阅读说明：本技术 基于两部分聚氨酯的热界面材料 (Thermal interface materials based on two-part polyurethanes ) 是由 S·S·孔 V·亚历克西斯 M·C·B·德耶苏 C·梅克尔-约纳斯 E·杰克逊 C·吴 于 2020-02-25 设计创作，主要内容包括：本文公开了基于两部分聚氨酯树脂的热界面材料,其包含聚氨酯树脂和分散在整个所述聚氨酯树脂中的导热填料,其中所述聚氨酯树脂由包含以下的两个部分形成：包含三醇的第一部分和包含异氰酸酯官能化组分的第二部分,其中所述第一部分和所述第二部分中的至少一个包含导热填料材料。(Disclosed herein is a two-part polyurethane resin-based thermal interface material comprising a polyurethane resin and a thermally conductive filler dispersed throughout the polyurethane resin, wherein the polyurethane resin is formed from two parts comprising: a first part comprising a triol and a second part comprising an isocyanate-functional component, wherein at least one of the first part and the second part comprises a thermally conductive filler material.)

1. a composition comprising a polyurethane resin and a thermally conductive filler dispersed throughout the polyurethane resin, wherein the polyurethane resin is formed from two portions comprising:

a first part comprising a triol, and

a second part comprising an isocyanate-functional component,

wherein at least one of the first portion and the second portion comprises a thermally conductive filler material.

2. The composition of claim 1 wherein the triol is a hydrophobic low glass transition temperature triol selected from the group consisting of polypropylene glycol triols, poly (trimethylene) glycol triols, poly (tetramethylene ether) glycol triols, 2-methyl-1, 3-propanediol adipate triols.

3. The composition of claim 1, wherein the triol has a molecular weight in the range of about 200 to about 5000 g/mol.

4. The composition of claim 1, wherein the first part further comprises a glycol.

5. The composition of claim 4, wherein the diol has a molecular weight in the range of from about 200 to about 5000 g/mol.

6. The composition of claim 1, wherein the triol is present in the first part in an amount of about 29 to about 100 wt% based on the total weight of the first part.

7. The composition of claim 1, wherein the isocyanate-functional component is a difunctional aliphatic isocyanate.

8. The composition of claim 1, wherein the isocyanate-functional component comprises pendant groups having a molecular weight of greater than about 100 g/mol.

9. The composition of claim 8, wherein the pendant groups of the isocyanate functional component are polyethers, linear or branched alkyl groups, esters, polyesters, which may contain unsaturation or heteroatoms, or combinations thereof.

10. The composition of claim 1, wherein each of the first and second parts has a molecular weight of less than about 5000g/mol and a viscosity of less than about 3000 mPa-s at room temperature.

11. The composition of claim 1, wherein the thermally conductive filler material is present in the first part in an amount in the range of about 30-95 wt% based on the total weight of the first part.

12. The composition of claim 1, wherein the thermally conductive filler material is present in the second part in an amount in the range of about 30-95 wt% based on the total weight of the second part.

13. The composition of claim 1, wherein the filler is present in the first part in an amount of about 85 wt% to about 95 wt%, based on the total weight of the first part.

14. The composition of claim 1, wherein the filler is present in the second part in an amount of about 85 wt% to about 95 wt%, based on the total weight of the second part.

15. The composition of claim 1, wherein the composition further comprises a catalyst.

16. The composition of claim 1, wherein the first part further comprises a catalyst.

17. The composition of claim 14, wherein the catalyst is selected from amine catalysts and Sn, Zn, Bi, Zr, V or Ti based metal catalysts.

18. The composition of claim 14, wherein the catalyst is a Zn-based complex, a Bi-based complex, or a combination thereof.

19. The composition of claim 1, wherein the first part and/or the second part further comprises an antioxidant blend, a pigment, an antifoaming agent, a phase change material, a rheology modifier, a plasticizer, a water scavenger, or a combination thereof.

20. The composition of claim 18, wherein the second part further comprises a water scavenger, wherein the water scavenger is selected from the group consisting of oxazolidines, p-toluenesulfonyl isocyanates, vinyloxysilanes, and combinations thereof.

21. The composition of claim 1, wherein the first part and the second part comprise a thermally conductive filler material selected from the group consisting of alumina, boron nitride, aluminum nitride, magnesium oxide, zinc oxide.

22. The composition of claim 1, wherein the composition has an NCO to OH ratio of less than about 1.3.

23. The composition of claim 1, wherein the composition is capable of curing at room temperature.

24. The composition of claim 1, wherein the cured composition is thermally stable between about-40 ℃ to about 125 ℃.

25. The composition of claim 1, wherein after curing, the composition has a shore OO hardness of less than about 90.

26. Composition according to claim 1 for use as a Thermal Interface Material (TIM), preferably in the form of a two-part gap filler or a pre-cured gap pad.

27. An electronic device comprising a heat source, a heat sink, and the composition of claim 1 disposed therebetween.

28. The electronic device of claim 25, wherein no air is disposed between the heat source and the heat sink.

Background

Electronic equipment typically generates a significant amount of heat during operation. To cool these devices, a heat sink is typically secured to the device in some manner. In operation, heat generated by the electronic device during use is transferred from the heat source of the device to the heat sink where the heat is harmlessly dissipated. Thermal interface materials typically operate by rejecting excess thermal energy generated by a heat source to a heat sink.

