KR101187664B1 - Method for measuring contact angle - Google Patents

Abstract

PURPOSE: A method for measuring a contact angle is provided to measure variation that a contact angle of a droplet is changed as time passed, thereby measuring the variation of the contact angle according to a shape varying process of the droplet even though the droplet is dried after being discharged. CONSTITUTION: A method for measuring a contact angle is as follows. A droplet is discharged on a substrate(1100). Images of the droplet discharged on the substrate is obtained(1200). An interest region is set on the images of the droplet(1300). A plurality of straight lines is formed in the interest region at a constant interval(1400). An X and a Y coordinates of a spot where an image value of the droplet is rapidly varied according to a direction of the straight line(1500). A curve fitting is performed by using the X and Y coordinates of the spot(1600). The contact angle of the droplet is obtained by using a slope of the straight line obtained by the curve fitting(1700). [Reference numerals] (1100) Step for discharging ink droplets on a substrate; (1200) Step for obtaining images of ink droplets discharged on a substrate; (1300) Step for setting an interest region on images of ink droplets; (1400) Step for drawing a straight line at a constant distance in an interest region; (1500) Step for obtaining X,Y coordinates of a point in which an image value is remarkably varied along a straight line direction; (1600) Step for performing a curve fitting by using a X,Y coordinates; (1700) Step for obtaining a contact angle by using a slope of a straight line; (AA) Start; (BB) Finish

Description

How to measure contact angle {METHOD FOR MEASURING CONTACT ANGLE}

The present invention relates to a contact angle measuring method, and more particularly, to a contact angle measuring method capable of precisely controlling the amount of droplets to be measured and measuring a change amount or a change degree of the contact angle with time.

As printing technology can be applied as a patterning technology in electronic device processing, material processing, biotechnology, etc. as well as text printing, related researches are being actively conducted. In particular, inkjet patterning technology is a non-contact three-dimensional (3D) printing-based patterning method, unlike the complicated optical lithography method of the semiconductor process, the display field such as LCD, OLED, PDP, PCB, RFID, micro lens (micro) It is applied as a process technology in the field of electronic material printing such as lens), various micro / nano sensors, bio chip, and biological cell culture.

The advantage of such inkjet patterning is that it is environmentally friendly in the direct printing process, low cost process due to material reduction, and large area patterning is possible. The ink ejected by using the ink jet forms a pattern on a substrate, and an important point is a contact angle.

Contact angle is the angle formed when a liquid is thermodynamically equilibrated on a solid surface. Contact angle measurement is a well known analytical technique in many fields, such as adhesion, surface treatment, and polymer surface analysis, where low contact angles are high wettability and high contact angles are low. Surface energy. In other words, when the contact angle is small, ink or droplets spread well on the substrate, and when the contact angle is large, it does not spread well. A device for measuring this quantitatively is a contact angle measuring device.

1 is a view schematically showing the configuration of a conventional contact angle measuring device, Figure 2 is a view showing a principle of measuring the contact angle using a conventional contact angle measuring device.

As shown in FIG. 1, a conventional contact angle measuring device includes a syringe-type dispenser capable of dispensing fluid, a fiber optic illumination, and a software capable of analyzing an image with a CCD camera. Includes onboard computer. In the conventional contact angle measuring device, since the dispenser for dispensing the fluid is in the form of a syringe, the contact angle is usually measured using a fluid of about 2 microliters (μL).

The conventional contact angle measuring device measures the contact angle by using a 2θ method. Referring to FIG. 2, a droplet D is present at an upper portion of the substrate S, and an image of the lower portion thereof is an image in which the droplet is reflected on the substrate. The length L and the height H of the triangle which consist of the height H of the point where the height of the droplet D becomes the highest with respect to the board | substrate S, and the length L of the board | substrate formed when the water line is cut off from the highest point. The angle θ is obtained from If the angle θ is doubled, the contact angle of the droplet can be obtained.

Once again, the conventional contact angle measurement method is described again, converting the image of the droplet obtained by using a camera to a binary image, and obtain the position of the highest value, leftmost and rightmost of the binary image The length L and the height H are calculated as pixel values, and the result of the calculation is drawn on the image to obtain a contact angle by the 2θ method.

