Patent Description:
Consumer tissue products such as toilet paper, napkins, kitchen towels, facial tissue, and the like are frequently embossed. One application of embossing is to bond together multiple plies of tissue layers to produce a final product that is thicker and more absorbent than a single ply might allow. Embossing typically introduces some degree of texture or topographical variation. While in some products certain texture may be desirable, in other products it may undesirable, such as facial tissue where a relatively flat, smooth, non-abrasive surface is preferred.

As shown in <FIG>, embossing on tissue is generally carried out by passing the tissue webs between two rolls - an embossing roll and a counter roll. The multiple plies of tissue, upon passing between a nip formed between the two rolls, get embossed together. The embossing roll generally has protrusions, such as in the shape of small pins. The shape and size of the pins, the number and concentration of pins, and the pattern in which they are arranged can all be varied to effect the bonding, tactile, and aesthetics properties of the final product. The manner in which the both the embossing roll and the counter roll are engraved or otherwise shaped will also impact the final product properties. Three conventional tissue embossing technologies know to those of skill in the art are "matched-steel" embossing, "pin-to-flat" embossing, and "pin-to-pin" embossing.

Referring to <FIG>, in "matched-steel" embossing, protrusions are disposed in a pattern on the embossing roll. The counter roll is configured to have small cavities in the same number, same concentration, same shape and in the exact same positions as the pins disposed on the embossing roll. Thus, conventionally, the "female" pattern of cavities engraved in the counter roll matches exactly the "male" pattern of protrusions disposed on the embossing roll. In operation in this matched-steel approach, the embossing roll and the counter roll typically do not contact one another (other than on the supporting gear units), in part because the cavities are typically marginally bigger than the pins. In the matched-steel approach, precise alignment of the rolls relative to each other is important to prevent the pins from missing the cavities, which would crush the embossing roll pins against the flat surface of the counter roll.

The tissue product created by a matched-steel approach is a multi-ply tissue product with projections on one side and cavities on the other side. The plies are attached to each other quite well, by virtue of the plies being firmed pressed together at the embossment points. However, the presence of the projections in the final tissue product can result in an undesirable rough surface. This technology has the advantage of low wear and long roll life due to the lack of metal-to-metal contact between the rolls.

Referring to <FIG>, in "pin-to-flat" embossing, protrusions are disposed in a pattern on the embossing roll, as with matched-steel embossing. The counter roll, in contrast, is completely flat and smooth in the pin-to-flat approach. The ply embossing in this case relies on compressing the tissue between the pin and the flat surface of the counter roll.

The tissue product created by a pin-to-flat approach is a multi-ply tissue with cavities on one side and substantially flat and smooth on the other side. As the embossing is less aggressive with this approach than with the matched-steel approach, the attachment between the plies of the final product tends to be weaker. However, the tissue will feel smoother to the touch and have a flatter appearance, because there are no rough surfaces but instead cavities on one side and a flat and smooth surface on the other. Since in this approach the counter roll is completely flat, no alignment or registration between the rolls is necessary. However, zero-gap or even positive interference of the pins with the counter roll is necessary to achieve adequate embossing using solely the pin-to-flat approach. This can cause undesirable wear on the pins, necessitating more frequent regrinding of the embossing rolls leading to increased equipment costs and increased "downtime" of converting machines. Furthermore, the recent increased use of short fibers in the tissue making industry further exacerbates these problems, because short fibers tend to be more abrasive to steel equipment, and short fibers can reduce tissue bulk which further increases the difficultly to satisfactorily emboss the plies together.

Referring to <FIG>, in "pin-to-pin" embossing, protrusions are disposed on both the embossing roll and the counter roll, such that both rolls resemble the embossing roll of the pin-to-flat approach. The counter roll is configured to have pins in the same number, same concentration, and in the same positions as the pins disposed on the embossing roll. Precise alignment between the rolls is necessary, so that the tissue layers are compressed between two pins whose heads are aligned at the nip. The tissue product created by a pin-to-pin approach is a multi-ply tissue with cavities on both sides.

The three approaches described above each have certain benefits but also certain drawbacks as noted. What is needed is an embossing technique that can deliver strong ply-to-ply attachment, yet provide a substantially non-abrasive texture and a substantially smooth and flat appearance, and also provide reduced roll wear and reduced machine downtime stemming from roll changes.

