AU9047098A - Method and apparatus for applying a coating material to sheets - Google Patents

Description

;r- -l;ici Our Ref: 706354 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT .4.

.4 a.ril 0~ .iI.

f s1 Ai u K -3 Applicant(s): 4 Address for Service: Invention Title: Minnesota Mining and Manufacturing Company 3M Center PO Box 33427 Saint Paul Minnesota 55133-3427 UNITED STATES OF AMERICA DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Method and apparatus for applying a coating material to sheets The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 -1 1METHOD AND APPARATUS FOR APPLYING A COATING MATERIAL TO

SHEETS

This application is a divisional of 29708/95. The ensuing description is substantially identical to the description of "parent" No. 29708/95. The parent description has been fully readopted to facilitate identification of the parent/divisional relationship. It is reiterated that the invention of this divisional application is as defined in the ensuing claims.

Technical Field The present invention relates to an apparatus and method for applying coating material to both opposing major surfaces of a plurality of individual sheets, for example sheets of paper.

Background of the Invention It is necessary in certain fields to apply coating material to paper and, in some 15 cases, to apply different coating materials to the two opposing major surfaces of the paper. For example, in the production of so-called repositionable notes it is known to S apply a primer material to one side of the paper from which the repositionable notes will be cut and to apply a low adhesion backsize, or release, material to the other side of the paper. The repositionable adhesive is applied to the paper on top of the primer S 2C material. Conventionally,.for the production of repositionable notes, the various coatings are applied to a web of paper from a roll. The coating materials are dispersed in solvents and coated directly on the paper. The web is dried between coatings and then rewound and the coated roll is subsequently cut into sheets which are used to produce the notes. When the paper web is coated with materials dispersed in an S' organic solvent and is under tension when the coatings are applied, the tendency of the p: per web to curl or wrinkle can be substantially eliminated, otherwise great care is required to balance the paper sheet's expansion during coating ~ii ;r la- A process for the production of repositionable notes, in which a release material and a primer material are coated successively on opposite sides ofa paper web is described in WO-A-87/05315. In some cases, it is desirable to apply coating material to cut sheets rather than to a web of paper. For example, in the production of repositionable notes it is desirable to have the option of using a stack of preprinted sheets as the supply source, instead of a plain paper web, to extend the flexibility of the production process. In addition, for environmental reasons, there is a desire to move away from the use of materials containing organic solvents in coating processes S 10 towards the use of water-based materials. Moreover, many inks are soluble in organic solvents, but insoluble in water. Problems can arise, however, in applying coating 0** *I .e e a1 4 S 9 WO 9610506 PCT/US9s5tO772 2 materials (and, particularly, water-based coating materials) to individual sheets because the risk that the sheets will curl or wrinkle is greatly increased. Any curling or wrinkling not only spoils the appearance of the sheets but can also make it difficult to apply further coating materials.

U.S. Patent No. 5,487,780 filed February 15, 1994 entitled "Method and Apparatus for Applying a Coating Material to a Sheet', discloses apparatus and a method for forming pads of repositionable notes from a stack of uncoated individual paper sheets- The sheets are fed from the stack in an overlapped condition to a coating station in which a continuousilayer of a water-based primer material is applied to one major surface of the web-like overlapped sheets and a continuous layer of a water-based low adhesion backsize (LAB) material is applied simultaneously to the other major surface. The overlapped sheets are then dried and S" fed to a second coating station in which stripes of repositionable adhesive are applied to the web-like overlapped sheets on the surface to which the primer was applied in the first coating station. Thereafter, the sheets are adhered together in a stack and S* trimmed to form pads of repositionable notes. In that process, curling or wrinkling of the sheets is avoided by applying the primer and LAB coatings simultaneously to both sides of the sheets and then drying both coatings simultaneously.