As printing technology (inkjet and offset printing) has been applied to the manufacture of electronic components, smaller line widths and smaller inks (liquids) are becoming patterns on substrates. Therefore, the contact angle may vary depending on the size of the droplets, which may vary depending on the roughness of the substrate, the characteristics of the ink absorbed on the substrate, and other patterns on the substrate. Therefore, in order to develop an ink and a printing process, it is necessary to be able to measure an accurate contact angle for a process (substrate and ink).

In addition, the contact angle changes with time. This change in contact angle should be able to be analyzed over time. However, in the case of the dispersion ink, the shape of the dispersion is changed as well as the contact angle change depending on the drying. At this time, if the contact angle is obtained by the existing contact angle measuring device and the measuring method, there is an error and there is a problem to be evaluated as a whole form.

In particular, in the case of electronic printing, the contact angle varies depending on the amount of ink, and the amount of ink discharged from the inkjet head is discharged in a very small amount of several tens of picoliters (pL). However, the conventional apparatus and method for measuring the contact angle is measured using an amount of several microliters (μL), which may result in a different result from the contact angle during the actual electronic printing process.

In addition, research is being conducted to obtain fine line widths in other printing electronic processes, such as gravure and offset printing, and requires accurate evaluation of ink and substrate. Therefore, it is necessary to evaluate the characteristics according to the characteristics of the substrate and the amount of ink.

Therefore, there is a need for a contact angle measuring device and measuring method capable of accurately producing a desired small amount of ink droplets (30 pL to 3 μL), accurately measuring them, and measuring the change in contact angle to the change in contact angle over time when it falls on a substrate. Is increasing.

Recently, research results suggest that super hydrophobic surfaces can be made by making nano shapes on the surface by the development of nano materials and fixation. However, in order to overcome the problems of the conventional contact angle measuring device, and to observe whether super water repellency can be applied to microdroplets in picoliter (pL) units and what phenomenon occurs as the droplets evaporate, It did not arrive.

Conventional contact angle measuring devices and methods have limitations in that they cannot fully observe and measure the phenomenon that ink is absorbed from the substrate. In addition, it is impossible to accurately measure the morphology change due to drying in suspension ink or the like in which nanoparticles are dispersed. Due to the coffee ring effect of the solids remaining after solvent evaporation of the ink, the shape after evaporation is sometimes undesirable.

In addition, the substrate may be reacted by the solvent of the ink, and the effective evaluation of the swelling, etc. at this time is essential for the electronic printing, but there are no contact angle measuring equipment and standardized methods for evaluating this. to be.

The present invention provides a contact angle measuring method capable of accurately controlling the amount or droplet number of droplets ejected using an inkjet head.

The present invention provides a contact angle measuring method capable of discharging the amount of droplets discharged from a small amount to a relatively large amount.

The present invention provides a contact angle measuring method capable of measuring the amount by which the contact angle of the droplet changes over time.

The present invention provides a contact angle measuring method capable of measuring the contact angle of the droplet in the desired position even in the state of ejecting a plurality of droplets.

The present invention provides a contact angle measuring method capable of measuring the contact angle of a plurality of droplets having various sizes on one substrate at a time.

The present invention provides a contact angle measuring method capable of measuring the profile of the droplet and the amount of change of the profile over time.

The present invention provides a contact angle measuring method capable of measuring the contact angle at the super water-repellent surface according to the size of the droplet.

The present invention provides a contact angle measuring method capable of analyzing the phenomenon when the ink reacts on the substrate and swells.

The present invention provides a contact angle measuring method capable of evaluating what shape the solid content solidifies as the solvent of the ink evaporates.

Contact angle measuring method according to an embodiment of the present invention for solving the above problems, the step of ejecting a droplet on the substrate; Obtaining an image of droplets ejected onto the substrate; Setting a region of interest on the image of the droplet; Forming a plurality of straight lines at regular intervals in the region of interest; Obtaining an X coordinate and a Y coordinate at a point where the image value of the droplet changes rapidly along the direction of the straight line; Performing curve fitting using the X and Y coordinates of the point; And obtaining the contact angle of the droplet using the slope of the straight line obtained by the curve fitting.

