EP0485892A1 - Striped material, process for its production and use - Google Patents

Abstract

A tape of unidirectionally aligned reinforcing and thermoplastic fibres which is built up of threads of reinforcing and/or thermoplastic fibres is described, the thread density being about 5 to 20 threads/cm width and the threads having a titre of about 1000 to 3000 dtex, and the matrix fibres being locally fused-on or fused-in with the formation of strengthening points, on at least one of the tape surfaces. The tape is suitable, for example, as a semi-finished product for the production of laminated materials. <IMAGE>

Description

The present invention relates to strip-shaped semifinished products which are suitable for producing composite materials, in particular fiber-reinforced thermoplastics.

It is already known to use so-called "organic sheets" for the production of fiber-reinforced thermoplastics. These generally consist of reinforcing fibers arranged in a band, which are melt-impregnated with thermoplastic material. Such semi-finished products are stiff and do not have the drapability of textile fabrics.

From DE-C-23 20 133 nonwovens made of unidirectionally arranged carbon fibers are known, which are impregnated with adhesive and which are held together by threads of thermoplastic material arranged perpendicular to the carbon fibers by melting these threads. DE-GBM 85 21 108 describes textile reinforcements for the production of layer structures from longitudinal and transverse thread layers. The number of crossing points between warp and weft threads is kept as low as possible. This is achieved there by an arrangement of superimposed longitudinal and transverse thread layers, which are interconnected by additional longitudinal threads made of thermoplastic material. Further configurations of textile reinforcements are described in EP-B-193 478, EP-B-193 479 and EP-B-198 776. From EP-A-144 939 a composite material of warp and weft threads made of reinforcing fibers is known, in which the warp and / or weft threads are wrapped with threads made of thermoplastic material, which causes the reinforcing fibers to be welded together by heating.

All these embodiments have in common that they have threads with different orientations.

Furthermore, DE-A-18 08 286 discloses nonwovens which consist of statistically stored threads or fibers and which have at least one thermoplastic polymer material. These nonwovens are characterized in that a consolidation has been carried out in part of the nonwoven, a certain number of binding points per unit area having a specific cross-sectional area of the binding point tips being generated in this part. The consolidation is e.g. by treating the fleece with a heated press that has a textured surface.

Finally, DE-A-34 08 769 discloses a process for the production of fiber-reinforced molded articles made of thermoplastic material, in which flexible textile structures are used which consist of reinforcing fibers that are largely unidirectional or parallel and a matrix composed of thermoplastic yarns or fibers . Essentially knitted fabrics made of these fibers are described, or strands or ribbons. These semi-finished products are then only deformed by heatable profile nozzles when they are finally shaped, with practically all thermoplastic fibers being melted.

New textile semi-finished products have now been found which have good drapability and can be processed in particular in structured press molds. The semi-finished products according to the invention have an essentially homogeneous distribution between the different types of fibers and the orientation of the reinforcing fibers is largely unidirectional. The drapability of the semifinished product according to the invention corresponds approximately to that of a woven or knitted fabric of the same basis weight made of these fibers and has the advantage over a woven or knitted fabric that the fibers are unidirectionally oriented and thus alignment of the fibers by stretching in the subsequent thermal shaping process can be omitted.

The invention relates to a band of essentially unidirectionally oriented reinforcing fibers and thermoplastic matrix fibers. It is characteristic of the tape according to the invention that it is essentially composed of yarns containing reinforcing fibers and / or matrix fibers, the yarn density of the tape is about 5 to 20 yarns / cm width, the titer of the yarns is about 1000 to 3000 dtex and the matrix fibers are locally melted or melted on at least one strip surface, forming solidification points.

For the purposes of this application, the term "yarn" is to be understood as meaning multifilament yarns, staple fiber yarns, mixed yarns made of multifilaments and staple fibers and also monofilaments. For the purposes of this application, the term “fiber” is understood to mean both staple fibers and endless filaments.

