HK1235810A1

HK1235810A1 - Heat-curable powder coating composition

Info

Publication number: HK1235810A1
Application number: HK17109655.8A
Authority: HK
Inventors: Johan Franz Gradus Antonius Jansen; Leendert Jan Molhoek; Jan Pieter Drijfhout
Original assignee: 帝斯曼知识产权资产管理有限公司
Priority date: 2008-11-07
Filing date: 2017-09-22
Publication date: 2018-03-16

Abstract

The invention relates to a heat curable powder coating composition suitable for being cured at a temperature from 60 to 130 DEG C. comprising: a thermal initiation system and a resin system, wherein the reactivity of the thermal initiation system is such that the thermal initiation system provides a geltime between 2.5 and 1000 minutes at 60 DEG C. in butane diol-dimethacrylate as measured according to DIN 16945 using 1 wt % of the thermal initiation system in 99 wt % of butane diol-dimethacrylate, wherein the amount of thermal initiation system is chosen such that when the powder coating composition is applied to a substrate and cured at a temperature of 130 DEG C. for 20 minutes, the resulting coating resists at least 50 acetone double rubs, wherein the resin system comprises a resin and a co-crosslinker, wherein the resin contains reactive unsaturations and wherein said reactive unsaturations are carbon carbon double bonds connected directly to an electron withdrawing group, wherein the co-crosslinker is chosen from the group of acrylates, methacrylates, vinylesters, vinylethers, vinyl amides, alkyn ethers, alkyn esters, alkyn amides, alkyn amines, propargyl ethers, propargyl esters, itaconates, enamines and mixtures thereof, wherein the weight per unsaturation in the resin system is between 100 and 1000 g/mole as determined using 1H NMR and wherein the powder coating composition is a one component system.

Description

Heat-curable powder coating composition

This application is a divisional application of chinese patent application No.200980144740.x (PCT/EP2009/064727) entitled "heat-curable powder coating composition", filed on 5/9/2011 and filed on 11/6/2009.

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.

Such as the article "overview of the book company works world 1/92, pp.15-22 by G.Maggiore in Pitture e Vernice Europe 1/92, and the report" Powder Coating "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.

Therefore, there is a need for a powder coating composition that balances curability at low temperatures (e.g., 60-130 ℃) and good processability in an extruder.

It is an object of the present invention to provide a heat-curable powder coating composition which is easy to process in an extruder and which is partially or completely heat-curable at low temperatures, for example between 60 and 130 ℃, making it suitable not only for non-heat-sensitive substrates but also in particular for heat-sensitive substrates.

This object is achieved by the powder coating composition of the present invention. In one embodiment, the present invention relates to a heat curable powder coating composition suitable for curing at a temperature of 60 to 130 ℃, comprising:

-a thermally initiated system and a resin system;

-wherein the reactivity of the thermally initiated system is: the thermally initiated system provided a gel time of 2.5 to 1000 minutes in butylene dimethacrylate at 60 ℃ as determined according to DIN 16945 with 1 wt% thermally initiated system in 99 wt% butylene dimethacrylate;

-wherein the amount of thermally initiating system is selected such that: after allowing the powder coating composition to coat onto a substrate and cure at a temperature of 130 ℃ for 20 minutes, the resulting coating is resistant to at least 50 acetone double rubs;

-wherein the resin system comprises a resin and a co-crosslinking agent;

-wherein the resin comprises a reactive unsaturated group, and wherein the reactive unsaturated group is a carbon-carbon double bond directly linked to an electron-withdrawing group;

-wherein the co-crosslinking agent is selected from the group consisting of: acrylate, methacrylate, vinyl ester, vinyl ether, vinyl amide, alkynyl ether, alkynyl ester, alkynyl amide, alkynyl amine, propargyl ether, propargyl ester, itaconate, enamine, and mixtures thereof;

in which use¹H NMR determination, the weight of the resin system per mole of unsaturated groups is 100-1000 g/mole; and is

-wherein the powder coating composition is a one-component system.

In another embodiment, the present invention relates to a heat curable powder coating composition suitable for curing at a temperature of 60 to 130 ℃, comprising:

-a thermally initiated system and a resin system;

-wherein the amount of thermal initiation system in the powder coating composition is selected such that: such that the peak of enthalpy of cure reaction of the powder coating composition after isothermal DSC onset is at most 60 minutes at 120 ℃ and at least 2.5 minutes at 60 ℃;

-wherein the resin system comprises a resin and a co-crosslinking agent;

-wherein the co-crosslinking agent is selected from the group consisting of: acrylate, methacrylate refers to, vinyl esters, vinyl ethers, vinyl amides, alkynyl ethers, alkynyl esters, alkynyl amides, alkynyl amines, propargyl ethers, propargyl esters, itaconate esters, enamines, and mixtures thereof;

-wherein the weight of the resin system per mole of unsaturated groups is 100-900 g/mole; and is

-wherein the powder coating composition is a one-component system.

