EP0077005B1

EP0077005B1 - Patterned dry laid fibrous web products of enhanced absorbency

Info

Publication number: EP0077005B1
Application number: EP82109199A
Authority: EP
Inventors: Michael P. Bouchette; Johannes A. Van Den Akker; William R. Watt
Original assignee: James River Dixie Northern Inc
Current assignee: Fort James Corp
Priority date: 1981-10-05
Filing date: 1982-10-05
Publication date: 1986-10-08
Also published as: JPS58144197A; DE3273640D1; DK439282A; ATE22713T1; EP0077005A1; CA1193919A

Abstract

A method of improving absorbency of air laid bonded fibrous cellulosic webs and tissue, towel and napkin products resulting therefrom comprising the step of imprinting at least one surface of the fibrous web (39) between a pair of cylindrical rolls (42) under a pressure of at least 100 pounds/lineal inch, the compacted area (51) of each imprinted web (50) surface being at least 40%, preferably at least 50%, of the total imprinted surface. In the preferred embodiment of the method, the fibrous web is first wetted with water, the imprinting step then being conducted with imprinting means heated to about 140 to about 180 DEG C.

Description

The present invention relates to a dry-laid fibrous web product of high bulk and enhanced absorbency rate comprising: (a) a web of randomly distributed wood pulp fibers; (b) an adhesive material substantially permeating said web, adjacent fibers being bonded to one another thereby, and (c) an imprinted pattern on at least one surface of said web, the pattern subdividing said surface into compacted regions and non-compacted regions in alternating relationship to one another, the area of the compacted regions being about 40% to about 80% of each imprinted surface and a method of making a dry-laid fibrous web product.
Imprinting of the web surface(s) to this degree densifies those interior portions of the web underlying each compacted area thereby promoting capillary tension and wicking to enhance web absorbency and wiping characteristics. The invention relates especially to tissue, towel and napkin products of high bulk and rapid absorbency obtained from bonded air laid cellulosic fibrous webs, in accordance with the method disclosed here. Preferably, a non-nesting pattern is imprinted on the web to prevent loss of final product size, e.g., product roll diameter.
Fibrous webs, particularly low basis weight webs between 3,6 and 27,2 kg per 279 m² (8 and 60 lbs. per ream (3,000 sq. ft.)), for use ultimately as tissue, towel and napkin products, are fabricated conventionally by two alternate processes. The older wet laid process dispenses an aqueous slurry of pulped paper-making fibers, generally natural cellulose fibers, onto a moving foraminous support means, e.g., a fourdrinier wire, the aqueous medium being removed through the support means by vacuum means. The wet laid web is thermally dried and taken up on a parent roll. Because of the presence of water, the wet laid fibers bond naturally to one another by means of hydrogen bonding. Such conventionally prepared webs are sometimes creped to improve feel and enhance absorbency. Similarly, the webs may be embossed to enhance softness and to provide a more aesthetic appearance.
The second, now conventional, yet relatively recent, process defiberizes cellulose pulp, the dry individual fibers being pneumatically transported to the dispensing means, and then dry laid (or air laid) onto the moving foraminous support means. Vacuum means below the support means is employed to ensure that the dry fibers remain on the web, which web has little inherent strength inasmuch as hydrogen bonds are not formed substantially in the absence of an aqueous medium. The dry, initially laid web is then sprayed with a synthetic bonding agent, such as a latex emulsion, preferably on both surfaces of the web. The bonding agent is cured by passing the thus treated web through a dryer, e.g. a through air dryer, before being taken up on a parent roll. These webs may also be creped and embossed.
Generally speaking, wet laid webs provide better wiping absorbency than dry laid webs. That is, under dynamic conditions of use, wet laid webs absorb liquid at a faster rate and retain the liquid thus absorbed better than their dry laid. counterpart. The slower rate of wiping absorbency associated with dry laid webs is primarily due to the greater volume of interstitial voids, existing within the reticulated structure of these webs.
The greater void volume is occasioned by the larger size, on average, of individual pores, as well as by the greater degree of reticulation extent in the overall web structure. These interstitial voids provide a greater interstitial liquid holding capacity under static conditions, but permit absorbed liquid to be squeezed back out more easily under dynamic wiping conditions. The net result is an appeared slower rate of wiping absorbency for dry laid webs. The advantages of greater void volume or bulk present in dry laid webs are several. Less fiber per ream is required to fabricate the web. The greater void size provides greater static liquid holding capacity, and typically contributes to a softer feeling web. Finally, dried laid webs have greater wet strength than conventional wet laid webs, and hence, do not break apart as readily during use. Thus, substantial improvement in wiping or dynamic absorbency characteristics would greatly improve product acceptance and usefulness.
Embossing and imprinting as used in this application are distinguished below, although terminology in the art is not uniform and does overlap.
