Note: Descriptions are shown in the official language in which they were submitted.
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PAPER MACHINE PRESSING FABRICS
DESCRIPTION
This invention relates to paper machine pressing
fabrics and has particular reference to paper machine
pressing fabrics formed of a polyamide material and
having improved longevity and resistance to flattening
in the surface layer.
In paper making machines, a slurry of paper making
constituents referred to as "furnish" is deposited on
a forming fabric or "wire" and the liquid constituent
furnish is drawn or extracted through the fabric or
wire to produce a self-cohesive sheet. This
self-cohesive sheet is then passed to a pressing and
then a drying section of the paper making machine.
In the pressing section, the paper sheet is
transported by a pressing fabric to a pair of rollers
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where the fabric and the paper sheet pass between the
nip of the rollers to dewater by mechanical pressure
the paper sheet.
The paper sheet itself may contain other types of .
chemical finishes and additives and could be, at the
same time, subjected to an elevated temperature in
order to aid the dewatering. The paper making
pressing fabric together with its sheet of paper
tends, therefore, to be subjected to immense pressure
at elevated temperatures in a rigorous chemical
environment. Paper making pressing fabrics are
generally produced by needling batt fiber to a woven
base fabric. The fabric has multiple functions: first,
to support the formed paper sheet through the press
section of the machine; secondly, to accept sheet
water expressed at each press nip; and last, to impart
a finish or surface texture to the paper sheet.
The batt fiber layer constitutes a "cushion" and
support for the paper sheet while the woven
base provides the primary channels or voids to accept
expressed sheet water. The quality of the batt fiber
layer and in particular its surface properties and its
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consistency of surface properties with time, is of
extreme importance. As the surface properties of the
batt fiber layer deteriorates, so does the quality
of the surface of the paper sheet being pressed, as
well as, the uniformity of water removal.
In the nip of the press rolls, the batt fibers are
bent and deformed under great pressure and at great
frequency. Hence the mechanical properties of the
batt fiber are of considerable importance in such
processes.
Polyamide 6 and polyamide 6,6 have been used
extensively in the manufacture of paper machine
pressing fabrics. These polymers are readily formable
as fibers and their fiber characteristics can be
controlled to make acceptable paper making pressing
fabrics.
Treatment of polyamide (PA) fibers in general has been
proposed, but none have been specifically concerned
with the improvement of the mechanical performance of
fibers as used in paper machine clothing. Among the
f~i
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prior proposals for the treatment of polyamide
fibers are the following:-
United States Patent Specification No. 2,434,247
issued to Lewis et al. relates to the modification
of synthetic linear polyamides with formaldehyde and
an alcohol to obtain a more elastic nylon for woven
fabrics .
United States Patent Specification No. 2,430,953
issued on November 18, 1947 to Schneider is
concerned with producing nylon yarns with a softer
hand, better drape, and in addition, a higher
melting point, better dye receptivity and increased
resistance to solvents. The polyamide yarns are
reacted with formaldehyde at a pH below 3 in
alcohol.
United States Patent Specification No. 2,425,334
issued on August 12, 1947 to McCreath relates to
modification of polyamides with formaldehyde at a pH
less than 3 so that they can be cold drawn by no
more than 75~ of their original lengths.
United States Patent Specification No. 3,276,839
issued on October 4, 1966 to Fruh describes a
process for finishing and dyeing synthetic nylon
textile materials in the presence of phenol and an
aliphatic anion-active compound in alkaline medium.
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United States Patent Specification No. 3,322,488
issued on May 30, 1967 to Feeman refers to
sulfomethylated bisphenol-formaldehyde condensation
products used as dye resists for synthetic polyamide
f fibers .
United States Patent Specification No. 2,533,100
issued to Flugel et al. relates to a process for
treating synthetic linear polyamides with thio
derivatives of phenols or their corresponding
reduction products.
United States Patent Specification No. 2,388,676
issued to Coffman et al. is concerned with improving
the light stability of polyamide fibers by forming a
catecholaldehyde resin within the nylon.
In each of the above cases the nylon materials
exhibit improved properties for use in apparrel or
decorative assembly, i.e. use in conditions that
will not be subjected to the aggressive physical and
chemical environment of a paper making machine.
As paper machine technology improves, speeds,
operating temperatures and pressures increase with a
result that the tendency of existing pressing
fabrics to compact and wear is increased.
Furthermore, increased degradation with increasing
temperature of operation and increasing speed of the
~.
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machine results in significantly shorter service life for these fabrics.
The present applicant has discovered that a paper making pressing fabric
using fibers of various polyamides having an increased amine end group
concentration can be fiu~ther processed and modified to produce signifi-
cantly improved properties.
