GB2380977A

GB2380977A - Embossing tissue paper

Info

Publication number: GB2380977A
Application number: GB0125337A
Authority: GB
Inventors: Peter Von Paleske; Thomas Heilemann
Original assignee: SCA Hygiene Products GmbH
Current assignee: Essity Germany GmbH
Priority date: 2001-10-22
Filing date: 2001-10-22
Publication date: 2003-04-23
Anticipated expiration: 2021-10-22
Also published as: GB0125337D0; GB2380977B; DE10241931A1

Abstract

Tissue paper sheets are embossed by two cooperating endless embossing belts (1, 2) being pressed together by pressure rolls (8) or such a belt and a roll at an embossing station where the tissue paper sheet (10) passes through a nip (9) provided there between the belts or belt and roll. Embossing belts are more simple for replacement when damaged than embossing rolls. Furthermore, the surface life of such a device is higher than that of usual embossing rolls used for embossing tissue paper sheets. Each belt (12) can be formed of linked elements, gaps between elements of one forming recesses accepting projections of the other belt.

Description

Device for Embossing Tissue Paper Technical Field The present invention relates to a device for embossing tissue paper as a single-ply or multi-ply tissue paper product.

Embossing can be made in different manner and different patterns wherein the embossing can be made in the single plies of a multi-ply tissue paper product or in the already laminated multi-ply tissue paper product. Embossing is usually made continuously on a web running continuously through the device for embossing tissue paper.

Tissue paper products, e. g. kitchen towels or toilet paper, are embossed for improving the performance of use and the appearance.

Background Art The usual methods for embossing tissue paper are based on the use of embossing rolls, wherein different roll surfaces are in use, e. g. steel/steel, steel/rubber'and steel/paper.

In case of embossing made by steel/rubber, a roll is used having embossing projections being imprinted into the rubber layer of the counter roll. Therewith the embossing projections are imprinted in the tissue paper provided in the nip between the rolls.

From US-A-4,740, 258 a process and a device are known for continuous embossing of the surface of flexible (i. e. , soft- elastic) sheets or length of film material optionally laminated to a synthetic resin film or a flat textile form or

facing. This film material is continuously fed through two pairs of rolls along an endless embossing belt.

Furthermore, a double band press is known from US-A-4,537, 810 and DE 37 26 345 Al. This press is used for manufacture of laminates, such as panels, foils, films and the like, on which an embossing pattern is provided by using press bands.

In US-A-4,740, 258 and US-A-4,537, 810 the material to be embossed has to be heated before and during the embossing.

This is unsuitable for a tissue product as a tissue product would age in an accelerated process by such heating. The ageing process would make the tissue paper brittle and stiff and the tensile strength and softness would be lowered. Furthermore, the tissue paper would become more yellow when aged, especially if the paper comprises mechanical and chemomechanical pulp. Additionally, such heating would dry the tissue paper and thus would affect the embossing.

The material being embossed in DE 37 26 345 Al is totally different from tissue paper as a substrate to be embossed. The laminate in this document has a much higher basis weight than tissue paper and also a higher tensile strength. A tissue paper is more flexible and pliable than the laminates in this document. The same is relevant for the two aforementioned US documents.

Disclosure of the Invention The present invention aims to provide a device for embossing tissue paper with improved simplicity and flexibility in use.

According to the invention, there is provided a device for embossing tissue paper sheets said device comprising one endless embossing belt or band cooperating with another endless embossing belt or band or an embossing roll as a counter embossing element forming with the one endless

embossing belt or band as an embossing element an embossing nip through which the tissue paper sheets can pass.

According to the invention the time for embossing is longer than in an ordinary roll nip. When using a belt embossing apparatus the paper web is predominantly treated in at least one nip of the guide rolls. However, the paper web is still in contact with the embossing projections for a longer time, e. g. during the time it takes for the paper web to run from one pair of guide rolls to the other pair of guide rolls when the guide rolls are used as pressure rolls. Thus, the embossing projections of the embossing belt acts a longer time on the paper web, which results in milder treatment with less loss of strength as a result. The longer embossing time also means that a lower embossing pressure can be used while the protrusions in the embossed paper web still will have the same depth as can be achieved by higher pressure in an ordinary two-roll-nip press. A further advantage of a lower possible pressure is that the choice of material for the projections on the embossing belts can be more flexible than in a conventional one, because there are less demands. For example, the material can be softer, such as rubber.

