Tissue product and method and apparatus for producing same

Abstract

A tissue product includes at least one ply with embossed protrusions defining an interior volume, the embossed protrusions including a base, a top surface and a sidewall extending from the top surface to the base, wherein the sidewall of at least 10% of the embossed protrusion is provided with an indent region shaped such that the sidewall bends towards the interior volume of the embossed protrusion.

Claims

1. A tissue product, comprising at least one ply with embossed protrusions defining an interior volume, the embossed protrusions comprising a base, a top surface and a sidewall extending from the top surface to the base, wherein the sidewall of at least 10% of the embossed protrusion is provided with an indent region shaped such that the sidewall bends towards the interior volume of the embossed protrusion.

2. The tissue product according to claim 1, wherein the embossed protrusions have general omega-shaped cross-section in a plane cutting through the sidewall and the top surface.

3. The tissue product according to claim 1, wherein the embossed protrusions comprise a first cross-sectional area (A.sub.1) at the base, a second cross-sectional area (A.sub.2) at the top surface parallel to the first cross- sectional area (A.sub.1), and a third cross-sectional area (A.sub.3) between and parallel to the first and second cross-sectional areas (A.sub.1, A.sub.2), wherein the third cross-sectional area (A.sub.3) is smaller than both the first and second cross-sectional areas (A.sub.1, A.sub.2).

4. The tissue product according to claim 3, wherein the third cross-sectional area (A.sub.3) between and parallel to the first and second cross-sectional areas (A.sub.1, A.sub.2) is at least 2% smaller than the second cross-sectional area (A.sub.2) at the top surface.

5. The tissue product according to claim 3, wherein the height (h) of the indent region over the base of the embossed protrusion is at least 5% of the total height (H) of the embossed protrusion extending from the first cross-sectional area (A.sub.1) at the base to the second cross-sectional area (A.sub.2) at the top surface.

6. The tissue product according to claim 1, further comprising at least one further ply, wherein the embossed protrusions extend towards the at least one further ply.

7. The tissue product according to claim 1, wherein the indent region runs around the circumference of the embossed protrusion and extends into the volume of a virtual truncated cone formed by the first cross-sectional area (A.sub.1), the second cross-sectional area (A.sub.2) and a mantle surface connecting the circumference of the first cross-sectional area (A.sub.1) and the circumference of the second cross-sectional area (A.sub.2).

8. The tissue product according to claim 1, wherein the indent region fully surrounds the embossed protrusion.

9. The tissue product according to claim 1, wherein the density of the embossed protrusions is at least 2 protrusions/cm.sup.2.

10. The tissue product according to claim 1, wherein the embossed protrusions have a minimum diameter at the top surface of about 0.3 mm.

11. The tissue product according to claim 1, wherein the height (H) of the embossed protrusions is between 0.1 mm and 5 mm.

12. The tissue product according to claim 1, wherein the angle (α) between the overall slope of the sidewall of the embossed protrusions and the direction perpendicular to the base is less than 40°.

13. The tissue product according to claim 6, wherein the plies are adhesively bonded to each other.

14. A method of producing a tissue product according to claim 1, comprising: (a) embossing a tissue material in an embossing unit for embossing a single web and/or embossing and laminating a multi-ply tissue web to create the embossed protrusions; (b) compressing the embossed tissue web in a protrusion compression unit in order to reduce its thickness and create the indent region of the sidewalls; and (c) directing the tissue web through a rewinding station.

15. The method of producing a tissue product according to claim 14, wherein the protrusion compression unit is either upstream of the rewinding station or an integral part of the rewinding station.

16. The method according to claim 15, wherein the operation of the protrusion compression unit upstream of the rewinding station comprises the step of directing the embossed tissue web into the gap between two parallel rolls, wherein the gap between the two parallel rolls has a size between 0 mm and 0.3 mm.

17. The method according to claim 14, wherein the protrusion compression unit is an integral part of the rewinding station and comprises a driven roll and a second roll parallel to the driven roll and not being driven, wherein the embossed tissue web is compressed in the gap between the driven roll and the second roll.

18. The method according to claim 14, further comprising, after step (c): (d1) rolling the tissue web to obtain a rolledtissue material product.

19. The method according to claim 14, further comprising, after step (c): (d2) folding the tissue web to obtain a folded tissue product.

20. The method according to claim 18, further comprising perforating the tissue web before step (d1) or (d2).

21. An apparatus for carrying out the method according to claim 14, comprising: an embossing unit for embossing a single web or embossing and/or laminating a multi-ply tissue web; a protrusion compression unit for reducing the thickness of the embossed tissue web and creating the indent region of the sidewalls; and a rewinding station.

22. The apparatus according to claim 21, wherein the protrusion compression unit is either upstream of the rewinding station or integral part of the rewinding station.

