MXPA06005814A - Needled glass mat - Google Patents

Abstract

The invention relates to a method of preparing a needled glass mat. The inventive method comprises the following steps consisting in:a) depositing or projecting fibres onto a conveyor in order to form a blanket of said fibres, which is driven by the conveyor;b) and needling using barbed needles which pass through the blanket and move in the direction of said blanket at essentially the same speed of same while passing therethrough, with a punch density varying between 1 and 25/cm2. The invention is quick and effective and the mat produced can be easily deformed by hand in order to be placed in a resin-injected composite production mould (RTM). The inventive mat can also be incorporated in a sheet moulding compound (SMC) and pressure moulded.

Description

MILLED GLASS HOLES The invention relates to the manufacture of glass fiber notches that can be used for the reinforcement of prepared composite materials, in particular, by injection (a method referred to as RTM Resin Transfer Molding) or preimpregnated lamination preparation (synonymous with SMC of Sheet Molding Compound). The mesh according to the invention can also be directly impregnated with a thermosetting resin, in particular to produce translucent boards. A mesh for reinforcement of composite materials should preferably have the following properties: have enough cohesion to be rolled and unrollable (for storage and transport), - have enough cohesion to cut into pieces, hold in hand and placed in the mold by the hand (RTM), do not chop hands when held or placed in the mold (RTM), easily deformed by the hand when placed in the mold manually (RTM), properly retain the shape given by the hand in the mold (RTM) ), impregnated as easily as possible with the injection resin or SMC (usually of the polyester type and • sometimes of the epoxy type), - have the most homogeneous structure possible, in particular without holes or other surface characteristic capable of causing a Mark on the surface of the final composite material, reinforce the composite material as much as possible. It is desirable, moreover, to be able to manufacture it - at the highest possible speed, with the least possible steps, using the least possible chemical products (such as binders). The final composite material should generally have the highest possible impact strength, the lowest uncontrolled porosity possible (without gas bubbles not intentionally trapped) and the best possible surface appearance, particularly the edge (narrow side) of the pieces final. The use of continuous fibers leads to an unexpected advantage in terms of 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. To be precise, the applicant discovered that the edge of the molded parts was much cleaner and smoother and better formed than when cut fibers were used. Without this explanation being able to limit the scope of the present application, it appears that the use of staple fibers includes a large number of cut fiber ends located on the surface or just below the surface of the edges of pieces. This phenomenon is due to the fact that naturally cut fibers have an orientation parallel to the main sides of the composite material. This accumulation of fiber ends cut at the edges seems to be conductive to the presence of porosities at the edges by the beginning of the method. The formed bubbles then expand under the effect of temperature (of the order of 200 ° C for the solidification of the thermosetting resin), thus tending to deform the appearance of the surface of the edges. It seems that the use of continuous fibers considerably reduces this phenomenon. To be precise, instead of a fiber end on the surface (situation where the staple fibers are used), instead there will be a continuous fiber cycle, thus extending to a smoother surface. As considered in the SMC application, the mesh must also be able to flow easily during press molding. It will be noted that, before molding, an SMC takes the form of a pre-impregnated sheet containing a thermosetting resin, said sheet containing in its middle part a coating of reinforcing fibers. According to the prior art, these fibers are, systematically, staple fibers. To be precise, in the mold, SMC undergoes a pressure and must flow easily to fill the total volume of the mold under the effect of pressure. For a person skilled in the art, this flow is possible due to the fact that the fibers are cut and can easily move with respect to each other.The area of SMC before pressing generally constitutes only about 30% of the area of the material, final composite. 