JP4527992B2 - 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 formed by press-molding a steel plate material or an aluminum alloy plate material to form inner members of the vehicle body such as floor panels and inner panels, and the obtained molded members are joined by welding or the like to form a chassis that is a vehicle body skeleton. To manufacture. Also, car body materials such as doors, roofs, fenders, bonnets, trunk lids, etc. are formed by press-molding steel plate materials and aluminum alloy plate materials, and the exterior members are joined to the chassis and painted to produce the car body.

  The above-mentioned coating processes include degreasing and cleaning processes, pre-coating processes such as chemical conversion after degreasing, and undercoating processes for the purpose of rust prevention by electrodeposition coating, etc., in order to improve the final appearance of the final topcoat The intermediate coating process is applied, and the top coating process is performed for the purpose of imparting aesthetics to the coating surface, weather resistance, chemical resistance, wear resistance and the like.

  The above-described conventional car body painting methods that have been generally used in the past require the above-mentioned processes, so the painting process includes the pretreatment process from the degreasing and cleaning process to the final topcoat. Becomes extremely large. Also, since the painting is carried out in a consistent line, the painting line becomes extremely long, and the rust prevention, undercoating, etc. use the electrodeposition coating method, so an immersion coating device is required and the equipment is large. This is disadvantageous in terms of equipment, and is disadvantageous in that the cost is high, such as maintenance of equipment and management man-hours.

  In order to simplify the painting of automobile bodies, focusing on pre-coated aluminum alloy plates, the painting process is aimed at simplifying the painting process by omitting the electrodeposition painting process, greatly reducing the number of painting steps, and facilitating painting work. Japanese Patent Laid-Open No. 2001-17915 (Patent Document 1) discloses that a pre-coated metal plate in which a coating containing a rust prevention layer and a lubricating component is formed on at least the outer surface of a metal plate is press-molded, and a bonnet, trunk lid, door , A process of manufacturing an exterior member constituting the outside of an automobile body such as a fender, and a pre-coated metal plate formed with a rust preventive layer containing a lubricating component on the surface of the metal plate, and then formed into a floor panel, an inner panel, etc. Forming a plurality of inner members constituting the inner side of an automobile body, and joining each of the inner members to manufacture a chassis of the vehicle; The timber was bonded to the chassis, then the intermediate coating on the surface of the exterior member, the vehicle body painting process of an automobile applying top coating successively is described.

  However, the method described in the above Japanese Patent Application Laid-Open No. 2001-17915 is formed by press-molding a pre-coated metal plate on which at least the outer surface of the metal plate is formed with a coating containing a rust-preventing layer and a lubricating component, and thereby forming a bonnet, trunk lid, door Since an exterior member constituting the outside of the automobile body such as a fender is used, there may be a problem in terms of weldability when each of the exterior members is joined to the chassis.

  In addition, automobile body made of aluminum material may be applied with extruded material, cast material, etc. made of aluminum material on the outer plate surface. Since the top coating material is applied, the rust prevention property of the application part such as a molding material or a casting material becomes a problem.

JP 2001-17915 A

  The object of the present invention is good coating appearance (underlying concealment property, coating film smoothness), corrosion resistance (salt warm water resistance, yarn rust resistance), adhesion to aluminum alloy material (water resistance adhesion), and electrodeposition coating. To provide a coating film forming method for an aluminum automobile body and a multilayer coating film formed by the coating film forming method for simplifying the coating process by omitting the process, greatly reducing the number of coating steps, and facilitating the painting work. It is.

  As a result of diligent research in view of the above-mentioned problems, the present inventors have degreased the surface to be coated of an automobile body made of an aluminum material, and then applied and dried a chemical conversion liquid mainly containing zirconium that does not contain phosphoric acid. Then, it was found that when a primer surfacer and a top coating material were applied and dried and cured thereon, a multilayer coating film excellent in rust resistance could be obtained. The reason for this is that zirconium is deposited on the surface to be coated by the chemical conversion treatment to form a zirconium coating, which suppresses excessive natural oxidation of the aluminum alloy material, and has a strong adhesion to the coating. It is conceivable to exhibit a function of suppressing the progress of corrosion to the interface between the aluminum alloy material and the coating film.

