Claims:We claim:
1. Powder coating composition comprising dry blend of dual cured polyester system including
(i) hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm cured with blocked polyisocyanate; and
(ii) acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm cured with TGIC (triglycidyl isocyanurate);
with said (i) and (ii) respectively taken in the ratio ranging from 35:65 to 65:35.
2. The powder coating composition as claimed in claim 1 that is free of any releasing agent that does not allow sublimed film to stick on substrate causing complete ink transfer on substrate being free of any releasing agent and adhesion promoter, and favours matt finish based on gloss value 29-30 units at 60° (ASTM D523).
3. The powder coating composition as claimed in anyone of claims 1 or 2 comprising dry blend dual cure polyester system including blocked polyisocyanate cured hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and TGIC cured acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm that remains stable and dry at accelerated stability testing for 7-14 days at 45 deg C.
4. The powder coating composition as claimed in anyone of claims 1-3 which composition includes degassing agent, flow and leveling additives, pigments, extenders.
5. The powder coating composition as claimed in anyone of claims 1-4 wherein said hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and melt viscosity at 200 ?C in the range of 50-90 poise is a reaction product of Neopentyl glycol (20-40 wt%), ethylene glycol (1-10 wt%), diethylene glycol (1-5 wt%), MP diol (0-10 wt%), butyl ethyl propanediol (1-3 wt%), trimethylolpropane (0-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (30-65 wt%), isophthalic acid (1-10 wt%), hexahydro phthalic anhydride (0-5 wt%) enabling equivalent ratio of polyols to polyacids between 1.10-1.15.
6. The powder coating composition as claimed in anyone of claims 1-5 wherein said acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm and melt viscosity at 200 ?C in the range of 50-90 poise is a reaction product of Neopentyl glycol (25-40 wt%), ethylene glycol (1-5 wt%), diethylene glycol (0-5 wt%), MP diol (1-10 wt%), trimethylolpropane (1-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (40-65 wt%), isophthalic acid (1-5 wt%), hexahydro phthalic anhydride (0-5 wt%) enabling equivalent ratio of polyacids to polyols between 1.10-1.15.
7. A process for preparing powder coating composition as claimed in claim 1-6 comprising the steps of
Providing (i) hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and cured with blocked polyisocyanate;
Providing (ii) acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm and cured with TGIC (triglycidyl isocyanurate);
blending (i) and (ii) respectively taken in the ratio ranging from 35:65 to 65:35 and obtaining dry blend of dual cured polyester system free of any releasing agent that does not allow sublimed film to stick on substrate thereby causing complete ink transfer on substrate being free of any releasing agent and adhesion promoter that favours matt finish on substrate based on gloss value 29-30 units at 60°.
8. The process for preparing powder coating composition as claimed in claim 7 wherein said step of providing (i) hydroxyl functional polyester having hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm is obtained by reacting Neopentyl glycol (20-40 wt%), ethylene glycol (1-10 wt%), diethylene glycol (1-5 wt%), MP diol (0-10 wt%), butyl ethyl propanediol (1-3 wt%), trimethylolpropane (0-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (30-65 wt%), isophthalic acid (1-10 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c to attain said final hydroxyl value and melt viscosity after vacuum application at 230 deg C.
9. The process for preparing powder coating composition as claimed in claim 6 or 7 wherein said step (ii) of providing acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm is obtained by reacting Neopentyl glycol (25-40 wt%), ethylene glycol (1-5 wt%), diethylene glycol (0-5 wt%), MP diol (1-10 wt%), trimethylolpropane (1-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (40-65 wt%), isophthalic acid (1-5 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c to attain said final acid value and melt viscosity after vacuum application at 230 deg C.
10. The process for preparing powder coating composition as claimed in claims 7-9 wherein said hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm thus attained is cured with blocked polyisocyanate that have deblocking temperature above 160°C and includes diisocyanates, polyisocyanates and urethdiones, as blocked or unblocked compounds including isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylalkyl diisocyanates, diphenylmethane diisocyanate, trimethylhexane diisocyanate, cyclohexane diisocyanate, cyclohexanedimethylene diisocyanate, tetramethylenexylylene diisocyanate, dicyclohexylmethane diisocyanate or the trimerization products, including aliphatic diisocyanate based isocyanurates or mixtures thereof.
11. The process for preparing powder coating composition as claimed in claim 7-10 wherein blocking proceeds with blocking agents including monoalcohols, glycol ethers, ketoximes, lactams, malonic acid esters, acetoacetic acid esters, including ethylene glycol monobutyl ether, butanone oxime, phenol, ethyl acetoacetate, dimethylpyrazole or caprolactam.

Dates this the 23rd day of March, 2022 Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)
IN/PA-199
, Description:FIELD OF INVENTION

The present invention provides for powder coating composition preferably thermally curable powder coating composition for decoration on substrates including aluminium substrate to enable wood grain appearance on powder coated metal substrates including aluminium substrate.

