CA1098275A

CA1098275A - Process for producing glass fiber-reinforced resin molded products

Info

Publication number: CA1098275A
Application number: CA286,785A
Authority: CA
Inventors: Osamu Yamamoto; Yoshiki Matsumoto; Hiromi Yamada; Keishin Takehara
Original assignee: Nitto Boseki Co Ltd
Current assignee: Nitto Boseki Co Ltd
Priority date: 1976-09-22
Filing date: 1977-09-15
Publication date: 1981-03-31
Also published as: AU512650B2; DE2739288C3; IT1090463B; DK417177A; CH624690A5; ZA774809B; AU2790477A; BE858914A; FR2365598B1; BR7706268A; NZ185225A; GB1583465A; DE2739288B2; PH14640A; MX146668A; JPS5341368A; NL164073B; FR2365598A1; NL164073C; DE2739288A1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for producing a glass fiber-reinforced resin molded article having superior transparency and mechanical properties and a greatly shortened curing time comprising dissolving about 10 to about 50 parts by weight of a copolymer of acrylo-nitrile and a vinyl aromatic hydrocarbon (e.g., styrene) in about 90 to about 50 parts by weight of a monomer selected from the group consisting of acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid esters and mixtures thereof, to produce a resin syrup, impregnating glass fibers with the resin syrup and curing the resin syrup with which the glass fibers are impregnated.

Description

BACKGROUND OF THE :INVENT_ON
1. Field of the Invention This invention relates to a process for producing a transparent molded article of a glass Eiber-reinforced resin by using a resin syrup composed mainly of acrylic acid, an acrylic acid ester, methacrylic acid, a methacrylic acid ester or a mixture thereof, with methyl methacrylate being a typical example thereof.

Molded articles of glass fiber-reinforced resins obtained by impregnating glass fibers with a resin syrup composed mainly of methyl methacrylate, and hardening the impregnated resin syrup have frequently been utilized ~utdoors as sheet-lika molded articles~ A technique is known to obtain a transparent molded article of a glass fiber-reinforced resin by causing ~h~ refractive index of the resin to correspond with that of the glass forming the glass fibers. One method of this l:ype can be achieved by~
copolymerizing methyl methacrylate and a vinyl aromatic hydrocarbon. A~ a result, the thus-obtained copolymer has a refractive index ranging from 1.49 to 1~60~ and thus, it is possible to adjust the refractive index of the copolymer to that of the glass fibers, as described in, for example, R.B~ Beevers, Trans. Faraday Soc., 58 1465 (1962). However, since the rate of reaction of the vinyl aromatic hydrocarbon is slow, the copolymerization of methyl methacrylate with the vinyl aromatic hydrocarbon does not proceed easily, and a viscous solution for glass fiber impregnation obtained by partially polymerizing ~hem (namely, a resin syrup) has a long hardening time. This has been the defect in the method of producing glass fiber-reinforced xesin products.

.,' ~

11 SUMMARY OF T~IE INVENTION

An object of this invention, therefore, is to provide a process for producing glass fiber reinforced resin products having superior mechanical properties within much shortened periods of hardening without impairing the transparency o the products.
Accordingly, thi~ invention provides a process for producing a molded article of a glass fiber-reinforced resin, which comprises dissolving about lO to about 50 parts by weight of a copolymer of about lO to about 50% by weight of acrylo-nitrile and about 90 to about 50% by weight of a vinyl aromatic hydrocarbon in about 90 to about 50 parts by weight of a monomer -~:
.
selected from the group consisting of acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid esters and mixtures :
thereof to produce a resin syrup, impregnating glass fibers with the rcsulting resin syrup, and thereafter hardening the resin syrup with which the glass fibers have been impregnated.
DETAILED DESCRIPTIQN ~F THE INVENTION