According to the preferred embodiment, when using two embossing belts measured between the guide rolls one embossing belt has a longer extension in the running direction than the other one so that the shorter embossing belt fits between the guide rolls of the longer embossing belt. Especially the longer embossing belt can be located above the shorter embossing belt and as viewed in the mutual running direction of both embossing belts the guide rolls of the shorter embossing belt overlaps the guide rolls of the longer embossing belt so that the shorter embossing belt deflects the longer embossing belt essentially perpendicularly to the mutual running direction of both embossing belts.

Advantageously there can be provided at least one pair of pressure rolls between the guide rolls.

Since there exists a longer embossing time, embossing of the paper is accomplished in a milder fashion and the embossing pressure, especially in the pressure nip between the pressure rolls, can be lower than in an ordinary two roll embossing nip. The two step process of increasing and decreasing the pressure upstream and downstream the pressure nip between the pressure rolls respectively exerted onto the tissue paper web also means that tensile forces on the paper web are reduced.

The milder embossing process and the lower pressure results in an embossed tissue paper web with less loss in tensile strength than in usual processes.

Different types of chemicals, such as wet and dry tensile strength agents, softener or lotion could be applied to a tissue paper web by using the embossing belts. The chemicals are first sprayed, printed, extruded or by any other method transferred to at least one of the embossing belts. The chemicals are then applied to the tissue paper web, when the web is brought into contact with the embossing belt. The pressure in the nip between the upstream guide rolls and pressure rolls between the guide rolls also contribute to press chemicals into the inner parts of the web. Thus, this apparatus is especially suitable for e. g. strength agents or softeners, which should act within the paper and not just on the outer surface of the paper.

The embossing nip can be formed between the one endless embossing belt and the embossing roll. When using two opposite endless embossing belts, an embossing nip can be formed between the two embossing belts especially at the location of opposite guide rolls for the belts or between the two embossing belts at a location where the two belts pass through a pressure nip of two pressure elements, preferably pressure rolls. There is a predominant embossing present as well.

In one favoured embodiment, the endless belt exhibits a formfit co-operation with at least one of the guide rolls, e. g. in a co-operation of complementary tooth formations.

Especially favoured are co-operations of embossing projections fitting into embossing recesses, because this should eliminate any offset between two embossing belts during the operation, with a more accurate and constant fit between the embossing projections and their complementary recesses.

When using two embossing belts, for a steel/rubber-embossing one embossing belt may be a steel belt and the other one a rubber belt and the steel belt has on its surface the male or female embossing means. Furthermore, for a steel/steelembossing both embossing belts may be steel belts, one thereof has a smooth surface or one having male embossing means and the other one has a surface with corresponding female embossing means.

In one favoured embodiment of the invention, at least the embossing belt provided with an embossing structure is made of a series of belt elements linked together to form an endless chain.

Such a belt can save manufacturing costs. Damage to portions of the embossing belt can be repaired simply by replacement of the respective damaged belt elements. Therefore, lower standstill time periods can be realized and the costs for replacing belt elements are lower than costs caused by replacing embossing rolls. There is furthermore a higher flexibility present due to a more simple and cheap change of the embossing pattern. Finally, by the improved device there is realized a higher surface life as well as a higher degree of freedom in the operation with steel/rubber embossing, because the rubber belt is not combined with a roll surface and therefore there is no risk of delamination.

It is also possible to mix the belt technology of the present invention with common technology. For example, it is possible to operate a rubber or steel belt on a usual steel embossing roll or a steel belt on an usual rubber embossing roll.

For a better understanding of the invention, and to show how it can be realised, reference will now be made to the accompanying drawings.

