CA2158529A1 - Curable pulverulent mixtures - Google Patents

Abstract

A curable pulverulent mixture including (A) a compound containing at least two 1,2-epoxide groups which is the reaction product of (A1) a compound having at least two 1,2-epoxide groups per molecule and (A2) a cyclic carboxylic anhydride, and optionally (B) a curing agent, is useful, for example, in adhesive and coating compositions.

Description

-1- 21 ~8529 CURABLE PULVERULENT MIXTURES

Background of the Invention Powder coatings are used, inter alia, for coating metal furniture such as camping equipment, refrigerators, garden furniture, and shelving, and for coating small objects and workpieces of complex shape, bicycles, sewing machines, and other metal articles. It is largely metal articles which are coated by this process, but powder coating technology can also be used to coat plastics, for example.
Compared with other coating processes, powder coating technology has a number of advantages. For instance, powder coating is a solvent-free operation and is thus environmentally friendly and more cost-effective.
The process is also advantageous with regard to waste disposal, workplace safety due to the absence of flammable solvents, industrial hygiene and environmental protection. In addition there is no need to wait for the coats to dry initially. The coated article is conveyed directly to the baking oven, thereby reducing the time expended on the overall coating procedure.
In addition to the production of coatings, powder resins can also be employed as adhesives. This is of advantage if, for example, it is necessary to adhesively bond nonporous materials such as metals from which it is not possible for volatile components to escape subsequently.
However, adhesive systems which are solvent-free and which do not give off elimination products are increasingly being preferred for the processing of porous materials too. These requirements are met by adhesives based on epoxy resins.
Among the heat-curable powder coating systems, it is predominantly epoxy resin combinations which are employed. These epoxy resins are mixed with curing agents, for example with amines, polyamides, acid -2- 21 ~8~29 anhydrides, boron trifluoride complexes, or dicyandi-amide. Many of these mixtures have disadvantages which restrict their industrial application. Both from an environmental standpoint and given economic considerations, there is currently a requirement for coating materials and adhesives which are free from solvent and from elimination products and which can be processed extremely rapidly.
It has now been found in practice that, for many applications, the curing time of the powder mixtures of the prior art is too long, since the reactivity of the known powder mixtures and methods is not sufficiently high. Thus the powder coating mixture should cure fully at the lowest possible temperature in the shortest possible time. A further requirement is that of good storage stability.
The curing of epoxy resins, especially glycidyl ethers, with numerous anhydrides, di- and polyanhydrides and various compounds in combination with anhydrides is known (cf. Lee, Neville, Handbook of Epoxy Resins, McGraw-Hill Book Company, Chapter 12 Acid-Anhydride Curing Agents for Epoxy-Resins).
As long ago as in the published German Patent Application D 7193 (September 4, 1952), resinous condensation products were described which comprise compounds containing ethyleneoxy or propyleneoxy groups in the molecule and polyanhydrides. According to published German Patent Application H 9989 (September 10, 1953) synthetic resins can be obtained by heating polyepoxy compounds which contain at least two glycidyl ether groups and are not derived from phenolic hydroxyl groups with anhydrides of polybasic carboxylic acids.
From among the plethora of patents, further mention may be made, for example, of GB-A 744,388, in which mixtures of epoxy resins and hexachloroendomethylenetetrahydro-phthalic anhydride and the full curing thereof are disclosed, and of GB-A 1,264,647, which discloses the curing of epoxy resins with polycarboxylic anhydrides containing at least one carbocyclic ring in the presence 215852~

of acidic polyesters which themselves contain carbocyclic and/or heterocyclic rings.
According to Patent SU 328134, epoxy block copolymers are prepared by condensation of carboxyl-containing compounds with excess epoxide. In this case, linear polyanhydrides of dicarboxylic acids or acidic polyesters are employed as acid component.

Summary of the Invention Accordingly, it is an object of the invention to provide epoxy compositions of improved storage stability and faster drying time.
It is also an object of the invention to provide methods of making and using such compositions.
It has now surprisingly been found that it is possible, by using specific epoxide compounds, to prepare powder mixtures which are stable on storage and which have a distinctly higher reactivity than the powder resin systems known from the prior art.
In accordance with these objectives, in accordance with a first aspect of the present invention there is been provided a curable pulverulent mixture including:
(A) a compound containing at least two 1,2-epoxide groups which is the reaction product of (Al) a compound having at least two 1,2-epoxide groups per molecule and (A2) a cyclic carboxylic anhydride, and optionally (B) a curing agent.
In accordance with other aspects of the invention, there is provided a substrate coated with a coating obtained by curing a mixture as described above.
Further objects, features, and advantages of the invention will become apparent from the details from the detailed description of preferred embodiments that follows.

Detailed Description of the Preferred Embodiments The epoxide compound (A) employed in accordance with the invention contains on average at least 2 epoxide groups per molecule. Any such compound or mixtures of such compounds prepared using (A1) and (A2) is useful.
Epoxy compound (A) may have any desired properties depending on the intended use of the composition.
The epoxide equivalent weight of (A) (molar mass divided by the number of epoxide groups in the molecule) is in general between 300 and 1500 g/mol, preferably between 400 and 800 g/mol and, in particular, between 500 and 700 g/mol, while the acid number is usually from 0.01 to 20 mg of KOH/g, preferably from 0.01 to 2 mg of KOH/g.
Furthermore, the epoxide (A) generally possesses a number-average molar mass Mn of from 500 to 10,000 g/mol, preferably from 800 to 3000 g/mol. Depending on the starting components (Al) and (A2) and their molar ratio and on the molar mass of (A), these epoxide compounds are generally solid products having a usual glass transition temperature (Tg) of at least 20C, preferably from at least 35 to 60C.
The epoxide compounds (A) are prepared by reacting the compounds (Al) with the cyclic carboxylic anhydrides (A2) in any desired manner, generally by heating the components for several hours with exclusion of oxygen at temperatures from 100 to 200C, preferably 120 to 160C, generally until an acid number of less than 20 mg of KOH/g, preferably of 2 mg of KOH/g or less, is reached.
In this context it is possible to employ as (A1) both epoxy resins which have been prepared in a one-stage process (for example from bisphenol and epichlorohydrin) and those which are obtainable in a two-stage process (for example from a low molar mass liquid epoxy resin and bisphenol). The epoxide compounds (A) are preferably prepared such that the synthesis of the epoxy resin (A1) is followed immediately by the reaction with the cyclic anhydride (A2).

