CA2314450A1 - Use of powder coatings and powder coating waste materials in anodically depositable electrodeposition lacquers - Google Patents

Abstract

Use of powder coatings and/or powder coating waste materials as additives in anodically depositable electrodeposition lacquers in order to improve the throwing power during anodic electrodeposition lacquering.

Description

Use of powder coatings and powder coating waste materials in aaodically depositable electrodeposition lacquers The invention provides the use of powder coatings and/or powder coating waste materials as additives inn anodically dcpositable electrodeposition lacquers, as well as the electrodeposition lacquers provided in this way, a process for pxeparing them and a process for anodic deposition lacquering which pxoduce improved throwing power, Coating with powder coatings is one of the particularly environmentally friendly methods of coating. Organic solvents can be largely dispensed with during the preparation and processing of powder coatings and also only small losses occur during their application.
lx~ general, powder coatings are prepared by mixing the individual constituents such as, for example, resin, hardener, additives and optionally pigments, and homogenising these in a melt process. The resultixig melt is cooled and crushed to a size suitable for a subsequent milling process. The product is then milled to the desired particle size in suitable milling equipment.
The finest particles arc removed from the range of particle sizes produced in so-called air separators, this being required for certain applications and also from the health and safety at work aspect (see H. Kittel, Lehrbuch tier Lacke and Beschichtungen, vol. VIII, part 2, appendix pages 13 to 24). In the first instance, the finest particles are a waste product.
When coating with powder coatings, it is inevitable that some of the coating powder does not reach the substrate or falls away from the substrate. In general, this powder coating overspray cannot be directly recycled to the coating process because the _Z_ original particle size distribution has been shi8ed and in the fast instance is also a waste product.
For economic and ecological reasons, it is desirable to take the waste products being produced through a procedure which makes them reuseable. A number of processes has been suggested for doing this and they all include a relatively costly working up procedure using remelting and milling.
The principle of elxtrodeposition lacquering is familiar to a person skilled in the art and is described extensively in the literature (for example in Metalloberflache 31 (1977) 10, pages 455 - 459), Electrodeposition lacquering is a fully automated, environmentally friendly and economic method of application and is us~1 in practice in the mass-production lacquering of electrically conductive surfaces, in particular of metal surfaces. It is then a fully automated method of application with a high degree of deposition, The process preferably takes place in sealed circuits and enables the recovery of excess lacquer material and of the auxiliary substances and operating matcnials used.
In the case of anodic electrodeposition lacquering (ADL), a workpiece with an electrically conductive surface consisting of metal or consisting of electrically conductive plastic material or consisting of a substrate provided with an electrically conducrive coating is placed in an aqueous ADL bath and connected to a source of direct current as the anode. On applying a direct electric current, the polymer particles which have been made water-soluble or water-dispersible by at least partial salt formation migrate from the aqueous dispersion in the ADL bath to the anode and there react with the ions being produced by simultaneous electrolysis of the water to again produce water-insoluble polymers which coagulate out of the aqueous phase and, with the additives dispersed therein, are deposited on the anode as a lacquer film.

DE-A-23 64 642 describes the preparation of thick, film-like coatings by means of anodic electmdeposition lacquering. In order to achieve a thick layer, water-insoluble resin powders with particle sizes of 10 to 100 p,m are added to the coating agents, wherein the most frequently occurring particle sixes are in the range 25 to 50 pm. The proportion of water-soluble resin in the coating agent is limited, It has been shown that coatings obtained with these coating agents have only a wary low throwing power and are not suitable for coating workpieces with multidimensional geometry or with cavities.
DE-A-33 66 973 describes the electrolytic deposition of powdered polymers on an anode. For this purpose, the polymer particles are coated with as amphoteric metal oxide or hydroxide in order to enable them to migrate to the anode under the effect of the charge. The fired-on film is slightly porous and has a reduced throwing power, DE-A-21 64 844 describes the electrophoretic deposition of powdered high molecular weight compounds at the anode. For this purpose, the powder particles are moistened with an organic solvent which is not miscible with water and are suspended in water which contains a surface-active compound. A resin support component is not used.
The object of the present invention is to provide a method for re-using powder coatings, for example non-recyclable powder coatings from overproduction and powder coating waste materials which are produced durix<g the pr~cparation and/or processing of powder coatings, in an economically viable and environmentally friendly manner without a costly conditioning step.
It has been shown that this object can be achieved by a use, forming one object of the in~cntion, of pawder coatings and/or powder coating waste materials as additives in anodically depositable electrodeposition lacquers.

Surprisingly, this is possible without impairing, rather in fact improving, the throwing power of an electrodeposiHon lacquer coating obtained from an eleEtrodeposition lacquer prepared via this use.
Powder coatings, powder coating waste materials or mixtures thereof which can be used according to the invention have a particle size distribution of 0,5 to 100 p,m, wherein preferably 40 to 60 wt.% of the powder coating and/or powder coating waste material has a particle size of less than 10 ~m and up to 20 wt.% has a particle size of less titan 5 p,m. The most frequently occurring sizes are particularly preferably in the xange 0.5 to 10 pro at the largest. It has been shown that the use of this type of fine powder in anodically depositable electzodeposition lacquers especially beneficially improves the throwing power of the anodieally deposited layers produced therefrom. For example, pigments and/or fillers and/or binders can also be at least partly replaced by this type of fine powder when formulating 1 S anodically depositable electrodeposition lacquers.
Accordingly, the present invention also provides anodicaUy depositable dip lacquers which contain one or more binders, water and optionally one or more cross-linlting agents, pigments, fillers andlor conventional additives and are characterised in that they contain one or. more powder coatings and/or one or more powder coating waste materials with a particle size distribution of 0.5 to 100 ~,m, wherein 40 to 60 wt.% of the powder coatings and/or powder coating waste materials has a particle size of less than 10 Nxn and up to 20 wt.% has a particle size of less than 5 pro.
The powder coatings and/or powder coating waste materials are preferably used, according to the invention, in such a way that the anodically depositable electrodeposition lacquer obtained contains 50 to less than 200 parts by weight of powder coating and/or powder coating waste material with respect to 100 parts by weight of binder plus optionally present cross-Linking agent.

