DE10214027A1 - Water-dilutable crosslinker - Google Patents

Abstract

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: 1, obtainable from the reaction of an alkanolamine with at least one partially blocked polyisocyanate with an NCO Equivalent weight between 600 and 10000 g / mol¶NCO¶ (based on free NCO groups) to an intermediate product that 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 derived from the alkanolamine and its use in automotive OEM painting.

Description

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 a spatial linkage of polymer chains (or also multifunctional monomers) cause each other to form a network polymer (crosslinking).

It is known to use blocked polyisocyanates as crosslinkers to coexist with OH-functional compounds - preferably with branched, saturated hydroxyl groups Polyesters and / or polyurethanes - to produce high quality coating compositions. By This crosslinking reaction creates polyurethanes that form the resulting coatings give excellent mechanical properties, especially in terms of mechanical Resilience of the hardened paint film.

As a result, polyurethanes are often used in the manufacture of conventional car paint layers used.

Such a car paint layer generally consists of a total of four different ones Layers (four-layer structure). These four layers are separated one after the other Paint systems applied.

The first layer located directly on the car sheet is an electrophoretically applied one Layer (Electrocoatschicht, KTL layer), which by electro-dipping - mainly cathodic dip painting (KTL) - applied for corrosion protection and then baked becomes.

The second, located on the electrocoat layer and about 30 to 40 microns thick is one so-called filler layer, which on the one hand protects against mechanical attacks (stone chip protection function) offers, on the other hand, ensures a sufficient level of topcoat, d. H. the rough surface of the The body-in-white for the subsequent top coat smoothes and fills in smaller bumps. The Lacquers 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 Topcoat level of the entire multi-layer coating and also on the gloss of the filler layer, as provided by is demanded by some automobile manufacturers. The filler layer is largely through application with electrostatic high-speed rotary bells and subsequent baking at temperatures generated above 130 ° C.

The third layer, which is on the filler layer, is the basecoat layer, which is provided by appropriate Pigments of the body give the desired color. The basecoat is used in conventional Spray applied. The layer thickness of this conventional basecoat is depending on the color between about 12 to 25 µm. This layer is usually divided into two, especially with metallic effect paints Process steps applied. In a first step, the application is carried out using electrostatic high-speed rotary bells, followed by a second application using pneumatic atomization. This layer is (when using aqueous basecoat) with infrared radiators and / or through Warm air convection temporarily dried.

The fourth and top layer on the basecoat is the clearcoat that mostly applied in one order using electrostatic high-speed rotary bells. It gives the body has the desired shine and protects the basecoat from environmental influences (UV radiation, salt water, etc.).

Then the basecoat and the clearcoat are baked together.

The fillers used in the manufacture are still based to a considerable extent on Solvent base and reach a solid concentration up to 60%. This high Solids concentration ensures efficient application and thus a good level of finish of the finished product Multi-layer coating. Examples of such a conventional filler are in WO 01/02457 called.

Especially against the background of the solvents used in conventional fillers and the associated environmental problems have recently been increasing developments on the Area of water-dilutable filler.

Such water-based fillers become water-soluble or water-dispersible OH-functional binders - mostly those based on branched, saturated polyester and / or based on Polyurethanes - combined with water-dispersible, blocked polyisocyanates. To the To ensure water dispersibility of these blocked isocyanates, they are included Modified carboxyl groups. Dimethylolpropionic acid is very often used for this modification. That so The carboxyl group-containing, blocked polyisocyanate prepared is then mixed with suitable Neutralized amines, for example with dimethylethanolamine and dispersed in water.

However, it has been shown that with the aforementioned water-dilutable Filler compositions on an industrial scale can only achieve solid concentrations up to about 50%. In comparison to conventional fountain pens, this difference creates a clearly visible difference Deterioration of the resulting multi-layer coating, especially with regard to the top coat level.

The object of the present invention is to provide a crosslinker which is in water-dilutable filler formulations can be used, these being water-dilutable Filler formulations reach a solids concentration of more than 50%.

Another object of the present invention is that the crosslinker Overall property level of the filler formulation produced in this way in comparison with the state of the Technology does not deteriorate. In this context, the essential property is Stone chip resistance with good sandability.

