NL1009254C2 - Heat curing polymeric powder coating compositions for coating metal and other substrates have a content of unsaturated long chain fatty acid or ester to improve adhesion and appearance after baking - Google Patents

Abstract

Incorporation of unsaturated fatty acids or esters of these into polymer based powder coatings to improve adhesion and appearance after stoving. Powder coating lacquers or binders for pigmented powder coatings which comprise one or more polymers (I) and 20-80 wt. % on total weight of binder of an unsaturated fatty acid (II) or an ester of this.

Description

Title: Powder paint

The invention relates to a powder paint and a binder therefor.

In recent years, there has been an increasing demand for low-solvent paint and coating systems. This question 5 is largely motivated by the desire to strongly limit the emission of volatile hydrocarbons (VOC) from paint. Powder paints are of great interest in this context, as these products are solvent-free.

10 Although powder paint is mainly used for coating metal objects, such as furniture, cars, utensils and the like, it is also possible to coat plastics (plastics) and wood. In addition to the obvious advantage of no or only negligible emission of volatile organic solvents, powder paint coatings provide good mechanical and chemical protection of a surface. In addition, a powder paint is quick and easy to apply and can be further processed. Powder paint 20 can be applied electrostatically to a surface, but also by spraying or dipping. The applied layer is then liquefied in an oven or 'cured' at a relatively high temperature (approximately 150-250 ° C) in an oven. For a general description of powder paints, reference can be made to T.A. Misev, "Powder Coatings, Chemistry and Technology", John Wiley & Sons, Chichester, 1991.

A powder paint typically includes one or more pigments, a binder and a number of additives, such as UV stabilizers and flow improvers. If no pigment is included in the paint, this is called a powder coating. Choosing a suitable binder ensures that the powder paint is a stable powder.

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Other important properties of a powder paint which are determined by the choice of the binder are the texture, the adhesion to a substrate, the flowing properties, elasticity and the like.

Binders for powder paints often consist of a polymer with reactive, functional groups, such as carboxyl, hydroxyl and / or amine groups. Due to the heat treatment, the molecules of the polymer are linked together via these functional groups. In many cases an additional substance, a cross-linking agent, is used here. However, it is also possible for the coupling to take place via an oxidative process, for example under the influence of air.

The invention aims to provide a binder system for a powder paint, which system imparts to the powder paint improved external properties, such as texture and gloss, and improved physical properties, such as adhesion, elasticity and flowability.

Surprisingly, it has been found that said goals can be achieved by incorporating an unsaturated fatty acid or an ester thereof into a powder coating or powder paint binder. The invention therefore relates to a powder coating or binder for a powder paint comprising one or more polymers and from 20 to 80% by weight, based on the weight of the binder, of an unsaturated fatty acid or an ester thereof.

It has been found that an unsaturated fatty acid or an ester thereof in a powder paint binder very favorably affects both the appearance and the adhesive properties of a powder paint. Due to the presence of an unsaturated fatty acid or an ester thereof, a binder for a powder paint is more flowable.

For the purposes of the invention, a fatty acid is understood to mean a compound consisting of a carbon chain with a carboxylic acid group. The carboxylic acid group of the fatty acid is preferably a terminal carboxylic acid group. The chain length of the carbon chain is preferably from 8 to 30 carbon atoms, particularly preferably from 18 to 24 carbon atoms.

According to the invention, an unsaturated fatty acid 5 is used, which means that the alkyl chain of the fatty acid comprises one or more double (C = C) bonds. The unsaturation preferably corresponds to an iodine number according to Wijs, as defined in NEN-ISO 3961: 1996, of at least 75, particularly preferably at least 150. The upper limit of the unsaturation is not critical. For practical reasons, according to Wijs, the iodine value will generally not exceed 300.

As ester of a fatty acid, any, preferably natural, ester of the above-described fatty acid can be used. Suitable esters are based on one or more fatty acids of the above-described nature and an alcohol. The nature of the alcohol is not critical; a wide variety of alcohols can be used. It has been found that both monoalcohols, such as methanol, ethanol or octanol, and polyalcohols, such as glycerol and glycols, including polyethylene glycol, can be used. It is preferably a glycerol ester of a fatty acid. These esters are commonly referred to as fats or oils. Mono-, di- and triesters (mono-, di-25 or triglycerides) are eligible, where different fatty acids can be linked to one glycerol molecule.

