Description

The present invention relates to a process for preparing a polyu rethane elastomer com pris ing the steps of (A) preparing an isocyanate prepolymer (a) by mixing (al) at least one iso cyanate reactive composition comprising a polyol, selected from polyester polyol polyether polyol or mixtu res thereof, having an average fu nctionality in the range of > 1.8 to < 2.5 and an OH value in the range of > 20 mg KOH/g to < 450 mg KOH/g and (a2) at least one polyi socyanate, and reacting the mixtu re to form the isocyanate prepolymer (a) , wherein the iso cyanate prepolymer has an isocyanate content in the range of > 1 wt.-% to < 9 wt.-%, and (B) preparing a reaction mixture by mixing at least one epoxy com pou nd (b) with the isocy anate prepolymer (a) in presence of at least one catalyst (c) , wherein the catalyst (c) is a mixtu re obtainable by introducing an al kali metal or al kaline earth metal salt into a com pound R-N H-CO-OR’, wherein R, and R’ can be same or different and can be any radical known in organic chemistry, and wherein the amount of the al kali metal or al kaline earth metal salt is 0,00001 to 0,1 mol per kg of the total weight of the isocyanate prepolymer (a) , the epoxy com pou nd (b) and the catalyst (c) , and heating the mixtu re to at least 80 ° C to obtain the polyu rethane elastomer. I n addition, the present invention relates to a polyu re thane elastomer obtained by a process according to the invention and the use of such a polyu rethane elastomer as part of a rol ler or as a sealant.

Especial ly for the production of large su rface area plastic parts, for exam ple wheels and rol lers for high load applications, a plastics system havi ng a long open assem bly ti me is re quired. Thus, for exam ple the molds may be fil led before the plastics system cures to afford the finished plastic. However, the plastics systems are also required to cu re to afford the plastic as fast as possible so that faster demolding times become possible and profitability is thus increased. A fu rther requirement, in particular of moldings su bjected to high loads, is a high mechanical strength and in particu lar com pression set. The required long open as sem bly time is general ly realized by slow-reacting chai n extenders, strongly reduced cataly sis or by setting with atmospheric humidity. However, the resu lt of this is that the demold ing time firstly can not be control led and second ly entails a long curing period.

One option for producing polyisocyanurate-polyu rethane elastomers is described in US 20110065885. Therein, a potassium acetate-based catalyst system is used and the open assembly time here is in the range of 10 minutes.

Patent docu ment EP0643086 describes the reaction of polyu rethane prepolymers in the presence of the 2-ethyl hexanoate salt of diazabicyclou ndecene (DBU) as the catalyst sys tem. The cu ring of the material is effected here as a one component system and may be initiated thermal ly from 50° C. Nevertheless, open times are stil l to be extended. WO 10121898 describes a polyisocyanate component, consisting in part of a urea prepoly mer (-N H-CO-N H-) bidentate towards the anion, which was mixed with lithiu m ch loride. When this com ponent is mixed with a diglycidy l-ether and polyol-com prising second com ponent and this mixtu re is heated to 80-90° C a rapid reaction takes place which resu lts in a th rough-curing of the material. Nevertheless, elastomers with a low com pression set are not mentioned in WO 10121898.

WO 2015/078740 is directed to the production of large fiber reinforced polyu rethane parts. To provide the production process of these parts with a long open time and a fast curing time WO 2015/078740 suggests the application of a polyu rethane catalyst mixtu re obtaina ble by introducing an al kali metal or al kaline earth metal salt into a u rethane grou p contain ing com pou nd. The production of elastomers is not suggested by WO 2015078740.

Object of the present invention is the provision of a process to produce a polyu rethane elas tomer wherein the reaction mixtu re for producing the polyu rethane elastomer shows a long open time allowing also the mold fil ling of larger parts and a rapid cu ring. Fu rther, it was object of the present invention to provide a polyurethane elastomer, obtainable by such a process, wherein the elastomer comprises a low com pression set.

The object according to the present invention has been achieved by means of a process for preparing a polyu rethane elastomer comprising the steps of (A) preparing an isocyanate prepolymer (a) by mixing (al) at least one isocyanate reactive com position com prising a polyol, selected from polyester polyol, polyether polyol or mixtu res thereof, having an aver age fu nctionality in the range of > 1.8 to < 2.5 and an OH value in the range of > 20 mg KOH/g to < 450 mg KOH/g and (a2) at least one polyisocyanate, and reacting the mixtu re to form the isocyanate prepolymer (a) , wherein the isocyanate prepolymer has an isocya nate content in the range of > 1 wt.-% to < 9 wt.-%, and (B) preparing a reaction mixture by mixing at least one epoxy compound (b) with the isocyanate prepolymer (a) in presence of at least one catalyst (c), wherein the catalyst (c) is a mixtu re obtainable by introducing an al kali metal or al kaline earth metal salt into a com pou nd R-N H-CO-OR' , and wherei n the amou nt of the al kali metal or al kaline earth metal salt is 0,00001 to 0,1 mol per kg of the total weight of the isocyanate prepolymer (a) , the epoxy com pou nd (b) and the catalyst (c) , and heating the mixtu re to at least 80 ° C to obtain the polyu rethane elastomer.

An elastomer according to the present invention com prises a elongation at break of at least 80 %, preferably at least 150 % more preferably at least 200 and especial ly at least 300% according to DI N 53504 and a shore hardness of at most 90 shore A, preferably at most 85 shore A, more preferably at most 75 shore A and most preferably at moat 70 shore A, while the shore A hard ness is preferably more than 20, more preferably more than 30 and most preferably more than 40 shore A. I n addition, an elastomer according to the invention pref erably com prises a compression set of not more than 40%, more preferably not more than 25% and most preferably not more than 15%.

