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Патент USA US3079939

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March 5, 1963v
Filed Nov. 12, 1958
3 Sheets-Sheet 1
„flueg- '
March 5, 1963
3 snèets-sneetz
Filed NOV. 12, 1958
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March 5, 1963
P. A. Mux-:LLER
Filed Nov. 12, 195s
s sneets-sneeis
States Patent _
Paul Adolf Mueller, Rosenhuegel, Herrliberg, Switzerland
Filed Nov. 12, 1958, Ser. No. 773,421
12 Claims. (Cl. 131-208)
The present invention relates to ülter plugs for cigarettes
and to a method of manufacturing a ülter -rope from
übrous material suitable for processing into such ülter
Patented Mar. 5, 1953
possesses -a gathering unit arranged at the end of a con
veyor line designed to change a üat pile web into a rope
with a cross-section at least substantially circular, and
which is designed to process the pile web delivered by the
ürst mechanism.
A number of embodiments of the invention is described
in greater detail in conjunction with the drawing in which:
FIG. 1 is a perspective diagrammatic view of the ülter
plug according to the present invention;
FIGS. 2 and 3 are sketched representations of micro
plugs, and to a device for the performance of the said 10
photographs of über cross-sections;
method. The method can preferably be employed for
FIG. 4 is a diagrammatic view of an embodiment of a
the manufacture of a ülter rope formed of a mixture of
device designed to consolidate a üat material web;
viscose übers and cotton and cellulose übers respectively.
FIGS. 5 to 9 are plan views of ñat über webs provided
A ülter rope capable of being processed into ülter plugs
for cigarettes can generally be produced in one of two 15 with an embossed design;
FIGS. l0 and l1 are perspective views of a two-ply and
basically different processes depending on the different
three-ply über web respectively;
raw material employed.
FIGS. 12a, 12b are diagrammatic representations of an
If a paper-type raw übrous material is used for raw
elevation and plan view respectively of a mechanism for
material, no diüiculties are generally encountered in the
processing of such material. However, the ültering action 20 producing a ülter rope from a consolidated über web; and
FIGS. 13a, 13b and 13C are diagrammatic cross-sections
of such materials is relatively small unless they are `sub
of über webs.
jected to a particular pretreatment. The pretreatment
The present ülter plug 10 according to FIG. 1 as usual
for such paper-type materials advantageously consists in
consists of a wrap 11 formed, by way of example, of thin
a loosening of the über structure of the paper employed,
i.e. in disintegrating the material. With such pretreat 25 paper enclosing a über bundle 12 having an oval or cir
cular cross-section. As shown by the front end of the
ment (see, by way of example the U.S. patent speciüca
ülter plug, the übers 13 should substantially extend in the
raxial direction of the plug. The entire über bundle 12.
is interspersed with a plurality of points of adhesion 14,
ready been largely adopted in practice.
However, if the raw material employed consists of 30 which FIG. l shows only diagrammatically, between cross
ing‘or laterally contacting übers. These points of ad
übers and über bundles, the principal diüiculty resides in
hesion 14 can readily be found when such a ülter plug 10
the necessity of taking measures designed to reinforce the
is opened either before or after using, and it canbe seen,
ülter rope formed of a bundle of übers. In the large
c_g. by means of -a magnifying glass, that the points of
majority of cases, a suitable binder must be employed to
consolidate the über tufts and to protect them against 35 adhesion are produced not by bonding> the contacting
tions Nos. 2,228,383 and 2,707,960), anexcellent ültering
action can be obtained so that such processes have al
sliding displacement, which involves considerable disad
übers by means of a binder or solvent butby a mechanical
vantages, such -as the emission in traces of solvents de
deformation of the übers.
Closer examination of the
points of adhesion reveals that their mechanical strength
is greater than that of the original über but that the
the taste. If such binders are not to be employed, the
übrous material must possess a sufficiently compact struc 40 absorptive and swelling capacity of the said points of
adhesion is substantially lower than that of the über por
ture, such as that of cotton wool or the like, from which
tions immediately adjacent such points of adhesion. Nat
only ülter plugs having an undesirable degree of resistance
urally, the points of adhesion are not necessarily points
to pulling can be produced.
-but may be elongated.
