FORMATION OF SHEET MATERIAL USING HYDROENTANGLEMENT

Abstract

A method is described for forming reconstituted leather sheet material from a mixture of base fibres, such as leather fibres, and bi-component synthetic fibres which have outer layers which melt at a lower temperature than their inner cores. The fibres are mixed, formed into a web and then heated so that the synthetic fibres fuse together to form a network within the web. The base fibres are then tangled, whilst constrained by the network, preferably using hydroentanglement. A high quality reconstituted leather sheet material is thus produced.

Claims

1. A reconstituted leather sheet material having a leather-like feel, the reconstituted leather sheet material being formed by a method comprising the steps of: evenly distributing and compressing a mixture of predominantly waste leather base fibres and additional synthetic fibres to form a web, wherein the additional synthetic fibres have meltable surface layers and the base waste leather fibres comprise leather fibres having fibrillated branches, heating the web to melt the surface layers of the additional synthetic fibres so as to cause such fibres to fuse together at intersections to form fused network intersections within the web mixture, and subjecting the web mixture to successive hydroentanglement stages to entangle the waste leather fibres with each other while initially constrained by the network, such that the increase in tensile strength arising from the hydroentanglement of the fibers within the web is greater than the tensile strength of the web prior to hydroentanglement.

2. A method of forming a reconstituted leather sheet material having a leather-like feel, comprising the steps of: evenly distributing and compressing a mixture of predominantly waste leather base fibres and additional synthetic fibres to form a web, wherein the additional synthetic fibres have meltable surface layers and the base waste leather fibres comprise leather fibres having fibrillated branches, heating the web to melt the surface layers of the additional synthetic fibres so as to cause such fibres to fuse together at intersections to form fused network intersections within the web mixture, and subjecting the web mixture to successive hydroentanglement stages to entangle the waste leather fibres with each other while initially constrained by the network, such that the increase in tensile strength arising from the hydroentanglement of the fibers within the web is greater than the tensile strength of the web prior to hydroentanglement.

3. The method according to claim 2, wherein the waste leather base fibres have a maximum fibre length of 6 mm.

4. The method according to claim 2, wherein at least 90% of the additional synthetic fibres have a maximum fibre length of 10 mm.

5. The method according to claim 2, wherein the additional synthetic fibres constitute less than about 10% of the weight of the formed sheet material.

6. The method according to claim 5, wherein the additional synthetic fibres constitute up to about 5% of the weight of the formed sheet material.

7. The method according to claim 2, wherein the additional synthetic fibres each has an inner core surrounded by a respective meltable outer surface layer that is formed by one or more outer layers having a melting point lower than the melting point of the inner core.

8. The method according to claim 7, wherein the one or more of the outer layers are polyethylene and the inner core is polyester or polypropylene.

9. The method according to claim 2, wherein the additional synthetic fibres have a denier in the range of 1.7 to 3.0 dtex.

10. The method according to claim 2, wherein the mixture of fibres also includes further synthetic fibres which are not melted to cause fusion together.

11. The method according to claim 2, wherein the further synthetic fibres have a denier less than 1.0 dtex.

12. The method according to claim 10, wherein the further synthetic fibres comprise less than 20% by weight of the reconstituted leather sheet material.

13. The method according to claim 2, wherein the leather base fibres have lengths of less than 3 mm.

14. The method according to claim 2, wherein the additional synthetic fibres constitute no more than 2% of the weight of the web.

15. The method according to claim 2, further comprising a fabric layer, and the leather fibres are caused to penetrate the fabric layer.

16. The method according to claim 2, wherein the additional synthetic fibres constitute 2 to 10% of the weight of the reconstituted leather sheet material formed by said method.

17. The method according to claim 2, wherein the hydroentanglement is performed using hydroentangling jets of liquid in multiple passes.

18. The method according to claim 17, further comprising using a collection device positioned adjacent the hydroentangling jets and a surface of the web to collect rebound liquid from the jets that rebounds off the surface of the web, such collection occurring before the liquid falls back onto the surface of the web thereby to minimize the amount of rebound liquid that falls back on the surface of the web.

19. The method according to claim 2, wherein the outer meltable surface layers of the additional synthetic fibres are melted by passing hot air through the web, and the web is held between porous belts during passage of the hot air through the web.