According to a preferred crnbodiment, the invention provides an anodically depositable electrodeposition lacquer containing A) 67 to 33 wt.% of a water-dilutable component consisting of one or more binders and optionally one or more cross-linking agents and optionally one or more pigments and/or fillers, B) 33 to 67 wt.% of one or more powder coatings and/or powder coating waste materials with a particle size distribution of 0.5 to 100 pcn, wherein 40 to wt.% has a particle size of less than 10 prn and up to 20 wt.% has a particle size of less than 5 ~.nn, as well as water and optionally one ox more conventional additives, wherein the ratio by weight of binder to cross-linking agent in component A) is 100 : 0 to 65 :
35 and the ratio by weight of pigment to binder in component A) is 0.1 : 1 to 1.5 :
1.
The anodically depositable electrodeposition lacquer is prepared by mixing one or mote suitable binder dispersions) with optionally one or more cross-linking agents) and optionally conventional additives, lacquer additives such as, fox example, catalysts, Light stabilisers, optical brighteners, biocidc components, neutral resins, layer-producers, emulsifiers and optionally pigments and/or fillers. The powder coating and/or powder coating waste material fraction can be admixed at any time.
Suitable binders far the aqueous binder dispersions in the anodically depositable electrodeposition lacquers provided in accordance with the invention are any conventional bindex systems for anodically depositable electrodeposition lacquers (ADLs). They contain anionic groups or acidic groups which can be converted into anionic groups by neutralisation. Acidic groups may be, for example, carboxyl groups, sulfonic acid groups, phosphoric acid groups, preferably carboxyl groups.
The acid value of the binder is preferably 20 to 150, particularly preferably to 120.

'- CA 02314450 2000-07-21 Binder systems which contain further functional groups, in particular hydroxyl groups, arc particularly preferably used. The hydroxyl value is preferably 20 to 150, particularly preferably 20 to 120.
Examples of binder systems acre those which are generally well-known for aqueous binder systems, in particular for anodic dectrodeposition lacquer coatings.
These include, for example, polyester, polyacrylate and polyurethane resins such as, for example, alkyd resins, uxethanised polyester resins or acrylated polyester or polyurethane resins, maleated oils, epoxyesters, maleated polybutadiene oils and mixtures of these resins. Polyester resins are preferred.
Suitable polyester resins are, for example, carboxyl group and hydroxyl group-containing polyesters with an acid value of 20 to 150 and a hydroxyl value of 20 to 150. They may be prepared, for example, by processes known to a person skilled in the art, by the reaction of polyhydric alcohols and polybasie carboxylic acids or carboxylic anhydrides, and optionally aliphatic and/or aromatic monocarboxylic acids. The hydroxyl group content is adjusted in a manner known per se by appropriate choice of the type and ratios by weight of the starting components. The carboxyl groups may be introduced, for example, by semi-ester formation from a previously prepared hydroxyl group-containing polyester resin, using acid anhydrides, The incorporation of carboxyl groups may also take place, for example, by the joint use of hydroxycarboxylic acids during the polycondensation reaction.
The polycarboxylic acids, for example dicarboxylic acids, and polyols may be aliphatic, cycloaliphatic or aromatic.
The polyols used to prepare the polyesters are, for example, diols such as alkylene glycols such as, for example, ethylene glycol, butylene glycol, hexanediot, hydrogenated bisphenol A, 2, 2-butyl-ethyl-propanediol, neopentyl glycol and/or other glycols such as, for example, dimethylolcyclohexaae. Higher functional or mixtures of higher and monofunctional OH components such as, for example, -7_ trimethylolpropane, pentaerythritol, glycerol, hexanetriol; polyethers which are condcnsates of glycols with alkylene oxides; monoethers of such glycols such as diethylene glycol monoethyl ether, tripropylene glycol monomethyl ether, mar also be used.
The acid component of the polyester preferably consists of low molecular weight dicarboxylic acids ar their anhydrides with 2 tol8 carbon atoms.
Suitable acids are, for example, phthalic acid, isophthalic acid, terephthalic acid, hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, malefic acid, glutaric acid, succinic acid, itaconic acid and/or 1,4-cyclohexanedicarboxylic acid. The methyl esters or anhydrides of these acids, if they exist, may also be used instead of the acids. It is also possible, in order to obtain branched polyesters, to add a proportion ofhigher functional carboxylic acids such as, for example, trifunctional carboxylic acids, trimellitic acid, malic acid, aconitic acid, bishydmxyethyltaurine and dimethylolpropionic acid, dimethylolbutyric acid or bisanhydrides.
Polycarboxylic acids which do not form cyclic anhydrides are preferred.
The polyester resins may also be modified, for example, by incorporating unsaturated compounds, isocyanate group-containing compounds or by fixation or graft polymerisation with cthylenically unsaturated compounds. Preferred polyesters are, for example, carboxyl group-containing polyesters with an said value of 20 to 120 and a hydroxyl value of 20 to 150, preferably 60 to 120. They are, for example, reaction products of di- and/or polyhydric aliphatic or cyeloaliphatic saturated alcohols, aliphatic, cycloaliphatic and/or monocyclic aromatic di- or polybasic polycarboxylic acids and optionally linear or branched, saturated or unsaturated aliphatic and/or cycloaliphatic C3 to C20 monoalcohols or monocarbvxylic acids.
The ratios by weight of stattit~g components are calculated from the molar ratios which lead to the desired acid values and hydroxyl values of the resin. The choice of individual starting components is known to a person skilled in the art, taking into consideration the objectives.