Brief Description of the Drawings In the drawings: Fig. 1 is a diagrammatic view of a device for embossing tissue paper sheets; Fig. 2 is an enlarged cross section of the embossing station of the Figure 1 device; and Fig. 3 is a diagrammatic view of another embodiment of a device for embossing tissue paper sheets.

In Fig. 1 an embossing station is illustrated where two endless embossing belts 1 and 2 are illustrated as cooperating belts running around guide rolls la and Ib as well as 2a and 2b, one of first or second mentioned guide rolls can be driven. In case of steel/rubber embossing, one embossing belt is made of belt elements 3 linked together to form a chain. Embossing projections 4 (male) are provided on the elements. The counter belt is in this case the rubber belt. In case of steel/steel embossing, both embossing belts are made of steel belt elements 3 as illustrated in Fig. 2 of the drawings. In this case, on one belt elements with embossing projections 4 are provided and on the other belt recesses (female) are provided between the belt elements. In a further embodiment these recesses provided on the other belt could have been provided as engravings in the separate belt

elements. In a further embodiment the belt elements of the other belt are provided with a flat surface and are fitted as to give the other belt a smooth paper contacting surface. In even a further embodiment the elements of the other belt are provided with projections.

The belt elements 3 are linked together by hinges 6 such that the belt can follow the circumference of the guide rolls la, 1b and 2a, 2b.

In order to avoid any relative movement (slippage) of the endless belts 1,2, especially when embossing projections have to fit with embossing recesses or when both belts have projections and the projections of both belts cooperate in a nested or foot-to-foot manner, there is a form-fit connection between the guide rolls and the embossing belts as illustrated by one of more teeth 7 illustrated in the guide rolls la, 2a of Fig. 1.

In the area between the guide rolls, there is provided a pair of pressure rolls 8. At the location of the pressure rolls 8 is formed a pressure nip 9, through which passes the tissue paper sheet 10 to be embossed. The pressure roll 8 can be made of steel but could also be cladded with rubber. A rubber cladded roll or roll pair enables an extended embossing nip due to compression of the rubber and exhibits lower raise of pressure until the maximum pressure is reached in the middle of the nip. This contributes to a lower risk of paper damage.

Rubber rolls having a hardness so low as 25-35 Shore A could be used.

There can be used more than one pair of pressure rolls one behind the other exerting the same or different pressure on the belts and the paper web.

At the station where the pressure rolls 8 are provided, the embossing operation is made in compliance with the illustration in Fig. 2.

In the embodiment according to Fig. 3 showing a device or apparatus comprising two parallel embossing belts, two are at least so much shorter than the other embossing belt 1 so that the shorter embossing belt 2 fits between the guide rolls la and 1b of the longer embossing belt 1. In this embodiment the longer embossing belt 1 is located above the shorter embossing belt 2. The shorter embossing belt 2 is placed so that according to the view in the running direction of the embossing belts 1, 2 the guide rolls la, 1b on the one hand and the guide rolls 2a, 2b on the other hand overlap to some extent. This means that the shorter embossing belt 2 presses into the lower part of the longer embossing belt 1. This pressing leads to a partial pressure increase against the tissue paper web 10 already upstream of a pair of pressure rolls 8 (zone 1) in this embodiment two pairs of pressure rolls 8 are provided. In the same manner the pressure is firstly just partially decreased directly downstream to the pressure nip, which pressure nip is present in the zone 2.

(zone 3). This means that the embossing of the paper web 10 starts upstream of the pressure nip (zone 2) in the zone 1 and continues downstream thereof. Such a longer embossing time means that the embossing of the tissue paper web is milder and that the embossing pressure especially in the pressure nip can be lower than in an ordinary two row embossing nip. The two step process of increasing and decreasing the pressure exerted on the tissue paper web 10 also means that tensile forces on the paper web is reduced. The milder embossing process and the lower pressure results in an embossed tissue paper web with less loss in tensile strength than in an usual process.

A spray device 11 is present for applying water, lotion or other chemicals.

