CA1129580A - High-speed pultrusion polyester resins and process - Google Patents

Abstract

Abstract The speed of pultrusion can be increased and the quantity of pul-truded products can be improved by using a polyester resin composition con-taining 4-10 parts of certain cellulose acetate butyrate resins per 100 parts of polyester resin.

Description

~z9s~o HIGH-SPEED PULTRUSION POLYESTER RESINS AND PROCESS

Background of the InYention This invention relates generall~ to a process for producing rein-forced polyester products employing a pultrusion process and to polyester resin compositions used therein. More particularly, it is directed to a pultrusion process that is run at significantly greater pulling or running speeds, and to particular new polyester resin compositions that make possible the use of such higher speeds.
Pultrusion is a newer process of producing reinforced plastic prod-ucts than are molding or hand-lay-up methods having its origin in the fifties.
lo Generally, the term "pultrusion" is used to describe any process of producing reinforced plastics in which continuous reinforcing material is impregnated with resin and pulled through a die of desired cross section to shape and cure the resin and produce continuous lengths of cured product having a uniform cross section and the shape of the die. Thermosetting-type resins are used almost exclusively at the present time with polyester resins comprising 85 to 90 percent of the total and expoxies the rest.
In pultrusion, the reinforcing material may be any filamentary mate-rial having strength, such as glass fiber, Aramid fibers, boron fibers or graphite fibers. Bustomarily, E-glass fibers constltute the majority of 20 reinforcing material used. Most commonly, filamentary reinforcing materials are used in the forms of: rovings, tows, mats, or cloth, or combinations of these forms.
Because pultrusion incorporates continuous strands of reinforcing material, it produces a product much stronger and flexible than those produced by older extrusion processes, which can only utilize discontinuous lengths of . . ~ ~
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11 ~129580 ~reinforcing f lement material, Beceuse of these characteristlcs, whenever high~strength products having the customary properties of polyester resins are desired, such as Corrosion resistanCe, electrical resistance or lightweight, then pultrusion will be used. The sizes and shapes of products, either solid or hollow, produced by pultrusion is virtually unlimited, as for example, I-beams, channel "Yide-flange beams, solid bars and rods, round and square tubing, rectangular beams, an91es, and eVen flat sheets. Customarily, the thickness of these parts can range from as little as 1/8 inch up to a practi-l cal maximunl of about three inches.
10 ¦ Ini-tially, pultrusion did not grow rapidly because it WdS costly and was limited to products With small cross-sectional areas. During the 1950's, however, radio frequency (RF) preheating was developed, which permitted faster line speeds and larger cross-sectional products to be made. However, even with RF-augmented heating, there is a prac-tical limit to pultrusion speed beyond which puliruded parts exhibit either internal -thermocracking due to excessive exotherm or external or internal cracking due to undercuring and monomer gaSsing. Typically, products having a thickness of about 0.25-0.375 inch made with relatively fast-curing polyester resins can be pultruded at a l maximum speed of about 8 to 9 feet per minute With fairly smooth surfaces;
¦ products having a -thickness of about 0.375 to 0.675 inch made With an inter-¦ mediate reactivity resin can be pultruded at speeds up to 6 feet per minute ¦ with only mildly abraded surfacesi while thick products over 0.67 inches in ¦ thickness and made with mediuM reactivity resins are limited to speeds of about 0.5-5 feet maximum depending on thickness and have pronounced surface abrasion and roughness. Additionally, because of the thermal cracking that occurs when the curing exotherm is excessive, thick parts generally can only be made With medium reaCtiVity resins having a maximum degree of unsaturation of about 50 to 55 mole percent of the total diacids (100 mole percent) em-: ' ' ' : ' . - ' ., . ' ' i ': :' :
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ployed in producing the resin. Because of their limited reactivity, these resins tend to sive softer cured surfaces that are more prone to be abraded in ~the die and to give products having rough, uneven surfaces.

