Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2000-08-31
2001-11-20
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S358200, C162S358400, C162S901000, C442S280000, C442S281000
Reexamination Certificate
active
06319365
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a web transfer belt with a web-receiving face on which water-repellent portions and water-condensing portions are dispersed, making it possible to break a water film formed between a web-receiving face and a web, and a production process for the same.
BACKGROUND OF THE INVENTION
As is well known to those skilled in the paper-making art, a web is dewatered by a pressing pressure applied in a press section of a paper-making machine. For example, it is known in the prior art to provide a web pressure-dewatering means and web transfer means, in the pressure section of a paper-making machine, in the form of a combination of a pair of press rolls with a pair of needled felts therebetween. More recently, a variety of means for imparting pressure onto a web have been provided with a combination of a single press roll and a shoe in order to improve the dewatering efficiency through an increase in the nip width, under application of a pressure, on the web. One example of the latter combination is known as a shoe-press assembly, whose simplified construction is illustrated in FIG.
8
(
a
)
Referring to the prior art arrangement shown in FIG.
8
(
a
), a shoe press assembly
20
includes a press roll
21
and a shoe
22
, wherein the shoe
22
is shaped so as to conform to the press roll
21
along its circumference. In this way a nip width N under an applied nip pressure is large when compared to an arrangement employing a pair of press rolls. A shoe-press belt
23
, that is constructed of a high-molecular elastic member, e.g., such as urethane, and a base cloth layer, runs between press roll
21
and shoe
22
. A web P runs between shoe-press belt
23
and press roll
21
, so as to be sandwiched between upper and lower needled felts
24
and
25
. As a consequence, web P is press-dewatered, under the nip-pressure produced between press roll
21
and shoe
22
, with the squeezed-out water migrating into upper and lower needled felts
24
and
25
.
In this situation, however, as the water migrates into the upper and lower needled felts
24
and
25
, they expand in sections where the felts are relieved of the nip pressure. As a result, the water accumulated in felts
24
and
25
actually migrates back into web P, by capillary action, thus rewetting the paper and causing a reduction in the efficiency of the dewatering process.
In order to solve the rewetting problem, a shoe press assembly
20
′, as illustrated in the prior art arrangement shown in FIG.
8
(
b
), has been proposed, and which is disclosed in U.S. Pat. No. 4,483,745. In the shoe press assembly
20
′, a web P is sandwiched between a single needled felt
24
and a shoe press belt
23
and dewatered under application of a nip pressure produced by a press roll
21
and a shoe
22
, such that the squeezed-out water migrates into needled felt
24
. This arrangement still rewets the paper, since even though needled felt
24
is only a single piece, a portion of the water absorbed in sections of the felt having lower applied pressure still migrates back to the web.
Also in the prior art arrangement shown in FIG.
8
(
b
), the web P of shoe-press assembly
20
′ and received on shoe press belt
23
has suffered from difficulties associated with paper transfer to and reception by a next step in the process. In particular, the surface of shoe press belt
23
is often highly polished so as to be very smooth. As a result, a water film of a uniform thickness is produced in a clearance between shoe press belt
23
and web P, whereby web P strongly adheres to shoe press belt
23
in the presence of the water, resulting in very poor paper release.
In order to solve the above-described problem, a shoe press belt
23
, as shown in FIG.
8
(
c
), is disclosed in Japanese Patent document No.: JP-A-94-57678. Here, shoe press belt
23
includes many recesses and protrusions formed on the surface of a web-receiving face
26
b
of a high-molecular weight elastic member
26
, which is reinforced with a base member
26
a.
The recesses and protrusions are formed in such a way that high-molecular elastic weight member
26
is mixed, in advance, with particulate filler of a material of a higher hardness, such as kaolin clay, inorganic material, metal or the like, and in a following step, the web-receiving face
26
b
is polished off to expose particles of the particulate filler
27
on the surface. Shoe press belt
23
includes many recesses and protrusions, formed from particulate filler
27
, on a surface of web-receiving face
26
b.
These recesses and protrusions are capable of breaking a wafer film formed between web P and web-receiving face
26
b
under application of the nip pressure, which decreases the adhesiveness between web P and shoe press belt
23
due to the presence of water. This arrangement enables transfer and reception of web P to and by the next step in the process.
This type of shoe press belt
23
, which has web-receiving face
26
b
having many recesses and protrusions made by particulate filler
27
requires the technically hard steps of mixing particulate filler
27
into a non-processed material of a high-molecular weight elastic member; coat impregnating the non-processed material, consisting of high-molecular weight elastic member
26
mixed with the particulate filler
27
, on and into a base member
26
a;
and curing the coat impregnated non-processed material. Further, the presence of particulate filler
27
creates an obstacle to controlling the global thickness of the belt after curing and polishing of the web-receiving face
26
b
to improve smoothness. In addition to this, while the polishing step is performed by pressing a polishing object onto the belt, which has been extended and driven between two rolls, many of the particles of particulate filler
27
that are exposed on web-receiving face
26
b
are hollowed out and fall off. Thus reducing the effectiveness of the particulate filler
27
.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly it is an object of the present invention to provide a web transfer belt with good paper releasability and having stable surface features.
It is another object of the present invention to provide a novel production process enabling easy production of a web transfer belt with good paper releasability and having stable surface features.
In order to achieve the above-described objects, the present invention provides a web transfer belt including a high-molecular weight elastic member having a web-receiving face for receiving a web thereon to transfer. A surface layer is formed on the high-molecular weight elastic member is exposed on the web-receiving face, wherein one of the web-receiving face and the surface layer forming member is made of a hydrophobic material. In this way, water-repellent portions and water-condensing portions are dispersed on the web-receiving face along with fine scale recesses and protrusions which can break a water film formed between the web-receiving face and a web.
In one embodiment of the invention, a web transfer belt is provided in which the surface layer forming member is constructed of at least one of a needled felt integrated by needling a fiber layer onto fibers, threads or a woven fabric, a non-woven fabric stacked with fibers, and a cloth woven with threads. In this way, the exposed portions of the surface layer are part of the surface layer forming member, and are easily formed on the web-receiving face so as to yield a stable surface.
In another embodiment of the invention, a web transfer belt is provided in which the surface free energy of the hydrophobic web-receiving face or the hydrophobic surface layer forming member is 30 dyn/cm or less. In this way, water-film repellent forces on the hydrophobic side and a water-film condensing forces on the hydrophilic side increase.
A production process for a web transfer belt is also provided comprising a first step of determining a non-processed material of one of a high-molecular weight elastic member and a surface layer formi
Chin Peter
Duane Morris & Heckscher
Hug Eric
Ichikawa Co., LTD
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