JP6420733B2 - Painting method - Google Patents

Description

  The present invention relates to a coating method in which three or more types of paints are laminated on a wet on wet basis and fired at the same time, and a coated body obtained thereby.

  When laminating three or more types of paints by wet-on-wet and then forming a layered coating by baking, all the layers that make up the layered coating are cured by baking after all the coatings 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 compared to the case where the lower layer is baked and then the coating material forming the intermediate layer and the upper 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. 2004-275966 (Patent Document 1) discloses a process in which an intermediate coating, a base coating, and a clear coating are sequentially applied by wet-on-wet, and a low-temperature heating step (temperature of 25 to 80% of the curing temperature). And a high-temperature heating stage (over 80% of the curing temperature and 30-130% of the curing time at a temperature of 120% or less). A method for forming a coating film is disclosed. Furthermore, it is also disclosed that the clearness of the coating film can be reliably ensured.

  However, the conventional coating technology has not paid attention to the unevenness of the layer interface of the multilayer coating film, which greatly affects the appearance quality such as skin (smoothness) and glossiness of the multilayer coating film. It has been difficult to improve the quality to the level required for the appearance quality of automobiles.

JP 2004-275966 A

  The present invention has been made in view of the above-described problems of the prior art. Even if three or more kinds of coatings are laminated on a wet on wet basis and simultaneously baked, each layer is cured to ensure high durability. An object of the present invention is to provide a coating method capable of obtaining a laminated coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed, and a coated body having a high appearance quality obtained thereby.

  As a result of intensive studies to achieve the above object, the present inventors have formed a lower layer for forming a lower layer when three or more types of thermosetting paints are laminated by wet-on-wet and simultaneously baked. Using a thermosetting paint as a paint for a coating, using a thermosetting paint as a paint for an intermediate layer for forming an intermediate layer, and using a thermosetting paint as a paint for an upper layer for forming an upper layer, The intermediate layer adjacent to the upper layer is defined as a first adjacent layer, and the intermediate layer coating material for forming the first adjacent layer is defined as a first adjacent layer coating material, adjacent to the first adjacent layer. When the intermediate layer or the lower layer is a second adjacent layer, and the intermediate layer paint or the lower layer paint for forming the second adjacent layer is a second adjacent layer paint, the upper layer Standard baking of each paint after the paint stoppage time The absolute value of the difference between the shrinkage rate of the upper layer paint and the shrinkage rate of the first adjacent layer paint until the end of the interval, the shrinkage rate of the first adjacent layer paint and the second The upper layer coating material, the first adjacent layer coating material, and the second adjacent layer coating material are selected such that the sum of the absolute value of the difference from the shrinkage rate of the adjacent layer coating material falls within a specific range. After the upper layer is cured and the fluidity is remarkably lowered, the amount of transfer to the upper layer of the interface unevenness between the upper layer and the first adjacent layer and / or the interface unevenness between the first adjacent layer and the second adjacent layer is increased. It was found that even when three or more kinds of paints were laminated by wet-on-wet and then baked at the same time, a highly superior laminated coating film was obtained by appearance quality, and the present invention was completed.

That is, the coating method of the present invention forms a laminated coating film comprising a lower layer formed on a substrate, at least one intermediate layer formed on the lower layer, and an upper layer formed on the intermediate layer. Painting method,
A thermosetting paint is prepared as a lower layer paint for forming the lower layer, a thermosetting paint is prepared as an intermediate layer paint for forming the intermediate layer, and an upper layer for forming the upper layer A preparation process for preparing a thermosetting paint as a paint
A forming step of laminating the lower layer coating material, the intermediate layer coating material and the upper layer coating material on the base material by wet-on-wet to form an uncured laminated coating film,
A baking process in which the uncured laminated coating film is subjected to a baking treatment to simultaneously cure the lower layer coating material, the intermediate layer coating material and the upper layer coating material,
Contains
In the preparation step, the intermediate layer adjacent to the upper layer is a first adjacent layer, the intermediate layer coating material for forming the first adjacent layer is a first adjacent layer coating material, and the first The intermediate layer or the lower layer adjacent to the adjacent layer is the second adjacent layer, and the intermediate layer paint or the lower layer paint for forming the second adjacent layer is the second adjacent layer paint. In the oscilloscope waveform measured using the electric field pickup viscometer with the standard baking temperature of 140 ° C. and the standard heating rate of 20 ° C./min for the upper layer coating material, the amplitude was reduced to 5% of the maximum amplitude. The time is _defined as the flow stop time t _{cU of the} upper layer paint, and the contraction rate of the upper layer paint from after the flow stop time t _cU of the upper layer paint to the end of the standard baking time t _bU is defined as ω _U , Flow stop time of upper layer paint The shrinkage rate of the first for the adjacent layer paint until the standard baking time t _BA1 end of the first for the adjacent layer coating and omega _A1 after _cU, flow down time of the layer-coating material t _cU after When the contraction rate of the second adjacent layer paint between the second adjacent layer paint and the end of the standard baking time t _{bA2 of} the second adjacent layer is ω _A2 , the shrinkage rate ω _U of the upper layer paint and the the difference between the absolute value and the first of the contraction ratio omega _A1 of paint adjacent layer a second for adjacent layer coating shrinkage omega _A2 of the difference between the shrinkage omega _A1 of the first for the adjacent layer coating The upper layer coating material, the first adjacent layer coating material and the second adjacent layer coating material are selected so that the sum of the absolute value and the absolute value is 8.0% or less.
It is the method characterized by this.

In the coating method of the present invention, the shrinkage rate ω _U of the upper layer coating material is in the range of 0 to 40%, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material is in the range of 0 to 40%. The shrinkage rate ω _{A2 of} the second adjacent layer coating material is preferably in the range of 0 to 40%. 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.

