TW201416431A - Thermally conductive polymer composites containing magnesium silicate and boron nitride - Google Patents

Abstract

A polymer composition is taught and claimed, the composition comprising polymer, boron nitride and magnesium silicate, wherein the composition has certain thermal conductivity and dielectric properties. Additionally, the composition may be injection moldable.

Description

Thermally conductive polymer composite comprising magnesium silicate and boron nitride [Reciprocal Reference of Related Applications]

The present application claims priority to Indian Patent Application No. 3301/DEL/2012, filed on Oct. 26, 2012. The entire disclosure of the above application is hereby incorporated by reference.

In some aspects, the invention relates to thermally conductive plastics, particularly those thermally conductive plastics comprising boron nitride, magnesium niobate and derivatives thereof.

This section provides background information related to the present invention and is not necessarily prior art.

Thermally conductive plastics (TCP or TCPs) are thermally conductive polymers and are often electrically insulating materials that can be used as fillers to achieve the desired properties. When the fillers are used in the correct proportions in the application, the final thermoplastic product provides a means of achieving thermal conductivity while maintaining electrical insulation at high dielectric strength. In view of the benefits of thermoplastics, those skilled in the art are continually looking for fillers or filler combinations that enhance these properties.

This section provides a general summary of the invention and is not a comprehensive disclosure of the full scope of the invention.

In one aspect, a polymer composite is described that includes at least one plastic resin, magnesium niobate, and one form of boron nitride, wherein the composite can be injection moldable.

In one embodiment, the polymer composite comprises at least 2% boron nitride by mass and about 1% magnesium silicate by volume. In another embodiment, the composite comprises at least 5% boron nitride by volume and about 2% magnesium silicate by volume. The polymer composite can exhibit a thermal conductivity greater than 2 W/m-K, and under certain conditions, the thermal conductivity can be as high as 18 W/m-K and above 18 W/m-K. The composite may have a dielectric strength greater than 4 kV/mm and may be as high as 28 KV/mm and 28 KV/mm under certain conditions.

Other specific examples and industrial applicability will become apparent from the description provided herein. The description and specific examples are intended to be illustrative only and not limiting of the scope of the invention.

Illustrative specific examples will now be further described.

TCP can be used in a variety of applications, including thermal management of electronic devices and components via, for example, injection molding or thermoset. These materials can serve as a substitute for metal or ceramic articles, but require other properties such as lower density, higher strength, and hardness. In addition, injection-molded TCP gives design flexibility, reduces secondary operations and increases throughput. Articles made by conventional injection molding techniques may include, but are not limited to, light emitting diode (LED) heat sinks, electronic housings, mobile phone battery covers, wireless base stations, and the like.

Magnesium citrate and its derivatives (commonly known as talc) are useful as components in thermoplastics, including as fillers in automotive applications to improve flame retardancy.

Boron nitride can be used as a filler in the polymer composite to increase thermal conductivity. One form of boron nitride used in conventional thermoplastics is hexagonal boron nitride (h-BN). Due to the hexagonal crystal structure of h-BN, its thermal conductivity depends on the direction. The average thermal conductivity of h-BN can vary between 250 and 300 W/m-K based on processing parameters.

Many types of h-BN will provide a particularly desirable synergistic effect when included in a polymer composite along with a certain ratio of magnesium citrate (3MgO, 4SiO2, H2O). As will be seen in the examples below, these results are surprising and novel in that the properties exhibited by the polymer composites are considered from the properties of a polymer composite having only one of boron nitride or magnesium niobate. It will be unpredictable. In addition, combining the two materials at the disclosed ratios results in enhanced injection moldability of the polymer composite, which has become a problem when injection molding a polymer composite having only one of boron nitride or magnesium ruthenate. .

Several types of h-BN are commercially available and are broadly classified as sheet h-BN (platelet h-BN), agglomerated h-BN (agglomerated h-BN) or spherical h-BN (spherical h-BN), There are various sizes ranging from a few microns to a few hundred microns.

