AQUEOUS URETDIONE GROUP-CONTAINING COMPOSITIONS AND METHOD FOR PRODUCING SAME

Abstract

The invention relates to aqueous uretdione group-containing compositions comprising or consisting of (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic, and/or aromatic polyisocyanates which do not contain chemically bonded hydrophilating groups; (B) at least one hydroxy group-containing polyol which contains at least one chemically bonded carboxylic acid group; (C) optionally solvents; and (D) optionally auxiliary agents and additives; wherein the quantity ratio of the components (A) and (B) is measured such that the molar ratio of the NCO groups of the curing agent (A), said groups being provided in the form of uretdione, to the NCO reactive groups of the polyol (B) equals 3.0:0.5 to 0.5:3.0, and A and B are provided as a physical mixture. The invention additionally relates to a method for producing a polyurethane layer using the aqueous uretdione group-containing composition according to the invention, to the polyurethane layer obtained therefrom, and to a substrate which is coated with or adhered to the polyurethane layer.

Claims

1. An aqueous uretdione group-containing compositions comprising; (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic or aromatic polyisocyanates that contains no chemically-bonded hydrophilizing groups; (B) at least one hydroxyl-containing polyol that contains at least one chemically-bonded carboxylic acid group; (C) optionally, solvents; and (D) optionally, auxiliaries and additives; wherein the quantitative ratio of components (A) and (B) is such that the molar ratio of the NCO groups of the curing agent (A) present as uretdione to NCO-reactive groups of the polyol (B) is 3.0:0.5 to 0.5:3.0 and wherein A and B are present as a mixture.

2. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) is obtained by reacting monomeric isocyanates comprising at least one monomeric isocyanate selected from the group consisting of tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate-, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, dicyclohexylmethane-2,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, tetramethylxylylene diisocyanate, triisocyanatononane, tolylene diisocyanate, diphenylmethane-2,4-diisocyanate, diphenylmethane-4,4-diisocyanate, triphenylmethane-4,4-diisocyanate, naphthylene-1,5-diisocyanate, and mixtures thereof.

3. The composition as claimed in claim 1, wherein hydroxyl-containing monomers or polymers are used as starting materials for the at least one uretdione group-containing curing agent (A).

4. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) has a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84 g/mol).

5. The composition as claimed in claim 1, wherein the aqueous composition has an acid value of 1 to 100 mg KOH/g.

6. The composition as claimed in claim 1, wherein the at least one hydroxyl-containing polyol (B) is obtained by reacting hydroxy- or aminocarboxylic acids comprising at least one carboxylic acid selected from the group consisting of 2,2-dimethylolacetic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, ,-diaminovaleric acid, and mixtures thereof.

7. The composition as claimed in claim 1, wherein the polyol (B) containing at least one hydroxyl group has an OH content greater than 1% by weight, calculated as OH groups based on the solids content, a molecular weight of 17 g/mol, and a number-average molecular weight Mn of 500 to 20 000 g/mol.

8. The composition as claimed in claim 1, wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters, and mixtures thereof.

9. The composition as claimed in claim 1, wherein the auxiliaries and additives are selected from the group consisting of leveling agents, light stabilizers, catalysts, fillers, and pigments, and mixtures thereof.

10. The composition as claimed in claim 1, wherein the sum of the proportions by weight of (A), (B), and (D) is 30% to 60% by weight based on the solids content of the total aqueous composition.

11. A process for producing a polyurethane layer comprising the steps of i) providing an aqueous uretdione group-containing composition as claimed in claim 1; ii) applying to a substrate the composition obtained in i) to produce a mixture; iii) drying the mixture from step ii), and iv) curing the mixture from step iii) by heating to from 40 C. to 180 C. for up to 180 minutes.

12. The process as claimed in claim 11, wherein the aqueous uretdione group-containing composition is obtained by mixing the uretdione group-containing curing agent (A) with the polyol (B) containing at least one hydroxyl group in the absence of water to obtain a mixture, and subsequently dispersing the mixture with water.

13. A polyurethane layer obtained by the process as claimed in claim 11.

14. A substrate coated or bonded with the polyurethane layer as claimed in claim 13.

Description

EXAMPLES

Raw Materials Used:

[0084] Polyester 1: an aliphatic polyester prepared from 1419 g of trimethylolpropane, 4773 g of neopentyl glycol, 3093 g of adipic acid, 4101 g of isophthalic acid, and 267 g of 1,2-propylene glycol, having an acid value of <3 mg KOH/g and an OH value of 181 mg KOH/g.