Therefore, in accordance with the present invention, there is provided a
treated polyamide fiber comprising treated polyamide fibers having an
1o initial amine end group concentration of at least 60 eq./106 g and an
initial ratio of amine end groups to carboxy end groups greater than 1.0,
the polyamide fibers being treated with a phenol/aldehyde treatment
which comprises contacting the polyamide fibers with a solution of
aldehyde at a temperature in excess of room temperature and a solution of
phenol at a temperature in excess of room temperature, the treatments
being carried out at a temperature and for a time sui~cient to increase the
intrinsic viscosity of the treated polyamide fibers by at least 4% when
compared to untreated polyamide fibers.
2 o Also in accordance with the present invention, there is provided a treated
paper machine pressing fabric comprising treated polyamide fibers having
an initial amine end group concentration of at least 60 eq./106 g and an
initial ratio of amine end groups to carboxy end groups greater than 1.0,
the polyamide fibers being treated with a phenol/aldehyde treatment
2 5 which comprises contacting the polyamide fibers with a solution of
aldehyde at a temperature in excess of room temperature and a solution of
phenol at a temperature in excess of room temperature, the treatments
being carried out at a temperature and time su~cient to increase the
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intrinsic viscosity of the treated polyamide fibers by at least 4% when
compared to the untreated polyamide fibers.
Further in accordance with the present invention, there is provided a
treated paper machine pressing fabric comprising treated polyamide
fibers, filaments and/or yarns having an initial amine end group
concentration of at least 60 eq./106 g and an initial ratio of amine end
groups to carboxy and groups greater than 1.0, the polyamide fibers,
filaments and/or yarns being treated with a phenol/aldehyde treatment
1 o which comprises contacting the polyamide fibers, filaments and/or yarns
with a solution of aldehyde at a temperature in excess of room
temperature and a solution of phenol at a temperature in excess of room
temperature, the treatments being carried out at a temperature and time
sufficient to increase the intrinsic viscosity of the treated polyamide fibers
by at least 4% when compared to the untreated polyamide fibers.
a
U
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According to the present invention there is provided
a paper making pressing fabric comprising a fiber
layer formed of various polyamides characterised in
that said polyamide has an amine end group
concentration such that the amine end group/carboxy
end group ratio is greater than 1 which has been
subjected to a phenol/aldehyde treatment process to
increase the intrinsic viscosity of by at least 4~
compared with the untreated material.
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In one embodiment of the invention, the amine end
group concentration is at least 60 equivalents/106g.
Where the polyamide is polyamide 6,6, the intrinsic
viscosity after treatment process is preferably not
less than 1.3 dl/g; said fiber layer can just be the
surface layer or layers of the batt structure and/or
any portion of the batt up to 100 of the batt
structure.
In another aspect of the present invention there is
provided a method of making a paper making pressing
fabric which method comprises treating a polyamide
fiber having an amine end group concentration of at
least 60 equivalent/106 gram with an aldehyde/phenol
treatment process by contacting the fiber with an
aqueous solution of an aldehyde at an elevated
temperature and with an aqueous solution of a phenol
at an elevated temperature, the treatment process
being carried out at a temperature for a time
sufficient to impart an increase in intrinsic
viscosity of the polyamide by at least 4~ and
thereafter forming a layer of said fibers and needling
onto a woven base fabric. The fiber may be formed into
1~~~~
_8_
a batt layer prior to attaching to the base fabric
either before or after the aldehyde/phenol treatment
procedure.
Since the woven base fabrics contain yarns of
monofilament, multifilament, or spun from staple
fibers, that are usually polyamide based, the
technology of the present invention can be utilized
for these yarn forms since they are also exposed to
the heat, pressure and chemical environment already
described. Benefits of dimensional stability,
strength retention and maintenance of water handling
capacity are all vital, and will be improved using
yarns prepared by this invention.
Also, while usual manufacturing techniques apply a
batt formed of fiber onto a woven base fabric, this
should not limit the scope of this invention. Other
methods to apply fiber, to anchor the fiber instead of
mechanically needling, whether the base is woven or
not, or whether there is even a support base should
all be considered in producing a pressing fabric.
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The word "fiber" should also not be limited in the
sense of size dimensions or shape, but be considered a
component. In this sense, therefore, for the
purposes of this specification, the use of the term
"fiber" should also include "yarns".
Phenols which can be used in this process include
phenol, pyrocatechol, resorcinol, hydroquinone,
pyrogallol and phloroglucinol, as well as, substituted
products of the aforementioned compounds provided at
least two reactive sites are left open on the aromatic
ring. In addition, bisphenols, dihydroxy-naphthalenes
and the like could also be utilized.
