Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing silicon
Reexamination Certificate
2002-09-13
2004-11-30
McAvoy, Ellen M (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing silicon
C508S204000, C508S207000, C508S211000, C508S213000, C106S038220
Reexamination Certificate
active
06825153
ABSTRACT:
The invention relates to a lubricating composition which is particularly appropriate for lubricating curing bladders used during the shaping and curing of pneumatic or semipneumatic tires.
The invention also relates to the curing bladders coated with a lubricating composition according to the invention as well as the pneumatic or semipneumatic tires coated with said lubricating composition.
According to two other of its aspects, the invention relates to a process for preparing the lubricating compositions of the invention as well as the use of said lubricating compositions for lubricating curing bladders.
Rubber tires for vehicles are usually manufactured by molding and curing a raw, or uncured and unshaped, envelope in a molding press in which the raw envelope is pressed toward the outside against the surface of a mold by means of a bladder which can expand by means of an inner fluid. By this process, the raw envelope is shaped against the outer surface of the mold which defines the design of the tire tread of the envelope and the configuration of t sides. On heating, the envelope 's cured. In general, the bladder is expanded by the inner pressure provided by a fluid such as a hot gas, hot water and/or steam, which itself also participates in the heat transfer for the curing. The envelope is then allowed to cool a little in the mold, this cooling being sometimes promoted by the introduction of cold or cooler water into the bladder. The mold is then opened, the bladder is deflated by releasing the pressure of the inner fluid and the envelope is removed from the envelope mold. This use of bladders for curing envelopes is well known in the art.
It is accepted that a notable relative movement occurs between the outer surface of contact of the bladder and the inner surface of the envelope during the bladder expansion phase before complete curing of the envelope. Likewise, a considerable relative movement also occurs between the outer surface of contact of the bladder and the cured inner surface of the envelope, after the envelope has been molded and cured, during the deflation and the extraction of the bladder from the pneumatic tire.
If adequate lubrication is not provided between the bladder and the inner surface of the envelope, the bladder generally tends to get warped, which causes deformation of the envelope in the mold and also excessive wear and depolishing of the surface of the bladder itself. The surface of the bladder also tends to stick to the inner surface of the envelope after curing of the envelope and during the part of the envelope curing cycle in which the bladder is deflated. In addition, air bubbles may be trapped between the surfaces of the bladder and of the envelope and may promote the appearance of envelope curing defects resulting from inadequate heat transfer.
For this reason, the outer surface of the bladder or the inner surface of the raw or uncured envelope is coated with an appropriate lubricant, sometimes called by the name “lining cement”.
Numerous lubricating compositions have been provided to this effect in the art.
Lubricating compositions described in FR 2 494 294 are known in particular which contain, as main constituents, a reactive polydimethylsiloxane preferably having terminal hydroxyl groups, a crosslinking agent, preferably comprising Si—H functional groups and optionally a polycondensation catalyst.
Examples of crosslinking agent with Si—H functional group(s) are methylhydrogensilane, dimethylhydrogensilane and polymethylhydrogenslane. The disadvantage of lubricating compositions of this type is their instability during storage. Indeed, creaming of the emulsion following the emission of hydrogen during transport and the preservation of the lubricating composition is observed. The emission of hydrogen, which is responsible for the instability of the compositions of the prior art, essentially results from the decomposition of the constituents with Si—H functional group(s).
The preparation of lubricating compositions from constituents not containing the Si—H functional group, and having nevertheless excellent properties of durability, lubrication and elasticity is therefore highly desirable.
The compositions forming the subject of EP 635 559 are lubricating compositions based on siloxane which partly meet these requirements. These compositions are in particular stable in that they do not emit hydrogen during storage.
These compositions, which exist in the form of emulsions, comprise as essential constituents, a nonreactive polydimethylsiloxane, a reactive polydimethylsiloxane, preferably with a hydroxyl or alkoxy terminus and a crosslinking agent. Their durability is however insufficient for practical use in the production of pneumatic or semipneumatic tires.
The present invention provides an improved lubricating composition which does not emit hydrogen and which moreover exhibits excellent sliding and durability characteristics, which makes them perfectly appropriate for lubricating the bladders used during the curing of pneumatic and semipneumatic tires.
The lubricating composition of the invention is an oil-in-water emulsion, based on siloxane which does not emit hydrogen. This composition comprises more precisely:
(a) a polydiorganosiloxane oil which is nonreactive to the lubricating properties, having a dynamic viscosity of the order of 5×10
−2
to 30×10
2
Pa.s at 25° C.;
(b) a polyorganosiloxane resin carrying, before emulsification, condensable hydroxyl substituents and containing, before emulsification, at least two different siloxyl units chosen from those of formula (R
0
)
3
SiO
1/2
(M); (R
0
)
2
SiO
2/2
(D); R
0
SiO
3/2
(T) and SiO
4/2
(O), at least one of these units being a T or Q unit, in which formulae R
0
represents a monovalent organic substituent, the average number per molecule of organic radicals R
0
for a silicon atom being between 1 and 2; and said resin having a weight content of hydroxyl substituents of between 0.1 and 10% by weight, and, preferably between 0.2 and 5% by weight;
(c) a crosslinking agent which is soluble in the silicone phase, comprising at least two functional groups capable of reacting with the polyorganosiloxane resin (b);
(d) a condensation catalyst capable of catalyzing the reaction of constituent (b) with constituent (c);
(e) a surfactant; and
(f) water,
said composition comprising
from 5 to 95 parts by weight of constituent (a);
from 0.5 to 50 parts by weight of constituent (b);
from 0.1 to 20 parts by weight of constituent (c);
from 0.05 to 10 parts by weight of constituent (d);
per 100 parts by weight of the sum of constituents (a)+(b)+(c)+(d);
the quantities of surfactants and water being sufficient to obtain an oil-in-water emulsion.
The constituents (a), (b), (c), (d) and (e) of the emulsion are defined with reference to their initial chemical structure, that is to say the structure which characterizes them before emulsification. As soon as they are in aqueous medium, their structure is likely to be greatly modified following hydrolysis and condensation reactions.
The expression dynamic viscosity is understood to mean, in the context of the invention, the Newtonian-type viscosity, that is to say the dynamic viscosity measured in a manner known per se at given temperature, at a gradient of shear rate which is sufficiently low for the measured viscosity to be independent of the rate gradient.
The nonreactive polydiorganosiloxane oil (a) has a dynamic viscosity which is generally between 5×10
−2
and 30×10
2
Pa.s at 25° C. Preferably, the dynamic viscosity varies between 5×10
2
and 30 Pa.s, better still between 0.1 and 5 Pa.s.
In the context of the invention, the expression “nonreactive” is understood to mean an oil which, under the conditions for emulsification, preparation of the lubricating composition and use, does not chemically react with any of the components of the composition.
As preferred constituent (a), there may be mentioned linear polydiorganosiloxanes with a recurring unit of formula V
1
V
2
SiO
2/2
, terminate
Giraud Yves
Guichard Gérald
Hawkins Ian
Burns Doane Swecker & Mathis L.L.P.
McAvoy Ellen M
Rhodia Chimie
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