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: 1, 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 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 to block the NCO groups as the starting product partially blocked polyisocyanate used, all suitable, customary blocking agents are used can. The term "blocking agent" does not include the alkanolamine used, however with the free NCO group of the partially blocked polyisocyanate to form a urea bond responding.

The choice of the NCO equivalent weight as a criterion for the partially blocked usable Polyisocyanate ensures that the alkanolamine is blocked with the partially blocked in such a manner Polyisocyanate reacts to ensure sufficient stability of the crosslinker in aqueous dispersion guarantee.

The implementation of the starting components takes place according to the well-known methods of organic chemistry (see e.g. Plastics Manual, Volume 7: Polyurethanes, edited by Dr. Y. Oertel, Carl Hanser Verlag, Munich, Vienna 1983).

The reaction is optionally carried out in the presence of water-miscible and volatile Solvents carried out which are inert to isocyanates. Methyl ethyl ketone is preferred and / or acetone used.

The crosslinker thus obtained is converted into an aqueous phase by neutralization the carboxyl groups by 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. The neutralization can in the organic phase or in the aqueous phase. Preference is given to the neutralizing agent Dimethylethanolamine used.

The crosslinker according to the invention is used in suitable water-dilutable filler formulations used, a solid concentration of more than 50% can be achieved.

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

The layers made from such filler formulations confer the resulting Multi-layer painting an excellent top coat level and a very good stone chip resistance.

• - einer Umsetzung eines mindestens drei freie NCO-Gruppen aufweisenden Polyisocyanats mit einem im stöchiometrischen Unterschuß eingesetzten Blockierungsmittel, gefolgt von einer weiteren Umsetzung mit mindestens einem Diol.
• - einer Umsetzung eines mindestens zwei freie NCO-Gruppen aufweisenden Diisocyanats mit einem im stöchiometrischen Unterschuß eingesetzten Blockierungsmittel, gefolgt von einer weiteren Umsetzung mit mindestens einem Polyol; und/oder
• - einer Umsetzung eines mindestens drei freie NCO-Gruppen aufweisenden Polyisocyanats mit einem im stöchiometrischen Unterschuß eingesetzten Blockierungsmittel.

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 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, 2,2-dimethylpropanediol, 2,2,4-trimethylpentanediol, 1,3-dimethylolcyclohexane, 1,4-dimethylolcyclohexane, hydroxypivalic acid neopentylglycol 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 can be used as polyols and / or di (trimethylolpropane). 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 solved by one of the aforementioned water-dilutable crosslinking agents, in a mixture with at least one additional polyisocyanate that completely blocked at least two Has NCO groups per molecule, that is at least difunctional.

This additional polyisocyanate is, in particular, one that does not Has carboxyl group, is consequently not water dispersible by itself.

Even if it is only a mixture of crosslinking agent according to the invention with one not water-dispersible polyisocyanate, the addition of the crosslinking agent according to the invention in appropriate amount of 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 become.

A preferred method of making this mixture according to the invention is not one blocked polyisocyanate and go out with a suitable blocking agent in one implement such a stoichiometric ratio that a sufficient number of free NCO Groups are left to after subsequent reaction with the alkanolamine and the cyclic Carboxylic anhydride enough free carboxyl groups in terms of stability and To allow dispersibility of the finished, aqueous dispersion.

Good results are obtained if the ratio of crosslinking agent according to the invention to not water-dispersible polyisocyanate is chosen so that the resulting mixture has an acid number of at least 15 mg KOH / g, in particular of at least 25 mg KOH / g.

All suitable compounds known to the person skilled in the art or their Mixtures are used. These include phenol, malonic acid diethyl ester, 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 anhydride is preferably selected from the group of Phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, Methylhexahydrophthalic anhydride, succinic anhydride and maleic anhydride. This is very particularly preferred cyclic carboxylic anhydride trimellitic anhydride.

As at least two free NCO groups polyisocyanate are preferred 3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Desmodur W), 1,3-bis (1-isocyanato-1-methylethyl) benzene (TMXDI), Hexamethylene diisocyanate (HDI), diphenylmethane-4,4'-diisocyanate (MDI), 2,4- and / or 2,6-tolylene diisocyanate (TDI) used.

