STRATIFIES

LAMINATE STRUCTURES

Abrégé anglais

Abstract
A PVC-impregnated textile fabric carcase, particularly a solid
woven conveyor belting fabric, is coated with a normally
PVC-incompatible synthetic rubber facing layer such as
polychloroprene by means of a fire resistant nitrile rubber
adhesive compound, the rubber facing layer incorporating a
minor proportion of a disintegrating agent comprising a
material compatible with the synthetic rubber, but which on
exposure to heating above 100°C causes breakdown of the
rubber matrix.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A pvc-impregnated textile fabric coated with a
normally pvc-incompatible synthetic rubber facing layer by means
of a nitrile rubber interlayer, wherein. the synthetic rubber
includes a minor proportion of a disintegrating agent comprising
a material which is compatible with the synthetic rubber but
which on exposure to heating above 100°C causes breakdown of the
rubber matrix.
2. A fabric according to claim 1 wherein the synthetic
rubber facing layer includes from 1 to 20 parts by weight per
100 parts of the rubber polymer of a disintegrating agent
compatible with the rubber, but which an exposure to heating in
the range 100 to 200 C causes breakdown of the rubber matrix.
3. A fabric according to claim 1 or 2 wherein the
synthetic rubber is a polychloroprene and the disintegrating
agent is selected from chlorinated polyethylene, high styrene
resins, ethylene vinyl acetate copolymers and aromatic hydrocar-
bon resins.
4. A fabric according to claim 1 or claim 2 wherein the
synthetic rubber is a chlorosulphonated polyethylene.

Description

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IMPROVEMEN~ IN AND RELATI~ TO LAMIMATE STRUCTURES
This invention relates to laminate structures in
which one polymeric material i8 employecl to provide a
different polymeric material with a surface or surface
laysr of desired physical and/or chemical properties. In
particular it relates to providing a polyvinylchloride
(PVC) - coated eubstrate with a rubber surface layer.
Our copending Canadian patent application No.
451,727 describes a method of providing a pvc-aoated
ubstrate with a surface layer of a normally pvc-
incompatible rubber by a proaess aomprising applying to
the sub6trate a thin layer of uncured, preferably fire
resistant nitrile rubber adhesive compound followed by
applying a cover layer of uncured, normally pvc-
incompatible rubber and thereafter 6ubjecting the
resultant la~inate to a curing treatment.
The process is particularly useful ~or making pvc
~onveyor belting having at lea6t one facing layer of
synthetic rubber such a8~ a polychloroprene rubber. The
belting may be ~olid woven, or plied.
Whil~t the products of~the proces6 ju t described
are extremely sati factory in terms of excsllent bond
strength betwee~ the layers, certain applications call
for compliance with fire resi;stance tests.
One such test i6 the "drum friction test" designed ~
to asse s the~behaviour of a conveyor belt under stalling
conditio~s. The test~ which~is described ~n B.S. 3289,
; comprises sub~ecting a stationary Iength of belt to the
action of a simulated driving drum which i8 rotated
again~t the belt Rurface. High frictional heating
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results and the test specifie6 amongst other things that
a ~atisfactory belt shall not glow, under the test
conditions, before it breaks.
Conveyor belting with PVC covers readily passes this
test, but this is not the case with rubber covered
belting. A solution to the problem has ]been proposed in
the U.K. Patent No. 1,310,291 by Fenner and Co. published
March 14, 1973 in which a thermoplastic layer is
interpo~ed between a pvc-impregnated belting carcase and
a nitrile rubber surface layer. Frictional heating under
drum friction test conditions melts the thermoplastic
interlayer, causing the belt to de-laminate. The nitrile
rubber peels off and leaves the pvc-based carcase to
break in the usual way, without glowing.
If an elastomeric adhesive interlayer is employed,
giving high interlaminar bond strength even at elevated
temperatures, using the method of our copending
application, then the above described solution to the
problem is inapplicable.
~0 According to the present invention a pvo-impregnated
textile fabric carcase coated with a normally-pvc
incompatible synthetic rubber facing layer by means of a
~fire resistant nitrile rubber adhesive compound includes
in said rubber facing layer a minor proportion of a
~ disintegrating agent comprising a material which is
compatible with~ the synthetic rubbe~r but which on
synthetic rubber but which on exposure to heating above
100-C causes breakdown o~ the rubber matrix. Breakdown
~ preferably takes place below 200 C, well below~the glow
temperature of the facing rubber~ Minor proportion"
~preferably means from 1 to 20 parts per 100 parts by
weight of the ynthetic rubber, aB otherwise the
~defiirable prQpertias of the latter may be unduly affected
by the presence of the disintegrating agent.
Suitable disintegrating~agents include various
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thermoplastics resins such as chlorinated polyethylene,
high styrene resins, ethylene vinyl a~etate copolymers
and aromatic hydrocarbon resins.
In assessing suitability it will usually be
necsssary to carry out experiments, since the precise
amount of disintegrating agent needed for a particular
synthetic rubber is not readily predictable.
Preferred synthetio rubbers are the
poly~hloroprenes, such as "NEOPRENE" and
chlorosulp~onated polyethylenes, such as "HYPALON"*.
It is normally essential to achievs a proper balance
between conflicting test specifications for the end
product; for example, the product may pass the drum
friction test, only to fail other tests described in
British Standrd 3289 or to be deficient in other
properties such as abrasio~ resistance or coefficient of
friction which are critical for satisfactory service.
In order that the invention be better understood an
example of it will now be given by way of illu~tration.
Exam~le
A cotton/nylon solid woven belting carcase was
- impregnated with pvc plastisol using the process of UK
patent No. 2036818. A Q.3mm layer of an uncured fire-
resi tant nitrile rubber adhesive compound was applied to
each surface of this carcase, by calendering. A 2mm
~hset of uncured polychloroprene rubber ("NEOPRE~E" GRT)
was applied to each nitrile~rubber layer prior to
consolidating/curing the assembly in a convention beltlng
press at 160~C. The polychloroprene rubber was a
aonventional carbon blaak reinforced, abrasion resistant
compound,~and included material for conferring fire
~resistance. It also included 10 parts (per 100 parts of
polychloroprene) by weight of a disintegrating agent, in
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this particular case an ethylene vinyl acetate copolymer,
sold under the brand ELVAX 360.
The resulting belting exhibited excellent
interlaminar adhesion in excess of 6KN per metre width;
it also passed the drum friction and other fire tests
carried out to B.S. 3289. In the drum friction text, the
synthetic rubber matrix broke down at about 180-C, as a
result of the inclusion of the disintegrating agent.
This was followed rapidly by breaXing of the belt,
without flame or even glow. This was especially
surprising in view of the fact that ELVAX 360 itself
burns ~uite readily. It follows that a good
disintegrating agent for present purposes may itself be
flammable, even where the end product incorporating it
must pass a relatively severe fire test.
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