Thermally conductive composition

Abstract

The thermally conductive composition includes a polymer formed from a condensation curable silyl-modified resin and a particulate alumina filler having a high total specific surface area. The composition exhibits a thermal conductivity of at least 1 W / m·K and is curable without the addition of environmental moisture and with reduced amounts of catalyst.

Description

[Technical field]

[0001] The present invention relates generally to thermally conductive materials, and more particularly to polymer-based thermal interface materials that can be dispensed from a two-component system and cured in low humidity environments with reduced catalyst dependency. [Background technology]

[0002] Thermally conductive materials, for example, are widely employed as interfaces between heat-generating electronic components and heat sinks, allowing the transfer of excess thermal energy from the electronic components to the thermally coupled heat sink. Numerous such thermal interface designs and materials have been implemented, with the best performance being achieved when gaps between the thermal interface and the respective heat transfer surfaces are substantially avoided, promoting conductive heat transfer from the electronic components to the heat sink. Thus, the thermal interface material preferably mechanically conforms to the somewhat uneven heat transfer surfaces of the respective components. Thus, key physical properties of high performance thermal interface materials are flexibility and low hardness. For dispensable materials, it is even more important that the thermal interface be able to wet the heat transfer surfaces, and provide adequate adhesion and cohesion to avoid delamination and maintain the shape and function of the interface over the expected service life. Thus, dispensable thermal interface materials may be designed with a yield stress to avoid significant spreading after dispensing, or without a yield stress to allow maximum flow and penetration into the surface. The curing behavior of the material can be tailored to avoid particle settling and provide sufficient pre-curing time for rework and handling.

[0003] Some examples of suitable thermally conductive compositions include silicone polymers that form a matrix filled with thermally conductive particles such as alumina (aluminum oxide) and boron nitride. The coatings are usually flexible enough to conform to the irregularities of the interfacial surface, both at room temperature and / or at elevated temperatures. However, silicone-based coatings are often not suitable for many applications due to the presence of low molecular weight volatile components that can contaminate surfaces and are difficult to remove. Alternative non-silicone polymer systems are limited in their temperature stability and glass transition behavior. Some conventional non-silicone systems that exhibit acceptable hardness also exhibit relatively high pre-cure viscosities, making dispensing and assembly challenging. Other non-silicone systems have suitable pre-cure viscosities for dispensing and assembly and acceptable post-cure hardness, but typically require either reactive diluents that can interfere with the cross-linking reaction of the polymer, or non-reactive diluents that tend to migrate out of the coating over time. Silyl-modified polymers are one type of material that has been explored for dispenseable non-silicone applications.

[0004] The development of thermally conductive coatings based on silyl-modified polymers is promising due to their desirable mechanical properties such as low hardness, high service temperature, and versatility. However, silyl-modified polymers have proven difficult to effectively cure due to their low reactivity and the need for multi-step reaction chemistry. These challenges are exacerbated in sealed applications such as battery cells where the materials are not exposed to atmospheric moisture that would promote the typical hydrolysis-condensation cure pathway.

[0005] Silyl-modified polymers, such as polyethers or polyureas containing one or more terminal alkoxysilane functional groups, are widely used in applications where the curable resin is exposed to atmospheric moisture, which is necessary to achieve the initial hydrolysis of the functional end groups and allow the subsequent condensation reaction. In the presence of moisture alone, the reaction proceeds at a slow rate. To obtain an adequate cure rate, a strong catalyst is usually required. These catalysts are usually based on organometallic catalyst compounds, which have known health and environmental hazards. Organometallic-free systems have been proposed, but have been found to lack the activity required to promote an effective polymerization reaction. Conventional silyl-modified polymer systems accordingly require the presence of moisture and the use of catalysts that may in some cases be environmentally toxic.

[0006] Condensation curable polymers, such as silyl modified polymers, present special challenges when used in a closed form, since atmospheric moisture is not available to initiate the hydrolysis portion of the cure reaction. One approach is to utilize a two-component system where water is added to the non-resin components prior to mixing. However, there are environmental limitations on the maximum amount of catalyst that can be used in such systems, limiting two-component systems to half the catalyst content of an equivalent one-component system. Additionally, increasing the amount of water in the formulation can cause problems related to incompatibility with hydrophobic plasticizers that are often included in coating compositions. This incompatibility can result in outgassing at high temperatures, leaving voids, promoting bleeding, and otherwise limiting the life of the product. A variety of silanes are available that can accelerate cure, but these tend to have little practical impact and do not aid in the hydrolysis portion of the reaction. Summary of the Invention

[0007] It is therefore an object of the present invention to provide a thermally conductive material that can be cured in low humidity environments without increasing the amount of catalyst, decreasing the shelf life or stability of the cured composition, or significantly changing the flow behavior and other functional properties of the formulation.

[0008] It is another object of the present invention to provide a thermally conductive composition formed from a two-part reactive composition that can be delivered via conventional dispensing equipment and cured in a low humidity environment.

[0009] It is a further object of the present invention to provide a thermally conductive composition formed from a condensation curable resin that exhibits high thermal conductivity while at the same time being capable of being dispensed at high speeds.

