Transfer fabric and papermaking machine using the same

BACKGROUND OF THE INVENTION

This invention relates to a transfer fabric for conveying wet paper from a sheet forming part to a hydro-extracting part and a papermaking machine using the fabric.

As means for receiving wet paper formed at a sheet forming part of a paper marking machine from a paper forming woven fabric of the machine and delivering the wet paper to a hydro-extracting part of the machine as the next step, a so-called needle felt obtained by applying vats of synthetic fibers one each to the obverse and the reverse face of a foundation formed by interweaving monofilaments or multifilaments and interlacing the vats by needling, and a wire which is a single-layer, double-layer woven fabric formed by using monofilaments have been known.

SUMMARY OF THE INVENTION

In a papermaking machine, delivery of wet paper is made at many places. This delivery process is generally effected by a forced aspirating device called transfer suction box or transfer suction roll. The method of harnessing the aspirating force is generally utilized because it is capable of most stably transferring wet paper. It nevertheless has disadvantages such as suffering the pressure of aspiration, when exerted more than that is proper, to extract fine fibers and filler together with water from the wet paper to the extent of adversely affecting the paper qualities, such as the evenness of surface smoothness on the obverse and the reverse side, curling property, and strength or inducing accelerated wear or abnormal wear on the paper forming woven fabric or felt. It also incurs higher cost for facilities and for maintenance and management thereof.

The needle felt has the vat densely gathered generally in the direction of z axis and, therefore, tends to accumulate fibers, filler, and chemical in the raw material for paper inside the body of felt. When a high-pressure washing shower is used for depriving the felt of such defiling substances, it tends to tear and bore holds in the vat of fibers and suffer from poor cleaning property. The papermaking machine of the type receiving the wet paper formed in the sheet forming part under nip pressure from the paper forming woven fabric and delivering the wet paper to the subsequent hydro-extracting part, therefore, is not allowed to increase the sheet forming speed but is prevented from improving the paper-producing property owing to the limited quality of the needle felt. For the purpose of conferring improved cleanability upon the needle felt, a woven fabric using monofilaments for both warps and wefts and keeping vats in an unneedled state have been tried. This woven fabric, however, has failed to withstand actual use because the transfer of water from the wet paper to the woven fabric is insufficient in the sheet forming part and the nip part and therefore the wet paper is not stably transferred to the woven fabric.

This invention, therefore, is aimed at providing a transfer fabric which is liberated from the drawback mentioned above and is enabled to manifest a satisfactory ability to transfer the wet paper and succumb fully to necessary cleaning and, as a result, improving the productivity of paper due to the use of this transfer fabric.

This invention relates to a transfer fabric used in a papermaking machine for receiving from a paper forming fabric the wet paper formed by a sheet forming part of the papermaking machine. The transfer fabric may be used for delivering the wet paper into a hydro-extracting part of the machine as the subsequent step. The transfer fabric is a clothed net produced by weaving monofilament wefts on the running face side thereof and plain yarn wefts of a small diameter so bound as to interpose water absorbing gaps therebetween on the wet paper receiving face side and monofilament or twisted monofilament warps. The wefts are in a plurality of layers and the warps are in a single layer. The warps of this invention can be monofilaments on the running face side of the fabric and can be monofilaments and/or plain yarns of a small diameter so bound as to interpose water absorbing gaps therebetween on the wet paper receiving face side of the fabric. The wefts can be disposed in a plurality of layers and the warps can be disposed in a plurality of layers.

The plain yarn wefts can be spun yarns, multifilaments, taslan finished yarns, twisted monofilaments, mole yarns, filament-processed yarns, yarns having spun yarns would on core lines of monofilaments, yarns having multifilaments wound on core lines of monofilaments, or yarns produced by co-twisting at least two kinds of yarns selected from any of yarns mentioned above.

A transfer fabric of the present invention may receive from the paper forming woven fabric wet papers formed by a plurality of sheet forming parts and delivers to the hydro-extracting part as the subsequent step the wet papers sequentially superposed in a plurality of layers. The transfer fabric of this invention will be discussed more in detail below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1

is a schematic diagram illustrating one example of the papermaking machine using the transfer fabric of this invention.

