DE1519327C3 - Highly resistant stoving enamels based on compounds containing epoxy groups or resins, melamine-formaldehyde resins etherified with butyl alcohol - Google Patents

Description

Stoving enamels based on epoxy resins and alcohol-etherified aminotriazine-formaldehyde condensation products have been in use for a long time, but the combination options are still available is bound to certain conditions. The production of etherified aminotriazine resins takes place in generally in such a way that initially in neutral or weakly alkaline aqueous, aqueous-alcoholic Medium made of an aminotriazine, possibly mixed with urea and / or urea derivatives and formaldehyde and / or formaldehyde-releasing agents such as Paraform, a relatively low molecular weight Condensation product is produced, which is then in an acidic condensation phase in aqueous-alcoholic or alcoholic solution further condensed and at the same time partially is etherified, or it becomes a priori in weakly acidic, aqueous-alcoholic or alcoholic Medium condenses and etherifies. Examples of etherified aminotriazine resins and their preparation can be found e.g. in DT-PS 9 70 453, 10 55 811 and 1127 083 as well as in J. S c h e i b e r: »Chemie und Technology of artificial resins ”, 1943, pp. 386-389.

Compounds or epoxy resins containing at least two epoxy groups are used as compounds containing epoxy groups for example in question: epoxidized diolefins, dienes or cyclic dienes, such as 1,2,5,6-diepoxihexane and 1,2,4,5-diepoxycyclohexane; epoxidized diolefinically unsaturated carboxylic acid esters, such as methyl 9,10,12,13-diepoxystearate; the dimethyl ester of 6,7,10,11-diepoxihexadecane-1,16-dicarboxylic acid; epoxidized compounds with two cyclohexenyl radicals, such as diethylene glycol bis - ^ - epoxycyclohexanecarboxylate) and 3,4-epoxicyclohexylmethyl-3,4-epoxicyclohexanecarboxylate. There are also polyesters with two epoxy groups, for example in question, how it can be achieved by reacting a dicarboxylic acid with epichlorohydrin or dichlorohydrin are accessible in the presence of alkali. Such polyesters can be derived from aliphatic dicarboxylic acids, how

Oxalic acid, succinic acid, glutaric acid,

Adipic acid, pimelic acid, suberic acid,

Acelaic acid, sebacic acid

and especially of aromatic dicarboxylic acids such as

Phthalic acid, isophthalic acid, terephthalic acid,

2,6-naphthylenedicarboxylic acid,

Diphenyl-O, O ', - dicarboxylic acid and

Ethylene glycol bis (p-carboxylphenyl) ether
derive. May be mentioned e.g. B. Diglycidyl adipate and diglycidyl phthalate. Preference is given to using diglycidyl esters which essentially have the formula

-CH-CH ₂ - (OOC-R ₁ -COO-CH ₂ -CHOH-CH ₂ -) "- OOC-R ₁ -COO-CH ₂ -CH-CH ₂

correspond, in which Ri is an aromatic carbon radical and η is zero or a small number, in particular in the range from zero to 2.

O (I)

Polyethers with two epoxy groups can also be used, such as those obtained by etherification of a bivalent one Alcohol or diphenol with epichlorohydrin or

Dichlorohydrin are accessible in the presence of alkali. These compounds can be derived from glycols, such as

Ethylene glycol, diethylene glycol, triethylene glycol,
Propylene glycol-1,2, propylene glycol-1,3,
1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol

1,4-dioxinaphthalene, bis (4-oxiphenyl) methane,
Bis- (4-oxiphenyl) -methylphenylmethane,
Bis- (4-oxiphenyl) -torylmethane, 4,4'-Dioxidiphenyl, Bis- (4-oxiphenyl) -sulfone and in particular
2,2-bis (4-oxyphenyl) propane

and in particular of diphenols such as

Resorcinol, catechol, hydroquinone,

CH ₂ -CH-CH ₂ - (Ο -R ₁ -Ο -CH ₂ CHOH-CH ₂ ) ,, - O - R ₁ -O O

derive. Ethylene glycol diglycidyl ether and resorcinol diglycidyl ether may be mentioned. It is preferred to use Diglycidyl ether, essentially of the formula

CH ₂ -CH

CH,

(Π)

correspond, in which R and η have the same meaning as in formula (I). Particularly preferred starting compounds are diglycidyl ethers, which essentially have the formula

