Thermoforming device

Abstract

The present application is a thermoforming device (100) that performs heating of a resin sheet (S) by means of a heating unit (110) and performs mold shaping of the resin sheet (S) using a mold (200), wherein the resin sheet (S) is held between a first chamber (101) disposed on an upper portion and a second chamber (102) disposed on a lower portion, the thermoforming device (100) is provided with a pressure control unit (270) that controls the first chamber (101) or the second chamber (102) to be an arbitrary pressure when the resin sheet (S) is molded, and the pressure control unit (270) controls a first valve (V1) connected to the first chamber (101) or a second valve (V2) connected to the second chamber (102) to switch the internal pressure of the first chamber (101) or the second chamber (102) in a multi-stage manner.

Description

Technical Field

[0001] The invention relates to a technique for thermoforming resin sheets, specifically a technique for improving molding accuracy by changing the heating conditions according to the location when heating a resin sheet with a radiant heating device to form it. Background Technology

[0002] Thermoforming machines are used to mold softened resin sheets into food containers or blister packs. They are also used to manufacture various plastic products such as automotive parts, home appliances, and industrial pallets. In recent years, thermoforming machines have also been used in applications such as transferring patterns, bonding resin sheets to the outer surface of molding substrates, and in molding processes requiring precise positioning.

[0003] Patent document 1 discloses a molding method for decorative molded articles. The method involves pre-shaping a resin sheet after heating it, followed by vacuum molding of the resin sheet after reheating it. In other words, by performing shaping in two stages, deep drawing and shaping of small R-shapes can be achieved. Existing technical documents Patent documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 62-255119 Summary of the Invention The problem the invention aims to solve

[0005] However, the technology described in Patent Document 1 makes it difficult to achieve high-precision positioning during the molding of resin sheets. When the resin sheet softens due to heating, it is prone to sagging due to its own weight, making high-precision positioning difficult. Therefore, even when using the method described in Patent Document 1, which involves pre-shaping followed by reheating for further shaping, the resin sheet must be sufficiently softened during heating to achieve high-precision positioning, making it impossible to avoid undulations or sagging of the resin sheet during heating. This results in misalignment or wrinkles due to variations in the state of the resin sheet in the molded product.

[0006] Therefore, the conventional method involves heating the resin sheet at a low temperature to prevent sagging, followed by molding with compressed air at ultra-high pressure, such as 3 MPa or higher. However, when molding transparent resin sheets using low-temperature heating and ultra-high pressure, residual stress can sometimes be generated inside the molded product, affecting the material's transparency. Furthermore, maintaining ultra-high pressure compressed air during molding results in problems such as expensive molding equipment and time-consuming molding processes.

[0007] Therefore, the object of the present invention is to provide a thermoforming apparatus that is less prone to misalignment or other defects when thermoforming resin sheets under relatively low pressure conditions. Technical means to solve the problem

[0008] To achieve the aforementioned objective, one aspect of the thermoforming apparatus of the present invention has the following features.

[0009] (1) A thermoforming apparatus that heats a sheet material using a radiant heating unit and uses a mold to shape the sheet material or to coat and bond it to a substrate, characterized in that... The sheet is held between the upper first chamber and the lower second chamber. The thermoforming apparatus includes a pressure control unit that controls the internal pressure of the first chamber or the second chamber during the forming of the sheet. The pressure control unit has the 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 to control 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 apparatus described in (1), Preferably, the pressure control unit can achieve the following multi-stage pressure control, namely, As a first control phase, the pressure in the first chamber is controlled to enter the first pressurized state after the sheet is brought close to the mold and the sheet has abutted against the protrusion of the mold; or the pressure in the second chamber is controlled to enter the first vacuum state after the sheet is brought close to the mold and the sheet has abutted against the protrusion of the mold. As a second control stage, the pressure in the first chamber is controlled either by changing to the second pressurized state or by changing to the second vacuum state during the forming of the sheet.

