JP2017218527A - Isocyanate curable coating composition and coating method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isocyanate curable coating composition capable of obtaining a laminated coating film in which occurrence of unevenness of a surface of an upper layer is sufficiently suppressed, even when two or more kinds of coating materials are laminated according to wet-on-wet method and are baked at the same time to cure each layer.SOLUTION: An isocyanate curable coating composition contains a thermosetting resin, an isocyanate-based curing agent and a flow stop retarder capable of bonded to an isocyanate group in an attachable/detachable manner.SELECTED DRAWING: None

Description

  The present invention relates to a coating method in which two or more kinds of paints are laminated on a wet on wet basis and fired at the same time, and an isocyanate curable paint composition used therefor.

  When two or more types of paints are laminated by wet-on-wet and then a multilayer coating film is formed by a baking method, all layers constituting the multilayer coating film are cured by baking after all the paints are laminated. Thus, a method of selecting a thermosetting coating material for forming each layer and curing the entire laminated coating film has been used. However, the conventional coating method has a problem that the skin and gloss of the laminated coating film are inferior as compared to the case where the lower layer is baked and then the upper layer forming coating is laminated and baked. For this reason, various methods have been proposed to improve the skin and gloss of the laminated coating film.

  For example, 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, and it is also disclosed that the sharpness of the coating film can be reliably ensured.

  Japanese Patent Application Laid-Open No. 2005-177680 (Patent Document 2) discloses a coating method in which at least three paints of an undercoat, an intermediate coat, and a top coat are applied to an object to be coated. After forming an undercoat film by coating on a coating, the intermediate coat film is formed by applying the intermediate coat paint to the undercoat film, and the top coat paint is applied to the uncured intermediate coat film. A coating method is disclosed in which a top coating film is formed, and the intermediate coating film is cured before the top coating film by a coating film curing means, whereby a coating film with good sharpness is formed. It is also disclosed. Further, in Patent Document 2, when a base resin having a hydroxyl group and a carboxyl group and a coating containing blocked isocyanate as a crosslinking agent is used as an intermediate coating, a short alkyl group is used as an alcohol-based blocking agent for blocking blocked isocyanate. It is described that the dissociation temperature of the blocking agent is lowered by using the alcohol-based blocking agent, and the reaction temperature of the intermediate coating can be lowered.

JP 2004-275966 A JP 2005-177680 A

  However, the conventional coating technology has not paid attention to the interfacial irregularities between the layers of the laminated coating film, which greatly affects the appearance quality such as skin (smoothness) and gloss of the coating film laminated wet-on-wet. It has been difficult to improve the appearance quality such as brightness and gloss to the level required for the desired appearance quality of automobiles and the like. In particular, a coating containing an isocyanate curing agent has a fast curing reaction at the time of baking, and when such a coating is used as an upper layer coating, the upper layer loses fluidity before the lower layer coating is cured. In the coating by wet-on-wet using a coating containing an isocyanate curing agent, after curing the upper layer, the unevenness present at the interface between the lower layer and the upper layer is transferred to the upper layer surface, the appearance quality is impaired, It has been difficult to improve skin and gloss to the level required for desired appearance quality.

  Under such circumstances, the present invention has been made in view of the above-described problems of the prior art, and even if two or more types of paints are laminated on a wet on wet basis and simultaneously baked to cure each layer, the upper layer It is an object of the present invention to provide a coating method capable of obtaining a laminated coating film in which the occurrence of unevenness on the surface is sufficiently suppressed, and an isocyanate curable coating composition used therefor.

  As a result of intensive research to achieve the above object, the inventors of the present invention, when laminating two or more kinds of paints by wet-on-wet and simultaneously baking them, In the case of three or more lowermost layers, two or more lowermost layers and at least one intermediate layer. The same shall apply hereinafter. In order to form an upper layer, a thermosetting paint is used as a lower layer paint, in the case of three or more layers, two or more kinds of paints of the lowermost layer and at least one intermediate layer paint. When an isocyanate curable coating composition is used as the upper layer coating, the isocyanate curable coating composition contains a flow stop retarder that can be detachably attached to an isocyanate group. For upper layer The flow stoppage time of the material becomes long, the upper layer is cured, and the fluidity is remarkably lowered. Yes, it is the lowest layer in the case of two layers, and it is an intermediate layer in the case of three or more layers.) The amount of transfer to the upper layer) can be reduced, Even when two or more kinds of paints are laminated by wet-on-wet and then baked at the same time, it has been found that a highly excellent laminated coating film can be obtained by appearance quality, and the present invention has been completed.

  That is, the isocyanate-curable coating composition of the present invention contains a thermosetting resin, an isocyanate-based curing agent, and a flow stop retarder that can be detachably bonded to an isocyanate group. Is.

  In the isocyanate curable coating composition of the present invention, the flow stop retarder includes phenolic hydroxyl group, lactam ring, ether bond, thiol group, urea bond, carbamate group, imino group, sulfite group, pyrazole ring, imidazole ring, A compound having at least one structure selected from the group consisting of an oxime group, an amino group, and an active methylene group is preferable. A phenol compound, a lactam compound, an ether compound, a mercaptan compound, a urea compound, a carbamate ester compound, and an imine compound More preferred is at least one compound selected from the group consisting of sulfites, sulfites, pyrazole compounds, imidazole compounds, oxime compounds, amine compounds, and active methylene compounds.

In the isocyanate curable coating composition of the present invention, the flow stop time t _c when the flow stop retarder is included is 1.1 relative to the flow stop time t _c0 when the flow stop retarder is not included. The flow stop time t _c when the flow stop retarder is included and the flow stop time t _c0 when the flow stop retarder is not included (t _c −t _c0 ) Is preferably 20 seconds or longer.

The coating method of the present invention is a coating method for forming a laminated coating film comprising at least one lower layer formed on a substrate and an upper layer formed on the lower layer,
Preparing a thermosetting paint as a lower layer paint for forming the lower layer, and preparing the isocyanate curable paint composition of the present invention as an upper layer paint for forming the upper layer;
A forming step of laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film,
A baking step of subjecting the uncured laminated coating film to a baking treatment to simultaneously cure the lower layer coating material and the upper layer coating material,
It is characterized by including.

