CA1307611C - Water-dilutable coating agent for preparing the base layer of a multilayer coatings - Google Patents

Abstract

Abstract of the Disclosure Basecoating compositions for preparing multilayered protective and/or decorative coat-ings comprise aqueous dispersions which contain a) as film-forming material one or more polyurethane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdiols and/or polyesterdiols having a molecular weight of from 400 to 3,000 (B) diisocyanates and (C) compounds which contain two groups which are reac-tive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation which have prefer-ably been neutralized before the reaction with a tertiary amine, an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with a polyol which contains three or more hydroxyl groups, preferably a triol, (b) pigments and (c) further customary additives.

Description

~3C)761 1 December 09, 1985 BASF Farben + Fasern AG, Hamburg Water-dilutable coating agent for preparing the base Layer_of a multilayer coat;ng The invention relates to a basecoating composition for preparing multilayered, protective and/or decorative coatings on substrate surfaces, comprising an aqueous dispers;on which contains a) as film-forming materiaL one or more polyurethane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdioLs and/or polyesterdiols having a molecular weight oF from 4~0 to 3,000 (B) diisocyanates and (C) compounds which contain two groups which are reac-tive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation which have prefer-ably been neutralized before the reaction with 3 tertiary amine, an:intermediate which has terminal isocyanate groups and whose f:ree isocyanate groups have subsequently been reacted wit~h (D) further compounds ~hich contain groups reactive toward isocyanate groups, (b) pigments and (c) further customary add;tives.

~.., .

1 3~76 1 ~

It is known in particular in automotive coating but also in other areas where coatings of pleasing decor-ative effect and at the same time high corrosion inhibition are desirable to provide substrates with a plurality of superposed coating layers.
Multilayer coatings are preferably applied by the basecoa~-clearcoat process~ wherein a pigmented basecoat is applied first and, after a short flashoff time, is overpainted wet-on-wet (ie. without prior bak;ng) with clearcoat. Basecoat and clearcoat are subsequently baked together.
The basecoat-clearcoat process has atta;ned par-ticularly great importance in the application of automotive metallic effect coat;ngs.
lS Economic and ecological reasons were beh;nd at-tempts to use waterborne basecoat;ng compositions in the preparation of multilayer coat;ngs.
Coating agents for preparing basecoats for multi-Layer automotive coatings must be processable by the cur-rently customary efficient wet on-wet process, ;e. they must be overcoatable after a very short predry;ng t;me with a (transparent) topcoat without show;ng unwanted signs of red;ssolving.
In the deveLopment of coat;ng agents for basecoats of metallic effect coat;ngs, it is additionalLy necessary to solve other problems~ The metall-ic effect depends crucially on the orientation of the metal pigment particles in the paint film. A metalLic effect basecoat wh;ch is processable wet-on-wet must accordingly produce pa;nt films , .. .. ..

~` 1 30761 1 in which the metal pigments are present after application in a favorab~e spatial orientation and in which this orien-tation is rapidly fixed in such a way that it cannot be disturbed in the course of the rest of the coating process.
S In the development of water-dilutable systems which are to meet the requirements described above, difficult problems arise due to the special physical properties of water, and to date there exist only few water-dilutable coating systems which can be used a~ basecoating compos-itions in the abovementioned sense~
For instance, US 4,558,090 discloses coating agents for preparing the base layer of multilayer coatings, which comprise an aqueous dispersion of a polyurethane resin having an acid number of 5 - 70. The aqueous polyurethane dispersion which, in addition to the binder, may also con-tain pigments and customary additives and if desired fur-ther binder components is prepared by reacting SA) a linear polyetherdiol and/or polyesterdiol having terminal hydroxyl groups and a molecular weight of from 400 to 3,000 with S~) a diisocyanate and SC) a compound which has two groups which are reactive toward isocyanate groups and one or more groups caP
able of anion formation, the group capable of anion ~formation having been neutralized before the reaction with a tertiary amine, to :give an intermediate having the terminal isocyanate groups, converting the intermediate obtained from SA), (B) and SC~ into a predo~inantly aqueous phase and . .

