HK1071763B - Radiation-curable urethane acrylates, based on a blend of various oxyalkylated polyols - Google Patents

Description

Radiation-curable urethane acrylates based on blends of different degrees of alkoxylated polyols

The invention relates to novel low-viscosity radiation-curable polyurethane acrylates which can be cured to form coatings having improved abrasion resistance, and to the use thereof as coating agents, in particular for flooring materials.

Radiation-curable coating agents based on the reaction product of a hydroxy-functional ester of (meth) acrylic acid and a diisocyanate are known as urethane acrylates, for example from p.k.t.oldring (eds.), Chemistry & Technology of UV & EB formulations for Coatings, Inks & paintts, vol.2, 1991, SITA Technology, london, pages 73 to 123. They are often used for coating parquet and other materials used as flooring. Most of these coating compositions have a high dynamic viscosity, usually greater than 10000 mPas (at 23 ℃), and can therefore be diluted with low molecular weight acrylates (reactive diluents) and hardened by various methods, for example using rollers, after application to the substrate to be coated, with additional photoinitiators and, if appropriate, additives, and by irradiation with UV light. Due to the dilution of the reactive diluent, the urethane acrylates often lose some important properties, such as abrasion resistance and viscoelasticity. For this purpose, particularly low viscosity urethane acrylates are used to keep the amount of reactive diluent low. In most cases, 2-hydroxyethyl-and 2-hydroxypropyl acrylate or methacrylate are used as starting products which are readily available industrially and as hydroxy-functional esters of (meth) acrylic acid for the production of urethane acrylates. The polyurethane acrylates produced are, however, highly viscous when undiluted (cf. examples of EP-A168173).

EP-A53749 discloses a process for the preparation of low-viscosity urethane acrylates based on diisocyanates or polyisocyanates, hydroxy-functional acrylates of 3 to 4.5-fold alkoxylated trimethylolpropane and optionally hydroxyalkyl acrylates. In the cited application, comparative experiments have shown that even if the degree of ethoxylation reaches 7, the stability of the corresponding products against polar solvents is still insufficient.

The object of the present invention is to provide low-viscosity urethane acrylates which are solvent-resistant and have better abrasion resistance than the prior art.

It has now been found that urethane acrylates based on diisocyanates or polyisocyanates and hydroxy-functional (meth) acrylates of mixtures of highly and lowly alkoxylated polyols have a low viscosity, are solvent-resistant and, in particular, are abrasion-resistant. This is a very surprising finding, since no substantial difference is to be expected between urethane acrylates containing, for example, a heptaethoxylated triol and urethane acrylates containing a mixture of high and low ethoxylation, on average corresponding to a heptaethoxylated triol.

The present disclosure therefore provides low-viscosity, radiation-curable urethane acrylates which can be prepared by reacting diisocyanates and/or polyisocyanates with hydroxy-functional partial esters of acrylic acid and/or methacrylic acid based on mixtures of polyols having different degrees of alkoxylation with three or more hydroxyl groups, and is characterized in that the alkoxylated polyol mixture consists of 25 to 75 mol% of a polyol having a degree of alkoxylation of between 3 and 5 and 75 to 25 mol% of a polyol having a degree of alkoxylation of between 8 and 25.

The invention also relates to a two-stage process for producing the urethane acrylates according to the invention, characterized in that in a first stage the alkoxylated polyol is partially esterified with acrylic acid and/or methacrylic acid [ hereinafter referred to as (meth) acrylic acid ], and in a second stage is reacted with a diisocyanate or polyisocyanate.

The invention also relates to the use of urethane acrylates as a constituent of coating agents which cure under the influence of high-energy radiation.

As base for the alkoxylated polyols, tri-and polyhydric alcohols having a molecular weight of 92 to 254, such as glycerol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol or sorbitol and mixtures thereof, are used. Preferred are glycerol and trimethylolpropane. The alkoxylation reaction is carried out according to methods known per se for producing polyethers. Ethylene oxide, propylene oxide and tetrahydrofuran, preferably ethylene oxide and/or propylene oxide, can be used as monomers for this purpose, it also being possible to use mixtures or successive different monomers ("block" preparation). The amount of alkoxylated monomer based on the amount of alcohol is referred to as the degree of alkoxylation (e.g., 7.0 moles of ethylene oxide per mole of trimethylolpropane corresponds to a degree of alkoxylation of 7.0).

