HK40014685A - Silicone rubber syntactic foam - Google Patents

Description

Silicone rubber composite foam material

Cross reference to related applications

This application is an international application under the patent cooperation treaty claiming priority of U.S. provisional application No.62/456484 filed on 8.2.2017, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a novel silicone rubber syntactic foam and to a silicone precursor for said silicone rubber syntactic foam. Such foams are useful when used in secondary battery packs, which exhibit improved thermal management. Such silicone rubber composite foams may be used in all Electric Vehicles (EV), plug-in hybrid vehicles (PHEV), Hybrid Electric Vehicles (HEV), or in batteries for batteries of other vehicles.

Background

Batteries may be broadly classified into primary and secondary batteries. Primary batteries, also called disposable batteries, are intended to be used until exhausted, after which they are simply replaced with one or more fresh batteries. Secondary batteries, more commonly referred to as rechargeable batteries, are capable of repeated recharging and reuse, and therefore offer the benefits of economy, environmental friendliness, and ease of use, as compared to disposable batteries. Examples of the secondary battery may include a nickel-cadmium battery, a nickel-metal hybrid battery, a nickel-hydrogen battery, a lithium secondary battery, and the like.

Secondary batteries, particularly lithium ion batteries, have emerged as a key energy storage technology and are now the primary technology for consumer electronics, industrial, transportation and power storage applications.

Due to their high potential and their high energy and power density and their good lifetime, secondary batteries are now the preferred battery technology, especially in the automotive industry, as it can now provide longer travel distances and suitable accelerations for electrically driven vehicles such as Hybrid Electric Vehicles (HEV), Battery Electric Vehicles (BEV) and plug-in hybrid electric vehicles (PHEV). In the current automotive industry, lithium ion battery cells of different sizes and shapes are manufactured and subsequently assembled into groups of different configurations. Automotive secondary battery packs are typically constructed of many cells, sometimes hundreds, or even thousands, to meet desired power and capacity requirements.

However, this switching in driving vehicle technology is not without its technical limitations, as the use of electric motors translates into a need for inexpensive batteries with high energy density, long operating life, and the ability to operate in a wide range of conditions. While rechargeable battery cells provide many advantages over disposable batteries, this type of battery is not without its disadvantages. In general, most of the disadvantages associated with rechargeable batteries are due to the battery chemistries used, as these chemistries tend to be less stable than those used in primary batteries. Secondary battery cells, such as lithium ion cells, tend to be more prone to thermal management problems that can occur when elevated temperatures trigger exothermic reactions that generate heat, further raising the temperature and potentially triggering more harmful reactions. During such an event, a large amount of thermal energy is rapidly released, heating the entire battery up to temperatures of 850 ℃ or higher. As a result of the elevated temperature of the cells undergoing such an increase in temperature, the temperature of adjacent cells in the battery pack will also increase. If the temperatures of these adjacent cells are allowed to increase without throttling, they may also enter unacceptable conditions with extremely high temperatures within the cells, resulting in a cascading effect where the temperature rise within a single cell begins to propagate throughout the entire battery pack. As a result, power from the battery pack is interrupted and the system using the battery pack is more likely to incur extensive collateral damage due to the scale of damage and associated thermal energy release. In the worst case scenario, the heat generated is large enough to cause combustion of the cell and materials adjacent to the cell.

In addition, the secondary battery pack operates in an ambient temperature range of-20 ℃ to 60 ℃ due to the characteristics of the lithium ion battery. However, even when operating in this temperature range, the secondary battery pack may begin to lose its charging and discharging capacity or ability (which should occur at ambient temperatures below 0 ℃). Depending on the ambient temperature, the life cycle capacity or charge-discharge capacity of the battery may be significantly reduced when the temperature starts to be lower than 0 ℃. However, it may be unavoidable to use lithium ion batteries where the ambient temperature is outside the optimal ambient temperature range (which is 20 ℃ to 25 ℃) as described. These factors not only significantly shorten the travel distance of the vehicle, but also cause much battery damage. The deterioration in the energy and power available at low temperatures is due to a reduction in capacity and an increase in internal resistance.

Due to the above, in a battery or a battery pack having a plurality of cells, a significant temperature variation occurs between different cells, which is detrimental to the performance of the battery pack. To facilitate long life of the entire battery pack, the cells must be below a desired threshold temperature. To facilitate stack performance, temperature differences between cells in a secondary battery stack should be minimized. However, different cells will reach different temperatures depending on the thermal path to the environment. Furthermore, for the same reason, different cells reach different temperatures during charging. Thus, if one cell is at a higher temperature than the other cells, its charge-discharge efficiency will be different, and so it can charge and discharge faster than the other cells. This will result in a degradation of the performance of the whole group.

Many solutions have been used to reduce the risk of thermal problems, or to reduce the risk of heat propagation. They may be found in U.S. patent 8367233, which discloses a battery pack thermal management system comprising at least one potted failure port integrated into at least one wall of the battery pack enclosure where the potted failure port remains closed during normal operation of the battery pack and opens during a battery pack thermal event whereby hot gases generated during the thermal event provide a flow path that is vented in a controlled manner from the battery pack enclosure.

Another solution is to develop new cell chemistries and/or change existing cell chemistries. Yet another solution is to provide additional shielding at the battery cell level, thereby inhibiting the flow of thermal energy from the cell where the thermal management problem occurs from propagating to adjacent cells. Yet another solution is to use a spacer assembly to maintain the position of the battery that is subjected to a thermal event at its predetermined position within the battery pack, thereby helping to minimize thermal effects to adjacent units.

Thermal insulation of the battery pack has also been described to reduce the risk of thermal deviations or their propagation. Document US2007/0259258, for example, describes a cell of a lithium generator in which the generators are stacked on top of each other and this stack is held in a position surrounded by a polyurethane foam. An embodiment is also disclosed wherein cooling fins are inserted between two generators.

Document DE202005010708 describes a starter lead-acid electrochemical generator and an electrochemical generator for industrial use, the casing of which comprises a plastic foam, such as polypropylene or polyvinyl chloride with closed cells.

Document US2012/0003508 describes a battery of a lithium electrochemical generator comprising a casing; a plurality of lithium electrochemical generators contained within a housing, each generator comprising a container; a rigid, flame retardant foam material having closed cells formed from an electrically insulating material filled into the space between the inner wall of the housing and the free surface of the container side wall of each electrochemical generator, the foam material covering the free surface of the container side wall of each electrochemical generator over a length occupying at least 25% of the height of the container. According to one embodiment, the foam material consists of a material selected from the group consisting of: polyurethane, epoxy, polyethylene, melamine, polyester, cresol, polystyrene, silicone or mixtures thereof, polyurethane and mixtures of polyurethane and epoxy being preferred. Expansion of polyurethane resins for foam form is described using the following chemical route to obtain foam materials:

a) CO production via the chemical route, i.e. reaction of water with isocyanate₂Which will cause the polyurethane to foam;

b) via a physical route, i.e. the evaporation of a low-boiling liquid under the action of heat generated by the exothermic reaction between isocyanate and hydrogen donor compound, or

c) Via air injection.

