RU2771822C2 - Composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a coating composition in the form of particles, in particular to a coating composition of powder material. The composition contains 30-60 wt.% of polyester polymer, 30-60 wt.% of hardener, at least 0.1 wt.% of metal pigment and polyorganosiloxane.

EFFECT: reduction or prevention of corrosion of metal pigment present in a composition is provided.

23 cl, 13 tbl, 2 ex

Description

The present invention relates to a coating composition in the form of particles, and in particular to a powder coating composition containing: at least one polyester polymer, at least one hardener, at least 0.1 wt. % of at least one metallic pigment and at least one polyorganosiloxane. The present invention also relates to a container containing this composition, to a kit containing the components of this composition, and to a method for manufacturing this composition. Additionally, the present invention relates to a coating containing this composition, to a substrate coated with this composition, and to methods for coating a substrate with this composition.

BACKGROUND OF THE INVENTION

Traditionally, coating powders have been made by extruding a mixture of polymers and hardeners (as well as standard additives, etc.) in order to obtain a homogeneous mixture, and then grinding the extrudate and screening the product in order to obtain the desired particle sizes and particle size distribution. The powder was then electrostatically deposited onto a substrate, often a metal substrate, and cured at high temperatures. The finish on the substrate can be controlled by adding additives to the coating powder.

A growing market for powder coatings is in the field of metal powder coatings that provide a metallic effect on the surface to be coated. The metallic effect is achieved by adding metallic pigments to the powder coating at the right time. However, these metallic effect pigments can corrode if exposed to oxygen, moisture, acid, alkali, etc. Corrosion very quickly destroys the appearance and integrity of the coating.

To avoid the problem of corrosion, one approach used is to apply an additional, separate layer of clearcoat over the metallic effect finish to provide protection. Essentially, the clear coat layer acts as a barrier between corrosive metallic pigments and the atmosphere. Unfortunately, applying this additional coating is time consuming and expensive. It also increases the overall thickness of the coating, which is undesirable in some applications.

In one alternative approach, the corrosion problem of metallic pigments has been solved by coating the metallic pigment particles themselves. This coating is ideally based on epoxy and polyester polymers and is therefore compatible with the binder that normally forms the bulk of the coating. The idea is that embedding metallic pigments in the epoxy/polyester polymer prevents the pigment from corroding. This is mainly why coated metal particles are provided to isolate the metal from air, moisture, acids and alkalis. Some manufacturers even use a double coating technique, for example based on an inorganic/organic double coating such as a silica coating followed by an acrylate coating or a polyester/epoxy coating.

The coating of the metal particles improves the stability of the pigments during storage, but the corrosion resistance of these particles after application to the substrate is still not ideal. Thus, while many metal particles are coated to allow storage for extended periods prior to application, our experience is that upon application, these particles are still subject to oxidation and degradation by acids and alkalis, as well as moisture.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a particulate coating composition, and preferably a powder coating composition, comprising:

(i) at least one polyester polymer;

(ii) at least one hardener;

(iii) at least 0.1 wt% of at least one metallic pigment; and

(iv) at least one polyorganosiloxane.

In one additional aspect, the present invention provides a container containing the particulate composition described above.

In yet another additional aspect, the present invention provides a kit comprising:

(i) a first container containing at least one polyester polymer, at least one hardener, and at least one polyorganosiloxane;

(ii) a second container containing at least 0.1 wt. % of said at least one metallic pigment based on the total weight of the contents of the kit containers; and

(iii) instructions for mixing at least one polyester polymer, at least one hardener, at least one polyorganosiloxane, and at least 0.1 wt. % of at least one metallic pigment.

In yet another additional aspect, the present invention provides a process for preparing a particulate coating composition, and in particular a powder coating composition, comprising:

(i) mixing at least one polyester polymer, at least one hardener and at least one polyorganosiloxane to form a mixture;

(ii) extruding said mixture to form particles; and

(iii) adding mentioned at least 0.1 wt. % of at least one metallic pigment to said particles.

In another additional aspect, the present invention provides a coating, preferably a cured coating, containing the particulate composition described above.

In another additional aspect, the present invention provides a coating obtained by spraying and curing the particulate composition described above.

In yet another additional aspect, the present invention provides a substrate coated with the particulate composition described above or the coating described above.

In yet another additional aspect, the present invention provides a method for coating a substrate with the particulate composition described above, as comprising:

i) applying said particulate composition to said support; and

ii) optionally curing said composition in particulate form.

In yet another additional aspect, the present invention provides for the use of the particulate composition described above to coat a substrate.

DEFINITIONS

As used herein, the term “particulate coating composition” refers to a mixture of particles that, when applied to a surface and heated, such as cured, forms a coating on that surface.

The term "powder coating composition" as used herein refers to a dry, flowable powder that, when applied to a surface and heated, such as cured, forms a coating on that surface. Typically, the particles that make up the powder have an average diameter of 10-120 µm.

As used herein, the term "polyester polymer" refers to a polymer containing ester (-COO-) linking groups.

As used herein, the phrase "acid value" refers to the amount of mg KOH required to neutralize alkali-reactive groups in 1 g of polymer, and is expressed in units of (mg KOH/g polymer). The acid number is determined according to the ASTM D974 method.

As used herein, the phrase "hydroxyl number" refers to the number of milligrams (mg) KOH equivalent to the hydroxyl groups present in each gram (g) of polymer, and is expressed in units of (mg KOH/g polymer).

As used herein, the phrase "epoxy equivalent weight" or "EEW" refers to the number of epoxy equivalents in 1 kg of resin. This amount is measured in accordance with ASTM D-1652.

As used herein, the term "hardener" refers to a compound which, when mixed with a polyester polymer, forms a cured coating. Hardeners are sometimes referred to as curing agents.

As used herein, the term "metal pigment" refers to a pigment containing a metal that is susceptible to corrosion. Metal salts are usually not metal pigments.

As used herein, the term "polyorganosiloxane" refers to a polymer containing repeating organosiloxane blocks. The repeating blocks of the organosiloxane contain a Si-O bond and at least one Si-organic group bond.

As used herein, the term "alkyl" refers to saturated linear, branched or cyclic groups. Alkyl groups may be substituted or unsubstituted.

As used herein, the term "cycloalkyl" refers to a saturated or partially saturated mono- or bicyclic alkyl ring system containing 3-10 carbon atoms. Cycloalkyl groups may be substituted or unsubstituted.

As used herein, the term "aryl" refers to a group containing at least one aromatic ring. The term aryl encompasses heteroaryl as well as ring-linked systems in which one or more aromatic rings are bonded to a cycloalkyl ring. Aryl groups may be substituted or unsubstituted. One example of an aryl group is phenyl, ie C ₆ H ₅ . Phenyl groups may be substituted or unsubstituted.

As used herein, the term "substituted" refers to a group in which one or more, for example up to 6, more specifically 1, 2, 3, 4, 5, or 6 hydrogen atoms in the group are independently substituted with the appropriate number of substituents described. As used herein, the term "optionally substituted" means substituted or unsubstituted.

As used herein, the term "aralkyl" or "arylalkyl" refers to an alkyl group substituted with an aryl group.

As used herein, the term "alkaryl" or "alkylaryl" refers to an aryl group substituted with an alkyl group.

As used herein, the term "halide" refers to Cl, F, and Br.

Used in this document, the term "molecular weight" refers to the average molecular weight (Mw), unless explicitly stated otherwise.

DESCRIPTION OF THE INVENTION

The present invention relates to a particulate coating composition, and in particular to a powder coating composition containing at least 4 components. These components are:

(i) at least one polyester polymer;

(ii) at least one hardener;

(iii) at least 0.1 wt. % of at least one metallic pigment; and

(iv) at least one polyorganosiloxane.

Optionally, the particulate coating composition of the present invention further comprises: (v) a filler; (vi) non-metallic pigment; (vii) a pour aid and/or (viii) a degassing aid.

Preferably, the powder coating composition of the present invention minimizes or prevents corrosion of the metallic pigment present therein. In particular, the powder coating composition of the present invention minimizes or prevents damage to the coating by acid, alkali or water. This means that the metallic effect, such as color and gloss, of the coating will last longer.

Polyester polymer

The coating composition of the present invention contains at least one polyester polymer. Preferably the polyester polymer is solid at room temperature (ie at 20°C). Preferably the polyester polymer has a glass transition temperature Tg above 40°C, and more preferably above 50°C. The maximum Tg value is preferably 100°C.

The polyester polymer present in the coating composition of the present invention preferably has a weight average molecular weight Mw of at least 1000, and more preferably at least 2000. Preferably, the polyester polymer has a weight average molecular weight Mw of 1000-10000, more preferably 2000-6000, and still more preferably 2500-5000.

The polyester polymer present in the coating compositions of the present invention preferably contains at least one reactive functional group. Preferably, the reactive functional groups present in the polyester polymer allow the polymer to react with the functional groups (eg, epoxide) present in the curing agent of the composition in order to achieve curing. Preferably, the reactive functional groups are pendant, terminal, or both pendant and terminal.

Preferably, the polyester polymer present in the coating composition of the present invention contains at least one functional group selected from a hydroxyl group, a carboxyl group, an ester group, and an isocyanate group. Particularly preferably, the polyester polymer contains at least one functional group selected from a hydroxyl group and a carboxyl group, and even more preferably a carboxyl group. Therefore, the polyester polymer is preferably a carboxylated or hydroxylated polyester polymer. Particularly preferred polyester polymers contain a plurality of carboxyl functionalities, and in particular a plurality of pendent carboxyl functionalities.

