Thermally conductive compositions based on silane-modified polymers

Abstract

The present invention relates to a composition comprising a) a thermally conductive filler; b) a first silane-modified polymer, which is functionalized with at least two C1-C4-alkyl-di-C1-C4-alkoxysilyl groups, or a tri-C1-C4-alkoxysilyl group, and b) a second silane-modified polymer, which is functionalized with at least two C1-C4-alkyl-di-C1-C4-alkoxysilyl groups; c) a second silane-modified polymer, which is functionalized with a C1-C4-alkyl-di-C1-C4-alkoxysilyl group, or a tri-C1-C4-alkoxysilyl group, and at least one silane-modified polymer, which is functionalized with a C1-C4-alkyl-di-C1-C4-alkoxysilyl group, which is functionalized with a C1-C4-alkyl-di-C1-C4-alkoxysilyl group; and d) at least one dialkoxysilane, the at least one dialkoxysilane being selected from the group consisting of a di-C1-C12-alkyl-di-C1-C4-alkoxysilane and an amino-C1-C12-alkyl-C1-C12-alkyl-di-C1-C4-alkoxysilane, and a method for preparing the same, and a method for preparing the same. The composition of the present invention can be used as an intermediate of a curable composition that can act as an interlayer between a heat dissipating substrate and a heat generating substrate.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a (SMP-based) thermally conductive composition based on a silane-modified polymer, and more particularly to a wet-curable SMP-based thermally conductive composition.

[0002] Thermal interface materials (TIMs) are used at the interface between heat-generating electronic components and heat sinks to prevent overheating of the electronic components. Liquid dispensed TIMs are preferred over preformed elastomeric TIMs because the liquid can conform to complex joint geometries and achieve thin bond lines and low thermal resistance. It is desirable for the liquid dispensed TIM to cure to an elastomeric state in less than 2 weeks, and even more desirable to cure to an elastomeric state in less than 24 hours. The cured hardness is desirably low enough to achieve vibration tolerance and easy peelability in non-adhesive applications. Most desirably, a thermal conductivity of 1 W / m·K or higher for the cured elastomer is achieved.

[0003] Silicone-based TIMs offer advantages such as high temperature resistance and soft-cured elastomers; however, some TIM users (especially automotive manufacturers) are reluctant to use silicones in their factories due to the perceived or actual risk of surface contamination that can damage other processes such as painting or adhesive assembly.

[0004] Although polyurethane-based TIMs avoid the silicone surface contamination problem, the presence of unreacted isocyanate groups generated from polyurethane precursors creates handling and toxicity issues. In addition, unacceptably high concentrations of potentially toxic plasticizers are typically required to obtain acceptable high flowability before curing and low hardness after curing. The need to reduce or eliminate plasticizers is further advantageous because plasticizers are known to migrate during the service life of the application. In addition, polyurethane-based TIMs are unstable under high temperature and high humidity conditions because the urethane bonds tend to dissociate under such conditions. Therefore, it is desirable to find a thermal interface material that: a) has a fast curing time to an elastomeric state; b) is silicone- and isocyanate-free; and c) has a low plasticizer content. SUMMARY OF THE INVENTION

[0005] The present invention addresses the needs in the art by providing, in one aspect, a composition comprising a) a thermally conductive filler; b) a first silane-modified polymer functionalized with at least two C 1 -C 4 -alkyl-di-C 1 -C 4 -alkoxysilyl groups or two tri-C 1 -C 4 -alkoxysilyl groups; c) a second silane-modified polymer functionalized with one C 1 -C4 -alkyl-di-C 1 -C 4 -alkoxysilyl group or a tri-C 1 -C 4 -alkoxysilyl group functionalized; and d) at least one dialkoxysilane selected from the group consisting of: di-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane and amino-C 1 -C 12 -alkyl-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane;

[0006] Wherein, based on the weight of the composition, the concentration of the thermally conductive filler is in the range of 70 wt% to 95 wt%; based on the weight of the composition, the concentration of the at least one dialkoxysilane is in the range of 0.1 wt% to 3 wt%; and the weight ratio of the second silane-modified polymer to the first silane-modified polymer is in the range of 0.8 to 3.0.

