CA2186715A1 - Polyisocyanates containing hydroxyl and uretdione groups - Google Patents

Abstract

Disclosed are polyaddition products containing hydroxyl groups and uretdione groups, and essentially comprising A) from 55 to 85% by weight of a uretdione, and at least one of:
B) from 2 to 15% by weight of a polyol with 3 hydroxyl groups, C) from 5.5 to 31% by weight of a diol, D) from 7.5 to 33% by weight of a chain extender with a functionality of 2 to 6, provided that when the polyol B is not contained, the chain extender D with a functionality of 3 must be contained, wherein the polyisocyanates carry terminal hydroxyl groups and have a functionality of 3, a molecular weight between 1,500 and 4,400 and a free isocyanate content of less than 0.5% by weight. The polyaddition products are useful as, components of polyurethane powder coating compositions.

Description

. ~
The invention relates to polyaddition products containing hydroxyl groups and uretdione groups and having a functiona~ity of at least 3, and to a process for their preparation and use for the preparation of polyurethane (PU) polymers, especi~lly of elimination-f ree PU coating systems, very preferably of PU powder coating systems, and to the PU
coatings prepared thereby.
Polyisocyanates for use in polyurethane powder coatings, containing uretdione groups, are known in particular from German Patent Publication (DE-A) 30 30 554. Such polyisocyanates, however, have only two ~rmin;~l ~ partially or completely blocked isocyanate groups and are strictly linear in structure. As revealed by European Patent Publication (EP-A)-254 152 (page 2, column 1, line 63 to end of sentence), this state of affairs is of great disadvantage in practice.
Described in EP-A-639 598 is a method based on the polyaddition reaction of polyisocyanates cQntaining uretdione groups with diols and/or with bifunctional chain extenders and, as evident from the examples, with monoalcohols. Owing to the use of monoalcohols, even the use of polyisocyanate-uretdiones containing isocyanurate groups and having more than two ~ICO
functions does not lead to more highly func~inn~1l7~ poly-addition products, the crQsslinking agents for PU powder coatings. EIowever, as mentioned above, this is a disadvantage for the quality of the coating.
In accordance with DE-A 19 505 566, it was possible for the first time to employ polyols having more than two O. Z. 5002 -. ~
hydroxyl groups for the preparation of the claimed polyiso-cyanates containing uretdione groups. However, for this purpose it was necessary to first partially block the isocyanate groups of the polyisocyanate-uretdiones in order - =
to avoid gelling. For economic reasons, removable blocking agents were employed. This, however, constitutes an ecological disadvantage .
A major object of the present invention, therefore, is to provide polyisocyanates containing uretdione groups, in order to use these crosslinking agents for the preparation of elimination-free PU polymers, especially of PU powder coatings, and the PU powder coatings prepared thereby, which no longer have the stated disadvantages of the prior art.
The present invention accordingly provides poly-addition products which contain hydroxyl groups and uretdione groups and consist essentially of:
A) from 55 to 859~ by weight of uretdiones derived from diiso-cyanates, and at least one hydroxyl compound selected from the group consisting of:
B) from 2 to 15% by weight of polyols having at least 3 hydroxyl groups, C) from 5.5 to 31% by weight of diols, and D) from 7.5 to 33% by weight of chain f~ n~l~rs having a functionality of from 2 to 6, provided that when the polyols B) are not contained, then the chain extenders D) having at least 3 hydroxyl groups must be contained, whereby the poly-addition products carry ~!~r~nin~l hydroxyl groups and have a .
functionality of three or more, preferably from. three to four, a molecular weight of between 1,500 and 4,400, preferably between 1,800 and 3,500, and a free isocyanate content of less than 0 . 5% by weight. The polyaddition products may also be called as polyisocyanates hereinunder since they are derived from diisocyanates, although they contain essentially no free isocyanate groups.
The invention additionally provides the use of the polyisocyanates containing hydroxyl groups and uretdione groups for the preparation of polyurethane (PU) polymers, especially in combination with hydroxyl-containing polymers, in elimination-free, transparent and pigmented polyurethane (PU) powder coatings of increased network density, very good reactivity and excellent gloss, and also provides elimination-free transparent and pigmented polyurethane (PU) powder coatings comprising the polyisocyanates according to the invention, containing hydroxyl groups and uretdione groups and having a functionality of at least 3.
The uretdiones employed in accordance with the invention (component A) are obtained from diisocyanates in accordance with the known methods, and it is posslble, in principle, to employ all known diisocyanates.
Preferred uretdiones, however, are derived from diisocyanates selected from the group consisting of hexa-methylene 1,6-diisocyanate (HDI), 2-methylpentamethylene 1,5-di i socyanate (DI 51 ), 2, 2, 4 ( 2, 4, 4 ) -trimethylhexamethylene diisocyanate and isophorone diisocyanate (IPDI). These diisocyanates may be employed individually or in mixtures as component A.
Typical uretdiones derived from diisocyanates have tPrm~nAl isocyanate groups and may be represented by the f ormula:

o Il OCN--R--N/ \N--R--NCO

n wherein n is an integer such as 1 to 6 and R is the residue of the diisocyanate.
Particularly preferred is the uretdione of isophorone diisocyanate.
The typical isocyanurate-free uretdione of isophorone diisocyanate (IPDI) is highly viscous at room temperature, i.e.
the viscosity is greater than 106 mPa-s; at 60C, it is 13 x 103 mPa-s and at 80C, it is 1.4 x 103 mPa-s. The free NCO content is between 16.8 and 18.5% by weight; in other words, more or less high proportions of polyuretdione of IPDI
must be present in the reaction product. The monomer content is about 1% ~y weight. The overall NCO content of the reaction product after heating at 180 - 200C is 37.5 - 37.896 by weight.
Wllen conventional catalysts and processes are used to dimerize aliphatic diisocyanates, isocyanurates are often formed as by-products in varying quantities, so that the NCO

' ~
functionality of the isocyanurate-contAining polyisocyanate-uretdiones employed is usually from about 2 to about 2 . 5 . It is therefore highly surprising that isocyanurate-containing -polyisocyanate-uretdiones of this type can be employed for the synthesis of polyisocyanates containing hydroxyl groups and uretdione groups and having a functionality of at least 3 without the occurrence of gelling.
Suitable polyols (component B) in accordance with the invention preferably have three to six hydroxyl groups and examples thereof include glycerol, trimethylolpropane, ditrimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, tris(~-hydroxyethyl) isocyanurate, penta-erythritol, mannitol and sorbitol, with preference being given to the use of trimethylolethane, trimethylolpropane (TMP) and trishydroxyethyl isocyanurate (THEIC). They are used individually or in mixtures.
The diols employed in accordance with the invention (component C) include all those customarily employed in PU
chemistry. Examples of particularly preferred diols include:
ethylene glycol (E), triethylene glycol (TEG), 1,4-butanediol (B), 1,5-pentanediol (P), 1,6-hexanediol (HD), 3-methyl-1,5-pentanediol (Pm), neopentylglycol (N), 2,2,4 (2,4,4)-trimethyl-hexanediol (T) and neopentylglycol hydroxypivalate (Eg).
The novel polyisocyanates may also contain chain extenders (component D) having a functionality of from 2 to 6, in particular f rom 2 to 4, in the f orm of li~ear and branched ' ~
hydroxyl-terminated polyesters having a molecular weight of between 180 and 2,000, preferably between 230 and 1,500, and a hydroxy number of between 900 and 50 mg of KOH/g, preferably between 700 and 100 mg of E~OH/g. They are prepared, for example, by condensing polyols (e.g., diols) and dicarboxylic acids or by polyerizing lactones or hydroxycarboxylic acids.
The "chain extenders" here generally mean oligomers and low polymerization polymers having t~rm;n~l hydroxyl groups.
Preferred chain extenders used are linear, hydroxyl-terminated polyesters or polycaprolactones having a molecular weight of between 180 and 2,000 and a hydroxyl number of between 625 and 50 mg of KOH/g.
Other preferred chain extenders used are branched polyesters or polycaprolactones having a functionality of 3 to 6, a molecular weight between 210 and 2, 000 and a hydroxyl number between 900 and 100 mg of KOH/g.
To prepare t~e chain e_tenders, it is preferred to employ the abovementioned polyols and/or diols, supplemented by 2-methyl-1, 3-propanediol, diethylene glycol, 1,12-dodecane-diol and trans- and cis-cyclf~ Y~nf~ thanol (CE~DM).
The preferred dicarboxylic acids include aliphatic acids with or without alkyl branching, such as succinic acid, adipic acld (As), suberic, azelaic and sebacic acid (Sb), 2, 2, 4 ( 2, 4, 4 ) -tr imethy ladipic ac id .
Alternatively, the chain extenders may be prepared by polymerizing lactones and hydroxycarboxylic acids, such as ~-caprolactone and hydroxycaproic acid. These lacto~es and 2~ ~67~
hydroxycarboxylic acids may further be used by partly replacing ~=
the dicarboxylic acid or the diols.
The hydroxyl-containing reactants, namely components B, C and D, are employed such that the OH component necessarily contains at least one of the polyol B and the chain extender D
having three or more OH groups. In a preferred embodiment, at least one mol of the polyols B or the chain extenders having three to OH groups per three mols of the uretdiones A may be employed .
The mixing ratio of the hydroxyl-containing reactants (i.e., B, C and D) with the uretdione must be chosen such that the iunctionality of the polyaddition products is at least 3.
The polyaddition products according to the invention can be obtained preferably by the process described as follows.
The reaction in solvent takes place in general at temperatures from 50 to 100C, preferably between 60 and 90C.
The OH component (one or more of the polyol B, diol C and chain extender D) is initially introduced into a reaction vessel, and the uretdione is added as rapidly as possible keeping the reaction tel[lperature within the abovementioned limits. The reaction is complete after from 30 to 150 minutes.
The solvent is then removed, suitably using evaporation screws, f ilmtruders or spray dryers .
Suitable solvents include benzene, toluene or other aromatic or aliphatic hydrocarbons, acetates such as ethyl acetate or butyl acetate, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, or chlorinated aromatic and 2~867~5 aliphatic hydrocarbons, and any desired mixtures of these or ~_ other inert solvents.
The invention additionally pro~ides the solvent-free and continuous preparation of the addition products by means of intensive kneading apparatus in a single-screw or multi-screw extruder, in particular in a twin-screw extruder. The solvent-free synthesis requires temperat~res o from 110 to 190C. It was surprising that such high temperatures can be used for the uretdione syntheses. These temperatures are already well within the recleaving range for uretdiones, with the poss~bility that high free isocyanate contents may result, whereby uncontrolled reaction processes might be expected.
This factor was significant for the synthesis of the hydroxyl-containing uretdione polyaddition product, and it was all the more surprising that the synthesis could be carried out. A
f actor which proved to be of advantage here was the short reaction times of less than 5 minutes, preferably less than 3 minutes, in particular less than 2 minutes.
Another matter of signi~icance is that the short-term exposure to heat is sufficient in order tD mix the reactants homogeneously, during which they are completely or extensively converted. The ~atch is subsequently cooled in a controlled manner, in accordance with the establishment of -equilibrium, and, if necessary, the conversion is completed (by further heating).
The reaction substrates are fed to the reaction kneading apparatus in separate substrate streams, it bein~

