WO2008031589A2

WO2008031589A2 - Powder paint composition

Info

Publication number: WO2008031589A2
Application number: PCT/EP2007/007973
Authority: WO
Inventors: Antonia Urmanova; Robert Van Den Berg Jeths
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2006-09-14
Filing date: 2007-09-13
Publication date: 2008-03-20
Anticipated expiration: 2009-03-14
Also published as: WO2008031589A3

Abstract

A thermosetting powder paint binder composition comprising thermosetting polyamide, a further polymer that is at least partly incompatible with the polyamide and crosslinker(s). The present invention further relates to processes for producing such compositions, the use of such compositions in powder paint compositions, and to substrates coated with such compositions.

Description

POWDER PAINT COMPOSITION

The present invention relates to a thermosetting powder paint binder composition comprising a polymer. The present invention further relates to a cross-linker and a powder coating with adjustable gloss levels based on said powder paint binder composition.

The semi- and low gloss powder paints are an important segment of the powder coating market. Low gloss coatings reduce the light reflection from the coated surface and visibility of surface defects like pinholes. For the indoor segment semi- and low gloss coatings play a major role in the design and styling trends of household appliances and metal furniture. For the outdoor segment coatings with reduced gloss are desirable for use with building materials, architectural window framing, motor vehicles and other traffic applications.

Reduction in gloss occurs when surface irregularities or imperfections, which are equal or larger in size compared to the incident wavelength decrease specular reflection and increase diffuse scattering. The intensity of reflection depends on the degree of surface-smoothness. Mirrors, for example, are recognised as high gloss surfaces as they reflect light with high clarity. In contrast, when micro-rough, irregular or micro textured paint films scatter light, only a reduced amount of light is reflected. In general, the rougher the surface the lower degree of gloss.

There isn't universally recognized classification for 'gloss'. However, the following general categories can be defined based on the gloss ranges at 60° as measured by ASTM D 523/70:

Gloss > 80% Semi gloss(semi matt) 40-80%

Low gloss(matt) < 40%

A reduced gloss powder-coated surface will result when incompatible or uniformly distributed matting additives have been introduced in the powder paint formulation. However, the use of large amounts of mineral matting additives such as silica and talc can result in limitations to the mechanical properties of the coating and excessive wear on the equipment. The use of incompatible organic additives such as waxes and cellulose derivatives can lead to insufficient UV and yellowing resistance, loss of adhesion, and poor mar or scratch resistance.

An alternative option for producing a reduced gloss coating is to use the dry blend technique. That is, mixing two powder coating paints with different reactivity's to each other. The disadvantages of dry blends include poor batch-to-batch reproducibility of gloss and appearance plus higher manufacturing costs. A further disadvantage is that the over-sprayed powder can only be re-used in combination with controlled, continuous dosing of virgin powder.

The "one-shot matt" technique is able to achieve reproducible semi- or low gloss powder paint compositions. In contrast to the dry blend process, in this technique the components of the binder formulation are usually subjected to a single extrudate.

The binders in a one-shot matt paint composition usually contain amorphous polyester and at least one other component that is at least partly incompatible with the amorphous polyester polymer. For example, (semi)-crystalline polyester, acrylic or methacrylic polymers, cross-linker or mixture of cross-linkers may be used.

Semi-crystalline resins can be expensive increasing the cost of the coating. Furthermore, (semi)-crystalline resins can have a low Tg and low melting viscosity and cause a sharp drop in gloss at phase separation point during the cure. The low melting viscosity of the (semi)crystalline component complicates the extrusion of the powder paint binder. A further disadvantage is that the relatively low Tg lowers the Tg of the paint composition and compromises the powder stability of the paint.

Coating formulations with acrylic and methacrylic polymers can give acceptable low gloss coatings. One major disadvantage of these systems is that the incompatibility between the acrylics and the polyesters is so severe that the slightest contamination leads to cratering. In addition, the gloss levels of these systems are not really adjustable.

