WO1990014383A1

WO1990014383A1 - Process for manufacturing a prepreg for use as a reinforcing inlay and use of said prepreg

Info

Publication number: WO1990014383A1
Application number: PCT/AT1990/000048
Authority: WO
Inventors: Walter Eichberger
Original assignee: ISOVOLTA Österreichische Isolierstoffwerke Aktiengesellschaft
Priority date: 1989-05-18
Filing date: 1990-05-18
Publication date: 1990-11-29
Also published as: AU5664390A; EP0431088A1; AT392646B; ATA120289A

Abstract

To manufacture a reinforcing prepreg, a woven fabric or a layer of high-strength reinforcing fibres, in particular a glass fibre woven fabric or layer of glass fibres with a basis weight between 150 and 1000 g/m2, preferably between 200 and 800 g/m2, is impregnated with a curable synthetic resin mixture containing a blowing agent which can be activated at high temperatures. The synthetic resin mixture is then heated - to remove the solvent, to lower the viscosity or possibly to subsequently raise the viscosity by a preliminary reaction - in such a manner that the blowing agent does not foam. This occurs, in particular, when the mixture is heated to temperatures below the temperature at which the half-life of the blowing agent is equal to 0.1 h. To manufacture laminated plastic products, the prepreg is placed in a mould, together with other starting materials; the prepreg foams to only 1.1 to 5 times, preferably 1.2 to 3 times, its original volume, filling any remaining voids in the mould cavity or pressing the surface layers against the inner surface of the mould cavity, while still retaining its reinforcing function.

Description

Process for producing a prepreg intended as a reinforcing insert and use of this prepreg.

Technical field

The invention relates to a method for producing a prepreg intended as a reinforcing insert, consisting of a fabric or scrim made of high-strength reinforcing fibers as the carrier material, which is impregnated with an optionally solvent-containing, curable synthetic resin mixture. The invention further relates to an advantageous use of the prepreg according to the invention in the production of a body by curing in a mold.

State of the art

A known semi-finished product of this type is e.g. a glass fiber fabric impregnated with an epoxy resin hardener mixture, commonly referred to as a "prepreg". Such prepregs are e.g. used for the production of tennis rackets. Blanks from these prepregs are wrapped around a tube to form a layer and - together with other curable, fiber-reinforced plastic pieces used to build the racket - inserted into a mold. This wound hose runs along the ski frame and is double-guided in the grip zone. The tube is then inflated and presses its prepreg wrapping against the inner surface of the mold. The fiber-reinforced epoxy resin introduced into the mold is then cured to the tennis racket body at elevated temperature, after which the tube is vented and pulled out of the tennis racket body.

In such a tennis racket manufacturer, however, because the cross-section of the racket frame is essentially rectangular and also has flat ribs at the corners, the problem arises that the pressure with which the prepreg is wound against the inner surface of the mold is pressed, is not inconsiderably less on the ribs than in the other areas. ^■ 2 -

However, this can lead to an unfavorable distribution of resin and fiber reinforcement over the circumference of the frame.

Presentation of the invention

The invention is first of all based on the object of specifying a prepreg as a reinforcing insert made of a fabric or scrim made of high-strength reinforcing fibers as the carrier material, which is impregnated with a synthetic resin mixture which may be present as a solution, which is used in the production of objects which are used manufactures in a mold at elevated temperature with the purpose of achieving the best possible distribution of the material in the mold, but the reinforcing function of the prepreg is retained.

This object is achieved in the process according to the invention for producing a prepreg, which is characterized in that the synthetic resin mixture used for impregnation contains a blowing agent which can be activated at elevated temperature and in that the synthetic resin mixture on or in the carrier material during and / or after the impregnation or Coating is heated without foaming the synthetic resin mixture by activating the blowing agent. In this case, heating advantageously takes place to temperatures which are lower than the temperatures at which the half-life of the blowing agent is 0.1 h.

In an advantageous embodiment of the invention, however, said heating takes place at temperatures which are lower than the temperature at which the half-life is 0.5 h.