[0011] (3) A thermoforming apparatus that heats a sheet material using a radiant heating unit and uses a mold to shape the sheet material or to coat and bond it to a substrate, characterized in that... The sheet is held between the upper first chamber and the lower second chamber. The thermoforming apparatus includes a pressure control unit that controls the internal pressure of the first chamber and the second chamber during the forming of the sheet. The pressure control unit has the function of controlling a first pressure control valve connected to the first chamber to switch the pressure in the first chamber to a first vacuum state and a second vacuum state with a vacuum level higher than the first vacuum state, and the 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 vacuum level higher than the first vacuum state. It can achieve the following multi-stage pressure control, namely... As a first control phase, after the sheet is brought close to the mold and the sheet has abutted against the protrusion of the mold, the pressure in the first chamber is controlled in a manner that changes to the first pressurized state, and the pressure in the second chamber is controlled in a manner that changes to the first vacuum state. As a second control stage, the pressure in the first chamber is controlled in a manner that changes to the second pressurized state midway through the forming of the sheet, and the pressure in the second chamber is controlled in a manner that changes to the second vacuum state.

[0012] By employing any of the forms described in (1) to (3) above, high-precision forming that is less prone to misalignment even under relatively low-pressure conditions can be achieved using a thermoforming apparatus that performs multi-stage pressure control. The reason for this is that by employing the following multi-stage pressure control, pressure corresponding to the forming stage of the sheet can be applied: as a first control stage, after the sheet is brought close to the mold and the sheet has abutted against the protrusion of the mold, the pressure in the first chamber is controlled in a first pressurized state, or the pressure in the second chamber is controlled in a first vacuum state, or the pressure in the first chamber and the pressure in the second chamber are controlled in a first pressurized state and a first vacuum state, as a second control stage, after a predetermined time, the pressure in the first chamber is controlled in a second pressurized state, or the pressure in the second chamber is controlled in a second vacuum state, or the pressure in the first chamber and the pressure in the second chamber are controlled in a second pressurized state and a second vacuum state.

[0013] After being heated to a non-sagging temperature by a radiant heating device, a sheet is placed against a preheated mold and further heated for forming. During the first control phase, the sheet is formed while maintaining pressure in the first chamber (either in a first pressurized state) or in the second chamber (either in a first vacuum state). After a predetermined time, the process transitions to a second control phase, where the sheet is either in a second pressurized state or a second vacuum state, and forming continues at a higher vacuum. Alternatively, both the pressure in the first and second chambers can be appropriately controlled for forming. If a sudden increase to a high vacuum occurs during forming, the sheet may stretch beyond the desired extent. By implementing multi-stage pressure control, the pressure can be increased according to the sheet's forming condition, resulting in easy shaping of the sheet into any form.

[0014] (4) In any of the thermoforming apparatuses described in (1) to (3), Preferably, the timing of switching from the first control stage to the second control stage is determined by the elapsed time.

[0015] (5) In any of the thermoforming apparatuses described in (1) to (3), Preferably, it includes a temperature verification unit for measuring the surface temperature of the sheet. The timing for switching from the first control stage to the second control stage is determined by using the temperature data obtained from the temperature confirmation unit as a trigger.

[0016] Through the forms described in (4) or (5) above, molding can begin at the appropriate time. As explained above, the purpose of multi-stage pressure control for molding is to use compressed air or vacuum molding on the sheet that has been heated to the appropriate temperature during molding, thereby enabling the molding of a product with a more uniform thickness or a target thickness. The timing of switching between control stages can be determined based on the passage of time or based on the temperature data provided by the temperature verification unit.

[0017] (6) In any of the thermoforming apparatuses described in (1) to (5), Preferably, the radiant heating unit is composed of multiple heaters arranged together, and has a first region formed by the heaters corresponding to the protrusions of the mold, and a second region formed by the heaters excluding the first region. The radiant heating unit is equipped with a heating control unit capable of different power controls in the first region and the second region. With the help 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. As part of the second heating stage, when the sheet is brought close to the mold and the sheet has abutted against the protrusion, the first region undergoes low-temperature heating with reduced power, while the second region undergoes high-temperature heating with increased power compared to the first region. The first control phase begins in the second heating phase.

[0018] With the configuration described above (6), high-precision forming can be achieved even under relatively low-pressure conditions by using a thermoforming apparatus with multi-stage heating control, making it less prone to misalignment. This is because the following method is employed: in the first heating stage, the sheet is initially heated to a temperature that prevents sagging; after the sheet comes into contact with the protrusion of the mold, in the second heating stage, low-temperature heating with reduced power is performed in the first region, and high-temperature heating with increased power is performed in the second region compared to the first region.

