GB1589800A

GB1589800A - Tissue paper-making machine

Info

Publication number: GB1589800A
Application number: GB15109/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-04-22
Filing date: 1978-04-18
Publication date: 1981-05-20
Also published as: BE866262A; BR7802481A; IT1094727B; FR2388076A1; CA1116452A; IT7822597A0; SE7804589L; DE2816581A1; CH627805A5; NO781397L; FI771295A7; JPS53134907A

Abstract

The tissue-paper machine contains, in a known way, a two-wire forming part with a run-on box (10a), a supporting cloth (11a), a covering cloth (12) and a forming roller (13) as well as, functioning as a drier, a glazing cylinder (50) which, together with a press-suction roller (40), forms a pressing point (N1). So that tissue paper with great softness, a high specific volume and high absorbency, at the same time with good strength, can be produced, a marking press cloth (32) is so arranged in the machine that it runs through the pressing point (N1), where it presses its marking into the paper web (W) and, in addition, also serves as an element further supporting the web (W), so that the web (W) is transferred on to the marking press cloth (32) by means of pick-up devices (30a, 30 alpha ). The supporting cloth (11a) can also itself be designed as a marking press cloth and be guided through the pressing point (N1). <IMAGE>

Description

(54) A TISSUE PAPER-MAKING MACHINE (71) We, KARI EBELING of Hasselbacka, 37120 Nokia 2, Finland, and RISTO TURUNEN of Kalervonkatu 13, 40200 Jyväskylä 20, Finland, both of Finnish nationality, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- This invention relates to a tissue papermaking machine of the kind in which there is a twin-wire former section with a headbox, a carrying fabric, and a covering fabric, and within the loop of the carrying fabric a forming roll on which the web is held between said fabrics, and there is a Yankee cylinder which together with a press suction roll~defines a press nip.The forming roll preferably has a smooth surface and the dewatering of the web on this roll is effected mainly by effect of centrifugal force.

Tissue paper is commonly manufactured by a method in which the web is formed on a comparatively short wire section resembling a normal planar wire and where the headbox supplies the pulp stock on to the breast roll, often open or provided with internal vacuum, whence the web passes, carried by the wire, past conventional dewatering elements such as table rolls, deflectors, foil strips, suction boxes and a suction roll, each of these removing water from the web. At the ultimate end of the wire section the partly dewatered web is transferred on to a so-called pickup felt, the web being carried by this felt to further drying in the press and drying sections. In some machines there is no planar wire section, and the web forming is then totally accompanished on a wire-coated suction breast roll, from which the web is transferred directly to the said pickup felt.

There are several known twin-wire formers intended for tissue paper manufacturing. Most of these twin-wire formers are so-called full throat formers, but such ave generally presented the drawback that, as a result of the use of a throat, a poor "formation" of the produced web is incurred. Various problems affecting the running of the machine are furthermore introduced, owing to the high dewatering rate at the initial draining step.

One object of the invention is to provide a tissue papermaking machine of the kind referred to and such that good qualities of softness, bulk and absorptivity, which are required of tissue paper, are achievable, preferably while improving the fibre retention and obtaining good strength in the finished paper without causing the above-mentioned qualities to suffer.

In many tissue paper manufacturing methods the wet paper web is pressed on the Yankee cylinder which effects the drying process, in such manner that the uniformity of the paper structure in the direction of the thickness dimension is maintained as exactly as possible. It is well known that with increasing machine speeds the drying capacity of the Yankee cylinder is the factor preventing any further increasing of production rate. In order that the drying capacity of the Yankee cylinder may be fully utilized in a crewed paper machine, it is common to subject the wet paper web to very powerful pressing with the aid of one or two Yankee cylinder presses prior to the start of evaporation drying proper.

Hereby it is achieved that the web is uniform over its whole breadth, but the softness and absorptivity characteristics of the end product are substantially impaired.

According to the present invention a machine of the kind referred to is characerized in that running through said press nip there is a pattern-embossing fabric or wire embossing its pattern on the web in said nip and which also serves to support and transport the web forwardly, the web being transferred on to or retained on the pattern-embossing fabric or wire by pick-up means.

