Inkjet printing method and inkjet printing apparatus

Abstract

The application discloses an inkjet printing method and an inkjet printing device, aiming at improving the uniformity problem during ink printing. The inkjet printing method comprises the following steps: constructing a first gas pressure environment for promoting the volatilization of a solvent in an inkjet printing ink, controlling the gas pressure of the first gas pressure environment to be less than the saturated vapor pressure of the solvent; placing a to-be-printed substrate in the first gas pressure environment; and performing inkjet printing on the surface of the to-be-printed substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film preparation, in particular to an inkjet printing method and an inkjet printing device. BACKGROUND

[0002] At present, OLED (Organic Light-Emitting Diode) is a kind of high-end display technology in the market, which gradually occupies an important position in the display high-end display panel market. From the manufacturing process, OLED display screen is composed of three kinds of RGB pixels that can self-emitting, each sub-pixel has a separate light-emitting layer, which is controlled by an independent circuit, so as to realize complete non-emitting display and improve the contrast. With the continuous development of OLED materials, the efficiency and service life are also higher and higher. However, at the same time, due to the limitation of the current layers of materials, the preparation of each organic functional layer is mainly realized by evaporation. The evaporation equipment itself occupies a large area. In order to ensure that each layer of material does not cross-contaminate in the evaporation process, most of the organic materials need independent evaporation chambers, so that in industrial production, there are more than ten organic evaporation chambers, which increases the production cost. On the other hand, more than 99% of the evaporation materials will adhere to the inner wall of the chamber and the mask, and less than 1% of the materials can be used for the substrate, which greatly increases the production cost.

[0003] At present, some preparation methods instead of evaporation method have appeared, such as OLED inkjet printing technology. Commercial printing equipment can control the printing precision to the micron level. The main factor restricting mass production is the lack of suitable printing ink. Each layer of functional layer required by OLED needs different performance. HIL (Hole Inject Layer) requires good hole injection ability, HTL (Hole Transport Layer) requires high hole carrier mobility, and EML (Emitting Layer) includes RGB three-color inks, which must meet the color gamut requirements of color coordinates, and also need sufficient efficiency and service life. In addition, the development of ETL (Electron Transport Layer) and EIL (Electron Inject Layer) inks suitable for inkjet printing is also difficult.

[0004] At present, OLED inkjet printing technology mainly prints each organic functional layer on the back plate after the back plate is manufactured, and the ink of each organic functional layer after printing is cured. The printing film layer of the optoelectronic device produced in the prior art often has poor optoelectronic effect. How to improve the optoelectronic effect of the printing film layer is a problem to be solved in the field. SUMMARY

[0005] Therefore, the present application provides an inkjet printing method and an inkjet printing device, aiming to improve the uniformity problem during ink printing.

[0006] The inkjet printing method provided in the embodiments of the present application comprises the following steps: constructing a first gas pressure environment for promoting the volatilization of a solvent in inkjet printing ink, controlling the gas pressure of the first gas pressure environment to be less than the saturated vapor pressure of the solvent; placing a substrate to be printed in the first gas pressure environment; and performing inkjet printing on the surface of the substrate to be printed.

[0007] Optionally, after the step of performing inkjet printing on the surface of the substrate to be printed, the method further comprises the following step: placing the substrate after inkjet printing in the first gas pressure environment for a first preset time length.

[0008] Optionally, the first preset time length is 2 min to 7 min, and the gas pressure of the first gas pressure environment is 10 Pa to 100000 Pa.

[0009] Optionally, the method further comprises the following step: simultaneously performing heating treatment on the substrate to be printed during the step of performing inkjet printing on the surface of the substrate to be printed.

[0010] Optionally, after the step of performing inkjet printing on the surface of the substrate to be printed, the method further comprises the following step: performing vacuum drying treatment on the substrate after inkjet printing.

[0011] Optionally, the vacuum drying treatment at least comprises the following steps: constructing a second gas pressure environment with gradually decreasing gas pressure, and the initial gas pressure of the second gas pressure environment is the same as the gas pressure of the first gas pressure environment.

[0012] Optionally, after the gas pressure of the second gas pressure environment decreases to a first preset value, the gas pressure of the second gas pressure environment is maintained at the first preset value, and the substrate is placed in the second gas pressure environment for at least 5 min.