The thermal interface material will desirably provide intimate contact between the heat sink and the heat source to facilitate heat transfer therebetween.

Typically, these thermal interface materials are used in conjunction with heat-generating electronic components, such as Integrated Circuits (ICs), Central Processing Units (CPUs), and the like. Generally, a paste-like heat conductive material (e.g., silicone grease) or a sheet-like heat conductive material (e.g., silicone rubber) is used as the thermal interface material. The performance of thermal interface materials is typically graded using both thermal conductivity and thermal resistance. For example, while some pastes and greases provide low thermal resistance, they must be applied in a liquid or semi-solid state, thus requiring manufacturing controls to optimize their application. In addition to enhanced control during application, handling of the paste or grease material can also be cumbersome and difficult. Furthermore, greases and pastes cannot be used on non-planar surfaces. Additional difficulties with existing materials include: control of reapplication of the paste, migration of grease to unwanted areas, and reworkability of the phase change material or thermoset paste. Conventional thermal interface pads address the handling and application of pastes and greases, however they typically have higher thermal resistance than pastes and greases. The thermal interface pad may be pre-cured, may be cured in situ, and may be made of a one or two part composition.

In addition, many thermal interface materials are made by dispersing thermally conductive fillers in a polymer matrix, and many contain silicon. Silicon-containing thermal interface materials have problems with bleeding and outgassing, and thus may contaminate equipment. On the other hand, a non-silicon-containing thermal interface material may have a low thermal conductivity and a high hardness.

The thermal interface plays an important role in the operation of the device in terms of performance and reliability. These materials can be used to accelerate heat dissipation and provide a cost effective method for reducing the flexibility of the overall size of the package.

Thus, there remains a need for a thermal interface material based on silicone replacement chemistry that does not release siloxane species (species) and thus does not contaminate surrounding structures and extends the life of the device. It would still be advantageous to provide a thermal interface material that is easy to handle and apply, but also provides low thermal resistance.

Disclosure of Invention

Compositions for use as thermal interface materials are provided. The composition comprises a polyurethane resin and a thermally conductive filler dispersed throughout the polyurethane resin, wherein the polyurethane resin is formed from two parts comprising: a first part comprising a triol and a second part comprising an isocyanate-functional component, wherein at least one of the first part and the second part comprises a thermally conductive filler material.

Another aspect of the invention provides an electronic device comprising a heat source, a heat sink, and a thermal interface material according to the description above disposed therebetween.

Drawings

Figure 1 depicts the rheological results of a composition of the invention based on a two-part polyurethane.

Fig. 2 depicts the rheological results for a composition of the present invention based on a two-part polyurethane resin and an alumina thermally conductive filler.

Detailed Description

Disclosed herein is a composition for use as a thermal interface material ("TIM"). The composition comprises a polyurethane resin formed of two parts and a thermally conductive filler dispersed throughout the polyurethane resin. The first part comprises a polyol and the second part comprises an isocyanate-functional component. The first portion and/or the second portion may comprise a thermally conductive filler material.

The two-part polyurethane comprises a lightly crosslinked polyurethane network having at least one long side group attached to each repeating urethane unit of the network, the long side group having a molecular weight greater than about 100g/mol, preferably greater than about 200 g/mol. These side groups minimize leaching or migration problems typically associated with thermal interface materials without the need to include plasticizers.

The first part may comprise a polyol, triol, diol, or combinations thereof. Preferably, the first part comprises a triol. In a preferred embodiment, the first part comprises a triol and a diol.

Triols that can be included in the first part of the compositions disclosed herein include, but are not limited to, low glass transition, low polarity resins built from trifunctional cores of trimethylolethane, trimethylolpropane or glycerol. Preferably, the triol has a molecular weight in the range of from about 500 to about 5000 g/mol. Particularly useful are: polyether triols made from polypropylene glycol (PPG), polytrimethylene glycol, polytetramethylene glycol (PTMG), and polyester triols made from 2-methyl-1, 3-propanediol adipate, and the like. These products and their diol analogs are available from Covestro (b)Series), Dow (Series), LyondellBasell (Polymeg), BASF (PolyTHF series), Kuraray (polyol series), Arkema (R) (Series) and the like.

Preferably, if a polyol is used in the compositions disclosed herein, the polyol has a hydroxyl functionality of at least 2 and a molecular weight in the range of from about 200 to about 5000 g/mol. Polyols contemplated for use in the compositions disclosed herein include, but are not limited to, polyester polyols, polyether polyols, polyolefin polyols, polycarbonate polyols, and mixtures and copolymers thereof. These polyols may further contain unsaturation (unsaturation), aromaticity, and/or heteroatoms as part of their structure. In addition to linear polyols, the polyols useful in the compositions may also be branched or cyclic.

In a preferred embodiment, the first part further comprises a polyol prepared by polymerization and copolymerization of a hydroxy-functional vinyl monomer with a low glass transition temperature monomer (e.g., butyl acrylate and 2-ethylhexyl acrylate).

