CA1116452A

CA1116452A - Tissue paper machine

Info

Publication number: CA1116452A
Application number: CA000301711A
Authority: CA
Inventors: Risto Turunen; Kari Ebeling
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-04-22
Filing date: 1978-04-21
Publication date: 1982-01-19
Also published as: DE2816581A1; CH627805A5; GB1589800A; FR2388076A1; BR7802481A; IT1094727B; JPS53134907A; SE7804589L; IT7822597A0; NO781397L; BE866262A; FI771295A

Abstract

ABSTRACT OF THE DISCLOSURE:
A paper machine for providing paper which has a pattern embossed therein includes a twin-wire former and a headbox for delivering pulp stock to the former to be formed into a web thereby. Situated beyond the twin-wire former is a structure which defines a press nip through which the web travels sub-sequent to the twin-wire former. A fabric structure which extends between the twin-wire former and the above press nip includes a former portion which forms part of the twin-wire former and participates in the formation of a web at the twin-wire former, this fabric structure also including a transfer portion which travels with the web through the press nip while transporting the web from the former portion of the fabric structure to the transfer portion thereof. At least the transfer portion of the above fabric structure has a mesh which embosses a predetermined pattern in the web as it travels through the above press nip, so that the transfer portion of the fabric structure serves not only to transport the web to the press nip but also to emboss a predetermined pattern in the web.

Description

S;~:

The present invention relates to paper machines and in particular to a paper machine capable of embossing a predetermined pattern in a web.
With previously known paper machines, tissue paper is commonly manufactured in such a way that the web is formed on a relatively short wire section similar to a normal planar wire situated at a location where a headbox supplied the pulp stock onto a breast roll which is in many cases of an open construction or provided with an internal vacuum.
From the breast roll the web travels, while carried by the wire, past conventional dewatering elements such as table rolls, deflectors, foil strips, suction boxes and a suction roll, each of the latter components serving to remove water from the web. ~t the end of the wire section the partly dried web is transferred to a so-called pick-up felt, with the web being carried by this felt to be further dried in the press and drying sections of the machine. In some designs this planar wire section has been totally omitted, ~16~2 and in this case the web formation is carried out entirely on a wire-coated suction breast roll fLom which the web is transferred directly to the pick-up felt.
The prior art also includes several twin-wire formers intended for manufacturing tissue paper. Most of the know twin-wire formers are so-called full throat forme-rs, but constructions of this type generally have the drawback that as a result of the use of such a throat former there is a poor "formation" of the web which is produced. Various problems affecting the running of the machine are furthermore introduced, as a result of the high rate of dewatering at the initial draining step.
In most widely used paper manufacturing methods, the wet paper web is pressed on a Yankee cylinder which carries out the drying operation, in such a way that the uniformity of the paper structure in the direction of the thickness dimension there-of is maintained as exact as possible. It is well known that with increasing machine speeds the drying capacity of the Yankee cylinder creates an obstacle to a further increase of the production rate. In order that the drying capacity of the Yankee cylinder shou]d be capable of being fully utilized in a creped paper machine, it is common to subject the wet paper web to very powerful pressure with the aid of one or two Yankee cylinder presses prior to starting of the evaporation drying proper. In this way it is possible to achieve a web which is uniform over its entire breadth, but the softness and absorptivity characteristics of the end product are substantially impaired.
It is a general object of the invention to achieve im-provements in tissue paper machines, in particular in connection with their total concept.
More specifically, it is an object of the invention to provide a tissue paper machine wherein it is possible to preserve in the web the qualities of softness, bulk, and absorptibity which are required of tisslle paper.

