GB2292339A

GB2292339A - A fibre-reinforced laminate suitable for the manufacture of light conveyor belts and flat drive belts

Info

Publication number: GB2292339A
Application number: GB9516720A
Authority: GB
Inventors: Andre Roetgers; Petra Herko
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1994-08-16
Filing date: 1995-08-15
Publication date: 1996-02-21
Anticipated expiration: 2015-08-15
Also published as: FR2723707A1; DE4428939A1; GB2292339B; GB9516720D0; FR2723707B1

Description

2292339 Fibre-reinforced laminate, its manufacture and use The present

invention relates to a laminate having thermoplastic layers and textile layers alternately and an upper and a lower thermoplastic covering layer, the textile layers being woven fabrics containing yarns having a fibrous surface consisting of synthetic fibres or filaments, and the surface fibres or filaments of the woven fabric layers being anchored in the thermoplastic layers.

Fibre-reinforced laminates, for example for the manufacture of conveyor belts and drive belts, consisting of layers of woven fabric sandwiched together with a plastics coating (for example PVC, PU etc.) or rubber are known. Also state of the art is bonding of the layers with adhesion promoters, some of which, however, are toxicologically hazardous and/or have to be applied by a I complicated procedure.

There is known from EP-A-472 436 a laminate consisting of a base layer of a nonwoven fabric, a polyolefin- impregnated nonwoven fabric layer lying on top of it, a layer of the same polyolefin lying on top of that and a covering layer of ultrahigh- molecular-weight polyethylene. All the layers are firmly bonded to one another. The polyolefin layer serves as an adhesion promoter between the layer of ultrahigh-molecular-weight polyethylene and the nonwoven fabric layer. The material serves to make surfaces slidable and at the same time insulates against sound and heat. It is used, for example, to line powder silos, skis, skids, guide rollers and transport belts.

There is known from FR-A-26 57 293 a laminate intended to be used for the manufacture of transport belts, hoses, vehicle tyres and the like, consisting of a card web of natural or synthetic organic or inorganic fibre materials which is coated on both sides with a thin layer of rubber. The manufacture is carried out by applying the pre- vulcanised rubber web to both sides of the nonwoven fabric and heating and pressing together all three layers.

Especially when coating with rubber, however, in order to ensure sufficient adhesion between the fibres and the rubber matrix, synthetic reinforcing fibres have to be subjected to a so-called dip treatment in which highly reactive epoxides are used concomitantly. Owing to their high reactivity, a considerable potential to endanger health is ascribed to such compounds.

If the hazardous and technically complicated dip processes are not carried out when rubber-coated textile supports are being manufactured, the products have a strong tendency to delaminate and therefore are totally unusable for some applications or have a greatly reduced service life. Another disadvantage of the known composite materials is that it is difficult to dispose of - 3 them properly after use.

It has now been found that, surprisingly, textile materials can be coated in a relatively simple work step in such a manner that operations that are hazardous to health are to a very large extent avoided and very good durability of the laminate is nevertheless achieved.

The present invention provides a laminate consisting of at least one layer of a textile sheet structure, a lower and an upper covering layer and, if more than one textile layer is present, adhesion layers lying between the textile layers, which is characterised in that the textile layers are woven fabrics containing yarns having a fibrous surface consisting of synthetic fibres or filaments, the covering layers and the adhesion layers are essentially unstructured thermoplastic layers and, at the interface between the textile woven fabric layer(s) and the covering layers and any adhesion layer(s) present, the surface fibres of the woven fabric layers are anchored in the covering layers and any adhesion layers present.

Essentially unstructured thermoplastic layers within the meaning of this invention are layers that, in contrast to the textile layers, do not exhibit any fibre structure but that can be obtained by softening or melting thermoplastic films. They thus form layers above, below and between the textile webs which are enriched with unformed thermoplastic composition.

4 - The laminate according the invention has a surprisingly high resistance to delamination, which can be attributed to the intimate bonding to the textile layers of the thermoplastic layers used as the covering layers and adhesion layers. The bonding is achieved by virtue of the fact that the yarns of the woven fabrics lying at the surface are penetrated by the adjoining softened or melted thermoplastic composition during the heating under pressure which is carried out in the manufacture of the laminate according to the invention, as a result of which the fibres or filaments of those yarns are firmly anchored in the thermoplastic matrix, that is to say, are embedded therein or adhere thereto.

