PAPER MAKING

Abstract: There is described a paper making machine (10) and a method of paper making wherein to create a paper embossed on both sides the web (17) after forming and before drying is subjected to an embossing nip (18, 19) having resilient surfaces. There is also described a resilient embossing nip component and a method of making a resilient embossing nip component for use in the paper making machine and method described.

Description: Paper Making This invention relates to paper making and in particular to the making of paper which has its surface or structure modified, for example by embossing. Embossed paper has been made in several ways. In one known way a dandy roll engaging the paper web during forming on the wire has been used to make an impression on one side of the web. After completion of the pressing and drying processes a paper is produced which has an embossed pattern on one side. The extent of such embossing is limited because of the effect of the subsequent pressing and drying on the pattern formed in the web. Further, if a paper is required which is embossed on both sides (which is most desirable) it is necessary to manufacture two half thickness paper webs and then laminate them together. Clearly this involves forming two webs in separate forming sections and bringing them together prior to pressing or double the amount of machine running time to produce two webs and then the cost of in house or contract lamination. Another previous known method of making embossed paper is to effect secondary treatment after the paper has been manufactured. Such secondary treatment involves passing it between embossing rollers. This process again, is expensive because it requires a secondary treatment machine. Further, after forming and drying the paper is relatively hard. For this reason, such embossing rollers have to be capable of dealing with paper in quite a hard condition and therefore need to be of metal or comparable material. To manufacture a pair of co-operating rollers to give double sided embossing requires heavy rollers with very close engagement. The cost of manufacturing such rollers and/or operating them with substantial nip pressures is undesirable and expensive. It is an object of the present invention to provide a method of paper making wherein the above disadvantages are reduced or minimised. The invention provides a method of paper making including forming a web on a fourdrinier wire, and pressing and drying the web, wherein the paper is embossed, characterised in that the web, before drying, is passed through a nip between a pair of rollers, at least one of which has been patterned by laser engraving. Desirably the nip is placed between the forming and drying stages and preferably during or after the pressing stage. Desirably the process is carried out at a stage where the paper web contains from 50% to 65% water, preferably 54% to 58% moisture. One component of the nip can have a textured surface and can operate against a plane component. Alternatively both components of the nip can be textured. In the latter case the two members of the nip can be driven in close synchronism. One or both components of the nip can have a surface of formed resilient plastics or rubber material. Desirably the material is rubber. Desirably natural rubber is used. The rubber surface can be formed by moulding in a press, but desirably is formed by laser engraving. In the case of a nip member in the form of a roller its surface can be made from the resilient material and the laser engraving can be performed on the actual roller surface. However, as paper web widths approach three metres it may not be economic to manufacture a laser etching machine of such a size. In these circumstances it can be desirable to mount a sheet of surface material on a dummy roll and laser engrave the surface thereof. The sheet, after -etching then being removed from the dummy roll and mounted on the embossing roll. Several sheets can be mounted side by side in register and secured to the embossing roll. The embossing roll can itself have an outer layer of resilient material compatible with the surface sheet. As the laser engraving process treats a sheet sequentially, rather than treating the entire sheet at the same time, the size of sheet which can be treated is not significantly limited. This is in contra-distinction to moulding or pressing of a rubber or elastic sheet, wherein the size of sheet to be produced is limited by the size of mould or press required and the difficulty of producing fine detail with great regularity on a large mould or press. Desirably the nip components are arranged and constructed so as to be capable of change between an operative nipping condition and an inoperative non-nipping condition so as to allow change from production to non-embossed paper to embossed paper and vice versa without interrupting paper production. In an advantageous development it can be possible for the nip to have a magazine arrangement so that different embossing patterns can be applied using different nip sets. Again it is desirable if this change can be effected whilst the paper web is running. When the nip is inoperative, for example when rollers are retracted, it