Allophanate-groups containing polyisocyanates

0001The invention relates to a novel process for producing allophanate -containing polyisocyanates, the compounds obtainable according to this method and their use as binders or binder components in coating compositions.

0002Polyisocyanates containing allophanate groups and their use in coating compositions have long been known (see. for example GB-PS 994 890, EP-A-0000194 or EP-A-0303150). The preparation of such allophanate Direction Polyisocyanates is generally carried out by reacting excess quantities of mostly aliphatic or cycloaliphatic diisocyanates with mono- or polyhydric Alcohols. After the urethanization and allophanatization is the excess of volatile isocyanate removed by distillation and results in products whose property profile depending on the used diisocyanate can be varied widely. The preparation of allophanate Polyisocyanates based on aromatic diisocyanates, for example, in U.S. Patent No. 3,769,318 described. One of the disadvantages of these aromatic allophanate is to be seen in their poor thermal stability, so that the Reaction products under the conditions of the thin film distillation, the built- split diisocyanates, indicating complete removal of the excess Diisocyanate following the allophanatization impossible power.

0003As has now been found, it is according to the invention described in detail below A process using different isocyanate components possible for the urethanization and the subsequent allophanatization, produce thermostable, allophanate groups, containing different isocyanate groups in chemically incorporated form and are thus referred to as "heteroallophanates". The properties this heteroallophanates, in particular its viscosity and Reactivity and Properties of the coatings produced from them, such as Hardness and elasticity, can easily by appropriate choice of the Urethanization one hand and for the allophanatization other part Isocyanate are controlled. Of particular importance is the thermal stability the process products invention described below even when using aromatic diisocyanates, in particular of Diisocyanatotoluene in the allophanatization.

0004The obvious idea, said variability of product and film properties by using isocyanate mixtures, in particular diisocyanate mixtures to achieve in the urethanization and subsequent allophanatization, fails partly due to the often inadequate thermal stability of such obtained "Mischallophanate" and is subject to another with the drawback that it is referred to in the corresponding reaction products in contrast to the Process products described in greater detail inventive polyisocyanates These isocyanate groups of different reactivity.

0005The invention is a process for producing allophanate containing polyisocyanates by reacting under allophanate containing urethane groups of compounds a) with respect to the urethane groups excess amounts of distillable organic polyisocyanates b) and subsequent distillative removal of the unreacted excess of the Component b), to a residual content of below 0.5 wt .-% and wherein the

0006Component a) is substantially free from isocyanate groups and hydroxyl, per Molecule having at least two urethane groups in the statistical average, a1 by reaction of organic isocyanates) with organic hydroxyl a2) compounds prepared a maximum average Molecular weight of 2,500 are characterized in that one b) used as a component of the component a1) different polyisocyanates wherein 2,2'-, 2,4'- and 4,4'-diisocyanatodiphenylmethane excluded.

0007Starting materials in the novel process are a) urethane containing compounds of the type b and detailed below) organic Polyisocyanates containing urethane groups with the compounds placed a) under allophanatization in a known manner to implement will.

0008The urethane group-containing compounds A) have (statistical average) per molecule, at least two urethane groups and from the stoichiometry the starting materials calculable molecular weight of at most 2,500, preferably a maximum of 1,500 on. The compounds a) are "substantially" Isocyanate and hydroxyl-free. This is to mean that the NCO content of the Compounds a) at max. 2, preferably at max. 0.5 and in particular at Max. 0.2 wt .-% and the hydroxyl group at max. 1, preferably at Max. 0.3 and in particular at max. 0.1 .-% is. This will substantially achieved in that in the preparation of the compounds a), the starting components a1) and a2) at an NCO / OH equivalent ratio of 1.2: 1 to 1: 1.2, preferably 1.1: 1 to 1: 1.1, and most preferably from 1: 1 are reacted. These urethane-forming reaction is generally within the Temperaturbereich- from 20 to 130, preferably 50 to 90 ° C, preferably carried out in bulk.

0009The isocyanate component a1) consists of any of (cyclo) aliphatic and / or aromatic mono-, di- and / or polyisocyanates of the molecular weight range 99-1000, preferably 140 to 300 having an NCO content of 10 to 56, preferably 18 to 56 and especially 30 to 50 wt .-%. The (average) NCO functionality component a1) is 1 to 6, preferably from 2 to 3.5 and most preferably 2. Preferably, the isocyanate component a1) exclusively of diisocyanates, in particular linear-or cyclic Diisocyanates. By "cyclic" diisocyanates are to be understood, per molecule at least one aromatic or at least one cycloaliphatic have ring.

0010Examples of monoisocyanates which contain as component a1) or as part of component a1) may be used, phenyl and (cyclo) aliphatic Monoisocyanates having 4 to 18 carbon atoms such as n-butyl isocyanate, Cyclohexyl or n-stearyl.

