JP2017023941A - Coating method and coated body obtained by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method whereby a laminated coating film in which occurrence of roughness of an upper-layer surface is sufficiently restricted can be obtained even when two or more coating materials are layered in a wet-on-wet manner and simultaneously baked to cure each layer.SOLUTION: A coating method for forming a laminated coating film comprising a lower layer formed on a base material, and an upper layer formed on the lower layer, comprises: a preparation step in which a thermoplastic coating material is prepared as a lower-layer coating material and an upper-layer coating material; a formation step in which an uncured laminated coating film is formed by layering, on the base material, the lower-layer coating material and the upper-layer coating material in a wet-on-wet manner; and a baking step in which the uncured laminated coating film is subjected to a baking process, thereby simultaneously curing the lower-layer coating material and the upper-layer coating material. In the preparation step, if the contraction coefficients of the upper-layer coating material and the lower-layer coating material for a period after the flow stop time tof the upper-layer coating material to the termination of a standard baking time tof each coating material are ωand ωrespectively, the upper-layer coating material and the lower-layer coating material are selected so that the absolute value of the difference between the contraction coefficient ωand the contraction coefficient ωis 6.0% or less.SELECTED DRAWING: None

Description

  The present invention relates to a coating method in which two types of paints are laminated by wet-on-wet and baked simultaneously, and a coated body obtained thereby.

  When two layers of paints are laminated on a wet-on-wet basis, and a multilayer coating film is formed by a baking method, all layers constituting the multilayer coating film are cured by baking after all the coating materials are laminated. Thus, a method of selecting a thermosetting coating material for forming each layer and curing the entire laminated coating film has been used. However, the conventional coating method has a problem that the skin and gloss of the laminated coating film are inferior as compared with the case where the lower layer is baked and then the upper layer forming coating 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, in Japanese Patent Application Laid-Open No. 2007-283271 (Patent Document 1), an aqueous base paint using a melamine resin as a curing agent and an aqueous clear paint using an isocyanate compound as a curing agent are applied wet-on-wet, and then both In the method for forming a multilayer coating film in which the coating film is heat-cured together, the solid content concentration of the base coating film is 85% by mass or more and the water absorption rate of the base coating film at 20 ° C. is 10% by mass or less when applying the water-based clear coating. By doing so, it is possible to suppress the diffusion and penetration of water from the clear layer to the base layer after the application of the water-based clear paint, and it is possible to suppress an increase in the viscosity of the clear paint film due to water absorption of the base paint film. It is disclosed. Furthermore, it is disclosed that it is possible to improve the finished appearance of the multilayer coating film.

  However, the conventional coating technology has not paid attention to the unevenness of the layer interface of the laminated coating film that greatly affects the appearance quality such as the skin (smoothness) and gloss of the coating film laminated wet-on-wet. It has been difficult to improve the appearance quality such as brightness and gloss to the level required for the appearance quality of automobiles. In particular, a clear coating film using an isocyanate compound as a curing agent as described in Patent Document 1 has a fast curing at the time of baking, and the clear coating film loses fluidity before the base coating is cured. In the wet-on-wet coating using the base paint and clear paint, the unevenness present at the interface between the base paint and the clear paint is transferred to the clear paint surface after the clear paint is cured. The appearance quality is impaired, and it is difficult to improve the skin and gloss to the level required for the appearance quality of automobiles. As described above, automobile steel sheets and the like have been demanded to have a coated body that is superior in appearance quality and durability, and further improvement of the coating method by wet-on-wet has been desired.

JP 2007-283271 A

  The present invention has been made in view of the above-described problems of the prior art, and even when two types of paints are laminated on a wet on wet basis and simultaneously baked to cure each layer, the occurrence of irregularities on the surface of the upper layer is sufficient. It is an object of the present invention to provide a coating method capable of obtaining a suppressed laminated coating film, and a coated body having a high appearance quality obtained thereby.

  As a result of intensive research to achieve the above object, the present inventors have made use of a lower layer for forming a lower layer in the case where two types of thermosetting paints are laminated by wet-on-wet and baked simultaneously. A thermosetting paint is used as a paint, and a thermosetting paint is used as an upper-layer paint for forming an upper layer. Between the time when the upper-layer paint stops flowing and the end of the standard baking time of each paint. By selecting the upper layer paint and the lower layer paint so that the absolute value of the difference between the shrinkage rate of the lower layer paint and the shrinkage rate of the upper layer paint falls within a specific range, the upper layer is cured. After the fluidity is significantly reduced, the amount of transfer to the upper layer of the upper and lower interface irregularities can be made smaller. Excellent multilayer coating film found that is obtained, and have completed the present invention.

That is, the coating method of the present invention is a coating method for forming a laminated coating film comprising a lower layer formed on a substrate and an upper layer formed on the lower layer,
Preparing a thermosetting paint as a lower layer paint for forming the lower layer, and preparing a thermosetting paint as an upper layer paint for forming the upper layer;
A forming step of laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film,
A baking step of subjecting the uncured laminated coating film to a baking treatment to simultaneously cure the lower layer coating material and the upper layer coating material,
Contains
In the preparation step, the shrinkage rate of the upper layer paint from after the upper layer paint flow stop time t _cU to the end of the standard baking time t _bU is ω _U , and the upper layer paint flow stop time t _cU. wherein when the shrinkage of the lower layer paint and omega _L, shrinkage of the layer-coating material and shrinkage omega _L of the lower layer paint between after until the standard baking time t _bL ends of the lower layer paint omega _The upper layer paint and the lower layer paint are selected so that the absolute value of the difference from _U is 6.0% or less.
It is the method characterized by this.

Wherein in the coating method of the present invention, the range shrinkage omega _U of 0-30% of the layer-coating material, shrinkage omega _L of the lower layer paint is preferably in the range of 0-30%. Moreover, it is preferable that the said upper layer coating material is a coating material which does not contain a melamine resin as a hardening | curing agent. Further, the upper layer coating material is preferably a thermosetting coating material that does not generate a volatile product in a curing reaction by heat treatment.

  Moreover, the coated body of the present invention is a coated body having a laminated coating film comprising a lower layer formed on a substrate and an upper layer formed on the lower layer, and was obtained by the coating method of the present invention. It is characterized by being.