  In the preparation step, it is preferable to prepare the isocyanate-curable coating composition by mixing the thermosetting resin and the flow stop retarder and then mixing the isocyanate-based curing agent into the obtained mixture. .

  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 a time-voltage waveform obtained at this time.

As shown in FIG. 1, in the obtained time-voltage 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 rate ω _U of the upper layer coating material, the shrinkage rate ω _L of the lowermost layer coating material, and the shrinkage rate ω _I of the intermediate layer coating material (when there are three or more layers) are expressed by the following formula (1):
ω _i = 100 (Y _i −Z _i ) / (Z _i −X) (1)
(Where ω _i represents the shrinkage of the paint resulting from volatilization of the volatile product of the curing reaction and the residual solvent such as the high boiling point solvent, X represents the mass (g) of the stainless steel foil, and Y _i represents the standard of the paint. This represents the mass (g) of the sample (stainless steel foil + coating film) after baking at the baking temperature up to the flow stop time t _cU , and Z _i is the sample after baking up to the standard baking time of the paint at the standard baking temperature of the paint. (It represents the mass (g) of (stainless steel foil + coating film), and i is U (upper layer coating material), L (lowermost layer coating material) or I (intermediate layer coating material).)
Is calculated by

The paint used for the first adjacent layer (hereinafter referred to as “first adjacent layer paint”) is a paint for the lowermost layer when the laminated coating film is two layers, and an intermediate layer when there are three or more layers. The absolute value (| Δω ₁ |) of the difference between the shrinkage rate ω _A1 of the paint for the upper layer and the shrinkage rate ω _U of the upper layer paint, and the k-th adjacent layer to the k−1th adjacent layer The absolute value (| Δω _k |) of the difference between the shrinkage rate ω _{A (k)} of the adjacent layer coating material and the shrinkage rate ω _{A (k-1) of} the k−1th coating material for the adjacent layer is Formulas (2-1) and (2-2):
| Δω ₁ | = | ω _A1 −ω _U | (2-1)
| Δω _k | = | ω _{A (k)} −ω _{A (k−1)} | (2-2)
(In the formula, k is an integer of 1 or more.)
Is calculated by

  In addition, even when two or more kinds of paints are laminated by wet-on-wet and baked at the same time to cure each layer by the coating method of the present invention, it is not always clear why the surface irregularities are 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 forming the upper layer is cured by heat treatment (baking process), the lower layer has already lost its fluidity due to the progress of curing of the thermosetting paint. 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 alleviated by the flow while the upper layer has sufficient fluidity, but when the fluidity of the upper layer is remarkably lowered by curing, the surface of the substrate or between each layer It is presumed that the unevenness of the interface 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 coating containing an isocyanate compound or isocyanate resin as a curing agent is used as an upper layer coating, the reactivity between the crosslinkable functional group in the base resin and the isocyanate group in the curing agent is extremely high. In other words, the upper layer often loses its fluidity before the lower layer is cured because the upper layer paint is fast. 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 surmised that the interfacial irregularities between the substrate surface and each layer are transferred to the upper layer surface, and the skin and gloss of the laminated coating film deteriorate.

  Accordingly, the present inventors first focused on the fact that the appearance quality such as skin (smoothness) and gloss of the laminated coating film is better as the surface roughness of the upper layer is smaller in order to achieve the above object. 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. Furthermore, the present inventors laminated at least one kind of coating material forming at least one lower layer and a coating material forming an upper layer on a substrate by wet-on-wet, and then baked simultaneously to form a laminated coating film. In this case, the above unevenness is mainly an interface unevenness between the layers formed when the lower layer paint and the upper layer paint are laminated by wet-on-wet (particularly, the interface unevenness between the upper layer and the first adjacent layer), After the fluidity of the upper layer is significantly reduced in the drying process, each layer is transferred to the surface of the upper layer by contraction of each layer.Each time between the time when the upper layer paint stops flowing and the end of the standard baking time of each paint It has been found that if the absolute value of the difference in shrinkage between the layers (particularly between the upper layer and the first adjacent layer) is small, the amount of transfer to the upper layer surface of the interface irregularities becomes small.

  And when the present inventors laminate two or more kinds of thermosetting paints by wet-on-wet and perform baking coating at the same time, the thermosetting paint is used as a lower layer paint for forming the lower layer, When an isocyanate curable coating composition is used as an upper layer coating material for forming the upper layer, the isocyanate curable coating composition contains a flow stop retarder capable of being detachably bonded to an isocyanate group. By using this, the flow stop time of the upper layer paint becomes longer, and the absolute value of the shrinkage rate difference between each layer (particularly between the upper layer and the first adjacent layer) after the upper layer flow stops is small. Therefore, the amount of transfer to the upper layer of the interfacial irregularities between each layer (particularly, the interfacial irregularities between the upper layer and the first adjacent layer) after the upper layer is cured and the fluidity is remarkably lowered. Can be reduced, and speculated that a highly superior multilayer coatings are obtained two or more kinds of coating materials by appearance quality be carried out baked simultaneously after laminating a wet-on-wet.

