EP0140878A1

EP0140878A1 - Textile-like reticular product derived from film material

Info

Publication number: EP0140878A1
Application number: EP19830901071
Authority: EP
Inventors: Ole-Bendt Rasmussen
Original assignee: RPD RASMUSSEN POLYMER DEVELOPMENT AG
Current assignee: RPD RASMUSSEN POLYMER DEVELOPMENT AG
Priority date: 1983-03-18
Filing date: 1983-03-18
Publication date: 1985-05-15
Also published as: WO1984003723A1

Abstract

Filet intégral bidimensionnel (1) possédant un duvet sous forme de fibres relativement longues (3) faisant partie intégrante du filet et saillant des bords qui entourent les ouvertures (2) du filet. D'après un procédé de production d'un tel filet à partir d'un fil, il faut chauffer des zones choisies du film jusqu'à ce qu'elles atteignent un état fondu, puis arracher ce matériau fondu pour en faire des fibres afin de pratiquer des ouvertures dans le film, tout en contrôlant l'opération d'arrachage au moyen d'un refroidissement par jet d'air.Two-dimensional integral net (1) having a down in the form of relatively long fibers (3) forming an integral part of the net and projecting from the edges which surround the openings (2) of the net. According to a method of producing such a net from a wire, it is necessary to heat selected zones of the film until they reach a molten state, then to tear off this molten material to make fibers of it in order to to make openings in the film, while controlling the tearing operation by means of air jet cooling.

Description

Textile-like reticular product derived from film material

The invention relates to a textile-like reticular product directly obtained from a thermoplastic film . Reticular products or nets of this kind are often used as reinforcement in paper articles or textiles, e. g . in sanitary paper articles . They are further used in heavy duty bags, paper cloth and non-woven upholstery fabrics . I n many cases, however, the utility of such nets is limited due to lack of textile feel and/or cover.

Thus, the sanitary articles where the net is in direct contact with the body, the surface of the net can irritate the skin . Also the relatively hard and smooth surface of the net gives some limitations to its use, e. g . as backing in thick carpets .

One object of the present invention is to overcome such drawbacks in nets obtained directly from films . Methods are known that provide sheets of continuous structure with a napped surface by casting or rolling the material in a mould that is a negative replica of the desired nap-surface. However, if a fine nap is desired , this method requires the polymer to be in a very low-viscous state. Besides, the notch effect highly reduces the strength of the sheet.

It is a further object of the invention to overcome these drawbacks and provide for a simple and convenient method for manufacturing a napped net directly from a film .

Other objects of the invention will appear from the following description .

The textile-like reticular product of the present invention consists of a body portion which forms a general ly two-dimensional integral net structure and a surface portion which consists of fibres materially integral with and protruding from at least part of the marginal edges of generally every aperture which is defined by the meshes of said net, and fibres being generally longer than any dimension of the aperture to which each fibre is adjacent.

This product can be manufactured by direct conversion of thermoplastic film material by the process of the invention which process comprises the steps of maintaining one surface of a length of such film material into face-to-face contact with a surface capable of adhering to said thermoplastic material when the latter is in molten condition , while said surface is heated in a pattern of heated surface regions separated by unheated surface regions to a temperature above the melting point of the film material; continuing the contact between the film surface and the selectively heated surface for a time sufficient to selectively melt the film areas contacting said heated surface regions, whereby said melted film areas adhere to said surface regions, while the remaining film areas remain in generally unmelted and non-adhering condition; then separating said selectively molten film from contact with said selectively heated surface whereby the molten adhering film areas are drawn out from the remainder of the film as fibre-like projections extending from the surrounding unmelted margins and thereby create apertures in said film generally corresponding to said heated surface regions; and directing a flow of cooling aϊr toward the surfaces undergoing each separation to control the drawing of said fibre-like projections.

The protruding relatively long fibres serve to eliminate the flat film-like character of the net, giving it improved bulk, and an improved ability for binding with similar or other materials, together with a more pfeasant appearance. The process can easily be carried out in an integrated manner with cheap and simple means. When suitable additional steps are taken - as it will be described - they also give the net a soft handle.