Summary of the Invent~on Accordingly, it is an objec-t of the present invention to provide new polyester resin composition for pultrusion which either do not have or have to a lesser degree the deficiencies of presently-used polyester resins. More particularly, it is an object of this invention to provide polyester resin compositions that can be pultruded more rapidly, thus Making possible higher-o productivity pultrusion processes.
¦ A further object is the provision of pultrusion polyester resins that ;-not only pultrude faster but also give pultruded products having smoother surfaces and diminished occurence of internal and/or external cracks.
Thes~ and other objects and advantages, which will become apparent from the following description and claims, are obtained with polyester resin compositions containing ~-10 parts of particular cellulose acetate butyrate resins per 100 parts of particular polyester resins, as hereinafter more fully described. Such compositions can be pultruded at greater speeds to give products having diminished sur~ace roughness and internal and/or external 20 cracking. Additionally, certain of these compositions have been found to glve bulk or sheet molding compositions capable of producing thick moldings that are crack-free.

Description of the Preferred Embodiments In the following description and claims:
(a) All parts, phr (parts per hundred of resin), and percentages are calculated and expressed on a weight basis;

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(c) The term "polyester resin" refers to a stable homogeneous solu-tion of the polyester and monomer(s), ~ereinafter described, copo1ymerizable with the polyester; and (d) The term "pultrusion (or invention) polyester resin" refers to a stable homogeneous solution formed by dissolving into the poly-ester resin a cellulose acetate butyrate resin useful in the lO ¦ invention process, as hereinafter described.
Polyesters employed in the invention polyester resins are the conden-sa-tion products of one or more dicarboxylic acids and/or anhydrides (100 moles %) with a slight excess of one or more glycols (about 105-110 mole %), chosen ¦ to provide a polyester, ~ich, when combined with the vinyl monomers, herein- ~-after described, and cured, give a Barcol hardness of about 45 or greater, as determined by ASTM test method, D 2583-75 employing a 0.125 inch-thick cured clear casting. For the polyester to provide this hardness and the reactivity ;
necessary for the invention process, at least about 60 mole percent of the total dicarboxylic acids (and/or anhydrides) used to make the resin should be 20 of the alpha, beta-unsaturated type, copolymerizable with the vinyl monomers.In some instances when high reactivity is desired, as for example when the polyester resin is to be u-tilized with a large quantity of the CAB resin, 90-100 mole percent of the dicarboxylic acids employed will be alpha, beta-unsaturated. More typical, however, are polyesters made with about 65 to 85 ...
- mole percent unsaturation, with about 75-~0 mole percent being optimum.
Examples of alpha, beta-unsaturated acids that can be employed to provide this unsaturation are: maleic, fumaric, chloromaleic, itaconic, and like acids and/or anhydrides. The balance of any diacids or anhydrides em-. . ;~
i 4 _ 12~S8() ployed to modify the reactivity and properties of the polyester may be eithersaturated or of the non-alpha, beta-unsaturated type, and may be, for example, phthalic, isophthalic, tetrahydrophthalic or tetrachlorophthalic acid, hexa-chloroendomethylenetetrahydrophthalic acid or low-molecular-weight aliphatic dicarboxylic acids, such as succinic, adiptic or diglycolic acid9 or their anhydrides. As previously described, the degree of alpha, beta-unsaturation and, hence, reactivity of the polyester and the modifying diacids should be chosen so as to give a polyester resin having the desired Barcol hardness. In this connection, it is known that the aliphatic diacids tend to impart soft-ness and, therefore, must be used in minor amounts. Conversely, it is knownthat the aromatic diacids, such as the phthalic or the halophthalic acids, impart hardness and can be used in larger quantities. When fire retardancy is desired, a halogenated diacid, such as tetrachlorophthalic acid or anhydride is used, or a non-alpha, beta-unsaturated acid, such as tetrahydrophthalic acid is used and then halogenated after condensation.
Examples of suitable glycols that may be used are ethylene glycol, propylene glycol, 1,4-butane diol, neopentyl glycol, 2,2-bis-(4-hydroxycyclo-hexyl)-propanë and the adduc-t of two moles of propylene oxide with bisphenol A. Polyether glycols, such as diethylene glycol and dipropylene glycol also may be utilized but only in small quantities, because of their softening effect on the polyester after cure. Similarly, it may be necessary to limit the quantity of ethylene glycol in the polyester when the resin is to be dissolved in large quantities of monomer, as for example 55 to 60 percent i monomer, since ethylene glycol lowers the monomer solubility of the polyester.The molecular weight of the invention polyester is not narrowly critical and varies typically between a~out 1500 and 3500 with an acid number in the range of about 20 to 35.

