JP2007229671A - Method for forming multilayer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient method for forming a three coat and one bake type multilayer coating film capable of yielding an excellent finish appearance. <P>SOLUTION: The three coat and one bake type coating method comprising steps of applying an intermediate-coat paint, applying a base topcoat paint, applying a clear topcoat paint, and heating the resulting layers employs a two-component type intermediate-coat paint comprising an isocyanate compound as a cross-linking agent, whereby the surface of the intermediate coat can be made flat and smooth with the flowability of its surface being improved and the intermixing thereof with the upper layer and the volume shrinkage of the intermediate coat caused by components detached and separated therefrom in the step of the cross-linking reaction can be avoided, and thereby a painted article having an excellent finish appearance can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a multilayer coating film, and more particularly to a method for forming a multilayer coating film suitably used for coating an outer plate of an automobile body.

  Conventionally, a three-coat two-bake (3C2B) method has been widely employed as a method for coating the outer plate of an automobile body. The general 3C2B coating method is to apply an intermediate coating material coating process, heating process, top coating base coating coating process, preheating process, top coating clear coating to an object that has been subjected to electrodeposition coating as an undercoat. A coating process and a heating process are sequentially performed to form a multilayer coating film. According to this coating method, since a coated product having a good finished appearance can be obtained, it is suitably used for coating the outer plate of an automobile body. However, this 3C2B coating system is not necessarily an efficient coating system because of the long coating process.

  As a more efficient coating method, there is a three-coat one-bake (3C1B) method, but when the paint used in the conventional 3C2B coating method is applied to this 3C1B method, the wet film after the top coating is formed. Since it became too thick, sagging and cracking occurred, resulting in a problem that workability deteriorated. For this reason, in recent years, various 3C1B coating methods that provide a good finished appearance have been studied.

  For example, in Patent Document 1, an intermediate coating film containing hygroscopic particles that absorb the solvent content of the top coating composition is applied onto the surface of the under coating film to form an uncured intermediate coating film, and then the top coating composition is applied. A 3C1B coating method has been proposed, in which the uncured intermediate coating and top coating are cured simultaneously. According to this coating method, since the solvent contained in the top coat layer is absorbed by the hygroscopic particles contained in the intermediate coat layer, the coating NV (NV: Non Volatile) of the top coat layer is promptly performed. It is said that the solvent of the top coat can be prevented from being transferred into the intermediate coat layer. Further, it is said that no mixed layer is formed at the boundary between the intermediate coating film layer and the top coating film layer, the smoothness of the top coating film is improved, and the occurrence of defects such as sagging can be prevented.

  In Patent Document 2, an intermediate coating is applied to form an uncured intermediate coating film, and then a top catalyst is applied after applying a curing catalyst that promotes the curing of the uncured intermediate coating layer. There has been proposed a coating method characterized by the above. According to this coating method, since at least the surface of the intermediate coating layer is cured, the presence of the surface cured film prevents the solvent of the top coating from being transferred into the intermediate coating layer after the top coating is applied. It can be prevented. In addition, a mixed layer does not occur at the boundary between the intermediate coating layer and the top coating layer, and the smoothness of the top coating layer is improved.

  Patent Document 3 discloses a first intermediate coat having a solid content concentration different from each other as an intermediate coat in a coating method including a step of forming an undercoat, an intermediate coat, and a top coat. There has been proposed a coating method characterized by sequentially applying a paint and a second intermediate coating to form a first intermediate coating and a second intermediate coating. According to this coating method, since there is a solid content concentration difference in the intermediate coating film, the smoothness and volume shrinkage of the intermediate coating film can be controlled, and the clarity of the coating film after curing can be improved. It is supposed to be possible.

  Patent Document 4 includes a thermosetting organic solvent-based intermediate coating (A) containing a neutralized product of a hydroxyl group-containing resin having an acid value of 5 to 100 and a crosslinking agent selected from block polyisocyanate and amino resin. There has been proposed a coating film forming method characterized in that a coating film comprising a thermosetting water-based colored top coating (B) is simultaneously cured on an uncured coating surface. According to this coating film forming method, the finished appearance such as the smoothness, sharpness, and gloss of the coating surface and the interlaminar adhesion of both coating films are excellent, and the deviation of the water-based top coating material can be achieved without strictly adjusting the humidity. It is said that it prevents falling off, prevents both coatings from mixing, and prevents the phenomenon of fogging.

  Non-Patent Document 1 discloses a three-wet-on-coating system in which an intermediate coating, top coating base coating, and top coating clear coating are applied in a wet state without baking, and urethane is contained in a polyester-melamine solvent one-component coating. There has been proposed a coating method in which a resin blend is applied as an intermediate coating. According to this coating method, the viscosity of the coating film after preheating is improved. As a result, the difference in viscosity between the uncured intermediate coating film and the top coating film is increased, so that it is possible to prevent a mixed layer at the time of top coating base coating. It is said that a painted product having a finished appearance can be obtained.

