A vacuum drying system for inkjet printing and a pressure control method thereof

Abstract

The application discloses a vacuum drying system for inkjet printing and a pressure control method thereof, and belongs to the technical field of inkjet printing. On the one hand, by setting a plurality of connection pipelines in parallel and with different pipe diameters, the pressure in the cavity is accurately controlled by using the different pressure reduction rates of the connection pipelines. On the other hand, the initial opening time value of the connection pipeline participating in each stage of air extraction is calculated according to the target pressure and target air extraction time in the cavity, and the opening time of each stage is further optimized to meet the set requirements; by rapid pressure reduction in the first stage and accurate pressure reduction in the second stage, a fast and non-overshoot pressure curve can be obtained. In addition, in the case that the vacuum drying system further comprises a third connection pipeline, the cavity pressure can be accurately adjusted around the allowed target pressure by switching on and off the third connection pipeline. In this way, the problems of pressure overshoot and instability during air extraction can be eliminated, and uniform film formation of ink droplets can be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of inkjet printing technology, and particularly discloses a vacuum drying system for inkjet printing and a pressure control method thereof. BACKGROUND

[0002] Inkjet printing is an additive manufacturing process, which is considered as a key technology in new display manufacturing due to its high material utilization, simple process flow and suitability for large-size flexible production. At present, many panel manufacturing enterprises have begun to develop inkjet printing related equipment and have carried out a series of printing OLED production experiments. In the preliminary stage of process route exploration, some problems that need to be solved urgently are encountered. For example, after the ink droplets evaporate on the ITO substrate, the "coffee ring" phenomenon appears on the surface of the dry film, which will damage the display effect and service life of the final display device. In view of this problem, the industry proposes to let the printed substrate evaporate quickly in a low vacuum environment to inhibit the "coffee ring" phenomenon, and the vacuum drying box is a device for generating a vacuum environment.

[0003] Although the existing vacuum drying box can complete the functions of vacuumizing and temporary pressure, it is prone to problems such as inconsistent film forming effect in different areas, pressure overshoot, cavity pressure failing to drop to the temporary pressure within the specified time, and poor pressure stabilization effect during the vacuumizing process. Therefore, it is necessary to optimize the structure scheme of the vacuum drying box, improve the function design of the vacuum drying box and propose a vacuumizing pressure control method. SUMMARY

[0004] In view of the defects and improvement needs of the prior art, the present application provides a vacuum drying system for inkjet printing and a pressure control method thereof, aiming to solve the technical problems of the existing vacuum drying box, such as inconsistent film forming effect in different areas, pressure overshoot, cavity pressure failing to drop to the temporary pressure within the specified time, and poor pressure stabilization effect during the vacuumizing process.

[0005] To achieve the above-mentioned purposes, in a first aspect, the present application provides a vacuum drying system for inkjet printing, comprising:

[0006] a cavity;

[0007] a carrier, which is installed at the bottom of the cavity and is used to place the substrate to be dried;

[0008] a temperature control circulation pipeline, which is laid inside the carrier and regulates the temperature of the carrier by circulating medium;

[0009] a vacuum pump, which is used to pump air out of the cavity;

[0010] N parallel connection pipes for connecting the vacuum pump and the cavity, and the opening and closing of each connection pipe is controlled by a separate vacuum electromagnetic valve; the pipe diameters of the N parallel connection pipes are different, and N≥2.

[0011] Further, the temperature control circulation pipeline is divided into two pipelines, one of which is laid in the central region of the carrier, and the other is laid in the peripheral region of the carrier, and the two pipelines are respectively connected to circulating media at different temperatures to achieve regional temperature control of the central and peripheral regions of the carrier, so that the ink drops in the central and peripheral regions of the substrate to be dried obtain different heat during evaporation.