The yarn density of the tape is chosen so that the distance between the yarns making up the tape is not too great, so that it is still possible to form consolidation points between adjacent yarns. Usually the distance between the yarns in the band should be less than about three times the diameter of a monofilament from the titer of the yarns. The titer of the yarns made of reinforcing and / or matrix fibers is generally 1000 to 3000 dtex, preferably 1500 to 2500 dtex.

Reinforcing fibers and matrix fibers can be in the form of separate yarns as well as mixed yarns. Bicomponent fibers made of reinforcement and matrix components can also be used. The reinforcing fibers in the yarns are preferably in the form of multifilaments. Mixed yarns made of reinforcing and matrix fibers are very particularly preferably used.

Blended yarns can be made using any of the conventional blending techniques such as Ring or 3-cylinder spinning, commingeling techniques, mixed twisting or DREF techniques.

It is particularly preferred to use multifilament blended yarns made from reinforcing and matrix fibers, in which at least part of the yarn consists of high-modulus individual filaments of an initial modulus of more than 50 GPa, in particular more than 80 GPa, which are mixed by means of a mixing medium, preferably air, are available, wherein the high modulus individual filaments have been preheated to a temperature of 0.25 Ts to 0.9 Ts prior to mixing and the mixing takes place at a temperature at which the matrix fibers are essentially retained; in particular, the mixing is carried out in the non-heated mixing medium. Here, Ts means the melting or decomposition temperature of the high modulus single filaments in ° C.

These particularly preferred multifilament blended yarns are characterized in that the average mixing distance of the yarn, measured in the needle test, is less than 150 mm and that the number of breaks in the individual filaments, measured in the light barrier method on one side of the yarn, is less than 20 / m .

Practically all non-meltable or high-meltable, high-modulus and / or high-strength fibers can be considered as reinforcing fibers. These fibers are selected so that they do not yet melt under the processing conditions suitable for the thermoplastic fiber fractions or practically do not deform thermoplastic and are present as reinforcing fibers in the resulting composite material.

Examples of such fibers are glass fibers, carbon fibers, fibers of various metals and Metal alloys, from a wide variety of metal nitrides or carbides, metal oxide fibers or fibers from organic polymers, such as from polyacrylonitrile, polyester, aliphatic and aromatic polyamide or polyimide.

Glass, carbon, metal or aramid fibers are preferably used.

All materials that can be reversibly processed thermoplastically are suitable as the thermoplastic material. Examples of this are metals and metal alloys, glasses and in particular organic materials. The organic materials are primarily known, optionally solvent-containing, but preferably solvent-free, known organic thermoplastic molding compositions.

Examples of thermoplastics are polymers, such as vinyl polymers, for example polyolefins, polyvinyl esters, polyvinyl ethers, polyacrylic and methacrylates, polyvinyl aromatics, polyvinyl halides, and a wide variety of copolymers, block, graft, liquid crystal, mixed polymers or polymer mixtures. Special representatives are: polyethylenes, polypropylenes, polybutenes, polypentenes, polyvinylchloride types, polymethyl methacrylates, poly (meth) acrylonitrile types, optionally modified polystyrenes or multiphase plastics such as ABS. Furthermore, polyaddition, polycondensation, polyoxidation or cyclization polymers, LC polymers, such as polyamides, polyurethanes, polyureas, polyimides, polyesters, polyethers, polyhydantoins, polyphenylene oxides, polyphenylene sulfides, polysulfones, polycarbonates, as well as their mixed forms, their mixtures and combinations with other polymers or polymer precursors, for example polyamide-6; Polyamide-6.6; Polyethylene terephthalate or bisphenol-A polycarbonate.

However, the polymers mentioned can also serve as reinforcing fiber material if they are processed with lower-melting fibers, which according to the invention act as thermoplastic components.

The filaments or staple fibers building up the yarns can have a practically round cross-section or can also have other shapes, for example a dumbbell-shaped, kidney-shaped, triangular or tri-or. have multilobal cross-section. Hollow fibers can also be used.

Bicomponent or multicomponent fibers can also be used in particular as thermoplastic fibers, for example of the core / jacket type or of the side / side type or of the matrix / fibril type.