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.

A further advantage of the composition according to the invention is that it has acceptable flowability and/or acceptable storage stability, for example the powder coating composition according to the invention can be stored physically and chemically stable for at least 6 weeks at 4 ℃.

"thermally curable" in the context of the present invention means that curing of the powder coating composition can be achieved by the use of 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.

The Acetone Double Rub (ADR) used for the purpose of the present invention means a coating weight of 980mg with cotton soaked in acetone and a contact surface area with the coating of 2cm²And then the hammer head is reciprocated on the surface of the coating layer 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 panel) is coated with the coating composition and cured at a temperature of 130 ℃, a coating prepared from the powder coating composition of the present invention is resistant to at least 60 ADRs, e.g., the coating is resistant to at least 70 ADRs, at least 80 ADRs, at least 90 ADRs, or at least 100 ADRs.

"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.

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. The at least two different powders may be mixed by physical mixing before placing the powder coating composition in 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.

EP1477534a2 discloses such 2K systems and in particular discloses powder compositions comprising one or more than one resin powder component in two or more than two separate parts; and for each resin powder component there is one or more than one powder, liquid or gaseous curing agent component in a single part, wherein for each resin powder component the ratio of the average particle size of the powder to the average particle size of the powder, droplets or gas droplets comprising the curing agent component is in the range of 1.3: 1 to 60: 1, and further wherein the resin component and curing agent component react to produce a cured powder coating when combined together at a temperature of 20-200 ℃ for a period of 0.01-600 seconds.

As used herein, the term "thermally initiated system" refers to a system that initiates free radical polymerization of reactive unsaturated groups in the resin with the co-crosslinker. The thermal initiation system comprises a free radical initiator. Initiation systems suitable for use in the present invention are those having a gel time of between 2.5 and 1000 minutes in the "BDDMA test" as described herein. Preferably, the thermal initiation system used has a gel time of at least 4 minutes, more preferably a gel time of at least 6 minutes and/or at most 800 minutes, such as at most 600 minutes, such as at most 400 minutes, such as at most 200 minutes.

Depending on the reactivity of the initiation system and the initiator, one or more inhibitors and/or one or more accelerators and/or one or more co-accelerators may optionally be present in the initiation system such that the gel time of the initiation system is between 2.5 and 1000 minutes as measured by the "BDDMA test" described herein.

The "BDDMA test" was used to determine "reactivity of the initiating system" herein. In this test 1 wt% of the initiation system was dissolved in 99 wt% butylene dimethacrylate (BDDMA) and the time to cure the BDDMA (gel time) was determined at 60 ℃ using DIN 16945 (section 6.2.2.2), which is incorporated herein by reference.

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. Solid initiators are preferred over liquid initiators.

The flow characteristics (flow) of the powder coating composition on the substrate can be determined by comparing the flow of the coating with a PCI powder coating flow plate (ACT Test Panels inc., APR22163(a) Batch: 50708816) at a coating thickness of about 75 μm. The flow rating is from 1 to 10, with 1 representing the most uneven coating and 10 representing the best flowing coating.

As used herein, the terms "thermal initiator", "free radical initiator" and "initiator" are used interchangeably.

The free radical initiator may be any free radical initiator known to one of ordinary skill in the art. Examples of free radical initiators include, but are not limited to, azo-type compounds such as Azobisisobutyronitrile (AIBN), 1 '-azobis (cyclohexanecarbonitrile), 1' -azobis (2, 4, 4-trimethylpentane); C-C labile compounds such as benzopinacol; peroxides and mixtures thereof.

Preferably, the initiator in the initiating system is a peroxide. The peroxide may be, for example, a percarbonate, a perester or a peracid anhydride. Suitable peracid anhydrides are, for example, Benzoyl Peroxide (BPO) or lauroyl peroxide (as Laurox)^TMTrade names are commercially available). Suitable peresters are, for example, tert-butyl perbenzoate and 2-ethylhexyl perlaurate. Suitable percarbonates are, for example, di-tert-butyl percarbonate, di (2-ethylhexyl) percarbonate or monopercarbonates.