To produce the isocyanate prepolymer (a) in step (A) , at least one isocyanate reactive com position (al) com prising a polyol, selected from polyester polyol polyether polyol or mixtu res thereof, having an average fu nctionality in the range of > 1.8 to < 2.5 and an OH value in the range of > 20 mg KOH/g to < 450 mg KOH/g and (a2) at least one polyisocyanate are mixed. The mixtu re is then reacted to form the isocyanate prepolymer (a) . This reaction can be performed in a wel l-known manner. For example, these polyisocyanate prepolymers are obtainable by reacting the isocyanates (a2) in excess, at temperatures for example of 30 to 100° C, preferably at about 80° C, with the isocyanate reactive com ponent (a2) , to give the prepolymer. The amou nt of the isocyanates (a2) and the isocyanate reactive component (al) is selected to result in an isocyanate content of the finished prepolymer in the range of > 1 wt.-% to < 9 wt.-%, preferably more than 2 wt.-% to less than 8 wt.-% and most prefer ably more than 4 wt.-% to less than 6 wt.-%.

As isocyanate reactive com position comprising a polyol, selected from polyester polyol, pol yether polyol and mixtu res thereof, polyester polyols and/or polyether polyols known in the field of polyu rethane chemistry having an average fu nctionality in the range of > 1.8 to <

2.5, preferably 1.9 to 2.3, more preferred 1.95 to 2.1 and especial ly preferred 2.0 and an OH value in the range of > 20 mg KOH/g to < 450 mg KOH/g, preferably 25 bis 200 mg KOH/g,

, more preferably 30 to 120 and especial ly preferred 35 to 70 mg KOH/g can be applied.

As Polyetherol having an average functionality in the range of > 1.8 to < 2.5, preferably 1.9 to 2.3, more preferred 1.95 to 2.1 and especial ly preferred 2.0 and an OH value in the range of > 20 mg KOH/g to < 450 mg KOH/g, preferably 25 to 200 mg KOH/g, more preferably 30 to 120 and especial ly preferred 35 to 70 mg KOH/g, it is possible to use customary polyeth er polyols featu ring these parameters. I n this contest, according to the present invention, the OH nu m ber is determined according to DI N 53240 and the functionality of the polyols applied is to be u nderstood as theoretical functionality. For polyether polyols this theoretical functionality for exam ple can be obtained by calcu lating the functionality based on the func tionality of the starting molecules. Effects of side reactions du ring the preparation of the polyether polyols, such as disproportionation, are not considered when determining the fu nctionality.

As isocyanate-reactive grou ps there may be groups such as OH, SH and N H grou ps present. The polyols preferably have su bstantial ly OH grou ps, more preferably exclusively OH groups, as isocyanate-reactive grou ps. The calcu lation of the average OH nu mber and the average functionality here is made on the basis of al l polyols used.

The polyether polyols are obtained in the presence of catalysts by known methods, as for example by anionic polymerization of al kylene oxides with addition of at least one starter molecu le, comprising 1 to 4, preferably 2 to 3 and more preferably 2 reactive hydrogen at oms in bound form. Catalysts used may be al kali metal hyd roxides, such as sodium or po tassiu m hydroxide, or al kali metal al koxides, such as sodium methoxide, sodium or potassi u m ethoxide or potassiu m isopropoxide, or Lewis acids in the case of cationic polymeriza tion, such as antimony pentachloride, boron trifluoride etherate or bleaching earth as cata lysts. As catalysts it is additional ly possible to use double metal cyanide com pou nds, known as DMC catalysts. As al kylene oxides, use is made preferably of one or more com pou nds having 2 to 4 carbon atoms in the al kylene radical, such as tetrahydrofu ran, 1,2-propylene oxide, or 1,2- and/or 2,3-butylene oxide, in each case alone or in the form of mixtu res, and preferably 1,2- propylene oxide, 1,2-butylene oxide and/or 2,3-butylene oxide, especial ly 1,2-propylene ox ide. I n a preferred embodiment the polyether polyols comprise at least 70 % by weight pro pylene oxide, more preferably at least 80% by weight and especial ly at least 90% by weight propylene oxide based on the total weight of the al kylene oxides.

Starter molecu les contemplated include, for exam ple, ethylene glycol, propylene glycol, di ethylene glycol, dipropylene glycol, glycerol, trimethylol propane, pentaeryth ritol, methyla- mine, ethylamine, isopropylamine, butylamine, benzylamine, aniline, toluidine, toluenedia- mine, naphthylamine, ethylenediamine, diethanolamine, triethanolamine, and other, espe cial ly dihydric alcohols.

I n another preferred em bodiment, the polyether polyols com prise polytetraethylene ether glycol (PTM EG) , also known as polytetrahyd rofu rane (PTH F) . If PTH F is present as polyeth er polyol, the amou nt of PTH F in the isocyanate reactive com ponent (al) is preferably at least 50%, more preferable at least 80% and most preferably at least 90%, based on the to tal weight of the isocyanate reactive component (al) .

As polyester polyols having an average fu nctionality in the range of > 1.8 to < 2.5, prefera bly 1.9 to 2.3, more preferred 1.95 to 2.1 and especial ly preferred 2.0 and an OH value in the range of > 20 mg KOH/g to < 150 mg KOH/g, preferably 25 bis 200 mg KOH/g, , more pref erably 30 to 120 and especial ly preferred 35 to 70 mg KOH/g, it is possible to use customary polyether polyols featu ring these parameters.

