Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-10-25
2004-01-06
Mayekar, Kishor (Department: 1741)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S404000, C525S113000, C204S489000
Reexamination Certificate
active
06673853
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel electrodeposition coating composition useful in the coating industry, in particular in the field of automobile coatings. More particularly, it relates to an electrodeposition coating composition capable of forming electrodeposited coating films having a multilayer structure comprising an anticorrosive layer and a shock-absorbing layer.
BACKGROUND ART
In recent years it has been urgently demanded that the coating process be curtailed in the field of coatings, in particular in the field of automobile coatings, so that the problems of saving resources, reducing costs and minimizing environmental impacts (VOC and HAPs, etc.) may be solved. In the conventional procedure for finishing coating automobiles, the three-coat three-bake coating technique has been used, namely the electrodeposited coating film, intermediate coating film and top coating film are baked each time after application of each corresponding coating. In recent years, however, it has been demanded that the coating film comparable in appearance, corrosion resistance and shock resistance (chipping resistance) to those which can be exhibited by the three-coat films obtained by the conventional three-coat three-bake coating technique be acquired by employing the three-wet coating system according to which the three coating steps, namely intermediate coating, base coating and clear coating, are carried out in the wet-on-wet manner following the step of electrodeposition coating and baking of the electrodeposited coating film and the resulting wet coating films are baked simultaneously, while thereby reducing the number of baking process steps.
The above-mentioned shock resistance, in particular the so-called chipping resistance to collision of pebbles or like obstacles with the car body during running, can be secured by the conventional three-coat three-bake coating technique, for example by providing a particular intermediate coating film having chipping resistance. In the three-wet coating system mentioned above, however, the conventional intermediate coatings cannot be used since the coating films obtained tend to be impaired in appearance due to such troubles as blurring or layer inversion. The coating films obtained by the three-wet coating system are disadvantageous in that they are low in shock resistance and chipping resistance.
Japanese Kokai Publication Sho-62-65765 discloses a technique according to which a resin layer capable of absorbing a shock to coating films (the so-called anti-chipping primer layer) is provided during multilayer film formation, in particular between the electrodeposited coating film and intermediate coating film. However, further incorporation of such a step in the car body coating process is against the market needs for curtailment of the above process and for cost saving.
While, generally, the intermediate coating film in the multilayer coating film formed on a car body or the like plays a role in building up the above-mentioned chipping resistance, there are technologies of providing the electrodeposited coating film with chipping resistance.
In Japanese Kokoku Publication Sho-56-41670, Japanese Kohyo Publication Hei-03-504396 and Japanese Kokai Publication Hei-07-82340, there are disclosed electrodeposition coating compositions in which an amine-modified epoxy-based cationic resin and an elastomer component having a shock absorbing capacity are integrated as a resin composition by reacting them each other in advance for the purpose of improving the shock absorbing property of the binder as a whole. Since, however, an amine-modified epoxy resin and an elastomer (rubber) component, which are intrinsically incompatible with each other, are reacted each other for integration on the molecular level for use in those resin compositions for electrodeposition coatings, the corrosion resistance decreases contrariwise when the amount of the elastomer component submitted to reaction is increased to an extent sufficient to provide a satisfactory level of shock resistance (chipping resistance), although the storage stability of the coatings is high. It is thus difficult for such compositions to perform the functions satisfactorily in the above-mentioned three-wet coating.
In Japanese Kokai Publication Hei-05-230402, Japanese Kokai Publication Hei-07-207196 and Japanese Kokai Publication Hei-09-208865, there are disclosed electrodeposition coating compositions characterized in that a hydrophilic (polar) or reactive functional group is introduced into the elastomer (rubber) component to thereby improve the compatibility thereof with the amine-modified epoxy-based cationic resin and thus secure the storage stability of the coatings. In these resin compositions for electrodeposition coatings, the elastomer (rubber) component is designed independently of the amine-modified epoxy-based cationic resin, namely the main binder in the electrodeposition coatings, so that when the proportion of the elastomer component is increased to an extent sufficient to provide a satisfactory level of shock resistance (chipping resistance), the corrosion resistance decreases contrariwise, like the case mentioned above. It is thus difficult for such compositions to perform the functions satisfactorily in the above-mentioned three-wet coating. Furthermore, the polar functional group introduction into the elastomer (rubber) component results in an unnecessary increase in resin glass transition temperature, producing such problems as a decrease in elasticity modulus and a decrease in shock resistance (chipping resistance).
Furthermore, the above-mentioned technologies each intends to form electrodeposited coating films having a single-layer structure while securing the compatibility between the elastomer (rubber) component, which is to provide the electrodeposited coating films with shock resistance, and the amine-modified epoxy-based cationic resin, which is to provide corrosion resistance. In that case, the shock resistance (chipping resistance) and corrosion resistance are attainable simultaneously only at an unsatisfactory level, although the storage stability of the coatings is high.
Accordingly, it is an object of the present invention to provide an electrodeposition coating composition excellent in storage stability and capable of forming a novel multilayer structure and thus useful in the three-wet one-bake coating technique which is intended for coating process curtailment, cost reduction and environmental impact reduction and by which coating films not only comparable in appearance, solvent resistance and corrosion resistance to the conventional three-coat films but also excellent in shock resistance (chipping resistance) can be formed.
SUMMARY OF THE INVENTION
The present invention provides an electrodeposition coating composition comprising
a particle A containing a resin (a) whose solubility parameter is &dgr;a as well as a particle B containing a curing agent and a resin (b) whose solubility parameter is &dgr;b,
wherein (1) the value of (&dgr;b-&dgr;a) is not less than 1.0,
(2) as regards the electrodeposited coating film formed from said electrodeposition coating composition, the resin film formed from said particle A shows a dynamic glass transition temperature of −110 to 10° C. and
the resin film obtained by film formation from said particle A alone shows an elongation percentage of not less than 200% and
(3) as regards the electrodeposited coating film formed from said electrodeposition coating composition, the resin film formed from said particle B shows a dynamic glass transition temperature of 60 to 150° C.
In the following, the present invention is described in further detail.
DETAILED DESCRIPTION OF THE INVENTION
The electrodeposition coating composition according to the present invention, in which two resin components incompatible with each other are used, can form an electrodeposited coating film having a multilayer structure so that a resin layer having corrosion resistance may be formed on the side in contact with the substrate and a r
Muramoto Hisaichi
Ohara Kouichi
Mayekar Kishor
Nippon Paint Co. Ltd.
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