CA2312462A1 - Epoxy-terminated polyaddition compounds containing uretdione groups, processes for preparing them and their use - Google Patents

Abstract

Disclosed are an epoxy-terminated polyaddition compound containing uretdione groups, obtainable by reacting:

A)40-84.5% by weight of at least one polyisocyanate component synthesized from: 1)at least 40% by weight of a polyisocyanate compound containing uretdione groups and having an average functionality of at least 2.0, and 2)not more than 60% by weight of at least one diisocyanate compound or isocyanurate compound without uretdione groups; B)50-15% by weight of at least one compound having at least two hydroxyl groups; and C)10-0.5% by weight of at least one compound having at least one epoxy group and at least one other group which is reactive with an isocyanate group; the polyaddition compound being present in solid form below 40°C and in liquid form above 130°C
and having a number-average molecular weight of between 1,000 and 15,000, and a free isocyanate group content (calculated as NCO; molecular weight=42) of from 0 to 2% by weight; a process for preparing it; and its use for preparing polyurethane (PU) polymers, especially a PU powder coating material which crosslinks to highly glossy, light-stable, and weather-stable films having improved chemical resistance.

Description

Epoxy-terminated polyaddition compounds containing uretdione groups, processes for preparing them and their use FIELD OF THE INVENTION
The present invention relates to a novel epoxy-terminated polyaddition compound containing uretdione groups, to a process for preparing it, and to its use for preparing polyurethane (PU) polymers, especially a PU powder coating material which crosslinks to highly glossy, light-stable and weather-stable films having improved chemical resistance.
BACKGROUND OF THE INVENTION
Blocked polyisocyanates which are solid at room temperature and contain uretdione groups are valuable crosslinkers for heat-crosslinkable polyurethane powder coating materials. German Patent Publication (DE-A) 30 30 554, for example, describes polyisocyanates having two terminal partially or fully blocked isocyanate groups. A disadvantage of these systems lies in the elimination of the blocking agent during the heat-induced crosslinking reaction. Since the blocking agent can be emitted into the environment in this way, it is necessary for reasons of ecology and workplace safety to take special measures to clean the outgoing air and/or to recover the blocking agent.
German Patent Publications (DE-A) 30 30 539 and 30 30 572 describe processes for preparing polyaddition products which contain uretdione groups and whose terminal isocyanate groups are irreversibly masked with monoalcohols or monoamines.
The chain-terminating constituents of the crosslinkers, which resulted in low network densities of the PU powder coatings and thus in moderate solvent resistance, were a particular disadvantage.

Hydroxyl-terminated polyaddition compounds containing uretdione groups are the subject of European Patent Publication (EP) 0 669 353. Their functionality of two gives them an enhanced resistance to solvents. For many applications, however, the resistance is not sufficient.
It would be advantageous, therefore, to provide polyisocyanates containing uretdione groups but free from blocking agent with the aim of using these crosslinkers to prepare PU polymers free from elimination products, and in particular to prepare environmentally valuable PU powder coating materials, with the PU powder coatings produced, accordingly no longer having the above-mentioned disadvantages of the prior art.
SZTi~IARY OF THE INVENTION
In one aspect, the present invention provides an epoxy-terminated polyaddition compound containing uretdione groups, obtainable by reacting: A)40-84.5% by weight of at least one polyisocyanate component synthesized from: 1)at least 40% by weight of a polyisocyanate compound containing uretdione groups and having an average functionality of at least 2.0, and 2)not more than 60% by weight of at least one diisocyanate compound or isocyanurate compound without uretdione groups;
B)50-15% by weight of at least one compound having at least two hydroxyl groups; and C)10-0.5% by weight of at least one compound having at least one epoxy group and at least one other group which is reactive with an isocyanate group; the polyaddition compound being present in solid form below 40°C
and in liquid form above 130°C and having a number-average molecular weight of between 1,000 and 15,000, and a free isocyanate group content (calculated as NCO; molecular weight=42) of from 0 to 2% by weight.