Preferably, the polyester polymer present in the coating composition of the present invention has an acid value (AV) in the range of 20-80 mg KOH/g, more preferably 30-70 mg KOH/g, and even more preferably 40-60 mg KOH/g. Polyester polymers having an AV value of 55-68 mg KOH/g or 60-70 mg KOH/g are particularly preferred. The carboxyl functionality, ie the average number of carboxyl groups present in each polymer molecule, is preferably greater than 2, eg 2.2-5.0. Similarly, the hydroxyl value of the hydroxylated polyester polymer is preferably 50-300 mg KOH/g, more preferably 60-200 mg KOH/g, and even more preferably 70-150 mg KOH/g. The hydroxyl functionality, ie the average number of hydroxyl groups present in each polymer molecule, is preferably greater than 2, eg 2.2-5.0.

The preferred polyester polymer present in the coating composition of the present invention is referred to as resin with a 50/50 to 80/20 type. For resin type 80/20 80 wt. % polyester polymer with carboxyl functionality are used with 20 wt. % hardener. The meaning of AV and EEW (described below) should preferably complement each other. For example, the AV value of a 50/50 type resin may be 60-80 mg KOH/g. Resins that are defined as 80/20 type resins will have a lower AV value, such as 20-40 mg KOH/g.

The polyester polymer present in the coating composition of the present invention may be saturated or unsaturated, but is preferably saturated. Saturated polyester polymers containing at least one functional group selected from hydroxyl and carboxyl groups are preferred, and even more preferred are saturated polyester polymers containing at least one carboxyl group. These functional groups are capable of reacting with a hardener such as epoxide. Alternatively, the polyester polymer may be an unsaturated polyester. These polymers can be cured using peroxide initiators, optionally in conjunction with infrared radiation, or using photoinitiators for ultraviolet radiation curing. The hardener in this case is the initiator. The term "unsaturated polyester" means the presence of multiple unsaturated bonds in the side chains of the polyester, for example introduced through (meth)acrylate. Preferred unsaturated polyesters are amorphous or crystalline. Suitable crystalline unsaturated polyesters are described in patent documents WO2011/138431 A1 and WO2011/138432 A1.

The polyester polymer present in the coating composition of the present invention is preferably derived from aromatic and/or saturated aliphatic acids and polyhydric alcohols. Preferred carboxylic acids (or anhydrides thereof) have an acid functionality of 2 or more. Preferred carboxylic acids are aromatic or aliphatic dicarboxylic acids, and more preferably aromatic dicarboxylic acids. Preferred polyhydric alcohols are diols.

Examples of multifunctional carboxylic acids suitable for inclusion in the polyester polymer of the present invention include benzene-1,2,4-tricarboxylic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, endobicyclo-2,2,1-5-heptin- 2,3-dicarboxylic acid, tetrachlorophthalic acid, cyclohexanedicarboxylic acid, isophthalic acid, terephthalic acid, trimesic acid, 3,6-dichlorophthalic acid, tetrachlorophthalic acid, benzophenone dicarboxylic acid, diphenic acid, 4,4-dicarboxydiphenyl ether, 2,5-pyridinedicarboxylic acid acid, trimellitic acid, azelaic acid, maleic acid, succinic acid, adipic acid, sebacic acid, glutaric acid, pimelic acid, subic acid, azelaic acid, diglycolic acid, 1,12-lauric acid, tetrapropenyl succinic acid, maleic acid, fumaric acid , itaconic acid and malic acid. Preferred acids are terephthalic acid and isophthalic acid.

Examples of suitable multifunctional alcohols for inclusion in the polyester polymer of the present invention include glycerol, trimethylolpropane, trimethylolethane, tris-hydroxyethylisocyanurate, pentaerythritol, ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, neopentyl glycol, 1,3-, 1,2-, and 1,4 -butanediols, heptanediol, hexanediol, octanediol, 2,2-'bis(4-cyclohexanol)propane, neopentylglycol, 2,2,3-trimethylpentan-1,3-diol, 1,4-dimethylolcyclohexane and 2,2,4- trimethylpentanediol. The preferred polyhydric alcohol is neopentyl glycol.

To obtain, for example, a carboxyl-functional polyester polymer of a given molecular weight, the mixture of monomers used to form the polyester polymer has a corresponding excess of carboxyl functionality over hydroxyl functionality. Alternatively, to obtain a hydroxyl-functional polyester polymer of a given molecular weight, the mixture of monomers used to form the polyester polymer has a corresponding excess of hydroxyl functionality over carboxyl functionality.

Coating compositions of the present invention may contain 1, 2, 3 or more polyester polymers. Preferably the coating composition contains 1 or 2 polyester polymers. Suitable polyester polymers can be prepared using conventional techniques known in the art. Suitable polyester polymers are also commercially available.

The coating composition of the present invention preferably contains 20-95 wt. %, more preferably 30-80 wt. % and even more preferably 40-60 wt. % polyester polymer.

Hardener

The coating composition of the present invention also contains a hardener. The hardener reacts with the polyester polymer during curing to form a coating, such as a film coating. Therefore, preferably the hardener reacts with the polyester polymer.

Preferably, the hardener present in the coating composition of the present invention is an epoxy-containing compound or a mixture of such compounds. More preferably, the hardener is an epoxy resin.

The preferred epoxy resins present in the coating compositions of the present invention are solid at room temperature, ie at 20°C.

Preferred epoxy resins present in the coating compositions of the present invention have an epoxy equivalent weight (EEW) in the range of 300-2000, more preferably 500-1500, and even more preferably 700-1000. Epoxies are sometimes described by their type, such as Type 2, 2.5, 3, 4, or Novalac. Type 2 resins may have EEW=550-700, eg Epikote 1002 resin, Epikote 3022-FCA resin. Type 2.5 resins may have EEW=600-750, e.g. Araldite GT 6450. Type 3 resins may have EEW=700-850, e.g. Epikote 3003 resin, Araldite GT 7004. Epikote 1055 resin. Modified Novalac type resins may include Epikote 2017 or Araldite GT 7255 resin. Preferred epoxy resins are type 3 resins.

Suitable epoxy resins for use in the coating composition of the present invention are known in the art and commercially available. Representative examples of suitable epoxy resins include TGIC (triglycidyl isocyanurate), Araldite PT 910/PT912, bisphenol A resins, novolac resins, modified novolac resins, 4,4'-isopropylidene diphenol epichlorohydrin (bisphenol F) resins, and glycidyl methacrylates ( GMA). Bisphenol A resins are preferred.

As an alternative to epoxy resins, other hardeners such as a hydroxyalkylamide hardener and a polyisocyanate hardener such as uretdione or caprolactam blocked isocyanate (eg, isophorone diisocyanate) may be present in the coating composition of the present invention. In particular, polyisocyanate hardeners are preferably used with hydroxyl-functionalized polyester polymers to form polyurethanes. Hydroxyalkylamide hardeners can be used with carboxy-functionalized polyester polymers. Suitable hardeners of this type are also commercially available.

Another alternative hardener is peroxide. Such hardeners may be used when the polyester polymer is an unsaturated polyester and may undergo an auto-cure reaction upon peroxide initiation.

Note that the hardener and polyester resin must react to cure the coating. Accordingly, it is preferred that these components are mixed in such a ratio that the reactive groups, eg carboxyl groups, in the polyester polymer and eg epoxy groups in the hardener are within ±25% of the stoichiometric ratio. The ratio of carboxyl groups and epoxy groups within ±10% of the stoichiometric ratio is more preferred. The ratio of carboxyl groups and epoxy groups within ±5% of the stoichiometric ratio is most preferred.

One skilled in the art will appreciate that some of the additives discussed below may contain carboxyl groups. When calculating the ratio of EEW to AV, the contribution of any carboxyl groups in standard additives used in powder coating should be taken into account. Therefore, it should be understood that this calculation is based on the total amount of carboxyl and epoxy groups present. Even if compounds contain many carboxyl or epoxy groups, which must be taken into account in these calculations, this will nevertheless be commonplace for a skilled chemist.

The coating composition of the present invention preferably contains 20-95 wt. %, more preferably 30-80 wt. % and even more preferably 40-60 wt. % hardener.

The combination of hardener and polyester polymer is referred to herein as the binder system. Preferably, the coating composition uses a hybrid epoxy-carboxy functional polyester polymer binder system. These systems are known in the art. Also within the scope of the present invention is the use of a pure polyester binder, which is an unsaturated polyester that can be cured with an epoxy.

Thus, the polyester polymer preferably forms 50-97 wt. % binder and more preferably 60-96 wt. % binder. The hardener preferably forms 3-50 wt. %, and more preferably 3-40 wt. % binder. The amount of polyester polymer is preferably about the same as the amount of hardener or more. When an unsaturated polyester binder is used, the polymer can form almost 100 wt. % binder with a small proportion of initiating hardener.

The coating composition of the present invention preferably contains 40-99 wt. %, more preferably 50-95 wt. % and even more preferably 55-90 wt. % binder.

metallic pigment

The particulate coating composition of the present invention contains a metallic pigment. The purpose of the metallic pigment is to provide a coating with a metallic color effect. Such coatings are used to coat a wide range of different products, including household appliances, furniture, building components, tools, vehicles, etc.

Preferably, the metallic pigment present in the particulate coating composition is susceptible to corrosion. An advantage of the particulate coating composition of the present invention is that it reduces corrosion of corrosive metallic pigments. For example, the composition of the particulate coating increases the resistance of the metallic pigment to both acids and alkalis, and hence the acid and alkali resistance of the coating as a whole. Humidity resistance is also greatly improved.