Aldehydes applicable to this process are formaldehyde,
formaldehyde liberating compounds, oxaldehyde,
malonaldehyde, succinaldehyde, glutaraldehyde,
adipaldehyde, pimelaldehyde, suberaldehyde,
azelaldehyde and sebacaldehyde, and the like, as well
as their substituted counterparts.
The treated polyamide batt fibers show an increase in
intrinsic viscosity up to 25~ depending on the
phenolic compound and subsequent heat treatment
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employed. These fibers also exhibit higher wet
elongations relative to standard polyamide fibers both
before, but especially after the treatment process.
There is also a significant improvement in chemical
resistance particularly in terms of resistance to
degradation of physical properties caused by oxidation
by chlorine containing compounds during use on a paper
making machine. Fibers also show increased resistance
to abrasion resulting from the pressing of papers
containing fillers, such as ground calcium carbonate.
Such pressing fabrics have exhibited as much as 100$
longer lifetime in use, particularly in hostile
chemical and mechanically abrasive environments.
Following is a description by way of example only of
methods of carrying the invention into effect.
L~YTMDT L~ 1
Polyamide 6,6 15d staple fiber having an amine end
group concentration of 66.4 equivalent/106 gram and an
intrinsic viscosity of 1.35 dl/g was subjected to a
phenolic treatment process as described below.
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The fiber was first immersed in an aqueous bath
consisting of 0.5$ ethylene diamine and 2.0~
formaldehyde at 130°F for 30 minutes. After a
rinse, the fiber is then subjected to a second aqueous
solution~of 1.5$ resorcinol and 1~ formaldehyde at
130°F for one hour. Followed by a rinse cycle,
the sample was subsequently air dried and heated 10
minutes at 300°F.
,-The Table 1 below compares intrinsic viscosities and
tensile properties of fiber processed with the above
formulation and untreated PA 6,6 fibers having high
and low amine end groups. Table 2 includes data
describing the properties after exposure to sodium
hypochlorite solution in a standard degradation test.
A 6$ increase in intrinsic viscosity is observed for
the high amine end group fibers after treatment. In
addition, these fibers have higher elongations
compared to the Control. This higher elongation
contributes to the higher Tensile Energy Absorption or
"toughness" values. This parameter is important in
considering end-use requirements such as resiliency
which is an important factor on a paper machine. The
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treated high amine end group fibers maintain high
elongation and tensile energy absorption relative to
the control even after exposure to hypochlorite.
EXAMPLE 2
Additional PA 6,6 fiber samples having low and high
amine concentration were treated as described in
Example 1 above (designated as "X" treatment) using
1/10 and 1/2 the chemical concentrations. The samples
were then subjected to a simulated papermaking test in
which they were exposed to repeated compression for a
given number cycles and were reviewed and judged on a
relative ranking on a scale of 0 to 5.
Examination of Table 3 below shows that the treated
high amine end group fibers give superior properties
in terms of improved ranking on the simulated
papermaking press. According to the table, the lower
the ranking the better the results.
EXAMPLE 3
One field trial was run on the third press position of
a paper machine which produces uncoated printing and
writing grades of paper, mainly bond and copy papers.
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The particular machine has been identified to have
extremely high chlorine residuals in their stock water
and shower water (in excess of 2.0 ppm).
The standard fabrics have been chemically treated with
the best known art to offer a degree of protection to
the polyamide fiber in the batt structure. Even so,
effective fabric life is less than three weeks, with
substantial wear and compaction causing loss of
efficient water removal. In extreme cases, fabrics
actually tore off the machine due to the degraded
state.
At the time of the trial, the previous three fabrics
had run 12 days each, one tearing off. The trial
fabric structure utilized was composed of 100 of the
modified polyamide fiber, with the addition of the
special process steps of the invention. Our trial ran
12 days and was scheduled off. The fabric showed no
signs of instability and our analysis of the used
fabric revealed low weight loss, no fiber fibrillation
and fatigue, and little loss to bulk and water
handling capacity.
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Subsequent fabrics exposed to the invention's process
have run as long as 39 days on this position with the
fabrics still in a usable physical condition at time
of removal. Competitive fabrics have run no longer
than 14 days during this time period.
. 2013852
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Table 3
Papermakina Press
Ranking (Scale 0-5)
Fibers Treatment 700,000 Cycles
High amine end group Control-- 3.5
High amine end group 1/10 X 2,2
High amine end group 1/2 X 1,g
High amine end group X
Low amine end group Control-- 3-7
Low amine end group 1/10 X 3.8
Low amine end group X 3-3