FIG. 2

is a schematic diagram illustrating another example of the papermaking machine using the transfer fabric of this invention.

FIG. 3

is a schematic diagram illustrating still another example of the papermaking machine using the transfer fabric of this invention.

FIG. 4

is a schematic diagram illustrating yet 35 another example of the papermaking machine using the transfer fabric of this invention.

FIG. 5

is a plan view illustrating one example of the transfer fabric of this invention.

FIG. 6

is a cross section along the line VI—VI

FIG. 5

which is in parallel to the warp direction.

FIG. 7

is a plan view illustrating one example of the transfer fabric of this invention.

FIG. 8

is a cross section along the line VIII—VIII in

FIG. 7

which is in parallel to the warp direction.

FIG. 9

is a cross section illustrating another 10 example of the transfer fabric of this invention as taken through the fabric along the warp direction.

FIG. 10

is a cross section illustrating still another example of the transfer fabric of this invention as taken through the fabric along the warp direction.

FIG. 11

is a cross section illustrating yet another example of the transfer fabric of this invention as taken through the fabric along the warp direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the transfer fabric in this invention to ensure 20 stable delivery of the wet paper, the invention must utilize the characteristics of the transfer fabric which is responsible for receiving the wet paper. The factors that determine the transferability of wet paper are the transfer fabric's surface density, area of contact with wet paper, ability to remove water from wet paper, etc. Particularly, the ability to remove water is important.

When the delivery of wet paper is effected by virtue of the nip pressure between two rolls, it is suspected that the nip pressure compresses the wet paper having a water content of about 85% and the transfer fabric playing the role of receiving the wet paper and that, after the rolls have loosed the pressure, the wet paper is transferred from the side of the paper forming woven fabric which has weak capillary attraction, namely the power to aspirate water from the wet paper, to the side of the transfer fabric which has a strong capillary attraction.

As viewed exclusively from the standpoint of this object, the needle felt which is filled throughout the entire depth from the obverse to the reverse surface thereof with a vat of fine synthetic fibers and, as a consequence, vested with high compressibility may well be rated as an optimum fabric on the receiving side. The fact that the water is aspirated from the wet paper as described above, however, automatically means that fine fibers, filler, chemical, etc. which are lodged in the wet paper enter the felt and that the felt must be cleaned. The dirt which has entered the felt defies removal and causes uneven spots and marks of dewatering because the felt has such a structure as is filled with a vat of fine synthetic fibers. When a high-pressure cleaning shower is used, the impact of the pressure of water tears and opens holes in the vat of fibers.

When a single layer woven fabric constructed by using monofilaments offering high resistance to the impact of the high-pressure cleaning shower for both warps and wefts or a two-ply woven fabric of wefts is adopted for the receiving side fabric with due consideration for the cleanability, the delivery of wet paper becomes unstable and the wet paper sustains breakage to the extent of degrading the rate of paper forming even when this fabric has finer mesh than the paper forming woven fabric. This phenomenon may be logically explained by a supposition that the fibers of paper, during the formation of a sheet of paper, thrust into the intersecting parts of the warps and wefts of the woven fabric and, as a consequence, the wet paper is not easily peeled from the paper forming woven fabric or it is not easily transferred even when the woven fabric on the wet paper receiving side has high surface density and contact area. An effort to stabilize the transfer by using a forced aspirating device results in degrading the quality of paper, aggravating the wear of the paper forming woven fabric, and posing the problem of a high cost of equipment and maintenance and management thereof.

