Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
The present invention pertains to a method of
making a pre-impregnated composite material of asbestos
fibre weaving.
! 5 BACRGROUND OF THE INVENTION
For sometime now, asbestos fibres have been
used as reinforcements in various plastic resins to form
a material, called "composite". Whether it be in the
form of brake linings, pipes or covering panels, asbestos
fibres have, in most cases, been used in the form of
short fibres. With the use of mixers, the asbestos
fibres have been dispersed and encapsulated using an
adhesive or a resinous matrix. This technology, which is
more or less known, is characterized by hazardous
environmental conditions and it has therefore become
necessary to evaluate a more modern technology with
improved results, whether it be at the level of
mechanical resistance or at the level of environmental
conditions of handling.
i 20 OBJECT8 OF THE INVENTION
An object of the present invention therefore
concerns the use of a composite in the shape of a pre-
impregnated material which is essentially constituted of
a weaving of asbestos fibres, the mechanical performances
of which after moulding or shaping are clearly superior
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to the materials which are constituted of short fibres
isotropically dispersed in accordance with the previous
method. A pre-impregnated material, commonly known as
3 "prepreg", is constituted of an assembly of reinforcing
fibres impregnated with a resinous matrix or adhesive,
which is maintained in a non-polymerization state or sub-
~ polymerization state prior to being moulded. The fibres
3 are in the shape of continuous strands and woven
according to different geometries, such as
unidirectional, biaxial or angular.
The pre-impregnated material is maintained in
a maturing chamber and then is refrigerated until its use
for the next stage, i.e. moulding. The orientation of
the fibres in the weaving enables to obtain mechanical
properties which vary in accordance with the laminating
pattern, and the selection of plastic resin ensures the
chemical resistance of the part.
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Therefore, the preparation of asbestos fibres
in the form "prepreg" enables moulders to have access to
the potential of performance of such a fibre without
having to be subjected to the inconveniences of air
contamination and the inherent risks of the previously
known technology of mixing and moulding asbestos fibres.
Also, this new technology enables moulders to obtain a
material which has improved mechanical, chemical and
thermal properties.
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8TATEMENT OF THE INVENTION
The present invention therefore relates to a
method of making a pre-impregnated composite material of
asbestos fibre weaving which comprises the steps of
passing a bidirectionally woven asbestos fabric in a
resin bath formed between a pair of impregnating rollers
to form an impregnated sheet, both faces of which are
then covered with a film of plastic material to form a
lamination which is then wound onto a roller.
10The roll of laminated fabric is matured and
refrigerated until it is later used for moulding.
Other objects and further scope of
applicability of the present invention will become
apparent from the detailed description given hereinafter.
15It should be understood, however, that this detailed
description, while indicating preferred embodiments of
the invention, is given by way of illustration only,
since various changes and modifications within the spirit
and scope of the invention will become apparent to those ~
20skilled in the art. -
BRIEF DESCRIPTION OF THE DRAWING8
Figure 1 is a schematic side representation of
an apparatus for carrying out the method of the present
invention; and
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Figure 2 is a schematic front view of the
apparatus shown in figure 1.
DE8CRIPTION OF PREFERRED EMBODIMENT8
A first step in the making of an asbestos woven
fabric consists in mixing chrysotile fibres of various
lengths with organic or synthetic fibres. In a second
step, this mixture is introduced in the form of a
sandwich in a mixer and it is conveyed to the hopper of
a card. The material is then carded in an apparatus
having an arrangement of cylinders rotating at varying
speeds. These cylinders are covered with many short
brushes perpendicular to the axis of the cylinders; this
operation removes impurities and brushes off unwanted
fibres. The mixture is then separated into bands of
various dimensions, called rovings, which are then either
wound separately or together with two, three or four
strands. A third step in the making of asbestos fabric
is the spinning operation during which the rovings pass
through a loom which transforms them by torsion into a
thread which is resistant to traction. This resistance
is also augmented by the addition of a further thread
which may be metallic, synthetic or organic. These
twisted threads, called strands, are wound and shipped to
clients where they are woven. During weaving, the
strands are placed on a loom where the cloth is formed by
the interweaving of two types of strands: the warp which
extends along the length of the cloth, and the weft which
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traverses the width of the cloth. This cloth is finally
vaporized with an adhesive of phenolic resin.
Thereafter, the resin is polymerized at high temperature
and the cloth is wound.
