CA1291290C

CA1291290C - Water-dilutable coating compositions for the production of heat-curable coatings

Info

Publication number: CA1291290C
Application number: CA000550049A
Authority: CA
Inventors: Lutz-Werner Gross; Ulrich Poth; Dieter Hille; Klaus Weidemeier
Original assignee: BASF Lacke und Farben AG
Current assignee: BASF Farben und Fasern AG
Priority date: 1986-10-25
Filing date: 1987-10-23
Publication date: 1991-10-22
Anticipated expiration: 2008-10-22
Also published as: DE3636368A1; EP0269828B1; AU8324587A; KR920009300B1; KR880701763A; EP0327589A1; WO1988003159A1; BR8707845A; AU607732B2; JPH0621272B2; DE3768441D1; ES2020987B3; JPH02501312A; EP0269828A1; ATE61379T1

Abstract

Abstract:

Water-dilutable coating compositions for the production of heat-curable coatings The invention relates to water-dilutable coating compo-sitions for the production of heat-curable coatings, in which the binders are composed, at least in part, of an epoxide resin-modified, water-dilutable polyester. The water-dilutable coating compositions according to the in-vention are characterized in that the epoxide resin-modi-fied, water-dilutable polyester has been prepared by (A) synthesizing a polyester from (a1) at least one polycarboxylic acid containing at least three carboxyl groups, or a reactive derivative of this acid, and/or (a2) at least one polyol containing at least one carboxyl group and (a3) at least one polycarboxylic acid containing two carboxyl groups, or a reactive derivative of this acid, and (a4) at least one polyol, at least 10 mol%, preferably 30-70 mol%, of the components (a1), (a2), (a3) and (a4) employed containing (relative to (a1) + (a2) +
(a3) + (a4) = 100 mol%) at least one (cyclo)-aliphatic structural element containing at least six C atoms, the polyester having an average molecular weight (num-ber average) less than 2,000, preferably 500 to 1,500, an acid number from 35 to 240 preferably 50 to 120, and an OH number from 56 to 320, preferably 80 to 200, and all the (a1) and (a3) components in the polyester being co-condensed via at least two carboxyl groups, and (B) subsequently reacting the polyester thus obtained with 0.3 to 1.5, preferably 005 to 1.0, equivalents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 1,000, preferably 170 to 500, and based on a bisphenol, preferably bis-phenol A, and/or with a derivative of this epoxide resin containing at least one epoxide group per mole-cule, under reaction conditions in which essentially only carboxyl groups react with epoxide groups, to give an epoxide resin-modified polyester which, after at least part of the free carboxyl groups have been neutralized, is present in a water-dilutable form.

Description

8~8.1986/b;
~ASF Lacke+Farben AG, Munster ~ater-dilutable_coating composi~ions for the production of heat-curable coatings The ;nvention relates to water-dilutable coating compo-sitions ~or the production of heat-curable coatings, in which the binders are composed, at least in part, of an epoxide resin-modified, water-dilutable polyester.

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In the assembly-line paint;ng of automobiles, a primer is usually first applied, then a f;ller and finally the top-1û coat.

In assembly-line painting, the filler layer is preferably applied by means of electrostatic spraying processes.
The use of electrostatic spraying processes compared with other spraying procYsses achieves a considerable saving in materials, associated with a high degree of automation.

It is extremely important for assembly-line painting that the filler material should have a good application be-havior, that is to say good sprayabiL;ty in, preferably, eleetrostatic or electrostatically assisted spraying pro-cesses, advantageous rheological properties, good absorp-tion of spray mist and advantageous drying behavior.

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One function of the filLer consists in filling in and covering inequalities in order to level the substrate for the subsequent topcoat. This covering of substrate structures and defects must be accomplished without carrying out e~tensive rubbing-down work on the filler layer; this is a requirement which can only be met if the filler material has good leveling properties.

As well as optical quality, important mechanical and technological properties of the paint coating, such as, for example, corrosion resistance and, above all, resis-tance to flying stones and other mechanical attacks, depend quite decisively on the quality of the filler layer.

