EP0745716A1 - Textile reinforcement fabric for the manufacture of composite materials - Google Patents

Abstract

The composite fibre reinforcement material, with a spring effect, is a layer of thicker fibres from a carding stage. Immediately after carding, continuous glass filaments are directed at the web surface, to lie on it in all directions. The web and filaments are mechanically bonded by needling, which draws the glass filaments through the web thickness. The web is of synthetic fibres to spring against the opposite face. The resultant material is coiled.

Description

The invention relates to an improvement made to the textile reinforcements used for the production of composite materials, that is to say arides of resin-based artides (polyester or others) armed with a textile reinforcement ply.

To date, depending on the applications and the characteristics sought, the reinforcing structures used in the field of composites are, for example fabrics, textile grids, unidirectional, bidirectional filament plies, or a combination of such elements.

In its French patent 2,646,442, the Applicant proposed a textile reinforcement which is particularly suitable for producing thick reinforcements, a characteristic necessary when it is desired to produce elements such as vehicle bodywork, pleasure boats, tanks, etc., which must have great rigidity. Such a frame is constituted by at least two layers of textile reinforcement proper, arranged on either side of a central layer giving the thickness to said material, and it is characterized in that said central layer consists of a ply based on synthetic fibers, of high unit strength, and which have received, prior to their forming in the form of plies, a treatment imparting to them a permanent waving or crimping, the different layers being linked together in particular by sewing / knitting.

Such a complex is entirely satisfactory with regard to the mechanical characteristics presented by the composite structures which it makes it possible to produce.

Furthermore, it is particularly suitable for producing structures of complex shape obtained by molding, for example according to the techniques known as "press molding with injection" or "vacuum molding".

For certain applications, it has however been observed that there could be risks of delamination in the area forming an interface between the central layer giving the thickness of the material and the surface layers giving the mechanical characteristics.

However, we have found, and this is what is the subject of the present invention, a simple and effective solution which makes it possible to virtually eliminate the risks of delamination.

In general, the invention therefore relates to an improvement made to the fibrous layers intended to constitute the central layer giving the thickness to a complex textile reinforcement used in the production of a composite material, said fibrous layers being based on fibers. , of high unitary title, having a "spring" effect.

The material according to the invention is characterized in that the conformation in the form of a sheet of said high titer fibers is carried out by carding, and in that, continuously, immediately after the carded sheet has been produced, this is projected onto the surface of this last of the continuous glass fibers or filaments which are distributed flat in a random manner in all directions, the assembly then being subjected to a mechanical needling treatment entraining said glass fibers or filaments through the entire thickness of the sheet of synthetic fibers, so that they or they emerge on the opposite face, the formed structure then being received in the form of a coil.

To make the carded fibrous web, it is also possible to use synthetic fibers having a high unit titer, such as polyester, polyamide, polyethylene, polypropylene fibers, which have received a treatment which communicates to them prior to their forming in the form of a web. a waviness or permanent crimp giving the effect of "spring", this treatment can be for example a stuffing treatment, as vegetable fibers such as flax, sisal, jute ...

By high titer is meant fibers whose titer is generally between 20 and 200 dtex and whose cutting length for synthetic fibers is generally between 40 and 120 mm, this length possibly being longer in the case vegetable fibers.

It could be envisaged to use finer fibers, but then this will be to the detriment of the quality of the composite material formed, since the fibrous web then has a higher density which disturbs the path of the resin during the production of the material. composite.

It can also be envisaged to use fibers having a titer greater than 200 dtex. However, in such a case, the carding operation is difficult to carry out and above all the carded web obtained can lack homogeneity.

Furthermore, the weight of said carded web will advantageously be between 150 g / m2 and 400 g / m2. Indeed, for a weight less than 150 g / m2, the complex lacks strength and regularity, while a weight greater than 400 g / m2 leads to thick products which are not justified in practice.

The thickness of the central ply will generally be between 3 and about 10 mm.

The glass fibers projected and implanted inside said ply are fibers having a cutting length of at least 10 mm, their titer being able to vary from 15 to 160 tex. These fibers are projected at a rate of 50 to 200 g / m2. There is no upper limit in the length of glass fibers which can be made of continuous filaments.

The invention and the advantages which it brings will however be better understood thanks to the example of embodiment which follows, given below by way of indication but not limiting.

Example

A material in accordance with the invention is produced on a production line successively comprising a conventional carding machine, a receiving mat for the carded web formed above which is arranged a projection assembly of cut glass fibers, a conventional mechanical needling machine equipped needles whose barbs are oriented in one direction so as to entrain the fibers only during the penetration phase, said needling machine being followed by a system for receiving the sheet formed.

On such an installation, a carded web is formed from polypropylene fibers, of 110 dtex title - cut 90 mm, crimped by stuffing, the web weighing, at the card outlet, 250 g / m2.

The sheet being kept flat on the conveyor belt, glass fibers having a titer of 25 tex are projected onto its surface, the cutting length being 50 mm, and this at a rate of 150 g / m2.

The call speed of the water table is 4m / min.

The assembly then passes inside a conventional needling machine adjusted to exert an action of 40 strokes / cm2.

At the exit from the production line, the complex formed weighs 400 g / m2 and has a thickness of the order of 8 mm.

Such a fibrous structure can be used as a central layer intended to give thickness to any complex textile structure for reinforcing laminated material, the textile reinforcements themselves being able to be arranged on either side of such a structure and which are associated with the latter by any appropriate means, in particular by a sewing / knitting, needling or gluing operation.

• des fils parallèles, jointifs ou espacés les uns des autres;
• des nappes bidirectionnelles, des nappes fibreuses, voire même des tissus et/ou combinaisons de tels éléments.

The additional reinforcements can be of any conventional type, namely for example:

• parallel, joined or spaced apart threads;
• bidirectional sheets, fibrous sheets, or even fabrics and / or combinations of such elements.

It has been found that such a material, when used to produce a composite structure to replace the central layer as described in FR-A-2 646 442, made it possible to virtually eliminate the risks of delamination as well as also to improve the characteristics of bending, rigidity and resistance to aging.

Claims (4)

Fibrous structure intended to constitute the central layer giving the thickness to a complex textile reinforcement used in the production of a composite material, consisting of fibers, of high unitary strength, having a "spring" effect, characterized in that the conformation in the form of a sheet of said high titer fibers is produced by carding, and in that, immediately, immediately after the carded sheet has been produced, continuous fibers or filaments of glass are projected onto the surface of the latter, which are distributed flat randomly in all directions, the assembly then being subjected to a mechanical needling treatment entraining said glass fibers or filaments through the entire thickness of the ply of synthetic fibers, so that it comes out on the opposite face, the structure formed then being received in the form of a winding. Fibrous structure according to claim 1, characterized in that the carded fibrous web is either based on synthetic fibers such as polyester fibers, polyamide, polyethylene, polypropylene ... which have received a treatment prior to their forming in the form of a web. communicating a permanent ripple or crimp conferring the "spring" effect, either based on vegetable fibers, such as flax, sisal, jute ... Fibrous structure according to claim 2, characterized in that the high titer fibers have a cutting length of between 20 and 120 mm, when they are made of synthetic fibers, this length possibly being greater in the case of vegetable fibers. Fibrous structure according to one of claims 1 to 3, characterized in that the glass fibers or filaments projected and implanted inside the sheet, have a cutting length of at least 10 mm, their titer being between 15 and 160 tex.