EP3062984A1 - Method for producing a thermoplastic component comprising a surface reinforcing sheet - Google Patents

Abstract

Method for producing a thermoplastic component reinforced with at least one reinforcing sheet situated at the surface of one of the faces of said component. This method involves the following steps: o a stack of sheets comprising at least one reinforcing sheet and at least one draining fabric sheet is placed in a mould; o the mould is closed and a thermoplastic is injected into the mould; and o the component thus obtained is demoulded.

Description

 Process for producing a thermoplastic part comprising a surface reinforcing sheet

 The invention relates to the technical field of plastic parts manufacturing processes, including motor vehicle parts.

 In the automotive field for example, many structural parts must combine mechanical strength and low weight.

 To do this, it is known to replace steel parts by plastic parts, thermosetting or thermoplastic.

 Various molding processes of plastic parts are known:

 · Compression method (for thermosetting materials)

 • Thermoforming process (compression with a thermoplastic material)

 • Injection process (for thermoplastics).

 The main advantage of the injection process is to be able to produce parts with great complexity of shape.

 The disadvantage is that the thermoplastic material is mechanically less resistant than thermosetting materials such as SMC (sheet molding compound).

 It is known to use reinforced thermoplastics. These materials consist of reinforcing fibers mixed with a resin. These reinforcements comprise glass, carbon or aramid fibers or a combination. These fibers can be cut or continuous. To obtain a good mechanical performance, continuous fibers are often used, preferably in the form of fabric.

 A method is known for producing a reinforced thermoplastic material part in which a reinforcement sheet, pre-impregnated or dry, is inserted directly into the mold. Then, the material (resin or reinforced resin) is injected into the mold.

However, this method does not make it possible to control the position, in the thickness of the finished part (that is to say, the mold outlet part), of the reinforcing sheets under the effect of the thrust of the injected material. . The sheet can then be positioned in the finished part in a random position between the two faces of the part. This heterogeneity locally causes a difference in mechanical behavior. The mechanical contribution of the reinforcement sheet is optimal when it is on the surface of the finished part.

Also known is a method for producing a reinforced thermoplastic material part in which a preformed reinforcement is produced, then this preformed reinforcement is placed in the mold, and finally, the material (resin or reinforced resin) is injected into the mold. If this method makes it possible to control the position of the preformed reinforcement, it requires an additional step, which lengthens the manufacturing time and therefore increases the manufacturing cost of the reinforced thermoplastic part.

 In certain process variants, the reinforcement must be able to be traversed by the resin during the injection, to be impregnated. In the context of a fabric, this ability is characterized by sufficiently open meshes. This type of open mesh fabric has lower mechanical properties than a more "dense" woven reinforcement with closed meshes. However, the woven reinforcements necessary to provide sufficiently large mechanical properties to obtain a high performance composite have a fiber density that is too high to be penetrated by resin injection.

 The invention makes it possible to overcome these constraints, by using a draining fabric to guide the material (resin with or without reinforcing fibers) injected along the reinforcing sheets, so as to hold them in place on the surface of the room.

 The object of the invention thus relates to a method for producing a thermoplastic material reinforced by at least one reinforcing sheet located on the surface of at least one of the faces of the part. This process comprises the following steps:

 - In a mold is arranged a stack of sheets comprising at least one reinforcing sheet and at least one sheet of draining fabric;

 the mold is closed and a thermoplastic material is injected into the mold; and - the part thus obtained is demolded.

Thanks to the draining effect used by this method, the respective positions of the reinforcing sheets in the thickness of the room are controlled. Thus, the piece has a better homogeneity and therefore a better mechanical performance.

 In addition, this method requires only one step in the mold, unlike methods using a preforming of the reinforcing sheets.

 The reinforcing sheet may be an assembly of unidirectional fibers (UD) or a fiber fabric, the fibers being selectable from glass, carbon or aramid fibers or a combination of these types of fibers.

 The backing sheet may be introduced cold into the mold, or it may be preheated before it is introduced into the mold.

 The reinforcing sheet may be pre-impregnated with a material before being introduced into the mold.

According to one embodiment, there is a stack comprising at least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of said part, and between which is interposed a layer of material and at least one sheet of draining fabric within said layer. According to a variant of this embodiment, a gas or an additive is introduced into the layer of material, so as to foam the resin.

 According to another embodiment, there is a stack comprising a superposition of a set of sheets, each set comprising:

 at least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of said part;

 a layer of material interposed between the reinforcing sheets;

 at least one sheet of draining tissue within said layer. According to the invention, it is possible to use a vertical mold, in which the sheets are suspended, and the reinforcement sheet is placed on the punching side or on the matrix side.

 Preferably, the material is injected through one end of the mold, or through openings created in the stack of sheets.

 Finally, the material used is preferably a resin, preferably a polyamide resin, or a resin loaded with reinforcing elements.

The invention also relates to a reinforced thermoplastic material part comprising at least one reinforcing sheet located on the surface of one of the faces of said part and a thermoplastic material. The part according to the invention comprises at least one sheet of draining fabric.

