Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-09-02
2002-03-12
Sergent, Rabon (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C528S060000, C528S061000, C528S068000, C560S026000, C560S115000, C560S158000, C560S190000, C560S204000, C560S205000, C564S058000, C564S059000, C564S060000
Reexamination Certificate
active
06355829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aspartate-terminated urea/urethane prepolymers and their use in combination with polyisocyanates for the production of coating compositions that have improved flexibility.
2. Description of the Prior Art
The reaction of polyaspartates with polyisocyanates to form polyurea coatings is disclosed in U.S. Pat. Nos. 5,126,170 and 5,236,741. The polyisocyanates are blended with polyaspartates and then reacted after the mixture has been applied to a suitable substrate to form a urea group-containing coating.
One of the deficiencies of these coatings is that they do not possess good flexibility, primarily because both of the reaction components are low molecular weight compounds. The reaction of these components results in a high concentration of urea groups, so-called “hard blocks,” which are known to result in rigid coatings.
One possibility for increasing the flexibility of the coatings is to blend the polyaspartates with the known high molecular weight polyols. However, when these systems are cured the coatings obtained have a waxy feel, which makes them unsuitable for commercial applications. It is believed that this is caused by the fact that aspartate groups react with isocyanate groups much faster than hydroxy groups. Therefore, during the curing process the polyisocyanates react with the aspartates, which hardens the coatings to such an extent that the isocyanate groups cannot react with the hydroxy groups of the polyol component. The polyols remain in the cured coating as a plasticizer resulting in a waxy feel.
One method of overcoming this difficulty is to prereact the polyol with the polyisocyanate to form an NCO prepolymer. The prepolymer can then be reacted with the polyaspartate to form a fully cured coating composition. One disadvantage of this process is that unreacted monomeric polyisocyanate is also present in the NCO prepolymer. To remove this free monomer, which is necessary for environmental reasons, requires an expensive stripping process.
Accordingly, it is an object of the present invention to improve the flexibility of coatings prepared from polyisocyanates and polyaspartates, while avoiding the high production costs associated with prior art processes.
These objects can be achieved with the aspartate-terminated urea/urethane prepolymers according to the present invention that are described hereinafter. These prepolymers can be combined with polyisocyanates to prepare solvent-containing or solvent-free coating compositions that may be cured to provide coatings with improved flexibility.
U.S. Pat. No. 5,397,930 is directed to aspartate-terminated hydantoin prepolymers that are prepared by reacting an excess of diaspartates with diisocyanates to form urea group-containing prepolymers and subsequently converting the urea groups to hydantoin groups. The prepolymers of the U.S. patent do not contain urethane groups. To the contrary the aspartate-terminated prepolymers of the present invention are prepared by reacting urethane group-containing NCO prepolymers with an excess of diaspartates.
SUMMARY OF THE INVENTION
The present invention relates to aspartate-terminated urea/urethane prepolymers that are based on the reaction products of NCO prepolymers with compounds corresponding to the formula
wherein
X represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100° C. or less,
R
1
and R
2
may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100° C. or less,
R
3
and R
4
may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100° C. or less and
n represents an integer with a value of at least 2, at an equivalent ratio of aspartate groups to isocyanate groups of 1.5:1 to 20:1.
The present invention also relates to coating compositions containing the aspartate-terminated urea/urethane prepolymers and a polyisocyanate.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention the term “urea/urethane prepolymers” refers to polymers containing urea groups and urethane groups. The aspartate-terminated urea/urethane prepolymers may be prepared by reacting NCO prepolymers with an excess amount of a polyaspartate. The NCO prepolymers are prepared by reacting a monomeric polyisocyanate or a polyisocyanate adduct, preferably a monomeric diisocyanate, with a high molecular weight polyol, and optionally a low molecular weight alcohol. The NCO prepolymers have an average functionality of 1.5 to 3.5, preferably 1.8 to 2.2, more preferably 2.
Suitable monomeric diisocyanates may be represented by the formula
R(NCO)
2
wherein R represents an organic group obtained by removing the isocyanate groups from an organic diisocyanate having a molecular weight of from about 112 to 1,000, preferably from about 140 to 400. Preferred diisocyanates are those in which R represents a divalent aliphatic hydrocarbon group having from 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group having from 5 to 15 carbon atoms, a divalent araliphatic hydrocarbon group having from 7 to 15 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms.
Examples of suitable organic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-isocyanato-cyclohexyl)-methane, 1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanatocyclohexyl)-methane, 2,4′-diisocyanato-dicyclohexyl methane, bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, &agr;,&agr;,&agr;′,&agr;′-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or 2,6-hexahydro-toluylene diisocyanate, 1,3- and/or 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, 2,4- and/or 4,4′-diphenylmethane diisocyanate and 1,5-diisocyanato naphthalene and mixtures thereof.
Monomeric polyisocyanates containing 3 or more isocyanate groups such as 4-isocyanatomethyl-1,8-octamethylene diisocyanate and aromatic polyisocyanates such as 4,4′,4″-triphenylmethane triisocyanate and polyphenyl polymethylene polyisocyanates obtained by phosgenating aniline/formaldehyde condensates may also be used.
Preferred organic diisocyanates include 1,6-hexamethylene diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-isocyanato-cyclohexyl)-methane, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or 2,6-toluylene diisocyanate, and 2,4- and/or 4,4′-diphenyl-methane diisocyanate. 1,6-hexamethylene diisocyanate is most preferred.
In accordance with the present invention the polyisocyanate component may also be in the form of a polyisocyanate adduct. Suitable polyisocyanate adducts are those containing isocyanurate, uretdione, biuret, urethane, allophanate, iminooxadiazine dione, carbodiimide and/or oxadiazinetrione groups. The polyisocyanates adducts, which preferably have an NCO content of 5 to 30% by weight, include:
1) Isocyanurate group-containing polyisocyanates which may be prepared as set forth in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589, EP-OS 47,452, U.S. Pat. No. 4,288,586 and U.S. Pat. No. 4,324,879. The isocyanato-isocyanurates generally have an average NCO functionality of 3 to 3.5 and an NCO content of 5 to 30%, preferably 10 to 25% and most preferably 15 to 25% by weight.
2) Uretdione diisocyanates which may be prepared by oligomerizing a portion of the isocyanate groups of a diisocyanate in the presence of a suitable catalyst, e.g., a trialkyl phosphine catalyst, and which may be used in admixture with other aliphatic and/or cycloaliphat
Gindin Lyubov K.
Hergenrother P. Richard
Roesler Richard R.
Bayer Corporation
Roy Thomas W.
Sergent Rabon
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