CA1141077A - Method of producing thermosetting one-component polyurethanes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE A method of producing one-component polyurethane varnishes for application on metal bands, characterized in that polyesters with a OH functionality of at least 2, an OH number of 70 - 150 mg KOH/g and a molecular weight of about 800 - 2500, from o-, m- and/or p-benzenedicarbolyllc acids and/or 1,2,5- or 1,3,5-benzenetricarboxylic acids or their alkyl esters with 1 - 4 C atoms with trifunctional alcohols and/or glycols, are converted with cycloaliphatic polyisocyanates blocked by means of dimethylketoxime, in the equivalent ratio of OH groups to blocked isocyanate groups of 1.0 : 0.7 to 1.0 : 1.1, especially 1.0 : 1.0 and resultant products.

Description

1~4~:377 Method of Producin~ Thermosetting One-component Polyurethanes Speclfication and Examples Polyurethanes would satisfy essential requirements for use as coatings in the production of varnished metal band wares.
For example, they have excellent surface hardness, wearability and chemical fastness~ Moreover, polyurethanes produced with the aid of aliphatic or cycloaliphatic polyisocyanates furnish varnish coatings which are further distinguished by excellent weather-fastness characteristics.
Nevertheless, polyurethanes are scarcely being used at all for the varnishin~ of bands because, owing to the reaction mechanism, they require two-component handling which, in the case of metal varnishing, leads to difficulties that in many cases are insuperable. Moreover, it has not hitherto been possible to achieve adequate surface hardness along with the good deformation values that are attainable nowadays without difficulty when using PVC organosols and PVDF systems.
There has been no lack of attempts, especially in the field of varnishes generally, to endow the basically two-compon-ent system with a pseudo one-component character. In these attempts, in principle the following two methods have been followed:
1. Resins have been produced possessing isocyanate groups, based on polyethers and polyesters. After application these resins react with the atmospheric moisture to produce cross-linked, high molecular polyether, or, as the case may be, polyester polyurea. In this case, therefore, the second component is water. It is from this fact that the difficulties of what is otherwise a very elegant method are derived. Before application care must be taken to exclude all water. Only resins, solvents and pigments etc. containing no water can be used. Since these conditions can be `~

- 2 -met only at great technological expense, the use of ~uch pro-duct~ has hitherto been restricted to only a few fields of ap-plication~

2. The second method is based generally on the fact that many organic bonds tend to split again above a certain temperature. A number of substances have been discovered which enter into stable com-pounds with isocyanate groups at room temperature, while at higher temperature, as a rule between 100 and 200 C they split again into isocyanate groups. In the technical literature such products are known as isocyanate splitters or or as blocked or masked isocyanates.

In the presence of hydroxyl groups no reaction of the isocyanate groups can take place at room temperature, so that one-componen~
processing becomes possible.

According to method 2, it is also part of the prior art that 2-butanoneoxime-blocked isocyanates are used as cro~s-linking agents for hydroxylacrylates (cf. U.S. patent 3,694,389). The dis-advantage of hydroxylacrylate~ for use as polyol component~ in the polyurethane varishing of metal bands lies in their poor deforma-bility. Good d~form~bility is an indispen~able condition for the application of coatings in the field of metal band varnishing.
Other, generally suitable polyols) are polyethers and higher mo-lecular epoxides. However, these two group~ of products, owing to their poor weathering propertiesD cannot be recommended for com-bining with aliphatic and cycloaliphatic isocyanate~ .
From German unexamined published pat. appln. (OS)23 45 818, now Patent ~o. 2,346,818 combinations of polyesters containing OH
groups with ~-caprolactam-blocked polyisocyanates are also known.
Owing to the high object temperature of about 240C required, such varnishes can be pigmented only with i ~