In conventional embossing, a raised pattern is formed on a portion of a first web surface (the raised portion), with corresponding depressions in the remaining portion of said web surface (the depressed portion). These discontinuities in the first surface of the web are occasioned by passing the web between two cylindrical rolls, one of which is resilient, the other being inextensible and having a plurality of bosses thereon. The bosses contact the second surface of the web forming the raised areas (and depressions) on the first surface in contact with the resilient roll. Typically, the raises comprise about 20 to 30% of the total first surface area, the depressions accounting for the remaining area. Surface depressions are also formed on the second surface where the bosses come into contact with the web, these depressions being in alignment with the raises on the first surface. Embossing of this nature may result in products having a raised area approaching 60%, as in U.S. Patent 3,337,388 to Wosaba, which embossing improves softness, bulkiness and sponginess.
U.S. Patent 3616157 discloses an embossed non-woven fabric having a textured character and fabric-like qualities of softness and hand and suitable for wiping surfaces comprising a fibrous web containing at least one layer of overlapping, intersecting fibers, a pattern of intermittently spaced, embossed compacted fibrous areas lying in the planes of both surfaces of said web of overlapping, intersecting fibers and a pattern of unembossed, uncompacted fibrous portions lying between said planes and connecting said embossed, compacted fibrous areas.
Furthermore, U.S. Patent 4135024 discloses a method of simultaneously strengthening and decorating a low integrity dry-formed nonwoven fibrous web, said method comprising the steps of: (a) forming spaced-apart densified regions in the web to strengthen the web by embossing a front surface of the web with spaced-apart raised surfaces of an embossing roll, the densified regions being able to transmit a treating fluid completely through the thickness of the web from a rear surface of the web to the front surface thereof, and simultaneous with the embossing; (b) applying a treating fluid that includes a coloring agent to the rear surface of the web from a treating fluid conveying surface that is free of raised, spaced-apart web embossing areas for causing the fluid to be transmitted completely through the thickness of the web from the rear surface to the front surface thereof in substantially only the densified regions to thereby impart a valley print decorative effect in the front surface, the treating fluid conveying surface being disposed opposite the raised surfaces on the embossing roll and constituting a backing surface for the web during the step of forming the densified regions in said web.
Imprinting, on the other hand, as the term is used herein, compresses certain portions of a web surface in intaglio, the other surface not being raised thereby. Necessarily, imprinting densifies the compressed surface portions substantially more than embossing.
Imprinting, as opposed to embossing, has heretofore been used in wet laid processing in conjunction with subsequent creping as disclosed in, for example, U.S. Patents 4,191,609 and 4,125,659. In doing so the finally creped product exhibits greater softness, improved stretch and tensile strength, and enhanced bulk.
In dry formed webs surface imprinting, as hereinbefore defined, has been performed to improve the application of bonding agent to the web. In U.S. Patent 4,127,637 between about 15 to 40% of the web surface is compressed by cylindrical rolls prior to bonding, the pattern being then stabilized with binder to retain the differential density. The web is then creped to improve softness and bulk. Similarily, U.S. Patent 4,135,024 imprints one web surface, simultaneously applying binder to the other web surface, thereby enhancing permeation of the binder into said web. U.S. Patents 3,692,622 and 3,776,807 respectively disclose spot bonding of dry laid webs wherein 5 to 40% of the web surface is imprinted. In U.S. Patents 4,207,367 and 4,138,848, a plurality of highly compressed, narrow regions, preferably about 30% of the surface, separate the high loft regions, the high loft regions being bonded only partially.
Finally, embossing and imprinting are employed to laminate two webs together as disclosed in U.S. Patents 3,867,225.
It is an object of the present invention to provide an air laid fibrous web product of high bulk and enhanced wiping absorbency rate characteristics.
Another object of the present invention is to provide a method for the manufacture of the web product of the present invention.
These objects are achieved by a dry-laid fibrous web product according to claims 1 to 11 and a method of making a dry-laid fibrous web product according to claims 12 to 25.
To obtain the soft, bulky products of the invention which have improved wiping absorbency properties, an air laid bonded web is imprinted with a depressed design, preferably with a non-nesting pattern to avoid loss of final product roll diameter. In one embodiment of the method, the bonded web to be imprinted is wetted optionally with a spray of water and subjected to an areal pressure of at least about 1,10.10⁵Pa (16 Ibs./in²) by platen means, said means having been heated to a temperature of between about 140 to about 180°C. To improve wiping absorbency at least one surface of the treated web must have a compacted area of at least about 40% of the total imprinted surface area, preferably between 50% to 80% of the total imprinted surface area. Each side of the web may be so imprinted.
In the preferred embodiment of the method, the imprinting means is a pair of non-resilient cylindrical rolls adapted for imprinting the web continuously. While the levels of compaction are analogous, the applied pressure is at least 45,3 kg per lineal 2,54 cm (100 lbs. per lineal inch). Again, the imprinting means are heated to 140 to 180°C., and a water spray is optional.
The diameter of individual product rolls or the composite thickness of packaged product sheets of the present invention are preferably reduced not more than 10% as compared to unimprinted products. Depending on the pressure applied by the imprinting means, said reduction may approach between 20 and 30%. However, the wiping absorbency of products of the present invention is increased by at least about 25%, preferably about 40% or more, as ascertained by relative values of mirror wipe time between imprinted and unimprinted products.