Preferably, the laminate according to the invention has from two to five, preferably two or three, textile layers. Preferably, at least 20 % by weight, more preferably at least 60 % by weight, of the yarns of the textile layers are yarns having a fibrous surface. 20 The woven fabrics may contain yarns having a fibrous surface in the warp and/or in the weft. one particular advantage of using woven fabrics is that the properties of the textile material can be adjusted differently in different directions so that it is possible to obtain optimum properties in use for the intended application. For example, for use of the laminate according to the invention as a light conveyor belt it is advantageous to have a high flexibility in the longitudinal direction whereas increased transverse stiffness is to be aimed at in the transverse direction. Such a deliberately created anisotropy of the properties can be achieved by using different fibre materials in the warp and the weft. A preferred embodiment of the laminate according to the invention consists in that the warp of the woven fabrics contains or consists of yarns having a fibrous surface and the weft contains or consists of monofilaments.

Preferably, the woven fabrics have in the warp and in the weft a thread sett of from 5 to 20, preferably from 7 to 15, threads/cm and have a surface weight of from 100 to 600, preferably from 350 to 500, g/M2.

As yarns having a fibrous surface it is possible to use in principle all types of yarn that, while being sufficiently strong, have fibre ends or fibre loops protruding from their surface. Thus, for example, yarns manufactured by secondary spinning of staple fibres (staple fibre yarn) are to be regarded as yarns having a fibrous surface within the meaning of this invention. For reasons of cost, but especially for reasons of strength, however, textured filament yarns are preferred as the yarns having a fibrous surface. 25 One especially advantageous type of yarn having a fibrous surface is blow-textured filament yarn. In view of the use of the laminate according to the 6 invention for technical applications, it is further preferred for the yarn having a fibrous surface to be a high-strength yarn.

In view of the fact that the woven fabric layers and the thermoplastic layers are melted together by a heat treatment, it has been found especially advantageous for the yarn having a fibrous surface to be a thermally prestabilised yarn.

As raw materials for the fibres or filaments of the yarns having a fibrous surface there come into consideration polymers and polycondensates that can be spun into filaments from solution or from the melt. Solutionspinnable polymers are, for example, polyacrylonitrile or modified aramides (= entirely aromatic polyamides), and melt-spinnable polymers or polycondensates are, for example, polyolefins, such as, for example, polypropylene, or araliphatic polyamides, such as, for example, the various types of (R)Nylon or polyesters. Preferred are yarns having a fibrous surface that consist of synthetic fibres or filaments of melt-spinnable polymers or polycondensates, and especially those which consist of polyesters, preferably predominantly of polyethylene terephthalate.

The covering layers and the adhesion layers of the laminate according to the invention are preferably thermoplastic layers having a surface weight of from 10 to 100, more preferably from 20 to 70, g/M2 per layer.

The thermoplastic layers preferably consist of a material having a melting point that is at least 100C, more preferably at least 200C, below the melting point of the fibres or filaments of the textile webs.

The thermoplastic layers advantageously consist of the same class of polymers as the fibres or filaments of the textile layers. By means of that measure laminates according to the invention that can be recycled especially advantageously are obtained. After use, such laminates according to the invention either can be directly regranulated without separating the fibres and thermoplastic constituents or can be subjected in their entirety to the same degradation reaction, with valuable raw materials for polymer manufacture being recovered.

The polymer materials for the textile fibres and the thermoplastic layers of the laminates according to the invention may be so modified, either by incorporating modifying units into the polymer chains or by mixing with other polymers or low-molecular-weight additives, that between them the melting point difference of at least 100C, preferably at least 200C, that is desirable between the textile material and the thermoplastic layer of the laminate according to the invention can be obtained.

Especially preferred are thermoplastic layers that consist of a polyester, especially when the fibres or filaments of the textile material contained in the laminate according to the invention also consist of - 8 polyesters.

As polyester materials there come into consideration in principle all known types that are suitable for the manufacture of fibres and films. Such polyesters consist predominantly of units derived from aromatic dicarboxylic acids and from aliphatic diols. Commonly used aromatic dicarboxylic acid units are the divalent radicals of benzenedicarboxylic acids, especially of terephthalic acid and isophthalic acid; commonly used diols have from 2 to 4 carbon atoms, ethylene glycol being especially suitable. Modified polyesters preferably contain at least 85 mol % ethylene terephthalate units. The remaining 15 mol % are then composed of dicarboxylic acid units and glycol units that act as so-called modifying agents and that allow the person skilled in the art to influence the physical and chemical properties of the manufactured Examples of such isophthalic acid filaments in a deliberate manner. dicarboxylic acid units are radicals of or of aliphatic dicarboxylic acids, such as, for example, glutaric acid, adipic acid, sebacic acid; examples of diol radicals having a modifying effect are those of longer-chained diols, for example of propanediol or butanediol, of di- or tri-ethylene glycol or, if present in small quantities, of polyglycol having a molecular weight of approximately from 500 to 2000. Especially preferred are polyesters that contain at least 95 mol % ethylene terephthalate units, especially those consisting of unmodified polyethylene terephthalate.

