WO1995015989A1

WO1995015989A1 - Low-temperature curing coating material, process for producing it and its use

Info

Publication number: WO1995015989A1
Application number: PCT/EP1994/003939
Authority: WO
Inventors: Peter Hoffmann; Udo Vorbeck; Werner Alfons Jung; Michael Brünnemann
Original assignee: Basf Lacke + Farben Ag
Priority date: 1993-12-10
Filing date: 1994-11-28
Publication date: 1995-06-15
Also published as: DE4342198A1

Abstract

The object of the present invention is a coating material curing at low temperatures of below 120 °C, containing: A) one or more carboxyl group-containing polymers with a number average molecular weight of 500 to 8000 and an acid number of 15 to 200 mg KOH/g as essential binder components; B) one or more epoxide group-containing compounds as cross-linking agents; and C) one or more organic solvents; This coating material is characterized in that the epoxide group-containing compound (B) can be produced from: 1. a biuret and/or isocyanate and/or urethane group-containing di and/or polyisocyanate compound and glycidyl alcohol of formula (I) in which R is an alkylene radical with 1 to 10 C atoms and R1 is H, a methyl or ethyl group, and/or: 2. a di and/or polyisicyanate and allyl alcohol followed by epoxiding the double bonds. The present invention also concerns a process for producing this coating agent and its use in car repair painting.

Description

Coating agent curable at low temperatures. Process for its production and its use

The present invention is a curable at low temperatures below 120 ^* C über¬ zugsmittel containing

A) one or more polymers containing carboxyl groups and having a number average molecular weight of 500 to

8000 and an acid number of 15 to 200 mg KOH / g as an essential binder component,

B) one or more compounds containing epoxy groups as crosslinking agents and

C) one or more organic solvents.

The present invention also relates to a method for producing the coating composition and its use in automotive refinishing.

Coating agents which contain carboxyl group-containing polymers as binders and epoxy group-containing compounds as crosslinking agents are known, for example in international PCT publication WO87 / 02041, EP-A-103 199, EP-B-51 275, EP-A-123 793, DE -B-26 35 177, JP-A-219 267/83, JP-A-76 338/77, JP-A-53 145/79 and DE-A-39 24 618.

Bisphenol-A or bisphenol-F-based epoxy resins are not suitable for use as crosslinkers in top coats and clear coats because of their tendency to yellowing. Crosslinkers based on aliphatic epoxy resins are often used here. However, the epoxy resins used are mostly very high molecular weight and therefore less reactive, especially if the coating agents are cured at low temperatures (ie generally <80 ° C).

From US-A-4,020,034 coating agents with good weather resistance are known which contain the reaction product of a (cyclo) aliphatic diisocyanate with glycidol as epoxy crosslinker and (cyclo) aliphatic acids or anhydrides as binder. A disadvantage of these coating compositions known from US Pat. No. 4,020,034 is the high baking temperature of the coating compositions, which precludes the use of the coating compositions for automotive refinishing.

Furthermore, from SU-A-83 60 17 coating agents are known which contain the reaction product of trimerized diisocyanate and glycidol as crosslinking agents and anhydrides as binding agents. The coating compositions are cured at elevated temperatures of 180 to 200 ° C., while curing at room temperature is not possible, so that these coating compositions are not suitable for automotive painting.

Furthermore, from DE-A-31 38 196 powder coatings are known which contain, in addition to an acid-functional binder as an epoxy-functional crosslinking agent, the reaction product of a di- and / or polyisocyanate and glycidyl alcohol. These powder coatings are cured at elevated temperatures of 150 to 260 ^° C, while curing at room temperature is not possible. These powder coatings described in DE-A-31 38 196 are therefore not suitable for use in the field of automotive refinishing.

Finally, from some other publications (eg DE-A-32 05 733 and DE-A-32 45 563) epoxy Resins are known which are based on reaction products of polyisocyanates and glycidol. These epoxy resins are used for a wide variety of other areas of application (for example casting resins, sealing compounds, adhesives and the like). However, references to the use according to the invention in coating compositions which can be hardened at low temperatures cannot be found in these documents.

The present invention was therefore based on the object of providing coating compositions based on binders containing carboxyl groups and crosslinkers containing epoxy groups, which can be cured at low temperatures of generally below 120 ° C., preferably below 80 ° C. so that they are suitable for auto repair painting. Even at these low temperatures, the coating agents should harden as quickly as possible (quick freedom from dust and tack as well as rapid hardening), but should have the longest possible processability (pot life). In addition, the coating agents should be as low in solvents as possible, i.e. that they should have as high a solids content as possible for the viscosity of 16 to 20 s, which is favorable for processing, measured in the DIN 4 discharge cup at 23 "C. Finally, the coatings produced using these coating compositions should have good weather resistance and high hardness with good flexibility and good chemical resistance.

Surprisingly, this object is achieved by a coating agent of the type mentioned at the outset, which is characterized in that compound B containing epoxide groups can be prepared

1. from a biuret and / or isocyanurate and / or Di- and / or polyisocyanate compound containing urethane groups and glycidyl alcohol of the formula

wherein R is an alkylene radical having 1 to 10 carbon atoms and RI is H, a methyl or ethyl group and / or

2. from a di- and / or polyisocyanate and allyl alcohol with subsequent epoxidation of the double bonds.

It is surprising and was not foreseeable that the use of the above-mentioned epoxy compounds based on a reaction product of an isocyanate compound gives coating compositions which, in comparison to the conventional systems, are faster in being free of dust and tack and in faster curing of the Mark coating. At the same time, the coating compositions according to the invention have an extended processability (improved pot life) compared to conventional 2K coating compositions. In addition, the coating compositions according to the invention are as low in solvents as possible, ie they have the highest possible solids content at the viscosity of 16 to 20 s, which is favorable for processing, measured in the outlet cup according to DIN 4 at 23 ^° C. Finally, the coatings produced using these coating compositions according to the invention have good weathering properties. resistance, high hardness with good flexibility and good chemical resistance.

In the following, the individual components of the coating agent according to the invention are first explained in more detail.

The polymers containing carboxyl groups used as binders are known and are described, for example, in DE-A-39 24 618, page 4, line 55, to page 10, line 24, DE-A-41 33 420, page 3, line 20, to page 7, line 18, and DE-A-41 19 857, page 3, line 46, to page 11, line 42. For details, please refer to these documents.

