JP5261061B2 - Coating method and coated body obtained thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method capable of obtaining a laminated coating film whose uppermost layer surface has scarce irregularities and excellent in adhesion to a base material even if three or more kinds of paints are laminated in a wet-on-wet condition and are baked. <P>SOLUTION: The painting method that forms the laminated coating film having the lowermost layer formed on the base material, an intermediate layer of one or more layers formed on the lowermost layer, and the uppermost layer formed on the intermediate layer includes steps of preparing a thermosetting coating material as the lowermost layer coating material to form the lowermost layer, preparing a non-thermosetting coating material that never causes a hardening reaction by heat-treatment at least as one kind of the intermediate coating materials to form the intermediate layer, and preparing a thermosetting coating material as the uppermost layer coating material to form the uppermost layer, a step of forming unhardened laminated coating film by laminating the lowermost, intermediate, and uppermost layer coating materials on the base material in a wet-on-wet condition, and a step of hardening the lowermost and uppermost layer coating materials by performing heat-treatment of the unhardened laminated coating film. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a coating method for laminating and baking three or more kinds of paints by wet-on-wet, and a coated body obtained thereby.

  When three or more types of paints are laminated by wet-on-wet and then a laminated coating film is formed by a baking method, conventionally, all the layers constituting the laminated coating film are cured by baking after all the coating materials are laminated. Thermosetting paint was used for all layers so that the reaction occurred and the entire laminated coating was cured. In this case, there is a problem that the skin and gloss of the laminated coating film are inferior compared to the case where the lowermost layer, or the lowermost layer and the intermediate layer are baked and then the coating for forming the uppermost layer is laminated and baked. For this reason, various methods have been proposed to improve the skin and gloss of the laminated coating film.

  For example, Japanese Patent Application Laid-Open No. 10-277478 (Patent Document 1) discloses a coating film in which a color base paint, a glittering material-containing base paint, and a clear paint are sequentially applied by a wet-on-wet method and then baked to cure each layer. A forming method is disclosed. In this method, the viscosity increase start time of each paint is adjusted to be longer in the order of the color base paint, the glitter-containing base paint, and the clear paint, and before the clear paint forming the uppermost layer increases in viscosity as it hardens. Curing of the color base paint and glittering material-containing base paint forming the lower layer is started.

  On the other hand, it is known that the cause of lowering the skin and gloss of the multilayer coating film is the residual solvent in the multilayer coating film before baking and curing. In particular, when the solvent in the laminated coating film is rapidly evaporated during the curing reaction, the surface of the laminated coating film becomes rough. In order to prevent this, the following method has been proposed. For example, in Japanese Patent Application Laid-Open No. 2004-275966 (Patent Document 2), a two-step heating process including a step of applying an intermediate coating, a base coating, and a clear coating in order by wet-on-wet, a low-temperature heating step, and a high-temperature heating step. A coating film forming method is disclosed. In these methods, the solvent in the paint is gently evaporated without curing the paint in the low-temperature heating stage, and then the thermosetting resin contained in each layer of paint is cured in the high-temperature heating stage.

As described above, various methods have been proposed in order to improve the skin and gloss of the laminated coating film. For example, in the case of an automotive steel sheet, a coated body having superior appearance quality and durability is provided. There is a need, and further improvement of the wet-on-wet coating method is desired.
Japanese Patent Laid-Open No. 10-277478 JP 2004-275966 A

  The present invention has been made in view of the above-described problems of the prior art, and at least the lowermost layer and the uppermost layer are provided for ensuring high durability by laminating and baking three or more kinds of paints by wet-on-wet. The present invention provides a coating method capable of obtaining a laminated coating film having less surface irregularities and having excellent adhesion to a substrate even when it is cured, and a coated body excellent in appearance quality obtained thereby. Objective.

  As a result of intensive research to achieve the above object, the inventors of the present invention, when laminating three or more kinds of paints by wet-on-wet and baking coating, among the layers other than the uppermost layer of the laminated coating film By forming at least one layer of the coating using a non-curing paint that does not cause a curing reaction by heat treatment, the shrinkage of the laminated coating after the uppermost layer is cured and the fluidity is remarkably reduced can be minimized. It was found that a laminated coating film having excellent appearance quality can be obtained even when baking is carried out after laminating three or more kinds of paints by wet-on-wet.

  However, the present inventors, when the lowermost layer of the multilayer coating film other than the uppermost layer is formed using a non-curable paint, a multilayer coating film having excellent appearance quality can be obtained. The present inventors have found that the laminated coating film tends to peel off from the substrate. Therefore, as a result of further earnest research, the present inventors formed the uppermost layer and the lowermost layer using a thermosetting paint that is cured by heat treatment, and a layer (intermediate layer) between them, By using non-curing paint, it is possible to obtain a laminated coating film that has excellent appearance quality and excellent adhesion to the substrate even if it is baked after laminating three or more kinds of paints by wet-on-wet. As a result, the present invention has been completed.

That is, the coating method of the present invention comprises a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer. A coating method for forming
A thermosetting coating is prepared as a lowermost layer coating for forming the lowermost layer, and at least one of the intermediate layer coatings for forming the intermediate layer is a non-curing type that does not cause a curing reaction by heat treatment Preparing a paint, and preparing a paint having a weight reduction rate of 0.5% by mass or less at the curing temperature as a top layer paint for forming the top layer,
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
It is the method characterized by including.

Also, other coating method of the present invention is provided with a top layer formed on the intermediate layer and the intermediate layer of at least one layer of the lowermost layer formed on a substrate formed on said bottom layer A coating method for forming a laminated coating film,
To prepare a thermosetting paint as a lowermost layer coating for forming the lowermost layer, to prepare a thermosetting coating as an uppermost layer coating for forming the uppermost layer, and to form the intermediate layer non-curable coating material is a by weight reduction rate in curing temperature of the uppermost layer-coating material that does not cause a curing reaction by a heat treatment as at least one of the intermediate layer coating to prepare a 0.5 wt% or less of the paint Process,
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
It is the method characterized by including .
Furthermore, another coating method of the present invention is a laminate comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer. A coating method for forming a coating film,
To prepare a thermosetting paint as a lowermost layer coating for forming the lowermost layer, to prepare a thermosetting coating as an uppermost layer coating for forming the uppermost layer, and to form the intermediate layer prepare those containing at least one as a curing reaction a non-curable coating is a by the melt viscosity of 500 Pa · s or less of the base resin in the curing temperature of the uppermost layer-coating material is not caused by the heat treatment of the intermediate layer-coating material And a process of
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
It is the method characterized by including .

Still another coating method of the present invention includes a lowermost layer formed on a base material, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer. A coating method for forming a laminated coating film,
A thermosetting coating is prepared as a lowermost layer coating for forming the lowermost layer, and at least one of the intermediate layer coatings for forming the intermediate layer is a non-curing type that does not cause a curing reaction by heat treatment Preparing a paint and preparing a thermosetting paint as a paint for the uppermost layer for forming the uppermost layer;
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
The heat-treated uncured multilayer coating film at a temperature less than [the curing temperature -20 ° C. in the uppermost layer-coating material, then facilities to heat treatment in the said curing temperature -20 ° C. of the uppermost layer-coating material] temperatures above Curing at least the lowermost layer paint and the uppermost layer paint,
It is the method characterized by including .

