Manufacturing method of painted metal sheets

Abstract

To provide a method for manufacturing painted metal sheets that reduces the risk of peeling of the coating layer. [Solution] The method for manufacturing a painted metal sheet includes a coating layer formation step S156. In the coating layer formation step S156, a coating layer 22 is formed from paint applied to the surface of a substrate 20. The substrate 20 has a metal, plate-shaped body 30. The coating layer 22 has an undercoat layer 40 and a topcoat layer 42. The undercoat layer 40 is placed on the surface of the substrate 20. The topcoat layer 42 is placed on the surface of the undercoat layer 40. The coating layer formation step S156 includes an undercoat painting step S170, an undercoat layer formation step S172, a topcoat painting step S174, and a topcoat layer formation step S176. The undercoat paint includes a urethane resin and a synthetic resin that hardens with the urethane resin.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a painted metal plate.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing a painted metal plate by an electron beam curing method. In this manufacturing method, first, the following-described paint is thermally cured to a solid state or a state close to a solid. The paint is composed of a composition containing, as an essential component, an oligo / polyester (meth)acrylate having two or more (meth)acryloyl groups in one molecule and a (meth)acryloyl group equivalent of 400 or less as the lowermost layer. Next, one or more layers of the following-described paint are applied on the paint. The paint is composed of a composition containing, as an essential component, an oligo / polyester (meth)acrylate having two or more (meth)acryloyl groups in one molecule and a (meth)acryloyl group equivalent of 400 or less. Next, all these paints are cured by electron beam irradiation. At that time, the ion permeation resistance of the coating film layer formed from the cured paint is set to 500 MΩ·cm 2 or more. According to the invention disclosed in Patent Document 1, a painted metal plate excellent in high hardness, stain resistance, antiglare property, and having sufficient corrosion resistance (for example, 5 years or more) even in a harsh corrosion environment is formed.

[0003] Patent Document 2 discloses a method for manufacturing a painted stainless steel sheet. In this manufacturing method, the painted stainless steel sheet is based on a stainless steel sheet containing 18% or more Cr. The bottom layer of the coating layer of this painted stainless steel sheet is a thermosetting type having flexible properties with a Tg (glass transition temperature) of 65°C or less, and is thermoset to a solid state. In this manufacturing method, one or more layers of the paint described below are applied on the bottom layer. The paint consists of a composition in which oligopolyester (meth)acrylate, which contains two or more (meth)acryloyl groups in one molecule and has an (meth)acryloyl group equivalent of 400 or less, is an essential component. Next, the paint containing the oligopolyester (meth)acrylate is cured by electron beam irradiation, ultraviolet irradiation, or heat. According to the invention disclosed in Patent Document 2, a painted stainless steel sheet is provided that has excellent cleaning and recovery properties in a tunnel environment, has a coating layer with high scratch resistance, and has excellent corrosion resistance of scratches in a severe corrosive environment. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-262136 [Patent Document 2] Japanese Patent Application Publication No. 8-281206 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the methods for manufacturing painted metal sheets disclosed in Patent Document 1 and the methods for manufacturing painted stainless steel sheets disclosed in Patent Document 2 have room for improvement regarding the peeling of the coating layer. The present invention aims to solve this problem. Its objective is to provide a method for manufacturing painted metal sheets that suppresses the risk of peeling of the coating layer. [Means for solving the problem]

