Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-22
2001-07-17
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S525000, C525S530000
Reexamination Certificate
active
06262146
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a resin composition for cationic electrocoating and to a cationic electrocoating composition, each excellent in throwing power and capable of providing coatings excellent in impact resistance.
PRIOR ART
Cationic electrocoating can provide substrates or coating target articles with coatings every nook and cranny even when said substrates are complicated in form or shape and can be performed automatically and continuously. Therefore, it is in general use as a technique of forming an undercoat on substrates, such as automotive bodies, which have a large size and are complicated in form or shape and are required to be highly resistant to corrosion. Furthermore, said technique is very highly efficient from the coating composition consumption viewpoint, hence economical, as compared with other methods of coating and, therefore, it has come into wide use as an industrial method of coating.
Cationic electrocoating is carried out by immersing a substrate, which is to serve as a cathode, in a cationic electrocoating composition and applying a voltage. The deposition of a coating layer on the substrate involves electrochemical reaction and the coating layer that has deposited on the substrate surface upon voltage application has an insulating property. Therefore, with the progress of deposition of the coating in the process of coating, hence with the increase in deposit layer thickness, the electric resistance of the coating layer increases in proportion to the increase in layer thickness. As a result, the deposition of the coating composition at that site decreases and, instead, the deposition of a coating layer on some other uncoated site begins. In this way, the deposition of emulsion particles of the coating composition takes place successively from uncoated site to uncoated site. In the present specification, such successive formation of a coating on uncoated sites of a substrate is referred to as “throwing power”.
Such cationic electrocoating is generally used in undercoat formation, mainly for the purpose of rust prevention and, therefore, it is required that even substrates having a complicated structure should be provided with a coating having a certain predetermined film thickness at any part thereof. For this reason, sufficient levels of throwing power are to be secured.
As a cationic electrocoating composition excellent in throwing power, WO 98/03701 for instance discloses a cationic electrocoating composition comprising a basic resin containing a triple bond such as an ethynyl or nitrile group within its molecule.
On the other hand, coating films to be formed on substrates such as automobiles should be protected from damages possibly resulting from collision with sand grains, small stones or the like during running. Thus, it is essential to make attempts to improve the so-called impact resistance. For attaining improved impact resistance, it is common practice to improve physical properties of the top coat and/or intermediate coat. However, it is not always possible to improve the impact resistance to a satisfactory extent by such a method alone. Coating film is generally constituted of a plurality of coating layers, so that it is necessary to improve the impact resistance of the film as a whole. In particular, if the impact resistance of the coating film as a whole can be improved through improvements in physical properties of an electrodeposition coating, there will arises the possibility that the impact resistance of the film might be markedly improved by combined use of some conventional impact resistance improving technology.
However, it is difficult to obtain a cationic electrocoating composition excellent in throwing power and capable of providing improved impact resistance using the conventional technology.
In view of the state of the art as mentioned above, the present invention has its object to provide a resin composition for cationic electrocoating and a cationic electrocoating composition, each excellent in throwing power and capable of providing coatings excellent in impact resistance.
SUMMARY OF THE INVENTION
The present invention provides an aliphatic hydrocarbon group-containing resin composition for cationic electrocoating, which comprises a resin having a skeleton of epoxy resin and has a number average molecular weight of 500 to 20,000, and which contains, per 100 grams of the nonvolatile matter in said resin composition,
(a) 5 to 400 millimoles of sulfonium group;
(b) 80 to 355 millimoles of at least one aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing unsaturated double bond within its chain; and
(c) 10 to 315 millimoles of at least one-remember selected from among propargyl group and a terminal unsaturated double bond-containing organic group containing 3 to 7 carbon atoms;
the total content of (a) the sulfonium group, (b) the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing unsaturated double bond within its chain and (c) the at least one member selected from among propargyl group and a terminal unsaturated double bond-containing organic group containing 3 to 7 carbon atoms being not more than 500 millimoles per 100 grams of the nonvolatile matter in said resin composition.
The present invention also provides a cationic electrocoating composition which comprises the above resin composition for cationic electrocoating as incorporated therein, and in particular a cationic electrocoating composition which comprises the above resin composition for cationic electrocoating and further a resin composition having a skeleton of epoxy resin and containing sulfonium group and propargyl group, wherein said cationic electrocoating composition have a number average molecular weight of its resin component of 500 to 20,000 and contains, per 100 grams of the resin solids,
(a) 5 to 400 millimoles of the sulfonium group;
(b) 10 to 300 millimoles of the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing unsaturated double bond within its chain; and
10 to 485 millimoles of the sum of propargyl group and the terminal unsaturated double bond-containing organic group containing 3 to 7 carbon atoms;
the total content of (a) the sulfonium group, (b) the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing unsaturated double bond within its chain, and the propargyl group and the terminal unsaturated double bond-containing organic group containing 3 to 7 carbon atoms being not more than 500 millimoles per 100 grams of the resin solids, with the proportion of said group (b) being 3 to 30% by weight relative to the resin solids.
REFERENCES:
patent: 709714 (1998-02-01), None
Izumiya Koji
Kawakami Ichiro
Kawanami Toshitaka
Saito Takao
Sakamoto Hiroyuki
Aylward D.
Connolly Bove Lodge & Hutz LLP.
Dawson Robert
Nippon Paint Co. Ltd.
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