The present invention constitutes -a novel solution of
The über bundle 12 reinforced by a plurality of points
the problems cited and it eliminates the former defects.
of adhesion 14 distributed at random is thereby provided,
lt relates to a ülter plug for cigarettes comprising übers
trimental to health during smoking, or the inüuencing of
`and über bundles and is characterized by the fact that a
as it were, with a supporting framework of mechani
cally stable points of adhesion which
supporting framework formed of points of adhesion free
altered when used, and with unprocessed
from binders and solvents is provided between contacting
übers Within the über bundle, the mechanical strength of 50 the spaces between the said framework.
rial in the spaces between the elements
the übers located at the points of adhesion being in
will hardly be
übrous areas in
The über mate
of these points
of adhesion can substantially swell and become soft dur
creased at the expense of a lower adsorptiveand swelling
ing use without markedly lessening the strength and sta
bility of the über bundle held together by the framework
The invention further relates to a method of manu
facturing such ülter plugs characterized by the fact that at 55 of points of adhesion. Against the ülter plugs so far
known, the strength of the ülter plug is largely independ
least one wide, loose web is produced ürst from übers
ent of the changes in strength of the übers during use.
which comprise at least a portion of such synthetic übers
For this reason it is now also possible to employ highly
which will form a point of adhesion when compressed,
absorbent über material and to obtain -a high degree of
the said web being continuously passed between emboss
ing means and thus consolidated by a pattern of points of 60 ültering action despite low resistance to pulling.
The framework of points of adhesion within the über
adhesion between contacting übers. The self-supporting
bundle further has the advantage that the -smoke is posi
web is then gathered transversely lto the direction of
travel and formed into a ülter having a cross-section which
tively conducted towards the highly adsorbent and/or
is at least approximately circular.
absorbent über material in the spaces. In particular this
The device according to the present invention for the 65 highly desirable effect _can be enhanced or reduced by
influencing- the spatial arrangement of the points of ad
performance of the said method is characterized by the
presence of two mechanisms of which the ürst one is
hesion within the über bundle in the event of the ülter
provided, at the beginning of a conveyor line, with a pile
plugs being produced in 'accordance with the method
web fabricating unit, possesses embossing means supplied
described hereunder.
-by the conveyor line and equipped with take-up devices 70
For the manufacture of the ülter plug according to this
at the end of the conveyor, while the second mechanism
invention, a synthetic über or ülament formed of viscose,
ie., a regenerated cellulosic material, is employed by
way of example, which is produced from cellulose
xanthate in diluted caustic soda and forced through spin
nerets in the form of viscous ülaments into a warm
Spinning bath containing strongly saline diluted sulphuric
acid. The bath causes the spinning solution to be pre
cipitatedto form viscosel filaments which can be cut into
desired staple lengths after washing and drying.
Such viscose übers or ülaments possess, by way of eX
behaviou-r of hydrophile synthetic übers has so far caused `
them to be considered entirely unsuitable for the purpose
of ültering smoke.
However, practically all these defects can be removed
if the bundle of fibers or ülaments forming the filter plug
is stabilized by a plurality of points of adhesion between
the individual übers as described above.
A method of producing such points of adhesion is`
based on the fact that crossing synthetic fibers adhere to
ample, a speciüc gravity of 1.5 gms/cm? and a. speciüc 10 one another if the point of crossing is sufficiently com
strength of 22 to 41 kg./mm.2. VOn the other hand, cellu
lose acetate ülaments commonly have a speciüc gravity
YIf a fiat loose über web formed of such synthetic fibers
of about 1.3 gms/cm.3 and a specificstrength of 13 to
21 Vlig/mm?.
or filaments is produced in which the fibers or filaments
lie in any direction, a large number of crossing points be
The' moisture absorption of 4such viscose übers or üla 15 .tween individual fibers corresponding Vto the very large
ments at 65% relative humidity amounts to about 13.5%
number of fibers present is obtained. If -a very loose über
and at 100% relative humidity to between 44 and 48%
web formed of viscose fibers is compressed, between fiat
against the corresponding values of about 6.0% and 15%
plates, vertically to the über web, the über Aweb which
respectively in cellulose acetate übers. The synthetic
could previously be transported only by means of a sup
viscose übers and filaments therefore display a far better 20 porting band is changed into a markedly stiffened, self'
absorptive capacity for moisture than cellulose acetate
supporting über web which is also fairly resistant in the
fibers. The reason therefor is found in the fact that the
transverse direction. However, a viscose über web so
cellulose acetate übers largely adsorb moisture at the sur
face only while viscose übers absorb the liquid deposited
Y _ treated is too rigid and strong for the purpose of manu
facturing ülter plugs.r A gradual consolidation of the " '
on the surface in the interior of the über thereby leaving 25 über web is quite sufiicient; the latter being compressed ' '
the surface free to take up more moisture.
