Coating material with high scratch resistance

Abstract

The present invention relates to a coating material comprising at least one aliphatic or cycloaliphatic polyisocyanate having an NCO functionality of at least 2, preferably 2.8 to 6, optionally at least one binder, preferably a hydroxyl-containing binder, at least one adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol, with more than 90, more preferably more than 95, most preferably more than 99 percent of the hydroxyl groups in the polyhydric alcohol having been converted by reaction with the isocyanatotrialkoxysilane, and less than 0.1 wt % of the isocyanate groups from the isocyanatotrialkoxysilane being reactive in the adduct, at least one catalyst selected from the group consisting of Lewis acids, phosphoric acid or phosphorous acid and esters thereof, blocked or non-blocked sulphonic acids, sulphuric acid, carboxylic acids having a melting point >60° C. and tetraalkylammonium carboxylates, optionally at least one auxiliary, preferably at least one further crosslinker, and/or adjuvant, and optionally organic solvents, and also to a process comprising providing, applying to a surface and curing the coating material, to a coating obtainable by curing the coating material, and to use of the coating material for coating a metal, glass, plastic or wood surface.

Claims

1. A coating material, comprising: an aliphatic or cycloaliphatic polyisocyanate having an NCO functionality of at least 2, optionally, a binder, an adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol, wherein more than 99 percent of the hydroxyl groups in the polyhydric alcohol have been converted by reaction with the isocyanatotrialkoxysilane, and less than 0.1 wt % of the isocyanate groups from the isocyanatotrialkoxysilane are reactive in the adduct, a catalyst selected from the group consisting of a Lewis acid, phosphoric acid, phosphorous acid and an ester thereof, blocked or non-blocked sulphonic acids, sulphuric acid, carboxylic acids having a melting point >60° C. and tetraalkylammonium carboxylates, optionally, an auxiliary selected from the group consisting of an isocyanate-free crosslinker, an additive, a stabilizer and an adjuvant, and optionally, an organic solvent.

2. The coating material according to claim 1, wherein the fraction of the aliphatic or cycloaliphatic polyisocyanate, based on the sum of the aliphatic or cycloaliphatic polyisocyanate, the binder and the adduct is 15 to 40 weight percent.

3. The coating material according to claim 1, wherein the fraction of the binder, based on the sum of the aliphatic or cycloaliphatic polyisocyanate, the binder and the adduct is 20 to 60 weight percent.

4. The coating material according to claim 1, wherein the fraction of the adduct, based on the sum of the aliphatic or cycloaliphatic polyisocyanate, the binder and the adduct is 10 to 70 weight percent.

5. The coating material according to claim 1, wherein the aliphatic or cycloaliphatic polyisocyanate is prepared by oligomerization of a diisocyanate.

6. The coating material according to claim 1, which contains the binder, and wherein the binder is selected from the group consisting of a hydroxyl-containing polyester, a hydroxyl containing polyether, a hydroxyl-containing polyacrylate, a hydroxyl-containing polyurethane and mixtures thereof, and wherein the binder has an OH number of 20 to 500 mg KOH/g.

7. The coating material according to claim 1, wherein the adduct of an isocyanatotrialkoxysilane and polyhydric alcohol is an adduct from the reaction of an isocyanatotrialkoxysilane, which represents an alkyl radical substituted by at least one Si(OR.sub.1)(OR.sub.2)(OR.sub.3) group and an isocyanate group, and a polyhydric alcohol, wherein the alkyl radical substituted by the at least one Si(OR.sub.1)(OR.sub.2)(OR.sub.3) group and an isocyanate group is a linear or branched alkane comprising 1 to 4 carbon atoms, and wherein R.sub.1, R.sub.2 and R.sub.3, in each case and independently of one another, are selected from the group consisting of methyl, ethyl, propyl and butyl.

8. The coating material according to claim 7, wherein the isocyanatotrialkoxysilane is a compound of the formula (I),
OCN—(CH.sub.2).sub.n—Si(OR.sub.1)(OR.sub.2)(OR.sub.3)  (I), wherein n is 1, 2, 3, 4, 5 or 6, and R.sub.1, R.sub.2 and R.sub.3, in each case and independently of one another, are selected from the group consisting of methyl, ethyl and propyl.

9. The coating material according to claim 1, wherein the polyhydric alcohol in the adduct is a non-cyclic polyhydric alcohol to an extent of at least 75%.

10. A process of coating a surface, comprising: (1) applying the coating material of claim 1 to a surface, and (2) curing the coating material.

11. The process according to claim 10, wherein curing the coating material is carried out at a temperature of 10 to 200° C.

12. A coating obtained by the process according to claim 10.

13. The coating material according to claim 1, which consists essentially of: the aliphatic or cycloaliphatic polyisocyanate, optionally, the binder, the adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol, the catalyst, optionally, the auxiliary, and optionally, the organic solvent.

14. The coating material according to claim 1, which consists of: the aliphatic or cycloaliphatic polyisocyanate, optionally, the binder, the adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol, the catalyst, optionally, the auxiliary, and optionally, the organic solvent.