The polyester alcohols used are prepared usual ly by condensation of polyfunctional alco hols, preferably polyfu nctional alcohols having 1 to 12 carbon atoms, such as ethylene gly col, diethylene glycol, butanediol, trimethylol propane, glycerol or pentaerythritol, with poly functional carboxylic acids having 2 to 12 carbon atoms, examples being succinic acid, glu- taric acid, adipic acid, su beric acid, azelaic acid, sebacic acid, decanedicarboxylic acid, ma leic acid, fu maric acid, phthalic acid, isophthalic acid, terephthalic acid, and the isomers of naphthalinedicarboxylic acids, or the anhyd rides thereof. Beside or in addition to the poly functional alcohols having 1 to 12 carbon atoms also al koxylation products of a preferably two fu nctional starting molecu les can be used. Such al koxylation products preferably have an OH num ber of less than 610 mg KOH/g. and preferably more than 100 mg KOH/g, more preferably more than 200 mg KOH/g and most preferably more than 400 mg KOH/g. I n a preferred em bodiment of the invention, the polyester polyols are obtained by esterification of adipic acid and butanediol. I n a more preferred embodiment the polyester com prises at least 70 % by weight, even more preferred at least 80% by weight and most preferred at least 90% by weight adipic acid and butanediol, based on diacid and diol used for the prepa ration of the polyester of the invention. As fu rther starting materials in the preparation of the polyesters it is possible to use hyd ro- phobic substances. The hyd rophobic substances are water-insolu ble su bstances which comprise an non-polar organic radical and also possess at least one reactive grou p, select ed from hyd roxyl, carboxylic acid, carboxylic ester or mixtu res thereof. The equivalent weight of the hydrophobic materials is preferably between 130 and 1000 g/mol. Use may be made, for exam ple, of fatty acids, such as stearic acid, oleic acid, pal mitic acid, lau ric acid or linoleic acid, and also fats and oils, such as, for exam ple, castor oil, corn oil, sunflower oil, soybean oil, coconut oil, olive oil or tal l oil, for example. Where polyesters com prise hyd ro- phobic su bstances, the fraction of the hyd rophobic substances among the total monomer content of the polyester alcohol is preferably 1 to 30 mol%, more preferably 4 to 15 mol%.

A further grou p of fatty-acid derived polyols used with preference may be obtained th rough ring opening of epoxidized fatty acid esters with simultaneous reaction of alcohols and, op tional ly, fu rther transesterification reactions su bsequently. The incorporation of hyd roxyl grou ps into oils and fats is accom plished primarily by epoxidation of the olefinic dou ble bond present in these products, fol lowed by the reaction of resu ltant epoxide grou ps with the mono- or polyhyd ric alcohol. This produces, from the epoxide ring, a hyd roxyl group or, in the case of polyfu nctional alcohols, a structu re having a higher num ber of OH groups. Since oils and fats are usual ly glycerol esters, paral lel transesterification reactions ru n addi tional ly du ring the reactions stated above. The compou nds thus obtained preferably have a molecular weight in the range from between 500 and 1500 g/mol. Products of this kind are available for exam ple from BASF under the product designation Sovermole ⁰ .

I n a preferred embodiment less than 30 % by weight, more preferred less than 10 and most preferred no additional com pou nds having isocyanate reactive groups are used besides the isocyanate reactive components (al) to prepare the isocyanate prepolymer (a).

As polyisocyanate (a2) al l aliphatic, cycloaliphatic, and aromatic isocyanate known for the preparation of polyurethanes can be used. They preferably have an average functionality of less than 2.5. Examples are 2,2'-, 2,4'-, and 4,4'-diphenyl methane diisocyanate, the mixtures of monomeric diphenyl methane diisocyanates and higher polycyclic homologs of diphenyl- methane diisocyanate (polymeric M DI) , isophorone diisocyanate (I PDI) or its oligomers, 2,4- or 2,6-tolylene diisocyanate (TDI) or mixtures thereof, tetramethylene diisocyanate or its oligomers, hexamethylene diisocyanate (H DI) or its oligomers, naphthylene diisocyanate (N DI), or mixtures thereof. As polyisocyanates (a2), preference is given to monomeric, aro matic diisocyanates preferably 2,4 - and 2.6- TDI, or especial ly preferred monomeric diphe nyl methane diisocyanate, for exam ple 2,2'-diphenyl methane diisocyanate,

2,4'-diphenyl methane diisocyanate, 4,4'-diphenyl methane diisocyanate, or mixtures thereof. Here, diphenyl methane diisocyanate may also be used as a mixtu re with its derivatives. I n that case, diphenyl methane diisocyanate may com prise with particu lar preference up to 10 wt%, with fu rther particu lar preference u p to 5 wt%, of carbodiimide-, u retdione- or u retonimine-modified diphenyl methane diisocyanate, especial ly carbodiimide-modified di phenyl methane diisocyanate. I n step (B) the isocyanate (a) and at least one epoxy compound (b) are mixed in presence of at least one catalyst (c). For the mixing step, the sequence is not relevant. I n one embod iment the epoxide (b) is al ready present du ring the formation of the isocyanate prepolymer (a) . I n a preferred embodiment, the isocyanate prepolymer is produced first and then the epoxide is added. Fu rther, in a preferred em bodiment, the catalyst (c) is not present while the isocyanate prepolymer (a) is formed.

I n a preferred embodiment the isocyanate prepolymer (a) to be used in step (B) com prises less than 1 wt.-%, more preferably less than 0.5 and most preferably less than 0.1 %by weight, based on the total weight of the isocyanate (a) monomeric diisocyanate. This can be ensured for example by removing an excess amount of u n reacted isocyanate by distil lation, for exam ple thin fil m distil lation.

As epoxide (b) any compound com prising one or more epoxide grou ps it is possible to use al l epoxide-com prising compou nds which are com mon ly used for the preparation of epoxy resins. The epoxide (b) comprising epoxide groups are preferably liquid at 25° C. Here it is also possible to use mixtures of such com pou nds, which are preferably likewise liquid at 25° C.