not across its entire fiat Width but only along a suitable
Absorption of moisture by viscose übers or filaments
fiat embossing design.
can easily be checked by their swelling and the enlarge
ment of their cross-section. By way of example, FIGS. 2
The embossing design may be produced, by way of
example, by means of fiat dies having a ribbed pressing
and 3 show two types of viscose filaments in cross-sec 30 surface or again by means of rotating rollers having a
tions enlarged at the rate of 1:550, the left side showing
corresponding design formed of projecting edges on the
a ülament in the dry state vas filament» 13a and the right
roller surface. The last-named case is represented, by
side showing the same filament in the swollen state as
Way of example, in the device according to FIG. 4, all
filament 13b. The enlargement ofV the cross-section, i.c.
less essential details îbeing omitted. The über web formed
the enlargement of the surface within the outer fiber 35 of
the synthetic or regenerated cellulosic fibers'such as
' skin, is clearly Visible.
viscose fibers is processed in the known manner by the
Examination of ülter plugs‘formed of such hydrophile
21. By Way of example, the mechanism 21
and swelling synthetic übers or filaments, preferably of Y; mechanism
may be designed as a card or a converter of usual design,
various viscose fibers„has shown that in order to obtain
it being of advantage for certain applications to employ
a satisfactory absorption of the liquid tar and nicotine 40 relatively short-stapled material. lThe mechanism 21 ap
components the synthetic übers or filaments should dis
plies a loose and thin über web 22 to the endless belt 23
play an enlargement of the cross-Section of Yat least 100
which travels in the direction indicated by the arrow.
percent after swelling. Moisture absorption should
amount to at least 10% yand 25% respectively in an
This belt 23 passes around the roller 24 which serves Ias a
for an embossing roller 25. The surface
atmosphere having a relative humidity of 65 % and 100% 45 counter-roller
of the embossing roller 25 is provided with a design of
projecting irregularities, e.g. intersecting oblique ribs -as
If these rules are observed, the ülter plugs formed
indicated in FIG. 4. The roller 25 forces the über web k22
of such synthetic or regenerated cellulosic Yübers or üla- ' `
passing beneath it against the supporting belt 23 and the
ments will, if the above steps are taken to strengthen the
counter-roller 24 so that the embossing ribs on the cir
ülter bundle, Ydisplay an absoiptive effect considerably 50 cumference
of the embossing roller 25 produce a cor
increased beyond that of cellulose acetate fibers. In ad
responding embossed design visible on therrconsolídated
dition, the hydrophilic and swelling synthetic fibers have
the great advantage over cellulose acetate übers that they i
are not foreign but akin to the human organs.
and self-supporting über web 26 which emerges from the n `
roller 25.
If desired, the embossing roller 25V can be heated in
fiber particles which, during use, pass into the respiratory 55 addition,
e.g. by means of lan electric heating element 27
organs and, in particular, into the lung in the form of
with heating current via the slip-rings 28
dust which can never be entirely elimina-ted, soon lose their
and the lines 29. Such heating of the embossing roller-25
dangerous splinter structure by swelling on the moist
particularly indicated when thermoplastic synthetic
mucous membranes, their edges and points will become " is
übers are employed.
rounded, they become supple and are then similarly 60
up after leav
harmless as natural über lengths. When swelled, the
ing the embossing roller 25 and formed into a rollV 30 Vby
hydrophile synthetic fibers have very little iioating power,
means of known take-up devices.
which facilitates their natural removal from the respiratory
organs. The term “synthetic übers” as used throughout
the specification and claims is meant to encompass also 65' ed to gradual consolidation of the über web. Although
the self-supporting über web produced is still very loose
regenerated cellulose fibers.