By the device illustrated before, an embossing method is possible in which by the extended belt time the embossing conditions can be enhanced and improved. It is known that a humid paper web is easier to emboss than a dry paper web especially a tissue paper web. In this case an embossing pattern imprinted into a humid tissue paper web is more prone to be stable when the final tissue paper is used in wet conditions. However, with apparatuses earlier known, it has been difficult to transfer an effective amount of water to a tissue paper web. A tissue paper web tended to become wavy because of non-uniform application of water and/or tended to break due to the lower strengths that a humid paper web exhibits. With the present apparatus, the tissue paper web is carried, supported and sandwiched between the two belts and is moisturised upstream to the pressure roll nip. This enables an equal distribution of humidity in all directions simultaneously due to the fact that the tissue paper web is sandwiched between the two belts and a wavy web is prevented. Since, finally, the web is carried on one of the embossing belts the risk of web ruptures is lowered.

For application of humidity a steam box 12 can be used at the place indicated in Fig. 3 within zone 1 between the guide roll 2a and the pressure rolls 8.

A dry tissue paper web normally has a humidity of 3% to 8%, depending on the humidity in the atmosphere. If the air is very humid, the humidity of the tissue paper web can be even higher than that and if the air is very dry the paper humidity can be lower. In the apparatus according to the present invention, the humidity of the paper web can be raised by 0,5% to 10%-units or preferably 1% to 5%-units, e. g. from 4% to 6% humidity. 1%-units'raise seems to be low but ameliorates the embossing result considerably. It is not necessary to raise the humidity to a value outside the normal humidity range to achieve a good result as it is the actual raise that gives a result.

If the tissue paper web has been embossed in a very humid state it may have to be dried in the step after the embossing.

This can be made by any common apparatus, e. g. infra-red (IR) or hot air fans. This is diagrammatically indicated in Fig. 3 in zone 3 by the box 13.

To be able to humidify and dry the paper web at least one of the tissue paper belts has to be foraminous. The belt could be made of a belt with holes or preferably of a woven fabric. It is even more preferred that both embossing belts are foraminiferous.

Claims

Claims 1. Device for embossing tissue paper sheets said device comprising one endless embossing belt or band (1) co- operating either with another endless embossing belt or band (2) or with an embossing roll as a counter embossing element forming with the one endless embossing belt or band (1) as an embossing element an embossing nip (9), through which, in use, the tissue paper sheets (10) to be embossed are advanced.
2. Device according to claim 1, wherein the embossing nip is formed between the one endless embossing belt (1) and the embossing roll.
3. Device according to claim 1, wherein, when using two opposite endless embossing belts (1, 2), the embossing nip is formed between the two embossing belts (1, 2) at the location of opposite guide rolls (la, 2a ; lb, 2b) for the belts (1, 2).
4. Device according to claim 1, wherein, when using two opposite endless embossing belts (1, 2), an embossing nip (9) is formed between the two embossing belts (1, 2) especially at a location, where the two belts (1, 2) pass through a pressure nip of two pressure elements, preferably pressure rolls (8).
5. Device according to claim 1, wherein the endless belt (1 ; 2) is in a form-fit connection with at least one of the guide rolls.

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6. Device according to claim 5, wherein the form-fit connection is a connection (7) formed between teeth on one of the embossing and counter- embossing element, and complementary recesses on the other of the embossing element and counter-embossing element.
7. Device according to claim 1, wherein, when using two embossing belts (1, 2), one embossing belt is a steel belt and the other one is a rubber belt.
8. Device according to claim 1, wherein, when using two embossing belts, both embossing belts (1, 2) are steel belts.
9. Device according to claim 1, wherein at least the embossing belt provided with an embossing structure is made of a series of belt elements (3) linked together to form an endless chain.
10. Device according to claim 9, wherein a gap between the linked belt elements (3) forms a recess (5) cooperating with an embossing projection (4) provided on the belt elements (3).

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11. Device according to at least one of the claims 3,7 or 8, wherein, when using two embossing belts (1, 2) measured between the guide rolls one embossing belt (1) has a longer extension in the running direction (14) than the other one (2) so that the shorter embossing belt (2) fits between the guide rolls (la, lb) of the longer embossing belt (1).
12. Device according to claim 11, wherein the longer embossing belt (1) is located above the shorter embossing belt (2).

