Thermoforming device

Abstract

This thermoforming device (100), which is for performing pneumatic molding or vacuum molding and in which a work space (50) is divided by a resin sheet (S) held in a state in which an upper chamber (101) and a lower chamber (102) are closed, and thus an upper compartment (51) is formed in the upper chamber (101) and a lower compartment (52) is formed in the lower chamber (102), comprises: a first main pipe path (121) that is connected to the upper compartment (51) to form an upper vacuum circuit (120); a first sub pipe path (122) in which the flow path narrows from the first main pipe path (121) and which branches from the first main pipe path (121); a second main pipe path (131) that is connected to the lower compartment (52) and forms a lower vacuum circuit (130); and a second sub pipe path (132) in which the flow path narrows from the second main pipe path (131) and which branches from the second main pipe path (131).

Description

thermoforming equipment

[0001] The present invention relates to a technology for controlling the pressure inside a thermoforming device, and more particularly to a technology for adjusting the degree of vacuum at the start of vacuum buildup in a top-and-bottom chamber thermoforming machine.

[0002] Thermoforming machines are now used in a wide range of fields, including food trays and packaging, and there are an increasing number of cases where higher precision molding is required. Also, when molded products are used in car dashboards and other applications, there are cases where texture is created by painting the molded product on the surface using decorative film, and there are also cases where equipment markings need to be displayed in a specific position. Therefore, there is an increasing demand for positional precision in molding.

[0003] Patent Document 1 discloses technology related to a vacuum forming machine. The vacuum forming machine seals a molding space between a lower box that opens upward and an upper box that opens downward. Within the molding space, a decorative film is adhered to the surface of an adherend. The upper molding space, separated by the decorative film held between the upper and lower boxes, is pressurized, while the lower molding space is depressurized, resulting in the decorative film adhering to the adherend through a pressure adjustment process. The technology prevents sagging of the decorative film, which can cause the film to lift, by stopping heating when a pressure difference is generated in the molding space.

[0004] JP 2015-107638 A

[0005] However, when thermoforming a product, if the degree of vacuum is increased to improve adhesion to the adherend, it takes time to reach the target vacuum. For this reason, it is necessary to increase the evacuation speed of the vacuum circuit to increase productivity, but the applicant has confirmed that doing so results in unstable behavior of the resin sheet or film used as the molded object. The technology described in Patent Document 1 does not mention this issue, making it difficult to resolve. Generally, drawdown is likely to occur during heating of a film or sheet depending on the thickness of the film or sheet, the physical properties of the material, and heating temperature control. In particular, when increasing the degree of vacuum to improve adhesion to the adherend, the impact of film drawdown is likely to be significant.

[0006] The applicant's investigation has confirmed that when a sheet or film is softened by heating, not only does it cause drawdown, in which the center of the film sags, but it also causes deformations that affect molding. When forming a film using a mold or other device in a closed work space formed by preparing an upper and lower container during pressure or vacuum forming, if a pressure difference occurs when increasing the vacuum between the upper and lower chambers separated by the film, the film will swell (droop) on the side with lower pressure. It has been found that increasing the exhaust speed causes the vacuum level to overshoot (exceed the target range) as the valve opens and closes, resulting in the differential pressure switching between the upper and lower chambers and causing the film to repeatedly move up and down. This can lead to defects such as wrinkles in the product.

[0007] Although this problem can be solved by narrowing the piping diameter and sufficiently slowing down the exhaust speed, this would then result in a decrease in productivity. Therefore, an object of the present invention is to provide a thermoforming device that can improve productivity while suppressing the behavior of the sheet or film.

[0008] In order to achieve the above object, a thermoforming apparatus according to one aspect of the present invention has the following features.

[0009] (1) A thermoforming device for performing pressure forming or vacuum forming, comprising an upper container having pressure resistance and opening downward, a lower container having pressure resistance and opening upward, a vacuum circuit connected to the upper container and the lower container, and a heating means for heating a resin molded body held in a working space formed when the upper container and the lower container are closed, wherein the working space is divided by the molded body held in the upper container and the lower container when the upper container and the lower container are closed, thereby forming an upper chamber on the upper container side and a lower chamber on the lower container side, the upper vacuum circuit connected to the upper chamber and regulating the pressure in the upper chamber comprises a first main piping line and a first sub-piping line whose flow path is narrowed from the first main piping line, and the lower vacuum circuit connected to the lower chamber and regulating the pressure in the lower chamber comprises a second main piping line and a second sub-piping line whose flow path is narrowed from the second main piping line, When the molding body is heated by the heating means, the flow rate is adjusted by switching the flow path from the first main piping line to the first sub-piping line and from the second main piping line to the second sub-piping line.

