ABSORBENT PAD

Abstract: The pad has a core (1) of an air laid web consisting of wood pulp fibre, super-absorbent fibre, and thermoplastic bonding material. The web is laid on a non-woven polyethylene tissue (2) and is coated with a release layer film (3) of polypropylene based material. The edges (4) of the pad are compressed, typically along a 3 mm wide margin (5), with the web being flattened and head bonded in its compressed state, with the backing and release layers united to it. This compression of the air laid web captivates fibres of the web from escaping from the cut edges. The pad is used in a meat tray, with the release layer uppermost. This avoids the meat sticking to the pad. Blood from the meat can flow around the edges of the pad and pass through the non-woven tissue to be absorbed into the web.

Description: ABSORBENT PAD The present invention relates to an absorbent pad, particularly though not exclusively for use in food trays, It is established practice to display meat for sale in covered trays having a pad for absorbing blood from the meat. Normally such pads are formed of an absorbent material with a top release layer, which prevents direct contact between the meat and the absorbent material and allows easy separation of the meat from the pad. So called "super-absorbent" materials are known, which absorb many times their dry weight of water. They are based on sodium acrylate copolymer. They are available from Technical Absorbents Ltd. of Grimsby in England. It is know to form webs by the "air laid" process on equipment from Dan- Webforming A/S of Risskov in Denmark. Such webs usually incorporate synthetic fibres, which soften under heat in the process and bond together with other fibres in the web. The object of the present invention is to provide an improved absorbent pad. In accordance with a first aspect of the invention there is provided an absorbent pad material comprising: a backing; an air laid web on the backing, the web incorporating super-absorbent material in fibrous form and bonding synthetic fibre; and a plastics material release layer on the side of the web opposite from the backing, wherein the plastics material of the release layer is based on a polymer having a melting point which is higher than at least a surface layer of the bonding synthetic fibre, whereby in use the air laid web can be heat bonded together in a compressed structure peripherally of a pad by application of heated members to the backing and/or the release layer. Preferably the synthetic fibre of the web is a copolymer of a polypropylene fibre with a polyethylene coating. The plastics material release layer is preferably a polypropylene based material, which has a higher melting point than polyethylene. Use of this material enables adequate softening of the polyethylene coating of the polypropylene, and hence satisfactory sealing of the edges, without softening of the release layer and without its adherence to the heat bonding members . Alternatively, the release layer can be a coextrusion of high and low density polyethylene, with the low density side in contact with the web. Alternatively again, a double laminate of PET or polypropylene with polyethylene may be used. The release layer may be printed on its inside, that is its side in contact with the air laid web. Normally, the backing will be a synthetic non-woven tissue. Preferably, the release layer is bonded to the air laid web, having been laminated onto the web as the web is being laid. The lamination provides good bonding and integrity of the pad in use, when it swells in thickness with absorbed water. Preferably, the air laid web includes wood pulp fibre to improve the texture and cost of the web. Insofar as the wood pulp fibre is least likely to be bonded to other fibres, it is likely to escape at the edges in the absence of peripheral heat-bonding compression. The super-absorbent material also may shed in the absence of peripheral compression. According to a second aspect of the invention, there is provided an absorbent pad cut from a sheet of the material of the first aspect, wherein the three layers of the pad, i.e. the backing, the air laid web and the release layer are compressed to a state thinner than that of the rest of the pad, with the material of the air lad web being bonded together in a compressed structure, at least at the cut edges of the pad, whereby fibres of the web are captivated at the cut edges. The backing, the air laid web and the release layer can be additionally sealed together in other areas of the pad, to show a logo for instance. Preferably, the ratio of thickness of the rest of the pad to the compressed edges is between 9: 1 and 2: 1 and normally between 7' 1 and 3 : 1. According to a third aspect of the invention, there