According to the present invention, the correspondence of the reEractive index of the resin with that of the glass fibers can be achieved by use of the resin s~rup which is obtained by dissol~ing a copolymer having a high refractive index .
in a monomer selected fxom the group consisting of acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters and mixtures thereof. In addition; to harden -the resin syrup : ~:~
with which the glass fibers are impregnated within short periods ~ ;
of time, the process comprises using a so-called polymeric syrup obtained by dissolving the copolymer in a monomer selected from acrylic acid, acrylic acid esters~ methacrylic acid~
methacrylic acid esters and mixtures thereof. Since the copolymer 1 used at this time is an acrylonitrile-modified vinyl aromatic hydrocarbon polymer of which a typical e~ample is an acrylonitrile/
styrene copolymer, the solubility parameter (calculated from the small equation) of the polymer is made equal to, or larger than, the soluhility parameter of the acrylic acid, the acrylic acid ester, the methacrylic acid or the methacrylic acid ester. This prevents a scattering of light caused by differences in the refractive index due to a phase separation between the dissolved polymer and the polymer obtained by polymerizing the monomer in the resin syrup. Hence, transparent glass ~iber-reinforced resin products can be obtained~
In order to produce resin molded products having especially good transparency by the process of this invention, it is necessary to use polymers having a calculated solubility parameter, as described hereinabove r Of at least about 9.30.
It ha~ been confirmed, however, that a transparency of a degree as is required for use in plastic panels used in green-houses can be achieved also by polymers having a calculated solubility parameter of about 9.25. The upper limit for the calculated solubility parameker is not particularly limited, but when the chain length of the acylonitxile unit in the copolymer is too long, an intramolecular cyclization takes place in the hardeniny step, which leads to problems in particle use.
The calculated solubility parameter of an acrylonitrile/
styrene copolymer, which is a typical example of the acrylonitrile/vinyl aromatic hydrocarbon copolymer used in this invention, is 9.25, 9.35 and 9 63, respectively, when the acrylonitrile content therein is 10, 20 and 30% by weight. Thus, the solubility parameter of the copolymer tends to increase as the content of acrylonitrile increases.. A feasible transparency can be sufficiently achieved when the acrylonitrile content is about 10~ by weiyht.

1 If the acrylonitrile content of the copolymer exceeds about 50% by weight, the sequence of the chain length of the acrylonitrile unit increases, and intramolecular cyclization occurs in the harde~ing step performed after impregnating the glass fibers with the resin syrup, thus impairing the transparency of the final product. Moreover, the styrene content o~ the copol~mer naturally decreases, and the refractive index of the polymer can be adjusted only within a narrow range. Thus, it is dif~icult to adjust the refractive index of the polymer when more than about 50%
10 hy weight acrylonitrile i5 used.
If the concentration of the acrylonitrile/vinyl aromatic hydrocarbon copolymer in the resin syrup used in this invention -is more than about 50~ by weight, the viscosity Qf the resin syrup is high and the syrup is di~ficult to handle. Preparatlon of a resin syrup which has too high a concentration should, therefore, be avoided. In order, however, to adjust the refractive index of the hardened resin product to near the refractive index tl.51 to l.55) of the glass fibers and to~avoid non-transparent glass fiber-reinforced resin products caused by the difference between the refractive index of the glass fibers ànd that of the resin impregnated therein9 the vinyl aromatic hydrocarbon adde~ to àdjus~ the refractive index of the resin syrup ~obtained by~dissolving an acrylonitrile/vinyl aromatic hydrocarbon copolymer in acrylic acld, an acrylic acid ester~
methacrylic acid, a methacrylic acid ester or a mixture thereof)~
must be present in an amount of at least about 5~ by weight in the resin syrup. It has been ascertained that in view of the amount of the vinyl aromatic hydrocarbon required, the concentration of the acrylonitrile/vinyl aromatic hydrocarbon copolymer in the resin syrup should be at least about 10% by weight. It has been found that, for example, a resin syrup obtained by dissolving an acrylonitrile/styrene (50:50 monomer ratio by weight) copolymer in a concentration o~ about 10% (the concentration of styrene being about 5~ by weight~ in me-thyl methacrylate has a refractive index of about 1.505, and that a gla5s fiber-reinforced resin product obtained by using such a resin syrup has a transparency which is feasible for practical applications such as for use as plastic panels in greenhouses.
A xesin syrup of a 50% by weight solution (the highest viscosity from the standpoint of handling the resin syrup, with a suitable viscosity ranging from about 3 to about 7 poises at the temperature of impregnation) of an acrylonitrile/styrene (10:90 monomer ratio by weight) copolymer has a refractive index of about 1.535, and a resin syrup composed of a 50% by weight solution of an acrylonitrile/styrene ~50:50 monomer ratio by weight) copolymer has a refractive index of about 1.516. Since glass fibers having a relatively low refractive index near 10510 are used in the art as reinforcing materials for molded articles of this kind, hardened resin products of a high refractive index of the degree intended by the pre~ent invelltion can be obtained, even i the amount of the vinyl aromatic hydrocarbon is confined within a range where the handling of ~he resin syrup is easy, namely even if the concentratlon of the acrylonitrile/vinyl ~ :-aromatic hydrocarbon copolymer in the resin syrup is limited to .:
not more than about 50% by weight.
Suitable vinyl aromatic hydrocarbons which can be used - in this invention are aromatic hydrocarbons in which one vinyl group is directly bonded to the aromatic ring, and which is copolymerizable with acrylonitrile. Suitable vinyl aromatic 3~ hydrocarbolls which can be used in -this invention include styrene, vinyltoluene, Yinylxylene, ~-methylstyrene and the like.