30% to 100% under the pressure effect According to the prior art, to prepare an SMC, the staple fibers are projected onto the slurry-based paste coating, and another paste coating is deposited at the top To catch the cut fibers in the same way as in a sandwich, SMC is subsequently rolled and stored and unrolled to cut a piece (usually called a "prepreg"), the area of which constitutes only 30% of the area of the The final piece, said piece is placed in a mold, and hot pressing molding is carried out.The hot-curing resin is cured during this treatment.Within the scope of the present invention n, it was discovered, in particular, that continuous fibers could be used instead of fibers cut in SMC technology. To be precise, unexpectedly, the continuous fiber coating can flow sufficiently during the SMC pressure. Meanwhile, according to the prior art, a cut fiber mesh is never used for the SMC application (since the staple fibers are projected and since a mesh is not isolated in an intermediate stage), it was then discovered that the meshing of fiber according to the invention (continuous or cut fibers) could be used within the structure of the SMC technique. The use of SMC of continuous fibers also leads to an unexpected advantage in terms of the surfaces and, more particularly, of the edges of the final composite materials. To be precise, the applicant discovered that the edge of the molded parts was much cleaner and smoother and better formed than when using staple fibers. In addition, if cut fibers are used, the necessary flow of the SMC during molding results in a preferred orientation of the fibers, which can give rise to the undulations of the surface. To be precise, since the staple fibers are independent, they follow the flows very easily and are oriented according to the flow lines. The fibers can still agglomerate or form bunches by following these flows very closely. In contrast, continuous fibers support any orientation considering their length, while at the same time sufficiently following the expansion of the SMC during pressure. Consequently, the use of continuous fibers leads to a greater homogeneity in the reinforcement of the composite material. With an identical fiber linear density, the use of continuous fibers generally leads to a composite having a higher stiffness of 5 to 12%, compared to a use of staple fibers. The manufacture of a mesh for the reinforcement of composite materials through the RTM method generally includes the deposition or projection of newly dimensioned fibers into a displaceable belt. However, the fiber bed at this stage has no consistency and can not be handled. Nor could it be rolled or unwound since its various layers of fiber would intermix. Therefore, it must be joined either chemically or mechanically. In order to chemically bind it, a chemical binder of the thermosetting or thermoplastic type, usually in powder form, is applied to it, and the heat treatment is subsequently carried out, which fuses the thermoplastic binder or polymerizes the binder of thermofixation and finally, after cooling it produces bridges between the fibers. However, this binder imparts a spring effect to the mesh structure which tends not to retain certain less progressive shapes (for example, at the corners of the mold). On the other hand, it is desirable to limit the use of chemical products in a spirit of respect for the environment. further, the heat treatment to fuse the thermoplastic binder is at a relatively high temperature (220-250 ° C), thus leading to a rough cooking of the size, which makes the fibers and therefore the mesh more rigid and more difficult to deform (the glass network is blocked then). To join a mesh mechanically, it can be subjected to conventional boring. However, this generally leads to the breaking of the fibers, thus causing a drop in the mechanical properties, and the formation of tips emerging from at least one side of the mesh. These tips then sting the hands of the handlers.

In addition, since the mesh advances while the needles planted with the mesh are fixed horizontally and placed only vertically, this gives rise to perforations larger than the cross section of the needles, thus tending to turn the needles. These perforations mark the surface, resulting in surface defects in the final part. To be precise, these holes are filled with resin, and due to the shrinkage of the resin after polymerization, the depressions remain visible on the surface. There are known meshes comprising a central core of crimped polypropylene (PP) fibers and outer layers of cut glass fibers, the total assembly being joined by means of a joined seam consisting of synthetic fiber, such as polyester (PET). Curly fiber tends to give volume to the mesh to make it easier for the resin to penetrate and fill the air space of the mold (the space between the two metal parts of the mold). However, neither PET nor PP fiber reinforces the composite material. In addition, the joined seam is visible in the final composite material, and in addition, the needles used for the joined seam give rise to holes in the surface. These holes are filled with resin and, due to the resin shrinkage after polymerization, the depressions remain visible on the surface. US 4277531 (or FR 2463221) teaches the drilling of continuous glass fiber filament meshing, typically producing 5 to 8% broken filaments. The hole produces 200 to 600 penetrations per 6.45 cm2 (that is, per square inch), therefore 31 to 93 penetrations per cm2. The manufacturing speed is necessarily very low (in the order of 1 to 2 meters per minute). US 4335176 (or FR 2494632) teaches a perforated mesh of continuous glass fibers which is produced by passing a mesh of unbonded continuous glass fibers through a felting loom or a conventional boring machine equipped with barbed needles. During passage through the piercing machine, the mesh is pierced by a series of rows of these needles, for wiring the glass fibers and separating the fibers to provide a mechanically assembled mesh containing short fibers and filaments.