23. The apparatus according to claim 22, further comprising: either a winding unit for forming a roll of the tissue product or a folding unit for providing a folded tissue product; and/or a perforating unit for perforating the tissue web in predetermined intervals perpendicular to the longitudinal extension of the tissue web.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings,

(2) FIG. 1 schematically shows an embodiment of a process for manufacturing an embodiment of the tissue product;

(3) FIG. 2 schematically shows a cross-sectional view of an embodiment of a two-ply tissue product with an embossed protrusion;

(4) FIG. 3 schematically shows a cross- sectional view of another embodiment of a two-ply tissue product with an embossed protrusion;

(5) FIG. 4 shows a cross-sectional view of a conventional two-ply tissue product.

(6) FIG. 5 shows a table comparing a tissue product according to an embodiment of the invention to a conventional product.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(7) In the following description of particular embodiments, the same reference numerals will be used for the same or similar elements.

(8) In FIG. 4, a cross-sectional view of a conventional two-ply tissue product is shown. A ply 10 of tissue material is provided with an embossed protrusion 12. In the example according to FIG. 4, the ply 10 is laminated to a second ply 20 in a nested arrangement. To this end, the second ply 20 is also provided with an embossed protrusion 22. The embossed protrusion 12 of the first ply 10 is arranged such that it extends into the embossed protrusion 22 of the second ply. Ply bonding between the plies 10 and 20 is achieved by means of a glue 30 applied to the top surface 14 of the embossed protrusion 12 before the two plies 10, 20 are laminated together in a conventional way. The embossed protrusion of FIG. 4 has a sloped sidewall connecting the top surface of the embossed protrusion and its base.

(9) Cross-sectional views of embossed protrusions in embodiments of a tissue product are shown with reference to FIGS. 2 and 3. In the examples of FIGS. 2 and 3, the two plies 10 and 20 are arranged in a pin to flat arrangement. This, however, is only an example and a nested arrangement as shown in the example of the conventional product in FIG. 4 is also possible like the arrangement of two plies in a pin-to- pin arrangement. Further, it should be noted that, although the specific examples of FIGS. 2 and 3 only refer to a two-ply product, the tissue product can be a single ply product, or can have more than two plies.

(10) As shown in both FIGS. 2 and 3, the embossed protrusion 12 is provided with a top surface 14 adhesively bonded with glue 30 to the second ply 20. Further, the sidewall 16 is provided with an indent region 18 within a certain part of the sidewall 16 in which the sidewall bends towards the interior volume 24 of the embossed protrusion 12. Although in the drawings, only cross-sectional views are shown, the indent regions in which the sidewall bends towards the interior volume of the embossed protrusions runs all around the embossed protrusion.

(11) As can be seen in FIGS. 2 and 3, the embossed protrusions 12 are compressed. Their height H is between 0.1 mm and 10 mm, between 0.2 mm and 8 mm, or between 0.25 mm and 5 mm. The shape of the embossed protrusions is such that they form an undercut in the indent region. Such indent region cannot be formed by using a conventional embossing process because an embossing protrusion in a conventional embossing roll cannot be shaped such that it generates such an undercut geometry of an embossed protrusion.

(12) When defining a first cross-sectional area A.sub.1 at the base and a second cross-sectional area A.sub.2 at the top surface 14 of the embossed protrusion 12, it can be seen that, like in the conventional embossed protrusion as shown in FIG. 4, the second cross-sectional area A.sub.2 is smaller than the first cross-sectional area A.sub.1. However, what is striking is that a third cross-sectional area A.sub.3 between and parallel to the first and second cross-sectional areas A.sub.1, A.sub.2 can be defined at the indent region. This cross-sectional area A.sub.3 is smaller than both the other two cross-sectional areas A.sub.1, A.sub.2 which characterizes the bending inwards of the sidewall 18 of the embossed protrusion 12.

(13) In particular embodiments, the cross-sectional area A.sub.3 is at least 2% and up to 60% smaller than the second cross-sectional area A.sub.2 at the top surface of the embossed protrusion.

(14) Further, it can be seen in FIG. 2 that the sidewall 16 of the embossed protrusion 12 folds inwards with relatively sharp turns which only have a very small radius. A slightly different geometry to that as shown in FIG. 2 is shown in FIG. 3 which can be compared generally to an Ω-shape. The indent region 18 of the embossed protrusion 12 is relatively close to the continuous base surface of the tissue web including the first cross-sectional area A.sub.1. The position at which the sidewall 16 has the most pronounced extension towards the interior volume 24 of the embossed protrusion is where the third cross-sectional area A.sub.3 is defined. As can be seen in FIG. 3, the third cross-sectional area A.sub.3 is at a height h above the base at the position of the first cross-sectional area A.sub.1. In particular embodiments, the height h of the third cross-sectional sectional area A.sub.3 above the first sectional-area A.sub.1 is considerably smaller than the height H between the first cross-sectional area A.sub.1 and the second cross-sectional area A.sub.2. The height h ranges between 5% and 30% of the total height H of the embossed protrusion 12.

(15) Further, in FIG. 3 the slope of the embossed protrusion 12 is shown. It can be defined as the angle between the extension perpendicular to the base surface of the web and the imaginary line connecting the rim of the first cross-sectional surface area A.sub.1 at the base and the rim of the second cross-sectional surface area A.sub.2 at the top surface of the embossed protrusion 12. The slope defines the initial shape of the embossed protrusion (not shown) which is similar to that as shown in FIG. 4 but before the compression leading to the claimed shape with the indent region 16 took place. For easy reference, the slope angle α is also shown in FIG. 4 referring to the conventional geometry of the embossed protrusion.