However, it has been found that existing systems for applying a coating material to sheets, including the aforementioned U.S. Patent No. 5,487,780, while having their own utility, are not as effective or efficient as desired in coating some materials onto certain sheet materials. Therefore, an improved method and apparatus for applying a coating material onto sheets is desired.

i i -7 !i i Z Smnmary of the Invention The present invention provides apparatus for applying water-based coating material to both sides of a plurality of sheet members, the apparatus comprising: a conveyor for conveying the sheet members sequentially along a sheet path a dual coating station positioned to receive the sheet members sequentially from the conveyor, the dual coating station comprising first and second coating stations located on opposite sides of the sheet path through the dual coating station, each of which first and second coating stations comprises a respective source of water based coating material and a respective 10 coating member positioned to contactthe sheet members at a point along the sheet path to apply coating material from the respective source to the respective side of each sheet member,

S.

an overlapping conveyor arranged to receive sheet members from the dual coating station and movable at such a speed that the leading edge portion of each sheet member leaving the dual coating station is deposited on the trailing edge po r ti on of the preceding sheet member on the conveyor thereby forming a pseudo-web of overlapping sheet members; an air knife positioned to direct a current of air at the overlapped sheets to change the relative positions thereof in the pseudo-web whereby the trailing edge portion of each sheet embdr overlies the leading edge portion of the succeeding sheet member, and a dryer in the sheet path for removing water from the coating material applied to the sheetmembers in the dual coating station- The sheets may then be fed to a second coating station which is operable to apply a further coating material to one side of the overlapped sheets.

SThe present invention also provides a method for applying water-based coating materials to both major surfaces of a plurality of sheet members, comprising the ordered steps of: conveying the sheet members sequentially along the sheet path applying awater-bad pime aeial to one major surface ofeach sheet member and a water-based low adhesion back material to the other major surf of each sheet member as the sheet members are being conveyed along the sheet path: Iz;/ -3adepositing the sheet members successively on conveying means in the sheet path, whereby the leading edge portion of each sheet member is deposited on the trailing edge portion of the preceding sheet member to form a pseudo-web of overlapped sheet members; directing a current of air at the overlapped sheet members to sequentially change the relative overlapped positions thereof, whereby the trailing edge portion of each sheet member overlies the leading edge portion of each succeeding sheet member, and drying the overlapped sheet members as they are being conveyed along the sheet path.

Preferably, when both sides of each sheet are being coated, the coating material(s) is/are applied simultaneously to both sides.

In another aspect, the present invention provides a method for applying water-based coating material to both opposing major surfaces of a plurality of sheet members, comprising the steps of: conveying the sheet members sequentially along a sheet path; applying water-based coating material simultaneously to both major surfaces of each sheet member individually as the sheet members are being conveyed along the sheet path; arranging the coated sheet members in sequential end-to-end overlapping relation and continuing to convey the sheet members along the sheet path; and drying the coated sheet members, continuously applying further coating material to at least one major surface of S 20 the overlapped sheet members as the sheet members are being conveyed along the sheet path.

S The coating materials may be a primer material and a low adhesion backsize material. The further coating material may be a repositionable adhesive.

i rr~ -3a- S(c) depositing the sheet members successively on conveying means in the sheet path, whereby the leading edge portion of each sheet member is depositedon the trailing edge portion of the preceding sheet member to form a pseudo-web of overlapped sheet members; directing a current of air at the overlapped sheet members to sequentially change the relative overlapped positions thereof, whereby the trailing edge portion of each sheet member overlies the leading edge portion of each succeeding sheet member, and drying the overlapped sheet members as they are being conveyed along the sheet path.

Preferably, when both sides of each sheet are being coated, the coating material(s) is/are applied S simultaneously to both sides.

In another aspect, the present invention provides a method for applying water-based coating material to both opposing major surfaces of a plurality of sheet members, comprising the steps of: conveying the sheet members sequentially along a sheet path; applying water-based coating material simultaneously to both major surfaces of each sheet member individually as the sheet members are being conveyed along the sheet path; I: arranging the coated sheet members in sequential end-to-end overlapping relation and continuing to convey the sheet members along the sheet path; and Si(d) drying the coated sheet members, continuously applying further coating material to at least one major surface of the overlapped sheet members as the sheet members are being conveyed along the sheet path.

