Patent Application
20190085174
This invention relates to metallic effect particulate coatings formed using pigments such as aluminium. In particular, the invention relates to the avoidance of corrosion of these pigments in the formed coating as well as the avoidance of scuff marks or finger marks on such a coating. The invention also relates to the use of the particulate coating to coat a substrate as well as to a process for the manufacture of the particulate coating, a process for curing the coating and uses of the coating. The particulate coating of the invention preferably forms a top coat on the substrate.
Traditionally, coating powders have been made by the extrusion of a mixture of resins and curing agents (and standard additives etc) to obtain a homogeneous mixture and then grinding the extrudate and screening the product to obtain the desired particle sizes and particle size distribution. The powder is then electrostatically sprayed onto a substrate, traditionally a metal substrate, and cured at high temperatures. The nature of the finish on the substrate was adjusted by the addition of additives.
A growing market for powder coatings is in the field of metallic powder coatings which provide a metallic effect on the surface of an article being coated. The metallic effect is achieved by adding metallic pigments into the powder coating at an appropriate time. These metallic effect pigments may corrode, however, if they are exposed to oxygen, humidity etc. Corrosion may also be caused by contact with acids, bases and water. This ruins the appearance and integrity of the coating. To avoid this problem, current practice involves the use of an extra clear coating layer applied separately over the metallic effect coating in order to provide protection against corrosion. The application of this further coat is time consuming and expensive however, and the customer wants a simpler solution to avoid the use of the extra clear coat. One coat less saves much time and money.
It is also observed that these metallic pigment containing powder coating compositions may suffer from inhomogeneity if the metallic pigment is not dispersed properly in the coating. A further issue of concern is scuff marks or finger marks on the formed coating. In order to keep an ideal aesthetic appearance, the avoidance of these marks is desired. It would be desirable to prepare a particulate coating composition that was able to address some or all of these issues.
The present inventors solve this problem through the addition of an amino alcohol to the powder coating. The present invention preferably relates to a polyester/epoxy powder coating composition which contains metallic effect pigments like aluminium powder/flakes and an amino alcohol. Surprisingly, this powder coating composition can be applied as a single coat without the need to apply an extra top coat.
This formulation surprisingly stabilises the metallic pigment against corrosion, e.g. improves acid resistance, base resistance and resistance to water/humidity. The need therefore, for a clear top coating layer is negated. The amino alcohol also aids the dispersability of the metallic pigment in the powder coating composition. The coating of the invention remarkably is less prone to discolouration by fingerprints when it is handled or touched.
The problem of corrosion of metallic pigments has been recognised before and attempts have been made to solve this problem in other ways, with limited success. In US2009/0264575, the inventors suggest coating the metallic pigment particles. The coating is ideally based on epoxy and polyester resins and is therefore compatible with the binder which generally forms the major part of the film forming coating. The idea is that embedding the metallic pigments within the epoxy/polyester resin prevents corrosion of the pigment. In essence therefore, this reference provides a metallic particle that is coated to isolate the metal from air and moisture. That coated metallic particle can be used as a masterbatch in a powder coating to provide the pigment in desired amounts. Some manufacturers even use a double coating technique, e.g. based on an inorganic/organic double coating such as a silica coating followed by an acrylate coating or polyester/epoxide coating.
Coating of the metal particles improves the stability of the pigments during storage, but the resistance of these particles to corrosion once applied to a substrate is still not ideal Thus whilst many metallic particles are coated to enable storage over a prolonged period before application, our experience is that on application, these particles are still susceptible to oxidation. Moreover, coating the particles is expensive and time consuming.
CN101225279A considers a composition that is designed to address the issue of fingerprint marks. It however employs epoxy resin, polyester resin, pigment and filler, and aluminum flakes. The aluminum flakes allegedly improves the flow performance, enhances the resistance to abrasion and scratch and has a defoam function.
CN103483979A discloses a powder coating composition which contains aluminium flakes, epoxy resin, polyester resin and vinyl tris(beta-methoxy ethoxy)silane as adhesion promoter. This combination allegedly improves wear resistance, anti-scratch property and defoaming function.
No one however, has previously suggested the possibility of using an amino alcohol in these powder coatings compositions. Not only therefore does the amino alcohol lead to better aesthetic appearance, but the dispersibility of the metallic pigment is improved. Moreover, the use of the amino alcohol leads to an improvement in corrosion resistance. This might manifest in an improvement in the acid or base resistance of the coating. Finally, humidity resistance can be improved.
Viewed from one aspect the invention provides a particulate coating composition, preferably a powder coating composition, comprising:
Viewed from another aspect the invention provides a substrate coated with a particulate coating composition, preferably a powder coating composition, comprising:
Viewed from another aspect the invention provides a substrate coated with a primer layer and thereover a particulate coating composition layer, preferably a powder coating composition layer, comprising:
a particulate coating composition, preferably a powder coating composition, comprising:
Viewed from another aspect the invention provides a substrate coated with a particulate coating composition or a substrate coated with a primer layer and thereover a particulate coating composition as herein defined wherein said powder coating composition is cured.
Preferably, said particulate coating composition forms the top layer on the substrate.
Viewed from another aspect the invention provides a kit comprising: a first composition comprising at least one hardener such as at least one epoxy containing compound, at least one polyester polymer, and at least one amino alcohol; and
a second composition comprising at least one metallic pigment.
Viewed from another aspect the invention provides a process for producing a particulate coating composition, preferably powder coating composition, comprising blending at least one hardener such as at least one epoxy containing compound, at least one polyester polymer, and at least one amino alcohol to form a mixture;
extruding said mixture to obtain particles;
adding at least one metallic pigment to form a particulate powder coating.
Viewed from another aspect the invention provides the product of the process as hereinbefore described.
Viewed from another aspect the invention provides a process for coating a substrate with a particulate coating as hereinbefore defined, e.g. using electrostatic spraying, comprising applying said particulate coating to said substrate, e.g. using electrostatic spraying and optionally curing the coating.
