Elimination of application streaks of coatings using short fibers

Abstract

Waterborne polyurethane coating compositions comprising a polyol, an isocyanate crosslinker, and a small amount of thermoplastic microfibers, e.g., polyolefin microfibers, having a length of less than 1 mm, exhibit a much less sag, roller lines and other surface imperfections upon application to a substrate, in particular a vertical substrate such as a wall, than analogous water borne polyurethane compositions that lack the microfibers.

Claims

1. A waterborne polyurethane coating composition comprising, by weight based on the total weight of the waterborne polyurethane coating composition: 10 to 60%, of a polyol, 5 to 60%, of an isocyanate crosslinker, 0.1 to 5.0%, thermoplastic microfibers having a fiber length of 1 mm or less and a diameter of from 0.001 to 0.025 mm, 10 to 40% TiO.sub.2, and 10 to 60% water, wherein the thermoplastic microfibers are polyolefin microfibers.

2. The waterborne polyurethane coating composition according to claim 1 wherein the polyol is a polymeric resin comprising hydroxy groups and the isocyanate crosslinker is an aliphatic isocyanate crosslinker.

3. The waterborne polyurethane coating composition according to claim 1 comprising, by weight based on the total weight of the waterborne polyurethane coating composition: 10 to 35% of a polymeric resin comprising hydroxyl groups, which resin comprises one or more acrylate and/or methacrylate polymer or co-polymer comprising a plurality of free hydroxyl groups, 10 to 35% of an aliphatic isocyanate crosslinker, 0.1 to 5.0%, polyolefin microfibers having a fiber length of 1 mm or less and a diameter of from 0.001 to 0.025 mm, 15 to 40% TiO.sub.2, and 15 to 50% water.

4. The waterborne polyurethane coating composition according to claim 3 wherein the polyolefin microfibers comprise high density polyethylene and/or low density polyethylene microfibers.

5. The waterborne polyurethane coating composition according to claim 3 wherein the polyolefin microfibers have a fiber length of 0.005 to 0.50 mm and a diameter of from 0.001 to 0.010 mm.

6. The waterborne polyurethane coating composition according to claim 5 wherein the polyolefin microfibers have a fiber length of from 0.010 to 0.25 mm, and a diameter of from 0.002 to 0.007 mm.

7. The waterborne polyurethane coating composition according to claim 1 wherein the isocyanate crosslinker comprises hexamethylene diisocyanate, hexamethylene diisocyanate dimer, hexamethylene diisocyanate trimer, and/or hexamethylene diisocyanate oligomers derived from 4 or more hexamethylene diisocyanate units.

8. The waterborne polyurethane coating composition according to claim 3 wherein the aliphatic isocyanate crosslinker comprises hexamethylene diisocyanate, hexamethylene diisocyanate dimer, hexamethylene diisocyanate trimer, and/or hexamethylene diisocyanate oligomers derived from 4 or more hexamethylene diisocyanate units.

9. The waterborne polyurethane coating composition according to claim 8 comprising: 15 to 25% of the polymeric resin comprising hydroxyl groups, 15 to 25% of the aliphatic isocyanate crosslinker, 0.2 to 3.0% of the polyolefin microfibers, 15 to 35% TiO.sub.2, 25 to 45% water, and 0 to 25% total of pigments, surfactants, dispersants, rheology modifiers, leveling agents, anti-foaming agents, other reactive or non-reactive resins, hardeners, cure accelerators, catalysts, delaying or blocking agent, solvents, reactive diluents, wetting agents, stabilizers, inhibitors, reinforcing agents, cement, sand, quartz silica, CaCO.sub.3, CaSO.sub.4, BaSO.sub.4, detergents, antistatic material, anti-slip agent, matting agent, UV blockers, hindered amine light stabilizers and/or antioxidants.

10. The waterborne polyurethane coating composition according to claim 9 comprising, 3 to 20% total of pigments, surfactants, dispersants, rheology modifiers, leveling agents, anti-foaming agents, other reactive or non-reactive resins, hardeners, cure accelerators, catalysts, delaying or blocking agent, solvents, reactive diluents, wetting agents, stabilizers, inhibitors, reinforcing agents, cement, sand, quartz silica, CaCO.sub.3, CaSO.sub.4, BaSO.sub.4, detergents, antistatic material, anti-slip agent, matting agent, UV blockers, hindered amine light stabilizers and/or antioxidants.

