HK1162188B - One component heat-curable powder coating composition - Google Patents

Description

One-component heat-curable powder coating composition

The present invention relates to a heat-curable powder coating composition, a process for its preparation, the use of the powder coating composition for coating a substrate, a substrate coated with the powder coating composition and a process for coating a substrate using the powder coating composition.

EP0844286a1 discloses dual heat and uv curable powder coating compositions wherein the composition in the form of solid particles comprises a mixture of:

a) a film-forming resin;

b) a second resin copolymerizable with the base resin;

c) a photoinitiator; and

d) a thermal initiator.

JP 55027423a discloses a composition comprising: a)100 parts by weight of an unsaturated polyester which is solid at room temperature; b) < 1 part by weight of metallic Pb (compound) or Mn (compound); and c) less than 5 parts by weight of a free radical initiator.

EP0957141a1 discloses a low temperature mixture of powder (a) and powder (B), wherein at least powder (a) comprises an unsaturated polyester resin and a free radical initiator for initiating polymerization of the unsaturated polyester resin in the powder coating composition, and component (B) comprises a polymerization accelerator.

Such as the article "overview of the Powder coatings market world" by G.Maggiore in Pitture e Vernice Europe 1/92, pp.15-22 and the report "Powder coatings" by D.Richart: current Developments, Future Trends (Waterborn, High-Solids and Powder Coatings Symposium, 1995, 2.s.22-24) have shown that Powder coating compositions that can cure with low substrate thermal stress and are therefore suitable for heat-sensitive substrates such as wood and plastics continue to be investigated.

In addition to the desire for powder coating compositions to be curable at low temperatures, it is also desirable for the powder coating compositions to be processable in an extruder.

Thus, there is a need for a powder coating composition that balances the ability to cure to an acceptable degree at low temperatures (e.g., up to 130 ℃) with good processability in an extruder. Such powder coating compositions will be suitable not only for non-heat sensitive substrates but also in particular for heat sensitive substrates.

Furthermore, it would be desirable to have a one-component powder coating composition that can provide a coating with better properties (e.g., appearance, acetone resistance, impact resistance, etc.) as opposed to a two-component powder coating composition.

It is therefore an object of the present invention to provide a one-component, heat-curable powder coating composition which is easy to process in an extruder and which can be cured to an acceptable degree if cured at low temperatures (e.g. at up to 130 ℃).

This object is achieved by a one-component, heat-curable powder coating composition comprising: a resin comprising reactive unsaturated groups and wherein all of said reactive unsaturated groups are carbon-carbon double bonds directly attached to an electron withdrawing group; a thermal initiation system comprising a transition metal catalyst and a peroxide, wherein the peroxide is selected from the group of peroxyesters, mono-peroxycarbonates, and mixtures thereof; a co-crosslinking agent selected from the group of vinyl ethers, vinyl esters, vinyl amides, itaconates, enamines, and mixtures thereof.

Another advantage of the compositions of the invention is that they can have satisfactory flow properties.

The flow characteristics (flow) of the powder coating composition on the substrate can be determined by comparing the flow of the coating (coating thickness of about 60 μm) with a PCI powder coating flow plate (ACT Test Panels Inc.). The flow rating is from 1 to 10, with 1 representing the most uneven coating and 10 representing the best flowing coating.

By "easy to process in an extruder" is meant that the powder coating composition can be extruded to form an extrudate without forming gel particles, preferably without forming a gel.

By "cured to an acceptable level" is meant that the powder coating resists at least 50 Acetone Double Rubs (ADR) when cured at up to 130 ℃, for example up to 20 minutes, preferably up to 15 minutes.

For the purposes of the present invention, "acetone double rubs"(ADR) means a weight of 980mg wrapped with cotton cloth soaked in acetone and a contact surface area of 2cm²And then reciprocating the hammer head on a coating surface having a thickness of about 60 μm. After each 20 rubs, the cloth was soaked in acetone. Testing was continued until the coating was removed (and the number of ADRs obtained was noted) or until 100 ADRs were reached.

Preferably, when a substrate (e.g. an aluminum substrate, such as an ALQ board) is coated with a powder coating composition of the invention and cured at a temperature of at most 130 ℃, for example for at most 20 minutes, preferably for at most 15 minutes, a coating prepared from said coating composition is resistant to at least 60 ADRs, such as at least 70 ADRs, at least 80 ADRs, at least 90 ADRs or at least 100 ADRs.

Within the scope of the present invention, "thermally curable" means that curing of the powder coating composition can be achieved by using heat. The presence of a thermal initiation system in the compositions of the present invention makes this thermal curing possible. The advantages of thermal curing are: in a one-step process that does not require the use of additional equipment (e.g., equipment that generates UV light or accelerates electrons) to heat the powder coating composition, the powder coating can be melted and cured on the substrate; radiation curing of powder coating compositions on substrates, in turn, requires two steps to melt and cure the powder coating on the substrate. In the two-step radiation curing, the powder coating composition is first melted on the substrate with heat and then cured with UV radiation or electron beam radiation. Thermal curing is particularly useful for coating 3D objects.

Preferably, the powder coating composition of the present invention is cured at a temperature of 60 to 130 ℃. More preferably, the curing temperature is at least 65 ℃, even more preferably at least 70 ℃, such as at least 75 ℃, such as at least 80 ℃. More preferably, the curing temperature is at most 125 ℃, even more preferably at most 120 ℃, in particular at most 115 ℃, in particular at most 110 ℃, such as at most 105 ℃ or such as at most 100 ℃. In particular examples, it may be advantageous to cure the powder coating composition at even lower temperatures (e.g., at temperatures below 100 ℃, below 95 ℃, below 90 ℃, or even below 85 ℃), for example, for more heat-sensitive substrates.

"powder coating composition" refers to a composition that can be used as a dry (without solvent or other carrier) fine particulate solid to coat a substrate, which when melted and fused forms a continuous film that adheres to the substrate.

The transition metal catalyst and peroxide content herein are calculated based on the amount of resin and co-crosslinker (resin system) in the powder coating composition. In other words, the resin system is a resin containing reactive unsaturated groups plus a co-crosslinker, excluding the usual powder coating composition additives such as pigments, fillers, etc.

The resin comprises a reactive unsaturated group, wherein the reactive unsaturated group is a carbon-carbon double bond directly attached to an electron-withdrawing group. "reactive unsaturated group" refers to a carbon-carbon double bond directly attached to an electron withdrawing group that can react with a free radical generated by an initiator. To avoid confusion, the reactive unsaturated groups do not contain aromatic rings.

Examples of suitable resins include polyesters, polyacrylates (═ acrylic resins), polyurethanes, epoxies, polyamides, polyesteramides, polycarbonates, polyureas, and the like, and mixtures thereof. The preferred resin is polyester.

The reactive unsaturated group (carbon-carbon double bond directly linked to the electron-withdrawing group) may be located on the main chain of the resin, a side chain of the resin (main chain), a terminal of the resin, or on a combination of these positions.

