TWO-PART CURABLE THERMALLY CONDUCTIVE COMPOSITION

FIELD

[0001] The present invention relates to thermally conductive compositions generally, and more particularly to two-part curable thermally conductive compositions with enhanced storage stability for extended shelf life.

BACKGROUND

[0002] Two-part curable thermally conductive compositions have been widely used as thermal interface materials, potting compounds, adhesives and sealants in electronics, power, and automotive applications. Both parts of the curable compositions are kept in dispensable form in separate containers and pumped through hoses and a mixing nozzle before they are applied onto substrates or injected to fill interstitial gaps. The material solidifies upon curing and functions to dissipate heat from heat generating devices to cooling devices. For high throughput applications, the viscosity of the liquid phase in the curable composition is typically reduced to facilitate a high flow rate when pumped out of the container. However, the thermally conductive fillers in conventional dispersions typically have a much greater density than the liquid phase. For example, widely used thermally conductive alumina filler is about 3.9 g/cc, silicon carbide is 3.2 g/cc, and zinc oxide is 5.6 g/cc, whereas a commonly used liquid phase such as silicone oil resin is only 0.97 g/cc. As a result, the solid conductive fillers tend to sediment, resulting in a liquid oil separation on the top of the package and a poor storage stability. It is therefore an aim to reduce particle sedimentation and composition separation to enhance storage stability.

[0003] For a typical curable thermally conductive composition, liquid oil separation during storage is a well known phenomena, and it is often used as an indicator of an expiration of shelf life due to its visually identifiable characteristic while in its packaging. The separated oil layer and subsequent oil rich layer from the bulk mixture is unusable as-is because such separated layer(s) lack sufficient particulate matter presence that otherwise provides the thermal conductivity properties to the composition. The composition gradient from oil-rich to particulate filler-rich layers due to filler sedimentation also creates large variation in rheological and other physical properties across the dispensable composition. These factors usually lead to a limited shelf life for high dispensing rate compositions. Otherwise, rheological modification must be performed on the composition, typically by increasing low-shear viscosity in order to achieve a suitable minimum shelf life.

[0004] Currently, many thermally conductive dispersions are pumped or dispensed at room temperature. However, it is known that viscosity of a fluid tends to decrease at higher temperature, so it is also a common practice to increase the dispensing flow rate by bringing the pumping equipment to a slightly elevated temperature, such 30-40C. In this approach, the tendency for oil separation during storage at room temperature can be mitigated but not eliminated. It is desired to minimize oil separation from the particulate filler for a long shelf life, but not at the cost of low pumping flow rates. Thus, it is desired to have both high flowability and long shelf life.

[0005] The fundamental cause of filler sedimentation in the storage of thermally conductive dispersions is the density difference between the filler and the liquid dispersing media. According to Stokes’ law, the terminal sedimentation velocity of a spherical particle in a dilute dispersion is:

(gravitationally downwards if p _P > pf, upwards if p _P < pt ), where:

• g is the gravitational field strength (m/s ² )

• R Is the radius or the spherical particle (m)

• p _P is the mass density of the particle (kg/m ³ )

• pt is the mass density of the fluid (kg/m ³ )

• is the dynamic viscosity (kg/(m*s)).

[0006] Even though this equation cannot be directly applied to high filler loading systems such as thermally conductive dispersions, it implies several factors that affect the filler sedimentation rate. Based on these factors, several approaches are commonly used to improve the storage stability of thermally conductive dispersions. [0007] One approach is to use a higher viscosity liquid dispersing media so that the solid particles will experience higher frictional drag force from the liquid media during sedimentation. However, this also negatively impacts the flowability of the dispersion, thereby limiting its pumping flow rate. Another approach is to use lower density filler to reduce the sedimentation rate. However, filler selection often is affected by many factors such as physical properties and cost. For example, alumina is by far the most popular filler in this field because of low cost and good thermal conductivity, but its density is close to 4 g/ml. Alumina trihydrate has lower density, but its thermal conductivity is also much lower. Boron nitride has lower density and high thermal conductivity, but its cost is very high and it has a less favorable morphology for dispersions. A third approach is to use fillers of smaller size. However, due to the high surface area of small-sized filler particles, more dispensing liquid is required to wet out the particulate filler, which significantly limits the maximum filler loading concentration. Although these approaches can improve the storage stability, they also detrimentally affect the performance of the thermally conductive materials.

[0008] To minimize the impact on the performance of thermally conductive materials, thixotropic rheological modifiers may be used to increase the viscosity of the dispersion at low shear rates while maintaining flowability at high shear rates. Common rheological modifiers include fumed silica and nanoclay. The modifiers may be dispersed as very fine particles and form aggregates in a controlled manner at rest state (no flow) to reduce particle settling. This approach works well in paints and coating dispersions, but it is less effective in thermally conductive dispersions which are already highly filled with inorganic particles. The nanoparticles in the rheological modifiers also compete with thermally conductive fillers for dispersing agents, so rheological modifiers also tend to increase the viscosity of the thermally conductive dispersions at high shear rates. This undesirably reduces the flow rate during dispensing. Another drawback of rheological modifier is that over time they can aggregate and become less effective.

[0009] Wax materials have shown to improve the storage stability of filler dispersions as rheology modifiers. For example, US patent no. 6,743,756 shows hydrogenated castor oil or wax improved dispersion of polyalkylene glycol. Such wax materials have been marketed as rheology modifiers, such as Efka™ RM 1463 from BASF, Disperlon™ 6500 from Kusumoto Chemicals, and Rheobyk™ 100 from BYK. Example waxes include polyamide, polyurea, or castor oil based waxes. However, the storage stability of the curable compositions relies on an activation by heat and shear forces below the wax's melting point for best performance. These waxes have high melting point, usually > 80 °C, and high molecular weight to facilitate aggregation or structuring of the molecules to function as rheology modifier. As such, at elevated temperatures up to standard operating conditions, these dispersions still do not exhibit significantly improved pumping rates.

SUMMARY

[0010] By means of the present invention, shelf life of curable thermally conductive compositions may be improved without detrimentally impacting high-shear flowability, such as in the case of pumping the composition from a container through an orifice. A low-melting point phase changing compound acts to increase composition viscosity at storage temperatures, while facilitating a viscosity reduction when being pumped at an elevated dispensing temperature. Preferably, the elevated temperature needed for viscosity reduction is only moderately above the storage temperature.

[0011] In one embodiment, a thermally conductive curable composition includes a first part that is initially separated from a second part, and a curable system having a curable component in the first part and a chemical cure activator in the second part. The chemical cure activator promotes a cure reaction involving the curable component to form a matrix when the curable component is exposed to the chemical cure activator. The thermally conductive curable composition further includes thermally conductive particulate filler in at least one of the first and second parts having a liquid phase. A phase changing compound is in at least one of the first and second parts including the thermally conductive filler. The phase changing compound is solid at 20 °C and is meltable or dissolvable into the liquid phase at temperatures above 20 °C. The phase changing compound has a melting point temperature of between 20 °C and 100 °C and is present in the respective one or more parts at an effective concentration so that the respective one or more parts exhibits a phase-change at between 0 °C and 50 °C. [0012] The first curable component of the thermally conductive curable composition may include a monomer, an oligomer, or a polymer, and the cure activator may be selected from a monomer, an oligomer, a polymer, a reaction initiator, a catalyst, a cross-linking agent, and combinations thereof. In some embodiments, the first curable component includes a first resin, and the cure activator includes a second resin that is reactive with the first resin to form the matrix.

[0013] In at least one of the first and second parts including the phase changing compound, the liquid phase may exhibit a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s' ¹ . In some embodiments, the composition includes a liquid diluent having a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s ^-1 .