234~3-580 ' ~i possible :Eor the starting components to be preheated at up to 120C, preferably up to 90C. Whe:re there are more than two product streams, they can also be = added together . Polyol and/or diol and/or chain extenders and/or catalysts and/or further customary paint additives, such as leveling agents and/or stabilizers, can be brought together to form one product stream; the same applies to those components which are inert towards isocyanate groups; catalysts and abovementioned paint additives.
The sequence of the substrate streams can also be =
varied, as can the point o~ entry of the substrate streams.

- 8a -234~3-580 ~i _ g _ o.Z. 5002 For after-reaction, cooling, comminution and bagging, known technigues and technologies are used.
.
In order to accelerate the polyaddition reaction it is also poscihl~ to use catalysts which are customary in 5 polyurethane chemistry, which are employed in a concen-tration of from 0.01 to 196 by weight, preferably from 0.03 to 0.596 by weight, based on the reaction components employed . C , ~ c which have proven particularly suitable to date are tin(II) and tin(IV) ~ ds.
10 Particular mention is made here of dibutyltin dilaurate (DBTL). However, other catalysts should not be regarded as being unsuitable in principle.
The present invention provides, furth~ e, for the use of polyisocyanates containing hydroxyl groups and 15 uretdione groups for the preparation of polyurethane polymers, especially in combination with hydroxyl-con-taining polymers and/or the additives which are customary in polyurethane chemistry, for the preparation of elimin-ation-free, ~rAncpArent and pigmented PU powder coatings 20 which are distinguished by very good reactivity and are therefore both ernn, -~~lly and r~rnlnrJic~lly s;qnifir-~nt, and which surprisingly, despite increased network den-sity, are of outstanding fl~Yihility.
The present invention also provides elimination-f ree EU
25 powder coatings consisting of the polyisocyanates accord-ing to the invention in combination with hydroxyl-con-taining polymers. Suitable co-reactants for PU powder . ~
- 10 - O. % . 5002 coatings are .ullds which carry functional groups which, during the curing process, react with isocyanate groups as a function of temperature and time, examples being hydroxyl, carboxyl, mercapto, amino, urethane and 5 ( thio ) urea groups . Polymers which can be employed are addition polymers, cnn~ n~tion polymers and polyaddition compounds .

Preferred c~ lLs are primarily polyethers, polythio-ethers, polyacetals, polyesteramides, epoxy resins with 10 hydroxyl groups in the molecule, amino resins and their modification products with polyfunctional alcohols, polyazomethines, polyurethanes, polysulf nn irl~
l~min~ derivatives, cellulose esters and cellulose ethers, partially hydrolyzed homo- and copolymers of 15 vinyl esters, but especially polyesters and acrylate resins .