11. The waterborne polyurethane coating composition according to claim 9 wherein the polyolefin microfibers have a fiber length of 0.005 to 0.50 m, a diameter of from 0.001 to 0.010 mm and comprise high density polyethylene and/or low density polyethylene microfibers.

12. The waterborne polyurethane coating composition according to claim 1, which is a wall coating composition.

Description

DESCRIPTION OF THE INVENTION

(1) In many broad embodiments, the waterborne 2-pack polyurethane coating composition of the invention comprises:

(2) 10 to 60%, e.g., 10 to 50%, by weight based on the total weight of the waterborne polyurethane coating composition of a polyol,

(3) 5 to 60%, e.g., 10 to 50%, of an isocyanate crosslinker,

(4) 0.1 to 5.0%, e.g., 0.2 to 3.0% polyolefin microfibers having a fiber length of 1 mm or less and diameter of from 0.001 to 0.025 mm, e.g., a diameter of from 0.001 to 0.10 mm,

(5) 10 to 40%, e.g., 15 to 35% TiO.sub.2, and

(6) 10 to 60%, e.g., 15 to 50% water.

(7) In some embodiments, the waterborne 2-pack polyurethane coating composition of the invention comprises:

(8) 10 to 40%, e.g., 10 to 35% or 15 to 25% of the polyol,

(9) 10 to 40%, e.g., 10 to 35% or 15 to 25% of the isocyanate crosslinker

(10) 0.1 to 5.0%, 0.2 to 3.0% of the thermoplastic microfibers,

(11) 15 to 40%, e.g., 15 to 35% TiO.sub.2, and

(12) 15 to 50%, e.g., 25 to 45% water.

(13) Typically the coating will also comprise up to 25%, e.g., 0 to 25% by weight, such as from 3 to 25% or 3 to 20 wt % total of components such as colorants, e.g., pigments, surfactants, dispersants, rheology modifiers, cure accelerators, catalysts, leveling agents and/or anti-foaming agents and other optional components. Other optional components include, e.g., other reactive or non-reactive resins, hardeners, delaying or blocking agent, solvents, reactive diluents, wetting agents, stabilizers, inhibitors, reinforcing agents, cement, sand, quartz (colored or non-colored), silica, clay and/or other fillers (CaCO3, CaSO4, BaSO4, etc.), detergents, antistatic material, anti-slip agent (Al2O3), matting agent, UV blockers, hindered amine light stabilizers, antioxidants, etc.

(14) In general, the 2 pack polyurethane coating composition of the invention are prepared by mixing dry microfibers into a composition comprising water, polyol, crosslinker and any other components desired in the final composition. In some embodiments the crosslinker may be added to the composition separately, e.g., just before, concurrent with, or some time after the microfibers have been added.

(15) As stated above, in many embodiments the polyol is an oligomeric or polymeric polyol e.g., a polyether polyol, polyester polyol, polycarbonate polyol, or co-polymer polyol such as a polyether/polyester polyol, etc., and in certain embodiments the polyol is a polymeric or copolymeric resin bearing two or more hydroxyl groups, for example, a hydroxyl bearing polyacrylate, polyacrylamide and the like. In particular embodiments, the hydroxy substituted polymer resin comprises one or more acrylate or methacrylate polymer or co-polymer comprising a plurality of free hydroxyl groups, many of which resins are commercially available.

