THERMOFORMING DEVICE

Abstract

This thermoforming device (100), which is used for performing compressed air or vacuum forming and in which a working chamber (50) is divided by a resin sheet structure (S) which is held in a state in which an upper chamber (101) and a lower chamber (102) are closed, thus forming an upper compartment (51) in the upper chamber (101) and a lower compartment (52) in the lower chamber (102), includes the following: a first main pipe path (121) which is connected to the upper compartment (51) to form an upper vacuum circuit (120); a first subordinate pipe path (122) in which the flow path narrows from the first main pipe path (121) and which branches off from the first main pipe path (121); a second main pipe path (131) which is connected to the lower compartment (52) and forms a lower vacuum circuit (130);and a second subordinate pipe path (132) in which the flow path narrows from the second main pipe path (131) and which branches off from the second main pipe path (131).

Description

AREA OF INVENTION

[0001] The present invention relates to a technique for controlling the internal pressure of a thermoforming device, specifically a technique for adjusting the degree of vacuum at a vacuum rise time of a thermoforming device of the type with an upper and a lower chamber. GENERAL STATE OF THE ART

[0002] It is increasingly necessary for thermoforming equipment, widely used for food trays, packaging, and other applications, to achieve highly accurate forming or shaping. Furthermore, when formed products are used, for example, as vehicle dashboards, decorative films are sometimes applied to their surface to allow for printing and adding texture. In such cases, the labels for displays or gauges must be printed in specific positions. Consequently, there is a growing need for positional accuracy in the forming process.

[0003] Patent document 1 discloses the technology relating to a vacuum forming machine. This vacuum forming machine is configured such that a forming chamber is hermetically sealed by a lower box opening upwards and an upper box opening downwards, and a decorative film is firmly applied to the surface of a substrate and shaped within the forming chamber. In this machine, the decorative film, clamped by the upper and lower boxes, thus dividing the forming chamber into an upper and a lower chamber, is brought into close contact with the substrate in a pressure setting step involving the creation of a high-pressure environment in the upper chamber and a low-pressure environment in the lower chamber. This technology prevents sagging of the decorative film, which can cause it to float, by stopping the heating process when a pressure differential is created between the forming chambers. DOCUMENTS ON RELATED TECHNOLOGY PATENT DOCUMENTS

[0004] Patent document 1: Japanese unexamined patent application, publication no. 2015-107638 SUMMARY OF THE INVENTION PROBLEMS THAT WILL BE SOLVED BY THE INVENTION

[0005] However, when products are thermoformed while the vacuum level is increased to improve adhesion to the substrate, reaching the target vacuum level takes time. Therefore, to improve productivity, it is necessary to increase the vacuum extraction rate of a vacuum circuit. The applicant has confirmed, however, that such an increased rate results in unstable behavior of a resin sheet or film, which is the workpiece to be formed. The technology disclosed in patent document 1 does not address this defect and therefore could not remedy it. Depending on the thickness and material properties of the film or sheet and the heating temperature control, the film or sheet is generally prone to sagging during heating.In particular, when the level of vacuum is increased to enhance adhesion to a substrate, the increased vacuum tends to cause significant sagging of the film.

[0006] The applicant has confirmed through investigations that when a sheet or film is heated and softened, it not only sags (i.e., a sagging of the film's center) but also undergoes deformation affecting the forming process. In pressure forming or vacuum forming, when film forming is carried out using a forming tool and other equipment in a workspace formed by an upper and lower container in a closed state, a pressure differential is created between the upper and lower compartments, which are separated by the film at the time the vacuum level is increased. This causes the film to bulge (sag) towards the side with the lower pressure. Increasing the suction rate causes the vacuum level to overshoot (exceed a target range) in conjunction with the opening and closing of the valve.This causes the differential pressure between the upper and lower compartments to reverse, resulting in the film repeatedly moving up and down. This can lead to product defects, such as creases.

[0007] The problems mentioned above could be solved by reducing the diameter of the pipes to sufficiently slow the extraction rate. However, such a configuration would reduce productivity. Therefore, the present invention aims to provide a thermoforming device capable of increasing productivity while suppressing the behavior of a sheet or film. MEANS TO SOLVE THE PROBLEMS

[0008] To achieve the above-mentioned goal, one aspect of the present invention provides the following configurations.