  However, when this method is actually performed, a high-performance coating film can be obtained at the beginning of coating, but as the number of treatments increases, the amount of zirconium deposited on the surface to be coated gradually decreases. A new problem was revealed that the rust prevention performance of the coating film was lowered.

  Therefore, the present invention uses a bath of a chemical conversion liquid mainly composed of zirconium that does not contain phosphoric acid, and when the chemical conversion treatment is performed by immersing the aluminum material in the bath, the performance of the coating film is increased by increasing the number of treatments. It is a direct object to provide a method for forming a multilayer coating film that does not decrease.

The present invention includes (1) a step of degreasing a painted surface of an automobile body made of an aluminum material;
(2) Using a bath of a chemical conversion liquid containing zirconium that does not contain phosphoric acid as a main component, containing aluminum ions, and having a fluorine ion source compound added thereto, the pH of the chemical conversion liquid, and addition to the chemical conversion liquid By controlling the mass ratio of the amount of fluorine formed and the amount of aluminum ions present in the chemical conversion liquid to the range shown in region A of FIG. A chemical conversion treatment step in which a chemical conversion liquid is applied and dried;
(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 top coating film forming step for applying and drying and curing the top coating material,
A method for forming a coating film on an aluminum automobile body including the above-described object is achieved.

  According to the method for forming a multilayer coating film of the present invention, when using a bath of a chemical conversion liquid mainly composed of zirconium that does not contain phosphoric acid and immersing an aluminum material in the chemical conversion treatment, The performance of the coating film does not deteriorate due to the increase of.

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

<Degreasing process>
The degreasing step applied to the method for forming a coating film of an aluminum automobile body according to 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, It is the process of processing by the spraying method of an aqueous solution or the dip immersion 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 hydrogen carbonate, sodium carbonate, potassium hydrogen carbonate, and potassium carbonate; caustic alkalis such as potassium hydroxide and sodium hydroxide, which can be used alone. Or two or more types are used together.

  Examples of the alkali silicate include alkali metal salts of orthosilicate such as orthosilicate sodium and potassium orthosilicate; alkali metal salts of metasilicate such as sodium metasilicate and potassium metasilicate; sesquisilicate such as sodium sesquisilicate and potassium sesquisilicate 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 step applied to the method of forming a coating film for an aluminum automobile body of the present invention is carried out by washing with water by spraying or dip dipping for 15 seconds to 5 minutes at room temperature after the degreasing treatment, and if necessary, titanium phosphate-based In this step, the surface is adjusted and then a chemical conversion treatment is performed using a chemical conversion liquid mainly containing zirconium not containing phosphoric acid. In the chemical conversion treatment, a chemical conversion time of 15 seconds to 5 minutes is applied at a chemical conversion temperature of 40 to 55 ° C., and the chemical conversion solution is applied to the surface to be coated of an automobile body made of an aluminum material and dried by a spraying method or a dip dipping method. .

  The chemical conversion liquid used for the coating film forming method for an aluminum automobile body of the present invention is mainly composed of zirconium not containing phosphoric acid.

Chemical conversion liquid mainly composed of zirconium not containing phosphoric acid:
Zr ion: 50 to 200 mg / L, preferably 80 to 120 mg / L,
F ion: 50-1500 mg / L, preferably 100-140 mg / L,
pH: 2.5-4.5, preferably 2.5-3.5
Zr ion source: ammonium zirconate, zircon hydrofluoric acid, zircon nitrate, etc.
F ion source: borofluoride, silicofluoride, etc. as complex fluoride, hydrofluoric acid, potassium fluoride, sodium fluoride, ammonium fluoride, potassium acid fluoride, sodium acid fluoride, acid fluoride as simple fluoride Ammonium etc.

  When the chemical solution excessively sprayed in the spraying method is collected and reused many times, or when the number of immersion of the aluminum material is increased in the dip dipping method, aluminum ions are eluted and accumulated in the chemical conversion solution.