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Lastly, in the invention polyester resin, either a single polyester may be employed or a mixture of two or more polyesters may be employed such that, after mixing, the combined total of the diacids and glycols present in each will give a final polyester resin system having the desired Barcol hard-ness and reactivity. An example of such a mixture is shown in Example 1.
Generally, such mixtures have the same physical properties as a single poly-ester made with the same to-tal quantity and types of condensation reactants used to make the two separate polyesters. The expression "polyester" used in the claims is intended to cover such mixtures.
Polyesters giving especially high pultrusion speeds and pultruded products with minimal or nO surface abrading or internal or external cracks, and hence constituting one of the preferred embodiments of the pultrusion polyester resins of this invention, are those having a styrene compatibility of about 25% or less and an alpha, beta-unsaturation (-C=C-) equivalent weight of about 200 to 275. Such polyesters are typically made by the condensation of about 65 to 85 mole percent of a suitahle alpha, beta-unsaturated diacid (usually maleic) and 15-35 mole percent of a suitable modifying diacid with a slight excess (e.g. 105-llO mole percent) of suitable glycol(s) - the conden-sation reactants being chosen to provide the polyester with this degree of 20 styrene compatibility. The definition and method of determining "styrene compatibility" is given in U.S. 3,940j350, column 4, lines 3-50.

In addition, pultrusion polyester resins made with polyesters having ~ this degree of styrene compatibility and (-C=C-) equivalent weight have been - discovered to give bulk and sheet molding compounds capable of being molded in thick sections (0.67 inch and greater) without cracking.
The monomers used in the invention polyester resin are, most prefer-ably, styrene or vinyl toluene or mixtures of the two employed in a quantlty

