EP3049231A1

EP3049231A1 - Method for using cutting remainders of fiber structures

Info

Publication number: EP3049231A1
Application number: EP14766691.1A
Authority: EP
Inventors: Matthias Scheibitz; Heiko Heß; Jens Cremer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2013-09-24
Filing date: 2014-09-12
Publication date: 2016-08-03
Also published as: KR20160062078A; CN105579214A; JP2016531960A; WO2015043985A1; US20160236376A1; BR112016006381A2

Abstract

The invention relates to a method for using cutting remainders of fiber structures, comprising the following steps: (a) cutting the cutting remainders to flakes, (b) admixing the flakes to a polymer melt, (c) kneading the polymer melt containing the flakes such that the flakes disintegrate into individual fibers, and (d) shaping the polymer melt containing the admixed fibers to a semi-finished product.

Description

Method for using cut remnants of fiber structures Description

The invention relates to a method for using cut remnants of fiber structures.

Fiber structures are, for example, knitted fabrics, woven fabrics or scrims made of fibers, as used for the production of continuous fiber-reinforced composite materials.

For the production of continuous-fiber-reinforced composite materials, fiber structures are usually placed in a mold and these are then poured out with a polymeric material, for example a thermoset or a thermoplastic. The fiber structures can be used, for example, in the form of a woven fabric, a knitted fabric or a fabric. In this case, it is possible to position a plurality of structures one above the other, which may be rotated relative to one another.

In particular, when the fiber structures in the form of woven, knitted or parallel fibers, which are connected to each other with auxiliary threads, present, they have a shape that does not match the shape of the component to be produced. For this reason, it is necessary first to cut the required fiber structures for the production of the component. In this case, cutting residues accumulate, which can no longer be used for the production of further endless fiber-reinforced components. The cut remnants are therefore usually supplied for disposal. In particular, cut remnants of carbon fibers are currently burned, but this is undesirable because of the high price of the carbon fibers.

In addition to thermal utilization, it is known from DE-A 10 2009 023 529 to first cut fiber composite wastes from unconsumed carbon fibers into sections of defined fiber length, to break them up to a fiber singulation and to restructure the resulting carbon fiber tangle into a fiber fleece or fiber fleece spun into an endless thread , This is particularly problematic that a largely non-destructive recycling by disassembly into single fibers by repetitive impact impact, for example in a hammer mill, as is performed for aramid or Kevlar fibers, for carbon fibers can not be applied. This is due in particular to the fragility of the carbon fibers, which are comminuted by such a process to form non-dosing or very short fibers, so that a sufficient reinforcement of polymer parts with these fibers can no longer be realized. A disadvantage of the process described in DE-A 10 2009 023 529 is, in particular, the great expense that has to be incurred in order to obtain a meterable material. An immediate use of cut pieces is not possible by the known methods. The object of the present invention was therefore to provide a method which makes it possible to use the cut remnants of fiber structures which do not have the disadvantages of the prior art. This object is achieved by a method for using cut remnants of fibrous structures, which comprises the following steps: a) cutting the cut remnants into flakes, b) admixing the flakes to a polymer melt, c) kneading the polymer melt with the flakes, so that the flakes in disintegrate individual fibers, d) forming the polymer melt with the mixed fibers to form a semifinished product.

By cutting the cut remnants to flakes, it is possible to mix the individual flakes in a simple manner in a polymer melt. Due to the comminution of the cut remnants into the flakes, the original connection of the fibers with one another is no longer sufficient to keep the flakes stable in shape, so that they disintegrate during mixing and kneading into individual fibers. In this way, the flakes can be used to make a fiber reinforced polymer that corresponds to a short fiber reinforced material.

In a preferred embodiment, the fiber structures from which the cut remnants originate are fabrics, scrims, knits, knits, braids, nonwovens or mats, which are usually made of continuous fibers. Any tissue that can be produced from continuous fibers can be used as the tissue. Also, any knit can be used. For the purposes of the present invention, the term "lies" is understood to mean that individual fibers are arranged parallel to one another. In this case, it is also possible that the fiber structure is made up of a plurality of layers, wherein the individual layers can be arranged parallel to one another or also rotated at an arbitrary angle relative to one another.

