WO2024024342A1

WO2024024342A1 - Printing device, control device, and printing method

Info

Publication number: WO2024024342A1
Application number: PCT/JP2023/022806
Authority: WO
Inventors: 智長田; 幸也臼井; 真弘室; 悌一木村; 修平中谷
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2022-07-25
Filing date: 2023-06-20
Publication date: 2024-02-01

Abstract

This printing device comprises: an inkjet head provided with a plurality of nozzles and a plurality of piezoelectric elements; a camera that captures an image of a droplet that is ejected from one of the plurality of nozzles and that lands on a target surface; and a control device that, on the basis of the image, acquires droplet brightness, which is the brightness of the droplet, and an orthographic projection shape, which is the shape of the orthographic projection of the droplet onto the target surface, calculates the volume of the droplet on the basis of on the droplet brightness and the orthographic projection shape, and adjusts a voltage applied to at least one of the plurality of piezoelectric elements on the basis of the calculated volume.

Description

Printing device, control device and printing method

The present disclosure relates to a printing device and a printing method.

As a method for manufacturing devices such as color filters for liquid crystal displays and organic EL displays, for example, a liquid containing a functional material is ejected as droplets from multiple nozzles using an inkjet method, and a film of the functional material is formed on the object to be ejected. There are known methods of forming . In this case, an important step is to obtain the correspondence between the settings of the control device that controls the droplet ejection amount and the actual droplet ejection amount, and to control the ejection amount to a constant value. This is because if the discharge amount becomes non-uniform, a difference will occur in the film thickness of the functional material, leading to device failure. For example, in the case of a color filter or an organic EL display, differences in film thickness are observed as color unevenness or brightness unevenness.

To check the actual discharge amount, for example, apply a predetermined number of droplets of ink containing a polymeric solute to a glass substrate, dry the solvent, and then measure the solute using a measuring instrument such as a white interference microscope. A method of measuring the volume of is known (for example, see Patent Document 1).

Furthermore, as a method of checking the actual discharge amount, a method is known in which the height of the droplet is measured using a laser distance measuring device and the volume of the droplet is calculated (see, for example, Patent Document 2).

In addition, as a method for manufacturing organic EL displays using the inkjet method, after coating ink on a glass substrate, the shape of the droplets after drying the solvent in the ink is measured using a confocal laser microscope, and the shape of the droplets after drying is measured. Obtain the volume value of the drop. Then, based on the solid content concentration in the ink, the volume value of the droplet after solvent drying is converted to the volume of the droplet in the wet state before solvent drying (hereinafter sometimes referred to as "droplet volume"). , obtain the volume value of droplets ejected from each nozzle of the inkjet head. A method is known in which printing with a uniform coating amount is achieved by adjusting the droplet volume value in a wet state between nozzles (for example, see Patent Document 3).

Japanese Patent Application Publication No. 9-48111 Patent No. 6524407 Japanese Patent Application Publication No. 2011-044340

A printing device according to one aspect of the present disclosure includes an inkjet head including a plurality of nozzles and a plurality of piezoelectric elements, and a camera that captures an image of a droplet ejected from one of the plurality of nozzles and landing on a target surface. , based on the image, obtain droplet brightness, which is the brightness of the droplet, and an orthogonal projection shape, which is the shape of the orthogonal projection of the droplet onto the target surface, and obtain the droplet brightness and the orthogonal projection. A control device that calculates the volume of the droplet based on the shape and adjusts the voltage applied to at least one of the plurality of piezoelectric elements based on the calculated volume.

A control device according to one aspect of the present disclosure includes an inkjet head including a plurality of nozzles and a plurality of piezoelectric elements, and a camera that captures an image of a droplet ejected from one of the plurality of nozzles and landing on a target surface. A control device for controlling a printing device comprising: an image acquisition unit that acquires the image from the camera; and a droplet brightness that is the brightness of the droplet by analyzing the image, and a droplet brightness that is the brightness of the droplet. an image analysis unit that obtains an orthogonal projection shape that is a shape of orthogonal projection onto the target surface; a volume calculation unit that calculates the volume of the droplet based on the droplet brightness and the orthogonal projection shape; A voltage adjustment section that adjusts a voltage applied to at least one of the plurality of piezoelectric elements based on the volume.

A printing method according to one aspect of the present disclosure is a printing method of printing by ejecting droplets from an inkjet head including a plurality of nozzles and a plurality of piezoelectric elements, the printing method being a printing method in which droplets are ejected from one of the plurality of nozzles to a target. An image of the droplet that has landed on the surface is captured, and the image is analyzed to determine the droplet brightness, which is the brightness of the droplet, and the orthogonal projection, which is the shape of the orthogonal projection of the droplet onto the target surface. obtaining the shape, calculating the volume of the droplet based on the droplet brightness and the orthogonal projection shape, and adjusting the voltage applied to at least one of the plurality of piezoelectric elements based on the calculated volume. Including doing.

Diagram showing a state in which ink is applied to a line bank in conventional technology Diagram showing a state in which ink is applied to a pixel bank in conventional technology Cross-sectional view taken along line AA in Figure 2 A diagram showing the overall configuration of a printing device according to an embodiment of the present disclosure Functional block diagram of a printing device according to an embodiment of the present disclosure A cross-sectional view showing the internal configuration of a head section of an inkjet head according to an embodiment of the present disclosure. A diagram showing the relationship between the volume of a droplet ejected from a nozzle of an inkjet head and the voltage applied to a piezoelectric element according to an embodiment of the present disclosure. A diagram showing the configuration of a coating unevenness observation device according to an embodiment of the present disclosure A diagram showing the arrangement of an optical system of a coating unevenness observation device according to an embodiment of the present disclosure A diagram showing a state in which droplets are printed on a substrate according to an embodiment of the present disclosure A diagram showing a method for measuring the area of a droplet according to an embodiment of the present disclosure Graph showing area measurement results of droplets according to embodiments of the present disclosure 13 is a graph showing the area measurement results of a droplet according to an embodiment of the present disclosure, in which the horizontal axis of the graph in FIG. 12 is corrected to the elapsed time from when the droplet lands until observation is performed. Graph showing the results of correcting the area measurement results of droplets according to the embodiment of the present disclosure A model diagram of a droplet landing on a substrate according to an embodiment of the present disclosure Graph showing the relationship between the area of a droplet and the elapsed time from landing to observation according to an embodiment of the present disclosure A diagram showing a method for measuring the area of a droplet according to a modification of the present disclosure. A diagram showing a state in which droplets are printed on a substrate according to a modified example of the present disclosure. A diagram showing a process flow of a method for adjusting coating unevenness according to an embodiment of the present disclosure A diagram showing a state in which printing is performed on a display panel in a coating unevenness adjustment flow according to an embodiment of the present disclosure. A diagram showing how ink applied in a cell according to an embodiment of the present disclosure spreads within the cell. Cross-sectional view taken along line AA in Figure 21 A diagram showing a state in which two patterns with different coating amounts are printed in a cell according to an embodiment of the present disclosure Block diagram of main parts of a printing device according to the present disclosure Top view of landed droplet Side view of landed droplet Graph showing the relationship between droplet volume and time Graph showing the relationship between the area and time of orthogonal projection of a droplet onto the target surface Diagram showing the side view shape of a droplet whose volume gradually decreases as it dries in CCR mode, arranged in chronological order. Diagram showing the plan view shapes of droplets dried in CCR mode arranged in chronological order An example of the relationship between the ratio of the size of the concentric circle to the size of the outer circle and the volume correction coefficient Diagram showing the plan view shapes of droplets dried in CCR mode arranged in chronological order An example of the relationship between the average brightness of the area surrounded by concentric circles and the volume correction coefficient Diagram showing the side view shape of a droplet whose volume gradually decreases as it dries in CCA mode, arranged in chronological order. Diagram showing the plan view shapes of droplets dried in CCA mode arranged in chronological order Diagram showing the process flow of how to calculate droplet volume using brightness

When manufacturing an organic EL display using an inkjet method, the area to which ink is applied is sometimes formed as a line-shaped bank (hereinafter sometimes referred to as a "line bank"). In this case, as shown in FIG. 1, the display panel 5006 is arranged so that the long axis direction of the line bank 2 formed on the display panel 5006 is parallel to the arrangement direction of the plurality of nozzles 101 of the inkjet head 30. By doing so, a plurality of nozzles 101 are assigned to the line bank 2 and ink is ejected to form a coating film. In this state, many nozzles 101 eject ink over a wide area formed in a line, so variations in the volume of droplets 310 between nozzles 101 are averaged out. As a result, variations in the thickness of the coating film formed within the line bank 2 do not pose much of a problem.

FIG. 1 shows an example of printing with 14 nozzles 101. The variation in the volume of droplets discharged from the 14 nozzles 101 is generally about 3%. However, since the droplets 310 from each nozzle 101 mix within the line bank 1, the originally existing variations in droplet volume are averaged out.

