THERMAL INTERFACE MATERIAL COMPRISING MAGNESIUM HYDROXIDE

Abstract

A thermal interface material (TIM) composition comprising a polymeric binder component and about 50-90 wt% of spherical magnesium hydroxide particles having a particle size distribution D50 ranging from about 20-100 .Math.m, with the total weight of the composition totaling to 100 wt%.

Claims

1. A thermal interface material (TIM) composition comprising: a) a polymeric binder component, and b) about 50-90 wt% of spherical magnesium hydroxide particles having a particle size distribution D50 ranging from about 20-100 .Math.m, with the total weight of the composition totaling to 100 wt%.

2. The thermal interface material composition of claim 1, wherein the spherical magnesium hydroxide particles have an oil absorption value of about 1-30 ml/100 g.

3. The thermal interface material composition of claim 1, wherein, the polymeric binder component is present at a level of about 10-50 wt%, based on the total weight of the composition.

4. The thermal interface material composition of claim 1, wherein, the polymeric binder component is formed of polyurethane based material.

5. The thermal interface material composition of claim 1, wherein, the spherical magnesium hydroxide particles have a particle size distribution D50 ranging from about 25-60 .Math.m.

6. The thermal interface material composition of claim 1, wherein, the spherical magnesium hydroxide particles have a particle size distribution D50 ranging from about 30-50 .Math.m.

7. The thermal interface material composition of claim 1, which further comprises about 2-50 wt% of spherical aluminum oxide particles.

8. The thermal interface material composition of claim 7, wherein the spherical aluminum oxide particles have a particle size distribution D50 ranging from about 5-100 .Math.m.

9. An article comprising the thermal interface material composition recited in claim 1.

10. The article of claim 10, which further comprises a battery module that is formed of one or more battery cells and a cooling unit, wherein, the battery module is connected to the cooling unit via the thermal interface material composition.

Description

DETAILED DESCRIPTION

[0014] Disclosed herein are thermal interface materials (TIM) comprising: a) a polymeric binder component and b) about 50-90 wt% of spherical magnesium hydroxide particles, with the total weight of the composition totaling to 100 wt%.

[0015] The polymeric binder component may be formed of any suitable polymeric material, which include, without limitation, binder material based on polyurethane, epoxy, silicone, modified silicone, acrylate, and etc. In one embodiment, the polymeric binder component is formed of a two-component polyurethane based binder material.

[0016] In accordance with the present disclosure, the polymeric binder component may be present in the TIM at a level of about 5-50 wt%, or about 10-40 wt%, or about 10-30 wt%, based on the total weight of the TIM composition.

[0017] The magnesium hydroxide particles used herein are spherically shaped. The term “spherically shaped” or “spherical” is used herein to refer to an isometric shape, i.e., a shape, in which, generally speaking, the extension (particle size) is approximately the same in any direction. In particular, for a particle to be isometric, the ratio of the maximum and minimum length of chords intersecting the geometric center of the convex hull of the particle should not exceed the ratio of the least isometric regular polyhedron, i.e. the tetrahedron. Particle shapes are often times defined by aspect ratios, which is expressed by particle major diameter/particle thickness. In accordance with the present disclosure, the aspect ratio of the spherically shaped or spherical magnesium hydroxide particles ranges from about 1-2.

[0018] Particle size distribution D.sub.50, also known as the median diameter or the medium value of the particle size distribution, is the value of the particle diameter at 50% in the cumulative distribution. For example, if D.sub.50=10 .Math.m, then 50 volume% of the particles in the sample have an averaged diameter larger than 10 .Math.m, and 50 volume% of the particles have an averaged diameter smaller than 10 .Math.m. Particle size distribution D.sub.50 can be determined using light scattering methods following, for example, ASTM B822-10. In accordance with the present disclosure, the spherical magnesium hydroxide particles used herein have a particle size distribution D.sub.50 ranging from about 20-100 .Math.m, or about 25-60 .Math.m, or about 30-50 .Math.m. Moreover, the spherical magnesium hydroxide particles used herein may have an oil absorption value of about 1-30 ml/100 g, or about 3-20 ml/100 g, or about 3-8 ml/100 g. Furthermore, the spherical magnesium hydroxide particles used herein also may be surface treated with, for example, fatty acid, silane, zirconium based coupling agent, titanate coupling agent, carboxylates, etc.

[0019] In accordance with the present disclosure, the spherical magnesium particles may be present in the composition at a level of about 50-95 wt% or about 55-90 wt%, or about 60-85 wt%, based on the total weight of the TIM composition.

[0020] In addition to the spherical magnesium hydroxide particles, spherical aluminum oxide particles also may be added in the TIM composition. The spherical aluminum oxide particles used herein may have a particle size distribution D.sub.50 ranging from about 5-100 .Math.m, or about 10-80 .Math.m, or about 20-60 .Math.m. And the spherical aluminum oxide particles may be present in the TIM composition at a level of about 2-50 wt%, or about 2-40 wt%, or about 2-30 wt%, based on the total weight of the TIM composition.

[0021] Furthermore, the TIM compositions disclosed herein may optionally further comprise other thermally conductive particles, such as, aluminum hydroxide, magnesium oxide, boron nitride, etc. The TIM composition disclosed herein also may comprise other suitable additives, such as, catalysts, plasticizers, stabilizers, adhesion promoters, fillers, colorants, etc. Such optional additives may be present at a level of up to about 10 wt%, or up to about 8 wt%, or up to about 5 wt%, based on the total weight of the TIM.

[0022] As demonstrated below by the examples, by incorporating spherical magnesium hydroxide particles, TIM material with high thermal conductivity was obtained. Moreover, the further addition of spherical aluminum oxide particles further decreases the viscosity of the TIM material, which is a very much desirable feature for TIM material.

[0023] Further disclosed herein are battery pack systems in which a cooling unit or plate is coupled to a battery module (formed of one or more battery cells) via the TIM described above such that heat can be conducted therebetween. In one embodiment, the battery pack systems are those used in battery powered vehicles.

EXAMPLES

[0024] Materials [0025] Prepolymer — a prepolymer prepared by the reaction of polyoxypropylene diol, polyoxypropylene triol, and diphenylmethane-4,4'-diisocyanate; [0026] PTSI — p-toluenesulfonyl isocyanate obtained from VanDeMark Chemicals; [0027] HDI — hexamethylene diisocyanate (HDI) obtained from Covestro under the trade name N3400; [0028] Plasticizer — polyester plasticizer obtained from Hallstar under the trade name Plasthall™ 190; [0029] Silane — polyethyleneglycol-functional alkoxysilane obtained from Evonik under the trade name Dynasylan™ 4148; [0030] Mg(OH).sub.2—S — spherical magnesium hydroxide particles obtained from Weifang Haolong Chemical CO.,LTD under the grade number HLG-05, which has a particle size distribution D.sub.50 of 46 .Math.m and oil absorption value of about 5 ml/100 g; [0031] Mg(OH).sub.2—P — platelet magnesium hydroxide particles obtained from Liaoning Haichen Chemical CO,.LTD under the grade number HM-15, which has a particle size distribution D.sub.50 of 3-4 .Math.m and oil absorption value of about 37 ml/100 g; [0032] Catalyst — 33% triethylenediamine dissolved in 67% dipropylene glycol, which is obtained from Evonik under the trade name Dabco™ 33-LV; [0033] Al.sub.2O.sub.3 — spherically shaped aluminum oxide particle obtained from Anhui Estone under the grade name SLA45, which has a particle size distribution D.sub.50 of 49 .Math.m; [0034] Polyol-1 — polyether polyol obtained from Dongda Chemical; [0035] Polyol-2 — Polyether polyol obtained from Dow Chemicals under the trade name Voranol™ 4701.

TABLE-US-00001 E1 E2 CE1 Part A Prepolymer (wt%) 11.5 11.3 11.5 PTSI (wt%) 1 1 1 HDI (wt%) 1 1.2 1 Plasticizer (wt%) 5.7 5.7 5.7 Silane (wt%) 0.8 0.8 0.8 Mg(OH).sub.2—S (wt%) 80 70 Al.sub.2O.sub.3 (wt%) 10 Mg(OH).sub.2—P (wt%) 80 Part B Silane (wt%) 0.8 0.8 0.8 Polyol-1 (wt%) 8 8 8 Polyol-2 (wt%) 2 2 2 Plasticizer (wt%) 6.6 6.6 6.6 Catalyst (wt%) 0.1 0.1 0.1 Mg(OH).sub.2—S (wt%) 82.5 72.5 Al.sub.2O.sub.3 (wt%) 10 Mg(OH).sub.2—P (wt%) 82.5 Properties Thermal conductivity (W/mk) 1.9 2.1 N/A* Viscosity (Part A), 10 S.sup.-1 35.6 25.9 Viscosity (Part B), 10 S.sup.-1 10.1 5.1 Lap shear strength (MPa) 0.37 0.38 *N/A: no homogenous dispersion was obtained.

Examples E1-E2 and Comparative Example CE1

[0036] The components of the TIM composition in each of E1-E2 and CE1 are listed in Table 1. First, Part A and Part B for each sample were prepared as follows: mixing all components (liquid component(s) first before adding solid component(s)) using a dual asymmetric centrifuge; mixing the mixture for about 30 minutes under vacuum; and storing the mixture in two-component cartridges. Then, the viscosity for Part A and Part B in each of E1-E2 was measured at a shear rate of 10 S.sup.-1 using AR1500EX Rheometer from TA Instruments and the results are tabulated in Table 1. For CE1, no homogenous dispersion was obtained for Part A or Part B.

[0037] To obtain the final TIM paste in E1 and E2, Part A and Part B were mixed at a weight ratio of 1:1 using a 2-component battery gun and a static mixer. The thermal conductivity of the TIM pastes was measured in accordance with ASTM D5470 at sample thickness of 1, 2, and 3 mm, and the Lap shear strength of the TIM pastes was measured in accordance with EN1465 at sample thickness of 1 mm. The results are tabulated in Table 1.

[0038] As demonstrated by the samples, by incorporating spherical magnesium hydroxide particles, homogenous TIM paste with high thermal conductivity was obtained. Moreover, the further addition of spherical aluminum oxide particles further decreases the viscosity of the TIM paste.