CA1246775A - Control of fiber prominence in vinyl ester resin compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Compositions of a curable vinyl ester or unsaturated polyester resin, a peroxide catalyst, a redox active metal salt, a scavenger, such as 2,4-pentanedione or maleic acid, and glass fibers sized with an acidic sizing material exhibit little fiber prominence during cure.

Description

-1- 1Z4~775 - CONTROL OF FIBER PROMINENCE
IN VINYL ESTER OR UNSATURATED
POLYESTER RESIN COMPOSITIONS

The glass used for fabrication of fiber reinforced plastic equipment is treated with an organo-silane sizing during its production. The purpose of the sizing is to improve the adhesion of resin and glass, and to protect the glass from abrasion during its production, shipping, and eventual use. These si~ings have been ~elected such that the organic portion of the sizing will be partially soluble in and react with the most common type of resins used in FRP - s~yrene diluted unsaturated polyesters.

When vinyl es~er resins and other similar resins are used with these glass reinforcements designed for compatibility with polyester resins and are cured with a system composed of an organic peroxide and a redox active metal salt, a problem known variously as "fiber prominence," "glints," "jackstraws," or "glass incompatibility" often occurs. In brief, the symptoms of the problem are:

29,613-F -1-

-2- 124~;~775 (a) When the glass reinforcement is placed in the liquid catalyzed resin, it gradually becomes nearly invisible as the resin wets the sizing and glass, displacing air.

(b) As the resin cures, the glass fibers reappear, particularly in areas of highest stress (knuckles of flanges, thick-walled small diameter pipe, the intersection of woven strands in woven roving, and the very ends of fiberglass bundles).

(c) Conditions that increase laminate stress exasperate the problem (high exotherm resins, thick laminates, and post cures following ' immediately after gel). Under extreme condi-tions this "fiber prominence" can actually lead to delamination.

This gradual "reajpearance" of the glass can be observed with a microscope. As the resin cures, there is a microscopic separation near the surface of the glass iber that starts in an area of high stress (crossed woven rovings or end of fiber bundle) and often progresses down the'length of the fiber as the cure progresses. The index of refraction change at this separation causes it to be visible. Because the separation has the same shape as the fiber, it is difficult to distinguish it from a poorly wet fiber.
As a result, equipment in which this phenomenon occurs is sometimes rejected by the buyer because he feels it is below standard quality.

29,613-F -2-" 12~6775

3--This invention is directed to a glass fiber reinforced, curable, resinous composition which, when cured, displays substantially reduced fiber prominence, said composition comprising: (A) sized glass fiber wherein the sizing contains acid functionality with a pKa of 3.0 or less; (B) a vinyl ester or unsaturated polyester resin prepared from an unsaturated carboxylic acid and a polyepoxide containing more than one oxizane group, said resin being curable with a peroxide and redox active metal wherein the resin or a mixture of resinq has a pH of at least 5.7 measured as a 10 percent methanol solution; (C) a peroxide catalyqt, selected from the group of organic peroxides and tertiary hydroperoxides; (D) a redox active metal salt soluble in said curable resin; and (E) a scavenger of the redox active metal said scavenger being an acid of pKa of 2.0 or le8s or a strong organic complexing agent with logs of stability oonstant of 5.0 or greater.
The thermosettable polymer used to form the glas8 fiber reinforced compositions is a vinyl ester resin or an unsaturated polyester or blends and mixtures of those two materials.
Vinyl eqter resins are described in U.S. Patent No. 3,367,992 wherein dicarboxylic acid half esters of hydroxylalkyl acrylates or methacrylates are reacted with polyepoxide resins. Bowen in U.S. Patent No.
3,066,112 and 3,179,623 describes the preparation of vinyl ester re9in9 from monocarboxylic acids such aq acrylic and metacrylic 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 e~ter re~ins based on epoxy novolac resins are described in U.S. Patent No. 3,301,743 to Fekete et al. Fekete et al.
also describe in U.S. Patent No. 3,256,226 vinyl ester resins wherein the molecular weight of the 29,613-F -3--~ -4- 1246775 polyepoxide is increased by reacting a dicarboxylic acid with the polyepoxide resin as well as acrylic acid, etc. Other difunctional compounds containing a group which is reactive with an epoxide group, such as an amine or a mercaptan, may be utilized in place of the dicarboxylic acid. All of the above-described resins, which contain the characteristic linkages O

OH

and terminal, polymerizable vinylidene groups, are classified as vinyl ester resins.

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 fatty acids or drying oil acids, epoxidized diolefins, epoxidized diunsaturated acid esters as well as epoxides of unsat-urated polyesters, as long as they contain more than one oxirane group per molecule.