  Furthermore, the flow of the upper layer coating material (isocyanate curable coating composition) can be obtained by using an isocyanate curable coating composition containing a flow stop retarder that can be detachably bonded to the isocyanate group. The reason why the stop time becomes long is not necessarily clear, but the present inventors infer as follows. That is, the conventional isocyanate curable coating composition is formed from the conventional isocyanate curable coating composition because the reactivity between the crosslinkable functional group such as a hydroxyl group in the base resin and the isocyanate group in the curing agent is very high. In the coated film, the crosslinking reaction proceeds by heat treatment or the like, the fluidity is gradually lost, and it stops at a certain time. On the other hand, the isocyanate-curable coating composition used in the present invention is blended with a flow stop retarder that can be detachably attached to the isocyanate group, and this flow stop retarder is contained in the curing agent. It is assumed that the crosslinkable reaction does not proceed and the fluidity of the coating film is maintained because the reaction with the isocyanate group in the curing agent and the crosslinkable functional group such as a hydroxyl group in the base resin is blocked by bonding with the isocyanate group. Is done. And since the bond between the flow stop retarder and the isocyanate group is cut by a heat treatment or the like in the drying process or baking process of the coating film, in the coating film after the bond is cut, a crosslinking reaction It is presumed that the fluidity gradually disappears and stops at a certain time. That is, in the isocyanate curable coating composition used in the present invention, the flow stop delay is caused along with the reaction between the crosslinkable functional group in the base resin and the isocyanate group in the curing agent by heat treatment in the drying process or baking process. Since the attachment / detachment reaction between the agent and the isocyanate group in the curing agent also proceeds at the same time, it is assumed that the crosslinking reaction is delayed and the time until fluidity stops (flow stoppage time) becomes longer.

  According to the present invention, it is possible to obtain a laminated coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed even when two or more kinds of paints are laminated on a wet-on-wet basis and simultaneously baked to cure each layer. Further, it is possible to obtain a coated body having a high appearance quality such as skin (surface smoothness) and gloss.

It is a time-voltage 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.

<Isocyanate curable coating composition>
First, the isocyanate curable coating composition of the present invention will be described. The isocyanate-curable coating composition of the present invention contains a thermosetting resin, an isocyanate-based curing agent, and a flow stop retarder that can be detachably attached to an isocyanate group. The isocyanate curable coating composition containing such a flow stop retarder has a long flow stop time. For example, when used as an upper layer paint, each layer (especially the upper layer) after the upper layer stops flowing is used. The absolute value of the difference in shrinkage ratio between the first layer and the first adjacent layer becomes small, and even if two or more types of paints are laminated on a wet-on-wet and baked simultaneously to cure each layer, irregularities on the surface of the upper layer are generated. A sufficiently suppressed laminated coating film can be obtained, and a coated body with excellent appearance quality such as skin (surface smoothness) and gloss can be obtained.

  The thermosetting resin is not particularly limited as long as it can be cured by the action of an isocyanate curing agent to form a coating film, and examples thereof include a hydroxyl group, a glycidyl group, a carboxyl group, and a silanol group. An acrylic resin, a polyester resin, an alkyd resin, a fluororesin, an epoxy resin, a urethane resin, a silicon-containing resin and the like containing at least one kind of crosslinkable functional group. These thermosetting resins may be used alone or in combination of two or more. Of these thermosetting resins, acrylic resin, polyester resin, and urethane resin containing the crosslinkable functional group are preferable from the viewpoint of sufficiently ensuring the coating film performance. Moreover, as content of such a thermosetting resin, 10-80 mass% is preferable with respect to the whole coating composition from a viewpoint of ensuring sufficient coating-film performance, and 20-70 mass% is more. preferable.

  The isocyanate curing agent is not particularly limited as long as it can react with the crosslinkable functional group of the thermosetting resin, and examples thereof include an isocyanate compound, a blocked isocyanate compound, an isocyanate resin, and a blocked isocyanate resin. . These isocyanate curing agents may be used alone or in combination of two or more. Of these isocyanate curing agents, an isocyanate compound is preferable from the viewpoint of sufficiently ensuring the coating film performance. Moreover, as content of such an isocyanate type hardening | curing agent, 1-40 mass% is preferable with respect to the whole coating composition from a viewpoint of ensuring coating-film performance fully, and 5-30 mass% is more. preferable.

  The flow stop retarder is one that can be detachably attached to an isocyanate group, that is, it binds to the isocyanate group of the isocyanate curing agent during the preparation of the isocyanate curable coating composition, There is no particular limitation as long as the bond is cleaved by heat treatment during drying or baking, for example, phenolic hydroxyl group, lactam ring, ether bond, thiol group, urea bond, carbamate group, imino group, sulfite group. , A compound having a detachable structure to at least one isocyanate group selected from the group consisting of a pyrazole ring, an imidazole ring, an oxime group, an amino group, and an active methylene group. Specific examples of such compounds include phenol compounds, lactam compounds, ether compounds, mercaptan compounds, urea compounds, carbamate compounds, imine compounds, sulfites, pyrazole compounds, imidazole compounds, oxime compounds, amine compounds, and activities. A methylene compound is mentioned. These compounds may be used individually by 1 type, or may use 2 or more types together. Of these compounds, lactam compounds, pyrazole compounds, imidazole compounds, oxime compounds, and active methylene compounds are preferable, and pyrazole compounds and oxime compounds are more preferable from the viewpoint of sufficiently ensuring the coating film performance. Moreover, as content of such a flow stop retarder, 1-20 mass% is preferable with respect to the whole coating composition from a viewpoint of ensuring sufficient coating-film performance, and 2-10 mass% is more. preferable.

  Moreover, in the isocyanate curable coating composition of 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 such an isocyanate curable coating composition of the present invention, the flow stop time t _c when the flow stop retarder is included is 1. with respect to the flow stop time t _c0 when the flow stop retarder is not included. It is preferably 1 or more times, more preferably 1.15 times or more, and particularly preferably 1.18 times or more. When the ratio (t _c / t _c0 ) of the flow stop time t _c when the flow stop delay agent is included to the flow stop time t _c0 when the flow stop delay agent is not included is less than the lower limit, for example, for the upper layer When used as a paint, the absolute value of the difference in shrinkage between each layer (especially between the upper layer and the first adjacent layer) after the flow of the upper layer stops increases, and two or more kinds of paints are wet-on-wet. When the layers are laminated and simultaneously baked to cure each layer, the occurrence of irregularities on the surface of the upper layer cannot be sufficiently suppressed, and the appearance quality of the resulting laminated coating film tends to deteriorate. Incidentally, preferably 2 times or less the upper limit of the ratio of the flow stop time t _c when including the flow stop retarder to flow stoppage time t _c when not including the flow stop retarder _(t c _/ t _c0) 1.5 times or less is more preferable.

