CH624690A5 - Process for the manufacture of moulded products made of glass fibre-reinforced resin - Google Patents

Description

The present invention relates to a process for the manufacture of a transparent molded article from a glass fiber reinforced resin, which uses a resin syrup composed mainly of acrylic acid, an ester of acrylic acid, methacrylic acid, an ester of methacrylic acid, or a mixture thereof, with methyl methacrylate as a typical example.

Glass fiber reinforced resin molded articles obtained by impregnating glass fibers with a resin syrup composed mainly of methyl methacrylate, and by curing the impregnated resin syrup have been frequently used as sheet molded articles. One technique is known for obtaining a transparent molded article of glass fiber reinforced resin, which matches the refractive index of the resin with that of the glass forming the glass fibers. A method of this type can be carried out by co-polymerization of methyl methacrylate and a vinyl aromatic hydrocarbon. As a result, the copolymer thus obtained has a refractive index of between 1.49 and 1.60, and it is thus possible to adjust the refractive index of the copolymer to that of glass fibers, as described, for example, by RB Beevers, in "Trans. Faraday Soc. ”, 58, 1465 (1962). However, since the reaction rate of the vinyl aromatic hydrocarbon is slow, the copolymerization of methyl methacrylate with the vinyl aromatic hydrocarbon does not occur easily, and a viscous solution for the impregnation of glass fibers obtained by partial polymerization (i.e. a resin syrup) has a long curing time. This constitutes a defect in the method of manufacturing such resin products reinforced with glass fibers.

The object of this invention is therefore to provide a process for the manufacture of glass fiber-reinforced resin products having superior mechanical properties in very short curing periods and without reducing the transparency of the products.

The object of this invention therefore consists of a process for the manufacture of an article molded from a resin reinforced with glass fibers, characterized in that 10 to 50 parts by weight of a copolymer are dissolved, 10 to 50% by weight of acrylonitrile and 90 to 50% by weight of a vinyl aromatic hydrocarbon in 90 to 50 parts by weight of a monomer chosen from the group comprising acrylic acid, esters of acrylic acid, l methacrylic acid, methacrylic acid esters, and mixtures thereof, in order to produce a resin syrup, by the fact that glass fibers are impregnated with this resin syrup, then hardened the resin syrup with which the glass fibers were impregnated.

According to the present invention, the correspondence of the refractive index of the resin with that of the glass fibers can be obtained by using a resin syrup which is obtained by dissolving a copolymer having a high refractive index in a chosen monomer from the group comprising acrylic acid, esters of acrylic acid, methacrylic acid, esters of methacrylic acid, and mixtures thereof. In addition, to harden in short periods of time the resin syrup with which the glass fibers have been impregnated, the method according to the invention comprises the use of a polymeric syrup obtained by dissolving the copolymer in a monomer chosen from the group comprising acrylic acid, esters of acrylic acid, methacrylic acid, esters of methacrylic acid, and mixtures thereof. Since the copolymer used is a polymer of a vinyl aromatic hydrocarbon modified by acrylonitrile, such as for example an acrylonitrile / styrene copolymer, the solubility parameter (calculated by the Small equation) of the polymer is made equal at or greater than the solubility parameter of acrylic acid, esters of acrylic acid, methacrylic acid or esters of methacrylic acid. This prevents the scattering of light caused by differences in the refractive index due to a separation phase between the dissolved polymer and the polymer obtained by polymerization of the monomer in the resin syrup. As a result, transparent resin products reinforced with glass fibers can be obtained.

In order to manufacture resin molded products having a particularly good transparency by the process according to the invention,

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it is necessary to use polymers having a calculated solubility parameter, as described above, of at least about 9.30. It has been confirmed, however, that a degree of transparency as required for use in plastic plates used for greenhouses can also be obtained with polymers having a calculated solubility parameter of about 9.25 . There is no particular upper limit for the calculated solubility parameter but, when the chain length of the acrylonitrile unit in the copolymer is too long, intramolecular cyclization occurs in the hardening step, which leads to problems during practical use.

The calculated solubility parameter of an acrylonitrile / styrene copolymer, which is a typical example of an acrylonitrile / vinyl aromatic hydrocarbon copolymer, used in the process according to the invention, is 9.25, 9.35 and 9.63 respectively, when the acrylonitrile content is 10.20 and 30% by weight. Thus, the solubility parameter of the copolymer tends to increase when the acrylonitrile content increases. Achievable transparency can be obtained satisfactorily when the acrylonitrile content is approximately 10% by weight.

If the acrylonitrile content of the copolymer exceeds about 50% by weight, the chain length sequence of the acrylonitrile unit increases, and intramolecular cyclization occurs during the curing step performed after impregnation of the fibers. of glass with the resin syrup, thus reducing the transparency of the final product. In addition, the styrene content of the copolymer naturally decreases, and the refractive index of the polymer can be adjusted only in a restricted range. Thus, it is difficult to adjust the refractive index of the polymer when acrylonitrile is used in an amount greater than about 50% by weight.

. If the concentration of the acrylonitrile / vinyl aromatic hydrocarbon copolymer in the resin syrup used in the process according to the invention is greater than approximately 50% by weight, the viscosity of the resin syrup is high, and this syrup is difficult to handle. The preparation of a resin syrup which has too high a concentration should therefore be avoided. However, in order to adjust the refractive index of the cured resin product around the refractive index (1.51 to 1.55) of the glass fibers and to avoid the non-transparency of the reinforced resin products by glass fibers produced by the difference between the refractive index of glass fibers and that of the impregnation resin, the vinyl aromatic hydrocarbon added to adjust the refractive index of the resin syrup (obtained by dissolving an acrylonitrile / vinyl aromatic hydrocarbon copolymer in acrylic acid, an ester of acrylic acid, methacrylic acid, an ester of methacrylic acid or a mixture thereof) must be present in an amount of at least about 5% by weight in this resin syrup. It has been determined, taking into account the required amount of vinyl aromatic hydrocarbon, that the concentration of 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 copolymer (monomer ratio 50:50 by weight) in a concentration of about 10% (the concentration of styrene being d (about 5% by weight) in methyl methacrylate has a refractive index of about 1.505, and that the glass fiber-reinforced resin product obtained by the use of such a resin syrup has a transparency which can be used for practical applications, such as plastic plates for greenhouses.

A resin syrup of a 50% by weight solution (the highest viscosity from the point of view of handling the resin syrup, with an appropriate viscosity of between approximately 3 and approximately 7 Po at the temperature of the impregnation ) of an acrylonitrile / styrene copolymer (monomer ratio of 10:90 by weight) has a refractive index of approximately 1.535, and a resin syrup composed of a 50% by weight solution of an acrylonitrile / styrene (monomer ratio 50:50 by weight) has a refractive index of about 1.516. Since glass fibers having a relatively low refractive index, close to 1.510, are generally used in the art of reinforcing materials for molded articles of this type, cured resin products having a high refractive index can be obtained , even if the quantity of the vinyl aromatic hydrocarbon is situated in an area where the handling of the resin syrup is easy, namely even if the concentration of the acrylonitrile / vinyl aromatic hydrocarbon copolymer in the resin syrup is limited to a value not greater than about 50% by weight.

Suitable vinyl aromatic hydrocarbons which can be used in the process according to the invention are aromatic hydrocarbons in which a vinyl group is directly linked to the aromatic ring, and which are copolymerizable with acrylonitrile. Such suitable vinyl aromatic hydrocarbons include styrene, vinyltoluene, vinylxylene, α-methylstyrene and the like.

The monomer for dissolving the acrylonitrile / vinyl aromatic hydrocarbon copolymer includes acrylic acid, ethyl acrylate, hydroxyethyl acrylate, methacrylic acid, butyl methacrylate and methyl methacrylate. These monomers can be used either individually or as a mixture of two or more of them. Of these, methyl methacrylate is most suitable for practical application.

As described above, according to the present invention, glass fibers are impregnated with a resin syrup obtained by dissolution of about 10 to about 50 parts by weight of an acrylonitrile / vinyl aromatic hydrocarbon copolymer of about 10 to 50 % by weight of acrylonitrile and from approximately 90 to approximately 50% by weight of a vinyl aromatic hydrocarbon in approximately 90 to approximately 50 parts of acrylic acid, of an ester of acrylic acid, of methacrylic acid, an ester of methacrylic acid or a mixture thereof. Thus, the impregnated resin comprises the vinyl aromatic hydrocarbon in the polymeric state, which does not delay the hardening of the resin syrup. Consequently, the curing speed of the resin syrup after impregnation can be increased sufficiently in comparison with the case of using a traditional monomeric resin syrup prepolymerized. This significantly increases the productivity of the process on an industrial scale.

Suitable glass fibers which can be used in the process according to the invention are those called chemical glass and which comprise a substantial quantity of alkali metal oxides with a relatively low refractive index, close to 1.510. The glass fiber strand which is used in the process according to the invention contains about 200 filaments having a fiber diameter of about 4.5 µm and is cut into 2 inch pieces for easy handling.

The curing time for the resin syrup with which the glass fibers have been impregnated can of course be shortened by using means generally employed for curing the resins, for example by increasing the reactivity of the resin by addition of catalysts, such as as benzoyl peroxide, acetyl peroxide and t-butyl peroxypivalate which can be used in small amounts to harden the resin syrup, to the composition, or by increasing the temperature to about 50 to about 80 ° C, or using a chain transfer agent. The chain transfer agent used here can reduce the molecular weight of the polymer obtained and, thus, 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 curing time can be further reduced by using a polyfunctional monomer in combination to lead to a gel effect, and to positively effect a tridi5 crosslinking reaction.

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monthly. A shorter curing time is of course preferred.

Useful chain transfer agents which can be employed in general include alkylmercaptans such as n-dodecylmercaptan, isopropylmercaptan and n-butylmercap-tan, arylmercaptans such as thiophenol, thiocresol and thionaphthol, and compounds sulfur containing active hydrogen, such as thioglycolic acid and esters thereof. An effective amount of the chain transfer agent is between about 0.1 and 1.0 parts by weight per 100 parts by weight of the monomer.

Examples of suitable polyfunctional monomers which can be employed include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene dimethacrylate, ethylene glycol diacrylate, trimethylolethane triacrylate, dimethacrylate triethylacrylate -butylene, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, divinylbenzene, triallyl cyanurate and triallyl isocyanurate. Among these compounds, 1,3-butylene dimethacrylate, ethylene dimethacrylate and trimethylolpropane trimethacrylate are especially effective. However, the use of such a polyfunctional monomer as a crosslinking agent is not essential. i

In the process according to the invention, when the monomer is dissolved in the resin syrup of the composition, it can be partially polymerized by the addition of a small amount of catalyst, such as benzoyl peroxide, azobSsisobuty-ronitrile, etc. The polyfunctional monomer can be used with equivalent results before or after the partial polymerization of the resin syrup.

When the quantity of a polyfunctional monomer is present up to approximately 5% by weight, this causes a shortening of the curing time according to this quantity and does not adversely influence the mechanical characteristics of the cured product. If the amount of the polyfunctional monomer exceeds about 5% by weight, the cured product becomes brittle. Consequently, it is necessary to restrict the amount of polyfunctional monomer up to about 5% by weight relative to the weight of monomer used. Generally, when such a crosslinking agent is employed in an amount of about 5% by weight, the cure time for the prepolymerized monomer resin syrup, which is generally about 30 min in the absence of such a crosslinking agent, can be shortened to around 20 to 22 min. It has been confirmed that the curing time for the polymeric syrup used in the process according to the invention, under the same conditions, can be shortened to approximately 8 to 10 min from approximately 16 min using the polyfunctional monomer .

In order to obtain good mechanical strength of the glass fiber reinforced plastic panel produced by the process according to the invention, the glass fibers are generally used in an amount of approximately 20 to approximately 30 parts by weight relative to 100 parts by weight of the resin syrup.

The following experimental examples and comparative experimental examples are given in order to illustrate in detail the synthesis of the resin syrup which forms the basis of the process according to the invention, as well as the various properties of the cured products obtained using a part by weight. t-butyl peroxypivalate, as a polymerization initiator, per 100 parts by weight of the resin syrup in comparison with the synthesis of a resin syrup using a conventional method, and the properties of the hardened product obtained by cooking the resin syrup . Unless otherwise indicated, all parts, percentages, reports and the like are by weight.

In the experimental examples and the comparative experimental examples, the various properties described are measured using the following methods.

Average molecular weight based on the viscosity of the polymer

Measured using an Ostwald capillary viscometer with benzene as the solvent (25 ° Q for the methyl methacrylate / styrene system and with dimethylformamide (25 ° C) as the solvent for the methyl methacrylate / styrene / acryloni system -trile.

Polymerization

Measured using a precipitation method with acé tone (good solvent) and methanol (bad solvent).

Viscosity

Measured by a standard viscometer of the BM type (a product of the firm Tokyo Keiki K.K.) with a rotor N ° 2 and a speed 15 of 30 rpm.

Hardening time

The time required for curing (baking) of a mixture of 100 parts of each of the resin syrups and one part of t-butyl peroxypivalate was measured using differential scanning calorimeter (DSC, a product of the Perkin-Elmer Co.) at 65 ° C.

Transparency 25 Evaluated by observation with the naked eye.

Light transmission

Light transmission at a wavelength of 350 n was measured using a double beam spectrophotometer 30 (a product of the firm Shimadzu Seisakusho K.K.).

Refractive index

Measured at 25 ° C using an Abbé refractometer (a product of Shimadzu Seisakusho K.K.).

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Flexural strength

Measured using a Tensi-lon resistance test device (a product of Toyo Baldwin Co., Ltd.) using a test piece having a width of 20 mm, a span of 50 mm and a thickness of 1 mm.

Tensile strength

Measured by means of a Tensi-lon resistance test device using a dumbbell-shaped test piece having a width 45 of 5 mm (the width of the central part being 3 mm), a length of 100 mm and a thickness of 1 mm.

Weather resistance

A test sample was exposed to a weatherometer (a proso duit from Suga Tester Co., Ltd) for 400 h, then the change in color of the sample was observed visually.

Experimental example 1

According to test No. 1 presented in table 1, a monomeric mixture 55 of 10 parts by weight of acrylonitrile and 90 parts by weight of styrene, 0.1 part by weight of t-butyl peroxypivalate as initiator of polymerization and 0.6 parts by weight of n-dodecylmercaptan as chain transfer agent were introduced into a reactor, and reacted at 60 ° C. in order to produce a precopolymer of acrylonitrile and styrene having an average molecular weight according to its viscosity of 70,000.

To 25 parts by weight of the prepolymer obtained were added 75 parts by weight of methyl methacrylate and 0.05 parts by weight of azobisisobutyronitrile as polymerization initiator, and these products were reacted in a reactor in order to produce a resin syrup having a polymerization rate of 31 to 33% and a viscosity of 5.5 Po (25 C) for use in the process according to the invention.

Then, t-butyl peroxypivalate was added in an amount of one part by weight per 100 parts by weight of the resin syrup. The mixture was poured into a mold in the form of a plate, and heated to about 65 ° C for 16 min to give a cured resin product having a thickness of about 1 mm.

The repetition of the above procedures confirmed that the cooking of the resin syrup was completed in 15 to 17 min.

The cured resin products obtained were semi-transparent, but sufficiently transparent that they could be used as transparent plates in practical applications. These products exhibited light transmission at 350 m | i of 82 to 83%, a refractive index of 1.513, a flexural strength of 10 to 12 kg / mm2, and a tensile strength of 5 to 7 kg / mm2.

The proportions of the monomers used to form the resin syrups, and the characteristics of the cured resin products above, as well as the results of the subsequent experimental examples are summarized in Table 1.

Experimental examples 2 to 4

In tests Nos 2 to 4 of table 1, a monomeric mixture of acrylonitrile and styrene in the proportions indicated in said table, 0.1 part by weight of t-butyl peroxypivalate as polymerization initiator and optionally 0, 6 parts by weight of n-dodecylmercaptan as chain transfer agent were introduced into a reactor, and reacted at 60 ° C to produce an acrylonitrile / styrene precopolymer.

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 left to stand in the form of a mixture. Resin syrups having the polymerization rates and viscosities listed in Table 1 were obtained.

Then, t-butyl peroxypivalate was added in an amount of 1 part by weight per 100 parts by weight of resin syrup, and the mixture was poured into a mold in the form of a plate, and heated to at approximately 65 ° C. for each of the periods indicated in table 1 in order to obtain cured resin products having a thickness of approximately 1 mm and having very good transparency.

In these examples, the use of a polyfunctional monomer as a crosslinking agent capable of shortening the curing time of the resin syrups has been omitted. However, as described above, the joint use of an appropriate amount of a polyfunctional monomer can reduce the curing time (16 to 19 min) for resin syrups up to about 8 to 10 min.

Table 1 shows that the mechanical strength characteristics of the cured products obtained from the resin syrups used in the process according to the invention are better than those of the cured products obtained in the experimental examples.

comparative mental (conventional method) which will be described later, and that, when the cured products are in the form of a plate, these plates are flexible and foldable. Because of this characteristic, plastic panels for greenhouses, which constitute one of the most important uses of products in the form of external panels of this type, can be provided with curvatures, and the operation of insertion or fixing products in the form of plates by bending or bending the product is made possible. Consequently, the resin products reinforced with glass fibers obtained by the process according to the invention are of great interest for industrial and commercial applications.

Comparative experimental examples 1 to 3

In tests 5 to 7 presented in table 1 below, a monomeric mixture of methyl methacrylate and of each of the vinyl aromatic hydrocarbons mentioned in this table 1 and in the proportions indicated in this table, 0.05 part by weight d azobisisobutyronitrile as the polymerization initiator and 0.6 part by weight of n-dodecylmercaptan as chain transfer agent, were introduced into a reactor, and reacted at 80 ° C. in order to produce a monomeric syrup having an average molecular weight based on its viscosity of 50,000.

Next, t-butyl peroxypivalate was added in an amount of 1 part by weight per 100 parts by weight of prepolymerized monomeric resin syrup. The mixture was poured into a plate-shaped mold in the same manner as in Experimental Examples 1 to 4, and heated to about 65 ° C to provide cured resin products having a thickness of about 1 mm. As shown in Table 1, the required cure time was more than 30 min in all tests. The flexural and tensile strengths of these products were lower than those of the products obtained in experimental examples 1 to 4.

Comparative experimental examples 4 and 5

In tests N05 8 and 9 of table 1, a styrene prepolymer was prepared, and mixed with methyl methacrylate in the proportions indicated in this table. The mixture was optionally heated in a reactor and resin syrups were obtained. Then, t-butyl peroxypivalate was added in an amount of 1 part by weight per 100 parts by weight of each of the resin syrups. The mixture was poured into a mold in the form of a plate and heated to about 65 ° C to provide cured resin products having a thickness of about 1 mm.

As can be seen from the results mentioned in Table 1, the required curing time can be reduced to about 15-20 min. However, the cured resin products obtained all had white stained surfaces, and the desired transparent products could not be obtained.

(Table on following pages)

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Table 1

1

2

Examples 3

4

1

2

Comparative examples 3 4

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Test No

1

2

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4

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S

Resin syrup

Polymerization system - Polymer-tion Monomer

Proportion of MMA syrup constituents: ST: AN resin (weight%) 75: 22.5: 2.5

Reaction conditions

Acrylonitrile (AN) 10 Ethyl acrylate (EA) -Vinyltoluene (VT)

Styrene (ST) 90

Methyl methacrylate (MMA) Azobisisobutyronitrile -T-butyl peroxypivalate 0.1

n-Dodecylmercaptan 0.6 Reaction temperature (° C) 60 Average molecular weight based on the viscosity of the polymer 70000

Resin syrup preparation conditions

Prepolymer 25 Methyl methacrylate 75 Azobisisobutyronitrile 0.05 n-Dodecylmercaptan -Reaction temperature (° C) 80

Properties of resin syrup

Polymerization rate (%) 31-33

Viscosity (Po at 25 ° C) 5.5

Polymer- Polymer- Polymer- Monomer Monomer Monomer

Monomere Monomere Monomere Monomere Monomere

MMA: ST: AN MMA: ST: AN MMA: ST: AN MMA: ST MMA: ST: EA MMA: VT MMA: ST MMA: ST

75: 20: 5 75: 18.5: 6.5 75: 17.5: 7.5 80:20 60:20:20 80:20 70:30 80:20

20

80

0.1 0.6

60

70000

25

75 0.05

80

30-32 5.5

25 75

0.1 60

250,000

25 75

25 6.0

30

70

0.1 0.6

60

70000

25

75 0.05

80

29-31 5.5

20

80 0.05

0.6 80

50,000

20

20

60 0.05

0.6 80

50,000

20

80 0.05

0.6 80

.100

0.05

0.6 100

50,000 50,000

30 70

34-36 5.0

34-36 4.8

34-36 5.2

30 4.5

100

0.05

0.6 100

50,000

20

80

0.05

0.3

80

34-36 5.5

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Glass fibers were impregnated with the same resin syrups as those produced in Experimental Example 2 and Comparative Experimental Example 1 in order to obtain cured resin products. The time required for cooking the resin syrup and the properties of the glass fiber-reinforced resin products obtained are described in the following examples.

Example

One part by weight of t-butyl peroxypivalate was added to 100 parts by weight of the same resin syrup as that obtained in experimental example 2 (MMA 75: ST 20: AN 5). After stirring, the mixture was used to impregnate cut filaments with 2 inches of chemical glass fibers having a refractive index of 1.517, the ratio of the weight of the glass to the weight of the resin syrup being kept at 1: 4 . Using a spa-cer to obtain a plastic plate having a uniform thickness of 1 mm, the impregnated glass fibers were heated at 65 ° C. for 17 min for the curing of the resin. A 2S postcook was then performed at 120 ° C for 5 min to produce a resin plate reinforced with glass fibers.

The characteristics of this resin plate obtained are presented in Table 2.

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Comparative example

One part by weight of t-butyl peroxypivalate was added to 100 parts by weight of the same monomeric syrup (MMA 80: ST 20) as that obtained in Comparative Experimental Example 1, and the products were mixed completely. The mixture thus obtained was used to impregnate cut filaments with 2 inches of chemical glass fibers, the ratio of the weight of the glass to the weight of the resin syrup being maintained at 1: 4. While being pressed by means of a spacer, 40 1 mm thick, the impregnated glass fibers were heated to 65 ° C.

More than about 34 minutes were necessary for the curing of the resin. Postcooking was carried out at 120 ° C for 5 min in order to provide a resin plate reinforced with glass fibers having the characteristics mentioned in Table 2.

Table 2

Molded plate

Characteristics

Example

Example

comparative

Transparency

Excellent

Excellent

Light transmission

350 m | x (%)

82-83

82-83

Weather resistance

No

No

discoloration discoloration

Flexural strength

(kg / mm2)

13-15

12-14

Tensile strength

(kg / mm2)

8-9

7-9

R

Claims (13)

624 690 1. Process for the manufacture of a molded article in resin reinforced with glass fibers, characterized in that one dissolves: a) 10 to 50 parts by weight of a copolymer, 10 to 50% by weight of acrylonitrile and 90 to 50% by weight of a vinyl aromatic hydrocarbon, in b) 90 to 50 parts by weight of a monomer chosen from the group comprising acrylic acid, esters of acrylic acid, methacrylic acid , esters of methacrylic acid and mixtures thereof, to provide a resin syrup; by the fact that glass fibers are impregnated with the resin syrup obtained, then that the resin syrup is hardened with which the glass fibers have been impregnated. 2. Method according to claim 1, characterized in that the vinyl aromatic hydrocarbon is chosen from the group comprising styrene, vinyltoluene, vinylxylene and α-methylstyrene. 2 3. Method according to claim 2, characterized in that the vinyl aromatic hydrocarbon is styrene. 4. Method according to claim 1, characterized in that the concentration of the copolymer of acrylonitrile and vinyl aromatic hydrocarbon in the resin syrup is between 10 and 50% by weight. 5. Method according to claim 1, characterized in that the monomer is methyl methacrylate. 6. Method according to claim 1, characterized in that one further dissolves a chain transfer agent for the preparation of resin syrup. 7. Method according to claim 6, characterized in that the chain transfer agent is chosen from the group comprising alkylmercaptans, arylmercaptans and sulfur compounds containing an active hydrogen. 8. Method according to claim 6, characterized in that the amount of chain transfer agent is between 0.1 and 1.0 part by weight per 100 parts by weight of the monomer. 9. Method according to claim 7, characterized in that the amount of chain transfer agent is between 0.1 and 1.0 part by weight per 100 parts by weight of the monomer. 10. Method according to claim 1, characterized in that one further dissolves a polyfunctional monomer for the preparation of resin syrup. 11. The method as claimed in claim 10, characterized in that the polyfunctional monomer is chosen from the group comprising ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene dimethacrylate, ethylene glycol diacrylate, trimethylolethane triacrylate, 1,3-butylene dimethacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, divinylbenzene, triallyl cyanurate and triallyl isocyanurate. 12. Method according to claim 10, characterized in that the amount of polyfunctional monomer is up to 5% by weight relative to the weight of the monomer. 13. The method of claim 11, characterized in that the amount of polyfunctional monomer is up to 5% by weight relative to the weight of the monomer.