Method for manufacturing molds and foams

Abstract

In the molding process, the internal pressure of the cavity is moderately reduced. [Solution] The mold 10 has a cavity 10a formed by a first recess 22 of the first mold 20 and a second recess 32 of the second mold 30, and is used to mold a foam. The first mold 20 has a first parting surface 28 that extends in a direction intersecting the mold opening direction of the mold 10, connected to a first mold side surface 26 which has a draft angle. The second mold 30 has a second parting surface 38 that extends in a direction intersecting the mold opening direction of the mold 10, connected to a second mold side surface 36 which has a draft angle. The mold 10 includes a cavity 12 provided between the first parting surface 28 and the second parting surface 38, and a communication part 14 provided between the first parting surface 28 and the second parting surface 38, which connects the cavity 10a and the cavity 12.

Description

Technical Field

[0001] This invention relates to a molding die and a method for manufacturing a foam.

Background Art

[0002] For example, there is a method of forming a foam by heating and pressurizing a molding die containing a thermoplastic resin containing a foaming agent and simultaneously releasing the pressure and opening the molding die to expand the thermoplastic resin with the foaming agent (see, for example, Patent Document 1). Such a molding method has the advantages that it is easy to control the cell diameter and it is easy to obtain a foam with low density and high strength.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since bubbles are affected by the internal pressure of the molding die, it is conceivable to lower the internal pressure of the molding die by appropriately discharging the gas generated during molding to the outside of the molding die. However, since the molten resin leaks out of the molding die together with the gas, if the sealing property of the parting surface is improved as a countermeasure, the gas cannot escape, so the internal pressure of the molding die cannot be lowered.

[0005] In view of the above problems in the prior art, the present invention has been proposed to preferably solve these problems, and an object thereof is to provide a molding die capable of appropriately lowering the internal pressure of a cavity.

Means for Solving the Problems

[0006] A first aspect of the molding die according to the present invention is a molding die having a cavity formed by a first recess of a first mold and a second recess of a second mold, and for forming a foam, The first mold has a first parting surface that extends in a direction intersecting the mold opening direction of the molding die, connected to the first mold side surface which is provided with a draft angle. The second mold extends in a direction intersecting the mold opening direction of the molding die, connected to the side surface of the second mold which has a draft angle, and has a second parting surface that faces the first parting surface when the molding die is closed. A cavity is provided between the first parting surface and the second parting surface, The gist of the invention is that it includes a communication portion provided between the first parting surface and the second parting surface, which connects the cavity and the void.

[0007] A second embodiment of the mold according to the present invention is, in the first embodiment, The first parting surface and the second parting surface have a sealing portion provided outside the cavity beyond the void, The sealing portion may have better sealing properties than the communicating portion.

[0008] A third aspect of the mold according to the present invention is, in the second aspect, The sealing portion may be a projection provided on one of the first parting surface and the second parting surface, which bites into the other.

[0009] A fourth aspect of the mold according to the present invention is, in any one of the first, second, and third aspects, The volume of the cavity may be 2% or more of the volume of the cavity.

[0010] A fifth aspect of the mold according to the present invention is, in any one of the first, second, third, and fourth aspects, The foam may be a cross-linked polyolefin foam.

[0011] One aspect of the method for producing foam according to the present invention is: The gist is that a foamed material with a volume more than 98% of the cavity volume is placed in any one of the molding dies of the first aspect, the second aspect, the third aspect, the fourth aspect, and the fifth aspect, heated and pressurized, and then the molding die is opened to expand the foamed material to obtain a foam.

Advantages of the Invention

[0012] According to the molding die of the present invention, the internal pressure of the cavity can be appropriately reduced. According to the method for manufacturing a foam of the present invention, the internal pressure of the cavity can be appropriately reduced.

Brief Description of the Drawings

[0013] [Figure 1] It is a cross-sectional view showing the molding die according to the embodiment. [Figure 2] It is a cross-sectional view showing the first die according to the embodiment. [Figure 3] It is a plan view showing the first die according to the embodiment. [Figure 4] It is a cross-sectional view showing the second die according to the embodiment. [Figure 5] It is a bottom view showing the second die according to the embodiment. [Figure 6] It is a cross-sectional view for explaining the manufacturing process of a foam using the molding die according to the embodiment. [Figure 7] It is a graph showing the result of measuring the change in the internal pressure of the cavity.

