Powder coating composition

Abstract

The present invention relates to a powder coating composition comprising at least one fluoropolymer resin, at least one polyester resin, and an isocyanate crosslinking agent, in which the molar ratio of isocyanate groups of the isocyanate crosslinking agent to hydroxyl groups of the polyester resin in the composition is 2.5 to 5. The present invention further relates to a method for producing the powder coating composition, a use of the powder coating composition for architectural powder coating, and a powder coating film obtained by applying and curing the powder coating composition.

Description

[Technical field]

[0001] The present invention relates to novel powder coating compositions based on fluoropolymers, polyester resins and isocyanate crosslinkers, and to a process for the preparation of such compositions. [Background technology]

[0002] Due to increasing concerns about environmental pollution, the coatings industry is shifting towards being volatile organic compounds (VOC)-free.

[0003] Powder coating is an environmentally viable technology because it contains no VOCs and does not require air or wastewater treatment, and excess material can be reused.

[0004] Powder coatings based on acrylic, polyester and epoxy resins have been used historically but have poor weatherability.

[0005] On the other hand, fluoropolymer-based paints have excellent weather resistance, but fluoropolymers are difficult to grind into powder, and coating materials containing fluorinated resins generally contain water or solvents and are not in powder form.

[0006] To address the above problems, attempts have been made to develop powder coatings that include a fluoropolymer and another resin.

[0007] Patent Document 1 relates to a resin composition comprising a blend of a) 10 to 90% by weight of at least one fluoropolymer resin and b) 90 to 10% by weight of at least one semi-crystalline polyester resin, based on the total weight of the fluoropolymer resin and the semi-crystalline polymer resin.

[0008] Patent Document 2 relates to a powder coating composition comprising a fluororesin, a polyester polymer, a curing agent, and an ultraviolet absorber, in which the polyester polymer is a polyester polymer comprising units derived from a C8-15 aromatic polybasic carboxylic acid compound and units derived from a C2-10 polyhydric alcohol compound.

[0009] Patent Document 3 relates to a composition for a powder coating material containing polyvinylidene fluoride and at least one resin selected from the group consisting of acrylic resins, polyester resins, and epoxy resins, in which the content of the polyvinylidene fluoride is 30 to 90 parts by mass per 100 parts by mass of the total of the polyvinylidene fluoride and the resin.

[0010] Patent Document 4 relates to a powder coating composition obtained by melt-kneading a mixture containing a fluororesin, a polyester resin, a pigment, crosslinkable resin particles, an epoxy resin, and an isocyanate compound, cooling, and then pulverizing the mixture.

[0011] However, such powder compositions tend to exhibit reduced weatherability, especially after extended use, resulting in coatings with poor adhesion. Indeed, a common method for assessing such weatherability involves immersing coated panels in boiling water for a period of time.

[0012] There is therefore a need for powder coating compositions that are capable of producing coatings with improved weatherability and adhesion properties, especially after extended use. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] European Patent Application Publication No. 3670570 [Patent Document 2] European Patent Application Publication No. 2868724 [Patent Document 3] International Publication No. 2016 / 002725 [Patent Document 4] Patent No. 5419828 Summary of the Invention

[0014] A first object of the present invention is to provide a powder coating composition comprising: a) at least one fluoropolymer resin; b) at least one polyester resin; and c) isocyanate crosslinkers; Here, the molar ratio of the isocyanate groups of the isocyanate crosslinking agent to the hydroxyl groups of the polyester resin in the composition is 2.5-5.

[0015] According to some embodiments, the polyester resin is preferably a semi-crystalline polyester resin having a linear aliphatic structure or / and an alicyclic structure.

[0016] According to some embodiments, the molar ratio of isocyanate groups of the isocyanate crosslinker to hydroxyl groups of the polyester resin in the composition is from 2.5 to 4.8, preferably from 2.8 to 4.5.

[0017] According to some embodiments, the isocyanate crosslinker is selected from blocked and unblocked isocyanate crosslinkers.

[0018] According to some embodiments, the isocyanate crosslinker is present in an amount of 1-20% based on the total weight of the resin components in the powder coating composition, and / or the fluoropolymer resin is present in an amount of 5-90% based on the total weight of the resin components in the powder coating composition, and / or the polyester resin is present in an amount of 5-90% based on the total weight of the resin components in the powder coating composition.

[0019] According to some embodiments, the polyester resin is a semi-crystalline polyester resin, the semi-crystalline polyester resin comprising, or preferably consisting of, units derived from: at least one polycarboxylic acid selected from linear aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids, and at least one polyol chosen from among linear aliphatic diols and / or cycloaliphatic diols, Wherein, the polycarboxylic acid is preferably selected from among linear aliphatic C4-C8 dicarboxylic acids, preferably linear aliphatic C4-C6 dicarboxylic acids, and / or alicyclic dicarboxylic acids, more preferably selected from among adipic acid, succinic acid, 1,5-pentanedioic acid, 1,4-cyclohexanedicarboxylic acid, and combinations thereof; and the polyol is preferably selected from among linear aliphatic C2-C8 diols, preferably linear aliphatic C2-C6 diols, more preferably linear aliphatic C4-C6 diols, and / or alicyclic diols, and more preferably selected from among 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and combinations thereof.

[0020] According to some embodiments, the polyester resin is a semi-crystalline polyester resin, wherein the melting temperature of the semi-crystalline polyester resin is 75-150°C, preferably 90-130°C.

[0021] According to some embodiments, the fluoropolymer resin is selected from among polyvinylidene fluoride homopolymer and poly(vinylidene fluoride-hexafluoropropylene) copolymer.

