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...
Utility Patent
1999-04-28
2001-01-02
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...
C524S506000, C524S507000, C524S589000, C524S838000, C524S864000, C525S100000, C525S101000, C525S102000, C525S123000, C525S127000, C525S128000, C525S455000, C528S028000
Utility Patent
active
06169140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to moisture-curable coating compositions containing polyisocyanates and polyacrylates having chemically incorporated alkoxysilane groups, and to coatings, sealants and adhesives prepared from these compositions.
2. Discussion of the Background
It is known that polyisocyanate resins are curable in the presence of atmospheric moisture to form polyurea coatings. During the curing mechanism an isocyanate group reacts with moisture to form an amino group, which then reacts with another isocyanate group to form a urea. One of the disadvantages of these moisture-curable resins is that the curing mechanism is relatively slow.
It is also known that resins containing alkoxysilane groups are curable in the presence of moisture by “silane polycondensation” during which the alkoxysilane groups are hydrolyzed to form Si—OH groups, which subsequently react to form siloxane groups (Si—O—Si).
A disadvantage of both of these moisture-curable resins is that their curing rates are relatively slow. Accordingly, it is an object of the present invention to increase the curing rate of these moisture-curable resins. This object may be achieved with the coating compositions of the present invention, which contain a mixture of polyisocyanates and polyacrylates that have been modified to contain alkoxysilane groups. The faster curing rates obtained according to the present invention are surprising because compounds containing alkoxysilane groups cure more slowly than polyisocyanates. However, when both isocyanate groups and alkoxysilane groups are present, a faster curing rate is obtained.
U.S. Pat. No. 5,162,426 and copending application, U.S. Ser. No. 09/172,750, disclose polyacrylates that have been modified to contain alkoxysilane groups. In U.S. Pat. No. 5,162,426 isocyanatoalkyl trialkoxysilanes are reacted with hydroxy-functional ethylenically unsaturated monomers and subsequently polymerized with other unsaturated monomers to form the silane-modified polyacrylates. In the copending application the alkoxysilane groups are incorporated by reacting polyacrylate polyols with compounds containing isocyanate, urea and alkoxysilane groups.
Copending applications, U.S. Ser. Nos. 09/172,751 and 09/172,584, describe compounds that contain both isocyanate groups and alkoxysilane groups and disclose that these compounds cure faster than compounds containing only one of these groups.
SUMMARY OF THE INVENTION
The present invention relates to moisture-curable compositions containing a mixture of
a) a polyisocyanate and
b) a polyacrylate resin which has an alkoxysilane group content (calculated as Si, MW 28) of 0.2 to 4.5% by weight, based on the weight of the polyacrylate resin, and contains less than 0.5% by weight of hydroxy groups, based on the weight of the polyacrylate resin,
wherein components a) and b) are present in amounts sufficient to provide an equivalent ratio of isocyanate groups to alkoxy groups, which are bound to Si, of 1.0:0.05 to 1.0:2.5.
The present invention also relates to coatings, sealants and adhesives prepared from these compositions.
DETAILED DESCRIPTION OF THE INVENTION
Suitable polyisocyanates for use as component a) according to the present invention include monomeric diisocyanates, polyisocyanate adducts and NCO prepolymers, preferably polyisocyanate adducts and NCO prepolymers and more preferably polyisocyanate adducts. The polyisocyanates have an average functionality of 1.5 to 6, preferably 1.8 to 6, more preferably 2 to 6 and most preferably 2 to 4.
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-hexahydrotoluylene 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 polyethylene 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-trimethylcyclohexane (isophorone diisocyanate or IPDI), bis-(4-isocyanatocyclohexyl)-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.
In accordance with the present invention the polyisocyanate component is preferably 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 cycloaliphatic polyisocyanates, particularly the isocyanurate group-containing polyisocyanates set forth under (1) above.
3) Biuret group-containing polyisocyanates which may be prepared according to the processes disclosed in U.S. Pat. Nos. 3,124,605; 3,358,010; 3,644,490; 3,862,973; 3,906,126; 3,903,127; 4,051,165; 4,147,714; or 4,220,749 by using co-reactants such as water, tertiary alcohols, primary and secondary monoamines, and primary and/or secondary diamines. These polyisocyanates preferably have an NCO content of 18 to 22% by weight and an average NCO functionality of 3 to 3.5.
4) Urethane group-containing polyisocyanates which may be prepared in accordance with the process disclosed in U.S. Pat. No. 3,183,112 by reacting excess quantities of polyisocyanates, preferably diisocyanates, with low molecular weight glycols and polyols having molecular weights of less than 400, such as trimethylol propane, glycerine, 1,2-dihydroxy propane and mixtures thereof. The urethane group-containing polyisocyanates have a most preferred NCO content of 12 to 20% by weight and an (average) NCO functionality of 2.5 to 3.
5) Allophanate group-containing polyisocyanates which may be prepared
Roesler Richard R.
Shaffer Myron W.
Bayer Corporation
Gil Joseph C.
Niland Patrick D.
Roy Thomas W.
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