BACKGROUND ART
Decorating a powder coated substrate providing enhanced properties of the decorated coating is required by the consumers that not only provides a coated substrate surface with permanent decorations on it and additionally with a very good anti-graffiti performance for a long time period, but the requirements is also to meet low gloss wood grain effect of powder coating on substrates including aluminium substrate that would act as an alternate to wood so as to preserve precious forests to thereby reduce global warming.
Low gloss powder coatings have been used for forming lusterless coating films based on polyester, in which the gloss value of the coating is reduced by incorporating an extender pigment, such as silica, talc or the like, have been known but while theses pigments reduce gloss surface irregularities occur due to the incorporation of the extender pigment, and also resulting coating film becomes hard and brittle together with a quite inferior appearance when high content of the extender pigment is employed.

On this several references are now drawn and admitted below:
WO2009070527A1 teaches a process of decorating a powder coated substrate comprising the steps (a) treating a substrate surface to be coated, (b) applying a powder coating composition on the treated substrate surface and curing the powder coating composition, and (c) covering the cured powder coating with a support comprising a decoration, and transfer the decoration onto the coated substrate surface by heating, wherein a powder coating composition is used comprising (A) 30 to 80 wt% of a mixture of at least one polyester resin A having a hydroxyl number in the range of 30 to 60 mg KOH/g, a weight average molar mass Mn in a range of 3100 to 5000 and a glass transition temperature Tg of 40 to 60 °C and at least one polyester resin B having a hydroxyl number in the range of 250 to 350 mg KOH/g, a weight average molar mass Mn in a range of 2000 to 3000, (B) 10 to 40 wt% of at least one hardener selected from the group consisting of diisocyanates, polyisocyanates and urethdiones, and (C) 0.01 to 40 wt% of at least one coating additive, pigment and/or filler, the wt% being based on the total weight of the powder coating composition, and wherein the transfer by heating is performed in a temperature range between 160 °C and 220 °C. The process provides a coated substrate surface with permanent decorations on it and additionally with a very good anti-graffiti performance for a long time period.
US5491202 teaches powder coating composition for forming a low gloss coating film, in particular to a powder coating composition based on polyester resins capable of adjusting the gloss of the resulting coating film at any voluntary value, as well as to a method for coating various substrates with it, wherein in said powder coating composition of this prior art the polyester resins involved of (A), (B) and (C) are hydroxyl group-containing polyester resins each having a glass transition temperature Tg of 35°-100°C.
EP1162241A2 teaches a thermally curing powder coating composition comprising a mixture of resins wherein at least one resin has a hydroxy number of less than 75 mg KOH/g, at least one resin has a hydroxy number of at least 75 mg KOH/g, and a curing agent for the resins.
EP0782934A1 teaches a white, powdery coating composition for image-receiving sheets for sublimation thermal transfer recording, which comprises a resin component, a white colorant and a cured product of reaction-curable silicone oils and which is characterized in that the composition comprises, as the resin component, from 70 to 95 % by weight of a resin mixture comprising from 50 to 90 % by weight of a saturated polyester resin having an acid value of from 1.0 to 20 mg KOH/g and a glass transition point of from 50 to 70°C and from 10 to 50 % by weight of a styrene-acrylic copolymer resin, and from 0.5 to 12 % by weight of a cured product of at least two reaction-curable silicone oils having functional groups capable of mutually reacting with each other.
RU2166381C2 discloses a method of coating surfaces and their decorative finishes with powders of various colors, in which at least one surface is applied to the surface subjected to decorative finishes, a layer of coating material of a color corresponding to the desired color background is applied to the surface thus treated powder of a color corresponding to the color of the reproduced pattern, distributing it in accordance with the desired pattern of this pattern, and dry the surface over time and at a temperature sufficient accurate for reliable attachment of the powder to the surface, characterized in that the coating is made of powder material, and after applying the powder coating material, the surface to be decorated is heated to a temperature lower than the drying temperature of the powder coating material, but sufficient to adhere the coating to specified surface.

CN101878119A is directed to a process of decorating a powder coated substrate comprising the steps (a) treating a substrate surface to be coated, (b) applying a powder coating composition on the treated substrate surface and curing the powder coating composition, and (c) covering the cured powder coating with a support comprising a decoration, and transfer the decoration onto the coated substrate surface by heating, wherein a powder coating composition is used comprising (A) 30 to 80 wt% of a mixture of at least one polyester resin A having a hydroxyl number in the range of 30 to 60 mg KOH/g, a weight average molar mass Mn in a range of 3100 to 5000 and a glass transition temperature Tg of 40 to 60 DEG C and at least one polyester resin B having a hydroxyl number in the range of 250 to 350 mg KOH/g, a weight average molar mass Mn in a range of 2000 to 3000, (B) 10 to 40 wt% of at least one hardener selected from the group consisting of diisocyanates, polyisocyanates and urethdiones, and (C) 0.01 to 40 wt% of at least one coating additive, pigment and/or filler, the wt.% being based on the total weight of the powder coating composition, and wherein the transfer by heating is performed in a temperature range between 160 DEG C and 220 DEG C. The process provides a coated substrate surface with permanent decorations on it and additionally with a very good anti-graffiti performance for a long time period.