In the isocyanate-curable coating composition of the present invention, the difference between the flow stop time t _c0 with and without flow stopping time t _c when including flow stop retarder the flow stop retarder (t _c -T _c0 ) is preferably 20 seconds or longer, more preferably 30 seconds or longer, and particularly preferably 40 seconds or longer. When t _c -t _c0 is less than the lower limit, for example, when used as an upper layer paint, the difference in shrinkage between each layer (particularly between the upper layer and the first adjacent layer) after the upper layer stops flowing. The absolute value of becomes large, and when two or more kinds of paints are laminated on wet and wet and simultaneously baked to cure each layer, it is not possible to sufficiently suppress the occurrence of irregularities on the surface of the upper layer, resulting in lamination The appearance quality of the coating film tends to deteriorate. The upper limit of t _c -t _c0 is preferably 200 seconds or less, and more preferably 150 seconds or less.

Furthermore, in the isocyanate curable coating composition of the present invention, the shrinkage ratio ω after the flow stop time t _c to the end of the standard baking time t _b is preferably 0 to 40%, and 0 to 30 % Is more preferable, 0 to 20% is further preferable, and 0 to 10% is particularly preferable. Thereby, it becomes possible to form a coating film with less unevenness on the surface, and it is possible to obtain a coated body with excellent appearance quality such as skin (surface smoothness) and gloss.

  In the isocyanate curable coating composition of the present invention, the combination of the thermosetting resin and the isocyanate curing agent is not particularly limited, but a volatile product is not generated in the curing reaction by the heat treatment, and the heat treatment is performed. It is possible to minimize shrinkage of the coating film due to, and when used as an upper layer coating, each layer after the flow of the upper layer stops (particularly between the upper layer and the first adjacent layer). From the viewpoint of reducing the absolute value of the difference in shrinkage ratio between (b) and (b), a combination of a hydroxyl group-containing acrylic resin and an isocyanate compound, or a combination of a hydroxyl group-containing acrylic resin and an isocyanate resin is preferable.

  Further, the form of the isocyanate curable coating composition of the present invention may be any of solvent type, aqueous type and powder. Furthermore, there is no restriction | limiting in particular as standard baking temperature of the isocyanate curable coating composition of this invention, Usually, it is 40-200 degreeC, and it is preferable that it is 80-160 degreeC. Further, in the isocyanate curable coating composition of the present invention, the weight reduction rate at the standard baking temperature is 0 to 20% by mass from the viewpoint that the shrinkage of the coating film due to heat treatment can be minimized. It is preferable that it is 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.

  Although there is no restriction | limiting in particular as a manufacturing method of the isocyanate curable coating composition of this invention, After mixing the said thermosetting resin and the said flow stop retarder, the said isocyanate type hardening | curing agent is mixed with the obtained mixture. It is preferable. By mixing the thermosetting resin, the flow stopping retarder, and the isocyanate curing agent in this order, the flow stopping time tends to be longer. On the other hand, when the thermosetting resin, the flow stopping retarder, and the isocyanate curing agent are mixed at once, the flow stopping time tends to be shortened.

<Coating method>
Next, the coating method of the present invention will be described. The coating method of the present invention is a coating method for forming a laminated coating film comprising at least one lower layer formed on a substrate and an upper layer formed on the lower layer,
A preparation step (raw material paint) for preparing a thermosetting paint as a lower layer paint for forming the lower layer and for preparing the isocyanate curable paint composition of the present invention as an upper layer paint for forming the upper layer Preparation process), and
A forming step (coating step) for laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film;
A baking process (baking process) in which the uncured laminated coating film is baked to simultaneously cure the lower layer paint and the upper layer paint,
Is included.

(Raw material preparation process)
In the coating method of the present invention, first, a thermosetting paint as a lower layer paint for forming a lower layer and an isocyanate curable paint composition of the present invention as an upper layer paint for forming an upper layer are prepared. . In addition, when a laminated coating film is two layers, the said lower layer is only one layer of the lowest layer, and prepares one kind of paint for the lowest layer as a paint for lower layers. On the other hand, when there are three or more laminated coating films, the lower layer is composed of two or more layers of the lowermost layer and at least one intermediate layer, and as the lower layer coating material, one type of the lowermost layer coating material and at least one type of coating material are used. Prepare two or more kinds of paints for the intermediate layer.

As the upper layer coating material according to the present invention, the isocyanate curable coating composition of the present invention is used. In the present invention, since the flow stop retarder is contained in this isocyanate curable coating composition, the flow stop time of the upper layer paint becomes longer, and after the flow stop time t _cU of the upper layer paint, between until the standard baking time t _b ends, the absolute value of a difference between the first adjacent layer coating shrinkage and the shrinkage of the layer-coating material is reduced (preferably 6.0% or less, more preferably 5.0% or less), and the shrinkage rate of the paint for the lowermost layer is also small. Even if two or more kinds of paints are laminated by wet-on-wet and simultaneously baked to cure each layer, unevenness on the surface of the upper layer It becomes possible to obtain a multilayer coating film in which the generation is sufficiently suppressed, and a coated body having a high appearance quality such as skin (surface smoothness) and gloss can be obtained.

In the present invention, shrinkage of the layer-coating material and the first adjacent layer coating of shrinkage during the after flow stop time t _cU of layer-coating material until the standard baking time t _b the end of each paint The combination of the thermosetting resin and the isocyanate-based curing agent is appropriately selected so that the absolute value of the difference between the thermosetting resin and the isocyanate-based curing agent is appropriately selected (preferably 6.0% or less, more preferably 5.0% or less). An upper layer coating material (the isocyanate curable coating composition) is prepared. As a combination of such a thermosetting resin and an isocyanate curing agent, a combination of an acrylic resin containing a hydroxyl group and an isocyanate compound, or a combination of an acrylic resin containing a hydroxyl group and an isocyanate resin is preferable.