2 ~S ~30 of about 45 to 55 weight percent of the total weigh~ of the polyester resin.
In certain instances, as little as 40 percent or as much as 60 percent monomer may be employed. Ho~YeYer, when less than about 45 percent mon~ner is used, low-molecular-weight cellulose acetate butyrates, such as EAB 551-0.01, may be required to give acceptably low resin viscosity. Alternatively, such low-monon~er resins may be heated in the impregnation tank to reduce viscosity to an acceptable level. This, of course, may require using catalysts having higher activation temperatures to prevent premature gellation. Conversely, more than about 55 percent monomer is usually only employed when physical properties are not especially critical and lower cost is paramount. Typical-ly, physical properties are maintained at high levels up to about 55 percent, at which point they start to drop.
Generally, the quantity of mon~ner is determined by the viscosity requirement of the intended pultrusion process, taking into consideration the type and molecular weight of the polyester and cellulose acetate butyrate being employed in the system--viscosity decreasing with increasing rnonomer.
In this connection, when the pultrusion composition is to be used for impreg-nating roving or tows, viscosities in the range of 800 to 1500 centiposes (cps) may be employed, with viscosities of 900 to 1000 cps generally being 20 1 preferred. With mat or fabric reinforcement, typical viscosities are of the order of about 1500 to 2000 cps. Bearing in mind that the impregnating poly-ester resin formulation can be compounded with varying amounts of filler, it can be appreciated that the raw or neat polyester resin may typically bè made to have a viscosity ranging ~rom about 500 to 2000 cps depending upon the type - I and quantity of filler subsequently added.
~ hen other monomers are used to partially replace styrene and/or vinyl toluene in the inventicin polyester resin, the type and quantity chosen should be such that they give a polyester resin having a length to peak exo-_ / -.. .
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thenn tLPE) not in excess of about 90 seconds when the resin is catalyzed ~lith 2 percent Percadox 16 (98 percent active bis-4-t butyl cyclohexyl peroxydicar-bonate) and tested for reactivity in accordance with the Society of the P~astic Industry (SPI) gel-time test. When very high reactivity resins are desired, the LPE should not exceed about 70 seconds. Illustrative of other monomers that may be employed are: divinyl benzene, for increased cured resin hardness; vinyl acetate, for lower resin viscosity, and acrylate esters, for improved light stability. Other monomers that might be considered for inclu-sion in the polyester resin are, for example, alpha-methylstyrene, chlorosty-rene, diallphthalate, and triallyphosphate. In addition to providing a poly-ester resin having the aforedescribed reactivity (LPE), any replacement monomers chosen should have in combination with the styrene and/or vinyl toluene an acceptable degree of solvating properties for the polyester.
The invention pultrùsion polyester resin contains, per 100 parts of the resin, 4 to 10 parts of a cellulose acetate butyrate resin (CAB) that is soluble in the polyester resin to give a stable one-phase solution, which, when cured in the neat form at a thickness of 0.125 inches, has a heteroge-neous opaque appearance. CAB resins having these properties typically have an average butyrate content of about 0.9 to 2.0 percent. Best results have been obtained with CAB resins having a butyrate content of about 49 to 55 percent by weight. Further, to obtain pultrusion polyester resins that are not exces-sively VlSCOUS, it is preferred to employ CAB's having a viscosity not exceed-ing about 5 seconds, as determined by ASTM test method, D 817-65 (Formula A), and D 1343-56. Most preferred are CAB resins having a viscosity of one second or less. Cellulose acetate butyrate resins having these characteristics are available from Eastman Kodak under the following designations: CAB-551-0.01, -0.1, -0.1, -0.2 and -1; CAB-500-5; and CAB-451-1. If desired, mixtures of suitable CAB reins may be used. Also, there could be used, if available, * Trademark - 8 -! ' , ,- ' , . ' . ~i lZ958(;~ ~

cellulose acetate pentoate or cellulose acetate or cellulose acetate hexoate resins having the aforedescribed solubility and cured~compatibility character- ¦istics in the polyester resin.
t~hen less than abou-t four parts of CAB resin are employed, pultruded products exhibit internal cracking and/or surface abrasion, ~hile more than ten parts of CAB can ~ive viscosities too high for satisfactory pultrusion.
Too-high viscosities require the use oF monomers in quantities greater than about 60 percent ~ere, as previously described, physical properties are diminished. Most preferred are pultrusion polyester resins containing 5-~ phr lo I of the CA resin.
¦ lypically, the amount of CAB resin added is adjusted to the reactiv-ity of the polyester resin being employed in the pultrusion invention composi-tions. For example, a polyester having high reactivity (i.e., one made with 95 to 100 mole percent of unsaturated acid) usually requires about 7 to 10 parts of CAB; a fairly high-reactivity resin (i.e., one made ~ith about 75 mole percent of unsaturated acid), about 5 to 8 parts of CAB; a polyester of intermediate reactivity (i.e., one made with about 67 mo1e percent of unsatu-rated acid), about 5 to 6 parts of CAB, while a low-reactivity polyester (i.e., one made with about 60 mole percent of unsaturated acid), about 4 to 5 20 ¦ parts of CAB. Generally, the higher the unsaturated content of the polyester, the grea-ter the cross-linking density and the peak exotherm temperature, and, hence, the shrinkage of the polyester upon cure. Both factors contribute to gross internal stresses, which result in internal cracking, and~ hence, pro-portionally increasing amounts of CAB are required as the resin reactivity increases to alleviate these effects.
^ The inven-tion polyes-ter resins utilized in the pultrusion invention process are easily prepared by dissolving the cellulose acetate butyrate resin in the polyester resin, by means known to those skilled in the art and then _ g _ ~ . . .. . .

