Radiation curable aqueous composition for low gloss coatings

Abstract

A radiation curable aqueous coating composition having a 85 gloss of 60 upon drying comprising (A) 10 to 99 wt % of a polyurethane, (B) 1 to 90 wt % of a radiation curable component; (C) 0.1 to 10 wt % of an associative thickener; wherein at least 80 wt % of (A)+(B)+(C) has a particle size greater than 500 nm and wherein the CC bond concentration of the composition is 0.2 to 5.0 mmol per g of (A)+(B)+(C).

Claims

1. An ultraviolet (UV) radiation curable aqueous coating composition comprising: (A) 10 to 99 wt % of a polyurethane obtained by the reaction of components comprising: (i) 5 to 65 wt % of at least one organic polyisocyanate; (ii) 0.1 to 6 wt % of at least one polyol containing ionic or potentially ionic water-dispersing groups having a molecular weight in the range of from 100 up to 500 g/mol; (iii) 0 to 30 wt % of at least one isocyanate-reactive component containing water-dispersing groups and having a molecular weight in the range of from 500 to 6000 g/mol; (iv) 0 to 80 wt % of at least one isocyanate-reactive component containing radiation curable functional groups and having a molecular weight in the range of from 70 to 6000 g/mol; (v) 0 to 50 wt % of at least one component not comprised by (i), (ii), (iii), (iv) or (vi); (vi) 0 to 50 wt % of at least one active-hydrogen chain extending compound; where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %; and where the NCO:OH ratio is in the range of from 0.4:1.0 to 10.0:1.0; (B) 1 to 90 wt % of a radiation curable component carrying two or more radiation polymerizable ethylenically unsaturated bonds which are capable of crosslinking; and (C) 0.1 to 10 wt % of an associative thickener; wherein (A)+(B)+(C) add up to 100 wt %; and wherein at least 80 wt % of the polyurethane (A)+(B)+(C) has a particle size greater than 500 nm; and wherein the CC bond concentration of the composition is 0.2 to 5.0 mmol per g of (A)+(B)+(C) and wherein crosslinking of the aqueous coating composition is initiated by UV radiation, and wherein the coating composition exhibits an 85 gloss of <60 upon curing in the absence of a flattening agent.

2. The UV radiation curable aqueous coating composition according to claim 1, which comprises <5% by weight of flattening agent by weight of the polyurethane (A).

3. The UV radiation curable aqueous coating composition according to claim 1, wherein the 60 gloss of the aqueous coating composition upon curing is <40.

4. The UV radiation curable aqueous coating composition according to claim 1, wherein at least 85 wt % of (A)+(B)+(C) has a particle size greater than 500 nm and less than 25000 nm.

5. The UV radiation curable aqueous coating composition according to claim 1, wherein the mean particle size (D[0.1]) of (A)+(B)+(C) is greater than 500 nm and less than 90000 nm.

6. The UV radiation curable aqueous coating composition according to claim 1, wherein polyurethane (A) comprises 0.5 to 3.0 wt % of neutralised component (ii).

7. The UV radiation curable aqueous coating composition according to claim 1, wherein radiation curable component (B) is selected from the group consisting of epoxy (meth)acrylates; urethane (meth)acrylates; multi-functional (meth)acrylate monomers; UV-curable urethane dispersions, amine-(meth)acrylate adducts and mixtures thereof.

8. The UV radiation curable aqueous coating composition according claim 1, wherein the radiation curable component (B) comprises a low molecular weight radiation curable component (B1) in an amount of 1 to 30 wt %, based on the weight of components (A), (B1) and (C).

9. The UV radiation curable aqueous coating composition according to claim 1, wherein the radiation curable component (B) comprises a high molecular weight radiation curable component (B2) in an amount of 10 to 90 wt %, based on the weight of components (A), (B2) and (C).

10. The UV radiation curable aqueous coating composition according to claim 1, wherein the associative thickeners component (C) is selected from the group consisting of hydrophobic modified water soluble polymers, hydrophobically modified alkali soluble emulsions and mixtures thereof.

11. The UV radiation curable aqueous coating composition according to claim 1 additionally comprising a vinyl polymer.

12. The UV radiation curable aqueous coating composition according to claim 11, wherein the ratio of the vinyl polymer to polyurethane (A) is in the range of from 10:90 to 90:10.

13. A process for preparing the aqueous coating composition according to claim 1 comprising the following steps: a) reacting components (i) to (vi) to form an polyurethane (A); b) forming an aqueous dispersion of the polyurethane (A) in water; c) optionally neutralising the polyurethane (A); d) adding at least a radiation curable component (B); e) adding at least an associative thickener; f) optionally adding a radiation initiator; g) optionally adding vinyl monomer; wherein steps b), c), d), e), f) and g) may be in any order.