The choice of peroxide is in principle not critical and can be any peroxide known to the person skilled in the art to be suitable for free radical curing of unsaturated resins. The peroxides include organic and inorganic peroxides, both in solid or liquid form (including supported peroxides); hydroperoxides may also be used. Examples of suitable peroxides include peroxycarbonates (of the formula-OC (O)); peroxyesters (of the formula-C (O) OO); diacyl peroxides, also known as peranhydrides (formula-C (O) OOC (O)); dialkyl peroxides or perethers (formula-OO-); hydroperoxides (of the formula-OOH), and the like. The peroxides themselves may be oligomeric or polymeric. Further examples of suitable peroxides can be found in e.g. US 2002/0091214-a1, paragraph [0018], which is incorporated herein by reference.

Preferably, the peroxide is selected from the group of organic peroxides. Examples of suitable organic peroxides are: tertiary alkyl hydroperoxides (e.g., t-butyl hydroperoxide); other hydroperoxides (e.g., cumene hydroperoxide); a particular type of peroxide formed from the group of ketone peroxides (perketones, which are addition products of hydroperoxides and ketones, such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide and acetylacetone peroxide); peroxyesters or peracids (e.g., t-butyl peroxide, benzoyl peroxide, peracetate, perbenzoate, lauroyl peroxide), including (di) peroxyesters; perethers (e.g. peroxy diethyl ether). It is of course also possible to use mixtures of peroxides in the powder coating compositions according to the invention. Also, the mixture may be a mixed type peroxide, i.e. a peroxide containing any two different peroxy-containing moieties in one molecule.

Particularly suitable for use in the present invention are any of the following initiators: peranhydrides (e.g., benzoyl peroxide or lauroyl peroxide); peroxydicarbonates (e.g., di (4-t-butylcyclohexyl) peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate).

If the reactivity of the initiating system is too high, i.e., the BDDMA test shows a gel time of less than 2.5 minutes, one or more inhibitors may be added to the initiating system. Alternatively, the inhibitor may be added during resin synthesis.

Examples of inhibitors are preferably selected from the following group: phenolic compounds, stable free radicals, catechols, phenothiazines, hydroquinones, quinones 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: aluminum-N-nitrosophenylhydroxylamine, diethylhydroxylamine and phenothiazine.

Mixtures of inhibitors (described above) may also be used. Preference is given to using hydroquinones or catechols as inhibitors, depending on the choice (type and amount) of the transition metal compound. If the reactivity of the initiating system is too low, i.e., the BDDMA test shows a gel time greater than 1000 minutes, one or more accelerators may be added to the initiating system.

The accelerator may be selected from the group of amines (preferably tertiary or aromatic amines): diamines, polyamines, acetoacetamides, ammonium salts, transition metal compounds, and mixtures thereof. Some preferred combinations of initiators and accelerators will be described below.

If the peroxide compound used comprises a structure of the formula-C (O) OO- (perester; percarbonate including peroxypolycarbonate; peranhydride, peroxyacid, etc.), the accelerator used is preferably an aromatic tertiary amine or a transition metal compound, the latter optionally being combined with a co-accelerator.

If the peroxide compound used comprises a structure of the formula-OOH- (hydroperoxides, including perketones and the like), it is preferred that the accelerator used is a transition metal, optionally in combination with a co-accelerator.

If the peroxide compounds used comprise structures of the formula-OO- (transition ethers, etc.), it is preferred that the accelerators used are transition metals, preferably in combination with co-accelerators.

Suitable tertiary aromatic amine accelerators include N, N-dimethylaniline, N-diethylaniline; toluidine and dimethylaniline, for example, N-diisopropanol-p-toluidine, N-dimethyl-p-toluidine, N-bis (2-hydroxyethyl) dimethylaniline, N-dimethylnaphthylamine, N-dimethyltoluidine and ethyl N, N-dimethylaminobenzoate.

Also, the accelerator may be selected from the group of transition metal compounds of transition metals 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.

The transition metal compound is preferably selected from the group of transition metal salts or complexes or mixtures thereof, preferably from the group of organometallic salts or complexes, most preferably from the group of metal salts of organic acids or derivatives thereof, such as transition metal carbonates or transition metal acetoacetates, such as transition metal ethylhexanoates. 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.

Depending on the reactivity of the transition metal compound, a co-accelerator may be used to enhance the reactivity of the initiating system.

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 structural 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 of which may optionally contain 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 sulfhydryl functionality of the sulfhydryl containing compound in the powder coating composition is preferably ≥ 2, more preferably ≥ 3.