[0010] According to the aspect (1) above, the pressure adjustment of the upper and lower chambers is achieved by switching between the first main and first sub-pipes in the upper vacuum circuit, and by switching between the second main and second sub-pipes in the lower vacuum circuit. Specifically, the flow rate of the first sub-pipe is narrower than that of the first main pipe, and the flow rate of the second sub-pipe is narrower than that of the second main pipe. This allows for the selection of an arbitrary pumping speed.

[0011] Considering the cycle time required to produce a molded product using a thermoforming device, a significant proportion of the time is required for heating or increasing the vacuum level. However, increasing the pipe diameter or flow rate of the first and second main pipes to increase the exhaust speed makes it difficult to control the vacuum level after it reaches the target level, as mentioned above. Therefore, by providing and switching between first and second sub-pipes with reduced flow rates, it becomes easier to control the vacuum level. As a result, it is possible to achieve both easy control of the exhaust speed and the vacuum level, and by controlling the pressure difference between the upper and lower chambers to be small, it is possible to prevent the effects of the pressure difference, such as drawdown of the molded film or sheet, from occurring.

[0012] (2) In the thermoforming apparatus described in (1), it is preferable that the upper vacuum circuit comprises a first main piping valve that connects and cuts off the first main piping line, a first sub-piping valve that connects and cuts off the first sub-piping line, and a first flow rate control valve used to throttle the flow path of the first sub-piping line; and the lower vacuum circuit comprises a second main piping valve that connects and cuts off the second main piping line, a second sub-piping valve that connects and cuts off the second sub-piping line, and a second flow rate control valve used to throttle the flow path of the second sub-piping line; and that after the degree of vacuum in the upper chamber and the lower chamber is reduced using the first main piping line and the second main piping line, the first main piping valve and the second main piping valve are closed, and then the flow rate of the upper vacuum circuit and the flow rate of the lower vacuum circuit are adjusted by opening and closing the first sub-piping valve and the second sub-piping valve, while the molding body is heated by the heating means.

[0013] According to the aspect (2) above, the pressure between the upper and lower chambers can be adjusted by adjusting the flow rate of air flowing in or out of the upper or lower chamber using either the first or second flow control valve, thereby enabling control of the behavior of the resin molded object. This is easily affected by the pressure difference between the upper and lower chambers, or by the flow velocity and flow rate. For example, when the air exhausted from the first main circuit connected to the upper chamber is throttled with the first flow control valve and the lower chamber is controlled for vacuum molding, the air exhausted from the second main circuit connected to the lower chamber can be throttled with the second flow control valve to reduce the differential pressure, thereby preventing the effects of the differential pressure, such as drawdown of the molded film or sheet. This reduces the incidence of defects such as wrinkles and deformation in the molded product.

[0014] (3) In the thermoforming device described in (2), it is preferable that a first vacuum meter for measuring the degree of vacuum is provided in the upper chamber or the first main piping line, a second vacuum meter for measuring the degree of vacuum is provided in the lower chamber or the second main piping line, and the degree of vacuum in the upper chamber or the lower chamber obtained by the first vacuum meter or the second vacuum meter is used to control the opening and closing of the first sub-piping valve or the second sub-piping valve.

[0015] According to the aspect (3) above, by providing the first and second vacuum gauges and using their data as a trigger, accurate control of vacuum adjustment becomes possible, which in turn makes it possible to start molding in a state where the pressure difference between the upper and lower chambers is suppressed and swelling of the molded body is suppressed.

[0016] (4) In the thermoforming apparatus described in either (2) or (3), it is preferable that a first vacuum pump for increasing the degree of vacuum in the upper chamber is connected to the first main piping line, and a second vacuum pump or the first vacuum pump for increasing the degree of vacuum in the lower chamber is connected to the second main piping line, and the flow rate of air exhausted by the upper vacuum circuit and the flow rate of air exhausted by the lower vacuum circuit are adjusted by opening and closing the first sub-piping valve and the second sub-piping valve.