[0009] (1) A thermoforming device for performing pressure forming or vacuum forming, the device comprising: an upper container having a pressure-resistant property and opening downwards; a lower container having a pressure-resistant property and opening upwards; and heating means for heating a workpiece made of resin which is held in a working chamber formed by the upper container and the lower container in a closed state, wherein the upper container and the lower container are connected to a vacuum circuit, is characterized in that the workpiece clamped by the upper container and the lower container in the closed state divides the working chamber into an upper compartment in the upper chamber and a lower compartment in the lower chamber, an upper vacuum circuit which is connected to the upper compartment to regulate the internal pressure of the upper compartment,comprising a first main line and a first branch line with a flow path that is more restricted than the first main line, a lower vacuum circuit connected to the lower compartment to regulate the internal pressure of the lower compartment, comprising a second main line and a second branch line with a flow path that is more restricted than the second main line, and a flow rate during heating of the workpiece using the heating medium, regulated by switching the flow paths from the first main line to the first branch line and from the second main line to the second branch line.

[0010] In the configuration described above in (1), the pressure setting of the upper and lower compartments is achieved by switching between the first main line and the first branch line in the upper vacuum circuit and between the second main line and the second branch line in the lower vacuum circuit. Specifically, the flow rate in the first branch line is restricted more than in the first main line, and the flow rate in the second branch line is restricted more than in the second main line. This allows for the arbitrary selection of the suction velocity.

[0011] When considering a sequence of cycle times in the production of a molded product using a thermoforming device, a large percentage of this time is taken up by either warm-up time or the time required to increase the vacuum level. However, if, as mentioned, the pipe diameters or flow velocities in the first and second main lines are increased to raise the extraction rates, it becomes difficult to control the vacuum levels once the target vacuum levels have been reached. Therefore, switching to the first and second branch lines, each providing a restricted flow rate, can facilitate vacuum level control. Consequently, both the extraction rates and the vacuum levels are easily controlled, while the differential pressure between the upper and lower compartments is reduced.This makes it possible to prevent the undesirable effects caused by differential pressure, such as wrinkling or sagging of the film or sheet material that is the workpiece to be formed.

[0012] (2) In the thermoforming device described in (1), the upper vacuum circuit preferably comprises: a first main line valve for opening and closing the first main line; a first branch line valve for opening and closing the first branch line; and a first flow control valve used to restrict the flow path of the first branch line, wherein the lower vacuum circuit comprises: a second main line valve for opening and closing the second main line; a second branch line valve for opening and closing the second branch line;and a second flow control valve used to restrict the flow path of the second branch line, and the device is configured to reduce the vacuum level of the upper compartment using the first main line and to reduce the vacuum level of the lower compartment using the second main line, and then to close the first main line valve and the second main line valve, after which the workpiece is heated by means of the heating medium while the first branch line valve and the second branch line valve are opened and closed to control a flow rate in the upper vacuum circuit and a flow rate in the lower vacuum circuit.

[0013] In the configuration described above in (2), the pressure of the upper compartment and the pressure of the lower compartment are controlled by regulating the flow rate of air that allows it to flow into or out of the upper or lower compartment(s) using the first or second main line valve. This enables control of the behavior of the resin-made workpiece. This behavior is sensitive to pressure differences between the upper and lower compartments, as well as the flow velocity or flow rate.Therefore, for example, when controlling the vacuum formation on the lower tray side by throttling or restricting the amount of air to be drawn from the first main circuit connected to the upper tray, the first flow control valve restricts the amount of air to be drawn from the second main circuit connected to the lower tray in order to reduce the differential pressure. This control can reduce the undesirable effects caused by the differential pressure, such as sagging of the film or sheet material being formed. This makes it possible to reduce the rate of defects, such as creases or deformation, in formed products.

[0014] (3) The thermoforming device described in (2) preferably comprises: a first vacuum gauge in the upper compartment or the first main line for measuring the degree of vacuum; and a second vacuum gauge in the lower compartment or the second main line for measuring the degree of vacuum, wherein the first main line valve or the second main line valve is controlled to open and close by using the degree of vacuum of the upper compartment or the lower compartment, measured by the first vacuum gauge or the second vacuum gauge.

[0015] In the configuration described above in (3), comprising the first vacuum gauge and the second vacuum gauge, and using their data as triggers, it is possible to precisely control the setting of vacuum levels. Consequently, this configuration can initiate forming from a state in which the workpiece is prevented from warping by preventing the generation of pressure differences between the upper and lower compartments.