[0019] During the first heating stage, the sheet heated by the radiant heating device experiences a temperature change at the contact point with the preheated mold. This is because the direct contact between the mold and the sheet causes temperature variations. Consequently, if the same heating continues, some areas will exceed the desired temperature while others will remain too low. To address this issue, heating can be performed in sections, allowing for further heating of desired areas while suppressing heating of unwanted areas, thus facilitating the shaping of the sheet into any desired form.

[0020] Specifically, the following forming process can be achieved: A first region is designated as a non-stretched area requiring alignment, for example. After first contacting the protrusion of the mold, the first region is heated at a low temperature, while a second region corresponding to the area to be deformed is heated at a higher power than the first region. By dividing the heating areas according to multi-stage heating control, the portion to be deformed can be heated precisely, thus deforming the sheet. As a result, forming with higher shape accuracy can be achieved.

[0021] (7) In the thermoforming apparatus described in (6) Preferably, the portion of the sheet material corresponding to the first region is designated as the portion on the molded article that requires alignment.

[0022] With the configuration described above (7), the portion of the sheet material corresponding to the first region first comes into contact with the protrusion 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 article that needs to be aligned, such as the printed portion or the portion used as a transparent window, as the portion of the sheet material corresponding to the first region, the effect of misalignment that occurs during molding can be minimized.

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

[0024] By means of the form described in (8) above, the temperature of the sheet material being tested can be determined by means of a radiation thermometer, thereby enabling more accurate control based on the heating control unit, thus achieving high shape accuracy molding. Attached Figure Description

[0025] Figure 1 The diagram illustrates the general structure of the thermoforming apparatus according to this embodiment. Figure 2 This is a plan view of the heater used in the thermoforming apparatus of this embodiment. Figure 3 This is an explanatory diagram illustrating the third molding process of this embodiment. Figure 4 This is an explanatory diagram illustrating the fourth molding process of this embodiment. Figure 5 This is an explanatory diagram illustrating the fifth molding process of this embodiment. Figure 6 This is a plan view of the heater in this embodiment, corresponding to the third process. Figure 7 This is a plan view of the heater in this embodiment, corresponding to the fourth step. Figure 8 This is a timeline showing the molding sequence of this embodiment. Figure 9 This is a schematic diagram of the thermoforming apparatus system of this embodiment. Detailed Implementation

[0026] First, a general description of the structure of the thermoforming apparatus 100 according to an embodiment of the present invention will be given. Figure 1This is an explanatory diagram illustrating the schematic structure of the thermoforming apparatus 100 of this embodiment. The thermoforming apparatus 100 includes a first chamber 101, a second chamber 102, a heating unit 110, and a mold 200. The structure of the thermoforming apparatus 100 is as follows: a resin sheet S, which is to be molded, is held in the first chamber 101 and the second chamber 102, and molding is performed while being heated by the heating unit 110 disposed on the upper side.

[0027] The thermoforming apparatus 100 has a compressor and a vacuum pump (described later) connected to its first chamber 101 and second chamber 102, respectively. The pressure in the first chamber 101 and second chamber 102 can be adjusted by operating the compressor and vacuum pump. The first chamber 101 opens downwards, and the second chamber 102 opens upwards. The apparatus is designed to hold the resin sheet S by raising and lowering the first chamber 101 and the second chamber 102.

[0028] A compressor or pressurizing tank (not shown) is connected to the first chamber 101, and a first valve V1 (described later) is installed along the first pipe P1, thereby pressurizing the interior of the first chamber 101 to any pressure. A vacuum pump (not shown) is connected to the second chamber 102, and a second valve V2 (described later) is installed along the second pipe P2, thereby depressurizing the interior of the second chamber 102 to any pressure. The first chamber 101 and the second chamber 102 are structures capable of withstanding the internal pressure generated during the pressurization and depressurization processes of the resin sheet S during molding. The first valve V1 and the second valve V2 are pressure control valves capable of detecting the internal pressure and arbitrarily controlling the pressure.