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13. Device according to claim 11 and/or 12, wherein as viewed in the mutual running direction (14) of both embossing belts (1,2) the guide rolls (2a, 2b) of the shorter embossing belt (2) overlap the guide rolls (la, lb) of the longer embossing belt (1) so that the shorter embossing belt (2) deflects the longer embossing belt (1) essentially perpendicularly to the mutual running direction (14) of both embossing belts (1, 2).
14. Device according to claim 4 or 11, wherein at least one pair of pressure rolls is provided between the guide rolls.
15. Tissue paper sheet embossing device substantially as hereinbefore described with reference to the accompanying drawings.
16. Use of a sheet embossing device substantially as hereinbefore described with reference to the accompanying drawings, for embossing sheets of tissue paper.
17. Method of embossing sheets of tissue paper substantially as described with reference to the accompanying drawings.

17. Method of embossing sheets of tissue paper substantially as described with reference to the accompanying drawings.

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Amendments to the claims have been filed as follows:

1. Device for embossing tissue paper sheets, said device comprising one embossing element being one endless embossing belt or band (1) cooperating with a counter-embossing element being another endless embossing belt or band (2), said one endless embossing belt or band forming with the counterembossing element an embossing nip (9), through which, in use, the tissue paper sheets (10) to be embossed are advanced, wherein the endless belt or at least one of the endless belts (1, 2) is/are in a formfit connection with at least one guide roll.

2. Device according to claim 1 wherein when using two opposite endless embossing belts (1, 2) the embossing nip (9) is formed between the two embossing belts (1, 2) especially at a location, where the two belts (1, 2) pass through a pressure nip of two pressure elements.

3. Device according to claim 2 wherein the pressure elements are pressure rolls (8).

4. Device according to claim 3 wherein a pair of guide rolls (la, 2a, lb, 2b) are used as the pressure rolls.

5. Device according to claim 1 wherein the formfit connection is a connection formed between teeth on one of the embossing and the counter-embossing element, and complementary recesses on the other of the embossing and counter-embossing element.

6. Device according to claim 1, wherein when using two embossing belts (1, 2), one embossing belt is a steel belt and the other one is a rubber belt.

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7. Device according to claim 1, wherein when using two embossing belts (1, 2), both embossing belts are steel belts.

8. Device according to claim 1 wherein at least the embossing elements and/or the counter-embossing elements is provided with embossing projections.

9. Device according to claim 1 or 8 wherein when using one embossing belt, the embossing belt provided with embossing projections is made of a series of belt elements (3) linked together to form an endless chain.

10. Device according to claim 1 or 8 wherein, when using two embossing belts (1,2), at least one of the embossing belts is/are provided with embossing projections, the embossing belt/s with embossing projections is/are made of a series of belt elements (3) linked together to form an endless chain.

11. Device according to claim 10 wherein, when using two embossing belts (1,2), the gaps between linked belt elements (3) of each belt form recesses cooperating with embossing projections (4) provided at corresponding locations on the belt members of the other belt.

12. Device according to claim 1" wherein when using two embossing belts (1,2), when measured between the guide rolls one embossing belt (1) has a longer extension in the running direction (14) than the other one (2) so that the shorter embossing belt (2) is shorter than the machine direction distance between the guide rolls (la, lb) of the longer embossing belt (1).

13. Device according to claim 12 wherein the longer embossing belt is located above the shorter embossing belt (2).

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14. Device according to claims 12 or 13, wherein in the mutual running direction (14) of both embossing elements (I, 2) the guide rolls (2a, 2b) of the shorter embossing belt (2) overlap the guide rolls (la, Ib) of the longer embossing belt (1) so that the shorter embossing belt (2) deflects the longer embossing belt essentially perpendicularly to the mutual running direction (14) of both embossing belts.

15. Device according to claim 3 or 11 wherein at least one pair of pressure rolls sandwiching the embossing belts is provided between the guide rolls.

16. Tissue paper embossing device substantially as hereinbefore described with reference to the accompanying drawings.