In this machine the paper web can be wet pressed so that the end product will display, side by side, structural areas which have been Powerfully compressed and which therefore meet the strength requirements imposed on the paper structure, and other areas which have not been strongly wet pressed and which endow the paper structure with the features of softness and absorptivity.

How the invention may be put into practice is described below with reference to tlic accompanying schematic drawings, in which: Figure 1 shows parts of a machine wherein a pick-up roll is used to transfer the web from the former section to a patternembossing wire, Figure 2 shows parts of a machine wherein in the former section is a patternembossing wire which transports the web immcdiately to a press nip in connection with a Yankee cylinder, and Figure 3 is a cross-section through tissue paper that has been produced with a machine according to the invention.

Each illustrated tissue paper-making machine comprises the twin-wire former section with a hydraulic headbox 10a or 101 and a forming roll 13 with smooth surface.

The two wires are a covering wire 12 and a carrying wire 1 la or 1 lib. The covering wire 12 has guide rolls 14, and carrying wire has guide rolls 15. A dotted line W represents the web that is being formed.

In order to obtain a long and favourable draining region the machine of Figure 1 has a singlc-wire initial part 20 of the draining region, this part 20 extending from a breast roll 14a up to the point of contact of the wires 1 la and 12 with the forming roll 13. On this initial part 20 of the draining region with only one wire there is within the loop of the wire 12 a forming board 21 to promote the dewatering action in well-known manncr by foil action and/or suction. In association with the hydraulic headbox 10er are means 22 by the aid of which the size of the lip slice of the hcadbox 10a and its direction with reference to the wire 12 are regulated.On the sector of of the forming roll 13 where the web is held between the fabrics 1 lea and 12, the dewatering is mainly effected by the draining pressure produced by centrifugal force. Of the guide rolls for the wire 12 at least one roll 14b is adjustable so that the vacuum at the uppcr tangential point of the covering wire 12 anct the forming roll 13 can be adjusted.This vacuum adjust ment may be used to influence the detach mcnt of the web W from the covering wire 12. so that lhe web W will follow positively along with the carrying fabric lia. Such re liablc web transfcr is achievable only if there is a high enough dry mattcr content after the forming process, and this is achieved by the present combination of forming board and small-diameter forming roll 13.

As shown in Figure 2, the lip slice of the hydraulic headbox is above the smoothsurfaced forming roll 13, and the carrying wire 1 lb is a pattern-embossing wire, which transports the web to a Yankee cylinder 50 without any intermediate steps.

As shown in Figure 1, the web W formed on the carrying wire 1 la is detached from the wire 1 la by effect of the suction zone 302 of a suction roll 30a and transferred to the underside of a patternembosisng wire or felt 32, the web W passing on, carried by this wire or fabric 32, to the sole press nip N1.

As shown in Figure 2, the web W departing from the sector 7 of rall 13, sandwiched between the wire 11b and 12, is guided by means of the suction zone 303 of a suction roll 30b, to pass along with with patternembossing wire 1 lb. The web W is transferred on the underside of the wire 1 lib to the press nip N,.

In each machine the press nip Nl is defined by a suction roll having a suction zone 401 and the Yankee cylinder 50 provided with a hood 51. A felt 42 laps the suction roll 40 and is guided by rolls 43 and has reconditioning means (not shown).

The pattern-embossing fabric or wire 32 or 1 Ib, serves also for supporting and conveying the web to the press nip N1, where the web W becomes embossed with the pattern of the fabric or wire 32 or I lb.

The felt 42 passing around the suction roll 40 may be arranged to lap the suction roll 30a. In certain instances the felt 42 may be totally omitted, in which case the suction roll 40 is very open having the highest possible fraction of its surface occupied by holes, for instance 72% thereof.

In such a case the pressure applied in the nip N, has to be light, at the most about 20 kNim line pressure. If a felt 42 is used, then the line presesure in the nip N, may be higher than about 20 kN/m, preferably about 20 to 60 kN/m. When the felt 42 is used and the suction roll 40 or other equivalent roll has a very open surface, large quantities of air will be passing through the web iW, while the vacuum is not strong. The use of low line pressures contributes to preservation of absorptivity and porosity in the web W.

On the other hand a certain minimum line pressure must be used in the nip N, so that the web W is induced to become adherent to the surface of the Yankee cylinder 50.