A phenomenon in which variation in droplet volume is alleviated by application from a plurality of nozzles will be explained in detail. For example, when coating with three nozzles, let σ _{mean be} the standard deviation of the overall droplet volume variation, and σ ₁ , σ ₂ , σ ₃ be the standard deviation of the droplet volume variation of three different nozzles. The following formula (1) holds true.

σ ₁ ² +σ ₂ ² +σ ₃ ² =σ _mean ² ...(1)
Assuming that the variations in droplet volume of each nozzle are equal, as in the following equation (2), the following equation (3) can be obtained from equations (1) and (2). Further, from equation (3), the following equation (4) is obtained, and from equation (4), the following equation (5) is obtained.

σ ₁ = σ ₂ = σ ₃ ...(2)
3σ ₁ ² =σ _mean ² ...(3)
σ ₁ ² = σ _mean ² /3...(4)
σ ₁ = σ _mean /3 ^1/2 ...(5)
Here, if the variation in the average value of the standard deviation is n% (however, n is 10 or less), the variation in droplet volume at each nozzle is calculated from equation (5) as follows: σ ₁ = n/3 ^1/2 For example, if n=3%, σ ₁ =1.7%. On the other hand, when applying with 14 different nozzles, σ ₁ =n/14 ^1/2 , and for example, if n=3%, σ ₁ =0.8%. In other words, even if the droplet volumes of the nozzles are adjusted to the same level, variations in the droplet volumes can be suppressed by applying the coating using a method using a larger number of nozzles.

Here, as shown in FIG. 2, inside the bank 2 divided into pixels (hereinafter sometimes referred to as "pixel bank") (hereinafter, the area surrounded by pixel bank 2 is referred to as "cell 2A"). When forming a coating film by discharging droplets 310 (in some cases), the number of nozzles 101 allocated to one cell 2A is reduced. As a result, as described above, the variations in droplet volume of the droplets 310 discharged into each cell 2A increase, and the influence of the variations in droplet volume on the variations in the thickness of the coating film increases.

FIG. 3 shows a cross-sectional view taken along line AA in FIG. 2 immediately after coating and before the ink solvent dries. The amount of ink in the coating films 311, 312, 313 formed by the droplets 310 ejected into each cell 2A changes depending on the variation in volume of the droplets 310 ejected from the inkjet head 30. In the example shown in FIG. 2, the number of nozzles 101 assigned to each cell 2A is three, so the effect of averaging the variations in droplet volume is small, and the amount of ink applied to each cell 2A is The dispersion becomes noticeable. This variation in the amount of ink is directly linked to the variation in the thickness of the coating film that remains after the ink solvent dries.

For this reason, the droplet volume is measured before drying. Variations in film thickness result in variations in luminance in organic EL displays, for example, and have a large impact on the display quality of the display. In particular, variations in luminance between adjacent cells 2A have a noticeable effect on the senses, and appear as streak-like unevenness in luminescence. Therefore, when printing on the pixel bank 2, it is necessary to suppress variations in droplet volume between the nozzles 101 more than ever. However, even at present, the variation in droplet volume is suppressed to about 3%, and it is not easy to further reduce the variation in droplet volume.

In view of this situation, an object of the present disclosure is to provide a printing device and a printing method that can suppress uneven light emission of a display panel.

An embodiment of the present disclosure will be described below.

[Printing device configuration]
First, the configuration of the printing device will be explained. FIG. 4 is a diagram showing the overall configuration of a printing device used in this embodiment. FIG. 5 is a functional block diagram of the printing device.

As shown in FIGS. 4 and 5, the printing apparatus 1000 includes a control device (PC) 15, an inkjet table 20, an inkjet head 30, a droplet observation device 40, and a coating unevenness observation device 50.

(Control device)
The control device 15 includes a CPU 150, a storage means 151 (including a large capacity storage means such as an HDD), an input means 152, and a display means 153. Specifically, a personal computer (PC) can be used as the control device 15. The storage unit 151 stores each control program for driving the inkjet table 20, inkjet head 30, droplet observation device 40, and coating unevenness observation device 50 connected to the control device 15, as well as characteristic data (all information) of the inkjet head 30. Characteristic data regarding the applied voltage of the piezoelectric element of the nozzle and the droplet volume) are stored. When the printing apparatus 1000 is driven, the CPU 150 performs predetermined control based on instructions input by the operator through the input means 152 and each control program stored in the storage means 151.

(inkjet table)
The inkjet table 20 is a so-called gantry-type work table, and two gantry units (movable frames) are disposed on a base table so as to be movable along a pair of guide shafts.

Specifically, the plate-shaped base 200 has column-shaped stands 201A, 201B, 202A, and 202B arranged at the four corners of its upper surface. In the area surrounded by these stands 201A, 201B, 202A, and 202B, there is a fixed stage ST for placing the object to be coated, and an ink pan (dish-shaped) used to stabilize ink ejection immediately before coating. container) 60 are provided, respectively.

Furthermore, guide shafts 203A and 203B are supported in parallel on the base 200 by the stands 201A, 201B, 202A and 202B along a pair of both sides along the longitudinal direction (Y direction). Two linear motors 204A and 204B are inserted through one guide shaft 203A. Two linear motors 205A and 205B are inserted through the other guide shaft 203B. A gantry section 210A is mounted on the linear motor 204A and the linear motor 205A so as to cross the base 200. A gantry section 210B is mounted on the linear motor 204B and the linear motor 205B so as to cross the base 200. With this configuration, when the printing apparatus 1000 is driven, the

linear motors

204A, 205A, 204B, and 205B are driven so that the two

gantry sections

210A and 210B are independently moved in the longitudinal direction of the guide shafts 203A and 203B. Move back and forth along the line.

A movable body (carriage) 220A, 220B consisting of an L-shaped pedestal is disposed in each of the

gantry parts

210A, 210B. Servo motors (moving body motors) 221A, 221B are provided in the moving bodies 220A, 220B. A gear (not shown) is arranged at the tip of the shaft of each servo motor 221A, 221B. The gears are fitted into guide grooves 211A, 211B formed along the longitudinal direction (X direction) of the

gantry parts

210A, 210B. Inside the guide grooves 211A and 211B, minute racks (not shown) are formed along the longitudinal direction. The rack meshes with the gears. Therefore, when the servo motors 221A, 221B are driven, the movable bodies 220A, 220B are reciprocated and precisely moved along the X direction by a so-called pinion rack mechanism. Here, the movable bodies 220A and 220B are each equipped with an inkjet head 30 and a coating unevenness observation device 50, and are driven independently of each other.

Note that the

linear motors

204A, 205A, 204B, 205B and the servo motors 221A, 221B are each connected to a control unit 213 for controlling driving. The control unit 213 is connected to the CPU 150 within the control device 15. When the printing apparatus 1000 is driven, the CPU 150 that has read the control program controls the driving of the

linear motors

204A, 205A, 204B, 205B and the servo motors 221A, 221B via the control unit 213 (FIG. 5).

Further, the

linear motors

204A, 205A, 204B, 205B and the servo motors 221A, 221B are merely examples of means for moving the

gantry sections

210A, 210B and the movable bodies 220A, 220B, respectively, and their use is not essential. For example, at least one of the gantry section and the moving body may be moved using a timing belt mechanism or a ball screw mechanism.

Note that in this embodiment, the inkjet head 30 is configured to move relative to the fixed stage ST, but the present invention is not limited to this. Alternatively, a configuration in which both the inkjet head 30 and the stage move may be used. Note that the number of inkjet heads 30 mounted on the movable body 220A does not need to be one, and a plurality of inkjet heads 30 may be mounted, or a line head in which a plurality of inkjet heads 30 are unitized is mounted. It's okay.

(inkjet head)
The inkjet head 30 is a head that employs a piezo system, and is composed of a head section 301 and a main body section 302 shown in FIG. 4, and a control section 300 shown in FIG. 5. A servo motor 304 is built into the main body 302 . The inkjet head 30 is fixed to the moving body 220A via the main body 302. As shown in FIG. 4, the head section 301 has a rectangular parallelepiped external shape, and is suspended from the shaft tip of the servo motor 304 of the main body section 302 near the center of its upper surface. Thereby, the plurality of nozzles 3030 (see FIG. 6) formed on the bottom surface of the head section 301 rotate above the fixed stage ST in accordance with the shaft rotation of the servo motor 304.

FIG. 6 is a cross-sectional view showing the internal configuration of the head section of the inkjet head. FIG. 6 partially shows three ink ejection mechanism sections formed adjacent to each other in the head section 301. In FIG.