Brief description of the drawings

Fig. 1 is a schematic diagram of a conventional dry laid papermaking operation, incorporating the imprinting means of the present invention.
Fig. 2 is a representation of a product web fabricated in accordance with the method of the present invention. The representation shown is not drawn to scale.
Figs. 3 and 4 are photomicrographs of conventional unimprinted and 100% compacted webs respectively, each enlarged 74 times.
Fig. 5 js a graph of absorbency rate as measured by mirror wipe time versus web density for totally compacted webs.
Fig. 6 is a representation of an alternate embodiment of the product web fabricated in accordance with the method of the present invention.

Referring to Fig. 1, a flow diagram of a process for making air laid webs, pulp sheets, laps or bales 10 are defiberized in defiberizer 11, here a hammermill, and transported pneumatically through line 12 to a distributor 14 by blower 13. Distributor arangements are well known in the art.
The individual fibers are dispersed onto an endless fourdrinier wire 15, which circles continuously about guide rolls 16. Vacuum means 17 draws and retains the loose fibers 18 onto the wire 15 to form a loose web 19 which has little integrity. The loose web 19 is typically pressed by consolidation rolls 21, which compaction increases web strength to a limited extent, and permits transfer of the pressed web 22 to a carrier wire 23. Wire 23 has larger perforations than wire 15 and is made typically from a synthetic plastic material. The use of a separate wire 23, then, is less likely to cause plugging with bonding material 26 from spray dispensing means 27, and will improve clean up. As shown in Fig. 1, the once bonded web 29, partially dried in dryer 28, is transferred from carrier wire 23 to a second carrier wire 31 where a second spray means 33 dispenses additional bonding material 32 onto the second surface of the web. While two bonding applications are shown, one application will suffice where the web is porous and has a low basis weight, e.g., less than about 9,1 kg per 279 m² (20 lbs. per 3000 sq. ft. ream). Additional information relating to a preferred process for bonding air laid webs is disclosed in commonly assigned U.S. Patent 4292271 entitled "Methods of Applying Bonding Materials Onto Fibrous Webs", filed December 28, 1979 by Pauls et al. After each bonding application, the web is at least partially cured in dryers 28, 35. If complete drying is not achieved in dryer 35, a curing oven 40 is provided.
As shown in Fig. 1, the bonded, cured web 39, and before take up on parent roll 41, is then imprinted at an imprinting station, here a pair of cylindrical rolls 42, although this location is not' critical. Alternatively, for example, station 42 can be situated between consolidation rolls 21 and bonding station 27, or between dryer 28 and bonding station 33. Indeed, the imprinting station may be located anywhere following the consolidation rolls 21. It should be noted that when the web is imprinted before the curing step, the compressive force applied by the imprinting means need not be as high as post curing imprinting because the pattern is less likely to "spring back". In another alternate embodiment, station 42 may be included as a step in the converting operation (not shown), either from parent rolls or individual product rolls. Preferably, it is less expensive to imprint webs before take-up on parent rolls rather than on individual product rolls during conversion because less capital investment is required. However, treatment of individual product rolls provides some additional flexibility in making products with several designs, which may be dictated by marketing considerations. If both sides of the web are to be imprinted, a second pair of cylindrical rolls is preferred. When platen means are used, however, only one pair of plates is necessary, each plate being provided with an etched surface.