15. The coating material according to claim 1, wherein the catalyst consists of a component selected from the group consisting of a Lewis acid, phosphoric acid, phosphorous acid and an ester thereof, blocked or non-blocked sulphonic acids, sulphuric acid, carboxylic acids having a melting point >60° C., tetraalkylammonium carboxylates, and mixtures thereof.

16. The coating material according to claim 1, wherein the catalyst consists of (1) a first component selected from the group consisting of a Lewis acid, phosphoric acid, phosphorous acid and an ester thereof, blocked or non-blocked sulphonic acids, sulphuric acid, carboxylic acids having a melting point >60° C., tetraalkylammonium carboxylates, and mixtures thereof, and, optionally, (2) a second component selected from the group consisting of metal complexes with chelate ligands, aluminium, zirconium, titanium and/or boron alkoxides and/or esters thereof, organic Sn(IV), Sn(II), Zn and Bi compounds, substituted phosphonic diesters and diphosphonic diesters, amine-blocked phosphoric esters, amine-blocked phosphoric acid catalysts, amine-blocked partial esters of phosphoric acid, and mixtures thereof.

17. The coating material according to claim 1, which comprises 15 to 40 weight percent of the aliphatic or cycloaliphatic polyisocyanate having an NCO functionality of at least 2, 20 to 60 weight percent of the binder, and 10 to 70 weight percent of the adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol, based on the total weight of the aliphatic or cycloaliphatic polyisocyanate having an NCO functionality of at least 2, the binder and the adduct of an isocyanatotrialkoxysilane and a polyhydric alcohol.

18. The coating material according to claim 1, which has a water content of at most 3 weight percent.

Description

EXAMPLES

(1) Unless otherwise indicated, the quantity figures in percent in the examples are given by weight.

Example 1: Preparation of an Adduct of Isocyanatosilane and Trimethyihexanediol (Component C of the Inventive Coating Composition)

(2) 27.4 g of an isomer mixture (approximately 50/50) of 2,2,4- and 2,4,4-trimethylhexanediol are charged to a 250 ml 3 necked flask and admixed with 0.2 g of dibutyltin dilaurate (DBTDL) with stirring. Under a continual stream of nitrogen, the mixture is heated to 60° C. in a water bath. Subsequently, with stirring, 72.4 g of 3-isocyanatopropyltrimethoxysilane are added dropwise at a rate such that the temperature does not climb above 70° C. Following complete addition, the reaction mixture is stirred at 60° C. for 6 hours. The free NCO content is then <0.1%. The product is a clear liquid of medium viscosity.

Example 2 (not Inventive): Preparation of a Silane-Modified Polyisocyanate

(3) 49.58 weight percent of a solvent-free, isocyanurate-based polyisocyanate based on hexamethylene diisocyanate (VESTANAT HT 2500/100, Evonik Industries) and 0.03% of dibutyltin dilaurate are dissolved in 15 weight percent of Solvesso 100 (aromatic solvent, ExxonMobil) and the solution is heated to 55 to 60° C. under N.sub.2. The heating bath is removed and, with stirring, 30.39 weight percent of bis(3-trimethoxysilylpropyl)amine (Dynasylan 1124, Evonik Industries) are added dropwise at a rate such that the temperature is maintained at about 55 to 60° C. After the end of the addition, 5 weight percent of Solvesso 100 are added to the mixture, followed by an hour of stirring at 60° C., and the NCO content is determined. The NCO content is 6.59%. The viscosity, measured at 23° C., is 620 mPas. The arithmetic solids content is 80%.

Example 3: Investigation of the Physical Properties of Various Inventive Coating Materials in Comparison to Conventional Coating Materials

(4) The inventive clearcoat materials and also the comparative based on a silane-modified polyisocyanate as per Example 2 (composition III) and a 2-component PU clearcoat material (composition VIII) were formulated in accordance with the amounts shown in Table 1.

(5) TABLE-US-00001 TABLE 1 Composition of the inventive coating materials III VIII (partly (comparative, silanized, 2-component Item comparative) IV V VI VII PU) 1 VESTANAT HT 2500 L / 18.30 16.68 15.32 12.72 19.24 (90% form) 2 Isocyanatosilane / 4.87 13.32 20.39 33.88 / adduct from Example 1 3 Non-inventive, silane- 36.43 / / / / / modified polyisocyanate from Example 2 4 Setalux ® C1767 VV-65 34.98 47.81 43.16 39.32 31.74 52.20 (65% form) 5 Byketol ® special 2.60 2.60 2.60 2.60 2.60 2.60 6 Byk ® 301 0.20 0.20 0.20 0.20 0.20 0.20 7 Butyl acetate/xylene 22.22 20.69 18.01 15.76 11.46 22.24 mixture (1:1) 8 TEAB (10% in Setalux 0.06 1.85 2.08 2.23 2.78 / C1767 VV-65) 9 Tinuvin ® 292 0.26 0.27 0.29 0.31 0.34 0.26 10 Tinuvin ® 900 3.25 3.41 3.66 3.87 4.28 3.26 Solids content: 51.9 53.5 57.6 61.0 67.6 51.3 (arithmetic, incl. trimethoxysilyl content) Arithmetic silicon content 3.5 0.9 2.3 3.3 4.9 0.0 based on solids [wt %] Setalux ® 1767 VV-65: Polyacrylate polyol, Nuplex Resins B.V. Byk ® 301: Polyether-modified polydimethylpolysiloxane, flow control agent, Byk Chemie Byketol ® Special: Flow control agent based on high-boiling solvents and polyether-modified polydimethylsiloxanes, Byk Chemie Tinuvin ® 292: sterically hindered amine, light stabilizer; BASF SE Tinuvin ® 900: UV absorber; BASF SE