2ls8529 The 1,2-epoxide compounds employed in accordance with the invention as component (A1) have on average at least two 1,2-epoxide groups per molecule. Any such epoxide compounds or mixtures can be used. Generally the compounds have an epoxide equivalent weight of from 160 to 1000 g/mol, preferably from 160 to 600 g/mol, and a glass transition temperature of at least 10C and up to 140C. They may be either saturated or unsaturated and aliphatic, cycloaliphatic, aromatic, or heterocyclic, and may also contain hydroxyl groups. They may additionally contain substituents which do not give rise, under the conditions of mixing or reaction, to any interfering side reactions, examples being alkyl or aryl substituents, ether groups, or the like.
Examples of such polyepoxide compounds (A1) include those based on polyhydric phenols, for example resorcinol, hydroquinone, 4,4'-dihydroxydiphenylmethane, isomer mixtures of dihydroxydiphenylmethane (bisphenol F), 4,4'-dihydroxy-3,3'-dimethyldiphenylmethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 4,4'-dihydroxydiphenylcyclohexane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl sulfone, tris(4-hydroxy-phenyl)methane, 4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)isobutane, 2,2-bis(4-hydroxy-3-tert-butylphenyl)propane, bis(2-hydroxy-naphthyl)methane, 1,5-dihydroxynaphthalene, bis(4-hydroxyphenyl) ether, and also those from the hydrogenation, chlorination and bromination products of the above-mentioned compounds, and from novolaks (i.e., from reaction products of mono- or polyhydric phenols with aldehydes, especially formaldehyde, in the presence of acidic catalysts).
The polyglycidyl ethers of polyhydric alcohols are also suitable as (Al). Examples of such polyhydric alcohols which may be mentioned are trimethylolpropane and 2,2-bis(4-hydroxycyclohexyl)propane.
Also suitable with or as component (Al) are solid acrylate resins which are compatible with any other components of (Al) and contain glycidyl groups, for example suitable polymers based on glycidyl methacrylate.
Other compounds which are suitable as (A1) are those such as (poly)glycidyl esters of the formula (I) R C--C--OCH2--CH--/H2)n C 1~

in which R' is a linear or branched, saturated or unsaturated hydrocarbon radical having from 1 up to 40, preferably up to 10, carbon atoms or a substituted or unsubstituted phenyl radical, the substituents being selected from among C1- to C8-alkyl and alkoxy radicals and halogen atoms, and n is at least 2, preferably from 2 to 5. Such polyglycidyl esters of polycarboxylic acids are obtained by reacting epichlorohydrin or similar epoxy compounds with an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, such as oxalic acid, adipic acid, glutaric acid, terephthalic acid, hexahydrophthalic acid, 2,6-naphthalenedicarboxylic acid and dimerized fatty acids. Examples of these esters are diglycidyl tereph-thalate and diglycidyl hexahydrophthalate.
Also suitable as polyepoxides (Al) are compounds such as triglycidyl isocyanurate and its oligomers and triglycidyl urazole and its oligomers, and corresponding mixtures.
These polyepoxide compounds can also be employed as a mixture with one another and, if desired, as a mixture with monoepoxides, with care preferably being taken to ensure that the mixture of the 1,2-epoxide compounds possesses a glass transition temperature of at least 10C. If 1,2-epoxide compounds having lower glass transition temperatures are used in the mixture, then they should preferably be employed only in a minor proportion and only in combination with correspondingly high-melting 1,2-epoxide compounds, so that the glass transition temperature of component (Al) is in the preferred range of at least 10C.