 The reinforcing sheet may be a unidirectional fiber (UD) assembly or a fiber fabric, the fibers being selected from glass, carbon or aramid fibers or a combination of these fiber types.

 According to one embodiment, the part comprises at least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of the part, between which is interposed a layer of material and at least one sheet of draining fabric with within the layer.

 The material may be in the form of a foam.

 Finally, the material is preferably a resin, preferably a polyamide resin, or a resin loaded with reinforcing elements.

The invention will be better understood on reading the description which follows, with reference to the appended drawings in which:

 FIG. 1 illustrates a piece of reinforced thermoplastic material resulting from the process according to the invention, comprising a reinforcing sheet (2) covering one of the faces of the part (1).

FIG. 2 illustrates a piece of reinforced thermoplastic material resulting from the process according to the invention, comprising two reinforcing sheets (2, 2 ') each sheet reinforcement covering a different face of the piece (1).

The method, according to the invention, for producing a thermoplastic material part reinforced by at least one reinforcing sheet located on the surface (apparently or not) of at least one of the faces of the part, comprises the following steps:

 - In a mold (preferably of injection) is arranged a stack of sheets comprising at least one reinforcing sheet and at least one sheet of draining fabric. The stack can be made in the mold, or outside the mold and then introduced into the mold.

 the mold is closed and a thermoplastic material is injected into the mold. The material is injected through one end of the mold at the level of the draining fabric sheet or through at least one opening created in the stack of reinforcing sheets. According to this method, a material comprising a resin, such as polyamide or polypropylene, is preferably used; and

 the part thus obtained is demolded.

 In the following description, we call "resin" the injected material which may be a resin or a resin filled with reinforcing fibers.

 The backing sheet may be an assembly of unidirectional fibers (UD) or a fiber fabric. The reinforcing fibers are generally chosen from glass, carbon or aramid fibers. The reinforcing fibers can also be a mixture of these three types of fiber. The reinforcing sheet may consist of several layers of tissue.

 A sheet of draining fabric is a fabric that facilitates the flow of a material in the plane defined by its surface. A material injected on such a fabric is thus drained on the surface of the fabric or in the thickness of the fabric.

 The material can be injected through one end of the mold. In this case, the material is injected at the level of the wad of the draining fabric, so that the draining fabric drains the material in the plane defined by its surface, thus preventing it from moving the reinforcing sheet perpendicularly to this "plane" in the thickness of the part, or more precisely in the air gap of the cavity of the mold (space between the punch and the matrix of the closed mold).

 The material may be injected in a direction substantially perpendicular to the draining tissue. It can be injected on the side of the draining fabric, or on the opposite side, through at least one hole made in the reinforcing sheet. In both cases, the draining fabric drains the material in the plane defined by its surface, thus preventing it from moving the reinforcement sheet.

The draining fabric thus makes it possible to promote the passage of the material (resin or resin charged), during its injection, in the plane defined by the surface of the draining fabric, thereby maintaining the reinforcing sheet surface of the workpiece.

 Different types of draining fabric are known, for example:

 • NET1® draining fabric (Chomarat, France): polyester knit 110 g / m2); · CFM® draining fabric (Chomarat, France): long fiber glass mat 150,

225, 300, 450 or 600 g / m2);

 • Airweave® range of drainage felt, Econoweave®, Ultraweave® (Airtech, Luxembourg);

 • Draining fabric from Cytec (United Kingdom).

 The reinforcing sheet may be introduced cold into the mold of the part, that is to say without preheating or substantially at room temperature. But it can also be preheated before it is introduced into the mold.

 Preferably, the reinforcing sheet is pre-impregnated with a material (resin or resin filled) before its introduction into the mold. This pre-impregnation makes it possible to give resistance to the sheet, which facilitates its handling. In addition, this step prevents the sheet from fraying and / or that the fibers do not break.

According to a preferred embodiment of the invention, the method comprises the production of a stack of at least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of the part, and at least one draining fabric sheet being interposed between the reinforcing sheets. Then, the material is injected so as to obtain a layer interposed between the reinforcing sheets, and comprising the draining fabric. Thus, it is possible to obtain following this method, a stack comprising a reinforcing sheet, a resin layer, and then a reinforcing sheet. The draining fabric sheet may be against one of the reinforcing sheets, or separated from the reinforcing sheets by resin (Figure 2).

 Stacking can be on the die side, or the punch side or both sides. The draining fabric then promotes the passage of the resin in the middle of the two reinforcing sheets, and thus allows the reinforcement sheets to be positioned on the surface of the part. As shown in FIG. 2, which is a result of the process, a piece having a homogeneous sandwich structure consisting of a layer of reinforcing fabric and then a layer of resin (comprising the sheet of fabric) is thus obtained. draining), then a second layer of reinforcement fabric.

It is possible, according to this method, to multiply the number of layers in the thickness by alternating layers of woven reinforcements and layers of draining. According to this configuration, some reinforcing sheet is not at the surface, but contributes to the mechanical reinforcement. In order to produce the part, a preferably vertical mold is used, in which the reinforcing sheets and the sheets of draining fabric are suspended in the mold, for example by means of needles, and the reinforcement sheet is placed on the side of the mold. punch or die side. In this case, the draining fabric sheet makes it possible to promote the vertical movement of the resin.