Combinations of initiators and optionally inhibitors and/or optionally accelerators in combination with co-accelerators suitable for use in the initiation system of the powder coating compositions of the present invention can be readily determined by one of ordinary skill in the art. This can be done, for example, by the BDDMA test described herein, by varying the initiator (amount), inhibitor (amount), accelerator (amount), and co-accelerator (amount) to find a combination that results in a gel time between 2.5 and 1000 minutes (e.g., at least 4 minutes and/or up to 200 minutes) as measured by the BDDMA test.

The resin system present in the powder coating composition of the invention comprises a resin and a co-crosslinking agent.

The resin contains 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.

By using¹The weight per mole of unsaturated group resin system (WPU) determined by H-NMR is between 100-1000g resin/mole unsaturated group, for example between 100-9000g resin/mole unsaturated group. The methods described in Journal Of applied Polymer Science, Vol.23, 1979, pp 25-38 (the entire contents Of which are incorporated herein by reference) or by the experimental section herein can be performed, for example, by¹H-NMR to determine WPU. In the method of the experimental part, the weight per mole of unsaturated groups (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.

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 unsaturation (carbon-carbon double bond directly attached to the electron withdrawing group) can be located on the resin backbone, a side chain of the resin (backbone), a terminal end of the resin, or a combination of these positions. Preferably, the resin with reactive unsaturation used in the powder coating composition of the present invention is based on fumaric acid, maleic acid and/or itaconic acid, more preferably the resin with reactive unsaturation is based on fumaric acid and/or maleic acid.

Examples of how these reactive unsaturated groups are introduced into the resin will be 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-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 more functional alcohols (collectively referred to as polyols) or acids may be used to obtain branched polyesters. Examples of suitable polyols or polyacids are glycerol, hexanetriol, trimethylolethane, trimethylolpropane, pentaerythritol and 1, 2, 4-trimellitic acid.

Monofunctional acids such as 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 for branching.

The polyester may be prepared by esterification and/or transesterification by a generally 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 dihydroxide, dibutyltin oxide, tetrabutyltitanate, 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 end product obtained is within the stated range for the value.

Preferably, the viscosity of the polyester resin is in the range of 2 to 30pa.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 (meth) acrylates, 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 contains hydroxyl functional (meth) acrylic acid, preferably in combination 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 a glycidyl functional group, the acrylic resin contains 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 in an amount of about 0.1 wt%, based on the total weight of the polyester.

Examples of (poly) alcohols that can be used to prepare the polyurethanes are the same as those used to prepare the 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 produce an epoxy resin, for example, a diglycidyl ether of bisphenol A (such as the commercially available Epicote)^TM1001) Or phenolic (Novolac) epoxide.

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

The diacid may be branched, nonlinear, or linear. Examples of suitable diacids 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-dodecane diamine, 1, 4-cyclohexane dimethylamine, piperazine, p-xylylenediamine and/or m-xylylenediamine. 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 the pendent groups of the resin by reacting the pendent epoxy-functional groups of the resin (e.g., glycidyl-functional acrylate) with an unsaturated carboxylic acid (e.g., a monoester of methacrylic or acrylic acid or fumaric acid, maleic acid, citraconic acid, itaconic or mesaconic acid).

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

Reactive unsaturation may also be attached at the end of the resin, for example by reacting a hydroxy 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 unsaturated groups due to peroxides that may be present in the ethylene glycol and instability due to esterification temperature.

By using¹The weight per mole of unsaturated groups (WPU) of the resin as determined by H-NMR is generally less than 7500, preferably less than 1500, examplesSuch as less than 1150 or less than 1100 or less than 1000 grams/mole and/or preferably greater than 100, more preferably greater than 250 grams/mole, for example greater than 500 grams/mole.

In the case of amorphous resins, the glass transition temperature (Tg) of the resin is preferably at least 20 deg.C, more preferably at least 25 deg.C. 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 an Acid Value (AV) in mgKOH/g of 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 value of 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-.

A co-crosslinking agent is also present in the powder coating composition. "Co-crosslinking agent" refers to a compound having a carbon-carbon double bond (the carbon-carbon double bond being directly attached to an electron-withdrawing group) that can react with a reactive unsaturated group in a resin.

The co-crosslinking agent used in the composition of the present invention is selected from the following group: acrylate, methacrylate, vinyl ester, vinyl ether, vinyl amide, alkynyl ether, alkynyl ester, alkynyl amide, alkynyl amine, propargyl ether, propargyl ester, itaconate, enamine and mixtures thereof, preferably selected from the group of vinyl ether, vinyl ester, (meth) acrylate or mixtures thereof.