The carboxyl-containing polymers used as binders in the coating compositions according to the invention have a number average molecular weight Mn of 500 to 8000 and an acid number of 15 to 200 mg KOH / g, preferably 30 to 120 mg KOH / g. The carboxyl groups can be introduced directly by using building blocks containing carboxyl groups when building up the polymers. However, it is also possible first to build up a hydroxyl- and optionally carboxyl-containing polymer with an OH number of 15 to 200 mg KOH / g and to convert the carboxyl groups in whole or in part in a second stage by reacting the hydroxyl- and if necessary to introduce carboxyl-containing polymers with carboxylic acid anhydrides. Carboxylic acid anhydrides suitable for addition to the hydroxyl group-containing polymers are the anhydrides of aliphatic, cycloaliphatic and aromatic saturated and / or unsaturated di- and polycarboxylic acids, such as, for example, the anhydrides of phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, succinic acid, succinic acid , Itaconic acid, glutaric acid, tri ellitic acid and pyromelitic acid and its halogenated or alkylated derivatives.

Anhydrides of phthalic acid, tetrahydro- and hexahydrophthalic acid and 5-methyl-hexahydrophthalic anhydride are preferably used.

Implementation of the hydroxyl groups _. Polymers with the carboxylic anhydrides are carried out at temperatures from 50 to 140 ° C, optionally in the presence of a catalyst, such as tertiary amines.

The carboxyl-containing polymers are copolymers containing carboxyl groups and / or polyesters containing carboxyl groups. The carboxyl group-containing polyesters can be prepared by the customary methods

(see, for example, B. Vol ert, floor plan of macromolecular chemistry, E. Volmert-Verlag, Karlsruhe 1982, volume 2, page 5 ff) are constructed from aliphatic and / or cycloaliphatic di-, tri- or higher-value alcohols, if necessary together with monohydric alcohols and from aliphatic and / or cycloaliphatic carboxylic acids and higher polycarboxylic acids.

Examples of suitable alcohols are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol , 1,5-pentanediol, 3-methyl-l, 5-pentanediol, 1,6-hexanediol, 2-ethyl-l, 6-hexanediol, 2,2,4, -trimethyl-1,6-hexanediol, 1, 4-dimethylolcyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, etherification products of diols and polyols, e.g. Di- and triethylene glycol, polyethylene glycol, neopentyl glycol ester of hydroxipivalic acid.

Examples of suitable carboxylic acids are adipic,

Azelaine, tetrahydrophthalic, hexahydrophthalic, endo methylene tetrahydrophthalic acid and its derivatives capable of esterification.

The carboxyl-containing polyesters used in the coating compositions according to the invention can optionally contain tertiary amino groups. These tertiary amino groups can be introduced into the polymer in various ways. On the one hand, tertiary amino groups containing carboxylic acids and / or alcohols can be used in the construction of the polyesters, on the other hand, the tertiary amino groups can also be introduced in a second stage. This can be done, for example, by reacting hydroxyl-containing polymers with carboxylic acids which contain a tertiary amino group or with compounds which contain on average 0.8 to 1.5, preferably one, free isocyanate group and at least one tertiary amino group per molecule. respectively. In addition, the carboxyl group-containing polymers can be reacted with compounds which, in addition to a tertiary amino group, also contain an alcohol, thiol or primary or secondary amino group. For further details, reference is made to the description below.

However, carboxyl group-containing acrylate copolymers, preferably in combination with the carboxyl group-containing polymers, are preferably used as carboxyl group-containing polymers. The carboxyl group-containing acrylate copolymers are preferably obtainable by

A) by means of radical solution polymerization

a- ^) 0 to 50% by weight of one or more monomers containing hydroxyl groups,

a ₂ ) 0 to 50% by weight of one or more carboxyl group-containing monomer and

a ₃ ) 30 to 85% by weight of at least one further ethylenically unsaturated, copolymerizable monomer,

an acrylate copolymer is prepared, the sum of the parts by weight of components a- ^ to a _{3 being} 100% by weight and the parts by weight of components a- _{j ^} and a ₂ not being both zero at the same time, and

B) if appropriate, the acrylate copolymer obtained in stage (A) is reacted with carboxylic acid anhydrides, the amount of carboxylic acid anhydrides used being selected so that the resulting copolymer has the desired acid number.

The acrylate copolymers are particularly preferably obtainable by first off

20 to 40% by weight of one or more monomers containing hydroxyl groups,

a ₂ ) 0 to 10% by weight of one or more monomers containing carboxyl groups and

a ₃ ) 40 to 60% by weight of at least one further ethylenically unsaturated, copolymerizable monomer,

wherein the sum of the parts by weight of components a ^ to a _{3 is in} each case 100% by weight, a hydroxyl-containing acrylate copolymer is prepared and this is then reacted in a second stage with carboxylic acid anhydrides, the amount of carboxylic acid anhydrides used in this way is chosen that the standing copolymer has the desired acid number.

Also preferred are acrylate copolymers which are obtainable by first off

a- ^) 0 to 20% by weight of one or more monomers containing hydroxyl groups,

a ₂ ) 20 to 50% by weight of one or more monomers containing carboxyl groups and

wherein the sum of the parts by weight of components a- ^ to a _{3 is in} each case 100% by weight, a carboxyl- and optionally hydroxyl-containing acrylate copolymer is prepared and this copolymer is optionally reacted with carboxylic anhydrides in a second stage, the amount of carboxylic acid anhydrides used is chosen so that the resulting copolymer has the desired acid number.

Hydroxyalkyl esters α, β-unsaturated carboxylic acids with primary or secondary hydroxyl groups can be used as component a ^ _^ . Hydroxyalkyl esters with primary hydroxyl groups are predominantly used, since they have a higher reactivity in the polymer-analogous reaction with the carboxylic anhydride. Mixtures of hydroxyalkyl esters with primary hydroxyl groups and hydroxyalkyl esters with secondary hydroxyl groups can of course also be used, for example if hydroxyl groups are required in the copolymer containing carboxyl groups, for example for adjusting the compatibility of the carboxyl group copolymer containing pen.

Examples of suitable hydroxyalkyl esters α, β-unsaturated carboxylic acids with primary hydroxyl groups are hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxibutyl acrylate and the corresponding methacrylates. Examples of usable hydroxyalkyl esters with a secondary hydroxyl group are 2-hydroxypropyl acrylate, 2-hydroxibutyl acrylate, 3-hydroxibutyl acrylate and the corresponding methacrylates. Of course, the corresponding esters of other α, β-unsaturated carboxylic acids, such as e.g. crotonic acid and isocrotonic acid.

Advantageously, component a ^ can be, at least in part, a reaction product of one mole of hydroxyethyl acrylate and / or hydroxyethyl methacrylate and an average of 2 moles of caprolactone. A component of a reaction product of monomers containing hydroxyl groups with ethylene oxide and / or propylene oxide can also be used at least in part. The number of ether groups in the reaction product is generally less than 15, preferably less than 10.

