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
2001-06-13
2003-03-04
Cain, Edward J. (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...
C524S589000
Reexamination Certificate
active
06528573
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to aqueous two-component polyurethane systems, to a process for producing them, and to their use for the production of coatings having an enhanced impact strength and good resistance to solvents.
Environmental questions play an important part in surface technology. One particularly pressing problem is to achieve a reduction in the amounts of organic solvents which are used for lacquers and coating materials.
For chemically crosslinking polyurethane lacquers, which on account of their outstanding properties are of considerable importance in the coating sector, it has not been possible hitherto to dispense with the use of organic solvents. The use of water instead of organic solvents in two-component polyurethane lacquers based on polyisocyanates comprising free isocyanate has hitherto seemed impossible, since it is known that isocyanate groups not only react with alcoholic hydroxyl groups, but also react with water. Furthermore, the concentration of active hydrogen atoms which originate from water is of course far higher than the concentration of hydroxyl groups in the organic component which reacts with NCO, so that it must be assumed from this that the main reaction which proceeds in a polyisocyanate/organic polyhydroxy compound/water ternary system is a reaction between isocyanate and water with the formation of urea and carbon dioxide, which firstly does not result in crosslinking of the organic polyhydroxy compounds and secondly results in foaming of the lacquer batch due to the formation of carbon dioxide.
It is known from EP-A 358 979 that if selected polyhydroxyl compounds based on vinyl polymers are used as co-reactants for organic polyisocyanates comprising free isocyanate groups, aqueous two-component polyurethane systems can be produced by the emulsification, in the aqueous polymer solution or dispersion, of the polyisocyanate comprising free isocyanate groups. The polyhydroxyl compounds described in EP-A 0 358 979 are preferably polymerised by a radical mechanism in organic solution and are subsequently converted, in an aqueous solution of a neutralising agent—mostly of ammonia or tertiary amines, into a form in which they are dissolved in water. The organic solvent can remain in the aqueous medium if need be, or can be removed by distillation.
Polymer polyols which are produced in this manner normally exhibit single-phase morphology, and therefore exhibit either thermoplastic or elastomeric properties after crosslinking and film formation with suitable hydrophobic polyisocyanates and/or polyisocyanates which have been rendered hydrophilic. A single-phase structure of a polymer polyol such as this is generally not satisfactory for the production of polyurethane films which exhibit the properties of a thermoplastic elastomer which possesses both excellent toughness properties and a high level of strength.
It has been shown that polymer polyol systems of two-phase or multi-phase structure, in combination with suitable polyisocyanates, result in polyurethane coatings with a high level of toughness, particularly at low temperatures.
SUMMARY OF THE INVENTION
The present invention therefore relates to two-component polyurethane coating media, which contain, as a binder vehicle component, a) a polyol component consisting of at least two polymer polyols, wherein the first is present as a discrete phase and as an elastic component a1) dispersed in a second thermoplastic component a2), and b) a polyisocyanate component which has a viscosity of at the most 10,000 mPa.s and which consists of at least one organic polyisocyanate, in amounts corresponding to an NCO/OH equivalent ratio from 0.2:1 to 5:1, characterised in that component a) constitutes an aqueous solution and/or dispersion of a mixture of at least two vinyl polymer polyols of the aforementioned type in which polyisocyanate component b) is present in emulsified or solubilised form.
DETAILED DESCRIPTION OF THE INVENTION
Component a) is a polyol component which consists of a mixture of at least two polyols a1) and a2) which are based on vinyl polymers. Polyols a1) and a2) are not chemically bonded to each other before they are crosslinked with isocyanate component b).
