EP0447428B1 - Process for the production of a multi-layer coating, water-dilutable coating compositions, water-dilutable emulsion polymers and process for the production of water-dilutable emulsion polymers - Google Patents

Abstract

The invention concerns a process for the production of multi-layer coatings, which uses a pigmented aqueous base coating composition containing a water-dilutable emulsion polymer as the film-forming material. The water-dilutable emulsion polymer is produced by two-stage emulsion polymerization. In the first stage, a polymer with a glass transition temperature (TG1) of +30 to +110°C is produced. In the second stage, a monomer mixture which, if polymerized alone, would give a polymer with a glass transition temperature (TG2) of -60 to +20°C is polymerized in the presence of the polymer produced in the first stage. The hydroxyl number of the emulsion polymer lies between 2 and 100.

Description

• (1) als Basisbeschichtungszusammensetzung eine pigmentierte wäßrige Beschichtungszusammensetzung, die als filmbildendes Material ein wasserverdünnbares Emulsionspolymer enthält, auf die Substratoberfläche aufgebracht wird
• (2) aus der in Stufe (1) aufgebrachten Zusammensetzung ein Polymerfilm gebildet wird
• (3) auf der so erhaltenen Basisschicht eine geeignete transparente Deckbeschichtungszusammensetzung aufgebracht wird und anschließend
• (4) die Basisschicht zusammen mit der Deckschicht eingebrannt wird.

The invention relates to a method for producing a multilayer protective and / or decorative coating on a substrate surface, in which

• (1) a pigmented aqueous coating composition containing a water-thinnable emulsion polymer as the film-forming material is applied as a base coating composition to the substrate surface
• (2) a polymer film is formed from the composition applied in step (1)
• (3) a suitable transparent top coating composition is applied to the base layer thus obtained and then
• (4) the base layer is baked together with the cover layer.

The invention also relates to water-thinnable coating compositions, water-thinnable emulsion polymers and a process for the preparation of water-thinnable emulsion polymers.

The process described above for the production of multilayer protective and / or decorative coatings is known and is used in particular for the production of metallic effect coatings on automobile bodies (cf. for example EP-A-89497, DE-A-3 628 124 and EP-A-38 127 ).

With the process in question, metallic effect coatings with a good metallic effect can only be produced if the aqueous base coating compositions used are composed such that they can be applied to the substrate in relatively thin, fast-drying layers, in particular with the aid of automatic painting systems, and after carrying out process steps (3) and (4), the metal pigment particles in parallel alignment to the substrate surface.

In addition, the aqueous base coating compositions must be composed in such a way that the base layer of the baked metal effect coating adheres well to the substrate and the transparent cover layer adheres well to the base layer. Furthermore, the aqueous base coating compositions must be composed in such a way that the baked-on metallic effect coating shows no matting, delamination phenomena or even bubbles after exposure to a constant temperature of condensed water.

Finally, it is desirable that the aqueous basecoat compositions exhibit high storage stability.

DE-A-36 28 124 discloses aqueous base coating compositions which contain, as film-forming material, a mixture of a water-dilutable emulsification polymer and a water-dilutable polyurethane resin. These basecoat compositions do not optimally meet the requirements set out above.

The object on which the present invention is based is to provide aqueous base coating compositions which are suitable for the process in question and which optimally meet the requirements set out above.

• (a) in einer ersten Stufe 10 bis 90 Gewichtsteile eines Gemisches aus
  • (a1) 100 bis 60, vorzugsweise 99,5 bis 75 Gew.-% eines cycloaliphatischen oder aliphatischen Esters der Methacrylsäure oder Acrylsäure oder eines Gemisches aus solchen Estern und
  • (a2) 0 bis 40, vorzugsweise 0,5 bis 25 Gew.-% eines mit (a1) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren
  in wäßriger Phase in Gegenwart eines oder mehrerer Emulgatoren und eines oder mehrerer radikalbildender Initiatoren polymerisiert werden, wobei die Summe der Gewichtsanteile von (a1) und (a2) stets 100 Gew.-% ergibt und (a1) und (a2) so ausgewählt werden, das in der ersten Stufe ein Polymer mit einer Glasübergangstemperatur (T_G₁) von +30 bis +110°C erhalten wird und
• (b) nachdem mindestens 80 Gew.-% des in der ersten Stufe eingesetzten ethylenisch ungesättigten Monomers bzw. Monomerengemisches umgesetzt worden sind, in einer zweiten Stufe 90 bis 10 Gewichtsteile eines Gemisches aus
  • (b1) 47 bis 99, vorzugsweise 75 bis 90 Gew.-% eines cycloaliphatischen oder aliphatischen Esters der Methacrylsäure oder Acrylsäure oder eines Gemisches aus solchen Estern
  • (b2) 1 bis 20, vorzugsweise 5 bis 15 Gew.-% eines mindestens eine Hydroxylgruppe tragenden mit (b1), (b3) und (b4) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren
  • (b3) 0 bis 8, vorzugsweise 2 bis 6 Gew.-% eines mindestens eine Carboxyl- oder Sulfonsäuregruppe tragenden mit (b1), (b2) und (b4) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren und
  • (b4) 0 bis 25, vorzugsweise 2 bis 15 Gew.-% eines weiteren mit (b1), (b2) und (b3) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren
  in Gegenwart des in der ersten Stufe erhaltenen Polymers polymerisiert werden, wobei die Summe der Gewichtsanteile von (b1), (b2), (b3) und (b4) stets 100 Gew.-% ergibt und (b1), (b2), (b3) und (b4) so ausgewählt werden, daß eine alleinige Polymerisation des in der zweiten Stufe eingesetzten Monomerengemisches zu einem polymer mit einer Glasübergangstemperatur (T_G2) von -60 bis +20°C führen würde und wobei die Reaktionsbedingungen so gewählt werden, daß das erhaltene Emulsionspolymer eine zahlenmittlere Molmasse von 200.000 bis 2.000.000 aufweist und wobei das in der ersten Stufe eingesetzte ethylenisch ungesättigte Monomer bzw. Monomerengemisch und das in der zweiten Stufe eingesetzte Monomerengemisch in Art und Menge so ausgewählt werden, daß das erhaltene Emulsionspolymer eine Hydroxylzahl von 2 bis 100 aufweist und die Differenz T_G1 - T_G2 10 bis 170°C beträgt.

This object is surprisingly achieved by aqueous base coating compositions which contain a water-dilutable emulsion polymer which can be obtained by

• (a) in a first stage 10 to 90 parts by weight of a mixture
  • (a1) 100 to 60, preferably 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters and
  • (a2) 0 to 40, preferably 0.5 to 25% by weight of a monomer copolymerizable with (a1) or a mixture of such monomers
  in the aqueous phase in the presence of one or more Emulsifiers and one or more radical-forming initiators are polymerized, the sum of the proportions by weight of (a1) and (a2) always giving 100% by weight and (a1) and (a2) being selected so that in the first stage a polymer with a glass transition temperature (T _G ₁) of +30 to + 110 ° C is obtained and
• (b) after at least 80% by weight of the ethylenically unsaturated monomer or monomer mixture used in the first stage has been reacted, in a second stage 90 to 10 parts by weight of a mixture
  • (b1) 47 to 99, preferably 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters
  • (b2) 1 to 20, preferably 5 to 15% by weight of a monomer carrying at least one hydroxyl group and copolymerizable with (b1), (b3) and (b4) or a mixture of such monomers
  • (b3) 0 to 8, preferably 2 to 6% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and can be copolymerized with (b1), (b2) and (b4) or a mixture of such monomers and
  • (b4) 0 to 25, preferably 2 to 15% by weight of another with (b1), (b2) and (b3) copolymerizable monomers or a mixture of such monomers
  are polymerized in the presence of the polymer obtained in the first stage, the sum of the parts by weight of (b1), (b2), (b3) and (b4) always giving 100% by weight and (b1), (b2), ( b3) and (b4) are selected so that a single polymerization of the monomer mixture used in the second stage would lead to a polymer with a glass transition temperature (T _G2 ) of -60 to + 20 ° C and the reaction conditions are chosen so that the emulsion polymer obtained has a number average molar mass of 200,000 to 2,000,000 and the type and amount of the ethylenically unsaturated monomer or monomer mixture used in the first stage and the monomer mixture used in the second stage are selected in such a way that the emulsion polymer obtained has a hydroxyl number of 2 to 100 and the difference T _G1 - T _{G2 is} 10 to 170 ° C.

