RU2773075C1 - Epoxy binder, pre-preg based thereon, and product made therefrom - Google Patents

Abstract

FIELD: polymers.

SUBSTANCE: invention relates to the field of creating mortarless single-component epoxy binders with accelerated energy-efficient hardening mode for producing structural polymer materials based on fibrous reinforcing fillers recycled according to the pre-preg technology, acceptable for use in the aviation, helicopter, shipbuilding, automotive, wind power, sports, electronic, construction and other industries. Epoxy binder includes a mixture of wt.%: polyepoxy resin 34.9 to 38.5, low molecular weight epoxy diane resin 17.0 to 22.0, and high molecular weight epoxy diane resin 25.0 to 29.3, a latent hardener - dicyandiamide 7.8 to 10.5, a hardening accelerator - asymmetrically disubstituted urea 2.4 to 3.2, and a modifier - "core-shell" rubber nanoparticles 4.4 to 5.2. A multifunctional epoxy resin selected from a homologous series of epoxy resins based on triphenols, epoxy novolac resins and halogen-containing epoxy resins, is used as a multifunctional epoxy resin. The product is manufactured by direct pressing or vacuum moulding of the pre-preg using the claimed binder, wherein the pre-preg includes said epoxy binder in an amount from 30.0 wt.% to 50.0 wt.% and a fibrous filler in an amount from 50.0 wt.% to 70.0 wt.%.

EFFECT: invention allows for an increase in the reaction activity of the binder and pre-pregs based thereon, and contributes to the formation of products made of structural polymer materials with improved stress-strain and impact-resistant characteristics.

8 cl, 3 tbl, 6 ex

Description

The invention relates to the field of creating solution-free one-component epoxy binders with an accelerated energy-efficient curing mode for obtaining structural polymer composite materials (PCM) based on fibrous reinforcing fillers processed using prepreg technology, which can be used in aviation, helicopter, shipbuilding, automotive, wind energy, sports , electronic, construction and other industries.

The intensification of the processing of epoxy polymers into PCM is impossible without the use of fast-curing, at low processing temperatures, one-component binders, since from an economic point of view, when obtaining products from PCM, it is desirable that their molding cycle be as short as possible and the curing temperature be lower.

An epoxy composition is known from the prior art, used as potting and impregnating materials in various industries (see SU 1525173 A1, IPC С08G59/68, publ. 11/30/1989), including epoxy resin, isomethyltetrahydrophthalic anhydride hardener and curing accelerator 2.2 -(diethylamino)diethyl ether. The main disadvantage of this epoxy composition, despite the presence of an effective amine accelerator in its composition, is the long high-temperature curing mode (temperature 100°C - 2 hours; temperature 120°C - 2 hours; temperature 150°C - 3 hours; temperature 200°C - 5 o'clock). This circumstance makes it economically inefficient to use the considered epoxy composition for the production of products from PCM, due to the need to use a long energy-consuming processing mode.

From the prior art, another solution-type epoxy binder is known for the manufacture of structural fiberglass products using solution prepreg technology (see SU 887595 A1, IPC C08L63 / 00, C08J5 / 24, C08G59 / 56, publ. 07.12.1981), containing epoxy diane resin brand ED-16, a complex curing system based on aromatic polyamine hardeners, which is a mixture of isomers of 4,4'-, 2,4'-, 2,2'-diaminodiphenylmethane and 4,4'-bis-( n - aminobenzyl)aniline and phenol-aniline-formaldehyde resin grade SF-340 and urea curing accelerator. In order to regulate the viscosity of this binder to the required technological index, a solvent - acetone - is introduced into the composition. The prepreg is made by impregnating T-11 fiberglass with the specified epoxy binder using mortar technology. The product is obtained by direct pressing of the assembled prepreg package at a temperature of 125°C in one technological cycle lasting 4 minutes.

The main disadvantage of this epoxy binder and prepreg based on it is their reduced technological viability at a temperature of 25 ° C (no more than 12 days), and in the case of storage of the prepreg without the use of refrigeration equipment, its technological characteristics rapidly decrease due to a decrease in drapeability, a decrease in elasticity. and flexibility, the disappearance of the necessary contact stickiness, etc., which greatly complicates the technological process of prepreg processing into final products from PCM. In addition, the presence of a highly volatile inert solvent acetone in the composition of an epoxy binder adversely affects the formation of final products based on it, since the removal of highly volatile components leads to the formation of a porous structure of the product, characterized by low and unstable elastic-strength characteristics.

The closest analogues taken as a prototype (see RU2263690 C1, IPC С08L63/00, С08J163/00, С08J5/24, B32B27/38, publ. 10.11.2005), are:

- epoxy composition, which is a mixture of polyepoxy epoxytriphenol resin - 46.1 wt. %, low molecular weight epoxy resin - 40.5 wt. %, high molecular weight epoxy resin - 3.5 wt. %, latent hardener dicyandiamide - 7.5 wt. %, accelerator for curing asymmetric disubstituted urea bis-(N,N'-dimethylurea)diphenylmethane - 1.2 wt. % and silica modifier in the form of white carbon powder - 1.2 wt. %.

- unidirectional prepreg containing the specified epoxy binder and carbon tow brand UKN-M-3K, with the ratio of components: binder - 37 wt. %, carbon fiber filler - 63 wt. %;

- products from prepreg are obtained by vacuum-autoclave molding according to a two-stage temperature-time regime: temperature 130 ° C - holding time 2 hours; temperature 180 °C - exposure 2 hours.

The disadvantages of these prototype materials are: the impossibility of forming for short-term energy-efficient modes at low temperatures of products from PCM based on them, with increased elastic-strength and impact-resistant characteristics.

The authors found that in the composition of the prototype binder, the total amount of the mixture of epoxy resins used, with an average epoxy equivalent weight of EEW = 245, accounts for a relatively small amount - 1.2 wt. % unsymmetrical disubstituted urea curing accelerator bis-(N,N'-dimethylurea)diphenylmethane (Hardener 9). The Epoxy Equivalent Weight (EEW) is used to determine the amount of curing components needed to cure and in general the higher the epoxy equivalent weight the less curing agent is required as it indicates that the active functional group content per unit weight of resin less.

Such a low content of the curing accelerator leads to an insufficient increase in the reactivity of this composition, does not contribute to a significant acceleration of the gelation process, and for these reasons, in order to obtain reliable structural products from PCM with high thermomechanical characteristics (glass transition temperature) and the degree of curing of the polymer matrix, it is necessary to use long-term energy-consuming high temperature molding. In addition, the composition of the considered prototype binder contains only 1.2 wt. % modifier of strength characteristics - silicon dioxide in the form of white carbon powder, which mainly performs the function of a regulator of viscosity characteristics, improves its thixotropy and rheological properties, gives a thickening effect, does not allow leakage of the binder from the prepreg during processing, however, such a small amount of modifier in the composition binder-prototype does not provide a significant increase in deformation resistance, growth of elastic-strength characteristics and crack resistance.

The technical problem to be solved by the invention is the insufficient amount of epoxy binders, which make it possible to obtain products with an increased level of elastic-strength characteristics and crack resistance using short-term energy-efficient modes for obtaining products from structural PCM.

The technical result achieved when solving a technical problem is to increase the reactivity of the binder, while maintaining the long-term technological viability of this binder in the prepreg at a storage temperature of 25 ° C, as well as reducing the duration and temperature of the curing of the binder and the mode of molding the prepreg based on it, while ensuring the achievement of a high value of the glass transition temperature and the degree of curing of the binder in the PCM, as well as an increase in the elastic-strength characteristics and crack resistance.

The technical problem is solved, and the technical result is achieved due to the fact that the epoxy binder for creating prepregs includes a mixture of polyepoxy resin, low molecular weight and high molecular weight epoxy resins, a latent hardener - dicyandiamide, a curing accelerator - asymmetrically disubstituted urea and a modifier, characterized in that as polyfunctional epoxy resin, a polyfunctional epoxy resin is used selected from a homologous series of epoxy resins based on triphenols, epoxy novolac resins and halogen-containing epoxy resins, and as a modifier, rubber nanoparticles of the "core-shell" type are used, consisting of a core of a copolymer of butadiene and styrene and a shell of an alkyl methacrylate polymer with the following ratio of components, wt. %:

- polyfunctional epoxy resin 34.9 - 38.5 - low molecular weight epoxy resin 17.0 - 22.0 - high molecular weight epoxy resin 25.0 - 29.3 - latent hardener dicyandiamide 7.8 - 10.5 - accelerator unsymmetrically disubstituted urea 2.4 - 3.2 - rubber nanoparticles of the "core-shell" type 4.4 - 5.2

To achieve a technical result, a prepreg is also proposed, including the specified epoxy binder and fibrous filler, in the following ratio of components, wt. %:

- epoxy binder 30.0 - 50.0 - fibrous filler 50.0 - 70.0.

Fibrous glass, carbon and organic fillers can be used as fibrous filler.

The product is made by direct pressing, vacuum or autoclave molding of a prepreg from the declared binder.

The composition of the proposed epoxy binder and the optimal balanced amount of the components used ensure its increased reactivity and prepregs based on it, and also contributes to the formation of PCM products based on it with improved elastic-strength and impact-resistant characteristics.

To create an epoxy binder as a polyfunctional epoxy resin in the invention, one of the resins selected from the following groups can be used: a homologous series of epoxy resins based on triphenols (for example, triglycidyl ether of triphenylmethane, an ETF brand resin, manufactured by OOO NPP Makromer), etc., a homologous a number of epoxy novolac resins (for example, based on phenol-formaldehyde oligomers of the novolac type, EN-6 and UP-643 resins, manufactured by Doros Enterprise LLC), etc., a homologous series of halogen-containing epoxy resins (for example, N,N-tetraglycidyl derivative 3.3 -dichloro-4,4-diaminodiphenylmethane resin brand EHD, manufactured by CJSC Himex Limited), etc.

The low molecular weight epoxy resin is selected from the following epoxy resins: for example, Araldite GY 250 brand resin (manufactured by Huntsman Advanced Materials), D.E.R. 330 (manufacturer Olin), resin brand ED-20 (manufacturer Ya.M. Sverdlov Plant) or resin brand NPEL128 (manufacturer Nan Ya Plastics Corporation), etc.

The high molecular weight epoxy resin is selected from the following epoxy resins: for example, YD-011 brand resin (manufactured by KUKDO Chemical Co., Ltd), NPES-901 brand resin (manufactured by Nan Ya Plastics Corporation), Araldite GT 7071 brand resin (manufactured by Huntsman Advanced Materials ) or resin grade E-40 (manufactured by OAO Kotovsky LKZ), etc.

As the hardener of the proposed binder, a latent amine-type hardener dicyandiamide is used, selected from the group of components with trademarks Dyhard 100S (manufacturer AlzChem), DICY 7 (manufacturer Japan Epoxy Resins) or Amicure CG1400 (manufacturer CVC Thermoset Specialties), etc.

The accelerator of the proposed binder is unsymmetrically disubstituted urea, which can be selected from a number of products with trademarks: bis-(N,N-dimethylcarbamide)-4-methylbenzene, AlzChem manufacturer), Dyhard URAcc 57 (AlzChem manufacturer), Dyhard URAcc 13 (AlzChem manufacturer), etc.

The role of the modifier in the claimed binder is performed by rubber nanoparticles of the "core-shell" type, consisting of a core of a copolymer of butadiene and styrene and a shell of an alkyl methacrylate polymer, which is selected from a number of products with the trademarks Paraloid EXL-2655 (manufactured by Dow Chemicals), Paraloid EXL-2691 (manufacturer Dow Chemicals) or Clearstrength XT100 (manufacturer Arkema S.A).

Unlike the prototype, the proposed binder contains a large amount of curing accelerator - asymmetrically disubstituted urea (2.4 ÷ 3.2 wt. % of the accelerator is introduced for the total amount of the mixture of epoxy resins used, with an average epoxy equivalent weight EEW = 244 ÷ 322), due to which increases the catalytic activity of the curing system, intensifies the gelling process of the binder, and achieves a high degree of curing when using an accelerated low-temperature, energy-efficient molding mode, but at the same time, the long-term technological viability of the binder in the prepreg at a storage temperature of 25 °C is maintained and PCM is formed with a high glass transition temperature of the polymer matrix .

The modifier in the proposed binder is rubber nanoparticles of the "core-shell" type, which are evenly distributed in the formed polymer matrix, forming phase microdomains in the form of a rubber-like material. Under critical loading of such structures, the deformation energy leads to cavitation of the core of rubber nanoparticles, which contributes to their significant absorption of the energy of destruction upon impact, and interrupts further destructive action, demonstrating the effectiveness of the modifier used to increase impact strength.

Implementation examples.

Preparation of the claimed epoxy binder.

Example 1 (Table 1).

In a clean and dry reactor is loaded 17.0 wt. % low molecular weight epoxy resin brand GY250, 29.3 wt. % high molecular weight epoxy resin brand GT7071, 4.2 wt. % rubber containing component brand Paraloid EXL-2655 and with the mixer running, the mixture is heated to a temperature of 100 °C. The reaction mixture is stirred at a speed of 250 rpm at a temperature of 100 °C until the components are completely combined.

Then, with the stirrer running, 7.8 wt. % dicyandiamide brand Dyhard 100S, while the stirrer speed is increased to 400 rpm. Stirring is carried out until a homogeneous mass is obtained.

The temperature is reduced to 80 °C and 3.2 wt. % Dyhard URAcc 57 unsymmetrically disubstituted urea curing accelerator with stirring at 250 rpm for at least 60 minutes until a completely homogeneous mass is obtained. After mixing, the finished binder is drained through the drain fitting into a dry and clean container.

The manufacture of epoxy binders according to examples 2 - 6 (table. 1) is carried out analogously to example 1.

Obtaining the declared prepreg.

Example 1 (Table 2).

The manufacture of the prepreg is carried out by applying 30 wt. % epoxy binder, prepared according to the recipe of example 1 (table. 1), by means of an impregnating machine at a temperature of 70 ° C on a carbon tow of the UMT42S-3K-EP brand in the amount of 70 wt. %.

Prepregs for examples 4, 6 were made using carbon tow brand UMT42S-3K-EP, for examples 2, 5 using glass roving brand T30 SE 1200 17-600 C-F, for example 3 using aramid fabric brand CBM art. 56313.

Manufacture of the claimed product.

Example 1 (Table 3).

A prepreg based on a binder and a carbon tow of the UMT42S-3K-EP brand, obtained according to the recipe of example 1 (Table 2), was cut according to templates, the cut blanks were laid out on a mold, and a technological package was assembled. The manufacture of the product (tennis racket body) was carried out by the method of vacuum-autoclave molding of the resulting technological package at an overpressure of 0.6-0.7 MPa, according to the temperature regime: 30 minutes at a temperature of (130 ± 5) °C.

Example 2 (Table 3).

From the cut prepreg based on binder and glass roving brand T30 SE 1200 17-600 C-F, obtained according to the recipe of example 2 (Table 2), a technological package was formed, which was placed in a mold, where the product (stick handle) was molded by direct pressing by heating molds on a thermosetting press at a temperature of (130 ± 5) °C for 30 ± 5 minutes and a pressure of 4-6 atm.

Example 3 (Table 3).

From cut prepreg based on binder and aramid fabric brand SVM art. 56313, obtained according to the recipe of example 3 (table 2), formed a technological package. The product (ski boot cuff) was manufactured by vacuum forming the resulting prepreg at a pressure of 0.095 MPa, according to the temperature regime: 30 minutes at a temperature of (130 ± 5) °C.

Also, products were made from prepregs according to examples 1 - 6 (Table 2):

- according to the technology similar to example 1 (by the method of vacuum autoclave molding): according to example 4 - skis for a snowmobile;

- according to the technology similar to example 2 (direct pressing method): according to example 5 - the walls of the mobile phone case;

- according to the technology similar to example 3 (vacuum forming method): according to example 6 - the lower knee of the spinning rod.

The compositions of the binders according to the invention and the prototype are shown in table 1, the compositions of the prepregs according to the invention and the prototype in table 2, the properties of the binders according to the claimed invention and the prototype, prepregs and PCMs made on their basis in table 3. The invention is not limited to the examples given.

Table 1. The composition of the epoxy binder prototype and the claimed invention.

Binder components The composition of the examples, wt. % Prototype
RU2263690 one 2 3 four 5 6 Polyepoxy resin / epoxy equivalent. the weight ETF/221 46.1 - - - - - 34.9 UP-643/195 - - 37.8 - - 36.3 - EHD/154 - - - 37.0 - - - EN-6/239 - 38.5 - - 36.0 - Epoxy
resin Low molecular weight resin grade / epoxy equivalent. the weight ED-20/215 40.5 - - - - - 22.0 GY 250/185 - 17.0 - - 20.5 - - NPEL128/
185 - - 17.9 - - - - DER 330/170 - - - 19.5 - 20.7 - High molecular weight resin grade / epoxy equivalent. the weight E-40/307 3.5 - - - - - 25.0 GT7071/510 - 29.3 - - - 25.4 - YD-011/450 - - 28.6 - 26.4 - - NPES-901/500 - - - 27.3 - - - Latent hardener dicyandiamide DCDA 7.5 - - - - - Dyhard 100S - 7.8 - - 10.1 - DICY 7 - - 8.3 - 9.6 - Amicure CG1400 - - - 8.8 - - 10.5 Accelerator unsymmetrically disubstituted urea Hardener 9 1.2 - - - - 2.5 - Dyhard UR-500 - - - - 2.7 - 2.4 Dyhard
URAcc 57 - 3.2 - 2.8 - - - Dyhard
URAcc 13 - - 3.0 - - - Modifier white soot 1.2 - - - - - - Paraloid EXL 2655 - 4.2 - 4.6 - 5.0 - Paraloid EXL 2691 Clearstrength XT100 - - 4.4 - 4.8 - 5.2

Table 2. The composition of the prototype prepreg and the claimed invention.

Name of components Prototype
RU2263690 Composition according to examples, wt.% one 2 3 four 5 6 Binder 37 thirty 45 40 43 37 fifty Carbon bundle brand UKN-M-3K 63 - - - - - - Carbon bundle brand UMT42S-3K-EP - 70 - - 57 - fifty Glass roving brand T30 SE 1200 17-600 C-F - - 55 - - 63 - Aramid fabric brand SVM art. 56313 - - - 60 - - -

Table 3. Properties of the binder of the claimed invention and the prototype, prepregs and PCMs made on their basis.

Name of characteristics No. of examples Prototype
RU2263690 one 2 3 four 5 6 Average epoxy equivalent weight, EEW, g/eq. 245 322 288 244 312 280 253 Binder gelation time at 120 °C, τ, min 7 6 6 5 four four 95 Viability of the binder in the prepreg during its storage at a temperature of 25 °C, at least days (technological viability of the prepreg) 33 35 35 40 38 40 90

, % .
Формование по режиму:The degree of curing of the binder in the PCM sample,

, %.
Forming by mode: single-stage - temperature 130 °C exposure 0.5 h 96.3 96.0 95.9 96.8 96.1 96.5 54.1 two-stage - temperature 130 °С holding time 2.0 h, temperature 180 °С holding time 2.0 h 97.5 97.1 97.6 98.3 98.1 98.5 95.7 Sample glass transition temperature
PKM, Tg dry, ^o C.
Forming by mode: single-stage - temperature 130 °C exposure 0.5 h 135 135 135 137 135 136 64 two-stage - temperature 130 °С holding time 2.0 h, temperature 180 °С holding time 2.0 h 176 175 174 175 174 175 135 Tensile strength of samples
PCM under compression (0°) σ _com , MPa.
Forming by mode: single-stage - temperature 130 °C exposure 0.5 h 1230 1220 1210 1210 1240 1230 -* two-stage - temperature 130 °С holding time 2.0 h, temperature 180 °С holding time 2.0 h 1320 1400 1370 1410 1390 1380 1100 Crack resistance of specimens
RMB in fashion I, G_1c(0°), J/m² _.
Forming by mode: single-stage - temperature 130 °C exposure 0.5 h 173 180 172 176 175 173 -* two-stage - temperature 130 °С holding time 2.0 h, temperature 180 °С holding time 2.0 h 175 180 176 174 175 172 125 *- due to the expectation of low strength indicators, the samples were not tested

Analysis and comparison of data from table 3 shows that the proposed epoxy binder has clear advantages over the prototype:

- is characterized by increased reactivity, since at a research temperature of 120 ° C it has a shorter gelation time τ ₁₂₀ ° _C = 4 ÷ 7 minutes, in comparison with the prototype binder, in which this process takes 14 times longer - τ ₁₂₀ ° _C = 95 minutes. However, such a high reactivity does not lead to a significant decrease in the technological viability of the binder in the prepreg during its storage at a temperature of 25 ° C, and its indicator is at least 35 days, which makes it possible to ensure the creation of long-lived prepregs that can be transported to their consumer and stored until the moment of processing, without the use of refrigeration equipment;

= 95,9 ÷ 96,8 %, а температура стеклования, которая характеризует степень сшивки сформированной полимерной матрицы в ПКМ, соответствует значениям - Tgdry= 135÷137 °С. Достигнуть близкие значения этих физико-химических показателей (степень отверждения связующего в образце ПКМ

= 95,7 % и температура стеклования образцов ПКМ Tgdry= 135 °С) у образцов ПКМ сформированных из рассматриваемого связующего- прототипа и препрега на его основе возможно только при использовании более длительного высокотемпературного двухступенчатого режима формования: - температура 130 °С выдержка 2,0 ч, температура 180 °С выдержка 2,0 ч ;- prepregs based on it make it possible to mold products from PCM according to the accelerated low-temperature, energy-efficient, low-cost one-stage curing mode: temperature 130°C - holding time 0.5 h.

= 95.9 ÷ 96.8%, and the glass transition temperature, which characterizes the degree of crosslinking of the formed polymer matrix in PCM, corresponds to the values - Tgdry= 135÷137 °С. To achieve close values of these physical and chemical parameters (the degree of curing of the binder in the PCM sample

= 95.7% and the glass transition temperature of PCM samples Tgdry = 135 °C) for PCM samples formed from the prototype binder under consideration and prepreg based on it is possible only when using a longer high-temperature two-stage molding mode: - temperature 130 °C exposure 2.0 h, temperature 180 °C exposure 2.0 h;

- forms products from PCM with increased elastic-strength characteristics and increased resistance to impact loads, since they are characterized by higher values of the crack resistance index of samples G _1c =172÷180 J/m ² , which is one of the criteria for assessing the resistance to impact fracture of the material and indicator of the ultimate strength of samples in compression σ _com = 1210÷1240 MPa, which is an indicator of the deformation resistance of the material. The values of the crack resistance index of PCM specimens based on the proposed materials exceed this index for the prototype specimens (G _1c =125 J/m ² ) by more than 38%, and the compressive strength index by more than 10% (for the prototype σ _com = 1110 MPa ).

Thus, the claimed epoxy binder and a prepreg made on its basis are capable of forming PCM products using energy-efficient low-cost modes, which are characterized by increased elastic-strength characteristics and crack resistance. This makes it possible to ensure significant efficiency and cost-effectiveness of production, shorten the technological cycle and reduce the labor intensity of manufacturing products from PCM, providing cost savings and increasing productivity without increasing production space, as well as creating products from PCM with a guarantee of long-term and reliable operation under conditions of critical mechanical and shock loads.

Claims (10)

1. An epoxy binder for structural polymer composite materials, including a mixture of polyepoxy resin, low molecular weight and high molecular weight epoxy resins, a latent hardener - dicyandiamide, a curing accelerator - asymmetrically disubstituted urea and a modifier, characterized in that a polyfunctional epoxy resin is used as a polyepoxy resin, selected from a homologous series of epoxy resins based on triphenols, epoxy novolac resins and halogen-containing epoxy resins, and as a modifier, rubber nanoparticles of the "core-shell" type are used, consisting of a core of a copolymer of butadiene and styrene and a shell of an alkyl methacrylate polymer, with the following ratio of components, wt. %: polyfunctional epoxy resin 34.9-38.5 low molecular weight epoxy resin 17.0-22.0 high molecular weight epoxy resin 25.0-29.3 latent hardener dicyandiamide 7.8-10.5 accelerator unsymmetrically disubstituted urea 2.4-3.2 rubber nanoparticles of the "core-shell" type 4.4-5.2 2. A prepreg comprising an epoxy binder according to claim 1 and a fibrous filler. 3. Prepreg according to claim. 2, characterized in that it contains components in the following ratio, wt. %: epoxy binder 30.0-50.0 fiberfill 50.0-70.0 4. Prepreg according to any one of paragraphs. 2 or 3, characterized in that it contains a fibrous carbon filler as a fibrous filler. 5. Prepreg according to any one of paragraphs. 2 or 3, characterized in that it contains a fibrous glass filler as a fibrous filler. 6. Prepreg according to any one of paragraphs. 2 or 3, characterized in that it contains a fibrous organ filler as a fibrous filler. 7. Product, characterized in that it is made by vacuum forming a prepreg according to any one of paragraphs. 2-6. 8. Product, characterized in that it is made by direct pressing prepreg according to any one of paragraphs. 2-6.