(D) reacting the isocyanate groups still present with a di- and/or polyamine having primary and/or secondary amino groups.
The coating agents disclosed in US
4,558,090 are highly suitable for preparing the base layer of multilayer coatings, but they are unsuitable for practical use, in particular in mass production coating processes, since the rapidly drying coating agents are so highly adherent to the application equipment used (for example paint spray guns;
automatic, electrostatically aided high-rotation units and the like) that they can only be removed with great difficulty. As a consequence, it is impossible to change the applied coating systems, for example to change the color, with the high speed which is very frequently required in particular in automotive mass production coating.
It is an object of the present invention to develop aqueous dispersions which can be used as basecoating compositions for preparing multilayered protective and/or decorative coatings on substrate surfaces and which meet all the abovementioned requirements of a basecoating composition and can also be processed without problems in the application equipment used.
We have found that, surprisingly, this object is achieved by using an aqueous dispersion which contains~
(a) as film-forming material one or more polyurethane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdiols and/or polyesterdiols having a molecular weight of from 400 to 3,000 (B) diisocyanates and . ~

....

- 4a -" 1 3076 1 1 (C) compounds which contain two groups which are reactive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation, an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with (D) further compounds which contain groups reactive toward isocyanate groups, (b) pigments and (c) further customary additives, wherein the aqueous polyurethane dispersion has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol, preferably a triol, which contains three or more hydroxyl groups, and transferring the reaction product thus obtained into an aqueous phase.

1 :~07~1 1 It is surprising and was not foreseeable that the difficulties in the removal of paint residues in the appli-cation equipment due to inherently desirable properties (rapid drying of the applied wet fil~, difficult redissol-ving of the dried film) can be solved by using the aqueouspolyurethane dispersion according to the invention and that no decrement in the quality of the completed multilayer coating need be incurred.
The dispersions according to the invention are obtained by reacting components (A), (8) and (C) to give an intermediate which has terminal ;socyanate groups. The reaction of components (A), (~) and (C) takes place in the conventional manner of organic chemistry, preferably in stages (for example formation of a first intermediate from components (A) and (8), which is then reacted with (C) to give a second intermediate). 8ut it is also possible to react components (A), (~) and (C) simultaneously.
The reaction is preferably carried out in solvents which are inert toward isocyanate groups and water-miscible.
It is advantageous to use solvents which, in addition to having the properties described above, are also good dis-solvers for the polyurethanes prepared and can be easily separated from aqueous mixtures. Particularly highly suit-able solvents are acetone and methyl ethyl ketone.
~ Component (A) can in principle be any diol custom-ary in the preparation of polyurethane-based coating agents.
su~itable polyether diols-conform to the general formula:

.

,...

, - 6 - 1 3 0 7 ~ 1 1 _ O ~ ( CHR )~ OH
n S -- _. m where R is hydrogen or lower alkyl with or without various substituents n is 2 - 6 and m is 10 - 50 or higher. Ex-amples are poly(oxyt~tramethylene) glycols poly(oxyethylene) glycols and poly(oxypropylene) glyccls~
The preferred polyalkylene ether polyols are poly-(oxypropylene) glycols having d molecular weight within the range from 400 to 3 000.
Polyesterdiols can likewise be used as polymeric diol component (component A) in the invention. The poly-esterdiols can be prepared by esterifying organic dicar-boxylic acids or the anhydrides thereof with organic diols.
The dicarbaxylic acids and the diols can be aliphatic or aromatic dicarboxylic acids and diols.
The diols used for preparing the polyesters include Z0 alkylene glycols such as ethylene glycol butylene glycol neopentylglycol and other glycols such as dimethylolcyclohexane.
The acid component of the polyester chief~y com-prises low molecular weight dicarboxylic acids or anhydrides thereof of 2 to 18 carbon atoms in the molecule.
Suitable acids are for example phthalic acid iso-phthalic acid terephthalic acid tetrahydrophthalic acid ; hexahydrophthalic acid~adipic acid azelaic acid sebacic acid maleic acid glutaric acid hexachloroheptanedicar-boxyl;c acid and tetrachlorophthallc acid. In place of . ,"f '''' , .

` - 7 ~ 1 3 0 76 1 1 these acids it is also possible to use their anhydrides, provided they exist.
F~rthermore, in the invention it is also possible to use polyesterdiols which are derived from lactones as component (A). These products are obtained for example by reacting an E-caprolactone with a diol. Products of this type are described in US Patent 3,169,945.
The polylactonepolyols which are obtained by this reaction have a terminal hydroxyl grouP ancl recurring poly-ester pc,rtions which are derived from the lactone. Theserecurring molecular portions can conform to the formula - C - ( R ) n C~20 .