[0029] The resin sheet S is composed of thermoplastic polycarbonate and is cut into rectangular sheets with a thickness of approximately 300 μm. This material and thickness are merely an example, and the material and thickness of the resin sheet S are not limited thereto. However, the purpose of this invention is to solve problems in the processing of relatively thin resin sheets; therefore, the thickness of the resin sheet S used as the processed product is envisioned to be approximately 250 μm to 500 μm. Furthermore, it can also be used with thicker sheets; applying this invention to the molding of thicker sheets is expected to yield effective results.

[0030] Figure 2 A plan view of the heaters used in the thermoforming apparatus 100 is shown. The heating unit 110 is positioned above the resin sheet S and is a group of radiant heaters 111 used for the purpose of heating the resin sheet S from its upper surface. Figure 2 As shown, the heaters 111 are arranged in a tile-like pattern on the lower surface of the upper lifting device 120. Figure 2The illustrations are arranged in 4 rows and 8 columns, but this does not preclude the addition or removal of rows and columns as needed. By adding rows and columns, more detailed shapes can be accommodated.

[0031] The heating unit 110 is held in the upper lifting device 120, which is a structure that allows the heating unit 110 to be moved to any height within the first chamber 101 by means of the first drive device 121 described later. Furthermore, each heater 111 is connected to the heating control unit 250 described later, allowing for arbitrary power adjustment.

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

[0033] The mold 200 is held in a lower lifting device 210 that can be raised and lowered to any height by means of a second driving device 211 described later, for molding the resin sheet S. A protrusion 200a is formed on the mold 200. The protrusion 200a is a portion corresponding to, for example, a portion of the molded article M produced from the resin sheet S where misalignment is not allowed for printing patterns, or a portion where transparency is required and internal deformation is not allowed. For convenience, the portion of the mold 200 other than the protrusion 200a is defined as the lower portion 200b.

[0034] Furthermore, the protrusion 200a of the mold 200 corresponds to Figure 2 The first region A1 in the heating unit 110 shown. The first region A1 is Figure 2 The area enclosed by double-dotted lines and containing four heaters 111 is designated as the second area A2. The mold 200 consists of a protrusion 200a and a lower portion 200b other than the protrusion 200a. The second area A2 of the heating unit 110 corresponds to the lower portion 200b and the portion around the lower portion 200b that the resin sheet S abuts against. Furthermore, it is not impossible to increase the area of ​​the heating unit 110 to two or more.

[0035] Figure 9A schematic diagram of the thermoforming apparatus system is shown. For ease of explanation, the heating unit 110 is omitted from the drawing, but the heaters 111 are connected to the heating control unit 250. Furthermore, a first thermometer S1 and a second thermometer S2, which function as temperature confirmation units, are connected to the heating control unit 250. The control of the heaters 111 is triggered using data from the thermometers (S1 and S2). The first thermometer S1 is configured to target the portion of the sheet material corresponding to the first region A1, and the second thermometer S2 is configured to target the portion of the sheet material corresponding to the second region A2. Moreover, the number of thermometers can be increased as needed. If the heating unit 110 extends beyond the first region A1 and the second region A2, additional thermometers can be added and connected to the heating control unit 250 accordingly.

[0036] The first drive unit 121 driving the upper lifting device 120 and the second drive unit 211 driving the lower lifting device 210 are connected to the drive control unit 260. Although Figure 9 The first chamber 101 and the second chamber 102 are not depicted, but 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. Furthermore, these heating control unit 250, drive control unit 260 and pressure control unit 270 are equipped on the control console 300.

[0037] Next, the molding sequence of the resin sheet S will be explained. The molding process is as follows: Figure 1 , Figures 3 to 5 It was shown in the middle, according to Figure 1 , Figure 3 , Figure 4 , Figure 5 The molding process is carried out in sequence. Figure 8 This diagram illustrates the timeline for controlling various functions during the molding process. The horizontal axis shows the elapsed times t1 to t6, dividing the process into stages. Below, it is divided into stages Pr1 (first stage) to Pr6 (sixth stage), based on... Figure 8 To explain the operation of each device.

[0038] First, in the first process Pr1, with the image Figure 1 The first chamber 101 and the second chamber 102 are closed in a manner shown by using the first chamber 101 and the second chamber 102 to hold the placed resin sheet S.

