EP4705391A1 - Castable composition comprising liquid silicone rubber and hollow glass microspheres - Google Patents

Castable composition comprising liquid silicone rubber and hollow glass microspheres

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Publication number
EP4705391A1
EP4705391A1 EP24736095.1A EP24736095A EP4705391A1 EP 4705391 A1 EP4705391 A1 EP 4705391A1 EP 24736095 A EP24736095 A EP 24736095A EP 4705391 A1 EP4705391 A1 EP 4705391A1
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EP
European Patent Office
Prior art keywords
composition
thixotropic agent
silicone rubber
castable
castable composition
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24736095.1A
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German (de)
French (fr)
Inventor
Stephen E. Amos
Robert W. Hunter
Kevin J. Rink
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3M Innovative Properties Co
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3M Innovative Properties Co
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Publication date
Application filed by 3M Innovative Properties Co filed Critical 3M Innovative Properties Co
Publication of EP4705391A1 publication Critical patent/EP4705391A1/en
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K7/00—Use of ingredients characterised by shape
    • C08K7/22—Expanded, porous or hollow particles
    • C08K7/24—Expanded, porous or hollow particles inorganic
    • C08K7/28—Glass
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/10—Esters; Ether-esters
    • C08K5/101—Esters; Ether-esters of monocarboxylic acids
    • C08K5/103—Esters; Ether-esters of monocarboxylic acids with polyalcohols
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K7/00—Use of ingredients characterised by shape
    • C08K7/02—Fibres or whiskers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
    • C08L83/04—Polysiloxanes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

Castable compositions are described. The castable composition comprise a liquid silicone rubber, a thixotropic agent comprising organic fibrils, and hollow glass microspheres. Cured compositions and methods of making the castable compositions, as well as battery modules comprising a plurality of battery cells and such cured compositions are also described.

Description

CASTABLE COMPOSITION COMPRISING LIQUID SILICONE RUBBER AND HOLLOW GLASS MICROSPHERES
Technical Field
The present disclosure relates to a castable composition comprising a liquid silicone rubber, a thixotropic agent, and hollow glass microspheres. The castable composition may be used for filling open space between battery cells in battery modules.
Background
Battery modules used in electric vehicles and energy storage devices are generally comprised of many lithium-ion battery cells in close proximity to one another in a module or pack. Oftentimes, a potting compound is used in these battery modules to maintain physical separation and electrical isolation between the individual battery cells and to provide thermal management to the battery module. These potting compounds have some unique attributes. First, the curable composition of the potting compounds needs to have a low viscosity of at most 6 pascal seconds (Pa-sec) (6000 centipoise (cP)) for flowability into very narrow channels between individual battery cells, i.e., the curable composition needs to be castable or pourable. Second, the curable composition of the potting compounds needs to be curable at room temperature, with the curing being only slightly exothermic so as not to harm the battery cells. Third, it is often desired that the cured composition of the potting compounds needs to have no or only low adhesion to the housing of the battery module, which allows for gas evolution in the case of a thermal runaway event and recyclability or repairability of the battery module. Fourth, the cured composition of the potting compounds needs to comprise porosity or void space to provide weight reduction, improved dielectric properties and thermal insulation.
US 10,501,597 discloses a room temperature cure liquid silicone rubber (LSR) composition containing up to 80 percent by volume of hollow glass microspheres. The viscosity of the unfilled LSR gel, i.e., of the LSR alone without hollow glass microspheres, is very low, around 100 mPa-sec; and the surface area of the hollow glass microspheres is very low, around 1 m2/g. A drawback of this LSR composition is the quick float-out or separation of the hollow glass microspheres in the filled LSR composition, which means that the hollow glass microspheres will separate from the liquid silicone rubber and will concentrate on the surface or in the upper part of the storage container, yielding very little, if any storage stability of a homogeneous dispersion.
A first solution to address the problem of poor storage stability is to mix the hollow glass microspheres with the LSR just before using the potting compound for addition to the battery module. A second solution is to pre-compound the composition but instruct the end-user on how to redisperse the floated- out, i.e., separated, hollow glass microspheres just before the addition of the filled LSR composition to the battery module. Both of these solutions are less desirable than a storage stable pre -compounded material. The first solution requires capital investment by the OEM or battery module/pack producer for handling, mixing and dispensing of hollow glass microspheres. The second solution has a risk of breakage of the hollow glass microspheres during redispersion. Breakage increases the specific gravity of the potting compound, reducing the weight reduction, and affecting thermal and electrical insulation properties. There is also a risk of releasing sulfur oxide gas that can foul the platinum catalyst, typically used in the room temperature cure liquid silicon rubber system, preventing a full cure and affecting physical properties.
There is still a need for a castable composition being usable as potting compounds comprising hollow glass microspheres and having an improved flowability, i.e., a low viscosity, and being curable at room temperature with limited exothermic reaction, and having good storage stability.
As used herein, "a", "an", "the", "at least one" and "one or more" are used interchangeably. The term “comprise” shall include also the terms “consist essentially of’ and “consists of’.
Summary
In a first aspect, the present disclosure relates to a castable composition comprising,
(a) a liquid silicone rubber,
(b) a thixotropic agent comprising organic fibrils, and
(c) hollow glass microspheres.
In another aspect, the present disclosure also relates to a masterbatch composition comprising
(a) a liquid silicone rubber, and
(b) a thixotropic agent comprising organic fibrils,
In yet a further aspect, the present disclosure also relates to a cured composition obtained by curing the castable composition as disclosed herein.
In yet a further aspect, the present disclosure also relates to a process for making the masterbatch composition as disclosed herein, the process comprising mixing the liquid silicone rubber and the thixotropic agent, and creating the organic fibrils of the thixotropic agent by shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C.
In yet a further aspect, the present disclosure also relates to a process for making the castable composition as disclosed herein, the process comprising mixing the liquid silicone rubber and the thixotropic agent, shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C to form the organic fibrils of the thixotropic agent, and combining the hollow glass microspheres with the mixture of liquid silicone rubber and thixotropic agent at a shear rate in the range of from 1 to 100 s '
In yet a further aspect, the present disclosure also relates to a battery module comprising a plurality of battery cells and open space between the battery cells, wherein the open space is at least partially filled with the cured composition as disclosed herein.
Surprisingly, it has been found that thixotropic agents can be used for liquid silicone rubber compositions comprising hollow glass microspheres which allow a thixotropic behavior for avoiding separation or float-out of the hollow glass microspheres during storage, preventing a hard packed concentration of hollow glass microspheres at the surface that requires moderate shear mixing and a significant amount of time to re-disperse, possibly breaking the hollow glass microspheres. For the storage stabilized castable composition as disclosed herein, at most a brief, low shear mixing may be needed to maintain homogenization of the dispersion.