(16) Other monomers aside from acrylate or methacrylate monomers may be present in the polymer resin, e.g., vinyl alcohols, vinyl acetates, vinyl amines, unsaturated acids, acrylamides, and polymer segments comprising amide, ester urethane or urea linkages, and the like may be present in the acrylate or methacrylate polymer or co-polymer. In some embodiments, polymers derived from these non acrylic monomers may also be present in the coating composition. For example, the hydroxy substituted polymer resin may comprise a co-polymer comprising different acrylate and/or methacrylate monomers, or a copolymer comprising one or more acrylate and/or methacrylate monomers segments and one or more amide, urethane, polyether, or hydroxy alkylene segments. There is generally no limit on where the free hydroxyl groups are located the polymer, e.g., they may be bound to the polymer backbone or be present on a pendent group such as a pendent ester group, e.g., the hydroxy group form a hydroxy ethyl acrylate or methacrylate monomer unit, a pendent amide group, e.g., from a hydroxyl alkyl acrylamide unit, a pendent hydroxy alkyl group from a vinyl alcohol unit, etc.

(17) A wide variety of polyisocyanate monomers are known and may be used e.g., aliphatic diisocyanates or tri-isocyanates, or aromatic diisocyanates or tris isocyanates. Common aliphatic diisocyanates include 1,6-hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene bis(p-cyclohexyl isocyanate) (H.sub.12MDI), 1,3-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate (CHDI), tetramethylene 1,4-diisocyanate, hexamethylene 1,4-diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate (TMDI), and the like.

(18) Common aromatic diisocyanates include diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate, 3,3-bitoluene diisocyanate (TODI), diphenyl 4,4-diisocyanate (DPDI), dibenzyl-4,4-diisocyanate, 1,3 and 1,4-xylene diisocyanates, tetramethylxylylene diisocyanate (TMXDI), para-phenylene diisocyanate (PPDI), stilbene-4,4-diisocyanate, benzophenone-4,4-diisocyanate, and the like.

(19) Dimers, oligomers and polymers of such isocyanates may also be used.

(20) The isocyanate crosslinker of the invention is typically an aliphatic polyisocyanate, e.g., an alkylene di- or tri-isocyanate or a dimer trimer or higher oligomer of an alkylene di- or tri-isocyanate. In many embodiments, the isocyanate crosslinker comprises hexamethylene diisocyanate or a dimer, trimer, higher oligomer or homopolymer of hexamethylene diisocyanate, for example, the isocyanate crosslinker often comprises hexamethylene diisocyanate and/or hexamethylene diisocyanate trimer

(21) Curing of the coating of the invention comprises reaction of hydroxy groups from the polyol, often comprising an acrylate or methacrylate polymer or co-polymer comprising free hydroxyl groups, and the isocyanate crosslinker, typically comprising hexamethylene diisocyanate or a dimer, trimer, higher oligomer or homopolymer of hexamethylene diisocyanate, to form a crosslinked polyurethane polymer.

(22) Thus the polyurethane film formed upon curing of the inventive coating composition is not a film formed by drying a dispersion of an already formed polyurethane resin. It is also not formed by the crosslinking of an isocyanate capped prepolymer formed from the reaction of a polyol with a polyisocyanate monomer.

(23) The microfibers or short fibers of the invention are thermoplastic fibers, often polyolefin, polystyrene, polyvinyl chloride or polyfluorocarbon microfibers, and in particular embodiments polyolefin microfibers such as polyethylene, polypropylene microfibers and the like, for example, high or low density polyethylene fibers. They have a fiber length of 1 mm or less, e.g. 0.001 to 1.0 or 0.005 to 0.50 mm, e.g., 0.010 to 0.50 or 0.010 to 0.25 mm, and diameter of from 0.001 to 0.025 mm, e.g., 0.001 to 0.015 or 0.001 to 0.010 mm, and in some embodiments 0.002 to 0.007 mm. In many embodiments, the microfibers have a surface area of 5 to 20 m.sup.2/gm as determined by gas absorption.

(24) Such microfibers are commercially available, for example, from MiniFibers Inc., under the trade name Short Stuff. The fibers of the invention are added to the formulation as dry materials, as opposed to being added in a slurry as found in US 2003/0119948 or as the wet pulp or fibers as found in US 2007/0149656. There is no particular limitation as to how or when the fibers are added.

(25) The coating of the present invention can be prepared and applied to a surface using any conventional means including roller, trowel, squeegee, spray, brush, etc., and can be cured at ambient temperatures.

