EP3941727A1

EP3941727A1 - Method for producing a self-reinforced thermoplastic composite material

Info

Publication number: EP3941727A1
Application number: EP20720338.1A
Authority: EP
Inventors: Michel Jansen
Original assignee: Fond Of GmbH
Current assignee: Fond Of GmbH
Priority date: 2019-03-18
Filing date: 2020-03-18
Publication date: 2022-01-26
Also published as: DE102019106772A1; US20220001628A1; CN113677508A; WO2020187371A1

Abstract

The invention relates to a method for producing a self-reinforced thermoplastic composite material comprising at least the following method steps: • providing strips (1) of a thermoplastic; • weaving the plastic strips (1) into a base fabric (10). The plastic strips (1) for this are produced by at least the following steps: • producing pre-stretched fibres (2) from a partially crystalline polyester homopolymer (PET), with a melting point T1, by extrusion on at least one spinning nozzle and subsequent stretching; • joining a plurality of pre-stretched endless fibres (2) lying next to and/or above one another to a matrix of an amorphous polyester homopolymer at a processing temperature T2 < T1, wherein the temperature difference between T1 and T2 is at least ΔΤ = 30°C.

Description

Method of making a self-reinforced

thermoplastic composite material

The invention relates to a method for producing a self-reinforced thermoplastic composite material with the features of the preamble of claim 1.

From WO 2005123369 A1 items of luggage are known in which structural elements, such as the half-shells in particular, are made of a polyolefinic composite material that has a high impact resistance and a low specific weight. The composite material consists of a Ge fabric of pre-stretched plastic strips, which are formed from blanks of a film made of polypropylene, polyethylene or a copolymer thereof. These cases have very good properties and are very durable. However, the production is very complex and requires high investments in the production facilities. A fundamental problem in production is that the plastic strips must be pre-stretched in order to achieve higher mechanical strength. The half-shells or the other structural elements are then produced by hot forming of cut fabric in a heated mold. During hot forming, however, the pre-stretched plastic strips partially shrink. To that Clamping frames are required, so that appropriate investments in systems and precise temperature control are required. The suitcases obtained in this way are indeed very shock-resistant, even at low temperatures, but they also have a high degree of elastic deformability. A higher form rigidity is particularly desirable for handling the still open case.

Another disadvantage is that the polyolefinic plastic, from which the half-shells and other structural elements are basically recyclable by type, the quality of the material decreases with each recycling process until ultimately only incineration is possible.

US Pat. No. 5,380,477 A describes a fiber-reinforced laminate that is formed from a matrix of polyamide (“nylon”) and so-called “Bico” fibers, which combine two plastics. A core consists e.g. B. made of polyester, while a jacket is also made of polyamide. So-called non-wovens are formed from the fibers, i.e. non-woven surfaces. Several pieces of tissue are then connected to one another in a mold under the action of pressure and temperature. The sheath of the reinforcing fibers melts and bonds with the similar plastic of the matrix fibers. The reinforcement fibers made of another plastic are embedded in the matrix. However, the laminates formed in this way contain two plastics, so that single-type recycling is not possible.

DE 10 2016 205 556 A1 describes how a mixture of amorphous and partially crystalline and amorphous polyester fibers is to be processed. In the end, a structural part with a partially crystalline matrix should be obtained as a result. That a fleece with amorphous fibers is brought to partial crystallization. However, such in-situ crystallization does not bring high mechanical strength. The object of the invention is thus to create a self-reinforced and highly resilient, thermoplastic composite material which is sustainably recyclable and which can also be produced and further processed more cost-effectively by dispensing with further processing in the clamping frame.

This object is achieved by a method for producing a self-reinforced thermoplastic composite material having the features of claim 1.

The invention retains the known concept of providing a composite material in the form of a ribbon fabric as a base fabric, from which structural elements can later be made by hot forming in a press mold. Essential to the invention is, on the one hand, the choice of material and the structure of the plastic strips used for this purpose.