[0039] Next, in the second process Pr2, the heating unit 110 is held in the position where the upper lifting device 120 has been lowered, and the resin sheet S is heated from above. Figure 1(State of the process). The heating unit 110 performs initial heating using the heater 111. At this time, the heating is set to a slightly softened state for the resin sheet S, and continues until the set temperature is confirmed by the first thermometer S1 and the second thermometer S2. In this embodiment, the resin sheet S is polycarbonate, whose softening temperature is approximately 150 degrees Celsius. Therefore, at this point, it is heated in a first heating stage to a temperature of approximately 140 degrees Celsius, where polycarbonate begins to undergo heat deformation. Since it is desirable to quickly complete the heating of the resin sheet S, the ignition rate (power) of the heater 111 is set to 100%.

[0040] Next, in the third process Pr3, as... Figure 3 As shown, the upper lifting device 120 is raised to lift the heating unit 110. Figure 8 (referred to as "heater"), while simultaneously using the lower lifting device 210 to raise the mold 200 so that it abuts against the resin sheet S ( Figure 8 (Referring to the lifting platform). At this time, the protrusion 200a of the mold 200 abuts against the resin sheet S before the other parts of the mold 200 (the lower part 200b). Thus, while the resin sheet S is heated by the heating unit 110, the mold abuts against the hot resin sheet S, thereby deforming the resin sheet S. Here, since the mold 200 is heated to a low degree (around 120 degrees Celsius), the temperature drops locally when the protrusion 200a abuts against the resin sheet S.

[0041] At this time, the heating control unit 250 receives the image Figure 6 As shown, the first heating stage, in which all heaters 111 perform heating at the same power, is switched to a state similar to... Figure 7 As shown, heating is performed by changing the temperature setting in the first region A1 and the second region A2 in the form of a second heating stage. Here, Figure 7 The first region A1 shown is the position of the heating unit 110 corresponding to the protrusion 200a of the mold 200, and the second region A2 is the position other than the first region A1. The heater 111 corresponding to the first region A1 is set to an ignition rate of 10% when entering the third process Pr3, and the ignition rate of the remaining heaters 111 (which are arranged in the position surrounding the heater 111 corresponding to the first region A1), including the second region A2, is set to 50%. Therefore, the portion of the resin sheet S that abuts against the lower part 200b is actively heated.

[0042] Next, in the fourth process Pr4, the first chamber 101 is pressurized and the second chamber 102 is depressurized to begin molding, triggered by the surface temperature of the resin sheet S reaching 170 degrees Celsius (detected by the second thermometer S2). In the fourth process Pr4, within a specified time period from time t3 to time t4, the pressurization of the first chamber 101 is controlled by limiting the amount of compressed air supplied by the first valve V1. Figure 8 The pressure reduction in the second chamber 102 is controlled by limiting the amount of air discharged through the second valve V2 (referred to as "upper micro-compressed air"). Figure 8 This is referred to as "lower microvacuum" to achieve low-pressure molding. The opening of the first valve V1 and the second valve V2 is controlled by the pressure control unit 270. 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 process Pr5, as... Figure 5 As shown, the supply of compressed air to the first chamber 101 is increased. Figure 8 (referred to as "upper compressed air") and increases the amount of air discharged from the second chamber 102. Figure 8 This is referred to as "lower formal vacuum," meaning that the first valve V1 and the second valve V2 are opened to perform molding at a higher pressure than the previous process. Here, as... 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 become 0.7 MPa, and the pressure in the second chamber 102 is controlled to become -0.1 MPa.

[0044] Finally, in the sixth process Pr6, the internal pressure of the first chamber 101 and the second chamber 102 is restored to atmospheric pressure. Thereafter, the first chamber 101 and the second chamber 102 are opened to remove the molded product M obtained by thermoforming the resin sheet S.

[0045] Since the thermoforming apparatus 100 of this embodiment has the above-described structure, it achieves the following functions and effects.

[0046] First, it enables thermoforming of molded products M with higher precision, making them less prone to misalignment. This is a thermoforming apparatus 100 that heats a resin sheet S using a radiant heating device (heating unit 110) and molds the resin sheet S using a mold 200. The resin sheet S is held in a clamping manner between a first chamber 101 located at the top and a second chamber 102 located at the bottom. The thermoforming apparatus 100 includes a pressure control unit 270 that controls the pressure in the first chamber 101 or the second chamber 102 to an arbitrary pressure during the molding of the resin sheet S.