[0016] (4) In the thermoforming device described in (2) or (3), preferably a first vacuum pump is connected to the first main line to increase the vacuum level of the upper compartment, a second vacuum pump or the first vacuum pump is connected to the second main line to increase the vacuum level of the lower compartment, and a flow rate of air to be extracted through the upper vacuum circuit and a flow rate of air to be extracted through the lower vacuum circuit are regulated by opening and closing the first branch line valve and the second branch line valve.

[0017] In the configuration described above in (4), it is possible to control the behavior of the film or sheet material to be formed during the process of increasing the vacuum level in the upper and lower compartments. This makes it possible to prevent defects such as wrinkles and deformation in the formed product. As mentioned above as the problems, it has been confirmed that when a pressure differential arises during the process of increasing the vacuum level in the upper and lower compartments, the workpiece bulges either towards the upper or the lower compartment, reversing the pressure equilibrium and causing the workpiece to move up and down. This phenomenon is particularly noticeable when the vacuum extraction rate in the vacuum circuit is increased to boost productivity. If this bulging of the workpiece (e.g.,If sagging occurs, the workpiece unintentionally sticks to the surface of the mold, resulting in a defective molded product. To prevent such problems, molding is carried out while controlling the vacuum levels to minimize the generation of differential pressure between the upper and lower trays.

[0018] Specifically, after reducing the vacuum to a predetermined level using the first and second vacuum pumps, the first main line valve, installed on the first main line, and the second main line valve, installed on the second main line, are closed. Then, while the flow rate of the first and second branch lines is regulated using the first and second flow control valves, the first and second branch line valves are opened and closed to control the vacuum levels until the target vacuum levels are reached. This control enables the forming process to begin while preventing the generation of pressure differentials between the upper and lower compartments and thus preventing warping of the workpiece.

[0019] It is therefore possible to finely control the vacuum levels in elevated conditions while increasing the vacuum extraction rates using the first and second main lines. This means that while the molding cycle time is improved, highly accurate molded products can be obtained. At this stage, only the first vacuum pump may be configured to control the first flow control valve, the second flow control valve, the first branch line valve, and the second branch line valve. This configuration can also achieve the same beneficial effects as described above. The configuration that includes a second vacuum pump in addition to the first allows for precise control by controlling each of these vacuum pumps. However, if the upper and lower compartments have small volumes and no complex control is required, only the first vacuum pump is selectively used, enabling cost optimization. BRIEF DESCRIPTION OF THE FIGURES [ Fig. Figure 1] is an explanatory diagram showing a schematic configuration of a thermoforming device in a first embodiment. [ Fig. 2] is a time graph before the forming process in the first embodiment. [ Fig. Figure 3] is an explanatory diagram showing a schematic configuration of the thermoforming device in a phase of beginning the heating of a resin sheet structure in the first embodiment. [ Fig. Figure 4] is an explanatory diagram showing a schematic configuration of the thermoforming device in which vacuum circuits have been changed in the first embodiment. [ Fig. Figure 5] is an explanatory diagram showing a schematic configuration of a thermoforming device based on a conventional prior art, manufactured for comparison. [ Fig. Figure 6] is an explanatory diagram showing a schematic configuration of a thermoforming device in a second embodiment. [ Fig. Figure 7] is an explanatory diagram showing a schematic configuration of a thermoforming device in a third embodiment. WAY OF EXECUTING THE INVENTION (First embodiment)

[0020] A schematic configuration of a thermoforming device 100 in a first embodiment according to the present invention is described first. Fig. Figure 1 is an explanatory diagram showing the schematic configuration of the thermoforming device 100 in the first embodiment. While clamping a resin sheet structure S between an upper chamber (an upper container) 101 and a lower chamber (a lower container) 102, the thermoforming device 100 performs the forming of the resin sheet structure S using a forming tool 150, while heating the resin sheet structure S using a heating medium 110 that can be moved up and down, such as a radiant heating device.

[0021] The resin sheet S, corresponding to a workpiece to be formed, is an ABS sheet material made from a thermoplastic resin with a thickness of approximately 500 µm. According to Japanese Industrial Standards (JIS), a sheet is defined as a plate-like material with a thickness of 250 µm or more, and a film is a membrane-like material with a thickness of less than 250 µm. However, the present invention can also be applied to the film. Furthermore, the material of the resin sheet S is not limited to ABS and can, if necessary, be selected from other resins, such as polypropylene.