0011Examples of suitable diisocyanates are tetramethylene, pentamethylene, Hexamethylene diisocyanate (HDI), Undecamethylendiisocyanat, dodecamethylene 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 4,4'-bis- (isocyanatocyclohexyl) -methane and mixtures thereof with the corresponding: 2,4'- and optionally 2,2'-isomers (HMDI), 1-methyl-2,4-diisocyanatocyclohexane or its mixtures with 1-methyl-2-6-diisocyanatohexane (HTDI), 1-isocyanato-4 (3) -isocyanatomethyl-1-methylcyclohexane or p-xylylene diisocyanate and mixtures thereof. Aromatic diisocyanates such as 2,4- and / or 2,6-diisocyanatotoluene (TDI) as component a1) or as part of this component into consideration.

0012Also biuret, uretdione or carbodiimide groups derivatives the above-mentioned isocyanates are in principle as component a1) or such as part of this component into consideration, however, the (co-) use Modification products is not preferred.

0013Component a1) preferably consists of HDI, HMDI, IPDI or HTDI.

0014The alcohol component a2) is from 1- to 6-hydric alcohols of the molecular weight range 32-900, preferably 74-300 or any mixtures such alcohols. Eligible alcohols are for example saturated monovalent alcohols such as methanol, ethanol, n-propanol, isopropanol, Methoxypropanol, the isomeric butanols, pentanol, hexanols, octanols, Decanols dodecanols, octadecanols; polyhydric alcohols such as Ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 2-methyl-1,3-propanediol, 2,2,4-trimethyl-1,3, dimer fatty alcohols, trimer, Glycerol, trimethylolpropane, trimethylolethane, the isomeric hexanetriols, Pentaerythritol or sorbitol. As a component or part of the component a2) also useful are unsaturated alcohols such as allyl alcohol, trimethylolpropane, Butenediol and monofunctional alcohols of corresponding to Acids or acid mixtures of unsaturated synthetic and natural fatty acids derived.

0015Basically possible, but by no means preferred, the (co-) use having ether groups alkoxylation way of example above said mono- and polyhydric alcohols and / or (co-) use having hydroxyl groups by transesterification of fats or oils with polyhydric alcohols such as in particular glycerol, trimethylolpropane, pentaerythritol.

0016The molecular weight of the component a) is by appropriate selection of the starting components a1) and a2) and in particular by their average functionality set. As component a) high molecular weight compounds can not be considered come, must accordingly as component a 1) and / or Component a2) monofunctional components (used to) to a chain terminator to effect during the urethane-forming reaction. This means that the average functionality of the components a1) and a2) under 2 lies.

0017The isocyanate component b) consists of distillable organic polyisocyanates mentioned already above in the description of component a1) Type with the exception of 2,2'-, 2,4'- and 4,4'-diisocyanatodiphenylmethane (S. Also US-A-5,319,054), but the b) component should have no monoisocyanates. The (Average) NCO functionality of component b) is from 2 to 4, preferably at 2, that is, it will preferably exclusively diisocyanates as component b) used.

0018are particularly preferred as component b) TDI, IPDI, HTDI, HMDI or HDI used.

0019The inventively essential point now is that a1 than component) one hand, and as component b) on the other hand different isocyanates of exemplary find mentioned type use. This means that when of isocyanate mixtures as component a1) and / or component b) maximum 10 wt .-% of the respective components present in the same isocyanates are. Preferably, of course, component b) exclusively from such isocyanates which are not present in component a1). Here are positional isocyanates same type, such as 2,4-and 2,6-TDI, 2,4-and 2,6-HTDI, 2,4'-, 2,2'- and 4,4'-MDI, 2,4'-, 2,2'- and 4, 4'-HMDI not as different isocyanates.

0020Particularly preferred combinations are consisting<ul><li>HDI as component a1) and TDI, as component b),</li><li>HDI as component a1) and IPDI as component b),</li><li>HDI as component a1) and HTDI as component b),</li><li>HMDI as as component a1) and HDI component b),</li><li>IPDI as as component a1) and HDI component b) and</li><li>HTDI as as component a1) and HDI component b).</li></ul>

0021the reaction of the urethane component a) with the isocyanate component b) in an NCO / urethane equivalent ratio of 3: 1 to 100: 1, preferably from 6: 1 to 60: 1 and particularly preferably from 8: 1 to 30: 1 in the temperature range of 40 ° C to 150 ° C, preferably 50 ° C to 120 ° C and more preferably 60 ° C to 90 ° C, preferably for accelerating the allophanatization reaction usual, literature known catalysts. Examples of usable Catalysts are tetraalkylammonium or arylalkylammonium, Metal salts such as iron (III) chloride, potassium octoate, zinc compounds such as zinc stearate, zinc octoate, zinc naphthenate, zinc acetylacetonate, tin compounds such as tin (II) octoate, tin (II) ethylhexanoate, tin (II) laurate, aluminum tri (ethlylacetoacetat), Dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, Dibutylzimimaleat or dioctyl, manganese, cobalt and Nickel compounds, and mineral acids such as trifluoroacetic acid, sulfuric acid, Hydrogen chloride, hydrogen bromide, phosphoric acid or perchloric acid.

