Aqueous radiation curable polyurethane compositions

Abstract

The invention relates to radiation-curable aqueous composition comprising an (meth)acrylated polyurethane pre-polymer obtained from the reaction of a polyisocyanate, optionally a polyol, at least one hydrophilic compound containing at least one reactive group capable to react with isocyanate groups and which is capable to render the polyurethane pre-polymer dispersible in aqueous medium either directly or after the reaction with a neutralizing agent to provide a salt, an (meth)acrylated compound containing at least two reactive groups capable to react with isocyanate groups and an (meth)acrylated compound containing essentially one reactive group capable to react with isocyanate groups, said composition comprising an amount of (meth)acrylated and polymerizable ethylenically unsaturated groups of at least 3 meq per g.

Claims

1. An aqueous radiation-curable composition comprising at least one (meth)acrylated polyurethane pre-polymer (A) obtained from the reaction of: at least one polyisocyanate compound (i), wherein the amount of the at least one polyisocyanate compound (i) is in the range of from 10 to 60 wt % of the polyurethane prepolymer (A), optionally, at least one polyol (ii), at least one hydrophilic compound (iii) containing at least one reactive group capable to react with isocyanate groups and which is capable to render the polyurethane pre-polymer dispersible in aqueous medium either directly or after the reaction with a neutralizing agent to provide a salt, at least one (meth)acrylated compound (iv) containing at least two reactive groups capable to react with isocyanate groups, wherein the amount of the at least one (meth)acrylated compound (iv) is in the range of from 5 to 30 wt % of the polyurethane prepolymer (A), at least one (meth)acrylated compound (v) containing essentially at least two (meth)acrylates and only one reactive group capable to react with isocyanate groups selected from poly(meth)acryloyl mono-hydroxy compounds, wherein the amount of the (meth)acrylated compound (v) is in the range of from 10 to 60% by weight of the polyurethane prepolymer (A), and at least one ethylenically unsaturated compound (B), wherein said composition comprises a total amount of (meth)acrylated and, optionally, polymerizable ethylenically unsaturated groups of at least 3 meq per total weight in g of (i), (ii), (iii), (iv), (v) and (B).

2. The radiation curable composition according to claim 1 obtained by a process comprising a first step comprising the reaction of compounds (i), (iii) and (iv), and optionally compound (ii), a second step comprising the reaction of the product of the first step with a compound (v) so that an end-capped (meth)acrylated polyurethane pre-polymer is obtained; the dispersing of said end-capped (meth)acrylated polyurethane pre-polymer obtained after the second step in an aqueous medium, an optional step comprising the reaction with a neutralizing agent in order to convert the hydrophilic groups provided by compound (iii) into anionic salts, and a step comprising the addition of an ethylenically unsaturated compound (B).

3. The radiation curable composition according to claim 1, wherein the polyisocyanate (i) is selected from aliphatic and cycloaliphatic polyisocyanates.

4. The radiation curable composition according to claim 1, wherein the polyol (ii) is a polyester polyol having a number average molecular weight of at least 400.

5. The radiation curable composition according to claim 1, wherein the amount of the polyol (ii) is in the range of from 2 to 50 wt % of the polyurethane prepolymer (A).

6. The radiation curable composition according to claim 1, wherein the hydrophilic compound (iii) is selected from hydroxycarboxylic acids represented by the general formula (HO)xR(COOH)y, wherein R represents a straight or branched hydrocarbon residue having 1 to 12 carbon atoms, and x and y independently are integers from 1 to 3.

7. The radiation curable composition according to claim 1, wherein the amount of the hydrophilic compound (iii) is in the range of from 1 to 25 wt % of the polyurethane prepolymer (A).

8. The radiation curable composition according to claim 1, wherein the (meth)acrylated compound (iv) is selected from the reaction products of diglycidyl compounds with (meth)acrylic acid.

9. The radiation curable composition according to claim 8, wherein the (meth)acrylated compound (iv) is the diacrylate ester of bisphenol A diglycidylether.

10. The radiation curable composition according to claim 1, wherein the (meth)acrylated compound (v) is selected from the esterification products of aliphatic and/or aromatic polyols with (meth)acrylic acid having a residual average hydroxyl functionality of about 1.

11. The radiation curable composition according to claim 1, comprising an ethylenically unsaturated compound (B) selected from the esterification products of (meth)acrylic acid with tri-, tetra-, penta and/or hexahydric polyols and their mixtures.

12. The radiation curable composition according to claim 1, comprising the ethylenically unsaturated compound (B) in an amount in the range of between 5 and 50% by weight relative to the total amount of pre-polymer (A).