After piercing, one of the meshing surfaces comprises a denser accumulation of fibers projecting from the surface, which may be referred to as spikes. The other side has 25 to 50% fewer tips than the dense surface. US 4404717 (or FR 2502199) teaches a method for manufacturing a felt perforated from a continuous coating of glass fibers containing an appreciable amount of moisture, the coating undergoing air treatment to be dried before entering the hole-equipped perforating machine. hooked needles. This treatment causes a lower staining of the piercing machine because of the fiber sizing binder. The invention solves the above-mentioned problems. According to the invention, a very special perforation is carried out in the mesh, giving the last sufficient consistency, without breaking any or only very few fibers and without forming any holes that are too long. The mesh according to the invention is sufficiently deformable by hand at room temperature, and is highly permeable to resin. According to the invention, the piercing is carried out by needles that move at the same time as the meshing, at substantially the same speed as the mesh, in a direction parallel to the direction of displacement of the mesh. In addition, the number of needle impacts is reduced and it is at most 25 strokes per cm2, preferably at most 15 strokes per cm2, and even more preferably at the most 10 strokes per cm2. In general, the number of needle impacts is at least one stroke per cm2, preferably at least two strokes per cm2. It will be recalled that meshes and felts differ markedly from one another as long as meshing is a flat article that can be used as a reinforcement, whereas a felt is an article that has volume and that can be used as thermal insulation. A mesh generally has a thickness that varies from 0.8 to 5 mm, more generally from 1 to 3 mm, while a felt is much thicker and generally has a thickness of 1 cm. A felt usually has a density ranging from 85 to 130 kg / m3. A mesh is much denser since its density can be of the order of 300 kg / m3. However, the density of a mesh is never expressed in mass per unit volume, but in mass per unit area, as a flat reinforcement. The invention, therefore, relates first of all to a method for preparing a mesh, comprising a) the deposition or projection of fibers onto a sliding belt to form a coating of said fibers that is driven by said belt, then b) boring by barbed needles passing through said covering and moving in the direction of the coating at substantially the same speed as when they pass through the latter, with a blow density varying from 1 to 25 strokes per cm2. Preferably, the beards of the needles are directed towards their support (usually called a needle board). Preferably, at least 1 barb, preferably 2 barbs, of each needle pass through the thickness of the mesh at each stroke. Preferably, the penetration depth of the needles (needle length emerging from the mesh after passing through the latter) varies from 5 to 20 mm. Preferably, the needles have a diameter (smaller circle completely containing any cross section of the needle, including the barbs) varying from 0.2 to 3 mm, still more preferably from 0.5 to 1.5 mm. Such perforation leads to a manageable mesh that is roll-up and uncoiling, is easily deformable by hand in the mold, does not pick at the hands and has no hole mark on the surface. By virtue of this very special perforation, meshing can be advanced at high speeds, for example at least 2 meters per minute and still at least 5 meters per minute and still at least 8 meters per minute. In general, the speed is at most 35 or at much more than 30 meters per minute, or even at most 20 meters per minute. During the passage of the needles through the meshing, the fibers are taken in the beards and act to form loops through the mesh, without any breaking of the fibers. These loops join the mesh and can easily deform, while at the same time retaining the function of a binder during insertion into the mold. These loops do not sting the hands because of the non-breaking of the fibers. To carry out such a hole, it is possible, for example, to use certain cylinder-type pre-needle machines normally designated for processing the polymer fiber felts, such as, for example, the machine designated PA169 or PA1500 or PA2000 sold by Asselin (NSC group). In this type of machine, the needles describe an elliptical movement with a horizontal component allowing the needles in the mesh to follow the last one in its movement. The mesh according to the invention generally has a mass per unit area ranging from 50 to 3000 g / m2. It can be a mesh with staple fibers or a mesh with continuous fibers. Thus, before cutting, staple fibers, generally with a length between 10 and 600 mm, more particularly between 12 and 100 mm, or continuous fibers are deposited or projected onto the belt by sliding in the direction of the piercing machine. Where the continuous fibers are related, these, the number of which can vary from 5 to 1200, are projected onto the sliding belt by means of a swinging arm transversely with respect to the direction of passage of the belt. For the continuous projection fiber technique, references can be made, for example, to WO 02/084005. Each of the projected fibers can comprise 20 to 500 unitary fibers (in fact, continuous filaments). Preferably, the fiber has a linear density ranging from 12.5 