EP1517936A1

EP1517936A1 - Water-dilutable cross-linking agent

Info

Publication number: EP1517936A1
Application number: EP03724850A
Authority: EP
Inventors: Hans-Dieter Hille; Karsten Jahny; Paul Lamers
Original assignee: PPG Industries Lacke GmbH
Current assignee: PPG Industries Lacke GmbH
Priority date: 2002-03-27
Filing date: 2003-03-25
Publication date: 2005-03-30
Also published as: DE10391698D2; DE10214027A1; DE10214027B4; WO2003080695A1; AU2003229271A1

Abstract

The invention relates to a water-dilutable cross-linking agent that does not comprise any free NCO groups but has at least two blocked NCO groups per molecule and a ratio of blocked NCO groups to OH groups of greater than 3: 1. Said cross-linking agent can be obtained by reacting an alkanolamine with at least one partially blocked polyisocyanate having an NCO equivalent weight ranging from 600 to 10,000 g/MolNCO (with regard to free NCO groups) to form an intermediate product comprising at least one urea linkage resulting from the nitrogen atom of the alkanolamine and of the free NCO group of the partially blocked polyisocyanate followed by adding a cyclic carboxylic acid anhydride, under decyclization, to the OH group of the intermediate product, said OH group originating from the alkanol amine. The invention also relates to the use of this water-dilutable cross-linking agent in the painting of automobiles.

Description

W a s s e rv e r d ü n n b a r e r V e r n e t z e r

The present invention relates to a new water-dilutable crosslinker, and its use in automotive OEM painting.

The term “crosslinking agent” is understood here and below to mean those compounds which bring about a spatial linkage of polymer chains (or else polyfunctional monomers) to one another to form a network polymer (crosslinking).

It is known to use blocked polyisocyanates as crosslinking agents in order to produce high-quality coating compositions together with OH-functional compounds, preferably with branched, saturated polyesters and / or polyurethanes containing hydroxyl groups. This crosslinking reaction gives rise to polyurethanes which give the resulting coatings excellent mechanical properties, in particular with regard to the mechanical strength of the cured paint film. As a result, polyurethanes are often used in the manufacture of conventional car paint layers.

Such a car paint layer generally consists of a total of four different layers (four-layer structure). These four layers are applied one after the other in separate painting systems. The first layer, which is located directly on the car sheet, is an electrophoretically applied layer (electrocoat layer, KTL layer), which is applied by electro-dip coating - mainly cathodic dip coating (KTL) - for corrosion protection and then baked. The second layer, located on the electrocoat layer and about 30 to 40 μm thick, is a so-called filler layer, which on the one hand offers protection against mechanical attacks (stone chip protection function) and on the other hand ensures a sufficient level of topcoat, ie smoothes the rough surface of the body shell for the subsequent topcoat and fills out minor bumps. The paints used to produce this filler layer contain not only binders but also pigments. The wettability of the pigments used has a decisive influence on the top coat level of the entire multi-layer coating and also on the gloss of the filler layer, as required by some automobile manufacturers. The filler layer is largely created by application with electrostatic high-speed rotary bells and subsequent baking at temperatures above 130 ° C. The third layer on the filler layer is the basecoat layer, which gives the body the desired color through the use of appropriate pigments. The basecoat is applied in the conventional spraying process. The layer thickness of this conventional basecoat is between about 12 and 25 μm depending on the color. This layer is usually applied in two process steps, especially with metallic effect paints. In a first step, the application is carried out by means of electrostatic high-speed rotary bells, followed by a second application by means of pneumatic atomization. This layer is dried (when using an aqueous basecoat) with infrared radiators and / or by hot air convection.

The fourth and uppermost layer on the basecoat is the clearcoat, which is usually applied in one application using electrostatic high-speed rotary bells. It gives the body the desired shine and protects the basecoat from environmental influences (UV radiation, salt water, etc.). The basecoat and the clearcoat are then baked together.

