DE2721989C3 - Liquid coating agents with a low solvent or solvent-free basis - Google Patents

Description

A. 45 to 10 percent by weight of aminoplasts and/or their low molecular weight precursors and

B. Contain 55 to 90 percent by weight of at least bifunctional, predominantly free hydroxyl and possibly free carboxyl end groups bearing polyesters or mixtures,

wherein the polyesters of component B are obtained by condensing a component 1 consisting of

Ll 0 to 50 molar percent of one or more aliphatic polyols with 3 or 4 hydroxyl groups and 3 to 6 carbon atoms and

L2 100 to 50 mole percent of a mixture II of diols,

The mixture 11 in turn

11.1 10 to 90 mole percent of ethylene glycol and
1L2 to 90 to 10 mole percent of propanediol-(O) and
113 to 0 to 40 mole percent of one or more other aliphatic or cycloaliphatic diols, in which the hydroxyl functions are separated by 2 to 8 carbon atoms and up to 2 of the carbon atoms can be replaced by oxygen atoms, which in turn should be separated from each other and from the hydroxyl groups by at least 2 carbon atoms,

consists of a component III, consisting of a mixture of

ULI Hexahydroterephthalic acid and
III.2 aromatic dicarboxylic acids

was produced;,i, where the polyesters or mixtures used as component B. have a molecular weight of 300 to 1500, and the binder can also have been obtained by co-condensation of aminoplasts and/or their low molecular weight precursors with the polyesters or by co-condensation of the starting products of the aminoplast production with the polyesters, where 8 to 33, preferably 12 to 25 mol percent of terephthalic acid is used as component II 1.2.

Examples of suitable polyols according to component 1.1 are glycerin, trimethylolethane, trimethylolpropane and pentaerythritol; the use of glycerin and trimethylolpropane is preferred. Component 1.1 is contained in the polyesters according to B, preferably in amounts of 0 to 20 mole percent; accordingly, the polyesters contain component 1.2, preferably in amounts of 80 to 100 mole percent.

Diols of component 113 can be, for example,

Propanediol-(1.3),
Butanediol-(1.2).
Butanediol-(2.3),
Butanediol-(13),
b'utandiol-(1.4),
2.2-Dimethylpropanediol-(1.3),
Hexanediol-(1.6),

1 A- bis(hydroxymethyl)cyclohexane,
*.8-Bis-(hydroxymethyl)-tricyclo-[5.2.1.0 ²⁶ ]decane,

where &khgr; is 3, 4 or 5, diethylene glycol or dipropylene glycol. Cycloaliphatic diols can be used in their cis or trans form or as a mixture of both forms. Component 15.3 is preferably used in amounts of 0 to 30 Mecl percent.

The hexahydroterephthalic acid is preferably contained in the acid component in amounts of 75 to 88 mol percent. The acids can be used as free acids for polyester production.

However, the lower alkyl esters are preferably used in the reaction, with dimethyl esters being particularly preferred. A cis-trans-!omer is preferred as dimethyl hydroxyhydroterephthalate, such as that obtained in the high-pressure hydrogenation of dimethyl terephthalate.

Preferably, the polyesters used according to the invention have a molecular weight of 600 to 1000. The molecular weight is the middle molecular weight. üi*s was determined by end group titration.

The use of polyols with more than 2 hydroxyl groups increases the inherent viscosity of the polyesters used according to the invention. The viscosity can also be controlled by the diols (113) that may be used. The use of longer-chain linear diols reduces the viscosity, whereas branched or cycloaliphatic diols cause an increase in viscosity.

The ratio of components II1.1:III.2 is critical for the polyesters to be used according to the invention.

At lower than inventive contents of terephthalic acid or its lower alkyl esters, only insufficiently hard coatings are obtained at baking temperatures of, for example, 120 ⁰ C, whereas too high terephthalic acid contents lead to crystalline

jo products that cannot be dissolved in conventional paint solvents.

The esters can be prepared by all known and conventional methods - with or without a catalyst, with or without passing through an inert gas sirome - as

J5 Solvent condensation. Melt condensation or azeotropic esterification can be carried out at temperatures up to 250 ⁰ C, if necessary also at higher temperatures, whereby the water or, for example, methanol ^released is removed. The esterification can be monitored by determining the hydroxyl number and, if free dicarboxylic acids are used, also by determining the acid number. As a rule, the esterification conditions are chosen so that the reaction is as complete as possible. The molecular weight of the esters can thus be regulated by the ratio of alcohol component (diol and, if necessary, polyol) and dicarboxylic acid or its ester.

