METHOD FOR PRODUCING A COMPOSITE MATERIAL, COMPOSITE MATERIAL PRODUCED THEREFROM AND ITS USE

Description

[0001] The present invention relates to a composite material. This can be used in particular as a housing for a rechargeable battery and / or as a component of an electronic component, part, or assembly. Furthermore, the present invention relates to a method for producing the composite material. State of the art

[0002] The housings of batteries in cordless drills and similar tools are typically made of organic polymer materials. While these offer good mechanical stability, they are insufficient in dissipating the heat generated by the battery.

[0003] It is known that a rechargeable battery achieves an increased service life with optimized heat dissipation. To improve heat dissipation, thermally conductive ceramic fillers can be incorporated into organic polymer masses. However, due to the processability of the organic polymer masses, only a small amount of these thermally conductive ceramic fillers can be incorporated.

[0004] Pure ceramic-cement composites exhibit very good heat dissipation. However, when used as battery housings, they have the disadvantage of being very brittle. Furthermore, their cement content causes porosity in such composites, which means that the housing's high sealing requirements cannot be met.

[0005] High heat dissipation is also desirable in electronic components, parts, and assemblies. However, this can only be achieved inadequately with organic polymer masses, or with poor processing properties and significantly higher material costs. At the same time, use at temperatures above 200 °C is usually critical for such polymer masses. Ceramic-cement composites are also sometimes too brittle and / or too permeable for this application.

[0006] US Pat. No. 5,275,655 A describes a cement composition with a reduced-adhesion surface. This composition contains 25 to 45 wt.% mineral fillers, 25 to 45 wt.% of a cement matrix, 10 to 20 wt.% of a polymeric binder, and 5 to 15 wt.% of a fluoropolymer.

[0007] WO 2014 / 029658 A1 describes a cement composition for construction. It contains 50 to 80 wt.% fillers and sand, 15 to 40 wt.% cement, and 0.1 to 3.5 wt.% of a polymer.

[0008] US 2016 / 0340251 A1 describes cement formulations based on Portland cement and calcium aluminate cement. Some formulations contain fillers such as aluminum oxide and an ethylene-vinyl acetate copolymer in addition to the cement.

[0009] DE 10 2015 223 449 A1 describes an electrical device with an encapsulating compound. The encapsulating compound comprises a layer system consisting of several discrete layers, each containing a cement compound. The cement may contain ceramic particles as fillers. Furthermore, it may contain a polymer as filler.

[0010] US Pat. No. 5,851,634 A describes inorganically filled composite materials. These comprise an inorganically filled matrix containing a homogeneous mixture of aggregate and organic binder. The matrix is ​​formed from an inorganically filled mixture containing water, a water-dispersible organic polymer binder, and an inorganic aggregate material. The aggregate comprises, for example, aluminum oxide and a cement. A coating material can be applied to the surface of the inorganically filled matrix.

[0011] WO 2014 / 180625 A1 discloses a process for producing plastic molded parts with increased thermal conductivity, comprising molding a molded part by injection molding a mixture of a polymer selected from the group consisting of polypropylene, polyethylene, polyurethane, polycarbonate, polyester, polyphenylene sulfide, polyetheretherketone, and polyamide and thermally conductive filler particles, wherein the filler consists of an electrically non-conductive compound, preferably boron nitride. The molded part can be a housing for electronic components.

[0012] Disclosure of the Invention The composite material according to the invention is produced by one of the processes described below. This composite material exhibits good thermal conductivity due to its high proportion of ceramic fillers. The combination of the ceramic fillers with the cement enables filling with at least one polymer without significantly impairing processability. This polymer fills pores in the structure of the cement, thus improving its mechanical stability and simultaneously counteracting its brittleness and porosity. Thus, permeability / water absorption is also reduced.

[0013] A cement is defined as any inorganic compound or mixture of inorganic compounds that sets hydraulically with water to form hydrate phases. High-alumina cements, Portland cements, and phosphate cements are particularly suitable as components of the composite material.

[0014] The at least one polymer makes up 1 to 20 vol.% of the composite material.