The metallic pigment present in the particulate coating composition of the present invention may be coated or uncoated. Coatings are sometimes provided on metallic pigments to improve their corrosion resistance, but they often also affect their metallic sheen. Metallic pigments may be coated with silica or other inert inorganic material for greater chemical resistance and durability. Alternatively, the metallic pigment may be coated with a polymeric material, such as acrylic, PTFE, or a thermosetting plastic material, or may be carried in a polymer or plasticizer that is compatible with the powder coating composition, such as a polyester/epoxy coating. As a further option, the metallic pigment may be coated with a dye such as a metal oxide pigment (eg iron oxide) to provide special color effects. The use of silica-coated metallic pigments is preferred to improve particle stability both during storage and during further coating. Double-coated particles (eg using an inorganic and then an organic coating) are also possible, but less preferred because their metallic effect is reduced. Optionally, the metallic pigments present in the coating of the present invention are uncoated. The protection provided by the polyorganosiloxane in the formulation means that coatings on metallic pigments may not be necessary.

The metallic pigment present in the particulate coating composition of the present invention is preferably in the form of flakes or particles. The metallic pigment present may be a flake or non-flake pigment. Non-flake metallic pigments are preferred. Flake pigments, such as flake aluminum flakes, typically orient themselves in a continuous layer on or near the surface of the coating to form an opaque silver finish. Non-flake pigments, such as non-flake aluminum pigments, generally orient themselves throughout the coating, providing a different aesthetic than flake pigments. Non-flake pigments are unique in their ability to produce flop, multicolor and sparkle effects. "Flop" is the ability to change color when viewed from different angles. This ability is directly related to the orientation of the flakes in the coating.

The metal pigment present in the particulate coating composition of the present invention preferably contains the metal in elemental or alloy form. Metal salts (eg oxides) are usually non-metallic pigments. Examples of suitable alloys include aluminum alloys, stainless steel, bronze or brass.

Preferably the metallic pigment contains at least Al, Sn or a transition metal, ie a metal of groups 3-12 of the periodic table (eg Cu, Zn), more preferably Al or Sn, and particularly preferably Al. Aluminum in elemental form is a particularly preferred metallic pigment. Combinations of two or more different metallic pigments may also be used.

The particle size d50 of the metallic pigment is preferably 3-50 µm, and more preferably 10-30 µm. Particle sizes can be measured using a Malvern machine which gives a size in d50. D50 is the mass median diameter (MMD). MMD is considered to be the average particle diameter by mass.

The metal pigment(s) are generally included in the powder material coating composition of the present invention after extrusion or other homogenization process (hereinafter referred to as "post blending"). One form of post-mixing process comprises dry mixing, and any available dry mixing method may be used. Metallic pigments may be added before and/or after milling, for example during the particle sifting step. Metallic pigments can also be added at the premixing stage, i.e. prior to extrusion. Products advertised under the brand name "Powdersafe" or "Powdersafe-02" are suitable for direct extrusion.

The pigment and other components of the powder coating composition are preferably "bonded". The bonding process is to be understood as a process of mixing a mixture containing a polyester polymer, a hardener, a polyorganosiloxane and a metallic pigment, in which the metallic pigment particles are physically bonded to the coating particles of the powder material by heating the mixture to the glass transition temperature of the polymers present. Therefore, adhesion of the metal pigments to the surface of the coating particles of the powder material is achieved.

A range of embossed and other textured metallic finishes can be produced using suitable structurants in addition to the metallic pigment.

The coating composition of the present invention preferably contains 0.1-15 wt. %, more preferably 0.5-10 wt. % and even more preferably 0.75-7.5 wt. % metallic pigment.

Polyorganosiloxane

The coating composition of the present invention contains polyorganosiloxane. Preferably, the polyorganosiloxane has a softening point of at least 40°C, and more preferably at least 45°C. Preferably, the polyorganosiloxane has a softening point of 40-100°C, and more preferably 40-90°C.

Preferably, the polyorganosiloxane has a weight average Mw of 1000-10000, more preferably 2000-6000, and even more preferably 2000-5000.

The polyorganosiloxane present in the coating composition of the present invention may have many different structures. The polyorganosiloxane may, for example, be linear or non-linear, branched or unbranched, or cyclic. Preferably, the polyorganosiloxane is cross-linked. Particularly preferably, the polyorganosiloxane is cross-linked via -O-Si-O- bonds. In some polyorganosiloxanes, the formation of cross-links creates a three-dimensional, cellular or network structure. Therefore, some preferred polyorganosiloxanes have a three-dimensional, cellular or network structure.

The polyorganosiloxane present in the coating composition of the present invention may be flake or non-flake, or a mixture thereof. Preferably, the polyorganosiloxane is flake.

Preferred polyorganosiloxanes present in the coating composition of the present invention contain OH and/or OR substituents, where R is C _{1 -24} alkyl or C _{6 -24} aryl. Particularly preferably, the polyorganosiloxane contains OH substituents. Preferred polyorganosiloxanes contain 1.0-15.0 wt. %, more preferably 2.0-12.0 wt. %, and even more preferably 2.5-10.0 wt. % OH groups based on the total weight of the polyorganosiloxane. The substituents, eg OH, present on the polyorganosiloxane may be pendant, terminal, or a combination thereof.

Preferably polyorganosiloxane contains 0.2 wt. % or less organic solvents, and more preferably 0.1 wt. % or less organic solvents. Most commercial polyorganosiloxanes contain some residual organic solvent as a consequence of their synthesis. Such an organic solvent tends to be trapped within the polyorganosiloxane, and is generally not removed when the polyorganosiloxane is melt-kneaded with other components to form a powder coating composition. Optionally, such residual organic solvent may be removed from the polyorganosiloxane prior to its use in the coating composition of the present invention. This is achieved by melting the polyorganosiloxane and removing the solvent from the molten polymer, for example by blowing with a gas such as nitrogen or by using a vacuum.

Preferred polyorganosiloxanes present in the coating composition of the present invention contain a repeating block of formula (I):

where

each R ¹ is independently a monovalent organic group;

each X is independently an OH, OR' or O- group;

each R' is independently C _{1 -24} alkyl or C _{6 -24} aryl; and

and equal to 0 or 1.

In preferred repeating units of formula (I), each R ¹ is selected from C _{1 -20} alkyl, C _{6 -20} aryl and C _{7 -20} aralkyl. More preferably, each R ¹ is independently selected from C _{1 -20} alkyl and C _{6 -20} aryl. Examples of suitable alkyl groups include methyl, ethyl, propyl, pentyl, octyl, decyl, dodecyl, undecyl, octadecyl, cyclopentyl, and cyclohexyl. Examples of suitable aryl groups include phenyl, tolyl and xylyl. Examples of suitable aralkyl groups are benzyl and 2-phenylethyl. Particularly preferably, each R ¹ is selected from methyl and phenyl.

In the preferred repeating units of formula (I), each X is selected from OH or O-. When X is O-, a cross-link is formed.

Further preferred polyorganosiloxanes present in the coating compositions of the present invention comprise a block of formula (II):

where

each of R ¹ and R ² is independently a monovalent organic group;

each X is independently an OH, OR' or O- group;

Y is an OH or OR' group;

each R' is independently C _{1 -24} alkyl or C _{6 -24} aryl;

and equal to 0 or 1;

b is 0, 1 or 2; and

c is 0, 1, or 2, with the condition that b+c ≤ 3.

In preferred repeating units of formula (II), R ¹ and R ² are each independently selected from C ^{1 -20} alkyl, C _{6 -20} aryl, and C _{7 -20} aralkyl. More preferably, each of R ¹ and R ² is selected from C ^{1 -20} alkyl and C _{6 -20} aryl. Examples of suitable alkyl groups include methyl, ethyl, propyl, pentyl, octyl, decyl, dodecyl, undecyl, octadecyl, cyclopentyl, and cyclohexyl. Examples of suitable aryl groups include phenyl, tolyl, xylyl and benzyl. An example of a suitable aralkyl group is 2-phenylethyl. Particularly preferably, each R ¹ is selected from methyl and phenyl. Particularly preferably, each R ² is selected from methyl and phenyl.

In the preferred repeating units of formula (II), each X is selected from OH or O-. When X is O-, a cross-link is formed.

In preferred units of formula (II), Y is OH. Y is an end group.

Preferred polyorganosiloxanes present in the coating composition of the present invention correspond to formula (III):

M _m D _n T _o Q _p (III)

where

M - group with the general formula (IIIa)

R ³ R ⁴ R ⁵ SiO _1/2 (IIIa),

D - group with the general formula (IIIb)

R ⁶ R ⁷ SiO _2/2 (IIIb),

T - group with general formula (IIIc)

R ⁸ SiO _3/2 (IIIc),

Q - block with the general formula SiO _4/2 ,

where each of R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ represents a monovalent organic group, OH or alkoxy group containing 1-10 C atoms, preferably 1-4 C atoms, and not more than 75% all groups R ³ -R ⁷ are hydroxyl or alkoxy groups,

m is an integer 0-20,

n is an integer 0-1000,

o is an integer 0-30,

p is an integer 0-20, and

m+n+o+p is an integer equal to at least 2.

In the preferred polyorganosiloxanes of formula (III), not more than 50%, even more preferably not more than 25%, and more particularly not more than 10% of all R ³ -R ⁸ groups are hydroxyl or alkoxy groups.