  In the present invention, the “flow stoppage time of the upper layer coating material” is the time until the coating film is not deformed when the coating film formed by the upper layer coating material is heated at the standard temperature rising rate, It is measured by the method. That is, an upper layer coating material is applied onto a stainless steel plate (40 mm × 50 mm × 0.5 mm) so that the film thickness after baking becomes 100 μm, and left at room temperature for 10 minutes, and then the sample is set in an electric field pickup viscometer. . The electric field pickup viscometer measures the deformation of the sample surface due to Maxwell stress in a non-contact manner by holding a needle as an electrode near the sample surface and applying a DC voltage by repeating on / off at regular intervals. It is a device that can. Needle-sample surface distance: 100 μm, voltage: 5 V, voltage on time: 1.0 sec, voltage off time: 1.0 sec. Heat to the standard baking temperature of the paint at the standard temperature rise rate of the upper layer paint. During this time, the deformation of the sample surface is measured at a measurement pitch of 0.01 seconds using the intensity of the laser beam irradiated with the laser beam and reflected from the sample surface as a detection voltage. FIG. 1 is an example of an oscilloscope waveform obtained at this time.

As shown in FIG. 1, in the obtained oscilloscope waveform, fluctuations of m detection voltages are observed in m + 1 seconds. It shows that the change in the sample surface due to the electric field is larger as the fluctuation width of the detection voltage is larger. Among these m detection voltage fluctuations, the time when the fluctuation width becomes the maximum (a _max ) is defined as t _max, and the time when the fluctuation width decreases to 5% of the a _max in the time range after t _{max. Let it be} the flow stop time t _cU (t _cU > t _max ) of the upper layer coating _material .

In the present invention, the “coating shrinkage” is caused by volatilization of a volatile product of a curing reaction and a residual solvent such as a high-boiling solvent, and is measured by the following method. In other words, weighed stainless steel foil (150mm x 30mm x 0.5mm) by air spray coating so that the film thickness after heat treatment becomes the target film thickness in the laminated coating film, and the coating film at the standard baking temperature of the paint Start baking. Thereafter, the coating film is baked (baking time: t _cU ) until the flow stop time t _cU of the upper layer coating material, and the sample (stainless steel foil + coating film) is weighed. Furthermore, the coating film is baked at the standard baking temperature of the paint (the latter baking time: t _b -t _cU ), and the sample (stainless steel foil +) so that the total baking time from the start of baking becomes the standard baking time t _b of the paint Weigh the coating film.

The shrinkage ω _U and ω _L of the upper layer coating material and the lower layer coating material are expressed by the following formula (1):
ω _i = 100 (Y _i −Z _i ) / (Z _i −X) (1)
(Where ω _i represents the shrinkage of the paint resulting from volatilization of the volatile product of the curing reaction and the residual solvent such as the high boiling point solvent, X represents the mass (g) of the stainless steel foil, and Y _i represents the standard of the paint. This represents the mass (g) of the sample (stainless steel foil + coating film) after baking at the baking temperature up to the flow stop time t _cU , and Z _i is the sample after baking up to the standard baking time of the paint at the standard baking temperature of the paint. (It represents the mass (g) of (stainless steel foil + coating film), and i is U (upper layer coating material) or L (lower layer coating material).)
Is calculated by The absolute value of the difference between the shrinkage omega _U shrinkage omega _L and layer-coating material of the lower layer paint (| [Delta] [omega |) is represented by the following formula (2):
| Δω | = | ω _L −ω _U | (2)
Is calculated by

  In addition, even if two types of paints are laminated by wet-on-wet and baked at the same time to cure each layer by the coating method of the present invention, the reason why the unevenness of the upper surface is sufficiently suppressed is not necessarily clear. The present inventors infer as follows. That is, in the conventional multilayer coating formed by wet-on-wet, thermosetting paint is used in all layers including the upper layer, and each layer is cured at the same heating temperature at the same time, or curing is started in order from the lower layer. Because it is designed, when the thermosetting paint that forms the upper layer is cured by heat treatment (baking treatment), the thermosetting paint is already cured in the lower layer and the fluidity has already been lost. It has become. In each layer of such a laminated coating film, the thermosetting paint is cured by an addition reaction after a condensation reaction or a deblocking reaction of a curing agent, so that volatile products generated by this condensation reaction or deblocking reaction remain. 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 relaxed by the flow while the upper layer has sufficient fluidity, but when the fluidity of the upper layer is significantly reduced by curing, the surface of the substrate and the interface of each layer It is presumed that the unevenness is transferred to the surface of the upper layer, and the skin and gloss of the laminated coating film deteriorate.

  In addition, when a thermosetting paint containing an isocyanate compound or an isocyanate resin as a curing agent is used as the upper layer paint, the upper layer has fluidity before the lower layer is cured because the upper layer paint has a fast curing speed. I often lose. In this case, the lower layer cures after the upper layer is cured, but the lower layer coating material used in conventional wet-on-wet coating has poor fluidity, and unevenness formed by shrinkage as the lower layer cures. Is not sufficiently relaxed, and it is assumed that the unevenness at the surface of the substrate and the interface of each layer is transferred to the surface of the upper layer, and the skin and gloss of the laminated coating film deteriorate.

  In order to achieve the above object, the present inventors first noticed that the appearance quality such as the skin (smoothness) and gloss of the laminated coating film is better as the surface roughness of the upper layer is smaller. And the unevenness that becomes the skin is caused by the amount of paint applied on the substrate surface during spraying and the shrinkage of the coating film in the drying process (including the baking process) being uneven in the surface direction. It was found that the unevenness (wavelength shorter than that in the case of skin) is caused by the amount of shrinkage of the coating film in the drying process being non-uniform in the surface direction. In addition, among the unevenness formed due to the above two causes, unevenness caused by uneven coating amount on the substrate surface during spraying is suppressed by improving the atomization of the paint. However, since the coating efficiency, which is the effective utilization rate of the paint, is reduced, it is not advantageous in terms of cost to improve the atomization of the paint more than necessary. For this reason, in order to improve the appearance quality such as skin (smoothness) and gloss, it is advantageous to reduce unevenness caused by unevenness of the shrinkage amount of the coating film in the drying process in the surface direction. I found. And when the present inventors laminate the paint for forming the lower layer and the paint for forming the upper layer on the base material by wet-on-wet, and then baked simultaneously to form a laminated coating film, the above unevenness is mainly Interfacial irregularities between the lower layer and the upper layer formed when the lower layer coating and the upper layer coating are laminated by wet-on-wet are transferred to the upper layer surface by contraction of each layer after the fluidity of the upper layer is significantly reduced in the drying process. It was found that the amount of transfer to the upper layer surface of the interface irregularities becomes smaller if the difference in shrinkage between the layers formed between the layers is small.

