Core for resin molding and resin molding method using the same

Abstract

To provide a core made of a material that can secure hardness and capable of being used regardless of a kind of resin, thereby realizing a resin mold having a hollow structure at low cost and with high precision.SOLUTION: An alloy-made core 11 is a core made of corrosive magnesium alloy, the core being to form a hollow part 32 in a resin molded body 30 by being introduced into a mold 21 that molds resin, where the alloy-made core 11 itself includes a core hollow part 12. And the alloy-made core includes an inflow port 13 to the core hollow part 12 in a non-contact part with resin 23 to be charged.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing a resin molded product having a hollow portion and a core used in the production. [Background technology]

[0002] Injection molding is the most commonly used method for molding resin products. Injection molding involves injecting heated and molten resin into a mold, cooling and hardening it, and then removing it from the mold to create a molded resin product. If you want to create a space inside this resin product, you can create a resin product in which the part with the core is not filled with resin by placing a core in the mold and then injecting the resin. However, if left as is, the core will be attached to the product, so this core must be removed after molding. Generally, sand that has good crumbling properties (casting sand) is used for the core. However, because casting sand is inherently prone to crumbling, it is difficult to make a core with a delicate shape, and there are limitations to the shape of the hollow part that can be formed.

[0003] Patent Document 1 discloses a method in which the core is formed from a water-soluble resin such as polyvinyl alcohol and the resin to be injection molded is a water-insoluble resin such as nylon resin, and the core is removed after molding by dissolving it with a medium such as water.

[0004] Furthermore, Patent Document 2 reports that when a magnesium alloy or aluminum alloy is used for the core (water-soluble core) and it is manufactured by heat spraying or sintering to form it into a mold with high porosity, the water-soluble core quickly dissolves through the pores.

[0005] Patent Document 3 presents an example of a magnesium alloy that can improve the corrosion rate by containing aluminum and copper, while Patent Document 4 also describes an example of a magnesium alloy that is susceptible to corrosion and contains nickel and copper in addition to aluminum and manganese. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-296748 [Patent Document 2] Japanese Patent Application Publication No. 10-311246 [Patent Document 3] International Publication No. 2021 / 075552 [Patent Document 4] International Publication No. 2017 / 168696 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the water-soluble resin described in Patent Document 1 is used for the core, there is a risk that the core will be destroyed due to insufficient strength if high pressure is applied when injecting the resin during injection molding. Also, the relationship between the resin used in the molded product and the water-soluble resin limits the resins that can be used.

[0008] As described in Patent Document 2, when a core with high porosity is formed from a magnesium alloy or an aluminum alloy, there is a problem that the surface of the molded product becomes rough due to the unevenness formed on the surface of the core. In addition, there is also a problem that the treatment to increase the porosity is time-consuming and expensive.

[0009] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a core that is made of a material that can ensure strength and can be used regardless of the type of resin, thereby enabling hollow resin molding to be achieved at low cost and with high precision. [Means for solving the problem]

[0010] In order to solve the above problems, A core for forming a hollow portion in a resin molded body by being introduced into a mold for resin molding, Made of corrodible magnesium alloy, The core itself has a core hollow portion, The above problem was solved by using an alloy core that has an inlet to the hollow portion of the core in a portion that does not come into contact with the injected resin.

[0011] That is, by using a magnesium alloy that corrodes in an aqueous environment, the strength of the core can be ensured. Meanwhile, a hollow core is provided inside the core, and an inlet to the hollow core is provided at a location (non-contact portion) that does not come into contact with the portion into which the resin is injected during injection molding, etc. This prevents the resin from entering the hollow core during injection molding, and the resin is removed from the entire outer shape of the core, so that the outer shape of the core becomes the hollow portion for the resin molded body. When an aqueous solvent such as water is poured into the hollow core from the inlet of this core, decomposition begins throughout the entire hollow core, even if fine pores are not formed on the surface of the core, and the core can be decomposed and removed quickly.

[0012] In the present invention, as the corrosive magnesium alloy constituting the alloy core, a magnesium alloy containing aluminum, copper, or both of them, or a magnesium alloy containing aluminum, manganese, and at least one of nickel and copper can be adopted. Magnesium alloys containing aluminum, copper, or nickel can increase the corrosion rate in water depending on the content, and can realize the decomposition and removal of the core at high speed.

[0013] This invention can employ a method for manufacturing a resin molded body, in which the above-mentioned alloy core is introduced into a mold for resin molding, and resin is injected between the outer periphery of the alloy core and the mold while preventing resin from entering the inlet.