[0010] According to the present invention, low hardness, high thermal conductivity materials can be formed from compositions that exhibit suitable viscosities for dispensing as liquid coatings through conventional liquid dispensing equipment. The curable compositions can cure at accelerated rates without increasing catalyst content and without significant environmental moisture. As used herein, the term "significant" is intended to mean more than trace or residual amounts. The curable compositions can use environmentally compatible catalysts that reduce or eliminate the dependency on organometallic catalyst compounds to promote the hydrolysis-condensation cure reaction. The curable compositions can also use polymers that are generally not preferred due to their relatively slow cure rates.

[0011] The composition generally comprises two main components: a condensation curable silyl modified resin and a thermally conductive particulate filler. The material before curing exhibits a liquid, dispensable viscosity and can be cured to form a soft solid with high thermal conductivity. High surface area alumina has been found to act as a cure accelerator in the composition of the present invention and can be used dually as a thermally conductive filler. The high surface area alumina is preferably unmodified.

[0012] In one embodiment, the composition comprises a polymer formed from a silyl-modified resin and at least 1 ml 2 and a particulate filler having a total specific surface area of ​​0.1 to 10 wt. % of the composition, a portion of the particulate filler being alumina having an average particle size of less than 1 μm, the portion constituting 0.1 to 10 wt. % of the composition. The composition further comprises less than 0.1 wt. % of an organometallic catalyst compound and less than 0.5 wt. % of water. The composition exhibits a thermal conductivity of at least 1 W / m·K.

[0013] The composition may exhibit a cured hardness of from 20 Shore 00 to 80 Shore A at 25°C.

[0014] The surface of the particulate alumina filler may be unmodified. At least a portion of the particulate alumina filler may be fumed alumina. At least a portion of the particulate alumina filler may exhibit predominantly alpha or gamma crystal structure, or a mixture thereof.

[0015] The total specific surface area of ​​the particulate filler is 4 to 150 m 2 / g.

[0016] The composition may comprise 1-5 wt.% of a polymer and 50-95 wt.% of a particulate filler. The composition may comprise 0.1-1 wt.% of a particulate alumina filler having an average particle size of less than 1 μm. The composition may comprise 5-10 wt.% of a plasticizer having a viscosity of less than 100 cP at 25° C.

[0017] The thermal interface material comprises 1-5 wt.% of a polymer formed from a silyl-modified resin and 50-95 wt.% of a thermally conductive particulate filler having a particle size distribution, a first portion of the particle size distribution comprising 0.1-10 wt.% of the thermal interface material. The first portion of the particle size distribution comprises an average particle size of 5-1000 nm and an average particle size of 4-150 nm. 2 The thermal interface material is an alumina particle with a specific surface area of ​​1000 nm / g. The thermal interface material exhibits a thermal conductivity of at least 1 W / m K and a hardness of 20 to 80 Shore 00 at 25 °C.

[0018] Thermally conductive particulate filler should be at least 1 m 2 / g.

[0019] The first portion of the particle size distribution may have an average particle size of from 5 to 250 nm.

[0020] The particulate alumina filler may have an unmodified surface.

[0021] The battery system includes a battery and a thermal interface material thermally coupled to the battery. The battery system may further include a heat sink thermally coupled to the thermal interface material.

[0022] The two-part curable composition includes a first part having a particulate filler having a particle size distribution, the first part of the particle size distribution constituting 0.1 to 10% by weight of the first part, having an average particle size of 5 to 1000 nm, and an average particle size of 4 to 150 nm. 2 The second part of the particle size distribution comprises 80-95% by weight of the first part and has an average particle size of 1-100 μm. The second part of the two-part curable composition comprises a condensation curable silyl-modified resin that is curable upon exposure to the first part to a cured material that exhibits a hardness of 20 Shore 00 to 80 Shore A at 25° C.

[0023] The two-part curable composition may be curable to a gelled state within 24 hours at 25°C.

[0024] The two-part curable composition may include a silane-terminated polyether.

[0025] The two-part curable composition may contain less than 0.1 wt.% of an organometallic catalyst compound and less than 0.5 wt.% of water.

[0026] The second part of the two-part curable composition may comprise 80-95% by weight of thermally conductive particulate selected from alumina, aluminum trihydrate, aluminum nitride, aluminum hydroxide, graphite, zinc oxide, magnesium oxide, silicon carbide, boron nitride, metal particles, and combinations thereof.

[0027] The two-part curable composition may exhibit a thermal conductivity of at least 1 W / m·K.

[0028] The hardened material from the two-part hardenable composition is at least 1 m 2 The particulate alumina has a total specific surface area of ​​ / g.

[0029] The two-part curable composition may include any combination of some or all of the above features, or may exclude one or more of the above features. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a graph showing cured hardness as a function of total specific surface area of ​​a particulate alumina filler. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The above-listed objects and advantages, together with other objects, features, and advancements represented by the present invention, are presented herein with respect to specific embodiments, however, it is recognized that other embodiments and aspects of the present invention are within the purview of those skilled in the art.

[0032] The thermally conductive compositions of the present invention may be formed as coatings on surfaces or self-supporting substrates for placement along a heat dissipation path to remove excess heat, typically from heat-generating electronic components. The thermally conductive compositions exhibit a desired thermal conductivity of at least 1 W / m·K, and sufficient wettability to completely coat a surface prior to curing. The compositions preferably exhibit sufficient flexibility and cohesion to provide a stable interface. The compositions preferably cure to a gel state within 24 hours, within which time the storage modulus exceeds the loss modulus as measured by a rheometer known in the art.

