|Title of Invention||
AN IMPROVED METHOD FOR MANUFACTURING SILICATE-CONTAINING FIBER
|Abstract||There is disclosed an improved method for manufacturing silicate-containing fiber, wherein silicon dioxide is added to viscose manufactured of cellulose, the formed mixture of viscose and silicon dioxide is directed via nozzles to an acidic regeneration solution, where silicate-containing fibers are formed, characterized in that soluble silicate is added to the acidic regeneration solution, whereby the solubility of the silicate in the fibers to the regeneration solution is decreased.|
|Full Text||Field of the invention
The invention relates to a method for manufacturing silicate-containing
fiber according to the preamble of the appended claim 1.
Background of the invention
Materials that are not easily burned or are non-combustible are
increasingly used in the production of furniture and textiles. For
example, in upholstery materials, such as fabrics, fibers that do not
catch fire easily, or are non-flammable, and prevent fire are used. This
kind of fibers include, inter alia, silicate-containing fibers.
One manner to manufacture silicate-containing fibers is to adapt
viscose manufactured of cellulose by adding silicon dioxide to it and by
spinning and processing the thus created silicate-containing fiber for
further use. This kind of a method is presented, for example, in the GB
patent 1064271, where the viscose-containing sodium silicate is spun
into an acidic spinning solution, where the regeneration of the viscose
into cellulose takes place, and at the same time, the sodium silicate in
the viscose precipitates into silicon acid, which is water-containing
silicon dioxide evenly distributed throughout the cellulose.
The method according to the above-mentioned patent is an
inexpensive manner to manufacture silicate-containing fibers. The
problem is that the silicon acid in the fibers formed by this method does
not endure the alkaline detergents used in washing of textiles. In
repeated washes, the silicon acid contained by the fibers dissolves into
the alkaline washing liquid, which leads into a decreased fire durability.
The above-mentioned problem is solved in the Fl patent 91778
(corresponds to US 5,417,752) by processing the spun silicate-
containing viscose fiber with sodium aluminate, wherein the silicon
dioxide that is in silicon acid form in the silicate reacts with the
aluminate and forms aluminum silicate groups in the silicon acid. The
solubility of the aluminum silicate groups-containing silicon acid to
alkaline detergents is very small, and therefore the product can be
washed with normal detergents without its fire prevention properties
being altered. In addition, the product containing aluminum silicate
groups has a significantly better fire protection efficiency than products
manufactured without aluminate.
The problem with the methods according to both of the above-
mentioned publications is, however, the tendency of the silicate
contained by the viscose, i.e. the silicon acid or silica (SiO2.nH2O) to
dissolve into the spinning solution in spinning. It has been detected that
a significant part of the silicate, even hundreds of milligrams/liter of
spinning solution, may remain in the spinning solution in spinning. The
uncontrolled dissolution of silicate and dispersion into the spinning
solution causes several problems. The silicate forms precipitate in the
spinning bath, which causes fouling of the spinning bath and increases
friction between the tow consisting of thousands of fibers that is formed
in the spinning bath and, and the stretch rolls, i.e. galets and stretch
stones. Friction between individual fibers also increases in the tow,
which weakens the stretchability of the tow and thus also the strength
of an individual fiber. The friction between fibers also causes fibers to
fray at the spinner.
The uncontrolled dissolution of silicate from the fibers into the spinning
solution also causes quality fluctuations in them. This can be seen as
fluctuations in the strength values and titer, i.e. the weight/length
values of the fiber, which deteriorates the textile properties of the fiber.
In addition, a decrease in the amount of silicate in a fiber leads to a
weakened fire durability of the finished fiber, because even only a
decrease of 1 to 2 % in the amount of silicate deteriorates fire
Brief description of the invention
Therefore, the purpose of the present invention is to provide an
improved method for manufacturing silicate-containing fiber, which
avoids the above-mentioned problems and where the fiber
manufactured according to the method has as high as possible silicate
To attain this purpose, the method according to the invention is
primarily characterized in what will be presented in the characterizing
part of the independent main claim 1.
The other, dependent claims will present some preferred embodiments
of the invention.
The invention is based on the idea that the composition of the
regeneration solution used in manufacturing silicate-containing fiber,
i.e. the spinning solution used as spinning bath is formed into such that
the silicate concentration of the fiber being manufactured can be kept
as high as possible. This can be implemented by means of the method
according to the invention, which utilizes the surprising observation that
by adding a suitable amount of soluble silicate in a controlled manner
into the spinning solution, the solubility of the silicate in the fibers to the
spinning solution decreases. Thus, the amount of silicate contained by
the viscose fiber can be kept as high as possible.