However, rigid foams (which are typically produced by reacting, for example, a polyisocyanate with an isocyanate-reactive material such as a polyol in the presence of a blowing agent) do not exhibit the desired high compression set when the foam is used to minimize the adverse effects of any fires and explosions associated with thermal events.

A modular lithium battery is described in document US4418127 and has a plurality of battery cells, with electrical connection means to connect the cells to the output terminals, and with ventilation means for releasing the exhausted by-products to the chemical scrubber. Stainless steel battery cell casings are potted in aluminum module casings with syntactic epoxy foam which is syntactic in nature to reduce weight and which has incorporated therein microballoons composed of a composition selected from the group consisting of glass and ceramic, and a flammability reducing additive.

Another major problem in the emerging field of electric vehicles relates to the powertrain system used, which integrates the engine, automated human-operated transmission, axles and wheels with the final drive to control speed and generate more torque to drive the vehicle. The main difference compared to conventional fuel-consuming vehicles is that there is no clutch or hydraulic torque converter in the electric vehicle, so the overall system configuration is inherently less flexible than an engine, and the transmission system is directly mechanically coupled. This configuration has little passive damping effect, which dampens disturbances and avoids vibrations, which is most common during low speed range driving. Indeed, the main sound is magnetic noise, which generates high-frequency squealing noise. Vehicles that are operated with only an electric motor will also have less masking sound at low frequencies. This means that other noise requirements for, for example, noise components such as liquid or air cooling/heating must therefore be changed for the electric battery. Noise during coasting (at coast down) regeneration (battery charging) is also important. Therefore, due to the low damping and lack of passive damping hardware in electric vehicles compared to conventional vehicles, a damping control strategy is required to minimize driveline vibrations.

While many solutions have been taken in an attempt to reduce the risk of heat ingress and heat propagation throughout the stack, it is critical that the risk of personnel and performance be minimized if a stack-level thermal event occurs. As the number of cells in a battery increases, and as the size of the cells increases, the necessity and benefit of providing suitable thermal management will also increase.

Furthermore, there is still a need to better insulate the battery cells, in particular lithium ion batteries, from the adverse effects of low temperatures which are encountered when the climate reaches severely low temperatures (which can reach-20 ℃ and even lower).

In this context, one of the basic objects of the present invention is to provide a new silicone rubber syntactic foam and a silicone precursor of said silicone rubber syntactic foam, which can be used in secondary batteries and which will minimize the personal and performance risks caused by uncontrolled thermal events while it is still waiting.

With the present invention, it is sought that a silicone rubber syntactic foam and a silicone precursor of said silicone rubber syntactic foam will solve said problems associated with uncontrolled thermal excursions, in particular for lithium batteries, which will provide effective low temperature insulation properties and will provide a damping control strategy that minimizes driveline vibrations.

All these objects are achieved in particular by the present invention, which relates to an addition-curing organopolysiloxane composition X comprising:

a) at least one organopolysiloxane a of the formula:

wherein:

-R and R' are independently from each other selected from C₁-C₃₀A hydrocarbyl group, and preferably R is an alkyl group selected from methyl, ethyl, propyl, trifluoropropyl, and phenyl, and most preferably R is methyl,

-R' is C₁-C₂₀Alkenyl, and preferably R 'is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl, and most preferably R' is vinyl,

-R "is alkyl such as methyl, ethyl, propyl, trifluoropropyl, phenyl and preferably R" is methyl, and

n is an integer value of from 5 to 1000, and preferably from 5 to 100,

b) at least one silicon compound B comprising at least two silicon-bonded hydrogen atoms per molecule, and preferably a mixture of two silicon compounds B, one of which comprises two silicon-bonded telechelic hydrogen atoms per molecule and has no pendant silicon-bonded hydrogen atoms per molecule, and the other of which comprises at least three silicon-bonded hydrogen atoms per molecule,

c) an effective amount of hydrosilylation catalyst C, and preferably a platinum-based hydrosilylation catalyst C,

d) hollow glass beads D, and preferably hollow borosilicate glass microspheres,

e) at least one reactive diluent E for reducing the viscosity of the composition and which reacts by hydrosilylation, and is chosen from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations of these, and all having terminal vinyl groups,

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl,

f) optionally at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminium trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

g) optionally at least one cure rate controlling agent G which slows the rate of cure.

To achieve this object, the applicant has in its reputation, entirely surprisingly and unexpectedly, demonstrated that the composition according to the invention, after curing, is capable of providing a silicone rubber syntactic foam comprising hollow glass beads, which makes it possible to overcome the problems that similar batteries using organic rubber syntactic foams cannot solve.

As used herein, the term "silicone rubber" includes the cross-linked product of any cross-linkable silicone composition. By "silicone rubber syntactic foam" is meant a matrix made of silicone rubber in which hollow glass beads are dispersed.

Furthermore, it is known that the travel distance of an electric vehicle between charges is calculated at ambient temperature. Electric vehicle drivers become aware of low temperatures which reduces the number of miles available. This loss is caused not only by electrically heating the compartments, but also by the inherent slowing down of the electrochemical reaction of the cell, which reduces capacity in cold conditions. Thus, the specific selection of silicone rubber as the binder in the syntactic foam makes it possible for the foam to exhibit excellent insulation against low temperature shutdown or below freezing points.

Another advantage of using a silicone rubber adhesive over an organic rubber adhesive for syntactic foams may be, for example, the point of embrittlement (or loss of ductility) which is-20 ℃ to-30 ℃ for typical organic rubber adhesives, compared to-60 ℃ to-70 ℃ for adhesives according to the invention.

Another advantage is also related to physical properties such as elasticity, which remains effective for silicone rubber adhesives even at low temperatures, when organic rubber adhesives become brittle.

Another advantage of using the silicone syntactic foam according to the present invention is that it has a very low water absorption and therefore optimally insulates the battery cell from water, which is not desired for its optimal application. Indeed, in contrast to silicone syntactic foams, conventional silicone foams contain only foamed gas bubbles and have voids that are completely or at least partially connected to each other, which have the ability to absorb and diffuse water, a feature that makes it difficult to use in electric vehicles, where the battery is most often located under the vehicle or in the vehicle floor, and problems can occur with such materials in rainy driving conditions.

