U.S. patent application number 11/848480 was filed with the patent office on 2009-03-05 for process for the continuous manufacturing of shaped articles and use of silicone rubber compositions in that process.
This patent application is currently assigned to MOMENTIVE PERFORMANCE MATERIALS GMBH. Invention is credited to Uwe Irmer, Yi-Feng Wang, Dieter Wrobel.
Application Number | 20090062417 11/848480 |
Document ID | / |
Family ID | 40343522 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090062417 |
Kind Code |
A1 |
Wrobel; Dieter ; et
al. |
March 5, 2009 |
Process For The Continuous Manufacturing Of Shaped Articles And Use
Of Silicone Rubber Compositions In That Process
Abstract
The present invention relates to a process for the manufacturing
of continuously shaped cured silicone articles, particularly
extrusions articles and the use of silicone compositions containing
a photoactivatable metal catalyst in said process, wherein the
curing is initiated by visible or UV-light.
Inventors: |
Wrobel; Dieter; (Leverkusen,
DE) ; Irmer; Uwe; (Leichlingen, DE) ; Wang;
Yi-Feng; (Waterford, NY) |
Correspondence
Address: |
RANKIN, HILL & CLARK LLP
925 EUCLID AVENUE, SUITE 700
CLEVELAND
OH
44115-1405
US
|
Assignee: |
MOMENTIVE PERFORMANCE MATERIALS
GMBH
Leverkusen
DE
|
Family ID: |
40343522 |
Appl. No.: |
11/848480 |
Filed: |
August 31, 2007 |
Current U.S.
Class: |
522/66 |
Current CPC
Class: |
C08G 77/80 20130101;
C08G 77/20 20130101; Y10T 428/1352 20150115; C08J 2383/04 20130101;
Y10T 428/13 20150115; C08G 77/12 20130101; C08G 77/70 20130101;
C08L 83/04 20130101; C08L 2666/52 20130101; C08L 83/00 20130101;
C08L 83/00 20130101; C08J 5/00 20130101; C08L 83/04 20130101; C08G
77/18 20130101; C08L 83/04 20130101 |
Class at
Publication: |
522/66 |
International
Class: |
C08F 2/46 20060101
C08F002/46 |
Claims
1. A process for the manufacture of shaped cured silicone articles
comprising the following steps: a) a shaping step, comprising the
continuous shaping of a mixture comprising: (i) at least one linear
polyorganosiloxane having at least three alkenyl groups and an
average number of diorganosiloxy units determined by GPC with
polystyrene as standard of at least 3000, (ii) optionally one or
more polyorganosiloxane having alkenyl groups, other than the
polyorganosiloxane according to the component (i), (iii) at least
one polyorganosiloxane having at least two SiH groups, (iv) at
least one photoactivatable transition metal catalyst, (v)
optionally one or more filler, (vi) optionally one or more
conventional additives, in a shaping apparatus, thereby obtaining a
shaped silicone article, b) at least one irradiation step to
photoactivate the photoactivatable transition metal catalyst, c)
optionally one or more heat treatment steps, d) optionally one or
more mixing steps, e) optionally one or more cutting and/or winding
and/or packaging steps of the continuously shaped cured silicone
article.
2. A process according to claim 1 wherein the polyorganosiloxane
(i) has at least one pendant alkenyl group.
3. A process according to claim 1 wherein the part of the uncured
mixture of the components (i) to (vi), which is soluble in
CDCl.sub.3 at 25.degree. C., has a content of vicinal Si-alkenyl
groups of less than 0.025 mol. %.
4. A process according to claim 1 wherein the polyorgano-siloxanes
(i) has a viscosity of at least 1.5 kpa*s (25.degree. C.; at a
shear rate of 1 s.sup.-1).
5. A process according to claim 1 wherein the mixture to be shaped
comprising the components (i). (iii), (iv) and optionally (ii), (v)
and (vi), has a viscosity of at least of 10 Mooney units.
6. A process according to claim 1 wherein the photoactivatable
transition metal catalyst is selected from the group of transition
metal complex compounds having sigma-bonded ligands.
7. A process according to claim 1 wherein the photoactivatable
transition metal catalyst is selected from the group of transition
metal complex compounds having at least one ligand selected from
the group consisting of cyclopentadienyl, cyclooctadiene,
cyclooctatetraene, norbornadiene.
8. A process according to claim 1 wherein the filler is selected
from the group reinforcing fillers.
9. A process according to claim 1 wherein the shaping apparatus
comprises at least one shape forming die.
10. A process according to claim 1 wherein the continuous shaping
step is an extrusion step and the shaping apparatus is an
extruder.
11. A process according to claim 10 wherein the extruder is
selected from single-screw extruders, twin screw extruders and gear
extruders.
12. A process according to claim 1 wherein the irradiation step b)
is carried out with light of a wavelength in the range from 190 to
600 nm.
13. A process according to claim 1 wherein the heat treatment step
(c) is performed at an oven temperature from 50.degree. C. to
250.degree. C.
14. A process according to claim 1 wherein the heat treatment step
(c) is performed at a surface temperature of the shaped article of
20 to 200.degree. C.
15. A shaped light-cured silicone extrudate obtained by the process
of claim 1.
16. A shaped light-cured silicone extrudate according to claim 15,
having the form of a sheet, a tube, a cable, a cable jacket, a wire
insulation, a profile, or a sheathing.
17. A shaped co-extrudate comprising the light-cured silicone
extrudates, obtained by the process of claim 1 in association with
at least one further extruded material.
18. A shaped light-cured co-extrudate according to claim 17 having
the form of a sheet, a tube, a cable, a cable jacket, a profile, a
sheathing.
19. A continuously formed shaped silicone article comprising at
least one polyorganosiloxane having at least three alkenyl groups,
an average number of diorganosiloxy units determined by GPC with
polystyrene as standard of at least 3000, and a the content of
vicinal alkenyl groups of less than 0.025 mol. %.
20. A composition comprising: (i) at least one polyorganosiloxane
having at least three alkenyl groups and an average number of
diorganosiloxy units determined by GPC with polystyrene as standard
of at least 3000, (ii) optionally one or more polyorganosiloxane
having alkenyl groups, other than the polyorganosiloxane according
to the component (i), (iii) at least one polyorganosiloxane having
at least two SiH groups, (iv) at least one photoactivatable
transition metal catalyst, (v) optionally one or more filler, and
(vi) optionally one or more conventional additives.
21. A composition according claim 20 comprising the components (i)
to (vi) in the amounts of: (i) 100 parts by weight, (ii) 0 to 100
parts by weight, (iii) 0.1 to 30 parts by weight, (iv) 1 to 100 ppm
(referring to the amount of the transition metal in the
photoactivatable transition metal catalyst in relation to the total
amount of components (i) to (iii)), (v) 0 to 100 parts by weight,
(vi) 0 to 15 parts by weight.
22. A cured composition, obtained by light-curing the compositions
according to claim 20.
23. A continuously formed cured shaped article comprising the
composition of claim 20.
24. An extrusion line, comprising: a) at least one extrusion means,
b) at least one irradiation means, c) optionally at least one
heating means, d) optionally at least one conveying means, and e)
at least one packaging means.
25. A continuous extrusion process for the manufacture of cured
silicone extrudates, comprising: mixing the following components:
(i) at least one linear polyorganosiloxane having at least three
alkenyl groups and an average number of diorganosiloxy units
determined by GPC with polystyrene as standard of at least 3000,
(ii) optionally one or more polyorganosiloxane having alkenyl
groups, other than the polyorganosiloxane according to the
component (i), (iii) at least one polyorganosiloxane having at
least two SiH groups, (iv) at least one photoactivatable transition
metal catalyst, (v) optionally one or more filler, (vi) optionally
one or more conventional additives, feeding said mixture obtained
into an extruder, extruding said mixture through a die to obtain a
continuously formed extrudate, conveying said extrudate obtained to
an irradiation stage, irradiating said extrudate with light of a
wavelength in the range from 190 to 600 nm to obtain a continuously
formed, cured silicone extrudate, collecting said continuously
formed, cured silicone extrudate, and optionally cutting said
continuously formed, cured silicone extrudate.
Description
[0001] The invention relates to a process for the continuous
manufacturing of shaped articles, particularly extrusions articles
and the use of silicone rubber compositions in that process,
wherein the curing is initiated by visible or UV light.
[0002] The silicone rubber polymers according to the prior art
comprise polydimethyl-siloxanes having a certain amount of vinyl
groups attached to silicon.
[0003] In the known industrial extrusion processes the rubber
compositions are thermally cured either with highly reactive
peroxides or silicone hydride crosslinkers and metal catalysts to
continuously extruded shaped articles. But there are a lot of
restrictions about the process conditions for the manufacture of
such extruded shaped articles.
[0004] Since the silicone compositions to be cured thermally
require a certain period of heating, the extrusion rate and
possibly the thickness of the extrudates are to be limited in order
to provide sufficient extrudate temperature, in order to achieve
sufficient curing in a reasonable time. Accordingly the processes
for thermally curable rubbers of the prior art must either provide
high temperatures along the extrusion line or provide a long
pathway while shifting the surface temperatures to a higher
level.
[0005] Otherwise if the cure is not almost complete the
continuously shaped article cannot be wound continuously on rolls
and the like for storage and further cutting or packing.
[0006] Therefore the usually applied means for heating, such as
ovens, salt baths, steam chambers or channels have a length of up
to 20 m in order to safeguard sufficient curing at high speed.
[0007] Further problems of thermally curing systems result from the
use of some of the high reactive peroxides such as
bis-2,4-dichlorobenzoyl peroxide, 2-monchloro or
4-monochloro-benzoyl peroxide as curing catalyst in current
silicone rubber extrusion processes. Such catalyst generates
unavoidably by-products under the cure such as chlorobenzoic acids,
which can weaken the mechanical properties of the cured rubbers by
so-called reversion. This effect has negative impact upon sealing,
compression set, and the dynamic resistance of the shaped articles.
Another disadvantage are biphenyls generated as trace by-products
and the malodor of these or other by-products. In order to separate
such by-products e.g. for complying with common food and health
related governmental requirements an additional secondary
post-curing operation is necessary, involving additional handling,
delays, and costs.
[0008] Furthermore the reactive compositions including peroxides as
well as metal catalysts have a limited shelf life or potting life
under storage conditions at room temperature. This time restricts
the period of storage time wherein extrusion is still possible
without showing negative effects such as scorching initiated by
premature cure. The resulting negative effects include rough
surfaces or higher die swelling after extrusion and finally the
higher degree of scorching decreases the extrusion rates.
[0009] Peroxide based systems having an appropriate cure rate may
have pot life times up to one months at 25.degree. C. whereas metal
catalyzed systems can only be stored for 1-10 hours. The latter
therefore are often designed as 2-component system whereby the
final reactive one-component mass composition is formed immediately
before extrusion. In some cases storage under cooling below room
temperature may extent the time for scorching.
[0010] Furthermore the wall temperature of the ovens in the
currently preferred shaping processes for thermally cured systems
can run up to 500.degree. C., but usually is 250 to 450.degree. C.
Therefore the surface temperature of the articles is around
100-350.degree. C. and can increase up to 500.degree. C. in case of
a standstill. In such a case this temperature destroys the silicone
rubber to give a kind of a hard ash and other volatile oxidation
products. Also, the need of a high temperature level for curing
extruded silicone rubber compositions requires sufficient
ventilation, in particular, in view of thermal decomposition of the
silicone rubber in case of a standstill in the heating
channels.
[0011] Also the strong temperature gradient and low heat transfer
rates of the silicone compositions may result in reversion and
surface embrittlement on the extruded articles leading to crazing
during modest extension and the so-called reversion leading to
depolymerisation. Reversion means that network weakening or
depolymerisation takes place by e.g. the reaction of splitting
products like water or organic acids that are enclosed at such high
temperature levels particularly in thick walled articles with the
polymer.
[0012] The surface temperature of thick walled articles can
increase up to more than 300.degree. C. while the inner part of the
article has a much lower temperature so that the thick-walled
article is not completely cured in the inner parts.