[0022] According to some embodiments, the isocyanate crosslinker is selected from tolylene diisocyanate, 4,4'-diphenylmethane isocyanate, xylene diisocyanate, hexamethylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis(methylisocyanate)cyclohexane-isophorone diisocyanate, dimer acid diisocyanate, lysine isocyanate, 1,5-naphthalene diisocyanate, and combinations thereof.

[0023] According to some embodiments, the powder coating composition has a particle volume median diameter Dv50, as determined by laser diffraction analysis, of 10 to 250 μm, preferably 30 to 150 μm.

[0024] According to some embodiments, the powder coating composition further comprises other additives selected from among pigments, flow agents, degassing agents, waxes, and combinations thereof.

[0025] The present invention also relates to a method of making the above powder coating composition which comprises mixing a blend comprising a fluoropolymer resin and a polyester resin with an isocyanate crosslinker.

[0026] According to some embodiments, the mixing is carried out by blending the blend comprising the fluoropolymer resin and the polyester resin with the isocyanate crosslinker in a blender, preferably an extruder, to form a molten blend, which optionally includes converting the molten blend into flakes, pellets, chips or powder after cooling.

[0027] The present invention also relates to the use of the above powder coating composition for architectural powder coating.

[0028] The present invention also relates to a powder coating obtained by applying and curing the above powder coating composition.

[0029] The present invention makes it possible to address the above-mentioned needs by providing a powder coating composition that makes it possible to produce coatings with improved weather resistance and adhesion properties, especially after long-term use.

[0030] This is achieved by using a composition comprising a fluoropolymer resin, a polyester resin and an isocyanate crosslinker, in which the molar ratio of blocked or unblocked isocyanate groups (NCO) of the isocyanate crosslinker to the hydroxyl groups (OH) of the polyester resin in the composition is between 2.5 and 5. More specifically, a specific NCO to OH molar ratio makes it possible to improve the weather resistance of the coatings produced, in other words to improve the adhesion of the coatings after prolonged weathering. In fact, compositions exhibiting lower NCO to OH molar ratios (for example about 1) show a worse weather resistance than that of the compositions according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The invention will be described in more detail in the following description, without being limited thereto.

[0032] Unless otherwise stated, percentages in this application are percentages by weight.

[0033] powder coating composition In a first aspect, the present invention relates to a powder coating composition comprising: a) at least one fluoropolymer resin; b) at least one polyester resin, and c) An isocyanate crosslinking agent, wherein the molar ratio of the isocyanate groups of the isocyanate crosslinking agent to the hydroxyl groups of the polyester resin in the composition is 2.5 to 5.

[0034] The polyester resin may be a semi-crystalline polyester resin or an amorphous polyester resin.

[0035] "Semicrystalline" means non-amorphous. The phase change that determines whether a resin is semicrystalline or amorphous can be detected by differential scanning calorimetry (DSC), the method of which is described in Encyclopedia of Polymer Science and Engineering, Vol. 4, pp. 482-519, 1986 (Wiley Interscience). If the resin does not show any discernible crystallization or melting peaks, the resin is considered amorphous. If the resin shows at least one crystallization or melting peak, the resin is considered semicrystalline. In general, if various melting peaks are observed in the DSC curve, these multiple peaks are identified by melting ranges. It should be noted that the term "semicrystalline" as defined herein strictly includes semicrystalline polymers (i.e., polymers that show a discernible glass transition temperature Tg) and crystalline polymers (i.e., polymers that do not show a discernible glass transition temperature Tg).

[0036] Semicrystalline (or crystalline) polyester resins differ from conventional amorphous polyester resins used in powder coatings in that they have a heterogeneous morphology (i.e., contain a mixture of phases), are usually opaque and white at room temperature, and, in addition to having a relatively low melt viscosity, are much more insoluble in common organic solvents, such as xylene, white spirits, and ketones, than their amorphous counterparts. Semicrystalline polyester resins generally have a high degree of structural regularity (i.e., chemical, geometrical, and / or spatial symmetry).

[0037] The powder coating composition of the present invention may comprise, based on the total weight of the resin components in the powder coating composition: a) 5 to 90% by weight of at least one fluoropolymer resin; b) 5 to 90% by weight of at least one polyester resin, and c) 1-20% by weight of an isocyanate crosslinker.

[0038] The powder coating composition according to the present invention is a curable (or crosslinkable) powder coating composition.

[0039] Preferably, the fluoropolymer resin is present in the powder coating composition in an amount of 10 to 90% by weight, more preferably 40 to 90% by weight, even more preferably 60 to 90% by weight, and even more preferably 70 to 80% by weight, based on the total weight of the resin components in the powder coating composition.

[0040] Preferably, the polyester resin is present in the powder coating composition in an amount of 10 to 90% by weight, more preferably 10 to 60% by weight, even more preferably 10 to 40% by weight, and even more preferably 20 to 30% by weight, based on the total weight of the resin components in the powder coating composition.

[0041] As mentioned above, the isocyanate crosslinker is present in an amount such that the molar ratio of isocyanate groups of the isocyanate crosslinker to hydroxyl groups of the polyester resin in the composition is from 2.5 to 5. According to a preferred embodiment, the isocyanate crosslinker is present in an amount such that the molar ratio of isocyanate groups of the isocyanate crosslinker to hydroxyl groups of the polyester resin in the composition is from 2.5 to 4.8, preferably from 2.5 to 4.5. The molar ratio can be calculated using the following formula:

[0042] Molar ratio = (561 / OH value (mgKOH / g)) * (NCO content (wt%) * crosslinker amount (g)) / 42 * semicrystalline polyester amount (g)

[0043] Here, OH number is the OH number of the polyester and NCO content is the NCO content of the crosslinker.