In the discharging of the droplets, the droplets may be discharged using an inkjet head, and the size or number of droplets may be controlled by adjusting a voltage applied to the inkjet head.

In the discharging of the droplets, the droplets may be discharged using a syringe, a dispenser, or a pipette.

The obtaining of the droplet image may include moving the substrate in X, Y, and Z directions to obtain an image of a desired droplet from among a plurality of droplets present on the substrate.

In the setting of the ROI, the ROI may be set to surround all of the images of the droplet.

In the forming of the plurality of straight lines, the plurality of straight lines may be identically formed for edge detection on the image of the droplet.

In the step of obtaining the X coordinate and the Y coordinate, the point at which the image value of the droplet changes abruptly is a point at which the straight line intersects the surface or boundary of the droplet.

In the obtaining of the X coordinate and the Y coordinate, the X coordinate and the Y coordinate may be obtained and stored over time to obtain a three-dimensional profile of the droplet.

Performing the curve fitting may reduce the influence of image noise by using the X coordinate and the Y coordinate of a plurality of points.

In the step of obtaining the contact angle of the droplet, the profile change of the droplet may be measured since the slope of the curve-fitted straight line changes over time.

In the obtaining of the contact angle of the droplet, the amount of change in the profile of the droplet over time may be measured by differentiating the Y coordinate of the point where the image value of the droplet changes rapidly with respect to the X axis.

As described above, since the contact angle measuring method according to an embodiment of the present invention can measure the amount by which the contact angle of the droplet changes with time, the droplet change process is performed even when the droplet is dried after being discharged. The change amount of the contact angle according to the measurement can be measured.

In the contact angle measuring method according to an exemplary embodiment of the present invention, when swelling occurs because ink or droplet reacts with time on a substrate, this may be evaluated by measuring a profile change.

The contact angle measuring method according to an embodiment of the present invention can overcome the limitations of the existing 2θ method and evaluate the superhydrophobic phenomenon.

Since the contact angle measuring method according to an embodiment of the present invention can measure the profile of the droplet over time and show the profile data in a three-dimensional shape, it is easy to understand how the droplet or the contact angle changes with time.

In the contact angle measuring method according to the exemplary embodiment of the present invention, since the contact angle of the droplet is obtained by performing curve fitting using coordinate values of a plurality of points on the droplet image, the contact angle change rate as well as the initial contact angle may be measured.

Since the contact angle measuring method according to the exemplary embodiment of the present invention calculates the contact angle by curve fitting, the influence of the image noise may be reduced.

1 is a view schematically showing the configuration of a conventional contact angle measuring device.
2 is a view showing the principle of measuring the contact angle using a conventional contact angle measuring device.
3 is a view showing a contact angle measuring device according to an embodiment of the present invention.
4 to 9 are exemplary views illustrating a programmed screen used in the contact angle measuring apparatus according to FIG. 3.
10 is a flowchart illustrating a method of measuring a contact angle using a contact angle measuring device according to an embodiment of the present invention.
11 and 12 are views illustrating a case where a contact angle measuring method according to an embodiment of the present invention is applied.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

3 is a view showing a contact angle measuring device according to an embodiment of the present invention, Figures 4 to 9 is an exemplary view showing a programmed screen used in the contact angle measuring device according to Figure 3, Figure 10 is an embodiment of the present invention 11 and 12 are flowcharts illustrating a method of measuring a contact angle using a contact angle measuring apparatus according to an example. FIG. 11 and FIG. 12 are views illustrating a case where a contact angle measuring method according to an embodiment of the present invention is applied.

Referring to FIG. 3, the contact angle measuring apparatus 100 according to an exemplary embodiment may include an inkjet head 110 for discharging droplets, a substrate 150 on which the droplets are attached, and a movement of the substrate 150. An image obtaining unit 130 which acquires an image of the droplet by capturing the droplets on the substrate moving unit 181, 183 and 185 and the substrate 150, and analyzing the image of the droplet obtained by the obtaining unit 130. And an image processing unit (not shown) for obtaining coordinates of a point at which the value changes rapidly, and a contact angle calculator (not shown) for calculating the contact angle of the droplet using the coordinates.