[0013] In view of the possible deterioration of the surface of the
extrudates, a higher temperature cannot compensate the lack of
incomplete cure. Accordingly lower extrusion rates are required in
order to increase residence times of the extrudates in the oven,
i.e. the efficiency is reduced.
[0014] Another problem of thermally curing systems may result, when
co-extrudates, like for example seals, insulations or sheathings,
with other materials are to be prepared. One example may be the
manufacture of sheathed cables where the final sheathing should
contact smoothly upon the underlying substrate, e.g. an insulated
cable. If the entrapped air under sheathing gets heated too
strongly and the rubber is not yet cured bubbles may appear between
cable and sheathing. Not only here but also in case of ordinary
extrusion of thick-walled articles bubbles or micro bubbles may be
a problem particular caused by low curing rates at higher
temperatures. Bubbles and thermal shrinkage are therefore a general
challenge if the curing rate is too low at high temperatures.
[0015] Other processes known in the prior art for the continuous
manufacturing of shaped articles, made out of silicone rubber
either apply ionizing high energy radiation such as gamma radiation
(wave lengths of less than 0.5 nm) or radiation of accelerate
electrons (Van-de-Graaff generator). Such processes do not achieve
sufficient cure rates under the condition of extrusion i.e. short
residence times and requires high investments for the radiation
sources.
[0016] For example, U.S. Pat. No. 4,490,314 discloses a process
wherein polydimethylsiloxanes having different functional groups
are cured in the presence of ammonia or amines and high energy
ionizing radiation. U.S. Pat. No. 5,346,932 teaches how one can
thermally cure a non colored silicone rubber with microwaves having
a frequency between 3000 to 10000 MHz (wavelength of 3-10 cm) when
using selected silicas.
[0017] WO 2006/-010763 discloses light curable siloxane
compositions comprising sigma platinum catalysts and polymers
having viscosities up to 10 Pas useful for coatings, casting and
molded parts.
[0018] US 2006/135689 describes polyorganosiloxane compositions
comprising platinum catalysts having cyclic or bicyclic dienes as
pi-ligands which can extend the pot life of thermally curable
silicone rubbers useful in casting, different extrusion and molding
processes.
[0019] U.S. Pat. No. 6,376,569 discloses polydimethylsioxanes
comprising sigma platinum catalysts and a free radical
photoinitiator, wherein the chain length of the
polydimethyl-siloxanes is up to about 3000 diorganosiloxy
units.
[0020] The light curable silicone composition known in prior art
are either low viscous compositions or cannot be used in an
efficient industrial extrusion process, because the curing rate is
too low.
[0021] Polysiloxane compositions comprising low viscous polymers,
i.e. a polymer with a short chain length cannot be used in an
extrusion process where a minimum of `green strength` is a
precondition for pulling the uncured, extruded shaped strand,
leaving the extrusion die, through the curing facilities. Also the
shape of the article cannot be maintained until the extruded
article is cured.
[0022] Other light curable silicone compositions are based on
organofunctional groups like acrylates, epoxides, thiols which
provide neither cured silicone rubbers having stable mechanical
properties after heat ageing nor good mechanical properties at room
temperatures, nor sufficient cure rates, nor are they free of
malodors.
[0023] In order to resolve the above mentioned problems of the
prior art there has been provided a continuous process for the
manufacture of continuously shaped cured silicone articles,
comprising the following steps: [0024] a) a shaping step,
comprising the continuously shaping of a mixture comprising: [0025]
(i) at least one linear polyorganosiloxane having at least three
alkenyl groups and an average number of diorganosiloxy units
determined by GPC with polystyrene as standard of at least 3000,
[0026] (ii) optionally one or more polyorganosiloxane having
alkenyl groups, other than the polyorganosiloxane according to the
component (i), [0027] (iii) at least one polyorganosiloxane having
at least two SiH groups, [0028] (iv) at least one photoactivatable
transition metal catalyst, [0029] (v) optionally one or more
filler, [0030] (vi) optionally one or more conventional additives,
in a shaping apparatus, thereby obtaining a shaped silicone
article, [0031] b) at least one irradiation step to photoactivate
the photoactivatable transition metal catalyst, [0032] c)
optionally one or more heat treatment steps, [0033] d) optionally
one or more mixing steps, [0034] e) optionally one or more cutting
and/or winding and/or packaging steps of the continuously shaped
cured silicone article.
[0035] A continuous process according to the present invention--in
contrast to a batch process--relates to the manufacture of endless
(continuously) shaped articles (like tubes, profiles, strands,
insulations of endless articles) through a die, in contrast to an
article that is discontinuously prepared by filling a mould and
releasing the article from the mould after curing.
[0036] Component (i) to be used in the shaping step a) of the
process of the invention is at least one linear
polydiorganosiloxane having at least three alkenyl groups and an
average number of diorganosiloxy units determined by GPC with
polystyrene as standard of at least 3000 as number average mol
weight of the linear molecules.
[0037] Preferably the linear polyorganosiloxane corresponding to
component (i) has at least 5, more preferably at least 10 alkenyl
groups in order to provide suitable cross-linking density.
[0038] Preferably the linear polyorganosiloxane corresponding to
component (i) has a maximum number of 100 alkenyl groups, still
more preferably of 50 alkenyl groups, because otherwise the
reactivity of the polyorganosiloxane may decrease.
[0039] The preferred viscosity range of the polyorganosiloxane(s)
(i) used according to the invention is preferably at least 1.5
kpa*s, more preferably 5 kpa*s, more preferably 10 kpa*s, more
preferably 15 kpa*s (25.degree. C.; at a shear rate of 1 s.sup.-1).
Such a viscosity is preferred in order to achieve a suitable
viscosity (green strength) of the mixture to be shaped, in
particular, to be extruded (in the following abbreviated as
"shaping mixture", in particular, "extrusion mixture").
[0040] The polyorganosiloxane(s) (i) having at least three alkenyl
groups may have pendant and terminal alkenyl groups. "Pendant
alkenyl groups" in accordance with the present invention is
intended to mean an alkenyl group of a R(alkenyl)SiO
(D.sup.alkenyl) or (alkenyl)SiO.sub.3/2 (T.sup.akenyl) group.
"Terminal alkenyl groups" in accordance with the present invention
is intended to mean an alkenyl group of a M.sup.alkenyl group.
Preferably the polyorganosiloxane(s) (i) in average have at least
one pendant alkenyl group, more preferably at least two pendant
alkenyl groups, still more preferably at least three pendant
alkenyl groups. Most preferably polyorganosiloxane(s) (i) are used
that have two terminal alkenyl groups and at least one pendant
alkenyl group in addition.
[0041] The use of such polyorganosiloxane(s) (i), in particular
those having at least one, preferably at least three pendant
alkenyl groups, and optionally two terminal alkenyl groups in
addition, in the continuous shaping, in particular, extrusion
process of the present invention, generally provides a sufficient
cross-linking density obtained upon irradiation, i.e. satisfactory
mechanical properties, like low permanent set and high recovery
properties after any deformation.
[0042] The linear polyorganosiloxane (i) having at least three
alkenyl groups preferably has an average number of diorganosiloxy
units P.sub.n determined by GPC with polystyrene as standard of at
least 3000, more preferably at least 3500, more preferably at least
4000, and still more preferably 5000 to 12000. Pn is determined by
the equation P.sub.n=(M.sub.n/molecular weight of the repeating
siloxy unit). The M.sub.n value is the number average molecular
weight wherein the low molecular weight polyorganosiloxanes up to
10 siloxy units are not counted. These low molecular weight
polyorganosiloxanes are mainly comprised of cyclic
polyorganosiloxanes.
[0043] The polyorganosiloxanes (i) to be used in accordance and in
particular the polyorganosiloxanes (i), having the preferred
viscosity, are essentially linear, i.e. being composed of M and D
units.
[0044] However, in addition to those linear polyorganosiloxanes (i)
there might be used low molecular branched alkenyl
polyorganosiloxanes having an average number of siloxy units of
about less than 1000 to a certain extent, in particular less than
30 weight-% based on the total amount of the mixture to be shaped.
Such branched alkenyl polyorganosiloxanes are comprised by the
definition of component (ii). These low molecular low molecular
branched alkenyl polyorganosiloxanes may be part of the mixture to
be shaped, in order to increase cross-linking density.
[0045] The average content of the alkenyl groups in the linear
polyorganosiloxane(s) (i) is preferably from about 0.02 to 1.57
mol. % Si alkenyl groups related to the number of silicon atoms in
the linear polyorganosiloxane(s) (i) (corresponding to about 0.003
to about 0.21 mmol/g SiVi), more preferably from 0.08 to 0.7 mol. %
(corresponding to about 0.01 to 0.095 mmol/g SiVi). The alkenyl
content is determined here by way of .sup.1H NMR--see A. L. Smith
(ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons
1991 Vol. 112 pp. 356 et seq. in Chemical Analysis ed. by J. D.
Winefordner.
[0046] The preferred polydiorganosiloxanes (i) can be described by
the general formula (I):
R.sub.(3-x)R.sup.1.sub.xSiO(R.sup.1RSiO).sub.a(R.sub.2SiO).sub.bSiR.sub.-
(3-x)R.sup.1.sub.x (I),
in which x is preferably 0, 1, 2 or 3, preferably 1, a is an
average value and is in the range of 0 to 100, preferably 1 to 50,
more preferably 1 to 20, b is an average value and is in the range
of 3000 to 12000, preferably 3500, more preferably 4000, and still
more preferably 5000 to 11000, more preferably 6000 to 10000, with
the proviso that the polydiorganosiloxanes (i) of the general
formula (I) have at least three alkenyl groups,
[0047] R=a saturated organic group, preferably unsubstituted or
substituted hydrocarbon radicals, more preferably n-, iso-, tert-
or C.sub.1-C.sub.12-alkyl,
C.sub.1-C.sub.12-alkoxy(C.sub.1-C.sub.12)alkyl,
C.sub.5-C.sub.30-cycloalkyl or C.sub.6-C.sub.30-aryl,
C.sub.1-C.sub.12-alkyl(C.sub.6-C.sub.10)aryl, each of these
radicals R can have substitution by one or more F atoms and/or can
contain one or more --O-- groups,
[0048] R.sup.1=an unsubstituted or substituted
C.sub.2-C.sub.12-alkenyl radical, these preferably being selected
from: unsubstituted and substituted alkenyl-containing hydrocarbon
radicals, such as n-, iso-, tert-, or cyclic
C.sub.2-C.sub.12-alkenyl, vinyl, allyl, hexenyl,
C.sub.6-C.sub.30-cycloalkenyl, cycloalkenylalkyl, norbornenylethyl,
limonenyl, C.sub.8-C.sub.30-alkenylaryl, in which, if appropriate,
one or more --O-- atoms can be present (corresponding to ether
radicals) and the radicals can have substitution by one or more
F-atoms.
[0049] Preferred examples of suitable monovalent hydrocarbon
radicals R include alkyl groups, preferably CH.sub.3,
CH.sub.3CH.sub.2, (CH.sub.3).sub.2CH, C.sub.8H.sub.17 and
C.sub.10H.sub.21 groups, cycloaliphatic groups, such as
cyclohexylethyl, aryl groups, such as phenyl, tolyl, xylyl, aralkyl
groups, such as benzyl and 2-phenylethyl groups. Preferred
monovalent halogenated hydrocarbon radicals R in particular have
the formula C.sub.nF.sub.2n+1CH.sub.2CH.sub.2--, where n is from 1
to 10, examples being CF.sub.3CH.sub.2CH.sub.2--,
C.sub.4F.sub.9CH.sub.2CH.sub.2--, and
C.sub.6F.sub.13CH.sub.2CH.sub.2--. A preferred radical is the
3,3,3-trifluoropropyl group.
[0050] Particularly preferred radicals R include methyl, phenyl,
and 3,3,3-trifluoropropyl.
[0051] Preferred radicals R.sup.1 are groups such as vinyl, allyl,
5-hexenyl, cyclohexenylethyl, limonenyl, norbornenylethyl,
ethylidenenorbornyl, and styryl, particular preference being given
to vinyl.