[0033] The thermally conductive material is formed from a two-part curable composition that can be dispensed from at least two separate containers to separate the reactive silyl-modified resin from the reaction catalyst and water until the time when it is desired to cure the material. The compositions of the present invention are mixed, dispensed, and cured in situ by silyl hydrolysis and condensation, with the reaction product having an irreversible soft solid form. In many applications, the hydrolysis pathway proceeds by absorption of environmental moisture. Insufficient environmental moisture can slow the hydrolysis reaction or prevent it from completing altogether. Increasing the water content in the two-part composition makes water available for the hydrolysis reaction, which is undesirable because it is incompatible with the hydrophobic plasticizer and the reactive resin. The compositions of the present invention overcome the challenge of insufficient environmental moisture by using high surface area alumina as a cure accelerator.

[0034] One or both parts of the two-part curable composition may further include thermally conductive fillers, including alumina, as well as rheology modifiers, compatibilizers, plasticizers, pigments, water scavengers, antioxidants, and other functional fillers.

[0035] The disclosed curable compositions, when mixed and ready to use, may have a low shear rate viscosity of less than 1,500,000 cP. In some applications, the disclosed curable compositions, when mixed, may have a viscosity of less than 750,000 cP. In some applications, the disclosed curable compositions, when mixed, may have a viscosity in the range of about 200,000 cP to about 500,000 cP. The low shear rate viscosity may be measured at 25° C. at a shear rate of 1 1 / s using a parallel plate rheometer equipped with 25 mm parallel plates.

[0036] In one embodiment, the compositions are thixotropic, exhibiting a decrease in viscosity at higher flow rates. These compositions have low viscosities, on the order of 5,000 cP for high volume dispensing applications, and up to 50,000 cP for other applications. High shear rate viscosity can be measured at 30° C. and a shear rate of 3,000 1 / sec, typically using a capillary rheometer according to ISO 11443. The disclosed curable compositions, when mixed, will have an extrusion rate appropriate for use in the application, taking into account extrusion pressure, nozzle type, etc. The extrusion rate can be determined by measuring the amount of each component extruded individually at 90 psi through a Nordson EFD syringe barrel without the addition of a nozzle. Each component should have an extrusion rate of greater than 50 g / min, preferably greater than 150 g / min, and in some cases greater than 300 g / min.

[0037] resin Various silyl modified resins may be used in the matrix of the present invention. Condensation curable silane terminated resins preferably participate in a hydrolysis condensation cure pathway at ambient temperature or higher. In some embodiments, the resin may be non-silicone, and the composition contains no more than trace amounts of silicone. In some embodiments, the composition does not contain silicone. In some embodiments, the non-silicone resin is substantially free of -Si-O- units therein. In other embodiments, the non-silicone resin excludes silicone and polysiloxane resins and does not have -Si-O- units therein.

[0038] The silyl-modified reactive resin employed herein is present in a range of about 1 to about 50 weight percent based on the total weight of the composition; in some embodiments, the composition comprises the silyl-modified reactive resin in a range of about 1 to about 20 weight percent; in some embodiments, the composition comprises the silyl-modified reactive resin in a range of about 1 to about 10 weight percent; in some embodiments, the composition comprises the silyl-modified reactive resin in a range of 1 to 7 weight percent.

[0039] Examples of suitable resins for the reactive resin of the present invention include reactive polymer resins having at least one silyl reactive functional group that includes at least one bond that can be activated with water. Exemplary silyl reactive functional groups include alkoxysilanes, acetoxysilanes, and ketoximesilanes.

[0040] The reactive polymer resin can be any reactive polymer that can participate in silyl hydrolysis reaction. For example, the reactive polymer resin can be selected from a wide range of polymers as polymer systems with reactive silyl groups, including silyl-modified reactive polymers. The silyl-modified reactive polymer can have a non-silicone backbone to limit or avoid silicone release when heated, such as when used in electronic devices. Preferably, the silyl-modified reactive polymer has a non-silicone backbone. Preferably, the silyl-modified reactive polymer has a flexible backbone to reduce elastic modulus and glass transition temperature. Preferably, the silyl-modified reactive polymer has a flexible backbone of polyether, polyester, polyurethane, polysiloxane, polyacrylate, polyisoprene, polybutadiene, polystyrene-butadiene, or polybutylene-isoprene.

[0041] Silyl-modified reactive polymers can be obtained by reacting a polymer with at least one ethylenically unsaturated silane in the presence of a radical initiator, and the ethylenically unsaturated silane has at least one hydrolyzable group on silicon atom.For example, the silyl-modified reactive polymer can be a dimethoxysilane-modified polymer, a trimethoxysilane-modified polymer, or a triethoxysilane-modified polymer.For example, the silyl-modified reactive polymer can include silane-modified polyether, polyester, polyurethane, polyacrylate, polyisoprene, polybutadiene, polystyrene-butadiene, or polybutylene-isoprene.

[0042] The ethylenically unsaturated silane may be selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxymethylsilane, vinyldiethoxymethylsilane, trans-β-methylacrylic acid trimethoxysilylmethyl ester, and trans-β-methylacrylic acid trimethoxysilylpropyl ester.