The sheet h-BN has a h-BN crystal in a sheet structure. The agglomerated h-BN can be a collection of h-BN crystals that combine to form separately distinguishable particles from non-agglomerated particles such as flakes or crystalline domains. The spherical h-BN is also made from a collection of h-BN crystals that are spherical in shape.

The above three h-BN forms have advantages and disadvantages during processing of the polymer composite. The agglomerated h-BN has advantages over other forms because it is easy to feed via conventional hoppers in twin screw extruders. However, due to the high shear rate in processing, the final composites disclosed herein often have h-BN crystals in the form of flakes.

Magnesium citrate, commonly known as talc (magnesium hydrated citrate - 3MgO, 4SiO2, H2O), is often used as a thermal insulating material. Several forms of magnesium citrate exhibit a thermal conductivity of about 4 to 6 W/m-K. This value is 10 to 20 times the value of some polymers in which the thermal conductivity is limited to 0.2 to 0.4 W/m-K.

Talc can be classified into different forms and shapes. As used herein, many of the talc systems used are in the form of 3MgO, 4SiO2, H2O. Like h-BN, talc has a thin structure. However, talc flakes have varying aspect ratios that can vary. In h-BN, since the sheet has a hexagonal shape, The aspect ratio is limited. High aspect ratio fillers used in polymer composites improve mechanical and thermal properties.

This technique does not show any example in which both magnesium silicate and boron nitride work synergistically to provide improved thermal conductivity and tunable electrical properties. The following specific examples provide thermoplastics that have not previously been found to have synergistic effects between magnesium silicate and boron nitride in the art.

A specific example is an injection molded composition comprising at least one plastic resin, magnesium silicate, and one form of h-BN. The plastic resin can be any suitable polymer such as polyamide 6, polycarbonate, polyphenylene sulfide, and liquid crystal polymer. The term "liquid crystal polymer" used in the various embodiments of the present technology is intended to mean a melt processable polymer having the property of regularly aligning polymer molecular chains in parallel with each other in a molten state. Liquid crystal polymer (LCP) is a class of materials that combine the properties of a polymer with the properties of a liquid crystal.

The particle size of the agglomerated boron nitride may range from about 25 μm to about 250 μm, and preferably from about 100 μm to about 150 μm. In another embodiment, magnesium citrate (3MgO, 4SiO2, H2O) has an aspect ratio of about 1, referred to as general purpose talc (hereinafter referred to as GP talc). In another embodiment, magnesium citrate (3MgO, 4SiO2, H2O) has an aspect ratio greater than 2 and is referred to as an aspect ratio talc (hereinafter referred to as AR talc). Those skilled in the art will appreciate that the aspect ratio as used herein refers to the ratio between the width and height of an object.

While polyamine 6, polycarbonate, polyphenylene sulfide, and liquid crystal polymers have been found to be suitable for the present application, other polymers, such as thermoplastics, may be included in the composition. Exemplary thermoplastics include, but are not limited to, polyamid-6,6, a blend of polycarbonate and acrylonitrile butadiene styrene (PC-ABS), polyether phthalimide, polyetheretherketone, Polyether oxime, polyfluorene, polypropylene and polybutylene terephthalate (PBT). Further, thermoplastic elastomers In the thermoplastics encompassed by the present invention, non-limiting examples thereof include polyester-based thermoplastic elastomers and olefin-based thermoplastic elastomers. Blends of any of the foregoing thermoplastics or thermoplastic elastomers are included within the scope of the invention.

When used at an appropriate ratio, as will be seen in the examples below, magnesium citrate and Boron nitride provides a synergistic effect that imparts a particularly desirable quality to the polymer composition. The disclosed fillers enable the polymer to crystallize at an improved level where the thermally conductive filler is optimally spaced from the polymer spherulity. This spacing achieves extremely high thermal conductivity compared to polymer composites having hexagonal boron nitride or agglomerated boron nitride in the absence of talc. In addition, this spacing enhances the dielectric properties of the polymer composite.