14. A coated substrate comprising a substrate and a cured coating on the substrate of a UV-cured coating composition having an 85 gloss of <60 in the absence of a flattening agent, wherein the cured coating is a UV-cured reaction product of an aqueous coating composition comprising: (A) 10 to 99 wt % of a polyurethane obtained by the reaction of components comprising: (i) 5 to 65 wt % of at least one organic polyisocyanate; (ii) 0.1 to 6 wt % of at least one polyol containing ionic or potentially ionic water-dispersing groups having a molecular weight in the range of from 100 up to 500 g/mol; (iii) 0 to 30 wt % of at least one isocyanate-reactive component containing water-dispersing groups and having a molecular weight in the range of from 500 to 6000 g/mol; (iv) 0 to 80 wt % of at least one isocyanate-reactive component containing radiation curable functional groups and having a molecular weight in the range of from 70 to 6000 g/mol; (v) 0 to 50 wt % of at least one component not comprised by (i), (ii), (iii), (iv) or (vi); (vi) 0 to 50 wt % of at least one active-hydrogen chain extending compound; where (i), (ii), (iii), (iv), (v) and (vi) add up to 100 wt %; and where the NCO:OH ratio is in the range of from 0.4:1.0 to 10.0:1.0; (B) 1 to 90 wt % of a radiation curable component carrying two or more radiation polymerizable ethylenically unsaturated bonds which are capable of crosslinking; and (C) 0.1 to 10 wt % of an associative thickener; wherein (A)+(B)+(C) add up to 100 wt %; and wherein at least 80 wt % of the polyurethane (A)+(B)+(C) has a particle size greater than 500 nm; and wherein the CC bond concentration of the composition is 0.2 to 5.0 mmol per g of (A)+(B)+(C).

15. The coated substrate as in claim 14, wherein the cured composition has a 60 gloss of <40.

16. A method of forming a coated substrate comprising coating the UV radiation curable aqueous coating composition according to claim 1 onto a substrate, and thereafter subjecting the coating on the substrate to UV radiation to cure the coating composition.

Description

EXAMPLES

(1) 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.

(2) UV Curing:

(3) Examples that were UV cured were cured in the following way: Coating layer thickness: 120 m wet on Leneta UV curing: 400 mJ/cm.sup.3, 240 nm/80 Watt after 2 minutes flash off at 120 C. Photoinitiator: 3 wt % Esacure KIP100F/IPA (2:5) on total composition
Gloss Measurements

(4) BYK Gardner micro-TRI-gloss 20-60-85 glossmeter in accordance with ASTM D523-89.

(5) Knig Hardness

(6) Knig Hardness as used herein is a standard measure of hardness, being a determination of how the viscoelastic properties of a film formed from the dispersion slows down a swinging motion deforming the surface of the film and is measured according to DIN 53157 using an Erichsen hardness tester.

(7) Chemical Resistances:

(8) Drops of the various testing liquids (water, 50% ethanol in water, coffee and Cif a commonly used Dutch detergent) were placed on the films and covered with a watch glass. The liquids were removed after 1 hour at room temperature and the damage to the coating was assessed immediately and after four hours recovery. 0 means that the coating is dissolved, 5 means that the coating is not affected at all.

(9) Resistance to MEK or Ethanol

(10) MEK (methyl ethyl ketone) or ethanol rub tests (being a measure of the resistance of the coating to the solvent) were performed on the coated glass plates using cotton wool soaked with the solvent which was rubbed over the surface of the coating, the number of rubs before failure being listed.

(11) The results of the tests are shown in Tables 2, 3, 5, 6, 8 and 9 below.

Examples 1, 2

UV Curable Dispersion

And Comparative Example 1

(12) TABLE-US-00001 TABLE 1 NeoRez R-1000 ethoxylated NeoRad R- UV- CC (grams) TMPTA (grams) 440 (grams) cured mol/g Comparative 100 0 0 No 0 Example 1 Example 1 90.9 9.1 0 Yes 0.64 Example 2 55.6 0 44.4 Yes 0.58

(13) TABLE-US-00002 TABLE 2 Gloss KH MEK 60 85 (s) rubs Comparative Example 1 1.4 51.1 49 10 Example 1 4.4 36.7 42 81 Example 2 0.6 22.6 70 100

(14) TABLE-US-00003 TABLE 3 Stain resistances Water Ethanol/water Cif Coffee Tea Total Comparative 4 2 4 2 2 14 Example 1 Example 1 5 4 4 2 3 18 Example 2 4 4 4 3 4 19

Comparative Example 3 and Example 4

UV Curable Dispersion

(15) A 2000 cm.sup.3 flask equipped with a thermometer and overhead stirrer was charged with IPDI (110.78 g) 9.0, DMPA (9.0 g), DC1248 (27.0 g), polyTHF 2000 (351.0 g), 2,6-di-tert-butyl-4-methyl phenol (0.23 g), ethoxylated TMPTA (48.0 g) and 0.1 tin octoate (0.1 g) and slowly heated to 85 C. and kept at this temperature for 2 hours. Subsequently Desmodur N3200 (54.0 g) was added and the measured NCO % of the resultant isocyanate terminated prepolymer was 5.39%.