Here, the image processor and the contact angle calculator may be regarded as a computer processing apparatus such as a computer.

The contact angle measuring apparatus 100 according to an exemplary embodiment of the present invention may easily obtain a contact angle with a small amount of droplets by measuring the contact angle of the droplets by ejecting the droplets using the inkjet head 110.

The inkjet head 110 may be connected to a supply conduit 120 for supplying ink or fluid to the inkjet head 110. The supply conduit 120 is formed to have a fine size and is supplied to the inkjet head 110. The amount of can be finely controlled.

The inkjet head 110 may be provided to be positioned above the substrate 150 so that droplets of ink or fluid may be dropped on the substrate 150 and contacted with the droplets. At this time, the inkjet head 110 is preferably provided fixed to the support structure.

One side of the substrate 150 is provided with an image acquisition unit 130 for acquiring an image of the droplets immobilized on the substrate 150, the image acquisition unit 130 may be configured as a CCD camera. The lighting 140 may be installed to face the image obtaining unit 130 based on the substrate 150. The lighting 140 may use LED lighting, and the image obtaining unit 130 may display an image of the droplet. Provides light for clearer shots or acquisition. Here, the illumination 140 may be always on, but may operate only at the moment when the droplet is ejected from the inkjet head 110 in synchronization with a trigger signal applied to the inkjet head 110.

The substrate 150 may be placed on an aluminum electrode plate (not shown), and the aluminum electrode plate may be placed on the insulating material 170.

Here, the electrode plate 150 and the insulating material 170 may be moved in the X-axis, Y-axis, and Z-axis directions by the substrate moving parts 181, 183, and 185. The substrate moving parts 181, 183, and 185 may include an X-axis moving part 181, a Y-axis moving part 183, and a Z-axis moving part 185 that may move in the respective axial directions by a lead screw method. have. Among these, since the Z-axis moving part may move in the vertical direction, the Z-axis moving part may move to a position in contact with the lower portion of the substrate 150 and the insulating material 170. As described above, the Z-axis moving unit 185 moves up and the X-axis moving unit 181 or the Y-axis moving unit 183 moves while the lower portion of the substrate 150 or the insulating material 170 is in contact with each other. The enemy may be positioned on a line connecting the image acquisition unit 130 and the illumination 140.

As described above, since the substrate moving parts 181, 183, and 185 that are movable in the three axis directions are used, images of all the droplets may be obtained even when a plurality of droplets are ejected onto the substrate 150. Therefore, compared with the conventional contact angle measuring apparatus which acquires the image with respect to one droplet, measurement efficiency can be improved.

In the drawings, reference numeral 160 denotes a vacuum switch.

On the other hand, the inkjet head 110 of the contact angle measuring apparatus 100 according to an embodiment of the present invention can control the discharge amount of the droplet using the number of droplets. That is, the inkjet head 110 may control the size or the number of droplets discharged according to the applied voltage.

For example, when one drop of the droplet is 50 pL, the number of droplets of the droplets discharged, such as one drop, ten drops, or 100 drops, may be controlled by the amount of the droplets discharged from the inkjet head 110. In addition, when the droplets are to be ejected in a minute or very small amount, the amount of droplets ejected may be controlled by adjusting the voltage applied to the inkjet head 110. For example, when the voltage applied to the inkjet head 110 is 40V, 50pL droplets may be discharged, and 40pL at 30V, 55pL may be discharged at 60V. As such, the contact angle measuring apparatus 100 according to the exemplary embodiment of the present invention may easily and accurately adjust the amount or droplet number of the ejected droplets by ejecting the droplets using the inkjet head 110. For this reason, the contact angle of the extremely small amount ink used for electronic printing can also be measured correctly.

As described above, in the contact angle measuring apparatus 100 according to the exemplary embodiment, a plurality of droplets may exist on the substrate 150. That is, since there are substrate moving parts 181, 183, and 185 capable of moving the substrate 150 in three axial directions, contact angles of multiple droplets on one substrate may be checked at once.

