JP2008086957A - Method of coating automobile body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of coating an automobile body having a coating film with an excellent appearance and durability capable of reducing a total number of processes while attaining resource-saving and space-saving. <P>SOLUTION: The method of intermediate-coating and finish-coating an undercoated automobile body includes the processes (a)-(f): the process (a) of coating an outer plate part of the automobile body with a solvent type intermediate coating composition, the process (b) of coating an inner plate part of the automobile body with a water-based coating composition 1, the first process (c) of heating to harden, the process (d) of further coating the outer plate part of the automobile body with a water base coating composition 2, the process (e) of further coating the outer plate part of the automobile body with a clear coating composition by a wet-on-wet method, and the second process (f) of heating to harden. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an undercoating and overcoating method for an undercoated automobile body.

  In the coating of automobile bodies, generally, after an undercoat film, particularly an electrodeposition film, is formed on an object to be coated, the coating is completed through intermediate coating, colored base coating, and clear coating. This colored base coating and clear coating are also called top coating.

  For example, JP-A-9-20667 (Patent Document 1), JP-A-11-165123 (Patent Document 2) and JP-A-2001-347223 (Patent Document 3) are technically different parts. However, in any technique, the painting is completed through three steps of an undercoating process, an intermediate coating process, and a topcoating process.

  In the case of painting a car body of an automobile, the painting process is further classified according to the painted part of the car body. One is the so-called “outer plate”, which is the part that can be seen from the outside of the car body, where the highest design and durability are required. The so-called “inner plate” is a part that cannot be seen directly from the outside and does not require a very high design, but it is difficult to apply mechanically. Is the part where Considering the painting process of each part, conventionally, a painting method as shown in the process diagram of FIG. 1 has been adopted.

  Specifically, for automobile bodies that have been undercoated, the intermediate coating of the outer panel is painted with a mechanical automatic coating device, and then the inner coating of the inner panel is painted by hand rather than mechanically. To do. Once the intermediate coating has been completed, the intermediate coating film is once heated and cured, and then the inner plate is manually sprayed with a base paint (for example, a colored paint or a metallic paint), and then the base is applied to the outer plate. The paint is automatically applied, and the base coating film is not cured by heating, but a clear coating is applied by so-called wet-on-wet. Similarly, in clear coating, after the inner plate is manually sprayed, the outer plate is mechanically automatically coated, and then the base coating and clear coating are heated and cured at the same time. A film is formed.

Up to now, even if each painting work increases in this basic process (that is, undercoating process, intermediate coating process, and topcoating process), it does not decrease much. Of course, there are cases where the number of processes is reduced by not performing clear coating or not performing intermediate coating, but in that case, a coating film having an inferior appearance is provided.
Japanese Patent Laid-Open No. 9-20667 JP 11-165123 A JP 2001-347223 A

  In the present invention, the conventional coating process of the intermediate coating process and the top coating process was reviewed, and by reducing at least one coating process, the total number of processes was reduced and resource saving and space saving were achieved. In addition, an object of the present invention is to provide a method for coating an automobile body having a coating film having a high appearance and durability similar to the conventional one.

  As a result of intensive studies, the present inventors applied a specific aqueous base coating composition directly to the inner plate portion of the primed automobile body without applying the intermediate coating to the inner plate portion of the primed automobile body. As a result, it was found that the total number of processes can be significantly reduced without changing the existing painting line. Accordingly, the present invention provides the following.

An undercoating and overcoating method for a primed automobile body comprising steps (a) to (f):
(A) coating the outer plate of the vehicle body with a solvent-type intermediate coating composition;
(B) coating the inner plate portion of the vehicle body with the aqueous base coating composition 1;
(C) a first heat curing step,
(D) a step of further coating the outer plate portion of the vehicle body with the aqueous base coating composition 2;
(E) a step of further coating the outer plate portion of the vehicle body with a clear coating composition by wet-on-wet, and (f) a second heat curing step.

  The coating method as described above, wherein the aqueous base coating composition 1 and the aqueous base coating composition 2 have the same composition.

  The coating method as described above, wherein the aqueous base coating composition 1 and / or the aqueous base coating composition 2 contains an acrylic emulsion resin and a curing agent.

  The acrylic emulsion resin emulsion polymerizes an α, β-ethylenically unsaturated monomer mixture (acid value 3 to 50 mgKOH / g) containing 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part. The above-described coating method.