[0044] The isocyanate crosslinker may be present in an amount of from 3 to 17% by weight, preferably from 6 to 17% by weight, based on the total weight of the resin components in the powder coating composition.

[0045] According to a preferred embodiment, in the powder coating composition of the present invention, the fluoropolymer resin, the polyester resin and the isocyanate crosslinker can be mixed by melting at least one of the resin components. In this case, the powder coating composition of the present invention comprises particles comprising the fluoropolymer resin, the polyester resin and the isocyanate crosslinker.

[0046] According to another embodiment, the powder coating composition of the present invention can be dry blended, in other words, the powder coating composition can be a mixture of a fluoropolymer resin powder, a polyester resin powder, and an isocyanate crosslinker powder.

[0047] Preferably, the particles of the powder coating composition have a volume median diameter Dv50 of 10 to 250 μm, preferably 30 to 150 μm, for example 10 to 30 μm, or 30 to 50 μm, or 50 to 100 μm, or 100 to 150 μm, or 150 to 200 μm, or 200 to 250 μm.

[0048] The Dv50 is the particle size at 50 percent (by volume) of the cumulative particle size distribution of the particles. This parameter can be determined by laser diffraction analysis.

[0049] In some embodiments, the powder coating composition consists essentially of, or consists of, at least one fluoropolymer resin, at least one polyester resin, and an isocyanate crosslinker.

[0050] Polyester Resin As mentioned above, the polyester resin may be a semi-crystalline polyester resin or an amorphous polyester resin.

[0051] According to a preferred embodiment, the polyester resin is a semi-crystalline resin, in which case the semi-crystalline polyester resin is preferably a linear semi-crystalline polyester resin.

[0052] The term "non-crystalline polyester" broadly defines a polyester that exhibits no or minimal crystallization or melting point as determined by differential scanning calorimetry (DSC).

[0053] The term "semicrystalline polyester" broadly defines a polyester that has a discernible crystallization or melting point by DSC.

[0054] The polyester resins may be based on the polycondensation reaction of (cyclo)aliphatic and / or aromatic polyols with (cyclo)aliphatic and / or aromatic polycarboxylic acids or anhydrides, esters or acid chlorides based on these acids. Examples of suitable polyols include 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol, 1-4-cyclohexanedimethanol, trimethylolpropane, 2-methylpropane-1,3-diol, hydrogenated bisphenol A (or 2,2-(dicyclohexanol)propane), 2,2,4-trimethyl-1,3-pentanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 3-hydroxy-2,2-dimethylpropyl, and 3-hydroxy-2,2-dimethylpropanoate (CA, Reg. No.=115-20-4). Suitable polycarboxylic acids that may be used include linear, (cyclo)aliphatic and / or aromatic polycarboxylic acids having 2 to 22 methylene groups, in particular succinic acid, adipic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, terephthalic acid, isophthalic acid, trimesic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid, trimellitic acid and naphthalenedicarboxylic acid.

[0055] However, preferably, the polyester resin is a semi-crystalline polyester resin, more preferably having a linear aliphatic and / or cycloaliphatic structure. In particular, such a semi-crystalline polyester resin may comprise units derived from: a polycarboxylic acid selected from at least linear aliphatic dicarboxylic acids and / or cycloaliphatic dicarboxylic acids, and a polyol chosen from at least linear aliphatic diols and / or cycloaliphatic diols;

[0056] Preferably, such semi-crystalline polyester resins do not include units derived from aromatic polycarboxylic acids (such as aromatic dicarboxylic acids) and / or aromatic polyols.

[0057] Additionally, such semi-crystalline polyester resins can consist essentially of or consist of units derived from: a polycarboxylic acid selected from at least linear aliphatic dicarboxylic acids and / or cycloaliphatic dicarboxylic acids, and a polyol chosen from at least linear aliphatic diols and / or cycloaliphatic diols;

[0058] Advantageously, the linear aliphatic dicarboxylic acid is a linear aliphatic C 4 -C 8 Dicarboxylic acids, more preferably straight chain aliphatic C 4 -C 6 It is a dicarboxylic acid. For example, it is a straight chain aliphatic C 4 Dicarboxylic acids, linear aliphatic C 5 Dicarboxylic acids, linear aliphatic C 6 Dicarboxylic acids, linear aliphatic C 7 Dicarboxylic acids and / or linear aliphatic C 8 It may be a dicarboxylic acid.

[0059] Advantageously, said cycloaliphatic dicarboxylic acid is 6 -C 8 It is an alicyclic dicarboxylic acid.

[0060] Preferably, the polycarboxylic acid is selected from adipic acid, succinic acid, 1,5-pentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and combinations thereof.

[0061] Preferably, the linear aliphatic diol is a linear aliphatic C 2 -C 8 diol, more preferably a straight chain aliphatic C 2 -C 6 diol, more preferably a straight chain aliphatic C 4 -C 6 The linear aliphatic diol is a linear aliphatic C 2 Diol, linear aliphatic C 3 Diol, linear aliphatic C 4 Diol, linear aliphatic C 5 Diol, linear aliphatic C 6 Diol, linear aliphatic C 7 Diol and / or linear aliphatic C 8 It may be a diol.

[0062] Advantageously, said cycloaliphatic diol is 6 -C 8 It may be a cycloaliphatic diol.

[0063] In a preferred embodiment, the polyol is selected from among 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and combinations thereof.

[0064] In a particularly preferred embodiment, the semicrystalline polyester resin having a linear aliphatic and / or cycloaliphatic structure is selected from among polybutylene succinate, polybutylene 1,4-cyclohexanedicarboxylate and 1,4-cyclohexanedimethanol pentadionate.

