Thixotropic molding material, method for producing thixotropic molding material, and thixotropic molded body

Abstract

To provide a thixomolded body with high thermal conductivity, and to provide a material for thixomolding capable of manufacturing such a thixomolded body and a manufacturing method thereof.SOLUTION: A material for thixomolding includes: a metal body mainly composed of Mg; and a coating part containing C particles adhering on the surface of the metal body via a binder, and mainly composed of C. A mass fraction of the C particles with respect to the total mass of the metal body and the C particles is 5.0 mass% or more and 40.0 mass% or less. Further, the binder preferably contains waxes. Furthermore, the C particles are preferably graphite particles.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a material for thixotropic molding, a method for producing a material for thixotropic molding, and a thixotropic molded article. [Background technology]

[0002] Magnesium has a low specific gravity and is excellent in electromagnetic shielding, vibration damping, machinability, and biological safety. For these reasons, magnesium alloy parts are beginning to be used in products such as automobiles, aircraft, mobile phones, and laptops.

[0003] Thixomolding is known as a method for manufacturing magnesium parts. Thixomolding is a molding method in which pellet-shaped or chip-shaped material is heated in a cylinder to create a solid-liquid coexistence state in which liquid and solid phases coexist, and then thixotropy is expressed by rotating a screw, and the resulting semi-solidified material is injected into a mold. According to this thixomolding method, the fluidity of the semi-solidified material is increased by heating and shearing, so that thinner parts and parts with complex shapes can be molded compared to the die casting method.

[0004] For example, Patent Document 1 discloses a method for producing molding chips in which 0.01 to 3% by weight of carbon black is added to magnesium chips and the two are mixed in a mixer to coat the surfaces of the magnesium chips with carbon powder. Such molding chips coated with carbon powder can improve the bending properties and tensile strength of molded products produced by injection molding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2012 / 137907 Summary of the Invention [Problem to be solved by the invention]

[0006] The molded product manufactured using the magnesium alloy chips described in Patent Document 1 has a problem of low thermal conductivity. It is difficult to apply a molded product with low thermal conductivity to parts that require heat dissipation. For this reason, there is a demand for further improvement in thermal conductivity in thixotropic molded products. [Means for solving the problem]

[0007] The thixomolding material according to the application example of the present invention is A metal body mainly composed of Mg 、 before a coating portion that is attached to a surface of the metal body and contains C particles having C as a main component; an adhesive portion that bonds the metal body and the coating portion and that includes a binder made of an organic material; having The mass fraction of the C particles in the total mass of the metal body and the C particles is 5.0 mass% or more and 40.0 mass% or less. the law of nature, In pellet or chip form, The average particle size is between 0.5mm and 10mm. .

[0008] A method for producing a thixomolding material according to an application example of the present invention includes the steps of: A metal body mainly composed of Mg, C particles mainly composed of C, Made of organic materials A preparation step of preparing a mixture including a binder and a solvent; A stirring step of stirring the mixture; a degreasing step of heating the stirred mixture to remove at least a portion of the binder contained in the mixture to obtain a thixotropic molding material; having a mass fraction of the C particles in the total mass of the metal body and the C particles is 5.0 mass% or more and 40.0 mass% or less; The content of the binder in the thixotropic molding material is 0.001% by mass or more and 0.200% by mass or less. the law of nature, The thixotropic molding material has the metal body, a coating portion that adheres to the surface of the metal body and contains the C particles, and an adhesive portion that bonds the metal body and the coating portion and contains the binder. The thixotropic molding material is in the form of pellets or chips, and has an average particle size of 0.5 mm or more and 10 mm or less. .

[0009] The thixotropic molded article according to the application example of the present invention is A matrix portion mainly composed of Mg; A particle portion dispersed in the matrix portion and containing C as a main component; having The average aspect ratio of the particle portion is 2.0 or more and 20.0 or less, The carbon content is 5.0% by mass or more and 40.0% by mass or less. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an injection molding machine used in thixomolding. [Diagram 2] FIG. 1 is a cross-sectional view showing a schematic diagram of a thixotropic molding material according to an embodiment. [Diagram 3] FIG. 2 is a process diagram for explaining a method for producing a thixotropic molding material according to an embodiment. [Figure 4] FIG. 2 is a partial cross-sectional view that shows a schematic view of a thixotropic molded article according to an embodiment. [Diagram 5] 2 is an image of a cut surface of a thixotropic molding corresponding to an example, observed with an optical microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The thixotropic molding material, the method for producing the thixotropic molding material, and the thixotropic molded article of the present invention will be described in detail below with reference to the embodiments shown in the accompanying drawings.

[0012] 1. Thixomolding First, a thixomolding method in which a thixomolding material according to an embodiment is used will be described. Thixomolding is a molding method in which pellet- or chip-shaped material is heated in a cylinder to create a solid-liquid coexistence state in which liquid and solid phases coexist, then thixotropy is expressed by rotating a screw, and the resulting semi-solidified material is injected into a mold. According to this type of thixomolding, the fluidity of the semi-solidified material is increased by heating and shearing, so that it is possible to mold thin-walled parts or parts with complex shapes compared to, for example, die casting. FIG. 1 is a cross-sectional view showing an example of an injection molding machine used in the thixomolding method.