[0022] The upper chamber 101 is connected to an upper vacuum circuit 120. The upper vacuum circuit 120 comprises a first main line 121, which is connected to the upper chamber 101, and a first branch line 122 located parallel to it. A first main line valve 123 is provided on the first main line 121 and is actuated to open and close, thereby enabling and blocking communication through the first main line 121. A first branch line valve 124 and a first flow control valve 125 are arranged on the first branch line 122. The first branch line valve 124 opens and closes, thereby enabling and blocking communication through the first branch line 122. The opening degree of the first flow control valve 125 is adjusted to regulate a flow rate in the first branch line 122.

[0023] The first branch line 122 is designed to branch off from the first main line 121 between the upper chamber 101 and the first main line valve 123, and to connect to the first main line 121 between the first main line valve 123 and a first vacuum pump 126. Therefore, when air is extracted by actuating the first vacuum pump 126, which is connected to the upper vacuum circuit 120, it is possible to extract air at a flow rate set by the first branch line 122. Here, the first main line valve 123 and the first branch line valve 124 are so-called vacuum valves, which are used in a vacuum circuit to enable or block communication through the circuit. Furthermore, the first flow control valve 125 is a control valve used in the vacuum circuit to regulate the flow rate.

[0024] The lower chamber 102 is connected to a lower vacuum circuit 130. This lower vacuum circuit 130 comprises a second main line 131 connected to the lower chamber 102 and a second branch line 132 running parallel to it. A second main line valve 133 is located on the second main line 131 and opens or closes, thereby enabling or blocking communication through the second main line 131. A second branch line valve 134 and a second flow control valve 135 are located on the second branch line 132. The second branch line valve 134 opens and closes, thereby enabling or blocking communication through the second branch line 132. The opening degree of the second flow control valve 135 is adjusted to regulate a flow rate in the first branch line 132.

[0025] The second branch line 132 is designed to branch off from the second main line 131 between the lower chamber 102 and the second main line valve 133, and to connect to the second main line 131 between the second main line valve 133 and the second vacuum pump 136. Therefore, when increasing the vacuum level by actuating the second vacuum pump 136, which is connected to the lower vacuum circuit 130, it is possible to extract air at a flow rate set by the second branch line 132. The second main line valve 133 and the second branch line valve 134 are vacuum valves used in a vacuum circuit to enable or block communication through the circuit. Furthermore, the second flow control valve 135 is a control valve used in the vacuum circuit to regulate the flow rate.

[0026] The first flow control valve 125 is adjusted so that the flow rate in the first branch line 122 is approximately 1 / 10 to 1 / 20 of that in the first main line 121. Similarly, the second flow control valve 135 is adjusted so that the flow rate in the second branch line 132 is approximately 1 / 10 to 1 / 20 of that in the second main line 131. The first flow control valve 125 and the second flow control valve 135 are preferably set to an opening degree that is appropriately selected based on the physical properties of the resin surface structure S.

[0027] The upper chamber 101 and the lower chamber 102 are connected by a connecting line 140 with a connecting line valve 141, which opens and closes, thus enabling or blocking communication between these chambers. When the upper chamber 101 and the lower chamber 102 are closed, the interior space formed therein is a working space 50, which is divided by the resin surface structure S into an upper compartment 51 and a lower compartment 52. Therefore, while the upper compartment 51 and the lower compartment 52 are communicating with each other via the connecting line 140, a differential pressure between this upper compartment 51 and this lower compartment 52 is less likely to occur. In contrast, when a flow path is blocked by the connecting line valve 141, it is possible to control the pressure in the upper vacuum circuit 120 and the pressure in the lower vacuum circuit 130 separately.

[0028] To perform pressure forming and vacuum forming using the upper vacuum circuit 120 and the lower vacuum circuit 130 as described above, 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. The upper chamber 101 is equipped with a first vacuum gauge 105 and the lower chamber 102 is equipped with a second vacuum gauge 106. The vacuum levels measured by the first vacuum gauge 105 and the second vacuum gauge 106 are used as triggers for the pressure control of the upper compartment 51 and the lower compartment 52.

[0029] The schematic configuration of the thermoforming device 100 according to the present invention is as described above. The following description is simplified by referring to the forming process using the thermoforming device 100.

[0030] Fig. Figure 2 is a time graph showing the process before the forming stage. The vertical axis indicates the processes of each component, and the horizontal axis indicates the time progression. On the left is a label "chamber" for the upper chamber 101 and the lower chamber 102, which form the working space 50. "Open" means that the upper chamber 101 and the lower chamber 102 are separated, and "Closed" means that the upper chamber 101 and the lower chamber 102 are clamped between them, enclosing the resin surface structure S.