[0012] In a second aspect, the present application provides a pressure control method suitable for the vacuum drying system for inkjet printing in the first aspect, the pressure control method comprising the following steps:

[0013] S1, obtaining the relationship between the pressure drop rate of each connection pipe and the pressure change in the cavity through pre-evacuation experiment fitting;

[0014] S2, given the target pressure in the cavity, and determine the connection pipes participating in each stage of evacuation; according to the ratio of the cavity volume to the pressure drop rate of each stage, the initial value of the opening time of the connection pipes participating in each stage of evacuation is calculated; wherein the pressure drop rate of each stage is the sum of the pressure drop rates of the connection pipes participating in the evacuation of the stage, and the pressure drop rates of each stage gradually decrease;

[0015] S3, according to the opening time of each stage and the pressure drop rate, the theoretical pressure in the cavity after completing all stages is calculated;

[0016] S4, if the theoretical pressure in the cavity is within the allowable range of the target pressure, and the sum of the opening times of all stages is within the allowable range of the target evacuation time, the opening times of each stage are output; otherwise, adjust the opening times of each stage, and execute S3.

[0017] Further, the adjustment of the opening time of each stage is specifically:

[0018] If the theoretical pressure in the cavity is greater than the upper limit of the target pressure, increase the opening time of the first stage;

[0019] If the theoretical pressure in the cavity is less than the lower limit of the target pressure, reduce the opening time of the first stage;

[0020] If the sum of the opening times of all stages is greater than the upper limit of the target evacuation time, reduce the opening time of the second stage;

[0021] If the sum of the opening times of all stages is less than the lower limit of the target evacuation time, increase the opening time of the second stage.

[0022] Further, the opening time initial values T1 and T2 of the connecting pipelines participating in the first stage and the second stage of the gas extraction are represented as:

[0023]

[0024]

[0025] wherein K q is a correction coefficient, V is the volume of the cavity, K1 is a preset pressure coefficient and K1 is greater than 1, P0 is the initial pressure in the cavity, P m is the target pressure in the cavity, v1(P0) is the sum of the pressure reduction rates of the connecting pipelines participating in the first stage of the gas extraction when the pressure in the cavity is P0, v2(K1P m ) is the sum of the pressure reduction rates of the connecting pipelines participating in the second stage of the gas extraction when the pressure in the cavity is K1P m .

[0026] Further, the theoretical pressure P r in the cavity after the completion of the first and second stages is represented as:

[0027]

[0028]

[0029] wherein p2 is the pressure in the cavity during the second stage of the gas extraction, and v2(p2) is the sum of the pressure reduction rates of the connecting pipelines participating in the second stage of the gas extraction when the pressure in the cavity is p2.

[0030] Further, the theoretical pressure in the cavity is within the allowable range of the target pressure, and the sum of the opening times of all stages is within the allowable range of the target gas extraction time, specifically:

[0031]

[0032] K t T m <T1+T2<T m

[0033] wherein K u is an upper limit coefficient of the target pressure, K d is a lower limit coefficient of the target pressure, K t is a lower limit coefficient of the target gas extraction time, and T m is the target gas extraction time.

[0034] In a third aspect, the present application provides a vacuum drying method for inkjet printing, comprising the following steps:

[0035] (1) input the temperature of the carrier, the rising distance, the target pressure in the cavity and the target pumping time;

[0036] (2) calculate the opening time of each stage by using the pressure control method of the second aspect;

[0037] (3) transfer the substrate to be dried onto the carrier in the cavity;

[0038] (4) start the vacuum pump, and open the corresponding vacuum electromagnetic valve to pump the cavity according to the calculated opening time of each stage;

[0039] (5) after sequentially performing the pumping time of each stage, close all vacuum electromagnetic valves.