(26) The coating formulation of present invention can be applied directly to a substrate, e.g., concrete, brick, tile, vinyl, other plastics, brick, wood, drywall, metal etc., or it can be applied over another coating film such as over a primer layer. The formulation can be used as primer, sealer, patch, intermediate coat, broadcast coat and top coat. It can also be mixed with cement, aggregates, sands, fillers, pigments, dye, anti-slip agent, anti-static agents and other additives to form a functional coating.

(27) Some embodiments of the invention provide a method for reducing or preventing roller line and/or sag from a waterborne 2 pack polyurethane coating, in particular a wall coating, by adding 0.1 to 5.0%, e.g., 0.2 to 3.0% by weight based on the weight of a waterborne 2 pack polyurethane coating composition, of the dry thermoplastic microfibers described above, for example, dry polyolefin microfibers to a composition comprising:

(28) 10 to 60%, e.g., 10 to 50%, by weight based on the total weight of the waterborne polyurethane coating composition, of a polyol, e.g., a polymeric resin comprising hydroxy groups,

(29) 5 to 60%, e.g., 10 to 50%, of an isocyanate crosslinker, e.g., an aliphatic isocyanate crosslinker,

(30) 10 to 40%, e.g., 15 to 35% TiO.sub.2, and

(31) 10 to 60%, e.g., 15 to 50% water;

(32) for example, adding the microfibers to a composition comprising:

(33) 10 to 40%, e.g., 10 to 35% or 15 to 25% of the polyol,

(34) 10 to 40%, e.g., 10 to 35% or 15 to 25% of the isocyanate crosslinker,

(35) 0.1 to 5.0%, 0.2 to 3.0% of the thermoplastic microfibers,

(36) 15 to 40%, e.g., 15 to 35% TiO.sub.2, and

(37) 15 to 50%, e.g., 25 to 45% water;

(38) or by adding, in any order,

(39) 5 to 60%, e.g., 10 to 50%, 10 to 40%, e.g., 10 to 35% or 15 to 25%, by weight based on the total weight of a resulting waterborne polyurethane, of the isocyanate crosslinker and from 0.1 to 5.0% of the dry thermoplastic microfibers described above to:

(40) 10 to 60%, e.g., 10 to 50%, 10 to 40%, 10 to 35%, or 15 to 25% of a polyol,

(41) 10 to 40%, e.g., 15 to 40%, or 15 to 35% TiO2,

(42) 10 to 60%, 15 to 50%, e.g., 25 to 45% water, and

(43) other optional components;

(44) and applying the thus formed waterborne polyurethane coating composition, to a surface, such as a vertical surface, e.g. a wall.

(45) Some particular embodiments of the invention provide a method for reducing or preventing roller line and/or sag from a waterborne 2 pack polyurethane coating, in particular a wall coating, by adding 0.1 to 5.0%, e.g., 0.2 to 3.0% by weight based on the weight of a waterborne 2 pack polyurethane coating composition, of dry polyolefin microfibers as described above to a composition comprising:

(46) 10 to 50% or 10 to 40%, e.g., 10 to 35%, or 15 to 25% by weight based on the total weight of the waterborne polyurethane coating composition of a polymeric resin comprising hydroxy groups,

(47) 10 to 50% or 10 to 40%, e.g., 10 to 35%, or 15 to 25% of an isocyanate crosslinker,

(48) 15 to 40%, e.g., 15 to 35% TiO.sub.2, and

(49) 15 to 50%, e.g., 25 to 45% water;

(50) or by adding, in any order,

(51) 10 to 50%, 10 to 40%, 10 to 35% or 15 to 25% of an aliphatic isocyanate crosslinker, and

(52) from 0.1 to 5.0%, dry polyolefin microfibers having a fiber length of 1 mm or less and a diameter of from 0.001 to 0.025 mm, to 10 to 50%, 10 to 40%, e.g., 10 to 35%, or 15 to 25% by weight based on the total weight of the waterborne polyurethane coating composition of a polymeric resin comprising hydroxy groups,

(53) 15 to 40%, e.g., 15 to 35% TiO.sub.2,

(54) 15 to 50%, e.g., 25 to 45% water, and

(55) other optional components;

(56) and applying the thus formed waterborne polyurethane coating composition, to a surface, such as a vertical surface, e.g. a wall.

