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Патент USA US2109676

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March 1, 1938.v
Filed Jan. 17, 1936
5 Sheets-Sheet 1
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March 1, 1938.
Filed Jan. 17, 1936
5 Sheets-Sheet 2
/4 /5 /0
March 1, 1938.
2,109,676 .
Filed Jan- 17, 1936
3 Sheets-Sheet s
-_F/' 57. 6.
20 ‘
30 '
gym ‘16%
' Patented Mar. 1, .1938 . ’
Henry B. Minor, Dayton, Ohio, assignor to -In
dustrial Process Corporation, Dayton, Ohio, at
corporation of New York '
Application January l7, 1936, Serial No. 595625
4 Claims. .(CI. 18-53)
This invention relates to rubber manuiacture, , p
stock attainsea certain degree. oiv plasticity with
and in particular, to methods for producing or I out su?icient heat tocause aset-upof the low
-. “temperature accelerators during the period that
treating sponge rubber.
7 ‘One object of_ this invention is tovprovide a
- 5 process of manufacturing‘ sponge-rubber by im
pregnating the rubber batch with carbon dioxide
the heat ,is applied;Ithas'been- ioundathat' ii
su?icient heat'isvapplied?to soiten thiys'stock, but 5
not enougliztojEca'nsefthev included gas to expand
iunder' highrpressure prior to vulcanization, this substantially'gii release of thegas pressure is then '
‘ vulcanization being preferably carried out in an? -' started ?a'uniiorm" ?ne cell structure is obtained.
and the expansion or blowing is preferably in a
‘ autoclave, either‘ simultaneously with, the imi, .
direction, which is much to bevdesired. l0
10 pregnation by the carbon dioxide or in successive
~ '" It the heat is still further maintained in amount
Another object is to providea process oi'man
uiacturing sponge'rubberwherein the uncured
'rubber batch is exposed simultaneously to high
15 pressure carbon dioxide‘ gas and to heat, the
temperature being caused to rise and the pres
sure to subside in a predetermined manner.
Another object is to provide a process of man
uiacturing sponge rubber wherein the rubber
batch is exposed to high pressure‘carbon dioxide
gas accompanied by a rise in temperature, after
" which the gas pressure is removed and the pres
sure around the batch reduced to a subatmos
pheric pressure by creating a partial vacuum
Another object is to provide ‘a process for man
ufacturing sponge rubber wherein a rubber batch
containing a “blowing agent" or gas-generating
substance, like sodium bicarbonate, is subjected,
sumcient to expand the included gas, then the
cell structure will be substantially larger and of
a reticular nature. It should be noted that if the
release of the gas pressure is started prior to the 15
attainment of the‘proper plastic state, then the
blowing or expansion tends to be in a horizontal
rather than a vertical direction, resulting in iold-- '
ing and poor formation.
Another object of this invention is to provide.
a process whereby the uncured stock may be ex
panded or blown under commercial conditions to
from 450 to 600 per cent. expansion, or from 25
to 50 per cent. greater expansion than is possible
or customary withchemical sponge. This object
is obtained by impregnating with carbon dioxide
gas at pressures between the ranges of 50 to 300
pounds, 170 pounds being very satisfactory. It _
under reduced pressure, so as to permit the batch
has been discovered that sufficient gas can be in
corporated or dissolved in the rubber in an hour 30
and arhalf period, or less, to cause blowing to
this degree; ' It should be noted that it is possible
to blow by this process, using the pressures here
to‘ expand not only under the in?uence of the
high pressure gas entrapped in the batch, but
also under the in?uence of the gas generated
within the batch by the gas generating substance,
per cent., but the particular requirements of com
mercial conditions are perhaps most easily met
when expansion is limited from 450 to 600 per
giving as a result a super-expanded sponge rub
before curing, ,to the action of a high pressure
~ inert gas, such as carbon dioxide, to impregnate
the batch with the gas, and is aiterwardheated,
Another object is to provide a mold for the
manufacture of sponge rubber articles, this mold
having perforated walls adapted to permit the
entrance of high pressure gases used for impreg
nating the rubber batch to enable the batch to be
‘ - 45 subsequently expanded into sponge rubber; this
, mold being optionally lined with a ioraminous or
inbeiore mentioned to as much as 1000 or more
Another object is to provide a condition during
impregnation or ‘carbonation such that penetra 40.