highly thermostable pigments. However, in many cases pigments of high thermostability are not entirely acceptable for toxicological reasons owing to their heavy metal bases. If the required object temperature can be lowered below 220C there are many pigments available from which no unhygienic effects need be feared.
Surprisingly, polyurethane raw materials have been dis-covered which are produced by combining blocked cycloaliphatic polyisocyanates with special polyesters containing hydroxyl groups which satisfy all essential conditions for use in the field of metal-band varnishing. In particular, they are characterized by extremely good deformability and good surface hardness, as well as excellent weathering properties. Their deformability remains in-tact even when these varnishes are adjusted by the addition of pyrolytically recovered silicic acid on semigloss or mat surfaces.
The subject of the invention, therefore, is a method of producing one-component polyurethane varnishes for applica~ion on metal bands, characterized in that polyesters with a OH function-ality of at least 2, an OH number of 70 - 150 mg KOH/g and a molecular weight of about 800 - 2500, from o-, m- and/or p-ben-zenedicarbolylic acids and/or 1,2,5- or 1,3,5-benzenetricarboxylic acids or their alkyl esters with 1 - 4 C atoms with trifunctional - alcohols and/or glycols, are converted with cycloaliphatic poly~
isocyanates blocked by means of dimethylketoxime, in the equi-valent ratio or OH groups to blocked isocyanate groups of 1.0 :
0.7 to 1.0 : 1.1, especially 1.0 : 1Ø
As trivalent alcohols for the production of polyesters, trimethylolpropane, trimethylolethane and triethanol propane are especially suitable. From the glycol side, especially suitable are ones with chains containing no heteroatoms and consisting of 5 - 8, especially 5 - 6 C atoms, e.g. 1,5-pentanediole, 1,6-hexa-nediole, 2,2,4- or 2,4,4-trimethylhexanediole and 3-methylpenta-nediole.
The OH number of polyesters with an OH functionality of at least 2 lies in the range of 70 - 150, especially 100 mg ~OH/g.

'77 The molecular wei~hts are 800 - 2500.

Suitable polyisocyanates are especially 2,4- andJor ~,6-hexahydrotoluylenediisocyanate 3 0-9 m- and p-xylylenediisocyanate,

3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate ~PDI) and

4,4'-dicyclohexylmethanediisocyanate.

The following polyisocyanate adducts are also suitables polyisocyanates based on the above-mentioned diisocyanates or mix-tures thereof and which are produced by an addition reaction with products containing QH groups and possessing a minimum functio-nality of 2, wherè the squivalent OH-to NCO ratio is made greater than 1 s 1.2, preferably 1 ~ 1,5 to 1 ~ 2s polyisocyanates produced by reaction of the above-mentioned diisocyanates with water accompanied by the formation o~ urea and/or biuret structures; polyisocyanates obtained by oligomerization of the above-mentioned diisocyanates to dimers, trimers or pentamers.

Obviously, mixtures of the various polyisocyanates can also be used.

As solvents for the formation of the invented polyurethanes the ~ollowing are suitable~ ketones such as methylisobutylketone, cyclopentanone, cyclohexanone~ isophoron, trimethylcyclohexanone, etc~ t aromatic compounds æuch as benzene, toluene, chloro-benzene~ mixtures of aromatic compound~. o~ C8, C11, etc.~ cyclic ethers such as tetrahydrofurane, dioxane etc.; esters such as n-butylacetate, isopropylacetate, cyclohexylacetate, ethylglycolace--tate~ methylglycolace~ate, butylglycolacetate, Beside the above-mentioned advantages oi the invented processt combined with the reduction of the required object tempera ture, there i~ a sa~ing of energy and an enhanced environmental ef-fect. Especially advantageous i8 the increase of band specd that now becomes possible with no increase of energy consumption.
As a measure of the extreme deformability it may be noted in particular, the T-bend test (Test Standards of the European Coil 7~
,~

coati~rAssociation) applied to 0.8 mm thick varnished sheet steel.
The steelsheet~ with the varnished side out, is bent 180 with ~various radii of curvature resulting from the interposition of no (coefficient of measure 0) unvarnished sheets or of several (coefficient of measure 0) unvarnished sheets of equal thickness as spacers during the bending. The"coefficient of measure indicates the conditions under which ~ending can still take place before cracks become recog-nizable under lOx magnification.
As a measure of the resistance of the varnishes to mechanical damage (surface hardness) one may cite in particular the pencil hardness test according to the Test Standard of the European Coil Coating Associ-ation and the pendulum hardness test according to DIN 53 157. Indic-ations and evidence of external weathering properties can be obtained by suitable quick weathering texts, e.g. in a Weatherometer.

