Inkjet printing method for thin film coatings

Abstract

The present invention relates to an inkjet printing method for thin film coating that overcomes the variation in ink ejection characteristics of each nozzle and minimizes the variation in thickness of a coating thin film, and the inkjet printing method for thin film coating of the present invention includes a dot pattern printing step of printing a dot pattern group by ejecting ink to a predetermined position on a surface of a target object using a dot pattern forming nozzle group so that the ejected droplets do not overlap each other, a connection pattern printing step of printing a connection pattern group by ejecting ink to a position between adjacent patterns using a connection pattern forming nozzle group so that the same attractive force acts on the adjacent patterns ejected on the surface of the target object, and a finish printing step of finishing the coating on the surface of the target object by ejecting ink to an area excluding the adjacent droplets using a finish nozzle group so that the same attractive force acts on the adjacent droplets ejected on the surface of the target object.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to an inkjet printing method for thin film coating, and more particularly to an inkjet printing method for thin film coating, which prevents deposited ink droplets from being attracted to each other and clumping together to have different thicknesses, overcomes variations in ink ejection characteristics of each nozzle, and minimizes variations in the thickness of a coating thin film.

[0002] [Background technology] Generally, the process of manufacturing a micro OLED display formed on a silicon substrate using inkjet printing technology includes forming a thin film coating.

[0003] For example, FIG. 1 shows the cross-sectional structure of a typical micro OLED display, in which the OCR layer and organic layer that make up the micro OLED display are formed by a thin film coating process.

[0004] In particular, since the pixel size of a micro OLED display is very small at less than 2.4 μm, the organic thin film of the micro OLED display must be coated as thin as 0.5 μm.

[0005] If the organic thin film of a micro OLED display is formed too thick, as shown in Figure 2, the diagonal light emitted from the micro OLED is likely to cause color interference with the adjacent pixels.

[0006] For the reasons mentioned above, in the manufacture of micro OLED displays, the organic thin film for sealing or the OCR layer for glass adhesion must be coated to a thickness of 0.5 μm or less.

[0007] Meanwhile, when coating to a thickness of 0.5μm or less using an inkjet head module, there are problems in that the thickness of the coated thin film is not uniform and uneven as shown in Figure 3 due to the variation in ink ejection characteristics caused by the difference in the volume of fine ejected ink droplets between the nozzles of the inkjet head module and the phenomenon in which the ejected ink droplets solidify due to the attractive force with other ink droplets depending on the surface condition after being impacted.

[0008] In other words, unevenness occurs due to thickness variations, as shown in green for thin coating areas and brown for thick coating areas. To prevent this, the coating should be applied evenly to a thickness of less than 2% of the total area.

[0009] Therefore, in order to solve the above-mentioned problem of variation in the thickness of the thin film, a solution is required to solve the problem of minute variations in the ink ejection characteristics between the nozzles of an inkjet head module, and the problem of ejected ink droplets not landing in the correct position due to the phenomenon in which the ejected ink droplets solidify due to the attractive force with other ink droplets depending on the surface condition after landing.

[0010] [Prior art documents] [Patent Documents] [Patent Document 1] Korean Patent Publication No. 10-2015-0130836, November 24, 2015 Summary of the Invention [Problem to be solved by the invention] In order to solve the problems of the prior art, the present invention provides an inkjet printing method for thin film coating that prevents ink droplets from being attracted to each other and clumping together to have different thicknesses, overcomes the variation in ink ejection characteristics of each nozzle, and minimizes the variation in the thickness of the thin coating film.

[0011] [Means for solving the problems] The inkjet printing method for coating a thin film according to the present invention for solving the above technical problems includes a dot pattern printing process of printing a dot pattern group by ejecting ink at a predetermined position on a surface of an object using a dot pattern forming nozzle group so that the ejected droplets do not overlap each other, a connective pattern printing process of printing a connective pattern group by ejecting ink at a position between adjacent patterns using a connective pattern forming nozzle group so that the same attractive force acts on the adjacent patterns ejected on the surface of the object, and a finish printing process of finishing a coating on the surface of the object by ejecting ink in an area excluding the adjacent droplets using a finish nozzle group so that the same attractive force acts on the adjacent droplets ejected on the surface of the object.

[0012] Preferably, the dot pattern forming nozzle group, the connection pattern forming nozzle group, and the finishing nozzle group are configured with different nozzles from each other within a head module.

[0013] Preferably, the size of the droplets ejected through the nozzle group for forming a dot pattern, the size of the droplets ejected through the nozzle group for forming a connecting pattern, and the size of the droplets ejected through the nozzle group for finishing are configured to be the same or different from each other.

[0014] Preferably, in at least one of the dot pattern printing process, the connected pattern printing process, and the finish printing process, a thickness of the coating is adjusted by discharging a plurality of droplets in an overlapping manner at the same position.

[0015] Preferably, in the dot pattern printing step, the connected pattern printing step and the finish printing step, the thickness of the coating is adjusted by adjusting the resolution in the printing direction.