[0013] As shown in FIG. 1, the injection molding machine 1 includes a mold 2, a hopper 5, a heating cylinder 7, a screw 8, and a nozzle 9. The mold 2 forms a cavity Cv. When the thixotropic molding material 10 is charged into the hopper 5, the thixotropic molding material 10 is supplied to the heating cylinder 7. The thixotropic molding material 10 supplied to the heating cylinder 7 is heated by the heater 6 and transferred while being sheared by the screw 8. As a result, the thixotropic molding material 10 is semi-melted and turned into a slurry. The obtained slurry is injected into the cavity Cv in the mold 2 through the nozzle 9 without coming into contact with the air. Then, the slurry injected into the cavity Cv is cooled to obtain a thixotropic molding. In addition to the thixotropic molding material 10, other materials may also be charged into the hopper 5.

[0014] 2.Thixo-molding material Next, a thixoforming material according to an embodiment will be described. FIG. 2 is a cross-sectional view that illustrates a thixotropic molding material according to an embodiment.

[0015] The thixomolding material 10 shown in FIG. 2 is a raw material used in the thixomolding method, and has a chip-shaped metal body 11, a coating portion 12 attached to the surface of the metal body 11, and an adhesive portion 13 containing a binder that bonds the metal body 11 and the coating portion 12 together.

[0016] 2.1. Metal objects The metal body 11 is, for example, a piece obtained by cutting or cutting an Mg-based alloy cast in a mold, etc. The method for producing the metal body 11 is not limited to this.

[0017] The metal body 11 contains Mg as a main component and various additive components. Examples of the additive components include lithium, beryllium, calcium, aluminum, silicon, manganese, iron, nickel, copper, zinc, strontium, yttrium, zirconium, silver, tin, gold, and rare earth elements, and one or a mixture of two or more of these is used. Examples of rare earth elements include cerium.

[0018] The main component refers to an element that is contained at the highest content in metal body 11. The content of the main component is preferably more than 50 mass %, more preferably 70 mass % or more, and even more preferably 80 mass % or more.

[0019] The additive components preferably contain aluminum and zinc. This lowers the melting point of the metal body 11 and improves the fluidity of the slurry. As a result, the moldability of the thixotropic molding material 10 can be improved.

[0020] In addition to aluminum and zinc, the additive component preferably contains at least one selected from the group consisting of manganese, yttrium, strontium, and rare earth elements, which can improve the mechanical properties, corrosion resistance, wear resistance, and thermal conductivity of the thixotropic molding.

[0021] The additive component may be present in the form of an element, an alloy, an oxide, an intermetallic compound, or the like in the metal body 11. Furthermore, the additive component may be segregated in the metal body 11 at the grain boundaries of the metal structure of Mg or an Mg alloy, or may be uniformly dispersed.

[0022] The average particle size of the thixotropic molding material 10 is not particularly limited, but is preferably 0.5 mm or more, and more preferably 1.5 mm or more and 10 mm or less. By setting the average particle size within the above range, the occurrence of bridges and the like within the heating cylinder 7 of the injection molding machine 1 can be suppressed.

[0023] The average particle size of the thixotropic molding material 10 is the average value of the diameters of circles having the same area as the projected area of ​​the thixotropic molding material 10. The average value is calculated from 100 or more randomly selected thixotropic molding materials 10.

[0024] The average aspect ratio of the thixotropic molding material 10 is preferably 5.0 or less, and more preferably 4.0 or less. The thixotropic molding material 10 having such an average aspect ratio improves the filling property inside the heating cylinder 7 and improves the temperature uniformity during heating. As a result, a thixotropic molding having high mechanical properties and high dimensional accuracy is obtained.

[0025] The average aspect ratio of the thixotropic molding material 10 is the average value of the aspect ratios calculated from the major axis / minor axis in the projected image of the thixotropic molding material 10. The average value is calculated from 100 or more randomly selected thixotropic molding materials 10. The major axis is the maximum length that can be taken in the projected image, and the minor axis is the maximum length in the direction perpendicular to that maximum length.

[0026] 2.2. Covering The coating portion 12 contains C particles 14 containing C as a main component. Specifically, for example, a plurality of C particles 14 are attached to the surface of the metal body 11, thereby forming the coating portion 12.

[0027] The coating portion 12 preferably covers the entire surface of the metal body 11, but may cover only a portion of the surface. The coating portion 12 imparts fluidity to the thixotropic molding material 10 due to the lubricity of carbon. In other words, it improves the flow of the slurry, making it difficult for internal defects due to blowholes or air entrapment to occur in the thixotropic molding. In addition, the C particles 14 have excellent thermal conductivity derived from carbon. For example, the thermal conductivity of magnesium alloys is about 50 to 80 W / (m·K), and the thermal conductivity of carbon is about 100 to 250 W / (m·K). Due to this difference in thermal conductivity, the thermal conductivity of a thixotropic molding containing the C particles 14 can be made higher than that of magnesium alloys.