The fillers used in the manufacture are still based to a considerable extent on solvents and reach a solids concentration of up to 60%. This high solids concentration ensures efficient application and thus a good top coat level of the finished multi-layer coating. Examples of such a conventional filler are mentioned in WO 01/02457.

Especially in view of the solvents used in conventional fillers and the associated environmental problems, developments in the field of water-dilutable fillers have recently been observed. In such water-based fillers, water-soluble or water-dispersible OH-functional binders - mostly those based on branched, saturated polyesters and / or on the basis of polyurethanes - are combined with water-dispersible, blocked polyisocyanates. In order to ensure the water dispersibility of these blocked isocyanates, they are modified with carboxyl groups. Dimethylolpropionic acid is very often used for this modification. The carboxyl group-containing, blocked polyisocyanate thus produced is then neutralized with suitable amines, for example with dimethylethanolamine, and dispersed in water.

However, it has been shown that only solid concentrations of up to about 50% can be achieved on an industrial scale with the aforementioned water-dilutable filler compositions. Compared to conventional fillers, this difference causes a clearly visible deterioration in the resulting multi-layer coating, particularly with regard to the level of the top coat.

The object of the present invention is to provide a crosslinking agent which can be used in water-dilutable filler formulations, these water-dilutable filler formulations reaching a solids concentration of more than 50%. Another object of the present invention is that the crosslinker does not degrade the overall property level of the filler formulation produced therewith in comparison with the prior art. In this context, the stone chip resistance with good grindability is an essential property.

This object is achieved according to the invention by a water-dilutable crosslinker without free NCO groups and with at least two blocked NCO groups per molecule and a ratio of blocked NCO groups to OH groups of more than 3: I, obtainable from the reaction of an alkanolamine with at least a partially blocked polyisocyanate with an NCO equivalent weight between 600 and 10,000 g / mol _NCO (based on free NCO groups) to an intermediate product which has at least one urea bond resulting from the nitrogen atom of the alkanolamine and the free NCO group of the partially blocked polyisocyanate , followed by addition of a cyclic carboxylic acid anhydride with ring opening to the OH group of the intermediate derived from the alkanolamine. It should be noted here that all suitable customary blocking agents can be used to block the NCO groups of the partially blocked polyisocyanate used as the starting product. This term “blocking agent” does not include the alkanolamine used, which reacts with the free NCO group of the partially blocked polyisocyanate to form a urea bond.

The choice of the NCO equivalent weight as a criterion for the partially blocked polyisocyanates that can be used ensures that the alkanolamine reacts with the partially blocked polyisocyanate in such a way as to ensure sufficient stability of the crosslinker in aqueous dispersion.

The starting components are implemented using the well-known methods of organic chemistry (see e.g. Plastics Manual, Volume 7: Polyurethane, published by Dr. Y. Oertel, Carl Hanser Verlag, Munich, Vienna 1983).

If appropriate, the reaction is carried out in the presence of water-miscible and volatile solvents which are inert to isocyanates. Methyl ethyl ketone and / or acetone is preferably used.

The crosslinker thus obtained is converted into an aqueous phase by neutralizing the carboxyl groups with amines and / or amino alcohols. Examples of suitable compounds are ammonia, tertiary amines, such as trimethylamine, triethylamine and / or amino alcohols, such as dimethylethanolamine, diethylethanolamine, methyldiethanolamine or triethanolamine. Neutralization can take place in the organic phase or in the aqueous phase. Dimethylethanolamine is preferably used as the neutralizing agent. If the crosslinking agent according to the invention is used in suitable water-dilutable filler formulations, a solids concentration of more than 50% can be achieved.

The crosslinker according to the invention is suitable in principle for crosslinking all resins which have OH groups and are compatible with it.

The layers produced from such filler formulations give the resulting multilayer coating an excellent topcoat level and very good stone chip resistance.

According to a preferred embodiment of the present invention, the partially blocked polyisocyanate is obtainable from

• a reaction of a polyisocyanate containing at least three free NCO groups with a blocking agent used in the stoichiometric deficit, followed by a further reaction with at least one diol.