tion of the uncured stock is facilitated. This ob
:Iect is accomplished by providing that ‘the ?rst
hour of the usual hour and a half of impregnation
time be at a temperature in the neighborhood‘ oi
between 125 and 1'75 degrees F._, "the ‘purpose
being to soften or plasticize the rubber so that
textileliner to permit the entrance and exit 01
the penetration will be more e?ective. It has
been round useful to cool the stock during the
last half-hour‘ oi impregnation to a temperature 50
- Another object is to providesimple means A)! 100 degrees F. or below, better ?lling and bet
whereby the formation in the mold and size .0! ter cell structure being obtained ‘when this is '
cell structure are under control. This object is done than when the higher temperature is main
the gas, yet retard the passage of rubber there
accomplished by application of heat subsequent
tained throughout. We have discovered that low
to the impregnation period, but prior to the re ' temperature accelerators can be successfully used
a lease oi the gas pressure such that the rubber
in conjunction with this process most advanta-'
‘geously, thereby achieving many improvements.
Another object of this invention is to provide
a process of manufacturing sponge rubber
through gas impregnation or carbonation, where
in the pressure required to e?ect it is relatively
low and requires no unusual commercial equip
Another object is to provide compounds adapt
ed to be vulcanized or cured at- temperatures be
lowthose'at which customary chemicals interact
to form blowing ingredients.
Another object is to provide simple means
whereby the uniformity of cell formation is under
Another object of this invention is to provide
a method whereby objects of variable thickness
or of relatively great thickness may be impreg
inated mold vemployed in the process of this in
vention. This ‘mold may be of any suitable
shape, according to the shape of the article to
be produced. As shown in the drawings, the
mold is in the shape of a rectangular block, with
inserted portions adapted to provide a sponge
rubber cushion-like article, with partitions there
in. To this end the mold, generally designated
I0, is provided with side walls ll of perforated or
foraminated material, such as punched metal 10'
plates or meta-l gauze, these side walls ll being
provided with outwardly extending ?anges I2. A
bottom plate I 3 and a top plate I! are provided
for engaging the ?anges l2 to provide a closed
container. ' Sheets l5 of lining material are pro
vided for the interior of the mold, these being
preferably of fabric or of very ?ne gauze. The
purpose of this lining material l5 isto permit the
passage of gas and impede the passage of rubber.
ing required.
therethrough. The top and bottom plates 14 20
Another object is to provide a process and and i 3 may be clamped ‘to the ?anges I 2 in. any
method whereby objects having portions in a ver "suitable manner, the means shown consisting of
tical plane, as well as in a horizontal plane,,may clamps l6 having knurled headed screws I‘! for
be made with equal uniformity.
applying clamping pressure to the jaws thereof.
Another object is to produce a product made
In the interior of the mold are arranged core 25
nated or carbonated without additional time be
from crude rubber of a kind not hitherto made
portions} l8, these also preferably having per
from this material.
forated walls to permit the passage of gas.
rubber portions adjacent these cores are
in the interior of the article, the slight
tions caused by the extrusion of the
In the drawings:
Figure l is a side elevation of a mold suit30 able for carrying out the‘process of this‘ inven
Figure 2 is a top plan view, partly broken away,
of the mold shown in Figure 1.
Figure 3 is a vertical section through the mold
.35 of Figures 1 and 2, along the line 3-3 of Figure
2, showing the rubber batch prior to its impreg
nation and expansion.
Figure 4 is. a view similar to Figure 3, but
As the
rubber 30
through .the perforations will not ordinarily be
objectionable, hence, a liner is not’ ordinarily used
around the cores. It will be understood, how
ever, that if‘a comparatively smooth wall is de
sired for the interior walls of the-compartments 35
formed by these cores, a suitable liner of fabric
or gauze may be provided in a manner similar to
the liner ‘l 5 employed in connection'with the outer
showing the rubberlbatch after its gas impreg-' walls of the‘ mold. In the embodiment shown in
40 nation and expansion to ?ll the mold with sponge the drawings the side walls II and top and bot 40
‘ rubber.