13. The radiation curable composition according to claim 1, further comprising non-ethylenically unsaturated compounds (C).

14. The radiation curable composition according to claim 13, wherein the amount of the non-ethylenically unsaturated compounds (C) in the range of between 0 and 30% by weight relative to the total amount of pre-polymer (A) and optionally compound (B).

15. The radiation curable composition according to claim 1 wherein said composition comprises a total amount of (meth)acrylated and, optionally, polymerizable ethylenically unsaturated groups of at least 3.5 meq per total weight in g of (i), (ii), (iii), (iv), (v) and (B).

16. The radiation curable composition according to claim 1 wherein said composition comprises a total amount of (meth)acrylated and, optionally, polymerizable ethylenically unsaturated groups of at least 4 meq per total weight in g of (i), (ii), (iii), (iv), (v) and (B).

17. The radiation curable composition according to claim 1 wherein the total amount of (meth)acrylated groups in the pre-polymer (A) is at least 3.0 meq, at least 3.5 meq of (meth)acrylated groups per total weight in g of compounds (i), (ii), (iii), (iv) and (v).

18. The radiation curable composition according to claim 2 which is obtained by a process further comprising a step wherein the (meth)acrylated polyurethane pre-polymer obtained after the second step is reacted with a chain extender (vii), which is an amine.

19. The radiation curable composition according to claim 1 wherein the (meth)acrylated polyurethane pre-polymer (A) is further reacted with at least one chain extender (vii) comprising active amino groups capable of making a chain extension of the remaining isocyanate end-groups of the pre-polymer.

20. The radiation curable composition according to claim 2 obtained by a process further comprising a step of reacting the (meth)acrylated polyurethane pre-polymer obtained after the second step with a chain extender (vii).

21. The radiation curable composition according to claim 1 wherein the (meth)acrylated polyurethane pre-polymer (A) is not further reacted with a chain extender (vii).

Description

EXAMPLE 1

(1) A double-wall glass reactor equipped with a mechanical stirrer, a thermocouple, a vapor condenser and a dropping funnel was charged with 45.3 g of a polyester polyol having an average molecular weight of 670, an hydroxyl number of 167 mg KOH/g and obtained from the polycondensation of neopentylglycol and a mixture of adipic acid and isophtalic acid in a 1:1 weight ratio, 109.2 g of the acrylic acid adduct of bisphenol A diglycidyl ether (BPAAA), 34.3 g of dimethylol propionic acid (DMPA), 231.3 g of 1,1-methylene bis(4-isocyanato cyclohexane)(H12MDI), 279 g of acetone, 3.1 g of TTNUVIN622 and 0.6 g of dibutyltinlaurate as a 10% solution in acetone. The reaction mixture was heated until 60 C. under stirring and kept under reflux until the isocyanate content reached a value of 1.09 mcq/g. Then 0.4 g of 4-methoxyphenol dissolved in 207.1 g of DTMPTA, a product comprising a mixture of ditrimethylolpropane triacrylate and ditrimethylolpropane tetraacrylate and having an hydroxyl number of 137 mg KOH/g was added slowly to the reactor and the reaction mixture was kept under reflux until the isocyanate content reached a value of 0.19 mcq/g. Then 209 g of EBECRYL01290, a hexafunctional aliphatic urethaneacrylate, was added to the reaction mixture and stirred until an homogeneous mixture was obtained. This mixture was then cooled down to 45 C. and 25.8 g of triethylamine was added under stirring. The resulting mixture was then added slowly to 1268 g of water at room temperature under high shear agitation until a stable dispersion was obtained. The acetone was stripped off under vacuum at a temperature of 50 C. until its level as measured by gas chromatography was below 0.15%. The polymer dispersion was then cooled down below 30 C. and 2.3 g of a biocide (ActicideMBS) was added. The dispersion was filtered over a 100 sieve and its solid content was adjusted to 40% by adding water. The dry content was measured by gravimetric method.

(2) The viscosity of the dispersion was 33 mPa.Math.s (measured at 25 C. with a Brookfield RVT viscometer using spindle N.sup.o 1 at 50 rpm).

(3) The average particle size of the aqueous polymer dispersion was 94 nm (measured by laser light scattering using a Malvern Autosizer Particle Analyzer).

(4) The grits content of the dispersion, that is the amount of residue from the polymer dispersion filtered on a 50 sieve, was lower than 100 mg/liter.

(5) The minimum film formation temperature (MFFT) of the dispersion measured on a gradient-heated metal plate was 0 C.

(6) The colloidal stability was assessed by observing the decantation and/or phase separation on a 200 g sample placed in an oven at 60 C.; it was more than 10 days prior to observable product deterioration. The properties of the dispersion are presented in Table 2 here below.

