Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2001-08-22
2003-04-29
Chen, Bret (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S410000, C523S463000, C523S400000
Reexamination Certificate
active
06555176
ABSTRACT:
This invention relates to coating compositions and to the use-thereof in the production of multilayer lacquer coatings, for example in the motor vehicle sector, in particular in the production of two layer coatings of the base lacquer/clear lacquer type.
Coating compositions which cure by forming esters and are based on a combination of epoxy-functional components and carboxy-functional components are known. They are distinguished by the good resistance to chemicals and acids of the stoved coatings produced therefrom and are thus particularly suitable as clear or topcoat lacquers in automotive original lacquer coating.
When producing base lacquer/clear lacquer two layer lacquer coatings, it is desirable to use clear lacquer coating compositions which are stabilised against sagging, in particular on vertical surfaces during the stoving operation.
WO 95/27012 discloses non-aqueous coating compositions based on a film-forming polymeric polyepoxide and a polyacid as crosslinking agent, which coatings are stabilised against sagging because they contain a colloidal dispersion of carboxy-functional polymer microparticles. The coating compositions may be used as clear lacquer coating compositions for overcoating base lacquer layers.
The storage stability of the coating compositions known from WO 95/27012 is dependent upon the solvent composition; satisfactory storage stability values are only obtained with formulations having a high polarity of the solvent composition. For example the solvent compositions substantially consist of polar solvents. However, when base lacquer layers are overcoated with clear lacquer coating compositions which comprise a polar solvent composition, the base lacquer layer often suffers solvent attack. Negative consequences of solvent attack are, for example, alteration of shade, mottling, impairment of the metallic or pearlescent effect of the resultant two layer lacquer coating.
The object of the present invention is to provide coating compositions cross-linkable by the reaction of carboxyl and epoxy groups, which coating compositions exhibit the advantages of a coating composition stabilised against sagging by a content of polymer microparticles, are stable in storage and nevertheless exhibit only slight solvent attack characteristics towards coating layers overcoated therewith. The coating compositions should in particular be usable as clear lacquer coating compositions for the production of base lacquer/clear lacquer two layer lacquer coatings by overcoating base lacquer layers, as are in particular conventional in automotive lacquer coating.
This object is achieved by curable coating compositions containing a binder/cross-linking agent system, one or more organic solvents, optionally together with pigments and/or extenders and optionally further conventional lacquer additives, wherein the binder/crosslinking agent system contains 20 to 80 wt. % of one or more dissolved carboxy-functional components A) selected from among carboxy-functional (meth)acrylic copolymers and/or carboxy-functional polyesters, the carboxy-functionality of which in each case corresponds to an acid value of 15 to 300 mg of KOH/g, and 20 to 80 wt. % of epoxy-functional crosslinking components B), wherein the weight percentages add up to 100 wt. % and wherein the crosslinking ratio between the component A) carboxyl groups and the component B) epoxy groups is between 1:1 and 1:3, characterised in that the epoxy-functional components B) comprise at least one epoxy-functional crosslinking component B
1
) which is dissolved in the continuous phase of the coating composition and at least one epoxy-functional component B
2
) dispersed in the continuous phase of the coating composition, wherein the ratio of the epoxy groups originating from the epoxy-functional components B
1
) and B
2
) is between 10:1 and 1:5, and wherein the organic solvents present in the ready-to-apply coating composition comprise 0 to 35 wt. % of one or more conventional organic lacquer solvents containing oxygen and 65 to 100 wt. % of one or more conventional lacquer hydrocarbons, wherein the weight percentages add up to 100 wt. %.
The solvent or solvent mixture which adds up to 100 wt. % and consists of 0 to 35 wt. % of conventional organic lacquer solvents containing oxygen and 65 to 100 wt. % of one or more conventional lacquer hydrocarbons is hereinafter denoted F).
The binder/crosslinking agent system of the coating compositions according to the invention contains components A), B
1
) and B
2
) as substantial components, optionally together with the optional components C), D) and/or E) explained below. For example, the coating compositions according to the invention may contain only components A), B
1
) and B
2
) as the binder/crosslinking agent system, or the binder/crosslinking agent system of the coating compositions according to the invention additionally contains the optional components C), D) and/or E).
The resin solids content of the coating compositions according to the invention comprises the sum of the resin solids contents or of the non-volatile fractions of components A), B
1
), B
2
) and of the optional components C), D) and E).
Curing of the coating compositions according to the invention is based upon the chemical reaction of the complementarily reactive groups of components A), B
1
) and B
2
) which proceeds during stoving; this reaction comprises an addition of the carboxyl groups onto the epoxy groups to form carboxylic acid ester bonds. The coating compositions according to the invention contain one or more carboxy-functional components A). The carboxy-functional component A) of the coating compositions according to the invention comprises carboxy-functional (meth)acrylic copolymers and/or carboxy-functional polyesters, the carboxy-functionality of which in each case corresponds to an acid value of 15 to 300 mg of KOH/g. The carboxy-functional (meth)acrylic copolymers and/or carboxy-functional polyesters may be urethanised and/or be modified by reaction with lactones.
The carboxy-functionalised component A) (meth)acrylic copolymers optionally containing urethane groups and/or modified with lactones preferably exhibit a number average molar mass (Mn) of 1000 to 30000 g/mol. The carboxy-functionalised component A) polyesters optionally containing urethane groups and/or modified with lactones preferably exhibit a calculated molar mass of 500 to 4000 g/mol. The acid value is in each case from 15 to 300 mg of KOH/g, preferably from 30 to 250 mg of KOH/g.
When producing the component A) (meth)acrylic copolymers or polyesters containing carboxyl groups, which may optionally in each case contain urethane groups and/or be modified with lactones, the carboxyl groups may be introduced directly by using structural units containing carboxyl groups. Examples of suitable monomers containing carboxyl groups which may be used for synthesising (meth)acrylic copolymers containing carboxyl groups are unsaturated carboxylic acids, such as for example acrylic, methacrylic, itaconic, crotonic, isocrotonic, aconitic, maleic and fumaric acid, semi-esters of maleic and fulmaric acid as well as carboxyalkyl esters of (meth)acrylic acid, such as for example beta-carboxylethyl acrylate and addition products of hydroxyalkyl (meth)acrylates with carboxylic anhydrides, such as for example phthalic acid mono-2-(meth)acryloyloxyethyl ester.
In the present description and the claims, the term (meth)acrylic is used and means acrylic and/or methacrylic.
When producing component A) (meth)acrylic copolymers or polyesters containing carboxyl groups which optionally contain urethane groups and/or are modified with lactones, it is, however, also possible initially to synthesise a polymer containing hydroxyl groups and optionally also carboxyl groups and to introduce the carboxyl groups entirely or in part in a second stage by reaction with carboxylic anhydrides. When this method is used, it is possible to work with quantity ratios such that sufficient hydroxyl groups optionally remain in order to permit urethanisation.
Carboxylic an
Dahm Ralf
Flosbach Carmen
Gawin Hans-Jürgen
Kerber Hermann
Manassis Apostolos
Chen Bret
Deshmukh Sudhir G.
E. I. du Pont de Nemours and Company
Fletcher, III William Phillip
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