[0065] To form polyester resins with significant crystallinity, it is preferred, but not essential, that the polycarboxylic acids and polyols used in the polycondensation reaction contain an even number of carbon atoms. The use of symmetrically substituted aliphatic cyclic reagents, such as 1,4-cyclohexanedicarboxylic acid or 1,4-cyclohexanedimethanol, tends to promote crystallinity. However, such reagents tend to produce semi-crystalline polyester resins that have melting temperatures higher than the normal cure temperatures of thermosetting polyester powder coatings. To produce semi-crystalline polyester resins with lower melting temperatures, they can be represented by the formula HO(CH 2 ) n OH or diol of formula HOOC(CH 2 ) n It may be preferable to use COOH in combination with a dicarboxylic acid, where n is an even number, preferably 2-8, for example 4 or 6.

[0066] However, this does not preclude the use of monomeric polycarboxylic acids or polyols containing an odd number of carbon atoms in the polycondensation reaction, or the use of certain experimental techniques known to promote polymer crystallization, such as maintaining the polyester product at a temperature intermediate its glass transition temperature (Tg) and melting temperature (Tm) for a period of time, or carrying out the synthesis in (or treating the final polyester resin with) a high boiling organic solvent such as 1,3-dichlorobenzene or diphenyl ether and maintaining the polyester above its Tm for a period of time before cooling to ambient temperature. These and other techniques for promoting crystallinity in carboxylic acid group-containing polyester resins may be used alone or in combination.

[0067] The polyester resin may be a mixture of two or more of the above mentioned resins.

[0068] When the polyester resin is an amorphous polyester, it may contain units such as terephthalic acid, neopentyl glycol, and trimethylolpropane. Specific examples of useful commercially available amorphous polyesters include Cargill 3000® resin, Rucote 105®, REAFREE® 17014, and REAFREE® 5709.

[0069] When the polyester resin is a semi-crystalline polyester resin, it may have a melting temperature of 75° C. to 150° C., preferably 90° C. to 130° C., for example, it may have a melting temperature of 75° C. to 90° C., or 90° C. to 100° C., or 100° C. to 110° C., or 110° C. to 120° C., or 120° C. to 130° C., or 130° C. to 150° C. The melting temperature may be measured according to ISO 11357-3:1999 Plastics - Differential scanning calorimetry (DSC) Part 3, but with a heating rate of 10° C. / min.

[0070] Specific examples of commercially available semi-crystalline polyester resins include UVECOAT® 9010, UV1605, UV2335, and Matflex AHA90.

[0071] The glass transition temperature Tg of the polyester resin is preferably lower than 100°C, and may be -20 to 50°C, more preferably -15 to 40°C. In some embodiments, the polyester resin has a glass transition temperature of -20 to -10°C, or -10 to 0°C, or 0 to 10°C, or 10 to 20°C, or 20 to 30°C, or 30 to 40°C, or 40 to 50°C, or 50 to 55°C. The glass transition temperature can be measured according to ISO 11357-2 Plastics - Differential scanning calorimetry (DSC) Part 2, but with a heating rate of 10°C / min. When examined by DSC, semi-crystalline polyester resins may show two glass transitions, one due to free-moving amorphous regions in the polyester resin and the other due to amorphous regions whose movement is constrained by adjacent crystallites. In these cases, the Tg values ​​are both within the above temperature range.

[0072] The polyester resin preferably has a hydroxyl number of at least 15 mgKOH / g. This ensures proper curing. Most preferably, the polyester resin has a hydroxyl number of at least 20 mgKOH / g. It preferably has a hydroxyl number of 70 mgKOH / g or less, most preferably 40 mgKOH / g or less. In particular, the hydroxyl number may be 15-20 mgKOH / g, or 20-25 mgKOH / g, or 25-30 mgKOH / g, or 30-35 mgKOH / g, or 35-40 mgKOH / g, or 40-50 mgKOH / g, or 50-60 mgKOH / g, or 60-70 mgKOH / g. The hydroxyl number can be measured according to DIN 53240-2.

[0073] Also preferably, the polyester resin has an acid number of less than or equal to 10 mg KOH / g, more particularly less than or equal to 5 mg KOH / g, which can be measured according to ASTM D-1639-90.

[0074] Polyester resins having such hydroxyl and acid values ​​can be prepared by the polycondensation reaction of polyols with polycarboxylic acids (or anhydrides, esters, or acid chlorides based on these acids) using an excess of alcohol relative to the acid.

[0075] In an alternative, less preferred embodiment, the polyester resin has an acid value of at least 15 mgKOH / g, most preferably at least 20 mgKOH / g. It may have an acid value of 70 mgKOH / g or less, most preferably 40 mgKOH / g or less. It may have an acid value of, for example, 15-20 mgKOH / g, or 20-30 mgKOH / g, or 30-40 mgKOH / g, or 40-55 mgKOH / g, or 55-70 mgKOH / g. It may have a hydroxyl value of 10 mgKOH / g or less, more particularly 5 mgKOH / g or less. Polyester resins having such hydroxyl and acid values ​​can be prepared by polycondensation reaction of polyols with polycarboxylic acids (or anhydrides, esters or acid chlorides based on these acids) using an excess of acid relative to the alcohol.

[0076] The number average molecular weight Mn of the polyester resin is preferably at least 1500. With such a number average molecular weight, the polyester resin can contribute to the toughness of the coating film. A number average molecular weight Mn of at least 2000 is particularly preferred.