[0052] In accordance with the invention it is possible to use a
mixture of different polyorganosiloxanes (i) having different
alkenyl contents, preferably vinyl contents in order to improve the
mechanical properties, such as tensile strength and tear
propagation resistance of the shaped crosslinked or cured silicone
rubber articles.
[0053] In accordance with the present invention for example a
mixture of a vinyl-rich polyorganosiloxane (I') and a vinyl-poor
polyorganosiloxane (II') (having a lower content of vinyl groups
than the vinyl-rich polyorganosiloxane) in a weight ratio of
100:0.5 to 1:10, preferably 10:1 to 1:1 may be used, in order to
suitably adjust satisfactory mechanical properties, like
elongation, tear strength, permanent set.
[0054] Furthermore in accordance with the present invention it is
possible to use in addition to the polyorganosiloxanes (i)
comprising at least three alkenyl groups, polyorganosiloxanes,
which are essentially linear alkenyl-endcapped polyorgano-siloxanes
having one alkenyl group on each terminal siloxy group (one of the
possible components (ii)). Such alkenyl polydiorganosiloxanes have
two alkenyl groups and are for example of the following formula
(II'):
R.sub.2R.sup.1SiO(R.sub.2SiO).sub.uSiR.sub.2R.sup.1 (II'), [0055]
in which the index `u` is an average value and is in the range of
3000 to 12000, preferably 5000 to 11000, more preferably 6000 to
10000, and R and R.sup.1 have the same meanings as given above for
formula (I).
[0056] The addition of those linear alkenyl-endcapped
polyorganosiloxanes having one alkenyl group on each terminal
siloxy group may help in maximizing the elongation and tear
strength of the cured continuously shaped silicone articles,
prepared with the process of the invention.
[0057] In order to provide silicone mixtures to be shaped and cured
having a good balance between cross-linking velocity and
cross-linking density the alkenyl (in particular vinyl content of
all polyorganosiloxane(s) in the mixture to be shaped (not only the
polyorganosiloxane(s) in accordance with the definition of
component (i)) should be set as high as possible, in particular, to
at least 0.03 mol-% Si alkenyl (corresponding to at least 0.004
mmol/g SiVi).
[0058] At the same time, however, the content of vicinal alkenyl
groups in the uncured mixture of components (i) to (vi) soluble in
CDCl.sub.3 at 25.degree. C. determined by .sup.29Si-NMR
spectroscopy preferably should be less than 0.025 mol. %.
[0059] The term "vicinal alkenyl groups" used in accordance with
the present invention means alkenyl groups attached to two
neighboring silicon atoms.
[0060] The content of vicinal alkenyl groups in the uncured mixture
of components (i) to (vi) is measured by .sup.29Si-NMR spectroscopy
in accordance to Maris J. Ziemelis and J. C. Saam, presented at the
132.sup.nd Meeting Rubber Division, American Chemical Society
Cleveland, Ohio Oct. 6-9, 1987.
[0061] In particular the uncured mixture of components (i) to (vi)
is mixed with CDCl.sub.3 in a weight-ratio of 30 wt-% of the
uncured mixture of components (i) to (vi) and 70 wt-% of CDCl.sub.3
with the exclusion of curing-inducing light. Thereafter the mixture
is optionally centrifuged. To the resulting dispersion is 0.8 wt. %
of Cr(AcAc).sub.3 is added, and the dispersion is subjected to
.sup.29Si-NMR spectroscopy measurement.
[0062] The content of vicinal Si-alkenyl groups in the component
(i) is measured in the same manner.
[0063] The method to determine the concentration of vicinal Si
alkenyl groups of the uncured mixture is exemplified for the
preferred vinyl groups attached to silicon atoms. The Si atoms in
the .sup.29Si-NMR spectroscopy having vicinal vinyl groups as
preferred embodiment of the invention have a chemical shift of
-35.47 to -34.89 ppm. The molar concentration of the vicinal Si
vinyl groups is thus calculated by:
[0064] Integral of the Si atoms in the range of -35.47 to -34.89
ppm/Integral over all Si atoms.times.100%.
[0065] Apart from this it is possible in the practice of the
invention, in particular, in the manufacture of the mixture to be
cured; to control the content of the vicinal Si alkenyl, in
particular, vinyl groups, by calculating the content of the vicinal
Si alkenyl groups, in particular, vinyl groups as follows:
[0066] Such method follows the equation:
(mol. % Si.sup.vicinal vinyl)=(mol. % Si.sup.vinyl*mol. %
Si.sup.vinyl),
wherein Si.sup.vinyl is determined as follows:
[0067] For each alkenyl containing polyorganosiloxane in the
mixture the content of the vinyl groups Si.sup.vinyl is determined
by .sup.1H-NMR spectroscopy, and for each alkenyl containing
polyorganosiloxane the content of the vicinal Si alkenyl groups is
calculated according to the formula:
(mol. % Si.sup.vicinal vinyl)=(mol. % Si.sup.vinyl*mol. %
Si.sup.vinyl).
[0068] Then the individual vicinal Si vinyl contents in mol. % are
multiplied with the relative weight in % (related to the total
weight of all alkenyl containing polyorganosiloxanes) of each
alkenyl containing polyorganosiloxane, and the sum of all such
products is divided by 100. For example, if there are three alkenyl
containing polyorganosiloxane in the mixture to be cured, x1, x2
and x3, having a vicinal Si vinyl content (mol. % Si.sup.vicinal
vinyl) of 0.03, 0.05 and 0.1 mol. %, respectively, and a weight
percentage of 20, 30 and 50 wt-%, respectively, then the
Si.sup.vicinal vinyl is calculated as follows:
(0.03.times.20+0.05.times.30+0.1.times.50)/100=(0.6+0.15+5)/100=0.0575
mol. %.
[0069] As a first approximation the content of vicinal Si alkenyl
groups calculated in this manner can be used to adjust the content
of vicinal Si alkenyl groups determined by
.sup.29Si-NMR-spectroscopy as explained above.
[0070] If the alkenyl content of all polyorganosiloxane(s) in the
mixture to be shaped is less than 0.03 mol-% the cross-linking
density may be too low to provide satisfactory mechanical
properties, (i.e. the permanent set and the elongation may be too
high).
[0071] If the part of the uncured mixture of the components (i) to
(vi), which is soluble in CDCl.sub.3 at 25.degree. C., has a
content of vicinal Si-alkenyl groups of more than 0.025 mol. %,
then the curing rate may be too slow in order to ensure economical
extrusion line speeds. A higher content of vicinal alkenyl groups
may be possible, but, however, would require higher catalyst
concentrations, which are again not desirable under economical
aspects. Under certain circumstances, where an increased pot life
is desired, it may be feasible, however, to adjust a total content
of vicinal alkenyl groups above 0.025 mol-%.
[0072] More preferably the content of the vicinal alkenyl groups in
the polyorganosiloxane (i) is less than 0.01 mol-%, and more
preferred the content is less than 0.005 mol-%. still more
preferred less than 0.001 mol-%.
[0073] In the present invention alkenyl-substituted
polyorganosiloxanes other than the polyorganosiloxanes (i), which
are referred to in this document as components(s) (ii) such as the
essentially linear alkenyl-endcapped polydiorganosiloxanes having
one alkenyl group on each terminal siloxy group, i.e. two alkenyl
groups, described before, may be used in the mixture to be shaped
in accordance with the continuous process of the invention. Such
alkenyl-substituted polyorgano-siloxanes (ii) other than the
polyorganosiloxane(s) (i) may include for example also those having
a lower number of diorganosiloxy units than 3000.
[0074] Polyorganosiloxanes (i) with a content of the vicinal
alkenyl groups of less than 0.025 mol % may be prepared by
equilibration polymerization reaction using basic or acidic
catalysts using both the various cyclosiloxanes, and linear
polyorganosiloxanes, and also symmetrical
1,3-divinyltetramethyldisiloxane, and other relatively long-chain
siloxanes having a trialkylsiloxy end cap or SiOH end groups.
Examples of those used for this purpose are the hydrolysates of
different alkylchlorosilanes, e.g. vinyidimethylchlorosilane and/or
dimethyldichlorosilane, other examples being the
trialkyl-terminated siloxanes per se obtained therefrom or these in
a mixture with other siloxanes.
[0075] The component(s) (iii) are preferably selected from linear,
cyclic or branched SiH-containing polyorganosiloxanes of the
general formula (III):
[M.sub.a2D.sub.b2T.sub.c2Q.sub.d2R.sup.2.sub.e2].sub.m (III) [0076]
in which [0077] M=R.sup.3R.sub.2SiO.sub.1/2, [0078]
D=R.sup.3RSiO.sub.2/2, [0079] T=R.sup.3SiO.sub.3/2, [0080]
Q=SiO.sub.4/2, in which
[0081] R=n-, iso-, tert- or C.sub.1-C.sub.12-alkyl,
C.sub.1-C.sub.12-alkoxy(C.sub.1-C.sub.12)alkyl,
C.sub.5-C.sub.30-cycloalkyl or C.sub.6-C.sub.30-aryl,
C.sub.1-C.sub.12-alkyl(C.sub.6-C.sub.10)aryl, each of these
radicals R can have substitution by one or more fluorine atoms
and/or can contain one or more --O-- groups,
[0082] R.sup.3=R, R.sup.1 or hydrogen, with the proviso that at
least two radicals R.sup.3 per molecule are hydrogen, and both here
can occur simultaneously in one molecule, but at least two radicals
R.sup.3 per molecule are hydrogen attached to a silicon atom, R
being defined above, R=methyl and R.sup.1=vinyl, if present, being
preferred.
[0083] R.sup.2=a divalent aliphatic n-, iso-, tert-, or cyclic
C.sub.1-C.sub.14-alkylene radical, or a C.sub.6-C.sub.14-arylene
or, respectively, alkylenearyl radical, which in each case bridges
two siloxy units M, D or T,
m=from 1 to 1000 a2=from 1 to 10 b2=from 0 to 1000 c2=from 0 to 50
d2=from 0 to 1 e2=from 0 to 300.
[0084] The polyhydrogensiloxanes (iii) are preferably linear,
cyclic, or branched polyorganosiloxanes whose siloxy units have
advantageously been selected from M=R.sub.3SiO.sub.1/2,
M.sup.H=R.sub.2HSiO.sub.1/2, D=R.sub.2SiO.sub.2/2,
D.sup.H=RHSiO.sub.2/2, T=RSiO.sub.3/2, T.sup.H=HSiO.sub.3/2,
Q=SiO.sub.4/2 in which these units are preferably selected from
MeHSiO units and Me.sub.2HSiO.sub.0.5 units alongside, if
appropriate, other organosiloxy units, preferably dimethylsiloxy
units.
[0085] The siloxy units present in the component (iii) can be
linked to one another in the polymer chain, blockwise or randomly.
Each siloxane unit of the polysiloxane chain can bear identical or
different radicals of the group R.
[0086] The indices of the formula (III) describe the average degree
of polymerization P.sub.n, measured as number average M.sub.n,
determined by GPC (polystyrene as standard) these being based on
polyhydrogenmethylsiloxane and, within the prescribed viscosity
limits, is to be appropriately adjusted on the basis of siloxy
groups using other substituents with other molecular weights.
[0087] The polyhydrogensiloxane (iii) in particular encompasses all
of the liquid, flowable, and solid polymer structures of the
formula (III) with the degrees of polymerization resulting from the
indices stated above. Preference is given to the
polyhydrogensiloxanes (iii) whose molar mass is smaller than about
60000 g/mol, preferably smaller than 20000 g/mol.
