Note: Descriptions are shown in the official language in which they were submitted.
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Com~osite lining material
This invention relates to a composite lining
material suitable for bonding to a reinforcement material.
U.S. Patent Specification No. 3l489,639 describes
such a lining material which comprises a thermoplastics
sheet bonded to a woven, knitted or non-woven fabric
comprising both glass fibres and thermoplastic fibres.
The thermoplastic fibres provide good adhesion to the
thermoplastics sheet~ and the fabric as a whole is a
receptive layer to which a bul~ reinforcement material
such as fibre-reinforced resin will bond. U.S. Patent
No. 4,228,208 describes the same type oE lining material
in which the fabric has a pile for improved bonding with
the reinforcement material.
One of the primary uses for such composite lining
materials is in the construction of chemical plant to
provide a chemically-resistant lining for vessels, tanks
and pipes. Clearly in such end uses, good adhesion
between the lining material and its reinforcement is
essential to the performance of the structure~ The term
'lining' i5 not meant to be confined to internal surfaces
only but is meant to include outer surfaces such as
facinys and claddings.
According to this invention a composite material
suitable for bonding to a reinforcement material comprises
a lining layer of a ~hermoplastic material having a lining
face and a reverse face, a non-woven fibrous web having
one of its faces bonded to the reverse face of the lining
layer and its other face exposed, and continuous filaments
which are stitched through the web and which pass back and
forth between the exposed face of the web and the reverse
face of the lining layer, the continuous filaments being
bonded to said reverse face of the lining layer at
multiple, spaced locations.
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As acknowledged earlier, non-woven fabrics have been
proposed previo~sly for this purpose because they are
inexpensive compared with woven fabrics. Those used
commercially have comprised needle-punched webs which give
S reasonable performance in many end uses but are not so
suitable where higher performance is required. An
examination of the mode of failure of structures
comprising a reinforced composite lining material made
with such fabrics has shown that failure tends to take
place within the fabric structure itself rather than by
delamination of the fabric from the lining layer or the
reinforcement layer.
The fabric used in the composite lining material of
the invention overcomes this disadvantage because the
fibrous web is itself reinforced by the continuo~s
filaments stitched through it, and furthermore these
filaments, being bonded at multiple, spaced locations to
the lining layer and also available to a reinforcement
material on the exposed face of the web, provlde a strong
direct link between the lining layer and the reinforcement
material.
The lining layer may be any thermoplastic material
which can be formed into sheet or other shapes,such as
moulded or extruded pipes or vessels, and which is
suitable for the lining duty required. For chemical
.
- plant, chemically-resistant thermoplastics are preferred,
particularly polypropylene and poly(vinylidene fluoride).
Other suitable ~hermoplastics include other polyolefins,
polycarbonates, polyethers, polyaldehydes, polyvinyls and
polystyrene~
The non-woven fibrous web may be a staple fibre web
formed by conventional carding and laying techniques.
The ter~ 'web' is meant to embrace multilayer web
assemblies such as fleeces. Continuous filament webs may
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also be used such as those formed by spreading a tow of
filaments by suspending the tow in ~iverging air currents
or in a diverging flow of liquid and then dry or wet
laying the spread tow to form a coherent web of filaments.
The fibres of the web are preferably synthetic
fibres. Polyester fibres are especially suitable because
of their chemical resistance. The continuous filaments
used to stitch through the web are required to have
adequate strength for their purpose of reinforcement and
the synthetic filaments are suitable in this respect, with
polyester filaments being preferred because of their
combination of strength and chemical resistance. Another
advantage of polyester filaments is that they do not
soften at the laminating temperatures used with the
preferred polypropylene lining layer.
The web may be stitched on any suitable stitching
machine, particularly the high output machines sold under
the "Mali" and "Arachne" names. The stitch construction
may be a simple chain stitch or a tricot stitch or a
combination of the two. The stitching guage and the
stitching rate may be selected to give the desired degree
of stitch reinforcement.
The stitched web may be bonded to the thermoplastic
lining layer using an intermediate adhesive material, but
the preferred method is to soften the reverse surface of
the lining layer using heat or solvent action and then to
fuse the face of the stitched web to the softened surface.
The exposed parts of the continuous filaments stitched
through the web also f~se to the softened surface of the
lining layer at multiple locations. With a lining layer
comprising a sheet, the stitched web may be calendered to
the sheet whilst its s~rface is still soft immediately
after extrusion as described in the aforementioned U.S.
Patent No. 3,489,639.
