Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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P ER MACHINE FELTS
DESCRIPTION
This invention relates to paper machine felts. In a
paper making machine, a slurry of paper making
constituents referred to as ~furnish~ is deposited on a
fabric or "wire" and the liquid constituents are drawn
or extracted therethrough to produce a self-cohesive
sheet which is then passed to the pressing and drying
sections of the paper-making machlne. In the pressing
section, the paper sheet is transported by ~ felt to a
pair of rollers where the felt and paper sheet pass
between the nip of the rollers to dewater and to dry the
`: paper sheet. The paper sheet itself may contain alltypes of chemical finishes and will be, at the same
time, subjected to an elevated temperature to aid the
dewatering and drying thereof. The paper making fel~
;: 20 together with its sheet of paper tends therefore, to be
subjected to immense pressure at elevated temperatures
in a rigorous chemical environment.
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Paper making felts are generally produced by needling
batt fibre to a woven backing which then supports the
forming paper sheet as it passes through the press. In
the nip of the press rolls, the batt fibres are bent and
deformed under great pressure and at great frequency and
hence the mechanical properties of the batt fibre are of
consi~erable importance in these processes.
Polyamide 6 and polyamide 6,6 (PA 6 and PA 6,6,) have
been used extensively in the manufacture of paper
machine felts. These polymers are readily formed as
fibres and their fibre characteristics can be controlled
to allow production into acceptable felts. Many prior
art proposals for the use of polyamide materials in
; 15 sheet and felt materials in general have been proposed.
For example, in British Patent Specification No.
1304732, there is a reference to the use of polyamide
such as nylon 6, nylon 6,6, nylon 6.10, nylon 6 r 7, nylon
8, nylon 9, nylon 11 and nylon 12. The specification is
concerned with the manufacture of fibrous sheet
materials and is not specifically concerned with paper
machine clothing.
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British Patent Specification No. 1329132 again relates
to a known woven fabric for use, for example, as an
interlining. Again, there is reference to the use of
polyamide such as nylon 6, nylon 11, nylon 12 and
copolyamides such as nylon 6,6 and copolymers of nylon 6
and nylon 6,6 with nylon 11 and nylon 12.
Prior British Specification No. 1585632 has been
; concerned with the manufacture of artificial leather and
like materials and again the use of nylon 6, nylon 6,6,
nylon 10 and nylon 11 and nylon 12 are disclosed
together with various copolymers of different variations
and combinations thereof.
In each of these cases, the nylon materials are used
primarily for their inherent strength in a clothing or
decorative assembly and would not be subjected to the
agressive physical and chemical environment of a paper
making machine.
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European Patent Specification No. 000708 relates to a
paper making machine felt comprising a woven heat set
belt which in the machine and transverse direction
comprises thermoplastic filaments, in which belt the
filaments in at least one of the machine and transverse
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directions are co-extruded and in which monofilaments
have a core of polymer selected from nylon 6,6,
polyethylene terephthalate and tetrapolymer of tera or
isophthalic acid and a sheet of copolymer selected from
nylon 11, nylon 12, nylon 6, nylon 6,10, nylon 6,12,
polybutylene terephthalate and a large number of other
materials.
In European Patent Specification No. 0070708, the
materials are being employed primarily for their well
known properties of strength and abrasion resistance.
Our co-pending European Application No. 88303201.3 shows
that nylon 12 can be used in the construction of a felt
for use in a paper making machine. Our researchers have
shown quite surprisingly, that nylon 11 has properties
which compare favourably with nylon 12 although this
would not have been expected from the normal structure
thereof. Polyamide 11 (polyundecanoamide) referred to
- 20 in this specification as "PA 11" is well known in
polymer technology and as an article of commerce.
Polyamide 11 was developed commercially for sources
directed primarily to injection moulding applications.
~; The polyamide 11 homopolymer without cross-linking
additives may be extruded to form a large number of
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items and is ideally suited to the formation of
monofilaments and fine denier continuous filament yarn.
While it would not be expected that this material would
provide satisfactory properties required in a paper
machine batt to provide the surface properties required,
the present Applicants, unexpectedly, have found that
batt materials of polyamide 11 when used in paper
machine felts have superior durability and enhance
recovery from compression and resistance to fibrillation
compared with felt materials currently employed. In
addition there is a superior chemical resistance to
hydrolysis and rPsistance to degradation of physical
properties by hypochlorite and other oxidation and we
have found surprisingly that polyamide 11 can exhibit a
50-100% greater lifetime use in particularly hostile
chemical and abrasive environments in paper making.
