JP2005131857A - Thermoforming mold and thermoforming method of resin sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoforming mold capable of obtaining a molded product excellent in transparency, glossiness and shaping properties without accompanying the lowering of a molding cycle or the additional consumption of energy in performing a thermoforming method. <P>SOLUTION: In the thermoforming mold for performing the thermoforming of a resin sheet so as to provide distribution in heating temperature by providing a low temperature part being a part wherein transparent surface properties are required after shaping and a high temperature part being a part wherein transparent surface properties are not required after shaping, a low temperature contact part coming into contact with the low temperature part of the resin sheet and a high temperature contact part bringing a mold into contact with the high temperature part of the resin sheet are thermally connected by a heat conductive member. Since the high and low temperature contact parts of the mold are thermally connected by the heat conductive member, the heat of the high temperature contact part can be efficiently transmitted to the low temperature contact part. Accordingly, high moldability can be held without bringing about the lowering of the molding cycle or an increase in cost by newly performing heating and a molded product excellent in transparency, glossiness and shaping properties can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, when a transparent resin sheet such as polycarbonate (PC) or polymethyl methacrylate (PMMA) is formed by a so-called thermoforming method such as vacuum forming, pressure forming, vacuum pressure forming, twin composite forming, etc., transparency The present invention relates to a thermoforming mold capable of obtaining a molded article excellent in gloss and formability with a short molding cycle and low energy consumption, and a method for thermoforming a resin sheet.

  Transparent resin is superior in impact resistance, light weight, and moldability compared to inorganic glass, so it is used in various industrial and daily necessities. For example, optical use such as camera lens and contact lens, transparency Used for building materials, automotive parts, electrical equipment parts, etc. Typical transparent resins include acrylic resins, polycarbonate resins, polyester resins, styrene resins, and cyclic olefin resins.

  A typical molding method for parts used in these applications is an injection molding method, and a molded product having excellent dimensional accuracy and appearance quality can be obtained. However, for example, if the injection molding method is applied to large parts such as building materials and automotive resin glass, a molding machine with a large clamping force is required, and the mold has a large and complicated structure, which increases costs. There is a possibility of connection.

  On the other hand, a so-called thermoforming method is required in which a resin sheet is heated and softened and then shaped using atmospheric pressure or compressed air pressure, such as vacuum forming, pressure forming, vacuum pressure forming, twin composite forming, etc. This molding method is advantageous in terms of cost in terms of the size of the molding machine and the structure and material of the mold.

  However, the dimensional accuracy is generally inferior to that of the injection molding method. On the other hand, if the heating temperature of the resin sheet is increased in order to obtain sufficient formability, the resin sheet is decomposed on the crimping surface of the mold, or due to local molding shrinkage. There is a problem that pinholes are generated, the appearance of the molded product is reduced, such as transparency and gloss, and it is difficult to obtain sufficient transparency for use in the above-described transparent application. As a measure for avoiding such problems, the heating temperature of the part where transparency is not required after molding of the resin sheet is high, the heating temperature of the part where transparency is required is set low, and the part where transparency is required It is effective to shape the material in a plastic deformation manner. In addition, the concept which performs the thermoforming of a resin sheet so that heating temperature may have distribution is shown in the schematic diagram of FIG. In FIG. 1, the mold is assumed to be a male mold used for vacuum forming.

  When this method is used, the occurrence of molding return (spring back) becomes a new problem, particularly around the low temperature heating section. That is, in the molded product having the shape shown in FIG. 2, the spring back of the bent portion indicated by the dotted line in FIG. 2 becomes a problem. As a method for reducing such spring back, partial heating by a heater embedded mold can be applied, and spring back can be reduced by an aging effect. The partial heating by the above-mentioned heater embedded mold is used for reducing the weld line in the injection molding method and shortening the molding time of a thin molded product. "Mold", JP-A-7-290540, "Plastic molded product manufacturing apparatus", JP-A-9-314610, "Injection molding method for preventing generation of weld line and mold used in this method". This method can also be applied to thermoforming, but it is disadvantageous in that it adds new heat to the mold, which can lead to lower molding cycles and energy consumption, leading to increased costs. is there. Particularly in the thermoforming of large parts, since the holding and cooling time from shaping to mold removal is long, the additional heat to the mold may cause a significant decrease in the molding cycle.