is provided a method of manufacturing absorbent pads of the second aspect, the method consisting in the steps of: heating bondingly compressing a sheet of the absorbent pad material by application of heated members to the backing and/or the release layer in strips to define absorbent pads wherein fibres of the web are captivated, and cutting the sheet to form the pads. Preferably, the pads are cut centrally of compressed strips, whereby the compression remains intact in both adjacent cut pads. The strips can be heat sealingly compressed by means of heated rollers rolled over the laminated web. Alternatively, the strips are heat sealingly compressed by means of heated dyes impressed into the laminated web. Where the width of the sheet is a multiple of the cut size of the pads, the sheet can be compressed at edges of the sheet corresponding to edges of the pads and the sheet cut widthwise and lengthwise between the pads. Where the width of the sheet is equal to the cut size of the pads, the sheet can be compressed at edges of the sheet corresponding to edges of the pads and the sheet cut widthwise between the pads. Again where the width of the sheet is greater than a multiple of the cut size of the pads, the sheet can be compressed at edges of the sheet corresponding to edges of the pads and the sheet cut widthwise between the pads and lengthwise between the pads and at the edges of the pads along the length of the sheet. It is convenient in certain applications to prepare the pads from rolls of the laminated pad material which are delivered in bulk to a factory where the pads placed into trays immediately after cutting. Thus in accordance with a particular feature of the invention, the method includes the step of placing and securing cut pads in trays. According to a fourth aspect of the invention there is provided a machine for manufacturing absorbent pads of the invention from a sheet of absorbent pad material of the invention, the machine comprising: means for successively feeding the said sheet, means for compressing the sheet at strips to define the pads by heat bonding the material of the air laid web, and means for cutting the sheet at the strips. Preferably the heat bonding compression means comprises a pair of heated platens having raised compression lands for defining the said strips and means for successively advancing the platens together for impressing the lands against the said sheet to heat bondingly compress the air laid web. To help understanding of the invention, specific embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a pad of the invention; Figure 2 is an end view of the pad; Figure 3 is a diagrammatic side view of production of a three part laminate for pad production; Figure 4 is a diagrammatic side view of a machine for making the pad; Figure 5 is a similar view of another pad making machine; Figure 6 is a front view of one of the heat sealing platens of the machine of Figure 5; Figure 7 is a diagrammatic side view of a third pad making machine; Figure 8 is an end view of the third pad making machine; and Figure 9 is a diagrammatic side view of a machine for cutting individual pads and inserting them into trays. The pad shown in Figures 1 & 2 has a core 1 of an air laid web consisting of: 52% of wood pulp fibre, 30% of super-absorbent fibre, 18% of thermoplastic bonding material. The super-absorbent fibre is 6mm long fibre sold under the OASIS trade mark by Technical Absorbents Ltd. The bonding material is polyethylene coated polypropylene fibre sold by Danaklon A/S of Varde in Denmark. The web is laid on a non-woven polyethylene tissue 2 and is coated with a release layer film 3 of polypropylene based material, suitably SWF film as sold under the TRESPAPHAN trade mark by Hoechst Trespaphan UK Ltd of Swindon. The material is corona discharge treated whereby it can be printed, on the side which is laminated to the air laid web, prior to the lamination. The printing is then visible through the film 3. The edges 4 of the pad are compressed, typically along a 3 mm wide margin 5, with the web being flattened and heat bonded in its compressed state, with the backing and release layers united to it. This compression of the air laid web captivates fibres of the web from escaping from the cut edges. Tests have shown this to be the case. In use, the pad is secured in a meat tray, with the release layer uppermost. This avoids the meat sticking to the pad. Blood from the meat can flow around the edges of the pad and pass through the non-woven tissue to be absorbed into the web. Figure 3 shows in outline a machine for manufacturing the material from which pad of Figures 1 & 2 is made. In the machine, the tissue layer 2 has the web layer 1 laid on it at forming station 10. These conformed layers are