[0013] Optionally, the first preset value is 10 Pa to 100000 Pa, and the time length consumed for the second gas pressure environment to decrease to the first preset value is less than or equal to 1 min. -3 to 10 -5 Pa.

[0014] Optionally, after the vacuum drying treatment, the method further comprises the following step: adjusting the gas environment of the substrate to be a third gas pressure environment, the gas pressure of the third gas pressure environment is a second preset value, and the second preset value is greater than the first preset value.

[0015] The embodiment of the present application also provides an inkjet printing device, comprising: a printing chamber for placing a substrate to be printed; a printing device arranged in the printing chamber and used for inkjet printing on the substrate to be printed; and a gas pressure adjusting assembly comprising a connecting pipeline connected to the printing chamber and used for building a first gas pressure environment to promote the evaporation of a solvent in inkjet printing ink, wherein the gas pressure of the first gas pressure environment is less than the saturated vapor pressure of the solvent.

[0016] Optionally, the gas pressure adjusting assembly comprises: an air pump connected to the printing chamber through the connecting pipeline and used for extracting gas in the printing chamber to reduce the gas pressure in the printing chamber; a gas source connected to the printing chamber through the connecting pipeline and used for introducing gas into the printing chamber to increase the gas pressure in the printing chamber, and a switch valve is arranged on the connecting pipeline where the gas source is located; and a controller used for controlling the working state of the air pump and the opening and closing state of the switch valve, so as to adjust the gas pressure environment in the printing chamber.

[0017] Optionally, the gas pressure adjusting assembly further comprises a gas pressure detection unit connected to the controller, and a detection end of the gas pressure detection unit is arranged in the printing chamber and used for detecting the actual gas pressure in the printing chamber.

[0018] Optionally, the device further comprises a heating device arranged in the printing chamber and used for heating the substrate to be printed.

[0019] The inkjet printing method and the inkjet printing device in the present application can promote the evaporation of the solvent in the inkjet printing ink by adjusting the gas environment where the substrate is located to be the first gas pressure environment, and the gas environment where the substrate is located is the first gas pressure environment, and the gas pressure of the first gas pressure environment is less than the saturated vapor pressure of the solvent, so that the solvent in the ink printed on the substrate to be printed can be quickly evaporated, the ink can be solidified into a film in a short time, the problem that the evaporation speeds of the solvents in the inks printed on different positions of the substrate are inconsistent can be solved, the problem that the function layer topographies of the optoelectronic devices prepared by inkjet printing on different positions of the substrate are different can be solved, and the uniformity of the devices formed based on different positions of the substrate can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0021] Figure 1is a step flow diagram of a method of inkjet printing provided by an embodiment of the present application;

[0022] Figure 2 is a structural diagram of an inkjet printing device provided by an embodiment of the present application;

[0023] Figure 3 is a top view structural diagram of another film layer provided by an embodiment of the present application;

[0024] Figure 4 is a side view structural diagram of a substrate of a film layer to be printed provided by an embodiment of the present application;

[0025] Figure 5 is a top view diagram of a substrate after inkjet printing provided by an embodiment of the present application;

[0026] Figure 6 is a pressure-time diagram of a vacuum compressor station of Comparative Group 1 and Comparative Group 2 when vacuum drying is performed on the film layer after printing;

[0027] Figure 7 is a pressure-time diagram of a vacuum compressor station of an experimental group when vacuum drying is performed on the film layer after printing. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, any other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application. In addition, it should be understood that the specific implementation described herein is only used to illustrate and explain the present application, and is not used to limit the present application. In the present application, the orientation words such as "upper" and "lower" are the directions of the drawing surface in the drawings. In addition, in the description of the present application, the term "comprising" means "including but not limited to". Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers in the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) in the indicated range.

[0029] It is found that, after printing the film layer of the photoelectric device, the printed ink needs a certain time to solidify, resulting in that the solidification degree of the ink in the area printed first on the substrate is different from that in the area printed later. In addition, after printing, the substrate needs to be sent to a vacuum drying machine for vacuum drying. During the vacuum drying process, the film layer will undergo two changes: one is that the liquid film layer volatilizes the solvent in the high-vacuum environment, leaving the solute and part of the solvent attached to the substrate; the other is that the solute and the un-volatilized solvent form their own unique film layer structure under lower air pressure, i.e. higher vacuum degree, which directly affects the uniformity and thickness of the finally formed film layer. Therefore, after the substrate is sent to the vacuum drying machine, the ink with different solidification degrees distributed in different areas of the substrate will directly lead to film layers with different thicknesses, resulting in the problem of uniformity of the film layer. These uniformity problems will lead to poor photoelectric effect of the film layer.

