AU667626B2 - Paper making - Google Patents

Description

41 P55492 WO 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 knewf- 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 -M en method of making embossed paper is to AMENDED SHEET ®4 i& effect secondary treatment after the paper has been manufactured.

j 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 reeasoti, 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 I engagement. The cost of manufacturing such rollers and/or operating them with substantial nip pressures is undesirable and.

expensive.

It s Vbectof the present invention to provide a method of making embossed paper wherein the above disadvantages are reduced or minimised.

DE-C-132665 and DE-C-71762 both disclose the use of resilient embossing nips in paper making machines in order to imprint watermarks as the paper is produced.

The present invention provideska method of making embossed paper including forming a web on a fourdrinier wire, and pressing and drying the web, and passing the web, before drying, through a nip between a pair of embossing rollers characterised in that at least one of those rollers has a resilient surface which has been patterned by laser engraving.

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2a Desirably the nip is placed between the forming and drying stages and preferably during or after the pressing stage.

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-3- 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 (patterned) 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.

The resilient surface of the patterned roller, or of both nip components, is preferably made of plastics or rubber material.

Desirably natural rubber is used.

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, is then 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 AMENDED SHEET 'r 0~ 4 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 of 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 provideska paper making machine including a _resilient embossing nip and a press section and a dryer section, AMENDED SHEET the resilient embossing nip being disposed upstream of the dryer section and comprising a pair of rollers, at least one of which has a resilient surface which has been laser engraved.

SThe nip can have two resilient surfaces, and one or both of these can be a textured surface formed by laser engraving.

The invention also provides in a third aspect a paper making nip embossing roller having a resilient textured surface j formed by laser engraving.

i t it The invention also provides in a fourth aspect a nonlaminated paper having embossed laid patterns on both sides I4,. t made in accordance with the first aspect of the invention.

S, 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 has been disclosed how 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, S951004,p:\oper\kay,61362-94.277,5 0W i 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 1 5 is not possible to produce a pattern 4 t 951004,p:\oper\kay,61362-94.277,6 OR- -7which 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 to~gether eafter their man~ufacture two thinner sheets of paper which have both been provided with a laid pattern on one surface. In both instance7,, however, the fact of lamination can be deduced by expert examina~tion of the f,,inished product.

By the use of the paper-making process and apparatus according tojithe invention it is possible to obtain for-~the first time nonlaminated 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 j 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 ~-~aper of lighter grades as well as board grades.

AmEN4DI SHEET -8 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 bossing 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 ie.silient 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.

Ijhe 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 pr\or ck icomnventt b paper making process; Figure 2 is a view similar to figure 1 but showing the process Ocr\ em-nbocrweA. c 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;

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AMENDED SHEET 0T 9 Figure 4 is a schematic illustration of the laser etching process; and Figure 5 is a partial side elevation of a preferred embossing e N J roller of kthe 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 4wno paper making machine, a iaen'enaianj breast box (11) a Fourdrinier wire presses 13, 14 and a dryer section When .embossihg is required the dandy roll 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 which can be transferred to the paper and will manifest itself, after pressing and drying and subsequent treatment of the paper, as 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 withAthe invention. After press (14) and before the dryer (15) the paper web (17) passes through a nip between a pair (o AMENDED SHEET AMENDED S~IEET 1004,q:\oper\kay,61362-94.277,5 of embossing rollers (18) Although f igure 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 o~f rollers (18) and (19) in a particular embodiment of paper making machine in rather more detail. In figure 3 the paper web travels from right to left rather than fr~om 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 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 (23) connected to the machine frame 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

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-11at 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 withkthe 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 AMENDED

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i- I 12 12 layer of natural 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 (29) a pattern is first produced.

The pattern can be in the form of a sheet of paper (31) 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 Sheet (31) is mounted on a drum (32) of the same diameter as the roller 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 A laser indicated at (36) directs its 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 FA. 9L AMENDED SHEET Doth sides the web (17) after forming and before drying is subjected to an emosn ni*1,1)hvn eiir ufcs hr 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.

-13 a laser indicated at (37) mounted on a carriage (38) which is traversable in a similar manner relative to drum Laser (37) differs from laser (36) in that it is a "write" laser rather than a "read" laser. The drum (34) is indexed and as the carriage (38) traverses it the laser (37) evaporates portions of the sheet (33) to form a textured sraein 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 For example a sample pattern of a small size can be fed 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 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 AMENDED SHEET AMENDED SHEET 7OB~~B LU i -i S 7 41 14 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 sloppj 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 or 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 to 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 way 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

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V AMENDED SHEET 7 patterned by laser engraving.

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15 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.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.

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Claims (15)

1. A method of making embossed paper including forming a web on a fourdrinier wire, and pressing and drying the web, and passing the web, before drying, through a nip between a pair of embossing rollers, characterised in that at least one of those rollers has a resilient surface which has been patterned by laser engraving.

2. A method as claimed in claim 1 wherein both rollers of 0oo the embossing nip are patterned and the two rollers are 00 edriven in synchronism. oo o« 0 0 0

3. A paper making machine including a resilient embossing 15 nip and a press section and a dryer section, the resilient embossing nip being disposed upstream of the dryer section and comprising a pair of rollers, at least one of which has ^a resilient surface which has been laser engraved.

4. A machine as claimed in claim 3 wherein the laser engraved resilient surface is provided by one or more sheets which are mounted on a supporting roller core.

A machine as claimed in claims 3 or 4 wherein the rollers of the embossing nip are arranged and constructed so as to be capable of change between an operative nipping condition and an inoperative non-nipping condition. 951004,p\oper\kay,61362-94.277,16 AMENDED SHEET i 1 i -17

6. A machine as claimed in any of claims 3 to 5 wherein the embossing nip has a magazine arrangement so that different embossing patterns can be applied using different nip sets.

7. A machine as claimed in any of claims 3 to 6, wherein the nip comprises a pair of laser engraved rollers having different patterns.

8. A machine as claimed in any of claims 3 to 7, wherein the or each laser engraved roller has been three- dimensionally engraved. I r

9. A paper making nip embossing roller having a resilient textured surface formed by laser engraving. t i,

10. Non-laminated paper having embossed laid patterns on et both sides, made by the method of claims 1 or 2 or by the i i i ct machine of any one of claims 3 to 8. i 20

11. Paper as claimed in claim 10, the patterns on the respective sides being independent of one another and not complementary.

12. A method substantially as hereinbefore described with reference to Figures 2 to 6 of the drawings.

13. A paper making machine substantially as hereinbefore described with reference to Figures 2 to 6 of the drawings. 951004,p.oper\kay,61362-94.277,17 L The invention also provides a paper making machine including a resilient embossing nip and a press section and a dryer section, 0 AMENDED SHEET WR I c-- i-- 18

14. A paper making nip embossing roller substantially as hereinbefore described with reference to Figures 2 to 6 of the drawings.

15. Non-laminated paper made substantially as hereinbefore described with reference to Figures 2 to 6 of the drawings. DATED this 4th day of October, 1995. James River UK Holdings Limited by its Patent Attorneys DAVIES COLLISON CAVE t Ii Ci C 951005,p\oper\kay,61362-94.277,18 r I i c