Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2000-08-31
2001-12-18
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S306000, C162S901000, C442S077000, C442S221000
Reexamination Certificate
active
06331231
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a web transfer belt adapted to easily 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.
7
(
a
)
Referring to the prior art arrangement shown in FIG.
7
(
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.
7
(
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.
7
(
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.
As a technique to improve the paper release, two concepts have recently been proposed. A first one, as illustrated in the prior art arrangement shown in FIG.
8
(
a
), is a shoe press belt
23
having a web-receiving face
26
b
, and on the surface of which are formed many of protrusions
27
. A second one, as illustrated in the prior art arrangement shown in FIG.
8
(
b
), is a shoe press belt
23
also having a web-receiving face, and on the surface of which are formed many of recesses
28
′. The first one, as illustrated in the prior art arrangement shown in FIG.
8
(
a
), is a technique disclosed in Japanese patent document JP-A-94-57678. In this prior art technique particulate filler
27
, such as kaolin clay, inorganic material, polymer material and metal, which have a higher hardness than a high-molecular weight elastic member
26
, is mixed into the high-molecular weight elastic member
26
, reinforced by a base member
26
a
, and a web-receiving face
26
b
is polished to make particles of the particulate filler
27
protrude from the surface of the web-receiving face
26
b
, thus producing many of protrusions
27
′ on web-receiving face
26
b
. The protrusions
27
′ function to break-up the water film that is easily formed between web P and web-receiving face
26
b
, thus decreasing the adhesive force between web P and web-receiving face
26
b
of shoe press belt
23
. This result in the web being transferred to or received by a next step in the process with ease.
The second one, as illustrated in the prior art arrangement shown in FIG.
8
(
b
), is a technique disclosed in U.S. Pat. No. 4,552,620. This technique is such that when a high-molecular weight elastic member
26
, that is reinforced by a base member
26
a
, is formed, a portion of the upper surface of the base member
26
a
is spray coated so that many of closed isolated bubbles
28
are formed. High-molecular weight elastic member
26
and a web-receiving face
26
b
are then polished so as to form a very large number of recesses
28
′ by the opening of the originally closed bubbles
28
, at the surface. The recesses
28
′ function to break the water film that is formed between web P and web-receiving face
26
b
, and also decrease the adhesive force between web P and web-receiving face of the belt
23
, such that the web is transferred to and received by a next step in the process with ease.
However, in order to attain the above-described effect, it is required to mix particulate filler
27
into a high-molecular weight elastic member
26
at a content ranging from 30 to 40 percent weight (wt %). Particulate filler
27
is harder than the high-molecular weight elastic resin so that belt
23
itself comes to have a high hardness, which results in easy cracking, especially at edge portions of a shoe, thereby decreasing the durability of the belt. In addition, since particulate filler
27
is mixed in the range of 30 to 40 wt % in content, the weight of belt
23
increases, which is problematic to operations, such as, looping belt
23
over in a shoe press assembly.
In addition, many hours are required to manufacture a high-molecular weight elastic member into which closed bubbles are mixed by, e.g., spray jetted synthetic resin. Also, closed bubbles once formed in the synthetic resin mass disappear over time due to fluidity of the resin resulting from conventional spraying methods. Thus, while there is a need to raise the viscosity of the sprayed resin, as the viscosity of the spraying resin is higher, spraying of the resin in a stable manner is harder to achieve and patches of coating are produced more easily, with the result that many kinds of problems such as unevenness of bubble size occur.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention solves the foregoing and other problems associated with the prior art. Accordingly, it is an object of the present invention to provide a web transfer belt having good paper releasability, and that can be produced with ease and at a low cost without increasing either its hardness or weight, and to provide a production process for the same.
In order to achieve the above described object, a web transfer belt and production process for the same are provided comprising a high-molecular weight elastic member formed using a resin material mixed with microcapsules, and having a web-receiving face for receiving a web thereon to transfer, upon which web-receiving face there are provided a mult
Chin Peter
Duane Morris & Hecksch LLP
Hug Eric
Ichikawa Co. Ltd.
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