- I ~LZ~5~0 adding additional monomer, if required, to give the specification viscosity desired. Alternatively, some of the monomer may be withheld from the poly-ester resin to predissolve the CAB resin, with the resulting CAB solution then ¦being admixed with the polyester resin and the viscosity adjusted with addi-tional monaner. If desired, solvation of the CAB resin can be accelerated by heating the polyester resin or monolner to moderately elevated temperdtures, such as 50 to 60C.
The invention pultrusion polyester resins are compounded into the final pultrusion compositions used to impregnate the reinforcing material by usual means and utilize the kinds and quantities of ingredients and adjuvants typically used for polyester resins in this process.
Thus, the level of catalyst chosen is such that the pultrusion poly-ester resin will be substantially fully cured during its residence time in the pultrusion die, and typically will be about 0.75 to 1.25 phr3 with about 1 phr most commonly being employed. Preferred are catalysts having a critical temperature (or activation temperature) of about 120-145F, such as Percadox 16 (98 percent active bis-~-t~butylcyclohexyl peroxydicarbonate having a critical tempèrature of about 120 to 122F) or Catalyst USP-245 (5-dimethyl-hexane-2,5-diper 2-ethylhexoate having a critical temperature of about 145F). Catalysts having this range of activation temperatures allow the pultrusion compound to be cured at lower temperatures which permits higher pultrusion speeds and minimizes internal thermal cracking. Catalysts having higher critical temperatures, however, mqy at times ~e used to advantage with RF-augmented heating to give high pultrusion speeds, but generally are less pre~erred because of the necessity of heating the resin-impregnated rein~orce-ment to d temperdture within 40 to 50F of the critical temperature of the catalyst. For example, temperatures of 100 to 120F may be needed when benzoyl peroxide having a critical temperature of 160F is used. At these .

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higher temperatures, monomer vapori~ation increases, changing the desired ratio of polyester to monomer-in the resin system. Additionally, increased monomer vapor in the air constitutes possible health and fire hazards to people working in the vicinity of the pu1trusion machine. Particularly, fire caused by sparking of the radio frequency heating equipment can be a threat that must be guarded against.
Besides benzoyl peroxide, other catalysts having high critical tem peratures, such as t-butyl perbenzoate having a critical temperdture of about ~ 200F, may be utilized, particularly in combination with catalysts having low activation temperatures. Such combinations may be advantageous when higher running speeds are to be utilized. Generally, undercuring due to insufficient catalyst results in monomer gassing causing internal voids and/or surface hairline cracks running for various lengths through the length of the pultru-sion. '~hen observed, increasing the level of catalyst will increase the degree of cure and eliminate these defects.
The kinds and quantities of other ingredients used in the pultrusion compositions of the invention are conventional and like those used in standard pultrusion colnpounds. Thus, fillers, such as calcium carbonate, clay and hydrated alumina, may be utilized in quantities varying from 0 to 100 phr of the pultrusion polyester resin, with the quantity being dictated primarily by the viscosity of the initial pultrusion polyester resin and the final viscos-ity required of the pultrusion composition for the intended use. Bearing this in mind, typically about 0 to 25 phr filler will be employed for tows and roving to give the desired 800-lS00 cps impregnation viscosity while about 10 _ to 100 phr filler will be required for mat and fabric pultrusion compositions to give the desired 1500-2000 cps final viscosity. In addition to adjusting viscosity, the use of fillers also reduces cost and further lowers cure shrinkage of the pultrusion composition.