Viewed from another aspect the invention provides a process for coating a substrate with a particulate coating composition, preferably powder coating composition, comprising blending at least one hardener such as at least one epoxy containing compound, at least one polyester polymer, and at least one amino alcohol to form a mixture;
extruding said mixture to obtain particles;
adding at least one metallic pigment to form a particulate powder coating;
applying said particulate coating to said substrate, e.g. using electrostatic spraying and optionally curing the coating.
Viewed from another aspect the invention provides use of an amino alcohol to prevent corrosion of a metallic pigment present in a powder coating composition comprising at least one hardener such as at least one epoxy containing compound, at least one polyester polymer, and at least one metallic pigment.
It is preferred if the coating described herein is a top coat. Thus, no further coating should be applied on the top of the coating of the invention.
This invention relates to a particulate coating composition such as a powder coating composition which can be used to coat a substrate. The particulate coating composition must contain at least four components: at least one hardener such as an epoxy containing compound, at least one polyester polymer, at least one amino alcohol and at least one metallic pigment. The particulate coating composition of the invention is preferably used as a top coat on a substrate, which may or may not be provided with a primer layer. The term top coat implies that no additional coating layer is applied on top of the particulate coating layer of the invention.
The amino alcohol is believed, inter alia, to prevent corrosion of the metallic pigment within the coating thus avoiding the need for the application of a clear top coat over the coating layer. Thus, the amino alcohol may help prevent acid, base and water damage to the coating. The amino alcohol also helps disperse the metallic pigment in the particulate coating. The amino alcohol helps to prevent aesthetic discoloration of the coating, e.g. via fingerprints or other human skin contact or via scuffing.
The particulate composition of the invention is preferably obtainable by the blending of two particulate, preferably powder compositions. A particulate composition containing an amino alcohol can be blended with a particulate composition containing a metallic pigment.
The coating composition of the invention contains at least one reactive polyester polymer. The term reactive implies that the polyester polymer must contain functional groups that are capable of reacting with the functional groups of the hardener to cure the coating. Suitable functional groups present on the polyester include carboxyl groups, ester groups, isocyanate groups and hydroxyl functional groups. Ideally, the polyester is solid. The polyester is further preferably a carboxylated or hydroxylated polyester, especially a saturated, carboxylated polyester resin or a saturated, hydroxylated polyester resin. Most preferably, the polyester is a carboxylated polyester resin and therefore comprises a plurality of pendant COOH groups.
Thus the polyester polymer is preferably a solid resin containing a plurality of free carboxyl groups or hydroxyl groups. Preferably, the polyester polymer has a Tg above 40° C., more preferably above 50° C.
Ideally, the polyester resin is characterised in terms of its acid value (AV). Most preferred are polyester resins with acid value (AV) between 20-80 mg KOH/g, such as 30 to 70 mg, KOH/g, preferably 40-60 mg KOH/g. Resins in the range of 55 to 68 mg KOH/g or 60 to 70 mg KOH/g are especially preferred.
More preferably, the polyester polymer is an acid functional polyester, especially one having the AV above.
The polyester polymer therefore preferably contains a plurality of carboxyl groups. These groups must be capable of reacting with the hardener, ideally epoxy groups and must therefore be available for reaction. That means carboxyl groups should be pendant on the molecule. Moreover, this component of the powder coating of the invention is a polymer, e.g. is formed from the polymerisation of monomers at least one of which is one containing a carboxyl group
It is possible to use a mixture of polyesters polymers or use one polyester polymer.
The use of carboxyl functional polyesters is preferred especially those designated 50/50 type resins to 80/20 type resins (i.e. where there is 80 wt % carboxy functional polyester is used to 20 wt % epoxy compound of the binders). The value of AV and EEW, should preferably complement each other. For example, the AV of a 50/50 type resin may be 60 to 80 mg KOH/g. Resins that are defined as 80/20 resins will have lower AV, such as 20 to 40 mg KOH/g.
The monomers used to form the polyesters of the invention may be based on terephthalic acid, isophthalic acid monomers together with, for example glycols such as neopentyl glycol.
Alternatively the polyester may be OH functional. Hydroxyl values are preferably about 50-300 mg KOH/g.
Another alternative may also be unsaturated polyesters. These can be hardened using peroxide initiators. The term unsaturated polyester implies the presence of multiple unsaturated bonds in the side chains of the polyester, e.g. introduced through (meth)acrylate. Unsaturated polyesters of use in this embodiment are amorphous or crystalline. Crystalline unsaturated polyesters are described in WO2011/138431 A1 and WO2011/138432 A1. These materials can be hardened using peroxides, optionally in conjunction with infrared radiation or radiation or using photo initiators for radiation cure with UV. The hardener in this regard is the initiator.
The polyester polymer is preferably one with a Mw of at least 1000, more preferably at least 2000. The upper Mw value may be 10,000. Preferred Mw values are 2000-6000, preferably 2500 to 5000, such as about 3000. The molecular weights are determined by gel permeation chromatography (GPC) using a polystyrene standard.
Such resins are well known in the art and are sold under the trade names such as Uralac from DSM and Crylcoat from Allnex.
It is also essential to use at least one hardener. The hardener reacts with the polyester polymer during the curing reaction to provide a film coating on the substrate.
It is preferred if the hardener is an epoxy containing compound such as an epoxy resin. It is also possible to use a mixture of epoxy containing compounds.
The epoxy containing compound is preferably an epoxy resin. Ideally it is a solid resin containing one or more epoxy groups. Suitable resins are again well known in the art and well known commercial products. Epoxy containing compound include TGIC (triglycidyl isocyanurate), Araldite PT 910/PT912, bisphenol A based resins, novolac resins, novolac modified resins, 4,4′-isopropylidenediphenol-epichlorohydrin resins (bisphenol F) based resins, glycidyl methacrylates (GMA) and so on.