[0017] The aspect described in (4) above allows for the suppression of the behavior of the film or sheet being molded as the vacuum level between the upper and lower chambers is increased. As a result, it is possible to prevent defects such as wrinkles and deformation in the molded product. As noted in the problem section, if a pressure difference occurs when increasing the vacuum level between the upper and lower chambers, the molded product will expand to either the top or bottom. We have also observed situations where the molded product moves up and down when the pressure balance is reversed. This phenomenon becomes more pronounced when the evacuation speed of the vacuum circuit is increased to increase productivity. If this expansion of the molded product (e.g., drawdown) occurs, it can unintentionally adhere to the mold surface, resulting in defective molded products. To solve these problems, molding is performed while controlling the pressure difference between the upper and lower chambers to prevent it from occurring.

[0018] Specifically, after the first vacuum pump and the second vacuum pump are used to reduce the pressure to a predetermined level, the first main piping valve provided on the first main piping line and the second main piping valve provided on the second main piping line are closed, and the flow rates of the first and second sub-piping lines are adjusted by the first and second flow control valves, and the first and second sub-piping valves are opened and closed to control the vacuum level and reach the target vacuum level. By performing this type of control, it is possible to start molding in a state where the pressure difference between the upper and lower chambers is suppressed and swelling of the molded body is suppressed.

[0019] As a result, it is possible to increase the evacuation speed using the first main piping line and the second main piping line, while finely adjusting the vacuum level at a high level, thereby improving the molding cycle time and producing highly accurate molded products. Note that the same effect can be achieved by providing only the first vacuum pump and controlling the first flow rate control valve, the second flow rate control valve, the first sub-piping valve, and the second sub-piping valve. When a second vacuum pump is provided in addition to the first vacuum pump, fine control can be achieved by controlling each vacuum pump separately. However, when the capacities of the upper and lower chambers are small and complex control is not required, selectively using only the first vacuum pump can optimize costs.

[0020] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a thermoforming device according to a first embodiment; FIG. 2 is a time chart of the first embodiment before molding; FIG. 3 is an explanatory diagram illustrating a schematic configuration of a thermoforming device according to the first embodiment at a stage when heating of a resin sheet is started; FIG. 4 is an explanatory diagram illustrating a schematic configuration of a thermoforming device according to the first embodiment in a state in which a vacuum circuit is switched; FIG. 5 is an explanatory diagram illustrating a schematic configuration of a thermoforming device of a conventional technology prepared for comparison; FIG. 6 is an explanatory diagram illustrating a schematic configuration of a thermoforming device according to a second embodiment; and FIG. 7 is an explanatory diagram illustrating a schematic configuration of a thermoforming device according to a third embodiment.

[0021] First Embodiment First, an outline of the configuration of a thermoforming apparatus 100 according to a first embodiment of the present invention will be described. Fig. 1 is an explanatory diagram illustrating the outline of the configuration of the thermoforming apparatus 100 according to the first embodiment. The thermoforming apparatus 100 holds a resin sheet S between an upper chamber (upper container) 101 and a lower chamber (lower container) 102, and performs molding using a mold 150 while heating the resin sheet S with a heating means 110 that can be raised and lowered, such as a radiant heating device.

[0022] The resin sheet S, which corresponds to the molded body, is an ABS sheet material made of a thermoplastic resin with a thickness of approximately 500 μm. According to the JIS standard, a sheet is defined as a plate-like material with a thickness of 250 μm or more, and a film is defined as a membrane-like material with a thickness of less than 250 μm, but this does not preclude the application of the present invention to a film. Furthermore, the material of the resin sheet S is not limited to ABS, and resins such as polypropylene can be appropriately selected as needed.

[0023] An upper vacuum circuit 120 is connected to the upper chamber 101. The upper vacuum circuit 120 includes a first main piping line 121 connected to the upper chamber 101 and a first sub-piping line 122 provided in parallel. A first main piping valve 123 is provided in the first main piping line 121, and opening and closing the first main piping valve 123 connects and disconnects the first main piping line 121. A first sub-piping valve 124 and a first flow rate adjustment valve 125 are provided in the first sub-piping line 122, and the first sub-piping line 122 can be connected and disconnected by opening and closing the first sub-piping valve 124, and the flow rate of the first sub-piping line 122 can be adjusted by adjusting the opening degree of the first flow rate adjustment valve 125.