Preferred polyepoxides are glycidyl poly-ethers of polyhydric alcohols or polyhydric phenols having weights per epoxide group of 150 to 2000. These polyepoxides are usually made by reacting at least 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 halohydrin. The products are characterized by the presence of more - 29,613-F _4-~5~ i2~775 .
.
than one epoxide group per molecule, i.e., a 1,2-epoxy equivalency greater than one.

Unsaturated monocarboxylic acids include, for example, acrylic acid, methacrylic acid, halo-genated acrylic or methacrylic acid, cinnamic acid and-mixtures thereof. Also included within the term "unsaturated carboxylic acids" are the hydroxyalkyl acrylate or methacrylate half esters of dicarboxyl acids as described in U.S. Patent No. 3,367,992 wherein the hydroxyalkyl group preferably has from 2 to 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 or the unsaturated polyester.

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 said vinyl ester resin in the presence of said unsaturated polyester.

These unsaturated polyesters are available commercially or may be generally prepared by heating a mixture of a polyhydric alcohol with an unsaturated dicarboxylic acid or anhydride and, if desired, an acid without vinyl unsaturation, in the proper molar propor-tions at elevated temperatures, usually at 150 to 225C
for a period of time ranging from 1 to 5 hours. The condensation reaction is contained until the acid 29,613-F -5-content drops to the desired level which for this inven-tion usually means that the resulting monomer diluted polyester has a pH greater than 5.7 measured as a 10 percent methanol solution.

Preferably, as is generally true in the thermosettable resin art, the resin phase is blended with a copolymerizable monomer.

Suitable monomers include vinyl aromatic com-pounds such as, for example, styrene, vinyl toluene, and divinyl benzene. Other useful monomers include the esters of saturated alcohols such as, for example, methyl, ethyl, isopropyl, and octyl, with acrylic acid or methacrylic acid; vinyl acetate, diallyl maleate, dimethallyl fumarate; mixtures of the same and all other monomers which are capable of copolymerizing with the vinyl ester resin.

Catalysts that may be used for the curing or polymerization are ketone peroxides, such as methyl ethyl ketone peroxide, tertiary peroxides such as cumene hydroperoxide, or peroxyesters, such as 2,5-dimethyl-2,5-bis(2-ethylhexoylperoxy)hexane. The amount of the catalyst added will vary preferably from 0.5 percent to 3.0 percent by weight of the resin phase.

The cure system also includes known redox active metal salts accelerating agents in an amount to provide from 0.0001 to 0.1 parts metal per 100 parts resin. Such salts include the naphthenates, octoates, and other salts of cobaltj manganese, nickel, vanadium and molybdenum.

- 29,613-F -6--7~ 124~775 Other accelerators and promoters which may be employed in addition to the metal salts typically are dimethylaniline, N,N-dimethyltoluidine and similar amines. The amount of these amines will vary, prefer-ably from 0.0 to 0.5 percent by weight of the resinphase.

The final essential part of the cure system is a scavenger for the redox active metal. The scavenger may be a strong complexing agent for the metal or a strong carboxylic acid having a pKa of 2.0 or less. A
preferred scavenger of the former class is an enolizable ketone, such as a ~-diketone. A preferred species within that class is 2,4-pentanedione. The amount of the ketone will vary preferably from 0.001 to 2.0 percent by weight of the resin phase.

A preferred acid scavenger is maleic acid which can be attached as a half ester to the resin molecule or to another molecule.

Optimum ratios of the resin and cure system ingredients can be easily determined by preliminary tests.

The concept of the present invention is especially adapted for use with glass fibers which are sized with a sizing that is or contains a stronger acid or a stronger complexing agent for redox metal ion than any acids in the resin and cure systems other than the added scavenger. Thus, the concept is independent of the type of glass fiber, the strand configuration and the physical form of the fiber. Included are continuous strand roving; woven rovin; woven fabrics; reinforcing, 29,613-F -7--8- ~2467~5 combination and surfacing mats; chopped strands and milled glass fibers.

The resin composition can be formulated in any order. Typically, the promoters (a redox metal and often dimethylaniline) are added to the resin and mixed followed by addition of peroxide and finally by glass fiber addition. The strong redox active metal scaveng-ing agent can be added at any time or may even be the vehicle for the redox active metal. Preferably, the glass fibers comprise from 1.0 to 70.0 percent of the weight of the composition.

It is believed that the fiber prominence phenomenon is caused by strong acid functionality in the glass sizing scavenging cobalt from the weakly acid vinyl ester resin at the interface of resin and glass.
This results in a poorly cured interface which tears or separates under the stress generated by the resin shrinkage on cure.