Exam~le 1 .

A. Production of a polyester containing hydroxyl groups 10 moles (1940 g) of terephthalic dimethyl ester was transesteri-fied in a suitable glass esterification apparatus with 8 moles (1280 g~ of a mixture o~ 2,2,4- or 2,4,4-trimethylhexanediol and 1,6 isomers (about 40 ~ 60), as ~ell as 3 moles (402 g) of 1,1,1-trimethylolpropane. The transesteri~ic tion was catalysed by 0.1 ~0 by weight dibutyl tin oxide. The reaction product~ were heated slowly while stirring until a homogeneous melt was ob-tained at a temperature of 140 C. The temperature was then in-creased to about 185 ~s at this temperature the f~ræt splitting off of methanol took place. Over a period of about 10 hours the transesterification temperature was raised to a maximum of 220 C~
during the last hour at 220 C practically no more methanol accumulated. During the entire transesterification process a a weak current of nitrogen was being passed through the reaction medium so that the condensation produ~t, methanol, could be dis-charged more effectively. In order to separate volatile components the temperature was dropped, after the transesterification, to . '~P
.~

200 C and volatile components were removed from the molten poly-ester for 39 minutes in a vacuum of 1 - 3 mm Hg.

Chemical and physical characteristics of the polyester~

OH number 93 mg KOH/g acid number ~1 mg KOH/g molecular weight 1650 glass transition temp. -5 C to ~8 C

~he polyester was dissolved in ethylglycol acetate/Solvesso 150*
(1 : 2) to give a 60 % solution, for subsequent use as a resin component for the preparation of a polyurethane varnish for coat-ing bands. (Solvesso 15~ is a mixture o~ aromatic compounds with boiling point limits of 177 - 206 C).

B. Production of the isocyanate component blocked with dimethylketoxime 500 g of a mixture consisting of 15 ~ by weight trimers tisocY-an~rate) and about 85 % of a dimer (uretdion) of isophorondiiso-cyanate was dissol~ed in 440 g of a mixture consisting of ethyl-glycol acetate and Solvesso 150 (1 ~ ~), then 159 g dimethylke-toxime was added in portions while stirringO The mixture of oli-gomers of the isophorondiisocyanate was produced in th* known manner under the catalytic influence of tributylphosphine and was subjected to thin film processing in order to separate mono-merlc isophorondiisocyanate. The monomeric isocyanate content after the thin film treatment was less than 1 % by weight;
the NCO oontent of the oligomeric mixture wa~ dsterminsd t9 be 18.4. When the free NCO groups of the mixture of oligomers was blocked the reaction mixture increased in temperature to abou~

", P~eparation of varnish On the basis of the resins described under A and B, a polyurethane * Trademark ~5 '77 varnish was prepared for varnishing bands by the following recipe:
49.2 % polyester solution, see under A
13.4 % blocked isocyanate adduct, see under ~
32.3 % white pigment, titanium dioxide (PVK 19) 3.9 % butylglycol acetate 1.2 % flow-promoting agent (silicone base) D. Technical testing of varnish 0.8 mm-thick sheets of aluminium were painted wîth a white varnish described under C and were hardened in a circulating 10 hot-air box at 310C for 55 sec, The maximum object tempera-ture was 220C.
Test results Thickness of coat 25 K~nig hardness (DIN 53 157) 173 Buchholz hardness (DIN 53 153) 100 Pencil hardness 2 H
Erichsen cupping (DIN 53 156) ~7 mm lattice incision (DIN 53 151) 0 T-bend (ECCA) 0 Examples 2 - 4 Similarly to Example 1, and using the polyester solution lA described there, baking varnishes were prepared. In doing so various acetone-blocked polyisocyanates were used.
B. Preparation of blocked polyisocyanates Example 2 231.6 g of 4,4'-dicyclohexylmethanediisocyanate was d.issolved in 160 g xylene and 80 g ethylglycol acetate and was converted in batches in a temperature range of 20 - 67C with the stoichiometric quantity o dimethylketoxime (128.4 g). After all the blockiny agent had been converted with the isocyanate groups, the content of free isocyanate groups was 0.25 % NCO.
The latent NCO content of the solution thus prepared was 12.3. ~ NCO.