and can be of practically any desired thinness, the surface
The hydrophilic and swelling synthetic übers or üla
of therweb facing the embossing roller clearly shows the
ments described and those of similar behaviour, however,
pressed design. This design can consist of lozenge-type in- '
could not vreadily be processed into filter plugs. Their
high swelling capacity-indispensable for the increase of 70 tersecting lines running obliquely to the web’s direction of
travel as shown in FIG. 5, or of lines parallel with or
their absorptive power and for hygienic reasons-causes
normal to the longitudinal axis of the said web as shown
the individual fibers to be come soft, tacky and supple
in FIG. 6. An Vembossing design without intersecting lines
When such filter plugs are used, while the bundled fibers
z is shown in FIG. 7 and other line designs `are represent
klose their shape and strength, which all results in a highly
undesirable increase of the resistance to pulling. This 75 ed in FIGS. 8 and 9. Essentially, any embossing design
can be employed which ensures that a sufficient number
56 of the waves are provided with consolidated areas 55
of points of crossing of individual übers or ülaments dis
which again extend substantially parallel with the ülter
posed in random directions will be pressed together. A
design comprising only embossed points is less suitable
unless the über web is extremely dense.
web axis. It is obvious that the meshing annular ribs
may be replaced by other suitable surface irregularities
projecting from the surface of the rollers 47 and 48, pro
vided that care is taken for the filter web passing between
It is also possible to add to the über web 22 formed of
the described hydrophilic and swelling synthetic übers a
certain quantity of other fibers of both natural and syn
them to obtain a longitudinal structure of consolidated
areas. These consolidated areas need not be continuous
thetic origin. If natural übers such as cellulose fibers, cot
in the longitudinal direction, but may be discontinuous.
ton übers and the like are added, the consolidation de
scribed can also be obtained by creating a network of 10 The wave-like structure of the ülter web substantially
resembling that shown in FIGS. 13a, 13b produced by
points of adhesion by means of embossing a design, ex
rolling with engaging annular grooves has proved par
perience showing that a natural fiber and a synthetic or
ticularly advantageous because über material so deformed
regenerated cellulosic fiber such as a viscose über will ad
can subsequently readily be transformed into a circular
here to one another at a point of crossing after embossing.
Instead of natural übers, the über web formed of hydro 15 filter rope 53 by the gathering device, and because this
filter rope possesses, after being processed into filter
philic and swelling synthetic or regenerated fibers may, by
way of example, be given an addition of a certain quantity
of synthetic fibers having a lesser swelling capacity, or of
cellulose acetate fibers, which may be Aadvantageous if the
plugs, particularly favourable properties. >In particular,
thus operate as a supporting framework for the softened
‘which is approximately fiat while still being provided
the consolidated longitudinal areas extending along the
ülter plug result in a further improvement of the mechani
absorptive action of the'hydrophilic -synthetic fibers is too 20 cal properties of the ülter plug during use, and their
action complements that of the framework of points of
powerful; in this case, too, consolidation may be obtained
by embossing a design. The fiber web consisting of hydro
If desired, a über web 51 may also be produced which
philic and non-hydrophilic synthetic übers may be advan
is not wavy but possesses a cross-section substantially
tageous also inasmuch as the non-swelling synthetic fibers
retain their stiffness also when the ülter plug is used and 25 similar to that shown diagrammatically in FIG. 13C, i.e.
with consolidated areas 55 extending in the longitudinal
direction of the web.
Mention should finally be made of the fact that several
In the diagrammatic views according to FIGS. 13a to
fiber webs consisting at least partly of hydrophilic synthet
ic übers can be superposed to produce an endless filter 30 13C, the consolidated areas formed by compressing the
fiber material are designated at 55, while the unprocessed
rope. Such individual über webs can `also be attached to
über material between the said areas is designated at 56.
one another as the two filter webs 33, 34 of FIG. 10
’ Attention is called to the fact that the second part of
which have individually been provided with a design of
the mechanism according to FIGS. 12a, 12b constitutes
points of adhesion, and which are'interconnected by a
plurality of embossing grooves oriented in the longitudi 35 only an embodiment. It is also possible to provide, in
stead of the two delivery rollers 45 and 46, a single
naldirection of the webs according to a predetermined
such roller and to supply only one filter web to the con
embossing design. Naturally, more than two über webs
hydrophilic synthetic fibers.
veyor unit. Conversely, more than two such filter webs
can be, interconnected in this manner, as the three such
may be superposed. If desired, the strength of the filter
webs according to FIG. 11.