[0024] The first sub-pipe line 122 is designed to branch off from the first main pipe line 121 between the upper chamber 101 and the first main pipe valve 123 and merge between the first main pipe valve 123 and the first vacuum pump 126. Therefore, when the first vacuum pump 126 connected to the upper vacuum circuit 120 is operated to exhaust air, the first sub-pipe line 122 can be used to evacuate air with a regulated flow rate. The first main pipe valve 123 and the first sub-pipe valve 124 are so-called vacuum valves, which are used in a vacuum circuit and have the function of connecting and disconnecting the circuit. The first flow rate adjustment valve 125 is an adjustment valve that can be used in a vacuum circuit and adjusts the flow rate.

[0025] A lower vacuum circuit 130 is connected to the lower chamber 102. The lower vacuum circuit 130 includes a second main piping line 131 connected to the lower chamber 102 and a second sub-piping line 132 provided in parallel. A second main piping valve 133 is provided in the second main piping line 131, and opening and closing the second main piping valve 133 connects and disconnects the second main piping line 131. A second sub-piping valve 134 and a second flow rate adjustment valve 135 are provided in the second sub-piping line 132, and the second sub-piping line 132 can be connected and disconnected by opening and closing the second sub-piping valve 134, and the flow rate of the second sub-piping line 132 can be adjusted by adjusting the opening degree of the second flow rate adjustment valve 135.

[0026] The second sub-pipe line 132 is designed to branch off from the second main pipe line 131 between the lower chamber 102 and the second main pipe valve 133 and merge between the second main pipe valve 133 and the second vacuum pump 136. Therefore, when the second vacuum pump 136 connected to the lower vacuum circuit 130 is operated to increase the degree of vacuum, the second sub-pipe line 132 can be used to perform evacuation while adjusting the flow rate. The second main pipe valve 133 and the second sub-pipe valve 134 are so-called vacuum valves, which are used in the vacuum circuit and have the function of connecting and disconnecting the circuit. The second flow rate adjustment valve 135 is an adjustment valve used in the vacuum circuit that can adjust the flow rate.

[0027] The first flow rate adjustment valve 125 is adjusted so that the flow rate of the first sub-pipe line 122 is, for example, about 1 / 10 to 1 / 20 of that of the first main piping line 121. The second flow rate adjustment valve 135 is similarly adjusted so that the flow rate of the second sub-pipe line 132 is, for example, about 1 / 10 to 1 / 20 of that of the second main piping line 131. The opening adjustments of the first flow rate adjustment valve 125 and the second flow rate adjustment valve 135 are preferably selected appropriately depending on the physical properties of the resin sheet S, etc.

[0028] The upper chamber 101 and the lower chamber 102 are connected by a connecting pipe 140, and communication between them is established or cut off by opening or closing a connecting pipe valve 141. When the upper chamber 101 and the lower chamber 102 are closed, the internal space becomes a working space 50, which is separated into an upper chamber 51 and a lower chamber 52 by a resin sheet S. Therefore, when the upper chamber 51 and the lower chamber 52 are in communication with each other via the connecting pipe 140, a pressure difference between the upper chamber 51 and the lower chamber 52 is unlikely to occur, but by cutting off the flow path with the connecting pipe valve 141, separate pressure control becomes possible in the upper vacuum circuit 120 and the lower vacuum circuit 130.

[0029] In this way, the upper vacuum circuit 120 is connected to the upper chamber 101, and the lower vacuum circuit 130 is connected to the lower chamber 102, so that compressed air / vacuum forming can be performed using the upper vacuum circuit 120 and the lower vacuum circuit 130. The upper chamber 101 is provided with a first vacuum gauge 105, and the lower chamber 102 is provided with a second vacuum gauge 106. The degree of vacuum is measured by the first vacuum gauge 105 and the second vacuum gauge 106, and the measured value is used as a trigger for pressure control of the upper chamber 51 and the lower chamber 52.

[0030] The outline of the configuration of the thermoforming apparatus 100 according to the present invention has been described above. Next, the molding procedure using the thermoforming apparatus 100 will be briefly explained.

[0031] 2 shows a time chart before molding. The vertical axis shows the operation of each device, and the horizontal axis shows the passage of time. The word "chamber" on the left side indicates the upper chamber 101 and lower chamber 102 that make up the working space 50. In the "open" state, the upper chamber 101 and the lower chamber 102 are separated, and in the "closed" state, the upper chamber 101 and the lower chamber 102 are held with the resin sheet S sandwiched between them.