Exam ples of such compounds com prising epoxide grou ps that can be used in the context of the invention are

I) Polyglycidyl and poly([beta] -methylglycidy I) esters, obtainable by reacting a com pou nd having at least two carboxyl grou ps in the molecule with in each case epich lorohyd rin and [beta] -methylepich lorohyd rin. This reaction is advantageously catalyzed by the presence of bases.

Aliphatic polycarboxylic acids may be used, for exam ple, as a compound having at least two carboxyl groups. Examples of such aliphatic polycarboxylic acids are oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, su beric acid, azelaic acid and dimerized or tri - merized linoleic acid. Additional ly, it is possible for cyclic, aliphatic acids to be used as wel l, such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahyd rophthalic acid or 4-methyl hexahydrophthalic acid. Aromatic carboxylic acids too, such as phthalic acid, isophthalic acid or terephthalic acid, and also any desired mixtu res of these carboxylic ac ids, may be used.

I I) Polyglycidyl or poly([beta] -methylglycidy I) ethers, obtainable by reaction of a com pou nd having at least two alcohol hydroxyl grou ps and/or phenolic hydroxyl groups with epich loro hyd rin or [beta] -methylepich lorohyd rin u nder al kaline conditions or in the presence of an acidic catalyst, and subsequent treatment with a base.

The glycidyl ethers of this type are derived for exam ple from linear alcohols, such as eth ylene glycol, diethylene glycol or higher poly(oxyethylene) glycols, propane-1, 2-diol or poly(oxypropylene) glycols, propane-1, 3-diol, butane-1, 4-diol, poly(oxytetramethylene) gly- col, pentane-1, 5-diol, hexane-1, 6-diol, hexane-2, 4, 6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol or sorbitol, and from polyepichlorohydrins.

Further glycidyl ethers of this type are obtainable from cycloaliphatic alcohols, such as 1,4- cyclohexanedimethanol, bis(4-hydroxycyclohexyl) methane or 2,2-bis(4-hydroxycyclo- hexyl) propane, or from alcohols which carry aromatic groups and/or other functional groups, such as N,N-bis(2-hydroxyethyl)aniline or p,p'-bis(2- hydroxyethyla- mino) diphenyl methane.

The glycidyl ethers may also be based on monocyclic phenols, such as p-tert-butylphenol, resorcinol or hydroquinone, or on polycyclic phenols, such as bis(4-hydroxyphenyl)methane, 4,4'-d i hyd roxybi phenyl , bis(4-hydroxyphenyl) sulfone, l,l,2,2-tetrakis(4- hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl) propane or 2,2-bis(3,5-dibromo-4- hydroxy phenyl) propane.

Further compounds comprising hydroxyl groups and suitable for the preparation of the glyc idyl ethers are novolacs, obtainable by condensing aldehydes, such as formaldehyde, acet aldehyde, chloraldehyde or furfuraldehyde, with phenols or bisphenols, which may be un substituted or substituted, by chlorine atoms or Cl to C9 alkyl groups, for example, such as phenol, 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol.

III) Poly(N-glycidyl) compounds, obtainable by dehydrochlorination of reaction products of epichlorohydrin with amines comprising at least two amine-bonded hydrogen atoms. Such amines are, for example, aniline, n-butylamine, bis(4-aminophenyl) methane, m- xylylenediamine or bis(4-methylaminophenyl) methane. The poly(N -glycidyl) compounds also include triglycidyl isocyanurates, N , N'-d iglycidyl derivatives of cycloalkyleneureas, like ethyleneurea or 1,3-propyleneurea, and diglycidyl derivatives of hydantoins, like 5,5- dimethylhydantoin.

IV) Poly(S-glycidyl) compounds, such as di-S-glycidyl derivatives, which are obtainable from dithiols, for example ethane-1, 2-dithiol or bis(4-mercaptomethylphenyl) ether.

V) Cycloaliphatic epoxy resins, such as bis(2,3-epoxycyclopentyl) ether, 2,3- epoxycyclopentyl glycidyl ether, l,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4- e poxycyc I o hexyl methyl 3',4'-epoxycyclohexanecarboxylate.

VI) Monofunctional epoxy resins, such as 2 -ethyl h exy I glycidyl ether, isopropyl glycidyl ether, butyl glycidyl ether or cresyl glycidyl ether.

In the context of the invention it is likewise possible to use epoxy resins wherein the 1,2- epoxy group is bonded to different heteroatoms or functional groups. These compounds include N , N ,0 -triglycidyl derivatives of 4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid, N-glycidyl-N'- (2 -glycidyl oxyp ro pyl)-5,5-dimethylhydantoin and 2-glycidyloxy- l,3-bis(5,5-dimethy 1-1 -glycidyl hydantoin-3-yl) propane. Particularly preferred epoxides (b) are the compounds of classes (I) and (II), more particu larly those of class (II).

The epoxide (b) is used preferably in an amount of 0.3 to 15 wt%, preferably 0.5 to 10 wt% and more particularly 0.8 to 5 wt%, based on the total weight of the isocyanate prepolymer (a) and the epoxide (b).

The catalyst (c) is a mixture obtainable by introducing an alkali metal or alkaline earth metal salt into a compound R-NH-CO-OR' .

The alkali metal salt or alkaline earth metal salt used in this context is a compound which accelerates the curing reaction of the isocyanate prepolymer (1) in presence of the epoxide. These compounds encompass, in particular, salts of sodium, lithium, magnesium, and po tassium, and ammonium compounds, preferably lithium or magnesium, with any desired anions, preferably with anions of organic acids such as carboxylates and more preferably of inorganic acids, such as nitrates, halides, sulfates, sulfites, and phosphates, more prefera bly still with anions of monoprotic acids, such as nitrates or halides, and especially nitrates, chlorides, bromides or iodides. Particular preference is given to using lithium chloride, lithi um bromide, and magnesium dichloride, and especially lithium chloride. Alkali metal or alka line earth metal salts of the invention can be used individually or as mixtures.