If the composition disclosed herein further comprises a diol, it is preferred that the diol is comprised in the first part. Preferably, the diol has a molecular weight in the range of about 200 to about 5000 g/mol. In addition to the above-mentioned polyether, polyester and polycarbonate diols, it is also possible to use polyolefin diols, such as polybutadiene diol, hydrogenated polybutadiene diol and polyfarnesene diol. Examples include: of Cray ValleyLBH-P series, HLBH P series, Krasol F3000, Nippon Soda G and GI series. Another type of non-polar diol is: from Croda as Pripol^TM2033 and its polyester oligomer diol.

In another preferred embodiment, the first part further comprises a silicone glycol. These materials typically contain very low levels of cyclic siloxane volatiles. Examples include Dow Corning 5562 Carbinol.

The balance between triols, diols, and monoalcohols (if present) can be adjusted to alter the hardness of the composition. The efficiency of the thermal interface material to transfer heat is significantly affected by the interface between the thermal interface material and the heat source, and the soft, conformable material can optimize contact at the interface. To optimize the hardness of the composition, in a preferred embodiment, the triol is present in the first part in an amount of from about 29 to about 100 wt% based on the total weight of the first part; more preferably, the triol is present in the first part in an amount of greater than about 57 wt% based on the total weight of the first part.

The isocyanate-functional component present in the second part of the composition comprises one or more of a variety of suitable mono-, di-and polyfunctional isocyanate resins and prepolymers.

Examples of suitable isocyanate-functional components for use in the composition include: aromatic isocyanates such as 1, 5-naphthylene diisocyanate, 2, 4-or 4,4 ' -diphenylmethane diisocyanate (MDI), carbodiimide-modified MDI, Xylylene Diisocyanate (XDI), m-and p-tetramethylxylylene diisocyanate (TMXDI), isomers of Toluene Diisocyanate (TDI), 4 ' -diphenyl-dimethylmethane diisocyanate, di-and tetraalkyldiphenylmethane diisocyanates, 1, 3-phenylene diisocyanate, 1, 4-phenylene diisocyanate, 4 ' -dibenzyl diisocyanate; aliphatic isocyanates, for example hydrogenated MDI (H12MDI), 1-methyl-2, 4-diisocyanatocyclohexane, 1, 12-diisocyanatododecane, 1, 6-diisocyanato-2, 2, 4-trimethyl-hexane, 1, 6-diisocyanato-2, 4, 4-trimethylhexane, 1-isocyanatomethyl-3-isocyanato-1, 5, 5-trimethylcyclohexane (IPDI), tetramethoxybutane-1, 4-diisocyanate, butane-1, 4-diisocyanate, hexane-1, 6-diisocyanate (HDI), dimeric fatty acid diisocyanate, dicyclohexylmethane diisocyanate, cyclohexane-1, 4-diisocyanate, mixtures of these diisocyanates, Ethylene diisocyanate or diisocyanatoethyl phthalate. Low molecular prepolymers, i.e. oligomers having a plurality of isocyanate groups, such as the reaction products of MDI and/or TDI with low molecular diols; the low molecular diol is, for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol or triethylene glycol. These oligomers are obtained with an excess of polyisocyanate in the presence of a diol. The diol present may have a molecular weight of less than about 1000 g/mol. The reaction product may optionally be freed of monomers by distillation. Crude MDI or liquefied diphenylmethane diisocyanate containing carbodiimides are likewise suitable. Suitable aliphatic isocyanates include isocyanurates, carbodiimides and biurets of isocyanates, in particular HDI or IPDI.

Further, a variety of isocyanates suitable for use herein are commercially available and/or can be obtained using known procedures. Aromatic diisocyanate and aliphatic diisocyanate prepolymers are commercially available from Covestro under the trade names Desmodur and Mondur, respectively, such as Mondur MRS-2, Mondur MRS-4, Desmodur LD, Mondur MA-2300, Desmondur XP 2599. Blocked isocyanates are also available from Covestro under the Desmodur BL trade name, for example Desmodur BL 1100/1. Other commercially available isocyanates are available from Mitsui Chemicals sold by Takenate. Preferably, the isocyanate-functional component comprises a difunctional isocyanate.

More preferably, the isocyanate-functional component comprises a difunctional aliphatic isocyanate having long pendant groups, wherein the long pendant groups are polyether, or linear or branched alkyl, ester, polyester structures, which may further comprise unsaturation or heteroatoms, or combinations thereof. Preferred aliphatic polyisocyanates are available from Vencorex under the trade name Tolonate^TMX FLO 100 is commercially available having the following structure, wherein R is an unpublished biologically derived long side group:

filler material

The compositions disclosed herein further comprise a filler, which preferably comprises a thermally conductive filler. The filler may be included in the first portion, the second portion, or both the first portion and the second portion.

Thermally conductive fillers are known in the art and are commercially available, see, for example, U.S. patent No. 6,169,142 (column 4, lines 7-33). The thermally conductive filler may be both thermally and electrically conductive. Alternatively, the thermally conductive filler may be thermally conductive and electrically insulating.

Specifically, useful thermally conductive fillers may include metallic fillers, inorganic fillers, carbon-based fillers, thermally conductive polymer particulate fillers, or combinations thereof.

The metal filler includes metal particles and metal particles having a layer on a surface of the particles. These layers may be, for example, metal nitride layers or metal oxide layers on the surface of the particles. Examples of suitable metal fillers are particles of metals selected from the group consisting of aluminum, copper, gold, nickel, silver, and combinations thereof. Further examples of suitable metal fillers are the above-mentioned metal particles having on their surface a layer selected from the group consisting of aluminum nitride, aluminum oxide, copper oxide, nickel oxide, silver oxide and combinations thereof. For example, the metal filler may include aluminum particles having an aluminum oxide layer on the surface thereof.