~r ~'-h ., ~.~4~77 Example 3 (comparison example) 354 g of the isomeric mixture from 2,2,4- and 2,4,4-trim~thylhexa-methylenediisocyanate was heated to about 60C and converted in portions with molten dimethylketoxime while stirring. The acetoneoxime (246 g) was added in such a way that the reaction temperature did not exceed 80C. When the reaction had prac-tically run its course, the blocked polyisocyanate was dissolved in 133 g n-butylacetate and 267 g xylene at about 70C. The content of free isocyanate groups in the solution was 0.15% NCO;
the content of blocked NCO groups was 14.1%.
Example 4 (comparison example) ~64 g of a 75~ solution in e-thylglycol acetate/xylene (1 : 1) of a hexamethylenediisocyanate-based polyisocyanate containing biuret groups was diluted with 136 g xylene and 68 g ethylglycol acetate, and was brought into reaction in portions, beginning at room temperature, with 132 g acetoneoxime.
This blocked-polyisocyanate solution can be described as having a 0.4~ content of free NC0 groups and a 9.6% content of latent isocyanate groups.
C. Preparation of varnish Baking varnishes were prepared, applied and tested similarly to Example 1. The polyester solution described in Example 1 was used as the polyol component.

~ - 8 ~

Table 1: Recipes of Examples 2 to 4 -Example Polyester solution Example lA 51.2 54.0 44.9Solvesso 150 4.7 4.7 6.5ethylglycol acetate 2.3 2.3 3.2white pigment TiO2 (rutile) 22.8 21.4 24.2flow-promoting agent 1.2 1.2 1.2 Blocked isocyanate - examp. 2 17.8 - -" " - cf. examp. 3 _ 16.4 " " - cf. examp. 4 - - 20.0 D. Technical testing of varnish Table 2 presents the various hardness conditions and the technical test figures of the hardened varnish films.
Table 2 - Technical figures of the baking varnishes described in Examples 2 to 4 Hardening Technical test figures Pen-conditions SD HK HB G2o G45 G~o ET GS T- cil ness . . _ _ Examp. 2 310C 55 s 23 165 91 83 55 87 7.9 00-1 H
cf. examp.3 300C 50 s 25 120 91 91 64 95 8.8 0 0 HB
cf. examp.4 300C 50 s 30 142 I00 73 54 8g 8.6 Q 2 H

Comparison Examples 3 and 4 show that the use of aliphatic poly-isocyanates i5 indeed possible in principle, but that a combina-tion of good surface hardness with high flexibility cannot be obtained.

9 _ Example 5 A. Production of a polyester containing hydroxyl groups 7 moles of isophthalic acid (1163 g), 4 moles of hexanediol-1,6 (472 g), 2 moles of 3-methylpentanediol-1,5 (236 g) and 2 moles of l,l,l-trimethylolpropane (268 g) were submitted to esterification in a g-litre glass flask while adding 0.1%
by weight dibutyl tin oxide. With increasing temperature a homogeneous melt formed and water separation occurred at approximately 195C. Over a period of 8 hours the tempera-ture was raised to a maxirnum of 220C, and at this tempera-ture the esterification ran its course during an additional 6 hours. The molten polyester was then cooled to about 200 C
and was exposed ~o a vacuum of 20 - 30 mm Hg for 30 - 45 minutes in order to eliminate the volatile components. The bright yellow, transparent polyester can be described analytically ~s having an OH number of 103 mg KOH/g and an acid number of 1 mg KOH/g. ~olecular weight determination showed a molecular weight of 2500. This polyester was dis-solved in a mixture of solvents consisting of ethylglycol acetate and solvesso 150 (1 : 2) to produce a 60% solution (Solvesso 150 is a mixture of aromatic compounds with boiling psint limits of 177 - 206C) B. Production of a dimethylketoxime-blocked polyisocyanate Similarly to the blocked isocyanate adducts described in Examples 1 to 4, 222.1 g of isophorondiisocyanate was dis-solved in 80 g ethylglycolacetate and 151 g Solvesso 150 (~Ihere Solvesso 150 i5 a mixture of aromatic compounds with boiling point limits of 177 - 206C). 124.3 g of dimethyl-ketoxime in solid form was added to this solution. By reason of thc exothermal reaction the temperature of the mixture increased to a maximum of 55C. When the reaction had finished the NCO content of the solution was 2.35%.
The latent NCO content of this solution of a blocked poly-isocyanate was 14.5 ~.

