JP4575008B2 - Coating method for aluminum car body - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film on a surface to be coated of an aluminum automobile body.

  The body of an automobile is a body frame by press-molding a steel plate base material or an aluminum alloy plate base material to form inner members of the vehicle body such as a floor panel and an inner panel, and joining the obtained molded members by welding or the like. Make a chassis. We also press-mold steel plate bases and aluminum alloy plate bases to form car body exterior members such as doors, roofs, fenders, bonnets, trunk lids, etc. To do.

  The general painting process for automobile bodies is a degreasing and washing process, after degreasing, a pre-coating process such as chemical conversion, and an undercoating process for the purpose of rust prevention by electrodeposition coating, etc. An intermediate coating process for the purpose of improving the appearance and a top coating process for imparting durability such as weather resistance, chemical resistance, and abrasion resistance to the painted surface.

  As described above, the general painting of a car body of an automobile has an extremely large number of painting processes including a pretreatment process from a degreasing and washing process to a final top coat. Also, since the painting is carried out in a consistent line, the painting line becomes extremely long. In addition, since the electrodeposition coating method is used for rust prevention and undercoating, etc., a dip coating device is required, the equipment is large, which is disadvantageous in terms of equipment, and requires maintenance and management man-hours. There are disadvantages such as high costs.

As a method for simplifying the coating process, Japanese Patent Application Laid-Open No. 2003-334490 (Patent Document 1) discloses the following processes (1) to (4):
(1) A process of degreasing the painted surface of an automobile body made of an aluminum material;
(2) a chemical conversion treatment step of applying and drying a chemical conversion treatment agent mainly containing zirconium phosphate not containing phosphoric acid, zinc phosphate not containing nickel, zirconium phosphate or titanium phosphate;
(3) As a vehicle, containing 40 to 80 parts by mass of a polyester resin, 10 to 50 parts by mass of a melamine resin, and 5 to 30 parts by mass of an epi-bis type epoxy resin in terms of solid content in the vehicle, A primer surfacer coating film forming step of applying and drying and curing a primer surfacer containing a flat pigment, a rust preventive pigment, a color pigment excluding these pigments, and a extender pigment in a solid mass ratio of the vehicle to the pigment of 30/70 to 80/20; And (4) A method for forming a coating film on an aluminum automobile body, which sequentially undergoes a top coating film forming step in which a top coating material is applied and dried and cured. A coating film excellent in corrosion resistance and the like can be formed by a method in which the coating process by omitting the electrodeposition coating process is simplified. On the other hand, however, reduction of raw material costs is becoming an important issue due to recent economic conditions. Therefore, if there is a method in which the coating process is simplified and a coating film excellent in corrosion resistance and the like can be formed even if a cheaper base material is used, it is very beneficial.

JP 2003-334490 A

  The object of the present invention is to form a coating film having good corrosion resistance (salt warm water resistance, yarn rust resistance, bare corrosion resistance) and adhesion to an aluminum alloy substrate (water resistance adhesion), and electrodeposition coating A coating film forming method for an aluminum automobile body and a multilayer coating film formed by the above coating film forming method, which can simplify the coating process by omitting the process, greatly reduce the number of coating steps, and facilitate the painting work. Is to provide.

The present invention
Degreasing the painted surface of an automobile body made of an aluminum substrate,
A chemical conversion treatment step for applying a chemical conversion treatment agent to the surface to be coated;
The vehicle contains 40 to 80 parts by mass of a polyester resin, 10 to 50 parts by mass of melamine resin, and 5 to 30 parts by mass of an epi-bis type epoxy resin in terms of solid content in the vehicle, and a flat pigment as a pigment , Anti-corrosion pigment, coloring pigment excluding these, and primer surfacer coating film forming step of applying and drying and curing primer surfacer containing 30/70 to 80/20 of solid matter mass ratio of vehicle and pigment, and top coating Applying and drying and curing the top coat film forming process,
Including a coating film forming method for an aluminum automobile body,
This chemical conversion treatment agent is a chemical conversion treatment agent containing at least one selected from the group consisting of zirconium, titanium, and hafnium, fluorine, and a water-soluble epoxy compound having an isocyanate group,
However, the content in at least one chemical conversion treatment agent selected from the group consisting of zirconium, titanium and hafnium is 20 to 10,000 mg / L,
The content of the water-soluble epoxy compound in the chemical conversion treatment agent is 5 to 5000 mg / L, which provides a method for forming a coating film on an aluminum automobile body, thereby achieving the above object.

  In the above method, the chemical conversion treatment agent preferably further contains at least one metal ion (A) selected from the group consisting of zinc ions, magnesium ions, and aluminum ions.

  Moreover, it is preferable that pH of the chemical conversion treatment agent in the chemical conversion treatment process of the said method is 1.5-6.5.

  The coating film forming method of the present invention is simplified by greatly reducing the number of coating steps by omitting the electrodeposition coating process. Furthermore, the method of the present invention can form a coating film excellent in corrosion resistance and the like even when a cheaper aluminum alloy substrate is used. The chemical conversion film obtained by the chemical conversion treatment step in the method of the present invention includes at least one inorganic component selected from the group consisting of zirconium, titanium, and hafnium, and an organic component that is an epoxy resin. Therefore, this chemical conversion film has excellent adhesion to the metal substrate and also excellent adhesion to the primer surfacer coating film formed on this chemical conversion film. Therefore, the multilayer coating film formed according to the present invention can give excellent corrosion resistance to the substrate.

<Aluminum car body>
In a vehicle body applied to the method for forming a coating film for an aluminum automobile body according to the present invention, an inner member, a chassis, and a vehicle body exterior member of the vehicle body are made of an aluminum base material. However, it shall include those in which the aluminum substrate is partially used.

  Here, the vehicle body inner member refers to a plurality of inner members such as various inner panels such as a floor panel member, a pillar member, a roof rail member, a side sill member, a bulkhead member, and a cross member member. The chassis refers to a vehicle body skeleton formed by molding an inner member of a vehicle body and joining the obtained molded member by welding, rivet connection, screw connection, or the like. The car body exterior members are fenders arranged on the front and rear sides of the press-molded chassis, the hood that is the hood of the front engine room, the trunk lid or tail gate on the rear, the doors arranged on the front and back of both sides, The roof panel etc. which comprise a ceiling exterior board. The exterior member is joined by a joining method such as rivet joining or screw joining to the chassis. An aluminum alloy is used as the aluminum substrate. By using an aluminum alloy, it has rust prevention and can eliminate the need for electrodeposition coating. As the chassis constituent member, an aluminum alloy base plate, profile, casting or the like is used.