If part of the acid component is in the form of

free acid and the other part as alkyl ester, it is more appropriate to carry out the reaction in two consecutive stages. In the first stage, the alkyl ester is transesterified with part or all of the diols and/or polyols required to produce the esters until the alcohol is almost completely removed. The remaining components are then added and condensed to the desired degree of conversion with elimination of water.

When using more highly reactive aminoplasts that cure without the addition of strongly acidic catalysts, it is advantageous to use polyesters with acid numbers of up to 30 mg KOH/g, preferably up to 20 mg KOH/g. Such products are obtainable when using free dicarboxylic acids, for example by stopping the reaction at the desired acid number. Polyesters obtained by transesterification that have practically no free carboxyl end groups, or those produced by esterification

Polyesters with an acid number < 5 mg KOH/g can have their acid number subsequently increased significantly by reacting them at 130 to 190 ^° C with relatively strongly acidic carboxylic acids or their anhydrides such as maleic acid, phthalic acid, trimellitic acid, pyromellitic acid, with the last two being preferred. Polyesters of this type are preferably acidified to such an extent that they have an acid number in the range of > 5 to 20 mg KOH/g.

The esterification or transesterification temperature is chosen so that the losses of easily volatile substances that make up the esters to be used according to the invention remain low, i.e. at least during the first period of esterification, the temperature is below the boiling point of the lowest boiling starting substance.

The properties of the coatings produced from the polyesters to be used according to the invention depend on the average molecular weight, the functionality and the composition of the polyesters. At higher average molecular weights, the hardness of the paint film is generally reduced while the elasticity increases. On the other hand, at lower molecular weights, the flexibility of the paint film decreases while the hardness increases.

The differences in the composition of the polyester have a similar effect. As the content of hexahydrourephthalic acid units in the polyester chain increases, the elasticity of the paint film increases, while its hardness decreases. As the chain length of the open-chain diols (II.3) used in minor amounts increases, and as the proportion of these diols in the polyester increases, the paint film becomes softer and more flexible. However, if diols with short and branched carbon chains or with cycloaliphatic rings are also used in the manufacture of the polyester, the coatings made from these esters generally produce harder and less elastic films as the proportion of these diols increases.

The molar ratio of polyol to diol is also important for the mechanical properties of the paint films: As the molar ratio of polyol to diol decreases, the hardness of the films also decreases, while their elasticity increases. Conversely, with larger molar ratios of polyol to diol, the flexibility of the paint films is reduced and the hardness improved.

With knowledge of these rules, it is easy for a person skilled in the art to select polyesters with optimal properties for the respective intended use of the coating agents according to the invention within the scope of the claimed range.

Suitable aminoplasts are the known reaction products of aldehydes, especially formaldehyde, with substances containing several amino or amido groups, such as melamine, urea, dicyandiamide and benzoguanamine. Mixtures of such products are also suitable. Aminoplasts modified with alcohols are particularly suitable.

Due to their low substance viscosity, low molecular weight, structurally defined aminoplasts are preferably used, which are practically infinitely miscible with the polyesters to be used according to the invention. Such structurally defined aminoplasts are, for example, dimethylolurea, tetramethylolbenzoguanamine, trimethylolmelamine or hexamethylolmelamine.

The latter can also be used in partially or fully etherified form, such as dimethoxymethylurea, tetrakis-(methoxymethyl)-benzoguanamine, tetrakis-(ethoxymethyl)-benzoguanamine, partial or complete etherification products of hexamethylolmelamine, such as tetrakis-(methoxymethyl)-tetrakis-(methoxymethyl)-bis-methylolmelamine. pentakis-(methoxymethyl)-mono-methylolmelamine and hexakis-(methoxymethyl)-melamine and mixtures of these

&iacgr;&ogr; three substances or hexakis-(butoxymethyl)-melamine. Particularly preferred are hexamethylolmelamine derivatives which are liquid in bulk at room temperature and etherified with alcohols having 1 to 4 carbon atoms.
When using these aminoplasts, the addition of strongly acidic catalysts, such as p-toluenesulfonic acid, is preferred to accelerate the curing process. In order to obtain paints with a longer shelf life, the use of blocked catalysts is particularly preferred.