The secondary battery pack according to the present invention allows uniform thermal conditions for all the battery cells in the battery pack or module because the temperature difference affects the resistance, self-discharge rate, coulombic efficiency, and irreversible capacity and power decay rate of the battery cells over a wide range of chemicals. The possibility of a charge-imbalanced cell condition and the possibility of early failure of good cells are further minimized.

Indeed, the silicone rubber syntactic foam partially or completely fills the open space of the battery module housing and/or partially or completely covers the battery cells. The silicone rubber binder provides mechanical flexibility and thermal stability over a wide temperature range (e.g., -70 ℃ to 200 ℃) to the syntactic foam. Furthermore, the decomposition of the silicone rubber binder into silica and silica at super-heated temperatures (up to 850 ℃) absorbs a large amount of heat. Therefore, the heat diffusion from the unit cell to the adjacent unit cell can be effectively insulated by the thermal insulation barrier, which is the silicon rubber syntactic foam. The thermal deviation is not propagated throughout the battery module and thus prevents a threat to the safety of the user. In addition, for some battery modules having a control circuit board located in the battery module housing, the silicone rubber syntactic foam of the present invention may be located between the battery cell and the circuit board and between the battery cell and the connecting circuitry to reduce battery heating problems caused by the circuit board and circuitry.

The silicone formulation comprises hollow glass beads and in a preferred embodiment the hollow glass beads have a melting point similar to the thermal event occurring in a cell or in a group of cells in an assembly, such heating will soften and melt the glass, thereby reducing heat transfer and protecting other cells around the overheated cell.

Hollow glass beads are used in the syntactic foam of the present invention and act to reduce the density of the foam. Hollow glass beads and in particular hollow glass microspheres are well suited for such applications because, in addition to having excellent isotropic compressive strength, they also have the lowest density of filler, which would be useful in making high compressive strength syntactic foams. The combination of high compressive strength and low density makes hollow glass microspheres a filler with many of the advantages according to the present invention.

According to one embodiment, the hollow glass beads are hollow borosilicate glass microspheres, also referred to as glass bubbles or glass microbubbles.

According to another embodiment, the hollow borosilicate glass microspheres have a true density in the range of 0.10 grams per cubic centimeter (g/cc) to 0.65 grams per cubic centimeter (g/cc).

The term "true density" is the quotient of the mass of a sample of glass bubbles divided by the true volume of the mass of glass bubbles, as measured by a gas pycnometer. The "true volume" is the aggregate total volume of the glass bubbles, not the gross volume.

According to another embodiment, the content of hollow glass beads is up to 80% volume loading in the silicone rubber syntactic foam or the liquid cross-linkable silicone composition precursor of the silicone rubber syntactic foam as described below, and most preferably 5% to 70% volume of the liquid cross-linkable silicone composition precursor of the silicone rubber syntactic foam as described below.

According to a preferred embodiment, the hollow glass beads are selected from 3M^TMGlass bubble float series (A16/500, G18, A20/1000, H20/1000, D32/4500 and H50/10000EPX glass bubble products) and 3M^TMThe series of glass bubbles (such as, but not limited to, the K1, K15, S15, S22, K20, K25, S32, S35, K37, XLD3000, S38, S38HS, S38XHS, K46, K42HS, S42XHS, S60, S60HS, iM16K, iM30K glass bubble products) are sold by 3M company. The glass bubbles exhibited varying crush strengths from 1.72 megapascals (250psi) to 186.15 megapascals (27000psi) at which 10 volume percent of the first plurality of glass bubbles collapsed. Other glass bubbles sold by 3M, e.g. 3M^TMGlass bubble-float series, 3M^TMGlass bubble-HGS series and 3M^TMSurface treated glass bubbles may also be used in the present invention.

According to a preferred embodiment, the glass bubbles are selected from those having a crush strength of 1.72 MPa (250psi) to 186.15 MPa (27000psi) at which 10 volume percent of the first plurality of glass bubbles collapse.

According to a most preferred embodiment, the hollow glass beads are selected from 3M^TMGlass bubble series S15, K1, K25, iM16K, S32 and XLD 3000.

In order to fill free spaces with the silicone rubber syntactic foam according to the invention, it is possible to:

a) the use of a liquid cross-linkable silicone composition precursor of the silicone rubber composite foam material comprising hollow glass beads according to the invention, which after injection or free-flowing begins to fill free space and cure via cross-linking,

b) either a machined or previously molded block of silicone rubber syntactic foam containing hollow glass beads is used, which is inserted into the housing at the time of assembly.

The use of a liquid cross-linkable silicone composition precursor of the silicone rubber composite foam comprising hollow glass beads in a battery facilitates its filling compared to conventional liquid cross-linkable silicone precursors of silicone foams, since the foaming process of conventional foams generates foaming bubbles and has voids that are completely or at least partially connected to each other, which leads to numerous defects and filling problems within the obtained silicone foam.

Indeed, conventional silicone foams are obtained by several methods, for example by adding thermally decomposable blowing agents, or by moulding and curing while generating hydrogen by-products. In the method of adding a thermally decomposable blowing agent, toxicity and odor of decomposed gas are problematic. Methods that utilize hydrogen gas by-product in the curing step suffer from such problems as potential explosion of hydrogen gas and careful handling of the uncured composition during back-up storage. In addition, the gas generation methods encounter difficulties in forming controlled, uniform cells.

Furthermore, conventional silicone foams comprise only foamed gas bubbles and have voids which are completely or at least partially connected to one another, so that very high water absorption levels result, whereas for the silicone rubber composite foams according to the invention the voids are brought about by the presence of hollow glass beads, which are gas-filled and therefore exhibit very low water absorption levels.

The use of an expandable silicone rubber syntactic foam is advantageous for filling the empty spaces within the battery, since the swelling pressure pushes the foam into all the cavities and depressions of the geometry to be filled. Also, this method allows filling any geometry, which is not possible with prefabricated blocks.

The addition-curable organopolysiloxane compositions according to the invention do not release reaction by-products so that they can be cured in a closed environment, their curing also being accelerated significantly by thermal curing.

According to another preferred embodiment, the reactive diluent E:

-is selected from dodecene, tetradecene, hexadecene, octadecene or combinations thereof, and all having terminal vinyl groups, or

Is a liquid organopolysiloxane of the formula I

Wherein:

-R and R²Independently of one another, from C₁-C₃₀Hydrocarbyl groups, and preferably they are selected from methyl, ethyl, propyl, trifluoropropyl and phenyl, and most preferably methyl,

-R¹is C₁-C₂₀Alkenyl, and preferably R¹Selected from vinyl, allyl, hexenyl, decenyl or tetradecenyl, and most preferably R¹Is vinyl, and

-X is 0 to 100, and X is selected such that the viscosity of the addition-curable organopolysiloxane composition X is reduced compared to the same composition without the reactive diluent.