Analytical Methods Used:

[0085] All viscosity measurements were carried out using a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219:1994-10.

[0086] NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

[0087] OH values were determined titrimetrically in accordance with DIN EN ISO 4629-2:2015-02.

[0088] Acid values were determined titrimetrically in accordance with DIN EN ISO 2114:2002-06.

[0089] Solids contents were determined in a circulating-air oven in accordance with DIN EN ISO 3251:2008-06, method B.

[0090] Mean particle sizes (MPS) were determined using a Zetasizer Nano from Malvern (DE) in accordance with DIN ISO 13321:2004-10.

[0091] pH determinations were carried out using a pH meter in accordance with DIN ISO 976:2008-07 in a 1:4 dilution with distilled water.

[0092] Residual monomer contents were measured in accordance with DIN EN ISO 10283 by gas chromatography with an internal standard.

[0093] Pendulum hardness was measured on a standardized coil test plate (coil coating blackCS 200570, from Heinz Zanders Priif-Blech-Logistik) in accordance with DIN EN ISO 1522:2007-04 using a Konig pendulum.

[0094] Chemical resistance was measured on a standardized coil test plate (coil coating blackCS 200570, from Heinz Zanders Priif-Blech-Logistik). A cotton pad soaked in the test substance (xylene or water) was laid on the coating surface and covered with a watch glass. After the specified contact time, the cotton pad soaked in test substance was removed and the contact site dried off and immediately examined. Softening and discoloration of the coating surface were assessed. The assessment was made in accordance with DIN EN ISO 4628-1 as follows:

0 no, i.e. no noticeable damage
1 very few areas of damage, i.e. small, just about significant number
2 a few areas of damage, i.e. small, but significant number
3 moderate number of areas of damage
4 considerable number of areas of damage
5 very many areas of damage

[0095] Unless indicated otherwise, all percentages refer to percentages by weight.

Preparation of a Uretdione Group-Containing Crosslinker (Crosslinker 1, Preparation Example)

[0096] 1000 g (4.50 mol) of isophorone diisocyanate (IPDI) was successively mixed at room temperature under dry nitrogen, and with stirring, with 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160 C. and a pressure of 0.3 mbar. This yielded a light yellow uretdione polyisocyanate having a free NCO group content of 17.0%, a calculated content of uretdione groups of 20.8%, a monomeric IPDI content of 0.4%, and a viscosity of more than 200 000 mPas.

[0097] 337 g of 1,4-butanediol, 108 of 2-ethylhexanol, and 569 g of -caprolactone were mixed at room temperature under dry nitrogen, 0.3 g of tin(II) octoate was added, and the mixture was stirred at 160 C. for 5 h and then cooled to room temperature. To this mixture was then added, over a period of 30 min, 1850 g of the above-described uretdione group-containing polyisocyanate based on IPDI, which was warmed to 80 C. The reaction mixture was stirred at a temperature of max. 100 C. until the NCO content of the reaction mixture had fallen after 7 to 8 h to a value of 0.8%. The reaction mixture was solidified by pouring it onto a metal sheet, comminuted, and then dissolved in acetone to give a solution with a solids content of 70% by weight.

Examples 1-3 (Inventive)

Example 1

[0098]

TABLE-US-00001 TABLE 1 Weight (g) Component 1: POLYESTER 1 875 DIMETHYLOLPROPIONIC ACID 55 TIN(II) 2-ETHYLHEXANOATE 1.4 ACETONE 471 Component 2: HEXAMETHYLENE DIISOCYANATE 169 Component 3: CROSSLINKER 1 (70% in ACETONE) 458 Component 4: DIMETHYLETHANOLAMINE 36 Component 5: DIST. WATER 1384

[0099] Component 1 from table 1 was weighed into a stirring apparatus under nitrogen and homogenized for 1 h at 60 C. Component 2 was then metered in at 55 C. such that the exothermicity caused the mixture to boil under reflux. The reaction mixture was kept under reflux until the NCO content had fallen below 0.05%. The reaction mixture was then cooled to 50 C. and component 3 added and stirred in for 1 h at 50 C. Component 4 was then added and stirring continued for 30 min. Finally, component 5 was stirred in over a period of 15 min and the acetone was distilled off under reduced pressure.

