Thermal forming device

Abstract

The present invention is a thermoforming apparatus (100) for heating a resin sheet (S) by means of a heating unit (110) and mold-shaping the resin sheet (S) using a mold (200), the resin sheet (S) being held between a first chamber (101) disposed at an upper part and a second chamber (102) disposed at a lower part, the thermal forming device (100) is provided with a pressure control unit (270) for controlling the pressure in the first chamber (101) or the second chamber (102) to be arbitrary when the resin sheet (S) is formed. A pressure control unit (270) controls a first valve (V1) connected to a first chamber (101) or a second valve (V2) connected to a second chamber (102) and switches the internal pressure of the first chamber (101) or the second chamber (102) in multiple stages.

Description

Technical Field

[0001] The present invention relates to a technology for thermoforming a resin sheet, and more specifically, to a technology for improving molding accuracy by changing the heating conditions according to the location when the resin sheet is heated and molded by a radiation heating device. Background Art

[0002] Thermoforming machines are used to shape softened resin sheets to produce food containers or blister packages. They are also used to produce various plastic products such as automobile parts, home appliances, and industrial trays. In recent years, thermoforming machines have also been used for applications such as transferring patterns or bonding resin sheets to the outer surface of a molding substrate, and for molding that requires positional accuracy.

[0003] Patent Document 1 discloses a technique related to a molding method for a decorative molded product. A resin sheet is pre-shaped after being heated, and then the resin sheet is vacuum-formed after being reheated. That is, by forming in two stages, deep drawing and forming in a small R shape can be achieved. Prior art literature Patent Literature

[0004] Patent document 1: Japanese Patent Laid-Open No. 62-255119 Summary of the invention Problem that the invention aims to solve

[0005] However, the technology described in Patent Document 1 makes it difficult to achieve high-precision position alignment during the molding of resin sheets. When the resin sheet softens due to heating, it is easy to sag due to the weight of the sheet itself, making it difficult to achieve high-precision position alignment. Therefore, even if the method of reheating after pre-shaping and further shaping as shown in Patent Document 1 is adopted, the resin sheet must be softened sufficiently when it is heated to achieve high-precision position alignment, so it is impossible to avoid the undulation or sagging of the resin sheet during heating. In this way, the problem of misalignment or wrinkles will occur due to the different states of the resin sheet of the molded product.

[0006] Therefore, the following method has been used in the past: the resin sheet is heated at a low temperature to a degree that the resin sheet does not sag, and then ultra-high pressure compressed air of, for example, 3MPa or more is applied to perform molding. However, when a transparent resin sheet is molded by low temperature heating and ultra-high pressure, residual stress may be generated inside the molded product, which may affect the transparency of the material. In addition, ultra-high pressure compressed air must be maintained during molding, so there are problems such as the molding device body becoming expensive and molding taking time.

[0007] Therefore, an object of the present invention is to provide a thermoforming apparatus that is less likely to cause positional displacement or the like when thermoforming is performed using a resin sheet even in a relatively low-pressure environment. Technical means of solving problems

[0008] To achieve the above-mentioned object, a thermoforming device according to one aspect of the present invention has the following features.

[0009] (1) A thermoforming device that heats a sheet material by means of a radiant heating unit and uses a mold to mold the sheet material or to cover and bond the sheet material to a substrate, wherein: The sheet is held between a first chamber disposed at the upper portion and a second chamber disposed at the lower portion, The thermoforming device includes a pressure control unit for controlling the internal pressure of the first cavity or the second cavity when the sheet is formed. The pressure control unit has a function of controlling a first pressure control valve connected to the first chamber to switch the pressure in the first chamber to a first pressurized state and a second pressurized state in which the internal pressure of the first chamber is higher than the first pressurized state, or a function of controlling a second pressure control valve connected to the second chamber to switch the pressure in the second chamber to a first vacuum state and a second vacuum state in which the vacuum degree is higher than the first vacuum state.