[0030] To solve the above problems, the present application provides an inkjet printing method and an inkjet printing device.

[0031] In an embodiment of the present application, an inkjet printing method is provided.

[0032] Referring to Figure 1 The inkjet printing method comprises the following steps:

[0033] Step S101: constructing a first gas pressure environment to promote the evaporation of the solvent in the inkjet printing ink, and controlling the gas pressure of the first gas pressure environment to be less than the saturated vapor pressure of the solvent;

[0034] Step S102: placing the to-be-printed substrate in the first gas pressure environment;

[0035] Step S103: inkjet printing on the surface of the to-be-printed substrate.

[0036] The inkjet printing method in the embodiment can promote the evaporation of the solvent in the inkjet printing ink by adjusting the gas environment in which the substrate is located during printing to be a first gas pressure environment, and the gas pressure of the first gas pressure environment is less than the saturated vapor pressure of the solvent, so that the solvent in the ink printed on the to-be-printed substrate can evaporate quickly, and the ink can be solidified into a film in a short time, thereby alleviating the problem that the evaporation speed of the solvent in the ink printed at different positions on the substrate is inconsistent, and thereby alleviating the problem that the functional layer morphology of the optoelectronic device prepared by inkjet printing at different positions on the substrate is different, and improving the uniformity of the devices formed at different positions on the substrate.

[0037] In some embodiments, after the step of inkjet printing on the surface of the to-be-printed substrate, the method further comprises the following step: placing the substrate after inkjet printing in the first gas pressure environment for a first preset time period, so that the solvent in the ink on the substrate can evaporate most in the first gas pressure environment, and the substrate printed with the ink has been substantially solidified before subsequent processes, thereby reducing the possibility of changes in the solidified film layer of the ink caused by changes in the environment of subsequent processes.

[0038] In some embodiments, the first preset time period is 2 min to 7 min. Research has found that when the first preset time period is 2 min to 7 min, the printing time and the solidification effect can be considered, and the printing time is prevented from being too long, and sufficient solidification effect can also be achieved. Research has found that when the first preset time period is 5 min, the solidification effect is better, and the printing time is also shorter.

[0039] In some embodiments, the gas pressure of the first gas pressure environment is 10 Pa to 100,000 Pa. In some other embodiments, the gas pressure of the first gas pressure environment can also be set according to the saturated vapor pressure of the required solvent.

[0040] When the air pressure of the first air pressure environment is low enough, the solvent of the ink can evaporate fast enough so that the ink printed on the surface of the substrate can be solidified substantially once the ink is printed on the surface of the substrate, or the solvent of the ink in each area of the surface of the substrate can evaporate to the maximum limit fast enough so that the solvent of the ink in each area evaporates equally, even if the substrate is further dried in vacuum later, the residual solvent of the ink in each area of the surface of the substrate will not be different, which can cause the film layer in each area of the surface of the substrate to be of different thickness and poor uniformity.

[0041] In some embodiments, the air pressure of the first air pressure environment is 10000 Pa to 50000 Pa. In practice, the air pressure of the first air pressure environment can also be smaller or larger to adapt to the saturated vapor pressure of the solvent of the ink at the current temperature. The air pressure of the first air pressure environment can also be larger, such as 90000 Pa, etc. The size of the first air pressure environment needs to be set according to actual needs to balance the printing effect and the solidification speed of the ink. When the air pressure of the first air pressure environment is too small, the printing effect of the ink can be affected, and when the air pressure of the first air pressure environment is too large, the solidification speed of the ink can be reduced.

[0042] In some embodiments, the air pressure of the first air pressure environment can be adjusted between 10 Pa and 100000 Pa as needed.