When the fibers are in the form of a slip, the individual parallel fibers are connected to one another, for example, by means of fibers or polymer threads. The connection takes place for example in the form of a seam of the synthetic fibers or continuous fibers. Preferably, a synthetic fiber, for example a polymer fiber, is used to produce the seam. In this case, a seam comprises, for example, a lower thread running perpendicular to the fiber web and an upper thread which is stung through the fibers at predefined intervals and wraps around the lower thread.

The fiber structures used may contain fibers which have been pretreated with a size or untreated fibers. Furthermore, it is also possible that the fiber structures are already impregnated with a polymer, in particular a thermoplastic polymer. loading However, it is preferable if the fibers are untreated or pretreated with a maximum size.

In particular, when the fibers of the blank remnants are untreated, it is preferred that the flakes be treated with a sizing agent after cutting the blank remainders into flakes and before blending into the polymer melt. Any arbitrary size known to the person skilled in the art can be used here. The treatment with a size has the advantage that the polymer adheres better to the fibers and thus improves overall the properties of the fiber-reinforced polymer produced by the process according to the invention. In particular, if individual fibers are used, or if the flakes are cut from Fasergelegen, it is advantageous to pretreat the fibers. In this case, it is particularly preferred to impregnate the fibers with a binder in order to bring them into a meterable form. As dosable form, for example, flakes are understood. Fiber flakes have the advantage over single fibers that they can more easily be mixed via a conventional conveyor into a machine for kneading the polymer melt with the flakes, for example an extruder or an injection molding machine.

The fibrous structures from which the cut remnants cut into the flakes can contain fibers of any known material. Common materials used for fibers are, for example, glass fibers, carbon fibers, arabite fibers, mineral fibers or synthetic fibers. The method according to the invention is particularly suitable for cut remnants of fiber structures which are made of carbon fibers for which the known recycling methods are not usefully applicable. At present, polymers containing carbon fibers for reinforcement or cutting residues of fiber structures made of carbon fibers are subjected to thermal utilization. However, this means a great waste of high quality material, as this is burned during thermal utilization and can not be used for its original purpose. The method according to the invention opens up a possibility, in particular for carbon fibers, of making use of blank remnants for the production of reinforced polymers.

The cutting of the cut remnants into flakes can take place, for example, with knives, for example punching knives or roller knives, a stamped grid or a laser. Also, the use of a CNC cutter for cutting the cut remnants into flakes is possible. In particular, it is preferred to use stamped grid or laser. The cutting into flakes is generally carried out by the same means with which the fiber structures are also brought into the mold for the production of continuous fiber-reinforced molded parts. Here, only the shape of the punched grid or the knife is to be adjusted so that are cut with these flakes.

The cutting of the cut remnants can take place simultaneously with the assembly of the fiber structure for the fiber-reinforced component to be produced. Alternatively, it is of course also possible to cut the cut remnants into the flakes in a separate second step. partners. If the cutting takes place simultaneously with the assembly, tools are used which allow a corresponding cut. For this purpose then appropriately designed punching or punching grid must be used. In this case, however, the blank is preferably cut with a CNC cutter.

If the cut remnants are comminuted in a separate step to flakes, any suitable cutting tool can be used, in particular, the above-mentioned cutting tools are suitable. When cutting the blank remainders into flakes in a separate step, it is possible to cut the blank remainders in individual layers or, alternatively, to layer several layers on blank remainders one above the other and to cut them into flakes. The number of layers that can be cut at the same time depends on the tool used. For reasons of efficiency, it is preferable to cut as many layers as possible at the same time, as long as this does not increase the cutting time, for example because of the necessary lower feed rates, as in the case of laser cutting.

The flakes to which the cut remnants of the fiber structures are cut preferably have an edge length of 10 to 50 mm, in particular in the range of 10 to 20 mm. The edge length is also dependent on the machine used, in which the flakes are added to the polymer melt.

By mixing the flakes into the polymer melt, the individual flakes disintegrate into individual fibers, which are then mixed into the polymer melt. Depending on the size of the flakes used and the shearing action in the device for mixing in the flakes, the fibers partially break, so that the properties of the fiber-reinforced polymer thus produced correspond to the properties of a short-fiber-reinforced polymer.