[0016] Preferably, the ratio of the diameter D of the droplets deposited by the dot pattern printing process to the pitch P1 between the deposited droplets is

[0017]

number

[0018] It is composed of:

[0019] Preferably, the ratio of the interval G of the patterns deposited by the connection pattern printing process to the pitch P2 between the deposited patterns is

[0020]

number

[0021] It is composed of:

[0022] Preferably, four pixel groups consisting of adjacent top left pixel, top right pixel, bottom left pixel, and bottom right pixel on the surface of the object are defined to be arranged in a grid, and the dot pattern printing process is configured to print only at a position corresponding to any one of the four pixels, the connected pattern printing process is configured to print only at a position corresponding to any one of the remaining three pixels, and the finishing printing process is configured to print only at a position corresponding to any one or two of the remaining two pixels.

[0023] Preferably, the linked pattern printing process includes a first linked pattern printing process of printing a first linked pattern group by ejecting ink between adjacent dot patterns using a first linked pattern forming nozzle group so that the same attractive force acts on adjacent dot patterns ejected on the surface of the target object, and a second linked pattern printing process of printing a second linked pattern group by ejecting ink between adjacent first patterns using a second linked pattern forming nozzle group so that the same attractive force acts on adjacent first linked patterns ejected on the surface of the target object.

[0024] Preferably, the first connection pattern forming nozzle group and the second connection pattern forming nozzle group are configured with different nozzles in a head module.

[0025] Preferably, the dot pattern printing process, the connection pattern printing process, and the finishing printing process further include a flattening process for waiting for the coating formed on the surface of the processed object to be flattened, and a hardening process for hardening the coating formed on the surface of the object.

[0026] [Effects of the Invention] The object of the present invention as described above is to prevent the impacted ink droplets from being attracted to each other and clumping together to have different thicknesses, and also to overcome the variation in ink ejection characteristics of each nozzle and minimize the variation in the thickness of the coating thin film.

[0027] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the cross-sectional structure of a typical micro OLED display.

[0029] [Figure 2] A diagram to explain the interference of light emitted from a micro OLED.

[0030] FIG. 3 is a diagram showing unevenness caused by the non-uniform thickness of the coated thin film.

[0031] FIG. 4 is a flow chart showing the steps of an inkjet printing method for thin film coating according to an embodiment of the present invention.

[0032] FIG. 5 is a diagram showing detailed printing processes of an inkjet printing method for thin film coating according to an embodiment of the present invention.

[0033] FIG. 6 illustrates droplet and pattern details of an inkjet printing method for thin film coating according to one embodiment of the present invention.

[0034] FIG. 7 illustrates droplet and pattern details of an inkjet printing method for thin film coating according to one embodiment of the present invention.

[0035] FIG. 8 is a diagram showing a state where a thin film is coated using an inkjet printing method according to an embodiment of the present invention.

[0036] FIG. 9 is a flow chart showing the steps of an inkjet printing method for thin film coating according to another embodiment of the present invention.

[0037] FIG. 10 is a diagram showing detailed printing processes of an inkjet printing method for thin film coating according to another embodiment of the present invention.

[0038] [Mode for carrying out the invention] The present invention can be embodied in various other forms without departing from the technical spirit or main characteristics thereof. Therefore, the present invention is to be construed as being merely illustrative in all respects and not restrictive.

[0039] Although the terms first, second, etc. are used to describe various components, the components are not limited to these terms.

[0040] The above terms are used only for the purpose of distinguishing one component from another component, for example, a first component may be named a second component, and similarly, the second component may be named a first component, without departing from the scope of the present invention.

[0041] The term and / or includes combinations of multiple items or any of multiple items.

[0042] When an element is referred to as being "coupled" or "connected" to another element, it may be directly coupled or connected to the other element, but it should be understood that there may be other elements in between.

[0043] On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

[0044] The terms used in this application are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless otherwise clearly indicated in the context.

[0045] In this application, the terms "including," "comprising," "having," and the like, are intended to specify the presence of any feature, number, step, operation, component, part, or combination thereof described hereinabove in the specification, but are to be understood as not precluding the presence or additional possibility of one or more other features, number, steps, operations, components, parts, or combinations thereof.

[0046] Unless otherwise defined, all terms, including technical or scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0047] Terms defined in commonly used dictionaries should be interpreted to have a meaning consistent with the meaning they have in the context of the relevant art, and not interpreted in an idealized or overly formal sense unless expressly defined in this application.

[0048] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Regardless of the reference numerals, the same or corresponding elements will be given the same reference numerals and redundant description thereof will be omitted.

[0049] In describing the present invention, if it is determined that a detailed description of related publicly known techniques may obscure the gist of the present invention, the detailed description will be omitted.

[0050] First, the definition of pixels on the surface of an object for thin film coating is described.