In Non-Patent Document 2, in a 3 wet-on coating system, an intermediate coating resin is selected from the viewpoint of SP value (polarity) and curing reaction speed, and control of the intermediate coating film interface with a dispersed acrylic resin is attempted. A painting method has been proposed. According to this coating method, as a result of forming a barrier layer on the surface layer of the intermediate coating film, a mixed layer at the interface between the intermediate coating film and the top coating base film is prevented, and a coated product having an excellent finished appearance is obtained. It is said that.
Japanese Patent Laying-Open No. 2005-21875 JP-A-2005-193107 Japanese Patent Laying-Open No. 2005-177631 JP-A-10-128224 Satoshi Kodama, Mitsuhiro Hamada, Akira Tanahashi, Mitsugu Endo, “Development of environmentally-friendly water-based coating technology”, Coating Engineering, 2005, Vol. 40, p. 429-439 Toshifumi Ogasawara, “Introduction of 3 Wet-on Painting”, Japan Paint Technology Association, 2002, 2nd Lecture Proceedings, p. 50-54

  As described above, the 3C1B system coating methods disclosed in these patent documents and non-patent documents mainly increase the viscosity of the intermediate coating film in order to ensure the wet coating property of the top coating film to the intermediate coating film. Is used. For this reason, in these coating methods, the surface flow property of the uncured intermediate coating film cannot be obtained at the time of baking and curing, and a good finished appearance cannot be obtained. Conventionally, as a method for improving the finished appearance of wet multilayer coating, a method of sequentially curing from the lower layer is generally used, but it is physically impossible to use this method for a 3C1B system coating method. Accordingly, development of a 3C1B type multilayer coating film forming method capable of obtaining a good finished appearance is required.

  This invention is made | formed in view of said subject, The objective is to provide the multi-layer coating-film formation method of 3C1B system which is efficient and can obtain a favorable finishing external appearance.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that the above-mentioned problems can be solved by using a two-pack type intermediate coating with an isocyanate compound as a crosslinking agent in the 3C1B system coating process, and the present invention has been completed. More specifically, the present invention provides the following.

  (1) A method for forming a multi-layer coating film, in which an undercoat paint is applied on an article to be coated, and an isocyanate compound is used as a cross-linking agent on the article to be coated that has undergone the primer coating process. An intermediate coating application process for applying a two-component intermediate coating, an overcoating base coating application process for applying an overcoating base coating on an object that has undergone the intermediate coating application process, and this overcoating base coating application process A method for forming a multi-layer coating film comprising: a top clear paint coating step for applying a top clear paint on a substrate to which the top coat has been applied; and a heating step for heating the target material that has undergone the top clear paint coating step.

  (2) The compound according to (1), further comprising a first preheating step for preheating the article that has undergone the intermediate coating coating step between the intermediate coating step and the top coating base coating step. Formation method of layer coating film.

  (3) The method for forming a multilayer coating film according to (2), wherein in the first preheating step, the preheating temperature is 40 ° C. or higher and 100 ° C. or lower.

  (4) The method further includes a second preheating step (1) to (3) for preheating the article that has undergone the top coating base coating application step between the top coating base coating coating step and the top coating clear coating coating step. ) A method for forming a multilayer coating film according to any one of the above.

  (5) The method for forming a multilayer coating film according to (4), wherein in the second preheating step, the preheating temperature is 40 ° C. or higher and 100 ° C. or lower.

  (6) The method for forming a multilayer coating film according to any one of (1) to (5), wherein in the intermediate coating material coating step, a chipping primer is applied before the intermediate coating material is applied.

  (7) The formation method of the multilayer coating film in any one of (1) to (6) using the to-be-coated object equipped with the 1st submaterial as the to-be-coated object which coats the said undercoat.

  (8) (1) to (7) further comprising a step of mounting a second auxiliary material on the article to be coated that has undergone the undercoat paint application step between the undercoat paint application step and the intermediate paint application step. The formation method of the multilayer coating film in any one.

  (9) The method for forming a multilayer coating film according to any one of (1) to (8), further including a step of mounting a third auxiliary material on the article that has undergone the heating step after the heating step.

  (10) The method for forming a multilayer coating film according to any one of (1) to (9), wherein the object to be coated is an outer plate of an automobile body.

  ADVANTAGE OF THE INVENTION According to this invention, the 3C1B type multilayer coating-film formation method which is efficient and can obtain a favorable finishing external appearance can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The flow showing an example of the multilayer coating film formation method which concerns on this embodiment is shown in FIG. The multi-layer coating film forming method according to the present embodiment is a 3C1B type multi-layer coating film forming method as shown in FIG. 1, and is compared with the conventional 3C2B type multi-layer coating film forming method as shown in FIG. And it differs greatly in the point that the heating process after the intermediate coating material coating process is not provided. Specifically, the method for forming a multi-layer coating film according to the present embodiment includes an intermediate coating material coating step in which an intermediate coating material is applied to an object to which an undercoat coating such as electrodeposition coating has been applied, and an intermediate coating material. First preheating step for preheating the coated object after the coating process, top coating base coating applying process for applying the top coating base paint, second preheating process for preheating the coated material after the top coating base coating process, top coating It has a heating process which heats an article to be coated which has undergone an overcoat clear paint application process for applying a clear paint and an overcoat clear paint application process.