で表される。 The precipitation reaction of zirconium ions on the aluminum material surface is

It is represented by

  When aluminum ions are present in the chemical conversion liquid, they react with fluorine ions. As a result, the fluorine ion concentration in the bath of the chemical conversion solution necessary for the reaction between the zirconium ions and the aluminum material is reduced, so that the precipitation reaction of zirconium ions on the aluminum material surface is inhibited.

  In particular, when the concentration of aluminum ions in the chemical conversion solution exceeds 50 mg / L, the amount of zirconium deposited on the surface to be coated, particularly the ground surface, decreases, the corrosion resistance of the aluminum substrate decreases, and the corrosion resistance as a coating film also decreases. Therefore, the amount of aluminum ions contained in the chemical conversion solution in the bath needs to be kept at a low concentration, particularly 50 mg / L or less.

  In order to prevent aluminum ions from accumulating in the chemical bath even when the aluminum material is immersed, there is a method of supplying a certain amount of chemical liquid to the chemical bath and causing it to overflow, or periodically updating the chemical liquid. Conceivable. However, if the chemical liquid is frequently discharged out of the system, the load required for wastewater treatment increases, adversely affects the environment, and the coating cost increases.

  On the other hand, in order to deposit zirconium on the surface to be coated, it is only necessary to promote the precipitation reaction of zirconium ions on the surface of the aluminum material. Therefore, it is effective to add a fluorine ion supply source to the chemical conversion liquid. . However, if fluorine ions are present excessively, the aluminum material is excessively etched and the formation of the zirconium film is hindered. Moreover, the fluorine compound is formed on the surface to be coated, and the corrosion resistance of the aluminum material is lowered. Therefore, the fluorine ion supply source needs to be added so as to supplement the amount of fluorine ions consumed in the reaction with aluminum ions in consideration of the amount of aluminum ions accumulated in the chemical conversion liquid.

  Then, since the amount of fluorine ions necessary for the adhesion reaction of zirconium is ensured, even when aluminum ions are accumulated in the chemical conversion liquid, a normal zirconium film is formed on the surface to be coated of the aluminum material. .

  In the method of the present invention, in the chemical conversion treatment step, a chemical conversion liquid containing zirconium containing no phosphoric acid as a main component, containing aluminum ions, and having a fluorine ion source compound added thereto is used. The amount of the fluorine ion source compound is such that the mass ratio of the amount of fluorine added to the chemical conversion solution and the amount of aluminum ions present in the chemical conversion solution (shown as “F / Al ratio”) is 1. Adjust to the range of 5-2.5.

The fluoride ion source compound may be a simple fluoride that releases fluoride ions in water. Examples of such simple fluorides include HF, NaF, KF, NH ₄ F, NaHF ₂ , KHF ₂ , NH ₅ F _{2 and the} like. The amount of aluminum ions present in the chemical conversion liquid is determined by calculating the aluminum ion equilibrium concentration from the amount of the aluminum alloy raw material dissolved in the bath of the chemical conversion liquid and the substitution amount of the chemical conversion liquid by the vehicle body.

  If the F / Al ratio is less than 1.5, the amount of fluorine ions necessary for the zirconium precipitation reaction becomes insufficient, and there is a possibility that the film is not formed normally. When the F / Al ratio exceeds 2.5, the amount of fluorine ions becomes excessive, so that the aluminum material is excessively etched and the formation of the zirconium film is inhibited. Moreover, the fluorine compound is formed on the surface to be coated, and the corrosion resistance of the aluminum material is lowered.

  In the method of the present invention, the pH of the chemical conversion solution is adjusted to a range of 3.0 to 4.5, preferably 3.5 to 4.3 during the chemical conversion treatment. If the pH of the chemical conversion solution is less than 3.0, the pH does not rise sufficiently in the vicinity of the surface to be coated, so that zirconium is difficult to precipitate and adhere, and there is a possibility that the film is not normally formed. If the pH of the chemical conversion solution exceeds 4.5, the deposition of zirconium may be excessive and the coating may not be formed normally. The pH of the chemical conversion solution is adjusted with hydrofluoric acid, silicohydrofluoric acid, borofluoric acid, sodium acid fluoride, potassium acid fluoride, ammonium acid fluoride, nitric acid, sulfuric acid, hydrochloric acid, sodium bicarbonate, potassium bicarbonate, Sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, aqueous ammonia or the like may be added.