In the unpublished EP-A-332 011 aqueous coating compositions are disclosed which can be used as wood lacquers and which contain a water-thinnable emulsion polymer which is free of hydroxyl groups and can be obtained via a two-stage emulsion polymerization process. U.S. Patent 4,150,005 discloses aqueous coating compositions containing a water-thinnable emulsion polymer which can be obtained by preparing a highly hydrophilic polymer with a low glass transition temperature in a first emulsion polymerization stage and in its presence in a second emulsion polymerization stage a hydrophobic polymer with a high glass transition temperature is produced. Multi-layer protective and / or decorative coatings of the type described above and the problems encountered in the manufacture of these coatings are not addressed in U.S. Patent No. 4,150,005. GB-A-2,034,334 describes aqueous coating compositions which contain a water-thinnable emulsion polymer which can be obtained via a two-stage emulsion polymerisation process and which must have N-methylol groups. GB-A-2,034,334 is not indicative of the fact that the two polymer stages have to differ in their glass transition temperatures in the manner according to the invention. Multilayer protective and / or decorative coatings of the type described above and the problems encountered in the manufacture of these coatings are not addressed in GB-A-2,034,334. EP-A-287 144 describes a process for producing a multilayer coating of the type described above, in which aqueous base coating compositions are used which contain a water-dilutable emulsification polymer which can be obtained via a two-stage emulsion polymerization process and which in the second stage ("shell" ) has a very high proportion of acid groups and in which the first and second polymer stages differ in their glass transition temperatures in such a way that the first stage has a lower glass transition temperature than the second stage.

The water-dilutable emulsion polymers used according to the invention are, in a known manner, for example in a stirred tank, by a two-stage emulsion polymerization in an aqueous medium with heating and cooling device, producible. The monomers can be added in such a way that a solution of all of the water, the emulsifier and part of the initiator is introduced and the monomer or monomer mixture and separately therefrom, but in parallel the rest of the initiator is slowly added at the polymerization temperature. However, it is also possible to introduce some of the water and the emulsifier and to prepare a pre-emulsion from the rest of the water and the emulsifier and from the monomer or monomer mixture, which is added slowly at the polymerization temperature, the initiator again being added separately.
It is preferred in the first stage to add the monomer or monomer mixture in the form of a pre-emulsion and in the second stage to add the monomer or monomer mixture in bulk, ie without water and emulsifier, and to add the initiator separately but in parallel. It is particularly preferred in the first stage to first prepare a seed polymer from a part (generally about 30% by weight of the total pre-emulsion to be used) of the pre-emulsion to be used in the first stage and then to add the rest of the pre-emulsion to be used in the first stage . The polymerization temperature is generally in the range from 20 to 100 ° C., preferably 40 to 90 ° C.

The quantitative ratio between the monomers and the water can be selected so that the resulting dispersion has a solids content of 30 to 60% by weight, preferably 35 to 50% by weight.

An anionic emulsifier is preferably used alone or in a mixture as the emulsifier.

Examples of anionic emulsifiers are the alkali metal salts of sulfuric acid half-esters of alkylphenols or alcohols, furthermore the sulfuric acid half-esters of oxethylated alkylphenols or oxethylated alcohols, preferably the alkali metal salts of sulfuric acid half-esters of a nonylphenol, alkyl or with 4-5 moles of ethylene oxide per mole Aryl sulfonate, sodium lauryl sulfate, sodium lauryl ethoxylate sulfate and secondary sodium alkane sulfonates, the carbon chain of which contains 8-20 carbon atoms. The amount of the anionic emulsifier is 0.1-5.0% by weight, based on the monomers, preferably 0.5-3.0% by weight. In addition, to increase the stability of the aqueous dispersions, a nonionic emulsifier of the ethoxylated alkylphenol or fatty alcohol type, for example an addition product of 1 mol of nonylphenol and 4-30 mol of ethylene oxide, can be used in a mixture with the anionic emulsifier.

A peroxide compound is preferably used as the radical-forming initiator. The initiator is water-soluble or monomer-soluble. A water-soluble initiator is preferably used.

Suitable initiators are the customary inorganic per compounds, such as ammonium persulfate, potassium persulfate, ammonium or alkali metal peroxydiphosphate and organic peroxides, such as e.g. Benzoyl peroxide, organic peresters, such as perisopivalate, partly in combination with reducing agents, such as sodium disulfite, hydrazine, hydroxylamine and catalytic amounts of accelerators, such as iron, cobalt, cerium and vanadyl salts, preferably alkali metal or ammonium peroxydisulfates. The redox initiator systems disclosed in EP-A-107300 can also be used.

In the first stage, 10 to 90, preferably 35 to 65 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers are emulsion polymerized. The monomer or monomer mixture used in the first stage is selected so that when the monomer or monomer mixture used in the first stage is completely polymerized out, a polymer with a glass transition temperature (T _G1 ) of + 30 ° C. to + 110 ° C, preferably 60 to 95 ° C is obtained. Since the glass transition temperature of emulsion polymers according to the equation

T_G

= Glasübergangstemp. des Copolymers in °K

W_n

= Gewichtsanteil des n-ten Monomers

T_Gn

= Glasübergangstemp. des Homopolymers aus dem n-ten Monomer

x

= Anzahl der verschiedenen Monomeren

näherungsweise berechnet werden kann, bereitet es dem Fachmann keine Probleme, das in der ersten Stufe einzusetzende Monomer bzw. Monomerengemisch so auszuwählen, daß bei völliger Auspolymerisation des in der ersten Stufe eingesetzten Monomers bzw. Monomerengemisches ein polymer mit einer Glasübergangstemperatur (T_G1) von + 30 bis + 110°C, vorzugsweise 60 bis 95°C erhalten wird.

T _G

= Glass transition temp. of the copolymer in ° K

W _n

= Weight fraction of the nth monomer

T _Gn

= Glass transition temp. of the homopolymer from the nth monomer

x

= Number of different monomers

can approximately be calculated, the person skilled in the art has no problem selecting the monomer or monomer mixture to be used in the first stage such that, when the monomer or monomer mixture used in the first stage is completely polymerized out, a polymer having a glass transition temperature (T _G1 ) of + 30 to + 110 ° C, preferably 60 to 95 ° C is obtained.

Examples of monomers which can be used in the first stage are: vinylaromatic hydrocarbons, such as styrene, α-alkylstyrene and vinyltoluene, esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates with up to 20 carbon atoms in the alcohol radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or methacrylate, acrylic and / or methacrylic acid, acrylic and / or methacrylamide, N-methylolacrylamide and / or N-methylol methacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, β-ethylenically unsaturated carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxyethyl methacrylate, 4-hydroxyl acrylate 4-hydroxybutyl methacrylate etc.