[0051] As shown in FIG. 5, the surface of the object is defined as a number of pixels arranged in a grid, more specifically, a pixel group consisting of four adjacent pixels (top left pixel, top right pixel, bottom left pixel, bottom right pixel) arranged in a grid in a specific area is repeatedly arranged in a grid in the horizontal and vertical directions.

[0052] For example, as shown in (a1) of Figure 5, the surface of the object is made up of a number of pixels, with the top left pixel being defined as the top left pixel (coordinates (1,1)), the pixel to the right of the top left pixel being defined as the top right pixel (coordinates (1,2)), the pixel below the top left pixel being defined as the bottom left pixel (coordinates (2,1)), and the pixel below the top right pixel being defined as the bottom right pixel (coordinates (2,2)).

[0053] Therefore, the four pixels with coordinates (1,1), (1,2), (2,1), and (2,2) come together to form one pixel group, and such pixel groups are repeatedly arranged in a grid in the horizontal and vertical directions, so that each pixel on the entire surface of the object is defined as one of the top left pixel, top right pixel, bottom left pixel, and bottom right pixel.

[0054] In other words, from the pixel with coordinates (1,1), the top left pixel, top right pixel, top left pixel, top right pixel, ..., top left pixel are repeated horizontally, and from the pixel with coordinates (1,1), the top left pixel, bottom left pixel, top left pixel, bottom left pixel, ..., top left pixel are repeated vertically.

[0055] In addition, from the pixel with coordinates (2,1), the bottom left pixel, bottom right pixel, bottom left pixel, bottom right pixel, ..., bottom left pixel are repeated horizontally, and from the pixel with coordinates (1,2), the top right pixel, bottom right pixel, top right pixel, bottom right pixel, ..., top right pixel are repeated vertically.

[0056] As described above, the surface of the object is defined as a group of pixels defined as the top left pixel, the top right pixel, the bottom left pixel, and the bottom right pixel, which are repeatedly arranged in a grid.

[0057] An inkjet printing method for thin film coating according to one embodiment of the present invention for performing a thin film coating on a surface of an object defined as above includes a dot pattern printing process S10, a connect pattern printing process S20 consisting of a first connect pattern printing process S21 and a second connect pattern printing process S22, a finishing printing process S30, a planarizing process S40, and a curing process S50, as shown in FIG. 4.

[0058] On the other hand, if we assume that the total amount of ink required for thin film coating on the surface of the object is 100 parts by weight, the sum of the amount of ink ejected by the dot pattern printing process S10, the amount of ink ejected by the connected pattern printing process S20, and the amount of ink ejected by the finishing printing process S30 is 100 parts by weight.

[0059] For example, as shown in FIG. 4, if printing is performed in four processes, such as a dot pattern printing process S10, a first connecting pattern printing process S21, a second connecting pattern printing process S22, and a finishing printing process S30, 25 parts by weight of ink, which is about 25% of the total ink of 100 parts by weight, is ejected in each process so that 100 parts by weight of ink is printed. However, the amount of ink ejected in each process may be appropriately adjusted so that different amounts of ink are ejected in each process, and when all printing processes are completed, the total amount of ink printed will be 100 parts by weight.

[0060] First, the dot pattern printing step S10 will be described.

[0061] The dot pattern printing process S10 is a process of printing a dot pattern landing group by ejecting ink at a predetermined position on the target surface using a dot pattern forming nozzle group so that the landed ink droplets (hereinafter referred to as "droplets") do not overlap each other.

[0062] For example, as shown in (a1) of Fig. 5, in the dot pattern printing step S10, droplets are printed only at the position of the upper left pixel. In other words, droplets are printed so as not to overlap with each other at pixel positions (1,1), (1,3), (1,5), ..., (3,1), ..., (5,1), ..., which correspond to the upper left pixel.

[0063] In this way, by printing only at the position of the upper left pixel so that the droplets do not overlap each other, the droplets are printed without any attractive force acting between adjacent droplets, and a dot pattern group is formed by this dot pattern printing process S10.

[0064] Here, the attractive force between impacted droplets refers to a force acting such that the interfaces of multiple droplets come into close contact with each other or overlap with each other, and the multiple droplets are attracted to each other and merge into one droplet.

[0065] Meanwhile, as shown in FIG. 6, the ratio of the diameter D of the droplets landed in the dot pattern printing process S10 to the pitch P1 between the landed droplets is

[0066]

number

[0067] This is determined by considering the pitch of the droplets and the diameter of the droplets after landing, the surface condition of the material (surface tension, roughness, etc.), the diameter of the droplets that will land on the next print path, the printing precision of the droplets, the behavior characteristics of the droplets formed when they are landed, the uniformity of the edge of the coating surface, and the spreading characteristics of the droplets over time on the surface, etc., depending on the target coating thickness.

[0068] The above-mentioned dot pattern printing process S10 forms a dot pattern landing group by printing in a state where no attractive force acts between the landing droplets. By printing in such a state where no attractive force acts between the landing droplets, it becomes possible to accurately print a predetermined amount of ink at a predetermined position.