The key is to use two polyols of different degrees of alkoxylation. On the one hand 25 to 75 mol%, preferably 30 to 45 mol%, of a polyol having a degree of alkoxylation of between 3 and 5 is used and on the other hand the polyol making up to 100 mol% parts, i.e.75 to 25 mol%, preferably 70 to 55 mol%, is used and has a degree of alkoxylation of between 8 and 25, preferably between 8 and 15, particularly preferably between 10 and 13.

The mixture of alkoxylated polyols is esterified with (meth) acrylic acid according to methods known per se, but preferably a method is employed in which the water of reaction can be distilled off by means of a solvent which forms an azeotrope with water (azeotropic entrainer). It is also possible to esterify the different alkoxylated polyols separately and subsequently and/or to mix the esters before further reaction with the polyisocyanate. If appropriate, it is also possible to react the remaining amount of acid and the epoxy compound further after the esterification reaction. These processes are described, for example, in EP-A54105, EP-A126341 and EP-A900778.

The acrylic acid and/or methacrylic acid are used in an equivalent ratio of acid to hydroxide of 1 to 1.1 to 1 to 2.4, preferably 1 to 1.2 to 1 to 1.8, particularly preferably 1 to 1.3 to 1 to 1.5, based on the hydroxyl groups of the alkoxylated polyol. Instead of pure acids, it is also possible to use their anhydrides or oligomerization products, such as methacrylic anhydride or dimeric acrylic acid, as long as they are available.

Hydrocarbons and their halogenated or nitro-substituted products, as well as other solvents which do not react with the reactants nor change due to the influence of the acid catalyst, are used as azeotropic entrainers. Unsubstituted hydrocarbons are preferably used. The ratio is as follows: aliphatic hydrocarbons such as hexane, heptane, octane, gasoline fractions of different boiling point ranges, alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, or aromatic hydrocarbons such as benzene, toluene or the isomeric xylenes. Preference is given to using those solvents having a boiling point of between 70 ℃ and 120 ℃. Particular preference is given here to cyclohexane, toluene or a gasoline fraction boiling between 70 ℃ and 120 ℃. The water-immiscible solvent may also be a mixture of the above. The amount of solvent used is between 10 and 100% by weight, preferably between 15 and 50% by weight, particularly preferably between 20 and 40% by weight, based on the weight of the reaction components to be esterified.

As acidic esterification catalysts, use may be made of inorganic or organic acids in an amount of from 0.1 to 3.0% by weight, preferably from 0.5 to 1.5% by weight, based on the weight of the reaction components to be esterified. Examples of such esterification catalysts are sulfuric acid, phosphoric acid, pyrophosphoric acid, p-toluenesulfonic acid, styrene-divinylbenzene sulfonic acid, chlorosulfonic acid, chloroformic acid, with sulfuric acid and p-toluenesulfonic acid being preferred. Also here, acid catalysts attached to solid resins, such as ion exchangers, can be used.

The reaction can be carried out in the presence of one or more inhibitors in an amount of from 0.01 to 1% by weight, preferably from 0.1 to 0.5% by weight, based on the mixture to be esterified. Such inhibitors are described, for example, in Houben-Weyl, Methoden der organischen Chemie, fourth edition, volume XIV/1, Georg Thieme Press, Stuttgart, 1961, see page 433. Examples are: sodium dithionite, sodium hydrosulfide, sulfur, hydrazine, phenylhydrazine, diphenylhydrazine, N-phenyl-beta-naphthylamine, N-phenylethanoldiamine, dinitrobenzene, picric acid, p-nitrosodimethylaniline, diphenylnitrosamine, phenols such as p-tert-butylcatechol, 2, 5-di-tert-amylhydroquinone, nitroxyl compounds, p-alkoxyphenols, di-tert-butylhydroquinone, tetramethylthiuram disulfide, 2-mercaptobenzothiazole and the sodium salt of dimethyldithiocarbamic acid. In addition, in a preferred embodiment, an oxygen-containing gas, preferably air, is introduced into the reaction mixture containing the solvent.