20. (canceled)

21. The reconstituted leather sheet material according to claim 1, wherein the sheet material includes a front web and a back web, wherein the front web is about 150 g/m2 and contains about 15% non-bicomponent synthetic fibres and the back web may be about 250 g/m2 and contain about 0% of non-bicomponent fibre, and wherein the bicomponent content for both webs may be constant at about 4%.

Description

BRIEF DESCRIPTION OF DRAWING

[0048] The invention will now be described further by way of example only and with reference to the accompanying drawings in which:

[0049] FIG. 1 is a schematic view of initial stages of one form of apparatus used in the performance of the method of the invention and which shows the main operating principles of a commercially available plant for making a fibre web with a fused bicomponent network; and

[0050] FIG. 2 shows further stages of the apparatus for combining such web with reinforcing fabric and hydroentangling the resulting sandwich.

DETAILED DESCRIPTION

[0051] Referring to FIG. 1, waste leather fibres made by textile reclaiming methods lightly chopped to a maximum length of approximately 6 mm are mixed with 4% of 1.7 dtex bicomponent fibres and 5% of 3.0 dtex standard polyester fibres both cut to constant 6 mm length. The mixture is evenly distributed at around 200 g/m2 onto a driven porous belt 1 by at least one pair of perforated drums 2 while the fibres are drawn onto the porous belt by vacuum box 3.

[0052] The resulting web 4 of evenly laid fibres is transferred by a conventional vacuum conveyor 5 to porous belts 6 and 7, which contain and partially compress the web while hot air from a box 8 is blown through belts 7 and 6 and web 4, and received by a suction box 9. The temperature of the hot air is sufficient to melt the outer sheath of the bicomponent fibres (but not the inner core) and thereby fuse the fibres together at their intersections.

[0053] Before the melted sheaths at the intersections of the bicomponent fibres solidify, the web may be compressed by nip rollers 10 to form a denser web consisting of un-bonded leather and polyester fibres supported by a three-dimensional network of fused bicomponent fibres. On solidification of the intersections the network provides sufficient strength for the web to be wound onto reel 11 for transport and/or storage.

[0054] Referring to FIG. 2, two such webs 4a and 4b unwind from reels 11a and 11b together with fabric reinforcement 4c from reel 12, and are brought together by rollers 13 to feed onto a porous belt 14. Webs 4a, 4b and fabric 4c comprising a composite web 15 are conveyed by belt 14 through hydroentangling jets 16, and water from the jets is drawn through web 15 and porous belt 14 by vacuum box 17. Water rebounding from the surface of the composite web is collected in trays 18 and conveyed away as described more fully in the prior application.

[0055] For complete hydroentanglement the composite web is passed through a plurality of successive hydroentanglement stages, one or more of which may incorporate a screen applied over the surface of the web 15. Hydroentanglement stages are arranged so that jets can be applied to both surfaces of the web, and for the present example, such application of jets is on alternate sides through 5 such stages at a speed of 10 m/min.

[0056] In this example perforated screens with an open area of approximately 60% made from chemically etched stainless steel of the type described in the prior application are applied to each side of the web for the final stage of hydroentangling in order to mask the furrow marks from the jets. To prevent coincidence lines forming on the surface, the pitch of the apertures of the screen is made the same as the pitch of the jet orifices.

[0057] Jet orifices for this example are 140 microns at 0.9 mm centres, and when applied through the screens, jet pressures can be at the maximum normally available in commercial hydroentangling equipment at 200 bar. Pressures without the screen may be reduced slightly to 180 bar, and unlike similar webs without a bicomponent network, this same high pressure can be applied at the first stage of hydroentangling without the need for an external screen. The resulting hydroentangled web may be finished by impregnating with emulsified oils, pigments and pigment fixatives as may be applied to natural leather, followed by drying and buffing both sides. The side that received three hydroentangling stages (and therefore has a higher degree of entanglement and attachment to the reinforcing fabric) dan then be coated with a leather-like finish by conventional means as used for coating synthetic leather.

[0058] The foregoing procedures may be suitable for shoe material, but for un-coated materials such as for clothing suede, web 4 may be on one side only of the reinforcing fabric and four hydroentangling stages applied, all onto the side having the web. After buffing and impregnation the web face may be treated with hot air to cause the projecting manmade fibres to melt and the surface brushed to remove any slight charring leaving a finish closely similar to natural leather.