  Therefore, the present inventors use a thermosetting paint as a lower layer paint for forming a lower layer in the case where two types of thermosetting paints are laminated by wet-on-wet and are baked at the same time. The thermosetting paint is used as the upper layer paint for forming the paint, and as these paints, the shrinkage rate of the lower layer paint from the time after the flow stop time of the upper layer paint to the end of the standard baking time of each paint By selecting a material whose absolute value of the difference between the shrinkage ratio of the upper layer coating material and the upper layer coating material is 6.0% or less, the transfer amount to the upper layer of the interface unevenness between the upper layer and the lower layer can be sufficiently reduced. It is presumed that even if the paints are laminated by wet-on-wet and then baked at the same time, a laminated film that is highly superior in appearance quality can be obtained.

  According to the present invention, it is possible to obtain a laminated coating film in which the occurrence of irregularities on the surface of the upper layer is sufficiently suppressed even when two types of paints are laminated by wet-on-wet and simultaneously baked to cure each layer. . Thereby, the coating body which was highly excellent in appearance quality, such as skin (surface smoothness) and gloss, can be obtained.

It is an oscilloscope waveform showing a deformation _| transformation of the coating-film surface when calculating the flow stop time _tcU of the upper layer coating material.

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

The coating method of the present invention is a coating method for forming a laminated coating film comprising a lower layer formed on a substrate and an upper layer formed on the lower layer,
Preparing a thermosetting paint as a lower layer paint for forming the lower layer, and preparing a thermosetting paint as an upper layer paint for forming the upper layer (raw material paint preparation step);
A forming step (coating step) for laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film;
A baking process (baking process) in which the uncured laminated coating film is baked to simultaneously cure the lower layer paint and the upper layer paint,
Contains
In the preparation step, the shrinkage rate of the upper layer paint from after the upper layer paint flow stop time t _cU to the end of the standard baking time t _bU is ω _U , and the upper layer paint flow stop time t _cU. wherein when the shrinkage of the lower layer paint and omega _L, shrinkage of the layer-coating material and shrinkage omega _L of the lower layer paint between after until the standard baking time t _bL ends of the lower layer paint omega _The upper layer paint and the lower layer paint are selected so that the absolute value of the difference with _U is 5.0% or less.
It is the method characterized by this.

(Raw material preparation process)
In the coating method of the present invention, first, a lower layer paint for forming a lower layer and an upper layer paint for forming an upper layer are prepared.

  A thermosetting paint is used as the upper layer paint according to the present invention. As the thermosetting paint used for such an upper layer coating, any thermosetting resin that can form a coating film and a curing agent may be used, and thermosetting used as an upper layer coating for ordinary baking coating. Mold paints. The form of the upper layer thermosetting coating may be any of solvent type, aqueous type, and powder. The standard baking temperature of the upper layer thermosetting paint is not particularly limited, and is usually 40 to 200 ° C, preferably 80 to 160 ° C. In addition, as such an upper layer coating material, it is preferable to use a coating material whose weight reduction rate at the standard baking temperature is 0 to 20% by mass. By doing in this way, it exists in the tendency which can minimize shrinkage | contraction of the coating film by heat processing. From such a viewpoint, it is most preferable to use a paint having a weight reduction rate of 0 to 10% by mass.

  In the present invention, the standard baking temperature of the paint means that the target paint is applied on the base material, subjected to a heat treatment to cure the coating film, and is cured such as a baking time for fixing on the base material. The temperature that can be baked most efficiently in relation to the conditions, and is generally set (designed) for each paint. In the present invention, a catalog value can be adopted as the standard baking temperature. Further, in the present invention, the standard baking time of the paint refers to a standard baking temperature or the like for coating the target paint on the base material, applying a heat treatment to cure the coating film, and fixing it on the base material. It refers to the time that can be baked most efficiently in relation to the curing conditions, and is generally set (designed) for each paint. In the present invention, a catalog value can be adopted as the standard baking time. Furthermore, in the present invention, the standard temperature increase rate of the paint refers to the standard baking temperature and the coating temperature for the purpose of coating the target paint on the substrate, applying the heat treatment to cure the coating film, and fixing it on the substrate. The rate of temperature rise of the coating film that can be baked most efficiently in relation to curing conditions such as standard baking time, and is generally set (designed) for each paint. In the present invention, a catalog value can be adopted as the standard temperature increase rate.

  Examples of the thermosetting resin capable of forming a coating film contained in such an upper layer coating material include acrylic resins, polyester resins, alkyd resins, epoxy resins, urethane resins containing hydroxyl groups, glycidyl groups, and carboxyl groups. However, it is not limited to these. Preferred curing agents include, but are not limited to, isocyanate compounds, blocked isocyanate compounds, isocyanate resins, amino compounds, melamine resins and the like. Moreover, these thermosetting resins and curing agents may be used alone or in combination of two or more.

  In addition, as a hardening | curing agent contained in such a coating material for upper layers, it is preferable that a melamine resin is not included. By doing in this way, it exists in the tendency which can minimize shrinkage | contraction of the coating film by heat processing.

  Moreover, as such a coating material for upper layers, it is preferable that it is a thermosetting coating material which does not produce | generate a volatile product in the hardening reaction by heat processing. By doing in this way, it exists in the tendency which can minimize shrinkage | contraction of the coating film by heat processing.

  Furthermore, examples of the combination of the thermosetting resin that does not generate a volatile product in the curing reaction by the heat treatment and the curing agent include a combination of a hydroxyl group-containing acrylic resin and an isocyanate compound and / or an isocyanate resin. It is done. In addition, in order to obtain an even higher level of appearance quality, in the present invention, a thermosetting paint cured by heat treatment is laminated on the upper layer of the laminated coating obtained by applying heat treatment to the laminated coating. Also good. The thermosetting paint is more preferably a paint that does not substantially generate a volatile product in a curing reaction by heat treatment.

In the present invention, the thermosetting resin and the curing agent contained in the upper layer coating material are _separated from the flow stopping time t _cU of the upper layer coating material until the end of the standard baking time t _{b of} each coating material. The upper layer coating material is selected and prepared in combination so that the absolute value of the difference between the shrinkage rate of the lower layer coating material and the shrinkage rate of the upper layer coating material falls within a specific range. The combination of the thermosetting resin and the curing agent includes a combination of an acrylic resin containing a hydroxyl group and an isocyanate compound, a combination of an acrylic resin containing a hydroxyl group and an isocyanate resin, an acrylic resin containing a hydroxyl group and a glycidyl group, and a carboxyl. A combination of acrylic resins containing groups is preferred.

  Furthermore, the upper layer coating material is preferably a so-called “clear coating” that forms a clear coating film (clear layer) used in automotive coatings and painting. For example, the thing containing the thermosetting resin and organic solvent which can form a transparent coating film, and the ultraviolet absorber etc. as needed is mentioned. Examples of the thermosetting resin include acrylic resins having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and an epoxy group, polyester resins, alkyd resins, fluororesins, urethane resins, and silicon-containing resins. Crosslinks of melamine resins, urea resins, (block) polyisocyanate compounds, epoxy compounds or resins, carboxyl group-containing compounds or resins, acid anhydrides, alkoxysilane group-containing compounds or resins that can react with these crosslinkable functional groups What consists of an agent is mentioned.