The castable composition disclosed herein has a good storage stability regarding separation or float-out of the hollow glass microspheres. Despite the castable composition disclosed herein is stabilized for storage, a low viscosity after mixing/shearing is still possible.
The castable composition disclosed herein is curable at room temperature (23 °C).
The performance of the cured product, i.e., properties such as thermal insulation, dielectric properties, and low density, are not adversely affected by the stabilization for storage. Some conventional additives that act as a thixotropic agent are dense inorganic fillers with high specific gravity, e.g., fumed silica and bentonite clay, that would significantly increase the density of the castable composition and reduce the weight reduction benefit of the hollow glass microspheres.
Brief Description of the Drawings
The present disclosure is explained in more detail on the basis of the drawings, in which
Figure 1 schematically shows a perspective view of a battery module with open space between battery cells to be filled with a castable composition as disclosed herein; and
Figure 2 schematically shows a top view of a battery module with open space between battery cells filled with a castable composition as disclosed herein. Detailed Description
Disclosed herein is a castable composition for fdling open space between battery cells in battery modules, the composition comprising (a) a liquid silicone rubber, (b) a thixotropic agent comprising organic fibrils, and (c) hollow glass microspheres.
A “battery module” comprises a plurality of battery cells and open space between the battery cells. The open space between the battery cells is partially or fully filled with the castable composition as disclosed herein. Typically, the battery module also comprises a battery module casing. Multiple battery modules may form a battery pack, which means that a battery module is a sub-assembly to a battery pack. A battery pack, in some cases, can have no modules, but still comprises a plurality of battery cells and open space between the battery cells which is partially or fully fdled with the castable composition as disclosed herein. For simplicity, the term battery module will be used to mean either a battery module or a battery pack. Typically, the battery module is a rechargeable battery, i.e., a rechargeable electrical energy storage system.
As used herein, “a liquid silicone rubber” is meant to refer to a curable silicone composition which is castable and curable at room temperature (23 °C). “Castable” means that the composition prior to crosslinking or curing can be poured, or dispensed, and will flow into narrow (~0.5 mm) channels or gaps and fully fill the gap without voids. The term “voids” refers to spaces which have not been filled with liquid silicone rubber or with hollow glass microspheres. Typically, a composition is castable if the viscosity is less than or equal to 6 Pa-sec, preferably less than or equal to 3 Pa-sec, and most preferably less than or equal to 2 Pa-sec. The curing of the liquid silicone rubber needs to be of limited exothermic reaction, so as not to harm the battery cells. Also, there should be only a limited amount, or no solvent comprised in the liquid silicone rubber, and the crosslinking or curing reaction should have no electrically conductive product, such as water.
Suitable liquid silicone rubbers are, for example, disclosed in US 10,501,597 and US 2018/0223069. Liquid silicone rubbers that can be used for the castable composition disclosed herein are, for example, available from Elkem under the trade designation Bluesil™, Dow Chemical under the trade designations DOWSIL™, SILASTIC™, and SYLGARD™, from Shin-Etsu, the KE series, and from Wacker Chemie under the trade designations ELASTOSIL® and LUMISIL®.
The thixotropic agent of this disclosure creates a high zero shear apparent viscosity. “Zero shear viscosity” is the viscosity of a material when it is effectively at rest. The “apparent viscosity” of each sample decreases greatly with increasing shear rate. Without wishing to be bound by theory, it is believed that the high zero shear apparent viscosity is obtained by creating a network of entangled long chain molecules and/or entangled fibrils. In addition, the long chain molecules and/or fibrils may also be connected by pseudo cross-links which are weak interactive forces like hydrogen bonding. This high zero shear apparent viscosity can be shear thinned upon stirring, mixing or flowing through a static mixer or nozzle. By shear thinning, the long chain molecules and/or fibrils may be aligned and the weak interactive forces may be temporarily disrupted. By adding the thixotropic agent to the castable composition, the separation or float-out of the hollow glass microspheres can be greatly slowed, or effectively prevented. The castable composition disclosed herein can be stored for weeks to months with limited to no separation of the hollow glass microspheres from the liquid silicone rubber visually observed and/or prevention of a concentrated hard pack of hollow glass microspheres on the surface. The castable composition remains easily stirred or mixed at low shear and for a relatively short period of time to maintain the homogeneous suspension of hollow glass microspheres in the liquid silicone rubber.
The thixotropic agent that is used for the castable composition disclosed herein may be selected from the group consisting of polyamide polymers, castor oil, castor oil derivatives, and combinations thereof. The polyamide polymers and the castor oil derivatives may be in the form of micronized waxes.
An example for a castor oil derivative is hydrogenated castor oil. Hydrogenated castor oil is also referred to as castor wax.
Suitable castor oil derivatives are available from Arkema, France, under the trade designation Crayvallac®, for example Crayvallac® PF, Crayvallac® MT, and Crayvallac®CVP.
Suitable polyamide polymers are available from Arkema, France, under the trade designation Crayvallac®, for example Crayvallac® SLT, Crayvallac® SLW, Crayvallac® SLX, Crayvallac® SL, and Crayvallac® Super, and from Kusumoto Chemicals, Ltd., Japan, under the trade designation Disparlon, for example Disparlon 6200, Disparlon 6250, and Disparlon 6500.
The polyamide polymer that may be used as a thixotropic agent for the castable composition disclosed herein may comprise silanol functional groups.
The thixotropic agent that is used in the castable composition disclosed herein comprises organic fibrils. The organic fibrils are created by shear heating the thixotropic agent to an elevated temperature of at least 40 °C. “Shear heating” means that the thixotropic agent is sheared by suitable shearing equipment, and by shearing the thixotropic agent, the thixotropic agent is heated up to an elevated temperature of at least 40 °C. Typically, the thixotropic agent is shear heated to an elevated temperature between 40 °C and 70 °C, preferably between 40 °C and 55 °C.
Suitable shearing equipment is, for example, a high-speed rotor-stator mixer such as a Silverson® L4-R mixer, or a high-speed mixer using a Cowles serrated blade such as a Dispermat® mixer. As an example, blade size of the Cowles serrated blade may be 2 ‘A” at settings of 4500 to 6000 rpm yielding effective tip speeds in the range of 10 to 20 m/s. Typically, shear heating of the thixotropic agent to an elevated temperature of at least 40 °C is performed in a mixture with the liquid silicone rubber.
