Note: Descriptions are shown in the official language in which they were submitted.
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In manufacturing certain types o~ floor material, a porous
sheet, having asbestos as its essential constituent, is used as
support felt. Asbestos, however, may create health risks and
it has therefore been proposed, in this connection as well as
in other connec ions, that the asbestos should be exchanged
with artificial mineral wool, for instance stone wool, glass
wool or the like, because artificial mineral wool will not
create the health risks, produced by the asbestos. Replacing
asbestos simply with a corresponding amount of mineral wool,
however, will produce a fibrous sheet wherein rigidity against
pulling, flexibility and impression resistance are much
inferior to the product using asbestos as the fibrous material.
The artificial mineral fibers, in contrast to the asbestos
fibers, are quite smooth and require quite a different binding
effect than the asbestos. Large quantities of binder, which
are obviously uneconomical, and also unsuitable from other
points of view, have proved incapable of overcoming this
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difference in fibrous properties.
In the present invention, however, a method is disclosed
whereby a fibrous sheet, based on artificial mineral wool, will
exhibit such properties, using reasonable amounts of binder,
- such that it may replace the corresponding asbestos products.
The method according to the present invention, however, is not
limited to replacing asbestos products.. The invention refers
to an aqueous process, where a suspension of artificial mlneral
fibers in water lS first prepared, a sheet is formed from the
fibrous suspension, and finally this sheet is dried.
According to the lnvention, the sheet is subjected to an
observable compression while drying. It has proved expecially
advantageous if the compression is subjected and removed so that ~ ; ;
the compression is retained during the major part of the drying
procedure, preferably so that it will remain until the sheet is
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almost completely dry. The reason for obtaining such a decisive
positve effect, which greatly supercedes the effect which an
increase of density proper will give, may, after studies, be
- assumed that the binder drops which in the initial part
comprise a given amount of water with one or more binder
particles contained therein, will also initially comprise or at
- least touch two or more fibers. When the water is removed, of
course, the volume of the drop is decreased so that the binder
- particles will be released. Then it may happen, and it obviously
` happens to an important extent, that the separate binder
particles no longer overlay the distance between the fibers.
Then, also, no binder action will occur.
The circumstances, however, are different if the fibers,
- which are in contact with a given binder dispersion drop, are
compressed so that the distance will be small. The binder
particles remaining after the evaporation of the water will
then be able to bind the fibers together. When the drying
procedure is finished and deloading takes place, the fiber sheet
will expand, but by that time, the binding is already esta-
blished. In principle, this effect could be achieved, for instance
- by a momentary compression of greater or lesser extent of the
fiber sheet after the drying procedure has been finished but
before the fiber sheet has been cooled. The effect which is
then achieved, however, is much smaller and therefore it seems
to be of importance that the binding between the fibers, due to
the compression adjacent to each other, takes place concurrent
with the removal of the water during the drying procedure.
In order to maximize the effect of the invention, it is
required that the compression during the drying be observable.
It should amount to at least 20 percent, and preferably, to at
least 40 percent of the thickness of the wet sheet. An
especially desirable apparatus for execution of the invention
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has proved to be a drying cylinder, which has, in an est~blishe~
way, its major part surrounded by a drying felt or a drylng
vira. The drying felt, however, or the drying vira must be so
arranged that it can be stretched to such a degree that the
- fiber sheet will get the required amount of compression.
A Yankee-type fiber machine has proved to be most favorable,
but multiple cylinder machines can be used as well, since it
has proved to be of no decisive importance that the pressure be
deloaded during the time when the sheet is moved from one
cylinder to another one. However, it is of greater importance
that the degree of compression on the different cylinders be
uniform.
The effects caused by the execution of the invention in
the above indicated process, according to what has been found
by investigation, is to be regarded as substantially the result
of an effective use of the binder. It has also been established
that the binder effect, such as it appears in the ready mineral
fiber sheet, is further improved by establishing sequential
feeding of the binder. Thus, it has proven to be of great
value that the binder is added in two steps. Thereby one part
of the binder should be added to the fiber suspension from which
the sheet is formed. A second part of the binder should there-
after be added to the wet sheet after dewatering has been
nearly or completely finished.
As binder during the first binder step, latex of an
- acrylate polymeric product in the form of a dispersio~ or some
binder comparable therewith seems to be optimal. The result
will be especially good if the dispersion is brought to a
coagualated state before the formation of the sheet. The
coagulation can take place in the fiber suspension after the
binder dispersion has been added, but it may preferably take
place before the addition of the dispersion to the fiber
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-~ suspension, because the conditions ~or coa~ulation will be
under better control then.
The binder which is added to the fiber suspension must
form at least 2 percent but should not exceed 25 percent of
the fiber weight. Preferably the amount-of binder should be
about 15 percenl of the fiber weight.
In the second binder step, it has been proved that
styrene-butadiene-latex or the like will give the best results.
However, it is of decisive importance that this binder be
distributed extremely evenly and in the form of small particles.
Spraying with a high degree of finely divided particles has
therefore been found to be the most suitable procedure. The
cloud of binder particles thereby created, however, is difficult
to control in practice, such that it has proved especially
advantageous to use electrostatic spraying. -
The amo~nt of binder in the second binder addition step
should also be at least 2 percent, and at a maximum 25 percent
- of the fiber weight. A suitable amount for most purposes will
be 10 percent of the fiber weight.
If the amount of binder in the first step is close to the
lower limit, then more binder should be added during the
second step relative to the amount added in the first step and
vice versa. The total amount of binder, therefore, should not
be less than 10 percent and, preferably, less than 20 percent
of the fiber weight. Alternatively, there are no essential
advantages to be gained by using over 40 percent by fiber
weight and little advantage in using over 30 percent.
The examples below show how the characteristics of the
invention produce an important result regarding the desirable
properties for the mineral fiber sheet. ~owever, it is under-
stood that the invention may be used in other ways within the
scope and spirit of the claims.
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` Example 1
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A fiber suspension comprising 0.1~ stone wool fibers in
water is provided with 15% acrylate latex, based on the fiber
weight, said latex having just been brought to a coagulated
- state by a lowering of the pH-value using alum solution. The
binder containing the fiber suspension is dewaterecl on an even
vira "Voith Hydroforme~'. After dewatering to 40~ dry substance
about 10~ based on the fiber weight, styrene butadiene latex
is sprayed thereon. The sheet was introduced on a drying
cylinder havin~ 1 m diameter, with its major part surrounded
- by a vira, having a controllable tension. The sheet was
dried and tested with respect to pulling rigidity and impression
rigidityl). The following results were obtained:
A B
Pulling force in the vira 0.4 kp/cm 20 kp/cm
Compression of the dry cylinder 10% 60%
- Pulling rigidity lengthwise 20.5 N/3cm 60 N/3cm
crosswise 17.3 N/3cm 53 ~/3cm
Impression rigidity durlng loadl) 1.4 mm 0.5 mm
after deloading 1.2 mm 0.38 mm
)a steel ball 20 mm ~ in diameter supplies a load to the sheet
for 5 minutes and the impression is measured. After deloading
- for 5 minutes, the impression is again measured.
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The sheet, which had been strongly compressed while drying
(test B) exhibited essentially better rigidity than the one
which had been compressed only nominally (A).
Example_2
In a test conducted principally accordin~ to example 1,
the following variations were made regarding the type of
binder utilized.
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