Low gloss powder coatings can also have inadequate mechanical properties. This is especially the case when the gloss level is les than 40% at 60°. Even more so when the gloss level is less than 30% at 60°. It is the object of the present invention to provide a thermosetting paint binder composition which has reproducible, adjustable gloss levels and/or superior mechanical properties. The compositions of the present invention are particularly attractive because of their flexibility to allow the user to adjust the gloss level to suit the application. The present compositions are particularly useful for low or semi-gloss applications.

One embodiment of the present invention relates to thermosetting powder paint binder compositions comprising thermosetting polyamide, a second polymer that is at least partly incompatible with the polyamide, and crosslinker(s).

A further embodiment of the present invention relates thermosetting powder paint compositions comprising carboxyl or hydroxyl functional polymer, thermosetting polyamide, and crosslinker(s).

A further embodiment of the present invention relates thermosetting powder paint compositions comprising polyamide that have a gloss of less than 80%, preferably less than 60%, more preferably less than 40%, at 60° as measured by ASTM D 523/70. The polyamide is preferably a thermosetting polyamide.

The carboxyl or hydroxyl functional polymer for use herein is preferably selected from polyesters and/or polyacrylates. Preferably the polymer is selected from polyesters, more preferably from carboxylic acid group-containing polyesters. Among the suitable polyesters are those based on a condensation reaction of linear aliphatic, branched aliphatic and cyclo-aliphatic polyols with aliphatic, cyclo-aliphatic and/or aromatic poly carboxylic acids and anhydrides. The ratio of polyol and acids or anhydrides is such that there is an excess of acid or anhydride over alcohol (so as) to form a polyester which has free carboxylic groups.

Polyesters for use herein can comprise units of, for example, isophthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-oxybisbenzoic acid, 3,6-dichloro phthalic acid, tetrachloro phthalic acid, tetrahydro phthalic acid, trimellitic acid, pyromellitic acid, hexahydro terephthalic acid (cyclohexane dicarboxylic acid), hexachloro endomethylene tetrahydro phthalic acid, phthalic acid, azelaic acid, sebacic acid, decane dicarboxylic acid, adipic acid, succinic acid, maleic acid and fumaric acid. These acids may be used as such, or, in so far as available as their anhydrides, acid chlorides or lower alkyl esters. Preferably, the polyester is based on at least one of isophthalic acid and/or terephthalic acid. Trifunctional or higher functional acids may be used also. Examples of suitable such acids include trimellitic acid or pyromellitic acid. These tri- or higher functional acids may be used as end groups or to obtain branched polyesters.

Hydroxy carboxylic acids and/or optionally lactones can also be used, for example, 12-hydroxy stearic acid, hydroxy pivalic acid and ε-caprolactone.

Monocarboxylic acids may also be used if desired. Examples of these acids are benzoic acid, tert. -butyl benzoic acid, hexahydro benzoic acid and saturated aliphatic monocarboxylic acids.

Useful polyalcohols, in particular diols, reactable with the carboxylic acids to obtain the polyester include aliphatic diols. Examples are ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, butane-1 ,2-diol, butane-1 ,4-diol, butane-1 ,3-diol,

2,2-dimethylpropanediol-1 ,3 (neopentyl glycol), hexane-2,5-diol, hexane-1 ,6-diol, 2,2-bis-(4hydroxy-cyclohexyl)-propane (hydrogenated bisphenol-A),

1 ,4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol, 2,2-bis[4-(2-hydroxy ethoxy)-phenyl] propane, the hydroxy pivalic ester of neopentyl glycol, 2-ethyl, 2-butyl propanediol-1 ,3 (butylethylpropane diol), 2-ethyl, 2-methyl propanediol-1 ,3 (ethylmethylpropane diol) and 2-methylpropanediol-1 ,3 (MP-Diol).

Tri- or higher functional alcohols may be used in order to obtain branched polyesters. Examples of suitable such polyols include glycerol, hexanetriol, trimethylol ethane, trimethylol propane tris-(2-hydroxyethyl)- isocyanurate, penta erythritol and sorbitol.