In the state where a plurality of droplets having various sizes are discharged onto the substrate 150 by the inkjet head 110, the image acquisition unit 130 is to photograph among the plurality of droplets existing on the substrate 150. The substrate 150 may be moved in the X-axis, Y-axis, and Z-axis directions so as to be positioned on the same line as the droplet.

4 and 5, the image processor sets a region of interest 202 in the image of the droplet, and the straight line 211 intersects with the image of the droplet 203 in the region of interest 202. A plurality of can be formed at the same interval. Here, the ROI 203 may be designated or input by the user, and the user may designate or input the same spacing of the plurality of straight lines 211 formed in the ROI 203. The region of interest 203 may be designated in the form of a rectangle or a closed curve having a square or a predetermined area so as to obtain a contact angle in the image of the droplet. An interval of the straight lines 211 formed in the ROI 202 may be designated as a predetermined pixel interval.

Referring to FIG. 5A, in order to find the point 212 where the straight line 211 and the image of the droplet intersect, the point where the image value defined along the direction of the straight line 211 changes rapidly may be found. That is, the image processor may find a plurality of points 212 on which the image values of the droplets rapidly change on the plurality of straight lines 211, and obtain X and Y coordinates of the plurality of points 212. In this case, an edge detection algorithm may be used to find a point 212 in which the image value of the droplet changes rapidly along the direction of the straight line 211.

When the image image of the droplet acquired by the image acquisition unit 130 is converted into a binary image through image processing, image values of the inside and outside of the image of the droplet are changed. For example, if the image value inside the image of the droplet is 1, the external image value may be 0.

As such, the point 212 where the image value changes abruptly in the outline or boundary of the image of the droplet and the image value changes rapidly can be found through the edge detection. It is preferable to find a point where the image value in the direction of the straight line 211 changes rapidly in order to obtain the X and Y coordinates of the point 212 where the image value changes rapidly. In this way, X coordinates and Y coordinates are obtained for a plurality of points 212 in which the image value changes rapidly.

The contact angle calculator may curve-fit the X coordinates and the Y coordinates of the plurality of points 212 to obtain a straight line 213, and calculate the contact angle of the droplet 203 from the inclination of the obtained straight line 213. have. As shown in FIG. 5B, a curve is formed using two or more points 212 at which image values of the droplets change rapidly along a plurality of straight lines 211 drawn at equal intervals in the ROI 202. It can be said that the inclination of the straight line 213 obtained by performing the fitting indicates the contact angle of the droplet 203.

Comparing FIG. 5 (a) showing a contact angle measuring method according to an embodiment of the present invention with FIG. 2 showing a conventional contact angle measuring method, the conventional contact angle measuring method uses a 2θ method based on a binary image. On the other hand, the contact angle measuring method according to an embodiment of the present invention is different in that it can measure not only the contact angle but also the shape of the droplet using edge detection technology. That is, the contact angle measuring method according to an embodiment of the present invention can measure the shape of the droplet or the change of profile with time, whereas the conventional contact angle measuring method cannot limit the profile of the droplet. There is.

Hereinafter, a method of measuring the contact angle of a droplet using the contact angle measuring apparatus 100 according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

First, as shown in FIG. 10, in the contact angle measuring method according to the exemplary embodiment of the present disclosure, the method may include: discharging droplets on the substrate 150 (1100); Step 1200, setting the region of interest 202 on the image of the droplet 203 (1300), and forming a plurality of straight lines 211 at regular intervals in the region of interest 202 (1400). Obtaining an X coordinate and a Y coordinate of a point 212 in which the image value of the droplet changes rapidly along the direction of the straight line 211 (1500), and curves using the X and Y coordinates of the point 212. The method may include performing a fitting 1600 and obtaining a contact angle of the droplet 1700 using the slope of the straight line 213 obtained by the curve fitting.

In the discharging of the droplet (1100), the droplet may be discharged using the inkjet head 110, and at this time, the size of the droplet or the number of droplets to be discharged may be controlled by adjusting a voltage applied to the inkjet head 110. Can be. The droplets discharged by the inkjet head 110 are present on the substrate 150, and the inkjet head 110 may discharge a plurality of droplets of various sizes on the substrate 150.