Air laid products made in accordance with the process of Fig. 1, including webs imprinted (or embossed as hereinbefore defined) to achieve aesthetic improvement wherein the compacted surface area of the webs represents less than about 40% of the total surface area, are notably poor in absorption properties. This failing of prior art products is attributed to the inherently large pore volume between fibers in air laid webs. As discussed above, wet laid webs begin to bond as soon as they are laid. The high moisture content of the wet laid web, which decreases from about 99% per weight water beneath the head box to between about 65% to 85% just prior to consolidation, facilitates densification of the web. The water "lubricates" the web and "plasticizes" the fibers so that the individual fibers can come into close physical relationship with one another.
Air laid webs do not have water to lubricate the fibers, resulting in less dense webs with greater bulk and larger interstitial void volumes. While bulk is highly advantageous, the consequences of excessively large void volume are not. Compaction by the vacuum means 17 and the consolidation rolls 21 is not intended to highly densify the webs. Although it would be possible to increase the pressure of the consolidation rolls to highly compact the webs, the beneficial bulk provided by the air laid process would be lost. Furthermore, densification of the web by the consolidation rolls 21 would compromise the ability to disperse bonding agent 26, 32 through the web.
The invention disclosed herein can be used with air laid webs of between about 3,6 and 27,2 kg per 279 m² (8 and 60 Ibs. per ream (3000 sq. ft.)) basis weight which have been consolidated by rolls 21 with pressures of between 22,7 and 135,9 kg/lineal 2,54 cm (50 and 300 lbs./lineal inch.) and then bonded with a latex emulsion bonding agent, the bonding agent typically representing between about 10 to 30%, preferably between 15 and 25%, of the web basis weight. Typically, such webs have a bulk of between 1,78.10-² to about . 3,05.10-2 mm/0,45 kg/279 m² (0.7 to about 1.2 mils/lb./ream) and a wet MD tensile strength of at least 200 g per 7,62 cm (3 inch) strip. Dry CD tensile is between 500 and 1500 g per 7,62 cm (3 inch) strip. Applicants test these webs for absorbency rate using a mirror wipe test. In this test, a given amount of distilled water, 1.4 ml, is placed on a flat 61 cmx91 cm (24"x36") mirror. A sheet of given size, 71 cm² (11 inches square), is used to remove the water under hand applied pressure, the time therefore being measured with a stop watch. The time required, mirror wipe time (MWT), is a measure of the rate of absorbency of the product. Although this test appears, at first inspection, to be more subjective than mechanical test methods known in the art, applicants, through extensive usage, have found that the test achieves nearly the same degree of accuracy. More importantly, applicants have found that the test is more indicative of consumer utilization than the mechanical test procedure.
Furthermore, it should be understood that the test is being used herein to determine gross differences in absorbency rate so that the standard deviations of individual measurements are negligible by comparison.
Fully compressed webs were prepared by compaction between two flat plates under various compression loads, and tested for absorbency as tabulated below. For comparison purposes, the results for wet laid and dry laid uncompacted webs are included.
Caliper was measured with a Testing Machines, Inc. (Amityville, New York) Model 551M Micrometer having a 5,08 cm (2 inch) anvil.
Fig. 3 and 4 are photomicrographs of a conventional uncompacted air laid web and a compacted air laid web, respectively, each enlarged 74 times. As readily seen in the photographs, the densified web of Fig. 4 has much smaller interstitial voids between fibers as compared to the uncompacted web. Hence, capillary tension and wiping absorbency is increased in the web of Fig. 4 web as demonstrated by reduction in mirror wipe time. Note, however, that a significant loss in caliper occurs as a consequence of the compaction. This loss is more than about 80% in each instance. In Fig. 2, a web 50 representative of the invention was prepared using a pair of etched plates each having raised areas representing 69% of the plate. That is, about 69% of each surface of