[0028] The C particles 14 are not particularly limited as long as they are particles mainly composed of carbon, and may be particles mainly composed of amorphous carbon such as carbon black, but are preferably graphite particles. The graphite particles are particles mainly composed of graphite, i.e., graphite having a plate-like crystal structure. The plate-like crystal structure of graphite is a structure in which sheet-like graphene is laminated, and the bond strength between the layers is weak, so that it imparts particularly high lubricity to the C particles 14. In addition, graphene has a characteristic that the bond strength in the in-plane direction is higher than the bond strength between the layers, and that it has excellent thermal conductivity in the in-plane direction. Therefore, even if a shear force is applied by the screw 8 and the bond between the layers is broken, the thermal conductivity of the coating portion 12 is maintained high. As a result, a thixotropic molding having excellent thermal conductivity and mechanical strength that is not easily reduced is obtained.

[0029] The average particle size of the C particles 14 is not particularly limited, but is preferably 1 μm or more and 100 μm or less, more preferably 1 μm or more and 25 μm or less, and even more preferably 2 μm or more and 15 μm or less. By setting the average particle size of the C particles 14 within the above range, it is possible to optimize the balance between the coverage of the coating portion 12 and the C content in the thixomolding material 10. In addition, when the C particles 14 are attached to the surface of the metal body 11, the C particles 14 are less likely to fall off.

[0030] If the average particle size of the C particles 14 is below the lower limit, the C particles 14 are difficult to disperse, which may deteriorate the balance described above. On the other hand, if the average particle size of the C particles 14 is above the upper limit, the C particles 14 may easily fall off.

[0031] In the thixotropic molding material 10, the mass fraction of the C particles 14 in the total mass of the metal body 11 and the C particles 14 is 5.0 mass% or more and 40.0 mass% or less, preferably 7.0 mass% or more and 25.0 mass% or less, and more preferably 10.0 mass% or more and 20.0 mass% or less. By setting the mass fraction of the C particles 14 within the above range, it is possible to sufficiently increase the thermal conductivity of the thixotropic molding while suppressing a significant decrease in the mechanical properties of the produced thixotropic molding. Such a thixotropic molding can be applied to parts where heat dissipation is required, for example.

[0032] If the mass fraction of the C particles 14 is below the lower limit, the thermal conductivity of the thixotropic molded body may not be sufficiently increased. On the other hand, if the mass fraction of the C particles 14 is above the upper limit, the mechanical properties of the thixotropic molded body may be degraded.

[0033] The coating portion 12 may contain a substance other than the C particles 14. In that case, the content of the substance other than the C particles 14 may be less than the content of the C particles 14 in terms of mass ratio.

[0034] Furthermore, the C particles 14 may contain elements other than C. In that case, the content of the elements other than C may be less than the content of C in terms of mass ratio.

[0035] 2.3.Adhesive part The adhesive portion 13 is interposed between the metal body 11 and the C particles 14 or between the C particles 14 themselves.

[0036] The adhesive portion 13 includes a binder. The binder is an organic material that bonds the metal body 11 and the covering portion 12, and examples of the binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, polyethers, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, as well as various resins such as waxes, alcohols, higher fatty acids, fatty acid metals, higher fatty acid esters, higher fatty acid amides, nonionic surfactants, and silicone lubricants. The binder may be a mixture containing at least one of these components and another component, or a mixture containing two or more of these components.

[0037] Of these, the binder preferably contains waxes, and more preferably contains paraffin wax or a derivative thereof. Waxes have good binding properties and can strongly bond between metal body 11 and C particles 14, and between C particles 14 themselves. In addition, by combining with degreasing conditions, a thixotropic molding material can be realized that can minimize gas generation during molding.

[0038] Examples of waxes include vegetable waxes such as candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax, ozokerite, and ceresin; natural waxes such as paraffin wax, microcrystalline wax, and petroleum wax; synthetic hydrocarbons such as polyethylene wax; modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives; hydrogenated waxes such as hydrogenated castor oil and hydrogenated castor oil derivatives; fatty acids such as 12-hydroxystearic acid, acid amides such as stearic acid amide, and synthetic waxes such as esters such as phthalic anhydride imide.

[0039] As described above, the thixotropic molding material 10 according to the embodiment has the metal body 11 and the coating portion 12, and the mass fraction of the C particles 14 in the total mass of the metal body 11 and the C particles 14 is 5.0 mass% or more and 40.0 mass% or less. The metal body 11 is mainly composed of Mg. The coating portion 12 adheres to the surface of the metal body 11 via a binder and contains C particles 14 mainly composed of C.