S" The coating materials may be a primer material and a low adhesion backsize material- The S: further coating material may be a repositionable adhesive.

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i-i Brief Description of the Drawines Embodiments of the invention will be described, by way of example, with reference to the accompanying drawings, wherein like structure is referred to by like 5 numerals in the several views, and in which: Figure 1 is a schematic side view of apparatus which includes a coating station, in accordance with the invention; Figure 2 is a schematic top view of the-apparatus shown in Figure 1; Figure 3 is a view of a coating station forming part of the apparatus shown in 10 Figure 1; Figure 4 is a view similar to Figure 3 showing par ofthe coating station in Sgreater detail; Figure 5 shows a cmGting material supply system for the coating station of Figs.

3 and 4; Figure 6 is a diagrammatic side view of part of an adhesive coating station at the downstream end of the apparatus shown in Figure 1 with an alternative coating section; SFigure 7 is a diagrammatic side view of a modified version of the apparatus shown in Figure 1 with an alternative guiding section; and

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3 PCT595J0877Z 4 Figure 8 is enlarged partial view of part of Figure 4- Detaileid Description of the Invention The apparatus Shown schematically in Figure 1 and 2 is specifically for use in the production of repositionable notes from sheets of any suitable substrate material.

example, Paper, polYmeric film or fogls, such as metallic foils and, in particular, for the application to indivdual sheets of a primer material, a low adhesion backsize (LAB) material, and a repositionable adhesive so that the sheets cani subsequently be used to form repositionaijie notes. In the following description, it will be assumed that the sheets (which may be pre-printed) are of paper. The paper may be any suitable paper.

such as the paper utilized to construct the Post-it®D brand repositionable notes available from Minnesota MininS and Manufacturing Company of St- Paul, MNIinnesota In the followiniz description, it will be assumed, unless otherwise noted. that the sheets (which may be pre-printed) are of paper.

The apparatus has a paper pat.h entry I which receives a s-iccession of'paper sheets (rot shown) from arny suitable source, for example a stack From the paper path entry 1, the sheets travel in the direction indicated by the a.-Tow 2 through a double coating station 3. a sheet overlapping station 4, a dryer 5, a sheer ouidine section 6 Conveniently, the apparatus may be used in conjunction -with an adhesive coating 20 station 7- The coating station 7 rmy be any quitable coating station. but the present iovention is most conveniently used in conjunction with the coautin station disclosed in co.-pending UnitEed States patent application filed of even date here-wuii centitled -Method and Apparatus for Applying a Coating Material to Sheets" and commonly assigned to the Assignee of the present invention (corresponds to WO 96/05065), and the contents of that co-pending application are incorporated herein by reference- 4 Alternatively, the output of the present invention may be stored such as in stacked form and independently and subsequently coated with a separate coating station- The control and synchronization of he drives of the various stations may be per-formed by a centra electronic control unit (not shown), for example a Siemens PLC 135.

Indlivdual sieetai veone af nteraat e aerpah etyI of the apparatus and are fed by anip roll pair 10 into the double coating station 3 (shown In greater detail in FIGs 3 and It is one of the advantrages of the present inetoasf WO 96105066 PCTFIUS9S772 -compared to other arrangements, such as in the above identified U.S.

Patent No. 5,487,780 filed February 15, 1994 entitled "Met-dd and Apparatus for Applying a Coating Material to a Sheet", that the sheets are fed into the coating station in a non-overlapped condition. This exposes all, or a substantial portion, of both major surfaces of the sheets to coating by the LAB and the primer.