According to other advantageous embodiments of the method according to the invention, a synthetic resin mixture is used which consists at least for the most part of an epoxy resin and a latent hardener. The epoxy resin can advantageously at least for the most part consist of an epoxy resin based on Bisphenol-A-diglycidyl ether with an epoxy equivalent between 175 and 400 or the epoxy-hardener mixture can advantageously contain an amine hardener.

According to further advantageous embodiments of the invention, the method according to the invention is characterized in that the epoxy resin-hardener mixture contains a hardener based on dicyandiamide and optionally an accelerator or that it contains a hardener based on aromatic amines and an accelerator, if appropriate Contains boron trifluoride-A i nkomplex.

According to other advantageous refinements of the method according to the invention, a glass fiber fabric or scrim with a surface weight between 150 to 1000 g / m ^z , preferably between 200 to 800 g / m ^z , or a laid and needled fiber mat, in particular a glass fiber mat, is used as the carrier material used.

According to other advantageous embodiments of the method according to the invention, at least the major part of the solvent contained in the synthetic resin mixture is driven off by the said heating and / or it initially lowers the viscosity of the synthetic resin mixture and, if necessary, to facilitate impregnation then, after impregnation and / or coating, the viscosity of the synthetic resin mixture is increased by a preliminary reaction.

The invention is also based on the object of specifying an advantageous use of the prepregs produced by the method according to the invention in the production of a body by curing in a mold.

This object is achieved in the use according to the invention, which is characterized in that when a body is produced by curing in a mold, the mechanically load-bearing surface layers and a hollow interior Rough or has a core of lower specific weight than these mechanically supporting surface layers, that the prepreg is attached within the mold between a temporary core or permanent core which creates the later cavity and the inner surface - at least over part of the inner surface of the mold is that the materials introduced into the mold are heated thereon, so that the prepreg material foams only to 1.1 - 5 times, but preferably to 1.2 - 3 times its original volume and thereby the between Fills the core and the free space still remaining in the mold surface and that the synthetic resin mixture of the prepreg finally hardens.

According to an advantageous embodiment of the use according to the invention, a non-foamable cover layer or layer is applied between the prepreg layers and the inner surface of the mold, against which the semi-finished material foams and presses it against the inner surface of the mold, after which the foamed prepreg material during of curing with the cover layer or layer.

According to a further advantageous embodiment of the use according to the invention, the prepreg material foams onto the permanent core and bonds to it during curing.

Brief description of the drawings

^Fi 9- ¹ shows a foamable prepreg for a charak¬ teristic preparation phase a schematic partial section of the mold used, and a cross-section of the ski to be produced Tennis äger framework for the manufacture of a tennis racket frame using.

In Fig. 2 is below for the manufacture of a surfboard -5-

Use of a foamable prepreg shows a schematic cross section through the mold used in the process or the arrangement of the materials introduced into the mold.

In Fig. 3 for the manufacture of a ski, in which a foamable prepreg is used, the ski structure within a press mold is shown schematically in cross section.

Some ways of carrying out the invention

The invention is explained in more detail below with reference to the figures, which illustrate some advantageous ways of carrying out the invention in the context of several examples.

Example 1:

For the production of a semi-finished product in the form of a prepreg, an epoxy resin mixture is used, which consists of an epoxy resin with a latent hardener, as is usually used for the production of prepregs for curing temperatures between about 130 and 160 ° C. The epoxy resin used is one based on bisphenol A diglycidyl ether with an epoxy equivalent of 230, with a hardener based on dicyandiamide and an accelerator. Hardeners based on aromatic amines with an accelerator such as boron trifluoride-amine complex can also be used. 3% by weight of azobisisobutyronitrile as blowing agent, which has a half-life of 0.1 h at a temperature of 102 ° C., and 1% by weight of a nonionic wetting agent are then added to this epoxy resin mixture and finely dispersed in the resin mixture by vigorous stirring . This mixture is then diluted to the viscosity required for later processing as an impregnation solution with acetone.

A glass fiber fabric in sheet form with a basis weight of 290 g / m ² is now π impregnation solution soaked and the impregnation agent applied by means of squeeze rollers. After evaporation of the acetone in a drying zone, which takes place at a temperature of 65-70 ° C for about 8 minutes, a dry or slightly sticky prepreg with a resin content of about 40% is obtained, which is coated with a release paper is rolled up as an intermediate layer.

For the production of a tennis racket, in addition to the above-described blowing agent-containing prepreg, a blowing agent-free prepreg is used, which - analogously as described above - was produced by impregnating a glass fiber fabric with a now but blowing agent-free epoxy resin hardener mixture. In the production of a tennis racket body, blanks made of the propellant-free prepreg and blanks made of the propellant-containing prepreg or other fiber-reinforced, hardenable plastic pieces provided for the construction of the tennis racket are placed on or on top of one another. This scrim is then wrapped around a tube, so that the propellant-free prepregs come to lie on the outside, and then - as already mentioned at the beginning of the description - the whole is introduced into a heated mold and the mate introduced into the mold rialien brought to a temperature of about 140 ° C. The blowing agent is activated and foams.

1 shows for this phase of the production process the mold used with the mold halves 1 and 2 and the Teπnisschäger frame to be produced with the outer region 3, which is occupied by the propellant-free prepregs, the regions 4 with the foamed propellant-containing prepregs and the inflated ones Hose 5. The pressure prevailing in hose 5 presses the hose wall and thus the prepregs of areas 3 and 4 in the direction of the mold surface 6. When the foaming agent-containing prepreg is foamed, a quantity of gas is generated which this prepreg at a free expansion (ie at 1 bar) and 140 ° C to about 6.5 times would let its original volume foam up. Since there are limits to such a free expansion due to the limited mold space, there is only a volume increase of 1.1 to 2.2 times here, the pressure in the area 4 of the prepregs containing blowing agent rises to approx. 3-6 bar, which means that in particular in the area of the ribs 9, the prepregs of area 3 are pressed against the inner surface 6 with sufficient pressure.

In an advantageous variant of this example described with reference to FIG. 1, a prepreg is used which is produced on the basis of a solvent-free epoxy resin mixture, as is usually already used today for producing prepregs in which the fibrous carrier material is elongated parallel fiber rovings arranged on a surface is formed. In this epoxy resin mixture, which consists of an epoxy resin and a latent hardener, has a viscosity of approx. 15,000 mPa.s at room temperature and can be cured well at temperatures between approx. 130 and 160 ° C, this becomes - analogous to the first variant Examples 1 to 3% by weight of Azobisi sobutyronitri 1 as a blowing agent, which has a half-life of 0.1 h at a temperature of 102 ° C., and 1% by weight of a nonionic wetting agent are finely dispersed.

In an impregnation machine designed as a so-called tape machine, the epoxy resin mixture containing blowing agent produced in this way is shaped at a temperature of 60 ° C., at which its viscosity is now approximately 700 mPa.s, by means of a heatable doctor blade device a film of a thickness of 0.25 mm evenly applied to a continuously supplied tape-shaped release film. In this thin, liquid resin film, glass fiber rovings drawn off from a creel are placed in parallel next to each other in the resin film. The weight per unit area of these parallel rovings is 360 g / m ² . The whole is then brought or maintained at temperatures between 65-70 ° C. when it is passed through a heating zone with a residence time in this zone of about 6 minutes. This is followed by a further reduction in the viscosity of the epoxy resin mixture, in which the rovings are well saturated with the resin mixture, and then a pre-reaction of the resin mixture with an associated increase in viscosity. After cooling while passing through a cooling zone, a slightly sticky, so-called unidirectional prepreg (ÜD-Pre-preg) lying on the tape-shaped separating film is finally obtained, which has a resin content of 40% by weight and which is rolled up with the tape-shaped separating film as an intermediate layer material becomes.

For the production of a tennis racket frame, in addition to the above-described blowing agent-containing UD prepreg, a UD prepreg is used which contains no blowing agent and which - like the blowing agent-containing UD prepreg - is produced using the blowing agent-free epoxy resin mixture .

The tennis racket frame is then produced in the same way as described with reference to FIG. 1.

Example 2:

This example, which relates to the use of propellant-containing prepregs in the production of a surfboard, will now be explained with reference to FIG. 2, which shows the mold with the mold halves 10 and 11 used in this method and the arrangement of the materials introduced into the mold.

For the production of the surfboard, propellant-free epoxy resin fiberglass prepregs, as they were also used according to Example 1, are first - with the upper mold half 11 raised - propellant-free in the lower mold half 10 to form a Layer 12 used, which protrudes over the edge of the mold inner surface of the lower mold half 10 at 13 brim. Thereafter, a lightweight core 14 made of polyurethane foam, which - somewhat reduced - already has approximately the final spatial shape of the surfboard to be produced, with blowing agent-containing epoxy resin glass fiber prepregs, as they were also used in Example 1, to form a foamable layer wound and the core 14 thus wound is inserted onto the layer 12 in the lower half 10. The same propellant-free prepregs as were used to form the layer 12 are then applied to this wound core 14 in a further layer 15, which also protrudes in the form of a pen at 13 on its edge. Then the mold is closed by placing the upper mold half 11.

The materials used in the mold are then heated to a temperature of 120 ° C. in the heated mold halves, the epoxy resins contained in the prepregs used flowing and the prepregs containing foaming agent foaming, the material of the layers 12 and 15 against the inner surface of the mold 16 press. The material 17 of the foaming prepregs completely fills the cavities that still exist in the molding space between the core 14 and the layer 15 and thereby compensates for any slight deviations from the ideal spatial shape of the lightweight core 14 that is used described in Example 1, produces a gas quantity which would increase to approximately 6 times if the prepreg volume were to expand freely. Since the limited space only allows an expansion to 1.5 3 times, a pressure of 2 -4 bar is generated in the foamed prepreg, with which the material of the layers 12 and 15 is pressed against the inner surface 16 of the mold. 2 shows this phase of the process sequence. The epoxy resin of the prepregs used then cures at a temperature of 130 ° C. for about 30 minutes, with all the materials used in the molding space stick together or bond intimately. The essentially finished surfboard blank is then removed from the mold and the 12 and 15 protruding and hardened layers 13 and 15 are removed by mechanical processing.

5 Example 3:

As an alternative to the expandable prepregs based on glass fiber fabrics described in Example 1, laid and needled glass fiber mats can advantageously also be used as carrier material for the blowing agent-containing epoxy resin hardener system for preparing the prepreg.

For this purpose, a glass fiber mat in sheet form with a basis weight of 500 g / m ² is impregnated in an impregnating machine with the blowing agent-containing epoxy resin mixture described in Example 1. A touch-dry or slightly tacky prepreg with a resin content of approx. 50% is obtained, which is rolled up with a release paper as an intermediate layer.

Such a prepreg can now be used in the production of surfboards, as described in Example 2, it being used instead of the epoxy resin-glass fabric prepregs containing blowing agent.

Example 4:

Another advantageous use of an epoxy resin-glass fiber prepreg containing blowing agent, which is implemented in the manufacture of a ski, will now be described with reference to FIG. 3.

In a customary ski manufacturing process, the individual ski components are connected to one another or bonded to one another in a press mold under pressure and at elevated temperature. Fig. 3 now shows, if one disregards the special components used to form the ski ends D, the ski structure incorporated in the mold. In this production process, an epoxy resin-glass fiber roving laminate 22 serving as an intermediate layer, an epoxy resin-glass fiber roving laminate 23 and a wooden core 24 stacked on top of one another. Layers 25 of a propellant-containing epoxy resin prepreg, of the type also used in Example 1, are then placed over the wooden core so that they also cover the side surfaces of the wooden core 24. In contrast to example 1, however, an approx. 700 g / m ² heavy glass fiber roving scrim is used, which is reinforced with approx. 70 g of cross-stitching and with a resin content of 40%. A shell-shaped outer shell 26, which was formed in a separate process, is now placed over the prepreg layers 25 and the mold is closed by applying the upper mold half 19. The shell-shaped outer shell used is produced in a separate manufacturing process and consists, for example, of an epoxy resin glass fabric on the inside, which is connected to a decorative, wear-resistant surface layer, such as an ABS layer, on the side that will later come to the outside.

The ski structure is then held in the mold under pressure at a temperature of about 125 ° C. for 20 minutes. The foaming agent-containing prepreg layers 25 foam and completely fill the space between the wooden core 24 and the shell-shaped outer shell 26. The pressure of the propellant, particularly on the side surfaces, creates a pressure that greatly promotes adhesion to the wood core. In the further sequence of the press cycle, while the binder or the foamed prepreg layers 25 are curing, the ski components used in the press mold are intimately connected to one another and the finished ski blank is finally joined to the press mold taken.

Commercial usability

With the aid of the plastic semifinished products containing propellant according to the invention, plastic composite bodies of the most varied types, such as tennis rackets, surfboards, skis and the like, can be produced in a simple manner and with high quality.

Claims

PATENT CLAIMS

1. A process for producing a prepreg intended as a reinforcing insert, consisting of a fabric or scrim made of high-strength reinforcing fibers as the carrier material, which is impregnated with an optionally solvent-containing, curable synthetic resin mixture, characterized in that the synthetic resin mixture used for impregnation coating in itself known manner contains a blowing agent which can be activated at elevated temperature and that the synthetic resin mixture in the carrier material is heated during and / or after the impregnation, without the synthetic resin mixture foaming by activating the blowing agent.

2. The method according to claim 1, characterized in that the heating takes place at temperatures which are lower than the temperature at which the half-life of the blowing agent is 0.1 h.

3. The method according to claim 1 or 2, characterized in that the heating takes place at temperatures which are lower than the temperature at which the half-life of the blowing agent is 0.5 h.

4. The method according to any one of claims 1 to 3, characterized ge indicates that a synthetic resin mixture is used which consists at least for the most part of an epoxy resin and a latent hardener.

5. The method according to claim 4, characterized in that the epoxy resin consists at least for the most part of an epoxy resin based on Bi sphenol -A-di glyc idyl ther with an epoxy equivalent between 175 and 400. - 1 4-

6. The method according to claim 4 or 5, characterized in that the epoxy resin-hardener mixture contains an aromatic hardener.

7. The method according to claim 6, characterized in that the epoxy resin-hardener mixture contains a hardener based on dicyandiamide and optionally an accelerator.

8. The method according to claim 6, characterized in that the epoxy resin-hardener mixture contains a hatcher based on aromatic amines and an accelerator, optionally boron tri * fluoride-amine complex.

9. The method according to any one of claims 1 to 8, characterized gekenn¬ characterized in that a glass fiber fabric or scrim with a basis weight between 150 to 1000 g / m ² , preferably between 200 - 800 g / m ^{2 is} used as the carrier material.

10. The method according to any one of claims 1 to 9, characterized gekenn¬ characterized in that a laid and needled fiber mat, in particular a glass fiber mat, is used as the carrier material.

11. The method according to any one of claims 1 to 10, characterized in that at least the major part of the solvent contained in the synthetic resin mixture is expelled by the heating.

12. The method according to any one of claims 1 to 11, characterized ge indicates that the heating initially lowers the viscosity of the synthetic resin mixture, if necessary, to facilitate impregnation, and that, if appropriate, then after impregnation has taken place, through a pre-reaction of the synthetic resin mixture Viscosity is increased.

13. Use of a prepreg manufactured according to one of claims 1 to 12 as a reinforcing insert, characterized in that, when a body is produced by curing in a mold, the mechanically load-bearing surface layers and inside a cavity or a core having a lower specific weight than these mechanically load-bearing surface layers, the prepreg is attached within the mold between a temporary core which creates the later cavity or the permanent core and the mold inner surface - at least over part of the mold inner surface - that the materials introduced into the mold are heated thereon, the prepreg material thereby foaming only to 1, 15 times, but preferably 1.2 to 3 times its original volume and thereby between the core and the Forminneπf1 fills the remaining free space and maintains its reinforcing properties oldest, and that the synthetic resin mixture of the prepreg finally hardens.

14. Use according to claim 14, characterized in that a non-foamable cover layer or layer is applied between the prepreg layers and the inner surface of the mold, against which the prepreg material foams and presses it against the inner surface of the mold and that the foamed prepreg Material bonds with the top layer or layer during curing.

15. Use according to claim 13 or 14, characterized in that the prepreg material foams onto the permanent core and connects to it during curing.