Figure 5 is a vertical section through an auto
clave suitable for carrying out the gas-impreg
nation and vulcanization steps, showing the mold
of'Figure 1 in position.
Figure 6 is a graph showing the relationship
between the pressure of the impregnating gas,
‘the temperature conditions and the percentage
of expansion of the rubber product obtained in
50 a modi?cation of the process.
In general, the process of this invention con
sists in preparing a suitable rubber batch of ma
terials known ‘to those skilled in the rubber art,
and suitable for sponge rubber, an example of
55 such a batch being given later. This batch is’
_ then placed in a perforated or foraminated mold,
tom plates l4 and I3 consist of metal sheets hav
'ing small holes is drilled or punched there-_
For the gas impregnation and/or the vulcaniza
tion steps of the process, the apparatus shown in 45
Figure 5 may be employed.‘ This consists of an
autoclave, ‘generally designated 20, and having’
outer and inner walls 2| and 22, respectively, with
a closed ‘space 23 therebetween. Pipes 24 and 25,
controlled by valves 26 and 21, serve for the ad 50
mission or discharge of steam or other suitable
heating agent, and also for the introduction of
such cooling agents as may be desirable. The
front of the autoclave 20 is closed by a door, gen 55
erally designated 28, and having outer and inner
the latter being placed within an autoclave and _ walls 29 and 30, separated by the space 3|, which
' subjected to high pressure carbon dioxide gas
The gas penetrates the pores f the rubber an
is preferably also connected to the source of heat
ing or cooling agent, in a manner similarto the
pace 23.
under pressure,
by the
process being‘
of heat,
the reduction of pressure of the gas. Under
these conditions the rubber batch expands to
65 ?ll the mold, due to the reduction in pressure, the
application of heat and the presence of the high
pressure gas within the cellular structure of the
rubber. >~The expanded rubber thus becomes
sponge rubber, and this is given apermanent
70 form by the vulcanization which is carried out
upon the expanded product.
Referring to the drawings in detaiLFigures 1
75 to 4 show various views of a perforated or foram
Clamping nuts 32cm the bolts 33, pivoted as
at 34, to the outer walls of the autoclave, serve
to clamp the door 28 securely to the remainder
of the autoclave and to provide a gas-tight junc
tion therebetween. The-door 28 is provided with 65
bosses 35 engaging corresponding projections 36
on the walls of the autoclave.
These, in connec
tion with the hinge pins 31, provide hinges upon
which the door may be swung to and fro into its
open or closed position.
Batch I
The vbatch of rubber stock from which the
sponge rubber is made may be of any suitable
composition, the’ following composition having
$109,678 '
been found suitable for the production of rubber.
tained for a suitable period or time. The exact _
by the apparatus and processdisclosed hereinz: '
depends upon the nature 0! the batch and the
time for the exposure of the batch to the gas also ‘
pressure employed, a period of one hour to one
100.00 and one-half hours being irequently used, at the
‘Rubber plastic
. Sulphur
Zinc oxide
_ Mercapto benzothiozole _______________ __
previously mentioned pressure 01- 170 pounds per
square inch,
Tetramethylthiuramdisul?de. _____ _;..____
Phenylbetanaphthylamine_- ____________ __
Stearic acid >_
Coloring agent
approximately 200 degrees F. and 235- pounds
Rubber Green
F. D.) ...._....' ________ "12-..; __________ .....
The valves 20 and. 21 are now opened and
steam is, admitted to the space: 23 between the
outer and inner walls 2| and. 22' or the autoclave. 10
Under the influence of this steam the tempera
ture and pressure inside the autoclave rise to
00' - per square inch, respectively.
This particular 7 compound loan“ be: very satisfac
The gas is then
?fteen to
' released. slowly over a period of from
tory when cured "40 min. at 35 .lbsifand 40 min. at: thirty minutes, the temperature rising as the gas
makes its exit with a steam pressure of 30 to 35
45 lbs. in an. autoclave. ,
pounds per square inch._ The‘ temperature within .