CN102634269A provides for wood grain powder coating for aluminum profile. The wood grain powder coating is prepared from the following raw materials in percentage by weight: 45-50% of saturated terminal carboxyl polyester resin, 3-4% of beta-hydroxyalkylamide, 0.6-0.7% of titanium dioxide, 39-42% of precipitated barium sulfate, 0.8-1.2% of brightening agent, 0.8-1.2% of flatting agent, 0.3-0.4% of transfer agent, 0.4-0.5% of polyethylene wax, 1.0-1.2% of everbright fast yellow, 2.0-2.5% of iron oxide red, 1.0-1.3% of everbright fast red and 0.5-0.7% of pigment carbon black. The invention also discloses a preparation method of the powder coating, which comprises five steps of: pre-mixing, melt extrusion, cooling, breaking and micro-fine crushing. When in use, the powder disclosed by this prior invention has obvious characteristics of low curing temperature, environment friendliness, no toxicity and the like.

CN103820010A provides glittering three-dimensional wood grain powder coating for aluminium profiles. The glittering three-dimensional wood grain powder coating comprises 98-99% of a powder coating and 1-2% of metal powder pigment, wherein the powder coating comprises saturated terminal carboxyl polyester resin A, saturated terminal carboxyl polyester resin B, a TGIC (triglycidyl isocyanurate) curing agent and the like. A preparation method of the glittering three-dimensional wood grain powder coating for the aluminium profiles comprises the steps as follows: firstly, the raw materials of the powder coating are premixed and then prepared into the powder coating through melt extrusion, tablet cooling, crushing, fine pulverization and sieving, the powder coating and the metal powder pigment are mixed in a bonded manner, and finally, a finished product is obtained through sieving. Formulas of high and low acid value resin are adopted, the metal powder pigment with the glittering effect is added, and a bonding technology and a dual-channel powder three-dimensional spraying and transfer technology are adopted, so that the decoration performance and the appearance of wood grain applied to workpieces are improved. A film of the coating glitters and has the colorful optical effect and the three-dimensional effect under the irradiation of light, so that the aesthetic experience is brought to people, and the cost performance of the aluminium profiles is improved.
US 3,907,974 provides heat resistant surfaces such as glass or metal using a heat transfer decoration comprising in sequence a temporary carrier, a transfer lacquer layer which is removably adhered to the surface of said carrier, at least one design print layer adhered over the lacquer layer and a heat-activatible adhesive layer adhered over said design print layer wherein at least the transfer lacquer and design print layers contain cross-linkable resin means and a crosslinking agent for cross-linking the resin intralayer and interlayer to form a unified adherent decoration resistant to abrasion and chemicals. The metal or glass surface may optionally be coated with a cross-linkable primer composition prior to application of the heat transfer decoration thereto.
EP2014732A1 thermally curable powder coating composition based on carboxy functional polyester resins with a high acid value dry blended with a low acid value resin and cured with a hydroxyalkylamide, and its use in the preparation of a decorated substrate, by transfer printing.

The problems or outstanding technical deficiencies present in the prior art are as follows:

>30 to 80 wt% of a mixture of at least one polyester resin A having a hydroxyl number in the range of 30 to 60 mg KOH/g, and at least one polyester resin B having a hydroxyl number in the range of 250 to 350 mg KOH/g used to be involved wherein high hydroxyl number polyester inherently exhibited lower Tg and melt viscosity.

>45-50% of saturated terminal carboxyl polyester resin having acid value 30-50 cured with 3-4% of beta-hydroxyalkylamide.