As shown in FIG. 6, a plurality of ink ejection mechanisms for ejecting ink are arranged in the head section 301 along the longitudinal direction. The ink ejection mechanisms are arranged in a line at regular intervals. Each ink ejection mechanism section includes a piezoelectric element 3010 (3010a, 3010b, 3010c), a liquid chamber 3020 (3020a, 3020b, 3020c), a nozzle 3030 (3030a, 3030b, 3030c), and a diaphragm 3040.

The diaphragm 3040 is arranged to cover the liquid chamber 3020. A piezoelectric element 3010 is stacked on the diaphragm 3040. The ink ejection mechanisms are each independently driven by applying a voltage to each of the piezoelectric elements 3010a, 3010b, and 3010c.

The liquid chamber 3020 and the nozzle 3030 are made of, for example, a metal material such as SUS or a ceramic material. The liquid chamber 3020 and the nozzle 3030 are each formed by machining, etching, or electrical discharge machining. The liquid chamber 3020 is a space that stores ink just before being ejected, and its volume is reversibly reduced and restored by driving the piezoelectric element 3010. The nozzles 3030 are formed in a line at a constant pitch so as to communicate with the liquid chamber 3020. Here, the pitch of each nozzle 3030 is structurally constant, but by adjusting the rotation angle of the shaft of the servo motor 304, the pitch of ink application on the object to be applied can be adjusted. . Note that the arrangement of the nozzles 3030 is not limited to the one row described above. For example, the pitch between the nozzles 3030 can be adjusted narrowly by forming the nozzles 3030 in multiple rows, or by forming the nozzles 3030 in multiple rows in a staggered manner.

The diaphragm 3040 is a thin plate made of stainless steel or nickel, and is arranged to be deformable together with the piezoelectric element 3010 laminated thereon. The piezoelectric element 3010 is a known piezo element, and has a laminate structure in which a plate-shaped piezoelectric body made of, for example, lead zirconate titanate is sandwiched between one or more pairs of electrodes. The energization of the electrodes is managed by the CPU 150 via the control unit 300, as shown in FIG. Based on a predetermined control program stored in the storage means 151, a rectangular pulse voltage with a width of several tens of μs is continuously applied to the electrodes at a driving frequency of several hundred Hz to several tens of kHz during ink ejection. . The piezoelectric element 3010 deforms in accordance with the rise of each rectangular pulse voltage, and as the piezoelectric element 3010 deforms, the diaphragm 3040 deforms so that the volume of the liquid chamber 3020 decreases or restores. When the volume of the liquid chamber 3020 decreases, ink is ejected from the nozzle 3030. Note that the pulse voltage is not limited to a rectangular shape, and may have a step shape or a partially curved waveform.

When driving each piezoelectric element 3010, the CPU 150 reads a predetermined control program from the storage means 151, and instructs the control unit 300 to apply a predetermined voltage to the target piezoelectric element 3010. As will be described later, in the printing apparatus 1000, if unevenness is confirmed when printing on an object to be coated, the printing apparatus 1000 controls the droplet volume to be corrected for each nozzle 3030. In this embodiment, an example is shown in which one inkjet head 30 is provided, but the number of inkjet heads 30 provided is not limited, and a plurality of inkjet heads 30 may be provided.

(Droplet observation device 40)
The droplet observation device 40 is configured using an ink discharge confirmation camera. As shown in FIG. 4, the droplet observation device 40 includes a droplet observation camera (CCD camera) 402 with a built-in light emitting light, a zoom lens 403 attached to the tip of the droplet observation camera in the objective direction, and a droplet observation camera (CCD camera) 402 that has a built-in light emitting light. It is composed of a control unit 400 for controlling the drive of a drop observation camera and a zoom lens 403, and the like. In the configuration shown in FIG. 4, the droplet observation camera is fixed to the fixed base 401, but the fixing method is not limited to this, and the droplet observation camera may be fixed directly to the base 200. Good too. The droplet observation camera is connected to the control unit 400 via a cable 404. The control unit 400 is connected to the CPU 150, as shown in FIG.

In the printing apparatus 1000, the droplet observation camera is directed to a position where it can image the state of droplets discharged from each nozzle 3030 of the head section 301, as shown in FIG. With such a configuration, when capturing images, image data of still images and moving images can be continuously obtained in synchronization with the strobe light emission of the light emitting light built into the droplet observation camera. The CPU 150 of the control device 15 stores captured image data in the storage means 151 and displays it on the display means 153 based on a predetermined control program.

Note that the droplet observation device 40 measures the velocity of droplets (hereinafter sometimes referred to as "droplet velocity"). If the droplet speed is too fast, secondary droplets called satellites will be generated, and if the droplet speed is too slow, the accuracy of the landing position will deteriorate due to air resistance during flight, so it is important to make sure that the droplet is flying at an appropriate speed. It is necessary to confirm that. Further, the droplet observation device 40 can measure the droplet volume for each nozzle 3030. Assuming that the flying droplet is spherical, the volume is estimated from the diameter of the droplet observed two-dimensionally. As described later, the droplet volume can be measured by coating on a droplet volume adjustment substrate, but it is also possible to measure the droplet volume using the droplet observation device 40.

(How to obtain droplet volume data for each nozzle)
In order to adjust the droplet volume for each nozzle 3030, voltage determination data indicating the correlation between the voltage applied to the piezoelectric element 3010 and the droplet volume is used. In order to obtain the voltage determination data, a droplet volume adjustment board is used. The droplet volume adjustment substrate used is one whose surface area on which ink is applied has been treated to be water-repellent by fluorine coating, plasma treatment, or the like. Such water-repellent finishing is a device for accurately measuring the volume of dropped ink droplets.

First, a predetermined number of droplets are applied from all nozzles 3030 onto the droplet volume adjustment substrate. After drying the solvent contained in the applied droplets by vacuum drying or the like, the volume of the remaining solute is measured. The volume is measured using a confocal laser microscope, a white interference microscope, or the like. Here, in general, with a confocal laser microscope or a white interference microscope, an image of only the focal portion can be obtained, so by changing the focal length, the area of the image at the height of each focal length can be measured. The ink droplet to be measured has a hemispherical shape, so its shape when viewed from above is approximately circular. Therefore, the shape of each droplet portion divided at predetermined fine constant height h intervals is regarded as a disk shape, and from the radius r of the disk at a constant height h, the partial volume of the disk shape (πr ² × h) seek. This disc-shaped partial volume is calculated up to the total height H of the droplet. Thereafter, by summing up each of the partial volumes previously determined, the ink droplet volume V can be calculated as an approximate value.

In addition, since the droplet volume of one droplet is very small, in the above calculation, the volume of a large droplet including a certain number of droplets is calculated based on the volume Vsum (for example, the droplet volume of 4 drops). calculate. That is, four drops of ink are dropped from each nozzle 3030 at the same position on the droplet volume adjustment substrate to form large droplets. By dividing the volume Vsum of this large droplet by the number of droplets (4 drops), the ink volume per droplet Vdr (=Vsum/4) is calculated.

By changing the voltage and measuring the droplet volume for each nozzle 3030 using the above method, voltage determination data as shown in FIG. 7 can be obtained. This voltage determination data is stored in the storage means 151 as a table for each nozzle 3030. This allows the voltage adjustment value when adjusting the droplet volume to be determined. Specifically, it can be seen that in order to change the droplet volume by 0.1 pL, it is sufficient to adjust the voltage applied to the piezoelectric element 3010 by 0.24V.

(Coating unevenness observation device 50)
The coating unevenness observation device 50 is one of the main features of the printing apparatus 1000, and is a means for observing unevenness in a coating film on a display panel, which is an object to be coated, placed on a fixed stage ST. FIG. 8 is a diagram showing the configuration of a coating unevenness observation device. FIG. 9 is a diagram showing the arrangement of the optical system of the coating unevenness observation device.

The coating unevenness observation device 50 is composed of a photographing unit 501 and a control section 500, as shown in FIG. As shown in FIG. 8, the photographing unit 501 includes a lighting 5001, a camera 5002, a lens 5003, a cylindrical lens 5004, and a rod lighting 5005. The cylindrical lens 5004 is provided with a lens function only in one direction. The cylindrical lens 5004 can uniformly illuminate the light in a straight line while condensing the light. As shown in FIG. 9, illumination light from a rod illumination 5005 is irradiated obliquely onto a coating film 5008 applied within a bank pattern 5007 (cell 5007A) on a display panel 5006. Reflected light is generated on the surface of the coating film 5008 according to the amount of coating liquid on the coating film 5008, and the reflected light is received by the camera 5002 arranged perpendicularly to the display panel 5006 via the lens 5003. . By irradiating the illumination light obliquely, it is totally reflected on the surface of the coating film 5008, eliminating loss of reflected light and improving observation sensitivity. The camera and illumination are not limited to those mentioned above, and any camera and illumination may be used as long as the coating film 5008 can be observed.

