DE3408769A1 - Process for producing fibre-reinforced mouldings and profiles - Google Patents

Abstract

The invention relates to a process for producing fibre-reinforced mouldings from thermoplastic material by hot press moulding of flexible textile formations from fibres or yarns with a thermoplastic character as matrix, the fibres being arranged substantially parallel, and from fibres or yarns of reinforcing material, the reinforcing fibres being aligned by stretching before or during melting for hot press moulding.

Description

Process for the production of fiber-reinforced molded articles

core and profiles are molded parts made of fiber-reinforced thermoplastics usually produced by incorporating fibers into thermoplastic granules or mixtures of thermoplastic granules or powders and fibers in the heat e.g. be deformed on extruders or injection molding machines.

These methods do not allow the incorporation of long fibers into the thermoplastic matrix, e.g. of fabrics, and due to the incorporation and processing problems mostly no more than 30% by weight of reinforcing fibers, e.g. Fiberglass, too.

If fabric made of reinforcing fibers is impregnated with thermoplastic materials, this gives rigid semi-finished products that can be hot-formed in presses to form molded parts with good properties. Even with these processes it is necessary because of the Uniformity of the impregnation the amount of reinforcement fabric to be incorporated limited.

However, the rigid semi-finished products are often disadvantageous because of their rigidity in handling and processing.

If you sprinkle fabric with thermoplastic powders, you have a flexible one Semi-finished product that can be conveniently placed in molds or the like when hot-pressed However, the viscosities and flow paths of the thermoplastic melt produced are so unfavorable that that the individual fibers of the fabric yarn are not or only very incompletely from the thermoplastic can be surrounded or enclosed, i.e.

molded parts with unsatisfactory mechanical properties result.

Glass fiber reinforced profiles with a high proportion of reinforcing fibers are obtained when fiber strands (rovings) with reactive resins, which in relative thin liquid form, soaked and then through heated calibration sections pulled and so hardened with deformation. Such profiles are, however duroplastic, i.e. they are cross-linked and cannot later be deformed in the heat will. This process is limited to reactive resins and for the use of prefabricated high molecular weight thermoplastic polymer materials not suitable. However, there is a need for reinforcing fiber-containing profiles made of thermoplastics.

The present invention leads to substantially void-free thermoplastic molded parts with reinforcement fiber contents up to more than 70% by weight (e.g. glass) with any fibers Length that is largely enclosed by the thermoplastic as a homogeneous matrix. she uses flexible textile semi-finished products made from mixtures of at least two types of fiber, in which at least one type of fiber can be melted and as a thermoplastic acts and at least one type of fiber when melting the aforementioned type of fiber as this is retained when the semi-finished textile products are hot-pressed with deformation will.

The fiber used below is an endless or limited length monofilament and as a yarn the combination of many fibers into a multifilament.

As usual, staple fibers are short-cut fibers.

The inventive method for the production of fiber-reinforced Molded bodies made of thermoplastic material by hot pressing of flexible textiles Formed from mixtures of at least two fiber types, with at least one fiber type is meltable under hot pressing conditions and acts as a thermal plastic and at least another fiber type is retained as such under the aforementioned conditions and acts as a reinforcing fiber in the finished part, is characterized in that a matrix made up of fibers or yarns (.A.) is used as the textile structure thermoplastic character is used, which is unidirectional or aligned in parallel, respectively.

largely before or after melting the thermoplastic components unidirectional or parallel orientable reinforcing fibers or yarns (.B.) contains in the composite, the fibers or yarns (.A.) wholly or partially made of reinforcing Material consist, and the reinforcing material (B) before or during melting is aligned unidirectionally or parallel for hot pressing by stretching.

When stretching, a tensile stress in the direction of the planned one is preferred Thread course of (.B.) Exercised.

Of particular interest are: either fibers with the character of Bi- or multi-component, fibers with star, dumbbell or core-jacket structure according to Figure 1c, d, e in addition to the normal structures according to Figure 1 a, b, and / or yarns or Fiber bundles, rovings with a bi- or multi-component structure according to Fig. 1f, g, h, i, k, where at least one component is thermoplastic (-) and at least one Component represents the reinforcing portion.