Preferably, shear heating to an elevated temperature of at least 40 °C is performed at a shear rate of at least 1000 s ' . This means that for shear heating to an elevated temperature of at least 40 °C, a high shear rate is applied, which means that shearing is performed with a high shear rate of at least 1000 s 1 Also shear rates higher than 1000 s’1 may be applied, for example, at least 2000 s’1, or at least 5000 s’1, or at least 10000 s’1, or at least 20000 s’1. Shear rates up to 60000 s’1 and higher may be applied. Shear heating to an elevated temperature of at least 40 °C is performed for the length of time it takes to reach the desired elevated temperature.
The thixotropic agent that is comprised in the castable composition disclosed herein comprises organic fibrils. Fibrils are composed of linear polymers, and are characterized by rod-like structures with high length-to-diameter ratios. Fibrils tend to have diameters in the sub-micron or nanometer scale range. Typically, the diameter of the fibrils ranges from 10-1000 nanometers and may even be from 10-100 nm. Fibrils are not to be confused with fibers, as fibers are micro to milli-scale structures.
The organic fibrils may be selected from the group consisting of polyamide polymer fibrils, castor oil fibrils, fibrils of a castor oil derivative, and combinations thereof. An example for fibrils of a castor oil derivative are fibrils of hydrogenated castor oil.
Preferably, the thixotropic agent that is comprised in the castable composition disclosed herein comprises a network of organic fibrils. As used herein, by “a network of organic fibrils” it is meant that the organic fibrils are entangled with one another and thus form a network, i.e., the organic fibrils are not chemically bonded together. The organic fibrils that form the network of organic fibrils may be selected from the group consisting of polyamide polymer fibrils, castor oil fibrils, fibrils of a castor oil derivative, and combinations thereof. An example for fibrils of a castor oil derivative are fibrils of hydrogenated castor oil.
The thixotropic agent typically is in powder form. By shear heating, the fine particles of the powder are converted to the network of organic fibrils. Without wishing to be bound by theory, it is the network of organic fibrils that provides the desired rheological behavior of the castable composition, i.e., a very high viscosity under the low shear rates associated with separation or float-out, and a low viscosity at the much higher application shear rates.
The mean particle size of the thixotropic agent may be measured by laser diffraction as described in the examples section. The mean particle size (d50) of the thixotropic agent may be at most 10 pm, or at most 8 pm, or at most 7 pm. Typically, the mean particle size (d50) of the thixotropic agent is from 1 to 10 pm. The d90 value of the particle size measurement of the thixotropic agent may be at most 20 pm, or at most 15 pm, or at most 12 pm. The d95 value of the particle size measurement of the thixotropic agent may be at most 25 pm, or at most 20 pm, or at most 15 pm.
The castable composition disclosed herein may comprise from 0.2 to 5 percent by weight of the thixotropic agent, based on the total weight of the castable composition.
The liquid silicone rubber that is comprised in the castable composition disclosed herein may comprise an addition curing type organopolysiloxane composition.
Such addition curing type organopolysiloxane compositions are well known by those skilled in the art of the silicone field. The addition curing type organopolysiloxane composition is preferably defined as primarily comprising (1) 100 parts by weight of an organopolysiloxane having at least two alkenyl groups attached to silicon atoms in a molecule, (2) 0.1 to 50 parts by weight of an organo-hydrogenpolysiloxane having at least two, preferably at least three hydrogen atoms attached to silicon atoms (i.e., SiH groups) in a molecule, and (3) a catalytic amount of an addition curing reaction catalyst.
Addition curing type organopolysiloxane compositions do not release reaction by-products so they can cure in closed environments. Their cure can also be greatly accelerated by heat curing however curing can be easily obtained without the need of heat, so at ambient temperature (23 °C, +/- 5 °C), by adjusting the level of inhibitor and/or catalyst which is a great advantage compared to, e.g., peroxide curing which needs to be heated to a temperature above 90 °C.
The addition curing type organopolysiloxane composition may comprise
(al) at least one organopolysiloxane having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing from 2 to 14 carbon atoms,
(a2) at least one silicon compound having at least two hydrogen atoms bonded to silicon per molecule, and
(a3) a hydrosilylation catalyst.
The alkenyl groups of the at least one organopolysiloxane may be chosen from the group consisting of vinyl, allyl, hexenyl, decenyl and tetradecenyl groups.
The at least one silicon compound may optionally have at least three hydrogen atoms bonded to silicon per molecule.
Hydrosilylation catalysts are well known in the art. The hydrosilylation catalyst is preferably a platinum based hydrosilylation catalyst. The addition curing type organopolysiloxane composition may optionally further comprise an inhibitor or cure rate controller which slows the curing rate of the addition curing type organopolysiloxane composition. Inhibitors are well known in the art.
The addition curing type organopolysiloxane composition is a two-part composition which is stored before use in two separate parts. The first part of the two-part composition may comprise at least one organopolysiloxane as defined above, and a hydrosilylation catalyst as defined above. The second part of the two-part composition may comprise at least one organopolysiloxane as defined above, at least one silicon compound having at least two hydrogen atoms bonded to silicon per molecule as defined above, and optionally a cure rate controller.
Hollow glass microspheres are also commonly known as "glass bubbles”, “glass microbubbles”, or “hollow glass beads”.
The hollow glass microspheres that are comprised in the castable composition disclosed herein may have an average true density of from 0.1 to 0.6 g/cm3. Preferably, the hollow glass microspheres have an average true density of from 0.1 to 0.3 g/cm3. Most preferably, the hollow glass microspheres have an average true density of from 0.1 to 0.28 g/cm3.
The term “average true density” is the quotient obtained by dividing the mass of a sample of hollow glass microspheres by the true volume of that mass of hollow glass microspheres as measured by a gas pycnometer. The “true volume” is the aggregate total volume of the glass bubbles, not the bulk volume.
For the purpose of this disclosure, average true density is measured using a gas pycnometer according to ASTM D2840-69, “Average True Particle Density of Hollow Microspheres”. The pycnometer may be obtained, for example, under the trade designation “Accupyc 1330 Pycnometer” from Micromeritics, Norcross, GA. Average true density can typically be measured with an accuracy of 0.001 g/cm3. Accordingly, each of the density values provided above can be +/- 0.003 g/cm3.
The hollow glass microspheres need to have a certain crush strength to survive mixing and dispensing of the castable composition. The hollow glass microspheres that are comprised in the castable composition disclosed herein may have a crush strength of at least 1.72 MPa (250 psi). The crush strength is defined as the hydrostatic pressure at which ten percent by volume of hollow glass microspheres collapses.
