Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-05-01
2002-08-06
Thibodeau, Paul (Department: 1773)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S404000, C427S405000, C427S407100, C427S409000, C427S412500, C428S423100, C428S425900
Reexamination Certificate
active
06428856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of a metallic coating film to be formed on an automotive body or automotive part and to a multilayer coating film obtained by the method.
PRIOR ART
The amount of an organic volatile solvent(s) in the step of application and curing by baking of coatings for automobiles is generally large and, for reducing the number of steps, attempts have been made to convert the coating form to a water-borne ones.
For example, Japanese Kokai Publication Sho-62-216671 proposes applying a resin particle-containing water-borne intermediate coating, applying a water-borne metallic coating, without curing the intermediate coating, and, after drying or curing, applying a clear coating. This technology, however, is not sufficient to obtain coating films capable of meeting the current high quality appearance requirement.
On the other hand, Japanese Kokai Publication Hei-09-235508 discloses a water-borne coating for a precoated metal as prepared by incorporating a mono- and/or polycarbodiimide compound in a water-borne coating containing, as a binder, an aqueous resin selected from among acrylic copolymer resins, polyester resins, polyurethane resins and modifications of these resins, each having carboxyl groups within the molecule and capable of being neutralized with a basic substance. This, however, is not satisfactory, from the appearance and performance characteristics viewpoint, in using for forming metallic coating films for automobiles.
SUMMARY OF THE INVENTION
Accordingly, the present invention has it for its object to provide a method of forming multilayer coating films having a high quality appearance while controlling the bleeding and inversion at the interface between the neighboring coating layers in applying a water-borne intermediate coating and a topcoat in that order to a substrate.
The present invention provides a method of forming coating films one after another on a substrate, namely forming an intermediate coating film using a water-borne intermediate coating, a metallic base coating film using a water-borne metallic base coating and a clear coating film using a clear coating,
wherein said water-borne intermediate coating and/or said water-borne metallic base coating contains a polycarbodiimide compound and a carboxyl-containing aqueous resin.
The invention also provides a method of forming coating films
wherein said polycarbodiimide compound is a carbodiimide compound modified for hydrophilicity obtainable by the step of reacting a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule with a hydroxy-terminated polyol (b) in a mole ratio such that the number of moles of the isocyanato groups of the polycarbodiimide compound (a) is in excess of the number of moles of the hydroxy groups of the polyol (b) and
the step of reacting the reaction product obtainable in the preceding step with a modifier for hydrophilicity (c) having an active hydrogen atom and a hydrophilic moiety.
The invention further provides a method of forming coating films
wherein said polyol (b) has a number average molecular eight of 300 to 5,000 and
the modifier for hydrophilicity (c) is a monoalkoxypolyalkylene glycol with a monoalkoxy group containing 4 to 20 carbon atoms.
The invention still further provides a method of forming coating films
wherein the clear coating film formation with the clear coating is carried out without curing of the intermediate coating film and metallic base coating film.
Furthermore, the invention provides a multilayer coating film obtainable by any of the methods mentioned above. In the following, the present invention is described in further detail.
DETAILED DESCRIPTION OF THE INVENTION
Intermediate Coating Film
In the above coating film forming method of the invention, a water-borne intermediate coating is used for the formation of the intermediate coating film. This water-borne intermediate coating may contain a polycarbodiimide compound and a carboxyl-containing aqueous resin. For obtaining multilayer coating films having a good appearance, this water-borne intermediate coating should preferably contain a polycarbodiimide compound and a carboxyl-containing aqueous resin. In the following, the case of its containing a polycarbodiimide compound and a carboxyl-containing aqueous resin is mentioned.
The polycarbodiimide compound may be the product of any of various methods. Fundamentally, an isocyanato-terminated polycarbodiimide synthesized by the condensation reaction, accompanying carbon dioxide elimination, of an organic diisocyanate.
More specifically, there can be mentioned those polycarbodiimide compounds modified for hydrophilicity which are obtained, in the production of polycarbodiimide compounds, by the step of reacting a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule with a hydroxy-terminated polyol (b) in a mole ratio such that the number of moles of the isocyanato groups of the polycarbodiimide compound (a) is in excess of the number of moles of the hydroxy groups of the polyol (b) and the step of reacting the reaction product obtained in the preceding step with a modifier for hydrophilicity (c) having an active hydrogen atom and a hydrophilic moiety.
In the above step of reacting a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule with a hydroxy-terminated polyol (b), the polycarbodiimide compound (a) having at least two isocyanato groups within the molecule is not particularly restricted but, from the reactivity viewpoint, it is preferably a carbodiimide compound having an isocyanato group at both termini. The method of producing carbodiimide compounds having an isocyanato group at both termini is well known in the art and the condensation reaction of an organic diisocyanate under elimination of carbon dioxide can be utilized.
As the organic diisocyanate, there can be mentioned an aromatic diisocyanate, an aliphatic diisocyanate, an alicyclic diisocyanate, or a mixture of these. As specific examples, there may be mentioned 1,5-naphthylene diisocyanate, 4,4′-diphenylmethanediisocyanate, 4,4′-diphenyldimethylmethanediisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophoronediisocyanate, dicyclohexylmethane-4,4′-diisocyanate, methylcyclohexanediisocyanate, tetramethylxylylene diisocyanate and the like.
The above-mentioned condensation reaction is generally carried out in the presence of a carbodiimidation catalyst. As specific examples of the carbodiimidation catalyst, there may be mentioned phospholene oxides such as 1-phenyl-2-phospholene 1-oxide, 3-methyl-2-phospholene 1-oxide, 1-ethyl-2-phospholene 1-oxide, 3-methyl-1-phenyl-2-phospholene 1-oxide and 3-phospholene isomers of these, among others. From the reactivity viewpoint, however, 3-methyl-l-phenyl-2-phospholene 1-oxide is preferred.
The hydroxy-terminated polyol (b) to be used in the process for producing polycarbodiimide compounds modified for hydrophilicity is not particularly restricted but, from the reaction efficiency viewpoint, it is preferred that its number average molecular weight be 300 to 5,000. Specifically, such polyol (b) includes polyether diols, polyester diols and polycarbonate diols. Typical examples are polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polyethylene-propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol and polyoctamethylene ether glycol, polyester diols such as polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene/butylene adipate and polyneopentyl/hexyl adipate, polylactone diols such as polycaprolactone diol, poly-3-methylvalerolactone diol, polycarbonate diols such as polyhexamethylene carbonate diol, and mixtures of these.
I
Harakawa Tsuyoshi
Kuwajima Teruaki
Masuda Kazuaki
Takeuchi Yutaka
Nippon Paint Co. Ltd.
Paulraj Christopher
Sughrue & Mion, PLLC
Thibodeau Paul
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