[0032] The "upper vacuum valve" refers to the first main piping valve 123, which is open when "ON" and communicates with the first main piping line 121. It is closed when "OFF" and blocks the first main piping line 121. The "upper vacuum retention valve" refers to the first sub-piping valve 124, which is open when "ON" and blocks the flow in the first sub-piping line 122. It is closed when "OFF" and blocks the flow in the first sub-piping line 122.

[0033] The "lower vacuum valve" refers to the second main piping valve 133, which is open when "ON" and communicates with the second main piping path 131. It is closed when "OFF" and blocks the second main piping path 131. The "lower vacuum retention valve" refers to the second sub-piping valve 134, which is open when "ON" and blocks the flow in the second sub-piping path 132. It is closed when "OFF" and blocks the flow in the second sub-piping path 132.

[0034] "Heater" indicates the overheated state of the heating means 110; "ON" energizes the heater to heat the resin sheet S, and "OFF" stops energizing the heater. "Upper vacuum" indicates the degree of vacuum in the upper chamber 101. "Lower vacuum" indicates the degree of vacuum in the lower chamber 102. Figure 3 shows a schematic configuration of the thermoforming device at the stage when heating of the resin sheet begins. Figure 4 shows a schematic configuration of the thermoforming device when the vacuum circuit is switched.

[0035] First, after the resin sheet S is loaded into the thermoforming device 100, the upper chamber 101 and the lower chamber 102 are brought close to each other so that the resin sheet S is sandwiched between the upper chamber 101 and the lower chamber 102. This is performed between t1 and t2 in Figure 2. Although not shown, the resin sheet S may be held in a holding frame fixed to the lower chamber 102 as needed.

[0036] Next, during the period from t2 to t5 that constitutes the early evacuation period p1, between t2 and t3, the first main piping valve 123, the first sub-piping valve 124, the second main piping valve 133, the second sub-piping valve 134, and the connecting piping valve 141 are all opened. The first vacuum pump 126 and the second vacuum pump 136 then increase the degree of vacuum in the upper chamber 101 and the lower chamber 102, respectively. This state is shown in FIG. 1 . The degree of vacuum in the upper chamber 101 and the lower chamber 102 is then reduced to approximately 700 Pa by t4, and heating by the heating means 110 is initiated. This state is shown in FIG. 3 .

[0037] Then, at timing t5, the first main piping valve 123 and the second main piping valve 133 are closed to shut off the first main piping line 121 and the second main piping line 131. The connecting piping valve 141 is also shut off. As a result, the degree of vacuum is increased in the first sub-piping line 122, the flow rate of which is determined by the first flow rate adjustment valve 125, and in the second sub-piping line 132, the flow rate of which is determined by the second flow rate adjustment valve 135, and the vacuum exhaust speed decreases.

[0038] Next, during the period from t5 to t16 that constitutes the latter exhaust period p2, the first sub-piping valve 124 is closed between t6 and t7 to stop the evacuation of the upper vacuum circuit 120. Furthermore, the first sub-piping valve 124 is opened between t8 and t9 to perform evacuation of the upper vacuum circuit 120. Furthermore, the first sub-piping valve 124 is controlled to be closed between t11 and t12 and opened between t14 and t15. This opening and closing control of the first sub-piping valve 124 is performed based on the value obtained by measuring the degree of vacuum in the upper chamber 51 with the first vacuum gauge 105. The first sub-piping valve 124 is closed when the upper vacuum degree lower limit b12 is reached, and is opened when the upper vacuum degree upper limit b11 is reached. In this way, the degree of vacuum in upper chamber 101 is controlled between upper vacuum upper limit value b11 and upper vacuum lower limit value b12.

[0039] Furthermore, between t9 and t10, the second sub-piping valve 134 is closed to stop evacuation in the lower vacuum circuit 130. Next, between t11 and t12, the second sub-piping valve 134 is opened to perform evacuation in the lower vacuum circuit 130. The opening and closing of the second sub-piping valve 134 is controlled based on the vacuum level in the lower chamber 52 measured by the second vacuum gauge 106. The second sub-piping valve 134 is closed when the lower vacuum level reaches the lower vacuum lower limit b22, and is opened when the lower vacuum level reaches the lower vacuum upper limit b21. In this way, the vacuum level in the lower chamber 102 is controlled to be between the lower vacuum upper limit b21 and the lower vacuum lower limit b22. The state of this final evacuation period p2 is shown in FIG. 4.