(7) The composition was then formulated with 1.5% of a photo-initiator (Additol BCPK) and the viscosity is adjusted to about 1500 mPa.Math.s (Brookfield) using AdditolVXW 6360:water (1:1) up to a maximum of 2%, and evaluated as to its reactivity, scratch resistance, stain resistance, hardness, flexibility and adhesion such as specified here below.

(8) Reactivity: The method covers the minimum UV-dose which is necessary to fully crosslink a coating of 36 wet applied to a non-porous substrate (white paper, Silico Ultraflat). The coating was dried for 1 minute at 120 C. and then cured under UV-lamp (Hg) of 80 W/cm at different conveyor speeds. The minimum dose is defined by the speed of the conveyer (m/min) that allows a solvent resistance equal or superior to 50 acetone double rubs. The rubs are made with a peace of cotton rag saturated with acetone; one double rub is equal to a forward and backward stroke on the coated surface. The reported number is the number of double rubs required to break through the coating.

(9) Scratch resistance: The method covers the scratch resistance a coating of 36 wet applied to a non-porous substrate (white paper, Silico Ultraflat). The coating was dried for 10 minute at 35 C. and then cured 2 times under UV-lamp (Hg) of 80 W/cm at a speed of 5 m/min. The scratch is assessed at room temperature using a piece of steel wool attached on a 800 g hammer and rubbed on the coated surface with a forward and backward motion. The reported number is the number of single rubs required to damage the surface and provide a visible loss of gloss due to abrasion.

(10) Stain resistance: The method covers the chemical resistance of a coating of 36 wet applied to a non-porous substrate (white, 5 mm thick PVC). The coating was dried for 1 minute at 120 C. and then cured under UV-lamp (Hg) of 80 W/cm at 5 m/min. The resistance is assessed by putting a test substance on the coating, covered with a microscope glass and left for 4 hours. The test substances used are tear, black polish, black alcohol pencil, BB750 colorant in water, SR380 colorant in white spirit and SG146 colorant in white spirit. The stains are washed with a couple of rubs using a tissue saturated with isopropanol. The remaining stains are assessed visually using a 1-5 scale, 5=best. A high value (5) is expected to provide the best protection against any household product spillage.

(11) Hardness: The method covers the surface hardness of a coating of 120 wet applied to glass. The coating was dried for 5 minute at 40 C., then 5 minutes at 80 C. and finally cured 3 times under an UV-lamp (Hg) of 80 W/cm at a speed corresponding to the reactivity. The coated samples are stabilized during 24 hours in a conditioned room (20 C., 50% humidity) and a pendulum hardness (Persoz) is determined in seconds on 3 places of the surface. The mean value is calculated.

(12) Pencil hardness: Pencil hardness (ASTM D-3363), The method covers the hardness of a coating of of 36 wet applied to polycarbonate sheets. It is used in the industry to determine scratch hardness of coatings. The coating was dried 10 minutes at 40 C. and was cured 2 times under an UV-lamp (Hg) of 80 W/cm at a speed of 2 times 5 m/min.

(13) The coated samples are stabilized during 24 hours in a conditioned room (20 C., 50% humidity). The pencil hardness is determined by scratching the surface of the coating with the pencils using a given force and with a given angle. The hardness is rated from softer to harder in a scale 2B-B-HB-F-H-2H-3H-4H-5H-6H, A high hardness level is whistled to provide an optimum mechanical protection from the coating.

(14) Flexibility: The method covers the flexibility of a coating of 36 g wet applied to a non-porous substrate (white, 5 mm thick PVC). The coating was dried for 1 minute at 120 C. and then cured under UV-lamp (Hg) of 80 W/cm at 5 m/min. The flexibility of the coated PVC can be assessed at room temperature after folding at 90 then at 180. The defects (cracks, loss of adhesion) are recorded on a 1-5 scale, 5=best. The attributions are 1=severe defects at 90; 2=moderate defects at 90; 3=severe defects at 180; 4=moderate defects at 180; 5=no defects at 180. A high value (5) is expected to generate no problem upon manipulation of flexible substrates and is a prerequisite for good temperature & dimensional stability onto rigid substrates.

(15) Water spot: The method covers the water resistance of a coating of 36 g wet applied to a non-porous substrate (white, 5 mm thick PVC). The coating was dried for 1 minute at 120 C. and then cured under UV-lamp (Hg) of 80 W/cm at 5 m/min. The resistance is assessed by cross cutting the coated surface with a knife and putting a drop of water in the middle for a period of 1 hour at room temperature. The water is removed using a dry tissue. The degradation of the surface is assessed visually for whitening or degradation using a 1-5 scale, 5=best. A high value (5) is expected to provide the best protection against water spillage.