The laminate according to the invention made of such polyesters, especially polyethylene terephthalate, is not readily flammable. The low flammability can be further 5 enhanced by the use of suitably modified polyesters. Such modified polyesters are known. They contain additives of halogen compounds, especially bromine compounds, or, as is especially advantageous, they contain phosphorus compounds which are condensed into 10 the polyester chain. Especially preferred, low-flammability laminates according to the invention contain monofilaments and yarns consisting of polyesters that contain, condensed into the chain, components of the formula 0 0 11 0 - P - R - C R' (1) 1 wherein R represents alkylene or polymethylene having from 2 to 6 carbon atoms or phenyl, and R' represents alkyl having from 1 to 6 carbon atoms, aryl or aralkyl.

In formula I, preferably, R represents ethylene, and R1 methyl, ethyl, phenyl or o-, m- or p-methylphenyl, especially methyl.

The polyesters contained in the laminates according to the invention advantageously have a molecular weight corresponding to an intrinsic viscosity (IV), measured in a solution of 1 g of polymer in 100 ml of dichloroacetic 5 acid at 250C, of from 0.5 to 1.4.

As polyolefins of which the yarns and thermoplastic layers of the laminates of the invention may consist there come into consideration also substituted polyolefins, especially polyolefins substituted by chlorine or cyano groups. Examples of such polyolefin materials are polyethylene, polypropylene, polyvinyl chloride and polyacrylonitrile. Preferred polyolefin yarns and polyolefin thermoplastic layers consist of polypropylene.

The present invention further provides a process for the manufacture of the laminate according to the invention by forming a stack (sandwich) that contains, on a thermoplastic film forming the base, alternately at least one textile layer and one thermoplastic film layer, and heating the stack under pressure to a temperature that is above the melting point of the thermoplastic film, which process is characterised in that the textile layers are woven fabrics containing yarns having a fibrous surface consisting of synthetic fibres or filaments, and the heating under pressure is continued until the surface fibres of the woven fabric layers have been anchored in the covering layers and any adhesion layers present. The stack is formed in such a manner that the lower and the upper layer is a thermoplastic film. In the simplest case, the stack consists of one woven fabric covered on both sides by a thermoplastic film. Preferably, stacks having from two to five, preferably two or three, textile layers and from three to six, preferably three or four, thermoplastic films are formed.

Preferably, at least 20 % by weight, more preferably at least 60 % by weight, of the yarns of the textile layers used are yarns having a fibrous surface.

Preferably, woven fabrics that contain yarns having a fibrous surface in the warp and in the weft are used. In view of the deliberate creation of an anisotropy described above, it may be advantageous to use woven fabrics in which the warp contains or consists of yarns having a fibrous surface and the weft contains or consists of monofilaments.

Preferably, woven fabrics that have in the warp and in the weft a thread sett of from 5 to 20, preferably from 7 to 15, threads/cm and that have a surface weight of from 100 to 600, preferably from 350 to 500, g/m2 are used.

It is furthermore preferred for the yarn having a fibrous surface of the woven fabrics used to be a textured, preferably a blow-textured, filament yarn.

In view of the use of the laminate according to the invention for technical purposes, it is advantageous for the yarn having a fibrous surface of the woven fabrics used to be a high- strength yarn.

The synthetic fibres or filaments of the yarn having a fibrous surface preferably consist of the abovementioned melt-spinnable polymers or polycondensates that have a melting point above the temperature at which the stack is treated under pressure.

More preferably, they consist of polyesters, especially those containing predominantly ethylene terephthalate units.

A commercial yarn having a fibrous surface that is very suitable for the manufacture of the woven fabrics to be used according to the invention is, for example, the high-strength, blow-textured yarn (R) TREVIRA HF, Type 702 dtex 1800 f 200 of Hoechst AG. A commercial weft material that is very suitable for transverse stiffening of the laminate according to the invention is, for example, (R) TREVIRA MONOFIL Type 900S, 0.30 mm of Hoechst AG.