The reason for using such a coating unevenness observation device 50 is as follows. The volume of droplets discharged from the nozzle 3030 is adjusted in advance to a predetermined volume. However, even if printing is performed in an adjusted state, depending on the position and number of nozzles 3030 assigned to the cells, there may be a difference in droplet volume between adjacent cells, resulting in uneven coating. In such a case, the volume of droplets discharged from the nozzle 3030 can be adjusted to an optimal state by directly observing the coating unevenness.

(Adjustment of droplet volume by measuring the area of landed droplets)
It is possible to adjust the volume of the droplet by observing the droplet that has landed on the workpiece from above with a camera and measuring the area of the droplet.This method will be explained below. The workpiece may be a portion of the display panel other than the cells, or may be a glass substrate whose surface area, on which droplets are to land, has been treated to be liquid repellent by a fluororesin coating, plasma treatment, or the like.

FIG. 10 shows a state in which droplets 321 are printed on a substrate 5010. The surface of the substrate 5010 is coated with a water-repellent material. Note that the surface of the display panel 5006 is also coated with a water-repellent material. The substrate 5010 has the property of repelling ink. When ink wets and spreads on the substrate 5010, adjacent droplets may connect with each other. In order to prevent such adjacent droplets from connecting, ink is prevented from getting wet and spread on the substrate 5010. There is a need. The contact angle of the ink to the substrate 5010 is approximately 30° to 70°.

First, before the droplet 321 lands on the substrate 5010, a dummy droplet 320 is printed in order to make the drying state of the droplet 321 that lands first and the droplet 321 that lands after that as similar as possible. . The dummy droplets 320 are obtained by landing several to several tens of droplets from each nozzle 3030.

After printing the dummy droplet 320, the droplet 321 is printed. If the density between the droplets 321 on the substrate 5010 is too high, it will be susceptible to drying, and there is a possibility that adjacent droplets 321 will connect with each other. In order to eliminate such effects of drying and to prevent adjacent droplets 321 from connecting with each other, printing is performed with a certain distance between droplets 321 secured. For example, the CPU 150 of the control device 15 prints the droplets 321 while moving the inkjet head 30 in the printing direction so as to eject the droplets 321 from adjacent nozzles 3030 at different times. Due to the actual positional relationship between the plurality of nozzles 3030, each droplet 321 is spread isotropically and applied. In this embodiment, when the row direction is the direction perpendicular to the printing direction, droplets 321 ejected from adjacent nozzles 3030 are printed in different rows on the substrate 5010.

FIG. 11 is an explanatory diagram of a method for measuring the area of the droplet 321 on the substrate 5010. As shown in FIG. 11, the area of the droplet 321 is measured by observing the droplet 321 that has landed on the substrate 5010 from above with a camera 5011. Note that the area here refers not to the surface area but to the area of the shadow when the droplet 321 is viewed from above (the projected area of the droplet 321 on the substrate 5010).

First, the camera 5011 is scanned to sequentially observe the droplets 321 in each row starting from the droplet 321 at the end of each row. After the observation of the droplets 321 in the first row is completed, the droplets 321 in the second row and the droplets 321 in the third row are observed in order. The CPU 150 of the control device 15 measures the area of the droplet 321 before the landed droplet 321 dries. The ink contains about 0.5 to 10% solid content, such as organic EL light-emitting materials. Although solid content remains after the ink solvent dries, the amount of solid content is very small, so the area of the droplet 321 becomes small. If the area of the droplet 321 becomes smaller, it becomes difficult to understand the difference in volume of the droplet 321 for each nozzle 3030, so the area of the droplet 321 is measured before the droplet 321 dries.

An experiment was conducted using the above method, and the area of the droplet 321 was measured. The measurement results of the area of the droplet 321 are shown in FIG. The horizontal axis of the graph in FIG. 12 indicates the measurement order of the droplets 321, and the vertical axis indicates the area of the droplets 321. FIG. 13 shows the results in which the horizontal axis of the results shown in FIG. 12 is corrected to the elapsed time from when the droplet 321 lands until observation is performed. From the relationship shown in FIG. 13, it can be seen that the longer the elapsed time after the droplet 321 lands, the smaller the area of the droplet 321 becomes. On the other hand, the area of the landed droplet 321 also changes depending on the volume of the droplet 321 discharged from the nozzle 3030. In order to obtain the correct area according to the volume of the droplet 321 discharged from the nozzle 3030, it is necessary to correct the value by taking into account that the droplet 321 becomes smaller due to drying and the area changes. .

Therefore, the drying of the droplet 321 on the substrate 5010 was considered using a model as shown in FIG. In the initial stage, the mode is called CCR (Constant Contact Radius) mode, in which the diameter of the droplet 321 remains constant at D ₀ and the contact angle changes from θ _C shown in the upper and left side of FIG. It decreases until it reaches θ ₁ as shown in the figure. After that, the mode shifts to CCA (Constant Contact Angle) mode, and the contact angle remains constant at θ ₁ , and the diameter of the droplet 321 changes from D ₀ shown in the upper and center figure of FIG. 15 to the upper and right figure. It decreases until it reaches _D2 as shown.

Furthermore, the droplet 321 that landed on the substrate 5010 was considered as a spherical crown (a part of a sphere cut by a plane) shown in the lower diagram of FIG. The radius of the sphere is r, the radius of the spherical crown is a (that is, the radius of the circle when the droplet 321 is observed from above), and the line from the center of the sphere to the apex (pole) of the spherical crown and the bottom of the spherical crown are Let the polar angle between the ends be θ. Here, θ is equal to the contact angle θ _C of the landed droplet 321 with respect to the substrate 5010. Further, the surface area of the spherical crown is expressed by the following equation (6), and the volume of the spherical crown is expressed by the following equation (7).

Surface area of spherical crown A = 2πr ² (1-cosθ) … (6)
Volume of the spherical crown V = (πr ² /3) × (2 + cos θ) (1 - cos θ) ² ... (7)
In this experiment, the volume of the droplet 321 discharged from the nozzle 3030 was 4100 μm ³ , and the contact angle θ _C was 61°. When calculated using equations (6) and (7) and experimental values, the relationship between the elapsed time after the droplet 321 lands and the area of the droplet 321 when viewed from above is as shown in FIG. expressed. From FIG. 16, it can be seen that in a region where the elapsed time is short, the area of the droplet 321 is expressed as a linear function with respect to the elapsed time. Therefore, it can be seen that the CPU 150 of the control device 15 can correct the area of the droplet 321 using the linear expression of the elapsed time after landing. FIG. 14 shows the results obtained by correcting the results shown in FIG. 13 using the above linear equation. Using the area values shown in FIG. 14, the CPU 150 of the control device 15 sets conditions for ejecting ink from the inkjet head 30 (for example, driving voltage ), it is possible to reduce variations in the volume of droplets 321 for each nozzle 3030.

Furthermore, it is preferable to correct the area of the droplet 321 for each line to be printed. For example, in FIG. 11, the first, second, and third rows are corrected separately. Although dummy droplets 320 are initially placed in order to equalize the drying conditions of the droplets 321, there is still a possibility that the drying conditions differ slightly from row to row. Therefore, it is possible to correct the area more accurately by correcting each row.

Furthermore, in order to make the drying state uniform, dummy droplets 320 may be placed at both ends of each row, as shown in FIG. 17. The nozzle 3030 corresponding to the droplet 321 at the end of each row may be treated as a dummy nozzle and operated as a nozzle 3030 whose volume is not adjusted. Further, as shown in FIG. 18, dummy droplets 320 may be placed before and after the droplets 321 printed row by row in the printing direction. In this way, the dry state of the droplet 321 becomes almost uniform within the plane.

Additionally, it is desirable to correct the area for each type of ink. This is because if the ink solvent is different, the drying state changes and the area correction formula changes. Even if the solvent is the same, the correction formula may change even if the type or concentration of the solid content differs, so it is desirable to perform correction for each ink. Alternatively, several droplets 321 ejected from one nozzle 3030 may be landed in multiple rows, and the average value may be used as the droplet area to be corrected. By averaging the area values of multiple droplets, it is possible to alleviate the influence on the corrected droplet area due to variations in repeatability of ejection and variations in wettability depending on the location of the substrate 5010.

[Method for adjusting coating unevenness]
Next, a coating unevenness adjustment method using the printing apparatus 1000 will be described. FIG. 19 is a diagram showing a process flow of the coating unevenness adjustment method. FIG. 20 is a diagram showing a state in which the display panel is printed in the coating unevenness adjustment flow. FIG. 21 is a diagram showing how ink applied inside a cell spreads within the cell. FIG. 22 is a cross-sectional view taken along line AA in FIG. 21. FIG. 23 is a diagram showing a state in which two patterns with different coating amounts are printed in a cell.