Examples of suitable monomers a ₂ containing carboxyl groups are unsaturated carboxylic acids, such as, for example, acrylic, methacrylic, itaconic, crotonic, isoerotonic, aconitic, maleic and fumaric acid, half-esters of maleic and

Fu aric acid and ß-carboxyethyl acrylate and adducts of hydroxyalkyl esters of acrylic acid and / or methacrylic acid with carboxylic acid anhydrides, such as, for example, phthalic acid mono-2-methacryloyloxyethyl ester, hexahydrophthalic acid mono-4-acryloyloxybutyl ester and caprolactone-modified carboxylate carboxylate groups, such as the commercial product Tone XM 300 from Union Carbide / USA, a polyester acrylate based on caprolactone with a molecular weight of approx. 500, with a polymerizable double bond and a carboxyl group. Also suitable as components a ₂ are the long-chain monomers which have carboxyl end groups and are described in EP-B1-230330 on page 2, line 29 to page 4, line 8. These long-chain monomers containing carboxyl groups can be prepared, for example, by first containing hydroxyl groups

Monomers are reacted with ethylene oxide and / or propylene oxide and the resulting products are then reacted with an acid anhydride to give the monomer containing carboxyl groups.

In addition, other ethylenically unsaturated, copolymerizable monomers are used to build up the acrylate copolymer. When selecting these monomers, care must be taken to ensure that the incorporation of these monomers a ₃ does not lead to undesirable properties of the copolymer. The choice of component a ₃ largely depends on the desired properties of the curable composition with regard to elasticity, hardness, compatibility and polarity.

For example, ₃ can be used as component a ₃ alkyl esters of ethylenically unsaturated carboxylic acids. Examples include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, 3,5,5-trimethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylic lat, hexadecyl (meth) acrylate, octadecyl (meth) acrylate,

Octadecenyl (meth) acrylate and the corresponding esters maleic, fumaric, tetrahydrophthalic, crotonic, isocrotonic, vinyl acetic and itaconic acid.

These alkyl esters of ethylenically unsaturated carboxylic acids are usually used in an amount of 5 to 50% by weight, preferably 15 to 35% by weight, based in each case on the total weight of the monomers used.

Also suitable as component a ₃ are vinylaromatic compounds, for example styrene, vinyltoluenes, α-methylstyrene, chlorostyrenes, o-, m- or p-methylstyrene, 2,5-dimethylstyrene, p-methoxistyrene, p-tertiary-butylstyrene, p- or m-vinylphenol and the like. Vinyl toluenes and, in particular, styrene are preferably used. These vinyl aromatic compounds are usually used in an amount of 0 to 30% by weight, preferably 5 to 15% by weight, in each case based on the total weight of the monomers used.

Monomers with at least two polymerizable, ethylenically unsaturated double bonds can also be used as component a ₃ , in particular in order to increase the reactivity and crosslinking density of the coating films.

Dimethacrylates of diols having 2 to 12 carbon atoms, for example glycol dimethacrylate, propanediol dimethacrylate, butanediol dimethacrylate, pentanediol dimethacrylate, hexanediol dimethacrylate, heptanediol dimethacrylate dimethacrylate, methyl methacrylate, and methylethane acrylate, are advantageously used as the monomer with at least two polymerizable double bonds. Reaction products of hydroxyethyl methacrylate and ethylene or propylene oxide and the resulting products are also preferred. Dimers used. The use of these branching monomers, which are preferably used, has the advantage, compared to other branching monomers, as described, for example, in EP-A-158 161, of a better color number of the end products and the advantage of reducing the required number of products amount of regulator. The use of branching monomers based on diacrylates can lead to gelling due to side reactions (Michael addition of the mercapto group of the regulator with the double bonds of the branching monomer, catalyzed by the tertiary amino groups of the copolymer). The use of divinylbenzene and its derivatives leads to a strong color number of the resins and to the brittleness of the resulting films.

Combinations of the polyunsaturated monomers can of course also be used. If ₃ monomers with at least two polymerizable, ethylenically unsaturated double bonds are used as component a, these compounds are usually used in an amount of more than 3 to 30% by weight, preferably 5 to 25% by weight, in each case based on the total weight of the monomers used.

As component a ₃ it is also possible to use polysiloxane macromonomers having a number average molecular weight of 1000 to 40,000, preferably 2000 to 10,000, and on average 0.5 to 3.0 ethylenically unsaturated double bonds per molecule. The use of these polysiloxane macromonomers leads to coatings which can be easily overpainted and have good weather resistance, good resistance to solvents and chemicals as well as a good topcoat level and sufficient scratch resistance. Suitable components a ₃ are, for example, those in DE-A-38 07 571 on pages 5 to 7, that in DE-A-37 06 095 in columns 3 to 7 and that in EP-B-358 153 on pages 3 to 6 and the polysiloxane macromonomers described in columns 5 to 9 of US-A-4,754,014.

Furthermore, other acryloxisilane-containing vinyl monomers with the abovementioned molecular weights and contents of ethylenically unsaturated double bonds are also suitable, for example compounds which can be prepared by reacting hydroxy-functional silanes with epichlorohydrin and then reacting the reaction product with (meth) acrylic acid and / or Hydroxyalkyl esters of (meth) acrylic acid.

As component a _3, preference is given to using polysiloxane macro monomers of the following formula:

with R ¹ = H or CH ₃ ,

R, R, R, R • = identical or different aliphatic hydrocarbon radicals with 1 to 8 carbon atoms, in particular methyl or phenyl radical, n = 2 to 5, preferably 3 and m = 8 to 30.

The α, U-acryloxiorganofunctional polydimethylsiloxane of the formula is particularly preferred

with n about 9, an acrylic oxide equivalent of

550 g / equivalent, an OH number of 102 mg KOH / g and a viscosity of 240 Pas (25 ^β C) used.

As component a ₃ , preference is also given to using polysiloxane macromonomers which have been prepared by reacting 70 to 99.999 mol% of a compound 1, represented by the formula (I)

in which R ^{1 represents} an aliphatic hydrocarbon group with 1 to 8 C atoms or a phenyl radical and R ² , R ³ and R ⁴ each represent a halogen radical or an alkoxy radical with 1 to 4 C atoms or a hydroxyl group, with 30 up to 0.001 mol% of a compound (2) represented by the formula (II)

CH ₂ = (II)

in which R ^{5 represents} a hydrogen atom or a methyl radical, R ⁶ , R ⁷ and R ⁸ each represent halogen, OH or an alkoxy radical having 1 to 4 carbon atoms or an aliphatic hydrocarbon group having 1 to 8 carbon atoms, wherein at least one of the radicals R, R ⁷ or R ^{8 is} OH or an alkoxy group and n represents an integer from 1 to 6.

