Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-07-02
2003-02-04
Sergent, Rabon (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C252S182200, C252S182210, C252S182220, C156S331400, C156S331700, C528S059000, C528S060000, C528S061000, C528S065000, C528S066000, C528S067000, C528S076000, C528S080000, C528S085000, C560S026000, C560S115000, C560S158000, C560S330000, C560S336000, C560S358000, C560S359000, C560S360000
Reexamination Certificate
active
06515164
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a low-monomer PU prepolymer containing free NCO groups obtainable from polyhydric alcohols and diisocyanates differing in their reactivity, to its production and to its use.
2. Discussion of the Related Art
PU prepolymers of the type in question are described in EP 0 150 444.
They are produced by a process in which
in a first reaction step, toluene-2,4-diisocyanate is reacted with polyhydric alcohols in an OH:NCO ratio of 4 to 0.55:1 in the absence of other diisocyanates and, after virtually all the NCO groups of relatively high reactivity have reacted off with some of the OH groups present,
a symmetrical dicyclic diisocyanate, which is more reactive than the sluggishly reacting NCO groups of the toluene-2,4-diisocyanate from reaction step 1, is added in a second reaction step in an equimolar quantity or in excess, based on free OH groups, or in a quantity of 5 to 80% by weight, based on the total quantity of diisocyanates in steps 1 and 2,
optionally at elevated temperature and/or in the presence of typical catalysts. Although this known PU prepolymer has a low monomer content, i.e. only 1 to 2.5% according to the Examples, it does not cure sufficiently quickly in many cases.
Accordingly, the problem addressed by the present invention was to provide a low-monomer PU prepolymer containing free NCO groups which would allow quicker but sufficiently safe processing.
SUMMARY OF THE INVENTION
The solution provided by the invention is defined in the claims and consists in a low-monomer PU prepolymer containing free NCO groups which is obtainable from polyhydric alcohols and at least two diisocyanates differing in their reactivity and which is characterized in that the ratio of the NCO groups of the partly slower-reacting diisocyanate to the NCO groups of the faster-reacting diisocyanate is greater than 6:1.
The ratio between the isocyanate groups is preferably greater than 10:1 and, above all, greater than 15:1.
DETAILED DESCRIPTION OF THE INVENTION
Various polyhydric alcohols may be used. Aliphatic alcohols containing 2 to 4 hydroxyl groups per molecule are suitable. Primary and secondary alcohols may be used, secondary alcohols being preferred. In particular, the reaction products of low molecular weight polyhydric alcohols with alkylene oxides containing up to 4 carbon atoms may be used. For example, the reaction products of ethylene glycol, propylene glycol, the isomeric butanediols or hexanediols with ethylene oxide, propylene oxide and/or butylene oxide are suitable. In addition, the reaction products of trihydric alcohols, such as glycerol, trimethylol ethane and/or trimethylol propane, or higher alcohols, for example pentaerythritol or sugar alcohols, with the alkylene oxides mentioned may be used.
Polyether polyols with a molecular weight of 100 to 10,000 and preferably 1,000 to 5,000, more especially polypropylene glycol, are particularly suitable. Thus, addition products of only a few moles of ethylene oxide and/or propylene oxide per mole or addition products of more than 100 moles of ethylene oxide and/or propylene oxide with low molecular weight polyhydric alcohols may be used according to the required molecular weight. Other polyether polyols may be obtained by condensation of, for example, glycerol or pentaerythritol with elimination of water. In addition, polyols widely used in polyurethane chemistry are obtained by polymerization of tetrahydrofuran. Among the polyether polyols mentioned, the reaction products of polyhydric low molecular weight alcohols with propylene oxide under conditions where at least partly secondary hydroxyl groups are formed are particularly suitable. Other suitable polyether polyols are described, for example, in DE-OS 2 559 759.
Polyester polyols having a molecular weight of 200 to 10,000 are also suitable for the process according to the invention. A first embodiment is characterized by the use of polyester polyols formed by reaction of low molecular weight alcohols, more particularly ethylene glycol, propylene glycol, glycerol or trimethylol propane, with 1 to 50 moles of caprolactone. Other suitable polyester polyols can be obtained by polycondensation. Thus, dihydric and/or trihydric alcohols may be condensed with less than the equivalent quantity of dicarboxylic acids and/or tricarboxylic acids or reactive derivatives thereof to form polyester polyols. Suitable dicarboxylic acids for this condensation reaction are succinic acid and higher homologs thereof containing up to 12 carbon atoms, unsaturated dicarboxylic acids, such as maleic acid or fumaric acid, and aromatic dicarboxylic acids, more particularly the isomeric phthalic acids. Suitable tricarboxylic acids include citric acid and trimellitic acid. Polyester polyols of the above-mentioned dicarboxylic acids and glycerol, which have a residual content of secondary OH groups, are particularly suitable for the purposes of the invention.
Polyols based on polycarbonates may also be used. Polycarbonates may be obtained, for example, by the reaction of diols, such as propylene glycol, butane-1,4-diol or hexane-1,6-diol, diethylene glycol, triethylene glycol to tetraethylene glycol, or mixtures of two or more of these diols with diaryl carbonates, for example diphenyl carbonate or phosgene.
Other suitable polyol components are OH-containing polyacrylates. These polyacrylates can be obtained, for example, by polymerization of ethylenically unsaturated monomers containing an OH group. Monomers such as these may be obtained, for example, by the esterification of ethylenically unsaturated carboxylic acids and dihydric alcohols, the alcohol generally being present in a slight excess. Ethylenically unsaturated carboxylic acids suitable for the esterification are, for example, acrylic acid, methacrylic acid, crotonic acid or maleic acid. Corresponding OH-containing esters are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof.
Finally, the polyols may also be based on polybutadiene, styrene/butadiene rubber or nitrile rubber.
In the context of the invention, the expression “two diisocyanates differing in their reactivity” applies to two different diisocyanates differing in their reactivity to alcohols. In selecting these different diisocyanates, the following observations should be taken into account: in the reaction of diisocyanates with alcohols, the reaction rate of the first diisocyanate group is considerably higher than that of the second diisocyanate group. This applies in particular to monocyclic diisocyanates and also to other diisocyanates containing groups in different chemical environments, i.e. generally speaking to non-symmetrical diisocyanates. It has also been found that dicyclic diisocyanates or, more generally, symmetrical diisocyanates have a higher reaction rate than the second isocyanate group of non-symmetrical or monocyclic diisocyanates.
Accordingly, the first diisocyanate is a non-symmetrical diisocyanate containing two NCO groups differing in their reactivity. Specific examples are toluene-2,4-diisocyanate (TDI), isophorone diisocyanate and 2,4-diphenyl methane diisocyanate. The second diisocyanate is a symmetrical isocyanate, preferably a dicyclic diisocyanate. It is important that the reactivity of its isocyanate groups to hydroxyl groups is higher than that of the terminal isocyanate groups of the non-symmetrical diisocyanate reacted on one side (reactive diluent). Accordingly, diaryl diisocyanates are especially suitable, 4,4′-diphenyl methane diisocyanate (MDI) and/or substituted 4,4-diphenyl methane diisocyanates, for example, being preferred.
The concentration of the NCO groups differing in their reactivity in the prepolymer according to the invention is determined by nuclear resonance spectroscopy (NMR).
By “low-monomer” is meant a low concentration of the starting diisocyanates. Their concentration is below 2, pre
Bolte Gerd
Henke Guenter
Kruedenscheidt Markus
Omoruyi Astrid
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Ortiz Daniel S.
Sergent Rabon
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