[0088] The preferred polyhydrogensiloxanes (iii) have structures
which are selected from the group which can be described via the
formula (IIIa-IIIeI)
HR.sub.2SiO(R.sub.2SiO).sub.z(RHSiO).sub.pSiR.sub.2H (IIIa)
Me.sub.2SiO(Me.sub.2SiO).sub.z(MeHSiO).sub.pSiMe.sub.2H (IIIb)
Me.sub.3SiO(Me.sub.2SiO).sub.z(MeHSiO).sub.pSiMe.sub.3 (IIIc)
Me.sub.3SiO(MeHSiO).sub.pSiMe.sub.3 (IIId)
{[R.sub.2R.sup.3Sio.sub.1/2].sub.0-3[R.sup.3SiO.sub.3/2][R.sup.4O).sub.n-
2}.sub.m2 (IIIe)
{[SiO.sub.4/2][R.sup.4O.sub.1/2].sub.n2[R.sub.2R.sup.3SiO.sub.1/2].sub.0-
.01-10[R.sup.3SiO.sub.3/2].sub.0-50[RR.sup.3SiO.sub.2/2].sub.1000}.sub.m2
(IIIf) [0089] where [0090] z=from 0 to 1000 [0091] p=from 0 to 100
[0092] z+p=b4=from 1 to 1000 [0093] n2=from 0.001 to 4 [0094]
m2=from 1 to 1000 [0095] in which R.sup.4O.sub.1/2 is an alkoxy
radical on silicon, and [0096] R.sup.3 is defined as above.
[0097] One preferred embodiment of the class (IIIe) and (IIIf)
compound is provided by way of example by monomeric to polymeric
compounds which can be described via the formula
[(Me.sub.2HSiO.sub.0.5).sub.kSiO.sub.4/2].sub.m2 wherein k can have
integer or decimal values from 0.01 to (2*m.sub.2+2).
[0098] The concentration of SiH is preferably in the range from 0.5
to 100 mol. % related to silicon atoms, or 0.1 to 17 mmol/g based
on polyhydrogen-methyl-siloxanes and, within the prescribed
viscosity limits, is to be appropriately adjusted on the basis of
siloxy groups using other substituents.
[0099] In one preferred embodiment of the invention, the
polyorganohydrogensiloxane (iii) is composed of at least one
polyorganohydrogensiloxane (iii-1) having per average two Si--H
groups per molecule and of at least one polyorgano-hydrogensiloxane
of type (iii-2) having more than two Si--H groups per molecule. In
this embodiment, component (iii) is composed of at least two
different polyorganohydrosiloxanes (iii), which produce different
crosslinking structures, in order to give high-strength silicone
elastomeric shaped articles. Bifunctional
polyorganohydrogensiloxanes (iii-1) act as so-called chain
extenders, and the polyhydrogensiloxanes (iii-2) of relatively high
functionality (>2) act as crosslinking agents. The silicone
composition to be shaped used according to the invention preferably
comprises at least one bifunctional chain extender (iii-1) and at
least one crosslinking agent (iii-2).
[0100] Examples of preferred structures of component (iii-1) in the
inventive silicone rubber composition include chain extenders
(iii-1) such as:
HMe.sub.2SiO-(Me.sub.2SiO).sub.zSiMe.sub.2H, and
Me.sub.3SiO-(Me.sub.2SiO).sub.z(MeHSiO).sub.2SiMe.sub.3
[(Me.sub.2SiO).sub.z(MeHSiO).sub.2].
[0101] The crosslinking agents (iii-2) comprise compounds such
as:
Me.sub.3SiO-(MeHSiO).sub.pSiMe.sub.3,
HMe.sub.2SiO(Me.sub.2SiO).sub.z(MePhSiO).sub.z(MeHSiO).sub.pSiMe.sub.2H,
(MeHSiO).sub.p,
(HMe.sub.2SiO).sub.4Si
MeSi(OSiMe.sub.2H).sub.3,
in which p and z are defined as above.
[0102] Mixtures of this type composed of what are known as chain
extenders and crosslinking agents can be used by way of example as
described in U.S. Pat. No. 3,697,473.
[0103] In a further preferred embodiment, the amount of components
(iii-1) and (iii-2) is from 0 to 70 mol-% of (iii-1), and
from 30 to 100 mol-% of (iii-2), based on (iii-1) and (iii-2).
[0104] If it is necessary to still further increase the cure rate,
this can by way of example be achieved via an increase of the ratio
of SiH to alkenyl, or an increased amount of catalyst (iv), or an
increase in the proportion of polyorganosiloxanes (iii-2) which
contain HMe.sub.2SiO.sub.0.5 units.
[0105] The polyorganosiloxanes (iii) are preferably
siloxane-soluble and, respectively, liquid at room temperature,
i.e. preferably have fewer than 1000 siloxy units, i.e. preferably
have viscosities below 40 Pas at 25.degree. C. and D=1
s.sup.-1.
[0106] The chain length of the crosslinking agents as component
(iii-2), which are mainly composed of MeHSiO units, is preferably
from 3 to 200, particularly preferably being from 15 to 60 MeHSiO
units.
[0107] The chain length of the chain extenders as component
(iii-1), these being mainly composed of Me.sub.2SiO units and
HMe.sub.2SiO.sub.1/2, is preferably from 2 to 100, particularly
preferably being from 2 to 60 Me.sub.2SiO units.
[0108] The SiH content in the present invention is determined by
way of .sup.1H NMR, see A. L. Smith (ed.): The Analytical Chemistry
of Silicones, J. Wiley & Sons 1991 Vol. 112 pp. 356 et seq. in
Chemical Analysis ed. by J. D. Winefordner.
[0109] The polyhydrogensiloxanes (iii) can be prepared by processes
known per se, e.g. using acidic equilibration or condensation, as
disclosed by way of example in U.S. Pat. No. 5,536,803. The
polyhydrogensiloxanes (iii) can also be reaction products generated
by a hydrosilylation reaction of organohydrosiloxanes using
siloxanes containing smaller amounts of alkenyl groups in the
presence of a hydrosilylation catalyst, where the resultant excess
SiH content is preferably within the limits defined above. This
gives organohydrogensiloxanes (iii) bridged by alkylene groups such
as R.sup.2 groups.
[0110] The polyhydrogensiloxanes (iii) can moreover also be
reaction products which have come from condensation of, for
example, organohydrogenalkoxysiloxanes (iii) using hydroxy- or
alkoxysilanes and, respectively, siloxanes, e.g. as described in
U.S. Pat. No. 4,082,726, e.g. columns 5 and 6.
[0111] According to the invention, it is preferable to select the
ratio of component (iii) to component (i) and optionally present
component (ii) in such a way that the molar ratio present of Si--H
to Si-alkenyl units is from about 0.5 to 20:1, preferably from 1 to
3:1.
[0112] The preferred amount of the polyhydrogensiloxanes (iii) is
from 0.1 to 200 parts by weight, based on 100 parts by weight of
component (i) and optionally present component (ii).
[0113] Many properties, such as vulcanizate properties,
crosslinking density, stability, and surface tack, can be
influenced by way of the ratio of SiH units to Si-alkenyl
units.
The Photoactivable Catalyst Component (iv)
[0114] Component (iv), the photoactivatable catalyst, preferably
contains at least one metal selected from the group composed of Pt,
Pd, Rh, Co, Ni, Ir or Ru. The photoactivatable catalyst preferably
comprises platinum.
[0115] Component (iv) is preferably an organometallic compound,
i.e., comprises carbon-containing ligands, or salts thereof. In a
preferred embodiment component (iv) has metal carbon bonds,
including sigma- and pi-bonds. Preferably the photoactivatable
catalyst is an organometallic complex compound having at least one
metal carbon sigma bond, still more preferably a platinum complex
compound having preferably one or more sigma-bonded alkyl and/or
aryl group, preferably alkyl group(s). Sigma-bonded ligands include
in particular, sigma-bonded alkyl groups, preferably sigma-bonded
C.sub.1 to C.sub.6-alkyl, more preferably sigma-bonded methyl
groups, sigma-bonded aryl groups, like phenyl, sigma-bonded silyl
groups, like trialkyl silyl groups. Most preferred photoactivatable
catalyst include .eta..sup.5-(optionally
substituted)-cyclopentadienyl platinum complex compounds having
sigma-bonded ligands, preferably sigma-bonded alkyl ligands.
[0116] The photoactivatable catalyst can be used as such or with a
carrier. Carriers that can be used for the catalysts are any solid
substances, which do not inhibit curing undesirably, or reduce
transparency for photoactivation undesirably. The carrier can be
solid or liquid. Solid carriers include for example silica,
alumina, organic resins etc. Liquid carriers include
polyorganosiloxanes, polyethers, solvents etc.
[0117] The photo-activatable catalyst is a catalyst, which provides
sufficient pot life, i.e. processing time prior to gelling of the
abovementioned components, once these have been combined.
[0118] Examples of photo-activatable catalysts include
.eta.-diolefin-.sigma.-aryl-platinum complexes, such as disclosed
in U.S. Pat. No. 4,530,879, EP 122008, EP 146307 (corresponding to
U.S. Pat. No. 4,510,094 and the prior art documents cited therein),
or US 2003-0199603, and also platinum compounds whose reactivity
can be controlled by way for example using azodicarboxylic esters,
as disclosed in U.S. Pat. No. 4,640,939 or diketonates.
[0119] Photoactivatable platinum compounds that can be used are
moreover those selected from the group having ligands selected from
diketones, e.g. benzoylacetones or acetylenedicarboxylic esters,
and platinum catalysts embedded into photo-degradable organic
resins. Other Pt catalysts are mentioned by way of example in U.S.
Pat. No. 3,715,334 or U.S. Pat. No. 3,419,593, EP 1 672 031 A1 and
Lewis, Colborn, Grade, Bryant, Sumpter, and Scott in
Organometallics, 1995, 14, 2202-2213, all incorporated by reference
here.
[0120] Photo-activatable catalysts can also be formed in-situ in
the silicone composition to be shaped, by using Pt.sup.0-olefin
complexes and adding appropriate photo-activatable ligands
thereto.
[0121] Pt.sup.0-olefin complexes are prepared by way of example in
the presence of 1,3-divinyltetramethyldisiloxane (M.sup.VI.sub.2)
via reduction of hexachloroplatinic acid or of other platinum
chlorides.
[0122] The photo-activatable catalysts that can be used here are,
however, not restricted to these above mentioned examples.
[0123] Particularly preferred catalysts in view of high reactivity
and cure rate include:
(.eta..sup.5-cyclopentadienyl)-trialkyl-platinum complexes with
(Cp=cyclopentadienyl) such as [0124] (Cp)trimethylplatinum [0125]
(Cp)ethyldimethylplatinum [0126] (Cp)triethylplatinum [0127]
(Cp)triallylplatinum [0128] (Cp)tripentylplatinum [0129]
(Cp)trihexylplatinum [0130] (methyl-Cp)trimethylplatinum [0131]
(trimethylsilyl-Cp)trimethyl platinum [0132]
(phenyldimethylsilyl-Cp)trimethylplatinum [0133]
(Cp)acetyldimethylplatinum [0134] (Cp)diethylmethylplatinum [0135]
(Cp)triisopropylplatinum [0136] (Cp)tri(2-butyl)platinum [0137]
(Cp)triallyiplatinum [0138] (Cp)trinonylplatinum [0139]
(Cp)tridodecylplatinum [0140] (Cp)tricyclopentylplatinum [0141]
(Cp)tricyclohexylplatinum [0142] (chloro-Cp)trimethyl platinum
[0143] (fluoro-Cp)trimethylplatinum [0144]
(Cp)dimethylbenzylplatinum [0145]
(triethylsilyl-Cp)trimethylplatinum [0146]
(dimethylphenylsilyl-Cp)trimethylplatinum [0147]
(methyldiphenylsilyl-Cp)trimethylplatinum [0148]
(triphenylsilyl-Cp)trihexylplatinum [0149]
[1,3-bis(trimethylsilyl)-Cp]trimethylplatinum [0150]
(dimethyloctadecylsilyl-Cp)trimethylplatinum [0151]
1,3-bis[(Cp)trimethylplatinum]tetramethyldisiloxane [0152]
1,3-bis[(Cp)trimethylplatinum]dimethyldiphenyfdisiloxane [0153]
1,3-bis[(Cp)dimethylphenylplatinum]tetramethyldisiloxane [0154]
1,3,5-tris[(Cp)trimethylplatinum]pentamethyltrisiloxane [0155]
1,3,5,7-tetra[(Cp)trimethylplatinum]heptamethyltetrasiloxane [0156]
(methoxy-Cp)trimethylplatinum [0157]
(ethoxymethyl-Cp)ethyldimethylplatinum [0158]
(methyoxycarbonyl-Cp)trimethylplatinum [0159]
(1,3-dimethyl-Cp)trimethylplatinum [0160]
(methyl-Cp)triisopropylplatinum [0161]
(1,3-diacetyl-Cp)diethylmethylplatinum [0162]
(1,2,3,4,5-pentachloro-Cp)trimethylplatinum [0163]
(phenyl-Cp)trimethylplatinum [0164] (Cp)acetyldimethylplatinum
[0165] (Cp)propionyldimethylplatinum [0166]
(Cp)acrloyldimethylplatinum [0167]
(Cp)di(methacryloyl)ethylplatinum [0168]
(Cp)dodecanoyldimethylplatinum [0169]
trimethylplatinumcyclopentadienyl-terminated polysiloxane.