In the first stage, preference is given to using ethylenically unsaturated monomers or mixtures of ethylenically unsaturated monomers which are essentially free of hydroxyl and carboxyl groups. "Substantially free" is intended to mean that it is preferred to use monomers or monomer mixtures which are free from hydroxyl and carboxyl groups, but that the monomers or monomer mixtures used also contain small amounts (for example as a result of impurities) of hydroxyl and / or may contain carboxyl groups. The content of hydroxyl and carboxyl groups should preferably be at most so high that a polymer prepared from the monomer or monomer mixture used in the first stage has an OH number of at most 5 and an acid number of at most 3.

• (a1) 100 bis 60, vorzugsweise 99,5 bis 75 Gew.-% eines cycloaliphatischen oder aliphatischen Esters der Methacrylsäure oder Acrylsäure oder eines Gemisches aus solchen Estern und
• (a2) 0 bis 40, vorzugsweise 0,5 bis 25 Gew.-% eines mit (a1) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren

eingesetzt, wobei die Summe der Gewichtsanteile von (a1) und (a2) stets 100 Gew.-% ergibt.In the first stage, a mixture of is particularly preferred

• (a1) 100 to 60, preferably 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters and
• (a2) 0 to 40, preferably 0.5 to 25% by weight of a monomer copolymerizable with (a1) or a mixture of such monomers

used, the sum of the proportions by weight of (a1) and (a2) always giving 100% by weight.

As component (a1) can be used, for example: cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and alkyl methacrylates with up to 20 carbon atoms in the alkyl radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate and methacrylate or mixtures of these monomers.

As component (a2) e.g. vinylaromatic hydrocarbons such as styrene, α-alkylstyrene and vinyltoluene, acrylic and methacrylamide and acrylonitrile and methacrylonitrile or mixtures of these monomers are used.

After at least 80% by weight, preferably at least 95% by weight, of the ethylenically unsaturated monomer or monomer mixture used in the first stage has been reacted, 90 to 10, preferably 65 to 35 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers is emulsion polymerized in the presence of the polymer obtained in the first stage, the monomer or monomer mixture used in the second stage being selected such that a sole polymerization of the monomer or monomer mixture used in the second stage into a polymer with a glass transition temperature (T _G2 ) of -60 to + 20 ° C, preferably -50 to 0 ° C would lead. This selection presents no difficulties for the person skilled in the art, since the glass transition temperatures of emulsion polymers - as already explained above - can easily be approximately calculated.

It is further essential to the invention that the monomer or monomer mixture used in the first stage and the monomer or monomer mixture used in the second stage are selected in such a way that the emulsion polymer obtained has a hydroxyl number of 2 to 100, preferably 10 to 50 and the difference T _G1 - T _{G2 is} 10 to 170, preferably 80 to 150 ° C.

Examples of monomers which can be used in the second stage are: vinylaromatic hydrocarbons, such as styrene, α-alkylstyrene and vinyltoluene, Esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates with up to 20 carbon atoms in the alcohol radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or - methacrylate, acrylic and / or methacrylic acid, acrylic and / or methacrylamide, N-methylolacrylamide and / or N-methylolmethacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, β-ethylenically unsaturated carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, etc.

• (b1) 47 bis 99, vorzugsweise 75 bis 90 Gew.-% eines cycloaliphatischen oder aliphatischen Esters der Methacrylsäure oder Acrylsäure oder eines Gemisches aus solchen Estern
• (b2) 1 bis 20, vorzugsweise 5 bis 15 Gew.-% eines mindestens eine Hydroxylgruppe tragenden mit (b1), (b3) und (b4) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren
• (b3) 0 bis 8, vorzugsweise 2 bis 6 Gew.-% eines mindestens eine Carboxyl- oder Sulfonsäuregruppe tragenden, mit (b1), (b2) und (b4) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren und
• (b4) 0 bis 25, vorzugsweise 2 bis 15 Gew.-% eines weiteren mit (b1), (b2) und (b3) copolymerisierbaren Monomeren oder eines Gemisches aus solchen Monomeren eingesetzt, wobei die Summe der Gewichtsanteile von (b1), (b2), (b3) und (b4) stets 100 Gew. % ergibt.

A mixture is preferably formed in the second stage

• (b1) 47 to 99, preferably 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters
• (b2) 1 to 20, preferably 5 to 15% by weight of a monomer carrying at least one hydroxyl group and copolymerizable with (b1), (b3) and (b4) or a mixture of such monomers
• (b3) 0 to 8, preferably 2 to 6% by weight of a monomer carrying at least one carboxyl or sulfonic acid group and copolymerizable with (b1), (b2) and (b4) or a mixture of such monomers and
• (b4) 0 to 25, preferably 2 to 15% by weight of a further monomer which can be copolymerized with (b1), (b2) and (b3) or a mixture of such monomers used, the sum of the parts by weight of (b1), (b2), (b3) and (b4) always giving 100% by weight.

As component (b1) e.g. are used: cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and alkyl methacrylates with up to 20 carbon atoms in the alkyl radical, such as e.g. Methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate and methacrylate or mixtures of these monomers.

The following can be used as component (b2): hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, β-ethylenically unsaturated carboxylic acid. These esters can be derived from an alkylene glycol esterified with the acid, or can be obtained by reacting the acid with an alkylene oxide. Hydroxyalkyl esters of acrylic acid and methacrylic acid, in which the hydroxyalkyl group contains up to 4 carbon atoms, or mixtures of these hydroxyalkyl esters are preferably used as component (b2). Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate or 4-hydroxybutyl methacrylate. Corresponding esters of other unsaturated acids, such as ethacrylic acid, crotonic acid and similar acids with up to about 6 carbon atoms per molecule, can also be used.
Acrylic acid and / or methacrylic acid and / or acrylamidomethylpropanesulfonic acid are preferably used as component (b3). However, other ethylenically unsaturated acids with up to 6 carbon atoms in the molecule can also be used. Examples of such acids are ethacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid.

As component (b4) e.g. are used: vinyl aromatic hydrocarbons, such as styrene, α-alkylstyrene and vinyl toluene, acrylic and methacrylamide and acrylonitrile and methacrylonitrile, or mixtures of these monomers.

The emulsion polymer used according to the invention should have a number average molar mass (determination: gel permeation chromatography using polystyrene as the standard) of 200,000 to 2,000,000, preferably 300,000 to 1,500,000.

The person skilled in the art knows how to select the reaction conditions during the emulsion polymerization in order to obtain emulsion polymers which have the number-average molar masses given above (see, for example, chemistry, physics and technology of the plastics in individual representations, dispersions of synthetic high polymers, part 1 of F Hölscher, Springer Verlag, Berlin, Heidelberg, New York, 1969).

It is preferred that the aqueous base coating compositions according to the invention contain, in addition to the emulsion polymer described above, a water-dilutable polyurethane resin as the film-forming material.

The base coating compositions according to the invention preferably contain water-thinnable, urea-containing polyurethane resins which have a number average molecular weight (determination: gel permeation chromatography using polystyrene as the standard) of 1000 to 60,000, preferably 1500 to 50,000 and an acid number of 5 to 70, preferably 10 to 30 and by reaction, preferably chain extension of prepolymers containing isocyanate groups with polyamines and / or hydrazine can be produced.