The semi-finished product according to the invention is so solidified by local melting of the matrix fibers that it can be handled without problems without losing its tape shape, but at the same time has good drapability, rollability and transportability. The semi-finished product according to the invention can be stored almost indefinitely and indefinitely, since there are practically no curing components. The consolidation points are located at least along one surface of the belt, but can also be along both surfaces. It may be sufficient in individual cases that only a surface fixation of the tape has taken place.

However, it is also possible that the local consolidation points run practically through the cross section of the entire band. It is essential in all of these embodiments that the melting of the matrix fibers takes place locally and that the individual matrix fibers and / or reinforcing fibers can each move practically freely between two solidification points. The mean free distance between two fastening points is preferably about 1 to 5 cm.

The density of the solidification points along the surface will depend, among other things, on the type and amount of the thermoplastic fibers and on the ratio of thermoplastic and reinforcing fibers. It is also possible to apply a pattern of solidification points to the tape, i.e. to provide only parts of the surface of the belt with consolidation points.

Usual values for the density of consolidation points, based on the unit area of the belt surface, are in the range from 40 to 500,000 points / m² surface, preferably 100 to 40,000 points / m² surface (with one-sided application of consolidation points to the surface; with two-sided Applying usually half the density per surface is sufficient). A consolidation point preferably connects several reinforcing yarns.

The volume ratio of the reinforcement to the matrix fibers in the semifinished product according to the invention can be chosen as desired within wide limits. The volume fraction of the reinforcing fibers can e.g. Amount to 10 to 90% and the volume fraction of the matrix fibers accordingly 90 to 10%. The volume fraction of the reinforcing fibers is preferably 20-80%, in particular 40-70%.

Preferred embodiments of the semi-finished product according to the invention are presented in claims 2 to 7.

• a) eine bandförmige Anordnung aus im wesentlichen unidirektional ausgerichteten Verstärkungsfasern und aus thermoplastischen Matrixfasern in Form von als Fadenkette angeordneten Garnen bereitstellt, und
• b) lokal begrenzt zumindest auf einer der Oberflächen dieser Anordnung erhöhte Temperaturen erzeugt, gegebenenfalls in Kombination mit erhöhten Drucken, so daß die Matrixfasern an diesen Stellen an- oder aufschmelzen und sich lokale Verfestigungspunkte ausbilden.

The semifinished product according to the invention can be produced by

• a) a band-shaped arrangement of essentially unidirectionally oriented reinforcing fibers and of thermoplastic matrix fibers in the form of yarns arranged as a thread chain, and
• b) locally, at least on one of the surfaces of this arrangement, produces elevated temperatures, possibly in combination with increased pressures, so that the matrix fibers melt or melt at these points and local solidification points form.

The method is also the subject of the present invention. Local elevated temperatures can be generated by treating the band-shaped arrangement with heated embossing rollers. The yarn strip can be passed between two embossing rollers or in particular between a roller with a smooth surface and a roller with a structured surface or partially structured surface. However, locally elevated temperatures can also be generated in any other way, for example by the action of hot gas streams or heated stamps or by ultrasound or high-frequency electromagnetic radiation (high-frequency welding).

These latter two embodiments are particularly preferred since they can be used to achieve a practically unlimited number of patterns at consolidation points, for example by guiding the heat sources in predetermined ways over the belt surface and by specifically switching the heat source on and off. This control can e.g. to be under the control of a computer.

FIGS. 1a, 1b, 2a and 2b show two exemplary embodiments of the method according to the invention.

FIG. 3 shows an example of an embodiment of the semi-finished product according to the invention.

Figure 1a relates to an embodiment in supervision, while this embodiment is shown in Figure 1b in side view.

The unidirectional yarn sheet (2) running from a warp beam (1) (shown in FIG. 1a only over part of the entire warp beam length) consists of at least one type of thermoplastic fiber, such as polyester, polyethylene, polyamide, polyphenylene sulfide, polypropylene, polyetherimide -, Polyetherketone, polysulfone or partially halogenated polyolefin fiber, and at least one type of reinforcing fiber, such as glass, carbon, metal, ceramic or aramid fiber.