The polyester may be prepared according to conventional procedures by esterification or transesterification, optionally in the presence of customary esterification catalysts for example dibutyltin oxide or tetrabutyl titanate. Preparation conditions and the COOH/OH ratio can be selected so as to obtain end products that have a particular desired acid number and/or a hydroxyl number.

Preferably, the polymer has an acid value between 20 and 200 mg KOH/gram resin and more preferably between 20 and 120 mg KOH/gram resin.

The number average molecular weight (Mn) of the polymer is preferably between about 1 ,000 and about 7,000, more preferably between about 1 ,400 and about 6,000. Preferably the polymer is an amorphous solid at room temperature.

The polymer preferably has a viscosity lower than 200 Pa.s (measured at 16O⁰C, Rheometrics CP 5), more preferably lower than 150 Pa.s. The glass transition temperature, Tg, of the polymer is preferably in the range between 20⁰C and100°C, more preferably from about 35⁰C to about 85⁰C, even more preferably from about 4O⁰C to about 75⁰C.

The polyamide herein may be any suitable polyamide or mixture of polyamides. For example, it may be an amorphous or a (semi)crystalline polyamide. Preferably the polyamide is an amorphous polyamide. As used herein "amorphous" means that the amorphous polyamide does not show a sharply defined melting on crystallization peak on a second DSC scan at a rate of 5°C/min. Generally, an amorphous polymer and/or polymer composition is characterized by a high degree of transparency (clarity) and a lack of a sharply defined melting point. With amorphous is meant here that the amount of crystallinity calculated from the DSC-measurement is less than 10%, preferably less than 5% and more preferably less than 1 %.

The polyamide preferably contains functional end groups such as for example carboxyl groups, epoxy groups, anhydride groups, hydroxyl groups, amino groups, acetoacetonate groups, phosphoric acid groups, phosphorous acid groups and/or thio groups.

In a preferred embodiment the polyamide is a carboxyl-, a hydroxyl- or an amine functional polyamide. More preferably, the polyamide contains functional carboxyl groups.

The amorphous polyamide preferably comprises the polycondensation reaction product (or residue) of at least one diamine component and at least one dicarboxylic acid component. It will be clear to the man skilled in the art that instead of, or in combination with, the dicarboxylic acid its anhydride can be used. Unless otherwise specified herein reference to a dicarboxylic acid is also meant to include anhydride.

The amorphous polyamides herein can be based on one type of amine and one type of carboxylic acid or can be based on one type of amine combined with more than one type of carboxylic acid or can be based on one type of carboxylic acid with more than one type of amine or can be based on a combination of more than one type of amine with more than one type of carboxylic acid. It is preferred that the polyamide is based on 2 to 4 diamines and 1 to 3 dicarboxylic acids.

Suitable dicarboxylic acids include, for example, dicarboxylic acids having from 3 to about 40 carbon atoms, and more preferably dicarboxylic acids selected from aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, and/or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms. The dicarboxylic acids may be branched, nonlinear or linear. Preferably, the dicarboxylic acids are branched or non-linear. Examples of suitable dicarboxylic acids include, for example, phthalic acid, isophthalic acid, terephthalic acid, 1 ,4-cyclohexanedicarboxylic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, phenylenedi (oxyacetic acid), sebacic acid, succinic acid, adipic acid, glutaric acid and/or azelaic acid.

The diamine can be any suitable diamine. For example, it can be of an aliphatic, cycloaliphatic, aliphatic-aromatic, or aromatic nature. The diamine component may comprise an aliphatic diamine having for example 2 to 12 carbon atoms. The aliphatic diamines may also contain aromatic groups in the molecule. With aromatic amines the glass transition temperature of the polyamide can be very high. It is preferred to use aliphatic and aromatic-aliphatic amines. With aliphatic amine is meant a compound in which the amine-group is directly coupled to an aliphatic chain. With aromatic amine is meant a compound in which the amine group is directly coupled to an aromatic ring structure. The aliphatic diamines also include cycloaliphatic diamines such as, for example, piperazine. Examples of suitable aliphatic diamines include, for example, isophorondiamine, 1 ,2-ethylenediamine, 1 ,3-propylenediamine, 1 ,6- hexamethylenediamine, 1 ,12-dodecylenediamine, 1 ,4 cyclohexanebismethylamine, piperazine, p-xylylenediamine and/or m-xylylenediamine. The amine component may also comprise branching components to obtain branched polyamides. Suitable examples include, for example, di-alkylene-triamines such as, for example, di-ethylene- triamine, di-alkylene-tetramines, di-alkylene- pentamines, di-hexamethylene-triamine, poly- functional acids such as, for example, 1 ,3,5-benzene tricarboxylic acid, trimellitic anhydride and pyromelitic anhydride and poly- functional amino acids such as, for example, aspartic acid and glutamic acid.