Of particular interest are: made of fibers and / or yarns or fiber bundles, Textile structures made up of rovings in accordance with the basic idealized structures Fig. 2 (1-10), the direction of the tensile stress being indicated by arrows in the preferred direction is specified.

In a particular embodiment, these are flexible textile Formed bundles or strands of the fibers or yarns described.

Thermoplastic are all materials that are reversible or intermediate have thermoplastic processing, for example metals and their alloys, Glasses and in particular organic materials. When it comes to organic materials they are above all, optionally containing solvents, but preferably solvent-free known organic thermoplastic molding compounds. But it can also be thermoplastic Reactive systems, i.e. thermosetting plastics that become thermoplastic when heated Go through phase and then with molecular enlargement or crosslinking their thermoplastic character lose irreversibly. Examples are polymers, especially vinyl polymers, e.g.

Polyolefins, polyvinyl esters, polyvinyl ethers, polyacrylates and methacrylates, Polyvinyl aromatics, polyvinyl halides, as well as a wide variety of copolymers, block, Graft, liquid crystal, mixed polymers or polymer mixtures.

Special representatives are: Polyethylene, Polypropylene, Polybutenes, Polypentenes, polyvinyl chloride types, polymethyl methacrylates, poly (meth) acrylonitrile types, optionally modified polystyrenes or multiphase plastics such as ABS. Further Polyaddition, polycondensation, polyoxidation or cyclization polymers, LC polymers such as polyamides, polyurethanes, polyureas, polyimides, polyesters, Polyethers, polyhydantoins, polyphenyloxides, 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, Bisphenol-A polycarbonate, etc. or as intermediate thermoplastic materials, which are mostly to be seen as precursors to higher polymer structures: Phenolic resin precursors, Furan resin precursors, melamine resins, epoxy compounds, compounds with polymerizable Double bonds or double bonds capable of addition, polyimide precursors, higher molecular weight Polyisocyanates or combinations of reactive polymers and when appropriate High temperature reactive crosslinking agent, e.g. containing OH, NH or COOH groups Polymers and crosslinkers with methylol groups.

However, the polymers mentioned can also be used as reinforcing fiber material serve when processed with deeper melting fibers, according to the invention act as thermoplastic components.

Flexible textile structures are understood to mean, for example, rovings, fiber strands, Fiber yarns, knitted fabrics, scrims, knitted fabrics, braids, woven fabrics, fleeces made of fibers or Yarns that still have a flexibility so that they can at least be rolled up or - without breaking - can be bent, preferably have such structures, e.g. in the form of strands, ribbons, tubes, flat structures, but a normal one, little stiff textile character.

The textile, flexible structures should consist of mixtures of at least two types of fibers exist.

According to the invention, it is also possible to use multicomponent fibers to use, e.g. to combine two types of fiber in one fiber by making a bifilar fiber or- core- Sheath fiber used; for a core-clad fiber the thermoplastic is preferably arranged as a fiber sheath. Usually they are different But fiber types are separated.

Here it is possible to mix the different fiber types with one another to process, with a mixture that is as uniform as possible and lying as parallel as possible Fibers of different types should be aimed for, but it is also possible in textile Yarns made from different fiber types, e.g. staple fibers or continuous fibers, to be processed in a mixture that is as uniform as possible, it can also be used, for example, in one The warp and weft fabrics consist of different types of fibers.

The statistical mixture of different fibers lying as parallel as possible Type is for endless fibers or long fibers by merging the different Fiber types, through joint spinning with adjacent spinnerets or easy through simultaneous feeding into the usual textile manufacturing processes achievable, with short fibers or the production of sandwich structures, the different fiber types e.g.

by electrostatic flocculation processes and later directional uniform folding over of the batt e.g.

mixed on heated rollers.

