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
1999-03-22
2001-02-06
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...
C523S455000, C525S530000, C525S922000
Reexamination Certificate
active
06184314
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a vinyl ester resin, and more particularly to a method prolonging the storage life of thermosettable vinyl ester resins.
BACKGROUND OF THE INVENTION
Thermosettable resins generally have limited shelf lives, i.e, upon storage at ambient temperatures the resins undergo premature gelation which, of course, is undesirable. Generally, the tendency of a resin to gel increases as the storage temperature increases and is also dependent on the choice of reactants and on the kind and amount of monomer which is generally mixed with the resin.
Thermosettable vinyl ester resins, unsaturated polyesters or mixtures thereof have similar shelf life or storage stability problems. In the past, attempts with known stabilizing materials to prevent gelation have also resulted in an undesirable increase in the catalyzed gel times of the resins and adversely affected the curability of the resin. Typical of inhibitors taught by the art are certain hydroxyamines as proposed in U.S. Pat. No. 3,408,422 and phenothiazine taught in U.S. Pat. No. 3,683,045.
SUMMARY OF THE INVENTION
The primary objective of the present invention is therefore to provide the method prolonging storage life of thermosettable vinyl ester resins by adding a stabilizer or stabilizing agent, maleic acid or maleic anhydride in small proportions, for greatly increasing the storage life of thermosettable vinyl ester resins without suppressing the exotherm or adversely affecting their curability.
The effective proportions of maleic acid or maleic anhydride range from 0.01% -5.0% by weight on the weight of resin.
DETAILED DESCRIPTION OF THE INVENTION
The thermosettable polymer compositions include a vinyl ester resin or an unsaturated polyester or blends and mixtures of those two materials.
Vinyl ester resins are described in U.S. Pat. No. 3,367,992 wherein dicarboxylic acid half esters of hydroxyalkyl acrylates or methacrylates are reacted with polyepoxide resins. Bowen in U.S. Pat. Nos. 3,066,112 and 3,179,623 describes the preparation of vinyl ester resins from monocarboxylic acids such as acrylic and methacrylic acid. Bowen also describes alternate methods of preparation wherein a glycidyl methacrylate or acrylate is reacted with the sodium salt of a dihydric phenol such as bisphenol A. Vinyl ester resins based on epoxy novolac resins are described in U.S. Pat. No. 3,301,743 to Fekete et al. Fekete et al also describes in U.S. Pat. No. 3,256,226 vinyl ester resins wherein the molecular weight of the polyepoxide is increased by reacting a dicarboxylic acid with the polyepoxide resin as well as acrylic acid, etc. Rubber modified vinyl ester resins are described in U.S. Pat. No. 3,892,819 to Daniel. Daniel describes vinyl ester resins modified by liquid carboxy terminated polybutadiene rubber. Other difunctional compounds containing a group which is reactive with an epoxide group, such as an amine, mercaptan, and the like, may be utilized in place of the dicarboxylic acid. All of the above-described resins, which contain the characteristic linkages
and terminal, polymerizable vinylidene groups, are classified as vinyl ester resins, and are incorporated herein by reference.
Briefly, any of the known polyepoxides may be employed in the preparation of the vinyl ester resins of this invention. Useful polyepoxides are glycidyl polyethers of both polyhydric alcohols and polyhydric phenols, epoxy novolacs, epoxidized diolefins, epoxidized diunsaturated acid esters, rubber-modified polyepoxides as well as epoxides of unsaturated polyesters, as long as they contain more than one oxirane group per molecule.
Preferred polyepoxides are glycidyl polyethers of polyhydric alcohols or polyhydric phenols having weights per epoxide group of about 150 to 2000. These polyepoxides are usually made by reacting at least about two moles of an epihalohydrin or glycerol dihalohydrin with one mole of the polyhydric alcohol or polyhydric phenol, and a sufficient amount of a caustic alkali to combine with the halogen of the halohyrin. The products are characterized by the presence of more than one epoxide group per molecule, i.e., a 1,2-epoxy equivalency greater than one.
Unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, halogenated acrylic or methacrylic acid, cinnamic acid and the like and mixtures thereof. Also included within the term “unsaturated carboxylic acids” are the hydroxyalkyl acrylate or methacrylate half esters of dicarboxylic acids as described in U.S. Pat. No. 3,367,992 wherein the hydroxyalkyl group preferably has from 2 to about 6 carbon atoms.
Polymerization inhibitors, commonly called process inhibitors, such as t-butyl catechol, monomethyl ether of hydroquinone (MEHQ) or hydroquinone, are advantageously added to prevent premature polymerization during the preparation of the vinyl ester resin.
Vinyl ester/unsaturated polyester resin blends are also effectively stabilized. The blends may be prepared either by physically mixing the two resins in the desired proportions or by preparing the vinyl ester resin in the presence of the unsaturated polyester.
Preferably, the thermosettable resin phase comprises from 40 to 70 weight percent of the vinyl ester and from 60 to 30 percent of a copolymerizable monomer.
Suitable monomers include vinyl aromatic compounds such as styrene, vinyl toluene, divinyl benzene and the like. Other useful monomers include the esters of saturated alcohols such as methyl, ethyl, isopropyl, octyl, etc., with acrylic acid or methacrylic acid:vinyl acetate, diallyl maleate, dimethyallyl fumarate:divinyl monomers or multifunctional (meth) acrylate monomers such as tripropylene glycol diacrylate, trimethylol propane triacrylate, mixtures of the same and all other monomers which are capable of copolymerizing with the vinyl ester resin.
When maleic acid or its anhydride is used as the sole stabilizer it is usually effective at a concentration of from 0.01 to 5 percent by weight on the weight of resin. Higher amounts than 5% can be used and will improve the stability. Preferably, the amount to be used is from 0. 1% to 2%.
Catalysts that may be used for the curing or polymerization are preferably the peroxide and hydroperoxide catalysts such as benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide (MEKP), t-butyl perbenzoate, and the like. The amount of the catalyst added will vary preferably from 0.1 percent to about 5 percent:by weight of the resin phase.
Preferably, the cure of the resin can be initiated at room temperature by the addition of known accelerating agents or promoters such as lead, potassium or cobalt naphthenate, cobalt octoate, N.N-dimethyl aniline, N.N-dimethyl-p-toluidine and the like usually in concentrations ranging from 0.01 to 1.5 weight percent. The promoted resin means that the promoter or accelerating agent have been added in the said unpromoted resin. The promoted composition of resin/monomer, when mixed with catalysts, will usually be converted to at least a gel state in a few minutes and cured to a solid state in 30 minutes to one or two hours. That time may vary widely depending upon the particular resin and vinyl monomer used, the catalyst/promoter system employed and its concentration, the temperature and other known factors. Similar results are observed when the usual process inhibitors are present that were added during the preparation of the resin. In amounts necessary to achieve that objective, such process inhibitors do not improve the storage stability of the composition to a significant extent. When used in amounts sufficient to provide storage stability, the gelation and cure rates are increased to unacceptable levels. It is an advantage of this invention that the process stabilizer can be employed in that minimum amount needed during resin preparation and that the stabilizer systems of this invention can be employed to provide the desired storage stability without unacceptable effects on gelation and cure.
The stabilizing agent is usually added to
Tsai Jan-Yang
Yur Shih-Wen
Harrison & Egbert
Sellers Robert E. L.
Swancor Industrial Co., Ltd.
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