> A thermally curable powder coating composition comprising a dry blended of powder based on a carboxy functional polyester resin with a high acid value (65-115 mg KOH/gm) and a carboxy functional polyester resin with a low acid value (10-55 mg KOH/gm) and both cured with a hydroxyalkylamide in ratio of 75/25 to 50/50.
> Mixture of at least one polyester resin A having a hydroxyl number above 75 mg KOH/g, and at least one polyester resin B having a hydroxyl number below 75 mg KOH/g,
> Involvement of anti-stick material such as silicon/fluoro/polyethylene wax etc are used to release decorative paper after sublimation.
Reference to the following prior arts are also invited:
CN11117554A discloses UV and moisture dual-curing polyurethane hot melt adhesive prepared from (by wt. parts) thermoplastic resin (thermoplastic polyurethane, thermoplastic acrylic resin, etc.) 20-50, polyester polyol (1,4-butanediol, diethylene glycol, etc.) 20-50, polyether polyol (PPG400, PPG600, etc.) 5-35, trifunctional small mol. polyol (trimethylolethane, trimethylolpropane, etc.) 1-10, hydroxyl-terminated acrylate (hydroxyethyl acrylate, hydroxyethyl methacrylate, etc.) or amino-terminated vinyl monomer (cyanuric acid and/or acrylamide) 1-10, polyisocyanate 2-20, catalyst (dibutyltin dilaurate, stannous octoate, etc.) 0.1-1, photoinitiator (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, etc.) 1-5, silane coupling agent 0.2-2 and defoaming agent 0.2-2. The hot melt adhesive has good pressure sensitivity and initial adhesion strength, and has the function of quickly positioning without pressure. Stated to involve silane coupling agent together with acrylics.
Dual-curable acrylic pressure-sensitive adhesives based on UV and thermal processes, From Macromolecular Research (2008), 16(2), 128-133, teaches several dual-curable acrylic pressure-sensitive adhesives (PSA) that were synthesized by the radical polymerization of acrylic monomers containing benzophenone, hydroxyl, and alkyl groups. The optimum extent of UV-induced cure was determined by varying the content of the benzophenone groups (the photoinitiator) from 0.5 to 1.5 wt%. The wt. av. mol. wt. of the polymers obtained ranged from 300,000 to 700,000 amu. The coated pressure-sensitive adhesives were cured either by short UV exposure to induce the grafting of acrylic polymers, or by heating for 6 h at 60 °C to promote the reactions between the polyisocyanates and hydroxyl groups. The dual-curing behavior was determined by monitoring both processes quant. by IR spectroscopy. The developed dual-curable acrylic pressure-sensitive adhesives were found to compensate for the limitations in UV-induced curing of thick coatings.
WO 2021089086 A1 is directed to coating material compositions based on dual-cure systems, coatings that can be produced using same, and use thereof for coating components and objects, in particular ships, aircraft or rail vehicles. This prior invention also relates to coating systems and layer structures, such as base coat clear-coat systems, containing the coatings according to the invention. The coating material composition according to this prior invention comprises a component A and a component B. The component A comprises 40 to 70 wt.% polyols (a), 2 to 10 wt.% OH-functional, unsaturated, aliphatic urethane acrylates (b), 0.2 to 5 wt.% photoinitiators (c) and a combination of amine synergists (d), which contains 1 to 10 wt.% acryloyl-functional amine synergists (d1) with amine values in the range of 130 to 190 mg/g and 1 to 10 wt.% acryloyl-functional amine synergists (d2) with amine values in the range of 60 to 105 mg/g. The component B comprises 40 to 100 wt.% aliphatic polyisocyanates and claim 4 therein teaches that the polyols (a) have OH numbers between 220 and 371, but involves amine synergists.
WO 2017148742 A1 discloses a coating composition, comprising: of at least one free radical-curable ethylenically unsaturated compound; at least one polyol; and at least one polyisocyanate. This prior invention also relates to a method of forming a coating on a surface of a substrate, comprising: applying at least one layer of the coating composition to the surface of the substrate; exposing the coating composition to an amount of radiation and/or of heat effective to initiate cure of the at least one free radical-curable ethylenically unsaturated compound; and reacting the at least one polyol and the at least one polyisocyanate. This prior invention also claims a precursor composition useful for forming a coating composition when precursor composition is combined with at least one polyol, wherein the precursor composition is comprised of at least one free radical-curable ethylenically unsaturated compound and at least one polyisocyanate, the precursor composition being free of any polyol. The invention also directs to a two part system useful for forming a coating composition, comprising as separate packaged components, either: (a-1) a part A-1 comprised of at least one free radical-curable ethylenically unsaturated compound and at least one polyisocyanate ; and (b-1) a part B-1 comprised of at least one polyol; or (a-2) a part A-2 comprised of at least one free radical-curable ethylenically unsaturated compounds and at least one polyol; and (b-2) a part B-2 comprised of at least one polyisocyanate. This prior invention also claims a method of making a coating, comprising: combining Part A-1 and Part B-1 or combining Part A-2 and Part B-2 to form a coating composition; applying the coating composition to a surface of a substrate; and curing the applied coating composition A coating comprised of at least one layer of a coating composition, wherein the coating composition is cured, is also claimed. An article of manufactured comprised of a substrate, wherein a surface of the substrate is at least partially coated with a coating composition, is also concerned. The invention also relates to the use of a composition in dual cure soft touch coatings and/or films, in particular coatings and/or films for automobiles and other motor vehicles such as coatings on arm rests, dashboards, seating, switches, controls and other interior components, aeronautic components, small appliances, packaging such as cosmetics packaging, printing enhancements (inks), coatings on leathers, and synthetic leathers and/or consumer electronics. This prior arts thus teaches free radical curable coating composition comprising comprised of at least one free radical-curable ethylenically unsaturated compound, at least one polyol and at least one polyisocyanate.

EP 1529793 A2 teaches solvent-based, dual cure coatings incorporating thermally curable blocked polyisocyanates, which also contain unsaturated linkages, and a method for preparing these coatings. The unsaturated linkages, such as acrylate groups, can be crosslinked by free-radical mechanisms such as UV curing. Therefore scopes a non-aqueous, dual-cure composition comprising: a) from about 5 to about 85% by weight of a blocked (cyclo)aliphatic polyisocyanate prepared by i) reacting a hydroxy-functional (meth)acrylate with an organic (cyclo)aliphatic polyisocyanate with an NCO to OH equivalent ratio of from about 1.5:1 to about 3:1, with the resultant partially blocked isocyanate having an isocyanate group content of from about 5 to about 13% by weight, and ii) reacting the remaining isocyanate groups with a blocking agent, b) from about 5 to about 85% by weight of a hydroxy-functional polymer having an OH number of from about 10 to about 250 and an acid number of from about 0.1 to about 50, with the equivalent ratio of blocked isocyanate groups to hydroxy groups being from about 0.8:1 to about 1.2:1, said hydroxy-functional polymer being selected from the group consisting of saturated polyesters, unsaturated polyesters, and mixtures thereof, c) from 0 to about 65% of an ethylenically unsaturated compound selected from the group consisting of ethylenically unsaturated monomers, polymers containing ethylenic unsaturation (other than unsaturated polyesters), and mixtures thereof and d) from about 0.1 to about 7.0% by weight of a UV initiator for free-radical polymerization, said percentages by weight totaling 100%, and with the proviso that if ingredient b) is a saturated polyester, ingredient c) is present in an amount of from about 20 to about 65% by weight, further teaches that the hydroxy-functional polymer comprises saturated polyester. Thus in this prior invention dual cure system composed of acrylic polyol and saturated/unsaturated polyester polyol were employed and both were cured with blocked isocyanates along with some UV crosslinking and is thus totally different form dual cure systems not prior known involving acid and hydroxyl functional polyester cured with blocked isocyanate and TGIC (triglycidyl isocyanurate) respectively.