[0040] By using such a thixotropic molding material 10, a thixotropic molding containing a relatively large amount of C can be easily manufactured. Such a thixotropic molding has high thermal conductivity due to the high concentration of C. As a result, a thixotropic molding applicable to a portion requiring heat dissipation can be obtained. In addition, a portion having a locally high C content is formed in the thixotropic molding due to the coating portion 12. This portion has a high aspect ratio, i.e., an elongated shape, since it inherits the shape of the coating portion 12. This allows this portion to function as a filler that enhances mechanical properties such as tensile strength and rigidity. As a result, by using the thixotropic molding material 10, a thixotropic molding having excellent mechanical properties can be manufactured.

[0041] Furthermore, the thixotropic molding material 10 may contain additives other than the above-mentioned metal body 11, coating portion 12, and adhesive portion 13. Examples of additives include coupling agents, surfactants, dispersants, lubricants, antioxidants, UV absorbers, thickeners, rust inhibitors, preservatives, and fungicides.

[0042] 3. Manufacturing method of thixomolding material Next, a method for producing the above-mentioned thixomolding material 10 will be described.

[0043] FIG. 3 is a process diagram for explaining the method for producing a thixotropic molding material according to the embodiment. The method for producing the thixomolding material 10 shown in FIG. 3 includes a preparation step S102, a drying step S104, a stirring step S106, and a degreasing step S108.

[0044] 3.1. Preparation process In the preparation step S102, a mixture containing metal bodies 11, C particles 14, a binder, and a solvent is prepared.

[0045] The solvent is not particularly limited as long as it is a liquid that disperses the binder. Examples of the solvent include water, isopropanol, acetone, etc. A mixer, a kneader, etc. are used for mixing. This step may be a step of preparing a mixture prepared in advance.

[0046] The content of the binder in the mixture is not particularly limited, but is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 15% by mass, and even more preferably 3% by mass to 10% by mass. By setting the binder content within the above range, the C particles 14 can be uniformly dispersed based on the dispersing action of the binder.

[0047] If the binder content falls below the lower limit, the amount of binder will be insufficient, making it difficult to uniformly adhere the C particles 14 to the metal body 11 and also difficult to uniformly disperse the C particles 14. On the other hand, if the binder content exceeds the upper limit, the amount of binder will be excessive, making the C particles 14 that are not adhered to the metal body 11 more likely to aggregate, which may increase the amount of binder residue in the degreasing step S108 described below and make the thixotropic molding more susceptible to internal defects.

[0048] The temperature of the solvent is preferably set to a temperature equal to or higher than the melting point of the binder, as necessary. This makes it easier for the binder to dissolve in the solvent. As a result, the binder can be dispersed more uniformly. The temperature of the solvent is preferably set to a temperature 10°C or higher than the melting point of the binder, and more preferably set to a temperature 20°C or higher and 50°C or lower.

[0049] In this case, the mixture is placed in a container, and the entire container is heated from the outside using a hot bath or the like.

[0050] The melting point of the binder used is not particularly limited, but is preferably 40°C or higher and 80°C or lower, more preferably 43°C or higher and 65°C or lower, and even more preferably 45°C or higher and 60°C or lower. If the melting point of the binder is within the above range, the binder can be melted efficiently in a short time. In addition, if the melting point of the binder is within the above range, the thixotropic molding material 10 produced will have good lubricity in thixotropic molding, and will be able to improve the fluidity of the slurry.

[0051] 3.2.Drying process In the drying step S104, the mixture is dried. As a result, the C particles 14 are adhered to the surface of the metal body 11 via the binder, and the solvent is volatilized to obtain a dried body. In this embodiment, the C particles 14 are dispersed using the binder, so that the C particles 14 can be adhered to the surface of the metal body 11 with a uniform thickness.

[0052] Drying can be performed by heating the mixture, exposing the mixture to a gas, or the like. When the mixture is heated, the entire container containing the mixture can be heated using a hot bath or the like. In the drying step S104, all of the solvent in the mixture may be removed, but some of the solvent may remain.

[0053] The temperature at which the mixture is heated may be equal to or higher than the temperature at which the solvent volatilizes and the binder softens, and is specifically set according to the composition of the solvent, preferably from 40° C. to 120° C., and more preferably from 50° C. to 80° C. This makes it possible to volatilize and remove the solvent while preventing the C particles 14 attached to the surface of the metal body 11 from falling off as the binder softens.

[0054] The time for heating the mixture is appropriately set depending on the heating temperature, but is, for example, preferably from 10 minutes to 300 minutes, and more preferably from 20 minutes to 200 minutes.

[0055] The drying step S104 may be performed as necessary, and may be omitted, or the drying step S104 and the stirring step S106 may be performed simultaneously.

[0056] 3.3.Mixing process In the stirring step S106, the mixture is stirred. If the drying step has been performed, the dried mixture is stirred. Stirring can be performed using a stirring rod or stirrer, or by shaking the mixture in a container with a lid on. By such stirring, the C particles 14 can be attached to the surface of the metal body 11 via the binder. Note that some of the C particles 14 may be directly attached to the surface of the metal body 11 without the binder. In addition, stirring can prevent the metal bodies 11 from agglomerating together to form lumps.