[0010] (2) In the thermoforming device described in (1), Preferably, the pressure control unit can realize the following multi-stage pressure control, namely, As a first control stage, after the sheet and the mold are brought close together and the sheet has abutted against the convex portion of the mold, the pressure in the first chamber is controlled in such a way as to be in the first pressurized state, or after the sheet and the mold are brought close together and the sheet has abutted against the convex portion of the mold, the pressure in the second chamber is controlled in such a way as to be in the first vacuum state. As a second control stage, the pressure in the first chamber is controlled to be in the second pressurized state or the pressure in the second chamber is controlled to be in the second vacuum state during the molding of the sheet.

[0011] (3) A thermoforming device that heats a sheet material by means of a radiation heating unit and uses a mold to mold the sheet material or to cover and bond the sheet material to a substrate, wherein: The sheet is held between a first chamber disposed at the upper portion and a second chamber disposed at the lower portion, The thermoforming device includes a pressure control unit for controlling the internal pressures of the first cavity and the second cavity when the sheet is formed. The pressure control unit has a function of controlling a second pressure control valve connected to the second chamber to switch the pressure in the second chamber to a first vacuum state and a second vacuum state with a higher vacuum degree than the first vacuum state, and a function of controlling a second pressure control valve connected to the second chamber to switch the pressure in the second chamber to a first vacuum state and a second vacuum state with a higher vacuum degree than the first vacuum state, and can realize the following multi-stage pressure control, namely, As a first control stage, after the sheet is brought close to the mold and the sheet has abutted against the convex portion of the mold, the pressure in the second chamber is controlled in such a way as to be in the first vacuum state, and the pressure in the second chamber is controlled in such a way as to be in the first vacuum state, As a second control stage, the pressure in the second chamber is controlled so as to be in the second vacuum state during the molding of the sheet, and the pressure in the second chamber is controlled so as to be in the second vacuum state.

[0012] According to the embodiment described in any one of (1) to (3), it is possible to realize high-precision molding that is less likely to cause misalignment even in a relatively low-pressure environment by using a thermoforming device that performs multi-stage pressure control. The reason for this is that the pressure corresponding to the molding stage of the sheet can be applied by adopting the following multi-stage pressure control: as a first control stage, after the sheet and the mold are brought close together and the sheet has abutted against the convex portion of the mold, the pressure in the first chamber is controlled to be in a first pressurized state, or the pressure in the second chamber is controlled to be in a first vacuum state, or the pressure in the first chamber and the pressure in the second chamber are controlled to be in a first pressurized state and a first vacuum state, and as a second control stage, after a predetermined time has passed, the pressure in the first chamber is controlled to be in a second pressurized state, or the pressure in the second chamber is controlled to be in a second vacuum state, or the pressure in the first chamber and the pressure in the second chamber are controlled to be in a second pressurized state and a second vacuum state.

[0013] After the sheet heated by the radiation heating device to a temperature that does not sag is placed against the preheated mold, it is further heated and molded. At this time, in the first control stage, the sheet held between the first chamber and the second chamber is molded while maintaining the pressure in the first chamber in a manner that changes to the first pressurized state or maintaining the pressure in the second chamber in a manner that changes to the first vacuum state and heating. After a predetermined time, the second control stage changes to the second control stage or the second vacuum state and continues molding with a higher vacuum degree. Alternatively, molding is performed by appropriately controlling both the internal pressure of the first chamber and the internal pressure of the second chamber. If a high vacuum state is suddenly entered during molding, the sheet may be stretched to a degree greater than required. By performing multi-stage pressure control, the pressure can be increased according to the molding condition of the sheet, and as a result, the sheet can be easily molded into any shape.

[0014] (4) In the thermoforming device described in any one of (1) to (3), Preferably, the timing of switching from the first control stage to the second control stage is determined using the passage of time as a trigger.

[0015] (5) In the thermoforming device described in any one of (1) to (3), Preferably, a temperature confirmation unit is provided to measure the surface temperature of the sheet. The timing of switching from the first control stage to the second control stage is determined using the temperature data obtained from the temperature confirmation unit as a trigger.

[0016] By means of the form described in (4) or (5) above, molding can be started at the appropriate time. As described above, the purpose of performing molding by multi-stage pressure control is to perform compressed air molding or vacuum molding at an appropriate pressure on the sheet heated to an appropriate temperature during molding, thereby molding a molded product with a more uniform thickness or a target thickness. The timing of switching the control stage can be determined based on the passage of time or based on the temperature data provided by the temperature confirmation unit.