  The aluminum base material used as the inner member of the vehicle body, the chassis, and the vehicle body exterior member is particularly required to have corrosion resistance. For this reason, JIS A6000 series Al-Mg-Si alloys having good corrosion resistance are generally used as aluminum base materials used in these applications, and among them, the copper (Cu) content is 0.1 mass% or less. Have been used. If copper is contained in the aluminum alloy substrate, the corrosion resistance will be poor. This is because copper has a lower ionization tendency than aluminum, and thus, when copper is contained in an aluminum alloy, ionization of aluminum (corrosion of aluminum) is promoted. The lower the copper content in the aluminum alloy, the better the corrosion resistance, but such substrates require more sophisticated purification and are expensive.

  In the coating film forming method of the present invention, not only an aluminum substrate having a Cu content of 0.1% by mass or less, but also an aluminum substrate containing about 1% by mass of Cu can be used. And the aluminum base material which has the multilayer coating film formed by the method of this invention is excellent in corrosion resistance. In the method of the present invention, even when an aluminum base material containing about 1% by mass of Cu is used as the aluminum base material, compared with the case of using a Cu content of 0.1% by mass or less. Excellent corrosion resistance can be given so as not to fade. The chemical conversion treatment agent used in the method of the present invention contains an organic resin component. Thereby, a coating film excellent in the concealability of the base material can be formed, and the base material becomes difficult to come into contact with the corrosive environment. Furthermore, when this chemical conversion treatment agent contains an organic resin component, the adhesion with the primer surfacer coating film formed thereafter is also improved, and the corrosion resistance of the resulting coated product is improved.

  Hereafter, the process in this invention is demonstrated sequentially.

<Degreasing process>
The degreasing step in the method of forming a coating film for an aluminum automobile body of the present invention uses an alkaline degreasing agent having a pH of 10.5 to 12.5, a degreasing temperature of 40 to 50 ° C., a degreasing time of 1 to 5 minutes, and an alkaline aqueous solution. It is a process of processing by a spraying method or a dip dipping method.

(Degreasing agent)
A degreasing agent applied to the degreasing step is subjected to a degreasing cleaning process to remove fats and oils such as mineral oil and animal and vegetable oil adhering to the surface of the object to be treated. As a degreasing detergent used for such a degreasing washing process, a builder mainly comprising an acid or an alkali and a non-ionic or anionic surfactant as a main component are generally used. As the alkali builder, those mainly composed of phosphate or silicate have been used from the viewpoint of detergency, but recently, alkali builder mainly composed of silicate is preferably used. Alkali builders in which carbonates and the like are further blended with such silicates are also used. It contains an alkali silicate, a water-soluble polycarboxylate, and a nonionic surfactant.

  In order to make the pH value of the degreasing liquid 10.5 or more, a chemical for increasing the pH value is blended in addition to the essential components. Examples of such agents include alkali carbonates such as sodium bicarbonate, sodium carbonate, potassium bicarbonate, and potassium carbonate; caustic alkalis such as potassium hydroxide and sodium hydroxide. These may be used alone or in combination of two or more.

  Examples of the alkali silicate include alkali metal salts of orthosilicates such as sodium orthosilicate and potassium orthosilicate; alkali metal salts of metasilicate such as sodium metasilicate and potassium metasilicate; sesquisilicates such as sodium sesquisilicate and potassium sesquisilicate. Examples include alkali metal salts of acids. These may be used alone or in combination of two or more. The water-soluble polycarboxylate is a homopolymer or copolymer of unsaturated carboxylic acids having one polymerizable double bond, and the carboxyl group is neutralized with an alkali metal such as sodium or potassium. Salt is preferred. As said nonionic surfactant, a conventionally well-known thing is mentioned, for example. Among various nonionic surfactants, from the viewpoint of excellent detergency and low fish toxicity, monoalkyl ether of polyethylene oxide is preferable, excellent detergency, low fish toxicity and antifoaming property. From the point of being excellent (low foaming property), a monoalkyl ether of polyethylene oxide polypropylene oxide is preferable. Among these monoalkyl ethers, an alkylene oxide adduct of an aliphatic alcohol, in which 50 mol% or more of the alkylene oxide is ethylene oxide, and less than 50 mol% is propylene oxide and / or butylene oxide, Is preferably a nonionic surfactant having a temperature in the range of 25 to 50 ° C. The pH value of the degreasing liquid needs to be 10.5 or more, and is preferably in the range of pH 10.5 to 12.5.

<Chemical conversion treatment process>
The chemical conversion treatment agent used in the method of the present invention contains at least one selected from the group consisting of zirconium, titanium, and hafnium, fluorine, and a water-soluble epoxy compound having an isocyanate group. In the chemical conversion treatment agent of the present invention, these components are dissolved and / or dispersed in an aqueous medium. And this chemical conversion treatment agent also has the advantage that it does not contain harmful heavy metal ions such as chromium. When this chemical conversion treatment agent is used to treat a metal substrate to be coated, at least one selected from the group consisting of zirconium, titanium, and hafnium forms a hydroxide or an oxide due to an increase in interface pH. These hydroxides or oxides are considered to precipitate on the substrate surface.

  When an epoxy compound is contained in such a chemical conversion treating agent, the epoxy compound chelates at least one selected from the group consisting of zirconium, titanium, and hafnium. Thereby, it is considered that strong adhesion can be obtained between the film made of at least one selected from the group consisting of zirconium, titanium and hafnium and the epoxy compound film. Since the epoxy compound film is composed of an organic component, it has a strong affinity with a resin component that forms a coating film and the like formed thereon, and it is considered that a strong adhesiveness can be obtained thereby. .

  Furthermore, since this chemical conversion treatment agent contains a component that acts as a curing agent, the above-mentioned epoxy compound film causes a crosslinking reaction, thereby being superior in physical properties, adhesion and corrosion resistance. A film layer can also be formed.

  At least one selected from the group consisting of zirconium, titanium and hafnium contained in the chemical conversion treatment agent is a chemical conversion film forming component. Here, the “chemical conversion film” refers to a coating film formed on the surface to be coated by a chemical conversion treatment process. By forming a chemical conversion film containing at least one selected from the group consisting of zirconium, titanium, and hafnium on the base material to be coated, the corrosion resistance and wear resistance of the base material are improved, and then Adhesion with the formed coating film can be enhanced.