In one preferred embodiment, the epoxy resin is TGIC, Araldite PT 910/PT912, bisphenol A based resins, novolac modified resins, or 4,4′-isopropylidenediphenol-epichlorohydrin resins (bisphenol F) based resins. Thus, in one embodiment the using of glycidyl methacrylate (GMA) or glycidyl methacrylates (GMA) in general is excluded. Especially preferred is bisphenol A resin.
Most preferred are solid epoxy resins with an equivalent epoxy weight (EEW) of 300-2000. These resins are often described by their “type”. Type 2, 2.5, 3, 4 and novalac modified type resins are all suitable here. Type 2 resins may have an EEW=550-700, e.g. Epikote resin 1002, Epikote resin 3022-FCA. Type 2.5 resins may have a EEW=600-750, e.g. Araldite GT 6450. Type 3 resins may have EEW=700-850, e.g. Epikote resin 3003, Araldite GT 7004. Type 4 type resins may have EEW=800-1000, e.g. Epikote resin 1055. Novalac modified type resins may include Epikote resin 2017 or Araldite GT 7255.
The use of an epoxy resin of EEW 730 to 840 (such as type 3) is especially preferred.
As an alternative to epoxy resins, the invention also envisages the use of other hardeners such as hydroxyalkyl amide hardeners and polyisocyanate hardeners such as one of the uretdione type, or caprolactam blocked isocyanates (e.g. isophorone diisocyanate). In particular, the polyisocyanate hardeners are preferably used with hydroxyl functionalised polyester resins to give polyurethanes. Hydroxy alkyl amide hardeners can be used with carboxylic functionalized polyester resins. The use of hydroxy alkyl amide hardeners is especially preferred such as Primid XL-552, available from Ems Primid.
A further alternative hardener is simply a peroxide where the polymer is an unsaturated polyester and can undergo a curing reaction with itself upon initiation with a peroxide.
It will be appreciated that the hardener and polyester need to react in order to cure the coating. Accordingly, it is preferred if these components are mixed in such a ratio that reactive groups, e.g. carboxyl, in the polyester and e.g. epoxy groups within the hardener are within ±25% of stoichiometric ratio. A carboxyl and epoxy ratio within ±10% of stoichiometric ratio is more preferred. A carboxyl and epoxy ratio within ±5% of stoichiometric ratio is most preferred.
The skilled man will be aware that some of the additives discussed below may contain carboxyl groups. When calculating the EEW to AV ratio, account should be taken of the contribution made by any carboxyl groups in the standard additives used in the powder coating.
It will be appreciated therefore that this calculation is based on the total number of carboxyl and epoxy groups present. If compounds contain multiple carboxyl or epoxy groups that must be considered in these calculations that will nevertheless be routine for the skilled chemist.
The combination of the hardener and polyester polymer is called the binder system herein. Ideally, the invention employs a hybrid epoxy-carboxyl functional polyester binder system. These systems are well known in the art. It is within the scope of the invention to employ a pure polyester binder where that binder is a unsaturated polyester which can be hardened via an epoxide.
Thus, the polyester may form 50 to 97 w % of the binder, preferably 60-96 wt % of binder. The hardener may form 3 to 50, preferred 3 to 40 wt % of the binder. The amount of polyester polymer will therefore be around the same as or exceed that of the hardener compound. Where an unsaturated polyester binder is employed the polymer can form almost 100 wt % of the binder, with a small contribution from the initiator hardener.
The amount of binder in the powder coating of the invention may be 40 to 99 wt %, preferably 50 to 95 wt %.
The particulate coating of the invention comprises a metallic pigment. The purpose of the metallic pigment is to provide a coated substrate with a metallic colour effect. These are used therefore to coat household appliances, furniture, building components, tools, vehicles and so on to provide a metallic effect coating.
Any metallic pigment can be used in this invention although the pigment should be one that is subject to corrosion. The present invention is related, inter alia, to a method of reducing the corrosion or preventing corrosion of the metal pigment. It will be clear therefore that the pigment in question should preferably be one that may corrode.
The metal in question is typically a transition metal (groups 3 to 12 of the periodic table), Al or Sn. The pigment can also be present as an alloy. The pigment ideally contains the metal in elemental or alloy form rather than as a salt (e.g. oxide) or in ionic form. It will be appreciated therefore that many powder coatings contain titanium dioxide and other metal salts as fillers. Titanium dioxide is a white powder and is not subject to corrosion and is not a metallic pigment. The metallic pigment must be capable of providing a metallic effect in the formed coating.
The metallic pigment is usually in flake form or particle form and may comprise aluminium or an aluminium alloy or another metal or alloy, for example, stainless steel, copper, tin, bronze or brass (gold is generally too expensive) and may be used to produce various metallic effects including those referred to as “lustre” or “glamour” finishes. Combinations of two or more different metallic pigments may be used.
The metallic pigment is advantageously aluminium or an alloy thereof. A “leafing” or a “non-leafing” system may be used. In a leafing system, the aluminium flakes orient themselves in a continuous layer at or near the surface of the applied coating film, producing an opaque silver finish.
Non-leafing aluminium pigments, which orient themselves throughout the coating film, provide aesthetics quite unlike leafing aluminium pigments. They are unique in their ability to project “flop”, polychromatic and sparkle effects. “Flop” is the ability to change colour when viewed at different angles. This capability is directly related to flake orientation in the film.
The metallic pigment(s) are usually incorporated in the powder coating composition after the extrusion or other homogenisation process (hereinafter “post-blended”). One form of post-blending method comprises dry-blending and any available dry-blending incorporation method may be used. Pigments can be added before or after milling, e.g. at the particle sieving stage. In theory however, metal pigments can be added at various stages of the manufacturing process, e.g. a portion before milling and a portion before sieving. The person skilled in the art can devise ways of adding the pigment to the powder coating. In one possible embodiment, pigments are added at the premix stage, i.e. before extrusion. Products advertised under the trade name “Powdersafe” or “Powdersafe-02” are suitable for direct extrusion. The use of these pigments forms a further aspect of the invention.