[0047] Furthermore, 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 to a first vacuum state and a second vacuum state with a vacuum degree higher than the first vacuum state.

[0048] The system enables multi-stage pressure control: In the first control stage, after the mold 200 is brought close to the resin sheet S and the resin sheet S has abutted against the protrusion 200a of the mold 200, the pressure in the first chamber 101 is controlled by changing to a first pressurized state, or the pressure in the second chamber 102 is controlled by changing to a first vacuum state. In the second control stage, during the thermoforming of the resin sheet S, the pressure in the first chamber 101 is controlled by changing to a second pressurized state, or the pressure in the second chamber 102 is controlled by changing to a second vacuum state. This prevents misalignment of the resin sheet S during thermoforming.

[0049] In other words, it is like... Figure 8 The molding process involved controlling the chamber pressure in multiple stages, as shown. The bottom "Vacuum Pressure" graph illustrates the following: during the period from time t3 to time t4, molding was performed with a low pressure (-0.05 MPa) in the second chamber 102. At this time, as described above, for the first chamber 101, the "Upper Micro Compressed Air" control was set to ON, and compressed air was supplied from the first pipe P1 via the pressure control unit 270 with the internal pressure reduced to 0.1 MPa and throttled through the first valve V1. For the second chamber 102, the "Lower Micro Vacuum" control was set to ON, and exhaust was performed from the second pipe P2 via the pressure control unit 270 with the internal pressure reduced to -0.05 MPa and throttled through the second valve V2. This is the first control stage.

[0050] Next, between time t4 and time t5, the process transitions to a second control stage where thermoforming is performed under even higher pressure (controlled at 0.7 MPa in the first chamber 101 and -0.1 MPa in the second chamber 102). This multi-stage pressurization allows for precise molding. Sudden application of high-pressure compressed air can easily cause the resin sheet S to become too thin or break; therefore, multi-stage pressurization ensures a uniform thickness for the molded product M.

[0051] Furthermore, regarding the timing of the switch from the first control stage to the second control stage, for example, data from the temperature confirmation unit (first thermometer S1 and second thermometer S2) can be used for judgment, instead of... Figure 8 As shown, the judgment is not based solely on the passage of time. 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, triggered by either the passage of time or temperature data. The purpose of switching to the second control stage is to improve the adhesion of the resin sheet S on the mold 200, through methods such as... Figure 5 As shown, further increasing the vacuum level (to reach a second vacuum state) when the resin sheet S has already taken the shape of the mold 200 makes it easier to transfer the shape of the mold 200 to the resin sheet S.

[0052] Furthermore, during the first heating stage, the resin sheet S is rapidly heated to a temperature that prevents sagging, and then the mold 200 contacts the resin sheet S, thereby preventing sagging of the resin sheet S. Furthermore, the heating area is divided into a first region A1, which heats at a low temperature, and a second region A2, which heats at a higher temperature than the first region A1. Thus, the portion of the resin sheet S to be deformed is heated as required in the second region A2, thereby achieving deformation. Therefore, multi-stage heating can be performed by controlling the heater 111 using the heating control unit 250, thereby preventing sagging of the resin sheet S 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 region A1 is designated as the portion requiring alignment. For example, if printing is done on the surface of the resin sheet S, misalignment would affect the performance of the product when it is molded into the molded article M, or the transparency would be affected by the deformation that occurs during molding. This prevents misalignment or internal deformation from causing the transparent portion to be difficult to transmit light. The portion of the resin sheet S corresponding to the first region A1 becomes the portion that first abuts against the protrusion 200a of the mold 200 during molding. Furthermore, the power of the first region A1 is further reduced compared to the second region A2 during the second heating stage, thus preventing overheating that could deform the resin sheet S to the required degree, or in some cases, cause wrinkles or damage, and thus molding the resin sheet S into the target shape.

[0054] By combining multi-stage heating and multi-stage pressurization in this way, and controlling the internal pressure of the chamber while thermoforming the resin sheet S, it is possible to prevent the resin sheet S from sagging during heating and to tightly press the resin sheet S onto the mold 200 during molding, thus achieving high shape accuracy. Furthermore, the previously used low-temperature heating and ultra-high-pressure molding methods are no longer required, thereby simplifying the device structure and potentially reducing costs.