[0006] To solve the above-mentioned problems, according to a certain aspect of the present invention, a method for manufacturing a painted metal sheet comprises a coating layer formation step S156. In the coating layer formation step S156, a coating layer 22 is formed from paint applied to the surface of a substrate 20. The substrate 20 has a metal, plate-shaped body 30. The coating layer 22 has an undercoat layer 40 and a topcoat layer 42. The undercoat layer 40 is placed on the surface of the substrate 20. The topcoat layer 42 is placed on the surface of the undercoat layer 40. The coating layer formation step S156 comprises an undercoat painting step S170, an undercoat layer formation step S172, a topcoat painting step S174, and a topcoat layer formation step S176. In the undercoat painting step S170, an undercoat paint is applied to the surface of the substrate 20. In the undercoat layer formation step S172, the undercoat paint is cured. This forms the undercoat layer 40. In the topcoat painting process S174, electron beam curable paint is applied to the surface of the undercoat layer 40. In the topcoat layer formation process S176, electron beams are irradiated onto the electron beam curable paint. This forms the topcoat layer 42. The undercoat paint is made of urethane resin and urethane resin as a hardening agent It contains a hardening synthetic resin. The electron beam curing paint contains a urethane acrylate oligomer.

[0007] Furthermore, it is desirable that the synthetic resin mentioned above be at least one of polyester and epoxy. [Effects of the Invention]

[0008] According to the present invention, the risk of peeling of the coating layer is reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This is a conceptual diagram of a cross-section of a painted steel sheet according to one embodiment of the present invention. [Figure 2] This figure shows the steps of a method for manufacturing a painted steel sheet according to one embodiment of the present invention. [Figure 3] This figure shows the components of the undercoat layer according to one embodiment of the present invention, as well as the results of an adhesion test to the processed area and a DuPont drop impact test. [Modes for carrying out the invention]

[0010] Embodiments of the present invention are described below. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are identical; therefore, detailed descriptions of them will not be repeated.

[0011] <Explanation of the composition of painted metal sheets> The painted metal sheet according to this embodiment is realized as a painted steel sheet. Of course, the scope of the present invention is not limited to painted steel sheets. For example, the painted metal sheet to which the painting method according to the present invention is applied may be an aluminum sheet to which the surface has been painted as described later. Figure 1 shows a conceptual diagram of the cross-section of the painted steel sheet according to this embodiment. In the following, the structure of the painted steel sheet according to this embodiment will be described based on Figure 1.

[0012] The painted steel sheet according to this embodiment comprises a base body 20, a coating layer 22, and a back surface layer 24.

[0013] The substrate 20 has a main body 30, plating layers 32, 32, and chemical conversion treatment layers 34, 34.

[0014] In this embodiment, the main body 30 is a well-known steel plate. As is clear from the above description, the material constituting the main body 30 is not limited to a steel plate, as long as it is a metallic, plate-like object on which the top coating layer 42 described later can be formed by electron beam curing paint.

[0015] In this embodiment, the plating layers 32, 32 are formed on both the front and back surfaces of the main body 30. Of course, the plating layers 32, 32 may be formed on only one of the front or back surfaces of the main body 30. If possible, the plating layers 32, 32 may not be formed on both the front and back surfaces of the main body 30.

[0016] In this embodiment, the chemical conversion treatment layers 34, 34 are formed on the surface of the plating layers 32, 32. The chemical conversion treatment layers 34, 34 may be formed only on the side of the main body 30 where the plating layer 32 is formed. The chemical conversion treatment layers 34, 34 do not need to be formed on both the front and back sides of the main body 30.

[0017] The coating layer 22 according to this embodiment is formed from a paint applied to the front surface of the substrate 20. The coating layer 22 according to this embodiment has an undercoat layer 40 and a topcoat layer 42.

[0018] In the case of this embodiment, the undercoat layer 40 is disposed on the front surface of the chemical conversion treatment layer 34 of the substrate 20. Of course, if the chemical conversion treatment layer 34 is not formed on the front surface of the substrate 20, the undercoat layer 40 is formed on the surface of the plating layer 32. If the plating layer 32 is not formed either, the undercoat layer 40 is formed on the surface of the main body 30. The undercoat layer 40 contains components formed by the curing of a paint described later. In the undercoat layer 40, components other than those components are not particularly limited.