[0014] In some embodiments, the thermally conductive particulate filler is present at a concentration of between 60-95% by weight of the composition. The thermally conductive filler may be selected from, for example, boron nitride, alumina, alumina trihydrate, aluminum, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, and combinations thereof.

[0015] The cure reaction to form the matrix may be selected from hydrosilylation from vinyl and hydride functional silicone resins, urethane reaction from hydroxyl and isocyanate functional monomers or resins, epoxy polymerization from epoxide and at least one of amino, mercapto, and anhydride functional monomers or resins, radical polymerization of vinyl or vinylidene functional monomers or resins, and condensation polymerization of silane- or silanol- terminated resins.

[0016] In some embodiments, the phase changing compound may be selected from esters, amides, urethanes, and ureas derived from C12-C20 alcohols or acids, and C12- C20 glycerides derived from animal fat or plant oil, hydrocarbon paraffins and combinations thereof. In some embodiments, the phase changing compound has a molecular weight of less than 2000 g/mol, and may be present in the composition at less than 10% by weight.

[0017] A thermally conductive curable composition includes a first part that is initially separated from a second part, and a liquid phase that is flowable at 20 °C with a viscosity of less than 500 cP at a shear rate of 1 s' ¹ . The liquid phase may include a first curable system having a first curable component in the first part and a first chemical cure activator in the second part, wherein the first chemical cure activator promotes a cure reaction involving the first curable component when the first curable component is exposed to the first chemical cure activator. In other embodiments, the liquid phase may include a second curable system having a second curable component in the first part and a second chemical cure activator in the second part, wherein the second chemical cure activator promotes a cure reaction involving the second curable component to form a second matrix when the second curable component is exposed to the second chemical cure activator. The second curable system may further include a liquid diluent exhibiting a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s ^-1 . The thermally conductive curable composition further includes thermally conductive particulate filler in at least one of the first and second parts, and a phase changing compound in the at least one of the first and second parts including the thermally conductive filler. The phase changing compound may exhibit a melting point temperature of between 20 °C and 100 °C.

[0018] In some embodiments, the liquid phase exhibits a viscosity of less than 200 cP at 20 °C at a shear rate of 1 s ^-1 .

[0019] In some embodiments, the thermally conductive curable composition includes less than 30% by weight liquid diluent.

[0020] A thermal interface may be formed from a two-part composition that includes a first part having a liquid phase that exhibits a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s' ¹ , one of a curable component or a chemical cure activator as a constituent of or mixed with the liquid phase, thermally conductive particulate filler, and a phase changing compound, wherein the first part preferably follows the formula of ps/pso > 5, wherein ps = the viscosity of the first part at 5 °C and a shear rate of no greater than 0.1 s' ¹ , and wherein pso = the viscosity of the first part at 50 °C and a shear rate of no greater than 0.1 s ^-1 . The second part of the two-part composition includes the other of the curable component or the chemical cure activator, wherein the thermal interface exhibits a hardness of at least 10 Shore OO and a thermal conductivity of at least 1 W/m*K. [0021] The thermal interface may include a liquid phase that exhibits a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s ^-1 in the second part, and thermally conductive filler in the second part.

[0022] In some embodiments, at least a portion of the thermally conductive particulate filler may be surface modified with a modifier having between 3 and 20 carbon atoms. In some embodiments, the modifier may be selected from a silane and a fatty acid.

[0023] An electronic package may include an electronic component and the thermal interface coupled to the electronic component. The electronic package may include a heat dissipater, wherein the thermal interface may be disposed along a heat dissipation pathway between the electronic device and the heat dissipater. The thermal interface may be in contact with at least one of the electronic component and the heat dissipater. [0024] A battery system may include a battery cell and the thermal interface coupled to the battery cell. The battery system may include a battery module having a plurality of battery cells contained within a case, wherein the thermal interface is disposed between adjacent ones of the battery cells, disposed between respective ones of the battery cells and the case, or both. The thermal interface may be disposed along a heat dissipation pathway between one or more of the battery cells and the case. The battery system may include a battery pack having a plurality of battery modules and a container, wherein the thermal interface is disposed along a heat dissipation pathway between one or more of the battery modules and the container.

[0025] A method for applying a thermally conductive material to a surface or a gap includes providing a two-part composition having a first part and a second part. The first part may be disposed in a first vessel, with the first part including a liquid phase that is liquid at 20 °C and 1 bar pressure, one of a curable component or a chemical cure activator as a constituent of or mixed with the liquid phase, thermally conductive particulate filler, and a phase changing compound having a melting point temperature of between 20 °C and 100 °C. The chemical cure activator promotes a cure reaction involving the curable component to form a matrix of the thermally conductive material. The second part of the two-part composition may be disposed in a second vessel, with the second part including the other of the curable component or the chemical cure activator. The method includes dispensing the first and second parts from their respective first and second vessels through respective first and second conduits to at least one orifice. At least the first part is heated to an elevated temperature exceeding 25 °C but no greater than 50 °C. Subsequent to heating at least the first part, the method further includes dispensing the composition through the at least one orifice to the surface or the gap.

[0026] In some embodiments, the method includes dispensing the first and second parts through respective first and second conduits to a mixing chamber, wherein the orifice is downstream from the mixing chamber. Heat may be applied to at least the first part in one or more of the vessel, the first follower if present, the first conduit, and the mixing chamber. In some embodiments, the second part may be heated to a temperature exceeding 25 °C but no greater than 50 °C.

[0027] The second part may include a liquid phase that is liquid at 20 °C and 1 bar pressure, thermally conductive filler, and a phase changing compound having a melting point temperature of between 20 °C and 100 °C.

[0028] The cure activator may be selected from a monomer, a polymer, a reaction initiator, a catalyst, and combinations thereof.

[0029] A heated dispensing rate of the first part at 50 °C is at least 50% greater than an unheated dispensing rate of the first part at 5 °C. In some embodiments, the heated dispensing rate is at least 200% greater than the unheated dispensing rate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic illustration of a heated dispensing system for a two-part curable composition of the present invention.

[0031] Figure 2A is a schematic illustration of a heated dispensing system for a two- part curable composition of the present invention stored in separated cartridges.

[0032] Figure 2B is a schematic illustration of a heated dispensing system for a two- part curable composition of the present invention stored in a two-part cartridge kit.

[0033] Figure 3 is a schematic illustration of an electronic package employing a thermal interface of the present invention.

[0034] Figure 4 is a schematic illustration of a battery system employing a thermal interface of the present invention.

[0035] Figure 5A is a chart depicting endothermic peaks that indicate phase transitions upon heating the curable compositions of the present invention.

[0036] Figure 5B is a chart depicting exothermic peaks that indicate phase transitions upon cooling the curable compositions of the present invention.

[0037] Figure 6A is a chart depicting viscosity changes that indicate phase transitions upon heating the curable compositions of the present invention.

[0038] Figure 6B is a chart depicting viscosity changes that indicate phase transitions upon cooling the curable compositions of the present invention.

[0039] Figure 7A is a chart depicting endothermic peaks that indicate phase transitions upon heating the curable compositions of the present invention.

[0040] Figure 7B is a chart depicting exothermic peaks that indicate phase transitions upon cooling the curable compositions of the present invention.

[0041] Figure 8A is a chart depicting viscosity changes that indicate phase transitions upon heating the curable compositions of the present invention.

[0042] Figure 8B is a chart depicting viscosity changes that indicate phase transitions upon cooling the curable compositions of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] The thermally conductive compositions may be formed as a coating on a surface or gap filler for placement along a thermal dissipation pathway, typically to remove excess heat from a heat-generating electronic component or a battery system. The cured thermally conductive composition exhibits a desired thermal conductivity of at least 1 W/m*K, and sufficient wettability to coat the respective surface. The composition preferably exhibits sufficient flexibility and cohesive strength to provide a stable interface.