[0040] Further, the vacuum drying system comprises three parallel connection pipelines, the first stage and the second stage only open the first connection pipeline and / or the second connection pipeline, and the pipe diameters of the first connection pipeline, the second connection pipeline and the third connection pipeline decrease in turn; the inkjet printing vacuum drying method further comprises the following steps:

[0041] (6) continuously detect the actual pressure in the cavity, if the actual pressure in the cavity is greater than the upper limit of the target pressure, open the third connection pipeline until the actual pressure in the cavity is within the allowed range of the target pressure, and then close the third connection pipeline.

[0042] Overall, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0043] (1) Unlike the existing vacuum drying system, the connection pipeline connecting the vacuum pump and the cavity has only one, or multiple but the same pipe diameter; the present application sets multiple parallel connection pipelines with different pipe diameters, the connection pipeline with large pipe diameter has large flow guide and can quickly reduce the cavity pressure to the vicinity of the target pressure at the beginning of pumping; the connection pipeline with small pipe diameter can further slowly pump the cavity pressure to the target pressure value and can ensure that the cavity pressure does not produce excessive overshoot. In this way, the size of the pressure in the cavity can be accurately controlled by using the different pressure reduction rates of the connection pipelines, realizing the stable and rapid pressure reduction and evaporation of the ink droplets in the vacuum drying system after inkjet printing, which is beneficial to obtain uniform drying film formation results.

[0044] (2) The present application can realize different heat fluxes of the ink droplets in the central region and the peripheral region of the printed substrate by controlling the temperature of the central region and the peripheral region of the carrier, thereby balancing the inconsistent evaporation speed of the ink droplets in the central region and the peripheral region, and finally obtaining consistent and uniform array film formation effect.

[0045] (3) The present application proposes a pressure control method based on a vacuum drying system, which can calculate the initial value of the opening time of the connecting pipeline participating in the evacuation of each stage according to the target pressure in the cavity and the target evacuation time, and further optimize to obtain the opening time of each stage that meets the set requirements. Through the rapid pressure reduction in the first stage and the accurate pressure reduction in the second stage, a fast and non-overshoot pressure curve can be obtained. In addition, in the case that the vacuum drying system further includes a third connecting pipeline, the cavity pressure can also be accurately adjusted around the allowed target pressure through the on-off of the third connecting pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 A structure schematic diagram of a vacuum drying system for inkjet printing is provided for the embodiments of the present application.

[0047] Figure 2 A structure schematic diagram of a carrier is provided for the embodiments of the present application.

[0048] Figure 3 A pressure control process flow chart is provided for the embodiments of the present application.

[0049] Figure 4 A pressure optimization algorithm flow chart is provided for the embodiments of the present application.

[0050] Figure 5 A pressure curve schematic diagram is provided for the embodiments of the present application.

[0051] Figure 6 A flow chart of an inkjet printing vacuum drying method is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as there is no conflict.

[0053] In the present application, the terms "first", "second", etc. (if any) in the present application and the drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0054] Figure 1 A structure schematic diagram of a vacuum drying system for inkjet printing is provided for the embodiments of the present application. The system mainly includes a cavity component, a temperature conduction device, a lifting mechanism, an evacuation pipeline, a vacuum pump, a controller, which will be explained one by one below.

[0055] The cavity component includes a cavity 11, a pressure gauge 12 and a gas source 13. Among them, the cavity 11 is a closed space forming a vacuum environment, which reduces the pressure of the ink droplets on the substrate after inkjet printing to evaporate and obtain uniform film morphology. The inside of the cavity component is used to integrate the temperature conduction device and the lifting mechanism, and the outside is connected to the air exhaust pipeline and the vacuum pump. The pressure gauge 12 is used to detect the pressure in the cavity and feedback to the controller to calculate the pressure reduction rate and dynamically control the pressure in the cavity. The gas source 13 is connected to the inside of the cavity, and after the ink droplets on the substrate are evaporated into a film by reducing the pressure, the gas source replenishes the gas in the cavity.