[Coating]
Examples of the object used in the present embodiment include metal materials and plastic materials used for outer plate parts of motorcycles and automobiles. These materials are preferably subjected to a pretreatment (surface treatment) such as a degreasing treatment or a chemical conversion treatment and then an undercoating treatment such as electrodeposition coating. According to the method for forming a multilayer coating film according to the present embodiment, since a coated product having a good finished appearance is obtained, an outer plate of an automobile body that requires a particularly good finished appearance is preferably used.

[Intermediate paint application process]
Conventionally, a one-pack type intermediate coating composition containing a crosslinking agent such as melamine resin or blocked isocyanate has been used. In this step, a two-pack type intermediate coating composition using an isocyanate compound as a crosslinking agent is used. . For this reason, the composition of the intermediate coating used in this step is greatly different from that of the conventional intermediate coating, and the curing system of the intermediate coating is also different.

  Conventionally, when the intermediate coating material used in the 3C2B method is applied to the 3C1B method, there has been a problem that the finished appearance is deteriorated. The following three can be considered as causes of the finished appearance deterioration.

  First, when the 3C2B system coating method is changed to the 3C1B system coating method, the heating (baking) process of the intermediate coating film is reduced. This is because the effect of reducing the skin round on the surface (unevenness seen on the surface of the coating film) cannot be obtained. Describing in more detail with reference to the drawings, as shown in FIG. 2A, unevenness called skin round is usually recognized on the surface of the intermediate coating film immediately after the intermediate coating is applied. By setting this to stand for a predetermined time, the unevenness of the skin round becomes gentle (see FIG. 2B). And this skin round becomes gentle at the time of heat hardening, the unevenness | corrugation of the coating-film surface is reduced and smoothed, and a finished external appearance improves (refer FIG. 2C). However, in the 3C1B method, since there is no heating step for such an intermediate coating film, the effect of reducing the skin round cannot be obtained, and the finished appearance is deteriorated. As a means to solve this, a means to improve the flowability of the surface of the intermediate coating film during setting after application of the intermediate coating can be considered, but when this means is applied, the viscosity of the coating during heating is also reduced. Therefore, the occurrence of a mixed layer of each coating layer as will be described later is expected, which is not a preferable solution.

  Secondly, the fluid phenomenon that occurs between the coatings during heating causes a mixture of the coating layers, resulting in a decrease in the finished appearance. More specifically, as the conventional intermediate coating, a coating using a crosslinking agent such as a melamine resin or a blocked isocyanate is generally used as in the case of the top coating or the clear coating. For this reason, the curing start temperature of the conventional intermediate coating is close to the curing start temperature of the top coating base coating or the top clear coating. Therefore, in the heating step, a flow occurs between the respective coating film layers due to a decrease in the coating film viscosity before the start of curing (see FIG. 3B). Then, as a result of the fluid phenomenon, the coating layers are mixed, and as a result, the flow trace remains as the outermost skin round, and the finished appearance is deteriorated. As means for solving this problem, in order to suppress mixing during heating, a means for increasing the viscosity of the coating film during heating can be considered. However, when this means is applied, the viscosity during setting is inevitably required. Since it becomes high, the flowability of the coating film surface at the time of setting is expected to be lowered, which is not a preferable solution.

  Third, since the low molecular weight detachment component generated by the curing reaction of the intermediate coating film is volatilized during heating, the volume of the intermediate coating film shrinks, causing skin rounds and the finished appearance may be reduced. It is cited as the cause. More specifically, as described above, since a conventional intermediate coating material uses a crosslinking agent such as melamine resin or blocked isocyanate, a reaction desorbed material or the like is generated during a curing reaction during heating. For this reason, in the conventional intermediate coating film, since the alcohol is volatilized during heating, the volume of the intermediate coating film shrinks and a skin round occurs (see FIG. 3C). This skin round is transferred to the upper layer, and the finished appearance is deteriorated. As a means for solving this problem, use of an intermediate coating material using a cross-linking agent that does not generate a desorbing component during the curing reaction can be considered, but it cannot be said to be common in conventional intermediate coating materials.

  For this reason, the method for forming a multilayer coating film according to the present embodiment has been developed to avoid the deterioration of the finished appearance caused by the above three causes. The specific means is to use a two-component paint having an isocyanate compound as a crosslinking agent as an intermediate coating, and the two-component paint having the isocyanate compound as a crosslinking agent is a conventional 3C2B system coating method. However, it can be said that the invention has been made based on a novel technical idea in that it is hardly used.