The product can easily be distinguished from those which would be formed by a simple partial cutting-up of well known net structures, since the latter could never exhibit the minimum length of protruding fibres defined above. Besides, it is easy to identify the protruding fibres manufactured by the present method, since the dragging in molten state produces a gradual tapering generally along each protruding fibre.

The number of fibres which form the "nap" (the protruding fibres) can with advantage be very much higher than the actual number of meshes or apertures.

If the protruding fibres of the invention are simple "tentacles" on the net, they should preferably have an average length which is many times the general mesh dimension of the net.

In a preferred embodiment, however, at least a substantial portion of the protruding fibres are not simple "tentacles" but are loop-formed, each protruding from different locations around the same aperture so as to bridge over the aperture. This loop-form serves to give the material further bulk and further capability for binding. In this case each fibre can with a similar effect be shorter. In another preferred embodiment of the net product at least a substantial portion of the protruding fibres are fibres with branches. This also further improves e.g. the bulk and ability for binding. The branching in question can start from one location on the net and at least a substantial portion of the protruding fibres can be interconnected through branching with at least one other similar fibre protruding from an adjacent position . Such interconnected fibres can further form bridges over the aperture as described above so that the nap becomes web-formed .

As mentioned above, the process for the production of napped net involves engaging the film with advancing surface means which comprise heated spaced areas placed in a pattern adapted to a desired , mesh pattern in the reticular product. In this connection, it is of course essential to maintain a net i.e. interconnected structure during the heat opening of the film. One way of achieving this is to let the heated areas form a dotted pattern. This can e. g . be circular, square or polyhedric spots arranged in a regular pattern or in mutually staggered dotted lines . The unheated areas will thereby form a reticular pattern which is generally the pattern for the final base net.

Another way of maintaining a net structure is to let the heated areas form a linear pattern (which may be continuous over the length of the film or span over the full width of the film) and in combination herewith use a starting film which incorporates an array of higher melting filaments which are maintained generally solid during the heat-dragging of the film. These higher melting filaments - and usually the surrounding regions of the matrix film polymer which remains adhered to said filaments during the heat opening - will thereby form one direction , while the film portions which are left (relatively) cold will form another direction of the net.

The higher melting filaments can be continuous or discontinuous . They can be incorporated by lamination between two films or incorporated by coextrusion. Further, such filaments can be incorporated in a transverse

(generally helical) direction by the extrusion apparatus schematically shown in Figs. 7, 8 and 9 of U .S. Patent No. 3.503.836, or by similar means. In such cases, the pattern of heated lines can be a continuous longitudinal pattern. In a preferred embodiment of the method according to the invention, the molten portions (which are dragged out to form the fibres) are embossed prior to the fibre-forming pulling action . This embossment is carried out in order to initiate the fibre formation . If the bosses traverse the molten area all the way from one side to the cither, a loop-formed, bridging nap can usually be formed at a suitable, relatively low temperature. Thus, the embossment also has the purpose to direct the form of fibres .

Further, the embossment can conveniently be in a pattern of linear mutually criss-crossing bosses . Hereby branching and/or web formation of the protruding nap can be achieved .

There is always a certain tendency for the molten material to be torn off from the net due to sticking to the heated surface means, whereafter it is later in the conveying cycle joined with the film at random . Such spin-off is significantly reduced by the criss- -crossϊng embossment which promotes branching and thereby gives each piece of fibre several ways of connection with the net.

For strength purposes, the net in its final state should preferably be strongly oriented . When a dense nap is preferable, at least a major proportion of the orientation is preferably carried out prior to the engagement with the heated surface means, while the material is still in film form.

As mentioned in the introduction, the invention has also for its object to provide improvements in the manufacture of napped film, and a method analogous to the above mentioned can with advantage be carried out on coextruded products, e.g . consisting of layers with different melting range. In this case the spaced or patterned areas contacting the heated surface are heated to a temperature at which the polymer in the layer with the lower melting range is molten or semimolten while the polymer in the other layer(s) is pronouncedly more solid. The resulting product may be a water impermeable sheet or film with a napped surface.