  Furthermore, the upper layer coating material (isocyanate curable coating composition) is preferably a so-called “clear coating” that forms a clear coating film (clear layer) used in automotive coatings and painting. For example, the thermosetting resin which can form a transparent coating film, an isocyanate type hardening | curing agent, the said flow stop retarder, the organic solvent, and the ultraviolet absorber etc. as needed are mentioned. Examples of the thermosetting resin include acrylic resins, polyester resins, alkyd resins, fluororesins, urethane resins, and silicon-containing resins having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and a glycidyl group. Examples of the isocyanate curing agent include polyisocyanate and block polyisocyanate.

  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 shrinkage ratio of the first adjacent layer paint and the shrinkage of the upper layer paint from the time after the flow stop time t _cU of the upper layer paint to the end of the standard baking time t _b of each paint. The absolute value of the difference from the rate, and the difference in shrinkage between the adjacent lower layer paints (the difference in shrinkage between the intermediate layer paints and the difference in shrinkage between the lowermost layer paint and the intermediate layer paint. The same applies hereinafter.) (Preferably 6.0% or less, more preferably 5.0% or less), and a combination of a thermosetting resin and a curing agent is appropriately selected to form the lower layer coating material. To prepare. Further, in the present invention, during the period from after the flow stop time t _cU of layer-coating material until the standard baking time t _b the end of the lowermost layer-coating material, as shrinkage of the lowermost layer-coating material is reduced, the bottom layer It is preferable to prepare a coating material for use. Such combinations of thermosetting resin and curing agent include acrylic resin and melamine resin combination, polyester resin and melamine resin combination, acrylic resin and (block) isocyanate compound, polyester resin and (block) isocyanate. A combination of compounds is preferred.

  Furthermore, as such a lower layer coating material, a so-called “base coating material” for forming a base coating film (base layer) used in automobile coating materials and painting, and a so-called “base coating film” (intermediate coating layer) are formed. An “intermediate paint” is preferred. For example, as the base paint, known solvent-based colored base paints and aqueous colored base paints are preferably used. As the intermediate coating, a thermosetting resin composition comprising a base resin and a crosslinking agent is preferably used.

  Examples of the water-based coloring base paint 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.

  Examples of the base resin used in the intermediate coating material include acrylic resins, polyester resins, and alkyd resins having two or more crosslinkable functional groups such as hydroxyl group, glycidyl group, isocyanate group, and carboxyl group in one molecule. In addition, examples of the crosslinking agent include amino resins such as melamine resins and urea resins, polyisocyanate compounds which may be blocked, carboxyl group-containing compounds, and the like.

  Furthermore, 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.

Note that in the raw material paint preparation step of the present invention, adjacent to the first adjacent layer coating (upper layer during the period from after the flow stop time t _cU of the layer-coating material until the standard baking time t _b the end of each paint The difference between the shrinkage rate of the lowermost layer paint (when the laminated coating is two layers) or the intermediate layer coating material adjacent to the upper layer (when the laminated coating is three or more layers) and the shrinkage rate of the upper layer coating The upper layer coating material and the first adjacent layer coating material are preferably selected so that the absolute value is 6.0% or less (more preferably 5.0% or less). As a result, it is possible to obtain a multilayer coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed even if two or more types of paints are laminated on a wet-on-wet and baked to cure each layer. A highly superior coated body can be obtained due to the appearance quality such as property) and gloss.

In the case where there are three or more layers, the lower layer paints adjacent to each other between the flow stop time t _cU of the upper layer paint and the end of the standard baking time t _b of each lower layer paint are used. It is preferable to select the coating material for the lower layer so that the absolute value of the difference in shrinkage rate is 6.0% or less (more preferably 5.0% or less). As a result, it is possible to obtain a laminated coating film in which the occurrence of irregularities on the upper layer surface is sufficiently suppressed even when three or more types of coatings are laminated and baked by wet-on-wet to cure each layer. A highly superior coated body can be obtained due to the appearance quality such as property) and gloss.

Further, in such a lower layer coating material, it is preferable that the shrinkage rate ω after the flow stop time t _cU of the upper layer coating _{material reaches the} end of the standard baking time t _b is 0 to 40%. More preferably, it is -30%, It is further more preferable that it is 0-20%, It is especially preferable that it is 0-10%. Thereby, it becomes possible to obtain a laminated coating film with less irregularities on the surface of the upper layer, and it is possible to obtain a coated body with excellent appearance quality such as skin (surface smoothness) and gloss. As such a lower layer coating material, a melamine curable coating material and an isocyanate curable coating material are preferable.

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

  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 lowermost layer coating is applied on a substrate, and if necessary, a solvent or the like is evaporated by drying or the like to form an uncured lowermost layer. Next, on the uncured lowermost layer, when the laminated coating film has two layers, the upper layer coating material (isocyanate curable coating composition of the present invention) is applied. When the laminated coating film has three or more layers, Applies an intermediate layer coating and, if necessary, evaporates the solvent by drying or the like to form an uncured upper layer or intermediate layer. This intermediate layer may be formed of only one layer or two or more layers. Next, when there are three or more laminated coating films, an upper layer coating material (isocyanate curable coating composition of the present invention) is applied onto the uncured intermediate layer, and a solvent or the like by drying or the like as necessary. Is evaporated to form an uncured upper layer. Examples of methods for applying each paint 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 lowermost 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. When the film thickness of the lowermost layer is less than the lower limit, it tends to be difficult to obtain a uniform film of the lowermost layer. On the other hand, when the upper limit is exceeded, the solvent tends to absorb a lot of solvents and the like contained in the laminated film. In addition, volatilization of the solvent contained in the lowermost layer itself 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. When the film thickness of the intermediate layer is less than the lower limit, it tends to be difficult to obtain a uniform intermediate film. On the other hand, when the upper limit is exceeded, the solvent tends to absorb a large amount of the solvent contained in the laminated film. In addition, volatilization of the solvent contained in the intermediate 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. When 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, when the upper limit is exceeded, the fluidity becomes excessively large, and the vertical direction When coating on the surface, defects such as sagging tend to occur.