Because the plastic strips according to the invention are chemically made of the same thermoplastic material, which is present in two different forms, namely crystallinities, there is a large difference between the temperature of the matrix material and the fiber material of at least 30 ° C, in particular even of 50 ° C created. This large distance between the temperatures allows the further processing of the base fabric on much simpler and therefore more cost-effective devices. Temperature control to the exact degree is not required, and the use of clamping frames in the manufacture of structural parts can be dispensed with.

A high mechanical strength is achieved according to the invention by using pre-stretched polyester fibers that are produced in continuous form and embedded in the matrix. It is therefore a matter of taut fibers that are aligned unidirectionally in the matrix. The pre-drawn reinforcing polyester fibers embedded in the matrix shrink the subsequent hot forming of the fabric blank or not to an extent that would impair the quality of the product. This means that elements that are free from shrinkage and distortion can be obtained without high manufacturing costs. This is primarily due to the large temperature difference between the individual components of the composite material, so that the fiber components remain unaffected in any case during the subsequent structuring by hot forming.

With regard to recycling, it is essential to the invention that both the matrix and the fibers contained therein as multifilament are made of polyester. The special feature of the invention is to use partially crystalline polyester for the fibers and amorphous polyester for the matrix.

Since flomopolymers or PET copolymers are preferably used in each case, but no other polymers, there are no interfering substances for a later recycling process.

The separation into partially crystalline polyester for the fibers and amorphous polyester for the matrix leads to the high temperature difference DT between the respective processing temperatures of the two components fibers and matrix, whereby the temperature at which the fibers are so impaired that their strength or even Lose dimensional stability, is significantly higher than the processing temperature of the matrix.

Due to this temperature difference, the fibers remain unaffected when they are embedded in the matrix. The fibers are not heated too much when the matrix is applied. In the subsequent hot forming of the base fabric made from the plastic strips, the matrix is only heated to the extent that permanent plastic shaping is possible and / or, if necessary, several layers of fabric can be connected to one another, but that the mechanical properties of the fibers contained in the matrix are retained not be affected. A very advantageous side effect of the selection of materials mentioned is that partially crystalline polyester can be stretched. By according to the invention pre-stretched fibers made of partially crystalline polyester can be subsequently embedded in a matrix, a high strength - under load in the stretching direction of the continuous fibers - of about 400 MPa can be achieved.

Choosing polyester as the starting material makes the product extremely sustainable, because with polyester as a thermoplastic polycondensate, the product properties can be specifically adjusted during the recycling process, and thus the recycled polyester, so-called R-PET, has at least the same product properties has like new goods. The reprocessing process can be repeated as often as required so that residual pieces of the composite material, but also parts made from it, can be reprocessed according to type after the end of their useful life. If, for example, suitcases are made from the composite material, suitcases returned by customers can be used to make new suitcases without any loss of quality. Furthermore, the polyester waste that arises in various forms around the world can be used.

The advantage of the selection of materials according to the invention is that all the other elements required for an item of luggage can also be produced from polyester. Textile elements can be welded or glued to the structural elements. Textile elements can be sewn to one another, and the seam can also be produced with a thread made of polyester. The half-shells can be connected by a polyester zipper. Injection molded parts can also be made from polyester, so that the suitcase manufactured in this way can be recycled according to type.

Further advantages of the selection of materials according to the invention are that the mechanical properties can be easily adjusted via the degree of stretching of the fibers, that the plastic tapes are easy to color and that there is a strong bond between the fibers and the matrix that does not come off even under load. The method described below is used to manufacture the case, with the temperature control of the overall process being particularly important in addition to the selection of the materials for manufacturing the plastic strips.

First the plastic straps are made. For this purpose, pre-stretched fibers are first produced from a partially crystalline polyester homopolymer with a melting temperature Tsi by extrusion on at least one spinneret and subsequent stretching. The partially crystalline polyester homopolymer has a relative degree of crystallization of more than 75%, based on the absolute crystallinity of the polymer, and a melting temperature of about 260 ° C. ± 10 °. The fibers are preferably wound up and then processed further from bobbins in order to be able to compensate for the different throughput speeds during fiber spinning and matrix production.

