Note: Descriptions are shown in the official language in which they were submitted.
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PARTING AGENT
FIELD OF THE INVENTION
This invention relates to a filler-free parting agent comprising an aqueous
emulsion
which contains silicone systems which react with each other and which contains
a
silica sol, and which in addition imparts good sliding properties to the
surface which
is treated. The parting agent is particularly suitable as a parting agent for
the produc
tion of tires and of other rubber articles, and is used during the molding and
vulcani
zation of said articles.
BACKGROUND OF THE INVENTION
According to the prior art, tires are molded and vulcanized by inserting the
tire blank
in a mold and pressing it against the mold using a heating membrane (bladder
or
blister membrane), whereupon it is vulcanized by the effect of heat. The
heating
membrane has to slide within the blank and has to be separable from the tire
after
vulcanization. The tire blanks are therefore introduced into a spray booth in
which
they are set in rotation by means of a mechanical device. A spray gun with
which a
solution of a parting agent is distributed inside the blanks is introduced
into said ro-
tating blanks. The overspray is mostly removed via a water curtain and is
taken up in
the water. This is followed by the molding and vulcanization of the blank in a
vul-
canization press by means of the heating membrane, the function of which is to
heat
the tire blank and to press the tire under a high pressure into the negative
mold.
Aqueous organopolysiloxane emulsions and the use thereof as parting agents in
tire
molding and vulcanization operations are known from the prior art. US-
4,184,880
describes parting agent emulsions, which, however, contain quite large amounts
of
inorganic silicates as fillers which have been treated with organosilicon
compounds
~0~-, in order to render their surface hydrophobic.
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US-4,431,452 describes an aqueous parting agent composition consisting of:
1) a polydimethylsiloxane which comprises SiOH terminal groups and which
has a viscosity of up to 25,000,000 centistokes at 25°C;
2) a polydimethylsiloxane which comprises SiOH terminal groups and which
has a viscosity of up to 120,000 centistokes at 25°C;
3) a polyalkylene glycol;
4) a bentonite clay; and
5) a surface-active agent.
US -x,359,340 describes aqueous parting agent preparations for use in tire
molding.
These emulsions consist of:
1) a polydimethylsiloxane with a viscosity of up to 25,000,000 centistokes at
25°C;
2) a methyl hydrogen silane with a viscosity of 20 to 40 centistokes or a di-
methyl hydrogen silane with a viscosity of 80 to 120 centistokes;
3) a metal salt of an organic acid, and
4) a surface-active agent.
EP-A-0,279,372 describes aqueous organopolysiloxane emulsions which can be
used
as parting agents in tire molding and vulcanization, particularly for coating
the blad
der, and which are composed of:
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1) a polydimethylsiloxane polymer which comprises SiOH terminal groups and
which has a plasticity of 50 to 100;
2) an organohydrogen polysiloxane comprising at least 2 Si-bonded hydrogen
atoms per molecule;
3) a lubricant with a melting point of 25 to 80°C;
4) an inorganic silicate (mica);
5) a thickener;
6) a surface-active agent; and
7) water.
The disadvantages of the aqueous parting agent compositions which have been de-
scribed hitherto are first, they contain relatively large amounts of inorganic
silicates
as fillers, which have a negative effect on the stability of the emulsion, and
second,
they crosslink via the reaction of an SiOH group with SiH, with the separation
of
hydrogen; this is undesirable due to the risk of an explosion.
EP-A-0,635,559 describes a parting agent composition for tire molding, which
acts
without this unwanted generation of hydrogen. The emulsion described is used
for
coating the bladder, and consists of
1) at least one non-reactive polydimethylsiloxane which has a kinematic viscos-
ity between 50 and 30,000,000 mm sec' at 25°C;
2) at least one reactive polydimethylsiloxane which has a kinematic viscosity
between 15 and 5,000,000 mm sec';
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3) a crosslinking agent;
4) a surface-active agent; and
5) water.
EP-A-0,111,100 describes a silicone-based parting agent for tire production,
which is
not only dissolved in an organic solvent and has to be used thus, but which
also has
to contain kaolin, chalk, powdered rock, hydrated silicas, carbon black or
graphite, if
the heating membrane does not already have a roughness from the outset which
is
sufficient to ensure the satisfactory escape of air.
A satisfactory sliding and parting effect can be achieved with lubricants
alone, e.g.
silicone oils or silicone oil emulsions, but total "de-airing", i.e. the
escape of air be-
tween the bladder and the tire blank, cannot, unfortunately, be achieved.
Air, included between the bladder and the tire blank means reject tires, since
satis-
factory vulcanization does not occur under the air bubble.
Fillers (mineral fillers or other types) are required as spacers between the
bladder and
the tire blank, so that air can escape before vulcanization.