This stock is mixed and calendered, in the man
the autoclaveis ‘maintained at a maximum of.
ner known to those skilled in the rubber art, the . from
260 to.- 265 degrees F. _When the gas pres‘-v '20,
able thickness, according, to the, nature 01.’ the sure drops ‘to a pressure 01.’ .irom 5 to .15» pounds
article to be made. These strips are cut to ap-‘ per square inch-‘the gas valve lil'lisiclosed. C'Un-_-_._ '‘
proximate dimensions and a weighed amount of der these conditions the rubber batch-becomes ;]
expands as
the"carbon dioxide gas, and this
this stock is placed in the mold, such as the one .gas
external gas pressure is low-’
IO Ol previously described and shown in Figures 1 to 5. ered, thereby forming cells within the rubber...‘ .
In the article shown by way oi illustration, the - and expanding the rubber itself to ?ll the mold,
stock consists preferably of relatively thin strips
as shown by a comparison of Figures 3 and 4.
these strips may be, for example,‘ .085 of an inch The lower the residual gas pressure the larger
are the cells formed in the sponge rubber.- when
'30 for the production of a sponge rubber article one
.the rubber has expanded to a suitable amount
half an inch thick, and .15 of an inch for sponge within the mold, the article is vulcanized and
rubber of'one inch thickness.
given its ?nal cure by being treated for ?fty min- '
The pieces or strips are inserted in the mold, utes
at a steam pressure of thirty pounds per
either ?at or edgewise, cushions having leg por
tions or. partitions being made by inserting strips . square inch, and afterward for another ?fty min
of stock on edge engaging the ?at portion of the
inch, using a temperature of approximately 240 .
cushion. The mold cores l8 serve to occupy the
or slabs of the rubber batch. The thickness of >
.space between the partitions. In the drawings
In Figure 6 is shown a graph giving the rela
the cover or top portion 38 and the partition or tionship
between the gas pressure and tempera 40 I
40 leg portions 39 are shown in this edge-to-?at rela
‘,ture for a particular procedure. In this proce- I
dure the carbon dioxide gas is admitted until it
The stock or batch described above is preferably reaches
a pressure of 170 pounds per square inch,
characterized by the use of low temperature ac
is steadily raised, beginning
celerators, which would be impracticable in the at roomtemperature
of approximately '15 de 45 I
45 manufacture of sponge rubber produced by the grees. The pressure and temperature rise con
use of gas generating substances in the batch be‘
currently, as shown in the graph, over a period oi!
cause of the necessity of having to attain relative
approximately 12 minutes until the gas reaches a?
chemicals react to form the gas for expanding the. pressure oi'about 235 pounds per square inch.
The gas pressureisthen released and allowed to so '
50 rubber into cellular form. _
fall rapidly between the times of 12 and 25 rninqv
ly high temperatures before the gas generating
The while
gas pressure
the temperature
subsides ismore
slowly :as the - "
With the moldjloaded with the batch or stock
in the above-described manner, the top and bot
tom plates I4 and It are clamped in position, with
the liners I! in proper locations, and the entire
assembly is then} placed in the autoclave 20'. The
door 28 oi’ the autoclave is then clamped tightly
temperature nears its peak of approximately 240
degrees, and decreases to atmospheric pressure 5s
after a period oi’ approximately 40 minutes.
Meanwhile, the rubber article has expanded to
approximately "1200 per cent. of its original vol
ume, as shown by the third curve on the chart oi’
against the walls so that the mold occupies a gas
tight inclosure. The gas valve 40 in the pipe ll
leading into the interior or the autoclave through
the passageway 02 is now'opened to permit the
entrance of high pressure carbon dioxide. The
temperature in the interior oi’ the autoclave is a
suitable temperature, which is high enough to
soften or plasticise the rubber so that the pene
tration will be moree?ective, ‘yet not so high as
to vulcanise the stock. Any temperature below
The point to which the pressure is released
while vulcanization takes place in connection with
the thickness of the batch inserted, determines ,,
the density of the rubber stock obtained. In re
leasing the pressure down to_5 pounds per square
inch. for example, a substantial increase inex
pansion is obtained over
when the f
release is only to 15 pounds per'souare inch.‘
oi theultimate pressureenables
140 degrees 1'‘. maybe employed. room tempera? .a control
of the density- and ?rmness oi the
ture being-preferable. The carbon dioxide gas
rubber. For ‘example, a su?icient amount oi ->
is allowed toenter until its pressure reaches ap
- proximately 170 lbs. per square inch, although
the upper or lower pressures maybe used, accord
ing to the particular-nature oi the batch. The
75, gas valve 40 is then closed and the pressure main
batch-to completely ?ll the mold when the pres
r square inch, iresure is reduced to'5 poun
quently gives'a'stock which is
soft and ?imsy.
