EP2961583A1 - Preparation of a semi-finished textile product intended for thermoplastic injection moulding, and resulting product - Google Patents

Abstract

A process for preparing a semi-finished textile product intended for thermoplastic injection moulding, according to which a multilayer complex comprising at least one reinforcing layer combined with a draining layer, is impregnated with at least one thermoplastic compound by passing into an aqueous solution containing said at least one thermoplastic compound. And also the product obtained by this process.

Description

 PREPARATION OF A SEMI-FINISHED TEXTILE PRODUCT INTENDED FOR

THERMOPLASTIC INJECTION, AND PRODUCT THUS OBTAINED

FIELD OF THE INVENTION

The invention relates to the preparation of a semi-finished textile product comprising a drainage layer associated with a reinforcing fabric impregnated with thermoplastic polymer core. The field of use of the present invention relates to composite materials that can be made by injection molding a thermoplastic resin. These composites can particularly find an application in the automotive industry, boating, sports and leisure. PRIOR STATE OF THE TECHNIQUE

The manufacture of composite parts combining textile reinforcements and resin, can be implemented according to different techniques well described in the prior art. It may especially be infusion molding or injection molding.

The infusion consists in making a composite part by stacking in a mold several layers of reinforcing fabrics and then spreading resin within this stack. The homogeneous distribution of the resin is ensured by putting the whole under vacuum. Once the air evacuated and the resin distributed, the latter is cured or crosslinked in the case of thermoset resins.

As described in WO 2005/118266, the distribution of the resin can be facilitated by positioning a drainage element between the reinforcing fabrics. In injection molding processes, a relatively viscous resin is injected at several points to penetrate a multilayer reinforcement. The homogeneous distribution of the resin can be ensured by the presence of a perforated structure within the reinforcement, forming a draining layer. The resin is then cured or cured in the case of a thermoplastic to form the composite part.

However, the distribution of thermoplastic resin can be problematic and this despite the improvement of multilayer reinforcements used in molding processes by injection of the prior art. Indeed, the reinforcements may include areas of porosity within the son constituting them, thus causing a decrease in the mechanical properties of the composite part. In other words, the injection of a thermoplastic material by nature viscous does not penetrate sufficiently to heart.

One could imagine that the penetration of the resin is improved by injection under high pressure, but this would cause a deformation / crushing of the draining layer and the reinforcement which would degrade the mechanical properties of the assembly. The Applicant has developed a method to overcome these problems by ensuring the impregnation of a thermoplastic compound in the core of the reinforcement, especially in the context of thermoplastic injection molding.

This method makes it possible to solve the problems of porosity during the injection of thermoplastic material on the reinforcement.

SUMMARY OF THE INVENTION

The method of the invention relates to the preparation of a semi-finished textile product for use in a conventional over-injection process. Only once this semifinished textile product has been produced is it placed in a mold in which a molten thermoplastic resin is injected so as to obtain, after cooling, a composite part. The product thus obtained can be assimilated to a partially pre-impregnated material in that it comprises a fraction of thermoplastic material and that the final composite material will be obtained by adding the additional resin fraction provided during the injection. This semi-finished textile product comprises at least one reinforcing layer whose threads are impregnated at the end of the process described hereinabove.

It involves impregnating the son of one or more thermoplastic compounds. In other words, the interstices between filaments constituting the son are better impregnated with thermoplastic material by means of the method according to the invention.

More specifically, the present invention relates to a process for the preparation of a semi-finished textile product for thermoplastic injection, according to which a multilayer complex comprising at least one reinforcing layer associated with at least one draining layer, is impregnated with at least one thermoplastic compound by passing through an aqueous solution containing said at least one a thermoplastic compound.

The thermoplastic compound used is thus distinguished in the impregnation of the multilayer complex, of the thermoplastic resin used later in the preparation of the semi-finished textile product in order to produce a composite part.

The multilayer complex is impregnated with the thermoplastic compound to form the semifinished textile product according to the method of the invention. The semi-finished textile product, that is to say the impregnated multilayer complex, can then be used to produce a composite part by injection of the thermoplastic resin.

For clarity, in the following description, the term "thermoplastic aqueous solution" is used to designate the aqueous solution containing at least one thermoplastic compound implemented in the method of the invention. Various variants can be envisaged concerning the multilayer complex.