  The coating method as described above, wherein the aqueous base coating composition 1 and / or the aqueous base coating composition 2 further contains a glittering material.

  The coating method as described above, further comprising a step of coating the inner plate portion of the vehicle body with a clear coating composition after the step (d).

  Car body painted by the above painting method.

  As a result of reviewing each painting process of the intermediate coating process and the top coating process, which was a conventional common sense, the present invention has a total number of processes less than that of the prior art by applying a specific aqueous base coating composition, In addition, it is possible to provide a method for painting an automobile body having a coating film having the same high appearance and durability as the conventional one. Further, since the total number of processes is reduced, it is possible to achieve a reduction in coating cost, resource saving and space saving. Furthermore, the method of the present invention can provide the same high appearance as before even if it is carried out by a person skilled in the art who is not skilled in coating technology.

Hereinafter, the method of intermediate coating and overcoating of an undercoated automobile body of the present invention including the following steps (a) to (f) will be described in detail with reference to the accompanying drawings:
(A) coating the outer plate of the vehicle body with a solvent-type intermediate coating composition;
(B) coating the inner plate portion of the vehicle body with the aqueous base coating composition 1;
(C) a first heat curing step,
(D) a step of further coating the outer plate portion of the vehicle body with the aqueous base coating composition 2;
(E) a step of further coating the outer plate portion of the vehicle body with a clear coating composition by wet-on-wet, and (f) a second heat curing step.

  When the coating method of the present invention is shown in a form contrasted with FIG. 1, the process diagram of FIG. 2 is obtained. As apparent from FIG. 2, the inner plate base coating process comes to the position of the inner plate intermediate coating process of the conventional intermediate coating process, and the conventional inner plate intermediate coating process is eliminated. In the process diagram of the present invention (FIG. 2), the inner plate portion may be omitted in the clear coating process. Although the omission of the clear coating itself can be performed by the prior art, a more excellent appearance can be obtained by using a specific water-based base coating composition, and it can be efficiently omitted.

  As is apparent from FIG. 2, before entering the coating method of the present invention, the undercoat of the automobile body is applied.

  In the present invention, the undercoated automobile body refers to an automobile body and an automobile part having an undercoat film obtained by coating an electrode body with an electrodeposition paint capable of forming an undercoat film.

  The electrodeposition paint that can form the undercoat film is not particularly limited, and general electrodeposition paints known to those skilled in the art, for example, cationic and anionic electrodeposition paints can be used. A cationic electrodeposition coating is preferred because it provides excellent laminated coating and corrosion resistance.

  The film thickness of the undercoat coating film is, for example, 10 to 30 μm.

  Examples of the base material constituting the automobile body include metals, but are not particularly limited. As the substrate, a metal that can be subjected to cationic electrodeposition coating is particularly preferable, and examples of the metal include iron, steel, copper, aluminum, tin, zinc, and alloys containing these metals. These metals are particularly preferably those that have been previously subjected to chemical conversion treatment with phosphate, chromate or the like.

  In addition, the undercoated automobile body is made of plastic (for example, polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin, etc.) and its foam. Auto parts are also included, and specifically include, but are not limited to, spoilers, bumpers, mirror covers, grills, door knobs, and the like. Further, these plastic products are preferably washed with pure water and / or a neutral detergent. Further, primer coating for enabling electrostatic coating may be applied.

  The outer plate of the car body is the part that can be seen from the outside of the car body, and the highest design and durability are required, but it is the part that can be mechanically painted. A part that cannot be seen directly from the outside and does not require a very high design, but is difficult to paint mechanically and is actually a part that is manually blown by a craftsman or painted by a dedicated robot (for example, an engine Room, luggage room, door opening, inside door, pillar, periphery and back of fuel lid, cabin interior, etc.).

Step (a): Intermediate Coating of Outer Plate Part Step (a) of the present invention is a process of coating the outer plate part of the undercoated automobile body with a solvent-type intermediate coating composition. The solvent-type intermediate coating composition is applied to the outer plate of the undercoated automobile body using an automatic coating machine. As a coating method, an electrostatic coating method is preferable from the viewpoint of coating efficiency.

  Examples of the automatic coating machine include an air atomizing type coating machine (Auto REA) and an electrostatic coating machine (for example, a (bell, microbell or micromicrobell type) rotary atomizing type electrostatic coating machine). .

