AQUEOUS COATING COMPOSITION

Abstract

The present invention relates to a radiation-curable aqueous coating composition comprising a polyurethane A comprising as building blocks at least: (a) a polyisocyanate(s) containing at least two cyclic groups, (b) a non-cyclic aliphatic diisocyanate(s) whereby the non-cyclic aliphatic group connecting the two isocyanate groups has from 4 to 36 carbon atoms, and (c) a component(s) containing an isocyanate-reactive group(s), whereby the summed amount of (a) and (b) is 10 to 60 wt. %, relative to the total weight amount of components used to prepare the polyurethane A; and optionally radiation-curable diluent; whereby the weight ratio between (a) and (b) is in the range from 50:50 to 99:1; and whereby the ethylenically unsaturated bond concentration of the coating composition is in the range from 0.5 to 6 milliequivalents per g of polyurethane A and radiation-curable diluent.

Claims

1. A radiation-curable aqueous coating composition comprising a polyurethane A comprising as building blocks at least: (a) a polyisocyanate(s) containing at least two cyclic groups, (b) a non-cyclic aliphatic diisocyanate(s) whereby the non-cyclic aliphatic group connecting the two isocyanate groups has from 4 to 36 carbon atoms, and (c) a component(s) containing an isocyanate-reactive group(s), whereby the summed amount of (a) and (b) is 10 to 60 wt. %, relative to the total weight amount of components used to prepare the polyurethane A; and whereby the weight ratio between (a) and (b) is in the range from 50:50 to 99:1; and the composition optionally further comprises radiation-curable diluent; whereby the ethylenically unsaturated bond concentration of the coating composition is in the range from 0.5 to 6 milliequivalents per g of polyurethane A and radiation-curable diluent.

2. The aqueous coating composition according to claim 1, wherein the weight ratio of (a) to (b) is from 60:40 to 95:5, preferably from to 65:35 to 90:10.

3. The aqueous coating composition according to claim 1, wherein component (a) is a polyisocyanate(s) containing at least two cycloaliphatic groups.

4. The aqueous coating composition according to claim 1, wherein component (a) is H12MDI (CAS number 5124-30-1).

5. The aqueous coating composition according to claim 1, wherein component (b) is a non-cyclic aliphatic C4-C9 diisocyanate(s), preferably C4-C8 diisocyanate(s).

6. The aqueous coating composition according to claim 1, wherein component (b) is 1,6-diisocyanatohexane (CAS number 822-06-0)).

7. The aqueous coating composition according to claim 1, wherein the ethylenically unsaturated bond concentration of the coating composition is introduced in the coating composition by the presence of (meth)acryloyl groups in the polyurethane (A) and/or the presence of radiation-curable diluent.

8. The aqueous coating composition according to claim 1, wherein the preparation of the polyurethane A is effected by using isocyanate-reactive component(s) containing at least one (meth)acryloyl group per molecule (component (c)(ii)).

9. The aqueous coating composition according to claim 1, wherein the polyurethane A is prepared by preparing a neutralized isocyanate-terminated polyurethane pre-polymer which is dispersed in water and which dispersed pre-polymer is subsequently chain-extended with a chain-extending compound selected from the group consisting of hydrazine, a primary diamine(s), a secondary diamine(s), a compound(s) containing a primary amino group and a secondary amino group, and any mixture thereof.

10. The aqueous coating composition according to claim 1, wherein the acid value of the polyurethane A is in the range from 4 to 60 mg KOH/g polyurethane A.

11. The aqueous coating composition according to claim 1, wherein the coating composition has a minimum film formation temperature of lower than 35 C. in the substantial absence of coalescent.

12. The aqueous coating composition according to claim 1, wherein the coating composition has a minimum film formation temperature of lower than 35 C. in the substantial absence of radiation-curable diluent.