The reaction between the compounds (1) and (2) is brought about by the dehydrating condensation of the hydroxyl groups which are contained in these compounds and / or of the hydroxyl groups which are on the Hydrolysis of the alkoxy groups of these compounds are to be returned. Depending on the reaction conditions, the reaction includes a dealcoholizing condensation in addition to the dehydration reaction. If the compounds (1) or (2) contain halogen radicals, the reaction between (1) and (2) is accomplished by dehydrohalogenation. For details of this implementation, reference is made to the above-mentioned documents.

If polysiloxane macromonomers are used as component a ₃ , their use amount is usually less than 5% by weight, preferably between 0.05 and 2.5% by weight and particularly preferably less than 1% by weight, each based on the total weight of the monomers used.

As component a ₃ unsaturated compounds with tertiary amino groups, such as N, N'-diethylamino ethyl methacrylate can, 2-vinylpyridine, 4-vinylpyridine, Vinylpyrrolin, vinylquinoline, vinylisoquinoline, N, N '-Dimethylaminoethylvinylether, 2-methyl-5- vinyl pyridine, vinyl imidazole and dimethylaminopropyl methacrylamide can be used.

Compounds such as acrylonitrile, methacrylonitrile, acrolein and methacrolein are also suitable as component a ₃ .

As component a ₃ can of course also

Mixtures of the monomers mentioned are used.

The preparation of the acrylate copolymers is carried out by means of solution polymerization in an organic solvent or solvent mixture at temperatures of ^β in allgmeinen between 80 and 150 C, preferably between 90 and 120 "C. The polymerization is preferably carried out in the absence of oxygen, for example by working in a nitrogen atmosphere. The reactor is equipped with appropriate stirring, heating and cooling devices and a reflux condenser in which volatile constituents are retained .

The polymerization takes place in the presence of initiators, such as azo initiators, e.g. Azobiscarboxylic acid amides and azobiscarboxylic acid nitriles, e.g. Azobisisovaleronitrile, azobis (2,4-dimethylvaleronitrile), azoisobutylvaleronitrile, azobisisobutyronitrile and azobiscyclohexanenitrile; organic peroxides, e.g. Dibenzoyl peroxide, dicuyl peroxide, cumene hydroperoxide, di-tert-butyl peroxide, tert-butylamyl peroxide, tert-butyl hydroperoxide, 2,2-di-tert-butyl peroxibutane, tert-amyl perbenzoate, 1,3-bis (tert. -butylperoxiisopropyl) benzene, diisopropylbenzene monohydroperoxide and diacyl peroxides, such as Diacetyl peroxide, peroxiketal, e.g. 2,2-di (tert-amylperoxipropane) and ethyl 3,3-di- (tert-amylperoxibutyrate), thermolabile, highly substituted ethane derivatives, for example based on sylol-substituted ethane derivatives and based on benzpinacol.

The amount of initiator is in most cases 0.1 to 5% by weight, based on the amount of monomer to be processed, but it may also be higher, usually the initiator is dissolved in a part of the polymer for the polymerization solvent used, gradually metered in during the polymerization reaction. The initiator feed preferably lasts about 0.5 to 2 hours longer than the monomer feed, so as to also have a good effect during the postpolymerization phase. If initiators with only a low disintegration rate, ie long shelf life below the the reaction conditions used, it is also possible to submit the initiator. Furthermore, the initiator can also be partially presented.

The reaction is preferably carried out in the presence of polymerization regulators, in particular if more than 5% by weight of difunctional monomers are used as component a _{3 in} order to restrict the dispersity of the resulting copolymers and thus to reduce the viscosity of the resins. Mercapto compounds are preferably suitable as regulators, mercaptoethanol being particularly preferably used. Other possible regulators are, for example, alkyl mercaptans, such as, for example, tert-dodecyl mercaptan, octyl mercaptan, phenyl erptane, octyldecyl mercaptan, butyl mercaptan, thiocarboxylic acids, such as thioacetic acid or thiolactic acids.

These regulators are used in an amount of up to 2% by weight, based on the amount of monomers to be processed. They are preferably dissolved in one of the monomer feeds and added with the monomers, insofar as it can be excluded that side reactions take place. The amount of regulator added is preferably constant over time.

The polymerization is carried out in an organic solvent which is inert to the monomers used and, if appropriate, to carboxylic acid anhydrides. The polymerization solid is preferably at least 30% by weight, particularly preferably between 45 and 60

% By weight, based on the total weight of the reaction mixture. Examples of suitable solvents are commercially available alkylated, aromatic hydrocarbons or mixtures with a boiling range from 130 to 220 ° C., toluene, xylene and other aromatic hydrocarbons, esters, such as butyl acetate, 1-methoxypropyl, Acetate-2, butyl glycol acetate, ethyl ethoxy propionate and the like, and aliphatic hydrocarbons and the like. If there is no addition of anhydrides after the polymerization, higher-boiling alcohols and / or ester alcohols, such as, for example, secondary butanol and 1-methoxypropanol, can also be used.

The components a ^ and / or a ₂ and / or a ₃ can also be introduced at least partially together with part of the total amount of solvent to be used and heated to the respective reaction temperature. As already described, the remaining amount of the solvent is preferably added gradually together with the catalyst. The remaining amount of the monomers, if any, is metered in.

The acrylate copolymers suitable for use in the coating compositions have an acid number of 15 to 200 mg KOH / g, preferably 30 to 120 mg KOH / g. The acrylate copolymers particularly preferably also have tertiary amino groups, the amine number preferably being 5 to 60 mg KOH / g, particularly preferably 10 to 40 mg KOH / g. This acrylate copolymer preferably also has an OH number of more than 20 mg KOH / g, since in this case there is particularly good compatibility with the epoxides. In addition, these acrylate copolymers preferably have number-average molecular weights from 500 to 8000, particularly preferably from 1000 to 5000 and very particularly preferably from 1500 to 3500.

As already mentioned above, the tertiary amino groups can be incorporated into the copolymer by using monomers with tertiary amino groups as component a ₃ .