where n is preferably 4 to 6 and the substituent ;5 hydrogen, alkyl, cycloalkyl or alkoxy, no subst;tuent conta;ning more than 12 carbon atoms and the total number of carbon atoms ;n the substituent on the lactone r;ng not exceeding 12.
The lactone used as starting material can be any desired lactone or any des;red comb;nat;on of lactones, although this lactone should contain not less than 6 car-bon atoms ;n the r;ng, for exampLe from 6 to 8 carbon atoms,and not less than 2 hydrogen substituents should be pres~
ent on the carbon atom wh;ch ;s bonded to the oxygen group of the r;n~. The lartone used as s~arting material can be . represented by the following general formula:

O

~.,, ~i ,,, ~ ' 8 - ~ 3076 1 1 where n and R have the previously mentioned meanings.
The lactones preferred in the invention for the preparation of the polyesterdiols are the caproLactones, where n is 4. The most preferable lactone is the unsub-stituted E-caproLactone, where n is 4 and all R substit-uents are hydrogen. This lactone is particularly preferred since it is available in large quantities and produces coatings having excellent properties. It is also Possible to use various other lactones individually or in combination.
Examples of aliphatic diols suitable for the reac-tion with the lactone include ethylene glycol, 1,3-propane-diol, 1,4-butanediol and dimethyLolcyclohexane.
Component (a) for the preparation of the polyureth-ane dispersion can be any desired organic diisocyanate.
Examples of suitable diisocyanates are trimethylene diiso-cyanate, tetramethylene diisocyanate, pentamethylene di-isocyanate, hexamethylene diisocyanate, propylene diisocy-anate, ethylethylene diisocyanate, 2,3-dimethylethylene di;socyanate, 1-methyltrimethylene diisocyanate, 1,3-cyclo-pentylene d1isocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene di;socyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluylene diisocyanate, 2,6-toluylene cliisocyanate, 4,4'-biphenylene diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanatef 1-isocyanatomethyl-5-isocyanato-1,3,3-trimethylcyclohexane, bis(4-isocyanatocyclohexyl)methane, bis(4-isocyanatophenyl)-methane, 4,4'-diisocyanatodiphenyl ether and 2,3-bis(8-iso-cyanatooctyl)-4-octyl-5-hexyl-cyclohexene.
Component (C) comprises compo~nds which contain t~o : :

'"'~'~ - 9 - 130761 1 groups reactive towards isocyanate groups, one or more of the compounds used as component (C) having one or more groups capable of anion formation which have preferably been neutralized before the reaction with a tertiary amine.
~y setting a certain mixing ratio between the com-pounds which contain groups capable of anion formation and the compounds which are free of these groups it is poscible to control the proportion of ionic groups in the poly-urethane molecule.
Suitable groups which react with isocyanate group,s are in particular hydroxyl groups. The use of compounds which contain primary or secondary amino groups can have an adverce effect on the above-described processability of the dispersions. The nature and amount of any amino-con-taining compounds to be used can be determined by the skilled worker by means of simple routine studies.
Suitable groups capable of anion formation are in particular carboxyl and sulfone groups. These groups can be neutralized before the reaction with a tertiary amine to avoid any reaction with the isocyanate groups~
Examples of compounds which contain two or more groups which react with isocyanate groups and one or more groups capable of anion formation are dihydroxypropionic acid, dimethylolpropionic ac;d~ dihydroxysuccinic acid and dihydroxybenzoic acid. Also suitable are polyhydro~y acids a~ccessible by oxidation of monosaccharides, for example gluconic acid, saccharic acid, mucic acid, glucurDnic acid and the like.
Amino-containing compounds are ~or example ~, -diaminovaleric .... .. .