To solve these problems, this invention contemplates using the construction of a clothed net having no use for a vat, namely by using on the wet paper receiving face side thereof such yarns as, for example, spun yarns, multifilaments, raising yarns, twisted monofilaments, mole yarns, filament-processed yarns, yarns having spun yarns wound on core lines of monofilaments, yarns having multifilaments wound on core lines of monofilaments, and yarns produced by co-twisting at least two species of yarns selected from thereamong and interweaving the yarns thereby giving rise to a multiplicity of capillary gaps in the fabric, improving the fabric in the ability to absorb water from the wet paper, heightening the power of the fabric to aspirate the wet paper, and stabilizing the reception of the wet paper and, meanwhile, using on the running face side thereof a reticular structure formed mainly of monofilaments thereby forming a polyfunctional woven fabric capable of securing three-dimensional empty spaces for easy passage of cleaning shower.

The term “spun yarn” as used in the present specification means what is obtained by bundling short fibers into a thread, namely a yarn produced by spinning, for example. The term “multifilament” means what is obtained by bundling fine short fibers into a thread, the term “raising yarn” means what is obtained by scratching and scuffing the surface of multifilaments with a needle-like object, and the term “filament-processed yarn” means a threadlike object obtained by subjecting filaments to such processings as stretching, bulking, and crimping and embraces yarns generally referred to as textured yarn, bulky yarn, and stretched yarn and even embraces wooly nylon. The term “mole yarn” means what is obtained by having short fibers disposed radially around the core of multifilament as the center. This term embraces what is produced by subjecting the radially disposed short fibers to a crimping treatment.

Further, this invention is furnished on the running face side with a reticular structure of monofilaments and, therefore, is enabled to acquire high rigidity for a woven fabric and diminish the dimensional changes (elongation in the direction of length and contraction in the direction of width) during service markedly as compared with the needle felt and produce a secondary effect of obviating the necessity for such devices as a stretcher and a measure roll. Further, the produced fabric suffers only a sparing decrease in thickness during service.

The needle felt gradually contracts with loss of 10 thickness and suffers gradual decrease in the ability to aspirate water in accordance as the cumulative duration of service increases. This invention incurs only sparing decrease in thickness and maintains a satisfactory ability to aspirate water until the termination of service life because the clothed net has high rigidity. As respects the resistance to the high-pressure cleaning shower, the vat of the needle felt is easily broken and expelled and compelled to sustain holes by the impact of the water of shower because this vat, though partially intertwined into the foundation, fundamentally has the individual fibers loosely interlaced mutually.

In contrast, the transfer fabric of this invention in its entirety has the construction of a clothed net, though the yarns forming the surface thereof are severally an aggregate of fine fibers similarly in the vat of the needle felt. Owing to this construction, the transfer fabric is neither broken or expelled by the impact of shower water because the wefts are interwoven in a short cycle into the warps and strongly restrained thereby and, by the same token, the warps into the wefts. This resistance to the impart of the high-pressure shower is another effect derived from the use of the construction of a clothed net for the wet paper receiving face.

The pattern of weaving is not particularly limited so long as the warps form layers of monofilaments or twisted monofilaments and the wefts have on the wet paper receiving face side thereof such yarns as are formed by binding plain threads of a small diameter in such a manner as to interpose water-absorbing gaps therebetween and have monofilaments so disposed in a multiplicity of layers on the running face side. Various constructions such as the combination of one ply of warps and two plies of wefts, combination of one ply of warps and three plies of wefts, combination of two plies of warps and three piles of wefts, and the construction of two layers each combining two plies of warps and two plies of wefts can be adopted.

The layer of monofilaments or twisted monofilaments in the warps fulfills the role of improving rigidity and dimensional stability and the monofilaments on the running face side the role of improving rigidity and resistance to abrasion. When the wefts on the running face side are made of polyamide, they excel in resistance to the pressure of nip and to the abrasion.

Polyester is adopted where rigidity forms an important consideration. Where the reconciliation of the two sets of properties is to be taken into account, polyamide and polyester may be alternately disposed. Where the warps are to be formed in two layers, those on the running face side may be monofilaments and those on the wet paper receiving face side such yarns as are obtained by binding plain threads so as to interpose water-absorbing gaps therebetween. The monofilaments on the running face main promote the improvement in rigidity and dimensional stability and the yarns on the wet paper receiving face side which result from winding plain threads so as to interpose water-absorbing gaps therebetween promotes the improvement in the ability to remove water.