The combination of fibers with different melting points to produce of thermoplastically deformable semi-finished products has in principle been known for a long time, e.g.

for the consolidation of nonwovens by means of integrated thermoplastic Hot-melt adhesive fibers or for the consolidation of fiber strands made from non-melting ones Fibers through thermoplastic adhesive fibers that are spaced apart perpendicular to them.

In general, however, these are textile constructions, which are not used directly for the production of fiber-reinforced thermoplastic molded parts can, but previously laminated with reactive resins or thermoplastic sheets or need to be equipped. It has also been proposed to use resins To compress finished fabric thermoplastically to form molded parts, their warp and their weft made of different types of fibers with melting points differing by at least 200C exist, or to process nonwovens from such fiber mixtures thermoplastically. The present invention, on the other hand, uses mixtures that are essentially parallel Reinforcement fiber types that are compressed by stretching and unidirectional and which can be processed without the need for additional resin.

The present invention particularly relates to knitted fabrics and their variants, in which the at least two types of fibers or yarns in a mixture of the arrangement shown schematically in cases a to h.

They are also possible by stitching, sewing, weaving, drawing in or Constructions with fibers or yarns A or B to be considered, some of which are exemplified according to 1 to 19 (page 4) are shown.

In addition to the arrangements shown, their combinations are also possible to draw, or strands, fiber or staple yarns made of bifilar or core / sheath fibers.

In the case of semi-finished products that are in the form of fiber strands, the arrangements are f to h of particular interest.

It goes without saying that multiples and combinations of those shown are also possible Arrangements possible, e.g. more than just one fiber or a fiber bundle (yarn) one fiber py each in cases a to h.

The textile structures should be made up of at least two types of fibers be, with at least one acting as a thermoplastic and at least one other is retained as such, while the former fiber type in the hot pressing process in the surrounding matrix is transferred.

The fibers can be sized or unsized.

Mostly sized fibers are used, which is an advantage can be to use sizes for the non-melting fibers, which on the are optimized for each type of thermoplastic. Such types of sizes e.g. for glass fibers are known.

It can also be oxidized, metallized or superficially elsewhere altered fibers should be considered.

The weight ratio of thermoplastic to other fiber types can fluctuate within the textile structure used as a semi-finished product, e.g. by special reinforcement effects on certain geometric areas of the desired molded part to achieve; Usually, however, the textile structure has a uniform structure, as far as the areal average fiber composition is concerned. Of course, e.g. by weaving in or embroidering or knitting in special patterns or geometries in the textile structure its overall character in relation to special requirements on the processability or the properties of the moldings to be produced therefrom be adjusted.

The weight ratio of the fiber types can in principle be chosen as desired will. The best molded part strength is obtained when it is not thermoplastic deforming fiber content 10 to 90% by weight, preferably 20 to 85% by weight, in particular Is 60 to 80 wt%.

The type of thermoplastic fiber can be selected from those described above Materials. The diameters and lengths of the thermoplastic are preferred Fiber proportions approximately the diameters and lengths of those that do not act as thermoplastics Fiber proportions the same.

Fibers that do not function as thermoplastics are understood to be those those among those for the thermoplastic Suitable fiber proportions Hot-pressing conditions do not yet melt or are thermoplastically deformed, i. E.

as such are preserved. It is quite possible that such fibers, glass fibers, for example, could also act as thermoplastics at higher temperatures. In addition to glass fibers, there are, for example, other inorganic and organic fibers suitable, such as carbon fibers, fibers made of various metals and metal alloys, made of steel, brass, copper, aluminum, a wide variety of metal nitrides or carbides, metal oxide fibers, such as Al oxide fibers, silicate fibers, e.g.

Kaolin fibers, calcium silicate fibers, calcium sulfate fibers, fibers made from a wide variety Glasses, fibers made from organic polymers such as polyacrylonitrile fibers, polyester, Polyamide fibers, polyimide fibers, such as those used under the trade names Dralon, Trevira, Perlon, Kevlar have become known.

The flexible textile structures composed according to the invention are particularly easy to handle. They can be rolled, wrapped or folded and if necessary specially structured by the manufacturing process of the textile structure and be specially adapted to the requirements of the molded part.