US 2009/0155462 A1 teaches a powder coating composition comprising (A) at least one hydroxyl functional polyester resin binder, and (B) at least one polyurethane resin as cross-linking agent containing blocked isocyanate groups, wherein the at least one hydroxyl functional polyester resin binder (A) and the at least one polyurethane resin (B) both having a melting temperature of 60 to 180°C., in particular, 60 to 160° C. The powder coating composition according to the invention provides the desired technological properties, in particular, thin films and high flexibility in combination with excellent mechanical properties of the coatings. Further teaches about a powder coating composition comprising (A) at least one hydroxyl functional polyester resin binder, and (B) at least one polyurethane resin as cross-linking agent containing blocked isocyanate groups, wherein the at least one hydroxyl functional polyester resin binder (A) and the at least one polyurethane resin (B) both have a melting temperature of 60 to 180° C. Also teaches that said composition comprises (A) 5 to 80 wt % of at least one hydroxyl functional polyester resin binder, (B) 95 to 20 wt % at least one polyurethane resin as cross-linking agent containing blocked isocyanate groups, (C) 0 to 30 wt % and optionally, 1 to 30 wt % of at least one binder different from (A) and (B), having functional groups reactive with the functional groups of (A) and (B), and (D) 0.1 to 60 wt % of pigments, fillers and/or coating additives, the wt % amounts based on the total weight of the powder coating composition (A) to (D), wherein the at least one hydroxyl functional polyester resin binder (A) and the at least one polyurethane resin (B) both having a melting temperature of 60 to 180° C. Again teaches that in said composition the polyester resin binder (A) has a hydroxyl value of 30 to 300 mg KOH/g and a number-average molar mass between 500 to 5000; (C) 0 to 30 wt % and optionally, 1 to 30 wt % of at least one binder different from (A) and (B), having functional groups reactive with the functional groups of (A) and (B), and (D) 0.1 to 60 wt % of pigments, fillers and/or coating additives, the wt % amounts based on the total weight of the powder coating composition (A) to (D), wherein the at least one hydroxyl functional polyester resin binder (A) and the at least one polyurethane resin (B) both having a melting temperature of 60 to 180° C. Also teaches that the polyester resin binder (A) has a hydroxyl value of 30 to 300 mg KOH/g and a number-average molar mass between 500 to 5000. Para [0080] therein also teaches powder coating compositions can be readily applied to metallic and non-metallic substrates. The powder coating composition of this prior art is also taught to be used to coat metallic substrates including, but not limited to, steel, brass, aluminum, chrome, and mixtures thereof, and also to other substrates including, for example, heat-sensitive substrates, such as, substrates based on wood, plastics and paper, and other substrates based, for example, on glass and ceramics. While this prior art teaches the concept of powder coating composition for decorating metal substrates such as aluminum, the acid value based polyester is not explicitly or implicitly taught by this prior art and though the claimed scope may appear to include an optional component (C) that is reactive to both component (A) and (B), but component (C) binder is not “acid” functional polyester, but rather a polyurethane and (meth) acrylic copolymer resins having hydroxyl value from 60 to 300 mg of KOH/g as per para [0061] of this prior patent.
Hence in the above backdrop there is a need to provide for powder coating composition that would be stable on storage free of any lump formation and would enable low gloss, complete ink transfer, and easy release (no sticking) of decorative paper design on substrate when free of silicon/fluoro based low surface energy material as releasing agent and adhesion promoter. There is also a need to achieve wood grain effect of powder coating on substrates including aluminium substrate as an alternate to using natural wood so as to preserve precious forests thereby reducing global warming.

OBJECTS OF THE INVENTION
Thus, the primary object of the present invention is to provide for powder coating composition for decoration on substrates including aluminium substrate to enable wood grain appearance on powder coated aluminium substrate.
Yet another object of the present invention is to provide for a solution towards decoration of aluminium substrates to enable wood grain appearance based on a composition of dry blend of dual cure polyester free of any involvement of releasing agent and advantageously free of high hydroxyl/acid value polyester which inherently exhibit the problems of low melt viscosity and lower Tg, as a result exhibiting lump formation during storage.

Another object of the present invention is to provide for said powder coating composition exhibiting low gloss, complete ink transfer, and easy release (no sticking) of decorative paper design on substrate free of any silicon/fluoro based low surface energy material as a releasing agent and adhesion promoters.