However, the polyisocyanate having at least two free NCO groups can also have at least one three free NCO groups containing polyisocyanate, 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 are a hydrogen atom bonded to the nitrogen atom exhibit. These include, for example, 1-amino-3-propanol and 1-amino-2-propanol (Isopropanolamine), 1-amino-4-butanol, 1-amino-5-pentanol, 1,1'-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 Alkanolamines with the nitrogen atom via a substituted or unsubstituted alkyl group 2 to 6 carbon atoms in the main chain are connected. As examples of this are Aminobutanol, 1-amino-5-pentanol, aminohexanol, 2- (2-aminoethoxy) ethanol, isopropanolamine, To name diisopropanolamine, 2-amino-2-methyl-1-propanol and 2-amino-2-methyl-1,3-propanediol.

Alkanolamine is particularly preferred for the preparation of the crosslinking agent according to the invention Bis (2-hydroxyethyl) amine (diethanolamine) and / or 1-amino-2-ethanol (monoethanolamine) used.

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

The crosslinked lacquer films available from it show compared to comparable lacquer films of the State of the art improved properties with regard to the top coat and the Chip resistance.

You can generally by spray painting, z. B. compressed air, hot or airless spraying, or by electrostatic painting processes, e.g. B. by means of rapidly rotating bells (minibells), electrostatic automatic or hand spray guns with air support, or by rolling, e.g. B. applied in a band painting process.

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

example 1 Preparation of a crosslinker according to the invention

In a glass flask with a volume of 4 l, equipped with a stirrer, one Reflux coolers and a temperature measurement were 894.3 g Desmodur N3300 (Bayer), 797.9 g Methyl ethyl ketone and 1.5 g of dibutyltin dilaurate presented. 212.4 g are added to the reaction mixture Methyl ethyl ketoxime was added so that the temperature did not exceed 75 ° C. Then were 90.0 g of 1,6-hexanediol are added and the reaction is continued until the NCO content is one constant value (1.09% NCO on solution). After the approach to a When the temperature had cooled from 40 ° C., 31.6 g of monoethanolamine were added (the molar ratio For this example, isocyanate to monoethanolamine was 1: 1).

The reaction mixture was then heated to 80 ° C and the reaction for one hour continued. The measured NCO content at this time was <0.01%. To this resin solution 65.9 g of trimellitic anhydride were added.

After a reaction time of one hour at 80 ° C, 61.1 g of dimethylethanolamine and 1374.3 g Deionized water metered in so that the temperature did not drop below 60 ° C. After removal of the methyl ethyl ketone in vacuo gave a stable dispersion with an acid number of 30 mg KOH / g, a solids content of 50% and a viscosity of 30 mPas.

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

In a glass flask with a volume of 4 l, equipped with a stirrer, one Reflux coolers and a temperature measurement were 566.9 g Desmodur N3300 (Bayer) and 141.1 g Methyl ethyl ketone submitted. 168.3 g of methyl ethyl ketoxime were metered into the reaction mixture in such a way that that the temperature did not exceed 75 ° C. The reaction was continued until a constant NCO content was reached. Then 64.8 g were successively Dimethlylolpropionic acid, 0.3 g of dibutyltin dilaurate and 125.6 g of methyl ethyl ketone were added. The reaction was at 80 ° C continued until the NCO content had fallen below 0.1%. Then 26.6 g Dimethylethanolamine and 1867 g of deionized water are added so that the temperature is not below Dropped to 60 ° C. After removing the methyl ethyl ketone in vacuo, a further 6.6 g Dimethylethanolamine and 533 g of deionized water were added. A clear dispersion with a Acid number of 34 mg KOH / g and a solids content of 25% with a viscosity of 12000 mPas.

Example 3 Production of a white pigment paste

In a stainless steel mixing vessel, the following components were in the above Weighed in sequence and homogenized by stirring after each addition: 775 g of one fatty acid-modified polyester dispersion (solids content = 30%) with an OH number of 160 mgKOH / g, 50 g 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 during the Grinding process kept below 40 ° C.