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¦ Similarly, inhibiters also are present in the invention resin compo-sitions to prevent premature gelation of the resin during mdnufactue and storage and subsequently during utilization in the pultrusion process. Illus-trative of useful inhibiters utilized in quantities giving the desired gel time according to standard industry practices are: hydroquinone, t-butyl catechol, and di-t-butyl-p-creosol. Other inhibiters, either individually or in combination, may alternatively be eMployed so long as the kinds and quanti-ties are judiciously chosen to provide the desired SPI gel time, previously described in connection with the mon~ners.
Lastly, the pultrusion compositions typically utilize standard mold release agents in quantities (1-5 phr) promoting smooth extrusion and rninimal die sticking. Exemplary of materials that may be used are: calcium or zinc stearate, phosphate esters or very fine (1 micron) polyethylene powder.
In the invention process, any type of reinforcement may be utilized that is customarily employed in standard pultrusion processes and includes filamentary reinforcelnents in the Form of rovings, tows, mats, woven cloth and the like, either singly or in various combinations. Glass fiber constitutes the majority of reinforcement material used today and will be normally em-ployed in the invention process. When special properties, such as higher 20 I strengths or lower weights, are desired, rnore esoteric reinforcements, such as ¦ Aramid, boron or graphite fibers may be used in any of the forms previouslydescribed. Conventionally, flat sheets are pultruded with mats or woven cloths--often reinforced with longitudinal lengths of fiber or rovi-ng--in quantities representing about 25 to 60 percent of the pultruded product, with about 50 percent being most typical. When maximuM adhesion between fiber reinforcement and pultrusion polyester resin is desired, che~ical coupling agents are applied to the reinforcing material.

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Similarly the invention pultrusion polyester resin is pultruded in a manner like the polyester of the prior art except for the pulling speed which can be two to four times more rapid than the speeds used for polyesters of the prior art. Ideally, pultrusion compounds employing the invention polyester resins are pultruded through a heated die, usually 3-5 feet long, arbitrarily divided for temperature sensing and control purposes into 4 zones. A typical die temperature profile for pultruding a compound like that used in Example 1 is sho~ln in Table A, which shows the temperatures used as the pultruding speed is increased.
o As can be seen fran Table A, the initial set point For the control probe in Zone I should be 325F. Zone II can go up to 340F and Zone III to 400F. Zone IV should be greater than 250F before processing begins. As line speed increases and the heat from the exotherm raises the die heat, the control temperature in Zone I is incrementally lowered so as to keep Zone IV
greater than 300F, preferably 325F. An indication of too low die heat will be the presence of internal voids. This is easily remedied by increasing the control temperature 10-20F or lowering the radio frequency plate current so as to reduce the resin temperature 5-10F. The speed and heat profiles shown in Table A are for R.F.-augmented-cure pultrusion equipment, but are equally applicable to thermal-only equipment, but at somewhat lower speeds.

