EP1799753A1

EP1799753A1 - Pre-impregnated sheet with bound fibers

Info

Publication number: EP1799753A1
Application number: EP05850638A
Authority: EP
Inventors: Claude Choudin; François ROEDERER
Original assignee: Saint Gobain Vetrotex France SA
Current assignee: Saint Gobain Adfors SAS
Priority date: 2004-10-07
Filing date: 2005-09-27
Publication date: 2007-06-27
Also published as: MX2007004053A; WO2006042984A1; BRPI0516258A; FR2876381A1; JP2008516038A; CN101039992A; EA200700802A1; FR2876381B1; US20080054530A1

Abstract

The invention concerns a pre-impregnated sheet material comprising a thermosetting resin and a fibrous structure bound with a soluble solvent in said thermosetting resin. During the hot-process and pressurized production of the composite material, the binder is solubilized and releases the fibers of the fibrous structure which may then creep and fill up the entire composite-manufacturing mould. A fibrous structure with continuous fibers or chopped fibers may be used, The binder enables the fibrous structure to be manipulated, wound and stored before it is incorporated into a pre-impregnated material.

Description

PREIMPREGNE SHEET WITH BONDED THREADS

The invention relates to the preparation of a prepreg sheet reinforced with cut or continuous son and its transformation into a composite material.

A sheet prepreg (SMC) is an assembly comprising a reinforcement and a thermosetting resin paste, said assembly being intended to be converted during a hot molding step into a piece of material. composite. Molding from an SMC is usually done as follows: a SMC sheet cut into the mold is cut according to the shape of the final part, but only represents part of the final total area, then - The hot sheet is pressed to fluidize and then harden the resin, the pressing being sufficient to flush the softened SMC so that it fills the entire inner surface of the mold.

The reinforcement is, according to the prior art, usually cut wire that is cut directly above a resin paste during the manufacture of the SMC. In the mold, the SMC is pressurized and must flow easily to fill the entire volume of the mold under the effect of pressure. For the skilled person, this creep is possible because the son are cut and unbound and can easily move relative to each other. The surface of SMC before pressing represents only a part of the surface of the final composite. We reach the entire surface under the effect of pressing. According to the prior art, to prepare a

SMC, cut yarns are projected on a moving sheet of resin-based paste, and another sheet of dough is put on top to trap the cut yarns as in a sandwich. The SMC is then rolled up and stored. It is rolled out to cut a workpiece (generally called a "prepreg blank") whose surface only represents a portion of the surface of the final workpiece, the workpiece is placed in a mold, and the workpiece is hot-molded. in press. The thermosetting resin cures during this treatment.

A manufacturing facility of SMC is therefore necessarily quite complex because it necessarily includes a cutter to cut the thread over- above the dough. However, it may be desirable to prepare the reinforcement at a site specialized in wire cutting, and assemble it in the SMC on a site specialized in the assembly of SMC. One can imagine preparing cut wire in one place and transport it to another to distribute it over a sheet of resin paste. However, handling cut threads is particularly difficult. The applicant then discovered that one could prepare a bonded son mat at first, then assemble said mat in a SMC, if necessary after a certain period of storage. This is made possible by the use of a binder to give consistency to the mat and to be able to wind, store and handle it, said binder being soluble in the thermosetting resin which makes it lose its binder character for the molding of the SMC. This disappearance of the binder allows the SMC to flow satisfactorily during the molding operation.

The reinforcement may for example comprise glass son. In particular, all the layers of the structure according to the invention may be made of glass fibers. Generally, the usable glass yarn is sized in a manner known to those skilled in the art. It is possible to use a glass yarn sized at 0.04 to 3% by weight and in particular from 1 to 2% by weight.

The material constituting the son may comprise a fibrable glass such as glass E or the glass described in FR2768144 or an alkaline-resistant glass called AR glass, which comprises at least 5% by mole of ZrO ₂ . In particular, the use of AR glass leads to a mat that effectively reinforces the cement matrices or can reinforce the thermosetting matrix composites that come into contact with a corrosive environment. The glass can also be free of boron.

The reinforcement may comprise cut son or continuous son. The reinforcement may comprise several layers of different yarns, for example a layer of continuous yarns and a layer of cut yarns.

The fibrous structure may comprise a central layer of continuous yarns placed between two layers of cut yarns. These two layers of cut son may be identical or different.

The manufacture of continuous wire mats has in particular been described in WO 98/10131 and WO 02/084005. The production of fibrous structures with several layers has been described in particular in WO 03/060218. We can use techniques described in these references for producing a mat or fibrous structure comprising a mat, since a binder soluble in the thermosetting resin used during the molding step is used as binder.

In the context of the present invention, it has furthermore been found that not only cut yarns but continuous yarns can be used in the context of SMC technology. Indeed, unexpectedly, the web of continuous son can flow sufficiently during the pressing of the SMC. While according to the prior art, no mat of cut son is used for SMC application (since the cut threads are projected and that one does not isolate a mat in an intermediate stage), it has now It was discovered that a continuous-wire mat could be used as part of the MSC technique.