[0077] The number average molecular weight Mn of the polyester resin is preferably less than or equal to 15000, most preferably less than or equal to 5000. Particular mention should be made of number average molecular weights of up to 4000. The number average molecular weight Mn can be determined by gel permeation chromatography (GPC).

[0078] In some embodiments, the number average molecular weight Mn of the polyester resin is 1500 to 2000, or 2000 to 3000, or 3000 to 4000, or 4000 to 5000, or 5000 to 6000, or 6000 to 7000, or 7000 to 8000, or 8000 to 9000, or 9000 to 10000, or 10000 to 11000, or 11000 to 12000, or 12000 to 13000, or 13000 to 14000, or 14000 to 15000.

[0079] When the polyester resin is a semi-crystalline polyester resin, it may have a heat of fusion of 20-100 J / g, preferably 25-90 J / g. The heat of fusion may be determined by DSC according to ISO 11357-3:1999, but at a heating rate of 10°C / min. In examples, the heat of fusion may be 20-25 J / g, or 25-30 J / g, or 30-40 J / g, or 40-50 J / g, or 50-60 J / g, or 60-70 J / g, or 70-80 J / g, or 80-90 J / g.

[0080] When the polyester resin is an amorphous polyester resin, it may have a heat of fusion of 0 to 20 J / g, preferably 0 to 5 J / g.

[0081] The above polyester resin is heated at 165℃ and a shear rate of 30 s -1 In particular, the melt viscosity at 165°C, 30s can be 0.005 to 10 Pa·s. -1 The melt viscosity may be from 0.005 to 0.05 Pa s, or from 0.05 to 0.5 Pa s, or from 0.5 to 1 Pa s, or from 1 to 2 Pa s, or from 2 to 3 Pa s, or from 3 to 4 Pa ​​s, or from 4 to 6 Pa s, or from 6 to 8 Pa s, or from 8 to 10 Pa s at a shear rate of 165° C. The melt viscosity may be measured according to ASTM D-4287-00 at 165° C.

[0082] The polyester resins can be prepared as described in DE 10 2006 057837.

[0083] Fluoropolymer Resin The fluoropolymer resin may contain at least one unit from a monomer selected from among vinyl monomers containing at least one fluorine atom, vinyl monomers containing at least one fluoroalkyl group, and vinyl monomers containing at least one fluoroalkoxy group in its backbone. By way of example, the monomer may be vinyl fluoride; vinylidene fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) or perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); or the monomer of formula CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 The product of X, where X is SO 2 F, C.O. 2 H, C.H. 2 OH, CH 2 OCN or CH 2 OPO 3 H); Formula CF 2 =CFOCF 2 CF 2 SO 2 F product; formula F(CF 2 )nCH 2 OCF=CF 2 where n is 1, 2, 3, 4 or 5; 1 CH 2 OCF=CF 2 (wherein R 1 is hydrogen or F(CF 2 ) m and m is 1, 2, 3 or 4; 2 OCF=CH 2 (wherein R2 is F(CF 2 )p, where p is 1, 2, 3, or 4); perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene, or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

[0084] The fluoropolymer resins may be homopolymers or copolymers and may contain units from non-fluorinated monomers such as ethylene.

[0085] Advantageously, said fluoropolymer resin is a polyvinylidene fluoride resin.

[0086] The polyvinylidene fluoride resin is preferably a homopolymer.

[0087] In other embodiments, the polyvinylidene fluoride resin may be a copolymer containing vinylidene fluoride units and units from one or more other monomers, such as vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) or perfluoro(propyl vinyl) ether (PPVE), perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), or a monomer represented by the formula CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 The product of X, where X is SO 2 F, C.O. 2 H, C.H. 2 OH, CH 2 OCN or CH 2 OPO 3 H); Formula CF 2 =CFOCF 2 CF 2 SO2 F product; formula F(CF 2 )nCH 2 OCF=CF 2 where n is 1, 2, 3, 4 or 5; 2 OCF=CF 2 where R' is hydrogen or F(CF 2 )z, where z is 1, 2, 3 or 4); Formula R''OCF=CH 2 where R″ is F(CF 2 )z, z being 1, 2, 3 or 4); perfluorobutylethylene (PFBE); 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene. Hexafluoropropylene is preferred. The polyvinylidene fluoride copolymer may also contain units from ethylene monomers. Preferably, when the polyvinylidene fluoride resin is a copolymer, it contains at least 50% by weight of vinylidene fluoride units, more preferably at least 60% by weight, more preferably at least 70% by weight, and even more preferably at least 80% by weight.

[0088] The polyvinylidene fluoride resin may be composed of vinylidene fluoride units and, optionally, units derived from one or more other monomers selected from the following: vinyl fluoride, trifluoroethylene, CTFE, 1,2-difluoroethylene, TFE, HFP, perfluoro(alkyl vinyl) ethers such as PMVE, PEVE or PPVE, perfluoro(1,3-dioxole), PDD, fluoroalkyl ethers of formula CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 The product of X, where X is SO 2 F, C.O. 2 H, -CH 2 OH, CH 2 OCN or CH 2 OPO 3 H), the formula CF 2 =CFOCF 2 CF 2 SO 2The product of F, formula F(CF 2 )nCH 2 OCF=CF 2 where n is 1, 2, 3, 4 or 5, a product of the formula R'CH 2 OCF=CF 2 where R' is hydrogen or F(CF 2 )z, where z is 1, 2, 3 or 4); R'OCF=CH 2 where R″ is F(CF 2 )z, where z is 1, 2, 3 or 4), PFBE, 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

[0089] The polyvinylidene fluoride resin may be composed of vinylidene fluoride units and, optionally, units derived from one or more other monomers selected from vinyl fluoride, trifluoroethylene, CTFE, 1,2-difluoroethylene, TFE and HFP.