-~ - 10 -acid, 3,4 diaminc,benzoic acid, 2,4-diaminotoluene-5-sulfonic acid, 4,4'-diaminodiphenyl ether sulfonic acid and the like.
Suitable tertiary amines for neutralizing anionic 5 groups are for example trimethylamine, triethylamine, di-methylaniline, diethylaniline, triphenylamine and the like.
Compounds which have two groups which are reactive toward isocyanate groups but are free of groups capable of anion formation can be for example low molecular weight diols or diamines having primary or secondary amino groups.
The isocyanato~containing intermediate formed from tA), (~) and (C) is reacted with the polyol which contains three or more hydroxyl groups, the consequence of which is most probably a cha;n lengthening and possibly even a bran-ching of the binder moleculeO
In this reaction care must be taken to ensure thatno crosslinked products are obtained. This can be achieved for example by adding an amount of polyol adapted to the isocyanate group content of the intermediate from (A), (B) and (C) and to the reaction conditions.
In principle, any polyol which contains three or more hydroxyL groups and can be reacted with the inter~
mediate obtained from ~A)~ (B) and (C) in such a way as to form no crosslinked products is suitable for preparing the ~25 ~polyurethane dispersion according to the inventionn Examples are trimethylolpropane, glycerol, erythritol, mesoerythritol, arabitol, adonitol, xylitol, mannitol, sorbitol, dulcitol, hexanetriol, (poly)p@ntaerythritol and the like.
Very particularly~ good results can be obtained when using trimethylolpropane as the polyol.
It is also conceivable that by reacting all.the four components, namely (A), (B), (C) and pOlyQl~ simul-taneously it is possible to prepare uncrosslinked poly-S urethanes ~hich can be processed to give usable basecoat-ing compositions.
After reaction of the intermediate obtained from (A), (~) and (C) with the polyol component, which has preferably been carried out in a water-miscible solvent which is inert toward isocyanate groups, which is a good solvent for the polyurethane formed and which is readily separable from aqueous mixtures, for example acetone or methyl ethyl ketone, and, if still to be carried out, neutraliz;ng the groups capable of anion formation, the reaction product is con-verted into an aqueous phase. This can be done for exampleby dispersing the reaction mixture in water and distilling off the organic solvent portions which boil below 100C.
~ or the purposes of the present invention, aqueous phase is water which can additionally contain organic sol-~0 vents. Examples of solvents which can be present in the~ater are heterocyclic, aliphatic or aromatic hydrocarbons, monohydric or polyhydrlc alcohols, ethers, esters and ket-ones, for example N-methylpyrrolidone, toluene, xylene, butanol, ethylglycol and butylglycol and acetates thereof, butyldiglycol, ethylene glycol dibutyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, acetone, lsophorone or ~ixtures thereof.
After the pH of the resulting polyurethane dispersion has been checked and if necessary been adjusted to a value within the range from 6 to 9, the dispersion forms the basis of the coating agents according to the invention into which the other constituents, ~or example additional binders, pigments, organic solvents and assistants, are homogeneousLy incorporated by dispersing, for example by means of a stir-rer or dissolver. Thereafter the p~ is checked again and if necessary adjusted to a value within the range from 6 to 9, preferably from 7.û to 8.5. Also the solids con-tent and the viscosity are set to values adapted to theparticular application conditions.
The ready-to-use coating agents generally have a solids content of from 10 to 30% by weight, and their efflux time in the IS0 cup 4 is from 15 to 30 seconds, pref-erably from 18 to 25 seconds. Their water content is from60 to 90~ by weight, and their organic solvent content from 0 to 20% by weight, in each case based on the total coating agent.
The advantageous actions of the coating compositions according to the invention can be ascribed to the use of the aqueous polyurethane d;spersion described above.
In many cases it is desirable to improve the prop-erties of the resulting surface roatings in a controlled manner by including further binder systems i~ the basecoat-ing composition.
The basecoat1ng cowpositions according to the inven-tion~advantageously contain as additional binder component a wa~ter-dilutable melamine resin in an amount of from 1 to 80% by weight, preferably from 20 to 60% by weight, based ~ - 13 - 1 30761 1 on the solids content of the polyurethane dispersion.
Water-soluble melamine resins are known per se and are widely used. They are etherified melamine-formaldehyde condensation products. Their water solubility depends not only on the degree of condensation, which should be as low as possible, but also on the etherification component, only the lowest members of the alkanol or ethylene glycol mono-ether series giving water-soluble condensates. The hexa-methoxymethylmelamine resins are of the greatest importance.
If solubilizers are used, even butanol-etherified melamine resins can be dispersed in the aqueous phase.
It is also possible to incorporate carboxyl groups in the condensate~ Transetherification products of highly etherified formaldehyde condensates with hydroxycarboxylic acids are water soluble after neutralization on account of their carboxyl group and can be used as crosslinker component in the coating agents according to the in-vention.
In place of the melamine resins described it is 2û also possible to use other water-soluble or water-dispers-ible amino resins, for example benzoguanamine resins.
When the basecoating composition according to the invention contains a melamine resin, it can advantageously a~dditionally contain, as a further binder component, a water-dilutable polyester resin and/or a ~ater-dilutable polyacrylate resin, the weight ratio of melamine resin:
polyester/polyacrylate resin being from 2:1 to 1:4 and the totaL amount of melamine resin and polyester/polyacrylate resin, basecl on the solids content of the polyurethane , , :

