WO1995006150A1

WO1995006150A1 - Non-woven fabrics

Info

Publication number: WO1995006150A1
Application number: PCT/GB1993/001833
Authority: WO
Inventors: Fred Kershaw
Original assignee: American Nonwovens, Corporation
Priority date: 1993-03-01
Filing date: 1993-08-27
Publication date: 1995-03-02

Abstract

A non-woven fabric (110) comprises a body layer (111) formed by hydro-entanglement at a station (31), and on to which fibres are deposited by passing through the layer (111), a stream of fluid such as process water at a station (33) to deposit the fibres by a filtration process. The fluid can be process fluid collected at station (32) or a separate fluid or a mixture thereof. Deposition fluid collected at station (34) can be returned for use in the hydro-entanglement process.

Description

Non-Woven Fabrics

This invention relates to the manufacture of non-woven fabrics by hydro-entanglement. In particular the process is concerned with the manufacture of barrier fabrics for once-only and limited use in such fields as surgical clothing, protective clothing and the like.

Non-woven fabrics are of particular usefulness in this area because they can be produced rapidly with the required properties at low cost which enables a low price to be maintained to allow disposability.

In view of their low cost, it is important that running costs and waste be minimised in the manufacture thereof.

In a known method of manufacturing a barrier fabric for use, for example, in surgical gowns and the like, an apparatus (10) (figure 1) is used. In the apparatus (10) a web (11) made of non-woven base fabric is fed to an entanglement zone (12) from a feed roll (13) . Simultaneously a tissue of cellulosic fibres (14) is fed thereto from a tissue feed roller (15) via a deflection roller (16) . After passing through the entanglement zone the combined web (11) and tissue (14) , united by the entanglement are treated with finish at station (17) and wound onto a take-up roll (18) Here it should be noted that the adding

SUBSTITUTE SHEET of the finish is a conventional step and is not described in detail. The finish applied can be a binder, an oil/water repellent or other type well known by those skilled in the art of finishing. It may also be a coating applied by conventional means such as spread coating, foam coating, screen print and so on.

In the entanglement zone process liquid, usually water engages the tissue (14) and the web (11) to connect them. After entanglement the process liquid is collected at (19) and fed to a filter (20) which separates washed out cellulosic fibres from the liquid. The fibres are discarded and the clean liquid is fed back to the entanglement zone for use as process liquid.

This apparatus and method has several disadvantages and/or undesirable features. Firstly, it is necessary to provide, maintain and clean the filter (20) and this adds to the cost of the process. Secondly, the amount of fibres lost and passed to waste can amount to up to 10% or more of the weight of the tissue (14) and this represents a serious material loss, it is not economic to recycle the fibres for the re-manufacturing of tissue.

A further, unconnected disadvantage of the known machine and method is that the hydro-entanglement process does tend to have a "liney" appearance some of the lines being more pronounced and to have occasional randomly arranged streaks and/or holes in the final fabric. This is a characteristic of the process and there has not been found thus far any satisfactory way of overcoming the problems which because they produce thin areas in the fabric can reduce the barrier properties significantly.

In the manufacture of non-woven fabrics by hydro-entanglement fibres of various sorts are cohered by jets of liquid, usually water. This process is efficient and is highly popular in the non-woven field because of its binder free bonding and special properties it produces. However, there are certain drawbacks with the process. The fabrics produced tend to have distinct longitudinal markings and irregularly spaced, partly, or wholly penetrating holes or depressions. The longitudinal markings tend to be caused by passage of the fibrous web under the hydro- entanglement jets in the treatment zone and can be exaggerated by incorrectly operating or slightly different entanglement nozzles creating distinct lines. The creation of the small holes and/or depressions is not easily understood, but it may be due to the hydro-entanglement process emphasising irregularities in the fibres as they reach the entanglement zone. In any case, these defects are undesirable in that they give a distinct visual and surface colour variation to the product which makes it unattractive. They also give rise to irregularities in the permeability of the material which reduces its capacity as a barrier or filter. It is an object of the present invention to provide a method of and an apparatus for making non-woven fabric wherein one or more of the above described disadvantages is obviated or reduced.

The invention provides, as a first feature thereof a method of manufacturing a non-woven fabric by laminating a web and a tissue of cellulosic fibres by means of hydro-entanglement characterised by the steps of collecting fibre-containing process liquid after entanglement, and passing it through the web to be filtered thereby so causing the fibres to be deposited on the fabric.

The invention provides, also, apparatus for manufacturing a non- woven fabric including means for feeding a web and a fibrous tissue to a hydro-entanglement zone, means for collecting the process liquid after hydro-entanglement, delivery means for delivering the collected, fibre-contaminated liquid and passing it through the web so as to be filtered thereby and deposit entrained fibres on the fabric.