The multilayer complex may thus consist of a single reinforcing layer associated, that is to say mechanically secured to a single draining layer. In practice, the multilayer complex is formed by the association between the reinforcing textile and the draining. The drainant, previously made from filaments (or son), is complexed with the reinforcement. A second reinforcement may be associated with the draining so as to form a sandwich structure. According to this particular embodiment, the multilayer complex comprises at least one draining layer interposed between two reinforcing layers, the draining layer being advantageously mechanically secured to the two reinforcing layers.

The draining layer may be in the form of a grid, a knit, or a three-dimensional knit.

According to the knowledge of those skilled in the art, a grid has a structure openwork ensuring a homogeneous distribution of the resin during the injection steps of the thermoplastic resin. The open areas between the crossings of the different son of the grid allow passage and creep of the aqueous solution of the thermoplastic resin.

A knit has a relatively loose and deformable structure, allowing not only the passage of the thermoplastic aqueous solution but also the passage of the thermoplastic resin. The knit has the advantage of having a relatively uniform thickness that is constant under pressure, and therefore, in a suitable manner, resists crushing to ensure permanent creep of the thermoplastics.

A three-dimensional knit, also known as a double-sided knit, has a thickness generated by knitting at least two plies of yarn with binding yarns.

In general, the draining layer may in particular be manufactured from synthetic yarns based on, for example, polyester, polyamide, or from twisted glass yarns. It may also be son made of thermoplastic material, preferably identical to the material injected or at least compatible with this material.

The twisted glass yarns exhibit good resilience and compressibility resistance in a manner similar to a synthetic monofilament, but with a much higher quality of mechanization.

As regards the reinforcing layer, it may advantageously be made from high-tenacity yarns, and especially glass, aramid, carbon or equivalent yarns.

The backing layer may also be in the form of a chopped fiber mat or a woven fabric from continuous yarns, or a sheet of straight NCF yarns ("Non Crimp Fabric"). "), Or the superposition of several plies of sewn rectilinear son, thus ensuring a multi-axial reinforcement.

The reinforcing layer may also result from the combination of several elementary layers of the same nature or of different natures. The draining / reinforcing association is generally carried out by gluing, by needling, or advantageously by sewing. Process

The impregnation of the multilayer complex is carried out at the core of the son forming the reinforcing layer or layers. It is a question of impregnating at best the interstices existing between the filaments constituting the threads.

At the end of the impregnation, a certain degree of deformability of the semifinished textile product is advantageously maintained.

In addition, the draining layer retains its permeability to the thermoplastic resin, once the multilayer complex impregnated.

The thermoplastic compound used in the impregnation of the multilayer complex is advantageously a polymer which may especially be chosen from the group comprising polyamides; acrylics (especially polymethyl methacrylate); polyurethanes and TPU (thermoplastic polyurethane), vinyl polyacetates; EVA (ethylene vinyl acetate); styrene / butadiene; polyesters; PE (polyethylene); PP (polypropylene); PPS (polyphenylene sulfide); and PEEK (polyetheretherketone or, in English "polyether ether ketone"). In general, the thermoplastic compound is water-dispersible, thus making it possible to prepare a homogeneous aqueous solution. In other words, it can be dispersed in water at concentrations of between 6 and 600 g / L of water.

As already indicated, it is used in aqueous solution. Advantageously, the concentration of thermoplastic compound in the aqueous solution is between 200 and 500 g / l, more advantageously between 200 and 300. The viscosity of the resulting aqueous solution is advantageously less than 100 mPa.s, which facilitates impregnation of the fibers with the aqueous solution. In general, the duration of impregnation, or speed of passage of the multilayer complex in the bath, is advantageously between 0.5 and 20 m / min, depending on the type of reinforcement to be impregnated. Once, the impregnated multilayer complex, it is advantageously dried at a temperature which can be between 100 and 300 ° C, more preferably between 150 and 200 ° C.

This drying step is preferably carried out in a hot air oven or on a heating cylinder.

According to a particular embodiment, the impregnation of the multilayer complex may comprise a passage in at least two baths, all having concentrations of thermoplastic compound that can be distinct.