[0044] The thermally conductive material is formed from a two-part curable composition that is dispensable from at least two separate vessels in order to separate a first curable component from a cure activator that promotes a cure reaction to the first curable component in order to form a matrix, such as a resin matrix. Low melting point phase-changing compounds (PCCs) are used to substantially improve the storage stability of the curable compositions while nevertheless maintaining their flowability, particularly at high shear rates. Thermally conductive particulate filler is included in at least one of the parts to provide the desired thermal conductivity characteristics.

Matrix Material

[0045] The matrix material of the compositions is formed from at least a curable component and a chemical cure activator. Preferably, a cure reaction is initiated with exposure between the curable component and the cure activator, in some cases when in the presence of an environmental cure reaction facilitator, such as water, heat, pressure, electromagnetic radiation, and the like. For the purposes hereof, the presence of an environmental cure reaction facilitator is assumed if necessary to the cure reaction initiated with exposure between the curable component and the cure activator. The cure activator therefore promotes a cure reaction involving the first curable component.

[0046] In some embodiments, the curable component may include a monomer, oligomer, or a polymer that is capable of undergoing a cross-linking reaction to form a network. The chemical cure activator is preferably an agent that is initially separated from the curable component to avoid a cure reaction, and subsequently introduced to the curable component when the cure reaction is desired. In some embodiments, the cure activator includes a cross-linking agent. The cure activator may also or instead include a monomer, an oligomer, a polymer, a reaction initiator, a catalyst, and combinations thereof. The curable component may include a first resin, and the cure activator may include a second resin that is reactive with the first resin. In some embodiments, the matrix may comprise an organic matrix including at least one of a thermoplastic resin and/or a thermoset resin.

[0047] The matrices formed from the curable component and cure activator of the present comprise in the range of about 0.01 up to about 40 percent by weight of the total composition, preferably in the range of about 0.1 up to about 40 percent by weight of the total composition, and more preferably in the range of about 0.5 up to about 40 percent by weight of the total composition. In some embodiments, the matrices formed from the curable component and cure activator comprise in the range of about 0.01 up to about 25 percent by weight of the total composition, preferably in the range of about 0.1 up to about 25 percent by weight of the total composition, and more preferably in the range of about 0.5 up to about 25 percent by weight of the total composition. In some embodiments, the matrices formed from the curable component and cure activator comprise in the range of about 0.01 up to about 15 percent by weight of the total composition, preferably in the range of about 0.1 up to about 15 percent by weight of the total composition, and more preferably in the range of about 0.5 up to about 15 percent by weight of the total composition.

[0048] The curable system of the curable component and the chemical cure activator may be selected from a wide variety of monomers, oligomers, and resins, wherein the term “resin” may include any natural or synthetic organic compound or mixture that is convertible into a polymer. An example cure reaction suitable for the curable systems is the hydrosilylation from vinyl and hydride functional silicone resins. An example silicone may be an organosiloxane having the structural formula: wherein “x" represents an integer ranging from between 1 and 1 ,000. The thermally conductive interface material may be prepared as a reaction product of the organosiloxane together with a chain extender/cross-linker such as a hydride functional polydimethyl siloxane having the structural formula: wherein “x” and “y” each represent an integer having a value of between 1 and 1 ,000. [0049] An example curable component includes polydiorganosiloxanes, such as various vinyl or siloxy-terminated polydimethylsiloxanes (PDMS). Example commercially-available PDMS materials include Nusil PLY-7500 and 7905 available from Avantor, Inc.; Evonik VS 100, 200, 500, 10000, 20000, and 65000 available from Evonik Industries AG; and Gelest DMS-V21 , V22, V41 , V42, and V43 available from Gelest, Inc. The curable component may include one or more polymers that differ in, for example, molecular weight, viscosity, and molecular structure.

[0050] The chemical cure activator may itself be reactive with the curable component, and may include a cross-linker for a hydrosilation reaction. The chemical cure activator may include a dihydroxy aliphatic chain extender such as a hydride- terminated polydimethylsiloxane. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or at both terminal and pendant positions. The chemical cure activator may include one or more organohydrogenpolysiloxanes that may differ in at least one of molecular weight, viscosity, and molecular structure. Example commercially-available methylhydropolydimethylsiloxanes useful as a chemical cure activator that is reactive with the first reactant composition include Nusil XL-112 and XL- 7505 available from Avantor, Inc.; Gelest HMS-071 , 082, and 991 available from Gelest, Inc.; and Andisil XL-1B and 1340 available from AB Specialty Silicones.

[0051] A variety of silane or silanol terminated resins may be employed in the matrices. Condensation-curable silane- or silanol-terminated resins participate in a hydrolysis-condensation cure pathway, preferably at and above ambient temperatures. In some embodiments, the resins are non-silicone, wherein no more than a trace amount of silicone is contained in the composition. In some embodiments, no silicone is contained in the composition.

[0052] Example resins suitable for the curable component include reactive polymer resins with at least one silyl-reactive functional group, including at least one bond that may be activated with water. Example silyl-reactive functional groups include alkoxy silane, acetoxy silane, and ketoxime silane.

[0053] The reactive polymer resin can be any polymer capable of participating in a silyl hydrolyzation reaction. For example, the reactive polymer resin can be selected from a wide range of polymers as polymer systems that possess reactive silyl groups, for example a silyl-modified reactive polymer. Preferably, the silyl-modified reactive polymer has a flexible backbone for lower modulus and glass transition temperature. Preferably, the silyl-modified reactive polymer has a flexible backbone of polyether, polyester, polyurethane, polyacrylate, polyisoprene, polybutadiene, polystyrenebutadiene, or polybutylene-isoprene.

[0054] The silyl-modified reactive polymer can be obtained by reacting a polymer with at least one ethylenically unsaturated silane in the presence of a radical starter, the ethylenically unsaturated silane carrying at least one hydrolyzable group on the silicon atom. For example, the silyl modified reactive polymer can be dimethoxysilane modified polymer, trimethoxysilane modified polymer, or triethoxysilane modified polymer. For example, the silyl modified reactive polymer may include a silane modified polyether, polyester, polyurethane, polyacrylate, polyisoprene, polybutadiene, polystyrenebutadiene, or polybutylene-isoprene.

[0055] The ethylenically unsaturated silane may be selected from the group made up of vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxymethylsilane, vinyldiethoxymethylsilane, trans-|3-methylacrylic acid trimethoxysilylmethyl ester, and trans-p-methylacrylic acid trimethoxysilylpropyl ester.

[0056] The silyl-modified reactive polymer preferably comprise(s) silyl groups having at least one hydrolyzable group on the silicon atom in a statistical distribution. For example, the silyl-modified reactive polymer can be a silane-modified polymer of general formula: in which; R is a mono- to tetravalent polymer radical, R ¹ > R ² ’ R ³ independently is an alkyl or alkoxy group having 1 to 8 carbon atoms, and A represents a carboxy, carbamate, amide, carbonate, ureido, urethane or sulfonate group or an oxygen atom, x = 1 to 8 and n = 1 to 4.

[0057] The silyl-modified reactive polymer can also be obtained by reacting a polymer with hydroxy group and alkoxysilane with isocyanate group. For example, the silyl modified reactive polymer can be dimethoxysilane modified polyurethane polymer, trimethoxysilane modified polyurethane polymer, or triethoxysilane modified polyurethane polymer. Further, the silyl-modified reactive polymer can be a o- ethoxysilane modified polymer of the average general formula: in which R is a mono- to tetravalent polymer residue, at most one third of the polymer of formula contained residues R ¹ ' R ² and R ³ are independently alkyl radicals having 1 to 4 carbon atoms, at least one-quarter of the polymer of the formula residues contained R ¹ , R ² , and R ³ are independently ethoxy residues that any remaining radicals

R ¹ , R ² , and R ³ independently of one another are methoxy radicals, and wherein n = 1 to 4.