[0007] The present invention meets the needs in the art by providing a composition that can be used as a thermal interface material with desired properties and low toxicity. Detailed Description

[0008] The present invention is a composition comprising a) a thermally conductive filler; b) a first silane-modified polymer functionalized with at least two C 1 -C 4 -alkyl-di-C 1 -C 4 -alkoxysilyl groups or two tri-C 1 -C 4 -alkoxysilyl groups functionalized; c) a second silane-modified polymer functionalized with one C 1 -C 4 -alkyl-di-C 1 -C 4 -alkoxysilyl group or one tri-C 1 -C 4 -alkoxysilyl group functionalized; and d) at least one dialkoxysilane selected from the group consisting of: di-C 1 -C 12 -alkyl-di-C 1 -C 4-alkoxysilane and amino-C 1 -C 12 -alkyl-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane;

[0009] wherein, based on the weight of the composition, the concentration of the thermally conductive filler is in the range of 70% to 95% by weight; based on the weight of the composition, the concentration of the at least one dialkoxysilane is in the range of 0.1% to 3% by weight; and the weight ratio of the second silane-modified polymer to the first silane-modified polymer is in the range of 0.8 to 3.0.

[0010] As used herein, "thermally conductive filler" refers to at least one thermally conductive filler. Examples of suitable thermally conductive fillers include zinc oxide; hydrates, hydroxides, oxides of aluminum such as aluminum oxide / alumina, aluminum hydroxide (ATH); aluminum; boron nitride, aluminum nitride; magnesium oxide, magnesium hydroxide; silver; amorphous carbon; graphite; and aluminosilicate; and combinations thereof. Based on the weight of the composition, the concentration of the thermally conductive filler is preferably in the range of 80% to 90% by weight.

[0011] The first and second silane-modified polymers (SMPs) include polyethers such as polyethylene oxide and polypropylene oxide; polybutadiene; polycarbonate; polyacrylate; polyurethane; and polyester. The first SMP is preferably functionalized with at least two C 1 -C 4 -alkyl-di-C 1 -C 2 -alkoxysilyl groups, or two C 1 -C 2 -alkyl-di-C 1 -C 2 -alkoxysilyl groups, or two terminal methyldimethoxysilyl groups. The second SMP is preferably functionalized with one C 1 -C 4 -di-C 1 -C 2 -alkoxysilyl group, or one C 1 -C 2 -alkyl-di-C 1 -C 2 -alkoxysilyl group, or one methyldimethoxysilyl group, or one tri-C 1 -C 2-alkoxysilyl group, or a trimethoxysilyl group. The weight ratio of the second SMP to the first SMP ranges from 0.8 or 1.0 to 3.0 or to 1.9. Based on the weight of the composition, the concentration of the sum of the first and second polymers is generally in the range of 5 wt% to 20 wt% or 15 wt%.

[0012] The composition further comprises one or more dialkoxysilanes. The first dialkoxysilane is represented by Structure I:

[0013]

[0014] where each R 1 is independently C 1 -C 4 -alkyl, preferably C 1 -C 2 -alkyl; and each R 2 is independently C 1 -C 12 -alkyl. An example of a suitable first dialkoxysilane is n-octylmethyldimethoxysilane.

[0015] The second dialkoxysilane is represented by the following Structure II:

[0016]

[0017] where each R 3 is independently C 1 -C 4 -alkyl, preferably C 1 -C 2 -alkyl; R 4 is C 1 -

[0018] C 12 -alkyl; and R 5 is a divalent C 1 -C 12 -alkylene or C 2 -C 4 -alkylene group. An example of the second alkoxysilane is 3-aminopropyl-methyl-dimethoxysilane.

[0019] Based on the weight of the composition, the total concentration of at least one dialkoxysilane is in the range of 0.1 wt% to 3 wt%. When the composition contains a first and a second dialkoxysilane (which is preferred for optimal cure time), the concentration of the first dialkoxysilane is generally in the range of 0.5 wt% to 2.0 wt% based on the weight of the composition; and the concentration of the second dialkoxysilane is generally in the range of 0.1 wt% or 0.2 wt% to 1 wt% or to 0.8 wt% or to 0.6 wt% based on the weight of the composition.

[0020] When the composition contains a first and a second dialkoxysilane, the weight ratio of the second alkoxysilane to the first alkoxysilane is preferably in the range of 0.15:1 or 0.20:1 or 0.25:1 to 0.65:1 or to 0.50:1 or to 0.45:1.

