A METHOD OF FORMING A PATTERNED NON-WOVEN

Abstract: A method and apparatus for forming a patterned, non-woven material involves wet laying of a porous fibrous base layer on a liquid permeable carrier. A fibrous stock is then applied to the exposed surface of the base layer in or through a patterned surface which is preferably an apertured rotary screen. Suction is applied to the carrier underneath the patterned surface to encourage liquid to drain through the base layer so leaving a residue of fibres forming a pattern on the base layer. The invention enables a patterned effect to be achieved without disruption of the base layer and has particular application to long fibred base layers for the manufacture of infusion pouches for example teabags. In this case the fibres of the intermittent layer are relatively short as compared to the fibres of the base layer.

Description: A method of forming a patterned non-woven This invention relates to non-wovens, i.e. non-woven fabrics such as paper intended particularly but not exclusively for the manufacture of infusion pouches for example tea bags and spice bags. European Patent 59608 by CH. Dexter Limited (the Dexter patent) relates to a method and apparatus for making a patterned- non-woven fabric for example paper for the manufacture of infusion pouches. The state of the art up to the time of the Dexter patent is described- in column 1, lin 10 to column 2, line 3 of the Dexter patent. That description is incorporated herein by reference. The Dexter patent concludes that there is a definite need for a patterned or decorative filter medium having a good pattern definition coupled with good filtration or sifting characteristics. The Dexter patent then proposes a method of and apparatus for producing a patterned non-woven fabric in which an apertured member overlies a web of non-woven fabric supported on a porous surface. A sheet of fluid is directed through the apertured member so as to cause discrete streams of fluid to pass through respective passageways in the apertured member and impinge upon the side of the web remot- from the porous surface. As explained in the Dexter paten.., the streams of fluid that impinge on the web act to displace fibres from discrete areas of the web in directions substantially in the plane of the web whilst maintaining a proportion of fibres within those areas and adjacent said porous surface. The invention of the Dexter patent is therefore the latest in a succession of techniques, some of which are acknowledged in the statement of prior art referred to above, in which patterning is effected by local disruption of the web with resultant changes in the filtration or sifting characteristics that are to some extent unpredictable. It is an object of the present inventio n to provide an improved method and apparatus for the manufacture of patterned non-woven fabrics in which the aforesaid disadvantage is obviated or mitigated. According to a first aspect of the present invention there is provided a method of forming a patterned, non-woven material, comprising wet-laying a porous fibrous base layer on a liquid permeable carrier, applying to the exposed surface of the base layer an intermittent layer of a liquid fibrous medium, permitting liquid to drain through said base layer and the carrier so as to leave a residue of fibres forming a pattern on the base layer, and drying the patterned material so formed, characterised in that said intermittent layer is delivered to the base layer in or through a patterned surface. According to a second aspect of the present invention there is provided apparatus for forming a patterned, non-woven material comprising a liquid permeable carrier, means for wet- laying a porous fibrous base layer on said carrier, means for applying to the exposed surface of the base layer an intermittent layer of a liquid fibrous medium, and drying means for drying the patterned material so formed, characterised in that the applying means has a patterned surface in or through which said intermediate layer is adapted to be delivered to the base layer. The invention will now be further described by way of example only with reference to the accompanying drawings, in which:- Fig. 1 is a diagrammatic side elevation of part of an inclined wire papermaking machine; Fig. 2 is a corresponding enlarged view of a rotary screen of Fig. 1; Fig. 3 is a view corresponding to Fig. 2 of an alternative embodiment of rotary screen with screen cleaning equipment, for use in the machine of Fig. 1; Fig. 4 is a diagrammatic view of the applicator of Fig. 3; Fig. 5 is a diagram illustrating the stock feed arrangement for the screens of Figs. 3 and 4; Fig. 6 is a diagrammatic illustration of an alternative pattern applying system; Fig. 7 is a plan view corresponding to Fig. 6, and Fig. 8 is a detail of the surface of the cylinder of Figs. 6 and 7. Referring now to Figs. 1 and 2 of the drawings, an inclined wire papermaking machine generally indicated at 1 comprises a pool box 2 in which the papermaking stock 3 is held prior to deposition on an upwardly inclined section 