Accordingly, they can also be processed continuously from the roll, for example or, if necessary, directly on site.

The textile structures used as semi-finished products are expediently used Dry as well as possible before processing. The processing is done by hot pressing, optionally with the application of a vacuum or a high vacuum or under protective gas according to methods familiar to the person skilled in the art.

According to the invention, the textile structure should preferably be used during processing be stretched in the direction of the grain of (B) (see page 4) in order to achieve unidirectionalization and to bring about extensive parallelization of the fibers of (B).

This can be the case with textile structures that have a simple mesh structure, for example (possibly only in selected areas) already largely before the melting process or also during the melting process and before or optionally take place during the pressing process.

It is preferable to work with a bias and during the Heating continues under tension with simultaneous elongation and with increasing Press pressure worked.

In the simplest cases, this is always guaranteed if that textile structures e.g. in the form of a strand through conical nozzles, the temperatures between 80 and 6000C, preferably 80-3800C, drawn or through Roller pairs can be drawn with appropriate heating. Leave on this path if necessary, stepwise or multi-step, highly reinforced strands and bands produce.

In the case of deep-drawing flat textile structures according to the invention Art, the stretching takes place at least partially during the deep-drawing process and the mostly combined with hot pressing in the specified temperature range.

The pressing pressures can be between 0.5 and over 200 bar, they direct as well as the pressing temperatures from approx. 80 to over 380 ° C, preferably 1500-3000C, according to the requirements of the fiber material, the construction of the textile structure and the shape for the molded part and can easily be carried out on a case-by-case basis by means of preliminary tests be determined.

The deformation process can also take place in several pressure and / or temperature stages be carried out, e.g. to first pre-consolidate the originally flexible To achieve the semi-finished product and later to connect the final deformation. Even partial hot pressing measures to modify the original semi-finished textile product are possible, e.g. partial consolidation or welding on special geometric Locations of the semi-finished product.

A particular advantage of the method according to the invention is that that such thermoplastic materials are also processed into fiber-reinforced molded parts which result in particularly highly viscous melts and are therefore less than conventional Processing conditions show poor flow behavior. By the in the prefabricated Semi-finished product, e.g. a knitted fabric, given spatial proximity of the two The fiber content is only a very short one in the final processing step into the finished part To provide flow path from the thermoplastic component.

It is also particularly easy to use the procedure according to the invention Molded parts made from combined reinforcing fibers such as glass / carbon or glass / aramids Etc.

to produce their simultaneous incorporation into thermoplastic Granules for injection molding in amounts greater than 20% extremely difficult if is not impossible.

If you work with textile flexible fiber bundles, then you can create profiles and molded bodies by drawing (continuously or intermittently) through heatable Nozzles or nozzle cascades with possibly different geometries or temperatures or pressures or speeds or in the pulling direction open molds or heated Create (metal) immersion baths with deformation.

Also deforming on heatable pairs of rollers, roller mills or split in rollers or without direct contact with mold surfaces, e.g. through Exercising a pull on the fiber strand or by wrapping a strand, e.g. also with thermally shrinkable threads, and simultaneous or previous or subsequent heating, if necessary under protective gas, comes into consideration here. The wrapping can also be with metal or mineral or. Glass fibers are made that Heating by conduction, heating gas, thermal radiation, high frequency, ultrasound, Microwaves or other processes.

The use of non-stick coatings or lubricants on the Deformation distance must be taken into account, e.g. fluoropolymers, waxes, fats, Silicone oils, etc.

The hot pressing of textile hoses, tapes, Strips or bundles of fibers under tension continuously between heatable Profile rolls or by means of heatable nozzles or nozzle sections. In this way it is particularly easy to create, preferably unidirectionally reinforced, endless profiles, e.g. round bars, bars with rectangular, triangular, T-shaped, U-shaped, Z-shaped or O-shaped cross-sections, e.g. produce pipes. Especially unidirectional fiber-reinforced thermoplastic profiles can be produced in such a way that, due to the high, Reinforcing fiber content achievable with this process has excellent tensile strengths own the longitudinal direction.