1 The monomer for dissolving the acrylonitrile/vi.nyl aromatic hydrocarbon copolymer includes acrylic acid, ethyl acrylate, hydroxyethyl acrylate~ methacrylic acid, butyl metha-crylate and methyl methacrylate. These monomers can be used either individually or as admixtures of two or more thereof. Of these, methyl methacrylate is most suitable for practical application.
As described above, according to this invention, glass fibers are impregnated with a resin syrup obtained by dissolving 1~ about 10 to about 50 parts by weight of an acrylonitrile/vinyl aromatic hydrocarbon copolymer of about lO to about 50~ by weigh-t of acrylonitrile and about 90 -to about 50% by weight o a vinyl ~ -~
aromatic hydrocarbon in about 90 to about 50 parts of acrylic :: -acid, acrylic acid esters, methacrylic acid, methacrylic acid esters or a mixture thereof. Thus, the impregnated resin includes the vinyl aromatic hydrocarbon in polymeric state, which does not retard the ha.rdening of the resin syrup. Hencei the rate of hardening of the resin syrup after the impregnation ca~ be sùfficiently decreased as compared with the case of using a conventional monomer-prepolymerized resin syrup. This greatly increases the productivity o the process in commercial ~ ~
operations. . .:
Suitable glass fibers which can be used in this invention are those of the so-called "chemical glass" including a substantial amount of alkali metal oxides wi~h a relatively low refractive index near 1.510. The strand of the glass fibers which is used in this invention conkains about 200 filaments having a fiber diameter of about 4.5 ~um and is cut into a size of 2 inches for ease of handling.
The hardening time for the resin syrup with which the ~8~7~

glass fibers are lmpregnat~d can, of course, be shortened further by using means generally used for promoting the hardening of resins, for example, by increasing the reactivity of the resin by adding a catalys-t such as benzoyl peroxide, acetyl peroxide and t-butylperoxypivalate, which can be employed in a small amoun-t to harden the resin syrup, to the composition or raising the temperature to about 50 to about 80C, or by using a chain transfer agent. The chain transfer agent used herein can reduce the molecular weight of the resulting polymer, and as a result, the viscosity of the resin syrup does not increase. Thus, it is possible to prepare a syrup having a relatively low viscosity which contains a high content of polymer. The hardening time can be decreased still further by using a polyfunctional monomer in combination therewith to promote a gel effect r and positively perfoxming a three-dimensional cross-linking reaction. A
shorter hardening time is preferred.
Useful chain transfer agents which can be used in general include alkyl mercaptans such as n-dodecyl mercaptan, isopropyl mercaptan and n-butyl mercaptan, aryl mercaptans such as thiophenol, thiocresol and thionaphtol and sulfur compounds containing an active hydrogen such as thioglycolic acid and the esters thereof. The effective amount of the chain transfer agent is about 0.1 to 1.0 part by weight per 100 parts by weight of monomer.
Examples of suitable polyfunctional monomers which can be employed include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane tri-methacrylate, ethylene dimethacrylate, ethylene glycol diacrylate, trimethylolethane triacrylate, 1,3-butylene dimethacrylate, glycidyl methacrylate, tetrahydrofurEuryl methacrylate, 8~75 l divinylben2ene, -triallyl cyanurate and triallyl isocyanurate.
Of these compounds, 1,3-bu-tylene dimethacrylate, ethylene dimeth-acrylate and trimethylol propane trimethacrylate are especially effective. However, the use of such a polyfunctional monomer as a cross-linking agent is not essential.
In the present invention, in dissolving the monomer in the resin syrup of the above-described composition can be partially polymerized by adding a small amount of a catalyst such as benzoyl peroxide, azobisisobutyronitrile, etc~ The polyfunctional monomer can be employed with equal results be~ore or after the partial polymerization of the resin syrup.
When the amount of the polyfunctional monomer is up to about 5% by weight, such promotes a shortening of the hardening time depending on the amount thereof, and does not adversely affect the mechanical characteristics of the hardened product.
If the amount of the polyfunctional monomer exceeds about 5~ ~ ;
by weight, the hardened product becomes brittle. Hence, it is neaessary to restrict the amount of the polyfunctional monomer within about S~ by weight based on the monomer used. Generally,