4 of an endless papermaking wire 5. The wire 5 may be any paper forming wire and may be plain or knuckled as desired. On deposition of the papermaking stock from the pool box 2 onto the inclined section 4 of the wire 5 liquid drains through the wire into a formation box 6 and a wet fibrous deposit remains on the upper surface of the wire and, in a conventional machine, is removed at the lefthand end couch roller 7 and passed to drying cylinders (not shown) . In the illustrated embodiment the inclined s. tion 4 of the wire 5 passes into a horizontal section 8 above which is provided pattern applying means 9 comprising a hollow cylinder or screen 10 whereof the axis of rotation extends transversely across the wire section 8. The cylir.ier 10 is mounted for rotation by a motor (not shown) about its axis and accommodates in the lower part thereof an applicator 11 comprising (as seen in Fig. 2) a horir ntally split pipe 12 with a downwardly di r ect. mouth 13 joined by means of two walls 14, 15 to rubber or piastics seals 16, 17 set at between lmm and 50mm apart to define a slot 18 which is in contact with the inside of the screen 10. . The screen 10 is preferably made of nickel by electrolytic deposition and is provided with a regular or irregular pattern of apertures of ->redetermined size and shape which may individually or in combination form letters, logos or other shapes as desired. The apertures may be straight sided or slightly tapered in the sense that their walls diverge slightly in the direction from the inner surface of the screen to the outer surface thereof or in the reverse direction. The screen 10 may be coated with release compositions such as silicone or PTFE in order to enhance its release characteristics so as to avoid pick-up of fibres. Alternatively, the screen 10 may be polished for the same reason. As indicated in Fig. 2, the screen 10 is pressed against the wire section 8 into contact with the fibrous deposit or base sheet 19 carried by the wire section 8. The contact region is short as seen in the direction of travel of the wire (see arrow in Fig. 2) and may approach line contact. Alternatively, as seen in Fig. 3, by increasing the contact pressure between the screen 10 and the wire section 8 there may be more intimate contact over not more than 90° and preferably less than 20° of the circumference of the screen 10 accompanied by downward deflection of part of the wire section 8. The preferred operational mode is between line contact and 10° lap. It may be possible to dispense with a motor drive for the screen 10 if a friction drive of the screen 10 by the wire 5 is possible. The position of the screen 10 lengthwise of the wire 5 may also be varied. Thus, compared to its position in Fig. 1, the screen 10 may be moved nearer the couch roller 7 or nearer the pool box 2 to any suitable location where there is sufficient space above and below the wire to accommodate the patterning means 9. Below the wire section 8 the patterning means 9 comprises a low vacuum box 20 followed in the direction of travel of the wire by a high vacuum box 21. The applicator pipe 12 is connected to a reservoir (not shown) containing a pulp mixture. The pulp mixture is applied to the applicator pipe 12 with the majority thereof passing through the pipe 12 and out of the other end for re- circulation. A small percentage of the pulp suspension comes into contact with the applicator pipe 12/screen 10 interface and emerges through the apertures in the screen 10 for deposition onto the base web 19 being formed on the wire section 8. The vacuum boxes 20, 21 under the wire section 8 in the region of the screen 10 assist in drainage of the pulp mixture so as to fix the residual fibres (which are effectively filtered out by the preformed wet paper sheet 19) to the paper sheet 19. An intermittent layer 22 of fibres so deposited conforms in pattern to the pattern of apertures in the screen 10. The high vacuum box 21 discourages the now composite sheet 19, 22 from adhering to the screen 10 causing wrap-round. In addition, the vacuum keys the intermittent layer 22 into the base sheet 19 to a predetermined extent depending upon the porosity of the base sheet 19 and the level of vacuum. The screen 10 may be rotated at speeds approaching that of the wire 5 but may run slower or faster dependent upon the desired pattern. The screen 10 may be provided at a different part of the wire 5 as described above and it is also contemplated that the same technique may be used for applying a pattern to partly finished paper in the drying train at the end of the papermaking machine beyond the couch roller 7, preferably at the position occupied by the size press. In either case, the deposition of the pa t terned fibrous layer 22 will take place in the way described above but will then require to be followed by a separate drying stage. It is also within the scope of the invention for the inte :iittent layer to be applied off-line, i.e. to a finished, dry base layer, but this has the disadvantage that the base layer has to be dried again following application