Preferred carboxylic acids for the preparation of polyesters can be aliphatic, cycloaliphatic, aromatic and/or heterocyclic in nature and may if desired be 20 substituted by halogen atoms and~or may be unsaturated.
Examples thereof are succinic, adipic (A~ ), suberic, azelaic, sebacic, phthalic, terephthalic (TS), iso-phthalic (Is), i-ri llitic, ~yl~ -llitic, tetrachloro-phthalic, endomethylenetetral.ydlu~lLhalic, glutaric, 25 maleic and fumaric acids and - where obtainable - their anhydrides, dimethyl terephthalate (D~T), bisglycol terephthalate, and also cyclic ~ylic acids, such as benzoic acid, p-tert-butylbenzoic acid and hexahydro-21867~5 - 11 - O . Z . 5002 benzoic acid.
- Examples of suitable polyhydric alcohols are ethylene glycol, 1, 2- and 1, 3-propylene glycol, 1, 4- and 2, 3-butylene glycol, di-~ ydlu~y~:Lhylbutanediol~ 1,6-hexane-5 diol , 1 , 8-octanediol , neopentylglycol , cycl~hF-Y~ n~ i o l, 1~4-bis(hydroxymethyl)cyclnh~y~n~ 2,2-bis(4-hydroxy-cyclûhexyl)propane, 2,2-bis[ (,~-llydlu~yl:Lhoxy)phenyl]-propane, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentane-diol, 2, 2, 4 ( 2, 4, 4 ) -trimethyl- 1, 6 -h~Y;I n~i i ol, glycerol, 10 trimethylolpropane, trimethylolethane, 1, 2, 6-hexanetriol, 1, 2, 4-butanetriol, tris ( 3-hydroxyethyl ) isocyanurate, pentaerythritol, mannitol and sorbitol and also diethyl-ene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polypropylene glycols, polybutylene 15 glycols, xylylene glycol and neopentylglycol ~ydlu~y,~uivalate .

It is also possible to employ mono- and polyesters as lactones, for example ~-caprolactone, or llyd- u~y~arbOx-ylic acids, for example hydroxypivalic acid, Q-hydroxy-20 decanoic acid, Q-l.ydlur.yuaproic acid, thioglycolic acid.
Polyesters of the ~buv~ ~ioned polycarboxylic acids and/or their derivatives and polyphenols, such as hydroouinone, bisphenol A, 4,4'-dilly~lLu~ybiphenyl or bis(~-l.ydlu~y~ul~llyl) sulfone; polyesters of carbonic acid 25 which are obtainable from hydro~uinone, diphenylol-propane, p-xylylene glycol, ethylene glycol, butanediol or 1, 6-h~Y~n~1 i ûl and other polyols by customary conden-sation reactions, for example with phosgene or with _ _ _ _ _ _ , . . ... . . ..... . .. .

2~86715 diethyl or diphenyl carbonate, or from cyclic carbonates such as glycol carbonate or vinylidene carbonate, by polymerization in a known manner; polyesters of silicic acid, polyesters of phosphoric acid, for example of methane-, ethane-, ~-chloro-ethane-, benzene- or styrene-phosphoric acid, -phosphoryl chloride or -phosphoric ester and polyalcohols or polyphenols of the abovementioned type; polyesters of boric acid; poly-siloxanes, for example the products obtainable by hydrolysis of dialkyldichlorosilanes with water and subsequent treatment with polyalcohols, and those obtainable by addition of poly-siloxane dihydrides onto olefins, such as allyl alcohol or acryl ic ac id .
Preferred polyesters are also for example the reaction products of polycarboxylic acids and glycidyl compounds, as described for example in DE-C 24 10 513.
The hydroxyl-containing polyesters which are employed with particular preference have an OH functionality of greater than 2, an OH number of from 20 to 200 mg of KOH/g, preferably from 30 to 150 mg of KOH/g, a viscosity of less than 60,000 mPa-s, preferably less than 40,000 mPa-s, at 140C and a melting point of from 70 to 120C, preferably from 75 to 100C.
Dicarboxylic acids ~hich can be used in this process are all of the polycarboxylic acids listed below urder 2.
Monocarboxylic acids which are listed below under 3., for example, can likewise be employed.

- 13 - O . Z . 5002 Other preferred ~~ I s are ~ esters, for example bis(hydroxy(alcohol)) dicarbo~ylates, monocarbox-ylic esters of more-than-dihydric polyols, and oligo-esters ~hich can be prepared by cn~ n~ation reaction from base materials which are customary in paint chemis-try. r ~ of c, Dullds which can be regarded as such are:
1. Alcohols having 2 to 24 carbon atoms, preferably 2 to 10 carbon atoms, and 2 to 6 OH groups attached to nonaromatic carbon atoms, for example ethylene glycol, propylene glycol, diethylene glycol, dipro-pylene glycol, butanediols, neopentylglycol, hr~-~nr~rl i ols, hexanetriols, perhydrobisphenol, dimethylolcye 1~)hr~Y~n F'~ glycero1, trimethylolethane, trimethylolpropane, pentaerythritolr dipentaerythri-tol and mannitol;
2. Di- and polycar}~oxylic acids having 4 to 36 carbon atoms and 2 to 4 carhoxyl groups, and est~ri f i ~hl e derivatives thereof, such as anhydrides and esters, for example phthalic acid (phthalic anhydride), isophthalic acid, terephthalic acid, alkyltetra-llydL~ alic acid, endomethylenetetrahydrophthalic anhydride, adipic acid, succinic acid, maleic acid, fumaric acid, dlmeric fatty acids, tri llitic acid, ~yl~ -llitic acid and azelaic acid;