(6) All of the clearcoat materials were formulated as 2-component systems, meaning that the curing component and the polyol component were mixed immediately prior to processing. Here, in the case of the inventive formulations (compositions IV-VII), the silane adduct (item 2) was mixed beforehand with the polyisocyanate (item 1).

(7) The viscosity of the formulations, determined as the flow time in the DIN 4 cup at 23° C., was approximately 20 seconds.

(8) The mechanical characteristics were determined by applying all of the coating materials by spraying with compressed air assistance, using an HPLV gun, to phosphatized steel panels (Chemetall Gardobond 26S/60/OC) and curing them at 140° C. for a time of 22 minutes.

(9) Testing for acid resistance and scratch resistance took place in a two-coat system, the clearcoat over a black basecoat. For this purpose, an aqueous black basecoat material (Autowave MM 245, jet black; blended 100:5 with Aktivator WB, curing: 15′ 50° C.) was applied by spraying to—in the case of acid resistance—metal test panels of special deep-drawn material with RP surface to DIN 1624, 570×98×0.8 mm, and—in the case of scratch resistance—to metal bodywork panels (steel, 190×105×0.8 mm DIN 1624) and, after a flash-off time of 10 minutes at room temperature, were dried in a forced air oven at 80° C. for 10 minutes. The dry film thickness in each case is about 10 μm.

(10) For the test for scratch resistance, a nylon fabric 45 mm×20 mm with a mesh size of 25 μm is weighted with a 2 kg weight, and placed on and locked to the test plate, which is in turn fixed on a carriage. Following application of 1 ml of an agitated, 0.25% strength detergent solution (Persil) immediately in front of the test area, the test plate is oscillated with a maximum deflection in each case of about 3.5 cm. After 80 double rubs (1 s.sup.−1), the remaining wash fluid is rinsed off with mains water and dried with compressed air. Gloss measurements (20° angle) are performed before and after the test in each case.

(11) Recovery (reflow) under effect of temperature: The damaged test plate is stored in a forced air oven at 40° C. for 2 h, after which the gloss of the coating is measured again.

(12) For the acid resistance test, drops (about 0.05 ml) of a 20% strength sulphuric acid solution are applied at a distance of 2 cm, using a pipette, to the metal test plates. In a temperature gradient oven (BYK-Gardner), they are subjected to a temperature gradient, in the longitudinal direction of the plate, from 35 to 80° C. for 30 minutes. Water is then used to wash off residues of the acid, and a visual examination is made after 24 hours. To assess the resistance, the range (temperature) of a first visible attack on the clearcoat, and also the range (temperature) of destruction of the basecoats, in ° C., are reported. The higher the respective temperature, the higher the evaluation of the resistance of the clearcoat.

(13) TABLE-US-00002 TABLE 2 Properties of the coatings Example No. VIII III (2-component (comparative) IV V VI VII PU, comparative) Curing 22′ 22′ 22′ 22′ 22′ 22′ 140° C. 140° C. 140° C. 140° C. 140° C. 140° C. Cupping (EN ISO 5.5 8.5 7.0 6.0 7.0 8 1520) [mm] Pendulum 166 174 164 162 143 171 hardness (König, DIN EN ISO 1522) [s], after 7 d Ball impact [in lbs] 80 >80 >80 >80 80 80 (DIN-EN-ISO 6272-1) MEK test [ASTM >150 >150 >150 >150 >150 >150 D 4752] (Double rubs, 1 kg applied weight) Acid resistance; <37/61° C. 47/67° C. 43/61° C. 40/61° C. 46/71° C. 47/65° C. gradient oven method [° C.] 1st Attack/ destruction of clearcoat Scratch 82/1 80/16 82/11 81/5 79/2 79/20 resistance Initial gloss/loss of gloss [scale divisions]

(14) The results in Table 2 demonstrate that the inventive coating materials, especially at relatively high levels of component C) (compositions with numbers VI, VII) exhibit outstanding scratch resistance, matching the relevant comparative based on trialkoxysilane-modified polyisocyanate crosslinkers (composition III) and being far superior to the 2-component PU coatings in this respect. The chemical resistance of the inventive coatings is significantly superior to that of the scratch-resistant clearcoat in the comparative example (composition III), expressed as acid resistance, and particularly so in relation to the temperature of the first discernible attack by sulphuric acid. Furthermore, Table 1 shows that the solids contents of the inventive coating composition (Examples IV-VII), especially those with outstanding scratch resistance (Examples VI and VII), are significantly increased relative to the scratch-resistant comparative system (Example III).