Viewed from another aspect the invention provides a process for producing a particulate coating composition, preferably powder coating composition, comprising blending at least one hardener such as at least one epoxy containing compound, at least one polyester polymer, at least one metallic pigment and at least one amino alcohol to form a mixture;
extruding said mixture and optionally milling and/or grinding to obtain a particulate powder coating.
In particular the pigment and the powder coating can be “bonded”. A bonding method is to be understood as being a mixing process of a powder coating and a metallic pigment in which the metallic pigment particles are physically bonded to the powder coating particles by heating the mixture to the glass transition temperature of the powder coating. Adhesion of the metallic pigments to the surface of the powder coating particles is therefore achieved.
A range of hammer and other textured metallic finishes can be produced using, in addition to the metallic pigment, an appropriate hammer or other structure additive.
The metallic pigment may be an uncoated or coated material. Examples of coated materials include pigments coated with silica or another inert inorganic material for greater chemical resistance and durability. Alternatively, the pigment may be coated with a polymeric material for similar purposes, for example, an acrylic, PTFE or thermosetting plastics material, or may be carried in a polymer or plasticiser which is compatible with the film-forming binder of the powder coating composition, such as a polyester/epoxide coating. As a further possibility, the metallic pigment may be coated with a colouring agent such as a metal oxide pigment such as, for example, iron oxide, to provide special colour effects. The use of metallic pigments coated with silica is preferred to improve the stability of the particles both during storage and during further coating. Double coated particles (e.g. using an inorganic then organic coating) are possible but less favoured as their metallic effect is reduced. It may also be possible to use a silane as an adhesive in the metallic pigment to bind a coating layer to the particle.
Ideally particles are not coated with an organic coating. Ideally particles are not coated with an oligomeric or polymeric coating.
The total proportion of metallic pigment(s) incorporated in the coating composition may be in the range of from 0.1 to 10% by weight (based on the weight of the coating composition, for example, from 0.4 to 8% by weight, preferably from 0.5 to 5% by weight, typically from 1 to 4% by weight. These values refer to the actual weight of particles which may or may not be coated.
The particle size, d50 of the metallic pigment may be in the range of 3-50 μm. Typically, the particle size is d50 10-30 μm. Ideal average particle sizes are no less than d50 10 μm. Particle sizes can be measured using a Malvern machine which gives size in d50. D50 is the mass-median-diameter (MMD). The MMD is considered to be the average particle diameter by mass.
The amino alcohol of the invention is a compound comprising at least one hydroxyl group and at least one primary, secondary or tertiary amine group. Salts thereof could also be used. Preferably, the amino alcohol of the invention will be formed from elements C, H, O and N only. The use of primary or secondary amino alcohols is preferred.
In general, the amino alcohols that may be used in accordance with the invention include those having the following formulas:
NH2R1
where R1 is a linear or branched alkyl group of 1 to 10 carbons, preferably 2 to 8 carbons, and more preferably 2 to 4 carbons, that contains at least one hydroxyl group; and
NHR1R2
where R1 is a linear or branched alkyl group of 1 to 10 carbons, preferably 2 to 8 carbons, and more preferably 2 to 4 carbons, or a linear or branched alkyl group of 1 to 10 carbons, preferably 2 to 8 carbons, and more preferably 2 to 4 carbons that contains at least one primary hydroxyl group and R2 is a linear or branched alkyl group of 1 to 10 carbons, preferably 2 to 8 carbons, and more preferably 2 to 4 carbons that contains at least one hydroxyl group.
Mixtures of these amino alcohols can also be employed. It is preferred if the hydroxyl group in these formula is primary, i.e. forming a —CH2—OH group with the carbon to which it is attached.
The amino alcohols used in accordance with the present invention can be in liquid or solid form. A person of ordinary skill in the art is familiar with the techniques that can be utilized to incorporate liquid amino alcohols into the powder mixture. For example, prior to adding the liquid amino alcohols to the powder coating mixture of the present invention, the liquid amino alcohols can be absorbed onto an inert carrier, such as silica.
Preferably, the amino alcohols of the present invention include, but are not limited to diethanolamines, ethanolamines, 2-amino-1-butanol, 2-amino-2-methyl-1-propanols, 2-amino-2-ethyl-1,3-propanediols, tris(hydroxymethyl)aminomethanes, 2-amino-2-methyl-1,3-propanediols, monomethylaminoethanols, isopropylaminoethanols, t-butylaminoethanols, ethylaminoethanols, n-butylaminoethanols, isopropanolamines, diisopropanolamines, and mixtures thereof. More preferably, the alkanolamines of the present invention are diethanolamines, tris(hydroxymethyl)aminomethanes, and mixtures thereof.
Preferably the amino alcohol of use in the invention will have a molecular weight of less than 500 g/mol such as 50 to 400 g/mol, e.g. 75 to 350 g/mol.
The amino alcohol may have 1 to 3 amino groups, preferably 1 to 2 amino groups, preferably 1 amino group. It is preferred if the amine functionality comprises an N—H bond, i.e. the amine is primary or secondary, especially primary (—NH2).
The amino alcohol may comprise one hydroxyl group or 2 to 5 hydroxyl groups, such as 2 or 3 hydroxyl groups.
Ideally, the amino alcohol has one amine group, ideally a primary amine, and 2 or more, such as 3, hydroxyl groups.