Acrylates are monomers, oligomers or polymers having an acrylate moiety (see formula (1) in table 1). A methacrylate is a monomer, oligomer or polymer having a methacrylate segment (see formula (2) in table 1). Examples of the liquid (meth) acrylate include butylene glycol dimethacrylate, hexylene glycol dimethacrylate, and hydroxypropyl methacrylate. Examples of other (meth) acrylates are given herein (see, for example, the resin portion modified with (meth) acrylates). Since the resin having an unsaturated group based on (meth) acrylic acid can be homopolymerized, the (meth) acrylic acid based resin can be used in combination with an oligomer or polymer containing an unsaturated group based on (meth) acrylic acid as a co-crosslinking agent.

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.

Vinyl ethers are monomers, oligomers or polymers having a vinyl ether moiety (see formula (4) 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) cyclohexylmethyl 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.

The vinyl amide is a monomer, oligomer or polymer having a vinyl amide segment (see formula (5) in table 1). Alkynyl ethers are monomers, oligomers or polymers having an alkynyl ether moiety (see formula (6) in table 1). Alkynyl esters are monomers, oligomers or polymers having an alkynyl ester moiety (see formula (7) in table 1). An alkynylamide is a monomer, oligomer or polymer having an alkynylamide moiety (see formula (8) in Table 1). Alkynylamines are monomers, oligomers or polymers having alkynylamine moieties (see formula (9) in table 1). Propargyl ether is a monomer, oligomer or polymer having a propargyl ether segment (see formula (10) in table 1). Propargyl esters are monomers, oligomers or polymers having a propargyl ester moiety (see formula (11) in table 1).

Itaconate is a monomer, oligomer or polymer having an itaconate fragment (see formula (12) 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 (13) 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.The co-crosslinking agent used in the composition of the invention is selected from monomers, oligomers or polymers comprising one or more of the following fragments: (meth) acrylate, vinyl ester, vinyl ether, vinyl amide, alkynyl ether, alkynyl ester, alkynyl amide, alkynyl amine, propargyl ester, propargyl ether, itaconate, 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 at which the powder coating composition is processed, applied and stored.

The weight per mole of unsaturated group co-crosslinker, as determined by 1H 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.

The amount of the initiation system is as follows: after application of the powder coating composition of the invention to a substrate and curing at a temperature of 130 ℃ for 20 minutes, the resulting coating is made resistant to at least 50, preferably at least 70 acetone double rubs. Methods of determining acetone double rubs are described herein.

In one embodiment of the invention, the powder coating composition has a peak enthalpy of curing reaction after the start of isothermal DSC of at most 60 minutes at 120 ℃ and at least 2.5 minutes at 60 ℃. Methods of performing isothermal DSC tests are described herein.

Alternatively, the amount of thermal initiation system in the powder coating composition is selected such that: such that the peak of enthalpy of curing reaction of the powder coating composition after the onset of isothermal DSC is at most 60 minutes at 120 ℃ and at least 2.5 minutes at 60 ℃. In another embodiment of the invention, the coating made from the powder coating composition is resistant to at least 50, preferably 70 acetone double rubs.

Preferably, the peak of the enthalpy of curing reaction is at least 4 minutes at 60 ℃, more preferably at least 6 minutes and/or at most 45 minutes at 120 ℃.

"isothermal DSC" refers to a thermal analysis test conducted with a differential scanning calorimeter at a constant temperature. The DSC used is, for example, a DSC Q2000 instrument from TA Instruments. Samples of the powder coating composition were used ranging from about 5 to about 10 mg. The sample is first stabilized at room temperature (2 minutes) and then heated at 60 ℃ or 120 ℃ at a rate of 5 ℃/min or 20 ℃/min, respectively, and held at that temperature for a period of time.

For fast scanning of powder coating compositions, in particular reactive (high) peroxides, samples of the powder coating compositions used for the DSC test were prepared by the following method: a20% solution of the resin system (resin and co-crosslinker) and the initiating system was prepared in a mixture of dichloromethane and ethanol (ratio 3: 2). The molar ratio of the resin to the unsaturated group of the co-crosslinking agent is 1: 1. A film of the powder coating composition solution was applied to a glass plate with a doctor blade to a thickness of 150 μm. The film was dried overnight. The dried film was scraped off from the glass plate, and then isothermal DSC test was performed with the resulting material.