JP-A-11-138557 JP 7-290540 A JP-A-9-314610

  The present invention has been made in view of such a conventional problem, and in performing the thermoforming method, the transparency, gloss, and formability can be achieved without reducing the molding cycle and consuming additional energy. It aims at providing the shaping | molding die for thermoforming for obtaining the outstanding molded object.

  In order to solve the above-mentioned problems, the present invention does not require a resin sheet low-temperature part in which a portion requiring a transparent surface property after shaping of the resin sheet is cooled, and a transparent surface property after shaping of the resin sheet. A molding die for thermoforming a resin sheet so as to have a distribution in heating temperature by providing a high temperature portion of the resin sheet having a high temperature part, the molding die being in contact with the low temperature portion of the resin sheet Or a low temperature contact portion which is at least a part of the periphery thereof and a high temperature contact portion which is at least a part of a portion where the mold comes into contact with the high temperature portion of the resin sheet are thermally connected by a heat conductive member. A mold for thermoforming is provided.

  Further, the present invention provides a resin sheet low-temperature part in which a portion where a transparent surface property is required after shaping of the resin sheet is lowered, and a resin sheet high temperature in which a portion where the transparent surface property is not required after shaping of the resin sheet is hot. In the thermoforming method, the heater temperature is set so as to provide a portion, the resin sheet is heated and softened according to the heater temperature, and the mold for forming the resin sheet is narrowed while being vacuumed. A portion in which the mold is in contact with the low temperature portion of the resin sheet or a low temperature contact portion that is at least a part of the periphery, and a high temperature contact portion in which the mold is in contact with the high temperature portion of the resin sheet are heated. The present invention also provides a method for thermoforming a resin sheet, characterized by being thermally connected by a conductive member.

  In the thermoforming mold of the present invention, since the high temperature contact portion and the low temperature contact portion are thermally connected by the heat conducting member, the heat of the high temperature contact portion is efficiently transmitted to the low temperature contact portion. For this reason, it is possible to prevent spring back around the low temperature heating part without applying new heat to the mold. Therefore, it is possible to obtain a molded article excellent in transparency, gloss, and formability without causing a reduction in molding cycle and an increase in cost.

Hereinafter, embodiments of the present invention will be described in detail together with the operation thereof.
As described above, the molding die for thermoforming of the present invention is a resin sheet low temperature part in which the heating temperature before shaping is set low to maintain transparency, and a resin sheet high temperature in which the heating temperature before shaping is set high. A molding die for thermoforming the resin sheet so as to have a distribution in the heating temperature by providing a portion, wherein the molding die is in contact with the low temperature portion of the resin sheet or at least a part of the periphery thereof A certain low temperature contact part and the high temperature contact part which is at least a part of the part which a molding die contacts with this resin sheet high temperature part are thermally connected by the heat conductive member, It is characterized by the above-mentioned. FIG. 3 is a schematic diagram of the molding die of the present invention, taking as an example the case where a convex vacuum molding die is used as the lower die.

  In the present specification, “thermally connected” means a state in which heat energy can be transferred because the high temperature contact portion and the low temperature contact portion are connected by the heat conducting member. Further, in the present specification, the “heat-absorbing / dissipating part of the heat pipe” means a heat-absorbing part and a heat-dissipating part of the heat pipe, and conforms to a normal definition in this technical field. That is, the heat absorption part of the heat pipe means a part where the working fluid evaporates and absorbs heat, and the heat dissipation part of the heat pipe means a part where the steam condenses and releases heat.

  In the present specification, the “low temperature contact portion” is a portion where the mold comes into contact with the low temperature portion of the resin sheet or at least a part of the periphery thereof in the mold of the present invention. That is, the low temperature contact portion includes not only the portion where the mold is in contact with the low temperature portion of the resin sheet but also the periphery of the contact portion, and means at least a part of such a portion. Here, the “part” is not limited to a specific part in the above part in the mold, but means any part thereof. Further, in the present specification, the “high temperature contact portion” is at least a part of a portion of the mold according to the present invention where the mold comes into contact with the resin sheet high temperature portion. Here, “a part” is not limited to a specific part in the above-mentioned part in the mold, but means any part thereof.