At the present time staving paints based on organic sol-vents are mainly used as the-filler materials~

The surface-coating industry is endeavoring, for economic and ecological reasons, to replace filler materials con-taining solvents by water-dilutable stoving paints.

The invention is based on the object of developing water-dilutable coating compositions for the production of ZO heat-curable coatings, which have the applicat;on pro-perties required for use in automobile assembly-line painting and which afford coatings having properties as good as, or even better than~ the coatings produced by means of conventional filler materials containing organic solvents.

This object is achieved, in accordance with the invention, by means of water-dilutable coating compositions in which the binders are composed, at least in part, of an epoxide S resin-modified, water-dilutable polyester which has been prepared by (A) synthesizing a polyester from (a1) at least one polycarboxylic acid containing at least three carboxyl groups~ or a reactive 1û derivative of this acid, and/or (a2) at least one polyol containing at least one carboxyl group and (a3) at least one polycarboxylic acid containing two carbo.xyl groups, or a reactive derivative of this acid, and (a4) at .least one polyol, at least 10 mol%, preferably 30-70 mol%~ of the components (a1), (a2), (a3) and (a4) employed containing (relative to (a1) + (a2) (a3) + (a4) = 100 mol%) at least one (cyclo)-aliphatic structural element containing at least six C atoms, the polyester having an average molecular weight (num-ber average) less than 2,000, preferably 500 to 1,500, an acid number from 35 to 240, preferably 50 to 120, and an OH number from 56 to 320, preferably 80 to 200, - ~t ~ /r.J'43!~
and all the ta1) and (a3) components in the polyester being co-condensed via at least two carboxyl groups, and (9) subsequently reacting the polyester thus obtained with 0.3 to 1.5, preferably 0.5 to 1~0, equivàlents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 1,000, preferably 170 to 500, and based on a bisphenol, preferably bis-phenol A, and/or with a derivative of this epoxide resin containing at least one epoxide group per mole-cule, under reaction conditions in which essentially only carboxyl groups react with epoxide groups, to give an epoxide resin-modified polyester which, after at least part of the free carboxyl groups have been neutralized, is present in a water-dilutable form.

In preparing the binders according to the invention, the type and amount of the components (a1), (a2), (a3) and (a4) should be so selected that at least 10 mol%, prefer-ably 30 to 70 mol%, of the components (a1), (a2), (a3) and (a4) employed contain (relative to (a1) + (a2) + (a3) + (a4) = 100 mol%) at least one (cyclo)aliphatic struc-tural element containing at least six C atoms, and that it is possible, on the basis of generally known principles of synthesis, to synthesize from the components (a1) and/or (a2), (a3) and (a4) a polyester which has an average molecular weight (number average) less than 2,000, pre~er-ably 500 to 1,500, an acl number from 35 t~ 240, prefer-- 5 ~
ably 50 to 120, and an OH number from 56 to 320, prefer-ably 80 to 200, and in which all the (a1) and (a3) com-ponents have been co-condensed via at least two carboxyl groups.

S The carboxyl groups of the polyester are supplied by the components (a1) and/or (a2)~ The polyester can be synthes;zed by using only the carboxyl group suppliers (a1) or ta2) or by using a mixture of the components (a1) and (a2)-8earing in mind bhe reqùirements mentioned above, the com-ponent (a1) employed can, in principle, be any polycar-boxylic acid, or a reactive derivative (for example an anhydride, ester or halide) suitable for the preparation of polyesters and containing at least three carboxyl groups, or a mixture of such acids or acid derivatives. Examples which may be mentioned are trimellitic acid, trimesic acid (1,3,5-benzenetricarboxylic acid), pyromellitic acid and trimeric fatty acids. It is preferable to employ trimel-litic acid~

Bearing in mind the requirements mentioned above, the com-ponent (a2) employed can, in principle, be any polyol suitable for the preparation of polyesters and containing carboxyl groups, or a mixture of such polyols, a polyol being understood to mean an organic compound carrying at least two hydroxyl groups. It is advantageous to employ ~ 3 dimethylolpropionic acid as the (a2) component.

