Note: Descriptions are shown in the official language in which they were submitted.
~074S~
It is known that batches of rubber and filler can be obtained in
the :~orm of pourable powders by precipitating rubbers from the latex phase
with the addition of fillers as is desired in German Offenlegungsschrift
No. 2,135,266 or 2,214,121 or U.S. Patent No. 3,714,087. The resulting
rubber-filler batches have, however, relatively low bulk densities (0.15
to 0.3 g/cm3).
It is the object of this invention to provide a process by which
a preground rubber powder which contains only small quantities of filler
as grinding aid and therefore still has the tendency to cake together, can
easily be converted into a permanently pourable pulverulent batch of rubber
and filler with the desired quantity and desired type of filler. me
fillers used as grinding aids may be silicic acids, ingredients which con-
tain silicic acid, chalk, talcum, metal stearates or metal oxides.
m is invention therefore provides a process for the preparation of
a pulverulent rubber-filler batch, wherein a comminuted rubber which still
has the tendency to cake is mixed with fillers by a rapid mixing process
and converted into a pourable powder.
According to the invention there is provided a process for the
preparation of a rubber-filler batch, in which a comminuted rubber which
contains smsll quantities of filler as grinding aid and which still has the
tendency to cake is mixed, immediately after grinding, with 5-100 parts of
filler per 100 parts of rubber by a rapid mixing process and converted into
a pourable powder, said mixing taking place in a mixing vessel having a mix-
ing element comprising a baton blade, double variant tool or impeller suction
blade with ground cleaning element, the material in the mixing vessel being
stirred at a temperature of from 20 to 80C and at a rotation of 200 to 5000
r.p.m.
To form the comminuted rubber, the rubber is ground with the addit-
ion of small quantities of the above mentioned fillers (e.g. 2 to 3 parts by
weight per 100 parts by weight of rubber) as grinding aid and then, according
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to the invention, mixed with larger quantities of filler in a stirrer
apparatus (e.g. at a speed of rotation of the stirrer of 1000 revs/min.)
immediately after the grinding process.
The fillers used may be carbon blacks, silicic acids, ingredients
containing silicic acid, chalk, talcum, metal stearates or metal oxides.
Suitable carbon blacks are summarized in Table 1. Carbon black
N-770 (according to ASTM D 75-68) was used in the Example.
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Table 1
Carbon black~
Classification of carbon blacks (accordi~ to ~STM-D 1765-68)
Nome~clature
AS~M ~y~e
N-110 SAF
N- 195 SCF
N-219 ISAF-IS
N-220 ISAF-HM
N-231 ISAF-IM
N-242 ISAF-HS
N-293 CF
N-294 SCF
N-296 CF
S-300 EPC
~-301 MPC
S-315 HAF-~S SC
. N-326 HAF-LS
: N-327 HAF-LS
N-330 HAF
N-347 HAF-HS
N-358 SPF
N 'l 40 FF
N-472 XCF
N.-539 FEF-~S
N-550 F~F
N-568 FEF-HS
N-601 HMF
N-660 GPF
N-683 APF
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N-761 SRF-LM
N-762 SRF-LM NS
N-770 SRF-HM
N-774 SRF-HM NS
N-785 MPF
N-880 FT
N-907 MT-NS
N-990 MT
~uring the stirring process, the filler is absorbed on the
rubber powder obtained from the mill, which still has a tendency
to cake and a freely pourable batch of rubber and filler is ob-
tained (bulk density 0.4 to 0.5 g/cm3).
The mixers used for mixing rubber and filler have a speed of
rotation of 200 to 5000 revs/min, preferably 1000 revs/min. The
stirrer vessel is equipped with a double jacket to provide for
cooling. The temperature of the wall has to be about 20C. The
material treated in the mixer has to have a temperature of 20 to
80C, preferably about 50C during the stirring process.
The capacity of the mixing vessel used can be from 10 to 2000 l.
The power voltage of 380 volts consumption is from 7 to 200 amps, pre-
ferably about 60 amps at 380 volts. In the case described here, an 80 l
mixing vessel was used and the mixer~ were driven by a 45 KW motor.
The amount of filler used was 70 %. The mixing t~r~ used may
consist of blades fixed to a vertical shaft or, a two-tier variant
took (Figure 1) or impellers operating with suction and equipped
with ground clearing devices may be used (Figure 2). These tools
are all available commercially. The stirring process may be com-
pleted within 1 to 5 minutes but is preferably carried out for one
minute at the given speed of rotation of 1000 revs/min. The mixing
vessel can be arranged either vertically or horizontally and i~ it
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is arranged horizontally, stirring can be carried out as a conti-
rLuous process.
It may therefore be regarded as an advantage of the above
mentioned process that rubber powders which have the tendency to
cake and which cannot be kept in a pourable state for a long time,
for example due to high cold flow (4 to 20 mg/min; for method of
measuring see below) can be converted into a pourable batch of
rubber and filler by a simple stirring process ~ollowing the grin-
ding process. The fluidity or caking resistance achieved is very
high, being 30 lbs determined according to ASTM-D 1937-62 (packing
force). The mixing tool can be separated from the grinding appara-
tus so that both light coloured batches of rubber and filler and
batches containing carbon black can easily be produced without
the grinding apparatus itself becoming soiled or requiring clea-
ning each time production is changed from one type of batch to
another.
In the process according to the invention, therefore, poura-
ble rubber powders are produced from rubber particles, preferably
with a diameter of 500 to 2000 which still have the tendency to
cake, the rubber powders being mixed with a filler (carbon black
or light coloured fillers of the type mentioned above) in a mixing
apparatus at speeds of rotation of 200 to 5000 revs/min, prefe-
rably 1000 revs/min, for 1 to 2 minutes, the power consumption of
the mixing apparatus being between 7 to 200 amps at 380 volts.
The filler (5 to 100 parts by weight per 100 parts by weight
of rubber) is absorbed so rapidly on the rubber particles which
are still slightly sticky that a completely pourable and non-
caking batch of rubber and filler is obtained within a very short
time (one minute). The particle size of the batch of rubber and
filler corresponds to that of the rubber particles used.
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Example:
Polybutadiene (microstructure: % cis 1,4 98 - 20 %;
% cis 1,2 2 - 90 %) was ground with the addition of 3 phr of
silicic acid. The powder, which had a strong tendency to cake,
was mixed with 10 phr of SRF carbon black (N-770) in a high
speed mixer at 1000 revs/min. The pourable product could be
removed after one minute. The particle size was 1.2 mm, the
bulk density determined according to DIN 53 468 is 0.5 g/cm3.
Natural rubber, styrene-butadiene copolymer, ethylene-
propylene terpolymer, polychloroprene, isoprene etc. were con-
verted into non-caking, pourable batches in the same manner.
The process is also applicable to all other types of
rubber.
Cold flow method of determination
The cylinder of the apparatus was filled with 1.5 g
of polymer. The outflow nozzle was loaded with a weight of
1 kg and kept at 50C for 10 minutes.
The load was then removed from the test apparatus
and any polymer overlfowing from it was cut off neatly.
The test apparatus was then kept at 50C under a load
of 1 kg for a further 30 minutes while free outflow was
provided for the polymer.
The amount of polymer which escaped from the apparatus
was cut off and weight to thousandths of a gram.
The cold flow was expressed in mg/min.
Each polymer was tested 6 times and the average value
~btained was taken as a result.
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