of the intermittent layer. Referring now to Figs. 3 and 4, a second embodiment of patterning means 9 is illustrated in which parts corresponding to those of Figs. 1 and 2 have been given the same reference numerals and are not further described. The pipe 12 of the applicator 11 has a rearwardly inclined outlet slot 18 at the end of a channel 23 terminating in rubber sealing blades 24, 25. The sides of the channel 23 at the ends of the screen 10 are closed by edge seals 26, 27. The applicator pipe 12 has inlets 28, 29 at opposite ends and a central overflow pipe 30. As shown in Fig. 5, the pulp suspension is supplied from a stock tank 31 with a mixing unit 32. The tank 31 is supplied with thick stock through a pipe 33 and with .luting water through a pipe 34. An outlet pipe 35 connected to the bottom of the tank 31 leads via a pump 36 and cleaner 37 to a head tank 38 from which a stock feed pipe 39 connects to the stock inlets 28, 29 of the applicator pipe 12. Flow control valves 40, 41 control the delivery of stock to the inlet pipes 28, 29. Stock flow meters 42, 43 are attached to the feed pipes 39 and the stock overflow pipe 30 respectively. The stock overflow pipe 30 leads back to the tank 31. The cleaner 37 may divert unusable liquid to drain 44 or re-usable liquid by a return pipe 45 back to the tank 31. The rate of flow to the applicator pipe 12 and the overflow through pipe 30 are so adjusted that the pipe 12 is always full thereby ensuring an even flow of stock down the flow channel 23 over the full length of the pipe 12. Two adjacent vacuum boxes 46, 47 are provided below the screen 10 in the region of contact with the wire section 8. The upper surface of the vacuum boxes 46, 47 is curved in conformity with the arcuate deflection of the wire section 8. The vacuum box 46 generates a relatively low vacuum whereas the vacuum box 47 generates a relatively high vacuum. Both vacuums are in the range 0 to 20 inches mercury and typically around 5 inches mercury. As in the case of the first embodiment the purpose of the low vacuum box is to draw the pulp suspension from the applicator 11 through the screen 10 in the direction of the wire section 8. A medium vacuum, i.e. having a level between the vacuums in the boxes 46 and 47, is applied by the vacuum box 48. The screen 10 is provided with an internal screen cleaning unit 49 and an external screen cleaning unit 50 which are intended to maintain the internal and external surfaces respectively of the screen 10 clear of pulp. The internal screen cleaning unit 49 comprises a doctor blade 51 engaging the internal surface of the screen 10 across the full width thereof. A water pipe 52 is provided with nozzles for directing jets of low pressure water in the direction of the arrows 53 towards the region of the doctor blade 51. The resultant washings 54 are caught in a tray 55 and removed at the rear side of the wire. In an alternative design of screen cleaning unit the doctor blade 51 is omitted and the pipe 52 merely sprays water over the inside surface of the screen 10. It will be appreciated that the internal screen cleaning unit 49 may be positioned at an alternative location along the circumference of the screen 10. The external screen cleaning unit 50 comprises a nozzle extendi-.g over the full width of the screen 10 and having a chamber 56 for entry of cleaning water and a chamber 57 to which a vacuum is applied for removing the water. The rear edge of the nozzle is in contact with the screen by means of a doctor-blade 5 A seal 59 is made inside the screen 10 so as to blind the screen and allow effective vacuum to be maintained. An alternative external screen cleaning unit may comprise a lick-up roll made from ' • tted felt with fibre picked up from the screen 10 being t. .sferred to a further felt roll from which it is removed by washing. The two embodiments of patterning apparatus described above with reference to Figs. 1 and 2 and Figs. 3 to 5 may be used to apply a variety of different patterns to a wide range of base sheets made on any t_ * of papermaking machine but as illustrated a preferred application is to the wire part of an inclined Fourdrinier machine used for long fibred papermaking, e.g. for making teabag paper. In such an application the base sheet may be a single sheet (as in the illustrated embodiments) or a multi-layered sheet using a corresponding number of successive pool boxes. In the case of a single sheet the fibres may be Abaca with admixture of hardwood and/or softwood fibres. Typically the Abaca fibre may have a length distribution of 0.8-11.3mm and a mean length of 4.26mm, the hardwood fibre length distribution may be in the range 0.53-2.6mm with a mean of 1.1mm and the softwood length distribution may be in the range 1-5.5mm with a mean of 3.6mm. Care is taken to retain the integrity and ler jth of the fibres, particularly the long Abaca fibres so as t maximise the strength rf the resultant sheet. A minimum of ±ibre treatment is there, re carried out conducive to achieving fibre to fibre bonding. By contrast, .he pulp suspension for * or ing