_8-The number average molecular weight Mn of suitable polyesters, measured against polystyrene as a calibration substance, is, for example, 1000 to 6000, preferably 2000 to 4000.
Carboxyl group-containing oil-free polyesters such as are described e,g. in D>r-A-32 47 756 are particularly preferred. These polyesters preferably contain 0.3 to 3.0, particularly preferably 0.5 to 2.5 milliequivalents of cocondensed aliphatic, cycloaliphatic and/or aromatic dicarboxylic acids per gram of resin. 0.8 to 2.0, preferably 0.9 to 1.8, particularly preferably 1,1 to I .5 millimoles of tribasic or polybasic cyclic carboxylic acids per gram of resin are expediently bonded via only one carboxyl group to the polyester. Tribasic and/or polybasic polycarboxylic acids, preferably tribasic and/or tetrabasic acids, are used as polycarboxylic acids.
The preparation of these polyesters may take place by polycondensation of the stating materials in a manner known per se, wherein the process is preferably performed stepwise in order to avoid turbidity and gel formation.
The esterification of preferably aromatic and cycloaliphatic diearboxyIic acids which cannot form an iuntramolecular anhydride, preferably takes place with dialcohoIs which contain either secondary OH groups or else primary OH groups which are sterically hindered by substituents, wherein an OH group-containing polyester is produced by using an excess of alcohol, The alcohols preferably contain 2 to 21, particularly preferably 4 to 18, carbon atoms. The dicarboxylic acids preferably contain 5 to 10 carbon atoms, particularly preferably 6 carbon atoms.
Bxamples of these are isophthalic acid, terephthalic acid, 1,3- and 1,4-cyclohexanedicarboxylic acid or alkyl-substituted dicarboxylic acids such as butylisophthalic acid. Isophthalic acid is particularly preferred.
On the other hand, dimethyl esters such as dimethyl tcrephthalate or dimethyl 1,4-cyclohexanedicarboxylatc may also be introduced into the polyester by transesterification, optionally in the presence of transesterification catalysts.

