Extended nip press belt having an interwoven base fabric and an impervious impregnant

An endless impervious, oil, abrasion, and crush resistant belt for use with papermaking machinery such as presses, especially of the extended nip type for the mechanical removal of water from a web of paper including a urethane coating impregnating a portion of a woven base providing multiple layers of base void of urethane and the portion impregnated impervious to oil, water, and air. The impregnated surface of the belt is made smooth and uniform in thickness through a grinding and polishing operation to act as a hydraulic bearing surface. The portion of the base void of urethane is capable of receiving and carrying water essential in the papermaking process.

BACKGROUND OF THE INVENTION 
The field of the invention relates to a belt used for extracting water from 
a web of material, and more particularly from a fibrous web formed in a 
papermaking machine. 
During the papermaking process, a web is formed by depositing a fibrous 
slurry on a forming wire. A large amount of water is drained from the 
slurry during this process, after which the newly-formed web proceeds to a 
press section. The press section includes a series of press nips. The web 
finally proceeds to a drying section including heated dryer drums where 
the water content is reduced to a desirable level. 
In view of the high cost of energy, it is desirable to remove as much water 
as possible from the web prior to its entering the drying section. The 
dryer drums in this section are often heated by steam and costs can be 
substantial if a large amount of water needs to be removed. 
The use of the extended nip press has been found to be advantageous over 
the use of nips formed by pairs of adjacent rollers. By extending the time 
the web is subjected to pressure in the nip, a greater amount of water can 
be removed. This fact has been recognized by those skilled in the art, and 
several patents have been granted in the area. These patents include Re. 
U.S. Pat. Nos. 30,268, 4,201,624, 4,229,253 and 4,229,254. 
Fibrous webs dewatered by a conventional belt in the extended nip press 
have been heavy weight flow controlled, sheets such as linerboard which 
has a basis weight of between 110 to 410 grams/sq. meter. The ability to 
dewater in "flow controlled" sheets is time dependent. The longer the 
dwell time in the press nip, the more water can be removed. The prior art 
sandwich felt system of dewatering linerboard in the extended nip press 
requires that the top roll be vented. Venting is generally accomplished by 
machining annular grooves in the top roll 0.100" deep by 0.02" wide at 8 
grooves to the inch of width. Water from the fibrous web is squeezed and 
passes into and through the sandwiched felts and channels into these 
grooves. Without the grooves, less water could be removed in the extended 
nip. 
Another consideration is that with the dewatering of lightweight webs of 
paper such as newsprint or fine paper which range from 40 to 95 grams/sq. 
meter, the function is more pressure controlled than flow controlled. 
Because lightweight paper dewatering is substantially pressure controlled, 
a grooved top roll would mark the sheet via the high loading in the 
extended nip press. The configuration of the extended nip press for use 
with fine paper or newsprint sheets would require the use of a smooth hard 
surface top roll and the elimination of the top sandwich felt which would 
provide the uniform pressure and impart a smooth surface to the web to be 
dewatered. 
The problem with this configuration is that there is no means for the 
expelled water to be evacuated from the extended nip with the grooves have 
been eliminated from the top roll. 
Attempts to make belts that have grooves on the felt side have been made. 
Unfortunately, the grooves mark the sheet and only provide a minimum of 
0.016 cubic inches of void per square inch of surface area. 
In using the extended press to dewater a fibrous web, the web has typically 
been sandwiched between two moisture-absorbing felts and a belt. The felts 
are trained around a cylindrical press roll with the web between them 
while the belt is arranged for applying pressure to the felts and roll. A 
pressure shoe exerts pressure on the belt in the press area and the shoe 
and belt are lubricated with hydraulic oil. 
SUMMARY OF THE INVENTION 
The invention is directed to a belt for dewatering a fibrous web used in an 
extended nip press provided by the roll and belt under the influence of 
the pressure shoe for applying pressure to the felt and fibrous web and 
belt in the nip. The belt comprises a base fabric which is partially 
impregnated with a thermoplastic or thermosetting polymeric material. The 
base fabric has a coated and impregnated side which would operate against 
the pressure shoe and a second side facing the felt and web. This second 
side contains voids into which water or other liquid could be transferred 
during passage of the felt and web through the nip. A significant 
advantage of this belt construction is that it can be made in any length 
since it does not require a mandrel during the manufacture thereof. A base 
fabric may be made endless using conventional fabric technology and then 
coated with the material. 
The present invention provides a means for the water to be evacuated from 
the nip when a solid top roll and single felt system is employed. The 
vented belt with its coated side running against the pressure shoe enables 
expelled web water to evacuate via the internal void volume on the 
uncoated side of the belt. 
The vented belt of this invention has a typical void volume of over 3 times 
that of a grooved belt. The belt of the present invention has a typical 
void volume of over 0.058 cubic inches/square inch of surface. This 
provides two functions. One--to be able to carry more water than a grooved 
belt, and second--to reduce hydraulic pressure which retards water flow. 
In addition to these advantages, the mere surface structure of the present 
invention provides a smoother surface to the wet felt and fibrous web thus 
reducing the possibility of mark to the fibrous web. 
The resulting structure is both light in weight and sufficiently stable to 
operate under paper machine conditions. It has sufficient abrasion 
resistance to resist any wear that might take place in the extended nip 
apparatus. Unlike materials which are built up in the manner of a rubber 
tire and can flow and/or delaminate, the invention provides a belt which 
will maintain its integrity. It also solves the problem of venting the nip 
press.