13. The aqueous coating composition according to claim 1, wherein the amount of 1-methyl-2-pyrrolidinone in the aqueous coating composition is less than 3 wt. % by weight of solids content of the coating composition, preferably less than 1 wt. %, more preferably less than 0.5 wt. % and even more preferably is 0 wt. %.

14. The aqueous coating composition according to claim 1, wherein the coating composition contains tin in amount of at most 2 ppm.

15. The aqueous coating composition according to claim 1, wherein the coating composition preferably contains tertiary amines in amount of at most 1.5 wt. %.

16. The aqueous coating composition according to claim 1 wherein the polyurethane A is present in the aqueous coating composition in an amount of from 20 to 55 wt. % (relative to the total weight of aqueous coating composition).

17. The aqueous coating composition according to claim 1 wherein the aqueous coating composition comprises a photo-initiator.

18. A process for preparing an aqueous coating composition according to claim 1 comprising the following steps I. preparing an isocyanate-terminated polyurethane pre-polymer by reacting at least components (a), (b), (c): (a) a polyisocyanate(s) containing at least two cyclic groups, (b) a non-cyclic aliphatic diisocyanate(s) whereby the non-cyclic aliphatic group connecting the two isocyanate groups has from 4 to 36 carbon atoms, and (c) a component(s) containing at least one isocyanate-reactive group comprising (c)(i) isocyanate-reactive component(s) containing ionic and/or potentially ionic water-dispersing groups, and/or (c)(ii) isocyanate-reactive component(s) containing at least one (meth)acryloyl group per molecule, and/or (c)(iii) isocyanate-reactive component(s) not comprised by (c)(i) and (c)(ii); whereby the summed amount of (a) and (b) is 10 to 60 wt. %, relative to the total weight amount of components used to prepare the polyurethane A; and whereby the weight ratio between (a) and (b) is in the range from 50:50 to 99:1; whereby preferably diluent is added in step I; II. either blending the isocyanate-terminated polyurethane pre-polymer with an aqueous phase comprising neutralizing agent and optionally further comprising chain extending compound or either neutralizing the isocyanate-terminated polyurethane pre-polymer by adding neutralizing agent to the isocyanate-terminated polyurethane pre-polymer and subsequently (i) adding the neutralized isocyanate-terminated polyurethane prepolymer to water optionally comprising further chain extending compound or (ii) adding water optionally comprising further chain extending compound to the neutralized isocyanate-terminated polyurethane prepolymer; and whereby the process comprises feeding to the reactor, at the start of the reaction to prepare the isocyanate-terminated polyurethane pre-polymer, either (A) components (a) and (b) and at least one of the components (c)(i), (c)(ii) and (c)(iii), either (B) component (a) and at least two of the components (b), (c)(i), (c)(ii) and (c)(iii) or either (C) component (b) and at least two of the components (a), (c)(i), (c)(ii) and (c)(iii); and whereby the preparation of the polyurethane A is effected in the presence of <3 wt. % of 1-methyl-2-pyrrolidone by weight of the polyurethane A.

19. Process according to claim 18, wherein the chain-extending of the isocyanate-terminated polyurethane pre-polymer is effected with hydrazine, a primary diamine(s), a secondary diamine(s), a compound(s) containing a primary amino group and a secondary amino group, and any mixture thereof.

20. A substrate having a coating obtained by (i) applying an aqueous coating composition according to claim 1 to a substrate and (ii) physically drying and curing by radiation (preferably UV-radiation) of the aqueous coating composition to obtain a coating.

21. A substrate according to claim 20, wherein the substrate is selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, packaging film and any combination thereof.

22. A substrate according to claim 20, wherein the substrate is selected from the group consisting of wood, PVC, linoleum and any combination thereof.

23. A method for coating a substrate selected from the group consisting of wood, metal, plastic, linoleum, concrete, glass, packaging film and any combination thereof; where the method comprises (i) applying an aqueous coating composition according to claim 1 to the substrate; and (ii) physically drying and curing by radiation (preferably UV radiation) of the aqueous coating composition to obtain a coating.

