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
2000-12-11
2002-08-20
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S108000, C525S110000, C525S111000, C525S114000, C525S117000, C525S118000, C525S119000, C525S124000, C525S125000, C525S127000, C525S128000, C525S161000, C525S162000, C525S163000, C525S166000, C525S170000, C525S207000, C525S208000, C525S454000, C523S456000
Reexamination Certificate
active
06437056
ABSTRACT:
The invention relates to coating compositions and their use in the production of multilayer lacquer coatings, for example in the automotive sector, especially in the production of two-layer lacquer coatings of the base lacquer/clear lacquer type.
Coating compositions that are based on a combination of an epoxy-functional component and a carboxyl-functional component and that cure with the formation of esters are known. They are distinguished by the fact that the coatings produced therefrom and stoved have good resistance to chemicals and acids, and they are therefore especially suitable as clear lacquers or finishing lacquers in the series lacquering of motor vehicles.
For example, there is known from DE-A-30 22 996 a stoving lacquer in which polymers containing carboxyl groups, such as, for example, (meth)acrylic copolymers based on acrylic acid or methacrylic acid, and acrylate resins containing glycidyl groups are mixed to form a curable composition.
DE-A-42 37 658 also describes stoving lacquer systems based on components containing carboxyl groups and components containing epoxy groups. In this case, the carboxyl groups are chain-lengthened with lactone in order to increase the reactivity.
The visual aesthetic effect of base lacquer/clear lacquer two-layer lacquer coatings is influenced essentially by the quality of the clear lacquer layer. Ideally, the structure of the clear lacquer layer is the same on horizontal and vertical surfaces of a three-dimensional substrate, for example a motor vehicle body. However, the described ideal case cannot readily be achieved in practice. For example, differences in the surface structure or in the flow of the outer clear lacquer layer may occur since, after application and especially during the heating phase of the stoving process, the clear lacquers tend to run or sag on surfaces that are outside the horizontal as a result of a temperature-related fall in the viscosity. That risk is greater, the greater the thickness of the clear lacquer layer.
It is known from DE-C-27 51 761 and EP-A-0 198 519 to use particular urea compounds as additives in aminoplastic-resin-curing stoving lacquers based on hydroxyl-functional binders, in order to counteract undesired sagging phenomena of the lacquer on stoving. It is additionally known from EP-A-0 192 304 to use urea compounds as anti-sagging agents in lacquers that contain hydroxyl-functional binders and aminoplastic resins or free or blocked polyisocyanates as crosslinking agents. The resistance to chemicals, especially the resistance to acids, of the stoved coating layers produced from those coating compositions is in need of improvement.
The object of the invention is to provide coating compositions that exhibit a reduced tendency to sag even when applied in relatively great layer thicknesses and that, in the stoved state, result in coatings having good resistance to acids and chemicals. The coating compositions are to be suitable especially as stoving coating compositions for the production of the outer clear lacquer or finishing lacquer layer of a multilayer lacquer coating.
The object is achieved by means of curable coating compositions containing binders and crosslinking agents, one or more organic solvents, anti-sagging agents and, optionally, pigments and/or extenders and, optionally, further additives conventionally employed in lacquers, wherein there are present as binders from 20 to 80 wt. % of one or more carboxyl-functional components A) selected from carboxyl-functional (meth)acrylic copolymers and/or carboxyl-functional polyesters, the carboxyl functionality of which corresponds in each case to an acid number of from 20 to 300 mg of KOH/g, and from 20 to 80 wt. % of one or more epoxy-functional crosslinking agents B), the percentages by weight adding up to 100 wt. % which coating compositions are characterised in that they contain as anti-sagging agents from 0.1 to 3 wt. % based on the resin solids, of one or more solid urea compounds D) which have previously been prepared in the presence of at least a portion of the epoxy-functional crosslinking agent(s) B) and which are insoluble in the coating composition, all percentages by weight in each case being based on the solids content.
The binder/crosslinking agent system of the coating compositions according to the invention contains components A) and B) as the essential components and, if desired, the optional components C) and/or E) and/or F) mentioned below. For example, the coating compositions according to the invention may contain only components A) and B) 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) and/or E) and/or F). The resin solid of the coating compositions according to the invention is formed from the sum of the resin solids or the non-volatile portions of components A), B) and the optional components C), E) and F) mentioned below.
Curing of the coating compositions according to the invention is based on the chemical reaction which takes place during stoving between the groups of components A) and B) that are complementarily reactive with respect to one another; it is an addition of the carboxyl groups to the epoxy groups with formation of carboxylic acid ester compounds.
The present invention provides curable coating compositions with which the stated object can be achieved. It was in no way to be expected that the object would be successfully achieved when the synthesis of the urea compounds D) from corresponding amine and isocyanate compounds, as discussed in greater detail below, is carried out in the presence of epoxy-functional crosslinking agents B). Surprisingly, the object is successfully achieved even though the urea compounds D) are prepared in the presence of epoxy-functional crosslinking agents B) that are reactive towards amine compounds. It is advantageous that the epoxy-functional crosslinking agents B), which are themselves a constituent of the coating composition according to the invention, can be used as the reaction medium for the synthesis of the urea compounds D). It is not necessary to synthesise the urea compounds D) in a separate reaction medium, addition of which to the binder/crosslinking agent system containing components A) and B) of the coating compositions according to the invention would possibly be undesirable and optionally even have an adverse effect.
The coating compositions according to the invention contain as component A) one or more carboxyl-functional components A). The carboxyl-functional component A) of the coating compositions according to the invention is carboxyl-functional (meth)acrylic copolymers and/or carboxyl-functional polyesters, the carboxyl functionality of which corresponds in each case to an acid number of from 20 to 300 mg of KOH/g. The carboxyl-functional (meth)acrylic copolymers and/or carboxyl-functional polyesters may be urethanised and/or modified by reaction with lactones.
The carboxyl-functional (meth)acrylic copolymers of component A) optionally containing urethane groups preferably have a number-average molecular weight (Mn) of from 1000 to 30,000 g/mol. The carboxyl-functional polyesters of component A) optionally containing urethane groups preferably have a calculated molecular weight of from 500 to 4000 g/mol. The acid number is in each case from 20 to 300 mg of KOH/g, preferably from 30 to 250 mg of KOH/g.
In the preparation of the carboxyl-group-containing (meth)acrylic copolymers or polyesters of component A), each of which may optionally contain urethane groups, the carboxyl groups may be introduced directly by the use of structural units containing carboxyl groups. Examples of suitable monomers containing carboxyl groups that may be used for the synthesis of carboxyl-group-containing (meth)acrylic copolymers are unsaturated carboxylic acids, such as, for example, acrylic, methacrylic, itaconic, crotonic, isocrotonic, aconitic, maleic and fumaric acid, half-esters of maleic and fumaric acid, and carboxyalkyl
Dahm Ralf
Flosbach Carmen
Kerber Hermann
Schubert Walter
Tückmantel Astrid
Deshmukh Sudhir G.
E. I. du Pont de Nmeours and Company
Sellers Robert E. L.
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