According to one aspect of the present invention,
therefore, there is provided an article of paper machine
clothing formed from a fibrous material having a woven
; base and an optional batt layer attached thereto
characterised in that said fibrous material comprises
fibres of poly(undecanoamide)(polyamide 11) formed by
the extrusion of a melt of polyamide 11 having an
intrinsic viscosity of at least 1.0 dl/gram.
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In a further aspect of the present invention the melt to
be extruded may contain 0.2 to 1.0% by weiqht of an
anti-oxidant and more preferably, 0.4 to 0.7% by weight.
The anti-oxidant may be selected from one or more of
alpha-tocopherol, condensation products of diphenylamine
and acetone and closely related structures derived from
diphenylamine and compatible phenolic stablisers with
amide functionality such, for example, as that made
commercially available by Ciba Geigy under the trade
name "IRGANOX 1098". Polyamide fibre containing
approximately 0.5 to 0.6% by weight of anti-oxidant
individually and separately or in combination results in
a further enhancement of durability.
Polyarnide 11 resin of the appropriate instrinsic
viscosity may be compounded during extrusion of
monofilament or continuous filament by the addition of
selec~ed anti-oxidants. Polyamide 11 monofilament
in accordance with the invention may be extruded at
temperatures across the barrel between 220C and
295C. The spinneret may be maintained at
temperatures of approximately 300C. Nonofilament
may be extruded with the drawdown of between 2.0 X and
4.5X in order to provide monofilaments of 0.1 - Q.25 mm
` 25 for manufacturing of Fourdrinier or other forming
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fabrics. A particular utility for improved durability
against abrasion, polyamide 11 monofilament may be
also used advantageously as shute filament and/or warp
filament in single, double or triple layer of press
fabrics.
Surprisingly, it has been found that the incorporation
of polyamide 11 high molecular weight monofilaments may
be employed in Fourdrinier forming fabrics as warp or
machine direction monofilaments. It is possible in
accordance with the invention to prepare high durability
all polyamide forming fabrics and avoid a mix of
materials presently employed in which polyamide
filaments must be alternatively inserted with polyester
monofilaments in the shute direction in order to provide
a measure of enhanced abrasion resistance without the
existence of dimensional instability which normally
results from the use of polyamide 6 or polyamide 6,6
material. The paper machine felts in accordance with
the present invention have a low moisture re~ain and are
relatively insensitive to physical properties in the
presence of water.
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Monofilaments may be extruded with variations in the
process to deliver this and other desirable tensile
properties for the weaving of base materials for needled
nonwovens employed in the pressing section of a paper
making machine. Monofilaments in large diameters may be
employed in both the warp and shute directions in dryer
screen applications.
Fine denier monofilaments of high molecular weight
polyamide 11 may be extruded with anti-oxidant employing
barrel temperatures within the range 215C to
277C with a spinneret temperature of approximately
270C. Continuous filament yarn of appropriate
denier desirable for various layers of the batt of press
felts can thus be extruded and later crimped and cut
into staple fibre for batt manufacture and thereafter
employed as a batt layer in press felts.
The advantage of the felts in accordance with the
present invention is that such felts have superior
durability due to enhanced resistance to fibre
fibrillation and recovery from compression which result
in compaction resistance. In addition to these
advantages there is superior chemical resistance
~`~ 25 particularly resistance to hydrolysis and resistance to
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degradation of physical properties by hypochlorite and
other oxidation. Such fibres in press felts exhibit
superior durability against abrasion damage experienced
with papers containing fillers especially including clay
or crushed limestone. Such felts exhibit at least
50-100% greater lifetime in use in particularly hostile
chemical and abrasive environments. These results are
quite surprising and outstanding and would not have been
expected from our previous experience with incumbent
polyamide materials.
Following is a description by way of example only of
methods and with reference to the accompanying drawings
of carrying the invention into effect:-
In the drawings:-
Figure 1 is a photomicrograph of a compression test of a
standard PA 6,6 fibre used in the manufacture of a
paper machine felt.
Figure 2 is a photomicrograph of a fibre in accordance
with the present invention.