It is furthermore an object of the present invention to provide a machine which is capable of improving the fiber retention and to achieve the highest possible strength in the finished paper without causing the above qualities to suffer~
According to the present invention, there is provided a tissue paper machine in which the twin-wire former section comprises a headbox, a carrying fabric, a covering fabric, within the loop of the carrying fabric a forming roll, this froming roll having a smooth surface and the dewatering of the web on this forming roll being mainly by centrifugal force effect while the web is impacted between the fabrics, and the tissue paper machine having as its dryer a Yankee cylinder with which together a press suction roll defines a press nip, characterized in that through the press nip is arranged to pass apattern embossing fabric embossing its pattern on the web in the nip and which is such that it also serves as a member trans-porting the web forwardly, the web being transferred onto the pattern embossing fabric by the aid of a pick-up means.
According to one aspect of the invention, in a paper machine, there are provided twin-wire former means for forming a web, headbox means cooperating with said twin-wire former means for supplying pulp stock thereto to be formed thereby into said web, press-nip means including a press suction roll, situated beyond said former means for providing at least one press nip through which the web travels, and fabric means ex-tending between said twin-wire former means and said press-nip means and including a former portion which participates in the formation of the web at said twin-wire former means and a trans-fer portion for transferring the formed web to said press-nip means while travelling with the web through said press nip, at least said transfer portion of said fabric means having a mesh - for embossing a predetermined pattern in the web as it travels through said press nip, so that 4~

sa.id transfer portion of said fabric means operates on the one hand to transport the web to said press-nip means and on the other hand to emboss a pattern in the web.
The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:
FIG. 1 is a schematic elevation of one possible embodi-ment of a machine of the invention;
FIG. 2 is a schematic elevation of another embodiment of a machine according to the invention; and FIG. 3 is a fragmentary sectional elevation illustrating the structure of paper manufactured with the machine of the invention.
FIGS. 1 and 2 respectively illustrate paper machines each of which has a twin-wire former means to which pulp stock is supplied by way of a hydraulic headbox means lOa, in the case of FIG. 1, and lOb in the case of FIG. 2, the twin-wire former means of both embodiments including a smooth-surfaced forming roll 13. In addition to the smooth-surfaced forming roll 13, the twin-wire forming means of FIGS. 1 and 2 each includes a pair of wires one of which is the outer wire 12, this wire 12 co-operating with the wire lla in FIG. 1 and with the wire llb in FIG. 2. The wire 12 is guided in both embodiments by way of guide rolls 14 while in both embodiments the other wire of the twin-wire former is guided by guide rolls 15. In both embodiments there is a schematic illustration of the web W which is formed.
In order to achieve in the twin-wire former means of FIG. 1 a draining region which is longer and more favorable than those previously known, the twin-wire former means of FIG. 1 in-cludes at the wire 12 an initial single-wire portion 20 situated at a draining region, this portion 20 oE the wire 12 oE FIG. 1 extending from the breast roll 14a up to the point where the 11'16~X'~