The unidirectional yarn group (2) is passed between the heated embossing rollers (3) and (4). One of these rollers can also have a smooth surface. Under the influence of pressure and heat at the locations of the raised parts of the embossing roller, local melting of the thermoplastic fiber occurs and thus melting points between two or more warp yarns lying next to one another. After leaving the area of the embossing rollers (3) and (4), the melting zones solidify and result in a positive connection between these warp yarns.

In Figure 1a, these solidified local melting zones (5) are shown in the form of a stripe pattern. After solidification, the band (6) can be wound onto a roll (7).

Figure 2a relates to a further embodiment in supervision, while this embodiment is shown in Figure 2b in side view.

The unidirectional yarn sheet (2) running from a warp beam (1) (shown in FIG. 2a only over part of the entire warp beam length) consists of at least one type of thermoplastic fiber, e.g. such fibers as mentioned by way of example in the description of FIG. 1a.

The unidirectional group of yarn (2) is carried out between a suitable base (8) and the selective melting unit (9). Such a selective melting unit can be, for example, an ultrasound probe, a hot gas supply, a heated stamp or an electromagnetic energy source. The melting unit can be moved parallel to the warp beam axis and in the vertical direction, a computer can control this process as well as switch the energy supply on and off. Likewise, the use of several melting units on a base as well as the use of several combinations consisting of melting unit (s) and base (s) one after the other. As a result, a higher throughput of the plant can be achieved.

The support (s) can be moved vertically (8a) in order to adjust the changes in diameter of the warp beam winding and roller (7).

Under the influence of heat at the locations of the reflow unit (9), the thermoplastic fiber melted locally and thus to fusion points between two or more warp yarns lying next to each other. After leaving the area of the melting unit (9), the melting zones solidify and result in a positive connection between these warp yarns.

These solidified local melting zones (5) are shown in FIG. 2a in the form of a striped pattern. After solidification, the band (6) can be wound onto a roll (7).

FIG. 3 shows an embodiment of the semi-finished product according to the invention. The band (6) is made up of a group of yarn (2). In this embodiment, mixed yarns (10) made of reinforcing and matrix fibers are used as yarns. The band (6) has solidified local melting zones (5), on each of which two adjacent yarns are connected to each other.

Claims (11)

Ribbon of essentially unidirectionally oriented reinforcing fibers and thermoplastic matrix fibers, characterized in that it is essentially composed of yarns which contain reinforcing fibers and / or matrix fibers, the yarn density of the ribbon is about 5 to 20 yarns / cm width, the yarn titer is about 1000 to 3000 dtex and the matrix fibers are locally melted or melted on at least one belt surface, forming solidification points. Belt according to claim 1, characterized in that it is made up of a mixture of yarns made from reinforcing fibers and yarns made from matrix fibers. Belt according to claim 1, characterized in that it is constructed as a mixed yarn from reinforcing and matrix fibers. Band according to claim 1, characterized in that it is made up of bicomponent fibers with a reinforcement and a matrix component. Belt according to claim 1, characterized in that the consolidation points are arranged in a regularly repeating pattern. Belt according to claim 1, characterized in that the consolidation points are statistically distributed over the belt surface. Belt according to claim 1, characterized in that the consolidation points make up about 5 to 50% of the surface of the belt. A method of making the tape according to claim 1 comprising the steps of: a) producing an arrangement of essentially unidirectionally oriented reinforcing fibers and of thermoplastic matrix fibers in the form of yarns arranged as a thread chain, and b) Generation of locally limited elevated temperatures and possibly increased pressures on at least one of the belt surfaces, so that the matrix fibers melt or melt at these points and local consolidation points form. A method according to claim 8, characterized in that the formation of local solidification points is carried out by means of a heated embossing roller. Method according to claim 9, characterized in that the formation of local solidification points takes place by means of ultrasound or high-frequency electromagnetic radiation. Use of the tape according to one of claims 1 to 7 for the production of composite materials, in particular fiber-reinforced thermoplastics.

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