Preferably means are provided for collecting the filtered liquid and returning it to the entanglement zone as process liquid.

The fibres filtered out of the process liquid during passage through the web can be deposited on either the web side or on the tissue side of the fabric but desirably are deposited on the tissue side. In the manufacture of a barrier fabric, the finish is desirably added after and over the deposited fibres so as to secure the deposited fibres firmly to the fabric.

The invention includes, of course, a non-woven fabric made by the method or apparatus aforesaid.

The invention will be described further, by way of example, with reference to the accompanying drawings wherein:-

Figure 1 is a schematic side elevational sketch illustrating a prior known apparatus for manufacturing non-woven fabrics;

Figure 2 is a view similar to figure 1 but illustrating a preferred apparatus of the invention;

Figure 3 is an enlarged schematic cross-section through a known non-woven fabric;

Figure 4 is a view similar to figure 3 but showing an non-woven fabric of the invention;

Figure 5 is a schematic cross sectional view illustrating a method of creating a fabric in accordance with the invention;

Figure 6a shows a first part of a process for creating a fabric of the invention in accordance with the second method;

SUBSTITUTE SHEET Figure 6b shows the second half of the process of figure 2a; and

Figure 7 is a cross sectional view through a preferred non-woven in accordance with the invention.

The prior art method and apparatus described in relation to figure 1 has already been discussed in detail and it will not be mentioned further here, it will be useful, for comparison purposes to mention briefly the prior known barrier non-woven fabric (21) which is shown in figure 3. The fabric (21) comprises a web (22) (which may itself be a non-woven base fabric web) , an overlying layer of cellulosic fibres (23) united to the web (22) by hydro-entanglement and an overlying treatment of binder (24) which renders the entire fabric waterproof. In fact, there is a significant amount of spreading of the binder (24) into the fibre (23) and web (22) but this is not shown in figure 3.

A preferred method of making a non-woven fabric is illustrated in figure 2 which shows a preferred apparatus (25) . The apparatus (25) includes respective feed rolls (26) and (27) for a face web (28) and a tissue (29) of cellulosic fibres respectively. The web (28) and tissue (29) pass a deflection roller (30) .

In the entanglement zone (31) jets of process liquid, usually water engage the tissue and the web and unite them. The used process water, which contains entrained fibres from the web tissue (29) is collected at (32) and passed to a filter delivery head (33) downstream of the entanglement zone (31) on the upper side of the fabric, that is to say on the side on which the tissue (29) has been laid. The water containing entrained fibres passes through the fabric, which acts as a filter with the fibres being deposited on the fibres of the tissues (29) and some of the web (28) . Clean water passing through the fabric is collected at (34) and returned as process water to the entanglement zone (31) . The filtered water could be passed to waste and fresh water used in the entanglement process but this would not usually be economic. Downstream of the filtration point finish is added to the fabric as indicated at (35) .

The finish may be a resin together with water/oil implants which further unites the various layers in the fabric and penetrates thereinto to create a barrier fabric. The addition of the finish also permeates the filtered fibres and firmly unites them with the body of the fabric.

It will be appreciated that the method and apparatus of the invention has significant economies in that the need for the filter (20) is eliminated along with its maintenance and care. Further, fibre normally lost with the process water is not passed to waste but is deposited on the fabric to increase its weight. Referring now to figure 4, it will be seen that the preferred fabric (36) of the invention includes the web (28) , a layer of cellulosic tissue fibres (29) united to the web (28) by the hydro-entanglement process, a thin layer of deposited fibres (37) and the finish (38) which permeates the fabric and further secures the layers together.

Figure 4 also illustrates a surprising advantage that has been found in using the non-woven fabric itself as a filter prior to the addition of the finish (28) . As has been mentioned earlier, the sole combination of the web (28) and fibres (29) tends, after the hydro-entanglement process, to have lines, holes and/or streaks which represent displacement of the fibres by the hydro- entanglement process. A typical such defect is illustrated by a cavity (39) penetrating the fibres (29) and partly into the web (28) . During the fibre deposition or filtration process, the fibre (37) fills into the cavity (39) preferentially building up a body (40) of fibres which can wholly or substantially fill the cavity (39) . This occurs because the web in the region of the cavity (39) has a greater permeability and therefore there tends to be a greater flow of water towards such area. Such greater flow of water entrains a greater number of fibres which enter into and tend to fill up the cavity.

The filling of cavities and areas of higher permeability provides improved levels of barrier properties and consistency and reproducibility of barrier properties.