C. Preparation of the resin solution and the prepared varnish 1295 g of the polyester solution described in A. was mixed in a glass flask with 400 g of the blocked polyisocyanate described in B. and was made to react for 60 minutes at 80 C.
A baking varnish was prepared according to the following recipe and was applied to 1 mm sheets of aluminium for hardening.
60.4 % by wt. resin solution (see above) 28.5 % by wt. white pigment TiO2 (rutile) 3.3 % by wt. ethylglycol acetate 6.7 ~ by wt. Solvesso 150 1.1 % by wt. flow-promoting agent (base: silicons and high-boiling esters) D. Technical varnish testing Table 3 summarizes the varlous hardening conditions and the technical test figures.
Table 3: hardening conditions and test figures of the varnish described in Example 5 -_ __ . _ _ _ _ Hardening Technical test figures Pen-conditions SD HK HB G20 G45 G60 E bend Hard-ness . - .
300 C 45 s 20 120 77 90 57 91 9.1 0 0 HB
300 C 50 s 20 143 lQ0 82 53 92 9.4 0 0 H-2H
300 C 60 s 23 137 100 82 55 90 9.3 0 0 H~2H
, ~ _ ~
Re Exam~s 2 to 5 Explanation of abbreviations used in Tables 1 - 3:
SD = coat thickness in;um HK = Konig hardness DIN 53 157 HB = Buchholz hardness DIN 53 153 - G = Gardner gloss values ET = Erichsen cupping DIN 53 156 GS = lattice incision DIN 53 151 Example ~
A. Production of a polyester containing hydroxyl groups 10 moles of phthalic acid anhydride (1480 g) and 12.5.moles of hexanediol-1,6 (1475 g) were submitted to esterification in a suitable apparatus. After a homogeneous melt had formed at a temperature of 155C, 3 g of dibutyl tin oxide was added as an esterifying catalyst~ The temperature was raised con-tinuously over a period of 6 hours to 220C and the esteri~i-cation was continued for a further 2~ hours in the temperature range of 2~0 - 232C. The molten polyester was then cooled to 190C and volatile components were removed in a vacuum of

5 mm Hg for 45 minutes. Analysis of the polyester thus pro-duced showed an OH number of 79 mg KOH/g and an acid number of 1.5 mg KOH/g. This polyester was dissolved in ethylglycol acetate/Solvesso 150 (1 : 2) to give a 60% solution.
B. Blocked polyisocyanate 466 g of the trimer of 3 isocyanatomethyl-3,5,5-trimethyl-cyclohexylisocyanate, produced in the known way, was dis-solved in 272 g Solvesso 150 and 136 g ethylglycol acetate and was converted with 146 g dimethylketoxime. The tempera-ture of the reaction mixture rose from room temperature to a maximum of 73C. After the solution had dropped back to room temperature, the free isocyanate content was still 0.5% by weight. This solution is taken into account in calculating the stoichiometric varnish batches with a latent NCO content o~ 8.4%.
C. Preparation of varnish A white polyurethane varnish was prepared with the resins described under A and B. Pigmentation was carried out in a bead mill.