The use of continuous filaments in SMC also leads to unexpected advantages in terms of the surface appearance and more particularly of the edge of the final composites, and in terms of the homogeneity of the distribution of the fibers in the final composite. Indeed the plaintiff discovered that the edge of the molded parts was much cleaner, smoother and better formed than when cut son were used. While this explanation can not limit the scope of the present application, it appears that the use of cut son implies that a large amount of cut ends son is found on the surface or just below the surface of the songs of parts . This phenomenon originates from the fact that the cut yarns naturally have an orientation parallel to the main faces of the composite. This accumulation of ends of son cut to the songs seems to favor the presence of porosity to the songs at the beginning of the process. The bubbles formed then expand under the effect of the temperature (of the order of 200 ° C for the solidification of the thermosetting resin), which tends to deform the appearance of the surface of the songs. It seems that the use of continuous threads considerably reduces this phenomenon. Indeed, instead of a wire end to the surface (case of the use of cut son), it will rather be a loop of continuous wire, which goes in the direction of a smoother surface. In addition, when cut wire is used, the necessary creep of the SMC during molding leads to a preferential orientation of the wires, which can lead to surface ripples. Indeed, as the cut son are independent, they too easily follow the flow and are oriented according to the flow lines. The wires can even agglomerate or form packets by following these flows too much. On the contrary, continuous yarns resist any orientation because of their length, while sufficiently following the expansion of the MSC during the pressing. As a result, the use of continuous wire leads to a better homogeneity of the reinforcement of the composite. At the same fiber rate, the use of continuous yarn generally leads to a composite having a rigidity greater than 5 to 12% in comparison with a use of cut yarn. The use of the continuous son also allows to make a thinner piece without degrading the surface appearance or mechanical properties: the son is not cut surface appearance is better (as already explained above). Finally, the Applicant has discovered that the mat with continuous yarn strengthens the piece in its thickness and not just in a plane (cut wire case), hence obtaining superior mechanical properties, such as breaking stress.

According to the invention, use is made of a fibrous structure comprising at least one mat with cut or continuous yarns bonded with a binder, said binder being soluble in the thermosetting resin at the latest during the molding, this solubilization being able to begin as soon as the mat is in contact with the mat. and and the thermosetting resin paste.

The invention particularly relates to a process for preparing a sheet prepreg comprising the combination of a thermosetting resin and a fibrous structure bound by a soluble binder in said thermosetting resin. In particular, the fibrous structure can be unwound continuously to be integrated continuously between two layers of thermosetting resin paste.

Remember that mats and felts are clearly differentiated to the extent that a mat is a flat object, usable as a reinforcement, while a felt is an object with volume, usable in thermal insulation. A mat generally has a thickness ranging from 0.8 to 5 mm, and more generally from 1 to 3 mm, whereas a felt is much thicker, and generally has a thickness greater than 1 cm. A felt usually has a density ranging from 85 to 130 kg / m ³ . A mat is much denser since its density can be of the order of 300 kg / m ³ . However, as a plane reinforcement, one never expresses the density of a mat in density but in mass per unit area. A fibrous structure for reinforcing composite materials by SMC technology should preferably have the following properties:

- have sufficient cohesion to be rollable, unwinding (for storage and transport), - do not prick hands when handling,

- be impregnated by the SMC resin (generally of the polyester type and sometimes of the epoxy type) as easily as possible,

- strengthen the composite as much as possible. The final composite should generally have the best impact resistance possible, the least uncontrolled porosity possible (no gas bubbles involuntarily trapped), and the best possible surface appearance, including the edge (narrow face) of the final pieces.

In the context of the present application, the fibrous structure (which may only be a mat) comprising the mat is chemically bonded. To do this, it has been applied a chemical binder of the thermoplastic or thermosetting type, generally powder, and then proceeds to a heat treatment that melts the thermoplastic or hardens the thermosetting (by polymerization and / or crosslinking) and finally after cooling creates bridges between the wires. The binder may be used in liquid form (which includes solution, emulsion, suspension), deposited by a cascade or spray type device, or in powder form, deposited by a powder dispenser, or in the form of a film.

In general, the binder can be used in the form of a powder, which can be sprayed onto the layer or structure to be bonded. This binder may also be used in the form of a film placed between the layers to be bonded. A suitable heat treatment then melts and eventually harden a compound of the binder so that it permeates the different points it must connect. For the case where the binder comprises a thermoplastic polymer, the heat treatment melts the polymer so that it impregnates different parts of the structure, the return to ambient temperature resulting in a solid bridging between the different points to be connected. . In the case where the binder comprises a thermosetting compound (in particular a polymer), the heat treatment causes this compound to crosslink and / or polymerize (if appropriate after melting) so that it connects the different locations by means of solid bridges. connect. In both cases (thermoplastic or thermosetting binder), the heat treatment is also used to evaporate any solvent used for its application. The chemical compound may be a polyester resin of the type thermosetting or thermoplastic. As crosslinkable binder (thermosetting), it is possible to use an acrylic polymer.