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

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

  Furthermore, in the present invention, in order to obtain a coated body having a higher-grade appearance, one or more kinds of paints are further applied on the upper layer of the coated body obtained by the coating method, and heat treatment is performed. It is preferable to form a surface layer. Such surface layer coating materials include thermosetting resins such as acrylic resins, polyester resins, alkyd resins, fluororesins, urethane resins, and silicon-containing resins having crosslinkable functional groups such as hydroxyl groups, glycidyl groups, and carboxyl groups. And a thermosetting paint containing a curing agent such as an isocyanate compound, a blocked isocyanate compound, an isocyanate resin, a blocked isocyanate resin, an amino compound, or a melamine resin. Such a surface layer coating material is preferably a coating material that does not substantially generate a volatile product in a curing reaction by heat treatment. Examples of the method for applying the surface layer coating material include conventionally known methods such as air spray coating, air electrostatic spray coating, and rotary atomizing electrostatic coating.

  Thus, the coating body manufactured by the coating method of the present invention has sufficiently less irregularities on the surface of the multilayer coating film than the conventional multilayer coating film manufactured by wet-on-wet, and the appearance quality is highly superior. In addition, by laminating the paint for forming the lower layer and the paint for forming the upper layer on the base material by wet-on-wet, and simultaneously baking to form a laminated coating film, significant energy reduction, cost reduction and process shortening are achieved. 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 a time-voltage waveform obtained at this time.

As shown in FIG. 1, in the obtained time-voltage 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>
To the weighed stainless steel foil (150 mm × 30 mm × 0.5 mm), the upper layer coating material and the lower layer coating material (when the laminated coating film is two layers, the lower layer coating material, when there are three or more layers, the lower layer coating material Air spray coating is applied so that the film thickness after heat treatment is equal to the target film thickness of the multilayer coating film, and the coating film is baked at the standard baking temperature (140 ° C). Started. 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 lowermost 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 (lowermost layer coating material).
Calculated by

In addition, the absolute value (| Δω ₁ |) of the difference between the shrinkage rate ω _{A1 of} the first adjacent layer paint adjacent to the upper layer and the shrinkage rate ω _U of the upper layer paint, and the second adjacent to the first adjacent layer. The absolute value (| Δω ₂ |) of the difference between the shrinkage rate ω _A2 of the adjacent layer coating material and the shrinkage rate 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 _A2 | (2-2)
(In the case of three layers, | Δω ₁ | and | Δω ₂ | are calculated. In the case of two layers, only | Δω ₁ | is calculated.)

(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. Was heated to 130 ° C. while 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-1 was obtained.

(Synthesis example 2) Preparation of acrylic emulsion R-2 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, the mixture was further reacted by stirring at 80 ° C. for 1 hour. 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-2 having a hydroxyl value of 86 and a nonvolatile content of 29 mass%.

(Synthesis example 3) Preparation of acrylic emulsion R-3 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, the mixture was further reacted by stirring at 80 ° C. for 1 hour. 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-3 having a hydroxyl value of 86 and a nonvolatile content of 29 mass%.

(Preparation example 1) Preparation of solvent-type clear paint C-1 In a container, 759.3 parts by mass of solvent-type clear acrylic resin R-1 obtained in Synthesis Example 1 as a thermosetting resin, 3 as a flow stop retarder , 5-dimethylpyrazole, 46 parts by mass, 197.4 parts by mass of butyl acetate, 9.9 parts by mass of Tinuvin 123 (manufactured by BASF), and 9.9 parts by mass of Tinuvin 384-2 (manufactured by BASF) were stirred. Then, BYK-370 (manufactured by BYK-Chmie), 2.8 parts by mass, BYK-306 (manufactured by BYK-Chmie), 5.1 parts by mass, and BYK-392 (manufactured by BYK-Chmie) while stirring the resulting mixture. 9 .5 parts by mass, Disparon NSH8430 (Tsubakimoto Kasei) 4.9 parts by mass, Disparon OX883 (Tsubakimoto Kasei) 1.2 parts by weight, Polyisocyanate (isocyanate-based curing agent) 175 parts by mass of “Duranate TPA-100” manufactured by Asahi Kasei Chemical Co., Ltd. was added and stirred to obtain an isocyanate-curing solvent-type clear paint C-1. The solvent-clear coating C-1 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 4.0% .

(Preparation Example 2) Preparation of solvent-type clear paint C-2 An isocyanate-curable solvent-type clear paint C-2 was prepared in the same manner as Preparation Example 1 except that 41 parts by mass of 2-butanone oxime was used as a flow stop retarder. Got. The solvent-clear coating C-2 of the flow stop time _{t cU} is 420 seconds, shrinkage omega _U between until the standard baking time _{t bU} ends after flow stop time _{t cU} was 3.5% .

(Preparation example 3) Preparation of solvent-type clear paint C-3 An isocyanate-curing solvent-type clear paint C-3 was obtained in the same manner as in Preparation Example 1 except that the flow stop retarder was not used. The solvent-clear coating C-3 of the flow stop time _{t cU} is 310 seconds, shrinkage omega _U between until the standard baking time _{t bU} ends after flow stop time _{t cU} was 0.9% .

(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-2 for aqueous intermediate coating obtained in Synthesis Example 2, and this is a methylated melamine resin while stirring. (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, alkali thickener (BASF Corporation, “Viscalex HV30”) 3.2 parts by mass, dimethylethanolamine 0.8 parts by mass, BYK-346 (byKy-Chmie) 2.5 parts by mass, Preparation Example 4 123.1 parts by mass of the obtained colored pigment paste was added to obtain an aqueous intermediate coating material P-1 having a nonvolatile content of 39.3% by mass. The shrinkage ratio ω _L of the waterborne intermediate coating P-1 is 6.0% when the flow stop time t _cU is 310 seconds, and 5.4% when the t _cU is 370 seconds, When t _cU was 420 seconds, it was 4.8%.