According to a preferred embodiment, the organopolysiloxane a is selected from dimethylpolysiloxanes containing dimethylvinylsilyl end groups.

According to another preferred embodiment, wherein:

-said organopolysiloxane a has a viscosity at 25 ℃ of from 5mpa.s to 60000 mpa.s; and preferably from 5 to 5000mPa.s, and most preferably from 5 to 350mPa.s, and

-said silicon compound B comprising two telechelic hydrogen atoms bonded to silicon per molecule and having no pendant hydrogen atoms bonded to silicon per molecule has a viscosity at 25 ℃ of from 5 to 100mpa.s, and

-said silicon compound B comprising at least three hydrogen atoms bonded to silicon per molecule has a viscosity at 25 ℃ of 5 to 2000 mpa.s.

All viscosities considered in this description correspond to dynamic viscosity levels, measured in a manner known per se at 25 ℃ with a Brookfield type machine. With regard to fluid products, the viscosity considered in the present description is the dynamic viscosity at 25 ℃, known as "newtonian" viscosity, i.e. the dynamic viscosity measured in a manner known per se at a sufficiently low shear rate gradient such that the measured viscosity is independent of the rate gradient.

According to a preferred embodiment, the viscosity at 25 ℃ of the organopolysiloxane a and the silicon compound B containing at least two hydrogen atoms bonded to silicon per molecule is selected such that the viscosity at 25 ℃ of the addition-curing organopolysiloxane composition X is from 500mpa.s to 300000mpa.s, so that it can be injected into the battery module case 102. If the option of pouring the composition into the battery module case 102 is selected, the components of the addition curing type organopolysiloxane composition X are selected so that its viscosity is 500mpa.s to 5000mpa.s and most preferably 500mpa.s to 2500 mpa.s.

Examples of hydrosilylation catalysts C are hydrosilylation catalysts such as Karstedt's catalyst shown in U.S. patent No.3715334 or other platinum or rhodium catalysts known to those skilled in the art, and also include microencapsulated hydrosilylation catalysts such as those known in the art, see, for example, U.S. patent No. 5009957. However, the hydrosilylation catalyst associated with the present invention may comprise at least one of the following elements: pt, Rh, Ru, Pd, Ni such as Raney nickel, and combinations thereof. The catalyst is optionally bound to an inert or active support. Examples of preferred catalysts that can be used include platinum-based catalysts such as chloroplatinic acid, alcohol solutions of chloroplatinic acid, complexes of platinum and olefins, complexes of platinum and 1, 3-divinyl-1, 1,3, 3-tetramethyldisiloxane, powders on which platinum is supported, and the like. Platinum catalysts are well described in the literature. Mention may in particular be made of the complexes of platinum and of organic products described in U.S. Pat. Nos. 3159601, 3159602 and 3220972 and European patents EP-A-057459, EP-188978 and EP-A-190530, and of the complexes of platinum and of vinylated organopolysiloxanes described in U.S. Pat. Nos. 3419593, 3715334, 3377432, 3814730 and 3775452 to Karstedt. In particular, platinum-based catalysts are particularly desirable.

Examples of cure rate control agents G (which are also referred to as inhibitors) are designed to slow the cure of compounded silicones, if desired. Cure rate controlling agents are well known in the art, and examples of such materials can be found in U.S. patents. U.S. patent 3923705 relates to the use of cyclic siloxanes containing vinyl groups. Us patent 3445420 describes the use of acetylenic alcohols. U.S. patent 3188299 shows the effectiveness of heterocyclic amines. U.S. patent 4256870 describes alkyl maleates for controlled curing. Olefinic siloxanes may also be used as described in U.S. patent 3989667. Polydiorganosiloxanes containing vinyl groups have also been used and this technique can be seen in us patent 3498945, 4256870 and 4347346. Preferred inhibitors for such compositions are methylvinylcyclosiloxane, 3-methyl-1-butyn-3-ol and 1-ethynyl-1-cyclohexanol, and most preferred is 1,3,5, 7-tetramethyl-1, 3,5, 7-tetravinyl-cyclotetrasiloxane, in an amount of 0.002% to 1.00% of the silicone compound, depending on the desired cure rate.

Preferred cure rate controlling agents G are selected from:

1,3,5, 7-tetramethyl-1, 3,5, 7-tetravinyl-cyclotetrasiloxane.

-3-methyl-1-butyn-3-ol, and

-1-ethynyl-1-cyclohexanol.

To achieve a longer working time or "pot life," the amount of cure rate control agent G is adjusted to achieve the desired "pot life. The concentration of catalyst inhibitor in the silicone composition of the invention is sufficient to delay the curing of the composition at ambient temperature without preventing or unduly prolonging the curing at elevated temperatures. This concentration will vary widely depending on the particular inhibitor used, the nature and concentration of the hydrosilylation catalyst, and the nature of the organohydrogenpolysiloxane. Inhibitor concentrations as low as 1mol inhibitor per mole of platinum group metal will in some cases result in satisfactory storage stability and cure rates. In other cases, inhibitor concentrations as high as 500 or more moles of inhibitor per mole of platinum group metal may be required. The optimum concentration of a particular inhibitor in a given silicone composition can be readily determined by routine experimentation.

According to a preferred embodiment, the weight proportions of organopolysiloxane a, reactive diluent E and silicon compound B are such that the overall molar ratio of hydrogen atoms bonded to silicon to all alkenyl groups bonded to silicon is from 0.35 to 10, and preferably from 0.4 to 1.5, for the addition-curing organopolysiloxane composition X.

Additives H such as pigments, dyes, clays, surfactants, hydrogenated castor oil, wollastonite or fumed silica (which alter the flow properties of the compounded silicone product) may also be used in the addition curable organopolysiloxane composition X.

By "dye" is meant an organic substance, colored or fluorescent only, that imparts color to a substrate by selectively absorbing light. By "pigment" is meant a colored, black, white or fluorescent particulate organic or inorganic solid that is generally insoluble in the carrier or substrate into which it is to be incorporated and is substantially unaffected by its physical and chemical effects. It changes appearance by selective absorption and/or by scattering light. Pigments generally retain a crystalline or granular structure throughout the coloring process. Pigments and dyes are well known in the art and need not be described in detail herein.