It is preferred to use a natural fatty acid or a natural ester of a fatty acid. By this is meant fatty acids and esters of fatty acids which can be obtained from animal and vegetable sources by means of physical processes, such as pressing or extracting.

Suitable examples of fatty acids or esters thereof on which a binder for a powder paint is based, according to the invention, include calendula oil, fish oil, palmitic acid, linseed oil, rapeseed oil, corn germ oil, sunflower oil and the like . Furthermore, boiled oils, such as poly- or oligomers based on fatty acid esters, such as boiled linseed oil, sunflower oil or mixtures thereof, are also very suitable. These oils appear to be extremely suitable for imparting favorable properties to a powder paint binder. In addition, they are economical to use in terms of availability and price. It is also possible to use mixtures of 10 fatty acids, fats and / or oils.

Preferably, the unsaturated fatty acid or its ester on which a powder coating or a powder paint binder of the invention is based is an activated fatty acid or an ester thereof. It has been found that an activated compound, in the form of a hydroperoxide fatty acid or an ester thereof, facilitates the formation of a powder paint. In a hydroperoxide fatty acid or ester thereof, one of the two carbon atoms of at least one of the unsaturated bonds (C = C) is substituted with a hydroperoxide group. It has been found that a greater number of hydroperoxide groups in the fatty acid or its ester leads to a simpler and faster preparation of the binder.

The amount of hydroperoxide groups in the fatty acid or its ester can be expressed in terms of a hydroperoxide number, as defined in NEN-ISO 6343: 1980. The fatty acid or its ester used preferably has a high hydroperoxide number. Extremely suitable fatty acids or esters thereof have a hydroperoxide number of at least 200. The upper limit of the hydroperoxide number of the fatty acid or its ester is determined by practical considerations and will usually not exceed 1500. The use of fatty acids or esters has been found. thereof having a hydroperoxide number within said limits results in a binder with which a powder paint with good powder stability and high curing speed can be prepared.

Activation of the C = C bonds of the fatty acid or its ester by the provision of hydroperoxide groups can be carried out in various ways. Possible ways are based on blowing an unsaturated fatty acid or its ester with an oxygen-containing gas. These ways are described in R.A. Hancock et al., Prog. Org. Coatings, 17 (1989), 321 and in 10 C.H. Hare, Paintindia, 59 (1994).

Another suitable method is based on an emulsion of the fatty acid or its ester in water. This emulsion is then flown at elevated temperature (50-80 ° C) in a closed vessel with an oxygen-containing gas, such as oxygen or air. The hydroperoxide number can be set by choosing suitable values for the temperature, time and pressure and the amount of oxygen flowing through. It is possible to use a catalyst, such as iron or an iron-EDTA complex, in the activation. An alternative method is based on the enzymatic application of hydroperoxide groups. Other ways of applying hydroperoxide groups known to those skilled in the art can also be used.

As mentioned, the unsaturated fatty acid or its ester according to the invention is present in the binder in an amount of from 20 to 80% by weight, preferably from 50 to 70% by weight, based on the weight of the binder.

Any polymer which can be prepared in an addition polymerization reaction and which can be used in a binder for a powder paint is suitable as a polymer for a binder according to the invention. Both homopolymers and copolymers can be used. Classes of monomers that can make up the polymer include acrylic monomers, such as,) * 2 5 4 6 alkyl (meth) acrylates having from 1 to 8 carbon atoms, dialkyl maleates, dialkyl fumarates, vinyl monomers, such as vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl-2 ethylhexoate, vinyl stearate, vinyl laurate, vinyl versatate, vinyl ethers, vinyl chloride and vinyl acetate, and olefins such as ethylene, propylene, isobutylene, butadiene, vinyl toluene, styrene, α-methylstyrene, p-methylstyrene and acrylonitrile. Preferably, a polymer is used which has a weight average molecular weight of at least 25000. Polymers meeting the above conditions provide a binder that imparts extremely suitable properties to a powder paint.

In addition to the unsaturated fatty acid or its ester and the one or more polymers, the binder may comprise a conventional additive. Examples of common additives are stabilizers, such as UV stabilizers, dispersants, emulsifiers, buffers, surfactants and the like.