Preferred amino alcohols are tris(hydroxymethyl)aminomethane (THAM) and diethanolamine. Possible amino alcohols therefore include:
3-Amino-1-propanol
Amino-2-propanol
3-Amino-1,2-propanediol
1,3-Diamino-2-propanol
1-Amino-2-methyl-2-propanol
1-Methoxy-2-propylamine
2-Amino-1-butanol
2-Amino-2-methyl-1-propanol
2-Amino-2-methyl-1-propanol
2-Dimethylamino ethanol
3-Methylamino-1-propanol
4-Amino-1-butanol
3-Methylamino-1,2-propanediol
meso-1,4-Diamino-2,3-butanediol
trans-2-Aminocyclopentanol hydrochloride
1-Dimethylamino-2-propanol
2-Amino-3-methyl-1-butanol
3-Dimethylamino-1-propanol
5-Amino-1-pentanol
2-Amino-1-pentanol
3-(Dimethylamino)-1,2-propanediol
1-Amino-1-cyclopentanemethanol
trans-2-Amino cyclohexanol
trans-4-Amino cyclohexanol
2-(tert-Butylamino)ethanol
2-Dimethylamino-2-methylpropanol
4-(Dimethylamino)-1-butanol
6-Amino-1-hexanol
2-Amino-1-hexanol
Bis(2-hydroxypropyl)amine
N,N′-Bis(2-hydroxyethyl)ethylenediamine
3-Diethylamino-1-propanol
3-(Diethylamino)-1,2-propanediol
1,3-Bis(dimethylamino)-2-propanol
The amount of amino alcohol in the composition of the invention may be 0.1 to 10 wt %, such as 0.2 to 5 wt %, preferably 0.2 to 4 wt %, e.g. 0.2 to 3 wt %.
Viewed from another aspect the invention therefore provides a particulate coating composition, preferably a powder coating composition, comprising:
The invention also provides a substrate coated with this particulate coating.
It is preferred if the amino alcohol forms 0.3 to 5 wt % of the coating composition such as 0.3 to 3 wt %.
The powder coating composition of the invention may also contain at least one silane. The present inventors have found that the problem of corrosion of metallic pigments can be addressed by adding a silane to the powder coating composition.
Such a silane should not be a coating on a metallic particle or act as an adhesive within a metallic particle. It is separate therefrom. By separate therefrom therefore means that the silane is not coated onto the metallic pigment.
Silanes of use are generally of low Mw such as less than 400 g/mol. Suitable silanes are of general formula (I) or (II)
Y—R(4-z)SiXz (I) or
Y—R(3-y)R1SiXy (II)
wherein z is an integer from 1 to 3,
wherein y is an integer from 1 to 2,
R is a hydrocarbyl group having 1 to 12 C atoms optionally containing an ether or amino linker,
R1 is a hydrocarbyl group having 1 to 12 C atoms;
Y is a functional group bound to R that can react with corresponding hardener functionalities, and
each X independently represents a halogen group or an alkoxy group.
Preference is given to isocyanate, epoxy, amino, hydroxy, carboxy, acrylate, or methacrylate groups as functional groups Y. The Y group can bind to any part of the chain R. It will be appreciated that where Y represents an epoxy group then R will possess at least two carbon atoms to allow formation of the epoxide ring system.
It is especially preferred if Y is an amino group or epoxy group. Amino groups are preferably NH2.
It is especially preferred if X is an alkoxy group such as a C1-6 alkoxy group, especially methoxy or ethoxy group. It is also especially preferred if there are two or three alkoxy groups present. Thus z is ideally 2 or 3, especially 3. Subscript y is preferably 2.
R1 is preferably C1-4 alkyl such as methyl.
R is a hydrocarbyl group having up to 12 carbon atoms. It may comprise an alkylene chain or a combination of an alkylene chain and rings such as phenyl or cyclohexyl rings. The term “optionally containing an ether or amino linker” implies that the carbon chain can be interrupted by a —O— or —NH— group in the chain, e.g. to form a silane such as [3-(2,3-Epoxypropoxy)propyl]trimethoxysilane: H2COCHCH2OCH2CH2CH2Si(OCH3)3. It is preferred if the group Y does not bind to a carbon atom which is bound to such a linker —O— or —NH—.
R might therefore represent (C6H5)—NH—(CH2)3— or Ph-NH—(CH2)3— or (C6H5)—(CH2)3 and so on.
R is preferably an unsubstituted (other than Y obviously), unbranched alkyl chain having 2 to 8 C atoms optionally containing an ether or amino linker.
A preferred silane general formula is therefore of structure (III)
Y′—R′(4-z′)SiX′z′ (III)
wherein z′ is an integer from 2 to 3, R′ is a unsubstituted, unbranched alkyl chain having 2 to 8 C atoms optionally containing an ether or amino linker, Y′ is an amino or epoxy functional group bound to the R′ group, and X′ represents an alkoxy group.
Examples of such silanes are the many representatives of the products manufactured by Degussa in Rheinfelden and marketed under the brand name of Dynasylan®D, the Silquest® silanes manufactured by OSi Specialties, and the GENOSIL® silanes manufactured by Wacker.
Specific examples include methacryloxypropyltrimethoxysilane (Dynasylan MEMO, Silquest A-174NT), 3-mercaptopropyltri(m)ethoxysilane (Dynasylan MTMO or 3201; Silquest A-189), 3-glycidoxypropyltrimethoxysilane (Dynasylan GLYMO, Silquest A-187), tris(3-trimethoxysilylpropyl) isocyanurate (Silquest Y-11597), gamma-mercaptopropyltrimethoxysilane (Silquest A-189), beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (Silquest A-186), gamma-isocyanatopropyltrimethoxysilane (Silquest A-Link 35, Genosil GF40), (methacryloxymethyl)trimethoxysilane (Genosil XL 33), isocyanatomethyl)trimethoxysilane (Genosil XL 43), aminopropyltrimethoxysilane (Dynasylan AMMO; Silquest A-1110), aminopropyltriethoxysilane (Dynasylan AMEO) or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (Dynasylan DAMO, Silquest A-1120) or N-(2-aminoethyl)-3-aminopropyltriethoxysilane, triamino-functional trimethoxysilane (Silquest A-1130), bis(gamma-trimethoxysilylpropyl)amine (Silquest A-1170), N-ethyl-gamma-aminoisobytyltrimethoxysilane (Silquest A-Link 15), N-phenyl-gamma-aminopropyltrimethoxysilane (Silquest Y-9669), 4-amino-3,3-dimethylbutyltrimethoxysilane (Silquest Y-11637), (N-cyclohexylaminomethyl)triethoxysilane (Genosil XL 926), (N-phenylaminomethyl)trimethoxysilane (Genosil XL 973), Deolink Epoxy TE and Deolink Amino TE (D.O.G Deutsche Oelfabrik) and mixtures thereof.