2i) In a preferred form of export, higher reactivity, relatively low viscosity, higher molecular weight melamine resins, specially developed for low-solvent stoving varnishes, are used, which are combined with the poly-

2-j esters without the addition of a catalyst to form hard, elastic films. These melamine resins, which are usually partially etherified with methanol and still contain a considerable number of unetherified methylol groups, are described by L A. Ruuer, for example [Adhäsion 1974 (Heft 6), Seile 178; Aminoharze der Gruppe 111

Of course, the polyesters used according to the invention can also be combined with higher molecular weight aminoplasts. As a rule, the

J5 polyesters according to the invention are miscible with such aminoplast resins in the claimed mixing ratios without clouding. However, if the mixtures of resinous aminoplasts with the polyesters according to the invention lead to clouding, the compatibility can be improved by reacting the polyester and aminoplasts with one another in a known manner in substance or in solution, whereby care must be taken that the reaction does not progress to crosslinking, for example

by briefly heating the mixture or a solution of the two resins, if necessary in the presence of a catalyst, such as organic or mineral acids.

It is also possible to

It is possible to add the polyester to be used to the batch before or during the production of the aminoplast resins from, for example, urea, benzoguanamine or melamine and aldehydes, whereby it is of course also possible to use additional conventional alkanols to modify the aminoplast resin thus formed. The methods for producing such amine/aldehyde resins are known. A large number of commercially available aminoplasts are available for combination with the polyesters to be used according to the invention.

To produce the coating agents, ester and aminoplast or aminoplast solution are usually mixed together. The weight ratio of polyester to aminoplast can be between 55:45 and

« 90:10, preferably between 65:35 and 85:15. The optimal ratio of the two components to each other for the respective application of the paint can easily be determined by preliminary tests.

It should be noted that increasing the aminoplast content often increases the hardness of the coatings and reduces their elasticity, while decreasing the aminoplast content reduces the hardness and increases the flexibility.

Depending on the intended use of the coating agent, its viscosity can be reduced by adding small amounts of conventional paint solvents, such as propanol, i-propanol, butanol, ethyl acetate, butyl acetate, ethyl glycol, ethyl glycol acetate, butyl glycol, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, 2-nitropropane, trichloroethylene or mixtures of various such solvents. It is also possible and, for economic reasons, may be advisable to add larger or smaller amounts of less polar solvents, such as xylene, higher-boiling aromatic fractions or aliphatic hydrocarbon mixtures.

such as mineral spirits. The proportion of these less polar solvents added can be freely selected within the scope of the solubility of the polyesters used according to the invention and their compatibility with the aminoplasts used. According to the invention, in no case is more than 30 percent by weight of solvent used in the coating agents.

The coating compositions according to the invention can contain, in addition to large amounts of pigment, the usual additives and auxiliary substances, in particular spreading agents, and additionally other binding agents, such as, for example, epoxy resins and silicone resins containing hydroxyl groups.

The binder/pigment ratio is determined by the intended use of the coating. For example, when the binders are used to produce automotive topcoats or industrial paints, they are pigmented in a ratio of 1:0.3 to 1:1. Even with a binder/pigment ratio of 1:1.1 to 1:13, as is usual in packaging coating or coil coating, the coatings show unusually good properties. The coating agent according to the invention can also have even higher pigment contents, as is usual, for example, in the production of primers.

The resulting coating agent is applied by conventional methods, for example by brushing, spraying, dipping or rolling - cold, warm or hot - and baked at temperatures between 100 and 250 ^° C, preferably between 110 and 200°C and in particular between 120 and 180 ^° C. When using almost completely etherified hexamethylolmelamine derivatives, an acidic catalyst such as p-toluenesulfonic acid is preferably added to accelerate crosslinking. Since the use of such strongly acidic catalysts can lead to an increase in the viscosity of the coating agent even at room temperature, it is advisable to use blocked catalysts which only develop their catalytic effectiveness at higher temperatures. For reasons of improved storage stability and better electrostatic processability, the use of blocked acids is preferred, as described in DE-AS 23 45 114 or DE-PS 23 56 768. When using the more highly reactive aminoplasts, curing is preferably carried out without the addition of a catalyst.