[0058] Silyl-modified reactive polymers are available, for example, as dimethoxysilane modified MS polymer with polyether backbone and XMAP™ polymer with polyacrylate backbone from Kaneka Belgium NV, trimethoxysilane modified ST polymer from Evonik, triethoxysilane modified Tegopac™ polymer from Evonik, silane modified Desmoseal™ polymer from Covestro, or di- or tri- methoxy silane modified Geniosil™ polymer from Wacker.

[0059] A wide variety of epoxy-functionalized resins are contemplated for use herein, e.g., liquid-type epoxy resins based on bisphenol A, solid-type epoxy resins based on bisphenol A, liquid-type epoxy resins based on bisphenol F (e.g., Epicion EXA-835LV), multifunctional epoxy resins based on phenol-novolac resin, dicyclopentadiene-type epoxy resins (e.g., Epicion HP-7200L), naphthalene-type epoxy resins, and the like, as well as mixtures of any two or more thereof.

[0060] Exemplary epoxy-functionalized resins contemplated for use herein include the diepoxide of the cycloaliphatic alcohol, hydrogenated bisphenol A (commercially available as Epalloy 5000), a difunctional cycloaliphatic glycidyl ester of hexahydrophthallic anhydride (commercially available as Epalloy 5200), Epicion EXA- 835LV, Epicion HP-7200L, and the like, as well as mixtures of any two or more thereof. [0061] In certain embodiments, the epoxy component may include the combination of two or more different bisphenol based epoxies. These bisphenol based epoxies may be selected from bisphenol A, bisphenol F, or bisphenol S epoxies, or combinations thereof. In addition, two or more different bisphenol epoxies within the same type of resin (such A, F or S) may be used.

[0062] Commercially available examples of the bisphenol epoxies contemplated for use herein include bisphenol-F-type epoxies (such as RE-404-S from Nippon Kayaku, Japan, and EPICLON 830 (RE1801), 830S (RE1815), 830A (RE1826) and 830W from Dai Nippon Ink & Chemicals, Inc., and RSL 1738 and YL-983U from Resolution) and bisphenol-A-type epoxies (such as YL-979 and 980 from Resolution). [0063] The bisphenol epoxies available commercially from Dai Nippon and noted above are promoted as liquid undiluted epichlorohydrin-bisphenol F epoxies having much lower viscosities than conventional epoxies based on bisphenol A epoxies and have physical properties similar to liquid bisphenol A epoxies. Bisphenol F epoxy has lower viscosity than bisphenol A epoxies, all else being the same between the two types of epoxies, which affords a lower viscosity and thus a fast flow underfill sealant material. The EEW of these four bisphenol F epoxies is between 165 and 180. The viscosity at 25°C is between 3,000 and 4,500 cps (except for RE1801 whose upper viscosity limit is 4,000 cps). The hydrolyzable chloride content is reported as 200 ppm for RE1815 and 830W, and that for RE1826 as 100 ppm.

[0064] The bisphenol epoxies available commercially from Resolution and noted above are promoted as low chloride containing liquid epoxies. The bisphenol A epoxies have a EEW (g/eq) of between 180 and 195 and a viscosity at 25°C of between 100 and 250 cps. The total chloride content for YL-979 is reported as between 500 and 700 ppm, and that for YL-980 as between 100 and 300 ppm. The bisphenol F epoxies have a EEW (g/eq) of between 165 and 180 and a viscosity at 25°C of between 30 and 60. The total chloride content for RSL-1738 is reported as between 500 and 700 ppm, and that for YL-983U as between 150 and 350 ppm.

[0065] In addition to the bisphenol epoxies, other epoxy compounds are contemplated for use as the epoxy component of invention formulations. For instance, cycloaliphatic epoxies, such as 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexylcarbonate, can be used. Also monofunctional, difunctional or multifunctional reactive diluents may be used to adjust the viscosity and/or lower the Tg of the resulting resin material. Exemplary reactive diluents include butyl glycidyl ether, cresyl glycidyl ether, polyethylene glycol glycidyl ether, polypropylene glycol glycidyl ether, and the like.

[0066] Epoxies suitable for use herein include polyglycidyl derivatives of phenolic compounds, such as those available commercially under the tradename EPON, such as EPON 828, EPON 1001 , EPON 1009, and EPON 1031 from Resolution; DER 331 , DER 332, DER 334, and DER 542 from Dow Chemical Co.; and BREN-S from Nippon Kayaku. Other suitable epoxies include polyepoxides prepared from polyols and the like and polyglycidyl derivatives of phenol-formaldehyde novolacs, the latter of such as DEN 431 , DEN 438, and DEN 439 from Dow Chemical. Cresol analogs are also available commercially under the tradename ARALDITE, such as ARALDITE ECN 1235, ARALDITE ECN 1273, and ARALDITE ECN 1299 from Ciba Specialty Chemicals Corporation. SU-8 is a bisphenol-A-type epoxy novolac available from Resolution. Polyglycidyl adducts of amines, aminoalcohols and polycarboxylic acids are also useful in this invention, commercially available resins of which include GLYAMINE 135, GLYAMINE 125, and GLYAMINE 115 from F.I.C. Corporation; ARALDITE MY-720, ARALDITE 0500, and ARALDITE 0510 from Ciba Specialty Chemicals and PGA-X and PGA-C from the Sherwin-Williams Co.

[0067] Appropriate monofunctional epoxy coreactant diluents for optional use herein include those that have a viscosity which is lower than that of the epoxy component, ordinarily, less than about 250 cps.

[0068] The monofunctional epoxy coreactant diluents should have an epoxy group with an alkyl group of about 6 to about 28 carbon atoms, examples of which include Ce- 28 alkyl glycidyl ethers, Ce-28 fatty acid glycidyl esters, Cs-28 alkylphenol glycidyl ethers, and the like.

[0069] In some embodiments, the epoxy component employed herein is a silane modified epoxy, e.g., a composition of matter that includes:

(A) an epoxy component embraced by the following structure: wherein:

Y may or may not be present and when Y present is a direct bond, CH2, CH(CH ₃ ) ₂ , C=O, or S,

R1 here is alkyl, alkenyl, hydroxy, carboxy and halogen, and x here is 1-4;

(B) an epoxy-functionalized alkoxy silane embraced by the following structure:

R ¹ - Si(OR ² ) ₃ wherein: R ¹ is an oxirane-containing moiety and

R ² is an alkyl or alkoxy-substituted alkyl, aryl, or aralkyl group having from one to ten carbon atoms; and

(C) reaction products of components (A) and (B).

[0070] An example of one such silane-modified epoxy is formed as the reaction product of an aromatic epoxy, such as a bisphenol A, E, F or S epoxy or biphenyl epoxy, and epoxy silane where the epoxy silane is embraced by the following structure:

R ¹ - Si(OR ² ) ₃ wherein

R ¹ is an oxirane-containing moiety, examples of which include 2- (ethoxymethyl)oxirane, 2-(propoxymethyl)oxirane, 2- (methoxymethyl)oxirane, and 2-(3-methoxypropyl)oxirane and

R ² is an alkyl or alkoxy-substituted alkyl, aryl, or aralkyl group having from one to ten carbon atoms. In one embodiment, R ¹ is 2-(ethoxymethyl)oxirane and R ² is methyl.

[0071] Idealized structures of the aromatic epoxy used to prepare the silane modified epoxy include wherein

Y may or may not be present, and when Y is present, it is a direct bond, CH ₂ , CH(CH ₃ )2, C=O, or S,

Ri is alkyl, alkenyl, hydroxy, carboxy or halogen, and x is 1-4.