In another aspect, the invention provides a process for preparing an epoxy-terminated polyaddition compound containing uretdione groups by reacting: A)40-84.5% by weight of at least one polyisocyanate component synthesized from: 1)at least 40% by weight of a polyisocyanate compound containing uretdione groups and having an average functionality of at least 2.0, and 2)not more than 60% by weight of at least one diisocyanate compound and/or isocyanurate compound; B)50-15% by weight of at least one compound having at least two hydroxyl groups; and C)10-0.5% by weight of at least one compound having at least one epoxy group and at least one other group which is reactive with an isocyanate group; the polyaddition compound being present in solid form below 40°C and in liquid form above 130°C and having number-average molecular weight of between 1,000 and 15,000, and free isocyanate group content (calculated as NCO; molecular weight=42) of from 0 to 2% by weight, in a solvent at 50-100°C or without solvent in an intensive kneading apparatus at 100-190°C.
In a further aspect, the invention provides for the use of polyaddition compounds for preparing PU polymers, especially in combination with hydroxyl-containing polymers and with additives customary in PU chemistry, in transparent and pigmented PU powder coating materials of heightened network density, very good reactivity and excellent gloss. Such, coating materials are free from elimination products.
In another aspect, the invention provides transparent and pigmented PU powder coating materials, free from elimination products, which comprise the polyaddition compounds of the invention.
In a further aspect, the invention provides a method of forming a glossy, light-stable and weather-stable film on a substrate, which comprises: applying the polyurethane powder coating material as defined in any one of claims 9 to 15 onto the substrate, and curing the powder coating material at a temperature of from 150 to 220°C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The polyisocyanate compounds A1) containing uretdione groups that are used in accordance with the invention. They generally have the formula:
O
I I
OCN-R N~ ~N-R NCO
C
I I
O n wherein n is an integer greater than O, preferably 1 to 10, and R is a divalent organic group. They are obtained from any desired diisocyanates, typically of formula OCN-R-NCO, by subjecting the isocyanate groups to catalytic dimerization.
The desired diisocyanates for preparing A1) may be aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates.
Preferred examples are 1,6-diisocyanatohexane (HDI), 2-methyl-pentamethylene-1,5-diisocyanate (DI-51), 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate, 4,4'-diisocyanatocyclohexylmethane, 1,3- and 1,4-diisocyanatocyclohexane, isophorone diisocyanate (IPDI), diphenylmethane 2,4'- and/or 4,4'-diisocyanate, xylylene diisocyanate or 2,4- and 2,6-tolylene diisocyanate and any desired mixtures of these isomers. It is possible to use these diisocyanates alone or in mixtures in order to prepare component A1). The polyisocyanate compounds A1) containing uretdione groups, as well, can be mixed with one another as desired and used for component A) in the sense of the invention.

Suitable catalysts for preparing component A1) from these diisocyanates are in principle all known compounds which catalyze the dimerization of isocyanate groups. Examples are tertiary organic phosphines (U. S. Patent No. 4,614,785, German Patent Publication Nos. 19 34 763 and 39 00 053), tris(dialkylamino)phosphines (German Patent Publication Nos. 30 30 513, 32 27 779 and 34 37 635), substituted pyridines (German Patent Publication Nos. 10 81 895 and 37 39 549), and substituted imidazoles or benzimidazoles (European Patent Publication No. 0 417 603, published March 20, 1991).
Preferred polyisocyanate compounds A1) are polyisocyanates which contain uretdione groups and have been prepared from diisocyanates having isocyanate groups attached to aliphatic and/or cycloaliphatic moieties.
Particular preference is given to the use of the uretdiones of isophorone diisocyanate (IPDI) and of 1,6-diisocyanatohexane (HDI).
An isocyanurate-free uretdione of isophorone diisocyanate is highly viscous at room temperature, for example more than 106 mPa~s; at 60°C the viscosity is 13x103 mPa~s and at 80°C it is 1.4x103 mPa~s. The free NCO content lies between 16.8 and 18.5% by weight; i.e., more or less high fractions of polyuretdione of IPDI must be present in the reaction product.
The monomer content is 1% by weight. The total NCO content of the reaction product after heating at 180-200°C is 37.5-37.8%
by weight.
In the course of the dimerization of aliphatic diisocyanates with conventional processes and catalysts, isocyanurate is formed as a byproduct in differing amounts, so that the NCO functionality of the polyisocyanate compounds A1) used is at least 2.