(Preparation Example 6) Preparation of water-based base coating material B-1 A container was charged with 69.6 parts by mass of the acrylic emulsion R-3 obtained in Synthesis Example 3, and this was stirred with methylated melamine resin (Ornex Japan Co., Ltd.). Manufactured, “Cymel 325”) 11.3 parts by mass and ion-exchanged water 54 parts by mass were added and stirred for 5 minutes. Furthermore, Viscalex HV30 4.0 mass part and dimethylethanolamine 1.2 mass part were added, and the aqueous resin liquid was obtained.

  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-1. The shrinkage rate ω _I of the water-based base coating material B-1 is 9.1% when the flow stop time t _cU is 310 seconds, 8.2% when the t _cU is 370 seconds, and t _{When cU} was 420 seconds, it was 7.2%.

Example 1
On the surface of the electrodeposited steel sheet (manufactured by Nippon Route Service Co., Ltd.), the water-based intermediate coating P-1 obtained in Preparation Example 5 (in the case of t _cU = 370 seconds, ω _L = 5.4%) 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-1 obtained in Preparation Example 6 (in the case of t _cU = 370 seconds, ω _I = 8.2%) was applied so that the film thickness after baking was 15 μm, and the temperature was 80 ° C. For 3 minutes to evaporate water and organic solvent. Next, the film thickness after baking the solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 370 seconds, ω _U = 4.0%) on the layer of the aqueous base paint B-1 is as _follows. The coating was applied to a thickness of 35 μm to obtain an uncured laminated coating film in which a water-based intermediate coating material P-1, a water-based base coating material B-1, and a solvent-type clear coating material C-1 were laminated by wet on wet.

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

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

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-1, and the second adjacent layer adjacent to the first adjacent layer is the aqueous layer. It is the lowest layer formed by the 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} 1 (first adjacent layer paint) is 4.2%, and the shrinkage rate ω of the water-based base paint B-1 (first adjacent layer paint) The absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of A1} and the water-based intermediate coating material P-1 (second adjacent layer coating material) was 2.8%. 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, the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the The sum (Δω ₁ + Δω ₂ ) with the absolute value | Δω ₂ | of the difference from the shrinkage rate ω _{A2 of} the second adjacent layer coating material was 7.0%.

(Example 2)
As the intermediate coating material, the aqueous intermediate coating material P-1 obtained in Preparation Example 5 (in the case of t _cU = 420 seconds, ω _L = 4.8%) was used, and the aqueous coating material obtained in Preparation Example 6 was used as the base coating material. Using the paint B-1 (in the case of t _cU = 420 seconds, ω _I = 7.2%), as a clear paint, the solvent-type clear paint C-2 obtained in Preparation Example 2 (t _cU = 420 seconds, ω _U = 3.5%) 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-1, and the second adjacent layer adjacent to the first adjacent layer is the aqueous layer. It is the lowest layer formed by the 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 3.7%, and the shrinkage rate ω of the aqueous base paint B-1 (first adjacent layer paint) The absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of A1} and the water-based intermediate coating material P-1 (second adjacent layer coating material) was 2.4%. 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, the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the The sum (Δω ₁ + Δω ₂ ) with the absolute value | Δω ₂ | of the difference from the shrinkage rate ω _{A2 of} the second adjacent layer coating material was 6.1%.

(Comparative Example 1)
As the intermediate coating material, the water-based intermediate coating material P-1 obtained in Preparation Example 5 (ω _L = 6.0% when t _cU = 310 seconds) was used, and the aqueous base material obtained in Preparation Example 6 was used as the base coating material. Using the paint B-1 (in the case of t _cU = 310 seconds, ω _I = 9.1%), as the clear paint, the solvent-type clear paint C-3 obtained in Preparation Example 3 (t _cU = 310 seconds, ω _U = 0.9%) 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-1, and the second adjacent layer adjacent to the first adjacent layer is the aqueous layer. It is the lowest layer formed by the 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 rate ω _{A1 of} 1 (first adjacent layer paint) is 8.2%, and the shrinkage rate ω of the aqueous base paint B-1 (first adjacent layer paint) The absolute value | Δω ₂ | of the difference between the shrinkage rate ω _{A2 of A1} and the water-based intermediate coating material P-1 (second adjacent layer coating material) was 3.1%. 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, the shrinkage rate ω _{A1 of} the first adjacent layer coating material, and the The sum (Δω ₁ + Δω ₂ ) with the absolute value | Δω ₂ | of the difference from the shrinkage rate ω _{A2 of} the second adjacent layer coating material was 11.3%.

As is clear from the results shown in Table 1, as in the present invention, a thermosetting paint is used for each of the two lower layers (intermediate layer and lowermost layer), an isocyanate curable paint is used for the upper layer, and wet. After obtaining an uncured laminated coating by laminating by on-wet, mixing a thermosetting resin and a flow stop retarder that can be detachably bonded to an isocyanate group in a coating method in which baking treatment is performed Then, by using an isocyanate curable paint prepared by mixing an isocyanate curing agent as the upper layer paint, the flow stop time t _cU of the upper layer paint becomes longer, and the upper layer after the upper layer flow stops and The absolute value of the shrinkage difference between the adjacent middle layer, the absolute value of the shrinkage difference between the middle layer and the lowermost layer after the upper layer stops flowing, and the upper layer The shrinkage rate of the lowermost layer adjacent to the base material after the flow of the liquid is stopped can be reduced, and as a result, an isocyanate curable paint that does not contain the flow stop retarder is used as the upper layer paint. It was found that a laminated coating film (Examples 1 and 2) having a smaller Wa to We was obtained as compared to the conventional laminated coating film (Comparative Example 1) formed in this manner.