advanced into a processing station 11, were hot air 12 is sucked through the layers, drawing the air laid web 1 to a uniform thickness and softening the polyethylene of the bonding material, acts as an adhesive to unite the layer and secure it to the web. At a lamination station 13 immediately down stream of the processing station, the release film 3 is laminated by rollers 14 onto the still hot web, whereby the three layers are united at their place of lamination. Air laying is a known technology and need not be described in detail. The lamination of the release film 3 is an additional step. Downstream of the lamination, the material is cooled and wound 15. Figure 4 shows diagrammatically one form of machine for manufacturing pads. This process is generally carried out at a site separate from the air laying and lamination. However, it could be carried out on the same site. The pad material 20 drawn from a roll 22 and fed by rollers 23 to a set of heated, longitudinal compression rollers 24 for forming sealing lines longitudinally of the material. These are lines where the rollers heat the air laid web sufficiently to again soften the polyethylene of the bonding material and cause it to hold the web in compressed state. Typically a 1.0- 1.5mm material is compressed to 0.3mm. (It will be appreciated that the material is so easily compressible that its free, uncompressed dimension is not easy to measure.) A set of slitting rollers 25 follows the compression rollers 24 for dividing the material into strips of a width equal to the end product. There then follow a further pair of lateral sealing and cutting rollers 26,27, having laterally extending, heated, compression elements 28 and cutting elements 29 for cutting off the individual pads 30. Figure 5 shows another machine, in which reciprocating compression and cutting stations 50,51 are employed. The pad material 40 is fed over a jockey roller 52 to a pneumatic feeding device 53, which comprises a clamp 54 and its actuator 55, which are connected to an advance bar 56 via short stroke actuators 57, a pair of which are provided at opposite end of the bar 56 corresponding to opposite sides of the material. The bar is movable vertically between stops 58,59 by a long stroke actuator 60. The clamp holds the material vertically and the feeding device is thus arranged to feed the material vertically downwards. Beneath the feeding device, an opposed pair of heated platens 61,62 are provided. These have lands 63 which define regions of compression of the material, the regions being a plurality of vertically arranged strips 64, with top and bottom horizontal strips 65, which together define the edges of a plurality of pads side by side. Typically the pads are 9.5 x 15.0mm, with the strips 64,65 being 0.5mm wide. One platen 61 is fixed and the other is reciprocatably mounted for movement towards and away from the other by a hydraulic actuator 66. Beneath the platens a cutter is provided in the form of a fixed array of anvil strips 67 laid out in the pattern of the lands 63 and a reciprocatable array of knives 68, also in the same pattern. A further hydraulic actuator 69 is provided for moving the knives. Within each pad area defined by the knives, a pneumatically operated pusher 70 is provided for pushing cut pads into reception trays 71. Beneath this cutter, a waste feeder 72 is provided with jaws 73 for gripping wasted left at the edges of the material. In operation, the actuators 66,69 are cycled together. The material is then fed by the feeders 53, 72 and the actuators recycled and so on. The material has a tendency to adhere to the platens when the actuator 66 is cycled. To pull it off, the short stroke actuators 57 draw up the clamp 54 before the long stroke actuators 60 feed the material down between the platens. The material with the previously compressed strips 64,65 is moved down to register with the knives 68, which are advanced to cut as the platens impress fresh strips above. Immediately on operation of the knives, the pushers 70 feed the cut pads into the trays 71, where lines 74 of pads accumulate for packing and distribution. The waste material is pulled down from the cutters by the feeder 72 in synchronisation with the long stroke actuator 60. All the feed devices return to their initial position during the operation of the actuators 66,69. Turning now to Figures 7 & 8 a larger machine in there shown. It comprises a compression device 101 having an actuator 102 and platens 103,104 arranged to impress strips defining pad in an array extending both across and along the pad material 100, which is fed from a roll 105 via a tensioning rollers 106. Between cycles of the compression device, the material is advanced by nip rollers 107, which incorporate in their length