0022The catalysts can before allophanatization or even before urethanization be added. They come in concentrations of 0.001 to 5 wt .-%, preferably 0.005 to 1 wt .-% are used. The catalyst can, if possible, be removed by distillation from the reaction mixture. It can but also be useful by suitable catalyst poisons its catalytic stop action.

0023By appropriate selection of the starting components a) and b) is the functionality the resulting products of the process set. The allophanatization when reaching the desired NCO-functionality of the reaction products terminated. Following the reaction the excess is not unreacted starting component b), preferably by film distillation, up to a residual content in the product is below 0.5, preferably below 0.2 wt .-% removed.

0024The products of the invention provide allophanate Polyisocyanates having an NCO content of 5 to 17, preferably 6 to 15 wt .-% and a content of distillable isocyanates of less than 0.5 and preferably less than 0.2 wt .-%. It is uni viscous to resinous Products.

0025Depending on the viscosity of the products according to the invention it may be useful be to dilute with inert solvent. For this purpose, suitable solvents for example, toluene, xylene, cyclohexane, chlorobenzene, butyl acetate, Ethyl acetate, ethyl glycol acetate, pentyl acetate, hexyl acetate, methoxypropyl, Tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, white spirit, more highly substituted Aromatics, such as under the name Solvent Naphtha, Solvesso®, Shellsol, Isopar, Nappar® and Diasol® commercially and mixtures such solvents.

0026The products of the invention provide, under the influence of humidity curable binders for one-component coating materials . Preferably, the process products according to the invention, however, are as Crosslinkers used in two-component polyurethane coatings. At least possible is also the use of the process products according to the invention with per se known blocking agents blocked form in combination with at is known polyhydroxyl compounds in thermosetting one-component coating systems.

0027Of course, in all coating compositions, in which according to the invention Process products used as binders or as binder component are known from coatings technology auxiliary substances and additives be used. respect to this, exemplified Wetting agents, flow control agents, antiskinning agents, antifoaming agents, Matting agents such as silica, aluminum silicates and high-boiling Waxes, viscosity regulators, pigments, dyes, UV absorbers or stabilizers against thermal and oxidative degradation.

0028The products according to the invention as a binder or binder component Coating compositions containing any can for coating Substrates such as wood, plastics, leather, paper, textiles, glass, Ceramics, plaster, masonry, metals or concrete. They can be by conventional methods such as spraying, brushing, flooding, pouring, Dipping and rolling.

0029all viscosity data relate pre- and well below the 23 ° C by rotational according to DIN 53 019 specific viscosities.

0030In the following examples, all figures in "%" on the Weight.

<b>example 1</b>

0031In a nitrogen-purged stirred reactor 29.5 g (0.226 mol) of 2-ethylhexanol submitted and at 60 ° C with 19 g (0.113 mole) of HDI are added. After about 6 hours reaction time at a temperature of 95 ° C, the NCO content of resulting diurethane had fallen to below 0.2%. Subsequently, by adding of 236 g TDI (2,4- and 2,6-diisocyanatotoluene in a weight ratio of 80:20) and subsequently catalyzed with 43 mg of zinc stearate at 88 ° C. The allophanatization started. After 6 hours, will once more with 14 mg of catalyst reactivated and further stirred until a constant NCO content reached 36.2% is. Excess TDI was then separated by thin film distillation (- 0.3 mbar 0.1) separated at a temperature of 150 ° C under high vacuum.

Product data:

0032<dl tsize="16" compact="compact"><dt>Yield:</dt><dd>83 g</dd><dt>NCO content:</dt><dd>10.8%</dd><dt>Viscosity:</dt><dd>75,000 mPas / 23 ° C</dd><dt>. fr TDI content:</dt><dd>&lt;0.03%</dd></dl>

0033The ¹³C-NMR spectrum shows characteristic peaks for allophanates, however, no signals for urethane. Also, the low content of free TDI has to a simple separation of the monomer during the distillation without cleavage out.

<b>example 2</b>

0034In a nitrogen-purged stirred reactor 29.5 g (0.226 mol) of 2-ethylhexanol submitted and at 60 ° C with 19 g (0.113 mole) of HDI are added. After about 6 hours reaction time at a temperature of 95 ° C, the NCO content of resulting diurethane had fallen to below 0.2%. Subsequently, by adding of 302 g (1.36 mol) IPDI and subsequently catalyzed with 0.35 g of zinc stearate at 88 ° C the allophanatization launched. After 6 hours, is a constant NCO content of 29.83% was reached. The excess IPDI was then separated by thin film distillation under high vacuum (0.1 to 0.3 mbar) at a temperature separated by 150 ° C.

Product data:

0035<dl tsize="17" compact="compact"><dt>Yield:</dt><dd>90 g</dd><dt>NCO content:</dt><dd>9.2%</dd><dt>Viscosity:</dt><dd>85 000 mPas / 23 ° C</dd><dt>. fr IPDI content:</dt><dd>0.15%</dd></dl>