Embodiments for Carrying Out the Invention

[0014] Next, the molding die and the method for manufacturing a foam according to the present invention will be described below with reference to the accompanying drawings by giving preferred embodiments. Note that the embodiments and drawings described below are examples of a part of the embodiments of the present invention, and are not used for the purpose of limiting to these configurations, and can be appropriately changed without departing from the gist of the present invention.

[0015] As shown in FIG. 1, the mold 10 according to the embodiment is used for molding the foam 40 (see FIG. 6(c)), and includes a first mold 20 and a second mold 30 that forms a cavity 10a between the first mold 20 when the mold is closed. The cavity 10a is formed by a first recess 22 of the first mold 20 and a second recess 32 of the second mold 30. In the mold 10 according to the embodiment, when the mold is closed, the second mold 30 is disposed above the first mold 20, and the second mold 30 moves relatively in the vertical direction with respect to the first mold 20 to close or open the mold. That is, in the mold 10 of the embodiment, the vertical direction is the mold opening direction. The second recess 32 according to the embodiment has a shape that is vertically symmetric with the first recess 22. Note that the mold 10 of the embodiment is exemplified as one for obtaining a rectangular parallelepiped foam 40.

[0016] Examples of the foam 40 include polyurethane-based foams and olefin-based foams, and are not particularly limited. However, it is suitable for a crosslinked polyolefin-based foam that is crosslinked by heating the foam material 50 (see FIG. 6(a)) in the mold 10 and expands by opening the mold 10. Further, the expansion ratio of the foam 40 is, for example, preferably in the range of 5 to 30 times.

[0017] As shown in FIGS. 2 and 3, the first mold 20 has a rectangular first mold bottom surface 24 and a first mold side surface 26 provided with a draft, and includes a first recess 22 that forms the cavity 10a. Further, the first mold 20 has a first parting surface 28 that extends in a direction orthogonal to the mold opening direction of the mold 10 (hereinafter simply referred to as the mold opening direction) along the first mold side surface 26. The first mold bottom surface 24 of the embodiment is a flat plane that extends horizontally when placed in a horizontal location. The first recess 22 has a first mold side surface 26 that extends in a direction intersecting the first mold bottom surface 24 from each of the four sides of the first mold bottom surface 24, and the four sides of the first mold bottom surface 24 are surrounded by four first mold side surfaces 26. In the first mold 20, the first parting surface 28 is provided so as to surround the entire outer periphery of the first recess 22.

[0018] As shown in Figures 4 and 5, the second mold 30 has a rectangular second mold bottom surface 34 and a second mold side surface 36 with a draft angle, and is equipped with a second recess 32 that forms a cavity 10a. The second mold 30 also has a second parting surface 38 that extends in a direction perpendicular to the mold opening direction, connected to the second mold side surface 36. The first mold bottom surface 24 in this embodiment is a flat plane that extends horizontally when placed on a horizontal surface. The second recess 32 has second mold side surfaces 36 that extend from each of the four sides of the second mold bottom surface 34 in a direction intersecting the second mold bottom surface 34, and the four sides of the second mold bottom surface 34 are surrounded by the four second mold side surfaces 36. The second parting surface 38 faces the first parting surface 28 when the mold 10 is closed (see Figure 1). At this time, a part of the first parting surface 28 and the second parting surface come into contact. Furthermore, in the second type 30, the second parting surface 38 is provided so as to surround the entire outer circumference of the second recess 32.

[0019] The draft angles of the first mold side 26 and the second mold side 36 are not particularly limited, as they can be changed depending on the type of foam, the foaming ratio of the foam 40, and the dimensions of the foam 40 such as its thickness. However, it is generally preferable to make it smaller than 90°, for example, setting it in the range of 45° to 80°. As the draft angle decreases (closer to the horizontal direction), the foam 40 becomes easier to remove from the first mold 20, while the excess portion 42 of the resulting foam 40 (see Figure 6(d)) increases. As the draft angle increases (closer to the vertical direction), the foam 40 becomes more difficult to remove from the first mold 20, while the excess portion 42 of the resulting foam 40 can be reduced.