Description

EXAMPLES

[0089] The following examples were prepared and coatings were obtained and tested. The compositions of the examples and results are as shown in the tables below.

Minimum Film Formation Temperature MFFT

[0090] The MFFT is the lowest temperature at which a polymer or solid portion of an aqueous polymer dispersion (also called latex or emulsion) self-coalesces in the semi-dry state to form a continuous polymer film, which in turn acts as a binder for the rest of the solids in the paint film. At temperatures at and above the MFFT of the polymer a continuous film is formed. At temperatures below its MFFT the polymer cannot coalesce to form a continuous film and thus cannot bind together itself (or any pigments and extenders that may be present) and a cracked, crazed or powdery layer results. MFFT is measured on a Rhopoint MFFT-90 Minimum Film Forming Temperature Instrument using a wet film thickness of 90 m.

[0091] Viscosity was determined with a Brookfield DV-I viscometer (spindle S61, 60 rpm, 23 C.)

Particle Size

[0092] The particle size was determined by photon correlation spectroscopy using a Malvern Zetasizer Nano zs. Samples are diluted until a concentration of approximately 0.1 g disp/liter.

Solids Content

[0093] The solids content of the dispersion was determined on a Mettler Toledo HB43-S Compact Halogen Moisture Analyzer. At the start of the measurement the Moisture Analyzer determines the weight of the sample, the sample is then heated to 130 C. by the integral halogen heating module and the volatile compounds vaporizes. During the drying process the instrument continually measures the weight of the sample. Once drying has been completed, the solids content of the sample is displayed as the final result.

Preparation of Radiation Curable Polyurethane Dispersion

Example 1

[0094] A 2000 cm.sup.3 flask equipped with a thermometer and overhead stirrer was charged with components DMPA (20.3 g), Priplast3192 (156.3 g), Agisyn1010 (112.5 g), H12MDI (128.7 g), HDI (32.2 g), acetone (250.0 g) and BHT (0.8 g). The reaction was heated to 50 C. and 0.16 g of Dabco T-9 was added. The reaction was kept at 60 C. until full conversion. The course of the reaction was monitored by NCO titration. When the NCO content of the resultant isocyanate-terminated prepolymer was 4.0% on solids (theoretically 4.2%), the prepolymer was cooled down to 35 C. and TEA was added (14.5 g). The NCO/OH molar ratio is 1.5.

[0095] A dispersion of the resultant isocyanate-terminated prepolymer was made by adding deionized water (1150 g) to the prepolymer mixture. After dispersing a mixture of EDA (10.3 g) and water (30 g) was added. Subsequently the acetone was removed from the dispersion by distillation under vacuum. The acryloyl concentration of the resulting dispersion was 1 meq/g solids.

[0096] The specifications of the resultant polyurethane dispersion are given in Table 2.

Examples 2, 4-9 and Comparative Example a and E

[0097] In Examples 2, 4-9 and Comparative Examples A-E the process described in Example 1 was repeated except that different quantities and different constituents were used such that the polyurethane prepolymer had a specific NCO/OH molar ratio (1.5) and hence the dispersability of the polyurethane prepolymer was not affected by using polyurethane prepolymer with different NCO/OH molar ratio. The amount of EDA was calculated on the experimental NCO content at the end of the prepolymer preparation and was kept constant (0.8 stoichiometric amount of EDA on NCO was added) for Examples 2, 4, 6-9 and Comparative Examples A-E. For Example 5, 0.7 stoichiometric amount of EDA on NCO was added. These quantities and components are specified below in Table 1. Unless specified otherwise, the amounts of the different components are expressed in grams. The specifications of the resulting compositions are represented in Tables 2, the film properties in Table 5.