Clays are products which are known per se and are described, for example, in the publication "minerals des argiles [ minerals of Clays ], S.Caillere, S.Henin, M.Rautureau, 2 nd edition 1982, Masson". Clays are silicates containing cations that can be selected from the following: calcium, magnesium, aluminum, sodium, potassium and lithium cations and mixtures thereof. Examples of such products which may be mentioned include clays of the smectite family such as montmorillonite, hectorite, bentonite, beidellite and saponite, and also the vermiculite, stevensite and chlorite families. These clays may be of natural or synthetic origin. The clays are preferably bentonite or hectorite, and these clays can be modified with chemical compounds selected from the group consisting of: quaternary amines, tertiary amines, amine acetates, imidazolines, amine soaps, fatty sulfates, alkyl aryl sulfonates and amine oxides and mixtures thereof. Clays that can be used in the present invention are synthetic hectorites (also known as laponites), such as the products sold by Laporte under the names Laponite XLG, Laponite RD and Laponite RDs (these products are sodium magnesium silicates and in particular lithium magnesium sodium silicates); bentonite, such as the product sold by Rheox under the name Bentone HC; magnesium aluminum silicates, in particular hydrated, such as the product sold under the name Veegum Ultra by the company r.t. vanderbilt, or calcium silicates and in particular synthetic form, which are sold under the name Micro-Cel C by the company CELITE ET WALSH ASS.

Many silicone polyether surfactants are available, but the preferred silicone polyether for thickening the silicone compounds of the present invention is SP3300 from Elkem Silicones USA.

Another preferred additive H is a rheology modifier such as Thixcin R, which is a hydrogenated castor oil from Elementis Specialties, new jersey, usa.

Wollastonite, also called calcium metasilicate, is a naturally occurring mineral which may be added as a flame retardant in an amount which will vary depending on the application and is 1 part by weight to 15 parts by weight based on 100 parts by weight of the addition curing type organopolysiloxane composition X. The wollastonite that can be used in the present invention is in the form of an ore, having a pointed morphology, which is needle-shaped. Preferred wollastonite grades are selected from the group consisting ofMaterials provided by Minerals, inc.

Aluminum Trihydrate (ATH) is a commonly used flame retardant filler. It decomposes when heated to above 180 ℃. — -200 ℃, at which temperature it absorbs heat and releases water to extinguish the fire. The thermal stability of magnesium hydroxide is higher than that of ATH. Endothermic (heat absorption) decomposition starts at 300 ℃, thereby releasing water, which can act as a flame retardant.

Huntite/hydromagnesite blends (Mg)₃Ca(CO₃)₄/Mg₅(CO₃)₄(OH)₂.4H₂O). Huntite and hydromagnesite are almost invariably always present in a mixture of properties. Hydromagnesite starts to decompose at 220 ℃ (open air) to 250 ℃ (under extruder pressure), which is high enough that it can be used as a flame retardant. Hydromagnesite gives off water and absorbs heat much like ATH and MDH do. In contrast, brucite decomposes above 400 ℃, absorbing heat, but releasing carbon dioxide.

Fumed silica can also be used as additive H to modify the rheology of these materials. Fumed silica can be obtained by high temperature pyrolysis of volatile silicon compounds in an oxyhydrogen flame, resulting in finely dispersed silica. This method makes it possible in particular to obtain hydrophilic silicas which have a high number of silanol groups on their surface, which will be more prone to thickening the silicone composition than silicas with a low silanol level. Such hydrophilic silicas are sold, for example, by Degussa under the names Aerosil 130, Aerosil 200, Aerosil 255, Aerosil 300 and Aerosil 380 and by Cabot under the names Cab-O-Sil HS-5, Cab-O-Sil EH-5, Cab-O-Sil LM-130, Cab-O-Sil MS-55 and Cab-O-Sil M-5. The surface of the silica can be chemically modified via a chemical reaction, which results in a reduction in the number of silanol groups. In particular, the silanol groups can be replaced by hydrophobic groups: thus obtaining hydrophobic silica. The hydrophobic group may be:

trimethylsiloxy, which is obtained in particular by treating fumed silica in the presence of hexamethyldisilazane. The silica thus treated is referred to as "silylated silica" according to CTFA (6 th edition, 1995). They are sold, for example, by Degussa under the name Aerosil R812 and by Cabot under the name Cab-O-Sil TS-530, or

Dimethylsiloxy or polydimethylsiloxane groups, obtained in particular by treating fumed silica in the presence of polydimethylsiloxane, or methyldichlorosilane.

The silica thus treated is referred to as "dimethylsilylated silica" according to CTFA (6 th edition, 1995). They are sold, for example, by Degussa under the names Aerosil R972 and Aerosil R974, and by Cabot under the names Cab-O-Sil TS-610 and Cab-O-Sil TS-720. Fumed silica preferably has a particle size that can range from nanometers to micrometers, e.g., about 5-200 nm.

According to another preferred embodiment, the addition-curing organopolysiloxane composition X is stored before use as a multicomponent RTV comprising at least two separate packages which are preferably gas-tight, whereas when it is a silicon compound comprising a single silicon hydride group per molecule, the hydrosilylation catalyst C is not present in the same package as the silicon compound B or as the reactive diluent E.

According to another preferred embodiment, the addition-curing organopolysiloxane composition X is stored prior to use as a multi-component RTV comprising at least two separate packages, which are preferably gas-tight:

a) the first package a1 comprises:

100 parts by weight of at least one organopolysiloxane A according to the invention and as defined above,

5 to 30 parts by weight of hollow glass beads D according to the invention and as defined above, and

5 to 30 parts by weight of at least one reactive diluent E according to the invention and as defined above, and

-4-150 ppm, based on metallic platinum, of a platinum-based hydrosilylation catalyst C;

b) the second package a2 contains:

100 parts by weight of at least one organopolysiloxane A according to the invention and as defined above,

10-70 parts by weight of a silicon compound B according to the invention and as defined above, comprising two telechelic hydrogen atoms bonded to silicon per molecule,

5-25 parts by weight of a silicon compound B according to the invention and as defined above, comprising at least three hydrogen atoms bonded to silicon per molecule,

5 to 30 parts by weight of hollow glass beads D according to the invention and as defined above, and

-an effective amount of at least one cure rate controlling agent G which slows the rate of cure.

According to another preferred embodiment, the present invention relates to a silicone rubber syntactic foam obtained by crosslinking said addition-curing organopolysiloxane composition X according to the present invention and as defined above.

Another embodiment of the present invention relates to a method for producing an addition-curable organopolysiloxane composition X, comprising the steps of:

a) supplying to the base supply line a liquid silicone base MS1 comprising:

i) at least one organopolysiloxane A having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups,

ii) hollow glass beads D, and preferably hollow borosilicate glass microspheres D1,

iii) at least one silicon compound B having at least two and preferably at least three hydrogen atoms bonded to silicon per molecule,

iv) at least one reactive diluent E for reducing the viscosity of the composition and which reacts by hydrosilylation and is selected from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably is selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations thereof,

and all have terminal vinyl groups, and

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl, and

v) an optional cure rate controlling agent G which slows the cure rate,

b) feeding a catalyst masterbatch MC to a catalyst feed line comprising:

i) at least one hydrosilylation catalyst C; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

c) feeding an inhibitor masterbatch MI to an inhibitor supply line, comprising:

i) a cure rate control agent G, which slows the rate of cure; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

d) optionally feeding an additive masterbatch MA to the additive feed line, comprising:

i) at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminum trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

ii) optionally at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

e) introducing said liquid silicone base MS1, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA into a tank to obtain an addition curing organopolysiloxane composition X.