[0069] Next, the connecting pattern printing step S20 will be described.

[0070] The linked pattern printing process S20 is a process of printing a linked pattern impact group by ejecting ink at positions between adjacent multiple patterns using a linked pattern forming nozzle group so that the same attractive force acts on the adjacent multiple patterns impacted on the surface of the target object.

[0071] For example, the connecting pattern printing process S20 is a process in which the same attractive force acts on droplets that land horizontally or vertically.

[0072] The linked pattern printing step S20 includes a first linked pattern printing step S21 and a second linked pattern printing step S22.

[0073] The first connection pattern printing process S21 is a process of printing a first connection pattern impact group by ejecting ink between adjacent dot patterns using a first connection pattern forming nozzle group so that the same attractive force acts on the adjacent dot patterns impacted on the surface of the target object.

[0074] For example, as shown in (a2) of Fig. 5, in the first connected pattern printing step S21, droplets are printed only at the positions of the upper right pixels, i.e., droplets are printed corresponding to the pixel positions (1,2), (1,4), (1,6), ..., (3,2), ..., (5,2), ..., which correspond to the upper right pixels.

[0075] In this way, by printing only at the position of the upper right pixel, each landing droplet is printed under conditions in which the same attractive force acts on the droplets already landed at the upper left pixels on either side, making it possible to accurately print a predetermined amount of ink at a predetermined position.

[0076] Meanwhile, through the above-mentioned first connected pattern printing step S21, as shown in FIG. 7, a linear first connected pattern impact group is formed.

[0077] At this time, as shown in FIG. 7, the ratio of the interval G of the patterns deposited by the first connecting pattern printing process S21 to the pitch P2 between the deposited patterns is

[0078]

number

[0079] This is determined by taking into consideration the surface condition of the material (surface tension, roughness, etc.), the thickness of the droplet that will land on the next print pass, the print precision of the droplet, the behavior characteristics of the droplet that is formed when it is landed, the uniformity of the edge of the coating surface, and the spreading characteristics and flattening characteristics of the droplet on the surface over time.

[0080] As described above, the first connecting pattern printing process S21 is performed in a state where the same attractive force acts between the droplets that have already landed on the upper left pixels on both sides, making it possible to accurately print a predetermined amount of ink at a predetermined position.

[0081] The second connection pattern printing process S22 is a process of printing a group of second connection patterns by ejecting ink between adjacent first connection patterns using a group of nozzles for forming a second connection pattern so that the same attractive force acts on the adjacent first connection patterns that are impacted on the surface of the target object.

[0082] For example, as shown in (a3) ​​of Fig. 5, in the second connected pattern printing step S22, droplets are printed only at the position of the bottom right pixel, i.e., droplets are printed corresponding to the pixel positions (2,2), (2,4), (2,6), ..., (4,2), ..., (6,2), ..., which correspond to the bottom right pixel.

[0083] In this way, by printing only at the position of the bottom right pixel, each landing droplet is printed under the same attractive force acting on the first connected patterns on both sides, making it possible to accurately print a predetermined amount of ink at a predetermined position, and forming a second connected pattern landing group in the form of black, as shown in (a3) ​​of Figure 5.

[0084] Next, the finishing print process S30 will be described.

[0085] This is a process for finishing the coating on the surface of the object by ejecting ink using a finishing nozzle group to an area excluding adjacent droplets so that the same attractive force acts on the multiple droplets that have landed on the surface of the object.

[0086] For example, as shown in (a4) of Fig. 5, in the finishing printing step S30, droplets are printed only at the bottom left pixel position, i.e., droplets are printed corresponding to the pixel positions (2,1), (2,3), (2,5), ..., (4,1), ..., (6,1), ..., which correspond to the bottom left pixel.

[0087] In this way, by printing only at the bottom left pixel position, droplets are completely deposited on the entire surface of the object.

[0088] In this way, by printing only at the position of the bottom right pixel, the droplets ejected and impacted in the finishing printing process are printed under conditions in which the same attractive force acts on each of the multiple droplets that have already impacted in the previous process, making it possible to accurately print a predetermined amount of ink at a predetermined position.

[0089] As described above, the dot pattern printing step S10, the first connected pattern printing step S21, the second connected pattern printing step S22, and the finishing printing step S30 enable a predetermined amount of ink to be printed accurately at a predetermined position over the entire surface of the object.

[0090] Meanwhile, in the above description, the dot pattern printing process S10 prints the upper left pixel, the first connected pattern printing process S21 prints the upper right pixel, the second connected pattern printing process S22 prints the lower right pixel, and the finishing printing process S30 prints the lower left pixel. However, it is of course possible to interchange the positions of the pixels printed in each process.

[0091] In other words, various modifications may be made as long as only pixels corresponding to one position are printed in one process, such as printing the bottom left pixel in the dot pattern printing process S10, the bottom right pixel in the first connected pattern printing process S21, the top right pixel in the second connected pattern printing process S22, and the top left pixel in the finishing printing process S30.