  Moreover, in the upper layer coating material according to the present invention, conventionally known color pigments, glitter pigments, and the like may be included 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.

  As the lower layer coating material according to the present invention, a thermosetting coating material is used. As the thermosetting paint used for such a lower layer coating material, any thermosetting resin that can form a coating film and a curing agent may be used, and thermosetting used as a lower layer coating material for ordinary baking coating. Mold paints. The form of the thermosetting paint for the lower layer may be any of solvent type, aqueous type, and powder. The standard baking temperature of the thermosetting paint for the lower layer is not particularly limited, and is usually 40 to 200 ° C, preferably 80 to 160 ° C.

  Examples of the thermosetting resin capable of forming a coating film contained in the lower layer coating material include, but are not limited to, an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, and a urethane resin. Examples of the curing agent include, but are not limited to, amino compounds, amino resins, isocyanate compounds, blocked isocyanate compounds, isocyanate resins and the like. Moreover, such a thermosetting resin and a hardening | curing agent may each be used individually by 1 type, or may use 2 or more types together.

In the present invention, the thermosetting resin and the curing agent contained in such a lower layer paint are mixed between the flow stop time t _cU of the upper layer paint and the end of the standard baking time t _{b of} each paint. The lower layer coating material is selected and prepared in combination so that the absolute value of the difference between the shrinkage rate of the lower layer coating material and the upper layer coating material is within a specific range. Examples of combinations of the thermosetting resin and the curing agent include a combination of an acrylic resin and a melamine resin, a combination of a polyester resin and a melamine resin, a combination of an acrylic resin and a (block) isocyanate compound, and a polyester resin and a (block) isocyanate compound. It is preferable that it is the combination of these.

  Furthermore, as such a lower layer coating material, a so-called “base coating material” for forming a base coating film (base layer) used in automotive coating materials and painting is preferable. For example, known solvent-based colored base paints and aqueous colored base paints are preferably used. Examples of such an aqueous colored base coating material include a pigment, a resin that can be dissolved or dispersed in water, a crosslinking agent as necessary, and water as a solvent. Examples of the resin that can be dissolved or dispersed in water include a resin containing a hydrophilic group such as a carboxyl group and a crosslinkable functional group such as a hydroxyl group in one molecule, and specifically, an acrylic resin or a polyester resin. And polyurethane resin. Moreover, as a crosslinking agent, hydrophobic or hydrophilic alkyl ether melamine resin, a block isocyanate compound, etc. are mentioned, for example. On the other hand, examples of the solvent-based coloring base paint include those containing a pigment, a resin similar to the above, and a crosslinking agent and a solvent as necessary.

  Moreover, in the lower layer coating material according to the present invention, conventionally known color pigments, glitter pigments, and the like may be included in 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 raw material paint preparation step of the present invention, the contraction rate of the upper layer paint from the time after the flow stop time t _cU of the upper layer paint to the end of the standard baking time t _bU is ω _U , When the contraction rate of the lower layer coating _material from after the paint flow stop time t _cU to the end of the standard baking time t _{bL of the} lower layer coating material is ω _L , the contraction rate ω _L of the lower layer coating material and The upper layer paint and the lower layer so that the absolute value of the difference from the shrinkage ratio ω _U of the upper layer paint is 6.0% or less (preferably 4.0% or less, more preferably 2.0% or less). It is necessary to select a paint for use. By doing so, it is possible to obtain a laminated coating film in which the occurrence of irregularities on the surface of the upper layer is sufficiently suppressed even when two types of paints are laminated on a wet on wet basis and baked to cure each layer. Thereby, the coating body highly excellent by external appearance quality, such as skin (surface smoothness) and glossiness, can be obtained.

In such an upper layer coating material and a lower layer coating material, the upper layer coating material has a shrinkage rate ω _{U in} the range of 0 to 30%, and the lower layer coating material has a shrinkage rate ω _{L in} the range of 0 to 30%. It is preferable. By doing in this way, it tends to be possible to obtain a laminated coating film with less irregularities on the surface of the upper layer, thereby obtaining a coated body with a high appearance quality such as skin (surface smoothness) and gloss. Tend to be able to.

  As such upper layer paint and lower layer paint, the upper layer paint is an acid epoxy curing type, isocyanate curing type, melamine curing type coating, and the lower layer coating is a melamine curing type, isocyanate curing type coating. Is preferred.

  Furthermore, as a combination of the upper layer coating and the lower layer coating, the upper layer coating / lower layer coating may be an acid epoxy curing system / melamine curing system, acid epoxy curing system / isocyanate curing system, isocyanate curing system / melamine curing system, isocyanate. A curing system / isocyanate curing system is more preferable.

(Painting process)
Next, in the coating method of the present invention, the lower layer coating material and the upper layer coating material prepared in the raw material coating material preparation step are laminated on the substrate in a wet on wet manner to form an uncured laminated coating film.

  The substrate according to the present invention is not particularly limited. For example, iron, aluminum, brass, copper, tin, zinc, stainless steel, tinplate, galvanized steel, alloyed zinc (Zn-Al, Zn- Ni, Zn-Fe, etc.) Metal materials such as plated steel, polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, etc. Examples thereof include plastic materials such as resins and various FRPs, inorganic materials such as glass, cement, and concrete, wood, fiber materials (paper, cloth, etc.), and foams. Of these, metal materials and plastic materials are preferable, and metal materials are particularly preferable. In particular, the present invention is suitably applied to automotive steel sheets having high required characteristics for appearance quality. The surface of these base materials may be previously subjected to treatment such as electrodeposition coating or electrodeposition coating and intermediate coating.

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

  In addition, although the film thickness of a lower layer can be suitably set with a desired use, it is preferable that it is 5-50 micrometers by the film thickness after heat processing, for example, and it is more preferable that it is 10-40 micrometers. If the film thickness of the lower layer is less than the lower limit, it tends to be difficult to obtain a uniform lower layer coating film.On the other hand, if it exceeds the upper limit, the lower layer itself tends to absorb much solvent contained in the upper layer coating film. Volatilization of the contained solvent is also suppressed, and the appearance quality of the laminated coating film tends to deteriorate.

  Moreover, although the film thickness of an upper layer can be suitably set with a desired use, For example, it is preferable that it is 15-60 micrometers by the film thickness after heat processing, and it is more preferable that it is 20-50 micrometers. If the film thickness of the upper 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, if the upper limit is exceeded, the fluidity becomes excessively large and the film is applied in the vertical direction. There is a tendency for defects such as sagging to occur.