[0040] Then, at timing t16, heating of the resin sheet S is completed. Furthermore, the degree of vacuum in the upper chamber 101 is controlled between an upper vacuum upper limit value b11 and an upper vacuum lower limit value b12, and the degree of vacuum in the lower chamber 102 is controlled between a lower vacuum upper limit value b21 and a lower vacuum lower limit value b22, so that the pressure difference between the upper chamber 101 and the lower chamber 102 is a specified value. In this state, molding of the resin sheet S begins using the mold 150.

[0041] The thermoforming device 100 of the first embodiment has the above-described configuration, and therefore provides the following functions and effects.

[0042] First, an effect can be achieved in that it is possible to provide a thermoforming apparatus 100 that can prevent drawdown of the resin sheet S during heating, which can lead to defective molded products. This thermoforming apparatus 100 includes an upper container (upper chamber 101) that is pressure-resistant and opens downward, and a lower container (lower chamber 102) that is pressure-resistant and opens upward, in which vacuum circuits (upper vacuum circuit 120, lower vacuum circuit 130) are connected to the upper chamber 101 and the lower chamber 102, and in which a resin body to be molded (resin sheet S) is held in a work space formed when the upper chamber 101 and the lower chamber 102 are closed and heated by heating means 110, thereby performing pressure forming or vacuum forming. In this thermoforming apparatus 100, a work space 50 is formed by the resin sheet S held in the upper chamber 101 and the lower chamber 102 being closed, so that an upper chamber 51 is formed in the upper chamber 101 and a lower chamber 52 is formed in the lower chamber 102.

[0043] The system further comprises a first main piping line 121 connected to the upper chamber 51 to form an upper vacuum circuit 120, a first sub-piping line 122 whose flow path is narrowed from the first main piping line 121 and branched off from the first main piping line 121, a second main piping line 131 connected to the lower chamber 52 to form a lower vacuum circuit 130, and a second sub-piping line 132 whose flow path is narrowed from the second main piping line 131 and branched off from the second main piping line 131.

[0044] Then, by switching the flow path from the first main piping path 121 and the second main piping path 131 to the first sub-piping path 122 and the second sub-piping path 132, the flow rate is adjusted, and the resin sheet S is heated by the heating means 110 and molded. Because of these characteristics, the effect of being able to prevent deformation such as drawdown when the resin sheet S is heated can be obtained.

[0045] This is believed to be due to the effect described below. Figure 5 shows a thermoforming machine prepared for comparison, in which a sub-pipe is not provided in the vacuum circuit. The thermoforming machine 200 prepared for comparison with the embodiment of the present invention is equipped with a first main piping line 121 and a first main piping valve 123, and a second main piping line 131 and a second main piping valve 133. A first vacuum pump 126 and a second vacuum pump 136 are connected to the machine, respectively, to enable evacuation.

[0046] In this configuration, evacuation is performed using the first vacuum pump 126 and the second vacuum pump 136, and when the target vacuum level is reached and the first main piping valve 123 and the second main piping valve 133 are closed, the evacuation stops. This may cause the resin sheet S to behave up and down as shown in FIG.

[0047] This is because differences in the capacity of the upper chamber 101 and the lower chamber 102, and differences in the lengths of the paths of the first main piping path 121 and the second main piping path 131, result in differences in the speed of evacuation, causing the degree of vacuum to increase more quickly in either the upper chamber 101 or the lower chamber 102, and as a result, swelling of the resin sheet S (also known as drawdown when swelling occurs in the lower chamber 102) occurs in the chamber with the lower degree of vacuum.

[0048] This problem is particularly likely to occur when the effective cross-sectional areas of the first main piping passage 121 and the second main piping passage 131 are increased to increase the vacuum exhaust speed during the process of manufacturing molded products using the thermoforming apparatus 100. While this is unlikely to be a problem during the early exhaust period p1, during the later exhaust period p2, the high exhaust speed at the timing of opening and closing the first main piping valve 123 or the second main piping valve 133 will have an effect, causing the exhaust pressure to fall below the lower limit when one side is opened.