The napped film according to the invention can in the latter case consist of a body portion formed of ribs of lower melting polymer interconnected through a thinner web of higher melting polymer and another portion which consists of fibres materially integral with and protruding in dense rows from a part at least of those edges of the ribs which are adjacent to the cavities defined by the ribs and the webs, and being generally longer than the distance between adjacent ribs.

There is a close analogy between this structure and the reticular structure described in the foregoing (the web-connected ribs and the nets being both examples of interconnected , two-dimensional lattices), and the steps to achieve the nap are therefore also similar. The napped film is preferably cross-laminated, e.g . with a similar napped film with the ribs and the nap extending outwardly. The invention will now be described in further detail with reference to the drawings . For the sake of clarity, the nap is generally shown very short, while in reality it should be at least longer than the biggest dimension of the adjacent aperture in the net. Fig . 1 schematically shows a napped netlike product according to the invention, Fig . 2 shows a preferred embodiment of a partially heated device for producing the net shown in

Fig . 1 , Fig . 3 schematically shows another napped net-like product according to the invention , Fig . 4 shows a device suitable for producing the product shown in Fig. 3,

Fig . 5 shows a third napped net-like product according to the invention, Fig . 6 shows a preferred device for producing the product shown in Fig . 5, Fig. 7 shows in enlarged scale part of Fig . 6,

Fig. 8 shows another preferred device for producing the product generally shown in Fig . 5 and more particularly with the special fibre forms shown in Figs . 10 or 11 , Fig . 9 shows in enlarged scale a part of Fig . 8,

Fig . 10 shows a branched nap on a net according to the invention ,

Fig. 11 shows a loop-formed , bridging nap on a net according to the invention . Fig. 11 is a net derived from a film 1 and with staggered hollows or apertures 2 edged by protruding filaments or naps 3. The arrow indicates the moving direction of the film during the process . The tapering of the protruding fibre is a result of the fibre dragging from molten state under cooling with an air jet . In Fig . 2 the hollow producing device is a roller 4 provided with an array of staggered, thermally conducting parts 5 separated by thermally insulated, coherent parts 6. The roller 4 is heated while a counter-roller 7 is cold . Fig. 2 shows only part of the overall process line. The sheet or film 1 is extruded in any known manner from an extruder (not shown), and If convenient stretched between nip rollers not shown . The thermally conducting parts of roller 4 are made of a material which sticks to the film when the latter is heated to generally molten condition . The counter-roller 7, preferably with a smooth surface, has the purpose of placing the film 1 into flat face to face contact on the roller 4 to which it sticks until it is conveyed away over a rod 8 in any known manner. During this process, the parts 5 are heated to a temperature slightly above the melting range of the film material , while the parts 6 have a temperature below this. While contacting the roller 4 some areas of the polymer film will stick to the heated regions 5 of the roller 4 and gradually become semimolten to molten and the time of contact is selected to achieve such conditions while the interjacent areas of the film corresponding to the parts 6 will be kept in a solid state by simultaneously cooling the surface of the roller 4 with air from two nozzles 11 , so as to keep the parts 6 cooled .

When the film is discharged over the rod 8, and cooling air as shown by 12 is blown directly against the zone of discharging , filaments or naps 3 will be dragged out from the sides of the apertures 2 that are now formed corresponding to the heated parts 5. A knife 10 cuts the naps 3 off at a convenient length .

Fig . 3 is a napped net-like product derived from a laminated e. g . coextruded film 14 with a layer 15 of a material with melting range pronouncedly above the melting range of another layer 16. The layer 16 is provided with parallel linear apertures 17 from the sides of which naps or filaments 18 are protruding, thus forming an array of filaments or filamentary strips on a continuous backing .

A similar product consisting of two criss-crossing arrays of filaments on a continuous backing is also available according to the invention .