The fibers are preferably processed as a multifilament, i.e. as a bundle of a large number of individual fibers, but without twisting, etc.

The unwound multifilaments are spread apart so that the fiber layer is wider and less high. This results in the adaptation to the ge desired thin rectangular profile of the cross section of the plastic strip.

The matrix is formed either by online extrusion or in the so-called film stacking process. Both make it possible to embed the fibers in a taut and directional manner in the matrix, so that in a linear extension of the plastic strips produced according to the invention, significantly higher strengths can be achieved than when using nonwoven webs according to the prior art mentioned above.

In online extrusion, the prepared fiber bundle is passed through a wetting tool of an extruder, i.e. through a nozzle tool that allows the fibers to pass through and at the same time applies liquid polyester melt to form a matrix that surrounds the fibers. The matrix is formed from a predominantly amorphous polyester homopolymer with a processing temperature T2 of about 210 ° C. This temperature is sufficient to press a flowable melt into the wetting tool and to produce the plastic tape with embedded fibers.

The fibers remain unaffected because the temperature difference DT between the processing temperature during extrusion and the melting point of the fibers is 50 ° C. The temperature difference should be at least 30 ° C, preferably 50 ° C.

The strand emerging from the wetting tool can then be cooled and calibrated in a known manner, for example by means of a pair of calender rollers.

It is even more advantageous to use the film stacking process for producing the plastic strips according to the invention. Two foils are rolled together while they are warm, enclosing the reinforcing fiber strands between them. According to the invention, two films made of amorphous polyester are used for this purpose. The pre-stretched reinforcing fibers made of partially crystalline polyester are inserted between the films and z. B. passed through a calender nip. The reinforcing fibers introduced in the endless strand can be guided well in the taut and linearly aligned state. The connection of the two foils then takes place under the influence of pressure and temperature in the roll gap. Here, too, a maximum processing temperature T2 is set as mentioned above. Since the pressure has an additional influence on the connection of the foils, the processing temperature can be even lower than with online extrusion, so that the temperature difference of 50 ° C between the processing temperature of the matrix and the temperature at which the fibers have a negative impact is preferably maintained can definitely be achieved. The trigger can follow in both manufacturing processes on rubberized rollers. For reasons of economy, a wide band is first extruded, which is then divided into several individual plastic bands with the desired width of 2 mm to 25 mm.

The plastic straps are then interwoven in a known manner in warp and weft, for example in plain weave or twill weave. The type of weave plays a subordinate role in the strength of the finished product. It is only important that with the desired number of fabric layers that are hot-pressed, a seamless, watertight surface is obtained.

In order to produce a structural element such as, in particular, half-shells of a suitcase, one or more layers of fabric cuttings are placed in a heated press mold and pressed under pressure and heat. The hot forming temperature T3 must be in the range from 190 ° C to 230 ° C. The processing temperature T2 of the matrix material lies in this interval.

In order to form a multi-layer composite material from several fabric cuts, the hot forming temperature T3 should correspond to the processing temperature T2 of the matrix material or even be a few degrees higher, for example 5 ° C to 10 °, so that the matrix material melts on the surface and the fabric layers pressed together firmly connect.

If a semi-finished product of the composite material is to be pressed into a three-dimensional structure, the hot forming temperature T3 should correspond to the processing temperature T2 of the matrix material, but if possible a little lower, preferably about 5 ° C to 10 ° C lower. This is sufficient for permanent shaping of the composite material and it prevents the matrix from being melted too far and fibers from being exposed.

Regardless of whether the hot forming temperature is selected a little higher or lower in relation to the processing temperature T2 of the matrix material: the advantage of the invention is that there is still a large temperature difference to the melting temperature Ti of the fiber material. In any case, the properties of the fibers are not impaired during hot forming, since their melting temperature is the highest temperature in the overall manufacturing process of the case element, but which is not nearly reached. With hot forming, the temperature window does not have to be adhered to to the exact degree in order to reliably avoid impairment of the mechanical properties.