Polyol a1) is an elastomer component which contains hydroxyl groups, sulphonate and/or carboxylate groups, preferably carboxylate groups, and which optionally contains sulphonic acid and/or carboxyl groups, preferably carboxyl groups. Component a1) comprises polymers of olefinically unsaturated monomers, which preferably have a (number average) molecular weight Mn as determined by the gel permeation chromatography method of 500 to 500,000 g/mol, particularly 1000 to 200,000 g/mol (with respect to the uncrosslinked constituents), a hydroxyl number of 8 to 264, preferably 16 to 198 mg KOH/g solid resin, and an acid number (with respect to the sum of the un-neutralised and neutralised acid groups) of 0 to 100, preferably 3 to 50 mg KOH/g solid resin. Elastomer component a1) has a glass transition temperature (as measured by the DSC or the DMA method) of 0° C. at most, preferably of −10° C. at most.
Thermoplastic constituent a2) is likewise a polyol which contains hydroxyl groups, sulphonate and/or carboxylate groups, preferably carboxylate groups, and which optionally contains sulphonic acid and/or carboxyl groups, preferably carboxyl groups. Component a2) is likewise a polymer of olefinically unsaturated monomers, which preferably has a (number average) molecular weight Mn as determined by the gel permeation chromatography method of 500 to 500,000 g/mol, particularly 1000 to 200,000 g/mol (with respect to the uncrosslinked constituents), a hydroxyl number of 16 to 264, preferably 33 to 198 mg KOH/g solid resin, and an acid number (with respect to the sum of the un-neutralised and neutralised acid groups) of 3 to 100, preferably 5 to 50 mg KOH/g solid resin. Thermoplastic component a2) has a glass transition temperature of at least 0° C., preferably of at least +10° C.
Elastomer components a1) which are synthesised from the following comonomer components are quite particularly preferred:
a1
a)
0.4-7.7% by weight
acrylic acid and/or methacrylic acid;
a1
b)
3.4-50.8% by weight
acrylic acid 2-hydroxyethyl ester and/or
acrylic acid hydroxypropyl ester and/or
methacrylic acid 2-hydroxyethyl ester
and/or hydroxypropyl methacrylate;
a1
c)
0-20% by weight
methyl methacrylate and/or acrylonitrile
and/or methacrylonitrile and/or styrene
or substituted styrenes as comonomers
with a strength- and hardness-imparting
character;
a1
d)
70-96% by weight
alkyl methacrylates comprising 2 to 12
C atoms in their alkyl radical and/or
alkyl acrylates comprising 1 to 12 C
atoms in their alkyl radical as
elasticising components;
a1
e)
0-5% by weight
crosslinking comonomers, such as
divinylbenzene, ethylene glycol
di(meth)acrylate, propylene glycol
di(meth)acrylate, butylene glycol
di(meth)acrylate or allyl (meth)acrylate;
wherein the sun of the percentages by weight of a1 a) to a1 e) is 100 and wherein the glass transition temperature is below −10° C.
Thermoplastic components a2) which are synthesised from the following comonomer components are quite particularly preferred:
a2
a)
0.6-7.7% by weight
acrylic acid and/or methacrylic acid;
a2
b)
6.8-50.8% by weight
acrylic acid 2-hydroxyethyl ester and/or
acrylic acid hydroxypropyl ester and/or
methacrylic acid 2-hydroxyethyl ester
and/or hydroxypropyl methacrylate;
a2
c)
30-80% by weight
methyl methacrylate and/or acrylonitrile
and/or methacrylonitrile and/or styrene
or substituted styrenes as comonomers
with a strength- and hardness-imparting
character;
a2
d)
5-40% by weight
alkyl methacrylates comprising 2 to 12
C atoms in their alkyl radical and/or
alkyl acrylates comprising 1 to 12 C
atoms in their alkyl radical
as elasticising components;
a2
e)
0-5% by weight
crosslinking comonomers, such as
divinylbenzene, ethylene glycol
di(meth)acrylate, propylene glycol
di(meth)acrylate, butylene glycol
di(meth)acrylate or allyl (meth)acrylate;
wherein the sum of the percen
Biskup Ulrich
Kobusch Claus
Probst Joachim
Bayer Aktiengesellschaft
Cain Edward J.
Gil Joseph C.
Roy Thomas W.
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