Apart from the alkali metal or alkaline earth metal salt, there are preferably no further com pounds used that accelerate the reaction of isocyanates with groups that are reactive to ward isocyanates.

The compound R-NH-CO-OR' is a compound comprising at least one urethane group. This compound preferably is solid or preferably liquid at 20 ° C. In a preferred embodiment R does not stand for hydrogen and/or not for COR". In this context, R, R’ and R” can be same or different and can be any radical known in organic chemistry.

The compound comprising urethane groups in catalyst (c) here is preferably obtainable by reaction from a second polyisocyanate and a compound having at least one OH group. Pref erence here is given to compounds which are liquid at 50° C, and more preferably those which are liquid at room temperature. A substance or component which is "liquid" in the context of the present invention means one which at the specified temperature has a vis cosity of not more than 10 Pas. Where no temperature is specified, the datum is based on 20° C. Measurement in this context takes place according to ASTM D445-11. The com pounds comprising urethane groups preferably have at least two urethane groups. The mo lecular weight of these compounds comprising urethane groups is preferably in the range from 200 to 15000 g/mol, more preferably 300 to 10000 g/mol, and more particularly 500 to 1300 g/mol. Compounds comprising urethane groups may be obtained, for example, by re action of aforementioned isocyanates (al) as second isocyanate with compounds which have at least one hydrogen atom that is reactive toward isocyanates, such as alcohols, ex- amples being monoalcohols, such as methanol, ethanol, propanol, butanol, pentanol, hexa- nol, or longer-chain propoxylated or ethoxylated monools, such as poly(ethylene oxide) monomethyl ether, such as, for example, the monofunctional Pluriol® products from BASF, dialcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butanediol, hexanediol, and/or reaction products of said isocyanates with the above-described polyols (al) and/or chain extenders - individually or in mixtures. To prepare the compound comprising urethane groups it is possible to employ not only iso cyanates but also polyols in a stoichiometric excess. Where monoalcohols are used, isocya nate groups and OH groups may also be used in a stoichiometric ratio. Where the com pound comprising urethane groups has two or more isocyanate groups per molecule, they may wholly or partly replace the polyisocyanates (a2). In this case prepolymer (a) is the compound comprising urethane groups in catalyst (c) and no further addition of prepolymer (a) is necessary.

Reaction takes place customarily at temperatures between 20 and 120° C, for example at 80° C. The second isocyanate, used for preparing the compound comprising urethane groups, is preferably an isomer or homolog of diphenylmethane diisocyanate. More prefera bly the second isocyanate is monomeric diphenylmethane diisocyanate, for example 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate,

4,4'-diphenylmethane diisocyanate, or a mixture thereof. This diphenylmethane diisocya nate may also be used as a mixture with its derivatives. In that case, diphenylmethane diisocyanate may with particular preference comprise up to 10 wt%, with further particular preference up to 5 wt%, of carbodiimide-, uretdione-, or uretonimine-modified diphenylme thane diisocyanate, especially carbodiimide-modified diphenylmethane diisocyanate. In a particularly preferred embodiment, the first isocyanate (a) and the second isocyanate for preparing the compound comprising urethane groups are identical.

The compound comprising urethane groups may also be obtained via alternative reaction pathways, as for example by reacting a carbonate with a monoamine to form a urethane group. For this purpose, for example, a propylene carbonate is reacted in a slight excess (1.1 eq) with a monoamine, e.g., a Jeffamin M 600, at 100° C.The resulting urethane may likewise be used as a compound comprising urethane group.

The mixtures comprising the alkali metal or alkaline earth metal salts and a compound comprising urethane groups may be obtained, for example, by mixing the alkali metal or al kaline earth metal salt into the compound comprising urethane groups, at room temperature or at elevated temperature, for example. This may be done using any mixer, such as a single stirrer, for example. The alkali metal or alkaline earth metal salt in this case may be used as a pure substance or in the form of a solution, in mono- or polyfunctional alcohols, for exam ple, such as methanol, ethanol, or chain extender, or water. In one particularly preferred embodiment, commercially available prepolymer-based isocyanate is admixed directly with the dissolved salt. Suitable for this purpose for example are isocyanate prepolymers having an NCO content of 15% to 30%, in particular based on diphenylmethane diisocyanate and a polyether polyol. Isocyanates of this kind are available commercially for example from BASF under the trade name Lupranat® MP 102.

In one particularly preferred embodiment of the present invention, the alkali metal or alka line earth metal salt is dissolved in a compound having hydrogen atoms that are reactive toward isocyanate, and this solution is subsequently mixed with the isocyanate, optionally at elevated temperature.

Particular preference is given to preparing the compound comprising urethane groups using a monool having a molecular weight of 30 to 15000 g/mol, preferably 100 to 900 g/mol and, in a particularly preferred version, of 400 to 600 g/mol.

According to the present invention the amount of the alkali metal or alkaline earth metal salt is adjusted that the salt is present in an amount of 0,00001 to 0,1 mol per kg of the total weight of the isocyanate prepolymer (a), the epoxy compound (b) and the catalyst (c). The amount of alkali metal ions or alkaline earth metal ions per urethane group in the catalyst (c) in a preferred embodiment is 0.0001 to 3.5, based on the number of alkali metal or alka line earth metal ions and urethane groups in catalyst (c).