By wrapping objects under tension and under melting conditions (e.g. optionally IR radiation) by means of textiles constructed according to the invention Ties or ribbons, hoses, bundles of fibers, can be used with these items a mechanically high-performance surface layer.

The semifinished products according to the invention should in principle be bundles or flocks of lying as parallel as possible or by pulling before or during the melting process process represent parallelizable reinforcing fibers.

But it should also be remembered that this fiber arrangement by not parallel fibers can be fixed, e.g. by wrapping or needling of fiber bundles or by placing fiber bundles through weft threads or interweaving or Welds, bonds are fixed. It is also to be considered that instead of or together with fiber bundles, ribbons made of fibers are also used can. These in turn can be knitted fabrics, scrims, braids, knitted fabrics, woven fabrics or nonwovens made of fibers, yarns or ribbons. It can also be attached to a fixation of the fibers within the fiber bundle by a partial or continuous, more or less loose bonding can be thought of using a wide variety of binders. Often, however, you can work without such fixation aids, it is enough then the natural parallel position of the fibers in the unidirectional fiber array the end.

There can also be strands of different fiber types in if necessary special geometries can be combined into a semi-finished product, so that e.g. profiles are available are, in some areas with glass fibers, in other areas with C-fibers are reinforced.

The flexible semi-finished products should consist of at least two types of fiber.

A special case to be considered here is that it is according to the invention It is also possible to combine two fiber types in one fiber by making a bifilar fiber or core-sheath fiber is used, in the case according to the invention is with a core-sheath fiber the thermoplastic is preferably arranged as a fiber sheath. Usually they are at least two types of fibers, however, contained as separate individuals in a mixture in a kind of roving.

It is possible to use the various fiber types preferably to be processed as such in a mixture with one another, with a uniform as possible A mixture of fibers of different types lying as parallel as possible is to be aimed for. But it is also possible to use yarns made of different fiber types in the textile structure, e.g. staple fibers or continuous fibers, to be processed in a mixture that is as uniform as possible. It can also be envisaged, e.g.

warp and weft made from the various fiber types in one fabric tape to use.

The statistically best possible mixture lying as parallel as possible Fibers of various types is for continuous fibers or long fibers by merging of the different fiber types through simultaneous feeding into the usual textile Processing processes easily possible in a manner familiar to the person skilled in the art.

A prototypical representation of various embodiments is provided given as an example on page 4 of this text.

The process products can be used, for example, for production of anchoring and spring elements, tensioning devices, suspension devices, Tension absorbing elements in sheaths or cores of electric, microwave or fiber optic cables, as pulling or sliding shafts for insertion into empty pipes, as reinforcement elements in plastics, organic and inorganic concretes, earths and mortars, as nails and screws, split pins, tubes and rods, as plate, housing, container and body material, as weldable construction material or thermally deformable, highly reinforced Semi-finished plastic products with a linear, flat or three-dimensional design.

In the following examples, parts are always parts by weight and percentages always percentages by weight, unless otherwise noted.

The following examples are with polyamide compatible (sized) Made of glass fibers (approx. 25 ßm ~) and polyamide. The polyamide is a perlon fiber (about 20 Am ~) and represents the thermoplastic. In place of the glass fibers can carbon or polyaramid or metal fibers also take the place of Perlon also aromatic polycarbonates, polystyrene, polypropylene or polyethylene terephthalate.

Example 1 By bringing together (monofilaments) fibers in a weight ratio 72 (glass) to 28 (Perlon) a kind of yarn (roving) is produced, which in weak twisted and untwisted form is wound.

From the untwisted material and from the lightly twisted material one knitted piece each (A and B) with a m2 weight of approx. 1,100 g is produced.

It is also made from a glass fiber roving and a polyamide roving in a weight ratio of 60% glass to 40% polyamide a knitted part of the same type (C) produced, in which, however, there is a row of stitches glass and a row of stitches Alternate polyamide.

All knitted parts are fully textile-flexible and can be rolled up, sew, thermally weld and fold.