~earing in mind the requ;rements mentioned above, the com-ponent (a3) employed can, in principle, be any polycar-boxylic acid, or a reactive derivative (for example an S anhydride, ester or halide), suitable for the preparation of polyesters and containing two carboxyl groups, or a mixture of such acids or acid derivatives. The following may be mentioned as examples of su;table acids: phthalic acid, isophthalic acid, terephthalic acid, fumaric acid, maleic acid, endomethylenetetrahydrophthalic acid, suc-cinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid.and dimeric fatty acids~ It is preferable to employ phthalic acid, isophthalic acid, adipic acid and dimeric fatty acids~

`15 ~earing in mind the requirements mentioned above, the com-ponent (a4) employed can, in principle, be any polyol or a mixture o-f polyols, suitable for the preparation of polyesters, a polyol being understood to mean an organic compound carrying at least 2 hydroxyl groups~ The fol-lowing are examples of suitable polyols: ethylene glycol,propanediols, butanediols, pentanediols, neopentyl glycol, hexanediols, diethylene glycol, glycerol, tri-methylolethane, trimethylolpropane, pentaerythritol, di-pentaerythritol, neopentyl glycol hydroxypivalate, 2-methyl-2-propyl-1,3-propanediol, Z,2,4-trimethyl~1,3-pentanediol and 2,2,5-tr~ ~thyl-1,6-hexanediol~ It is .

preferable to employ neopentyl glycol, 1,6-hexanediol and neopentyl glycol hydroxypivalate.

The polyester prepared -from the components (a1) and/or (a2), (a3) and (a~,) and having the characterist;c data mentioned above is reacted with 0.3 to 1.5, preferably 0.5 to 1.0, equivalents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 1,000, preferably 170 to 500, and based on a bisphenol, prefer-ably bisphenol A, or with a derivative of this epoxide resin containing at least one epoxide group per molecule, under reaction conditions in which essentially only car-boxyl groups react with epoxide groups, to give an epoxide resin-modified polyester according to the invention, which, after at least part of the free carboxyl groups have been neutralized, is présent in a water-dilutable form.

The epoxide resins based on a bisphenol, preferably bis-phenol A, are, as a rule, reaction products of bisphenols with epichlorohydrin. These epoxide resins should have an epoxide equivalent weight of 170 to 1,000, preferably 170 to 500, and should preferably contain on average one to two, particularly preferably two, epoxide groups per molecule~

It is also possible to employ derivatives of these epoxide resins containing at leaj ~ne epoxide group per molecule.

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Suitable derivatives which can be used are reaction pro-ducts containing at least one epoxide group per molecule and formed from the epoxide resins mentioned above and from a (cyclo)aliphatic monocarboxylic or polycarboxylic acid, preferably a monocarboxylic or polycarboxylic acid having a (cyclo)al;phatic structural element containing at least 6 C atoms. These derivatives can be prepared by reacting the epoxide resins in question with, for example, polymeric, preferably dimeric, fatty acids, adipic acid, 1û azelaic acid, dodecanedicarboxylic acid, long-chain mono-carboxylic acids, tetrahydrophthalic acid or hexahydro-phthalic acid, in such a way that reaction products which st;ll contain at least one epoxide group per molecule are formed.

Water-dilutable coating compositions which are very par-ticularly preferred are obta;ned if the polyester syn-thesized in stage (A) has been reacted with 0.3 to 1.5, preferably 0.5 to 1.0, equivalents per polyester molecule of a reaction product containing at least one epoxide 2û group per molecule and formed from an epoxide resin based on a bisphenol, preferably bisphenol A, having an epoxide equivalent weight of 17û to 1,000, preferably 170 to 500, and from a (cyclo)aliphatic monocarboxylic or polycarboxy-lic acid having a (cyclo)aliphatic structural element con-taining at least 18 C atoms, preferably a polymeric fattyacid and particularly a dimeric fatty acid.