Beside catalyst (c) the remaining compounds (a) and (b) and potentially additional com pounds pesent, comprise preferably less than 0.0001 wt%, based on the total weight of components (a) and (b), of alkali metal ions or alkaline earth metal ions. With particular preference the amount of alkali metal or alkaline earth metal ions in components (a) and (b) is less than 0.00005, more preferably 0.00003, and more particularly 0.00001 wt%, based on the total weight of components (a) and (b) and, if present, further compounds.

The amount of alkali metal or alkaline earth metal ions per epoxy group is preferably greater than 0.00001 and is more preferably 0.00005 to 0.3, based in each case on the number of alkali metal or alkaline earth metal ions and epoxy groups.

The reaction mixture in step (B) may further comprise additional isocyanate reactive com pounds as polyols, chain extenders or crosslinkers.

As polyols it is possible for example to use polyethers, polycarbonate polyols or polyesters that are known in polyurethane chemistry and that are same or different from compounds (al). If additional polyols are added to the reaction mixture in step (B), they are added in a preferred embodiment after the formation of the isocyanate prepolymer (a) is completed. As additional polyols it is possible for the purposes of this invention to use compounds having at least two isocyanate-reactive groups and having a molecular weight of at least 350, pref erably at least 400 g/mol, and more preferably at least 500 g/mol. Isocyanate-reactive groups present may be groups such as OH-, SH-, NH-, and CH-acid groups. The polyols preferably have essentially OH groups, more preferably exclusively OH groups, as isocya nate-reactive groups. In one preferred embodiment the polyols have at least 40%, preferably at least 60%, more preferably at least 80%, and more particu larly at least 95% of secondary OH grou ps, based on the nu mber of isocyanate-reactive grou ps.

The polyols preferably employed are polyetherols and/or polyesterols having nu m ber- average molecu lar weights of between 350 and 12 000, preferably 400 to 6000, more partic u larly 500 to less than 3000, and having preferably an average, nominal functionality of 2 to 6, preferably of 2 to 3. I n a preferred em bodiment, additional polyols, if used in mixing step (B) , are identical to polyols (al) .

Where low molecu lar weight chain extenders and/or crosslinking agents are used, it is pos sible to use chain extenders that are known in the context of polyurethane production, while chain extenders have a functionality of 2 and crosslinkers have a fu nctionality of 3 or more. These are preferably low molecular weight compounds having at least two isocyanate- reactive grou ps and used for molecular weights of less than 350 g/mol, more preferably of 60 to less than 300 g/mol. Chain extenders and/or crosslin king agents can be used to ad just mechanical properties such as hard ness or elongation. This is known to a person skil led in the art. Exam ples of chain extenders and crosslinkers wil l include aliphatic, cyclo aliphatic and/or araliphatic or aromatic diols having 2 to 14, preferably 2 to 10 carbon at oms, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10- decanediol and bis(2-hyd roxyethyl) hyd roquinone, 1,2-, 1,3-, 1,4-dihydroxycyclohexane, di ethylene glycol, dipropylene glycol, tripropylene glycol, triols, such as 1,2,4-, 1,3,5- trihyd roxycyclohexane, glycerol and trimethylol propane, and hyd roxyl-containing poly- al kylene oxides of low molecu lar weight that are based on ethylene oxide and/or on

1,2-propylene oxide and on the aforementioned diols and/or triols as starter molecu les. Fur ther possible low molecu lar weight chain extenders and/or crosslin king agents are specified for example in "Kunststoffhandbuch, volu me 7, Polyu rethane", Carl Hanser Verlag, 3rd edi tion 1993, sections 3.2 and 3.3.2. If chain extender is used preferably propane diol, 1,4 bu tane diol or 1,6-Hexane diol is used. With preference no chain extender is used.

The addition of additional polyol to the reaction mixture produced in the mixing step (B) is optional. Preference is given to not using additional polyol. I n case that additional polyol is used the fraction of polyol (d) , based on the total weight of components (a) , (b) and (c) , is preferably in an amount that the mixing according to step (B) is performed at an isocyanate index of more than 200, preferably more than 500 more preferably more than 1000 most preferably no fu rther compou nds having isocyanate reactive grou ps are added in step (B) . The isocyanate index for the pu rposes of the present invention is the stoichiometric ratio of isocyanate grou ps of the isocyanate prepolymer (a) for isocyanate-reactive grou ps added to the mixture in step (B) , mu ltiplied by 100. Isocyanate-reactive grou ps are al l isocyanate- reactive grou ps present in the reaction mixture, including those of chemical blowing agents and com pou nds having epoxide grou ps, but not the isocyanate grou p itself.

It is possible to add to the reaction mixtu re produced in step (B) additional additives. Such additives are wel l known in polyu rethane chemistry and include filers, additives for water adsorption, flame retardants, hyd rolysis in hibitors, antioxidants, and internal release agents. Such su bstances are stated for exam ple in "Ku nststoffhand buch, volu me 7, Polyu rethane", Carl Hanser Verlag, 3rd edition 1993, sections 3.4.4 and 3.4.6 to 3.4.11.

Additives for water adsorption used are preferably aluminosilicates, selected from the group of sodiu m alu minasilicates, potassium alu minasilicates, calciu m alu minasilicates, cesium aluminasilicates, barium alu minasilicates, magnesiu m alu minasilicates strontiu m alumi nasilicates, sodiu m alu minophosphates, potassiu m alu minophosphates, calciu m alu mino- phosphates, and mixtures thereof. Particu larly preferred are mixtures of sodiu m, potassiu m, and calcium aluminasilicates, used in castor oil as carrier substance.

The additive for water absorption preferably has an average particle size of not greater than 200 mΐti, more preferably not greater than 150 mΐti, and more particularly not greater than 100 mΐti. The pore size of the additive of the invention for water absorption is preferably 2 to 5 Angstroms. As wel l as the inorganic additives for water adsorption, it is also possible to use known organic additives for water adsorption, such as orthoformates, triisopropy- lorthoformate for exam ple.