An intermediate layer formed of monofilaments or of the same wefts as used on the wet paper receiving face side may be interposed between the wet paper receiving face side and running face side of wefts for the purpose of enabling the woven fabric to acquire cushionability and improved ability to remove water. Depending on the conditions being sought, the disposition of monofilaments may be relied on to improve the rigidity and the deposition of such yarns as are produced by binding plain threads of a small diameter so as to interpose water-absorbing gaps therebetween similarly to the wet paper receiving face side may be relied on to improve further the ability to absorb water. The quality intermediate the two sets of properties mentioned above may be attained by alternately disposing monofilaments and fib, plain threads of a small diameter.

The embodiments of this invention will be described with reference to working examples illustrated in the accompanying diagrams.

FIGS. 1 through 4

are schematic diagrams illustrating a papermaking machine using a transfer fabric

1

of this invention.

With reference to

FIG. 1

, the pulp slurry elected from a head box

3

is dewatered by paper forming woven fabrics

2

and

2

′, the wet paper consequently formed is received by the transfer fabric

1

by virtue of the nip pressure in the wet paper receiving part A. The plurality of wet papers thus formed are sequentially superposed and delivered to a hydro-extracting part (press part) B. In the part A, the wet papers are transferred to the transfer fabric. The A part has a nip pressure in the range of 3.5 7 kg/cm and is not fitted with a forced aspirating device.

FIG. 2

depicts another working example, which is identical with that of

FIG. 1

, excepting that the transfer fabric plays the roll of removing water and forming a base in the place of the paper forming woven fabric

2

′ on the left end side of the sheet forming machine.

FIG. 3

depicts still another working example which attains the transfer of the wet paper from the paper forming woven fabric

2

to the transfer fabric

1

by virtue of the pressure of contact of faces. It is not furnished with a forced aspirating device or a roll nip.

FIG. 4

represents yet another working example using the transfer fabric

1

for receiving the wet paper formed in a reticular cylinder

5

in the wet paper receiving part A by virtue of the nip pressure and sequentially superposing the wet papers, and delivering the superposed wet papers into the hydro-extracting part B.

FIG. 5

is a plan view illustrating one example of the 5 transfer fabric according to this invention and

FIG. 6

is a cross section taken along the line VI—VI of

FIG. 5

which is parallel to the warps.

For warps

6

, 90 polyamide monofilaments, 0.35 mm in diameter, are disposed per inch. For wefts

7

on the wet paper receiving face side, 28 yarns each obtained by co-twisting crimped yarns of polyamide multifilaments, 800 deniers in fineness and polyamide raising yarn, 540 deniers in fineness, are disposed per inch. For intermediate layer wefts

8

, 28 polyester monofilaments, 0.45 mm in diameter, are disposed per inch. For running face side wefts

9

, 28 polyamide monofilaments and 28 polyester monofilaments, 0.40 mm in diameter are disposed per inch. They jointly form eight shafts of weave of the combination of one ply warps and three plies of wefts.

FIG. 7

is a plan view illustrating one example of the transfer fabric of this invention and

FIG. 8

is a cross section taken along the line VIII—VIII of

FIG. 7

is parallel to the warps.

For warps

6

, polyester monofilaments are disposed. For wet paper receiving face side wefts

7

, polyamide spun yarns are disposed. For intermediate layer wefts

8

and running face side wefts

9

, polyamide monofilaments are disposed. Thus, eight shafts of the combination of one ply of warps and three plies of wefts are completed.

FIG. 9

is a cross section illustrating another example of the transfer fabric of this invention, as taken along the direction of warps.

For warps

10

, twisted polyester monofilaments are disposed. Fig wet paper receiving face side wefts

11

, polyamide spun yarns are disposed. For intermediate layer yarns, intermediate layer wefts

12

of twisted polyamide monofilaments and intermediate layer wefts

13

of polyamide monofilaments are alternately disposed. For running face side wefts

14

, polyamide monofilaments are disposed. Thus eight shafts of three piles of wefts are completed.