Example 3

[0098] A 1000 cm.sup.3 flask equipped with a thermometer and overhead stirrer was charged with components DMPA (20.0 g), pTHF1000 (136.6 g), H12MDI (138.8 g), HDI (24.5 g), Agisyn2884 (80.0 g), Agisyn 2811 (100 g) and BHT (0.6 g). The reaction was heated to 90 C. and 0.16 g of Dabco T-9 was added. The reaction was kept at 90 C. until full conversion. The course of the reaction was monitored by NCO titration. When the NCO content of the resultant isocyanate-terminated prepolymer was 4.23% (theoretically 5.0%), the prepolymer was cooled down to 80 C. and TEA was added (14.3 g).

[0099] A dispersion of the resultant isocyanate-terminated prepolymer was made by feeding 414 gram of the prepolymer mixture to deionized water (596 g) over the course of 45 minutes.

[0100] After dispersing a mixture of hydrazine (16% solids in water, 36.3 g) and water (20 g) was added. The acryloyl concentration of the resulting dispersion was 3.7 meq/g solids.

[0101] The specifications of the resultant polyurethane dispersion are given in Table 2.

TABLE-US-00001 TABLE 1 Compositions Comp. Comp. Compounds Ex A Ex. 2 Ex B Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 DMPA 20.3 20.3 20.3 20.3 20.3 22.5 22.5 20.3 Priplast 3192 141.5 pTHF1000 132.7 121.6 126.5 132.5 103.7 Desmophen 145.8 C2200 PEC 205 143.6 H12MDI 175.8 156.9 195.7 162.2 157.0 179.6 143.8 147.6 TMDI 28.6 HDI 27.7 27.7 31.7 25.4 26.0 AgiSyn1010 112.5 112.5 112.5 112.5 112.5 112.5 112.5 Laromer LR- 112.5 8765 Dabco T-9 0.16 0.16 0.16 0.16 0.24 0.16 0.16 Bismuth 0.24 Neodecanoate Acetone 200 150 150 150 150 150 150 150 BHT 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 NCO % 3.6 4.5 4.1 5.3 4.7 5.5 4.1 4.7 prepolymer on solids TEA 14.5 14.5 14.5 14.5 14.4 14.4 14.5 KOH (15% in 56.5 water) Water 885 885 885 885 902 927 902 956 EDA 9.3 11.6 10.4 13.6 10.6 14.1 10.6 12.1 ADH 15.5 Comp. Comp. Comp. Compounds Ex 9 Ex. C Ex D Ex E DMPA 20.3 20.3 20.3 20.3 Priplast 3192 106.8 94.4 119.3 125.9 H12MDI 152.1 191.3 IPDI 166.5 135.9 HDI 26.9 24.0 AgiSyn1010 144.0 144.0 144.0 144.0 Bismuth 0.24 0.24 0.24 0.24 Neodecanoate Acetone 150 150 150 250 BHT 0.8 0.8 0.8 0.8 NCO % 4.9 4.8 5.2 4.6 prepolymer on solids TEA 10.7 14.5 14.5 14.5 Water 885 885 885 885 EDA 12.6 12.3 13.3 11.8 Note: The amount of acetone used in Example 1 differs from amount used in Comp Ex A. However, since acetone is distilled off, the amount of acetone does not influence the performance of the coating composition.

TABLE-US-00002 TABLE 2 Specifications Example Comp. Comp. Ex. 1 Ex. A Ex. 2 Ex B Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 NCO/OH 1.5 1.5 1.5 1.5 1.8 1.5 1.5 1.5 1.5 1.5 molar ratio prepolymer CC theor on 1.0 1.0 1.0 1.0 3.7 1.0 1.0 1.4 1.0 1.0 prepolymer solids [meq/g solids] Solids (%) 28 32 33 33 35 34 30 32 36 32 pH 7.7 7.9 7.1 7.5 7.1 7.1 8.2 7.8 7.1 6.9 Viscosity * 97 50 17 18 30 26 410 185 37 135 Particle size 98 32 53 63 78 62 167 43 63 99 (nm) MFFT ( C.) 17 43 7 28 <5 14 <5 <5 31 37 Example Comp. Comp. Comp. Ex. 9 Ex C Ex. D Ex. E NCO/OH 1.5 1.5 1.5 1.5 molar ratio prepolymer CC theor on 1.3 1.3 1.3 1.3 prepolymer solids [meq/g solids] Solids (%) 33.1 35.3 33.8 34.9 pH 7.4 7.0 8.2 8.2 Viscosity * 23 24 18 35 Particle size 74 46 96 93 (nm) MFFT ( C.) 44 60 46 39 * A Brookfield viscosity at 25 C. (mPa .Math. s)