_7_ 21 $8529 Examples of suitable monoepoxides include epoxidized monounsaturated hydrocarbons (butylene oxide, cyclohexene oxide and styrene oxide), halogen-containing epoxides, for example epichlorohydrin, epoxide ethers of monohydric alcohols (methyl, ethyl, butyl, 2-ethylhexyl and dodecyl alcohol); epoxide ethers of monohydric phenols (phenol, cresol and other o- or p-substituted phenols); glycidyl esters of unsaturated carboxylic acids, epoxidized esters of unsaturated alcohols or unsaturated carboxylic acids, and the acetals of glycidaldehyde.
Other epoxide compounds having suitable melting points useful in or as component (A1) are described in the handbook "Epoxidverbindungen und Epoxidharze"
[Epoxide compounds and epoxy resins] by A.M. Paquin, Springer Verlag, Berlin 1958, Chapter IV, in Lee, Neville "Handbook of Epoxy Resins", 1967, Chapter 2 and in Wagner/Sarx, "Lackkunstharze" [Synthetic resins for coatings], Carl Hanser Verlag (1971), p. 174 ff.
Preferred epoxide compounds (Al) are:
20 poly(epoxyalkyl) ethers of aliphatic or cycloaliphatic polyhydroxy compounds, such as of trimethylolethane, trimethylolpropane, tris(hydroxy-ethyl) isocyanurate and pentaerythritol;
reaction products of epihalohydrins such as epichlorohydrin with monomeric polyhydric phenols such as 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxy-phenyl)methane, 4,4'-dihydroxydiphenyl sulfone, hydroquinone, resorcinol, dihydroxybiphenyl, dihydroxynaphthalene, and also trisglycidyl isocyanurate;
glycidyl ethers of polyhydric phenolic compounds, such as novolaks and resols obtained from the condensation of phenol and/or cresols with formaldehyde;
polyglycidyl esters of polycarboxylic acids, such as diglycidyl esters of phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, polyglycidyl esters derived 2l~8529 from polyesters, or else compounds containing free carboxyl groups.
It is particularly preferred to use as (A1), epoxy resins based on bisphenol A and/or bisphenol F with epichlorohydrin, having epoxide equivalent weights in the range from 160 to 1000 g/mol.
Suitable cyclic carboxylic anhydrides (A2) include any known in the art and are expediently those containing from 4 to 20, and preferably from 4 to 10 carbon atoms, which may if desired also contain substituents such as halogen, especially chlorine, and/or carboxyl groups.
They may be derived from (cyclo)aliphatic, olefinically unsaturated or aromatic polycarboxylic acids having 2 or more carboxyl groups. Examples which may be mentioned include succinic anhydride, alkenylsuccinic anhydrides such as, for example, dodecenylsuccinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride (methylmaleic anhydride), dichloromaleic anhydride, aconitic anhydride (l-propene-1,2,3-tricarboxylic 1,2-anhydride), tricarballylic anhydride (propane-1,2,3-tricarboxylic anhydride), itaconic anhydride (methylenesuccinic anhydride), cyclopentanetetracarboxylic dianhydride, ~4-tetrahydro-phthalic anhydride, 4-methyl-~4-tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexa-hydrophthalicanhydride,3,6-endomethylene-~4-tetrahydro-phthalic anhydride (= nadic anhydride), 4-methyl-3,6-endo-methylene-~4-tetrahydrophthalic anhydride (= methylnadic anhydride); 3,4,5,6,7,7-hexachloro-3,6-endomethylenetetrahydrophthalic anhydride (= chlorendic anhydride), the Diels-Alder adduct of 2 mol of maleic anhydride and 1 mol of 1,4-bis(cyclopenta-dienyl)-2-butene or Diels-Alder adducts of maleic anhydride and conjugated fatty acids such as 2,4-hexa-dienoic acid (sorbic acid), 9,11-octadecadienoic acid (ricinenic acid), 9,11,13-octadecatrienoic acid (eleostearic acid), 9,11,13,14-octadecatetraenoic acid, and also aromatic polycarboxylic anhydrides such as phthalic anhydride, trimellitic anhydride, pyromellitic 2ls8529 anhydride or benzophenonetetracarboxylie bisanhydride.
It is also useful to use other cyclic polycarboxylic anhydrides whose carboxyl groups are on different rings, whieh may be fused, one example of such compounds being 1,8-naphthalenedicarboxylic anhydride.
Particular preference is given to succinic anhydride, phthalic anhydride and the cycloaliphatic dicarboxylic anhydrides which can be obtained by Diels-Alder addition from inexpensive petrochemical raw materials, for example ~4-tetrahydrophthalic anhydride or hexahydrophthalic anhydride.
Components (A1) and (A2) are employed in quantities to give the desired product and are usually employed in quantities such that in general 0.01 - 1 mol, preferably 0.05 - 0.5 mol and particularly preferably 0.1 - 0.4 mol of cyclic anhydride (A2) is used per mole of epoxide compound (A1).
Catalysts can optionally be used in the reaction of (A1) and (A2) to form (A). Examples of catalysts which ean be employed for the targeted and aecelerated reaction of the anhydride and/or carboxyl groups of component (A2) and of the epoxide groups of component (A1) include Bronsted bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium earbonate; ehromium eompounds such as CrCl3, CrO3, ehromium aeetyl aeetonate;
imidazoles; quaternary ammonium and phosphonium eompounds sueh as benzyl-trimethylammonium ehloride, tetraethyl-ammonium ehloride, tetramethylammonium ehloride, benzyl-trimethylammonium ehloride, benzyldodeeyldimethylammonium ehloride, methyltriphenylphosphonium iodide, triphenyl(2,5-dihydroxyphenyl)phosphonium hydroxide, ethyltriphenylphosphonium aeetate, triphenylethyl-phosphonium bromide and Lewis bases, sueh as organie phosphines (e.g., triphenylphosphine, trieyelohexyl-phosphine, tributylphosphine, eyelohexyloetylphosphine)and amines, whieh may be aromatic (N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-di-ethyl-p-toluidine) and (cyclo)aliphatic (triethylamine, tributylamine, benzyldimethylamine, benzyldiethylamine, triethylenediamine, N-methylmorpholine, N-methyl-piperidine, N-butylamine) as well as alkanolamines such as diethanolamine, dimethylethanolamine, diethylethanol-amine, dibutylethanolamine, methyldiethanolamine and di(3-phenoxy-2-hydroxypropyl)alkylamines, for example di(3-phenoxy-2-hydroxypropyl)-n-butylamine.
Preferred catalysts in this context are those of the formula (II) R--N ~ I 1) in which 0 R = hydrogen, a branched or unbranched alkyl radical having 1 to 18, preferably 1 to 4, carbon atoms, a cycloaliphatic alkyl radical having 5 to 12, preferably 5 to 8, carbon atoms, or is -R10H; 5 R1 = a branched or unbranched alkylene radical having 2 to 6, preferably 2 or 3, carbon atoms, which may additionally carry substituents -OR2, R2 = a branched or unbranched alkylene radical having 2 to 6, preferably 2 or 3, carbon atoms or a substituted or unsubstituted aromatic ring.
Particularly preferred compounds of the formula (II) are triisopropanolamine and/or triethanolamine.
These optional catalysts when employed, are employed in a catalytic effective amount and in general in quantities of from 0.01 to 1~, preferably from 0.05 to 2%, based on the sum of the masses of (Al) and (A2).
The reaction products (A) of (Al) and (A2) can be used in compositions with known epoxy resins, for example those based on bisphenol A or bisphenol F, in which case their proportion is preferably allowed to be between 5 -11- 21 ~8~29 and 70% of the overall mass of the epoxide components (A).
Suitable curing agents (B) include all compounds which are known for this purpose, especially anhydride curing agents such as, for example, phthalic anhydride, tetrahydrophthalic anhydride, 4-methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexa-hydrophthalic anhydride, methylnadic anhydride (trivial name for isomers ofmethylendomethylenetetrahydrophthalic anhydride), chlorendic (HET) anhydride (3,4,5,6,7,7-hexa-chloro-3,6-endomethylenetetrhydrophthalic anhydride), pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, trimellitic anhydride, curing agents in accordance with component (B) of DE-A 25 56 182 (hereby incorporated by reference), dodecenylsuccinic anhydride, isooctenylsuccinic anhydride, other acidic curing agents, dicyandiamide, phenolic curing agents such, for example, as the Dow hardeners ~D.E.H. 80, ~D.E.H. 82, ~D.E.H. 84, carboxylic salts of imidazole or imidazoline compounds, meltable, soluble adducts which are obtained by reacting an epoxide compound with imidazole or imidazoline compounds or the carboxylic salts thereof (cf.
DE-C 19 10 758, hereby incorporated by reference).
Polyesters which contain carboxyl groups are preferred as curing agents (B). The epoxide compounds (A) and the carboxyl polyesters as curing agents (B) are present in the mixture according to the invention, in general, in quantities such that the ratio of equivalents of carboxyl groups of the curing agents to epoxide and hydroxyl groups in (A) is from 0.7 to 1.3, preferably from 0.9 to 1.1. For this to apply, the quantity of carboxyl polyesters as curing agent (B) will usually be from 50 to 90~, preferably from 65 to 85~, based on the sum of the masses of (A) and (B). In this way, a suffi-cient crosslinking density is generally obtained.
The carboxyl-containing polyesters employed as component (B) usually possess an acid number of from 15 to 150 mg of KOH/g, preferably from 30 to 100 mg of KOH/g and a glass transition temperature of at least 35C, pre-ferably from at least 40 to 60C. The number-average molar mass Mn (gel chromatography, polystyrene standard) is in general between 600 and 12,000 g/mol, preferably between 2000 and 8000 g/mol. The carboxyl groups are preferably disposed at the ends of the molar chains, which may be linear or branched. The end groups of the carboxyl polyester in general consist of carboxyl groups to the extent of more than 70%, preferably more than 90%.
The chain ends preferably predominantly have on average 2 or more carboxyl groups, some of which are present as carboxylic anhydride groups.
The melt viscosities of the carboxyl polyester at 200C are in general between 1000 and 8000 mPa.s, preferably between 2000 and 6000 mPa.s.
The carboxyl polyesters are prepared in a known manner in a one-stage process or, preferably, in a two-stage process as described, for example, in DE-A 2 163 962 (hereby incorporated by reference), by reacting appropriate polyols with appropriate poly-carboxylic acids or derivatives thereof, especially anhydrides. In this context, the polycarboxylic acids and anhydrides are employed in excess. The quantitative ratio is generally such that the ratio of equivalents of hydroxyl to acid and/or anhydride groups is from 1:3 to 1:1.1, preferably from 1:2.2 to 1:1.8.
Compounds which are especially suitable as polyol component include those having hydroxyl numbers in the range from 10 to 80 mg of KOH/g, preferably from 15 to 40 mg of KOH/g, and number-average molar masses Mn (gel chromatography) of from 600 to 10,000 g/mol, preferably from 2000 to 8000 g/mol, and also softening points of from 35 to 110C, preferably from 40 to 90C (differen-tial thermal analysis). Examples which may be mentioned here include OH-containing polyesters, polyethers, poly-thioethers, polyacetals, polycarbonates and polyester-amides. Linear or branched polyesters are preferred in this context.
Examples of such hydroxyl-containing polyesters are reaction products of polyhydric, preferably dihydric and, -13- 21 ~8529 if desired, additional trihydric, alcohols with poly-basic, preferably dibasic, carboxylic acids. In place of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or polycarb-oxylic esters of alcohols having 1 to 6 carbon atoms, mixtures thereof, to prepare the polyesters. The reac-tion can also be carried out in the presence of conven-tional esterification catalysts. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic in nature and may, if desired, be substi-tuted, for example, by halogen atoms, and/or unsaturated.
Examples of useful carboxylic acids and derivatives thereof for making the polyester curing agents include the saturated aliphatic dicarboxylic acids, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid; also phthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhyd-ride,endomethylenetetrahydrophthalicanhydride,glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimerized and trimerized unsaturated fatty acids, if desired as a mixture with monomeric unsaturated fatty acids, such as oleic acid, and also dimethyl terephtha-late and bisglycol terephthalate.
Examples of suitable polyhydric alcohols useful in making the polyester curing agents include ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-buty-lene glycol, 1,6-hexanediol, 1,8-octanediol, neopentyl-glycol, 1,4-bishydroxymethylcyclohexane, 2-methyl-1,3-propanediol, glycerol, trimethylolpropane, 1,2,6-hexanetriol, 1,2,4-butanetriol, trimethylolethane, pentaerythritol, quinitol, mannitol and sorbitol, methyl-glycoside, and also diethylene glycol, triethylene glycol, tetraethylene glycol and higher polyethylene glycols, dipropylene glycol and higher polypropylene glycols, and dibutylene glycol and higher polybutylene glycols. It is also useful to employ polyesters of lactones, for example, ~-caprolactone, or of hydroxy-carboxylic acids, for example, ~-hydroxycaproic acid.