However, the tertiary amino groups are preferred by Reacting the polymer containing hydroxyl and carboxyl groups with compounds (V) which contain 0.8 to 1.5, preferably one, free isocyanate group and at least one tertiary amino group per molecule. However, it is also possible to first react the hydroxyl-containing copolymer with the compounds (V) and only then to introduce the carboxyl groups into the copolymer by reaction with the carboxylic anhydride. In this case, the reaction with the anhydride can take place at lower temperatures.

The amount of compound (V) is chosen so that the resulting resin has the desired amine number. The compounds (V) used to introduce the tertiary amino group are prepared by reacting diisocyanates or polyisocyanates with a stoichiometric deficit on a tertiary amine. Suitable for this reaction are tertiary amines of the general formula NR ¹ R ² R ³ , where R ^{1 is} preferably an alkanol radical or another hydroxyl-containing radical and R ² or R ^{3 can be} alkyl or cycloalkyl radicals. Dialkylalkanolamines, such as, for example, dimethylethanolamine, diethylethanolamine and their higher homologs or isomers, are preferred.

Examples of suitable di- or polyisocyanates are: aromatic isocyanates, such as, for example, 2,4-, 2,6-tolylene diisocyanate and mixtures thereof, 4,4'-diphenylmethane diisocyanate, m-phenylene, p-phenylene , 4,4'-diphenyl, 1,5-naphthalene, 1,4-naphthalene, 4,4'-toluylene, xylylene diisocyanate and substituted aromatic systems, such as, for example, dianisidine diisocyanates, 4,4 '-Diphenyl ether diisocyanates or chlorodiphenyl diisocyanates or higher functional aromatic isocyanates such as 1,3,5-triisocyanatobenzene, 4,4', 4 '' triisocyanate triphenyl methane, 2,4,6-triisocyanatotoluene and 4,4'-diphenyl dimethyl methane-2,2 ', 5,5'-tetraisocyanate; cycloaliphatic see isocyanates such as 1,3-cyclopentane, 1,4-cyclohexane, 1,2-cyclohexane and isophorone diisocyanate; aliphatic isocyanates such as trimethylene, tetra methylene, pentamethylene, hexamethylene, trimethyl hexamethylene-l, 6-diisocyanate and tris-hexamethylene triisoeyanate.

Diisocyanates with different reactive isocyanate groups are preferably used, e.g. Isophorondiisoeyanat.

The reaction between the amine and the isocyanate is carried out at temperatures of 0 to 80 ° C, preferably from 20 to 50 C. The proportions of the ^β Reaktions¬ partner are that the compound (V) formed 0.8 to 1.5 is selected, , preferably contains a free isocyanate group.

In addition, there is also the possibility of reacting the hydroxyl- and optionally carboxyl-containing copolymer with carboxylic acids which contain a tertiary nitrogen atom. Examples of such carboxylic acids are 3- and 4-dimethylaminobenzoic acid, picolinic acid and dimethylaminosalicylic acid.

Finally, it is also possible to introduce tertiary amino groups into the copolymer containing carboxyl groups by reacting some of the carboxyl groups or, if appropriate, carboxylic anhydride groups of the copolymer with compounds which, in addition to a tertiary amino group, also contain an alcohol or primary or secondary amino group or a thiol group . Examples of suitable compounds are mentioned, for example, in DE-A-39 24 618 on page 7, line 12 to line 31.

Of course, the tertiary amino groups can also be introduced into the copolymer by combining different methods.

Finally, the carboxyl group-containing copolymers described in German patent application DE-A-39 18 669 are also suitable as binders (A). These copolymers containing carboxyl groups can be prepared by means of radical solution polymerization using one or more vinyl esters of aliphatic monocarboxylic acids with 5 to 15 carbon atoms per molecule which are branched in the alpha position.

To promote the copolymerization and reduce the homopolymerization of the individual components, they are prepared by the process described in DE-A-3918669 on page 9, lines 23 to 54.

In addition to the described carboxyl group-containing polyesters and / or copolymers, it is of course also possible to use other carboxyl group-containing polymers with the specified number average molecular weight and the specified acid number, provided that they lead to the desired properties of the coating agents.

It is essential to the invention that the coating compositions contain, as crosslinking agents, an isocyanate-based compound containing epoxy groups. These compounds containing epoxy groups are known per se and are described, for example, in DE-A-31 38 196, DE-A-32 05 733 and DE-A-32 45 563.

For example, the reaction product of a biuret and / or isocyanurate and / or urethane groups containing di- and / or polyisocyanate compound with glycine dyl alcohol used.

To produce component (B), the trimerizates of aliphatic or cycloaliphatic or aromatic diisocyanates can be used as the isocyanate component. The production of trimerizates of 1,6-diisocyanatohexane is described for example in EP-A-10 589 or US-A-4,324,879. However, the isocyanurate group-containing trimerizates of other diisocyanates are also suitable, in particular the isocyanurized isophorone diisocyanate and the isocyanurate group-containing trimerizates of, for example, 4,4-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthylene diisocyanate, 2,4- and 2,6 -Toluylene diisocyanate, trimethylhexamethylene diisocyanate and others. The tri erisate of hexamethylene diisocyanate and isophorone diisocyanate is preferably used as the isocyanate component.

Compounds of the formula are suitable as glycidyl alcohol

where R is an alkylene radical having 1 to 10 carbon atoms and RR ^{11 is} hydrogen, a methyl or ethyl group.

Glycidol (2,3-epoxypropanol-1-glycid) is preferably used.

The reaction of the isocyanate groups with the glycidyl alcohol takes place in particular when catalysts, such as, for example, tertiary amines or β-caprolactam or organotin compounds, for example dibutyltin dilaurate, are added. at temperatures between about -5 "and +40 ^β C. In this reaction, inert organic solvents are generally added, such as ketones, hydrocarbons, chlorinated hydrocarbons and ethers and esters. In the reaction of the glycidyl alcohol with the

Isocyanate component is preferably used with a deficit of glycidyl alcohol in order to reduce the presence of toxic residual monomers (epoxy monomers). The ratio of isocyanate and glycidyl alcohol is particularly preferably between 1: 0.98 and 1: 0.95. Free NCO groups are replaced by lower alcohols, e.g. Butanol, propanol, pentanol, iso-butanols, iso-propanol and iso-pentanols

Also suitable as a crosslinking agent (B) containing epoxy groups is the reaction product of a di- and / or polyisocyanate containing urethane groups with glycidyl alcohol. The di- and / or polyisocyanates containing urethane groups can be prepared, for example, by reacting terminal hydroxyl-containing polyesters and / or polyethers with low molecular weight di- and / or polyisocyanates.

