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Патент USA US2119620

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Patented June 7, '1938
Ernst Benzing and. Johannes Jaenicke, Frank
fort-on-the-Main, Germany, assignors, by
mesne assignments, to Revertex Limited, Lon
d0n,'England, a corporation of England .
No Drawing. Application November 29, 1935,
Serial No. 52,193. In Germany December 5,
9 Claims.
(01. 18-50)
vThis invention relates to a process for concen-
resulting from the ?rst step concentrated di
trating rubber latex and similar vegetable juices,
rectly. It is also possibleto revert the order of the.
and to the product of such process.
?rst two steps.
Heretofore attempts to produce ‘rubber latex
5 concentrates were made with pure rubber latex
or with latex such as contained antiputrefactive
agents. In this manner, but a slightly increased
The desensitized latex is admirably adapted for
the production of concentrates by evaporation .5"
because, in consequence of its exceedingly small
content of substances that are sensitive to heat,
concentration could be obtained because coagula-
it can be inspissated to form surprisingly stable ,
tion very soon set in during the operation due
concentrates, without skinning and coagulation,
10 to the fact that natural rubber latex contains
non-rubber substances which counteract its powers of resistance to coagulating in?uences.
The object of the present invention is to treat
the latex ?rst by partially coagulating it and
l5 removing the coagulated matter thereby desensitizing the latex by eliminating those substances ,
even without the addition of protective colloids.
1o '
The latex derived from latex which has been
pre-treated in accordance with the present in
Vention can be employed with advantage for the
production of latex concentrates by centrifuging. _
In such case not only is the high degree of purity 15
of the resulting cream of importance, but also
which render it susceptible toward coagulating
influences and second by concentrating the vdesensitized latex previous to which concentrating,
the fact that the e?iciency of the centrifuge is
increased because, owing to the greater mechan
ical stability of theldesensitized latex, the trouble
20 the desensitized latex may, if desired, be treated
with adsorptive media by which treatment the
some cleaning of the centrifuge, hitherto neces- 20
sary after short working periods has to be un
content of sensitizing substances in the latex is
dertaken only at comparatively rare intervals. ‘
still further reduced.
Moreover, in the case of desensitized latex, the
The present invention accordingly comprises . centrifuging can be easily performed at elevated
25 ?rst removing a portion of the sensitizing sub-
temperature, which hitherto has been a matter 25
stances from the rubber latex and then concentrating the latter'in known manner and in an
of considerable di?iculty owing to the known '
sensitiveness of latex to the influence of tem
alkaline or acid condition, for example by evap-
oration, creaming, centrifuging, ?ltering, ‘or by
30 several of these methods in combination. Particularly good results are obtained when the stability of the rubber latex is improved by adding
stabilizing agents, such as protective colloids, in
addition to removing the sensitizing substances.
35 The stabilizing agents may be added before, during, or after concentration.
pretreatment of the latex in accordance with the 30
present invention. The separation of serum is
accelerated to a greater degree than in the case
of untreated latex, and a cream characterized by
‘a high rubber content and particularly low con
tent of non-rubber constituents is obtained, to-"- 3;’;
gether with a remarkably clear serum.
The non-rubber constituents which lower the
stability of the latex may be removed, in accord-
ance with this invention as/follows.
Creaming also is facilitated by the desensitizing
In respect of ?ltration properties, the pretreat
ment ofv the present invention also’ has an ex
First, the; tremely favorable effect'on the latex. Compara
40 alkaline or acid latex, treated with protective col- , tively coarse deposits are obtained on the ?lter, 4c .
loids and/or preservatives if desired, is partially
coagulated and the coagulum separated, prefer‘
and the pores of the latter become clogged'far
less rapidly than in the case of ordinary latex. ‘
ably by a sieve. In such ‘case, the coagulants may
consist for example, of electrolytes and/or non-
in accordance with the present invention, the risk
15 electrolytes, such as alcohol or colloidal ferric
oxide in a state of true or colloidal solution.
Second, the remaining latex is treated with active charcoal, silica gel, aluminum oxide or ferric
oxide by which any soluble non-rubber substances
,0 which counteract the powers of resistance to co- -
In the case of the latex concentrates produced
of decomposition by bacteria islessened to an 4,7.
eXtraordinary degreasince the concentrates con
tain only fractional amounts of the decompos
able substances normally present (proteids and
carbohydrates in particular). This advantage of
the present process ?nds expression in a sensible 50
agulating in?uence are adsorbed. Third, the latex economy of preservatives.
thus desensitized is concentrated in any of the
Hitherto, it has been impossible inv practice to
various methods mentioned above. If desired ‘produce concentrates with such a high degree of
the second step, that of treating the latex with purity asis obtainable by the process of the pres
,5 adsorbing media, may be omitted and the latex
It has already been proposed, it 55 Y
1. A process for producing a relatively’ stable
is true', to obtainvery pure latex'concentratesby
. removing a portion of the serum, b-y'centrifuging,
?ltration or'c'reaming, andto repeat these oper
- aliens-after the addition'iof clean water in each
case-until theseparated sera: contain the bulk
of the non-rubber constituents. This procedure,
however, is so expensive and complicated that it
is suitable only for laboratory work, but not for.
concentrated rubber latex which comprises the '
steps of desensitizing the latex by partially co
agulating the latex, separating the coagulum!