Example 4.1 Production of a filler formulation according to the invention

The filler was made by mixing 441 g of the pigment paste according to Example 3 and 313 g of a polyacrylate latex (produced according to US Pat. No. 5,830,928 with a solids content of 42%), 276 g of the crosslinking agent from Example 1 with 26 g of Cymel 325 and 20 g of 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 prepared by mixing 441 g of the pigment paste according to Example 3 and 313 g of a polyacrylate latex (produced according to US Pat. No. 5,830,928 with a solids content of 42%), 552 g of the crosslinking agent 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

Common and well-known steel test boards were used for the production of the multi-layer coating used with a 20 µm thick electrocoat, made from a commercially available cationic electrocoat, were coated.

The test panels were pneumatically coated with the filler according to Example 4.1 or 4.2. The resulting filler layers were pre-dried at 80 ° C for eight minutes and then 20 min. baked at a temperature of 140 ° C for a long time. There was a filler layer with one Obtained layer thickness of 35 microns.

A commercially available conventional solid color top coat was applied pneumatically to the filler layer and after a ten-minute flash at room temperature and an eight-minute predrying 80 ° C baked at 140 ° C for 30 min. The solid color finish of the resulting Multi-layer painting had a layer thickness of 30 µm.

The multicoat paint systems produced in this way were in relation to the top coat level and the rockfall resistance was examined. The results of the investigations are in the summarized the following table 1:

Determination of the solid concentration

The solids determination was carried out in a convection oven by baking at a temperature of 120 ° C carried out. For this purpose, 1 g of the substance to be tested was placed on a patent lid (diameter 75 mm), evenly distributed over the surface, applied and dried in the oven for one hour. The non-volatile content was then determined by weighing the lids back. It is one Triple determination was 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 hoze-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 quenched twice at a pressure of 2 bar, each with 500 g Iron shot "diamond", angular, size 4-5 mm shot.

Determination of the pendulum hardness according to König

The pendulum hardness was determined using a pendulum hardness tester from BYK-Gardner. Table 1

From the values listed in Table 1 it is clear that the using the Filler produced according to the invention with respect to the solid concentration of the ready-to-use filler formulation and the top coat level of the finished multi-layer coating have improved properties compared to the fillers of the prior art.

Claims (18)

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: 1, 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 _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 anhydride with ring opening to the OH group of the intermediate originating from the alkanolamine. 2. Water-dilutable crosslinker according to claim 1, characterized in that the partially blocked polyisocyanate from a reaction of at least three free NCO groups having polyisocyanate with a stoichiometric deficit used Blocking agent is available, 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 1, characterized in that the Partially blocked polyisocyanate is available from a reaction of at least two free ones Diisocyanate containing NCO groups with a stoichiometric deficit blocking agent used, 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 1, characterized in that the partially blocked polyisocyanate from a reaction of at least three free NCO groups containing polyisocyanate with a stoichiometric deficit used Blocking agent originates. 7. Water-dilutable crosslinker according to one of the preceding claims, characterized characterized that it is mixed with at least one completely blocked, at least difunctional polyisocyanate is present. 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 available from the Reaction of a polyisocyanate having at least two free NCO groups with one Blocking agent. 10. Water-dilutable crosslinker according to one of claims 2 to 9, characterized in that that the blocking agent is selected from the group of methyl ethyl ketoxime, 3,5- Dimethylpyrazole and ε-caprolactam. 11. Water-dilutable crosslinker according to one of the preceding claims, characterized characterized in that the cyclic carboxylic anhydride is selected from the group of Phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, Methylhexahydrophthalic anhydride, succinic anhydride and maleic anhydride. 12. Water-dilutable crosslinker according to one of claims 1 to 10, characterized characterized in that the cyclic carboxylic anhydride is trimellitic anhydride. 13. Water-dilutable crosslinker according to one of the preceding claims, characterized characterized in that the polyisocyanate having at least two free NCO groups is selected from the group of 3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Desmodur W), 1,3-bis (1-isocyanato-1- 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 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 crosslinker 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-1,3,5-triazine (Desmodur N3300). 16. Water-dilutable polyurethane according to one of the preceding claims, characterized characterized in that at least one OH group of the alkanolamine with its nitrogen atom via a substituted or unsubstituted alkyl group having 2 to 6 carbon atoms in the main chain is connected. 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.