[0092] The detailed configurations and relationships of the dot pattern forming nozzle group, the first connected pattern forming nozzle group, the second connected pattern forming nozzle group, and the finishing nozzle group that eject droplets in the dot pattern printing process S10, the connected pattern printing process S20, and the finishing printing process S30 as described above will be described in detail.

[0093] The nozzle group for forming the dot pattern, the nozzle group for forming the first conductive pattern, the nozzle group for forming the second connecting pattern, and the finishing nozzle group are composed of different nozzles that do not overlap with each other within the head module, and will be described with reference to (a1) to (a4) of Figure 5.

[0094] For example, the dot pattern forming nozzle group is composed of nozzles a1, a2, a3, . . . an selected from a plurality of nozzles configured in an inkjet head module.

[0095] Meanwhile, the first connecting pattern forming nozzle group is composed of nozzles b1, b2, b3, . . . bn selected from a plurality of nozzles configured in an inkjet head module.

[0096] The second connection pattern forming nozzle group is composed of nozzles c1, c2, c3, . . . cn selected from a plurality of nozzles formed in the inkjet head module.

[0097] Finally, the finishing nozzle group is composed of nozzles d1, d2, d3, . . . dn selected from a plurality of nozzles configured in the inkjet head module.

[0098] Here, the multiple nozzles constituting the nozzle group for forming a dot pattern are selected from nozzles having the same pitch as the pitch P1 between the impacted droplets, and the multiple nozzles of the nozzle group for forming a first connection pattern, the multiple nozzles of the nozzle group for forming a second connection pattern, and the multiple nozzles of the finishing nozzle group are also selected from nozzles having the same pitch as P1.

[0099] As a specific example, if an inkjet head module is formed by arranging a total of 100 nozzles in series with the pitch P1, the nozzle group for forming a dot pattern is composed of nozzles No. 1 to No. 25, the nozzle group for forming a first connection pattern is composed of nozzles No. 26 to No. 50, the nozzle group for forming a second connection pattern is composed of nozzles No. 51 to No. 75, and the finishing nozzle group is composed of nozzles No. 76 to No. 100.

[0100] As another example, the dot pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 1 to No. 50, the first connection pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 20 to No. 70, the second connection pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 40 to No. 90, and the finishing nozzle group may be composed of odd or even numbered nozzles among nozzles No. 50 to No. 100. In other words, the nozzle groups are composed with an interval of one or many nozzles.

[0101] In other words, the dot pattern forming nozzle group, the first conductive pattern forming nozzle group, the second connecting pattern forming nozzle group, and the finishing nozzle group are configured with nozzles that are completely different from one another within the head module.

[0102] It is preferable that the head module is formed longer than the width of the object to be coded. In particular, the head module is composed of one head formed longer than the width of the object, or composed of a plurality of heads formed shorter than the width of the object connected in series.

[0103] As another example, the nozzle group for forming the dot pattern, the nozzle group for forming the first conductive pattern, the nozzle group for forming the second connecting pattern, and the finishing nozzle group may be composed of different nozzles with some overlapping within the head module, but this will be explained with reference to (a5) to (a8) of Figure 5.

[0104] For example, the dot pattern forming nozzle group is composed of nozzles a1+α, a2+α, a3+α, . . . an+α selected from a plurality of nozzles configured in an inkjet head module.

[0105] Meanwhile, the first connecting pattern forming nozzle group is composed of nozzles a1+β, a2+β, a3+β, . . . an+β selected from a plurality of nozzles configured in an inkjet head module.

[0106] The second connection pattern forming nozzle group is composed of nozzles a1+γ, a2+γ, a3+γ, . . . an+γ selected from a plurality of nozzles configured in the inkjet head module.

[0107] Finally, the finishing nozzle group is composed of nozzles a1+δ, a2+δ, a3+δ, . . . an+δ selected from a plurality of nozzles configured in the inkjet head module.

[0108] Here, the multiple nozzles constituting the nozzle group for forming a dot pattern are selected from nozzles having the same pitch as the pitch P1 between the impacted droplets, and the multiple nozzles of the nozzle group for forming a first connection pattern, the multiple nozzles of the nozzle group for forming a second connection pattern, and the multiple nozzles of the finishing nozzle group are also selected from nozzles having the same pitch as P1.

[0109] As a specific example, if an inkjet head module is formed by arranging a total of 55 nozzles in series with the pitch P1, the nozzle group for forming a dot pattern is composed of nozzles No. 1 to No. 25, the nozzle group for forming a first connection pattern is composed of nozzles No. 11 to No. 35, the nozzle group for forming a second connection pattern is composed of nozzles No. 21 to No. 45, and the finishing nozzle group is composed of nozzles No. 31 to No. 55.

[0110] In other words, the nozzle group for forming the dot pattern, the nozzle group for forming the first conductive pattern, the nozzle group for forming the second connecting pattern, and the finishing nozzle group are shifted in the longitudinal direction by a distance equivalent to the spacing between a predetermined number of nozzles within the head module, and are composed of different nozzles with some overlapping.