[0015] On the one hand, this ensures that the polymer compensates for the porosity, brittleness and resulting low mechanical stability of the cement, but on the other hand, the thermal conductivity of the composite is essentially determined by the cement and the ceramic fillers, not the polymer.

[0016] Preferred polymers for the composite material are selected from the group consisting of polysiloxanes or silicones, epoxy resins, polyurethane resins, vinyl acetate-ethylene copolymers, and mixtures thereof. These synthetic resins or resin-like compounds are particularly well suited to imparting the necessary elasticity to the composite material to compensate for the otherwise rather brittle properties of the cement and ceramic fillers.

[0017] The ceramic fillers intended to increase thermal conductivity are preferably selected from the group consisting of oxides, nitrides, carbides, and mixtures thereof. The oxides are, in particular, aluminum oxide. The nitrides are, in particular, aluminum nitride, boron nitride, or silicon nitride. The carbides are, in particular, silicon carbide or tungsten carbide. These ceramic fillers not only increase the thermal conductivity of the composite material but also meet electrical insulation requirements that may be placed on the composite material when used as a component of electronic components, parts, or assemblies with high operating voltages.

[0018] In the process for producing the composite material, a formulation of the following composition is mixed with water: 40 to 85 vol% ceramic fillers, 14 to 59 vol% at least one cement, 1 to 20 vol.% at least one polymer, 0 to 2 vol.% additives.

[0019] The formulation is then hydraulically set. The additives contained in the formulation are primarily flow agents that facilitate the processability of the formulation, such as polycarboxylate ethers (PCEs), polycondensates, polymer-based defoamers, polysiloxanes, or wetting agents.

[0020] The at least one polymer partially forms a polymer lattice. This encloses the ceramic fillers and the cement. Such a polymer lattice, which can also be referred to as a macroscopic matrix, further improves the mechanical stability of the composite.

[0021] The composite material is manufactured by injecting a cement paste into the polymer lattice using injection molding. The polymer lattice can also be formed using injection molding. To combine the advantages of the polymer lattice as a macroscopic polymer matrix with the advantages of the polymer bonded to the cement and ceramic fillers at the microscopic level, the cement paste formulation described above is used. The composite material therefore contains the polymer both in the cement paste and in the macroscopic matrix.

[0022] To cure the composite and reduce its water absorption, it is preferable to subject it to a heat treatment at a temperature in the range of 60°C to 350°C. This temperature range is sufficient to expel water that has not reacted with the cement from the composite, while being low enough to prevent thermal deformation or decomposition of the polymer, which could lead to the formation of cracks in the composite.

[0023] The composite material combines high thermal conductivity with good mechanical stability, low water absorption, and high electrical resistance. Therefore, it is particularly suitable for use as a housing for a rechargeable battery and / or as a component of an electronic device, electronic component, or electronic assembly. Short description of the drawings

[0024] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Fig. 1 shows a schematic representation of a microscopic matrix of a composite material. Fig. 2 compares the water absorption of the microscopic matrix of composite materials. Fig. 3 compares the thermal expansion of the microscopic matrix of a composite material with several conventional materials. Fig. 4 schematically shows a composite material according to an embodiment of the invention. Embodiment of the invention

[0025] According to Table 1 below, two formulations B1 and B2 were used to produce two examples of the microscopic matrix of composite materials. Furthermore, two formulations VB1 and VB2 were used to produce two comparative examples of conventional composite materials. Table 1 Example VB1 VB2 B1 B2 Alumina cement [Vol.%] 23,5 21,65 17,5 16,3 aluminum oxide [Vol.%] 49,5 51,7 49,5 51,7 Flow agent [Vol.%] 1,0 0,65 1,0 0,65 Polysiloxane resin [Vol.%] 6,0 polymer dispersion [Vol.%] 5,35 Water [Vol.%] 26,0 26,0 26,0 26,0

[0026] A mixture of a polycarboxylate ether and a defoamer was used as the flow agent. A saturated dispersion of a vinyl acetate-ethylene copolymer was used as the polymer dispersion.

[0027] All formulations were hydraulically set to obtain test specimens.