[0043] The silyl-modified reactive polymer preferably comprises silyl groups with at least one hydrolyzable group on the silicon atom in statistical distribution. For example, in one embodiment, the silyl-modified reactive polymer has the general formula:

[0044] [ka] where R is a monovalent to tetravalent polymer radical, R 1 , R 2 , R 3 are independently an alkyl or alkoxy group having 1 to 8 C atoms, and A is a carboxy, carbamate, amide, carbonate, ureido, urethane or sulfonate group, an oxygen atom or a covalent bond, with x=1 to 8 and n=1 to 4. In some embodiments, R does not contain any -Si-O- units.

[0045] The silyl-modified reactive polymer can also be obtained by reacting a polymer having a hydroxyl group with an alkoxysilane having an isocyanate group. For example, the silyl-modified reactive polymer can be a dimethoxysilane-modified polyurethane polymer, a trimethoxysilane-modified polyurethane polymer, or a triethoxysilane-modified polyurethane polymer. Furthermore, the silyl-modified reactive polymer can be represented by the average general formula:

[0046] [ka] In the formula, R is a monovalent to tetravalent polymer residue, and the residue R1 , R 2 and R 3 at most one third of the radicals are independently alkyl radicals having 1 to 4 carbon atoms, and the residues R 1 , R 2 and R 3 At least one-quarter of the radicals R are independently ethoxy residues, and the remaining radicals R 1 , R 2 and R 3 are each independently a methoxy radical, and n=1 to 4. In some embodiments, R does not contain any -Si-O- units.

[0047] Silyl-modified reactive polymers are available, for example, as dimethoxysilane-modified MS polymers with a polyether backbone and XMAP™ polymers with a polyacrylate backbone from Kaneka Belgium NV, trimethoxysilane-modified ST polymers from Evonik, triethoxysilane-modified Tegopac™ polymers from Evonik, silane-modified Desmoseal™ polymers from Covestro, or di- or tri-methoxysilane-modified Geniosil™ polymers from Wacker.

[0048] Alumina hardening accelerator Applicants have discovered that alumina with relatively high surface area, preferably unmodified alumina, accelerates the cure of silyl-modified reactive resins, such as silane-terminated resins. The cure acceleration varies with the total surface area of ​​the filler. However, in the dispensable compositions of the present invention, a balance must be struck between cure acceleration and viscosity / dispenseability, as excessive alumina loading can adversely affect dispenseability. It has been found that a range of alumina loadings and total alumina surface area combinations can achieve the most favorable performance for cure acceleration of silane-terminated reactive resins.

[0049] Alumina useful as a cure accelerator is preferably a high surface area particle having an unmodified surface. As used herein, the term "unmodified" or "unmodified surface" means that the alumina particles are not chemically, physically, or electrically modified by an applied treatment process. Changes in the alumina particles as a result of exposure to the surrounding environment are not considered to be an applied treatment process. An example of an unmodified alumina is fumed alumina. In some embodiments, the particulate alumina may be surface modified. An example of a surface modification of particulate alumina may be to render it hydrophobic, such as silane treatment.

[0050] It has been found that certain surface crystallinity of alumina particles can promote cure acceleration properties. In particular, aluminas having either or both alpha and gamma crystallinity have shown desirable results for accelerating the cure of silyl-modified reactive resins.

[0051] It has also been found that the particle size of the alumina plays an important role in promoting accelerated hardening. In some embodiments, the alumina particles have an average particle size (d 50 ). In some embodiments, the average particle size of the alumina is in the range of 5 nm to 20 μm. In some embodiments, the average particle size of the alumina is in the range of 5 nm to 1000 nm. In some embodiments, the average particle size of the alumina is in the range of 5 nm to 250 nm. The alumina particles may be of any suitable shape, such as spherical, rod-like, plate-like, or branched particles, and one or more particle shapes may be used in the compositions of the present invention.

[0052] In useful embodiments, the particulate alumina filler constitutes a portion of the thermally conductive filler in the composition. In some embodiments, the first portion of the thermally conductive filler is a particulate alumina filler having an average particle size of less than 1 μm. In some embodiments, the particulate alumina filler of the first portion has an average particle size of 5 nm to 500 nm. In some embodiments, the particulate alumina filler of the first portion has an average particle size of 5 nm to 250 nm. In some embodiments, the particulate alumina filler of the first portion has an average particle size of 5 nm to 100 nm. The first portion of the thermally conductive filler preferably constitutes 0.1 to 10% by weight of the total composition. In some embodiments, the first portion of the thermally conductive filler preferably constitutes 0.1 to 1% by weight of the total composition.

[0053] The second portion of the thermally conductive filler may have an average particle size of greater than 1 μm. In some embodiments, the second portion of the thermally conductive filler has an average particle size of 1 μm to 100 μm. In some embodiments, the second portion of the thermally conductive filler has an average particle size of 1 μm to 60 μm. The second portion of the thermally conductive filler preferably comprises 20 to 95% by weight of the total composition. In some embodiments, the second portion of the thermally conductive filler preferably comprises 40 to 95% by weight of the total composition. In some embodiments, the second portion of the thermally conductive filler preferably comprises 50 to 95% by weight of the total composition.

[0054] The thermally conductive filler preferably constitutes 50-95 wt.% of the total composition. The amount of the particulate alumina portion of the thermally conductive filler is preferably within a range that does not excessively inhibit the dispersibility of the uncured two-part composition and does not excessively restrict the flexibility of the cured composition. Therefore, it is preferable to balance the cure acceleration properties and the viscosity / hardness effect in the amount range and particle size range of the particulate alumina filler. In some embodiments, the particulate alumina filler is present in the total composition at 1-1000 phr. In some embodiments, the particulate alumina filler is present in the total composition at 1-100 phr. In some embodiments, the particulate alumina filler is present in the total composition at 1-50 phr.

