GB2108045A - Laminated films - Google Patents

Abstract

The present invention provides a non-woven material comprising a pair of overlaid stretch orientated films with the direction of stretch orientation of the films extending substantially transversely to each other, the films being stitch bonded together with the stitching causing fibrillation of at least one of the films. Preferably the films are arranged obliquely so that the stitching creates a structure comprising weft elements formed from the films bonded by the stitching yarn, and a series of saltire form fibril pairs also formed from the films linking successive weft elements. Such a structure provides a material of considerable strength and stability particularly by virtue of the presence of the saltire form fibrils. The material could be used for example in the manufacture of bags and sacks. <IMAGE>

Description

SPECIFICATION Improvements in stitched film This invention concerns non-woven sheet material.

In the Applicant's U.K. Patent No. 1437179 there is described and claimed a non-woven sheet material made by stitch-bonding a film of stretch orientated synthetic resinous material, the direction of stitching being transverse to the direction of stretch of the film whereby the film is slit into strips by the stitching needles, which strips extend transversely of the direction of the stitching to form therewith a weavelike material.

It is an object of the present invention to provide improvements in the above non-woven sheet material.

According to one aspect of the present invention, a non-woven material comprises two overlaid stretch-oriented films, with the directions of stretch orientation of the films lying at rightangles to each other and secured together by stitching, at least one of the films being slit into strips by the stitching needles. The stitching may constitute parallel stitching extending transversely to the direction of stretch orientation of one of the films. The stitching may be conveniently carried on a stitch-bonding machine of appropriate type. As an alternative, the films may be secured together by securing a fibrous web thereto, again conveniently by means of needling on an appropriate type of stitch-bonding machine. This material is useful for backing tufted carpets.

According to a second aspect of the present invention, a non-woven material comprises film stretch-oriented in the longitudinal direction and continuously cross-laid to provide two layers of films which are secured together by parallel lines of stitching extending transversely of the layers.

This can be done in a continuous manner on an appropriate type of stitch-bonding machine, for example on a Malimo (RTM) machine.

Preferably, in the transverse laying of the film which results in the double layer film, one layer of the double layer film extends obliquely to the superimposed layer of the film, so that the stitching extends at an angle to the stretch orientation of both layers. It has been found that with this film arrangement, the splitting of the film layers is not continuous, but there is a series of short fibrils extending diagonally between successive split wefts of each layer and oppositely to the orientation of the fibrils between the two respective wefts of the superimposed layer. This material consequently has the interesting visual effect of stitch-bonded wefts additionally by a plurality of saltire patterned fibrils. Further, it has been found that this fibril pattern considerably improves the dimensional stability of the material.

The stitching yarn can be nylon, polyester, polypropylene or other stretchable material and as described and claimed in the applicants' copending application the basic fabric material can be stretched in the longitudinal direction possibly after heating. It has been found that this increases the tenacity of the stitching yarn chain very considerably, in addition to providing the advantage of an increase in the area of the material and the stability of the material is also improved.

Several embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 shows schematically the cross-laying of film for carrying out a first embodiment of the present invention, and Fig. 2 shows a stitched film fabric according to the present invention and utilising the cross-laid film of Fig. 1.

Referring to Figs. 1 and 2 in the first embodiment of the present invention, a band of longitudinally oriented polypropylene film 1 is supplied to the weft carrier 9 of a Malimo (RTM) stitch-bonding machine which carrier traverses back and forth transversely to the direction of warp feed, to cross-lay the film strip continuously. In Fig. 1 , the top layer is 1 a and the bottom layer 1 b.

The weft carrier is modified so as to pre-perforate the band 1 at appropriate intervals, causing it to separate into short lengths about 2.5 millimetres wide, which can then be looped about the hooks (not shown) which normally receive the weft.

Alternatively, the carrier motion may be such as to impale the band on the latter hooks, likewise causing short splits and narrow strands which can be looped above the hoqks. In this way, a continuous length of cross-laid film 1 a, 1 b is fed by the hooks to the stitching needles of the machine. An appropriate supply of stitching yarn 2 is provided of nylon, polypropylene or other heat stretchable plastics material and the stitching yarn can be in the form of tape. The stitching yarn should be moderately orientated to enable the stitching process to proceed satisfactorily. The stitch needles are arranged to form spaced parallel rows of chain stitches 3, longitudinally of the cross-laid film, so securing the cross-laid layer la, 1 b together.