The inorganic filler may include: metal oxides such as aluminum oxide, beryllium oxide, magnesium oxide, and zinc oxide; nitrides such as aluminum nitride and boron nitride; carbides, such as silicon carbide and tungsten carbide; and combinations thereof. Other examples include aluminum trihydrate, silicon dioxide (silicone dioxide), barium titanate, magnesium hydroxide.

Carbon based fillers may include carbon fibers, diamond, graphite. Carbon nanostructured materials, such as one-dimensional Carbon Nanotubes (CNTs) and two-dimensional (2D) graphene and Graphite Nanoplatelets (GNPs), can also be used in the composition due to their high intrinsic thermal conductivity.

Examples of thermally conductive polymeric fillers include oriented polyethylene fibers and nanocellulose. Other examples of polymers that can be used to make the thermally conductive filler include polythiophenes, liquid crystal polymers based on polyesters or epoxy compounds, and the like.

The shape of the thermally conductive filler particles that can be used is not limited; however, when the load of the thermally conductive filler in the composition is high, the round or spherical particles can prevent the viscosity from increasing to an undesirable level. The thermally conductive filler may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property, such as particle shape, average particle size, particle size distribution, and filler type. For example, a combination of inorganic fillers (e.g., a first aluminum oxide having a larger average particle size and a second aluminum oxide having a smaller average particle size) can be included in the composition. Alternatively, a combination of alumina having a larger average particle size and zinc oxide having a smaller average particle size may be included in the composition. A combination of metal fillers (e.g., a first aluminum having a larger average particle size and a second aluminum having a smaller average particle size) may alternatively be included in the composition. Furthermore, combinations of metallic and inorganic fillers may alternatively be included in the compositions disclosed herein, for example: a combination of aluminum and alumina fillers; a combination of aluminum and zinc oxide fillers; or a combination of aluminum, aluminum oxide and zinc oxide fillers. The use of a first filler having a larger average particle size and a second filler having a smaller average particle size than the first filler can improve packing efficiency, can reduce viscosity, and can enhance heat transfer.

The thermally conductive filler may further comprise a filler treatment agent. The filler treating agent may be any treating agent known in the art. The amount of filler treatment may vary depending on various factors including the type and amount of thermally conductive filler. In a preferred embodiment, the filler treating agent is included in the composition in an amount in the range of from about 0.1% to about 5.0% by weight of the filler.

The filler may be treated with the filler treating agent in situ or pre-treated prior to combining with the resin to make the composite. The filler treating agent may include: silanes, such as alkoxysilanes; alkoxy-functional oligosiloxanes, cyclic polyorganosiloxanes, hydroxy-functional oligosiloxanes, such as dimethylsiloxanes or methylphenylsiloxanes; stearate esters or fatty acids. Alkoxysilane filler treatments are known in the art and examples are hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, phenyltrimethoxysilane, phenethyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, and combinations thereof.

Alternatively, the filler treating agent may be any organosilicon compound commonly used to treat silica fillers. Examples of such organosilicon compounds include, but are not limited to: organochlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, and trimethylmonochlorosilane; organosiloxanes such as hydroxy-terminated dimethylsiloxane oligomers, hexamethyldisiloxane and tetramethyldivinyldisiloxane; organosilazanes, such as hexamethyldisilazane and hexamethylcyclotrisilazane; organoalkoxysilanes such as methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane.

Alternatively, polyorganosiloxanes capable of hydrogen bonding may be used as filler treating agents.

In certain embodiments, the filler may comprise, in addition to the thermally conductive filler, a reinforcing filler, an extending filler, or a combination thereof.

When the compositions disclosed herein are in a thermal interface material, they typically comprise a thermally conductive filler that is electrically insulating. Preferably, the thermally conductive filler material used in the compositions disclosed herein is selected from the group consisting of alumina, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, or combinations thereof. For commercial sources, CB-A205 and Al-43-Me are alumina fillers of different particle sizes commercially available from Showa-Denko, DAW-45 is an alumina filler commercially available from Denka, and AA-04, AA-2, and AA18 are alumina fillers commercially available from Sumitomo Chemical Company. Zinc oxide is available from Zochem LLC.

Other suitable fillers and/or additives may also be added to the compositions disclosed herein to achieve various composition characteristics. Examples of additional components that may optionally be added include pigments, plasticizers, processing aids, flame retardants, extenders, electromagnetic interference (EMI) or microwave absorbers, electrically conductive fillers, magnetic particles, and the like. According to exemplary embodiments, a wide range of materials may be added to the thermal interface material, such as carbonyl iron, iron silicide, iron particles, iron-chromium compounds, metallic silver, carbonyl iron powder, SENDUST (an alloy containing 85% iron, 9.5% silicon, and 5.5% aluminum), permalloy (an alloy containing approximately 20% iron and 80% nickel), ferrites, magnetic alloys, magnetic powders, magnetic flakes, magnetic particles, nickel-based alloys and powders, chromium alloys, and any combination thereof. Other embodiments may include one or more EMI absorbers formed from one or more of the above materials, wherein the EMI absorber includes one or more of particles, spheres, microspheres, ellipsoids, irregular spheres, ribbons, flakes, powders, and/or a combination of any or all of these shapes. Thus, some example embodiments may thus include thermal interface materials comprising or based on thermally reversible gels, wherein the thermal interface materials are also configured (e.g., comprise or are loaded with EMI or microwave absorbers, electrically conductive fillers, and/or magnetic particles, etc.) to provide shielding.