(16) Adhesion: The method covers the adhesion of a coating of 36 g wet applied to a non-porous substrate (white, 5 mm thick PVC). The coating was dried for 1 minute at 120 C. and then cured under UV-lamp (Hg) of 80 W/cm at 5 m/min. 5 cuts of 1 cm and spaced by 1 mm are made in the coating using a knife, followed by 5 similar cuts in the transversal direction. The adhesion was measured using an adhesive tape firmly pressed on the cross-cut coating and removed rapidly; the damage to the cross-cut surface area of the coating due to adhesion loss is expressed in a 1-5 scale, 5=best. A high adhesion (5) is necessary to ensure a strong permanent bond between the coating and the substrate.

(17) The results obtained are represented in Table 3 here below.

(18) Examples 2 to 5, 7 to 16 and comparative example 6R:

(19) In Examples 2 to 5 and 7 to 16 the process described in Example 1 was repeated except that different quantities and different constituents were used as specified in Table 1 here below. Unless specified otherwise, the amounts of the different compounds are expressed in g.

(20) In Examples 2 to 5, 6R and 7 to 16, the hexafunctional urethaneacrylate EB1290 was omitted.

(21) In Example 4, DPHA, a mixture of dipentaerythrytol hydroxy pentaacrylate and dipentaerythrytol hexaacrylate, having an hydroxyl number of 67 mg KOH/g, was used instead of DTMPTA

(22) In Example 5, DPHA, a mixture of dipentaerythrytol hydroxy pentaacrylate and dipentaerythrytol hexaacrylate, having an hydroxyl number of 67 mg KOH/g, was used instead of DTMPTA and DPHA was also used instead of EBCD1290.

(23) In comparative example 6R, no compound (iv) was used: the acrylic acid adduct of bisphenol A diglycidyl ether (BPAAA) was replaced by 15.4 g of ethylene glycol.

(24) In example 7, PCDL T4691 (Asahi Kasei), a polycarbonate of butane diol: hexane diol (9:1) of average molecular weight of 1000 and having an average hydroxyl number of 110 mg KOH/g, was used instead of the polyester diol.

(25) In example 8, dimethylol propionic acid (DMPA) was replaced by dimethylol butanoic acid (DMBA). The neutralization with triethylamine happens stoichiometrically based on the moles of carboxylic acid.

(26) In example 9, the polyester diol is replaced stoichiometrically by an excess of the acrylic acid adduct of bisphenol A diglycidyl ether (BPAAA).

(27) In example 10, the polyester polyol is replaced by 2-ethyl-2-butyl-1,3-propanediol.

(28) In example 11, the polyester polyol is replaced stoichiometrically by PRIPOL2033 (Unichema) which is a fatty acid dimer diol composed with 36 carbon atoms and having an average molecular weight of 600 Daltons and an hydroxyl value of 196-206 mg KOH/g.

(29) In example 12, the diisocyanate (H12MDI) is replaced by a mixture of 199 g H12MDI and 15.4 g of DESMODURN3300 (HDI isocyanurate) in a 95:5 molar ratio.

(30) In example 13, neutralization was done with 32.1 g ammonia (110 mole % in comparison with carboxylic acid) in the water phase instead of triethylamine (100 mole % in comparison with carboxylic acid) in the pre-polymer.

(31) In example 14, 24.8 g of IRR154, which is a urethane acrylate based on silicone oil, was added at a level of 5% based on the total weight of the pre-polymer instead of to EBECRYL01290

(32) In example 15, 0.6 g of ADDITOLHGX83, which is a fluorinated acrylate, was added at a level of 0.1% based on the total weight of the pre-polymer instead of EBECRYL1290.

(33) In example 16, 6.01 g SILCLEAN3700, which is a silicone modified hydroxyl-functional polyacrylate of average molecular weight 15000 Daltons supplied as a 25% solution in methoxy propyl acetate, was added at a level of 7% based on the total weight of the pre-polymer instead of EBECRYL01290.

(34) The properties of the compositions are represented in Tables 2 and 3.