_ 9 _ The reaction between the polyester synthesized ;n stage ~A) and the epoxide resin or epoxide resin derivative must be carried out in such a way that essentially only the carboxyl groups of the polyester are reacted with the epoxide groups of the epoxide resin, and that competitive reactions, such as, for example, the reaction of hydroxyl groups with epoxide groups, only take place to a minor extent.

Suitable reaction conditions are, for example: a reaction temperature of 25-180C, preferably 80-160C. The reactlon can be carried out in an inert solvent or without a dil-uent and is advantageously catalyzed by means of basic catalysts, such as, for example, tertiary amines.

After at least part of the carboxyl groups present in the epoxide resin-modified polyester according to the inven-tion have been neutralized with basic compounds, such as, for example, ammonia, aliphatic secondary and tertiary amines, such as diisopropanolamine, dimethylaminoethanol and diethylaminoethanol, and trimethylamine, triethylamine and tripropylamine, preferably with tertiary amines, the epoxide resin-modified polyester according to the invention is present in a water-dilutable form.

The coating compositions according to the invention are prepared by processing the epoxide resin-modifled polyesters according to the inven~ion, crosslinking agents (for ~ L?,~
example amino resins, in particular those of the type of hexamethoxymethylmeLam;ne, urea resins, water-dilutable epoxide res;ns and the l;ke), ;f appropriate, further binders, pigments, f;llers and further customary additives to give a water-dilutable coating compos;t;on.

In add;tion to water, the water-dilutable coating com-positions accord;ng to the ;nvention can also contain, as diluents, minor amounts of solvents.

A great advantage of the polyesters accord;ng to the ;n-vention consists:in their good compat;b;l;ty w;th the other paint components, in part;cular with crosslinking agents and further binders wh;ch may be present in the coating compos;t;on.

In an advantageous embod;ment~ the coat;ng compos;tions according to the invention contain the polyester according to the invention as the sole binder; th;s embodiment is made possible by the fact that, by virtue o~ its excellent pigment wetting properties, the polyester accord;ng to the invention can also be used as a gr;nding resin~

The coating composit;ons accord;ng to the ;nvent;on exhib;t excellent application properties, even at fluctuat;ng humidity values, and are very suitable for use in assembly-line painting. Above all, they can be readily applied by means of electrostat;c, or electrostatically assisted, , spraying processes and display advantageous rheological properties, good absorption of spray mist, good leveling properties, an advantageous drying behavior and a good wetting behavior towards PVC.

The stoved films obtained by means of the coating com-positions according to the invention display not only a good anti-corrosion action, but also a reduced tendency to yelLowing, compared with known systems, and optimum intercoat adhesion properties. In cooperation with the primer and the topcoat film(s) they result in paint coatings which have a very good topcoat appearance and - even at very high and very low temperatures -an ex-cellent resistance to flying stones and other mechan-ical attacks.

The possible uses of the coating compositions according to the invention are not limited to the painting of auto-mobiles. They can also be used for applying a mono-layer or multi-layer coating to any other substrates. Suitable substrates can be composed, for example, of ceramics, glass, concrete, plastics or preferably metals, such as iron, zinc, copper, aluminum, steel and the like.

The coating compositions according to the invent;on make it possible to obtain coatings having a particularly high g l'o s s .

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Additionally, the coating compositions according to the invention afford coatings which adhere excellently to the substrates~ if appropr;ate after pretreatment, and wh;ch exhibit very good values of resistance to mechanical at-tacks and organic solvents.

The invention is illustrated in greater detail in the following examples. Unless anything to the contrary is expressly stated, all data relating to parts and percen-tages are by weight.