The structural element formed in this way can also initially be a plate-shaped flat product made of the composite material. The fabric layers are then welded and pressed by the folded product manufacturer. The processor can produce three-dimensional structural elements from the flat sheet metal by heating them again up to the hot forming temperature or slightly above and then immediately inserting them into a press mold and forming them. The surface temperature of the cavity of the press mold is preferably below T2, so that no surface melts whatsoever are caused. In any case, the surface temperature is clearly Lich, namely at least 30 ° C, preferably 50 ° C, below Ti _in order to avoid any Liche effect on the fibers embedded in the tapes or bands. The advantage for the processor is that the energy expenditure for heating a flat product z. B. in the furnace is significantly less than a prolonged heating of the entire press tool.

In particular, the mold is kept in the range between room temperature and approximately 60 ° C. even by cooling. This enables safe handling without any special protection measures.

The invention is tert erläu below with reference to the drawings. The figures show in detail:

1 shows a cross section of a plastic band;

2 shows a fabric of plastic bands in plan view; 3 shows an opened suitcase in a perspective view

Figure 1 shows a plastic strip 1 that is Herge in the manner according to the invention. It consists of pre-stretched fibers 2, which are formed from a partially crystalline polyester flomopolymer. They are embedded in a matrix 3, which is also formed by a polyester flomopolymer, but in amorphous form, ie with a very low degree of crystallization of less than 10% crystalline fractions. On the other hand, the fibers 2 consist of a partially crystalline polyester, the degree of crystallization in the material of the fibers being between 30% and 40%.

It is essential that there is a sufficiently large gradient between the polyester materials used in terms of the degree of crystallization.

From the maximum achievable degree of crystallization with polyester, which from absolute, d. H. Based on the total volume, which is 30% to 40%, the PET polymer from which the matrix is formed has a relative proportion of a maximum of 10%. The PET fiber material, however, has a relative degree of crystallization of 75% to 100% - again based on the absolute maximum achievable with the PET type used. Through this relative distribution of the different degrees of crystallization and the relative distance of over 60 percentage points in the two materials used, the large temperature difference in the melting and processing temperatures is achieved, which leads to an uncomplicated and inexpensive production option of structural elements from the composite material according to the invention.

The individual plastic strips 1 are then woven together so that a base fabric is formed. A section of a base fabric 10, in which the plastic strips 1 are interwoven, for example in a simple canvas weave, is shown in FIG. 2. The relatively large width of the plastic strips used is advantageous in order to impress the base fabric 10 with a certain rigidity. With complicated ones Three-dimensional shapes with narrow radii can be advantageous with a finer fabric. The advantage of using large widths of the tapes, in particular up to 25 mm, has the further advantage that a water- and gas-tight structural element can be produced with a few layers stacked on top of one another and connected to one another, because the gaps in the tissue are small anyway and due to the connection several layers of fabric can be completely closed under pressure and temperature.

Another criterion for the number of layers of the base fabric that are pressed together results from the desired strength of the structural element or the mechanical requirements that prevail in later use. It has been shown that 3 to 6 layers of a fabric are sufficient, the plastic bands in the fabric each having a thickness of 80 μm to 200 μm.

Figure 3 shows the use of structural elements formed from the composite material according to the invention, using the example of a suitcase 100. The suitcase 100 has two suitcase shells 101, 102, each of which are three-dimensional structural elements which have been formed from the composite material of the invention . The case shells 101, 102 are connected to one another via a textile web 105, which preferably also consists of polyester, in particular a textile cut made of polyester yarn. The zip fasteners 103, 104, which are each attached to the edge of the Kofferscha len 101, 102, are preferably made of polyester. This means that the majority of the suitcase can be recycled according to type. Polyester materials are also used as much as possible for the other add-on parts, such as rollers 108 or an extendable bracket 109, so that a modern and durable, but completely recyclable suitcase 100 is available after use.