[0056] The temperature conduction device includes a metal platform 21, a first temperature control circulation pipeline 22, a second temperature control circulation pipeline 23 and a temperature control machine 24. Among them, the metal platform 21 is installed at the bottom of the cavity component through the lifting mechanism; the first temperature control circulation pipeline 22 and the second temperature control circulation pipeline 23 are laid inside the metal platform 21, and the temperature of the metal platform 21 is adjusted by circulating medium (preferably, water bath circulating medium can be used); the temperature control machine 24 is used to control the temperature of the circulating medium (preferably, a water temperature machine is used), and the circulating medium flows through the first temperature control circulation pipeline 22 and the second temperature control circulation pipeline 23. The temperature conduction device is the carrier of the display substrate, which supplies heat when the ink droplets evaporate to obtain an array film with good consistency.

[0057] In a preferred embodiment, as shown in Figure 2 The temperature conduction device can realize temperature control of the metal platform 21 in different regions. The temperature control circulation pipeline is divided into two parts, wherein the first temperature control circulation pipeline 22 is laid in the central region of the metal platform, and the second temperature control circulation pipeline 23 is laid in the peripheral region of the metal platform. The two pipelines are respectively connected to circulating media with different temperatures (preferably, the circulating medium in the central pipeline has a higher temperature than the circulating medium in the peripheral pipeline), so as to realize temperature control of the central and peripheral regions of the metal platform, so that the ink droplets in the central and peripheral regions of the substrate obtain different heat when evaporating.

[0058] The lifting mechanism includes a transmission mechanism 31 and a driving element 32. Among them, the transmission mechanism 31 is used to connect the temperature conduction device and the cavity 11; the driving element 32 is used to adjust the position of the temperature conduction device relative to the cavity (preferably, a stepping motor can be used as the driving element), so as to change the gas velocity distribution during air exhaust to obtain an orderly and uniform flow field.

[0059] The evacuation pipeline includes vacuum solenoid valves 41, 42, 43, and 44, and a connecting passage 45. Connecting passage 45 connects the vacuum pump and the cavity components. Connecting passage 45 consists of parallel pipes of different diameters, divided into three stages according to diameter. The first-stage connecting pipe has the largest diameter and the largest conductance, quickly reducing the cavity pressure to near the target pressure at the beginning of evacuation. The second-stage connecting pipe has a smaller diameter, slowly reducing the cavity pressure to the target pressure value after the first-stage connecting pipe has completed evacuation, ensuring that the cavity pressure does not experience excessive overshoot. The third-stage connecting pipe has the smallest diameter; after the cavity pressure reaches a temporary pressure, the vacuum solenoid valves on the first and second-stage connecting pipes close, and the cavity pressure is dynamically adjusted only through the proportional valve on the third-stage connecting pipe. Vacuum solenoid valves 41, 42, 43, and 44 control the on / off state of the connecting pipelines, achieving precise control of the pressure within the cavity components.

[0060] Vacuum pump 51 is an actuator for evacuating air from the cavity, which can create a high vacuum environment by evacuating air from the cavity components.

[0061] The controller 61 is the storage and calculation element of the vacuum drying system. It can receive information on the chamber environment variables from the pressure gauge 12, the drive element 32, and the temperature controller 24. The controller 61 calculates the pressure drop rate at different pressures based on the pressure inside the chamber during evacuation and sends commands to the vacuum solenoid valves 41, 42, 43, and 44 on each stage of the connecting pipeline to control their opening and closing.

[0062] like Figure 3 and Figure 4 The figures shown are the pressure control process flow diagram and the pressure optimization algorithm flow diagram of this embodiment, respectively. The pressure control method provided by this embodiment mainly includes the following steps:

[0063] S1, the relationship between the pressure drop rate of each connecting pipe and the change in pressure inside the cavity was obtained by fitting the pre-evacuation experiment.