<CIT> discloses a method of manufacturing a multilayer sheet that takes advantage of an elongation capacity of the material, conferred by the crepe, to emboss it. <CIT> discloses a tool and method for embossing layers of sheet-like materials, wherein stamping surfaces are arranged to extend at least partially at different distances or at certain angles to a reference line.

<CIT> which represents the closest prior art to the subject matter of claim <NUM> discloses a process to mate a plurality of tissue webs to form a composite web whereby a first steel roll having a first steel roll primary surface provided with protrusions and a second steel roll having a second steel roll primary surface with corresponding recesses, wherein the plurality of tissue webs is fed through the nip formed there between.

The present invention provides a process to mate a plurality of tissue webs as claimed in claim <NUM>.

In one embodiment, the process includes providing an embossing roll having an embossing roll primary surface, the embossing roll having first protrusions and second protrusions. Each first protrusion protrudes a first height from the primary surface, and each second protrusion protrudes a second height from the primary surface. The first height is greater than the second height. The embodiment further includes providing a counter roll having a counter roll primary surface, and the counter roll has recesses. The embodiment further includes forming a nip between the embossing roll and the counter roll; rotating the embossing roll about a first axis of rotation and rotating the counter roll about a second axis of rotation; and advancing the plurality of tissue webs through the nip. The first protrusions press a first series of portions of the plurality of tissue webs into the recesses proximate the nip as the embossing roll and counter roll simultaneously rotate to create a series of first embossments connecting the tissue webs to one another. Furthermore, the second protrusions press a second series of portions of the plurality of tissue webs against the counter roll primary surface as the embossing roll and counter roll simultaneously rotate to create a series of second embossments connecting the tissue webs to one another. The plurality of tissue webs thereafter define a composite web.

In the present invention, the process includes providing a first steel roll and a second steel roll, the first steel roll having a first steel roll primary surface and the second steel roll having a second steel roll primary surface. The first steel roll has first protrusions, and the second steel roll has recesses. The present invention further includes; forming a nip between the first steel roll and the second steel roll; rotating the first steel roll about a first axis of rotation and rotating the second steel roll about a second axis of rotation; and advancing the plurality of tissue webs through the nip. The present invention further includes embossing a series of first embossments and a series of second embossments into the plurality of tissue webs to connect the tissue webs to one another as the tissue webs advance through the nip. The first protrusions press a first series of portions of the plurality of tissue webs into the recesses proximate the nip as the first steel roll and second steel roll simultaneously rotate to create the series of first embossments. The second embossments are created by one of pin-to-flat and pin-to-pin embossing. The plurality of tissue webs thereafter define a composite web.

Referring to <FIG>, in embodiments, the present invention uses an apparatus <NUM> to mate a plurality of tissue webs 22a, 22b via embossing. The plurality of tissue webs can include two or more tissue webs, such as two, three, four, five, or more tissue webs. The apparatus <NUM> includes an embossing roll <NUM> having an embossing roll primary surface <NUM>. The embossing roll <NUM> includes first protrusions <NUM> and second protrusions <NUM>. In particular embodiments, each first protrusion <NUM> protrudes a first height <NUM> from the primary surface <NUM>, and each second protrusion <NUM> protrudes a second height <NUM> from the primary surface <NUM>. The first height <NUM> is greater than the second height <NUM>. In particular embodiments, the second height <NUM> is less than <NUM>%, more preferably less than <NUM>%, and still more preferably less than <NUM>% of the first height <NUM>. "Embossing roll primary surface" means the surface and regions, defined by the circumferential plane occupied by the substantially flat portions of the embossing roll <NUM>, that extend between and around the first and second protrusions <NUM>, <NUM>. The protrusions <NUM>, <NUM> can take any suitable form, such as pins, cones, pyramids, lines, bars, and the like. The cross-section of the protrusions can define any suitable shape, such as circular, rectangular, triangular, oval, rhomboid, irregular, or other shape.

The apparatus also includes a counter roll <NUM> having a counter roll primary surface <NUM>. The counter roll includes recesses <NUM>. "Counter roll primary surface" means the surface and regions, defined by the circumferential plane occupied by the substantially flat portions of the counter roll <NUM>, that extend between and around the recesses <NUM>. "Substantially flat portions" as used in the context of the preceding definition includes portions that have a slight curvature attributable to the convexity of the counter roll <NUM> itself, and further includes portions that have a minimal recess due to such factors as manufacturing wear or to a minimal recess imparted by the manufacturing process of the counter roll. "Minimal recess" as used in the context of the preceding definition means a recess or indentation having a depth, measured from the circumferential plane to the deepest part of the recess, of <NUM> millimeters or less.