The diisocyanates A2) may be the abovementioned diisocyanates suitable for preparing component A1). They can account for up to 60% of the overall weight of component A1) and A2). Suitable mixtures include, for example, solutions of uretdiones in diisocyanates, as are obtained following catalytic dimerization and without separating off the unreacted diisocyanate.
The diisocyanates A2) may be the trimers of the diisocyanates used to prepare the polyisocynate compounds A1) containing uretdione groups. The isocyanurates can be added separately to the polyisocyanate compound A1), or are already part of the polyisocyanate compound A1), having been formed in part as byproducts of the dimerization of diisocyanates.
Suitable compounds B) are any diol commonly used in polyurethane chemistry which have molecular weight of at least 62. Examples that may be mentioned include ethylene glycol, triethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2,2,4(2,4,4)-trimethylhexanediol, and neopentyl glycol hydroxypivalate. They are generally monomeric diols, have a relatively low molecular weight, and may be used alone or in mixtures..
Further suitable compounds B) are polymeric diols containing further functional groups. These may be linear hydroxyl-containing polyesters, polycarbonates, polycaprolactones, polyethers, polythioethers, polyesteramides, polyurethanes or polyacetals which are known per se. They preferably have a number-average molecular weight of from 134 to 3500. Preference is given to linear hydroxyl-containing polyesters, namely, polyester polyols, or to mixtures of such polyesters. They are prepared, for example, by reacting diols with substoichiometric amounts of dicarboxylic acids, -corresponding dicarboxylic anhydrides, corresponding dicarboxylic esters of lower alcohols, lactones, or hydroxy carboxylic acids.
Diols suitable for preparing the polyester polyols, in addition to the abovementioned diols, include 2-methyl-propanediol, 2,2-dimethylpropanediol, diethylene glycol, 1,12-dodecanediol, 1,4-cyclohexanedimethanol, and 1,2- and 1,4-cyclohexanediol.
Dicarboxylic acids or derivatives thereof suitable for preparing the polyester polyols can be aliphatic, cycloaliphatic, aromatic and/or heteroaromatic in nature and can if desired be substituted - halogen atoms for example -and/or.unsaturated.
The preferred dicarboxylic acids or derivatives include succinic acid, adipic acid, suberic acid, azelaic acid, and sebacic acid, 2,2,4(2,4,4)-trimethyladipic acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, dimethyl terphthalate, tetrahydrophthalic acid, malefic acid, malefic anhydride, and dimeric fatty acids.
Further suitable polyester polyols are those preparable in a known manner by ring opening from lactones such as s-caprolactone and simple diols as starter molecules.
The diols and dicarboxylic acids and/or derivatives thereof used to prepare the polyester polyols can be used in any desired mixtures.
Compounds C) are compounds which in addition to an epoxy group carry at least one further functional group, such as carboxyl, hydroxyl, mercapto or amino groups, for example, which is capable of reacting with an isocyanate group.
Particular preference is given to 2,3-epoxy-1-propanol and - 7a -epoxidized soybean oil.
The polyaddition compounds of the invention are prepared in accordance with the general process specified above. Depending on the nature of the components used, this process can be varied in accordance with the details given below.
The reaction in a solvent takes place in general at temperatures from 50 to 100°C, preferably between 60 and 90°C, with the use of catalysts being possible as well.
The polyisocyanate component A) is introduced initially and the hydroxyl-bearing component B) is added as quickly as possible without the reaction temperature exceeding the abovementioned limits. Subsequently, component C) is added. Alternatively, the reaction of component A) with component C) can be carried out first, followed by the reaction with component B). Another possibility is to add components B) and C) as a mixture to component A). The mixture of B) and C) can also be introduced initially, and A) added. After reaction has taken place the solvent is removed. This is suitably done using devolatilization screws, film extruders or spray dryers.
Suitable solvents include benzene, toluene or other aromatic and/or aliphatic hydrocarbons, acetates such as ethyl or butyl acetate, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, or chlorinated aromatic and aliphatic hydrocarbons, and any desired mixtures of these or other inert solvents.
The invention also provides for a solventless and continuous preparation of the polyaddition compounds of the invention by means of intensive kneading apparatus.
Preparation takes place preferably in a single-screw or multiscrew extruder, in particular in a twin-screw extruder.

- 7b -The solventless synthesis requires temperatures of from 110 to 190°C. It was a surprise that such high temperatures could be used. These temperatures are already well within the range in which uretdiones undergo deblocking, so that high free isocyanate contents can result and, consequently, uncontrolled reaction events were to be expected. This fact was significant for the synthesis of the hydroxyl-containing uretdione polyaddition product, and it was all the more surprising that it could be realized. The short reaction times of less than 5 minutes, preferably less than 3 minutes, in particular less than 2 minutes, proved advantageous in this context.
It was not possible to predict that the brief thermal treatment would be sufficient to provide for homogenous mixing of the co-reactants accompanied by their complete, or substantial, reaction. Subsequently, in accordance with the establishment of equilibrium, controlled cooling is carried out and, if necessary, the reaction is brought to completion.
The co-reactants are supplied to the kneading apparatus in separate product streams. It is possible to preheat the starting components at up to 120°C, preferably up to 90°C. Where there are more than two product streams, they can also be metered in bundled form.
Components B) and/or C), leveling agents or stabilizers can be combined into one product stream, as can those constituents which are inert toward isocyanate groups:
catalysts, and additives mentioned above accordingly.
It is likewise possible to vary the sequence of the product streams, and the entry point for the product streams can be different.
Known processes and technologies are used for subsequent reaction, cooling, comminution, and bagging.