(16) With respect to the dimensions of an embossed protrusion 12, the tissue product was found to show good properties if the embossed protrusions 12 has a minimum diameter at the base of about 0.3 mm, preferably of about 0.4 mm. In an embodiment, the minimum diameter at the base is about 1 mm. The minimum diameter at the top surface is about 0.3 mm. In an embodiment, the minimum diameter at the top surface of the embossed protrusions is about 1 mm. With respect to the density of the protrusions on the ply 10, it was found to provide good properties in terms of absorbency and softness if there are at least 2 protrusions/cm.sup.2, or at least 5 protrusions/cm.sup.2. The best results were achieved if there are at least 10 protrusions/cm.sup.2 and up to 50 protrusion/cm.sup.2.

(17) In FIG. 1, the general process for manufacturing a product according to FIG. 2 or FIG. 3 is shown. Referring to a two-ply or three-ply embossing and lamination apparatus, the ply 10 is embossed in the nip between a first embossing roll 40 and a cooperating anvil roll 42. In particular embodiments, the embossing roll 40 is made of steel, whereas the cooperating anvil roll 42 is made of rubber. When the ply 10 has been embossed and runs over the embossing surface of the steel embossing roll 40, adhesive is applied to the top surfaces of the embossed protrusions by means of the glue applicator device 44 as is conventionally used. It can be used to apply colored glue to all or a part of the embossed protrusions. The second ply 20 also runs through the embossing nip of a steel embossing roll 46 and a rubber anvil roll 48. Such an embossing equipment, however, can be omitted if, like in the case of FIGS. 2 and 3, a pin-to-pin flat arrangement of the two plies is contemplated. If, however, a nested arrangement of the plies 10 and 20 of the plies 10 and 20 is contemplated, the second embossing station with the steel embossing roll 46 and the rubber anvil roll 48 is used.

(18) The two plies 10 and 20 are laminated together by means of a conventional marrying roll 50 cooperating with the steel embossing roll 40. By means of the marrying roll 50 made of an elastic material, the plies 10 and 20 pressed together and laminated together by means of the glue which has been aligned by means of the glue applicator device 44. The two-ply product which received a conventional embossing is directed to a protrusion compression unit 60 which includes two cooperating rolls 62, 64 which are arranged with a very small gap in-between. The protrusion compression unit 60 works like a calendaring unit known in the prior art but with a very small gap which is specifically adapted to the desired result of the protrusion compression unit. The size of the gap depends on the number of plies of the product and on the desired thickness of the product and ranges between 0 mm and 0.3 mm. Depending on the selection of the gap and the geometry of the embossed protrusions, different degrees of compression leading to different geometries of the compressed embossed protrusions will be generated.

(19) After the protrusion compression unit 60, which serves as a dot-folding unit, the tissue web with reduced thickness is directed to a rewinder 70 including infeed draw rolls 71, 72 and outfeed draw rolls 73, 74. Between the infeed draw rolls and outfeed draw rolls, perforation of the web might be performed at a perforating station 80 which is operated in a conventional way.

(20) After leaving the rewinder 60 incorporating an optional perforating station 80, the product is directed to a further processing unit 90 which might either windup the tissue product to a roll or fold it into a stack of individual sheets.

(21) In Table 1 as shown in FIG. 5, a tissue product according to an embodiment of the invention is compared to a conventional product (lower curve) marked “DC (nip)” which is a product with a smaller nip in the conventional embossing station so that a smaller degree of embossing takes place.

(22) Such product which received a lower degree of embossing has a pronounced reduction of absorbency when reducing the thickness of the product. The product according to the embodiment of the invention with the “folded” sidewalls of the compressed embossing protrusions also has a lower absorbency with reduced thickness of the product. However, the decrease of absorbency when reducing the thickness is only about half of that of a conventional product using a smaller nip with a lower degree of embossing. As a result, the product according to the embodiment of the invention is brought to the level of a conventional TAD product “TAD (nip)” which is conventionally superior with respect to the loss of absorbency when reducing the thickness as compared to dry creped products like that according to an embodiment of the invention and the comparative example with the smaller nip (“DC (nip)”). It can be seen that the tissue product according to an embodiment of the invention can be provided with a reduced thickness without suffering from a largely reduced absorbency as is common in conventional products.

(23) Besides the superior properties in absorbency, the perceived softness of the tissue product according to an embodiment of the invention is superior to a product in which a smaller degree of embossing is provided by means of a smaller nip in the embossing station. Also in comparison to a product in which the thickness is reduced by rewinding the tissue web with high tension, the perceived softness both of the individual sheets of tissue product and a roll of tissue product is higher according to embodiments of the invention.

(24) Therefore, the tissue product according to embodiments of the invention are especially useful when a product with low thickness is contemplated which has a long paper length per roll. Among conventional products with such properties, the product according to embodiments of the invention has a higher softness because of the very specific shape of the embossed protrusions.