A reaction of a diisocyanate containing at least two free NCO groups with a blocking agent used in the stoichiometric deficit, followed by a further reaction with at least one polyol; and or

A reaction of a polyisocyanate having at least three free NCO groups with a blocking agent used in the stoichiometric deficit.

It should be noted here that the partially blocked polyisocyanate thus obtainable still has an _NCO equivalent weight between 600 and 10,000 g / mol _NCO (based on free NCO groups).

Ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, hexaethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol can be used as diols for this purpose. 2,2-dimethylpropanediol, 2,2,4-trimethylpentanediol, 1,3-dimethylolcyclohexane, 1,4-dimethylolcyclohexane, hydroxypivalic acid neopentyl glycol monoester and / or perhydrogenated bisphenol A. The diol is preferably selected from the group of hexanediol, neopentyglycol, 1, 4 - Dimethylolcyclohexane, ethylene glycol and propylene glycol.

Trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol and / or di (trimethylolpropane) can be used as polyols. The polyol is preferably selected from the group of trimethylolpropane and dimerized trimethylolpropane.

According to a further, likewise preferred embodiment, the object of the present invention is achieved by one of the aforementioned water-dilutable crosslinking agents which is present in a mixture with at least one additional polyisocyanate which has at least two completely blocked NCO groups per molecule, that is to say is at least difunctional.

This additional polyisocyanate is, in particular, one which has no carboxyl group and is consequently not water-dispersible by itself. Even if it is only a mixture of the crosslinking agent according to the invention with a non-water-dispersible polyisocyanate, the addition of the crosslinking agent according to the invention in an appropriate amount results in sufficient dispersibility and stability of the resulting mixture. This corresponding amount can easily be determined by a person skilled in the art by simple experiments.

A preferred process for the preparation of this mixture according to the invention is to start from an unblocked polyisocyanate and to react it with a suitable blocking agent in a stoichiometric ratio such that a sufficient number of free NCO groups remains to react with the alkanolamine and the Cyclic carboxylic acid anhydride to create enough free carboxyl groups with regard to stability and dispersibility of the finished, aqueous dispersion.

Good results are obtained if the ratio of crosslinking agent according to the invention to non-water-dispersible polyisocyanate is chosen such that the resulting mixture has an acid number of at least 15 mg KOH / g, in particular at least 25 mg KOH / g.

All suitable compounds known to those skilled in the art or mixtures thereof can be used as blocking agents. These include phenol, diethyl malonate, acetoacetic ester, butanone oxime and / or ε-caprolactam. The blocking agent is preferably selected from the group of methyl ethyl ketoxime, 3,5-dimethylpyrazole and ε-caprolactam.

The cyclic carboxylic acid anhydride is preferably selected from the group of phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, succinic anhydride and maleic anhydride. The cyclic carboxylic anhydride trimellitic anhydride is very particularly preferred.

3,5,5-Trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Desmodur W), 1,3-bis (l.) Are preferably used as polyisocyanate having at least two free NCO groups -isocyanato-l -methylethyl) benzene (TMXDI), hexamethylene diisocyanate (HDI), diphenylmethane-4,4'-diisocyanate (MDI), 2,4- and / or 2,6-tolylene diisocyanate (TDI).

The polyisocyanate containing at least two free NCO groups can also be a polyisocyanate containing at least three free NCO groups, in particular 2,4,6-trioxo-1,3,5-tris (6-isocyanatohexyl) hexahydro-1,3. 5-triazine (Desmodur N3300).

