Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to the production of
aqueous dispersions oE chrysotile asbestos fibre and
in particular to the production of dispersions for use
in the manufacture of coherent bodies such as strands
and filaments and textile yarns made therefrom.
Asbestos fibres can be dispersed in water with the aid
of a surfactant, for example as described in British
atent specification No. 689,692, or with the aid of
a mixture of a soap and an andanionic surfactant, for
; 10 example as described in British Patent specification
No. 1,143,573. This latter specification discloses a
process in which a substance capable of reacting with
and precipitating the soap is added to such a dispersion
in an amount insufficient to cause the dispersion to
begin to coagulate but which is in excess of the amount
of any such substance forming the natural hardness of
the water in the dispersion. One effect of this addition
is to improve the quality of the dispersion as regards
its homogeneity and smoothness. Suitable additives
recited in the specification include various water-
soluble salts of, for example, aluminum, zinc or copper,
and acids such as sulphuric and hydrochloric acid.
Although dispersions prepared by the techniques discloses
in sritish patent specification No. 1,143,573 are appreciably
more homogeneous and contain fibre opened to a greater
extent than was previously possible, they are still
not ideal for use in strand-or filament-forming processes
using fine, easily blocked nozzles, for example those
having at least one dimension less than 2 mm, because
the incidence of nozzle blockages due to bundles of
u~opened fibre is unacceptably high for anything other
than experimental production. Furthermore, the use
of any additive which yields a precipitate of a polyvalent
metal soap makes the removal of the residual organic
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processing chemicals to obtain a substantially pureasbestos yarn more difficult, whether this is carried
out by solvent extraction or by the volatilisation of
the organic material in a non-oxidising atmosphere,
(referred to hereafter as "heat cleansing"~.
According to the present invention, a dispersion of
asbestos fibre in an aqueous medium is essentially comprised
of water, soap and up to 100 percent molar excess of
free acid. "Excess" in the present context means an
` 10 amount in excess of that present in, or used to make,
the soap. In practice, a 25% molar excess appears to
be the minimum necessary with the optimum in the vicinity
of a 50% excess. Beyond about 100% excess there is
a progressively increasing tendency for the dispersion
to become unstable, yielding poor quality strands/filaments.
Other additives are not necessary; in fact the water
need not even contain any hardness - imparting salts,
as has previously been though essential to the production
of dispersions suitable for use in making coherent bodies
such as strands/filaments.
The soap may be a commercial product or may be made
from a pure fatty acid or a commercially available
~ mixture of fatty acids by reaction with a suitable base.
;~ The acid in the soap and the acid forming the excess
preferably have a chain length of at least 12 carbon
atoms, equivalent to a minimum molecular weight of about
200. It is not necessary for the excess fatty acid to
have the same composition as that in the soap.
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The base may be an alkali metal hydroxide, for example
sodium or potassium hydroxide, or may be ammonia or
one of its derivatives such as hydroxylamine, hydrazine
and most saturated amines and quaternary ammonium hydroxides;
unsaturated amines and their derivatives are, on the
; ~ whole, unsuitable.
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t is important to a~preciate that the excess fatty
acId required ~y the present invention does not react
with and precipitate the soap as described in British
patent specification No. 1,143,573 referred to previously
and that, in view of this apparent contradiction of
the teaching of the latter specification, the mechanism
whereby the present invention operates is not fully
understood.
The dispersions of the present invention can be made
in at least three different ways. For example, the
asbestos fibre may be slurried in water before adding
the fatty acid soap, mixing for a period and then adding
fatty acid to provide the desired excess, followed by
further mixing to thoroughly homogenise the dispersion.
Alternatively, the soap may be prepared in situ by the
addition of a stoichiometric amount of fatty acid to
a hot solution of a base before adding the fibre and
excess fatty acid.
Preferably, however, the fibre is slurried in a hot
aqueous solution of the base and the fatty acid is added
all at once, followed by mixing thoroughly. Although
: it offers no obvious technical advantage, this method
has the benefit of extreme sim~licity.
; In order tha-t the invention be ~etter understood, it
: 25 will now be described with reference to the following
six examples. In all but example 6, the dispersion was
formed with the aid of a mixer of the kind generally
described as a hydrapulper and widely used in the paper
making industry for stock preparation.