- 7c -In order to accelerate the polyaddition reaction it is possible to use the catalysts customary in PU chemistry.
They are used in a concentration of from 0.01. to 2% by weight, preferably from 0.03 to 0.5% by weight, based on the reaction component used. Examples of catalysts are tertiary amines such as triethylamine, pyridine or N,N-dimethylaminocyclohexane or metal salts such as iron iron (III) chloride, molybdenum glyconate, and zinc chloride. Tin (II) and tin (IV) compounds have proven particularly suitable. Particular mention may be made here of dibutyltin dilaurate (DBTL) and tin octoate.
The polyaddition compounds of the invention may be suitable for preparing polyurethane polymers, especially in combination with hydroxyl-containing polymers and/or with the additives customary in PU chemistry, for preparing transparent and pigmented PU powder coatings which are free from elimination products, are distinguished by very good reactivity and are thus both economically and environmentally significant, and which, surprisingly, exhibit excellent flexibility despite an increased network density.
In one aspect, the present invention provides polyurethane polymers and especially PU powder coating materials free from elimination products.
The PU powder coating materials essentially comprise the above-described polyaddition compounds in combination with hydroxyl-containing polymers. Suitable coreactants for PU
powder coating materials are compounds carrying functional groups which react with isocyanate groups during the curing process as a function of the temperature and time, examples being hydroxyl, carboxyl, mercapto, amino, _ g _ urethane, and (thio)urea--groups. The polymers used can be addition polymers, polycondensates and polyaddition compounds.
In principle it is possible to use any polymer which contains more than two OH
groups and melts at not less than 70°C. These include polyester poiyols, polyether polyols, polyesteramide poiyols, polyurethane poiyois, hydroxyiated acryiate resins, epoxy resins with hydroxyl groups in the molecule, amino resins and their modification products with polyfunctional alcohols; polyazomethines, polysulfonamides, melamine derivatives, cellulose esters and cellulose ethers, whose OH groups are intended for crossiinking with the polyaddition compounds of the invention.
Among the numerous possibilities for polymers carrying hydroxyl groups, particular preference is given in the context of the invention to polyester poiyois and hydroxyiated acryiate resins.
Carboxylic acids which are preferred for the preparation of polyesters can be aliphatic, cycioaliphatic, aromatic and/or heterocyclic in nature and can if desired be substituted by halogen atoms and/or unsaturated. Examples thereof that may be mentioned include succinic, adipic, suberic, azelaic, sebacic, phthalic, terephthalic, isophthalic, trimellitic, pyromellitic, tetrahydrophthalic, hexahydrophthalic, hexahydroterephthalic, dichlorophthalic, teirachlorophthaiic, endo-methylenetetrahydrophthalic, glutaric, malefic and fumaric acids and - where obtainable - their anhydrides, dimethyi terephthalate, bisglycol terephthalate, and also cyclic monocarboxylic acids such as benzoic acid, p-tert-butyibenzoic acid, or hexahydrobenzoic acid.
Examples of suitable polyhydric alcohols are ethylene glycol, propylene 1,2-and 7 ,3-glycol, butylene 1,4- and 2,3-glycol, di-~i-hydroxyethylbutanediol, 1,6-hexanediol, 1,8-octanedioi, neopentyl glycol, cyciohexanedioi, 1,4-bis(hydroxymethyl)cyclohexane, 2,2-bis(4-hydroxycyclohexyi)propane, 2,2-bis[4-{~i-hydroxyethoxy)phenyi]propane, 2-methyl-1,3-propanediol, 2-methyl-1,5-pentanediol, 2.2,4(2,4,4)-trimethyi-1,6-hexanediol, glycerol, trimethylvlpropane, trimethylolethane, 1,2.6-hexanetriol, 1,2,=>~-butanetriol, tris(~3-hydroxyethyl) isocyanurate, pentaerythritol, mannitol and sorbitol, and also diethyiene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polypropylene giycols, polybutylene giycols, xyiylene glycol, and neopentyl glycol hydroxypivalate.