Further, handling of the sheets is more convenient, since the "pseudo-web" is of uniform thickness The sheets are preferably all of the same size, for example A2, and weight, for example 70 gsm. The paper may be of any convenient weight, including but not limited to papers having a weight between 45 grams per square meter (gsm) and gsm The double coating station 3 comprises an upper coating station 11 and a lower coating station 12 located, respectively above and below the paper path. As the sheets pass through the double coating station the upper station 11 applies a coating of prirer material to one side of each sheet and the lower station 12 simultaneously applies a 15 coating ofLAB material to the other side of each sheet In one embodiment of the S present invention, the primer material and the LAB mateial are coated over substantially both major surfaces of the sheets. Typically, mechanical means are used a. to grip and advance the sheets through the apparatus, preventing the primer and LAB i to be coated over the entire major surfaces of the sheets.

Paper is commonly formed by accumulating paper fibers on a wire mesh or screen and compressing the accumulated fibers between the screen and a "felt" or cloth layer opposite the screen layer This produces paper having a "wire" side and a "felt" S side. It has also been found advantages to convey the sheets S through the apparatus of the present invention with the "wire" side presented for coating of the release material and the "felt" side presented for coating of the primer and ultimately for coating of the adhesive.

The primer material may, for example be a water-based solution of an organic i- binding agent and a cleaved mineral pigment_ More specifically, the primer material may be obtained by mixing approximately 3-7% by weight of the binding agent MOWIOL (Trade Mark) arailable from Hoechst AG, Frankf;Jr/Main, Germany and g approximately 3-8% by weight of the pigment AEROSIL (Trade Mark) availble from -I Degussa AG, Frankfurt/Main, Germany with approximately 9Y0 by weight of water.

WO 96-05066 PCTfUS95BST72 6 The LAB matefial may be any suitable_ nateltal, including, but lirotted to, acrylate co-polymners, silicone materials, urethanes, and fluor 3 h xape the LAB may be a water-based solution of the material des-tdir4inEJ? 618509, filed March 31, 1994 and commonly a.;sigrned to the Assigne of the present (equivralent of EP 618509), the contents of which are incorporated herein by reference- The solution comprising typically from about 5% to about solid material- Other LAB materials that may be employed with the present invention include those disclosed in United States Patent Nos-. 5,202,190 and 5,032,460- The upper coating station I1I con.prises a metering roller 13 and a coating roller 14, located above the path of the sheets of paper throught he double coating.

station- The coating roller 14 cooperates With a coating drum 16 of the lower coating station 12 which also comprises a metering roller 17 and a transfer roller 1 8, all locared below the paper path through tht double coating station-. The coating drum 16 has a 15 cut-out portion 9 of rectangular cross-section (shown in greater detail in Figure 8) 'which contains a conventional sheet gripper 9A (shrwn closed in Finure 8) for graspinag sheets from the feed nip 10. In addition, the drum is covered, around less than half its circumference. with a blanket 20 (not shown in Fig- 8) whereby, as decrbed below, the coating roll-- 14 and coarine drum 16 form a coating nip only when the blanket is located directly adjacent the coating roller 14., .A--r.described beiow, the upper coating station I11 provides substantialy fulil surface roll coating oprimer j ~material on the upper surface ofthe sheets, nd the lower coating station 12 proildes substantially full suface roll coating of LAB material on the lower surfaze of .he 9=ets- In each casethe portions engaged with the gippers (as described herein) are 425 not coatedg In the upper coating station, a trough 15 for the printer material is formed by the sunfaces; of the metering and coating rollers 13. 14 adjacent the nip between the rollers and on the upper side thereof together with two opposed end walls (not shown) which engage in grooves (not shown) adacent' the ends ofzthe rollers. As the rollers; 13, 14 rotate, the priner material forms afilm on the coatinigroller14 and is traifrircd to a sheet passing undernecath the wller.