40 webs can be influenced by more than one such pair of
An embodiment of the second unit’of the mechanism
rollers and various types of longitudinal structures be
for the manufacture of a filter rope suitable for process
created in the filter web. Furthermore, the rollers pro
ing into filter plugs is shown in FIGS. 12a and 12b. A
vided to influence the filter webs may also be heated
conveyor device comprising the two rollers 4i) and 41
similarly to the roller 2S in the mechanism according to
and the conveyor band 42 is supplied with two ülter webs
FIG. 4.
43 and 44 already consolidated, which are delivered by
The present method enables a web of thin and loose
delivery rolls 4S and 46 respectively. The preceding con
4fibers in which the individual fibers o_r über tufts are not
solidation of these loose and very thin filter webs in a
interconnected to be transformed'into a self-supporting
first mechanism such as the one according to FIG. 4 '
enables such webs to be wound up and off at least once. 50 über web of the nature of a- particularly light fabric
similar to a muslin bandage used for medical purposes.
The two superposed filter webs 43 and 44 are here sup
Instead of weaving the individual fibers, which is not
plied, by the conveyor unit, to a pair of rollers 47 and
possible with conventional means at the disposal of tex
4S which are, by way of example, equipped with'a large
tile processes owing to the very- thin fibers, the present
number of meshing annular ribs- 49 and 50 respectively
method provides a pressing process. Accordingly, if the
of which the annular ribs 49 of the top roller 47 are
shown in FIG. 12b. The ülter web 51 emerging from
between the rollers 47 and 48 passes into a gather
ing device 52 of known design and is there gathered into
embossed design is selected properly, the product may
be described as constituting a “pressed fabric.”
novelty of the ülter plugs according to this invention thus
resides in the fact that when opened-«prior or subsequent
a filter rope 5S _transversely to its direction of travel, the
said ülter rope having a circular or oval cross-section as 60 to use-it can be spreadL to form a fabric-type über
'web which constitutes the said “pressed fabric.” This
constitutes a characteristic difference when compared with
The engaging annular ribs 49 and 50 of the two
rollers 47 and 4S can be designed so that the faces of
the known filter plugs also consisting of fibers or a fiber
the ribs force the ülter web passed beneath them against
I claim:
the sole surfaces of the corresponding groove in the 65
1. A filter lplug for cigarettes and the like, consisting
counter-roller or that the ülter web is compressed be
essentially of superposed layers of comparatively loose
tween the opposing flanks of the individual ribs of the
fibrous material arranged so that abutting faces of said
two rollers. In the one case, a filter web having a wavy
superposed layers extend in axial direction of said filter
cross-section as shown diagrammatically in FIG. 13a
will be produced, which is provided with consolidated 70 plug, each of said layers of fibrous material comprising
haphazardly arranged übers, which are adapted lto absorb
areas at the highest and lowest points, which are sub
moisture under simultaneous swelling and which are also
stantially parallel with the axis of the filter web. In the
adapted to 'be mechanically deformed by compression
second case, a wavy filter web is again obtained of which
of selected portions of the layer and thereby adhere and
the cross-section substantially corresponds to that shown
diagrammatically in FIG. 13b, in which the lateral fianks 75 be joined together `due to such mechanical deformation
so that the compressed portions of said layer composed
of said mechanically deformed liber por-tions have greater
deformed by compression of selected portions of the
Yweb and thereby adhere and be joined together `due to
such mechanical deformation so that the compressed por
tions of said web composed of s-aid mechanically de
formed fiber portions have greater mechanical strength
and lesser capability of -absorbing moisture and of swelling
than uncompressed portions of said web, said fibrous web
including a plurality of said compressed portions com
posed of mechanically deformed and thereby joined fiber
mechanical strength and lesser capability of absorbing
moisture and of Iswelling than uncompressed portions of
Isaid layer, each of said fibrous layers including a plu
rality -of `said compressed portions composed of mechan
ically deformed and thereby joined fiber portions extend
ing throughout the thickness of the respective layer, there
by forming reinforcing structures which will be »substan
tially unaffected by moisture passing through said filter
plug during use of the same.
