outer panel, an inner panel, and an adhesive that joins the outer panel and the inner panel, The edge of the outer panel is folded back to enclose the edge of the inner panel, forming a hemmed portion, the adhesive contains thermally responsive microcapsules encapsulating anti-rust wax; A hemming structure in which the surfaces of the adhesive exposed from the outer panel and the inner panel are covered with a coating of the rust-preventive wax.

2. The hemming structure according to claim 1 , wherein the thermoresponsive microcapsules are unevenly distributed on the surface side of the adhesive that is exposed from the outer panel and the inner panel.

3. 3. The hemming structure according to claim 1, wherein the adhesive is a thermosetting adhesive, and the curing temperature thereof is lower than the response temperature of the thermoresponsive microcapsules.

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