In one useful embodiment, the thermally conductive filler material is present in the first part of the composition in an amount of about 30 to 95 weight percent, such as about 85 to 95 weight percent, based on the total weight of the first part. In another useful embodiment, the thermally conductive filler material is present in the second part in an amount in the range of about 30 wt.% to about 95 wt.%, for example about 85 wt.% to about 95 wt.%, based on the total weight of the second part.

Catalyst and process for preparing same

The isocyanate functional compounds and polyols contained in the compositions disclosed herein can react at ambient temperature to form crosslinked/cured polyurethanes without the need for catalysts. The optional inclusion of a catalyst in the composition is effective to accelerate the reaction.

Preferably, one or several catalysts may be included in the compositions disclosed herein to adjust the cure speed according to application and process requirements. In the two-part compositions disclosed herein, the isocyanate and polyol components are each dispensed and then mixed to effect the reaction. If the catalyzed reaction is too fast, the reactants may clog the dispensing mechanism. If the catalyzed reaction is too slow, the composite may flow out of the area intended to solidify after application and contaminate other surrounding components. Thus, the reaction rate is critical to achieving the desired properties of the composition. Suitable catalysts include, but are not limited to, lewis acids and bases and metal compounds.

Preferably, the composition may comprise a catalyst selected from amine catalysts or metal catalysts based on Sn, Zn, Bi, Zr, V or Ti. More preferably, the catalyst used in the composition is a Zn-based complex, a Bi-based complex, or a combination thereof.

Tin-based compounds are conventional catalysts for the reaction of hydroxyl-containing organic molecules with isocyanates to form urethane groups. Representative members of such tin compounds include: stannous salts of carboxylic acids; organic stannoic acids such as butyl stannoic acid; an organic thiostannic acid; diorganotin oxides such as dibutyltin oxide; diorganotin sulfides; mono-and diorganotin halides, such as dimethyltin dichloride; mono-and diorganotin carboxylates, such as dibutyltin dilaurate, dibutyltin adipate and dibutyltin maleate; mono-and diorganotin mercaptides, such as dibutyltin bis (lauryl mercaptide); mono-and diorganotin derivatives of mercaptocarboxylic acid esters and mercaptoalkyl esters, such as dibutyltin-S, S '-bis (isooctylmercaptoacetate) and dibutyltin S, S' -bis (mercaptoethyl stearate); diorganotin oxides such as dibutyltin oxide; and mono-and diorganotin derivatives of beta-diketones, such as dibutyltin bisacetylacetonate.

The composition may also include a tertiary amine catalyst. Tertiary amine catalysts can activate isocyanate groups to nucleophilic substitutions to promote reaction with water to form carbon dioxide and with polyhydroxy compounds to form carbamates. Examples of tertiary amine catalysts include N, N-dimethylaminoethanol, tris (dimethylaminopropyl) amine, N, N-dimethylcyclohexylamine, bis- (2-methylaminoethyl) ether, N, N-dimethylbenzylamine, diaminobicyclooctane, triethylamine, tributylamine, N-methylmorpholine, N-ethylmorpholine, N-cocomorpholine (N-coco-morpholine), N, N, N ', N "-tetramethylethylenediamine, 1, 4-diaza-bicyclo- (2,2,2) -octane, N-methyl-N' -dimethyl-amino-ethylpiperazine, N, N-dimethylbenzylamine, bis- (N, N-diethyl-aminoethyl) -adipate, N, N-diethylbenzylamine, Pentamethyldiethylenetriamine, N-dimethylcyclohexylamine, N' -tetramethyl-1, 3-butanediamine, N-dimethyl- β -phenylethylamine, 1, 2-dimethyl-imidazole, 2-methylimidazole and mixtures thereof. Also useful are commercially available tertiary amines, such as Niax A-1 available from WITCO.

Plasticizer

The composition may optionally further comprise up to about 80 wt% of a liquid plasticizer in the first and/or second parts, based on the weight of the composition. Suitable plasticizers include paraffinic oils, naphthenic oils, aromatic oils, long chain partial ether esters (long chain partial ether esters), alkyl monoesters, epoxidized oils, dialkyl diesters, aromatic diesters, alkyl ether monoesters, polybutenes, phthalates, benzoates, adipates, acrylates, and the like. Particularly preferred plasticizers include plasticizers having functional groups that can further react with the polyol in the first part or the isocyanate in the second part and are part of the polyurethane network.

Water removing agent

In one embodiment, the curable composition further comprises a water scavenger. Preferably, the water scavenger is selected from the group consisting of oxazolidines, p-toluenesulfonyl isocyanates, vinyloxysilanes (vinyloxy silanes), and combinations thereof. P-toluenesulfonyl isocyanate is a particularly useful water scavenger.

Antioxidants or stabilizers

The compositions disclosed herein may optionally further comprise not more than about 3.0 wt.%, for example from about 0.1 wt.% to about 2.5 wt.%, and preferably from about 0.2 wt.% to about 2.0 wt.%, based on the weight of the resin composition in each part, of one or more of an antioxidant or stabilizer.

