Papermakers felt with a resin matrix surface

A press felt base (single or multiple layer) having a plastic, fiber reinforced resinous matrix surface, wherein the surface is composed of a resin. The press felt base also having textile fibers distributed throughout the resin and having open air channels and voids throughout the resin once it is hardened.

BACKGROUND OF THE INVENTION 
Field of the Invention 
This invention pertains to fabrics used in the papermaking industry. More 
particularly it relates to felts used in the wet section of a papermaking 
machine. 
During the papermaking process, felts are used to dewater the paper web. 
The felts undergo severe environmental stresses, i.e., changes in 
temperature, pressure, humidity, etc. Despite these changes, the felts 
must retain compaction resistance, resiliency, wear resistance, 
dimensional stability and ability to uniformly distribute pressure. 
Various felts have been developed to meet these demands, however none have 
been found to be completely satisfactory. 
SUMMARY OF THE INVENTION 
The invention consists of an endless woven press felt base having any of 
the normal numbers of layers, with a plastic, fiber reinforced, resinous 
matrix surface replacing the normal needle-punched staple fiber surface. 
The resinous matrix consists of three phases, the first is a resin chosen 
for a given application. As an example polyurethane is used when 
workability and resiliency is desired and polyvinyl chloride is used when 
hardness and compact resistance is desired. 
The second phase is a network of textile fibers whose distribution, 
composition and size is engineered to enhance the mechanical properties of 
the total matrix. These fibers may be added to the molten resin prior to 
application onto the woven base, or may be present on the base prior to 
the application of the resin. 
The third phase is open channels and voids throughout the matrix to permit 
fluid flow. The overall void volume is controlled by fiber reinforcement 
structure, chemical additions and the method of resin application. After 
the resin is cured on the base, a separate grinding operation takes place 
to open sealed voids and channels and to impart a smooth, highly uniform 
surface to the felt. 
An object of the present invention is to provide a felt with superior 
compaction resistance. The matrix of the present invention will maintain 
caliper longer when subjected to the successive loading/unloading cycles 
in a nip press of a papermaking machine. 
Another objection of the present invention is to provide a felt with 
superior resiliency. The present matrix may be formed with resinous 
materials, such as polyurethane, which have an ability to recover from 
deformation which is superior to staple fibers. This results in a longer 
operational life of the felt and a cost savings from a reduced machine 
downtime associated with felt replacement. 
Yet another object of the present invention is to provide a felt with a 
better resistance to wear. This increased wear resistance arises from 
superior matrix material and the improved bonding mode. The 
thermo-mechanical and chemical adhesion of the present invention is by far 
better than the fiber entanglement used in the prior art. 
Still another object of the present invention is to provide a felt that is 
easy to keep clean. The resinous materials used in the present invention 
have an intrinsically low affinity for the contaminants found in the paper 
machine environment. 
An additional object of the present invention is to provide a felt which 
provides a uniform and complete pressure distribution between the paper 
web and felt surfaces in the nip. This feature of the present invention 
results in improved dewatering of the paper sheet. 
These and various other advantages and features of novelty which 
characterize the invention are pointed out with particularity in the 
claims annexed hereto and forming a part hereof. However for a better 
understanding of the invention, its advantages, and objects attained by 
its use, reference should be had to the drawings which form a further part 
hereof, and to the accompanying descriptive matter, in which there is 
illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 1 the woven press felt 20 is made endless to obtain the 
papermakers felt 10 of the present invention. The press felt base may be 
either constructed endless, seamed or joined. The felt 10 may be mounted 
in the press section of a papermakers machine after being treated as will 
be described hereinafter. 
FIG. 2 is an enlarged cross-sectional view of the felt 10 shown in FIG. 1 
and shows that the woven base 20 having a matrix coating 25 which is 
comprised of a thermoplastic resin 40, a network of fibers 30 and voids, 
and open channels 50 throughout the matrix. The voids and channels permit 
fluid flow in the matrix. 
The resin 40 is applied to the woven base 20 by conventional techniques, 
such as by dipping, spraying and the like of the liquid pre-former of the 
resin. The method and rate of application of the resin, along with the 
fiber reinforcement structure, will control the volume of voids within the 
matrix. The pre-former of the resin may contain fibers 30 prior to its 
application on the base. An alternative method is to have the fibers 30 on 
the woven base 20 prior to application of the resin. 
Following application, the resin 40 is dried and cured, employing 
conventional drying and heating apparatus. The temperature of curing will 
be dependent on the type of resin employed. A wide variety of such resin 
are known an many are commercially available. Representative resin which 
may be used are polyurethane for resiliency and cleanability and polyvinyl 
chloride for hardness and compaction resistance. Flexible coatings may 
also be formed from mixtures of polymeric resins. 
While the woven base 20 shown in FIG. 2 is a single layer, a greater number 
of layers in the woven base is also possible. Other modifications would be 
obvious to one skilled in the art without departing from the scope of the 
invention as defined in the appended claims.