Preferably the resin with reactive unsaturation used in the powder coating composition of the invention is based on fumaric acid, maleic acid, itaconic acid, acrylic acid and/or methacrylic acid, more preferably the resin with reactive unsaturation used is based on fumaric acid and/or maleic acid. Examples of how these reactive unsaturated groups can be introduced into the resin are described below.

Polyesters are generally polycondensation products of polyols and polycarboxylic acids.

Examples of polycarboxylic acids which may be used to prepare the polyester include isophthalic acid, terephthalic acid, hexahydroterephthalic acid, 2, 6-naphthalenedicarboxylic acid and 4, 4' -oxybis-benzoic acid, 3, 6-dichlorophthalic acid, tetrachlorophthalic acid, tetrahydrophthalic acid, hexahydroterephthalic acid, hexachloroendomethyltetrahydrophthalic acid, endomethyltetrahydrophthalic acid, phthalic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, adipic acid, succinic acid and 1, 2, 4-trimellitic acid. These exemplary acids may be used in the acid form or in other useful forms, such as the anhydride, acid chloride or lower alkyl esters thereof. Mixtures of acids may also be used. In addition, hydroxycarboxylic acids and lactones may also be used. Examples include hydroxypivalic acid and epsilon-caprolactone.

Polyols, particularly diols, may be reacted with the carboxylic acids and analogs thereof described above to produce polyesters. Examples of the polyhydric alcohol include aliphatic diols such as ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 4-butanediol, 1, 3-butanediol, 2-dimethyl-1, 3-propanediol (neopentyl glycol), 2, 5-hexanediol, 1, 6-hexanediol, 2-bis (4-hydroxycyclohexyl) propane (hydrogenated bisphenol a), 1, 4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol and 2, 2-bis [4- (2-hydroxyethoxy) phenyl ] propane, hydroxypivalate of neopentyl glycol and 4, 8-bis (hydroxymethyl) tricyclo [5, 2, 1, 0] decane (═ tricyclodecanedimethanol) and 2, 3-butanediol.

Trifunctional or higher functional alcohols (collectively referred to as polyols) or acids may be used to prepare the branched polyesters. Examples of suitable polyols or polyacids are glycerol, hexanetriol, trimethylolethane, trimethylolpropane, pentaerythritol and 1, 2, 4-trimellitic acid.

Monofunctional acids (e.g., p-tert-butylbenzoic acid, benzoic acid, m-methylbenzoic acid, cinnamic acid, crotonic acid) may be used for the end-capping of the polymer chain.

Preferably, the resin in the powder coating composition of the invention is a polyester made from at least the following monomers: terephthalic acid, neopentyl glycol and/or propylene glycol. Trimethylolpropane may be present in the polyester for branching.

The polyester can be prepared by esterification and/or transesterification by a known polymerization method, or by esterification and/or transesterification using an enzyme. For example, if desired, the usual esterification catalysts can be used, such as butyltin chlorohydroxide, dibutyltin oxide, tetrabutyl titanate or butylstannoic acid. These esterification catalysts are generally used in an amount of about 0.1 weight percent based on the total weight of the polyester.

The conditions for the preparation of the polyester and the COOH/OH ratio can be selected so that the acid or hydroxyl value of the final product obtained is within the stated range for the value.

Preferably, the viscosity of the polyester resin is in the range of 2 to 30 pa.s measured at 160 ℃ by the method described herein.

The resin may also be a polyacrylate (also referred to as an acrylic resin). Typically, the acrylic resin is based on alkyl esters of (meth) acrylic acid, optionally in combination with styrene. These alkyl (meth) acrylates may be replaced by hydroxy-or glycidyl-functional (meth) acrylic acid. Examples of the alkyl (meth) acrylate include: ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, n-propyl (meth) acrylate, isobutyl (meth) acrylate, ethylhexyl acrylate, cyclohexyl (meth) acrylate, and mixtures thereof.

In order to obtain an acrylic resin having hydroxyl functional groups, the acrylic resin comprises hydroxyl functional (meth) acrylic acid, and is preferably combined with an alkyl (meth) acrylate. Examples of hydroxy-functional (meth) acrylates include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and the like.

In order to obtain an acrylic resin having glycidyl functional groups, the acrylic resin comprises a glycidyl functional (meth) acrylate, preferably in combination with an alkyl (meth) acrylate. Examples of glycidyl functional (meth) acrylates include glycidyl (meth) acrylate and the like.

It is clear that it is also possible to synthesize acrylic resins having both hydroxyl and glycidyl functions.

Polyurethanes can be prepared, for example, by polyaddition reactions known per se of (poly) alcohols and (poly) isocyanates in the presence, if desired, of catalysts and further additives.

For example, if desired, customary catalysts can be used, for example tertiary amines or organometallic compounds, such as monobutyltin tris (2-ethylhexanoate), tert-butyl titanate or dibutyltin dilaurate. These catalysts are generally used, for example, in an amount of about 0.01% by weight, based on the total weight of the resin.

Examples of (poly) alcohols useful in the preparation of polyurethanes are the same as those useful in the preparation of polyesters.

Examples of (poly) isocyanates that may be used to prepare the polyurethanes include, but are not limited to: diisocyanates, such as toluene 2, 4-diisocyanate, toluene 2, 6-diisocyanate, 4 ' -diphenylmethane diisocyanate, 2 ' -diphenylmethane diisocyanate, 1, 6-hexamethylene diisocyanate, 5-isocyanato-1- (isocyanatomethyl) -1, 3, 3-trimethylcyclohexane (isophorone diisocyanate), m-tetramethylxylylene diisocyanate, dicyclohexylmethane 4, 4 ' -diisocyanate, naphthylene 1, 5-diisocyanate or 1, 4-phenylene diisocyanate; and triisocyanates, such as triphenylmethane-4, 4', 4 "-triisocyanate.

The resin may also be a polyepoxide (also referred to as an epoxy resin). Epoxy resins can be prepared, for example, by combining a phenolic compound with epichlorohydrin to provide an epoxy resin, such as bisphenol A diglycidyl ether (such as the commercially available Epicote)^TM1001) Or phenolic (Novolac) epoxide.

Polyamides can be prepared, for example, by polycondensation of diamines and dicarboxylic acids.

The dicarboxylic acids may be branched, non-linear or linear. Examples of suitable dicarboxylic acids are for example: phthalic acid, isophthalic acid, terephthalic acid, 1, 4-cyclohexanedicarboxylic acid, naphthalene-2, 6-dicarboxylic acid, cyclohexanediacetic acid, biphenyl-4, 4' -dicarboxylic acid, phenylenedi (glycolic acid), sebacic acid, succinic acid, adipic acid, glutaric acid and/or azelaic acid.