In this invention, the phenomenon can be reduced or eliminated by the addition of a strong cobalt scavenger to the resin, which counteracts the strong acid of the glass sizing and allows more uniform cure of resin and interface.

The following examples illustrate the inven-tive concept and the best mode for carrying out thatconcept. In the examples:

E glass fibers are electrical grade glass fibers intended for chemical resistant service and are manufactured by Fiberglas Canada. The fibers are 29,613-F -8-9 ~246775 believed to be an organosilane containing malei~ anhy-dride to provide reactive vinyl functionality.

Resin A is a vinyl ester resin prepared by reacting 1 equivalent of methacrylic acid with 0.75 equivalent of an epoxy novolac having an epoxide equivalent weight (EEW) between 175 and 182 (D.E.N.~ 438 epoxy novolac available from The Dow Chemical Company) and 0.25 equivalent of a glycidyl polyether of bisphenol A having an EEW between 186 and 192 (D.E.R.~ 331 epoxy resin availabLe from The Dow Chemical Company). The above reactants were heated to 115C with catalyst and hydroquinone present until the carboxylic acid content reached about 1 percent. The reaction products were cooled and then styrene containing 50 ppm of t-butyl catechol was added to a styrene content o 36 percent. The inal resin diluted with styrene had a pH of 7.3.

Resin B is a vinyl ester resin prepared by catalytically reacting 1,;equivalent of bisphenol A with 2.2 equivalents of a diglycidyl ether of bisphenol A
having, an epoxy equivalent weight (EEW) between 172 and 176 at 150C under a nitrogen atmosphere for one hour to orm a polyepoxide having an EEW of 535. After cooling to 110C, an additional equivalent of the diglycidyl ether of bisphenol A was added with 1.6 equivalents of methacrylic acid and hydroquinone and reacted to a carboxylic acid (COOH) content of 3 percent. Then, 0.4 equivalent of maleic anhdride was added to the reaction mixture and reacted therewith to an acid content of 1 percent. The final resin diluted with styrene containing 50 ppm of t-butyl catechol to a styrene content of 45 percent, had a pH of 1.7.

29,613-F ,' -9--10~ 4677s Resin C is a vinyl ester resin prepared by catalytically reacting 0.05 equivalent of bisphenol A
with 0.25 equivalent of the diglycidyl ether of bisphenol A having an EEW between~186 and 192 to form a polyepoxide having an EEW of 275. After cooling 1 equivalent of an epoxy novolac having an EEW between 172 and 182 and 1.05 equivalent of methacrylic acid are added and reacted to an aci,d content of 1 percent.
Then, 0.75 equivalent of maleic anhydride is added and reacted to an acid content of S percent. The final resin, diluted with styrene containing 50 ppm of t-butyl catechol to a styrene content of 33 percent, had a pH
of 4.5.

Exam~le 1 lS Laminates were made from 3 layers of 1.5 oz chopped strand mat of E glass fibers, Resin A and a cure system of 0.3 percent level of 6 percent cobalt naphthenate and 1.5 percent methyl ethyl ketone peroxide.
Laminates were allowed to cure for 48 hours at room temperature.

', Other laminates were made with the same system except the glass was exposed to 1200F for 2 , hours to burn off the sizi,ng,bef,ore applying Resin A
and the cure system.

All of the laminates were checked for fiber prominence. The laminates using sized glass showed about 1000 glints per 10 square inches. The laminates using glass with no sizing showed no glints. This demonstrates the dependence of the fiber prominence phenomenon on the sizing.

.
~ 29,613-F -10-Example 2 Laminates were made from 3 layers of E glass fibers 1.5 oz. chopped strand mat using the resin and cure system of the previous example. Resin A was used S alone and in combination with Resin c. After cure at 48 hours at room temperature the laminates were examined for fiber prominence. The results are shown in Table I.

TABLE I

pH of 10Resin Resin APPearance 100% Resin A 7.3 Approx. 1000 glints/10 in2 96% Resin A 6 0 50 glints/10 in2

4% Resin C
94% Resin A 5 7 10 glints/10 in2 156% Resin C

This demonstrates the effectiveness of a strong acid as the redox metal active scavenger. The acid was the maleic half ester with the secondary hydroxyl of the vinyl ester Resin C.

ExamPle 3 The following laminates were made from 3 layers of E glass fibers 1.5 oz chopped strand mat.
Laminates were made from the combinations of Resin A
and cure systems; allowed to cure for 48 hours at room temperature and then checked for fiber prominence.
The results are shown in Table II.