the web was compacted. The web so treated had a grid pattern illustrated in Fig. 2. As shown therein, the compacted areas 51 were about 2,02 cm² (5/16 inch square) (dimension x) and the non-compacted surfaces 52, e.g., the essentially uncompacted zones which appear as intersecting ribs or bridge regions, were about 0,16 cm (1/16") wide (dimension y). The depth of the compacted areas is dependent upon the pressure applied by the plates. The uncompacted web (Table I) had a basis weight of 19,5 kg/279 m² (43 lbs./ream), and a caliper of 1,13 mm (44.6 mils). Ideally, the imprinting of the web does not reduce the caliper of the non-compacted portions of the web, that is, dimension C_i, remains about 1,12 mm (44 mils). However, some reduction occurs, typically less than about 10%, but possibly approaching 20 to 30%. A compression load of about seven tons was applied between the plates for about 20 seconds.
The caliper C, of the imprinted web was measured as 0,79 mm (31 mils) with the Model 551 M Micrometer, as compared to 1,13 mm (44.6 mils) for the uncompacted web and as compared to less than 0,23 mm (9.04 mils) for the compacted webs. The loss in caliper is about 30% versus about at least 80% for the totally compacted webs. Conversely relative to the wet laid web, the caliper of the imprinted web is about 30% greater. Mirror wipe time for the imprinted web was measured at 17 seconds, which is an improvement of 46.9% over the conventional dry laid web.
While the actual pattern is not critical, it is essential that at least 40%, preferably more than 50%, of the area of one web surface be compacted. If both surfaces of web are compacted, each should be compacted to at least 40%, each preferably more than 50%. In the preferred embodiment, the plates or cylinders are heated to between 140 and 180°C., with water sprayed on the towel before pressing. The spray of water is not critical to the process, but it does aid in retention of the compaction.
Although the grid pattern of Fig. 2 is not critical to the concept of improved web absorbency rate by high compaction imprinting, the grid pattern does affect the end product beneficially in that the grid pattern prevents nesting of the compacted zones within one another when the web is taken up on a product roll. Thus, the roll of the invention web has essentially the same diameter as conventional products, which is preferred.
Fig. 6 illustrates an alternate embodiment of the web of the present invention. Although only one surface has received an imprinted pattern, both surfaces may be imprinted if desired. In this embodiment web 60 has compacted area 61 and a plurality of non-compacted areas. In contradistinction to the contiguous non-compacted bridge regions 52 of the web of Fig. 2, the web of Fig. 6 has contiguous compacted channel regions 61, which regions likewise represent at least 40% of the surface of the web so imprinted. As before, densified zones, here indicated by numeral 63, exist beneath the compacted area 61. These contiguous channel regions are desirable because they provided pathways for lateral wicking.
The data of Table I is reproduced graphically in Fig. 5. This graph, a plot of compacted web density versus Mirror Wipe Time, shows that the improvement in MWT is rapid until a density of about 0.35 g/cm³ is achieved, which value corresponds to a compression force of about 1,0.10⁵ Pa (15 Ibs./in.²). Thereafter, MWT increases slightly, an asymptote being reached at about 0.80 g/cm^3. It is believed that analogous relationships between MWT and web density are applicable to the product of this invention. The reduction in absorbency at the higher density values in Fig. 5 apparently occurs because the interstitial voids are too small to permit large amounts of water to be absorbed. For this reason, the densities of the densified web region are between about 0.20 to about 0.50 g/cm³, which would correspond roughly to MWT's below 14 and 13 seconds, respectively, for the webs of this invention. It should be noted that the optical density of 0.35 g/cm³ provides essentially equal absorbency as compared to conventional wet laid webs, that is, an MWT of about 11.5 seconds.