[0019] The topcoat layer 42 is disposed on the surface of the undercoat layer 40. The topcoat layer 42 according to the present invention contains components formed by the curing of an electron beam curable paint. Examples of such components include a monomer having an acryloyl group and a polymer having an acryloyl group. When these are polymerized by an electron beam, the topcoat layer 42 is formed. In the case of this embodiment, in the topcoat layer 42, specific components contributing to the curing in response to the irradiation of an electron beam and components other than those components are not particularly limited. The electron beam curable paint cures when irradiated with an electron beam Contains urethane acrylate oligomer Any paint may be used as long as it is a paint.

[0020] The back surface layer 24 according to this embodiment is formed by applying a well-known paint to the back surface of the substrate 20 and curing it. Since the specific configuration of the back surface layer 24 is not directly related to the present invention, its detailed description will not be repeated.

[0021] <Explanation of the manufacturing method> FIG. 2 shows the steps of the manufacturing method of the painted steel sheet according to this embodiment. Based on FIG. 2, the manufacturing method of the painted steel sheet according to this embodiment will be described.

[0022] The method for manufacturing a painted steel sheet according to this embodiment comprises a plating step S150, a chemical conversion treatment step S152, a back surface painting step S154, and a coating layer formation step S156.

[0023] In the plating process S150, a well-known zinc plating is applied to both the front and back surfaces of the main body 30. This forms plating layers 32, 32 on both the front and back surfaces of the main body 30. The specific means for this are well known, so a detailed explanation will not be repeated here. In this invention, any plating may be applied instead of zinc plating. Examples of such platings include zinc-aluminum alloy plating, nickel plating, chromium plating, and tin plating. Furthermore, this step is not essential in this invention.

[0024] In the chemical conversion treatment step S152, the plating layers 32, 32 on both the front and back surfaces of the main body 30 are subjected to chemical conversion treatment. This forms chemical conversion treatment layers 34, 34 on the surfaces of the plating layers 32, 32. The formation of the chemical conversion treatment layers 34, 34 on the surfaces of the plating layers 32, 32 completes the substrate 20. In this invention, the specific content of the chemical conversion treatment is not particularly limited. Examples of chemical conversion treatments that can be applied in this invention include zinc phosphate treatment, zirconium treatment, and silane treatment. If the plating layers 32, 32 are zinc plating or zinc alloy plating, chromate treatment may be performed as a chemical conversion treatment. Examples of chromate treatments include hexavalent chromium treatment and trivalent chromium treatment. Of course, if the plating layers 32, 32 are zinc plating or zinc alloy plating, well-known chromate-free treatment may be performed. The specific procedures for these chemical conversion treatments are well known, so a detailed explanation will not be repeated here. Furthermore, this step is not essential in this invention.

[0025] In the back surface coating process S154, paint is applied to the surface of the chemical conversion treatment layer 34 on the back side of the substrate 20, and the paint is cured. This paint then becomes the back surface layer 24. The specific means for this are well known, so a detailed explanation will not be repeated here. If the chemical conversion treatment layer 34 is not formed on the back surface of the substrate 20, the paint is formed on the surface of the plating layer 32. If the plating layer 32 is also not formed, the paint is formed on the surface of the main body 30.

[0026] In the coating layer formation step S156, a coating layer 22 is formed from the paint applied to the surface of the chemical conversion treatment layer 34 on the front side of the substrate 20. In this embodiment, the coating layer formation step S156 includes a primer coating step S170, a primer layer formation step S172, a topcoat coating step S174, and a topcoat layer formation step S176.

[0027] In the undercoat painting process S170, an undercoat paint is applied to the surface of the chemical conversion treatment layer 34 on the front side of the substrate 20. In this embodiment, the undercoat paint includes a urethane resin (used as a curing agent in the following description) and a synthetic resin that hardens with the curing agent (referred to as the "main resin" in the following description). The main resin is preferably a thermosetting resin. Examples of thermosetting resins include polyester resin and epoxy resin. The specific means for applying the undercoat paint are well known, so a detailed explanation will not be repeated here.

[0028] In the primer layer formation process S172, the primer coating applied to the surface of the chemical conversion treatment layer 34 on the front side of the substrate 20 is cured. The specific means for this curing are well known, so a detailed explanation will not be repeated here. This curing forms the primer layer 40.