3. ~onocarboxylic acids having 6 to 24 carbon atoms, for example caprylic acid, 2-ethylhexanoic acid, 21867~5 - 14 - O . Z . 5~02 benzoic acid, p-tert-butylbenzoic acid, hexahydro-benzoic acid, monocarboxylic acid mixtures of natu-ral oils and fats, such as coconut fatty acid, soya oil fatty acid, rieinr~nic fatty acid, hydrogenated and isomerized fatty acids, such as "Ronjuvandol"
fatty acid and mixtures thereof. It is also possible for the fatty acids to be employed as glycerides and to be reacted in t ~llse~ Lerification and/or dehydration reactions;
10 4. II~ ully~lLic ;~lcnhol~ having 1 to 18 carbon atoms, for example methanol, ethanol, isopropanol, cyclohex-anol, benzyl alcohol, isodecanol, nonanol, octanol and oleyl alcohol.
The polyesters can be obtained in a manner known per se by ~nn~ n~ tion in an inert gas ai ~_L,he ~d at tempera-tures o~ from 100 to 2607C, preferably from 130 to 220C, in the melt or by an azeotropic procedure, as described for example in Methoden der Organischen Chemie (Houben-~eyl), Vol. 14/2, 1 - 5, 21 - 23, 40 - 44, t,eorg Thieme Verlag, SLuLLyt~l L, 1963 or in C.R. Martens, Alkyd Resins, 51 - 59, R~inhnl~i Plastics ~ppl. Series, Reinhold Publishing Comp., New York, 1961.
Preferred acrylate resins which can be used as OII compon-ent are homo- or copolymers in which case, for example, the following can be chosen as starting com-pounds: esters of acrylic acid and methacrylic acid with dihydric, saturated, aliphatic alcohols having 2 to - 15 - 0. Z . 5002 4 carbon atoms, for example 2-1lydLu~.y~:Lhyl acrylate, 2-IIYdLV~Y~LU~Y1 acrylate, 4-1~ydlu~yLuLyl acrylate and the corr-~cpnn-lin~ methacrylates; acrylic and methacrylic alkyl esters having 1 to 18 carbon atoms in the alcohol _ , L, for example methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate and the uuL~ ul~ding methacrylatefi; cyclohexyl acrylate and cyclohexyl methacrylate; acrylonitrile and methacrylonitrile, acrylamide and methacrylamide; and N-methoxymethyl (meth ) acrylamide .
Particularly preferred acrylate resin5 are copolymers ûf a) from 0 to 50% by weight of esters of acrylic or methacrylic acid with dihydric or polyhydric alco-hols, such as 1, 4-butanediol monoacrylate, hydroxy-propyl (meth)acrylate; and also vinyl glycol, vinyl thioethanol, allyl alcohol and 1, 4-butanediol mono-vinyl ether;
b) from 5 to 959~ by weight of esters of acrylic acid or methacrylic acid with ~' yd~ic alcohols containing 1 to 12 carbon atoms, such as methyl methacrylate, ethyl acrylate, n-butyl acrylate or 2-ethylhexyl acrylate;
c) from 0 to 509s by weight of aromatic vinyl ~- rlc such as styrene, methylstyrene or vinyltoluene;