[0055] The thermoforming apparatus 100 of the present invention has been described above, but the present invention is not limited thereto, and various modifications can be made without departing from its spirit. For example, the illustrated materials and temperatures can be modified as appropriate. Furthermore, 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 closer to the resin sheet S during the second heating stage. Moving the heater 111 during the second heating stage is an effective method for molding complex shapes with many protrusions and depressions. Conversely, if the heating unit 110 is moved away from the resin sheet S, the temperature gradient can be made gentler.

[0056] Furthermore, as a multi-stage heating process, the initial heating of the resin sheet S in the first heating stage is described by setting the ignition rate of heater 111 to 100%. However, this does not preclude the heating unit 110 from being divided into different zones than the first region A1 and the second region A2, or from being heated by changing the ignition rate according to the division of the first region A1 and the second region A2. For example, consider the case where the ignition rate of the central portion of the resin sheet S is set lower than that of the surrounding area to uniformly heat the resin sheet S. The aim of this first heating stage is to achieve smooth heating of the resin sheet S and avoid problems such as sagging, so it is different from the objective of minimizing the temperature rise of specific areas sought in the subsequent second heating stage. By performing multi-stage heating with different heating conditions in the first and second heating stages, the present invention achieves high-precision molding of the resin sheet S.

[0057] Furthermore, this embodiment demonstrates an example of mold forming using mold 200, but it does not preclude the use of the present invention for thermoforming of a resin sheet S coated and bonded to a substrate. When the present invention is used for coating bonding, the adhesion of the resin sheet S to the substrate can be improved, and higher precision molding can be achieved. In addition, in this 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. However, besides using temperature data as the triggering method, time or observation of vacuum degree could also be considered as triggering methods, so modifications can be made as appropriate.

[0058] Furthermore, this embodiment illustrates the internal pressure of the first chamber 101 and the second chamber 102 of the thermoforming apparatus 100. Figure 8 The timing of these internal pressure changes is explained. The main purpose of the invention is to perform multi-stage control, setting the pressure to low in the first control stage and higher in the second control stage, so it is not impossible to slightly increase or decrease these timing values ​​according to the thickness and temperature of the resin sheet S. Symbol Explanation

[0059] S…Resin Sheets A1…First Area A2…Second Zone 100…Thermoforming apparatus 110… Heating Unit 111… heater 250… Heating Control Unit 200… mold 200a…convex part

Claims

1. A thermoforming apparatus that heats a sheet material using a radiant heating unit and uses a mold to shape the sheet material or coat it onto a substrate, characterized in that... The sheet is held between the first chamber located in the upper part and the second chamber located in the lower part. The thermoforming apparatus includes a pressure control unit that controls the internal pressure of the first chamber or the second chamber during the forming of the sheet. The pressure control unit has the 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 to control 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 achieve the following multi-stage pressure control, namely, As a first control phase, after the sheet is brought close to the mold and the sheet has abutted against the protrusion of the mold, the pressure in the first chamber is controlled in a manner that changes to the first pressurized state, or the pressure in the second chamber is controlled in a manner that changes to the first vacuum state. As a second control stage, the pressure in the first chamber is controlled either by changing to the second pressurized state or by changing to the second vacuum state during the forming of the sheet. The radiant heating unit is composed of multiple heaters arranged together, and has a first region formed by heaters that correspond to the protrusions of the mold and to the part of the sheet that first contacts the mold during molding, and a second region formed by heaters that do not include the first region. The radiant heating unit is equipped with a heating control unit capable of different power controls in the first region and the second region. With the help 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. As part of the second heating stage, when the sheet is brought close to the mold and has abutted against the protrusion, the first region undergoes low-temperature heating with reduced power, while the second region undergoes high-temperature heating with increased power compared to the first region. The first control phase begins in the second heating phase.

2. The thermoforming apparatus according to claim 1, characterized in that, The timing of switching from the first control stage to the second control stage is determined by the elapsed time.

3. The thermoforming apparatus according to claim 1, characterized in that, Equipped with a temperature verification unit for measuring the surface temperature of the sheet. The timing for switching from the first control stage to the second control stage is determined by using the temperature data obtained from the temperature confirmation unit as a trigger.

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