The breakage of the fibers is due, in particular, to the brittleness of the carbon fibers and to the processing in a screw-type reciprocating machine in which the material is sheared due to the rotation of the screws.

For mixing and kneading the flakes into the polymer melt, in particular, screw-type piston machines, for example injection molding machines or extruders, in particular extruders, are suitable. The addition of the flakes takes place at a customary for the addition of fibers position. The position for adding the fibers is usually located behind the feed zone in a region in which the polymer added to the screw machine is completely melted. If a polymer melt is already supplied to the screw-type piston machine, the point of addition for the flakes can be located immediately after the addition point of the polymer melt. Since a pellet machine usually polymer granules, ie a plastic is added in solid form, it is necessary to first melt the polymer before the flakes are added. The addition of the flakes in the polymer melt allows a more homogeneous mixing of the melt with the Flakes and thus a more uniform distribution of the resulting individual fibers in the polymer melt.

If the employed screw-type piston machine is an extruder, both single-screw extruders and multi-screw extruders, for example twin-screw extruders, can be used. Particularly preferred is the use of twin-screw extruders, since they have a better mixing action than single-screw extruders. Furthermore, a twin-screw extruder makes it easier to meter in fillers and it is possible to operate the twin-screw extruder with a variable degree of filling, which also results in a good degassing performance and the product properties can be better adjusted. In addition, a twin-screw extruder, in contrast to the single-screw extruder, has very good self-cleaning properties.

The addition of the flakes into the screw-type piston machine, for example the extruder, takes place via an addition point, which preferably comprises a delivery spindle. With the feed screw it is possible to meter the flakes evenly into the polymer melt. When adding the flakes without a feed screw, for example via an addition opening, there is a risk that the flakes are not absorbed by the polymer melt or that only occasionally flakes get into the polymer melt, so that the proportion of fibers in the polymer would be too low.

The feed screw makes it possible to adjust the amount of flakes added to the polymer melt. In particular, it is possible to use a feed spindle to provide forced conveyance of the flakes so that a proportion of flakes and thus of fibers in the polymer melt of up to 50% by weight is possible. Preferably, the proportion of flakes and thus fibers after metering in the polymer melt in the range of 1 to 50 wt .-%, in particular in the range of 1 to 40 wt .-%.

The length of the fibers in the semifinished product results, on the one hand, from the shearing of the fibers in the screw-type piston machine and, on the other hand, from the dimensioning of the granulate, which is cut from the polymer melt. The maximum fiber length corresponds to the maximum length expansion of a single granule. If longer fibers are desired, it is necessary to cut a flake with a larger edge length and on the other to produce a larger granules. The granules are preferably cylindrical and the largest extent is usually the height of the cylinder. Alternatively, however, it is also possible to choose a larger diameter and a lower height. However, since the fibers are aligned substantially parallel in the axial direction to the axis of the holes in the perforated plate due to the promotion of the polymer melt, usually the axial extent of the granule gives the maximum fiber length.

The polymer to which the flakes are admixed may be a thermoplastic, thermoset or elastomeric polymer. Particularly preferably, the polymer melt contains a thermoplastic plastic polymer, most preferably the polymer melt is a melt of a thermoplastic polymer.

The thermoplastic polymer is preferably selected from polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyoxymethylene (POM), polyamide (PA), polypropylene (PP), polyethylene (PE), polyethersulfone (PES) or a mixture of at least two of these polymers. In addition to the abovementioned thermoplastic polymers, it is also possible to use any other thermoplastic polymer. The semi-finished product produced by the process according to the invention is particularly preferably a granulate. In addition to granules, however, the semifinished product can also be in the form of plates or strands. If the semifinished product is a granulate containing fibers, this is produced, as is customary with granules, by pressing the polymer melt through a perforated plate and cutting it off with a knife into granules. On the one hand, it is possible to first produce a polymer strand which is cooled and then cut into granules. Alternatively and usually, the polymer pressed through the perforated plate is cut directly on the plate. The cutting can take place in air, wherein the cut granules preferably falls into a cooling liquid and solidifies. As a cooling liquid is for example water. Alternatively, it is also possible to carry out an underwater granulation, wherein the polymer melt is pressed through the perforated plate into a cooling liquid and cut directly to the granules on the plate. In both cases, the granules are discharged with the cooling liquid, then removed from the cooling liquid and dried. The granules thus produced can then be further processed in any way in which plastic granules can be processed into a finished part. For example, the plastic granulate can be formed into a finished part by extrusion or injection molding. In this case, any injection molding machine or extrusion machine can be used, which can be used for the production of finished parts and is particularly suitable for the processing of fiber-reinforced plastics.