The zirconium source is not particularly limited, and examples thereof include alkali metal fluorozirconates such as K ₂ ZrF ₆ ; fluorozirconates such as (NH ₄ ) ₂ ZrF ₆ ; fluorozirconate acids such as H ₂ ZrF _6, etc. And soluble fluorozirconate, etc .; zirconium fluoride; zirconium oxide and the like.

The titanium source is not particularly limited. For example, alkali metal fluorotitanate, fluorotitanate such as (NH ₄ ) ₂ TiF ₆ ; soluble fluorozirconate such as fluorotitanate such as H ₂ TiF ₆ ; Titanium; titanium oxide and the like can be mentioned.

The source of hafnium is not particularly limited, and examples thereof include fluorohafnate acids such as H ₂ HfF ₆ ; hafnium fluoride. The at least one source selected from the group consisting of zirconium, titanium and hafnium is at least one selected from the group consisting of ZrF ₆ ²⁻ , TiF ₆ ²⁻ , and HfF ₆ ²⁻ due to high film forming ability. The compound which has is preferable.

  The content of at least one selected from the group consisting of zirconium, titanium and hafnium contained in the chemical conversion treatment agent is within the range of the lower limit of 20 mg / L and the upper limit of 10,000 mg / L as the metal ion concentration contained in the chemical conversion treatment agent. Is preferred. If it is less than the above lower limit, the resulting chemical conversion film may have insufficient performance. Further, when the above upper limit is exceeded, no further effect can be expected, which is economically disadvantageous. The lower limit is more preferably 50 mg / L, and the upper limit is more preferably 2000 mg / L.

  The fluorine contained in the chemical conversion treatment agent serves as an etching agent for the substrate. The fluorine supply source is not particularly limited, and examples thereof include simple fluorides such as hydrofluoric acid, ammonium fluoride, boron fluoride acid, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. it can. Examples of the complex fluoride include hexafluorosilicate, and specific examples thereof include hydrofluoric acid, zinc silicofluoride, manganese silicofluoride, magnesium silicofluoride, and hydrosilicofluoride. Examples thereof include nickel, iron silicohydrofluorate, and calcium silicohydrofluoride.

  The chemical conversion treatment agent used in the present invention contains a water-soluble epoxy compound. When the water-soluble epoxy compound is added to the chemical conversion treatment agent, the epoxy skeleton improves the affinity with the coating resin, so that the adhesion of the coating film is increased and good stability can be exhibited.

  The water-soluble epoxy compound is not particularly limited as long as it has a solubility sufficient to dissolve a necessary amount in the chemical conversion treatment agent, and may be an epoxy resin as a skeleton. The epoxy resin is not particularly limited. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydrogenated bisphenol F type epoxy resin, bisphenol A propylene oxide addition type epoxy resin, bisphenol F propylene oxide addition type epoxy resin, novolak type epoxy resin, etc. can be mentioned. Among these, bisphenol F type epoxy resin is preferable, and bisphenol F epichlorohydrin type epoxy resin is more preferable.

The water-soluble epoxy compound preferably has an amino group. Such a water-soluble epoxy compound having an amino group is a cationic compound and has a property of insolubilizing and precipitating as the pH of the aqueous solution increases because the balance between hydrophilicity and hydrophobicity is adjusted. It is. For this reason, the said epoxy compound becomes easy to precipitate on the metal surface, when pH raises in a metal / water solution interface. As a result of analysis by X-ray photoelectron spectroscopy, it was found that the water-soluble epoxy compound having the amino group was deposited on the chemical conversion film made of at least one selected from the group consisting of zirconium, titanium and hafnium. . It is presumed that the adhesiveness can be improved when the obtained chemical conversion film has such a structure. The amino group is not particularly limited, and examples thereof include -NH ₂ group, monoalkylamino group, dialkylamino group, monohydroxyamino group, dihydroxyamino group, and other compounds having primary to tertiary amines. Can do.

  The reaction for introducing an amino group into the epoxy resin forming the skeleton is not particularly limited, and examples thereof include a usual method such as a method of mixing an epoxy resin and an amine compound in a solvent.

  As an example of the water-soluble epoxy compound having an amino group, commercially available products such as Adeka Resin EM-0436 series, Adeka Resin EM-0436F series, Adeka Resin EM0718 series (all manufactured by Asahi Denka Kogyo Co., Ltd.) can be used.

  The water-soluble epoxy compound may have a phosphorus element. The phosphorus element is preferably contained in the water-soluble epoxy compound as a phosphate group. The phosphate group may be partially alkylated. The phosphate ester group can be introduced into the epoxy compound by a reaction between the epoxy group and a phosphate compound.

The film formed by the chemical conversion treatment agent used in the present invention has curability. That is, by containing a component that causes a curing reaction after film formation, the physical properties of the coating film are improved, and an organic film layer having excellent adhesion and corrosion resistance is formed.
In this invention, sclerosis | hardenability can be given to the film | membrane obtained by including the water-soluble epoxy compound which has an isocyanate group as said water-soluble epoxy compound. A cross-linking reaction occurs due to the isocyanate group in the water-soluble epoxy compound, and a cured film can be formed.

  The said isocyanate group can be introduce | transduced in a water-soluble epoxy compound, for example by making the half block diisocyanate compound blocked with the blocking agent react with a water-soluble epoxy compound.

  The said half block diisocyanate compound can be obtained by making a diisocyanate compound and a blocking agent react in the ratio in which an isocyanate group becomes excess.

  The polyisocyanate compound is not particularly limited. For example, aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4,4′-methylenebis ( And cycloaliphatic polyisocyanates such as cyclohexyl isocyanate), aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate.

  The blocking agent is not particularly limited, and examples thereof include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol. Cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono 2-ethylhexyl ether; phenols such as phenol, para-t-butylphenol and cresol; dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, Examples include oximes such as cyclohexanone oxime; lactams represented by ε-caprolactam and γ-butyrolactam. Oxime and lactam blocking agents dissociate at low temperatures, and are more preferable from the viewpoint of resin curability.

  The synthesis of the half-block diisocyanate compound and the reaction between the half-block diisocyanate compound and the water-soluble epoxy compound are not particularly limited and can be performed by a known method.

  The chemical conversion treatment agent used in the present invention preferably contains the above water-soluble epoxy compound having an isocyanate group within the range of a lower limit of 5 mg / L and an upper limit of 5000 mg / L in terms of solid content concentration. When it is less than 5 mg / L, there is a possibility that proper post-coating performance may not be obtained in the resulting chemical conversion coating. On the other hand, when it exceeds 5000 mg / L, the chemical conversion film may not be formed efficiently. A more preferred lower limit is 30 mg / L, and a more preferred upper limit is 2000 mg / L.