the intermittent layer requires a generally shorter ribre length in order to achieve ease of application and good pattern definition. Regard must however be had to the maximum pore size of the base paper at the point of application of the pulp suspension. If the fibres of the pulp suspension are too short to be entrapped by the base sheet (i.e. if they pass through the pores in the base sheet) it will not be possible to achieve the desired effect of the intermittent layer being retained on top of the base sheet. The pulp suspension may contain long fibred Abaca but in this case, in contrast with the stock for the base sheet, the suspension is treated by means of refining or beating so that the majority of the fibres are cut or fibrillated to lengths less than in the base sheet stock but sufficient to be entrapped by the base layer. A typical length range for the Abaca of the intermittent layer may be 0.096-4.5mm with an average of 0.5mm. The pulp suspension may have a Schopper Reigler value of 8°SR to 80°SR preferably 40-50°SR as measured by the Schopper Reigler drainage test which is related to specific surface area. In general longer fibred suspensions will have a lower SR value than shorter fibred suspensions. It is preferred that the SR values of the intermittent layer pulp suspension be greater than those of any of the fibrous components forming the base layer. A heat-sealable base paper is typically composed of a heat-sealing layer on the wire side of the machine and an insulation layer on the top side. The component fibres may be natural cellulosic or man-made or mixtures of both. A typical base layer of this kind is composed of rayon (regenerated cellulose) which is man-made and cut to fibre lengths in the range 3mm-15mm. A preferred range is 4-6mm and a mean length of 5mm. The rayon component is mixed with polypropylene or other thermoplastic material to render the paper heat sealable. The polypropylene fibre length may be varied from 3-15mm e.g. it may be cut to 5mm with a range of 4-6mm. The insulation layer may be made of cellulosic fibres of any type but more generally hardwood or softwood or mi:: ures of both. T ~~ - fibres are generally refined or beaten to the following dimensions: for hardwood the length range of 0.25-2mm with a mean of 0.9mm; for softwood the length range of 0.4-2mm with a mean of 1.2mm. For application to the heat sealable base paper the stock for the intermittent layer may be made from any natural fibrous source but will more typically be made from either softwood or hardwood or a mixture of both. In addition, in order to aid contrast a brightening agent such a precipitated calcium carbonate may be used. Depending on the desired effect (e.g. fixing the intermittent layer to the base sheet, enhancing definition etc.) other additives may be added to this and other stocks for making the intermittent layer e.g. carboxy methyl cellulose, titanium dioxide, fluorbcarbons, natural gums, polyamine epichlorohydrins, dyes etc. The stock is beaten to the same extent as or preferably to a greater extent than the insulation layer of the base paper in order to reduce fibre length thereby to a ' pattern definition. Preferably, the softwood fibres hav<_ a length range of 0.096mm-1.36mm with a mean of 0.22mm and the hardwood fibres have a length range of 0.04bmm-l.3mm with a mean of 0.18mm. The SR value of the intermittent layer pu-p suspension is greater than the SR value of any of the fibrous components within the base layer the heat-sealing layer of the base paper and is preferably greater than but may be the same as or even less than the SR value of the insulating layer of the base paper. In a further example the heat sealable base paper again comprises an insulation layer and a heat sealing layer but in this case the heat sealing layer is on the upper side of the sheet. The composition of these layers may be the same as in the previous example. However, since the intermittent layer w_.ll be deposited on the heat sealing layer it is desirable to use only thermoplastics fibres in the intermittent layer. The thermoplastics fibres of the intermittent layers may be of the same kind and length as those used in the heat sealing layer. Alternatively, shorter fibres may be used. In order to enhance definition the heat sealing layer may contain different fibres from the intermittent layer, for example the heat sealing layer may be made of polypropylene fibres while the intermittent layer is made of vinyon fibres; the heat sealing layer may be made of a vinyon/polypropylene mixture while the intermittent layer is made of pulpex. It is also possible for the heat sealing layer of the base layer to be omitted and to rely upon the intermittent layer to provide the heat sealing capability. An alternative system for applying the patterned fibrous layer is now described with reference to Figs. 6 to 8. This involves application of a pulp suspension as described above but using an engraved cylinder 100 whereof the recessed areas 101 are shaped and dimensioned both individually and relative to each other so as to achieve