  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 rates ω _U , ω _I and ω _L of the upper layer coating material, the intermediate 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 foil + coating film), and i is U (coating for upper layer), I (coating for intermediate layer) or L (coating for lower layer).)
Is calculated by

Further, the absolute value (| Δω ₁ |) of the difference between the shrinkage rate ω _{A1 of} the first adjacent layer paint and the shrinkage rate ω _U of the upper layer paint, and the shrinkage rate of the second adjacent layer paint The absolute value (| Δω ₂ |) of the difference between ω _A2 and the shrinkage ratio ω _{A1 of} the first adjacent layer coating material is expressed by the following equations (2-1) and (2-2):
| Δω ₁ | = | ω _A1 −ω _U | (2-1)
| Δω ₂ | = | ω _A2 −ω _A1 | (2-2)
Is calculated by

  Further, even if three or more kinds of paints are laminated on the wet-on-wet and simultaneously baked to cure each layer by the coating method of the present invention, it is not always clear why the unevenness on the upper layer surface is sufficiently suppressed. However, 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. The present inventors then baked at the same time after laminating the paint for forming the lower layer on the substrate, at least one paint for forming at least one intermediate layer, and the paint for forming the upper layer by wet-on-wet. When the laminated coating film is formed, the above unevenness is mainly the interface between the upper layer and the first adjacent layer formed by laminating the lower layer coating material, the intermediate layer coating material, and the upper layer coating material by wet-on-wet. The unevenness and the unevenness of the interface between the first adjacent layer and the second adjacent layer are formed by being transferred to the surface of the upper layer by contraction of each layer after the fluidity of the upper layer is significantly reduced in the drying step. The absolute value of the shrinkage rate difference between the upper layer and the first adjacent layer from the time when the coating material flow stops until the end of the standard baking time of each paint, and the difference between the first adjacent layer and the second adjacent layer Small sum of absolute shrinkage difference Transfer amount to the upper surface of the interface roughness if Kere found that smaller.

  Therefore, the present inventors use a thermosetting paint as a lower layer paint for forming a lower layer when laminating three or more kinds of thermosetting paints by wet-on-wet and simultaneously baking coating, The thermosetting paint is used as the intermediate layer paint for forming the intermediate layer, the thermosetting paint is used as the upper layer paint for forming the upper layer, and the flow stop time of the upper layer paint as these paints The absolute value of the difference between the shrinkage rate of the upper layer coating material and the shrinkage rate of the first adjacent layer coating material after the standard baking time of each coating material is reached, and the first adjacent layer coating material By selecting the sum of the shrinkage rate and the absolute value of the difference between the shrinkage rates of the second adjacent layer paints to be 8.0 or less, the interface unevenness between the upper layer and the first adjacent layer and Interfacial irregularities between the first adjacent layer and the second adjacent layer The amount of transfer to the upper layer can be made sufficiently small, and it is speculated that even if three or more types of paints are laminated by wet-on-wet and then baked at the same time, a highly superior laminated coating film can be obtained depending on the appearance quality .

  According to the present invention, even when three or more kinds of paints are laminated on and wet and wet and each layer is cured to ensure high durability, the occurrence of unevenness on the upper layer surface is sufficiently suppressed. A coating film can be obtained. 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 coating material for upper layers.

  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, at least one intermediate layer formed on the lower layer, and an upper layer formed on the intermediate layer. Because
A thermosetting paint is prepared as a lower layer paint for forming the lower layer, a thermosetting paint is prepared as an intermediate layer paint for forming the intermediate layer, and an upper layer for forming the upper layer A preparation process (raw material paint preparation process) for preparing a thermosetting paint as a paint for coating,
A forming step (coating step) for laminating the lower layer coating material, the intermediate 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 subjected to a baking treatment to simultaneously cure the lower layer coating material, the intermediate layer coating material and the upper layer coating material;
Contains
In the preparation step, the intermediate layer adjacent to the upper layer is a first adjacent layer, the intermediate layer coating material for forming the first adjacent layer is a first adjacent layer coating material, and the first The intermediate layer or the lower layer adjacent to the adjacent layer is the second adjacent layer, and the intermediate layer paint or the lower layer paint for forming the second adjacent layer is the second adjacent layer paint. The contraction rate of the upper layer paint from 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, and after the flow stop time t _cU of the upper layer paint, The shrinkage rate of the first adjacent layer coating material until the end of the standard baking time _{tbA1 of} one adjacent layer coating material is ω _A1, and after the flow stop time t _cU of the upper layer coating material, the second wherein between until the standard baking time of coating adjacent layers t _BA2 End When the shrinkage rate of the paint for a two adjacent layers and omega _A2, the absolute value of the difference between the shrinkage omega _A1 shrinkage omega _U and the first for the adjacent layer coating of the layer-coating material, the first The upper layer coating material, the sum of the difference between the shrinkage rate ω _A1 of the adjacent layer coating material and the absolute value of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material is 8.0% or less, Selecting the first adjacent layer coating and the second adjacent layer coating;
It is the method characterized by this.

  In the coating method of the present invention, when the intermediate layer is one layer, the intermediate layer is the first adjacent layer, and the lower layer is the second adjacent layer. On the other hand, when the intermediate layer has two or more layers, the intermediate layer adjacent to the upper layer is the first adjacent layer, and the intermediate layer adjacent to the first adjacent layer is the second adjacent layer. Become.

(Raw material preparation process)
In the coating method of the present invention, first, a lower layer paint for forming a lower layer, at least one intermediate layer paint for forming at least one intermediate layer, and an upper layer paint for forming an upper layer Prepare.