The polyesters containing terminal OH groups are known compounds which, if desired, can be obtained from polyfunctional alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, trimethylolpropane, butanediol, hexanediol and polyhydric acids or their anhydrides, e.g. Maleic anhydride,

Phthalic anhydride or terephthalic acid or adipic acid can be obtained by esterification. The OH numbers of such polyesters are generally between about 80 and 250 mg KOH / g. These OH group-containing polyesters are then known per se

Way with the low molecular weight di- or polyisocyanate implemented. Examples of isocyanates used are hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, tolylene diisocyanate (mixture of isomers) or diphenylmethane diisocyanate.

Furthermore, the reaction products of the di- and / or polyisocyanates just mentioned with hydroxyl-containing polyethers can also be used to prepare the crosslinking agent (B) containing epoxy groups. Preferred polyether diols are derived from glycols containing 2 to 4 carbon atoms. Accordingly, polyethylene and / or polypropylene glycol and / or polytetramethylene glycol (produced by ring-opening polymerization of tetrahydrofuran) are suitable. Adducts of ethylene oxide and / or propylene oxide with polyhydric alcohols, such as glycerol, trimethylolpropane and pentaerythritol, can also be used.

The reaction of the di- and / or polyisocyanate with the hydroxyl-containing compound (polyester, polyether, OH-acrylate) is usually carried out in the presence of solvents and suitable catalysts based on organotin compounds or tertiary amines. The subsequent reaction of the di- and / or polyisocyanate containing urethane groups with the glycidyl alcohol is carried out analogously to the reaction of the di- and / or polyisocyanate containing isocyanurate groups with the glycidyl alcohol, so that reference is made here only to the corresponding points in the description .

Finally, the crosslinking agent (B) containing epoxide groups is the reaction product of a di- and / or polyisocyanate with allyl alcohol and subsequent epoxidation of the double bond. Examples of suitable di- and / or polyisocyanates are already listed isocyanates. The reaction with the allyl alcohol and the epoxidation of the resulting double bonds are known per se and therefore do not need to be explained in more detail.

The coating compositions according to the invention usually contain the carboxyl group-containing polymer (component A) in an amount of 10 to 70% by weight, based on the total weight of the coating composition. The epoxy group-containing compound (component B) is usually used in an amount of 10 to 50% by weight, based on the total weight of the coating composition. The content of organic solvents is usually 20 to 50% by weight, based on the total weight of the coating agent.

If appropriate, the coating compositions can also contain a crosslinking catalyst. Tertiary amines, quaternary ammonium compounds such as e.g. Benzyltrimethylammonium hydroxide and

Benzyltrimethylammonium chloride, special Chromverbin¬ connections and tin compounds. Of course, the use of a crosslinking catalyst is unnecessary in most cases in which tertiary amino groups are already incorporated in the copolymer or in the polyester. By using an internal or external cross-linking catalyst, lower stoving temperatures and shorter stoving times are achieved. The crosslinking catalyst is preferably used in an amount of 0.5 to 10% by weight, based on the total weight of the di- or polyepoxide component and the binder component.

The coating compositions according to the invention can also contain customary pigments and fillers in customary amounts, preferably 0 to 60% by weight, based on the total Composition, as well as other auxiliaries and additives, such as leveling agents, silicone oils, plasticizers, such as phosphoric acid esters and phthalic acid esters, viscosity-controlling additives, matting agents, UN absorbers and light stabilizers in customary amounts, preferably 0 to 10% by weight, based on the overall composition.

These coating agents can be applied by spraying, flooding, dipping, rolling, knife coating or brushing onto a substrate in the form of a film, the film then being cured to form a firmly adhering coating.

The coating compositions according to the invention are suitable for automotive serial painting and - if low curing temperatures between 20 and 80 ° C. can be used by appropriate selection of the hardener component - also particularly suitable for the refinishing of motor vehicles. They are used as primers, top coats or clear coats.

The coating compositions according to the invention are produced by mixing binders and crosslinking agents, if appropriate with the addition of solvents. Pigments and / or fillers can optionally be added to the binder or the crosslinking agent by customary methods (dispersing, dissolving and the like). Any additional additives that may be used can be added both to the binder or the crosslinking agent and to the finished coating agent.

The present invention therefore also relates to a process for the preparation of coating compositions comprising A) one or more polymers containing carboxyl groups with a number average molecular weight of 500 to 8000 and an acid number of 15 to 200 mg KOH / g as the essential binder component,

B) one or more compounds containing epoxy groups as crosslinking agents and

C) one or more organic solvents,

in which the binder component (A) and the crosslinking agent (B) are mixed only shortly before the coating agents are applied. The process is characterized in that the compound (B) containing epoxide groups can be prepared from

1. a biuret and / or isocyanurate and / or urethane groups containing di- and / or poly-isocyanate compound and glycidyl alcohol of the formula

where R stands for an alkylene radical with 1 to 10 C atoms and RR ¹¹ for H, a methyl or ethyl radical. and or

2. a di- and / or polyisocyanate and allyl alcohol with subsequent epoxidation of the double bonds.

With regard to the description of the components used in the method and the implementation of this method, reference is made to the previous pages of this description. The invention is explained in more detail in the following examples. All parts and percentages are by weight unless expressly stated otherwise.

I. 1. Preparation of the epoxy crosslinker Bl

In a 41 stainless steel kettle equipped with a stirrer,

Thermometers and dosing devices are weighed:

307 parts glycidol (2,3-epoxypropanol) 132 parts xylene.

A mixture of the following components is allowed to run into this mixture over the course of 4 hours:

1540 parts of a commercially available isocyanurate based on isophorone diisocyanate in

70% solution in solvent naphtha (commercial product Desmodur ^ Z 4370 from Bayer) 6.94 parts dibutyltin dilaurate (10% solution in xylene).

The reaction mixture is kept at 40 ° C. during the feed. The progress of the reaction is determined via the content of free isocyanate, optionally after-catalyzed with a further 0.05% DBTL. The reaction is complete when the free isocyanate content is less than 0.2%. In the present example, a residual NCO content of 0.15% was achieved. Then it is dissolved with xylene to a solids content of 65% and further with methoxypropanol to a solids content of 60%. End dates of the networker: Solids: 65.1% (60 minutes 130 * C; lg substance + 3 ml xylene) rest NCO: 0% epoxide equivalent weight: 365

Viscosity (55% in butyl acetate): 2.0 dPa.s

1.2. Production of epoxy crosslinker B2

Analogously to the example B1, a mixture of the following components is weighed in a 41 stainless steel bowl equipped with a stirrer and metering device:

436.6 parts glycidol (2,3-epoxypropanol) 187 parts xylene.