to 100 tex (g / km). The material forming the fibers (continuous filaments) and therefore the fibers may comprise a glass fiber, such as glass E, or the glass described in FR2768144 or an alkaline resistant glass, called glass AR, comprising at least 5 mol% of Zr02. Particularly, the use of AR glass leads to a meshing effectively reinforcing the cement matrices or capable of reinforcing thermofixing matrix composite materials that come into contact with a corrosive environment. The glass can also be boron free. Furthermore, it is also possible to use a mixture of glass fibers and fibers consisting of polymer, such as polypropylene, in particular the blended fibers sold under the Twintex® brand by Saint-Gobain Vetrotex France. The fibers used to produce the fiber therefore comprise glass fibers (filaments). The invention also relates to a method for the manufacture of a mesh, comprising the step of previously described hole. Prior to piercing, the staple or continuous fibers are deposited or cast on a sliding belt. In this step, the fibers can be dried, either because they come from wicks (or spindles) or because they have dried after sizing and before the piercing according to the invention. However, the applicant noted that it was advantageous for the fibers that are wet to enter the hole punching machine. To be precise, the passage of the belt (having served to receive the fibers) of the piercing machine takes place much easier because the fibers stick together a little due to the adhesive effect imparted by impregnating them with liguid. This adhesive effect can, in particular, be that originating naturally from the sizing of the fibers just after the fiberization. In this way, the jump or step of the machine belt - 1! The perforation, even when the fibers are not yet bonded, takes place more efficiently because of the coherence of the coating due to its impregnated state. If the fibers are dried at the beginning, they can still be deliberately impregnated before the perforation, to facilitate the steps from one device to the other, more particularly the balance of the belt that receives the fiber in the needlework machine. The mesh according to the invention can undergo at least one drying, depending on the circumstances. If the fibers used are dried at the beginning and if the fibers are not impregnated with any liquid, drying is not necessary. Drying is necessary if the fibers are impregnated with a liquid at a time of the manufacture of the mesh according to the invention. In general, the fibers are newly dimensioned at the time of their use in the method according to the invention. In this way, it is possible to dry the fibers on the slidable belt before piercing. However, as already stated, it is preferable to preserve the impregnated state of the hole, and the coating of the fibers is therefore preferably dried only after boring. Drying can be carried out by passing the slidable belt through an oven at a temperature ranging from 40 to 170 ° C, more particularly from 50 to 150 ° C. Such heat treatment does not result in an excessive hardening of the dimensioning of the fibers which retain their total flexibility. The mesh according to the invention can be integrated into a complex comprising a plurality of juxtaposed layers. In particular, the mesh according to the invention, in its variant using continuous fibers, can form the layer, with randomly distributed continuous fibers, of the fibrous structure which is the subject of WO 03/060218, the text of which is incorporated in the present for reference. More particularly, the mesh according to the invention can be incorporated into a multilayer complex having the following structure: the mesh according to the invention + the layer of staple fibers on one side of the fiber according to the invention or mesh of according to the invention + fiber layer cut on both sides of said mesh (complex with two or three layers). In this way, it is possible to deposit a first layer of fibers (for example, staple fibers, for example, to a length of between 12 and 100 mm) on the slidable belt and then deposit the fibers on this layer to form the mesh according to the invention , then carry out the perforation according to the invention and thus join the two layers together by means of the hole. A third layer (for example, staple fibers, for example, at a length between 12 and 100 mm) can also be added before the perforation according to the invention. At the end of the manufacture of the mesh, it is possible, if appropriate, to carry out a cutting of the edges of the formed meshing tape, since the edges may possibly have a structure or density a little different from the central part. There will be no deviation from the scope of the invention if one of the following procedures is adopted: a) bond the fibers of the mesh by means of a water-soluble binder (example: a polyvinyl alcohol) before the hole, then remove the binder when dissolving in water or in an aqueous solution before piercing; b) joining the fibers of the mesh by means of a water-soluble binder (example: a polyvinyl alcohol) before boring, after removing the binder on dissolving in water or in an aqueous solution after boring; c) depositing or projecting the fibers onto a film, by itself resting on a sliding belt, then joining the non-bonded fiber covering at the same time as the film (the latter preventing the various