the desired patterned effect. Thus, for example, Fig. 7 shows the cylinder 100 with a pattern of recesses or pockets in the form of a C and Fig. 8 shows an L shaped recess in a similar cylinder. The engraved cylinder 100 and its backing roller 102 (which may have a hollow interior to which a vacuum is applied) may be arranged in the size press area of a paper machine of the kind described above, i.e. in the middle of the drying train where size or other liquid impregnant is sucked into the sheet by squeezing the sheet in a roller nip and then relaxing it so that it takes up the liquid applied to the surface thereof. The pulp suspension, the viscosity of which may be adjusted as necessary, is applied to the engraved cylinder 100 by an applicator 108 so as to fill the recesses or pockets 101 of the cylinder 100 with the suspension which is then deposited onto the base substrate at the nip of the cylinder 100 with the backing roller 102. The nip is followed by a high vacuum box 103 below the web which has the effect of promoting drainage of the liquid portion of the pulp suspension so leaving the patterned deposit or intermittent layer 104 of fibrous material on the upper surface of the base substrate 105. The pulp suspension may be modified so that the liquid part thereof contains a constituent which it is desired to apply to the paper web, e.g. size. Drainage of the liquid portion of the ulp suspension through the paper web will thus le 'e a residue of this component within the web. The cylinder 100 may be cleaned by means of a vacuum box 106 and a low turbulence wash section 107. Application of the intermittent layer gives effective control over the characteristics, e.g. sifting and infusion characteristics, of the finished paper in a way which is not possible with the disruptive techniques such as described in the Dt ter patent referred to in the introduction.

Claims: CLAIMS 1. A method of forming a patterned, non-woven material, comprising wet-laying a porous fibrous base layer on a liquid permeable carrier, applying to the exposed surface of the base layer an intermittent layer of a liquid fibrous medium, permitting liquid to drain through said base layer and the carrier so as to leave a residue of fibres forming a pattern on the base layer, and drying the patterned material so formed, characterised in that said intermittent layer is delivered to the base layer in or through a patterned surface. 2. A method as claimed in claim 1,» wherein said patterned surface is provided by a rotary screen having apertures of predetermined size and shape arranged in a regular or irregular pattern. 3. A method as claimed in claim 1 or 2, wherein suction is applied to the carrier underneath the patterned surface. 4. A method as claimed in any one of the preceding claims, wherein the base layer comprises two or more sub¬ layers of different composition. 5. A method as claimed in any one of the preceding claims, wherein the fibres of the liquid fibrous medium have a higher SR value as measured by the Schopper Reigler drainage test than any of the fibrous components of the base layer. 6. A method as claimed in any one of the preceding claims, wherein the liquid fibrous medium contains additives for improving the contrast of the fibres thereof with the base layer. 7. Apparatus for forming a patterned, non-woven material comprising a liquid permeable carrier, means for wet-laying a porous fibrous base layer on said carrier, means for applying to the exposed surface of the base layer an intermittent layer of a liquid fibrous medium, and drying means for drying the patterned material so formed, characterised in that the applying means has a patterned surface in or through which said intermediate layer is adapted to be delivered to the base layer. 8. Apparatus as claimed in claim 7, wherein the applying means is a rotary screen having apertures of predetermined size and shape arranged in a regular or irregular pattern. 9. Apparatus as claimed in claim 8, wherein the applying means includes a delivery channel stationary within the rotary screen, said channel having side walls terminating in seals engaging the internal surface of the screen, means being provided for supplying said delivery channel with liquid fibrous medium. 10. Apparatus as claimed in any one of claims 7 to 9, wherein means is provided for applying variable suction to the carrier underneath said patterned surface. 11. Apparatus as claimed in claim 10, wherein said suction applying means is adapted to apply a relatively low vacuum in one section thereof and a relatively high vacuum in an adjacent downstream section thereof. 12. Apparatus as claimed in any one of claims 7 to 11, wherein means is provided for internally and/or externally cleaning said patterned surface. 13. A papermaking machine including apparatus as claimed in any one of claims 7 to 12.

Inventors: GBUR IVAN, ROSE JOHN EDWARD, TOMKINSON BRIAN, GBUR, IVAN, ROSE, JOHN, EDWARD, TOMKINSON, BRIAN
Applicants: CROMPTON J R PLC, J.R. CROMPTON PLC
Application year: 1990
Main classification: D04H1
IPC codes: D04H1, D21F11