There is thus produced a double-layer film and the orientation K of the superimposed film layers 1 a, 1 b will run oppositely to each other and obliquely to the direction of warp feed of the machine.

The relative angularity of the cross-laid layers 1 a, 1 b of the film will depend on the machine settings and it will be clear that this angularity can be varied within certain limits.

It has been found that the stitch needles, on penetrating the cross-laid double layer film 1 a, 1 b, substantially split the two layers of film into strips 4 extending across the fabric with a width substantially equal to the length (L) of stitch. There are also left two series of fibrils 5a, Sb connecting successive "weft elements" and running diagonally on saltire formation (see Fig. 2). The first series 5a consists of a fibril running diagonally across each space defined by successive "weft elements" and adjacent rows of stitches, in the direction of orientation of the one layer 1 a of the film and the other series 5b consists of a similar fibril running across each space but in the direction of orientation of the other 1 b superimposed layer of the cross-laid film.These fibrils 5a, Sb improve the dimensional stability of the material to a considerable degree in that the resistance to biasing is very substantially increased.

If the stitching yarns are of polypropylene, nylon, polyester or other thermoplastic material moderately oriented, it is possible, after the material has been taken from the machine, to substantially further orientate it by passing it over a heated surface to soften the stitching yarn 2 as described and claimed in the applicants' copending application. This can be conveniently done since the stitching yarn 2 stands proud of the weft film 4. Alternatively, the fabric could be completely heated causing softening of the stiching yarn 2, if the stitching has a lower melting temperature than the rest of the fabric.

Simultaneously with the heat softening, the stiching yarn 2 is tensioned longitudinally and stretched and in this way, the length of the fabric can be as much as doubled and there is no corresponding reduction in its width. When the double layer film is stretched in the longitudinal direction, the "weft elements" 4 which were created by the needles and stitching, which elements 4 extend transversely across the film and being linked by the diagonally extending fibrils 5a, Sb as described in the previous paragraph, move apart but remain joined by the diagonally extending fibrils 5a, 5b. This improves further the dimensional stability of the product.

The advantages to be gained from producing the fabric in this form and thereafter stretching it can be listed as follows 1. For every one square metre of basic fabric produced, two square metres of finished fabric will result.

2. If fabric can be produced with a resultant chain yarn tex of 22 from an initiai tex of 44, then this will result in a cheaper yarn cost per kilo, as it is normal for the lower tex yarns to be more expensive per kilo than the higher tex yarns. The effect of stretching the chain formation in the warp direction results in 3 reasons for increased tenacity in grammes per dtex of the chain: a. The yarn elements, because of increased orientation, have a resultant increased tenacity.

b. Any tension load subsequently applied to the chain will be evenly distributed over the 3 legs of the chain, resulting in a higher breaking load.

c. When the chain is stretched, the amount of orientation resulting at the curved end of the loop is less than the orientation in the legs of the chain loop, which results in an improved strength at the loop end, which is normally the weak part of the link in the chain.

4. The combination of heating and tensioning the chain formation during the stretching process results in the chain's formation gripping more tightly around the strips 4 of weft film and after cooling, this may result in a bonding between the film 1, and the chain stitch 2 or a permanent improvement in the mechanical lock between the chain formation of the warp stitching 2 and the strips of weft 4, resulting in a fabric of improved stability.

5. The stretching of the double layer film 1 in the longitudinal direction pulls and tensions the saltire form fibrils 5a, Sb, resulting in considerable improvement of the dimensional stability of the material, in that the resistance to biasing stresses is very substantially increased.

6. It will be appreciated that a basic fabric constructed from weft film, using a different polymer, film weight and thickness, could be used and that in the warp direction, stitching yarns of other thermoplastic materials of varying tex and orientation ratio and material, could be used. it will also be appreciated that the amount of stretch applied in the process could vary from 1% upwards.

This could be used commerciallyforthe manufacture of open weave sacks and bags for vegetables, where lightness and good stability are required in the product, along with a low cost of production.

A second commerical use for this fabric would be as a reinforcement for needle punch products such as coir mattress pads.

A third commercial use for the material in its unstretched form could be for tufted carpet primary backing, where improved tuft lock and a reduction in loss of weft strength during the tufting operation can be achieved.