Preparation of an epoxide res;n-modif;ed, water-dilutable polyester according to the invention (polyester A) 442.4 g of 1,6-hexanediol and 166.6 g of a techn;cal polymeric fatty acid (dimer content at least 80% by weight, trimer content not more than 20% by weight and monomer content not more than 1% by weight) are weighed out into a stainless steel reaction vessel which can be heated by means of heat transfer oil and is equipped with an anchor stirrer, a packed column, a vapor condenser with a re-ceiver, a protective gas inlet (N2) and temperature sen-sors for the temperature of the reaction material and thevapor temperature at the head of th0 column, and are heated to 130C. 184.3 g of isophthalic ac;d are then added and heating is continued. As soon as water from the conden-sation reaction is formed (above about 160C) the tem-ZS perature of the reaction material is increased, while the 2~- 13 -water from the condensation reaction is distilled off, to not more than 220C sufficiently sLowly for the vapor temperature at the head of the coLumn not to exceed 103C.
Condensation is carried out at 220C until the acid number of the reaction material has reached 10.5. After cooling to 140C, 266.7 9 of trimell;tic anhydride are intro-duced into the reaction material in portions and with stirring. The reaction material is then heated to 150C
and esterification is continued until the acid number has reached 67.7. The material is then cooled to 120C and diluted with sufficient ethylene glycol monobutyl ether to give a solution having a solids content of 85% by weight (determined after drying for 60 minutes at 130C
in a circulating air drying cabinet). A sample diluted to 50% by weight with ethylene glycol monobutyl ether has a solution viscosity of 4Z0 mPa.s (23~C ICI plate-cone viscometer).

The 85% strength polyester solution is heated to 140C, and 209.6 9 of an epoxide res;n formed from bisphenol A
and epichlorohydrin and having an epoxide equivalent weight of 490 are added in portions, with stirring. The mixture is then reacted at 140C until an epoxide equivalen~
weight of more than 50,000 and an acid number of 42.1 (relative to solids) have been reached. It is then cooled to 100C and neutralized with 64.6 9 of N,N-dimethyl-ethanolamine. The reaction material is then discharged, with stirring, into 2,0G~ j of demineralized water, previously heated to 60C, and vigorous stirring is applied to produce a stable binder dispersion, which is adjusted with 180 9 of demineralized water and N,N-d;methylethan-olam;ne to a solids content of 35% by weight tdeterm;ned after drying for 60 minu~es at 130C in a circulating air drying cabinet) and to a pH of 6.67 at 23C.

Preparation of an epoxide resin-modified, water-dilutable polyester according to the invention (polyester ~) 922.5 9 of an epo~ide resin formed from bisphenol A and epichlorohydrin and having an epoxide equivalent weight of 185 and Z.5 g of N,N-dimethylbenzylamine are weighed - out into the apparatus described in the preparation of polyester A, the packed column and the vapor condenser being replaced by a reflux condenser, and are heated to 1û0C with stirring. 600~0 g of the polymeric fatty acid used for the preparation of polyester A are then added in portions at 100C, and the mixture is heated to 140C. Reaction is continued until an acid number of 1.5 and an epoxide equivalent weight of 535 have been reached. T~e mixture is then diluted with 380 9 of di-ethylene glycol monobutyl ether. (A 50% strength by weight solution of the product in diethylene glycol monobutyl ether has a solution viscosity of 120 mPa.s (Z3C, ICI
plate-cone viscometer).

1,110 g of a 90~ strength by weight solution in ethylene glycol monobutyL ether of the polyester prepared in the first stage of the preparation of polyester A are prepared, and 270 9 of the epoxide resin solution prepared by the process described above are added. The mixture is heated to 140C and is reacted at 140C unt;l the product has an acid number of 40.9 (relative to solids) and an epoxide equivalent weight of more than 50,000. The reaction mat-erial is then cooled to 100C, neutralized with 63~0 9 of N,N-dimethylethanolamine and converted, analogously to the preparation of polyester A, into an aqueous dispersion having a solids content of 35% by weight and a pH of 6.60.

Preparation of some coating compositions according to the invention Deionized water and N,N-dimethylethanolamine are added, in accordance with the weight ratios indicated in Table 1, to the aqueous polyester dispersions obta;ned by the instructions described above, the mixtures are made into a paste with after-treated titanium dioxide of the rutile type, and an unsaturated, branched diol is added as an anti-foaming àgent. These mixtures are filled into a dis-continuous laboratory sand mill and are dispersed until a fineness of not more than 10 ~m, determ;ned ;n a Hegmann ~rindometer, is reached. The coating compositions 1, 2, 3 and 4 according to the invention (see Table 1) are then obtained from the dispersion mixtures by generally known methods by adding further ~olyester dispersion, low-....
.. : :,. ' '' ' ' ' ~ molecular melamine resin highly etherified with methanol, ethylene glycol ethers, water-dilutable acrylic resin as a leveling agent and demineralized water.