  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, during a such a thermosetting resin contained in the layer-coating material curing agent, after flowing down time t _cU of layer-coating material until the standard baking time t _b the end of each paint The absolute value of the difference between the shrinkage rate of the upper layer coating material and the shrinkage rate of the first adjacent layer coating material, the shrinkage rate of the first adjacent layer coating material and the shrinkage rate of the second adjacent layer coating material. The upper layer coating material is selected and prepared in combination so that the sum of the difference and the absolute value 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 intermediate layer coating material according to the present invention, a thermosetting coating material is used. As the thermosetting paint used for such an intermediate layer coating material, any thermosetting resin that can form a coating film and a curing agent may be used, and it is used as an intermediate layer coating material for ordinary baking coating. A thermosetting paint is mentioned. The form of such a thermosetting coating for the intermediate layer may be any of solvent type, aqueous type, and powder. The standard baking temperature of the thermosetting paint for intermediate layers 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 such an intermediate layer coating material include acrylic resins, polyester resins, alkyd resins, epoxy resins, and urethane resins, but are not limited thereto. . 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 an intermediate layer paint are _separated from the flow stop time t _cU of the upper layer paint until the end of the standard baking time t _{b of} each paint. The absolute value of the difference between the shrinkage ratio of the upper layer paint and the shrinkage ratio of the first adjacent layer paint, the shrinkage ratio of the first adjacent layer paint and the shrinkage of the second adjacent layer paint The intermediate layer paint is selected and prepared in combination so that the sum of the difference and the absolute value of the difference falls 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, the intermediate layer coating material is preferably a so-called “base coating material” that forms a base coating film (base layer) used in automotive coating materials and painting. 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 coating material for intermediate | middle layers concerning this invention, the conventionally well-known coloring pigment, the luster pigment, etc. may be contained in the conventionally well-known range as needed. 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 absolute value of the difference between the shrinkage rate of the upper layer coating material and the shrinkage rate of the first adjacent layer coating material, the shrinkage rate of the first adjacent layer coating material and the shrinkage rate of the second adjacent layer coating material. The lower layer coating material is selected and prepared in combination so that the sum of the difference and the absolute value falls 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.

  Further, the lower layer coating material is preferably a so-called “intermediate coating material” which forms an intermediate coating film (intermediate coating layer) used in automotive coating materials and painting. For example, a thermosetting resin composition composed of a base resin and a crosslinking agent is preferably used. Examples of such base resins include acrylic resins, polyester resins, alkyd resins having two or more crosslinkable functional groups such as hydroxyl group, epoxy group, isocyanate group, and carboxyl group in one molecule, and crosslinking. Examples of the agent include amino resins such as melamine resins and urea resins, polyisocyanate compounds that may be blocked, carboxyl group-containing compounds, and the like.

  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 coating material preparation step of the present invention, the intermediate layer adjacent to the upper layer is used as a first adjacent layer, and the intermediate layer coating material for forming the first adjacent layer is used as the first adjacent layer. The intermediate layer or the lower layer adjacent to the first adjacent layer is the second adjacent layer, and the intermediate layer paint or the lower layer paint for forming the second adjacent layer is the first coating. The upper layer paint shrinkage rate is ω _U 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 , and the flow stop of the upper layer paint. the shrinkage rate of the first for the adjacent layer coating between the later time t _cU until the standard baking time t _BA1 end of the first for the adjacent layer coating and omega _A1, flow stop time t of the layer-coating material the later _cU second standard baking time of coating adjacent layers t _BA2 When the shrinkage rate of the second neighboring-layer paint until Ryoji and omega _A2, the difference between the shrinkage omega _A1 shrinkage of the layer-coating material omega _U and the first for the adjacent layer coating of the absolute value, said first sum 8.0% and the absolute value of the difference between the shrinkage omega _A1 of coating adjacent layer and the second for coatings adjacent layer shrinkage omega _A2 or less (preferably It is necessary to select the upper layer coating material, the first adjacent layer coating material, and the second adjacent layer coating material so as to be 6.0% or less, more preferably 4.0% or less. By doing so, it is possible to obtain a laminated coating film in which the occurrence of unevenness on the surface of the upper layer is sufficiently suppressed even if each layer is cured by laminating and baking three or more kinds of paints wet-on-wet. . Thereby, the coating body highly excellent by external appearance quality, such as skin (surface smoothness) and glossiness, can be obtained.

In the upper layer coating material, the first adjacent layer coating material, and the second adjacent layer coating material, the upper layer coating material has a shrinkage ratio ω _{U in} the range of 0 to 40%, and the first adjacent layer material It is preferable that the shrinkage ratio ω _{A1 of the} paint for coating is in the range of 0 to 40%, and the shrinkage ratio ω _{A2 of the} paint for the second adjacent layer is in the range of 0 to 40%. 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, intermediate layer paint and lower layer paint, the upper layer paint is an acid epoxy curing type, isocyanate curing type, melamine curing type paint, and the intermediate layer coating is a melamine curing type, isocyanate curing type. It is preferable that the lower layer coating is a melamine curing type or isocyanate curing type coating.

  Furthermore, as a combination of the upper layer paint, the intermediate layer paint, and the lower layer paint, the upper layer paint / the intermediate layer paint / the lower layer paint is an acid epoxy curing system / melamine curing system / melamine curing system, acid epoxy curing system. / Melamine curing system / isocyanate curing system, acid epoxy curing system / isocyanate curing system / melamine curing system, acid epoxy curing system / isocyanate curing system / isocyanate curing system, isocyanate curing system / melamine curing system / melamine curing system, isocyanate curing system More preferred are: / melamine curing system / isocyanate curing system, isocyanate curing system / isocyanate curing system / melamine curing system, and isocyanate curing system / isocyanate curing system / isocyanate curing system.

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

  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 intermediate 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 intermediate layer. This intermediate layer may be formed of only one layer or two or more layers. Next, an upper layer coating material is applied onto the uncured intermediate layer, and a solvent or the like is evaporated by drying or the like as necessary to form an uncured upper layer. Examples of methods for applying the lower layer coating material, the intermediate 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 intermediate | middle 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 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 upper coating film and the intermediate layer. Volatilization of the solvent contained in the layer itself is also suppressed, and the appearance quality of the laminated coating film tends to deteriorate.