[0064] Specifically, to determine the pressure reduction rate of each connecting pipe under different pressures, an individual evacuation experiment needs to be conducted on each connecting pipe. The evacuation experiment follows these steps: First, the vacuum pump 51 is turned on, and the controller 61 sends a command to open the main vacuum solenoid valve 44 on the evacuation pipe. Then, the cavity 11 is evacuated by opening the vacuum solenoid valve 41 on each primary connecting pipe individually. During the evacuation and pressure reduction process, the pressure gauge 12 monitors the pressure change within the cavity over time in real time and transmits the data to the controller 61.

[0065] Furthermore, the controller 61 obtains data on pressure changes over time and calculates the pumping capacity (pressure reduction capacity) of each connecting pipeline at different pressures. The pressure reduction rate function of each connecting pipeline is then fitted using the following formula. Preferably, a cubic polynomial is used for fitting:

[0066] f1(p) = a3p 3 +a2p 2 +a1p+a0

[0067] In the formula, f1(p) represents the pressure reduction rate function of the first connecting pipeline, p is the pressure in the cavity; a0, a1, a2, a3 are polynomial fitting coefficients.

[0068] Further, the above steps are repeated to obtain the pressure reduction rate functions f2(p) and f3(p) of the second and third connecting pipelines, respectively.

[0069] S2, a target pressure in the cavity is given, and the connecting pipelines participating in each stage of pumping are determined; according to the ratio of the cavity volume to the pressure reduction rate of each stage, the initial value of the opening time of the connecting pipeline participating in each stage of pumping is calculated; wherein the pressure reduction rate of each stage is the sum of the pressure reduction rates of the connecting pipelines participating in the stage, and the pressure reduction rates of the stages gradually decrease.

[0070] It should be noted that the entire drying process of the present application can be regarded as a plurality of continuous pumping stages, and the pressure reduction rates of the stages gradually decrease. Taking two stages as an example, since the pipe diameter of the first connecting pipeline is greater than that of the second connecting pipeline in the present embodiment, the first stage can only open the first connecting pipeline, and the second stage can only open the second connecting pipeline; the first stage can open the first and second connecting pipelines, and the second stage can only open the first connecting pipeline; the first stage can open the first and second connecting pipelines, and the second stage can only open the second connecting pipeline.

[0071] When the target pressure P m and the target pumping time T m in the cavity are input according to the process requirements, the opening time T1 of the first stage and the opening time T2 of the second stage need to be calculated and optimized.

[0072] Further, the initial values of T1 and T2 are calculated by the following formula:

[0073]

[0074]

[0075] In the formula, K q is a correction coefficient, and the reference value is 2.3; V is the cavity volume; K1 is a preset pressure coefficient and K1 is greater than 1, and the reference value is 1.1; P0 is the initial pressure in the cavity, P m is the target pressure in the cavity, v1(P0) is the sum of the pressure reduction rates of the connecting pipelines participating in the first stage of pumping when the pressure in the cavity is P0, v2(K1P m) is the sum of the pressure reduction rates of the connection pipelines participating in the second stage of pumping. m

[0076] For example, when the first stage only opens the first connection pipeline and the second stage only opens the second connection pipeline, v1(P0) = f1(P0), v2(K1P m ) = f2(K1P m ); when the first stage opens the first connection pipeline and the second connection pipeline and the second stage only opens the first connection pipeline, v1(P0) = f1(P0) + f2(P0), v2(K1P m ) = f1(K1P m ).

[0077] S3, according to the opening time of each stage and the pressure reduction rate, calculate the theoretical pressure in the cavity after all stages are completed.

[0078] Specifically, the theoretical pressure P r in the cavity after the first and second stages are completed is represented as:

[0079]

[0080]

[0081] In the formula, p2 is the pressure in the cavity during the second stage of pumping, and v2(p2) is the sum of the pressure reduction rates of the connection pipelines participating in the second stage of pumping when the pressure in the cavity is p2.