  In addition, even when three or more kinds of paints are laminated by wet-on-wet and baked by the coating method of the present invention, there are few surface irregularities of the laminated coating film, and the reason why the laminated coating film becomes difficult to peel from the substrate is Although not necessarily certain, the present inventors infer as follows. That is, in the conventional multilayer coating film formed by wet-on-wet, thermosetting paint is used in all layers including the uppermost layer, so the thermosetting paint forming the uppermost layer is subjected to heat treatment (baking treatment). When cured, the thermosetting paint is cured even in the lower layer. At this time, in each layer of the laminated coating film, the thermosetting paint is cured by an addition reaction after the condensation reaction or the deblocking reaction of the curing agent. Therefore, a volatile product is generated and remains by this condensation reaction or deblocking reaction. It volatilizes with the solvent to be formed, the laminated coating film shrinks, and irregularities are formed on the coating film surface. The unevenness on the surface of the coating film is alleviated by the flow while each layer has sufficient fluidity, but the unevenness is not alleviated if the fluidity of each layer, particularly the uppermost layer, is significantly reduced by curing. Concavities and convexities at the surface of the material and the interface of each layer are transferred to the surface of the uppermost layer, and the skin and gloss of the laminated coating film deteriorate.

  On the other hand, in the coating method of the present invention, at least one of the uppermost layer and the layer other than the lowermost layer (intermediate layer) is formed using a non-curable paint, and therefore the uppermost layer is formed using a thermosetting paint. However, when this thermosetting paint is cured by heat treatment, the intermediate layer formed using the non-curable paint does not substantially undergo a curing reaction and substantially does not produce volatile products. In addition, fluidity is maintained. As a result, the volatilization of the volatile product that affects the shrinkage of the conventional multi-layer coating film does not occur, and the shrinkage of the multi-layer coating film is suppressed to the minimum due to only the volatilization of the remaining solvent. Further, the present inventors infer that the unevenness of the coating film surface due to this shrinkage and the shrinkage of the uppermost layer and the lowermost layer is alleviated by the fluidity of the intermediate layer.

  Further, in the coating method of the present invention, since the lowermost layer is formed using a thermosetting paint, the lowermost layer is formed between the lowermost layer and the base material more than when the lowermost layer is formed using a non-curable paint. The present inventors infer that the chemical bond is formed, delamination does not easily occur at the interface between the lowermost layer and the substrate, and the adhesion of the laminated coating film to the substrate is improved. Further, during the heat treatment, a part of the curing agent in the uppermost layer and the lowermost layer moves to the intermediate layer, and a chemical bond is formed at the interface between the uppermost layer and the intermediate layer and the interface between the lowermost layer and the intermediate layer. It is presumed that peeling between layers is difficult to occur and interlayer adhesion is improved.

  In the present invention, “substantially does not generate a volatile product” and “volatilization of a volatile product does not substantially occur” includes shrinkage of a coating film due to volatilization of a volatile product. The case where the volatile product is generated and volatilized to such an extent that the surface smoothness of the coating film is not affected is included. Specifically, if the weight reduction rate of the coating film is 0.5% by mass or less even if a volatile product is generated and volatilized by heat-treating the paint, the paint is substantially volatile. It shall not produce product and will not volatilize.

  According to the present invention, even when at least the lowermost layer and the uppermost layer are cured by laminating and baking three or more types of paints on a wet-on-wet basis to ensure high durability, the surface of the uppermost layer has less unevenness. It becomes possible to obtain a laminated coating film having excellent adhesion to the substrate. Thereby, the coating body which is excellent in external appearance quality, such as skin (surface smoothness) and glossiness, and a multilayer coating film cannot peel easily can be obtained.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

The coating method of the present invention forms a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer. A painting method,
A thermosetting coating is prepared as a lowermost layer coating for forming the lowermost layer, and at least one of the intermediate layer coatings for forming the intermediate layer is a non-curing type that does not cause a curing reaction by heat treatment Preparing a paint and preparing a thermosetting paint as a paint for the uppermost layer for forming the uppermost layer;
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
It is the method characterized by including.

  In the coating method of the present invention, first, a lowermost layer coating is applied on a substrate, and if necessary, a solvent or the like is evaporated by drying or the like to form an uncured lowermost layer. Next, one or more kinds of intermediate layer paints are applied on the uncured lowermost layer, and if necessary, the solvent is evaporated by drying or the like to form an uncured intermediate layer. Further, the uncured laminated coating film obtained after applying the uppermost layer coating on the uncured intermediate layer and evaporating the solvent by drying or the like as necessary to form an uncured top layer. Is subjected to heat treatment (baking treatment) to cure at least the uppermost layer coating material and the lowermost layer coating material.

  The substrate used in the present invention is not particularly limited, and examples thereof include metals (iron, copper, aluminum, tin, zinc and alloys of these metals), steel plates, plastics, foams, paper, wood, cloth, Glass etc. are mentioned. Especially, this invention is applied suitably for the steel plate for motor vehicles with the required characteristic with respect to external appearance quality. These substrate surfaces may be subjected to a treatment such as electrodeposition coating in advance.

  In the present invention, a thermosetting coating is used as the lowermost layer coating. Thereby, the adhesiveness of the laminated coating film with respect to a base material improves. As such a thermosetting paint for the lowermost layer, a thermosetting paint used for ordinary baking coating can be used, and examples thereof include an intermediate paint described in JP-A-2004-275966. The form of the thermosetting paint for the lowermost layer may be either a solvent type or an aqueous type, but an aqueous type is preferred in that the discharge amount of volatile organic compounds can be reduced. In addition, the thermosetting paint for the lowermost layer is the weight at the curing temperature of the uppermost layer paint used from the viewpoint of minimizing the shrinkage of the coating after the uppermost layer is cured by heat treatment and the fluidity is significantly reduced. The smaller the reduction rate, the better.

  Specific examples of the thermosetting paint for the lowermost layer include thermosetting resins such as acrylic resins, polyester resins, alkyd resins, epoxy resins and urethane resins, and curing agents such as amino compounds, amino resins, isocyanate compounds and isocyanate resins. However, it is not limited to these. Moreover, the thermosetting resin and the curing agent may be used alone or in combination of two or more.

  The thermosetting paint for the lowermost layer may contain conventionally known color pigments, glitter pigments, and the like within a conventionally known range, if necessary. In order to adjust various physical properties, various additives such as a viscosity control agent, a surface conditioner, a thickener, an antioxidant, an ultraviolet absorber, and an antifoaming agent may be blended within a conventionally known range.