The invention further relates to a process for the preparation of a binder as described above. According to this method, a mini-emulsion is formed from one or more monomers, the unsaturated fatty acid or its ester and any additives in the desired proportions. For a general description of mini-emulsions and conducting a polymerization reaction therein, reference may be made to P.A. Lovell, M.S. El-Aasser (eds.), "Emulsion Polymerization and Emulsion Polymers", John Wiley & Sons, Chichester, 1997. The nature and number of the monomers will depend on the desired polymer in the binder.

The emulsion is formed by high shear mixing, for example using conventional emulsification techniques such as stirring, mixing or homogenizing.

A surfactant and a co-surfactant, often referred to as 1 5 4 7 hydrophobic, are used as additives to form a homogeneous mini-emulsion. Suitable surfactants are non-ionic and anionic surfactants. Examples of surfactants include alkyl carboxylic acids, alkyl sulfates, alkyl sulfonates, alkyl phosphates, alkyl amines, alkyl aryl sulfonates, alkyl polyethylene glycol ethers, alkyl aryl polyethylene glycol ethers, and the like. Preferably anionic surfactants are used. A co-surfactant or hydrophobic is usually a long carbon chain alkane or alcohol, for example longer than 8 carbon atoms. Suitable co-surfactants are, for example, hexadecane, dodecane, hexadecanol and cetyl alcohol.

In addition, it can be advantageous to add a buffer. Examples of suitable buffers include carbonate buffers, such as sodium hydrogen carbonate, and phosphate buffers.

An addition polymerization reaction is then carried out in the obtained mini-emulsion in the usual manner to obtain the desired polymer. For this purpose an initiator is added to the emulsion. As initiator, any initiator customary in addition polymerization reactions can be used. Examples of these include Fe-EDTA complexes, persulfates, hydrogen peroxide, peroxides and azo compounds.

The temperature during the polymerization is preferably between -15 and 100 ° C, particularly preferably between 0 and 90 ° C. When operating at a temperature below 0 ° C, it is advantageous to conduct the polymerization in the presence of an anti-freeze, such as glycol. The polymerization is preferably carried out under an inert atmosphere, for example under nitrogen pressure. The progress of the reaction can be monitored using known techniques. The skilled person is able, on the basis of his normal professional knowledge, to assess when the desired degree of polymerization has been reached.

In order to vary the properties of a powder paint, it may be desirable to combine the properties of 1009254 different polymers in one powder paint system. A binder created by combining different polymers is referred to as a hybrid binder. An example of a hybrid binder is the combination of an acrylic polymer and a polyester. A powder paint based on this binder combination has an improved abrasion resistance compared to a powder paint in which only an acrylic polymer is used as a binder, and a higher mechanical stability compared to a powder paint in which only a polyester is used as a binder. Other properties of the powder paint, such as the adhesive properties, the texture or the gloss, can also be added to the binder by combining polymers.

It is one of the advantages of the present process that it is possible to combine the properties of more than one polymer in the binder. For this purpose, the necessary monomers for the various desired polymers can be simultaneously emulsified in the unsaturated fatty acid or its ester. Then, an addition polymerization reaction is carried out in the manner described above. However, it is also possible to include an already formed oligomer or polymer in the mini-emulsion of the unsaturated fatty acid or its ester and the monomer from which another polymer is prepared. Care must be taken here to obtain a homogeneous mini-emulsion in order for the addition polymerization reaction to proceed smoothly.

It will be clear that the invention also relates to a powder paint comprising the above-described binder a pigment. In fact, all pigments customary in powder paints can be included in the powder paint. Different pigments customary for dispersion paints can also be included.

The choice of a particular pigment will mainly depend on. : i 9 u -I%) '1 9 the desired color of the paint and the nature of the surface to which the paint is to be applied. The person skilled in the art will otherwise be perfectly able to match the nature of the binder according to the invention to the pigment required in the powder paint.

Examples of suitable pigments include both organic and inorganic pigments. In particular, titanium dioxide, iron oxides, chromium oxide, carbon black, lime and azo pigments can be mentioned. For other examples of suitable pigments, reference can be made to T.C. Patton, Pigment Handbook, John Wiley & Sons, New York, 1973.

The amount of binder in a powder paint according to the invention will usually be between 10 and 100, preferably between 20 and 80% by weight, based on the weight of the powder paint.