[0082] S4, if the theoretical pressure in the cavity is within the allowable range of the target pressure, and the sum of the opening times of all stages is within the allowable range of the target pumping time, output the opening time of each stage; otherwise, adjust the opening time of each stage, and execute S3.

[0083] Specifically, the theoretical pressure in the cavity is within the allowable range of the target pressure, and the sum of the opening times of all stages is within the allowable range of the target pumping time, specifically:

[0084]

[0085] K t T m <T1+T2<T m

[0086] In the formula, K u is the upper limit coefficient of the target pressure, with a reference value of 1.05; K d is the lower limit coefficient of the target pressure, with a reference value of 0.95; K t is the lower limit coefficient of the target pumping time, with a reference value of 0.9; and T m ​is the target evacuation time.

[0087] When , it indicates that the pressure in the chamber cannot be evacuated to the target pressure value under the current time allocation, and the first stage opening time needs to be increased.

[0088]

[0089] In the formula, ΔT is the time step, and the reference value is 1s.

[0090] When , it indicates that the pressure in the chamber will overshoot under the current time allocation, and the first stage opening time needs to be reduced.

[0091]

[0092] When T1+T2>T m , it indicates that the pressure reduction rate under the current time allocation is too slow, and the second stage opening time needs to be reduced.

[0093]

[0094] When T1+T2<K t T m , it indicates that the pressure reduction rate under the current time allocation is too fast, and the second stage opening time needs to be increased.

[0095]

[0096] As shown in Figure 6 , the present application also provides a method for inkjet printing vacuum drying, comprising the following steps:

[0097] (1) input the temperature of the carrier, the rising distance, and the target pressure and target evacuation time in the chamber;

[0098] (2) calculate the opening time of each stage by using the above pressure control method;

[0099] (3) transfer the substrate to be dried onto the carrier in the chamber;

[0100] (4) start the vacuum pump, and open the corresponding vacuum electromagnetic valve to evacuate the chamber according to the calculated opening time of each stage;

[0101] (5) after sequentially executing each stage evacuation time, close all vacuum electromagnetic valves.

[0102] Further, the ink droplet pressure reduction evaporation film forming is completed, the controller 61 sends a command to perform air supplement to atmospheric pressure, and the substrate is taken out.

[0103] In addition, if the vacuum drying system comprises three parallel connection pipelines, only the first connection pipeline and / or the second connection pipeline are opened in the first stage and the second stage, and the diameters of the first connection pipeline, the second connection pipeline and the third connection pipeline are sequentially reduced; the inkjet printing vacuum drying method further comprises the following steps:

[0104] (6) continuously detecting the actual pressure in the cavity, if the actual pressure in the cavity is greater than the upper limit of the target pressure, the third connection pipeline is opened until the actual pressure in the cavity is within the allowable range of the target pressure, and then the third connection pipeline is closed.

[0105] Those skilled in the art will easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pressure control method, characterized in that, Suitable for vacuum drying systems used in inkjet printing, including: cavity; A stage, which is installed at the bottom of the cavity, is used to place the substrate to be dried; A temperature-controlled circulation pipeline is laid inside the platform and the temperature of the platform is regulated by circulating a medium. A vacuum pump, used to evacuate the cavity; N parallel connecting pipes are used to connect the vacuum pump and the cavity, and the opening and closing of each connecting pipe is controlled by a separate vacuum solenoid valve; the diameters of the N parallel connecting pipes are all different, and N≥2; The pressure control method includes the following steps: S1, the relationship between the pressure drop rate of each connecting pipe and the change in pressure inside the cavity was obtained by fitting the pre-evacuation experiment; S2, Given the target pressure inside the cavity, determine the connecting pipelines involved in the pumping at each stage; calculate the initial value of the opening time of the connecting pipelines involved in the pumping at each stage based on the ratio of the cavity volume to the pressure drop rate of each stage; wherein, the pressure drop rate of each stage is the sum of the pressure drop rates of the connecting pipelines involved in the pumping at that stage, and the pressure drop rate of each stage gradually decreases. S3, calculate the theoretical pressure inside the cavity after all stages are completed, based on the opening time and pressure reduction rate of each stage; S4. If the theoretical pressure inside the cavity is within the allowable range of the target pressure, and the sum of the opening times of all stages is within the allowable range of the target evacuation time, then output the opening time of each stage; otherwise, adjust the opening time of each stage and execute S3.