[0014] Furthermore, in the present invention, a method for removing the alloy core can be employed in which, after the resin molded body is produced, a decomposition liquid is introduced from the inlet to cause decomposition to proceed from the inner surface of the hollow portion of the core. Effect of the Invention

[0015] According to the present invention, a resin molded article having a smooth hollow portion without unnecessary unevenness in the portion that was in contact with the core can be produced at low cost. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an embodiment of an alloy core according to the present invention; [Diagram 2] A diagram showing the state in which the alloy core shown in Figure 1 is introduced into a die. [Diagram 3] Cross-sectional view showing resin being inserted between the die and alloy core [Figure 4] Cross-sectional view showing the resin part removed together with the alloy core [Diagram 5] A cross-sectional view showing a resin molded body including an alloy core being immersed in a dissolving solution to decompose the alloy. [Figure 6] Cross-sectional view of the alloy core after it has been completely disassembled [Figure 7] A cross-sectional view of the final resin molded body having a hollow portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The alloy core according to the present invention and the method for manufacturing a resin molded body using the same will be described in detail. The alloy core 11 is introduced into a die 21 and resin is then injected into the die 21 in order to form a hollow portion 32 therein when forming a resin molded body 30. The core is removed after the resin has solidified.

[0018] A front view of an embodiment of the alloy core 11 is shown in Fig. 1. The outer shape of this alloy core 11 corresponds to the shape of the hollow portion 32 to be formed inside the resin molded body 30. This alloy core 11 is dissolved in a dissolving liquid and removed after the resin molded body 30 is formed. For this reason, the alloy must be one that dissolves in the dissolving liquid.

[0019] The alloy core 11 according to the present invention has a core hollow 12 inside and an inlet 13 leading to the core hollow 12 from the outside. This core hollow 12 is for introducing the above-mentioned dissolving liquid into the alloy core 11 to facilitate the progress of decomposition. The core hollow 12 is preferably formed so as to occupy a portion of the alloy core 11 that is sufficiently thick. It takes time to dissolve and remove all of the thick portions, but if the core hollow 12 is formed with the alloy portion missing so that the inside is hollowed out, the portion is removed in advance even if it is not dissolved, so that the time required to completely remove the alloy core 11 can be significantly reduced. In addition, in the decomposition process, the dissolving liquid quickly fills the core hollow 12 from the inlet 13, and the dissolution of the alloy portion progresses from each part of the inner surface of the core hollow 12, so that a wide interface where the dissolution reaction occurs can be secured. This allows a sufficient decomposition rate to be ensured without forming pores or the like on the surface of the alloy core 11, and the alloy core 11 itself may be in a solid material state except for the core hollow portion 12.

[0020] However, as described later, the location where the inlet 13 is provided needs to be a non-contact area that does not come into contact with the resin injected when molding the resin molded body 30. This is to prevent the resin from entering the core hollow portion 12.

[0021] It is not necessary that the number of core hollows 12 is one and that they are all connected, and a plurality of independent core hollows 12 may be formed inside the alloy core 11. However, when there are a plurality of independent core hollows 12, it is necessary that an inlet 13 connected to each of those core hollows 12 is formed.

[0022] The dissolving liquid for dissolving the alloy core 11 is easy to handle if it is water or an aqueous solution rather than an organic solvent. However, if it is strongly acidic or strongly alkaline, depending on the type, there is a risk that it may dissolve the resin molded body 30 along with the alloy core 11, so it is preferable to use a dissolving liquid that does not dissolve the resin molded body 30. An example of an aqueous solution that accelerates the decomposition rate while minimizing the effect on the resin molded body 30 is a neutral sodium chloride aqueous solution. The inclusion of an electrolyte makes it easier to advance dissolution due to corrosion.

[0023] As an alloy that can be decomposed in such an environment, a corrosive magnesium alloy can be used. Among them, a magnesium alloy containing aluminum, copper, or both of them (first magnesium alloy) and a magnesium alloy containing aluminum, manganese, nickel, and copper (second magnesium alloy) are particularly preferable in terms of decomposition performance.

[0024] The Al content of the first magnesium alloy is preferably 7.0% by mass or more. If the Al content is too small, the fluidity during casting decreases, and the amount of Cu-Al-Mg intermetallic compounds that are easily dissolved in water is insufficient, but if the Al content is 7.0% by mass or more, sufficient fluidity and the amount of Cu-Al-Mg intermetallic compounds can be ensured. On the other hand, the Al content is preferably 13.0% by mass or less. If the Al content is too high, the amount of Cu-Al-Mg intermetallic compounds becomes excessive, and if it exceeds 13.0% by mass, the Cu-Al-Mg intermetallic compounds hinder the progress of Mg dissolution, causing a rapid decrease in the dissolution rate.