[0029] In the topcoat painting process S174, on the surface of the undercoat layer 40 on the front side of the substrate 20 Contains urethane acrylate oligomer An electron beam curable coating is applied. The specific method for this application is well known, so a detailed explanation will not be repeated here. An example of an electron beam curable coating applied in this process is one containing a monomer with an acryloyl group and a polymer with an acryloyl group. In addition to urethane acrylate oligomers Some paints contain acryloyl groups. Examples of monomers containing acryloyl groups include 2-ethylhexyl acrylate, and examples of polymers containing acryloyl groups include polyester acrylates.

[0030] In the topcoat formation step S176, an electron beam is irradiated onto the electron beam-curable paint applied to the surface of the undercoat layer 40 on the front side of the substrate 20. This irradiation hardens the electron beam-curable paint. The specific means for this hardening are well known, so a detailed explanation will not be repeated here. The hardening of the electron beam-curable paint forms the topcoat layer 42. The formation of the topcoat layer 42 completes the coating film layer 22. The completion of the coating film layer 22 completes the painted steel sheet according to this embodiment. In this step, ultraviolet light may be irradiated before the electron beam irradiation. The purpose of ultraviolet light irradiation is to create a wrinkled pattern on the surface of the topcoat layer 42.

[0031] <Explanation of variations> The embodiments disclosed herein are illustrative in all respects. The scope of the present invention is not limited based on the embodiments described above, and various design modifications may be made without departing from the spirit of the invention.

[0032] <Description of the Examples> The following are examples of the present invention, but the present invention is not limited to the following examples.

[0033] [Example 1] (Manufacturing of painted steel sheets) The worker immersed the steel plate (0.4 mm thick) that would become the main body 30 in molten zinc. After that, the worker removed the steel plate from the molten zinc. The worker then air-cooled the removed steel plate. This caused the molten zinc to solidify. The solidified zinc became the plating layers 32,32 on both the front and back surfaces of the main body 30 (S150). Next, the worker applied a chemical conversion treatment to the plating layers 32,32 on both the front and back surfaces of the main body 30 using ZM-1300AN manufactured by Nippon Parkerizing Co., Ltd. This formed chemical conversion treatment layers 34,34 on both the front and back surfaces of the main body 30 (S152). After that, paint was applied to the surface of the chemical conversion treatment layer 34 on the back side of the main body 30 and cured (S154). Next, the worker applied GLOBAL PRIMER paint manufactured by AkzoNobel Coatings Inc. to the surface of the chemical conversion treatment layer 34 on the front side of the main body 30 (S170). The paint consisted of a polyester resin as the main resin and a urethane resin as the hardener. The worker then heated and cured the paint. This formed a primer layer 40 on the surface of the chemical conversion treatment layer 34 on the front side of the main body 30 (S172). The thickness of the primer layer 40 was 5 μm. Once the primer layer 40 was formed, the worker applied the electron beam curing paint described below to the surface of the primer layer 40 (S174). The electron beam curable coating contained 25% by mass of M1100 urethane acrylate oligomer manufactured by Toagosei Co., Ltd., 3% by mass of M-6250 polyester acrylate manufactured by Toagosei Co., Ltd., 10% by mass of trimethylolpropane triacrylate manufactured by Toagosei Co., Ltd., 15% by mass of tripropylene glycol diacrylate manufactured by Tokyo Chemical Industry Co., Ltd., 1% by mass of 89-0065-37 methanol primary grade 3L CAS No: 67-56-1 13002087 manufactured by Hayashi Pure Chemical Industries, Ltd., and 46% by mass of titanium dioxide "R-820" manufactured by Ishihara Sangyo Co., Ltd. Next, the worker irradiated the electron beam curable coating with an electron beam. The electron beam acceleration voltage was 150 kilovolts, the electron beam current was 4.7 milliamperes, the transport speed of the main unit 30 was 9 millimeters per minute, the number of electron beam irradiations was 1, and the electron beam irradiation dose was 60 kilogray. As a result, the electron beam curing paint hardened, and a topcoat layer 42 was formed (S176). The thickness of the topcoat layer 42 was 20 μm. The painted steel sheet according to this embodiment is the one on which the topcoat layer 42 has been formed in this manner.Four test pieces of the same size were cut from this painted steel sheet. The size of the test pieces was 200 mm x 100 mm.