[0017] (6) In the thermoforming device described in any one of (1) to (5), Preferably, the radiation heating unit is composed of a plurality of heaters arranged in an array, and has a first area composed of the heaters corresponding to the convex portion of the mold and a second area composed of the heaters excluding the first area. The radiant heating unit is equipped with a heating control unit capable of performing different power controls in the first area and the second area, By means of the heating control unit, the following multi-stage heating control can be achieved, namely, As the first heating stage, the radiant heating unit performs initial heating of the sheet material. As the second heating stage, when the sheet and the mold are brought close to each other and the sheet has abutted against the convex portion, the first region is subjected to low-temperature heating with reduced power, and the second region is subjected to high-temperature heating with increased power compared to the first region. The first control phase begins during the second heating phase.

[0018] According to the embodiment described in (6) above, a high-precision molding that is less likely to cause misalignment, etc., can be achieved by using a thermoforming device that performs multi-stage heating control even in a relatively low-pressure environment. This is because the sheet is initially heated to a temperature that does not cause sagging in the first heating stage, and after the sheet abuts against the convex portion of the mold, low-temperature heating with reduced power is performed in the first region in the second heating stage, and high-temperature heating with increased power compared to the first region is performed in the second region.

[0019] After the sheet is heated by the radiation heating device in the first heating stage, the temperature of the abutting part changes when it abuts against the preheated mold. The reason is that the mold and the sheet are in direct contact, causing the temperature to change. As a result, if the same heating is continued, there will be parts where the temperature rises above the required level and parts where the temperature is insufficient. In order to deal with this problem, the required heating can be performed in different zones, thereby further heating the parts to be processed and suppressing the heating of the parts not to be processed, making it easier to form the sheet into any shape.

[0020] Specifically, the following molding can be achieved: the first area is set as a part that does not want to be stretched, for example, which requires position alignment, so that after first contacting the convex part of the mold, the first area is heated at a low temperature in a manner that becomes low temperature, and the second area corresponding to the part to be deformed is heated at a higher power than the first area. By performing multi-stage heating control in this way and dividing the area to be heated, the part to be deformed can be heated intensively to deform the sheet. As a result, molding with higher shape accuracy can be achieved.

[0021] (7) In the thermoforming device described in (6), It is preferable that the portion of the sheet corresponding to the first region is set as a portion requiring positional alignment on the molded product.

[0022] According to the embodiment described in (7), the portion of the sheet corresponding to the first region first contacts the convex portion of the mold and is heated at a low temperature in the second heating stage, so it is not easily affected by deformation during molding. Therefore, by setting the portion of the molded product that requires position alignment, such as a printed portion or a portion used as a transparent window, as the portion of the sheet corresponding to the first region, the influence of misalignment occurring during molding can be suppressed to a minimum.

[0023] (8) In the thermoforming device described in (6) or (7), It is preferable that the heating control means includes a temperature confirmation means for confirming the temperature of the sheet material, and the multi-stage heating control is performed using temperature data of the sheet material measured by the temperature confirmation means.

[0024] According to the aspect described in (8) above, the temperature of the sheet to be measured can be grasped by the radiation thermometer, thereby enabling more accurate control by the heating control unit, thereby achieving molding with high shape accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an explanatory diagram regarding the schematic structure of the thermoforming device according to the present embodiment. Figure 2 This is a plan view of a heater used in the thermoforming device of this embodiment. Figure 3 It is an explanatory diagram showing the third step of molding in this embodiment. Figure 4 It is an explanatory diagram showing the fourth step of molding in this embodiment. Figure 5 It is an explanatory diagram showing the fifth step of molding in this embodiment. Figure 6 This is a plan view of the heater of this embodiment, corresponding to the third step. Figure 7 This is a plan view of the heater of this embodiment, corresponding to the fourth step. Figure 8 It is a time chart showing the molding sequence of this embodiment. Fig. 9 This is a schematic diagram of the system of the thermoforming device of this embodiment. DETAILED DESCRIPTION

[0026] First, the outline of the structure of the thermoforming apparatus 100 according to the embodiment of the present invention will be described. Figure 1This is an explanatory diagram for explaining the schematic structure of the thermoforming device 100 of this embodiment. The thermoforming device 100 includes a first cavity 101, a second cavity 102, a heating unit 110, and a mold 200. The thermoforming device 100 has the following structure: a resin sheet S to be molded is held by the first cavity 101 and the second cavity 102, and molded while being heated by the heating unit 110 disposed on the upper side.