  Furthermore, the film thickness of the upper layer can be appropriately set depending on the desired application. For example, the film thickness after the heat treatment is preferably 15 to 60 μm, and more preferably 20 to 50 μm. 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. Tends to cause defects such as sagging.

(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 apply the lower layer coating material, the intermediate layer coating material, and the upper layer coating material. Harden. 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, the coating material that forms the lower layer, the coating material that forms the intermediate layer, and the coating material that forms the upper layer on the base material are laminated by wet-on-wet and then baked at the same time to form a multilayer coating film, resulting in significant energy savings. 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, shrinkage rate difference and sum of paints>
Air spray so that the film thickness after heat treatment of the upper layer paint, intermediate layer paint, or lower layer paint on the weighed stainless steel foil (150 mm x 30 mm x 0.5 mm) becomes the target film thickness in the laminated coating film. After coating, baking of the coating film was started at a standard baking temperature (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 rates ω _U , ω _I and ω _L of the upper layer coating material, the intermediate 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 coating material), I (intermediate layer coating material), or L (lower layer coating material).
Calculated by

Further, the absolute value (| Δω ₁ |) of the difference between the shrinkage rate ω _{A1 of} the first adjacent layer paint and the shrinkage rate ω _U of the upper layer paint, and the shrinkage rate ω _{A2 of} the second adjacent layer paint The absolute value (| Δω ₂ |) of the difference from the shrinkage ratio ω _{A1 of} the first adjacent layer coating is expressed by the following formulas (2-1) and (2-2):
| Δω ₁ | = | ω _A1 −ω _U | (2-1)
| Δω ₂ | = | ω _A2 −ω _A1 | (2-2)
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 intermediate coating First, 31.5 parts by mass of 2-ethylhexyl acrylate, 78.8 parts by mass of butyl methacrylate, 52.9 parts by mass of styrene, 4-hydroxy acrylate 72.5 parts by weight of butyl, 16.4 parts by weight of acrylic acid, 63.0 parts by weight of methyl methacrylate, 3.2 parts by weight of n-dodecyl mercaptan, 119 parts by weight of ion-exchanged water, and lathemul (PD-104) 17.5 Mass 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%.

(Synthesis example 5) Preparation of acrylic emulsion R-5 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-5 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% 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 (Tsubakimoto Kasei) 4.9 parts by mass, Disparon OX883 (Tsumoto Kasei) 1.2 Mass part, 175 parts by mass of polyisocyanate (Asahi Kasei Chemical Co., Ltd., “Duranate TPA-100”) was added, and the mixture was further stirred for 10 minutes to give an isocyanate hardness of 59% nonvolatile content. Chemical-type 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 solvent-type clear paint C-3 In a container, 759.3 parts by mass of the acrylic resin R-3 for solvent-type clear 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 (Tsubakimoto Kasei) 4.9 parts by mass, Disparon OX883 (Tsumoto Kasei) 1.2 Part by weight, half of isocyanate group of blocked isocyanate (polyisocyanate (manufactured by Asahi Kasei Chemical Co., Ltd., “Duranate TPA-100”) is 3,5-dimethylpyrazo 175 parts by mass) was added, and the mixture was further stirred for 10 minutes to obtain an isocyanate-curable solvent-type clear paint C-3. The solvent-clear coating C-3 of the flow stop time _{t cU} is 370 seconds, shrinkage omega _U between until the standard baking time _{t bU} ends after flow stop time _{t cU} was 5.8% .

(Preparation Example 4) Preparation of Colored Pigment Paste In a container, 450 parts by mass of ion-exchange water, 50 parts by mass of a wetting and dispersing agent (Byk-Chemie, “Disperbyk-180”), rutile titanium oxide (Ishihara Sangyo Co., Ltd., "CR-90") 495 parts by mass, carbon black (manufactured by Mitsubishi Chemical Co., Ltd., "MA-100") 5 parts by mass, and after premixing for 10 minutes, glass beads having the same volume as the charged volume (particle size 1.6 mm), and dispersed for 1 hour with a desktop sand mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less.

(Preparation Example 5) Preparation of aqueous intermediate coating material P-1 A container is charged with 185.7 parts by mass of the acrylic emulsion R-4 for aqueous intermediate coating obtained in Synthesis Example 4, and this is stirred with methylated melamine resin. (Ornex Japan, "Cymel 325") 30.0 parts by mass and 32 parts by mass of ion-exchanged water were added and stirred for 5 minutes. Furthermore, 3.2 parts by mass of an alkali thickener (manufactured by BASF, “Viscalex HV30”), 0.8 parts by mass of dimethylethanolamine, 2.5 parts by mass of BYK-346 (manufactured by BYK-Chmie), and coloring pigment paste 123 .1 part by mass was added to obtain an aqueous intermediate coating P-1 having a nonvolatile content of 39.3% by mass. The shrinkage ratio ω _L of the waterborne intermediate coating P-1 is 5.8% when the flow stop time t _cU is 320 seconds, and 5.4% when the t _cU is 370 seconds, When t _cU was 400 seconds, it was 5.0%.

(Preparation Example 6) Preparation of aqueous intermediate coating material P-2 In a container, 132.6 parts by mass of the aqueous emulsion for aqueous intermediate coating R-4 obtained in Synthesis Example 4 was charged, and ion-exchanged water 16 was added thereto while stirring. 0.0 part by mass was added and stirred for 5 minutes. Furthermore, 1.6 parts by mass of Viscalex HV30, 0.4 parts by mass of dimethylethanolamine, 1.0 part by mass of BYK-346, and 61.5 parts by mass of a color pigment paste were added, and the non-volatile content was 39.3% by mass. Water-based intermediate coating material P-2 was obtained. The shrinkage ratio ω _L of the water-based intermediate coating material P-2 was 3.2% when the flow stop time t _cU was 320 seconds, and 2.4% when the t _cU was 400 seconds. .