Typically, the hollow glass microspheres that are comprised in the castable composition disclosed herein have a crush strength ranging from 1.72 MPa (250 psi) to 186.15 MPa (27,000 psi).
The hollow glass microspheres that are comprised in the castable composition disclosed herein may have a size distribution comprising a median size by volume in a range from about 15 micrometers to about 65 micrometers. In the measurement of size “about” a given size can include a value +/- one percent. In some embodiments, the median size by volume of the hollow glass microspheres may be from 30 to 65 micrometers, from 35 to 65 micrometers, or even from 35 to 60 micrometers. The median size by volume is also called the d5o size, where 50 percent by volume of the hollow glass microspheres in the distribution are smaller than the indicated size. As used herein, the term size is considered to be equivalent with the diameter and height of the hollow glass microspheres. For the purposes of the present disclosure, the median size by volume is determined by laser light diffraction by dispersing the hollow glass microspheres in deaerated deionized water. Laser light diffraction particle size analyzers are available, for example, under the trade designation “SATURN DIGISIZER” from Micromeritics.
Hollow glass microspheres useful for practicing the present disclosure can be made by techniques known in the art (see, e.g., U.S. Pat. Nos. 2,978,340 (Veatch et al.); 3,030,215 (Veatch et al.); 3,129,086 (Veatch et al ); and 3,230,064 (Veatch et al.); 3,365,315 (Beck et al ); 4,391,646 (Howell); and 4,767,726 (Marshall); and U.S. Pat. App. Pub. No. 2006/0122049 (Marshall et al ). Techniques for preparing hollow glass microspheres typically include heating milled frit, commonly referred to as “feed”, which contains a blowing agent (e.g., sulfur or a compound of oxygen and sulfur).
Although the frit may have any composition that is capable of forming a glass, typically, on a total weight basis, the frit comprises from 50 to 90 percent of SiOj, from 2 to 20 percent of alkali metal oxide, from 1 to 30 percent of B2O3, from 0.005-0.5 percent of sulfur (for example, as elemental sulfur, sulfate or sulfite), from 0 to 25 percent divalent metal oxides (for example, CaO, MgO, BaO, SrO, ZnO, or PbO), from 0 to 10 percent of tetravalent metal oxides other than Si O2 (for example, TiOz. MnCL, or ZrCL), from 0 to 20 percent of trivalent metal oxides (for example, AI2O3, FczO;. or SbzCL). from 0 to 10 percent of oxides of pentavalent atoms (for example, P2O5 or V2O5), and from 0 to 5 percent fluorine (as fluoride) which may act as a fluxing agent to facilitate melting of the glass composition. Additional ingredients are useful in frit compositions and can be included in the frit, for example, to contribute particular properties or characteristics (for example, hardness or color) to the resultant hollow glass microspheres.
Hollow glass microspheres useful for practicing the present disclosure can be obtained commercially and include those prepared by a plurality of processes including spray drying and marketed by Potters Industries LLC, Malvern, PA, under the trade designations “SPHERICEL Hollow Microspheres” (e.g., grades 25P45 and 34P30) and Q-Cel 6019, 6028, 6036, 7028, and hollow glass microspheres marketed by Sinosteel Maanshan New Material Technology Co., Ltd., China, under the trade designation “H Series Hollow glass microspheres” (e.g., grades H20, H25, H32 H40) and hollow glass microspheres marketed by 3M Company, St. Paul, MN, under the trade designation “3M GLASS BUBBLES” (e.g., grades KI, K15, S15, K20, K20HS, S22, XLD3000, K25 and S28HS).
The castable composition as disclosed herein may comprise up to 60 percent by volume of hollow glass microspheres, based on the total volume of the castable composition. The castable composition as disclosed herein typically comprises from 20 to 60 percent by volume of hollow glass microspheres, based on the total volume of the castable composition.
The castable composition as disclosed herein may have a viscosity of at most 6 Pa-sec. Preferably, the viscosity of the castable composition is at most 3 Pa-sec, and most preferably, the viscosity of the castable composition is at most 2 Pa-sec.
The castable composition disclosed herein is curable at room temperature (23 °C).
Typically, the castable composition has a gel time of about 5 minutes. As used herein, the “gel time” is the time required to effectively solidify the castable composition at the curing temperature, i.e., at room temperature, such that further filling with the castable composition is impossible.
Further disclosed herein is a masterbatch composition for producing the castable composition as disclosed herein, the masterbatch composition comprising
(a) a liquid silicone rubber, and
(b) a thixotropic agent comprising organic fibrils.
The organic fibrils that are comprised in the thixotropic agent that is comprised in the masterbatch composition are created by shear heating the thixotropic agent to an elevated temperature of at least 40 °C.
Typically, the thixotropic agent is shear heated to an elevated temperature between 40 °C and 70 °C, preferably between 40 °C and 55 °C.
Preferably, shear heating is performed at a shear rate of at least 1000 s’1. Also shear rates higher than 1000 s’1 may be applied, for example, at least 2000 s’1, or at least 5000 s’1, or at least 10000 s’1, or at least 20000 s’1. Shear rates up to 60000 s’1 and higher may be applied.
The thixotropic agent that is comprised in the masterbatch composition disclosed herein comprises organic fibrils.
Preferably, the thixotropic agent that is comprised in the masterbatch composition disclosed herein comprises a network of organic fibrils.
Further specific and preferred details of the liquid silicone rubber and the thixotropic agent comprised in the masterbatch composition are as described above in the context of the castable composition. The castable composition as disclosed herein may be obtained by mixing the masterbatch composition disclosed herein with hollow glass microspheres and optionally additional liquid silicone rubber. Typically, the concentration of the thixotropic agent is higher in the masterbatch composition than in the castable composition, and the thixotropic agent is let-down from the higher concentration of the masterbatch composition to the final concentration in the castable composition. With a high concentration of the thixotropic agent in the masterbatch composition, shear forces may be effectively applied to the thixotropic agent to generate the fibrillation. The hollow glass microspheres are mixed with the masterbatch composition at low shear rate.
As used herein, a “low shear rate” is a shear rate in the range of from 1 to 100 s’1.
By mixing the hollow glass microspheres with the liquid silicone rubber and the let-down concentration of the masterbatch composition at low shear rate, breakage of the hollow glass microspheres is prevented.
A cured composition may be obtained by curing the castable composition as disclosed herein. Curing may be performed at room temperature (23 °C).
Typically, the castable composition comprises a first part and a second part, i.e., the castable composition is in the form of a two-part composition which is stored before use in two separate parts. Curing may be started by mixing the first part and the second part of the two-part composition.