[0020] As shown in Figure 1, the mold 10 includes a cavity 12 provided between a first parting surface 28 and a second parting surface 38, and a communication portion 14 provided between the first parting surface 28 and the second parting surface 38, which connects the cavity 10a and the cavity 12. The mold 10 also has a sealing portion 16 provided between the first parting surface 28 and the second parting surface 38, which is located outside the cavity 10a beyond the cavity 12.

[0021] As shown in Figure 1, the cavity 12 according to this embodiment is formed when the mold 10 is closed by a first groove 12a recessed from the first parting surface 28 and a second groove 12b recessed from the second parting surface 38. As shown in Figure 3, the first groove 12a is a groove shape that extends along the edge of the first parting surface 28 on the side of the first mold 26. The extension dimension of the first groove 12a may be shorter than the extension dimension of the edge, but it is preferable to make the extension dimension of the first groove 12a greater than or equal to the extension dimension of the edge, as this allows the foaming gas to escape from the cavity 10a in a balanced manner. In this embodiment, the first groove 12a is the same length as or approximately the same length as the edge of the first parting surface 28 on the side of the first mold 26. That is, the first recess 22 is surrounded by the first groove 12a, except for the outer position of the corner of the first recess 22 on the first parting surface 28. The first recess 22 may be surrounded by the first groove 12a, including the outer position of the corner of the first recess 22 on the first parting surface 28. The cross-sectional shape of the first groove 12a can be an arc shape such as a semicircle, a polygon shape such as a triangle or a square, and in this embodiment, the cross-sectional shape of the first groove 12a is a square (see Figure 2).

[0022] As shown in Figure 5, the second groove 12b is a groove shape that extends along the edge of the second parting surface 38 on the side of the second mold side 36. The extended dimension of the second groove 12b may be shorter than the extended dimension of the edge, but it is preferable to make the extended dimension of the second groove 12b greater than or equal to the extended dimension of the edge, as this allows the foaming gas to escape from the cavity 10a in a balanced manner. In the embodiment, the second groove 12b is the same length as or approximately the same length as the edge of the second parting surface 38 on the side of the second mold side 36. That is, the second recess 32 is surrounded by the second groove 12b, except for the outer position of the corner of the second recess 32 on the second parting surface 38. The second recess 32 may be surrounded by the second groove 12b, including the outer position of the corner of the second recess 32 on the second parting surface 38. The cross-sectional shape of the second groove 12b can be an arc shape such as a semicircle, or a polygon shape such as a triangle or a square. In this embodiment, the cross-sectional shape of the second groove 12b is a square (see Figure 4). In this embodiment, the first groove 12a and the second groove 12b are formed in a vertically symmetrical shape, and when the mold 10 is closed, the opening of the first groove 12a and the opening of the second groove 12b align. Note that if the cavity 12 is not provided at the outer position of the corners of the first recess 22 and the second recess 32 as in this embodiment, it becomes easier to remove burrs formed in the cavity 12.

[0023] The volume of the cavity 12 is preferably 2% or more of the volume of the cavity 10a. More preferably, the volume of the cavity 12 is in the range of 2% to 10% of the volume of the cavity 10a. Setting the volume of the cavity 12 to 2% or more of the volume of the cavity 10a allows for an appropriate release of foaming gas from the cavity 10a. If the volume of the cavity 12 is less than 2% of the volume of the cavity 10a, the effect of releasing foaming gas from the cavity 10a decreases, making it difficult to obtain foam 40 of the desired quality.

[0024] As shown in Figure 1, the communication portion 14 has one end that connects to the cavity 10a and the other end that connects to the cavity portion 12, allowing the flow of foaming gas from the cavity 10a to the cavity portion 12. The communication portion 14 is formed in a groove shape that extends along the edge of the first parting surface 28 on the side of the first mold side 26 (see Figure 3). The extended length of the communication portion 14 may be shorter than the extended length of the edge, but it is preferable that the extended length of the communication portion 14 be the same as the extended length of the edge, as this allows the foaming gas to escape from the cavity 10a in a balanced manner. In this embodiment, the communication portion 14 is the same length as or approximately the same length as the edge of the first parting surface 28 on the side of the first mold side 26. That is, the first recess 22 is surrounded by the communication portion 14, except for the outer position of the corner of the first recess 22 on the first parting surface 28. In this embodiment, the second parting surface 38 does not have a recess corresponding to the communication portion 14, and when the mold 10 is closed, the second parting surface 38 covers the upper side of the communication portion 14.