In the preferred polyorganosiloxanes of formula (III), each of R ³ -R ⁸ is preferably a monovalent organic group having 1-20 carbon atoms, which is unsubstituted or substituted with a halogen compound, alkoxy group, ammonium or silyl, hydroxyl group or alkoxy group, having 1-10 C atoms. Unsubstituted alkyl groups, cycloalkyl groups, aryl groups, alkylaryl groups and arylalkyl groups are particularly preferred. Each of R ³ -R ⁸ preferably contains 1-8 carbon atoms.

Examples of suitable unsubstituted alkyl groups for R ³ -R ⁸ include methyl, ethyl, n-propyl, 2-propyl (=isopropyl), 3,3,3-trifluoropropyl, vinyl, 1-n-butyl, 2-methylpropyl ( =isobutyl), 2-butyl, tert-butyl, n-pentyl, cyclopentyl, cyclohexyl, n-nonyl, n-decyl, n-undecyl, 10-undecyl, n-dodecyl, isotridecyl, n-tetradecyl, n-hexadecyl, allyl, phenyl, benzyl, p-chlorophenyl, o-(phenyl)phenyl, m-(phenyl)phenyl, p-(phenyl)phenyl, 1-naphthyl, 2-naphthyl, 2-phenylethyl, 1-phenylethyl, 3-phenylpropyl , 1-n-hexyl, 1-n-heptyl, 1-n-octyl, 2,4,4-trimethyl-1-pentyl, 2-ethyl-1-hexyl, 2-methyl-1-pentyl, isohexyl and isooctyl . Preferred groups R ³ -R ⁸ are methyl, ethyl, propyl, isobutyl, 1-n-hexyl, 1-n-octyl, isohexyl, isooctyl and phenyl, in particular methyl and phenyl.

Examples of suitable substituted alkyl groups for R ³ -R ⁸ include 3-chloropropyl, chloromethyl, methoxymethyl, ethoxymethyl, 2-trimethylsilylethyl, 2-trimethylsilyloxyethyl, 2-trimethoxysilylethyl, 2-dimethylmethoxysilylethyl, 2-dimethoxymethylsilyl, 3-trimethylammonium propyl, and 3- dimethylbenzylammonium propyl. Additional examples of suitable substituted alkyl groups for R ³ -R ⁸ correspond to the general formula:

-(CR ⁹ R ¹⁰ ) _r O) _s -R ¹¹ (IV)

where r is 1-6, s is 1-100, and R ⁹ , R ¹⁰ and R ¹¹ are each independently H or a monovalent organic group containing 1-20 C atoms, optionally interrupted by heteroatoms. Optionally, various groups of general formula (IV) are present in the form of blocks, for example -CH ₂ CH ₂ CH ₂ -O-(CH ₂ CH ₂ O) ₆ -CH ₃ , -CH ₂ CH ₂ CH ₂ -O-(CH ₂ CH (CH ₃ )O) ₈ -H, -CH ₂ CH ₂ CH ₂ -O-(CH ₂ CH ₂ CH ₂ CH ₂ O) ₁₀ -CH ₂ CH ₂ CH ₂ CH ₃ and -CH ₂ CH ₂ CH ₂ - O-(CH ₂ CH ₂ O) ₁₀ -(CH ₂ CH (CH ₃ )O) ₈ -CH ₂ CH ₂ CH ₂ CH ₃ .

Further preferred polyorganosiloxanes present in the coating composition of the present invention contain blocks M and Q. Preferred polyorganosiloxanes correspond to formula (V):

R ¹² _v R ¹³ ₍₃ - _v) SiO _1/2 and SiO _4/2 (V)

where

each of R ¹² and R ¹³ is independently a monovalent organic group; and

v is 0, 1, or 2.

Representative examples of suitable monovalent organic groups include alkyl (eg methyl, ethyl, propyl, pentyl, octyl, decyl, dodecyl, undecyl and octadecyl); cycloalkyl (eg cyclopentyl and cyclohexyl); aryl (eg phenyl, tolyl, xylyl and benzyl); aralkyl (eg 2-phenylethyl); chlorinated alkyl groups (eg chloromethyl and chloropropyl); fluorinated alkyl groups (e.g. fluoromethyl, 2-fluoropropyl, 3,3,3-trifluoropropyl, 4,4,4-trifluorobutyl, 4,4,4,3,3-pentafluorobutyl, 5,5,5,4,4,3 ,3-heptafluoropentyl, 6,6,6,5,5,4,4,3,3-nonafluorohexyl and 8,8,8,7,7-pentafluorooctyl; chlorinated cycloalkyl groups (e.g. 2,2-dichlorocyclopropyl, 2, 3-dichlorocyclopentyl); fluorinated cycloalkyl groups (e.g. 2,2-difluorocyclopropyl, 2,3-difluorocyclobutyl, 3,4-difluorocyclohexyl and 3,4-difluoro-5-methylcycloheptyl); and other monovalent organic groups such as hydrocarbon groups , substituted with oxygen atoms, such as glycidoxyalkyl, and hydrocarbon groups substituted with nitrogen atoms, such as aminoalkyl, and cyanide functional groups, such as cyanoethyl and cyanopropyl.

The polyorganosiloxane of formula (V) is sometimes referred to as MQ resin. Preferred polymers have a molar ratio of M blocks to Q blocks (M:Q) ranging from 0.5:1 to 1.5:1. These molar ratios are conveniently measured by Si ²⁹ NMR spectroscopy.

Preferably polyorganosiloxane contains approximately 2.0 wt. % or less, more preferably about 0.7 wt. % or less, even more preferably about 0.3 wt. % or less end blocks represented by the formula X''SiO _3/2 where X'' represents a hydroxyl or alkoxy group such as methoxy and ethoxy groups.

Further preferred polyorganosiloxanes present in the coating composition of the present invention comprise a T block. Preferred polyorganosiloxanes are silsesquioxanes, and especially those corresponding to formula (VI):

(R^fourteenSiO_3/2) (VI)

where

each R ¹⁴ is hydrogen or a monovalent organic group.

Representative examples of suitable monovalent organic groups include alkyl (eg methyl, ethyl, propyl, pentyl, octyl, decyl, dodecyl, undecyl and octadecyl); cycloalkyl (eg cyclopentyl and cyclohexyl); aryl (eg phenyl, tolyl, xylyl and benzyl); aralkyl (eg 2-phenylethyl); halogenated alkyl groups (eg chlorinated alkyl groups such as chloromethyl and chloropropyl); fluorinated alkyl groups (e.g. fluoromethyl, 2-fluoropropyl, 3,3,3-trifluoropropyl, 4,4,4-trifluorobutyl, 4,4,4,3,3-pentafluorobutyl, 5,5,5,4,4,3 ,3-heptafluoropentyl, 6,6,6,5,5,4,4,3,3-nonafluorohexyl and 8,8,8,7,7-pentafluorooctyl; chlorinated cycloalkyl groups (e.g. 2,2-dichlorocyclopropyl, 2, 3-dichlorocyclopentyl); fluorinated cycloalkyl groups (e.g. 2,2-difluorocyclopropyl, 2,3-difluorocyclobutyl, 3,4-difluorocyclohexyl and 3,4-difluoro-5-methylcycloheptyl); other monovalent organic groups such as hydrocarbon groups substituted oxygen atoms such as glycidoxyalkyl, nitrogen substituted hydrocarbon groups such as aminoalkyl, and cyanide functional groups such as cyanoethyl and cyanopropyl, and any combinations thereof.

Silsesquioxanes suitable for use herein are known in the art and are publicly available. For example, a methylmethoxysiloxane-methylsilsesquioxane resin having a DP of about 15 and an average molecular weight (Mw) of about 1200 g/mol is available as DOW CORNING® US-CF 2403 resin from Dow Corning Corporation. Alternatively, the silsesquioxane may have phenylsilsesquioxane blocks, methylsilsesquioxane blocks, or a combination thereof. Such resins are known in the art and are available, such as XIAMETER® Flake resins such as RSN-0217, RSN-0220, RSN-0233, RSN-0249, RSN-0255, also available from Dow Corning Corporation. .

Alternatively, the polyorganosiloxane present in the coating composition of the present invention may contain a DT block. Preferred polyorganosiloxanes correspond to formula (VII):

(R ¹⁵ ₂ SiO _2/2 ) and/or (R ¹⁵ R ¹⁶ SiO _2/2 ) and (R ¹⁵ SiO _3/2 ) and/or (R ¹⁶ SiO _3/2 ) (VII)

where R ¹⁵ is hydrogen or a monovalent organic group, and R ¹⁶ is an OH group or an alkoxy group. Examples of suitable monovalent organic groups are described above for R ¹⁴ .

DT resins are known in the art and are available, for example, as methoxyfunctional DT resins, including XIAMETER® RSN-3074 and XIAMETER® RSN-3037 resins; and silanol-functional resins, including XIAMETER® RSN-0804, RSN-0805, RSN-0806, RSN-0808, and RSN-0840 resins, which are also available from Dow Corning Corporation. Other suitable resins include DT resins containing methyl and phenyl groups.

Alternatively, the polyorganosiloxane present in the coating composition has the formula (VIII):

R ¹⁷ _t R ¹⁸ _u SiO ₍₄ - _t - _u)/2 (VI)

where

each of R ¹⁷ and R ¹⁸ is independently a monovalent organic group, another group of formula (VI), or OR ¹⁹ where R ¹⁹ is H or an alkyl or aryl group having 1-24 carbon atoms, where each of t and u represents is a positive number such that 0.8 ≤ (x+y) ≤ 4.0. Exemplary polyorganosiloxanes contain blocks including dimethyl, diphenyl, methylphenyl, phenylpropyl, and mixtures thereof.