As can be seen from the following examples, a specific example of the present invention is a composition comprising a polymer comprising magnesium niobate in an amount of at least 2% of the total integral number and boron nitride in an effective amount as a whole of the integral number for nitriding. A synergistic effect occurs between boron and magnesium citrate. In another embodiment of the invention, the composition comprises a polymer comprising magnesium niobate in an amount of at least 2% of the total number of points and boron nitride in an integral fraction of at least 1%. Other fillers may be added to the thermally conductive composition, including those having thermal conductivity.

In one embodiment, the composite comprises a polymer, boron nitride, and magnesium niobate in a ratio sufficient to produce a synergistic effect, whereby the composite is thermally conductive. Preferably, the composite is additionally dielectric and injection moldable. Experiments have shown that synergy is observed at a ratio as low as 97:2:1 by weight (as will be seen in the following composition K), although the spirit and scope of the present invention encompasses a higher volume percentage of the polymer. Other ratios.

The following examples and the formulations are intended to illustrate the general principles and characteristics of certain embodiments of the invention and are not intended to limit the scope of the claims.

Example 1: LCP type heat conduction composite

Case 1a: A heat transfer composite was prepared by melt mixing based on the formulation given in Table 1a.

The composition seen in Table 1a (referred to as Composition A) contained 60 V% coalesced h-BN in a 40 V% liquid crystal polymer (LCP). The resulting melt-mixed composite may not be suitable for injection molding at 290 degrees Celsius. However, the composite is suitable for compression molding, thereby providing a thermal conductivity of about 16 W/m-K.

Case 1b: A heat transfer composite was prepared by melt mixing based on the formulation given in Table 1b.

The composition seen in Table 1b (referred to as Composition B) contained 60 V% GP talc in a 40 V% liquid crystal polymer (LCP). The resulting melt-mixed composite may not be suitable for injection molding at 290 degrees Celsius. However, it is suitable for compression molding. The resulting sample exhibited a thermal conductivity of about 2 W/m-K.

Case 1c: A heat transfer composite was prepared by melt mixing based on the formulation given in Table 1c.

The composition seen in Table 1c (referred to as Composition C) contained 45 V% agglomerated h-BN and 15 V% GP talc in a 40 V% liquid crystal polymer (LCP). The resulting melt-mixed composite was found to be suitable for injection molding at 290 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 18 W/m-K.

In the three formulations seen in Example 1 above, the total volume percentage of filler remained constant at 60. Composition A containing agglomerated BN but no talc is non-shot moldable using current technology. However, the compression molded sample exhibited a thermal conductivity of about 16 W/m-K. Composition B, which contains talc but no agglomerated h-BN, is also non-shot moldable using current technology. After compression molding, the sample exhibited only a thermal conductivity of 2 W/m-K. This is because talc is a material having a lower thermal conductivity (5 W/m-K) than boron nitride (about 300 W/m-K) when measured through a plane of hexagonal boron nitride crystals.

In comparison, composition C comprising 45 V% agglomerated h-BN and 15 V% GP talc was injection moldable and the resulting sample exhibited an enhanced thermal conductivity of about 18 W/m-K. The replacement of 15V% high thermal conductivity BN with talc, which is less thermally conductive, allows the composite to be injection moldable and provides a small increase in thermal conductivity when compared to composition A.

Example 2: Polyamine heat transfer composite

Case 2a: A heat transfer composite was prepared by melt mixing based on the formulation given in Table 2a.

The composition seen in Table 2a (referred to as Composition D) contained 15 V% agglomerated h-BN in 85 V% Polyamide 6. The resulting melt-mixed composite is suitable for injection molding at 270 degrees Celsius. The resulting sample exhibited a thermal conductivity of about 4.7 W/m-K.

Case 2b: A thermally conductive composite was prepared by melt mixing based on the formulation given in Table 2b.

The composition seen in Table 2b (referred to as Composition E) contained 15 V% agglomerated h-BN and 23 V% GP talc in 62 V% Polyamide 6. The resulting melt-mixed composite is suitable for injection molding at 270 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 8 W/m-K.

