Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/16—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies using synthetic lacquers or varnishes

Definitions

• the present invention relates to a method of coating a metal assembly including at least one aluminum member and other metal members such as steel parts, particularly to a method of coating assembled metal members for automobile bodies etc.
• Jitsumu Hyomen Gijutsu (Metal Finishing Practice) Vol. 35, No. 1, 1988 discloses a method of coating assembled members consisting of aluminum parts and steel parts in which the aluminum parts and the steel parts are treated separately in their exclusive treatment lines and the treated aluminum parts and the steel parts are combined in a final stage.
• the exclusive lines are necessary for both of the aluminum parts and the steel parts, and the treated aluminum parts and the steel parts should be handled very carefully in assembling.
• painted parts may have slightly different finish colors.
• an object of the present invention is to provide a method of coating a metal assembly including at least one aluminum member in which the aluminum member and the other metal members such as steel parts can be treated simultaneously, thereby effectively coating the aluminum member for automobile bodies, etc.
• an aluminum member coated with a conductive primer is highly resistant to a treatment chemical solution which is necessary for chemically treating steel members, and that the aluminum member coated with a conductive primer can be easily stamped to provide deep-drawn products, etc. without using lubricating oils.
• the present invention is based on these findings.
• the method of coating a metal assembly including at least one aluminum member comprises the steps of applying a conductive primer to the aluminum member; combining the aluminum member with other metal members; and providing the resulting assembled members with chemical coatings and electrodeposition coatings.
• the method of coating a metal assembly including at least one aluminum member comprises the steps of applying a conductive primer to the aluminum member; stamping the aluminum member; combining the stamped aluminum member with other metal member; and then providing the resulting assembled members with an intermediate coat and/or a top coat.
• the method of coating a metal assembly including at least one aluminum member comprises the steps of applying a conductive primer to the aluminum member; combining the aluminum member with at least one second aluminum member; and providing the resulting assembled members with chemical coatings and electrodeposition coatings.
• the metal assembly to which the coating method of the present invention can be applied may be constituted by at least one aluminum member and at least one other metal member.
• a typical combination of aluminum members and other metal members are aluminum parts and steel parts (including zinc-plated steel parts). Accordingly, the present invention will be explained referring to aluminum parts and steel parts for simplicity.
• One combination is at least one aluminum parts and at least one Steel parts, and another combination is at least one first aluminum parts and at least one second aluminum parts.
• the first aluminum parts is coated with a conductive primer, while the second aluminum parts may not be coated with a conductive primer.
• a metal assembly of these plates are provided with chemical coatings and electrodeposition coatings, optionally followed by the formation of an intermediate coat and/or a top coat.
• Second aluminum parts which may not be coated with a conductive primer.
• the first aluminum parts After the first aluminum parts is stamped, they are assembled together and then provided with an intermediate coat and/or a top coat.
• plastic members are used for automobile bodies, electric appliances, etc.
• plastic members may be combined with aluminum parts and steel parts.
• the conductive primer which may be used in the present invention comprises:
• the solid content of the conductive primer is 10 to 50 weight %, which makes it possible to form a thin, uniform, conductive primer layer with excellent corrosion resistance, high conductivity in electrodeposition coating, etc., improved formability, and excellent adhesion to an electrodeposition coating layer., etc.
• binder resin (A) is a bisphenoltype epoxy resin soluble in an organic solvent and having a number average molecular weight of 300 to 100,000, which is excellent in water resistance, alkali resistance, and good adhesion to a substrate material as well as a top coat.
• examples are the epoxy resins represented by the formula:
• the number average molecular weight of the epoxy resin is less than 300, it is unable to get a high polymer when reacted with a polyisocyanate, making the resulting conductive primer layer deficient in anti-corrosive properties.
• it is more than 100,000 a cross-linking degree decreases, providing the resulting conductive primer layer with poor anti-corrosive properties.
• the above bisphenol-type epoxy resin (A) should be 30 weight % or more on a solid basis of the conductive primer layer, because, if otherwise, the resulting conductive primer layer is likely to be brittle and have poor adhesion after stamping.
