Note: Descriptions are shown in the official language in which they were submitted.
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5 Process for the continuous productioll of liquid silicone rubbers
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The object of the present invention is a process for the continuous production of
10 silicone rubbers, in particular of two-component liquid silicone rub'oers.
Rub~rs of this type consist essentially of crosslinlcable diorganosilo%anes and
silylated finely-dispersed silicic acids9 as well as small amounts of crosslir~ng agents,
catalysts and inhibitors, and, optionally9 other non-reinforcing or semi-reinforcing
1 5 fillers.
There are several well-known processes (e.g. ~3P-A-2589159, US-4,737,561, US-
4,649,005~ for the continuous production of silicone rubbers.
20 US-4,649,005 dessribes the continuous production of base r~xtures for liquid silicone
rubbers which crosslink after addition of crosslinking agent and catalyst in accordance
with the addition principle. In this connection a mixed process is described in which
compounding is effected in a temperature range firOQI 200C to 300C whereby t~ecoating of the filler to allow reaction with the silicon polymer is avoided.
~P-A 258 159 discloses a process for the continuous production of base mixtures for
silicone elastomers that are capable of hot vulcanisation and based on highly viscous
polymers with a viscosity of 1000 Pa.x. 1l1 this connection so-called anti-structural
agents are also used which according to the description can be, e.g. a,~
30 dihydroxydiorganopolysiloxanes with a viscosity of 20 to 100 mPas. Silazanes are
only mentioned in connec~ion with t~e use of coated fillers (exterllal coating).A further characteristic of the hlown process is a short residence-time of 30 seconds
to 10 minutes.
35 It is an aim of the present invention, on the other hand, to provide a process for the
tot~l, continuous compounding of crosslinkable silicone rubbers,~in particular for the
parallel production of bo~h the components of li~quid silicone rubbçrs.
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An aiin of the present invention is ~urthermore the continuous implementation ofin-situ coating, as completely as possible, of f~nely-dispersed silica with silazanes
and/or silanols.
10 Such in-situ coating with silazanes and/or silanols requires longer residence-~mes than
compounding processes with other filler-coating agents (e.g. dihydroxy-diorganopoly-
siloxanes~, which only cover the filler s~face incompletely. Incompletely silylated
(made hydrophobic) fillers result however in relatively high mixing viscosi1des and a
strong crepe hardening (increase in viscosi~ after storage). For this reason silicone
15 rubbers with ill-situ silazane coating, produced in the hereto~ore described aggregates
with short residence-time, exhibit the disadvantages of the other coa~ng agents
described above.
A further aim of the present invention consists in keeping to a mil~imum the amount of
2o coating agent required for the coating step.
The problem is solved according to the invention in that the coating agent is used in
excess in a continuous n~ing process, excess coating agent is distilled off be~ore or
during the actual coating reaction, and the distilled coating agent is recycled.
With the process according to the invention it is possible to produce all formulations
which have hitherto becn produced discontinuously. Fur~hermore, in comparison with
the discontinuous mode of operation whereby the same product quality is obtained,
the process according to the invention pennits the required amounts of coating agents
30 to be reduced.
Polydiorg~nosiloxanes of the formula
R' . R R'
R - Si- o - - SiO- - Si - R
R~ Rl x
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R and R' are alkyl residues with 1 to 8 carbon atoms,
aryl residues, vinyl residues and fluoroaL~cyl
residues with 3 to 8 car~on atoms, and
x has a value from 10 to 6000.
:
Instead of diorganopolysiloxanes, copolymers with units not containing silicon can
also be used. In aWition, branched polymers, namely those of the formulae SiO4/2,
15 RSiO3/2 and R3SiOl/2 can also be used, wherein R has the meaning s~ed above.
Hydrogen siloxanes having at least 3 SiH groups or peroxides can be used as
crosslinking agents. Fur~ermore, chain-extenders with 2 SiH groups can also be
used. All~nols can be used as inhiWtors. Suitable catalysts for the crosslin~dng20 reaction are vinylsiloxane-platinum complexes.
By way of reinforcing fillers, fumed or precipitated finely-disperæd silica with a BE~T
surface of more than 50 m2/g can be use~. Such fillers exhibit bulk densities of 0.1
kg/l, t~pically 0.05 down to 0.025 kg/l. In addition, carbon blacks and non-reinforcing
25 or semi-reinforcing fillers can also be used, such as diatomaceous e~lrths or quartz
powders. Thc amount of filler shall be about 10 to 60 % by weight of the total
mixture. As coating agents, hexaalkyldisilaz~nes with methyl and vinyl groups can be
used together with water. ~urthermore, silanols are also suitable, e,g. trimethylsilanol
and dimethylvinylsilanol, together with small amounts of aqueous solution OI a~nmonia
30 or disi1azane/water by way of coating agent"n amounts to ensure an aLlcaline pH of
the solution (pH >7) Mixture of silanols can also be used.