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, to obtain a powder coating composition of suitable particle size. 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 at a 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 for at least partial curing of 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 typically 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. It is to be noted that none of these conventional additives are considered transition metal compounds. Examples of leveling agents include Byk^TM361N. Examples of suitable fillers/pigments include metal oxides, silicates, carbonates or sulfates. 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 one embodiment of the invention, the powder coating composition of the invention comprises a resin (preferably a polyester, such as a fumaric-based polyester), comprising a co-crosslinking agent (such as a vinyl ether, for example commercially available from DSM Resins under the name Uracross @)^TMVinyl ether of P3307) and a thermal initiator (e.g., a peroxydicarbonate, such as Perkadox, respectively^TM16 and Perkadox^TMDi (4-t-butylcyclohexyl) peroxydicarbonate and dimyristyl peroxydicarbonate, commercially available from akzo nobel, and inhibitors (e.g., hydroquinones such as t-butylhydroquinone or 2, 3, 5-trimethylhydroquinone).

The present invention therefore especially relates to a powder coating composition according to the present invention, wherein the resin is a fumaric-based polyester, wherein the co-crosslinking agent is a vinyl ether, and wherein the thermally initiated system comprises a peroxydicarbonate, preferably di (4-tert-butylcyclohexyl) peroxydicarbonate and dimyristyl peroxydicarbonate; and hydroquinone, preferably tert-butylhydroquinone or 2, 3, 5-trimethylhydroquinone.

In one embodiment of the invention, the powder coating composition of the invention comprises a resin, preferably a polyester, e.g. a fumaric-based polyester, a co-crosslinking agent, e.g. a vinyl ether, e.g. commercially available from DSM Resins under the name Uracross^TMVinyl ether of P3307) and thermal initiators (e.g., Benzoyl Peroxide (BPO)).

The invention therefore especially relates to a powder coating composition according to the invention, wherein the resin is a fumaric-based polyester, wherein the co-crosslinking agent is a vinyl ether, and wherein the thermal initiator is benzoyl peroxide.

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 present 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 and wood substrates, for example 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); substrates with cellulosic fibers, such as cardboard, paper substrates; 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.

Examples

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

Experimental part

Determination of the reactivity of the initiating System in butanediol dimethacrylate (BDDMA)

The determination of the reactivity of the initiation system was carried out by monitoring the curing of BDDMA with a standard gel time device. The gel time (T) was determined by testing the exothermic reaction of BDDMA when it was cured at 60 ℃ using 1% of the initiation system shown in Table 2, according to the method in DIN 16945 (section 6.2.2.2)_gelOr T_60-＞70℃). For this purpose, the equipment used was a Soform gel time apparatus equipped with the Peakpro software package and National Instruments hardware; the water bath and thermostats used were Haake W26 and Haake DL30, respectively.

In table 2, the amount of the transition metal compound (accelerator) is expressed as mmol of the transition metal compound per kg of BDDMA used.

TABLE 2

This indication shows that a variety of peroxides are suitable for use in the initiation system of the present invention. In addition, the table shows that various relatively inert peroxides can become more reactive in the presence of an accelerator, and thus have the reactivity required according to the invention (see table entry 22 and table entry 30). In addition, the table shows that the various reactive peroxides with inhibitors can become less reactive and thus give more suitable reactivity (see table entry 4 and table entry 38). The table also shows that combinations of accelerators and inhibitors can be used to alter the reactivity (table entry 39).

Synthesis and application of powder coatings

Table 3: chemical product

Synthesis of resin: general procedure

The chemicals used in the following examples are described in table 3 above.

Synthesis of resin (resin B)

The tin catalyst and the monomers used in the first step (all of the (poly) alcohol and terephthalic 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 230 ℃. The benzoic acid used in the second step is then added at a temperature of 140 ℃ and then esterified at 230 ℃. When the acid number reached less than about 8mg KOH/g resin, the reaction mixture was cooled to 160 ℃. Fumaric acid and a small amount of a radical inhibitor were added and esterification was carried out by raising the temperature to 200 ℃. The last step of the polyester preparation is carried out under reduced pressure.

Synthesis of resin (resin C, D, E, K)

The tin catalyst and the monomers used in the first step (all of the (poly) alcohol and terephthalic 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 benzoic acid and fumaric acid used in the second step and a small amount of a free radical inhibitor are then added at a temperature of 160 ℃ and then esterified at 210 ℃. When the acid number reached about 5mg KOH/g resin, the esterification step was carried out under reduced pressure. The acid value of the resin was brought to less than 5mg KOH/g resin by reaction of the remaining acid groups of the resin with epoxy groups or alkylene carbonate (see chemicals used in Table 4). The amount depends on the acid number before addition.