• the hardener (B) used in the present invention is selected from the group consisting of polyisocyanates and blocked polyisocyanates.
• polyisocyanates examples include aliphatic or alicyclic diisocyanates including hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenyl methane diisocyanate and the like; aromatic diisocyanates including tolylene diisocyanate, diphenyl methane-4,4′-diisocyanate and the like; triisocyanates as adducts of 1 mol of trimethylol propane and 3 mol of either one of the above-­mentioned diisocyanates, trimers of hexamethylene diisocyanate, trimers of tolylene diisocyanate and the like.
• any of the above-­mentioned polyisocyanates blocked with blocking agents may be used.
• Such blocking agents must be compounds capable of reacting with an isocyanate group and forming addition products which are stable at a room temperature but dissociated at a high temperature encountered at a baking stage, thereby making the isocyanate group free.
• the blocking agents are lactam blocking agents such as ⁇ -­caprolactam, ⁇ -butyrolactam and the like; oxime blocking agents such as methyl ethyl ketoxime, cyclohexanone oxime and the like; alcohol blocking agents such as methanol, ethanol, isobutyl alcohol and the like; phenol blocking agents such as phenol, p-t-butyl phenol, cresol and the like; and ⁇ -diketone blocking agents as ethyl acetoacetate, methyl acetoacetate, acetyl acetoacetate, dimethyl malonate, diethyl malonate and the like.
• lactam blocking agents such as ⁇ -­caprolactam, ⁇ -butyrolactam and the like
• oxime blocking agents such as methyl ethyl ketoxime, cyclohexanone oxime and the like
• alcohol blocking agents such as methanol, ethanol, isobutyl alcohol and the like
• the above-mentioned hardener (B) is contained in the conductive primer in an amount of one-tenth to 2 times the weight of the epoxy resin (A) on a solid basis.
• the epoxy resin (A) and the hardener (B) react with each other at a relatively low baking temperature in a short period of time, for example, at a maximum temperature of about 100°C or more, preferably at 120°C to 200°C, in 5 to 60 seconds.
• the mixing ratio of (B)/(A) is less than 1/10, the cross-­linking reaction is insufficient, resulting in poor corrosion resistance of the conductive primer layer.
• the ratio (B)/(A) is more than 20/10, the conductive primer layer are provided with poor water resistance, alkali resistance and adhesion to an overlying coat.
• Particularly preferable mixing ratio of the hardener (B) to the epoxy resin (A) is such that NCO equivalent of the hardener (B)/OH equivalent of the epoxy resin (A) is within a range of 0.1/1 - 1.0/1. Under these conditions, excellent anti-corrosion properties can be achieved.
• the above-mentioned hardener (B) may be used together with a resol-type phenyl resin, if desired. This is especially effective in accelerating the film-forming reaction at a relatively low baking temperature, for example, at a maximum temperature of 100°C to 130°C.
• Particularly preferable resol-type phenol resins are the compounds of the formula: wherein n is an integer 0 to 4; W is -CH2- or -CH2-O-CH2-; R is CH3, H, or
• Such a resol-type phenol resin is preferably added in an amount up to 10 times the weight of the hardener (B) on a solid basis. If the weight ratio of the phenol resin/hardener (B) is more than 10/1, alkali resistance of the resulting conductive primer layer is likely to be lowered.
• fumed silica (C) having an average particle size of 0.1 to 100 milli- ⁇ m serves to provide the primer layer with electric conductivity, because ions can pass through pores generated by the fumed silica in the primer layer in the processes of chemical coating and electrodeposition coating. If the average particle size of the silica is less than 0.1 milli- ⁇ m, the conductive primer layer is insufficient not only in electric conductivity but also in adhesion to an overlying layer and alkali resistance. On the other hand, when the average particle size of the fumed silica exceeds 100 milli- ⁇ m, the corrosion resistance of the resulting conductive primer layer is lowered.
• the fumed silica (C) is 5 to 50 weight %, preferably 15 to 30 weight %, on a solid basis of the conductive primer.