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SWO 9WNW 6 PCTIUS95/08772 Thethii ne~ ofth pir film on the coating roller 14, and hence the amount S:of primer coated onto asheet, is dependent on the viscosity of the primer and on the pressure between the metering and coating rollers 13, 14 and, for a given primer, can be adjusted by moving e metering roller towards or away from the coating roller thereby adjusting the pressure between therollers. The trough 15 is supplied with p rimer. nozzles 60 (see also Figure 5) which rceivethe primer from a tank 61 by m- eans ofa pump 62. The trough 15 also has overflow outlet through which excess primer is returned to the tank.

In the lower coating station 12, a trough 19 for LAB material is similarly 10 formed between the metering roller 17 and the transfer roller 18. As in-the-upper;_ S- station, thecoating material forms a film on the transfer roller, the thickness of which can be adjusted by moving the metering roller 17 towards or away from the transfer roller 18, thereby controlling the amount of LAB material that passes from the transfer roller to the blanket covering 20 on the coating drum 16 (but not on to the remainder '15 of the drum, which the transfer roller 18 does not contact).

In a'similar manner to the trough 15 in the upper coating station I Hthe trough S19 is supplied with LAB material by respective nozzles 60 (see also Figure 5) which receive the LAB material from a respective tank 61A by means of a pump 62A. The Strough 19 has overflow outlets 63A through which excess LAB material is returned to the tank 61A. As the blanket covers part of the drum 16 moves around adjacent ,he coating roller 14 of the upper station, a sheet that is incoming from the feed nip 10 of Sthe double coating statin 3 will be picked-up by the gripper 9A in the drim, ai carried through the coating nip between the roller 14 and the blanket 20 on the drum S. 16 and, as t h esheet passes through the nip, it will be coated on one side with the LAB material. Sheet strippers (not shown) are lcated on the downstream sides of the coating roller and the coating drum to ensure that sheets donot wrap around either the i roller or thedrum but are fed out to the overlapping station 4. The next sheet from the Sfeed roll nip 10 will be picked up and carried between the coating roller and the coating drum when the blaket covering onceagain moves around adjacent the roller S, '-30 14. It-will be appreciated that the coating in the double coating station 3 is discontinuous because it occurs only when the blanket covering 20 on the coating .Wo 96/s5066 PCT/US95/072 drum 16 is adjacent the coating roller 14 when a sheet is passing through the coating nip). A typical coating weight for the LAB material on the sheets is from about 0.5 gsm to about 12.0 gsm and the coating weight of the primer material would be matched to that to ensure that the coated sheets remain flat. Because the primer and the LAB materials are applied to the paper sheets simultaneously in the coating Sstation and are preferably selected to have appropriately selected characteristics, such as viscosity, solids, coating weights, the risk that the sheets will curl or wrinkle is substantially eliminated.

The blanket covering 20 on the coating drum 16 can be of any suitable type, for example a DuPont "CYRELL" polyurethane blanket available from E.I DuPont i Demours of Wilmington, Delaware.

.On the exit side of the coating nip 14, 16, in the sheet overlapping station 4 a gripper unit 27 is positioned to take sheets as they emerge from the coating nip and deposit them on a conveyor 30 (not shown in Figure The gripper unit 27, which is S 15 conventional, comprises sheet grippers 28 carried on an endless chain 29 the ovement of which is synchronized with the sheet feed so that a gripper 28 is positioned to receive ech sheet that leaves the coating nip. A blower 31, located below the paper path on the exit side of the coating nip, provides a cushion of air to i support the sheet as they are being carried by the sheet grippers 28. The blower 31 incorporates a heater (not shown) which serves to dry the LAB coating on thesheet to some extent, to prevent the sheets from sticking to the conveyor. The conveyor 30 is run at a slower speed than the chain 29 of the gripper unit so that each sheet is deposited on the conveyor with the leading edge of the sheet lying on top of the .Trailing edgeof the preceding sheet, forming a pseudo-web of sheets. Typically, the extent of the overlap is from about I centimeter (cm) to about 2 cm. The conveyor is a vacuum conveyor connected to a source32 of low pressure so that the sheets are positively held on the conveyor andthe overlapped relationship between them is maintained.