It has not been possible, mainly on account of the need for de-airing, to
employ filler-
free inner solutions consisting of combinations of lubricants or parting
agents only.
Fillers perform the function of a spacer between the bladder and the inner
liner of the
tire blank.
The use of conventional silicone oils has hitherto resulted in troublesome
separation
phenomena at the tire faces.
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SUMMARY OF THE INVENTION
There is accordingly a need, as before, for an aqueous, solvent-free parting
agent,
which can be sprayed on to the inside of the tire blank and/or on to the
surface of the
bladder, which parting agent fulfils all the requirements for vulcanization,
namely
sliding, separation and de-airing, and which at the same time does not exhibit
the
disadvantages described above, such as a content of fillers and/or
crosslinking with
the separation of hydrogen. In addition, separation phenomena at the tire
faces
should be prevented.
The present invention relates to parting agents comprising, in an aqueous
emulsion,
- a system consisting of at least two silicone components which react with
each
other with crosslinking, said system being selected from the group consisting
of
(A) silicone components which react with each other by condensation, or
(B) silicone components which react with each other by addition, and
- an aqueous colloidal hydrated silica (silica sol).
Accordingly, the present invention also relates to a process for vulcanizing
pneu-
matic tires, which is characterized in that the parting agent composition
according to
the invention is applied to the bladder and/or to the tire surface before
vulcanization.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the invention is extremely environmentally friendly,
since it
employs only 10 % of the effective solids content of the parting substances
used in
conventional, prior art processes and is accordingly more economical as a
whole.
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The silicone systems (A) and (B) according to the invention, which react with
crosslinking, comprise mixtures of emulsions of silicone components (A) which
react
(crosslink) with each other by condensation or mixtures of emulsions of
silicone
components (B) which react (crosslink) with each other by addition, and are de-
scribed in detail below. Both these reaction systems are catalyzed by suitable
cata-
lysts.
A. Silicone systems which crosslink with each other by condensation
These systems are mixtures of aqueous emulsions of polydimethyl-siloxanes (A-
1)
which comprise SiOH terminal groups, and of alkoxy-functional silicones (A-2).
The emulsion of the polydimethylsiloxane (A-1) which comprises SiOH terminal
groups contains the siloxane in an amount of 20 to 80 % by weight, preferably
30 to
60 % by weight, with respect to emulsion A-1.
The emulsion of the alkoxy-functional silicone (A-2) which is capable of
crosslink-
ing contains the siloxane in an amount of 20 to 80 % by weight, preferably 25
to 60
by weight, with respect to emulsion A-2.
The two emulsions are mixed with each other in a quantitative ratio of A-1 to
A-2
which ranges from 20:80 to 80:20, preferably from 40:60 to 60:40. Both
emulsions,
of course, contain suitable emulsifiers as determined by the manner in which
they are
produced.
Emulsion A, which is produced from emulsion A-1 and emulsion A-2, contains 20
to
80 % by weight, preferably 30 to 60 % by weight, of silicone with respect to
emul-
sion A.
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A-1: Emulsions of polydimethylsiloxanes which comprise SiOH terminal groups:
The polydimethylsiloxanes which comprise SiOH terminal groups are polymers of
general formula I
HO[Si(CH3)2-O]PH (I)
where p = 400 to 3000, preferably 800 to 2000.
The production of emulsions of long chain silicone oils which comprise SiOH
termi-
nal groups by emulsion polymerization is known to one skilled in the art from
US--
2,891,920 or GB-A-1,024,024, for example. The process disclosed in GB-A-
1,024,024, which employs an alkyl-benzenesulphonic acid as a catalyst, is most
pref
erably used, since the emulsifier and polymerization catalyst are present as
one sub-
stance here. After polymerization is complete, the acid is neutralized, so
that the
catalyst properties are subsequently blocked whilst the emulsifier properties
are
completely retained or are even enhanced. Accordingly, the concentration of
emulsi-
fier can be kept low, and after production of the emulsion is complete there
are no
troublesome extraneous molecules from the catalyst in the finished product. N-
alkyl-
sulphonic acids can also be used instead of the aforementioned alkyl-
benzenesul-
phonic acids. It is also possible to use other emulsifiers as co-emulsifiers
in addition
to the catalytically active sulphonic acid.
Co-emulsifiers of this type can be either of a non-ionic nature or of an
anionic nature.
Suitable anionic co-emulsifiers include salts of the aforementioned n-alkyl-
or alkyl-
benzenesulphonic acids. Non-ionogenic co-emulsifiers are polyoxyethylene
deriva-
tives of fatty alcohols, fatty acids and the like. Examples of emulsifiers of
this type
include POE (3)-lauryl alcohol, POE (20)-oleyl alcohol, POE (7)-nonylphenol
and
POE (10)-stearate (the nomenclature POE (3)-lauryl alcohol means that 3 units
of
ethylene oxide have been added to one molecule of lauryl alcohol, with the
number 3
constituting an average value). Non-ionogenic emulsifiers of this type are
familiar in
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principle to one skilled in the art. These added co-emulsifiers firstly
increase the sta-
bility of the emulsion which results after emulsion polymerization, and
secondly they
simultaneously have an effect on the chain length of the long chain silicone
oil which
comprises SiOH terminal groups and which is formed by the polymerization
process.
