Manufacturing method and molding die for composite material

Abstract

To provide a molding die capable of obtaining a composite material in which oblate particles are dispersed in resin in a highly orientated manner.SOLUTION: A molding die according to the present invention comprises: a first die part having flow paths that guide a mixture in which oblate particles are mixed in a molten or softened resin; and a second die part that constitutes a cavity in which the mixture is filled from the flow paths. The flow paths are made up of a plurality of parallel flow paths, and the flow paths and the cavity satisfy the following formula. I=(p / d)×(t / d)3≥2.6×10-5, where p: the sum of circumferential length (the total circumferential length) of flow path outlets (filling ports), d: a width of the cavity, and t: a cavity depth. For example, flow paths of the first die part are cylindrical, and the cavity of the second die part is hollow discoid. The oblate particles are made up of hexagonal system boron nitride. The composite material is used for a thermal conductive component (sheet) or the like.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a molding die and the like used for molding a composite material in which flat particles are dispersed in a resin. [Background technology]

[0002] Electronic devices (such as semiconductor modules) that have become increasingly dense and sophisticated require sufficient heat dissipation (including thermal diffusion) to maintain their functionality and lifespan. Heat dissipation from electronic devices is typically achieved through heat dissipation components (heat sinks, housings, etc.) made of metal or other materials. In this case, a flexible heat dissipation sheet (such as a thermally conductive sheet or a thermally conductive insulating sheet) is inserted between the electronic device (heat source) and the surface of the heat dissipation component to absorb any irregularities or undulations.

[0003] The heat dissipation sheet uses, for example, a composite material (including a composition) in which a highly thermally conductive filler is dispersed in a synthetic resin (including elastomer, rubber, etc.) that is highly flexible or elastic. Various proposals have been made regarding such composite materials, and for example, there are related descriptions in the following patent documents. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-128940 [Patent Document 2] Patent Publication No. 2016-79353 [Patent Document 3] Patent Publication No. 2011-74303 [Patent Document 4] Patent Publication No. 2011-218504 [Patent Document 5] Patent Publication No. 2015-45019 [Patent Document 6] Patent Publication No. 2015-216387 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Documents 1 and 2 propose a composite material in which hexagonal boron nitride particles (BN particles) with anisotropic thermal conductivity are oriented and dispersed in a (synthetic) resin by utilizing centrifugal force.

[0006] Patent Documents 3 and 4 describe a resin sheet obtained by slicing a molded body (laminate) in which flake graphite (filler) is dispersed in a resin, but do not substantially describe the orientation of the filler.

[0007] Patent Documents 5 and 6 describe thermally conductive sheets obtained by slicing a molded product obtained by extruding a mixture of silicone resin and carbon fiber. The molded product, which contains carbon fibers oriented longitudinally through a slit provided at the outlet of the extruder, is sliced ​​with an ultrasonic cutter to ensure the orientation of the carbon fibers within the sheet. Patent Documents 5 and 6 are based on the premise of using a fibrous filler, and do not address flat (plate-like or scale-like) fillers (e.g., BN particles).

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide a molding die or the like for obtaining a composite material in which flat particles are oriented and dispersed in a resin. [Means for solving the problem]

[0009] Through extensive research, the inventors have discovered that by using a molding die with a desired shape, a composite material in which flat particles are highly oriented in the resin can be obtained. By expanding on this finding, the present invention, which will be described below, has been completed.

[0010] 《Mold》 The present invention provides a molding die that is used to mold a composite material in which flat particles are dispersed in resin, and that comprises a first mold section having a flow path that guides a mixture of molten or softened resin and flat particles mixed therein, and a second mold section that forms a cavity into which the mixture is filled from the flow path, and the flow paths consist of multiple parallel flow paths, and the flow paths and the cavity satisfy the following formula: I = (p / d) × (t / d) 3 ≧ 2.6×10 -5 p: total circumference of the flow channel outlet (filling port), d: cavity width, t: cavity depth

[0011] By using a molding die in which the above index I is equal to or greater than a predetermined value, the flat particles can be highly oriented in the resin, so that, for example, a composite material (molded body, processed product of molded body, etc.) can be obtained that has improved desired properties (e.g., thermal conductivity) in a specific direction (orientation direction) while reducing the amount of flat particles used.