CH-CH ₂

-O

/ Z

CH ₃

-C

CH ₃

O-CH, -CHOH-CH,

/ n

-O

\ / Z

Q-CH ₇ -CH-

-CH,

(III)

correspond, where η has the average value from zero to 2, in particular from zero to 0.5. Other epoxies and / or epoxy resins with at least two epoxy groups are described in large numbers in the book "Epoxydverbindungen und Epoxyharze" by AM Paquin, Springer-Verlag, 1958, Berlin / Göttingen / Heidelberg. If one tries to mix the etherified aminotriazine resins prepared by the processes described in the German patents cited above with epoxy resins at room temperature, one finds a severe incompatibility between the two components and the very cloudy mixtures cannot be processed into stoving finishes. However, due to the high chemical and solvent resistance that characterize the cured epoxy resin films, etherified aminotriazine resins, which can be combined with epoxy resins and / or compounds containing epoxy groups and which cause them to cure when stoving at higher temperatures, are very popular in the paint industry.

This is why paint technology has hitherto managed to use the epoxy resin and the aminotriazine-formaldehyde condensation product etherified with alcohols in the presence of organic solvents and basic catalysts, such as dicyandiamide or ammonia, and acidic catalysts, such as adipic acid, oxalic acid, glacial acetic acid or ^{Benzoic acid has been heated to temperatures of 80 to 10O 0} C until the mixtures become homogeneous for a long time, possibly up to 4 hours (DT-PS 9 35 390). According to the teachings of DT-PS 895 833, dicyandiamide and polybasic carboxylic acids or their anhydrides as catalysts together with the epoxy resin and etherified aminotriazine resin can be heated for a long time in the presence of solvents. In GB-PS 8 48 678, epoxy and aminotriazine resins are heated in the presence of solvents with catalytic amounts of phosphoric acid until they are compatible. In the DT-AS 1156 558 condensing the two resins while keeping constant the amount of solvent at temperatures of 70 to 12O ⁰ C with acid catalysts such as phosphoric acid or p-toluenesulfonic acid or their morpholine. For this “precondensation”, however, considerable expenditure on equipment and time is necessary, which unnecessarily makes these stoving enamels even more expensive.

In DT-AS 10 52 026, highly resistant paints based on epoxy resins and etherified melamine resins are already described above, which are characterized in that they contain solutions of epoxy resins with a molecular weight of more than 1000, optionally with the addition of other paint raw materials, and solutions of melamine resins, which . Are etherified with secondary butyl alcohol or isopropyl alcohol. The melamine resins etherified with secondary butyl or isopropyl alcohol and described in this last-named German patent application are also dealt with in "Fette-Seifen-Anstrichmittel", 1958, No. 7, page 553. However, these proposed paint combinations various disadvantages: In burnt 18O ⁰ C, this paint combinations are still clouded films. These films are also very brittle and show only poor solvent resistance, for example to acetone, methyl isobutyl ketone and aromatics. These disadvantages are confirmed in "Fette-Seifen-Anstrichmittel", 1958, No. 7, page 553, right column, last paragraph. Baked at 220 ^° C. and higher, the result is also very brittle films which also show strong yellowing . With baking temperatures of 22O ⁰ C and higher, you get a statement about life of a paint film and the protection he z treated him objects. B. metal parts

len, can offer. Both are only in this lacquer material given for a short time in order to be able to use them in practice. A statement about that The so-called weather-o-meter test, in which Paint films exposed to UV light, heat and moisture over a longer period of time are exposed to. In this test, too, a strong paint or film material is shown very quickly Increase in the yellowing values and a strong embrittlement, recognizable by the sharp drop in the Erichsen deepening (DIN 53136) and the behavior at the ASTM kink (D 522-11).

The aim of the proposed invention is to produce high resistance stoving lacquers based on epoxy group-containing compounds or resins and etherified melamine-formaldehyde resins which can be used without going through a pre-condensation, and baked in a wide temperature range of 180 to 25O ⁰ C, Provide films with excellent properties such as high gloss, good yellowing resistance, great elasticity and solvent resistance. Above all, the aim of the present invention is to produce highly stable stoving enamels which are distinguished by a long service life and excellent aging resistance compared to other proposed enamel combinations, which likewise do not require precondensation.