In general, silicone oils such as these, which are formed by emulsion
polymerization
in the presence of non-ionogenic co-emulsifiers, have lower molecular weights
than
those for which no co-emulsifier was used. The molecular weight of a silicone
oil
which comprises SiOH terminal groups and which is formed by emulsion polymeri-
zation can also be controlled via the temperature at which equilibrium occurs
be-
tween the siloxane, water and the silanol which is first formed by ring
opening of the
siloxane.
The process described below is particularly preferred for the production of an
emul-
sion of a long chain silicone oil which comprises OH terminal groups.
Octamethylcyclotetrasiloxane (D 4) is used as the monomer, in an amount such
that a
40 % emulsion is formed. The sulphonic acid which acts as a catalyst for the
emul-
sion polymerization is an n-alkylsulphonic acid. 4 % of this sulphonic acid is
used
with respect to the amount of D 4. The Na salt of the sulphonic acid which is
used as
the catalyst, as well as POE (5)-lauryl alcohol, are employed as co-
emulsifiers. The
temperature during emulsion polymerization is 60°C, and neutralization
is effected
with triethanolamine.
One particularly preferred emulsion of a polydimethylsiloxane which is blocked
by
terminal groups is a 40 % by weight emulsion of a polydimethylsiloxane of
formula
I, wherein p is between 800 and 2000.
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A-2: Emulsions of alkoxy-functional silicone oils:
The silicone oil which is contained in emulsion A-2 according to the
invention, and
which is capable of crosslinking, consists of units which have the general
structure
R"R'mSiO(4_"_m)2 (11)
wherein
R denotes identical or different hydrocarbon radicals or hydrocarbon oxyradi-
cals, which are optionally substituted and which each comprise 1 to 18 carbon
atoms,
R' denotes identical or different Si-C-bonded, substituted hydrocarbon
radicals
which contain polar groups,
n is an integer with a value of 0, 1, 2 or 3, and
m is an integer with a value of 0, 1, 2 or 3,
wherein the sum of n + m has an average value from 1.8 to 2.2, and m is
selected so
that the polyorganosiloxane comprises at least one R' radical.
Preferably, the sum of n + m has an average value from 1.9 to 2.1. Examples of
hy-
drocarbon radicals R include alkyl radicals such as methyl, ethyl, n-propyl,
iso-
propyl, n-butyl, iso-butyl, tert.-butyl, n-pentyl, iso-pentyl, neopentyl or
tert.-pentyl
radicals; hexyl radicals such as the n-hexyl radical; heptyl radicals, such as
the n-
heptyl radical; octyl radicals such as the n-octyl radical and iso-octyl
radicals such as
the 2,2,4-tri-methylpentyl radical; nonyl radicals such as the n-nonyl
radical; decyl
radicals such as the n-decyl radical; dodecyl radicals, such as the n-dodecyl
radical;
octadecyl radicals such as the n-octadecyl radical; alkenyl radicals such as
vinyl, allyl
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and 5-hexen-1-yl radicals; cycloalkyl radicals. such as cyclopentyl,
cyclohexyl and
cycloheptyl radicals and methylcyclohexyl radicals; aryl radicals such as
phenyl,
naphthyl, anthryl and phenanthryl radicals; alkaryl radicals such as o-, m- or
p-tolyl
radicals, xylyl radicals and ethylphenyl radicals; and aralkyl radicals, such
as benzyl
radicals and alpha- and (3-phenylethyl radicals.
Examples of hydrocarbon oxyradicals R, which may optionally be substituted, in-
chide substituted and unsubstituted hydrocarbon radicals R according to the
afore-
mentioned examples which are bonded via an oxygen atom which is directly
bonded
to a silicon atom, particularly alkoxy radicals comprising 1 to 1 8 carbon
atoms and
phenoxy radicals, especially methoxy, ethoxy, n-propoxy, iso-propoxy and
phenoxy
radicals. It is preferred that 10 % at most of the radicals R are hydrocarbon
oxyradi-
cats which are optionally substituted.
The radicals R are preferably methyl, ethyl, phenyl, methoxy and/or vinyl
radicals.
On account of their more ready accessibility, 50 % the radicals R,
particularly at
least 80 % of the radicals R, are preferably methyl radicals.