2~ when such a cross~linking agent is emp:Loyed in an amount of about 5% by weight, the hardening time for the monomer-pre pol~merized resin syrup, which is generally about 30 minutes in the absence of such a cross-linking agent r can be shortened to ~ , about 20 to 22 minutes. It has been confirmed that the hardening time for the polymeric syrup used in this invention, under the same conditions, can be shortened to about 8 to lO `
minutes from about 16 minutes by using the polyfunctional monomer.
To obtain good mechanical strength in a glass fiber-reinforced plastic panel produced in accordance with this

3~ invention, the glass fibers are generally employed in an amount ~r~2~5 1 of about 20 to 30 parts by weight based on 100 parts by weight of the resin syrup.
The following experimental examples and comparative ~xperimental examples are given to illustrate in detail the synthesis of the resin syrup which forms a basis for the dis-covery of the process for producing glass fiber~reinforced resin products in accordance with this invention, and the various properties of the hardened products obtained by using 1 part by weight of t-butylperoxypivalate~ as a polymerization initiator, per 100 parts by weight of the resin syrup in com-parison with the synthesis of a resin syrup using a conventional method and the properties of the hardened product obtained by curing the resin syrup. Unless otherwise indicated herein, all parts, percents, ratios and the like are by weight.
In the experimental examples; comparative experimental examples, example and comparative example given hereinafter, the various properties described were measured using the following methods.
Viscosity Averaqe Molecular Weiqht o ;~y~
Measured using an Ostwald capillary viscometer using benzene (25C) as a solvent for the methyl methacrylate/styrenesystem and dimethyl formamide ~25C) as a solvent for the methyl methacrylate/styrene/acrylonitrile system.

Polymerization Conversion Measured by a precipitation method using acetone (good solvent)-methanol (poor solvent).
Viscosity Measured with a BM-type standard viscometer (a product of Tokyo Keiki K.K.) using a No. 2 rotor at a speed of 30 rpm.

32~

1 Hardening Time -- -, ~
The time required to harden ~cure) a mixture of 100 parts of each of the resin syrups and 1 part of t-butylperoxy~ ~ -pivalate was measured using a differential scanning calorimeter (DSC, a product of Perkin-Elmer Company) at 65 C.

Transparenc~
Evaluated by visual observation with the naked eye.

Light Transmittance 1~ Transmittance of light at a wavelength of 350 m~ which was measured using a double-beam spectrophotometer (a product of Shimadzu Seisakusho K.K.).

Refractive Index Measured at 25C using an Abbe refractometer (a product of Shimadzu SeisàXusho K.K.).

Flexural Stren ~ ~ -Measured with a tensile tester ~"Tènsilon", a product of Toyo Baldwin Co., Ltd.) using a test piece having a width 2~ of 20 mm, a span of 50 mm and a thickness of 1 mm.

Tensile Stren~th Measured with a tensile tester ("Tensilon") using a dumbbell-shaped test piece having a width of 5 mm ~central width of 3 mm), a length of 100 mm and a thickness of 1 mm.

Weatherability A test sample was exposed to a weather-ometer (a product of Suga Tester Co., Ltd.) for 400 hours, and then the change in the colour of the sample was visually observed.

7~i 1 Experimental Exam~le 1 In accordance with Run No. 1 shown in Table 1 below, a monomeric mi~ture of 10 parts by weight of acrylonitrile and 90 parts by weight of styrene, 0.1 part by weight of t-butylperoxypivalate as a polymerization initiator and 0.6 part by weight of n-dodecyl mercaptan as a chain transfer agen~ were charged into a reactor, and reacted at 60C to product a pre-copolymer of acrylonitrile and styrene having a viscosity average molecular weight of 70,000.