In the silicate-containing fibers formed in the spinning bath the silicate
is evenly distributed in the fiber. The silicate on the outer surface of the
fibers, however, comes into contact with the spinning solution during
the spinning of fibers and dissolves into the spinning solution and
crystallizes into it. This crystallization is completely uncontrolled and
causes the above-described problems. By adding soluble silicate
according to the invention to the spinning solution, the uncontrolled
dissolution and crystallization of the silicate on the surface of the fibers
can be prevented.
The silicate added to the spinning bath can be water-soluble alkali
metal silicate, such as sodium silicate, for example, water glass
(Na2OnSiO2) or water-soluble precipitated silicate. The silicate
concentration of the spinning bath can vary between 50 and 1,000 mg/l
of spinning solution, advantageously it is between 100 and 700 mg/l of
spinning solution. The silicate is added directly to the spinning bath,
among the other chemicals forming the spinning solution. The spinning
solution is continuously recirculated between the processes of the
spinning bath and the spinning solution during spinning.
According to an advantageous embodiment of the invention, the
spinning solution is kept saturated or nearly saturated by the soluble
silicate by removing or adding silicate in a controlled manner to the
spinning bath. The extra silicate precipitated in the spinning bath can
be removed by means of any filtering method known as such, for
example, by sand filtration, pressure filtration or a curved screen.
According to a second embodiment of the invention, in the
manufacturing process of silicate-containing fiber, silicate-containing
solutions are used also in the stretching and washing stages of the
fiber, which follow the spinning stage.
Further, according to a third embodiment of the invention, the silicate
concentration of the silicate-containing fiber can be controlled onto a
desired level by controlling the amount of silicate added to the spinning
By means of the method, the uncontrolled dissolution of silicate from
the silicate-containing fiber into the spinning solution can be eliminated
and the problems caused by the friction between the fibers caused by
the silicate powder precipitating in the spinning bath can be removed.
As a result of that, the fluctuations in the quality properties of the fibers
also decrease. The deviations of the strength and titer values
measured of the fibers are smaller than that of the fibers manufactured
by means of the methods according to prior art, which improves their
textile properties. In addition, the increase in the amount of silicate
contained by the fibers improves the fire protection properties of the
By means of the method it is also possible to produce viscose fibers
whose silicate concentration has been controlled onto a specific level
according to the desires of the customer.
Application of the method is easy and simple and it is easy to apply to
the already existing plants manufacturing silicate-containing fiber.
Brief description of the drawings
In the following, the invention is described more in detail with reference
to the appended figure, which schematically shows the method for
manufacturing silicate-containing fiber according to the invention.
Detailed description of the invention
The figure shows a manufacturing method for viscose fiber, wherein in
stage 1, the dissolving cellulose processed by means of sodium
hydroxide (NaOH) is sludged into slush pulp. After this, the cellulose is
pressed in stage 2 for removing the sodium hydroxide from it, and the
resulting alkali cellulose is shredded in stage 3. The shredded alkali
cellulose is directed to stage 4, i.e. prematuring, where it stays under
the effect of the oxygen in air for about 3 to 5 hours in a temperature of
approximately 35 to 45 °C. In prematuring, the alkali cellulose is partly
Next, the prematured alkali cellulose is directed to sulphurization (stage
5), where carbon bisulphide (CS2) is mixed into the alkali cellulose, in
which case cellulose xanthate is formed. After the sulphurization, weak
sodium hydroxide (NaOH) is added in stage 6 to the xanthate while
mixing at the same time, which leads to dissolution of xanthate, which
is almost complete after 1 hour of dissolution. The orange-yellow,
syrupy viscose received from stage 6 is directed through the ageing
tanks of stage 7.
During the ageing and after that in stage 8, the viscose is filtered. The
next process stage 9 is deaeration. Before deaeration, for example at
the point marked with the arrow 10, silicon dioxide solution is added to
the viscose resulting in a mixed viscose formed by viscose and silicon
dioxide. If desired, the silcon dioxide can also be added in an earlier
process stage, i.e. in any suitable process stage/point before the
spinning bath. The silicon dioxide added to the viscose can be, for
example, commercial silicon dioxide, such as water glass (Na2O
nSiO2) or a mixture of silicon dioxide and sodium hydroxide. In the
deaeration stage 9 the air and gas bubbles are removed from the
viscose/silicon dioxide -mixture viscose.
Next, the mixed viscose is directed to the spinning stage 11, where the
formation of viscose fibers takes place. The mixed viscose is directed
to the spinning bath, below the surface of the spinning solution, through
the small-perforation nozzles, spinnerettes of the spinning candle.