[0043] In some embodiments, the method further comprises the step of heating the substrate to be printed while the step of performing inkjet printing on the surface of the substrate to be printed is performed. Heating the substrate after inkjet printing can accelerate the evaporation speed of the solvent of the ink. In this embodiment, the evaporation speed of the solvent of the ink is further accelerated under the condition of heating. In some other embodiments, the combination of heating and decompression can reduce the requirement for the decompression amplitude. For example, originally, the air pressure of the first air pressure environment needs to be adjusted to 10000 Pa at a temperature of 25°C to have the required evaporation speed, after the heating function is added, the temperature of the substrate is adjusted to 60°C, and the air pressure of the first air pressure environment is adjusted to 30000 Pa, which can achieve the required evaporation speed.

[0044] In some embodiments, after the step of performing inkjet printing on the surface of the substrate to be printed is performed, the method further comprises the step of drying the substrate after inkjet printing in vacuum to further solidify the ink.

[0045] In some embodiments, a vacuum dryer (VCD) is used to perform the vacuum drying process. The vacuum dryer can be used to dry heat-sensitive, decomposable and oxidizable substances, remove moisture inside the container by extracting air inside the container to a predetermined vacuum degree, and can fill inert gas into the inside.

[0046] In some embodiments, the substrate after inkjet printing is placed in the first gas pressure environment for a first preset time period, and then the substrate after inkjet printing is subjected to vacuum drying treatment.

[0047] In some embodiments, the substrate to be printed is subjected to vacuum drying treatment by using a vacuum dryer, and the vacuum drying treatment at least includes: constructing a second gas pressure environment with gradually decreasing gas pressure, and the initial gas pressure of the second gas pressure environment is the same as the gas pressure of the first gas pressure environment.

[0048] In some embodiments, after the gas pressure of the second gas pressure environment is reduced to a first preset value, the gas pressure of the second gas pressure environment is maintained at the first preset value, and the substrate is placed in the second gas pressure environment for at least 5 minutes to enhance the curing effect of the ink.

[0049] In some embodiments, the first preset value is 10 -3 to 10 -5 Pa, and the time period for reducing the second gas pressure environment to the first preset value is less than or equal to 1 minute.

[0050] The initial gas pressure is equal to the gas pressure of the first gas pressure environment, which can prevent the ink that has not completely cured from fluctuating due to the pressure difference between the first gas pressure environment and the second gas pressure environment when the substrate is placed in the second gas pressure environment, thereby affecting the uniformity of the film layer formed by the ink. The first preset value is 10 -3 to 10 -5 Pa can ensure the vacuum drying effect, and the time period for reducing the second gas pressure environment to the first preset value is less than or equal to 1 minute, which helps to control the total time period of the vacuum drying treatment.

[0051] In some other embodiments, the initial gas pressure can also be other gas pressures, which can be set as needed by those skilled in the art.

[0052] In some embodiments, the time period for reducing the second gas pressure environment to the first preset value is 20 seconds, because the ink has been preliminarily cured in the first gas pressure environment, and further low-pressure curing can be directly performed here, thereby saving the time period required for curing the ink.

[0053] In some embodiments, after the vacuum drying process, a step of adjusting the gas environment of the substrate to a third gas pressure environment is further included, the third gas pressure environment has a second preset value of gas pressure, and the second preset value is greater than the first preset value. In some embodiments, the first, second, and third gas pressure environments are all nitrogen environments, and the second preset value is equal to the atmospheric pressure outside the vacuum drying machine or the working gas pressure of the machine corresponding to the next process of the vacuum drying machine, so as to prevent the substrate from being damaged due to a large pressure difference when the substrate is taken out of the vacuum drying machine.

[0054] An inkjet printing device is also provided in the embodiments of the present application.

[0055] Please refer to Figure 2 , which is a structural schematic diagram of the inkjet printing device in an embodiment.

[0056] In this embodiment, the inkjet printing device includes a printing chamber 204 for placing a substrate 205 to be printed, a printing device arranged in the printing chamber for performing inkjet printing on the substrate 205 to be printed, and a gas pressure adjusting assembly 200 including a connecting pipeline 203 connected to the printing chamber 204 for establishing a first gas pressure environment to promote the evaporation of a solvent in inkjet printing ink, and the gas pressure of the first gas pressure environment is less than the saturated vapor pressure of the solvent.