Examples of suitable aliphatic diamines include, for example: isophorone diamine, 1, 2-ethylene diamine, 1, 3-propane diamine, 1, 6-hexamethylene diamine, 1, 12-dodecyl diamine, 1, 4-cyclohexane dimethylamine, piperazine, p-xylylene diamine and/or m-xylylene diamine. The polyamines can also be branched with a branching component. Suitable examples of branching components include amines, for example dialkylene-triamines (such as diethylene-triamine or di-hexamethylene-triamine); dialkylene-tetraamines or dialkylene-pentaamines; acids, such as 1, 3, 5-benzenetricarboxylic acid, 1, 2, 4-trimellitic anhydride or 1, 2, 4, 5-pyromellitic anhydride; and polyfunctional amino acids such as aspartic acid and glutamic acid.

Polyesteramides are resins containing both ester (in polyesters) and amide (in polyamides) linkages and may be prepared, for example, from mono-, di-, tri-or polyfunctional monomers, such as monomers having carboxylic acid functionality, monomers having hydroxyl functionality, monomers having amine functionality, and/or monomers having combinations of these functionalities.

In principle, any solid polycarbonate which is hydroxy-functional can be used. Hydroxy-functional polycarbonates are commercially available from a variety of sources.

Polyureas can be prepared, for example, by polyaddition reactions known per se of (poly) isocyanates and (poly) amines in the presence, if desired, of catalysts and other additives analogous to those described above for polyurethanes. Suitable (poly) amines for preparing the polyureas include those listed above for the polyamides. Suitable (poly) isocyanates for preparing the polyureas include those listed above for the polyurethanes.

Reactive unsaturation can be built into the resin backbone, for example, by reacting a hydroxy-functional monomer (such as the aforementioned polyols) with an unsaturated carboxylic acid or anhydride (such as fumaric, maleic, citraconic, itaconic or mesaconic acid).

Resins in which reactive unsaturation can be built into the resin backbone by reaction of a hydroxy-functional monomer with an unsaturated carboxylic acid are for example polyesters.

Likewise, reactive unsaturation may be attached to pendant groups of a resin (e.g., glycidyl functional acrylate) by reacting the pendant epoxy functional groups with unsaturated carboxylic acids (e.g., methacrylic or acrylic acids or monoesters of fumaric, maleic, citraconic, itaconic or mesaconic acids, preferably with methacrylate or acrylic acids).

Likewise, reactive unsaturation may be attached to a pendent group of a resin (e.g., a hydroxy-functional acrylate) by reacting the pendent hydroxy-functional group with an unsaturated carboxylic acid (e.g., methacrylic or acrylic acid) or an unsaturated carboxylic acid anhydride (e.g., anhydride of itaconic, maleic or citraconic acid).

Reactive unsaturation can also be attached at the ends of the resin, for example, by reacting a hydroxyl functional, epoxy functional, or amine functional end group with an unsaturated carboxylic acid (e.g., fumaric acid, maleic acid, citraconic acid, itaconic acid, mesaconic acid, or monoesters thereof, methacrylic acid, acrylic acid). Thus, resins having hydroxyl, amine or glycidyl end groups can be reacted with the carboxylic acids.

Also or alternatively, the hydroxyl or amine functional resin may be modified with a hydroxyl functional compound containing reactive unsaturation by reaction with a diisocyanate to form urethane or urea linkages. Such modifications may be made at the pendant or terminal hydroxyl groups.

Sometimes, a small amount of inhibitor is also present during the esterification reaction to prevent: loss of unsaturation due to peroxide that may be present in the ethylene glycol and instability due to esterification temperature.

By using¹The weight per unit unsaturated group resin (WPU) as determined by H-NMR is typically less than 7500, preferably less than 1500, such as less than 1150 or less than 1100 or less than 1000 g/mole and/or preferably more than 100, more preferably more than 250 g/mole, such as more than 500 g/mole.

The methods described, for example, in Journal Of Applied Polymer Science, Vol.23, 1979, pp25-38 (the entire contents Of which are incorporated herein by reference) or described in the Experimental section herein can be used¹H-NMR to determine WPU. In the procedure of the experimental part, the weight per unit unsaturated group (WPU) was determined by¹H-NMR was measured on a 300MHz Varian NMR spectrometer using pyrazine as an internal standard or the WPU was determined theoretically by dividing Mn by the amount of unsaturated groups added in the synthesis of the resin and/or co-crosslinker.

In the case of amorphous resins, the glass transition temperature (Tg) of the resin is preferably at least 20 ℃, more preferably at least 25 ℃. Preferably, the resin is a polyester having a Tg of at least 40 ℃, preferably at least 45 ℃ and/or a Tg of at most 65 ℃, preferably at most 60 ℃ (e.g. at most 55 ℃, e.g. at most 50 ℃).

The acid group content of the resin was determined by titration of the acid/anhydride groups with KOH. The content of acid groups is expressed as the acid number (AV) in mg KOH/g resin.

The hydroxyl content of the resin was determined by titration of hydroxyl groups with acetic anhydride and back titration of KOH. The hydroxyl group content is expressed as the hydroxyl number (OH-number or OHV) in mg KOH/g resin.

If the hydroxyl number is less than the acid number, the resin is classified as acid functional. If a carboxyl functional resin is desired, the hydroxyl number of the resin is generally less than 10mg KOH/g resin.

If the acid number is less than the hydroxyl number, the resin is classified as hydroxyl functional. If a hydroxy-functional resin is desired, the acid value of the resin is generally less than 10mg KOH/g resin.

The hydroxyl number of the resin in the powder coating composition of the invention is generally in the range of from 0 to 70mg KOH/g resin.

If a vinyl ether or vinyl ester co-crosslinker is used in the powder coating composition of the invention, it is desirable to obtain a resin, preferably a polyester, having an acid number of less than 10, preferably less than 5mg KOH/g resin. If the co-crosslinking agent used is not a vinyl ether or vinyl ester, the acid number of the resin, preferably a polyester, may be in the range of from 0 to 250, for example from 0 to 60mg KOH/g resin.

The number average molecular weight (Mn) of the resin is in principle not critical and may be, for example, 1000-. Preferably, the Mn of the resin is at least 1500Da, such as at least 2000Da and/or preferably at most 8000Da, such as at most 4000Da in the case of amorphous resins and/or preferably at most 15000Da in the case of crystalline resins. Preferably, the resin is a polyester having a number average molecular weight (Mn) in the range of 1500-.

As used herein, the term "thermally initiated system" refers to a system that initiates free radical polymerization.

The curing of the powder coating composition according to the invention is carried out by means of heat; i.e. the powder coating composition is heat curable. The thermal initiator in the thermally initiated system generates (free) radicals during heating that initiate the following polymerization reactions: polymerization of the reactive unsaturated group in the resin in combination with the unsaturated group of the co-crosslinking agent or polymerization in combination with the reactive unsaturated group in the resin.

The transition metal catalyst may be selected from the group of transition metal salts, transition metal complexes or mixtures thereof. Transition metals are elements having atomic numbers from (including equal to) 21 to (including equal to) 79. In chemistry and physics, the atomic number (also called proton number) is the number of protons present in a nucleus. Generally denoted by the symbol Z. Atomic number uniquely represents a chemical element. Because of the electrical neutrality of atoms, the atomic number is equal to the number of electrons. Examples of suitable transition metal compounds are the following transition metal compounds: sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, etc., preferably Mn, Fe, Co, or Cu. From the viewpoint of environmental protection, Cu, Fe or Mn is most preferably used.