The thermoplastic films used advantageously have a surface weight of from 10 to 100, preferably from 20 to 70, g/m2. They preferably consist of a material having a melting point that is at least 100C, more preferably at least 200C, below the melting point of the fibres or filaments of the textile webs used.

It is especially preferred to use thermoplastic films that consist of the same class of polymers as the fibres or filaments of the textile layers used, since, as already mentioned above, as a result the used laminate according to the invention can be recycled especially advantageously. When polyester woven fabrics are used, therefore, polyester films will preferably also be used as the thermoplastic films. A commercial polyester film is, for example, the fusible copolyester film (R) PLATILON H5 of ATO-CHEM.

Special advantages with regard to fire protection are offered by the use of woven fabrics and films consisting of one of the low-flammability polyesters mentioned above.

The laminate according to the invention is outstandingly suitable for the manufacture of light conveyor belts and flat drive belts. The present invention therefore relates also to those products made of the laminate according to the invention.

The following working examples illustrate the manufacture of the laminates according to the invention.

Example 1 a) A warp of high-strength blow-textured polyester yarn of the type (R) TREVIRA HF Type 702 dtex 1800f200 is woven with the same yarn as the weft material to form a woven fabric in linen weave with 10 threads/cm in the warp and 10 threads/cm in the weft.

b) On a fusible polyester film of the type Platilon H5 having a surface weight of 35 g/m2 and a melting point of 1200C, 3 layers of the woven fabric produced in a) and 3 layers of the same fusible polyester film are laid alternately. The stack so obtained is subjected to a surface pressure of 20 bar between two metal plates and heated to 1300C. That temperature is maintained for 5 minutes, then the system is cooled while maintaining the pressing pressure, and the laminate according to the invention is removed.

The laminate has a very good layer adhesion of 18.8 N/cm. It is outstandingly suitable for the manufacture of light conveyor belts and flat drive belts.

ExamiDle 2 a) A warp of high-strength blow-textured polyester yarn of the type (R) TREVIRA HF Type 702 dtex 1800f200 is woven with a monofilament (R)TREVIRA MONOFIL Type 900S, 0.30 mm as the weft material to form a woven fabric having 11 threads/cm in the warp and 10 threads/cm in the weft.

b) On a fusible polyester film of the type Platilon H5 having a surface weight of 35 g/m2 and a melting point of 1200C, 3 layers of the woven fabric produced in a) and 3 layers of the same fusible polyester film are laid alternately. The stack so obtained is subjected to a surface pressure of 20 bar between two metal plates and heated to 1300C. That temperature is maintained for - 15 minutes, then the system is cooled while maintaining the pressing pressure, and the laminate according to the invention is removed.

The laminate so produced has a good layer adhesion of 21 N/cm. It is outstandingly suitable for the manufacture of light conveyor belts with increased transverse stiffness.

claims 1. A laminate comprising at least one layer of a textile sheet structure comprising woven fabric containing yarns having a fibrous surface comprising synthetic fibres or filaments, a lower and an upper covering layer and, if more than one textile layer is present, an adhesion layer lying between each pair of textile layers, the covering layers and any adhesion layer(s) being essentially unstructured thermoplastic layers, and the surface fibres of the woven fabric layer(s) being anchored at the interfaces between the textile woven fabric layer(s) and the covering layers and any adhesion layer(s) present in the covering layers and any adhesion layer(s) present.

2. A laminate as claimed in claim 1, wherein the laminate has from two to five textile layers.

3. A laminate as claimed in claim 2, wherein the laminate has two or three textile layers.

4. A laminate as claimed in any one of claims 1 to 3, wherein at least 20 % by weight of the yarns of the textile layer(s) are yarns having a fibrous surface.

5. A laminate as claimed in claim 4, wherein at 17 least 60 % by weight of the yarns of the textile layer(s) are yarns having a fibrous surface.

6. A laminate as claimed in any one of claims 1 to 5, wherein the woven fabric contains yarns having a 5 fibrous surface in the warp and in the weft.

7. A laminate as claimed in any one of claims 1 to 6, wherein the warp of the woven fabric contains or consists of yarns having a fibrous surface and the weft contains or consists of monofilaments.

8. A laminate as claimed in any one of claims 1 to 7, wherein the woven fabric has a surface weight of from 100 to 600 g/m2.