therefrom as by a sieve, and Vtreatinggthe remain
1 ing latex with’ media‘ to 'adsorb the ‘non-rubber
substances which tend vto render the'lat'ex sensi
._tive to coagulating influences and concentrating ’'
the production of concentrates onamanufactur- ' ‘
said desensitized latex;
2. A process ‘for producing a relatively stable 7
concentrated. rubber. latex which comprises the
The latex, concentrates produced by the process
steps of desensitizing the latex by 'partiallyco
of the present’ invention form -a valuable new agulating the latex; ‘separating the coagulum
starting material
for the inudustrie‘s employing Q therefrom
__ .as
_ by a sieve, and treating the remain- ‘
rubber latex; and, since they furnish colorless,
and non¢tacky ?lms, areadmirably
715 quick-drying
adapted 'for the production of dipped and spread
ing latex?withrmedia to adsorb the'non-rubber.
substances whichite'nd vto render the latex sen
sitiveto coagulating influences and concentrat
ingr said desensitized‘. latex by evaporation;
3. A process for" producing a relatively stable.
7 From a large stock of Hevea rubber latex, pre- ' concentrated rubber latex which comprises the
20 served by adding a little sodiumbisulphite in. the
steps of desensitizing; the-latex, by" partially 'co-y
' tapping cups,_100l)_kg’s.' weretreated by gradually‘ " agulating the latex; separating: 'the‘fcoagulumi; 7
adding '36 litres of ‘formic acid (0.8%’ tstrengthh“ . therefrom as by a/vsieve; and‘ treating the ‘remain? ’
After gently stirring for‘3/hours, a coarse, yellowj ing latex 'with media to v‘ adsorbjthe non-‘rubber
coagulum'had/ formedpln order tobhechthe, substances‘ whichtend toirender- the latexyseh
progressof the ‘coagulation, ammonia" was; added g
V " untilititrationfof} the’ latex with methyl red'as'in
'sitiveto ‘coagulatingtinfluences‘andr;concentrat-,
. '
14. said
A process
latex by centrifuging.
trated rubber latex. which comprises thewsteps; v
of desensitizing the latex bypartially coagulating‘
' 'dicato'r disclosed'analkalinityof-ZSO'milli-equivaf
lents ‘per litre. The] coagulum' was then-'sepaQ
rated'by means of anickelsieve. ' The latexiprey
therlatex and separating the coagulum therefromv
cont‘zentra‘ted,v by, evaporation} to' a content; of as by'a sieve,- and concentrating the desensitized:- '
‘78.7% of dry substancei and "containing. only’
5. A‘process'for producing ‘a stable concentraté’
0.4% of. coagulated matter. Dry ?lmsproduced
treatediby partial coagulation in this manner was
’ the concentrate hadsmerelyfa slightly yelf
tE'xample I1,
‘ Rubber latex'pretreated by partial coagulation:
sensitizing the latex .by partially'coagulating the
'ylatex andseparating; the coagulum therefromiajs’»
by a sieve, and- concentrating the desensitized
, 6. A processior producinga stable iconcenllratg
with formic acid, as
ed’ rubberlatex which ‘comprises the steps of de,-_ -
low’ tinge andwlow hygroscopic ‘properties.’
' -
was-concentrated in thecentrifuge, 'at 60—65°' C.
‘ed rubber vlatexywhich-comprises the stepsjo‘fi
~afterthe additionof 250imil1i-equivalents of NH! ldesensitizing- the latex by‘ partially coagulating!’
per‘ litre. The "resulting cream ‘contained 6'1‘.8%5 the latex and separating the coagulumi?ere-y
offdry substance andless than 0.1 % of coagulated ,from asby a-sieve, and concentratingythedesen- V
vmatter. I No non-reversible’ substances ‘were rpre—>
" '
sitized latex , by - centrifuging.
“ cipitated Jon, dilution of the cream‘ with water.
'LA, process ' for producing; _a _'stab1e¢¢¢ri¢eA-fi
Rubber precipitated fromiithec‘ream hadla pro- . tratedi rubber latex'which comprises the'stepsofj
tein icontent‘ of10.9% “and 1 a content of ~1'.4%' of‘ desensitizing' the latex by‘ partially ’ coagulating
substances soluble in acetone.’ I
j ' the latex and separating-the coagulumgtherefrom;
as by a sieve, and concentrating'the ‘desensitized, { '
. m
. Rubberslatex pretreated by partialcoagulationi;
¢latex by creamingp»
'- i
> '
l-j 7‘
I 8; A process>for-producing‘a'stable'rubber' latex '_
with formic acid and subsequently renderedal-i which comprises-the steps’ of- "desensitizing the? ‘ 7
kaline as in. Example 1, Waspallowed topass; a latex by partially ‘coagulating it byan'organic;
layer of activeicharcoal whichshad been‘ steamed; acid; separating the rcoavgulum from the latex as; r s a.
and slightly dried. The latex was then ;concen-.
byv a, sieve, and concentrating the-desensitized i”
in the copendingjapplication ‘Serial No. 509,660.
9. ,A processfor producing-stable ‘rubbery
‘ ‘
The concentrate contained, ,715.6%,> of ‘dry sub: which’ comprisesthe-‘steps of ¢desensitizingj the‘ ' I
stance; The content of non-coagulable'dissolved} latexby
partially coagulatingit by a‘ formiceacid
>o1'; dispersed constituents in- the’ concentrate';_ separating; the . coagulum; from the latex as bya
trated by evaporation in a concentrator described‘ 7
Ibased‘on the crepe‘ content, was'only>2.9t%
The‘ 1 sieve, and concentrating‘the desensitizedglatex
amount of irreversible matter'presentin'the con
centrate was as low-as 0.2.per mille, ~
‘We claim:
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