The transition metal salt or transition metal complex portion of the transition metal catalyst is preferably organic, for example an organic acid transition metal salt or derivative thereof, for example a transition metal carbonate or a transition metal acetoacetate, for example a transition metal ethylhexanoate may be used. If a copper compound is used, this may be, for example, Cu⁺Salt or Cu²⁺In the form of a salt. If a compound of manganese is used, this may be, for example, Mn²⁺Salts or Mn³⁺In the form of a salt. If a compound of cobalt is used, it may be, for example, Co²⁺In the form of a salt.

The optimum amount of transition metal catalyst will depend on the choice of transition metal and the choice of peroxyester or monoperoxycarbonate, but can be readily determined by one of ordinary skill in the art through routine experimentation. Typically, the amount of transition metal catalyst selected is in the range of from 0.00001 to 25mmol transition metal catalyst per kg resin system.

Preferably, the peroxide is a monoperoxycarbonate or peroxyester of formula (1),

(1)

wherein R is¹、R²And R³Each independently represents an alkyl group, and wherein X represents R⁴OR OR⁴Wherein R is⁴Represents an alkyl group, an aryl group or an oligomer or polymer.

Preferably, R¹、R²And R³Each independently represents an alkyl group of 1 to 6 carbon atoms, more preferably methyl or ethyl. Most preferablyThe peroxide is a compound of formula (1) wherein R¹Represents methyl, R²Represents methyl and R³Represents ethyl or methyl. Preferably, the peroxide is tert-butyl peroxybenzoate, tert-butyl peroxy2-ethylhexanoate, tert-amyl peroxy2-ethylhexanoate or tert-butyl peroxy2-ethylhexyl carbonate.

Preferably R⁴Represents an aryl radical having 6 to 20 carbon atoms, preferably R⁴Represents phenyl or R⁴Represents an alkyl group of 1 to 20 carbon atoms, more preferably an alkyl group of 6 to 12 carbon atoms.

Monoperoxycarbonates and/or peroxyesters of formula (1) useful in the compositions of the present invention are peroxides capable of initiating free radical crosslinking reactions with reactive unsaturation on resins in powder coating compositions.

Examples of peroxyesters include tert-butyl peroxybenzoate (Trigonox C), tert-butyl peroxyacetate (Trigonox F-C50), tert-amyl peroxybenzoate (Trigonox127), tert-amyl peroxyacetate (Trigonox133-CK60), tert-butyl peroxy2-ethylhexanoate (Trigonox21S), tert-butyl peroxydiethylacetate (Trigonox27), di-tert-butyl peroxypivalate (Trigonox25-C75), tert-butyl peroxyneoheptanoate (Trigonox257-C75), and cumyl peroxyneodecanoate (Trigonox 99-C75). Examples of monoperoxycarbonates include t-butyl peroxy-2-ethylhexyl carbonate (Trigonox117), t-butyl peroxy-isopropyl carbonate (Trigonox BPIC75), and t-amyl peroxy-2-ethylhexyl carbonate (Trigonox 131). It is noted that Trigonox is a trademark from Akzo Nobel.

It is of course also possible to use mixtures of peroxides of formula (1) in the powder coating compositions of the invention.

The optimum amount of peroxide of formula (1) depends on the choice of transition metal and the choice of peroxyester or monoperoxycarbonate, but can be readily determined by one of ordinary skill in the art through routine experimentation. Generally, the amount of peroxide of formula (1) is at least 1mmol peroxide per kg resin system, preferably at least 10, more preferably at least 25mmol peroxide per kg resin system. In general, the amount of peroxide of formula (1) is at most 1000mmol peroxide per kg resin system, preferably at most 500, such as at most 250 or at most 200mmol peroxide per kg resin system.

Preferably, the amount of the initiation system is chosen such that after applying the powder coating composition of the invention to a substrate and curing at a temperature of 130 ℃ for 20 minutes, the resulting coating resists at least 50, preferably at least 70, acetone double rubs. Methods of determining acetone double rubs are described herein.

The co-crosslinking agent used in the composition of the present invention is selected from the following group: vinyl ethers, vinyl esters, vinyl amides, itaconates, enamines and mixtures thereof, preferably selected from the group of vinyl ethers, vinyl esters and mixtures thereof.

Vinyl ethers are monomers, oligomers or polymers having a vinyl ether moiety (see formula (2) in table 1). The co-crosslinking agent in the powder coating composition of the invention is for example a vinyl ether. Examples of liquid vinyl ethers include mono (alcohol) -functional vinyl ethers such as ethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether or 4- (hydroxymethyl) cyclohexyl methyl vinyl ether (1, 4-cyclohexanedimethanol vinyl ether); diol-functional vinyl ethers, e.g. butanediol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, poly-THF^TM290-divinyl ether, hexanediol divinyl ether, 1, 4-cyclohexanedimethanol divinyl ether; triol-functional vinyl ethers such as trimethylolpropane trivinyl ether, 1, 2, 4-trivinylcyclohexane; and monoamino-functional vinyl ethers, such as 3-aminopropyl vinyl ether.

For example, vinyl ethers can be prepared with dimethyl esters and hydroxy-functional vinyl ethers to form vinyl ether esters.

Examples of amorphous or semi-crystalline vinyl ethers include vinyl ether urethanes, vinyl ether polyester urethanes, vinyl ether ureas, and vinyl ether polyester ureas. The polyester portion of the vinyl ether polyester polyurethane is typically a polycondensation product of a polyol and a polycarboxylic acid, possibly with the same monomers and may be synthesized by methods similar to those described above for polyester synthesis. The polyester portion of the vinyl ether polyester polyurethane may be saturated or unsaturated and may be similar to the resin.

To prepare the vinyl ether urethanes, isocyanates can be reacted with hydroxy-functional vinyl ethers and/or polyols. To prepare the vinyl ether polyester polyurethane, an isocyanate may be reacted with a hydroxy-functional vinyl ether and a hydroxy-functional polyester (such as the polyesters described above). These reactions are the well-known polyaddition reactions of (poly) isocyanates and (poly) alcohols in the presence of catalysts and, if desired, further additives. Some examples of catalysts, other additives, polyols and isocyanates are given herein (see for example the polyurethane section).

Examples of vinyl ethers also include vinyl ether polyesters, which can be prepared, for example, by reacting an acid functional polyester (such as those listed herein) with a hydroxy functional vinyl ether (such as those listed herein). Of course, the vinyl ether polyesters can also be prepared by transesterification of hydroxy-functional or alkyl-functional polyesters with hydroxy-functional vinyl ethers.