wires 12 and ]la of FrG. 1 start to travel along a common path around the forming roll 13. This initial par~ 20 of the wire 12 of FIG. 1 where the web is carried only by one wire travels along a forming board 21 situated within the loop of the wire 12, this forming board 21 promoting the dewatering action in a well known manner by foil action and/or suction. FIG. 1 schematically shows connected to the headbox means lOa a suitable means 22 which serves to adjust the size and direction of the lip slice of the headbox means lOa, for purposes which are well known.
At the sector ~ of the forming roll 13 where the web is compress-ed between the pair of fabrics lla and 12, dewatering is carried out primarily by the draining pressure produced by centrifugal force (by kinetic energy). The guide rolls for the wire 12 in FIG. 1 include the roll 14b which is arranged to be adjustable in its location, as indicated by the double-headed arrow, so that the vacuum at the upper tangetial point where the wire 12 departs from the forming roll 13 can be adjusted. This vacuum adjustment is utilized to influence the detachmen-t of the web of the web W from the wire 12, so that the web W will positively continue to travel with the fabric lla of the twin-wire former means. Such reliableweb transfer is only achieved by producing a high enough dry matter content after the web-forming process, and this result is achieved by way of the illustrated combina-tion ~of the forming board 20 and the relatively small diameter of the former roll 13.
In the embodiment of FIG. 2, the hydraulic headbox means lOb has been arranged so that its lip slice is above the smooth-surface forming roll 13, and as is illustrated in FIG. 2, the rolls 14 which guide the wire 12 include the roll 14c which can be adjusted as indicated by the double-headed arrow.
In both embodiments drying of the fabric takes place by way of a Yankee cylinder 50 with which a hood 51 cooperates in a known way. This Yankee cylinder 50 ~orms part of a press-nip means which includes the press suction roll 40 which defines the single press nip Nl with the Yankee cylinder 50. In both embodi-ments of the invention a fabric means extends between the twin-wire former means and the prcss nip means wherc the nip Nl is situated. This fabric means includes in both embodiments a former portion which forms part of the twin-wire former means and a transfer portion which transfers the web to the press nip means to travel with the web through the nip Nl. In the case of FIG. 2, the former portion and transfer portion form parts of a single fabric, this being the fabric llb. However, in the case of FIG. 1, this fabric means includes separate endless fabrics lla and 32.
It will be seen that in the embodiment of FIG. 2 the fabric means extending between the twin-wire former means and the press-nip means is in the form of a single endless fabric llb which at its left, as viewed in FIG. 2, has a portion forming part of the twin-wire former means and participating in the formation of the web and at its right has the transfer portion which transfers the web fromthe twin-wire former means to the press-nip means to travel through the nip Nl. The fabric means llb of FIG. 2 has a mesh which will provide embossing of a predetermined pattern in the web as the fabric means llb together with the web travel through the nip Nl. Thus the fabric with the mesh which provides the predetermined embossing pattern also is utilized in the twin-wire former means in the embodiment of FIG. 2. The former portion and transfer portion of the fabric means llb of FIG. 2 are located one next to the other at a jonction where the pick-up means 30b is situated, this pick-up means 30b being in the form of a rotary suction pick~up roll.'rhus the pick-up means 30b assures that the web will be picked up fro-m the wire 12 and delivered reliably to the transfer portion of the fabric means llb at the l.ocation where this transfer portion continues to travel forwardly to the right, as viewed in FIG. 2, beyond the pick-up means 30b.
In the embodiment of FIG. 1, however, the fabric means which extends between the twin-wire former means and the press nip Nl formed by the press-nip means includes separate former and transfer portions, the former portion of this fabric means being formed by the endless fabric lla while the transfer portion of the fabric means of FIG. 1 is formed by the separate endless wire 32 which has a mesh which will provide embossing of a pre-determined pattern in the web as the wire 32 travels together with the web through the nip Nl. In FIG. 1 also the former portion and transfer portion of the fabric means are situated one next to the other at a junction where the pick-up means 30a of FIG. 1 is situated, this pick-up means 30a of FIG. 1 being in the form of a pick-up roll which assures that the web W will be picked up from the former wire lla, which forms the former portion of the fabric means, and delivered to the transfer portion thereof whi.ch is formed by the embossing wire 32.
As is i.ndicated in FIG. 1, the web W which is transported away from the forming roll 13 by way of the wire lla is detached from the latter as a result of the effect of suction acting at the suction zone 30 ~ of the suction roll 30a, with the web being delivered to the underside of the pattern-embossing wire 32 or in the alternative to an equivalent special felt provided for this purpose. The web W continues to travel, while carried by the fabric 32, to the first and only press nip Nl. In the case of FIG. 2, the web W travelling downwardly beyond the forming roll 13 where it is sandwiched between the wires llb and 12, is guided by way of the suction zone 30 ~ of the suction roll 3nb, so as to be delivered to the underside of the pattern-embossing wire llb, with the web W being transported to the press nip ~1 6~5;~