Applicat;on to phosphated steel sheets The coating compositions prepared by the instructions described above were set with demineralized water to a viscosity of 25 s, measured in a viscosity cup as specified in DIN 4 at 20C, and were sprayed onto phos-phated steel sheets in two cross-way operations with a 1 minute period of:;ntermediate exposure to the air, using a flow cup gun (nozzle orifice 1.2 mm; air pressure 4.5 bar). Application was carried out at an air temperature of 23C and a relative humidity of 60%. The sprayed panels were exposed to the air for 10 minu~es at 23C and for 10 minutes at 80C in a circulating air oven and were then stoved for 20 minutes at 160C in a circulating air oven and were cooled and assessed.

The coating compositions prepared by the instructions described above were also applied by electrostatic means.
This was effected using an Esta-~ehr apparatus having a TOS 300/5/8 cone and at a d;stance of 30 cm and a speed of 30,000 revolutions per minute at a relative humidity of 40-70%.

Although no special conditioning of the spray booth was . .

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carr;ed out, coatings having h;gh gloss and very good leveL;ng were obtained both w;th thin (approx. 30 ~m) ~;lm thicknesses and with thicker film thicknesses (approx. 54 ~m). The coatings had an excellent elasticity, good ad-S hesion, high resistance to yellowing and good wetting be-havior for PVC (see Table 2).

Application of the coating compositions according to the invention to steel sheets coated with an electrodipping primer Coating compositions 1 to 4 according to the invention were sprayed by the process descr;bed above onto phos-phated steel sheets coated with an electrodipping paint as specified in Example 6 of German Offenlegungsschrift 2,701,002~ The resulting coatings exhibited very good leveling, covered the structure of the electrodipping paint very well and exhibited good intercoat adhesion to the primer of electrod;pping pa;nt (see Table 3).

Application_of the coating compositions according to the invention as fillers The coating composit;ons according to the invention were applied as described above to electrod;pped steel sheets and ~ere stoved. After cool;ng, the panels were then ad-d;t;onally oversprayed with a wh;te stov;ng topcoat containing solvent and based on an alkyd resin containing saturated and unsaturated fatty acids ~acid number 1Z, OH number 110) in combination with a medium molecular weight melamine resin (ratio 2:1) partly etherified with n-butanol, and pigmented with an after-treated titanium S diox;de of the rutile type (PVC 21~) and containing solvents and additives customarily employed for processing a paint for assembly-line painting of automobiles, and the panels were stoved for 30 minutes at 130C (dry film thickness 37 to 40 ~m~.

The coatings are distinguished by good leveling, good covering of the structure of the primer and good inter-coat adhesion tsee Table 4).

Table 1 Coating composition 1 2 3 4 .
Polyester A Z0.0 20.0 Polyester P - - 20.0 20.0 Demineralized water5.8 5.8 5.8 5.8 N,N-dimethylethanolamine 0.1 0.1 0.1 0.1 Titanium dioxide 20.0 20.020.0 20.0 Anti-foam (50% solution ~10 in ethylene glycol 0.3 0.3 0.3 0.3 monobutyl ether) D;spersion mixture46.2 46.246.2 4602 .
Polyester A 44.3 37.1 Polyester B - - 44.3 37.1 Melam;ne res;n (100%) 2.6 5.1 2.6 5.1 Diethylena glycol monobutyl ether 3.0 3.0 3.0 3.0 Ethylene glycol mono-butyl ether 2;0 2.0 2.0 2.0 Leveling agent (50% solution in ethylene glycol monobutyl ether) 1.0 1.0 1.0 1.0 Demineralized water0.9 5.6 _0.9 5.6 100.0 100.0 100~0100.0 (all data in % by weight) ~"~"'~