Discussion: In the two formulations seen in Example 2, the volume percentage of agglomerated h-BN remained constant at 15. However, the addition of 23V% GP talc together with 15V% agglomerated h-BN resulted in a thermal conductivity of the resulting excipient-forming material (which is composition E) that was enhanced by about 70 compared to the composition D of only agglomerated h-BN. %.

Example 3: PC-ABS heat transfer composite

A heat transfer composite was prepared by melt mixing based on the formulation given in Table 3, wherein the PC-ABS was polycarbonate/acrylonitrile butadiene styrene.

The composition of Table 3 (referred to as Composition F) contained 15 V% agglomerated h-BN and 23 V% GP talc in 62 V% PC-ABS. The resulting melt-mixed composite is suitable for injection molding at 270 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 8 W/m-K.

Comparing the composition F with the composition E of the above Example 2, the ratio of the raw materials remained the same except that the matrix polymer was changed. The use of a more amorphous polymer PC-ABS in place of the more crystalline polymer polyamide 6 does not affect thermal conductivity or injection moldability.

Example 4: Polyphenylene sulfide-based heat transfer composite

The heat transfer composite was prepared by melt mixing based on the formulation given in Table 4.

The composition of Table 4 (referred to as Composition G) contained 15 V% agglomerated h-BN and 23 V% GP talc in 62 V% polyphenylene sulfide. The resulting melt-mixed composite is suitable for injection molding at 290 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 8 W/m-K.

Composition G maintains the same ratio of matrix polymer to agglomerated h-BN to talc as in composition F and composition E, but differs from other compositions in that high heat polyphenylene sulfide is used instead of polyamine 6. As can be seen in Table 4, this substitution did not affect thermal conductivity and injection moldability. It is thus concluded that the synergistic effect observed between talc and BN is not only independent of the polymer, but is also suitable for all high heat polymer matrices and blends thereof.

It is apparent from these examples that the synergistic effect observed between talc and BN is independent of the polymer used in the composition. Accordingly, the spirit and scope of the present invention fully encompasses and supports the inclusion of a synergistic ratio of talc to BN in a plurality of polymer matrices and blends thereof that exceeds the ratios disclosed herein.

Example 5: Comparison of agglomerated BN and flake BN

The heat transfer composite was prepared by melt mixing based on the formulation given in Table 5.

The composition of Table 5 (referred to as Composition H) contained 15 V% flake h-BN and 23 V% GP talc in 62 V% Polyamide 6. The resulting melt-mixed composite is suitable for injection molding at 270 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 8 W/m-K.

The composition H maintained the same composition ratio as the composition E of Example 2 except that the type of h-BN was changed. Replacing agglomerated h-BN with the same volume percentage of non-agglomerated sheet h-BN does not affect thermal conductivity and injection moldability. It is concluded that the synergistic effect observed between talc and BN is independent of the h-BN type. It is suitable for all types of h-BN and combinations thereof.

Example 6: Comparison of GP talc and AR talc

The heat transfer composite was prepared by melt mixing based on the formulation given in Table 6.

The composition in Table 6 (referred to as Composition I) contained 15 V% flake h-BN and 23 V% AR talc in 62 V% Polyamide 6. The resulting melt-mixed composite is suitable for injection molding at 270 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 8 W/m-K.

In Composition I, the composition ratio remained the same as the composition ratio of Composition E of Example 2, except that the type of talc in the composition was changed. Replacing GP talc with high aspect ratio AR talc in the same volume percentage does not affect thermal conductivity and injection moldability. It is inferred between talc and BN The synergistic effects of observations are independent of the type of talc. It is suitable for all types of talc and combinations thereof. In addition, AR talc enhances mechanical properties due to its high aspect ratio.

Example 7: Polycarbonate-based heat transfer composite with low filler loading

The heat transfer composite was prepared by melt mixing based on the formulation given in Table 7.

The composition of Table 7 (referred to as Composition J) contained 5V% agglomerated h-BN and 2V% AR talc in 93V% polycarbonate. The resulting melt-mixed composite is suitable for injection molding at 280 degrees Celsius. The injection molded sample exhibited a thermal conductivity of about 4 W/m-K.