Fig . 4 is a frontal view of two rollers 20 and 21 constituting a preferred device for producing the laminated net-like product shown in Fig . 3. The aperture-forming parts of the roller 20 are in the shape of parallel circumferential rings 22 separated by grooves 23. The two rollers 20 and 21 function in the overall process-line analogously to the rollers 4 and 7 in Fig . 2. However, it is not necessary to keep the grooves 23 cool during the process e. g. by air, as shown in Fig . 2, because of the continuous backing layer 15 with a higher melting range .

Fig . 5 is a napped scrim derived from a film 25 provided with incorporated coextruded longitudinal flat filaments 26 e .g . of nylon . The nylon threads form one array of the network and segments or strips 27 of film material form the other array leaving apertures 28. Filaments or naps 29 protrude from the side of the last mentioned strips, but as the nylon threads are surrounded by a certain amount of film material some naps 30 will protrude from the sides of the threads also.

Fig . 6 is a side view of the rollers constituting a preferred device for producing the net according to Fig . 5 from the starting film material incorporating the flat filaments (not visible in Fig . 6) , and functioning in an overall process-line analogously to the rollers

4 and 7 in Fig . 2.

A heated roller 31 is provided with axially extending ribs 32, the ribs are provided with slots or channels 33 in the middle of the top, and are separated by grooves 34. Two counter-rollers 35 and 36 are shown, but there may be more according to the necessary length of contact between film 25 and roller 31 . The rollers 35 and

36 are cooled and are provided on their surfaces with axially extending lands 38 that keep the strip-like film-parts of the resulting net cooled and solid during the aperture formation process . Like in Fig .

2, the net is discharged from the roller over a rod 39, while an air-jet 41 cools the dragging zone, and a knife 40 cuts off the dragged filaments in convenient lengths . The temperature of the ribs 32 is chosen so that it lies slightly above the melting range of the film material , but under the melting range of the coextruded filamental threads 26 (not apparent in Fig . 6), e. g . of nylon .

When the film 25 leaves the extruder (not shown) it may be stretched longitudinally but should advantageously be stretched transversely in a tenter frame before the aperture formation . In this way the napping will become denser in the final product compared to the density of the naps if the stretching is effectuated after the napping process . Besides it is advantageous that the heat-dragging is parallel to the direction of orientation of the film material as it has been found that heat-dragging parallel to the direction of orientation is easier than heat-dragging under a pronounced angle to this direction, and also easier than with unoriented material . If the above mentioned air-cooling 41 of the discharging zone is omitted, protruding naps will normally not be the result, but the described process still provides for a most practical way of producing net-like products .

The process line of Fig . 8 is essentially like that of Fig . 6 (and also devised for film with higher melting filaments incorporated), but designed for a more precise and controlled formation of the nap.

The film 42 with longitudinal reinforcement filaments of higher melting polymer (not apparent in Fig . 8) Is taken over a guide roller 43 onto a water-cooled roller 44 which has a semi-hard surface (e. g . polytetrafluorethytene reinforced with fabric) which has the function to act as backing for the initial embossment. Roller 44 carries the film into the nip which it forms with an embossed roller 45 rotating with the same circumferential velocity as roller 44 and having linear bosses 46 generally perpendicular to the machine direction of the film, i . e. to the incorporated filaments .

The embossed roller - 45 is heated evenly to a temperature above the melting point of the matrix film polymer. The main bosses are supplied - as shown in the detail drawing Fig . 9 - with a fine subembossment, preferably (as shown) forming relatively sharp points 47 and further (as also shown) adapted to produce a criss--crossing pattern of fine bosses on the heated portions of the film. The film Is heated where it is attached to the bosses 46 but maintained relatively cold at the portions which are adjacent to the grooves . in order to reach a convenient temperature with a relatively high throughput, the film thereafter follows the hot embossed roller over a substantial part of its circumference, while a jet 48 blows on air - as shown by the arrow - in order to maintain the temperature low at those portions which are not in direct contact with the embossed roller.

