DE4231071A1 - Coating material for prodn. of transparent top coats - Google Patents

Abstract

Coating material suitable for the prodn. of transparent topcoats is claimed (I), contg. binder(s) based on OH-functional (meth)acrylic copolymer (II), crosslinker(s) based on (cyclo)aliphatic polyisocyanates (III), solvent(s) and normal paint additives. The binders contains mixts. of (A) 40-60 wt.% copolymer (IIA) and 60-40 wt.% copolymer (IIB). (IIA) is obtd. by copolymerisation of (al) 50-70 wt.% acrylate ester(s) mixed with sufficient hydroxyalkyl acrylate(s) to give a mixt. with OH no. 40-70 mg KOH/g and (a2) 30-50 wt.% methacrylate ester(s) mixed with sufficient hydroxyalkyl methacrylate to give OH no. 180-450. (IIB) is obtd. by copolymerisation of (b1) 27-40 wt.% alkyl acrylate(s), (b2) 49-55 wt.% methacrylate ester(s) mixed with hydroxyalkyl methacrylate to give OH no. 240-300, (b3) 1-3 wt.% acrylic acid and (b4) 10-15 wt.% vinyl ester(s) of unsatd. aliphatic monocarboxylic acid(s) with the COOH gp. on a tert. C atom.Also claimed are (1) prepn. of (I), by mixing 40-60 wt.% (A) with 60-40 wt.% (B) and with solvent(s) and additives, then adding (III) immediately before use, in amts. such that the mixt. contains 0.5-2.0 NCO gps. per OH gp. in (A + B); and (2) prepn. of a multilayer coating on a substrate which may be precoated with primer, filler and/or other intermediate layers, by applying a basecoat (pref. a water-based basecoat), briefly drying or hardening, and then applying (I) as the topcoat, pref. by spraying at a solids content of above 55 wt.%.Pref. amt. of polyisocyanate (III) is as given above. Component (A) has OH no. 120-170, Mw 3000-5000 and Tg 10-30 deg.C; component (B) has acid no. 25-50, OH no. 120-160, Mw 5000-8000 and Tg 20-50 deg.C..

Description

The invention relates to a coating agent that is used to manufacture transpa renter top layers on multi-layer coatings is suitable.

Coating compounds for the production of transparent cover layers on Mehr layer coatings are known. In DE-A 33 22 037 such Describe coating compositions based on (meth) acrylic copolymers. These coating agents contain a mixture of special (meth) acrylic Copolymers that have a solids content of up to Allow 55% by weight.

It is for environmental protection and occupational safety reasons however, the solids content of coating agents, in particular especially applied in the spray process, to further increase thus the content of volatile and possibly toxic solvents to further reduce. For the same reasons, the Use of heavy metal catalysis as used in these systems Practice is customary to be dispensed with.

The object of the invention is therefore to provide a coating agent, especially for the production of transparent cover layers in Multilayer coatings are suitable, with an increased solids content can be applied and have a good flow and excellent the top coat level results.

It has been shown that this problem can be solved by a Coating agent which forms an object of the present invention  and the binder based on one or more (meth) acrylic Contains copolymers that are a mixture of

• A) 40-60 wt .-% of one or more hydroxyl-containing (meth) acrylic copolymers, obtainable by copolymerization of
  a1) 50-70 wt .-% of one or more acrylic acid esters which are present in a mixture with such a proportion of one or more acrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 20-40 mg KOH / g, and
  a2) 30-50 wt .-% of one or more methacrylic acid esters, which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 100-120 mg KOH / g, and
• B) 60-40% by weight of one or more (meth) acrylic copolymers containing hydroxyl groups, which are obtainable by copolymerization of:
  b1) 27-40% by weight of one or more alkyl acrylates,
  b2) 49-55% by weight of one or more methacrylic acid esters which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 120-150 mg KOH / g,
  b3) 1-3% by weight of acrylic acid,
  b4) 10-15% by weight of one or more vinyl esters of aliphatic saturated monocarboxylic acids in which the carboxyl group is bonded to a tertiary carbon atom,

where the sum of components A) and B), the sum of components a1) and a2) and the sum of components b1) to b4) in each case 100% by weight is composed.

The coating compositions according to the invention contain the first two defined (meth) acrylic copolymers as crosslinking agents or several aliphatic and / or cycloaliphatic polyisocyanates, which also can be present in the mixture. The coating agents also contain one or several organic solvents, as well as conventional additives, for example Sunscreen.