Table 2 Coating composition 1 2 3 4 _ Film thickness (~m) 41 45 45 45 Cross-cut test as 5 specified in DIN 53,151 (Gt B) Gt 2 Gt 1-2 Gt 2Gt 2 Erichsen cupping 8.5 7.1 8.77.5 Gloss tGardner 60~ 94 96 94 92 Buchholz hardness 91 118 91 105 Yellowing~ 3 hours/

PVC wetting*
Intercol 0787 Togol~ 1 1 1-2 Unitecta~ 1-2 1 2 2 * Scale of ratings 0 (very good) to 5 (very poor) Table 3 Coating composition 1 2 3 4 Film thickness (~m)41 45 45 45 20 Cross-cut test as specified in DIN 53,151 (Gt B) Gt 0-1 Gt 1Gt 0-1 Gt 1 Buchholz hardness 91 105100 105 Erichsen cupping 6.7 5.86.9 6.2 25 Gloss (Gardner 60) 96 97 94 94 Table 4 Coating compos;t;on 1 2 3 4 Film thickness of filLer (~m) 40 43 46 45 5 Cross-cut test as specified in DI~ 53,151 (Gt G) Gt 1 Gt 2-3 Gt 1-2Gt 1-2 Erichsen cupping 6.2 5~8 6.0 5.8 Flying stones test 3 3-4 2-3 3 The flying stones test was carried out using a VDA
("Automobile Industries Association") flying stones test apparatus (model 508) tsingle bombardment w;th 1,000 g of steel shot inside 20 seconds; pressure 2 bar). The as-sessment scale ranges from 1 (very good) to 10 (very poor).

Claims

1. A water-dilutable coating composition for the production of heat-curable coatings, which water-dilutable coating composition contains a binder composed, at least in part, of an epoxide resin-modified, water-dilutable polyester which has been prepared by (A) synthesizing a polyester from (a1) at least one polycarboxylic acid containing at least three carboxyl groups, or a reactive derivative of this acid, and/or (a2) at least one polyol containing at least one car-boxyl group and (a3) at least one polycarboxylic acid containing two carboxyl groups, or a reactive derivative of this acid, and (a4) at least one polyol, at least 10 mol% of the com-ponents (a1), (a2), (a3) and (a4) employed containing (relative to (a1) + (a2) + (a3) + (a4) = 100 mol%) at least one (cyclo)-ali-phatic structural element containing at least six C atoms, the polyester having an average molecular weight (number average) less than 2,000, an acid number from 35 to 240, and an OH number from 56 to 320, and all the (a1) and (a3) components in the poly-ester being co-condensed via at least two carboxyl groups, and (B) subsequently reacting the polyester thus obtained with 0.3 to 1.5 equivalents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 1,000, and based on a bisphenol, and/or with a derivative of this epoxide resin con-taining at least one epoxide group per molecule, under reaction conditions in which essentially only carboxyl groups react with epoxide groups, to give an epoxide resin-modified polyester which, after at least part of the free carboxyl groups have been neutralized, is present in a water-dilutable form.

2. A water-dilutable coating composition as claimed in claim 1 wherein 30 - 70% of the components (a1), (a2), (a3) and (a4) contain at least one (cyclo)aliphatic structural element con-taining at least six C atoms and the polyester has an average molecular weight in the range 500 to 1,500, an acid number in the range 50 to 120 and an OH number in the range 80 to 200.

3. A water-dilutable coating composition as claimed in claim 2 wherein the polyester has been reacted with 0.5 to 1.0 equivalents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 500 and based on bisphenol A.

4. A water-dilutable coating composition as claimed in claim 1, 2 or 3 wherein part of the components (a1) and/or (a3) has been composed of at least one polymeric fatty acid.

5. A water-dilutable coating composition as claimed in claim 1, 2 or 3 wherein part of the components (a1) and/or (a3) has been composed of at least one dimeric fatty acid.

6. A water-dilutable coating composition as claimed in claim 1, 2 or 3, wherein the polyester obtained in stage (A) has been reacted with 0.3 to 1.5, equivalents per polyester molecule of a reaction product containing at least one epoxide group per molecule and formed from an epoxide resin based on a bisphenol having an epoxide equivalent weight of 170 to 1,000, and from a (cyclo)aliphatic monocarboxylic or polycarboxylic acid.