The amount of coating agent shall at leas~ be su~ficient for a complete coating of the
~iller particles, tyically at least abou~ 0,12 g of coating agent per 300 m2 of filler
35 surface area
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5 In the first step of the process according to the invention the diorganopolysiloxanesare com~Jined with the fillers and coating agents in a mixer working continuous~y. The
air ca~ied in with the filler is withdrawn through domes in which separation of filler
particles and air takes place. Large-volume mixers with ~ree volume and which are
capable of being cooled are suitable for this step; e.g. a Contin~lous Universal Mixer
10 omrnercially available from Baker Perkins, or an Ap-conti reactor, commercially
available from ~ist, with a discharge screw.
In the second step of the process according to the invention, in-situ coating of the
fillers employed is ef~ected with the coating agents at the boiling-temperature of the
15 reacted or original coating agents (silanols). The distillates arising are condensed in a
cooler, separated into org~c and aqueous phase, and either the organic phase only or
both phases are in part recycled into the mixer. In a further variant a parlial flow of
the distillates is conveyed to the f;~st mixer. Mixers capable of being heated and
having rela~vely high residence-time and a free volume are suitable for this step, e.g.
20 an Ap-conti reacts~r, commercially available from List, with discharge s¢rew.
In the third step, the residues of coating agent that are still prese~ are removed a~
elevated temperature (up to 1 80C) ~n a vacuum in a double-shafted screw, e.g. ZSK
commercially available from Werner u. Pfleiderer, or a double-shafted screw availabh
25 from Baker Perlcins, and are optionally re-diluted in the second part of the aggregate
with polydiorganosiloxane.
I;or example, a Co-Kneader commerc,ially available from Buss is also suitable for this
step of the process.
In the last step of ~e process according to the invention - in case both components of
liquid silicone rubbers are being produced in parallel - ~e mixh~e is l'irs~dy split into
two partial flows with separate conveyor pumps and then combined n~xing ~d
cooling is effected in static mixers capable of being cooled. One partial ~ow is mixed
with catalyst and diorganopolysiloxanes and the other partial flow is mixed wi~
crosslinking agents, inhibitors and diorganopolysiloxane.
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5 Alternatively, in the case of production of only one component, the last step of the
process can be effected together with the third step in an aggregate (e.g. a
double-shafted screw of sufficient leng~h).
Fig. 1 describes an example of a plant for implementing the process according to the
10 invention. The figures in the diagrarn describe in particular:
Mixer for the 1 st step:
Ap-conti reactor made by List, type AR 12C,
15 having a free volume of 30,6 l,
2 Mixer for the 2nd step:
Ap-conti reactor made by Lis~, type AP 12C,
20 3 Mixer for the 3rd step:
Double-shafted screw available from Werner und
Pfleiderer, type ZSK 37,
having a free volume of 1,31,
25 4 Condensation de~ice for silanol,
5, 6 Static mixers for mixing catalyst or crosslinking
agent and inhibitors for producing components A
and B of the two-component system, e.g. type SMX
30 available from Sulzer.
The polyrner mixture and the f;ller are introduced into the mixer through feed lines 7
and 8, water is introduced via feed line 9, and the coating agent via feed line 10~ in
each case via metering devices. Air contai~ing powder is withdrawn via line 11.
The temper~ture in m~xer 1 is maintained at 20 to 40C; the pressure is sligh~y below
normal pressure - e.g. not more than 100 mbar below normal pressure. The
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5 residence-time in mixer 1 lies between 5 and 40 minutes in order to ensure sufflcient
mixing of filler, polymer and coating agent.
The mix~ure is conveyed to mixer 2 through line 12. Here the reaction between
coating agent and filler takes place subject to the formation of silanols at a
10 temperature of 80 to 110C and at normal pressure. The silanolsj water and other
volatile components leave n~ixer 2 at line 13. Silanols are condensed in condenser 4
and corlveyed back into the mixture through line 14, op~ionally partly ~hrough line 15.
Non-condensed volatile components leave the system vialine 16.