  The mechanism of the multilayer coating film forming method according to this embodiment will be described in detail with reference to FIG. FIG. 4 shows a case where a water-based top coat base material is wet-on applied to a two-component intermediate coating material using an isocyanate compound as a crosslinking agent (this embodiment), and a one-component intermediate coating method using a melamine resin as a crosslinking agent. For each multi-layer coating film when a water-based top coating base material is wet-on-painted on the coating material (conventional), measurement is carried out using a pendulum viscoelasticity measuring device (FDOM) “DDV-OPAIII” manufactured by Orientec Co., Ltd. It is a figure which shows the time-dependent change of the viscosity obtained in this way. As shown in FIG. 4, the multilayer coating film according to this embodiment has a large variation in coating film viscosity in the temperature rising process as compared with the conventional multilayer coating film. Specifically, the viscosity of the multilayer coating film according to the present embodiment is once greatly reduced in the temperature rising process up to 80 ° C. (see A in FIG. 4). This decrease in viscosity is due to the effect of the melt viscosity of the intermediate coating film, and since the flowability of the coating film surface becomes good due to this decrease in viscosity, the coating film surface is smoothed and a good finished appearance is obtained. It is considered to be obtained. Moreover, in the temperature rising process from 80 ° C. to 140 ° C., the viscosity of the multilayer coating film is rapidly increased. This is because the isocyanate crosslinking reaction proceeds and the viscosity of the intermediate coating film rapidly increases. (See B in FIG. 4). It is considered that this rapid increase in the viscosity of the coating can avoid a mixed layer with the clear clear coating.

  Further, as described above, in the cross-linking reaction in the conventional intermediate coating film, alcohol is eliminated and volatilized as a reaction product (see FIG. 6), whereas in the intermediate coating film according to this embodiment, Since a two-component paint using an isocyanate compound as a crosslinking agent is used, reaction products such as alcohol do not occur (see FIG. 5). For this reason, it is considered that the volume of the intermediate coating film does not shrink during heating, and a good finished appearance can be obtained.

  In addition, as an isocyanate compound, a conventionally well-known thing can be used and it does not specifically limit. For example, an alicyclic, aromatic group-containing aliphatic or aromatic polyfunctional isocyanate compound can be used, and diisocyanate or its isocyanurate (triisocyanate of diisocyanate) is preferably used.

  As the diisocyanate, those having 5 to 24, preferably 6 to 18 carbon atoms can be used. Examples of such diisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,6-diisocyanatohexane (HDI), 2,2,4-trimethylhexane diisocyanate, undecane diisocyanate- (1,11 ), Lysine ester diisocyanate, cyclohexane-1,3- and 1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (IPDI), 4,4′-diisocyanatodi Cyclomethane, ω, ω′-dipropyl ether diisocyanate, thiodipropyl diisocyanate, cyclohexyl-1,4-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,5- Dimethyl-2,4-bis (isocyanatomethyl) benzene, 1,5-trimethyl-2,4-bis (ω-isocyanatoethyl) -benzene, 1,3,5-trimethyl-2,4-bis (isocyanate) Natomethyl) benzene, 1,3,5-triethyl-2,4-bis (isocyanatomethyl) benzene, dicyclohexyldimethylmethane-4,4′-diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, And diphenylmethane-4,4′-diisocyanate. 2,4-diisocyanatotoluene and / or 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 1,4-diisocyanatoisopropylbenzene, cyclohexyl-1,4-diisocyanate, Aromatic diisocyanates such as toluene diisocyanate and hexamethylene diisocyanate can also be used. Furthermore, as said isocyanurate, the trimer of the diisocyanate mentioned above is mentioned. In addition, such a polyfunctional isocyanate compound can also be used independently and can also use 2 or more types together. Moreover, it can also be used as a mixture of said diisocyanate and isocyanurate (trimer). The molecular weight of these isocyanate compounds is not particularly limited.

  The base resin is not particularly limited as long as it causes a crosslinking reaction with an isocyanate compound, and conventionally known resins can be used, but a hydroxyl group-containing resin is preferably used. The hydroxyl group-containing resin is not particularly limited as long as it is a polymer containing a hydroxyl group, and examples thereof include a hydroxyl group-containing acrylic copolymer, a hydroxyl group-containing polyester copolymer, a hydroxyl group-containing alkyd resin, and a hydroxyl group-containing silicon resin. These hydroxyl group-containing resins may further have a carboxyl group, an epoxy group, or the like. Further, the molecular weight of the base resin is not particularly limited.

  Moreover, you may mix | blend the curing catalyst which accelerates | stimulates an isocyanate crosslinking reaction in intermediate coating. Specifically, an organic tin compound curing catalyst such as dibutyltin dilaurate, dibutyltin diacetate, or dibutyltin dioctate may be blended. Thereby, without providing a preheating step, the crosslinking reaction proceeds to some extent even at room temperature, and the viscosity of the intermediate coating film is increased to avoid mixing with the upper layer, so that the finished appearance can be improved.