(Baking process)
Next, in the coating method of the present invention, the uncured laminated coating film obtained in the coating step is subjected to a baking treatment (heat treatment) to simultaneously cure the lower layer coating material and the upper layer coating material. In the coating method of the present invention, it is preferable that the heat treatment includes a heat treatment at least at a temperature equal to or higher than a temperature at which the upper layer is cured, for example, [standard baking temperature of the upper layer paint −20 ° C.]. The heating time is preferably 50% or more and 150% or less of the standard baking time _tbU of the upper layer coating _material .

  Moreover, in the coating method of this invention, in order to stabilize the uncured coating film laminated | stacked by wet-on-wet, it is preferable to make it stand at room temperature (setting) before the said baking process (heat processing). The setting time is usually set to 1 to 20 minutes.

  Furthermore, 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 upper layer of the coated body obtained by the coating method, and heat treatment is performed. It is preferable to form a surface layer. As the paint, those exemplified as the paint for the upper layer 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 above-described coating method of the present invention, and the unevenness of the surface of the laminated coating film is sufficiently less than the conventional laminated coating film produced by wet-on-wet, and the appearance quality is high. Are better. In addition, by laminating the paint that forms the lower layer on the substrate and the paint that forms the upper layer by wet-on-wet, and simultaneously baking to form a laminated coating film, significant energy reduction, cost reduction and process shortening Can be realized. Furthermore, by adopting an aqueous paint using water as the main solvent, emission of volatile organic compounds (VOC) can be reduced. 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. It should be _noted that the upper layer paint flow stop time t _cU , the upper layer paint flow stop time t _{cU and the} end of the standard baking time t _b of each paint, and the difference in contraction rate of each paint. The absolute value of was calculated by the following method.

<Calculation of Flow Stop Time t _cU of Upper Layer Paint>
The upper layer paint was applied to a stainless steel plate (40 mm × 50 mm × 0.5 mm) using a bar coater so that the film thickness after baking was 100 μm, and allowed to stand at room temperature for 10 minutes. It was set in Kyoto Electronics Industry Co., Ltd. model number RM-01T. Needle-sample surface distance: 100 μm, voltage: 5 V, voltage on time: 1.0 sec, voltage off time: 1.0 sec. It heated at the standard temperature increase rate (20 degreeC / min) of the upper layer coating material to the standard baking temperature (140 degreeC) of the paint. During this time, the deformation of the sample surface was measured at a measurement pitch of 0.01 seconds using the intensity of the laser beam irradiated with the laser beam and reflected from the sample surface as a detection voltage. FIG. 1 is an example of an oscilloscope waveform obtained at this time.

As shown in FIG. 1, in the obtained oscilloscope waveform, fluctuations of m detection voltages are observed in m + 1 seconds. Among these m detection voltage fluctuations, the time when the fluctuation width becomes the maximum (a _max ) is defined as t _max, and the time when the fluctuation width decreases to 5% of the a _max in the time range after t _max. The flow stop time t _cU (t _cU > t _max ) of the upper layer coating _material was used.

<Calculation of shrinkage rate and shrinkage rate difference of each paint>
A standard baking temperature is applied to a weighed stainless steel foil (150 mm x 30 mm x 0.5 mm) by spraying the upper layer paint or the lower layer paint so that the film thickness after heat treatment becomes the target film thickness in the laminated coating film. The coating was baked at (140 ° C.). Thereafter, the coating film was baked (baking time: t _cU ) until the flow stop time t _cU of the upper layer coating material, and the sample (stainless steel foil + coating film) was weighed. Further, the coating film is baked at the standard baking temperature (140 ° C.) of the paint so that the total baking time from the start of baking becomes the standard baking time t _b (30 minutes) of the paint (the baking time at the subsequent stage: t _b -t _cU ) and a sample (stainless steel foil + coating film) were weighed.

The shrinkage ω _U and ω _L of the upper layer coating material and the lower layer coating material are expressed by the following formula (1):
ω _i = 100 (Y _i −Z _i ) / (Z _i −X) (1)
(Where ω _i represents the shrinkage of the paint resulting from volatilization of the volatile product of the curing reaction and the residual solvent such as the high boiling point solvent, X represents the mass (g) of the stainless steel foil, and Y _i represents the standard of the paint. It represents the mass (g) of the sample (stainless steel foil + coating film) after baking at the baking temperature up to the flow stop time t _cU , and Z _i is after baking to the standard baking time t _b of the paint at the standard baking temperature of the paint. (I) is U (upper layer paint) or L (lower layer paint).
Calculated by The absolute value of the difference between the shrinkage omega _U shrinkage omega _L and layer-coating material of the lower layer paint (| [Delta] [omega |) is represented by the following formula (2):
| Δω | = | ω _L −ω _U | (2)
Calculated by

(Synthesis Example 1) Preparation of Solvent-type Clear Acrylic Resin R-1 First, Solvesso 100 was added to a normal acrylic resin production reaction vessel equipped with a stirrer, thermometer, dropping funnel, reflux condenser, nitrogen inlet tube, and the like. 235 parts by mass, and the temperature was raised to 130 ° C. with stirring.

  Next, in this reaction vessel, 95 parts by mass of 2-ethylhexyl acrylate, 120 parts by mass of 2-hydroxyethyl methacrylate, 150 parts by mass of styrene, 135 parts by mass of glycidyl methacrylate, a polymerization initiator (manufactured by NOF Corporation, "Percure O") 40 parts by mass of the mixture was added dropwise with stirring over 3 hours. After completion of the dropwise addition, stirring was continued at 130 ° C. for 1 hour for reaction. Thereafter, 10 parts by mass of Percure O was added, and stirring was continued at 130 ° C. for 2 hours, followed by reaction. After cooling to room temperature, an acrylic resin R- having a hydroxyl value of 94, an epoxy value of 107, and a nonvolatile content of 70% by mass. 1 was obtained.

(Synthesis Example 2) Preparation of solvent-type clear acrylic resin R-2 First, Solvesso 100 was added to a normal acrylic resin production reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen inlet tube, and the like. Was heated to 130 ° C. while stirring.

  Next, in this reaction vessel, 125 parts by mass of butyl methacrylate, 225 parts by mass of 2-ethylhexyl methacrylate, 150 parts by mass of maleic anhydride, 50 parts by mass of Solvesso 100, a polymerization initiator (NOF Corporation) Manufactured, “Percure O”) was added dropwise over 3 hours with stirring over a period of 3 hours. After completion of the dropwise addition, stirring was continued at 130 ° C. for 1 hour for reaction. Thereafter, 10 parts by mass of Percure O was added, and stirring was continued for 2 hours at 130 ° C., followed by reaction, followed by cooling to 60 ° C. After cooling, 4.6 parts by mass of triethylamine and 73.5 parts by mass of methanol were added, and stirring was continued at 60 ° C. for 12 hours for reaction. Then, it cooled to room temperature and obtained acrylic resin R-2 with an acid value of 172 and 61 mass% of non volatile matters.