[0111] In this case, it is preferable that the dot pattern forming nozzle group, the first conductive pattern forming nozzle group, the second connecting pattern forming nozzle group, and the finishing nozzle group are configured so that the positions of at least two nozzles are shifted.

[0112] In other words, if the nozzle group for forming the dot pattern is composed of nozzles No. 1 to No. 25, and the nozzle group for forming the first connection pattern is composed of nozzles No. 2 to No. 35, the result will be that nozzle No. 1 and nozzle No. 2 will be printed immediately adjacent to each other, but it is preferable to prevent nozzles that are immediately adjacent to each other from being used in each process in this manner.

[0113] On the other hand, in the above explanation, an example was given of the case where the nozzles of the nozzle group for forming the dot pattern, the nozzle group for forming the first conductive pattern, the nozzle group for forming the second connecting pattern, and the finishing nozzle group are all different, but this does not exclude the possibility that the same nozzles may be used for some of the groups. In other words, the nozzles of the dot pattern forming nozzle group and the finishing nozzle group may be the same nozzles, and only the nozzles of the first conductive pattern forming nozzle group, the second connecting pattern forming nozzle group, and the finishing nozzle group may be different nozzles.

[0114] Meanwhile, the size of droplets ejected through the nozzle group for forming a dot pattern, the size of droplets ejected through the nozzle group for forming a connecting pattern, and the size of droplets ejected through the nozzle group for finishing are configured to be the same or different from each other.

[0115] In addition, in at least one of the dot pattern printing process S10, the connected pattern printing process S20, and the finishing printing process S30, the thickness of the coating may be adjusted by ejecting multiple droplets in an overlapping manner at the same position.

[0116] That is, the coating thickness is adjusted so that discharging two droplets at the same position has a greater thickness than discharging one droplet at the same position.

[0117] Also, in the dot pattern printing process S10, the connection pattern printing process S20, and the finishing printing process S30, the thickness of the coating is adjusted by adjusting the resolution in the printing direction.

[0118] In other words, when printing at 500 dpi (dots per inch) in the printing direction, the density of the impacted droplets is increased compared to when printing at 400 dpi, resulting in a thicker coating thickness.

[0119] According to the detailed configurations and relationships of the dot pattern forming nozzle group, the first conductive pattern forming nozzle group, the second connecting pattern forming nozzle group, and the finishing nozzle group as described above, the use of immediately adjacent nozzles of the inkjet head module is limited when printing on immediately adjacent pixels.

[0120] That is, in terms of pixels with coordinates (1,1), (1,2), (1,3), ..., (1,n), nozzle 1 is used for the pixel with coordinates (1,1), nozzle 2 is used for the pixel with coordinates (1,2), nozzle 3 is used for the pixel with coordinates (1,3), and nozzle n is used for the pixel with coordinates (1,n). However, unlike the conventional technique, which causes variations in the volume of droplets ejected depending on different rows of nozzles or nozzle regions, as shown in FIG. 3, this prevents unevenness caused by the variations in the volume of droplets of various shapes, overcomes the variations in the ink ejection characteristics of each nozzle, and minimizes the variations in the thickness of the coating thin film, thereby enabling coating in a good condition as shown in FIG. 8.

[0121] The most important concept of the present invention is to prevent the ink droplets from overlapping and solidifying in the dot pattern printing process where printing is performed first. This is to fundamentally eliminate the phenomenon where ink droplets that are dropped very quickly and finely attract ink droplets that are dropped later and solidify due to the attractive force (the force that attracts each other) that occurs when ink droplets overlap.

[0122] Meanwhile, after the dot pattern printing process, the nozzle positions are adjusted to be different in the connection pattern printing process and the finish printing process, so that droplets discharged from nozzles at other positions are landed between droplets already landed in the previous process, and a uniform attractive force acts from the droplets already landed, thereby accurately maintaining the landing positions of the droplets in all processes.

[0123] In other words, by restricting the use of the same nozzle or the immediately adjacent nozzle of the inkjet head module for the top left pixel, top right pixel, bottom left pixel, and bottom right pixel that make up one pixel group, nozzles that are at least two nozzle intervals apart are applied to the top left pixel, top right pixel, bottom left pixel, and bottom right pixel of one pixel, respectively, thereby overcoming variations in the ink ejection characteristics of each nozzle.

[0124] For example, if the printing process is divided into four steps, such as a dot pattern printing process S10, a first connected pattern printing process S21, a second connected pattern printing process S22, and a finishing printing process S30, the entire print image can be made up of four images with uniform pixel intervals.

[0125] When coating each image, the same nozzle or the immediately adjacent nozzles are not used in each area, but nozzles in other positions are used to print, so that differences in the volume of ink droplets produced by each nozzle can be compensated for.