Exemplary polyorganosiloxanes of the present invention contain random mixtures of methyl and phenyl groups, dimethylsiloxane and diphenylsiloxane groups, or methylphenylsiloxane groups, wherein the ratio of phenyl to methyl groups is from 0.5 to 1.5:1, more preferably from 0.7:1 to 1 ,1:1.

The polyorganosiloxane present in the coating composition of the present invention preferably contains silanol, SiOH groups. Preferably, the content of silanol in polyorganosiloxane is 0.25 wt. % or more, for example, 0.5 wt. % or more, or 1 wt. % or more, or 1.3 wt. % or more, or 2.5 wt. % or more, or 3 wt. % or more based on the total weight of the polyorganosiloxane. The content of condensable hydroxyl in polyorganosiloxane can be up to 7 wt. %, or up to 5 wt. % by total weight of polyorganosiloxane.

Examples of suitable polyorganosiloxanes of formula (VI) include the polyorganosiloxanes sold by Wacker under the trademark Silres® as Silres® 601, 603 and 604 products.

The coating composition of the present invention preferably contains 0.5-30 wt. %, more preferably 0.75-25 wt. %, and even more preferably 1.0-20 wt. % polyorganosiloxane.

Additives

The powder coating composition of the present invention may contain a variety of additives. Examples of additives that are optionally present in the composition of the present invention include silane, metal phosphate, metal borate, amino alcohols, filler, non-metal pigments, flow aids, degassing agent, gloss modifiers, scratch-resistance agents, dyes, waxes, antioxidants, optical brighteners and surface modifiers. Additional additives are preferably present in an amount of from 0 to 60 wt. %, more preferably 1-40 wt. %, even more preferably 2-20 wt. %, and especially preferably 5-10 wt. % by total weight of the composition.

Examples of suitable silanes correspond to the following formula:

YR ₍₄ - _z) SiX _z -

where z is an integer from 2 to 3;

R is an unsubstituted, straight chain alkyl chain having 2-8 C atoms, optionally containing an ether or amine coupling agent;

Y is an amino or epoxy functional group linked to an R group; and

X represents an alkoxy group.

Examples of such silanes are products from Degussa (Rheinfelden) sold under the brand name Dynasylan(R)D, as well as Silquest(R) silanes from OSi Specialties and GENOSIL(R) silanes from 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-l 110), aminopropyltriethoxysilane (Dynasylan AMEO), or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (Dynasylan DAMO, Silquest A-l 120) or N-(2-aminoethyl)-3-aminopropyltriethoxysilane, triamino-functional trimethoxysilane (Silquest A-l 130), bis(gamma-trimethoxysilylpropyl)amine (Silquest A-l 170), N-ethyl-gamma- aminoisobutyltrimethoxy silane (Silquest A-Link 15), N-phenyl-gamma-aminopropyltrimethoxysilane (Silquest Y-9669), 4-amino-3,3-dimethylbutyltrimethoxysilane (Silquest Y-l1637), (N-cyclohexylaminomethyl)triethoxysilane (Genosil XL 926) , (N-phenylaminomethyl)trimethoxysilane (Genosil XL 973), Deolink Epoxy TE and Deolink Amino TE (D. O. G Deutsche Oelfabrik), as well as mixtures thereof.

When present, the amount of silane in the powder compositions of the present invention is preferably 1-10 wt. %, more preferably 0.2-6 wt. %, even more preferably 0.4-3 wt. % and most preferably 0.6-3 wt. % by total weight of the composition.

Examples of suitable phosphates and borates are metal phosphates and metal borates. The preferred borate is barium metaborate monohydrate.

Phosphates are the preferred additive present in the compositions of the present invention, especially metal phosphates. Preferred phosphates are orthophosphate, hydrogen phosphate or polyphosphate. Particularly preferred phosphates are orthophosphates, and even more preferably orthophosphates of alkali metals or alkaline earth metals.

Specific examples of suitable phosphates are dicalcium phosphate dihydrate, dimagnesium phosphate trihydrate, zinc phosphate (e.g. zinc phosphate di- or tetrahydrate, preferably in the form of spheroidal particles as described in US Pat. Fe(II) and Fe(III) phosphate, zinc phosphate (preferably in spheroidal form) modified with zinc molybdate and rendered organophilic by suitable surface treatment or zinc aluminum phosphate), alkaline earth hydrogen phosphates in conjunction with alkaline earth carbonates, optionally also comprising one or more additives selected from fluorosilicates, fluoroborates, alkali and alkaline earth fluorides, mixtures of magnesium hydrogen phosphate and calcium hydrogen phosphate, polyphosphates and polyphosphate hydrates, including ammonium polyphosphates, modified strontium aluminum polyphosphate hydrates, such as those available under the trade names HEUCOPHOS SAPP and HEUCOPHOS SRPP; zinc aluminum polyphosphate hydrates such as those available under the tradename HEUCOPHOS ZAPP; modified zinc calcium aluminum polyphosphate silicate hydrates such as those available under the trade name HEUCOPHOS ZCPP; and modified calcium aluminum polyphosphate silicate hydrates such as those available under the trade name HEUCOPHOS CAPP; orthophosphate hydrates, including modified zinc, calcium and strontium orthophosphate silicate hydrates, such as those available under the tradename HEUCOPHOS ZCP; modified zinc and aluminum orthophosphate hydrates such as those available under the trade name HEUCOPHOS ZPA; organically processed basic zinc orthophosphate hydrates such as those available under the trade name HEUCOPHOS ZPO; modified basic zinc molybdenum orthophosphate hydrates such as those available under the trade name HEUCOPHOS ZMP and organic/inorganic modified basic zinc orthophosphate hydrates or basic zinc phosphate silicate hydrates such as those available under the trade names HEUCOPHOS ZPZ and ZBZ , respectively; phosphosilicates such as, for example, calcium strontium zinc phosphosilicate (such as the material available under the trade name Halox SZP391 from Halox Pigments), calcium phosphosilicate and zinc aluminum phosphosilicate; organophosphorus compounds, including metal organophosphorus compounds, such as, for example, salts of a multivalent metal cation and an organic phosphonic acid containing at least two phosphonic acid groups, such as calcium etidronate (1-hydroxyethane-1,1-diphosphonic acid monocalcium dihydrate). A particularly preferred phosphate is dicalcium phosphate dihydrate.

When it is present, the amount of phosphate or borate in the powder compositions of the present invention is preferably 1-10 wt. %, more preferably 0.2-6 wt. %, even more preferably 0.4-3 wt. % and most preferably 0.6-3 wt. % by total weight of the composition.

Amino alcohols are the preferred additive present in the compositions of the present invention. Examples of suitable amino alcohols have the formula:

NH ₂ R ¹

where R ¹ is a linear or branched alkyl group of 1-10 carbon atoms, preferably 2-8 carbon atoms, and more preferably 2-4 carbon atoms, which contains at least one hydroxyl group; and

NHR ¹ R ²

where R ¹ is a linear or branched alkyl group of 1-10 carbon atoms, preferably 2-8 carbon atoms, and more preferably 2-4 carbon atoms, or a linear or branched alkyl group of 1-10 carbon atoms, preferably 2-8 atoms carbon, and more preferably 2-4 carbon atoms, which contains at least one primary hydroxyl group, and R ² is a linear or branched alkyl group of 1-10 carbon atoms, preferably 2-8 carbon atoms, and more preferably 2-4 carbon atoms, which contains at least one hydroxyl group.

Preferably, the amino alcohol has a molecular weight of less than 500 g/mol, more preferably 50-400 g/mol, and even more preferably 75-350 g/mol.

Preferably the amino alcohol has 1-3 amino groups, more preferably 1-2 amino groups, and even more preferably 1 amino group. Preferably the amine functionality contains an NH bond, ie the amine is primary or secondary, especially primary (-NH ₂ ).

The amino alcohol preferably contains one hydroxyl group or 2-5 hydroxyl groups, for example 2 or 3 hydroxyl groups. Preferably, the hydroxyl group in these formulas is primary, ie forming a -CH ₂ -OH group with the carbon to which it is attached.

Preferably the amino alcohol has one amino group, ideally a primary amine, and 2 or more, and more preferably 3, hydroxyl groups.

Preferably, amino alcohols 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, tert-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.

Preferred amino alcohols are tris(hydroxymethyl)aminomethane (THAM) and diethanolamine. Therefore, possible amino alcohols include: ethanolamine, 2-(methylamino)ethanol, 3-amino-1-propanol, amino-2-propanol, DL-alaninol, amino-1,2-propanediol, serinol (C3H9NO2), 1, 3-diamino-2-propanol, 1-amino-2-methyl-2-propanol, 1-methoxy-2-propylamine, 2-(ethylamino)ethanol, 2-amino-1-butanol, 2-amino-2-methyl -1-propanol, 2-amino-2-methyl-1-propanol, 2-dimethylaminoethanol, 3-methoxypropylamine, 3-methylamino-1-propanol, 4-amino-1-butanol, 2-(2-aminoethoxy)ethanol, 3-methylamino-1,2-propanediol, diethanolamine, tris(hydroxymethyl)aminomethane, N-(2-hydroxyethyl)ethylenediamine, meso-1,4-diamino-2,3-butanediol, trans-2-aminocyclopentanol hydrochloride, 1- dimethylamino-2-propanol, 2-(isopropylamino)ethanol, 2(propylamino)-ethanol, 2-amino-3-methyl-1-butanol, 3-dimethylamino-1-propanol, 3-ethoxypropylamine, 5-amino-1- pentanol, 2-amino-1-pentanol, 3-(dimethylamino)-1,2-propanediol, N-methyldiethanolamine, 2-(3-aminopropylamino)ethanol, 1-amino-1-cyclopentanemethanol, trans-2-aminocyclohexanol, trans -4-aminocyclohexanol , 2-(butylamino)ethanol, 2-(diethylamino)ethanol, 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-ethyldiethanolamine, triethanolamine, N,N'-bis(2-hydroxyethyl)ethylenediamine, 3-diethylamino-1-propanol, 3-(diethylamino)-1 ,2-propanediol, 1,3-bis(dimethylamino)-2-propanol, 2-{[2-(dimethylamino)ethyl]methylamino}ethanol, 2-(diisopropylamino)ethanol, N-butyldiethanolamine, N-tert-butyldiethanolamine, 2-(dibutylamino)ethanol, as well as any mixtures thereof. A particularly preferred amino alcohol is tris(hydroxymethyl)aminomethane (THAM).

