JP7603219B2 - Inkjet printing apparatus, device manufactured using the same, coating film formation unevenness detection method, and device manufacturing method - Google Patents

Description

This disclosure relates to an inkjet printing apparatus, a device manufactured using the same, a method for detecting unevenness in coating formation, and a method for manufacturing the device.

Inkjet printing is also used in the manufacture of various devices such as solar cells and displays. For example, in the manufacture of organic electroluminescence displays, inkjet printing is used in the process of applying ink containing functional materials to the surface of a substrate.

A method is known in which a plurality of cells partitioned by banks are provided on the surface of a substrate to be printed, and ink is applied to each cell. Here, if the amount of ink filled in each of the plurality of cells is not uniform, differences will occur in the thickness of the coating film formed in each cell, and uneven coating film formation may occur on the surface of the substrate. Uneven coating film formation can cause device defects. For example, in the case of an organic EL display, uneven coating film formation appears as uneven color and brightness, impairing the display's functionality. Therefore, it is preferable that the amount of ink filled in each cell by inkjet printing is uniform.

For example, Patent Document 1 discloses an inspection method for inspecting coating film formation unevenness by imaging a coating object with an angle of 70 to 80 degrees between the perpendicular to the surface of the coating object and the imaging optical axis.

JP 2007-205873 A

However, in inspections using optical means such as those described in Patent Document 1, coating film formation unevenness is not detected, and coating film formation unevenness is sometimes only detected in the lighting inspection carried out at the final stage of the manufacturing process. For example, in the case of organic EL displays, coating film formation unevenness can only be detected as color unevenness or brightness unevenness by passing electricity through the functional material during the lighting inspection, causing the functional material to emit light.

If unevenness in the coating formation is not detected until the final lighting inspection stage, this will result in a poor yield, which is undesirable.

This disclosure has been made in light of these points, and its main purpose is to detect unevenness in coating film formation by inkjet printing with high sensitivity using optical means.

The inkjet printing device according to the present disclosure is an inkjet printing device that performs printing by ejecting ink onto a substrate having a plurality of cells on its surface, and includes a printing means that ejects liquid ink from a plurality of nozzles to fill each of the plurality of cells with ink, thereby forming a coating film in each of the cells, a moving means that moves the substrate relative to the printing means, and an observation means that observes the state of the coating film in each of the cells by optical means before the ink filled in each of the cells dries.

The device according to the present disclosure is manufactured by the inkjet printing apparatus described above.

The coating formation unevenness detection method according to the present disclosure is a coating formation unevenness detection method for a coating formed in each of a plurality of cells by filling each of the cells with ink in inkjet printing, which involves ejecting liquid ink onto a substrate having a plurality of cells on its surface, and observes the state of the coating in each of the cells before the ink filled in the cells dries.

The device manufacturing method according to the present disclosure is a method for manufacturing a device in which a coating film is formed in a plurality of cells provided on the surface of a substrate, and includes a printing process for forming a coating film in each of the plurality of cells by ejecting and filling each of the cells with liquid ink, and an inspection process for observing the state of the coating film in each of the cells before the ink filled in each of the cells dries.

According to the present disclosure, unevenness in coating film formation by inkjet printing can be detected with high sensitivity using optical means.

FIG. 1 is a diagram illustrating a schematic diagram of an inkjet printing apparatus according to an embodiment of the present disclosure. FIG. 2A is a schematic diagram illustrating a method of printing with an inkjet printing device. FIG. 2B is a schematic cross-sectional view taken along line IIB-IIB in FIG. 2A. FIG. 3A is a diagram showing a schematic diagram of a coating film formed in each cell in a state where no coating film formation unevenness occurs. FIG. 3A is a view equivalent to FIG. 3A in a state in which unevenness in coating film formation has occurred. FIG. 4A is a diagram showing a schematic diagram of a method for observing a coating film formed in each cell in a state where no coating film formation unevenness occurs. FIG. 4B is a view equivalent to FIG. 4A in a state in which unevenness in coating film formation has occurred. FIG. 5 is a diagram showing a schematic diagram of the change in shape of a coating film over time. FIG. 6 is a graph showing the change in diameter of the coating over time in the examples. FIG. 7A is a photograph of a defect formed on the surface of a substrate in an example. FIG. 7B is a diagram showing defects formed on the surface of a substrate in an embodiment, which are highlighted by a predetermined algorithm.