  In the present invention, the heat conducting member is preferably a heat pipe. This is because both the thermal conductivity and the heat transfer rate are large and can be easily installed in the mold. However, if the thermal conductivity is good, the usable thermal conductive member is not limited to the heat pipe. The material of the heat pipe container or wick is not particularly limited and may be appropriately selected according to the molding temperature of the resin material to be molded. However, considering the heat resistance, durability, cost, etc. when installed in the mold Copper, stainless steel, or aluminum is preferable. The working fluid to be sealed is not particularly limited, and water, acetone, methanol, etc. can be used. However, water can be used because it can cover the molding temperature of many resins, is highly safe and hardly corrodes. Is particularly preferred.

  The resin molded by the thermoforming mold of the present invention is not particularly limited. Examples of the resin to be molded include transparent resins such as acrylic resins, polycarbonate resins, polyester resins, styrene resins, and cyclic olefin resins. However, the present invention is not limited thereto, and the thermoforming mold of the present invention can be used for thermoforming various resins.

  In the present invention, the position of installation of the heat pipe is not particularly limited, and may be appropriately determined depending on the position and area of the low-temperature contact portion and the high-temperature contact portion described above. In FIG. 4, the aspect which installed the heat pipe in the various positions is shown. For example, one heat pipe may be arranged linearly as shown in FIG. 4 (1), or the shape of the heat pipe is U-shaped and inverted U-shaped as shown in (2) to (5) of FIG. A mold, a U-shape, and a pseudo-loop type may be used to increase the contact area between the low temperature contact portion / high temperature contact portion and the heat pipe heat sink. Further, in order to further increase the contact area between the low temperature contact portion / the high temperature contact portion and the heat pipe heat sink, the shape of the heat pipe contact portion is corrugated and S-shaped as shown in FIGS. 4 (6) and (7). It may be a mold.

  In general, it is difficult for a general heat pipe to transfer heat continuously from a high place to a low place in the direction of gravity. For example, as shown in FIG. 5, when a concave vacuum forming die is used as the lower die, the low temperature contact portion is positioned below the high temperature contact portion in the weight direction. In a general heat pipe, the enclosed working fluid evaporates, moves downward, and does not return upward when condensed, which may cause a lack of action. In such a case, as shown in FIG. 5 (8), it is a preferred embodiment in the present invention to use a capillary pump droop (CPL) type heat pipe. By using a CPL-type heat pipe, the working fluid becomes a closed circulation system, and the capillary force due to the change in the internal pressure distribution can be used, so that continuous heat transfer is possible regardless of the direction of gravity.

  In the present invention, at least one heat pipe is required to connect the pair of low temperature contact portions and the high temperature contact portions. However, in order to achieve more efficient heat conduction, it is a preferable aspect in the present invention to install a plurality of heat pipes as shown in FIG. 6 according to the position and area of the low temperature contact portion / high temperature contact portion. . In this case, it is possible to install a plurality of linear heat pipes as shown in (9a) of FIG. 6, and a plurality of pseudo-loop heat pipes as shown in (9b) of FIG. It is also possible to install.

  The material and manufacturing method of the mold main body in the present invention are not particularly limited. The material of the mold main body may be any of a metal mold such as an iron-based or aluminum-based alloy, a resin mold such as a wood powder mixed resin or a thermosetting resin, or a ceramic mold. As a method of manufacturing the mold body, first, a cast block may be formed and ground, or the mold may be divided into pieces that can be easily processed in advance and separately formed.

  In addition, the back surface of the mold may be solid or hollow, but is preferably a hollow for ease of installation of the heat pipe. The left side of FIG. 7 shows the case where the back surface of the mold is solid, and the right side of FIG. 7 shows the case where the back surface of the mold is hollow. When the material of the mold main body is a resin mold, a member having high smoothness such as a metal plate can be inserted into a low temperature contact portion where high transparency and gloss are required.

  Moreover, the installation method of the heat pipe of this invention is not specifically limited, What is necessary is just to contact the heat absorption / radiation part of a heat pipe, and the low temperature contact part / high temperature contact part of a shaping | molding die, respectively. For example, a pipe introduction hole may be opened in advance in a mold, and a heat pipe may be inserted here. However, in order to carry out heat transfer more efficiently, for example, it is preferable that a part of the molding die has a nested structure as shown in FIG. 8 and the heat pipe is connected thereto by welding or the like. It is. Further, at this time, it is a more preferable aspect in the present invention that the connection portion is formed into a wave shape or an S shape as described above. Thus, connecting the heat pipe with the mold as a nested structure is also preferable in terms of the convenience of installing the heat pipe.