dispersion, ranging from 1 to 80% by weight, preferably from 20 to 60% by weightO
Water-dilutable polyesters are those having free carboxyl groups, ie. polyesters of high acid number.
There are in principle two known methods for incor-porating the necessary carboxyl groups in the resin system.
The first method comprises terminating the esterification at the desired acid number. After neutraLization with bases, ~he polyesters thus obtained are soluble in water and undergo film ;ormation in the course of baking. The second method comprises forming partial esters of dicarb-oxylic or polycarboxylic acids with high-hydroxyl polyesters of low acid number. This reaction is customarily carried out with the dicarboxylic acids in anhydride form, which reacts under mild conditions with the hydroxyl component by forming a free carboxyl group.
The water-dilutable polyacrylate resins, like the polyester resins described above, contain free carboxyl groups. They generally comprise acrylic or methacrylic copolymers, and the carboxyl groups come from the acrylic or methacrylic acid portions.
Suitable crosslinking agents include blocked poly-isocyanates. According to the invention, it is possible to use any desired polyisocyanate where the isocyanate groups have been reacted with a compound so that the blocked polyisocyanate formed is resistant to hydroxyl groups at room temperatures but reacts~ a~ elevated temperatures, in general within the range from about 90 to 300C. In the preparation o~ the blocked polyisocyanates it is possible to .:
.. .

' .. ' '' , ' ,. ~ .

use any desired organic polyisocyanates which are suitable for th~ crosslinking. Preference is given to those iso-cyanates which contain from about 3 to about 36, in par-ticular from about 8 to 15, carbon atoms~ Examples of suit-5 able diisocyanates are the abovementioned diisocyanatestcomponent 8).
It is also possible to use polyisocyanates of higher iso-cyanate functionality. Examples thereof are tris(4-isocy-anatophenyl)methane, 1,3,5-triisocyanatobenzene, 2,4,6-10 triisocyanatotoluene, 1,3,5-trist6-isocyanatohexyl)biuret, bis(2,5-d;isocyanato-4-methylphenyl)methane and polymeric polyisocya~ates, such as dimers and trimers of diisocyanato-toluene. It is also possible to use mixtures of polyiso-cyanates.
The organic polyisocyanates which are suitable for use as crosslinking agents in the invention can be prepoly-mers which are derived for example from a polyol, includ-ing a polyetherpolyol or a polyesterpolyol. To this end it is known to react polyols with excess polyisocyanates to 2~ form prepolymers having terminal isocyanate groups. Ex-amples of polyols which can be used for this purpose are simple polyols, such as glycols~ for example ethylene glycol and propylene glycol, and other polyols, such as glycerol, trim~thylolpropane, hexanetriol and pentaeryth-ritol, furthermore monoethers, such as diethylene glycoland dipropylene glycol, as well as polyethers which are adducts of such polyols and alkylene ox;des. Examples of ; alkylene oxides wh;ch are su;table for polyaddition onto these polyols to form polyethers are ethylene oxide, ,,, - ~ , ~ - 16 - 1307611 propylene oxide, butylene oxide and styrene oxide. These polyaddition products are generaLly referred to as polyethers having terminal hydroxyl groups. They can be linear or branched. Examples of such polyethers are polyoxyethylene glycol having a molecular weight of 1,540, polyoxypropylene glycol having a molecular weight of 1,025, polyoxytetra-methylene glycol, polyoxyhexamethylene glycol, polyoxynona-methylene glycol, polyoxydecamethylene glycol, polyoxy-dodecamethylene glycol and mixtures thereof. Other types 1G of polyoxyalkylene glycol ethers can likewise be used.
Particularly suitable polyether polyols are those which are obtained by reacting such Polyols as ethylene glycol, di-ethylene glycol, triethylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol and mixtures thereof, glycerol-trimethylolethane, trimethylolpropane, 1,2,6-hexanetriol, dipentaerythritol, tripentaerythritol, polypentaerythritol, methylglucosides and sucrose with alkylene oxides, such as ethylene oxide, propylene oxide or mixtures thereof.
To block the polyisocyanates it is possible to use any desired suitable aliphatic, cycloaliphatic or aromatic alkyl monoalcohols. Examples thereof are aliphatic alco-hoLs, such as methyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexyl, decyl and lauryl alcohol, aromatic alkyl alcohols, such as phenylcarbinol and methylphenylcarbinol. It is also Pos-sible to include small amounts of higher molecular weight and relatively ;nvolatile monoalcohols, if desired, these al-cohols, after detachmentr functioning as plasticizers in the coatings.

