Method of Producing Multi-Ply Embossed Fibrous Webs

The invention will be more readily understood with reference to the accompanying drawings wherein FIG. 1 is a diagrammatic elevational view illustrating the basic elements of apparatus for carrying out the method of this invention; FIG. 2 is a perspective view illustrating operation of the apparatus of FIG. 1, and FIG. 3 is a fragmented view of a section of the two ply embossed web of FIGS. 1 and 2.

With reference to FIG. 1 of the drawings, webs or plies 11 and 12 of creped tissue stock suitable for use in multi-ply bathroom tissue products are drawn from supply rolls 13 and 14 and fed into the nip of embossing roll 16 and back up impression roll 17 where the webs are embossed simultaneously. The embossing roll typically has a steel surface provided with a plurality of engraved raised embossing elements. In a specific preferred embodiment, the embossing elements of roll 16 are essentially those disclosed in U.S. Pat. No. 4,659,608 wherein each design is made up of several embossing elements, each of which comprise lands about 0.02 inch wide and about 0.06 inch deep with sides of the lands sloped inwardly from bottom to top at an angle of about 25.degree. relative to the radii of the roll. Each design pattern measures about one inch in its longest dimension. In this preferred embodiment, the patterns are spaced apart about one quarter inch. A resilient back up roll 17 of rubber or similar material permits deep clean embossments in the tissue without rupturing the tissue.

In the method of this invention, as in the parent application, the plies of the multi-ply embossed sheet formed by the embossing roll 16 and its back up roll 17 are separated from one another after embossing. In the apparatus illustrated in the drawings, embossed web 12', after leaving the embossing roll, is passed directly to the first of the in-feed rolls 20, 21, 22, whereas embossed web 11' passes over rolls 18 and 19 before rejoining web 12' at in-feed roll 21. As illustrated in FIG. 2, rolls 18 and 19 serve not only as a positive means for separation of the embossed webs 11' and 12' but also serve to displace web 11' relative to web 12' in the longitudinal or machine direction and to smooth web 11'. In accordance with this invention, a smoothing roll 18 is provided between the impression roll 17 and in-feed roll 21 where it comes in contact with the raised embossments on web 11' tending to flatten embossed web 11' by smoothing out its embossments. The sheet 11' is held against smoothing roll 18 by displacement roll 19.

By displacing the embossed webs relative to one another, the originally nested bosses are so displaced relative to one another as to preclude nesting with one another as illustrated in FIG. 3. The extent to which the web 11' is longitudinally displaced relative to web 12' is determined by the relative lengths of the paths of the webs during their passage from embossing roll 16 to in-feed roll 21. The extent of displacement is easily adjusted to suit the particular embossment pattern by changing the position of the rolls 18 and 19 relative to the path of web 12' to shorten or lengthen the path of web 11' in passing from the embossing roll to the in-feed rolls. The smoothing roll may be placed on either side of the displacement roll relative to the path of the web 11'.

After the embossed webs have been recombined at rolls 21, and 22, the resulting multi-ply product is perforated by conventional perforating rolls (not illustrated).

Typical two-ply bathroom tissue is formed by first joining two webs of creped tissue and then embossing both webs simultaneously. The caliper of the resultant product may be tested on TMI Special Model 551-M motorized micrometer available from Testing Machines Incorporated, Amityville, New York. Eight two-ply sheets are interposed as a stack between parallel, two-inch diameter anvils and subjected to 539.+-.30 grams dead weigh load. Using this test method, two ply bathroom tissue embossed by the method of this invention has a caliper of from about 0.55 to about 0.95 inch which is preferably made essentially the same as or greater than that of two-ply bathroom tissue embossed with the same pattern which is not separated and recombined after it is embossed.

Leveling of the embossments in web 11', which in the finished product is the underside or hidden side of the towel or tissue when rolled on a hollow core, further "works" and softens web 11' increasing its absorbency and softness to the touch.