The esterification of the (meth) acrylic acid is first carried out at a temperature in the range from 60 ℃ to 140 ℃, preferably from 70 ℃ to 120 ℃, particularly preferably at the boiling point of the solvent used. The solvent is continuously removed from the reaction mixture by distillation, then concentrated in a water separator outside the reactor and separated from the entrained water before being returned to the reaction mixture. The reaction is ended when the amount of water removed in the reaction corresponds to the desired degree of reaction or the acid number of the reaction mixture has dropped to a value corresponding to the desired degree of reaction. The acid number in this case is from 0.1 to 15, preferably from 1 to 5mg of potassium hydroxide per gram of reaction mixture. The esterification catalyst can then optionally be neutralized, precipitated and/or filtered off, the solvent can optionally also be distilled off, and the residual acid can be reacted with the epoxide compound optionally having unsaturated groups. In a preferred variant, from 0.8 to 1.5, preferably from 0.9 to 1.1, mol of glycidyl methacrylate are added per mole of residual acid and the reaction is carried out at from 70 to 130, preferably from 80 to 110 ℃ until an acid number of less than 3, preferably less than 1mg of potassium hydroxide per gram of reaction mixture is reached.

If the solvent is not distilled off before the reaction with the epoxy compound, it is necessary to remove it after the reaction. Here, the distillation is preferably carried out under reduced pressure until the flash point of the sample is above 100 ℃.

In a variant which is likewise known in principle, it is also possible to replace the esterification of the acid with the polyol by a transesterification process. The principle of the above-described method is described, for example, in DE-A4019788. Here, instead of (meth) acrylic acid, an ester of (meth) acrylic acid with a low molecular weight alcohol such as methanol or ethanol may be used. In this case, no water is split off, but the low molecular weight alcohol is distilled off from the reaction mixture. Azeotropic entrainers can be omitted from the process.

The hydroxy-functional partial esters formed from different alkoxylated polyols and (meth) acrylic acid generally have a dynamic viscosity of less than 1000 mPas at 23 ℃ and are transparent, water-clear or slightly colored. In a second step, these products are reacted with diisocyanates and/or polyisocyanates, hereinafter referred to as polyisocyanates.

In addition to the hydroxy-functional partial esters prepared from different alkoxylated polyols and (meth) acrylic acids, it is also possible, if appropriate, to use further compounds which are reactive toward isocyanates. For the urethane acrylates of the present invention, the amount thereof is limited: i.e. less than 0.4 equivalents, preferably less than 0.2 equivalents, of other compounds reactive with isocyanates are used per isocyanate equivalent.

This class of compounds may be: esters of acrylic or methacrylic acid with diols having a free hydroxyl group, such as 2-hydroxyethyl-, 2-or 3-hydroxypropyl-or 2-, 3-or 4-hydroxybutyl- (meth) acrylate, and their reaction products with lactones, such as epsilon-caprolactone, or any mixtures of such compounds, i.e. (cyclo) alkanediols having a molecular weight in the range from 62 to 286, i.e. diols with hydroxy groups linked to cyclo (aliphatic) hydrocarbons, such as ethylene glycol, 1, 2-and 1, 3-propanediol, 1, 2-, 1, 3-and 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, neopentyl glycol, cyclohexane-1, 4-dimethanol, 1, 2-and 1, 4-cyclohexanediol, 2-ethyl-2-butylpropanediol, 2-diethyl-1, 3-propanediol, 2, 2-dimethyl-1, 3-propanediol, 2-ethyl-1, 3-hexanediol, 2, 5-dimethyl-1, 6-hexanediol, 2, 2, 4-trimethyl-1, 3-pentanediol, (3-hydroxy-2, 2-dimethylpropyl) -3-hydroxy-2, 2-dimethylpropionate, glycols which contain ether oxygen and have a maximum molecular weight of about 2000, preferably about 1000 and particularly preferably about 500, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol or polybutylene glycol. The reaction products of the above diols with epsilon-caprolactone or other caprolactones may likewise be used as diols. In addition, it is also possible to use polyester diols known per se which are obtained from the aforementioned diols and aromatic and/or preferably from (aliphatic) dicarboxylic acids or their anhydrides (such as phthalic acid, phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, cyclohexanedicarboxylic acid, maleic anhydride, fumaric acid, malonic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid, and hydrogenated dimeric fatty acids).