coiled layers from intermingling), for storage possible intermediate, then unwinding the film / double coating layer, removing the film and replacing the coating on a slidable strap to continue the method according to the invention. The mesh obtained by means of the method according to the invention does not contain any binder. It is symmetric with respect to a plane that is parallel to it and passes through its center. It has enough cohesion to roll up into the shape of a roller and can unwind itself for use. The invention leads, in particular, to a perforated mesh of continuous fibers or staple fibers (preferably of continuous fibers) consisting of fiberglass, if properly sized, and without any hole per needle visible to the naked eye. This mesh, therefore, contains maximum glass to reinforce the composite material as much as possible, in the absence of synthetic materials based on polymers (PP, polyester, etc.) that are not reinforcing the composite material, with the exception of the possible organic components of the dimensioning of the fibers. This meshing is advantageously used to reinforce a composite material - in the closed mold injection (RTM) method or within the structure of the SMC technology, or to directly impregnate with resin to produce panels that, in particular, are translucent.

The mesh obtained by means of the method according to the invention can be integrated into a prepreg sheet (SMC). The mailing according to the invention is then continuously inserted between two layers of hot-melt resin paste. Said mesh is unwound and then integrated directly between two layers of resin paste. In addition to the mesh according to the invention, the addition of other reinforcing layers in SMC, such as, for example, staple fibers, especially glass, is not ruled out. For example, the following procedure can be adopted: unwinding the mesh according to the invention horizontally in a layer of resin paste, then projecting the staple fibers onto the mesh, then unwinding a layer of resin paste onto staple fibers. A layer of staple fibers can also be applied before the mesh according to the invention is unwound. The sheet SMC 'can be used for the manufacture of a composite material by molding the sheet by pressing on its main sides, thus resulting in a broadening of the sheet in the mold before the solidification of the resin. If the mesh should have continuous fibers, the cut SMC sheet preferably has, before molding under pressure, an area constituting 50 to 80% of the area of the mold (and therefore the area of the final piece). The fact that a chemical binder is not used to produce the mesh according to the invention makes it possible to produce particularly translucent composite materials. To be precise, the applicant found that the absence of binder significantly improved the translucency of the final composite. In order to produce such translucent composites, it is possible, in particular, to use the method illustrated in Figure 4. According to this method, a backing film 41 (generally consisting of polyester) is unwound and has applied to it a coating layer 42 of gel (usually a polyester resin). The mesh 43 according to the invention is substantially unrolled on said gel coating layer. Another support film 44 is unwound to receive a gel coating layer 45, this assembly 44/45 being applied to the mesh according to the invention on the side of the gel coating layer. The assembly is subsequently subjected to the heat treatment by means of the unit 46 to cure the gel coating, then the two support films 41 and 44 are separated and the solid composite is received in 47. If appropriate, the composite material can be give a special shape or profile just before solidification, for example, a corrugation (example of use: ceilings). Figure 1 highly illustrates in a diagrammatic manner the principle of perforation by virtue of which the needles accompany the mesh when they penetrate the latter. The mesh 1 advances under the board 2 provided with barbed needles 3 oriented towards its support (bubble board), said board being operated in one movement having two components, one horizontal CH and the other vertical CV, by means of a system of rods of connection rotating around a fixed point 4. These various elements of the machine are dimensioned so that the horizontal component CH is substantially identical to the speed of the VM mesh when the needles are in the mesh. The illustration of figure 1 is highly diagrammatic, and what is preferred for a simple circular motion suggested by figure 1, even though it is already satisfactory, is an elliptical movement (the main axis of the ellipse being vertical and the minor axis of the ellipse being horizontal), making it possible for the horizontal component to be more efficient to maintain the mesh speed, which is generally constant. Figure 2 illustrates a needle 3 clamped on the needle board 2. It can be seen that the needle is equipped with barbs 5 directed towards the needle board, ie up when the mesh is under the needle board (the beards are directed in the same way as a hook for fish). Figure 3 illustrates in a diagrammatic manner the method according to the invention: the fibers impregnated with sizing liquid and forming the coating 1 advance in the direction of the piercing machine 7 by means of the belt 6. The coating passes on 8 of the strap 6 to the perforating machine 7.