[0027] The first chamber 101 and the second chamber 102 of the thermoforming device 100 are respectively connected to a compressor and a vacuum pump described later, and the pressure in the first chamber 101 and the second chamber 102 can be adjusted by operating the compressor and the vacuum pump. The first chamber 101 opens downward, and the second chamber 102 opens upward. The first chamber 101 and the second chamber 102 are provided with a structure that can clamp the resin sheet S by raising and lowering the first chamber 101 and the second chamber 102, thereby holding the resin sheet S.

[0028] The first chamber 101 is connected to a compressor or a pressure tank (not shown), and a first valve V1 (described later) is provided in the middle of the first pipe P1, thereby the inside of the first chamber 101 can be pressurized to any pressure. The second chamber 102 is connected to a vacuum pump (not shown), and a second valve V2 (described later) is provided in the middle of the second pipe P2, thereby the inside of the second chamber 102 can be depressurized to any pressure. The first chamber 101 and the second chamber 102 are structures that can withstand the internal pressure generated during the pressurization and depressurization during the molding of the resin sheet S. The first valve V1 and the second valve V2 use pressure control valves that can detect the internal pressure and control the pressure arbitrarily.

[0029] The resin sheet S is made of polycarbonate, a thermoplastic resin, and is cut into a rectangular sheet with a thickness of about 300 μm. This material and thickness are just an example of one form, so the material and thickness of the resin sheet S are not limited to this, but the purpose of the present invention is to solve the problem in the processing of relatively thin resin sheets, so the thickness of the resin sheet S to be processed is assumed to be a sheet of about 250 μm to 500 μm. Furthermore, it does not prevent the use of thick plates, and the application of the present invention to the molding of thick plates can also be expected to achieve effective results.

[0030] Figure 2 A plan view showing a heater used in the thermoforming apparatus 100. The heating unit 110 is disposed above the resin sheet S and is a group of heaters 111 for performing radiant heating for the purpose of heating the resin sheet S from the upper surface. Figure 2 As shown, the heaters 111 are arranged in a tiling shape on the lower surface of the upper lifting device 120 . Figure 2Although the drawing is performed in 4 rows and 8 columns for the purpose of explanation, it does not prevent the number of rows and columns from being increased or decreased as needed. By increasing the number of rows and columns, more detailed shapes can be handled.

[0031] The heating unit 110 is held by the upper lifting device 120, which is a structure that can move the heating unit 110 to any height in the first chamber 101 by means of a first driving device 121 described later. In addition, each heater 111 is connected to a heating control unit 250 described later and can adjust the power arbitrarily.

[0032] Thermometers (S1, S2) are provided on the upper part of the upper lifting device 120, and the thermometers (S1, S2) measure the temperature by aiming at the surface of the resin sheet S from the gap provided between the upper lifting device 120 and the heating unit 110. The first thermometer S1 and the second thermometer S2 use radiation thermometers that measure the temperature of the resin sheet S in a non-contact manner. In addition, for reasons described later, the number of thermometers is provided as needed.

[0033] The mold 200 is held by a lower lifting device 210 that can be raised and lowered to any height by a second driving device 211 described later, and is used for molding a resin sheet S. A convex portion 200a is formed on the mold 200. The convex portion 200a is a portion that corresponds to a portion of a molded product M produced by molding the resin sheet S, such as a portion for printing a pattern that cannot be misaligned or a portion that requires transparency and cannot be deformed internally. For convenience, the portion other than the convex portion 200a of the mold 200 is defined as a low portion 200b.