Useful stabilizers or antioxidants include, but are not limited to, high molecular weight hindered phenols and multifunctional phenols, such as sulfur and phosphorus-containing phenols. Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds that also contain sterically bulky groups immediately adjacent to their phenolic hydroxyl groups. In particular, the tertiary butyl group is generally substituted onto the phenyl ring in at least one ortho position relative to the phenolic hydroxyl group. The presence of these sterically bulky substituents in the vicinity of the hydroxyl group serves to retard the stretching frequency and, correspondingly, to reduce the reactivity thereof; thus, this hindrance provides the phenolic compound with its stabilizing properties. Representative hindered phenols include: 1,3, 5-trimethyl-2, 4, 6-tris- (3, 5-di-tert-butyl-4-hydroxybenzyl) -benzene; pentaerythritol tetrakis-3 (3, 5-di-tert-butyl-4-hydroxyphenyl) -propionate; n-octadecyl-3 (3, 5-di-tert-butyl-4-hydroxyphenyl) -propionate; 4, 4' -methylenebis (2, 6-tert-butylphenol); 4, 4' -thiobis (6-tert-butyl-o-cresol); 2, 6-di-tert-butylphenol; 6- (4-hydroxyphenoxy) -2, 4-bis (n-octyl-thio) -1,3, 5-triazine; di-n-octylthioethyl 3, 5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol hexa [3- (3, 5-di-tert-butyl-4-hydroxy-phenyl) -propionate ].

Useful antioxidants are commercially available from BASF and include those which are hindered phenols565. 1010, 1076 and 1726. These are the primary antioxidants used as radical scavengers and may be used alone or with other antioxidants such as phosphite antioxidants (as available from BASF)168) Are used in combination.

The inclusion of antioxidants and/or stabilizers in the compositions disclosed herein should not affect other characteristics of the compositions.

Retarding agent

One or more retarders may also be included in the composition to provide an induction period between mixing and the onset of curing of the two parts of the composite composition. Preferably, the retardant may be 8-hydroxyquinoline.

Optional Components

Other optional components may be added to the composition, such as nucleating agents, elastomers, colorants, pigments, rheology modifiers, dyes, mold release agents, adhesion promoters, flame retardants, defoamers, phase change materials, rheology modifiers, processing aids (e.g., thixotropic agents and internal lubricants), antistatic agents, or mixtures thereof, which are known to those skilled in the art and may be selected from a wide variety of commercially available products depending on the desired characteristics. The amount of these additives added to the composition may vary depending on the purpose for which the additives are added.

The OH functionality of a compound is understood to mean its average OH functionality. It represents the average number of hydroxyl groups per molecule. The average OH functionality of a compound can be calculated based on the number average molecular weight and the hydroxyl number. Unless otherwise stated, the hydroxyl number (OH number) is obtained from the supplier's proof of Analysis (Certificate of Analysis).

The NCO functionality of a compound is understood to mean its average NCO functionality. It represents the average number of NCO groups per molecule. The average NCO functionality can be calculated based on the number average molecular weight of the compound and the NCO number. Unless otherwise stated, the isocyanate content (NCO content,% NCO) is obtained from the supplier's analytical certificate.

The molar ratio of NCO to OH groups ("NCO/OH ratio") represents the stoichiometric balance between the second part and the first part. If the NCO/OH ratio is higher than 1, this indicates that the formulation is stoichiometrically unbalanced and that an excess of isocyanate is present. If the NCO/OH ratio is below 1, this indicates that the formulation is stoichiometrically unbalanced and that there is an excess of hydroxyl groups.

In exemplary embodiments, the NCO/OH ratio in the composition is less than 1.3.

TIM material

The compositions according to the present invention can be used as thermal interface materials to ensure consistent performance and long-term reliability of heat-generating electronic devices. In particular, these compositions are useful as liquid gap filler materials that can conform to complex topographies, including multi-level surfaces. Due to the increased fluidity prior to curing, the composition can fill small air voids, cracks, and cavities, thereby reducing the overall thermal resistance of the heat-generating device. In addition, a thermal interface gap pad can be prepared from the composition.

The composition can be applied directly to a target surface using manual or semi-automatic dispensing tools, thereby making efficient use of the material with minimal waste. By the implementation of an automated dispensing apparatus, a further maximization of material utilization may be achieved, which allows for precise material placement and reduces the application time of the material. Thus, the viscosity of each part of the composition must be maintained so that the parts can be dispensed through the dispensing tool. Each of the first and second parts has a viscosity of less than about 3000 mPa-s at room temperature, preferably from about 200 to about 1000 mPa-s at room temperature.

The first and second parts of the composition may be mixed to form a composition that is curable at room temperature. The blended composition has a pot life of greater than about 10 minutes, preferably greater than about 20 minutes. The composition, after curing at room temperature, has a glass transition temperature (Tg) of less than about-20 ℃, preferably less than about-30 ℃, and a shore OO hardness of less than about 90, preferably less than about 80, and even more preferably less than about 70. In addition, the cured composition is thermally stable at about-40 ℃ to about 125 ℃.