  The chemical conversion treatment agent used in the present invention further contains at least one selected from the group consisting of zinc ions, magnesium ions, and aluminum ions (sometimes referred to as “metal ions (A)” in the present specification). It is preferable to do. By including these components, the substrate adhesion of the coating film can be further improved.

  The content of at least one metal ion (A) selected from the group consisting of zinc ions, magnesium ions and aluminum ions is such that the metal ion concentration contained in the chemical conversion treatment agent is a lower limit of 1 mg / L and an upper limit of 5000 mg / L. It is preferable to be within the range. If it is less than 1 mg / L, the corrosion resistance of the resulting chemical conversion film may be lowered, which is not preferable. If it exceeds 5000 mg / L, no further improvement of the effect is observed, which is economically disadvantageous, and the adhesion after coating may be reduced. The lower limit is more preferably 20 mg / L, and the upper limit is more preferably 2000 mg / L.

  The supply source of these metal ions (A) is not particularly limited, and for example, the metal ion (A) can be blended in the chemical conversion treatment agent as nitrate, sulfate, fluoride, or the like. Of these, nitrate is preferable because it does not adversely affect the chemical conversion reaction.

  In the chemical conversion treatment agent used in the present invention, the pH is preferably adjusted within the range of the lower limit of 1.5 and the upper limit of 6.5. If the pH is less than 1.5, the water-soluble epoxy compound is hardly precipitated, and thus the coating film adhesion may not be sufficiently improved. If the pH exceeds 6.5, the chemical conversion treatment reaction may not sufficiently proceed. The lower limit is more preferably 2.0, and even more preferably 2.5. The upper limit is preferably 5.5, and more preferably 5.0. Since the chemical conversion treatment agent used in the present invention may contain complex fluoride ions, nitrates, sulfates, fluoride salts, and the like as described above, in order to adjust the pH within the above range, an alkali is used. It is preferred to add the components. It does not specifically limit as an alkali component which can be used in order to adjust pH, Sodium hydroxide, potassium hydroxide, ammonia, an amine compound, etc. can be mentioned.

  The chemical conversion treatment agent used in the present invention is preferably substantially free of phosphate ions. The phrase “substantially free of phosphate ions” means that the phosphate ions are not contained so much as to act as a component in the chemical conversion treatment agent. Phosphoric acid generated when the zinc phosphate treating agent is used without substantially using phosphorous that causes environmental burden, if the chemical conversion treating agent is substantially free of phosphate ions. Generation of sludge such as iron and zinc phosphate can be suppressed. Furthermore, there is no environmental load due to phosphorus, which is a great advantage in terms of wastewater workability.

  The chemical conversion treatment step for applying the chemical conversion treatment agent used in the present invention to the surface to be coated of the automobile body is not particularly limited, and can be performed by bringing the chemical conversion treatment agent into contact with the surface to be coated. It does not specifically limit as a method to contact, For example, the dipping method, the spray method, the roll coat method etc. can be mentioned.

  In the said chemical conversion treatment process, it is preferable to carry out by adjusting the temperature of a chemical conversion treatment agent in the range of the minimum 20 degreeC and the upper limit 70 degreeC. By performing the reaction within such a temperature range, the chemical conversion treatment reaction can be performed efficiently. The lower limit is more preferably 30 ° C, and the upper limit is more preferably 50 ° C. The treatment time varies depending on the concentration of the chemical conversion treatment agent and the treatment temperature, but is preferably 20 to 300 seconds.

  In the said chemical conversion treatment process, it is preferable to perform a water washing process after apply | coating a chemical conversion treatment agent. This water washing treatment is performed once or more so as not to adversely affect the adhesion, corrosion resistance, and the like after the subsequent various coatings. In this case, it is appropriate that the final water washing is performed with pure water. In this water washing treatment, either spray water washing or immersion water washing may be used, and these methods may be combined for water washing. Moreover, since the chemical conversion treatment using the chemical conversion treatment agent used in the present invention does not need to be subjected to a surface conditioning treatment or the like, it is excellent in terms of workability.

  In the chemical conversion treatment step of the present invention, it is not always necessary to dry after the water washing treatment. Even if the chemical conversion coating is applied in a wet state without performing a drying step, the obtained performance is not affected. Moreover, when performing a drying process, it is preferable to perform cold air drying, hot air drying, etc. When performing hot air drying, in order to prevent decomposition | disassembly of organic content, 300 degrees C or less is preferable.

The chemical conversion treatment film obtained by the chemical conversion treatment agent used in the present invention has a lower limit of 0.1 mg / m ² and an upper limit of 500 mg / m ² in terms of the total amount of the total amount of metal and the amount of carbon contained in the epoxy compound. Preferably there is. If it is less than 0.1 mg / m ² , a uniform chemical conversion coating cannot be obtained, which is not preferable. If it exceeds 500 mg / m ² , it is economically disadvantageous. The lower limit is more preferably 5 mg / m ² , and the upper limit is more preferably 200 mg / m ² .

<Primer surfacer coating film formation process>
The primer surfacer coating film forming step applied to the method for forming a coating film of an aluminum automobile body of the present invention is carried out by applying the primer surfacer by spray coating or roll coating, and the primer surfacer coating film formed is preferably 120 to 180 ° C., 15 to 15 ° C. This is a step of baking and drying for 60 minutes. As for the dry film thickness of the said primer surfacer coating film, 20-100 micrometers is preferable. If it is less than 20 μm, it is difficult to conceal the base, and if it exceeds 100 μm, there is a risk of poor appearance of the coating.

[Primer surfacer]
The primer surfacer used in the method for forming a coating film for an aluminum automobile body according to the present invention is, as a vehicle, 40 to 80 parts by mass of a polyester resin, 10 to 50 parts by mass of a melamine resin, and 5 to 30 parts by mass in terms of solid content in the vehicle. Part of an epi-bis type epoxy resin, a pigment containing a flat pigment, a rust preventive pigment, a colored pigment excluding these pigments, and an extender pigment in a solid content mass ratio of vehicle / pigment of 30 / 70-80 / 20 is there.