The polyamide may have, for example, a linear or nearly linear, branched, star or dendritic structure. The present invention is not directed to the use of a polyesteramide as the thermosetting amorphous polyamide. With polyesteramide is meant here and hereinafter a polymer that contains both ester-bonds as well as amide-bonds, where the polyamide according to the invention does not contain ester-bonds.

The composition may also comprise branching components to obtain branched polymers. Suitable examples include di-alkylene-triamines such as di-ethylene- triamine, di-alkylene-tetramines, di-alkylene- pentamines, di-hexamethylene-triamine, poly functional acids such as 1 ,3,5-benzene tricarboxylic acid, trimellitic anhydride and pyromelitic anhydride and poly functional amino acids such as aspartic acid and glutamic acid.

The polyamide may have, for example, linear or nearly linear, branched, star or dendritic structure.

Preferably, the polyamide has an acid number between 20 and 200 mg of KOH/gram of resin (polymer).

According to a further preferred embodiment of the invention the glass transition temperature (T₉) of the polyamide is between 2O⁰C and 200°C. More preferably the glass transition temperature (T₉) is between 40°C and 12O⁰C.

The polyamide preferably has a viscosity lower than 200 Pa. s (measured at 16O⁰C, Rheometrics CP 5), more preferably lower than 150 Pa. s.

Preferably the molecular weight (Mn) of the polyamide ranges between 1000 and 10,000 g/mol, and more preferably between 1400 and 6000 g/mol.

Any suitable crosslinker(s) may be used herein. Preferably the cross-linkers are capable of reacting with carboxyl-functional polymers. Various types of crosslinkers or mixtures of crosslinkers may be used herein. Examples of suitable crosslinkers include triglycidylisocyanurate (TGIC), epoxy resin, a crosslinker containing hydroxylamide group for example PRIMID, aliphatic oxirane, isocyanate, diglycidyl phtalate containing crosslinker, hexamethoxy-methylmelamine (HMMM), glycoluril(derivative), benzoguanamine (derivative), amino resin, phenolic resin

According to a preferred embodiment of the invention the reduced gloss powder binding compositions herein are obtained by mixing the carboxyl or hydroxyl functional polymer, thermosetting polyamide, and crosslinker(s) in a single extrusion. More preferably all the components of the powder paint binder composition are mixed in a single extrusion.

The present invention provides reduced gloss powder coatings which can be obtained with adjustable gloss levels by selecting the ratio between the polymers and the cross- linker. The present invention also provides reduced gloss powder coatings which can be obtained with reproducible gloss levels.

Furthermore, the present invention provides reduced gloss powder coatings having improved mechanical properties at low gloss levels, excellent appearance, good powder stability, solvent resistance, outdoor durability, and/or resistance to yellowing during curing.

Preferably the weight ratio of polymer comprising the carboxyl functional polymer and the thermosetting polyamide to cross-linker ranges between 50:50 and 98:2. More preferably this ratio ranges between 75:25 and 95:5.

The preparation of thermosetting powder coatings in general and the chemical reactions for curing powder paints to form cured powder coatings are described by Misev in Powder Coatings, Chemistry and Technology (1991 , John Wiley) on pp. 42- 54, pp. 148 and 224-226. Test procedures are described at pages 284-300. A thermosetting powder paint binder composition is generally defined as the resinous part of the powder paint composition consisting of polymer and crosslinker(s) and this composition generally contains more than 50 wt.% polymer and less than 50 wt.% crosslinker(s).

