Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-01
2001-06-19
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06248819
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermosetting water-borne coating composition excellent in storage stability and capable of providing coating films excellent in workability, a method of forming a coating film using the same, and a method of forming a multilayer coating film.
PRIOR ART
It is a recent trend to use water-borne coatings, in place of solvent-borne coatings, as coatings for automobile or motorcycle or its parts where the substrates to be coated are metals.
As such water-borne coatings so far disclosed, there may be mentioned, among others, the one whose basis is an aqueous dispersion containing a finely divided crosslinked polymer and showing pseudoplasticity or thixotropy (Japanese Kokai Publication Hei-02-97564), the one which contains a polyether-polyurethane dispersion and an intercalation compound as a viscosity modifier (Japanese Kokai Publication Hei-02-55720), the one which contains the product of polymerization of an acrylic monomer in the presence of a polyester resin and a polyurethane dispersion (Japanese Kokai Publication Sho-63-51471), and the one which contains an amido-containing acrylic resin and a urethane-containing aqueous dispersion (Japanese Kokai Publication Hei-06-233965).
Furthermore, in recent years, plastic materials have also been used as articles or substrates to be coated from the light weight and/or easy molding viewpoint. A water-borne base coat has been disclosed as a coating for such articles or substrates not so high in heat resistance. According to Japanese Kokai Publication Hei-02-289630, for instance, such coating comprises an aqueous acrylic resin and a polyurethane resin-based emulsion.
However, these water-borne coatings, when dryed at ordinary temperature or baked at relatively low temperature not higher than 120° C., show insufficient curability. Even when baked at a high temperature exceeding 120° C., they sometimes show reduced coating film performance characteristics, for example reduced water resistance, due to carboxyl groups remaining in coating films.
As regards other water-borne coatings differing from those mentioned above, Japanese Kokai Publication Sho-62-72742 and Japanese Kokai Publication Hei-05-271611 disclose carbodiimide compounds which can be used in aqueous systems and thermosetting water-borne coating compositions containing them. However, the coating films obtained by using these coatings are insufficient in solvent resistance and the water-borne coatings themselves have a problem with their storage stability, although it has been proved that the water resistance of said coating films is improved as a result of disappearance of carboxyl groups by their reacting with carbodiimide groups.
Accordingly, it is an object of the present invention to provide a thermosetting water-borne coating composition showing a balance between sufficient curability and sufficient storage stability and giving coating films having good water resistance and a method of forming a coating film using said composition as well as a method of forming a multilayer coating film.
SUMMARY OF THE INVENTION
The present invention provides a thermosetting water-borne coating composition comprising a polycarbodiimide compound modified for hydrophilicity and a carboxyl-containing aqueous resin composition,
wherein the polycarbodiimide compound modified for hydrophilicity has a structure such that a carbodiimide unit and a polyol unit occur alternately via a urethane bond and repeatedly and
a hydrophilic unit occurs at both molecular termini and is bound to such carbodiimide unit via a urethane bond. The number of repetitions of the carbodiimide unit and polyol unit is preferably 1 to 10.
Said carbodiimide unit is, for example, obtainable from a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule by removal of the isocyanato groups, said polyol unit is obtainable from a polyol (b) having at least two hydroxy groups within each molecule by removal of the active hydrogen atoms, and said hydrophilic unit is obtainable from a modifier for hydrophilicity (c) having an active hydrogen atom and a hydrophilic moiety by removal of the active hydrogen atom.
The modifier for hydrophilicity (c) is preferably a monoalkoxy-polyalkylene glycol, more preferably one in which an alkoxy moiety contains 4 to 20 carbon atoms.
Furthermore, it is preferred that the mole ratio of the total number of carboxyl groups within said water-borne coating composition to the total number of carbodiimide groups within said polycarbodiimide compound modified for hydrophilicity is 1/0.05 to 1/3.
The above thermosetting water-borne coating composition may further comprise a coloring component.
The invention also provides a method of forming a coating film
comprising applying the thermosetting water-borne coating composition defined above to the surface of an article or substrate to be coated and curing the resulting water-borne coat by heating.
The invention further provides a method of forming a multilayer coating film
comprising applying a clear coating to the surface of the coating film obtainable by the above method of forming a coating film and curing the resulting clear coat by heating, or
comprising the step (1) of applying a thermosetting water-borne coating composition to the surface of an article or substrate to be coated to thereby provide a water-borne coat, the step (2) of applying a clear coating onto the water-borne coat to provide a clear coat, and the step (3) of curing both coats obtainable by the steps (1) and (2) simultaneously by heating,
wherein said thermosetting water-borne coating composition is defined as mentioned above.
The above step (1) may comprise applying a thermosetting water-borne coating composition, followed by heating, to provide a water-borne coat.
Furthermore, the invention provides a method for producing a polycarbodiimide compounds modified for hydrophilicity
which comprises the step (1) of reacting a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule with a polyol (b) having hydroxy groups at molecular termini 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 (2) of reacting the reaction product obtainable in the above step with a modifier for hydrophilicity (c) having an active hydrogen atom and a hydrophilic moiety.
The modifier for hydrophilicity (c) may be a monoalkoxy-polyalkylene glycol. The monoalkoxy group of the monoalkoxy-polyalkylene glycol preferably contains 4 to 20 carbon atoms. Further, the polyol preferably has a number average molecular weight of 300 to 5,000.
The present invention is directed to a polycarbodiimide compound modified for hydrophilicity as obtainable by the above production process. The polycarbodiimide compound modified for hydrophilicity has a structure such that a carbodiimide unit and a polyol unit occur alternately via a urethane bond and repeatedly and a hydrophilic unit occurs at both molecular termini and is bound to such carbodiimide unit via a urethane bond. The number of repetitions of the carbodiimide unit and polyol unit is preferably 1 to 10.
The carbodiimide unit is, for example, obtainable from a polycarbodiimide compound (a) having at least two isocyanato groups within each molecule by removal of the isocyanato groups, said polyol unit is obtainable from a polyol (b) having at least two hydroxy groups within each molecule by removal of the active hydrogen atoms, and the hydrophilic unit is obtainable from a modifier for hydrophilicity (c) having an active hydrogen atom and a hydrophilic moiety by removal of the active hydrogen atom. The modifier for hydrophilicity (c) is preferably a monoalkoxy-polyalkylene glycol, more preferably one in which the alkoxy group contains 4 to 20 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
Thermosetting Water-borne Coating Composition
The thermosetting water-borne coating composition of the present invention
Harakawa Tsuyoshi
Kuwajima Teruaki
Masuda Kazuaki
Ohsugi Hiroharu
Michl Paul R.
Nippon Paint Co. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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