7. A water-dilutable coating composition as claimed in elaim 1, 2 or 3 wherein the polyester obtained in stage(A) has been reacted with 0.5 to 1.0 equivalents per polyester molecule of a reaction product containing at least one epoxide group per mole-cule and formed from an epoxide resin based on bisphenol A having an epoxide equivalent weight of 170 to 500 and from a monocarboxylic or polycarboxylic acid having a (cyclo)aliphatic structural ele-ment containing at least 6 C atoms.

8. A water-dilutable coating composition as claimed in elaim 1, 2 or 3, wherein the polyester obtained in stage (A) has been reacted with 0.3 to 1.5 equivalents per polyester molecule of a reaction product containing at least one epoxide group per mole-cule and formed from an epoxide resin based on a bisphenol, having an epoxide equivalent weight of 170 to 1,000 and from a (cyclo)-aliphatic monocarboxylic or polycarboxylic acid having a (cyclo)-aliphatic structural element containing at least 18 C atoms.

9. A water-dilutable coating composition as claimed in claim 1, 2 or 3, wherein the polyester obtained in stage (A) has been reacted with 0.5 to 1.0 equivalents per polyester molecule of a reaction product containing at least one epoxide group per mole-cule and formed from an epoxide resin based on bisphenol A, having an epoxide equivalent weight of 170 to 500 and from a (cyclo)-aliphatic monocarboxylic or polycarboxylic acid having a (cyclo)-aliphatic structural element containing at least 18 C atoms.

10. A water-dilutable coating composition as claimed in claim 1, 2 or 3, wherein the polyester obtained in stage IA) has been reacted with 0.3 to 1.5 equivalents per polyester molecule of a reaction product containing at least one epoxide group per molecule and formed from an epoxide resin based on a bisphenol, having an epoxide equivalent weight of 170 to 1,000 and from a (cyclo)aliphatic monocarboxylic or polycarboxylic acid having a (cyclo)aliphatic structural element containing at least 18 C atoms, which (cyclo)aliphatic monocarboxylic or polycarboxylic acid is a polymeric fatty acid.

11. A water-dilutable coating composition as claimed in claim 1, 2 or 3, wherein the polyester obtained in stage (A) has been reacted with 0.5 to 1.0 equivalents per polyester molecule of a reaction product containing at least one epoxide group per molecule and formed from an epoxide resin based on bisphenol A
having an epoxide equivalent weight of 170 to 500 and from a (cyclo)aliphatic monocarboxylic or polycarboxylic acid having a (cyclo)aliphatic structural element containing at least 18 C atoms, which (cyclo)aliphatic monocarboxylic or polycarboxylic acid is a dimeric fatty acid.

12. A polyester obtainable by reacting (a1) at least one polycarboxylic acid containing at least three carboxyl groups, or a reactive derivative of this acid, and/
or (a2) at least one polyol containing at least one carboxyl group, and (a3) at least one polycarboxylic acid containing two carboxyl groups, or a reactive derivative of this acid, and (a4) at least one polyol, at least 10 mol % of the components (a1), (a2), (a3) and (a4) employed containing (relative to (a1) + (a2) + (a3) + (a4) = 100 mol %) at least one (cyclo)-aliphatic structural element containing at least six carbon atoms, the polyester having an average molecular weight (number average) less than 2,000, an acid number from 35 to 240 and an OH number from 56 to 320, all the (a1) and (a3) components in the polyester being co-condensed via at least two carboxyl groups.

13. An epoxide resin-modified polyester obtainable by reacting a polyester as claimed in claim 12 with 0.3 to 1.5 equivalents per polyester molecule of an epoxide resin having an epoxide equivalent weight of 170 to 1,000 and based on a bisphenol and/or with a derivative of this epoxide resin containing at least one epoxide group per molecule, under reaction conditions in which essentially only carboxyl groups react with epoxide groups.