Typically, the gel time is about 5 minutes.
The liquid silicone rubber comprises a first part and a second part, the first part being comprised in the first part of the castable composition, and the second part being comprised in the second part of the castable composition. The hollow glass microspheres may be comprised in the first part or the second part, or in both parts of the two-part composition. The thixotropic agent may be comprised in the first part or in the second part, or in both parts of the two-part composition.
Further disclosed herein is a process for making the masterbatch composition as disclosed herein, the process comprising mixing the liquid silicone rubber and the thixotropic agent, and creating the organic fibrils of the thixotropic agent by shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C.
Typically, the mixture of liquid silicone rubber and thixotropic agent is shear heated to an elevated temperature between 40 °C and 70 °C, preferably between 40 °C and 55 °C. The specific and preferred details of the liquid silicone rubber and the thixotropic agent are as described above in the context of the castable composition.
Preferably, shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C is performed at a shear rate of at least 1000 s’1. This means that for shear heating to an elevated temperature of at least 40 °C, a high shear rate is applied, which means that shearing is performed with a high shear rate of at least 1000 s ' . Also shear rates higher than 1000 s 1 may be applied, for example, at least 2000 s’1, or at least 5000 s’1, or at least 10000 s’1, or at least 20000 s’1. Shear rates up to 60000 s’1 and higher may be applied. Shear heating to an elevated temperature of at least 40 °C is performed for the length of time it takes to reach the elevated temperature.
By shear heating of the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C, the organic fibrils of the thixotropic agent are created. After shear heating the thixotropic agent in the mixture of thixotropic agent and liquid silicone rubber, the thixotropic agent comprises organic fibrils, preferably a network of organic fibrils.
Further disclosed herein is a process for making the castable composition as disclosed herein, the process comprising mixing the liquid silicone rubber and the thixotropic agent, shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C to form the organic fibrils of the thixotropic agent, and combining the hollow glass microspheres with the mixture of liquid silicone rubber and thixotropic agent at a shear rate in the range of from 1 to 100 s’1.
Typically, the mixture of liquid silicone rubber and thixotropic agent has a higher concentration of the thixotropic agent than the final castable composition, i.e., let-down composition. After shear heating the mixture of liquid silicone rubber and thixotropic agent, the mixture of liquid silicone rubber and thixotropic agent is let-down to the final concentration of the thixotropic agent, and the hollow glass microspheres are combined and mixed with the mixture of liquid silicone rubber and thixotropic agent.
Typically, the mixture of liquid silicone rubber and thixotropic agent is shear heated to an elevated temperature between 40 °C and 70 °C, preferably between 40 °C and 55 °C.
Combining the hollow glass microspheres with the mixture of liquid silicone rubber and thixotropic agent is performed at low shear rate, to prevent breakage of the hollow glass microspheres. By “low shear rate” it is meant that the shear rate typically is from 1 to 100 s’1. Preferably, shear heating the mixture of liquid silicone rubber and thixotropic agent is performed at a shear rate of at least 1000 s’1. Also shear rates higher than 1000 s’1 may be applied, for example, at least 2000 s’1, or at least 5000 s’1, or at least 10000 s’1, or at least 20000 s’1. Shear rates up to 60000 s’1 and higher may be applied.
By shear heating of the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C, the organic fibrils of the thixotropic agent are formed. After shear heating the thixotropic agent in the mixture of liquid silicone rubber and thixotropic agent, the thixotropic agent comprises organic fibrils, preferably a network of organic fibrils.
Further disclosed herein is a battery module comprising a plurality of battery cells and open space between the battery cells, wherein the open space is at least partially filled with the cured composition as disclosed herein. In some cases, at least 80% by volume of the open space is filled with the cured composition, e.g., in some cases at least 90%, at least 95%, or even at least 99% by volume of the open space is filled with the cured composition. In some cases, the cured composition totally fills the open space.
The battery module may further comprise a battery module casing, and the open space between the battery cells and the battery module casing is partially or fully filled with the cured composition disclosed herein.
The battery module may be used in electric vehicles.
Figure 1 schematically shows a perspective view of a battery module 100 comprising a plurality of battery cells 102 and a battery module casing 104. Between the battery cells 102, there is open space 106 which is to be filled with a castable composition as disclosed herein.
Figure 2 schematically shows a top view of a battery module 100 comprising a plurality of battery cells 102 and a battery module casing 104. The battery cells 102 can be very close together in the battery module 100. Between the battery cells 102, there is open space 106. By pouring a castable composition 108 as disclosed herein into the battery module casing 104, i.e., into the open space 106 between the battery cells 102, the open space 106 is filled with the castable composition 108. After pouring the castable composition 108 into the open space 106 between the battery cells 102, the castable composition is cured, yielding a cured composition. Examples
Test Methods
Crush strength test
The crush strength of the hollow glass microspheres was measured using ASTM D3102-72 “Hydrostatic Collapse Strength of Hollow Glass Microspheres”; with the following modifications. The sample size (in grams) was equal to 10 times the density of the hollow glass microspheres. The hollow glass microspheres were dispersed in glycerol (20.6 g), and data reduction was automated using computer software. The value reported is the hydrostatic pressure at which 10 percent by volume of the hollow glass microspheres collapse (crush strength at 90% survival).
Particle size measurement
Particle size of the thixotropic agent was measured by laser diffraction, using a Laser Diffraction Particle Size Analyzer S3500 from Microtrac. For the measurements, a 0.5% dilution of BYK-333 (available from BYK-Chemie GmbH, Wesel, Germany) in deionized water was used as surfactant. The mean particle size d50, and the d90 and d95 values were reported.
True density measurement
True density of hollow glass microspheres can most conveniently be measured using gas pycnometry, which is a common analytical technique that uses a gas displacement method to measure volume accurately. In this method, the sample weight is measured on an analytical balance (Ms) and then sealed in the instrument compartment of known volume, the appropriate inert gas (e.g., helium, nitrogen) is admitted, and then expanded into another precision internal volume. The pressure before and after expansion is measured and used to compute the sample volume (Vs) using the ideal gas law. The true density of the sample (ps) is the sample mass divided by the sample volume (ps = Ms/Vs).