A corresponding amount of tricarboxylic acids such as trimellitic anhydride may be cocondensed into the resin molecule instead of some of the dicatboxylic acid in order to produce a branched structure.
Neopentyl glycol, neopentyl glycol hydroxypivalate, hexane-2,5-diol, 1,4-bis(hydroxymethyI)cyclohexane,1,1-isvpyrilidine-bis-(p-phenoxy)-2-propanol, 2,2,4-trimethylolpentane-1,3-diol, and mixtures thereof are preferably used as dialcohols.
The glycidyl esters of branched fatty acids, such as versatic acid, may also be used for example as dialcohols because the fatty acid is incorporated into the molecular structwe in a hydrolysis-stable form. rn special cases, the use of epoxide resins in which the epoxy groups have been reacted with monoalcohols is also possible.
A proportion of polyols with more than two OH groups, such as tnimethylolpropane or pentaerythritol, may also be used in order to adjust to suitable hydroxyl values and viscosities. This also applies to elastification due to a very small degree of modification with long-chain dialcohols such as hexatle-1,6-diol, or aliphatic dicarboxylic acids such as adipic acid.
fisterification (first stage) is performed azeotropically or in the melt at elevated temperature (above 190°C) in a known way cad provides a clear product with an acid value of 0 to 50, preferably 5 to 25 and a viscosity of 200 to 3000 mPas, measured at 25°C in a 75 % strength butyl glycol solution.
Additional carboxyl groups have to be introduced into the OH group-containing polyester in order to facilitate solubility in the aqueous alkaline medium.
Reaction at temperatures below 190°C (second stage) with an aromatic or cycloaliphatic dicarboxylic acid which has preferably boon produced from a polycarboxylic acid with three or four carboxyl groups such as, for example, trimesie acid, hemimellitic acid, prehnitic acid and mellophanic acid by dcfunctionalisation with a long-chain, aliphatic hydrophobic monoalcohol is performed for this purpose. A process which makes use of anhydride-containing compounds such as trimellitic anhydride, pyromellitic anhydride or corresponding hydrogenated ring systems, as well as cyclopentanetctracarboxylic anhydride or pyrazinetetracarboxylic anhydride is particularly simple.
Mo~noalcohols which may be used are, for example, straight-chain and/or branched saturated and/or unsaturated primary, secondary and/or tertiary, preferably primary and/or secondary, alcohols. Mixtures may also be used, in particular isomeric mixtures of these alcohols. Aliphatic C6 to C18 monoaleohols and benzyl alcohol and its alkyl-substitution products arc preferred. Hranched C8 to C13 iso-monoalcohols are particularly preferred. Particularly hydrolysis resistant semi-esters are obtained by the use of branched monoalcolnols or secondary monoalcohols such as cyclohexanol or secondary methyloctyl alcohol. The structure of the resin ensures that optional breakdown products (monoalcohols and monoesters of trimellitic acid) which may be produced by hydrolysis are electrophoretically deposited with the film without causing problems.
The polycarboxylic acids may be stoichiometrically reacted, for example in a two-pot process, with enough monoalcohol to make sure that a dicarboxylic acid is still present and this is subsequently added to the OH group-containing polyester at temperatures of about 150 to 190°C.
In practice, it has been shown that preparation of the carboxyl group-containing polyester in a one-pot process can be achieved by adding approximately stoichiometric amaunts of monoalcohol and trimellitic anhydride to tho OI-T
group-containing polyester ran the given sequence.
The incorporation of carboxyl groups may also be performed, for example, by the use of hydroxyearboxylic acids, such as e.g. diznethylolpropionic acid, during the polycondensation reaction, the free carboxyl groups in these generally not participating in the polycondensation reaction due to steric hindrance so that the incorporation of these acids takes place exclusively via the hydroxyl groups.
The molar ratios in the overall formulation for preparing the polyester sure chosen so that a viscosity which is appropriate for the particular ultimate purpose is achieved.
This is, for example, about 200 to 3000, preferably 250 to 2000 and in particular 300 to 1500 mPas, measured at 50 % strength in butyl glycol at 25°C. It can also be adjusted, as can the molecular weight, by mixing in resins with lower and higher viscosities or lower and high molecular weights respectively. The upper limit for the acid value is preferably less than 100, particularly preferably less than 60;
the lower limit for the acid value is preferably greater than 35, particularly preferably greater than 40. The carboxyl group-containing polyester contains at Feast one, preferably at least two, carboxyl groups per molecule in order to produce water dilutability due to salt formation with a low molecular weight base. If the acid value is too low, then the solubility is inadequate; if it is too high, then the high degree of neutralisation can cause increased electrolysis in the ADL bath, which can lead to surface defects.
The excess of alcohol chosen produces a hydroxyl value, in the final resin, of about to 150, preferably 60 to 120. Preferred resins have a relatively high hydroxyl value and a low acid value.
Polycondensation is performed, for example, azeotropically or in the melt, for example at reaction temperatures between 160 and 240°C, preferably between 160 and 2I0°C. After reaching the desired final value with respect to viscosity and acid value, the mixture is cooled to a temperature at which the product has a viscosity which enables the incorporation of water. In practice, that means that the melt viscosity should not be greater than 40 000 mPa.s. If not working under pressure, the temperatures arc up to about 100°C. At least some of the carboxyl groups in the polycondensation product are neutralised by the addition of a neutralising agent, in order to convent to an aqueous solution or dispersion. The neutralising agent may be added before or during the addition of water, but it may also be initially introduced in the water in which the polycondensation product is dispersed. High-speed disc agitators, rotor/stator mixers or high pressure homogenisers, foi example, are used for this. Organic solvents rnay optionally be removed by distillation during or after conversion into the aqueous solution or dispersion.
Suitable neutralising agents arc conventional bases such as, for example, arnmonia, NaOH, KOH, LiOH, primary, secondary and tertiary amines such as diethylamine, triethylamine, rnorpholine; alkanolamincs such as diisopropanolaminc, dimethylaminoethanol, triisopropanolamine, dimethylamino-2-methylpropanol;
quaternary ammonium hydroxides or optionally also sraall amounts of alkylene polyarrrines such as ethylene diamine. Mixtures of these types of neutralising agents may also be used.
The amount of neutralising agent is chosen so that a MEQ value of 15 to 90, preferably 20 to 60, is achieved.
Suitable polyacrylate resins are, for example, carboxyl group-containing and/or sulfone group-containing copolymers which may also contain hydroxyl groups with an acid value of 20 to 150 and a number average molecular weight Mn of 1000 to 10 000 and, if hydroxyl groups are present, with a hydroxyl value of 20 to 200.
They are prepared by conventional processes, by copolymerisation of olefinically unsaturated monomers, wherein monomers containing acid groups are copolymerised with other monomers. The use of acid group-containing monomers has the objective of incorporating carboxyl and/or sulfonic acid groups in the copolymers in order to ensure the water solubility or water dispersibility of the copolymers by at least partial neutralisation of these groups.
Suitable monomers which contain acids groups are in principle any oleftnieally unsaturated polymerisable compounds which contain at least one carboxyl and/or sulfonic acid group such as, for example, olefinically unsaturated monocarboxylic or dicarboxylic acids such as (meth)acrylic acid, crotonic acid, fumaric acid, malefic acid, itaconic acid or the semi-esters of fumaric acid, malefic acid and itaconic acid or sulfonic acid group-containing olefinically unsatwated compounds such as, for example, 2-acrylamido-2-methylpropanesulfo~nic acid or any mixture of these types of olefinically unsaturated acids. Acrylic acid and methacrylic acid are particularly preferred.
In order to produce desired application oriented properties in the final lacquer, the copolymers may contain other monomers which contain functional groups with which, for example, cross-linking reactions may be performed, in addition to the acid groups. Thus, both self cross-linking of the copolymer and also external cross-linking with other components which have also been introduced into the lacquer can take place. Furthermore, in principle, any non-functional olefinically unsaturated monomers may also be used when preparing the copolymers.
Examples of these types of functional groups aro hydroxyl, amino, amido, keto, aldehyde, lactam, 'lactone, isocyanate, epoxy and silane groups. Olehnically unsaturated monomers which contain these types of functional groups are known.
Hydroxyl and epoxy groups are preferred.
Suitable noon-functional monomers are, for example, esters of acrylic and methacrylic acids in which the alcohol component contains 1 to 18 carbon atoms, vinylaromatic compounds, vinyl esters of aliphatic monocarboxylic acids, acrylonitrile and methacrylonitrile.
The copolymers may be prepared by polymerisation using conventional processes.
The copolymers are preferably prepared in organic solvents. Continuous or batchwise polymerisa'on processes may be used.
Suitable solvents are aromatic compounds, esters, ethers and ketones. Glycol ethers are preferably used.

Copolymerisation is preferably performed at temperatures between 80 and 180°C
using conventiou~al initiators such as, for example, aliphatic azo compounds or peroxides. In order to regulate the molecular weight of the copolymers, conventional regulators may be used. After completion of polymerisation, the copolymers, as described for polycondensation resins, are neutralised and converted into an aqueous solution or dispersion, wherein the organic solvent may optionally be distilled off, Examples of basic neutralising agents are those described above for neutralising polyester resins.
Suitable polyurethane resins are, for example, anionic polyurethane resins which contain carboxyl, sulfonic acid and/or phosphoric acid groups present in the salt form. They arc prepared in a manner known per se from polyols, polyisocyaaates and optionally chain-lengthening agents.
The polyurethane resins may be prepared either in bulk or also in organic solvents which do not react with isocyanates, They are, as described for the polycondensation resins, converted into the aqueous phase after neutralisation of the acid groups. In many cases it is expedient to prepare polyurethane resins in a stepwise manner.
Thus, for example, it is possible to first prepare a prepolymer with acid groups and terminal isocyanate groups in organic solvents and then, after neutralisation of the acid groups with tertiary amines, to chain-Icngthe~n this prcpolymer and convert it into the aqueous phase, wherein the organic solvents may be removed by distillation.
The polyols used to prepare tln~e prepolymers may be of low or high molecular weight and may also contain anionic groups.
Low molecular weight polyols preferably have a number average molecular weight Mn of 60 to 400 and may contain aliphatic, alicyclic or aromatic groups. They may be used as up to 30 wt.% of the total polyol constituents.