[0034] Furthermore, the convex portion 200a of the mold 200 corresponds to Figure 2 The first area A1 of the heating unit 110 is shown. The first area A1 is Figure 2 The area surrounded by the double-dashed line in the figure includes four heaters 111, and the area outside this area is set as the second area A2. The mold 200 is composed of a convex portion 200a and a low portion 200b other than the convex portion 200. The second area A2 of the heating unit 110 corresponds to the low portion 200b and the portion around the low portion 200b where the resin sheet S abuts. In addition, there is no problem in increasing the area of ​​the heating unit 110 to more than two.

[0035] Fig. 9A schematic diagram showing a system of a thermoforming device. For ease of explanation, the heating unit 110 is omitted from the drawing, but the heaters 111 are respectively connected to the heating control unit 250. In addition, the first thermometer S1 and the second thermometer S2, which are equivalent to the temperature confirmation unit, are connected to the heating control unit 250, and the control of the heater 111 is triggered using the data of the thermometers (S1 and S2). The first thermometer S1 is set to target the portion of the sheet corresponding to the first area A1, and the second thermometer S2 is set to target the portion of the sheet corresponding to the second area A2. Furthermore, there is no obstacle to increasing the number of thermometers as needed. In the case where the heating unit 110 further increases areas in addition to the first area A1 and the second area A2, thermometers can be added accordingly and used in the heating control unit 250.

[0036] The first driving device 121 driving the upper lifting device 120 and the second driving device 211 driving the lower lifting device 210 are connected to the driving control unit 260. Fig. 9 Although the first chamber 101 and the second chamber 102 are not shown, the first valve V1 and the second valve V2 connected to the first chamber 101 and the second chamber 102 are connected to the pressure control unit 270. The heating control unit 250, the driving control unit 260 and the pressure control unit 270 are provided in the console 300.

[0037] Next, the procedure for molding the resin sheet S is described. Figure 1 , Figures 3 to 5 It was demonstrated in Figure 1 , Figure 3 , Figure 4 , Figure 5 The molding is carried out in the order of. Figure 8 A schematic diagram showing a time chart for controlling each function during molding. The horizontal axis shows the time t1 to t6, dividing the process. Figure 8 The operation of each device is described below.

[0038] First, in the first step Pr1, Figure 1 As shown, the first chamber 101 and the second chamber 102 are closed so that the resin sheet S put in is sandwiched between the first chamber 101 and the second chamber 102 .

[0039] Next, in the second step Pr2, the heating unit 110 is held at the position where the upper lifting device 120 has been lowered, and the resin sheet S is heated from the upper side ( Figure 1The heating unit 110 performs initial heating using the heater 111. The heating at this time is set to a degree that the resin sheet S is slightly softened, and is heated until the first thermometer S1 and the second thermometer S2 confirm that the set temperature has been reached. In this embodiment, the resin sheet S is set to polycarbonate, and its softening temperature is about 150 degrees. Therefore, at this point in time, it is heated in the form of the first heating stage to a temperature of about 140 degrees at which polycarbonate begins to thermally deform. At this time, it is desired to quickly complete the heating of the resin sheet S, so the ignition rate (power) of the heater 111 is set to 100%.

[0040] Next, in the third step Pr3, as Figure 3 As shown, the upper lifting device 120 is raised to lift the heating unit 110 ( Figure 8 The mold 200 is raised by the lower lifting device 210 to make it contact with the resin sheet S ( Figure 8 At this time, the convex portion 200a of the mold 200 contacts the resin sheet S before the other parts (lower portion 200b) of the mold 200. In this way, the mold contacts the hot resin sheet S while the resin sheet S is heated by the heating unit 110, thereby deforming the resin sheet S. Here, since the mold 200 is heated to a low degree (about 120 degrees), the convex portion 200a contacts the resin sheet S to locally reduce the temperature.

[0041] At this time, the heating control unit 250 is used to Figure 6 As shown in the figure, the first heating stage in which all heaters 111 perform heating at the same power is switched to Figure 7 As shown in the figure, the state of heating is performed by changing the temperature setting in the first area A1 and the second area A2 in the form of the second heating stage. Here, Figure 7 The first area A1 shown is a position of the heating unit 110 corresponding to the convex portion 200a of the mold 200, and the second area A2 is a position other than the first area A1. The heater 111 corresponding to the first area A1 is set to have an ignition rate of 10% when entering the third step Pr3, and the ignition rate of the remaining heaters 111 (arranged at the position surrounded by the heater 111 corresponding to the first area A1) including the second area A2 is set to 50%. Therefore, the portion of the resin sheet S abutting against the low portion 200b is actively heated.