Another heat transfer composite was prepared by melt mixing based on the formulation given in Table 8.

Significantly and unexpectedly, there is a synergistic effect of BN and talc even at very low loadings. This phenomenon is seen in composition J and composition K, in which the total filler loading is extremely low (7V% and 3%, respectively), but significant thermal conductivity is still observed (4W/mK, respectively). And 2W/mK).

As can be seen from the examples shown in Table 9, below, the composition maintains a high dielectric strength in each case.

As can be seen in Table 9, these compositions each provide a highly effective dielectric strength result. Using the results in Table 9, it was theoretically calculated that the dielectric strength of the composition A and the composition B was in the range of 12 to 15 kV/mm.

From a practical point of view, the urgent need in this technology has been met. Due to the synergy between boron nitride and talc, the inventors have produced thermally conductive polymer compositions that are significantly less expensive than currently available compositions in the market. Conventional thermoplastics containing only boron nitride must carry a large amount of BN to produce the desired thermal characteristics. Talc is essentially less expensive than boron nitride, and therefore the combination of talc and boron nitride maintains attractive thermal conductivity and low electrical conductivity at low loadings (up to 2% to 7%, or less). It also offers significant advantages over the technology and has not been seen before. The low loadings disclosed herein provide an additional advantage with regard to the flexibility of injection molding that has not been seen in high load boron nitride compositions in the absence of talc.

An additional advantage of some of the specific examples described above is the flexibility with respect to the color of the shaped thermoplastic article. Many of the compositions disclosed herein are white in color and various known colorants can be added to the thermoplastic composite without loss of thermal or dielectric efficacy. Articles made by conventional injection molding techniques may include, but are not limited to, light emitting diode (LED) heat sinks, electronic housings, mobile phone battery covers, wireless base stations, and the like. Composites made in accordance with the teachings herein can meet most industry standard requirements for electronic applications and additionally have a low coefficient of thermal expansion.

Articles made of the thermally conductive dielectric composite of the present invention may be formed using manufacturing methods such as extrusion, injection molding, and compression molding, although the composite of the present invention is preferably formed by injection. Type to form. For example, injection molding allows the composite of the present invention to be formed into many different shapes and sizes using available equipment and systems. These manufacturing methods can also be carried out in a continuous manner (for example using a twin screw extruder) to provide benefits in terms of manufacturing time and cost effectiveness.

The foregoing description of the present invention is intended to be illustrative of the nature of the subject matter of the present invention, and is not intended to limit the scope of the invention as claimed in the application. The scope, application or use of the invention or the patent issued therewith. The following definitions and non-restrictive criteria must be considered when reviewing the technical descriptions set forth herein.

The headings (such as "Background" and "Summary") and subheadings used herein are intended to be used only in the general organization of the subject matter of the present technology, and are not intended to limit the disclosure of the present technology or any Aspect. In particular, the subject matter disclosed in the "Prior Art" may include novel technology and may not constitute a description of the prior art. The subject matter disclosed in the "Summary of the Invention" is not an exhaustive or comprehensive disclosure of the full scope of the technology or any specific examples thereof. It is convenient for the material to be classified or discussed as having a particular utility within the specification, and it should not be inferred from the fact that when the material is used in any given composition, it must or can only be The classification works.

The description and specific examples, while indicating specific examples of the present invention, are intended for purposes of illustration In addition, the description of a plurality of specific examples of the features is not intended to exclude other specific examples of other features, or other specific examples that incorporate different combinations of the features. The specific embodiments are provided for the purpose of illustrating how to make and use the compositions and methods of the present technology, and are not intended to indicate that a particular embodiment of the present technology has been or has not been manufactured or tested unless specifically stated otherwise.

As used herein, the terms "preferred" and "preferably" refer to specific examples of the present technology that provide certain benefits in certain instances. However, other specific examples may also be preferred under the same or other circumstances. In addition, the recitation of one or more preferred embodiments does not imply that other specific examples are not applicable and do not exclude other specific examples. Beyond the scope of the technology of the present invention.