A first advantage of the preferred embodiment is that the reaction rate for crosslinking the addition-curable organopolysiloxane composition X is regulated by the addition of a cure rate-controlling agent G. Since the addition of this base component is done via the use of a specific feed line, the level of inhibitor can be easily changed by the operator, which allows him to increase the curing rate or to reduce the temperature at which rapid curing is initiated. This is a key advantage because the construction of newly designed secondary battery packs involves increasingly complex shapes, meaning that the curing rate is carefully adjusted from case to case.

The second major advantage is that the inhibitor level and thus the temperature at the onset of rapid cure can now be reduced. This can be important if the components present in the battery pack are somewhat temperature sensitive.

Another embodiment of the present invention also relates to a method for producing an addition-curable organopolysiloxane composition X, comprising the steps of:

a) supplying to the base supply line a liquid silicone base MS2 comprising:

i) at least one organopolysiloxane a having at least two silicon-bonded alkenyl groups per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups, and

ii) at least one silicon compound B having at least two and preferably at least three hydrogen atoms bonded to silicon per molecule,

iii) optionally a curing rate controlling agent G, which slows down the curing rate,

iv) at least one reactive diluent E which reduces the viscosity of the composition, reacts by hydrosilylation and is selected from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations thereof, and all having terminal vinyl groups, and

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl, and

b) feeding a catalyst masterbatch MC to a catalyst feed line comprising:

i) at least one hydrosilylation catalyst C; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

c) feeding an inhibitor masterbatch MI into an inhibitor feed line, comprising:

i) a cure rate control agent G, which slows the rate of cure; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

d) optionally feeding an additive masterbatch MA into the additive feed line comprising:

i) at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminum trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

ii) optionally at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

e) introducing said liquid silicone base MS2, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA into a stirred tank; and

f) operating said stirred tank whereby said liquid silicone base MS1, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA are mixed, preferably using a high flow low shear mixer, and

g) the hollow glass beads D and the preferably hollow borosilicate glass microspheres D1 were added to the stirred tank to obtain the addition curing organopolysiloxane composition X, preferably by using a gravity discharge or screw feeder.

Drawings

Fig. 1 and 2 provide illustrations of two preferred embodiments of the process for producing an addition-curable organopolysiloxane composition X in which an inhibitor masterbatch MI and a catalyst masterbatch MC are separately fed to the other components to control the curing rate.

Fig. 1 shows a method for producing an addition curing type organopolysiloxane composition X according to one embodiment of the present invention, in which the liquid silicone base MS1 is stored in the holding tank 1, the catalyst master batch MC is stored in the holding tank 20, the inhibitor master batch MI is stored in the holding tank 50 and the additive master batch MA is stored in the holding tank 65 and fed into their respective supply lines 200, 210, 220, and 230, respectively. The holding tank 1 of liquid silicone base MS2 is connected to the agitation tank 80 via a feed pump 10 (which may be any large reciprocating pump) and via an optional feed rate adjuster 15. The holding tank 20 for the catalyst masterbatch MC is connected to the agitation tank 80 via a feed pump 25 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other active reciprocating pump), and via an optional feed rate adjuster 30. The holding tank 50 for the inhibitor masterbatch MI is connected to the agitation tank 80 via a feed pump 55 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other actively reciprocating pump), and via an optional feed rate adjuster 60. The holding tank 65 for the additive masterbatch MA is connected to the agitation tank 80 via a feed pump 70 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other active reciprocating pump), and via an optional feed rate adjuster 75. When said liquid silicone base MS2, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA are introduced into said agitation tank 80; the resulting mixture is preferably mixed by using a high flow low shear mixer to produce the addition curing organopolysiloxane composition X according to the present invention. The composition can now be used for introduction into a battery module housing, e.g. of an electric battery, by means of an apparatus 100, which apparatus 100 can be introduced via an injection device or via a pump to allow free flow to fill the free space of the battery module housing and cured via cross-linking.

Fig. 2 shows a method for producing an addition curing type organopolysiloxane composition X according to another embodiment of the present invention, in which the liquid silicone base MS2 is stored in the holding tank 1, the catalyst master batch MC is stored in the holding tank 20, the inhibitor master batch MI is stored in the holding tank 50 and the additive master batch MA is stored in the holding tank 65 and fed into their respective supply lines 200, 210, 220, and 230, respectively. The holding tank 1 of liquid silicone base MS2 is connected to the agitation tank 80 via a feed pump 10 (which may be any large reciprocating pump), and via an optional feed rate adjuster 15. The holding tank 20 for the catalyst masterbatch MC is connected to the agitation tank 80 via a feed pump 25 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other active reciprocating pump), and via an optional feed rate adjuster 30. The holding tank 50 for the inhibitor masterbatch MI is connected to the agitation tank 80 via a feed pump 55 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other actively reciprocating pump), and via an optional feed rate adjuster 60. The holding tank 65 for the additive masterbatch MA is connected to the agitation tank 80 via a feed pump 70 (which may be any small piston reciprocating pump, gear pump, micro-motion injection pump, or other active reciprocating pump), and via an optional feed rate adjuster 75. When said liquid silicone base MS2, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA are introduced into said agitation tank 80; the resulting mixture is preferably mixed by using a high flow, low shear mixer. To the resulting mixture, hollow glass beads D and preferably hollow borosilicate glass microspheres D1, which are stored in a holding tank 90 (preferably a hopper), are transferred by gravity discharge directly or via a screw feeder 95 to the agitation tank 80 to produce the addition curing type organopolysiloxane composition X according to the present invention. The composition can now be used to introduce, for example, a battery module housing of an electric battery through the apparatus 100, which apparatus 100 can be introduced via an injection device or via a pump to allow free flow to fill the free space of the battery module housing and cured via crosslinking.

Other advantages offered by the present invention will become apparent from the examples of the specification which follow.