[0042] Next, in the fourth step Pr4, the first chamber 101 is pressurized and the second chamber 102 is depressurized, and molding is started by triggering the surface temperature of the resin sheet S reaching 170 degrees (detected by the second thermometer S2). In the fourth step Pr4, the first chamber 101 is pressurized by controlling the amount of compressed air supplied by the first valve V1 in a flow-limiting manner within a predetermined time, that is, from the elapsed time t3 to the elapsed time t4. Figure 8 The decompression of the second chamber 102 is controlled by limiting the amount of air discharged by the second valve V2 ( Figure 8 The first valve V1 and the second valve V2 are controlled by the pressure control unit 270 to control their openings. Specifically, the pressure in the first chamber 101 is controlled to be 0.1 MPa, and the pressure in the second chamber 102 is controlled to be -0.05 MPa.

[0043] Next, in the fifth step Pr5, as Figure 5 As shown, the amount of compressed air supplied to the first chamber 101 is increased ( Figure 8 The amount of air discharged from the second chamber 102 is increased ( Figure 8 In other words, the first valve V1 and the second valve V2 are opened to perform molding at a higher pressure than the previous process. Figure 8 As shown, the opening timing of the first valve V1 is controlled to be later than the opening timing of the second valve V2. Specifically, the pressure in the first chamber 101 is controlled to be 0.7 MPa, and the pressure in the second chamber 102 is controlled to be -0.1 MPa.

[0044] Finally, in the sixth step Pr6, the internal pressures of the first chamber 101 and the second chamber 102 are returned to atmospheric pressure. Thereafter, the first chamber 101 and the second chamber 102 are opened to take out the molded product M obtained by thermoforming the resin sheet S.

[0045] Since the thermoforming device 100 of the present embodiment has the above-described structure, the following operations and effects are achieved.

[0046] First, it is possible to realize thermoforming of a molded product M with higher precision and less prone to misalignment. This is a thermoforming device 100 that heats a resin sheet S by means of a radiation heating device (heating unit 110) and uses a mold 200 to mold the resin sheet S, wherein the resin sheet S is held in a manner of being sandwiched between a first cavity 101 disposed at an upper portion and a second cavity 102 disposed at a lower portion, and the thermoforming device 100 includes a pressure control unit 270 that controls the pressure in the first cavity 101 or the second cavity 102 to be an arbitrary pressure when molding the resin sheet S.

[0047] In addition, the pressure control unit 270 has the function of controlling the first pressure control valve (first valve V1) connected to the first chamber 101 and the second pressure control valve (second valve V2) connected to the second chamber 102 to arbitrarily switch the pressure in the second chamber 102 between a first vacuum state and a second vacuum state having a higher vacuum degree than the first vacuum state.

[0048] The following multi-stage pressure control can be realized, that is, as a first control stage, after the resin sheets S are brought close to each other and the resin sheets S have abutted against the convex portion 200a of the resin sheet S, the pressure in the first chamber 101 is controlled to be in a first pressurized state, or the pressure in the second chamber 102 is controlled to be in a first vacuum state, and as a second control stage, the pressure in the first chamber 101 is controlled to be in a second pressurized state, or the pressure in the second chamber 102 is controlled to be in a second vacuum state during the thermoforming of the resin sheet S. Thus, displacement of the resin sheet S during the thermoforming is prevented.

[0049] That is, the process is like Figure 8 The molding is performed by controlling the internal pressure of the chamber in multiple stages as shown. The graph of "vacuum pressure" shown at the bottom shows the following situation: between the time t3 and the time t4, molding is performed in a state where the pressure in the second chamber 102 is low pressure (-0.05MPa). At this time, as described above, for the first chamber 101, the control of "upper slightly compressed air" is set to ON (open), and compressed air is supplied from the first pipe P1 by means of the pressure control unit 270 in such a way that the internal pressure becomes 0.1MPa while the first valve V1 is throttled. For the second chamber 102, the control of "lower slightly vacuum" is set to ON, and the internal pressure becomes -0.05MPa by means of the pressure control unit 270 while the second valve V2 is throttled and exhaust is performed from the second pipe P2. This is the first control stage.