21~6715 , - 16 - O. Z . 5002 d) from 0 to 2096 by weight of other ~ containing functional groups, for example acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, maleic anhydride, maleic monoesters, acrylamide, methacrylamide, acrylo-nitrile or ~i-methylol(meth)acrylamide and glycidyl (meth ) acryla~e, the proportion of group a ) and/or b ) being at least 596 by weight.
The acrylate resins can be prepared by the customary methods, i.e. by solution, suspension, l~ nn or precipitation polymerization; however, they are preferab-ly ~ al~ by bulk polymerization, which can in turn be initiated by means of W light.
Other polymerization initiators used are the customary peroxides or azo compounds, examples being dibenzoyl peroxide, tert-butyl L,~ ~ oate or ~r~rli i, l uLy ~J-nitrile . The molecular weight can be regulated with, f or example, sulfur ~ u--ds, such as tert-dodecyl mercaptan .
Preferred polyethers can be prepared, for example, by polyaddition of epoxides, such as ethylene oxide, propylene oxide, butylene oxide, tri ylene oxide, 3,3-bis(chlul ' yl)oxacyclobutaner tetrahydrofuran, styrene oxide, the 2, 5-bis ( ~pO~y~ y 1 ) ether of diphenylolprop-ane or r~rirl~ln~ohydrin with itself, for example in the presence of BF" or by addition reaction of these epoxides, individually in a mixture or in succession, - 17 - O. Z . 5002 with starting r ~ ~nts containing reactive llydl~y~
atoms, such as alcohols or amines, for example water, ethylene glycol, 1, 3- or 1, 2-propylene glycol, pentameth-ylene glycol, h~Y~nf-linl, ~If Lhylene glycol, tri-S methylolpropane, 4,4'-dillydl~J~y~iphenylpropane~ aniline, ammonia, ethanolamine, ethylf-ne~ minf~, di(~-hydroxy-propyl)methylamine, di(,~-hydlu~y~Lhyl)aniline~ hydrazine and also hydroYyalkylated phenols, f or example di ( B-hydroxyethoxy)rf~qorl-innl .
It is likewise possible to employ hydroxyl-containing polyurethanes and/or polyureab.
The mixing ratio of the hydroxyl-containing polymers and the polyisocyanates according to the invention is gen-erally chosen such that there are 0 . 5 - 1. 2, pref erably 0.8 - 1.1, NCO groups per OH group, with very particular pref erence 1. 0 NCO group per OH group .
For the production of PU powder cn~tin~q~ the isocyanate component is mixed with the i~rFrQ~ri Ate hydroY~yl-contain-ing polymer and, if desired, catalysts and also pigments and customary ~I~Yi l i~ries, such as fillers and leveling agents, for example ~ilicnn~ oil, acrylate resins, and the mixture is homogenized in the melt. This can take place in suitable apparatus, for example heatable knead-ing equipment, but preferably by extrusion, in which case upper temperature limits of from 130 to 140C should not be exceeded. The extruded composition, after cooling to room temperature and after appropriate comminution, is 2~86715 - 18 - O. Z . 5002 ground to a ready-to-spray powder. The application of the ready-to-spray powder to suitable suhstrates can be carried out by the known methods, for example by electro-static powder spraying, fluidized-bed sintering, or electrostatic f ~ i 7e~l-bed sintering. Following applica-tion of the powder, the coated ~nrkr;e~-~c are heated for curing ~ oses for from 4 to 60 minutes at a temperature of from lS0 to 220C, rr~f-~r~hly for from 6 to 30 minutes at from 160 to 200C.
~he suhject-matter of the invention is illustrated in more detail below with rf-f,~r~nr- to e~amples. The abbrev-iations used are ~r' ~ i n~od in the description at the appropriate points ( pages 3 and 4 ) .
A Pre~aration of the hydrox~l and uretdione grou~-c~n~aining ~olyisocyanates aCcQr~l i ncz to the inven-~n A 1 ~olyol ~-h;l i n extenders r.on~r~ 1 preparation procedure The starting ~ n~nts - cf. Tables 1 and 2 - are placed in a reactor and heated with the aid of an oil bath to Y 140C. After the substances have been largely melted, 0.1% hy weight of di-n-butyltin oxide is added as catalyst. Initial elimination of water takes place at from 150 to 160C. The tempera-ture is raised to fro~ 180 to 190C over the course 21867~5 - 19 - O . Z . 5002 of from 2 to 3 hours and the est~ri~ic~tion is brou~ht to an end over zl f urther 8 to 10 hours .
During the entire ro~ rfirn period, the bottom prod-uct is stirred and a weak stream of nitrogen is pa~sed through the reaction mixture. The acid nur~ber of the polye~ters is always less than 2 mg of l~OH/g.

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2 1 867~ 5 - 22 - O.Z. 5002 A 2 Poly; F ocyanates cont ~ i n i n ~7 h~rl rox yl ~ n~l uret ri i ~n~
g~Q~
- General pr ~p~rAtion ~L.,~edu~s A 2.1 Wi~h solvent The polyol c , I - cf. Table 3 - ~Lnd the catalyst (0.03 - 0.5% by weight DBTL) are intro-duced into the reactor as a solution in the solvent. With vigorous stirring and under an inert gas atmosphere, the calculated quantity of uretdione, as a solution in the solvent, is added rapidly at a rate such that the reaction tempera-ture does not exceed 100C. The reaction is monitored by means of titrimetric NCO determina-tion and is over af ter 1 to 3 hours . The solvent is subsec~uently removed, and the product is cooled and, if desired, comminuted.
A 2 . 2 w~ ~h~ut ~olvent The llre~ n~ was fed at a t~ l_u~ of from 60 to 110C into the entry barrel of a twin-screw extruder, the polyol ~ ~ 1 - cf. Table 3 -being metered in simultaneously at a temperature of from 25 to 110C. The uretdione and~or the polyol component contained, if ~p~ iate, the quantity of catalyst required - f rom 0 . 0 3 - O . 5 96 by weight DBTL -, based on thQ end product.