  Moreover, in this invention, it is preferable that parts other than the heat absorption / radiation part of each heat pipe are coat | covered with the heat insulating material. If there is heat transfer at a portion other than the low temperature contact portion / high temperature contact portion of the mold, the efficiency of achieving the object of the present invention is lowered, and this is disadvantageous in terms of the formability and the molding cycle that are the aims of the present invention. Because it becomes. The heat insulating material to be used is not particularly limited, and any heat insulating material can be used as long as heat resistance at the resin molding temperature is ensured. Among them, a cured resin foam such as urethane is particularly preferable.

  In the present invention, as shown in FIG. 9, a material having high thermal conductivity is interposed between the heat absorbing / dissipating part of the heat pipe and the mold (upper right of FIG. 9), or a material having high thermal conductivity is provided in the heat absorbing / dissipating part of the heat pipe. This high thermal conductivity material can be exposed to the mold surface (lower right in FIG. 9). In the case of a metal mold, it is not essential because the mold itself has a high thermal conductivity. However, a resin mold having a low thermal conductivity is effective for improving the formability.

  Next, examples of the thermoforming mold according to the present invention will be described in detail, but the present invention is not limited thereto.

(Molding mold)
A convex vacuum forming mold was used to be positioned below the resin sheet. The material of the mold was an aluminum alloy (ZAS). The projected area of the mold is 800mm x 800mm. FIG. 10 shows an outline of the mold. In this mold, it is possible to confirm the formability by measuring the angle after shaping with a low temperature contact part that is a transparency requirement part with a convex part as a smooth surface and a bent part of 110 ° I made it.

(Molding and evaluation)
The same resin sheet was used in both Examples and Comparative Examples. Specifically, a polycarbonate resin sheet (Iupilon sheet NF-2000: manufactured by Mitsubishi Engineering Plastics) and an acrylic resin sheet (Acrylite L: manufactured by Mitsubishi Rayon) having a size of 800 mm × 800 mm and a thickness of 2 mm were used. Clamp the entire circumference of the resin sheet, and as shown in Fig. 1, set the heater temperature around the convex top to a low temperature, set the heat temperature around this to a high temperature, heat and soften the resin sheet, and then vacuum the mold While pressing, the resin sheet was shaped. The heater used was a 9 × 9 = 81 array of near infrared heaters (0.4 kW), and the temperature of each block could be adjusted.

The evaluation items after molding are the following two.
(1) Shapeability: The above-mentioned bent part (110 ° with the mold) was cut out from the molded body, and this angle was measured.
(2) Transparency: The above-mentioned convex upper smooth surface was cut out from the molded product, and the haze value (%) was measured with a haze meter.
The resin sheet temperature and molding cycle during molding are shown in Table 1 together with the evaluation results.

(Example 1)
A heat pipe (φ8 mm, container and wick: made of copper, working fluid: water) installed in the mold shown in FIG. 10 as shown in FIG. 6 (9b) and FIG. 8 was used. The above-mentioned polycarbonate resin sheet was used for the resin sheet.

(Example 2)
A heat pipe (φ8 mm, container and wick: made of copper, working fluid: water) installed in the mold shown in FIG. 10 as shown in FIG. 6 (9 b) and FIG. 8 was used. The above-mentioned acrylic resin sheet was used for the resin sheet.

(Comparative Example 1)
The mold shown in FIG. 10 was used without installing a heat pipe. The above-mentioned polycarbonate resin sheet was used for the resin sheet.

(Comparative Example 2)
The mold shown in FIG. 10 was used without installing a heat pipe. The above-mentioned acrylic resin sheet was used for the resin sheet.

  Comparing the example and the comparative example, regardless of the type of resin, the example in which the heat pipe was arranged was superior in formability. In addition, since the cooling time of the molded body and the mold was shortened, the molding cycle was also shorter in the examples. On the other hand, with respect to the haze value, although the example was slightly better, there was no significant difference. The power consumption was exactly the same in the examples and comparative examples.