All suitable compounds can be used as alkanolamine. It should be noted that the alkanolamines used according to the invention have a hydrogen atom bonded to the nitrogen atom. These include, for example, I-amino-3-propanol, I-amino-2-propanol (isopropanol-amine), I-amino-4-butanol, I-amino-5-pentanol, l, r-iminodi-2-propanol ( Diisopropanolamine), 2- (2-aminoethoxy) ethanol. For the purposes of the present invention, tertiary alkanolamines are not to be used. Alkanolamines are preferably used in which at least one OH group of the alkanolamine is connected to the nitrogen atom via a substituted or unsubstituted alkyl group having 2 to 6 carbon atoms in the main chain. Examples include aminobutanol, 1-amino-5-pentanol, aminohexanol, 2- (2-aminoethoxy) ethanol, isopropanolamine, diisopropanolamine, 2-amino-2-methyl-1-propanol and 2-amino-2 -methyl- 1, 3-propanediol to name. Bis- (2-hydroxyethyl) amine (diethanolamine) and / or 1-amino-2-ethanol (monoethanolamine) are particularly preferably used as alkanolamine for the preparation of the crosslinking agent according to the invention.

The crosslinker according to the invention is particularly suitable for crosslinking OH-containing polymers, in particular in fillers based on saturated polyesters.

The crosslinked lacquer films obtainable therefrom show improved properties in relation to the topcoat level and the stone chip resistance compared to comparable lacquer films of the prior art.

They can generally be spray painted, e.g. Compressed air, hot or airless spraying, or by electrostatic painting processes, e.g. by means of rapidly rotating bells (mini bells), electrostatic automatic or hand spray guns with air support, or by rollers, e.g. applied in a band painting process.

The following examples serve to illustrate the invention without restricting it thereto:

Example I: Preparation of a crosslinker according to the invention:

894.3 g of Desmodur N3300 (Bayer), 797.9 g of methyl ethyl ketone and 1.5 g of dibutyltin dilaurate were placed in a glass flask with a volume of 4 l, equipped with a stirrer, a reflux condenser and a temperature measurement. 212.4 g of methyl ethyl ketoxime were added to the reaction mixture in such a way that the temperature did not exceed 75 ° C. 90.0 g of 1,6-hexanediol were then added and the reaction was continued until the NCO content had reached a constant value (1.09% -NCO in solution). After the mixture had cooled to a temperature of 40 ° C., 31.6 g of monoethanolamine were added (the molar ratio of isocyanate to monoethanolamine was 1: 1 for this example).

The reaction mixture was then heated to 80 ° C and the reaction continued for one hour. The measured NCO content at this time was <0.01%. 65.9 g of trimellitic anhydride were added to this resin solution. After a reaction time of one hour at 80 ° C., 61.1 g of dimethylethanolamine and 1374.3 g of deionized water were metered in, so that the temperature did not drop below 60 ° C. After removal of the methyl ethyl ketone in vacuo, a stable dispersion with an acid number of 30 mg KOH / g, a solids content of 50% and a viscosity of 30 mPas was obtained.

Example 2: Preparation of a crosslinking agent not according to the invention

566.9 g of Desmodur N3300 (Bayer) and 141.1 g of methyl ethyl ketone were placed in a glass flask with a volume of 4 l, equipped with a stirrer, a reflux condenser and a temperature measurement. 168.3 g of methyl ethyl ketoxime were metered into the reaction mixture in such a way that the temperature did not exceed 75.degree. The reaction was continued until a constant NCO content was reached. Then 64.8 g of dimethlylolpropionic acid, 0.3 g of dibutyltin dilaurate and 125.6 g of methyl ethyl ketone were added in succession. The reaction was continued at 80 ° C until the NCO content fell below 0.1%. Then 26.6 g of dimethylethanolamine and 1867 g of deionized water were metered in, so that the temperature did not drop below 60.degree. After the methyl ethyl ketone had been removed in vacuo, a further 6.6 g of dimethylethanolamine and 533 g of deionized water were added. A clear dispersion with an acid number of 34 mg KOH / g and a solids content of 25% at a viscosity of 12000 mPas was obtained.