[0100] This yielded a dispersion with the following properties:

TABLE-US-00002 Solids content 49.8% by weight Acid value (100%) 20 mg KOH/g OH content (100%, calculated) 1.9% by weight Mean particle size 143 nm Viscosity 640 mPas pH 7.8

[0101] The dispersion remained stable for 14 months at 23 C.

Example 2

[0102] Example 2 was prepared in the same way as example 1, except that 718 g of the crosslinker 1 solution and 38 g of dimethylethanolamine were used. The dispersion obtained has the following properties:

TABLE-US-00003 Solids content 42.6% by weight Acid value (100%) 18 mg KOH/g OH content (100%, calculated) 1.7% by weight Mean particle size 180 nm Viscosity 850 mPas pH 8.0

[0103] The dispersion remained stable for 14 months at 23 C.

Example 3

[0104] Example 3 was prepared in the same way as example 1, except that the amounts shown below in table 2 were used.

TABLE-US-00004 TABLE 2 Weight (g) Component 1: POLYESTER 1 759 DIMETHYLOLPROPIONIC ACID 60 TIN(II) 2-ETHYLHEXANOATE 1.3 ACETONE 667 Component 2: HEXAMETHYLENE DIISOCYANATE 181 Component 3: CROSSLINKER 1 (70% in ACETONE) 1043 Component 4: DIMETHYLETHANOLAMINE 42 Component 5: DIST. WATER 1690

[0105] The dispersion obtained has the following properties:

TABLE-US-00005 Solids content 40.0% by weight Acid value (100%) 17 mg KOH/g OH content (100%, calculated) 1.2% by weight Mean particle size 261 nm Viscosity 320 mPas pH 7.6

[0106] The dispersion remained stable for 10 months at 23 C.

Example 4 (Comparative)

[0107] 1000 g (4.50 mol) of isophorone diisocyanate (IPDI) was successively mixed at room temperature under dry nitrogen, and with stirring, with 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160 C. and a pressure of 0.3 mbar.

[0108] A light yellow uretdione polyisocyanate having a free NCO group content of 17.0% and a viscosity of more than 200 000 mPas was obtained.

[0109] 219 g of the above-described uretdione group-containing polyisocyanate, based on IPDI and having a free isocyanate group content of 17.0% and a calculated uretdione group content of 20.8%, was under dry nitrogen to 80 C. was weighed into a stirring apparatus under nitrogen and dissolved in 849 g of acetone at room temperature. 22.9 g of dimethylolpropionic acid and 2.11 g of tin(II) 2-ethylhexanoate were then metered into the homogeneous solution such that the exothermicity caused it to boil under reflux. The reaction mixture was kept under reflux until an NCO content of 2.2% was reached. 265.9 g of polyester 1 was then added and the reaction mixture was stirred under reflux until the NCO content of the reaction mixture had fallen to a value below 0.1%. cooled to 50 C. After cooling to 23 C., 16.8 g of dimethylethanolamine was added to the reaction mixture and stirring was continued for 30 min. Finally, 1451 g of distilled water was stirred in over a period of 15 min and the acetone was distilled off under reduced pressure. This yielded a dispersion with the following properties:

TABLE-US-00006 Solids content 37.62% by weight Mean particle size 91 nm Viscosity 30 mPas pH 8.0

[0110] After 6 months at 23 C. this dispersion had developed sediment and after 6 days of storage at 40 C. it had gelled completely.

Tests of Coating Properties

Examples 5-7 (Inventive)

[0111] Clear coatings were produced from the following compositions (all weights are in g):

TABLE-US-00007 TABLE 3 Example 5 6 7 Composition from example 1 10.00 Composition from example 2 10.00 Composition from example 3 10.00

[0112] The dispersions were mixed in a SpeedMixer at 2000 rpm for 1 minute and then applied to a metal coil test plate in a layer thickness of 180 m (wet) using a coating blade. The plates with the applied wet coatings were flashed off for 5 min at room temperature and then baked for 30 min at 180 C. and stored for 4 days at room temperature. The performance of the stored films was assessed (table 4).

TABLE-US-00008 TABLE 4 Example 5 6 7 Appearance of the coating satisfactory satisfactory satisfactory (visual examination) Film thickness (dry, ) 50 60 50 Pendulum hardness (s) 95 145 200 Resistance to xylene 3 3 3 (5 minutes) Deionized water (1 hour) 1 1 0

[0113] As can be seen from table 4, the uretdione-containing dispersions of the invention afford hard and resistant coatings.