  In the coating method of the present invention, at least one intermediate layer is formed on the lowermost layer, but at least one of the intermediate layers is a non-curing type that does not cause a curing reaction by heat treatment as a coating for the intermediate layer It is formed using paint. Specifically, when the intermediate layer is one layer, this intermediate layer is formed using a non-curable paint, and when the intermediate layer is two or more layers, at least one of them is a non-curable paint. It forms using. In addition, when there are two or more intermediate layers formed using a non-curable paint, these layers are adjacent to each other from the viewpoint that there are few chemical bonding points at the interface between the intermediate layer and the intermediate layer, and delamination easily occurs. Preferably not.

  The non-curable coating material that does not cause a curing reaction by heat treatment used in the present invention may be any coating material that does not substantially cause a curing reaction by heat treatment, and the weight reduction rate at the curing temperature of the uppermost layer coating material to be used is 0. 5% by mass or less is preferable, 0.3% by mass or less is more preferable, and 0.1% by mass or less is particularly preferable. When a non-curing coating material having a small weight reduction rate due to such heat treatment is used, the shrinkage of the laminated coating film after the fluidity of the uppermost layer is remarkably lowered by curing tends to be reduced. Therefore, from this point of view, the non-curable paint is most preferably a paint that includes a base resin that can form a coating film and that does not contain a curing agent. What contains the hardening | curing agent can also be used, The content rate is 5 mass% or less with respect to 100 mass% of total of base resin and a hardening | curing agent, and 3 mass% or less is more preferable.

In the present invention, the “coating temperature of the paint” refers to a curing condition such as a curing time for coating the target paint on the base material and applying a heat treatment to cure the coating film and fix it on the base material. The temperature at which curing can be performed most efficiently is generally referred to, and generally the baking temperature set (designed) for each paint. In the present invention, a catalog value can be adopted as the curing temperature (baking temperature). The “weight reduction rate of the paint” is a value measured by the following method. That is, the target paint was coated on the aluminum foil so that the film thickness after heat treatment was the target film thickness in the laminated coating film, and the obtained aluminum foil sample was 40 ° C. higher than the curing temperature of the top layer paint. After drying at a low temperature and a vacuum condition of 10 ⁻² Torr or less for 90 minutes, a gas chromatograph / mass spectrometer (for example, 6890GC / 5975MSD manufactured by Agilent) equipped with a thermal desorption introduction device (for example, Thermal Desorption System manufactured by GERSTEL) is used. The volatile product amount (Rc (unit: g)) and the residual solvent amount are quantified by heating at the curing temperature of the uppermost layer coating material for 30 minutes, and the weight reduction rate is calculated by equation (1). This weight reduction rate is a ratio of the volatile product amount to the total binder amount in the coating film.

Weight reduction rate = 100 × Rc / W × 100 / (100-P) (1)
In formula (1), W is the mass (unit: g) of the coating film obtained in the vacuum drying step, and P is the mass (unit: g) of the pigment contained in 100 g of the coating film. In addition, the value (catalog value etc.) of the recipe of a coating material can be employ | adopted for the mass of a pigment.

  The base resin contained in the non-curable paint used in the present invention preferably has a melt viscosity of 500 Pa · s or less, more preferably 100 Pa · s or less, at the curing temperature of the uppermost layer paint to be used. 50 Pa · s or less is particularly preferable. When such a non-curable coating containing a base resin having a low melt viscosity at the curing temperature of the uppermost layer coating is used, the fluidity of the intermediate layer is ensured even during heat treatment (during baking), and the fluidity of the uppermost layer is improved. There is a tendency that shrinkage of the laminated coating film after remarkably lowering by curing can be reduced.

The “melt viscosity of the base resin” is a value measured by the following method. That is, a target base resin is applied to a glass plate and naturally dried at room temperature for 12 hours to sufficiently volatilize moisture in the base resin. Thereafter, the sample is dried for 90 minutes at a temperature lower by 40 ° C. than the curing temperature of the uppermost layer paint and 10 ⁻² Torr or less, and further heated at the curing temperature of the uppermost layer paint for 30 minutes to prepare a measurement sample. The melt viscosity (unit: Pa · s) of this measurement sample is measured using a viscoelasticity measuring device (for example, ARES viscoelasticity measuring device manufactured by TA Instruments). The measurement is performed at a shear rate of 0.1 s ⁻¹ using a 25 mm cone plate by raising the temperature of the sample to the curing temperature of the uppermost layer paint and keeping it in a steady state.

  Further, the base resin preferably has a standard polystyrene equivalent weight average molecular weight measured by high performance liquid chromatography of 1000 to 100,000, more preferably 5000 to 50000. When the weight average molecular weight of the base resin is less than the lower limit, the durability of the laminated coating film tends to be inferior. On the other hand, when the upper limit is exceeded, the smoothness of the coated surface tends to be inferior.

  Such a base resin may be a resin that does not cause a curing reaction by heat treatment alone. For example, a resin component obtained by removing a curing agent from a base paint described in JP-A-2004-275966, specifically, Examples of the resin include, but are not limited to, acrylic resin, polyester resin, alkyd resin, epoxy resin, and urethane resin. Two or more of these resins that do not cause a curing reaction by heat treatment may be selected and used in combination. Of these base resins, a resin containing a hydroxyl group is preferable, and a hydroxyl group-containing acrylic resin is more preferable from the viewpoint of improving the adhesion between the uppermost layer and the intermediate layer, the lowermost layer and the intermediate layer, and the intermediate layers.

  Examples of the curing agent that may be included in the non-curable coating material include amino compounds, amino resins, isocyanate compounds, and isocyanate resins.

  The form of the non-curable coating used in the present invention may be either solvent-based or water-based, but water-based is preferable in that the amount of volatile organic compounds discharged can be reduced. In addition, the non-curable coating material may contain conventionally known color pigments, glitter pigments, and the like within a conventionally known range, if necessary. In order to adjust various physical properties, various additives such as a viscosity control agent, a surface conditioner, a thickener, an antioxidant, an ultraviolet absorber, and an antifoaming agent may be blended within a conventionally known range.

  In the present invention, when there are two or more intermediate layers, if at least one layer is a layer formed using the non-curable paint, the remaining layers may be formed using a thermosetting paint.

  As the thermosetting paint for the intermediate layer, a thermosetting paint used in ordinary baking coating can be used, and examples thereof include a base paint described in JP-A-2004-275966. The form of the thermosetting coating for the intermediate layer may be either a solvent type or an aqueous type, but an aqueous type is preferable in that the amount of volatile organic compounds discharged can be reduced. In addition, the thermosetting paint for the intermediate layer is the weight at the curing temperature of the coating material for the uppermost layer used from the viewpoint of minimizing the shrinkage of the coating film after the uppermost layer is cured by heat treatment and the fluidity is significantly reduced. The smaller the reduction rate, the better.

  Specific examples of thermosetting coatings for intermediate layers include thermosetting resins such as acrylic resins, polyester resins, alkyd resins, epoxy resins and urethane resins, and curing agents such as amine compounds, amino resins, isocyanate compounds and isocyanate resins. However, it is not limited to these. Moreover, the thermosetting resin and the curing agent may be used alone or in combination of two or more.