• fumed silica (D) is 5 to 50 weight %, preferably 15 to 30 weight %, on a solid basis of the conductive primer.
• the fumed silica (C) is less than 5 weight % on a solid basis of the conductive primer, the corrosion resistance of the resulting conductive primer layer becomes poor. On the other hand, if it exceeds 50 weight %, adhesion properties of the conductive primer layer after stamping tend to be undesirably decreased.
• the epoxy resin (A), the hardener (B) and the fumed silica (C) are dissolved or dispersed in a ketone solvent.
• the ketone solvent (D) should be 40 weight % or more to adjust the solid content of the conductive primer to 10 to 50 weight %.
• the solid content of the conductive primer is less than 10 weight %, it is uneconomical because too much solvent is consumed. On the other hand, if it exceeds 50 weight %, it is hardly possible to form a thin, uniform conductive primer layer.
• ketone solvents (D) are methyl isobutyl ketone, acetone, cyclohexanone, isophorone and the like. If desired, additional solvents other than the ketone solvent may be used together therewith. However, solvents reactive with polyisocyanates, e.g. water, alcohol and the like, should be avoided.
• the conductive primer may further contain 0.1 to 10 weight % based on the conductive primer, of such lubricants as polyolefins, carboxylates, metal carboxylates, polyalkylene glycols, molybdenum disulfide, silicone compounds, fluorinated compounds and the like.
• lubricants are polyethylene waxes having densities of 0.94 or more, molecular weights of 1,000 to 10,000 and acid values of 15 KOH mg/g or less.
• conductive material powder such as carbon black, graphite powder, zinc oxide powder, titanium oxide powder, aluminum powder, copper powder, etc. may be added in proper proportions.
• the conductive primer may further contain known anti-corrosive pigments (e.g. chromate pigments, especially zinc chromate, lead chromate and barium chromate, phosphate pigments, plumbate pigments and the like), extender pigments (e.g. carbonate pigments, silicate pigments and the like), coloring pigments (e.g. titanium oxide, carbon black and the like), anti-corrosive agents (e.g. amine compounds, phenolic carboxylic acids and the like), dispersion stabilizers and the like.
• anti-corrosive pigments e.g. chromate pigments, especially zinc chromate, lead chromate and barium chromate, phosphate pigments, plumbate pigments and the like
• extender pigments e.g. carbonate pigments, silicate pigments and the like
• coloring pigments e.g. titanium oxide, carbon black and the like
• anti-corrosive agents e.g. amine compounds, phenolic carboxylic acids and the like
• the conductive primer used in the present invention forms an organic coating layer which is electrically conductive for the purpose of the present invention.
• conductive used herein means that the aluminum parts coated with the conductive primer can be provided with chemical coatings and electrodeposition coatings, namely meaning that electric conductivity can be achieved through the conductive primer in the process of electrodeposition coating, etc. The reasons therefor may be considered that since the conductive primer layer is thin and porous, electrodeposition coating composition can be attracted to the aluminum parts via the conductive primer.
• the conductive primer provides the aluminum parts with excellent workability, thereby making it unnecessary to use lubricating oils. This is an outstanding advantage because the process of removing lubricating oils from the stamped aluminum parts can be omitted.
• the aluminum parts is coated with the conductive primer on one or both sides thereof, and then conveyed to an automobile body manufacturing line, etc., where the aluminum parts is stamped and combined with steel parts for subsequent treatments.
• the conductive primer may be applied to the assembled members by spraying, etc. and then baked.
• the conductive primer is usually applied to the aluminum parts in a dry film thickness of 10 ⁇ m or less.
• the dry film thickness exceeds 10 ⁇ m, the conductive primer shows high insulation, making it difficult to provide it with chemical coatings and electrodeposition coatings. Accordingly, the resulting coated aluminum parts has poor corrosion resistance, impact resistance and workability.
• the preferred dry film thickness of the conductive primer layer is 0.1-5 ⁇ m.
• the conductive primer-coated aluminum parts is vulnerable to erosion in a zinc phosphate treatment bath, permitting a large amount of aluminum to be dissolved into the zinc phosphate treatment bath.