Each machine comprises pick-up means 30a, 15 or 30b, 14d which serves in addition to its inherent pick-up action, also as a dewatering means. With this in mind, the pick-up suction rolls 30a; 30b have very open surfaces; the surface area covered by holes is, for instance, about 72 of the whole roll shell surface. Hereby the web W is traversed by large air quantities, while the vacuum is not strong. In the machine of Figure 1; for instance, the dry matter content of the web W following after the pair of rolls 30a, 15 is in the order of 250/, by weight and that after the nip Nl is in the order of 42 to 45%.

To be noted is the way in which the pattern-embossing fabric or wire 32 or llb is arranged. Herein a "pattern-embossing wire" is understood to be a fairly loosely woven wire with density lower than about 20 wires per cm. It is known, of course, that normal wires are in the order of 28 to 31 wires per cm. There may be used as the pattern-embossing wire a double fabric which has a " base " of higher density, for instance one equivalent to a normal wire, and upon this a less dense pattern embossing fabric (relief pattern) with a density e.g. of the lower order of magnitude above described, and which then impresses its pattern on the web W.

In the operation of the tissue papermaking machine of the invention the endeavour is to avoid excessive pressing, and the dewatering is accomplished mainly with the aid of suction.

In Figure 1 is shown a heating means 60 which heats the web W on the wire 1 la and thereby promotes the dewatering on the pick-up roll 30a and possibly also on the suction roll 40. The operation of the means 60 may be based on steam supply and/or infrared heating, for instance. There is also a dewatering means and/or a heating means 61. The means 61 may, for instance, include a planar perfusion dryer. The purpose of the means 60 and 61 is to control the dry mater content of the web W in the pattern-embossing step to be appropriate for different tissue papers.

Figure 3 shows a cross-section of a paper web 100 manufactured by the procedure of the invention, this web being characterized by a pattern 101 impressed by the patternembossing wire 32 or 1 ib on one side of the web 100. The structure of the web 100 shows absorptive high bulk areas 103 and greater density areas 102 which impart mechanical strength to the web 100, these latter being indicated in Figure 3 by heavier cross-hatching. The areas 102 will occur in the web 100 at those points where the fabric or wire 32 or lib has impressed the pattern 101.

The inner felt 42 may be omitted, particularly when producing thin paper, for instance paper of less than 30 g/m2 basis weight. As has been observed, it is then necessary to have an open surface of the press roll 40.

Such a tissue paper-making machine, when open suction rolls are used, can lead to economy in dewatering and simplicity in construction, and modifications are possible within the scope of the Claims following below.

WHAT WE CLAIM IS:- 1. A tissue paper-making machine of the kind in which there is a twin-wire forming section with a headbox (lox; lOb), a carrying fabric (1 lea; llb), and a covering fabric (12), and within the loop of the carrying fabric (lea;; llb) a forming roll (13) on which the web (W) is held between said fabrics (11, 12), and there is a Yankee cylinder (50) which together with a press suction roll (40) defines a press nip (no), characterized in that running through said press nip (N,) there is a pattern-embossing fabric or wire (32, llb) which embosses its pattern on the web (W) in said nip (Nl) and which also serves to support and transport the web (W) forwardly, the web (W) being transferred on to or retained on the patternembossing fabric or wire (32; llb) by pickup means (30v, 301; 30b, 30ss).

2. A machine according to Claim 1, wherein the forming roll has a smooth surface and the dewatering of the web (W) on this forming roll (13) is effected mainly by centrifugal force.

3. A machine according to Claim 1 or 2, wherein said press suction roll (40) and its suction sector (402) are lapped by a felt (42) upon which the pattern-embossing fabric or wire (32; llb) and the web (W) on the surface of the latter lap the said press suction roll (40).

4. A machine according to Claim 1, 2, or 3, comprising a pick-up suction roll (30) by which the web (W) is transferred from the carrying fabric (1 la) of the former section on to the pattern-embossing fabric (32), said pick-up suction roll (30) having an open surface so that it serves also as a component removing a substantial amount of water from the web (W) (Figure 1).