The present invention is concerned with a
method of making a pre-impregnated composite material
that includes such asbestos fibre fabric. Referring to
figure 1, it comprises the step of passing the
bidirectionally woven asbestos fabric 10 taken from roll
12 in a resin bath 14 formed between a pair of
i impregnating rollers 16 and 18. The bath contains a
plastic resin, such as polyester, vinylester, phenolic,
etc., catalysts and other additives. The impregnated
fabric 10' thus obtained is covered on both faces thereof
with a plastic film 20, 22 mounted on transverse
rotatable supports 21 and 23 respectively and is
simultaneously wound to form a roll 24 supported on
transverse support 25.
Thereafter, the roll of impregnated sheet is
stored at ambient temperature for maturing, that is until
the viscosity of the resin is sufficiently high to enable
- it to be properly handled. It is thereafter refrigerated
~ in order to increase its shell life and until it is
s1 wished to utilize it in a moulding operation. The shell
life of the prepreg is about three to six months.
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One type of resin which can be used is a liquid
unsaturated polyester of the isophtalic type which is
diluted in a styrene monomer. This resin is classified
among those which are thermosetting and is largely
utilized in cases where corrosion resistance is required.
Another resin is a liquid vinylester which also
forms part of the thermosetting resin family. This resin
is obtained from an epoxy made from bisphenol A to which
an elastomer is added to obtain a flexibilized vinylester
resin offering excellent adhesive properties.
Another resin among thermosetting resins is an
epoxide having excellent electrical properties which is
also made of bisphenol A and epichlorohydrin.
Another semi-solid thermosetting resin is
novalac epoxide which combines, in a molecule, the
thermal stability of a phenolic resin with the reactivity
and the versatility of epoxy resin. This resin offers
good chemical resistance at high temperatures.
Another resin is phenolic resin which is a
phenol formaldehyde copolymer in liquid form. This
thermosetting resin forms part of the resol family which
has a ratio of formol-to-phenol higher than one. This
resin has high fire resistance and low smoke emission
properties.
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, The resin bath may also include catalysts.
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Perkadox 16 (trade name) may be used; it i5 a
solid catalyst in powder form of the peroxide family. It
is used as a curing agent for unsaturated polyester
~ 5 resins and vinylester resins.
¦ Another catalyst is DEH 40, which i5 a
f commercial name for a solid hardener in powder form and
which is used during moulding operations at high
temperature using epoxy resins (DEH 40 is a dicyandiamide
accelerated with 2-methylimidazole).
Another catalyst is BF3MEA which is a solid
hardener in the shape of flakes which is used for
moulding at high temperature using epoxy resin~. Its
chemical denomination is boron trifluoride monomethyl
amine.
f
Certain phenolic resins have a catalytic system
which is very particular, in that they do not necessitate
a catalyst to polymerize during moulding at high
temperature. This is due to their ratio of formol-to-
phenol being higher than one.
The resin bath used with the present invention
may also contain solvents, such as Dowanol PM which is a
commercial name given to propylene glycol monomethyl
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ether; it is used as a solvent for dissolving the
catalyst DEH 40. Also used as a solvent, is
dimethylformamide which is used to dissolve DEH 40.
The resin bath may also contain additives such
as Aerosil (trade name), MgO, MgOH, CaO, Ca OH, talc and
hollow glass balls. Aerosil is a powder of fine
particles of silicium dioxide; it is a thixotropic agent
which prevents drainage of the resin on a vertical wall.
Magnesium oxide, such as Maglite D (trade name), is
highly reactive; it is a thickening agent used to
increase the viscosity of the resin at ambient
temperature. Talc is an inert material, in powder form,
forming part of the family of silicates; it has high
chemical resistance and is used to thicken the resin and
reduce the cost of materials. Finally, hollow glass
balls are used as reinforcing elements, mainly to reduce
the density of the molded parts.
Referring to figures 1 and 2, once the resin is
mixed, it is fed from a container 29 to a distribution
system that includes pipe lines 26 and 28 connected to a
pair of parallel conduit systems 30 and 32 equipped with
a series of nozzles 34, 36.
Although the invention has been described above
with respect with one specific form, it will be evident
to a person skilled in the art that it may be modified
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and refined in various ways. It is therefore wished to ~ ,
have it understood that the present invention should not
be limited in scope, except by the terms of the following
claims.
