Method of compressing tissue bundles

Abstract

A method is disclosed for forming a tissue bundle from a stack of folded absorbent tissues. The method includes the steps of forming a stack of folded absorbent tissues; compressing the stack to an initial density in a first compression step; wrapping the stack a first time in a supporting wrapper to form an initial bundle and maintain the initial density; subsequently applying a second compression step to compress the stack to a final density that is higher than the initial density; and wrapping the stack a second time to form a final bundle and to maintain the final density.

Claims

1. A method of forming a tissue bundle comprising a stack of folded absorbent tissues, the method comprising: forming a stack of folded absorbent tissues; compressing the stack to an initial density in a first compression step; wrapping the stack a first time in a supporting wrapper to form an initial bundle; subsequently applying a second compression step to compress the stack to a final density that is higher than the initial density; and re-wrapping the same stack a second time to form a final bundle and to maintain the final density, wherein the tissues are of structured tissue and the final density is greater than 0.2 g/cm.sup.3; or the tissues are of hybrid tissue and the final density is greater than 0.25 g/cm.sup.3; or the tissues are of dry crepe tissue and the final density is greater than 0.3 g/cm.sup.3.

2. The method according to claim 1, wherein the stack is wrapped the second time in a final wrapper that is different to the supporting wrapper.

3. The method according to claim 1, wherein the stack is wrapped the second time by re-wrapping the supporting wrapper.

4. The method according to claim 1, wherein the second compression step is carried out without removing the supporting wrapper.

5. The method according to claim 1, wherein the initial density is less than 0.25 g/cm.sup.3.

6. The method according to claim 1, wherein the stack is compressed in a height direction during the second compression and the final bundle has a height that is less than 70% of the initial bundle.

7. The method according to claim 1, wherein the stack is compressed in a height direction during the second compression with a pressure of greater than 120 kN/m2.

8. The method according to claim 1, wherein the second compression step takes place at a time or location that is distant from the first compression step.

9. The method according to claim 1, wherein the initial bundle is in the form of an elongate log and the method comprises cutting the log transverse to its elongate dimension to form a plurality of tissue packages.

10. The method according to claim 9, wherein the log is cut into tissue packages subsequent to the second compression step.

11. The method according to claim 1, wherein the tissues comprise dry crepe material.

12. The method according to claim 1, wherein the tissues are interleaved in a V, M or Z configuration.

13. The method according to claim 1, wherein the initial bundle is in the form of an elongate log and the second compression step takes place by transporting the log along a compression path that is aligned with an elongate direction of the log.

14. The method according to claim 1, wherein a portion of the supporting wrapper is cut away, prior to wrapping the stack a second time to form a final bundle.

15. The method according to claim 14, where the portion cut away is a portion that has been previously adhered on wrapping the stack a first time.

16. A tissue bundle comprising a stack of folded absorbent tissues, wrapped in a wrapper to form a final bundle and compressed in a two-step compression process according to the method of claim 1.

17. The tissue bundle according to claim 16, wherein the wrapper is nipped and folded to tightly wrap the final bundle and to maintain the final density.

18. A packaging machine for forming a tight final tissue bundle from a loose wrapped initial bundle containing a stack of folded absorbent tissues, the packaging machine comprising: a transport station for conveying an initial bundle having a supporting wrapper to a compression station; and a compression station for compressing the wrapped initial bundle from an initial density to a final tissue bundle having a higher final density and a wrapping station for re-wrapping the same final tissue bundle to maintain the final density, wherein the wrapping station comprises a nip and fold provision to take up excess material in the supporting wrapper and fold it around the final tissue bundle.

19. The packaging machine of claim 18, wherein the packaging machine has a cutter for cutting away at least a portion of the supporting wrapper prior to forming the final tissue bundle.

20. A packaging machine for forming a tight final tissue bundle from a loose wrapped initial bundle containing a stack of folded absorbent tissues, the packaging machine comprising: a transport station for conveying an initial bundle having a supporting wrapper to a compression station; and a compression station for compressing the wrapped initial bundle from an initial density to a final tissue bundle having a higher final density and a wrapping station for re-wrapping the same final tissue bundle to maintain the final density, wherein the wrapping station comprises replacement provision to remove the supporting wrapper and replace it with a high-tensile wrapper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

(2) FIG. 1 is a schematic side view of an output part of a conventional tissue production machine;

(3) FIG. 2 is a schematic view in the direction II of FIG. 1;

(4) FIG. 3 is a schematic view of operation of a process according to the present disclosure

(5) FIGS. 4a-c are cross-sectional views through the stations of FIG. 3 in the directions IVa, IVb and IVc respectively; and

(6) FIGS. 5-7 depict alternative methods of wrapping a final bundle in the stations of FIG. 3.

DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 is a schematic side view onto an output part of a conventional tissue production machine 1 that may be used according to the present invention. In this embodiment, the machine 1 is for the production of 2-ply dry-crepe tissue 10 according to the SCA article number 140299, each of the plies being 18 gsm. The skilled person will nevertheless understand that any other suitable tissue may also be used.

(8) The machine 1 provides its output as two webs 11, 12 of tissue 10, that are passed around output rollers 3, 4 and cut and folded together at a folding station 6. The tissue 10 coming from the respective webs 11, 12 is folded together in Z-formation, with folds of the respective webs 11, 12 interleaved together as is otherwise well known in the art. The folded tissue 10 is collected as a stack 14 in stacking station 8 until the stack reaches an uncompressed height H0, which in this case is around 130 mm. The stack 14 has a stack width W, which in this case is around 85 mm, being a standardized dimension for use in certain tissue dispensers. These dimensions can of course be adjusted according to the tissue material, the process and/or the required end use.

(9) FIG. 2 is a schematic view in the direction II of FIG. 1, in the process direction of the machine 1. It will be understood that the machine 1 is a complex installation having many more components that are neither shown nor discussed as they are otherwise not relevant to the present invention.

(10) According to FIG. 2, the roller 4 is shown above the folding station 6 and the stacking station 8. The tissue webs 11, 12, the rollers 3, 4, the folding station 6 and the stacking station 8 all have an effective width L, which defines the length of the stack 14. In the present embodiment, this length L is 2200 mm although the skilled person will understand that this is a variable that will be determined by the machine and/or the end use.

(11) Aligned with the stack 14, is a compressing and wrapping line 20, comprising a first transport station 22, a first compression station 24 and a first wrapping station 26. The first transport station 22 comprises first transport bands 28, that engage the stack 14 and move it laterally out of the machine 1 in the direction X. This takes place once the stack 14 has reached the uncompressed height H0. Additional rollers, grippers, guides and transport provisions may be present to facilitate this movement. The stack 14 proceeds in the lateral direction X through the first compression station 24, where first compression bands 30 apply compression to the stack 14 to reduce it in height from the uncompressed height H0 to an initial height H1, which in this embodiment is around 120 mm.

(12) In the first wrapping station 26, further transport bands 32 move the stack 14 in the lateral direction X, while a supporting wrapper 34 is applied around the stack 14 to form an initial loose bundle or log 40. The supporting wrapper is in the form of a wrap-around strip, extending over the full length and width of the stack 14, joined to itself along a longitudinal seam by a hotmelt adhesive. It will be understood that a two part wrapper may also be used, employing two seams. The wrapper material is Puro Performance™, available from SCA Hygiene products, with surface weight 60 gsm. In this context, it should be noted that although reference is given to a loose bundle 40, the bundle may be relatively tightly packed due to the first compression step. Nevertheless, at this stage, it is clear to a user that it is a stack of tissues and individual tissues may be immediately identified. As compressed to the initial height H1, the loose bundle 40 has an initial density of around 30 g/cm3. This value is based on a simple L×W×H1 calculation of its volume and will be subject to the normal measurement tolerances. It should also be pointed out that the process and equipment up to this point may be otherwise conventional, with the exception of the wrapping material, which is of virgin 80 gsm paper and significantly stronger than a wrapper conventionally used for a loose bundle of this density.

(13) FIG. 3 shows operation of a process according to the present disclosure, which in this case takes place at a location distant from the machine 1 of FIG. 1. It will however be understood that the process and equipment of FIG. 3 could be implemented directly following the first wrapping station 26 of FIG. 2.

(14) According to FIG. 3, a pallet 48 of loose bundles or logs 40 is provided. These may be provided from storage or as a buffer within a production line. In an initial stage, a loose bundle 40 is loaded onto a second transport station 42, which moves it by means of second transport bands 62, in the lateral direction X towards a second compression station 44. The second compression station 44 comprises second compression bands 64 that operate to pinch the loose bundle 40 as it progresses. The second compression station 44 acts at a considerably higher pressure than the first compression station 24. The pressure of the first compression station may be around 20 kN/m2, while the pressure of the second compression station may be around 160 kN/m2, according to requirements. This compression is sufficient to reduce the height of the stack 14 from the initial height H1 to a final height H2. In the present example, the compression is 2 bar, the final height H2 is around 60 mm and the final density is around 60 g/cm3. At this value, the tissue 10 is still viable and will spring back if not contained. As explained above, due to the presence of the supporting wrapper 34, distortion of the upper- and lowermost tissues 10 within the stack 14 is avoided. A number of factors are believed to further assist in achieving a high quality result. Due to the fact that the compression takes place in two steps, distortion may be reduced. To this end, the amount of compression during the respective first and second compressions may be adjusted. Furthermore, the use of a relatively strong wrapping material may further prevent distortion. In fact, the supporting wrapper may be chosen specifically for the purpose of facilitating the second compression step with the final wrapper being dedicated to withstanding the high compression.