[0170] The most preferred photoactivatable catalysts to be used in
the process of the invention are optionally alkyl or trialkylsilyl
substituted cyclopentadienyl-tris-alkyl-platinum compounds, in
particular, alkylcyclopentadienyl-trimethyl-platinum, in
particular, methylcyclopentadienyl-trimethyl-platinum.
[0171] Further photoactivatable catalysts include
(.eta.-diolefin)-(sigma-aryl)-platinum complexes (see e.g. U.S.
Pat. No. 4,530,879) as exemplified in the following (wherein for
the sake of simplification, "COD" signifies cyclooctadiene, "COT"
signifies cyclooctatetraene, and "NBD" signifies norbornadiene):
[0172] (1,5-COD)diphenylplatinum [0173]
(1,3,5,7-COT)diphenylplatinum [0174] (2,5-NBD)diphenylplatinum
[0175] (3a,4,7,7a-tetrahydro-4,7-methanoindene)diphenylplatinum
[0176] (1,5-COD)-bis(4-methylphenyl)platinum [0177]
(1,5-COD)-bis(2-methylphenyl)platinum [0178]
(1,5-COD)-bis(2-methoxyphenyl)platinum [0179]
(1,5-COD)-bis(3-methoxyphenyl)platinum [0180]
(1,5-COD)-bis(4-phenoxyphenyl)platinum [0181]
(1,5-COD)-bis(4-methylthiophenyl)platinum [0182]
(1,5-COD)-bis(3-chlorophenyl)platinum [0183]
(1,5-COD)-bis(4-fluorophenyl)platinum [0184]
(1,5-COD)-bis(4-bromophenyl)platinum [0185]
(1,5-COD)-bis(4-trifluoromethylphenyl)platinum [0186]
(1,5-COD)-bis(3-trifluoromethylphenyl)platinum [0187]
(1,5-COD)-bis(2,4-bis(trifluoromethyl)phenyl)platinum [0188]
(1,5-COD)-bis(4-dimethylaminophenyl)platinum [0189]
(1,5-COD)-bis(4-acetylphenyl)platinum [0190]
(1,5-COD)-bis(trimethylsilyloxyphenyl)platinum [0191]
(1,5-COD)-bis(trimethylsilylphenyl)platinum [0192]
(1,5-COD)-bis(pentafluorophenyl)platinum [0193]
(1,5-COD)-bis(4-benzylphenyl)platinum [0194]
(1,5-COD)-bis(1-naphthyl)platinum [0195]
(1,5-COD)-naphthylphenylplatinum [0196]
(1,5-COD)-bis(2H-chromen-2-yl)platinum [0197]
(1,5-COD)-bis(xanthen-1-phenyl)platinum [0198]
(1,3,5-cycloheptatriene)diphenylplatinum [0199]
(1-chloro-1,5-COD)diphenylplatinum [0200]
(1,5-dichloro-1,5-COD)diphenylplatinum [0201]
(1-fluoro-1,3,5,7-COT)diphenylplatinum [0202]
(1,2,4,7-tetramethyl-1,3,5,7-COT)-bis(4-methylphenyl)platinum
[0203] (7-chloro-2,5-NBD)diphenylplatinum [0204]
(1,3-cyclohexadiene)diphenylplatinum [0205]
(1,4-cyclohexadiene)diphenylplatinum [0206]
(2,4-hexadiene)diphenylplatinum [0207]
(2,5-heptadiene)diphenylplatinum [0208]
(1,3-dodecadiene)diphenylplatinum [0209]
bis[.eta..sup.2-2-(2-propenyl)phenyl]platinum [0210]
bis[.eta..sup.2-2-(ethenylphenyl)platinum [0211]
bis[.eta..sup.2-2-(cyclohexen-1-ylmethyl)phenyl]platinum.
[0212] Further photoactivatable catalysts include (.eta.-diolefin)
(sigma-alkyl)-platinum complexes, like [0213]
(1,5-COD)Pt(methyl).sub.2 [0214] (1,5-COD)Pt(benzyl).sub.2 [0215]
(1,5-COD)Pt(hexyl).sub.2.
[0216] The amount of component (iv) is preferably 0.1-1000 ppm,
preferably 0.5-500 ppm, more preferably 1-100 ppm, particularly
preferably 2-50 ppm, most preferably 2 to 20 ppm calculated as
metal, based on the weight of components (i) to (iii).
[0217] The curing rate is inter alia determined by the selected
catalyst compound, by its amount, and also by the nature and amount
of an optionally present additional inhibitor component covered by
components (vi).
Component (v) Filler
[0218] The silicone mixtures to be shaped and cured used according
to the process of the invention moreover optionally comprise one or
more, if appropriate surface-modified, fillers (v).
[0219] In general, if such fillers inhibited the photoactivation of
the photoactivatable catalyst (iv), in particular due to their
non-transparency or low light-transmittance, the process of the
present invention would require that such fillers, if intended to
be in the final shaped article, are admixed after the
photoactivation or irradiation step as described below.
[0220] The fillers include by way of example all of the
fine-particle fillers, i.e. those having particles smaller than 100
.mu.m, i.e. preferably composed of such particles. These can be
mineral fillers, such as silicates, carbonates, nitrides, oxides,
carbon blacks, or silicas. The fillers are preferably those known
as reinforcing silicas, which permit production of opaque
elastomers having better transparency, i.e. those which improve
vulcanizate properties after crosslinking, and increase strength,
examples being fumed or precipitated silica whose BET surface areas
are from 50 to 400 m.sup.2/g, these preferably having been
specifically surface-hydrophobicized here. If component (v) is
used, its amounts are from 1 to 100 parts by weight, preferably
from 10 to 70 parts by weight, even more preferably from 10 to 50
parts by weight, based on 100 parts by weight of component (i) and
optionally (ii).
[0221] Fillers whose BET surface areas are above 50 m.sup.2/g
permit production of silicone elastomers with improved vulcanizate
properties. It is only above 90 m.sup.2/g that vulcanizate strength
and transparency increase with, for example, fumed silicas, and
these are therefore preferred, and even more preferred silicas are,
for example, Aerosil.RTM. 200, 300, HDK.RTM. N20 or T30,
Cab-O-Sil.RTM. MS 7 or HS 5 more than 200 m.sup.2/g BET surface
area. As BET surface area rises, the transparency of the silicone
mixtures in which these materials are present also rises. Examples
of trade names of the materials known as precipitated silicas, or
wet silicas, are Vulkasil.RTM.VN3, or FK 160 from Degussa, or
Nipsil.RTM.LP from Nippon Silica K. K. and others.
[0222] It is preferred to use silica fillers having surface areas
above 50 m.sup.2/g leading to compositions in which the catalyst
(v) can be photoactivated due to sufficient transparency.
[0223] Examples of materials serving as non-transparent fillers
known as non-reinforcing fillers are powdered quartz, diatomaceous
earths, powdered crystoballites, micas, aluminum oxides, aluminum
hydroxides, Ti oxides, Fe oxides, Zn oxides, chalks, or carbon
blacks whose BET surface areas are from 0.2 to 50 m.sup.2/g or
higher if carbon black is used. These fillers are available under
variety of trade names, examples being Sicron.RTM., Min-U-Sil.RTM.,
Dicalite.RTM., Crystallite.RTM.. The materials known as inert
fillers or extenders with BET surface areas below 50 m.sup.2/g
should advantageously comprise no particles (<0.005% by weight)
above 100 .mu.m for use in silicone rubbers, in order that further
processing generates no problems during downstream processing, e.g.
passage through sieves or nozzles, or the mechanical properties of
the articles produced therefrom are adversely affected. Among the
opacifying fillers are also in particular non-transparent, in
particular inorganic, pigments or carbon black.
[0224] The use of these opacifying fillers is preferred only when
pigmentation is necessary or the physical function like thermal or
electrical conductivity is a requirement.
[0225] The use of opaque non-transparent fillers requires changing
the usual sequence of the activation and shaping steps in the
process. Normally, if no or transparent fillers are used, the
photoactivation through irradiation is carried out after the final
shaping process. If opaque non-transparent fillers, which would
inhibit the photoactivation of the photoactivatable catalyst, are
used, the photoactivation step is carried out before the opaque
non-transparent fillers are incorporated and the mixture is
shaped.
[0226] As the person skilled in the art knows, a filler can also be
a pigment. For clarification, the intention is that all of the
inorganic pigments included in the term filler as component (v) for
the present invention, whereas all of the remaining pigments and
dyes, in particular organic dyes and stabilizers, be included in
the definition of the auxiliaries (vi).
[0227] The fillers (v) may be subject of any suitable conventional
surface-treatment with suitable surface-treatment agents (belonging
to components (vi), such as hydrophobizing treatment with suitable
hydrophobizing agent, dispersing treatment with suitable dispersing
agents which influence the interaction of the filler with the
silicone polymer, e.g. influence thickening action. The surface
treatment of the fillers is preferably hydrophobation with silanes
or with siloxanes. It can by way of example take place in situ via
addition of silazanes, such as hexamethyldisilazane and/or
1,3-divinyltetramethyldisilazane, with addition of water, and
in-situ hydrophobation is preferred. It can also take place with
other familiar filler-treatment agents, for example with
vinylalkoxysilanes, e.g. with vinyltrimethoxysilane, or with other
silanes having unsaturated organofunctional groups, for example
with methacryloxypropyltrialkoxysilanes, or else with
poly-organosiloxanediols whose chain lengths are from 2 to 50 and
which bear unsaturated organic radicals, with the aim of providing
reactive sites for the crosslinking reaction. As explained above,
however, for the purpose of the present invention the
alkenyl-substituted polyorganosiloxanes used as hydrophobizing
agent will be also subsumed under component (ii).
[0228] In order to establish examples of commercially available
silicas pre-hydro-phobized with various silanes are: Aerosil R 972,
R 974, R 976, or R 812, or, for example, HDK 2000 or H30 Examples
of trade names for materials known as hydrophobized precipitated
silicas or wet silicas are Sipernat D10 or D15 from Degussa.
[0229] These pre-hydrophobized silicas are less preferred than the
silicas hydrophobized in-situ with silazanes. Vulcanizate
properties and rheological properties, i.e. technical processing
properties, of the silicone rubber mixtures can be influenced by
the selection the amount of the type of the filler, its amount, and
the nature of hydrophobation.
[0230] In one preferred embodiment, the silicone composition to be
shaped according to the process of the invention comprises at least
one reinforcing filler (v) which has at least a BET surface area of
more than 50 m.sup.2/g, preferably more than 80 m.sup.2/g of BET
surface area.
[0231] According to the invention, it is also possible to use a
mixture of one or more, in particular two, fillers with different
specific surface areas. Suitable selection of different, in
particular two, fillers with different specific surface areas or
treatment processes in order support the requirements of good
extrusion properties, i.e. namely retaining high flowability at
high level of green strength of unhardened polymer compositions and
avoiding self-leveling of the continuously shaped articles. This
can be achieved best by using fillers having preferably surface
areas above 90 m.sup.2/g BET and a surface treatment with
polyorganosiloxanediols, polyorganosiloxanes, chloro or
alkoxysilanes which ensure a high degree of thickening properties,
high viscosity level and shear thinning. Another assumption is a
sufficient polymer viscosity. In addition one can increase the
performance for effective extrusion by using specific auxiliary
additives such as PTFE powders, PTFE emulsions or boron derivative
in smaller amounts i.e. below 1 wt. %.