[0057] After the stirring step S106, the drying step S104 and the stirring step S106 may be repeatedly performed as necessary. This causes the adhesion of the C particles 14 to be repeated, so that the C particles 14 can be adhered to the surface of the metal body 11 in multiple layers. As a result, a larger number of the C particles 14 can be adhered to the surface of the metal body 11. The number of repetitions is not particularly limited, but is, for example, 2 to 10 times. In this case, the drying step S104 and the stirring step S106 may be performed simultaneously.

[0058] 3.4. Degreasing process In the debinding step S108, the stirred mixture is subjected to a debinding treatment. This results in a thixotropic molding material 10. Examples of debinding treatments include a method of heating the mixture and a method of exposing the mixture to a gas that decomposes the binder. This makes it possible to remove at least a portion of the binder contained in the mixture. As a result, it is possible to prevent a large amount of binder from being transferred into the heating cylinder 7, and to suppress the generation of a large amount of gas in the heating cylinder 7.

[0059] The heating temperature of the mixture in the degreasing treatment is not particularly limited as long as it is a temperature at which the binder can be thermally decomposed, but is preferably from 200° C. to 500° C., and more preferably from 250° C. to 450° C. By setting the heating temperature within the above range, the binder can be appropriately removed while suppressing adverse effects on the metal body 11 caused by the degreasing treatment.

[0060] If the heating temperature is below the lower limit, a large amount of binder may remain unremoved, and a large amount of gas may be generated inside the heating cylinder 7. On the other hand, if the heating temperature is above the upper limit, the heat may adversely affect the metal body 11, or the binder may be completely removed, causing the C particles 14 to fall off from the metal body 11.

[0061] The heating time of the mixture in the degreasing treatment is not particularly limited and may be, for example, 5 minutes or more, but is preferably 1 hour to 100 hours, more preferably 10 hours to 50 hours. This makes it possible to appropriately remove the binder while suppressing adverse effects on the metal body 11 due to the degreasing treatment.

[0062] The amount of binder after degreasing, i.e., the binder content in thixotropic molding material 10, is not particularly limited, but is preferably 0.001% by mass to 0.200% by mass, more preferably 0.010% by mass to 0.100% by mass, and even more preferably 0.015% by mass to 0.040% by mass. By setting the binder content in thixotropic molding material 10 within the above range, it is possible to ensure the adhesion of covering portion 12 by adhesive portion 13, while preventing the amount of binder thermally decomposing in heating cylinder 7 from becoming more than necessary.

[0063] If the binder content falls below the lower limit, the amount of binder may be insufficient, and the covering portion 12 may easily fall off. On the other hand, if the binder content exceeds the upper limit, the amount of binder may be excessive, and a large amount of decomposition gas may be generated in the heating cylinder 7, and voids may easily occur in the thixotropic molded body.

[0064] As described above, the manufacturing method of the thixotropic molding material 10 according to this embodiment includes the preparation step S102, the stirring step S106, and the degreasing step S108. In the preparation step S102, a mixture containing the metal body 11 mainly composed of Mg, the C particles 14 mainly composed of C, a binder, and a solvent is prepared. In the stirring step S106, the mixture is stirred. In the degreasing step S108, the stirred mixture is heated to remove at least a portion of the binder contained in the mixture, thereby obtaining the thixotropic molding material 10. In the thixotropic molding material 10 obtained in this manner, the mass fraction of the C particles 14 in the total mass of the metal body 11 and the C particles 14 is 5.0 mass% or more and 40.0 mass% or less, and the content of the binder is 0.001 mass% or more and 0.200 mass% or less.

[0065] According to this configuration, it is possible to obtain a thixotropic molding material 10 that contains a high concentration of C and that can easily produce a thixotropic molding body with high thermal conductivity. In addition, because the binder content is optimized, it is possible to obtain a thixotropic molding material 10 in which the adhesiveness of the covering part 12 by the adhesive part 13 is ensured and the amount of the binder that thermally decomposes in the heating cylinder 7 is suppressed.

[0066] It should be noted that the thixotropic molding material 10 does not necessarily have to be manufactured by this manufacturing method. In other words, the thixotropic molding material 10 may be manufactured without going through, for example, the degreasing step S108.

[0067] 4. Thixoplastic molding Next, the thixotropic molding according to the embodiment will be described. FIG. 4 is a partial cross-sectional view that typically shows a thixotropic molded article according to an embodiment.

[0068] The thixotropic molded body 100 shown in Fig. 4 is a molded body obtained by the thixotropic molding method, and has a matrix portion 200 and a particle portion 300. The matrix portion 200 is a portion that originates mainly from the metal body 11 of the thixotropic molding material 10, and is mainly composed of Mg. The particle portion 300 is a portion that originates mainly from the coating portion 12 of the thixotropic molding material 10, and is mainly composed of C.