2ls8529 Examples of the anhydrides useful as curing agents (B) are, in particular, trimellitic anhydride (TMAA) and pyromellitic anhydride or maleic anhydride adducts with, for example, piperylene.
Further carboxyl-containing polyesters which are suitable in accordance with the invention as curing agents (B) are, for example, those described in DE-C 36 18 355 and in DE-A 21 63 962, and 26 18 729, each of which are hereby incorporated by reference.
Particularly preferred curing agents are carboxyl-containing polyesters whose acid number is between 15 and 150 mg of KOH/g and whose number-average molar mass is between 600 and 12,000 g/mol.
Other preferred curing agents are imidazolines of the formula (III) R ¦ ¦ R

R--N~ N
R

in which each substituent R, independently of the others, is hydrogen or a C1 to C20-alkyl, aryl, aralkyl, cycloalkyl or heterocyclic radical, R' is the same as R
or is an alkylene or arylene radical connecting two imidazole or imidazoline groups, any of R and R' may possibly be substituted by one or more C1 to C20-alkyl, aryl, aralkyl, cycloalkyl or heterocyclic radicals, and where two or more radicals may be connected, possibly also by heteroatoms, and/or imidazoles of the formula (IV) R R

H N~N ~ I V~ ' in which R and R' are as defined for formula (III).