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EXAMPLE 1
Continuous filament of PA 11 was prepared according
to the following procedure. Commercially available
PA 11 w~s purchased as pellets from Rilsan Corp., New
Jersey, having an intrinsic viscosity of 1.20 dl/g when
determined in concentrated sulfuric acid. These
polyamide pellets were vacuum dried at 80C for 16
hours to a final vacuum measured outside`the vacuum oven
of 140 microns Hg. The pellets were transferred in a
lQ manner so as to avoid absorption of moisture from the
; air to a hopper of a single screw extruder. The
extruder was equipped with a 2.5 cm diameter low
compression screw. The extruder was fitted with a
filter pack of 55 micron nominal porosity. Downstream of
the filter the extruder was fitted with a Zenith gear
pu~p metering-the melt to a spinneret. The spinneret
had 30 holes, each hole of diameter 0.5 mm. The extruder
had a temperature profile ranging from 243C at the
hopper throat to 271C at the pump with 5 zones of
independent temperature monitoring and control. The
spinneret was maintained at 270C. Filaments were
extruded at approximately 195ft/min with a maximum
draw-down such that the radial change was approximately
7-8/1 between spinneret and the first Godet. Yarn was
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taken up on a cylinder attached to a Leesona winder
after the Godet.
A typical fibre as-spun according to this procedure was
S drawn in two stages with a third stage of relaxation all
with heat to provide an overall 2.3X draw ratio. The
first temperature of drawing was at 110C;
relaxation occurred in the 2nd stage at 160C.
Fibre from such a process was prepared to be 12.8 dpf
(denier per filament). Fibre thus prepared had 4.6 gpd
tenacity with an initial modulus of 26 gpd and an
elongation at break of 45%. The stress-strain curve
exhibited a deflection at an elongation of 10% at 3.5
gpd specific stress.
Such fibre was crimped in a heated stuffer box crimper
to provide continuous yarn with a variable random crimp
with approximately 4 crimps/cm. It was cut into staple
of approximately 7.0 cm length. Such fibre was carded,
lapped and needled into a press felt to provide a batt
structure at an overall batt weight of approximately
; 1000 g/m2. A felt having such a batt structure
exhibited at least 50% increased life in comparison to
similar PA 6 felts when challenged with the same furnish
on the same position on a paper machine.
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EXAMPLE 2
Fibres were prepared as described in Example 1 with the
following exceptions. Prior to drawing, pellets were
tumbled with powdered Irganox 109~ (Ciba-Geigy) at a
loading such that the blend would be 0.7% wt/wt.
Pellets appeared to be uniformly coated with the powder
antioxidant prior to transfer to the hopper. W
analysis of the as spun fibre indicated a uniform
concentration in several samples tested at a
concentration of approximately 0.5% wt/wt.
EXANPLE 3
Polyamide fibres produced in accordance with Example 1
were for~ed into a batt structure. Comparable filaments
of a standard polyamide 6,6 currently used as an
industry standard in the manufacture of paper machine
clothing and commercially available under the trade
reference T-100 supplied by DuPont was formed into a
similar batt. Each of the batts was then incorporated
by needling to the backing of a test felt to be run on a
compression test machine. The felt containing the two
`; batt samples was installed on the test machine and the
machine was run to pass the felt between a pair of nip
rollers with a predetermined nip loading. The test felt
was run on the compression tester for one million
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compressions. After the one million compressions, the
felt was removed and the batt examined under an electron
microscope.
The results are shown in Figures 1 and 2 of the
accompanying drawings. The results were assessed on a
scale of 1 to 5 by inspection and comparison against
prepared standards and given a ranking accordingly. The
DuPont polyamide 6,6 was given a ranking of 4.0 on a
scale of 1 to 5 in which 5 is the worst. An examination
of the photomicrographs will show extensive fibrillation
and fracture of the flattened filaments. By comparison
examination of the polyamide 11 candidate batt shows
a marked lack of fibrillation of the fibres and with
only flattening and some transverse fracture of some of
the fibres. It was given a ranking of 3.3 on a similar
scale as above.
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The candidate fibre PA 11 was, therefore, in
~ 20 substantially better condition after a million
; compressions than the industry standard. This result
~ was a significant improvement over and above that which
; would have been expected for polyamide 11 filaments.
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Samples of commercial PA 6,6 fibre of instrinsic
: viscosity 1.36; commercial PA 6 fibre of instrinsic
viscosity 1.46; staple fibre of Examples 1 and 2 above
with fibre instrinsic viscosities of 1.05 and 1.12
respectively were each subjected to 35% hydrogen
peroxide aqueous solution at pH2 and at 60C for 24
hours. Retained IV results were as follows:
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Candidates Initial IVFinal IV % Retained
Example 1 PA 11 1.05 0.87 83%
Example 2 PA 11/AO 1.12 0.97 87%
PA 6 1.47 0.49 31%
PA 6,6 1.36 0.62 47
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