The preparation of those contained in the coating composition according to the invention (Meth) acrylic copolymers can be polymerized by conventional methods Process, e.g. B. the substance, solution or pearl polymerization leads. The various polymerization processes are well known and described in: Houben-Weyl, Methods of Organic Chemistry, 4. Ed., Vol. 14/1, pp. 24-255 (1961).

The solution polymerization process is used to manufacture the Coating agents according to the invention used (meth) acrylic copolymers prefers. In this process, the solvent is in the reaction vessel installed, heated to boiling temperature and the monomer / initiator mixture metered continuously in a certain time.

The polymerization is carried out at temperatures between 60 ° C and 160 ° C preferably carried out at 120 ° C to 150 ° C.

The polymerization reaction is carried out using known polymerization initiators started. Suitable initiators are per and azo compounds, which in a first order reaction thermally decompose into radicals. Initiator type and amount are chosen so that at the polymerization temperature radical supply is as constant as possible during the inflow phase.

Examples of preferred initiators for the polymerization are: dialkyl peroxides, such as di-tert-butyl peroxide, di-cumyl peroxide;  Diacyl peroxides such as di-benzoyl peroxide, di-lauroyl peroxide; Hydroperoxides, such as cumene hydroperoxide, tert-butyl hydroperoxide; Perester, like tert.- Butyl perbenzoate, tert-butyl perpivalate, tert-butyl per-3,5,5-trim ethyl hexanoate, tert-butyl per-2-ethylhexanoate; Peroxydicarbonates such as Di-2-ethylhexyl peroxydicarbonate, dicyclo-hexyl peroxydicarbonate; Perk tals, such as 1, 1-bis (tert-butylperoxy) -3,5,5-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane; Ketone peroxides, such as cyclohexanone peroxide, Methyl isobutyl ketone peroxide; Azo compounds, such as 2,2′-azo-bis (2,4- dimethylvaleronitrile), 2,2'-azo-bis (2-methylbutyronitrile), 1,1'-azo-bis- cyclohexane carbonitrile, azo-bis-isobutyronitrile.

The peroxide initiators, in particular the peresters in, are preferred an amount of 3 to 8 wt .-% to use on the monomer weight.

As an organic solvent, which is expediently used in the solution polymer station and later also in the coating agent according to the invention are suitable, for example: glycol ethers, such as ethylene glycol dimethyl ether; Glycol ether esters, such as ethyl glycol acetate, butyl glycolace tat, 3-methoxy-n-butyl acetate, butyl diglycol acetate, methoxy propyl acetate, Esters such as butyl acetate, isobutyl acetate, amyl acetate; Ketones, such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isopho ron; aromatic hydrocarbons, such as xylene, Solvesso 100 (registered trademark) and aliphatic hydrocarbons can also be found in Waste with the solvents mentioned above can be used.

To regulate the molecular weight can be preferred in particular chain transfer agents can also be used. Examples are mercaptans, thioglycolic acid esters, chlorinated hydrocarbons, cumene, dimeric α-methylstyrene.

The polymerization conditions (reaction temperature, feed time of the Monomer mixture, solution concentration) are set up so that the (Meth) acrylic copolymers for the coating produced according to the invention average a weight average molecular weight (determined by Gelper meation chromatography using polystyrene as calibration sub  punch) between 3000-5000 for component A) and 5000-8000 for compo nente B) have.

The hydroxyl-containing (meth) acrylic copolymers of the invention The coating agent produced is in a glass transition temperature range from 10 ° C to + 30 ° C for component A) and + 20 ° C to 50 ° C for Component B), calculated from the glass transition temperature of the homopolyme risks of the individual monomers specified in the literature (FOX- Equation, see e.g. B. Polymeric materials, Batzer, 1985, page 307).

As monomer components for the production of hydroxyl-containing (Meth) acrylic copolymers (component A) and B) are alkyl esters Acrylic acid or methacrylic acid used: methyl acrylate, methyl meth acrylate, ethyl acrylate, ethyl methacrylate, iso-propyl methacrylate, tert.- Butyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, iso- Butyl methacrylate, cyclohexyl methacrylate, trimethylcyclohexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl meth acrylate, stearyl acrylate, stearyl methacrylate, isobornyl acrylate, isobornyl methacrylate; Hydroxyalkyl esters of acrylic acid or methacrylic acid, such as Hydroxyethyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate, butanediol-1,4-monoacrylate, butanediol-1,4- monomethacrylate, hexanediol-1,6-monoacrylate, hexanediol-1,6-monometh acrylate.