[0031] A label "upper vacuum valve" refers to the first main line valve 123. "ON" means that the first main line valve 123 is open, allowing communication through the first main line 121, and "OFF" means that the first main line valve 123 is closed, blocking communication through the first main line 121. A label "upper vacuum holding valve" refers to the first branch line valve 124. "ON" means that the first branch line valve 124 is open, blocking flow communication through the first branch line 122, and "OFF" means that the first branch line valve 124 is closed, blocking flow communication through the first branch line 122.

[0032] A label "lower vacuum valve" refers to the second main line valve 133. "ON" means that the second main line valve 133 is open, allowing communication through the second main line 131, and "OFF" means that the second main line valve 133 is closed, blocking communication through the second main line 131. A label "lower vacuum holding valve" refers to the second branch line valve 134. "ON" means that the second branch line valve 134 is open, blocking flow communication through the second branch line 132, and "OFF" means that the second branch line valve 134 is closed, blocking flow communication through the second branch line 132.

[0033] A label labeled "Heating" indicates a superheated state of the heating medium 110. When "ON," the heating is switched on to heat the resin surface structure S. When "OFF," the heating is switched off. A label labeled "Upper Vacuum Level" indicates the vacuum level in the upper chamber 101, and a label labeled "Lower Vacuum Level" indicates the vacuum level in the lower chamber 102. Fig. Figure 3 is an explanatory diagram showing a schematic configuration of the thermoforming device in the phase of beginning the heating of a resin sheet structure. Fig. Figure 4 is an explanatory diagram showing a schematic configuration of the thermoforming device in which the vacuum circuits have been changed.

[0034] First, the resin sheet structure S is inserted into the thermoforming device 100, and then the upper chamber 101 and the lower chamber 102 are moved closer together so that the resin sheet structure S is clamped between the upper chamber 101 and the lower chamber 102. This process is carried out between t1 and t2 in Fig. 2. Although not shown, the resin surface structure S can, if necessary, be held in place by a holding frame attached in the lower chamber 102.

[0035] Secondly, during an early-phase suction period p1 from t2 to t5, the first main line valve 123, the first branch line valve 124, the second main line valve 133, the second branch line valve 134, and the connecting line valve 141 between t2 and t3 are opened. Then, the vacuum level of the upper chamber 101 and the vacuum level of the lower chamber 102 are increased by the first vacuum pump 126 and the second vacuum pump 136, respectively. This state is in Fig. 1 shown. Then the vacuum level of the upper chamber 101 and the lower chamber 102 is reduced to approximately 700 Pa at t4, and heating is started using the heating medium 110. This state is shown in Fig. 3 shown.

[0036] At the point when t5 is reached, the first main line valve 123 and the second main line valve 133 are closed, thereby isolating the first main line 121 and the second main line 131. The connecting line valve 141 is also closed. In this state, the vacuum levels are increased by both the first branch line 122, which provides a flow rate determined by the first flow control valve 125, and the second branch line 132, which provides a flow rate determined by the second flow control valve 135. Consequently, the vacuum extraction rates decrease.

[0037] Subsequently, during a late-phase extraction period p2 from t5 to t16, the first branch line valve 124 is closed between t6 and t7, thus terminating the vacuum extraction through the upper vacuum circuit 120. Furthermore, the first branch line valve 124 is opened between t8 and t9, thereby continuing the vacuum extraction through the upper vacuum circuit 120. Afterward, the first branch line valve 124 is controlled to close between t11 and t12, and then to open between t14 and t15. This control of the opening and closing of the first branch line valve 124 is based on measurements obtained from the first vacuum gauge 105 as the vacuum level of the upper compartment 51.The control system is designed to close the first branch valve 124 when a lower limit b12 of the vacuum level in the upper chamber 101 (a "lower limit b12 of the upper vacuum level") is reached, and to open the first branch valve 124 when an upper limit b11 of the vacuum level in the upper chamber 101 (a "upper limit b11 of the upper vacuum level") is reached. In this way, the first branch valve 124 is controlled to maintain the vacuum level of the upper chamber 101 between the upper limit b11 of the upper vacuum level and the lower limit b12 of the upper vacuum level.