  In the molding die for thermoforming of the present invention, the high temperature contact portion and the low temperature contact portion are thermally connected by the heat conducting member, so that the heat of the high temperature contact portion can be efficiently transmitted to the low temperature contact portion. For this reason, it is possible to maintain a high moldability without lowering the molding cycle and increasing the cost due to new heating in the mold, and to obtain a molded article with excellent transparency, gloss and formability. It is. Therefore, the thermoforming mold and the resin sheet thermoforming method of the present invention are particularly useful for the purpose of molding large parts such as building materials and automotive resin glass.

FIG. 1 is a diagram showing a state in which the heating temperature is distributed in order to ensure the transparency of the resin. FIG. 2 is a view showing the spring back of the molded product. FIG. 3 is a schematic view showing an outline of the molding die of the present invention. FIG. 4 is a diagram illustrating a state in which heat pipes are installed at various positions. FIG. 5 is a diagram showing a state in which a capillary pump droop (CPL) type heat pipe is used. FIG. 6 is a diagram showing a state in which a plurality of heat pipes are installed. FIG. 7 is a view showing a state in which the back surface of the mold is solid and hollow. FIG. 8 is a diagram showing a heat pipe installed in a nested structure. FIG. 9 is a view showing a state in which a heat pipe is installed with a high thermal conductivity material interposed. FIG. 10 is a diagram showing an outline of the mold used in the examples and comparative examples of the present invention.

Claims (12)

  Provide a resin sheet low-temperature part in which the part that requires a transparent surface property after shaping the resin sheet is made low temperature, and a resin sheet high-temperature part in which a part that does not require a transparent surface property after shaping the resin sheet is made high temperature Thus, a molding die for thermoforming the resin sheet so as to have a distribution in the heating temperature, wherein the molding die is a part in contact with the low temperature part of the resin sheet or at least a part of the periphery thereof. A thermoforming mold characterized by thermally connecting a contact portion and a high temperature contact portion, which is at least a part of a portion where the mold comes into contact with the high temperature portion of the resin sheet, by a heat conductive member.   2. The thermoforming mold according to claim 1, wherein the heat conducting member comprises a heat pipe.   The said low temperature contact part and the said high temperature contact part are connected by installing the said heat pipe in the shape of a U-shape or an inverted U shape in the said shaping | molding die, The Claim 2 characterized by the above-mentioned. Mold for thermoforming.   3. The molding for thermoforming according to claim 2, wherein the low-temperature contact portion and the high-temperature contact portion are connected by installing the heat pipe in a U-shape in the mold. Type.   3. The mold for thermoforming according to claim 2, wherein the low-temperature contact portion and the high-temperature contact portion are connected by installing the heat pipe in the shape of a pseudo loop in the mold. .   The mold for thermoforming according to claim 2, wherein a shape of a connecting portion between the heat pipe and the low temperature contact portion and / or the high temperature contact portion is a corrugated shape.   The thermoforming mold according to claim 2, wherein a shape of a connection portion between the heat pipe and the low temperature contact portion and / or the high temperature contact portion is an S-shape.   3. The mold for thermoforming according to claim 2, wherein the heat pipe is a capillary pump droop (CPL) type heat pipe.   The thermoforming mold according to any one of claims 2 to 8, wherein two or more heat pipes are installed in the same mold.   The thermoforming mold according to any one of claims 2 to 9, wherein the heat pipe other than the heat absorbing / dissipating part is covered with a heat insulating material.   A material having a high thermal conductivity is interposed between the heat absorbing / dissipating part of the heat pipe and the mold, or a material having a high thermal conductivity is attached to the heat absorbing / dissipating part of the heat pipe so that the material having the high thermal conductivity is added. The thermoforming mold according to any one of claims 2 to 10, wherein the mold is exposed on the surface of the mold.   Provide a resin sheet low-temperature part in which the part that requires a transparent surface property after forming the resin sheet is cooled, and a resin sheet high-temperature part in which the part that does not require a transparent surface property after forming the resin sheet is hot In a thermoforming method, comprising setting a heater temperature, heat-softening the resin sheet according to the heater temperature, and narrowing the mold for forming the resin sheet while evacuating the mold, the mold is the resin sheet A thermal contact member thermally connects a low temperature contact portion that is in contact with the low temperature portion or at least part of the periphery thereof, and a high temperature contact portion that is at least part of the portion in which the mold is in contact with the resin sheet high temperature portion. A method for thermoforming a resin sheet, wherein

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