upper, circular slitting cutters 108 and lower anvil discs 109, whereby the material is fed onto a suction table 110 already slit longitudinally into pad widths and having a rectangular array of pad edge strips impressed into it. For separation of the pads widthwise of the material, the material is held by suction onto the table 110 and further circular slitting cutters 111 rolled across the table in line with anvil strips 112 -set in it. At the end of this cutting stroke, a suction head 113 is in register with the cut pads 114. The head 113 is lowered by an actuator 115 onto the pads. The suction of the table 110 is released and that of the head applied. The head is lifted by actuator 115 and returned by a long stroke actuator 116 to its initial position, where release of the suction deposits the pads on a stack 117. A pad making device is shown in Figure 8. Its reel of pad material 150 is one pad wide. The material is fed by feed rollers 151 through a pair of single pad, impression platens 152, with an actuator 153. Beneath the rollers, the strip-impressed material hangs down in front of a pad applicator device 154, in the form of a suction head 155, on an actuator 156. Above the actuator, an anvil strip 157 and laterally movable circular slitting cutter 158 are provided. On cycling of the impression platens 152, the material is pulled down by the rollers and the pad 159 aligns with the suction head. Suction is applied and the cutter is operated. The actuator is then advanced, to apply the pad to a meat tray 160, which has been presented by another machine in front of the actuator. The tray has already had adhesive applied to, whereby the actuator causes the pad to adhere to the tray, when the suction is released and the actuator withdrawn. As an alternative to use of adhesive, the pads can be ultrasonically welded in place after placement. Whilst it is envisaged that the primary use of the pads will be in meat trays, they or indeed sealed but uncut sheets of them may find use in providing a convenient means of holding water against perishable goods which are frozen. The pads freeze and assist in maintaining the goods at or below freezing point. The pads have particular advantage in being flat and able to take up moisture very quickly. This enables them to be used after freezing to line a container of frozen food. In another use, they can be shaped to contact the food and then frozen.

Claims: CLAIMS: 1. An absorbent pad material comprising: a backing; an air laid web on the backing, the web incorporating super-absorbent material in fibrous form and bonding synthetic fibre; and a plastics material release layer on the side of the web opposite from the backing, wherein the plastics material of the release layer is based on a polymer having a melting point which is higher than at least a surface layer of the bonding synthetic fibre, whereby in use the air laid web can be heat bonded together in a compressed structure peripherally of a pad by application of heated members to the backing and/or the release layer. 2. An absorbent pad material as claimed in claim 1, wherein the synthetic fibre of the web is a copolymer of a polypropylene fibre with a polyethylene coating. 3. An absorbent pad material as claimed in claim 1 or claim 2, wherein the plastics material release layer is a polypropylene based material. 4. An absorbent pad material as claimed in claim 1 or claim 2, wherein the plastics material release layer is a coextrusion of high and low density polyethylene, with the low density side in contact with the web. 5. An absorbent pad material as claimed in claim 1 or claim 2, wherein the plastics material release layer is a double laminate of PET or polypropylene with polyethylene. 6. An absorbent pad material as claimed in any preceding claim, wherein the release layer is printed on its inside, that is its side in contact with the air laid web. 7. An absorbent pad material as claimed in any preceding claim, wherein the backing is a synthetic non-woven tissue. 8. An absorbent pad material as claimed in any preceding claim, wherein the release layer is bonded to the air laid web, having been laminated onto the web as the web is being laid. 9. An absorbent pad material as claimed in any preceding claim, wherein the air laid web includes wood pulp fibre. 10. An absorbent pad cut from a sheet of the material claimed in anyone of claim 1 to 9, wherein the three layers of the pad, i.e. the backing, the air laid web and the release layer are compressed to a state thinner than that of the rest of the pad, with the material of the air lad web being bonded together in a compressed structure, at least at the cut edges of the pad, whereby fibres of the web are captivated at the cut edges. 