[0025] The spacing D1 in the mold opening direction at the connecting section 14 should be set to a range of, for example, 0.1 mm to 1.0 mm. In particular, when the mold 10 is used to manufacture a cross-linked polyolefin foam, it is preferable that the spacing D1 in the mold opening direction at the connecting section 14 be within the above range, as this allows for the flow of foaming gas while suppressing the flow of foam material 50. Furthermore, the spacing D1 in the mold opening direction at the connecting section 14 should be set to be narrower than the spacing D2 in the mold opening direction at the cavity section 12. The length W from the cavity 10a to the cavity section 12 at the connecting section 14 is not particularly limited, but it should be set to a range of, for example, 5 mm to 20 mm.

[0026] As shown in Figure 1, the sealing portion 16 is a projection provided on the first parting surface 28 that bites into the second parting surface 38. The sealing portion 16 is provided outside the first groove portion 12a and is positioned on the opposite side of the communication portion 14, with the first groove portion 12a in between. The sealing portion 16 extends along the edge of the first parting surface 28 on the first mold side surface 26 side and surrounds the first recess 22 (see Figure 3). The cross-sectional shape of the sealing portion 16 according to this embodiment is a roughly triangular shape that tapers as it protrudes from the first parting surface (see Figure 2). The sealing portion 16 has better sealing performance than the communication portion 14.

[0027] The manufacturing process for producing a crosslinked polyolefin foam using the mold 10 described above will now be explained. The foam material 50 is filled into the cavity 10a formed by the first recess 22 and the second recess 32 (see Figure 6(a)), and the first mold 20 and the second mold 30 are closed. The foam material 50 is a solid. The filling rate of the foam material 50 in the cavity 10a should be set to, for example, in the range of 98% to 100%. By heating and pressurizing the mold 10, the foaming agent contained in the foam material 50 is decomposed, and the crosslinking reaction proceeds, filling the cavity 10a with foam 40 before expansion containing foaming gas (see Figure 6(b)). By opening the mold 10 and releasing the pressure, the block-shaped foam 40 that has expanded according to the shape of the cavity 10a comes out from the first recess 22 and the second recess 32 (see Figure 6(c)). As shown in Figure 6(c), the sides of the foam 40 have a tapered shape that conforms to the draft angles of the first mold 20 and the second mold 30. Therefore, the excess tapered portion 42 is removed by cutting or other processes to refine the shape of the foam 40 (see Figure 6(d)). In this way, the foam material 50 is expanded by opening the mold 10 to obtain the foam 40. The mold 10 is suitable for compression molding (pressure foaming).

[0028] The foam 40, such as a cross-linked polyolefin foam, obtained by compression molding (pressure foaming) is low-density and high-strength, and the bubble diameter can be controlled to be uniform within the product. Here, the control of the bubble diameter depends on the resin viscosity, the decomposition rate of the foaming agent, the clamping pressure, etc., and since these factors are affected by the foaming pressure (internal pressure) of the cavity, the foaming pressure can be adjusted by releasing the foaming gas from the cavity 10a. The higher the foaming pressure, the smaller the bubble diameter, but there is a tendency for unintended large bubbles to be scattered, so sometimes the foaming pressure is lowered than conventional methods to increase the bubble diameter. However, if communication holes that communicate with the outside are provided in the parting surfaces 28, 38 to lower the foaming pressure, the foam material 50 will leak out of the mold 10 along with the foaming gas. If the sealing performance of the parting surfaces 28, 38 is improved to suppress leakage, the foaming gas will not escape. Thus, with conventional molding dies, it is difficult to adjust the foaming pressure by releasing the foaming gas, which tends to result in large variations in bubble diameter.