It is particularly preferred, however, to dispense with the use of the abovementioned compounds which can be reacted further with isocyanates.

Suitable polyisocyanates are any organic polyisocyanates known per se from polyurethane chemistry which carry aliphatically, cycloaliphatically and/or aromatically attached isocyanate groups and which preferably have a molecular weight of from 144 to 1000, more preferably from 168 to 300. Suitable examples are butylene diisocyanate, 1, 6-Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), 3(4) -isocyanatomethyl-methylcyclohexyl-isocyanate (IMCI), trimethylhexamethylene diisocyanate (═ 2, 2, 4 and/or 2, 4, 4-trimethylhexamethylene diisocyanate), the isomeric bis (4, 4' -isocyanatocyclohexyl) methanes (H)₁₂MDI), the isomeric bis (isocyanatomethyl) -methylcyclohexanes, isocyanatomethyl-1, 8-octanediocyanates, 1, 4-cyclohexylene diisocyanate, 1, 4-phenylene diisocyanate, 2, 4-and/or 2, 6-Toluene Diisocyanate (TDI), 1, 5-naphthalene diisocyanate, 2, 4 ' -and/or 4, 4 ' -diphenylmethane diisocyanate (MDI), triphenylmethane-4, 4 ' -triisocyanates or their mixtures with urethane-, isocyanurate-, allophanate-, biuret, uretdione (urea) structures and/or mixtures thereof and also aliphatic and aromatic di-and/or polyisocyanate mixtures. Generally, these derivatives have an average molecular weight of up to about 1000. The production and preparation of such derivatives is described in documents such as US-A3124605, US-A3183112, US-A3919218, US-A4324879 or EP-A798299.

Preferably HDI, IPDI, TD are usedI、H₁₂MDI and/or polyisocyanates having isocyanate groups obtained by trimerization of HDI, TDI or IPDI. Particularly preferred are HDI and IPDI and mixtures thereof.

When polyisocyanates are used, the equivalent ratio of isocyanate groups to hydroxyl groups is from 1 to 3, preferably from 1 to 2, particularly preferably from 1 to 1.5. The degree of conversion is generally monitored by tracking the isocyanate content of the reaction mixture. For this purpose, spectroscopic measurements (infrared or near-infrared spectroscopy) or chemical analyses (titration) can be carried out on the extracted sample. The reaction is preferably carried out until the isocyanate content is 0.2% or less. The reaction temperature is kept at 20 to 100 ℃ and particularly preferably 50 to 80 ℃. The starting components may be added to the reaction in any order as the reaction proceeds. The reaction is preferably carried out in the presence of a suitable catalyst for the urethanization reaction, such as zinc (II) octoate, zinc dibutylacetate or a tertiary amine such as diazabicyclooctane.