'porti-ons, extending through the thickness of said web
thereby yforming reinforcing structures which will be sub
2. A filter plug for cigarettes and the like, consisting
essentially of a vspirally wound layer of comparatively
stantially unaffected by moisture passing through said
pression of selected portions -of the layer and thereby
thetic fibers capable of absorbing at «their surfaces liquid
adhere and be joined together due to such mechanical
deformation so that the compressed portions of said layer
components of tobacco smoke.
filter plug >during use of the same.
loose fibrous material arranged so that abutting face por
I 5. A fil-ter plug »according to claim 1, wherein said
tions of said spirally wound layer extend in axial direc 15 haphazardly arranged fibers consist at least partly of syn
tion of said filter plug, said layer of fibrous material com
thetic fibers >and filaments the cross sections of which
prising haphazardly arranged fibers which Iare adapted to
are adapted to increase at least by 100% on swelling.
absorb moisture under simutlaneous swelling and which
6. A filter plug according to claim 1 vwherein said Y
are also adapted to be mechanically deformed by com
haphazardly arranged fibers vcomprise >hydrophilic syn
7. A filter plug according to claim 1 wherein said i
composed of said mechanically deformed fiber portions
haphazardly arranged fibers comprise synthetic fibers with
have greater mechanical strength and lesser capabil-i-ty of
a moisture absorption of at least 10% in an atmosphere
absorbing moisture >and of swelling than uncompressed 25 of 65% relative humidity.
portions of said layer, each of `said fibrous layers including
y 8. A rl'ilter plug according to claim l wherein said
a plurality of said compressed portions composed of me
haphazardly arranged fibers comprise synthetic fibers with
chanically deformed and thereby joined fiber portions
a moisture absorption of at least 25% in an atmosphere
extending throughout -the thickness of said layerthere‘by
-of 100% relative humidity. w
forming reinforcing structures which will be substantially 30
9». A filter plug according _to claim _l wherein said
unaffected by moisture passing through said filter plug
haphazardly arranged fibers comprise cellulose and vis
4during use of the same.
3. A filter plug for cigarettes and the like, consisting
essentially of superposed layers of comparatively loose
fibrous material arranged so that abutting faces of said
superposed layers extend in axial direction of said filter
plug, each of said layers of fibrous material comprising
haphazardly arranged viscose fibers which are adapted
to absorb moisture under simultaneous swelling -and which
l0. A fìlterrplug laccording toclaim9 wherein said
haphazardly arranged fibers include between 5 and 50%
by weight of Íviscose fibers. Z
l1. A filter plug according to claim 1 wherein said
haphazardly arranged fibersconsist essentially of cellulose
fibers and thermoplastic synthetic fibers`-v
12. A filter plug accordingto claim` I_wherein said
are also 'adapted to be mechanically deformed by com 40 haphazardly arranged fibers consist essentially of cellulose
pression of selected portions of the layer and thereby ' fibers and hydrophilic acetate fibers.
adhere and be joined together due to such mechanical
deformation so that the compressed portions of said layer
composed of said mechanically deformed fiber portions
have greater mechanical strength and lesser capability of 45
absorbing moisture and of swelling than uncompressed
portions of said layer, each of said fibrous layers including
a plurality of said compressed portions composed of
mechanically deformed and thereby joined fiber portions
extending throughout the thickness of the respective layer, 50
lthereby forming reinforcing structures which will be sub
References Cited in the file of this patent
Goldman ____________ __ Apr. 16, 1907
Van Nostrand ________ __ Mar.- 14, 1922 ,
Butiington .__ __________ __ June 29, 1937
Berl _________ _______ __ Jan. 14, `1941
Francis _____ ____ _____ __ Mar. 15, 1949
Ryberg ____ ______ _______ Apr. s, 1952
Ness et al. ___ _________ __ Apr. 5, 1955
filter plug during use of the same.
‘Petterson __'___« ________ __ Apr. 5, 1955
4. A filter plug for cigarettes -aud the like, consisting
essentially of a gathered flexible web of comparatively 55
loose fibrous material forming a plurality of folds with
abutting faces of adjacent folds engaging each other and
extending in axial direction of said filter plug, said web
of fibrous material comprising haphazardly arranged fibers
Janecke ______________ __ May 10, 1955
Himmelheber et al _____ __ Mar. 13, 1956
Müller ______________ __ Sept. 18, 1956'
stantially unaffected by moisture passing through `said
which are adapted to absorb moisture under simultaneous 60
swelling and which are also adapted to be mechanically
Schur et al. _____'___-_____ Aug. 6, 1957
Touey _ ______________ __ Apr. 14, 1959
Neumann ____________ __ lune 23, 1959
Kiefer et al ...... ______.. Sept. 15, 1959
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