The invention relates to highly resistant stoving enamels based on epoxy groups Compounds or resins and melamine-formaldehyde resins etherified with butyl alcohols, wherein the paint contains the components mixed at room temperature, characterized in that as Etherified melamine-formaldehyde resins contain those that are produced in one step by heating together n-butanol or mixtures of n- and i-butanol therein dissolved formaldehyde and / or formaldehyde-releasing compounds, and melamine, in the presence weak acids, condensed by heating and then dehydrated.

This solution found for the composition of the new stoving enamels must be surprising be considered, since in DT-AS 10 52 026, column 3, lines 14 to 22, the following statements are literal have been hit:

»Based on the known state of the art, it was not to be expected that the compatibility of the Melamine ethers with epoxy resins of the type used to etherify methoxylated melamine Alcohol as well as the molecular size of the epoxy resin used. Will etherification is carried out with normal or isobutanol or an even higher alcohol, so are these melamine ethers are incompatible with epoxy resins. Even if only small amounts are used, about up to 15% of the melamine ether results in cloudy mixtures or films with a cloudy or cloudy appearance. "

The melamine-formaldehyde resins contained according to the invention can be obtained by adding n-butanol or mixtures of n- and i-butanol, Formaldehyde and / or formaldehyde-releasing compounds and melamine in the presence of weak compounds Acids first heated together under reflux and then by further heating with dehydration condensed by circulation distillation. N-Butanol or mixtures of n- and i-butanol, the mixing ratio should be 1: 1.

Paraform is useful as a formaldehyde-supplying compound. Weak acids can be acetic acid, Formic acid, coconut fatty acid, acrylic acid or half or partial esters of polybasic acids, e.g. B. Use half esters or maleic acid, individually or in a mixture. Glacial acetic acid is preferred as the weak acid, in particular, 0.5 to 5 ml, preferably 0.5 to 1 ml, of glacial acetic acid are used per mole of melamine.

In the preparation of the melamine resin obtained according to the invention, 3.5 to 6.5 mol of n-butanol or Mixtures of n- and i-butanol, preferably in a mixing ratio of 1: 1, 3.5 to 6 mol of formaldehyde in Form of Paraform, preferably 4 to 4.5 moles of formaldehyde as Paraform with 1 mole of melamine and in Presence of a weak acid, preferably glacial acetic acid, together under reflux for some time heated and then dehydrated with further heating while performing the circular distillation.

The reaction mixture is heated to boiling under reflux for 2 to 5 hours, preferably 1 to 2 hours and then dehydrated in 2 to 7 hours, preferably in 3 to 5 hours, by circulating distillation. Circulatory drainage can be supported by adding 10 to 50 g of benzene per mole of melamine.

Instead of the heated n-butanol or n- and i-butanol-paraform acid mixture, one can also a corresponding equal amount of acid-containing solution of anhydrous, gaseous formaldehyde in Use butanol.

The following formulations for the melamine resins A to C are intended to facilitate the production of the new aminotriazine resins explain in more detail:

Melamine resin A

300 g of n-butanol, 300 g of i-butanol, 210 g Para form (95 weight percent) and 1 ml glacial acetic acid are heated together with stirring at 80 to 85 ° C and held for I ¹ A hours at this temperature. The mixture is then allowed to cool slightly and 189 g of melamine are added at 65.degree. The mixture is heated to the boiling point and refluxed for 1 hour. The boiling temperature drops from 110 to 98.5 ⁰ C. Then there is 25 g.

Benzene is added through the condenser and 70 g of aqueous water is removed in 3 hours by circulatory dewatering Phase. In a weak vacuum, so that the distillation temperature is between 85 and 90 ° C., 133 g are withdrawn Distillate. The residue is diluted to 50 percent by weight with 30 g of xylene and approx. 125 g of i-butanol Solid resin content.

The viscosity of the resin solution is 97 DIN seconds (20 ^° C.), the gasoline compatibility 1: 2.9 and the acid number 0.99.

Melamine resin B

200 g of n-butanol, 400 g of i-butanol, 210 g Para form (95 weight percent) and 1 ml of glacial acetic acid are heated with stirring to 80 to 85 ⁰ C V / a hours at this temperature. The mixture is then allowed to cool slightly and 189 g of melamine are added at about 65.degree. The mixture is heated to the boiling point and refluxed for 2 hours. Then 25 g of benzene are added through the condenser and 69 g of aqueous phase are removed by circulatory dehydration in 3 hours. In the weak vacuum so that the distillation temperature between 85 and 9O ⁰ C, is drawn off 80 g of distillate. With 30 g of xylene and 80 g of i-butanol, 51

Weight percent solid resin content diluted. The viscosity of the resin solution is 97 DIN seconds (20 ^° C.), the gasoline compatibility 1: 3.1 and the acid number 0.95.