[0090] The polyvinylidene fluoride resin may be composed of vinylidene fluoride units and optionally HFP units.

[0091] The fluoropolymer resin may be a mixture of two or more of the above resins.

[0092] The fluoropolymer may have a viscosity, measured by capillary rheometry according to ASTM D3835 at a shear rate of 100 s-1 and 230°C, of ​​less than 3000 Pa·s, more preferably less than 1500 Pa·s.

[0093] Advantageously, the fluoropolymer resin has a melting temperature higher than the melting temperature of the polyester resin or the glass transition temperature of the amorphous polyester.

[0094] Isocyanate Crosslinker "Isocyanate crosslinker" means a crosslinker containing at least one isocyanate (NCO) group, preferably more than one isocyanate (NCO) group. The isocyanate crosslinker may contain blocked and / or unblocked isocyanate groups. Thus, when the ratio of each component is mentioned and measured, isocyanate groups refers to the sum of blocked and / or unblocked isocyanate groups.

[0095] The isocyanate crosslinker reacts with the polyester resin, allowing the composition to cure (crosslink) at a particular temperature.

[0096] In a preferred embodiment, the fluoropolymer resin does not react with an isocyanate crosslinker. In particular, in a preferred embodiment, the fluoropolymer resin does not contain hydroxy groups and / or does not contain any reactive groups that can react with isocyanate groups.

[0097] By "blocked isocyanate" is meant the reaction product of an isocyanate whose isocyanate functionality has already reacted with a "blocking agent." Thus, the blocked isocyanate will not react until and is unblocked at a deblocking temperature.

[0098] According to a preferred embodiment, the isocyanate crosslinking agent is a blocked isocyanate crosslinking agent, i.e. a crosslinking agent comprising blocked isocyanate groups.

[0099] The blocking agent may be chosen in particular from methanol, ethanol, n-propanol, n-butanol, n-pentanol, iso-propanol, w-hydroperfluoroalcohol, 1-chloro-2-propanol, 1,3-dichloro-2-propanol, ethylene chlorohydrin, phenol, 2-methyl-2-propanol, m-cresol, o-nitrophenol, p-nitrophenol, p-chlorophenol, guaiacol, resorcinol, phloroglucinol, 1-dodecanethiol, benzenethiol, ethyl acetoacetate, diethyl malonate, ε-caprolactam, ethyl carbamate, boric acid and acetylacetone.

[0100] The isocyanate crosslinker can be selected from tolylene diisocyanate, 4,4'-diphenylmethane isocyanate, xylene diisocyanate, hexamethylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis(methylisocyanate)cyclohexane, isophorone diisocyanate, dimer acid diisocyanate, lysine isocyanate, 1,5-naphthalene diisocyanate, and combinations thereof.

[0101] Specific examples of commercially available crosslinkers include Vestagon® B1530, Vestagon® B1400, Vestagon BF1320, Vestagon® BF1321, and Vestagon® BF1540.

[0102] Other Additives The powder coating composition may also contain other additives, for example selected from pigments, flow agents, degassing agents, waxes, leveling agents for reducing gloss, additives for improving scratch resistance, surfactants, antioxidants, UV absorbers and stabilizers, and combinations thereof. These other additives are preferably present in an amount of 10-30% by weight, preferably 15-27% by weight, based on the total weight of the powder coating composition. These additives are described in "Coatings Formulation", Bodo Mueller, Ulrich Poth, 2nd Revised Edition, Hanover: Vincentz Network, 2011, European Coatings Tech Files, ISBN 978-3-86630-891-6.

[0103] According to some embodiments, the powder coating composition is pigment-free.

[0104] According to another embodiment, the powder coating composition includes one or more pigments to provide an opaque coating when applied to a substrate. These pigments may be present in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, of the total weight of the resin components in the powder coating composition.

[0105] Preparation process In another aspect, the present invention relates to a method for producing the above powder coating composition.

[0106] Such a method involves mixing the fluoropolymer resin with the polyester resin and the isocyanate crosslinker, and optionally other additives.

[0107] The mixing step may be a dry blending of the powdered ingredients.

[0108] Alternatively and preferably, the mixing step may be a step of melt blending some or all of the components, which blend is then ground to a powder after solidification. If only some of the components are melt blended and ground to a powder, the resulting particles are dry blended with the remaining components in powder form.

[0109] In the case of melt blending, the fluoropolymer resin and the polyester resin are preferably already homogeneously blended, but can be blended with the isocyanate crosslinker and potentially additives at a temperature below the temperature at which the isocyanate crosslinker initiates cure of the composition, in other words, the isocyanate crosslinker remains inactive during melt blending.

[0110] The melt blending can be carried out at a temperature of 60 to 160°C, preferably 60 to 140°C, and more preferably 80 to 140°C.

[0111] By "homogeneous blend" is meant a macroscopically homogeneous blend, ie, a blend in which no phase separation is visible to the naked eye.

[0112] The blender is preferably an extruder or a co-kneader, more preferably a twin-screw extruder or a co-kneader.

[0113] Preferably, the blend is first formed into a solid compound such as flakes, chips or pellets, and the solid compound is ground into a powder. Any grinding technique can be used to carry out this step, such as a hammer mill, a pin mill, a grinder using an abrasive disk or an impact classifier mill.

[0114] The method may include the step of selecting powder particles having a desired particle size distribution, for example by passing the powder through a sieve.

[0115] The present invention also relates to a powder coating composition produced according to the above-described process.