Of course, when x is 2-4, chain extended versions of the aromatic epoxy are also contemplated as being embraced by this structure.

[0072] For instance, a chain extended version of the aromatic epoxy may be embraced by the structure below

[0073] In some embodiments, the siloxane modified epoxy resin has the structure: -(O-Si(Me)2-O-Si(Me)(Z)-O-Si(Me) ₂ -O-Si(Me) ₂ )n- wherein:

Z is -O-(CH ₂ )3-O-Ph-CH2-Ph-O-(CH2-CH(OH)-CH2-O-Ph-CH2-Ph-O-)n- CH ₂ -oxirane, and n falls in the range of about 1-4.

[0074] In some embodiments, the siloxane modified epoxy resin is produced by contacting a combination of the following components under conditions suitable to promote the reaction thereof:

Me2Si(OMe)2

+

(MeO)3Si-(CH2)s-O-CH2-oxirane

+ oxirane-CH ₂ -O-Ph-CH ₂ -Ph-O-(CH ₂ -CH(OH)-CH2-O-Ph-CH2-Ph-O-)n-CH2- oxirane, wherein “n” falls in the range of about 1-4.

[0075] The silane modified epoxy may also be a combination of the aromatic epoxy, the epoxy silane, and reaction products of the aromatic epoxy and the epoxy silane. The reaction products may be prepared from the aromatic epoxy and epoxy silane in a weight ratio of 1 :100 to 100:1 , such as a weight ratio of 1 :10 to 10:1.

[0076] Epoxy cure agents are optionally employed in combination with epoxy monomer(s). Examples of epoxy cure agents include ureas, aliphatic and aromatic amines, amine hardeners, polyamides, imidazoles, dicyandiamides, hydrazides, ureaamine hybrid curing systems, free radical initiators (e.g., peroxy esters, peroxy carbonates, hydroperoxides, alkylperoxides, arylperoxides, azo compounds, and the like), organic bases, transition metal catalysts, phenols, acid anhydrides, Lewis acids, Lewis bases, and the like. [0077] When epoxy cure agents are present, the compositions comprise in the range of about 0.1 - 2 wt % thereof. In certain embodiments, the compositions comprise in the range of about 0.5 - 5 wt % of epoxy cure agent.

[0078] Other examples of curing reactions contemplated for the curable component and cure activator include urethane reaction from hydroxyl and isocyanate functional monomers, oligomers, or resins, epoxy polymerization from epoxide and at least one of amino, mercapto, and anhydride functional monomers, oligomers, or resins, and radical polymerization of vinyl or vinylidene functional monomers, oligomers, or resins.

[0079] In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure, and exhibit a viscosity of less than 500 cP at 20 °C at a shear rate of 1 s ^-1 . In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure, and exhibit a viscosity of less than 200 cP at 20 °C at a shear rate of 1 s ^-1 .

[0080] In some embodiments, the cure activator may include a catalyst, such as a reaction catalyst. A reaction catalyst may, for example, be employed to further facilitate the hydrosilylation reactions described above. Examples of the reaction catalysts include platinum compounds, and organotin and organo-zinc and organo-titanium compounds (together referred to herein as “organo-metal catalyst”) that facilitate moisture cure of the silyl-modified reactive resins.

[0081] Reaction catalysts may be present in the range of 0 up to 0.1 percent by weight. In some embodiments, the compositions comprise in the range of 0.01 up to 0.5 percent by weight reaction catalyst. In some embodiments, the compositions comprise in the range of 0.01 up to 0.02 percent by weight reaction catalyst.

[0082] The thermally conductive compositions may be curable in the presence of water (moisture curable) at ambient temperature. Depending upon the application, the moisture may be available from the ambient environment or from water released from the object(s) to which the composition is applied. In some embodiments, the compositions are curable without addition of environmental moisture. In some embodiments, water may be included as an ingredient in a non-resin part of the multiple part curable composition, for mixture with the reactive constituents in situ. Preferably, however, the amount of water required in the composition itself is minor so as not to interfere with functional properties of the thermal material. In some embodiments, water is present in the compositions in the range of 0 up to 0.5 wt%. In some embodiments, the compositions comprise in the range of 0.01 up to 0.3 wt% water. In some embodiments, the compositions comprise in the range of 0.01 up to 0.2 wt% water.

[0083] The term “ambient temperature” is intended to mean the temperature of the environment within which the reaction occurs, and within a temperature range of 15-30 °C, and preferably 25 °C. The thermally conductive compositions are curable at ambient temperature within 72 hours, and preferably within 24 hours. The thermally conductive compositions may also be curable at elevated temperatures. For the purposes hereof, the term “curable” is intended to mean reactable to form a solidus body.

Diluent

[0084] The compositions may include a diluent to adjust the viscosity of the dispensable mass. The cured compositions exhibit a relatively low modulus or hardness of between 10 Shore OO and 80 Shore A to mitigate the stress in electronic component assembly and to promote conformability of the thermal material to respective contact surfaces of the electronic component.

[0085] Diluents are those which are effective in facilitating fluency of the coherent mass making up the composition. The diluents are compatible with and may be solvents for the selected monomers, oligomers, or resins, and may preferably be low- volatility liquids that reduce the viscosity of the overall pre-cured composition so that the composition is readably dispensable through liquid dispensing equipment. The diluent may therefore exhibit a viscosity of less than 500 cP at 25 °C at a shear rate of 1 s ^-1 . In another embodiment, the diluent may exhibit a viscosity of less than 200 cP at 25 °C at a shear rate of 1 s" ¹ . In a further embodiment, the diluent may exhibit a viscosity of less than 100 cP at 25 °C at a shear rate of 1 s ^-1 . Preferably, the diluent exhibits a viscosity of between 1-200 cP at 25 °C at a shear rate of 1 s ^-1 .

[0086] The diluent is preferably added to the composition in an amount suitable to appropriately adjust viscosity for pre-cured dispensability, and post-cured softness. In some embodiments, the diluent may represent between about 0.01 and about 10 percent by weight of the total composition.- In some embodiments, the diluent may represent between about 0.1 and about 5 percent by weight of the total composition. In some embodiments, the diluent may represent between about 0.5 and about 2 percent by weight of the total composition. The diluent may preferably be present at less than 10% by weight of the composition. The diluent may be included in one or more parts of the multiple-part curable composition. In preferred embodiments the diluent may be included at least in one or more of the parts of the curable composition that would benefit from a reduced viscosity.

[0087] Examples of inert diluents include non-reactive silicone oils, benzoates, oleates, ricinoleates, phthalates, trimellitates, teraphthalates, adipates, sebacates, azelates, maleates, citrates, epoxidized vegetable oils, organosulfates, organophosphates, glycols and polyethers, ether esters, polyolefins, and combinations thereof.

Thermally Conductive Particulate Filler

[0088] Conductive fillers contemplated for use herein include, for example, boron nitride, aluminum nitride, alumina, alumina trihydrate, silicon, silicon carbide, graphite, diamond, magnesium oxide, magnesium hydroxide, zinc oxide, gold, silver, copper, platinum, palladium, nickel, aluminum, indium, alloy of nickel (e.g., alloy 42), alloy of zinc, alloy of iron, alloy of indium, silver-plated copper, silver-plated aluminum, bismuth, tin, bismuth-tin alloy, silver-plated fiber, silver-plated graphite, silver-plated silicon carbide, silver-plated boron nitride, silver-plated diamond, silver-plated alumina, silver- plated alloy 42, graphene, silver-plated graphene, silver-coated polymer, cadmium and alloys of cadmium, lead and alloys of lead, antimony and alloys of antimony, and the like, as well as mixtures of any two or more thereof. Said particulate, conductive filler typically has a particle size in the range of about 1 nm up to about 200 pm; in some embodiments, the conductive filler has a particle size in the range of about 10 nanometers up to about 20 micrometers.