15 ~e mixture from mixer 2 is conveyed via line 17 to mixer 3 after a residence-time of
10 to 40 minutes. Here the reaction is completed at a ternperature of 130 to 160C
and remaining volatile components are withdrawn via line 18 at a pressure of less than
100 mbar. Silicone polymers of low viscosity ("re-dilution polymers") can be
conveyed through line 19 to adjust the viscosity of the rnixture. The liquid silicone
20 ~ubber, still free of catalyst or crosslinhng agent, leaves mixer 3 at 20.
Further admixture of catalyst 26 for producing cornponent A and of crosslinldng
agent and, optionally, of inhibitors 25 for producing component B now takes place in
separate rnixers 5 and 6 respectively, either simultaneously in parallel, wherein the
25 polymer feed is split up in line 20 by a divîder 21 into lines 22 and 23, or in series,
when 21 denotes a valve.
Re-dilution polymers can likewise be conveyed to the mixers 5 and 6 via lines 24.
~o The following examples illustrate the present invention but are not intended to lirnit its
scope in any way.
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Use is made of a device such as depicted in Fig. 1.
To mixer 1 are charged:0 1~ kg/h of apolydimethylsiloxanemixturewith
vinyl terminal groups, polymer 1
(visc.: 10 Pa.s), polymer 2 (~isc.: 65 Pa.s),
mixingratio: 1:2.5;
1.1 kg~ hexamethyldisilazane as coating agen~;
15 0.6 kg/h water and
8.3 k~/h fumed silica (BET 300 m2/g~.
The temperature is maintained at 30C. The air containing powder is removed at 0.98
bar. The aYerage residence-~rne of the polysiloxane mixt~ arnounts to 34 minutes.
Mixer 2:
0.5 kg/h organic phase is condensed and recycled into n~ixer 2. The residence~meamounts to 33 minutes, the pressu~e 1 bar, the temperature 90 to 100C.
z~ Mixer 3:
Temperature = 150C
Vacuum: 20 mbar; residence-time: 2 minutes.
To bring about re-dilution, 3.7 kg/h of polymer 1 are adde~!.
3t~ Separation ratio of the main flow: 1:1.
Static mixer 5:
1.9 g/h Pt catalyst and, to bring about further re-dilution, 1600 g~ of polymer 1 are
added. Residence-time 2.5 minutes.
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5 Static mixer 6:
500 glh hydrogensiloxane ~4 mmol SiHJg) as crosslinking agent and 13 ~/h
2-methylbutyne-3-ol-2 as inhibitor, as well as llQ0 g/h of polymer 1, to bdng about
further re-dilution, are added. Residence-time 2.5 minutes,
10 The two par~al flows have a discharge temperature of 50C. After mixing of the two
components and curing at 175C
(10 min) a highly transparent vulcanisate is obtained.
Exa~pplQ2 :.
Example 1 is repeated, with the difference that to mixer 1 are charged
1.1 kg/h of a mixture consisting of
20 parts hexame~yldisilazane and
1 part tetramethyldivinyldisilazane
by way of coating agent.
After mixing of the components ~ and B and curing at 175C for over 10 min a highly
2~ transparent vulcanisate is obtained.
Example 1 is repeated, with the difference that to rnixer 1 are charged
1.3 k~/h trimethylsilanol and
0.005 kg/h aqueous solution of ammonia as the coating
agent, and no extra water is supplied.
35 After mixing of the components A and B and curing at 175C for over 10 rnin a highly
transparent vulcanisate is obtained.
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Device as in Example 1.
To mixer 1 are charged:
10 38 l~g/h of a polydime~ylsiloxane mixture with
vinyl terminal groups, polymer 1
(visc.: 10 Pas), polymier 2 ~visc.: 65 Pas),
mixing ratio: 1:2.5;
2.2 kg/.h hexamie~hyldisilazane;
15 1.2 k~/h water and
16.6 kg/.h compressed fumed silica (BET 300 m2/g).
.
Temperature: 33C, pressure: 0.98 bar; residence-time: 17 minutes.
20 Mixer 2:
Temperature = 90 to 100C, residence-time: 16 minutes, pressure: 1 bar, condensate:
1.0 g/hi organic phase are recycled into mixer 2.
Mixer 3:
Temperature = 150C, pressure: 20 mbar, residence-time: 1 minute, re~dilution: 7.4
kg/h of polymer 1.
Separation ratio of the main flow: 1:1.
30 Static mixer 4: '.
3.8 g/h Pt catalyst and
3200 g/h of polymer 1, : ;
residence-time: 1.3 minutes.