Claims

1. A dry-laid fibrous web product of high bulk and enhanced absorbency rate comprising:

(a) a web of randomly distributed wood pulp fibers;

(b) an adhesive material substantially permeating said web, adjacent fibers being bonded to one another thereby, and

(c) an imprinted pattern on at least one surface of said web, the pattern subdividing said surface into compacted regions and non-compacted regions in alternating relationship to one another, the area of the compacted regions being about 40% to about 80% of each imprinted surface,

characterised in that the portions of the web underlying the compacted regions have a density in the range of about 0.2 g/cm² to about 0.5 g/cm².

2. The product of claim 1 characterised in that the compacted regions preferably represent between 50 and 70% of each imprinted surface.

3. The product of claim 2 characterised in that the pattern is in the form of a grid comprising a plurality of discontinuous compacted regions and contiguous non-compacted bridge regions.

4. The product of claim 3 characterised in that each compacted region has an area between about 0,323 to 3,626 cm² (0.05 to 0.562 sq. in.) and the bridge regions have a width between about 0,127 to 0,254 cm (0.05 to 0.10 inch).

5. The product of claim 2 characterised in that the pattern is in the form of a grid comprising a plurality of discontinuous non-compacted regions and contiguous compacted channel regions.

6. The product of claim 5 characterised in that each non-compacted region has an area of between about 0,516 to 1,613 _CM ² (0.08 to 0.25 sq. in.) and the channel regions have a width of between about 0,381 to 0,914 cm (0.15 to 0.36 inch).

7. The product of claims 3 or 5 characterised in that the absorbency rate as measured by mirror wipe time (MWT) which is the time required for removing water under hand applied pressure on a flat mirror is reduced by at least 25% as compared to corresponding unimprinted web products.

8. The product of claim 7 characterised in that the densified web portions preferably have a compacted area density of between about 0.2 to about 0.5 g/c_m ³.

9. The product of claim 8 characterised in that the absorbency rate as measured by mirror wipe time (MWT) which is the time required for removing water under hand applied pressure on a flat mirror is reduced by at least 40% as compared to corresponding unimprinted web products.

10. The product of claim 8 characterised in that the absorbency rate as measured by mirror wipe time (MWT) which is the time required for removing water under hand applied pressure on a flat mirror is less than about 15 seconds.

11. The product of claims 1, 3 or 5 characterised in that each surface of the web is imprinted.

12. A method of making a dry-laid fibrous web product comprising

(a) randomly distributing dry fibers onto a moving foraminous support means to provide a dry loose web,

(b) bonding said web with an adhesive material, said adhesive material substantially permeating said web,

(c) curing said adhesive material prior to take-up of the cured web on a parent roll, and

(d) imprinting at least one surface of the web, each imprinted web surface having a pattern characterised by a compacted area of at least 40% of the total imprinted surface area,

characterised in that the dry loose web is consolidated between step (a) and (b) and the imprinting is performed at any step in the method subsequent to the consolidation of the dry loose web under a pressure sufficient to densify the portions of the web underlying the compacted areas to a density in the range of about 0.2 g/cm³ to about 0.5 g/cm³.

13. The method of claim 12 characterised in that the imprinting means is a pair of platen pressers, the pressure being at least 1,10.10⁵ Pa (16 !bs./sq. in.), and further comprising the step of first wetting the web with a spray of water, the imprinting step being further characterised in that the imprinting means are heated to a temperature of between about 140 to about 180°C.

14. The method of claim 12 characterised in that the imprinting means is a pair of cylindrical rolls, the pressure being at least 45,3 kg per lineal 2,54 cm (100 lbs. per lineal inch).

15. The method of claim 14 characterised in that the compacted area is preferably more than 50% of the total imprinted surface.

16. The method of claim 15 characterised in that the absorbency rate as measured by mirror wipe time (MWT) which is the time required for removing water under hand applied pressure on a flat mirror is reduced by at least 25% as compared to corresponding unimprinted web products.

17. The methods of claim 16 characterised in that the pressure applied to the web by the imprinting means is preferably between about 45,3 to about 226,5 kg per lineal 2,54 cm (100 to 500 Ibs/lineal inch).

18. The method of claims 12, 14 or 17 characterised in that it further comprises the step of first wetting the web with a spray of water, the imprinting step being further characterised in that the imprinting means are heated to a temperature of between about 140 to about 180°C.

19. The method of claim 18 characterised in that it further comprises the step of converting the parent roll into product rolls.

20. The method of claim 18 characterised in that the imprinting occurs between steps (a) and (b).

21. The method of claim 18 characterised in that the imprinting occurs between steps (b) and (c).

22. The method of claim 21 characterised in that the bonding step. (b) comprises the steps of (i) applying a first application of bonding material to one web surface, (ii) partially drying said first application of binding material, (iii) applying a second application of bonding material to the other surface, and (iv) partially drying said second application of bonding material, the imprinting step being performed after either drying operation.

23. The method of claim 18 characterised in that the imprinting occurs after curing.

24. The method of claim 19 characterised in that the imprinting occurs during the converting operation.

25. The methods of claims 12, 16, 18 or 22 characterised in that each surface of the web is imprinted.