[0055] It has been found that the specific surface area (total surface area of ​​material per unit mass, "SSA") of the particulate alumina filler in the composition of the present invention contributes to the hardening acceleration properties. As used herein, the term "total specific surface area" refers to the specific surface area of ​​all the alumina fillers in the composition. In some embodiments, the total specific surface area of ​​the particulate alumina filler is at least 0.2 m 2 In some embodiments, the total specific surface area of ​​the particulate alumina filler is at least 1 m 2 In some embodiments, the total specific surface area of ​​the particulate alumina filler is 1 to 200 m 2 In some embodiments, the total specific surface area of ​​the particulate alumina filler is 4 to 150 m 2 / g.

[0056] In some embodiments of the present invention, in addition to the particulate alumina filler, thermally conductive particles may be included to increase the thermal conductivity of the composition. The particles may be both thermally conductive and electrically conductive. Alternatively, the particles may be thermally conductive and electrically insulating. Examples of thermally conductive particles include aluminum trihydrate, zinc oxide, graphite, magnesium oxide, silicon carbide, aluminum nitride, boron nitride, metal particles, and combinations thereof. The thermally conductive particles may be of various shapes and sizes, and it is contemplated to employ a particle size distribution to meet the parameters of a particular application.

[0057] It is desirable for the compositions of the present invention to exhibit a thermal conductivity of at least 1 W / m·K, more preferably at least 2 W / m·K.

[0058] Plasticizer The compositions of the present invention may include a plasticizer to adjust the viscosity of the dispensed material, especially under shear, and to maintain flexibility / softness properties when the composition is in the cured state. The cured compositions exhibit a relatively low modulus or hardness of less than 80 Shore A, which relieves stress during electronic component assembly and promotes compatibility of thermal materials with the respective contact surfaces of electronic components.

[0059] The plasticizers useful in the compositions of the present invention are those that are effective in promoting the flowability of the aggregates that make up the composition. The plasticizers of the present invention may preferably be low volatility liquids that reduce the overall viscosity of the composition before hardening so that the composition is easily dispenseable through a liquid dispensing device. Thus, the plasticizer may exhibit a viscosity of less than 1000 cP at 25°C. In another embodiment, the plasticizer may exhibit a viscosity of less than 500 cP at 25°C. In a further embodiment, the plasticizer may exhibit a viscosity of less than 100 cP at 25°C. Preferably, the plasticizer exhibits a viscosity of 1 to 50 cP at 25°C.

[0060] The plasticizer is preferably added to the composition in an amount suitable to properly adjust the viscosity for dispersibility before curing and softness after curing. In some embodiments, the plasticizer may comprise about 1-50 weight percent of the composition. In some embodiments, the plasticizer may comprise about 1-20 weight percent of the composition. In some embodiments, the plasticizer may comprise about 5-10 weight percent of the composition. The plasticizer may preferably be present at less than 20 weight percent of the composition.

[0061] Examples of plasticizers include sebacates, adipates, terephthalates, dibenzoates, gluterates, phthalates, azelates, benzoates, sulfonamides, organic phosphates, glycols, polyethers, trimellitates, polybutadienes, epoxies, amines, acrylates, thiols, polyols, isocyanates, and the like.

[0062] The silyl-modified reactive polymer that forms the bulk matrix of the composition preferably does not react with the plasticizer to form a network. Applicants have found that silyl-modified polymers (SMPs) such as those described in U.S. Pat. No. 3,632,557 and U.S. Patent Application Publication No. 2004 / 0127631, the contents of which are incorporated herein in their entirety, may be particularly useful in preparing the thermally conductive material of the present invention.

[0063] Rheology Modifiers The compositions of the present invention may contain certain rheology modifiers, sometimes called "thickeners", to aid in flow properties, thixotropy, and stability of the dispensed form. Rheology modifiers useful in the present invention include thickeners such as fumed silica, organoclays, polyurethanes, and acrylic polymers. Rheology modifiers may also include dispersants for thermally conductive fillers. In some embodiments, the rheology modifiers themselves may contribute to the thermal conductivity and / or hardening of the composition. Rheology modifiers may inhibit settling of fillers during storage.

[0064] The thickening agent used in the compositions of the present invention is present in the range of about 0 to about 3 weight percent. In some embodiments, the composition comprises a thickening agent in the range of about 0.01 to about 1 weight percent. In some embodiments, the composition comprises a thickening agent in the range of about 0.05 to about 0.5 weight percent. In some embodiments, the composition comprises less than 0.5 weight percent of the thickening agent.

[0065] Reaction catalyst Reaction catalysts may be used to further accelerate the hydrolysis-condensation cure reaction of the silyl-modified reactive resin. Examples of reaction catalysts useful in the compositions of the present invention include organotin, organozinc and organotitanium compounds (collectively referred to herein as "organometallic catalysts") that accelerate the moisture cure of the silyl-modified reactive resin.