In some exemplary embodiments, the thermal interface material may comprise an adhesive layer. The adhesive layer may be a thermally conductive adhesive to maintain overall thermal conductivity. The adhesive layer may be used to secure the thermal interface material to an electronic component, a heat sink, an EMI shield, or the like. The adhesive layer may be formulated using a pressure sensitive thermally conductive adhesive. Pressure Sensitive Adhesives (PSAs) may generally be based on compounds including acrylics, silicones, rubbers, and combinations thereof. For example, the thermal conductivity is improved by containing ceramic powder.

In some exemplary embodiments, a thermal interface material comprising a thermoreversible gel may be attached or secured (e.g., adhesively bonded, etc.) to one or more portions of an EMI shield, such as: attached or secured to a single piece EMI shield (single piece EMI shield), and/or attached or secured to a cover (cover), lid (lid), frame or other portion of a multi-piece EMI shield (multi-piece shield), attached or secured to a discrete EMI shielding wall, or the like. Alternative securing methods, such as mechanical fasteners, may also be used. In some embodiments, a thermal interface material comprising a thermally reversible gel may be attached to a removable cover or lid of a multi-piece EMI shield. A thermal interface material comprising a thermally reversible gel may be disposed on an interior surface of, for example, a cover or lid such that the thermal interface material is compressively sandwiched between an EMI shield and an electronic component on which the EMI shield is disposed. Alternatively, a thermal interface material comprising a thermoreversible gel may be disposed on an exterior surface of, for example, a cover or lid, such that the EMI shield is compressively sandwiched between the EMI shield and the heat sink. The thermal interface material comprising the thermoreversible gel may be disposed over the entire surface of the cover or lid or less than the entire surface. The thermal interface material comprising the thermoreversible gel can be applied in virtually any location where it is desirable to have an EMI absorber.

Also contemplated herein is an apparatus comprising a heat source, a heat sink, and the composition disclosed herein disposed therebetween. In a preferred embodiment, the device leaves no air gap between the heat source and the heat sink.

Examples

The compositions listed in the following examples were prepared according to the following procedure, unless otherwise indicated. The first part of the composition (part A) was prepared by mixing the polyol, catalyst and thermally conductive filler under vacuum at 80 ℃ for about 1 hour using a double planetary mixer (Ross model DPM-1Qt) manufactured by Charles Ross & Sons corporation. The second part of the composition (part B) was prepared by mixing the isocyanate, antioxidant and thermally conductive filler under vacuum at 80 ℃ for about 1 hour using a double planetary mixer (Ross model DPM-1Qt) manufactured by Charles Ross & Sons corporation.

The cured composite was obtained by mixing part a and part B in a mixing apparatus, a Loctite double barrel applicator (applicator) equipped with a 50cc or 200cc 2K barrel and a 6.3-21 static mixer attached to the end of the barrel, at 0.52MPa for 1 minute. During dispensing, parts a and B are thoroughly mixed as they move through the static mixer under an applied pressure, typically 0.5 to 0.65 MPa.

Shore OO hardness was measured according to ASTM D2240 using a Shore durometer OO. The storage modulus (G') of the composite was measured by Rheometric Scientific RDA III from TA Instruments. The dynamic temperature sweep test was performed by placing a sample of the composite material between two parallel plates and then measuring from about-70 ℃ to about 200 ℃ at a constant frequency of 10 rad/sec. Throughout the experiment, the temperature was raised gradually by 5 ℃. The stable plateau modulus (plateau modulus) at higher temperatures indicates that the composite is thermally stable and can maintain the shape required to act as a thermal interface material in use.

Example 1: aromatic isocyanates having pendant groups

TABLE 1

Mondur MRS 4(Covestro) is a polymeric diphenylmethane-diisocyanate (pMDI) having an average functionality of 2.4, which means that it contains both difunctional and trifunctional aromatic isocyanates. In part B, it is partially pre-reacted with the monohydroxy polyether (consuming approximately 27% of the NCO groups). This results in a mixture of monofunctional and difunctional aromatic isocyanates with long side groups and unreacted difunctional and trifunctional isocyanates.

A sample mixture of part a resin and part B resin (50/50 by weight, without filler) was cured at room temperature and the rheology of the samples was measured. Figure 1 shows the thermal stability of the mixture up to about 160 ℃.

Example 2: aliphatic isocyanates with pendant groups

TABLE 2

Example 2 illustrates a composition based on aliphatic isocyanates with pendant groups (Tolonate)^TMX FLO 100) and triol/diol mixtures (table 2). The rheology curve of the cured composite is shown in fig. 2, which shows thermal stability up to about 170 ℃.

Example 3: high filler low hardness composition

TABLE 3

Example 3 illustrates that higher filler loading can be achieved while maintaining low shore OO hardness by adjusting the triol/diol ratio and thermally conductive filler package (table 3).

Examples 4 and 5: formulations containing isocyanate-functionalized water scavenger p-toluenesulfonyl isocyanates

TABLE 4

Part A (weight)	Example 4	Example 5
			PPG triol, MW:～700g/mol	98	88.8
PPG triol, MW: -3300 g/mol	0	10.3
			Bismuth Complex 2	1.5	0.73
Carbon black	2	2
			Alumina Filler bag #3	1000	1000
Part A totals	1102	1102
			Part B (weight)	Example 4	Example 5
TolonateTM X FLO 100	95	95
			P-toluenesulfonyl isocyanate	5	5
Antioxidant agentBlends	2	2
			Alumina Filler bag #3	1000	1000
Part B Total	1102	1102
			Parameter(s)	Example 4	Example 5
NCO/OH ratio	0.74	0.80
			Triol in part A resin%	98	99.1
Characteristics of	Example 4	Example 5
			Shore OO hardness (at 25 ℃/50% RH)	88	82
(initial) g/min of distribution	12.9	na

Examples 4 and 5 illustrate the successful addition of isocyanate-functional water scavengers to our polyurethane composite formulation (table 4).