Before explaining the present invention, let me explain how I came up with the idea.

A method for manufacturing organic EL displays using inkjet printing is known. In this method, multiple cells are provided on the surface of a substrate, and each cell is filled with ink containing a functional material to form a coating film in each cell.

Here, if there is a non-uniformity in the thickness of the coating film between each cell, unevenness in the coating film formation will occur on the surface of the substrate. Unevenness in the coating film formation is undesirable as it impairs the quality of the product. In particular, in the case of organic EL displays, unevenness in the coating film formation can cause a loss of image quality.

The final stage of the manufacturing process for organic EL displays is usually a lighting test. In a lighting test, electricity is passed through the functional material to actually light up the display. This allows any unevenness in the coating film formation to be detected as uneven color or brightness.

To prevent the deterioration of yield due to uneven coating formation, it is preferable to detect uneven coating formation as early as possible in the manufacturing process.

Here, a method is known in which coating formation unevenness is detected by observing the surface of the substrate with optical means during the manufacturing process. Examples of methods for detecting coating formation unevenness using optical means include a method that uses the difference in the amount of diffusely reflected light due to differences in coating thickness, and a method that uses the difference in the directionality of transmitted light due to differences in coating thickness.

However, inspection using optical means during the manufacturing process sometimes fails to detect unevenness in the coating formation on the surface of the substrate. In such cases, unevenness in the coating formation is only detected during the lighting inspection at the final stage of the manufacturing process, resulting in a poor yield.

In other words, in order to improve yields, it is effective to detect unevenness in coating formation with high sensitivity by inspection using optical means performed during the manufacturing process.

The inventors of the present application therefore conducted extensive research to improve the sensitivity of detecting unevenness in coating film formation by optical means. As a result, they discovered that there is a difference in the direction of change in the shape of the ink before and after it is dried after it is ejected onto the substrate. They also found that the difference in the direction of change in the shape of the ink affects the sensitivity of detecting unevenness in coating film formation by optical means.

The following describes in detail the embodiments of the present invention with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the present invention, its applications, or its uses.

Figure 1 shows a schematic diagram of an inkjet printing apparatus 1 according to this embodiment. The inkjet printing apparatus 1 is an apparatus for manufacturing an organic EL display as a device, and performs printing by applying ink P to a substrate 10.

The inkjet printing device 1 includes a print head 20 as a printing means. The print head 20 is disposed above the substrate 10. The print head 20 is provided with a plurality of nozzles 21, 21, .... Liquid ink P is ejected from each nozzle 21 toward the surface of the substrate 10. The ink P contains at least a functional material that becomes a light-emitting element of the organic EL display, and a solvent. The amount and direction of ejection of each nozzle 21 in the print head 20 are controlled by the processing unit 2.

The inkjet printing device 1 is equipped with an observation means 30 that observes the surface condition of the substrate 10 by optical means. The observation means 30 has an illumination 31 as a light source unit and a light sensor camera 32 as an imaging unit. The illumination 31 is disposed above the substrate 10 and irradiates the substrate 10 with illumination light L1. The light sensor camera 32 is disposed above the substrate 10. Specifically, the illumination 31 is disposed at a predetermined angle θ with respect to the perpendicular to the surface of the substrate 10.

The licenser camera 32 is positioned on a perpendicular line to the surface of the substrate 10. That is, the imaging axis T2 of the licenser camera 32 has a predetermined angle θ with respect to the irradiation axis T1 of the illumination light L1. The image data captured by the licenser camera 32 is input to the processing unit 2.

The illumination axis T1 refers to the central axis of the light emitted from the illumination 31. The imaging axis T2 refers to the direction in which the lens of the imaging camera 32 faces (the central axis of the lens).

The inkjet printing device 1 includes a stage 3 as a moving means. The stage 3 moves the substrate 10 relative to the print head 20. Specifically, the stage 3 places the substrate 10 on its upper surface and transports the substrate 10 from the print head 20 to the observation means 30. In the figure, X indicates the transport direction of the substrate 10 (stage 3) and indicates the relative movement direction of the substrate 10 with respect to the print head 20 (hereinafter simply referred to as "transport direction X"). The observation means 30 is disposed in a position in the transport direction X where the surface of the substrate 10 is observed immediately after ink P is applied from the nozzle 21 of the print head 20 to the surface of the substrate 10.

Figure 2A shows a schematic diagram of a method of printing with the inkjet printing device 1. Figure 2B shows a schematic diagram of a cross section taken along line IIB-IIB in Figure 2A. A plurality of cells 11, 11, ... are provided on the surface of the substrate 10. Each cell 11 is arranged in the transport direction X and in a direction perpendicular to the transport direction X. Here, a plurality of banks 12, 12, ... are provided on the surface of the substrate 10. Each bank 12 in the plurality of banks 12, 12, ... is a wall that protrudes upward from the surface of the substrate 10. Each bank 12 extends in a direction perpendicular to the transport direction X and is parallel to the transport direction X. Cells 11, 11 adjacent to each other in the transport direction X are separated by a bank 12.

Here, the multiple nozzles 21 in the print head 20 are arranged in the transport direction X and in a direction perpendicular to the transport direction X. In addition, multiple liner cameras 32 are arranged in a direction perpendicular to the transport direction X (not shown).

As shown in FIG. 2B, ink P is filled into each cell 11. This forms a coating in each cell 11.

In this embodiment, inks Pa, Pb, and Pc, which are red, green, and blue in the RGB color system, are prepared as ink P. Each cell 11 is filled with one of the inks Pa, Pb, and Pc. Cells 11a, 11b, and 11c corresponding to the inks Pa, Pb, and Pc are provided on the surface of the substrate 10 and are arranged in the transport direction X.

Here, it is preferable that the thickness of the coating film of ink Pa, Pb, Pc filled in each cell 11a, 11b, 11c is equal to each other. This is because non-uniformity in the coating film thickness causes uneven coating film formation on the surface of the substrate 10. In order to make the thickness of the coating film of ink Pa, Pb, Pc filled in each cell 11a, 11b, 11c equal, the discharge amount, discharge direction, etc. of each nozzle 21 are controlled by the processing unit 2.

Figure 3A shows a schematic diagram of the coating film formed in each cell 11 in a state where no coating film formation unevenness occurs (hereinafter referred to as a normal state). Figure 3B shows a schematic diagram of the coating film formed in each cell 11 in a state where coating film formation unevenness occurs (hereinafter referred to as an abnormal state). As shown in Figure 3A, in a normal state, ink Pc is ejected directly downward from each nozzle 21. Therefore, ink Pc is not filled into cell 11b adjacent to cell 11c, and is entirely filled into cell 11c. The same thing happens with cells 11a and 11b.

In this case, the thicknesses of the coatings of the inks Pa, Pb, and Pc filled in the cells 11a, 11b, and 11c are approximately equal to each other. Therefore, no unevenness in the coating is generated on the surface of the substrate 10.

As shown in FIG. 3B, in an abnormal state, due to clogging of the nozzle 21, manufacturing errors, etc., some of the ink Pc may not be ejected directly downward from the nozzle 21, but may be ejected toward the cell 11b side. As a result, some of the ink Pc fills the cell 11b, not the cell 11c. This reduces the amount of ink Pc filled in the cell 11c, and the thickness of the coating in the cell 11c becomes smaller. On the other hand, the cell 11b is filled with ink Pb and some of the ink Pc, so the thickness of the coating in the cell 11b becomes larger.

Figure 4A shows a schematic diagram of a method for observing the coating film formed on each cell 11 in a normal state. Figure 4B shows a schematic diagram of a method for observing the coating film formed on each cell 11 in an abnormal state. As shown in Figure 4A, in a normal state, illumination light L1 irradiated from the illumination 31 becomes specularly reflected light L2 from the surface of the substrate 10.

As shown in FIG. 4B, in an abnormal state, the illumination light L1 emitted from the light 31 is diffusely reflected by the side of the raised portion P1 of the coating film in the cell 11b, and is input to the light sensor camera 32 as diffused light L3 from the substrate 10. In other words, the light sensor camera 32 receives the diffusely reflected light L3 of the illumination light L1 from the substrate 10. By receiving more diffusely reflected light L3 by the light sensor camera 32, the detection sensitivity of coating film formation unevenness is improved.

Here, if the specified angle θ is too small, specifically, if it is smaller than 70 degrees, the light sensor camera 32 will also receive the specularly reflected light L2, making it difficult to detect the minute diffusely reflected light L3, and the detection sensitivity for coating formation unevenness will decrease. On the other hand, if the specified angle θ is too large, specifically, if it is greater than 80 degrees, the lighting 31 will interfere with the stage 3, making installation difficult. Therefore, it is preferable that the specified angle θ be greater than 70 degrees and less than 80 degrees.

Image data captured by the line sensor camera 32 is input to the processing unit 2. Here, as shown in FIG. 2A, the substrate 10 placed on the stage 3 moves in the transport direction X relative to the nozzle 21 of the print head 20. Therefore, if the unevenness of the coating thickness between the cells 11 (uneven coating formation) is caused by a defect in any of the nozzles 21, 21, ..., a linear defect extending in the transport direction X is formed on the surface of the substrate 10 (see FIGS. 7A and 7B). Note that examples of defects in the nozzles 21 include a decrease in the discharge amount due to clogging of the nozzle 21, and a mismatch in the discharge direction due to a manufacturing error of the nozzle 21. When the observation means 30 observes the linear defect, the processing unit 2 detects the linear defect as the unevenness of the coating thickness between the cells 11 (uneven coating formation) caused by a defect in any of the nozzles 21, 21, ....

Furthermore, the processing unit 2 highlights the linear defect in comparison to other defects, making it easier to distinguish between defects caused by uneven coating formation due to a malfunction of the nozzle 21 and other defects (e.g., defects caused by the surface condition of the substrate 10, etc.).

The manner in which the shape of the coating of ink P that is ejected onto the surface of the substrate 10 and fills each cell is changed will be described with reference to FIG. 5. FIG. 5 shows a schematic diagram of the change in shape of the coating over time. Ink P ejected onto the surface of the substrate 10 from the nozzle 21 of the print head 20 fills each cell 11. The solvent in the ink P starts to evaporate immediately after it is ejected from the nozzle 21. In other words, the ink P starts to dry immediately after it is ejected from the nozzle 21.

Here, the ink P ejected from the nozzle 21 onto the surface of the substrate 10 first becomes thinner as time passes. At this time, the diameter of the ink P film hardly changes. Then, after a certain time has passed, the ink P dries and the thickness of the film becomes sufficiently small. After that, the diameter of the ink P film starts to become smaller. At this time, the thickness of the ink P film hardly changes.

That is, after a certain time has passed since the ink P was ejected from the nozzle 21 and the ink P filled in each cell 11 has dried and the thickness of the coating film has become sufficiently small, there is almost no difference in the thickness of the coating film between each cell 11. Therefore, it becomes difficult to detect unevenness in the thickness of the coating film between each cell 11 (unevenness in the coating film formation) by optical means. Therefore, in this embodiment, the state of the coating film in each cell 11 is observed by the observation means 30 before the ink P filled in each cell 11 dries (before the thickness of the coating film becomes sufficiently small).

As described above, in this embodiment, by observing the state of the coating in each cell 11 before the ink P filled in each cell 11 dries (before the thickness of the coating becomes sufficiently small), unevenness in the coating formed by inkjet printing can be detected with high sensitivity by the observation means 30, which is an optical means. This makes it possible to detect unevenness in the coating formation before the lighting inspection performed in the final stage, thereby improving the yield.

The observation means 30 uses diffuse reflected light from the surface of the substrate 10, so unlike the case where transmitted light is used, it is possible to detect coating formation unevenness formed on the surface of the substrate 10 even if the substrate 10 is opaque.

By setting the predetermined angle θ to be between 70 degrees and 80 degrees, the light sensor camera 32 receives almost no specular reflected light L2 and only diffuse reflected light L3. This allows for accurate detection of coating formation unevenness. In addition, interference between the lighting 31 and the stage 3 can be suppressed.

When linear defects are observed on the surface of the substrate 10, the processing unit 2 identifies them as uneven coating formation caused by a defective nozzle 21, allowing the cause of the defect to be discovered at an early stage.

The present invention has been described above using preferred embodiments, but these descriptions are not limiting and various modifications are possible.

For example, the inkjet printing device 1 may be equipped with a landing camera. The landing camera captures the ink P ejected from the nozzles 21. As described above, when a linear defect is found on the surface of the substrate 10, the cause of the linear defect is identified as a defect in one of the multiple nozzles 21, 21, ... At this time, by checking the image captured by the landing camera, it is possible to further identify which nozzle 21, 21, ... is causing the defect.

The observation means 30 is not limited to using diffuse reflected light L3, but may also use transmitted light, for example.

The device manufactured by the inkjet printing device 1 is not limited to an organic EL display. For example, it may be a solar cell, etc.

The coating formation unevenness detection method according to the present disclosure is a method for detecting coating formation unevenness in a coating formed in each of a plurality of cells 11, 11, ... by filling each of the cells 11 with ink P in inkjet printing, which involves ejecting liquid ink P onto a substrate 10 having a plurality of cells 11 on its surface, and observes the state of the coating in each cell 11 before the ink P filled in each cell 11 dries.

The device manufacturing method according to the present disclosure is a method for manufacturing a device in which a coating film is formed in a plurality of cells 11 provided on the surface of a substrate 10, and includes a printing process in which liquid ink P is ejected and filled into each of the plurality of cells 11, 11, ... to form a coating film in each of the cells 11, and an inspection process in which the state of the coating film in each of the cells 11 is observed before the ink P filled in each of the cells 11 dries.

Next, we will explain the specific implementation examples.

Ink was dropped onto a glass substrate. The amount of ink dropped was the amount that filled the cell. The change in diameter of the coating film due to the evaporation of the solvent contained in the ink after dropping was measured. Figure 6 is a graph showing the change in diameter of the coating film over time. As shown in Figure 6, no significant change in diameter was observed for about 60 seconds after dropping, but a significant change was observed after 60 seconds. From the time of dropping to about 60 seconds, the reduction in the liquid volume due to the evaporation of the solvent changes in the height direction of the coating film. Then, after about 60 seconds, when the thickness of the coating film becomes sufficiently small, the diameter of the coating film begins to decrease. Therefore, it was found that with the ink measured this time, it is necessary to observe the coating film within 60 seconds after it is ejected from the nozzle.

A line sensor camera (model number: VT-9K7C-H80, manufactured by ViewWorks) was used as the observation means. Four line sensor cameras were arranged in a direction perpendicular to the substrate transport direction X.

A bar light (model number: PDL-T-1500-1, manufactured by Nippon PI) and an LED light source (model number: SLG-150V-R, manufactured by REVOX) were prepared as the lighting section. A personal computer (model number: LR-41S49, manufactured by Logitec) was prepared as the processing section. An image input board (model number: APX-3800, manufactured by Aval Data) was installed in the personal computer and connected to a line sensor camera. The specified angle θ was set to 70 degrees.

The observation means was disposed immediately behind the print head in the transport direction X. This made it possible to observe the surface of the substrate by the observation means immediately after ink was ejected from the nozzles.
(Ink application)
A 730 mm x 920 mm glass substrate (model number: AN100, manufactured by AGC) was prepared as the substrate. The glass substrate was placed on the stage of an inkjet printing device. Then, ink was applied from the nozzle of the print head to the surface of the glass substrate. The application time was 27 seconds.
(Method for detecting unevenness in coating film formation)
After the ink was applied to the surface of the glass substrate, the glass substrate was transported to the observation means at 150 mm/s by the stage. The total transport time and observation preparation time was 15 seconds. Then, the surface of the glass substrate was imaged by four line sensor cameras. The image capture time was 10 seconds. As a result, image data was obtained 25 to 52 seconds after application, and the surface of the substrate could be observed within 60 seconds after the ink was applied. The captured image data was sent to a processing unit, and coating film formation unevenness was detected.