[0059] The resulting sheet material is a high quality reconstituted leather having an excellent feel, strength and surface finish.

[0060] It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

[0061] Thus, for example, the web may be wet laid, although there can be disadvantages with this.

[0062] As described in the prior patent application, webs can be wet laid by methods normally used for paper making or by carding if sufficiently long textile fibres are included to carry the leather fibres through the carding process. The use of bicomponent fibres which are added or which make up the carrier fibres provides a screen for hydroentangling according to the present invention. For effective carding, normally over 5% of 1.7 decitex carrier fibres of 20 mm or more is needed, and the leather fibres need to be made by textile reclaiming methods to be long enough to avoid excessive ejection of fines. For wet laying, the bicomponent fibres need to be short and the webs dried before fusing. This may not be wholly satisfactory when the next step is to wet the webs again for hydroentangling, while the disadvantages of carding include slow rates of production and wastage from the ejection of fine fibres.

[0063] A wide variety of variations are feasible within the scope of this invention. Jet orifice size, screen details, production speeds and other details provided in the prior application can broadly apply to the present invention. The main departure is the reduced application of surface screens, and to ensure good attachment to the reinforcing core, it is often desirable to hydroentangle on alternate sides of the fabric so that fibres are pushed evenly into the interstices of the fabric. Also, due to the stabilising effect of the bicomponent network, pressures can be higher and leather fibres shorter than in the method of the prior application.

[0064] Product compositions can vary widely and thickness of the web between the final coated surface and the internal reinforcing layer can differ substantially from the web forming the back layer. For example, instead of the equal webs implied in the previously described example, the front one may be 150 g/m2 and contain 15% non-bicomponent synthetic fibres and the back may be 250 g/m2 and contain 0% of non-bicomponent fibre. The bicomponent content for both webs, however, may be constant at 4%.

[0065] Fibre lengths can be determined largely by the production limitations of commercial web laying equipment and, where alternative web laying equipment (such as carding) can handle long manmade fibres, it may not be necessary to incorporate fabric reinforcement. Also, where jet markings are acceptable in the finished product, there may be no need for surface applied screens. Alternatively, screens may be used extensively to supplement the internal screens of the bicomponent network, particularly if the latter are very light and the leather fibres are particularly short.

[0066] Hydroentangling speeds can vary widely depending on a whole range of parameters, including weight per unit area of material being hydroentangled, open area of fabric reinforcement, jet pressures, jet diameter, jet spacing, number of passes through the jets, weight of bicomponent network, type of leather fibre, number of passes using external screens, and open area of screens. Generally lighter webs can be hydroentangled at faster speeds, and typically 600 g/m2 material may require 6 m/minute while 200 g/m2 may entangle fully at 15 m/min.

[0067] The choice of using relatively long waste leather fibres made by textile reclaiming methods or short ones made by milling (such as conventional hammer or disk milling) can depend on the cost and availability of the different types of waste leather. Milling is cheaper and can use waste leather shavings, which are usually cheaper than the sheet waste used in textile reclaiming plant. However end product quality can be lower and more costly manmade fibre additions may be needed to achieve acceptable performance. Blends of both types of waste fibre can also be used for intermediate quality products.

[0068] As with the prior application, the main limitation in weight of composite webs that can be hydroentangled is the onset of hydroentanglement itself as this reduces permeability to the jets and constricts further entanglement. Such constriction is far greater with leather fibres than conventional synthetic fibres but, by using the methods of this invention, it is possible to make acceptable product at relatively high composite web weights of around 600 g/m2. Producing acceptable quality end product at much above this weight is possible but becomes increasingly difficult. Lighter webs are easier to hydroentangle, and minimum web weights can be set more by limits of web forming accuracy and limited market demand for exceptionally thin leather products.

[0069] The inter-relationships between all the foregoing parameters are complex and can vary considerably for different types of end product. An optimum balance between output rate, cost and finished product performance can be established by conducting empirical trials within the broad guidance provided in this patent application. The bicomponent network and associated features of the present invention assist considerably in improving production rate and product quality at lower cost compared to the methods of the prior application.