Here, the step 1100 of ejecting the droplets does not necessarily eject the droplets using the inkjet head 110, but ejects the droplets using a conventional syringe, dispenser, or pipette. You can also That is, the contact angle measuring method according to an embodiment of the present invention may be used in existing contact angle measuring equipment. Hereinafter, for convenience of description, a contact angle measuring method using a contact angle measuring apparatus using the inkjet head 110 will be described.

In order to acquire an image of a desired droplet in a state where a plurality of droplets are ejected onto the substrate 150, the substrate 150 must be moved to position the droplet to be photographed toward the image obtaining unit 130. To this end, obtaining an image of the droplet 1200 may move the substrate 150 in the X, Y, and Z directions to obtain an image of a desired droplet from among a plurality of droplets present on the substrate. Can be. At this time, the substrate 150 may move in the X-axis, Y-axis, and Z-axis directions by the substrate moving parts 181, 183, and 185. The substrate moving parts 181, 183 and 185 place the desired droplets on the same line as the image acquisition unit 130 and the illumination 140, and then photograph the droplets by the image acquisition unit 130 to obtain an image of the droplets.

After acquiring the image of the droplet, the image processor performs image processing and edge detection on the image of the droplet. The setting of the region of interest 202 (1300) may be performed by the image processor, and may set the region of interest 202 to surround all of the images of the droplet. As shown in FIG. 4, the ROI 202 may be set to have a square shape or a predetermined area to surround the image of the droplet 203. 4, which shows a programmed screen for processing an image of a droplet, an image of the droplet is displayed in a left window 201, and a result of image processing of the droplet is displayed on the right side. That is, a graph 205 showing the contact angle 204 and the contour or boundary of the droplet over time is shown on the right side.

As described above, after setting the ROI 202, a plurality of straight lines 211 are drawn in the ROI 202 at regular intervals. The step 1400 of forming the plurality of straight lines 211 may also be performed by the image processor, and the plurality of straight lines may be identically formed for edge detection on the image of the droplet.

After drawing a plurality of straight lines 211 in the region of interest 202, in the step 1500 of obtaining the X and Y coordinates, a plurality of points 212 at which the image values of the droplets change rapidly are obtained (1500). The point 212 at which the image value of the droplet changes rapidly may be a point at which the straight line 211 intersects the surface or boundary of the droplet. When the image processing unit performs image processing on the image of the droplet, a binary image of the droplet may be obtained. The binary image is rapidly changed from the boundary or surface of the droplet image. Thus, the method according to the invention can obtain the surface or contour of the droplet image. Obtaining the X coordinate and the Y coordinate 1500 may obtain a profile of the droplet. For example, looking at the bottom right of FIG. 4, it can be seen that the profile or contour of the droplet image is represented by a plurality of points (see 205 of FIG. 4). Here, in the step 1500 of obtaining the X coordinate and the Y coordinate, the X coordinate and the Y coordinate may be obtained and stored according to time, thereby forming the profile of the droplet in three dimensions.

In the step 1600 of performing curve fitting using the X coordinates and the Y coordinates of the plurality of points 212 obtained as described above, an optimal straight line 213 may be obtained through the curve fitting. In this case, two points may be used for curve fitting, or X and Y coordinates of a plurality of adjacent points may be used.

In the performing of the curve fitting 1600, the influence of image noise may be reduced by deriving a straight line 213 using the X and Y coordinates of the plurality of points 212.

6 illustrates a programmed screen 220 for performing curve fitting using a plurality of points 212. Referring to FIG. 6, a straight line derived by performing curve fitting using a plurality of points is illustrated. The straight line derived by curve fitting may be expressed in the form of a linear equation, that is, y = ax + b. Here, the a value corresponding to the inclination of the straight line is the degree of change of the contact angle with time, that is, the rate of change of the contact angle with time, and the b value corresponding to the y-axis intercept of the straight line is the initial contact angle. Referring to FIG. 6, the initial contact angle of the straight line is approximately 30 degrees, and since the a corresponding to the slope has a negative value, the contact angle decreases with time. Therefore, it can be said that the contact angle obtained through this process is relatively less sensitive to noise than the initial value.