2~8~7~
- 23 - O.Z. 5002 The extruder employed is , s~l of ten barrels, of which five are heating zones. The temperatures of the heating zones are within a wide ran~e -between 50 and 190C - and can be controlled individually. All temperatures are ~etpoint ~ ~ Lu~s, and regulation in the barrels takes place by electric heating and pneumatic cooling.
The die element i8 heated by an oil thermostat.
The rotary speed of the twin screw, fitted with conveying elements, was between 50 and 380 rpm.
The reaction product, o~tained at a rate of from 10 to 130 kg/h, is either cooled, then comminuted or shaped and bagged, or else the melt itself is shaped, cooled and bagged.
The physical and chemical characteristics of the novel process products and the molar compositions are collated in Tables 3 to 5.
The uretdiones prepared by known processes had the f ollowing characteristics:
IPDI uretdione NCO-free: from 16 . 8 to 18 .5% by weight Total NCO: from 37.4 to 37.896 by weight DI 51 uretdione NCO-free: from 20.1 to 21.2% by weight - 24 - O.Z. 5002 Total NCO: from 43 . 7 to 44 . 99~ by weight HDI uretdione (DE:SNOD~ 1~ 3400) NCO-free: from 20.9 to 22.196 by weight Total ~ICO: from 35.6 to 36.596 by weight 21867~5 . ~
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~ 34 ~ O. Z . 5002 C Polynrethane powder coatinqs r.on~r~l ~reparation yLu~
The nllt~ products - polyisocyanates containing llr~triinnF. groups (croF:Slinkin ~ agents), polyesters, leveling agent masterbatch and, if ~?rrorrii~te, catalyst masterbatch - are intimately mixed with or without the white pigment in an edge runner mill and then homogenLzed in an ~LLUde1 at a maximum tem-perature of 130C. After cooling, the extrudate is fractionated and ground with a pinned-disk mill to a particle s~7e less than 100 ~n. The paAder thus pre~ared is applied with an electrostatic power spraying unit at 60 kV to ri~r~ edr optionally pretreated iron panels which are baked in a convection oven at t-emperatures between 160 and 200C.
T.~V~l i nn agent masterbatch 1096 by weight of the leveling agent - a commercially available copolymer of butyl acrylate and 2-ethyl-hexyl acrylate - are homogenized in the melt in the ~ulL ~ n~ polyester and comllL~ nuted after having sol i-li f i~,~, Catalyst master~atch 596 by weight of the catalyst - DBTL - are homogen-ized in the melt in the ~ol~ ul.ding polyester and comminuted af ter having s~ l i f i ~
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Claims (31)

1. A polyaddition product containing hydroxyl groups and uretdione groups, and being formed essentially of:
A) from 55 to 8596 by weight of a uretdione derived from a diisocyanate, and at least one hydroxyl compound selected from the group consisting of:
B) from 2 to 15% by weight of a polyol having at least 3 hydroxyl groups, C) from 5.5 to 31% by weight of a diol, and D) from 7. 5 to 33% by weight of a chain extender having a functionality of from 2 to 6, provided that when the polyol B) is not contained, then the chain extender D) having a functionality of 3 to 6 must be contained, wherein the polyaddition product carry terminal hydroxyl groups and have a functionality of at least 3, a molecular weight between 1,500 and 4,400 and a free isocyanate content of less than 0.5% by weight.

2. A polyaddition product as claimed in claim 1, which has a functionality of from 3 to 4 and a molecular weight between 1, 800 and 3, 500.

3. A polyaddition product as claimed in claim 1 or 2, wherein the uretdione is of at least one diisocyanate selected from the group consisting of hexamethylene 1,6-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, 2,2,4 (2,4,4)-trimethylhexamethylene diisocyanate and isophorone diisocyanate.

4. A polyaddition product as claimed in any one of claims 1 to 3, wherein the polyol is at least one member selected from the group consisting of glycerol, trimethylol-propane, ditrimethylolpropane, trimethylolethane, 1, 2, 6-hexanetriol, 1, 2, 4-butanetriol, tris (.beta.-hydroxyethyl) isocyanurate, pentaerythritol, mannitol and sorbitol.

5. A polyaddition product as claimed in any one of claims 1 to 4, wherein the diol is at least one member selected from the group consisting of ethylene glycol, triethylene glyco1, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 3-methyl-1, 5-pentanediol, neopentylglycol, 2, 2, 4 ( 2, 4, 4 ) -trimethylhexanediol (isomeric mixture) and neopentylglycol hydroxypivalate.

6. A polyaddition product as claimed in any one of claims 1 to 5, wherein the chain extender is a linear hydroxyl-terminated polyester or polycaprolactone having a molecular weight between 180 and 2,000 and a hydroxyl number between 625 and 50 mg of KOH/g.

7. A polyaddition product as claimed in claim 6, wherein the linear hydroxyl-terminated polyester is derived from at least one diol selected from the group consisting of ethylene glycol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanedio1, 3-methyl-1, 5-pentanediol, 2, 2, 4 ( 2, 4, 4 ) -trimethylhexanediol, neopentylglycol hydroxypivalate, 2-methylpropanediol, 2,2-dimethylpropanediol, diethylene glycol, 1,12-dodecanediol and trans- and cis-cyclohexanedimethanol and at least one dicarboxylic acid selected from the group consisting of succinic, adipic, suberic, azelaic, sebacic and 2,2,4 (2,4,4)-trimethyladipic acid (isomer mixture), or is derived from .epsilon.-caprolactone or hydroxycaproic acid.

8. A polyaddition product as claimed in any one of claims 1 to 5, wherein the chain extender is a branched poly-ester or polycaprolactone having a functionality of at least 3, a molecular weight between 210 and 2,000 and a hydroxyl number between 900 and 100 mg of KOH/g.