First, as shown in FIG. 19, the display panel before printing is observed (step S1). Specifically, by observing the display panel before printing with the coating unevenness observation device 50 and acquiring image information from the panel before printing ink, information on the base is acquired, and later cell observation is performed. The background noise of the coating unevenness observation device 50 is removed.

Next, the printing device 1000 performs printing on the display panel observed in step S1 (step S2). Specifically, as shown in FIG. 20, ink is applied inside the cells 2A formed in the bank 2 and to locations other than the cells 2A.

Next, the CPU 150 of the control device 15 calculates the volume of droplets for each nozzle 3030 (step S3). When the droplet 310 is applied inside the cell 2A as shown in FIG. 20, the droplet 310 immediately spreads to form coating films 311, 312, 313 filling the inside of the cell 2A as shown in FIG. The volume of the droplet 310 for each nozzle 3030 cannot be calculated based on the coating films 311, 312, and 313 in the cell 2A. Therefore, the CPU 150 calculates the volume of droplets applied to locations other than the cell 2A for each nozzle 3030. As shown in FIG. 22, it is desirable that the droplet 315 applied to areas other than the cell 2A be placed above the bank 2. This is because the upper part of the bank 2 is highly liquid repellent to the droplets 315, and the applied droplets 315 are likely to be stably formed into a hemispherical shape. By making the shape of the droplet 315 into such a hemispherical shape, the diameter and height of the droplet 315 tend to change regularly according to the droplet volume of the droplet 315, and the droplet 315 can be viewed from above by the camera 5002. The droplet volume can be accurately measured when observed at . The intensity of the reflected light correlates with the height of the droplet 315. Therefore, the CPU 150 calculates the volume of the droplet 315 as follows.

First, in advance, droplet height calculation data indicating the relationship between the intensity of reflected light from a droplet applied to a location other than the cell 2A and the height of the droplet is created in a database and stored in the storage means 151. I'll keep it. The coating unevenness observation device 50 observes the droplets 315 on the bank 2 and outputs image data indicating the observation results to the control device 15. By observation using the coating unevenness observation device 50, image data of a gray scale of 256 gradations from 0 to 255 is obtained. Note that the image data is not limited to grayscale, and may be color. Based on the image data, the CPU 150 of the control device 15 calculates the area of the droplet 315 (the area of the orthogonal projection of the droplet onto the coating surface, that is, the cross-sectional area of the droplet, in other words, the circular area visible to the observer). , and the intensity of reflected light from the droplet 315. The CPU 150 calculates the volume of the droplet 315 based on the area and reflected light intensity of the droplet 315 calculated based on the image data and the droplet height calculation data. Note that as a simple method for measuring the droplet 315, it is also possible to estimate the volume from only the area of the droplet 315 described above. This is because the height of the droplet is determined by the contact angle of the droplet 315 on the bank 2, and is considered to be approximately constant regardless of the droplet volume.

With reference to the droplet volume of each nozzle 3030 measured by the above method, the nozzle 3030 to be adjusted when adjusting the droplet volume of each cell 2A is determined. This is because it is difficult to make a droplet that originally has a large volume even larger, or to make a droplet that originally has a small volume even smaller.

Next, the coating unevenness observation device 50 observes the printed cells 2A (step S4). It is desirable that the printed cell 2A be observed before the ink solvent dries. This is because if the cell 2A is observed after the ink solvent has dried, the volume of the droplet ejected from the nozzle 3030 cannot be accurately calculated.

Next, the CPU 150 of the control device 15 calculates the volume of the droplets applied in each area of each cell 2A based on the image data obtained in step S4 (step S5). When the cell 2A is observed from above with the camera 5002 of the coating unevenness observation device 50, the area of the droplet displayed in the image data (the area of the orthogonal projection of the droplet onto the coating surface, that is, the cross-sectional area of the droplet, in other words The area of the circle visible to the observer is determined by the size of the cell 2A and is constant. Therefore, the volume of the droplet can be estimated based on the difference in the intensity of the reflected light, which varies depending on the height of the applied droplet. The intensity of the reflected light can be determined from the image data obtained in step S4. Using the method described above, the data for calculating the cell coating amount representing the relationship between the intensity of reflected light from the coating film in the cell 2A (image data) and the volume of the droplet is created in advance into a database, and the data is stored in the storage means 151. By accumulating the droplet volume, the droplet volume can be calculated. Note that creating a database of droplet volumes may use supervised machine learning in which input information is cell image data and output information is volume numerical data for each cell.

The diagram at the left end of FIG. 23 shows the cell 2A before printing, and the diagrams at the center and right end of FIG. 23 show the state in which the coating film 316 is printed on the cell 2A with different amounts of ink. As shown in the center and rightmost diagrams of FIG. 23, the shape of the four corners of the coating area in cell 2A, which is the area surrounded by the dashed-dotted line, the measured values of the horizontal width and vertical width of the coating area, and the gray scale. It is also possible to estimate the shape of the coating film 316 and calculate the droplet volume from the contrast of the image data. In this case, data for calculating the cell coating amount representing the relationship between the shapes of the four corners, the measured values of the horizontal and vertical widths of the coating area, the contrast, and the droplet volume obtained from the image data are compiled into a database and stored in the storage unit 151. You can store it in

The CPU 150 of the control device 15 calculates the value of the droplet volume to be adjusted for each cell 2A, based on the above-mentioned calculated value of the droplet volume for each cell 2A, so that the droplet volume for each cell 2A becomes equal ( Step S6). At this time, the volume of each cell 2A is determined so that uneven streaks do not occur, that is, so that the difference in droplet volume between the cells 2A calculated in step S5 disappears (reduces). In particular, since droplet volume variations between adjacent cells 2A lead to uneven streaks, it is necessary to adjust with high precision.

The CPU 150 of the control device 15 uses the position information of the nozzle 3030 assigned to each cell 2A, the droplet volume value of each nozzle 3030 calculated in step S3, and the droplet volume value to be adjusted for each cell 2A calculated in step S6. The adjusted droplet volume value is determined for each nozzle 3030 from the volume value and the voltage determination data shown in FIG. 7 (step S7). The droplet volume can be adjusted by voltage; however, increasing the applied voltage increases the droplet velocity. When the droplet speed increases beyond a certain level, sub-droplets called satellites are generated in addition to the main droplet. Since satellites may reduce the accuracy of droplet landing positions, it is necessary to eject droplets without generating satellites. Also, when the voltage is reduced, the droplet velocity becomes slower. If the droplet speed becomes slower than a certain level, the droplet will wander due to air resistance during flight, which may reduce the accuracy of the landing position. Therefore, although it is possible to adjust the droplet volume by applying voltage, the adjustment range is limited from the viewpoint of droplet velocity. Therefore, it is difficult to adjust the volume of a droplet with a high droplet velocity to a larger value or to make the volume of a droplet with a lower droplet velocity smaller. Therefore, the CPU 150 of the control device 15 needs to select an appropriate nozzle 3030 for adjusting the droplet volume from the viewpoint of the droplet speed. In other words, it is necessary to select a nozzle 3030 whose droplet volume can be adjusted within a droplet volume adjustable range excluding the range in which volume adjustment is difficult.

Further, the CPU 150 of the control device 15 determines the nozzle 3030 whose droplet volume is to be adjusted, taking into account the arrangement of the nozzles 3030 assigned to the cell 2A and the balance of the droplet volume ejected from each nozzle 3030. For example, in FIG. 20, three nozzles 3030 are assigned to one cell 2A, and the CPU 150 of the control device 15 makes sure that the total volume of droplets 310 ejected from these three nozzles 3030 is as equal as possible. The nozzle 3030 whose volume is to be adjusted is determined. The volume of which nozzle 3030 is adjusted is determined based on the original droplet volume value (preset value of the droplet volume) of each nozzle 3030 assigned to the cell 2A. Specifically, the CPU 150 of the control device 15 calculates the volumes of the three droplets 310 arranged in one cell 2A.
(Pattern 1)
Decrease the volume of the droplet on the left side, reduce the volume of the droplet in the center, and increase the volume of the droplet on the right side.
(Pattern 2)
It is conceivable to select a nozzle 3030 that adjusts the droplet volume so that the droplet volume on the left side is small, the center droplet volume is large, and the right droplet volume is small. However, in the case of pattern 1, the volume of droplets printed to the left of the center in cell 2A becomes smaller, and the volume of droplets printed to the right becomes larger, which may result in an asymmetrical shape within cell 2A. There is. On the other hand, under the conditions of pattern 2, the droplet volume distribution within the cell 2A becomes symmetrical on the left and right sides. From the above, from the viewpoint of the distribution of the film shape formed in the cell 2A, it is desirable to select the nozzle 3030 that adjusts the droplet volume like pattern 2. The CPU 150 of the control device 15 determines the adjusted droplet volume of the selected nozzle 3030.

The CPU 150 of the control device 15 rewrites the applied voltage data for each nozzle 3030 (step S8). Specifically, the CPU 150 of the control device 15 determines the adjusted application voltage for each nozzle 3030 based on the adjusted droplet volume of the nozzle 3030 determined in step S7 and the voltage determination data shown in FIG. Determine the voltage. The CPU 150 of the control device 15 transmits the determined applied voltage value to the control unit 300 of the inkjet head 30, and rewrites the applied voltage data in real time. The applied voltage data is rewritten by directly rewriting the memory (RAM) mounted on the head control board of the control unit 300.

After the display panel on the fixed stage ST is replaced with a new display panel, the printing device 1000 prints on the cells of the display panel based on the rewritten applied voltage data. The coating unevenness observation device 50 observes coating unevenness on the display panel. If the CPU 150 of the control device 15 determines that there is a coating unevenness based on the observation result of the coating unevenness observation device 50 (step S9: YES), it performs the process of step S1, and if it determines that there is no coating unevenness ( Step S9: NO), the coating unevenness adjustment is ended.

As described above, the coating unevenness observation device 50 observes the ink coating state (coating film formation state) within the cell 2A. Based on the observation results of the coating unevenness observation device 50, the CPU 150 of the control device 15 calculates the droplet volume for each nozzle 3030 that ejects ink into the cell 2A so that the difference in droplet volume for each cell 2A becomes small. adjust. In this way, by adjusting the droplet volume for each nozzle 3030 based on the observation results of the droplet volume for each cell 2A to which ink is actually applied, variations in droplet volume between cells 2A are suppressed. be able to. As a result, uneven light emission of the display panel can be suppressed.

[Volume adjustment using ink brightness]
As described above, the printing apparatus 1000 according to the present disclosure includes the inkjet head 30 including a plurality of nozzles 3030 and a plurality of piezoelectric elements 3010. Furthermore, the printing apparatus 1000 includes at least one of the camera 5002 (see FIG. 8) and the camera 5011 (see FIG. 11) of the coating unevenness observation device 50. The printing apparatus 1000 also includes a control device 15 . Such a printing apparatus 1000 may adjust the volume of the droplet discharged from the nozzle 3030 using the brightness of the droplet that landed on the target surface (for example, the surface of the substrate 5010 or the pixel bank 2). A printing apparatus and a printing method that adjust the volume of droplets ejected from the nozzle 3030 using the brightness of the droplets will be described below.

[Printing device configuration]
The main parts of the printing apparatus 1000 that function when adjusting the volume of droplets discharged from the nozzle 3030 using the brightness of the droplets are as follows. Note that content that overlaps with the previous explanation will be omitted as appropriate. In other words, the printing apparatus 1000 described below also includes the components described above using FIGS. 4, 5, and the like. Also, the same components are given the same reference numerals.

FIG. 24 is a block diagram of the main parts of the printing apparatus 1000. The main parts of the printing apparatus 1000 include a control device 15, an inkjet head 30, and a camera 5002. Note that the main part of the printing apparatus 1000 may include a camera 5011 instead of the camera 5002. That is, the functions of the camera 5002 described below may be performed by the camera 5011. Further, the main parts of the printing apparatus 1000 include a camera 5002 and a camera 5011, and these may be switched and used for each process.

The camera 5002 detects the dummy droplet 320 (see FIGS. 10 to 11) that landed on the surface of the substrate 5010 (an example of the target surface) or the droplet 315 that landed on the surface of the pixel bank 2 (see FIGS. 20 to 22). ) is used for observation. Hereinafter, a case where the liquid droplet 315 is observed will be exemplified. At this time, the camera 5002 captures an image of the droplet 315. Camera 5002 transmits the captured image to control device 15.

The control device 15 includes a CPU 150 and a storage means 151. The CPU 150 functions as an image acquisition section 154, an image analysis section 155, a volume calculation section 156, and a voltage adjustment section 157 by reading and executing a program stored in the storage means 151.

The storage unit 151 stores the volume correction coefficient of the droplet 315 that landed on the target surface in association with a parameter that has a correlation with the brightness of the droplet.

The image acquisition unit 154 acquires an image from the camera 5002.

The image analysis unit 155 analyzes the image acquired by the image acquisition unit 154.

The volume calculation unit 156 calculates the volume of the droplet 315 using the image analysis result by the image analysis unit 155 and the volume correction coefficient acquired from the storage unit 151.

The voltage adjustment unit 157 transmits a signal to the inkjet head 30, specifically, the control unit 300, based on the volume of the droplet 315 calculated by the volume calculation unit 156. The signal transmitted at this time is a signal for adjusting the voltage applied to the piezoelectric element 3010 corresponding to the nozzle 3030 whose ejection amount needs to be adjusted, that is, at least one of the plurality of piezoelectric elements 3010.

As shown in FIG. 6, the inkjet head 30 includes a plurality of nozzles 3030 and a plurality of piezoelectric elements 3010 corresponding to each nozzle 3030 on a one-to-one basis. The control unit 300 controls each piezoelectric element 3010 based on instructions (that is, signals) from the control device 15.

(Relationship between brightness and volume)
Before describing a specific printing method using the printing apparatus 1000 having the main parts as described above, the relationship between the brightness and volume of droplets that have landed on the target surface will be described.

FIGS. 25 and 26 are a plan view and a side view of a droplet 315 that has landed on the surface of the bank 2, which is an example of the target surface. 315A, 315B, and 315C shown in FIGS. 25 and 26 are minute regions on the surface of the droplet 315. The micro region 315A is located near the center of the droplet 315, the micro region 315C is located near the edge of the droplet 315, and the micro region 315B is located between the micro region 315A and the micro region 315C. positioned.

When observing the droplet 315 along the direction perpendicular to the target surface on which the droplet 315 landed, the brightness differs depending on the position of the surface of the droplet 315. Specifically, the brightness is higher at a position where the angle between the plane in contact with the surface of the droplet 315 and the target surface is smaller, and the brightness is higher at a position where the angle between the plane in contact with the surface of the droplet 315 and the target surface is larger. It gets expensive. Furthermore, since the droplet 315 has a spherical crown shape, the plane that is in contact with the center of the droplet 315 is parallel to the object plane. Therefore, at the center of the droplet 315, the angle between the plane in contact with the surface of the droplet 315 and the object plane is the minimum 0, and the brightness is the highest. Furthermore, at the outermost periphery of the droplet 315, the angle between the plane in contact with the surface of the droplet 315 and the target surface is maximum (contact angle), and the brightness is the lowest.

In the case of the example shown in FIGS. 25 and 26, the brightness of the minute area 315A is high, the brightness of the minute area 315C is low, and the brightness of the minute area 315B is between the brightness of the minute area 315A and the brightness of the minute area 315C. becomes.

If the volume of the droplet ejected from the nozzle 3030 differs, the shape of the spherical crown formed on the target surface will also differ, and the brightness distribution will also differ. Further, while the droplet landed on the target surface is observed, as the droplet dries and the volume of the droplet decreases, the shape of the spherical crown also changes, and the brightness distribution also changes. By using this property, the volume of the droplet can be determined with high accuracy based on the brightness.

(Relationship between drying mode, volume and orthographic area)
FIG. 27 is a diagram showing an example of a change in volume of an ejected droplet over time. As shown in FIG. 27, droplets 315 are first dried in CCR mode and then in CCA mode. When drying through these modes, the droplet 315 decreases in volume as shown in FIG. 27. That is, in the CCR mode, the volume gradually decreases over time. Furthermore, in the example shown in FIG. 27, the volume decreases at a slower pace in the CCA mode than in the CCR mode. That is, the rate of volume reduction is different between the CCR mode and the CCA mode.

Furthermore, the area of the orthogonal projection of the droplet 315 onto the target surface changes as shown in FIG. 28. That is, in the CCR mode, the area of the orthogonal projection of the droplet 315 onto the target surface does not change. Furthermore, in the CCA mode, the area of the orthogonal projection of the droplet 315 onto the target surface decreases as time passes.

(Relationship between brightness and volume in CCR mode)
FIG. 29 is a diagram chronologically arranging the side view shape of a droplet 315 whose volume gradually decreases as it dries in the CCR mode. Moreover, FIG. 30 is a diagram chronologically arranging the plan view shapes of droplets 315 dried in the CCR mode. Each droplet 315 shown in FIG. 30 corresponds one-to-one with each droplet 315 shown in FIG. 29. Note that FIG. 29 shows only the outline of the droplet 315. FIG. 30 also shows the level of brightness; the closer the color is to white, the higher the brightness, and the closer to black, the lower the brightness.