Examples

I) Definition of Components

-organopolysiloxane a1 ═ polydimethylsiloxane, having dimethylvinylsilane terminal units, the viscosity at 25 ℃ being from 80mpa.s to 120 mpa.s;

organopolysiloxane a2 ═ polydimethylsiloxane, having dimethylvinylsilane-terminal units, and having a viscosity at 25 ℃ of from 500mpa.s to 650 mpa.s;

an organopolysiloxane B1(CE) ═ polydimethylsiloxane as chain extender, having dimethylsilylhydride end units, having a viscosity at 25 ℃ of from 7mpa.s to 10mpa.s andhaving the formula: m' D_xM'

Wherein:

d is formula (CH)₃)₂SiO_2/2A siloxy unit of (a);

-M' is formula (CH)₃)₂(H)SiO_1/2Siloxy units of

-and x are integers from 8 to 11;

organopolysiloxane B2(XL) as crosslinker, having a viscosity at 25 ℃ of 18mpa.s to 26mpa.s, there being more than 10 SiH-reactive groups (16 to 18 SiH-reactive groups on average): poly (methylhydrogen) (dimethyl) siloxane having SiH groups (. alpha./omega.) in the chain and at the chain ends,

hollow glass beads D1: 3M^TMGlass bubble series S15, sold by 3M company, particle size (50% by volume) 55 microns, isostatic crush strength: the test pressure was 300psi (2.07MPa) and the true density (g/cc) was 0.15.

Hollow glass beads D2: 3M^TMiM16K glass bubble, sold by 3M company, particle size (50 vol%) 20 microns, isostatic crush strength: test pressure 16000psi, true density (g/cc) ═ 0.46.

Curing rate control agent G1: 1,3,5, 7-tetramethyl-1, 3,5, 7-tetravinyl-cyclotetrasiloxane.

Curing rate control agent G2: 1-ethynyl-1-cyclohexanol (ECH).

Curing rate control agent G3-MB: 90% by weight of organopolysiloxane a1 and 10% by weight of curing rate-controlling agent G2.

-catalyst C: 10% platinum in 350cS dimethyl vinyl dimer as Karstedt's catalyst, sold by Johnson Matthey Company.

Catalyst C-MB: 98% by weight of organopolysiloxane a1 and 2% by weight of catalyst C.

-reactive diluent E ═ 1-tetradecene.

Component A	Parts by weight
		Organopolysiloxane A1	81.88
Reactive diluent E	5.03
		Catalyst C	0.037
Hollow glass bead D1	13.05
		Component B
Organopolysiloxane A1	81.88
		Organopolysiloxane B2(XL)	8.6
Organopolysiloxane B1(CE)	53.41
		Curing Rate-controlling agent G1	0.01
Hollow glass bead D1	13.05

Table 1: two-component formulation 1 silicone rubber syntactic foam precursor of the present invention

Component A	Parts by weight
		Organopolysiloxane A1	78.27
Reactive diluent E	8.62
		Catalyst C	0.063
Hollow glass bead D1	13.05
		Component B
Organopolysiloxane A1	69.23
		Organopolysiloxane B2(XL)	2.46
Organopolysiloxane B1(CE)	15.26
		Curing Rate-controlling agent G1	0.0029
Hollow glass bead D1	13.05

Table 2: the precursor of the two-component formulation 2 silicone rubber syntactic foam of the present invention.

For two-component formulation 1, components a and B were mixed in a ratio of 6: 1w/w (weight ratio) were combined to prepare composition I.

For two-component formulation 2, components a and B were mixed in a ratio of 1: 1w/w (weight ratio) were combined to prepare composition II.

Each of compositions 1 and 2 was cured at room temperature to produce a silicone rubber syntactic foam comprising a silicone rubber binder and hollow glass beads.

Other ingredients were prepared according to the present invention and are described in table 3. Each formulation was cured to produce a silicone rubber syntactic foam according to the present invention. The thermal conductivity (W/mK) and specific gravity (g/cm) were measured³). Thermal conductivity was measured using a Thermtest Hot Disk TPS (transfer plant Source)2500S tester.

Table 2: the two-component formulations 3, 4 and 5 of the present invention are precursors to silicone rubber syntactic foams.

Claims (13)

1. An addition-curable organopolysiloxane composition X comprising:

a) at least one organopolysiloxane a of the formula:

wherein:

-R and R' are independently from each other selected from C₁-C₃₀A hydrocarbyl group, and preferably R is an alkyl group selected from methyl, ethyl, propyl, trifluoropropyl, and phenyl, and most preferably R is methyl,

-R' is C₁-C₂₀Alkenyl, and preferably R 'is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl, and most preferably R' is vinyl,

-R "is alkyl such as methyl, ethyl, propyl, trifluoropropyl, phenyl and preferably R" is methyl, and

n is an integer value of from 5 to 1000, and preferably from 5 to 100,

b) at least one silicon compound B comprising at least two silicon-bonded hydrogen atoms per molecule, and preferably a mixture of two silicon compounds B, one of which comprises two silicon-bonded telechelic hydrogen atoms per molecule and has no pendant silicon-bonded hydrogen atoms per molecule, and the other of which comprises at least three silicon-bonded hydrogen atoms per molecule,

c) an effective amount of hydrosilylation catalyst C, and preferably a platinum-based hydrosilylation catalyst C,

d) hollow glass beads D, and preferably hollow borosilicate glass microspheres,

e) at least one reactive diluent E for reducing the viscosity of the composition and which reacts by hydrosilylation, and is chosen from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations of these, and all having terminal vinyl groups,

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl,

f) optionally at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminium trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

g) optionally at least one cure rate controlling agent G which slows the rate of cure.

2. The addition curable organopolysiloxane composition X according to claim 1, wherein the hollow glass beads are hollow borosilicate glass microspheres.

3. The addition curable organopolysiloxane composition X according to claim 2, wherein the true density of the hollow borosilicate glass microspheres is 0.10 grams per cubic centimeter to 0.65 grams per cubic centimeter.

4. The addition curable organopolysiloxane composition X according to claim 1, wherein the level of hollow glass beads is up to 80% volume loading in the silicone rubber syntactic foam, and preferably 5% to 70% volume loading of the silicone rubber syntactic foam.

5. The addition-curable organopolysiloxane composition X according to claim 1, wherein the ratio of reactive diluent E:

-is selected from dodecene, tetradecene, hexadecene, octadecene or combinations thereof, and all having terminal vinyl groups, or

Is a liquid organopolysiloxane of the formula I

Wherein:

-R and R²Independently of one another, from C₁-C₃₀Hydrocarbyl groups, and preferably they are selected from methyl, ethyl, propyl, trifluoropropyl and phenyl, and most preferably methyl,

-R¹is C₁-C₂₀Alkenyl, and preferably R¹Selected from vinyl, allyl, hexenyl, decenyl or tetradecenyl, and most preferably R¹Is vinyl, and

-X is 0 to 100, and X is selected such that the viscosity of the addition-curable organopolysiloxane composition X is reduced compared to the same composition without the reactive diluent.