Molded parts which can be produced from the granules produced by the process according to the invention are all particularly geometrically demanding molded parts which can also be produced with commercially available fiber-reinforced thermoplastics, for example cylinder head covers, intake pipes for turbochargers, switch housings.

example

For the production of a fiber-reinforced polyamide, a commercially available twin-screw extruder with a dosing unit for carbon fiber flakes was converted. For this purpose, a storage container with a spindle attached to the bottom was mounted centrally above the side feeder of the twin-screw extruder. For the production of a 20 wt .-% carbon fiber reinforced polyamide 66 Gelegereste a continuous carbon fiber mat were first cut by means of a CNC cutter into flakes of size 20x20 mm. The flakes thus cut were then placed in the reservoir above the side feeder of the twin screw extruder and metered into the melt of the polyamide 66 gravimetrically via the side feeder. The material thus produced was granulated directly after the extruder.

From the material thus obtained, specimens were produced by means of an injection molding machine in a further processing step. The characteristic values measured on the test specimens and the characteristic values which were measured on specimens of a commercially available polyamide reinforced with 20% by weight short carbon fibers (Ultramid® A3WC4 from BASF SE) are shown in Table 1. Here, the characteristic values of the test specimens from the polyamide produced according to the invention are listed as an "example", and the characteristic values of the test specimens from the commercially available polyamide are listed as a "comparison".

From the comparison of the characteristics it can be seen that the properties essentially correspond to those of a conventional polymer reinforced with short carbon fibers.

Table 1: Characteristics of a fiber-reinforced polyamide 66 produced by the process according to the invention and of a commercially available fiber-reinforced polyamide 66

Properties Test Method Example Comparison

Density [kg / m ³ ] EN ISO 1 183-2: 2004-10 1230 1220

Modulus of elasticity [MPa] DIN EN ISO 527-1 / -2: 2012-06 14600 16800

Breaking stress [MPa] DIN EN ISO 527-1 / -2: 2012-06 200 235

Elongation at break [%] DIN EN ISO 527-1 / -2: 2012-06 2.8 2.4

Impact strength at 23 ° C [kJ / m ² ] DIN EN ISO 179-1: 2010-1 1 54 57

Notched impact strength at 23 ° C [kJ / m ² ] DIN EN ISO 179-1: 2010-1 1 4,7 6

Claims

Patent claims

Method for using cutting residues from fiber structures, comprising the following steps:

(a) cutting the blanks into flakes,

(b) mixing the flakes into a polymer melt,

(c) kneading the polymer melt with the flakes so that the flakes break down into individual fibers,

(d) Forming the polymer melt with the added fibers into a semi-finished product.

Method according to claim 1, characterized in that the fiber structures are fabrics, scrims or knitted fabrics made of continuous fibers.

Method according to claim 1 or 2, characterized in that the fiber structures are made of carbon fibers.

Method according to one of claims 1 to 3, characterized in that the flakes are treated with a size before being mixed into the polymer melt.

Method according to one of claims 1 to 4, characterized in that the blank residues are cut into flakes with a knife, a lead frame or a laser.

Method according to one of claims 1 to 5, characterized in that the admixing of the flakes and kneading of the polymer melt with the flakes is carried out in a screw-piston machine.

7. The method according to claim 6, characterized in that the screw piston machine is an extruder.

8. The method according to claim 7, characterized in that the extruder for mixing the flakes into the polymer melt comprises an addition point with a conveyor spindle. Method according to one of claims 1 to 7, characterized in that the polymer melt contains a thermoplastic polymer.

0. The method according to claim 9, characterized in that the thermoplastic polymer is selected from polybutylene terephthalate, polyethylene terephthalate, polyoxymethylene, polyamide, polypropylene, polyethylene, polyethersulfone or mixtures of at least two of these polymers.

1 . Method according to one of claims 1 to 10, characterized in that the semi-finished product is granules containing fibers.