Materials Used in the Examples
A masterbatch composition was prepared by first dispersing 20 g of Crayvallac® SLT in 80 g of BlueSil™ ESA 7203 (Part A, i.e., the first part of the two-part composition of liquid silicone rubber) at 600 rpm with an impeller mixer for 5 minutes (low shear) and then mixing the obtained premix by using a Silverson L4R Mixer equipped with a tubular mixing head and rotor/stator configuration at 13500 rpm (corresponding to a shear rate of 75000 s 1 (high shear)) for 3 minutes. The mixing operation with the Silverson L4R Mixer raised the temperature of the slurry to 50 °C, shear heating the Crayvallac® SLT and creating a fibrillated network. The BlueSil™ ESA 7203 (Part A) has a starting viscosity of 100 mPa-sec.
The final composition, i.e., the first part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 71.5 g of BlueSil™ ESA 7203 and 12.5 g of the masterbatch which results in an amount of Crayvallac® SLT of 2.5 wt.-% in the final composition. The content of the BlueSil™ ESA 7203 (Part A) in the final composition was 81.5 wt.-%. The mixing was performed in a Dispermat® mixer using a Cowles serrated blade at 700 - 900 rpm for 5 minutes in a 250 ml plastic beaker. By mixing the glass bubbles with low shear rate, breakage of the glass bubbles was avoided (as evidenced by measuring pycnometer density and comparing to theoretical density), while the fibrillated network of the thixotropic agent was maintained. The obtained sample of the final composition was stored for visual examination in a regular walled/ straight sided 16 oz polypropylene jar.
The obtained sample of the final composition is homogeneous and remains homogeneous even after keeping the mixture for 60 days at ambient conditions, no visual separation could be observed. After 75 days, visual separation could be observed, with a clear phase width of 5 mm (see Table 1).
A composition having the same amounts and grades of LSR, thixotropic agent and glass bubbles as the final composition of Example 1 was prepared in a one-step process, i.e., without first preparing a masterbatch. 81.5 g of BlueSil™ ESA 7203 (Part A), 2.5 g of Crayvallac® SLT and 16 g of glass bubbles K25 were mixed in a Dispermat® mixer using a Cowles serrated blade at 3000 rpm (moderate shear rate) for 5 minutes in a 250 ml plastic beaker. By the mixing, the temperature of the slurry was raised slightly above room temperature to 25 °C. A higher shear rate would break a significant portion of the glass bubbles releasing sulfur oxides that foul the platinum catalyst of the LSR, inhibiting cure. The obtained sample of the composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar. The obtained sample of the composition was homogeneous after the mixing, but the glass bubbles separated from the silicone oil in less than a day and were concentrated on the surface of the slurry (see Table 1).
Comparative Example 2 (CEX2)
A composition having the same amount and grade of glass bubbles and the same grade of LSR as the final composition of Example 1 was prepared. No thixotropic agent was used. The composition was prepared by mixing 16 g of glass bubbles K25 with 84 g of BlueSil™ ESA 7203 (Part A) in a Dispermat® mixer using a Cowles serrated blade at 700 - 900 rpm for 5 minutes (low shear) in a 250 ml plastic beaker. The obtained sample of the composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar.
The obtained sample of the composition was homogeneous after the mixing, but the glass bubbles separated from the silicone oil in only a few hours (i.e., less than 24 hours) and were concentrated on the surface of the slurry. After 3 days, a hard pack of glass bubbles formed on the surface of the slurry (see Table 1).
Example 2 (EX2)
For Example 2, Crayvallac® PF was used as thixotropic agent. The particle size of Crayvallac® PF was measured as described above in the test methods section. The mean particle size (d50) is 5 pm, the d90 value is 9 pm, and the d95 value is 11 pm.
A masterbatch composition was prepared by first dispersing 20 g of Crayvallac® PF in 80 g of BlueSil™ ESB 7203 (Part B, i.e., the second part of the two-part composition of liquid silicone rubber) at 600 rpm with an impeller mixer for 5 minutes (low shear) and then mixing the obtained premix by using a Silverson L4R Mixer equipped with a tubular mixing head and rotor/stator configuration at 9600 rpm (corresponding to a shear rate of 57000 s"1 (high shear)) for 5 minutes. The mixing operation with the Silverson L4R Mixer raised the temperature of the slurry to 53 °C as measured with an IR thermometer, shear heating the Crayvallac® PF and creating a fibrillated network.
The final composition, i.e., the second part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 64 g of BlueSil™ ESB 7203 and 20 g of the masterbatch which results in an amount of Crayvallac® PF of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESB 7203 (Part B) in the final composition was 80.0 wt.-%. The mixing was performed in a 250 ml plastic beaker, gently by hand, with a stainless steel spatula, to achieve a homogeneous mixture. The obtained sample of the final composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar. The obtained sample of the final composition is initially homogeneous and is easily re-homogenized even after keeping the mixture for 35 days at ambient conditions (see Table 2).
Comparative Example 3 (CEX3)
For Comparative Example 4, Thixcin® R was used as thixotropic agent. The particle size of Thixcin® R was measured as described above in the test methods section. The mean particle size (d50) is 11 pm, the d90 value is 24 pm, and the d95 value is 29 pm.
A masterbatch composition was prepared by first dispersing 20 g of Thixcin® R in 80 g of BlueSil™ ESB 7203 (Part B) at 600 rpm with an impeller mixer for 5 minutes and then mixing the obtained premix by using a Silverson L4R Mixer equipped with a tubular mixing head and rotor/stator configuration at 9600 rpm (corresponding to a shear rate of 57000 s’1 (high shear)) for 5 minutes. The mixing operation with the Silverson L4R Mixer raised the temperature of the slurry to 52 °C as measured with an IR thermometer.
The final composition was prepared by mixing 16 g of glass bubbles K25 with 64 g of BlueSil™ ESB 7203 and 20 g of the masterbatch which results in an amount of Thixcin® R of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESB 7203 (Part B) in the final composition was 80.0 wt.-%. The mixing was performed in a 250 ml plastic beaker gently by hand with a stainless steel spatula, to achieve a homogeneous mixture. The obtained sample of the final composition was stored for visual examination in a regular walled/ straight sided 16 oz polypropylene jar.
Unlike Example 2, this comparative example exhibited visual separation of the glass bubbles from the LSR in 2 days and had a hard pack of glass bubbles concentrated at the surface of the slurry after 35 days requiring moderate work and significant time to re-homogenize (see Table 2).
Example 3 (EX3)
100 g of a masterbatch composition of 80 wt.-% BlueSil ESA 7203 (i.e., Part A) and 20 wt.-% Crayvallac PF was prepared using a combination of mixing techniques, starting with a FlackTec Speed Mixer at 1000 rpm in a wide-mouth polypropylene mixer cup, using three 1 :00 minute mixing cycles, followed by a 1:00 minute mixing cycle in a Silverson L4R Mixer equipped with the tubular mixing head and rotor/ stator configuration at the lowest setting (approx. 6000 rpm), followed by 5 minutes at 9000 rpm (corresponding to a shear rate of 52360 s’1) with cup movement by hand to move the mixer element through the entire volume of the mixing cup to achieve a mass temperature of 50 °C.