The consistent selection of PET as the material also ensures the possibility of hot welding. The zippers 103, 104 can preferably be cut directly during the hot forming of the fabric are also inserted and are then pressed into the composite at the edge. But they can also be welded on later. The same also applies to the central web 105 and, if necessary, to other elements that can be welded to the case shells 101, 102, which are the structural components of the case 100.

Claims

FONP 001 WO A5.docx WO 2020/187371 PCT / DE2020 / 100217 patent claims

1. Process for producing a self-reinforced thermoplastic composite material, with at least the following process steps:

- Provision of strips (1) made of a thermoplastic material;

- Weaving the plastic strips (1) to form a base fabric (10); characterized in that the plastic strips (1) are produced by at least the following steps:

- Production of pre-stretched continuous fibers (2) from a partially crystalline polyester homopolymer (PET) with a melting temperature Ti by extrusion on at least one spinneret and subsequent stretching;

- Connecting a large number of pre-stretched continuous fibers (2) lying next to one another and / or on top of one another with a matrix made of an amorphous polyester homopolymer at a processing temperature T2 <Ti, the temperature difference between Ti and T2 being at least DT = 30 ° C.

2. The method according to claim 1, characterized in that the fiber and

Matrix materials are chosen such that the temperature difference between Ti and T2 is at least DT = 50 ° C.

3. The method according to claim 1 or 2, characterized in that the

Melting temperature Ti of the PET fiber material is between 250 ° C and 270 ° C.

4. The method according to at least one of the preceding claims, characterized in that the relative degree of crystallization of the PET fiber material is more than 75%, based on the maximum achievable in the PET polymer from absolute degree of crystallization.

5. The method according to any one of claims 1 to 4, characterized in that the matrix is produced in a wetting tool of an extruder by applying a liquid polyester melt to the adjacent and / or superimposed, pre-stretched fibers (2). FONP 001 WO A5.docx

WO 2020/187371 PCT / DE2020 / 100217

6. The method according to any one of claims 1 to 4, characterized in that the matrix is formed by joining at least two films, each of which consists of the amorphous polyester homopolymer and which include the pre-stretched continuous fibers between them.

7. The method according to any one of the preceding claims, characterized in that the processing temperature T2 of the PET matrix material when applying to the fibers is between 160 ° C and 230 ° C.

8. The method according to any one of the preceding claims, characterized in that the relative degree of crystallization of the PET matrix material, based on the maximum absolute degree of crystallization achievable in the PET polymer, is less than 10%.

9. The method according to any one of the preceding claims, characterized in that the continuous fibers (2) are connected to the matrix in a tightened state.

10. A method for producing a structural element from a composite material produced according to one of the preceding claims, characterized by the following steps:

- cutting the base fabric (10) to at least one fabric blank;

- Placing a fabric cut or several superimposed fabric cuttings in a press mold;

- heating the at least one fabric blank to a hot stamping mold temperature T ₃ while simultaneously applying pressure to form the structural member, wherein the hot-forming temperature T ₃ is lower than or equal to T2, and at least 30 ° C is less than Ti; and

- Cooling of the structural element and removal from the mold.

11. The method according to any one of the preceding claims, characterized in that during the hot forming and structuring of the fabric cut on the edge side at the same time a textile fabric cut made of polyester fabric is welded. FONP 001 WO A5.docx

WO 2020/187371 PCT / DE2020 / 100217

12. The method according to any one of the preceding claims, characterized in that first a planar structural element is formed as a semi-finished product, which it is heated again to the hot forming temperature T3 and formed in a mold with a three-dimensionally shaped cavity to a three-dimensional structure element, the The surface temperature in the mold cavity at the beginning of the deformation of the preheated planar structural element is less than Ti.

13. Case (100) with at least one according to one of claims O to 12 Herge provided structural element.

14. Case according to claim 13, characterized in that at least one structural element is verbun with at least one textile element (105) made of polyester.

15. Case (100) according to claim 13 or 14, characterized in that two structural elements are provided as case shells (101, 102), which are secured by at least one zipper made of polyester (103, 104) and / or a textile bridge element (105 ) are connected to each other.