Examples of suitable imidazolines include the following compounds: 2-methylimidazoline, 2-ethyl-4-methylimidazoline, 2-phenylimidazoline, 2-undecyl-imidazoline, 2-heptadecylimidazoline, 2-ethylimidazoline, 2-isopropylimidazoline, 2,4-dimethylimidazoline, 2-phenyl-4-methylimidazoline, 2-benzylimidazoline, 2-(o-tolyl)imidazoline, 2-(p-tolyl)imidazoline, tetra-methylenebisimidazoline,1,1,3-trimethyl-1,4-tetramethy-lenebisimidazoline, 1,3,3-trimethyl-1,4-tetramethylene-bisimidazoline, 1,1,3-trimethyl-1,4-tetramethylenebis-4-methylimidazoline, 1,2-phenylenebisimidazoline, 1,3-phenylenebisimidazoline,1,4-phenylenebisimidazoline and 1,4-phenylenebis-4-methylimidazoline. It is also useful to employ any desired mixtures of the imidazo-lines.
Examples of suitable imidazoles include imidazole itself, 1-methylimidazole, 2-methylimidazole, 4-methyl-imidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethyl-imidazole, 1-propylimidazole, 2-propylimidazole, 2-isopropylimidazole, 1-butylimidazole, 2-octylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-cyclohexyl-imidazole, 1-phenylimidazole, 2-phenylimidazole, 2,4-dimethylimidazole, 1,2-dimethylimidazole, 4,5-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-ethyl-2-methylimidazole, 1-methyl-2-isopropylimidazole, 4-butyl-5-ethylimidazole, 2-cyclohexyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 4,5-diphenylimidazole, 2-ethyl-4-phenylimidazole, 2,4,5-trimethylimidazole, 2,4,5-tricyclohexylimidazole, 1,2,4,5-tetramethylimidazole and benzimidazoles and derivatives thereof. It is also useful to employ any desired mixtures of the imidazoles and/or imidazolines.
The quantity of curing agents in the pulverulent mixtures according to the invention depends on the nature of the curing agent and can fluctuate within wide limits to give the desired curing. The quantity of curing agent is generally from 0.01 to 90%, preferably from 0.5 to 85%, based on the sum of the masses of the two components (A) and (B). In the case of imidazoles or imidazolines, a mass fraction of 0.01 to 70%, preferably of 0.5 to 40%, of curing agent in the composition is usually chosen.
In addition to components (A) and (B), the mixtures according to the invention may contain additives which are conventional for powder coatings, such as leveling agents or anticrater agents, dyes, pigments, fillers, matting agents, thixotropic agents, deaerating agents, W
stabilizers, oxidation inhibitors, quenchers (free-radical scavengers, for example, N-alkyl-substituted piperidines), catalysts for accelerating the crosslinking reaction, plasticizers, additional curing agents, addi-tional curable resins, and the like. Any of these addi-tives or mixtures thereof can be used. These additives are generally employed in effective quantities of from 0 to 50%, preferably from 0.1 to 40%, based on the overall mass of the powder coating mixture. Any liquid or pasty additives here can be used, inter alia, as a mixture with highly active silicic acid as a masterbatch (see DE-A 22 02 907).
Leveling agents which can be employed include, for example, acetals such as polyvinylformal, polyvinyl-acetal, polyvinylbutyral, polyvinylacetobutyral, and the like, polyethylene glycols and polypropylene glycols, silicone resins, mixtures of zinc soaps, of fatty acids and aromatic carboxylic acids, and in particular commer-cially available products based on polyacrylates. The leveling agents can be added to component (A) in effec-tive quantities, for example, of from 0.1 to 4%, prefer-ably from 0.2 to 2.0%.
Examples which may be mentioned of the dyes or pigments, which may be inorganic or organic in nature, are titanium dioxide and zinc oxide. The organic dyes or pigments should of course be selected such that they are stable at the curing temperatures and do not lead to any intolerable alterations in shade.
Examples of suitable fillers include ground quartz, silicates, chalk and gypsum.