The knitted pieces represent 5 cm wide ribbons, the thread run (i.e. In the context of the present text, the direction in which the thread runs through the The textile part runs regardless of local diversions, e.g.

due to the mesh structure) is parallel to the longitudinal axis of the belt.

This tape is dried over silica gel and pulled using a traction device under constant tension of 9 N by a metal bath drawn from 2500C, with an elongation of approx. 300 8 and at the same time a Reduction of the width to approx. 20%.

The resulting strand leaves the metal bath through a conical slot nozzle with a cross-section of 2 mm x open to the subsequent air-cooling section 10 mm.

An almost unidirectional reinforced polyamide strip profile is obtained, which can be permanently deformed at 1800C and has high rigidity.

A visual examination reveals that the one from the knitted part A profile produced a weak wavy line of the reinforcing fibers in the direction of the thread results, and that the individual strands of the reinforcing fibers penetrate each other. The deviation from a strictly unidirectional arrangement of the reinforcing fibers however, it is only minor.

The profile from the knitted part also offers an almost identical picture B. When made from the knitted part C profile shows a strict, itself non-penetrating parallel layer of the reinforcing fibers with only very little corrugation in the direction of pull of the profile.

The profiles from A, B and C have the following tensile strengths measured in the direction of the profile axis: A 1 200 Nimm2 B 1 055 N / mm2 C 910 N / mm2 The lower tensile strength at C with a more ideal structure is explained from the lower proportion of glass in this sample.

Example 2 A zigzag stitch is used on a 5 cm wide polyamide tape a fiberglass yarn in several rows that overlap in the axial direction of the tape brought on both sides, so that the resulting textile structure (band) the structural elements 12 represented on page 4 in repetitive order. In the resulting volume the weight ratios of polyamide to glass are 40 to 60.

This tape is on the apparatus described in Example 1 below pulled through the heated drawing section under the same conditions. A band profile is obtained with a strength of 855 Nimm, in which the glass threads are almost parallel.

Example 3 One by combining bisphenol A polycarbonate fibers (endless filament yarn, approx. 10 dtex) and E-glass fibers (endless) made fiber bundle (so-called combination roving) in a ratio of 20:80 is under low tension so Pulled through a heated nozzle (> 2000C) so that the polycarbonate fibers melt and penetrate between the E-glass fibers under the shaping force of the nozzle. (The The nozzle can also be under vacuum -> 1 Torr inside.) Immediately behind the heated nozzle is the so formed reinforced thermoplastic profile with a suitable device, as it is the prior art, more or less closely with an organic or inorganic fiber material wound around the transverse compressive strength of the resulting profile.

A 3 mm round profile produced in this way has a tensile strength of approx. 1600 N / mm2 and a breaking force of approx.

8000 N.

Example 4 A procedure analogous to Example 3 can take place of a mixed roving also a roving made of core / sheath fibers (sheath polycarbonate or other thermoplastics, core E-glass or S-glass) can be used. Man When using bisphenol-A-polycarbonate and E-glass, it gets the same Profile with the properties mentioned in Example 3.

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Claims (2)

Claims Process for the production of fiber-reinforced molded bodies Made of thermoplastic material by hot pressing of flexible textile structures from mixtures of at least two fiber types, with at least one fiber type under Hot pressing is meltable and acts as a thermoplastic and at least one other fiber types are retained as such under the aforementioned conditions and in the finished part acts as a reinforcing fiber, characterized in that as textile structure consisting of a thermoplastic matrix composed of fibers or yarns (A) Character used, the unidirectional or parallel aligned or in front of or after melting the thermoplastic components largely unidirectional or parallel contains orientable fibers or yarns (B) in the composite, the fibers or yarns (A) consist entirely or partially of parts functioning as thermoplastic and the Fibers or yarns (B) consist entirely or partially of reinforcing material, and the reinforcing material prior to or during the melting for hot pressing Stretching is aligned unidirectionally or in parallel. 2. The method according to claim 1, characterized in that the stretching tension when stretching in the direction of the thread path of the fibers or yarns (B) onto the textile Structure is exercised.