For example, the discharge amount is 200 to 400 cc / min, the cone diameter is 50 to 80φ, the rotation speed is 15000 to 30000 rpm, and the shaping air pressure is 1.5 to 2.5 kg / cm ² . Yes, the coating film thickness is preferably 20 to 60 μm.

  After the step (a), before proceeding to the subsequent step (b), an operation for making a time interval called an interval can be performed.

  By this interval, the organic solvent contained in the intermediate coating film can be sufficiently volatilized, and the appearance of the resulting multilayer coating film is improved. The interval is preferably 60 seconds to 10 minutes.

  Moreover, you may perform the heating operation called preheating during the said interval. By this preheating, the organic solvent contained in the intermediate coating film can be volatilized efficiently in a short time. This heating operation does not positively cure the intermediate coating film, and the heating condition is, for example, 60 to 100 ° C. for 1 to 5 minutes. The preheating can be performed using, for example, a warm air heater or an infrared heater.

  By the step (a), as shown in FIG. 3, the intermediate coating film 3 is formed on the outer plate portion. FIG. 3 is a schematic view showing a cross section of the coating film formed by the coating method of the present invention. After the undercoat coating film 2 is formed on the surface of the base material 1 of the automobile body, the above step (a The intermediate coating film 3 is formed on the outer plate portion.

Step (b): Inner Plate Base Coating Step (b) of the present invention is a step of coating the inner plate portion of the automobile body with an aqueous base coating composition. Conventionally, the intermediate coating is also applied to the inner plate portion here, but in the present invention, the inner plate portion is colored using an aqueous base coating. That is, according to the present invention, the aqueous base coating composition can be applied to the inner plate portion in the intermediate coating zone by wet-on-wet with the intermediate coating. The water-based base coating composition used here will be described in detail later, but the role of the intermediate coating film is high, that is, the adhesion with the undercoat film is high, the hue concealment of the undercoat film is high, It is necessary to have an excellent balance of sagging properties and an appropriate gloss.

  In particular, by using the aqueous base coating composition used in the present invention, it is possible to form an inner plate coated surface having an excellent appearance.

  In the step (b), the water-based base coating composition is applied to the inner plate portion of the automobile body using a usual means such as an air gun.

For example, the discharge amount is 100 to 400 cc / min, the air pressure is 3.0 to 4.0 kg / cm ² , and the coating film thickness is 10 to 20 μm.

  After the step (b), before proceeding to the subsequent step (c), an operation for making a time interval called an interval can be performed.

  By this interval, the organic solvent / water contained in the base coating film can be sufficiently volatilized, and the appearance of the resulting multilayer coating film is improved. The interval is preferably 7-15 minutes.

  Moreover, you may perform the heating operation called preheating during the said interval. By this preheating, the organic solvent / water contained in the base coating film can be volatilized efficiently in a short time. This heating operation does not positively cure the base coating film, and the heating condition is, for example, 80 to 100 ° C. for 2 to 5 minutes. The preheating can be performed using, for example, a warm air heater or an infrared heater.

  By the step (b), the inner plate base coating film 4 shown in FIG. 3 is formed.

  The boundary between the vehicle body outer plate and the inner plate substantially becomes a wet-on-wet coating of water-based paint onto the solvent-type intermediate coating film. Both interfaces are maintained by the interaction between the paint and the water-based paint that is hydrophilic, and the appearance can be satisfactorily applied. Further, due to the molecular weight effect of the specific acrylic emulsion resin contained in the aqueous base coating composition, even when the coating film is thick, sagging is unlikely to occur and the management range of the film thickness is widened. Therefore, a sufficiently good coating layer can be obtained even when an inexperienced painter performs painting.

Step (c): Heat-curing Step (c) of the present invention is a first heat-curing step and can be performed using a conventional baking and drying furnace. For example, the heat curing temperature is 120 to 160 ° C., and the heat curing time is 20 minutes to 1 hour.

Step (d): The outer plate portion base coating step (d) is a step in which the outer plate portion of the automobile body is further coated with an aqueous base coating composition. In the coating method of the present invention, since the base coating film 4 has already been formed on the inner plate portion, the outer plate is directly applied after the heat curing step (c) without performing the base coating of the inner plate portion as in the prior art. Apply the aqueous base coating composition to the part.