shown in FIG. 2 at the underside of the wire llb.
As is indicated in FIGS. 1 and 2, the first and only -actual press nip of the illustrated tissue paper machines, namely the nip N1, is defined by a press suction roll 40 having the suction zone 40 d~and the Yankee cylinder 50 which -Eorms part of the drying section of the tissue paper machine. As was indicated above, the Yankee cylinder 50 cooperates with a hood 51 in a known way.
As is indicated in FIGS. 1 and 2, an endless felt 42 laps the press suction roll 40, this felt 42 being guided by the guide rolls 43. Thus between the transfer portion of the fabric means, which provides the web with a predetermines pattern em-bossed therein, and the press suction roll 40 there is the felt 42 which is acted upon by a reconditioning means which is not illustrated. An important feature of the invention resides in the fact that the pattern-embossing wire 32 or llb, which in and of itself may be known, serves at the same time as a conveyor for transporting the web in the closed conduction, which is to say without any open draw, all the way up to and through the first press nip N1 where the web W is embossed with the pattern of the wire 32 or llb, for achieving in this way the eEfects desired by the present invention.
With respect to the felt 42, instead of providing an arrangement as shown in FIG. 1 where this felt laps only the suction roll 40, the arrangement can be such that the felt 42 also laps the pick-up roll 30a. Moreover, in some cases the felt 42 may be entirely omitted, and in this event the suction roll 40 has an outer surface which is recessed to a large extent so as to be open to a large extent, having the highest possible fraction of its surface occupied by holes. For example in such a case 72% of the outer surface of the rol] 40 may be occupied by holes. In this latter event, the pressure which is applied 131.~1Lf;~rj~:

at the nip Nl must be relatively light, at a maximum on the order of 20kN/m line pressure. However, iE the felt 42 is used and the suction roll 40 or another equiva]ent roll has a very open surface, then large quantities of air will pass through the web W, while the vacuum level remains minimal. The use of low line pressures contributes to the preservation of the absorp-tivity and porosity in the web W. On the other hand, a certain minimum line pressure must be utilized at the nip Nl so that the web W will reliably adhere to the surface of the Yankee cylinder 50.
With the embodiment of FIG. 1, as well as with the em-bodiment of FIG. 2, the pick-up means, formed by the rolls 30a and 15 of FIG~ 1 and by the rolls 30b and 14d of FIG. 2 serves, in addition to its inherent pick-up action, also as a dewatering means. With this latter function in mind, the pick-up suction rolls 30a, 30b have a;so surfaces which are relatively open, which is to say surfaces formed with a relatively large number of recesses. For example the outer surfaces of the pick-up - rolls 30a, 30b may have openings or holes passing therethrough which occupy approximately 72% of the entire outer roll shell surface~ In this way as the web travels past the pick-up roll it is traversed by large quantities of air, while the vacuum levels remain relatively moderate. As a result it is possib]e in th~e embodiment of FIG. 1, for example, to provide for the web W a dry matter content immediately subsequent to the rolls 30a, 15 which is on the order of 25% and immediately subsequent to the nip Nl a dry matter content on the order of 42-45%.
An important new feature of the present invention resides in the manner in which the course of the pattern-embossing wire 32 or llb has been arranged. With the present invention the pattern-embossing wire is understood to be fairly losse woven wire having a mesh whose density is less than about 20 wi{es per _9_ cm. As is known, normal wires have a mesh density determined by on the order of 28-31 wires per cm.
Also in accordance with the invention it is possible to utilize as the fabric means which provides the embossed pattern a pattern-embossing wire which has a "base" of a higher density, for example a density equivalent to a normal wire, while upon this latter "base" wire there is a pattern-embossing fabric which has a lesser density, providing a relief pattern, with this lesser density being on the order referred to above, so that it is this mesh of lesser density which has its pattern impressed on tlle web W.
When operating the tissue paper machine of the invention, an attempt is made to avoid excessive pressing of the web, and dewatering is carried out primarily by way suction and adhesion.
FIG. 1 illustrates a heating means 60, in a schematic manner, this heating means 60 serving to heat the web W residing on the wire lla, so as to promote in this way the dewatering at the pick-up roll 30a and possibly also at the suctionroll 40.
The operation of the heating means 60 is based on steam supply and/or infrared heating, for example.
Moreover, just before the web W reaches the press suction roll 40, the water in the web is influenced by a means 61. This water-influencing means 61 can take the form either of a de-watering means and/or a heating means equivalent to the heating means 60. The means 61 when influencing the water by dewatering action may for example, be in the form of a planar perfusion dryer. The purpose of the means 60 and 61 is to control the dry-matter conten-t of the web W at the pattern-embossing stage so that this dry-matter content will be appropriate for different ~issue paper brands.
FIG. 3 shows a cross section of a web lOn manufactured with the machine of the invention, this web 100 being characte-,,~. ,. --10--,~, rized by the pattern 101 which is impressed by the pattern-embossing wire 32 or llb on one side only of the web 100. When the tissue paper machine of the invention is utilized, the paper web 100 which is produced thereby has a structure which is characterized by absorptive, high-bulk areas 103 and areas 102 of greater density which impart mechanical strength to the web 100, these latter areas 102 of greater density being indicated in FIG. 3 by heavier cross hatching than the other areas. The areas 102 will be situated at the web 100 at those locations where there wire 32 or llb has impressed the pattern 101.
As was indicated above, the inner felt 42 may be omitted, and this is particularly the case when producing thin paper, for example paper of less than 30 g/m base weight. As has been in-dicated above, it is then necessary to utilize for the press roll 40 a roll which has an outer shell which is open to a very large extent.
The tissue paper machine of the invention is characte-rized, when relatively open suction rolls are utilized, as described above, by economy of dewatering and furthemore by simplicity of its construction.
Of course, the invention is not to be narrowly confimed to the details presented above by way of example only, inasmuch as these details may vary within the inventive concept defined - by the claims which follow below.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Tissue paper machine in which the twin-wire former section comprises a headbox, a carrying fabric, a covering fabric, within the loop of the carrying fabric a forming roll, this forming roll having a smooth surface and the dewatering of the web on this forming roll being mainly by centrifugal force effect while the web is impacted between said fabrics, and said tissue paper machine having as its dryer a Yankee cylinder with which together a press suction roll defines a press nip, characterized in that through said press nip is arranged to pass a pattern embossing fabric embossing its pattern on the web in said nip and which is such that it also serves as a member transporting the web forwardly, the web being transferred onto the pattern embossing fabric by the aid of a pick-up means.

2. Tissue paper machine according to claim 1, characterized in that said press suction roll and its suction sector are lapped by a felt upon which the pattern embossing fabric and the web on the surface of the latter lap the said press suction roll.

3. Tissue paper machine according to claim 1 or 2, characterized in that the web is transferred from the carrying fabric of the former section by means of a pick-up suction roll onto the pattern embossing fabric and that said pick-up suction roll has an open surface so that it serves in addition to its inherent task, also as a component removing from the web a substantial amount of water.

4. Tissue paper machine according to claim 1, characterized in that the former section of the machine comprises a pattern embossing wire as carrying fabric, conveying the web over pick-up suction roll without any intermediate steps to a first and only press nip and that said pick-up suction roll has an open surface so that it also operates as a component removing from the web appreciable amounts of water.

5. Tissue paper machine according to claim 4, charac-terized in that the headbox of the former section is placed above the smooth-surface forming roll.

6. Tissue paper machine according to claim 1 or 2, characterized in that the surface of said press suction roll is open so that a substantial amount of water departs from the web on the suction sector of the press suction roll.

7. Tissue paper machine according to claim 1 or 2, characterized in that adjacent to the carrying fabric before the pick-up roll there is a heating means heating the water in the web.

8. Tissue paper machine according to claim 1 or 2, characterized in that adjacent to the pattern embossing fabric there is, before the suction roll, a dewatering means and/or heating means by the aid of which water is removed from the web and/or the water in the web is heated.