[0034] (Adhesion test of processed area) The worker bent one of the test specimens so that the topcoat layer 42 was exposed. The test specimen was bent so that the back layers 24 were in close contact with each other from both ends up to just before the bent portion. Once the bending was complete, the worker applied cellophane tape to the bent portion of the test specimen. The worker then removed the cellophane tape. No peeling was observed in the topcoat layer 42 after the cellophane tape was removed. No peeling fragments were observed on the cellophane tape.

[0035] Next, the worker bent one of the other test specimens so that the topcoat layer 42 was exposed. The test specimen was bent so that the back layers 24 faced each other at intervals equal to the thickness of the specimen, from both ends up to just before the bent portion. Once the bending was complete, the worker attached cellophane tape to the bent portion of the test specimen. The worker then removed the cellophane tape. No peeling was observed in the topcoat layer 42 after the cellophane tape was removed. No peeling fragments were observed on the cellophane tape.

[0036] Next, the worker bent one of the four test pieces cut from the painted steel sheet, different from the two test pieces described above, so that the topcoat layer 42 was exposed. The test piece was bent so that the back layers 24 faced each other at a distance equal to twice the thickness of the test piece, from both ends up to just before the bent part. Once the bending was complete, the worker attached cellophane tape to the bent part of the test piece. The worker then removed the cellophane tape. No peeling was observed in either the topcoat layer 42 or the cellophane tape after it was removed.

[0037] (DuPont drop impact test) Next, the worker performed a DuPont test as specified in Japanese Industrial Standard K5600-5-3:1999 using the remaining one of the four test pieces cut from the painted steel sheet. The mass of the weight was 500 grams. The height of the weight immediately before dropping was 50 centimeters. The weight was dropped on both the front and back sides of the test piece. As a result, concave and convex areas were formed on both the front and back sides of the test piece. After the test, the worker applied cellophane tape to the uneven areas on the front side of the test piece, including the concave area caused by the direct impact of the weight, and the convex area that formed on the front side of the direct impact area on the back side of the test piece. The worker then removed the cellophane tape. There was no peeling on any of the uneven areas on the front side.

[0038] [Example 2] (Manufacturing of painted steel sheets) The worker applied paint KP8211, manufactured by Kansai Paint Co., Ltd., to the surface of the chemical conversion treatment layer 34 on the front side of the main body 30 (S170). The paint's main resin was epoxy resin, and its hardener was urethane resin. Other than these points, it was the same as in Example 1. Therefore, a detailed explanation will not be repeated here.

[0039] (Adhesion test of processed area) The results of the adhesion test of the processed area were the same as in Example 1. Therefore, a detailed explanation will not be repeated here.

[0040] (DuPont drop impact test) The results of the DuPont drop impact test were the same as in Example 1. Therefore, a detailed explanation will not be repeated here.

[0041] [Comparative Example 1] (Manufacturing of painted steel sheets) The worker applied paint FX39, manufactured by AkzoNobel Coatings Inc., to the surface of the chemical conversion treatment layer 34 on the front side of the main body 30 (S170). The paint's main resin was polyester resin, and its hardener was melamine resin. Other than these points, it was the same as in Example 1. Therefore, a detailed explanation will not be repeated here.

[0042] (Adhesion test of processed area) The worker bent one of the test specimens so that the topcoat layer 42 was exposed. The specimen was bent so that the back layers 24 were in close contact with each other from both ends up to just before the bent portion. Once the bending was complete, the worker applied cellophane tape to the bent portion of the specimen. The worker then removed the cellophane tape. At least 80% of the topcoat layer 42 was found to have peeled off after the cellophane tape was removed.