If an additive for water absorption is added, it is added preferably in amounts greater than one part by weight, more preferably in the range from 1.2 to 2 parts by weight, based on the total weight of the polyisocyanurate system. prior art. Exam ples of suitable flame retardants are brominated ethers (Ixol B 251) , bromin- ated alcohols, such as dibromoneopentyl alcohol, tribromoneopentyl alcohol and PHT-4- diol, and also ch lorinated phosphates, such as, for example, tris(2— ch loroethyl) phosphate, tris(2-chloroisopropyl) phosphate (TCPP), tris(l,3— d ich loroisopropy I) phosphate, tris(2,3- dibromopropyl) phosphate and tetrakis(2-chloroethyl) ethylene diphosphate, or mixtu res thereof.

Apart from the halogen-su bstituted phosphates al ready stated, use may be made of inor ganic flame retardants, such as red phosphorus, preparations comprising red phosphorus, expandable graphite, alu minum oxide hydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate and calciu m su lfate, or cyanu ric acid derivatives, such as melamine, or mix tu res of at least two flame retardants, such as am monium polyphosphates and melamine, and also, optional ly, starch, or rendering the rigid polyu rethane foams, produced in accord ance with the invention, flame retardant.

As fu rther liquid, halogen-free flame retardants it is possible to use diethyl ethanephospho- nate (DEEP) , triethyl phosphate (TEP) , dimethyl propyl phosphonate (DM PP) , diphenyl cre- syl phosphate (DPC) , and others.

The flame retardants are used for the pu rposes of the present invention preferably in an amou nt of 0 to 60 wt%, more preferably of 5 to 50 wt%, more particu larly of 5 to 40 wt%, based on the total weight of components (a) to (c) . As internal release agents it is possible to use al l release agents customary in polyu rethane production, examples being metal salts, such as zinc stearate, in diamine solution, and de rivatives of polyisobutylene succinic acid.

A polyurethane system of the invention preferably has less than 0.5 wt%, more preferably less than 0.3 wt%, of water, based on the total weight of com ponents (a) to (c) .

Reaction mixtu res of the invention have a long open time at 25° C, of more than 60 minutes for example, preferably of more than 90 minutes, and more preferably of more than 120 minutes. This open time is determined as described above via the increase in viscosity. On temperatu re increase to tem peratu res greater at least 80° C, preferably greater than 80 to 200° C, and more preferably to 90 to 150° C, the reaction mixtu re of the invention cures rapidly, in less than 50 minutes for example, preferably in less than 30 minutes, more pref erably in less than 10 minutes, and more particularly in less than 5 minutes. For the pu rpos es of the invention the cu ring of a reaction mixture of the invention is u nderstood as the increase in the initial viscosity to 10 times the initial viscosity. The difference here between the open time at 25° C and the open time at 130° C is preferably at least 40 minutes, more preferably at least one hour, and very preferably at least 2 hou rs. I n a preferred embodiment curing is performed in a heated mold.

With the process of the invention, preferably, a compact material is obtained, meaning that no blowing agent is added. Smal l amou nts of blowing agent, as for exam ple smal l amou nts of water, which pass by condensation into the reaction mixtu re or the starting components during processing, by way of atmospheric moistu re, are not included here. A compact polyu rethane is a polyurethane which is su bstantial ly free from gas inclusions. The density of a com pact polyurethane is preferably greater than 0.8 g/cm ³ , more preferably greater than 0.9 g/cm ³ and, more particu lar greater than 1.0 g/cm ³ .

A polyurethane elastomer obtainable by a process according to the present invention shows good mechanical properties as a low compression set, a high elasticity and a high tensile strength at relatively low hardness values of preferably less than 90 shore A and low abra sion values. Fu rthermore, the production pf a polyu rethane according to the present inven tion resu lts in low shrin kage values. Therefore, the method according to the present inven tion perfectly suits to the production of polyu rethane sealants or polyurethane rol lers, espe cial ly large rol lers or large sealants which require a long open time and a fast cu ring.

I n the text below, the present invention is il lustrated using exam ples:

I n put materials:

Isocyanate 1 is 4,4’-diphenyl methanediisocyanate (4,4’- M DI), molar mass 250.26 g/mol

Isocyanate 2 is a mixtu re of 2,4-tol uene diisocyanate and 2,6-toluene diisocyanate

(80:20) Isocyanate 3 is a carbodiimide-modified 4,4’-diphenylmethane diisocyanate (4,4‘- MDI), NCO: 29.5% (e.g. Lupranat ^® MM 103 from BASF)

Polyol 1 polyether diol having OH number of about 56 constructed from tetra- hydrofuran (MW: approx. 2000)

Polyol 2 polyether diol having OH number of about 56 constructed from propyl ene glycol and propylene oxide (PO) having functionality of about 2 (MW: approx. 2000)

Polyol 3 Polyester diol having OH number of about 56 constructed from adipic acid, 1,2-ethanediol and 1,4-butanediol having functionality of 2 (MW: approx. 2000)

Polyol 4 polyester diol having OH number of about 56 constructed from adipic acid and 1,4-butanediol having functionality of 2 (MW: approx. 2500) Polyol 5 polyether diol having OH number of about 104 constructed from pro pylene glycol and propylene oxide (PO) having functionality of about 2 (MW: approx. 1000)

Polyol 6 polyether diol having OH number of about 248 constructed from pro pylene glycol and propylene oxide (PO) having functionality of about 2 (MW: approx. 450)

Polyol 7 polyether diol having OH number of about 28 constructed from propyl ene glycol and propylene oxide (PO) having functionality of about 2 (MW: approx. 4000)

Epoxy bisphenol-A-based diglycidyl ether, e.g. Araldite GY 250 from Hunts man

Additive 1 diethylene glycol bischloroformate

Additive 2 antifoam, e.g. AF9000 NE Silicone Antifoam from Momentive

Additive 3 K-Ca-Na-Zeolite A in castor oil

Catalyst 1 the reaction product of isocyanate 3 with a monofunctional polyeth ylene oxide having a number average molecular weight of 500 g/mol obtainable under the trade name "Pluriol ^® A 500 E” from BASF as a mixture with LiCI; 0.50 eq. of LiCI based on number of urethane com pounds according to the invention

Catalyst 2 potassium acetate

Catalyst 3 noninventive mixture of LiCI and urea prepolymer obtainable by reac tion of Jeffamin M600 and isocyanate 3 and also 0.70 equivalents of LiCI based on the number of urea compounds in the prepolymer amount such as described accordingly in WO10121898.