-At e output end of theconveyor 30, the sheets pass over an air knife 33 ged to dir a re ti which is arranged to reverse the direction in which the sheets are verlapped. The air kfe 33 is arranged to direct a current ofair at the sheets sothat the trailing edge of each sheet is moved out from ndeeath the leading edge of thesucceeding heet and I s: f' r W09 066 PCT/US95t08772 9 deposited instead on top of that leading edge. Instead of using an air knife 33 to change the direction of overlap of the sheets, an equivalent mechanical arrangement could be employed, for example an arrangement similar to that described in GB-A-2 166 717.

The double coating station 3 together with the sheet overlapping station 4 may be based on the "GUILA SPEED GS GS 8000" coater available from Billhofer Maschinenfabrik GmbH of Nfrnberg, Germany.

Returning to Figure 1, the pseudo-web ofsheets now moves out of the sheet overlapping station 4 and into the dryer 5 in which moisture is removed from the primer and LAB coatings. The dryer 5 is preferably a radio-frequency dryer, for example a particularly adapted version of the Model No. SP 890 GF'C" -AG S. manufactured by Proctor Strayfield Ltd. of Berkshire, England. The dryer 5 is S' provided with a control unit (not shown) which adjusts the power of the dryer in S. accordance with the line speed of the apparatus. That control unit may, for example, S, 15 be a Siemens PLC 55 95U interconnected with the central electronic control unit of the whole apparatus. The overlapped sheets move through the dryer 5 continuously on an endless belt 40 and are dried to attenuate the tendency of the sheets to curl but which .ensures that they emerge substantially dry. The use of a radio-frequency dryer is not S essential and the overlapped sheets could, instead, be dried using infra-red heating or hot air. Alternatively, the endless belt 40 could be heated to dry the sheets. However, I *d i t im ity radio-frequency drying is preferred for its simplicity and lower energy, consumption.

Downstream of the dryer 5, the overlapped sheets move through the guiding I. section 6 in which they are side registered and aligned with each other in preparation for advancement to further processing stations, such the adhesive coating station 7, previously identified as the subject of a co-pending United States patent application filed of even date herewith, entitled "Method and Apparatuslbr Applyng a Coating SMaterial to Sheets", and commonly assigned to theAsigee of the present invention (correspondsto WO 96/05065). As described in the above indicated co-pending Sapplication, the overlapped sheets pass through a transfer nip 50 (see also Fig. 6) where 30 they contact an endless transfer belt 51 to which an adhesive coating has previously ben i i 3 revilt The applied in the form of a plurality of stripes extending longitudinally othe belt. The adhesive my bea pressure-sensitive adhese,preferably a repositionable microsphere p: ressure-sensitive~ adhesive, S WO 910566 PCr/US9nmso72 for example as described in U.S. Patent No. 4,495,318 to Howard, or U.S. Patent No.

3,691,140 to Silver. Adhesives for use with the present invention also includes filmforming materials known in the art, including those containing organic solvents.

At the transfer nip 50, the adhesive is transferred in continuous stripes to the pseudo-web of overlapped sheets on the surface to which primer was applied in the double coating station 3. The adhesive-coated sheets are then pulled away from the transfer belt 51 at a vacuum roller 52 (shown in Figure 6) the interior of which is connected to a source of low pressure. The removal of the sheets from the transfer belt 51 is facilitated by the direction in which the sheets overlap by the fact that the air knife 33 has caused the leading edge of each sheet to underlap the trailing edge of the preceding sheet). Following removal from the transfer belt 51, the sheets are held to a vacuum belt 53 which passes around the roller 52 and carries the sheets (still S. overlapped) out of the adhesive coating station 7 to the sheet exit 8 of the apparatus.

'The sheets may then be stacked and trimmed to form pads of repositionable notes, for 15 example those available under the trademark "Post-it"® available from the Minnesota Mining and Manufacturing Company of St. Paul, Minnesota.

