Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-08-27
2002-02-26
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S453000, C525S454000, C528S075000, C528S076000
Reexamination Certificate
active
06350826
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to thermoset resins. More particularly, this invention relates to a curable resin composition including a mixture of epoxy vinyl ester resins and urethane vinyl ester resins.
Thermoset resins prepared from a mixture of epoxy vinyl ester resins and urethane vinyl ester resins are described in U.S. Pat. No. 4,824,919 (the '919 patent). The '919 patent describes the use of urethane oligomers as flexibilizers added to epoxy vinyl esters to impart a toughening effect, that is, increased impact resistance, to the vinyl ester resin. The '919 teaches that vinyl ester/styrene mixtures are flexibilized by adding thereto minor amounts of urethanes which (1) comprise at least one polyglycol moiety and two urethane groups and are terminated by vinyl-reactive end groups, and (2) form a dispersed second phase in the cured mixture. The flexibilized compositions otherwise largely retain the characteristic properties of the unflexibilized mixtures.
The flexibilizer described in the '919 patent “is of a nature such that the uncured mixture of resin, monomer and flexibilizer is a homogeneous liquid at ordinary temperatures.” Phase separation of the flexibilizer on cure is seen as essential to obtain the desired good flexibilization effect.
The preferred flexibilizers described in the '919 patent are urethane oligomers derived from one molecular proportion of a polyalkylene glycol (for example, polyether glycols such as VORANOL* (Trademark of The Dow Chemical Company)), about two molecular proportions of an aromatic diisocyanate and about two molecular proportions of a hydroxyalkyl acrylate or methacrylate.
The thermoset resins described in the '919 patent are known to have good impact resistance when using urethane vinyl ester resins in combination with epoxy vinyl ester resins. These type of resins, which show microphase separation on cure, give better impact resistance and good thermal performance than other comparable known resins based on CTBN (carboxy-terminated-butadiene-acrylonitrile) rubber.
While the urethane oligomers disclosed in the '919 patent provide resins with good impact resistance, there still exists a need for more suitable flexibilizers which exhibit a phasing behavior (that is, phase separation upon curing) for vinyl ester resin systems and which are compatible with and stable with vinyl ester resin prior to cure. It is desired to provide resins with good impact resistance using such flexibilizers.
SUMMARY OF THE INVENTION
It has been found that the properties of oligomeric urethanes used as flexibilizers in the composition of the present invention are critically dependent on the structure of the diisocyanate component and the mixture of polyalkylene glycols used in preparing the oligomeric urethane flexibilizer. Thus, the choice of diisocyanate component and mixture of polyalkylene glycols used in the present invention is important in obtaining a final resin product with good properties.
Accordingly, one aspect of the present invention is directed to a curable thermoset resin composition which contains a homogeneous mixture of:
(a) an epoxy vinyl ester resin;
(b) a urethane vinyl ester resin having a weight average molecular weight of greater than 8,000 which forms a dispersed second phase in the epoxy vinyl ester resin upon curing of the curable formulation; and
(c) optionally a co-reactive monomer, characterized in that the urethane vinyl ester resin is preparable by reacting:
(1) an alkylene bis(phenyl isocyanate) compound;
(2) at least two polyalkylene glycols having different molecular weights, including a first polyalkylene glycol with an average molecular weight of from about 1,500 to about 10,000 wherein the amount of the first polyalkylene glycol is from about 1.45 to about 12.6 weight percent based on the curable resin composition; and a second polyalkylene glycol with an average molecular weight of from about 200 to about 800 wherein the amount of the second polyalkylene glycol is from about 0.15 to about 3.75 weight percent, based on the curable resin composition; and, optionally a branched-polyalkylene polyol with a hydroxy functionality of greater than 2 and an average molecular weight of from about 450 to about 4600; and
(3) a hydroxyalkyl acrylate or hydroxyalkyl methacrylate.
The invention also provides a urethane vinyl ester resin having a weight average molecular weight of greater than 8,000 which may be prepared by reacting
(1) an alkylene bis(phenyl isocyanate) compound with
(2) at least two polyalkylene glycols having different molecular weights, including a first polyalkylene glycol with an average molecular weight of from about 1,500 to about 10,000 and a second polyalkylene glycol with an average molecular weight of from about 200 to about 800 and, optionally,
(3) a branched polyalkylene polyol with a hydroxy functionality of greater than 2 and an average molecular weight of from 450 to 4600, and
(4) a hydroxyalkyl acrylate or hydroxyalkyl methacrylate.
Such vinyl ester resins may be compounded with an epoxy vinyl ester resin and, optionally, other co-reactive monomers, to produce the curable resin.
Another aspect of the present invention is directed to a process of making a curable composition comprising blending such a urethane vinyl ester resin with an epoxy vinyl ester resin.
Still another aspect of the present invention is a process of making a cured article comprising curing such a composition
It has been found that the properties of oligomeric urethanes used as flexibilizers in the composition of the present invention are critically dependent on the structure of the diisocyanate component and the mixture of polyalkylene glycols used in preparing the oligomeric urethane flexibilizer. Thus, the choice of diisocyanate component and mixture of polyalkylene glycols used in the present invention is important in obtaining a final resin product with good properties.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to thermoset resins comprising blends or mixtures of epoxy vinyl ester resins and urethane vinyl ester resins. The epoxy vinyl ester resins as well as the urethane vinyl ester resins used in the present invention can be dissolved in a solvent monomer such as, for example, styrene, resulting in transparent and clear solutions at room temperature and elevated temperatures. When styrene solutions of epoxy vinyl ester resins are blended with urethane vinyl ester resins at various blend ratios surprisingly, depending on the composition of the urethane vinyl ester resin and the amount of urethane vinyl ester resin blended with the epoxy vinyl ester resin, a solution is obtained which has a clear transparent to a slight hazy visual appearance and which undergoes a microphase separation on cure. Resins with a turbid or opaque visual appearance show a phase- instability and separate in a short period of time (for example, a maximum of one day) in two separate resin layers. Such resins which phase separate prior to cure do not provide the improvements of the present invention. The resin blends of the present invention that give a microphase separation on cure provide a much better impact resistance than comparable vinyl ester resins that contain, for example, a CTBN rubber as a flexibilizer. In addition, the thermal performance (glass transition temperature) of the epoxy/urethane vinyl ester blends of the present invention is only slightly decreased compared to unmodified epoxy vinyl ester resins.
Epoxy Vinyl Ester Resins
The epoxy vinyl ester resins used in the present invention may be, for example, the epoxy vinyl ester resins described in U.S. Pat. No. 4,824,919 incorporated herein by reference.
The epoxy vinyl esters suitable for the practice of the present invention are generally preparable by the adduction of an at least difunctional epoxide with at least two molecules of an unsaturated monocarboxylic acid in which the carbon-to-carbon double bond is vinyl reactive.
Exemplary of suitable epoxy resins are the well-known polyglicid
Sellers Robert E. L.
The Dow Chemical Company
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