Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PAPE:RMAKING FELTS AND FIBERS HAVING IMPROVED ANTIREDEPOSITION
PROPERTIES
Backt~rr~und of the Invention
1. Field of the Invention
The present invention relates to papermaking felts and the fibers used to make the felts.
More specifically, the invention relates to felts and the fibers used to make the felts which
10 have coated thereon a polymer which is capable of inhibiting the formation of conla""nants onto the felts and fibers.
2. Technology Description
In general, papermakers' wet felts comprise an endless belt having a smooth paper-
receivin~g surface and an abrasion-resistant machine roll contacting surface. The press
felts pelform the function of supporting the paper web during the dewatering process,
advancing the paper web to the next stage in the papermaking process, and serving as a
receptacle for water removed during the dewatering process, the water also being conveye d away from the processing by the press felt.
During processing as it is known in today's papermaking industry, tremendous roll
pressures and high speeds are developed. Accordingly there is a tendency for the wet
press felts to wear rapidly due to abrasion and, additionally, to lose porosity and therefore
the abilily to remove water from the paper web.
Since the 1960's, the paper industry has witnessed and experienced the impact of a paper
machine clothing evolution, especially in the press section. The older batt-on-base needled
felts have been replaced by more sophisticated batt-on-mesh needled designs which yield
greatemiewatering efficiencies and longer felt life. These early needled felts had a base
woven from spun staple fibers into which the batt fibers, generally nylon, were inserted by
the needling process. The weight percentage of the base fibers was relatively high and
these fibers were mainly oriented in the machine and cross-machine directions. Thus only
a smalH3mount of the capillary volume in the felt was formed by the batt fibers which were
mainly \lertically oriented. When these felts underwent dewatering on the paper machine
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by passing through the nip of squeeze rollers, the fibers in the base fabric became
compressed, particularly at the crossover points. As the base fibers compressed, the
overall felt rapidly lost porosity and capillary structure, yielding poor dewatering properties.
Additionally, the compressed fibers increasingly trapped fine particles from both paper and
fracturecl felt fibers which further led to early felt failure. The newer batt-on-mesh felts
utilize high-strength twisted multifilament yams or monofilaments. The mesh base not only
has greater open area between machine and cross-machine yams, but also resists
compaction to a greater degree than the spun yam base. This greater initial porosity and
resistance to compaction has resulted in improved felt life. However, these yams have the
disadvantage of reduced retention of the batt fibers and lower abrasion resistance of the
mesh under certain conditions due to fibrillation of the filament surface.
Also known to the prior art is a mesh base which contains highly twisted multifilaments,
usually nylon, impregnated with phenolic resin. These twisted yarns are impregnated
before weaving by immersing the yarns in a solution of phenolic rein followed by drying at
a sufficiently low temperature to evaporate the solvent without curing the resin. The treated
yams in this state remain reasonably flexible to facilitate weaving of the mesh fabric. After
needling the batt onto the mesh, the felt is then heat treated at a temperature which will
crosslink the phenolic resin into a finally cured stage. However, these phenolic resin-
impregnated yarns suffer from poor batt retention and are difficult to weave due to the high
friction surface characteristics of the impregnated material.
The fibers and papermaker's belts can also be negatively effected by contaminants which
can be present during the paper making cycle. Contaminants typically are hydrophobic
material; such as waxes, glues, naturally occurring pitch, hot melts, latexes, oils and the
like which contaminate the machine clothing and thereby hinder the performance of the
clothing. Attempts have been made in the art to improve the fibers and belts produced
thereby to improve their durability.
U.S. Pal:. No. 4,093,512, discloses a papermakers' belt comprising ultrahigh modulus load
bearing yarns which may be resin coated or wrapped and then resin coated to improve
their abrasion resistance. Among the resins suggested for coating the high modulus yarn
are acrylic resins, phenolic resins, and nylon resins.
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U.S. Pat. No. 4,259,394, discloses a papermaking fabric composed of a base having a
fibrous batt needled to one surface thereof. The base is formed of interwoven core
wrapped yams comprising core yams which are effectively heat infusible and wrapping
5 yams which are effectively heat fusible. Polyethylene and polypropylene are the only
resins disclosed as wrapping materials.
U.S. Patent No 4,520,059 discloses the use of ionomer-coated yarns and their use in
papermaker's wet press felts. The ionomer resin coating tends to be a metal salt of a
10 copolyrner of ethylene and a vinyl monomer containing an acid group.
U.S. Patent No. 4,861,429 discloses a process for inhibiting white pitch deposition in
papermaking felts. The process includes the addition to the felts of an effective inhibiting
amount of an organic, anionic polyelectrolyte.