Melamine resins

200 g of n-butanol, 100 g of i-butanol, 500 g of a commercial solution of formaldehyde in 40gewichtsprozentigen i-butanol and 1 ml of glacial acetic acid are heated with stirring to about 60 to 70 ⁰ C. 189 g of melamine are added. The mixture is heated to the boiling point and allowed to reflux for 11/2 hours. The further procedure is as described for the preparation of the melamine resin A or B. The viscosity of the resin solution obtained is 91 DIN seconds, measured at 20 ^° C., the white spirit compatibility 1: 3.5 and the acid number 0.87.

The melamine resin was made into stoving enamels in the same way as described for melamine resins A and B processed.

To obtain the stoving enamels according to the invention, a mixture consisting of 10 to is used 70 percent by weight of the melamine formaldehyde resins according to the invention and 90 to 30 percent by weight of the Epoxy resins. The combination of 10 to 40 percent by weight of the new melamine-formaldehyde resins is particularly favorable and 90 to 60 percent by weight of the compounds or epoxy resins containing epoxy groups. The stoving enamels can also be used in a pigmented state. That in the examples and Comparative tests mentioned epoxy resin is a commercially available solid epoxy resin, manufactured by alkaline condensation of bisphenol A with epichlorohydrin with the following key figures: epoxy equivalent weight 1550 to 2000, softening point according to D u r r a n 114 to 125 ° C, viscosity of the 40% solution in Butyl diglycol at 25 ° C 1750 to 2700 centipoise (dissolved 40 percent by weight in ethyl glycol acetate / toluene = 1: IJ.

For comparison, commercial melamine resins etherified with isobutanol alone were also used according to the Example 2 of the DT-AS 10 65 552 and according to example 2 of the DT-AS 1127 083, which are in checked area proved to be completely incompatible. The table (see below) also shows the Properties of the stoved films made from the resin mixtures, compiled, namely by the pendulum hardness according to König and the resistance to acetone. the Acetone resistance was determined in the following way: On the films stoved on metal strips 0.5 ml of acetone were pipetted in the same layer thickness and immediately rubbed in with the fingertip.

It means:

1 = film without change,

2 = film slightly softened,

3 = film softened, sticky,

4 = film loosened, strongly adhesive and

5 = film released immediately.

example 1

225 g epoxy resin, 40 percent by weight in ethyl glycol acetate (ÄGA) / toluene = 1: 1, and 20 g melamine formaldehyde resin A, 50 percent by weight in xylene / butanol, were mixed. A uniform film was applied to two degreased metal sheets by dipping and after drying in the air, baked for 30 minutes at 180 ° C and 200 ° C. After 24 hours were Pendulum hardness and acetone strength determined.

Example 2

200 g of the 40 percent by weight epoxy resin solution and 40 g of melamine formaldehyde resin A in 50 percent by weight Solution were mixed. The rest of the procedure was as in Example 1.

Example 3

175 g of the 40 percent by weight epoxy resin solution and 60 g of melamine formaldehyde resin A in 50 percent by weight Solution were mixed. The rest of the procedure was as in Example 1.

Example 4

150 g of the 40 weight percent epoxy resin solution and 80 g of melamine formaldehyde resin A in 50 weight percent Solution were mixed. The rest of the procedure was as in Example 1.

Example5

225 g of the 40 weight percent epoxy resin solution and 20 g melamine formaldehyde resin in 50 weight percent Solution were mixed. The rest of the procedure was as in Example 1.

Example 6

200 g of the 40 percent by weight epoxy resin solution and 40 g of melamine formaldehyde resin B in 50 percent by weight Solution were mixed. The rest of the procedure was as in Example 1.

Example 7

175 g of the 40 percent by weight epoxy resin solution and 60 g of melamine formaldehyde resin B in 50 percent by weight Solution were mixed. The rest of the procedure was as in Example 1.

Example 8

150 g of the 40 weight percent epoxy resin solution and 80 g of melamine formaldehyde resin B in 50 weight percent Solution were mixed. The rest of the procedure was as in Example 1.