3443-70_>

_ g _ The foilowirig monoesters and polyesters are also suitable for use in principle:
a s-ca rolactone, or of hydroxy carboxylic acids, e.g., Polyesters of lactones. .g.. p hydroxypivalic acid, a hydrcxydecanoic acid, cc hydroxycaproic acrd, and thioglycolic acid: polyesters of the abovementioned polycarboxyiic acids or derivatives thereof and poiyphenols such as hydroquinone, bisphenol A, 4,4'-dihydroxybiphenyl, and bis(4-hydroxyphenyl) sulfone; polyesters of carbonic acid obtainable from hydroguinone, diphenylolpropane, p-xyiyiene glycol, ethylene glycol, butanediol or 1,6-hexanedioi.---and other pools-.. by customary condensation-Factions, with phosgene or diethyl or dipi~enyl carbonate, far example. or from cyclic carbonates such as glycol cart;cnate or ninyiidene carbonate by addition polymerization in a known manner, polyesters--cf-silicic acid; polyesters of phospi~,oric acid;
and polyesters cf boric acid.
E,~camples of other preferrec polyesters are the reaction produces ~of poiycarbey iic acids and Qiycidyl compcuncs. as are described, far example, inGer~an Patent Application Vo. ~4 1O5i3.
The hydroxyl-containing polyesters used with particular preference have an OH
functionality of > 2. an CH number of from 20 to ?00 rng KOH/g, preferably from 30 to 150 mg KOH/g, a viscosity of < 60,000 mPa~s, preferably < 4Ø000 mPa~s, at ia0°C, and a melting point of > 70 to 120°C, preferably from 75 to 100°C.
EYamples of glycidy! compounds which can be used are esters of 2,3-epoxy-1-propanol with monobasic acids having 4 to 18 carbon atoms, suc~ as glycidyi palmitate, giycidyl !aurate and glyc;dy! stearate, and alkyiene oxides having 4 to 18 carbon atoms. such as buryiene oxide, and glycidyi ethers, suc;~ as octy!
glycidyf ether.
Dicarboxyiic acids which can be used in this process are ail of the polycarboxyiic acids set out under II 'oeiow. or monocarboxylic acids, ~rohich are exemplified under II1, can likewise be used.
Cther preferred components inc;ude monomeric asters, such as dicarboxyiic acid bis(hydrexy~afcnhol)) asters, monocarboxylic esters of more than dihydric polyols, and oligoesters. whic~ can be prepared by condensation reactions from raw materials customary in coatings chemistry. Examples of compounds to be regarded as such are the following:
I. alcohols having 2 to 24, preferably 2 to 10 carbon atoms, and 2 to 6 OH
groups attached to nonaromatic carbon atoms, e.g., ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butanediols, neopentyl glycol, hexanediols, hexanetriois, perhydrobisphenol, dimethylolcyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and mannitol;
I I. di- and polycarboxylic acids having 4-to 36 carbon. atoms and 2 to 4 carboxyl groups, and esterifiable derivatives of these acids, such as anhydrides and esters, e.g. phthalic acid (anhydride), isophthalic acid, terephthalic acid, alkyltetrahydrophthaiic- acid, endo-methyienetetrahydrophthalic anhydride, adipic acid, succinic acid, malefic acid, fumaric acid, dimeric fatty acids, trimellitic acid, pyromellitic acid, and azelaic acid;
III. monocarboxylic acids having 6 to 24 carbon atoms, e.g., caprylic acid, 2-ethylhexanoic acid, benzoic acid, p-tert-butylbenzoic acid, hexahydrobenzoic acid, monocarboxylic acid mixtures from natural oils and fats, such as coconut fatty acid, soybean oil fatty acid, ricinene fatty acid, hydrogenated and isomerized fatty acids, such as "Konjuvandol" fatty acid, and mixtures thereof, it also being possible to use the fatty acids as glycerides and to subject them to transesterification and/or dehydration reactions;
IV. monohydric alcohols having 1 to 18 carbon atoms, e.g., methanol, ethanol, isopropanol, cyclohexanol, benzyl alcohol, isodecanol, nonanol, octanol, and oleyl alcohol.
Such polyesters can be obtained in a manner known per se by condensation in an inert gas atmosphere at temperatures from 100 to 2fi0°C, preferably from 130 to 220°C, in the melt or in an azeotropic procedure, as is described in Methoden der Organischen Chemie (Houben-Weyl), vol. 14/2, 1-5, 21-23, 40-44,Georg Thieme Verlag, Stuttgart, 1963 or in C.R. Martens, Alkyd Resins, 51-59, Reinhold Plastics Appl. Series, Reinhold Publishing Comp., New York and in German Patent Publication Nos. 19 57 483, 25 42 191, 30 04 876, and 31 43 060.