R' can be selected from the group comprising the radicals R. R' is preferably
selected
from the group comprising amino-functional hydrocarbon radicals, for example
aminoalkyl radicals, such as the 'y-aminopropyl radical and the (3-aminoethyl-
y-
aminopropyl radical; aminoaryl radicals; or Si-C-bonded, cyclic amino-
functional
radicals.
Examples of preferred amino-functional radicals R' include radicals of general
for-
mula
-R'-[NRZ(CHZ)a]bNHR2 (III)
wherein
RI denotes a divalent C~ to C~g hydrocarbon radical,
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RZ denotes a hydrogen atom or a C, to C,g hydrocarbon radical which is option-
ally substituted,
a has the value 2, 3, 4, S or 6, and
b has the value 0, 1, 2, 3 or 4.
Examples of the divalent C, to C,g hydrocarbon radicals RI include saturated
straight-chain, branched-chain or cyclic alkylene radicals such as methylene
and
ethylene radicals, as well as propylene, butylene, pentylene, hexylene, 2-
methylpropylene, cyclohexylene and octadecylene radicals, or unsaturated
alkylene
or arylene radicals such as hexenyl radicals and phenylene radicals, wherein
the n-
propylene radical and the 2-methyl-propylene radical are particularly
preferred.
The examples given for R constitute examples of C, to C,g hydrocarbon radicals
RZ
which are optionally substituted.
The meanings of the constituents of the above general formula (III) are
preferably as
follows:
R' denotes a divalent CZ to C6 hydrocarbon radical,
RZ denotes a hydrogen atom, or a methyl or cyclohexyl radical,
a denotes the values 2 or 3, and
b denotes the values 0 or 1.
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Silicones which are capable of crosslinking and which also contain amino
groups,
and which are particularly preferred, are partially branched
polydimethylsiloxanes of
structure
O(SiMe2)xOR"
R'-Si-O(SiMe2)XOR"
O(SiMez)XOR"
where R' = HZN(CHz)zNH(CHZ)3- or HzN(CHZ)3-
i Hs
and where R" = CZHS or -C-CHZNHZ
H
and where Me = CH3, x=20 to 200.
Reference is made to EP-A-0,646,618 for the production of compounds of this
type
and of suitable emulsifiers.
In addition, the emulsion which contains the alkoxyfunctional silicone which
is
capable of crosslinking may also contain 2 to 20 % by weight, preferably 5 to
15
by weight, of an alkoxy-functional silicone resin of formula V
R3dSi(OR4)eO~a-a-e~z (V)
wherein
R3 is a monovalent hydrocarbon radical comprising 1 to 14 C atoms, preferably
a
methyl radical,
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R4 is a monovalent hydrocarbon radical comprising 1 to 18 C atoms, preferably
a
methyl radical,
d has a value from 0.75 to 1.5, preferably of about 1, and
a has a value from 0.2 to 2, preferably from 0.4 to 1.2.
The viscosity of this resin ranges from 2 to 2000 mPa.s, preferably from 20 to
200
mPa. s.
The production of these alkoxy-functional silicone resins is known and is
effected by
the reaction of corresponding alkyl- and/or arylchlorosilanes with alcohol and
water
(see GB-A-685,173, DE-A-958,702, FR-A-1,475,709, US-3,668,180, DE-A-
2,061,189, DE-A-2,444,529, DE-A-2,532,887, EP-A-0,003,610 and DE-A-
3,000,782, for example).
The most preferred methyl-methoxy silicone resin is produced by the reaction
of
methyltrichlorosilanes with methanol and water. Mixtures of
methyltrichlorosilane
and other alkyl- and/or arylchlorosilanes and/or tetrachlorosilanes can also
optionally
be used for the production of the alkoxy-functional silicone resins, without
impairing
the stability of the emulsion according to the invention. Mixtures of
different alcohols
can also be used for the production of the resin and/or different alkoxy-
functional
silicone resins can be mixed with each other without impairing the stability
of the
emulsion.
The preparation of emulsions of the alkoxy-functional silicone resins
described above
is known from DE-A- 3,323,909.
Suitable catalytically active substances (catalyst emulsions) for the
crosslinking re-
action between the polydimethylsiloxanes which comprise terminal Si-OH groups
and the amino-functional silicones in the emulsion are those which are
described in
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the known literature for condensation and esterification reactions. The
catalysts are
used in the customary concentrations which are described in said literature.
B. Silicone systems which crosslink with each other by addition
These systems constitute an emulsion B which comprises a mixture of an
emulsion
which contains an organopolysiloxane B-1 comprising at least two unsaturated
hy-
drocarbon groups, and an emulsion which contains a methyl hydrogen
polysiloxane
B-2 in addition to a catalyst.
Emulsion B, which is produced from emulsions B-1 and B-2, contains 20 to 80 %
by
weight, preferably 30 to 60 % by weight, of silicone with respect to emulsion
B.