  From the viewpoint of cost, simplicity, finished appearance of the coating film, and hue difference between the inner and outer plates, the aqueous base coating composition used in step (d) has the same composition as the aqueous base coating composition used in step (b). Preferably there is.

  As the coating method, an electrostatic coating method using an automatic coating machine is preferable from the viewpoint of coating efficiency.

  As an automatic coating machine, for example, an air atomizing type coating machine (Auto REA), an electrostatic coating machine (for example (bell, microbell or micromicrobell type), a rotary atomizing type electrostatic coating machine (for example, ABB cartridge) Type rotary atomizing electrostatic coating machine, etc.).

For example, the discharge amount is 150 to 400 cc / min, the cone diameter is 50 to 80φ, the rotation speed is 20000 to 30000 rpm, and the shaping air pressure is 1.0 to 2.0 kg / cm ² . Yes, the coating thickness is preferably 10 to 20 μm.

  After step (d), before proceeding to the subsequent step (e), operations can be performed with a time interval called an interval.

  By this interval, the organic solvent / water contained in the base coating film can be sufficiently volatilized, and the appearance of the resulting multilayer coating film is improved. The interval is preferably 7-15 minutes.

  Moreover, you may perform the heating operation called preheating during the said interval. By this preheating, the organic solvent / water contained in the base coating film can be volatilized efficiently in a short time. This heating operation does not positively cure the base coating film, and the heating condition is, for example, 80 to 100 ° C. for 2 to 5 minutes. The preheating can be performed using, for example, a warm air heater or an infrared heater.

  By the step (d), the outer plate base coating film 5 shown in FIG. 3 is formed.

Step (e): Clear coating The outer plate portion of the automobile body and, if necessary, the inner plate portion may be further coated with a clear coating composition. Clear coating of the inner plate is less necessary than clear coating of the outer plate, so it is optionally painted. Therefore, first, clear coating on the outer plate portion will be described. Clear coating on the outer plate is important because it greatly contributes to the appearance of the car and gives an excellent appearance.

  Clear coating on the outer plate of the vehicle body can be performed using an automatic coating machine. As a coating method, an electrostatic coating method is preferable from the viewpoint of coating efficiency.

  Examples of the automatic coating machine include an air atomizing type coating machine (Auto REA) and an electrostatic coating machine (for example, a (bell, microbell or micromicrobell type) rotary atomizing type electrostatic coating machine). .

For example, the discharge amount is 150 to 300 cc / min, the cone diameter is 50 to 80φ, the rotation speed is 15000 to 25000 rpm, and the shaping air pressure is 1.0 to 7.0 kg / cm ² . Yes, the coating film thickness is preferably 20 to 60 μm.

  Also in this step, an operation for making a time interval called an interval can be performed.

  By this interval, the solvent contained in the clear coating film can be sufficiently volatilized, and the appearance of the resulting multilayer coating film is improved. The interval is preferably 7-15 minutes.

  The clear coating on the outer plate portion performed in this step is performed wet-on-wet on the base coating film formed in step (d). The advantage of wet-on-wet coating is that the process can be simplified and resources can be saved by omitting the heat curing process once.

  In FIG. 4, the schematic cross section of the laminated coating film which formed the clear coating film only in the outer-plate part before the heat-hardening process (f) after the coating process (a)-(d) of this invention is shown. In FIG. 4, coating films 1 to 5 are the same coating films as in FIG. 3, but a clear coating film 6 is formed on the outer plate portion on those coating films.

  Moreover, you may perform clear coating to an inner-plate part as mentioned above. However, when a clear coating film is formed on the inner plate portion, it is necessary to be after the step (d) and before clear coating on the outer plate portion. This is because it is necessary to finish the outer plate portion with a higher aesthetic appearance, and it is necessary to finish the coating of the outer plate portion so that paint dust or the like does not appear on the appearance. The clear coating of the inner plate part is also performed using the hand-blown coating means as described above.

  FIG. 5 shows a schematic cross-sectional view of a composite coating film when clear coating films (6 and 6 'respectively) are formed on the outer plate portion and the inner plate portion. In the figure, coating films 1 to 5 are the same as those in FIGS.

Step (f): Heat curing Step (f) of the present invention is a second heat curing step and can be performed using a conventional baking drying furnace.