2. The pressure control method according to claim 1, characterized in that, The adjustment of the opening time for each stage is as follows: If the theoretical pressure inside the cavity is greater than the upper limit of the target pressure, the opening time of the first stage will be increased. If the theoretical pressure inside the cavity is less than the lower limit of the target pressure, reduce the opening time of the first stage. If the sum of the opening times of all stages is greater than the upper limit of the target evacuation time, reduce the opening time of the second stage. If the sum of the opening times of all stages is less than the lower limit of the target evacuation time, increase the opening time of the second stage.

3. The pressure control method according to claim 2, characterized in that, Initial values ​​of the opening time of the connecting pipelines involved in the first and second stages of air extraction and , is represented as: In the formula, It is a correction factor. It refers to the cavity volume. It is a preset pressure coefficient and Greater than 1, It is the initial pressure inside the cavity. It is the target pressure inside the cavity. The pressure in the cavity of the first-stage evacuation connecting pipe is... The sum of the rate of voltage drop at different times, The pressure in the cavity of the connecting pipe involved in the second stage of air extraction is... The sum of the rate of decrease in voltage at different times.

4. The pressure control method according to claim 3, characterized in that, Theoretical pressure inside the cavity after completing the first and second stages of evacuation , is represented as: In the formula, This refers to the pressure inside the cavity during the second stage of air extraction. The pressure in the cavity of the connecting pipe involved in the second stage of air extraction is... The sum of the rate of decrease in voltage at different times.

5. The pressure control method according to claim 4, characterized in that, The theoretical pressure within the cavity is within the allowable range of the target pressure, and the sum of the opening times for all stages is within the allowable range of the target evacuation time, specifically: In the formula, It is the upper limit coefficient of the target pressure. It is the target pressure lower limit coefficient. It is the lower limit coefficient of the target evacuation time. This is the target evacuation time.

6. The pressure control method according to any one of claims 1 to 5, characterized in that, The temperature control circulation pipeline is divided into two lines. One line is laid in the central area of ​​the stage, and the other line is laid in the peripheral area of ​​the stage. The two lines are respectively filled with circulating media at different temperatures to achieve regional temperature control of the central and peripheral areas of the stage, so that the ink droplets in the central and peripheral areas receive different amounts of heat during the evaporation of the substrate to be dried.

7. A vacuum drying method for inkjet printing, characterized in that, Includes the following steps: (1) Input the stage temperature, rising distance, target pressure in the cavity, and target evacuation time; (2) Calculate the activation time of each stage using the pressure control method according to any one of claims 1 to 6; (3) Transfer the substrate to be dried onto the stage inside the cavity; (4) Start the vacuum pump and open the corresponding vacuum solenoid valves in sequence according to the calculated start-up time of each stage to evacuate the cavity; (5) After each stage of evacuation time has been completed, close all vacuum solenoid valves.

8. The inkjet printing vacuum drying method according to claim 7, characterized in that, The vacuum drying system includes three parallel connecting pipes. In the first and second stages, only the first connecting pipe and / or the second connecting pipe are activated. The diameters of the first, second, and third connecting pipes decrease sequentially. The inkjet printing vacuum drying method further includes the following steps: (6) Continuously monitor the actual pressure inside the cavity. If the actual pressure inside the cavity is greater than the upper limit of the target pressure, open the third connecting pipe until the actual pressure inside the cavity is within the allowable range of the target pressure, and then close the third connecting pipe.

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