Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2001-09-19
2004-05-04
Mayekar, Kishor (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S506000
Reexamination Certificate
active
06730203
ABSTRACT:
This application has benefit of the priority of Japanese Patent Application No. 00/285312, filed on Sep. 20, 2000, and Japanese Patent Application No. 00/285313, filed on Sep. 20, 2000.
BACKGROUND ART
(1) Field of the Invention
The present invention firstly relates to a multi-layer coating film-forming method which comprises coating a cationic electrodeposition coating composition and a water based intercoat coating composition by the wet-on-wet coating method, followed by heating and crosslink-curing both coating films simultaneously by the so called two coats one bake (2C1B) coating method to form a multi-layer coating film including an intercoat coating film having a thin film thickness, and showing good substrate-opacifying properties and good weather resistance.
The present invention secondly relates to a multi-layer coating film-forming method which comprises coating a cationic electrodeposition coating composition and a water based intercoat coating composition by the wet-on-wet coating method, followed by beating and crosslink-curing both coating films simultaneously by the so called two coats one bake (2C1B) coating method to form a multi-layer coating film improved in anti-chipping properties, water resistance, finished appearance such as gloss, interlayer adhesion properties and the like.
(2) Description of Background Art
It is known in the art that a multi-layer coating film is formed by a method which comprises coating a cationic electrodeposition coating composition and a water based intercoat coating composition onto an electrically conductive substrate such as an automobile body and the like by the 2C1B coating method to form a multi-layer coating film.
However, the use of the above intercoat coating composition may easily develop sagging and bubbling, consequently makes it difficult to form a thick coating film, and results in that an unsatisfactory ultraviolet light-shielding power of the intercoat coating film makes it easy for an ultraviolet light permeating through a topcoating film to reach an electrodeposition coating film and to reduce weather resistance thereof.
It is an object of the present invention to provide a multi-layer coating film-forming method which is capable of solving the above problems of the multi-layer coating film formed by coating the cationic electrodeposition coating composition and the water based intercoat coating composition by the 2C1B coating method, and capable of forming a multi-layer coating film including an intercoat coating film having good substrate-opacifying properties and showing good weather resistance.
Now, it was found that on coating the cationic electrodeposition coating composition and the water based intercoat coating composition by the 2C1B coating method, use of a water based intercoat coating composition containing a hydroxyl group and carboxyl group-containing base resin, a crosslinking agent, a fine aluminum powder and a titanium oxide white pigment can achieve the above object, and results in improving the substrate-opacifying properties of the intercoat coating film, and weather resistance of a multi-layer coating film formed by coating the cationic electrodeposition and the water based intercoat coating composition, and in accomplishing the present invention.
On the other hand, it is also known in the art that a multi-layer coating film is formed by a method which comprises coating a cationic electrodeposition coating composition containing a blocked polyisocyanate compound as a crosslinking agent, and a water based intercoat coating composition containing a polyester resin and a blocked polyisocyanate compound by the 2C1B coating method to form a multi-layer coating film.
However, the above method had such problems that the resulting multi-layer coating film shows such unsatisfactory finished appearance or gloss as difficult to be solved by coating a topcoating composition, may develop chipping or peeling between both coating films when hit by jumping stones while the automobile is running, and shows unsatisfactory water resistance.
It is another object of the present invention to provide a multi-layer coating film-forming method which is capable of solving the above problems of the multi-layer coating film formed by coating the cationic electrodeposition coating composition and the water based intercoat coating composition by the 2C1B coating method, and capable of forming a multi-layer coating film showing good properties in finished appearance, anti-chipping properties, water resistance and the like.
Now, it was found that on coating the cationic electrodeposition coating composition and the water based intercoat coating composition by the 2C1B coating method, use of a water based intercoat coating composition containing a hydroxy group and carboxyl group-containing base resin, a blocked polyisocyanate crosslinking agent and an alicyclic epoxy compound can achieve the above object to accomplish the present invention.
SUMMARY OF THE INVENTION
The present invention firstly provides a multi-layer coating film-forming method which comprises coating a cationic electrodeposition coating composition (A) containing a blocked polyisocyanate compound as a crosslinking agent to form a non-cured electrodeposition coating film, coating a water based intercoat coating composition (B
1
) containing a hydroxyl group and carboxyl group-containing base resin, a blocked polyisocyanate crosslinking agent, a fine aluminum powder and a titanium oxide white pigment onto the non-cured electrodeposition coating film to form a non-cured intercoat coating film, followed by heat curing both coating films simultaneously (hereinafter may be referred to as a first invention).
The present invention secondly provides a multi-layer coating film-forming method which comprises coating a cationic electrodeposition coating composition (A) containing a blocked polyisocyanate compound as a crosslinking agent to form a non-cured electrodeposition coating film, coating a water based intercoat coating composition (B
2
) containing a hydroxyl group and carboxyl group-containing base resin, a blocked polyisocyanate crosslinking agent and an alicyclic epoxy compound to form a non-cured intercoat coating film, followed by heat curing the both coating films simultaneously (hereinafter may be referred to as a second invention).
Preferably in the method of the present invention, for the purpose of achieving the above objects of the present invention, a crosslink-curing reaction of the non-cured coating film formed from the cationic electrodeposition coating composition (A) may be controlled so as to take place earlier than a crosslink-curing reaction of a non-curing coating film formed from a water based intercoat coating composition (B
1
) or B
2
).
In the method of the present invention, measurement of a crosslink-curing reaction starting time of a coating film formed from the cationic electrodeposition coating composition (A), or the water based intercoat coating composition (B
1
) or (B
2
) may be carried out by use of a pendulum type viscoelastometer such as Rheovibron DDV-OPA Type (marketed by Toyo Baldwin Co., Ltd.). Specifically, a pendulum having a weight of 22 g and a moment of inertia of 850 g•cm
2
is placed on a non-cured coating film coated onto a steel sheet so as to be a cured coating film of 30 &mgr;m, followed by heating at a predetermined temperature for crosslink-curing the non-cured coating film, for example, in the range of 140 to 180° C. to determine a time when a logarithmic decrement of the pendulum starts increasing as a crosslink-curing starting time, and to determine a time period from a starting time of heating to a crosslink-curing starting time as a period of time for starting curing, wherein a shorter period of time for starting curing means that the crosslink-curing reaction takes place earlier, and comparison of the crosslink-curing starting time between both coating films is made based on the results measured at the same temperature.
DETAILED DESCRIPTION OF THE INVENTION
Details of the multi-layer coating f
Ikenoue Syuichi
Kasari Akira
Fisher Christen & Sabol
Kansai Paint Co. Ltd.
Mayekar Kishor
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