[0043] Next, the worker bent one of the other test specimens so that the topcoat layer 42 was exposed. The test specimen was bent so that the back layers 24 faced each other at a distance equal to the thickness of the specimen, from both ends up to just before the bent portion. Once the bending was complete, the worker applied cellophane tape to the bent portion of the test specimen. The worker then removed the cellophane tape. At least 65% of the topcoat layer 42 was found to have peeled off after the cellophane tape was removed.

[0044] Next, the worker bent one of the four test pieces cut from the painted steel sheet, different from the two test pieces described above, so that the topcoat layer 42 was exposed. The test piece was bent so that the back layers 24 faced each other at a distance equal to twice the thickness of the test piece, from both ends up to just before the bent point. Once the bending was complete, the worker applied cellophane tape to the bent part of the test piece. The worker then removed the cellophane tape. At least 50% of the topcoat layer 42 was found to have peeled off after the cellophane tape was removed.

[0045] (DuPont drop impact test) Next, the worker performed a DuPont test as specified in Japanese Industrial Standard K5600-5-3:1999 using the remaining one of the four test pieces cut from the painted steel sheet. The mass of the weight was 500 grams. The height of the weight immediately before dropping was 50 centimeters. The weight was dropped on both the front and back sides of the test piece. As a result, concave and convex areas were formed on both the front and back sides of the test piece. After the test, the worker applied cellophane tape to the uneven areas on the front side of the test piece, including the concave area on the front side due to the direct impact of the weight, and the convex area on the front side of the back side of the test piece due to the direct impact of the weight. The worker then removed the cellophane tape. The topcoat layer 42 peeled off completely from all of these uneven areas on the front side.

[0046] <Explanation of the effects of the painted steel sheet and its manufacturing method according to this embodiment> Figure 3 shows the components of the undercoat layer 40 for Example 1, Example 2, and Comparative Example 1, as well as the results of the adhesion test and DuPont drop impact test for the processed area. In the results shown in Figure 3, the "0TT" column indicates that the test piece was bent so that the back layers 24 were in close contact with each other. The "1TT" column indicates that the test piece was bent so that the back layers 24 were facing each other with a gap equal to the thickness of the plate. The "2TT" column indicates that the test piece was bent so that the back layers 24 were facing each other with a gap equal to twice the thickness of the plate. From Figure 3 and the above explanation, it is clear that when the undercoat layer 40 contains urethane resin as a curing agent, it is significantly superior in terms of adhesion to the processed area and resistance to weight drop compared to when it contains melamine resin. [Explanation of Symbols]

[0047] 20...Base 22…Coating layer 24…Back layer 30...Main unit 32…Plating layer 34...Chemical treatment layer 40…Undercoat layer 42...Top coat layer

Claims

1. The process includes a coating layer formation step in which a coating layer is formed from paint applied to the surface of a base body having a metal, plate-shaped body, The aforementioned coating layer A primer layer disposed on the surface of the substrate, It has a top coat layer that is placed on the surface of the undercoat layer, The aforementioned coating layer formation step is A primer coating step in which a primer paint is applied to the surface of the substrate, A primer layer formation step in which the primer coat is formed by hardening the primer paint, A topcoat painting step in which an electron beam curing paint is applied to the surface of the aforementioned undercoat layer, A method for manufacturing a painted metal sheet, comprising a top coat layer forming step in which the top coat layer is formed by irradiating the electron beam-curable paint with an electron beam, The undercoat paint is Urethane resin and The urethane resin is cured with a synthetic resin, A method for manufacturing a coated metal sheet, characterized in that the electron beam curable coating contains a urethane acrylate oligomer.

2. The method for manufacturing a painted metal plate according to claim 1, characterized in that the synthetic resin is at least one of a polyester resin and an epoxy resin.

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