For example, when two baths are used to impregnate the multilayer complex, the concentration of the second bath may be lower than that of the first.

According to another embodiment, the concentration of the first bath may be lower than that of the second bath, in order to favor the impregnation of the core fibers. The second bath, having a higher concentration and viscosity, allows for a more surface coating of the fiber or to increase the level of thermoplastic compound of the semi-finished product.

The impregnation makes it possible to penetrate the thermoplastic compound to the core. However, the monofilaments constituting the draining layer being very open, the thermoplastic aqueous phase does not close the draining layer which retains its resin permeability properties.

In general, the thermoplastic compound is of the same nature as the thermoplastic resin subsequently used to manufacture the composite part. However, the polymer chains are preferably of higher molecular weight for the thermoplastic resin.

In addition, advantageously, the impregnating composition is not charged.

Preferably, the melting temperature of the thermoplastic compound is such that the compound remains stable during the subsequent injection process. The impregnation with the thermoplastic compound makes it possible to bind the filaments and to preserve the self-draining nature during the injection. The skilled person will know how to choose the compound thermoplastic depending on the final properties desired for the composite part.

In addition, according to a particular embodiment, the thermoplastic aqueous solution comprises a crosslinking agent of the thermoplastic compound. Thus, the aqueous solution may comprise between 0.5 and 20% by weight of crosslinking agent.

The partial crosslinking of the thermoplastic compound makes it possible in particular to improve the temperature resistance during the injection step to manufacture the composite part. The cohesion between the son of the reinforcement, improved by this partial crosslinking, also allows the holding of the composite part itself during its subsequent use, if the latter occurs at high temperatures. The crosslinking phenomenon remains a minority and does not alter the essentially thermoplastic character of the impregnating compound. The partial crosslinking can in particular be carried out by firing as a result of the heating step to remove water from the aqueous solution.

The crosslinking agent may especially be chosen from the group comprising amines, melamines, epoxies, methacrylic and acrylic esters. The impregnation of the multilayer complex makes it possible to obtain a semi-finished textile product having draining channels whose quality and regularity are obtained by fixing the self-draining structure. Thus, the presence of the thermoplastic compound makes it possible to maintain the self-draining structure until the thermoplastic compound particles are melted by the resin subsequently injected.

In the impregnated semi-finished textile product, the thermoplastic compound is in fact deposited in the heart of the yarns. The thermoplastic compound and the thermoplastic injection resin fulfilling distinct functions, various combinations of thermoplastic compound / thermoplastic resin can therefore be envisaged.

For example, the resin may have strong bonding properties to create bonds between son and avoid micro-stress and delamination between son.

In any event, the thermoplastic impregnating compound and the thermoplastic injection resin must be compatible in order to limit the risk of delamination on the surface of the fibers. The present invention makes it possible to improve and make the interface the reinforcement and the resin more compatible. This increases the mechanical performance of the final composite. In addition, the thermoplastic compound impregnated at the core of the reinforcement makes it possible to keep the wires in their initial position and to limit the deformation of the reinforcement under the injection pressure.

The method of the invention allows the impregnation of the filaments in the heart of the son, which is not possible with the thermoplastic resin during injection because the latter has a viscosity too high. On the other hand, the speed of the injection process does not promote this impregnation heart of the fiber.

The method according to the invention thus makes it possible to reduce the porosity of the core of the reinforcements and thus to improve the mechanical properties of the resulting composite part.

Semi-finished textile product

Advantageously, the semi-finished textile product obtained after the process described above comprises between 2 and 40% of thermoplastic compound retained after impregnation, in dry weight relative to the dry weight of the semi-finished textile product, plus advantageously still between 5 and 15%. The presence of this amount of thermoplastic compound within the semifinished textile product makes it possible to supplement the quantity necessary for the improved production of the part during the injection process.

As already stated, the multilayer complex may have a plurality of unitary reinforcing layer / draining layer elements.

Therefore, the semi-finished textile product may comprise a stack of n draining layers and n + 1 reinforcing layers, each draining layer being interposed between two layers of reinforcements, n being an integer greater than or equal to 2.

Advantageously, each draining layer is associated (mechanically secured) to at least one of the reinforcements with which it is in contact.

In other words, according to this particular embodiment, the product is constituted a stack of reinforcement / draining.