The organopolysiloxane B-1 which comprises at least two unsaturated
hydrocarbon
groups in the sense of the invention is preferably a cyclic, linear or
branched poly-
siloxane which contains units of general formula
(RS)~R6)hSlO~4_f_h)/2
where RS = CZ-Cg alkenyl and/or unsaturated C3-C,° ether radicals, such
as vinyl,
allyl, 1-butenyl, 1-hexenyl and/or -CHZ-CHZCHZOCHzCH = CHz, etc.,
R6 = a monovalent, saturated hydrocarbon radical which is optionally
substituted and
which comprises up to 10 carbon atoms, from the group comprising substituted
and
unsubstituted alkyl, aryl and arylalkyl radicals, wherein
f and h are integers within the following limits: 0<_f<_3 or 0<_h<3 and
0<f+h<_4 and
each individual RS or R6 within the molecule can be identical or different.
RS is preferably vinyl or allyl, most preferably vinyl.
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Examples of R6 include methyl, ethyl, propyl, isopropyl, butyl, octyl, etc.,
cyclo-
butyl, cyclopentyl, cyclohexyl, etc., phenyl, tolyl, xylyl, naphthyl, etc.,
benzyl, phen-
ylethyl and phenylpropyl. In one embodiment of the invention, some or all of
the
hydrogen atoms of the R6 alkyl, aryl, and arylalkyl radicals are replaced by
fluorine,
chlorine, bromine or iodine atoms and/or by cyano radicals. In this situation,
for ex-
alnple, R6 corresponds to chloromethyl-, trifluoropropyl, chlorophenyl,
dibromo-
phenyl-, (3-cyanoethyl, ~3-cyanopropyl or y-cyanopropyl radicals. At least 90%
of the
R6 radicals are preferably methyl, however.
In one preferred embodiment of the invention, f equals 0 or 1.
Using nomenclature which is familiar to one skilled in the art, namely
M = (CH3)3'510,/2
D = (CH3)zSlOZ~2
T = (CH3)Si03,z
M"' _ (CHZ CH)(CH3)ZSiO"Z, and
D"' _ (CHZ CH) (CH3)SiOz,z, the following examples of component B-1 can be
given:
MzDiooD"~3~ M"~zD~ao~ Mv'11D1ooDvi3~ TsDssoM'~~~ T3DsooM~zMs and/or
T6DsooD"'M4M"'4.
The molar proportion of unsaturated radicals of type RS can be selected
arbitrarily.
In component B-l, the molar proportion of unsaturated radicals of type R
should pref
erably be between 0.01 and 10 mmole/g, more preferably between 0.05 and
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1 mmole/g, and most preferably 0.1 to 0.7 mmole/g of component B-1. The
viscosity
of component B-1 is preferably between 10 and 100,000 mPa.s, most preferably
50-10,000 mPa.s, at 25°C.
In one preferred embodiment of the invention, the organopolysiloxanes
described in
DE-A-43 28 657 are used as component B-1, since these are branched, the ratio
of
the number of diorganosiloxy units (D units) to the number of branching
locations is
between 15 and 40 on average there, at least one triorganosiloxy unit (M unit)
and a
maximum of half of all the M units are free from unsaturated radicals there
and the
remaining M units only comprise one unsaturated radical, and the content of
unsatu-
rated radicals ranges from 0.1 to 1 mmole/g.
The branching locations of component B-1 are preferably monoorganosiloxy
units,
i.e. tri-functional siloxy units (T units), which, however, can also be
replaced in part
by tetra-functional siloxy units (SiO4,z units, Q units).
The terminal groups of the branched organopolysiloxane which are free from
unsatu-
rated radicals perform the function of an internal plasticizer. The
flexibility of the
crosslinked film can be controlled via the number terminal groups which are
free
from unsaturated radicals (M units).
Examples of compounds which are preferred as component B-1 are compounds of
formulae
TsDzooM~sMz~ T~DzaoM~~sMa~
T6D~soD°~ZM"~4M4 and/or TBDZSOM"~7M3.
Branched organopolysiloxanes B-1 which comprise at least two unsaturated hydro-
carbon groups can be produced by customary methods, such as the hydrolysis of
chlorosilanes and subsequent polymerization with low molecular weight cyclic
dior-
ganopolysiloxanes.
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The methyl hydrogen polysiloxane B-2 preferably contains units of general
formula
H~(R')kSlO~4 ~_ky2 (VII)
where R' = monovalent, saturated hydrocarbon radicals, which are optionally
substi-
tuted and which comprise up to 10 carbon atoms, from the group comprising
substi-
tuted and unsubstituted alkyl, aryl, arylalkyl and/or CZ-C8 alkenyl radicals,
wherein
j and k are integers, where 0 <_ k 5 3, 0 <_ j <_ 2 and 0 S j+k <_ 4,
preferably 0 5 j < 1.