[0021] The composition of the present invention can be used as an intermediate for a curable composition that also contains a plasticizer, a condensation catalyst, water, and an antioxidant. A plasticizer is a substance added to a material to reduce its viscosity and hardness. Examples of plasticizers include esters such as phthalates, terephthalates, adipates, glycols, polyalkylene glycols, glycol ether esters, and low-viscosity polyethers. Based on the weight of the composition, the plasticizer is generally used at a concentration in the range of 0.2 wt% or 0.5 wt% or 1.0 wt% or 2.0 wt% to 10 wt% or to 8 wt% or to 6 wt%.

[0022] Suitable condensation catalysts include organotin catalysts such as dibutyltin dilaurate and dibutyltin diacetate, and bismuth catalysts such as bismuth octoate, the concentration of which is preferably in the range of 0.01 wt% or 0.05 wt% to 1.0 wt% or to 0.5 wt% or to 0.2 wt% based on the weight of the composition.

[0023] Based on the weight of the composition, water is present in the curable composition at a concentration of 0.1 wt% or 0.5 wt% to 2.0 wt% or to 1.2 wt%. Based on the weight of the composition, the antioxidant is present in the curable composition at a concentration preferably in the range of 0.05 wt% or 0.2 wt% to 1.0 wt% or to 0.5 wt%. Di-C 6 -C 16 -diphenylamine is an example of a suitable antioxidant, and a commercial example is the Irganox 5057 antioxidant (bis(4-octylphenyl)amine).

[0024] The curable composition of the present invention is advantageously prepared by blending two pre-prepared intermediate compositions as follows: The first intermediate composition (Part A) is advantageously prepared by mixing a plasticizer and a portion of one or more thermally conductive fillers in a container and then heating the mixture under vacuum. After cooling the contents of the container, a catalyst and water are then added to the container and further mixed.

[0025] The second intermediate composition (Part B) is advantageously prepared by mixing a first and a second silane-modified polymer, an antioxidant, and the remaining one or more fillers and then heating the mixture under vacuum. One or more dialkoxysilanes are then added to the mixture and further mixed. Parts A and B are then advantageously mixed, typically by static or active mixing methods well known in the art, and the Part A:Part B w / w ratio is preferably in the range of 20:1 or 10:1 or 2:1 or 1:1 to 1:2, 1:5 or 1:10 or 1:20 and then used as a curable interlayer between a heat-generating substrate (such as a battery or a semiconductor chip) and a heat-dissipating substrate. This multi-layer article is advantageously prepared by applying the mixed two-component composition to one of the substrates and then pressing the other substrate onto the composition to spread the composition into a uniform layer and then curing the composition.

[0026] Thus, on the other hand, the present invention is a multi-layer article comprising a heat-dissipating substrate, a cured or curable interlayer superposed on the heat-dissipating substrate, and a heat-generating substrate superposed on the interlayer.

[0027] It has been found that the curable composition of the present invention meets the performance criteria of a sufficiently low extrusion pressure, curing time, and curing hardness at the target thermal conductivity value.

[0028] Examples

[0029] Example 1 - Preparation of a Curable Silane-Modified Polymer Composition

[0030] Preparation of Part A

[0031] The first component (Part A) is prepared by the following steps: Add Plasthall 190 plasticizer (10.28 g) and ZOCO104 ZnO particles (17.57 g) to a 100 MAX Flacktek high-speed mixer cup covered with a lid. Use the Flacktek high-speed mixer to mix the contents at 1800 rpm for 20 seconds. Then add DAM-40K alumina particles (32.98 g) to the cup, and mix the contents in the high-speed mixer at 2000 rpm for 30 seconds. Then add MX 200 aluminum hydroxide powder (36.87 g) to the cup, and mix the contents in the high-speed mixer at 1500 rpm for 30 seconds, and then mix at 2000 rpm for another 10 seconds. Remove the lid and place the cup in a vacuum chamber preheated to 80 °C. Evacuate the chamber to 50 Torr, and keep the contents in the chamber for 1 hour. Then take the cup out of the chamber, cover it with a lid, and then let it cool to room temperature.

[0032] Add dibutyltin dilaurate (0.29 g) and deionized water (2.00 g) to the cup, and mix the contents in the high-speed mixer at 2000 rpm for 20 seconds. Then manually stir the contents in the cup, and then mix at 2000 rpm in the high-speed mixer for another 5 seconds.