The different layers of the fibrous structure are interconnected by the binder. The entire final fibrous structure (ready for use in the SMC application) may comprise 0.5 to 15% and even 1 to 10% by weight of binder.

The nature of the binder may vary depending on the nature of the thermosetting resin, since a characteristic of the binder is to be soluble in the resin during SMC molding, in order to release the wires from each other and allow creep into the mold. The binder is at least soluble in the thermosetting resin at the curing temperature of said thermosetting resin. However, the binder can already be solubilized in this resin from its contact with the thermosetting resin paste at room temperature. Generally, the binder solubilizes sufficiently between 50 ° C and 200 ° C in the thermosetting resin. The thermosetting resin generally cures at 150 to 300 ° C.

When the thermosetting resin is a polyester, it is possible in particular to use as binder a polyester, in particular of the thermoplastic type. In particular, a high molecular weight unsaturated bisphenol polyester may be used.

The fibrous structure is integrated in a sheet prepreg (SMC). The fibrous structure is then inserted continuously between two layers of thermosetting resin paste. This structure is unrolled and integrated directly between two layers of resin paste. In addition to said structure, it is not excluded to add other reinforcing layers in the SMC, such as cut son, especially glass. For example, we can proceed as follows:

- running horizontally of the fibrous structure on a first layer of resin paste, then

- Throwing son cut on said structure, then - unwinding a second layer of resin paste on the cut son.

One can also put a layer of cut son before unrolling the fibrous structure. The SMC sheet generally comprises about 90 to 50 and more particularly 80 to 60% by weight of thermosetting resin, the remainder being constituted by the fibrous structure which comprises the fibers and their size and the binder. The prepreg sheet may be wound, stored and handled in the same manner as the prepreg sheets of the prior art.

The SMC sheet may be used to manufacture a composite material by molding the sheet by pressing on its main faces leading to an expansion of the sheet in the mold before solidification of the resin. Before molding, the cut SMC sheet generally has a surface area of from 20 to 80% of the surface of the final piece. For the case where the fibrous structure comprises a layer with continuous yarns, the cut SMC sheet has, before molding under pressure, preferably a surface representing 40 to 80% of the surface of the mold (and therefore of the surface of the final piece ). If the SMC comprises only cut yarns, the cut SMC sheet may have, before molding under pressure, a surface area representing 20 to 80% and more generally 25 to 40% of the surface of the mold (and thus the surface area of the mold). final piece).

EXAMPLES: Two series of sheet prepregs were made comprising 23% glass fibers and 77% polyester resin paste, one with glass in cut wires (50 mm length), the other with glass in continuous threads. Prior to insertion into the SMC, the fibrous structures were bound as a mat by an unsaturated bisphenol polyester. Rectangular pieces representing 40% of the surface of the final article are cut and placed in an SMC mold. Pressurized hot molding is carried out. The creep lasts 3 seconds. After demolding, it is observed that the pieces are well formed. Continuous-wire parts have ten times less surface porosity than cut-wire parts (by visual observation: possible presence of blisters or punctures). Furthermore, in 3-point flexion (Afnor 50 705 standard) the following breaking stresses were obtained: Cut yarns: 175 MPa Continuous yarns: 185 MPa.

Claims

A process for preparing a sheet prepreg comprising the combination of a thermosetting resin and a binder structure bound by a binder soluble in said thermosetting resin.

2. Method according to the preceding claim characterized in that the fibrous structure is unwound continuously to be integrated continuously between two layers of thermosetting resin paste.

3. Method according to one of the preceding claims, characterized in that the fibrous structure comprises a layer of continuous son.

4. Method according to one of the preceding claims characterized in that the fibrous structure comprises glass son.

5. Method according to one of the preceding claims, characterized in that the binder is thermoplastic.

6. Prepreg sheet comprising a thermosetting resin and a fibrous structure bound by a binder soluble in said thermosetting resin.

7. Sheet according to the preceding claim, characterized in that the fibrous structure comprises a layer of continuous son.

8. Sheet according to one of the two preceding claims, characterized in that the fibrous structure comprises glass son.

9. Sheet according to one of the preceding claims of sheet, characterized in that the thermosetting resin is a polyester and in that the binder is a polyester.

10. Sheet according to one of the preceding sheet claims, characterized in that the binder is a thermoplastic.

1. Sheet according to one of the preceding claims of sheet, in the form of a roll.

A method of manufacturing a thermoset matrix composite material comprising press-molding a sheet of one of the preceding sheet claims.

13. Method according to the preceding claim, characterized in that before molding, the sheet represents only 20 to 80% of the surface of the final composite material.

14. Method according to the preceding claim characterized in that the fibrous structure comprises a layer of continuous son and in that the surface of the sheet represents 40 to 80% of the surface of the final composite material.