Vinyl esters are monomers, oligomers or polymers having vinyl ester moieties (see formula (3) in table 1). Examples of vinyl esters include monofunctional vinyl esters such as vinyl stearate, vinyl palmitate, vinyl benzoate, vinyl laurate, vinyl caproate, vinyl pivalate, vinyl oleate, vinyl methacrylate, vinyl caprate, vinyl bromoacetate, vinyl myristate, vinyl valerate, vinyl pelargonate, vinyl heptanoate, vinyl phenylacetate, vinyl (di) maleate, vinyl undecanoate, vinyl iodoacetate, vinyl 2-naphthoate, vinyl 3-chloro-butyrate, vinyl 4-chloro-butyrate, vinyl 2-chloro-butyrate; difunctional vinyl esters, such as divinyl adipate, divinyl fumarate, divinyl sebacate, divinyl phthalate and divinyl terephthalate; and polyfunctional vinyl esters, such as 1, 2, 4-trimellitic acid trivinyl ester.

The vinyl amide is a monomer, oligomer or polymer having a vinyl amide segment (see formula (4) in table 1).

Itaconate is a monomer, oligomer or polymer having an itaconate fragment (see formula (5) in table 1). Examples of liquid itaconates include diethyl itaconate, dibutyl itaconate, and the like. Examples of solid itaconates include dimethyl itaconate. Examples of amorphous itaconate esters are given above (see resin moieties modified with monoesters of itaconic acid or itaconic acid). Since the resin having an itaconic acid-based unsaturated group may be homopolymerized, the resin having an itaconic acid-based unsaturated group may be used in combination with an oligomer or polymer including an itaconic acid-based unsaturated group as a co-crosslinking agent.

Enamines are monomers, oligomers, or polymers having an enamine moiety (see formula (6) in table 1).

As defined herein: the Mn of the monomers is less than 500Da, the Mn of the oligomers is less than 1500Da, and the Mn of the polymer is at least 1500 Da.

Table 1. co-crosslinkers used in the composition of the invention are selected from the group of monomers, oligomers or polymers comprising one or more of the following fragments: vinyl esters, vinyl ethers, vinyl amides, itaconates and/or enamine fragments. For joining of segmentsAnd (4) showing.

If the carbon-carbon double bond in the resin directly attached to the electron withdrawing group is capable of reacting with the resin itself (i.e., the resin is homopolymerizable), such as some resins containing acrylate, methacrylate, or itaconate moieties, then the resin and the co-crosslinking agent may contain the same moieties, and thus in one embodiment, the presence of a separate co-crosslinking agent is optional, and the resin and the co-crosslinking agent may be the same.

If the resin is not homopolymerizable, a separate co-crosslinking agent is required to effect cure. To avoid confusion, it is considered within the scope of the present invention that the resin can homopolymerize if the unsaturated groups in the resin can react with each other upon free radical initiation by the free radical initiator.

The individual co-crosslinking agents may be (semi-) crystalline or amorphous. Also, a liquid co-crosslinking agent may be used. Preferably, the co-crosslinking agent is non-volatile at the temperatures and pressures used in processing, applying and storing the powder coating composition.

By using¹The weight per unit of unsaturated group co-crosslinker, as determined by H NMR, is preferably below 870 g/mole, such as below 650 g/mole, such as below 630 g/mole and/or preferably above 70, more preferably above 100, such as above 150 g/mole. The Mn of the co-crosslinking agent is not critical and may vary within wide limits, for example the Mn may be between 100 and 20000 Da.

The amount of co-crosslinker used in the powder coating composition is in principle not critical, especially when the resin used is homopolymerizable. If the resin is not homopolymerizable, for example, the molar ratio of unsaturated groups in the co-crosslinking agent to unsaturated groups in the resin may be between 9: 1 and 1: 9, preferably between 2: 1 and 1: 2. Preferably, in this case, the co-crosslinking agent is used in an approximately equimolar amount with respect to the unsaturated group in the resin.

As used herein, "one-component system" (also referred to as a 1K system) means that all (reactive) components of the powder coating composition form part of one powder. This is in contrast to two-component systems (also referred to as 2K systems), in which the powder coating composition consists of at least two powders having different chemical compositions, which allow the reactive components to be physically separated. Such at least two different powders may be mixed by physical mixing before placing the powder coating composition into a storage container or just before applying the 2K system on a substrate for a curing reaction. The composition of the at least two different powders in the 2K system is generally chosen such that: so that each powder contains ingredients that need to be solidified but are not present in the other powders. This separation allows the preparation of individual powder compositions in a heated state (e.g., by melt mixing) without initiating a curing reaction.

Depending on the reactivity of the initiating system and the peroxide and transition metal catalyst, one or more inhibitors and/or one or more co-accelerators may optionally be present in the initiating system. If the reactivity of the initiating system is too high, one or more inhibitors may be added to the initiating system. Alternatively, the inhibitor may be added, for example, during resin synthesis. Accordingly, the present invention also relates to a powder coating composition according to the invention further comprising an inhibitor.

Examples of inhibitors are preferably selected from the following group: phenolic compounds, stable free radicals, catechols, phenothiazines, hydroquinones, benzoquinones and mixtures thereof, more preferably selected from the group consisting of stable free radicals, catechols, phenothiazines, hydroquinones, benzoquinones and mixtures thereof.

Examples of phenolic compounds include: 2-methoxyphenol, 4-methoxyphenol, 2, 6-di-tert-butyl-4-methylphenol, 2, 6-di-tert-butylphenol, 2, 6-di-tert-butyl-4-ethylphenol, 2, 4, 6-trimethylphenol, 2, 4, 6-tris-dimethylaminomethylphenol, 4 ' -thio-bis (3-methyl-6-tert-butylphenol), 4 ' -isopropylidenediphenol, 2, 4-di-tert-butylphenol and 6, 6-di-tert-butyl-2, 2 ' -methylene-di-p-cresol.

Examples of stable free radicals include: 1-oxo-2, 2, 6, 6-tetramethylpiperidine, 1-oxo-2, 2, 6, 6-tetramethylpiperidin-4-ol (a compound also known as TEMPOL), 1-oxo-2, 2, 6, 6-tetramethylpiperidin-4-one (a compound also known as TEMPON), 1-oxo-2, 2, 6, 6-tetramethyl-4-carboxy-piperidine (a compound also known as 4-carboxy-TEMPO), 1-oxo-2, 2, 5, 5-tetramethylpyrrolidine, 1-oxo-2, 2, 5, 5-tetramethyl-3-carboxypyrrolidine (also known as 3-carboxy-PROXYL and gammahloranyloxy (2, 6-di-tert-butyl-alpha- (3, 5-di-tert-butyl-4-oxo-2, 5-cyclohexadien-1-ylidene) -p-tolyloxy)).

Examples of the catechols include catechol, 4-tert-butylcatechol, and 3, 5-di-tert-butylcatechol.

Examples of the hydroquinones include hydroquinone, 2-methylhydroquinone, 2-tert-butylhydroquinone, 2, 5-di-tert-butylhydroquinone, 2, 6-dimethylhydroquinone and 2, 3, 5-trimethylhydroquinone.

Examples of benzoquinones include benzoquinone, 2, 3, 5, 6-tetrachloro-1, 4-benzoquinone, methylbenzoquinone, 2, 6-dimethylbenzoquinone, and naphthoquinone.