9. In a paper machine, twin-wire former means for forming a web, headbox means cooperating with said two-wire former means for supplying pulp stock thereto to be formed thereby into said web, press-nip means including a press suction roll, situated beyond said former means for providing at least one press nip through which the web travels, and fabric means extending between said twin-wire former means and said press-nip means and including a former portion which participates in the formation of the web at said twin-wire former means and a transfer portion for transferring the formed web to said press-nip means while travelling with the web through said press-nip, at least said transfer portion of said fabric means having a mesh for embossing a predetermined pattern in the web as it travels through said press-nip, so that said transfer portion of said fabric means operates on the one hand to transport the web to said press-nip means and on the other hand to emboss a pattern in the web.

10. The combination of claim 9 and wherein said twin-wire former means includes a pair of fabrics between which a web is formed by said twin-wire former means, said former portion said fabric means forming one of said pair of fabrics, and said twin-wire former means including a smooth-surface forming roll lapped by said pair of fabrics and providing for dewatering of the web during formation thereof by said twin-wire former means primarily by centrifugal force at said forming roll while the web which is being formed is compressed between said pair of fabrics while the latter lap said smooth-surface forming roll.

11. The combination of claim 10 and wherein said press-nip means further includes a Yankee cylinder which cooperates with said press suction roll to define said press-nip therebetween, said transfer portion of said fabric means travelling with the web between said Yankee cylinder and press suction roll so that said pattern is embossed on the web at the latter press-nip, said Yankee cylinder forming part of a drying means for drying the web subsequent to travel thereof through the press-nip.

12. The combination of claim 11 and wherein said former portion and transfer portion of said fabric means define between themselves a junction where the web travels from said former portion to said transfer portion of said fabric means, and pick-up means situated at said junction for picking up the web from said former portion of said fabric means and delivering the web to said transfer portion of said fabric means.

13. The combination of claim 12 and wherein a felt means laps said press suction roll and directly engages the latter while travelling through said press nip, said felt means being situated between said press suction roll and said transfer portion of said fabric means while the web is situated between said transfer portion of said fabric means and said Yankee cylinder.

14. The combination of claim 12 and wherein said pick-up means includes a pick-up suction roll means having a recessed outer surface for dewatering the web while said pick-up roll means also acts to pick up the web from said former portion and deliver the same to said transfer portion of said fabric means.

15. The combination of claim 14 and wherein said fabric means is in the form of a single endless fabric one part of which forms said former portion of said fabric means and another part of which forms said transfer portion thereof so that the embossing pattern provided by the mesh of said fabric means participates in the formation of the web at said twin-wire former means while the web is transported to said press nip by way of said single endless fabric of said fabric means.

16. The combination of claim 15 and wherein said headbox means is situated over said smooth-surfaced forming roll so that the web is formed while travelling downwardly around said forming roll between the pair of fabrics of said twin-wire former means.

17. The combination of claim 11 and wherein said press suction roll is formed with openings passing therethrough for providing for a substantial amount of dewatering at a suction sector of said press suction roll.

18. The combination of claim 12 and wherein a heating means is situated adjacent said junctionin advance of said pick-up means for heating water in the web just before the web reaches said junction.

19. The combination of claim 1 and wherein a means for influencing the water in the web is situated adjacent said transfer portion of said fabric means in the region of but in advance of said press suction roll.

20. The combination of claim 19 and wherein said means for influencing the water is a heating means.

21. The combination of claim 19 and wherein the means for heating the water is a dewatering means.

22. The combination of claim 12 and wherein said former portion and transfer portion of said fabric means are in the form of separate endless fabrics situated next to each other at said junction while the separate fabric which forms said transfer portion of said fabric means defines a closed loop in in which said pick-up means is situated at said junction for transferring the web from the endless fabric which forms said former portion to the endless fabric which forms said transfer portion of said fabric means.