Preferred acrylate resins which can be used as the OH component are homopoiymers .or copolymers, the following monomers being examples of starting materials that can be chosen: esters of acrylic acid and methacrylic acid with dihydric, saturated aliphatic alcoho(s having 2 to 4 carbon atoms, such as 2-hydroxyethyl acryiate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate and the corresponding methacrylates, for example; acrylic acid and methacrylic acid alkyl esters having 1 to 18 carbon atoms in the alcohol component, such as methyl acrylate, ethyl acryiate, propyl acrylate, isopropyl acryiate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acryiate, stearyi acrylate, and the con-esponding methacrylates, for example; acrylic acid and methacrylic acid cyclohexyl esters;
acryionitriie and methacrylonitrile, acryiamide and methacrylamide; and N-methoxymethyi(meth)acrylamide.
Particularly preferred acrylic resins are copolymers of a, from 0 to 50°o by ~Neight of esters of acrylic or methacryiic acid with dihydric or poiyhydric alcohols, such as 1,4-butanediol monoacryiate, hydroxypropyi (meth)acrylate; and also vinyl glycol, vinyithioethanol, allyi alcohol, and 1,4-butanedioi monovinyi ether, b. from 5 to 95°,'° by weight of esters of acrylic acid or methacrylic acid with monohydric alcohols containing 1 to 12 carbon atoms, such as methyl methacryiate, ethyl acryiate, n-butyl acryiate or 2-ethylhexyl acryiate, for example;
c. from 0 to 50°'° by weight of aromatic vinyl compounds, such as styrene, methylstyrene or vinyitoluene;
d. from 0 to 20°,'° by weight of other monomers having functional groups, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, malefic acid, fumaric acid, malefic anhydride, malefic monoesters, acrylamide, methacryiamide, acrylonitriie or N-methyiol(meth)acryiamide, and also giycidyi (meth)acrylate, the proportion of group a. and/or b. being at least 5% by weight. The acryiate resins can be prepared by the customary methods, i.e., by solution, suspension, emulsion or precipitation polymerization, but preferably by bulk polymerization, which in tum can be initiated by means of UV light. Further polymerization initiators used are the customary peroxides or azo compounds, such as dibenzoyi peroxide, tert-butyl perbenzoate or 23443-702 ca 02312462 2000-06-20 azodiisobutyronitrile, for example. The molecular weight can be regulated using, for example, sulfur compounds, such as tert-dodecyi mercaptan.
The hydroxyl-containing polyacrylates prepared in this way have an OH number of from 20 to 150 mg KOH/g, preferably from 25 to 100 mg KOH/g.
The mixing ratio of the hydroxyl-containing polymers and the polyaddition compounds of the invention is generally chosen such that there is 0.5 - 1.2, preferably 0.8 - 1.1, very preferably 1.0 NCO group per OH group.
In order to increase the gelling rate of the heat-curable powder coating materials it is possible to add catalysts. Catalysts used are organotin compounds such as dibutyltin dilaurate- (DBTL), Sn(II) octoate, dibutyitin-maleate, etc. The amount of catalyst added is 0.1 - 5 parts by weight per 100 parts by weight of the hydroxyi-carrying polyester.
For the preparation of PU powder coating materials, the isocyanate compound is mixed with the appropriate hydroxyl-containing polymer and, if desired, catalysts and also pigments and customary auxiliaries such as fillers and leveling agents, e.g., silicone oil, acrylate resins, and the mixture is homogenized in the melt.
This can be done in suitable equipment, examples being heatable kneading apparatus, but prefefably by extrusion, in the course of which the temperature ought not to exceed upper limits of from 130 to 140°C. After cooling to room temperature and appropriate comminution, the extruded mass is ground to the ready-to-spray powder. The application of this powder to appropriate substrates can be carried out in accordance with the known processes, such as, for example, by means of electrostatic powder spraying, fluidized-bed sintering, or electrostatic fluidized-bed sintering.
After powder application the coated workplaces are cured by heating at a temperature of from 150 to 220°C for from 60 to 4 minutes, preferably from 160 to 200°C
for from 30 to 6 minutes.
The subject-matter of the invention is illustrated below with reference to examples.