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The invention includes a wall structure comprising a
lining layer of a thermoplastic material having a lining
face and a reverse face, a layer of reinforcement
material, a non-woven fibrous web having one of its faces
bonded to the reverse face of the lining layer and the
other of its faces bonded to the layer of reinforcement
material, and continuous filaments which are stitched
through the web and which pass back and forth between the
lining layer and the reinforcement layer, being bonded to
each of said layers at multiple, spaced locations.
The reinforcement material may be a synthetic resin
reinforced with fibres such as G.R.P. (glass reinforced
polyester resin). It may be applied to the exposed face
of the stitched web by any of the usual techniques
including hand lay-up, spraying, moulding and casting.
Resins do not simply bond to the face of the stitched web
but are absorbed by it and thereby envelop both the web
fibres and the stitching filaments to provide a strong
mechanical bond.
A certain amount of resin usually is applied to the
stitched web to wet it O-lt prior to application of the
G.R.P., and it has been found that for this purpose less
resin per unit area is required with the stitched web than
with a needle-punched fabric of similar basis weightO In
addition to the saving in resin, there is a valuable
saving in fabrication time.
The wall structure of the invention may comprise the
wall of a pipe, vessel or tank for which the lining layer
provides an internal lining. It may also be the wall of
a building having an external or internal lining.
The wall structure of the invention has improved
properties in shear and in peel as measured by the tests
described in the following Examples. Measured at 20C.,
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shear forces of greater than 100 kg/cm~ and steady peel
forces of greater than 7.0 kg/cm are obtainable.
Moreover, these properties do not fall off drastically at
elevated temperatures. At 50~C., shear forces greater
than 100 kg/cml are maintained, and at 100C., the value
of shear ~orce -is still in excess of 50 kg/cm~ . In
steady peel, the maintenance of properties is even more
impressive because, over the temperature range of 0C. to
lOO~C., the rate at which steady peel force falls is less
than 0.01 kg/cm per 1C. rise in temperature.
, .
The invention is illustrated by the accompanying
drawings in which:
Figure 1 comprises a graph plotting values of shear
force for wall structures according to the invention
against temperature;
Figure 2 comprises a graph plotting values of steady
peel force for wall structures according to the invention
against temperature;
Figure 3 is a schematic perspective, partly cut
away, of a wall structure according to the invention;
Figure 4 is a cross-section through a wall structure
according to the invention adjacent to a line of chain
stitch in the fibrous web; and
Fig~re ~ is a enlarged plan view of a series of
interconnected stitch loops forming part of such a line of
chain stitch.
Figures 1 and 2 of the drawing are referred to in
Example 2. Figures 3 and 4 show a wall structure 1 which
is according to the invention and which comprises a lining
layer 2 of a thermoplastic material, a layer 3 of a
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reinforcement material, and bonded between those layers, a
non-woven fibrous web 4 reinforced by continuous filaments
5 stitched through it in lines of chain stitch 6.
Figure 5 shows an enlarged view of a series of
interconnected stitch loops 7 forming part of such a line
of chain stitch 6. These loops lie against that face 8
of the fibrous web which remains exposed after the web has
been fused to the lining layer 2, and to which the
reinforcing layer 3 is subsequently bonded.
As shown in Figure 4, the continuous filaments 5
which are stitched through the web 4 provide a direct
mechanical link between the lining layer 2 to which they
are fused at locations 9, and the reinforcement layer 3
which bonds to the stitch loops 7.
The invention is illustrated by the following
Examples:-
Example 1
Polyester fibres of 4.4 dtex and lOOmm staple length
were carded into a web which was then cross-folded to form
a fleece. The fleece was stitched using a continuous
filament polyester stitching yarn of 78 dtex and
comprising 24 filaments on a Maliwatt multiple needle
stitching machine. A single needle bar was used,
stitching chain stitch at a stitch ~uage of 8.8
stitches/cm and a stitch rate of 6 stitches/cm. The
basis weight of the stitched fleece produced was 165
gms/m.
The stitched fleece was bonded to a 2mm thick sheet
of polypropylene extruded at a temperature of 240C by
passing the freshly-extrucled sheet and the stitched fleece
together through a three roll calender with that face of
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the fleece on which the chain loops are exposed uppermost
and the reverse face against the soft surface of the
sheet. The temperatures of the calender surfaces were:-
Top roll 70C.
Centre roll 90C.
Bottom roll 85C.
The sheet and the stitched fleece were passed
together between the nip of the top and centre rolls,
partially lapped around the centre roll, passed through
the nip of the centre and bottom rolls and then partially
lapped around the bottom roll.