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Example 1 A polyester resin ~Jas made by admixing together:
Polyester A 20.9%
Polyester B 23.8%
Styrene 55.3%
Total 100.0% -¦Polyester A and polyester B and the mixture of the two c~nprised:
Polyester A Pollyester B Mixture maleic anhydride (moles) 0.5 1.0 0.765 isophthalic acid (moles) 0.5 ' 0.235 propylene glycol (moles) 1.05 1.11 1.085 Properties Styrene Compatibility 10% 40~ 25%
LPE (2% Percadox 16) 57 sec.
¦ (-c = c-) equivalent weight37.0 160 225 ¦ Cured Barcol hardness 45 60 55 ~ viscosity 500 cps ¦ A pultrusion polyester resin was then prepared by admixing and dis-¦ solving into 100 parts of the polyester resin, 5.7 parts of Eastman Kodak's j CAB-551-0.1 resin (cellulose acetate butyrate resin having about 55% b~tyl, 2%¦ acetyl and 1.6% hydroxyl average content). Finally, a pultrusion composition having a viscosity of 1000 cps was prepared by homogeneously admixing: :~
Parts .- pultrusion polyester resin 105.7 mold release agent (,phosphate ester) 1.06 catalyst USP-245 1.06 calcium carbonate fil`ler 10.6 . - 15 -- llZ9580 This compound was used to impregnate 66-end-count glass roving that was subsequently pulled through a die producing a -flat bar, 1-1/2 inch x 1/4 ¦ inch having bbed e~ges, utilizing the processing conditicn- shown in Table , ~1 ~3 29 V " ,o, ~o ~
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Example 2 A pultrusion polyester resin having.a viscosity of lO00 cps was prepared by admixing and dissolving together first: I
Parts Polyester of Example 1 47.6 Styrene 52.4 CAB-551-0.1 7.85 and then admixing into the resulting solution:
Parts ¦ mold release agent 1.08 . I catalyst USP-245 1.08 The resulting pultrusion composition was used to impregnate a 68-end-count glass roving that was pulled through the same die as used in Example 1 ¦ utilizing he processing cond~tions llown in 'able 2.

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The physical properties of the bars produced in Examples 1 and 2 are given in Table 3, which also gives the properties of a one-inch diameter pultruded bar made ~ith 69 percent glass roving and a polyester -typically used for thick-pultruded products. All property values are in pounds per square inch (psi).

Typical ! Example 1 Example ? Prior Art Flexural Strength 134,600 136,700 128,000 Flexural Modulus 5.6 x 106 6.1 x 106 5.3 x 106 Tensile Stren~th 131,200 125,700 154,000 Tensile Modulus 6.1 x 106 6.7 x 106 4.8 x 106 Compressive Strength 78,000 55,000 58,000 Compressive Modulus 5.9 x 106 6.8 x 106 3,5 x 105 From the data in Tables 1, 2 and 3, it is apparent that the invention pultrusion resins can be pultruded at high speeds to give products having smooth surfaces and no internal or external cracking. Additionally, the data shows that the invention pol~ester resins give pultruded products having superior physical properties as compared to products made with polyester resins typically employed at the present time.
In production runs at two different pultrudersj a pultrusion poly-ester resin like that of Example 1 was used to: a) increase the pultrusion speed of a one-inch-diameter rod from 3 feet/minute to 6 feet/rninute, and b) increase the pultrusion speed of a ~ammer handle frorn 8 inches/minutes to 36 inches/minute.

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Claims (5)

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

1. In a pultrusion process the improvement which comprises using a polyester resin composition comprising a homogeneous admixture of:
(A) 40-60 parts of a polyester made by the condensation of reactants consisting essentially of from about 65-85 mole percent of an alpha, beta-unsaturated diacid or anhydride, from about 15-35 mole percent of a saturated diacid or anhydride and up to about 110 mole percent of a glycol, the polyester having an alpha, beta-unsaturation equivalent weight of about 200-275 and a monomer compatibility of about 25 percent or less;
(B) 40-60 parts of a monomer or mixture of monomers copolymer-izable with the polyester, the total of (A) and (B) being 100 parts, and giving a polyester resin which when cured has a Barcol hardness of at least 45;
(C) 4-10 parts of a cellulose acetate butyrate resin that is:
(1) soluble in the polyester resin;
(2) causes the admixture when cured to be opaque.

2. The process as in Claim 1 wherein the monomer consists essen-tially of styrene, vinyl toluene or mixtures thereof.

3. The process as in Claim 1 wherein the quantity of cellulose acetate butyrate resin is 5-8 parts.

4. The process as in Claim 1 wherein the cellulose acetate butyrate resin has an average butyrate content of about 44 percent or higher.

5. The process as in Claim 1 wherein there is used 45 to 55 parts of the polyester and 55 to 45 parts of the monomer.