23443-702 ca 02312462 2000-06-20 Ex-1es A prep- aration of the polyaddition compounds of the invention A1 Polyol chain extenders General preparation procedure The starting components - cf. Tables 1 and 2 - are placed in a reactor and heated to 140°C with the aid of an oil bath. After the substances have largely melted, 0.1 % by weight of di-n-butyltin oxide is added as catalyst. initial elimination of water occurs at from 150 to 160°C. Over the course of 2 to 3 hours, the temperature is increased to from 180 to 190°C and the esterification is- brought to completion over the course of a further 8 to 10 hours. Throughout the reaction period the bottom product is stirred and a gentle stream of nitrogen is passed through the reaction product. The acid number of the polyesters was always < 5 mg KOH/g.

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23443-7(7?. CA 02312462 2000-06-20 A2 ~poxy-terminated polyaddition compounds containing uretdione groups General areaaration procedures A2.1 From solvent Components B) and C) and the catalyst (dibutyitin dilaurate) are initially introduced into a reactor and dissolved in a solvent. With vigorous stirring and under an inert gas atmosphere, the calculated amounts of the uretdione (component A)) in solution in a solvent is added at a rate such that the reaction temperature does not exceed 100°C. The reaction is monitored by means of titrometric NCO
determination and is over after from 1 to 3 hours. Subsequently, the solvent is removed and the product is cooled and, if appropriate; is comminuted.
A2.2 Solventless Component A) was fed at a temperature of from 60 to 110°C into the intake zone of a twin-screw extruder, components B) and C) being metered in simultaneously at a temperature of from 25 to 110°C. If desired, the required amount of catalyst was admixed to the starting components.
The extruder used was composed of ten zones, of which five are heating zones.
The temperatures of the five heating zones are between 50 and 180°C and can be controlled individually. All temperatures are setpoint temperatures.
Regulation within the zones takes place by means of electrical heating and pneumatic cooling.
The die element is heated by means of an oil thermostat. The rotary speed of the twin screws, fitted with conveying elements, was between 50 and 380 rpm.
The reaction product, which is obtained at a rate of from 10 to 130 kg/h, is either cooled, then comminuted or shaped and bagged, or the melt itself is shaped, cooled and bagged.
The physical and chemical characteristics of the process products of the invention, and the molar compositions, are collated in Table 2.
The IPDI uretdione produced by a known process had the following characteristics:

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Table 3: Polyesters Chemical and Dhvsical characteristics Trad e Example Name OH Aad MeltingTg Viscosity No.

i~Ianuf acture numbernumber range (C] at 160 /country (m9 (m9 (C1 (mPa.sl KOH/ KOH/

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C) Polyurethane Aowder coatin4 materials General prec~aration procedure The milled products - poiyaddition compound of the invention, polyester(s), leveling agent, and white pigment - are intimately mixed in an edge runner mil( and then homogenized in an extruder at 80 - 140°C. After cooling, the extrudate is crushed and ground using a pin mill to an particle size < 100 um. The powder prepared in this way is applied to degreased and optionally pretreated iron panels at 60 kV using an eiecirostatic powder spraying unit and the panels are baked in a circulating-air drying oven at 200°C far 15 minutes.
* Trade-marl:

Levelling anent masterbatch 10°,'a by weight of the leveling agent - a commercially customary butyl acryiate polymer - are homogenized in the melt in the corresponding polyester, and the melt, following its solidification, is comminuted.
Catafyst masterbatch ~ Q~~a by weight of the catalyst dibutyitin diiaurate (DBTL) are homogenized in the melt in the corresponding polyester, and the melt, following its solidification, is comminuted.
The curing agent vNas mixed ~roith the polyoi in an NCO : OH ratio of ~ :1.
Additives were as 'oilows:
40.4°,a by mass ~RCNCS 2160 0.~','a by mass leveling agent 0.5'/o by mass benzoin The abbreviations in Table ~ below have the following meanings:
CT = coat thic:~ness in um Ei - Erichsen indentation in mm (DIN 53 15v) GG o0° ~ = Gardner gloss measurement (ASTM-0 523) 81 dir. = direct ball impact in inch-~ lb MEK = methyl ethyl ketone *Trade-mark W *

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The coatings prepared with the polyaddition compounds of the invention are highly glossy and very flexible. in comparison to the prior art, they possess markedly improved resistance to chemicals such as methyl ethyl ketone, far example.

Claims (16)

1. An epoxy-terminated polyaddition compound containing uretdione groups, obtainable by reacting:

A) 40-84.5% by weight of at least one polyisocyanate component synthesized from:

1) at least 40% by weight of a polyisocyanate compound containing uretdione groups and having an average functionality of at least 2.0, and

2) not more than 60% by weight of at least one diisocyanate compound or isocyanurate compound without uretdione groups;

B) 50-15% by weight of at least one compound having at least two hydroxyl groups; and C) 10-0.5% by weight of at least one compound having at least one epoxy group and at least one other group which is reactive with an isocyanate group;

the polyaddition compound being present in solid form below 40°C and in liquid form above 130°C and having a number-average molecular weight of between 1,000 and 15,000, and a free isocyanate group content (calculated as NCO; molecular weight=42) of from 0 to 2% by weight.

2. The polyaddition compound according to claim 1, wherein the polyisocyanate compound A1) containing uretdione groups is prepared from a diisocyanate selected from the group consisting of 1,6-diisocyanatohexane (HDI), 2-methylpentyl-methylene 1,5-diisocyanate (DI 51), 2,2,4(2,4,4)-trimethylhexamethane diisocyanate, 4,4'-diisocyanatodicyclyhexylmethane, 1,3- and 1, 4-diisocyanatocyclohexane,isophorone diisocyanate (IPDI), and, mixtures thereof.