[0025] The first magnesium alloy may contain Mn. However, the Mn content is preferably less than 0.10 mass %. If the Mn content increases, Mn is contained in the Cu-Al-Mg intermetallic compound, and the Cu-Al-Mg intermetallic compound is likely to become coarse. If the Cu-Al-Mg intermetallic compound becomes coarse, the dissolution rate decreases.

[0026] The Cu content of the first magnesium alloy is preferably 4.5% by mass or more. By adding Cu, a Cu-Al-Mg intermetallic compound having a noble potential is generated in the alloy core 11. The potential difference between α-Mg and the Cu-Al-Mg intermetallic compound promotes the loss of α-Mg due to macrocell corrosion, and the dissolution rate can be improved. In a normal Mg alloy, the dissolution rate tends to decrease when the above-mentioned Al is contained, but if the Cu content is 4.5% by mass or more, the alloy core 11 can achieve a practical dissolution rate even in the above-mentioned Al content range. In particular, the Cu content is more preferably 7.0% by mass or more. If the Cu content is 7.0% by mass or more, the amount of the Cu-Al-Mg intermetallic compound increases, and it is thought that the Cu-Al-Mg intermetallic compound is easily crushed when the alloy core 11 is strained, and the Cu-Al-Mg intermetallic compound phase is made fine, making it easier to improve the dissolution rate. On the other hand, the Cu content is preferably 13.0% by mass or less. If the Cu content exceeds 13.0% by mass, coarse block-shaped Cu-Al-Mg intermetallic compounds are generated during casting, which impede the progress of Mg dissolution and reduce the effect of improving the dissolution rate due to macrocell corrosion caused by adding Cu.

[0027] The first magnesium alloy may contain elements other than the above-mentioned elements as inevitable impurities. These inevitable impurities are those that are unavoidably contained against the intention due to manufacturing problems or raw material problems. Examples of the inevitable impurities include elements such as Ag, Fe, Ca, Cd, Ga, In, Li, Mm (misch metal), Ni, Pb, Se, Si, Ti, Y, Zn, and Zr. It is preferable that the content of each element is less than 0.2 mass%, and more preferably less than 0.1 mass%. The smaller the content, the more preferable it is because uncertain factors that should be considered are eliminated, and it is particularly preferable that the content is below the detection limit.

[0028] On the other hand, the second magnesium alloy preferably has an Al content of 3.9 mass% or more, and more preferably 7.0 mass% or more. Although the addition of Al has the effect of improving strength, if the content is less than 3.9 mass%, the effect becomes insufficient. On the other hand, the Al content is preferably 14.0 mass% or less, and more preferably 13.0 mass% or less. If the content of Al is too high, deformation may occur more easily, which may reduce the strength, and if the content of Al exceeds 14.0 mass%, it may become difficult to maintain the shape of the member.

[0029] The Mn content of the second magnesium alloy is preferably 0.1% by mass or more. Mn has the effect of removing some elements contained as impurities, and if the content is too small, the dissolution rate of the decomposable Mg alloy may deviate significantly from the value adjusted by Ni and Cu described below, resulting in insufficient control. On the other hand, the Mn content is preferably 0.6% by mass or less, and more preferably 0.5% by mass or less. If the content is too high, a large amount of intermetallic compounds of Mn and Al and simple Mn precipitates, making the alloy brittle and reducing its strength.

[0030] The second magnesium alloy may contain 1.0 mass % or less of Zn. Zn has the effect of improving strength. If it exceeds 1.0 mass %, not only will the ductility become insufficient, making the forming process of the alloy core 11 itself, such as extrusion or forging, difficult, but it will also have the effect of suppressing the dissolution rate, which is not preferable. On the other hand, Zn does not have to be contained, and may be contained in a range that is included as an inevitable impurity, which will be described later.

[0031] The second magnesium alloy may contain Ni, Cu, or both. By containing a predetermined amount of Ni or Cu, the dissolution rate of the alloy in an aqueous environment can be adjusted as desired. In other words, the alloy core 11 manufactured from this second magnesium alloy can be quickly decomposed when it is no longer needed. However, although both Ni and Cu contribute to decomposability, their influences are different.

[0032] When the second magnesium alloy contains Ni, the Ni content is preferably 0.01% by mass or more. Although Ni has a greater effect on the dissolution rate than Cu, if the Ni content is less than 0.01% by mass, it is difficult to obtain the necessary dissolution effect as a corrosive magnesium alloy. On the other hand, the Ni content is preferably 7.0% by mass or less. Even if an excessive amount is contained, the dissolution rate cannot be significantly improved, and the physical properties become difficult to control. In addition, if the Ni content is too high, the burden in terms of cost becomes too large.