9. A laminate as claimed in claim 8, wherein the 1 woven fabric has a surface weight of from 350 to 500 g/m2.

10. A laminate as claimed in any one of claims 1 to 9, wherein the yarn having a fibrous surface is a blowtextured filament yarn.

11. A laminate as claimed in any one of claims 1 to 10, wherein the yarn having a fibrous surface is a high-strength thermally pre-stabilised yarn.

12. A laminate as claimed in any one of claims 1 to 11, wherein the synthetic fibres or filaments consist of melt-spinnable polymer or polycondensate.

13. A laminate as claimed in any one of claims 1 to 12, wherein the covering layers and any adhesion layer(s) are thermoplastic layers having a surface weight of from 10 to 100 g/m2 per layer.

14. A laminate as claimed in claim 13, wherein the covering layers and any adhesion layer(s) are thermoplastic layers having a surface weight of from 20 to 70 g/m2 per layer.

15. A laminate as claimed in any one of claims 1 to 14, wherein the thermoplastic layers consist of a material having a melting point that is at least 100C below the melting point of the fibres or filaments of the textile layer(s).

16. A laminate as claimed in claim 15, wherein the thermoplastic layers consist of a material having a melting point that is at least 200C below the melting point of the fibres or filaments of the textile layer(s).

17. A laminate as claimed in any one of claims 1 to 19 - 16, wherein the thermoplastic layers consist of the same class of polymer as the fibres or filaments of the textile layer(s).

18. A laminate as claimed in claim 1, substantially 5 as described in Example 1 or 2.

19. A process for the manufacture of a laminate as claimed in claim 1, which comprises forming a stack that comprises at least one layer of a textile sheet structure comprising woven fabric containing yarns having a fibrous surface comprising synthetic fibres or filaments, a lower and an upper covering layer and, if more than one textile layer is present, an adhesion layer lying between each pair of textile layers, the covering layers and any adhesion layer(s) being essentially unstructured thermoplastic layers, and heating the stack under pressure to a temperature that is above the melting point of the thermoplastic film until the surface fibres of the woven fabric layer(s) have been embedded in the covering layers and any adhesion layer(s) present.

20. A process as claimed in claim 19, wherein a stack having from two to five textile layers and from three to six thermoplastic films is formed.

A process as claimed in claim 20, wherein a stack having two or three textile layers and three or four thermoplastic films is formed.

22. A process as claimed in any one of claims 19 to 21, wherein at least 20 % by weight of the yarns of the textile layer(s) are yarns having a fibrous surface.

23. A process as claimed in claim 22, wherein at least 60 % by weight of the yarns of the textile layer(s) are yarns having a fibrous surface.

24. A process as claimed in any one of claims 19 to 23, wherein woven fabric having a surface weight of from 100 to 600 g/m2 is used.

25. A process as claimed in claim 24, wherein woven fabric having a surface weight of from 300 to 500 g/m2 is used.

26. A process as claimed in any one of claims 19 to 25, wherein the yarn having a fibrous surface is a blowtextured filament yarn.

27. A process as claimed in any one of claims 19 to 26, wherein the synthetic fibres or filaments consist of melt-spinnable polymer or polycondensate that has a melting point above the temperature at which the stack is treated under pressure.

28. A process as claimed in any one of claims 19 to 27, wherein the thermoplastic films used have a surface weight of from 10 to 100 g/m2 per layer.

29. A process as claimed in claim 28, wherein the thermoplastic films used have a surface weight of from 20 to 70 g/M2 per layer.

30. A process as claimed in any one of claims 19 to 29, wherein the thermoplastic films used consist of a material having a melting point that is at least 100C below the melting point of the fibres or filaments of the textile layer(s) used.

31. A process as claimed in claim 30, wherein the thermoplastic films used consist of a material having a melting point that is at least 200C below the melting point of the fibres or filaments of the textile layer(s) used.

32. A process as claimed in any one of claims 19 to 31, wherein the thermoplastic films used consist of the same class of polymer as the fibres or filaments of the textile layer(s) used.

- 22 33. A process as claimed in claim 19, carried out substantially as described in Example 1 or 2.

34. A laminate whenever produced by a process as claimed in any one of claims 19 to 33.

35. Use of a laminate as claimed in any one of claims 1 to 18 and 34 for the manufacture of light conveyor belts and flat drive belts.

36. A light conveyor belt, comprising a laminate as claimed in any one of claims 1 to 18 and 34.

37. A flat drive belt comprising a laminate as claimed in any one of claims 1 to 18 and 34.