Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-04-20
2002-05-28
Dawson, Robert (Department: 1712)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C428S413000, C523S466000, C528S403000, C528S407000, C528S408000, C528S418000, C528S421000
Reexamination Certificate
active
06395340
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an organic solvent type thermosetting coating composition capable of forming a rigid coating film having a Tukon hardness (20° C.) of at least 25, excellent in stain resistance, and from which pollutants can easily be removed even when they are adhered, and further relates to a method to form a multilayered topcoating film with use of said coating composition.
BACKGROUND ART
As a topcoat paint (in particular clear paint) for automobile body panel, there are usually used organic solvent type paints which comprise, as main components, hydroxyl group-containing acrylic resin and melamine resin. Although good in weatherability, finished appearance, etc., a coating film made from these paints has yet to have sufficient “acid rain resistance” which has been high-lighted recently. As a topcoat paint which has improved in this acid rain resistance, there have been proposed organic solvent type paints (generally called acid epoxy type paints) which comprise, as main components, carboxyl group-containing resin and epoxy group-containing resin, and which are free of melamine resin. Although excellent in weatherability and finished appearance and also in acid rain resistance, a cured film formed from said acid epoxy type paints has a problem of poor stain resistance which makes it difficult to remove adhered pollutants tracelessly.
The surface of top coating film on outer body panel of automobile which is mostly used outdoors is apt to be stained with pollutants (e.g., bird droppings, pollens, dead insects etc.), iron powder, sand mud, exhaust soot (carbon, paraffin, etc.) which adhere to, soak or sink into said coating film. For example, bird droppings which have stuck on the coating film condense as they are dried and solidified, with the result that the surface of top coating film shrinks together, causing decrease in the appearance of portions concerned, such as gloss and distinctness-of-image-gloss. When wetted with rain etc., pollens and dead insects which have adhered to the coat surface elute protein or amino acid, which may possibly penetrate into the coating film to cause stains. Iron powder, sand mud, exhaust soot etc. also adhere to, or sink into coating film to cause stains.
Automobile body panel, when left outdoors, may raise its temperature to 60° C. or higher by solar heat. Top coating film is softened at such a high temperature, and, thus, staining by the above-mentioned causes becomes more likely to be accelerated.
Once a coating film is stained in such a manner, the stains cannot be removed by simply wiping or using cleanser or wax, and, thus, appearance is damaged.
Thus, the main purpose of the present invention is to provide a novel organic solvent type paint capable of forming a coating film which is equivalent or superior, in weatherability, finished appearance, acid resistance, etc., to coating film of conventional organic solvent type paints (e.g., those which comprise, as main components, acrylic resin and melamine resin, such as acid epoxy type paints) used as an automobile topcoat paint, and which is also good in stain resistance.
DISCLOSURE OF INVENTION
As a result of assiduous study with a view to achieving the above-mentioned purpose, inventors of the present invention have found out that an organic solvent type thermosetting paint which contains a compound having alicyclic epoxy group, a secondary amino group-containing compound and a thermally latent cationically polymerizable catalyst, and, if necessary, colloidal silica as well, gives a coating film which is excellent in crosslinking curing reactivity, and which, once cured, is rigid and hardly softened even when exposed to a temperature of 60° C. or higher, does not allow pollutants to soak or sink into, can easily be freed from pollutants, even though they have stuck, by water washing or dry cloth rubbing without using deter-gents, and, further, is also excellent in weatherability, finished appearance, acid resistance, etc., and thus have completed the present invention.
Thus, the present invention provides an organic solvent type thermosetting paint (hereinafter referred to as “the paint of the present invention”) which is characterized by containing (A) a compound with a number-average molecular weight of less than 2000 and having at least two alicyclic epoxy groups in a molecule, (B) a secondary amino group-containing compound and (C) a thermally latent cationically polymerizable catalyst, and, if necessary, (D) colloidal silica as well.
The present invention further provides a coating method (hereinafter referred to as “the coating method of the present invention”) which is characterized in that, in a method for forming a multilayered top coating film by coating a substrate with at least one colored paint and at least one clear paint in order, the paint of the present invention is used as a clear paint which is to be uppermost applied.
The paint of the present invention is capable of forming a cured coating film which has a Tukon hardness (20° C.) of at least 25, a breaking stress of at least 500 kg/cm
2
and a Young's modulus of at least 20000 kg/cm
2
. A coating film having these property values is more rigid and tough than film of conventional paints, is hardly softened even when exposed to a temperature of 60° C. or higher, does not allow pollutants to soak or sink into, and can easily be freed from pollutants even though they have stuck, and thus has markedly improved stain resistance.
In this description, “Tukon hardness (20° C.)” value is obtained as follows. A paint is applied on a glass plate so that the cured coating film may have a thickness of 30 &mgr;m, and is then heated under a certain condition, for example, at 140° C. for 30 minutes. Thus cured coating film is measured at 20° C. by a TUKON microhardness tester made by American Chain & Cable Company. The larger the value is, the harder is the film. A cured coating film which is formed from known thermosetting paints has usually a Tukon hardness of about 5 to 10. It would be understood therefore how hard a cured film with a Tukon hardness (20° C.) of at least 25 which can be formed by the paint of the present invention is.
“Breaking stress” value is obtained as follows. A paint is applied on a glass plate so that the cured coating film may have a thickness of 30 &mgr;m, and is then heated under a certain condition, for example, at 140° C. for 30 minutes. Thus cured coating film is peeled off the glass plate, and is measured at 20° C. by a tensilon meter made by Orientech Corporation. The larger the value is, the higher the strength of the coating film. A cured coating film which is formed from known thermosetting paints has usually a breaking stress of about 300 to 500 kg/cm
2
. Hence, a coating film with a breaking stress of at least 500 kg/cm
2
, which can be formed by using the paint of the present invention has a higher breaking stress and is more tough than coating film formed from conventional thermosetting paints.
“Young's modulus” is a value which is measured in a manner similar to the above-mentioned breaking stress. The larger the value is, the higher is the hardness of coating film. A cured coating film which is formed from known thermosetting paints has usually a Young's modulus of about 10000 to 20000 kg/cm
2
. Hence, a coating film with a Young's modulus of at least 20000 kg/cm
2
, which can be formed by using the paint of the present invention is more rigid than coating film formed from conventional thermosetting paints.
The paint and coating method of the present invention are described in more detail below.
BEST MODE FOR CARRYING OUT THE INVENTION
The paint of the present invention is an organic solvent type thermosetting paint which is characterized by comprising (A) a compound with a number-average molecular weight of less than 2000 and having at least two alicyclic epoxy groups in a molecule, (B) a secondary amino group-containing compound and (C) a thermally latent cationically polymerizable catalyst, and, if necessary, (D) colloidal silica as
Aida Haruhiko
Ikushima Satoshi
Sugai Hideo
Wada Seiji
Aylward D.
Dawson Robert
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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