[0057] Since the printing chamber 204 is provided with the gas pressure adjusting assembly 200, the gas pressure environment inside the printing chamber 204 can be adjusted to the first gas pressure environment, and the first gas pressure environment promotes the evaporation of the solvent in the inkjet printing ink to the saturated vapor pressure of the solvent, so that the solvent in the ink printed on the substrate 205 can be quickly evaporated, and the ink can be solidified into a film in a short time, thereby alleviating the problem of inconsistent evaporation speed of the solvent in the ink printed at different positions on the substrate 205, and alleviating the problem of functional layer morphology difference of the optoelectronic device prepared by inkjet printing at different positions on the substrate 205, and improving the uniformity of the devices formed at different positions on the substrate 205.

[0058] In some embodiments, the air pressure adjusting assembly 200 comprises: a gas pump 206 connected to the printing chamber 204 through the connecting pipeline 203, for pumping out the gas in the printing chamber 204 to reduce the air pressure in the printing chamber 204; a gas source 202 connected to the printing chamber 204 through the connecting pipeline 203, for supplying gas into the printing chamber 204 to increase the air pressure in the printing chamber 204, and a switch valve 201 is arranged on the connecting pipeline 203 where the gas source 202 is located; and a controller 207 for controlling the working state of the gas pump 206 and the opening and closing state of the switch valve 201, so as to adjust the air pressure environment in the printing chamber 204.

[0059] Since the gas pump 206 and the gas source 202 are provided, the air pressure adjusting assembly 200 can at least increase the air pressure in the printing chamber 204 and reduce the air pressure in the printing chamber 204, so as to adjust the air pressure in the printing chamber 204 to the required air pressure environment.

[0060] In some other embodiments, an electromagnetic valve 208 is arranged on the connecting pipeline 203 connected to the gas pump 206, and the electromagnetic valve 208 is connected to the controller 207, and the opening and closing of the electromagnetic valve 208 is controlled by the controller 207, so as to control the gas pumping of the gas pump 206 to the printing chamber 204.

[0061] In some embodiments, the switch valve 201 is also an electromagnetic valve, which can be controlled by the controller to change the opening and closing state.

[0062] Since the controller 207 is provided, in some embodiments, the air pressure environment in the printing chamber 204 can be accurately controlled by accurately controlling the gas pump 206 and the switch valve 201.

[0063] In some embodiments, the gas source 202 comprises a nitrogen sub-source. The nitrogen sub-source is used to provide nitrogen for the air pressure adjusting assembly 200. Since most of the ink used to prepare the film layer has a large reaction to water and oxygen, nitrogen is often used to fill the printing chamber 204 to prevent the influence of water and oxygen on the film layer.

[0064] In some embodiments, when other gas environment is required, other gas sub-sources can also be used to provide corresponding gas.

[0065] In some embodiments, the air pressure regulating assembly 200 further comprises an air pressure detecting unit 210 connected to the controller 207, and a detecting end of the air pressure detecting unit 210 is arranged in the printing chamber 204 for detecting an actual air pressure in the printing chamber 204, and the actual air pressure can be acquired by the controller 207. The controller 207 can adjust the air pressure in the printing chamber 204 according to the actual air pressure, and precisely control the air pressure in the printing chamber 204.

[0066] In some embodiments, the air pressure detecting unit 210 comprises an air pressure sensor arranged in the printing chamber 204, and the air pressure sensor comprises a high-precision air pressure sensor which uses MEMS technology to process a vacuum cavity and a Wheatstone bridge on a single silicon wafer. The output voltage at both ends of the bridge arm of the Wheatstone bridge is proportional to the applied pressure, and after temperature compensation and calibration, the high-precision air pressure sensor has the characteristics of small volume, high precision, fast response speed, and is not affected by temperature changes.

[0067] In fact, the specific configuration of the air pressure detecting unit 210 can also be selected as needed.

[0068] In some embodiments, the controller 207 comprises an I / O port which is used at least for acquiring a target air pressure, and the controller 207 is configured to adjust the control of the air pump 206 and the on-off valve 201 according to the actual air pressure and the target air pressure. Therefore, the inkjet printing device can adjust the air pressure of the gas environment in the printing chamber 204 according to the actual needs. Therefore, the inkjet printing device can adjust the air pressure in the printing chamber 204 during printing according to the properties of the specific ink being printed.