can be arranged for the rollers to be detached and replaced so as to allow the embossing pattern to be changed. The invention also provides a paper making machine including a resilient embossing nip and a press section and a dryer section, characterised in that the resilient embossing nip is disposed upstream of said dryer section and comprises a pair of rollers, at least one of which has a surface which has been laser engraved. The nip can have one or two resilient surfaces. The or each resilient surface can be a textured surface. The surface can be formed by laser engraving. The invention also provides a paper making nip embossing roller having a resilient textured surface formed by laser engraving. The invention also provides a method of creating a surface for a paper making embossing nip roller including scanning a pattern to produce data representative of the pattern, mounting resilient material, scanning the material with an engraving laser and modifying the laser output in accordance with said data to produce an engraved surface on the material derived from the pattern. The pattern can itself be in the form of a sheet, for example of paper. Alternatively, the pattern could be built up on a computer screen and the scanning thereof effected by storing information from he computer screen on memory. The pattern can be a full size replica of the intended sheet surface or can be of a different size or scale. The data can be processed prior to engraving so as to modify the pattern. In particular, in the case of a pattern which is to form the basis of engraving on a large sheet of resilient material, the pattern can be only a fraction of the size of the sheet, the data derived from the pattern being electronically expanded to produce the same engraving over the entire sheet. The invention also provides a method of making a resilient paper making embossing roller including the steps of providing a roll body having a cylindrical surface, making a plurality of resilient textured sheets by a method as claimed in any of claims 36 to 45 and securing said sheets to the roll body in mated relationship. The invention also provides non-laminated paper, especially of board weight, having embossed laid patterns on both sides. By laid pattern is meant a pattern of essentially parallel lines having for example a spacing of 0.5mm -2mm such as 1mm between them forming alternative small projections and dips in the surface of the paper. It is known to form a laid pattern on paper of lighter grades (generally well below 150 g/m 2 ) using a dandy roll on the wire of a conventional paper making machine so that the pattern formed on one surface of- the paper by the dandy roll appears in reverse on the other side. However, for the heavier grades of paper, essentially those referred to as board and having a weight of about 150 g/m 2 or more, it is not possible to produce a pattern which extends through from one side to the other in this way by means of a conventional dandy roll on the wire because the paper is too thick and heavy. Although it has been possible to use a specialist twin-wire machine to produce heavier paper grades embossed with a laid pattern on both surfaces, this involves in situ laminating of two thinner paper webs after they have each had a laid pattern formed on one surface but before manufacture is complete. A further alternative is to laminate together after their manufacture two thinner sheets of paper which have both been provided with a laid pattern on one surface. In both instances, however, the fact of lamination can be deduced by expert examination of the finished product. By the use of the paper-making process and apparatus according to the invention it is possible to obtain for the first time non- laminated heavier-grade paper having a laid pattern on both sides. It also becomes possible to obtain non-laminated paper having different laid patterns on the two sides. Preferably, the lines of the laid pattern on the two sides of the heavier-grade paper run parallel to one another and are in register with one another so that dips on one side correspond to projections on the other, but this is not necessary. As the patterns are independent of one another they may vary from one to the other in spacing or direction of the lines or in displacement of the lines. This provides an additional possibility for non-laminated paper of lighter grades as well as board grades. To form the laid pattern on both sides of the paper the two component rolls of the resilient embossing nip in the paper making machine are both formed with a corresponding pattern of essentially parallel lines of appropriate spacing and orientation, as by laser engraving or etching. The paper web of appropriate weight is then passed through the resilient embossing nip in the manner described as part of the otherwise conventional manufacturing process. With the paper according to the invention produced by the use of the resilient nip it is possible to make the chain lines less prominent than on paper produced by a conventional twin wire machine. The sheets can be applied by adhesive and/or vulcanisation. The invention will be described further, by way of example, with reference to the accompanying