(Preparation Example 7) Preparation of aqueous base paint B-1 99.5 parts by mass of the acrylic emulsion R-5 obtained in Synthesis Example 5 was charged into a container, 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 _I of the water-based base coating material B-1 is 2.8% when the flow stop time t _cU is 320 seconds, 2.0% when the t _cU is 370 seconds, and t _{When cU} was 400 seconds, it was 0.9%.

(Preparation example 8) Preparation of water-based base coating material B-2 A container is charged with 84.5 parts by mass of the acrylic emulsion R-5 obtained in Synthesis Example 5, 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 _I 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 t _cU was 400 seconds.

(Preparation example 9) Preparation of water-based base coating material B-3 The amount of the acrylic emulsion R-5 obtained in Synthesis Example 5 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 8 except that the amount of addition was changed to 4.0 parts by mass. The shrinkage rate ω _I of the 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 10) Preparation of aqueous base paint B-4 69.6 parts by mass of acrylic emulsion R-5 obtained in Synthesis Example 5 was charged into a container, and 11.3 parts by mass of Cymel 325 was added to this while stirring. 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 _I of this 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 11) 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 10, and obtained water-based base coating material B-5. The shrinkage rate ω _I 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 12) 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 10, and obtained water-based base coating material B-6. The shrinkage rate ω _I 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.

(Preparation Example 13) Preparation of aqueous base paint B-7 The addition amount of 2-ethylhexanol was 30.0 parts by mass, the addition amount of butyl glycol was 15.0 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 10, and obtained water-based base coating material B-7. The shrinkage rate ω _I of this water-based base coating material B-7 was 12.7% when the flow stop time t _cU was 320 seconds, and 12.0% when the t _cU was 400 seconds.

Example 1
On the surface of the electrodeposited steel sheet (manufactured by Nippon Route Service Co., Ltd.), the waterborne intermediate coating P-1 obtained in Preparation Example 5 (in the case of t _cU = 400 seconds, ω _L = 5.0%) Was coated so that the film thickness after baking was 20 μm, and heated at 80 ° C. for 3 minutes to volatilize water and organic solvent. Next, the aqueous base paint B-3 obtained in Preparation Example 9 (in the case of t _cU = 400 seconds, ω _I = 6.4%) was applied so that the film thickness after baking was 15 μm, and 80 ° C. For 3 minutes to evaporate water and organic solvent. Next, the film thickness after baking the solvent-type clear coating material C-1 (t _cU = 400 seconds, ω _U = 7.7%) obtained in Preparation Example 1 on the layer of the aqueous base coating material B-3. The coating was applied to a thickness of 35 μm to obtain an uncured laminated coating film obtained by laminating water-based intermediate coating material P-1, water-based base coating material B-3, and solvent-type clear coating material 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 <0.3 mm), Wb (wavelength 0.3 to 1 mm), Wc, Wc using a 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)] were measured. 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 the du or Wa, the better the gloss, and the smaller the Wd or We, the better the skin.

Moreover, in the obtained multilayer coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-3, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 3 (first adjacent layer paint) is 1.3%, and the shrinkage of the aqueous base paint B-3 (first adjacent layer paint) rate omega _A1 and aqueous intermediate coating composition P-1 the absolute value of the difference between the shrinkage omega _A2 of (second adjacent layer paint) _| Δω ₂ | was 1.4. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 2.7%.

(Example 2)
As the intermediate coating, the aqueous intermediate coating P-1 obtained in Preparation Example 5 (ω _L = 5.0% in the case of t _cU = 400 seconds) was used, and the aqueous base obtained in Preparation Example 11 was used as the base coating. Using paint B-5 (in the case of t _cU = 400 seconds, ω _I = 9.2%), as a clear paint, solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Further, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-5, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 5 (first adjacent layer paint) is 1.5%, and the shrinkage of the water-based base paint B-5 (first adjacent layer paint) rate omega _A1 and aqueous intermediate coating composition P-1 the absolute value of the difference between the shrinkage omega _A2 of (second adjacent layer paint) _| Δω ₂ | was 4.2. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 5.7%.

(Example 3)
As the intermediate coating, the aqueous intermediate coating P-1 obtained in Preparation Example 5 (ω _L = 5.0% when t _cU = 400 seconds) was used, and the aqueous base obtained in Preparation Example 12 was used as the base coating. Using the paint B-6 (in the case of t _cU = 400 seconds, ω _I = 10.3%), as a clear paint, the solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Further, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-6, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 6 (first adjacent layer paint) is 2.6%, and the shrinkage of the water-based base paint B-6 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-1 (the second adjacent layer paint) _| Δω ₂ | was 5.3%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 7.9%.

Example 4
As the intermediate coating, the aqueous intermediate coating P-2 obtained in Preparation Example 6 (ω _L = 2.4% in the case of t _cU = 400 seconds) was used, and the aqueous base obtained in Preparation Example 9 was used as the base coating. Using the coating material B-3 (in the case of t _cU = 400 seconds, ω _I = 6.4%), as the clear coating material, the solvent-type clear coating material C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained multilayer coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-3, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating P-2. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 3 (first adjacent layer paint) is 1.3%, and the shrinkage of the aqueous base paint B-3 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and an aqueous intermediate coating P-2 (the second adjacent layer paint) _| Δω ₂ | was 4.0%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 5.3%.

(Example 5)
As the intermediate coating material, the aqueous intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 5.8% when t _cU = 320 seconds) was used, and the aqueous base material obtained in Preparation Example 7 was used as the base coating material. Using paint B-1 (in the case of t _cU = 320 seconds, ω _I = 2.8%), as a clear paint, solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-1, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 1 (first adjacent layer paint) is 1.4%, and the shrinkage of the aqueous base paint B-1 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-1 (the second adjacent layer paint) _| Δω ₂ | was 3.0%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) was 4.4%.