  More preferably, both the pH of the chemical conversion liquid and the F / Al ratio are controlled within the range indicated by the shaded area A in the graph of FIG. In this graph, the conditions of pH and F / Al ratio indicated by black dots are tested in Reference Examples, Examples and Comparative Examples.

<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 performed by spray coating or roll coating of the primer surfacer, and the formed primer surfacer coating film is preferably 120 to 180 ° C., 15 It 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 material 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 an aluminum flake pigment, talc or clay having an average particle diameter of 5 to 25 μm. If the average particle diameter is less than 5 μm, there is a fear that the concealment improvement of the base roughness may be insufficient, and it exceeds 25 μm. There is a fear that the coating film appearance is 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 zinc phosphate, calcium phosphate, aluminum phosphate, zinc phosphite, calcium phosphite, or aluminum phosphite, and the rust preventive pigment is preferably 0.1% of all pigments. -10 mass%. By using a rust preventive pigment, corrosion resistance can be 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.

  Further, as the colored pigment, organic pigments such as azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, etc. Inorganic pigments such as yellow lead, yellow iron oxide, bengara, titanium dioxide, and carbon black.

  Further, the extender pigment preferably includes barium sulfate, barium carbonate, calcium carbonate, magnesium carbonate, silica and the like.

  Further, the organic bentonite is preferably 0.1 to 1% by mass with respect to the solid content of the paint, and if the organic bentonite content is less than 0.1% by mass, the base concealing property may be lowered. The paint appearance and gloss may be reduced. 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.

Furthermore, the crosslinkable resin particles are preferably contained in an amount of 0.3 to 2.5% by mass 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 resin handling properties will be reduced, and if the lower limit is not reached, the resin having emulsifying ability will be detached or the solvent resistance will be reduced if 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, phenyl acid phosphate, methane Examples thereof include at least one selected from sulfonic 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]
The multilayer coating film of the present invention is formed by the above-described method for forming a coating film for an aluminum automobile body.

  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.

Reference example 1
(Degreasing treatment)
Degreased "Surf Cleaner SD280A" (made by Nippon Paint Co., Ltd.) using aluminum material cut out of aluminum alloy (JIS A 6022 alloy equivalent) with car body exterior member joined to chassis with car body inner member joined ) And “Surf Cleaner SD280B” (manufactured by Nippon Paint Co., Ltd.) (water concentration A is adjusted to 1.5 mass%, B is adjusted to 0.75 mass%, pH is about 11) at 42 ° C. for 2 minutes. Degreased and then washed with water for 15 seconds at room temperature using tap water.

(Chemical conversion treatment)
Subsequently, the chemical conversion liquid containing the components shown in Table 1 in water was filled in a container to obtain a chemical conversion bath. In Table 1, zircon hydrofluoric acid was used as the complex fluoride. The bath temperature was adjusted to 40 ° C., and an aluminum material was immersed here for 90 seconds. After pulling up the aluminum material from the chemical bath, leave it at 25 ° C. for 30 seconds, use tap water, wash with spray water at 25 ° C. for 15 seconds, use ion-exchanged water, and wash with spray water at 25 ° C. for 15 seconds. And dried with hot air at 80 ° C. for 10 minutes.

(Adjustment of primer surfacer)
Primer surfacer (in the table, indicated as “Plasaf”) was blended in the types and proportions shown in Table 2.

  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.

(Formation of multilayer coating)
The primer surfacer was coated on the aluminum material subjected to the 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. Next, “Super Lac M-80” (acrylic / melamine resin-based metallic paint manufactured by Nippon Paint Co., Ltd.) was spray-applied in an amount to a dry film thickness of 15 μm, set for 5 minutes, and then “Super Lac 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 at a temperature of 140 ° C. for 30 minutes to obtain a test piece.