(Verification of effectiveness)
Fig. 7A is a photograph of a defect formed on the surface of a substrate taken by an observation camera (model number: HS-80-04K40/manufactured by DALSA), and Fig. 7B is a diagram showing the defect formed on the surface of the substrate photographed by a licenser camera, which is highlighted by a predetermined algorithm in a processing unit.

The observation camera is installed perpendicular to the surface of the stage (not shown). The observation camera shines light from directly above the surface of the glass substrate and observes the specularly reflected light from the glass substrate. As a result, as shown in Figure 7A, in the image captured by the observation camera, defective areas (uneven coating formation) are captured in black compared to normal areas.

In addition, in the image captured by the licenser camera, a large amount of diffuse reflected light from defective areas (uneven coating formation) is detected, so the defective areas are imaged as white compared to normal areas, as shown in Figure 7B. Note that, as shown in Figure 7B, the processing unit uses a predetermined algorithm to highlight defects that are formed in a straight line in the conveying direction X. When comparing the image captured by the observation camera shown in Figure 7A with the image shown in Figure 7B in which the defective areas are highlighted by the processing unit, it was confirmed that the positions of the defective areas matched.

P: Ink X: Transport direction L1: Illumination light L2: Regularly reflected light L3: Diffusely reflected light T1: Irradiation axis T2: Imaging axis 1: Inkjet printing device 2: Processing section 3: Stage (moving means)
10 Substrate 11 Cell 20 Print head (printing means)
21 Nozzle 30 Observation means 31 Illumination (light source unit)
32 Licenser camera (imaging unit)

Claims (7)

An inkjet printing apparatus that performs printing by ejecting ink onto a substrate having a plurality of cells on its surface,
a printing means for ejecting liquid ink from a plurality of nozzles to fill each of the plurality of cells with ink, thereby forming a coating film in each of the cells;
a moving means for moving the substrate relative to the printing means;
an observation means for observing a state of the coating film in each of the cells by an optical means before the ink filled in each of the cells dries;
The observation means is
a light source unit that irradiates the substrate with illumination light;
an imaging unit that receives diffuse reflected light of the illumination light from the substrate,
an imaging axis of the imaging unit has a predetermined angle with respect to an irradiation axis of the illumination light;
The predetermined angle is equal to or greater than 70 degrees and equal to or less than 80 degrees,
The substrate is provided with a plurality of banks,
Each of the plurality of banks protrudes from the substrate , extends in a direction perpendicular to a relative movement direction of the substrate with respect to the printing means, and is aligned in the relative movement direction;
the cells adjacent to each other in the moving direction are partitioned by the bank,
An inkjet printing apparatus , wherein the imaging axis is along a normal to the substrate . In claim 1,
An inkjet printing device, wherein the imaging unit receives the diffuse reflected light from the substrate when the ink runs over the bank, and does not receive the specular reflected light from the substrate when the ink does not run over the bank . In claim 1 or 2 ,
An inkjet printing apparatus, wherein the imaging units are arranged in a direction perpendicular to the direction of movement of the substrate relative to the printing means. In any one of claims 1 to 3 ,
the light source unit is disposed above the substrate,
The inkjet printing apparatus, wherein the imaging unit is disposed above the substrate. In any one of claims 1 to 4 ,
The inkjet printing device further includes a processing unit that, when the observation means observes a linear defect on the surface of the substrate extending in the relative movement direction of the substrate with respect to the printing means, detects the defect as an unevenness in the thickness of the coating film between the cells caused by any one of the multiple nozzles. A device manufactured by an inkjet printing apparatus according to any one of claims 1 to 5 . In claim 6,
A solar cell,device.

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