The prepolymer containing isocyanate groups can be prepared by reacting polyalcohols having a hydroxyl number from 10 to 1800, preferably 50 to 500, with excess polyisocyanates at temperatures up to 150 ° C., preferably 50 to 130 ° C., in organic solvents which do not react with isocyanates can, succeed. The equivalence ratio of NCO to OH groups is between 1.5 and 1.0 to 1.0, preferably between 1.4 and 1.2 to 1. The polyols used to prepare the prepolymer can be low molecular weight and / or high molecular weight and they can contain inert anionic groups.

Low molecular weight polyols can be used to increase the hardness of the polyurethane. They have a molecular weight from 60 to about 400 and can contain aliphatic, alicyclic or aromatic groups. Amounts of up to 30% by weight of the total polyol constituents, preferably about 2 to 20% by weight, are used. The low molecular weight polyols with up to about 20 carbon atoms per molecule, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol, are advantageous , Trimethylolpropane, castor oil or hydrogenated castor oil, di-trimethylolpropane ether, pentaerythritol, 1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol F, neopentylglycol, hydroxypivalic acid-neopentylglycol ester, hydroxyethylated or hydroxypropylated bisphenol A, bisphenol A, mixtures thereof .
In order to obtain a high flexibility NCO prepolymer, a high proportion of a predominantly linear polyol with a preferred hydroxyl number of 30 to 150 should be added. Up to 97% by weight of the total polyol can consist of saturated and unsaturated polyesters and / or polyethers with a molecular weight Mn exist from 400 to 5000. Aliphatic polyether diols are suitable as high molecular weight polyols of the general formula H - (- 0 - (- CHR) _n -) _m -OH in which R = hydrogen or a lower alkyl radical which is optionally provided with different substituents, where n = 2 to 6, preferably 3 to 4 and m - Is 2 to 100, preferably 5 to 50. Examples are linear or branched polyether diols, such as poly (oxyethylene) glycols, poly (oxypropylene) glycols and / or poly (oxybutylene) glycols. The selected polyether diols should not introduce excessive amounts of ether groups, otherwise the polymers formed will swell in water. The preferred polyether diols are poly (oxypropylene) glycols in the molecular weight range Mn from 400 to 3000. Polyester diols are produced by esterification of organic dicarboxylic acids or their anhydrides with organic diols or are derived from a hydroxycarboxylic acid or a lactone. To produce branched polyester polyols, polyols or polycarboxylic acids with a higher valency can be used to a small extent. The dicarboxylic acids and diols can be linear or branched aliphatic, cycloaliphatic or aromatic dicarboxylic acids or diols.
The diols used to prepare the polyesters consist, for example, of alkylene glycols, such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and other diols, such as dimethylcyclohexane. The acid component of the polyester consists primarily of low molecular weight dicarboxylic acids or their anhydrides with 2 to 30, preferably 4 to 18, carbon atoms in the molecule. Suitable acids are, for example, o-phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, glutaric acid, hexachlorheptanedicarboxylic acid, tetrachlorophthalic acid and / or. Instead of these acids, their anhydrides, if they exist, can also be used. When forming polyester polyols, smaller ones can also be used Amounts of carboxylic acids with 3 or more carboxyl groups, for example trimellitic anhydride or the adduct of maleic anhydride with unsaturated fatty acids, are present.

in der n und R die bereits angegebene Bedeutung haben. Für die Herstellung der Polyesterdiole wird das unsubstituierte -Caprolacton, bei dem n den Wert 4 hat und alle R-Substituenten Wasserstoff sind, bevorzugt. Die Umsetzung mit Lacton wird durch niedermolekulare Polyole, wie Ethylenglykol, 1,3-Propandiol, 1,4-Butandiol, Dimethylolcyclohexan gestartet. Es können jedoch auch andere Reaktionskomponenten, wie Ethylendiamin, Alkyldiakanolamine oder auch Harnstoff mit Caprolacton umgesetzt werden.According to the invention, polyester diols are also used which are obtained by reacting a lactone with a diol. They are characterized by the presence of a terminal hydroxyl group and recurring polyester content of the formula - (- CO- (CHR) _n -CH₂-0 -) -. Here, n is preferably 4 to 6 and the substituent R is hydrogen, an alkyl, cycloalkyl or alkoxy radical. No substituent contains more than 12 carbon atoms. The total number of carbon atoms in the substituent does not exceed 12 per lactone ring. Examples include hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid and / or hydroxystearic acid. The lactone used as a raw material can be represented by the following general formula

in which n and R have the meaning already given. Unsubstituted -caprolactone, in which n has the value 4 and all R substituents are hydrogen, is preferred for the preparation of the polyester diols. The reaction with lactone is started by low molecular weight polyols, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, dimethylolcyclohexane. However, other reaction components, such as ethylenediamine, alkyldiacanolamines or urea, can also be reacted with caprolactone.

Also suitable as higher molecular weight diols are polylactam diols, which are produced by reacting, for example, ε-caprolactam with low molecular weight diols.

Aliphatic, cycloaliphatic and / or aromatic poly are used as typical multifunctional isocyanates isocyanates with at least two isocyanate groups per molecule. The isomers or isomer mixtures of organic diisocyanates are preferred. Suitable aromatic diisocyanates are phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, naphthylene diisocyanate and diphenylmethane diisocyanate.
Due to their good resistance to ultraviolet light, (cyclo) aliphatic diisocyanates produce products with a low tendency to yellowing. Examples include isophorone diisocyanate, cyclopentylene diisocyanate and the hydrogenation products of aromatic diisocyanates, such as cyclohexylene diisocyanate, methylcyclohexylene diisocyanate and dicyclohexylmethane diisocyanate. Examples of aliphatic diisocyanates are trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylethylene diisocyanate, dimethylethylene diisocyanate, methyltrimethylene diisocyanate and trimethylhexane diisocyanate. Isophorone diisocyanate and dicyclohexyl methane diisocyanate are particularly preferred as diisocyanates. The polyisocyanate component used to form the prepolymer can also contain a proportion of higher-quality polyisocyanates, provided that this does not cause gel formation. Products which have been found to be suitable as triisocyanates are those which are formed by trimerization or oligomerization of diisocyanates or by reaction of diisocyanates with compounds containing polyfunctional OH or NH groups. These include, for example, the biuret of hexamethylene diisocyanate and water, the isocyanurate of hexamethylene diisocyanate or the adduct of isophorone diisocyanate with trimethylolpropane.
The average functionality can optionally be reduced by adding monoisocyanates. Examples of such chain terminating monoisocyanates are phenyl isocyanate, cyclohexyl isocyanate and stearyl isocyanate.
Polyurethanes are generally not compatible with water Lich, if special components are not incorporated in their synthesis and / or special manufacturing steps are carried out. So large an acid number is built in that the neutralized product can be dispersed stably in water. For this purpose, compounds are used which contain two H-active groups reacting with isocyanate groups and at least one group capable of forming anions. Suitable groups which react with isocyanate groups are, in particular, hydroxyl groups and primary and / or secondary amino groups. Groups which are capable of forming anions are carboxyl, sulfonic acid and / or phosphonic acid groups. Carboxylic acid or carboxylate groups are preferably used. They should be so inert that the isocyanate groups of the diisocyanate preferably react with the other groups of the molecule that are reactive toward isocyanate groups. For this purpose, alkanoic acids with two substituents on the carbon atom are used. The substituent can be a hydroxyl group, an alkyl group or an alkylol group. These polyols have at least one, generally 1 to 3 carboxyl groups in the molecule. They have two to about 25, preferably 3 to 10, carbon atoms. Examples of such compounds are dihydroxypropionic acid, dihydroxysuccinic acid and dihydroxybenzoic acid. A particularly preferred group of dihydroxyalkanoic acids are the α, α-dimethylolalkanoic acids, which are characterized by the structural formula RC (CH₂OH) ₂COOH, in which R = hydrogen or an alkyl group having up to about 20 carbon atoms. Examples of such compounds are 2,2-dimethylol acetic acid, 2,2-dimethylol propionic acid, 2,2-dimethylol butyric acid and 2,2-dimethylol pentanoic acid. The preferred dihydroxyalkanoic acid is 2,2-dimethylolpropionic acid. Compounds containing amino groups are, for example, -diaminovaleric acid, 3,4-diaminobenzoic acid, 2,4-diaminotoluenesulfonic acid and 2,4-diaminodiphenyl ether sulfonic acid. The polyol containing carboxyl groups can be 3 to Make up 100% by weight, preferably 5 to 50% by weight, of the total polyol component in the NCO prepolymer.
The amount of ionizable carboxyl groups available through the carboxyl group neutralization in salt form is generally at least 0.4% by weight, preferably at least 0.7% by weight, based on the solid. The upper limit is about 6% by weight. The amount of dihydroxyalkanoic acids in the unneutralized prepolymer gives an acid number of at least 5, preferably at least 10. The upper limit of the acid number is 70, preferably 40, based on the solids.
Before the reaction with isocyanates, this dihydroxyalkanoic acid is advantageously at least partially neutralized with a tertiary amine in order to avoid a reaction with the isocyanates.
The NCO prepolymers used according to the invention can be prepared by simultaneously reacting the polyol or polyol mixture with an excess of diisocyanate. On the other hand, the implementation can also be carried out in stages in the prescribed order.
Examples are described in DE 26 24 442 and DE 32 10 051. The reaction temperature is up to 150 ° C, with a temperature in the range of 50 to 130 ° C being preferred. The reaction continues until practically all of the hydroxyl functions have been converted.