~ 17 - 1 3076 1 1 Other suitable blocking agents are oximes, such as methyl ethyl ketone oxime, acetone oxime and cyclohexanone oxime, as well as caprolactams, phenols and hydroxamic acid esters.
Preferred blocking agents are malonic esters, acetoacetic 5 esters and B-diketones.
The blocked polyisocyanates are prepared by reac-ting a sufficient amount of an alcohol with the organic polyisocyanate, so that no free isocyanate grouPs are present.
The basecoating compositions according to the in-vention may contain any known pigment or dye customary in the paint industry.
; Examples of dyes and pigments which may be of in-organic or organic nature are titanium dioxide, graphite, 15 carbon black, zinc chromate~ strontium chromate, barium chromate, lead chromate, lead cyanamide, lead silicochrom-ate, zinc oxide, cadmium sulfide, chromium oxide, zinc sulfide, nickel titanic yellow, chromium titanic yellow, ;ron oxide red, iron oxide black, ultramarine blue, phthalo-20 cyanine ~omplexes, naphthol red, quinacridones, halogenatedthioindigo pigments or the like.
Particularly preferred p;gments are metal powders alone or a nixture, such as copper, copper alloys, aLuminum and;steel, preferably aLuminum powder, used in an not less 25 than~predominant amount, namely in an amount of from 0.5 to ZS~X by weight, based on the total solids content of binders in the coating agents.; Preferred metallic pigments are those commercially available metal powders which ha~e been specifically pretreated for aqueous systems.

'i The metal po~ders can also be used together w1th one or more of the abovementioned non-metallic pigments or dyes.
In this case, the amount thereof is chosen in such a way that the desired metallic effect is not suppressed.
The basecoating compositions according to the in-vention can also contain further customary additives such as solvents, fillers, plasticizers, stabilizers, wetting agents, dispersants, flow control agents, anti~oams and catalysts individually or in mixture in the customary amounts. These substances can be added to the individual components and/or to the mixture as a whole.
Examples of suitable fillers are talcum, mica, kaolin, chalk, quartz powder, asbestos powder, slate powder, barium sulfate, various silicas, silicates, glass fibers, organic fibers and the like.
The coating compos;tions described above are used according to the invention in processes for preparing mult;layered coatings on substrate surfaces, wherein ~1) an aqueous dispersion is applied as a basecoating Z0 composition (2) from which a polymer f;lm is formed on the substrate surface (3) to the basecoat thus obtained is applied a suitable transparent topcoat composition and subsequently (4) the basecoat is baked together with the topcoat.
Suitable topcoat composit;ons are in principle aLl known nonpigmented or merely transparently pigmented coating agents~ They may be conventional solvent-contain-ing clearcoats, water-dilutable clearcoats or powder clearcoats.

, _ 19 _ -~ ~ Suitable substrates to be coated ar~3i~7p~rlt~cular pretreated metal substrates, but it is also Possible to coat the nonpretreated metalc and any other desired sub-strates such as, for examPle, ~ood, ~lastics and the ~ike with a multilayered protective andtor decorative coating using the basecoating compositions according to the invention.
The invention is exDlained in more detail in the following examples. Parts and percenta~es are by weight, unless otherwise stated.
PreDaration of a polyurethane dispersion according to th~
..... . . . .
invention 255 9 of a polyester of 1,6-hexanediol and iso-phthalic acid with an average molecular ~eight of 614 are heated together with 248 9 of polypropylene glycol having an average molecular ~eight of 600 and 100 9 of dimethylols propionic acid to 100C and dehydrated for 1 hour under reduced pressure. At 80 C 526 9 of 4,4'-dicyclohexyl-methane diisocyanate and 48û 9 of methyl ethyl ketone are added. Stirring is continued at 80C until the free isocyanate group content is 1.69%, based on the total starting weight.
Z8.5 g of trimethylolpropane are then added, fol-lowed by 0.4 9 of dibutyltin dilaurate, and 2 hours of stirring at 80C. After addition of 1,590 9 of methyl ethyl ketone the temperature of 80 C is maintained until the viscosity, measured in the DIN cup, is 65 s (sample dissolved in a ratio of 203 in N-methylpyrrolidone)~
After addition of a mixture of 22.4 g of dimethyl-; ethanolamine and 2,~50 9 of deionized water~ methyl ethyl . i ,.,~
'' ~, , .

