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
2000-01-28
2002-05-28
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
06395824
ABSTRACT:
The present invention relates to aqueous dispersions comprising a polyurethane which comprises carbodiimide structural units of the formula (I)
—N═C═N— (I).
The invention also relates to processes for coating, bonding and impregnating articles made from various materials with these dispersions and to the articles coated, bonded and impregnated with these dispersions.
The use of aqueous dispersions comprising polyurethanes (PU dispersions for short) for coating substrates such as textile or leather has long been known. Owing to their outstanding mechanical properties, PU dispersions based on polyesterols are preferably employed for this purpose.
In many cases the substrates thus coated are exposed to the influence of a warm and humid atmosphere. When this occurs it is found that the coatings lose their mechanical stability, as a result of hydrolytic degradation.
U.S. Pat. No. 4,113,676 discloses that aqueous PU dispersions can be protected against hydrolytic degradation by the addition of monocarbodiimides which carry no other functional groups. A disadvantage of these systems, however, is the presence of the low molecular mass carbodiimides, which may, for example, migrate from the coating and thus lead to hygiene problems. Another disadvantage is that the acylureas formed by reaction of the carbodiimide (CDI) with carboxyls split into amide and into the parent isocyanate of the CDI (Williams & Ibrahim; Chem. Rev. 81 (1981) 603), which may likewise migrate and cause problems.
WO 96/08 524, EP-A-207 414 and DE-A-4 039 193 describe aqueous dispersions of acylurea-comprising polyisocyanate adducts. To prepare them, first of all carbodiimide-containing polyurethanes or prepolymers are prepared and, before the polyurethanes are dispersed, the carbodiimide groups are reacted with carboxylic acids such as stearic acid to form the acylurea groups.
It is an object of the present invention to find PU dispersions which do not have the disadvantages of the prior art and from which it is possible to produce coatings and films which suffer no deterioration in their mechanical properties, especially their elongation at break, when stored under warm and humid conditions.
We have found that this object is achieved by the dispersions specified at the outset, by processes for producing coatings, bonds and impregnated materials and by the coated, bonded and impregnated articles themselves.
The novel dispersions comprise the carbodiimide structural units of the formula (I) preferably in amounts from 5 to 200, particularly preferably in amounts from 5 to 150 and, with very particular preference, in amounts from 10 to 100 mmol per kg of polyurethane.
A particularly simple way to incorporate the carbodiimide structural units of the formula (I) into the novel aqueous polyurethane dispersion is to construct the polyurethanes using, in whole or in part, diisocyanates (a1) which contain on average from 1 to 10, preferably from 1 to 4, structural units of the formula (I).
Examples of suitable diisocyanatocarbodiimides (a1) are those of the formula (Ia1)
OCN—(R
1
—N═C═N)
m
—R
1
—NCO (Ia1)
where R
1
is a divalent hydrocarbon radical with or without urethane, ester and/or ether groups, as is obtained by removing the isocyanate groups from a simple organic isocyanate or from a prepolymer which contains urethane groups and possibly ether or ester groups and which is terminated by isocyanate groups; if there are two or more radicals R
1
in the same molecule then different radicals R
1
conforming to the given definition may be present simultaneously; and
m is an integral or (on average) fractional number from 1 to 10, preferably from 1 to 4.
The radicals R
1
are preferably derived by abstracting the isocyanate groups from monomers (a) which are the diisocyanates commonly employed in polyurethane chemistry.
Monomers (a) are, in particular, diisocyanates X(NCO)
2
, where X is an aliphatic hydrocarbon radical of 4 to 12 carbons, a cycloaliphatic or aromatic hydrocarbon radical of 6 to 15 carbons or an araliphatic hydrocarbon radical of 7 to 15 carbons. Examples of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,2-bis(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate, 1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of bis(4-isocyanatocyclohexyl)methane (HMDI), such as the trans/trans, the cis/cis and the cis/trans isomer, and mixtures of these compounds.
Particularly important mixtures of these isocyanates are the mixtures of the respective structural isomers of diisocyanatotoluene and diisocyanatodiphenylmethane, especially the mixture comprising 80 mol-% 2,4-diisocyanatotoluene and 20 mol-% 2,6-diisocyanatotoluene. In addition, the mixtures of aromatic isocyanates such as 2,4-diisocyanatotoluene and/or 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanates such as hexamethylene diisocyanate or IPDI are particularly advantageous, the preferred mixing ratio of aliphatic to aromatic isocyanates being from 4:1 to 1:4.
In the case of the radicals R
1
derived by abstracting the isocyanate groups from a prepolymer which contains urethane groups, possibly ether or ester groups and terminal isocyanate groups, the preferred radicals are those built up from the diols (b) and the diisocyanates (a2).
The preparation of monomers (a1) is known per se and is described, for example, in U.S. Pat. Nos. 2,840,589, 2,941,966, EP-A-628 541 and by P. W. Campbell and K. C. Smeltz in Journal of Organic Chemistry 28 (1963) 2069. Diisocyanatocarbodiimides can also be prepared, in a particularly gentle process with no by-products, by a heterogeneous catalysis in accordance with DE-A 2 504 400 and 2 552 350. The carbodiimidization of diisocyanates in the presence of very small amounts of phospholine oxide and with subsequent block ing of th e catalyst with acid chlorides is described in DE-A 2 653 120.
In addition to preparing the diisocyanates (a1), the diisocyanates (a2) are also generally employed directly to synthesize the polyurethanes which are present in novel polyurethane dispersions, since to synthesize the polyurethanes it is often necessary to have more isocyanate than is required to introduce the carbodiimide groups.
In addition to the isocyanates listed above, isocyanates which can be employed as compounds (a2) to synthesize the polyurethanes are those which carry not only the free isocyanate groups but also further, capped isocyanate groups, such as uretdione groups.
With a view to good filming and elasticity, compounds which are ideally suitable as diols (b) are diols (b1) which have a relatively high molecular weight of from about 500 to 5000, preferably from about 1000 to 3000 g/mol.
The diols (b1) are, in particular, polyesterpolyols which are known, for example, from Ullmanns Encyklopädie der technischen Chemie, 4th edition, Vol. 19, pp. 62 to 65. It is preferred to employ polyesterpolyols that are obtained by reacting dihydric alcohols with dibasic carboxylic acids. Instead of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof in order to prepare the polyesterpolyols. The polycarboxylic acids can be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and can be unsubstituted or substituted, for example by halogens, and/or saturated or unsaturated. Examples are suberic, azelaic, phthalic and isophthalic acids, phthalic, tetrahydrophthalic, hexahydrophthalic, tetrachlorophthalic, endomethylenetetrahydrophthalic, glutaric and maleic anhydride, maleic and fumaric acid and dimeric fatty acids. Preference is given to dicarboxylic acids of the formula HOOC—(CH
2
)
y
—COOH where y i
Beutler Kuno
Götz Thomas
Häberle Karl
Hummerich Rainer
Kaehs Helmut
BASF - Aktiengesellschaft
Niland Patrick D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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