Other specific silanes of interest include 3-Aminopropyltriethoxysilane, 3-Aminopropyltrimethoxysilane, N-(Aminoethyl)-aminopropyltrimethoxysilane H2NCH2CH2NHCH2CH2CH2Si(OCH3)3, 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, (H2NCH2CH2NHCH2CH2CH2SiCH3(OCH3)2), [3-(2,3-Epoxypropoxy)propyl]triethoxysilane (H2COCHCH2OCH2CH2CH2Si(OCH2CH3)3, [3-(2,3-Epoxypropoxy)propyl]trimethoxysilane (H2COCHCH2OCH2CH2CH2Si(OCH3)3).
The use of silane ([3-(2,3-Epoxypropoxy)propyl]-triethoxysilane or 3-aminopropyltriethoxysilane is especially preferred. A mixture of silanes might also be used.
separate from said metallic pigment.
The amount of silane present in the powder coating as a whole may be 0.1 to 10 wt %, preferably 0.2 to 6 wt %, more preferably 0.4 to 3 wt % on total weight, ideally 0.6 to 3 wt %.
The silane can be supported on a carrier or it can be added in its native form (or as part of a solution). The use of a carrier makes the addition of the silane easier as the silane can be added as a solid rather than liquid. Thus, silane materials in which 50 wt % is carrier material and 50 wt % is the silane can be employed. It will be clear that the amounts of silane quoted above in the powder coating as a whole refer to silane “per se” and do not count carrier material weight. If a carrier is used then the skilled person needs to adjust his weights accordingly.
Viewed from another aspect the invention therefore provides a particulate coating composition, preferably a powder coating composition, comprising:
The invention also provides a substrate coated with this particulate coating.
It is preferred if the polyester polymer, hardener and the amino alcohol are premixed and extruded. Extrusion conditions are known and will generally be kept at low temperature to avoid premature curing.
The ingredients can be mixed and extruded to form particles as is known in the art, and the particles can then be milled to form powder. Metal pigments can be added after extrusion or, using the Powdersafe technology discussed above, they could also be added before extrusion. Metallic pigments and particulate coatings can be bonded together in a process in which the pigment and the particulate coating are mixed and heated to the glass transition temperature of the particulate coating. Adhesion of the metallic pigments to the surface of the particulate coating particles is therefore achieved.
Pigments can be added before or after milling, preferably after. After milling, sieving can be used to maximise particle distribution homogeneity.
In order to ensure homogeneity before extrusion, the components of the blend must be well mixed. It is preferred to keep the extrudate temperature below 140° C. to prevent premature curing.
The extruded granulates can be milled by all types of conventional mills and the particles thereafter classified by a method of choice, to a particle size found most suitable for powder application. The particle size distribution d50 of the powder coating composition may be in the range of 10 to 120 μm with a preferred particle size d50 in the range of from 15 to 75 μm, preferably at least 20 or 25 μm, advantageously not exceeding 50 μm, more especially 20 to 45 μm. In general, particle sizes can be established using a Malvern particle size analyser.
It will also be appreciated that the particulate coatings of the invention may contain a wide variety of standard industry additives. Additives of use include gloss modifiers, scratch resistors, pigments (non corrodible metallic and non-metallic pigments), fillers, degassing additives, flow control agents, waxes, antioxidants, optical brighteners and surface modifying agents. These additives in total can generally form up to about 60 wt % of the powder coating, e.g. up to 40 wt %, ideally up to 20 wt %, such as up to 10 wt % of the coating. Additives might be present in as little as 2 wt % or less of the particulate coating, in particular when a primer layer is also present.
Fillers include micronized minerals. Pigments of interest include organic pigments and inorganic pigments such as carbon black.
In particular pigments and fillers may form up to 50 wt % of the coating such as up to 40 wt % on total weight, preferably 2.0-20 wt %. These numbers include therefore the metallic pigment discussed in detail above.
Other additives might form 0.1 to 15 wt % on total weight of the powder coating, such as 0.5 to 15 wt %, preferably 0.7 to 10 wt %, especially 1 to 8 wt %. It will be appreciated that the powder coating of the invention must be dry and free of water and other volatile organic solvents.
In this regard, the inventors have also found that the addition of certain stabilising additives to the particulate coating of the invention leads to a significant improvement in properties, such as a synergistic improvement. In particular, the presence of the stabilsiing additive maintains gloss over a much longer period and improves acid resistance (ΔL) and humidity resistance (ΔE).
The stabilising additive may comprise at least one silicate material selected from the group consisting of: (a) materials obtainable by admixture or, preferably, reaction of silica or a silicate with a compound of a trivalent metal; and (b) naturally occurring or synthetic metal silicates.
Advantageously, the stabilising additive also includes an oxide selected from zinc oxide, magnesium oxide or silica, preferably zinc oxide, which may be incorporated in an amount in the range of from 2 to 30% by weight, based on the total weight of the stabilising additive, advantageously at least 5%, 10% or 15% by weight, more especially not exceeding 20% or 25% by weight.
The preferred trivalent metal in embodiment (a) is chromium, iron or aluminium, especially aluminium. Embodiment (b) advantageously uses a silicate of a trivalent metal.
The compound of the trivalent metal may, for example, be a phosphate (preferably a mono- or di-hydrogen phosphate), a fluoride, silicofluoride, chloride, sulphate or alkane carboxylate. Aluminium phosphates or sulphate are preferred.
The silica in embodiment (a) is advantageously amorphous silica or a precursor thereof.
Examples of naturally occurring metal silicates for use in embodiment (b) are china clay and bentonite.