  If the polyester resin is less than 40 parts by mass in terms of solid content in the vehicle, the adhesion with the top coat film and the chipping resistance may be reduced, and if it exceeds 80 parts by mass, the curability is lowered and the aluminum substrate is reduced. There is a possibility that the adhesiveness with the lowering. If it is less than 10 parts by mass in terms of solid content in the vehicle of melamine resin, the curability may be lowered and the adhesion to the aluminum substrate may be reduced, and if it exceeds 50 parts by mass, the adhesion with the top coat film will be reduced. Chipping resistance may be reduced. If it is less than 5 parts by mass in terms of solid content in the vehicle of the epi-bis type epoxy resin, the adhesion to the aluminum substrate may be reduced, and if it exceeds 30 parts by mass, the coating appearance may be reduced.

  When the above flat pigment, rust preventive pigment, colored pigment excluding these, and extender pigment are in a mass ratio of the solid content of the vehicle and the pigment, preferably less than 30/70, the adhesion to the aluminum substrate is lowered and the coating appearance is lowered. If it exceeds 80/20, the base concealing property may be lowered.

  Preferably, the primer surfacer comprises, as a vehicle, 50 to 70 parts by mass of a polyester resin, 15 to 45 parts by mass of melamine resin, and 10 to 20 parts by mass of an epi-bis type epoxy resin in terms of solid content in the vehicle. The pigment contains a flat pigment, a rust preventive pigment, a colored pigment excluding these pigments, and an extender pigment in a solid content mass ratio of 40/60 to 70/30 between the vehicle and the pigment.

  The film-forming resin in the vehicle is a polyester resin and an epi-bis type epoxy resin. The polyester resin preferably has a number average molecular weight of 2000 to 4000, a hydroxyl value of 50 to 150, and an acid value of 5 to 20. is there. A preferred number average molecular weight of the epi-bis type epoxy resin is 3000 to 10,000. The unit of hydroxyl value and acid value is mgKOH / g.

  If the number average molecular weight of the polyester resin is less than 2,000, the coating film hardness may be lowered, and if it exceeds 4000, the coating appearance may be lowered. If the hydroxyl value is less than 50, the coating film hardness may be lowered and the crosslinking density may be insufficient, and if it exceeds 150, the coating appearance may be deteriorated. If the acid value is less than 5, the coating film hardness may be lowered and the crosslinking density may be insufficient, and if it exceeds 20, the coating appearance may be deteriorated. The number average molecular weight of the polyester resin is more preferably 2500 to 3500, the hydroxyl value is 70 to 120, and the acid value is 8 to 15. The number-average molecular weight of the epi-bis type epoxy resin is more preferably 3500 to 6000. If the number average molecular weight of the epi-bis type epoxy resin is less than 3000, the adhesion to the aluminum substrate may be lowered, and if it exceeds 10,000, the coating appearance may be lowered.

  As the polyester resin, a resin that is a condensation product of a polyhydric alcohol and a polycarboxylic acid is used. It also includes alkyd resins obtained by adding components that provide fatty acid residues derived from natural or semi-dry oils. These resins contain a proportion of free hydroxyl and / or carboxyl groups that are available for reaction with conventional crosslinking agents.

  Polyhydric alcohols suitable for the production of the polyester resin include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol. Including trit, tripentaerythritol, hexanetriol, and condensation products of trimethylolpropane with ethylene oxide or propylene oxide.

Polycarboxylic acids suitable for the production of polyester resins are succinic acid (or its anhydride), adipic acid, azelaic acid, sebacic acid, maleic acid (or its anhydride), fumaric acid, muconic acid, itaconic acid, phthalic acid (Or its anhydride), isophthalic acid, terephthalic acid, trimellitic acid (or its anhydride), and pyromellitic acid (or its anhydride). Fatty acids derived from flaxseed oil, soybean oil, tall oil, dehydrated castor oil, fish oil, and tung oil as derived from natural or semi-drying oils Fatty acids derived from safflower oil, sunflower oil, and cottonseed oil Include. Usually, it is preferable that the oil length of such an alkyd resin does not exceed 50%. A monofunctional saturated carboxylic acid can be further blended for the purpose of imparting plasticity to the polyester. Examples of such acids may include saturated aliphatic acids C ₄ -C _20, benzoic acid, p- tert-butyl benzoic acid, and abietic acid.

  As said epi-bis type | mold epoxy resin, what has at least 2 or more epoxy group in 1 molecule is used suitably, Specifically, resin etc. which are obtained by reaction of bisphenol and epichlorohydrin are mentioned. Examples of bisphenol include bisphenol A and F. Examples of the epi-bis type epoxy resin include Epicoat 1007 and Epicoat 1009 (both are trade names, manufactured by Shell Chemical Co., Ltd.), and these are chained using a chain extender such as diol, dicarboxylic acid, or diamine. Extended ones can also be used. For example, an epibisepoxy resin, which is obtained by extending the chain with a diol, dicarboxylic acid, diamine or the like can be used. By using the epi-bis type epoxy resin, the corrosion resistance and the adhesion with the aluminum substrate can be improved.

  The melamine resin is more preferably a methylated melamine resin etherified with a methyl group alone, a n-butyl group or i-butyl group, and a methyl / butyl mixed etherified melamine resin etherified with a methyl group. By using a methylated melamine resin or a methyl / butyl mixed etherified melamine resin, it is possible to improve the base concealing property by controlling the coating film shrinkage.

  As the pigment, flat pigments, rust preventive pigments, colored pigments excluding these, and extender pigments are used.

  The flat pigment is preferably at least one selected from the group consisting of aluminum flake pigments having an average particle diameter of 5 to 25 μm, talc and clay. If these average particle diameters are less than 5 μm, there is a fear that the concealment improvement of the base roughness will be insufficient, and if it exceeds 25 μm, the appearance of the coating film may be insufficient. The flat pigment is preferably 0.1 to 3.5% by mass in the total pigment. By using a flat pigment, it is possible to improve the hiding of the surface roughness. If the above flat pigment is less than 0.1% by mass in the total pigment, there is a fear that the concealment improvement of the base roughness will be insufficient, and if it exceeds 3.5% by mass, the coating film appearance may be insufficient. .

  The rust preventive pigment is preferably at least one selected from the group consisting of zinc phosphate, calcium phosphate, aluminum phosphate, zinc phosphite, calcium phosphite and aluminum phosphite, and the rust preventive pigment is preferably It is 0.1-10 mass% in all the pigments. Use anti-corrosion pigments. By using this, the corrosion resistance can be further improved. If the rust preventive pigment is less than 0.1% by mass in the total pigment, the corrosion resistance may be insufficiently improved, and if it exceeds 10% by mass, the coating film appearance may be insufficient.