  When mixing and coating the isocyanate compound of the crosslinking agent and the base resin, a conventionally known mixed coating apparatus, for example, a two-component mixed coating apparatus as disclosed in Utility Model Registration No. 2506381 is used. be able to. A schematic configuration diagram of this two-component mixed coating apparatus is shown in FIG. As shown in FIG. 7, in this two-component mixed coating apparatus, the pressure-feed paths 2 a and 2 b are respectively stored in storage tanks 1 a and 1 b in which a base (base resin) X and a crosslinking agent (isocyanate compound) Y are stored. One end is disposed, and the other ends of the pressure feed paths 2 a and 2 b are connected to the inlet of the mixer 3, and the coating gun 4 is connected to the outlet of the mixer 3. Gear pumps 5a and 5b are disposed in the middle of the pressure feed paths 2a and 2b, respectively. The gear pump 5a is connected to the air motor 7a via the transmission 6a, while the gear pump 5b is connected via the transmission 6b. It is connected to the air motor 7b. Instead of these transmissions, a reduction gear may be provided.

  In such a configuration, in order to set the mixing ratio of the base X and the crosslinking agent Y, the rotational speeds of the gear pumps 5a and 5b are adjusted by the transmissions 6a and 6b. Next, the air motors 7a and 7b are started at a predetermined rotational speed, and the base X and the cross-linking agent Y are discharged from the storage tanks 1a and 1b to the mixer 3 at a predetermined flow rate under the driving action of the gear pumps 5a and 5b. . Further, the base X and the cross-linking agent Y are mixed by the mixer 3 and supplied to the coating gun 4, and are discharged from the coating gun 4 to an object not shown.

[Chipping primer]
In the intermediate coating material application step in the present embodiment, a chipping primer may be applied before application with the intermediate coating material (not shown). The chipping primer protects the coating film by absorbing the impact of a stone or the like that jumps up while the vehicle is running, and is generally applied in the coating of the outer plate of the vehicle. This chipping primer is applied in the same or different coating booth as the intermediate coating before the intermediate coating. The painting is performed manually or by an automatic machine, and the application range is determined according to the shape of the vehicle, but generally a part that is easily damaged by rock jumping is common.

  The chipping primer material is not particularly limited, and both aqueous and organic solvent systems are used. For example, a cross-linking type using a polyolefin resin, a polyester resin, a polyurethane resin or the like as a main component and using a cross-linking agent and a non-cross-linking type using no cross-linking agent are used. In addition, you may give preliminary drying after chipping primer coating.

[First preheating step]
In the method for forming a multilayer coating film according to the present embodiment, it is preferable to provide a first preheating step for preheating the article to be coated that has undergone the intermediate coating material coating step. As the preheating means, conventionally known means such as hot air drying (flash-off that blows high-speed hot air or the like) and infrared heating are used. The heating conditions for the preheating are appropriately set according to the composition of the intermediate coating. More specifically, the heating condition is set such that the viscosity of the intermediate coating film is reduced and the surface flow property of the intermediate coating film is improved. Specifically, for example, heating conditions of 40 to 100 ° C. and a heating time of 3 to 30 minutes can be mentioned.

  When the heating temperature is less than 40 ° C., the solvent in the intermediate coating film does not volatilize sufficiently, so that a mixed layer with the top coating base coating film during the top coating base coating is produced and the finished appearance is deteriorated. On the other hand, when the heating temperature exceeds 100 ° C., the intermediate coating film is completely cured, the flowability is not obtained after the top coating base coating, and the finished appearance is deteriorated. In addition, the high-temperature drying furnace requires equipment specifications such as heat resistance, which increases the investment amount and increases the energy cost of heating, thereby impairing the economy. Furthermore, for the top coat base coating after the first preheating, the temperature of the object to be coated needs to be lowered to near room temperature. However, if it is 100 ° C. or higher, it takes time for cooling and the process becomes longer.

  When the heating time is less than 3 minutes, the solvent in the intermediate coating film does not evaporate sufficiently and is hardly cured, so the intermediate coating film absorbs the solvent in the top coating film during top coating. However, the finished appearance deteriorates. On the other hand, when the heating time exceeds 30 minutes, the intermediate coating film is completely cured, the flowability is not obtained after the top coating, and the finished appearance is deteriorated. Moreover, since a normal drying furnace is 30 minutes or more, the effect of shortening the process cannot be obtained with a drying furnace longer than this. Furthermore, the amount of investment increases and the energy cost of heating increases, resulting in a loss of economic efficiency.

  By this 1st preheating process, the flow property of the intermediate coating film surface improves more, and the skin round of the surface of an intermediate coating film is reduced. For this reason, a coated product having a better finished appearance can be obtained by providing the first preheating step.