To equip the (meth) acrylic copolymer with carboxyl groups Polymerized acrylic acid in such amounts that for component B) an acid number of 25 to 50 mg KOH / g results.

The coating agents used according to the invention are crosslinked Combined as polyisocyanates or polyisocyanate prepolymers Production of transparent cover layers of a multilayer coating.

The proportion of polyisocyanate crosslinker is preferably chosen so that a hydroxyl group of the binder components 0.5 to 2.0 isocyanate Groups are dropped. Excess isocyanate groups can be damp  react and contribute to networking. It can be aliphatic and / or cycloaliphatic polyisocyanates can be used, such as Hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorondi isocyanate; Biuret, allophanate, urethane or isocyanurate groups containing polyisocyanates. The polyisocyanates can optionally partially blocked with CH-, NH- and / or OH-acidic compounds.

Examples of such polyisocyanates include a biuret group of the reaction product from 3 moles of hexamethylene diisocyanate with 1 mole Water with an NCO content of approx. 22% (corresponding to the commercial product Desmodur N® BAYER AG) and a polyisocyte containing isocyanurate groups anat by trimerization of 3 moles of hexamethylene diisocyanate is produced with an NCO content of about 21.5% (corresponding to the Commercial product Desmodur N 3390® BAYER AG).

The coating agents, which are the binders to be used according to the invention can contain, in addition to the solvents already mentioned customary paint additives contain: leveling agents such. B. (meth) acrylic Homopolymers, silicone oils and castor oil, which can be hydrogenated, Plasticizers, such as phosphoric acid, phthalic acid or citric acid esters, Anti-settling agents, optionally transparent pigments such as B. pyrogenes Silicon oxide, rheology control agents, such as. B. microgels, NAD's (Non aqueous dispersions = non-aqueous dispersions) and substituted Polyureas, light stabilizers, such as. B. benzotriazole and / or HALS Derivatives (hindered amine light stabilizers = sterically hindered amines as light stabilizers).

The coating compositions according to the invention can be conventional curing accelerators contain, but are particularly characterized in that they, too without (heavy metal) catalysts, at temperatures of 110- 160 ° C, preferably cured below 150 ° C to high-gloss coatings can be.

The coating compositions of the invention can be opaque for production Coatings usual opaque pigments can be added.  

The coating agents according to the invention can consist of the individual components are produced by customary processes familiar to the person skilled in the art. The polyisocyanate component is preferred shortly before application added.

The coating compositions according to the invention are produced by known methods, such as e.g. B. spraying, dipping, rolling or knife application. Doing so the substrate, which may already have been provided with further layers of lacquer the top coat is applied. After an evaporation phase, the appli ornamental coating agent preferably crosslinked by heating. The branded temperatures are between 110 to 160 ° C, preferably between 120 to 150 ° C. However, crosslinking can also take place at lower temperatures, for example at 20-110 ° C, preferably at 25 to 80 ° C. become. The layer thickness of the baked film is approximately 15-50 µm. This creates a cross-linked, hard, glossy lacquer coating. A the preferred embodiment is the application of the invention Coating agent as a clear coat on a basecoat, preferably one aqueous basecoat. You can work wet-on-wet, or the Basecoat is dried beforehand by heating. This creates one particularly good adhesion of the two layers.

With coating compositions formulated according to the invention as clear lacquers For example, basecoats are overcoated, the usual topcoat paint may contain elements, preferably they contain effect pigments, such as. B. Metallic pigments. Preferred as the binder base of the basecoat Polyester, polyurethane or acrylic resins are used. These binders can optionally via crosslinkers, e.g. B. melamine or isocyanate derivatives te, be networked.

The coating compositions according to the invention are particularly suitable for top coats or clear coats, which are preferred in the automotive sector, however in other areas. The use of the fiction moderate coating agent in the multi-layer coating is particularly for the Automobile series painting suitable, but it can also be used for others  Purposes are used such. B. for household appliances or in furniture Industry.

The coating compositions according to the invention can be held with solids Apply over 55% by weight with excellent flow and they allow the production of high-gloss multi-layer coatings with excellent Top coat stand.