  The thermosetting paint for intermediate layer may contain conventionally known color pigments, glitter pigments, and the like within a conventionally known range, if necessary. In order to adjust various physical properties, various additives such as a viscosity control agent, a surface conditioner, a thickener, an antioxidant, an ultraviolet absorber, and an antifoaming agent may be blended within a conventionally known range.

  In the present invention, a thermosetting paint is used as the paint for the uppermost layer. As the thermosetting paint for the uppermost layer, a thermosetting resin capable of forming a coating film and a curing agent (for example, a compound or resin having two or more functional groups capable of reacting with the functional group of the thermosetting resin). Any thermosetting paint (for example, clear paint described in JP-A-2004-275966) used as an uppermost-layer paint for ordinary baking coating may be used. The form may be any of solvent type, aqueous type and powder. The curing temperature of the uppermost layer thermosetting paint is not particularly limited, but is usually 40 to 200 ° C, preferably 60 to 160 ° C.

  Examples of the thermosetting resin capable of forming a coating film contained in the uppermost layer-coating material include acrylic resins, polyester resins, alkyd resins, epoxy resins, and urethane resins, but are not limited thereto. Preferred curing agents include, but are not limited to, amino compounds, amino resins, isocyanate compounds, and isocyanate resins. These resins and curing agents may be used alone or in combination of two or more.

  In the coating method of the present invention, the uppermost layer-coating material is preferably a coating material that does not substantially generate a volatile product in a curing reaction by heat treatment. Such a coating material preferably has a weight reduction rate of 0.5% by mass or less at the curing temperature, more preferably 0.3% by mass or less, and particularly preferably 0.1% by mass or less. When such a thermosetting paint having a small weight reduction rate is used as the uppermost layer paint, shrinkage of the coating film due to heat treatment tends to be minimized. From this point of view, a paint that does not generate a volatile product (weight reduction rate of 0% by mass) is most preferable.

  The combination of the thermosetting resin that does not generate a volatile product in the curing reaction by heat treatment and the curing agent includes a combination of a hydroxyl group-containing acrylic resin and an isocyanate compound and / or an isocyanate resin, an epoxy group-containing acrylic resin, and a combination. Examples thereof include a combination with a polyvalent carboxylic acid compound and / or a carboxyl group-containing resin.

  Further, the uppermost layer coating material may contain conventionally known color pigments, glitter pigments, and the like within a conventionally known range, if necessary. In order to adjust various physical properties, various additives such as a viscosity control agent, a surface conditioner, a thickener, an antioxidant, an ultraviolet absorber, and an antifoaming agent may be blended within a conventionally known range.

  In the coating method of the present invention, first, the lowermost layer-coating material is applied onto the substrate, and if necessary, the solvent is evaporated by drying or the like to form an uncured lowermost layer. Examples of the method for applying the lowermost layer coating material include conventionally known methods such as air electrostatic spray coating and rotary atomizing electrostatic coating.

  The film thickness of the lowermost layer can be appropriately set depending on the desired application. For example, the film thickness after the heat treatment is preferably 5 to 50 μm, and more preferably 10 to 40 μm. When the film thickness of the lowermost layer is less than the lower limit, it tends to be difficult to obtain a uniform lowermost film. On the other hand, when it exceeds the upper limit, it tends to absorb a lot of solvent contained in the uppermost film. The volatilization of the solvent contained in the layer itself is also suppressed, and the appearance quality of the laminated coating film tends to deteriorate.

  Next, the intermediate layer coating material is applied onto the uncured lowermost layer, and the solvent is evaporated by drying or the like as necessary to form an uncured intermediate layer. At this time, when the intermediate layer is one layer, the intermediate layer is formed using the non-curable coating material. When there are two or more intermediate layers, at least one layer can be formed using the non-curable coating material, and the remaining layers can be formed using the intermediate layer thermosetting coating material. Further, when two or more intermediate layers are formed using a non-curable paint, these layers are preferably not adjacent to each other.

  When applying the coating for the intermediate layer, apply a conventionally known method such as air electrostatic spray coating or rotary atomizing electrostatic coating, regardless of whether non-curing paint or thermosetting paint is used. Can do.

  Although the film thickness of each layer of an intermediate | middle layer can be suitably set with a desired use, For example, it is preferable that it is 5-50 micrometers by the film thickness after heat processing, and it is more preferable that it is 10-40 micrometers. If the thickness of each intermediate layer is less than the lower limit, it tends to be difficult to obtain a uniform intermediate layer coating film. On the other hand, if it exceeds the upper limit, it tends to absorb a large amount of the solvent contained in the uppermost coating layer. At the same time, the volatilization of the solvent contained in the layer itself is also suppressed and the appearance quality of the laminated coating film tends to deteriorate.

  Next, the uppermost layer-coating material is applied on the uncured intermediate layer, and if necessary, the solvent is evaporated by drying or the like to form an uncured uppermost layer. Conventionally known methods such as air electrostatic spray coating and rotary atomizing electrostatic coating can be used as the coating method for the uppermost layer coating material.

  The film thickness of the uppermost layer can be appropriately set depending on the desired application. For example, the film thickness after heat treatment is preferably 15 to 60 μm, and more preferably 20 to 50 μm. When the film thickness of the uppermost layer is less than the lower limit, the fluidity is insufficient and the appearance quality of the laminated coating film tends to deteriorate. On the other hand, when the upper limit is exceeded, the fluidity becomes excessively large and the coating is applied in the vertical direction. There is a tendency for defects such as sagging to occur.

  In this way, the uncured multi-layer coating film formed by laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material in a wet-on-wet manner is subjected to a heat treatment (baking treatment) to at least the uppermost layer coating. The upper layer paint is cured. In the coating method of the present invention, the heat treatment is a heat treatment (hereinafter referred to as “high temperature heat treatment”) at a temperature higher than at least the temperature at which the uppermost layer is cured, for example, [the curing temperature of the paint for the uppermost layer−20 ° C.]. ) Is preferably included.

  Further, the high temperature heating temperature is preferably in a range of [the curing temperature of the top layer coating material ± 20 ° C.]. Specifically, when the curing temperature of the uppermost layer-coating material is 140 ° C., the high temperature heating temperature is preferably 120 ° C. or higher, and preferably 120 ° C. or higher and 160 ° C. or lower. The high temperature heating time is preferably 50% or more and 150% or less, and preferably 60% or more and 100% or less, of the curing time of the uppermost layer coating material. Specifically, when the curing time of the uppermost layer-coating material is 30 minutes, the high-temperature heating time is preferably 15 minutes to 45 minutes, and more preferably 18 minutes to 30 minutes.

  Moreover, in the coating method of this invention, it is preferable to reduce the volatile matter density | concentration of a laminated coating film, without hardening the uppermost layer, before performing the said high temperature heat processing. This tends to minimize the shrinkage of the laminated coating after the uppermost layer is cured by heat treatment and the fluidity is significantly reduced.