[0089] The particulate, conductive filler employed herein can be substantially nanoparticulate, or the particulate, conductive filler employed herein can be substantially larger, non-nanoparticulate, or the particulate, conductive filler employed herein can be a combination of nanoparticulate and non-nanoparticulate.

[0090] The particulate conductive filler employed herein may be present in the range of about 60 up to about 98 wt % of total composition; in some embodiments, the compositions comprise in the range of about 80 up to about 98 wt % of a particulate, conductive filler; in some embodiments, the compositions comprise in the range of about 85 up to about 98 wt % of a particulate, conductive filler; in some embodiments, the compositions comprise in the range of about 90 up to about 98 wt % of a particulate, conductive filler; in some embodiments, the compositions comprise in the range of about 60 up to about 95 wt % of a particulate, conductive filler; in some embodiments, the compositions comprise in the range of about 80 up to about 95 wt % of a particulate, conductive filler; in some embodiments, the compositions comprise in the range of about 90 up to about 95 wt % of a particulate, conductive filler.

[0091] The particulate, conductive filler may be allocated to one or more parts of the curable composition, such that the cured material exhibits a thermal conductivity of at least 0.5 W/m*K, and more preferably at least 1 W/m*K. In some embodiments, the particulate conductive filler may be allocated to one or more parts of the curable composition including a liquid phase. Examples of liquid phases include one or more of a diluent and a curable component, wherein at least one of the diluent and curable component exhibit liquidous behaviour. In some embodiments, at least one of the diluent and curable component exhibit a liquid phase viscosity of less than 500 cP at 20 °C at a shear rate of 1 s ^-1 .

[0092] In some embodiments, the particulate, conductive filler may be surface treated with organic modifiers containing between 3 and 20 carbon atoms to the improve the dispersion properties of the particulate filler in the liquid phase(s) of the curable compositions. Examples of surface modifiers include silanes and fatty acids.

Phase Changing Compound

[0093] The phase changing compounds as used in the curable compositions are substances that are in solid form at 20 °C, a typical room temperature, and are meltable or dissolvable into the liquid phase(s) of the curable composition at temperatures exceeding 20 °C to establish a “phase changing” characteristic to the curable compositions wherein the viscosity decreases significantly as the compositions are heated to temperatures exceeding 20 °C but no greater than 50 °C. The phase changing characteristic imparted to one or more parts of the multiple part curable composition follows the following relationship: ps/pso > x wherein: ps = the viscosity of the part at 5 °C and a shear rate of no greater than 0.1 s- ¹ ; p5o = the viscosity of the part at 50 °C and a shear rate of no greater than 0.1 s ^-1 ; and x = at least 5; and preferably at least 10.

[0094] Thus, the part viscosity at 50 °C is substantially lower than the part viscosity at 5 °C, and preferably at least an order of magnitude lower.

[0095] Consistent with the reduced viscosity of the curable composition part(s) containing the phase changing compounds is an increased dispensing rate at the elevated temperatures of above 20 °C up to 50 °C. A dispensing rate is determined by dispensing the material from a containment vessel through an orifice under a given dispensing force. In one embodiment, the dispensing rate may be determined by dispensing the material from a 30 mL Nordson EFD syringe under 90 psi pressure for one or several seconds at various test temperatures. The dispensed mass value is divided by the dispensing time to calculate the dispensing rate. A heated dispensing rate is determined at a dispensing temperature exceeding 25 °C but no greater than 50 °C. An unheated dispensing rate is determined at a dispensing temperature of less than 25 °C. In some embodiments, the curable composition part containing the phase changing compound exhibits a heated dispensing rate at 50 °C that is at least 50% greater than an unheated dispensing rate at 5 °C. In some embodiments, the curable composition part containing the phase changing compound exhibits a heated dispensing rate at 50 °C that is 100% greater than an unheated dispensing rate at 5 °C. In some embodiments, the curable composition part containing the phase changing compound exhibits a heated dispensing rate at 50 °C that is at least 200% greater than an unheated dispensing rate at 5 °C. In some embodiments, the curable composition part containing the phase changing compound exhibits a heated dispensing rate at 50 °C that is at least 1000% greater than an unheated dispensing rate at 5 °C.

[0096] Storage stability of curable compositions is enhanced thereby increasing shelf life. Storage stability of the curable compositions may be enhanced by reducing or eliminating separation of liquid phase from the thermally conductive composition. The phase changing compounds provide the curable composition with a relatively high viscosity at room temperatures, while facilitating a significant viscosity reduction at elevated temperatures up to 50 °C for dispensing the curable composition. Accordingly, the phase changing compounds are preferably utilized in the at least one part of the multiple part curable compositions that contain the thermally conductive particulate filler. In some embodiments, the phase changing compound is employed only in one part of the multiple part curable composition. In some embodiments, the phase changing compound is employed in more than one part of the multiple part curable composition. [0097] In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 100 °C. in some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 90 °C. In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 80 °C. In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 70 °C. In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 60 °C. In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 50 °C. In some embodiments, the phase changing compound has a melting point temperature of between 20 °C and 40 °C.

[0098] The phase changing compound is preferably present in the respective one or more parts of the multiple part curable composition at an effective concentration so that the respective one or more parts exhibits a phase change at between 0 °C and 50 °C. In some embodiments, the phase changing compound is present in the respective one or more parts of the multiple part curable composition at an effective concentration so that the respective one or more parts exhibits a phase change at between 5 °C and 45 °C. In some embodiments, the phase changing compound is present in the respective one or more parts of the multiple part curable composition at an effective concentration so that the respective one or more parts exhibits a phase change at between 5 °C and 40 °C. In some embodiments, the phase changing compound is present in the respective one or more parts of the multiple part curable composition at an effective concentration so that the respective one or more parts exhibits a phase change at between 10 °C and 50 °C.

[0099] In some embodiments, the phase changing compound may be present at a concentration of between 0.01 and 10 % by weight of the respective one or more parts of the multiple part curable composition. In some embodiments, the phase changing compound may be present at a concentration of between 0.05 and 5 % by weight of the respective one or more parts of the multiple part curable composition. In some embodiments, the phase changing compound may be present at a concentration of between 0.1 and 3 % by weight of the respective one or more parts of the multiple part curable composition. In some embodiments, the phase changing compound may be present at a concentration of between 0.4 and 1.5 % by weight of the respective one or more parts of the multiple part curable composition.

[0100] The phase changing compound may include, for example, organic waxy compounds. Examples of phase changing compounds include esters, amides, urethanes, and ureas derived from C12-C20 alcohols or acids, and C12-C20 glycerides derived from animal fat or plant oil, hydrocarbon paraffins and combinations thereof. In some embodiments, the phase changing compound has a molecular weight of less than 2000 g/mol. In some embodiments, the phase changing compound has a molecular weight of less than 1000 g/mol.

[0101] In some embodiments, the phase changing compound may be solid at room temperature and dispersed in the liquid phase of the respective one or more parts of the multiple part curable composition. The phase changing compound may, in some embodiments, be particulated or crystallized solid at 20 °C. Solidification of the phase changing compound in the respective one or more parts of the multiple part curable composition effectively reduces the fraction of the liquid phase in the respective part, and results in less liquid phase to separate at room temperature. The dispersed phase changing compound may also enhance viscosity characteristics of the part, particularly at low shear rates, which further reduces the tendency for filler sedimentation and liquid separation.

Optional Additives

[0102] In some embodiments, the compositions described herein may further comprise one or more flow additives, adhesion promoters, rheology modifiers, toughening agents, fluxing agents, film flexibilizers, phenol-novolac hardeners, curing agents (catalysts, promoters, initiators, etc.), and the like, as well as mixtures of any two or more thereof.