[0012] <<Manufacturing method of composite materials>> The present invention can be understood as a method for producing a composite material. For example, the present invention may be a method for producing a composite material using the above-mentioned molding die to obtain a molded body by solidifying a mixture of flat particles mixed in a resin. For example, the production method of the present invention may include at least a preparation step of mixing (kneading) a molten or softened resin with flat particles to obtain a fluid mixture, a filling step of flowing the fluid mixture from the flow path of the first mold part into the cavity of the second mold part, and a solidification step of solidifying (coagulating) the fluid mixture filled in the cavity.

[0013] According to the research of the present inventors, within a reasonable range where molding is possible, the viscosity and density of the fluid mixture, the particle size distribution and volume fraction of the flat particles, the pressure and feed rate of the fluid mixture, etc. have little effect on the orientation of the flat particles. In other words, the shape of the molding die described above has a dominant effect on the orientation of the flat particles.

[0014] In addition to the resin and flat particles, the fluid mixture may contain particles of different shapes (spherical, fibrous, etc.), solvents, processing agents (hardeners, surfactants, etc.), etc. The mixture is usually pumped from the first mold section to the second mold section by a plunger, screw, rotating device (centrifugal force imparting device), etc., located upstream of the first mold section.

[0015] 《Composite material》 Furthermore, the present invention can be understood as a composite material (member) obtained by the manufacturing method. The composite material may be the molded body itself solidified in the cavity, or may be a member (such as a thermally conductive sheet) obtained by processing (e.g., slicing) the molded body into a desired shape.

[0016] "others" Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." Unless otherwise specified, "x to y μm" in this specification means x μm to y μm. The same applies to other unit systems. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 10 is a perspective view illustrating a model of a forming die used in a simulation. [Figure 1B] FIG. 10 is a perspective view showing another example of a molding die having a different shape. [Figure 1C] FIG. 10 is a perspective view showing another example of a molding die having a different shape. [Figure 2A] FIG. 2 is a longitudinal cross-sectional view of a molded body showing the dispersion state of flat particles. [Figure 2B] FIG. 2 is a cross-sectional view of a molded body showing the dispersion state of flat particles. [Figure 3] FIG. 2 is an explanatory diagram showing a reference angle when calculating the degree of orientation of flat particles. [Figure 4] FIG. 2 is a scatter diagram showing the relationship between the mold index (I) and the degree of orientation of flat particles in a molded body. [Figure 5] 1 is a graph showing the flow velocity gradient (shear rate) at each position in the thickness direction of the cavity. DETAILED DESCRIPTION OF THE INVENTION

[0018] One or more components arbitrarily selected from the present specification may be added to the components of the present invention. The contents described in this specification apply not only to molding dies but also to composite materials (molded bodies, processed products, etc.) and their manufacturing methods, as appropriate. Even method-related components can be considered as product-related components. Which embodiment is best depends on the target, required performance, etc.

[0019] 《Mold》 The molding die has a first mold portion on the upstream side along the flow direction of the mixture containing the resin and flat particles, and a second mold portion on the downstream side thereof.

[0020] (1) First mold part The first mold section has multiple parallel flow paths, and the flowing mixture (simply referred to as "mixture") is guided along the flow paths from the upstream side to the cavity on the downstream side. The cross-sectional shape (shape, size) of each flow path may be circular, elliptical, square, etc. The cross-sectional shape of the flow path may change along the flow direction or may change for each flow path. It is usually sufficient for each flow path to have a uniform cylindrical cross section.

[0021] The multiple flow paths do not need to be uniform in direction or distribution, but are usually arranged parallel to the depth (thickness) direction of the cavity (normal direction of the cavity surface) and at equal or equal intervals. In this specification, the upstream end face or downstream end face of the cavity will be referred to as the "cavity surface" as appropriate.

[0022] The total perimeter (total perimeter: p) of the channel outlet (filling port to the cavity) changes depending on the size and number of channels. The larger the total perimeter (p), the larger the index (I), resulting in a composite with many flat particles oriented in a specific direction.

[0023] As the number of flow paths increases for a given cavity surface, the spacing between the filling ports that introduce the mixture into the cavity decreases and the area occupied by the filling ports also increases. This is thought to cause the expanding flow that occurs during filling to act stably (and even dominantly) on the flattened particles, promoting their orientation.

[0024] For example, the total perimeter is 5 to 10,000 mm, 10 to 5,000 mm, or 15 to 2,500 mm. Depending on the size (width) of the cavity surface, the inner diameter (filling port diameter) of each flow path is 0.5 to 100 mm, 1 to 50 mm, or 5 to 25 mm, the number of flow paths is 2 to 200, 5 to 100, or 10 to 50, and the spacing (minimum distance between adjacent flow paths) is 1 to 20 mm, 2 to 10 mm, or 3 to 5 mm. The ratio (p / d) of the total perimeter (p) to the cavity width (d) is, for example, 0.15 to 20, 0.2 to 15, 0.3 to 13, or 0.5 to 12.

[0025] (2) Second mold part The second mold section has a cavity into which the mixture is filled from the flow path of the first mold section. The cross section of the cavity (transverse cross section in the filling (flow) direction) may be circular, elliptical, rectangular, etc., and does not have to be constant in the filling direction. A typical example is a hollow disk-shaped (low cylindrical) cavity with a constant cross section.

[0026] By changing the size of the cavity (width, depth), the ratio (t / d) of the depth (t) to the width (d) can be adjusted. As this ratio increases, the index (I) also increases significantly, resulting in a composite with many flat particles oriented in a specific direction.

[0027] As the depth (t) increases, the flow velocity of the mixture in the cavity decreases, and the shear rate acting on the mixture also decreases. This is thought to stably maintain the expansion flow that affects the orientation of the flattened particles, promoting the orientation of the flattened particles.

[0028] For example, the cavity width (d) is 25 to 500 mm, 50 to 300 mm, or 100 to 200 mm, and the cavity depth (t) is 1 to 50 mm, 5 to 30 mm, or 10 to 20 mm. The ratio (t / d) of the cavity width (d) to the depth (t) is, for example, 1 to 50, 3 to 25, 5 to 20, or 7 to 15. The cavity width (d) is the maximum width of the cavity cross section. For a cylindrical or hollow disk-shaped cavity, the width (d) is the diameter (cavity diameter).

[0029] (3) Indicators A mold having such a first mold portion and a second mold portion has, for example, an index I=(p / d)×(t / d) 3 (×10 -5 ) is preferably 2.6 to 5000, 3 to 2500, 10 to 2000, or 30 to 1800. If the mold has an excessively small index, the flat particles will not be sufficiently oriented along the filling direction (the direction in which the flow channels extend). The larger the index of the mold used, the more highly oriented the flat particles will be, but it is not easy to manufacture a mold with an excessively large index. Furthermore, even if the index is made excessively large, a significant improvement in the degree of orientation cannot be expected.

[0030] 《Flat particle》 Flat particles are particles with a sufficiently large aspect ratio (ratio of maximum length to thickness, simply referred to as "particle size" regardless of shape). The aspect ratio is, for example, 10 to 1000, 20 to 500, or 30 to 100.

[0031] The particle size (maximum length) of the flat particles is, for example, 0.1 to 100 μm, 0.5 to 50 μm, 1 to 40 μm, or 3 to 30 μm, and the thickness (plate thickness) is, for example, 0.01 to 10 μm, 0.1 to 5 μm, 0.3 to 3 μm, or even 0.5 to 2.5 μm.

[0032] The particle size of the raw material powder or powder recovered from the composite material is specified, for example, by the 50% diameter (D50: median diameter) determined from the particle size distribution of the powder. The particle size distribution is determined by laser diffraction. The "thickness" is calculated as the arithmetic mean value of the thicknesses measured for multiple particles randomly selected within the field of view observed under a microscope.

[0033] An example of a flat particle is h-BN particles (simply referred to as "BN particles"), which have a hexagonal lattice structure and a mesh-like structure. BN particles can be single layers, laminates, or aggregates (aggregates, secondary particles). Flat (plate-like, scale-like) BN particles have thermal conductivity anisotropy, in which the thermal conductivity differs significantly between the in-plane direction (a-axis direction) and the plate thickness direction (c-axis direction). Composites in which BN particles are oriented in the in-plane direction (filling direction) can exhibit high thermal diffusivity and other properties along that direction.