The coating compositions according to the invention are particularly suitable for the manufacture a transparent top layer of an air drying or oven drying multilayer coating. They are particularly suitable for the Series painting of motor vehicle bodies and their parts. they have the advantage that they have a high processing solids can be applied.

The coating compositions according to the invention can be wet-on-wet on conventional le, d. H. solvent-based or aqueous layers of lacquer are applied, whereupon both layers are hardened together at elevated temperature. For example, it is possible to use the transparent cover layers applied from the clear varnishes containing polyisocyanate according to the invention be, according to the wet-on-wet method on conventional or aqueous Apply basecoats. The two layers can then harden together be tested. For example, curing temperatures are of the order of magnitude 120 to 150 ° C. The curing times are, for example The order of 20 to 40 minutes.

The invention therefore also relates to the production of multilayer coatings gene or the use of the coating agent according to the invention for the manufacture development of topcoat layers, e.g. B. clear lacquer layers, for curable more layer coatings.

The following examples serve to illustrate the invention. Parts and Percent refer to the weight.  

Examples 1 to 3 Preparation of the (meth) acrylic copolymers of components A) and B). Production of component A)

In a 2 liter three-neck ground flask, with an agitator, contact thermometer, ball cooler and dropping funnel, item I (the amounts are given in Table 1) and under Stirring heated to approx. 145 ° C with reflux cooling switched on. Inner pos. II (monomer mixture + initiator) is continued continuously within 6 hours dier dosed out of the dropping funnel. After the end of the feed, the Rinsing funnel rinsed with item III and added to the reaction material. The batch is then polymerized for 3 hours at about 143 ° C. so that the conversion is <99%. Then it is cooled to 100 ° C and with Item IV diluted to a solid of approx. 65%.

Production of component B)

In a 2 liter three-neck ground flask, with an agitator, contact thermometer, ball cooler and dropping funnel, item I (the amounts are given in Table 1) and under Stirring heated to approx. 139 ° C with reflux cooling switched on. Inner half of 5 hours, item II (monomer mixture + initiator) is continued dier dosed out of the dropping funnel. After the end of the feed, the Rinsing funnel rinsed with item III and added to the reaction material. The batch is then polymerized for 5 hours at about 135 ° C., so that the conversion is <99%. Then it is cooled to 100 ° C and with Item IV diluted to a solid of approx. 50%.

Table 1

(The numbers refer to the weight in grams)

Manufacture of multi-layer coatings Example 4

409 parts of the resin solution from Example 3 and 323 parts of the resin solution Example 1 are mixed homogeneously and then are under the current Stirrer 21 parts of a commercial phthalate, 24 parts of a mixture commercial light stabilizers (HALS and benzotriazole derivative in Ratio 1: 1), 23 parts of a 1% xylene solution commercially available cher silicone oils (leveling and wetting agents) and 180 parts of one Solvent mixture of butyl diglycol acetate, ethoxypropyl acetate, butyl glycol acetate and high-boiling aromatic hydrocarbons in the Ratio 13: 10: 12: 65 added.

In 100 parts of this solution, 30 parts of an 82% solution are one aliphatic isocyanurate polyisocyanate in xylene / butyl acetate (1: 1) homogeneously stirred. This clearcoat was used as follows Production of a multi-layer paint used:

With commercially available katho used in automotive OEM painting separable electrodeposition paint (KTL) (18 µm) and commercially available Filler (35 µm) pre-coated body panels were coated with commercial  chem water-thinnable metallic basecoat in a dry layer thickness painted of 15 µm and 6 min. predried at 80 ° C. Immediately afterwards became the clear coat described above in a dry layer thickness of 35 µm applied by spray application wet-on-wet and after 5 min. Flash off at room temperature for 20 min. at 140 ° C (object temperature) burns.

Example 5

The procedure is analogous to Example 4, with the difference that instead of le of 409 parts of the resin solution from Example 3 and 323 parts of the Resin solution from Example 1, 414 parts of the resin solution from Example 3 and 318 parts of the resin solution from Example 2 were used.

Example 6

The procedure is analogous to Example 4, with the difference that instead of le of 409 parts of the resin solution from Example 3 and 323 parts of the Resin solution from Example 1, 156 parts of the resin solution from Example 1 and 581 parts of the resin solution from Example 3 were used.