Suitable low molecular weight polyols are, for example, diols, triols and polyols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol,1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane, castor oil or hydrogenated castor oil, pentaerythritol, 1,2-cyclohexanediol, 1,4-cyclohexane-dimethanol, bisphenol A, bisphcnol F, hydrogenated bispheaol A and mixtures of these polyols.
High molecular weight polyols consist of linear or branched polyols with an OH
value of 30 to 150. They are preferably saturated or unsaturated polyesterdiols and/or polyetherdiols and/or polycarbonatediols with a molecular weight Mn of to 5000 or mixtures of these.
Suitable linear or branched polyetherdiols are, for example, poly(oxyethylcne)glycols, poly(oxypropylene)glycols and/or poly(oxybutylene)glyeols.
Polycsterdiols are preferred and arc prepared in a known manner by esterification of dicarboxylic acids or their anhydrides with diols. In order to produce branched polyesters, small amounts of polyols or polycarbvxylic acids with a higher functionality may be used.
The groups capable of forming anions may arise from the polyester or they are incorporated into the prepolymers by using compounds which have two H-active groups which can react with isocyanates and at least one group capable of forming an anion. Suitable groups which can react with isocyanates are in particular hydroxyl groups and also priimary and/or secondary amine groups. Groups which are capable of forming anions are, for example, carboxyl, sulfonic acid and/or phosphoric acid groups. Examples of such compounds are dihydroxycarboxylic acids such as dihydroxypmpionic acid, dihydroxybutyric acid, dihydroxysuccinic acid, diaminosuccinic acid and, preferably, oe,a-dimethylolalkanoic acids such as e.g, dimcthylolpropionic acid.

Suitable polyisocyanates are aliphatic, cycloaliphatic and/or aromatic polyisocyanates with at least two isocyanate groups per molxule and the derivatives of these diisocyanates knowm per se containing biurct, allophanate, urethane and/or isocyanurate groups and also mixtures of these polyisocyanates. Ysomers or isomeric mixtures of organic diisocyanates are preferably used, The polyisocyanate component used to prepare the prepolymer may also contain small proportions of higher functional polyisocyanates.
The prepolymer is expediently prepared in the presence of catalysts such as e.g.
organotin compounds or tertiary amines.
Conversion of the polyurethane resin into the aqueous phase is performed, as described in the case of polyester resins, by neutralisation of the acid groups in the polyurethane resin with a basic neutralising agent, optionally with removal of organic solvents by distillation.
Examples of basic neutralising agents are those described above for neutralising polyester resins.
The binder dispcrsion(s) according to the invention are cross-linked, preferably during stoving, by reaction with a cross-linking component, Cross-linking components are familiar to a person skillod in the art. Examples are amino resins, in particular melamine/fotmaldehyde resins; phenol resins; blocked polyisocyanates or transesterification cross-linking agents such as polyesters or polyurethane esters with hydroxyalkyl ester groups, alkyl ester derivatives of acetoacetic acid or malonie acid, tris(alkoxyearbonylamino)triazine derivatives and mixtures of these components which can produce highly cross-linked coatings with or without the use of catalysts. Blocked polyisocyanates are preferred.