(15) The stack 14 then progresses to a second wrapping station 46, where the stack 14 is rewrapped to form a final tight bundle 50 to maintain the final density and the final height H2, thus preventing it from springing back to the uncompressed state. The second wrapping station 46 may comprise a replacement provision 461 to remove the supporting wrapper 34 and replace it with a high-tensile wrapper. In the following, reference to a tight bundle is intended to refer to the bundle in its final condition. From the second wrapping station 46, the tight bundle advances to a sawing station 52, where it is cut into a number of shorter tissue packages 54. In this case, the tight bundle 50 is cut into 10 tissue packages 54, each having a length of 212 mm.

(16) FIGS. 4a-c show cross-sectional views through the second transport station 42, second compression station 44 and second wrapping station 46 of FIG. 3 in the directions IVa, IVb and IVc respectively. As can be seen in FIG. 4a, the stack 14 in its supporting wrapper 34 is held between the second transport bands 62. At this position, it is still under its initial compression and has its initial height H1. Individual tissues 10 are still visible.

(17) FIG. 4b illustrates a cross-section at a position through the second compression station 44 where the stack 14 is fully compressed to its final density. The second compression bands 64 exert a force F on the stack 14 to maintain it at the final height H2. As indicated above, this force F is around 2 bar and the final height H2 is around half of the initial height H1. As a result of this reduction in height, the supporting wrapper 34 develops slack at the sides of the stack 14, which is gathered together as the stack 14 progresses through the compression station by an appropriate guide into a nip 66. It may also be noted here that the compression of the stack 14 is such that individual tissues can no longer be discerned and at this density, the stack is brick-like. In this embodiment, it can be seen that the nip 66 on the right of the stack 14 is gathered at the base of the stack 14 and the nip 66 on the left is gathered at the top of the stack 14.

(18) FIG. 4c, is a view through the tight bundle 50 at the exit to the second wrapping station 46. The supporting wrapper 34 has been tightly wrapped around the stack 14 by folding this nips 66 against the stack 14 and adhering them to the supporting wrapper 34 using adhesive tape 68. In this state, the compression of the tight bundle 50 is maintained entirely by the supporting wrapper 34, which must be sufficiently strong to withstand the spring-back force. It will be understood that although the tight bundle 50 is shown with flat upper and lower surfaces, these will inevitably become bowed as the stack 14 relaxes. It will also be noted that the positions of the nips 66 allows them to be folded upwards and downwards respectively, limiting an increase in width of the tight bundle 50.

(19) FIG. 5A shows an alternative way in which a tight bundle 50 may be rewrapped. In this embodiment, the nips 66 are formed at the position at which the supporting wrapper 34 has been glued to form the loose bundle. Cuts K are made through the nip 66 to remove the glued portion 68. In FIG. 5B, the supporting wrapper 34 is re-glued by overlapping the ends 70 of the supporting wrapper 34 at the location of the cut.

(20) A further alternative method of rewrapping is shown in FIGS. 6A and 6B. In this case, compression of the tight bundle 50 allows nips 66 to be formed in the supporting wrapper 34 as indicated above. In this case, each nip 66 is cut at two separate locations K′ and K″ to remove the glued portion 68, which is at the upper side of the nip 66. In FIG. 6B, the ends 70 comprising the lower side of the nip 66 are folded upwards and adhered to the remainder of the supporting wrapper 34.

(21) A still further alternative for rewrapping the supporting wrapper 34 is shown in FIGS. 7A and 7B. In this case, cutting takes place of the supporting wrapper 34 while the stack 14 is still a loose bundle 40. Cuts K′, K″ on either side of the loose bundle 40 remove the glued portion 68. Subsequent compression of the stack 14 as shown in FIG. 7B allows the ends 70 of the supporting wrapper 34 to overlap where they can be again glued together to form the tight bundle 50.

(22) The invention has been described by reference to the embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, it will be understood that various alternative wrapping processes may be employed for the wrapping or rewrapping of the tight bundle. Additionally, although the process of FIGS. 3 and 4 has been explained as a continuous process using transport bands to transport elongate logs through the respective stations, a similar result may be achieve using a batch process whereby individual logs or packages are compressed and wrapped sequentially.

(23) Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.