The film is thereafter withdrawn by pulling over a bar 49 with a relatively sharp edge at a short distance from the surface of the roller, and is gufded by roller 50, while extra air is blown directly from nozzle 51 into the gap where the nap is formed . Fig . 10 shows branched protruding fibres . 53 is a portion of the base net from which the fibres protrude, and 54 an aperture defined by a mesh of this net. At a point 55 on 53 adjacent to the aperture 54 a fibre 56 protrudes. The fibre has branches 57. Fig . 11 shows fibres in a loop-formed bridging arrangement. The base net consists of portions 58 which were kept relatively cold during the heat-dragging, and intervening portions 59 formed of the higher melting incorporated filaments (not shown) and matrix film polymer which has stuck to the solid filaments during the heat- -splitting . Protruding fibres 60 form loops and bridge over two adjacent parallel portions of the net.

It is to be understood that the protruding fibres are extensions of the margins of portions 58 and at the start of the protrusions have the same thickness as these edge-portions . The bridging fibres 60 are tapered like the other protruding fibres, but in this case they are thinnest at the middle.

The fibres 60 can have branches like in Fig. 10, and can even be totally interconnected to a branched web.

The embossment pattern of Fig . 9 will normally produce the branched fibres of Fig . 10. However, at a relatively low temperature at which the probability of rupture is reduced (but still in at least partly molten state) they can produce bridging fibres like in Fig . 11 , but at the same time be branched . The nonbranched bridging fibres of Fig . 11 are produced under similar circumstances , but with a one-directional sub-embossment pattern instead of the criss--crossing pattern produced by the device shown in Fig . 9 .

When the heat-dragging is carried out at such relatively low temperatures, it may be necessary to use lower melting polymers - which may be applied in very small amounts - to improve the adhesive bonding between the film and the bosses 46. Such material may be applied as layers by coextrusion or may be dusted onto the embossed roller .

Like most other processes for producing nets from films, the present process has a tendency to result in a structure with scratchy feel . This is mainly due to the feel of the edges of the flat (generally ribbon-formed) net portions when the skin is rubbed over the surface of the structure, but is also due to the prickle-form of the fibres at their protrusion locations . However, this draw-back can be minimized by several measures taken alone or in combination , viz. : using very thin film, e.g . 10-20 gr per sq . m, carrying out the heat-dragging at the lowest possible temperature, retaining sufficiently wide - and close interconnections in the base net, using the product in laminated form, e. g . spot-glued, so as to eliminate the possibility for the ribbon-formed portions to turn on edge.

The napped net (scrim) according to the invention can with particular advantages be used in combination with cellulosic fibres for diapers and other textiles . The scrim is then applied so as to face the body, whereby there is made use of the pleasant feel caused by the nap . At the same time it serves as reinforcement. When used as outer layer in diapers and other materials to absorb the fluid discharged from a human or animal body, it will be preferable to produce the napped scrim from a pronouncedly hydrophobic polymer, in particular a polyolefin such as polypropylene. Provided the density of the nap is not exaggerated, the hydropho bϊcϊty will not prevent the discharge from passing through and being absorbed in the cellulosic fibres, but will make the sanitary textile with its wet contents feel more dry. It will also prevent coagulated blood etc. from sticking to the textile. The scrim can also be used for non-woven apparel , either facing the body or as interlining, where the nap serves as heat insulator, or at the outside of apparel with a fur-like effect. For such purpose, it is preferably produced from a tougher type of polymer, such as a polyamlde or polyethylene terephthalate. It can also in several cases with advantage be produced from e.g. polyvinylchlorlde or polyvinylidene chloride, or copolymers between the latters. On principle, any thermoplastic film and fibre-forming polymer can be applied .

In order to increase the tendency to form fibres by the dragging in molten state and to improve the look of the nap, the film used for the scrim production may with advantage be a slightly expanded (foamed) film.

Further examples of suitable uses of the napped net according to the invention are: for blankets, preferably in form of a laminate of several layers napped net, for wiping cloth - alone or as a layer, as a layer or layers in carpet backing, for filter material , as paper reinforcement and as scrim reinforcement for turf and the like. EXAMPLE

Flat threads of nylon 6 (1 part by weight) are coextruded in a 300 g per m² polypropylene (10 parts by weight) film wholly surrounded by the polypropylene. The distance from center to center of the threads was 0.8 mm . Thickness of the film : 300 g per m². Melt flow index of polypropylene: 5 according to ASTM condition

I . Melt flow index of nylon : adjusted to give distinct but flat filaments in the coextrusion . The film was stretched at ratio 2: 1 in the length and 7.5 : 1 in the transverse direction . It was then taken through the line shown in Fig . 8. Temperature of the embossed roller was kept between the melting points of the two polymers, while the exact adjustment of this and the air jets were adjusted by experimenting and observing the results obtained .