For comparison, in the same mixing ratios as indicated in the above examples, the about 50 percent by weight melamine-formaldehyde resins etherified with isobutanol according to DT-AS 10 65 552 and DT-AS 11 27 083, mixed with the 40 weight percent epoxy resin solution. In all mixing ratios only very cloudy solutions resulted, which could not be made into perfect films.

Example 9 to 12

225 g, 200 g, 175 g and 150 g of the 40 weight percent solution of the polyglycidyl ether of bisphenol A with an epoxide equivalent of 1550 to 2000, dissolved in ethyl glycol acetate / toluene = 1: 1, were with 20 g, 40 g, 60 g and 80 g of melamine resin C, about 50gewichtsprozentig in xylene / butanol, mixed by diving was placed a uniform film on degreased metal sheets and baked after drying in air, 30 minutes each at 180 ⁰ C and 200 ° C after 24 hours, pendulum hardness, pencil hardness, and Acetone resistance determined (see Table 2).

(See table 1)

So one obtains in the technically used mixing range, namely from 9: 1 to 6: 4, with the marked melamine-formaldehyde and epoxy

609 529/440

ίο

Resins well-compatible resin combinations that can be easily mixed without another Have heat treatment or post-condensation established. The technical properties of these coatings according to the invention Resin combinations are also to be regarded as very good, as Table 1 shows what a Another advantage of these stoving enamels is.

Further comparative tests

The melamine resin A according to the invention was mixed with an etherified melamine-formaldehyde resin according to FIG DT-AS 10 52 026, compared. The combination resins used were 50 percent by weight solutions of epichlorohydrin and bisphenol A commercially available polyglycidyl ethers with an epoxy equivalent from 1550 to 2000 in xylene ethyl glycol acetate 1: 1. Pigmented was based on T1O2 in a ratio of 1: 1 on the resin solid content. The mixtures were diluted with xylene-ethylglycol acetate (1: 1) and in a Ball mill abraded. The paint was adjusted to a spray viscosity of 27 sec / DIN 4 with xylene. the Film was applied in two cross-coats to glass plates or to bonded metal sheets, accordingly an average dry film thickness of 65 μ. Testing the Erichsen cupping and kink resistance was carried out on Bonder 97 sheets.

The combination ratios (based on solid resin

Table 1

gen) from epoxy to melamine resin were 9: 1.8: 2, 7: 3, 6: 4; the wet film thickness = 0.003 inch. The baking conditions were 18O ⁰ C, 200 ° C and 220 ° C per 30 minutes. ,

The test extended to the pendulum hardness (DIN 53 157), Erichsen cupping (DIN 53 156) and ASTM-Knick (D 522 to 41) before and after aging, surface hardness, gloss according to Lange (45 ° optics), Gloss retention after exposure in the Weather-o-meter (CAM 7 program disc), yellowing (with leukometer after Lange) before and after aging and on the acetone resistance (0.5 ml of acetone each are mixed with a Put the pipette on the hardened film and rub it in immediately with the fingertip.

Evaluation:

1 = film without change;

2 = film slightly softened;

3 = film softened, sticky;

4 = film loosened, strongly adhesive;

Table 3 shows the results of the measurements. It is from them that the superiority of the Stoving enamel according to the invention clearly stands out compared to the known lacquer binders. compatibility of epoxy resin and melamine resin according to the invention was of course in all mixing ratios given.

Compatibility of the solution 9: 1 to melamine resin) 7: 3 6: 4 Burn-in Pendulum hardness 8: 2 7: 3 6: 4 Acetone resistance 9: 2 7: 3 6: 4 (Mixing ratio of epoxy 8: 2 tempVtime (sec) Etherified 9: 1 9: 1 Melamine shape aldehyde resin strong strong strong According to cloudy strong cloudy cloudy DT-AS 10 65 552 cloudy Example 2 strong strong strong - - - - - - According to cloudy strong cloudy cloudy DT-AS 1127 083 B.l cloudy B.3 B.4 - - B.2 B.3 B.4 - B.2 B.3 B.4 Example 2 clear B.2 clear clear 200 200 200 3 2 2 clear 160 ° / 30 ' B.l 195 184 190 B.l 1 1 1 According to B.5 B.7 B.8 200 ° / 30 ' 196 B.6 B.7 B.8 3 B.6 B.7 B.8 invention clear B.6 clear clear 205 202 202 202 2 4th 3 2 clear B.5 210 205 210 B.5 1 1 1 According to 160 ° / 30 ' 210 5- invention 200 ° / 30 ' 225 2. (B. = example.) Ex. 10 Ex. 12 Table 2 Ex. 9 Ex. 11