  Examples of the colored pigment include organic pigments such as azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments, Examples thereof include inorganic pigments such as yellow lead, yellow iron oxide, red iron oxide, titanium dioxide, and carbon black.

  Examples of the extender pigment include barium sulfate, barium carbonate, calcium carbonate, magnesium carbonate, and silica.

  The primer surfacer used in the present invention may further contain an organic bentonite, preferably 0.1 to 1% by mass, more preferably 0.3 to 0.7% by mass, based on the solid content of the paint. If the content of the organic bentonite is less than 0.1% by mass, the base concealing property may be lowered, and if it exceeds 1% by mass, the coating appearance and gloss may be lowered. More preferably, it is 0.3-0.7 mass%. By using the organic bentonite, the underlying concealment can be improved by controlling the viscoelasticity of the coating film.

The primer surfacer used in the present invention may further contain 0.3 to 2.5% by mass of crosslinkable resin particles based on the solid content of the paint. If the crosslinkable resin particles are less than 0.3% by mass, the base concealing property may be lowered, and if it exceeds 2.5% by mass, the effect commensurate with the addition may be insufficient. As the crosslinkable resin particles, for example, emulsification of alkyd resin or polyester resin synthesized by using a monomer having a zwitterionic group in the molecule described in JP-A-58-129066 as one of polyhydric alcohol components. Those obtained by emulsion polymerization of an ethylenically unsaturated monomer in an aqueous medium in the presence of a resin having a function and a polymerization initiator are preferred. As the monomer having a zwitterionic group of the in the molecule, -N (+) - R- COO (-) or -N (+) - R-SO 3 (-) shown as (R is alkylene or a phenylene group C ₁ -C _6, which may have a substituent group), further, may be preferably used those having two or more hydroxyl groups in one molecule. As such a monomer, a hydroxyl group-containing aminosulfonic acid type zwitterionic compound is preferable in terms of resin synthesis.

  The resin having a zwitterionic group having emulsifying ability synthesized in the above monomer in the molecule has an acid value of 30 to 150 mg KOH / g, preferably 40 to 150 mg, KOH / g, number average molecular weight. It is good to use the polyester resin of 500-5000, Preferably it is 700-3000. If the upper limit is exceeded, the handling properties of the resin may be reduced, and if it is less than the lower limit, the resin having emulsifying ability may be detached or the solvent resistance may be reduced when a coating film is formed. Moreover, the ethylenically unsaturated monomer that is emulsion-polymerized in the synthesis of the crosslinkable resin particles is a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule. Such a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule is preferably contained in the range of 0.1 to 10% by mass in the total monomers. This amount is selected to such an extent that sufficient crosslinking is provided so that the particulate polymer does not dissolve in the solvent.

  The crosslinkable resin particles generally do not contain a low molecular emulsifier or protective colloid contained in an emulsion resin, and copolymerize monomers having two or more radically polymerizable ethylenically unsaturated groups in the molecule. Therefore, cross-linkable resin particles having water resistance, solvent resistance, gloss and the like that are insoluble in organic solvents and having an average particle size of 0.02 to 0.5 μm are preferable. By using the crosslinkable resin particles, the underlying concealment can be improved by controlling the viscoelasticity of the coating film.

  The primer surfacer can have an effect of suppressing the occurrence of repelling by adding a curing catalyst as necessary. Examples of the curing catalyst include metaphosphoric acid, orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, phosphoric acid, trimetaphosphoric acid, triphosphoric acid, tetrametaphosphoric acid, phosphorous acid, monobutyl phosphoric acid, monoethylhexyl phosphoric acid, monolauryl phosphoric acid, Examples thereof include at least one selected from phenyl acid phosphate, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, toluenesulfonic acid, nonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. More preferred is monolauryl phosphoric acid, dodecylbenzenesulfonic acid, toluenesulfonic acid, dinonylnaphthalene disulfonic acid, or dinonylnaphthalenesulfonic acid.

  In addition to the above components as additives, the primer surfacer includes an anti-settling agent and an ultraviolet absorber that are a polyamide wax which is a lubricating dispersion of an aliphatic amide and a polyethylene wax which is a colloidal dispersion mainly composed of polyethylene oxide. Antioxidants, leveling agents, surface conditioners such as silicone and organic polymers, sagging inhibitors, thickeners, antifoaming agents, lubricants and the like can be added as appropriate. These additives can improve the performance of paints and coating films by blending them at a ratio of 15 parts by mass or less with respect to 100 parts by mass of the total solid content of the resin and the crosslinking agent. .

  The above-mentioned primer surfacer is usually provided with the above-described components dissolved or dispersed in a solvent. Any solvent can be used as long as it dissolves or disperses the vehicle, and an organic solvent and / or water can be used. Examples of the organic solvent include those usually used in the paint field. Examples thereof include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, cellosolve acetate and butyl cellosolve, alcohols and the like. Water is preferably used when the use of organic solvents is restricted from an environmental point of view. In this case, an appropriate amount of a hydrophilic organic solvent may be contained.

<Top coat formation process>
The top coat film forming step applied to the coating film forming method for an aluminum automobile body of the present invention includes a top coat solid paint containing a color pigment as a top coat, or a top coat base paint containing a glitter pigment and / or a color pigment. This is a step of forming a top coat film using a transparent top coat top clear paint to be formed on the top coat base film formed by this top coat base paint.

  Formation of the above-mentioned top coat solid coat or top coat base coat is performed by spray coating or roll coating, but when the top coat film formed is baked and dried, it is preferably 120 to 180 ° C., 20 to 30 minutes, Bake and dry.

  As for the dry film thickness of the said top coat solid coating film, 20-100 micrometers is preferable. As for the dry film thickness of the said top coat base coating film, 10-100 micrometers is preferable. The dry film thickness of the top-coated top clear coating film is preferably 20 to 100 μm. When the preferable lower limit is less than 10 or 20 μm, it is difficult to conceal the base, and when it exceeds 100 μm, there is a possibility that poor appearance of the coating may occur. A top coat film is formed on the outer surface of the exterior member of the vehicle body, coating of the vehicle body is completed, and then the process proceeds to the outfitting process.

(Top coat)
The above topcoat paint is composed of at least one thermosetting resin selected from an acrylic resin, a polyester resin, a fluororesin, an epoxy resin, a polyurethane resin, a polyether resin, and a modified resin thereof, and various crosslinks. Various pigments, solvents, and additives such as modifiers, ultraviolet absorbers, leveling agents, dispersants, antifoaming agents, and the like can be blended with the mixture of the agent. Various additives can be used. However, the top-coated top clear paint contains no pigment, or even if it contains a pigment in an amount that does not impair the transparency. In these resins, the resin system may be any of organic solvent type, aqueous type and powder type.