EXAMPLES

(57) The following examples employ one or more of the following commercial materials: ESS5F MiniFibers dry HDPE fibers 0.1 mm long, 0.005 mm diameter Bayhydrol HD 2016 acrylic polyol resin in water-42% Solids Bayhydrol HD 2017 acrylic polyol resin in water-51% Solids Bayhydur HD 2018 hexamethylene diisocyanate based crosslinker Disperbyk 190 block copolymer dispersant Byk 3455 polyether modified siloxane flow leveling agent Byk 028 polysiloxane/polyglycol defoamer Byk 3441 Solution of an acrylate copolymer with 47%-48% of 2-Methoxymethylethoxypropanol DSX1514 thickener

Examples 1-4

(58) A series of coating compositions according to the table below were prepared using standard means and applied by roller to a wall and allowed to cure. Formulations 1, 2 and 3 were white matte coatings, formulation 4 contained additional colorants as shown.

(59) TABLE-US-00001 Formulation 1 2 3 4 Approx. total wt % water ~37% ~37% water water ~40% water ~36% water Water 14.20 14.0 18.9 12.66 Disperbyk 190 0.70 0.70 0.60 0.60 Byk 3455 0.00 0.80 0.00 0.70 Byk 028 0.85 0.00 0.70 0.76 Byk 3441 0.00 0.80 000 000 DSX 1514 3.80 2.85 4.72 2.60 13.4% solids ESS5F MiniFibers 0.40 1.9 1.90 0.35 TiO.sub.2 22.25 22.90 20.60 20.70 Bayhydrol HD 2016, 28.35 27.87 18.80 25.22 43% solids Bayhydrol HD 2017, 7.10 7.00 12.57 6.30 51% solids Total hydroxy resin solids 20.00 19.60 17.20 17.10 Bayhydur HD 2018 21.50 21.25 21.15 19.25 Color package 0.00 0.00 0.00 10.9

(60) The Color package for Formulation 4:

(61) TABLE-US-00002 Total wt % wt % due to water Pure Options B Lamp Black 4.04 1.62 Pure Options F Red Oxide 1.35 0.34 Pure Options AX Yellow 4.71 1.65 Pure Options C Yellow Oxide 0.81 0.20
Comparative coatings with a similar composition but without the microfibers were also prepared applied to a wall and cured.

(62) Examination of the cured coatings revealed that each of the polyurethane coatings 1 through 4 of the invention containing the microfibers shown had a smooth surface with no unwanted lines and no sag. The comparative coatings exhibit roller lines and varying degrees of sag.

(63) Also for comparison, polyacrylate coating formulations according to the table below were prepared using the same microfibers used in the two pack polyurethane systems. The preparation of the polyacrylate formulations comprised adding the microfibers to a mixture containing the first 5 components of the table, mixing for 40 minutes, adding the benzoyl peroxide and mixing for 30 to 60 seconds, after which the formulation was immediately applied to a substrate for testing.

(64) TABLE-US-00003 C1 C2 C3 C4 Methyl methacrylate 74.30 73.90 72.80 71.30 Triethylene glycol dimethacrylate 6.00 5.95 5.85 5.74 Methyl methacrylate/butylacrylate 17.20 17.20 16.95 16.60 copolymer Hydroxyethyl p-toluidine 1.0 1.0 1.0 1.0 BHT 0.10 0.10 0.10 0.10 ESS5F MiniFibers 0.13 0.50 2.0 4.0 Benzoyl peroxide 1.0 1.0 1.0 1.0

(65) A drawdown bar was used to prepare 15 mil and 30 mil coatings of the above polyacrylate coating formulations, which were cured for 40 to 60 minutes. The resulting films all exhibited noticeable sagging and were not smooth. A similar polyacrylate coating formulation containing 3.8 wt % Cab-O-Sil M5 silica powder in place of the microfiber of the invention was also prepared and produced smooth films with no sagging when tested accordingly.

(66) Results similar to those from the above polyacrylate films were obtained when repeating the tests with an epoxy coating formulation.