A mixture of the following raw materials is metered in with stirring over the course of 4 hours:

1296 parts of a commercially available trimerized

Hexamethylene diisocyanates (isocyanurate form) as a 90% solution (commercial product Tolonate HDT 90 from Rhönen-Poulenc)

186 parts of xylene

8 parts of dibutytin dilaurate as a 10% solution in xylene.

The reaction is highly exothermic. After the

The exothermic reaction was kept at room temperature for 3 hours until a residual NCO content of 0.2% was reached. The mixture was then dissolved with methoxypropanol to a solids content of 70%. Solids: 72.1% (60 minutes 130 ° C; lg substance +

3 ml xylene) balance NCO: 0% epoxide equivalent weight: 277 viscosity (70% in butyl acetate): 6.8 dPa.s

I. 3. Production of epoxy crosslinker B3

63.8 parts of a commercially available, aliphatic epoxy resin with a molecular weight of approx. 1200 and an epoxide equivalent weight of approx. 250-550 based on a dinuclear melamine resin, reacted with acrylamide and subsequent epoxidation of the acrylic double bonds (commercial product Santolink LSE 4114 or Monsanto) and 36.2 parts of methoxypropanol are mixed.

II. L. Production of a Binder Al (Acrylate) Containing Carboxyl Groups

The acrylate copolymer (AI) was prepared in a 4 liter stainless steel polymerization kettle with stirrer, reflux condenser, two monomer feeds and an initiator feed. The components specified in each case are weighed in and the template is then heated to 110 ° C.

The start of all feeds is started simultaneously, the two monomer feeds are metered in uniformly within 3 h, and the initiator feed is metered in within 4 h. During the polymerization, the temperature in the boiler is kept at 108-110 ° C. The mixture is then polymerized for a further 2 h. The acrylic resin solution thus obtained has a solids content of 50%. There are then 309.8 parts of hexahydrophthalic anhydride (HHPSA) was added and added at 110 C ^β of the acrylate resin. After the acid number determination in aqueous and alcoholic KOH results in the same values, sec. Butanol diluted to 50% solids.

The commercial product became a siloxane macromonomer

Marubenr. <S * ^) AK 5 from Toagosei. Chemi .cal Industries

Co., LTD. used. It has a number average molecular weight of approximately 5000 and on average one ethylenically unsaturated double bond per molecule.

Preparation of an acrylate copolymer (A-.)

Template:

13 parts of siloxane macromonomer (Marubenr ** 'AK5) 552.2 parts of butyl acetate 552.2 parts of xylene

Monomer feed A:

130 parts of dimethylaminoethyl methacrylate

130 parts ethylhexyl acrylate 195 parts hydroxibutyl acrylate

312 parts of n-butyl acrylate

Monomer feed B:

208 parts hexanediol dimethacrylate 195 parts hydroxyethyl methacrylate 130 parts styrene

6.5 parts mercaptoethanol 0.7 parts triisodecyl phosphite Initiator inflow:

65 parts of ^2,2-azobis (2-methylbutanenitrile) 130 parts Butyl acetate 130 parts Xylene

Viscosity (original):> 40 dPa.s (23 ^β C) acid number (aqueous / alcoholic): 67.5 / 71.1 mgKOH / g

II. 2 Production of a Binder A2 Containing Carboxyl Groups (Polyester.

In a 4 liter polycondensation kettle with stirrer, steam-heated column and water separator, 488 parts of hexahydrophthalic anhydride and 515 parts

1,4-Cyclohexanedicarboxylic acid, 752 parts trimethylolpropane, 72.5 parts neopentyl glycol, 82.8 parts methyl diethanolamine, 200 parts isononanoic acid, 77 parts benzoic acid, 88 parts xylene and 1.14 parts triisodecyl phosphite and slowly heated up. It is at a temperature of max. 190 "C up to an acid number of 20 mgKOH / g and a viscosity of 2.0 dPa.s (50% in butylglycol) condensed, then it is cooled and dissolved at 130 ° C with 886 parts of xylene. After further cooling to 50 ° C are then added to this solution 321.3 parts of hexahydrophthalic anhydride and 1.12 parts of triisodecyl phosphite. the addition of the anhydride is carried out at max. 50 ^β C until an acid number of 68 mg KOH / g and a viscosity of 2.4 dPas (50% ig in butylglycol) and then 377 parts of xylene and 147 parts of sec-butanol are dissolved in. The polyester thus obtained has a solids content of 61.5%, an acid number of 68 mgKOH / g and a viscosity of 13 , 5 dPa.s (original). III. Production of a catalyst solution

1.90 parts of diazobicyclooctane are mixed with 98.1 parts of butyl acetate 98/100.

Examples 1 and 2

A clear lacquer solution is prepared from the components listed in Table 1 by mixing. The crosslinking agent solutions EV1 and EV2 (examples according to the invention) and W1 (comparative example) are prepared from the components given in Table 2 by mixing.

The clear coat solution is adjusted with lacquer thinner to a viscosity measured in a DIN 4 flow cup at 20 ^β C, 21 s. 100 parts of this clear lacquer solution are then mixed with 50 parts of the crosslinking agent solution EV1 or EV2 or Wl and 30 parts of the catalyst solution. The paint is then applied to phosphated and coated steel sheets. For this purpose, the phosphated steel sheets are coated with a commercially available conventional filler (commercial product Glasurit basic filler EP AC01-1492 from Glasurit GmbH, Münster, with an epoxy-functional binder and an amino-functional hardener), dried overnight and then with a commercially available conventional metallic Basecoat (commercial product basecoat series AE 54 from Glasurit GmbH, Münster, based on a hydroxyl-containing polyester, cellulose acetobutyrate, wax and a melamine resin). After a flash-off time of 30 min. the clear coat is applied. The panels are then dried at 60 ° C for 30 minutes. The results of the paint test are shown in Table 3.

Table 1: Composition of the clear coat solution

Binder AI containing carboxyl groups 55.0 parts Tinuvin® 1130 ¹ ) 1.0 Tinuvin 900 ²⁾ 1.0

Butylglycol acetate 3.0 parts l-methoxypropyl acetate-2 13.0 parts Carboxyl group-containing binder A2 27.0 parts

1.) commercial light stabilizer from Ciba Geigy based on benzotriazole

2) commercial light stabilizer from Ciba Geigy based on a sterically hindered amine

Table 2: Composition of the crosslinking solutions EV1, EV2 and Wl

EV1 EV2 Wl

Epoxy crosslinker Bl 99.0 - -

Epoxy crosslinker B2 - 99.0 -

Epoxy crosslinker B3 - - 99.0

1-methoxy propyl acetate -2 -2 1.0 1.0 1.0

Explanations to Table 3:

--- ⁾ Dust-free:

Approximately 15 minutes after spraying the varnish, the bar is sprinkled with a small sample of sea sand (3 - 4 g) on one corner. The board is then pushed open from a height of 30 cm with the edge (free fall). Dust-free is achieved if there is no sand adherence. The test is repeated every 15 minutes; shortly before dust-free is reached, the repetition interval is reduced to 5 minutes.