3. The polyaddition compound according to claim 1 or 2, wherein the diisocyanate compound or isocyanurate compound A2) is selected from the group consisting of 1,6-diisocyanatohexane (HDI), 2-methylpentylmethylene 1,5-diisocyanate (DI 51), 2,2,4 (2,4,4)-trimethylhexamethylene diisocyanate,

4,4'-diisocyanatodicyclohexylmethane, 1,3- and 1,4-diisocyanatocyclohexane, isophorone diisocyanate (IPDI), and mixtures thereof.

4. The polyaddition compound according to claim 1, 2, or 3, wherein the compound of B) is a diol selected from the group consisting of ethylene glycol, triethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,

5-pentadiol, neopentyl glycol, 2,2,4(2,4,4)-trimethylhexanediol, neopentyl glycol hydroxypivalate, and mixtures thereof.

5. The polyaddition compound according to any one of claims 1 to 3, wherein the compound B) is selected from the group consisting of linear hydroxyl-containing polyesters, polycarbonates, polycaprolactones, polyethers, polythioethers, polyesteramides, polyurethanes, and polyacetals, and mixtures thereof.

6. The polyaddition compound according to any one of claims 1 to 3, wherein the compound B) is a combination of (1) at least one diol consisting of ethylene glycol, triethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentadiol, neopentyl glycol, 2,2,4(2,4,4)-trimethylhexanediol, neopentyl glycol hydroxypivalate, and mixtures thereof and (2) at least one polymeric diol having a number-average molecular weight of 134 to 3,500 selected from the group consisting of linear hydroxyl-containing polyesters, polycarbonates, polycaprolactones, polyethers, polythioethers, polyesteramides, polyurethanes, polyacetals, and mixtures thereof.

7. The polyaddition compound according to any one of claims 1 to 6, wherein 2,3-epoxy-1-propanol, epoxidized soybean oil, or mixtures thereof are used as component C).

8. A process for preparing an epoxy-terminated polyaddition compound containing uretdione groups by reacting:
A)40-84.5% by weight of at least one polyisocyanate component synthesized from:
1)at least 40% by weight of a polyisocyanate compound containing uretdione groups and having an average functionality of at least 2.0, and 2)not more than 60% by weight of at least one diisocyanate compound and/or isocyanurate compound;
B)50-15% by weight of at least one compound having at least two hydroxyl groups; and C)10-0.5% by weight of at least one compound having at least one epoxy group and at least one other group which is reactive with an isocyanate group;
the polyaddition compound being present in solid form below 40°C and in liquid form above 130°C and having number-average molecular weight of between 1,000 and 15,000, and a free isocyanate group content (calculated as NCO; molecular weight=42) of from 0 to 2% by weight, in a solvent at 50-100°C
or without solvent in an intensive kneading apparatus at 100-190°C.

9. A transparent or pigmented and polyurethane powder coating material free of elimination products, comprising a polyaddition compound according to any one of claims 1 to 7, in combination with a hydroxyl-containing polymer.

10. The polyurethane powder coating material according to claim 9, wherein the hydroxyl-containing polymer is selected from the group consisting of polyester polyols, polyether polyols, polyesteramide polyols, polyurethane polyols, hydroxilated acrylate resins, epoxy resins with hydroxyl groups in the molecule, amino resins and their modification products with polyfunctional alcohols, polyazomethines, polysulfonamides, melamine derivatives, cellulose esters, and cellulose ethers.

11. The polyurethane powder coating according to claim 10, wherein the hydroxyl-containing polymer is a polyester polyol having an OH functionality of more than 2, an OH number of from 20 to 200 mg KOH/g, a viscosity at 140°C of less than 60,000 mPa.s, and a melting point of from 70 to 120°C.

12. The polyurethane powder coating material as according to claim 10, wherein the hydroxyl-containing polymer is a hydroxylated acrylate resin having an OH number of from 20 to 150 mg KOH/g.

13. The polyurethane powder coating material according to claim 9, 10 or, 12, wherein the hydroxy-containing polymer contains more than two OH groups and melts at a temperature of not less than 70°C.

14. The polyurethane powder coating material according to any one of claims 9 to 13, which further comprises at least one member selected from the group consisting of a catalyst, a pigment, a filler, and a leveling agent.

15. The polyurethane powder coating material according to any one of claims 9 to 14, which has an OH/NCO ratio of from 1:0.5 to 1:1.2.

16. A method of forming a glossy, light-stable and weather-stable film on a substrate, which comprises:
applying the polyurethane powder coating material as defined in any one of claims 9 to 15 onto the substrate, and curing the powder coating material at a temperature of from 150 to 220°C.