The embossing roll <NUM> is rotatable about a first axis of rotation <NUM> and the counter roll <NUM> is rotatable about a second axis of rotation <NUM>. The embossing roll <NUM> and the counter roll <NUM> together form a rotary nip <NUM>, and are positioned with respect to each other such that the first protrusions <NUM> individually extend into the recesses <NUM> proximate the nip <NUM> as the embossing roll <NUM> and counter roll <NUM> simultaneously rotate. The embossing roll <NUM> and counter roll <NUM> are further positioned next to each other such that the second protrusions <NUM> do not extend into the recesses <NUM> as the embossing roll <NUM> and counter roll <NUM> simultaneously rotate. In particular embodiments, the second protrusions <NUM> contact the counter roll <NUM> proximate the nip <NUM> as the embossing roll <NUM> and counter roll <NUM> simultaneously rotate when no tissue webs 22a, 22b are present, as representatively illustrated in <FIG>.

The first protrusions <NUM> and the second protrusions <NUM> together define a total number of protrusions. In particular embodiments, the first protrusions <NUM> make up less than <NUM>% of the total number of protrusions, and/or the second protrusions make up at least <NUM>% of the total number of protrusions. In another embodiment, the first protrusions <NUM> make up less than <NUM>% of the total number of protrusions, and/or the second protrusions <NUM> make up at least <NUM>% of the total number of protrusions. In yet another embodiment, the first protrusions <NUM> make up less than <NUM>% of the total number of protrusions, and/or the second protrusions <NUM> make up at least <NUM>% of the total number of protrusions. In particular embodiments, no first protrusion <NUM> is adjacent another first protrusion <NUM>. In alternative embodiments, every first protrusion <NUM> is adjacent at least one other first protrusion <NUM>.

Referring again to <FIG>, the present invention pertains to a process <NUM> to mate a plurality of tissue webs 22a, 22b. In embodiments, the process <NUM> includes providing an embossing roll <NUM> and a counter roll <NUM> as described above in conjunction with the apparatus aspect of the invention. In these embodiments, the process further includes forming a rotary nip <NUM> between the embossing roll <NUM> and the counter roll <NUM>, rotating the embossing roll <NUM> about a first axis of rotation <NUM>, and rotating the counter roll <NUM> about a second axis of rotation <NUM>. In these embodiments, the process further includes advancing the plurality of tissue webs 22a, 22b through the nip <NUM>. As the webs 22a, 22b pass through the rotary nip <NUM>, the first protrusions <NUM> press a first series of portions <NUM> of the plurality of tissue webs 22a, 22b into the recesses <NUM> proximate the nip <NUM> as the embossing roll <NUM> and counter roll <NUM> simultaneously rotate to create a series of first embossments <NUM> connecting the tissue webs 22a, 22b to one another. The second protrusions <NUM> press a second series of portions <NUM> of the plurality of tissue webs 22a, 22b against the counter roll primary surface <NUM> as the embossing roll <NUM> and counter roll <NUM> simultaneously rotate to create a series of second embossments <NUM> connecting the tissue webs 22a, 22b to one another. After being embossed together, the plurality of tissue webs 22a, 22b together define a composite web <NUM>.

The series of first embossments <NUM> and the series of second embossments <NUM> together define an embossing pattern <NUM>. <FIG> representatively illustrates a composite web <NUM>. One embossing pattern <NUM> defines one product length <NUM> in the machine direction <NUM> of the process <NUM> and one product width <NUM> in the cross-machine direction <NUM> of the process <NUM>. In particular embodiments, the process further includes cutting individual tissue products <NUM> from the composite web <NUM>, wherein each individual tissue product <NUM> includes one embossing pattern <NUM>. The exemplary composite web <NUM> shown in <FIG> has a composite web width equal to four product widths <NUM>.