drawings wherein; Figure 1 is a schematic illustration showing part of a conventional paper making process; Figure 2 is a view similar to figure 1 but showing the process modified in accordance with the invention; Figure 3 is a side elevation of part of a paper making machine modified in accordance with the invention; Figure 4 is a schematic illustration of the laser etching process; and Figure 5 is a partial side elevation of a preferred embossing roller of the invention. Figure 6 is an enlarged perspective view, partially in section, of a portion of a sheet of non-laminated paper of board grade having an embossed laid pattern on both sides, the two patterns being not fully in register. Figure 1 shows part of a prior known paper making machine, a conventional breast box (11) a Fourdrinier wire (12) , presses 13, 14 and a dryer section (15) . When embossing is required the dandy roll (16) which usually applies a water mark is constructed to be textured by having a cylindrical surface on which are mounted very fine projections, for example, in the form of copper wires so as to form a desired control pin to which can be transferred to the paper and will manifest itself, after pressing and drying and subsequent treatment of the paper has an embossed surface. Such embossing is only on one side of a sheet. Figure 2 shows the same paper making machine (10) but modified in accordance with the invention. After press (14) and before the dryer (15) the paper web (17) passes through a nip between a pair of embossing rollers (18) (19) . Although figure 2 shows the machine being extended to accommodate the rollers (18) (19) in practice there is usually sufficient room to place the rollers without increasing the overall machine length. This is important in relation to existing machines wherein lengthening the machine is not practical. At the position of the rolls (18) and (19) the paper web has a water content of from 50 to 65%, preferably from 54 to 58%. Figure 3 shows the incorporation of rollers (18) and (19) having a particular embodiment of paper making machine in rather more detail. In figure 3 the paper web travels from right to left rather than from left to right as it is in figures 1 and 2. Paper web (20) passes through press (13) and press (14) wherein it is preliminary dewatered by the absorbent felts (20) . From the nip of press (14) the web (20) passes to the first dryer drum (22) and on its way passes the nip between rollers (18) and (19) . Roller (18) is fixed on a mounting (20) connected to the machine frame (24) . Roller (19) has a mounting (25) pivotable at (26) and influenced by a hydraulic or comparable ram arrangement (27) . Ram arrangement (27) can serve either to maintain steady nip pressure during use or it can be used to withdraw the roll (19) completely away from the web. With the roll (19) withdrawn paper passing over the roller (18) is not significantly influenced thereby and a plain unembossed paper is produced. This allows production to be switched between embossed and plain paper to be changed at will. If desired roll (18) can also be rendered retractable. Normally rollers (18) and (19) will have textured surfaces which are complimentary and which interengage. However, by having one of the rollers textured and the other a plain resilient cylindrical surface, perhaps of a slightly lower hardness than the other, a nip can be produced which will produce a web which is embossed on both sides. This reduces the amount of work necessary to produce the nip. In the case where one of the rollers is retractable away from the web this can conveniently be the textured roller. When removed from the web the textured roller can be replaced with a roll having a different pattern, thus changing the nature of the embossing during use. If both rollers are textured then both rollers can be rendered retractable and changeable in situ. If space permits the embossing rollers could be arranged in a magazine type arrangement to allow different nips of different embossing patterns to be introduced at will, even during running on the machine. Figures 4 and 5 illustrate a method of making an embossing roller in accordance with the invention. A roller (28) in accordance with the invention may be perhaps 3 metres long and about 500mm in diameter. The roller (28) can have a cylindrical metallic core (not shown) surrounded by a base layer of nature rubber, also cylindrical and also not shown. A plurality of sheets (29) engraved in accordance with the following method are adhered to the resilient rubber base layer on the roller and arranged to mate at their joins (30) with adjacent sheets and secured by adhesive and/or vulcanisation so as to produce an embossing roller having a resilient surface throughout its length. In the manufacture of sheet (19) a pattern is first produced. The pattern can be in the form of a sheet of paper (30) upon which is marked the desired pattern. The art work can be in the form of a black and white representation of the desired pattern of texture required on the surface. The art work can be prepared on a single sheet and then enlarged photographically or electronically to form the sheet (31) which is of the same size as the final resilient sheet (29) . Sheet (31) is mounted on a drum (32) of the same diameter as the roller (28) . A plain sheet of resilient natural rubber (33) which will eventually form the sheet (29) is mounted on a comparable dummy roll or drum (34) . Drum (32) is indexed and rotated about its axis. At each index position a carriage (35) makes a traverse of the length of the drum (32) . A laser indicated at (36) directs the beam at the sheet (31) as the carriage traverses and the sheet (31) reflects back to the laser a signal which depends on the pattern at any particular point. This information is stored on memory. The information stored in the memory, (which can be part of a computer controlling the whole process,) is then used to modify a laser indicated at (37) mounted on a carriage (38) which is traversable in a similar manner relative to drum (32) . Laser (37) differs from laser (36) in that it is a quote "write" laser rather than a "read" laser. The laser (37) and drum (34) is indexed and as carriage (38) traverses it evaporates portions of sheet (33) to form a textured surface in accordance with the pattern formed on sheet (31) . Although this is not strictly necessary, it is possible for the data to be modified before feeding to laser (37) . For example a sample pattern on a small size can be feed into the computer, the computer can generate the pattern for a full size sheet (33) by repeating the pattern. This can be useful when a new formed pattern is needed and the expense of creating the pattern as art work in full is not justified. However, the use of a full size pattern and synchronised drum (32) and (34) operating simultaneously can have advantages in that data storage and later retrieval are unnecessary. The invention is relevant to text covered paper, printing writing and paper of board weight. The invention has particular applicability to papers of board weight, but is not necessarily so limited. The laser engraving used can be "three dimensional". This means that the strength of the laser beam as it travels in lines across the surface has two values, namely high and a low value. When the beam is on its high value material is vaporised and removed. When the beam is on its low value little or no material is removed. This produces a surface which is composed entirely of lands and pits or channels. Desirably, however, the surface is laser engraved using a machine which can produce a "three dimensional" engraving pattern. This means that the laser beam has several, for example possibly five but desirably ten different levels giving not merely lands and pits, but also texture on the surfaces which can be graded from 0 to maximum depth as in the manner of a stepped pyramid or any stepped formation. This can give a better product because the paper does not need to be forced into the sharp corners of a sheer sided pit, but can more happily take up the softer contours of a curved or diagonally slopping side or stepped in accordance with the chosen power variation of the laser beam. This has a further advantage that within a particular chosen shape of pattern motif, for example a square or diamond motif, additional minor patterning can be provided which can vastly improve the range of patterns which can be applied to the paper being treated. The use of this technique in relation with cylindrically mounted nip forming material, either a sheet on a dummy roll to be mounted on a master roll, or a smaller roll being itself engraved in situ provides a particularly cheap and simple to produce such rolls and in a wide range of sizes and with a very wide range of possible embossing patterns. It is to be emphasised that much of the prior art is directed to off machine embossing wherein paper which has already been formed, pressed, dried and rolled is unwound, wetted and then passed between engraving rollers in order to produce a pattern thereon. These prior methods are very time and heat consuming because as the paper has to be wetted and then, eventually, re-dried, very significant energy has to be expended in both the winding, un-winding and then re-drying of the paper. The invention is not limited to the precise details of the foregoing and variations can be made thereto.

Claims: Claims 1. A method of paper making including forming a web on a fourdrinier wire, and pressing and drying the web, wherein the paper is embossed, characterised in that the web, before drying, is passed through a nip between a pair of roller, at least one of which has been patterned by laser engraving. 2. A method as claimed in claim 1 wherein the nip is disposed intermediate the pressing stage. 3. A method as claimed in claim 1, wherein the nip is often the pressing stage. 4. A method as claimed in claim 1, 2 or 3 wherein the process is carried out at a stage where the paper web contains from 50% to 65% water. 5. A method as claimed in claim 4 wherein the paper web contains 54% to 58% water. 6. A method as claimed in any preceding claim wherein one roller of the nip has a textured surface and the other component is plain. 7. A method as claimed in any of claims 1 to 5 wherein both rollers of the nip are textured. 8. A method as claimed in claim 7 wherein the two rollers are driven in synchronism. 