[0049] In other words, the controllable degree of vacuum fluctuates widely, and the overshoot in the degree of vacuum that occurs when the first main piping valve 123 or the second main piping valve 133 is opened or closed causes the resin sheet S to move up and down. This can cause wrinkles in the resin sheet S, resulting in a defective product. To prevent this, it is possible to adjust the degree of vacuum by opening the connecting piping valve 141 to leak air from the upper chamber 51 and the lower chamber 52, but this is not desirable because it can lead to problems such as air getting between the mold 150 and the resin sheet S.

[0050] To prevent such effects, the thermoforming apparatus 100 of the present invention switches the flow paths so that the first main piping path 121 and the second main piping path 131 are used during the early exhaust period p1, and the first sub-piping path 122 and the second sub-piping path 132 are used during the later exhaust period p2. Because the flow rates of the first sub-piping path 122 and the second sub-piping path 132 are restricted by the first flow control valve 125 and the second flow control valve 135, it is possible to prevent vacuum overshoot even when adjusting the vacuum level in the upper chamber 101 and the lower chamber 102 by opening and closing the first sub-piping valve 124 and the second sub-piping valve 134.

[0051] Furthermore, by separating the upper vacuum circuit 120 and the lower vacuum circuit 130, it is possible to set the upper vacuum upper limit b11 and the upper vacuum lower limit b12, and the lower vacuum upper limit b21 and the lower vacuum lower limit b22, in separate ranges. In this example, for example, if the upper vacuum upper limit b11 is 585 Pa, the upper vacuum lower limit b12 is 580 Pa, the lower vacuum upper limit b21 is 605 Pa, and the lower vacuum lower limit b22 is 600 Pa, setting the upper vacuum circuit 120 to a higher vacuum than the lower vacuum circuit 130 will result in pressure adjustment such that the resin sheet S is pulled toward the upper chamber 51.

[0052] For this reason, even if drawdown of the resin sheet S occurs due to the influence of heating by the heating means 110 that begins at a time as shown in Fig. 3 (around t4 to t6 in Fig. 2), drawdown of the resin sheet S can be suppressed by closing the first sub-piping valve 124 during the latter exhaust period p2 (around t8 to t15 in Fig. 4), separating the upper vacuum circuit 120 from the lower vacuum circuit 130, and setting a higher degree of vacuum on the upper vacuum circuit 120 side. This results in improved manufacturing accuracy of the molded product.

[0053] Second Embodiment Next, a second embodiment of the present invention will be described. The thermoforming apparatus of the second embodiment has substantially the same configuration as the thermoforming apparatus of the first embodiment, but differs in the configurations of the upper vacuum circuit 120 and the lower vacuum circuit 130. FIG. 6 is an explanatory diagram illustrating the schematic configuration of the thermoforming apparatus of the second embodiment. In the upper vacuum circuit 120, a first main piping line 121 and a first sub-piping line 122 are each connected to the upper chamber 101. The first main piping line 121 is provided with a first main piping valve 123 and a first vacuum pump 126. The first sub-piping line 122 is provided with a first sub-piping valve 124, a first flow rate adjustment valve 125, and a third vacuum pump 127.

[0054] In the lower vacuum circuit 130, a second main piping line 131 and a second sub-piping line 132 are each connected to the lower chamber 102. A second main piping valve 133 and a second vacuum pump 136 are provided in the second main piping line 131. A second sub-piping valve 134, a second flow rate adjustment valve 135, and a fourth vacuum pump 137 are provided in the second sub-piping line 132. The valves of the upper vacuum circuit 120 and the lower vacuum circuit 130 configured as described above can be controlled in the same way as in the thermoforming apparatus 100 of the first embodiment, and similar effects can be obtained.

[0055] Third Embodiment Next, a third embodiment of the present invention will be described. The thermoforming apparatus of the third embodiment has substantially the same configuration as the thermoforming apparatus of the first embodiment, but differs in the configurations of the upper vacuum circuit 120 and the lower vacuum circuit 130. Figure 7 shows an explanatory diagram illustrating the schematic configuration of the thermoforming apparatus of the third embodiment. The upper vacuum circuit 120 and the lower vacuum circuit 130 are configured to evacuate using a common fifth vacuum pump 128. The valve control of the upper vacuum circuit 120 and the lower vacuum circuit 130 configured in this manner can be the same as that of the thermoforming apparatus 100 of the first embodiment, and similar effects can be obtained.