As shown in FIG. 29, in the CCR mode, the contact angle of the droplet 315 with respect to the surface of the pixel bank 2, which is an example of the target surface, decreases over time. As shown in FIG. 30, in the CCR mode, the orthogonal projection shape, which is the shape of the orthogonal projection of the droplet 315 onto the target surface, does not change over time. In other words, the size (ie, area, diameter, radius, etc.) of the outer circumferential circle 315D, which is the outline of the orthogonal projection shape, does not change.

Further, as shown in FIG. 30, the brightness of the droplet 315 dried in the CCR mode changes as the volume of the droplet 315 decreases (that is, changes in shape). Specifically, as the contact angle decreases and the droplet 315 becomes flat, the region of high brightness spreads from the center toward the periphery.

Therefore, in the CCR mode, as the volume of the droplet 315 decreases (that is, the shape changes), the circle 315E connecting the predetermined brightness increases. This circle 315E is a concentric circle of the outer circumferential circle 315D.

Therefore, the ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D (for example, area ratio, diameter ratio, radius ratio, etc.) changes when the volume of the droplet 315 changes and the brightness of the droplet changes. In other words, the ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D is one of the parameters that has a correlation with the droplet brightness.

Note that the predetermined brightness may be an absolute value of brightness, or a relative value between the maximum value (that is, the brightness at the center) and the minimum value (that is, the brightness at the outer periphery) of the brightness of the droplet 315. It may be.

The ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D changes as the volume of the droplet 315 changes, that is, it is determined according to the volume of the droplet 315, so it is an index indicating the volume of the droplet 315. becomes. Therefore, by determining the relationship between the ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D and the volume correction coefficient, which is a coefficient for correcting the volume of the droplet 315, in advance through experiments, etc. A volume correction factor can be obtained from the ratio.

FIG. 31 shows an example of the relationship between the ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D and the volume correction coefficient. The volume correction coefficient becomes smaller as the ratio of the size of the concentric circle 315E to the size of the outer circumferential circle 315D becomes larger (the height of the droplet 315 becomes lower and the volume becomes smaller).

For example, a more accurate volume of the droplet 315 can be calculated by calculating the provisional volume, which is the provisional volume of the droplet 315, based on the above-mentioned formula (7), and multiplying the provisional volume by a volume correction coefficient. can. That is, by using the brightness of the droplet 315, the volume of the droplet 315 can be calculated more accurately.

Similar to FIG. 30, FIG. 32 is a diagram in which the plan view shapes of droplets 315 dried in the CCR mode are arranged in chronological order. Each droplet 315 shown in FIG. 32 corresponds one-to-one with each droplet 315 shown in FIG. 29. FIG. 32 shows a concentric circle 315F whose diameter is the value obtained by multiplying the diameter of the outer circumferential circle 315D by a predetermined value. Note that the predetermined value can be any value greater than 0 and less than or equal to 1.

In the CCR mode, the diameter of the outer circle 315D does not change. Therefore, the diameter of the concentric circle 315F also does not change. In other words, the shape of the concentric circle 315F does not change, and the area surrounded by the concentric circle 315F also does not change.

However, the brightness of the droplet 315 that dries in the CCR mode changes as the volume of the droplet 315 decreases (that is, the shape changes).

Therefore, the average value of the brightness of the area surrounded by the concentric circle 315F changes when the volume of the droplet 315 changes and the brightness of the droplet changes. That is, the average value of the brightness of the area surrounded by the concentric circle 315F is one of the parameters that has a correlation with the droplet brightness.

The average value of the brightness of the area surrounded by the concentric circles 315F changes as the volume of the droplet 315 changes, that is, it is determined according to the volume of the droplet 315, and therefore serves as an index indicating the volume of the droplet 315. Therefore, by determining the relationship between the average value of the brightness of the area surrounded by the concentric circle 315F and the volume correction coefficient, which is a coefficient for correcting the volume of the droplet 315, in advance through experiments, etc., it is possible to calculate the relationship from this average value. A volume correction factor can be obtained.

FIG. 33 shows an example of the relationship between the average brightness of the area surrounded by the concentric circle 315F and the volume correction coefficient. The volume correction coefficient becomes smaller as the average value of the brightness of the area surrounded by the concentric circle 315F becomes larger (the height of the droplet 315 becomes lower and the volume becomes smaller).

(Relationship between brightness and volume in CCA mode)
FIG. 34 is a diagram chronologically arranging the side view shape of a droplet 315 whose volume gradually decreases as it dries in the CCA mode. Moreover, FIG. 35 is a diagram chronologically arranging the plan view shapes of droplets 315 dried in the CCA mode. Each droplet 315 shown in FIG. 35 corresponds one-to-one with each droplet 315 shown in FIG. 34. Note that only the outline of the droplet 315 is shown in FIG. FIG. 35 also shows the level of brightness; the closer the color is to white, the higher the brightness, and the closer to black, the lower the brightness.

Further, FIG. 35 shows a concentric circle 315F whose diameter is the value obtained by multiplying the diameter of the outer circumferential circle 315D by a predetermined value. Note that the predetermined value can be any value greater than 0 and less than or equal to 1.

As shown in FIG. 34, in the CCA mode, the contact angle of the droplet 315 with the surface of the pixel bank 2, which is an example of the target surface, does not change over time. As shown in FIG. 35, in the CCA mode, the orthogonal projection shape, which is the shape of the orthogonal projection of the droplet 315 onto the target surface, changes over time. In other words, the size (that is, the area, diameter, radius, etc.) of the outer circumferential circle 315D, which is the outline of the orthogonal projection shape, decreases over time.

That is, when drying in the CCA mode, the shapes of the droplets 315 at each time are similar to each other.

Therefore, the average value of the brightness of the area surrounded by the concentric circle 315F does not change while the droplet 315 dries in the CCA mode.

However, the higher the height of the droplet 315 when the drying mode is switched from the CCR mode to the CCA mode (that is, the larger the contact angle), the smaller the average value of the brightness of the area surrounded by the concentric circle 315F becomes. In other words, when the droplet 315 is drying in the CCA mode, the higher the average value of the brightness of the area surrounded by the concentric circle 315F, the lower the height of the droplet 315 and the smaller the volume of the droplet 315.

Therefore, also in the CCA mode, the average value of the brightness of the area surrounded by the concentric circle 315F is one of the parameters that has a correlation with the droplet brightness. Also, in the CCA mode, the relationship between the average brightness of the area surrounded by the concentric circle 315F and the volume correction coefficient, which is a coefficient for correcting the volume of the droplet 315, can be determined in advance through experiments, etc. , a volume correction coefficient can be obtained from this average value. In the CCA mode, the relationship between the average brightness value of the area surrounded by the concentric circle 315F and the volume correction coefficient is similar to the relationship shown in FIG. 33.

(Printing method with volume adjustment using brightness)
Next, a printing method using the printing apparatus 1000 that involves volume adjustment using brightness will be described.

The basic flow of the printing method is the same as that described above with reference to FIG. However, instead of step S3, which is the step of calculating the volume of the droplet 315 (see FIGS. 20 to 22) for each nozzle 3030, the steps shown in FIG. 36 are performed. Therefore, first, a method of calculating the droplet volume executed by the printing apparatus 1000 will be described with reference to FIG. 36.

First, an image of the droplet 315 is captured by the camera 5002 (S11). When the image is captured, the control device 15, specifically the image acquisition unit 154, acquires the image from the camera 5002. Note that the camera 5002 may take an image with the optical axis of the camera 5002 perpendicular to the target surface, or may take an image with the optical axis of the camera 5002 inclined with respect to the target surface. Good too.

Next, the image is analyzed by the image analysis unit 155, and the droplet brightness, which is the brightness of the droplet 315, and the orthogonal projection shape, which is the shape of the orthogonal projection of the droplet 315 onto the target surface, are obtained (S12). . This means that even if an image is captured with the optical axis of the camera 5002 tilted with respect to the target surface, the image analysis unit 155 can obtain the droplet brightness and orthographic shape by image analysis. Needless to say.

Next, the image analysis unit 155 further analyzes the image, and obtains the value of a parameter that has a correlation with the brightness of the droplet 315 (S13). Specifically, it is a concentric circle of the outer circumferential circle that is the outline of the orthogonal projection shape that is the shape of the orthogonal projection of the droplet 315 onto the target surface, and has a predetermined brightness. The ratio of the sizes of concentric circles connecting the points is obtained (see FIG. 30). Alternatively, it is a concentric circle of the outer circumferential circle that is the outline of the orthogonal projection shape that is the shape of the orthogonal projection of the droplet 315 onto the target surface, and the diameter is the value obtained by multiplying the diameter of the outer circumferential circle by a predetermined value. The average value of the brightness of the area surrounded by concentric circles is obtained (see FIG. 32 and FIG. 35).