-~ - 12 -7~

Varnish preparation recipe:
43.7 ~ polyester solution, see in A
1805 % blocked`polyisocyanate, see under B
29.6 % white pigment TiO2 (PVK 19) 7.0 % ethylglycol acetate/Solvesso 150 (1 : 2) 1.2 % flow-promoting agent (silicon resins dissolved in high-boiling esters) This white varnish was mixed in a ratio of 20 : 80 with the white varnish of Example 5 (use of monomeric diisocyanate) and was applied in the usual way to 1 mm-thick sheets of aluminium and subjected ~o hardening at 310C in circulating air. The varnish was hardened for 50 seconds in the circulat-ing-air hot box, during which the maximum object temperature established itself at 210C.
D. Technical testing of varnish Test results:
Coat thickness 23 ~m Konig hardness (DIN 53 157) 162 : Buchholz hardness (DIN 53 153) 100 Pencil hardness H - 2 H
Erichsen cupping (DIN 53 156) ~7 mm Lattice incision (DIN 53 151) 0 T-bend (ECCA) O
Example 7 (comparison example) A. Production of a polyester containing hydroxyl groups 7 moles of isophthalic acid (1163 g), 6 moles of 3,3-dimethyl-pentanediol-1,5 (624 g) and 2 moles of l,l,l-trimethylol-propane (268 g) were submitted to esterification in a 4-litre glass flask, with the addition of 0.1~ by weight n-dibutyl tin dioxide, As the temperature rose, a homogeneous melt formed and the first water separa~ion occurred at about 195C. Over a period of 8 hours the temperature was increased to 220C

and the esterification was brought to completion at this temperature over an additional six hours. The acid number at this time was 1.7 mg KOH/g. The molten polyester was exposed in the usual way to a vacuum treatment of 10 mm Hg at approximately 200C, expelling the volatile components in 30 minutes. During the entire reaction a weak current of nitrogen was passed through the reaction system. By analysis the OH number was found to be 105 mg I~OH/g and an acid number of 1.7 mg KOH/g was obtained. The polyester was dissolved for subsequent use in ethylglycol acetate/Solvesso 150 to produce a 60% solution.
B. Blocked polyisocyanate In this example the blocked oligomeric mix~ure of isophorondi-isocyanate described under B in Example 1 was used. The blocking agent was again dimethylketoime; a 60~ solution of this material in ethylglycol acetate/Solvesso 150 (1 : 2) was employed.
C. Preparation of the varnish A polyurethane varnish was prepared with the resins described under A and B. Pigm~ntation was carried out in a sand mill.
Varnish recipe:
49.0 ~ polyester solution, see under A
14,7 % blocked isocyanate adduct, see under B
32.0 % white pigment TiO2 (PVK 19) 3.2 ~ butylglycol acetate 1.1 % flow-promoting agent (varnish-compatible silicon resins in high-boiling ester solvents3 D. Technical testing 0.3 mm-thick sheets of aluminium were coated in the usual manner with the white varnish described under C and were hardened at a circulating-air temperature of 310C for 55 seconds.
.
~ 14 Test results:
Coat thickness 23)um Konig hardness (DIN 53 157) 185 Buchholz hardness (DIN 53 153) 111 Pencil hardness 3 H
Erichsen cupping (DIN 53 156) 3 mm Lattice incision (DIN 53 151) 0 T-bend tECCA) ~5 The purpose of this example is to show that when glycols other than the invented ones are used in the preparation of the polyester, adequate flexibility cannot be attained.

.~

Claims (25)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OF
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the production of single-component polyurethane lacquers which comprises:
reacting (1) a polyester having an OH-functionality of at least 2, an OH-count of 70-150 mg KOH/g and a molecular weight of about 800-2500, derived from (A) an acid selected from the group consisting of ortho-, meta-, and para-dicarboxylic acids, 1,2,5-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, C1-C4 alkyl esters thereof and mixtures thereof and (B) a glycol with a heteroatom-free chain which chain consists of 5-8 C atoms with (2) a dimethylketoxime-blocked cycloaliphatic polyisocyanate;
wherein the equivalence ratio of said OH groups to said blocked isocyanate group is 1.0:0.7 to 1.0:1.1.