The stabilizers can be aromatic diketones such as benzoin, which prevent localized decomposition and thus suppress the formation of pores.
The stabilizers are generally added in quantities of from 0.1 to 3%, preferably from 0.2 to 2~, based on the mass of the overall binder mixture.
In order to prepare the pulverulent mixtures according to the invention for testing, processing and practical application, the individual components are generally mixed with one another. When using liquid constituents, generally the solid components are finely ground and the liquid components are distributed uniform-ly therein. In order to prepare the curable mixtures according to the invention, the components are homo-genized in the melt after mixing. This can take place in suitable equipment, for example, heatable kneading appa-ratus, double-Z mixers, or extruders, preferably the latter, the extrusion temperature being chosen such that maximum shear force acts on the mixture. In this con-text, an upper temperature limit of 130C should not be exceeded. When using catalysts it may be advantageous to add these to component (A) or (B). This addition can also be made, for example, during the preparation of component (A).
The homogenized mass is then allowed to cool to room temperature and, after suitable precomminution, is ground to give a curable, pulverulent mixture (powder coating).
The target average particle sizes depend on the intended use and are generally from about 40 to 90 ~m, but pre-ferably about 50 ~m. Any oversize present, with a particle size of more than 90 ~m, is generally removed by screening.
On the basis of their high reactivity, the mixtures according to the invention are particularly suitable as adhesives and coating compositions. The mixture can be made solvent free, thereby achieving the advantages mentioned at the outset.
The powder coatings thus produced can be applied to suitable substrates, for example, metal, wood, glass, 21$8S29 concrete, plastic and ceramic, by known methods, for example, by electrostatic powder spraying, powder application by the triboelectric method, fluidized-bed sintering, electrostatic fluidized-bed sintering or by flame spraying.
After the powder coating has been applied by one of the methods mentioned, the coated workpieces are general-ly heated, to achieve full cure, to a temperature of from 90 to 270C, preferably from 120 to 220C, for a time which is sufficient to achieve full curing, in general from 0.5 to 60 minutes. The resulting coatings are distinguished by good properties in terms of paint technology, such as good mechanical properties, good chemical resistance, good weathering resistance and good adhesion. The powder coatings according to the invention are consequently suitable, in particular, for coating materials such as, for example, metal, glass, fabrics, paper, and ceramic.
In addition to the use as coatings, the mixtures according to the invention can also be employed as adhesives. The production of adhesive formulations is in principle carried out in the same way as described for the powder coating mixtures. In other words the solid epoxy resins (component A) are first comminuted and then intimately mixed with the curing agent (B), care being taken to ensure uniform distribution of the components.
The formulations thus obtained may if desired be admixed with conventional additives as described above, such as fillers, pigments, and/or dyes. The mixtures according to the invention can be used for adhesive bonding of all types of materials, for example, metals, light metals, but also nonmetallic materials such as ceramic, glass, leather, rubber, paper, cardboard, wood and plastics with themselves or with other materials.
They can also be employed in the preparation of sandwich constructions of metals and other materials.
A point worthy of particular emphasis is the possibility of constructing sandwich systems from wood (chipboard, plywood, etc.) and fabrics, for example, 2l5852~

polyester fibers (~Trevira). In the course of the adhesion process the fabric is embedded completely in the binder system, forms a homogeneous surface and adheres in an optimum manner to the substrate. The laminate obtained in this way, even with a lower thickness of material, has a high flexural strength in relation to plain chipboard or plywood panels. This procedure makes it possible to obtain panels which, while of the same quality, are of lower weight in comparison to standard materials.
When the mixtures according to the invention are used for adhesive bonding they can be applied by electrostatic means, for example, with an electrostatic powder spray gun. In this way it is possible to apply uniformly thin coats, for example, on films. Because of the rapid reaction of the individual components of the mixtures according to the invention at low temperatures, it is also possible to achieve high rates of production throughput.
An outstanding advantage in this application means is that yellowing, combustion, and gas escape can be avoided. The pulverulent mixture on the coated materials generally cures fully at temperatures of from 120 to 220C, preferably from 130 to 210C, in an adequate time of from 2 to 60 minutes.
The compositions according to the invention are particularly suitable for the coating of filter papers which can be used in the production of filters for low-and medium-viscosity liquids, for example, oils. In this case either the epoxy resin/curing agent mixture is applied to untreated filter paper in the form of a fine powder and incipiently melted for a brief period, or the paper is coated with a melt of the mixture. Full curing is then carried out at the stage of ultimate fabrication and adhesive bonding.
The present invention is further illustrated by the following examples, which are for illustrative purposes only and do not limit the invention.

EXAMPLES:

Epoxy resin I (comparison) Commercially available bisphenol A epoxy resin for the preparation of powder coatings, having the following characteristics:
Epoxide equivalent weight about 800 g/mol Viscosity at 25C about 500 mPa.s 40% strength in butyldiglycol in accordance with DIN 53 015 Melting point about 70C
Capillary method in accordance with DIN 53 015 Glass transition temperature about 50~C

Epoxy resin II (according to the invention) Preparation 1464 g of a liquid bisphenol A epoxy resin having an epoxide equivalent weight of 183 g/mol (8 mol of epoxy groups) and 456 g of bisphenol A (2 mol) are heated to 125C in a four-necked flask with stirring under a nitrogen atmosphere, and 4 g of triethanolamine are added. By exothermic reaction and additional heating, the temperature is brought to 160C over the course of 15 minutes and maintained for 4.5 hours. The epoxide equivalent weight is then 468. After a holding time of a further hour at 160C, the temperature is reduced to 150C and 91. 4 g (0. 6 mol) of tetrahydrophthalic anhydride are added. After 1. 25 hours, the acid number is 0.9 mg of KOH/g. After a further 0. 5 hour, the flask is emptied.

Characteristics:
Epoxide equivalent weight 601 g/mol Acid number (toluene/ethanol) 0. 2 mg of KOH/g Viscosity 25C (40% in butyldiglycol 519 mPa.s Glass transition temperature 45.7C

21~8529 Example 1 Gel time determination The gel time was measured in accordance with DIN 16 916 Part 2 (September 1987) section 5.7.1, "Determination of the B-stage time", at 180C. The results for various mixtures according to the invention in comparison with those of the prior art are listed in Table 1.
The pulverulent mixtures according to the invention exhibit surprisingly short gel times in comparison with the mixtures containing a prior art epoxy resin. This is a measure of the high reactivity of the mixtures accord-ing to the invention which are used, and demonstrates the great influence of the epoxy resin component A on the rate of reaction of the overall system.