Still another object of the present invention is to provide for said powder coating composition that would be commercially attractive in achieving wood grain effect on aluminum substrate as an alternate to using a natural wood that are already jeopardized through excess use that would thus aid in conserve precious forest and reduce global warming.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided powder coating composition comprising dry blend of dual cured polyester system including
(i) hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm cured with blocked polyisocyanate; and
(ii) acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm cured with TGIC (triglycidyl isocyanurate);
with said (i) and (ii) respectively taken in the ratio ranging from 35:65 to 65:35.

Preferably said powder coating composition is free of any releasing agent that does not allow sublimed film to stick on substrate causing complete ink transfer on substrate being free of any releasing agent and adhesion promoter, and favours matt finish based on gloss value 29-30 units at 60° (ASTM D523).

According to a preferred aspect of the present invention there is provided said powder coating composition comprising dry blend dual cure polyester system including blocked polyisocyanate cured hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and TGIC cured acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm that remains stable and dry at accelerated stability testing for 7-14 days at 45 deg C.

Preferably said powder coating composition is provided which composition includes degassing agent, flow and leveling additives, pigments, extenders.

According to yet another preferred aspect of the present invention there is provided said powder coating composition wherein said hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and melt viscosity at 200 ?C in the range of 50-90 poise is a reaction product of Neopentyl glycol (20-40 wt%), ethylene glycol (1-10 wt%), diethylene glycol (1-5 wt%), MP diol (0-10 wt%), butyl ethyl propanediol (1-3 wt%), trimethylolpropane (0-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (30-65 wt%), isophthalic acid (1-10 wt%), hexahydro phthalic anhydride (0-5 wt%) enabling equivalent ratio of polyols to polyacids between 1.10-1.15.

Preferably said powder coating composition is provided wherein said acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm and melt viscosity at 200 ?C in the range of 50-90 poise is a reaction product of Neopentyl glycol (25-40 wt%), ethylene glycol (1-5 wt%), diethylene glycol (0-5 wt%), MP diol (1-10 wt%), trimethylolpropane (1-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (40-65 wt%), isophthalic acid (1-5 wt%), hexahydro phthalic anhydride (0-5 wt%) enabling equivalent ratio of polyacids to polyols between 1.10-1.15.

According to another aspect of the present invention there is provided a process for preparing powder coating composition comprising the steps of
Providing (i) hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm and cured with blocked polyisocyanate;
Providing (ii) acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm and cured with TGIC (triglycidyl isocyanurate);
blending (i) and (ii) respectively taken in the ratio ranging from 35:65 to 65:35 and obtaining dry blend of dual cured polyester system free of any releasing agent that does not allow sublimed film to stick on substrate thereby causing complete ink transfer on substrate being free of any releasing agent and adhesion promoter that favours matt finish on substrate based on gloss value 29-30 units at 60°.

Preferably in said process for preparing powder coating composition said step of providing (i) hydroxyl functional polyester having hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm is obtained by reacting Neopentyl glycol (20-40 wt%), ethylene glycol (1-10 wt%), diethylene glycol (1-5 wt%), MP diol (0-10 wt%), butyl ethyl propanediol (1-3 wt%), trimethylolpropane (0-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (30-65 wt%), isophthalic acid (1-10 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c to attain said final hydroxyl value and melt viscosity after vacuum application at 230 deg C.
According to yet another preferred aspect of the process of the present invention there is provided said powder coating composition wherein said step (ii) of providing acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm is obtained by reacting Neopentyl glycol (25-40 wt%), ethylene glycol (1-5 wt%), diethylene glycol (0-5 wt%), MP diol (1-10 wt%), trimethylolpropane (1-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (40-65 wt%), isophthalic acid (1-5 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c to attain said final acid value and melt viscosity after vacuum application at 230 deg C.
Preferably in said process for preparing powder coating composition said hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm thus attained is cured with blocked polyisocyanate that have deblocking temperature above 160°C and includes diisocyanates, polyisocyanates and urethdiones, as blocked or unblocked compounds including isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylalkyl diisocyanates, diphenylmethane diisocyanate, trimethylhexane diisocyanate, cyclohexane diisocyanate, cyclohexanedimethylene diisocyanate, tetramethylenexylylene diisocyanate, dicyclohexylmethane diisocyanate or the trimerization products, including aliphatic diisocyanate based isocyanurates or mixtures thereof.
More preferably in said process for preparing powder coating composition wherein blocking proceeds with blocking agents that are conventional including monoalcohols, glycol ethers, ketoximes, lactams, malonic acid esters, acetoacetic acid esters, including ethylene glycol monobutyl ether, butanone oxime, phenol, ethyl acetoacetate, dimethylpyrazole or caprolactam.
BRIEF DESCRIPTION OF FIGURES

Fig. 1a and 1b: are illustrative images of (i) before film sublimation and (ii) after film sublimation
DETAILED DESCRIPTION OF THE INVENTION
As discussed hereinbefore, the present invention provides for powder coating composition for decoration on substrates including aluminium substrate to enable wood grain appearance on powder coated aluminium substrate.
The solution of the aforementioned problems in the art could be surmounted by the present invention by providing a solution in respect of providing said powder coating composition comprising a dry blend dual cure polyester based on hydroxyl functional polyester ranging from 25-45 mg KOH/gm cured with blocked polyisocyanate and acid functional polyester with acid value ranging from 25-45 mg KOH/gm and cured with TGIC respectively taken in the ratio ranging from 35:65 to 65:35 without any releasing agent, to attain matt finish.
As a result, the process of synthesizing high hydroxyl/acid value polyester which inherently exhibit low melt viscosity and lower Tg, as a result exhibiting lump formation during storage as apparent from the prevailing state of the arts JP6597806B2 and WO2001029107A1, could be completely eliminated.