  For example, the heat curing temperature is 120 to 160 ° C., and the heat curing time is 20 minutes to 1 hour.

  When providing a clear coating process, a heat-hardening process is performed after a clear coating process.

  As is clear from the above, the present invention can reduce the total number of processes compared to the prior art by reviewing each coating process of the intermediate coating process and the top coating process, which was the conventional common sense, Moreover, by using a specific aqueous base coating composition, it is possible to obtain a coating film having the same high appearance and durability as before. Therefore, reduction of coating cost, resource saving and space saving can be achieved. Furthermore, since the present invention can omit the intermediate coating manual blow coating process of the inner plate portion, problems caused by sagging, skin defects, contact with wet coating, and adhesion of dust by those skilled in the art of coating technology can be avoided. It is possible to provide an excellent finished appearance efficiently.

  Hereinafter, each coating composition used in the method of the present invention will be described.

Solvent-type intermediate coating composition A solvent-type intermediate coating composition is used to form an intermediate coating film. The solvent-type intermediate coating composition contains a film-forming resin, a curing agent, various organic and inorganic color pigments, and extender pigments.

  The film-forming resin contained in the intermediate coating composition is not particularly limited, and film-forming resins such as acrylic resin, polyester resin, alkyd resin, epoxy resin, and urethane resin can be used. Is used in combination with the curing agent mentioned in the aqueous base coating composition described later. An amino resin and / or a blocked isocyanate resin is generally used in view of various performances and costs of the obtained coating film.

  As the pigment contained in the intermediate coating composition, those mentioned in the description of the aqueous base coating composition described later can be used in the same manner, but carbon black and titanium dioxide are typically used as the main pigment. A so-called color intermediate coating composition, which is a combination of a gray-based intermediate coating composition and a set gray that matches the lightness of the top coating and various coloring pigments, can be used. Furthermore, flat pigments such as aluminum powder and mica powder may be added.

  In these intermediate coating compositions, in addition to the above components, additives usually added to the coating, for example, surface conditioners, antioxidants, antifoaming agents and the like may be blended.

Water-based base coating composition The water-based base coating composition used in the present invention has high adhesion to the undercoat film, high hue concealment of the base coat film, excellent balance between flow and sagging properties, and moderate Since it has a high gloss, it can be applied directly to the inner plate of an undercoated automobile. Further, the aqueous base coating composition has high adhesion to the intermediate coating film, high hue concealment of the intermediate coating film, and excellent wet-on-wet property with the intermediate coating film. The present invention can also be suitably applied to a coating film comprising an intermediate coating composition.

  The aqueous base coating composition contains an acrylic emulsion resin and a curing agent, and may further contain a glittering material.

  The acrylic emulsion resin contained in the aqueous base coating composition is, for example, an α, β-ethylenically unsaturated monomer mixture (acid value) containing 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part. An emulsion resin obtained by emulsion polymerization of 3 to 50 mgKOH / g) can be mentioned, but is not limited thereto.

  When the amount of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part contained in the α, β-ethylenically unsaturated monomer mixture is less than 65% by mass, the appearance of the resulting coating film is deteriorated. To do. Examples of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part include methyl (meth) acrylate and ethyl (meth) acrylate. In addition, in this specification, (meth) acrylic acid ester shall mean both acrylic acid ester and methacrylic acid ester.

  The particle diameter of the acrylic emulsion resin is preferably in the range of 0.01 to 1.0 μm. When the particle diameter is less than 0.01 μm, the effect of improving workability is small, and when it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions. In addition, the particle diameter of acrylic emulsion resin in this specification is a volume average particle diameter calculated | required by the laser light scattering method.

  The acrylic emulsion resin can be used at pH = 5 to 10 by neutralizing with a base as necessary. This is because the stability in this pH region is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

  In addition, it is preferable that the water-based base coating composition contains 50 to 90 parts by mass of the acrylic emulsion resin per 100 parts by mass of the resin solid content. When the content of the acrylic emulsion resin is less than 50 parts by mass, the coating workability is lowered, and when it exceeds 90 parts by mass, the curability is lowered. Especially preferably, it is 60-80 mass parts.

  The aqueous base coating composition further includes a curing agent. As said hardening | curing agent, what is generally used for the coating material can be used, An amino resin, blocked isocyanate, etc. are mentioned as such a thing. Amino resins and / or blocked isocyanates are generally used in view of various performances and costs of the obtained coating film.