[0034] The flat particles may be a mixture of multiple types with different shapes and types. Furthermore, other particles (cubic boron nitride (c-BN) particles, ceramic particles, metal particles, spherical particles, etc.) may be included in the mixture or composite material in addition to the flat particles.

[0035] "resin" The resin serves as the matrix (base material) of the composite material or as a binder for the particles (filler). The resin may be of a single type or multiple types, and is selected appropriately depending on the specifications of the composite material.

[0036] The resin may be a thermosetting resin or a thermoplastic resin. Examples of thermosetting resins include epoxy resin, phenol resin, and silicone resin. Examples of thermoplastic resins include polystyrene, polymethyl methacrylate, polycarbonate, and polyphenylene sulfide. In addition, rubbers such as ethylene-propylene-diene rubber (EPDM) and butyl rubber, and elastomers may also be used as the resin (or a part thereof).

[0037] 《Composite material》 (1) Content rate The ratio (content) of particles (filler) contained in the entire composite material is, for example, 30 to 85 volume %, 40 to 75 volume %, or 50 to 65 volume %. The particles may be dispersed uniformly or in a gradient.

[0038] (2) Degree of orientation The degree of orientation of flat particles is indicated, for example, by the angle (tilt angle) of the flat surface relative to a reference direction. The average value of the tilt angles (average angle) determined for the observed particles may be, for example, 1 to 45°, 3 to 40°, 5 to 35°, or 10 to 30°. The reference direction is, for example, the flow direction (0°) of the mixture filled from the flow channel.

[0039] The degree of orientation of the flat particles in the component (molded body) can be determined, for example, by image processing of an observation image (e.g., SEM image) of a cross section of the composite cut along a desired direction. The degree of orientation may be uniform or gradient throughout the composite.

[0040] (3)Applications A composite material in which highly thermally conductive flat particles are oriented and dispersed in a resin can exhibit excellent thermal conductivity in a specific direction. When the flat particles are BN particles, for example, their thermal diffusivity is 1.5 to 10 mm 2 / s, 2~7mm 2 / s, 2.5~5mm 2 / s. Unless otherwise specified, the thermal diffusivity and thermal conductivity are determined along the direction in which the flat particles are oriented (reference direction).

[0041] Such composite materials are used, for example, for heat dissipation members, substrates, housings, etc. of electronic devices, etc. The heat dissipation members may be in the form of a block or a sheet. [Example]

[0042] The influence of the molding die for the composite material on the degree of orientation of the flat particles (filler) was evaluated by simulation. The present invention will be described in more detail with reference to such specific examples.

[0043] <Analysis Model> An example model of the mold used in the analysis is shown in Figure 1A. Models with different shapes are shown in Figures 1B and 1C. In this example, we assumed that a fluid mixture of flat particles (filler) dispersed in a resin (matrix) was injection molded into a mold to produce a disk-shaped molded body (composite material).

[0044] The mold comprises a first mold section on the upstream side having a flow path for guiding a mixture of resin and flat particles, and a second mold section on the downstream side that forms a cavity corresponding to the molded body.

[0045] The cavity of the second mold section was a hollow disk, and its thickness (t: cavity thickness / cavity depth) and diameter (d: cavity diameter / cavity width) were variously changed as shown in Table 1. The ratio (t / d) of cavity thickness (t) to cavity diameter (d) is also shown in Table 1. Based on this second mold section, the first mold section was set as follows:

[0046] In the first mold section, multiple cylindrical flow paths (gates) with a constant cross section parallel to the thickness direction of the cavity (molded body) (perpendicular to the cavity surface (circular)) were arranged in parallel. Each flow path within one model had the same shape.

[0047] The inner diameter (q: 1 to 5 mm) of the outlet (filling port) of the flow path and the number of flow paths (n: 1 to 741) were changed for each model. As shown in Table 1, these were normalized by the ratio (p / d) of the total perimeter (p = q × n) to the cavity diameter (d) of the total perimeter (p = q × n). The index I calculated for each model was then expressed as (p / d) × (t / d). 3 are also shown in Table 1.