Synthesis of resin (A)Resin A, G, H, J)

The tin catalyst and the monomers used in the first step (all of the (poly) alcohol and terephthalic 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 ℃. Followed by addition of a second step of fumaric acid and a small amount of a free radical inhibitor at a temperature of 180 c and subsequent esterification at 220 c. When the acid number reached less than about 15mg KOH/g resin, the reaction mixture was cooled to 205 ℃. The third step of the polyester preparation was carried out under reduced pressure until an acid value of about 5mgKOH/g of resin was reached. The acid value of the resin was brought to less than 5mg KOH/g resin by reaction of the remaining acid groups of the resin with epoxy groups or alkylene carbonate (see chemicals used in Table 4). The amount depends on the acid number before addition.

Synthesis of resin (resin F)

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 230 ℃. When the acid number reached less than about 10mg KOH/g resin, the reaction mixture was cooled to 160 ℃. Itaconic acid and a small amount of free radical inhibitor were added and esterification was carried out by raising the temperature to 220 ℃. The last step of the polyester preparation is carried out under reduced pressure.

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 heating rate of 5 deg.C/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 mole 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 mole of 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).

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

Method for determining 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 (II)

The isocyanates as listed in Table 5 were charged into a reactor equipped with a thermometer and a stirrer. Stirring was then applied and a small nitrogen stream was passed through the reaction mixture while the temperature was kept below 15 ℃. Next, vinyl ether as listed in Table 5 was added, and the reaction mixture was maintained below 15 ℃ during the addition. After all the vinyl ether was added, the temperature was raised to 65 ℃ and the tin catalyst was added. The alcohol as listed in table 5 was then added while the temperature was kept below 75 ℃. After all the alcohol was added, the temperature was set to 105 ℃ 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 115 ℃ and vacuum (0.1bar) was applied to remove all volatiles. The contents of the container are released after the vacuum treatment.

Synthesis of Co-crosslinking Agents (III/IV/V)

The tin catalyst and the monomers used in the first step as listed in Table 5 (all of the (poly) alcohols, terephthalic acid and isophthalic acid) were charged to a reactor equipped with a thermometer, a stirrer and distillation equipment. Stirring was then applied and a small stream of nitrogen was passed through the reaction mixture while warming to 220 ℃. Next, the vinyl ethers and tin catalysts as listed in Table 5 for the second step were added at a temperature of 100 ℃. The isocyanate as listed in table 5 was then added, and the reaction mixture was maintained below 100 ℃ during the addition. After all the isocyanate had been added, the temperature was maintained or set at 105 ℃ 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 115 ℃ and vacuum (0.1bar) was applied to remove all volatiles. The contents of the container are released after the vacuum treatment.

Table 5: 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 20 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.

Preparation of powder coating compositions

The molar ratio of the unsaturated groups in the resin and the co-crosslinking agent is selected to be 1: 1. The amount of initiator used in the initiation system is based on the total weight of the resin system (e.g., x moles initiator per kg resin system; the so-called resin system in the amounts of initiator and inhibitor is defined as resin containing reactive unsaturated groups plus co-crosslinker, excluding conventional powder coating composition additives such as pigments, fillers, etc.). The amount of inhibitor used in the initiating system is based on the total weight of the resin system. The amount of accelerator used in the initiating system is based on the total weight of the resin system (e.g., x moles accelerator per kg resin system). The levelling agents and pigments are used in amounts of wt.%, calculated with respect 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 6, the following initiation systems can be used as initiation systems for curing powder coating compositions: the reactivity in BDDMA as measured by the BDDMA test described herein is between 2.5 and 1000 minutes.

It is also shown that: by selecting the initiation system within the desired reactivity range, the powder coating composition can be cured to acceptable levels at relatively low temperatures, i.e., T_{＞50 ADR}(bringing the coating toThe curing temperature required for at least 50 ADRs) is below 130 ℃. Likewise, T_{＞70 ADR}(curing temperature required to achieve at least 70 ADR times) of the coating is less than 130 ℃.

As can be seen from table 7 above: different initiation systems may be used in the powder coating compositions of the present invention. Likewise, the resin system may also vary, and thus different combinations of resins and co-crosslinking agents may be used.

The results in Table 7 also show that the amount of inhibitor used in the initiation system can vary.