[0050] Next, between time t4 and time t5, the second control stage of thermoforming is performed at a higher pressure (the first chamber 101 is controlled to be 0.7 MPa, and the second chamber 102 is controlled to be -0.1 MPa). By performing multi-stage pressurization in this way, precise molding can be achieved. If high-pressure compressed air is suddenly applied, the resin sheet S is likely to become thinner than necessary or break, so multi-stage pressurization is performed to achieve molding in which the thickness of the molded product M becomes uniform.

[0051] In addition, the timing of switching from the first control stage to the second control stage may be determined by using the data of the temperature confirmation unit (the first thermometer S1 and the second thermometer S2), instead of using the temperature confirmation unit as shown in FIG. Figure 8 The switch from the first control stage to the second control stage should be determined based on the progress of the molding of the resin sheet S, and its trigger is based on either the time or the temperature data. The purpose of switching to the second control stage is to improve the adhesion of the resin sheet S to the mold 200. Figure 5 As shown, when the resin sheet S has taken the shape of the mold 200 , further increasing the degree of vacuum (reaching a second vacuum state) makes it easier to transfer the shape of the mold 200 to the resin sheet S.

[0052] Furthermore, when the resin sheet S is quickly heated to a temperature at which it does not sag in the first heating stage, the mold 200 is brought into contact with the resin sheet S, thereby preventing the resin sheet S from sagging. Furthermore, the heating portion is divided into a first area A1 that is heated at a low temperature and a second area A2 that is heated at a higher temperature than the first area A1, thereby heating the portion of the resin sheet S that needs to be deformed in the second area A2 as required, thereby achieving deformation. As a result, multi-stage heating can be performed while the heater 111 is controlled by the heating control unit 250, thereby preventing the resin sheet S from sagging and improving the molding accuracy of the molded product M.

[0053] At this time, the portion of the resin sheet S corresponding to the first area A1 is set as a portion that requires positional alignment, for example, a portion where printing is made on the surface of the resin sheet S, and if misaligned, the performance of the product will be affected when it is shaped into the molded product M, or the transparency will be affected due to the influence of deformation during molding, thereby preventing the transparent portion from being difficult to transmit light due to misalignment or internal deformation. The portion of the resin sheet S corresponding to the first area A1 becomes the portion that first abuts against the convex portion 200a of the mold 200 during molding. In addition, the first area A1 further reduces the power compared to the second area A2 in the second heating stage, so it is possible to prevent the resin sheet S from being deformed to a greater extent than required due to overheating, and wrinkles or damage in some cases, and mold the resin sheet S into a target shape.

[0054] By combining multi-stage heating and multi-stage pressurization to thermoform the resin sheet S while controlling the internal pressure of the chamber, it is possible to prevent the resin sheet S from sagging during heating and to tightly press the resin sheet S against the mold 200 during molding to achieve molding with high shape accuracy. In addition, it is no longer necessary to use low-temperature heating and ultra-high pressure as in the past to mold the resin sheet S, thereby simplifying the equipment calibration and reducing costs.

[0055] The above is a description of the thermoforming device 100 of the present invention, but the present invention is not limited thereto, and various changes can be made without departing from the scope of the present invention. For example, the materials and temperatures illustrated do not prevent changes as appropriate. In addition, if it is desired to further enhance the temperature gradient, the temperature gradient on the resin sheet S can be significantly enhanced by bringing the heating unit 110 close to the resin sheet S in the second heating stage. To form a complex shape with many concave and convex shapes, moving the heater 111 in the second heating stage is an effective method. Conversely, if the heating unit 110 is moved away from the resin sheet S, the temperature gradient can be made gentle.