[0033] Preparation of Part B

[0034] The second component (Part B) is prepared by the following steps:

[0035] Add bis-(methyldimethoxysilyl)-terminated polypropylene oxide with a dynamic viscosity of 600 mPa·s (SMP1, 7.08 g), mono-(methyldimethoxysilyl)-terminated polypropylene oxide with a dynamic viscosity of 1000 mPa·s (SMP2, 5.66 g), Irganox 5057 antioxidant (0.53 g) and ZOCO 104 ZnO particles (17.04 g) to a 100 MAX Flacktek high-speed mixer cup covered with a lid. Use the Flacktek high-speed mixer to mix the contents at 1800 rpm for 20 seconds. Then add DAM-40K alumina particles (31.98 g) to the cup, and mix the contents in the high-speed mixer at 2000 rpm for 30 seconds. Then add MX 200 aluminum hydroxide powder (35.76 g) to the cup, and mix the contents in the high-speed mixer at 1500 rpm for 30 seconds, and then mix at 2000 rpm for another 10 seconds. Remove the lid and place the cup in a vacuum chamber preheated to 80 °C. Evacuate the chamber to 50 Torr, and keep the contents in the chamber for 1 hour. Then take the cup out of the chamber, cover it with a lid, and then let it cool to room temperature.

[0036] Octyldimethoxysilane (OMDMS, 1.45 g) and 3-aminopropyldimethoxysilane (APMDMS, 0.50 g) were added to a cup. The cup was covered and the contents were mixed in a high-speed mixer at 2000 rpm for 20 seconds. Then the contents of the cup were stirred manually and then mixed again in the high-speed mixer at 2000 rpm for 5 seconds.

[0037] Preparation of the Composition

[0038] A portion of Part A (15.00 g) and a portion of Part B (28.66 g) were added to a high-speed mixer cup. The cup was covered with a lid and mixed in the high-speed mixer at 1800 rpm for 20 seconds. The contents of the cup were stirred manually and then mixed again in the high-speed mixer at 1500 rpm for 5 seconds.

[0039] The blend of Part A and B was immediately transferred to a sealed square Teflon plate. The poured composition was flattened by gently tapping the plate.

[0040] Preparation of Comparative Example 1 - Curable Silane-Modified Polymer Composition

[0041] Part A was prepared as described in Example 1. Part B was prepared as described in Example 1, except that Polymer 1 (12.74 g) was the only polymer used.

[0042] Preparation of Comparative Example 2 - Curable Silane-Modified Polymer Composition

[0043] Part A was prepared as described in Example 1. Part B was prepared as described in Example 1, except that Polymer 2 (12.74 g) was the only polymer used.

[0044] Examples 2 - 5 were prepared substantially as described in Example 1, except that the relative amounts of Polymer 1 and Polymer 2 were varied, with the sum of the total polymer amounts remaining constant. Table 1 shows the relative amounts by weight of the components of the blend of Part A and Part B when the parts were combined. SMP2:SMP1 refers to the w / w ratio of SMP2 to SMP1.

[0045] Table 1 - Composition of SMP Composition

[0046]

[0047]

[0048] Curing Hardness Measurement

[0049] Pour the fresh mixture of Part A and Part B onto a Teflon plate. Determine the cure hardness as the median of five measurements using a Shore A durometer. Stack four sheets, each with a thickness of approximately 1 mm, before making the measurements. The sample is considered cured when no residue transfers to a gloved finger gently pressed against the slab, and the sample can also be peeled from the Teflon plate with a spatula.

[0050] Thermal Conductivity Measurement

[0051] Measure the thermal conductivity from the cured slab using a Hot Disk TPS2500 unit according to the ISO 22007-2 standard.

[0052] Measure the cure time, cure hardness, and thermal conductivity (TC) of the samples and present them in Table 2. The cure hardness is measured in Shore A; cured coatings with a Shore A index between 2 and 65 passed the hardness requirement. Samples cured within 2 weeks passed the cure time requirement (P); samples cured within 24 hours are particularly desirable (Hi P). Samples cured for more than 2 weeks did not pass the cure test (F).

[0053] Table 2 - Characteristics of Cured Coatings

[0054] Characteristics CE1 IE1 IE2 IE3 IE4 IE5 CE2 Curing Time P P Hi P Hi P Hi P Hi P F Curing Hardness 78 65 44 44 36 26 0 TC 2.1 2.1 2.1 2.2 2.0 2.1 N / A

[0055] Prepare Examples 6-9 as in Example 2, except that the ratio of the dialkoxysilane OMDMS to APMDMS is changed as shown in Table 3.