[0069] In some embodiments, the solvent of the ink is n-hexane with a boiling point of 68°C (standard atmospheric pressure). In some other embodiments, the solvent of the ink is a DMF (N,N-dimethylformamide) solution with a boiling point of 153°C (standard atmospheric pressure). In fact, the specific type of solvent of the ink can also be selected as needed. In fact, the solvent of the ink can also be other monohydric alcohols, polyhydric alcohols, etc. When the target air pressure is input through the I / O port, it can be set according to the boiling point of the solvent.

[0070] In some embodiments, the inkjet printing device further comprises a heater arranged in the printing chamber 204 for heating the substrate 205 during inkjet printing. The heater can be at least one of a heating wire, a heating lamp tube, an induction heating device, etc.

[0071] In some embodiments, the air pressure adjusting assembly can be loaded on an existing inkjet printing device to form the inkjet printing device in the embodiments, thereby saving the cost of replacing the inkjet printing device. During the printing of the organic functional layer, the air pressure of the N2 environment of the environment where the substrate is located can be adjusted, so that the liquid film layer can realize solvent evaporation in a high vacuum environment during the printing process, leaving the solute and part of the solvent attached to the substrate.

[0072] In addition, changing the environmental air pressure during printing can cause the liquid film layer printed on the substrate to solidify into a film in a short time. In combination with the easily volatile ink, the effect of rapid solidification of the just-printed ink can be achieved, so that the substrate can achieve uniform solidification into a film at each position, thereby minimizing the problem of inconsistent evaporation speed at each position of the substrate caused by saturated vapor pressure. In addition, the use of the inkjet printing device in the embodiments can expand the solvent selection range of the inkjet printing ink. For ink with poor volatility, the same printing effect as ink with good volatility can be achieved by reducing the printing environmental air pressure.

[0073] The following provides Embodiment 1:

[0074] Please refer to Figure 3 、 Figure 4 and Figure 5 , wherein Figure 3 is another top view structural schematic diagram of a film layer provided in the embodiments of the present application; Figure 4 is a side view structural schematic diagram of a substrate to be printed film layer provided in the embodiments of the present application; Figure 5 is a top view schematic diagram of a substrate after inkjet printing provided in the embodiments of the present application.

[0075] 1. A substrate 401 is provided, which is a transparent substrate. A TFT (Thin-Film Transistors) layer 402 is prepared on the substrate 401. The TFT layer 402 can be prepared by using metal oxide indium tin oxide (ITO).

[0076] 2. A planar layer 403 is prepared on the TFT layer 402. The planar layer 403 is subjected to laser etching, developing and other processes to form a pixel opening.

[0077] 3. An anode ITO layer 405 is prepared in the pixel opening by using a magnetron sputtering film plating method. Finally, a pixel definition layer 404 is coated and a laser etching process is used to form a pixel area as shown in Figure 4 . Figure 4 The pixel area in Figure 5 corresponds to the area to be printed with an organic film layer, and the shape of the pixel area is as shown by the outer contour shape of the pixel 501 in Figure 4After printing the organic film layer in the pixel region in the substrate 205, the pixel 501 is formed.

[0078] 4. The substrate 205 finally formed is a square substrate with a size of 2 cm*2 cm as shown in FIG. 4, and the light-emitting region 301 includes a plurality of pixels 501, and the light-emitting region 301 is controlled by the anode pattern to be four regions with a size of 4 mm*4 mm, which are distributed in the pixel distribution region 302. Figure 3

[0079] 5. After the anode ITO layer 405 on the substrate 205 is prepared, the substrate 205 can be transferred to an OLED inkjet printing device for printing of an organic film layer, which includes a HIL (Hole Injection Layer), a HTL (Hole Transport Layer), an EML (Emission layer), an ETL (Electron Transport Layer), and an EIL (Electron Injection Layer).

[0080] 6. The same batch of substrates are printed with the same ink for printing research. The following uses ink to print ETL, and the solvent used is an alcohol or a mixture of several alcohol compounds, which are monohydric alcohol or polyhydric alcohol, including methanol, ethanol, ethylene glycol, butanol, heptanol, propylene carbonate, butene glycol, acetylene glycol, ethylene glycol, etc. The proportion of the solvent in the ink is 50% to 99%. The example uses a 95.5% mixed solvent of two monohydric alcohols with a proportion of 1:3, and the temperature in the printing chamber 204 is 25°C. At this temperature, the saturation vapor pressure of the solvent in the ink is known to be greater than 20,000 Pa and less than one standard atmospheric pressure:

[0081] Comparative group 1: The substrate 205 is placed on the stage of the printing chamber 204 (see FIG. 2), the temperature of the printing chamber 204 is set to 25°C, the N2 pressure in the printing chamber 204 is slightly greater than the standard atmospheric pressure, which is 110,000 Pa, 60 pl of ink is printed on the surface of the substrate 205, the film thickness is about 100 nm, and after all the printing is completed, it is transferred to a vacuum drying machine for drying and curing. The drying and curing conditions are shown in FIG. 3. Specifically, the drying condition is to reduce the chamber pressure of the substrate from the standard atmospheric pressure to 50,000 Pa within 20 s, maintain for 5 min, then reduce the pressure to 0.00001 Pa, maintain for 2 min, and finally fill N2 until the pressure in the chamber where the substrate is located returns to the standard atmospheric pressure. Figure 2 Figure 6

[0082] ​​​Comparative Group 2: The substrate 205 is placed on the stage of the printing chamber 204 (see Figure 2 ), the temperature of the printing chamber 204 is set to 5°C, the same volume of ink as in Comparative Group 1 is printed on the surface of the substrate, the N2 pressure in the printing chamber 204 is slightly higher than the standard atmospheric pressure, which is the same as the N2 pressure in Condition 1, and after all the printing is completed, the substrate is transferred to the vacuum drying machine for drying and curing, and the drying conditions are the same as in Comparative Group 1. The purpose of this condition is to slow down the evaporation speed of the ink during printing at low temperature, so that the evaporation speed of the ink just printed into the pixel is consistent with that of the last printed ink, and the solvent evaporation is delayed.

[0083] Experimental Group: The substrate 205 is placed on the stage of the printing chamber 204 (see Figure 2 ), the temperature of the printing chamber 204 is set to 25°C, the printing chamber pressure is stabilized to 20,000 Pa, then the same volume of ink as in Comparative Group 1 is printed on the surface of the substrate, and after all the printing is completed, the substrate is maintained for 5 minutes without moving, and then transferred to the vacuum drying machine for further curing. The further curing conditions are shown in Figure 7 , which are to reduce the pressure of the printing chamber 204 in which the substrate 205 is located from the standard atmospheric pressure to 0.00001 Pa within 20 seconds, maintain for 2 minutes, and finally fill N2 to increase the pressure of the vacuum drying processing chamber of the vacuum drying machine to the standard atmospheric pressure. It should be noted that when the pressure of the printing chamber 204 in which the substrate 205 is located is reduced to 0.00001 Pa in the experimental group, a molecular pump is used for pumping, so it is not accurate to control to 0.00001 Pa within 20 seconds, but the pressure will become lower and lower until it reaches 0.00001 Pa.

[0084] The dried printed substrates obtained from the two comparative groups and one experimental group are tested using a white light interferometer. Specifically, the substrates produced by the two comparative groups and one experimental group are uniformly baked, and after 20 minutes, an aluminum film with a thickness of 100 nm is evaporated in an evaporation chamber. After evaporation, the white light interferometer is used for testing, and for each substrate, pixel points at different positions of the substrate are selected for testing at 9 positions, i.e. 9-point testing method is used for testing, and the results are as follows:

[0085] The uniformity of Comparative Group 1 is the worst among the three conditions, with an average thickness of 105 nm, and the difference between the minimum film thickness and the maximum film thickness is 20 nm;

[0086] In the test results of Comparative Group 2, the average film thickness is 103 nm, and the difference between the minimum film thickness and the maximum film thickness is 10 nm;

[0087] In the test results of the experimental group, the average film thickness is 102 nm, and the difference between the minimum film thickness and the maximum film thickness is 6 nm;

[0088] In the present embodiment, the experimental group realizes the optimal substrate topography uniformity by changing the air pressure during printing, which is superior to the other two schemes, ensures that the ink printed first and the ink printed last is solidified immediately after printing is completed, avoids the instability of the liquid state, and the transfer substrate after solidification avoids shaking and other external factors during transmission, ultimately achieving good results.