2. The method of claim 1 wherein the ratio of OH groups to said blocked isocyanate groups is 1.0:1Ø

3. The method of claim 1 wherein said glycol has a chain which contains 5-6 C atoms.

4. The method of claim 3 wherein said glycol is selected from the group consisting of 1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethylhexanediol, 2,4,4-trimethylhexanediol and 3-methylpentanedio.

5. The method of claim 1 wherein the OH count of said polyester is 100 mg KOH/g.

6. The method of claim 1 wherein in addition to said glycol, said polyester is also derived from a trifunctional alcohol.

7. The method of claim 6 wherein said trifunctional alcohol is selected from the group consisting of trimethylolpropane, trimethylolethane triethanolpropane.

8. The method of claim 1 wherein sald polyisiocyanate is selected from the group consisting of 3,4-hexahydrotoluylenediisocyanateJ 2,6-hexahydro-toluylenediisocyanate, o-, m-, and p-hexahydroaylylenediisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, 4,4'-dicyclohexyl-ethanediisocyanate, and mixtures thereof.

9. The method of claim 8 wherein said polyisocyanate is reacted with an OH-group-containing product with at least a functionality of 2, wherein the equivalence ratio of OH:NCO is greater than 1:1.2.

10. The method of claim 9 wherein said equivalence ratio is 1:1.5 to 1:2.

11. The method of claim 8 wherein said polyisocyanate is an adduct formed by reacting a cycloaliphatic polyisocyanate with water.

12. The method of claim 8 wherein said polyisocyanates are selected from the group consisting of dimers, trimers and pentamers of said polyisocyanates.

13. The method of claim 1 wherein said polyurethane lacquers are formulated in a solvent.

14. A single-component duroplastic lacquer composition which comprises:
(1) a polyester having an OH functionality of at least 2, an OH count of 70-150 mg KOH/g and a molecular weight of about 800-2500, derived from (A) an acid selected from the group consisting of ortho-, meta- and para-dicarboxylic acids, 1,2,5-benzenetricarboxylic acid, 1,3,5-benzenetri-carboxylic acid, Cl - C4 alkyl esters thereof and mixtures thereof and (B) a glycol with a heteroatom-free chain which chain consists of 5-8 carbon stoms, and (2) a dimethylketoxime-blocked cycloaliphatic polyisocyanate; wherein the equivalence ratio of said OH groups to said blocked isocyanate groups is 1.0:0.7 to 1.0:1.1.

15. The composition of claim 14 wherein the ratio of OH groups to said blocked isocyanate groups is 1.0:1Ø

16. The composition of claim 14 wherein said glycol has a chain which contains 5-6 carbon atoms.

17. The composition of claim 16 wherein said glycol is selected from the group consisting of 1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-hexanediol, 2,4,4-trimethylhexanediol and 3-methylpentanediol.

18. The composition of claim 14 wherein the OH functionality of said polyester is 100 mg KOH/g.

19. The composition of claim 14 wherein in addition to said glycol, said polyester is derived from a trifunctional alcohol.

20. The composition of claim 19 wherein said trifunctional alcohol is selected from the group consisting of trimethylolpropane, trimethyloethane and triethanolpropane.

21. The composition of claim 14 wherein said polyisocyanate is selected from the group consisting of 3,4-hexahydrotoluylenediisocyanate, 2,6-hexahydrotoluylenediisocyanate, o-xylylenediisocyanate, m-xylylenediiso-cyanate, pexylylenediisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl-diisocyanate, 4,4'-dicyclohexylmethanediisocyanate, and mixtures thereof.

22. The composition of claim 21 wherein said polyisocyanate is reacted with an OH-group-containing product with at least a functionality of 2, wherein the equivalence ratio of OH:NCO is greater than 1:1,2.

23. The composition of claim 22 wherein said OH group containing product is water.

24. The composition of claim 21 wherein said polyisocyanates are selected from the group consisting of dimers, trimers and pentamers of said polyisocyanates.

25. The composition of claim 14 which further comprises a solvent.