The NCO prepolymer contains at least about 0.5% by weight of isocyanate groups, preferably at least 1% by weight of NCO, based on the solid. The upper limit is approximately 15% by weight, preferably 10% by weight, particularly preferably 5% by weight. The reaction can optionally be carried out in the presence of a catalyst such as organotin compounds and / or tertiary amines. In order to keep the reactants in a liquid state and to enable better temperature control during the reaction, the addition of organic is Solvents that do not contain Zerewitinoff active hydrogen are possible. Usable solvents are, for example, dimethylformamide, esters, ethers, such as diethylene glycol dimethyl ether, keto esters, ketones, such as methyl ethyl ketone and acetone, ketones substituted with methoxy groups, such as methoxy hexanone, glycol ether esters, chlorinated hydrocarbons, aliphatic and alicyclic hydrocarbon pyrrolidones, such as N-methylpyrrolidone Furans, aromatic hydrocarbons and their mixtures. The amount of solvent can vary within wide limits and should be sufficient to form a prepolymer solution with a suitable viscosity. Mostly 0.01 to 15 wt .-% solvent, preferably 0.02 to 8 wt .-% solvent, based on the solid. If the water-insoluble solvents boil lower than water, they can be gently distilled off after the production of the urea-containing polyurethane dispersion by vacuum distillation or thin-film evaporation. Higher boiling solvents should be water soluble and remain in the aqueous polyurethane dispersion to facilitate the confluence of the polymer particles during film formation. Particularly preferred solvents are N-methylpyrrolidone, optionally in a mixture with ketones, such as methyl ethyl ketone.
The anionic groups of the NCO prepolymer are at least partially neutralized with a tertiary amine. The resulting increase in dispersibility in water is sufficient for infinite dilutability. It is also sufficient to permanently disperse the neutralized polyurethane containing urea groups. Suitable tertiary amines are, for example, trimethylamine, triethylamine, dimethylethylamine, diethylmethylamine, N-methylmorpholine. After neutralization, the NCO prepolymer is diluted with water and then results in a finely divided dispersion. Shortly thereafter, the isocyanate groups still present are included Di- and / or polyamines reacted with primary and / or secondary amino groups as chain extenders. This reaction leads to a further linkage and increase in the molecular weight. The competitive reaction between amine and water with the isocyanate must be well coordinated (time, temperature, concentration) in order to obtain optimum properties and well monitored for reproducible production. Water-soluble compounds are preferred as chain extenders because they increase the dispersibility of the polymeric end product in water. Hydrazine and organic diamines are preferred because they usually build up the highest molecular weight without gelling the resin. However, the prerequisite for this is that the ratio of the amino groups to the isocyanate groups is selected appropriately. The amount of chain extender is determined by its functionality, the NCO content of the prepolymer and the duration of the reaction. The ratio of the active hydrogen atoms in the chain extender to the NCO groups in the prepolymer should generally be less than 2: 1 and preferably in the range from 1.0: 1 to 1.75: 1. The presence of excess active hydrogen, especially in the form of primary amino groups, can result in polymers with undesirably low molecular weights.
Polyamines are essentially alkylene polyamines having 1 to 40 carbon atoms, preferably about 2 to 15 carbon atoms. They can carry substituents that have no hydrogen atoms that are reactive with isocyanate groups. Examples are polyamines with a linear or branched aliphatic, cycloaliphatic or aromatic structure and at least two primary amino groups. The diamines include ethylenediamine, propylenediamine, 1,4-butylenediamine, piperazine, 1,4-cyclohexyldimethylamine, 1,6-hexamethylenediamine, trimethylhexamethylenediamine, methanediamine, isophoronediamine, 4,4'-diaminodicyclohexylmethane and aminoethylethanolamine. Preferred diamines are alkyl or cycloalkyl diamines, such as propylenediamine and 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.
The chain can be extended at least partially with a polyamine that has at least three amine groups with a reactive hydrogen. This type of polyamine can be used in such an amount that unreacted amine nitrogen atoms with 1 or 2 reactive hydrogen atoms are present after the polymer has been extended. Such useful polyamines are diethylenetriamine, triethylenetetraamine, dipropylenetriamine and dibutylenetriamine. Preferred polyamines are the alkyl or cycloalkyl triamines, such as diethylenetriamine. To prevent gelling during chain extension, small amounts of monoamines, such as ethylhexylamine, can also be added.

The water-dilutable polyurethane resins to be used according to the invention and their preparation are also described in EP-A-89497 and US Pat. No. 4,719,132.

The mixture of emulsion polymer and polyurethane resin contained in the preferred aqueous base coating compositions as a film-forming material consists of 95 to 40% by weight of emulsion polymer and 5 to 60% by weight of polyurethane resin, the proportions each referring to the solids content and their total always 100% by weight .-%.

In addition to the emulsion polymer or the mixture of emulsion polymer and polyurethane resin, the aqueous base coating compositions according to the invention advantageously also contain further compatible water-dilutable synthetic resins, such as, for example, aminoplast resins, polyesters and polyethers, which generally serve as grind resins for the pigments.

The aqueous base coating compositions according to the invention preferably contain 5 to 20, particularly preferably 10 to 16% by weight, based on the total solids content of the base coating compositions, of a water-dilutable aminoplast resin, preferably melamine resin and 5 to 20, preferably 8 to 15% by weight, of a water-dilutable polyether (eg polypropylene glycol with a number average molecular weight of 400 to 900).