Subsequently, the volume calculation unit 156 obtains a volume correction coefficient (S14). Specifically, the volume calculation unit 156 calculates the volume correction coefficient based on the value of the parameter acquired by the image analysis unit 155 and the relationship between the volume correction coefficient and the parameter, which is stored in advance in the storage unit 151. get.

Next, the volume calculation unit 156 calculates a provisional volume that is a provisional volume of the droplet 315 (S15). The temporary volume is, for example, the volume assuming that the shape of the droplet 315 is a hemisphere. From the orthogonal projection shape acquired by the image analysis unit 155, the radius of this hemisphere can be determined and the temporary volume can be calculated.

Alternatively, the tentative volume may be determined from equation (7) by predetermining the contact angle of the droplet 315 with respect to the target surface based on experiments or the like. In this case, the radius of the circle drawn by the orthogonal projection shape is the radius a (=rsinθ) of the spherical crown shown in FIG. Therefore, the radius r of the sphere shown in FIG. 15 can be calculated from the orthogonal projection shape. Then, by substituting this radius r and a predetermined contact angle into equation (7), the tentative volume of the droplet 315 can be calculated.

Next, the volume calculation unit 156 calculates the volume of the droplet 315 by multiplying the temporary volume by the volume correction coefficient (S16).

Through the above flow, the printing apparatus 1000 can accurately calculate the volume of the droplet 315 using the brightness of the droplet 315. By performing these steps for each droplet 315 ejected from each nozzle 3030, the volume of the droplet 315 for each nozzle 3030 can be accurately calculated. Then, by going through steps S4 to S8 described above, the voltage applied to at least one of the plurality of piezoelectric elements 3010 is adjusted based on the calculated volume of the droplet 315.

Note that the type of parameter that has a correlation with the brightness of the droplet 315 may be changed depending on the drying mode of the droplet 315 at the time when the image is captured by the camera 5002. That is, in step S13, if the drying mode of the droplet 315 at the time of imaging is the CCR mode, the image analysis unit 155 sets the value of the first parameter as the value of the parameter having a correlation with the brightness of the droplet 315. You may obtain it. Further, in step S13, if the drying mode of the droplet 315 at the time of imaging is the CCA mode, the image analysis unit 155 determines that the first parameter is the type You may acquire the value of the second parameter which is different. The first parameter is, for example, the average brightness of an area surrounded by concentric circles of an outer circumferential circle that is the outline of an orthogonal projection shape, and whose diameter is a value obtained by multiplying the diameter of the outer circumferential circle by a predetermined value. Can be a value. Further, the second parameter is, for example, the ratio of the size of a concentric circle of the outer circumferential circle that connects points having a predetermined brightness to the size of the outer circumferential circle that is the outline of the orthogonal projection shape. can do.

The image analysis unit 155 determines whether the drying mode of the droplet 315 is the CCR mode or the CCA mode based on the elapsed time from when the droplet 315 is ejected from the nozzle 3030 until it is imaged by the camera 5002. can do. That is, if the elapsed time is less than a predetermined time, it is determined that the drying mode is the CCR mode, and if the elapsed time is greater than or equal to the predetermined time, the drying mode is determined to be the CCA mode. It can be determined that

Further, the orthogonally projected shape of the droplet 315 does not change when the drying mode is the CCR mode, but changes and gradually becomes smaller when the drying mode is the CCA mode. Therefore, the image analysis unit 155 analyzes a plurality of still images of the droplet 315 or a moving image of the droplet 315, and determines that the drying mode of the droplet 315 is the CCR mode based on the change in the orthogonal projection shape of the droplet 315. or CCA mode.

By switching the types of parameters used depending on the drying mode, more appropriate parameters can be used for each drying mode, and as a result, a more accurate volume correction coefficient can be obtained. Therefore, the volume of the droplet 315 can be calculated more accurately for each drying mode.

According to the printing device, control device, and printing method of the present disclosure, uneven light emission of the display panel can be suppressed.

The printing apparatus and printing method of the present disclosure can suppress uneven light emission even when display panels are manufactured by printing on pixel banks, and can be applied to display panel manufacturing.

1 Line bank 2 Pixel bank 2A, 5007A Cell 15 Control device 20 Inkjet table 30 Inkjet head 40 Droplet observation device 50 Application unevenness observation device 60 Ink pan (dish-shaped container)
101 Nozzle 150 CPU
151 Storage means 152 Input means 153 Display means (display)
154 Image acquisition unit 155 Image analysis unit 156 Volume calculation unit 157 Voltage adjustment unit 200 Base 201A, 201B, 202A, 202B Stand 203A, 203B Guide shaft 204A,

204B Linear motor

204A, 204B, 205A,

205B Linear motor

210A, 210B Gantry Parts 211A, 211B Guide groove 213 Control part 220A, 220B Moving body 221A, 221B Servo motor 300 Control part 301 Head part 302 Main part 304 Servo motor 310, 315

Droplet

315A, 315B, 315C Micro area 315D Outer circle 315E, 3 15F concentric circles 311, 312, 313, 316 Coating film 320 Dummy droplet 321 Droplet 400 Control unit 401 Fixed stand 402 Droplet observation camera (CCD camera)
403 Zoom lens 404 Cable 500 Control unit 501 Photographing unit 1000 Printing device 3010, 3010a, 3010b, 3010c Piezoelectric element 3020, 3020a, 3020b, 3020c Liquid chamber 3030, 3030a, 3030b, 3030c Nozzle 3040 Vibration plate 5001 Lighting 5002 Camera 5003 Lens 5004 Cylindrical lens 5005 Rod illumination 5006 Display panel 5007 Bank pattern 5008 Coating film 5010 Substrate 5011 Camera ST Fixed stage

Claims

an inkjet head including multiple nozzles and multiple piezoelectric elements;
a camera that captures an image of a droplet ejected from one of the plurality of nozzles and landing on a target surface;
Based on the image, obtain droplet brightness, which is the brightness of the droplet, and an orthogonal projection shape, which is the shape of the orthogonal projection of the droplet onto the target surface,
calculating the volume of the droplet based on the droplet brightness and the orthogonal projection shape;
A printing apparatus, comprising: a control device that adjusts a voltage applied to at least one of the plurality of piezoelectric elements based on the calculated volume.
The control device includes:
The volume correction coefficient of the droplet is stored in association with a parameter having a correlation with the droplet brightness,
Calculating the temporary volume of the droplet from the orthogonal projection shape,
obtaining the value of the parameter from the droplet brightness and the orthogonal projection shape;
obtaining the volume correction coefficient from the obtained value of the parameter;
calculating the volume based on the provisional volume and the acquired volume correction coefficient;
The printing device according to claim 1.
The parameter is an average value of luminance of an area surrounded by concentric circles of an outer circumferential circle that is the outline of the orthogonal projection shape, and whose diameter is a value obtained by multiplying the diameter of the outer circumferential circle by a predetermined value. is,
The printing device according to claim 2.
The parameter is a ratio of the size of a concentric circle of the outer circumferential circle connecting points having a predetermined brightness to the size of the outer circumferential circle that is the outline of the orthographic projection shape.
The printing device according to claim 2.
The control device obtains a first parameter value as the parameter value when the droplet drying mode is the CCR mode, and obtains the first parameter value as the parameter value when the droplet drying mode is the CCA mode. obtaining a value of a second parameter different in type from the first parameter as a value;
The printing device according to claim 2.
The control device determines whether the drying mode is a CCR mode or a CCA mode based on an elapsed time from when the droplet is ejected until when the image is captured by the camera.
The printing device according to claim 5.
The control device determines whether the drying mode is a CCR mode or a CCA mode based on a change in the orthogonal projection shape.
The printing device according to claim 5.
A control device for controlling a printing device including an inkjet head including a plurality of nozzles and a plurality of piezoelectric elements, and a camera that captures an image of a droplet ejected from one of the plurality of nozzles and landing on a target surface. hand,
an image acquisition unit that acquires the image from the camera;
an image analysis unit that analyzes the image to obtain droplet brightness that is the brightness of the droplet and an orthogonal projection shape that is the shape of the orthogonal projection of the droplet onto the target surface;
a volume calculation unit that calculates the volume of the droplet based on the droplet brightness and the orthogonal projection shape;
a voltage adjustment unit that adjusts a voltage applied to at least one of the plurality of piezoelectric elements based on the calculated volume;
Control device.
A printing method in which droplets are ejected from an inkjet head including a plurality of nozzles and a plurality of piezoelectric elements, the method comprising:
capturing an image of the droplet ejected from one of the plurality of nozzles and landing on the target surface;
Analyzing the image to obtain droplet brightness, which is the brightness of the droplet, and an orthogonal projection shape, which is the shape of the orthogonal projection of the droplet onto the target surface,
calculating the volume of the droplet based on the droplet brightness and the orthogonal projection shape;
adjusting a voltage applied to at least one of the plurality of piezoelectric elements based on the calculated volume;
Printing method.