[0126] In addition, since this is a coating method that makes the attraction of ink droplets that are landed vertically or horizontally uniform, if the width of the head module is smaller than the width of the area to be coated, in a connected pattern printing process in which ink droplets land between already landed ink droplets, the attraction of the ink droplets may occur at the end of the nozzle of the head module, resulting in a visible discontinuous line. In this case, in the line where discontinuity occurs, that is, when printing the next printing area using the head module, the position of the head module, that is, the position of the nozzle is adjusted in the conventional printing direction more than the conventional pitch to adjust the discontinuous line so that it appears small. However, in order to basically improve this problem, it is necessary to set the width of the head module sufficiently larger than the width of the coating image, mix the nozzle positions, and easily print the entire area, or to print so that the discontinuous boundary is not visible at all.

[0127] Next, the planarization step S40 will be described.

[0128] The flattening step S40 is a step of waiting for the coating formed on the surface of the object processed in the dot pattern printing step S10, the connection pattern printing step S20, and the finish printing step S30 to be flattened.

[0129] In detail, the dot pattern printing step S10, the link pattern printing step S20, and the finish printing step S30 are to stabilize the uncured coating formed on the surface of the treated object.

[0130] Next, the curing step S50 will be described.

[0131] The curing step S50 is a step of curing the coating formed on the surface of the object.

[0132] In detail, the dot pattern printing step S10, the connection pattern printing step S20, and the finishing printing step S30 are performed on the surface of the treated object, and then the stabilized coating is irradiated with ultraviolet light and cured.

[0133] FIG. 9 is a flow chart showing the procedure of an inkjet printing method for thin film coating according to another embodiment of the present invention, and FIG. 10 is a diagram showing a detailed printing process of an inkjet printing method for thin film coating according to another embodiment of the present invention. Another embodiment of the present invention will be described with reference to FIG. 9 and FIG. 10.

[0134] In the inkjet printing method for thin film coating according to the embodiment of FIGS. 9 and 10, the second connecting pattern printing process S22 and the finishing printing process S30 of the above-mentioned embodiment are performed in one step.

[0135] In detail, in the dot pattern printing step S10, droplets are printed only at the upper left pixel position, in the connecting pattern printing step S20, droplets are printed only at the upper right pixel position, and in the finishing printing step S30, droplets are printed simultaneously at the lower right pixel and the lower left pixel position.

[0136] As a specific example, if an inkjet head module is formed by arranging a total of 100 nozzles in series with the pitch P1, the nozzle group for forming a dot pattern is composed of nozzles No. 1 to No. 25, the nozzle group for forming a connecting pattern is composed of nozzles No. 26 to No. 50, and the finishing nozzle group is composed of nozzles No. 51 to No. 100.

[0137] As another example, the dot pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 1 to No. 50, the first connection pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 20 to No. 70, the second connection pattern forming nozzle group may be composed of odd or even numbered nozzles among nozzles No. 40 to No. 90, and the finishing nozzle group may be composed of odd or even numbered nozzles among nozzles No. 50 to No. 100. In other words, the nozzle groups are composed with an interval of one or many nozzles.

[0138] As another specific example, if an inkjet head module is formed by arranging a total of 55 nozzles in series with the pitch P1, the nozzle group for forming a dot pattern is composed of nozzles No. 1 to No. 25, the nozzle group for forming a connection pattern is composed of nozzles No. 11 to No. 35, and the finishing nozzle group is composed of nozzles No. 21 to No. 55.

[0139] As described above, the method is composed of three steps, namely, the dot pattern printing step S10, the connecting pattern printing step S20, and the finishing printing step S30. Although the method may be less able to eliminate the variation in the ink ejection characteristics of each nozzle than the four-step embodiment described above, it allows for coating at a faster speed.

[0140] Although the present invention has been described with reference to the accompanying drawings and focusing on the preferred embodiment, it will be apparent to those skilled in the art that many various and obvious modifications can be made from such description without departing from the scope of the present invention. Therefore, the scope of the present invention should be interpreted by the claims written to include many such modifications. [Brief description of the drawings]

[0141] [Figure 1] FIG. 1 is a diagram showing the cross-sectional structure of a typical micro OLED display. [Diagram 2] 1 is a diagram for explaining interference of light emitted from a micro OLED. FIG. [Diagram 3] FIG. 13 is a diagram showing unevenness caused by non-uniform thickness of the coated thin film. [Figure 4] 1 is a flow chart showing a procedure of an inkjet printing method for thin film coating according to an embodiment of the present invention. [Diagram 5] 2A to 2C are diagrams illustrating detailed printing processes of an inkjet printing method for thin film coating according to an embodiment of the present invention. [Figure 6] 2A-2C are diagrams illustrating droplet and pattern details of an inkjet printing method for thin film coating according to one embodiment of the present invention. [Figure 7] 2A-2C are diagrams illustrating droplet and pattern details of an inkjet printing method for thin film coating according to one embodiment of the present invention. [Figure 8] 1 is a diagram showing a state where a thin film is coated using an inkjet printing method according to an embodiment of the present invention; [Figure 9] 4 is a flow chart showing a procedure of an inkjet printing method for thin film coating according to another embodiment of the present invention. [Figure 10] 4A to 4C are diagrams illustrating detailed printing processes of an inkjet printing method for thin film coating according to another embodiment of the present invention.