The blocked polyisoeyanates contain on average more than one isocyanate group, preferably ax least two isocyanate groups, per molecule. They should be storage stable in the aqueous phase at an approximately neutral to weakly basic pH, decompose under the effect of heat at about 100 to 200°C and cross-link with the reactive hydroxyl andlor carboxyl groups present in the rosin structure.
Blocked polyisocyanates are obtained by reacting polyisocyanates with monofunctional compounds with active hydrogen atoms, Polyisocyanates which are suitable for use individually or as a mixture in the blocked form as cross-linking agents are any organic diisocyanates and/or polyisocyanates with aliphatically, cycloaliphatically and/or aromatically bonded, free isocyanate groups.
Polyisocyanates which contain about 3 to 36, preferably 8 to 15, carbon atoms are preferred. Examples of suitable diisocyanates are toluylene diisocyanate, diphenylmethane diisocyanate and in particular hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, dicylohexylmethane diisocyanate and cyclohexanc diisocyanate.
Extremely suitable polylsocyanates are, for example, "lacquer polyisocyanates"
based on hexamethylene diisoeyanate, isophorone diisocyanate and/or dicyclohexylmethane diisocyanate, wherein the polyisocyanates are derivatives of these diisocyanates known per se which contain biuret, urethane, uretdione and/or isocyanurate groups.
Monofunctional compounds with active hydrogen atoms which can be used to block the polyisocyanates are known to a person skilled in the art. The following are examples of compounds which may be used: CH-acid compounds such as acetylacetone; CH-acid esters such as alkyl acetoacetates, dialkyl rnalonaxes;
(cyclo)aliphatie alcohols such as n-butanol, 2-ethylhexanol, cyclohexanol;
glycol ethers such as butyl glycol, butyl diglycol; phenols such as cresol, tert.-butylphenol;
diaminoalcohols such as dimethylaminoethanol; oximes such as butanone oxime, acetone oxime cyclohexanone oxime; lactams such as ~-caprolactam or pyrrolidone-2; imides; hydroxyalkyl esters; hydroxamic acids and their esters; pyrazoles.
The polyisocyanates may be blocked with identical or different blocking agents within one molecule. Mixtures of identically or differently blocked polyisocyanates may also be used, Melamine/formaldehyde resins cross-link with the hydroxyl groups in the polyester resin to form ether groups, ~'hese cross-linking agents are, for example, triazines such as melamine or benzoguanamine condensed with aldehydes, in particular formaldehyde, in the presence of alcohols such as methanol, ethanol, propanol, butanol or hexanol, using known industrial methods. They are preferably methanol-I S etherified znelamin.e resins such as e.g. Cymel 325m, Cymel 32'7, Cymel 350, Cymel 370~, Maprenal MF 92'1; butanol or isobutanol ethcrified melamine resins such as e.g. Setamin US 138m or Maprenal MF 610; mixed etherified melamine resins and in particular hexamethylolmelamine resins such as e.g. Cymel 301e or Cymel 303m.
Conventional pigments, fillers, corrosion inhibitors and lacquer auxiliary substances may be used to pigment the anodic elxtmdeposition lacquer, as long as they do not enter into any disruptive reaction with water in the weakly basic to neutral pH range and do not introduce any water-soluble foreign ions which could cause problems.
The pigments and fillers are fillers which are conventionally used in the lacquer industry and inorganic or organic colour and/or effect-providing pigments and anti-corrosive pigments. Examples of inorganic colour-providing pigments are titanium dioxide, micronised titanium dioxide, zinc sulfide, lithopone, lead carbonate, lead sulfate, tin oxide, antimony oxide, iron oxides, chrome yellow, nickel titanium yellow, chrome orange, molybdenum red, mineral violet, ultramarine violet, ultramarine blue, cobalt blur, chro~anium oxide green and carbon black, Examples of colour-providing organic pigments are those from the group of azo, phthalocyanine, quinacridone, perylene, perinone, anthraquinone,. thioindigo and diketopyrrolvpyrrole pigments. Examples of effect-providing pigments are metal pigments, for example of aluminium, copper or other metals; interference pigments such as for example, metal oxide coated metal pigments or metal oxide coated mica;
pearl gloss pigrnemts and optically variable pigments (OVPs).
Examples of anti-corrosive pigments are zinc chromate, strontium chromate, zinc phosphate, lead silicochromate, barium metaborate arid zinc berate.
Examples of fillers are calcium carbonate, barium sulfate, talcum, silicon oxide, aluminium silicates, magnesium silicates, mica, aluminium hydroxide and silicas.
The fillers may also be modif ed (coated) with organic compounds, wherein the organic compounds may also contain W-curable groups. Examples of fillers modified in this way are coated microniscd aluminium oxide or coated micronised silicon dioxide.
The pigments may be dispersed in conventional ways, known to a person skilled in the art, in some of the binder dispersion or in a special paste resin. The composition of the constituents for optimum dispersion is determined separately for each dispersing unit. Suitable dispersing units are, for example, disc agitators, throe-roll mills, ball mills or preferably sand or pearl mills, During the dispersion procedure, conventional auxiliary substances such as, for example, antifoam agents, dispersion aids and agents for controlling the Theology may also be added.
The anodically depositable aqueous elcctrodeposition lacquers according to the invention may also contain conventional lacquer auxiliary substances and additives such as biocides, light stabilisers, flow control agents, Further hydrophilic and/or hydrophobic polymers with or without reactive ~roups or mixtures of these polymers may also be used, Examples of such polymers are saturated or unsaturated acrylate, polyurethane or polyester resins, acrylic-modified acrylate, polyurethane or polyester resins, epoxide resins, amino resins, phenol resins, hydrocarbon resins, silicone-modified acrylatc, polyurethane or polyester resins, copolymers of butadiene and acrylonitrile, styrene/aJ.lyl aleohal copolymers.
A,ny known powder coatings may be used in the process according to the invention, wherein they preferably do not contain any low molecular weight acidic water-soluble constituents.
Examples of powder coating compositions are described in Kittel "Lehrbuch der Lacke and Beschichtungen", vol. VIII, part 2, in the appendix, page 11 et seq.
Powder coatings which can be used according to the invention contain a binder component consisting of a film-forming resin component and a hardener component, wherein the resin component generally makes up at least 50 wt.% of the basic resinlhardener mixture, while the hardener component amounts to at most 50 wt.%
of this combination, Suitable resin components arc, for example, plastics resins which are conventionally used in the preparation of powder coatings such as polyester resins, epoxide resins, poly(meth)acrylate resins, phenol resins, polyurethane resins and siloxane resins with a number average molecular weight Mn of S00 to 20 000, preferably 500 to 10 000 and a glass transition temperature between +20°C and +100°C, preferably between +40°C and +'70°C.
The hardener components have, for example, number average molecular weights Mn of 84 to 3 000, preferably 84 to 200.
The resin and hardener components contain functional groups which are complementary one to the other and react with each other under the stowing conditions for powder coating and thus lead to cross-linking of the powder coating.
Examples of such functional groups are epoxide groups, hydroxyl groups, carboxyl groups, anhydride groups, isocyanate groups, blocked isocyanate groups, primary or secondary amine groups, blockod amine groups, N-heterocyclic groups capable of ring-opening addition such as, for example, oxazoline groups, (meth)aeryloyl groups, CH-acid groups such as, for example, acctoacetate groups, aminoether groups.
The choice of functional groups which react with each other is familiar to a person skilled in the art (see also H. I~ittel, Lehrbuch der r,acke and Beschichtungen, vol.
VIII, part 2, page 12).
Clptionally, several different functional groups may also be combined with each other, provided these do not react with each other under the conditions of preparation of powder coatings. This situation may occur, for example when the resin component contains different functional groups or when mixtures of dit~erent resin and/or hardener components are used.
The resin and hardener components contain on average at least two functional groups per molecule. In general, the ratio of resin to hardener component is 98 : 2, to 50 : 50; it is preferably between 95 : 5 and 70 : 30, The binder component should be present in a brittle and muillable condition at room temperature. A sharp drop in melt viscosity should take place in the temperature range from +100°C; to +160°C in order to favour wetting of the substrate, flow of the coating and Frlm formation.
The process is particularly suitable for using or re-using powder coatings based on epoxy-functional, hydroxy-functional and carboxy-functional binder components or mixtures thereof.

