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
2000-12-05
2002-09-03
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...
C524S839000, C524S840000, C428S423100
Reexamination Certificate
active
06444746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aqueous polyurethane dispersions containing amide groups, which are pendant to the backbone of the polyurethane; to aqueous, one-component, thermoset compositions containing these dispersions and a cross-linking component; and to coatings, sealants and adhesives prepared from these compositions.
2. Description of the Prior Art
One-component polyurethane coating compositions containing polyisocyanates blocked with reversible, monofunctional blocking agents for isocyanate groups and polyols are an important class of materials for applications such as automotive OEM coatings. While these one-component compositions overcome the difficulties of two-component coating compositions with regard to accurate metering of the components, the one-component coating compositions also have disadvantages, which are primarily caused by the presence of organic solvents and the volatilization of the blocking agent.
The release of the blocking agent can cause blistering and yellowing in thick films and oven fouling. In addition, the blocking agents are considered to be volatile organic compounds (VOC's) in the same manner as organic solvents. Therefore, it is difficult for these coating compositions to satisfy environmental regulations due to the presence of organic solvents and blocking agents.
It is an object of the present invention to overcome the known disadvantages of one-component coating compositions caused by the release of blocking agents during cure and the presence of organic solvents without affecting the advantages of these coating compositions when compared to two-component coating compositions.
This object can be achieved with the aqueous, one-component compositions according to the present invention, which are based on aqueous polyurethane dispersions containing amide groups, which are pendant to the backbone, and crosslinking agents that are reactive with amide groups.
U.S. Pat. No. 5,780,559 discloses polyurethanes containing amide groups; however, the amide groups are present in terminal positions as opposed to being present in the backbone. As shown in the comparison examples hereinafter, polyurethanes containing amide groups in terminal positions are not stable when dispersed in water.
SUMMARY OF THE INVENTION
The present invention relates to aqueous polyurethane dispersions containing amide groups that are pendant to the backbone of the polyurethane, wherein the amide groups (calculated as NH—CO—, MW 43) are present in an amount of 1 to 14% by weight, based on the weight of the polyurethanes.
The present invention also relates to aqueous, one-component, thermoset compositions containing the polyurethanes with amide groups in the backbone and a cross-linking component that is reactive with amide groups. Finally, the present invention relates to coatings, sealants and adhesives prepared from these aqueous, one-component, thermoset compositions.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention the term “polyurethane” means polymers containing urethane and/or urea groups.
The aqueous polyurethane dispersions according to the invention may be prepared by either a one-step or a two-step process, preferably by a two-step process. In the one-step process all of the components are mixed together and reacted in one step. In the two-step process an NCO prepolymer is formed in the first step and is subsequently reacted with a compound corresponding to formula II and optionally a low molecular weight, isocyanate-reactive chain extender in the second step to form the polyurethane either before, during or after being mixed with an aqueous medium. The NCO prepolymer is prepared by reacting an organic polyisocyanate with a high molecular weight polyol, an isocyanate-reactive compound containing hydrophilic groups and optionally a low molecular weight polyol.
The polyurethanes may be dispersed in water by either the inverse process or the direct process. In the direct process water is added to the polymer to initially form a water-in-oil emulsion, which after passing through a viscosity maximum, is converted into an oil-in-water emulsion. In the inverse process the polymer is added to water, which avoids the need to pass through the viscosity maximum.
Even though more energy is required for preparing a dispersion by the direct process, it may be necessary to use this process if the viscosity of the polymer is too high to add it to water. A high viscosity polymer is often obtained when a fully reacted polyurethane is prepared in the organic phase, especially when large amounts of solvent are not used to reduce the viscosity.
To obtain a suitable viscosity for using the inverse process without the use of large amounts of solvent, the NCO prepolymer can be dispersed in water and then reacted with the compounds corresponding to formula II and optionally with an amine chain extender.
In addition to the one-step process in which all of the components are reacted to form the polyurethane in one step and the preferred two-step process previously set forth, it is also possible to incorporate the compounds corresponding to formula II into the NCO prepolymers, which are then chain extended with polyamine chain extenders or crosslinking agents in known manner.
Any of the known starting materials for preparing polyurethane dispersions may be used for preparing the dispersions according to the invention, provided that sufficient isocyanate groups are reacted with the compounds corresponding to formula II to obtain the required amide group content.
In accordance with the present invention the amide groups are pendant to the backbone of the polyurethane. The amide groups either connected directly to carbon or nitrogen atoms present in the backbone of the polyurethane or are connected to the polyurethane by optionally substituted hydrocarbon groups that are bound to carbon or nitrogen atoms present in the backbone of the polyurethane. The pendant hydrocarbon groups correspond to the formulas
wherein
R is a covalent bond or a divalent hydrocarbon group that is optionally substituted by one or more groups that do not contain isocyanate-reactive hydrogen atoms, preferably an aliphatic hydrocarbon group having 1 to 10, more preferably 1 to 6 carbon atoms, and
R′ is hydrogen or a monovalent hydrocarbon group that is optionally substituted by one or more groups that do not contain isocyanate-reactive hydrogen atoms, preferably hydrogen or an aliphatic hydrocarbon group having 1 to 10, preferably 1 to 4 carbon atoms.
To ensure that the amide groups are present in a pendant position as opposed to a terminal position, it is important that the compound used to incorporate the amide groups into the backbone of the polyurethane contains two isocyanate-reactive groups, i.e., either hydroxy groups or primary or secondary amino groups. These compounds may be prepared by several methods.
In one method a compound containing two isocyanate-reactive groups, preferably hydroxyl groups, and one or more acid groups, preferably one acid group, is reacted with either ammonia or a compound containing a primary amino group to form a primary or secondary amide group. Suitable compounds containing two isocyanate-reactive groups and one or more acid groups include those set forth hereinafter for incorporating hydrophilic carboxylate groups into the water dispersible polyurethanes.
Suitable primary monoamines include the known aliphatic, cycloaliphatic, araliphatic and aromatic amines, preferably aliphatic amines. Examples include ethyl amine and the isomeric propyl and butyl amines.
In another method the compounds containing pendant amide groups are prepared by reacting a compound containing two isocyanate-reactive groups, preferably hydroxyl groups, and a primary amino group with a compound containing a carboxylic acid group to form a secondary amide group. Suitable compounds containing two isocyanate-reactive groups and a primary amino group include those set forth hereinafter for incorporating hydrophilic ca
Gindin Lyubov K.
Henderson Karen M.
Lee Sze-Ming
Long Brian
Bayer Corporation
Gil Joseph C.
Niland Patrick D.
Roy Thomas W.
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