When it is present, the amount of amino alcohol in the composition of the present invention is preferably 0.1-10 wt. %, for example 0.2-5 wt. %, and more preferably 0.2-4 wt. %, for example 0.2-3 wt. %.

The powder coating composition of the present invention preferably contains a filler. Representative examples of fillers include wollastonite (calcium metasilicate), wollastonite mixed with barite, mica, mica mixed with barite, wollastonite mixed with mica, barite, calcium phosphate, magnesium phosphate, perlite, and other porous fillers having a low thermal coefficient. extensions (CTE), alumina; clays such as layered silicates including phyllosilicates, smectite, hectorite, montmorillonite and kaolin; Na or Mg metasilicate, Mg silicate, talc, chalk, feldspar, CaCO3, sintered glass frit, quartz glass powder, glass rods and glass whiskers having an aspect ratio of 8:1 to 40:1, crushed glass fibers having an aspect ratio 8:1 to 40:1, sodium titanate, silicon carbide, silicon nitride, polytitananocarbosilane, phosphate glass frit having a Tg of 420 to 450°C, MgO, magnesium oxide.

When present, the amount of filler in the powder compositions of the present invention is preferably 0-15 wt. %, more preferably 0.5-12.5 wt. %, and even more preferably 1.0-12 wt. % by total weight of the composition.

The powder coating composition of the present invention preferably contains non-metallic pigments. Examples of non-metallic pigments include inorganic pigments such as titanium dioxide, red and yellow iron oxides, chromium pigments, and carbon black. Examples of organic pigments include phthalocyanine, axo, anthraquinone, thioindigo, isodibenzanthrone, triphendioxane, quinacridone pigments, and vat dye pigments.

When they are present, the amount of non-metallic pigments in the powder compositions of the present invention is preferably 0-5 wt. %, and more preferably 0.1-2 wt. % by total weight of the composition.

The powder coating composition of the present invention preferably contains a spreading agent. Examples of suitable pour aids include acrylics, silicon compounds, and fluorine-based polymers. The pour aids improve the melt flow characteristics of the compositions and help eliminate surface defects during curing.

When they are present, the amount of additives to improve filling in the powder compositions of the present invention is preferably 0-5 wt. %, and more preferably 0.1-2 wt. % by total weight of the composition.

The powder coating composition of the present invention preferably contains a degassing agent. A suitable example is benzoin. When it is present, the amount of degassing additive in the powder compositions of the present invention is preferably 0-5 wt. %, and more preferably 0.1-1 wt. % by total weight of the composition.

Containers and kits

The present invention also relates to a container containing the particulate coating composition described above. Suitable containers include cans and drums.

Alternatively, the particulate coating composition of the present invention may be provided in the form of a kit. In the kit, the metallic pigment is preferably contained separately from the other components of the powder coating composition. Therefore, the kits contain:

(i) a first container containing at least one polyester polymer, at least one hardener, and at least one polyorganosiloxane;

(ii) a second container containing at least 0.1 wt. % of at least one metallic pigment based on the total weight of the kit components; and

(iii) instructions for mixing at least one polyester polymer, at least one hardener, at least one polyorganosiloxane, and at least 0.1 wt. % of at least one metallic pigment.

Production

The present invention also relates to a process for preparing the particulate composition described above, comprising:

(i) mixing at least one polyester polymer, at least one hardener and at least one polyorganosiloxane to form a mixture;

(ii) extruding said mixture to form particles; and

(iii) adding mentioned at least 0.1 wt. % of at least one metallic pigment to said particles.

Preferred processes of the present invention further comprise milling the extruded particles. Other preferred processes of the present invention further comprise screening the ground particles. Thus, the preferred process of the present invention comprises:

(i) mixing at least one polyester polymer, at least one hardener and at least one polyorganosiloxane to form a mixture;

(ii) extruding said mixture to form extruded particles;

(iii) grinding said extruded particles to form milled particles;

(iv) screening said ground particles; and

(iii) adding mentioned at least 0.1 wt. % of at least one metallic pigment to said particles.

Non-metallic pigments may be added to the mixture in step (i) or after extrusion. Preferably non-metallic pigments are added to the mixture in step (i).

Preferably the polyester polymer, hardener, polyorganosiloxane and optionally non-metallic pigments are premixed and extruded. Any conventional mixing method may be used. Preferred extrusion conditions are conventional, and will typically be maintained at a low temperature, eg below 140° C., to avoid premature curing.

In the preferred process of the present invention, extruded particles containing a polyester polymer, hardener, polyorganosiloxane, and optionally a non-metallic pigment are ground to form a powder. Grinding can be carried out in any conventional mill to the particle size most suitable for powder application. The particle size distribution d50 of the powder coating composition is preferably in the range of 10-120 µm, and even more preferably 15-75 µm. The preferred particle size d50 is at least 20 or 25 µm, and preferably does not exceed 50 µm, such as 20-45 µm. In most cases, particle sizes can be determined using a Malvern particle size analyzer. After grinding, sieving is preferably performed to maximize the uniformity of particle distribution.

Metallic pigments may be added before or after extrusion, but are preferably added after extrusion. Preferably, metallic pigments are also added after milling or other homogenization processes. The metal 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. Therefore, the adhesion of the metallic pigments to the surface of the coating particles of the powder material is achieved.

Metal effect pigments such as mica can also be added before or after extrusion, but are preferably added after extrusion. Preferably, metallic effect pigments are also added after milling.

Application to substrates and coating

The present invention also relates to a method for coating a substrate with a particulate composition as described above, comprising:

i) applying the particulate composition to said support; and

ii) optionally curing said composition in particulate form.

The particulate coating of the present invention may be applied to a substrate by any conventional powder coating method. Preferred is atomization, such as electrostatic. Triboelectric guns can also be used. Coating techniques are known in the art and will be understood by a person skilled in the art.

The present invention also relates to a coating containing the particulate composition described above. Preferably the coating is cured. Alternatively, the present invention relates to a coating obtained by spraying and curing the particulate coating composition described above.

The particulate coating composition of the present invention may be used to form a single coat or may be used over a primer to form an overcoat. Preferably, however, the particulate coating composition of the present invention is used to form the outer coating layer used on any substrate. Therefore, preferably the coating is an outer coating. Optionally, the coating further comprises an underlying primer layer.

Curing

After the substrate has been coated with the powder material coating composition of the present invention, the coating is preferably cured. Thermal or thermal curing is preferred. The coated substrate can be cured in a conventional convection oven, in a combined infrared/convection oven, in a convection/induction oven, or in a convection/induction/infrared oven. When heat is used for curing, the temperature is preferably in the range of 100-250°C, such as 150-200°C. Preferably, the powder coating composition of the present invention can be cured in short cycles, for example 15 minutes or less.

The powder coating composition is preferably fluid during the curing operation. Preferably, this results in a smooth and even finish. The film thickness of the cured coating is preferably 20-200 µm, for example 30-120 µm, and in particular 40-100 µm.

It is a feature of the present invention that the powder material coating composition of the present invention does not corrode. The absence of corrosion manifests itself in good color fastness and low gloss change. This coating is preferably resistant to acids, alkalis and water.

Substrate and products

The present invention also relates to a substrate coated with a particulate composition as described above or a coating as described above. The particulate coating composition of the present invention may be applied to any substrate. Representative examples of substrates include metal substrate (steel, galvanized steel, aluminium), wood, medium density fibreboard (MDF), high density fibreboard (HDF), plywood, fibreboard, particle board, plastic, glass, ceramic, filled graphite composites, etc. The preferred substrate is a metal substrate. The substrates may ultimately be intended for internal or external use.

The substrate may be partially or completely coated with the particulate composition or coating of the present invention. In some cases, for example, only the top surface of the substrate is coated. In other cases, all surfaces of the substrate are preferably coated. Preferably, the substrate is at least part of the surface of the article. Product examples include appliances, building components, furniture, vehicles, fittings and pipe fittings, etc.

The article to be coated may be provided with a primer layer, although this is not essential. The primer can use zinc or zinc-free powder or liquid primer for corrosion inhibition. Typical epoxy and epoxy/polyester primers contain 0-85 wt. % zinc. The coating of the present invention preferably forms an outer coating on any substrate. Thus, preferably no additional coating layer is applied to it. Therefore, the substrates may comprise a primer layer and an overcoat containing the powder composition of the present invention, or simply comprise an overcoat of the present invention without a primer primer.

Further, the present invention will now be illustrated using the following non-limiting examples.

EXAMPLES

Test Methods

Film thickness: Measured according to ISO 2178.