² > freedom from tack:

Approximately 20 minutes after the absence of dust has been reached, the lacquered board is covered with an approximately 3 cm ² plate of paper. A small plate made of hard plastic is placed on this paper, on which a weight of 100 g is then placed. After exactly one minute, as in the test for freedom from dust, it is checked whether the paper is still adhering. Time interval as for the dust-free test.

³ 'Drying recorder:

The test is carried out with a device of type BK Dryingrecorder, manufacturer: The Mickle Laboratory Engineering Company Ltd., Gomshall, Great Britain, according to the following rule: Before the steel sheets are coated with the basecoat, 25 mm wide and 30 cm long glass strips are applied lengthways ¬ device glued to the respective test panels. The test panels together with glass strips are then coated with the basecoat after a drying time of 30 minutes coated with the clear coat. The glass strips are removed and clamped in a special test device (drying recorder). With the help of the drying recorder, a needle with a diameter of 1 mm is now pulled over the lacquer within 6 hours. Due to the drying of the paint, 3 different scratch marks appear, called phases. In the first phase the needle penetrates to the glass, the lacquer still flows together. In the second phase there is a clear scratch mark, the paint no longer flows together. In the third phase the needle penetrates the lacquer surface only very slightly and leaves a barely visible trace. The middle of the transition between two clearly definable phases is specified as the phase change.

Petrol resistance: As described in Example 1, the clearcoat is applied to phosphated, coated steel sheets coated with the filler and basecoat described above and dried at room temperature. After 24 hours of storage at room temperature, gasoline resistance is tested for the first time.

Implementation: A cotton pad (filter grade, type T950, size 2.3 from Seitz) impregnated with 1 ml of premium petrol (lead-free), which has a grid-like structure on the underside, is placed on the lacquer layer and weighed 100 g Minutes charged. The structure caused by the swelling of the lacquer surface is then assessed visually: not marked, marked, very lightly marked, slightly marked, marked, strongly marked, very strongly marked. It is stated Duration of storage at room temperature in days after which the petrol test is OK, ie no marking is visible.

5) The viscosity is measured as the flow time in a DIN 4 cup at 20 * C

6) Volvo Crack Test:

Test conditions 1 cycle: 4h at 50 ° C in the oven

2h at 35 ^β C and 95-100% rel. Humidity 2h at 35 ° C and 95-100% rel. Air humidity and 21 sulfur dioxide 16h at -30 ° C in the freezer

Wash the plate with water and dry

Evaluation:

Degree of bubbles according to DIN 53209

Cracks ASTM D660

⁷ 'Compatibility check on glass board:

After dilution to spray viscosity, the lacquer is poured onto a glass sheet with an inclination of approximately 45 °. The paint is allowed to flash off at room temperature for about 2 hours. If the paint components are compatible, a speck-free film results.

Summary of test results

When the clearcoats 1 and 2 according to the invention were stirred together, in contrast to the clearcoat of comparative example 1, there was no turbidity when the components were stirred together. The clearcoat of example 1 is distinguished by a shorter absence of dust and tack than the clearcoat of comparative example 1. It is advantageous Clear varnish of comparative example 1. It is particularly advantageous to extend the pot life of the clearcoats of Examples 1 and 2 according to the invention in comparison with the clearcoat of Comparative Example 1. In addition, the gasoline test for the clearcoat of Example 1 is already after 5 days after storage at room temperature, for the clearcoat of the example 2 after 12 days, in the case of the clearcoat of comparative example 1, on the other hand, only in order after 20 days. In the short-term weathering in the Volvo test, the clearcoat of Example 1 and

Example 2 better than the clearcoat of Comparative Example 1.

Claims

claims

1. Containing hardenable coating agent at low temperatures of below 120 ^β C.

A) one or more polymers containing carboxyl groups with a number average molecular weight of 500 to 8000 and an acid number of 15 to 200 mg KOH / g as essential binder component,

B) one or more compounds containing epoxy groups as crosslinking agents and

C) one or more organic solvents,

characterized in that the epoxy group-containing compound (B) can be prepared from

1. a biuret and / or isocyanurate and / or urethane groups containing polyisocyanate compound and glycidyl alcohol of the formula

H0-R-CH ₂ -C - CH ₂ k ¹

wherein

R for an alkylene radical with 1 to 10 carbon atoms and

R ^{1 represents} hydrogen, a methyl or ethyl group. and or

2. a di- and / or polyisocyanate and with

Allyl alcohol followed by epoxidation of the double bonds.

2. Coating agent according to claim 1, characterized gekenn¬ characterized in that the epoxy group-containing compound B is a reaction product based on isophorone di-isocyanate as the isocyanate component.

3. Coating agent according to claim 1 or 2, characterized ge indicates that the epoxy group-containing connection is a reaction product which has been prepared using 2,3-epoxypropanol-1 as glycidyl alcohol.

4. Coating agent according to one of claims 1 to 3, characterized in that the carboxyl-containing polymers used as binder A have an acid number of 30 to 120 mg KOH / g and / or an amine number of 0 to 50 mg KOH / g, preferably 10 to 40 mg KOH / g.

5. Coating agent according to one of claims 1 to 4, characterized in that the carboxyl-containing polymers used as binder A have been prepared by first producing a hydroxyl-containing polymer with an OH number of 30 to 200 mg KOH / g , which was then reacted with carboxylic anhydrides to give the corresponding carboxyl-containing polymers.

6. coating agent according to one of claims 1 to 5, characterized in that the coating agent A) 10 to 70% by weight of binder A containing carboxyl groups,

B) 10 to 50% by weight of crosslinking agent B containing epoxide groups

C) 0 to 60 wt .-% pigments and / or fillers and

D) contains 0 to 10% by weight of conventional auxiliaries and additives, the sum of the proportions by weight of components A to D being 100% by weight in each case.

7. A process for the preparation of coating compositions according to one of claims 1 to 6, in which the binder component A and the crosslinking agent B are mixed only shortly before the application of the coating composition.

8. Use of the coating agent according to one of claims 1 to 6 for automotive refinishing.

9. Use of the coating agent according to one of claims 1 to 6 for automotive serial painting.