(Example 6)
As the intermediate coating material, the aqueous intermediate coating material P-1 obtained in Preparation Example 5 (in the case of t _cU = 320 seconds, ω _L = 5.8%) was used, and the aqueous coating material obtained in Preparation Example 8 was used as the base coating material. The paint B-2 (when t _cU = 320 seconds, ω _I = 6.3%) was used as the clear paint, and the solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-2, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 2 (first adjacent layer paint) is 4.9%, and the shrinkage of the aqueous base paint B-2 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-1 (the second adjacent layer paint) _| Δω ₂ | was 0.5%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) was 5.4%.

(Example 7)
As the intermediate coating material, the aqueous intermediate coating material P-2 obtained in Preparation Example 6 (in the case of t _cU = 320 seconds, ω _L = 3.2%) was used, and the aqueous coating material obtained in Preparation Example 7 was used as the base coating material. Using paint B-1 (in the case of t _cU = 320 seconds, ω _I = 2.8%), as a clear paint, solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-1, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating P-2. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 1 (first adjacent layer paint) is 1.4%, and the shrinkage of the aqueous base paint B-1 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-2 (the second adjacent layer paint) _| Δω ₂ | was 0.4%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 1.8%.

(Example 8)
As the intermediate coating material, the aqueous intermediate coating material P-1 obtained in Preparation Example 5 (in the case of t _cU = 370 seconds, ω _L = 5.4%) was used, and the aqueous coating material obtained in Preparation Example 7 was used as the base coating material. Using the paint B-1 (in the case of t _cU = 370 seconds, ω _I = 2.0%), as a clear paint, the solvent-type clear paint C-3 obtained in Preparation Example 3 (t _cU = 370 seconds, ω _U = 5.8%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-1, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-3 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 1 (first adjacent layer paint) is 3.8%, and the shrinkage of the aqueous base paint B-1 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-1 (the second adjacent layer paint) _| Δω ₂ | was 3.4%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 7.2%.

(Comparative Example 1)
As the intermediate coating material, the water-based intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 5.0% when t _cU = 400 seconds) was used, and the aqueous base material obtained in Preparation Example 13 was used as the base coating material. Using paint B-7 (in the case of t _cU = 400 seconds, ω _I = 12.0%), as a clear paint, solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed of the water-based base coating material B-7, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint (the first paint) 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. absolute value of the difference between the shrinkage omega _A1 of the one adjacent layer paint) _| Δω ₁ | is 4.3%, shrinkage of the water-based base coating material B-7 (first adjacent layer paint) omega _A1 The absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _A2 of the water-based intermediate coating material P-1 (the second adjacent layer coating material) was 7.0%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 11.3%.

(Comparative Example 2)
As the intermediate coating, the aqueous intermediate coating P-2 obtained in Preparation Example 6 (ω _L = 2.4% when t _cU = 400 seconds) was used, and the aqueous base obtained in Preparation Example 13 was used as the base coating. Using paint B-7 (in the case of t _cU = 400 seconds, ω _I = 12.0%), as a clear paint, solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed of the water-based base coating material B-7, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating P-2. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 7 (first adjacent layer paint) is 4.3%, and the shrinkage of the aqueous base paint B-7 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-2 (the second adjacent layer paint) _| Δω ₂ | was 9.6%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 13.9%.

(Comparative Example 3)
As the intermediate coating material, the aqueous intermediate coating material P-1 obtained in Preparation Example 5 (in the case of t _cU = 320 seconds, ω _L = 5.8%) was used, and the aqueous coating material obtained in Preparation Example 9 was used as the base coating material. Using paint B-3 (in the case of t _cU = 320 seconds, ω _I = 8.2%), as a clear paint, the solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained multilayer coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-3, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating material P-1. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 3 (first adjacent layer paint) is 6.8%, and the shrinkage of the water-based base paint B-3 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-1 (the second adjacent layer paint) _| Δω ₂ | was 2.4%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 9.2%.

(Comparative Example 4)
As the intermediate coating, the aqueous intermediate coating P-2 obtained in Preparation Example 6 (ω _L = 3.2% in the case of t _cU = 320 seconds) was used, and the aqueous base obtained in Preparation Example 9 was used as the base coating. Using paint B-3 (in the case of t _cU = 320 seconds, ω _I = 8.2%), as a clear paint, the solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 1 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained multilayer coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-3, and the second adjacent layer adjacent to the first adjacent layer. Is a lower layer formed by the water-based intermediate coating P-2. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 3 (first adjacent layer paint) is 6.8%, and the shrinkage of the water-based base paint B-3 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition P-2 (the second adjacent layer paint) _| Δω ₂ | was 5.0%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 11.8%.

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, the intermediate layer and the upper layer, and is laminated by wet-on-wet to obtain an uncured laminated coating film. Thereafter, in the coating method in which the baking process is performed, the shrinkage rate ω _U of the upper layer paint (solvent type clear 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 _b of each paint The absolute value | Δω ₁ | of the difference between the shrinkage rate ω _{A1 of} the first adjacent layer coating material (water-based base coating material) and the second shrinkage rate ω _{A1 of} the first adjacent layer coating material (water-based base coating material) The upper layer coating material, the first layer coating (first aqueous coating material) so that the sum (Δω ₁ + Δω ₂ ) with the absolute value | Δω ₂ | of the difference from the shrinkage rate ω _A2 of the layer coating material (water-based intermediate coating material) The laminated coating film formed by selecting the adjacent layer coating material and the second adjacent layer coating material (Examples 1 to Any Wa~Wd of), the absolute value of the sum (Δω ₁ + Δω ₂₎ is smaller than that of a conventional multilayer coating film exceeds 8.0% (Comparative Example 1-4), high appearance quality It was confirmed to be excellent. That is, as in the present invention, the upper layer coating material, the first adjacent layer coating material, and the second adjacent layer coating material are adjusted so that the sum of the absolute values (Δω ₁ + Δω ₂ ) is 8.0% or less. Wa of the coating films (Examples 1 to 8) selected and wet-on-wet laminated was 25 or less and satisfied the required appearance quality. On the other hand, an upper layer coating material in which the sum of the absolute values (Δω ₁ + Δω ₂ ) exceeds 8.0%, a first adjacent layer coating material, and a second adjacent layer coating material are laminated by wet on wet. Wa of the film (Comparative Examples 1 to 4) exceeded 25, and it was confirmed that the required appearance quality was not satisfied.