The methyl hydrogen polysiloxanes B-2 are preferably linear. At least half the
D
units preferably comprise hydrogen atoms which are directly bonded to silicon
(H(CH3)Si0 groups). The number of groups comprising hydrogen atoms which are
directly bonded to silicon is preferably between 70 and 85 % of the di-
functional
units.
Within the scope of the aforementioned structural limitations, the molar
proportion of
hydrogen atoms which are directly bonded to a silicon atom in component B-2
can be
selected arbitrarily.
In component B-2, the molar proportion of hydrogen atoms which are directly
bonded to a silicon atom is preferably between 0.01 and 17 mmole, more
preferably
between 0.1 and 17 mmole and most preferably between 1 and 17 mmole/g compo-
nent B-2.
Examples of component B-2 include compounds of formulae
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H H H H
M zD~o~ MzD~oD ~o~ M zD zoD~o~
M"'zD 11 and/or MZD"'3DH8, where
MH = H(CH3)zSiO"z and
DH = H(CH3)SiOz,z.
Components B-1 and B-2 are preferably present in aqueous emulsion B in a
quantita-
tive ratio such that the molar ratio of hydrogen atoms which are directly
bonded to a
silicon atom (SiH) in component B-2 to the unsaturated radicals (Si-vinyl) in
com-
ponent B-1 is between 0.05 and 20, more preferably between 0.5 and 10 and most
preferably between 1 and 3.
In addition, emulsion B may also contain an organopolysiloxane which comprises
units of general formula
(R')rSi0~4_r~, z (VIII),
wherein
R' represents monovalent, hydrocarbon radicals which are optionally
substituted and
which comprise up to 10 carbon atoms, from the group comprising substituted
and
unsubstituted alkyl, aryl, and arylalkyl radicals, and which can be the same
or differ-
ent within the molecule, and wherein r can assume the value of integers
between 0
and 3.
The preferred organopolysiloxane is a linear polydimethylsiloxane which
comprises
trimethylsiloxy terminal groups, such as that sold by Bayer AG under the
description
Baysilone~-Ole M, for example. The use of Baysilone~-Ole M such as these which
have a viscosity between 50 mmzsec' and 5000 mmzsec' is particularly
preferred.
Emulsion B also contains a catalyst from the platinum group, preferably the
elements
platinum, rhodium, iridium, nickel, ruthenium and/or palladium, in elemental
form,
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on a support or in the form of compounds thereof. Platinum compounds or
platinum
complexes are preferred, such as HZPtCIb, platinum-olefine complexes, platinum-
al-
cohol complexes, platinum-vinylsiloxane complexes or even elemental platinum
on a
support substance, such as activated carbon, A1203 or Si02. A platinum-
vinylsiloxane
complex is particularly preferred as the catalyst. Said platinum-vinylsiloxane
com-
plexes preferably have at least 2 olefinically unsaturated double bonds in the
siloxane
entity. They are described in US-3,715,334, for example.
The term siloxanes includes polysiloxanes, i.e. it also includes
vinylpolysiloxanes.
The proportion of catalyst with respect to the sum of all the constituents is
preferably
between l and 1000 ppm, more preferably between 1 and 500 ppm and most prefer-
ably between 25 and 250 ppm.
A catalyst from the platinum group can also be pre-dissolved in part of
polymer B-1,
for example.
Emulsion B may also contain an inhibitor, suitable emulsifiers, thickeners
and/or
customary additives and adjuvant substances (but no fillers). Reference is
made to
EP-A-0,819,735 for the production of emulsion B
Aqueous colloidal hydrated silica
The aqueous colloidal hydrated silica (silica sol) is an aqueous colloid
containing 15
to 40 % by weight, preferably 25 to 35 % by weight, of hydrated silica with an
aver-
age particle diameter of 6 to 50 nm, preferably 7 to 15 nm. Colloidal hydrated
silica
systems of this type are known to one skilled in the art from the literature
and are
commercially available.
The aqueous parting agent emulsion according to the invention contains 5 to 35
% by
weight, preferably 8 to 24 % by weight, of silicone emulsion A or B as
described
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above, as well as 0.5 to 5 % by weight, preferably 0.8 to 4 % by weight, of
aqueous
colloidal hydrated silica as described above, with respect to the total
emulsion.
The total silicone content in the parting agent according to the invention
ranges from
2 to 20 % by weight, preferably 5 to 15 % by weight, with respect to the
parting
agent.
The emulsion according to the invention may additionally contain,
independently of
each other, germ prevention agents, rot prevention agents (bactericides),
additional
wetting agents, thickeners, stabilizers, additional emulsifiers, anti-foaming
agents,
corrosion inhibitors and colorants, preferably organic colorants and
particularly col-
orants which can be activated by UV light.