[0056] Table 3 - Effect of Curing Hardness and Curing Time on the Relative Amount of Dialkoxysilane

[0057] Component Type IE6 IE7 IE2 IE8 IE9 OMDMS 15.3 13.3 11.4 9.4 0 APMDMS 0 2 3.9 5.9 15.3 OMDMS:APMDMS 0 0.15:1 0.35:1 0.63:1 ∞ Curing Time P P Hi P Hi P Hi P Curing Hardness 10 25 44 60 52

[0058] Data shows that acceptable cure hardness can be achieved with either or both of the dialkoxysilanes, and the most desirable cure time is achieved using a combination of the dialkoxysilanes.

Claims

1. A composition, the composition comprising a) a thermal conductive filler; b) a first silane-modified polymer, the first silane-modified polymer being functionalized with at least two C 1 -C 4 -alkyl-di-C 1 -C 4 -alkoxysilyl groups or two tri-C 1 -C 4 -alkoxysilyl groups; c) a second silane-modified polymer, the second silane-modified polymer being functionalized with one C 1 -C 4 -alkyl-di-C 1 -C 4 -alkoxysilyl group or one tri-C 1 -C 4 -alkoxysilyl group; and d) at least one dialkoxysilane, the at least one dialkoxysilane selected from the group consisting of: di-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane and amino-C 1 -C 12 -alkyl-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane; Wherein, based on the weight of the composition, the concentration of the thermal conductive filler ranges from 70% by weight to 95% by weight; based on the weight of the composition, the concentration of the at least one dialkoxysilane ranges from 0.1% by weight to 3% by weight; and the weight ratio of the second silane-modified polymer to the first silane-modified polymer ranges from 0.8 to 3.

0.

2. The composition according to claim 1, wherein the thermal conductive filler is one or more fillers selected from the group consisting of: zinc oxide, alumina, aluminum hydroxide, aluminum, boron nitride, aluminum nitride, magnesium oxide, magnesium hydroxide, silver, amorphous carbon, graphite, and aluminosilicate; and the silane-modified polymer is selected from the group consisting of: polyether, polybutadiene, polycarbonate, polyacrylate, polyurethane, and polyester.

3. The composition according to claim 2, wherein the first silane-modified polymer is functionalized with at least two C 1 -C 4 -alkyl-di-C 1 -C 2 -alkoxysilyl groups and the second silane-modified polymer is functionalized with one C 1 -C 4 -di-C 1 -C 2 -alkoxysilyl group.

4. The composition according to claim 3, wherein the first silane-modified polymer is functionalized with two C 1 -C 2 -alkyl-di-C 1 -C 2 -alkoxysilyl groups and the second silane-modified polymer is functionalized with one C 1 -C 2 -alkyl-di-C 1 -C 2 -alkoxysilyl group; and the thermally conductive filler is a mixture of zinc oxide, aluminum oxide and aluminum hydroxide.

5. The composition according to claim 4, wherein the at least one dialkoxysilane is a mixture of a first dialkoxysilane and a second dialkoxysilane, the first dialkoxysilane being a di-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane, and the second dialkoxysilane being an amino-C 1 -C 12 -alkyl-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane.

6. The composition according to claim 5, wherein the di-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane is n-octylmethyldimethoxysilane and the amino-C 1 -C 12 -alkyl-C 1 -C 12 -alkyl-di-C 1 -C 4 -alkoxysilane is 3-aminopropyl-methyl-dimethoxysilane; wherein the weight ratio of the second dialkoxysilane to the first dialkoxysilane is in the range of 0.15:1 to 0.65:

1.

7. The composition according to claim 6, wherein the weight ratio of the second dialkoxysilane to the first dialkoxysilane ranges from 0.20:1 to 0.50:

1.

8. The composition according to any one of claims 1 to 7, wherein the silane-modified polymer is a silane-modified polyethylene oxide or a silane-modified polypropylene oxide.

9. The composition according to any one of claims 1 to 7, wherein the composition is a curable composition further comprising a plasticizer, a condensation catalyst, water, and an antioxidant.

10. A multi-layer article, the multi-layer article comprising a heat dissipation substrate, a curable interlayer stacked on the heat dissipation substrate, and a heat generating substrate stacked on the interlayer.

11. The multi-layer article according to claim 10, wherein the curable interlayer is cured.

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