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
2002-04-02
2004-07-27
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...
C428S423100, C524S591000, C524S839000, C524S840000, C525S123000, C525S127000, C525S455000
Reexamination Certificate
active
06767954
ABSTRACT:
The present invention relates to latently crosslinking aqueous polyurethane dispersions containing
I) a disperse phase (P.I) containing
Ia) a polyurethane (Ia) which, in addition to hydrophilic groups which produce water dispersibility, carries carbodiimide groups and substantially no carboxyl groups or
Ib) a physical mixture of
Ibi) a polyurethane (Ibi) which carries hydrophilic groups which produce water dispersibility and carries substantially no carbodiimide or carboxyl groups, and
Ibii) a carbodiimide (Ibii) which carries substantially no hydrophilic groups which produce water dispersibility, and
II) a disperse phase (P.II) containing another polymer (II) which carries substantially no carbodiimide groups and is substantially derived from
II.1) from 30 to 99.98% by weight of main monomers selected from C
1
- to C
20
-alkyl (meth)acrylates, vinyl esters of carboxylic acids of up to 20 carbon atoms, vinylaromatics of up to 20 carbon atoms, ethylenically unsaturated nitrites, vinyl halides and aliphatic hydrocarbons having 2 to 8 carbon atoms and 1 or 2 double bonds,
II.2) from 0.01 to 20% by weight of a carboxylic acid having an olefinic double bond and
II.3) from 0.01 to 10% by weight of a monomer differing from the monomers II.1 and II.2 and selected from the group consisting of N-methylol (meth)acrylamide (AMOL), (MAMOL), acetoacetoxyethyl (meth)acrylate, diacetone (meth)acrylamide, glycidyl (meth)acrylate, ureido (meth)acrylate and (meth)acrylic anhydride, and
II.4) if required, monomers differing from (II.1), (II.2) and (II.3) and capable of free radical polymerization.
The present invention furthermore relates to the use of the novel aqueous dispersions as an impregnating composition, coating material or adhesive and to the impregnated, coated or adhesively bonded articles produced using these dispersions.
Aqueous dispersions which contain a polyurethane in dispersed form are generally known. In order for coatings produced from the polyurethane to have particularly good mechanical properties, a crosslinking component is added to these dispersions. It is particularly desirable for the crosslinking agent to increase the molecular weight of the polyurethane only when the polyurethane dispersion has formed a film after application to the workpiece to be coated. Under these circumstances, films which have particularly high cohesion are obtained since the polymer molecules of a dispersion particle can then also be linked to the polymer molecules of another neighboring dispersion particle via a covalent bond.
Particularly good cohesion of the films is required, for example, in the adhesive sector, particularly when the adhesive bond is subjected to mechanical load under the action of heat.
In order to obtain adhesive bonds which still have sufficient strength even under these conditions, for example EP-A-206059 recommends adding a water-emulsifiable polyisocyanate as a crosslinking agent to the dispersions shortly before they are processed as an adhesive.
However, the disadvantage of these two-component systems is that the pot life, i.e. the period in which these systems can be processed after they have been mixed, is subject to narrow limits. Since the two-component system cannot be stored over a relatively long period and the processor has to specially prepare a specific amount of adhesive which he can process within a working cycle, more work is required on the part of the processor of the adhesives in the case of two-component systems than one-component systems.
U.S. Pat. Nos. 4,977,219 and 5,117,059 disclose mixtures of an aqueous dispersion of a carbodiimide and an aqueous dispersion of an emulsion polymer having carboxylate groups, the first-mentioned dispersion being stabilized with the aid of conventional surfactants.
U.S. Pat. No. 5,574,083 relates to a mixture of an aqueous dispersion of carbodiimides, the dispersion being stabilized by hydrophilic polyalkylene oxide radicals which the carbodiimides carry. These dispersions are mixed with aqueous dispersions of an emulsion polymer having carboxylate groups.
EP-A-792908 discloses mixtures of an aqueous dispersion of a carboxyl-carrying polyurethane and an aqueous dispersion of a carbodiimide, the dispersion being stabilized with the aid of conventional surfactants.
EP-A-198343 relates to polyurethanes having carbodiimide groups and having hydrophilic groups which permit water dispersibility. According to said patent, the carboxyl-containing polymer dispersions are added and result in a crosslinking effect in the polymers.
According to the 5 abovementioned publications, the carbodiimides result in an increased molecular weight of the carboxyl-containing polymers with which they are mixed. However, the strength of adhesive bonds produced by means of these dispersions is still unsatisfactory, particularly at elevated temperatures. Furthermore, the pot life of such mixtures is limited.
DE-A-19733044 relates to aqueous dispersions of a polyurethane which carries carbodiimide groups.
DE-A-19828251 describes aqueous dispersions which contain two different types of dispersion particles, the first of which contain polyurethanes having carbodiimide groups or mixtures of polyurethanes and carbodiimides and the second of which contain other polymers having carboxyl groups.
The dispersions prepared according to the two last-mentioned publications comply with the requirement profile for adhesives technology. However, workpieces pretreated with these dispersions have insufficient blocking resistance. Blocking resistance is understood as meaning the property whereby workpieces which were wetted with the dispersion do not stick together or to other articles after drying, with application of only slight pressure. Thus, when they are stacked one on top of the other and the pressure applied to the adhesive surfaces is less than 1 kg/cm
2
, the prepared workpieces should still be capable of being separated without force even after prolonged storage. Only on application of a pressure of about 0.5 N/mm
2
, as is typically applied during the adhesive bonding of the pretreated workpieces, should a very strong adhesive bond form.
This substantially simplifies the organization of work in the production of adhesively bonded articles. Only with substantially nonblocking workpieces coated with adhesive is it possible in practice to separate the processing step of adhesive coating from the actual adhesive bonding of the adhesive-coated workpieces in terms of space or time since this requires efficient storage and transport.
It is an object of the present invention to provide a further one-component polyurethane dispersion which does not have the disadvantages of the prior art. It should in particular have a long shelf-life and be further improved with regard to the blocking resistance of the workpieces prepared therewith.
We have found that this object is achieved by the aqueous dispersions defined at the outset.
The disperse phase P.I contains in general from 0.01 to 1, preferably from 0.1 to 0.5, particularly preferably from 0.15 to 0.4, mol of carbodiimide groups per kg of monomers used for the synthesis of the polyurethanes Ia or Ibi and Ibii.
Suitable polyurethanes (Ia) are described, for example, in EP-A-792908.
In principle, all hydrophilic polyurethanes in the synthesis of which monomers having carbodiimide structural units are concomitantly used are suitable as polyurethanes (Ia). The carbodiimide structural units are introduced into the polyurethane (Ia) preferably via polyisocyanates (Ia1.1) containing one or more of the carbodiimide structural units. Such polyisocyanates (Ia1.1) are preferably of the formula Ia1.1.1
OCN—(R
c
—N═C═N)
n
—R
c
—NCO (Ia1.1.1)
where R
c
is a divalent hydrocarbon radical which may have urea, urethane, ester and/or ether groups, as is obtained by removing the isocyanate groups from a simple organic isocyanate or from a prepolymer having urethane groups and, if required, ether or ester groups and carrying terminal isocyanate groups, where, with the presence of a plurality of radicals R
Burghardt Andre
Licht Ulrike
Meyer-Roscher Bernd
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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