The composite lining material so formed was
reinforced with G.R.P. by applying resin and 'E' ylass in
the form of chopped strand mat to the exposed surface of
the stitched fleece to a depth of 4mm. The resin was a
polyester resin formulation sold by Scott Bader under the
trade mark "Crystic" 474 PA. After curing the resin, the
bond strength between the composite lining material and
the G.R.P. reinforcement was measured in shear and in peel
using a Hounsfield tensometer.
The peel test used is one developed by Courtaulds
PLC which peels the composite lining material away from
the G.R.P. reinforcement at an angle of ~0 degrees to the
reinforced composite lining material and records the
steady value of peel force attained during steady peel
following the peak initial value. This test has been
found to give more reproduceable results than the peel
test specified in British Standard 4994 which measures the
value of force to initiate peel.
The values of shear force and peel force were
measured at 20C. and are shown in the following table in
comparison with values obtained with prior art composite
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lining materials. In both cases 2mm sheets of poly-
propylene were used and the procedures of lamination,
reinforcement and testing were the same as were used with
the composite lining material of the invention, but the
stitched fleece was replaced by, respectively, a woven
fabric and a needle-punched fabric.
The woven fabric was woven in a four shaft satin
weave at 10 ends/cm and 10 picks/cm and had a basis weight
of 280 gms/mq O The warp yarn was of 1,500 dtex and
comprised 50 per cent by weight of 693 dtex/70 filament
polypropylene yarn and 50 per cent by weight of 666 dtex
glass yarn. The weft yarn was a 100 per cent glass yarn
of 1,200 dtex. The needle-punched fabric comprised a
blend of polyester staple fibres, 50 per cent by weight of
3.6 dtex, 58mm staple length fibres and 50 per cent by
weight of 5.3 dtex, 50mm staple length fibres~ It was
needle-punched at a punch guage of 100/cm and a punch rate
of 2.35/cm and had a basis weight of 160 gms/m~.
The quantity of resin required to completely wet-out
the exposed face of each of ~he fabrics bonded to a
polypropylene sheet is also shown in the following table.
Composite Steady Peel Shear Resin
lining force (kg/cm) force Wet-out
material (kg/cm~) (kg/m~)
.
Woven fabric 4~3 74 0.60
Needle-punched
fabric 6.9 81 1.44
Stitched fleece
(invention) 7O3 112 0.625
The composite lining material according to the
invention using the stitched fleece gives superior peel
and shear strengths compared with each of the prior art
;
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materials, and requires only the ~ame arnount of resin to
wet out the stitched fleece as is required by the woven
fabric, which is less than half that required by the
needle-punched fabric. The stitched fleece was purchased
at a price which was about 35 per_cent of that of the
woven fabric and about 70 per cent of that of the needle-
punched fabric.
Example 2
The procedure of Example 1 was repeated except that
3mm thick polypropylene sheet was used in all cases.
Samples of the reinforced composite lining material of the
invention and of the prior art reinforced composite lining
material which uses a needle-punched fabric were tested in
shear and in peel over a range of temperatures. The
results are shown in the graphs plotting shear foLce
against temperature and steady peel force (Courtaulds'
test) against temperature which comprise Figures 1 and 2
respectively of the accompanying drawing. In each case
the results obtained with material according to the
invention are shown by a continuous line and those with a
prior art needle-punched fabric by a dashed line.
The values of shear force and peel force obtained at
20C. for all three composite lining materials are shown
in the following table:-
25 Composite Steady Peëi Shear force
lining force (kg/cm) (kg/cm~)
material
_ _ _ . _ _ _ _
Woven fabric 5.0 116
Needle punched
30 fabric 7.0 74
Stitched fleece
; ~invention) 8.0 124
... . ~
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The superiority of the composite lining material ofthe invention in peel and in shear is shown again with the
thicker polypropylene sheetO Moreover, the improved
properties are maintained over the temperature range
shown. Thus, the value of shear force is about 107 kg/cm~
at 50C. and about 75 kg/cm~ at 100C. The value of peel
force remains above 7O5 kg/cm over the whole temperature
range, and falls less than l kg/cm as the temperature is
raised over that range.
Example 3
The procedure of Example 1 was repeated except that
6mm thick polypropylene sheet was used in all cases. The
Courtaulds' peel test was carried o~t in the same way but
the values of peel force quoted in this Example are the
initial values because steady peeling was not possible
with this thickness of sheet. The comparative
performances of the three samples are seen to be
maintained with the much thicker 6mm polypropylene sheet.
Composite Initial Peel Shear force
20 lining force tkg/cm) (kg/cm~)
material
Woven fabric 12.6 103~2
Needle-punched
fabric 16.6 93.7
25 Stitched-fleece
(invention) 18.3 147.5
.