Example 9
On the surface of the electrodeposited steel sheet (manufactured by Nippon Route Service Co., Ltd.), the waterborne intermediate coating P-1 obtained in Preparation Example 5 (in the case of t _cU = 400 seconds, ω _L = 5.0%) Was coated so that the film thickness after baking was 20 μm, and heated at 80 ° C. for 3 minutes to volatilize water and organic solvent. Next, the aqueous base paint B-3 obtained in Preparation Example 9 (in the case of t _cU = 400 seconds, ω _I = 6.4%) was applied so that the film thickness after baking was 15 μm, and 80 ° C. For 3 minutes to evaporate water and organic solvent. Next, the water-based base paint B-4 obtained in Preparation Example 10 (in the case of t _cU = 400 seconds, ω _I = 8.1%) was applied so that the film thickness after baking was 15 μm, and 80 ° C. For 3 minutes to evaporate water and organic solvent. Subsequently, the film thickness after baking the solvent-type clear coating material C-1 (t _cU = 400 seconds, ω _U = 7.7%) obtained in Preparation Example 1 on the layer of the aqueous base coating material B-4. An uncured laminated coating film coated to 35 μm and laminated with water-based intermediate coating material P-1, water-based base coating material B-3, water-based base coating material B-4, and solvent-type clear coating material C-1 in a wet-on-wet manner. Got.

  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 <0.3 mm), Wb (wavelength 0.3 to 1 mm), Wc, Wc using a 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)] were measured. The results are shown in Table 2.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-4, and the second adjacent layer adjacent to the first adjacent layer. Is an intermediate layer formed of the water-based base coating material B-3. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 4 (first adjacent layer paint) is 0.4%, and the shrinkage of the water-based base paint B-4 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition B-3 (the second adjacent layer paint) _| Δω ₂ | was 1.7%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (2.1ω ₁ + Δω ₂ ) and 2.1%.

(Example 10)
As the intermediate coating material, the water-based intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 5.8% when t _cU = 320 seconds) was used, and the base coating material was replaced with the aqueous base coating material B-3. The aqueous base paint B-2 obtained in Preparation Example 8 (ω _I = 6.3% when t _cU = 320 seconds) was used, and the aqueous base paint obtained in Preparation Example 7 was used instead of the aqueous base paint B-4. Using paint B-1 (in the case of t _cU = 320 seconds, ω _I = 2.8%), as a clear paint, solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 9 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-1, and the second adjacent layer adjacent to the first adjacent layer. Is an intermediate layer formed by the water-based base paint B-2. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 1 (first adjacent layer paint) is 1.4%, and the shrinkage of the aqueous base paint B-1 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition B-2 (the second adjacent layer paint) _| Δω ₂ | was 3.5%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 4.9%.

(Comparative Example 5)
As the intermediate coating material, the water-based intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 5.0% when t _cU = 400 seconds) was used, and the base coating material was replaced with the aqueous base coating material B-3. The aqueous base paint B-7 obtained in Preparation Example 13 (in the case of t _cU = 400 seconds, ω _I = 12.0%) was used, and the aqueous base paint obtained in Preparation Example 7 was used instead of the aqueous base paint B-4. Using the paint B-1 (in the case of t _cU = 400 seconds, ω _I = 0.9%), as the clear paint, the solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 400 seconds, ω _U = 7.7%) was used in the same manner as in Example 9 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

In the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-1, and the second adjacent layer adjacent to the first adjacent layer. Is an intermediate layer formed of the water-based base paint B-7. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-1 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage ratio ω _{A1 of} 1 (first adjacent layer paint) is 6.8%, and the shrinkage of the aqueous base paint B-1 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition B-7 (the second adjacent layer paint) | Δω ₂ | was 11.1%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 17.9%.

(Comparative Example 6)
As the intermediate coating material, the water-based intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 5.8% when t _cU = 320 seconds) was used, and the base coating material was replaced with the aqueous base coating material B-3. The aqueous base paint B-7 obtained in Preparation Example 13 (ω _I = 12.7% when t _cU = 320 seconds) was used, and the aqueous base paint obtained in Preparation Example 8 was used instead of the aqueous base paint B-4. Using paint B-2 (in the case of t _cU = 320 seconds, ω _I = 6.3%), as a clear paint, the solvent-type clear paint C-2 obtained in Preparation Example 1 (t _cU = 320 seconds, ω _U = 1.4%) was used in the same manner as in Example 9 to obtain a laminated coating film. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 1.

Moreover, in the obtained laminated coating film, the first adjacent layer adjacent to the upper layer is an intermediate layer formed by the water-based base coating material B-2, and the second adjacent layer adjacent to the first adjacent layer. Is an intermediate layer formed of the water-based base paint B-7. Therefore, the shrinkage rate ω _U of the solvent-type clear paint C-2 (upper layer paint) and the water-based base paint B- from the time 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. The absolute value | Δω ₁ | of the difference from the shrinkage rate ω _{A1 of} 2 (first adjacent layer paint) is 4.9%, and the shrinkage of the aqueous base paint B-2 (first adjacent layer paint) absolute value of the difference between the shrinkage omega _A2 rate omega _A1 and aqueous intermediate coating composition B-7 (the second adjacent layer paint) _| Δω ₂ | was 6.4%. In addition, the absolute value | Δω ₁ | of the difference between the shrinkage rate ω _U of the upper layer coating material and the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the shrinkage rate ω _{A1 of} the first adjacent layer coating material. And the absolute value | Δω ₂ | of the difference between the shrinkage ratio ω _{A2 of} the second adjacent layer coating material (Δω ₁ + Δω ₂ ) and 11.3%.