As an indication of the relative proportions of silica and trivalent metal compound in embodiment (a), the ratio of silicon to trivalent metal atom may be, for example, 1.5 to 30:1, advantageously at least 1.5:1, 2.5:1 or 3.5:1, preferably not exceeding 20:1, 15:1 or 10:1. In general, the same silicon:metal ratios are also applicable to embodiment (b), especially in the case where the metal silicate is a silicate of a trivalent metal.
Other classes of materials which may be used as stabilising additive include materials based on or comprising phosphates or borates, generally a metal phosphate or borate. A phosphate is preferably an ortho-phosphate, but may also be a hydrogen phosphate or a polyphosphate.
Thus, for instance, another stabilising additive which may be used comprises dicalcium phosphate dihydrate, for example, the material “Budit 222” as supplied by Budenheim Chemische Fabrik. Mention may also be made of dimagnesium phosphate trihydrate, such as the materials “Budit 229” and “Budit 246” (Budenheim Chemische Fabrik).
The stabilising additive may be a zinc phosphate, for example: (a) Zinc phosphate di- or tetra-hydrate; (b) spheroidal zinc phosphate as a crystalline phase in admixture with an amorphous phase comprising Fe (II) phosphate and Fe (III) phosphate; (c) zinc phosphate modified with zinc molybdate and rendered organophilic by suitable surface treatment.
Further materials which come into consideration as stabilising additives include: (i) alkaline earth hydrogen phosphates in conjunction with alkaline earth carbonates, optionally also including one or more additives selected from fluorosilicates, fluoroborates, alkali and alkaline earth fluorides;
(ii) mixtures of magnesium hydrogen phosphate and calcium hydrogen phosphate;
(iii) polyphosphates and polyphosphate hydrates, including ammonium polyphosphates; modified strontium aluminium polyphosphate hydrates; zinc aluminium polyphosphate hydrates; modified zinc calcium aluminium polyphosphate silicate hydrates; and modified calcium aluminium polyphosphate silicate hydrates;
(iv) orthophosphate hydrates including modified zinc calcium strontium orthophosphate silicate hydrates; modified zinc aluminium orthophosphate hydrates; organically treated basic zinc orthophosphate hydrates; modified basic zinc molybdenum orthophosphate hydrates and organic/inorganic modified basic zinc orthophosphate or basic zinc phosphate silicate hydrates, respectively;
(v) phosphosilicates such as, for example, calcium strontium zinc phosphosilicate, calcium phosphositicate, and zinc aluminium phosphosilicate;
(vi) organophosphonates including metal organophosphonates such as, for example, salts of a polyvalent metai cation and an organic phosphonic acid containing at least two phosphonic acid groups, for instance, calcium etidronate (1-hydroxyethane-1,1-diphosphonic acid monocalcium dihydrate). Further information concerning such materials may be found in GB 2 121 419A.
(vii) barium metaborate monohydrate;
(viii) zinc salts of organic nitro compounds;
(ix) zinc oxide/cinnamic acid combinations; and
(x) molybdates, including basic molybdates such as, for example, zinc molybdates) and calcium zinc molybdate complexes which comprises a calcium zinc molybdate complex on a core of calcium carbonate.
In a particularly preferred embodiment the stabilising additive is a metal phosphate, such as a transition metal, alkali metal or alkaline earth metal phosphate, especially an alkaline earth metal phosphate such as dicalcium phosphate dihydrate. The amount of stabilising additive present may be 0.25 to 3.0 wt %, such as 0.25 to 2.0 wt %. We have established that the combination of stabilising additive and amino alcohol may lead to a synergistic improvement in properties. In particular the combination of dicalcium phosphate dihydrate and THAM leads to synergy.
We show in the examples that the combination of low amounts of THAM, such as 0.25 to 1.5 wt % with low amounts of dicalcium phosphate dihydrate, such as 0.25 to 1.5 wt % leads to synergy.
Viewed from another aspect the invention therefore provides a particulate coating composition, preferably a powder coating composition, comprising:
Stabilising additives used according to the invention may be incorporated by intimate mixing with the other constituent (s) of the composition, before the extrusion or other homogenisation process and/or may be incorporated during the process.
Alternatively, the additive (s) of the invention may be incorporated in the coating composition by any available post-blending method as described hereinbefore in relation to the incorporation of the metallic pigment (s).
The particulate coating of the invention can be applied to a substrate by any conventional powder coating method such as spraying, e.g. electrostatically. The use of triboelectric guns can also be used. Coating techniques are well known in the art and will be familiar to the skilled man. The coating composition may be used as a one layer coating or be used on top of a primer forming a top coat. In any embodiment, it is preferred if the coating of the invention forms the top layer employed on any substrate. Thus, the inventive coating can serve as a dual primer and top coat layer or may be applied on a conventional primer layer.
The substrate onto which the particulate coatings of the invention should be applied can be any substrate such as a metal substrate (steel, galvanized steel, aluminium), wood, MDF, HDF, plywood, fibreboard, particleboard, plastic, glass, ceramic, graphite-filled composites and so on. Substrates for interior or exterior use are envisaged.
Coated articles include appliances, building components, furniture, vehicles, fixtures and fittings and so on.
The object being coated may be provided with a primer layer although this is not essential. The primer may use zinc or zinc free powder or liquid corrosion inhibiting primer. Typical epoxy and epoxy/polyester primers comprise 0-85 wt % zinc. The powder coating of the invention forms the top coat on any substrate. Thus, no additional coating layer is applied thereon. Substrates may therefore comprise a primer layer and top coat comprising the powder composition of the invention or simply comprise the top coat of the invention without a base primer layer.
Once a substrate is coated with the powder coating, the coating must be cured. The coated substrate may be cured in a conventional convection oven or an IR/convection combination oven. It is also possible to use inductive heating. The use of a convection/induction oven or even convection/induction/IR oven is also contemplated. The use of heat curing is preferred.