Other suitable inhibitors may for example be selected from the group of aluminium-N-nitrosophenylhydroxylamine, diethylhydroxylamine and phenothiazine.

Mixtures of inhibitors (described above) may also be used. Preference is given to using hydroquinones or catechols as inhibitors, more preferably hydroquinones, most preferably 2-methylhydroquinone or 2-tert-butylhydroquinone, depending on the choice (type and amount) of transition metal compound.

Examples of suitable co-accelerators include 1, 3-dioxo compounds, bases and sulfhydryl-containing compounds.

The 1, 3-dioxo compound is preferably a1, 3-dioxo compound having the following formula:

wherein X, Y is H, C₁-C₂₀Alkyl radical, C₆-C₂₀Aryl, alkylaryl, arylalkyl, part of the resin chain, OR₃、NR₃R₄；R₁、R₂、R₃And R₄Each independently of the others hydrogen (H) or C₁-C₂₀An alkyl, aryl, alkylaryl or arylalkyl group, each optionally containing one or more heteroatoms (such as oxygen, phosphorus, nitrogen or sulfur atoms) and/or substituents; r₁And R₂R is₁And R₃And/or R₂And R₄There may be a ring in between; r₃And/or R₄May be part of the polymer chain, may be attached to the polymer chain or may comprise a polymerizable group. Preferably, X and/or Y is C₁-C₂₀Alkyl and/or C₆-C₂₀And (4) an aryl group. More preferably, X and/or Y are methyl groups. Preferably, the 1, 3-dioxo compound is acetylacetone. The 1, 3-dioxo compound may be a resin or may be polymerizable.

Other examples of 1, 3-dioxo compounds include 1, 3-diketones, 1, 3-dialdehydes, 1, 3-ketoaldehydes, 1, 3-ketoesters, and 1, 3-ketoamines.

Examples of suitable base co-accelerators are organic or inorganic bases. The organic base is, for example, a compound of an alkali metal or an alkaline earth metal. The organic base is preferably a nitrogen-containing compound, preferably an amine.

Examples of suitable sulfhydryl-containing compounds that may be used as co-accelerators include aliphatic thiols, more preferably primary aliphatic thiols. The aliphatic thiol is preferably alpha-mercaptopropionate, alpha, beta-mercaptopropionate, dodecanethiol, and mixtures thereof. The thiol functionality of the sulfhydryl containing compound in the powder coating composition is preferably ≥ 2, more preferably ≥ 3.

Misev, in Powder Coatings, Chemistry and Technology (pp.224-300; 1991, John Wiley), describes the preparation of Powder coating compositions, which is incorporated herein by reference.

The conventional method for preparing powder coating compositions is: the weighed components are mixed in a premixer, the obtained premix is heated (e.g. in a kneader, preferably in an extruder) to obtain an extrudate, the obtained extrudate is cooled until it solidifies, and then it is crushed into small particles or flakes, further ground to reduce the particle size, and subsequently, by suitable classification, a powder coating composition of suitable particle size is obtained. The present invention therefore also relates to a process for preparing the powder coating composition of the invention, which comprises the following steps:

a. mixing the components of the powder coating composition to obtain a premix;

b. heating the obtained premix, preferably in an extruder, thereby obtaining an extrudate;

c. cooling the resulting extrudate, thereby obtaining a solidified extrudate; and is

d. The resulting solidified extrudate is broken up into smaller particles to provide a powder coating composition.

Preferably, the pre-mix is heated at a temperature at least 5 ℃ lower, more preferably at least 10 ℃ lower than the temperature at which the powder coating composition is intended to be cured. If the premix is heated in the extruder, temperature control is preferably used in order to avoid excessive temperatures which may lead to curing of the powder coating composition in the extruder.

In another aspect, the present invention relates to a method of coating a substrate comprising the steps of:

1) applying the powder coating composition according to the invention on a substrate (thereby partially or completely coating the substrate with the coating);

2) the resulting (partially or fully coated) substrate is heated (for a time and temperature to at least partially cure the coating).

The powder coating compositions of the present invention may be applied by techniques known to those of ordinary skill in the art, for example, using electrostatic spraying or electrostatic fluidized bed.

Heating of the coated substrate can be carried out using conventional methods, for example with convection ovens and/or (near) infrared lamps. Even microwave equipment may be used to heat the substrate.

If a convection oven is used to heat the coating, the time to at least partially cure the coating is preferably less than 60 minutes and typically greater than 1 minute. More preferably, if a convection oven is used to heat the coating, the cure time is less than 40 minutes.

The temperature at which the coating is cured is preferably below 130 ℃ and usually above 60 ℃. Preferably, the curing temperature is below 120 ℃, more preferably below 110 ℃, most preferably below 100 ℃, most preferably below 95 ℃. Preferably, the curing temperature is at least 65 ℃, more preferably 70 ℃, even more preferably at least 75 ℃.

The powder coating compositions of the invention may optionally comprise customary additives, such as fillers/pigments, deaerators, levelling agents or (photo) stabilizers. Examples of leveling agents include Byk^TM361N. Examples of suitable fillers/pigments include metal oxides, silicates, carbonates or sulfates. It is to be noted that none of these conventional additives are considered transition metal catalysts. Examples of suitable stabilizers include UV stabilizers, such as phosphonites, thioethers or HALS (hindered amine light stabilizers). Examples of deaerators include benzoin, cyclohexane dimethanol dibenzoate. Other additives (e.g., additives that improve triboelectric chargeability) may also be used.

In another aspect, the present invention relates to a substrate which is coated in whole or in part with a powder coating based on the heat-curable powder coating composition of the invention.

In one embodiment of the invention, the substrate is a non-heat sensitive substrate, such as glass, ceramic, fiber cement board, or metal (e.g., aluminum, copper, or steel). In another embodiment of the present invention, the substrate is a heat sensitive substrate. The invention therefore also relates to the use of the powder coating composition of the invention for coating heat-sensitive substrates, preferably wood.

Heat-sensitive substrates include plastic substrates, wood substrates, e.g., solid wood, such as: hardwood, softwood, plywood; veneers, particle-, low-, medium-and high-density fibreboards, OSB (oriented strand board), wood laminates, chipboards and other substrates of which wood is an important component, such as metal foil-clad wood substrates, composite wood floors, plastic-modified wood, plastic substrates or wood-plastic composites (WPC); a substrate having cellulosic fibers, such as a cardboard or paper substrate; textile and leather materials.

Other heat-sensitive substrates include objects in which a metal substrate is combined with a heat-sensitive component (e.g., plastic hose, heavy metal component, strip), such as an aluminum alloy vehicle frame with a heat sink strip.

Examples of plastic substrates include unsaturated polyester-based composites, ABS (acrylonitrile-butadiene-styrene), melamine-formaldehyde resins, polycarbonates, polystyrenes, polypropylenes, Ethylene Propylene Diene Monomer (EPDM), Thermoplastic Polyolefins (TPO), Polyurethanes (PU), polypropylene oxide (PPO), polyethylene oxide (PEO), polyethylene terephthalate, and nylons (e.g., polyamide 6, 6), and combinations thereof, such as polycarbonate-ABS.

