Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-04-03
2003-08-12
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C522S081000, C522S083000, C522S074000, C522S126000, C528S059000, C528S060000, C528S065000
Reexamination Certificate
active
06605669
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to coating compounds based on binders curable by high-energy radiation and to the use of the coating compounds for multi-layer coatings in the field of automotive and industrial coating.
DESCRIPTION OF RELATED ART
It is already known to use coating compounds curable by high-energy radiation in automotive coating. This application also utilizes the advantages of radiation-curable coating compounds such as, e.g., the very short curing times, the low solvent emission of the coating compounds and the good hardness and mar resistance of the resulting coatings.
In automotive coating, binders used in the coating compounds curable by high-energy radiation are generally those containing (meth)acryloyl groups and cure by free-radical polymerization initiated by UV radiation. However, coating compounds that cure by UV radiation, in addition to their undisputed advantageous properties, also have some disadvantages. Volume shrinkage of the coating applied occurs during curing, which may lead to tensions and cracking in the film and ultimately to detachment from the substrate. Moreover, particularly when coating three-dimensional objects, insufficient curing and hence unsatisfactory surface properties may occur in areas that are unexposed or underexposed to UV radiation. In order to overcome these problems, it is also already known to use so-called dual-cure systems in which free-radical polymerization initiated by UV radiation is combined with a further chemical crosslinking mechanism.
For example, WO-A-98/00456 describes a binder system containing OH—, NH
2
—, COOH—, NCO— or epoxy-functional compounds with at least one olefinic double bond capable of free-radical polymerization, photoinitiators and a binder system based on polyacrylate and/or polyester polyols with melamine resins or optionally, with blocked polyisocyanates, or a binder system based on carboxy-, anhydride- or amino-functional polyesters and/or polyacrylates with epoxy-functional polyesters and/or polyacrylates
DE-A-197 09 560 describes a clear coat coating compound for automotive coating which contains binders curable by high-energy radiation and, in addition, a binder system curable by addition and/or condensation reactions and that is free from double bonds capable of free-radical polymerization. DE-A-198 18 735 describes a coating compound curable by high-energy radiation that contains components with double bonds capable of free-radical polymerization and with additional reactive groups and components with double bonds capable of free-radical polymerization and with additional reactive groups that are complementary to the reactive groups of the first component.
Moreover, coating systems curable by UV radiation which are based on urethane (meth)acrylates with (meth)acryloyl groups and free isocyanate groups, photoinitiators and compounds with groups that are reactive with isocyanate groups, and optionally, additional polyisocyanates are known from DE-A-198 00 528.
The dual-cure systems known from the prior art are still in need of improvement, however. For example, the adhesion to the substrate is still sometimes insufficient and does not guarantee rapid further treatment of the coated surfaces, e.g., by polishing or sanding. A well known general shortcoming of UV-curable coating compounds is the initial yellowing of the coatings obtained brought about by UV irradiation, with the result that the use of these binder systems in clear coats and top coats, particularly top coats containing pale pigments, e.g., white pigments, is considerably restricted.
This invention provides coating compounds based on binders curable by high-energy radiation that form coatings with defect-free surfaces and good adhesion to the substrate. The coatings are also uniformly and completely curable in shadow regions. The coatings also permit rapid further treatment, e.g., by sanding or polishing. The coating compounds result in non-yellowing or at least low-yellowing coatings after UV irradiation.
SUMMARY OF THE INVENTION
This invention is directed to coating compounds based on binders curable by high-energy radiation, comprising
A) at least one (meth)acrylic copolymer containing olefinic double bonds capable of free-radical polymerization and hydroxyl groups with a C═C equivalent weight from 100 to 10,000 and an OH value from 20 to 250 mg KOH/g, which is prepared from monomers, comprising:
A1) at least one olefinically unsaturated epoxy-functional monomer capable of free-radical polymerization,
A2) at least one olefinically unsaturated carboxy-functional monomer capable of free-radical polymerization, and
A3) at least one further olefinically unsaturated monomer capable of free-radical polymerization which is different from A1) and A2), and
B) at least one component with free isocyanate groups.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The coating compounds according to the invention are based on a combined crosslinking mechanism of free-radical polymerization initiated by high-energy radiation and a polyaddition reaction between hydroxyl and isocyanate groups.
Component A), the (meth)acrylic copolymers, preferably contain olefinic double bonds in the form of (meth)acryloyl groups. Reference will always be made hereinafter to (meth)acryloyl groups. The terms “(meth)acryloyl” and “(meth)acrylic” mean acryloyl and/or methacryloyl, and acrylic and/or methacrylic.
Component A) of the coating compound according to the invention concerns (meth)acrylic copolymers capable of free-radical polymerization containing olefinic double bonds and hydroxyl groups that preferably have a C═C equivalent weight from 300 to 8,000, particularly preferably from 500 to 5,000 and a hydroxyl value from 20 to 200 mg KOH/g, particularly preferably from 80 to 150 mg KOH/g.
The (meth)acrylic copolymers (component A) are preferably prepared from:
10-50 wt. %, particularly preferably 15-35 wt. % of component A1),
5-40 wt. %, particularly preferably 5-25 wt. % of component A2) and
10-80 wt. %, particularly preferably 20-60 wt. % of component A3).
The number-average molecular mass Mn of the (meth)acrylic copolymers (component A) may be, for example, 1,000-10,000 g/mole, preferably 2,000-8,000 g/mole.
The (meth)acrylic copolymers (component A) are prepared from the monomer components A1), A2) and A3). Examples of suitable olefinically unsaturated epoxy-functional monomers capable of free-radical polymerization (component A1) include (meth)allylglycidyl ether, 3,4-epoxy-1-vinylcyclohexane, epoxycyclohexyl (meth)acrylate, vinylglycidyl ether, 2-methylglycidyl (meth)acrylate and glycidyl (meth)acrylate. The use of glycidyl (meth)acrylate is preferred.
Examples of suitable olefinically unsaturated carboxy-functional monomers capable of free-radical polymerization (component A2) include olefinically unsaturated mono- and/or dicarboxylic acids, such as, (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid and isocrotonic acid and the corresponding half esters and anhydrides of the olefinically unsaturated dicarboxylic acids. The use of (meth)acrylic acid is particularly preferred.
Component A3) concerns any olefinically unsaturated monomers capable of free-radical polymerization, which are different from A1) and A2). Component A3) preferably comprises:
A3a) esters of olefinically unsaturated carboxylic acids capable of free-radical polymerization, optionally
A3b) olefinically unsaturated hydroxy-functional monomers capable of free-radical polymerization, and optionally
A3c) further olefinically unsaturated monomers capable of free-radical polymerization, which are different from A3a) and A3b).
Examples of suitable esters of olefinically unsaturated carboxylic acids capable of free-radical polymerization (monomers A3a) include, in particular, esters of alpha,beta-olefinically unsaturated monocarboxylic acids with aliphatic, cycloaliphatic or aromatic alcohols. Examples of suitable olefinically unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid and isocrotonic acid. The alcohols are, in particu
Awokola Morenike
Flosbach Carmen
Loeffler Helmut
Paschmann Volker
Berman Susan W.
E. I. du Pont de Nemours and Company
Lerman Bart E.
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