(Synthesis Example 3) Preparation of solvent-type clear acrylic resin R-3 First, Solvesso 100 was added to a normal acrylic resin production reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen inlet tube, and the like. Was charged with 195 parts by mass and 65 parts by mass of butyl acetate, and the temperature was raised to 130 ° C. with stirring.

  Next, in this reaction vessel, 162.5 parts by mass of butyl methacrylate, 149.5 parts by mass of 4-hydroxybutyl acrylate, 78 parts by mass of styrene, 260 parts by mass of isobornyl acrylate, a polymerization initiator (manufactured by NOF Corporation, "Percure O") 52 parts by mass of the mixture was added dropwise with stirring over 3 hours. After completion of the dropwise addition, stirring was continued at 130 ° C. for 1 hour for reaction. Thereafter, 13 parts by mass of Percure O was added, and the mixture was further reacted by stirring at 130 ° C. for 2 hours. Then, 75 parts by mass of butyl acetate was added and cooled to room temperature, with a hydroxyl value of 90 and a nonvolatile content of 65 parts by mass. % Acrylic resin R-3 was obtained.

(Synthesis example 4) Preparation of acrylic emulsion R-4 for aqueous base First, 31.5 parts by mass of 2-ethylhexyl acrylate, 78.8 parts by mass of butyl methacrylate, 37.8 parts by mass of butyl acrylate, 2-methacrylic acid 2- 63.0 parts by mass of hydroxyethyl, 16.4 parts by mass of acrylic acid, 87.6 parts by mass of styrene, 3.2 parts by mass of n-dodecyl mercaptan, 119 parts by mass of ion-exchanged water, and 17.5 parts of latem (PD-104) The parts were mixed and stirred using a mixer to emulsify to prepare a monomer pre-emulsion.

  Next, 280 parts by mass of ion-exchanged water, Latemul PD-104 (manufactured by Kao Chemical 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, a nitrogen introduction tube and the like. 3.5 parts by mass and an APS aqueous solution (polymerization initiator: ammonium persulfate, 0.7 part by mass of APS (manufactured by Aldrich) and 7 parts by mass of water) were charged and heated to 80 ° C. while stirring. Next, 5% by mass of the monomer pre-emulsion was added to the reaction vessel and held at 80 ° C. for 10 minutes. Thereafter, the remaining monomer pre-emulsion was dropped into the reaction vessel with stirring over 3 hours. After completion of the dropwise addition, stirring was further continued at 80 ° C. for 1 hour for reaction. Thereafter, 322 parts by mass of ion-exchanged water was added and cooled to room temperature. After cooling, 40.5 parts by mass of a 50 mass% dimethylethanolamine aqueous solution was added and stirred for 10 minutes to obtain an acrylic emulsion R-4 having a hydroxyl value of 86 and a nonvolatile content of 29 mass%.

(Preparation Example 1) Preparation of solvent-type clear paint C-1 443.3 parts by mass of solvent-type clear acrylic resin R-1 obtained in Synthesis Example 1 in a container and solvent-type clear acrylic obtained in Synthesis Example 2 300.3 parts by mass of resin R-2, 123.8 parts by mass of n-butanol, 24.8 parts by mass of Solvesso 100, 14.9 parts by mass of xylene, 39.6 parts by mass of 2-methoxy-1-propanol, Tinuvin 123 (BASF) 9.9 parts by mass, Tinuvin 384-2 (BASF) 9.9 parts by mass, tributylammonium bromide solution (tributylammonium bromide 0.9 parts by mass and n-butanol 9 parts by mass) 9.9 parts by mass was charged into this, and 2.8 parts by mass of BYK-370 (manufactured by BYK-Chmie) and BYK-306 (manufactured by BYK-Chmie) 5.2 with stirring. Mass parts, 9.5 parts by mass of BYK-392 (manufactured by BYK-Chmie), 5.0 parts by mass of Disparon NSH8430 (manufactured by Enomoto Kasei), 1.2 parts by mass of Disparon OX883 (manufactured by Enomoto Kasei) are added, and further 10 minutes By stirring, an acid epoxy curable solvent-type clear paint C-1 having a nonvolatile content of 52% by mass was obtained. The solvent-clear coating C-1 of the flow stop time _{t cU} is 400 seconds, shrinkage omega _U between until the standard baking time _{t bU} ends after flow stop time _{t cU} was 7.7% .

(Preparation Example 2) Preparation of Solvent Type Clear Paint C-2 In a container, 759.3 parts by mass of solvent type clear acrylic resin R-3 obtained in Synthesis Example 3 and 197.4 parts by mass of butyl acetate, Tinuvin 123 ( 9.9 parts by mass of BASF) and 9.9 parts of Tinuvin 384-2 (BASF) were charged, and 2.8 parts by mass of BYK-370 (BYK-Chmie), BYK-, while stirring. 306 (BYK-Chmie) 5.1 parts by mass, BYK-392 (BYK-Chmie) 9.5 parts by mass, Disparon NSH8430 (Enomoto Kasei) 4.9 parts by mass, Disparon OX883 (Enomoto Kasei) 1.2 Mass part, 175 parts by mass of polyisocyanate (manufactured by Asahi Kasei Chemical Co., Ltd., “Duranate TPA-100”) was added, and the mixture was further stirred for 10 minutes to obtain an isocyanate having a nonvolatile content of 59% by mass. A curable solvent-type clear paint C-2 was obtained. This solvent-type clear paint C-2 had a flow stop time t _cU of 320 seconds, and a shrinkage rate ω _U from the flow stop time t _cU to the end of the standard baking time t _bU was 1.4%. .

(Preparation Example 3) Preparation of water-based base coating material B-1 Into a container, 99.5 parts by mass of the acrylic emulsion R-4 obtained in Synthesis Example 4 was charged, and 54 parts by mass of ion-exchanged water was added to this while stirring. Stir for 5 minutes. Furthermore, 2.0 parts by mass of an alkali thickener (manufactured by BASF, “Viscalex HV30”) and 1.2 parts by mass of dimethylethanolamine were added to obtain an aqueous resin solution.

  In another container, 9.9 parts by mass of butyl glycol and 9.9 parts by mass of aluminum paste (Ekcart, “Hydrolan 2156”) were charged, and further stirred for 1 hour to obtain an aluminum paste solution.