EXAMPLE 3 use of additives

TABLE 8 influence of the use of additives (pigments and levelling agents) on the powder coating compositions according to the invention

As can be seen from table 8: the powder coating composition may contain additives without affecting the cure temperature (T) required to obtain an acceptable cure_{＞50 ADR}Held at less than 130 c).

The additive-containing composition was coated on an aluminum substrate (ALQ board) and a white oak substrate. The coated substrate was cured at 100 ℃ for 25 minutes to give a very good cure and the coating was able to withstand 100 ADR's. This example thus shows that the powder coating composition of the invention is particularly suitable for coating heat-sensitive substrates (e.g. wood).

EXAMPLE 4 itaconic acid based polyester resin

TABLE 9 itaconic acid based polyester resins as both resins and co-crosslinking agents

As can be seen from table 9: the itaconic acid based polyester resin may be homopolymerized, and thus the resin and the co-crosslinking agent may be the same.

Example 5 different Co-crosslinkers

TABLE 10 different Co-crosslinkers

As can be seen from table 10: the powder coating compositions of the invention may use different co-crosslinkers. Also, both amorphous and crystalline co-crosslinkers can be used.

EXAMPLE 6 WPU of resin System, WPU of resin and WPU of Co-crosslinker pairs to give acceptable powder coatings Influence of the required curing temperature of the layer

TABLE 11 influence of WPU

As can be seen from table 11 above: by using¹The WPU (actual WPU) of the resin system as determined by H NMR needs to be below 1000, preferably below 900. Furthermore, it is preferable to use¹WPU (actual WPU) of resin determined by H NMR is lower than 1170 and/or¹The WPU (actual WPU) of the co-crosslinking agent as determined by HNMR is less than 870g/mol, preferably 630 g/mol.

Example 7 Effect of the amount of initiating System

TABLE 12 influence of the amount of initiating System used

As can be seen from table 12: one of ordinary skill in the art can readily determine to cure the powder coating composition to an acceptable degree (T) by using conventional techniques_{＞50 ADR}(DEG C) less than 130 ℃) of the minimum amount of initiation system required.

Claims

1. A heat curable powder coating composition suitable for curing at a temperature of from 60 to 130 ℃, comprising:

-a thermally initiated system and a resin system;

-wherein the amount of thermal initiation system in the powder coating composition is selected such that: after allowing the powder coating composition to coat onto a substrate and cure at a temperature of 130 ℃ for 20 minutes, the resulting coating is resistant to at least 50 acetone double rubs;

-wherein the resin system comprises a resin and a co-crosslinking agent;

-wherein the powder coating composition is a one-component system.

2. The composition of claim 1, wherein the gel time provided by the thermal initiation system is at least 6 minutes.

3. A composition according to claim 1 or 2, wherein the thermal initiation system comprises a peroxide, preferably an organic peroxide.

4. The composition of any one of claims 1-3, wherein the thermal initiation system comprises hydroquinone or catechol.

5. The composition of any of claims 1-4, wherein the resin is a polyester.

6. The composition of any of claims 1-5, wherein the co-crosslinking agent is selected from the group consisting of: vinyl ethers, vinyl esters, methacrylates, acrylates, itaconates, and mixtures thereof.

7. The composition of any of claims 1 to 6, wherein the weight of co-crosslinking agent per mole of unsaturated groups is preferably less than 630 g/mole and/or the resin weight per mole of unsaturated groups is less than 1150 g/mole.

8. The composition of any of claims 1-5 or 7, wherein the resin and the co-crosslinking agent are the same.

9. The composition of any one of claims 1-7, wherein the resin is a fumaric-based polyester, wherein the co-crosslinking agent is a vinyl ether, wherein the thermally initiated system comprises a peroxydicarbonate (preferably di (4-t-butylcyclohexyl) peroxydicarbonate or dimyristyl peroxydicarbonate) and a hydroquinone (preferably t-butylhydroquinone or 2, 3, 5-trimethylhydroquinone).

10. The composition of any of claims 1-3 or 5-7, wherein the resin is a fumaric-based polyester, wherein the co-crosslinking agent is a vinyl ether, and wherein the thermal initiator is benzoyl peroxide.

11. A process for preparing a powder coating composition according to any one of claims 1 to 10, comprising the steps of:

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

12. A method of coating a substrate comprising:

1) applying the powder coating composition according to any one of claims 1 to 10 to a substrate to obtain a coated substrate;

2) the coated substrate is heated.

13. A substrate partially or completely coated with a powder coating composition according to any one of claims 1 to 10.

14. Use of the powder coating composition according to any one of claims 1 to 10 for coating heat-sensitive substrates, preferably wood.