[0066] As a result of the discovered cure-accelerating properties of particulate alumina, the compositions of the present invention preferably have a low dependency on reaction catalysts. In some embodiments, the use of organometallic catalyst compounds may be avoided entirely ... This may be preferred in view of the environmental and health toxicity of such compounds. In other embodiments, the use of organometallic catalyst compounds may be reduced. Furthermore, other alternative, safer reaction catalysts may be used in place of at least a portion of the organometallic catalyst compounds, which are inappropriate for accelerating the moisture cure reaction of silyl-modified resins.

[0067] The reaction catalyst used in the compositions of the present invention may be present in the range of 0 to 0.1 weight percent. In some embodiments, the composition includes a reaction catalyst in the range of 0.01 to 0.5 weight percent. In some embodiments, the composition includes a reaction catalyst in the range of 0.01 to 0.02 weight percent. As used herein, a concentration "less than" a particular amount may include 0.

[0068] The thermally conductive compositions of the present invention are preferably curable in the presence of water (moisture curable) at ambient temperature. Depending on the application, moisture may be available from the ambient environment or from water released from the object(s) to which the composition is applied. The compositions of the present invention significantly reduce the amount of water required to facilitate the hydrolysis-condensation cure reaction of the silyl-modified resin. Preferably, the compositions of the present invention are curable without the addition of environmental moisture. In some embodiments, water may be included as an ingredient in the non-resin part of a multi-part curable composition for mixing with the reactive resin in situ. However, preferably, the amount of water required in the composition itself is small so as not to interfere with the functional properties of the thermal material. In some embodiments, water is present in the compositions of the present invention in the range of 0-0.5% by weight. In some embodiments, the compositions include water in the range of 0.01-0.3% by weight. In some embodiments, the compositions include water in the range of 0.01-0.2% by weight.

[0069] As used herein, the term "ambient temperature" is intended to mean the temperature of the environment in which the reaction occurs, within a temperature range of 15 to 30°C, preferably 25°C. The thermally conductive composition is curable at ambient temperature within 72 hours, preferably within 24 hours. The thermally conductive composition may also be curable at elevated temperatures. As used herein, the term "curable" is intended to mean that the composition is capable of reacting under appropriate conditions and the reaction product has an irreversible solid form.

[0070] Water Scavenger The composition of the present invention preferably contains a water scavenger to prevent the reaction of resin-containing components before dispensing so as to extend shelf life.The water scavenger may be, for example, alkyltrimethoxysilane, oxazolidine, zeolite powder, p-toluenesulfonyl isocyanate, oxocalcium, and ethyl orthoformate.The water scavenger is preferably vinyltrimethoxysilane.If there is too much water scavenger in the composition, curing will be slow.The water scavenger may be present in an amount of more than about 0.05% by weight and less than about 0.5% by weight, for example about 0.1% by weight, of the composition.

[0071] Optional Additives In accordance with some embodiments of the present invention, the compositions described herein may further comprise one or more additives selected from fillers, stabilizers, adhesion promoters, solvents, pigments, wetting agents, dispersants, flame retardants, extenders, and corrosion inhibitors. In some embodiments, the compositions may be free of any or all of the additives. EXAMPLES

[0072] The examples described herein are two-component curable compositions that utilize alkoxysilane-modified polyether resins as the reactive polymer component.

[0073] Example 1 Example 1 is a two-component thermally conductive material with Part A containing an organotin catalyst and Part B containing a silyl-modified reactive resin. The composition is summarized in Table 1. Part A contained 8 wt% plasticizer with a viscosity of less than 100 cP, 3 wt% thickeners (fumed silica, organoclay, and liquid rheology additives), 0.1 wt% organotin catalyst, 0.2 wt% pigment, 0.4 wt% water, and 88 wt% thermally conductive filler. Standard Part B contained 4 wt% plasticizer with a viscosity of less than 100 cP, 4 wt% alkoxysilane-modified polyether resin with dimethoxysilane end groups, 1 wt% thickeners (fumed silica, organoclay, liquid rheology modifiers), 0.2 wt% resin additives (water scavenger, antioxidant), and 90 wt% thermally conductive additives. The fillers were mixed at elevated temperature and vacuum prior to adding the reactive resin to avoid hydrolysis, or were dried at ambient temperature with optional addition of water scavenger.

[0074] [Table 1]

[0075] The formulations were initially prepared using a planetary mixer. Part A was then modified using various strategies to alter the cure reaction as shown in Table 2. The same Part B was used for each test. The separate parts were loaded into two-component cartridges and mixed while dispensing with a static mixer. Samples were dispensed into small aluminum trays and evaluated for hardness after various time intervals in a controlled environment at 74°F and 50% relative humidity. Hardness was measured with a Shore 00 or Shore A durometer.

[0076] [Table 2]

[0077] The evolution of Shore 00 hardness for selected formulations is shown in Table 3. In an open tray exposed to air, the base formulation (containing the maximum allowable level of organotin catalyst to avoid hazard classification labeling and 0.4 wt.% water to accelerate the initial hydrolysis step of the curing reaction) required more than 24 hours at room temperature to develop a measurable hardness on the Shore 00 scale and did not reach a hardness plateau at 7 days. In a closed container, the material did not cure even after a week and showed a variety of surface defects with delamination and cracking due to slow development of mechanical strength, which is unacceptable for many applications.