A final composition, i.e., the first part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 64 g of BlueSil™ ESA7203 and 20 g of the masterbatch which results in an amount of Crayvallac® PF of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESA 7203 (Part A) in the final composition was 80.0 wt-%. The masterbatch and glass bubbles were added and mixed by hand at minimal shear. The obtained sample of the final composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar. The obtained sample of the final composition is initially homogeneous and is easily re-homogenized even after keeping the mixture for 100 days at ambient conditions (see Table 3).
Example 4 (EX4)
100g of a masterbatch of 80 wt.-% BlueSil™ ESB 7203 (i.e., Part B) and 20 wt.-% Crayvallac PF was made by using a FlackTec Speed Mixer at 2400 rpm in a wide-mouth polypropylene mixer cup for multiple cycles to achieve a temperature of > 40 °C (47 °C as measured with an IR thermometer).
A final composition, i.e., the second part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 64 g of BlueSil™ ESB 7203 and 20 g of the masterbatch which results in an amount of Crayvallac® PF of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESB 7203 (Part B) in the final composition was 80.0 wt.-%. The masterbatch and glass bubbles were added and mixed by hand at minimal shear. The obtained sample of the final composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar. The obtained sample of the final composition is initially homogeneous and is easily rehomogenized even after keeping the mixture for 100 days at ambient conditions (see Table 3).
Example 5 (EX5)
100 g of a masterbatch combining 90.0 wt.-% BlueSil™ ESA 7203 (i.e., Part A) with 10.2 wt.-% Crayvallac PF was made in two steps. First the BlueSil™ ESA 7203 was weighed into a polypropylene mixing cup (6“ x 6“ diameter) and the Crayvallac PF was weighed in on top. The mixture was dispersed using an impeller mixer (Dispermat) equipped with a timer and digital speed display, and fitted with a 2“ diameter Cowles blade, at 1000 rpm for 10 minutes. This resulted in a 1-2 °C temperature increase maximum as measured by infrared thermometer, but dispersed the lumps of the additive completely. Next this premix was shear heated using the same Dispermat mixer and Cowles blade arrangement over a 95 minute mixing time with increasing speeds up to a maximum of 6600 rpm (corresponding to a shear rate of 1134 s’1), which resulted in a temperature rise to > 45 °C.
A final composition, i.e., the first part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 44 g of BlueSil™ ESA 7203 and 40 g of the masterbatch which results in an amount of Crayvallac® PF of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESA 7203 in the final composition was 80.0 wt.-%. The masterbatch and glass bubbles were added and mixed by hand at minimal shear. The obtained sample of the final composition was stored for visual examination in a regular walled/straight sided 16 oz polypropylene jar. The obtained sample of the final composition is initially homogeneous, and at 100 days the surface re-levels when perturbed, no separation is seen and is easily remixed (see Table 4). Example 6 (EX6)
100 g of a masterbatch combining 90.0 wt.-% BlueSil™ ESB 7203 (i.e., Part B) with 10 wt.-% Crayvallac PF was made in two steps. First the BlueSil™ ESB 7203 was weighed into a polypropylene mixing cup (6“ x 6“ diameter) and the Crayvallac PF was weighed in on top. The mixture was dispersed using an impeller mixer (Dispermat) equipped with a timer and digital speed display, and fitted with a 2“ diameter Cowles blade, at 1000 rpm for 10 minutes. This resulted in a 1-2 °C temperature increase maximum as measured by infrared thermometer, but dispersed the lumps of the additive completely. Next this premix was shear heated using the same Dispermat mixer and Cowles blade arrangement over a 95 minute mixing time with increasing speeds up to a maximum of 6600 rpm, which resulted in a temperature rise to > 45 °C.
A final composition, i.e., the second part of a castable composition according to the present disclosure, was prepared by mixing 16 g of glass bubbles K25 with 44 g of BlueSil™ ESB 7203 and 40 g of the masterbatch which results in an amount of Crayvallac® PF of 4.0 wt.-% in the final composition. The content of the BlueSil™ ESB 7203 in the final composition was 80.0 wt.-%. The masterbatch and glass bubbles were added and mixed by hand at minimal shear. The obtained sample of the final composition was stored for visual examination in a regular walled/ straight sided 16 oz polypropylene jar. The obtained sample of the final composition is initially homogeneous, and at 100 days the surface re-levels when perturbed, no separation is seen and is easily remixed (see Table 4).
Example 7 (EX7)
A final castable composition, i.e., a castable composition according to the present disclosure, was made by combining Examples 6 and 7 in equal amounts (50/50 vol.-%). Gel time was observed to be the same (5 minutes) as the 50/50 vol.% combination of Part A and Part B with the same loading of glass bubbles but no thixotropic agent. This confirms that the addition of thixotropic agent does not affect the cure kinetics of the castable composition.
Comparative Example 4 (CEX4)
100 g of a commercially available castable composition comprising a liquid silicone rubber and glass bubbles (Bluesil™RT Foam 3250, Part A, available from Elkem, Norway), were poured into a regular walled/ straight sided 16 oz polypropylene jar and stored for visual examination.
Already after one week, the glass bubbles separated from the silicone oil and were concentrated on the surface of the slurry. A hard pack of glass bubbles formed on the surface of the slurry, the silicone oil is at the bottom of the polypropylene jar. With a stainless steel spatula poking through the surface, the hard pack at the surface doesn’t relevel. The hard pack is dry (i.e., the spatula is not wetted by the hard pack) and has a stiff consistency similar to peanut butter. The sample is hard to remix, it requires significant force to penetrate with a stainless steel spatula and more than 10 minutes to re-homogenize (corresponding to a surface toughness value of 3, with the surface toughness indicated as explained below).
The same result was obtained with Part B of the commercially available castable composition comprising a liquid silicone rubber and glass bubbles (Bluesil™RT Foam 3250, Part B, available from Elkem, Norway).
Compositions and results for the examples and comparative examples are summarized in Tables 1 to 4.
In the tables, “Clear phase width” is the height of the clear phase measured off the bottom of the beaker; “0 mm” means that there is no separation. The higher the clear phase width, the more separation occurred.