Next, 19.8 parts by mass of this aluminum paste solution was added to 156.7 parts by mass of the aqueous resin solution while stirring, and further stirred for 1 hour to obtain an aqueous base paint B-1. The shrinkage rate ω _L of this water-based base coating material B-1 was 2.8% when the flow stop time t _cU was 320 seconds, and 0.9% when t _cU was 400 seconds.

(Preparation example 4) Preparation of water-based base coating material B-2 A container is charged with 84.5 parts by mass of the acrylic emulsion R-4 obtained in Synthesis Example 4, and this is stirred with methylated melamine resin (Ornex Japan). 5.6 parts by mass, “Cymel 325”) and 54 parts by mass of ion-exchanged water were added and stirred for 5 minutes. Further, 3.0 parts by mass of Viscalex HV30 and 1.2 parts by mass of dimethylethanolamine were added to obtain an aqueous resin solution.

  In another container, 9.9 parts by mass of butyl glycol and 9.9 parts by mass of aluminum paste (Ekcart, “Hydrolan 2156”) were charged, and further stirred for 1 hour to obtain an aluminum paste solution.

Next, 19.8 parts by mass of this aluminum paste solution was added to 148.3 parts by mass of the aqueous resin solution while stirring, and the mixture was further stirred for 1 hour to obtain an aqueous base paint B-2. The shrinkage rate ω _L of this water-based base coating material B-2 was 6.3% when the flow stop time t _cU was 320 seconds, and 3.2% when the t _cU was 400 seconds.

(Preparation Example 5) Preparation of water-based base coating material B-3 The amount of the acrylic emulsion R-4 obtained in Synthesis Example 4 is 69.6 parts by mass, the amount of Cymel 325 is 11.3 parts by mass, and the Viscalex HV30. A water-based base coating material B-3 was obtained in the same manner as in Preparation Example 4 except that the amount of addition was changed to 4.0 parts by mass. The shrinkage rate ω _L of this water-based base coating material B-3 is 8.2% when the flow stop time t _cU is 320 seconds, 7.2% when the t _cU is 370 seconds, and t _{When cU} was 400 seconds, it was 6.4%.

(Preparation example 6) Preparation of water-based base coating material B-4 In a container, 69.6 parts by mass of the acrylic emulsion R-4 obtained in Synthesis Example 4 was charged, and while stirring, 11.3 parts by mass of Cymel 325 was obtained. 54 parts by mass of ion-exchanged water, 7.5 parts by mass of 2-ethylhexanol, and 3.8 parts by mass of butyl glycol were added and stirred for 5 minutes. Further, 3.0 parts by mass of Viscalex HV30 and 1.2 parts by mass of dimethylethanolamine were added to obtain an aqueous resin solution.

  In another container, 9.9 parts by mass of butyl glycol and 9.9 parts by mass of aluminum paste (Ekcart, “Hydrolan 2156”) were charged, and further stirred for 1 hour to obtain an aluminum paste solution.

Next, 19.8 parts by mass of this aluminum paste solution was added to 150.4 parts by mass of the aqueous resin solution while stirring, and the mixture was further stirred for 1 hour to obtain an aqueous base paint B-4. The shrinkage rate ω _L of the water-based base coating material B-4 was 10.3% when the flow stop time t _cU was 320 seconds, and 8.1% when the t _cU was 400 seconds.

(Preparation Example 7) Preparation of aqueous base paint B-5 The addition amount of 2-ethylhexanol is 15.0 parts by mass, the addition amount of butyl glycol is 7.5 parts by mass, and the addition amount of Viscalex HV30 is 2.0. Except having changed into the mass part, it carried out similarly to the preparation example 6, and obtained water-based base coating material B-5. The shrinkage rate ω _L of this water-based base coating material B-5 was 9.9% when the flow stop time t _cU was 320 seconds, and 9.2% when t _cU was 400 seconds.

(Preparation Example 8) Preparation of aqueous base paint B-6 The addition amount of 2-ethylhexanol was 22.5 parts by mass, the addition amount of butyl glycol was 11.3 parts by mass, and the addition amount of Viscalex HV30 was 2.0. Except having changed into the mass part, it carried out similarly to the preparation example 6, and obtained water-based base coating material B-6. The shrinkage rate ω _L of this water-based base coating material B-6 was 10.4% when the flow stop time t _cU was 320 seconds, and 10.3% when t _cU was 400 seconds.

Example 1
On the surface of a steel sheet (manufactured by Nippon Route Service Co., Ltd.) subjected to intermediate coating and electrodeposition coating, the water-based base coating B-2 obtained in Preparation Example 4 (when t _cU = 400 seconds, ω _L = 3. 2%) was coated so that the film thickness after baking was 15 μm. Water and an organic solvent were volatilized by heating at 80 ° C. for 3 minutes. Next, the film thickness after baking the solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _L = 7.7%) on the layer of the aqueous base paint B-2. An uncured laminated coating film was obtained by coating to 35 μm and laminating the aqueous base paint B-2 and the solvent-type clear paint C-1 by wet-on-wet.

  After leaving this uncured laminated coating film at room temperature for 10 minutes (setting), a heat treatment (baking process) is performed at 140 ° C. for 30 minutes to cure the layers, and a multilayer coating film is obtained. It was.

  About the obtained laminated coating film, wave scan values [Wa (wavelength 0.1 to 0.3 mm), Wb (wavelength 0.3 to 1 mm) using wave scan (“Wave-Scan Dual” manufactured by BYK-Gardner). ), Wc (wavelength 1 to 3 mm), Wd (wavelength 3 to 10 mm), We (wavelength 10 to 30 mm)]. The results are shown in Table 1. These wave scan values indicate that the smaller the value, the fewer the irregularities of the wavelength on the surface of the upper layer, and the better the appearance quality. Incidentally, the smaller Wa is, the better the gloss is, and the smaller Wd and We are, the better the skin is.

In addition, the shrinkage ratio ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) from the flow stop time t _cU of the upper paint to the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 4.5%.

(Example 2)
The water-based base paint B-3 obtained in Preparation Example 4 (ω _L = 6.4% when t _cU = 400 seconds) was used as the base paint, and the solvent-type clear paint obtained in Preparation Example 1 was used as the clear paint. A laminated coating film was obtained in the same manner as in Example 1 except that C-1 (t _cU = 400 seconds, ω _L = 7.7%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 1.3%.

(Example 3)
The water-based base paint B-6 obtained in Preparation Example 8 (ω _L = 10.3% in the case of t _cU = 400 seconds) was used as the base paint, and the solvent-type clear paint obtained in Preparation Example 1 was used as the clear paint. A laminated coating film was obtained in the same manner as in Example 1 except that C-1 (t _cU = 400 seconds, ω _L = 7.7%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 2.6%.