Although the above description refers to the sheets as being paper, they could S (as already mentioned) be formed of other materials, for example polymeric films or metallic foils, as previously described. When the sheets are paper, they are preferably fed through the apparatus with the "machine direction" of the paper sheets aligned with the machine process direction; in that way, the tendency of the sheets to curl or wrinkle can be further attenuated.

Sapers of different weights and textures can be used if desired. For example, s although the above description refers to a sheet size of A2, the described apparatus is S' 25 readily adaptable to handle sheets of A4 size. Likewise, although the above S description refers to sheets of weight 70 gsm, the apparatus could also handle sheets of higher weight e.g90gsm) andsheets of a lower ight 70 gsm and possibly even as low as 45 gsm).

If the sheets supplied to the double coating station 3 are pre-printed, the above- S:des:bed i method results in the LAB coating material being applied over theprinted matter on the sheets. The LAB coating then serves to protect the printed matter, especially against removal by the adhesive n an adjacent sheet when the sheets are V- II i i iii:,ii~l)' .I SWO 96/05066 PCTIUS95/08772 11 subsequently stacked and cut to form pads of repositionable notes. The protection offered by the LAB coating enables the use of stronger adhesives on printed notes to be considered. Of course, the sheets maybe printed on after the double coating station 3, whether or not pre-printed, using any conventional printing operation.

Although it is advantageous for the primer and LAB coating to be applied to the sheets simultaneously in the double coating station 3 as described above, that is not essential. However, the simultaneous application of the coatings is preferred, particularly when the coating materials are water-based, since it assists in maintaining the sheets in a flat condition.

Apparatus in which the primer and LAB coatings are not applied simultaneously is illustrated in Fig. 7. In that apparatus, the primer coating station I1 is located prior to the LAB coating station 12 and, consequently, the coating roller 14 of the upper station 11 and the coating drum of the lower station 12 both require a j respective counter-pressure roller 14A, 16A. In each coating station, the arrangement I S' 15 for supplying coating material to the coating roller/drum also differs from that shown S in Fig. I in that, in each case, the metering roller 13, 17 dips into a respective tank SI3A, 17A of coating material and applies the coating material to a respective transfer roller which, in turn, applies the coating material to the coating roller/drum 14, 16.

The remainder of the apparatus shown in Fig. 7 (comprising the overlapping station 4, the dryer 5, the guiding section 6 and the adhesive transfer station 7) is effectively as Sdescribed above with reference to Fig. 1.

SThe present invention has now been described with respect to several embodiments thereof. It will be apparent to those skilled in the art that many changes may be made in the embodiments described without departing from the spirit and scope of the invention. Thus, the scope of the present invention should not be limited to the structures and processes described herein, but rather by the language of the S claims, and the equivalents thereof.

Claims (6)

12- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method for applying water-based coating materials to both major surfaces of a plurality of sheet members, comprising the ordered steps of: S conveying the sheet members sequentially along the sheet path; applying a water-based primer material to one major surface of each sheet Smember and a water-based low adhesion backsize material to the other major surface of each J sheet member as the sheet members are being conveyed along the sheet path; depositing the sheet members successively on conveying means in the sheet path, S 10 wh-eby the leading edge portion of each sheet member is deposited on the S trailing edge portion of the preceding sheet member to form a pseudo-web of overlapped sheet S members; S directing a current of air at the overlapped sheet members to sequentially change Sthe relative overlapped positions thereof, whereby the trailing edge portion of each sheet member overlies the leading edge portion of each succeeding sheet member; and drying the overlapped sheet members as they are being conveyed along the sheet path. So.. S 2. The method of claim 1, further including the step of: applying a water-based adhesive material to the overlapped sheet S embers as they are being conveyed along the sheet path, the adhesive material being applied to the sheet members on the major surface to which primer material was applied in step 3: A method as claimed in claim 1, in which some at least of the sheet members S arepre-printed at least on the major surface to which the low adhesion backsize material is applied in step S L 1 t- 1paDOCSUWSEM3mD.rV-27/lO,99