FIG. 10

is a cross section illustrating still another example of the transfer fabric of this invention, taken along the direction of warps. For wet paper receiving face side warps

15

, polyamide multifilaments are disposed. For running face side warps

16

, polyester monofilaments are disposed. For wet paper receiving face side wefts

17

, polyamide multifilaments are disposed. For intermediate layer wefts

18

, twisted polyamide monofilaments are disposed. For running face side wefts

19

, polyamide monofilaments are disposed. Thus, eight shafts of the combination of two plies of warps and three plies of wefts are completed.

FIG. 11

is a cross section illustrating a further example of the transfer fabric of this invention taken along the direction of wefts.

For wet paper receiving face side warps

20

, yarns having polyamide spun yarns wound around the core yarns of polyester monofilaments are disposed. For running face side warps

21

, polyester monofilaments are disposed. For wet paper receiving face side wefts

22

, wooly nylon yarns are disposed. For running face side wefts

23

, polyamide monofilaments are disposed. For binding yarns

24

, polyamide monofilaments are disposed. Thus, eight shafts of a two-layer woven fabric each combining two plies of warps and two plies of wefts are completed.

Next, the effect of this invention will be described below by citing the results of a comparative study conducted on the transfer fabrics of the working examples of this invention and the needle felt and the clothed net according to the conventional examples.

EXAMPLE 1

According to this invention adopted, the working 35 example illustrated in

FIGS. 5 and 6

and comparative examples adopted the conventional needle felt and the clothed net of monofilaments tested formerly.

COMPARATIVE EXAMPLE 1

This is a needle felt obtained by intertwining by needling a vat of polyamide at a rate of 1 kg per m

2

of foundation using twisted polyamide monofilaments for warps and polyamide monofilaments for wefts.

COMPARATIVE EXAMPLE 2

This is a 7-shaft woven fabric of the combination of one ply of warps and two plies of wefts, produced by disposing 180 polyester monofilaments, 0.15 mm in diameter, per inch for warps, alternately disposing a total of 96 nylon monofilaments, 0.13 mm in diameter, and polyester monofilaments, 0.17 mm in diameter, per inch for wet paper receiving face side wefts, and alternately disposing a total of 48 polyester monofilaments and polyamide monofilaments, each 0.22 mm in diameter for running face side wefts.

COMPARATIVE TEST

1. Sheet transfer

Discarded cardboard paper as raw material was processed on a paper forming woven fabric to produce wet paper. In a Tappi Standard Sheet Tester, the sample wet papers of the example and the comparative example were mounted as inverted on the wet paper receiving face, roll pressed (80 mm in diameter, about 0.75 kg/cm), and then relieved of a paper forming net to find which of the opposed faces the wet paper adhered to. At the same time, the wet paper samples were tested for water content.

The results are shown in Table 1. The transferability was superior in the decreasing order of working example and Comparative Example 1. The sample of Comparative Example

2 could not be stably transferred.

In terms of the water content of wet paper, Example 1 and Comparative Example 1 were on a par and Comparative Example 2 was slightly higher.

The paper forming woven fabric used in the test was a 7-shaft combination of one ply of warps and two plies of wefts, having 155 polyester monofilaments, 0.17 mm in diameter, disposed per inch for warps, a total of 86 polyester monofilaments and polyester monofilaments, 0.20 mm in diameter, alternately disposed per inch for wet paper receiving face side wefts, and a total of 43 polyester monofilaments and polyamide monofilaments, 0 22 mm in diameter, alternately disposed per inch for running face side wefts.