Example 4
As the base paint, the water-based base paint B-1 obtained in Preparation Example 3 (in the case of t _cU = 320 seconds, ω _L = 2.8%) is used, and the solvent-type clear paint obtained in Preparation Example 2 is used as the clear paint. A laminated coating film was obtained in the same manner as in Example 1 except that C-2 (t _cU = 320 seconds, ω _L = 1.4%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 1.4%.

(Example 5)
As the base paint, the water-based base paint B-2 obtained in Preparation Example 4 (in the case of t _cU = 320 seconds, ω _L = 6.3%), and as the clear paint, the solvent-type clear paint obtained in Preparation Example 2 A laminated coating film was obtained in the same manner as in Example 1 except that C-2 (t _cU = 320 seconds, ω _L = 1.4%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 4.9%.

(Comparative Example 1)
As the base paint, the water-based base paint B-1 obtained in Preparation Example 3 (in the case of t _cU = 400 seconds, ω _L = 0.9%) is used, and as the clear paint, the solvent-type clear paint obtained in Preparation Example 1 A laminated coating film was obtained in the same manner as in Example 1 except that C-1 (t _cU = 400 seconds, ω _L = 7.7%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 6.8%.

(Comparative Example 2)
As the base paint, the water-based base paint B-3 obtained in Preparation Example 5 (in the case of t _cU = 320 seconds, ω _L = 8.2%) was used, and as the clear paint, the solvent-type clear paint obtained in Preparation Example 2 A laminated coating film was obtained in the same manner as in Example 1 except that C-2 (t _cU = 320 seconds, ω _L = 1.4%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 6.8%.

(Comparative Example 3)
As the base paint, the water-based base paint B-4 obtained in Preparation Example 6 (ω _L = 10.3% in the case of t _cU = 320 seconds) was used, and the solvent-type clear paint obtained in Preparation Example 2 was used as the clear paint. A laminated coating film was obtained in the same manner as in Example 1 except that C-2 (t _cU = 320 seconds, ω _L = 1.4%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 8.9%.

(Comparative Example 4)
As the base paint, the water-based base paint B-5 obtained in Preparation Example 7 (in the case of t _cU = 320 seconds, ω _L = 9.9%) was used, and the solvent-type clear paint obtained in Preparation Example 2 was used as the clear paint. A laminated coating film was obtained in the same manner as in Example 1 except that C-2 (t _cU = 320 seconds, ω _L = 1.4%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1. Note that the shrinkage ω _L of the water-based base paint (lower paint) and the solvent-type clear paint (upper paint) after the flow stop time t _cU of the upper paint and after the end of the standard baking time t _b of each paint. absolute value of the difference between the shrinkage ω _U | Δω | was 8.5%.

As is clear from the results shown in Table 1, as in the present invention, a thermosetting paint is used for each of the lower layer and the upper layer and is laminated by wet-on-wet to obtain an uncured laminated coating film, which is then baked. In the coating method, the shrinkage ratio ω _L of the lower layer paint (water-based base paint) and the upper layer paint (solvent) from after the flow stop time t _cU of the upper layer paint to the end of the standard baking time t _b of each paint Layer clear coating) is formed by selecting a lower layer paint and an upper layer paint so that the absolute value | Δω | of the difference from the shrinkage rate ω _U is 6.0% or less (Examples 1 to 5) Wa to Wd are all smaller than the conventional laminated coating film (Comparative Examples 1 to 4) in which the absolute value | Δω | exceeds 6.0%, and the appearance quality is excellent. It was confirmed that. That is, as the absolute value | Δω | decreases, Wa to We tend to decrease. As in the present invention, the lower layer paint and Wa of the coating film (Examples 1-5) which selected the upper layer coating material and laminated | stacked wet-on-wet was 25 or less, and satisfy | filled the required external appearance quality. On the other hand, Wa of the coating film (Comparative Examples 1 to 4) obtained by laminating the lower layer coating material and the upper layer coating material in which the absolute value | Δω | It was confirmed that the quality was not met.

As described above, in the case of forming a coating film by laminating two types of paints by wet-on-wet, for the lower layer between the time after the flow stop time t _cU of the upper layer paint and the end of the standard baking time t _{b of} each paint. It was confirmed that a laminated coating film having a high appearance quality can be obtained by setting the absolute value of the difference between the shrinkage ratio of the paint and the shrinkage ratio of the upper layer paint to 6.0% or less.

  As described above, according to the present invention, even when two types of paints are laminated by wet-on-wet and simultaneously baked to cure each layer, a laminated coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed is obtained. Can be obtained. Thereby, the coating body which was highly excellent in appearance quality, such as skin (surface smoothness) and gloss, can be obtained.

  Therefore, the present invention is useful as a coating method capable of obtaining a coated body having a high appearance quality even when two types of paints are laminated by wet-on-wet and baked at the same time, and is particularly useful for passenger cars, trucks, It is useful as a method for painting automobile bodies such as buses and motorcycles and parts thereof.

Claims (5)

A coating method for forming a laminated coating film comprising a lower layer formed on a substrate and an upper layer formed on the lower layer,
Preparing a thermosetting paint as a lower layer paint for forming the lower layer, and preparing a thermosetting paint as an upper layer paint for forming the upper layer;
A forming step of laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film,
A baking step of subjecting the uncured laminated coating film to a baking treatment to simultaneously cure the lower layer coating material and the upper layer coating material,
Contains
In the preparation step, the shrinkage rate of the upper layer paint from after the upper layer paint flow stop time t _cU to the end of the standard baking time t _bU is ω _U , and the upper layer paint flow stop time t _cU. wherein when the shrinkage of the lower layer paint and omega _L, shrinkage of the layer-coating material and shrinkage omega _L of the lower layer paint between after until the standard baking time t _bL ends of the lower layer paint omega _The upper layer paint and the lower layer paint are selected so that the absolute value of the difference from _U is 6.0% or less.
A painting method characterized by that. Paint according to claim 1, shrinkage omega _U of the layer-coating material is in the range of 0-30%, the shrinkage rate omega _L of the lower layer paint is in the range of 0-30%, it is characterized by Method.   The coating method according to claim 1, wherein the upper layer coating material is a coating material that does not contain a melamine resin as a curing agent.   The said upper layer coating material is a thermosetting coating material which does not produce | generate a volatile product in the hardening reaction by heat processing, The coating method as described in any one of Claims 1-3 characterized by the above-mentioned.   It is a coating body which has a laminated coating film provided with the lower layer formed on the base material, and the upper layer formed on this lower layer, Comprising: Obtained by the coating method as described in any one of Claims 1-4 Painted body characterized by being made.