[Top coat base coating process]
The topcoat base paint used in this step can be the same as that conventionally used, and is not particularly limited. It does not matter whether it is aqueous or organic solvent. Examples of the resin component blended in the topcoat base paint include base resins such as alkyd resins, polyester resins, acrylic resins, and epoxy resins, and cured (crosslinked) resins such as amino resins, polyisocyanate resins, and carboxylic acid resins. Can be used.

  The topcoat base paint used in the present embodiment may contain a glitter pigment. Examples of glitter pigments include aluminum flakes, vapor-deposited aluminum, colored pigment-coated aluminum flakes, metal oxide-coated alumina flakes, metal oxide-coated silica flakes, graphite pigments, metal oxide-coated mica, titanium flakes, stainless steel flakes, and chloride. Examples thereof include oxybismuth, iron oxide pigments on plates, metal-plated glass flakes, metal oxide-coated glass flakes, and hologram pigments. These glitter pigments can be used alone or in combination of two or more.

  Moreover, the top coat base paint used in the present embodiment may contain a color pigment in addition to the glitter pigment. Examples of the color pigment include titanium dioxide, carbon black, zinc white, molybdenum red, Prussian blue, cobalt blue, phthalocyanine pigment, azo pigment, quinacridone pigment, isoindoline pigment, selenium pigment, and perylene pigment. These color pigments can be used alone or in combination of two or more.

[Second preheating step]
In the method for forming a multilayer coating film according to the present embodiment, it is preferable to provide a second preheating step of preheating the article to be coated that has undergone the top coating base coating application step. As the preheating means, conventionally known means such as hot air drying (flash-off that blows high-speed hot air or the like) and infrared heating are used. The heating conditions for the preheating are appropriately set according to the composition of the intermediate coating material and the top coating base coating material. More specifically, the heating conditions are set such that the viscosity of the top coat base coating is reduced and the surface flow of the top coat base coat is good. Specifically, for example, heating conditions of 40 to 100 ° C. and a heating time of 3 to 30 minutes can be mentioned.

  When the heating temperature is less than 40 ° C., the intermediate coating film is not cured, so that after the top clear coating, the intermediate coating film absorbs the solvent in the top coating clear film and the finished appearance is deteriorated. On the other hand, when the heating temperature exceeds 100 ° C., the intermediate coating film is completely cured, the flowability is not obtained after the top coating base coating, and the finished appearance is deteriorated. In addition, the high-temperature drying furnace requires equipment specifications such as heat resistance, which increases the amount of investment and increases the energy cost of heating, thereby impairing the economy. Furthermore, for the clear coating of the top coat after the second preheating, it is necessary to lower the temperature of the object to be close to room temperature.

  When the heating time is less than 3 minutes, the solvent in the intermediate coating film does not evaporate sufficiently and does not cure, so the intermediate coating film absorbs the solvent in the top coating film during clear coating. However, the finished appearance deteriorates. On the other hand, when the heating time exceeds 30 minutes, the intermediate coating film is completely cured, the flowability cannot be obtained after the top clear coating, and the finished appearance is deteriorated. Moreover, since a normal drying furnace is 30 minutes or more, the effect of shortening the process cannot be obtained with a drying furnace longer than this. Furthermore, the amount of investment increases and the energy cost of heating increases, resulting in a loss of economic efficiency.

  In the second preheating step, the intermediate coating film and the top coating base coating film are preheated so as not to prevent these coating films from being in a semi-cured state. That is, before the top clear coating is applied, curing of the intermediate coating film and the top coating film may be started. Thereby, a mixed layer with the top clear film can be effectively avoided, and a coated product having a better finished appearance can be obtained.

[Topcoat clear coating application process]
The topcoat clear paint used in this step can be the same as that conventionally used, and is not particularly limited. It does not matter whether it is aqueous or organic solvent. Resin components to be blended in the clear clear coating include base resins such as alkyd resins, polyester resins, acrylic resins, epoxy resins, fluororesins and silicon-containing resins, and curing of amino resins, polyisocyanate resins, carboxylic acid resins, etc. The thing which mix | blended (crosslinking) resin is mentioned.

[Heating process]
This step is a step of completely curing each of the uncoated or semi-cured intermediate coating film, top coating base coating film, and top coating clear coating film. As the heating means, conventionally known means such as hot air drying and infrared heating are used. The heating conditions are appropriately set according to the composition of the intermediate coating, top coating base coating, and top coating clear coating. Specifically, for example, the heating temperature is 120 ° C. to 170 ° C. and the heating time is 15 minutes to 60 minutes.

〔Auxiliary materials〕
In this embodiment, you may provide suitably the process of equip | providing a submaterial between each above-mentioned coating process (refer FIGS. 8-11). Moreover, as shown in FIGS. 9-11, as a to-be-coated object used by this embodiment, what used the undercoat film formed after the auxiliary material (1st auxiliary material) was equipped to the above-mentioned raw material was used. May be. The first auxiliary material in the present embodiment is a variety of polymer materials provided at predetermined positions of the article (vehicle) to be coated, and means other than paint. Specifically, for example, sealing, grommet, mel sheet, undercoat and the like can be mentioned.

