METHOD FOR PRODUCING A SELF-REINFORCED THERMOPLASTIC COMPOSITE MATERIAL

Abstract

The invention relates to a method for producing a self-reinforced thermoplastic composite material including: providing strips of a thermoplastic and weaving the plastic strips into a base fabric. The plastic strips for this are produced by at least the following steps: producing pre-stretched fibres from a partially crystalline polyester homopolymer with a melting point by extrusion on at least one spinning nozzle and subsequent stretching and joining a plurality of pre-stretched endless fibres 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 ΔT=30° C.

Claims

1. A method of producing a self-reinforced thermoplastic composite material, comprising: providing strips having a rectangular cross-section and made of a thermoplastic material; and weaving the strips into a base fabric, wherein strips are produced by: producing pre-stretched continuous fibers from a partially crystalline polyester homopolymer having a melting temperature T.sub.1 by extrusion with at least one spinneret and subsequent drawing; forming a plurality of multifilaments each bundling a plurality of pre-stretched fibers; spreading the multifilaments to obtain a layer of fibers adapted to the thin rectangular profile of the cross-section of the plastic strip, the width of which is greater than the height; and bonding a plurality of juxtaposed and/or superimposed pre-stretched continuous fibers, which are in the form of the spread multifilaments and are under prestress, to a matrix of an amorphous polyester homopolymer at a processing temperature T.sub.2<T.sub.1, the temperature difference between T.sub.1 and T.sub.2 being at least ΔT=30° C.

2. The method according to claim 1, wherein the fiber and matrix materials are selected such that the temperature difference between T.sub.1 and T.sub.2 is at least ΔT=50° C.

3. The method according to claim 1, wherein the melting temperature T.sub.1 of the PET fiber material is between 250° C. and 270° C.

4. The method according to claim 1, wherein the relative degree of crystallization of the PET fiber material is more than 75%, based on the maximum absolute degree of crystallization achievable in the PET polymer.

5. The method according to claim 1, wherein the processing temperature T.sub.2 of the PET matrix material when applied to the fibers is between 160° C. and 230° C.

6. The method according to claim 1, wherein 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%.

7. A method of making a structural member from a composite material made according to claim 1, the method comprising: cutting the base fabric into at least one fabric blank; Inserting a fabric blank or several fabric blanks lying on top of each other into a press mold; heating the at least one fabric blank to a hot working temperature T.sub.3 while substantially simultaneously applying pressure to form the structural member, the hot working temperature T.sub.3 being less than or equal to T.sub.2 and is at least 30° C. below T.sub.1; and cooling the structural element and removing the structural element from the mold.

8. The method according to claim 7, wherein during the hot forming and structuring of the fabric blank, a textile fabric blank made of polyester fabric is substantially simultaneously welded on at the edge.

9. The method according to claim 7, wherein a planar structural element is first formed as a semi-finished product, which is heated again to the hot forming temperature T.sub.3 and is formed into a three-dimensional structural element in a press mold having a three-dimensionally shaped mold cavity, the surface temperature in the mold cavity at the beginning of the forming of the preheated planar structural element being lower than T.sub.1.

10. A suitcase comprising at least one structural element made according to claim 7.

11. The suitcase according to claim 10, wherein at least one structural element is bonded to at least one textile element made of polyester.

12. The suitcase according to claim 10, wherein two structural elements are provided as suitcase shells that are connected to one another by at least one zipper formed of polyester and/or a textile bridging element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0037] FIG. 1 shows a cross-section of a plastic belt;

[0038] FIG. 2 shows a top view of a woven fabric of plastic straps; and

[0039] FIG. 3 shows an opened case in perspective view

DETAILED DESCRIPTION

[0040] FIG. 1 shows a plastic tape 1 manufactured in accordance with the invention. It includes pre-stretched fibers 2 formed from a partially crystalline polyester homopolymer. They are embedded in a matrix 3 which is also formed by a polyester homopolymer, but in amorphous form, that is to say with a very low degree of crystallization of less than 10% crystalline content. On the other hand, the fibers 2 are made of a partially crystalline polyester, the degree of crystallization being between 30% and 40% for the material of the fibers.

[0041] It is essential that there is a sufficiently large gradient between the polyester materials used with regard to the degree of crystallization. Of the maximum degree of crystallization achievable with polyester, which is 30% to 40% in absolute terms, i.e., based on the total volume, the PET polymer from which the matrix is formed has a relative proportion of no more than 10%. The PET fiber material, on the other hand, has a relative degree of crystallization of 75% to 100%—again based on the absolute maximum achievable with the PET type used. This relative distribution of the different degrees of crystallization and the relative difference of more than 60 percentage points between the two materials used result in the large temperature difference in the melting or processing temperatures, which leads to an uncomplicated and cost-effective manufacturing possibility of structural elements from the composite material according to the invention.

[0042] The individual plastic bands 1 are then woven together to form a base fabric. A section of a base fabric 10, in which the plastic tapes 1 are woven together, for example in a simple plain weave, is shown in FIG. 2. The relatively large width of the plastic tapes used is advantageous in order to impart a certain rigidity to the base fabric 10. In the case of complicated three-dimensional shapes with tight radii, a finer weave can be advantageous. 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 only a few superimposed and interconnected layers, because the gaps in the fabric are small anyway and the interconnection of several fabric layers completely closes them under pressure and temperature.

[0043] A further criterion for the number of layers of the base fabric which are pressed together results from the desired strength of the structural element or the mechanical requirements prevailing thereon 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.

[0044] FIG. 3 shows the use of structural elements which are formed from the composite material of the invention, using the example of a suitcase 100. The suitcase 100 has two suitcase shells 101, 102, which are each three-dimensional structural elements which have been formed from the composite material of the invention. The suitcase shells 101, 102 are connected to each other by a textile web 105, which is preferably also made of polyester, in particular of a textile blank made of polyester yarn. The zippers 103, 104, each of which is attached at the edges to the suitcase shells 101, 102, are also preferably made of polyester. Thus, the major part of the suitcase is already recyclable by type. Polyester materials are also used as far as possible for the other attachments, such as castors 108 or an extendable handle 109, so that a modern and durable suitcase 100 is present which is, however, completely recyclable after the end of use.

[0045] The consistent selection of PET as a material also ensures the possibility of hot welding. The zippers 103,104 can preferably be inserted directly during hot forming of the fabric blanks and are then pressed into the composite at the edges. However, they can also be welded on subsequently. The same 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.

[0046] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.