  As a method of reducing the volatile content concentration of the laminated coating film without curing the uppermost layer, heat treatment (hereinafter referred to as “low temperature heat treatment”) at a temperature lower than [the curing temperature of the uppermost layer coating material—20 ° C.] The method of applying is preferred. Further, the low-temperature heating temperature is preferably less than [the curing temperature of the uppermost layer paint −30 ° C.], particularly preferably less than [the curing temperature of the uppermost layer paint −40 ° C.]. Specifically, when the curing temperature of the paint for the uppermost layer is 140 ° C., the low temperature heating temperature is preferably less than 120 ° C., more preferably less than 110 ° C., and particularly preferably less than 100 ° C. . The low temperature heating time is preferably 10% or more and less than 50%, and preferably 20% or more and 40% or less of the curing time of the uppermost layer coating material. Specifically, when the curing time of the uppermost layer-coating material is 30 minutes, the low-temperature heating time is preferably 3 minutes to 15 minutes, and more preferably 6 minutes to 12 minutes. When the uncured laminated coating film is heat-treated in the range of the low temperature heating temperature and the low temperature heating time, the volatile content concentration of the laminated coating film tends to be reduced without substantially curing the uppermost layer.

  Furthermore, in the coating method of the present invention, in order to stabilize the uncured coating film laminated by wet-on-wet, it is preferable to leave it at room temperature (setting) before the heat treatment. The setting time is usually set to 1 to 20 minutes.

  In the present invention, in order to obtain a coated body having a higher-grade appearance, one or more kinds of paints are further applied on the uppermost layer of the coated body obtained by the coating method and subjected to a curing treatment. It is preferable to form a surface layer. As the coating material, those exemplified as the top layer coating material can be used. Examples of the method for applying the paint include conventionally known methods such as air spray coating, air electrostatic spray coating, and rotary atomizing electrostatic coating.

  The coated body of the present invention is manufactured by the coating method of the present invention, and has fewer irregularities on the surface of the multilayer coating film than the conventional multilayer coating film manufactured by wet-on-wet, and is excellent in appearance quality. Moreover, this laminated coating film is hard to peel off from a base material, and is excellent in the adhesiveness with respect to a base material. Such a coated body is particularly useful as a vehicle body for automobiles such as passenger cars, trucks, buses, motorcycles, and parts thereof.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. The measurement of the melt viscosity of the base resin and the weight reduction rate of the laminated coating film and the evaluation of the adhesion of the laminated coating film were carried out by the following methods.

(Melt viscosity)
The target base resin was applied to a glass plate and naturally dried at room temperature for 12 hours to sufficiently volatilize water in the base resin. Thereafter, the sample was dried for 90 minutes at a temperature 40 ° C. lower than the curing temperature of the uppermost layer paint and 10 ⁻² Torr or less, and further heated for 30 minutes at the curing temperature of the uppermost layer paint to prepare a measurement sample. The melt viscosity (unit: Pa · s) of this measurement sample was measured using a viscoelasticity measuring device (ARES viscoelasticity measuring device manufactured by TA Instruments). The measurement was performed at a shear rate of 0.1 s ⁻¹ using a 25 mm cone plate by raising the temperature of the sample to the curing temperature of the coating material for the uppermost layer and maintaining the steady state.

(Weight reduction rate)
The target paint is coated on the aluminum foil so that the film thickness after the heat treatment becomes the target film thickness of the laminated coating film, and the obtained aluminum foil sample is at a temperature 40 ° C. lower than the curing temperature of the uppermost layer paint. After drying for 90 minutes under a vacuum condition of 10 ⁻² Torr or less, using a gas chromatograph / mass spectrometer (for example, 6890GC / 5975MSD manufactured by Agilent) equipped with a thermal desorption introducing device (for example, Thermal Destruction System manufactured by GERSTEL) The amount of volatile products (Rc (unit: g)) and the amount of residual solvent were quantified by heating at the curing temperature of the upper layer coating material for 30 minutes, and the weight reduction rate was calculated by equation (1). This weight reduction rate is a ratio of the volatile product amount to the total binder amount in the coating film.

Weight reduction rate = 100 × Rc / W × 100 / (100-P) (1)
In formula (1), W is the mass (unit: g) of the coating film obtained in the vacuum drying step, and P is the mass (unit: g) of the pigment contained in 100 g of the coating film. In addition, the mass of the pigment used the value of the coating composition table.

(Adhesiveness)
The adhesion of the laminated coating film was evaluated by a cross cut test (2 mm) described in JIS K5400 8.5.1. Cellotape (registered trademark) CT-24 (manufactured by Nichiban Co., Ltd., width 24 mm) was used as the tape.

(Synthesis example 1) Acrylic emulsion R-1
The following monomers were mixed to prepare a monomer mixed solution (acid value: 20 (calculated value), hydroxyl value: 69 (calculated value), Tg: −20 ° C. (calculated value)).

<Monomer mixture composition>
Methyl methacrylate 10.7 parts by mass Butyl acrylate 198.5 parts by mass 2-hydroxyethyl methacrylate 50.4 parts by mass Styrene 47.3 parts by mass Acrylic acid 8.2 parts by mass n-dodecyl mercaptan 4.0 parts by mass.

  319 parts by weight of this monomer mixture, 105 parts by weight of water, and 14 parts by weight of an anionic surfactant (“New Coal 707-SN” manufactured by Nippon Emulsifier Co., Ltd.) are mixed and stirred to emulsify using a mixer. A monomer pre-emulsion was prepared.

  Next, 280 parts by mass of water and an anionic surfactant (manufactured by Nippon Emulsifier Co., Ltd.) were added to a reaction vessel for producing an acrylic resin emulsion equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser and a nitrogen introduction tube. 5.6 parts by mass of Newcol 707-SN "), 0.7 parts by mass of an aqueous solution of ammonium persulfate (hereinafter referred to as" APS ") as a polymerization initiator (APS (manufactured by Aldrich)) and 13.3 parts by mass of water, Were prepared by stirring and mixing), and the temperature was raised to 80 ° C. while stirring. To this solution, 5% by mass of the monomer pre-emulsion was added and held at 80 ° C. for 10 minutes. Thereafter, the remaining monomer pre-emulsion was added dropwise with stirring over 4 hours. After completion of the dropwise addition, the reaction was further continued at 80 ° C. for 1 hour with stirring. Thereafter, 56 parts by mass of water was added and cooled to room temperature. After cooling, the pH of the reaction solution was adjusted to 7.4 using a 10% by mass aqueous dimethylethanolamine solution to obtain an acrylic emulsion R-1 having a nonvolatile content of 38.1% by mass.

(Synthesis example 2) Acrylic emulsion R-2
The following monomers were mixed to prepare a monomer mixed solution (acid value: 20 (calculated value), hydroxyl value: 97 (calculated value), Tg: −12 ° C. (calculated value)).