The powder paint can conveniently be prepared by mixing the binder as described above with a dispersion of the pigment in water. In such a dispersion, often referred to as "mill-20 base", the pigment will usually be present in a dilute amount such that the so-called pour point is reached. Pour point refers to the point at which a pigment paste becomes liquid. This point can be ascertained in that the pigment paste transitions from a dull paste into a more liquid, glossy substance. The amount of pigment in a mill base will usually be between 10 and 60% by weight, based on the weight of the dispersion. The mixture of binder and dispersion can then be homogenized and dried, eg by freeze-drying, spray-drying or supercritical drying, to form a fine, dry powder. This powder can be applied to a surface of a material such as wood, metal, glass, plastic (plastic) and the like in any manner usual for powder painting. Examples of suitable methods for applying the powder paint include electrostatic application, dipping and spraying. In this context, reference can again be made to the aforementioned T.A. Misev, "Powder Coatings, Chemistry and Technology", John Wiley & Sons, Chichester, 1991.

The invention will now be further elucidated by means of the following examples.

Sunflower oil with a hydroperoxide number of 1500 10 (+/- 10%) was mixed with a 1 high-solid alkyd resin (a prepolymerized oil, see Ullmann's Encyclopedia of Industrial Chemistry, Vth ed., 1985, VCH, Weinheim, "Alkyd Resins, vol. Al, pp. 409-423, in this case Uralac AH98 DSM, oil length about 83%, content of isophthalic acid about 15 13%) in a weight ratio of about 1: 3, so that an average hydroperoxide number between 400 and 500 was obtained .

The resulting mixture was mixed in a 1: 1 weight ratio with ethyl methacrylate previously purified by distillation. Then a suspension was prepared of 8 grams of millipore Q, 6.5 mM SDS (sodium dodecyl sulfate surfactant), 20 mM NaHCO 3 (buffer) and 22.5 mM hexadecane (co-surfactant)). This suspension was added to the mixture of the oil, the alkyd resin and ethyl methacrylate in a ratio of 20 wt% solids based on water.

The resulting two-phase system was emulsified under cooling with an ice bath using an ultrasonic rod (mode 7, 100% duty cycle, 4 minutes) and homogenized at a pressure of 800 bar (second stage 80 bar, at least 4 circulations). The emulsion obtained in this way was transferred to a 300 ml reactor (heating reactor at 30 ° C), after which SFS was added from an SFS stock solution (2.5 M SFS (sodium formaldehyde sulfoxylate)) in such an amount that the final concentration SFS in 11 the emulsion was 7.5 mM based on the water present in the reactor.

After stirring for 20 minutes under a nitrogen atmosphere, a polymerization reaction was initiated by adding an iron-EDTA complex (weight ratio iron: EDTA was 1: 2.2). The course of the reaction was followed by taking samples from the emulsion and allowing it to dry after adding a few drops of 5% hydroquinone solution. The weight gain was a measure of the conversion of monomer ethyl methacrylate to polymer. Also, the molecular weight of the forming polymer and the particle size of the resulting latex during the reaction were followed by characterizing a few drops of the emulsion at different times, each time stopping the polymerization reaction in the drops by adding hydroquinone solution. After about 5 hours, the polymerization reaction was completed and a latex having a solid content of 22.1% by weight was obtained.

After freeze-drying the latex, a dry powder was obtained. This powder was sprayed onto a metal substrate which was then heated to 140 ° C in an oven. After cooling, a transparent film had formed.

Example II

The CPVC (Critical Pigment Volume Concentration) was determined for four pigments (all available from Bayer). For this, the oil absorption values (OA oil) and the densities (p) of the four pigments were used as mentioned in the product information of the pigments. The formula used is: CPVC = 1 / (l + OA * p / 93.5).

The pigments used were the following: white: Bayertitan R-KB (tons no. A / 99) green: Chromoxidgrün GN-M Standard (Lot No 137/94) red: Bayerferrox 130 M Standard 84 (Auftrag 251408 D6) 35 yellow: Bayerferrox 915 Standard 95 (Suftrag 548 529 H6).

1009254 12

Table 1 shows the different parameters.

Table 1

Pigment p (g / cmj) 0A oil CPVC

(g / 100g)

White 471 26 0.47

Green 5.2 11 0.62

Red 5.0 26 0.42

Yellow 4.0 32 0.42 5 ——

So-called mill bases were formed from the four pigments. That is, an amount of water was added to the pigment powders that the flow point was reached. The amounts of pigment in the mill-base 10 for the pigments used are shown in Table 2.