9. A polyaddition product as claimed in claim 8, wherein the chain extender comprises in addition to a dicarboxylic acid, hydroxycarboxylic acid or lactone at least one mol of a polyol selected from the group consisting of trimethylol-ethane, trimethylolpropane, tris (hydroxyethyl) isocyanurate and pentaerythritol.

10. A polyaddition product as claimed in any one of claims 1 to 5, wherein the chain extender is based on .epsilon.-capro-lactone or a hydroxycaproic acid.

11. A polyaddition product as claimed in any one of claims 1 to 5, wherein the chain extender is a linear or branched hydroxyl-terminated polyester having a hydroxyl functionality of 2 to 6, a molecular weight of 180 to 2, 000 and a hydroxyl number of 900 to 50 mg of KOH/g.

12. A polyaddition product as claimed in any one of claims 1 to 11, wherein the chain extender has a functionality of from 2 to 4.

13. A process for preparing the polyaddition product as claimed in any one of claims 1 to 12, which comprises:
reacting the uretdione derived from a diisocyanate A with at least one of the hydroxyl-containing reactants B, C
and D, provided that when the polyol B is not employed, then the chain extender having a hydroxyl functionality of 3 to 6 must be employed.

14. A process for preparing the polyaddition product as claimed in any one of claims 1 to 12, which comprises:
reacting the uretdione A having terminal isocyanate groups and being derived from a diisocyanate, with a mixture of the polyol B, the diol C and the chain extender D, wherein the mixture contains at least 1 mol of the polyol B or the chain extender D having three to six hydroxyl groups per molecule relative to 3 mols of the uretdione A; and the uretdione A, the polyol B, the diol C and the chain extender D are employed in such amounts that the resulting polyaddition product has a functionality of at least 3.

15. The process as claimed in claim 13 or 14, wherein the reaction is carried out at a temperature of from 50 to 100°C
in a solvent which is removed after the reaction has taken place.

16. The process as claimed in claim 13 or 14, wherein the reaction is carried out without solvent in an intensive kneading apparatus at a temperature of from 110 to 190°C.

17. The process as claimed in claim 16, wherein the reaction is carried out in a twin-screw extruder.

18. The process as claimed in any one of claims 13 to 16, wherein a catalyst is employed for the reaction in a concentration of from 0.01 to 1% by weight, based on the starting materials employed.

19. The process as claimed in claim 18, wherein an organic tin compound is employed as the catalyst.

20. The process as claimed in claim 18 or 19, wherein from 0.03 to 0.5% by weight of the catalyst is employed.

21. An elimination-free, transparent or pigmented poly-urethane powder coating, which comprises the polyaddition product as claimed in any one of claims 1 to 12, in combination with a hydroxyl-containing polymer.

22. A polyurethane powder coating as claimed in claim 21, which is based on an OH/NCO ratio of from 1:0.5 to 1.2.

23. A polyurethane powder coating as claimed in claim 21 or 22, which also contains a catalyst in a concentration of from 0.03 to 0.5% by weight, including a catalyst which may be employed in, the production of the polyaddition product.

24. A polyurethane powder coating as claimed in claim 23, wherein an organic tin compound is contained as the catalyst.

25. A polyurethane powder coating as claimed in claim 23 or 24, wherein from 0.05 to 0.15% by weight of the catalyst is contained.

26. A polyurethane powder coating as claimed in any one of claims 21 to 25, wherein the hydroxyl-containing polymer is a polyester having a functionality of greater than 2, an OH
number of from 20 to 200 mg of KOH/g, a viscosity of less than 60,000 mPaS at 160°C and a melting point of from 70 to 120°C.

27. A polyurethane powder coating as claimed in claim 26, wherein the polyester has a functionality of greater than 2, an OH number of from 30 to 150 mg of KOH/g, a viscosity of less than 40,000 mPas at 160°C and a melting point from 75 to 100°C.

28. A method of coating a substrate according to any one of claims 21 to 27, which comprises:
applying the powder coating composition to a substrate, and curing the so-applied powder coating composition at a temperature of 160 to 200°C for from 4 to 60 minutes, wherein the substrate is one which can withstand the curing conditions.

29. A polyaddition product having terminal hydroxyl groups and uretdione groups, and being formed essentially of:

A) from 55 to 85% by weight of a uretdione which is derived from a diisocyanate and has terminal isocyanate groups, B) from 2 to 15% by weight of a polyol having at least hydroxyl groups, C) from 5.5 to 31% by weight of a diol, and D) from 7.5 to 33% by weight of a chain extender having a functionality of 2 to 6, wherein the polyaddition product has a functionality of at least 3, a molecular weight of between 1,500 and 4,400 and a free isocyanate content of less than 0.5% by weight.

30. A polyaddition product as claimed in claim 29, wherein the chain extender is a linear or branched hydroxyl-terminated polyester having a hydroxyl functionality of 2 to 6, a molecular weight of 180 to 2,000 and a hydroxyl number of 900 to 50 mg of KOH/g.

31. A polyaddition product as claimed in claim 29 or 30, which has a functionality of from 3 to 4 and a molecular weight of between 1,800 and 3,500.