[0038] The second branch valve 134 closes between t9 and t10, thus terminating the vacuum extraction through the lower vacuum circuit 130. Then, the second branch valve 134 opens between t11 and t12, thereby initiating vacuum extraction through the lower vacuum circuit 130. This control of opening and closing the second branch valve 134 is based on measurements obtained using the second vacuum gauge 106 as the vacuum level of the lower compartment 52. The control is performed to close the second branch valve 134 when a lower limit b22 of the vacuum level in the lower compartment 102 (a "lower limit b22 of the lower vacuum level") is reached, and to open the second branch valve 134 when an upper limit b21 of the vacuum level in the lower compartment 102 (a "upper limit b21 of the lower vacuum level") is reached.In this way, the second branch line valve 134 is controlled so that it sets the vacuum level of the lower chamber 102 between the upper limit b21 of the lower vacuum level and the lower limit b22 of the lower vacuum level. This state during the late-phase extraction period p2 is in . Fig. 4 shown.

[0039] At time t16, the heating of the resin sheet S is complete. Furthermore, since the vacuum level of the upper chamber 101 is controlled between the upper limit b11 and the lower limit b12 of the upper vacuum level, and the vacuum level of the lower chamber 102 is controlled between the upper limit b21 and the lower limit b22 of the lower vacuum level, the pressure difference between the upper chamber 101 and the lower chamber 102 is a specified value. In this state, the forming of the resin sheet S is started using the forming tool 150.

[0040] The thermoforming device 100 configured as above in the first embodiment can achieve the following processes and effects.

[0041] As a first advantage, the thermoforming device 100 can be provided to prevent the resin sheet S from sagging during heating, which would lead to defectively shaped products. This thermoforming device 100 comprises an upper container (the upper chamber 101), which is pressure-resistant and opens downwards, and a lower container (the lower chamber 102), which is pressure-resistant and opens upwards. The upper chamber 101 and the lower chamber 102 are connected to vacuum circuits (the upper vacuum circuit 120 and the lower vacuum circuit 130). In the working space formed when the upper chamber 101 and the lower chamber 102 are closed, a workpiece made of resin (the resin sheet S) is held and heated by the heating medium 110, and pressure forming or vacuum forming is carried out.The resin surface structure S, clamped between the upper chamber 101 and the lower chamber 102 in the closed state, divides the working space 50 into the upper compartment 51 in the upper chamber 101 and the lower compartment 52 in the lower chamber 102.

[0042] The thermoforming device 100 comprises the first main line 121, which is connected to the upper compartment 51, thereby forming the upper vacuum circuit 120, the first branch line 122, which branches off from the first main line 121 and has a flow path that is more restricted than the first main line 121, the second main line 131, which is connected to the lower compartment 52, thereby forming the lower vacuum circuit 130, and the second branch line 132, which branches off from the second main line 131 and has a flow path that is more restricted than the second branch line 132.

[0043] Forming is carried out by controlling the flow rates by changing the flow paths from the first main line 121 and the second main line 131 to the first branch line 122 and the second branch line 132 and by heating the resin sheet S using the heating medium 110. The thermoforming device 100, configured as above, can achieve the advantageous effect of preventing deformation of the resin sheet S, such as sagging, during heating, as described above.

[0044] This is considered the result of the following processes. Fig. Figure 5 shows a thermoforming device for comparison, which does not include a branch line in the vacuum circuits. A thermoforming machine 200, prepared for comparison with the embodiment of the present invention, comprises a first main line 121 and a first main line valve 123, and a second main line 131 and a second main line valve 133. Furthermore, a first vacuum pump 126 and a second vacuum pump 136 are each connected to a corresponding line for carrying out vacuum extraction.

[0045] In this configuration, when vacuum extraction is started using the first vacuum pump 126 and the second vacuum pump 136, and a target vacuum level is reached, the first main line valve 123 and the second main line valve 133 are closed, thus ending the vacuum extraction. This can cause the resin surface structure S to behave, for example, by moving up and down, as shown in Fig. 5 shown.

[0046] This is because differences in volume between the upper chamber 101 and the lower chamber 102, and differences in path length between the first main line 121 and the second main line 131, result in differences in the vacuum evacuation rate, causing the vacuum level to increase more rapidly in either the upper chamber 101 or the lower chamber 102. This leads to a bulging of the resin surface structure S towards the chamber with the lower vacuum level (the bulging towards the lower chamber 102 is called sagging).

[0047] The problem described above is likely to occur, particularly in the process of manufacturing molded products using the thermoforming device 100, if the first main line 121 and the second main line 131 are each designed with a larger effective cross-sectional area to increase the vacuum evacuation rate. This problem is unlikely to occur during the early-stage evacuation period p1. However, during the late-stage evacuation period p2, at the time of opening / closing either the first main line valve 123 or the second main line valve 133, such a rapid evacuation rate causes the vacuum level to fall below the lower limit when either valve 123 or 133 opens.