[0028] Fig. 1shows the structure of microscopic matrices 1 of composite materials produced according to formulations B1 and B2, as they can be partially visualized in micrographs using light microscopy or scanning electron microscopy, or indirectly detected using mercury indentation porosimetry or resistance measurements. It can be seen that the ceramic fillers 2, in the form of aluminum oxide particles of varying sizes, are embedded in the cement matrix 3 together with a microscopic organic matrix made of the respective polymer 4, i.e., a polysiloxane or the vinyl acetate-ethylene copolymer.

[0029] Composites produced according to formulations VB1 and B1 were each first cured for 48 hours at a temperature of 60°C, then dried at a temperature of 80°C, and then stored at 22°C for more than 24 hours. One sample of each composite produced according to formulation B1 was subjected to a one-hour heat treatment at a temperature of 150°C after drying and before storage at room temperature. All samples were then stored underwater, and their percentage water absorption WA was determined by weighing after two hours and after 24 hours. As described in Fig. 2As shown, the composite exhibits significantly lower water absorption than a conventional ceramic-cement composite that does not contain a polymer. This can be significantly improved through heat treatment and is then comparable to that of silicone casting compounds. It was thus demonstrated that the composite's water absorption reflects the positive properties of the polymer it contains, rather than the negative properties of the cement it contains.

[0030] One sample each of composite materials, manufactured according to recipes VB2 and B2, was heated from a temperature of 22°C in the undried state at a rate of 2°C per minute to a temperature of 300°C and then cooled back to the initial temperature. The percentage elongation (rel. DL) of the composite materials during heating and cooling is shown in Fig. 3The composite material exhibits significantly lower thermal shrinkage than a conventional ceramic-cement composite material that does not contain a polymer. This demonstrates that such a composite material exhibits lower stress at the interfaces with metallic substrates, such as those found in electronic components, parts, and assemblies, than the conventional composite material. This is shown in Fig. 3 The thermal expansion of aluminum and copper is also demonstrated. Better adhesion of the composite material under the influence of temperature is also expected than can be achieved with conventional composite materials.

[0031] Fig. 4schematically shows a mechanically particularly stable composite material 5 according to an embodiment of the invention. This is produced by embedding formulation B1 or B2 into a polymer lattice as a macroscopic polymer matrix by injection molding. The polymer used in formulation B1 is polysiloxane, and in formulation B2, vinyl acetate-ethylene copolymer. The composite material 5 thus consists of a microscopic matrix 1 comprising ceramic fillers, a cement, and the polymer, which in turn is embedded in a macroscopic matrix of the polymer 4.

[0032] The composite materials 5 which can be produced from the formulations B1 and B2 according to the exemplary embodiment of the invention described above can be used as a housing for a battery of a cordless drill or as a component of an electronic semiconductor component, an electronic semiconductor device or an electronic semiconductor assembly.

Claims

1. Process for producing a composite material (5) by injecting a cement composition into a polymer lattice by means of injection moulding, wherein as the cement composition a formulation having the following composition is admixed with water: 40 to 85% by volume of ceramic fillers (2), 14 to 59% by volume of at least one cement (3), 1 to 20% by volume of at least one polymer (4), 0 to 2% by volume of additives, based in each case on 100% by volume of the composite material (5), and then hydraulically setting the formulation.

2. Process according to Claim 1, characterized in that the polymer (4) is selected from the group consisting of polysiloxanes, epoxy resins, polyurethane resins, vinyl acetate-ethylene copolymers and mixtures thereof.

3. Process according to Claim 1 or 2, characterized in that the ceramic fillers (2) are selected from the group consisting of oxides, nitrides, carbides and mixtures thereof.

4. Process according to any of Claims 1 to 3, characterized in that the composite material (5) is subjected to a heat treatment at a temperature in the range from 60°C to 350°C.

5. Composite material produced by one of the processes according to Claims 1 to 4.

6. Use of a composite material (5) according to Claim 5 as a housing for a rechargeable battery and / or as a constituent of an electronic component, an electronic structural part or an electronic assembly.