11. An absorbent pad as claimed in claim 10, wherein the backing, the air laid web and the release layer are additionally sealed together in other areas of the pad. 12. An absorbent pad as claimed in claim 10 or claim 11, wherein the ratio of thickness of the rest of the pad to the compressed edges is between 9: 1 and 2:1 and preferably between 7: 1 and 3:1. 13. A method of manufacturing absorbent pads as claimed in claim 10, the method consisting in the steps of: heating bondingly compressing a sheet of the absorbent pad material by application of heated members to the backing and/or the release layer in strips to define absorbent pads wherein fibres of the web are captivated, and cutting the sheet to form the pads. 14. A method of manufacturing absorbent pads as claimed in claim 13, wherein the pads are cut centrally of compressed strips, whereby the compression remains intact in both adjacent cut pads. 15. A method of manufacturing absorbent pads as claimed in claim 13 or claim 14, wherein the strips are heat sealingly compressed by means of heated rollers rolled over the laminated web. 16. A method of manufacturing absorbent pads as claimed in claim 13 or claim 14, wherein the strips are heat sealingly compressed by means of heated dyes impressed into the laminated web. 17. A method of manufacturing absorbent pads as claimed in any one of claim 13 to 16, wherein the width of the sheet is a multiple of the cut size of the pads, the sheet is compressed at edges of the sheet corresponding to edges of the pads and the sheet is cut widthwise and lengthwise between the pads. 18. A method of manufacturing absorbent pads as claimed in any one of claim 13 to 16, wherein the width of the sheet is equal to the cut size of the pads, the sheet is compressed at edges of the sheet corresponding to edges of the pads and the sheet is cut widthwise between the pads. 19. A method of manufacturing absorbent pads as claimed in any one of claim 13 to 16, wherein the width of the sheet is greater than a multiple of the cut size of the pads, the sheet is compressed at edges of the sheet corresponding to edges of the pads and the sheet is cut widthwise between the pads and lengthwise between the pads and at the edges of the pads along the length of the sheet. 20. A method of manufacture as claimed in any one of claims 13 to 18, including the step of placing and securing cut pads in trays. 21. A machine for manufacturing absorbent pads as claimed in claim 10 from a sheet of absorbent pad material as claimed in claim 1, the machine comprising: means for successively feeding the said sheet, means for compressing the sheet at strips to define the pads by heat bonding the material of the air laid web, and means for cutting the sheet at the strips. 22. A machine as claimed in claim 21, wherein the heat bonding compression means comprises a pair of heated platens having raised compression lands for defining the said strips and means for successively advancing the platens together for impressing the lands against the said sheet to heat bondingly compress the air laid web. 23. A machine as claimed in claim 21 or claim 22, wherein the feeding means is a pair of driven rollers between the nip of which the sheet passes downstream of the platens. 24. A machine as claimed in claim 21 or claim 22, wherein the feeding means is a pair of jaws closable against the sheet and means for moving the jaws towards the platens, the moving means preferably including means for moving the jaws slightly away from the platens with the sheet before moving them forward again to release the sheet from the platens. 25. A machine as claimed in any one of claims 21 to 24, wherein the cutting means comprises a set of longitudinal knife blades advanceable into the material against an anvil plate. 26. A machine as claimed in claim 25, wherein the anvil has cut-outs and the machine includes plungers for pushing the cut pads through the cut-outs. 27. A machine as claimed in any one of claims 21 to 24, wherein the cutting means comprises at least one rolling knife advanceable across the sheet against an anvil. 28. A machine as claimed in claim 27, including a vacuum plate, at least one second rolling knife and anvil for cutting the sheet transversely and means for transferring the cut pads from the vacuum plate, the transfer means preferably being a second plate. 29. A machine as claimed in claim 21, the machine including: means for placing cut pads in trays, and means for securing the pads into the trays.

Inventors: DAVIDSON RODERICK IAIN, HALL ROBERT SINCLAIR, DAVIDSON, RODERICK, IAIN, HALL, ROBERT, SINCLAIR
Applicants: DAVIDSON RODERICK IAIN, DYECOR LIMITED, HALL ROBERT SINCLAIR, DAVIDSON, RODERICK, IAIN, HALL, ROBERT, SINCLAIR
Application year: 1998
Main classification: B32B27
IPC codes: B32B5, B32B27, B65D81