Suitable epoxy-functional binder components are, for example, epoxide group-containing polyacrylate resins, epoxide group-containing condensation resins or oligomeric polyepoxides with, for example, polycarboxylic acids, polycarboxylic anhydrides, acid polyesters, acid acrylate resins, dieyanodiamide and its derivatives, amino and/or amide group-containing compounds, blocked polyisocyanates, phenolic compounds or mixtures thereof as the hardener component, Epoxide group-containing polyacrylate resins can be prepared by generally known methods by rauiical polymerisation o;f at least one ethylenically unsaturated monomer with at least one cpoxide group in the molecule and at least one other ethylenically unsaturated monomer without epoxide groups in the molecule.
Glycidyl acrylate, glycidyl rnethacrylate and/or allyl glycidyl ether or mixtures of these monomers, for example, may be used as ethylcnically unsaturated monomers with at least one epoxide group.
Examples of ethylenically unsaturated monomers which do not contain an epoxide group are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon atoms in the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or vinylidene halides. Small amounts of compounds with more than one ethylenically unsaturated centre xnay also be used. The ethylenically unsaturated monomers which do not contain an epoxide group are preferably used as a mixture. Epoxide group-containing condensation resins may be prepared, for example, by etherification of polyhydric phenols or polyhydric aliphatic or cycloaliphatic alcohols with epichlorhydrin in the presence of an alkali.
Suitable hydroxyl-functional binder components may be, for example, polyester, polyether, polyurethane and/or polyacrylate resins with, for example, carboxylic anhydrides, acid polyester resins, acid acrylate resins, blocked polyisocyanates, ~i-hydroxyalkylamides, substituted glycolurils or mixtures thereof as hardener components.

Suitable hydroxyl-functional polyesters have, for example, an OH value of 10 to 200 mg KOH/ g of resin and an acid value of less than 5 mg KOH/g of resin.
They are prepared by methods known to a person skilled in the art, by esterification of organic dicarboxylic acids and/or their anhydrides with organic dialcohols and/or polyalcohols.
Suitable hydroxyl-functional polyethers are, fox example, polyalkylene ethers with 2 to 100 alkylene units per polymer molecule and at least one free OH group per alkylene unit, Suitable hydroxyl-functional polyurethanes are obtained by reacting aliphatic and/or cycloaliphatic and/or aromatic diisocyanates with aliphatic and/or cycloaliphatic and/or araliphatic aleohols with 2 to 6 OH groups and/or with the previously mentioned hydroxyl-functional polyesters and/or polyethers.
Hydroxyl-functional polyacrylate resins may be prepared by generally known methods by radical polymerisation of at least one ethylenically unsaturated monomer with at least one hydroxyl group in the molecule and at least one other ethylenically unsaturated monomer without hydroxyl groups in the molecule.
Ethylenically unsaturated monomers with at least one hydroxyl group which may be used are, for example, hydroxyalkyl esters of (meth)acrylic acid such as e.g.
hydroxyethyl (meth)acrylate and/or hydroxypropyl (meth)acrylate and/or hydroxybutyl (meth)acrylatc or mixtures thereof.
Examples of ethylenically unsaturated monomers which do not contain hydroxyl groups are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon atoms in the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or vinylidene halides_ Small amounts of compounds with more than one ethylenically unsaturated centre may also be used. The ethylenically unsaturated monomers which do not contain hydroxyl groups are preferably used as a mixture, Suitable carboxyl-functional binder components are, for example, acid polyester or acid acrylate resins with epoxide resins, epoxyacrylate resins, hydroxyl group-containing polyester or polyacrylate resins, oxazolines, triglycidyl isocyanurate, (3-hydroxy-alkylamides, substituted glycolurils ox mixtures thereof as hardener components.
Suitable carboxyl-functional polyesters have, for example, an acid value of 20 to I 00 mg KOH/g of resin and an OH value of less than 10 mg KOH/g of resin. They are prepared by methods known to a person skilled in the art by esterification of organic dicarboxylic acids and/or their anhydrides with organic dialcohols andlor polyalcohols, Carboxyl-functional polyacrylate resins may be prepared by generally known methods by radical polymerisation of at least one ethylenicalIy unsaturated monomer with at least one carboxyl group in the molecule and at least one other ethylenically unsaturated monomer without carboxyl groups in the molecule, Ethylenically unsaturated monomers with at least one carboxyl group which may be used are, for example, olefinically unsaturated mono or dicarboxylic acids such as e.g, acrylic acid, methacrylic acid, malefic acid, itaconic acid or mixtures thereof.
Examples of ethylenically unsaturated monomers which do not contain hydroxyl groups are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon atoms in the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or vinylidene halides. Small amounts of compounds with more than one ethylenically unsaturated centre may also be used. 'The ethylenically unsaturated monomers which do not contain hydroxyl groups are preferably used as a mixture.
However, self cross-linking powder coatings may also be used in the process according to the invention, these containing, for example, polymers with olefinically unsaturated groups as binder components. Suitable polymers are, for example, unsaturated polyester resins, unsaturated acrylate resins, polyurethane resins with (meth)acryloyl groups or mixtures of these resins which cure at the stowing temperature far anodic deposition lacquers or under additional energy-rich iwadiation.
The powder coatings may also contain pigments such as, for example, those which are specified for anodic electrodeposition lacquers.
Furthermore, conventional additives for powder coatings may be contained in the powder coatings, such as, for example, flow control agents, catalysts, waxes, degassing agents, antioxidants, light stabilisers, adhesion promoters and agents to control the melt rheology.
The powder coatings are prepared by methods lmown to a person skilled in the art 1 S such as are descr;bed, for example, in "Lehrbuch der Lacke and Beschichtungen", Dr. Hens Kittel, vol. V~Z, part 2, pages 1 to 25.
For use according to the invention, the particle sizes in the powder coating may be 1 to 100 ~Cm.
These are preferably powder coating residues or powder coating waste materials in which ai least 40 to 60 % has a particle size of less than 10 pm and up to 20 % has a particle size of less than 5 lun.
Examples:
1. Preparation of an aqueous binder dispersion for anodic electrodeposition lacquering A mixture of 1.80 parts by weight of diethanolamine and 3 parts by weight of fully deionised water are added to 57.00 parts by weight of a polyester resin with an acid value of 49 and a hydroxyl value of 60 (prepared from 26.17 parts by weight of neopentyl glycol, 5.43 parts by weight of trimethylolpropane, 10.83 parts by weight of isophthalic acid, 21.45 parts by weight of isodecanol and 36.12 parts by weight of trimcllitic anhydride) at 100°C in a reaction vessel provided with stirrer, thermometer and reflux condenser and stirred homogeneously for 10 minutes, then 0.15 parts by weight of a commercial biocide are added and the mixture is again stirred homogeneously for 10 minutes. 38.05 parts by weight of fully deionised water are added, with stirring. The mixture is stirred for 90 minutes at 80°C
and then rapidly cooled to 25°C, Characteristics:
Solids: 53.5 (30 minutes 180°C') MBQ value; 27.1 nailliequivalents of a~anine per 100 g of solid resin Solvent content: < 0.1 2. Particle size distribution of the powder coating fines fraction The paxticle size distribution of a powder coating fines fraction from a white powder coating (prepared from 910 parts by weight of Crylcoat 801 (UCB
Co.), 90 parts by weight of Araldite PT 910 (CIBA Co.), 540 pacts by weight of titanium dioxide 2160 (Kronos Co.) and 3 parts by weight of benxoin) was determined using a Master Sizer X from the Malvern Co.
60 % of all the particles had a particle size of less than 10 Nxrt, 20 % of all the particles had a particle size of less than 5 pm.