Acid resistance: Coatings are exposed to 5% HCl solutions for 15, 30, 60, 90 or 120 minutes. The difference in darkness ΔL before and after the test describes the level of corrosion of the panels. Panels with high corrosion performance have a low absolute ΔL value, while highly corrosive panels have high absolute ΔL values. ΔL values are measured using the Largo Coloreye 3000 instrument.

Alkali resistance Coatings are exposed to 1% NaOH solution and the time required for visual darkening is recorded.

The humidity test is performed in accordance with ISO 6270-2. Coatings are exposed to a condensing atmosphere of constant humidity (CH). The air temperature is 40±3°C and the relative humidity is approximately 100% with condensation on the test pieces. Gloss and color are measured before and after the test. Gloss is measured according to ISO 2813 at a measuring angle of 60°. Color change ΔE is measured using a Largo Coloreye 3000 instrument. Differences in darkness and gloss change describe panel corrosion. Panels with high corrosion performance have little gloss change and low absolute ΔE, while highly corroded panels have high gloss change and high absolute ΔE.

materials

All polymers and compounds used in the examples were obtained commercially.

The properties of the polyorganosiloxanes used in the examples are shown in the table below:

Name Softening T (°C) OH groups (wt.%) MW PS1 Polyorganosiloxane containing phenyl groups 65-85 4.5-6.5 1200-2600 PS2 Flaky polyorganosiloxane containing phenyl and methyl groups (1:1 ratio) 55-80 3.5-7.0 1800-2400 PS3 Flaky polyorganosiloxane containing phenyl and methyl groups (0.8:1 ratio) 5.0 4000 PS4 Flaky polyorganosiloxane containing phenyl and methyl groups (2:1 ratio) 5.0 2500

General production procedure

Powder preparation:

The ingredients (except for the metallic pigment) were dry mixed in a high speed mixer to ensure sufficient dispersion of the powder mixture. This premix was then added to a Theyson TSK 20-24 twin screw extruder and extruded under the following conditions: 30° feed, 50° melt, 100° mix and disperse, and 100° die, 500 rpm, at a torque of 60-65.

The extruded material was fed to a chilled roll and passed through a crusher to reduce the cooled material to flaky particles. The crushed flocculent particles were then fed into the mill. The extruded particles were milled and screened through a 125 µm rotary sieve to ensure a particle size distribution (PSD) (d50) of 25-50 µm (determined using a Malvern particle size analyzer).

The metallic pigment was then carefully mixed into the powder.

Applying the powder to the substrate

The powder was applied to phosphated cold rolled steel panels using a standard corona gun.

Film Curing

The powder coated substrates were cured by conventional convection heat transfer using a conventional Heraeus benchtop oven. The curing temperature of the object was 180°C, and curing at this temperature took 10 minutes.

Example 1

Powder Coating Compositions

The examples in this document are based on the powder coating composition described in Table 1 below. 1.5 wt. % aluminum pigment was added after the extruder. All other components were premixed and extruded as described above. The films produced had a thickness of 50-100 µm.

Test results

Acid resistance

The results are shown in Table 2 below.

Table 1

Name Description CE one 2 3 4 5 6 7 eight nine ten Polyester polymer with carboxyl functionality (AV60-70) Polyester polymer 37.4 35.5 33.6 35.5 33.6 37.0 36.6 35.5 37.0 36.6 35.5 Polyester Polyester with Carboxyl Functionality (AV55-68) Polyester polymer 8.6 8.2 7.8 8.2 7.8 8.5 8.5 8.2 8.5 8.5 8.2 Epoxy Type 3 Epoxy hardener 40.3 38.3 36.3 38.3 36.3 39.9 39.5 38.3 39.9 39.5 38.3 Degassing additive 0.3 0.2 0.2 0.2 0.2 0.3 0.3 0.2 0.3 0.3 0.2 Filling additive 1.1 1.1 1.0 1.1 1.0 1.1 1.1 1.1 1.1 1.1 1.1 _TiO2 Non-metallic white pigment 1.5 1.4 1.3 1.4 1.3 1.5 1.4 1.4 1.5 1.4 1.4 Sodium feldspar Filler 4.3 4.1 3.9 4.1 3.9 4.3 4.2 4.1 4.3 4.2 4.1 _BaSO4 Filler 6.5 6.2 5.8 6.2 5.8 6.4 6.3 6.2 6.4 6.3 6.2 PS1 Polyorganosiloxane - 5.0 10.0 - - - - - - - - PS2 Polyorganosiloxane - - - 5.0 10.0 - - - - - - PS3 Polyorganosiloxane - - - - - 1.0 2.0 5.0 PS4 Polyorganosiloxane - - - - - - - - 1.0 2.0 5.0 Aluminum pigment, non-flake metallic pigment 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5

table 2

Exposure time 5% HCl solution [min] Comparative Example one 2 3 4 5 6 7 eight nine ten ΔL ΔL ΔL ΔL ΔL ΔL ΔL ΔL ΔL ΔL fifteen 0.08 0.04 0.09 0.02 0.00 0.1 0.08 0.05 0.09 0.06 0.01 thirty -0.5 -0.4 -0.06 -0.3 -0.1 -0.1 -0.07 0 -0.05 0.01 0.02 60 -2.4 -1.5 -0.9 -1.46 -0.90 -1.4 -1.3 -0.8 -1.3 -1.1 -0.6 90 -4.8 -2.6 -2.3 -2.5 -2.2 -3.1 -3.0 -2.2 -3.3 -2.8 -1.9 120 -6.8 -3.1 -3.7 -3.3 -3.4 -4.8 -4.8 -4.8 -5.3 -4.5 -3.4

The results in Table 2 show that the polyorganosiloxane-containing coatings have lower absolute ΔL values than the comparative example. This shows that polyorganosiloxane-containing coatings have improved acid resistance than coatings without polyorganosiloxane.

Alkali resistance

The results are shown in Table 3 below.

Table 3

Comparative Example one 2 3 4 5 6 7 eight nine ten Exposure time 1% NaOH without darkening (min) 5 ten 25 ten 25 ten ten fifteen 7.5 ten fifteen

These results show that polyorganosiloxane-containing coatings can remain in 1% NaOH solution without browning for a significantly longer time than a comparative coating without polyorganosiloxane. This shows that polyorganosiloxane-containing coatings have improved alkali resistance compared to comparative coatings without polyorganosiloxane.

moisture resistance

The results are shown in Tables 4, 5 and 6 below. Table 4 shows the results for the powder coating compositions 1-4 described in the above table, and Table 5 shows the results for the powder coating compositions 5-10 described in the above table. Table 6 shows the results for a powder coating composition containing 1.0 wt. % aluminum flake pigment instead of non-flake pigment. In all other respects, these compositions were identical to compositions 1-4.

Table 4

Humidity test, 40°C Comparative Example one 2 3 4 ΔE, 24 hours 6.5 0.02 0.06 0.03 0.07 ΔE, 48 hours 8.4 0.2 0.1 0.2 0.1 ΔE, 72 hours 8.8 0.6 0.2 0.3 0.2 ΔE, 96 hours stopped 0.9 0.2 0.8 0.2 ΔE, 192 hours 3.8 0.5 3.5 0.5 ΔE, shine, 336 hours 6.4/37 0.9/84 5.5/46 3.4/64 ΔE, shine, 700 hours 7.3/35 1.6/79 7.6/35 5.5/45 ΔE, shine, 800 hours 7.3/28 1.7/78 7.6/34 7.1/28 ΔЕ, shine, 1000 hours 7.6/32 6.3/28 8.4/31 7.8/22

Table 5

Humidity test, 40°C Comparative Example 5 6 7 eight nine ten ΔE, shine, 0 hour 0/100 0/88 0/82 0/81 0/86 0/84 0/79 ΔE, shine, 24 hours 0.3/98 0.6/84 0.5/81 0.2/81 3.4/59 0.9/79 0.1/80 ΔE, shine, 72 hours 7.6/18 6.1/37 5.2/47 1.6/71 8.6/26 6.5/41 1.3/74 ΔE, shine, 144 hours stopped 8.6/22 8.7/38 6.4/41 - 9.1/35 4.9/62 ΔE, shine, 192 hours - - - - - 6.5/56

Table 6

Humidity test, 40°C Comparative Example one 2 3 4 ΔE, 24 hours 36.2 17.2 4.2 13.9 6.5 ΔE, 48 hours stopped stopped 10.5 stopped 11.3 ΔE, 72 hours 12.2 13.0

Panels with high corrosion performance have low absolute ΔE values and little gloss change, while highly corroded panels have high absolute ΔE values and significant gloss changes. From the results shown in Tables 4-6, it is apparent that the powder coating compositions of the present invention significantly improve the moisture resistance of the coatings. In Table 4, the ΔE values are significantly lower for Examples 1-4 compared to the Comparative Example. The same trend is also observed in Table 5 where lower amounts of polyorganosiloxane are present in the powder coating composition.

Table 6 shows the results obtained by including a flake aluminum pigment in the powder composition instead of a non-flake pigment. Because the flake aluminum pigment flows to the surface of the coatings, it is more difficult to protect them. However, these results show that the polyorganosiloxane-containing powder material coating compositions of the present invention significantly improve the moisture resistance of coatings containing flake metal pigments.

Example 2

Powder Coating Compositions

These examples are based on the powder coating composition described in Tables 7 and 8 below. In Table 7, 1.5 wt. % non-flake aluminum pigment was added after the extruder. In table 8, 1.0 wt. % flake aluminum pigment was added after the extruder. All other components were premixed and extruded as described above, except that the metallic pigments were more gently mixed into the powder. The films produced had a thickness of 50-100 µm.