  The amino resin is not particularly limited, and a water-soluble melamine resin or a water-insoluble melamine resin can be used.

  The blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, and is blocked by heating. Examples include agents that dissociate to generate isocyanate groups that react with the functional groups in the resin component and cure.

  When the said hardening | curing agent is contained, it is preferable that the content is 10-50 mass parts with respect to 100 mass parts of resin solid content in an aqueous base coating composition, and it is further more preferable that it is 20-40 mass parts. . When the amount is less than 10 parts by mass, the curability and the like are reduced, and when the amount exceeds 50 parts by mass, the adhesion, hot water resistance, and the like may be reduced.

  The glittering material that may be contained in the aqueous base coating composition is not particularly limited, and may be colored with a pigment. For example, the average particle diameter (D50) is 2 to 50 μm, and the thickness is Is preferably 0.1 to 5 μm. Those having an average particle diameter in the range of 10 to 35 μm are excellent in glitter and are more preferably used. Specific examples include non-colored or colored metallic luster materials such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, or alloys, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, glass flake pigments, and the like can also be included. In addition, the average particle diameter (D50) of the luster material in this specification is a value obtained by a laser light scattering method.

  The pigment concentration (PWC) of the glitter material is preferably 18.0% or less. When it exceeds 18.0%, the appearance of the coating film is deteriorated. More preferably, it is 0.01 to 15.0%, and particularly preferably 0.01 to 13.0%. In addition, the pigment concentration of the above-mentioned glitter material is a calculation formula including other pigments described below, (total mass of all glitter materials) / (total mass of all glitter materials, all pigments, and all resin components) × 100 (%) It is calculated from

  If necessary, the aqueous base coating composition of the present invention may contain other film-forming resin. Such additional film-forming resin is not particularly limited, and film-forming resins such as acrylic resins, polyester resins, alkyd resins, and epoxy resins can be used.

  The aqueous base coating composition can further contain a pigment. It does not specifically limit as a pigment, A coloring pigment, an extender, etc. can be mentioned. Examples of the color pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. Pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like. Examples of inorganic pigments include yellow lead, yellow iron oxide, bengara, carbon black, and titanium dioxide. Examples of the extender pigment include calcium carbonate, barium sulfate, clay and talc.

  In this case, the total pigment concentration (PWC) in the aqueous base coating composition is preferably 0.1 to 50%. More preferably, it is 0.5 to 40%, and particularly preferably 1.0 to 30%. If it exceeds 50%, the coating film appearance may be deteriorated. The total pigment concentration is represented by (total mass of all pigments and all glitter materials) / (total mass of all glitter materials, all pigments and all resin components) × 100 (%).

  Furthermore, a viscosity control agent can be further added to the aqueous base coating composition in order to prevent the compatibility with the laminated coating film and to ensure the coating workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, polyamide-based ones such as crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long-chain polyaminoamide phosphates. Viscosity develops depending on the shape of polyethylene, such as colloidal swelling dispersion of polyethylene oxide, organic bentonite such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, etc. A flat pigment or the like can be mentioned as a viscosity control agent.

  In the aqueous base coating composition of the present invention, in addition to the above-mentioned components, additives usually added to the coating, for example, surface conditioners, thickeners, antioxidants, UV inhibitors, antifoaming agents and the like are blended. May be. These compounding amounts are within the range known to those skilled in the art.

  The method for producing the aqueous base coating composition of the present invention is not particularly limited, and may include all methods well known to those skilled in the art, such as kneading and dispersing a compound such as a pigment using a kneader or a roll. .

Clear coating composition The clear coating composition is used to smooth the unevenness, flickering, etc. of the base coating that can be attributed to the glitter pigment, and to protect the base coating and improve the appearance. Can be formed on top.

  It does not specifically limit as said clear coating composition, For example, the coating composition containing a film-forming resin and a hardening | curing agent and another additive as needed can be mentioned.

  The film-forming resin is not particularly limited, and examples thereof include acrylic resins, polyester resins, epoxy resins, and urethane resins.

