Coating agent, the manufacture and uses thereof

Details Coating agent, the manufacture and uses thereof Coating agent, the manufacture and uses thereof

1999-06-14

2001-03-13

Short, Patricia A. (Department: 1712)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S388200, C427S388400, C427S407100, C427S409000, C427S410000, C524S507000, C524S513000, C524S517000, C525S125000, C525S131000, C525S176000, C525S194000, C525S208000

Reexamination Certificate

active

06200639

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to aqueous and/or solvent-containing coating agent compositions which are suitable for coatings which are stoved at elevated temperature, and in particular for the production of multilayer lacquerings, for example in the motor vehicle sector.
BACKGROUND OF THE INVENTION
A stoving lacquer in which polymers containing carboxyl groups, such as e.g. acrylates based on acrylic acid or methacrylic acid and acrylates containing glycidyl groups, are mixed to give a curable composition is known from DE-A-30 22 996.
WO 84/00771 describes a multi-component system in which four types of binder are mixed with one another and the mixture is then applied. The components are acrylate containing hydroxyl groups, acid anhydride, at least 50% being alkylhexahydrophthalic acid anhydrides, epoxy resin and melamine resin. The systems have a high solids content.
DE-A-23 33 384 describes a binder based on acrylated polyesters which are obtained by polymerization of an acrylate containing hydroxyl groups in a polyester or alkyd resin containing hydroxyl groups. The crosslinking can be carried out with melamine resins and simultaneously epoxy resins.
DE-A-38 00 389 describes the modification of copolymers containing hydroxyl groups with lactones, in particular with epsilon-caprolactone.
U.S. Pat. No. 4,501,829 described polyesters with hydroxyl and carboxyl groups which are reacted with lactones. The reaction takes place on the hydroxyl groups.
U.S. Pat. No. 4,082,816 describes compositions of (meth)acrylic copolymers modified with caprolactone and containing carboxyl groups and melamine-formaldehyde resins.
The known coating compositions in some cases lead to film of high hardness and good resistance to weathering. However, they do not meet the constantly increasing requirements of high resistance to acids and resistance to solvents.
DE 44 16 282 describes stoving lacquers which are based on crosslinking of acid polyesters, which are urethanized, with polyepoxides. DE 42 37 658 also describes carboxyepoxy lacquers for stoving systems. In these, the carboxyl group chains are lengthened with caprolactone to increase the reactivity. These systems are distinguished by excellent resistance to chemicals. All these systems have the common feature that they tend to run, especially in very high coating thicknesses.
EP-A-0 509 392 and EP-A-0 517 536 describe powder lacquer resins in which tert-butyl (meth)acrylate and glycidyl methacrylate are copolymerized. This monomer combination is said to lead to an increased reactivity.
SUMMARY OF THE INVENTION
The object of the invention is to provide a binder system which can be processed to aqueous and/or solvent-containing coating compositions which can be stoved at elevated temperature and lead to coating with a good hardness, good resistance to weathering and high elasticity, and which furthermore are resistant to acids and resistant to solvents. The coating compositions should furthermore have a good application reliability (reduced tendency to run), even at high coating thicknesses. In particular, the coating compositions should show no yellowing at all on stoving and have a high storage stability. A high boiling resistance is an essential requirement.
It has been found that this object can be achieved by an aqueous or solvent-containing coating composition which comprises a binder system based on carboxyl-functional (meth)acrylic copolymers and/or polyesters with an epoxide-functionalized (meth)acrylic copolymer as the crosslinking agent, the epoxide-functionalized (meth)acrylic copolymer having been prepared co-using tert-butyl (meth)acrylate as a monomer unit.
The invention thus provides a coating composition comprising a binder composition, solvent and/or water and optionally pigments and/or fillers and optionally the conventional additives in lacquers, which is characterized in that the binder composition comprises:
A) 25 to 75 wt. % of one or more carboxyl-functional (meth)acrylic copolymers and/or one or more carboxyl-functional polyesters, the carboxyl functionality of which in each case corresponds to an acid number of 15 to 300 mg KOH/g,
B) 25 to 75 wt. % of one or more epoxide-functionalized crosslinker resins, at least one of these crosslinker resins being a (meth)acrylic copolymer which has been prepared co-using tert-butyl (meth)acrylate as the monomer unit,
C) 0 to 50 wt. % of one or more polyols which have at least two hydroxyl functions in the molecule and differ from a component A) optionally containing hydroxyl functions,
D) 0 to 40 wt. % of components which crosslink with hydroxyl groups to form ethers, and/or of a crosslinking agent based on triazine,
E) 0 to 40 wt. % of one or more polyisocyanates, which can optionally be masked,
F) 0 to 50 wt. % of an anhydride component comprising at least one organic polyanhydride with at least two cyclic carboxylic acid anhydride groups per molecule,
G) 0 to 20 wt. % of one or more reactive thinners with an epoxide function,
H) 0 to 10 wt. % of one or more catalysts to catalyse the reaction of carboxyl and epoxide groups,
the sum of the wt. % of components A) to H) adding up to 100 wt. %.
According to a preferred embodiment of the invention, the epoxide-functional crosslinker resin is based on (meth)acrylic copolymers which have been prepared co-using 3 to 50 wt. % tert-butyl (meth)acrylate, based on the total weight of the monomer units.
According to another preferred embodiment of the invention, a crosslinker component B) is employed which comprises at least one crosslinker resin based on (meth)acrylic copolymers which has been prepared using the following monomer units:
b1) 5 to 60 wt. % of one or more epoxide-functional olefinically unsaturated monomers, in particular glycidyl (meth)acrylate,
b2) 3 to 50 wt. % tert-butyl (meth)acrylate,
b3) 0 to 60 wt. % of one or more aromatic vinyl-functional monomers,
b4) 0 to 20 wt. % of one or more hydroxyl-functional (meth)acrylic monomers,
b5) 0 to 92 wt. % of one or more monomers which differ from b1) to b4),
the sum of the wt. % of b1) to b5) adding up to 100 wt. %.
It has been found, surprisingly, that the aqueous or solvent-containing coating compositions according to the invention lead to coatings which, in spite of an expected possible formation of cleavage products during the advanced crosslinking reaction, achieve a high boiling resistance, the other requirements according to the object being at an unchanged high level.
In component A) of the binder or coating agent compositions according to the invention, the carboxyl groups can be modified by reaction with lactones. A “chain-lengthening” of the carboxyl groups takes place by the adding on of lactones. By ring-opening of the lactone to be added on, the carboxyl groups originally on the (meth)acrylic copolymer matrix and/or on the polyester matrix are esterified, but the lactone carboxyl groups are liberated and reaction products which contain exposed carboxyl groups on the short side chains corresponding to the lactone are thus formed.
According to a preferred embodiment of the invention, the carboxyl-functionalized (meth)acrylic copolymers, which optionally contain urethane groups and can be reacted with lactone, have a number-average molecular weight (Mn) of 1,000 to 30,000 g/mol. The carboxyl-functionalized polyesters which optionally contain urethane groups and can correspondingly be employed preferably have a calculated molecular weight of 500 to 4,000 g/mol, for example 800 to 4,000 g/mol. The acid number of these starting materials is 15 to 300 mg KOH/g, preferably 30 to 250 mg KOH/g, and particularly preferably 60 to 200 mg KOH/g.
In the preparation of (meth)acrylic copolymers or polyesters which contain carboxyl groups, can optionally each contain urethane groups and can be employed as component A), the carboxyl groups can be introduced directly by using units containing carboxyl groups, for example, in the build-up of polymers, such as (meth)acrylic copolymers. Examples of suitable monomers which contain carboxyl groups and can be used for this pu

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