[0048] In other words, the controllable vacuum level can fluctuate significantly. The surge in vacuum level that occurs when the first main line valve 123 or the second main line valve 133 opens / closes causes the resin sheet assembly S to move up and down. This can lead to wrinkling of the resin sheet assembly S, resulting in product defects. To prevent such defects, it is conceivable to adjust the vacuum levels of the upper compartment 51 and the lower compartment 52 by opening the connecting line valve 141 to allow air to escape. However, this can lead to undesirable problems, such as air entering between the mold 150 and the resin sheet assembly S.

[0049] To prevent the undesirable effects described above, the thermoforming device 100 of the present invention is configured to switch the flow paths, using the first main line 121 and the second main line 131 during the early-phase extraction period p1 and the first branch line 122 and the second branch line 132 during the late-phase extraction period p2. The flow paths of the first branch line 122 and the second branch line 132 are restricted with respect to the flow rate by the first flow control valve 125 and the second flow control valve 135, respectively. Therefore, even when the first branch line valve 124 and the second branch line valve 134 are opened and closed to adjust the vacuum level of the upper chamber 101 and the vacuum level of the lower chamber 102, respectively, it is possible to prevent the vacuum level from being forced out.

[0050] Furthermore, since the upper vacuum circuit 120 and the lower vacuum circuit 130 are provided separately, the range from the upper limit b11 of the upper vacuum level to the lower limit b12 of the upper vacuum level and the range from the upper limit b21 of the lower vacuum level to the lower limit b22 of the lower vacuum level can be set to different ranges. In this embodiment, for example, if the upper limit b11 of the upper vacuum level is set to 585 Pa, the lower limit b12 of the upper vacuum level is set to 580 Pa, the upper limit b21 of the lower vacuum level is set to 605 Pa, and the lower limit b22 of the lower vacuum level is set to 600 Pa, the vacuum level controlled by the upper vacuum circuit 120 is set higher than the vacuum level controlled by the lower vacuum circuit 130, thereby adjusting the pressure that pulls the resin sheet structure S towards the upper compartment 51.

[0051] Therefore, even if, as a result of the approximately t4 to t6 in Fig. 2 initiated warming by the in Fig. 3. Heating medium 110 shows that a sagging of the resin surface structure S occurs; it is possible to prevent the sagging of the resin surface structure S. This is because during the late-phase extraction period p2 (in Fig. 4 (approximately from t8 to t15) the first branch line valve 124 is closed, the upper vacuum circuit 120 and the lower vacuum circuit 130 are separated by blocking the communication between them, and a higher degree of vacuum is set on the side of the upper vacuum circuit 120. This results in improved accuracy of the manufactured products. (Second embodiment)

[0052] A second embodiment of the invention is described below. A thermoforming device in the second embodiment is structurally identical to the thermoforming device in the first embodiment, but differs in the configuration of the upper vacuum circuit 120 and the configuration of the lower vacuum circuit 130. Fig. Figure 6 is an explanatory diagram showing a schematic configuration of the thermoforming device in the second embodiment. In the upper vacuum circuit 120, the first main line 121 and the first branch line 122 are connected to the upper chamber 101. The first main line valve 123 and the first vacuum pump 126 are provided on the first main line 121. The first branch line valve 124, the first flow control valve 125, and a third vacuum pump 127 are provided on the first branch line 122.

[0053] In the lower vacuum circuit 130, the second main line 131 and the second branch line 132 are each connected to the lower chamber 102. The second main line 131 is connected to the second main line 131, along with the second main line valve 133 and the second vacuum pump 136. The second branch line 132 is connected to the second branch line valve 134, the second flow control valve 135, and a fourth vacuum pump 137. The valve control for the upper vacuum circuit 120 and the lower vacuum circuit 130, configured as above, can be the same as for the thermoforming device 100 in the first embodiment and can achieve the same advantageous effects. (Third embodiment)

[0054] A third embodiment of the invention is described below. A thermoforming device in the third embodiment is structurally identical to the thermoforming device in the first embodiment, but differs in the configuration of the upper vacuum circuit 120 and the configuration of the lower vacuum circuit 130. Fig.Figure 7 is an explanatory diagram showing a schematic configuration of the thermoforming device in the third embodiment. This device is configured to extract air using a fifth vacuum pump 128, which is shared between the upper vacuum circuit 120 and the lower vacuum circuit 130. The valve control for the upper vacuum circuit 120 and the lower vacuum circuit 130, configured as above, can be the same as for the thermoforming device 100 in the first embodiment and can achieve the same advantageous effects.