The coatings produced with the coating agents according to the invention have a wealth of good properties. They are high-gloss, easy to pigment and adhere very well - especially to metals. In salt spray tests, tropical tests and weatherometer tests they show excellent corrosion protection and weather resistance. Furthermore, they show good storage stability, especially when using non-ionic blocked catalysts or using more highly reactive melamine resins. In addition, the systems are characterized by good stability on vertical surfaces during baking.

&iacgr;&ogr; out.

An outstanding property of the coating agents according to the invention is the possibility of obtaining hard-elastic coatings even when the baking temperature is varied over ^a wide range. The previously known solvent-free or low-solvent polyester/aminoplast binders only produce hard-elastic and burnable coatings when they have been baked at temperatures of >130°C or >150°C.

With the products of the state of the art, lower baking temperatures can be used, but in this case the baking time must be extended to a time that is not appropriate in practice, or the amount of catalyst must be increased so much that the quality of the coatings no longer meets the practical requirements in all areas of application. The coatings according to the invention are able to avoid the disadvantages described.

In other words, the coating agents according to the invention provide the processor with a system that allows him to carry out curing at both higher and lower temperatures, regardless of the type of curing units present.

Since the coating agents according to the invention contain no or only a small amount of organic solvents, they are extremely environmentally friendly, so that the costs for afterburning can be reduced or even saved. Due to this fact and the good overburning stability, the coating agents according to the invention are particularly suitable for

&bull; industrial mass-production painting.

Examples
1. Polyester production

A mixture of 248 g ethylene glycol (4 mol), 1«g propanediol-(1.2) (1 mol), 600 g dimethyl hexahydroterephthalate (3 mol) and 194 g dimethyl terephthalate (1 mol) is heated to 180 to 190°C for 2 to 3 hours after adding 0.8 ml of a titanium tetraisopropylate solution (10% by volume in isopropanol) with stirring, a gentle stream of nitrogen and constant distillation of the methanol formed. The temperature is then slowly increased to 210 ⁰ C. After a total of 22 hours, almost 256 g of methanol have been split off. The clear

µm colorless ester mixture has an acid number of 0.9 mg KOH/g and a hydroxyl number of 128 mg KOH/g - corresponding to an average molecular weight of 869. A solution of the polyester is prepared in ethyl glycol acetate (80 percent)

II. Acidification of a polyester

To 100 g of a solvent-free polyester according to I. 1.72 g of trimellitic acid are added at 170°C with stirring.

hydride and left at this temperature for about 1 h under nitrogen. After cooling, the product obtained has an acid number of 9.7 mg KOH/g. The polyester is then dissolved in ethyl glycol acetate (80%).

Holy preparation of a binding agent

The polyester or the polymerization solution is mixed with a commercially available hexamethylolmelamine derivative or a solution of a melamine-formaldehyde-alkanol condensate in the desired solids ratio. If the ester and aminoplast are not compatible with each other, the mixture of the two components, which contains solvent when using aminoplast solutions, is heated to 50 to 100 ^° C for 10 to 60 minutes.

IV. Preparation of a coating agent

To produce a coating agent, pigmentation is carried out in the desired binder/pigment ratio by incorporating the appropriate amount of pigment, e.g. on a three-phase pigment mill, possibly after adding solvents.

V. Production and testing of coatings

For testing, the coating agent is applied to test sheets and glass plates at room temperature and baked. To reduce the baking temperature, p-toluenesulfonic acid or a non-ionic blocked catalyst is added when using the less reactive aminoplasts. The layer thickness of the films on which the test is carried out is usually approx. 40 μm. The hardness test is carried out in accordance with DIN 53 157 by determining the pendulum strength according to König. The elasticity of coatings is determined by the Erichsen cupping test (DIN 53 156). The cupping of the painted sheet in mm at which the coating begins to crack is given as a measure of the extensibility. The slow deformation of the coating (feed rate: 0.2 mm/sec) is essential for this test method.

Examples marked with letters are comparative examples. All information on proportions, time, etc. that are not mentioned under IH. to V. can be found in the tables.

Approximately 36 g of water gives a clear polyester with a hydroxyl number of 237 mg KOH/g and an acid number of 4.7 mg KOH/g, which corresponds to an average molecular weight of approx. 465. A coating agent is produced from this polyester and a commercially available, largely methyl-etherified hexamethylolmelamine, which is liquid at room temperature, and titanium dioxide, which contains 70 parts of polyester, 30 parts of aminoplast, 80 parts of titanium dioxide, 8 parts of a

in a 50 percent solution of a commercially available non-ionic blocked acid catalyst and 20 percent by weight of ethyl glycol acetate. The coatings baked at 120°C/30min show the following values:

Example A
(DE-PS 23 43 436. Example 8)

A mixture of 62 g of ethylene glycol (1 mol) and 100 g of dimethyl hexahydroterephthalate (0.5 mol) is heated to 180 to 190°C for 2 to 3 hours with stirring, a gentle stream of nitrogen and constant distillation of the methanol after addition of 1 ml of a 10% by volume isopropanolic solution of titanium tetraisopropylate. The temperature is then slowly increased to 200°C. After a total of 16 hours, approximately 32 g of methanol have been split off. After cooling the mixture, 124 g of ethylene glycol (2 mol), 148 g of phthalic anhydride (1 mol) and 73 g of adipic acid (0.5 fvioi) are added and heated according to the following temperature-time schedule: 2 h at 140 ⁰ C, 2 h at 160 ⁰ C, 4 h at 180°C, 4 h at 190 ⁰ C and 3 to 4 h at 200°C After elimination of

< 50 sea

>10mm

Example B
DE-PS 24 57 775, Example 8)

i. From 3.5 moles of ethylene glycol, 0.5 moles of propanediol-(1.2) and 3 moles of DMHT, a polyester is produced using the method described under Polyester production, which has a hydroxyl number of 170 mg KOH/g, corresponding to an average molecular weight of 659. From 75 parts of the polyester, 25 parts of the aminoplast used in Example A, 80 parts of titanium dioxide, 2.5 or 5.0 parts of a

A coating agent is produced using 20 percent isopropanolic p-toluenesulfonic acid solution and 43 g ethyl glycol acetate, which produces coatings with the following values:

Table 1

Burn-in Type and quantity H T condition of the catalyst (Wt.% based [°C/min] on binders) [lake] [mm]

120/30

120/30

120/90

0.5 pTS
1.0 pTS
0.5 pTS

83
127
149

ii. If the 2.5 parts of the p-toluenesulfonic acid solution are replaced by 8 parts of the catalyst solution described in Example A, the following coating properties result at 120°C/30 min:

H:<50sec
T:>10mm

iii. 333 g of a commercially available solution of a partially methylated, highly reactive melamine resin (90 percent in isopropanol) are added to 87.5 g of an 80 percent solution of the polyester acidified with trimellitic anhydride to an acid number of 9.9 mg KOH/g in ethyl glycol acetate as per Example B/i. The mixture is then pigmented with 80 g of titanium dioxide and, after adding 24.2 g of ethyl glycol acetate, baked at 120 ⁰ C/ 30 min:

H:56sec
T: >10mm

Example C (DE-QS 24 37 217, Example 1)

i. 519.4 g phthalic anhydride, 57 g adipic acid, 160 g propanedioic acid, 159.6 g ethylene glycol and 81 g neopentyl glycol are heated to 200°C over 8 hours with a gradual increase in temperature and reacted to an acid number of 12.6 mg KOH/g while passing through nitrogen and continuously removing the resulting water of reaction and then dissolved in ethyl glycol acetate (80 percent). The polyester solution is mixed with hexakis-(methoxy)-methylmelamine in a solids ratio of 80:20 and then rubbed with 80 parts titanium dioxide. After adding 1 g of a 20% isopropanolic p-toluenesulfonic acid solution, it is diluted with 24 g of ethyl glycol acetate and, after coating, baked for 30 minutes at 12°C. The resulting coating is hard and brittle.

H: 188 sea
T: 1.2mm

ii. The 80% solution of the polyester described in Example C/i. is mixed in a solids ratio of 7:3 with the partially methylated melamine resin described in Example B/iii., then pigmented with titanium dioxide in a ratio of 1:0.8.

2u

Table

Burn-in condition

(°C/min)

(sec)

[mm]

120/30
170/30

126
182

9.5
0.7

iii. A coating agent is prepared from 100 parts of the 80 percent polyester solution according to Example C/i, 20 parts of the melamine resin described in Example A, 80 parts of titanium dioxide and 1 part of a 20 percent by weight isopropanolic p-toluenesulfonic acid solution. By adding ethyl glycol acetate it is diluted to a viscosity of 40 see in a DIN 4 mm cup (20°C). A 1 mm thick sheet metal plate (70 x 200 mm) is then coated with a doctor blade so that after baking in the horizontal layer thicknesses of 50±3μπα would result. The lower part of the plate (5 cm) is not coated. After 10 minutes of drying time, the plate is baked hanging vertically. (If the stability is insufficient, a layer thickness gradient forms - the measurement points are 1.5 cm from the upper and lower edges of the coating. If there is a strong tendency to run off, runs can be seen in the uncoated lower area of the panel.)

Table 3

Coating agents Burn-in II T Layer thickness (μΙΠΕΛ) runner conditions 1.5 cm from j°C/minj [soul [mm] upper lower edge edge Example C/iii 120/30 141 10 41 59 many 170/30 197 1.6 43 61 indicated Example 5 120/30 156 >10 49 51 no 170/30 189 8.6 49 50 no

Example D

A polyester with a hydroxyl number of 163 mg KOH/g and an acid number of 0.6 mg KOH/g, corresponding to a molecular weight of 685, is prepared from 3 moles of ethylene glycol, 1 mole of propanediol-(1.2), 1.8 moles of dimethyl hexahydroerephthalate and 1.2 moles of dimethyl terephthalate using the method described. The product obtained is partially crystalline at room temperature and does not dissolve clearly in paint solvents such as xylene, butyl acetate, n-butanol, ethyl glycol acetate, etc.

All quantities refer to the weight unless otherwise stated

Abbreviations

PES: saturated PES

EG: Ethylene glycol

PG: Propanediol-(1.2)

CHDM: 1.4-Bis(hydroxymethyl)cyclohexane

GIy: Glycerin

DM HT: Dimethylhexahydroterephthalate

DMT: Dimethyl terephthalate

TMSA: Trimellitic anhydride

pTS: p-To!ulenesulfonic acid

HMM: largely methyl etherified commercially available hexmethylomelamine

MFK: highly reactive, partially methyl etherified commercial melamine-formaldehyde condensation product; 90 percent in isopropanol

blown cat: approx. 50% solution of a non-ionic blocked commercial catalyst acid

S-Z.: Acid number

H: Pendulum hardness (DIN 53 157)

T: Elasticity (DIN 53 156)

Table 4

Example PES from medium Weight loss Type of Type and quantity Burn-in H T No. PES-MoI- Ratio PES: Amino of the catalyst conditions weight Aminoplast: plastics (Weight per unit, based gene _TiO2 on binders) [mol] [°C/min] [tsec] [mm]

1.25 EC
1.25 PG
1.275 DMHT
0.225 DMT

3 EC

1 PG

2.5 DMHT

0.5 DMT

385

710

EC
PG

DMHT
DMT

865

1020

1 EC

3 PG

1 CHDM

3.5 DMHT

0.5 DMT

(with TMSA for
SZ 9.6 implemented)

3.5 EC 1425

3.5 PG

5.05 DMHT

0.95 DMT

7.5:2.5:8 7.5:2.5:8

7.5:2.5:0 7.5:2.5:0 7.5:2.5:8 7.5:2.5:8 7.5:2.5:0 7.5:3 ,5:0

8:2:0 8:2:0 8:2:8 8:2:8

7:2,7:8

7.5:2.5:8 7.5:2.5:8

hmmmmm

HIVIM HMM HMM HMM HMM HMM

hmmm hmmm hmmm

MFK MFK

hmmmmm

0.5 pTS
0.5 pTS

0.5 pTS
0.5 pTS
0.5 pTS
0.5 pTS

O 1_| &Igr;&Lgr;_*

O KCUI. IVd I.

blown cat.

0.5 pTS
0.5 pTS
0.5 pTS
0.5 pTS

0.5 pTS
0.5 pTS

120/30
170/30

120/30
140/30
120/30
140/30

IZWJU

140/30

120/30
170/30
120/30
140/30

120/30
160/30

120/30
170/30

173 184

224 225 154 162

t nc

1 7 years

209

197 232 157 187

139 170

156 189

3.2 EC 715 7.5:24 :8th hmmm 04pTS 120/20 139 9.7 0.5 PG 74:24 :8th hmmm 0.5 pTS ¹ 120/30 153 9.1 0.3 GIy 24 DMHT 0.5 DMT

Claims (2)