[0103] As used herein, the term “flow additives” refers to compounds which modify the viscosity of the formulation to which they are introduced. Examples of such compounds which impart such properties include silicon polymers, ethyl acrylate/2- ethylhexyl acrylate copolymers, alkylol ammonium salts of phosphoric acid esters of ketoxime, and the like, as well as combinations of any two or more thereof.

[0104] As used herein, the term “adhesion promoters” refers to compounds which enhance the adhesive properties of the formulation to which they are introduced.

[0105] As used herein, the term “rheology modifiers” refers to additives which modify one or more physical properties of the formulation to which they are introduced.

[0106] As used herein, the term “toughening agents” refers to additives which enhance the impact resistance of the formulation to which they are introduced.

[0107] As used herein, the term “fluxing agents” refers to reducing agents which prevent oxides from forming on the surface of the molten metal.

[0108] As used herein, the term “film flexibilizers” refers to agents which impart flexibility to the films prepared from formulations containing same.

[0109] As used herein, the term “phenol-novolac hardeners” refers to materials which participate in the further interaction of reactive groups so as to increase the crosslinking thereof — thereby enhancing the stiffness thereof.

[0110] As used herein, the term “curing agents” refers to reactive agents which participate in or promote the curing of monomeric, oligomeric or polymeric materials.

[0111] In order to realize high pumping flow rates, at least the part of the curable composition containing the phase changing compound is preferably heated to a point at which the phase changing compound melts or dissolves into the liquid phase. A method of applying a thermally conductive material to a surface or a gap between surfaces therefore includes heating at least the part of the curable composition containing the phase changing compound to an elevated temperature exceeding 25 °C but no greater than 50 °C. The parts of the curable composition may then be dispensed through at least one orifice to the surface or the gap. In some embodiments, first and second parts of the curable composition may be dispensed from their respective first and second containment vessels through respective first and second conduits to the at least one orifice.

[0112] An example of a dispensing system 100 of the present invention is illustrated in Figure 1 , wherein a first vessel 110 contains a first part 112 of a two-part curable composition, and a second vessel 120 contains a second part 122 of the two-part curable composition. The first and second vessels 110, 120, in the illustrated embodiment, may be pails or drums for relatively large volume dispensing applications. A first conduit 114 flu idically couples first vessel 110 to a mixing chamber 130 for conveying first part 112 from first vessel 110 to mixing chamber 130. Likewise, a second conduit 124 fluidically couples second vessel 120 to mixing chamber 130 for conveying second part 122 from second vessel 120 to mixing chamber 130. As illustrated in Figure 1 , mixing chamber 130 may include an orifice 132 through which the curable composition may be dispensed.

[0113] A first follower plate or other heating mechanism 116 may be disposed at or in first vessel 110 to selectively apply heat to first part 112, and a second follower plate or other heating mechanism 126 may be disposed at or in vessel 120 to selectively apply heat to second part 122. A first conduit heating mechanism 118 may be coupled to or integrated with first conduit 114 for applying heat to first part 112 conveyed through first conduit 114. A second conduit heating mechanism 128 may be coupled to or integrated with second conduit 214 for applying heat to second part conveyed though second conduit 124. A mixing element heating mechanism 134 may be coupled to or integrated with mixing chamber 130 for applying heat to first and second parts 112, 122 mixed in mixing chamber 130. [0114] Another example of a dispensing system 200 of the present invention is illustrated in Figures 2A and 2B, wherein a first vessel 210 contains a first part 212 of a two-part curable composition, and a second vessel 220 contains a second part 222 of the two-part curable composition. The first and second vessels 210, 220, in the illustrated embodiment, may be cartridges for relatively small volume dispensing applications. A first conduit 214 fluidically couples first vessel 210 to a mixing apparatus 230 for conveying first part 212 from first vessel 210 to mixing apparatus 230. Likewise, a second conduit 224 fluidically couples second vessel 220 to mixing apparatus 230 for conveying second part 222 from second vessel 220 to mixing apparatus 230. As illustrated in Figure 2A and 2B, mixing apparatus 230 may include an orifice 232 through which the curable composition may be dispensed.

[0115] Mixing apparatus 230 may include a mixing chamber 236 at which first and second parts 212, 222 may be mixed for a cure reaction, and thereafter dispensed through orifice 232. A first conduit heating mechanism 218 may be coupled to or integrated with first conduit 214 for applying heat to first part 212 conveyed through first conduit 214. A second conduit heating mechanism 228 may be coupled to or integrated with second conduit 214 for applying heat to second part conveyed though second conduit 224. A mixing element heating mechanism 234 may be coupled to or integrated with mixing chamber 230 for applying heat to first and second parts 212, 222 mixed in mixing chamber 236.

[0116] Figure 2B illustrates an alternative embodiment in which first and second conduits 214, 224 are eliminated, and a dual-chamber cartridge kit 240 combines first and second vessels 210, 220 into first and second chambers 242, 244 that directly feed into mixing chamber 236.

[0117] In each of these example embodiments, the first and/or second parts of the curable composition may be heated to an elevated temperature exceeding 25 °C but no greater than 50 °C in order to affect a phase change in the respective first and/or second parts, and to facilitate a high dispensing rate of the first and/or second parts through the orifice.

[0118] An electronic package 310 incorporating a thermal interface 320 formed from the multiple part curable composition is illustrated in Figure 3. Electronic package 310 includes a substrate 312 and an electronic component array 314 including a plurality of electronic components 316 secured to substrate 312. Electronic package 310 further includes a heat dissipater 318 and thermal interface 320 positioned in a heat dissipation pathway (designated by dashed arrow 322) between electronic component array 314 and heat dissipater 318. Electronic package 310 is arranged to dissipate thermal energy generated by electronic components 316 by providing a highly thermally conductive path from electronic component array 314 to a heat-absorbing fluid media 324 in contact with heat dissipater 318. In typical applications, fluid media 324 may be a gas, such as air, motivated by an air mover to absorb thermal energy from heat dissipater 318. Electronic package 310 is an example arrangement that may be modified as appropriate to accommodate a variety of electronic applications, such as data processors, data memory, communication boards, antennae, and the like. Such devices may be utilized in computing devices, communication devices, and peripherals therefor. In a particular example embodiment, electronic package 310 may be employed to support various functions in a cellular communication device.

[0119] Substrate 312 may serve one or more of a variety of functions in addition to being a support for electronic component array 314. For the purpose of simplicity in describing electronic package 310, substrate 312 may be a circuit board, such as a printed circuit board with electrically conductive traces on a mounting surface 313 for electrically connecting electronic components 316 as needed in the assembly. Components 316 may be electrically connected to wiring traces through soldering or other known techniques. In operation, electronic components 316 generate significant excess thermal energy which must be dissipated in order to maintain optimal performance, Electronic components 316 may be any of a variety of elements useful in an electronic process, and may include, for example, integrated circuits, resistors, transistors, capacitors, inductors, and diodes.

[0120] Thermal interface 320 provides a thermally conductive bridge between electronic component array 314 and heat dissipater 318 generally along heat dissipation pathway 322. Heat dissipater 318 may be thermally coupled to thermal interface 320 in a manner that most efficiently transmits thermal energy to heat dissipater 318. As schematically illustrated, heat dissipater 318 may have a configuration that incorporates a relatively high surface area, such as through fins 328. The use of heat dissipaters is well understood, and it is contemplated that conventional and custom designs may be utilized in these arrangements.

[0121] Figure 4 illustrates a battery system 410 including a battery cell 412 having a case 414 and first and second terminals 416, 418. Battery cell 412 may be any of a variety of battery types, wherein a need for a thermally conductive interface 420 is identified. A particular embodiment of battery system 410 may employ lithium ion-type battery cells 412, which may be assembled into a battery module 422 of a plurality of battery cells 412, as well as in a battery pack (not shown) having a plurality of battery modules 422. Battery cells 412 may be secured together into battery module 422 within an external clamp or housing 424 that may be positioned about the group of battery cells 412 in battery module 422.