There are generally about 8,000 to 50,000 holes in the spinnerettes,
whose diameter is between 50 and 80 urn. The spinning solution is
acidic liquor, which typically contains sulphuric acid (H2SO4), zinc
sulphate (ZnSO4) and sodium sulphate (Na2SO4). The sodium sulphate
is formed in the solution when the sulphuric acid contained by the
solution and the sodium hydroxide in the mixed viscose react. The
temperature of the spinning solution is approximately 0 to 100 °C,
typically approximately 40 to 70 °C. According to the invention, soluble
silicate, for example, sodium silicate, is also added to the spinning
solution, which results in that the silicate in the viscose/silicon dioxide -
fiber forming in the spinning bath does not dissolve into the spinning
bath, but remains in the fiber. The ratio of the components contained
by the spinning solution may vary in the following way:
sulphuric acid 40 to 150g/l of spinning solution
sodium sulphate 20 to 40 wt-%
zinc sulphate 0 to 100 g/l of spinning solution
sodium silicate 50 to 1,000 mg/l of spinning solution,
advantageously 100 to 700 mg/l,
calculated as SiO2
The composition of the spinning bath varies depending on the quality
targets and properties of the fiber being manufactured, for example its
Silicate is added in a controlled manner into the spinning bath, i.e. in
the manner that the silicate concentration of the fiber being spun
remains as high as possible, but the properties of the spinning solution
and the silicate precipitating in it do not cause problems in spinning and
in the operation of the spinning apparatus. Thus, silicate can be added
to the bath in suitable portions continuously or at set intervals. The
silicate precipitated in the spinning bath is removed in a controlled
manner as well, depending on the amount of the precipitated silicate.
The solid cellulose-filament fibers forming in the spinning bath are
collected from the bath in such a manner that the tow formed by the
thousands of fibers coming from one spinnerette is in stage 12 wound
around smaller stretch rolls first, and then further via a stretch bath to
other, bigger stretch rolls, i.e. stretch stones. The stretch not only
lengthens the fibers 50 to 100%, but also increases their strength. After
the stretch the tow formed of the fibers is directed to the cutting stage
13 where it is cut into a desired length. The cut fibers are rinsed with
water to the washing stage 14. Thus, the fiber bundles break up and
the washing of individual fibers can be continued in stage 14.
In the drawing and washing stages it is possible to also use silicate-
containing solutions, which assists in keeping the silicate concentration
in the fibers as high as possible.
In the washing stage 14 it is also possible, if desired, to treat the fibers
with some aluminum containing solution, such as, for example, sodium
aluminate solution (NaAIO2). As a result of this, the silicon acid
contained by the fibers is modified into aluminum silicate, which results
in a fiber that endures washing and even bleaching chemicals well,
which, however, feels the same as a normal viscose fiber.
After the possible sodium aluminate processing, the fibers are
processed further in stage 14 in a normal manner, i.e. they are
washed, the pH is adjusted and they are processed with surface-active
agents. After this the fibers are dried.
According to an advantageous embodiment, the amount of silicate
added to the spinning bath is such that the bath is saturated in relation
to dissoluble silicate, or almost saturated. The extra silicate precipitated
in the spinning bath is removed in connection with the circulation of the
The devices use in the above-described manufacture of viscose fiber
and their operation are known as such to a man skilled in the art, which
is why they are not described more in detail here.
In the following, some test results of the method according to the
invention for manufacturing silicate-containing fiber will be presented.
In the test, the silicate concentration of the spinning solution was varied
and at the same time the silicate concentration of the viscose fibers
resulting from the spinning was monitored.
The viscose was manufactured by means of the viscose method
described above and known as such, wherein sodium silicate, i.e.
water glass, was added to the viscose as silicon dioxide. Thus, the
result was a mixed viscose containing 3.6 % of SiO2, 8.2 % of alpha-
cellulose, and 7.4 % of NaOH. 3.5 dtex of fiber was spun of this mixed
viscose. The temperature of the spinning solution was 50 °C and its
composition without the silicate addition was as follows:
sulphuric acid 65 g/l of spinning solution
sodium sulphate 20 wt-%
zinc sulphate 45 g/l of spinning solution
A certain amount of silicate was added into the spinning bath at set
intervals in such a manner that the silicate concentration of the
spinning solution increased gradually. Commercially available water
glass (SiO2:Na2O 2,5:1, 30,9% SiO2) was used as the added silicate.
After each addition, fibers were spun to the solution in the manner
presented above. After the spinning bath the fiber was stretched 90%
longer than original in the stretching bath, in which the temperature
was 90 °C and which contained 3g/l of sulphuric acid.
The silicon dioxide content of the spinning solution was determined by
a spectraphotometer by using the so-called molybdenum sine method.
Before the determination the spinning solution was circulated for about
and hour in order for the acid balance to normalize.