[0029] As described above, the mold 10 according to the embodiment includes a cavity 12 provided between a first parting surface 28 and a second parting surface 38, and a communication portion 14 provided between the first parting surface 28 and the second parting surface 38, which connects the cavity 10a and the cavity 12. Therefore, foaming gas generated during molding can be released from the cavity 10a to the cavity 12 via the communication portion 14. By releasing foaming gas from the cavity 10a, the mold 10 can adjust the foaming pressure inside the cavity 10a to an appropriate level, thereby enabling the production of a high-quality foam 40 with uniform bubble diameters. Similarly, the method for manufacturing the foam 40 using the mold 10 allows for the adjustment of the foaming pressure inside the cavity 10a during molding, thereby enabling the production of a high-quality foam 40 with uniform bubble diameters.

[0030] When the foaming gas is released from the cavity 10a, there is a risk that the foaming material 50 may also leak out. However, by retaining the foaming material 50 in the cavity 12, the possibility of the foaming material 50 leaking out to the outside of the mold 10 can be reduced. In addition, by retaining the foaming material 50 in the cavity 12, the internal pressure of the cavity 10a can be adjusted. Since the foaming material 50 will not leak out of the cavity 10a into the cavity 12 in an amount exceeding the volume of the cavity 12, the amount of foaming material 50 leaking out of the cavity 10a can be controlled by the volume of the cavity 12. As a result, leakage of foaming material 50 outside the mold 10 before heating and pressurizing can be suppressed, the amount of foaming material 50 that does not become foam 40 can be reduced, and the yield of foam 40 obtained from the foaming material 50 filled in the cavity 10a can be improved. The mold 10 does not use special components or materials such as pumps or valves, but has a simple structure consisting of a cavity 12 and a connecting section 14 that can control the release of foaming gas and the leakage of foam material 50. Since the cavity 12 is formed between the parting surfaces 28 and 38, the inflow of oxygen into the cavity 12 during molding is suppressed, and the crosslinking reaction of the foam material 50 that flows into the cavity 12 can proceed. Therefore, it is easy to remove the residue formed from the foam material 50 that flows into the cavity 12 from the cavity 12.

[0031] The mold 10 has a sealing portion 16 located outside the cavity 10a, beyond the cavity 12, between the first parting surface 28 and the second parting surface 38. Because the sealing portion 16 is located outside the cavity 12, the possibility of the foam material 50 flowing into the cavity 12 leaking out of the mold 10 is reduced. Furthermore, the sealing portion 16 outside the cavity 12 suppresses the inflow of oxygen into the cavity 12 during molding, allowing the crosslinking reaction of the foam material 50 into the cavity 12 to proceed. Therefore, it is easier to remove residue formed from the foam material 50 into the cavity 12. Moreover, because the sealing portion 16 has a higher sealing performance than the communication portion 14, foaming gas can easily escape from the cavity 10a into the cavity 12. If the sealing portion 16 is a projection provided on the first parting surface 28 that bites into the second parting surface 38, a linear seal is formed where the first parting surface 28 and the second parting surface 38 come into contact linearly, thereby improving the sealing performance between the first parting surface 28 and the second parting surface 38 by the sealing portion 16.

[0032] (Example test) The change in internal pressure of a cavity was measured when a cross-linked polyolefin foam was manufactured using a mold having a cavity formed by a first recess and a second recess with a vertically symmetrical shape. The results are shown in Figure 7.

[0033] The construction of the sealing section and the manufacturing conditions, such as heating of the mold, are the same in Test Examples 1 to 5. The cavity volume is also the same in Test Examples 1 to 5. The connecting section has a spacing of 0.5 mm in the mold opening direction, and the length from the cavity to the hollow section in the connecting section is 5 mm. Test Example 1 involves filling a cavity formed with a volume of 4% of the cavity's total volume with 800g of foam material. In Test Example 2, 810g of foam material was filled into a cavity formed to a volume of 4% of the cavity's total volume. When the volume of the cavity is calculated considering the amount of foam material used, it becomes 2.75%. In Test Example 3, 820g of foam material was filled into a cavity formed to a volume of 4% of the cavity's total volume. When the volume of the cavity is calculated considering the amount of foam material used, it becomes 1.5%. Test Example 4 involves filling a cavity formed with a volume of 1% of the cavity's total volume with 800g of foam material. Test Example 5 involves filling a mold cavity without voids or connecting sections with 800g of foam material.