As the pigments, the base coating compositions according to the invention can contain coloring pigments on an inorganic basis, such as e.g. Titanium dioxide, iron oxide, soot, etc., coloring pigments on an organic basis as well as common metal pigments (e.g. commercially available aluminum bronzes, stainless steel bronzes ...) and non-metallic effect pigments (e.g. pearlescent or interference pigments). The base coating compositions according to the invention preferably contain metal pigments and / or effect pigments. The pigmentation level is in the usual ranges.

Furthermore, crosslinked polymeric microparticles, such as are disclosed in EP-A-38 127 and / or customary rheological inorganic or organic additives, can be added to the base coating compositions according to the invention. For example, water-soluble cellulose ethers, such as hydroxyethyl cellulose, methyl cellulose or carboxymethyl cellulose, as well as synthetic polymers with ionic and / or associative groups, such as polyvinyl alcohol, poly (meth) acrylamide, poly (meth) acrylic acid, polyvinyl pyrrolidone, styrene-maleic anhydride or ethylene-maleic anhydride, act as thickeners Copolymers and their derivatives or also hydrophobically modified ethoxylated urethanes or polyacrylates. Carboxyl group-containing polyacrylate copolymers are particularly preferred with an acid number of 60 to 780, preferably 200 to 500.

The base coating compositions according to the invention generally have a solids content of about 15 to 50% by weight. The solids content varies with the intended use of the coating compositions. For metallic paints, for example, it is preferably 17 to 25% by weight. For plain-colored paints it is higher, for example 30 to 45% by weight.
The coating compositions according to the invention can additionally contain customary organic solvents. Their share is kept as low as possible. For example, it is below 15% by weight.

The base coating compositions according to the invention are generally adjusted to a pH between 6.5 and 9.0. The pH can be adjusted with conventional amines, e.g. Ammonia, triethylamine, dimethylaminoethanol and N-methylmorpholine can be adjusted.

With the provision of the base coating compositions according to the invention, the task explained at the outset is solved.
With the base coating compositions according to the invention, high-quality coatings can be produced even without overcoating with a transparent top coating composition.
The coating compositions according to the invention can be applied to any substrates, such as metal, wood, plastic or paper.

The invention is explained in more detail in the following examples.

A. Preparation of the emulsion polymers Emulsion polymer dispersion 1

1344 g of deionized water and 12 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate (Fenopon® EP 110 from GAF Corp., emulsifier 1) are placed in a cylindrical glass double-walled vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer. submitted and heated to 82 ° C. An emulsion is prepared in the stirrable feed vessel from 720 g deionized water, 24 g emulsifier 1, 10.8 g acrylamide, 864 g methyl methacrylate and 216 g n-butyl methacrylate. 30% by weight of this emulsion are added for presentation. 28% by weight of a solution of 3.1 g of ammonium peroxodisulfate (APS) in 188 g of deionized water are then added dropwise over the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the ammonium peroxodisulfate solution has ended, the remaining 70% by weight of the emulsion together with the remaining 72% by weight of the ammonium peroxodisulfate solution are added over the course of an hour, the temperature being kept at 85.degree. The mixture is then cooled to 82 ° C. and within 2 hours a mixture of 842 g n-butyl acrylate, 108 g hydroxypropyl methacrylate, 43 g methyl methacrylate, 43.2 g methacrylic acid, 32.4 g acrylamide and 5.4 g eikosa (ethylene glycol) nonylphenyl ether (Antarox® CO 850 from GAF Corp., emulsifier 2) and 343 g of deionized water were added. When the addition is complete, the reaction mixture kept at 85 ° C for 1.5 hours. It is then cooled and the dispersion is passed over a 30 μm mesh. A finely divided dispersion having a non-volatile content of 45% by weight, a pH of 3.4, an acid number of 13 and an OH number of 20 is obtained.

Emulsion polymer dispersion 2

1344 g of deionized water and 12 g of a 40% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate (Fenopon® EP 110 from GAF Corp., emulsifier 1) are placed in a cylindrical glass double-walled vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer. submitted and heated to 80 ° C. An emulsion is prepared in the stirrable feed vessel from 720 g deionized water, 24 g emulsifier 1, 10.8 g acrylamide, 518 g methyl methacrylate, 292 g n-butyl methacrylate and 205 g styrene.
30% by weight of this emulsion are added for presentation. A solution of 0.9 g of ammonium peroxodisulfate APS in 55 g of deionized water is then added dropwise in the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 80 and 85 ° C. 15 minutes after the addition of the above-mentioned APS solution has ended, a solution of 2.2 g of APS in 480 g of water is added within 3 hours and the remaining 70% by weight of the above-mentioned emulsion are added within one hour, the reaction temperature being 80 ° C is maintained. After the addition of the emulsion has ended, the mixture is cooled to 77 ° C. and within 2 hours a mixture of 745 g of n-butyl acrylate, 119 g of methyl methacrylate, 108 g of hydroxypropyl methacrylate, 54 g of styrene, 42.7 g of ethylhexyl acrylate, 42.7 g of methacrylic acid, 21.6 g of acrylamide and 2.2 g of emulsifier 2 were added. After the addition has ended, the reaction mixture is kept at 80 ° C. for a further 1.5 hours.

It is then cooled and the dispersion is passed over a 30 μm mesh. A finely divided dispersion with a non-volatile content of 45% by weight, a pH of 3.8, an acid number of 13 and an OH number of 19 is obtained.

Emulsion polymer dispersion 3

1109 g of deionized water and 10 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate (Fenopon®EP 110 from GAF Corp., emulsifier 1) are placed in a cylindrical glass double-walled vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer. submitted and heated to 82 ° C. An emulsion is prepared in the stirrable feed vessel from 748.2 g deionized water, 20.3 g emulsifier 1, 9.0 g acrylamide, 718.1 g methyl methacrylate and 179.5 g n-butyl methacrylate. 30% by weight of this emulsion are added for presentation. 10% by weight of a solution of 7.2 g of ammonium peroxodisulfate in 305 g of deionized water are then added dropwise over the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the ammonium peroxodisulfate solution has ended, the remaining 70% by weight of the emulsion together with the remaining 90% by weight of the ammonium peroxodisulfate solution are added over the course of an hour, the temperature being kept at 82.degree. A mixture of 700 g of n-butyl acrylate, 89.8 g of hydroxypropyl methacrylate, 35.9 g of methyl methacrylate, 35.9 g of methacrylic acid, 26.9 g of acrylamide and 4.5 g is then added within 2 hours
Eikosa (ethylene glycol) nonylphenyl ether (Antarox®CO 850 from GAF Corp., emulsifier 2) was added. After the addition has ended, the reaction mixture is kept at 82 ° C. for a further 1.5 hours. It is then cooled and the dispersion is spread over a fabric 30 µm mesh size given. A finely divided dispersion with a non-volatile content of 45% by weight, a pH of 2.5, an acid number of 14 and an OH number of 20 is obtained.