In addition to the component mentioned above the present compositions may comprise one or more additives such as, for example, pigment, filler, degassing agent, flow agent and/ or stabilizer. Suitable pigments include inorganic pigments such as titanium dioxide, zinc sulphide, iron oxide and chromium oxide, and also organic pigments such as azo compounds. Suitable fillers include for example metal oxides, silicates, carbonates and/or sulphates. Primary and/or secondary antioxidants, UV stabilizers such as quinones, (sterically hindered) phenolic compounds, phosphonites, phosphites, thioethers, HALS compounds (hindered amine light stabilizers) and aromatic amines, may for example be used as stabilizers. Examples of degassing agents include benzoin and cyclohexane dimethanol bisbenzoate. Examples of flow agents include polyalkylacrylates, fluorohydrocarbons and silicone fluids. Other suitable additives include, for example, additives for improving tribocharging, such as sterically hindered tertiary amines that are described in EP-B-371528.

One preferred additive for use herein is copper halogenides, particularly in combination with at least one other halogenide. Examples of suitable other halogenides include potassium and sodium halogenide, preferably potassium halogenide is used.

The invention further relates to a process for coating a substrate with a thermosetting powder paint composition according to the invention comprising at least the following steps: a. Optionally pre-treating and/or pre-heating the substrate, b. Applying a thermosetting powder paint composition comprising a binder composition as described hereinabove to the substrate, c. Heating the coated substrate from step b) to a temperature and for such a period that the coating is at least partially cured, d. Optionally applying a second cure step.

The process according to the invention is preferably used without the use of step a) and/ or d).

The process can be used in various temperature regimes. The man skilled in the art can readily determine which temperature regime is most suitable for his application.

The process according to the invention can be used to coat all kinds of substrates. Examples of suitable substrates include metal, (galvanized) steel, cast iron, other alloys, glass, ceramic, bricks, plastic, paper, cardboard, cork, solid wood, veneer, chip wood, wood composite material, for example particle board, high, medium or low density fibre board, plywood and other substrates that contain a significant amount of wood.

The present invention also relates to a substrate fully or partially coated with a composition according to the invention or obtained by a process according to the invention. Thermosetting coatings intended for industrial applications are described further in general in Powder Coatings, Chemistry and Technology, Misev, pages 141-173 (1991).

Thermoplastic powder paint compositions comprising a polyamide are disclosed for example at pages 28-34 of Powder Coatings, Chemistry and Technology, Misev,

(1991). However, these thermoplastic powder paint compositions are different from the thermosetting powder paint composition according to the present invention because of, amongst others, the different crosslink mechanism, the different crystallinity and the different molecular weight. Thermoplastic compositions comprising polyamide generally result in coatings that have insufficient or at least decreased hardness.

This invention also relates to the use of the present binder compositions in powder paint compositions, especially in reduced gloss paint compositions.

Powder paints according to the invention can be applied to a suitable substrate in the usual manner, for example by electrostatically spraying the powder onto an earthed substrate and curing the powder paint to a powder coating by exposing the powder paint composition to heat at a suitable temperature for a sufficient length of time. The applied powder can for example be heated in a gas oven, an electric oven or with the aid of infrared radiation or UV-radiation.

The invention will be elucidated with reference to the following non-limiting examples.

Example 1 The preparation of carboxyl functional polvamide resin 1

369,34 grams of isophorone diamine, 708,87 grams of decane dionic acid and 200 grams of water were charged in a 2 liter reaction flask equipped with a stirrer, nitrogen sparge, a temperature control unit and distillation glassware. The reaction mixture was stirred until all the ingredients were dissolved. The mixture was heated slowly to 220⁰C, while the water was distilled off. After reaching the reaction temperature of 220⁰C the mixture was vacuum distilled for 30 minutes, the vacuum was set off and the resin discharged. The obtained resin was an amorphous, crystal clear polyamide having an acid value of 150 mg KOH/gram resin, a Tg of 34,0°C and a viscosity of 35.4 Pa.s at 160⁰C.