9. A method as claimed in any preceding claims wherein the textured roller has a surface of plastics or rubber material. 10. A method as claimed in claim 9, wherein the surface is natural rubber. 11. A method as claimed in any of claims 1 to 10, wherein the pattern on the roller is an overall uniform pattern. 12. A method of paper making substantially as described with reference to the accompanying drawings. 13. A paper making machine including a resilient embossing nip and a press section and a dryer section that the resilient embossing nip is disposed upstream of said dryer section and comprises a pair of rollers, at least one of which has a surface which has been laser engraved. 14. A machine as claimed in claim 13 wherein the nip has at least one resilient surface. 15. A machine as claimed in claim 14 wherein the resilient surface is said laser engraved surface. 16. A machine as claimed in claim 13, 14 or 15 wherein the surface is provided by one or more sheets mounted on a support. 17. A machine as claimed in claim 20 wherein the support is a roller core. 18. A machine as claimed in claim 16, wherein the or each sheet is produced by laser engraving. 19. A machine as claimed in any of claims 15 to 18 wherein the nip rollers are arranged and constructed so as to be capable of change between an operative nipping condition and an inoperative non-nipping condition. 20. A machine as claimed in claim 19 wherein change can occur without interrupting paper production. 21. A machine as claimed in any of claims 13 to 20 wherein the nip has a magazine arrangement so that different embossing patterns can be applied using different nip sets. 22. A machine as claimed in claim 27 wherein the change can be effected whilst the paper web is running. 23. A machine as claimed in claim 21 or 22 wherein nip components are detachable and replaceable. 24. A paper making machine substantially as described with reference to the accompanying drawings. 25. A paper making nip embossing roller having a resilient textured surface formed by laser engraving. 26. A paper making nip embossing roller substantially as described with reference to the accompanying drawings. 27. A method of creating a surface for a paper making embossing nip roller including scanning a pattern to produce data representative of the pattern, mounting resilient material, scanning the material with an engraving laser and modifying the laser output in accordance with said data to produce an engraved surface on the material derived from the pattern. 28. A method as claimed in claim 27 wherein the pattern sheet is of paper. 29. A method as claimed in claim 27 wherein the pattern is built up on a screen and information from the screen is stored in memory. 30. A method as claimed in any of claims 27 to 29 wherein the pattern is a full size replica of the intended sheet surface. 31. A method as claimed in any of claims 27 to 29 wherein the pattern is of a different size or scale. 32. A method as claimed in any of claims 27 to 30 wherein the data is processed prior to engraving to modify the pattern. 33. A method as claimed in any of claims 27 to 31 wherein the sheet, after etching is demounted and mounted on the embossing roll. 34. A method as claimed in claim 32 wherein several sheets are mounted sid-e by side in register and secured to the embossing roll. 35. A method as claimed in any of claims 27 to 33 wherein the embossing roll itself has an outer layer of resilient material compatible with the surface material. 36. A method of creating a surface for a paper making embossing nip roller substantially as described with reference to the accompanying drawings. 37. A method of making a resilient paper making embossing roller including the steps of providing a roll body having a cylindrical surface, making a plurality of resilient textured sheets by a method as claimed in any of claims 36 to 45 and securing said sheets to the roll body in mated relationship. 38. A method as claimed in claim 35 wherein the sheets are secured by adhesive and/or vulcanisation. 39. Non-laminated paper of board weight having embossed laid patterns on both sides. 40. Non-laminated paper having embossed laid patterns on both sides, the patterns being independent of one another and not complementary. 41. A method of making non-laminated paper having embossed laid patterns on both sides, made by the method of any of claims 1 to 12 or the machine of any of claims 13 to 224. 42. Paper as claimed in claim 40 and made by the method of any of claims 1 to 12 or by the machine of any of claims 13 to 24. 43. Paper as claimed in claim 39, made by the method of any of claims 1 to 12 or by the machine of any of claims 13 to 24, wherein the nip comprises a pair of laser engraved rollers having different patterns. 44. A method as claimed in any of claims 1 to 12, or a machine as claimed in any of claims 13 to 24, wherein the laser engraved roller has been three-dimensionally engraved.

Inventors: DODGSON BARRY STEPHEN, MILNE ALLAN MCRAE, DODGSON, BARRY, STEPHEN, MILNE, ALLAN, MCRAE
Applicants: DODGSON BARRY STEPHEN, JAMES RIVER UK HOLDINGS LTD, MILNE ALLAN MCRAE, JAMES RIVER UK HOLDINGS LIMITED
Application year: 1993
Main classification: D21F11
IPC codes: D21F11