[0122] Thermal interface 420 may be applied to various portions of battery cell 412, battery module 422, and/or housing 424 to facilitate heat transfer of excess thermal energy generated by each battery cell 412. In some embodiments, thermal interface 420 may be disposed between adjacent battery cells 412 in a battery module 422, between battery module 422 and a cooling plate (not shown), and between respective parts of a container for a plurality of battery modules 422. Thermal interface 420 is preferably applied along a heat dissipation pathway between the battery cells 412, the battery module 422, and one or more heat dissipating elements.

EXAMPLES

EXAMPLE 1

[0123] This example illustrates a two-part system in which a phase changing compound is added into each part to improve storage stability. The curing chemistry is based on hydrosilylation of vinyl-functional and hydride-functional silicone resin. The vinyl to hydride ratio in this example is maintained at 3.5.

[0124] Two phase changing compounds, methyl stearate with a melting point temperature of 38-42 °C, and palm kernel oil with a melting point temperature of 25- 30 °C were used to demonstrate the efficacy of using phase changing compounds to reduce or eliminate oil separation at room temperature while nevertheless maintaining desired dispensing flow rates at 40°C.

[0125] All ingredients except the phase changing compounds were blended together first, and after the phase changing compounds were added, the mixture was heated to 60 °C and mixed thoroughly. After a brief degassing under vacuum, the mixture was discharged into respective containers.

Table 1 Test methods:

[0126] Dispensing flow rate: The material was filled into a standard 30 ml Nordson EFD syringe barrel (Part# 7012136), then subjected to dispensing at 90 psi for 1 second. Whenever possible, multiple dispensing trials were carried out to calculate the average dispensed mass per second. Syringe barrels were equilibrated at 20 °C or 40 °C for at least 45 min before dispensing.

[0127] Oil separation: The material was filled into 100ml clear polypropylene graduated cylinders, and then stored at room temperature for 16 days.

[0128] Thermal conductivity: The two-part composition was cured at 85 °C into a 6.35 mm-thick disk and then cut to test in TIM1400 tester based on the standard ASTM D5470 method.

[0129] Hardness: The two-part composition was cured at 85 °C into a 6.35 mm-thick disk and then tested with a Shore 00 durometer with 15s delayed reading.

[0130] In this example, after adding the phase changing compounds into the thermally conductive dispersion, the dispensing flow rates at 20 °C are decreased compared to EX 1-1 A or EX 1-1B. However, after the samples were warmed to 40C, above the melting point of the phase changing compounds, the dispersions showed significantly improved flow rates with values comparable with EX 1-1 A or EX 1-1B. A drastic improvement in oil separation was observed with the addition of the phase changing compounds. Examples EX 1-2A/B, EX 1-3A/B and EX 1-4A/B showed zero oil after being stored at room temperature for 16 days.

[0131] In this example, the transition for phase changing compound melting or crystallization was characterized by both differential scanning calorimeter and rheometer.

[0132] Figures 5A and 5B illustrate heating (Fig. 5A) and cooling (Fig. 5B) of each of the part A dispersions of Example 1 , as measured by differential scanning calorimeter between 0 °C and 40 °C at 5 °C/min. Examples EX 1-2A/B, EX 1-3A/B, and EX 1-4A/B show exothermic or endothermic peaks indicating a phase transition originating from the phase changing compounds. [0133] Figures 6A and 6B illustrate heating (Fig. 6A) and cooling (Fig. 6B) of each of part A dispersions of Example 1 , as measured by a rheometer operating at a shear rate of 0.1 s ^-1 between 16 °C and 40 °C at 5 °C/min. Examples EX 1-2A/B, EX 1-3A/B, and EX 1-4A/B show more significant viscosity changes than Example EX 1-1A/B.

EXAMPLE 2

[0134] This example illustrates a two-part system in which a phase changing compound is only added to one part (Part A in this case) to improve storage stability. The curing chemistry is based on moisture curing of silane modified resins, so Part A includes diluent oils, a catalyst and water, and Part B includes diluent oils and curable silyl modified resins. In this example, Part B has sufficient storage stability without the phase changing compound, whereas Part A has poor storage stability due to the low viscosity of diluent oils.

[0135] In this example, two phase changing compounds, methyl stearate with a melting point temperature of 38-42 °C, and lauryl stearate with a melting point temperature of 39-43 °C were used to demonstrate the efficacy of using phase changing compounds to reduce or eliminate oil separation of Part A at room temperature while nevertheless maintaining a desired dispensing flow rate at 40 °C. [0136] For Part A mixing, all ingredients except the phase changing compound and water were mixed first, then the phase changing compound was added to the mixture while it was heated to 60 °C and mixed thoroughly. The mixture was then cooled to room temperature before water was added. After a brief degassing, the mixture was discharged into respective containers.

Table 2

Test method:

[0137] Dispensing flow rate: The material was filled into a standard 30 ml Nordson EFD syringe barrel (Part# 7012136), then subjected to dispensing at 90 psi for 1 second. Whenever possible, multiple dispensing trials were carried out to calculate the average dispensed mass per second. Syringe barrels were equilibrated at 20 °C or 40 °C for at least 45 min before dispensing.

[0138] Oil separation: The material was filled into 100ml clear polypropylene graduated cylinders, and then stored at room temperature for 16 days. [0139] Thermal conductivity: The two-part composition was cured at 85 °C into a 6.35 mm-thick disk and then cut to test in TIM1400 tester based on the standard ASTM D5470 method.

[0140] Hardness: The two-part composition was cured at 85 °C into a 6.35 mm-thick disk and then tested with a Shore 00 durometer with 15s delayed reading.

[0141] Samples EX2-A3 and EX2-A4 have different phase changing compounds, and both exhibit decreased dispensing flow rates at 20 °C compared to the samples of EX 2-A1 and EX 2-A2. However, after the samples have been warmed to 40 °C, above the melting point of the phase changing compounds, the dispersions showed significantly improved flow rates with values comparable with EX 2-A1 . A drastic improvement in the minimization of oil separation was observed with the addition of the phase changing compounds, wherein each of samples EX 2-A3 and EX2-A4 showed zero oil after being stored at room temperature for 16 days. In contrast, EX2-A2 with a higher viscosity oil only showed a very little improvement in oil separation in comparison to EX 2-A1 , and the dispensing rate of sample EX 2-A2 was significantly reduced in comparison to sample EX2-A1 at both 23 °C and 40 °C. This demonstrates that using phase changing compounds is advantageous comparted to high viscosity oils in maintaining high dispensing flow rates and low/no oil separation.

[0142] In this example, the transition for phase changing compound melting or crystallization was characterized by both differential scanning calorimeter and rheometer.

[0143] Figures 7A and 7B illustrate heating (Fig. 7A) and cooling (Fig. 7B) of each of the part A dispersions of Example 2, as measured by differential scanning calorimeter between 0 °C and 40 °C at 5 °C/min. Examples EX 2-A3 and EX 2-A4 show exothermic or endothermic peaks indicating a phase transition originating from the phase changing compounds.

[0144] Figures 8A and 8B illustrate heating (Fig. 8A) and cooling (Fig. 8B) of each of part A dispersions of Example 2, as measured by a rheometer operating at a shear rate of 0.1 s' ¹ between 16 °C and 40 °C at 5 °C/min. Examples EX 2-A3 and EX 2-A4 show more significant viscosity changes than Examples EX 2-A1 and EX 2-A2, reflecting the effect of the presence of the phase changing compounds in Examples EX 2-A3 and EX 2-A4.