Component (vi): Conventional Additives
[0232] The auxiliary or conventional additives can comprise for
example organic dyes or pigments if not already defined under (v),
stabilizers introduced in silicone rubbers in order to improve heat
stability i.e. resistance against hot air, reversion, such as i.e.
depolymerisation under attack of traces of acids or water at high
temperature. The auxiliary or conventional additives further
include e.g. plasticizers, or release oils, or hydrophobicizing
oils, such as polydimethylsiloxane oils, without reactive alkenyl
or SiH groups, with viscosity which is preferably 0.001-10 Pas at
25.degree. C. Additional mold-release or flow improving agents can
also be used, examples being fatty acid derivatives or fatty
alcohol derivatives, fluoroalkyl surfactants. Compounds
advantageously used here are those which separate rapidly and
migrate to the surfaces. Stability after exposure to hot air can by
way of example be increased using known hot-air stabilizers, such
as Fe-, Mn-, Ti-, Ce- or La-compounds, and organic salts of these,
preferably their organic complexes. Another class of the
conventional additives (vi) are additives which can improve
rheological properties, to provide higher flow and smooth surfaces
of the shaped articles. Such additives are known for the persons
skilled in the art and include PTFE-powders, boron oxide
derivatives, flow additives like fatty acid derivative, esters and
its salts or fluoroalkyl surfactants. The auxiliary additives (vi)
may also include so-called inhibitors for controlling the
crosslinking reaction. However the presence of those inhibitors is
in general not preferred. However, if it is intended to extent the
pot life of the silicone composition to be shaped, for example, in
case non-transparent fillers are to be compounded after
photoactivation, the use of such inhibitors may be suitable to
decrease the cure rate. Examples of advantageous inhibitors include
for example vinylsiloxanes, 1,3-divinyltetra-methyldisiloxane, or
tetravinyl-tetramethyl-tetracyclosiloxanes (for sake of clarity it
is pointed out that if inhibitors belong to the class of alkenyl
polyorganosiloxanes they are formally subsumed under component (i)
or (ii)). It is also possible to use other known inhibitors, for
example ethynylcyclohexanol, 3-methylbutynol, or dimethyl
maleate.
[0233] The mixture to be shaped, in particular, to be extruded
comprising the components (i), (iii) and (iv) and optionally (ii),
(v) and (vi), preferably has a viscosity of at least of 10 Mooney
units. If the viscosity of the shaping or extrusion mixture is less
than a certain viscosity, extrusion rate might be too low, because
the extrusion pressure might be too low, and also the so-called
`green-strength` of the extrudates leaving the extruder before
curing might be too low, so that in particular it might be
impossible to pull the extrudates through the extrusion line
downstream. Preferably the viscosity of the shaping mixture is at
least 10 Mooney units, more preferably at least 15 Mooney units at
room temperature (25.degree. C.). Mooney will be measure
accordingly to DIN 53523 at 25.degree. C. as so-called
MI.sub.0=(starting value at time 0+15 sec/max after 0 sec and
MI.sub.4=value 4 min after MI.sub.0.
Shaping Process
[0234] The shaping apparatus used in the process of the invention,
preferably comprises at least one shape forming die, through which
the mixture to be shaped is passed, with the formation of the
continuously formed silicone article. Preferably the continuous
shaping step is an extrusion step and the shaping apparatus is an
extruder. The extruder is preferably selected from single-screw
extruders, twin-screw extruders and gear extruders, with the
single-screw extruders and gear extruders being the most preferred
extruders. It may be also possible to use other shaping apparatus
than extruders with a die to prepare the endless shaped article,
like shaping rollers, but those are less preferred.
[0235] One of the major advantages of the process according to the
present invention is that the composition cures by irradiation.
Therefore, --in contrast to thermally curing systems, like
peroxide- or metal catalyst initiated systems--it is normally not
necessary to cool the extruder in order to prevent curing of the
mixture to be cured in the extruder. Therefore, the continuous
light-induced shaping process according to the invention is quite
favorable in terms of energy saving and operation costs, including
costs for extrusion equipment.
[0236] In the process according to the present invention the
irradiation step b) is carried out preferably with light of a
wavelength in the range from 190 to 600 nm. Usually a non-laser
light source emits a spectrum of wavelengths, and according to the
present invention preferably the maximum of the light emitted lies
in the range of 190 to 600 nm, more preferably in the range of 200
to 460 nm.
[0237] In the process according to the invention an optional heat
treatment step (c) may be performed after initiation of the curing
process through irradiation, in order to accelerate curing. Such
optional heat treatment step (c) may be carried out by passing an
oven, having a temperature of for example 50.degree. C. to
250.degree. C. and at an extrudate surface temperature of
20.degree. to 200.degree. C., more preferred 35-150.degree. C.,
still more preferred 40 to 90.degree. C. In general, however,
thermal stress of the extrudates prepared in accordance with the
process of the present invention is much lower than of extrudates
subjected to thermal curing, resulting in an improved surface, i.e.
reduced embrittlement, reduced reversion and reduced thermal
shrinkage.
[0238] Accordingly the present invention also relates to the shaped
light-cured silicone extrudates, obtained by the process of the
invention.
[0239] Such shaped light-cured silicone extrudates for example have
the form of a sheet, a tube, a cable, insulation on wire, a cable
jacket, an insulation or sheathing of temperature sensitive other
substrate, a profile, particularly embracing a carrier substrate
made of plastic or natural polymers, or a sheathing of cable or
tubes etc.
[0240] The present process of the invention is particularly
suitable for the manufacture of shaped co-extrudates, in
particular, co-extrudates with thermally sensitive substrates, like
thermoplastics, rubbers, leather, natural polymers, like cellulose,
collagen, wood, low-melting metals, comprising the light-cured
silicone extrudates, obtained by the process of the invention in
association with at least one further extruded material. Such
shaped co-extrudates may have the forms of strands, tubes, profiles
for sealing in all forms and dimensions, insulations, seals,
sheathings etc.
[0241] The present invention further is related to the use of at
least one polyorgano-siloxane having at least three alkenyl groups
and an average number of diorganosiloxy units determined by GPC
with polystyrene as standard of at least 3000, and having a content
of vicinal alkenyl groups of less than 0.025 mol. %, preferably
less than 0.005 mol-% determined by .sup.29Si--NMR spectroscopy or
calculation as described above for the manufacture of continuously
formed shaped articles.
[0242] The present invention further is related to a novel
composition, comprising: [0243] (i) at least one polyorganosiloxane
having at least three alkenyl groups and an average number of
diorganosiloxy units determined by GPC with polystyrene as standard
of at least 3000, and having in average less than 0.025 mol-%
vicinal alkenyl groups, preferably less than 0.005 mol. %, the
mol-% being based on integral of the .sup.29Si-NMR signal at -34.89
to -35.47 ppm related to the integral of the signals for all vinyl
substituted Si atoms (P.sup.vinyl tot=total concentration of Si
vinyl atoms as described above), [0244] (ii) optionally one or more
polyorganosiloxanes having alkenyl groups, other than the
polyorganosiloxane according to the component (i), [0245] (iii) at
least one polyorganosiloxane having at least two SiH groups, [0246]
(iv) at least one photoactivatable transition metal catalyst,
[0247] (v) optionally one or more filler, [0248] (vi) optionally
one or more conventional additives, which can be used, in
particular, for the manufacture of continuously formed shaped
articles.
[0249] Preferably such composition comprises the components (i) to
(vi) in the amounts of components (i) to (vi) in the following
amounts: [0250] (i) 100 parts by weight, [0251] (ii) 0 to 100 parts
by weight, preferably 0 to 30 parts by weight, [0252] (iii) 0.1 to
30 parts by weight, preferably 1 to 10 parts by weight, [0253] (iv)
1 to 100 ppm, preferably 2 to 20 ppm, (referring to the amount of
the transition metal in the photoactivatable transition metal
catalyst in relation to the total amount of components (i) to
(iii)), [0254] (v) 0 to 100 parts by weight, preferably 15 to 60
parts by weight, [0255] (vi) 0 to 15 parts by weight, preferably
0.01 to 10 parts by weight. which can be used for the manufacture
of continuously formed shaped articles.
[0256] The shaped light-cured silicone extrudates according to the
invention can be used preferably in food and beverage industry, in
medical care applications, in the electro and electronic industry,
as glass fiber isolation, elastomer seal for or upon temperature
sensitive substrates, etc.
[0257] The present invention also relates to an extrusion line,
comprising: [0258] a) at least one extrusion means, [0259] b) at
least one irradiation means, [0260] c) optionally at least one
heating means, [0261] d) optionally at least one conveying means,
and [0262] e) at least one packaging means, which can be used, in
particular, to prepare the shaped light-cured silicone extrudates
according to the invention.
[0263] The extrusion line as mentioned before may have additional
mixing means, where the extrusion mixture is prepared. Such mixing
means may include for example a kneader, two roll-mixers, mixing
extruder, in particular twin screw extruders, a LIST-mixer,
ZSK-extruders, HENSCHEL-mixers, BANBURY-mixers, BUSS-co-kneader
(oscillating one screw mixer).
[0264] Preferably a two-step mixing process is used, wherein in a
first step an extrusion mixture is prepared with the components
without the photoactivatable transition metal catalyst, and in a
second mixing step the photoactivatable transition metal catalyst
optionally together with other components is incorporated to
prepare the photoactivatable extrusion mixture. During the
incorporation of the photoactivatable transition metal catalyst and
after the photoactivatable extrusion mixture is prepared, care must
be taken for preventing premature cross-linking, which would make
the subsequent extrusion difficult or even impossible. Premature
cross-linking of the photoactivatable extrusion mixture can be
prevented for example by using closed apparatuses, or depending on
the specific catalyst used, light of selected wavelength ranges,
e.g. yellow light (600 to 650 nm) or red light (650 to 1000 nm). If
light of selected wavelength ranges, which do not activate the
photoactivatable transition metal catalyst, is used, of course open
apparatuses can be used, like two-roll mixers, etc.
[0265] The specific kind of extrusion line is also depending on the
pigments or fillers used. If those pigments or fillers are opaque
(that is light-proof), then the photoactivation cannot be carried
out anymore after such opaque fillers or pigments are added. In
such case it is necessary to first photoactivate the mixture, and
thereafter mixing the mixture with such opaque fillers or pigments.
In such case it is preferred that the average residence time of the
extrusion mixture between the activation step and the final shaping
step when passing the extruder die is smaller than the scorch time
(MI.sub.min+5 i.e. the time wherein the Mooney viscosity increases
of more than 5 units above the minimum), because otherwise the
final shaping step becomes difficult or even impossible.
[0266] In this respect it has to be emphasized that in the present
invention the enumeration of the process steps a) to e) does not
necessarily determine the order of carrying out such steps. As
explained before, in accordance with the present invention it is
also possible to carry out the irradiation step before the final
shaping, preferably extrusion step, if the use of opaque fillers or
pigments requires so.
[0267] In a preferred embodiment of the process of the invention
however, translucent mixtures are prepared, where the irradiation
step is carried out after the final shaping, preferably extrusion
step. That is, such process usually includes a first step of mixing
the mixture to be extruded, which may preferably include a separate
step of admixture of the photoactivatable catalyst. In the second
step the mixture obtained is fed into shape-forming extruder. It is
also in the scope of the invention to carry out a mixing step for
the components of the mixture to be shaped directly in the
shape-forming apparatus, preferably in the extruder. Such extruders
have means to introduce the several components. It lies also in the
ambit of the present invention to perform the mixing of all
components of the mixture except for the photoactivatable catalyst
in a conventional mixing unit such as a kneader, and to incorporate
the photoactivatable catalyst in the shape-forming apparatus,
preferably the extruder, which has means for introducing additional
components into the mixture to be extruded.