The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example, the advantages of fibre economy and elimination of the filter can be useful even when a finish is not to be used to make a barrier fabric. In this case the fibres can be deposited, again, either on the side of the tissue or on the side of the face web. It is important, here, that the fibres (relatively loosely adhered) are firmly secured and to this end a conventional binder can be applied or adhesion can be by a powdered adhesive or by incorporation of a fusible component in the fibres, when application of heat can cause firm adhesion. It is, however, expected that in the field of barrier fabrics where a finish is added that the invention will find most application.

Referring now to figure 7, it will be seen that a preferred non- woven fabric (110) of the invention comprises a body layer (111) during the formation of which a hydro-entanglement process has been used. In the specific embodiment illustrated the body (111) is made up of a base layer (112) which has itself been formed by hydro-entanglement from a web of textile fibres, and a second layer (113) formed by hydro-entanglement cellulosic fibres (for example in the form of a tissue) with the fibres of the base layer (112) . The fibres of the second layer (113) can be such as to convey a barrier property to the non-woven and typically can be of cellulosic, or of other natural or a synthetic fibre or combination of fibres having appropriate properties. In general, the textile fibres in the base layer (112) import flexible textile like nature to the product whereas the cellulosic or other fibres in the second layer (113) decrease the permeability of the fabric and therefore improve its barrier properties.

During the one or two processes of hydro-entanglement jet streaks and/or holes may be formed. In the drawing three types of defect have been illustrated. Defect (114) is a jet streak extending longitudinally of the web of fabric (the cross section in figure 3 has been taken transversely thereto) . Defect (115) is a minor jet streak which may be apparent across the full width of the fabric. A hole (116) is shown in the form of a closed depression, usually not extending right through the fabric but on occasions it may do so. In the drawings the defects (114) , (115) and (116) have been shown as being entirely at the upper surface of the second layer (113) . In practice, such defects can be formed on the upper layer of the base layer (112) thus causing the layer (113) to have an uneven surface upon which are imposed the defects during its own entanglement.

In accordance with the invention, the non-woven is provided with a layer of deposited fibres (117) . These, it will be seen, wholly or substantially fill the defects (114), (115) and (116) leaving a smooth surface to the fabric (110) and greatly improving its uniformity, colour consistency and overall hydrostatic resistance, that is to say its uniform permeability.

As will be apparent, the layer (117) has desirably been deposited in such a way that it does not form a layer of uniform thickness on top of the body (111) . On the contrary, it is preferably deposited in a way that ensures that it has a relatively flat outer surface and its thickness varies in accordance with the irregularities in the surface of the body (111) . This can be achieved in many ways, for example, by application and use of a doctor or a comparable mechanism. Desirably, however, the layer (117) is deposited by a filtration system wherein fibres are suspended in a fluid be it gas or liquid which is caused to pass from the top to the bottom side of the fabric (in the drawing). As the body (111) is of lower permeability in register with the defects (114), (115) and (116) there is greater fluid flow in those areas and therefore greater deposition of the fibres which are, as far as possible, suspended throughout the fluid supply.

The fibre layer (117) can be composed entirely of a special fibre supply different from or the same as or including the same sort of fibres are in layer (113) or (114) or both. However, desirably they include or consist of fibres included in the process water used during hydro-entanglement. This way the benefits of the improved fabric (110) are accompanied by savings in water filtration. The fibres in layer (117) are united either through entanglement into the fabric and by locally-formed hydrogen bonding in intimate contact. The binder/finish can assist in fixing the applied fibre layer.

Referring now to figure 5, there is shown a schematically, first process in which a fabric in accordance with the invention can be manufactured. In the process shown in figure 1 a body fabric (118) is formed by a body fibres being passed to a treatment zone beneath a hydro-entanglement head (119) , water passing through body fabric (118) being collected by a collector (220) and passed to a depositor (121) which supplies the process water carrying entering fibres to the top surface of the body fabric (118) and deposits them as a layer of fibre (122) . Clean water is collected at (123) and can be passed to waste or re-used as indicated by arrow (124) . Downstream of deposition of the layer (122) the combined fabric (125) is treated with a finish or binder applied by an applicator (126) . As indicated the binder (127) permeates the entire fabric and confers desired characteristics thereto. These can include oil and/or water repellency, coherency, lack of fluffing and the like.

In the process the fibres which go up to make the body fabric (118) can be pure textile fabrics, or a mixture of textile and cellulosic fibres. Typical fibres could be conventional fibres such as viscose, polyester, polyamide, polypropylene, cotton, with or without pulp or high performance fibres such as para/eta aramids, polyphenylene sulphide and the like.