[0034] As shown in Figure 7, it was found that test examples 1 to 4, which have cavities and connecting sections, reduced the internal pressure of the cavity compared to test example 5, which does not have cavities or connecting sections. In particular, in test examples 1 and 2, where the volume of the cavities was 2% or more, it was found that a moderate reduction in the internal pressure of the cavity resulted in foam with smaller and more uniform bubble diameters, improving the quality of the resulting foam.

[0035] In the mold cavity used in Test Example 1, the obtained foam was compared under three conditions: when the same volume of foam material as the cavity was filled (100% foam material filling rate), when 98% of the cavity's volume was filled (98% foam material filling rate), and when 96% of the cavity's volume was filled (96% foam material filling rate). It was found that good quality foam was obtained at 100% and 98% filling rates, but at 96% filling rate, the surface of the resulting foam may be rough. Thus, it is desirable to fill the cavity with foam material at 98% or higher.

[0036] (Example of change) The present invention is not limited to the aforementioned matters, but may also be applied as follows, for example. Furthermore, the present invention is not limited to the embodiments and the following specific examples of modifications. (1) In the embodiments described above, the first recess of the first mold and the second recess of the second mold are vertically symmetrical in shape, but the invention is not limited to this, and the first recess and the second recess may have different shapes. Furthermore, in a mold for forming a cross-linked polyolefin foam, the second mold may not have a second recess, and the first recess may be closed by the second mold. Moreover, in a mold for forming a cross-linked polyolefin foam, the second mold may have a protrusion, and the protrusion may be positioned to correspond to the first recess and close the first recess. (2) In the embodiment, the first parting surface and the second parting surface extend in a direction perpendicular to the mold opening direction of the molding die, but the embodiment is not limited to this, and the first parting surface and the second parting surface may extend in a direction that intersects the mold opening direction of the molding die at an angle. (3) In this embodiment, a cavity is formed by the first groove of the first type and the second groove of the second type, but the invention is not limited to this, and a cavity may be formed by grooves formed in either the first type or the second type alone. (4) In this embodiment, the communication portion is formed by a recess formed in the first mold, but the invention is not limited to this, and the communication portion may be formed by recesses formed in both the first mold and the second mold. (5) The configuration of the sealing portion is not limited to the embodiment. [Explanation of symbols]

[0037] 10 Molding mold, 10a Cavity, 12 Hollow section, 14 Connecting section, 16 Seal section, 20 Type 1, 22 First recess, 26 Type 1 side, 28 First parting surface, 30 Type 2, 32 Second recess, 36 Type 2 side, 38 Second parting surface, 40 Foam, 50 Foam material

Claims

1. A mold for molding a foam, having a cavity formed by a first recess of a first type and a second recess of a second type, The first mold has a first parting surface that extends in a direction intersecting the mold opening direction of the molding die, connected to the first mold side surface which is provided with a draft angle. The second mold extends in a direction intersecting the mold opening direction of the molding die, connected to the side surface of the second mold which has a draft angle, and has a second parting surface that faces the first parting surface when the molding die is closed. A cavity is provided between the first parting surface and the second parting surface, A molding die comprising a communication portion provided between the first parting surface and the second parting surface, which connects the cavity and the hollow portion.

2. The first parting surface and the second parting surface have a sealing portion provided outside the cavity beyond the void, The molding die according to claim 1, wherein the sealing portion has better sealing performance than the communicating portion.

3. The molding die according to claim 2, wherein the sealing portion is a projection provided on one of the first parting surface and the second parting surface and bites into the other.

4. The mold according to claim 1, wherein the volume of the cavity is 2% or more of the volume of the cavity.

5. The mold according to claim 1, wherein the foam is a crosslinked polyolefin foam.

6. A method for producing a foam, comprising: filling a mold according to any one of claims 1 to 5 with a foam material in an amount greater than 98% of the cavity volume, heating and pressurizing it, and then opening the mold to expand the foam material and obtain a foam.

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