As is clear from the results shown in Table 2, as in the present invention, a thermosetting paint is used for each of the lower layer, the intermediate layer and the upper layer, and the uncured laminated coating film is laminated by wet-on-wet. In the coating method in which the baking process is performed, the shrinkage rate ω of the upper layer paint (solvent type clear paint) 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 The absolute value | Δω ₁ | of the difference between the shrinkage rate ω _{A1 of U} and the first adjacent layer coating material (first aqueous base coating material), and the first adjacent layer coating material (first aqueous base coating material) absolute value of the difference between the shrinkage omega _A2 and shrinkage omega _A1 second adjacent layer coating material (second aqueous base paint) _| Δω ₂ | sum of (Δω _{1 +} Δω ₂₎ is 8.0% or less Select the upper layer paint, the first adjacent layer paint, and the second adjacent layer paint so that Both were Wa~Wd the multilayer coating film (Example 9-10), the sum of the absolute values (Δω ₁ + Δω ₂₎ conventional laminated coating film is greater than 8.0% (Comparative Example 5-6 ) And the appearance quality was confirmed to be highly superior. That is, as in the present invention, the upper layer coating material, the first adjacent layer coating material, and the second adjacent layer coating material are adjusted so that the sum of the absolute values (Δω ₁ + Δω ₂ ) is 8.0% or less. Wa of the coating films (Examples 9 to 10) selected and wet-on-wet was 30 or less and satisfied the required appearance quality. On the other hand, an upper layer coating material in which the sum of the absolute values (Δω ₁ + Δω ₂ ) exceeds 8.0%, a first adjacent layer coating material, and a second adjacent layer coating material are laminated by wet on wet. Wa of the film (Comparative Examples 5 to 6) exceeded 30 and it was confirmed that the required appearance quality was not satisfied.

As described above, in the case where a coating film is formed by laminating three or more kinds of paints by wet-on-wet, the upper layer from the flow stopping time t _cU of the upper layer paint to the end of the standard baking time t _{b of} each paint. The absolute value of the difference between the shrinkage of the paint for the first layer and the shrinkage of the paint for the first adjacent layer, and the absolute value of the difference between the shrinkage of the paint of the first adjacent layer and the shrinkage of the second layer It was confirmed that by making the sum with the value 8.0% or less, it is possible to obtain a laminated coating film having a high appearance quality.

  As described above, according to the present invention, even when three or more kinds of paints are laminated on a wet-on-wet basis and simultaneously baked to cure each layer, the multilayer coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed. 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 three or more kinds of paints are laminated on a wet on wet basis and simultaneously baked. It is useful as a method for painting automobile bodies such as buses and motorcycles and parts thereof.

Claims (4)

A coating method for forming a laminated coating film comprising a lower layer formed on a substrate, at least one intermediate layer formed on the lower layer, and an upper layer formed on the intermediate layer,
A thermosetting paint is prepared as a lower layer paint for forming the lower layer, a thermosetting paint is prepared as an intermediate layer paint for forming the intermediate layer, and an upper layer for forming the upper layer A preparation process for preparing a thermosetting paint as a paint
A forming step of laminating the lower layer coating material, the intermediate layer coating material and the upper layer coating material on the base material by wet-on-wet to form an uncured laminated coating film,
A baking process in which the uncured laminated coating film is subjected to a baking treatment to simultaneously cure the lower layer coating material, the intermediate layer coating material and the upper layer coating material,
Contains
In the preparation step, the intermediate layer adjacent to the upper layer is a first adjacent layer, the intermediate layer coating material for forming the first adjacent layer is a first adjacent layer coating material, and the first The intermediate layer or the lower layer adjacent to the adjacent layer is the second adjacent layer, and the intermediate layer paint or the lower layer paint for forming the second adjacent layer is the second adjacent layer paint. In the oscilloscope waveform measured using the electric field pickup viscometer with the standard baking temperature of 140 ° C. and the standard heating rate of 20 ° C./min for the upper layer coating material, the amplitude was reduced to 5% of the maximum amplitude. The time is _defined as the flow stop time t _{cU of the} upper layer paint, and the contraction rate of the upper layer paint from after the flow stop time t _cU of the upper layer paint to the end of the standard baking time t _bU is defined as ω _U , Flow stop time of upper layer paint The shrinkage rate of the first for the adjacent layer paint until the standard baking time t _BA1 end of the first for the adjacent layer coating and omega _A1 after _cU, flow down time of the layer-coating material t _cU after When the contraction rate of the second adjacent layer paint between the second adjacent layer paint and the end of the standard baking time t _{bA2 of} the second adjacent layer is ω _A2 , the shrinkage rate ω _U of the upper layer paint and the the difference between the absolute value and the first of the contraction ratio omega _A1 of paint adjacent layer a second for adjacent layer coating shrinkage omega _A2 of the difference between the shrinkage omega _A1 of the first for the adjacent layer coating The upper layer coating material, the first adjacent layer coating material and the second adjacent layer coating material are selected so that the sum of the absolute value and the absolute value is 8.0% or less.
A painting method characterized by that. The shrinkage rate ω _U of the upper layer coating material is in the range of 0 to 40%, the shrinkage rate ω _{A1 of} the first coating material for the adjacent layer is in the range of 0 to 40%, and the second coating material for the adjacent layer The coating method according to claim 1, wherein the shrinkage ratio ω _A2 is in the range of 0 to 40%.   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.