Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-04
2001-09-04
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C427S372200, C427S385500, C428S423100, C524S839000, C524S840000
Reexamination Certificate
active
06284836
ABSTRACT:
The invention relates to aqueous polyurethane dispersions, processes for their preparation, aqueous polyurethane systems containing them and their use for coating leather.
Polyurethane-based binders for the aqueous finishing of leathers are already known.
The finishing of leather imparts to the leather articles their fashion aspect and their suitability for use. Finishing is understood as meaning the application of binders, dyes, pigments, waxes, handle compositions and further auxiliaries, by customary application techniques, such as spraying, printing, pouring, knife-coating, application with a plush pad, to the tanned hide. This application may be effected in one coat but as a rule is carried out in a plurality of coats, further process steps, such as intermediate drying, plating, embossing, milling, being customary. After each application of a finish coat, the leathers are usually stacked. This is possible only if the freshly applied finish coat does not stick after drying. The technical possibilities for drying an aqueous finish coat on leather are limited; only 90° C. to—briefly—100° C. can be reached because otherwise the shrinkage temperature of the leather is exceeded. The drying time, too, is short.
Owing to these limitations, inherently film-forming polymer dispersions which, after drying on, give a nontacky finish coat having good mechanical strength are used in the aqueous finishing of leather.
However, such binders have substantial disadvantages; for example, the levelling is not optimum and the formation of a continuous film is made more difficult. In industrial finishing, an attempt is made to compensate these disadvantages by adding levelling assistants—so-called levellers. Good levelling and optimum film formation of the binders of a finish system are essential for obtaining the required aspect and fastness level of the finish. This applies in particular to the uppermost finish coat, the so-called top coat.
Such binders are polymer dispersions. Low molecular weight—non-film-forming—polyurethane dispersions have not been used to date in the aqueous finishing of leather because, after drying on, such products are tacky, preventing industrial use.
It was the object of the present invention to overcome these disadvantages. Surprisingly, an aqueous polyurethane dispersion has now been found which contains a polyurethane which is composed of:
a) at least one polyol, preferably one diol, having an average molecular weight, determined as the number average, of 500 to 6000 g/mol, preferably 1000 to 4000, in particular 1500 to 3000 g/mol,
b) at least one polyol, preferably diol, having a molecular weight of less than 500 g/mol, preferably 61 to 499 g/mol,
c) at least one aliphatic polyisocyanate, preferably diisocyanate, preferably having a molecular weight of less than 500 g/mol, preferably 112 to 400, in particular 168 to 262 g/mol,
d) at least one diol having a molecular weight of less than 450 g/mol, which carries one or more ionic groups and/or one or more potentially ionic groups, preferably at least one carboxyl or carboxylate group,
e) at least one amine which is reactive towards NCO groups, carries hydroxyl groups and has an OH functionality of 1 to 6,
f) water and optionally
g) a monoalcohol, characterized in that the molar ratio of polyol of the component a) to the sum of the polyols b) and d) is 1:1.5 to 1:4, preferably 1:2 to 1:3, the molar ratio of the sum of the polyols a), b) and d) to the polyisocyanate c) is 1:1.1 to 1:2.5, preferably 1:1.2 to 1:1.7, the OH functionality of the polyurethane being 2 to 6, preferably 2 to 4, and the average molecular weight, determined as the number average, of the polyurethane being less than 15,000, preferably from 2500 to 10,000, in particular from 3000 to 7000, g/mol.
In general, the polyols a) and b) have no ionic groups or potentially ionic groups, apart from terminal carboxyl groups in polyester polyols, a proportion of which cannot always be avoided in their preparation.
The following may be used as a suitable polyol of the component a) or as suitable polyols of the component a): polyesters, polyethers, polycarbonates and polyesteramides of the molecular weight range 500 to 6000.
For example, the following may be mentioned as such: reaction products of polyhydric, preferably dihydric, alcohols with preferably dibasic carboxylic acids. Instead of the polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof may also be used for the preparation of the polyesters. The polycarboxylic acids may be of an aliphatic, cycloaliphatic, aromatic and/or heterocyclic nature and may be optionally substituted, for example by halogen atoms, and/or unsaturated. The following may be mentioned as an example thereof: succinic acid, adipic acid, suberic acid, azeleic acid, sebacic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric fatty acids, such as oleic acids, optionally as a mixture with monomeric fatty acids, dimethyl terephthalate, bis-glycol terephthalate.
Suitable polyhydric alcohols are, for example, ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4-, 1,3- and 2,3-butylene glycol, 1,6-hexanediol, 1,8-octanediol, neopentylglycol, cyclohexanedimethanol (1,4-bis-hydroxymethylcyclohexane), 2-methyl-1,3-propanediol, furthermore diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, and polybutylene glycol. The polyesters may have a proportionate amount of terminal carboxyl groups. Polyesters obtained from lactones may also be used.
The particularly preferred polyester polyols, in particular polyester diols, are dicarboxylic acid polyester polyols whose dicarboxylic acid component comprises at least 50 carboxyl equivalent %, particularly preferably exclusively, adipic acid and whose polyol component preferably comprises at least 50 hydroxyl equivalent % of 1,4-dihydroxybutane, 1,6-dihydroxy-hexane, or neopentylglycol.
Polycarbonates having hydroxyl groups are also suitable as component a) or as part of the component a), for example those which can be prepared by reacting diols, such as 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, with dicarbonates, for example diphenyl carbonate or phosgene. Any mixtures of the polyhydroxy compounds mentioned by way of example may likewise be used as component a).
The following may be particularly preferably mentioned: dihydroxypolyesters of dicarboxylic acids or their anhydrides, e.g. adipic acid, succinic acid, phthalic anhydride, isophthalic acid, terephthalic acid, suberic acid, azeleic acid, sebacic acid, tetrahydrophthalic acid, maleic anhydride, dimeric fatty acids and diols, e.g. ethylene glycol, propylene glycol, 1,4-propanediol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylenepentanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, 1,8-octanediol; polyesters and polycarbonates based on lactones, in particular based on &egr;-caprolactone, polycarbonates as obtainable by reacting, for example, the abovementioned diols with diaryl or dialkyl carbonates or phosgene. Polyethers, as can be obtained, for example, using diols or water as initiator molecule by polymerization with ethylene oxide and/or propylene oxide and by polymerization of tetrahydrofuran, are likewise suitable.
Particularly suitable polyols of the component a) are polycarbonate diols, polylactonecarbonate diols and polytetrahydrofuran diols.
Among these particularly suitable polyols, hexanediol-polycarbonate diols, caprolactone-hexanediol-polycarbonate diols and tetrahydrofuran diols are preferred, in particular those of the molar mass range 1000 to 3000 g/mol.
The following are suitable as preferred polyols, in parti
Hassel Tillmann
Meixner Juergen
Muenzmay Thomas
Reiners Juergen
Schoob Jörg
Bayer Aktiengesellschaft
Gil Joseph C.
Henderson Richard E. L.
Niland Patrick D.
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