Chain extender 1 1,4-butanediol

Comparative examples and inventive examples: 1. Prepolymers

Production of the prepolymer

Isocyanate is initially charged at about 50° C into a 4000 ml round-necked flask fitted with a PT100 thermocouple, nitrogen feed, stirrer and heating mantle and a polyol is added at this temperature. The reaction mixture is heated to 80° C and stirred for 2 hours at 80° C. The resulting prepolymer is then allowed to reach room temperature and without further treatment is used for the following application.

2. Elastomers, sealants and adhesives

Production of the polyurethane based on prepolymers

The components (see formulation) were mixed for 20 seconds in a vacuum speed mixer at 1800 rpm and subsequently poured into the stepped mold (110° C). The cured test sheets were subsequently conditioned at 90° C for 24h.

Properties of the solid polyurethane and resulting test specimens:

The following properties of the obtained polyurethanes were determined by the recited methods:

Density: DI N EN ISO 1183-1, A.

Hardness (Shore A/D): DI N ISO 7619-1

Tensile strength/elongation at break: DI N 53504

Tear resistance: DI N ISO 34-1, B (b)

Measurement of abrasion: DI N ISO 4649

Glass transition temperature: The T _g was determined by differential scanning calorime try.

Curing and mechanical properties: Formulation of reactive mixture:

Comparative 1 Comparative 2

Prepolymer Prepolymer 1 Prepolymer 1

Catalyst 2 3

Open assembly time at melting temp of No complete curing

< 1 minute

prepolymer (max 55 ° C)

Hardness [Shore A]

Tensile Strength [Mpa]

Elongation at break [%]

Tear resistance [kN/m]

Compression set (23/70° C) [%]

Example 1 Example 2 Example 3

Prepolymer Prepolymer 1 Prepolymer 2 Prepolymer 3

Catalyst 1 1 1

Open assembly time at melting > 48 h

> 48 h > 48 h temp of prepolymer (max 55 ° C)

Hardness [Shore A] 57 64 59

Tensile Strength [Mpa] 6 5 10

Elongation at break [%] 240 180 310

Tear resistance [kN/m] 8 7 10

Rebound resilience [%] 42 54 18

Abrasion (mm ³ ) 94 46 56

Shrinkage (%) 0.8 0.8 0.8

Compression set (23/70° C) [%] 17/15 20/21 3/3

Example 4 Example 5 Comparative 3

Prepolymer Prepolymer 4 Prepolymer 5 Prepolymer 6

Open assembly time at melting

> 48 h > 48 h > 48 h temp of prepolymer (max 55 ° C)

Hardness [Shore A] 51 88 74 ShD

Tensile Strength [Mpa] 4 18 53 Elongation at break [%] 400 80 10

Tear resistance [kN/m] 7 20 40 Compression set (23/70° C) [%] 3/5 26/4 V- Example 6 Com parative 4 Com parative 5

Prepolymer 7 8 9

Open assembly time at melting

> 48 h > 48 h > 48 h temp of prepolymer (max 55 ° C)

Hardness [Shore A] 92 93 74 Sh D

Tensile Strength [M pa] 19 23 65 Elongation at break [%] 90 100 10

Tear resistance [kN/m] 21 43 102 Com pression set (23/70° C) [%] 32/8 66/38 97/107

Example 7 Com parative 6

Prepolymer 10 9

Open assem bly time at melting tem p of > 48 h

> 48 h

prepolymer (max 55 ° C)

Hardness [Shore A] 83 38

Tensile Strength [M pa] 8 2

Elongation at break [%] 40 240

Tear resistance [kN/m] 7 7

Com pression set (23/70° C) [%] V- 12/14

The examples show that in the selected NCO range the prepolymer and, if polyols according to the invention are used to produce the prepolymers, very good mechanical properties are obtained, especial ly for elongation and com pression set with a hardness of less than 90 shore A. If non-inventive catalysts which are bidentate towards the anion, for example such catalysts as disclosed in WO10121898, are used, cu ring at elevated tem peratu res is not suf- ficient for a reasonable catalyst amount. When used in larger quantities, e.g. in 10 parts by weight instead of 1 part by weight, cu ring may take place at elevated tem peratu re, but such a high amou nt of catalyst is undesirable and leads to undesirable deterioration of the me chanical properties of the elastomer obtained. The fol lowing table shows formu lations which are cu red in presence of additional isocya nate reactive components. Formulation of the reactant mixture with copolyol or chain extender:

Mechanics/P re polymer Example 12 Example 13

Open assembly time at melting

> 5 h

temp of prepolymer (max 55 ° C)

Flardness [Shore A] 92 38

Tensile Strength [Mpa] 19 2

Elongation at break [%] 90 240

Tear resistance [kN/m] 21 7

Compression set (23/70° C) [%] 32/8 12/14

Also formulations according to the invention which are cured in presence of additional iso cyanate reactive components show long open time at room temperature and a fast curing at temperatures above 80 ° C.