According to another embodiment (foaming), a gas or an additive is introduced into the material so as to foam it. This foaming operation can take place before injection into the mold, or after the injection, it is being injected.

 The additive is added to the resin. It may be Hydrocerol® (Clariant, Switzerland), for example.

 The gas is injected into the feed screw of the material.

 To increase the foaming it is possible to slightly open the tool after the injection of the material with the gas or the additive.

 The foaming improves, for the same amount of material, the beam effect (a core separating and separating two reinforcing sheets from the average bending line), and therefore the mechanical strength of the part. In addition, the foaming contributes to the lightening of the room.

 With this method, it is no longer necessary to add a reported product such as a honeycomb core to achieve the same benefits. This method therefore simplifies the known method because the part is produced in a single step.

Illustrated in Figure 1, the invention also relates to a reinforced thermoplastic material part (1), obtained by the method according to the invention. It comprises at least one reinforcing sheet (2) located on the surface of one of the faces of said part (1) and a thermoplastic resin (3), characterized in that it comprises at least one sheet of draining fabric (4). ).

 According to one embodiment (FIG. 2) the part (1) comprises at least two reinforcing sheets (2, 2 '), each reinforcing sheet being situated on the surface of a different face of the part (1), between which a resin layer (3) and at least one draining fabric sheet (4) are interposed within the layer (3).

 This piece (1) has good mechanical strength thanks to the reinforcing sheets (2, 2 '). The resin core (3) makes it possible to stiffen the reinforcing sheets (2, 2 ') while limiting the weight of the piece (1).

 The spacing between the reinforcing sheets (2, 2 ') makes it possible to maintain the resistance of the part (1).

The draining fabric (4) makes it possible to obtain a piece (1) homogeneous from the point of view of the mechanical strength, because the reinforcing sheets (2, 2 ') remain on the surface of the workpiece (1).

 According to another embodiment, the resin (3) is in the form of a foam. The resin is preferably polyamide.

 Preferably, the mold is a vertical mold, and therefore, the Z axis represents the vertical axis of the mold.

Claims

1. Process for producing a thermoplastic material reinforced by at least one reinforcing sheet situated on the surface of one of the faces of said part, characterized in that it comprises the following steps:  - In a mold is arranged a stack of sheets comprising at least one reinforcing sheet and at least one sheet of draining fabric;  the mold is closed and a thermoplastic material is injected into the mold; and the part thus obtained is demolded. The method of claim 1, wherein the backing sheet is a unidirectional fiber (UD) assembly or a fiber fabric, the fibers being selected from glass, carbon or aramid fibers or a combination thereof. types of fibers.  3. Method according to one of the preceding claims, wherein the reinforcing sheet is introduced cold in the mold.  4. Method according to one of claims 1 to 2, wherein the reinforcing sheet is preheated before its introduction into the mold.  5. Method according to one of the preceding claims, wherein the reinforcing sheet is pre-impregnated with a material before its introduction into the mold. 6. Method according to one of the preceding claims, wherein there is a stack comprising at least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of said part, and between which is interposed a layer of material and at least one sheet of draining tissue within said layer. 7. The method of claim 6, wherein a gas or an additive is introduced into said layer of material, so as to foam the resin.  8. Method according to one of claims 6 and 7, wherein there is a stack comprising a superposition of a set of sheets, each set comprising:  At least two reinforcing sheets, each reinforcing sheet being located on the surface of a different face of said part;  A layer of material interposed between the reinforcing sheets;  At least one sheet of draining tissue within said layer.  9. Method according to one of the preceding claims, wherein using a vertical mold, wherein the sheets are suspended, and the reinforcing sheet is placed on the punch side or the die side. 10. Method according to one of the preceding claims, wherein the injection is material through an end of the mold, or through openings created in the stack of sheets.  11. Method according to one of the preceding claims, wherein the material used is a resin, preferably a polyamide resin, or a resin filled with reinforcing elements.  12. Part reinforced thermoplastic material (1) comprising at least one reinforcing sheet (2) located on the surface of one of the faces of said part (1) and a thermoplastic material (3), characterized in that it comprises at least one sheet of draining fabric (4). 13. Part according to claim 12, wherein the reinforcing sheet (2) is an assembly of unidirectional fibers (UD) or a fiber fabric, the fibers being chosen from glass, carbon or aramid fibers or a combination of these types of fiber.  14. Part according to one of claims 12 and 13, comprising at least two reinforcing sheets (2, 2 '), each reinforcing sheet (2, 2') being located on the surface of a different face of said part ( 1), between which is interposed a layer of material (3) and at least one sheet of draining fabric (4) within said layer.  15. Part according to claim 14, wherein the material (3) is in the form of a foam. 16. Part according to one of claims 12 to 15, wherein the material (3) is a resin, preferably a polyamide resin, or a resin loaded with reinforcing elements.