  In order to prevent intrusion of water or outside air, the sealing is performed by discharging a sealing material from a nozzle of an application (discharge) device or the like and filling the seam or hemming portion of the steel plate to close these portions. As the sealing material, a semi-liquid polymer material that solidifies upon drying is used, and examples thereof include acrylic vinyl sol and bituminous materials. As the sealing material, a colored material is usually used, but a transparent material may be used for a portion having a problem in appearance. When this sealing material is discharged and installed, a part of the sealing material may grow due to viscosity and adhere to the painted part. Also, dust can be attached to the work.

  Grommets are intended to avoid the risk of short circuiting (fire) due to damage to the cable sheath due to vibration or the like when a through hole is provided in an iron plate or the like (object to be coated) for wiring. As the grommet, a conventionally known rubber-made grommet is used. When this grommet is equipped, a part of the grommet becomes dust and adheres to the painted part, and dust may be attached due to work.

  The mel sheet is a sheet having functions such as vibration proofing and sound proofing, and is installed at a predetermined position of an object to be coated (vehicle). A bituminous sheet or a rubber sheet is used as the melt sheet. The bituminous sheet is a polymer material that is fused by heating, and examples thereof include an asphalt material. Bituminous seats are also called fusible insulators, and are provided on the left and right front of the front seat of the floor, the left and right front of the front seat, the rear seat, the rear room floor, the dashboard, and the like. When this melt sheet is equipped, a part of the melt sheet becomes dust and adheres to the painted portion, and dust can be attached to the work.

  Undercoat is applied to the floor underside and the joints of steel plates in the wheel house to improve waterproofing, dustproofing, rusting, and chipping resistance (preventing damage caused by hopping). Or it forms by spraying. Examples of the undercoat material include the same material as the sealing material. When this undercoat is provided (formed), a part of the undercoat may scatter and adhere to the painted part, and dust may be attached to the work.

  For example, as shown in FIGS. 8, 10, and 11, a step of mounting the second auxiliary material on the object to be coated may be provided before the above-described intermediate coating material coating step. It does not specifically limit as a 2nd secondary material, The various secondary materials which were illustrated by description of the above-mentioned 1st secondary material are used.

  Or as shown in FIG.10 and FIG.11, you may provide the process of equip | installing the 3rd submaterial on the to-be-coated article which passed the heating process after the heating process mentioned above. It does not specifically limit as a 3rd submaterial, Various submaterials which were illustrated by description of the above-mentioned 1st submaterial are used.

  In addition, as shown in FIGS. 8 to 11, when the auxiliary material is equipped before and after the entire coating process, drying (baking or room temperature drying) is performed individually. On the other hand, when sub-materials are equipped during the painting process, heat drying can be performed at the same time as the pre-coating process and heating process of the paint film, so there is no need to perform individual drying. Is. Moreover, you may provide the cleaning process for the purpose of removing the dust adhering to the to-be-coated object surface between each coating process suitably.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Example 1>
As Example 1, 3C1B system coating using a two-pack type intermediate coating with an isocyanate compound as a crosslinking agent was performed according to the flow shown in FIG. Specifically, for cold-rolled steel sheets (however, hot-dip galvanized steel sheets, electrogalvanized steel sheets, aluminum steel sheets, etc. are also considered, and this test does not prescribe the base steel sheet type) Kansai Paint Co., Ltd. Cationic electrodeposition paint “HG350E” manufactured by Electrodeposition was applied and dried by heating at 170 ° C. for 20 minutes. Next, an intermediate coating “KP30” manufactured by Kansai Paint Co., Ltd. was applied, preheated at 70 ° C. for 5 minutes, and then a top coating base coating “WT700” manufactured by Kansai Paint Co., Ltd. was applied, followed by 10 minutes at 80 ° C. Preheated. Finally, an overcoat clear coating “KINO # 430” manufactured by Kansai Paint Co., Ltd. was applied and dried by heating at 140 ° C. for 30 minutes.

<Comparative Example 1>
As Comparative Example 1, 3C2B system coating using a one-pack type intermediate coating with melamine resin as a crosslinking agent was performed according to the flow shown in FIG. Specifically, a cationic electrodeposition paint “HG350E” manufactured by Kansai Paint Co., Ltd. was electrodeposited on the cold-rolled steel sheet, and heat-dried at 170 ° C. for 20 minutes. Next, an intermediate coating “WP404” manufactured by Kansai Paint Co., Ltd. was applied and dried by heating at 140 ° C. for 30 minutes, and then a top coating base coating “WT700” manufactured by Kansai Paint Co., Ltd. was applied, followed by 80 minutes at 80 ° C. Preheated. Finally, an overcoat clear coating “KINO # 430” manufactured by Kansai Paint Co., Ltd. was applied and dried by heating at 140 ° C. for 30 minutes.