ketone is distilled off under reduced pressure, to leave a finely divided dispersion having a solids content of 30%, a pH of 7.4 and a viscosity of 48 s, measured in the DIN

c u p .
Preparation of two-layer coatings by the oasecoat/clearcoat . .. . . _ .
method using the polyurethane dispersion according to the . . . _ invention prepared by the above method .
The two-layer coating was prepared in accordance with the experimental directions given in U~ 4,558,090.
It proved possible to process a metallic effect basecoat prepared using the polyurethane dispersion accor-ding to the invention into a high-quality two-layer metal-lic effect coating giving an excellent metallic effect.
The removability of paint residues remaining be-hind in the appl;cation equipment is demonstrated by meansof the following comparative experiment:
A glass plate was knife-coated in a wet film thickness of 100 ~m with a metallic effect basecoat in accordance with US 4,558,090 and a metall;c effect basecoat in accordance ~ith the present ;nvention.
After 2 hours of drying at room temperature a mix-ture of 50 parts of water and 50 parts of n-propanol was used to try to remove the dried paint film from the ~lass plate by guiding under slight pressure a brush which had been impregnated w;th this cleaning mi~ture in circular ; ~ovements over the dried pa;nt film. The paint film formed from the.metallic effect basecoat prepared according to the invention dissolved homogeneously after the first few circular movements. The paint film prepared using the , ,~

, dispersion disclosed in US 4,558,090, by contrast, first became swollen and only became detached from the substrate in relatively large connected flakes after many circular movements.
This experiment was repeated with a large number of different solvent and solvent mixtures. Similar results were obtained in all cases.

~,,,, ~, ,

Claims (27)

1. A basecoating composition for preparing multilayered, protective and/or decorative coatings, comprising an aqueous dispersion which contains (a) as film-forming material one or more poly-urethane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdiols and/or poly-esterdiols having a molecular weight of from 400 to 3,000 (B) diisocyanates and (C) compounds which contain two groups which are reactive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation, an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with (D) further compounds which contain groups reactive toward isocyanate groups, (b) pigments and (c) further customary additives, wherein the aqueous polyurethane dispersion has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol which contains three or more hydroxyl groups, and transferring the reac-tion product thus obtained into an aqueous phase.

2. A basecoating composition as claimed in claim 1, wherein one or more of the compounds used as component (C) have one or more groups capable of anion formation which have been neutralized before reaction with a tertiary amine.

3. A basecoating composition as claimed in claim 1, wherein the polyol with which the inter-mediate obtained from (A), (B) and (C) has been reacted is a triol.

4. A basecoating composition as claimed in claims 1, 2 or 3, wherein the reaction of the inter-mediate obtained from (A), (B) and (C) with the polyol has been carried out in a water-miscible organic solvent which boils below 100°C, is inert toward isocyanate groups and is readily separable from aqueous mixtures.

5. A basecoating composition as claimed in claims 1, 2 or 3, wherein the reaction of the inter-mediate obtained from (A), (B) and (C) with the polyol has been carried out in acetone.

6. A basecoating composition as claimed in claims 1, 2 or 3, wherein the intermediate obtained from (A), (B) and (C) has been reacted with tri-methylolpropane.

7. A basecoating composition as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as an additional binder component a water-dilutable melamine resin in an amount from 1 to 80%
by weight, based on the solids content of the poly-urethane dispersion.

8. A basecoating composition as claimed in claims 1, 2 or 3 r wherein the basecoating composition contains as an additional binder component a water-dilutable melamine resin in an amount from 20 to 60 by weight, based on the solids content of the poly-urethane dispersion.

9. A basecoating composition as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as a further binder component a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the weight ratio of melamine resin: polyester resin and/or polyacrylate resin being from 2:1 to 1:4 and the total proportion of melamine resin, polyester resin and polyacrylate resin, based on the solids content of the poly-urethane dispersion, ranging from 1 to 80% by weight.

10. A basecoating composition as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as a further binder component a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the weight ratio of melamine resin: polyester resin-and/or polyacrylate resin being from 2:1 to 1:4 and the total proportion of melamine resin, polyester resin and polyacrylate resin, based on the solids content of the poly-urethane dispersion, ranging from 20 to 60% by weight.

11. A basecoating composition as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as an additional binder component a blocked polyisocyanate together with a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the proportion of polyisocyanate, polyester resin and/or polyacrylate resin as a whole ranging from 1 to 80% by weight, based on the solids content of the polyurethane dispersion.

12. A basecoating composition as claimed in claims 1, 2 or 3, wherein the basecoating composition contains from 0.5 to 25% by weight of metal pigments, based on the total solids content of the polyurethane dispersion.