Other substrates particularly suitable for coating with the powder coatings of the invention are those for which low-temperature curing is desired for efficient production, for example heavy metal parts.

In another aspect, the invention relates to the use of the composition of the invention for coating a substrate, either entirely or partially.

The invention likewise relates to the use of the powder coating compositions according to the invention as tints, primers and top coats.

Specific wood coating applications in which the powder coating compositions of the present invention may be used include household furniture, such as tables, chairs, cabinets and the like; bedroom and bathroom furniture; office furniture; custom furniture such as school and children's furniture, hospital furniture, restaurant and hotel furniture, kitchen cabinets and furniture; (flat) panels for interior design; indoor and outdoor windows and doors; indoor and outdoor window and door frames; outdoor and indoor siding and wood flooring.

Specific plastic coating applications in which the powder coating compositions of the present invention may be used include the automotive industry, such as interior automotive parts, wheel covers, bumpers, underbody parts, and the like; a resilient floor; sporting goods; a cosmetic; audiovisual applications, such as televisions, computer housings, telephones, and the like; household appliances and satellite antennas.

In a particular embodiment, the present invention relates to the use of the inventive powder coating composition for coating heat-sensitive substrates, preferably wood.

Examples

The invention will be illustrated in more detail with reference to the following non-limiting examples.

Examples

Synthesis and application of powder coatings

Table 2: chemical product

Synthesis of resin: general procedure

The chemicals used in the following examples are described in table 2 above.

Synthesis of resin (resin A)

The tin catalyst and the monomers used in the first step as listed in table 3 (all (poly) alcohols and terephthalic acid) were charged to a reactor equipped with a thermometer, a stirrer and a distillation apparatus. Stirring was then applied and a small stream of nitrogen was passed through the reaction mixture while the temperature was raised to 220 ℃. The fumaric acid used in the second step and a small amount of a free radical inhibitor are then added at a temperature of 180 ℃ and subsequently esterified at 220 ℃. When the acid number reached less than about 15mg KOH/g resin, the reaction mixture was cooled to 205 ℃. The third step of preparing the polyester was carried out under reduced pressure at 205 ℃ until an acid value of about 5mgKOH/g of resin was reached. The acid number of the resin was made less than 5mg KOH/g resin by reaction of the remaining acid groups of the resin with an epoxide (see Table 3 for chemicals). The amount depends on the acid number before addition.

Synthesis of resin (resin B)

The tin catalyst and the monomers used in the first step as listed in table 3 (all (poly) alcohols and terephthalic acid) were charged to a reactor equipped with a thermometer, a stirrer and a distillation apparatus. Stirring was then applied and a small stream of nitrogen was passed through the reaction mixture while the temperature was raised to 220 ℃. The fumaric acid used in the second step and a small amount of a free radical inhibitor are then added at a temperature of 180 ℃ and esterified at 205 ℃. When the acid number reaches less than about 30mg KOH/g resin, the third step of preparing the polyester is conducted under reduced pressure at 205 ℃ until an acid number of less than about 5mg KOH/g resin is reached. The acid number of the resin was made less than 5mgKOH/g of resin by reaction of the remaining acid groups of the resin with an epoxide (see the chemicals used in Table 3). The amount depends on the acid number before addition.

Analysis of resin and Co-crosslinker

The glass transition temperature (Tg) test (inflection point) and the melting temperature test were performed by Differential Scanning Calorimetry (DSC) on Mettler Toledo, TA DSC821 under the following test conditions: n is a radical of₂Atmosphere and 5 deg.CHeating rate/min. Viscosity measurements were performed on a Rheometric Scientific CT 5(Rm 265) instrument (Mettler Toledo) at 160 ℃. A 30mm conical plate was used. Applied shear rate of 70s^-1. The acid value and hydroxyl value of the resin were determined by titration according to ISO 2114-2000 and ISO 4629-1978, respectively.

By passing¹H-NMR the weight per unit of unsaturated groups (WPU) was determined on a 300MHz Varian NMR spectrometer using pyrazine as an internal standard. The recorded spectra were all analyzed with ACD software and the peak areas of all peaks were calculated.

The weight per unit unsaturated group resin is calculated using the formula:

W_pyrand W_resinWeights of pyrazine (internal standard) and resin, respectively, are expressed in the same units. MW_pyrIs the molecular weight of pyrazine (═ 80 g/mol). A. the_C＝CIs the peak area of hydrogen attached to the carbon-carbon double bond of the reactive unsaturated group (C ═ C component) in the resin; n is a radical of_C＝CIs the amount of hydrogen of the C ═ C component. A. the_pyrIs the peak area of pyrazine, and N_pyrIs the number of hydrogens (═ 4).

Table 3: synthesis and Properties of the resins used

Synthesis of vinyl ether-based co-crosslinking agent: general procedure

Method for determining the presence of free-NCO

FT-IR spectra were recorded on a Varian Excalibur instrument equipped with an ATR (golden Gate) accessory. At 2250cm^-1Characteristic peaks of free NCO can be found. The presence of peaks here indicates free NCO groups.

Synthesis of Co-crosslinking agent (I)

The tin catalyst and the monomers used in the first step (all (poly) alcohols and isophthalic acid) as listed in table 4 were charged to a reactor equipped with a thermometer, a stirrer and a distillation apparatus. Stirring was then applied and a small stream of nitrogen was passed through the reaction mixture while the temperature was raised to 220 ℃. The vinyl ether and tin catalyst for the second stage as listed in Table 4 were then added at a temperature of 120 ℃. The isocyanate as listed in table 4 was then added while maintaining the reaction mixture temperature below 120 ℃ during the addition. After all the isocyanate had been added, the temperature was maintained or set at 120 ℃ and maintained at this temperature for about half an hour. Subsequently, n-butanol was added until all free NCO had reacted (tested by FT-IR as described above). The temperature was raised to 120 ℃ and vacuum (0.1bar) was applied to remove all volatiles. The contents of the container are released after the vacuum treatment.

Table 4: synthesis and Properties of Co-crosslinkers

Preparation, application and analysis of powder coating compositions

The compositions of the powder coating compositions to be tested are given in the table below. The components were extruded at 60 ℃ using a Prism twin-screw extruder (200rpm, torque > 90%). Grinding and sieving the extrudate; a sieve fraction of less than 90 microns is used as the powder coating composition. The powder coating compositions were applied to aluminum ALQ panels with a corona powder coating spray gun and cured for 15 minutes at different temperatures in a convection oven (Heraeus UT 6120). The coating thickness was about 60 μm.

Acetone two-way friction

Acetone Double Rubs (ADRs) as described herein were performed to determine cure.