In the tables, the indication “high shear”, “medium shear” and “low shear” means that the samples have been prepared as follows, corresponding to the indicated shear rate ranges:
High Shear: Silverson L4R or Cowles or Speed Mixer for long enough period of time to generate > 40 °C (shear rate at least 1000 s’1)
Medium Shear: Cowles or Speed Mixer for a short period of time that doesn't generate shear heating (shear rate from 100 s’1 to below 1000 s’1)
Low Shear: hand mixing or impeller mixer (shear rate at most 100 s’1)
In the tables, the row “Thixotropic agent form” includes a short description of how the thixotropic agent was introduced into the composition. “MB” means masterbatch.
In the tables, “Surface Toughness” is indicated by a scale of 1 to 3, where the numbers 1, 2 and 3 have the following meaning:
1 = soft, surface relevels when perturbed (with a stainless steel spatula poking through the surface), easily remixed (can be re-homogenized by hand stirring in < 1 minute), stainless steel spatula is wetted by the sample when poked through the surface
2 = soft, surface doesn't relevel when perturbed (with a stainless steel spatula poking through the surface), easily remixed (can be re-homogenized by hand stirring in < 1 minute), stainless steel spatula is wetted by the sample when poked through the surface
3 = hard, surface doesn't relevel when perturbed (with a stainless steel spatula poking through the surface), hard to remix (surface is stiff and dry and forms a hard pack, and requires significant force to penetrate with a stainless steel spatula, potentially breaking the glass bubbles, and more than 10 minutes to re-homogenize), stainless steel spatula is not wetted by the sample when poked into the hard pack at the surface Intermediate values of 1.5 (between 1 and 2) and 2.5 (between 2 and 3) are also possible.
Table 1
Table 2
Table 3
Table 4
No visual separation when surface toughness was observed.

Claims

Claims
1. A castable composition comprising,
(a) a liquid silicone rubber,
(b) a thixotropic agent comprising organic fibrils, and
(c) hollow glass microspheres.
2. The castable composition of claim 1, wherein the thixotropic agent comprises a network of the organic fibrils.
3. The castable composition of claim 1 or 2, wherein the thixotropic agent is selected from the group consisting of polyamide polymers, castor oil, castor oil derivatives, and combinations thereof.
4. The castable composition of claim 3, wherein the thixotropic agent comprises a polyamide polymer, wherein the polyamide polymer comprises silanol functional groups.
5. The castable composition of any one of the preceding claims, wherein the thixotropic agent has a mean particle size (d50) of at most 10 pm.
6. The castable composition of any one of the preceding claims, comprising from 0.2 to 5 percent by weight of the thixotropic agent, based on the total weight of the castable composition.
7. The castable composition of any one of the preceding claims, wherein the liquid silicone rubber comprises an addition curing type organopolysiloxane composition.
8. The castable composition of claim 7, wherein the addition curing type organopolysiloxane composition comprises
(al) at least one organopolysiloxane having at least two alkenyl groups bonded to silicon per molecule, said alkenyl groups each containing from 2 to 14 carbon atoms,
(a2) at least one silicon compound having at least two hydrogen atoms bonded to silicon per molecule, and
(a3) a hydrosilylation catalyst.
9. The castable composition of any one of the preceding claims, wherein the hollow glass microspheres have an average true density of from 0.1 to 0.6 g/cm-f
10. The castable composition of any one of the preceding claims, wherein the hollow glass microspheres have a crush strength of at least 1.7 MPa, wherein the crush strength is defined as the hydrostatic pressure at which ten percent by volume of hollow glass microspheres collapses.
11. The castable composition of any one of the preceding claims, wherein the castable composition comprises from 20 to 60 percent by volume of hollow glass microspheres, based on the total volume of the castable composition.
12. The castable composition of any one of the preceding claims, wherein the castable composition has a viscosity of at most 6 Pa-sec.
13. The castable composition of any one of the preceding claims, wherein the castable composition is curable at 23 °C.
14. A cured composition obtained by curing the castable composition of any one of the preceding claims.
15. A battery module comprising a plurality of battery cells and open space between the battery cells, wherein the open space is at least partially filled with the cured composition of claim 14.
16. A process for making the castable composition of any of claims 1 to 13, the process comprising mixing the liquid silicone rubber and the thixotropic agent, shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C to form the organic fibrils of the thixotropic agent, and combining the hollow glass microspheres with the mixture of liquid silicone rubber and thixotropic agent at a shear rate in the range of from 1 to 100 s’1.
17. The process of claim 16, wherein shear heating the mixture of liquid silicone rubber and thixotropic agent is performed at a shear rate of at least 1000 s’1.
18. A masterbatch composition comprising
(a) a liquid silicone rubber, and
(b) a thixotropic agent comprising organic fibrils.
19. The masterbatch composition of claim 18, wherein the thixotropic agent comprises a network of the organic fibrils.
20. A process for making the masterbatch composition of claim 18 or 19, the process comprising mixing the liquid silicone rubber and the thixotropic agent, and creating the organic fibrils of the thixotropic agent by shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C.
21. The process of claim 20, wherein shear heating the mixture of liquid silicone rubber and thixotropic agent to an elevated temperature of at least 40 °C is performed at a shear rate of at least 1000 s .
EP24736095.1A 2023-07-21 2024-06-19 Castable composition comprising liquid silicone rubber and hollow glass microspheres Pending EP4705391A1 (en)

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Publication number Priority date Publication date Assignee Title
NL232500A (en) 1957-10-22
US3230064A (en) 1960-10-21 1966-01-18 Standard Oil Co Apparatus for spherulization of fusible particles
US3365315A (en) 1963-08-23 1968-01-23 Minnesota Mining & Mfg Glass bubbles prepared by reheating solid glass partiles
US4391646A (en) 1982-02-25 1983-07-05 Minnesota Mining And Manufacturing Company Glass bubbles of increased collapse strength
US4767726A (en) 1987-01-12 1988-08-30 Minnesota Mining And Manufacturing Company Glass microbubbles
US20060122049A1 (en) 2004-12-03 2006-06-08 3M Innovative Properties Company Method of making glass microbubbles and raw product
JP4952882B2 (en) * 2006-01-13 2012-06-13 信越化学工業株式会社 Liquid silicone rubber coating composition, curtain airbag and method for producing the same
EP3580278A1 (en) 2017-02-08 2019-12-18 Elkem Silicones USA Corp. Silicone rubber syntactic foam
EP3580790B1 (en) 2017-02-08 2024-01-24 Elkem Silicones USA Corp. Secondary battery pack with improved thermal management

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Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC ME MK MT NL NO PL PT RO RS SE SI SK SM TR