Emulsion polymer dispersion 4

1344 g of deionized water and 12 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate (Fenopon® EP 110 from GAF Corp., emulsifier 1) are placed in a cylindrical glass double-walled vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer. submitted and heated to 82 ° C. An emulsion is prepared in the stirrable feed vessel from 477 g of deionized water, 66.7 g of emulsifier 1, 10.8 g of acrylamide, 864 g of methyl methacrylate and 216 g of n-butyl methacrylate. 30% by weight of this emulsion are added for presentation. Then 3.6% by weight of a solution of 8.6 g of ammonium peroxodisulfate in 183 g of deionized water are added dropwise within 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the ammonium peroxodisulfate solution has ended, the remaining 70% by weight of the emulsion together with the remaining 96.4% by weight of the ammonium peroxodisulfate solution are added over the course of an hour, the temperature being kept at 82.degree. A mixture of 842 g of n-butyl acrylate, 108 g of hydroxypropyl methacrylate, 43.2 g of methyl methacrylate, 43.2 g of acrylamidomethylpropanesulfonic acid, 32.4 g of acrylamide, 66.7 g of emulsifier 1 and 5.4 g of eikosa ( ethylene glycol) nonylphenyl ether (Antarox® CO 850 from GAF Corp., emulsifier 2) added. After the addition has ended, the reaction mixture is kept at 82 ° C. for a further 1.5 hours. It is then cooled and the dispersion is passed over a 30 μm mesh. You get a finely divided Dispersion with a non-volatile content of 46% by weight, a pH of 2.5, an acid number of 6 and an OH number of 19.

Emulsion polymer dispersion 5

1344 g of deionized water and 12 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate (Fenopon® EP 110 from GAF Corp., emulsifier 1) are placed in a cylindrical glass double-walled vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer. submitted and heated to 82 ° C. In the stirrable feed vessel 720 g of deionized water, 24 g of emulsifier 1, 43.2 g of acrylamide, 907 g of methyl methacrylate and 216 g of n-butyl methacrylate, 842 g of n-butyl acrylate, 108 g of hydroxypropyl methacrylate, 43.2 g of methacrylic acid and 5.4 g emulsifier 2 an emulsion is prepared. 10% by weight of this emulsion are added for presentation. A solution of 0.87 g of ammonium peroxodisulfate in 53 g of deionized water is then added dropwise in the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the APS solution has ended, the remaining 90% by weight of the emulsion are added within 3 hours and a solution of 2.23 g of APS in 478 g of deionized water is added within 3.5 hours, the temperature being at Is held at 82 ° C.

After the addition has ended, the reaction mixture is kept at 82 ° C. for a further 1.5 hours. It is then cooled and the dispersion is passed over a 30 μm mesh. A finely divided dispersion with a non-volatile content of 45% by weight, a pH of 5.8, an acid number of 13 and an OH number of 20 is obtained.

B Production of the polyurethane resins used according to the invention Polyurethane resin dispersion 1

570 g of a commercially available polyester made from caprolactone and ethylene glycol with a hydroxyl number of 196 are dewatered at 100 ° C. for 1 hour in vacuo. 524 g of 4,4'-dicyclohexylmethane diisocyanate are added at 80 ° C. and the mixture is stirred at 90 ° C. until the isocyanate content is 7.52% by weight, based on the total weight. After cooling to 60 ° C., a solution of 67 g of dimethylolpropionic acid and 50 g of triethylamine in 400 g of N-methylpyrrolidone are added and the mixture is stirred at 90 ° C. for 1 hour. The mass obtained is poured into 1840 g of cold deionized water with vigorous stirring. 86 g of a 15% hydrazine solution are added to the dispersion obtained within 20 minutes, with vigorous stirring. The resulting, very finely divided dispersion has a solids content of 35% and a run-out time of 27 seconds in the DIN cup 4.

Polyurethane resin dispersion 2

830 g of a polyester composed of neopentyl glycol, 1,6-hexanediol and adipic acid with a hydroxyl number of 135 and an acid number below 3 are dewatered at 100 ° C. for 1 hour in vacuo. 524 g of 4,4'-dicyclohexylmethane diisocyanate are added at 80 ° C. and the mixture is stirred at 90 ° C. until the free isocyanate group content is 6.18% by weight, based on the total weight. After cooling to 60 ° C., a solution of 67 g of dimethylpropionic acid and 50 g of triethylamine in 400 g of N-methylpyrrolidone are added and the mixture is stirred at 90 ° C. for 1 hour.
The mass obtained is poured into 2400 g of cold deionized water with vigorous stirring. You get a finely divided Dispersion. 80 g of a 30% strength aqueous solution of ethylenediamine are added to this dispersion with vigorous stirring within 20 minutes. The resulting, very finely divided dispersion has a solids content of 35% and a run-out time of 23 seconds in the DIN cup 4.

C. Manufacture of base coating compositions

18.2 g of butyl glycol, 3.7 g of a commercially available melamine-formaldehyde resin (Cymel® 301), 3.1 g of polypropylene glycol (average molecular weight = 400) and 7.2 g of an aluminum bronze according to DE-OS-36 36 183 (aluminum content: 60 wt .-%) with a high speed stirrer for 15 minutes at 300-500 U / min. touched. A mixture 1 is obtained.
27.2 g of emulsion polymer dispersion 1, 2, 3 or 4 are mixed with 11.6 g of polyurethane resin dispersion 1 and 19.6 g of deionized water. The mixture is adjusted to a pH value of 7.7 with a 5% aqueous dimethylethanolamine solution and with 9.4 g of a 3.5% solution of a commercially available polyacrylic acid thickener (Viscalex®HV 30 from Allied Colloids, pH value: 8 , 0) offset. Mixture 2 is obtained.

Mixtures 1 and 2 are produced at 800-1000 rpm for 30 minutes to produce the basecoats of the invention. mixed and then adjusted to a pH of 7.7 with a 5% aqueous solution of dimethylethanolamine. The viscosity is then adjusted to an outflow time of 25 seconds in a DIN 4 cup by adding deionized water. The base coating compositions BB1, BB2, BB3 and BB4 according to the invention are obtained.

The base coating composition BB5 is obtained by incorporating 36.2 g of the emulsion polymer dispersion 1 into the mixture 2. BB5 does not contain a polyurethane resin dispersion.

The base coating compositions thus obtained show excellent storage stability.

The base coating compositions are sprayed onto well-known methods onto phosphated steel sheets (Bonder 132) coated with a commercially available electrodeposition coating and a commercially available filler, overcoated with a commercially available clearcoat after a flash-off time of 10 minutes and baked at 140 ° C. for 20 minutes.
The metallic effect coatings obtained in this way show a good metallic effect, good adhesion to the filler, good adhesion between the basecoat and topcoat, good gloss and good resistance in a condensed water constant climate according to DIN 50 017. BB1, BB2, BB3 and BB4 show a better metallic effect than BB5.

A part of the painted sheets is coated again with the base coating compositions BB1, BB2, BB3, BB4 and BB5 and overcoated with a commercially available clear coat. The coatings obtained in this way are baked at 80 ° C. for 40 minutes. The coatings baked at 80 ° C adhere well to the coatings baked at 140 ° C.

Comparative example

A basecoat composition prepared as described above using the emulsion polymer dispersion 5 shows insufficient storage stability.