Mixing ratio 9: 1 8: 2 7: 3 6: 4 Compatibility of the solution clear clear clear clear Compatibility before stoving clear clear clear clear Compatibility after baking at 180 ° / 30 ' clear clear clear clear Compatibility after 200 ° / 30 'stoving clear clear clear clear Pendulum hardness 160 ° / 30 ' 204 " 212 " 211 " 202 " Pendulum hardness 200 ° / 30 ' 225 " 189 " 195 " 210 " Pencil hardness 160 ° / 30 ' HB 2H HB HB (= Scratch resistance) 200 ° / 30 ' HB 2H 2H 2H Acetone resistance 180 ° / 30 ' 2 1 1 1 Acetone resistance 200 ° / 30 ' 2 1 1 1

Table 3

Stoving conditions I. A resin according to 200 ° C / 30min ■ Resin according to 220 ° C / 30min Resin ge 180 ° C / 30 min DT-AS Melamine resin A DT-AS Melamine resin A according to DT-AS Epoxy resin Melamine resin 10 52 026 10 52 026 10 52 026 210 206 203 3.5 255 4.0 252 3.2 Pendulum hardness 250 3.1 9.8 3.1 9.5 2.5 Erichsen depression 8.0 9.9 9.7 Ditto after 7 days 8.9 3 3 4th Wheatherometer aging 4th 1 5 1 5 ASTM kink 1 2 2 Ditto after 7 days 1 107 98 93 Wheatherometer aging 95 115 87 110 80 Shine 120 113 110 Shine retention after 7 days 115 -22 -21.5 -20.5 Wheatherometer aging 83.9 -27 85.2 -28 86.7 Yellowing initial value -28 57.2 55.2 Ditto after 7 days 56.6 4-5 2 2 Wheatherometer aging weak / cloudy 1 clear 1 clear Acetone resistance 2 clear clear Film texture before clear cloudy clear clear the branding clear clear After burning in clear

Comparative examinations as evidence
the distinctness of the products of the invention

A melamine-formaldehyde resin was prepared in accordance with the prior art (example 14 on pages 368 and 369 from Houben - Weyl, »Methods of

Melamine-formaldehyde resin I *)

126 g melamine

400 g 30 weight percent

tiger formaldehyde
500 g n-butanol

Formic acid content
in 30 weight percent formaldehyde:
approx. 0.01% by weight

The dehydration of the reaction batches took about 4 hours. This was followed by on concentrated to a solids content of approx. 50% by weight.

*) Note: When using formaldehyde solutions for the production of melamine-formaldehyde resin I, which are free from Were formic acid or where the formic acid content of organic chemistry «, Volume 14,2 '[1963]) (Melamine-formaldehyde resin I).

A melamine-formaldehyde resin II contained in the stoving enamel according to the invention was produced according to the code of the present invention.

Melamine-formaldehyde resin II

126 g melamine
500 g n-butanol

120 g formaldehyde dissolved in it

0.65 ml glacial acetic acid

Formic acid content
in the butanolic
Formaldehyde solution:
0.0001 wt%

was not more than 0.0001 wt .-%, cloudy, highly viscous condensation products were obtained, which do not Can be processed further and are therefore useless for 'lacquer-technical purposes.

The following characteristics were obtained for the melamine-formaldehyde resins I and II produced:

Melamine-formaldehyde resin I

Melamine-formaldehyde resin II

yield
Solids content
Acid number
Light petrol compatibility

Viscosity (DIN cup 4 / 2O ⁰ C)
Formaldehyde content (hydroxylamine chlorohydrate method)

540 g

50.8% by weight

0.25

Part resin / 3 parts light petrol

625 sec 0.27 wt% 550 g

51% by weight

0.94

1 part resin /

5 parts light petrol

50 sec

1.14 wt%

As the above information shows, the melamine-formaldehyde resin II contained in the invention has higher acid numbers, gasoline compatibility and formaldehyde content, and the viscosity is significantly lower than that of melamine-formaldehyde resin I. This means that the slight

Differences in condensation resins with significant differences can be obtained.