  From the viewpoint of transparency or acid etching resistance, a combination of an acrylic resin and / or polyester resin as the coating film-forming resin and an amino resin and / or polyisocyanate resin as the curing agent, or a carboxylic acid / epoxy group curing system It is preferable to use acrylic resin and / or polyester resin having

  For example, when a clear coating composition is applied on the above base coating, the clear coating composition is applied onto the wet base coating formed by the aqueous base coating (ie, wet-on-wet coating). It is preferable to contain a viscosity control agent as an additive in order to prevent familiarity, inversion or sagging between coating layers. The addition amount of the viscosity control agent is 0.01 to 10 parts by mass, preferably 0.02 to 8 parts by mass, with respect to 100 parts by mass of the resin solid content of the clear coating composition. Preferably, it is 0.03 mass part-6 mass parts. When the addition amount exceeds 10 parts by mass, the appearance of the obtained coating film is deteriorated, and when it is less than 0.01 part by mass, the viscosity control effect cannot be obtained, causing a problem such as sagging when forming the coating film It becomes.

  The clear coating composition may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-water-dispersed type, and powder type, and if necessary, a curing catalyst, surface conditioning. An agent or the like can be used.

  In addition, as an example of the said water-type clear coating composition, the film-forming resin contained in what was mentioned as an example of the said clear coating composition, a base (for example, tertiary amine, dimethylethanolamine, triethylamine, Examples thereof include those containing a resin neutralized with trimethylamine, triethanolamine, sodium hydroxide, potassium hydroxide, ammonia, etc.) and made aqueous. This neutralization can be performed by adding a base before or after the polymerization.

  Hereinafter, the present invention will be described in detail with specific examples, but the present invention is not limited to the following examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

Example 1
Coating step Step (a): Nippon Paint Co., Ltd. polyester resin / melamine resin curable solvent-type intermediate coating composition “Olga P-5-1 Gray (trade name)” It apply | coated with the rotary atomization type electrostatic coating machine (discharge amount: 300 cc / min).
Interval: 2 minutes Step (b): Nippon Paint Co., Ltd. acrylic emulsion / melamine resin curable water-based base coating composition “AQUALEX AR-2000 Silver (trade name)” was painted on an air gun coating machine. (Wider w-200 air gun; discharge amount: 150 cc / min).
Interval: 7 minutes Step (c): Baking and drying were performed in a drying furnace (140 ° C., 30 minutes).
Step (d): Acrylic emulsion / melamine resin curable water-based base coating composition “AQUALEX AR-2000 Silver (trade name)” manufactured by Nippon Paint Co., Ltd. is applied to the outer skin of the vehicle body using an ABB cartridge type rotary atomizing electrostatic coating. It was painted with a machine (discharge amount: 200 cc / min).
Preheat: 80 ° C. × 3 minutes Process (e): Nippon Paint Co., Ltd. acid / epoxy curable clear coating composition “McFlow O-1800 Clear (trade name)” is rotated and atomized electrostatically. It painted with the coating machine (wet / wet, discharge amount: 250 cc / min).
Interval: 7 minutes Step (f): Baking and drying were performed in a drying furnace (140 ° C., 30 minutes).

Example 2
In the painting process of Example 1, a clear painting process for the inner plate portion was added. Otherwise, coating was performed in the same manner as in Example 1.

Comparative Example 1
Coating process 1st process: Nippon Paint Co., Ltd. intermediate coating composition “Olga P-5-1 Gray (trade name)” is applied to the outer plate of the undercoated automobile body in the same manner as in Example 1. It apply | coated with the electrostatic coating machine (discharge amount: 300 cc / min).
Interval: 2 minutes Second process: Nippon Paint Co., Ltd.'s intermediate coating composition “Orga P-5-1 Gray (trade name)” was applied to the inner plate of the vehicle body with an air gun coating machine (Wider w-200 Air Gun (REA Hand gun), discharge rate: 150 cc / min).
Interval: 7 minutes Third step: Baking and drying were performed in a drying furnace (140 ° C., 30 minutes).
Fourth step: A water base coating composition “AQUALEX AR-2000 Silver (trade name)” manufactured by Nippon Paint Co., Ltd. was applied to the inner plate of the vehicle body in the same manner as in Example 1 (Wider w-200 Air Gun). : Discharge amount: 150 cc / min).
Fifth step: A water base coating composition “AQUALEX AR-2000 Silver (trade name)” manufactured by Nippon Paint Co., Ltd. is applied to the outer plate of the vehicle body in the same manner as in Example 1 with an ABB cartridge type rotary atomizing electrostatic coating machine. Painted (discharge amount: 200 cc / min).
Preheating: 80 ° C. × 3 minutes Sixth step: A clear paint composition “Mac Flow O-1800 Clear (trade name)” manufactured by Nippon Paint Co., Ltd. was painted on the inner plate of the vehicle body with an air gun coating machine (wet / wet, weider w -200 air gun, discharge rate: 250 cc / min).
Seventh step: A clear paint composition “McFlow O-1800 Clear (trade name)” manufactured by Nippon Paint Co., Ltd. was applied to the outer skin of the vehicle body with a rotary atomizing electrostatic coating machine (wet / wet, discharge amount: 250 cc) / Min).
Interval: 7 minutes Eighth step: Baking and drying were performed in a drying furnace (140 ° C., 30 minutes).