Example 6: formulations containing biobased diols

TABLE 5

Part A (weight)	Portions are
		PPG triol, MW: -700 g/mol	80
Polybutadiene diol, Krasol F MW: -3000 g/mol	19
		Bismuth/zinc complex 1	1
Carbon black	2
		Alumina Filler bag #3	800
Part A totals	902
		Part B (weight)	Portions are
TolonateTM X FLO 100	100
		Antioxidant blends	2
Alumina Filler bag #3	800
		Part B Total	902
Parameter(s)
		NCO/OH ratio	0.84
Triol weight% in part A resin	80
		Characteristics of
Shore OO hardness (curing at 25 ℃/50% RH)	87
		(initial) g/min of distribution	51

Example 6 was prepared by the following method. Part A was prepared by using a speed mixer device manufactured by Flacktek (model DAC 150 FVZ-K). Part A was mixed at 2000RPM for 30 seconds. Part B was prepared by using a speed mixer device manufactured by Flacktek (model DAC 150 FVZ-K). Part B was mixed at 2000RPM for 30 seconds. The cured composite was obtained by mixing part a with part B in a mixing apparatus, a Loctite dual barrel applicator equipped with a 50cc or 200cc 2K barrel and a 6.3-21 static mixer attached to the end of the barrel, at 0.52MPa for 1 minute. During dispensing, parts a and B are thoroughly mixed as they move through the static mixer under an applied pressure, typically 0.5 to 0.65 MPa.

Example 6 illustrates the addition of sustainable polybutadiene diol from non-petroleum feedstock to a polyurethane composite formulation (table 5) with appropriate properties (e.g., hardness and partitioning) that can be used as a thermal interface material.

Comparative example 7: low triol weight% and low NCO/OH ratio compositions

TABLE 6

Part A (weight)	Portions are
		PPG triol, MW: -700 g/mol	29
PPG diol, MW: 425g/mol	70
		Bismuth/zinc complex 1	1
Carbon black	2
		Alumina Filler bag #3	800
Part A totals	902
		Part B (weight)	Portions are
TolonateTM X FLO 100	100
		Antioxidant blends	2
Alumina Filler bag #3	800
		Part B Total	902
Parameter(s)
		NCO/OH ratio	0.66
Triol weight% in part A resin	29
		Characteristics of
Shore OO hardness (curing at 25 ℃/50% RH)	Too soft
		(initial) g/min of distribution	na

Comparative example 7 illustrates that when the level of triol is below 30 wt% and the NCO/OH ratio is reduced to 0.68, the cured composite is too soft and loses integrity due to lack of sufficient crosslinking (table 6).

Comparative example 8: flexible polyurethane without pendant groups

TABLE 7

Part A (weight)	Portions are
		PPG triol, MW: -3300 g/mol	60
PPG diol, MW: -2000 g/mol	10
		PPG diol, MW: 3025g/mol	29
Bismuth/zinc complex 1	1
		Carbon black	2
Alumina Filler bag #3	800
		Part A totals	902
Part B (weight)	Portions are
		PPG (PPG) blocked by toluene 2, 4-diisocyanate, MW: -2300 g/mol	100
Antioxidant blends	2
		Alumina Filler bag #3	800
Part B Total	902
		Parameter(s)
NCO/OH ratio	0.96
		Triol weight% in part A resin	60
Characteristics of
		Shore OO hardness (curing at 25 ℃/50% RH)	96
(initial) g/min of distribution	NA

Comparative example 8 was prepared by the following method. Part A was prepared by using a speed mixer device manufactured by Flacktek (model DAC 150 FVZ-K). Part A was mixed at 2000RPM for 30 seconds. Part B was prepared by using a speed mixer device manufactured by Flacktek (model DAC 150 FVZ-K). Part B was mixed at 2000RPM for 30 seconds. The cured composite was obtained by mixing part a with part B in a mixing apparatus, a Loctite dual barrel applicator equipped with a 50cc or 200cc 2K barrel and a 6.3-21 static mixer attached to the end of the barrel, at 0.52MPa for 1 minute. During dispensing, parts a and B are thoroughly mixed as they move through the static mixer under an applied pressure, typically 0.5 to 0.65 MPa.

In comparative example 8, toluene 2, 4-diisocyanate terminated poly (propylene glycol) was obtained from Aldrich. This material has a MW of 2300g/mol and an isocyanate content level of 3.6% by weight. In this design, we chose an NCO/OH ratio close to 1.0(0.96) so that almost all of the reactive groups are consumed and a negligible amount of the triol/diol or diisocyanate can contribute to the formation of long pendant groups after curing. After curing, we obtained a hard composite with a shore OO hardness of 96, which is not suitable for our intended application (table 7).

Toluene 2, 4-diisocyanate terminated poly (propylene glycol) has the following structure: