Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-07
2001-07-24
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S840000, C524S841000
Reexamination Certificate
active
06265468
ABSTRACT:
BACKGROUND OF THE INVENTION
1). Field of the Invention
The present invention relates to two- and three- component aqueous polyurethane dispersions which are cured at ambient temperatures and to the coatings prepared therefrom which have excellent chemical resistance without reduction in abrasion resistance and flexibility. More particularly, the present invention relates to a coating composition comprised of a hydroxy functional aliphatic polyurethane dispersion in water combined with an aromatic polyether and crosslinked with an aliphatic or aromatic polyisocyanate compound. More specifically the aromatic polyether can be an epoxy resin or a phenoxy resin.
2) Prior Art Description
Aqueous polyurethane dispersions and their use for the production of coatings are known. The dispersions may be cured at ambient temperature by evaporation of water and coalescence of the individual polyurethane particles. These water-based products have been developed in an effort to reduce the amount of organic solvents which are present in corresponding solvent-based coating compositions. Even though the prior art dispersions possess many valuable properties, it has not been possible to obtain coatings which possess all of the properties of coatings obtained from solvent-based coating compositions, especially with regard to hardness and solvent resistance.
The known aqueous polyurethane dispersions do not possess the amount of crosslinking which is required to obtain these properties. One method of increasing the amount of crosslinking is to blend the polyurethane dispersion with a water dispersible, blocked polyisocyanate as disclosed in U.S. Pat. No. 4,098,933. U.S. Pat. No. 4,608,413 discloses the use of water dispersible, blocked polyisocyanates in combination with polyurethanes which contain hydroxyl groups as crosslinking sites. While the systems disclosed in these patents make it possible to obtain improved hardness and crosslinking, they suffer from the disadvantage that the coating compositions must be heated to high temperatures in order to release the blocking agent and initiate crosslinking. Obviously, these coating compositions are not suitable for application to substrates which cannot withstand the unblocking temperature of the polyisocyanate.
Accordingly, it is an object of the present invention to provide aqueous polyurethane dispersions which may be cured at ambient temperature to provide coatings with excellent hardness, flexibility, solvent resistance and surface appearance.
SUMMARY OF THE INVENTION
The present invention relates to a two- or three-component aqueous polyurethane dispersion useful as a coating composition which is cured at ambient temperature and contains:
i) a hydroxy functional aliphatic polyurethane dispersion in water;
ii) a crosslinker selected from the group consisting of aliphatic or aromatic polyisocyanate compounds; and
iii) an aromatic polyether selected from the group consisting of epoxy resins and phenoxy resins, or mixtures thereof.
More specifically, the polyurethane of component i) is a hydroxyl group containing polyurethane obtainable by two-step reaction of
a polyisocyanate A having at least two isocyanate groups,
a polyol B having a M
n
of at least 400 g/mol, selected from the group consisting of polyester polyols, polyether polyols, polyurethane polyols, and polyacrylate polyols, with a hydroxyl number of from 30 to 280 mg/g,
a compound C that has at least one group capable of forming anions, and at least two groups that are reactive towards isocyanate groups, and optionally,
a low molar mass polyol D with M
n
of from 60 to 400 g/mol to form an isocyanate-terminated intermediate, which is then reacted with at least one of
a low molar mass polyol E carrying no other isocyanate-reactive group,
a compound F which is either monofunctional towards NCO or contains active hydrogen of different reactivity,
a compound G selected from the group consisting of water, hydrazine and aliphatic diprimary amines like ethylene diamine, diamino propane and diamino hexane, with an OH number of from 30 to 200 mg/g and M
n
of from 1600 to 50000 g/mol.
When an epoxy resin is employed as the aromatic polyether, the coating compositions of the present invention are generally three-component systems as set forth in i)-iii) above. When the aromatic polyether is a phenoxy resin, the phenoxy resin is generally blended with the polyurethane dispersion, so that a two-component system (the polyurethane/phenoxy component and the crosslinker polyisocyanate component) results.
The present invention also relates to a cured coating which comprises the dried film (dried residue) of a uniformly mixed and reacted composition comprising:
i) a hydroxy functional aliphatic polyurethane dispersion as described supra;
ii) an aliphatic or aromatic polyisocyanate; and
iii) either an epoxy resin or a phenoxy resin.
The disclosed invention is an improvement over conventional water based polyurethanes which are crosslinked with polyisocyanate in that the chemical resistance is greatly improved by the addition of the aromatic polyether compound but no reduction in flexibility is seen. The increase of the chemical resistance is due to the polyether of the invention and it was discovered that maintaining the same flexibility and abrasion resistance as a non-aromatic polyether system was unexpected and unique. The coating composition may further comprise solvents, in a mass fraction of from 1 to 20 per cent of the sum masses of components i), ii) and iii).
The applications for this invention are in floor coatings, anti-graffiti coatings, general metal coatings, and aerospace coatings, but these uses are not exhaustive.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable hydroxy functional aliphatic polyurethane dispersions i) are obtainable by two-step reaction of
a polyisocyanate A having at least two isocyanate groups,
a polyol B having a M
n
of at least 400 g/mol, selected from the group consisting of polyester polyols, polyether polyols, polyurethane polyols, and polyacrylate polyols, with a hydroxyl number of from 30 to 280 mg/g,
a compound C that has at least one group capable of forming anions, and at least two groups that are reactive towards isocyanate groups, and optionally,
a low molar mass polyol D with M
n
of from 60 to 400 g/mol to form an isocyanate-terminated intermediate, which is then reacted with at least one of
a low molecular mass polyol E carrying no other isocyanate-reactive group,
a compound F which is either monofunctional towards NCO or contains active hydrogen of different reactivity,
a compound G selected from the group consisting of water, hydrazine and aliphatic diprimary amines like ethylene diamine, diamino propane and diamino hexane, with an OH number of from 30 to 200 mg/g and M
n
of from 1600 to 50000 g/mol.
Suitable polyisocyanates A (which means compounds having a plurality of isocyanate groups) for preparing the hydroxy functional polyurethane include any organic polyisocyanate, preferably monomeric diisocyanates. Especially preferred are polyisocyanates, especially diisocyanates, having aliphatically- and/or cycloaliphatically-bound isocyanate groups, although polyisocyanates having aromatically-bound isocyanate groups are not excluded and may also be used.
Examples of suitable polyisocyanates which may be used include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane- 1,3- and/or -1,4-d iisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane(isophorone diisocyanate or IPDI), 2,4- and/or 2,6-hexahydrotoluylene diisocyanate, 2,4′- and/or 4,4′-dicyclohexylmethane diisocyanate, &agr;,&agr;,&agr;′,&agr;-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate, 1,3- and 1,4-xylylene dilsocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl-cyclohexane, 1,3- and 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, dip
Carpenter Brian S.
Chambers Douglas Ronald
LeBlanc David
Pschaidt Mario
Slocki Allen T.
Aylward D.
Dawson Robert
Frommer & Lawrence & Haug LLP
Vianova Resins, Inc.
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