<Monomer mixture composition>
2-ethylhexyl methacrylate 100.8 parts by mass Butyl acrylate 69.3 parts by mass 4-hydroxybutyl methacrylate 78.8 parts by mass Styrene 58.0 parts by mass Acrylic acid 8.2 parts by mass n-dodecyl mercaptan 4.0 parts by mass.

  Acrylic emulsion R-2 having a non-volatile content of 38.1 mass% and a weight average molecular weight of 12,000 in the same manner as in Synthesis Example 1 except that 319 parts by mass of this monomer mixture was used instead of the monomer mixture described in Synthesis Example 1. Got. The melt viscosity (140 ° C.) of this acrylic emulsion R-2 was 27 Pa · s.

(Synthesis example 3) Acrylic emulsion R-3
The following monomers were mixed to prepare a monomer mixed solution (acid value: 20 (calculated value), hydroxyl value: 97 (calculated value), Tg: 10 ° C. (calculated value)).

<Monomer mixture composition>
2-ethylhexyl methacrylate 91.4 parts by mass Butyl acrylate 25.2 parts by mass 4-hydroxybutyl methacrylate 78.8 parts by mass Styrene 111.5 parts by mass Acrylic acid 8.2 parts by mass n-dodecyl mercaptan 4.0 parts by mass.

  Acrylic emulsion R-3 having a non-volatile content of 38.1% by mass and a weight average molecular weight of 12,000 in the same manner as in Synthesis Example 1 except that 319 parts by mass of this monomer mixture was used instead of the monomer mixture described in Synthesis Example 1. Got. The melt viscosity (140 ° C.) of this acrylic emulsion R-3 was 93 Pa · s.

(Synthesis example 4) Acrylic emulsion R-4
The following monomers were mixed to prepare a monomer mixed solution (acid value: 20 (calculated value), hydroxyl value: 97 (calculated value), Tg: 10 ° C. (calculated value)).

<Monomer mixture composition>
2-ethylhexyl methacrylate 91.4 parts by mass Butyl acrylate 25.2 parts by mass 4-hydroxybutyl methacrylate 78.8 parts by mass Styrene 111.5 parts by mass Acrylic acid 8.2 parts by mass n-dodecyl mercaptan 2.0 parts by mass.

  Acrylic emulsion R-4 having a non-volatile content of 38.0% by weight and a weight average molecular weight of 30000 in the same manner as in Synthesis Example 1 except that 317 parts by mass of this monomer mixture was used instead of the monomer mixture described in Synthesis Example 1. Got. The melt viscosity (140 ° C.) of this acrylic emulsion R-4 was 490 Pa · s.

(Preparation Example 1) Colored pigment paste In a SUS container, 123 parts by mass of water, 30 parts by mass of urethane dispersion (“Hydran WLS-202” manufactured by DIC Corporation), a wetting dispersant (“Disperbyk-181” manufactured by BYK Chemie) 1.5 parts by mass, 1.5 parts by mass of an antifoaming agent (“SN deformer 1340” manufactured by San Nopco Co., Ltd.) and 323.4 parts by mass of rutile titanium oxide (“CR-90-2” manufactured by Ishihara Sangyo Co., Ltd.) After the parts were premixed for 3 minutes, glass beads (particle size: 1.6 mm) having the same volume as the total charged volume were charged and dispersed for 1 hour with a desktop sand mill. The particle size at the end of dispersion as measured with a grind gauge was 5 μm or less.

(Preparation Example 2) Melamine curable aqueous intermediate coating P-1
A container is charged with 244.9 parts by mass of the color pigment paste obtained in Preparation Example 1, and 171.4 parts by mass of the acrylic emulsion R-1 obtained in Synthesis Example 1 and methylated melamine resin (Japan) while stirring. 40.3 parts by mass of "Cymel 325" manufactured by Cytec Industries Co., Ltd. was added and stirred for 5 minutes. Thereafter, 20 parts by mass of water, 8 parts by mass of butyl diglycol and 16 parts by mass of butyl glycol were added and stirred for 5 minutes. Further, an alkali thickener (“Viscalex HV30” manufactured by Ciba Specialty Chemicals Co., Ltd.), dimethylethanolamine and water are added in an appropriate amount, and a melamine curable aqueous intermediate coating P- having a non-volatile content of 48.3% by mass and a pH of 8.4. 1 was obtained. The curing temperature of this aqueous intermediate coating P-1 was 140 ° C. Further, the total pigment content mass (%) (hereinafter referred to as “PWC”) with respect to the total solid content mass in the formulation of the aqueous intermediate coating material P-1 was 42.

(Preparation Example 3) Isocyanate-curable aqueous intermediate coating P-2
Except for changing the amount of acrylic emulsion R-1 to 197.7 parts by mass and using 25.0 parts by mass of water-dispersible polyisocyanate (“Birnock DNW5000” manufactured by DIC Corporation) instead of methylated melamine resin. In the same manner as in Preparation Example 1, an isocyanate curable aqueous intermediate coating P-2 having a nonvolatile content of 47.3% by mass, pH 8.2, a curing temperature of 140 ° C., and PWC42 was obtained.

(Preparation Example 4) Non-curing aqueous intermediate coating P-3
In a container, 244.9 parts by mass of the color pigment paste obtained in Preparation Example 1 was charged, and 250.5 parts by mass of the acrylic emulsion R-1 obtained in Synthesis Example 1 was added to this while stirring and stirred for 5 minutes. Thereafter, in the same manner as in Preparation Example 1, a non-curable aqueous intermediate coating material P-3 having a nonvolatile content of 45.0% by mass, pH 8.0, and PWC42 was obtained.

  Table 1 shows the compositions of the water-based intermediate coating materials P-1 to P-3.

(Preparation Example 5) Non-curable water-based base paint B-1
A container was charged with 263.6 parts by mass of the acrylic emulsion R-2 obtained in Synthesis Example 2, and 150 parts by mass of water and 20 parts by mass of butyl glycol were added thereto and stirred for 5 minutes. Thereafter, an alkali thickener (“Viscalex HV30” manufactured by Ciba Specialty Chemicals), dimethylethanolamine and water were added in an appropriate amount to obtain an aqueous resin solution having a nonvolatile content of 21% by mass and a pH of 8.5.

  In another container, 61.5 parts by mass of butyl glycol and 5.0 parts by mass of a phosphate ester compound (“Lublizol 2062” manufactured by Nippon Lubrizol Co., Ltd.) were charged and stirred for 5 minutes. To this solution, 20.0 parts by weight of two types of aluminum paste (“Hydrolan 2154” manufactured by ECKART GmbH and “Hydrolan 2156” manufactured by ECKART GmbH) were added, and then stirred for 1 hour to obtain an aluminum dispersion.

  Next, 58.6 parts by mass of this aluminum dispersion was added to 497.6 parts by mass of the aqueous resin solution, and the mixture was further stirred for 1 hour to obtain a non-curable aqueous base having a nonvolatile content of 22% by mass and a pH of 7.8. A paint B-1 was obtained. The weight loss rate of this water-based base coating material B-1 at 140 ° C. was 0% by mass (calculated as P = 14.5).

