Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2001-12-27
2004-03-02
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S901000, C428S167000, C428S351000
Reexamination Certificate
active
06699368
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to papermaking and more particularly to a shoe press belt, for use in a papermaking machine, having a superior water draining effect, and to a method of manufacturing the belt.
BACKGROUND OF THE INVENTION
Shoe press devices adopted for use in the press stage of a papermaking process in recent years may be roughly divided into two types. One is shown in
FIG. 8
, and another is shown in FIG.
9
. In both of these shoe press devices, a shoe
62
is in opposed relationship with a roll
61
, with upper and lower endless felts
63
and
64
provided between the shoe and the roll, and a wet web P therebetween. A press belt
65
is arranged between the lower felt
64
and the shoe
62
so that the press belt
65
runs along with the lower felt
64
. The shoe
62
raises the press belt
65
, thereby pressing the felts
63
and
64
against the roll
61
. Thus, a relatively wide nip area is formed and water squeezing is effected by the pressure between the roll
61
and the shoe
62
.
The press belt
65
of
FIG. 8
is a comparatively long belt, spanning a plurality of rolls
66
, there being four such rolls in the particular shoe press device depicted in FIG.
8
. The press belt
65
is adapted to run under tension. On the other hand, the press belt
65
of
FIG. 9
is a comparatively short belt.
As shown in FIG.
10
(
a
), the press belt
65
, used for the two types of shoe press, is generally composed of a base member
65
a
sandwiched by a wet web side layer
65
b
and a shoe side layer
65
c
, both of which layers are composed of high molecular weight elastic members. The surface of the high molecular weight elastic member
65
b
is either a flat surface H as shown in FIG.
10
(
a
), or has a grooved water-holding section M as shown in FIG.
10
(
b
).
The press belt
65
, having a flat surface H as shown in FIG.
10
(
a
), may be completed at low cost, since only grinding the wet web side is necessary in the manufacturing process. The low manufacturing cost is the reason why this type of press belt is still in wide use. On the other hand, in the use of the press belt
65
of FIG.
10
(
b
), having a water-holding section M, the water squeezed from the wet web P (
FIGS. 8 and 9
) by the pressure applied by the roll
61
and the shoe
62
, is retained within the water holding section M, so that the water squeezing efficiency of the belt of FIG.
10
(
b
) is far greater than that of the belt of FIG.
10
(
a
). Unexamined Japanese Utility Model Publication No. 54598/1984 is representative of the belt having a water-holding section. In this case, a material having a hydrophilic property, such as polyurethane resin, is used as a high molecular weight elastic material.
Notwithstanding the improved water squeezing efficiency afforded by the press belt of FIG.
10
(
b
), the amount of moisture which remains in the belt has increased as result of the use of increased nip pressures and greater operating speeds in recent years, and this moisture retention has been an obstacle to water squeezing efficiency improvement. That is, when the nip pressure of the roll
61
and shoe
62
is increased, more water is squeezed from the wet web, but the result is that more water is held on the flat surface H (FIG.
10
(
a
)) or the water holding section M (FIG.
10
(
b
)) of the press belt
65
. Therefore, in some cases, because of the strong affinity of the press belt surface for moisture, resulting from hydrogen bonding, when the press belt is made hydrophilic as taught in Unexamined Japanese Utility Model Publication No. 54598/1984, water may not be shaken off adequately from the press belt
65
in the tangential direction.
Under the nip pressure in such a situation, because of the moisture saturation in the felts
63
and
64
, and in the press belt
65
, it has not been possible to drain water effectively from the wet web. The tendency of the belt to retain water has become more significant with the recent demand for higher speed operation in papermaking machinery. The underlying reason for the greater water retention at higher operating speeds is that the more rapid movement of the press belt
65
results in the shortening of the time interval between the successive compressions of given parts of the press belt
65
by the roll
61
and the shoe
62
. Consequently, the time available for water to be shaken off a given area of the press belt
65
between compression cycles inevitably becomes shorter. This has become a particularly acute problem in the operation of the shoe press device of FIG.
9
. Excessive water retention was not only a problem in the case of a press belt
65
having a water holding grooved section M, but was also encountered as a problem in the case of a press belt
65
having a flat surface H.
An object of this invention is to provide a belt for a shoe press, which is capable of solving the above-mentioned problems, thereby improving the water-squeezing function. Another object of the invention is to provide a novel method for the manufacture of such a belt.
SUMMARY OF THE INVENTION
To achieve the above-mentioned objectives, the shoe press belt in accordance with the invention is a shoe press belt in which a wet web side layer of a main body of the belt comprises a high molecular weight elastic material, characterized in that the surface of the wet web side layer is hydrophobic. Consequently, water squeezed from the wet web under compression in the shoe press device, and shifting to the surface of the wet web side layer of the main body of the belt through the felt, may be shaken off reliably before the belt is again subjected to compression.
If the main body of the belt also comprises a water holding section on the surface of the wet web side layer, both the surface of the wet web side layer and at least a part of the water holding section are preferably hydrophobic. Thus, the moisture which is squeezed from the wet web under compression in a shoe press device, passed through the felt, and held on the surface of the wet web side layer of the main body of the belt, and in the water holding section, may be shaken off reliably before the belt is again is subjected to compression.
In another embodiment of the invention in which a water holding section is provided on the surface of the wet web side layer of the belt, the surface of the wet web side layer may be hydrophilic, but at least a part of the inner surface of the water holding section is hydrophobic. In this case, moisture which is squeezed from the wet web under compression in the shoe press device, passed through the felt, and held on the surface of the wet web side layer of the main body of the belt, may be shaken off reliably by virtue of the hydrophobic property of the water holding section before the belt is again subjected to compression.
Preferably, the hydrophobic property is such that the contact angle between a drop of water and a reference plane corresponding to the surface of the belt is at least 50°, thereby enhancing the effect of the hydrophobic property of the surface of the wet web side layer, or of the water holding section, in promoting shaking of moisture off the belt.
The belt is preferably manufactured by forming a wet web side layer of a main body of the belt with a high molecular weight elastic material having a hydrophobic property, and forming a hydrophobic surface by grinding the surface of the wet web side layer. Thus, a surface having a hydrophobic property may be easily produced on the wet web side layer of the main body of the belt.
The method of manufacture may optionally include a third step, in which a water holding section is formed on the surface of the wet web side layer. Thus, both the surface of the wet web side layer of the main body of the belt and the inner surface of the water holding section, can be easily made hydrophobic.
In an alternative method, a wet web side layer of the main body of the belt is formed of a high molecular weight, hydrophobic elastic material, a film comprising a high molecular weight elastic material of hyd
Ishii Hirofumi
Ito Nobuyuki
Watanabe Kazumasa
Griffin Steven P.
Howson and Howson
Hug Eric
Ichikawa Co. Ltd.
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