TABLE I

Weight of

Weight of

Paper

Amount

Water

Number

Accepted/

Wet paper

Absolutely

of water

content

Cycles

Rejected

(g)

Dried

(g)

(g)

EXAMPLE 1

1

Accepted

9.523

0.928

8.595

90.3

2

Accepted

9.125

0.944

8.181

89.7

3

Accepted

9.558

0.989

8.569

89.7

4

Accepted

10.177

1.002

9.175

90.2

5

Accepted

9.971

0.956

9.015

90.4

COMP EX 1

1

Accepted

11.883

1.172

10.711

90.1

2

Accepted

11.521

1.160

10.361

89.9

3

Accepted

12.117

1.201

10.916

90.1

4

Accepted

12.145

1.199

10.946

90.1

5

Accepted

11.742

1.193

10.549

89.8

COMP EX 2

1

Rejected

11.560

1.087

10.473

90.6

2

Accepted

11.621

1.111

10.510

90.4

3

Rejected

11.648

1.137

10.511

90.2

4

Accepted

11.931

1.124

10.807

90.6

5

Rejected

11.691

1.138

10.531

90.2

2. Property to resist shower

The samples of Example 1 and comparative examples were set in frames and exposed to high-pressure shower under the following conditions, and were examined to rate durability to resist the impact of shower.

Shower pressure: 20, 30 kg/cm

2

Nozzle diameter: 1 mm

Distance: 100 mm

Sliding distance: 50 mm in the direction of warps and 50 mm in the direction of wefts

Speed of sliding: 50 mm/30 sec. in the direction of warps and 50 mm/7 sec.

Under the shower pressure of 20 kg/cm

2

, the sample of Comparative Example 1 were observed to have sustained a fair number of holes, that of Comparative Example 2 showed absolutely no sign of trouble after one hour of test, and that of Example 1 was not observed to sustain any discernible rupture or breakage of yarns in spite of slight scuffing in 30 minutes of test.

Under the shower pressure of 30 kg/cm

2

, the sample of Comparative Example 1 sustained a hole before completion of one cycle, that of Comparative Example 2 showed absolutely no sign of trouble, and that of Example 1 showed no sign of either rupture or breakage of yarn in spite of slight scuffing in 10 minutes of test.

3. Property to resist nip

The samples were nipped between two opposed rolls and 30 slid therebetween under pressure under the following conditions and rate for fibrillation or disintegration of yarns.

Tension: 2.5 kg/cm

Nip roll: 40 mm (in diam)×2 (made of steel and plated with chromium)

Nip conditions: Dry 15 kg/cm

Stroke: 100 mm

Sliding speed: 50 cycles/mm

Number of sliding motions: 15,000 reciprocations

The sample of Comparative Example 1 suffered a decrease of 36.25% in thickness, though it showed no marked variation in appearance. The sample of Comparative Example 2 sustained fibrillation in the warps and upper and lower polyester monofilaments. It showed a decrease of 4.3% in thickness.

The sample of Example 1 showed absolutely no sign of fibrillation but barely suffered a slight crush into a flat face to occur in the yarns obtained by co-twisting raising yarns of polyamide multifilaments and crimped polyamide multifilaments for the wet paper receiving face side wefts. The decrease in thickness was 8.4%.

It is clearly noted from the test results described above that the transfer fabric of this invention was satisfactory in sheet transferring property, i.e. on a par with the needle felt, that it was decidedly superior to the needle felt though slightly inferior to the woven fabric produced with monofilaments in terms of the shower-resisting property, and that it was superior to the other two samples in terms of nip-resisting property.

The transfer fabric of this invention is capable of receiving stably and satisfactorily the wet paper formed in the sheet forming part from the paper forming woven fabric and then delivering it to the hydro-extracting part as the subsequent step.

It excels in the shower-resisting property, allows ready removal of the dirt therefrom by high-pressure shower cleaning, and consequently permits addition to the speed of paper formation.

It further excels in the nip-resisting property and incurs only a sparing decrease in thickness. It shows no sign of degradation in the cushionability and the ability to remove water even after a protracted use and, therefore, maintains a satisfactory sheet transfer property until the termination of service life.

Use of the transfer fabric which manifests satisfactory wet paper-transferring property and cleanability as described above ought to allow accomplishment of the ultimate object of this invention which resides in enhancing the productivity of paper.

The contents of Japanese Patent Application No. 9-238798 filed Aug.1, 1997 was incorporated herein by reference in its entirety.