- 21S8~29 -Table 1: Gel time determinations at 180C
Epoxy Curing agentParts by wt. (pbw) of curing Seconds resin agent per 100 pbw of epoxy resin 2-Heptadecylimidazole 0.5 > 600 II 2-Heptadecylimidazole 130 2-Heptadecylimidazole 1 > 600 II 2-Heptadecylimidazole 62 2-Heptadecylimidazoline2.5 725 II 2-Heptadecylimidazoline 172 1 0 I 2-Ethyl~methylimidazoline 1 219 II 2-Ethyl~methylimidazoline 35 2-Methylimidazoline 1 282 II 2-Methylimidazoline 111 2-Phenylimidazole 2.5 85 1 5 II 2-Phenylimidazole 37 2-Phenylimidazoline 2.5 337 II 2-Phenylimidazoline 103 Curing agent B31 (Huls) 1 > 600 II Curing agent B31 (Huls) 376 I Curing agent B31 (Huls) 2.5 324 II Curing agent B31 (Huls) 79 Curing agent B68 (Huls) 2.5 > 600 II Curing agent B68 (Huls) 221 Curing agent B55 (Hals) 2.5 > 600 II Curing agent B55 (Huls) 190 Curing agent EH 694 (Hoechst) 15 234 II Curing agent EH 694 (Hoechst) 80 Trimellitic anhydride 6 587 II Trimellitic anhydride 108 3 0 I Pyromellitic anhydride 5 314 II Pyromellitic anhydride 112 Dicyandiamide 2.5 684 II Dicyandiamide 280 Dyhard~ lW (SKW Trostberg) 2.7 623 II Dyhard~ 100 (SKW Trostberg) 225 Curing agent B31: cyclic amidine Curing agent B55:~ salt of a polycarboxylic acid and of a Curing agent B68:J cyclic amidine Curing agent EH694: resinous anhydride Dyhard~ 100: dicyandiamide 2l~8.529 Example 2 Coatings testing The powder coatings tested in Table 3 were prepared by extruding the powder coating mixtures comprising carboxyl polyester, epoxy resin, pigment and additives in the mixing ratio given in Table 2 and are comparable with one another in respect of the preparation process and the particle size distribution (average particle size 50 ~m).
The extruded powder coating mixtures were applied to degreased steel panels using a Corona spray gun. The coating thickness was on average about 63 ~m and the stoving temperature was 160C (see Table 3). The tests were carried out in accordance with the standards indicated.
The tendency toward yellowing was determined by dividing the coated panels together with the baked films and overbaking one half at 200C. The ~E color differ-ence measurement was carried out on a Tricolor LFM 3 colorimeter from Lange in accordance with DIN 6174, CIE-LAB 1976, against a white standard or, in the case of the overbaked films, against the portion of the film which was not overbaked.

- 21s8s29 Table 2: Powder coating mixtures (composition in parts by weight) FY~mpl~. 2 a)Example 2 b) Comparison Epoxy resin I 170 Epoxy resin II - 157 Polyesterl) 397 410 Titanium dioxide2)300 300 Blanc fixe F 100 100 Leveling agent3) 30 30 Benzoin 3 3 l) Carboxyl polyester~ Alftalat AN 770 (Hoechst) having the following characteristics:
Acid number (DIN 53 402): 34 + 4 mg of KOH/g Glass transition temperature: 53 + 2C
(measured by DSC, Mettler TA 3000, at 10C/min) Viscosity at 200C: 5,000 to 6,500 mPa.s (measured with ICI Cone & Plate) 2) ~Kronos 2160 from Kronos Titan 3) ~Additol XL 396 (Hoechst) - 21 S85~9 Table 3: Test results for the coating films Example 2c Example 2d Example 2e Example 2f (Co~)dlis(,ll)(C~ lis~,ll) Powder coating mixture 2a 2a 2b 2b example Overbaking Ov~ kii.g Drying temperature (C) 160 200 160 200 5 Drying time (min) 10 60 10 60 Coat thickness (~Im)60 - 66 56 - 62 60 - 66 66 - 70 Gloss 60 perspective DIN 95 94 95 94 67 530 (%) Leveling (+) 2 2 Cratering (+) 0 0 Erichsen indentation11.2 11.8 11.5 11.7 DIN 53 156 (mm) Impact testing ASIIM

direct Nm (Ib-in) 1 8 (16) 18.1 (160) 6.8 (60)18.1 (160) indirect NM (Ib-in)<0.5 (<4) 18.1 (160) 4.5 (40)18.1 (160) Butyl acetate test 3 min 5 4 4 3 (+) Xylene test 30 min (+) 5 5 5 4 I~E rel. to powder white 1.21 1.35 standard AB rel. to powder white 0.12 0.04 standard AE rel. to normal curing 3.15 1.94 ~B rel. to normal curing 2.79 1.93 Blocking resistance of the powder coating mixture 2 2 40C acc. to DIN 55990 7 days 3 0 Gel time of the powder coating mixture at 180C 197 85 (S) ( + ) = visual assessment in accordance with DIN 53 230 0 = very good, 5 = very poor ` -26- 21 58529 From the examples in Table 3 it is evident that the powder coating films of the powder coating mixture according to the invention give test results which are equal to (gloss, leveling, cratering, Erichsen indentation) and in some cases better than (solvent test, yellowing resistance) those of the comparison powder coating mixture. In particular, the powder coating mixture 2 b (2 e) according to the invention exhibits substantially greater reactivity (lower gel time) than that of the prior art 2 a (2 c). Furthermore, it was found that the impact testing values of the coating film according to the invention (2 e) at the chosen baking temperature are higher than those of the comparison (2 c). In practice, therefore, powder coating films can advantageously be stoved at lower temperatures with the resins according to the invention than with those according to the prior art.

Example 3 Bonding of polyester fabric The resin/curing agent mixture (e.q., 92 parts by weight of epoxy resin II and 8 parts by weight of curing agent B 31, cyclic amidine from Huls Aktiengesellschaft) is mixed in an MTI mixer to a particle size of < 5 mm and extruded at 80C with a residence time of 10-15 seconds, and the liquid melt of the binder/curing agent mixture, directly after the dispersion in the extruder, is passed together with the polyester fabric through a calender, in the course of which operation the liquid melt material is distributed uniformly on the fabric. The coated fabric is stored at ambient temperature prior to its subsequent use or adhesive bonding.
The fabric treated with the powder mixture is punched out, cut and then adhesively bonded with chipboard panels under a pressure of 40 bar over 40 seconds at 200C. Under the process conditions chosen, the powder mixture melts, wets the substrate (chipboard and fabric) very thoroughly and then cures fully. In 21 ~8~2g this procedure the polyester fabric is completely embedded in the binder system, forms a homogeneous surface and adheres to the substrate in an optimum manner.