(35) TABLE-US-00001 Example 1 2 3 4 5 6R 7 8 9 Isocyanate 231.3 283.4 289.0 192.7 192.7 340.0 198.9 210.2 217.7 Polyol 45.3 99.3 56.6 37.8 37.8 119.2 62.7 41.2 EG 15.4 DMPA 34.3 42.0 42.8 28.6 28.6 50.4 29.5 32.2 DMBA 34.4 BPAAA 109.2 100.3 136.5 91.0 91.0 93.9 99.2 135.1 DTMPTA 207.1 258.8 275.9 312.6 DPHA 319.0 373.3 422.6 411.4 448.8 DPHA 241.1 Acetone 279 261 267 223 332 280.0 269 265 278 Dibutyltin 0.6 0.7 0.7 0.5 0.5 0.7 0.5 0.5 0.5 laurate Tinuvin 622 3.1 3.9 4.0 3.3 3.6 4.2 4.0 4.0 4.2 4-methoxy 0.4 0.5 0.5 0.4 0.4 0.5 0.9 0.9 0.9 phenol Triethylamine 25.8 31.6 32.2 21.5 21.5 38 22.4 26.1 24.4 Biocide 2.3 2.3 2.3 2.8 2.8 2.4 2.3 2.3 2.4 Deionized water 1268 1476 1508 1802 1802 1577 1514 1493 1562 Example 10 11 12 13 14 15 16 Isocyanate 260.4 225.6 199.0 + 15.4 385.4 122.4 157.5 208.5 Polyol 46.4 19.5 40.9 75.5 24.0 30.8 40.8 EG DMPA 31.5 33.4 31.0 57.1 18.1 23.3 30.9 DMBA BPAAA 46.7 106.5 98.7 182.0 57.8 74.3 98.4 DTMPTA DPHA 504.9 475.0 426.4 782.0 248.4 319.5 401.0 DPHA Acetone 297 287 270 494 165 202 280 Dibutyltin 0.5 0.5 0.5 1.0 0.3 0.4 0.5 laurate Tinuvin 622 4.4 4.3 4.1 7.4 2.4 3.0 3.9 4-methoxy 1.1 1.0 1.0 1.8 0.6 0.7 0.9 phenol Triethylamine 23.8 25.3 23.5 13.8 17.7 23.4 Biocide 2.5 2.4 2.4 4.3 1.4 1.7 2.4 Deionized water 1666 1611 1521 2778 928 1136 1573

(36) TABLE-US-00002 TABLE 2 Example 1 2 3 4 5 6R 7 8 Solid 40 35 35 35 35 35 35 35 content (%) pH 7.1 7.6 7.2 7.1 7.7 7.5 7.4 7.4 Viscosity 33 27 23 25 12 50 26 28 (mPa .Math. s) Particle 94 65 63 60 271 50 91 63 size (nm) Acetone <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 (%) Grits <100 <100 <100 <100 <100 <100 <100 <100 (mg/l) MFFT ( C.) 0 0 0 0 0 0 0 0 Stability >10 >10 >10 >10 10 >10 >10 >10 60 C. (d) Acrylates 3.9 3.1 3.3 5.1 6.5 2.8 5.5 5.5 (meq/g) Example 9 10 11 12 13 14 15 16 Solid 35 35.2 34.6 34.1 35.1 35.1 35.2 34.7 content (%) pH 7.1 6.9 7 6.7 6.9 7.3 7.1 7.3 Viscosity 23 17 19 21 27 18 23 23 (mPa .Math. s) Particle 60 188 131 72 118 186 58 111 size (nm) Acetone <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 <0.15 (%) Grits <100 <100 <100 <100 <100 <100 <100 <100 (mg/l) MFFT ( C.) 0 0 0 0 0 0 0 0 Stability >10 >10 >10 >10 7 5 >10 >10 60 C. (d) Acrylates 5.8 5.7 5.8 5.6 5.6 5.3 5.6 5.1 (meq/g)

(37) TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 6R 7 8 9 10 11 16 Reactivity 40 20 20 45 55 15 45 45 50 45 50 45 (m/min) Hardness (s) 274 318 331 308 330 207 322 328 325 327 314 348 Pencil hardness 3-4H 3-4H 4H 4-5H 3H 4H 3-4H Scratch (rubs) 20 10 15 30 50 5 30 25 45 20 35 15 Stains (0-5) 4.91 4.88 4.91 5.00 5.00 4.33 5 5 5 4.95 5 5 Flexibility (0-5) 2 4 5 3 4 5 5 5 5 5 5 5 Water spot (0-5) 4 4 5 5 5 5 5 Adhesion (0-5) 4.5 5 2 5 5 4 4 3 5 5 5 5

(38) The comparison of Examples 1 to 5 and 7 to 12 with Comparative example 6R show the better performances of the coatings obtained with the compositions according to the invention. Especially comparison of Example 2 with Comparative Example 6R obtained with exactly the same constituents except for the compound (iv) shows the benefit of the compositions according to the invention.