Example 7

The procedure is analogous to Example 4, with the difference that instead of le of 180 parts of the solvent mixture only 100 parts can be used.

Despite the high processing solids with those in Examples 4 to 6 The clearcoats described the course was excellent and resulted high-gloss multi-layer coatings with excellent topcoat level.

Claims (11)

1. Coating agent, suitable for the production of transparent cover layers, containing one or more binders based on hydroxy-functional (meth) acrylic copolymers, one or more crosslinkers based on aliphatic and / or cycloaliphatic polyisocyanates, one or more solvents and customary lacquers Additives, characterized in that the binders contain mixtures of

• A) 40-60% by weight of one or more (meth) acrylic copolymers containing hydroxyl groups, obtainable by copolymerization of
  a1) 50-70% by weight of one or more acrylic acid esters which are present in a mixture with such a proportion of one or more acrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 20-40 mg KOH / g, and
  a2) 30-50% by weight of one or more methacrylic acid esters which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 100-120 mg KOH / g, and
• B) 60-40% by weight of one or more (meth) acrylic copolymers containing hydroxyl groups, which can be obtained by copolymerizing:
  b1) 27-40% by weight of one or more alkyl acrylates,
  b2) 49-55% by weight of one or more methacrylic acid esters which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 120-150 mg KOH / g,
  b3) 1-3% by weight of acrylic acid,
  b4) 10-15% by weight of one or more vinyl esters of aliphatic saturated monocarboxylic acids in which the carboxyl group is bonded to a tertiary carbon atom,

where the sum of components A) and B), the sum of components a1) and a2) and the sum of components b1) to b4) each 100 % By weight. 2. Coating agent according to claim 1, characterized in that the aliphatic and / or cycloaliphatic polyisocyanate in one such an amount is present that on a hydroxyl group of the bandage middle components A) and B) each 0.5 to 2.0 isocyanate groups omitted. 3. Coating agent according to claim 1 or 2, characterized in that component A) has a hydroxyl number of 120 to 160 mg KOH / g Weight average molecular weight (Mw) from 3000 to 5000 and a glass transition temperature Tg from 10 ° C to + 30 ° C. 4. coating agent according to claim 1, 2 or 3, characterized in that component B) has an acid number of 25 to 50 mg KOH / g, a Hydroxyl number of 120-150 mg KOH / g, a weight average molecular weight (Mw) from 5000 to 8000 and a glass transition temperature Tg of + 20 ° C to + 50 ° C.   5. A process for the preparation of the coating agent according to one of the preceding claims, characterized in that

• A) produces a copolymer by copolymerization of
  a1) 50-70% by weight of one or more acrylic acid esters which are present in a mixture with such a proportion of one or more acrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 20-40 mg KOH / g, and
  a2) 30-50% by weight of one or more methacrylic acid esters which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 100-120 mg KOH / g, and
• B) produces another copolymer by copolymerization of
  b1) 27-40% by weight of one or more alkyl acrylates,
  b2) 49-55% by weight of one or more methacrylic acid esters which are present in a mixture with such a proportion of one or more methacrylic acid hydroxyalkyl esters that the hydroxyl number of the mixture is 120-150 mg KOH / g,
  b3) 1-3% by weight of acrylic acid,
  b4) 10-15% by weight of one or more vinyl esters of aliphatic saturated monocarboxylic acids in which the carboxyl group is bonded to a tertiary carbon atom

and then 40-60% by weight of the copolymer A) obtained with 60- 40% by weight of the copolymer B) obtained with one or more  Solvents, and optionally additives common in paint and mixed immediately before use one or more aliphatic and / or Add cycloaliphatic polyisocyanates in such an amount that 0.5 to a hydroxyl group of the copolymers A) and B) up to 2.0 isocyanate groups are eliminated. 6. Process for producing a multilayer coating, characterized records that one on a substrate that with a primer layer, a filler and / or other intermediate layers can be a basecoat based on solvent-based gene or aqueous basecoats and after a short time Flash off or harden a topcoat from a coating agent according to applies one of claims 1 to 4. 7. The method according to claim 6, characterized in that one Apply basecoat layer based on aqueous basecoats. 8. The method according to claim 6 or 7, characterized in that one apply the topcoat by spray application while doing that Coating agents with a solids content of over 55 wt .-% puts. 9. Use of the coating agent according to one of claims 1 to 4 Production of transparent cover layers on multi-layer coatings.