Referring to <FIG>, in particular embodiments of the process <NUM>, individual tissue products <NUM> emerge from the process <NUM>, and the first embossments <NUM> and the second embossments <NUM> together define a total number of embossments <NUM>. In particular embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up at least <NUM>% of the total number of embossments <NUM>. In other embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up at least <NUM>% of the total number of embossments <NUM>. In yet other embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> comprise at least <NUM>% of the total number of embossments <NUM>.

For example, in the embodiment of <FIG>, the first embossments <NUM> make up <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up <NUM>% of the total number of embossments <NUM>. The pattern <NUM> of <FIG> is predominantly made up of rhomboid figures defined by intersecting wavy lines of dot embossments. In this embodiment, half of the intersection points of these wavy lines of dot embossments are first embossments <NUM> (i.e., "matched steel" embossments). In <FIG>, the first embossments <NUM> appear as dots, and each first embossment <NUM> is labeled on the top side region of the tissue product <NUM>. All dots not labeled <NUM> are second embossments <NUM> (i.e., "pin to flat" embossments). The remaining three side regions of the tissue product <NUM> contain a distribution and arrangement of first and second embossments <NUM>, <NUM> that is similar to that in the top side region.

In another example, in the embodiment of <FIG>, the first embossments <NUM> make up <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up <NUM>% of the total number of embossments <NUM>. The pattern <NUM> of <FIG> is, like that of <FIG>, predominantly made up of rhomboid figures defined by intersecting wavy lines of dot embossments. In this embodiment, all of the intersection points of these wavy lines of dot embossments are first embossments <NUM> (i.e., "matched steel" embossments). In <FIG>, the first embossments <NUM> appear as dots, and each first embossment <NUM> is labeled on the top upper left region of the tissue product <NUM>. All dots not labeled <NUM> in this top upper left region are second embossments <NUM> (i.e., "pin to flat" embossments). The remaining portions of the tissue product border region contain a distribution and arrangement of first and second embossments <NUM>, <NUM> that is similar to that in the top upper left region.

In another example, in the embodiment of <FIG>, the first embossments <NUM> make up <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up <NUM>% of the total number of embossments <NUM>. The pattern <NUM> of <FIG> is, like that of <FIG> and <FIG>, predominantly made up of rhomboid figures defined by intersecting wavy lines of dot embossments. In this embodiment, each point embossment having no other embossment along an imaginary straight that extends between it and the perimeter edge <NUM> (and that is perpendicular to the perimeter edge <NUM>) of the tissue product <NUM> is a first embossment <NUM> (i.e., "matched steel" embossment). In <FIG>, the first embossments <NUM> appear as dots, and each first embossment <NUM> is labeled on the top upper left corner of the tissue product <NUM>, and all similarly positioned dot embossments around the periphery region of the tissue product <NUM> are first embossments <NUM>. All other dots are second embossments <NUM> (i.e., "pin to flat" embossments).

In particular embodiments, no first embossment <NUM> is adjacent another first embossment <NUM>. Examples of such embodiments are shown in <FIG> and <FIG>. In other embodiments, every first embossment <NUM> is adjacent at least one other first embossment <NUM>. An example of such an embodiment is shown in <FIG>.

It should be noted that modifications of the above-described apparatus and process aspects of the invention can be made, and still achieve certain advantages offered by particular embodiments of the invention. For example, as noted in <FIG>, the second protrusions <NUM> can be moved from the roll <NUM> to the roll <NUM>. In such an embodiment, the second protrusions <NUM> will press the multi-ply tissue web (not shown) against the primary surface <NUM> of the roll <NUM>. Thus, the embodiment still combines aspects of both "matched steel" and "pin-to-flat" techniques, but, as representatively illustrated in <FIG>, the depressions <NUM> of the second embossments <NUM> of the resulting tissue product will have been moved from the first side <NUM> to the second side <NUM>. In another example, as noted in <FIG>, the roll <NUM> can further include third protrusions <NUM>. In such an embodiment, the second protrusions <NUM> of the roll <NUM> will press the multi-ply tissue web (not shown) against the third protrusions <NUM> of the roll <NUM>. Thus, the embodiment combines aspects of both "matched steel" and "pin-to-pin" techniques, and, as representatively illustrated in <FIG>, the second embossments <NUM> on the first side <NUM> of the resulting tissue product will have second depressions <NUM> on the first side <NUM> and third depressions <NUM> on the second side <NUM> that are perfectly aligned with the second embossments <NUM> in the machine direction and cross-machine direction of the process.