[0033] When the second magnesium alloy contains Cu, the Cu content is preferably 10.0 mass % or less. Even if an excessive amount of Cu is contained, the dissolution rate cannot be significantly improved and the physical properties become difficult to control.

[0034] The above-mentioned first magnesium alloy and second magnesium alloy are only examples of the alloys constituting the alloy core 11, and there are no particular limitations on the alloys as long as they can be similarly quickly dissolved in the decomposition liquid.

[0035] The method for producing the alloy core 11 from these alloys can be appropriately selected from techniques such as casting, extrusion, and forging. Any of these methods can form the core hollow 12 and the inlet 13 communicating with it. Among these, casting is a preferred technique because sand casting and die casting methods provide a high degree of freedom in size and shape, and it is easy to form the core hollow 12 that matches the shape of the alloy core 11.

[0036] The procedure for producing a resin molded body 30 having a hollow portion using such an alloy core 11 will be described with reference to the drawings. The alloy core 11, which conforms to the shape of the hollow portion 32 to be formed in the resin molded body 30, is introduced into a mold 21 having an internal shape conforming to the outer shape of the resin molded body 30 to be produced. The state of introduction into the mold 21 is shown in FIG. 2. In the embodiment shown in the figure, the inflow ports 13 open above and below the alloy core 11 are both blocked by the inner wall of the mold 21 to prevent resin from flowing in, and are non-contact portions where the resin does not come into contact. A cavity 22 is formed between the outer surface of the alloy core 11 and the inner surface of the mold 21, and molten resin 23 is injected into this cavity 22. FIG. 3 shows a cross-sectional view of the mold 21 in a state where the molten resin 23 has solidified and the resin portion 31, which will be the outer shape of the resin molded body 30 to be finally obtained, has solidified. Since the inlet 13 is located in a non-contact portion that does not come into contact with the resin 23, the resin 23 does not flow into the hollow portion 12 of the core, and the hollow portion remains hollow. A cross-sectional view of the core removed from the mold 21 is shown in Figure 4. The resin portion 31 contains the alloy core 11.

[0037] The resin molded body 30 (resin portion 31) containing the alloy core 11 thus obtained is exposed to the dissolving liquid S to decompose the alloy core 11. As an example, FIG. 5 shows the state of immersion in the dissolving liquid S. Without the inlet 13 and the core hollow portion 12, the area in contact with the decomposition liquid S is small, and it takes a certain amount of time for the alloy core 11 to decompose from the lower end to the upper end. By having the core hollow portion 12 as in the present invention, the decomposition liquid penetrates the inside at once, and the decomposition reaction progresses over the entire inner surface of the core hollow portion 12 that comes into contact with the decomposition liquid, and the decomposition of the alloy core 11 progresses at an extremely high speed. FIG. 6 shows the state after the removal of the alloy core 11 is completed. In this way, a resin molded body 30 (FIG. 7) is obtained that has a resin portion 31 with an outer shape that matches the mold 21 and has a hollow portion 32 inside where the alloy core 11 was.

[0038] In addition to simple immersion, exposure to a flowing dissolving liquid (flowing water) can further accelerate the decomposition. In a configuration with two or more inlets 13, the dissolving liquid can be poured in from one inlet 13 and withdrawn from another inlet 13, and the inner surface of the core hollow portion 12 can be continuously exposed to flowing water to further accelerate the decomposition. In addition, although not shown, electrolysis in the decomposition liquid S can further accelerate the decomposition. In this case, by passing a current so that the alloy core 11 becomes the anode and the counter electrode becomes the cathode, the magnesium alloy quickly dissolves in the decomposition liquid. [Explanation of symbols]

[0039] 11 Alloy core 12 Core hollow part 13 Inlet 21 Mold 22 Cavity 23 Resin 30 Resin molding 31 Resin part 32 Hollow part S solution

Claims

1. A core for forming a hollow portion in a resin molded body by being introduced into a mold for resin molding, Made of corrodible magnesium alloy, The core itself has a core hollow portion, An alloy core having an inlet into the hollow portion of the core at a portion that does not come into contact with the resin to be injected.

2. 2. The alloy core according to claim 1, which is made of a magnesium alloy containing aluminum, copper, or both.

3. 2. The alloy core according to claim 1, which is made of a magnesium alloy containing aluminum, manganese, and at least one of nickel and copper.

4. A method for producing a resin molded body, comprising: introducing the alloy core according to any one of claims 1 to 3 into a mold while preventing resin from entering the inlet, and injecting resin between the outer periphery of the alloy core and the mold.

5. A method for removing an alloy core, comprising introducing a decomposition liquid from the inlet into a resin molding containing the alloy core described in any one of claims 1 to 3, and causing decomposition of the alloy core from the inner surface of the core hollow portion.

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