Corresponding to the data before Example 1 of the present invention in connection with Table 1 became the known melamine-formaldehyde resin I and the melamine-formaldehyde resin used according to the invention II with the commercially available solid epoxy resin described there as a lacquer in its technological Behavior checked.

The epoxy resin, prepared by alkaline condensation of bisphenol A with epichlorohydrin having the following characteristics: epoxide equivalent weight of from 1550 to 2000, softening point Dürr at 114-125 ° C, viscosity of 4O ° / o solution measured in butyl glycol at 25 ⁰ C, 1750-2700 Centipoise, was 40 wt% in ethyl glycol acetate / toluene ratio

I: 1 solved; in a technically usual ratio of 3: 7 parts of melamine-formaldehyde resin I / epoxy resin were resin mixtures of melamine-formaldehyde resin I and epoxy resin or melamine-formaldehyde resin

II made with epoxy resin. Of the 5% by weight solutions of the resins in tetrahydrofuran were IR spectra recorded, which are shown in FIG. 1 and F i g. 2 are reproduced.

It was found that the melamine-formaldehyde resin-II-epoxy resin mixture according to FIG. 2, which contains the melamine-formaldehyde resin used according to the invention, for the following wave ranges deviations from the melamine-formaldehyde resin-I-epoxy resin mixture according to F i g. 1, d. H. the special melamine-formaldehyde resin II contained in the paint according to the invention shows the following characteristic deviations in the bands in the IR spectrum:

1. CH ₂ band at 2930 cm - 'is sizes

2. Band at 740 cm - 'is smaller.

3rd gang at 1560 cm - 'is small

4. Band at 1085 cm - 'is larger.

Further chemical comparative tests

Further comparative tests with the above mixtures had the following results:

Mixture with mixture with

Melamine melamine

Formaldehyde resin I formaldehyde resin II

Formaldehyde 0.08 wt% 0.34 wt%

salary

Viscosity 150OcP (25 ° C) 65OcP (25 ° C)

1 sheet of drawings

Claims (8)

Patent claims: 1. Stoving enamels that provide solvent-resistant coatings with high mechanical strength based on compounds or resins containing epoxy groups and with butyl alcohols etherified melamine-formaldehyde resins, whereby the varnish mixed those at room temperature Contains components, characterized that as etherified melamine-formaldehyde resins are included, the one-stage through Joint heating of n-butanol or mixtures of n- and i-butanol, with formaldehyde dissolved therein and / or formaldehyde-releasing compounds and melamine, in the presence of weak compounds Acids have been condensed by heating and then dehydrated. 2. Stoving enamel according to claim I _1, characterized in that it contains an epoxy resin with the epoxy equivalent 1550 to 2000 and the softening point according to Dur ran of 114 to 125 ° C. 3. Stoving enamel according to claim 1 or 2, characterized in that it is such a melamine-formaldehyde resin contains, in the preparation of which, based on 1 mole of melamine, 3.5 to 6.5 moles of n-butanol or mixtures of n- and i-butanol, has used. 4. Stoving enamel according to one or more of claims 1 to 3, characterized in that this contains such a melamine-formaldehyde resin, in the production of which one 3.5 to 6 mol, preferably 4 to 4.5 mol of formaldehyde or compounds which release formaldehyde Formaldehyde, based on 1 mole of melamine, has been used. 5. Stoving enamel according to one or more of claims 1 to 4, characterized in that this contains such a melamine-formaldehyde resin, in the manufacture of which 0.5 to 5 ml, has preferably used 0.5 to 1 ml, glacial acetic acid per mole of melamine. 6. stoving enamel according to one or more of claims 1 to 5, characterized in that this contains such a melamine-formaldehyde resin, in the preparation of which the reaction mixture is used first 0.5 to 5 hours, preferably 1 to 2 hours, for the purpose of refluxing the condensation Has heated to the boil. 7. stoving enamel according to one or more of claims 1 to 6, characterized in that this contains such a melamine-formaldehyde resin, in the preparation of which the reaction mixture is used after the condensation by refluxing in 2 to 7 hours, preferably 3 to 5 hours Hours, has drained in the circuit. 8. stoving enamel according to one or more of claims 1 to 7, characterized in that this contains such a melamine-formaldehyde resin, the production of which involves circulatory drainage supported by the presence of 10 to 50 g of benzene per mole of melamine used has.