[0069] 4, when the cross section of the thixotropic molding 100 is viewed, the area occupied by the matrix portion 200 is larger than the area occupied by the particle portion 300. Therefore, the particle portion 300 is in a state of being dispersed within the matrix portion 200.

[0070] In addition, the particle portion 300 has an elongated cross section as shown in Fig. 4. The average aspect ratio of the particle portion 300, i.e., the ratio of the length of the major axis A1 to the length of the minor axis A2, is 2.0 or more and 20.0 or less, preferably 4.0 or more and 15.0 or less, and more preferably 5.0 or more and 10.0 or less.

[0071] Since the particle portion 300 has the above-mentioned average aspect ratio, the thermal conductivity of the particle portion 300 itself has a large anisotropy. That is, in the cross section shown in Fig. 4, the particle portion 300 has a high thermal conductivity in the extension direction of the major axis A1, but has a low thermal conductivity in the extension direction of the minor axis A2.

[0072] On the other hand, the thixotropic molded body 100 contains a high proportion of particle portions 300 having anisotropic thermal conductivity. Specifically, the C content in the thixotropic molded body 100 is 5.0 mass% or more and 40.0 mass% or less, preferably 7.0 mass% or more and 25.0 mass% or less, and more preferably 10.0 mass% or more and 20.0 mass% or less.

[0073] By setting the C content within the above range, when the particle portions 300 have the average aspect ratio as described above, the particle portions 300 in the thixotropic molded body 100 are more likely to come into contact with or be close to each other. This makes it easier for heat conduction to occur between the particle portions 300, and the thermal conductivity of the thixotropic molded body 100 can be improved.

[0074] In addition, since the particle portion 300 has the average aspect ratio as described above and the C content is within the above range, the particle portion 300 functions as a filler that enhances mechanical properties such as tensile strength and rigidity. As a result, a thixotropic molding 100 with excellent mechanical properties can be realized.

[0075] When the average aspect ratio of the particle portions 300 is below the lower limit and when the C content is below the lower limit, the probability that the distance between the particle portions 300 will be large increases, making it difficult for heat conduction to occur between the particle portions 300. On the other hand, when the average aspect ratio of the particle portions 300 exceeds the upper limit and when the C content exceeds the upper limit, the mechanical properties of the thixotropic molded body 100 may decrease.

[0076] The C content can be measured, for example, by the oxygen flow combustion (high-frequency induction heating furnace combustion)-infrared absorption method specified in JIS G 1211: 2011. An example of an analytical device compatible with this measurement method is a carbon-sulfur analyzer manufactured by LECO Japan Co., Ltd.

[0077] Further, the average value of the major axis A1 of the particle portion 300 is not particularly limited, but is preferably 10 μm or more, and more preferably 20 μm or more and 100 μm or less.

[0078] The average aspect ratio and the average value of the major axis A1 are obtained by observing the cross section of the thixotropic molded body 100 with an optical microscope and processing the image. For example, image analysis software such as OLYMPUS Stream can be used for image processing. The magnification of the observed image is preferably 300 times or more.

[0079] The C content can be measured, for example, by the oxygen flow combustion (high-frequency induction heating furnace combustion)-infrared absorption method specified in JIS G 1211: 2011. An example of an analytical device compatible with this measurement method is a carbon-sulfur analyzer manufactured by LECO Japan Co., Ltd.

[0080] The thermal conductivity of the thixotropic molded body 100 is preferably 53 W / (m·K) or more, more preferably 58 W / (m·K) or more, and even more preferably 62 W / (m·K) or more. The thixotropic molded body 100 having such a thermal conductivity can be applied to, for example, parts where heat dissipation is required.

[0081] The thermal conductivity of the thixotropic molded body 100 is measured by, for example, a laser flash method.

[0082] The thixotropic molding material, the method for producing a thixotropic molding material, and the thixotropic molded body of the present invention have been described above based on the illustrated embodiments, but the thixotropic molding material and the thixotropic molded body of the present invention are not limited to the above-mentioned embodiments, and may be, for example, the above-mentioned embodiments to which any component has been added. Also, the method for producing a thixotropic molding material of the present invention may be the above-mentioned embodiments to which any purpose has been added. EXAMPLES

[0083] Next, specific examples of the present invention will be described. 5. Manufacturing of materials for thixomolding 5.1. Sample No. 1 First, magnesium alloy chips, which are metal bodies, graphite particles, which are C particles, a binder, and a solvent were mixed to obtain a mixture. The magnesium alloy chips used were 4 mm x 2 mm x 1 mm chips made of AZ91D alloy manufactured by STU Co., Ltd. The AZ91D alloy is a Mg-based alloy containing 9 mass% Al and 1 mass% Zn. The binder used was "Paraffin Wax 115" manufactured by Nippon Seiro Co., Ltd. The melting point of Paraffin Wax 115 was 48°C. Furthermore, 35 mL of isopropanol was used as the solvent per 4.5 g of binder.