Within the scope of the present invention, "acceptable cure" is defined as the ability of the powder coating composition to withstand at least 50 ketone double rubs (ADRs), more preferably at least 70 ketone double rubs (ADRs), after 15 minutes of curing. The curing temperature that renders the coating resistant to at least 50 ADR's or at least 70 ADR's, respectively, is defined as T_{＞50 ADR}And T_{＞70 ADR}For the purposes of the present invention, this temperature is below 130 ℃.

Preparation of powder coating compositions

The molar ratio of the resin to the unsaturated groups in the co-crosslinking agent is selected to be 3: 2. The initiator content of the initiation system is based on the total weight of the resin system (e.g., x moles initiator per kg resin system; resin system is defined as the resin containing reactive unsaturated groups plus co-crosslinking agent, excluding conventional powder coating composition additives such as pigments, fillers, etc.). The amount of inhibitor in the initiating system is based on the total weight of the resin system. The accelerator content of the initiating system is based on the total weight of the resin system (e.g., x moles accelerator per kg resin system). The content of the levelling agent is calculated in wt% relative to the total weight of the powder coating composition. In all powder coating compositions, 0.8% by weight of leveling agent was used, unless otherwise stated.

As can be seen from Table 5 above, coatings produced using peroxyesters and monoperoxycarbonates (preferably peroxyesters) cure to acceptable levels even at relatively low temperatures (below 130℃.) for 15 minutes, whereas coatings produced using other peroxides do not cure to acceptable levels at these low temperatures.

These experiments were performed using a resin with WPU of 1130; if a similar initiation system (peroxide + transition metal catalyst and optional inhibitor) is used but the resin has a lower WPU, T_{＞50 ADR}Will be lower.

Claims (33)

1. A one-component, heat-curable powder coating composition comprising:

-a resin containing reactive unsaturated groups and wherein all of said reactive unsaturated groups are carbon-carbon double bonds directly linked to electron-withdrawing groups, with¹A weight per unit unsaturated group (WPU) determined by H-NMR of the resin, which is a polyester, higher than 250 g/mole and lower than 1500 g/mole; and

-a thermal initiation system comprising a transition metal catalyst and a peroxide, wherein the transition metal catalyst is a salt or complex of Mn, Fe, Co or Cu and wherein the peroxide is a monoperoxycarbonate or peroxyester of formula (1) or a mixture thereof,

wherein R is¹、R²And R³Each independently represents an alkyl group, and wherein X represents R⁴OR OR⁴Wherein R is⁴Represents an alkyl, aryl or oligomer or polymer and the amount of peroxide is at least 10mmol peroxide per kg resin containing reactive unsaturated groups and co-crosslinking agent; and

a co-crosslinking agent, its use¹A weight per unit unsaturated group (WPU) determined by H-NMR higher than 150 g/mole and lower than 870 g/mole, the co-crosslinking agent being selected from the following group: vinyl ethers, vinyl esters, vinyl amides, itaconates, enamines, and mixtures thereof.

2. The composition of claim 1, wherein the WPU of the resin is above 250 g/mole and below 1150 g/mole.

3. The composition of claim 1, wherein the WPU of the resin is above 500 g/mole and below 1500 g/mole.

4. The composition of claim 1, wherein the WPU of the resin is above 500 g/mole and below 1150 g/mole.

5. The composition according to any of claims 1 to 4, wherein the WPU of the co-crosslinking agent is higher than 150 g/mole and lower than 650 g/mole.

6. The composition according to any of claims 1 to 4, wherein the WPU of the co-crosslinking agent is higher than 150 g/mole and lower than 630 g/mole.

7. The composition according to any one of claims 1 to 4, wherein the hydroxyl value of the resin is in the range of 0 to 70mg KOH/g resin.

8. The composition of any of claims 1-4, wherein the reactive unsaturation of the resin is based on maleic acid, fumaric acid, itaconic acid, acrylic acid, and/or methacrylic acid.

9. The composition of any one of claims 1-4, wherein the reactive unsaturation of the resin is based on maleic acid, fumaric acid, citraconic acid, itaconic acid, and/or mesaconic acid.

10. The composition of any of claims 1-4, wherein the reactive unsaturated groups of the resin are based on fumaric acid and/or maleic acid.

11. The composition of any of claims 1-4, wherein the reactive unsaturated group of the resin is based on fumaric acid.

12. The composition of any of claims 1-4, wherein the peroxide is t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, t-amyl peroxy (2-ethyl) hexanoate, or t-butyl peroxy-2-ethylhexyl carbonate.

13. The composition of any of claims 1-4, wherein the transition metal catalyst is a salt or complex of Mn, Fe, or Cu.

14. The composition according to any one of claims 1 to 4, wherein the co-crosslinking agent is selected from the group of vinyl ethers, vinyl esters and mixtures thereof.

15. The composition of any of claims 1-4, wherein the co-crosslinking agent is a vinyl ether.

16. The composition of claim 14, wherein the resin has an acid value of less than 10mgKOH/g of resin.

17. The composition of claim 15, wherein the resin has an acid value of less than 10mgKOH/g of resin.

18. The composition of claim 14, wherein the resin has an acid value of less than 5mgKOH/g of resin.

19. The composition of claim 15, wherein the resin has an acid value of less than 5mgKOH/g of resin.

20. The composition of any one of claims 1-4, wherein the composition further comprises an inhibitor.

21. The composition of claim 20, wherein the inhibitor is hydroquinone or catechol.

22. The composition of any of claims 1-4, wherein the resin has a glass transition temperature of at least 25 ℃ as measured by DSC at a heating rate of 5 ℃/min.

23. The composition of any of claims 1-4, wherein the resin has a glass transition temperature of at least 40 ℃ as measured by DSC at a heating rate of 5 ℃/min.

24. The composition of any of claims 1-4, wherein the resin has a glass transition temperature of at least 45 ℃ as measured by DSC at a heating rate of 5 ℃/min.

25. The composition of any one of claims 1-4, wherein the glass transition temperature of the resin is at least 40 ℃ and at most 65 ℃, as measured by DSC at a heating rate of 5 ℃/min.

26. The composition of any one of claims 1-4, wherein the resin has a number average molecular weight in the range of 1500 to 8000 Da.

27. The composition of any one of claims 1-4, wherein the resin has a number average molecular weight in the range of 2100 to 4000 Da.

28. A process for preparing a powder coating composition as claimed in any one of claims 1 to 27, comprising the steps of:

a. mixing the components of the powder coating composition to obtain a premix;

b. heating the premix to obtain an extrudate;

c. cooling the extrudate to obtain a solidified extrudate; and is

d. The resulting solidified extrudate is broken up into smaller particles to provide a powder coating composition.

29. A method of coating a substrate comprising:

1) coating a substrate with a powder coating composition according to any one of claims 1 to 27;

2) the substrate is heated.

30. A substrate partially or completely coated with a powder coating composition according to any one of claims 1 to 27.

31. Use of the powder coating composition according to any one of claims 1 to 27 for coating heat-sensitive substrates.

32. Use according to claim 31, wherein the heat-sensitive substrate is wood.

33. The use of claim 31, wherein the heat-sensitive substrate is a plastic.