3. Preparing a powder coating-containing electrodeposition lacquer bath 150.0 parts by weight of the powder coating fines fraction from example 2 were added slowly, with stirring, to 280.0 parts by weight of the binder dispersion from example 1. Then, with further stirring, the batch was dilutod with a mixture of 1554.9 parts by weight of fully deionised water and 15.1 parts by weight of dimethylethanolamine.
Characteristics:
Solids: 15 MEQ value: 70 milliequivalents of amine per 100 g of solid resin Powder : binder 1 : 1 Pigment : binder 0.2 : 1 4. Comparison trial 50.0 parts by weight of titanium dioxide 2160 (Kronos Co.) were worked into 467.3 parts by weight of binder dispersion from example 1 in as agitator.
Then, with further slow stirring, the batch was diluted with a mixture of 1470.1 paxts by weight of fully deionised water and 12.6 parts by weight of dimethylethanolarnine.
Characteristics:
Solids: 15 MEQ value: 70 milliequivalents of amine pcr 100 g of solid resin Pigment : binder 0.2 : 1 5. Testing the throwing power Throwing power determinations were performed in accordance with "Ford Laboratory Test Method B 1 120-02" at a total immersion depth of 24 cm, in electmdepasition lacquer baths according to examples 3 and 4.

. 28 _ Example 3 Example 4 (comparison) Bath temperature 30C 30C

Coating voltage 250 Volts 250 Volts Coating time 2 minutes 2 minutes Thickness of layer, 18 ~m 21 ~m outside Thickness of layer, 20 1 N,m 23 1 ~m inside 7 ~.m lirnit 15 cm 11 cm 1 ~m limit I S cm 13 cm Range, inside, total85.7 % 59

Claims (8)

1. Use of powder coatings and/or powder coating waste materials with a particle size distribution of 0.5 to 100 µm, wherein 40 to 60 wt.% has a particle size of less than 10 µm and up to 20 wt.% has a particle size of less than 5 µm, as additives for anodically depositable electrodeposition lacquers.

2. An anodically depositable electrodeposition lacquer containing one or more binders, water and optionally one or more cross-linking agents, pigments, fillers and/or conventional additives, characterised in that it contains one or more powder coatings and/or powder coating waste materials with a particle size distribution of 0.5 to 100 µm, wherein 40 to 60 wt.% has a particle size of less than 10 µm and up to 20 wt.% has a particle size of less than 5 µm.

3. An anodically depositable electrodeposition lacquer according to Claim 2, characterised in that it contains 50 to less than 200 parts by weight of powder coating and/or powder coating waste material with respect to 100 parts by weight of binder plus optionally present cross-linking agent.

4. An anodically depositable electrodeposition lacquer in accordance with Claim 2 or 3, characterised in that it contains:
A) 67 to 33 wt,% of a water-dilutable component consisting of one or more binders and optionally one or more cross-limiting agents and optionally one or more pigments and/or fillers, B) 33 to 67 wt.% of one or more powder coatings and/or powder coating waste materials with a particle size distribution of 0.5 to 100 µm, wherein 40 to 60 wt.% has a particle size of less than 10 µm and up to 20 wt,% has a particle size of less than 5 µm, as well as water and optionally one or more conventional additives, wherein the ratio by weight of binder to cross-linking agent in component A) is 100:0 to 65:35 and the ratio by weight of pigment to binder in component A) is 0.1:1 to 1,5:1.

5. A process for preparing an anodically depositable electrodeposition lacquer by mixing an aqueous dispersion of a binder with one or more powder coatings and/or powder coating waste materials with a particle size distribution of 0.5 to 100 µm, wherein 40 to 60 wt,% has a particle size of less than 10 µm and up to 20 wt.% has a particle size of less than 5 µm, and optionally with one or more cross-linking agents, pigments, fillers and/or conventional additives.

6. A process for improving the throwing power during anodic electrodeposition lacquering, characterised in that an anodically depositable electrodeposition bath is used to which are added one or more powder coatings and/or powder coating waste materials.

7. A process for anodic electrodeposition lacquering, characterised in that an anodically depositable electrodeposition lacquer in accordance with one of Claims 2 to 4 is used.

8. A substrate, coated by the process in Claim 7.