DETAILED DESCRIPTION OF THE INVENTION 
An extended nip press for dewatering a travelling web of material is shown 
in FIG. 1. The nip 10 is defined by a cylindrical press roll 12, a 
pressure shoe 14 having an arcuate surface facing the press roll, and the 
belt 16 of the invention arranged such that it bears against the surface 
of the press roll. The arcuate surface of the pressure shoe has about the 
same radius of curvature as the press roll. The distance between the press 
roll and the pressure shoe may be adjusted by means of conventional 
hydraulic or mechanical apparatus (not shown) connected to a rod 18 
pivotally secured to the shoe 14. The rod may also be actuated to apply 
the desired pressure to the shoe. It will be appreciated that the pressure 
shoe and press roll described above and shown in FIG. 1 are conventional 
and that other arrangements may be utilized in accordance with the 
invention. 
An embodiment of a two-layer belt 16 constructed in accordance with the 
invention is shown in detail in FIG. 2. The belt 16 comprises a two-layer 
woven monofilament base fabric 20 with multifilament or spun stuffer yarns 
21. The belt is partially impregnated with a polymeric material 22 with 
the stuffer yarns acting as barriers to the impregnation of the belt on 
the remaining side, which is the lower side as shown in FIG. 2. 
Thermosetting resins such as polyurethanes have been found to be suitable 
impregnating materials. Thermoplastic polymers such as polypropylene are 
also acceptable. 
The base fabric 20 is sufficiently open to allow impregnation to eliminate 
the possibility of undesirable voids forming in the final fabric on the 
pressure shoe side. These voids are undesirable because they allow the 
lubrication used between the belt and shoe to pass through the belt and 
contaminate the felt and fibrous web. The stuffer yarns 21 provide a 
barrier of sufficiently low permeability to prevent passage of the resin 
during the coating and impregnating process to the side with voids. It is 
endless in final construction and uniform in thickness. The fabric must 
also be made to have sufficient stability under paper machine conditions. 
In other words, it must have length stability, width stability, and 
guidability. 
The thermoplastic resin or thermosetting resin used should be substantially 
one hundred percent solid composition to avoid the formation of bubbles 
during the curing process of the resin in the belt structure which . could 
cause voids on the coated side. 
Side 17 of the belt can be ground smooth for contact with the pressure shoe 
14. The opposite side contains voids, as a result of the weave and absence 
of impregnation, into which liquid can be transferred during the passage 
of the web, felt and belt through the nip. It has been found that the 
preferred range of void volume on the vented (nonimpregnated) side of the 
belt is from 0.005 cubic inches per square inch of surface area to 0.20 
cubic inches per square inch of surface area. 
A three-layer embodiment of the invention is shown in FIG. 3. The 
components are similar to those in FIG. 2. The components of FIG. 3 are 
numbered as those of FIG. 2 with a prime following. Belt 16' of FIG. 3 is 
a multilayer structure with a barrier layer provided by stuffer yarns 21'. 
These stuffer yarns, 21', can be multifilament or spun. The belt is coated 
and impregnated as described previously to provide a smooth impervious 
surface 17' and a surface with voids 18' on the remaining side. The use of 
belt 16' is the same as previously described for belt 16. 
A four-layer embodiment of the invention is shown in FIG. 4. The components 
are similar to those in FIGS. 2 and 3 and are numbered the same with a 
double prime following. Belt 16'' of FIG. 4 is a four-layer structure with 
a barrier layer provided by stuffer yarns 21'' which can be multifilament 
or spun. The belt is coated and impregnated as previously described to 
provide a smooth impervious surface 17'' and a surface voids 18''. An 
example of the embodiment of FIG. 4 is the four-layer duplex weave having 
a spun yarn stuffer the cross machine direction and located between the 
first and second layers. 
A single system of warp yarns 24 comprised of 0.016 inch diameter 
monofilament nylon arranged in a density of 80 to the inch. 
A multiple system of weft yarns 26 comprised of four layers of 0.021 inch 
diameter monofilament nylon arranged in a density of 64 to the inch. 
Between the first and second layers, a spun stuffer 21" comprised of 100% 
polyester staple fiber 6 denier, 31/2" staple, single ply, at a weight of 
1,000 grams per 100 yards, at a density of 16 to the inch. 
The entire base structure weights 5.4 ounces per square foot and after 
impregnating on the spun stuffer side, 11.46 ounces per square foot. 
Belts manufactured in accordance with the invention have been found to have 
many desirable characteristics. They move easily over the pressure shoe 
and are capable of transmitting pressure from the shoe to the web and 
press roll. Sufficient flexibility is obtained, and the belts have proven 
to be unaffected by lubricant applied prior to entering the press nip. 
The manufacture of the belt according to the invention may be accomplished 
economically and without the need for mandrels or autoclaves which limit 
the size of other belts. A belt of any length can accordingly be produced. 
A web may be needled into the woven base if desired. If the base structure 
has not been woven endless it is joined endless using conventional joining 
techniques applicable to forming fabrics in the paper industry. 
The belt is easily repaired should a hole or other surface irregularity 
develop therein. The damaged portion can be cleaned with a solvent and a 
suitable amount of coating applied to the affected area. A heat gun can 
then be employed to cure the surface which can then be sanded. 
Because of the excellent flexibility characteristics of the base structure 
and the fact that the coating layers can be kept to a minimum, the surface 
of the belt will have less tendency to fail due to bending fatigue. This 
is due to the fact that, because of the low caliper, the surface plane of 
the coated surface is at a minimum distance from the neutral axis of 
bending. 
It will be appreciated that the belt utilized in the invention may include 
a base fabric made from various polymeric materials having the necessary 
properties for application in papermaking machines. Materials other than 
polyurethane and polypropylene may also be employed as the coating 
material. Also the weave of the belt may be altered although a 
multilayered belt is desirable for creation of the voids. Known coating 
and impregnating techniques may be employed in the practice of this 
invention.