To 25 parts by weight of the resulting prepolymer were added 75 parts by weight of methyl methacrylate and 0.05 part by weight of azobisisobutyronitrile as a polymerization initiator, and these materials were reacted in a reactor to produce a resin syrup having a polymerization conversion of 31 to 33~ and a viscosity of 5.5 poises ~25C) for use in this invention.
Then, t-butylperoxypivalate was added in an amount of 1 part hy weight per 1~0 parts by weight of the resin syrup~
The mixture was poured into a mold having the shape o~a flat ~ plate, and heated at about 65C;for 16 minutes to produce a resin hardened produ~t having a thic]cness of about 1 mm.
Repetition of these procedures confirmed that the curing of the resin syrup en~ed in 15 to 17 minutes.
The resulting resin hardened products were semi-;

transparent but sufficiently transparent that they could beused as transparent plates in practical application. The product had a light transmittance at 350 my o~ 82 to 83~, a refractive index of 1.513, a flexural strength of 10 to 12 kg/mm~, and a tensile strength of 5 to 7 k.g~mm .

The propOrtlonS of the monomers used to form resin syrups, 2~5 1 and the characteristics of the resin :hardened products in the a~ove and subsequent experimental examples are summarized in the following Table 1.

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1 Experimen-tal Examples 2 to 4 In Run Nos. 2 to 4 ln Table 1, a monomeric mixture of acrylonitrile and styrene in the proportion indicated in Table 1, 0~1 part by weight of t-butylperoxypivalate as a poly-merization initiator and optionally 0.6 part by weight of n-dodecyl mercaptan as a chain transfer agent were charged in-to a reactor, and reacted at 60C to produce a pre-copolymer of acrylonitrile/styrene.
To 25 parts by weight of the prepolymer were added 75 parts by weight of methyl methacrylate and optionally 0.05 part by weight of azobisisobutyronitrile as a polymerization initiator~ These materials were reacted in a reactor, or allowed to stand as a mixture. Resin syrups having the polymerization conversions and viscosities shown in Table 1 were obtained.
Then, t-bu-tylperoxypivalate was added in an amount of 1 part by weight per 100 parts by weight of the resin syrup, and the mixture was poured into a mold having the shape of a f1at plate, and heated at about 65C for each of the periods indicated in Table 1 below to produce resin hardened products having a thickness of a~sut 1 mm and very good transparency. -In these examples, the use o~ a polyfunctional monomeras a cross-linking agent capable of shortening the hardening time ~or resin syrups was omit-ted. ~owever,as described hereinabove r the joint use of a suitable amount of a poly- -functional monomer can reduce the hardening time (16 to 19 minutes) for the resin syrups to about 8 to 10 minutes.
Table 1 shows that the mechanical strength character-istics of the hardened products obtained from the resin syrups used in this invention are somewhat better than those of hardened products obtained in the comparative experimental ~ 9 1 examples (conventional method) to be given hereinbelow, and that whe~ the hardened products are in the form o a plate, the plates are flexible and thus pliable when bent. Because of this characteristic, plastic panels for greenhouses, which are one important use of plate-like products of this kind outdoors, can be designed with a curvature, and the insertion or fitting operation of the plate-like product by bending the product is made possible. Accordingly, the glass fiber-reinforced resin products obtained by the present invention have very good utility 10 in commercial applications.

Comparative Experimental Examples 1 to 3 In Run Nos. 5 to 7 shown in Table l, ~ monomeric :
mixture of methyl methacrylate and each of the vinyl aromatic hydrocarbons indicated in Table l, in the proportions .
indicated, 0.05 part by weight of azobisisobutyronitrile as a polymerization initiator and 0.6 part by weight o n-dodecyl mercaptan as a chain transfer agent were charged into a reactor, and reacted at 80& to produce a monomeric syrup having a viscosity average molecular weight of 50,000.
Then, t~butylperoxypivalate was added in an amount of l part by weight per lO0 part3 by weight o~ the monomex-prepolymerized resin syrup. The mixture was poured into a mold having the shape of a flat plate in the same manner as in Experimental Examples l to 4, and heated at about 65C to produce resin hardened products having a thickness of about 1 mm.
As indicated in Table l below, the required hardening time was more than 30 minutes in all of the runs. The flexural strengths and tensile strengths of these products were inferior to those of the products obtained in Experimental Examples l to 4.

1 Comparative Experimental Examples 4 and 5 In Run Nos. 8 and 9 in Table 1, a prepolymer of styrene was prepared, and mixed with methyl methacrylate in the proportions shown in Table 1 . The mixture was optionally heated in a reactor and resin syrups were obtained.
Then, t-butylperoxypivalate was added in an amount of 1 part by weight per 100 parts by weight of each resin syrup. The mixture was poured into a mold having the shape of a flat plate, and heated at about 65C to produce resin hardened products having a thickness of about 1 mm.
As can be seen from the results in Table 1, the required hardening time could be shortened to about 15 to 20 minutes.
However, the resulting resin hardened products all had white cloudy areas therein, and the transparent products intended by the invention could not be formed.
Glass fibers were impregnated with the same resin syrups as produced in Experimental Example 2 and Comparative Experimental Example 1 to obtain resin hardened products.
The time re~uired to cure the resin syrup and the properties of the resulting glass fiber-reinforced resin products are described in the following examples.