Claims

1. a dot pattern printing process in which ink is ejected onto a predetermined position on the surface of the object using a dot pattern forming nozzle group so that the impacted droplets do not overlap each other, thereby printing a dot pattern impact group; a connected pattern printing process for printing a connected pattern impact group by ejecting ink at a position between the adjacent patterns using a connected pattern forming nozzle group so that the same attractive force acts on the adjacent patterns impacted on the surface of the target object; a finishing printing step of forming a coating on the surface of the object by ejecting ink onto an area excluding the plurality of droplets that have already landed on the surface of the object in the dot pattern printing step and the connected pattern printing step, using a finishing nozzle group, so that the same attractive force acts on the plurality of droplets that have already landed on the surface of the object, the dot pattern forming nozzle group, the connection pattern forming nozzle group, and the finishing nozzle group are configured with different nozzles in a head module, a size of droplets discharged through the nozzle group for forming a dot pattern, a size of droplets discharged through the nozzle group for forming a connection pattern, and a size of droplets discharged through the nozzle group for finishing, the size of droplets being the same as each other.

2. 2. The inkjet printing method for thin film coating according to claim 1, wherein a thickness of the coating is adjusted by ejecting a plurality of droplets in an overlapping manner in at least one of the dot pattern printing process, the connected pattern printing process, and the finish printing process.

3. 2. The inkjet printing method for thin film coating according to claim 1, wherein the thickness of the coating is controlled by controlling the dot density of the deposited droplets in the dot pattern printing process, the connected pattern printing process, and the finish printing process.

4. The ratio of the diameter D of the droplets deposited by the dot pattern printing process to the pitch P1 between the deposited droplets is [0010] The inkjet printing method for thin film coating according to claim 1, comprising:

5. The ratio of the interval G between adjacent groups of connected patterns that are impacted by the connection pattern printing process to the pitch P2 between adjacent groups of connected patterns that are impacted by the connection pattern printing process is [0025] The inkjet printing method for thin film coating according to claim 1, comprising:

6. Four pixel groups, each consisting of an upper left pixel, an upper right pixel, a lower left pixel, and a lower right pixel, are defined to be arranged in a grid on the surface of the object. The dot pattern printing process is configured to print only at a position corresponding to one of the four pixels, The connection pattern printing process is configured to print only at a position corresponding to one of the remaining three pixels, 2. The inkjet printing method for thin film coating according to claim 1, wherein the finishing printing process is configured to print only at positions corresponding to one or two of the remaining two pixels.

7. The connecting pattern printing step includes: a first connection pattern printing step of printing a first connection pattern landing group by ejecting ink between adjacent dot patterns using a first connection pattern forming nozzle group so that the same attractive force acts on adjacent dot patterns that are impacted on the surface of the target object; and a second connection pattern printing process for printing a group of second connection patterns by ejecting ink between the plurality of adjacent first connection patterns using a group of nozzles for forming a second connection pattern so that the same attractive force acts on the plurality of adjacent first connection patterns impacted on the surface of the target object.

8. 8. The inkjet printing method for thin film coating according to claim 7, wherein the first and second connection pattern forming nozzle groups are composed of different nozzles in a head module.

9. The connecting pattern printing step includes: a first connection pattern printing step of printing a first connection pattern landing group by ejecting ink between adjacent dot patterns using a first connection pattern forming nozzle group so that the same attractive force acts on adjacent dot patterns that are impacted on the surface of the target object; a second connection pattern printing step of ejecting ink between the adjacent first connection patterns by using a second connection pattern forming nozzle group to print the second connection pattern landing group so that the same attractive force acts on the adjacent first connection patterns that are impacted on the surface of the target object, 2. The inkjet printing method for thin film coating according to claim 1, further comprising: an inkjet head module having a plurality of nozzles arranged in series, wherein the nozzle group for forming a dot pattern, the nozzle group for forming a first connection pattern, the nozzle group for forming a second connection pattern, and the nozzle group for finishing are shifted in a length direction by a distance corresponding to a predetermined number of nozzle intervals within the head module, and are composed of different nozzles with some overlapping, and the nozzle group for forming a dot pattern, the nozzle group for forming a first connection pattern, the nozzle group for forming a second connection pattern, and the nozzle group for finishing are configured such that the positions of at least two nozzles are shifted.

10. a flattening step for waiting for a coating formed on the surface of the object as a result of the dot pattern printing step, the connection pattern printing step, and the finishing printing step to be flattened, the flattening step stabilizing a coating that has been formed on the surface of the object as a result of the dot pattern printing step, the connection pattern printing step, and the finishing printing step and that has not been hardened; 2. The inkjet printing method for thin film coating according to claim 1, further comprising: a curing step of curing the coating formed on the surface of the object.

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