According to a further embodiment of the present invention a non-woven material is made from two polypropylene films each of which is uniaxially oriented. The two films are laid one on the other with their directions of stretch orientation at right-angles to each other. They are then processed on a Malimo (RTM) stitch-bonding machine, being fed therethrough in place of the normal warp. The stitching elements of the machine are supplied with continuous filament nylon yarn, and they operate to form two parallel rows of tricot stitches lying transversely to the direction of orientation of one of the films. The penetration of the stitching elements, that is the needles, causes the film to split in the directions of orientation, and this gives rise to a generally woven appearance. Furthermore, the perforations and splits caused by the needles impart a considerable degree of flexibility to the material which can be used as a primary carpet backing for tufting.

In a modification of the above described embodiments, instead of using a stitchng yarn a fibrous web is laid on top of the overlaid film and this web can be of any suitable material. The fibres of the web are picked up by the needles in the stitch-bonding machine, drawn through the film, formed into loops in lieu of the stitching yarn threads and this will result in the film being stitched together by the looped fibres drawn from the fibrous web. A modified Malimo (RTM) machine can be used which is equipped with special needles which penetrate the web and the films, and by pulling bundles of fibre from the web through the films and forming a stitch causes the films to be secured together, and also cause the web to be secured to the films. The needles cause the film to be split in the direction of orientation, and this gives rise to a generally woven appearance. This material is suitable for use as a primary or secondary tufted carpet backing. The greater part of the nylon fibres will be located at one side of the film laminate, and it is from this side that the carpet tufts will extend. The nylon has a good dye receptivity and enhances the appearance of the printed carpet.

In a further modification the fibrous web could be used in the stitch-bonding and fibrillation of a single stretch oriented film.

Claims (20)

1. Non-woven material comprising two overlaid stretch-oriented films, with the directions of stretch orientation of the film lying at right-angles to each other and secured together by stitching, at least one of the films being slit into strips by the stitching needles.

2. Non-woven material as claimed in Claim 1, wherein the strips constitute weft yarn of the material, the stitching constituting warp yarn.

3. Non-woven material comprising film stretchoriented in the longitudinal direction and continuously cross-laid to provide two layers of film which are secured by parallel lines of stitching extending transversely of the layers.

4. Non-woven material as claimed in Claim 3, wherein one layer of the film extends obliquely to the other layer of the film so that the stitching extends at an angle to the stretch orientation of the both layers.

5. Non-woven material as claimed in Claim 4, wherein there are provided warp yarns defined by the stitching yarn and weft yarns formed by splitting of the film, successive weft yarns being linked by a series of diagonally orientated fibril pairs.

6. Non-woven material as claimed in any one of the preceding Claims, wherein the stitching comprises thread or tape.

7. Non-woven material as claimed in Claim 1, wherein a web of fibres is laid on the film, and the stitching comprises fibres drawn from the web.

8. Non-woven material comprising a stretch orientated film, and a web of fibres located on the film, said web being stitch-bonded to the film utilising fibres of the web, said stitch bonding serving to fibrillate the film.

9. Non-woven material as claimed in any one of the preceding claims, wherein the film comprises synthetic resinous plastics material.

10. Non-woven material as claimed in any one of Claims 1 to 6, wherein the stitching comprises synthetic resinous plastics material.

11. Non-woven material as claimed in any one of the preceding claims wherein the stitching is applied by means of a stitch-bonding machine.

12. A method of making non-woven material comprising providing a double layer film, each layer comprising stretch orientated material with the direction of stetch of the layers extending substantially transversely to each other, and stitch-bonding the layers with thread so that at least one of the layers is fibrillated.

13. A method as claimed in Claim 12, wherein one layer extends obliquely to the other layer, the stitching extending at an angle to both layers.

14. A method as claimed in Claim 13, wherein the double-layer film is formed by cross laying a continuous film sheet.

15. A method as claimed in any one of Claims 12 to 14, wherein the stjtch-bonding is carried out on a stitch-bonding machine.

16. A method as claimed in any one of Claims 12 to 1 5, wherein the double-layer film is made from synthetic resinous plastics material.

17. A method as claimed in any one of the preceding claims, wherein the stitching thread comprises synthetic resinous plastics material.

1 8. Non-woven material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 9. A method of making non-woven material as claimed in Claim 12 and substantially as hereinbefore described.

20. Composite material including non-woven material as claimed in any one of Claims 1 to 11 and 18.