Thus a need has continued to exist for a yam suitable for forming the mesh layer of
papemlakers' wet felt which has good abrasion resistance, good durability, good
toughness, good resistance to compression, good adhesion at the crossover points, low
frictional characteristics, good needling characteristics regarding both integrity of the base
20 yams and batt retention, and good handling characteristics during weaving.
The use of copolymers of polyethylene terephthalate and polyoxyethylene terephthalate
has been suggested as soil release promoting materials for polyester fabrics. This use is
suggestled in U.S Patent Nos. 4,785,060, 4,873,003, 4,569,772 and 5,234,753 and is
25 directed for fabrics which are worn as clothing items whereby the copolymer is present in
laundry detergent. The above patents have not suggested the use of these copolymers in
connect on with fabrics and fiber webs used in paper making.
Despite the above teachings, there still exists a need in the art for forming fabrics, press
felts and drying felts used in paper making and the fibers used to fomm such fabrics and
felts which have excellent durability and resistance to hydrophobic deterioration.
Brief Summary of the Invention
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In accordance with the present invention novel forming fabrics, press felts and drying felts
used in paper making and the fibers used to form such fabrics and felts which has
excellent durability and resistance to hydrophobic deterioration are provided. The
durability and hydrophobic deterioration resistance properties are obtained by applying to
5 fabric or the fibers a hydrophilic material such as a copolymer of polyethylene
ter~phlllalate and polyoxyethylene terephthalate in the case of polyester fabrics or a
hydrophilic polyamine or polyamide in the case of nylon or nylon-blend fabrics.
One embodiment of the present invention comprises polyester-based novel forming
fabrics, press felts and drying felts used in paper making having associated therewith a
hydrophilic material, preferably a copolymer of polyethylene terephthalate and
polyoxyethylene terephthalate.
Another embodiment of the present invention comprises nylon-based novel forming
fabrics, press felts and drying felts used in paper making having associated therewith a
hydrophilic polyamine or polyamide.
In preferred embodiments of the present invention the hydrophilic material is either
topically heat set into the final product, is included as a coating to the extruded fibers used
to form l:he final fabrics or felts or is used in topical cleaning of the final product. Presence
of the hydrophilic material renders the surface hydrophilic and, accordingly capable of
either repelling or releasing hydrophobic contaminants which would otherwise deteriorate
the clothing surface.
Still another embodiment of the present invention comprises a process for improving the
durability of a polyester forming fabric, press felt or drying felt used in paper making
col"prising the step of associating with the fabric or felt a hydrophilic material, preferably a
copolynner of polyethylene terephthalate and polyoxyethylene terephthalate to render the
fabric or felt hydrophilic.
Yet another embodiment of the present invention comprises a process for improving the
durability of a nylon forming fabric, press felt or drying felt used in paper making
comprising the step of associating with the fabric or felt a hydrophilic polyamine or
polyamide to render the fabric or felt hydrophilic.
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An object of the present invention is to provide forming fabrics, press felts or drying felts
used in paper making having improved resistance against deterioration by hydrophobes.
Still ancther object of the present invention is to provide a process for rendering fomming
fabrics, press felts or drying felts used in paper making resistant against deterioration by
hydrophobes.
These, and other objects, will readily be apparent to those skilled in the art as reference is
10 made tc the detailed description of the preferred embodiment.
Detailed Description of the Preferred Embodiment
In describing the preferred embodiment, certain terminology will be utilized for the sake of
clarity. Such terminology is intended to encompass the recited embodiment, as well as all
technical equivalents which operate in a similar manner for a similar purpose to achieve a
similar result.
The present invention provides improved properties to forming fabrics, press felts or drying
felts used in paper making as well as the fibers used to form such fabrics or felts. For
purposes of this document the term "fabric" will encompass all such embodiments. In
practice, the final fibrous substrate is either a polyester or a nylon material. The fibers
used to form the final products may be either monofilament or multifilament yarns,
including highly twisted yarns. Twisted yarns are preferred because of their round core
and low compressibility. Most preferred are twisted yarns of plied construction, the plied,
twisted yarns demonstrating the lowest degree of compressibility.
Techniques for fabricating final fabrics and felts from yarn are well known to the art. The
base fabrics may be of the woven or non-woven type. Any of the conventional weaving
patterns known in the art are contemplated as within the scope of this invention, with the
final product being used in both the machine and cross-machine direction, in the case of a
woven fabric, and as the principal yarn, in the case of a non-woven fabric.