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o o o ~ ~ o ~1 ~1 ~
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X ~n u~ u~ ~ ~ ~n .
r~ O O'r~
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, , , , , ~o ~ ~ l l ' ' o X~ ,,,,,P~

o C~

~ o~ . . . . ..
E~ ~ 1 ~4 ~ Zo æO Zo ~ Z ~ Zo o ~ ) X
o ~ ~ ~ ~ ~ o P~
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~ ~ ~ ~ $
~ ~ ~ ~ o~ o~
tl~ ~5:1 :~ ~3 N N ~:1 ~ C ~
~ x ~ m ~ ~ o ~ ~ ~

~1 ~ ~ ~ U~ ~ O ~rl ~ o o o o o ,~
d ~ ~ ~ ~ ~ ~ O
U~ ~ ~ ~ Z
O O O O O ~:1N O
c~ u o ~ m c~ a N

29, 613-F -12-~ -13- ~Z4~775 This demonstrates the dependence of the fiber prominence on the cure system requiring a redox active metal. The Bz2O2/DMA curing system did not induce fiber prominence. Even the addition of cobalt naphthenate to this system failed to produce the phenomenon because the cobalt napthenate in no way effects the Bz202/DMA
.cure rate. The methyl ethyl ketone peroxide cure system which is dependent on the cobalt naphthenate did produce fiber prominence at all levels of cobalt.
Finally the addition of 2,4-pentane dione, one of a broad group of organic complexing agents with log of stability constant greater than 5.0, dramatically reduced the fiber prominence.

. Exam~le _ Two laminates were made from S layers of E
glass fibers chopped strand mat. The formulation used Resin B plus 0.1 percent dimethylaniline; 0.3 percent cobalt naphthenate and 1 percent methyl ethyl ketone peroxide. To the second formulation was added 0.05 percent of 2,4-pentanedione(2,4-P).

Upon curing, the control without 2,4-P exhi-; bited glinting while the laminate with 2,4-P showed no glinting.

Other portions of the compositions were wound and cured on a 2-inch pipe mandrel with the same results.

In the examples it is shown that the unmodified combination of thermosetting resin, redox active metal salt, and organic peroxide will consistently develop fiber prominence when it is used with glass fiber reinforcement treated with a sizing that is or contains 29,613-F -13--14- ~246775 acid functionality of pKa of 2.0 or less. It is believed that the strong acid functionality in the sizing scavenges the redox active metal from the weaker naphthenate carrier. Both the napthenate and the residual vinyl acids typical of vinyl ester resins have pKas of approxi-mately 4.5 to 5Ø The end result of the loss of cobalt from the resin at the interface of resin and sizing is that the interface cures more slowly than the resin resulting in a tear or separation under the stress generated as the resin cures.

The examples show that fiber prominence is easily reduced or eliminated by adding an equally powerful scavenger to the resin. Two broad classes have been identified: acids of pKa of 2.0 or less and strong organic complexing agents with logs of stability constant of 5.0 or greater.

.29,613-F -14-

Claims (8)

THE EMBODIMENTS OF THE INVENTION FOR WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A glass fiber reinforced, curable, resinous composition which, when cured, displays substantially reduced fiber prominence, said composition comprising:

A. sized glass fiber wherein the sizing contains acid functionality with a kPa of 3.0 or less;

B. a vinyl ester or unsaturated polyester resin prepared from an unsaturated carboxylic acid and a polyepoxide containing more than one oxizane group, said resin being curable with a peroxide and redox active metal wherein the resin or a mixture of resins has a pH of at least 5.7 measured at a 10 percent methanol solution;

C. a peroxide catalyst, selected from the group of organic peroxides and tertiary hydroperoxides.

D. a redox active metal salt soluble in said curable resin; and E. a scavenger of the redox active metal said scavenger being an acid of pKa of 2.0 or less or a strong organic complexing agent with logs of stability constant of 5.0 or greater.

2. The composition of Claim 1 wherein said glass fibers are from 1.0 to 70.0 percent of the weight of the composition.

3. The composition of Claim 1 wherein said scavenger of redox active metal is an organic complexing agent with log of stability constant of 5.0 or greater.

4. The composition of Claim 3 wherein said organic complexing agent is an enolizable diketone.

5. The composition of Claim 4 wherein said enolizable diketone is 2,4-pentanedione.

6. The composition of Claim 1 wherein said strong redox active metal scavenging agent is an organic acid with pKa of 2.0 or less.

7. The composition of Claim 6 wherein said organic acid is maleic acid.

8. The composition of Claim 6 wherein said organic acid is pendant to the resin backbone.