[0089] The inkjet printing method and inkjet printing device provided in the embodiments of the present application can realize the solidification process of the liquid film during printing, ensure that the liquid film is also solidified after printing is completed, speed up the process flow, and keep the film formation environment of the area printed first and the area printed last consistent, thereby improving the uniformity of the film layer at each position of the substrate and increasing the yield. Moreover, the environmental air pressure in the printing chamber can be adjusted specifically for solvents of inks with different volatilities, thereby optimizing the topography of the film layer, improving uniformity, and also increasing the selection range of inks. If the boiling point of the solvent of the ink is relatively low, the further solidification corresponding to the vacuum compression process can also be completed in the printing chamber, thereby simplifying the preparation process.

[0090] The electronic transport film layer and the preparation method thereof, the optoelectronic device and the preparation method thereof, and the display device provided in the embodiments of the present application are described in detail above, and the principles and implementation manners of the present application are described by applying specific examples in the present text; the above description of the embodiments is only used to help understand the method of the present application and the core idea thereof; meanwhile, for those skilled in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application, and the above description of the present specification should not be understood as a limitation of the present application.

Claims

1. An inkjet printing method, characterized by, The method comprises the following steps: constructing a first gas pressure environment, and controlling the gas pressure of the first gas pressure environment to be less than the saturated vapor pressure of a solvent in inkjet printing ink; placing a substrate to be printed in the first gas pressure environment; carrying out inkjet printing on the surface of the substrate to be printed; carrying out heating treatment on the substrate to be printed while carrying out the step of inkjet printing on the surface of the substrate to be printed.

2. The inkjet printing method according to claim 1, characterized by, After the step of carrying out inkjet printing on the surface of the substrate to be printed, the method further comprises the following steps: placing the substrate after inkjet printing in the first gas pressure environment for a first preset time period.

3. The inkjet printing method according to claim 2, characterized by, The first preset time period is 2 min to 7 min, and the gas pressure of the first gas pressure environment is 10 Pa to 100,000 Pa.

4. The inkjet printing method according to claim 1, characterized by, After the step of carrying out inkjet printing on the surface of the substrate to be printed, the method further comprises: carrying out vacuum drying treatment on the substrate after inkjet printing.

5. The inkjet printing method according to claim 4, characterized by The vacuum drying treatment at least comprises: constructing a second gas pressure environment with gradually decreasing gas pressure, and the initial gas pressure of the second gas pressure environment is the same as the gas pressure of the first gas pressure environment.

6. The inkjet printing method according to claim 5, characterized by After the gas pressure of the second gas pressure environment is reduced to a first preset value, the gas pressure of the second gas pressure environment is maintained at the first preset value, and the substrate is placed in the gas pressure of the first preset value for at least 5 min.

7. The inkjet printing method according to claim 6, characterized by, The first preset value is 10 -3 Pa 10 -5 Pa, and / or the time length for reducing the air pressure of the second air pressure environment to the first preset value is less than or equal to 1 min.

8. The inkjet printing method according to claim 7, characterized by, After the vacuum drying treatment, the method further comprises the following steps: adjusting the gas environment of the substrate to be a third gas pressure environment with a second preset value of gas pressure, which is greater than the first preset value.

9. An inkjet printing apparatus, characterized by comprising: It comprises: a printing chamber for placing a substrate to be printed; a printing device arranged in the printing chamber for inkjet printing on the substrate to be printed; a gas pressure adjusting assembly comprising a connecting pipeline connected to the printing chamber, for constructing a first gas pressure environment to promote the volatilization of a solvent in inkjet printing ink, and the gas pressure of the first gas pressure environment is less than the saturated vapor pressure of the solvent; and a heating device arranged in the printing chamber for heating treatment on the substrate to be printed.

10. The inkjet printing device according to claim 9, wherein The gas pressure adjusting assembly comprises: a gas suction pump connected to the printing chamber through the connecting pipeline, for sucking out the gas in the printing chamber to reduce the gas pressure in the printing chamber; a gas source connected to the printing chamber through the connecting pipeline, for introducing gas into the printing chamber to increase the gas pressure in the printing chamber, and a switch valve is further arranged on the connecting pipeline of the gas source; a controller for controlling the working state of the gas suction pump and for controlling the opening and closing state of the switch valve, so as to adjust the gas pressure environment in the printing chamber.

11. The inkjet printing device according to claim 10, wherein The gas pressure adjusting assembly further comprises a gas pressure detection unit connected to the controller, and a detection end of the gas pressure detection unit is arranged in the printing chamber for detecting the actual gas pressure in the printing chamber.

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