To render the fabrics resistant to deterioration as a result of the presence of hydrophobic
con~a",inants such as waxes, glues, naturally occurring pitch, hot melts, latexes, stickies,
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oils and the like that can otherwise contaminate the fabric and hence hinder theperfomm,ance of the fabric, a hydrophilic material is associated with the fabric. If the fabric
is made from polyester yam, the hydrophilic material is preferably a copolymer of
polyethylene terephthalate and polyoxyethylene terephthalate. If the fabric is made from
nylon yam, the hydrophilic material comprises a hydrophilic polyamine or polyamide.
In the embodiment wherein the hydrophilic material is a copolymer of polyethylene
lerephthalate and polyoxyethylene terephthalate, such materials are defined in any of U.S
Patent Nos. 4,785,060, 4,873,003, 4,569,772 and 5,234,753 for their soil releasing
0 properties when used in association with laundry detergents. To the extent necessary for
completion, these patents are hereby expressly incorporated by reference.
More specifically, in the preferred embodiment, the hydrophilic material is a non-fiber
fomming polyester-polyether copolymer, more specifically, polyethylene terephthalate -
polyoxyethylene terephthalate (PET - PEOT) copolymers. Such PET-PEOT copolymers,typically having an average molecular weight in the range of from about 5000 to about
50000, may be prepared by polymerization of dimethyl terephthalate (DMT) and ethylene
glycol (E.G) in the presence of a mixed catalyst system.
The copolymer material of which the hydrophilic properties are provided is comprised
preferably from about 10 to 50 percent by weight of ethylene terephthalate repeat units
together with from about 90 to 50 percent by weight of polyoxyethylene terephthalate
repeat units which have been derived from a polyoxyethylene glycol having an average
molecul;ar weight of from about 1000 to about 4000, and wherein the molar ratio of
ethylene terephthalate repeat units to polyoxyethylene terephthalate repeat units is from
about ~':1 to about 6:1. A preferred copolymer material for use in the composition of the
invention comprises the reaction product of ethylene glycol, dimethyl terephthalate and a
polyoxyethylene glycol, containing from about 1 to about 50 ethylene oxide repeat units.
A preferred commercial product which has been sold for use as a soil release polymer and
is as deFined above is sold under the REPEL-O-TEX~ or LUBRIL~ brands from Rhône-Poulenc Inc.
Production of this PET - PEOT copolymer involves at low temperature, 160~C - 180~C,
transesterification between methyl terephthalate and dimethyl 5-sulfo-isophthalate and
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ethylene glycol in the presence of catalyst, at high temperature, 1 80~C - 230~C,
e~l~rir,~lion of isophthalic acid and terephthalic acid and ethylene glycol, and finally
polycondensation at 230~C - 250~C. A preferred catalyst for use is a titanium catalyst
which is registered under CAS Registration Number 15879-01-3.
Alternative materials which can be associated with polyester-based fabrics include
polyalkylene terephthalate and polyethylene glycol, sulfonated polyethylene terephthalate,
polyester polyurethane and acetic acid ethenyl esters.
0 When the fabric is derived from nitrogen containing polymers such as nylon, an amine or
amide having hydrophilic properties is selected. A preferred agent is ethoxylated
tetraethylenepentamine. Exemplary ethoxylated amines are further described in U.S. Pat.
No. 4,'i97,898 to VanderMeer, issued Jul. 1, 1986, incorporated herein by reference.
Other examples of hydrophilic polyamines or polyamides which may be selected for use in
accordance with the present invention include those disclosed in the following U.S.
Patents: 4,891,160; 4,372,882; and 5,174,927. To the extent necessary for completion,
these patents are hereby incorporated by reference.
A particularly preferred commercial polyamide material which can function in accordance
with the claimed invention is sold by Rhône-Poulenc Inc. under the name LUBRIL~ NLF.
This material is a hydrophilic polyamide which is a polymer of polyamide and ethoxylated
polyamides.
Association of the hydrophilic material to the fabric can occur by one of several methods.
In a first preferred method, the hydrophilic material is permanently heat set onto the fabric,
including the individual fibers. This process typically involves coating the outer surfaces of
the fabric with an aqueous solution of the hydrophilic material and thereafter heating the
substrate to set the hydrophilic material permanently into the fabric.
In the case of the individual fiber coatings, it is recommended that the fibers be first
immersed in the solution containing the hydrophilic material, followed by heating the
coated fibers. In the case where the fibers have first been woven into a final product, the
hydrophilic material is applied to the product (felt or fabric) by advancing the fabric through
a coating apparatus such as a kiss roll applicator which would function to apply the
hydrophilic material to the fabric, followed by heating the fabric to set the hydrophilic
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material onto the surface of the fabric. Any other coating apparatus such as a dip or spray
device could alternatively be selected. This procedure may be repeated for multiple
passes to insure complete coating of the fabric. Heating temperatures are selected to set
the coating material, and are typically between about 250~F to about 400~F. As would be
appreciated by one skilled in the art, the heating temperature should directly correlate with
the cure temperature of the hydrophilic material.