[0116] Purpose In another aspect, the present invention relates to the use of the powder coating composition.

[0117] Preferably, the coating composition is used as an architectural powder coating (for example, for painting the exterior walls of buildings) or an automotive coating.

[0118] Therefore, the architectural powder coating has high weather resistance, for example, it can show gloss retention of 60% or more after 4500 hours when measured according to ASTM D-523-60E.

[0119] Architectural powder coatings can last for 10 years or more.

[0120] In another aspect, the present invention relates to a process for coating a substrate comprising: applying the powder coating composition onto a substrate; The powder coating composition is melted.

[0121] The substrate may be wood or metal such as aluminum or steel grades.

[0122] The coating of the substrate may be performed by electrostatic spraying. In that case, the process for coating the substrate may include the following steps: - charging the powder coating composition; Spraying electrically charged powder onto a substrate; The substrate coated with the powder is heated to a temperature above the melting temperature of the powder.

[0123] The powder coating composition can be melted by heating the substrate covered with the powder to a temperature higher than the melting temperature of the powder, for example, 160°C to 280°C, preferably 180°C to 250°C.

[0124] The process of coating the substrate includes a step of curing the powder coating composition applied on the substrate, which may be performed simultaneously with the step of melting the powder coating composition. Curing may be induced by heating the powder coating composition, for example to a temperature of 160°C to 280°C, preferably 180°C to 250°C.

[0125] The present invention also relates to a powder coating obtainable by applying and curing at least one powder coating composition as described above.

[0126] The present invention also relates to an object comprising the above-described powder coating. EXAMPLES

[0127] The following examples illustrate the invention without limiting it.

[0128] Example 1 Compounds A and B were prepared as follows: Compound A (comparison compound): PVDF homopolymer with a melting point of 169°C and a melt viscosity of 6 kPo; PVDF-HFP copolymer with a melting point of 112°C and a viscosity of 0.7 kPo, A semi-crystalline polyester (polybutylene succinate) having a melting point of 110°C, a heat of fusion of 20.9 J / g, a hydroxyl number of 30-45 mg KOH / g, and a melt viscosity of less than 1 Pa.s; · Isocyanate crosslinkers (Vestagon B-1530, Evonik), Benzoin (a degassing agent), and TiO 2 Pigment (CR95, Ishihara) were blended at 140° C. in a weight ratio of 49.21 / 3.99 / 19.74 / 3.06 / 1.00 / 23.00. The molar ratio of NCO / OH was 1 / 1.

[0129] Compound B (according to the invention): PVDF homopolymer with melting point of 169℃ and melt viscosity of 6kPo, PVDF-HFP copolymer with melting point of 112°C and viscosity of 0.7 kPo, A semi-crystalline polyester (polybutylene succinate) with a melting point of 110°C, heat of fusion of 20.9 J / g, hydroxyl number of 30-45 mg KOH / g and melt viscosity according to ISO 3129 of less than 1 Pa·s; · Isocyanate crosslinkers (Vestagon B-1530, Evonik), Benzoin (a degassing agent), and TiO 2 Pigment (CR95, Ishihara) were blended at 110°C in a weight ratio of 43.26 / 7.64 / 14.89 / 10.21 / 1 / 23. The NCO / OH molar ratio was 4.42 / 1.

[0130] All compounds were individually ground in a high-speed blender and sieved through a 125 μm mesh. The sieved powders were electrostatically sprayed onto chromated aluminum panels and baked at 240 °C for 15 min.

[0131] The coatings were then evaluated for the following properties: · Crosshatch adhesion per AAMA 2605-13 8.4.1.1; · Cross-hatch adhesion with reverse impact per ASTM D3359-02; · Direct and reverse impact per AAMA 2605-13 A5.2.2; -MEK solvent resistance according to ASTM D4752 (200 double rubs) Weatherability is evaluated by gloss retention after 4500 hours of QUV testing according to ASTM D3451. If gloss retention is 60% or more, the coating is considered to be "passed" and if it is less than 60%, the coating is considered to be "failed"; · Adhesion after boiling water by immersing the painted panel in boiling water for 5 hours and then performing the cross-hatch adhesion test according to AAMA 2605-13 8.4.1.1.

[0132] The results are shown in the table below:

[0133] [Table 1]

[0134] From the above table it is clear that compositions according to the invention provide improved adhesion properties after extended use compared to compositions having NCO to OH molar ratios outside the claimed ranges.

[0135] Example 2 Compound C (molar ratio of NCO / OH=1.1) is a comparative compound, compounds D (molar ratio of NCO / OH=3), E (molar ratio of NCO / OH=4), F (molar ratio of NCO / OH=4) and G (molar ratio of NCO / OH=5) are compounds according to the invention.

[0136] Compounds C through G were prepared using: • A blend consisting of a PVDF homopolymer with a melting point of 169°C and a melt viscosity of 6 kPo and a semicrystalline polyester with a melting point of 110°C, a heat of fusion of 20.9 J / g, a hydroxyl number of 30-45 mg KOH / g and a melt viscosity of <1 Pa.s; ● Isocyanate crosslinker (Vestagon B1530 from Evonik); ● Benzoin (a degassing agent); and ● TiO 2 Pigment (Kronos 2160).

[0137] The weight ratios of the different components and the equivalent weight of crosslinker with respect to the hydroxyl number of the polyester are reported in the table below. In compounds C, D, E and G the hydroxyl number of the resin is about 9.5 mg KOH / g, in compound F the hydroxyl number is 7.4 mg KOH / g.

[0138] [Table 2]

[0139] The resin comprises PVDF homopolymer and semi-crystalline polyester as reported in the table below, where the weight ratio of the PVDF homopolymer and the semi-crystalline polyester is based on the total weight of the resin.