Table 2

Pigment Amount of pigment in mill-base (wt%) _____ _

Green 34

Red 68

Yellow 15

Of the four mill bases, together with the binder prepared according to Example I, powder paints were prepared. To this end, mill base was added to the binder in a ratio calculated as a ratio of the weight of the mill base to the binder solids content (22.1 wt%). The stated ratio was 15% by weight for the pigments white and red and 54% by weight for the pigments yellow and green. The four mixtures of the pigments and the binder were found to be stable emulsions which were frozen at -80 ° C and then lyophilized.

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The resulting powders were ground for a few minutes in a steel mill universal mill set at 20,000 rpm. The ground powders were sprayed as a free flowing powder and applied to a glass substrate. The applied powders were pressed and cured in an oven at 140 ° C. a stable, hard, colored film was obtained.

Example III

Linseed oil (Iodine number 180) was mixed 1: 1 (w / w) with ethyl methacrylate. Then, a suspension, buffer and co-surfactant were added as described in Example I. The mixture was ultrasonically emulsified at about 2 ° C and homogenized at a pressure of 170 bar (second stage 80 bar, 5 circulations). The mixture was then placed in a reactor (30 °), after which SFS was added to a concentration of 7.5 mM.

After stirring for 20 minutes under nitrogen, the polymerization reaction was initiated by adding Fe-20 EDTA complex and 5 mM butyl peroxide. The mixture was stirred at 50 ° C for 15 hours. .

A latex was obtained, which was spray dried into a dry powder. This powder was sprayed on a glass plate and then heated to 150 ° C in an oven. After cooling, a transparent hard film had formed.

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Claims (9)

A powder coating or binder for a powder paint comprising one or more polymers and from 20 to 80% by weight, based on the weight of the binder, of an unsaturated fatty acid or an ester thereof. The binder of claim 1, wherein the fatty acid comprises a carbon chain of 8 to 30 carbon atoms. The binder of claim 1 or 2, wherein the ester of the fatty acid is a glycerol ester. Binder according to any of the preceding claims, wherein the fatty acid or its ester has a hydroperoxide number of at least 200. Binder according to any of the preceding claims, comprising one or more polymers based on one or more monomers selected from the group of acrylic monomers, such as 15 alkyl (meth) acrylates with from 1 to 8 carbon atoms, dialkyl maleates, dialkyl fumarates, vinyl monomers, such as vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl 2-ethylhexoate, vinyl stearate, vinyl laurate, vinyl versatate, vinyl ethers, vinyl chloride and vinyl acetate, and olefins such as ethylene, propylene, isobutylene, butadiene, vinyl toluene, styrene, a-methyl styrene, p-methyl styrene . 6. A process for preparing a binder according to claims 1-5, wherein a mini-emulsion is formed from one or more monomers and a fatty acid or an ester thereof, after which the monomers are polymerized in an addition polymerization reaction. Powder paint comprising a pigment and a binder according to any one of claims 1-5. 8. Substrate provided with a coating of a powder paint according to claim 7. 9. Use of an unsaturated fatty acid or an ester thereof in a powder paint binder to improve the appearance and adhesive properties of the powder paint. • if - * /! ·; j; · <^ COOPERATION TREATY (PCT) REPORT ON NEWNESS RESEARCH OF INTERNATIONAL NATIONAL APPLICATION TYPE LICENSE Identification of the applicant or of the authorized Nw 2070 Dutch application no. request for an examination of international type Granted by the International Research Authority of the USA to the request for an examination of international type No SN 31227 EN I. CLASSIFICATION OF THE SUBJECT (when using different classifications, indicate all classification symbolsI According to the International classification (IPC) Int.Cl.6: C 09 D 5/03, C 08 F 291/00 II AREAS OF TECHNIQUE EXAMINED ____ Minimum Documentation Examined __Classification System_j_ Clamfication Symbols Int.Cl.6: C 09 D, C 08 F Other Examined documentation than aa minimum documentation insofar as such do Comments on the areas under investigation are presented "L I I CANNOT EXAMINE CERTAIN CONCLUSIONS (remarks oo supplement sheet) lv 'LACK OF UNITY OF INVENTION (remarks oo supplementinosoladl:, llm ° 1' - * Ι ', Λ, ΖΟιίιΙ 07 l