[0056] Therefore, by connecting the fifth vacuum pump 128 to the upper vacuum circuit 120 and the lower vacuum circuit 130, the number of vacuum pumps used can be reduced, which can contribute to cost reduction. Depending on the capacities of the upper chamber 51 and the lower chamber 52 and the required responsiveness, even if a configuration is adopted in which only one fifth vacuum pump 128 is provided, the same effects as those of the first or second embodiment can be obtained and costs can be optimized. Furthermore, the simplified device configuration can be expected to contribute to the miniaturization of the device.

[0057] The thermoforming apparatus 100 according to the present invention has been described above, but the present invention is not limited thereto, and various modifications are possible without departing from the spirit of the present invention. For example, the first sub-pipe line 122 and the second sub-pipe line 132 may be used for a short period of time during the early exhaust period p1 to reduce the influence of the vacuum exhaust immediately after startup, thereby controlling the vacuum exhaust speed. Furthermore, the configurations of the upper vacuum circuit 120 and the lower vacuum circuit 130 shown in the first through third embodiments are merely examples, and other configurations that achieve similar effects are also possible. For example, a combination of the first embodiment for the upper vacuum circuit 120 and the second embodiment for the lower vacuum circuit 130 may be used.

[0058] Furthermore, although the first to third embodiments each describe thermoforming using a mold, this does not preclude the use of the configuration of the present invention for coating or molding onto a substrate or transferring onto a substrate.

[0059] S: Resin sheet 50: Working space 51: Upper chamber 52: Lower chamber 100: Thermoforming device 101: Upper chamber 102: Lower chamber 110: Heating means 120: Upper vacuum circuit 130: Lower vacuum circuit

Claims

1. A thermoforming device for performing pressure forming or vacuum forming, comprising an upper container having pressure resistance and opening downward, a lower container having pressure resistance and opening upward, a vacuum circuit connected to the upper container and the lower container, and heating means for heating a resin molded body held in a work space formed when the upper container and the lower container are closed, wherein the work space is divided by the molded body held in the upper container and the lower container are closed, forming an upper chamber on the upper container side and a lower chamber on the lower container side, an upper vacuum circuit connected to the upper chamber and regulating the pressure in the upper chamber comprises a first main piping line and a first sub-piping line having a flow path narrowed from the first main piping line, and a lower vacuum circuit connected to the lower chamber and regulating the pressure in the lower chamber comprises a second main piping line and a second sub-piping line having a flow path narrowed from the second main piping line, and when the molded body is heated by the heating means, a flow rate is adjusted by switching a flow path from the first main piping path to the first sub-piping path and from the second main piping path to the second sub-piping path, respectively.

2. A thermoforming device as claimed in claim 1, wherein said upper vacuum circuit comprises a first main piping valve for connecting and cutting off said first main piping line, a first sub-piping valve for connecting and cutting off said first sub-piping line, and a first flow rate control valve used for the purpose of throttling the flow path of said first sub-piping line, and said lower vacuum circuit comprises a second main piping valve for connecting and cutting off said second main piping line, a second sub-piping valve for connecting and cutting off said second sub-piping line, and a second flow rate control valve used for the purpose of throttling the flow path of said second sub-piping line, wherein after the degree of vacuum in said upper chamber and said lower chamber is reduced using said first main piping line and said second main piping line, said first main piping valve and said second main piping valve are closed, and then said flow rate in said upper vacuum circuit and said flow rate in said lower vacuum circuit are adjusted by opening and closing said first sub-piping valve and said second sub-piping valve while said heating means heats said molded body, A thermoforming device comprising:

3. A thermoforming device as claimed in claim 2, characterized in that: a first vacuum gauge for measuring the degree of vacuum is provided in the upper chamber or the first main piping line; a second vacuum gauge for measuring the degree of vacuum is provided in the lower chamber or the second main piping line; and the degree of vacuum in the upper chamber or the lower chamber obtained by the first vacuum gauge or the second vacuum gauge is used to control the opening and closing of the first sub-piping valve or the second sub-piping valve.

4. A thermoforming device as claimed in claim 2, characterized in that: a first vacuum pump for increasing the degree of vacuum in the upper chamber is connected to the first main piping path; a second vacuum pump for increasing the degree of vacuum in the lower chamber or the first vacuum pump is connected to the second main piping path; and the flow rate of air exhausted by the upper vacuum circuit and the flow rate of air exhausted by the lower vacuum circuit are adjusted by opening and closing the first auxiliary piping valve and the second auxiliary piping valve.

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