  As the top coat, a top coat solid paint containing a color pigment, or a top coat base paint containing a glitter pigment and / or a color pigment, and a top coat top clear having transparency formed on a coating film formed by the top coat base paint Use paint.

  In addition, as a top-coated top clear coating, a coating containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in JP-B-8-19315 is a top-coated base coating film containing a pigment in a measure against acid rain and wet on wet. It is preferably used from the viewpoint of not disturbing the orientation of the glittering pigment when coated on the surface.

[Multi-layer coating film]
A multilayer coating film is formed on the vehicle body that is the object to be coated by the above-described aluminum vehicle body coating film forming method.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited only to these Examples.

Example 1
1. Degrease treatment Cu content 0.1% or less aluminum alloy base material (JIS A 6022 alloy equivalent), degreasing agent "Surf Cleaner SD280A" (manufactured by Nippon Paint) and "Surf Cleaner SD280B" (manufactured by Nippon Paint) And then degreased by immersing it in a mixture (water concentration A of 1.5% by mass, B adjusted to 0.75% by mass, pH of about 11) at 42 ° C. for 2 minutes, and then using tap water at room temperature. Washed with water for 2 seconds.

2. Chemical treatment
2-1. Preparation of chemical conversion treatment agent
2-1 (a) Production of amino group-containing water-soluble epoxy compound To 190 parts by mass of bisphenol F epichlorohydrin type epoxy compound having an epoxy equivalent of 190, 30 parts of diethanolamine and 110 parts of cellosolve acetate were added and reacted at 100 ° C. for 2 hours, and non-volatile A 70% amino group-containing water-soluble epoxy compound was obtained.

2-1 (b) Production of partially blocked polyisocyanate 100 parts of trimethylolpropane 2,4-toluene diisocyanate precopolymer with 13.3% NCO and 75% non-volatile content, 44 parts nonylphenol, 5 parts dimethylbenzylamine Then, 65 parts of cellosolve acetate were mixed and stirred and reacted at 80 ° C. for 3 hours under nitrogen to obtain a partially blocked polyisocyanate having a nonvolatile content of 70% and an NCO% of 20%.

2-1 (c) Production of amino group-containing water-soluble epoxy compound having an isocyanate group 70 parts of the produced amino group-containing water-soluble epoxy compound and 30 parts of partially blocked polyisocyanate were mixed and stirred at 80 ° C. for 4 hours. After the reaction, it was confirmed by infrared spectroscopic analysis that the absorption of the NCO group was completely eliminated. Thereafter, 3 parts of acetic acid was mixed and further diluted with ion-exchanged water to obtain an amino group-containing water-soluble epoxy compound having an isocyanate group and having a nonvolatile content of 25% and a pH of 4.1.

2-2. Preparation of chemical conversion treatment agent and chemical conversion treatment A chemical conversion treatment agent having the composition shown in Table 6 was prepared. Here, zircon hydrofluoric acid was used as the complex fluoride. Chemical conversion treatment was performed by immersing the degreased aluminum base material in the chemical conversion treatment agent. The pH of the chemical conversion treatment agent, the time of immersion in the chemical conversion treatment agent (immersion time), and the temperature of the chemical conversion treatment agent are as described in Table 6. Moreover, nitric acid and sodium hydroxide were used for adjustment of the pH of the chemical conversion treatment agent. The treated aluminum substrate is pulled up from the chemical conversion treatment agent, left at 25 ° C. for 30 seconds, washed with tap water at 15 ° C. for 15 seconds, and further ion-exchanged water at 25 ° C. After spray water washing for 15 seconds, it was dried with hot air at 80 ° C. for 10 minutes.

3. Preparation of primer surfacer and coating surface formation primer surfacer (in the table, indicated as “prasaf”) were blended in the types and proportions shown in Table 1.

  Next, the primer surfacer was prepared by stirring and mixing together with an organic solvent (toluene / xylene / ethyl acetate / butyl acetate mass ratio = 70/15/10/5) with a stirrer so as to obtain an appropriate coating viscosity.

  The primer surfacer was coated on the aluminum base material subjected to chemical conversion treatment so that the dry film thickness was 50 μm, set at room temperature for 10 minutes, and baked at 140 ° C. for 30 minutes.

4). Topcoat formation then spray applied in an amount to provide a dry film thickness of 15μm to "Superlac M-80" (Nippon Paint Co., Ltd. acrylic-melamine resin-based metallic paint), and setting 5 minutes, then, "Superlac O −80 ”(acrylic / melamine resin-based top clear paint manufactured by Nippon Paint Co., Ltd.) was spray-applied in an amount to give a dry film thickness of 35 μm and set for 10 minutes. Thereafter, the coated plate was baked for 30 minutes at a temperature of 140 ° C. to obtain a multilayer coating film. This was a test piece.

Evaluation method and evaluation criteria About the obtained test piece, Zr adhesion amount (mg / m ² ), corrosion resistance (salt warm water resistance, yarn rust resistance, bare corrosion resistance), adhesion to aluminum alloy substrate (water adhesion resistance) Was evaluated by the following evaluation method. The results are shown in Table 6.

Measurement of Zr adhesion amount (mg / m ² ) : The amount of Zr contained in the obtained film was analyzed using “XRF1700” (fluorescence X-ray analyzer manufactured by Shimadzu Corporation).

Salt hot water resistance : The test piece was cross-cut, immersed in a 5% NaCl aqueous solution at 55 ° C. for 240 hours, and the swelling and peeling of the coating film were visually evaluated.

Yarn rust resistance : After cross-cutting a test piece, a salt spray test (5% NaCl aqueous solution, 35 ° C. continuous spray) is performed for 24 hours, and then a moisture resistance test (70% at 40 ° C.) is 240 hours. After the cycle, the swelling from the cut portion was visually evaluated.

Water-resistant adhesion : The test piece was immersed in warm water at 40 ° C. for 240 hours, cooled to room temperature, then subjected to a cross-cut adhesion test, and the degree of peeling was evaluated.

Naked corrosion resistance : Two years after exposure to Okinawa, the degree of corrosion was evaluated visually.

Example 2
Example 1 except that an aluminum alloy base material having a Cu content of 0.7 to 1.0% (JIS A 6111 alloy equivalent) was used instead of the aluminum alloy base material having a Cu content of 0.1% or less. In the same manner, a multilayer coating film was formed. Table 6 shows the evaluation results.