(Preparation Example 6) Fine melamine curable aqueous base paint B-2
A container is charged with 255.7 parts by mass of the acrylic emulsion R-2 obtained in Synthesis Example 2, and 4.0 parts by mass of a methylated melamine resin (“Cymel 325” manufactured by Nippon Cytec Industries, Ltd.) while stirring. Then, 150 parts by mass of water and 20 parts by mass of butyl glycol were added and stirred for 5 minutes. Further, an appropriate amount of an alkali thickener (“Viscalex HV30” manufactured by Ciba Specialty Chemicals), dimethylethanolamine and water was added to obtain an aqueous resin solution having a nonvolatile content of 21% by mass and a pH of 8.5.

  Instead of the aqueous resin solution described in Preparation Example 5, the same procedure as in Preparation Example 5 except that 493.7 parts by mass of this aqueous resin solution was used. A fine melamine curable aqueous base paint B-2 was obtained. The weight reduction rate of this water-based base coating material B-2 at 140 ° C. was 0.4% by mass (calculated as P = 14.5).

(Preparation Example 7) Melamine curable aqueous base paint B-3
Except for changing the amount of the acrylic emulsion R-2 to 184.6 parts by mass and changing the amount of the methylated melamine resin to 40.0 parts by mass, in the same manner as in Preparation Example 6, the nonvolatile content was 23% by mass, pH 8. 5 aqueous resin solution was obtained.

  Instead of the aqueous resin solution described in Preparation Example 5, the same procedure as in Preparation Example 5 except that 458.6 parts by mass of this aqueous resin solution was used. The non-volatile content was 24% by mass, the pH was 7.8, and the curing temperature was 140 ° C. A melamine curable aqueous base paint B-3 was obtained. The weight loss rate of this water-based base coating material B-3 at 140 ° C. was 3.8% by mass (calculated as P = 14.5).

(Preparation Example 8) Non-curable water-based base paint B-4
An aqueous resin solution having a nonvolatile content of 21% by mass and a pH of 8.5 in the same manner as in Preparation Example 5 except that 263.6 parts by mass of the acrylic emulsion R-3 obtained in Synthesis Example 3 was used instead of the acrylic emulsion R-2. Got.

  A non-curable aqueous base having a non-volatile content of 22% by mass and a pH of 7.8 in the same manner as in Preparation Example 5 except that 497.6 parts by mass of this aqueous resin solution was used instead of the aqueous resin solution described in Preparation Example 5. A paint B-4 was obtained. The weight loss rate of this water-based base coating material B-4 at 140 ° C. was 0% by mass (calculated as P = 14.5).

(Preparation Example 9) Non-curable water-based base paint B-5
An aqueous resin solution having a nonvolatile content of 21% by mass and a pH of 8.5 in the same manner as in Preparation Example 5 except that 263.6 parts by mass of the acrylic emulsion R-4 obtained in Synthesis Example 4 was used instead of the acrylic emulsion R-2. Got.

  A non-curable aqueous base having a non-volatile content of 22% by mass and a pH of 7.8 in the same manner as in Preparation Example 5 except that 497.6 parts by mass of this aqueous resin solution was used instead of the aqueous resin solution described in Preparation Example 5. A paint B-5 was obtained. The weight loss rate of this water-based base coating material B-5 at 140 ° C. was 0% by mass (calculated as P = 14.5).

  Table 2 shows the compositions of the aqueous base paints B-1 to B-5.

(Preparation Example 10) Thermosetting clear paint C-1
A main component of a two-component thermosetting clear paint was prepared by mixing polyol, additive and solvent in the proportions shown in Table 3. Moreover, the isocyanate hardening | curing agent shown in Table 3 was used as a hardening | curing agent of the said thermosetting type clear coating material. What mixed this main ingredient and the hardening | curing agent in the ratio shown in Table 3 (solid content concentration of 55 mass%) was used as the thermosetting clear coating material C-1. The curing temperature of this clear paint C-1 was 140 ° C., and the weight reduction rate at 140 ° C. was 0% by mass (calculated as P = 0).

Example 1
The film after baking the melamine curable aqueous intermediate coating P-1 (curing temperature 140 ° C.) obtained in Preparation Example 2 on the surface of the electrodeposition coating plate (trade name “Sucsade 80V Gray” manufactured by Shinto Herberts) The coating was applied to a thickness of 20 μm and heated at 100 ° C. for 3 minutes to volatilize water and organic solvent. Next, the non-curable water-based base paint B-1 obtained in Preparation Example 5 was applied on the layer of the water-based intermediate coating P-1 so that the film thickness after baking was 15 μm, Water and organic solvent are volatilized by heating for a minute, and then the film thickness after baking the thermosetting clear paint C-1 obtained in Preparation Example 10 on the layer of the aqueous base paint B-1 is 35 μm. To obtain an uncured laminated coating film obtained by laminating a melamine curable aqueous intermediate coating material P-1, a non-curable aqueous base coating material B-1, and a thermosetting clear coating material C-1 in a wet-on-wet manner. It was.

  This uncured laminated coating is allowed to stand (setting) at room temperature for 10 minutes, and then subjected to heat treatment (baking treatment) at 90 ° C. for 10 minutes and heating treatment (baking treatment) at 140 ° C. for 30 minutes in sequence. Type waterborne intermediate coating P-1 and thermosetting clear coating C-1 were cured. At this time, wave scan values [Wa (wavelength <0.3 mm), Wb (wavelength 0.3 to 1 mm), Wc (wavelength 1 to 3 mm) using wave scan (“Wave-Scan Dual” manufactured by BYK-Gardner). ), Wd (wavelength 3 to 10 mm)]. These wave scan values mean that the smaller the Wa, the better the gloss, and the smaller the Wd, the better the skin. Table 4 shows Wa to Wd of the laminated coating film at the end of baking.

  After the baking was finished, the coated plate was allowed to stand at room temperature for 30 minutes, and then the adhesion of the laminated coating film (hereinafter referred to as “adhesion after baking”) was evaluated. Moreover, after leaving the coating plate after baking for 24 hours at room temperature, it was immersed in a constant temperature water bath at 40 ° C. for 240 hours. Thereafter, the coated plate was pulled up from the water tank and allowed to stand at room temperature for 30 minutes, and then the adhesion of the laminated coating film (hereinafter referred to as “adhesion after water resistance test”) was evaluated. Table 4 shows the number of cells in which the laminated coating film did not peel off.