Figures 2a and 2b illustrate a process shown in figures 2 and 3 a body of textile fabrics (128) is deposited on a wire or comparable belt by a depositor (29) . The fibres (28) pass a hydro-entanglement head (130) to which process water is supplied at (131) . The hydro-entanglement creates a base layer (112) and used process water containing fibres is collected in a collector (132) .

In a second fibre depositor (133) cellulosic or like fibres in the form of loose fibres or supplied in tissue from a roll are deposited on to the upper surface of the base layer (112) and passed to a second hydro-entanglement head (135) where they are compacted and united with the base layer (112) forming a second layer (113) . Process water from head (135) is collected by a collector (136) . To the upper surface of the layer (113) is applied a layer of fibres (117) by means of a filter head (137) which can be supplied with a suspension of slurry of fibres from collector (132) and/or collector (136) and/or a separate independent fibre supply (138) . After deposition of layer (117) the entire fabric (139) has a finish applied by an applicator (140).

The fabric is (139) the equivalent to the fabric (110) of figure

SUBSTITUTE SHEET 3, but made in accordance with specific method disclosed in figures 2a and 2b.

In a typical process the amount of fibre in layer (117) can be from 0.5 gm " or greater. Generally, 0.5 up to 3 g m'² is achieved using filtered process water with added fibre, a separate fibre 0.5 up to 5 or more gm m'² can be achieved.

In the filtration, it has been found that at least 75% of previously washed fibre is recovered and deposited, and up to 90% or 95% is possible.

The fabric of the invention has improved appearance, a better handle, and better barrier properties.

The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example instead of being deposited by a filtration method the layer of fibres can be deposited by any convenient process is applicable to a wide range of fibres and fabrics and, of course, the fibres deposited can be the same as fibres already incorporated in the fabric, or can be different in order to achieve different properties.

Many other variations are possible. The layer of deposited fibres need not be limited to the quantity available from the circulated water but can be supplemented by addition of pre-disposed pulp fibres to this water stream. Thus allowing a much larger range of weight additions.

Many other variations are possible within the scope of the invention.

Claims

1. A non-woven including a base product which has been subjected to hydro-entanglement and a layer of fibres deposited on the base and united therewith.

2. A non-woven as claimed in claim 1, wherein the fibres are deposited by a filtration process which ensures maximum deposition on areas of maximum permeability.

3. A non-woven as claimed in claim 1 or 2 wherein the fibres are carried in a fluid medium be it gas or liquid.

4. A non-woven as claimed in claims 1, 2 or 3 wherein the fibres are applied in a liquid medium such as water.

5. A non-woven as claimed in any preceding claim wherein the body is a single layer formed in a wet laid or dry laid manner.

6. A non-woven as claimed in any of claims 1 to 5 wherein the body is of a multiple layer construction.

7. A non-woven as claimed in any preceding claim wherein the body comprises a base layer of one type of fibres to which a second layer of the same or a different sort of fibres has been united by hydro-entanglement.

8. A non-woven as claimed in any preceding claim wherein the fibres deposited on the body of the non-woven are entrained in used hydro-entanglement process water thereby submitting the process water to a filtration step.

9. A non-woven as claimed in any of claims 1 to 7 wherein the fibres supplied are from a separate source or are a combination of the fibres suspended in the process water and a separate source of fibres.

10. A non-woven as claimed in any preceding claim wherein the fibres are the same as or different from those in the body of the non-woven.

11. A non-woven substantially as described with reference to the accompanying drawings.

12. A method of manufacturing a non-woven fabric by laminating a web and a tissue of cellulosic fibres by means of hydro- entanglement characterised by the steps of collecting fibre-containing process liquid after entanglement, and passing it through the web to be filtered thereby so causing the fibres to be deposited on the fabric.

13. Apparatus for manufacturing a non-woven fabric including means for feeding a web and a fibrous tissue to a hydro-

SUBSTITUTE SHEET entanglement zone, means for collecting the process liquid after hydro-entanglement, delivery means for delivery the collected, fibre-contaminated liquid and passing it through the web so as to be filtered thereby and deposit entrained fibres on the fabric.

14. Apparatus as claimed in claim 13 wherein means are provided for collecting the filtered liquid and returning it to the entanglement zone as process liquid.

15. A method as claimed in claim 12 wherein the fibres filtered out of the process liquid during passage through the web can be deposited on either the web side or on the tissue side of the fabric but desirably are deposited on the tissue side.

16. A method as claimed in claim 12 or claim 15 wherein, in the manufacture of a barrier fabric, a finish is desirably added after and over the deposited fibres so as additionally to secure the deposited fibres firmly to the fabric.

17. A method of manufacturing a non-woven substantially as described with reference to the accompanying drawings.