[0102] Comparing Ex 9 with Comp Ex C and comparing Comp Ex D with Corn Ex E shows that the additional use of HDI results in a MFFT reduction and that the MFFT reduction is much more pronounced when HDI is used in combination with H12MDI compared to when HDI is used in combination with IPDI.

[0103] To 30 g of the final dispersions of Examples 1-2 and Comparative Examples A and B different amounts of coalescent, Dowanol DPM (DDPM) or Agisyn 2836 were added in amounts of respectively 0.3 [1%], 0.6 [2%], 1.2 [4%] grams. The radiation curable binders according to the invention show a low minimal film formation temperature and coalescent demand is low as demonstrated in Table 3 & 4.

TABLE-US-00003 TABLE 3 MFFT [ C.] MFFT [ C.] MFFT [ C.] MFFT [ C.] Sample [0% DDPM] [1% DDPM] [2% DDPM] [4% DDPM] Ex. 1 17 <5 Comp. 43 37 27* 22* Ex. A Ex. 2 7 <5 Comp. 28 26 25 20 Ex. B Note: *= BYK-346 (from BYK) added for good levelling

TABLE-US-00004 TABLE 4 MFFT [ C.] MFFT [ C.] MFFT [ C.] MFFT [ C.] MFFT [ C.] Sample MFFT [ C.] [1% Agisyn 2836] [2% Agisyn 2836] [3% Agisyn 2836] [5% Agisyn 2836] [7% Agisyn 2836] Ex. 1 17 16 9 <5 Comp. Ex. A 43 43 37 33 22 19 Ex. 2 7 <5 Comp. Ex. B 28 30* 26* 19* 16** Note: *= BYK-346 (from BYK) added for good levelling

[0104] The radiation curable binders prepared in Examples 1-9 and Comparative Examples A-E were formulated with 2% Irgacure 500 (relative to dispersion), available from BASF. If required BYK-346 was added to improve substrate wetting. The formulated compositions (see Table 5 for amounts of Dowanol DPM) were cast onto a Leneta test chart using a wire rod at a wet film thickness of 125 micron. Coalescent was added to the dispersion in such an amount that a continuous defect-free film could be formed at the applied temperature conditions in order to be able to determine the stain resistances of the cured coating. The cast films were then allowed to dry at room temperature for 10 minutes, followed by 20 minutes at 50 C. Then the films were cured by UV radiation using a Mercury lamp [500 mJ/cm.sup.2, 80 W]. The panels were stored for 4-6 hours at room temperature before aging for 16 hours at 50 C. in an oven with air flow (=1.2 m/s). The coatings were allowed to cool to room temperature for 1 hour. The stain resistance of the coated cards towards the following stains were then assessed: ammonia, water, red wine, ethanol (48%), coffee, tea and mustard. In all cases, a spot (1 cm.sup.2) of the respective stain was placed on the coating and covered with a piece of filter paper and a watch glass. After the test periods, the spot was gently wiped off with a tissue and the film was assessed for its integrity. This was rated between 0 to 5, where:

Grade 5No change; Test area indistinguishable from adjacent surrounding area.
Grade 4Minor change; Test area distinguishable from adjacent surrounding area, only when the light source is mirrored on the test surface and is reflected towards the observer's eye, e. g. discoloration, change in gloss and color. No change in the surface structure, e.g. swelling, fiber raising, cracking, blistering.
Grade 3Moderate change; Test area distinguishable from adjacent surrounding area, visible in several viewing directions, e. g. discoloration, change in gloss and colour. No change in the surface structure, e.g. swelling, fibre raising, cracking, blistering.
Grade 2Significant change; Test area clearly distinguishable from adjacent surrounding area, visible in several viewing directions, e. g. discoloration, change in gloss and colour.
Grade 1Strong change; Test area clearly distinguishable from adjacent surrounding area, visible in several viewing directions, e. g. discoloration, change in gloss and colour, and/or the surface material being totally or partially removed.

[0105] Stain resistances of the coatings of the Examples versus of the Comparative Examples clearly demonstrate that with low amount of coalescent sufficient and mostly similar level of stain resistances can be achieved. Lowering the amount of Dowanol DPM of Comparative Example A-E resulted in that no continuous, defect-free film could be obtained and hence stain resistances of the coating were very poor.

TABLE-US-00005 TABLE 5 Formulation and resulting stain resistances Comp. Comp. Ex. 1 A Ex. 2 B Ex. 3 Ex. 4 Ex. 5 WFT m 125 125 125 125 125 125 125 Dispersion g 30 30 30 30 30 30 30 Irg 500 g 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Water g 0 2 3 3 0 0 0 Dowanol DPM g 0.3 1.5 0.3 0.6 0 1.2 0 BYK 346 g 0 0 0.06 0.08 0 0 0 Solid content % 30 30 30 30 35 33 29 formulation Stains Ammonia 2 min 5 5 5 5 5 5 5 Ethanol 48% 1 h 5 5 5 5 5 5 5 Red Wine 6 h 4 4 3 4 5 5 5 Mustard 6 h 1 3 1 2 3 3 3 Coffee 1 h 5 5 5 5 5 5 5 Coffee 16 h 4 4 3 3 5 3-4 3-4 Water 16 h 5 5 5 5 5 5 5 Water 24 h 5 5 5 5 5 5 5 Tea 16 h 5 5 5 5 5 5 5 Comp. Comp. Comp. Ex. 6 Ex. 7 Ex. 8 Ex. 9 C D E WFT m 125 125 125 125 125 125 125 Dispersion g 30 30 30 30 30 30 30 Irg 500 g 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Water g 0 4 0 0 0 0 0 Dowanol DPM g 0.6 1.2 1.5 2.7 3.0 2.1 2.1 BYK 346 g 0 0.08 0 0.2 0.2 0.16 0.04 Solid content % 30 31 31 30 31 31 32 formulation Stains Ammonia 2 min 5 5 5 5 5 5 5 Ethanol 48% 1 h 5 5 5 5 5 5 5 Red Wine 6 h 5 5 5 5 5 5 5 Mustard 6 h 2 4 4 5 5 3 2 Coffee 1 h 5 5 5 5 5 5 5 Coffee 16 h 3 5 3-4 5 5 4 3 Water 16 h 5 5 5 5 5 5 5 Water 24 h 5 5 5 5 5 5 5 Tea 16 h 5 5 5 5 5 5 5

[0106] The results as shown in Table 2 and 5 show that the use of H12MDI in combination with HDI results in that a MFFT comparable to when IPDI is used can be obtained (i.e. 44 C. vs 46 C., see Table 3, Ex. 9 and Comp Ex D), while the stain resistances (ammonia, ethanol, red wine, water and tea) of a coating obtained with a composition comprising a polyurethane comprising H12MDI and HDI as building blocks compared to a coating obtained with a composition comprising a polyurethane comprising IPDI as building block are at the same level and the resistances against mustard and prolonged exposure to coffee (16 h) are even improved (see Table 5, Ex. 9 and Comp Ex D).