(Example 2)
Laminated coating in the same manner as in Example 1 except that the isocyanate curable aqueous intermediate coating material P-2 (curing temperature 140 ° C.) obtained in Preparation Example 3 was used instead of the melamine curable aqueous intermediate coating material P-1. A film was prepared, and Wa to Wd were measured. Table 4 shows Wa to Wd of the laminated coating film at the end of baking. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

(Example 3)
A laminated coating film in the same manner as in Example 1 except that the fine melamine curable aqueous base paint B-2 (curing temperature 140 ° C.) obtained in Preparation Example 6 was used instead of the non-curable aqueous base paint B-1. And Wa to Wd were measured. Table 4 shows Wa to Wd of the laminated coating film at the end of baking. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

Example 4
A laminated coating film was produced in the same manner as in Example 1 except that the non-curable water-based base paint B-4 obtained in Preparation Example 8 was used instead of the non-curable water-based base paint B-1, and the baking was completed. Wa to Wd of the multilayer coating film were measured. The results are shown in Table 4. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

(Example 5)
A laminated coating film was prepared in the same manner as in Example 1 except that the non-curable water-based base paint B-5 obtained in Preparation Example 9 was used instead of the non-curable water-based base paint B-1, and the baking was completed. Wa to Wd of the multilayer coating film were measured. The results are shown in Table 4. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

(Comparative Example 1)
A laminated coating film was prepared in the same manner as in Example 1 except that the melamine curable aqueous base paint B-3 (curing temperature 140 ° C.) obtained in Preparation Example 7 was used instead of the non-curable aqueous base paint B-1. It produced and Wa-Wd of the laminated coating film at the time of completion | finish of baking was measured. The results are shown in Table 4. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

(Comparative Example 2)
In place of the melamine curable aqueous intermediate coating material P-1, the non-curable aqueous intermediate coating material P-3 obtained in Preparation Example 4 was used, and instead of the non-curable aqueous base coating material B-1, in Preparation Example 7. A laminated coating film was produced in the same manner as in Example 1 except that the obtained melamine curable water-based base coating B-3 (curing temperature 140 ° C.) was used, and Wa to Wd of the laminated coating film at the end of baking were measured. . The results are shown in Table 4. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

(Comparative Example 3)
A laminated coating film was prepared and baked in the same manner as in Example 1 except that the non-curable aqueous intermediate coating material P-3 obtained in Preparation Example 4 was used instead of the melamine-curable aqueous intermediate coating material P-1. Wa to Wd of the laminated coating film at the end were measured. The results are shown in Table 4. Table 4 shows the results of evaluating the adhesion after baking and after the water resistance test in the same manner as in Example 1.

  As is clear from the results shown in Table 4, as in the present invention, a thermosetting coating is used for the uppermost layer and the lowermost layer, and a non-thermosetting or slightly curable coating is used for the intermediate layer. Wa to Wd of the multilayer coating films (Examples 1 to 5) are all conventional multilayer coating films (comparative example 1) using the thermosetting paint for all of the uppermost layer, the intermediate layer and the lowermost layer, and the uppermost layer. And the thermosetting paint is used for the intermediate layer, and it is smaller than the multi-layer coating film (Comparative Example 2) using the non-curing paint for the lowermost layer. It was confirmed that it was improved over the laminated coating films of Comparative Examples 1 to 4.

  Further, as is apparent from the results shown in Table 4, a laminated coating film using a thermosetting paint for the uppermost layer and the lowermost layer and a non-thermosetting or slightly curable paint for the intermediate layer (Example 1) ~ 5) are not peeled off at all, and are excellent in adhesion as in the case of a conventional multilayer coating film (Comparative Example 1) using a thermosetting paint for all of the uppermost layer, the intermediate layer and the lowermost layer. Was confirmed. On the other hand, in the case of a laminated coating film (in Comparative Examples 2 to 3) using a non-thermosetting paint for the lowermost layer, the substrate (electrodeposition coating plate) and the outermost layer are used in all the cells after the heat resistance test. Peeling occurred at the interface with the lower layer (non-curable paint), and the adhesion was poor. This is because the lowermost layer does not harden in the laminated coating films of Comparative Examples 2 to 3, so that there are very few chemical bonding points at the interface between the lowermost layer and the base material, and warm water penetrates into the laminated coating film. In this case, it is assumed that the hot water entered the interface and the bond was broken.

  As described above, according to the present invention, even when at least the uppermost layer and the lowermost layer are cured by laminating and baking three or more types of paints in a wet-on-wet manner, the surface of the uppermost layer is less uneven, and the substrate It is possible to obtain a laminated coating film having excellent adhesion to the film. Thereby, the coating body which was excellent in external appearance quality, such as skin (surface smoothness) and glossiness, and excellent in the adhesiveness of a base material and a coating film can be obtained.

  Therefore, the present invention provides a coating method capable of obtaining a coated body having excellent appearance quality and excellent adhesion between a base material and a coating film even when three or more kinds of paints are laminated and baked wet-on-wet. It is particularly useful as a method for painting automobile bodies such as passenger cars, trucks, buses, motorcycles, and parts thereof.

Claims (4)

A coating method for forming a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer,
A thermosetting coating is prepared as a lowermost layer coating for forming the lowermost layer, and at least one of the intermediate layer coatings for forming the intermediate layer is a non-curing type that does not cause a curing reaction by heat treatment Preparing a paint, and preparing a paint having a weight reduction rate of 0.5% by mass or less at the curing temperature as a top layer paint for forming the top layer ,
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
Painting how to comprising a. A coating method for forming a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer,
To prepare a thermosetting paint as a lowermost layer coating for forming the lowermost layer, to prepare a thermosetting coating as an uppermost layer coating for forming the uppermost layer, and to form the intermediate layer non-curable coating material is a by weight reduction rate in curing temperature of the uppermost layer-coating material that does not cause a curing reaction by a heat treatment as at least one of the intermediate layer coating to prepare a 0.5 wt% or less of the paint Process,
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
Painting how to comprising a. A coating method for forming a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer,
To prepare a thermosetting paint as a lowermost layer coating for forming the lowermost layer, to prepare a thermosetting coating as an uppermost layer coating for forming the uppermost layer, and to form the intermediate layer prepare those containing at least one as a curing reaction a non-curable coating is a by the melt viscosity of 500 Pa · s or less of the base resin in the curing temperature of the uppermost layer-coating material is not caused by the heat treatment of the intermediate layer-coating material And a process of
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
Applying a heat treatment to the uncured laminated coating to cure at least the lowermost layer coating and the uppermost layer coating;
Painting how to comprising a. A coating method for forming a laminated coating film comprising a lowermost layer formed on a substrate, at least one intermediate layer formed on the lowermost layer, and an uppermost layer formed on the intermediate layer,
A thermosetting coating is prepared as a lowermost layer coating for forming the lowermost layer, and at least one of the intermediate layer coatings for forming the intermediate layer is a non-curing type that does not cause a curing reaction by heat treatment Preparing a paint and preparing a thermosetting paint as a paint for the uppermost layer for forming the uppermost layer;
A step of laminating the lowermost layer coating material, the intermediate layer coating material and the uppermost layer coating material on the base material by wet-on-wet to form an uncured laminated coating film;
The heat-treated uncured multilayer coating film at a temperature less than [the curing temperature -20 ° C. in the uppermost layer-coating material, then facilities to heat treatment in the said curing temperature -20 ° C. of the uppermost layer-coating material] temperatures above Curing at least the lowermost layer paint and the uppermost layer paint,
Painting how to comprising a.