[0055] This configuration with the fifth vacuum pump 128, connected to the upper vacuum circuit 120 and the lower vacuum circuit 130, results in a reduced number of vacuum pumps and can thus contribute to cost reduction. Depending on the volumes of the upper compartment 51 and the lower compartment 52, or the required reaction properties, even the configuration using only a fifth vacuum pump 128 can achieve the same advantageous effects as in the first or second embodiment and can optimize costs. Furthermore, the simplified device configuration described above can be expected to contribute to a reduction in size.

[0056] The foregoing embodiments are given to the thermoforming device 100 according to the present invention, but the present invention is not limited thereto and can be implemented in other specific forms without deviating from its essential features. For example, during the early-phase extraction period p1, the first branch line 122 and the second branch line 132 can also be used only for a short period immediately after start-up to control the vacuum extraction rate in order to avoid the influence of vacuum extraction. The configurations of the upper vacuum circuit 120 and the lower vacuum circuit 130 shown in the first to third embodiments are merely examples, and these circuits can have different configurations that achieve similar advantageous effects.For example, the upper vacuum circuit 120 can be combined using the system shown in the first embodiment and the lower vacuum circuit 130 can be combined using the system shown in the second embodiment.

[0057] Furthermore, each of the first to third embodiments shows thermoforming using a forming tool; however, the present invention can be applied to coating forms on a substrate, transfer to a substrate and other processes. REFERENCE MARK LIST S resinous surface formations 50 workspace 51 upper compartment 52 lower compartment 100 thermoforming devices 101 upper chamber 102 lower chamber 110 heating fuel 120 upper vacuum circuit 130 lower vacuum circuit QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2015-107638

[0004]

Claims

[1] A thermoforming device for carrying out pressure forming or vacuum forming, the device comprising: an upper container having a pressure-resistant property and opening downwards; a lower container having a pressure-resistant property and opening upwards; and heating means for heating a resin workpiece held in a working space formed by the upper container and the lower container in a closed state, the upper container and the lower container being connected to a vacuum circuit, characterized by , that the workpiece, clamped between the upper and lower containers in the closed state, divides the working space into an upper compartment in the upper chamber and a lower compartment in the lower chamber, an upper vacuum circuit connected to the upper compartment for regulating the internal pressure of the upper compartment, comprising a first main line and a first branch line with a flow path that is more restricted than the first main line, a lower vacuum circuit connected to the lower compartment for regulating the internal pressure of the lower compartment, including a second main line and a second branch line with a flow path that is more restricted than the second main line, When the workpiece is heated using the heating medium, a flow rate is regulated by changing the flow paths from the first main line to the first branch line and from the second main line to the second branch line. [2] Thermoforming apparatus as described in claim 1, wherein the upper vacuum circuit comprises: a first main line valve for opening and closing the first main line; a first branch line valve for opening and closing the first branch line; and a first flow control valve, which is used to the To restrict the flow path of the first branch line, The lower vacuum circuit includes the following: a second main line valve for opening and closing the second main line; a second branch valve for opening and closing the second branch line; and a second flow control valve, which is used to regulate the to restrict the flow path of the second branch line, and The device is configured to reduce the vacuum level of the upper compartment using the first main line and to reduce the vacuum level of the lower compartment using the second main line, and then to close the first main line valve and the second main line valve, after which the workpiece is heated by means of the heating medium while the first branch line valve and the second branch line valve are opened and closed to regulate a flow rate in the upper vacuum circuit and a flow rate in the lower vacuum circuit. [3] Thermoforming device as described in claim 2, comprising: a first vacuum gauge in the upper compartment or the first main line for measuring the degree of vacuum; and a second vacuum gauge in the lower compartment or the second main line for measuring the degree of vacuum, wherein the first main line valve or the second main line valve is operated by using the vacuum level of the upper compartment or the lower compartment, measured by the first vacuum gauge or the second vacuum gauge, It is controlled for opening and closing. [4] Thermoforming device as described in claim 2, wherein a first vacuum pump is connected to the first main line to increase the vacuum level of the upper compartment, a second vacuum pump or the first vacuum pump is connected to the second main line to increase the vacuum level of the lower compartment, and The flow rate of air to be extracted through the upper vacuum circuit and the flow rate of air to be extracted through the lower vacuum circuit are regulated by opening and closing the first branch line valve and the second branch line valve.

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