[0048] Numerical Analysis A simulation was conducted to determine the degree of orientation of the flat particles that occurs within the cavity when a flow mixture (slurry in which flat particles are dispersed in molten resin) is pumped from the flow path in the first mold section to the cavity in the second mold section. It was assumed that the movement of the flat particles does not affect the flow of the molten resin, and calculations were performed for the number of flat particles required to calculate the degree of orientation. 3D TIMON (manufactured by Toray Engineering D Solutions Co., Ltd.) was used as the analysis software.

[0049] The density and viscosity of the mixture were calculated using data for common thermoplastic resins pre-installed in the analysis software. The flat particles were square fillers (particle size: 1 to 40 μm) that were assumed to be BN particles. The analysis was performed without setting any particular filler density, assuming that the effect of filler inertia was small.

[0050] The mixture introduced into each flow path had a total flow rate (Q) of 30 cc / sec and a temperature of 255°C. The mold temperature was also set to 80°C.

[0051] 《Analysis results》 (1) Molded body The longitudinal and transverse cross sections of the molded article (sample No. 7 in Table 1) obtained by the above-mentioned injection molding are shown in FIGS. 2A and 2B, respectively.

[0052] (2) Degree of orientation The angles formed by the plane direction of the flat particles with respect to the reference angle set as shown in Figure 3 were calculated, and the arithmetic mean value (average angle) of these was shown as the degree of orientation in Table 1. The smaller the angle, the higher the degree of orientation of the flat particles in the packing direction (thickness direction).

[0053] For a flat particle size of 20 μm, the relationship between the index I shown in Table 1 and the degree of orientation is shown in FIG. 4. As is clear from FIG. 4, when the index I reaches a critical value (for example, 2.6×10 -5 ) or more, the filler was found to be in a highly oriented state with an orientation degree of less than 45°.

[0054] (3) Molding mold The effect of cavity thickness (t) on the velocity gradient (shear rate) acting on the mixture (especially flat particles) filled into the cavity is shown in Figure 5. As is clear from Figure 5, when the cavity was thick (e.g., sample No. 17 in Table 1, t = 17 mm), the velocity gradient was small and stable in the cavity thickness direction. On the other hand, when the cavity was thin (e.g., sample No. 7 in Table 1, t = 3 mm), the velocity gradient fluctuated greatly in the cavity thickness direction.

[0055] As can be seen from Table 1, when the cavity was sufficiently thick, the filler was highly oriented even if the shape of the filling port (p or p / d) changed, allowing for greater freedom in the shape of the filling port.

[0056] Conversely, when the cavity is thin, it is possible to achieve a high filler orientation by increasing the total perimeter of the filling ports (p or p / d). For example, when the cavity is thin, it is possible to provide a large number of flow channels with small filling ports (short perimeters) for a given cavity diameter (d), thereby shortening the spacing between the filling ports that serve as inlets to the cavity and increasing the opening area leading to the cavity (see Figure 1C). In either case, it is believed that by using a mold that satisfies indicator I of the present invention, the influence of the expanding flow that orients the filler in the filling direction is stably maintained, resulting in the production of a molded product with a highly oriented filler.

[0057] From the above, it was confirmed that the molding die of the present invention can produce a molded body (composite material) in which flat particles (filler) are highly oriented in a resin (matrix).

[0058] [Table 1]

Claims

1. a first mold portion having a flow path for guiding a mixture of molten or softened resin and flat particles therein; a second mold portion that forms a cavity into which the mixture is filled from the flow path, The flow path is made up of a plurality of parallel flow paths, The flow path and the cavity satisfy the following formula: A molding die used to mold a composite material in which the flat particles are dispersed in the resin. I=(p / d)×(t / d) ３ ≧ 2.6×10 -５ p: Total circumference of the flow channel outlet (filling port) (total circumference) d: cavity width t: cavity depth

2. the flow channel is cylindrical; 2. The mold according to claim 1, wherein the cavity is a hollow disk.

3. 3. The mold according to claim 2, wherein the depth of the cavity is 5 to 30 mm.

4. 2. The mold according to claim 1, wherein the flat particles have a particle size of 0.1 to 100 μm.

5. 2. The mold according to claim 1, wherein the flat particles are made of hexagonal boron nitride.

6. A method for producing a composite material, comprising using the mold according to any one of claims 1 to 5 to obtain a molded product by solidifying a mixture of molten or softened resin and flat particles mixed therein.

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