Example 3: Preparation of a white pigment paste:

The following constituents were weighed in a stainless steel stirred vessel in the order mentioned and, after each addition, homogenized by stirring: 775 g of a fatty acid-modified polyester dispersion (solids content = 30%) with an OH number of 160 mgKOH / g, 50 g of Disperbyk 181 (Wetting and dispersing additive), 10 g Aerosil R 972 (Degussa), 505 g barium sulfate (Blanc Fixe® micro), 700 g titanium dioxide (Tiona RCL 628), 50 g butyl glycol and 85 g deionized water. The mixture was predispersed in a dissolver for thirty minutes and then ground on a sand mill to a grain fineness <10 μm. The temperature was kept below 40 ° C during the milling process.

Example 4.1: Preparation of a filler formulation according to the invention:

The filler was prepared by mixing 441 g of the pigment paste according to Example 3 and 313 g of a polyacrylate latex (manufactured according to US Pat. No. 5,830,928 with a solids content of 42%), 276 g of the crosslinking agent from Example I with 26 g of Cymel 325 and 20 g Butyl diglycol and 2.2 g of dimethylethanolamine and 37.6 g of deionized water.

The viscosity of the filler was 28 s with a solids content of 53%.

Example 4.2: Preparation of a filler formulation not according to the invention (comparative example): The filler was made by mixing 441 g of the pigment paste according to Example 3 and 313 g of a

Polyacrylate latex (manufactured according to US 5,830,928 with a solids content of 42%), 552 g of the

Crosslinker from Example 2 with 26 g of Cymel 325 and 20 g of butyl diglycol and 2.2 g of dimethylethanolamine and 17.3 g of deionized water.

The viscosity of the filler was 27 s with a solids content of 43%.

Application of the filler:

For the production of the multi-layer coating, customary and known steel test panels were used, which were coated with a 20 μm thick electrocoat, produced from a commercially available cationic electrocoat.

The test panels were pneumatically coated with the filler according to Example 4.1 or 4.2. The resulting filler layers were predried at 80 ° C for eight minutes and then for 20 minutes. long baked at a temperature of 140 ° C. A filler layer with a layer thickness of 35 μm was obtained.

A commercially available conventional solid-color topcoat was applied pneumatically to the filler layer and after ten minutes of flashing off at room temperature and eight minutes of predrying at 80 ° C. for 30 minutes at 140 ° C. The solid color coating of the resulting multi-layer coating had a layer thickness of 30 μm.

The multicoat paint systems produced in this way were examined with regard to the top coat level and the stone chip resistance. The results of the tests are summarized in Table I below: Determination of the solid concentration:

The solids determination was carried out in a convection oven by baking at a temperature of 120 ° C. For this, I g of the substance to be tested were applied to patent lids (diameter 75 mm), evenly distributed over the surface, and dried in the oven for one hour. The non-volatile content was then determined by weighing the lids back. A triple determination has been carried out.

Determination of the layer thickness:

The layer thickness was determined using the Surfix device from Phynix.

Determination of the gloss level

The degree of gloss was determined using the haze-gloss device from BYK Gardner at an angle of 60 °.

Stone chip resistance test:

The stone chip resistance was tested using a stone chip tester according to VDA, model 508 from Erichsen GmbH + Co KG.

The test sheets were bombarded twice with a pressure of 2 bar each with 500 g quenched iron shot "diamond", square, size 4-5 mm.

Determination of the pendulum hardness according to König

The pendulum hardness was determined using a pendulum hardness tester from BYK-Gardner.

Table I

^a) Visual assessment ^b) Cross cut test according to DIN ISO EN 2409 It is clear from the values listed in Table I that the filler produced using the crosslinking agent according to the invention has improved properties compared to the fillers of the prior art in relation to the solids concentration of the ready-to-use filler formulation and the top coat level of the finished multilayer coating.

Claims

P at claims

1. Water-dilutable crosslinker without free NCO groups and with at least two blocked NCO groups per molecule and a ratio of blocked NCO groups to OH groups more than 3: I, obtainable from the reaction of an alkanolamine with at least one partially blocked polyisocyanate with a NCO equivalent weight between 600 and 10,000 g / mol of _NCO (based on free NCO groups) to an intermediate product which has at least one urea bond resulting from the nitrogen atom of the alkanolamine and the free NCO group of the partially blocked polyisocyanate, followed by addition of a cyclic one Carboxylic acid anhydride with ring opening to the OH group of the intermediate originating from the alkanolamine.