Example 4 Bonding of polyester fabric The resin/curing agent mixture (e.q., 92 parts by weight of epoxy resin II and 8 parts by weight of curing agent B 31, cyclic amidine from Huls Aktiengesellschaft) is mixed in an MTI mixer to a particle size of < 5 mm and is extruded at 80C with a residence time of 10-15 seconds. The extrudate emerging at 100C is cooled, broken, ground and screened to a particle size of < 125 ~m.
The powder mixture obtained in this way is applied using an electrostatic powder spray gun to polyester fabric and the coated material is processed further either by a) immediately pressing and adhesively bonding the polyester fabric provided with the powder mixture onto chipboard to be laminated, or by b) fusing the powder mixture for 2 minutes at 100C
onto the Trevira fabric, placing the material in intermediate storage and then adhesively bonding it to chipboard.
The adhesive bonding of the fabric treated in this way is carried out under pressure (40 bar) over 40 seconds at 200C to chipboard. Owing to the chosen process conditions, the powder mixture melts, wets the substrate (chipboard and fabric) very thoroughly and then cures fully.

Example 5 Filter paper coating The epoxy resin/curing agent mixture (e.g., 92 parts by weight of epoxy resin II and 8 parts by weight of curing agent B 31, cyclic amidine from Huls Aktiengesellschaft) is mixed in an MTI mixer to a 2l58s29 particle size of < 5 mm and is extruded at 80C with a residence time of 10-15 seconds.- The extrudate emerging at 100C is cooled, broken, ground and screened to a particle size of < 125 ~m.
The powder mixture obtained in this way is applied using an electrostatic powder spray gun to filter paper, fused to the paper at about 100C for 2 minutes, and placed in intermediate storage until adhesive bonding is carried out.
An alternative procedure which is possible is to cut the filter paper, which has been provided with the as yet unfused powder coating, to the desired shape, to punch it out and then immediately to carry out adhesive bonding.
Instead of the electrostatic application, the liquid melt of the binder-curing agent mixture can be applied directly, following its dispersion in an extruder, to the paper. To this end the liquid material is passed together with the filter paper through a calender, resulting in a uniform coat on the paper. The coated filter paper is then placed in intermediate storage until adhesive bonding is carried out.
The papers treated with the powder coating are punched out to shape, cut and then bonded to one another under pressure and with heating. Owing to the chosen process conditions, the powder melts, sufficiently wets the papers to be bonded and cures in a very short time (e.g., a few seconds at 180C) to give adhesive bonds which are suitable for the production of oil filters.
While the invention has been described with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the preferred embodiments are possible without departing from the spirit and scope of the invention.

Claims (20)

1. A curable pulverulent mixture comprising (A) a compound containing at least two 1,2-epoxide groups which is the reaction product of (A1) a compound having at least two 1,2-epoxide groups per molecule and (A2) a cyclic carboxylic anhydride, and (B) optionally a curing agent.

2. A curable mixture as claimed in claim 1, wherein the compound (A1) has an epoxide equivalent weight of between 160 and 1000 g/mol.

3. A curable mixture as claimed in claim 1, wherein the compound (A1) is selected from the group consisting of the diglycidyl ethers of bisphenol A and bisphenol F.

4. A curable mixture as claimed in claim 1, wherein the cyclic anhydride (A2) is selected from the group consisting of succinic anhydride, phthalic anhydride, .DELTA.4-tetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

5. A curable mixture as claimed in claim 1, wherein the compound (A) has an epoxide equivalent weight of from 300 to 1500 g/mol.

6. A curable mixture as claimed in claim 1, wherein the glass transition temperature of the compound (A) is at least 20°C.

7. A curable mixture as claimed in claim 1, wherein the compound (A) has an acid number of from 0.01 to 20 mg of KOH/g.

8. A curable mixture as claimed in claim 1, wherein the compound (A) has a number-average molar mass of from 500 to 10,000 g/mol.

9. A curable mixture as claimed in claim 1, wherein to synthesize component (A), from 0.01 to 1 mol of cyclic carboxylic anhydride (A2) is employed per mole of epoxide compound (A1).

10. A curable mixture as claimed in claim 1, wherein to synthesize component (A), from 0.05 to 0.5 mol of cyclic carboxylic anhydride (A2) is employed per mole of epoxide compound (A1).

11. A curable mixture as claimed in claim 1, wherein a curing agent (B) is present which comprises a carboxyl-containing polyester.

12. A curable mixture as claimed in claim 11, wherein the acid number of the carboxyl-containing polyester is from 15 to 150 mg of KOH/g.

13. A curable mixture as claimed in claim 11, wherein the number-average molar mass Mn of the carboxyl-containing polyester is between 600 and 12,000 g/mol.

14. A curable pulverulent mixture as claimed in claim 1, wherein a curing agent (B) is present which comprises an imidazoline of the formula (III) or an imidazole of the formula (IV), (III) (IV) in which each radical R, independently of the others, is hydrogen or an alkyl, aryl, aralkyl, cycloalkyl, or heterocyclic radical, R' is the same as R or is an alkylene or arylene radical;
wherein R and R' may optionally be substituted by one or more alkyl, aryl, aralkyl, cycloalkyl or heterocyclic radicals, and where two or more radicals may be connected, optionally by heteroatoms.

15. A curable mixture as claimed in claim 14, wherein curing agent (B) is present and comprises 2-phenylimidazoline.

16. A curable mixture as claimed in claim 1, wherein curing agent (B) is present and comprises dicyandiamide.

17. A curable mixture as claimed in claim 1, wherein the quantity of curing agent (B) is from 0.01 to 90%, based on the sum of the masses of (A) and (B).

18. A substrate coated with a coating obtained by curing a mixture as claimed in claim 1.

19. An adhesive comprising a curable mixture as claimed in claim 1.

20. Filter paper coated with a curable mixture as claimed in claim 1.