Example 1
The mixer was filled with 300 litres of hot water at
about gaoc and 10 kg of grade 3 fibre added The mixer
was run briefly to slurry the fibre and then 2.5 kg
of a commercial sodium soap of mixed tallow fatty acids
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was added. The soap was 70% active; i.e. it had a water
content of 30~ by weight. After mixing for 40 minutes,
; the fibre was largely present as small fibres or bundleswhich were readily visible to the eye. Stearic acid
, 5 (90% pure~ was then added slowly and the dispersion
carefully observed. After about 0.5 kg of acid had been
added the dispersion was clearly no longer flocculent
but smooth and homogeneous. Mixing was continued for
a further 20 minutes and then a thin film of the dispersion
was examined between two glass sheets against a diffuse
light source. Very few flocs or spelks (coarse fibre
bundles) could be seen wîth the naked eye. The fatty
acid molar excess was in this example about 30%.
Example 2
Using the same mixer, 336 g of sodium hydroxide was
dissolved in 300 litres of water at about 70C and
2.37 kg of oleic acid added. After a few minutes agitation
the latter dissolved to form a soapy solution to which
15 k~ of grade 3 asbestos was added. The mixer was
~ 20 then run for 1 hour, after which the fibre was present
,~ in the same finely flocculated form observed in Example
1. Then 1 kg of oleic acid was added ~with the mixer
~` still running) and the dispersion was rapidly transformed
to a smooth, homogeneous consistency. It was rather
more viscous than that discribed in the previous Example
because of its greater fibre content but otherwise
it was very similar when examined between two glass
` sheets. The fatty acid molar excess in this case was
about 42~.
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3 a Example 3
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Again using the same mixer, 600 ml of 14 molar ammonia
' solution was added to 300 litres of water at about 65C.
15 kg of grade 3 asbestos fibre was added and the mixer
run to slurry the fibre before adding 3 kg of myristic
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acid and running the mixer for 75 minutes. The dispersion
was then examined between two glass sheets, as in Example
1, and its quality was extremely good. It will be appreciated
that in this, and all subsequent Examples the soap was
not only formed in situ but the excess fatty acid was
introduced at the same time. The fatty acid molar excess
in this case was of the order of 57%.
Example 4
The procedure of Example 3 was repeated using 1.25 kg
of triethanolamine instead of the ammonia. The dispersion
produced was once again of high quality. The fatty
acid molar excess was again of the order of 57%.
Example 5
Example 3 was repeated with 480 g of potassium hydroxide
instead of the ammonia and 3.75 kg of stearic acid instead
of the myristic acid. The dispersion was smooth, homogenous
and of good quality. The fatty acid molar excess was
this case about 54%.
Example 6
A tank fitted with a pump arranged to re-circulate
the contents was filled with 540 litres of water at
about 70C, to which was added 405 of sodium hydroxide
and 18 kg of grade 3 asbestos fibre. After pumping
the mixture around for a while to slurry the fibre,
2.75 kg of lauric acid was added and pumping continued
for 3 hours, yielding a smooth, homogenous dispersion.
`~ The fatty acid molar in this case was of the order of
; 36%.
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; The range of dispersions possible using the method of
the invention appears to be very wide. The asbestos
fibre content may be in the range from about 0.5 to
about 10% by weight; preferably it is from about 1.5
i~ to about 7.5%. Above 10% it becomes increasingly difficult
to mix effectively.
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The possible permutations of bases and fatty acids are
- numerous and the exact amount of excess fatty acid does
; not appear to be critical, quite unlike, for example,
the technique disclosed in specifications 1,143,573.
In any particular instance the amount of excess acid
needed can, with experience, be assessed quite easily
by eye, because the quality of the dispersion improves
markedly as the acid is added, although naturally the
effect becomes progressively less noticeable after the
initial acid additions. The optimum excess for a given
dispersion is also related to the characteristics of
the fibres used.
Although it is possible to make, store and/or use dispersions
at ambient temperature where the fibre content is very
low, it is important to appreciate that the dispersions
should preferably be kept at above their gel ~oint,
the latter being a matter for experiment in any given
~; case as it is a function of the materials/quantities
; employed.
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` 20 Dispersions made according to the invention are useful
in yarn/strand/filament-making processes. All can be
solidified by coagulation with polyvalent metal salts
as described in British patent specifications 824,446
and 1,129,815 though the benefits which are obtained
by omitting such slats from the dispersion, outlined
~` previously, are lost thereby and, in some cases, the
strands are of marginal strength. Dispersions made
according to the invention which gel at room temperature
are very suita~le for use in the strand-forming process
disclosed in our Bri~ish patent 1,484,401.
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