2. Water-dilutable crosslinker according to claim I, characterized in that the partially blocked polyisocyanate is obtainable from a reaction of a polyisocyanate containing at least three free NCO groups with a blocking agent used in the stoichiometric deficit, followed by a further reaction with at least one diol.

3. Water-dilutable crosslinker according to claim 2, characterized in that the diol is selected from the group of hexanediol, neopentyglycol, 1, 4-dimetylolcyclohexane, ethylene glycol and propylene glycol.

4. Water-dilutable crosslinker according to claim I, characterized in that the partially blocked polyisocyanate is obtainable from a reaction of at least two free ones

Diisocyanate containing NCO groups with a blocking agent used in the stoichiometric deficit, followed by a further reaction with at least one polyol.

5. Water-dilutable crosslinker according to claim 4, characterized in that the polyol is selected from the group of trimethylolpropane and dimerized trimethylolpropane.

6. Water-dilutable crosslinker according to claim I, characterized in that the partially blocked polyisocyanate from a reaction of at least three free NCO groups containing polyisocyanate with a blocking agent used in the stoichiometric deficit.

7. Water-dilutable crosslinking agent according to one of the preceding claims, characterized in that it is present in a mixture with at least one completely blocked, at least difunctional polyisocyanate.

8. Water-dilutable crosslinker according to claim 7, characterized in that the mixture has an acid number of at least 15 mg KOH / g, in particular at least 25 mg KOH / g.

9. Water-dilutable crosslinker according to claim 7 or 8, characterized in that the completely blocked, at least difunctional polyisocyanate is obtainable from the reaction of a polyisocyanate having at least two free NCO groups with a blocking agent.

10. Water-dilutable crosslinker according to one of claims 2 to 9, characterized in that the blocking agent is selected from the group of methyl ethyl ketoxime, 3,5-dimethylpyrazole and ε-caprolactam.

1 1. Water-dilutable crosslinker according to one of the preceding claims, characterized in that the cyclic carboxylic anhydride is selected from the group of phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyl hexahydrophthalic anhydride, succinic anhydride and maleic anhydride.

12. Water-dilutable crosslinking agent according to one of claims I to 10, characterized in that the cyclic carboxylic anhydride is trimellitic anhydride.

13. Water-dilutable crosslinker according to one of the preceding claims, characterized in that the polyisocyanate which has at least two free NCO groups is selected from the group consisting of 3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Desmodur W), 1,3-bis (l-isocyanato-l-methylethyl) benzene (TMXDI), hexamethylene diisocyanate (HDI), diphenylmethane-4,4'-diisocyanate (MDI), 2 , 4- and 2,6-tolylene diisocyanate (TDI).

14. Water-dilutable crosslinker according to one of the preceding claims, characterized in that the polyisocyanate having at least two free NCO groups is a polyisocyanate having at least three free NCO groups.

15. Water-dilutable crosslinking agent according to claim 14, characterized in that the polyisocyanate containing at least three free NCO groups 2,4,6-trioxo-1,3,5-tris (6-isocyanatohexyl) hexahydro- l, 3.5 -triazine (Desmodur N3300).

16. Water-dilutable polyurethane according to one of the preceding claims, characterized in that at least one OH group of the alkanolamine is connected to its nitrogen atom via a substituted or unsubstituted alkyl group having 2 to 6 carbon atoms in the main chain.

17. Water-dilutable crosslinker according to claim 16, characterized in that the alkanolamine is selected from the group of diethanolamine and monoethanolamine.

18. Use of a water-dilutable crosslinker according to one of the preceding claims for crosslinking OH-containing polymers, especially in fillers based on saturated polyesters.