13- 4. A method as claimed in claim 1, in which step comprises the steps of: conveying the overlapped sheet members along the sheet path on a belt which is non-reactive to radio-frequency radiation; and (ii) exposing the water based materials on the sheet members to radio frequency radiation to reduce the water content of the water-based materials to a desired level. A method as claimed in claim 1, including the further step of partially drying the sheet members after step on the major surface that is then deposited on the conveying 10 means. a 6. A method as cl2med in claim 1, in which the sheet members are overlapped by from about 1 cm to 2 cm. 7. A method as claimed in claim 2, including the step of aligning the sheet S members before the adhesive material is applied in step Apparatus for applying water-based coating material to both sides of a plurality :o of sheet members, the apparatus comprising: a conveyor for conveying the sheet members sequentially along a sheet path a dual coating station positioned to receive the sheet members sequentially from the conveyor, the dual coating station comprising first and second coating stations located on o pposite sides of the sheet path through the dual coating station, each of which first and second coating stations comprises arespective source of water based coating materialand a respective 25 coating member comprising a coatin rolle, the respective coating rollers being disposed in oppositerelationshi on opposite sides ofthe sheet path to form a coating nip whereby coating material from the respective source is applied simultaneously to both sides of a sheetmember an overlappingcnveyor arranged to receive sheet members from the dual 30 coating station and movable at such a speed that the leading edge portion of each sheet member Mlc VPDOCSALSPECU33LMrD-27flVW .fl. *e U r. U a A ai. as a S -14- leaving the dual coating station is deposited on the trailing edge portion of the preceding sheet member on the conveyor thereby forming a pseudo-web of overlapping sheet members; an air knife positioned to direct a current of air at the overlapped sheets to change the relative positions thereof in the pseudo-web whereby the trailing edge portion of each sheet member overlies the leading edge portion of the succeeding sheet member; and a dryer in the sheet path for removing water from the coating material applied to the sheet members in the dual coating station. 9. The apparatus of claim 8, further including: a further coating station comprising a source of water-based coating material, and a coating member positioned to contact the pseudo-web of overlapping sheet members at a point along the sheet path to apply coating material from the respective source to one side of the pseudo-web of overlapping sheet members. 10. Apparatus as claimed in claim 8, including a covering member over part of the circumference of one of the coating rollers whereby the coating nip is formed only when that part of the roller is located adjacent the other coating roller. 11. Apparatus as claimed in claim 10, in which the said one of the coating rollers 20 includes a sheet gripper for pulling each sheet member through the coating nip. 12. Apparatus as claimed in claim 11, including a further sheet gripper downstream of the dual coating station for removing each sheet member from the dual coating station and depositing the sheet member on the overlapping conveyor. cushion of air to su S- station. 4i-~- aratus as claimed in claim 8, including a blower positioned to provide a pportthe sheet members as they are being removed from the dual coating

14. Apparatus as claimed in claim 13, in which the blower includes a heater for partially drying the sheets on the side that is then deposited on the overlapping conveyor. Apparatus as claimed in claim 8, in which the dryer comprises a conveyor which is non-reactive to radio-frequency radiation and is arranged to convey the overlapped sheet member along part of the sheet path, and a source of radio frequency radiation directed to the water-based coating material on the sheet members.

16. Apparatus as claimed in claim 9, further including an aligning station located *I 10 in the sheet path to align the overlapping sheet members before they enter the further coating S station_

17. Apparatus as claimed in claim 9, in which the coating member in the further f coating station comprises a transfer belt having a transfer surface positioned to contact the overlapping sheet members at a point along the sheet path. or i

18. An apparatus for applying water-based coating material to a plurality of sheet members, substantially as hereinbefore described with reference to the accompanying drawings. s o DATED this 27th day of October, 1998. MINNESOTA MINNG AND MANUFACTURING COMPANY By Its Patent Attorneys SDAVIES COLLISON CAVE I