6. The addition-curable organopolysiloxane composition X according to claim 1, wherein:

-said organopolysiloxane a has a viscosity at 25 ℃ of from 5mpa.s to 60000 mpa.s; and preferably from 5 to 5000mPa.s, and most preferably from 5 to 350mPa.s, and

-said silicon compound B comprising two telechelic hydrogen atoms bonded to silicon per molecule and having no pendant hydrogen atoms bonded to silicon per molecule has a viscosity at 25 ℃ of from 5 to 100mpa.s, and

-said silicon compound B comprising at least three hydrogen atoms bonded to silicon per molecule has a viscosity at 25 ℃ of 5 to 2000 mpa.s.

7. The addition-curable organopolysiloxane composition X according to claim 1, wherein the viscosities of the organopolysiloxane a and the silicon compound B comprising at least two hydrogen atoms bonded to silicon per molecule at 25 ℃ are selected such that the viscosity of the addition-curable organopolysiloxane composition X at 25 ℃ is from 500mpa.s to 5000mpa.s and most preferably from 500mpa.s to 2500 mpa.s.

8. The addition-curable organopolysiloxane composition X according to claim 1, wherein the weight proportions of organopolysiloxane a, reactive diluent E, and silicon compound B are such that the overall molar ratio of hydrogen atoms bonded to silicon to all alkenyl groups bonded to silicon is from 0.35 to 10, and preferably from 0.4 to 1.5.

9. The addition-curable organopolysiloxane composition X according to claim 1, which is stored prior to use as a multi-component RTV comprising at least two separate packages, which are preferably gas-tight, whereas when it is a silicon compound comprising a single silicon hydride group per molecule, the hydrosilylation catalyst C is not present in the same package with the silicon compound B or with the reactive diluent E.

10. The addition-curable organopolysiloxane composition X according to claim 1, which is stored prior to use as a multi-component RTV comprising at least two separate packages, which are optionally air-tight:

a) the first package a1 comprises:

100 parts by weight of at least one organopolysiloxane A,

5 to 30 parts by weight of hollow glass beads D, and

5 to 30 parts by weight of at least one reactive diluent E, and

-4-150 ppm, based on metallic platinum, of a platinum-based hydrosilylation catalyst C;

b) the second package a2 contains:

100 parts by weight of at least one organopolysiloxane A,

10-70 parts by weight of a silicon compound B comprising two telechelic hydrogen atoms bonded to silicon per molecule,

5-25 parts by weight of a silicon compound B comprising at least three hydrogen atoms bonded to silicon per molecule,

5 to 30 parts by weight of hollow glass beads D,

which is stored prior to use as a multicomponent RTV comprising at least two separate packages which are preferably gas-tight, whereas when it is a silicon compound comprising a single silicon hydride group per molecule, the hydrosilylation catalyst C is not present in the same package as the silicon compound B or as the reactive diluent E, and

-an effective amount of at least one cure rate controlling agent G which slows the rate of cure.

11. A silicone rubber syntactic foam obtained by crosslinking the addition-curable organopolysiloxane composition X defined in any one of the preceding claims.

12. A process for preparing the addition-curable organopolysiloxane composition X according to any one of claims 1 to 8, comprising the steps of:

a) supplying to the base supply line a liquid silicone base MS1 comprising:

i) at least one organopolysiloxane A having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups,

ii) hollow glass beads D, and preferably hollow borosilicate glass microspheres D1,

iii) at least one silicon compound B having at least two and preferably at least three hydrogen atoms bonded to silicon per molecule,

iv) at least one reactive diluent E for reducing the viscosity of the composition and which reacts by hydrosilylation and is selected from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably is selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations thereof, and all having terminal vinyl groups, and

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl, and

v) an optional cure rate controlling agent G which slows the cure rate,

b) feeding a catalyst masterbatch MC to a catalyst feed line comprising:

i) at least one hydrosilylation catalyst C; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

c) feeding an inhibitor masterbatch MI to an inhibitor supply line, comprising:

i) a cure rate control agent G, which slows the rate of cure; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

d) optionally feeding an additive masterbatch MA to the additive feed line, comprising:

i) at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminum trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

ii) optionally at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

e) introducing said liquid silicone base MS1, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA into a tank to obtain an addition curing organopolysiloxane composition X.

13. A process for preparing the addition-curable organopolysiloxane composition X according to any one of claims 1 to 8, comprising the steps of:

a) supplying to the base supply line a liquid silicone base MS2 comprising:

i) at least one organopolysiloxane a having at least two silicon-bonded alkenyl groups per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups, and

ii) at least one silicon compound B having at least two and preferably at least three hydrogen atoms bonded to silicon per molecule,

iii) optionally a curing rate controlling agent G, which slows down the curing rate,

iv) at least one reactive diluent E which reduces the viscosity of the composition, reacts by hydrosilylation and is selected from:

-a silicon compound comprising a single silicon hydride group per molecule, and

-an organic compound containing a single ethylenically unsaturated group, preferably said organic compound is an organic alpha-olefin containing from 3 to 20 carbon atoms, and most preferably selected from the group consisting of dodecene, tetradecene, hexadecene, octadecene and combinations thereof, and all having terminal vinyl groups, and

an organopolysiloxane having a single telechelic alkenyl group, and preferably said telechelic alkenyl group is selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably is vinyl, and

b) feeding a catalyst masterbatch MC to a catalyst feed line comprising:

i) at least one hydrosilylation catalyst C; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

c) feeding an inhibitor masterbatch MI into an inhibitor feed line, comprising:

i) a cure rate control agent G, which slows the rate of cure; and

ii) optionally, at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups; and

d) optionally feeding an additive masterbatch MA into the additive feed line comprising:

i) at least one additive H such as a pigment, a dye, a clay, a surfactant, hydrogenated castor oil, wollastonite, aluminum trihydrate, magnesium hydroxide, halloysite, huntite, hydromagnesite, expanded graphite, zinc borate, mica or fumed silica, and

ii) optionally at least one organopolysiloxane a having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing 2 to 14 carbon atoms, preferably said alkenyl groups are selected from vinyl, allyl, hexenyl, decenyl and tetradecenyl groups, and most preferably said alkenyl groups are vinyl groups;

e) introducing said liquid silicone base MS2, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA into a stirred tank; and

f) operating said stirred tank whereby said liquid silicone base MS1, said catalyst masterbatch MC and said inhibitor masterbatch MI and optionally said additive masterbatch MA are mixed, preferably using a high flow low shear mixer, and

g) the hollow glass beads D and the preferably hollow borosilicate glass microspheres D1 were added to the stirred tank to obtain the addition curing organopolysiloxane composition X, preferably by using a gravity discharge or screw feeder.