(16) A dispersion of the resultant isocyanate-terminated prepolymer was made by feeding this prepolymer (424.25 g), neutralised with TEA (4.8 g), to water (862.5 g) containing Nopco DSX 1514 (33.9 g), Disponil AFX 3070 (9.1 g), Tegofoamex 805 (4.2 g). After the prepolymer was fed to the water phase hydrazine (49.35 g, 15.2 wt %) was added.

(17) The final solids content of the resulting UV curable polyurethane dispersion (comparative example 3) was 32%, the Brookfield viscosity was 412 mPa.Math.s, the acid value was 6 mg KOH/g and the pH was 7.3.

Example 4

(18) Example 4 was prepared by adding NeoRad R-440 to the dispersion of comparative example 3 (see table 4 below). Example 4 was UV cured at 120 m wet films, flash off time 10 minutes at 60 C.

(19) TABLE-US-00004 TABLE 4 Example 3 NeoRad R-440 UV- CC (grams) (grams) cured mol/g Comparative Example 3 100 0 No 0.18 Example 4 80 20 Yes 0.25

(20) TABLE-US-00005 TABLE 5 Gloss KH MEK Ethanol 60 85 (s) rubs Rubs Comparative Example 3 0.8 12.8 31 7 7 Example 4 3 7.8 45 101 131

(21) TABLE-US-00006 TABLE 6 Stain resistances Water Ethanol/water Cif Coffee Tea Total Comparative 3 0 3 2 2 10 Example 3 Example 4 3 4 4 3 4 18

Example 5

UV Curable Polyurethane Dispersion

(22) A 2000 cm.sup.3 flask equipped with a thermometer and overhead stirrer was charged with IPDI (124.4 g), DMPA (9.0 g), DC1248 (27.0 g), polyTHF 2000 (312.7 g), Bisphenol A diepoxy diacrylate (24.9 g), ethoxylated TMPTA (48.1 g) and Tin octoate (0.1 g) and slowly heated to 85 C. and kept at this temperature for 2 hours. Subsequently Desmodur N3200 (54.0 g) was added and the measured NCO % of the resultant isocyanate terminated prepolymer was 5.70%.

(23) A dispersion of the resultant isocyanate-terminated prepolymer was made by feeding the prepolymer (424.25 g), neutralised with TEA (3.85 g), to water (863.4 g) containing Nopco DSX 1514 (33.9 g), Disponil AFX 3070 (9.1 g) and Tegofoamex 805 (4.2 g). After the prepolymer was fed to the water phase hydrazine (51.52 g, 15.2 wt %) was added.

(24) The final solids content of the resulting UV curable polyurethane dispersion was 32%, the Brookfield viscosity was 457 mPa.Math.s, the acid value was 6 mg KOH/g, and pH was 7.1.

Example 5

(25) Example 5 was prepared by adding NeoRad R-440 to the dispersion (see table 7 below)

(26) TABLE-US-00007 TABLE 7 Example 5 UV- CC (grams) NeoRad R-440 (grams) cured mol/g Example 5 70 30 Yes 0.32

(27) TABLE-US-00008 TABLE 8 Gloss KH MEK Ethanol 60 85 (s) rubs Rubs Example 5 0.6 1.4 46 200 93

(28) TABLE-US-00009 TABLE 9 Stain resistances Water Ethanol/water Cif Coffee Tea Total Example 5 3 4 4 3 4 18
Particle Size Measurements

(29) A Mastersizer 2000 from Malvern, which measures the particle size and particle size distribution by laser diffraction, was used to measure the particle size of the whole composition, i.e. (A)+(B)+(C) and the results are shown in Table 10 below.

(30) The technique of laser diffraction is based on the principle that particles passing through a laser beam will scatter light at an angle that is directly related to their size. The observed scattering intensity is also dependent on particle sizes. Large particles scatter light at narrow angles with high intensity, whereas small particles scatter light at wider angles but with low intensity.

(31) TABLE-US-00010 TABLE 10 Particle size X (m) D(0.1) D(0.5) D(0.9) Comparative Example 1 1.605 3.122 7.671 Example 1 1.633 3.094 6.621 Example 2 1.541 2.954 6.642 Example 4 1.304 9.108 19.094 Example 5 1.598 9.553 22.215 D(0.1) = first 10% of the particle size distribution has a mean particle size < X D(0.5) = first 50% of the particle size distribution has a mean particle size < X D(0.9) = first 90% of the particle size distribution has a mean particle size < X