Where heating is used during cure, the temperature should preferably be in the range of 100 to 250° C., e.g. 150 to 200° C.
The powder coating of the invention can be cured using short curing cycles, e.g. of 15 minutes or less.
The powder coating is preferably free flowing during the curing operation and therefore this leads to smooth, even finishes.
The film thickness of the cured coating is preferably 20 to 200 microns such as 30 to 120 microns especially 40 to 100 microns.
It is a feature of the invention that the powder coating of the invention does not corrode. The lack of corrosion also manifests itself in good colour retention and low gloss change. The coating is preferably therefore resistant to acid, base and water.
It will be appreciated that the coating should also provide an acceptable metallic effect. The whole point of the coatings of the invention is to provide a coated substrate with a metallic paint effect. The coatings of this invention are able to provide a good metallic effect whilst also reducing corrosion. Ideally, the coatings offer a “wet paint” effect. The wet paint look is achieved when the gloss difference between gloss measured at 200 and 60° is minimised. It preferred if the delta gloss value measured at these angles is 50 or less.
The invention will now be described with reference to the following non limiting examples.
Film thickness: Measured according to ISO 2178.
Gloss: Measured according to ISO 2813 at 60° or 20° measurement angle.
EEW: Measured according to ASTM D-1652
Acid Value (AV): Measured according to ASTM D974
Color changes, ΔL and ΔE were measured using a Largo Coloreye 3000 instrument.
The ingredients (except metallic pigment) were dry-mixed in a high speed mixer in order to ensure sufficient dispersion of the powder pre-mix. The pre-mix was then added to a Theyson TSK 20-24 twin-screw extruder and extruded under the following conditions: 30 degrees in the feed zone, 50 degrees in the melting zone, 100 degrees in the mixing & dispersion zone, 100 degrees at the head, 500 rpm. 60-65 torque
The extruded material was fed to a chilled roll and passed through a crusher, reducing the chilled material to flakes. The crushed flakes were then fed to a mill. The extruded chips were milled in a mill and sieved through a 125 μm rotational sieve in order to ensure a particle size distribution (PSD) (d50) of 25-50 μm (determined using a Malvern particle size analyzer).
The metallic pigment was then gently mixed with the powder.
The powder was applied to panels of iron phosphated cold roll steel using a standard corona charging spray-gun.
Substrates coated with powder were cured in conventional heat transfer by convection using a Heraeus conventional benchtop oven.
Curing temperature was 180° C. object temperature, with 10 minutes curing time at object temperature.
The examples of the invention are based on a powder coating composition as described in Table 1. 1.5 wt % Standard Aluminium Powder Special PCR 901 was added post extruder. All other components are preblended and extruded.
Typical film thickness: 50-100 μm.
Table 1 summarises components in each example:
Human fingers were pressed against the coated surface to leave fingerprint on the surface. The coatings that contain the amino alcohol are less prone to becoming discoloured by fingerprints when they are handled or touched and are easier to remove with a paper tissue. The scale below was used to evaluate the fingerprint resistance performance.
F1=Severe fingerprinting which is difficult to remove
F2=Pronounced fingerprinting which is difficult to remove
F3=Evident fingerprinting which is quite easy to remove
F4=Slight visible fingerprinting which is easy to remove.
F5=No visual fingerprinting
The coatings were also assessed according to appearance. Lower gap between gloss measured at 200 angle and gloss measured at 600 angle was defined as “wet-paint look”. We perceive a difference of 50 or less to reflect a “wet paint” look.
The panels were coated on both sides. Half of the panel was dipped into a 5% HCL solution for a given time. The difference in darkness, ΔL, before and after the test, describes the corrosion of the panels. The panels with high performance with respect to corrosion have low absolute ΔL value, while the panels which are highly corroded have high absolute ΔL values.
The coatings with an amino alcohol showed little change in darkness. For THAM the performance increased with the level of THAM.
1 cm2 Whatman filter paper 597 was dipped into a 1% NaOH solution, and immediately placed on the coated panels. The time to visual darkening was recorded. It takes a longer time before the coatings that contain amino alcohol are corroded by the NaOH solution. The performance is also increasing with increasing level of additive.
Corrosion test/humidity test according to ISO 6270-2 was performed. The coatings are exposed to condensation atmosphere with constant humidity (CH). Air temperature is 40±3° C., relative humidity is approximately 100% with condensation on test specimens. Gloss and colour before and after the test are measured.
The difference in colour, ΔE, describes the corrosion of the panels. The panels with high performance with respect to corrosion have low ΔE value, while the panels which are highly corroded have high ΔE values. The performance also increases with increasing level of additive.
A multiple cutting tools with 6 cutting edges as per ISO 2409 Standard is used to make a crosscut in the coating with cutting rate 2-5 cm/sec. Then 5 mm Erichsen is made in the middle of the crosscut, and adhesive tape (3M No#250) is pressed onto the lattice pattern. The tape is then removed and a classification Gt0 to Gt5 is made. Gt0 describes that no coating has been removed, whereas Gt5 describes that all coating has been removed. The coatings of the invention have better adhesion to the surface.
Further examples of the invention were based on a powder coating composition as described in Table 7. 1.5 wt % Standard Aluminium Powder Special PCR 901 was added post extruder. All other components are preblended and extruded.
Table 7 summarises components in each example:
To the components in the reference example 1 above are added tris(hydroxymethyl) aminomethane (THAM) and/or calcium hydrogen phosphate dihydrate CaHPO4. The amounts added are shown in table 8 below are based on wt % relative to the composition of ref 1 above. Coatings were applied to panels and cured as discussed above. Film thickness was 50 to 100 microns.
The resulting coatings were tested for humidity resistance, alkaline resistance and fingerprint resistance following the methods above.
It is clear seen that the combination of THAM and CaHPO4 offers improvements in humidity (corrosion), alkaline resistance and fingerprint resistance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16167780.2 | Apr 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/060110 | 4/27/2017 | WO | 00 |