[0084] Next, the mixture was heated to obtain a dried product. The obtained dried product was then stirred. After that, the stirred dried product was further heated and then stirred three times. For stirring, a method of shaking the container containing the dried product was used.

[0085] Next, the stirred dried body was subjected to a degreasing treatment. As a result, at least a portion of the binder was removed to obtain a material for thixotropic molding. In the obtained material for thixotropic molding, almost the entire surface of the magnesium alloy chips was covered with graphite particles. The manufacturing conditions in the above manufacturing method are shown in Table 1. In Table 1, the amount of C particles added is the ratio of the mass of the added C particles to the total mass of the magnesium alloy chips and C particles. Also, the amount of binder added is the ratio of the mass of the added binder to the total mass of the material for thixotropic molding.

[0086] 5.2. Samples No. 2 to 4 A thixomolding material was obtained in the same manner as Sample No. 1, except that the production conditions were changed as shown in Table 1.

[0087] 5.3. Sample No. 5 A thixomolding material was obtained in the same manner as Sample No. 1, except that the graphite particles and binder were not used.

[0088] 5.4. Samples No. 6-8 A thixomolding material was obtained in the same manner as Sample No. 1, except that the production conditions were changed as shown in Table 1.

[0089] 5.5. Sample No. 9 A thixomolding material was obtained in the same manner as sample No. 1, except that carbon black was used instead of the graphite particles.

[0090] 5.6. Samples No. 10 to 13 A thixomolding material was obtained in the same manner as Sample No. 1, except that the production conditions were changed as shown in Table 1.

[0091] 5.7. Sample No. 14 A thixomolding material was obtained in the same manner as Sample No. 1, except that graphite particles were used while no binder was used.

[0092] In Table 1, among the thixomolding materials of each sample number, those that correspond to the present invention are labeled "Examples," and those that do not correspond to the present invention are labeled "Comparative Examples."

[0093] 6. Evaluation of thixotropic molding materials 6.1. Amount of C particles after degreasing For each sample number of the thixomolding material, the amount of C particles after degreasing was calculated by the following method.

[0094] First, the mass M1 of the thixotropic molding material was measured. Since the thixotropic molding material had been degreased, the remaining binder was considered to be almost zero and was not taken into account in the calculation. Next, the thixotropic molding material was immersed in acetone and washed with an ultrasonic cleaner for 10 minutes. This allowed the adhering C particles to fall off and only the magnesium alloy chips to be extracted. Next, the washed magnesium alloy chips were removed from the acetone and dried, after which the mass M2 was measured.

[0095] The mass fraction of C particles relative to the magnesium alloy chips, calculated by (M1-M2) / M1 x 100, was taken as the amount of C particles after degreasing [%]. The calculation results are shown in Table 1.

[0096] 6.2.C particle adhesion rate The amount of C particles after degreasing was divided by the amount of C particles added to calculate the adhesion rate of C particles. The calculation results are shown in Table 1.

[0097] 6.3.Amount of binder after degreasing For each sample number of the thixomolding material, the amount of binder after degreasing was calculated by the following method.

[0098] First, the thermogravimetric change of one pellet of thixotropic molding material was measured in the temperature range of 50 to 450°C using a Mettler Toledo TGA / DSC 1LF. The temperature was increased at a rate of 10°C / min under atmospheric conditions while air was flowed in at a flow rate of 30mL / min. When the weight change per unit time dropped to 0.03% by weight or less, it was determined that debinding was complete, and the weight loss from 50°C to the completion of debinding was calculated. The calculated weight loss was taken as the amount of binder after debinding. The calculation results are shown in Table 1.

[0099] [Table 1]

[0100] As shown in Table 1, in the thixomolding material corresponding to the examples, although the amount of binder was reduced to a minimum by degreasing, it was found that the C particles adhered at a sufficient adhesion rate.

[0101] 7. Manufacturing of thixotropic moldings 7.1. Sample No. 15 The thixomolding material of Sample No. 1 was put into an injection molding machine to obtain a thixomolded body of Sample No. 15. The injection molding machine used was a magnesium injection molding machine JLM75MG manufactured by The Japan Steel Works, Ltd.

[0102] 7.2. Samples No. 16 to 28 A thixotropic molding was obtained in the same manner as in Sample No. 15, except that the production conditions were changed as shown in Table 2.

[0103] 8. Analysis of thixotropic moldings 8.1.Cross-section observation The thixotropic molded bodies of each sample number were cut and the cut surfaces were observed under an optical microscope. FIG. 5 shows an image of the cut surface of the thixotropic molded body corresponding to the example, observed under an optical microscope. In FIG. 5, dark-colored particle parts and light-colored matrix parts are observed. Most of the particle parts have a relatively large aspect ratio and are elongated. The average aspect ratios of the particle parts thus obtained are shown in Table 2.

[0104] 8.2.C Content The C content of each thixotropic molded body of sample No. was measured by elemental analysis. The measurement results are shown in Table 2.