(Example 3)
On the surface of the electrodeposited steel sheet (manufactured by Nippon Route Service Co., Ltd.), the aqueous base paint B-1 obtained in Preparation Example 6 (in the case of t _cU = 370 seconds, ω _I = 8.2%) The film was baked to a film thickness of 15 μm and heated at 80 ° C. for 3 minutes to volatilize water and organic solvent. Next, the film thickness after baking the solvent-type clear paint C-1 obtained in Preparation Example 1 (t _cU = 370 seconds, ω _U = 4.0%) on the layer of the aqueous base paint B-1 is as _follows. An uncured laminated coating film was obtained by coating to 35 μm and laminating the aqueous base paint B-1 and the solvent-type clear paint C-1 by wet-on-wet.

  This uncured laminated coating film was subjected to setting and heat treatment (baking treatment) 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 2.

Moreover, in the obtained laminated coating film, the 1st adjacent layer adjacent to an upper layer is the lowest layer formed with the said water-based base coating material B-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} 1 (the first adjacent layer coating material) was 4.2%.

(Comparative Example 2)
As the base paint, the water-based base paint B-1 obtained in Preparation Example 6 (ω _I = 9.1% in the case of t _cU = 310 seconds) was used, and the solvent-type clear paint obtained in Preparation Example 3 was used as the clear paint. A laminated coating film was obtained in the same manner as in Example 3 except that C-3 (t _cU = 310 seconds, ω _U = 0.9%) was used. About the obtained laminated coating film, Wa-We were measured like Example 1. FIG. The results are shown in Table 2.

Moreover, in the obtained laminated coating film, the 1st adjacent layer adjacent to an upper layer is the lowest layer formed with the said water-based base coating material B-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 rate ω _{A1 of} 1 (the first adjacent layer coating material) was 8.2%.

As is clear from the results shown in Table 2, as in the present invention, a thermosetting paint is used for the lowermost layer, an isocyanate curable paint is used for the upper layer, and lamination is performed by wet-on-wet to form an uncured laminated coating. After obtaining the film, in the coating method in which baking treatment is performed, after mixing the thermosetting resin and the flow stop retarder that can be detachably bonded to the isocyanate group, the isocyanate curing agent is mixed. By using the isocyanate curable paint prepared in this way as the upper layer paint, the flow stop time t _cU of the upper layer paint becomes longer, and the shrinkage between the upper layer and the adjacent lowermost layer after the upper layer flow stops Both the absolute value of the rate difference and the shrinkage rate of the lowermost layer adjacent to the base material after the flow of the upper layer is stopped can be reduced. As a result, the flow stop retarder Compared to a conventional multilayer coating film (Comparative Example 2) formed by using an isocyanate-curable coating material that does not contain bismuth as a coating material for the upper layer, a multilayer coating film (Example 3) having a smaller Wa to We is obtained. I understood.

  From the above results, the thermosetting paint is applied to at least one lower layer (the lowermost layer in the case of two laminated coatings, two or more layers in the lowermost layer and at least one intermediate layer in the case of three or more layers). In the coating method in which an isocyanate-curable coating material is used as an upper layer, and an uncured laminated coating film is obtained by laminating by wet-on-wet, and then subjected to baking treatment, a thermosetting resin and the flow stop retarder After mixing, it was confirmed that by using an isocyanate curable coating prepared by mixing an isocyanate curing agent as a coating for the upper layer, a laminated coating film having a high appearance quality can be obtained.

  As described above, by using the isocyanate curable coating composition of the present invention, even when two or more types of coatings are laminated on a wet on wet and simultaneously baked to cure each layer, unevenness on the surface of the upper layer is generated. A sufficiently suppressed laminated 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.

  In addition, since the coating method of the present invention uses such an isocyanate curable coating composition, the appearance quality is highly excellent even when two or more types of coatings are laminated by wet-on-wet and baked simultaneously. It is useful as a coating method for obtaining a painted body, and particularly useful as a method for coating automobile bodies such as passenger cars, trucks, buses, motorcycles, and parts thereof.

Claims (7)

  An isocyanate-curable coating composition comprising a thermosetting resin, an isocyanate-based curing agent, and a flow stop retarder capable of being detachably attached to an isocyanate group.   The flow stop retarder comprises a phenolic hydroxyl group, lactam ring, ether bond, thiol group, urea bond, carbamate group, imino group, sulfite group, pyrazole ring, imidazole ring, oxime group, amino group, and active methylene group. The isocyanate-curable coating composition according to claim 1, which is a compound having at least one structure selected from the group.   The flow stop retardant is a phenol compound, a lactam compound, an ether compound, a mercaptan compound, a urea compound, a carbamate ester compound, an imine compound, a sulfite, a pyrazole compound, an imidazole compound, an oxime compound, an amine compound, and an active methylene compound. The isocyanate-curable coating composition according to claim 1 or 2, wherein the isocyanate-curable coating composition is at least one compound selected from the group consisting of: The flow stop time t _c when the flow stop delay agent is included is 1.1 times or more than the flow stop time t _c0 when the flow stop delay agent is not included. The isocyanate curable coating composition according to any one of the above. The difference (t _c −t _c0 ) between the flow stop time t _c when the flow stop delay agent is included and the flow stop time t _c0 when the flow stop delay agent is not included is 20 seconds or more. The isocyanate curable coating composition according to any one of claims 1 to 4. A coating method for forming a laminated coating film comprising at least one lower layer formed on a substrate and an upper layer formed on the lower layer,
The isocyanate curable type according to claim 1, wherein a thermosetting paint is prepared as a lower layer paint for forming the lower layer, and the upper layer paint for forming the upper layer. A preparation step of preparing a coating composition;
A forming step of laminating the lower layer coating material and the upper layer coating material on the substrate by wet-on-wet to form an uncured laminated coating film,
A baking step of subjecting the uncured laminated coating film to a baking treatment to simultaneously cure the lower layer coating material and the upper layer coating material,
The coating method characterized by including.   In the preparation step, after mixing the thermosetting resin and the flow stop retarder, the isocyanate curing agent is mixed with the obtained mixture to prepare the isocyanate curable coating composition. The coating method according to claim 6.