Claims (11)

1. Process for the preparation of a multicoat protective and/or decorative coating on a substrate surface, in which process

   (1) a pigmented aqueous coating composition which comprises as the film-former a water-thinnable emulsion polymer, is applied to the substrate surface as basecoat composition

   (2) a polymeric film is formed from the composition applied in stage (1)

   (3) a suitable clear topcoat composition is applied to the basecoat obtained in this manner and subsequently

   (4) the basecoat and the topcoat are baked together, characterised in that the basecoat composition comprises a water-thinnable emulsion polymer, which polymer can be obtained

   (a) by polymerising in a first stage 10 to 90 parts by weight of a mixture of

   (a1) 100 to 60 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid, or a mixture of such esters, and

   (a2) 0 to 40 % by weight of a monomer which is copolymerisable with (a1), or a mixture of such monomers

   in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the total of the weight percentages of (a1) and (a2) always being 100 % by weight and (a1) and (a2) being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T_G1) of + 30 to + 110°C, and

   (b) by polymerising in a second stage 90 to 10 parts by weight of a mixture of

   (b1) 47 to 99 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid, or a mixture of such esters

   (b2) 1 to 20 % by weight of a monomer which carries at least one hydroxyl group and is copolymerisable with (b1), (b3) and (b4), or a mixture of such monomers

   (b3) 0 to 8 % by weight of a monomer which carries at least one carboxyl or sulphonyl group and is copolymerisable with (b1), (b2) and (b4), or a mixture of such monomers, and

   (b4) 0 to 25 % by weight of a further monomer which is copolymerisable with (b1), (b2) and (b3), or a mixture of such monomers

   after at least 80% by weight of the monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the total of the weight percentages of (b1), (b2), (b3) and (b4) always being 100 % by weight and (b1), (b2), (b3) and (b4) being chosen such that an exclusive polymerisation of the mixture of monomer used in the second stage gives rise to a polymer having a glass transition temperature (T_G2) of - 60 to + 20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T_G1 - T_G2 is 10 to 170°C.
2. Process according to Claim 1, characterised in that the basecoat composition comprises a metallic pigment, preferably an aluminium pigment.
3. Process according to Claim 1 or 2, characterised in that 99.5 to 75 % by weight of component (a1) and/or 0.5 to 25 % by weight of component (a2) and/or 75 to 90 % by weight of component (b1) and/or 5 to 15 % by weight of component (b2) and/or 2 to 6 % by weight of component (b3) and/or 2 to 15 % by weight of component (b4) are polymerised.
4. Process according to one of Claims 1 to 3, characterised in that the film-former consists of 95 to 40% by weight of the emulsion polymer and 5 to 60% by weight of a water-thinnable polyurethane resin, the weight percentages in each case referring to the solids content and their sum being always 100% by weight.
5. Water-thinnable coating compositions characterised in that they contain as the film-former a water-thinnable emulsion polymer which can be obtained

   (a) by polymerising in a first stage 10 to 90 parts by weight of a mixture which consists of

   (a1) 100 to 60 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and

   (a2) 0 to 40 % by weight of a monomer which is copolymerisable with (a1) or a mixture of such monomers, in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the total of the weight percentages of (a1) and (a2) always being 100 % by weight and (a1) and (a2) being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T_G1) of +30 to +110°C, and

   (b) by polymerising in a second stage 90 to 10 parts by weight of a mixture of

   (b1) 47 to 99 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters

   (b2) 1 to 20 % by weight of a monomer which carries at least one hydroxyl group and is copolymerisable with (b1), (b3) and (b4), or a mixture of such monomers

   (b3) 0 to 8 % by weight of a monomer which carries at least one carboxyl or sulphonic acid group and is copolymerisable with (b1), (b2) and (b4), or a mixture of such monomers, and

   (b4) 0 to 25 % by weight of a further monomer which is copolymerisable with (b1), (b2) and (b3), or a mixture of such monomers after at least 80 % by weight of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the total of the weight percentages of (b1), (b2), (b3) and (b4) always being 100 % by weight and (b1), (b2), (b3) and (b4) being chosen such that an exclusive polymerisation of the mixture of monomers used in the second stage gives rise to a polymer having a glass transition temperature (T_G₂) of - 60 to + 20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T_G1 - T_G2 is 10 to 170°C.
6. Coatings compositions according to Claim 5, characterised in that they contain a metallic pigment, preferably an aluminium pigment.
7. Coating compositions according to Claim 5 or 6, characterised in that 99.5 to 75 % by weight of component (a1) and/or 0.5 to 25 % by weight of component (a2) and/or 75 to 90 % by weight of component (b1) and/or 5 to 15 % by weight of component (b2) and/or 2 to 6 % by weight of component (b3) and/or 2 to 15 % by weight of component (b4) are polymerised.
8. Water-thinnable emulsion polymers, characterised in that they can be obtained

   (a) by polymerising in a first stage 10 to 90 parts by weight of a mixture of

   (a1) 100 to 60 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid, or a mixture of such esters and

   (a2) 0 to 40 % by weight of a monomer which is copolymerisable with (a1), or a mixture of such monomers, in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the total of the weight percentages of (a1) and (a2) always being 100 % by weight and (a1) and (a2) being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T_G₁) of + 30 to + 110°C, and

   (b) by polymerising in a second stage 90 to 10 parts by weight of a mixture of

   (b1) 47 to 99 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid, or a mixture of such esters

   (b2) 1 to 20 % by weight of a monomer which carries at least one hydroxyl group and is copolymerisable with (b1), (b3) and (b4), or a mixture of such monomers

   (b3) 0 to 8 % by weight of a monomer which carries at least one carboxyl or sulphonyl group and is copolymerisable with (b1), (b2) and (b4), or a mixture of such monomers, and

   (b4) 0 to 25 % by weight of a further monomer which is copolymerisable with (b1), (b2) and (b3), or a mixture of such monomers, after at least 80% by weight of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the total of the weight percentages of (b1), (b2), (b3) and (b4) always being 100 % by weight and (b1), (b2), (b3) and (b4) being chosen such that an exclusive polymerisation of the mixture of monomers used in the second stage gives rise to a polymer having a glass transition temperature (T_G2) of - 60 to + 20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T_G1 - T_G2 is 10 to 170°C.
9. Emulsion polymers according to Claim 8, characterised in that 99.5 to 75 % by weight of component (a1) and/or 0.5 to 25 % by weight of component (a2) and/or 75 to 90 % by weight of component (b1) and/or 5 to 15 % by weight of component (b2) and/or 2 to 6 % by weight of component (b3) and/or 2 to 15 % by weight of component (b4) are polymerised.
10. Process for the preparation of water-thinnable emulsion polymers characterised in that

    (a) in a first stage 10 to 90 parts by weight of a mixture which consists of

    (a1) 100 to 60 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and

    (a2) 0 to 40 % by weight of a monomer which is copolymerisable with (a1) or a mixture of such monomers,

    in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the sum of the parts by weight of (a1) and (a2) always being 100 % by weight and (a1) and (a2) being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T_G₁) of +30 to +110°C, and

    (b) by polymerising in a second stage 90 to 10 parts by weight of

    (b1) 47 to 99 % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters

    (b2) 1 to 20 % by weight of a monomer which carries at least one hydroxyl group and is copolymerisable with (b1), (b3) and (b4), or a mixture of such monomers

    (b3) 0 to 8 % by weight of a monomer which carries at least one carboxyl or sulphonic acid group and is copolymerisable with (b1), (b2) and (b4), or a mixture of such monomers, and

    (b4) 0 to 25 % by weight of a further monomer which is copolymerisable with (b1), (b2) and (b3), or a mixture of such monomers,

    after at least 80 % by weight of the monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the sum of the parts by weight of (b1), (b2), (b3) and (b4) always being 100 % by weight and (b1), (b2), (b3) and (b4) being chosen such that an exclusive polymerisation of the mixture of monomers used in the second stage gives rise to a polymer having a glass transition temperature (T_G₂) of -60 to +20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T_G₁ - T_G₂ is 10 to 170°C.
11. Process according to Claim 10 characterised in that 99.5 to 75 % by weight of component (a1) and/or 0.5 to 25 % by weight of component (a2) and/or 75 to 90 % by weight of component (b1) and/or 5 to 15 % by weight of component (b2) and/or 2 to 6 % by weight of component (b3) and/or 2 to 15 % by weight of component (b4) are polymerised.