EXAMPLES:

Low gloss, complete ink transfer, and easy release (no sticking) of decorative paper design on substrate without use of silicon/fluoro based low surface energy material as a releasing agent could be demonstrated as per Figure 1.
The advantages being: No film sticking is observed; Ink is completely transferred to substrate; Gloss value is 29-30 units at 60° (ASTM D523).
Polyesters based on hydroxyl functional polyester ranging from 25-45 mg KOH/gm of Table 1 and acid functional polyester ranging from 25-45 mg KOH/gm, were prepared based on analogous protocol by involving the following ingredients as per the Table 1 below:
For hydroxyl functional polyester having hydroxyl functionality ranging from 25-45 mg KOH/gm, the same is a reaction product of Neopentyl glycol (20-40 wt%), ethylene glycol (1-10 wt%), diethylene glycol (1-5 wt%), MP diol (0-10 wt%), butyl ethyl propanediol (1-3 wt%), trimethylolpropane (0-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (30-65 wt%), isophthalic acid (1-10 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c and final hydroxyl value and melt viscosity were achieved after vacuum application at 230 deg C.
Table 1:
Raw Materials Formula 1 Formula 2 Formula 3
Ethylene glycol 4 8 1
MP Diol - 8 7.66
Neopentyl glycol 35 20.64 28.81
Trimethylolpropane - - 1.63
Terephthalic acid 52.84 63.2 56.74
Isophthalic acid 8 - 4
Tg 65 61 62.46
Melt viscosity in Poise @ 200 deg C 57 60 87
GPC Mn-3730 Mw-7780 PDI-2.08
Mn-4431
Mw- 9078
PDI-2.04 Mn-4767
Mw- 12886
PDI-2.7

For acid functional polyester having acid functionality ranging from 25-45 mg KOH/gm, the same is a reaction product of Neopentyl glycol (25-40 wt%), ethylene glycol (1-5 wt%), diethylene glycol (0-5 wt%), MP diol (1-10 wt%), trimethylolpropane (1-3 wt%), Adipic acid (0-3 wt%), terephthalic acid (40-65 wt%), isophthalic acid (1-5 wt%), hexahydro phthalic anhydride (0-5 wt%) using tin based catalyst and triphenyl phosphite as antioxidant at the temperature range from 190-240 deg c and final hydroxyl value and melt viscosity were achieved after vacuum application at 230 deg C.
The synthesis process of the above is analogous to the procedures flowing from US5405920, WO1989005320A1, US4859760, WO2017074835A1, but for the purposes of the present invention higher molar ratio of polyol for moderate to higher hydroxyl value is employed and similarly higher molar ratio of polyacids is employed for moderate to higher acid value polyester as per the reactor charges below:
Synthetic protocol for hydroxyl functional polyester: A 2000 mL, 3-necked, round bottom flask equipped with a stirrer, a short pack column, dean stark, condenser and an inlet for nitrogen, was charged with ethylene glycol (64 gm), neopentyl glycol (560 gm), tin based catalyst, and triphenyl phopshite, material was heated to 120-140 °C followed by addition of isophthalic acid (128 gm), terephthalic acid (845.4 gm). After complete addition, the reaction was heated to 190° Cover 30 minutes. The reaction was then maintained, under nitrogen, at 190° C. for 1-2 hours with stirring. Reaction temperature was taken to 240 °C gradually over 10-12 hrs. After cold and hot clarity of material is obtained, vacuum applied to reduce acid value below 5 mg KOH/gm and desired melt viscosity that is important. After attaining the desired constants molten mass is discharged in stainless steel tray. Hydroxyl value is controlled by controlling the wt. of the reagents leading to hydroxyl functional polyester polyol thus attained based on equivalent ratio of polyols to polyacids between 1.10-1.15.
Synthetic protocol for acid functional polyester: A 2000 mL, 3-necked, round bottom flask equipped with a stirrer, a short pack column, dean stark, condenser and an inlet for nitrogen, was charged with ethylene glycol (180.8 gm), MP Diol (284.8 gm), diethylene glycol (4.8 gm), trimethylol propane (30.4 gm), tin based catalyst, and triphenyl phopshite, material was heated to 120-140 °C followed by addition of terephthalic acid (926.4 gm). After complete addition the reaction was heated to 190°C over 30 minutes. The reaction was then maintained, under nitrogen, at 190° C. for 1-2 hours with stirring. Reaction temperature was taken to 240 °C gradually over 10-12 hrs. After hot and cold clarity achieved, terephthalic acid (160 gm) was added and reaction continued at 240 °C till cold and hot clarity of material is obtained followed by vacuum applied to achieve desired melt viscosity that is important. After attaining the desired constants molten mass is discharged in stainless steel tray. Acid value of acid functional polyester polyol thus attained is controlled by controlling the wt. of the reagents leading to said acid functional polyester polyol based on equivalent ratio of polyacids to polyols between 1.10-1.15.
The curing agents of blocked polyisocyanates comprise such isocyanates that have deblocking temperature above 160°C and includes diisocyanates, polyisocyanates and urethdiones, as blocked or unblocked compounds. Examples of diisocyanates and polyisocyanates are isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), toluylene diisocyanate, diphenylmethane diisocyanate, trimethylhexane diisocyanate, cyclohexane diisocyanate, cyclohexanedimethylene diisocyanate, tetramethylenexylylene diisocyanate, dicyclohexylmethane diisocyanate or the trimerization products, for example, aliphatic diisocyanate based isocyanurates or mixtures thereof. Aromatic diisocyanate compounds may also be present, such as, for example, tolylene diisocyanate (TDI), diphenylalkyl diisocyanates or mixtures thereof.
The diisocyanates, polyisocyanates and urethdiones can be used also in blocked form. Blocking may proceed with conventional agents, e.g., with monoalcohols, glycol ethers, ketoximes, lactams, malonic acid esters, acetoacetic acid esters, for example, ethylene glycol monobutyl ether, butanone oxime, phenol, ethyl acetoacetate, dimethylpyrazole or caprolactam.