• the aluminum parts tends to have cracks and strains.
• the more preferred dry film thickness of the conductive primer layer is 0.5-3 ⁇ m.
• the chemical coating can be conducted by using known coating chemicals.
• the preferred coating chemicals for the purpose of the present invention are zinc phosphate chemicals which contain zinc ion, phosphate ion, hydrochloric ion, nitrite ion, and, if necessary, nickel ion, nitrate ion, chlorine ion, etc. in proper proportions.
• a typical example of the coating chemicals consists essentially of about 0.4 to about 1 g/l of zinc, about 5 to about 40 g/l of phosphate, about 0.01 to about 0.2 g/l of nitrite and about 2 to about 5 g/l of chlorate.
• Such coating chemicals suitable as primers for forming electrodeposition coatings are exemplified in Japanese Patent Laid-­Open No. 55-145180.
• the coating chemicals may be applied to the aluminum parts and the Steel parts separately or in combination. It should be noted that the coating chemicals are not necessarily indispensable for the aluminum parts, but that the coating chemicals can provide the aluminum parts with better corrosion resistance.
• the precoated aluminum parts is not eroded by the chemical treatment bath so that substantially no aluminum sludge is formed in the bath.
• the electrodeposition coating composition may be either one of a cation type and an anion type which are known in the art.
• a uniform electrodeposition coating layer having a good appearance can be formed on the precoated aluminum parts and the chemically treated steel parts.
• an intermediate coat and/or a top coat can be formed on the assembled members thus treated.
• electrodeposition coating can be conducted, optionally followed by the formation of an intermediate coat and/or a top coat.
• oils, dusts, strains, etc. are attached to the conductive primer layers, it is preferable that they are removed by solvents, etc. before subsequent treatments.
• Preferred examples of the coating process according to the present invention are as follows:
• the steps (a-1), (a-2) may be conducted in aluminum-working lines, and the steps (b-1), (b-2) ... may be conducted in assembly lines of automobile bodies, etc.
• Example 1 The same coating process as in Example 1 is conducted except for changing the dry film thickness of NIPPE METALCOAT P19 CLEAR to 5 ⁇ m. Various properties are evaluated, and the results are shown in Table 1.
• Example 4-1 The same coating process is conducted as in Example 4-1 except for omitting the chemical coating process. Various properties are evaluated, and the results are shown in Table 1.
• Example 4-1 The same coating process is conducted as in Example 4-1 except for omitting the formation of chemical coatings and the electrodeposition coatings. Various properties are evauated, and the results are shown in Table 1.
• Example 4-1 The same coating process is conducted as in Example 4-1 except for conducting the electrodeposition coating process under the following conditions: Undercoat Applying an epoxy-resin type primer (ORGA SELECT 30 PRIMER, manufactured by Nippon Paint Co., Ltd.) to the automobile body in a dry film thickness of 30 ⁇ m, and baking it at 130°C for 30 minutes. Various properties are evaluated, and the results are shown in Table 1.
• an epoxy-resin type primer ORGA SELECT 30 PRIMER, manufactured by Nippon Paint Co., Ltd.
• Example 4-1 The same coating process is conducted as in Example 4-1 except for stamping one aluminum parts, assembling it with another aluminum parts to provide an automobile body, and then applying NIPPE METALCOAT P19 CLEAR in a dry film thickness of 3 ⁇ m.
• a metal assembly including at least one aluminum member and at least one other metal member such as steel member can be provided with chemical coatings and electrodeposition coatings without suffering from the erosion of the aluminum parts.
• the aluminum parts coated with the conductive primer can be stamped to any shape, such as a deep drawn shape without using a lubricating oil. This is greatly advantageous in terms of productivity because the operation of removing a lubricating oil from the stamped aluminum parts usually takes a lot of time and labor.

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Citations (4)

• 1990
  • 1990-02-28 EP EP19900103924 patent/EP0385448B1/fr not_active Expired - Lifetime
  • 1990-02-28 DE DE1990602481 patent/DE69002481T2/de not_active Expired - Fee Related

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