<Comparative example 2>
As Comparative Example 2, 3C1B system coating using a one-pack type intermediate coating with melamine resin as a crosslinking agent was performed according to the flow shown in FIG. Specifically, a cationic electrodeposition paint “HG350E” manufactured by Kansai Paint Co., Ltd. was electrodeposited on the cold-rolled steel sheet, and heat-dried at 170 ° C. for 20 minutes. Next, an intermediate coating “WP404” manufactured by Kansai Paint Co., Ltd. was applied, preheated at 70 ° C. for 5 minutes, and then a top coating base coating “WT700” manufactured by Kansai Paint Co., Ltd. was applied, followed by 10 minutes at 80 ° C. Preheated. Finally, an overcoat clear coating “KINO # 430” manufactured by Kansai Paint Co., Ltd. was applied and dried by heating at 140 ° C. for 30 minutes.

<Evaluation>
The finished appearance of the multilayer coating films obtained in Examples and Comparative Examples was evaluated using a finished characteristic value measuring device “wave scan” (manufactured by BYK-Gardner). Specifically, the horizontal and vertical surfaces of each multilayer coating film have long (LW wavelength: 1.2 mm to 12.0 mm) and short (SW wavelength: 0 wavelength) rounds (swells) on the coating film surface. .3 mm to 1.2 mm) and the respective amplitudes were measured. The results are shown in Table 1. As shown in Table 1, since the multi-layer coating film of this example has a smaller amplitude value than the multi-layer coating film of the comparative example, the surface of the coating film is smooth and the finished appearance is It was confirmed to be good.

It is a flowchart of the multilayer coating-film formation method which concerns on this embodiment. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure for demonstrating the mechanism of the multilayer coating-film formation method. It is a figure which shows the time-dependent change of the viscosity of a multilayer coating film. It is a schematic diagram of the crosslinking reaction of the intermediate coating film of this embodiment. It is a schematic diagram of the crosslinking reaction of the conventional intermediate coating film. It is a schematic block diagram of a 2 liquid mixing type coating apparatus. It is a flowchart of the multilayer coating-film formation method which concerns on the modification of this embodiment. It is a flowchart of the multilayer coating-film formation method which concerns on the modification of this embodiment. It is a flowchart of the multilayer coating-film formation method which concerns on the modification of this embodiment. It is a flowchart of the multilayer coating-film formation method which concerns on the modification of this embodiment. It is a flowchart of the conventional multilayer coating-film formation method.

Explanation of symbols

1a, 1b Storage tank 2a, 2b Pressure feed path 3 Mixer 4 Paint gun 5a, 5b Gear pump 6a, 6b Transmission 7a, 7b Air motor

Claims (10)

A method for forming a multilayer coating film, comprising:
An undercoat paint process for applying an undercoat paint on an object to be coated;
An intermediate coating application step of applying a two-component intermediate coating with an isocyanate compound as a cross-linking agent on the article that has undergone the undercoat coating step;
A top coat base paint application process for applying a top coat base paint on the article to be coated through the intermediate coat paint application process;
A top clear paint coating step for applying a clear top paint on an object that has undergone the top base paint coating step;
A method of forming a multilayer coating film, comprising: a heating step of heating an object to be coated that has undergone the top clear coating application step.   The multilayer coating film according to claim 1, further comprising a first preheating step of preheating the article that has undergone the intermediate coating coating step between the intermediate coating step and the top coating base coating step. Forming method.   The method for forming a multilayer coating film according to claim 2, wherein in the first preheating step, the preheating temperature is set to 40 ° C. or more and 100 ° C. or less.   4. The method according to claim 1, further comprising a second preheating step of preheating the article that has undergone the top coating base coating application step between the top coating base coating coating step and the top coating clear coating coating step. 5. A method for forming a multilayer coating film.   The method for forming a multilayer coating film according to claim 4, wherein in the second preheating step, the preheating temperature is set to 40 ° C. or more and 100 ° C. or less.   The method for forming a multilayer coating film according to any one of claims 1 to 5, wherein, in the intermediate coating material coating step, a chipping primer is applied before the intermediate coating material is applied.   The formation method of the multilayer coating film in any one of Claim 1 to 6 using the to-be-coated object equipped with the 1st submaterial as a to-be-coated object which coats the said undercoat.   8. The compound according to claim 1, further comprising a step of mounting a second auxiliary material on the article that has undergone the undercoat paint application step between the undercoat paint application step and the intermediate paint application step. Formation method of layer coating film.   The formation method of the multilayer coating film in any one of Claim 1 to 8 which further has the process of equip | installing the 3rd submaterial on the to-be-coated article which passed through the said heating process after the said heating process.   The method for forming a multilayer coating film according to claim 1, wherein the object to be coated is an outer plate of an automobile body.

Images