10 15 20 Patent claims: 1. Liquid coating agents on a low-solvent or solvent-free basis consisting of a mixture of binder and, if appropriate, conventional auxiliary materials, where the coating agents act as binders A. 45 to 10 percent by weight of aminoplasts and/or their low molecular weight precursors and B. Contain 55 to 90 percent by weight of at least bifunctional polyesters or mixtures containing predominantly free hydroxyl and possibly free carboxyl end groups. wherein the polyesters of component B are obtained by condensing a component 1 consisting of 1.1 0 to 50 mole percent of one or more aliphatic polyols with 3 or 4 hydroxyl groups and 3 to 6 carbon atoms and 1.2 100 to 50 Mo'prGzent from a mixture !! of diols, The mixture 11 in turn 11.1 to 10 to 90 mole percent of ethylene glycol and ,. IL2 to 90 to 10 mole percent of propanediol-(l^) and 113 to 0 to 40 mol percent of one or more other aliphatic or cycloaliphatic diols in which the hydroxyl functions are separated by 2 to 8 carbon atoms and up to 2 of the carbon atoms can be replaced by oxygen atoms, which in turn should be separated from each other and from the _hydroxyl groups by at least 2 carbon atoms. consists of a component III, consisting of a mixture of 111.1 Ilcxahydrotcrcphthalic acid and _A(j 111.2 aromatic dicarboxylic acids were produced, the polyesters or mixtures used as component B. having a molecular weight of 300 to 1500, and the binder can also have been obtained by co-condensation of aminoplasts and/or their low molecular weight precursors with the polyesters or by co-condensation of the starting products of the aminoplast production with the polyesters, characterized in that 8 to 33 mol percent of terephthalic acid are used as component 111.2. 2. Coating agent according to claim 1, characterized in that the polyester according to B. contains 12 to 25 mole percent of terephthalic acid units as component III.2. The invention relates to liquid coating agents on a low-solvent or solvent-free basis, wherein the coating agents - optionally containing conventional auxiliaries - consist of a mixture of aminoplasts and polyesters. Such environmentally friendly coating agents have been known for some years (DE-AS 20 19 282). Also known are coating agents which contain polyesic acid whose acid component is formed entirely or partly from hexahydroterephthalic acid units (DE-PS 16 44 766, 23 43 436, 24 57 775; DE-OS 24 37 217). DE-PS 16 44 766 expressly does not claim low-solvent or solvent-free coating agents. DE-PS 23 43 435 restricts the acids which can be used in addition to hexahydroterephthalic acid to aromatic dicarboxylic acids with carboxyl groups in the M or IJ position. DE-PS 24 57 775 aims in the same direction (see column 5, line 20). As our own detailed tests have shown, the coating materials of the state of the art have a decisive disadvantage: if coatings are to be obtained that meet the high requirements of practice, curing temperatures of > 130° C, and in most cases even > 150° C, have to be used (DE-OS 24 37 217, Example 3). In order to save energy costs, the curing temperatures should be reduced - while of course retaining the good final properties. With the products of the state of the art, curing temperatures of < 150° C or < 130° C can be used, but it is then necessary to extend the curing times considerably, so that hardening is no longer cost-effective and practical. Likewise, higher amounts of catalyst do not achieve the desired effect, as they impair the properties of the coatings, such as the gloss. DE-OS 24 37 217 describes coating agents which, according to the examples, can be baked at 120°C within a practical time and produce good coatings. Our own tests have shown, however, that the coating agents described here, in contrast to the other products of the state of the art mentioned above, cannot be baked at 170 to 180°C, a temperature commonly used in practice for certain production processes, without defects in the coating occurring. Because of these defects that occur at higher temperatures, the binding agents according to DE-OS 24 37 217 prove to be extremely critical under increased heat loads, such as can occur when a strip stops during series painting. On the other hand, these coating agents do not have sufficient stability during baking, as is shown, for example, by coating agents according to DE-PS 24 57 775. The object of the invention is to develop a clearly dissolved coating agent of the type according to the invention which, while maintaining the good properties already known for this product group, including the over-stability, makes it possible to be baked even at baking temperatures below 130 ^° C. This problem was solved by using polyesters containing predominant proportions of hexahydroterephthalic acid in the coating medium, which contain 8 to 33 mole percent, preferably 12 to 25 mole percent, of terephthalic acid as the second acid component. The invention relates to liquid coating agents on a low-solvent or solvent-free basis from a mixture of binder and optionally conventional auxiliary materials, the coating agents as binder