Referring to <FIG> and <FIG>, an example of a tissue product <NUM> includes a first tissue ply 122a and a second tissue ply 122b superposed over the first tissue ply 122a. The first tissue ply 122a and second tissue ply 122b are connected together via first embossments <NUM> and second embossments <NUM>. The tissue product <NUM> has a first side <NUM>, a second side <NUM>, and a primary plane <NUM>. The first embossments <NUM> define a series of first depressions <NUM> on the first side <NUM> and a series of protuberances <NUM> on the second side <NUM>. The second embossments <NUM> define a series of second depressions <NUM> on the first side <NUM>. The second embossments <NUM> have substantially no protuberances on the second side <NUM>. "Substantially no protuberances" as used herein means both no protuberances and with slight protuberances having a height of <NUM> millimeters or less.

Referring to <FIG>, in particular embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up at least <NUM>% of the total number of embossments <NUM>. In other embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> make up at least <NUM>% of the total number of embossments <NUM>. In yet other embodiments, the first embossments <NUM> make up less than <NUM>% of the total number of embossments <NUM>, and the second embossments <NUM> comprise at least <NUM>% of the total number of embossments <NUM>.

In particular embodiments, the first side <NUM> of the tissue product <NUM> defines a first side area, and an aggregate area of the first embossments <NUM> and the second embossments <NUM> occupies at most <NUM>% and more particularly at most <NUM>% of the first side area. In particular embodiments, an aggregate area of the first embossments <NUM> and the second embossments <NUM> occupies at most <NUM>% and more particularly at most <NUM>% of the area of the first side extending within a <NUM> centimeter wide outermost periphery of the product (where the majority of the embossments holding the plies together are in particular embodiments located). In particular embodiments, at least <NUM>% of the first embossments are adjacent the perimeter edge <NUM>. "Adjacent the perimeter edge" as used herein means within <NUM> centimeter of the perimeter edge <NUM>.

Preferably, the first depressions <NUM> are deeper than the second depressions <NUM>, as representatively illustrated in <FIG>. In particular embodiments of the tissue product <NUM>, the second embossments <NUM> comprise no protuberances on the second side <NUM>. In other embodiments, the second embossments <NUM> can include third depressions <NUM> on the second side <NUM>, as representatively illustrated in <FIG>. This latter embodiment could occur when the second embossments are created via a "pin-to-pin" technique, as opposed to "pin-to-flat.

In particular embodiments, this invention merges "matched steel" techniques with one or both of "pin to flat" and "pin to pin" embossing techniques in a single dual-roll embossing unit. The resulting surface effect of this product in particular embodiments is one in which many or most regions are relatively smooth to the touch (being associated with the "pin to flat" or "pin to pin" techniques), with a minority of points having protuberances (being associated with the "matched steel" technique).

Claim 1:
A process to mate a plurality of tissue webs (22a. 22b), the process comprising:
providing a first steel roll (<NUM>) and a second steel roll (<NUM>), the first steel roll (<NUM>) having a first steel roll primary surface (<NUM>) and the second steel roll (<NUM>) having a second steel roll primary surface (<NUM>), wherein the first steel roll (<NUM>) comprises first protrusions (<NUM>), and wherein the second steel roll (<NUM>) comprises recesses (<NUM>);
forming a nip (<NUM>) between the first steel roll (<NUM>) and the second steel roll (<NUM>);
rotating the first steel roll (<NUM>) about a first axis of rotation and rotating the second steel (<NUM>) roll about a second axis of rotation;
advancing the plurality of tissue webs (22a, 22b) through the nip (<NUM>); and
embossing a series of first embossments (<NUM>) and a series of second embossments (<NUM>) into the plurality of tissue webs (22a, 22b) to connect the tissue webs (22a, 22b) to one another as the tissue webs (22a, 22b) advance through the nip (<NUM>),
wherein the first protrusions (<NUM>) press a first series of portions (<NUM>) of the plurality of tissue webs (22a, 22b) into the recesses (<NUM>) proximate the nip (<NUM>) as the first steel roll (<NUM>) and second steel roll (<NUM>) simultaneously rotate to create the series of first embossments (<NUM>),
wherein the second embossments (<NUM>) are created by one of pin-to-flat and pin-to-pin embossing,
the plurality of tissue webs (22a, 22b) thereafter defining a composite web (<NUM>).