[0056] In addition, as a multi-stage heating, the description of the initial heating of the resin sheet S in the first heating stage is that the ignition rate of the heater 111 is set to 100%, but this does not prevent the heating unit 110 from being divided into different first areas A1 and second areas A2 as needed, or the ignition rate is changed according to the division of the first area A1 and second area A2 to perform heating. For example, consider the case where the resin sheet S is uniformly heated by setting the ignition rate of the central part of the resin sheet S lower than that of the surrounding area. Such a first heating stage seeks to achieve smooth heating of the resin sheet S and avoid sagging and other problems, so it is different from the purpose of the subsequent second heating stage, which seeks to minimize the temperature rise of a specific part. The present invention achieves high-precision molding of the resin sheet S by performing such multi-stage heating in which different heating conditions are set in the first heating stage and the second heating stage.

[0057] In addition, the present embodiment shows an example of mold shaping using the mold 200, but it does not prevent the present invention from being used for thermoforming of a resin sheet S coated and bonded on a substrate. When the present invention is used for mold shaping, the adhesion of the resin sheet S on the substrate can be improved, and molding with higher precision can be achieved. In addition, in the present embodiment, the triggering of the first heating stage and the second heating stage uses data obtained from the first thermometer S1 and the second thermometer S2. In addition to the method of using temperature data as a trigger, it is also possible to consider using time as a trigger or observing the vacuum degree as a trigger, so it does not prevent it from being changed as appropriate.

[0058] In addition, in this embodiment, the internal pressures of the first chamber 101 and the second chamber 102 of the thermoforming device 100 are exemplified. Figure 8 The timing of these internal pressure changes is described in . The main purpose of the invention is to perform multi-stage control, that is, to set the pressure to low in the first control stage and to set the pressure to higher in the second control stage. Therefore, it does not prevent the values ​​of these timings from being slightly increased or decreased as appropriate according to the thickness and temperature of the resin sheet S. Explanation of symbols

[0059] S…Resin sheet A1…First Area A2…Second area 100…Thermoforming device 110…Heating unit 111…Heater 250...Heating control unit 200…Mold 200a…convex part

Claims

1. A thermoforming device, which heats a sheet by means of a radiant heating unit and uses a mold to mold the sheet or to cover and bond the sheet to a substrate, wherein: The sheet is held between a first chamber disposed at the upper portion and a second chamber disposed at the lower portion, The thermoforming device includes a pressure control unit for controlling the internal pressure of the first cavity or the second cavity when the sheet is formed. The pressure control unit has a function of controlling a first pressure control valve connected to the first chamber to switch the pressure in the first chamber to a first pressurized state and a second pressurized state in which the internal pressure of the first chamber is higher than the first pressurized state, or a function of controlling a second pressure control valve connected to the second chamber to switch the pressure in the second chamber to a first vacuum state and a second vacuum state in which the vacuum degree is higher than the first vacuum state. The pressure control unit can realize the following multi-stage pressure control, namely, As a first control stage, after the sheet is brought close to the mold and the sheet has abutted against the convex portion of the mold, the pressure in the first chamber is controlled so as to be in the first pressurized state or the pressure in the second chamber is controlled so as to be in the first vacuum state. As a second control stage, the pressure in the first chamber is controlled to be in the second pressurized state or the pressure in the second chamber is controlled to be in the second vacuum state during the molding of the sheet.

2. The thermoforming device according to claim 1, characterized in that: The timing of switching from the first control stage to the second control stage is determined using the passage of time as a trigger.

3. The thermoforming device according to claim 1, characterized in that: A temperature confirmation unit is provided to measure the surface temperature of the sheet, The timing of switching from the first control stage to the second control stage is determined using the temperature data obtained from the temperature confirmation unit as a trigger.

4. The thermoforming device according to claim 1, characterized in that: The radiation heating unit is composed of a plurality of heaters arranged in an array, and has a first area composed of the heaters corresponding to the convex portion of the mold and a second area composed of the heaters excluding the first area. The radiant heating unit is equipped with a heating control unit capable of performing different power controls in the first area and the second area, By means of the heating control unit, the following multi-stage heating control can be achieved, namely, As the first heating stage, the radiant heating unit performs initial heating of the sheet material. As the second heating stage, when the sheet and the mold are brought close to each other and the sheet has abutted against the convex portion, the first region is subjected to low-temperature heating with reduced power, and the second region is subjected to high-temperature heating with increased power compared to the first region. The first control phase begins during the second heating phase.

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