[0078] [Table 3]

[0079] Increasing the amount of organotin catalyst to three times the acceptable loading resulted in faster cure but a decrease in final hardness and strength (Test A-2), a change that indicates an undesirable change in the framework structure. Other tests based on changing the type of organotin catalyst, adding a second catalyst (Test A-3), and increasing the amount of water (Test A-4) similarly did not improve cure speed enough to remain within the acceptable range for the application.

[0080] The most significant improvement was observed with the addition of untreated alumina filler. Three small spherical aluminas were used, each of which showed more than 50% cure after 24 hours. At a given loading, the rate scaled with the specific surface area (SSA) of the filler, and increasing loadings further improved the reaction rate. This confirms that alumina surface interactions are driving the reaction. Importantly, the addition of untreated alumina did not result in a significant change in the final hardness of the material, as observed with changing the catalyst, nor was there any change in volatile components such as water. The high thermal conductivity of alumina also allows partial replacement of treated alumina to compensate for changes in viscosity or dispensing speed without changing the thermal performance of the material.

[0081] [Table 4]

[0082] Example 2 In Example 2, the amount of organotin catalyst was increased to accelerate cure to an acceptable level. A description of the two-part formulation is shown in Table 5. Dimethoxysilane terminated reactive resin was present in Part B at 4 wt % and Part A contained 0.4 wt % water.

[0083] [Table 5]

[0084] Trays were prepared using the method described in Example 1 and left exposed to air to accelerate curing. The change in hardness after dispensing is shown in Table 6. At an organotin loading of 0.1 wt%, the material did not cure after 24 hours and did not reach final hardness by 72 hours. In closed packs, the material did not cure within 7 days and exhibited cracks and mechanical defects due to slow outgassing of the uncured material. Increasing the loading to 0.8 wt% allowed the material to reach approximately 80% of its final cure within 24 hours, but further increases tended to decrease hardness and create inhomogeneities within the material.

[0085] [Table 6]

[0086] This example highlights that it is possible to accelerate cure by increasing catalyst levels, but only by increasing the loading to undesirable levels. For most applications, the maximum amount of organotin that can be included is 0.1 wt. % tin. This approach is not preferred due to the environmental and health hazards associated with tin-based catalysts.

[0087] Example 3 Untreated fillers tend to have a greater impact on viscosity and flow rate than treated fillers, limiting the maximum loading in many gap-filling applications. To minimize the effect of the filler addition on dispensing characteristics, it is desirable to use a filler that has a high surface area relative to the volume area. In Example 3, fumed alumina was selected, which offers a very high surface area, thereby maximizing the amount of alumina surface for a given volume fraction of filler.

[0088] [Table 7]

[0089] The materials were prepared using a planetary mixer and dispensed into an open aluminum tray using a static mixer. Hardness after 24 hours was measured using a Shore 00 durometer and is shown in Table 8. In Example 3, one Part B was used to prepare various Part A's with varying amounts of fumed alumina from 0 to 0.5 wt%.

[0090] [Table 8]

[0091] The base formulation without fumed alumina showed no measurable hardness after 24 hours. At 0.5 wt.% fumed alumina content, hardness increased with fumed alumina content up to 40 Shore 00, which is 70% of the final hardness. Increasing the amount of larger diameter untreated alumina further improved hardness (Example C-6), but the significantly lower specific surface area severely limited the rate at which it could be compounded.

[0092] Example 4 The percent hardness increase was used as a proxy to evaluate the ability of various fillers to accelerate the cure of the silane modified resin. Example 4 contains the results of many experiments using various types of alumina as well as silica and zinc oxide, and for various types of surface treatments. Typical parameter ranges for the mix compositions are shown in Table 9.

[0093] [Table 9]

[0094] In Example 4, the rate of cure of the dimethoxy-terminated polyether was primarily driven by the total amount of untreated surface area (USA) of a given filler (i) in the composition, such as alumina. This parameter was calculated by the USA for each particle. i =SSAi*c i where SSAi is the specific surface area of ​​filler i (m 2 / g), and c i is the weight percent of the composition. For compositions with multiple fillers, the total surface area (TUSA) of the fillers is calculated as TUSA=Sum{USA i * A i} where A is the activity index.

[0095] A summary of the Shore 00 hardness after 24 hours is shown in Figure 1. The results show a very strong correlation between the amount of active surface area of ​​the untreated alumina and hardness. This effect is more pronounced than changes in water content and catalyst loading; no similar effects were observed with zinc oxide or silica.

[0096] The importance of the alumina surface is highlighted by the observation that no cure rate enhancement was observed after surface treatment of the same grade of alumina with silane groups. Increasing the levels of compatibilizers or other dispersing aids designed to coat the surface of the alumina had the same effect of slowing down the cure rate by limiting the amount of exposed surface area and / or complexing with the organometallic catalyst, thereby reducing its activity.

[0097] 1 provides a summary of the activity index of various fillers, which was obtained by optimizing the relationship between the total surface area of ​​various fillers and the 24 hour hardness of the trays, as described in the examples above.

[0098] [Table 10]

[0099] Example 5 Additional compositions Table 11 shows another slow-cure composition incorporating multiple types of thermally conductive fillers. The zinc oxide filler is untreated, but not enough to provide a significant effect on cure acceleration. Even with 0.15 wt. % organometallic catalyst, this composition fails to form a solid with measurable hardness. To clearly demonstrate the cure-accelerating effect of the high surface area alumina, a 100 m2 sample was used. 2 / g unmodified surface and average particle size (d 50 Fumed alumina having a fluorine atom number of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31

[0100] Table 12 shows the 1-day and 4-day Shore 00 hardness with various amounts of fumed alumina, showing that the 1-day hardness increases approximately linearly with the amount of fumed alumina added.