[0268] After the mixture has been formed it is discharged from the
shaping apparatus and than passed on with suitable conveying means
to an irradiation stage, wherein irradiation is carried out in
order to activate the photoactivatable catalyst and to initiate the
curing of the shaped silicone composition. Usually a heating step
after the irradiation step is not required in order to complete
curing, since the mixture is cured by the action of the
photoactivated catalyst, but a heating step can be used
additionally to shorten the curing time, if desired. Normally, the
silicone composition formed according to the process of the
invention does require higher temperatures during its manufacture,
which is a particular advantage of the process of the invention,
because it is energy saving, because it neither requires heating
nor cooling means, and moreover, thermal shrinking of the shaped
silicone composition can be almost completely avoided.
[0269] On the other hand, it is according to the invention normally
not necessary to cool the shape-forming apparatus, in particular,
the extruder, because the composition is not thermally sensitive,
i.e. does not cure, before photoactivation of the catalyst through
irradiation has been initiated. In particular on an industrial
scale it represents a great advantage that the process of the
present invention does not require cooling of the shape forming
apparatus. However, in the specific case, where opaque fillers or
pigments are used to prepare the shaped silicone articles with the
process of the present invention, which requires an additional
mixing step and the subsequent forming step after the irradiation
step to activate the catalyst is carried out, it might be necessary
to have the activated mixture cooled after the irradiation step to
increase the scorch time of the mixture.
[0270] As the shape-forming apparatuses in the present invention
there can be used for example extruders, shaping rolls, etc.
[0271] The extruders that can be used as shape-forming apparatuses
in the present invention include in particular single-screw
extruders, twin screw extruders and gear extruders, having suitably
integrated dies for shaping, in particular, the extruder according
to WO 03/024691, because such extruders can unify mixing and
extruding with one srew. The extruders include extruders feeding a
crosshead for shaping sheathings or insulations. Extruders useable
in the present invention may have the following throughput: 0.01 to
5000 kg/hour of the silicone composition. The preferred dimension
is designed for an output of 1 to 500 kg/h. The extrusion rate
therefore can run up to 600 m/min or more if the length of the
channel for irradiation can provide exposure times for round about
1 sec or more. Thick-walled tubes or profiles are preferably
extruded between 1-20 m/min. Higher extrusions rates can be applied
purposively for e.g. wire insulations.
[0272] Single screw extruders and gear (pump) extruders useable in
the present invention may have the following typically
(length-to-diameter) L/D-ratio of 10:1 to 25:1. Screw diameters may
be between 10 and 150 mm, preferably 30 to 90 mm, screw length may
be between 5 to 1000 mm. The screw rotation (number of
revolutions/min) may be 10 to 150 RPM. The screw should have a
compression rate of 1:1.1 to 1:3 which can be obtained with
constant core diameter and varying flight distance or with varying
core diameter and constant flight distance. For trouble free
continuous feeding and high output, the flight should be quite deep
and should be hardened or hard metal coated to prevent wear. In the
process of the invention it is not necessary to cool the
composition to prevent scorch due to the shear heat generated
during the extrusion process as explained above. The twin-screw
extruders may have co-rotating or counter-rotating screws of the
same dimension as the single screw extruders. They are however less
preferred in the process of the invention except as mixing unit in
the mixing step as explained above.
[0273] The shape-forming apparatuses, in particular, the extruders
used in the process of the invention can be operated in vertical
units, wherein the formed composition is dropped downwards by its
own weight or pulled upwards by a motor-driven drum at the top.
Horizontal shape forming apparatuses, in particular, extruders are
preferably used in the process of the invention. Such kind of
operation usually requires the use of a conveyor belt.
[0274] In accordance with the invention it also possible to prepare
co-extrudates, where the silicone composition is attached to any
kind of other material, including thermoplastic substrates (which
can be processed particularly advantageous with the process of the
invention, because the process does not require thermal curing),
like polyethylene, polypropylene, polyvinylacetate, natural
biodegradable polymers, like polylactic acid, polycarbonate, foam
plastic articles, like foam extrudates, like endless foam
profiles.
[0275] The process offer a method for the manufacture of seals for
plastic boxes wherein the shaped extrudate is placed immediately
after the shaping process.
[0276] As the irradiation means in the process of the present
invention and in the extrusion line of the present invention
conventional irradiation units providing light whose wavelength is
in the range of preferably from 180 to 600 nm, more preferably
190-500 nm, are used. If the light-activatable curable compositions
comprise appropriate sensitizers or photoinitiators, selected from
the class of anthracene, xanthonone, anthraquinone derivatives,
then irradiation sources providing light of a wavelength range of
180 to 700 nm can also be used. The addition of commercially
available sensitizers, such as benzophenones, etc., permits
activation using longer-wavelength light or with better yields of
light. As the irradiation sources preferably UV radiation sources
are used for light-activation selected from xenon lamps which can
be operated as flash lamps, undoped or iron- or gallium-doped
mercury lamps, black-light lamps, excimer lasers and LEDs. The
light-irradiation intensity (radiation dose*exposure time per unit
of volume) is selected as a function of the selected process, of
the selected composition of the temperature of the composition in
such a way as to give a sufficient processing time. Commercially
available irradiation sources may be used in the irradiation step
of the present invention. Such irradiation sources may have power
consumption of 0.5 to 20 kW and length of irradiation units of 5 cm
to 1 m, which may be arranged in series of more than one
irradiation unit to achieve increased exposure time. Additional
reflectors radial assembled can help to increase the yield of
light. The distance between shaped extrudate and light source is
preferred between 1 cm to 100 cm.
[0277] Average exposure times (time which is required to pass the
irradiation unit(s)) is for example at least 1 second, preferably 2
to 50 seconds.
[0278] Optionally useable additional heating means arranged after
the irradiation unit may include conventional ones, i.e. hot air
chambers, strip heaters, heat radiator units, heating mantles,
etc.
[0279] Optionally the process is carried out with at least one
conveying means, at least one packaging means and/or cutting means,
for cutting the endless extrudates into pieces.
[0280] The endless extrudate is conveyed by for example conveyor
belts and finally it is cutted, and/or wound and/or packed to
obtain the final shaped light-cured silicone article.
[0281] The present invention still further provides a continuous
extrusion process for the manufacture of cured silicone extrudates,
comprising: [0282] mixing the following components: [0283] (i) at
least one linear polyorganosiloxane having at least three alkenyl
groups and an average number of diorganosiloxy units determined by
GPC with polystyrene as standard of at least 3000, [0284] (ii)
optionally one or more polyorganosiloxane having alkenyl groups,
other than the polyorganosiloxane according to the component (i),
[0285] (iii) at least one polyorganosiloxane having at least two
SiH groups, [0286] (iv) at least one photoactivatable transition
metal catalyst, [0287] (v) optionally one or more filler, [0288]
(vi) optionally one or more conventional additives, [0289] feeding
said mixture obtained into an extruder, [0290] extruding said
mixture through a die to obtain a continuously formed extrudate,
[0291] conveying said extrudate obtained to an irradiation stage,
[0292] irradiating said extrudate with light of a wavelength in the
range from 190 to 600 nm to obtain a continuously formed, cured
silicone extrudate, [0293] collecting said continuously formed,
cured silicone extrudate, and [0294] optionally cutting said
continuously formed, cured silicone extrudate.
EXAMPLES
Example 1
[0295] Example according to the invention 75 parts per wt. of a
polydimethylsiloxane having 0.03 mol-% terminal vinyldimethylsiloxy
units and 0.2 mol-% pendant vinylmethylsiloxy units with a
viscosity of 20*10.sup.3 Pas at 25.degree. C. (P.sub.n 8000), 25
parts per wt. of a polydimethylsiloxane having 0.03 mol-% terminal
vinyidimethylsiloxy units and 0.08 mol-% pendant vinylmethylsiloxy
units with a viscosity of 20*10.sup.3 Pas at 25.degree. C. (P.sub.n
8000) as components (i), 36 parts per wt. of a fumed silica treated
with 6 wt.-% octamethylcyclotetrasiloxane and a BET surface of ca.
200 m.sup.2/g as component (v), 1 part per wt. of an
.alpha.,.omega.-polydimethylsiloxanediol having an OH-content of
6.5 wt. %, 0.15 parts per wt. of tetramethyldivinyldisilazane, 1
part per wt. of an .alpha.,.omega.-dimethoxypolydimethyl-siloxane
having a methoxy content of 7 wt.-% (all three as component (vi))
are admixed at 110.degree. C. in a two-blade-kneader for 90 minutes
and the volatiles evaporated for 2 hours at 180-190.degree. C. in a
vacuum of 20 mbar.
[0296] After subsequently cooling down to 65.degree. C. the mixture
for 15 minutes 0.85 parts per wt. of a trimethylsiloxy-endstopped
polyhydrogenmethyl-dimethylsiloxane having a SiH-content of 8.9
mmol/g and a viscosity of 45 mPas as component (iii) are mixed to
the previous composition. This mixture is admixed for 10 minutes in
the dark or presence of filtered light (`yellow light`) with
5-methylcyclopentadienyl)-trimethyl-platinum related to 4 ppm
platinum metal as component (iv) as metal related to the components
(i) to (iii).
[0297] The complete composition therefore has 0.20 mol. % Mvi and
Dvi groups and a calculated content of vicinal vinyl groups of
0.00043 mol. % in the components (i) and (iii).
[0298] The mixture including the catalyst then was photoactivated,
extruded with a single screw extruder Rheomex combined with
Rheocord EU 3 Fa. Haake (screw diameter 19 mm, L/D=14), 24 RPM
(revolutions/min) and cured under following conditions:
[0299] The shaped extrudate passed a UV-lamp iron doped having a
bulb length of 10 cm and an power of 2.4 kW with an extrusion rate
of 1.5 m/min.
[0300] The shaped article is a tube having a diameter outside of 5
mm and inside of 3 mm. A continuous strand as the extruded article
was collected about 1 m after the irradiation channel. The
transparent elastomeric extrusion tube was almost completely cured
and could be wound up and stored without any problems. The hardness
according to DIN 53501 of the extrusion strand was nearly exactly
the same as the hardness of a 6 mm test sheet made by exposure to
60 sec UV-light and 12 h after exposure to daylight at 25.degree.
C. from the same composition. A hardness of 46 Shore A was measured
for 3.times.2 mm sheets of the tube.
[0301] The extrusion rate can be increased up to 6.1 m/min, upon
which the extrusion strand is still crosslinked enough to prevent
deformation of the shaped extrudate and to allow winding-up the
tube. During subsequent storage at room temperature the strand gets
cured completely after a few minutes. This shows that irradiation
in the process of the present invention basically is required only
for the initiation of the cross-linking process, which in turn
allows high extrusion rates, which is a major advantage in the
industrial production of silicone elastomers. A further increase of
the extrusion rate can be achieved by increasing the irradiation
power and/or the length of the irradiation unit.
[0302] The silicone composition of example 1 are formed into sheets
of 2-6.4 mm thickness which are irradiated under the same UV-lamp
at different irradiation times, in order to determine reasonable
irradiation times for continuous extrusion at certain thicknesses
of the extrusion articles. Table 1 shows the physical properties of
the cured sheets:
TABLE-US-00001 TABLE 1 Irradiation Thickness time Hardness [mm] [s]
[.degree. Shore A] 3.2 1 <30 3.2 3 46 6.4 5 38
[0303] Table 1 shows that required irradiation time does not depend
strongly on the thickness of the articles to be extruded.
Example 2
[0304] 100 parts per weight of a polydimethylsiloxane having 0.03
mol. % terminal vinyl-dimethylsiloxy units and 0.42 mol-%
vinylmethylsiloxy units i.e. 0.45 mol. % (0.0609 mmol/g) for all
vinyl groups and a viscosity of 11*10.sup.3 Pals at 25.degree. C.
(P.sub.n=6500) as component (i). The composition further comprises
45 parts per weight of a fumed silica having a BET-surface of ca.