Stadc rnixer 5:
1000 g/h hydrogensiloxane (4 mmol SiH/g),
26 g/h 2-methylbutyne-3-ol-2 and
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5 2200 g/h of polymer 1,
residence-time: 1.3 minutes.
The two pa~al flows have a discharge temperature of 61C. After mixing of the two
components and curing at 175C
10 (10 min) a highly ~ansparent vulcanisate is obtaine~l.
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Apparatus as in Example 1.
15 To mixer 1 are charged:
19 kg/h of a polydimethylsiloxane mixture wi~h
vinyl terminal groups, polymer 1
(visc.: 10 Pas), polymer 2 (visc.: 65 Pa.s),
mixirig ratio: 1:2.5;
1.0 kg/h hexamethyldisilazane,
0.3 k~ org. phase of the condensates from mixer 2,
0.6 k~h water and
8.3 l~g/ fumed silica (13ET 300 m2/g).
25 Temperature: 30C, pressure: 0.98 bar; residence-time: 34 miautes.
Mixer 2;
Temperature = 90 to 100C, pressure: I bar, residence-time: 34 millutes;
~o Condensate:
0.5 glh of organic phase, of which 0.2 kg/h are recycled into mixer 2.
Mixer 3:
Temperature = 1 50C, pressure: 20 mbar, ~esidence-time: 2 minutes
35 Re-dilution: 3.7 kg/h of polymer }.
Separation ratio of the main flow~
A 27 982-FC - 10 -
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Static mixer 4~
1.9 g/h Pt catalyst and
1600 g/h of polymer 1.
Residence-time: 2.5 minutes.
Static mixer 5:
500 g/h hydrogensiloxane (4 mmol SiH/g),
13 ~/h 2-methylbu~ne-3-ol-2 and
1 lOû g/h of polymer 1.
~, 5 Residence-time: 2.5 minutes.
The two partial flows have a discharge temperaeure of 50C. Afier mixing of the two
components and curing at 175C
(10 n~in) a highly transparent vulcanisate is obtained.
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Example 1 is repeated7 with the differ~nce that to each of static mixers 4 and 5 are
added
70 g/h 215-dimethyl-2,5-(tert-butylperoxy)-hexane
instead of catalyst, crosslinking agent, inhibitor and dilution polymer.
'' 3~ The one-component system obtained results after curing at 175C for over 10 min in a
highly transparent vulcanisate.
~mllLel (reference)
35 Instead of mixers 1, 2 and 3, use is made of a double-shafted screw of ~yp,e æK
34/2VlS00, available from Werner und Pfleiderer.
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5 Into the screw are charged:
2.4 kglh of a polydimethylsiloxane mixture with
vinyl terminal groups, polymer 1
(visc.: 10 Pa.s), polymer 2 (visc.: 65 Pas),
mixingratio: 1:2.5;
0.14 kglll hexamethyldisilazane
0.û8 kg/h water and
1.05 kg/h fumed silica (BET 300 m2/g).
15 A short distance be~ore the end of the screw re-dilu~ion takes place with:
0.47kg/h of polymer 1.
The total residence-time in the screw arnounts to 5.7 minutes. A short distance behind
the ir~et the temperature is maintained at 100C for in-situ coating of the filler
20 material. The pressure here amounts to about 1.5 bar.
At the back end of ehe screw the temperature is raised to 160C with a view to vapour
discharge at a pressure of 20 mbar.
The discharge temperature sti}l amounts to 150C.
25 The discharge pressure amounts to about 2 bar.
The base rnixture produce~l in this way (without cat~lyst or crosslinking agent)exhibits a doubling of viscosity a~ter just a short storage ~ime (2 weeks) at room
temperature.
~0
Table 1 shows the characteristics of the rubbers and vulcan~isates obtained from t~e
Examples.
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5 Ta~lelL
Example: 1 2 3 4 5 6 7
Rubber: Component B Base mixture
Viscosity ~Pas~ (D=10/s) 710 700 720 690 715 810 740
Vlsc.after63 days 720 750 760 800 770 830 >5000
Vulcanisate:
Hardness (Shore A) 35 45 36 34 35 38 - ~
Tensile strength (MPa) 9.2 9.5 9.3 9.0 9.3 9.4 - :
Elongation at break (q'o) 920 800 880 930 910 800
Transparency 0.05 0.07 0.06 0.07 0.06 0.06 -
(2 mm, 600 nm)
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