The urethane acrylates thus produced can be advantageously used as a main component of a coating agent. The coating compositions may in turn contain auxiliaries and auxiliaries, such as initiators which are known per se and which, after irradiation with sufficiently energetic radiation, for example UV radiation, initiate free-radical polymerization. Such photoinitiators are described, for example, in p.k.t.oldring (eds.), the chemistry and technology of UV and EB formulations for coatings, inks and paints, volume 3, 1991, SITA technology, london, (pages 61-325). Specific examples are 1-hydroxycyclohexylphenylketone, benzil ketals such as benzil dimethyl ketal, acylphosphine oxides such as bis (2, 4, 6-trimethylbenzoyl) phenylphosphine oxide, diacetylphosphine oxide, benzophenone and derivatives thereof. They may be used alone or in mixtures, where appropriate together with further accelerators or coinitiators as additives, in amounts of from 0.1 to 10 parts by weight, preferably from 2 to 7 parts by weight, particularly preferably from 3 to 4 parts by weight, based on the solids in the coating system. The photopolymerization can also be carried out in an inert atmosphere, in which case the photoinitiator can be chosen to be significantly smaller than when curing is carried out in air. If the coating agent is cured by means of an electron beam, the photoinitiator can be discarded.

The coating agent may be mixed with a diluent which is an auxiliary agent capable of (co) polymerization upon UV curing. Such reactive diluents are described in p.k.t.oldring (editors), UV and EB formulation chemistry and technology for use in coatings, inks and paints, volume 2, 1991, SITA technology, london, pages 237 and 285. Specific examples are esters of acrylic acid or methacrylic acid, preferably acrylic acid, with the following alcohols. The monoalcohols include the various isomeric butanols, pentanols, hexanols, heptanols, octanols, nonanols and decanols, and also cycloaliphatic alcohols such as isoborneol, cyclohexanol and alkylated cyclohexanols, dicyclopentanol, arylaliphatic alcohols such as phenoxyethanol and nonylphenylethanol, and tetrahydrofurfuryl alcohol. Alkoxylated derivatives of these alcohols may additionally be used. Dihydric alcohols are, for example, ethylene glycol, propylene glycol-1, 2, propylene glycol-1, 3, diethylene glycol, dipropylene glycol, the various isomeric butanediols, neopentyl glycol, hexanediol-1, 6, 2-ethylhexanediol and tripropylene glycol or also alkoxylated derivatives of these alcohols. Preferred diols are hexanediol-1, 6, dipropylene glycol and tripropylene glycol. The trihydric alcohol is glycerol or trimethylolpropane or an alkoxylated derivative thereof. Propoxylated glycerol is preferred. Since the urethane acrylates of the invention have a relatively low viscosity, less reactive diluent is generally required to adjust to the same viscosity than the urethane acrylates of the prior art.

Furthermore, it is also possible to blend the coating agents prepared according to the invention with different types of auxiliaries and additives (adjuvants). Fillers, pigments, dyes, smoothing agents, matting agents, degassing agents (Entluftungsmittel) such as polyacrylates, binders such as aminoalkyl trialkoxysilanes and flow control agents such as polysiloxanes can be added, these auxiliaries being used in the customary amounts known in coating technology. To improve the weathering resistance, for example the light resistance, light stabilizers, for example UV absorbers and sterically hindered amines, can be used in the customary amounts. If UV-absorbers are used, it is generally necessary to use a proportion of a photoinitiator of the long-wave absorption type. Methods of use of light stabilizers and their various types are described, for example, in a. valet, lichtschuttzmitl fur Lacke, Vincentz press, hannover, 1996. It is also possible to use solvents which are inert with respect to free-radical polymerization and are then removed between the coating and curing process, optionally with the introduction of heat.

The coating compositions containing the urethane acrylates according to the invention are suitable for the production of high-grade coatings, coverings and lacquers on various substrates, for example paper, cardboard, leather, textiles, glass, plastics, metals such as aluminum or steel sheets which have been pretreated if necessary, but also metals in the form of so-called "foils", wood, in particular parquet, or wood materials such as medium-density fiberboard, plastics materials such as polycarbonate or polyvinyl chloride sheets (PVC), inorganic materials such as cement, china clay, mineral, ceramics or substrates which are composed of said materials and have been coated, such as automobiles or automobile parts. Substrates composed of a plurality of such materials may also be coated. The coating agent of the invention is particularly suitable for wear-resistant coatings of materials which can be used for floors. In particular parquet and PVC sheeting.