The effect of the silicate additions on the silicate concentration of tie
viscose fibers resulting from the spinning was monitored by analyzing
the SiO2-content of the spun fibers after each silicate addition. The
Sip2-content of the fibers was determined by ashing the fiber in the
furnace in 750 °C for an hour and by weighing the resulting ash. The
silicon dioxide in the fibers was found to be almost pure SiO2.
The following table presents the effect of the silicate concentration of
the spinning bath on the SiO2-concentration of the fiber:
Table 1. The amount of silicate added to the spinning bath, the
measured silicate concentration of the bath, and the SiO2-concentration
of the fibers spun to the bath in question
From the results of Table 1 it is detected that the addition of silicate to
the spinning bath increases the silicate concentration of the fibers
received as a result of spinning, i.e. the dissolution of the silicate in the
fibers into the spinning bath is decreased. The saturation point of the
solution in relation to silicate was reached in test 4. The larger silicate
additions after that to the spinning bath did not have an effect on the
silicate concentration of the fiber any more, but it remained constant.
In addition, when fibers are compared, of which one was spun to the
spinning solution that was saturated with silicate (test 4) and the other
to a solution to which was added very little or no silicate (tests 1 and 2),
it is noticed that without the silicate addition, an approximately 8%
weight loss took place in the fiber in the spinning, i.e. the dissolution of
the silicate from the fibers into the spinning solution was significant.
This has an effect on the fire protection properties of the fiber. In fact,
the fibers produced in tests 1 and 2 are inadequate in their fire
protection properties and the unanticipated weight loss impedes the
control of the fiber dtex (weight/length). By keeping the silicate
concentration of the spinning bath on a suitable level, these problems
can be removed.
A part of the fibers manufactured in the above-presented tests (tests 1
to 7) were also processed with aluminate. Processing with sodium
aluminate solution (3 g/l of Na aluminate calculated as AI2O3, solution
ratio 1:10, temperature 50 °C) increased the ash content of the fiber 2
to 2.5% of the values presented in Table 1. Thus, the ash also
The invention is not intended to be limited to the above embodiments
presented as an example, but the invention is intended to be applied
widely within the scope of the inventive idea as defined in the
1. An improved method for manufacturing silicate-containing fiber, wherein silicon
dioxide is added to viscose manufactured of cellulose, the formed mixture of viscose and
silicon dioxide is directed via nozzles to an acidic regeneration solution, where silicate-
containing fibers are formed, characterized in that soluble silicate is added to the acidic
regeneration solution, whereby the solubility of the silicate in the fibers to the regeneration
solution is decreased.
2. The method as claimed in claim 1, wherein the silicate added to the regeneration
solution is water-soluble alkali metal silicate or water-soluble precipitated silicate.
3. The method as claimed in claim 1 or 2, wherein 50 to 1,000 mg/l of silicate,
advantageously 100 to 700 mg/l, calculated as SiO2, is added to the regeneration solution.
4. The method as claimed in claim 1 or 2, wherein the amount of silicate added to the
regeneration solution is such that the regeneration solution is saturated by the soluble silicate.
5. The method as claimed in claim 4, wherein the silicate precipitated into the
regeneration solution is removed from the regeneration solution in connection with its
6. The method as claimed in claim 1, wherein silicate is added to the regeneration
solution directly to the spinning stage (11) before the mixture of viscose and silicon dioxide is
directed to the regeneration solution.
7. The method as claimed in any of the claims 1 to 6, wherein the regeneration solution
also contains sulphuric acid, sodium sulphate and zinc sulphate.
8. The method as claimed in claim 1, wherein that silicate is added to and removed from
the regeneration solution.
9. The method as claimed in claim 8, wherein adding and removing silicate from the
regeneration solution is performed in a controlled manner in such a way that the silicate
concentration of the regeneration solution remains on a level to control the silicate
concentration of the silicate-containing fiber onto a desired level.
There is disclosed an improved method for manufacturing silicate-containing fiber,
wherein silicon dioxide is added to viscose manufactured of cellulose, the formed mixture of
viscose and silicon dioxide is directed via nozzles to an acidic regeneration solution, where
silicate-containing fibers are formed, characterized in that soluble silicate is added to the
acidic regeneration solution, whereby the solubility of the silicate in the fibers to the
regeneration solution is decreased.
|Indian Patent Application Number||3342/KOLNP/2006|
|PG Journal Number||13/2012|
|Date of Filing||13-Nov-2006|
|Name of Patentee||SATERI INTERNATIONAL CO. LTD.|
|Applicant Address||PORTCULLIS TRUSTNET CHAMBERS ROAD TOWN, TORTOLA|
|PCT International Classification Number||D01F1/07; D01F2/08|
|PCT International Application Number||PCT/FI2005/050187|
|PCT International Filing date||2005-06-01|