Test results

Acid resistance

The results are shown in Tables 9 and 10 below.

Table 7

Name Description CE1 CE2 CE3 eleven 12 Polyester polymer with carboxyl functionality (AV60-70) Polyester polymer 37.4 37.0 37.0 33.3 33.3 Polyester Polyester with Carboxyl Functionality (AV55-68) Polyester polymer 8.6 8.5 8.5 7.7 7.7 Epoxy Type 3 Epoxy hardener 40.3 39.9 39.9 35.9 35.9 Degassing agent 0.3 0.3 0.3 0.2 0.2 Filling additive 1.1 1.1 1.1 1.0 1.0 _TiO2 Non-metallic white pigment 1.5 1.5 1.5 1.3 1.3 Sodium feldspar Filler 4.3 4.3 4.3 3.8 3.8 _BaSO4 Filler 6.5 6.4 6.4 5.8 5.8 PS1 Polyorganosiloxane - - - 10.0 10.0 Tris(hydroxymethyl)aminomethane (THAM) Amino alcohol - 1.0 - 0.9 - Dicalcium Phosphate Dihydrate metal phosphate - - 1.0 - 0.9 Aluminum pigment, non-flake metallic pigment 1.5 1.5 1.5 1.5 1.5

Table 8

Name Description CE4 CE5 CE6 thirteen fourteen Polyester polymer with carboxyl functionality (AV60-70) Polyester polymer 37.4 37.0 37.0 33.3 33.3 Polyester Polyester with Carboxyl Functionality (AV55-68) Polyester polymer 8.6 8.5 8.5 7.7 7.7 Epoxy Type 3 Epoxy hardener 40.3 39.9 39.9 35.9 35.9 Degassing additive 0.3 0.3 0.3 0.2 0.2 Filling additive 1.1 1.1 1.1 1.0 1.0 _TiO2 Non-metallic white pigment 1.5 1.5 1.5 1.3 1.3 Sodium feldspar Filler 4.3 4.3 4.3 3.8 3.8 _BaSO4 Filler 6.5 6.4 6.4 5.8 5.8 PS1 Polyorganosiloxane - - - 10.0 10.0 Tris(hydroxymethyl)aminomethane (THAM) Amino alcohol 1.0 0.9 Dicalcium Phosphate Dihydrate metal phosphate - 1.0 - 0.9 - Aluminum pigment, flake metallic pigment 1.0 1.0 1.0 1.0 1.0

Table 9

Exposure time 5% HCl solution [min] CE1 CE2 CE3 eleven 12 2 ΔL ΔL ΔL ΔL ΔL ΔL fifteen 0.09 -0.01 0.1 0.01 0.02 0.0 thirty -0.3 -0.01 0.1 0.03 0.02 -0.1 60 -2.0 -0.3 -0.5 -0.02 -0.3 -0.9 90 -3.5 -0.8 -1.8 -0.4 -1.1 -2.2 120 -4.6 -1.4 -3.1 -1.0 -2.1 -3.4

Table 10

Exposure time 5% HCl solution [min] CE4 CE5 thirteen 2* ΔL ΔL ΔL ΔL fifteen 0.02 0.02 -0.01 -0.01 thirty 0.04 0.05 0.0 -0.02 60 -0.09 0.01 0.01 -0.05 90 -1.46 -1.0 0.0 -0.4 120 -2.7 -3.8 -0.6 -1.4

*Same as composition 2, but with 1.0 wt. % flake pigment

The results in Tables 9 and 10 show that coatings containing polyorganosiloxane and either amino alcohol or metal phosphate have lower absolute ΔL values than the comparative example without polyorganosiloxane, amino alcohol and metal phosphate. The results in Tables 9 and 10 also show that the presence of an amino alcohol or metal phosphate in combination with the organopolysiloxane further improves the acid resistance of the nonflake pigments present therein compared to the organopolysiloxane alone.

moisture resistance

The results are shown in Tables 11 and 12 below.

Table 11

Humidity test, 40°C CE2 CE3 eleven 12 2 ΔE, 24 hours 0.1 0.16 0.07 0.05 ΔE, 144 hours 3.78 0.31 0.1 0.03 0.13 ΔE, 192 hours stopped 0.28 0.04 0.03 ΔE, 312 hours 0.14 0.2 0.13 0.73 ΔE, 576 hours 0.17 1.07 0.14 2.24 Initial shine 78 95 76 81 88 Maintained shine, 144 hours 100 100 100 100 98 Maintained gloss, 312 hours 100 100 99 95 Maintained shine, 576 hours 100 99 99 80

Table 12

Humidity test, 40°C CE6 thirteen fourteen 2* ΔE, 24 hours 6.34 0.09 0.25 1.23 ΔE, 48 hours 7.79 0.11 3.14 5.83 Initial shine 88 101 95 98 shine, 24 hours 38 101 95 95 shine, 48 hours 21 101 65 39

*Same as composition 2, but with 1.0 wt. % flake pigment

The results in Tables 11 and 12 show that the polyorganosiloxane-containing powder coating compositions have improved moisture resistance. These results also show that the presence of an amino alcohol or metal phosphate in combination with the organopolysiloxane further improves the moisture resistance of both the non-flake and flake pigments present therein compared to the organopolysiloxane alone.

Claims (56)

1. A particulate coating composition comprising: (i) 30-60% by weight of at least one polyester polymer; (ii) 30-60% by weight of at least one hardener; (iii) at least 0.1 wt.% at least one metallic pigment, where the specified metallic pigment contains a metal in elemental form or in the form of an alloy; and (iv) at least one polyorganosiloxane. 2. The composition of claim 1 which is a powder coating composition. 3. A composition according to claim 1 or 2, wherein said metallic pigment is susceptible to corrosion. 4. Composition according to any one of paragraphs. 1-3, in which said metallic pigment contains Al or Sn. 5. Composition according to any one of paragraphs. 1-4, in which said polyorganosiloxane has a softening point of at least 40°C. 6. Composition according to any one of paragraphs. 1-5, wherein said polyorganosiloxane contains OH and/or OR substituents, where R is C _1-24 alkyl or C _6-24 aryl. 7. Composition according to any one of paragraphs. 1-6, in which said polyorganosiloxane contains 1.0-15 wt.% OH groups based on the total mass of polyorganosiloxane. 8. Composition according to any one of paragraphs. 1-7, in which said polyorganosiloxane contains a repeating block of formula (I):

, where each R ¹ is independently a monovalent organic group; each X is independently an OH, OR', or O– group; each R' is independently C _1-24 alkyl or C _6-24 aryl and and equal to 0 or 1. 9. Composition according to any one of paragraphs. 1-8, in which said polyorganosiloxane has the general formula (III): M _m D _n T _o Q _p (III), where M is the end group with the general formula (IIIa) R ³ R ⁴ R ⁵ SiO _1/2 (IIIa), D is a difunctional group with the general formula (IIIb) R ⁶ R ⁷ SiO _2/2 (IIIb), T is a trifunctional group with the general formula (IIIc) R ⁸ SiO _3/2 (IIIc), Q is a block with the general formula SiO _4/2 , where each of R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ is independently selected from a monovalent organic group, hydroxyl group or alkoxy group containing 1-10 C atoms, preferably 1-4 C atoms, and not more than 75% of all these groups are hydroxyl or alkoxy groups, m is an integer 0–20, n is an integer 0–1000, o is an integer 0–30, p is an integer 0–20 and m+n+o+p is an integer equal to at least 2. 10. The composition according to any one of paragraphs. 1-9, wherein said polyorganosiloxane is a silsesquioxane. 11. The composition according to any one of paragraphs. 1-10, additionally containing a silane, metal phosphate, metal borate and/or amino alcohol. 12. Composition according to claim 11 containing an amino alcohol. 13. A composition according to claim 11 or 12, wherein said amino alcohol has one amino group and 2 or more hydroxyl groups. 14. Composition according to claim 11 containing metal phosphate. 15. A composition according to claim 11 or 14, wherein said metal phosphate is an orthophosphate. 16. A container containing a composition in the form of particles according to any one of paragraphs. 1–15. 17. A kit for preparing a particulate coating composition according to any one of claims 1 to 15, comprising: (i) a first container containing at least one polyester polymer, at least one hardener, and at least one polyorganosiloxane; (ii) a second container containing at least 0.1 wt.% mentioned at least one metallic pigment based on the total weight of the contents of the kit containers, where the specified metallic pigment contains a metal in elemental form or alloy form; and (iii) instructions for mixing at least one polyester polymer, at least one hardener, at least one polyorganosiloxane, and at least 0.1% by weight of at least one metallic pigment. 18. The process for preparing a composition in the form of particles according to any one of paragraphs. 1–15 containing: (i) mixing at least one polyester polymer, at least one hardener and at least one polyorganosiloxane to form a mixture; (ii) extruding said mixture to form particles and (iii) adding said at least 0.1% by weight of at least one metallic pigment to said particles. 19. Coating, preferably a cured coating containing a particulate composition according to any one of paragraphs. 1–15. 20. The coating obtained by spraying and curing the composition in the form of particles according to any one of paragraphs. 1–15. 21. Substrate coated with a composition in the form of particles according to any one of paragraphs. 1-15 or a coating according to item 19 or 20. 22. A method for coating a substrate with a particulate composition according to any one of paragraphs. 1–15 containing: i) applying said particulate composition to said support, and ii) optionally curing said composition in particulate form. 23. The use of a composition in the form of particles according to any one of paragraphs. 1-15 to cover the substrate.