With regard to the applicability of the powder coating composition first base coat is applied and cured. The cured base cost is wrapped with a sublimation film and sublimed under vacuum at 200°C for desired time. This results in transfer of wooden design of film to substrate completely and without any sticking of film to substrate.
The following experiments were carried out by involving only TGIC as the curing agent, blocked polyisocyanate as curing agent and by varying mixture ratio of TGIC and blocked isocyanate as the curing system. The results are displayed in Table 1 below:
Gloss standard test method of measurement being: ASTM D523

Table 2:
For dry blend dual cure polyester based on hydroxyl functional polyester ranging from 25-45 mg KOH/gm cured with blocked polyisocyanate and acid functional polyester ranging from 25-45 mg KOH/gm cured with TGIC, and its related curing and gloss as below, in accordance with the present invention.
Gloss Pure hydroxy functional Polyester cured with blocked polyisocyanate (A) Pure acid functional polyester cured with TGIC PU (B) A:B (35:65) A:B (50:50) A:B (65:35)
Gloss @60° before film sublimation
45-46
37-38
24-25
28-29
30-31
Gloss @60° after film sublimation
46-47
38-39
24-25
29-30
31-32

Thus, from the above Table 1 it is evident that matt finish only in mixture of TGIC and polyisocynate as a curing system could be achieved only when maintained at a select ratio of TGIC (A): Blocked Isocyanate (B) in the ratio range of 35:65 to 65:35 and further when the dry blend dual cure polyester for curing is based on hydroxyl functional polyester ranging from 25-45 mg KOH/gm and acid functional polyester ranging from 25-45 mg KOH/gm.
The distinctive aspect of powder coating composition of the present invention enables matt finish/ wood grain appearance on powder coated metal substrates including aluminium substrate achieved by dry blend dual cured hydroxyl & acid functional polyesters instead of using low and high hydroxyl value based polyester or low and high acid number polyester,
and also, advantageously, in the absence of silicon/fluoro based low surface energy material no sticking issues was observed and complete ink transfer on substrate without using any releasing agent and adhesion promoter could be achieved.
A thermally curable powder coating composition could be thus achieved comprising a dry blended dual cured powder based on hydroxyl functional polyester ranging from 25-45 mg KOH/gm and acid functional polyester ranging from 25-45 mg KOH/gm curable with blocked polyisocyanate and TGIC (triglycidyl isocyanurate) respectively.

It is thus possible for the present invention to attain the distinctive attributes/ aspects of the powder coating composition based on the following:
1) Matt finish wood grain coating obtained by dry blend dual cure (hydroxyl and acid functional polyesters) instead of using low and high hydroxyl number polyester or low and high acid number polyester

2) No sticking and complete ink transfer on substrate without using any releasing agent and adhesion promoter, as shown in Fig.1.
Advantageously the present powder coating composition could be exploited in commercial powder coating to achieve wood grain effect on aluminium substrate as an alternate to using a natural wood which are jeopardized through excess use of it and can help to conserve precious forest and acts as a helping hand in reducing global warming.
Further advantageous aspect of the powder coating composition of the present invention being that low hydroxy functional polyester reduced the demand for blocked polyisocyanate as otherwise if high hydroxyl polyester is involved that also causes handling issues inherently exhibiting low melt viscosity and lower Tg as a result exhibiting lump formation during storage, could be completely eliminated, and also demand for blocked isocyanate goes up leading to higher cost of coating material. By involving lower -OH value polyester not only such storage and handling issues could be avoided but also demand of blocked isocyanate could be brought down leading to an alternative coating that is economically significant.
Also similarly, with regard to higher acid value (80-120 mg KOH/gm) polyester, handling issues arise that again requires more TGIC for curing. In general, 1% of TGIC reduces the Tg of system by 2-3 deg C, and lesser requirement of costly TGIC is important that could be achieved by the present invention.