The piercing machine comprises two large perforated cylindrical elements 9 and 9 'driven in rotation in correspondence with the speed of the belt 6. These two cylindrical elements grab the coating to cause it to advance without any distortion or elongations of the latter. The board 2 with needles 3 is located within the upper cylindrical element (the same system in the lower cylinder) and is driven in an elliptical movement 10, the horizontal component of which corresponds substantially to the speed VM of advancing the mesh. The needles pass through the upper cylindrical element which is equipped with suitable holes, then the covering to pierce the latter, then, if appropriate, the lower cylindrical element, and then rise upwards along an elliptical path. Leaving the perforating machine 7, the meshing again passes (or jumps) in 11 on another belt 12 that supplies it in the furnace 13. At the exit of the furnace, the meshing can be rolled up and stored. At the time of its use, it can be unrolled, cut, moved, handled, placed and deformed in the injection mold in the most satisfactory way. It can be easily impregnated with the injection resin. It has good permeability to the resin, above all if it is obtained from continuous fibers.

Claims (21)

1. CLAIMS 1. Method for preparing a mesh comprising glass fiber, comprising: a) the deposition or projection of fibers comprising glass fibers on a sliding belt to form a coating of said fibers that is driven by said belt, then b) punched by barbed needles passing through said coating and moving in the direction of the coating at substantially the same speed as that when they pass through the latter, with a blow density varying from 1 to 25 strokes per cm2. Method according to the preceding claim, characterized in that the puncture density of the hole is at most 15 strokes per cm2. Method according to the preceding claim, characterized in that the puncture density of the hole is at most 10 strokes per cm2. Method according to one of the preceding claims, characterized in that the puncture density of the hole is at least 2 strokes per cm2. Method according to one of the preceding claims, characterized in that the fibers are continuous fibers comprising glass fibers. Method according to one of claims 1 to 4, characterized in that the fibers are staple fibers comprising glass fibers. Method according to one of the preceding claims, characterized in that the piercing is carried out by needles fastened to a support, the beards of the needles facing said support. Method according to one of the preceding claims, characterized in that the coating and the mesh that is derived from it advance at a speed of 2 to 35 meters per minute. Method according to one of the preceding claims, characterized in that the coating and the mesh that is derived from it advance at the speed of at least 8 meters per minute. Method according to one of the preceding claims, characterized in that the coating and the mesh that is derived from it advance at a speed of at most 20 meters per minute. Method according to one of the preceding claims, characterized in that the needles describe an elliptical movement. Method according to one of the preceding claims, characterized in that the mesh does not contain any binder. 13. A perforated mesh of continuous fibers consisting of fiberglass, if appropriately sized, and without any needle holes visible to the unaided eye, said meshed joining by means of loops of said fibers. 14. Mesh according to the preceding claim is in the form of a roll. 15. Method for preparing a thermosetting matrix composite material comprising impregnating the mesh of claim 13 with a thermosetting resin. Method according to the preceding claim, characterized in that it is with closed mold injection (RTM). 17. Method for preparing a prepreg sheet (SMC) comprising the continuous insertion of the mesh of claim 13 between the two layers of the heat set resin paste. 18. Prepreg sheet comprising the mesh of claim 13 and a thermosetting resin. 19. Method for manufacturing a composite material by molding the sheet of the preceding claim by pressing on its main sides, thus resulting in a broadening of the sheet before solidification of the resin. 20. Composite material obtained by means of the method of one of claims 15, 16 or 19. 21. Composite material with a thermofixation matrix and with a reinforcement comprising continuous glass filaments.