Comparative Example 2
Coating was performed in the same manner as in Comparative Example 1 by omitting the sixth and seventh steps of Comparative Example 1.

Comparative Example 3
Coating was performed in the same manner as in Comparative Example 1, omitting the fourth and fifth steps of Comparative Example 1.

The laminated coating film obtained by the method of the present invention was compared with the laminated coating film obtained in the comparative example, and the results are summarized in Table 1.

○: There is a coating film-: There is no coating film A: There is no problem at all B: There is a problem that there is no need for reworking C: Problems are likely to occur and reworking is required, but reworking does not take time Level D: Problems are likely to occur, and it takes time to rework E: Levels that have problems and require repainting from the beginning * 1: Sauce / skeke is a term that generally represents coating unevenness. Means the state where the paint film is dripping due to excessive coating, and the scale means the state where the coating is not sufficiently applied and the base can be seen through. Means a bug.
* 2: No problem in the finished appearance means that the visual haze and gloss are good.
* 3: “There is no problem in hue” means that there is no difference between the outer plate portion and the inner plate portion by visual inspection.

  By reviewing each painting process of the intermediate coating process and top coating process, which was the conventional common sense, the total number of processes is smaller compared to the conventional technology, and the same high appearance and durability coating film as before It is possible to provide a method for painting a car body having the same. Further, since the total number of processes is reduced, it is possible to achieve a reduction in coating cost, resource saving and space saving. Furthermore, the method of the present invention is less likely to cause defects such as sagging of the inner plate portion and skin defects even by those skilled in the art who are not skilled in coating technology, and efficiently provides the same high appearance as before. Can do.

FIG. 1 is a process diagram showing a conventional coating process. FIG. 2 is a process diagram showing the painting process of the present invention. FIG. 3 is a schematic cross-sectional view of a coating film formed by the method of the present invention. FIG. 4 is a schematic cross-sectional view of a coating film formed by the method of the present invention. FIG. 5 is a schematic cross-sectional view of a coating film formed by the method of the present invention.

Explanation of symbols

1: Base material 2: Undercoat paint film 3: Intermediate paint film 4: Inner plate part base paint film 5: Outer plate part base paint film 6: Outer plate part clear paint film 6 ': Inner plate part clear paint film

Claims (7)

An undercoating and overcoating method for a primed automobile body comprising steps (a) to (f):
(A) coating the outer plate of the vehicle body with a solvent-type intermediate coating composition;
(B) coating the inner plate portion of the vehicle body with the aqueous base coating composition 1;
(C) a first heat curing step,
(D) a step of further coating the outer plate portion of the vehicle body with the aqueous base coating composition 2;
(E) a step of further coating the outer plate portion of the vehicle body with a clear coating composition by wet-on-wet, and (f) a second heat curing step.   The coating method according to claim 1, wherein the aqueous base coating composition 1 and the aqueous base coating composition 2 have the same composition.   The coating method according to claim 1, wherein the aqueous base coating composition 1 and / or the aqueous base coating composition 2 contains an acrylic emulsion resin and a curing agent.   The acrylic emulsion resin emulsion polymerizes an α, β-ethylenically unsaturated monomer mixture (acid value 3 to 50 mgKOH / g) containing 65% by mass or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part. The coating method of Claim 3 obtained by these.   The coating method according to claim 3, wherein the aqueous base coating composition 1 and / or the aqueous base coating composition 2 further contains a glittering material.   The coating method of Claim 1 which further includes the process of coating the inner-plate part of the said vehicle body with a clear coating composition after a process (d).   An automobile body painted by the method according to claim 1.

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