[0105] 9. Evaluation of thixotropic moldings 9.1. Formability The thixotropic moldings of each sample number were observed, and the molding state of the thixotropic moldings was evaluated based on the fluidity of the molten metal and the presence or absence of internal defects due to blowholes or air entrapment. Specifically, those with poor fluidity or many internal defects were rated as "NG," and those with relatively few such defects were rated as "OK." The evaluation results are shown in Table 2.

[0106] 9.2. Dispersibility of particle part The dispersibility of the particles was evaluated from the observation images of the thixotropic moldings of each sample No. Specifically, those in which significant aggregation of the particles was observed were rated as "NG," and those in which no such aggregation was observed were rated as "OK." The evaluation results are shown in Table 2.

[0107] 9.3.Thermal Conductivity The thermal conductivity was measured for the thixotropic molded body of each sample No. The measurement results are shown in Table 2.

[0108] 9.4.Tensile strength The tensile strength was measured for the thixotropic molded bodies of each sample No. Specifically, test pieces conforming to the JIS standard were formed from the thixotropic molded bodies, and the tensile strength was measured at 25°C using a tensile tester. The measurement results were evaluated against the following evaluation criteria.

[0109] A: Relatively high tensile strength B: Tensile strength is relatively high C: Relatively low tensile strength The evaluation results are shown in Table 2.

[0110] [Table 2]

[0111] As is clear from Table 2, it was confirmed that the thixotropic molded bodies corresponding to the Examples had higher thermal conductivity than the thixotropic molded bodies corresponding to the Comparative Examples. Also, it was confirmed that when the C content was too low, the thermal conductivity could not be increased sufficiently, while when the C content was too high, the moldability was poor and the mechanical properties of the thixotropic molded body were low.

[0112] Furthermore, in the comparative example in which no binder was added during the production of the thixotropic molding material, the thermal conductivity of the thixotropic molding could not be increased. The reason for this is that the C particles fell off the magnesium alloy chips and could not be sufficiently dispersed. [Explanation of symbols]

[0113] Reference Signs List 1... injection molding machine, 2... mold, 5... hopper, 6... heater, 7... heating cylinder, 8... screw, 9... nozzle, 10... thixomolding material, 11... metal body, 12... coating part, 13... adhesive part, 14... C particles, 100... thixomolded body, 200... matrix part, 300... particle part, A1... long axis, A2... short axis, Cv... cavity, S102... preparation process, S104... drying process, S106... mixing process, S108... degreasing process

Claims

1. A metal body mainly composed of Mg, A coating portion adhering to the surface of the metal body and containing C particles mainly composed of C, An adhesive portion that adheres the metal body and the coating portion and contains a binder made of an organic material, having, The mass fraction of the C particles in the total mass of the metal body and the C particles is 5.0% by mass or more and 40.0% by mass or less, in the form of pellets or chips, A thixotropic molding material characterized in that the average particle size is 0.5 mm or more and 10 mm or less.

2. The thixotropic molding material according to claim 1, wherein the binder contains waxes.

3. The thixotropic molding material according to claim 1 or 2, wherein the C particles are graphite particles.

4. The thixotropic molding material according to any one of claims 1 to 3, wherein the average particle size of the C particles is 1 μm or more and 100 μm or less.

5. The thixotropic molding material according to any one of claims 1 to 4, wherein the content of the binder is 0.001% by mass or more and 0.200% by mass or less.

6. The thixotropic molding material according to any one of claims 1 to 5, wherein the coating portion contains the C particles adhered in multiple layers.

7. A preparation step of preparing a mixture containing a metal body mainly composed of Mg, C particles mainly composed of C, a binder made of an organic material, and a solvent, A stirring step of stirring the mixture, A degreasing step of heating the stirred mixture to remove at least a part of the binder contained in the mixture to obtain a thixotropic molding material, having, The mass fraction of the C particles in the total mass of the metal body and the C particles is 5.0% by mass or more and 40.0% by mass or less, The content of the binder in the thixotropic molding material is 0.001% by mass or more and 0.200% by mass or less, The thixotropic molding material has the metal body, a coating portion adhering to the surface of the metal body and containing the C particles, and an adhesive portion that adheres the metal body and the coating portion and contains the binder, A method for producing a thixotropic molding material, characterized in that the thixotropic molding material is in the form of pellets or chips and has an average particle size of 0.5 mm or more and 10 mm or less.

8. The method for producing a thixotropic molding material according to claim 7, further having a drying step provided between the preparation step and the stirring step to dry the mixture.

9. The method for manufacturing a thixotropic molding material according to claim 8, wherein the drying step and the stirring step are repeated.

10. A matrix part mainly composed of Mg, A particle part mainly composed of C, dispersed in the matrix part, having, wherein the average aspect ratio of the particle part is 2.0 or more and 20.0 or less, and the thixotropic molded body is characterized in that the content of C is 5.0% by mass or more and 40.0% by mass or less.

11. The thixotropic molded body according to claim 10, having a thermal conductivity of 53 W / (m·K) or more.

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