All composition percentages are by weight of the total composition as mentioned herein unless otherwise specified. As used herein, the words "comprise", "include", and variations thereof are intended to be non-limiting, and the items recited in the list do not exclude the materials and compositions that are also applicable to the technology. Other similar items in the objects, devices and methods. Similarly, the terms "can" and "may" and variations thereof are intended to be non-limiting, and thus a specific example may or may not contain certain elements or features without excluding such elements. Or other specific examples of the techniques of the present invention.

As used herein, "a" (a/an) indicates the presence of "at least one" item; if possible, there may be a plurality of such items. "About" when applied to a value indicates that the calculation or measurement allows the value to be slightly inaccurate (to some extent an exact value that approximates the value; approximate or moderately close to the value; similar). If, for some reason, the inaccuracy provided by "about" is not otherwise understandable in this technology for this general meaning, the "about" indication as used herein may be measured or used. At least some of the changes caused by the general method. In addition, the disclosure of the scope includes the disclosure of all the various values and further sub-ranges throughout the scope.

The foregoing description of specific examples has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. The individual elements or features of a particular embodiment are generally not limited to the specific embodiments, but are also interchangeable and can be used in the specific embodiments as appropriate, even if not specifically shown or described. It can also vary in a number of ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims (11)

A thermally conductive composite comprising a polymer, at least about 2% boron nitride by volume, and at least about 1% by volume magnesium ruthenate. The thermally conductive composite of claim 1 which comprises at least about 5% by volume of boron nitride and at least about 2% by volume of magnesium ruthenate. The thermally conductive composite of claim 2, comprising at least about 15% boron nitride by volume, and at least about 23% by volume magnesium ruthenate. The heat transfer composite according to claim 1, wherein the polymer is selected from the group consisting of polyamine 6, polyamine 6, 6, polyester, polyphenylene sulfide, polycarbonate, and propylene. The nitrile butadiene styrene, the liquid crystal polymer or any combination thereof; and/or the boron nitride is selected from the group consisting of agglomerated hexagonal boron nitride, flake hexagonal boron nitride, and spherical hexagonal boron nitride. According to the heat transfer composite of claim 1, wherein the chemical composition of magnesium niobate is 3MgO, 4SiO2, H2O, and the aspect ratio thereof is greater than 1. The thermally conductive composite of any one of clauses 1 to 5 wherein: the composite exhibits a thermal conductivity of at least about 2 W/mK, at least about 4 W/mK, or at least about 8 W/mK; and / Or the composite exhibits an average dielectric strength of at least about 4 kV/mm, at least about 15 kV/mm, or at least about 20 kV/mm. A thermally conductive composite comprising a polymer, boron nitride, and magnesium niobate, wherein the polymer, the boron nitride, and the magnesium niobate are present in an amount sufficient to produce a synergistic effect whereby the composite exhibits at least 2W /mK thermal conductivity. The thermally conductive composite of claim 7 wherein the composite exhibits a thermal conductivity of at least about 4 W/m-K or at least about 8 W/m-K. A thermally conductive composite comprising a polymer, at least 2% by volume of boron nitride, and At least 1% by volume of magnesium citrate, wherein: the polymer is selected from the group consisting of polyamine 6, polyamine 6,6, polyester, polyphenylene sulfide, polycarbonate, acrylonitrile Butadiene styrene, liquid crystal polymer or any combination thereof; the boron nitride is selected from the group consisting of agglomerated hexagonal boron nitride, thin hexagonal boron nitride and spherical hexagonal boron nitride; and chemistry of magnesium citrate The composition is 3MgO, 4SiO2, H2O, and the aspect ratio is 1 or more. The heat transfer composite according to claim 9 which comprises: at least about 5% by volume of boron nitride, and at least about 2% by volume of magnesium ruthenate; or at least about 15% by volume of nitrogen Boron, and at least about 23% by volume of magnesium ruthenate. The thermally conductive composite according to claim 9 or 10, wherein the composite exhibits a thermal conductivity of at least about 2 W/m-K or at least about 4 W/m-K.