The semi-finished textile product thus obtained has deformability properties. In practice, some applications require a more limited deformability of the complex, the association between the draining layer (s) and the reinforcing layer (s) can be obtained by combining the characteristic bonding with an assembly by sewing or knitting the different layers between they. This makes it possible to retain a deformability of the appreciable assembly in the case of producing pieces of complex geometry, while increasing the resistance to delamination. This type of assembly makes it possible not to compress the layers too strongly while ensuring good bonding thereof.

This aspect may be particularly important especially when the reinforcement is preformed hot.

When the final injection is complete and the resin is conveyed (by the self-draining structure) throughout the room, the melting of the particles of the dispersion releases the reinforcing filaments and thus allows a spreading of the reinforcement threads and thus an optimization of the mechanical performances. by removing areas rich in resin and unreinforced.

This phenomenon will be all the more marked as the temperature of the mold is maintained at the melting temperature of the dispersion particles

The invention and the advantages thereof will become more apparent from the following examples given to illustrate the invention and not in a limiting manner.

EXAMPLES OF CARRYING OUT THE INVENTION

Example 1

A multilayer complex comprising two reinforcing fabrics of 600 g / m ² plain weave based on glass yarns of unitary title 1200 Tex disposed on either side of a draining net formed of a knit fabric, with a weight per unit area 110 g / m ² , 0.7 mm thick (measured at 0.6 bar pressure), and made from monofilament polyester yarns with a unit weight of 280 dTex is prepared. The three layers are sewn with 167 dTex polyester yarn. This multilayer complex is then immersed for 30 seconds in an aqueous solution containing a copolyamide dispersion whose concentration (20%) makes it possible to obtain a semifinished textile product containing 10% by dry weight of thermoplastic compound. The whole is then dried in an oven at 150 ° C. to evacuate all the water present in the semi-finished textile product for a period of approximately a few minutes. These impregnation and drying phases are continuous from rolls of multilayer complex. Example 2

A complex analogous to that of Example 1 is impregnated with an aqueous dispersion of styrene-butadiene resin crosslinked with 10% by weight of melamine resin relative to the amount of styrene butadiene. The dry matter concentration of the aqueous dispersion is 26% in order to achieve a content of 20% by weight of styrene-butadiene resin relative to the total weight. The whole is then dried in an oven to evacuate the residual water present on the product. The speed of this continuous process from complex roll is 2 m / min.

Claims

Process for preparing a semi-finished textile product intended for thermoplastic injection, in which a multilayer complex comprising at least one reinforcing layer associated with a draining layer is impregnated with at least one thermoplastic compound by passage through an aqueous solution containing said at least one thermoplastic compound. Process according to Claim 1, characterized in that the multilayer complex comprises at least one draining layer interposed between two reinforcing layers. Method according to claim 1 or 2, characterized in that the draining layer is in the form of a grid, a knit, or a three-dimensional knit. Process according to one of Claims 1 to 3, characterized in that the thermoplastic compound is a polymer chosen from the group comprising polyamides; acrylics; polyurethanes; polyvinyl acetate; ethylene vinyl acetate; styrene / butadiene; polyesters; polyethylene; polypropylene; poly (phenylene sulfide); and polyetheretherketone. Process according to one of Claims 1 to 4, characterized in that the concentration of thermoplastic compound in the thermoplastic aqueous solution is between 6 and 600 g / l. Process according to one of Claims 1 to 5, characterized in that the impregnation of the multilayer complex comprises a passage through at least two baths, all having different concentrations of thermoplastic compound. Process according to one of Claims 1 to 6, characterized in that the rate of passage of the multilayered complex in the aqueous solution is between 0.5 and 20 m / min. Method according to one of claims 1 to 7, characterized in that it further comprises a drying step, after impregnation, preferably at a temperature between 100 and 300 ° C. Process according to one of Claims 1 to 8, characterized in that the semi-finished textile product comprises between 2 and 40% by dry weight of thermoplastic compound retained after impregnation. Semi-finished textile product obtained according to the method according to one of claims 1 to 9, characterized in that it comprises a stack of n draining layers and n + 1 reinforcing layers, each draining layer being interposed between two layers reinforcements, n being an integer greater than or equal to 2.