13. A process for preparing a multi-layered, protective and/or decorative coating on a substrate surface by (1) applying as a basecoating composition an aqueous dispersion which contains (a) as film-forming material one or more poly-urethane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdiols and/or poly-esterdiols having a molecular weight of from 400 to 3,000 (B) diisocyanates and (C) compounds which contain two groups which are reactive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation, an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with (D) further compounds which contain groups reactive toward isocyanate groups, (b) pigments and (c) further customary additives, (2) forming from the composition applied in step (1) a polymer film on the surface, (3) applying to the basecoat thus obtained a suitable tansparent topcoat composition and then baking the basecoat together with the topcoat, wherein the polyurethane dispersion forming the basecoating composition has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol which contains three or more hydroxyl groups, and transferring the reaction product thus obtained into the aqueous phase.

14. A process as claimed in claim 13, wherein one or more of the compounds used as component (C) have one or more groups capable of anion formation which have been neutralized before reaction with a tertiary amine.

15. A process as claimed in claim 13, wherein the polyol with which the intermediate obtained from (A), (B) and (C) has been reacted is a triol.

16. A process as claimed in claims 13, 14 or 15, wherein the reaction of the intermediate obtained from (A), (B) and (C) with the polyol has been carried out in a water-miscible organic solvent which boils below 100°C, is inert toward isocyanate groups and is readily separable from aqueous mixtures.

17. A process as claimed in claims 13, 14 or 15, wherein the reaction of the intermediate obtained from (A), (B) and (C) with the polyol has been carried out in acetone.

18. A process as claimed in claims 13, 14 or 15, wherein the intermediate obtained from (A), (B) and (C) has been reacted with trimethylolpropane.

19. A process as claimed in claims 13, 14-or 15, wherein the basecoating composition contains as an additional binder component a water-dilutable melamine resin in an amount from 1 to 80% by weight, based on the solids content of the polyurethane dispersion.

20. A process as claimed in claims 13, 14 or 15, wherein the basecoating composition contains as an additional binder component a water-dilutable melamine resin in an amount from 20 to 60% by weight, based on the solids content of the polyurethane dispersion.

21. A process as claimed in claims 1, 2 or 3, wherein wherein the basecoating composition contains as a further binder component a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the weight ratio of melamine resin: polyester resin and/or polyacrylate resin being from 2:1 to 14 and the total proportion of melamine resin, polyester resin and polyacrylate resin, based on the solids content of the polyurethane dispersion, ranging from 1 to 80% by weight.

22. A process as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as a further binder component a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the welght ratio of melamine resin: polyester resin and/or polyacrylate resin being from 2:1 to 1:4 and the total proportion of melamine resin, polyester resin and polyacrylate resin, based on the solids content of the polyurethane dispersion, ranging from 20 to 60% by weight.

23. A process as claimed in claims 1, 2 or 3, wherein the basecoating composition contains as an additional binder component a blocked polyisocyanate together with a water-dilutable polyester resin and/or a water-dilutable polyacrylate resin, the proportion of polyisocyanate, polyester resin and/or polyacrylate resin as a whole ranging from 1 to 80%
by weight, based on the solids content of the poly-urethane dispersion.

24. A process as claimed in claim 1, 2 or 3, wherein the basecoating composition contains from 0.5 to 25% by weight of metal pigments, based on the total solids content of the polyurethane dispersion.

25. A substrate coated with a multi-layered, protective and/or decorative coating which has been obtained by (1) applying as a basecoating composition an aqueous dispersion which contains (a) as film-forming material one or more polyure-thane resins having an acid number of from 5 to 70, which has been prepared by preparing from (A) linear polyetherdiols and/or polyesterdiols having a molecuiar weight of from 400 to 3,000 (B) diisocyanates and (C) compounds which contain two groups which are reactive toward isocyanate groups, one or more of the compounds used as component C having one or more groups capable of anion formation, an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with (D) further compounds which contain groups reactive toward isocyanate groups, (b) pigments and (c) further customary additives, (2) forming from the composition applied in stage (1) a polymer film on the surface, (3) applying to the basecoat thus obtained a suitable transparent topcoat composition and then (4) baking the basecoat together with the topcoat, wherein the polyurethane dispersion forming the basecoating composition has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol which contains three or more hydroxyl groups, and transferring the reaction product thus obtained into an aqueous phase.

26. A substrate as claimed in claim 25, wherein one or more of the compounds used as component (C) have one or more groups capable of anion formation which have been neutralized before reaction with a tertiary amine.

27. A substrate as claimed in claim 25 or 26, wherein the polyol with which the intermediate obtained from (A), (B) and (C) has been reacted is a triol.