(Evaluation method and evaluation criteria)
Evaluation of coating appearance (undercoating concealment, smoothness of coating film), corrosion resistance (salt warm water resistance, yarn rust resistance), and adhesion to aluminum alloy material (water resistance adhesion) using the following evaluation methods. The results are shown in Table 6.

  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.

Example 1
Aluminum nitrate was added to the chemical conversion solution shown in Table 1 to adjust the aluminum ion concentration in the bath to 500 ppm. This is for reproducing the state in which the number of immersion of the aluminum material is increased in the dip dipping method and aluminum ions are accumulated in the chemical conversion liquid. Thereafter, hydrofluoric acid was added to the chemical conversion solution in an amount of 790 mg / L. As a result, the F / Al ratio was 1.50. A multilayer coating film was formed and evaluated in the same manner as in Reference Example 1 except that the chemical conversion liquid thus obtained was used. The evaluation results are shown in Table 6.

Examples 2-6 and Comparative Examples 1-5
A multilayer coating film was formed and evaluated in the same manner as in Reference Example 1 except that the amount of fluorine ions in the simple fluoride to be added and the pH of the chemical conversion solution were changed as shown in Tables 6 and 7. The evaluation results are shown in Tables 6 and 7. At this time, zircon hydrofluoric acid was used as the complex fluoride, and hydrofluoric acid was used as the simple fluoride, and the pH was adjusted by adding nitric acid or aqueous ammonia.

  As is apparent from the results of Tables 6 and 7, this example is a coating film formation method for an aluminum automobile body of the present invention, a chemical conversion solution, and a multilayer coating film formed by a primer surfacer. A multilayer coating film having good concealability, coating film smoothness), corrosion resistance (salt warm water resistance, yarn rust resistance), and adhesion to an aluminum alloy material (water adhesion resistance) was obtained. On the other hand, in the comparative example, the multilayer coating film as obtained in the above example was not obtained.

It is the graph which showed the range of the conditions of preferable pH and F / Al ratio for performing the method of this invention.

Explanation of symbols

A: Preferred condition region.

Claims (7)

(1) A process of degreasing a painted surface of an automobile body made of an aluminum material;
(2) Using a chemical conversion bath containing a zirconium ion, an aluminum ion, and an F ion and containing a fluorine ion source compound in addition to a phosphoric acid-containing chemical conversion solution and having an F ion concentration of 50 to 1500 mg / L. And the mass ratio of the pH of the chemical conversion liquid and the amount of fluorine released as F ions and the amount of aluminum ions present in the chemical conversion liquid when the fluorine ion source compound is added to the chemical conversion liquid. Is controlled to the range shown in the region A of FIG. 1, and by performing a dip dipping method, a chemical conversion treatment step of applying and drying a chemical conversion liquid on the surface to be coated,
(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 top coating film forming step for applying and drying and curing the top coating material,
A method for forming a coating film on an aluminum automobile body including   The number average molecular weight of the polyester resin is 2000 to 4000, the hydroxyl value is 50 to 150, the acid value is 5 to 20, and the number average molecular weight of the epi-bis type epoxy resin is 3000 to 10,000. Coating method for aluminum automobile body.   The method for forming a coating film on an aluminum automobile body according to claim 1 or 2, wherein the melamine resin is a methylated melamine resin or a methyl / butyl mixed melamine resin.   The flat pigment is an aluminum flake pigment, talc or clay having an average particle diameter of 5 to 25 µm, and the flat pigment is 0.1 to 3.5% by mass in the total pigment. A method for forming a coating film on an aluminum automobile body according to claim 1.   The said rust preventive pigment is zinc, calcium or aluminum phosphate or phosphite, and the said rust preventive pigment is 0.1 to 10% by mass in the total pigment. Coating method for aluminum automobile body.   The primer surfacer further contains 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. 5. A method for forming a coating film on an aluminum automobile body according to any one of 5 to 5.   The multilayer coating film formed by the coating-film formation method of the aluminum vehicle body of any one of Claim 1 to 6.

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