[0140] [Table 3]

[0141] All compounds were prepared in a twin-screw extruder, then milled at room temperature using an ultra-centrifugal hammer mill and sieved through a 120 μm mesh to obtain powders with a Dv50 of 35 μm. The sieved powders were electrostatically sprayed onto non-chromated aluminum panels of types 5005 and 6060 conforming to Qualicoat Class 3 and AAMA2605-13 and baked at 220 °C for 15 min. The coating thicknesses formed were 80-100 μm.

[0142] According to Qualicoat 3, the coatings were evaluated for the following properties: ● Cross-hatch adhesion of AL 5005 panels according to AAMA 2605-13 8.4.1.1 and ISO 2409 (Qualicoat Class 3 2.4.1). Test results range from 0 (perfect adhesion) to 5 (complete removal of coating during test); • Boiling water adhesion by immersing the painted panel in boiling water for 5 hours and performing cross-hatch adhesion test according to AAMA 2605-13 8.4.1.1 and ISO 2409 (Qualicoat Class 3 2.16). • Adhesion after mechanical deformation following bending test with conical mandrel according to ISO 1519 (Qualicoat Class 3 2.7); ● Weather resistance evaluated by gloss retention after 4500 hours of QUV testing in accordance with ASTM D3451. If the gloss retention is 60% or more, the coating is considered to be "passed", and if it is less than 60%, the coating is considered to be "failed".

[0143] The results are shown in the following table:

[0144] [Table 4]

[0145] From the above table it is clear that compositions according to the invention provide improved adhesion properties after extended use compared to compositions having NCO to OH molar ratios outside the claimed ranges.

Claims

1. A powder coating composition comprising a) at least one fluoropolymer resin b) at least one polyester resin; and c) an isocyanate crosslinking agent; wherein the molar ratio of the blocked or unblocked isocyanate groups of the isocyanate crosslinking agent to the hydroxyl groups of the polyester resin in the composition is 2.5 to 5. The powder coating composition.

2. The powder coating composition according to claim 1, wherein the polyester resin is preferably a semi-crystalline polyester resin having a linear aliphatic structure and / or an alicyclic structure.

3. The powder coating composition according to claim 1, wherein the molar ratio of the isocyanate groups of the isocyanate crosslinking agent to the hydroxyl groups of the polyester resin in the composition is 2.5 to 4.8, preferably 2.8 to 4.

5.

4. The powder coating composition according to claim 1, wherein the isocyanate crosslinking agent is selected from a blocked isocyanate crosslinking agent and an unblocked isocyanate crosslinking agent.

5. The isocyanate crosslinking agent is present in an amount of 1 to 20% based on the total weight of the resin components in the powder coating composition, and / or the fluoropolymer resin is present in an amount of 5 to 90% based on the total weight of the resin components in the powder coating composition, and / or the polyester resin is present in an amount of 5 to 90% based on the total weight of the resin components in the powder coating composition. The powder coating composition according to claim 1.

6. The powder coating composition according to claim 1, wherein the polyester resin is a semi-crystalline polyester resin, the semi-crystalline polyester resin comprises units derived from the following, and preferably consists of the units: - at least one polycarboxylic acid selected from linear aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids, and - at least one polyol selected from linear aliphatic diols and / or alicyclic diols Here, the polycarboxylic acid is preferably selected from linear aliphatic C4-C8 dicarboxylic acids, preferably linear aliphatic C4-C6 dicarboxylic acids, and / or alicyclic dicarboxylic acids, more preferably selected from adipic acid, succinic acid, 1,5-pentanedioic acid, 1,4-cyclohexanedicarboxylic acid, and combinations thereof; and the polyol is preferably selected from linear aliphatic C2-C8 diols, preferably linear aliphatic C2-C6 diols, more preferably linear aliphatic C4-C6 diols, and / or alicyclic diols, more preferably selected from 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and combinations thereof.

7. The powder coating composition according to claim 1, wherein the polyester resin is a semi-crystalline polyester resin, and the melting temperature of the semi-crystalline polyester resin is 75 to 150°C, preferably 90 to 130°C.

8. The powder coating composition according to claim 1, wherein the fluoropolymer resin is selected from polyvinylidene fluoride homopolymer and poly(vinylidene fluoride - hexafluoropropylene) copolymer.

9. The powder coating composition according to claim 1, wherein the isocyanate crosslinking agent is selected from tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis(isocyanatomethyl)cyclohexane isophorone diisocyanate, dimer acid diisocyanate, lysine isocyanate, 1,5-naphthalene diisocyanate, and combinations thereof.

10. The powder coating composition according to claim 1, having a particle volume median diameter Dv50 of 10 to 250 μm, preferably 30 to 150 μm, as determined by laser diffraction analysis.

11. The powder coating composition according to claim 1, further comprising other additives selected from pigments, flow agents, degassing agents, waxes, and combinations thereof.

12. A method for producing the powder coating composition according to any one of claims 1 to 11, comprising mixing a blend containing the above fluoropolymer resin and the above polyester resin with the above isocyanate crosslinking agent.

13. The above mixing forms a melt blend by blending a blend containing the above fluoropolymer resin and the above polyester resin with the above isocyanate crosslinking agent in a blender, preferably an extruder, and the method optionally includes cooling the melt blend and then converting it into flakes, pellets, chips or powder. The method according to claim 12.

14. Use of the powder coating composition according to any one of claims 1 to 11 for architectural powder coating.

15. A powder coating film obtained by applying and curing the powder coating composition according to any one of claims 1 to 11.