Comparative Example 1
As shown in Table 6, the chemical conversion treatment agent does not contain an epoxy compound and a metal ion (A), and the pH of the chemical conversion treatment agent is changed as shown in Table 6 in the same manner as in Example 1. A multilayer coating was formed and evaluated. The evaluation results are shown in Table 6. The pH of the chemical conversion treatment agent was adjusted by adding nitric acid or aqueous ammonia.

Comparative Example 2
Instead of an aluminum alloy substrate having a Cu content of 0.1% or less, an aluminum alloy substrate having a Cu content of 0.7 to 1.0% is used, and as a chemical conversion treatment agent, as shown in Table 6 A multilayer coating film was formed and evaluated in the same manner as in Example 1 except that the epoxy compound and the metal ion (A) were not contained and the pH of the chemical conversion treatment agent was changed as shown in Table 6. The evaluation results are shown in Table 6. The pH of the chemical conversion treatment agent was adjusted by adding nitric acid or aqueous ammonia.

Comparative Example 3
As shown in Table 6, the chemical conversion treatment agent does not contain Zr ions, epoxy compounds, and metal ions (A). Instead, complex fluoride: 500 (mg / L), simple fluoride: 350 (mg / L L), Zn ion: 1000 (mg / L), Ni ion: 1000 (mg / L), Mn ion: 1300 (mg / L), PO ₄ ion: 20000 (mg / L), NO ₂ ion: 120 ( mg / L), containing NO ₃ ions: 4500 (mg / L) were used. Others are the same as in the first embodiment. In the coating film forming method, a surface treatment using titanium phosphate was performed before the chemical conversion treatment, and the pH and immersion time of the chemical conversion treatment agent were changed as shown in Table 6. The evaluation results are shown in Table 6. The pH of the chemical conversion treatment agent was adjusted by adding sodium hydroxide.

Note 1) The concentration of Zr ions is the concentration due to H ₂ ZrF ₆ .
As Note 2) complex fluorides, Examples 1 and 2 _H 2 ZrF ₆ In and Comparative Examples 1 and 2, were used _H 2 SiF ₆ in Comparative Example 3.
Note 3) NaHF ₂ was used as simple fluoride.
Note 4) The chemical conversion treatment agent of Comparative Example 3 has the following components:
Zn ion: 1000 (mg / L)
Ni ion: 1000 (mg / L)
Mn ion: 1300 (mg / L)
PO ₄ ion: 20000 (mg / L)
NO ₂ ion: 120 (mg / L)
NO ₃ ion: 4500 (mg / L)
Is included.

As is apparent from the results in Table 6, the present example is a method in which the coating process is simplified by omitting the electrodeposition coating process, the coating film forming method of the present invention, a chemical conversion treatment agent, and a primer surfacer. A coating film was formed, and a multilayer coating film having good corrosion resistance (salt warm water resistance, yarn rust resistance, bare corrosion resistance) and adhesion to an aluminum alloy substrate (water adhesion resistance) was obtained. And even when an aluminum substrate having a high Cu content was used as the “adherent”, a multilayer coating film having good properties was obtained. On the other hand, in the comparative example, when using an aluminum substrate having a high Cu content, a multilayer coating film having excellent effects as obtained in the above examples could not be obtained particularly remarkably.

Claims (10)

Degreasing the painted surface of an automobile body made of an aluminum substrate,
A chemical conversion treatment step of applying a chemical conversion treatment agent to the surface to be coated;
The vehicle contains 40 to 80 parts by mass of a polyester resin, 10 to 50 parts by mass of melamine resin, and 5 to 30 parts by mass of an epi-bis type epoxy resin in terms of solid content in the vehicle, and a flat pigment as a pigment , Anti-corrosion pigment, coloring pigment excluding these, and primer surfacer coating film forming step of applying and drying and curing primer surfacer containing 30/70 to 80/20 of solid matter mass ratio of vehicle and pigment, and top coating Applying and drying and curing the top coat film forming process,
Including a coating film forming method for an aluminum automobile body,
The chemical conversion treatment agent is a chemical conversion treatment agent containing at least one selected from the group consisting of zirconium, titanium, and hafnium, fluorine, and a water-soluble epoxy compound having an isocyanate group,
However, the content in at least one chemical conversion treatment agent selected from the group consisting of zirconium, titanium and hafnium is 20 to 10,000 mg / L,
The content of the water-soluble epoxy compound in the chemical conversion treatment agent is 5 to 5000 mg / L.
Coating method for aluminum automobile body.   The method of forming a coating film for an aluminum automobile body according to claim 1, wherein the chemical conversion treatment agent further contains at least one metal ion (A) selected from the group consisting of zinc ions, magnesium ions, and aluminum ions.   The coating film forming method for an aluminum automobile body according to claim 1 or 2, wherein the chemical conversion treatment agent in the chemical conversion treatment step has a pH of 1.5 to 6.5. The chemical conversion film obtained by a chemical conversion treatment process contains 0.1-500 mg / m < ² > of the total amount of the carbon contained in a metal and an epoxy compound, The coating film of the aluminum vehicle body in any one of Claims 1-3 Forming method.   5. The polyester resin has a number average molecular weight of 2000 to 4000, a hydroxyl value of 50 to 150, and an acid value of 5 to 20, and the epi-bis type epoxy resin has a number average molecular weight of 3000 to 10,000. The coating method of the aluminum vehicle body of description.   The method for forming a coating film on an aluminum automobile body according to any one of claims 1 to 5, wherein the melamine resin is a methylated melamine resin or a methyl / butyl mixed melamine resin.   The flat pigment is at least one selected from the group consisting of aluminum flake pigment, talc and clay having an average particle diameter of 5 to 25 μm, and the flat pigment is 0.1 to 3.5 mass in the total pigment. The method for forming a coating film on an aluminum automobile body according to any one of claims 1 to 6.   The rust preventive pigment is at least one selected from the group consisting of zinc, calcium or aluminum phosphates and phosphites, and the rust preventive pigment is 0.1 to 10% by mass in the total pigments, The coating film formation method of the aluminum vehicle body in any one of Claims 1-7.   The primer surfacer further comprises 0.1 to 1% by mass of organic bentonite based on the solid content of the paint, and 0.3 to 2.5% by mass of the crosslinkable resin particles based on the solid content of the paint. The method for forming a coating film on an aluminum automobile body according to any one of -8. The multilayer coating film formed by the coating-film formation method of the aluminum vehicle body in any one of Claims 1-9.