Claims

C l a i m s

1 . A textile-like reticular product directly obtained from a thermoplastic film, characterized in that it consists of a body portion which forms a generally two-dimensional integral net structure and a surface portion which consists of fibres materially integral with and protruding from at least the marginal edges of generally every aperture which is defined by the meshes of said net, such fibres being generally longer than any dimension of the aperture to which each fibre is adjacent.

2. A textile-like reticular product according to claim 1 , characterized in that at least a substantial portion of the protruding fibres are loop-formed, each protruding from different locations acound the same aperture so as to bridge over said aperture.

3. A textile-like reticular product according to claim 1 or claim 2, characterized in that at least a substantial portion of the protruding fibres are fibres with branches .

4. A textile-like reticular product according to any of the preceeding claims, characterized in that at least some of the fibres are interconnected with at least one other fibre by common branches .

5. A process for the direct conversion of thermoplastic film material into open-work sheet material having fibers on one surface thereof, characterized in that it comprises the steps of maintaining one surface of a length of such film material into face-to-face contact with a surface capable of adhering to said thermoplastic material when the latter is in molten condition, while said surface is heated in a pattern of heated surface regions separated by unheated surface regions to a temperature above the melting point of the film material ; continuing the contact between the film surface and the selectively heated surface for a time sufficient to selectively melt the film areas contacting said heated surface regions , whereby said melted film areas adhere to said surface regions, while the remaining film areas remain in generally unmelted and nonadhering condition; then separating said selectively molten film from contact with said selectively heated surface whereby the molten adhering film areas are drawn out from the remainder of the film as fiber-like projections extending from the surrounding unmelted margins and thereby create apertures in said film generally corresponding to said heated surface regions; and directing a flow of cooling air toward the surfaces undergoing each separation to control the drawing of said fiber-like projections .

6. A process according to claim 5, characterized in that the heated areas form a dotted pattern.

7. A process according to claim 5, characterized in that the starting material film incorporates an array of higher melting filaments having a higher melting point than the temperature of said heated surface regions and the heated areas in said pattern are each generally linear in shape and extend in the same direction , which is different from the direction of said higher melting filaments.

8. A process according to claim 5, characterized in that said molten portions are embossed prior to said drawing away.

9. A process according to claim 8, characterized in that the bosses are formed in a linear criss-crossing pattern .

10. A process according to claim 5, characterized in that the film material is strongly oriented prior to contact with the selectively heated surface .

11 . The process according to claim 5, characterized in that said thermoplastic film material comprises at least two layers, the layer on the surface contacting the selectively heated surface being a polymeric material having a melt temperature lower than the temperature of the heated regions of said surface and the next adjacent layer being a polymeric material having a melt temperature higher than the temperature of the heated surface regions .

12. The process according to claim 5, characterized in that the heated surface regions are formed as bosses separated by recesses and the surface of said bosses carry a pattern of generally fine pyramidal sub-embossments .

13. The process according to ciaϊm 5, characterized in that said selectively molten film material is separated from said selectively heated surface by deflection away from the latter over a fixed edge arranged in closely spaced proximity to said heated surface.

14. The process according to claim 5, characterized in that said selectively heated advancing surface comprises a rotatably driven cylinder.

15. A process for the direct conversion of thermoplastic film material into open-work sheet material having fibers on one surface thereof, characterized in that it comprises the steps of selectively heating said film material in a pattern of heated areas separated by unheated areas until the material in said heated areas is at least substantially molten; and drawing out the thus molten material in said heated areas from one surface of the materiai into filaments with consequential creation of perforations by the drawing out of said filaments therefrom, said filaments having a length greater than any dimension of the corresponding perforation .