5. A machine according to Claim 1, 2, or 3, wherein the forming section of the machine comprises a pattern-embossing wire (ill) acting as a carrying fabric for conveying the web (W) over a pick-up suction roll (30b) without any intermediate steps to a sole press nip (no), and said pickup suction roll (30b) has an open surface so that it also operates as a component removing appreciable amounts of water from the web (W) (Figure 2).

6. A machine according to Claim 5, wherein the headbox (lOb) is placed above the smooth-surface forming roll (13) (Figure 2).

7. A machine according to any one of the preceding Claims, wherein the surface of said press suction roll (40) is open so that a substantial amount of water departs from the web (W) on the suction sector of the press suction roll (40).

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. is traversed by large air quantities, while the vacuum is not strong. In the machine of Figure 1; for instance, the dry matter content of the web W following after the pair of rolls 30a, 15 is in the order of 250/, by weight and that after the nip Nl is in the order of 42 to 45%. To be noted is the way in which the pattern-embossing fabric or wire 32 or llb is arranged. Herein a "pattern-embossing wire" is understood to be a fairly loosely woven wire with density lower than about 20 wires per cm. It is known, of course, that normal wires are in the order of 28 to 31 wires per cm. There may be used as the pattern-embossing wire a double fabric which has a " base " of higher density, for instance one equivalent to a normal wire, and upon this a less dense pattern embossing fabric (relief pattern) with a density e.g. of the lower order of magnitude above described, and which then impresses its pattern on the web W. In the operation of the tissue papermaking machine of the invention the endeavour is to avoid excessive pressing, and the dewatering is accomplished mainly with the aid of suction. In Figure 1 is shown a heating means 60 which heats the web W on the wire 1 la and thereby promotes the dewatering on the pick-up roll 30a and possibly also on the suction roll 40. The operation of the means 60 may be based on steam supply and/or infrared heating, for instance. There is also a dewatering means and/or a heating means 61. The means 61 may, for instance, include a planar perfusion dryer. The purpose of the means 60 and 61 is to control the dry mater content of the web W in the pattern-embossing step to be appropriate for different tissue papers. Figure 3 shows a cross-section of a paper web 100 manufactured by the procedure of the invention, this web being characterized by a pattern 101 impressed by the patternembossing wire 32 or 1 ib on one side of the web 100. The structure of the web 100 shows absorptive high bulk areas 103 and greater density areas 102 which impart mechanical strength to the web 100, these latter being indicated in Figure 3 by heavier cross-hatching. The areas 102 will occur in the web 100 at those points where the fabric or wire 32 or lib has impressed the pattern 101. The inner felt 42 may be omitted, particularly when producing thin paper, for instance paper of less than 30 g/m2 basis weight. As has been observed, it is then necessary to have an open surface of the press roll 40. Such a tissue paper-making machine, when open suction rolls are used, can lead to economy in dewatering and simplicity in construction, and modifications are possible within the scope of the Claims following below. WHAT WE CLAIM IS:-

1. A tissue paper-making machine of the kind in which there is a twin-wire forming section with a headbox (lox; lOb), a carrying fabric (1 lea; llb), and a covering fabric (12), and within the loop of the carrying fabric (lea;; llb) a forming roll (13) on which the web (W) is held between said fabrics (11, 12), and there is a Yankee cylinder (50) which together with a press suction roll (40) defines a press nip (no), characterized in that running through said press nip (N,) there is a pattern-embossing fabric or wire (32, llb) which embosses its pattern on the web (W) in said nip (Nl) and which also serves to support and transport the web (W) forwardly, the web (W) being transferred on to or retained on the patternembossing fabric or wire (32; llb) by pickup means (30v, 301; 30b, 30ss).

8. A machine according to any one of

the preceding Claims, wherein adjacent to the carrying fabric (lea) there is a heating means (60) heating the water in the web (W) before the web (W) reaches the pick-up roll (30a).

9. A machine according to any one of the preceding Claims, wherein before the suction roll (40) and adjacent to the pattern embossing fabric (32; llb) there is a dewatering means and/or heating means (61) by the aid of which water is removed from the web (W) and/or the water in the web (W) is heated.

10. A tissue paper-making machine constructed and arranged substantially as hereinbefore described with reference to and schematically illustrated in Figure 1 or Figure 2 of the accompanying drawings.