~ E_e 1 part by weight of t-butylperoxypivalate was added to 100 parts by weight o~ the same resin s~rup as obtained in Experimental Example 2 (MMA 75 : ST 20 : AN 5). After thorough mixing, the mixture was used to impregnate a 2-inch chopped strand of chemical glass fibers having a refractive index of 1.517 with the weight ratio o~ the glass to the resin syrup being maintained at 1 : 4. By using a spacer to obtain a plastic plate having a uniform thickness of 1 mm, the impregnated glass 7~;i 1 fibers were heated at 65C for 17 minu-tes to cure the resin.
Post-curing was subsequently performed at 120C for 5 minutes to produce a glass fiber-reinforced resin plate.
The characteristics of the resulting resin plate are shown in Table 2.

Comparative Example 1 part by weight of t-butylperoxypivalate was added to 100 parts by weight of the same monomeric syrup (MMA 80 ~ 5T
20j as obtained in Comparative Experimental Example 1, and the materials were thoroughly mixed. The mixture was used to impregnate a 2-inch chopped stra~d of chemical glass fibers with the weight ratio o~ the glass to ~he resin syrup being maintained at 1 : 4. While bein~ pressed with a spacer having a thickness of 1 mm, the impregnated glass fibers were ~eated at 65C. More than about 34 minutes were required to cure the resin. Post-curing was performed at 120C for 5 minutes to produce a glass ~iber-reinforced resin plate having the characteristics shown in Table 2 below.

T~BLE 2 Molded Plate Characteristics of Comparative Molded Plate Exam~l~ Example Transparency Excellent Excellent Light Transmittance82-83 82-83 at 350 m~
WeatherabilityNo discolourationNo discolouration Flexural Strength (kg/mm2) 13-15 12-14 Tens~le Strength 8-9 7-9 (kg/mm ) -32~i While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from:the ,-spirit and scope thereof.

1~ ' 3~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A process for producing a glass fiber-reinforced resin molded article, which comprises dissolving (a) about 10 to about 50 parts by weight of a copolymer of about 10 to about 50%
by weight of acrylonitrile and about 90 to about 50% by weight of a vinyl aromatic hydrocarbon selected from the group consisting of styrene, vinyltoluene, vinylxylene and .alpha.-methylstyrene, in (b) about 90 to about 50 parts by weight of a monomer selected from the group consisting of acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters and mixtures thereof to produce a resin syrup; impregnating glass fibers with the result-ing resin syrup; and thereafter hardening the resin syrup with which the glass fibers are impregnated.
2. The process of claim 1, wherein the vinyl aromatic hydrocarbon is styrene.
3. The process of claim 1, wherein the concentration of the copolymer of acrylonitrile and the vinyl aromatic hydrocarbon in the resin syrup is about 10 to about 50% by weight.
4. The process of claim 1, wherein the monomer is methyl methacrylate.
5. The process of claim 1, including dissolving a chain transfer agent therein in producing the resin syrup.
6. The process of claim 5, wherein the chain transfer agent is selected from the group consisting of alkyl mercaptans, aryl mercaptans and sulfur compounds containing an active hydrogen.
7. The process of claim 5, wherein the amount of the chain transfer agent is about 0.1 to about 1.0 part by weight per 100 parts by weight of the monomer.
8. The process of claim 6, wherein the amount of the chain transfer agent is about 0.1 to about 1.0 part by weight per 100 parts by weight of the monomer.
9. The process of claim 1, including dissolving a poly-functional monomer therein in producing the resin syrup.
10. The process of claim 9, wherein the polyfunctional monomer is selected from the group consisting of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylol-propane trimethacrylate, ethylene dimethacrylate, ethylene glycol diacrylate, trimethylolethane triacrylate, 1,3-butylene dimethacrylate, glycidyl methacrylate, tetrahydrofurfuryl meth-acrylate, divinylbenzene, triallyl cyanurate and triallyl isocyanurate.
11. The process of claim 9, wherein the amount of the polyfunctional monomer is up to about 5% by weight based of the monomer.
12. The process of claim 10, wherein the amount of the polyfunctional monomer is up to about 5% by weight based of the monomer.