Example 2

The preparation of carboxyl functional polvamide resin 2 488,30 grams of isophorone diamine, 615,10 grams of adipic acid and 200 grams of water were charged in a 2 liter reaction flask equipped with a stirrer, nitrogen sparge, a temperature control unit and distillation glassware. The reaction mixture was stirred until all the ingredients were dissolved. The mixture was heated slowly to 220⁰C, while the water was distilled off. After reaching the reaction temperature of 220⁰C the mixture was vacuum distilled for 30 minutes, the vacuum was set off and the resin discharged. The obtained resin was an amorphous, crystal clear polyamide having an acid value of 148 mg KOH/gram resin, a Tg of 76,0°C and a viscosity of 63,0 Pa. s at 160⁰C.

Examples I-X:

The preparation of powder paints:

Three DSM Resins polyester products with the end specifications given in Table 1 were use together with the polyamides according to the Example 1 and 2 for the preparation of the powder paint binder compositions. Beta-hydrxoalkyl amide with trade name

Primid was used as a cross-linker.

' 600 parts binder,300 parts TiO2, 9 parts resiflow PV5, 2.5parts benzoine

Table 1 : End specifications and properties DSM resins products

All components of the powder paint compositions were premixed in dry blender and extruded with Prism at 12O⁰C. The extrudate was cooled, ground and sieved. The sieve fraction smaller than 90 micrometers was used as powder paint.

The exact composition of the powder paints are given in Table 2.

Table 2: Powder coating composition

The powder paint was applied by Corona gun on to aluminium substrate A-36 and cured 10' at 200⁰C in electrical oven.

The various tests were performed according to the following methods:

Reverse impact is determined via ASTM 2794/69

Appearance -The coatings are viewed at in the reflection of a light source and are compare visually.

Flow -The flow is visually evaluated on coated panels according PRA standards.

Gloss is determined via ASTM D 523/70

Gel time is determined via ISO 8130 part 6 at 200⁰C

Powder stability is determined via DIN 2409. Storage stability is determined via DIN 55990-7 at 40 ⁰C

The results of the tested coatings I-X are given in table 3

^*n m - not measured

Table 3 Test results of powder coating paints I-X

Claims

1. A thermosetting powder paint binder composition comprising thermosetting polyamide, a second polymer that is at least partly incompatible with the polyamide, and crosslinker.

2. A thermosetting powder paint binder composition according to Claim 1 wherein the second polymer comprises a carboxyl or hydroxyl functional polymer.

3. A composition according to any preceding claim wherein the polyamide is amorphous.

4. A composition according to Claim 1 or 2 wherein the polyamide is a carboxyl-, a hydroxyl- or an amine functional polyamide.

5. A composition according to any preceding claim wherein the carboxyl or hydroxyl functional polymer is polyester and/or polyacrylate.

6. A composition according to any preceding claim wherein the carboxyl or hydroxyl functional polymer is polyester.

7. A thermosetting powder coating obtained by curing a powder paint composition comprising polyamide wherein the coating has a gloss of less than 80% at 60°.

8. A coating according to Claim 7 wherein the gloss is less than 40% at 60°.

9. A coating according to Claim 7 or 8 wherein the polyamide is amorphous.

10. A coating according to Claim 7-9 wherein the polyamide is a thermosetting polyamide.

11. A coating according to Claim 7-10 wherein the composition comprises carboxyl or hydroxyl functional polymer.

12. Process for coating a substrate with a thermosetting powder paint composition comprising: a. Optionally pre-treating and/or pre-heating the substrate, b. Applying a thermosetting powder paint composition carboxyl or hydroxyl functional polymer, thermosetting polyamide, and crosslinker to the substrate, c. Heating the coated substrate from step b) to a temperature and for such a period that the coating is at least partially cured , d. Optionally applying a second cure step

13. A substrate fully or partially coated with a composition according to Claim 1-6, a coating according to Claim 7-11 or obtained by a process according to Claim 12.

14. Use of the composition according to Claim 1-6 in a powder coating composition.