In particular, the emulsion according to the invention may contain
~ 0.01 to 0.1 % by weight, preferably 0.03 to 0.06 % by weight, of customary
germ
prevention agents,
~ 0.1 to 1 % by weight, preferably 0.3 to 0.7 % by weight, of
thickeners/stabilizers,
particularly polysaccharides,
~ 0.1 to 2 % by weight, preferably 0.3 to 0.6 % by weight, of wetting agents,
pref
erably non-ionic wetting agents, which give rise to a homogeneous distribution
(spray pattern) when surfaces are sprayed, due to the improved wetting
thereof,
~ 0.5 to 4 % by weight, preferably 0.8 to 2 % by weight, of polyethylene
waxes,
particularly hard polyethylene waxes having an average particle size of 1 to 9
~m
and a melting point between 90 and 110°C,
~ 0.1 to 4 % by weight, preferably 0.3 to 2 % by weight, of
polytetrafluoroethylene
micro-powders (waxes) which are known from DE-A-4,024,565, for example and
which have a molecular weight between 30000 and 200,000 and an average parti-
cle size of 1 to 20 Vim.
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The parting agent emulsions according to the invention can be mixed together
from
the respective individual components by customary methods known to one skilled
in
the art.
The emulsion as used has a viscosity (DIN 53211, 4 mm Ford Cup) of 20 to 80
sec-
onds, preferably of 30 to 60 seconds.
The composition according to the invention is preferably used as a parting
agent for
vulcanization. In this application, the parting agent is sprayed on to the
bladder
(heating membrane) and/or on to the inner liner of the tire blank before the
bladder is
inserted in the interior of the (green) tire blank. The amount of parting
agent which is
deposited is between 8 and 50 g/mz, preferably between 11 and 25 g/mz of the
surface
which is sprayed. The requisite amount of sprayed-on parting agent for a
conven-
tional private car tire is 6 to 40 g, preferably 8 to 18 g.
The bladder is subsequently inserted in the tire. The heating membrane heats
the tire
blank and simultaneously presses it, under high pressure, into the negative
mold,
where it is vulcanized. The bladder is then removed from the tire again.
The use of the composition according to the invention as a parting agent in
the proc-
ess described above for the vulcanization of tires has the advantages that not
only can
the bladder easily be inserted in and subsequently removed again from the tire
blank,
but also that air escapes completely from the intermediate space between the
bladder
and the tire inner liner, due to the formation of fine fissures in the semi-
elastic coat-
ing which is formed. Included air means reject tires, since satisfactory
vulcanization
does not take place under an air bubble. Moreover, the bladder can be
separated from
the vulcanized tire without problems. Furthermore, if a variable spraying
technique is
used with the parting agent compositions according to the invention it is
possible that
each tyre does not have to be sprayed. Due to the use of silicone components
which
crosslink under vulcanization conditions, separation phenomena at the tire
faces can
be eliminated. In addition, part of the coating is formed on the bladder and
has a
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positive effect on bladder life. It is also possible to apply an additional
coating to new
bladders, in order to facilitate the start of new bladders in the press.
As a whole, the use of the parting agents according to the invention can not
only im-
prove the quality of tires and the tire reject rate, but can also drastically
reduce both
the cost per tire and the amount of contaminants (soiling of the production
installa-
tion/reduction of waste), as a direct consequence of the smaller amount of
spray so-
lutions which are used.
The invention is explained in more detail by the following examples.
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EXAMPLES
Example 1 : (Prior art parting agent composition - aqueous dispersions of a
tire
inner spray solution).
Silicone oil emulsions: % by weight
Silicone oil, viscosity (1-1000 m2/s)
100 - 100,000 cSt 5-15%
Fillers:
carbon black 1-2%
mica, French chalk, etc. 20 - 40
Glycols, wetting agents 10 - 20
Water balance
Amount sprayed on per private
car tire blank 16 - 30 g
22 g on average of a prior art aqueous inner spray solution containing about
40 - 60
of active ingredient (all the constituents apart from water) were uniformly
sprayed
into a private car tire blank. This corresponded to about 11 g of active
ingredients per
private car tire. Subtracting the amount of overspray of about 25 - 30 % which
did
not reach the tire blank leaves a remainder of about 8 g of active ingredients
per pri
vate car tire. The individual constituents, which are given below in the form
of a
Table in g/private car tire, fulfil the following requirements:
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Molding Demolding
Active ingredi-g/private Sliding De-airingParting Bladder
car ef
ents tire blank effect fect/slidingservice
ef life
fect
Silicone about 0.96 X X X
oil
Glycols about 1.44 X X X
+surfactants
Mineral about 5.6 X
fillers
+ carbon
blacks
Total about 8.0
The following components were used in the experiments detailed below:
Propel~ GXL is a bactericide (a commercial product of ICI).
Kelzon~ D is a polysaccharide which acts as a thickener and stabilizer (a
commercial
product of Langer & Co.).