The coating agents can be applied to the material to be coated by methods customary and well known in painting technology, such as spraying, knife coating, roller coating, pouring, dipping, spin coating and spraying (vacuum). The curing process of the liquid coating agent is accomplished by irradiation with ultraviolet rays or electron beams. For this purpose, the coated material is placed under a medium-pressure radiator, for example of mercury. The curing process with UV radiation is carried out in a known manner and the relevant contents are described, for example, in p.k.t.oldring (editors), the chemistry and techniques of UV and EB formulations for coatings, inks and paints, pp.1, 1991, SITA technique, london, 167-.

Examples

Partial esters were prepared from alkoxylated polyols and acrylic acid:

A) 860.6g of an average 12-fold ethoxylated polyether starting from trimethylolpropane (hydroxyl number 255, dynamic viscosity at 23 ℃ 265 mPas), 214.2g of an average 4-fold ethoxylated polyether starting from trimethylolpropane (hydroxyl number 550, dynamic viscosity at 23 ℃ 505 mPas), 309.6g of acrylic acid, 9.3g of 4-toluenesulfonic acid, 3.9g of 4-methoxyphenol, 0.3g of 2, 5-di-tert-butylhydroquinone and 560.1g of isooctane were weighed in a device with a water separator, stirrer, gas conduit and thermometer with through-air (one-fold device volume per hour) and nitrogen (two-fold device volume per hour). The reaction mixture is then heated to reflux temperature (about 94-108 ℃ C.) with stirring and maintained under vigorous reflux until the acid number reaches a value of less than 4.5. During this time, about 77g of water were separated. The batch was then cooled to 50 ℃ and slowly evacuated at 50 ℃ and the solvent was distilled off until no more solvent was distilled off at 90 ℃ and under vacuum (< 50 mbar). After ventilation, 26.3g of glycidyl methacrylate were added uniformly with stirring. Stirring was then continued for one hour at 100 ℃ and the acid number of the product was below 2 and the hydroxyl number was between 80 and 90.

B) Test A) was repeated with the difference that 214.2g of an average 3-fold propoxylated and trimethylolpropane-initiated polyether (hydroxyl number 550, dynamic viscosity 1800 mPas at 23 ℃) were used instead of an average 4-fold ethoxylated trimethylolpropane-initiated polyether.

Urethane acrylate

According to the following table, the partial ester formed from the alkoxylated polyol and acrylic acid, and 0.1% by weight, based on the total mass, of 2, 6-di-tert-butyl-4-methylphenol and 0.05% by weight, based on the total mass, of tin (II) ethylhexanoate were weighed into an apparatus equipped with a stirrer, a gas conduit and a thermometer while introducing air (one-time apparatus volume per hour) and nitrogen (two-time apparatus volume per hour) through the apparatus, and heated to 55 ℃ with stirring. The corresponding isocyanate is then added dropwise so that the temperature is maintained at 55 to 60 ℃ by means of an exothermic reaction. After the addition was complete (about 1h), the temperature was adjusted to 60 ℃ and maintained until the NCO content was below 0.1% (about 8 h).

Production of urethane acrylates				Testing of the paint
						Example No. 2	Partial esters	Isocyanates	Viscosity [23 deg.C]	Wear resistance	Stability of
1	A[450.9g]	TDI[25.0g]And HDI [24.2g]Mixture of	2600mPa s	7900 cycles per 100 μm thick coating	1(NaOH)/2 (ethanol)
						2	B[430.0g]	IPDI[62.0g]	4300mPa s	5600	1/3
3	A[450.9g]	First HDI [24.2g]Then TDI [25.0g]	3100mPa s	10100	1/2
						4	A[444.1g]	IPDI[56.0g]	8000mPa s	7300	1/2
5	A[450.0g]	TDI[50.0g]	5600mPa s	7000	1/2
						And (3) comparison: re-calibration example 6 of EP-A53749				4000	1/2
And (3) comparison: re-calibration example 3 of EP-A53749				4300	1/2

TDI-Desmodur* T80，Bayer AG，Leverkusen，DE；HDI-Desmodur*H，Bayer AG，Leverkusen，DE；IPDI-Desmodur* I，Bayer AG，Leverkusen，DE.