200 m.sup.2/g as component (v), 6.5 parts per weight of an
.alpha.,.omega.-dihydroxydimethylsiloxane having a content of
OH-groups of 7.5 wt.-% as component (vi) and 0.5 parts per weight
of hexamethyl-disilazane as component (vi).
[0305] All components (i), (v) and (vi) are admixed in a kneader at
120.degree. C. for 90 minutes and then for additional 120 min at
160.degree. C. the volatiles were evaporated and externally
condensed.
[0306] After cooling down to 65.degree. C. the composition was
admixed together with 1 part per weight of a
trimethylsiloxy-terminated polyhydrogenmethyl-dimethylsiloxane
having a content of SiH-groups of 7.4 mmol/g and a viscosity of 40
mPas for 15 minutes.
[0307] The aforementioned composition is admixed for 10 minutes
under exclusion of light or under `yellow` light with
.eta..sup.5-(methylcyclopentadienyl)-trimethyl-platinum according
to 4 ppm platinum calculated as metal related to the components (i)
to (iii).
[0308] The total amount of the vinyl units in the composition was
0.45 mol. % and the total amount of the vicinal Si-vinyl groups are
calculated to be 0.0020 mol. % in the components (i) and (iii).
[0309] The tube having the dimension an outer diameter 5 mm and an
inner diameter 3 mm could be extruded with an extrusion rate of 1.7
m/min at 24 RPM. The Mooney viscosity was measured to be
MI.sub.0/MI.sub.4=34/32 units. If photoactivation or the catalyst
(iv) is omitted, then the uncured tube maintained its shape over
more than 1 min after the shaping process through the die.
[0310] The composition could be extruded under the same conditions
as those used in example 1. A continuously shaped strand as the
extruded article could be collected about 1 m after the irradiation
channel. The transparent elastomeric extruded tube could be almost
completely cured and could be wound up and stored without any
problems.
[0311] In addition a shaped test sheet of this composition having a
thickness of 2 mm was exposed for 5 and 10 sec. to the irradiation
of a iron doped UV-lamp having a length of 10 cm and a power of 2
kW with a distance to the sheet of 4 cm. A hardness of 20.degree.
and 22.degree. Shore A was measured on a sheet of 3.times.2 mm, for
each 2 mm sheet the hardness was 33.degree./35.degree., which shows
that the composition can be cured after a irradiation time
reasonable for an extrusion operation.
Example 3
[0312] 100 parts per weight of a polydimethylsiloxane having 0.03
mol. % terminal vinyldimethylsiloxy units and 0.08 mol-%
vinylmethylsiloxy units and a viscosity of 20*10.sup.3 Pas at
25.degree. C. as component (i). The composition further comprises
29 parts per weight of a fumed silica having a BET-surface of ca.
200 m.sup.2/g, which has been treated with 6 wt.-% of
octamethylcyclotetrasiloxane as component (v), 1 part per weight of
an .alpha.,.omega.-dihydroxydimethylsiloxane having a content of
OH-groups of 6.5 wt.-% as component (vi).
[0313] All components (i), (v) and (vi) are admixed in a kneader at
50-65.degree. C. for 90 minutes and then for additional 15 minutes
together with 1.3 part per weight with a trimethylsiloxy-terminated
polyhydrogenmethyl-dimethylsiloxane as component (iii) having a
content of SiH-groups of 8.9 mmol/g and a viscosity of 45 mPas.
Subsequently the aforementioned composition is admixed for 10
minutes under exclusion of light or under `yellow` light with
.eta..sup.5-(methylcyclopentadienyl)-trimethyl-platinum according
to 4 ppm platinum calculated as metal related to the components (i)
to (iii) as component (iv). The total amount of the vinyl units in
the soluble components (i) to (iii) was 0.11 mol. % whereas the
total amount of the vicinal Si-vinyl groups calculated for the
composition (i) to (iii) was 0.00012 mol. %.
[0314] This composition was extruded through a die for shaping a
tube having an outer diameter of 5 mm and an inner diameter of 3 mm
at an extrusion rate of 2.4 m/min subsequently passed downstream a
mercury doped UV-lamp (one sided placed) having a length of 10 cm
and a power of 2 kW. A tube having the dimension of an outer
diameter 5 mm and an inner diameter 3 mm maintained its shape over
more than 1 min after the shaping process through the die if it is
not photoactivated or the catalyst is omitted.
[0315] After passing the UV-channel the extruded tube was almost
completely cured and could be stored without any problems.
Example 4
[0316] 100 parts per weight of a polydimethylsiloxane having 0.03
mol. % terminal vinyldimethylsiloxy units and 0.18 mol-%
vinylmethylsiloxy units and a viscosity of 16*10.sup.3 Pas at
25.degree. C. (P.sub.n=7500) as component (i). The composition
further comprises 45 parts per weight of a fumed silica having a
BET-surface of ca. 200 m.sup.2/g as component (v), 6.5 parts per
weight of .alpha.,.omega.-dihydroxydimethyl-siloxane having a
content of OH-groups of 7.5 wt.-% as component (vi) and 0.5 parts
per weight of hexamethyldisilazane as component (vi).
[0317] All components (i), (v) and (vi) are admixed in a kneader at
120.degree. C. for 90 minutes and then for additional 120 min at
160.degree. C. the volatiles were evaporated and externally
condensed.
[0318] After cooling down to 65.degree. C. the composition was
admixed together with 1 part per weight of a
trimethylsiloxy-terminated polyhydrogenmethyl-dimethylsiloxane as
component (iii) having a content of SiH-groups of 7.4 mmol/g and a
viscosity of 40 mPas for 15 minutes.
[0319] The aforementioned composition is admixed for 10 minutes
under exclusion of light or under `yellow` light with
.eta..sup.5-(methylcyclopentadienyl)-trimethyl-platinum according
to 4 ppm platinum calculated as metal related to the components (i)
to (iii).
[0320] The total amount of the vinyl units in the components (i) to
(iii) was 0.21 mol. % and the calculated total amount of the
vicinal Si-vinyl for the components (i) to (iii) soluble in
CDCl.sub.3 is 0.00044 mol. %.
[0321] The composition could be extruded under the same conditions
as those used in example 1. A continuously extruded tube could be
collected about 1 m after the irradiation channel. The transparent
elastomeric tube could be almost completely cured and could be
wound up and stored without any problems.
[0322] Also a shaped test sheet of this composition having a
thickness of 2 mm was exposed for 5, 10 and 120 sec. to the
irradiation of an iron doped UV-lamp having a length of 10 cm and a
power of 2 kW with a distance of 4 cm. A hardness of 36, 38 and
47.degree. Shore A was measured for a sheet of 3.times.2 mm, and
44, 45 and 51.degree. Shore A for each 2 mm sheet, which shows that
the composition can be cured after an irradiation time reasonable
for an extrusion operation.
[0323] The Mooney viscosity was measured to be
MI.sub.0/MI.sub.4=39/33 units.
[0324] When this material was placed in a lab extruder having srew
diameter of example 1 a tube with the dimension of example 1 could
be continuously shaped. The extrusion rate was 1.7 m/min. The
extruded tube exposed to the lamp of example 1 has almost no tacky
feeling. When the shaped tube was not photactivated after passing
the die or the catalyst (iv) is omitted then the shaped form after
the die could be maintained over more than 1 min.
Example 5
[0325] 85 parts per weight of a polydimethylsiloxane having 0.03
mol. % terminal vinyidimethylsiloxy units and 0.18 ml-%
vinylmethylsiloxy units and a viscosity of 16*10.sup.3 Pas at
25.degree. C. (P.sub.n 7500) and 15 parts per weight of a
polydimethylsiloxane having 0.035 mol. % terminal
vinyidimethylsiloxy units and 5.4 mol-% vinylmethyl-siloxy units
and a viscosity of 10*10.sup.3 Pas at 25.degree. C. (P.sub.n=6000),
both as component (i).
[0326] The composition further comprises 45 parts per weight of a
fumed silica having a BET-surface of ca. 200 m.sup.2/g as component
(v), 6.5 parts per weight of an
.alpha.,.omega.dihydroxydimethylsiloxane having a content of
OH-groups of 7.5 wt.-% as component (vi), and 0.5 parts per weight
of hexamethyldisilazane.
[0327] All components are admixed in a kneader at 120.degree. C.
for 90 minutes and then for additional 120 min at 160.degree. C.
the volatiles were evaporated and externally condensed.
[0328] After cooling down to 65.degree. C. the composition was
admixed together with 2.7 parts per weight of a
trimethylsiloxy-terminated polyhydrogenmethyl-dimethylsiloxane as
component (iii) having a content of SiH-groups of 7.4 mmol/g and a
viscosity of 40 mPas for 15 minutes.
[0329] The aforementioned composition is admixed for 10 minutes
under exclusion of light or under `yellow` light with
.eta..sup.5-(methylcyclopentadienyl)-trimethyl-platinum according
to 4 ppm platinum calculated as metal related to the components (i)
to (iii).
[0330] The total amount of the vinyl units in the components (i) to
(iii) was 0.99 mol.-% and the total amount of the vicinal Si-vinyl
groups for the components (i) to (iii) was calculated to be 0.045
mol. % as sum of the weighted individual concentrations in each of
the polymers in the mixture of component (i) to (iii).
[0331] A shaped test sheet of this composition having a thickness
of 2 mm was exposed for 60 sec. to the irradiation of an iron doped
UV-lamp having a length of 10 cm and a power of 2 kW. The article
is cured to a certain extent but the hardness could not be measured
in a satisfactory manner according to a standard method.
[0332] In a second run the irradiation time was extended to 150
sec, the tube appears to be more elastic than after 60 sec but it
has not been fully cured.
[0333] This example shows that the degree of cross-linking achieved
for a certain period of irradiation depends on the content of the
vicinal alkenyl groups. Accordingly a lower content of vicinal
alkenyl groups is preferred in order to reduce irradiation time
required for cross-linking in the extrusion line.
Example 6
[0334] Example 1 was repeated with a modified concentration level
of the catalyst (iv), which is now adjusted to 8 ppm platinum
related to the components (i) to (iii). The composition was
extruded to a tube having the dimension of an outer diameter of 10
mm and an inner diameter of 3 mm (0.375/0.125 inches) using a
single screw extruder having an L/D of 10.5:1, srew diameter 6.35
cm (2.5 inch) compression rate/progression of 2.6:1, and a belt
speed of 4 m/min (13 ft/min) while passing a 15.2 cm (6 inch) iron
halide lamp having a power of 2.82 kW (0.47 kW per inch).
[0335] The extrudate is already cured to a certain extent but is
still a little bit tacky.
Example 7
[0336] The example 6 was repeated with a modified concentration
level of the catalyst (iv) which is now adjusted to 16 ppm Pt. The
composition was shaped to a tube having the dimension of an outer
diameter of 16 mm and an inner diameter of 3 mm (0.625/0.125
inches) and a belt speed of 7 m/min (23 ft/min) while passing a
15.2 cm (6 inch) iron halide lamp having a power of 0.47 kW per
inch.
[0337] The extrudate is almost completely cured having a hardness
of 46.degree. Shore A, with no tackiness of the surface.
Example 8
Comparative
[0338] The composition of example 4 was mixed again wherein the
polydimethyl-siloxane (i) having terminal vinyldimethylsiloxy and
vinylmethylsiloxy units was replaced by a polydimethylsiloxanes
having a viscosity of 1 kPas at 25.degree. C. and an average number
of siloxy units of 2500.
[0339] When this material was placed in lab extruder of example 1
for shaping a tube with dimension of example 1 then an extrusion
rate of 2.1 m/min at 24 RPM could be achieved.
[0340] But the form of the tube not photoactivated could not be
maintained, the tube collapsed 1 cm after the shaping die of the
extruder to a flat strand, corresponding to not more than 2 sec
after passing the shaping die. The Mooney viscosity was measured to
be MI.sub.4=19 units.
[0341] The surface of the non-cured tube is tackier than that of
the non-cured tube of example 4 or 2. The example shows that
polymer (i) for continuous shaping process must have a minimum
viscosity i.e. chain length to maintain the shaped form during the
curing process.
* * * * *