Levasil~ 200A30 (a commercial product of Bayer AG) is a silica sol which
contains
30 % by weight SiOz and which has a specific surface of 200 m2/g. Its particle
size
ranges from 7 to 15 nm. Levasil~ 200A30 promotes better curing of the
formulation
and on dilation contributes to the formation of fissures in the coating, which
in turn
has a positive effect on de-airing.
Lanco~ Wachs PEW 1555 (a commercial product of Langer & Co.) is a hard poly-
ethylene wax with an average particle size of 2.5 ~m and a melting point of
102°C.
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Rewopal~ LA 6 (a commercial product of Rewo) is a non-ionic wetting agent
which
results in a homogeneous distribution (spray pattern) on spraying due to
improved
wetting of the inner liner compound.
Oil emulsion 1 (see Example 2) is Baysilon~ N (Bayer AG)
Oil emulsion 2 (see Example 3) is Baysilon~ VP AI 3632 (Bayer AG)
Oil emulsion 3 (see Example 3) is Baysilon~ VP AI 3628 Z 343 (Bayer AG)
Oil emulsion 4 (see Example 3) is Baysilon~ VP AI 3629 Z 344 (Bayer AG)
Example 2: Experiment using the condensation crosslinking system
Constituents % by weight
ater 83 .10
roxel~ CXI 0.05
(germ prevention agent)
elzan~ D 0.45
(thickener)
ewopal~ LA 6 0.40
(emulsifier)
il emulsion 1 6.50
il emulsion 2 6.50
anco~ PEW 1 S55 1.00
evasil~' 200 A 30 2.00
In experiments with the composition according to Example 2, about 13 g of
product
were sprayed on. The content of active ingredients (percentage of all the
constituents
in the composition apart from water) was about 10 %. If the amount of
overspray of
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about 25 - 30% is taken into account, there remained about 1.0 g of active
ingredi-
ents/tire blank.
Molding Demolding
Active g/privateSliding De-air- Parting Bladder
in- car tire effect ing ef durability
gredients blank fect/sliding
effect
Silicone 0.8 X X X X
polymers
Surfactants0.2 X X X
Total 1.0
In a production trial in a tire factory, about 3000 private car tires of all
tire sizes were
produced using the condensation crosslinking system according to the
invention. All
the vulcanized tires were of the best quality.
An aspect which should be emphasized is the total transparency of the inner
tire,
which enabled markings (such as bar codes) to be identified. No marks or other
de-
fects could be ascertained, even during possible overspraying on to the
outside.
The silicone polymers formed an extremely thin layer which polymerized during
vulcanization, whereby any separation effect was partly eliminated (no
separation at
the splice). This effect was confirmed by separation loading tests according
DIN
53539.
The function of de-airing, which in prior art systems which contain fillers is
per-
formed by the fillers, was also observed as a result of the parting layer
formed by the
condensation crosslinking system according to the invention.
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Comparison of the amounts sprayed on to private car tires
Tire inner spray solutions
(solids content of the amounts sprayed on per private car tire blank)
Prior art composition Composition according to
according to Example 1 Example 2
Solids content/private car tire blank Solids content/private car tire blank
about 11 g about 1.0 g
Silicone oil/private car tire blank Silicone polymers/private car tire blank
about 1.32 g about 0.8 g
The solids content which had to be sprayed on per tire blank in order to
achieve the
desired effects was reduced by about 90 % (from 11 g to 1.0 g). If the
proportion of
silicone oil is compared with that of the silicone polymer, a reduction of
about 40
was achieved (from 1.32 g to 0.8 g).
This means that the water loading due to overspray (overspray = about 25 - 30
% the
total amount sprayed) in spraying installations is reduced to the said amounts
(< 90
% in total, < 40 % for the silicone oil or polymer), i.e. the pollutant burden
is reduced
by the same ratio.
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Example 3: Experiment using a Pt-catalyzed addition system
onstituents % by weight
ater 77.05
roxel~' GXL 0.05
elzan~' D 0.5
ewopal~ LA 6 0.4
il emulsion 3 9.5
il emulsion 4 9.5
anco~ PEW 1555 1.0
evasil~ 200A30 9.0
About 200 private car tires of different popular sizes were sprayed and
vulcanized.
These results corresponded to those which were also obtained for the
condensation
crosslinking system. The tires were all of the best quality.
These examples clearly show that, compared with prior art parting agent
systems,
better results are obtained, with the use of lesser amounts of active
ingredients, by
employing the crosslinking silicone systems according to the invention.
Although the invention has been described in detail in the foregoing for the
purpose of
illustration, it is to be understood that such detail is solely for that
purpose and that
variations can be made therein by those skilled in the art without departing
from the
spirit and scope of the invention except as it may be limited by the claims.
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