85 parts by weight of a urethane acrylate were applied to the etched Medium Density Fiberboard (MDF) by means of a spiral blade with 16 parts by weight of dipropylene glycol diacrylate (BASF AG, Ludwigshafen, DE) and 2.5 parts by weight of a photoinitiator Darocur * 1173, Ciba specialty Chemicals, Lampertheim, DE, and cured by means of UV light (ribbon arrangement, 1 radiator, 80W/cm lamp radiation [ CK-radiator, IST, Metzingen, DE ]). For the abrasion resistance test, a coating film was prepared as follows: one pass with a hand coater #2[ about 18 μm ] at a band speed of 15m/min for 2 times, and then a second pass with a hand coater #3[ about 30 μm ] at a band speed of 5m/min for 1 time. The thickness of the coating obtained was determined by optical microscopy. For the stability test, a coating film of about 120 μm was produced on MDF by means of a spiral doctor blade and cured in one pass at a belt speed of 5 m/min.

For the abrasion resistance test, Taber Abraser model 5130 and Taber Abraser Grip Feeder model 155 from Erichsen were used, and a smoothing agent of alumina (Alodur * EPL) from Treibacher Schleifmittel (Villach, Austria) which had been sieved (200 μm mesh) and dried (80 ℃ C., 1 hour) was used. The abrasion resistance test was carried out according to the Erichsen test Condition guidelines BA 155/D-VI/1995, under a load of 1000g per axis and a dissipation of 85 (corresponding to 34g per 100 revolutions). Calibration was performed using acrylic sheets. An abrasion resistance of 142mg (ideal 127. + -.18 mg) was found at 2000 revolutions. The number of cycles was measured in each case until the coating was destroyed. By calculating the measured layer thickness, a given number of periods per 100 μm thick layer can be obtained.

The stability test was performed using 48% aqueous ethanol and 16% sodium hydroxide. The impregnated cotton yarn lumps were each covered on the coating for 16 h. The surface was then wiped clean with a piece of dry and soft fabric and visually inspected. The results obtained were evaluated in points (0-no change up to 5-destruction).

Claims (8)

1. Low-viscosity, radiation-curable urethane acrylates obtainable by reacting diisocyanates and/or polyisocyanates with hydroxy-functional partial esters of acrylic and/or methacrylic acid, wherein the partial esters are based on a mixture of polyols with different degrees of alkoxylation with three or more hydroxy groups, characterized in that the mixture of alkoxylated polyols consists of 25 to 75 mol% of a polyol with a degree of alkoxylation between 3 and 5 and 75 to 25 mol% of a polyol with a degree of alkoxylation between 8 and 25.

2. Urethane acrylates according to claim 1, characterised in that they do not contain acrylic hydroxyl-C_1-4Alkyl esters and hydroxy-C methacrylate_1-4-an alkyl ester.

3. A polyurethane acrylate according to claim 1 characterised in that the mixture of alkoxylated polyols consists of 30 to 45 mol% of a polyol with a degree of alkoxylation between 3 and 5 and 70 to 55 mol% of a polyol with a degree of alkoxylation between 8 and 15.

4. A polyurethane acrylate according to claim 1, characterised in that a mixture of aliphatic and aromatic diisocyanates and/or polyisocyanates is used.

5. A process for producing the low-viscosity, radiation-curable polyurethane acrylates according to claim 1, characterised in that in a first stage the alkoxylated polyol is partly esterified with acrylic acid and/or methacrylic acid; and in a second stage, reacting it with a diisocyanate and/or a polyisocyanate.

6. Use of the urethane acrylates according to claim 1 as a coating agent component which can be cured under the influence of high-energy radiation.

7. Use of the urethane acrylates according to claim 1 for coating paper, cardboard, leather, textiles, glass, metal and plastics.

8. Use of the urethane acrylates according to claim 1 for coating floors, wood panels, PVC panels and parquet panels made of wood and plastic.