‘ 2,109,6 76
but undesirable for other purposes, such as ?llers
where a greater density‘ of vstock- or body is re
quired. In the ?rst instance‘ the maximum ex
pansion would be secured with the minimum
amount of stock being used. In the second in
stance, however, more stock would be used, or
an increase might be made in the thickness
. thereof, and by halting the release of the pressure
at 15 pounds per square inch the exact ?lling
would take place.
The temperatures given are approximate and
may be varied as they represent thermometer
temperatures. For instance, it is possible to have
the temperature'range from 205 degrees F. to 270
15 degrees F., depending upon the compound.
It will be understood that I. desire to compre
' hend within my invention such modi?cations as
come within the scope of the claims and the in
while continuing to elevate the temperature,
whereby to bring about expansion‘ of the-rubber
in sponge form prior to vulcanization; and (c)
the step of thereafter releasing substantially all
of the pressure prior to vulcanization and con
tinuing the heating to complete the vulcaniza~
tion of the rubber in its fully expanded sponge __
3. A-process of making- sponge rubber includ
ing the following steps: (a) the step of subject‘
ing the rubber to heat at a temperature below
a vulcanizing temperature not exceeding ap
proximately 140 degrees F. and simultaneously
impregnating the rubber with gas under a pres~ ‘
sure not exceeding 170 pounds per square inch; 15
(b) the step of subsequently increasing the tem
perature and pressure to approximately 200 de
grees F. and 230 pounds per square inch, respec
tively; (c) the step of. thereafter releasing sub
Having thus fully described my invention, ' stantially all of the pressure to cause the spong 20
what I claim as new and desire to secure by Let
ing of the rubber while continuing to elevate the
ters Patent, is:
temperature, whereby to bring about the maxi
l. A process of. making sponge rubber includ- , mum sponging'of the rubber prior to the setting
ing the following steps: (a) the step of subject-.
25 ing the rubber toiheat at a sub-vulcanizing tem
perature sufficient to soften the rubber yet in
sufiicient to vulcanize it and simultaneously im
of the rubber’ consequent to vulcanization; and
(d) the step of thereafter continuing to elevate
the temperature to vulcanize the rubber.
4. A process of making sponge rubber includ
' pregnating the rubber with gas; (b) the step of
ing the following steps: (a) the step of subject
- subsequently reducing the pressure to cause the
ing the rubber ‘to gas pressure to impregnate the
30 sponging of the rubber by expansion of the gas = rubber while applying heat thereto suf?cient to 30
while continuing to elevate the temperature,
whereby the gas is substantially released prior
to the vulcanization of the rubber; and (c) the
step of thereafter heating the rubber to a vul
35 canizing temperature to vulcanize the rubber in
its sponged condition.
2. A process of making sponge rubber includ
ing the following steps: (a) the step of subject
ing raw rubber stock to heat at a sub-vulcaniz
ing temperature sufficient to soften the stock yet
insufficient to‘ vulcanize it while impregnating
the rubber with substantially dry inert gas; (17) _
- the step of subsequentlylreducing the pressure
raise the temperature yet to maintain the tem
perature below a vulcanization temperature; (27)
the subsequent step of decreasing the pressure to
cause the sponging of the rubber while increas
ing the temperature whereby to progressively 35
sponge the rubber; and (c) the step of complet
ing the sponging of the rubber by continuing to
increase the temperature while releasing sub
stantially all of the pressure substantially prior
to the setting of the rubber by its becoming 40
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