The coating solution typically is an aqueous emulsion of the hydrophilic material, which
typically is present in emulsion form. For example, in the case of polyester fabrics, the
coating solution typically is between about 1 to about 10 weight percent of the emulsion,
more preferably between about 3 to about 8 weight percent of the emulsion, most
preferably between about 5 to about 7 weight percent of the emulsion, which typically
contains, between about 5 to about 30 percent, more preferably between about 10 to about
25 percent, most preferably between about 15 to about 20 percent by weight solids.
The emulsion may be used in "neat" form, i.e., only the hydrophilic material and water, or
may include additives which can be used to provide other properties to the coating. These
additives include, but are not limited to, antioxidants, dispersants, surfactants and other
surface active agents, softeners, biocides, stabilizers and the like. In particularly preferred
embodirnents, the emulsions are coated in neat form onto the substrate.
In yet another embodiment, the hydrophilic material may be associated with the fabric
during il:s operation at the paper mill. At the mill it is common to periodically pass a
cleaning solution, typically containing, for example, water, surface active agents,
detergent builders, enzymes, and the like, throughout the mill unit operations in order to
remove the contaminants from the system, and more particularly, the fabrics and felts
present. The hydrophilic material of the present invention would be added to such a
solution in amounts sufficient to protect the fabric webs. Under such a process, it is
particularly preferred that the fabric first have been coated with the hydrophilic material so
that it is already resistant to hydrophobic contaminants so that the risk of hydrophobic
conlan, ~ation is minimized. The amount of addition of the hydrophilic material, in
emulsion form, would comprise between about 0.1 to about 5.0 percent by weight of the
entire cleaning solution.
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While not wishing to be bound to any specific scientific theory, the inventors theorize that
the application of the hydrophilic material to the fabric is to hinder the adhesion of the
hydrophobic contaminants to the fabric itself by either repelling or allowing for easy release
of the contaminants from the fabric surface. As paper mills move to cheaper furnish or
5 more r~cycled paper, the problems associated with hydrophobic contaminants will
increase. Use of the hydrophilic material under proper conditions either in the fiber
fo"~a~ion or the fabric cleaning stage should allow for enhanced performance and life of
the paper machine fabric. This results in a significant economic advantage for the paper
mill as huge sums of money are lost to the mill when the unit operations are not in proper
10 working order, or if there is a break in the paper being formed as a result of the
hydrophobic contaminants.
The invention is described in greater detail by the following non-limiting examples.
Example 1
A 6.0 percent by weight aqueous solution of a 15 percent by weight solids emulsion of a
hydrophilic polyester, more particularly, REPEL-O-TEX~ WVX sold by Rhône-Poulenc Inc.
is prepared and poured into the applicator storage tank of a kiss roll applicator. This
material is a polyethylene terephthalate - polyoxyethylene terephthalate (PET - PEOT)
copolyrrer. A polyester woven fabric which is used in paper mills as a wire fabric blanket is
passed over the kiss roll applicator at an agitation rate of about 5.5 yards per minute with
the fabric passing over the kiss roll applicator at a rate of about 5 yards per minute and
through an oven at 280~- 300~F for 30 to 45 seconds to coat and set the entire exterior
surfaces of the blanket with the hydrophilic material. The woven fabric is made of 100
percent polyester filament yarns which is woven into a blanket which is 127.6 yards long
and 182 inches wide. This procedure is repeated three times. The fabric is then passed
through an oven at 370~F for 30 to 45 seconds. This process is repeated four times. The
fabric actually reaches a temperature of 360~F, which is sufficient to enable the PET-
PEOT to heat set onto the fabric.
The coated fabric is placed on a paper machine and is used in the manufacture of paperstock. 1~he coated fabric demonstrates excellent resistance against deterioration resulting
from hydrophobic contaminants. When the contaminants come into contact with the
coated fabric, they easily separate from the fabric thereby making them easy to isolate and
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remove from the paper making process. This enables the fabric to have excellent
durability and reduce the down-time of the paper making process. By comparison, a fabric
which does not have the hydrophilic material coated thereon does not easily repel and
release hydrophobic contaminants and hence reduces the efficiency of the overall paper
5 making process. In addition, the treated fabric demonstrates excellent water drainage,
permeability and wear life properties. These properties are enhanced when the fabric is
additionally cleaned with the hydrophilic material while present on the rollers used to
l,ansporl the fabric during the paper making process.
0 Having described the invention in detail and by reference to the preferred embodiments
thereof, it will be apparent that modifications and variations are possible without departing
from the scope of the appended claims.