[0101] [Table 11]

[0102] [Table 12]

Claims

1. A thermally conductive composition comprising: A condensation-curing silyl-modified resin; and Particulate alumina filler having a total specific surface area of at least 1 m ２ / g, wherein a part of the particulate alumina filler has an average particle size of less than 1 μm, and the part constitutes 0.1 to 10% by weight of the composition; Less than 0.1% by weight of an organometallic catalyst; and Containing less than 0.5% by weight of water, The composition exhibits a thermal conductivity of at least 1 W / m·K. A thermally conductive composition.

2. The thermally conductive composition according to claim 1, wherein the particulate alumina is unmodified.

3. The thermally conductive composition according to claim 1 or 2, wherein at least a part of the particulate alumina filler contains fumed alumina.

4. The thermally conductive composition according to claim 1 or 2, wherein the alumina filler contains at least one of alpha and gamma crystal structures.

5. Having a total specific surface area of 4 m ２ / g to 150 m ２ / g. The thermally conductive composition according to claim 1 or 2.

6. 1% to 7% by weight of the silyl-modified resin; and Containing 50% to 95% by weight of the particulate alumina filler. The thermally conductive composition according to claim 1 or 2.

7. The thermally conductive composition according to claim 1 or 2, containing 0.1% to 1% by weight of a part of the particulate alumina filler having an average particle size of less than 1 μm.

8. Containing 5% to 20% by weight of a plasticizer having a viscosity of less than 100 cP at 25°C. The thermally conductive composition according to claim 1 or 2.

9. The silyl-modified resin is a silane-terminated polyether; and / or The silyl-modified non-silicone polymer contains an alkoxysilane end group; and / or The silyl-modified non-silicone polymer does not contain -Si-O- units; and / or The heat-conductive composition according to claim 1 or 2, wherein the silyl-modified non-silicone polymer is a two-part composition.

10. The heat-conductive composition according to claim 1 or 2, wherein each component has an extrusion rate greater than 50 g / min, preferably greater than 150 g / min, more preferably greater than 300 g / min when extruded through a Nordson EFD syringe barrel at 90 psi.

11. The cured reaction product of the heat-conductive composition according to claim 1 or 2.

12. The cured reaction product of the heat-conductive composition according to claim 1 or 2, having a cured hardness of 20 Shore 00 to 80 Shore A at 25°C.

13. A battery; and A battery system including the heat-conductive composition according to claim 1 or 2 thermally bonded to the battery.

14. A thermal interface material, 1 to 7% by weight of a condensation-curable silyl-modified resin; and 50 to 95% by weight of a heat-conductive particulate filler having a particle size distribution, wherein a first portion of the heat-conductive filler is alumina, constituting 0.1% to 10% by weight of the thermal interface material, having an average particle size of 5 nm to 1000 nm and a specific surface area of 4 m ２ / g to 150 m ２ / g, The thermal interface material exhibits a thermal conductivity of at least 1 W / m·K and a cured hardness of 20 Shore 00 to 80 Shore A at 25°C.

15. The particulate alumina filler has a total specific surface area of at least 1 m ２ / g; and / or The first portion of the thermal conductivity filler has an average particle size of 5 nm to 250 nm; and / or The particulate alumina filler is unmodified, the thermal interface material according to claim 14.

16. A two-part curable composition, A first part containing a thermal conductivity filler having a particle size distribution, wherein the first portion of the thermal conductivity filler is alumina, constituting 0.1% to 10% by weight of the first part, having an average particle size of 5 nm to 1000 nm and 4 m ２ / g to 150 m ２ / g specific surface area, the second portion of the thermal conductivity filler constitutes 80% to 95% by weight of the first part, having an average particle size of 1 μm to 100 μm, the first part; and A second part containing a condensation-curable silyl-modified resin, wherein the resin can be cured to a gel state having a hardness of 20 Shore 00 to 80 Shore A at 25°C by being exposed to the first part, the second part A two-part curable composition comprising.

17. The silyl-modified resin is a silane-terminated polyether; and / or The silyl-modified non-silicone polymer contains an alkoxysilane end group; and / or The silyl-modified non-silicone polymer does not contain -Si-O- units, the two-part curable composition according to claim 16.

18. The first part contains less than 0.5% by weight of an organometallic catalyst and less than 0.5% by weight of water, the two-part curable composition according to claim 16 or 17.

19. The two-part curable composition according to claim 16 or 17, wherein the second part contains 80% to 95% by weight of a thermally conductive filler selected from alumina, aluminum trihydrate, aluminum nitride, aluminum hydroxide, graphite, zinc oxide, magnesium oxide, silicon carbide, boron nitride, metal particles, and combinations thereof.

20. The two-part curable composition according to claim 16 or 17, wherein the cured material exhibits a thermal conductivity of at least 1 W / m·K.

21. The two-part curable composition according to claim 16 or 17, wherein the cured material contains particulate alumina having a total specific surface area of at least 1 m ２ / g.

22. Use of the thermally conductive composition according to claim 1 or the two-part curable composition according to claim 16 as a thermally conductive coating or a thermal interface material.

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