As described above, in the step 1700 of obtaining the contact angle of the droplet, the profile change of the droplet may be measured from the change in the slope of the curve-fitted straight line 213 over time. In the contact angle measuring method according to an exemplary embodiment of the present invention, the X and Y coordinates of the point 212 at which the image value of the droplet changes rapidly are found, and the slope of the initial contact portion using the relationship of tanθ = Y / X using the same. The contact angle can be calculated. In addition, since the droplet profile is measured, the characteristic of the droplet when drying is also known, and the change in profile and the change in contact angle can be effectively measured using the characteristic with time.

In operation 1700, the contact angle of the droplet may be measured by differentiating the Y coordinate of the point at which the image value of the droplet rapidly changes with respect to the X axis to measure the amount of change in the profile of the droplet over time. For example, as shown in FIG. 7, it can be seen how the profile of the droplet changes with time.

8 and 9, the contact angle measuring method according to an exemplary embodiment of the present invention obtains the coordinates of the point 212 at which the image value of the droplet rapidly changes in the ROI 202, and with respect to time. Storing each coordinate and displaying it in a three-dimensional graph also reveals the characteristics of the droplet drying process. That is, the contact angle measurement method according to the present invention may analyze the change process of the droplet profile or droplet shape as well as the contact angle. 8 illustrates a plurality of points in which image values change rapidly in three dimensions, and FIG. 9 illustrates a profile or a shape connecting the plurality of points displayed in three dimensions. Referring to FIG. 9, it can be seen how the profile of the droplet or the shape of the droplet changes, that is, the width and height of the droplet.

11 and 12, when the contact angle measuring method according to an embodiment of the present invention is used, the contact angle may be measured, but the conventional contact angle measuring method may not measure the contact angle. First, FIG. 11 is a view for explaining a method for measuring and analyzing how a solid or coffee ring comes out when ink or droplets are absorbed and evaporated on a substrate. As illustrated in FIG. 11, when a droplet or ink evaporates with time, a form of a droplet that cannot be measured or analyzed by a conventional contact angle measuring method remains. A contact angle measuring method according to an embodiment of the present invention. Using 3D allows you to express the profile of time in three dimensions so you can see at a glance how solids are produced. In addition, although not shown, the contact angle measuring method according to the present invention may analyze the swelling, that is, the swelling of the droplets when the ink reacts on the substrate, and three-dimensionally analyze the phenomenon.

Meanwhile, a display having a touch panel such as a smart phone and a tablet PC has been used in recent years. When the touch panel is touched with a finger, surface treatment is necessary so that fingerprints and the like do not remain. FIG. 12 is a photograph showing the appearance of fingerprints and sweat components of a person remaining on the surface of the touch panel. FIG. The contact angle measuring method according to the present invention can be effectively used for evaluating the relationship between the liquid and the substrate according to various applications, such as used in the surface treatment technique of the touch panel.

According to the contact angle measuring apparatus and the measuring method according to an embodiment of the present invention as described above, not only measuring the contact angle of the droplet, but also about how the profile of the droplet changes over time or what characteristics the droplet dries. Able to know.

In addition, since the contact angle measuring method according to an embodiment of the present invention measures the entire profile of the droplet, the relationship between the substrate and the droplet can be evaluated and three-dimensional shaping over time is possible. Through this, the evaluation of the super water-repellent substrate, which was not possible to measure by the conventional contact angle measurement method, the droplet shape during the drying process, and the swelling by the reaction between the substrate and the droplet can be evaluated.

The contact angle measuring method according to the exemplary embodiment of the present invention described above is not limited to an apparatus using an inkjet head to form droplets, and the image processing is performed when the droplets are dropped onto the surface by a conventional droplet dispensing apparatus. Through this, it can be applied to profile measurement and evaluation method through it.

In the present invention as described above has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from these descriptions. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

100: contact angle measuring device 110: inkjet head
130: image acquisition unit 140: lighting
150: substrate 181,183, 185: substrate moving part

Claims (10)

Ejecting a droplet onto the substrate;
Obtaining an image of droplets ejected onto the substrate;
Setting a region of interest on the image of the droplet;
Forming a plurality of straight lines at regular intervals in the region of interest;
Obtaining an X coordinate and a Y coordinate at a point where the image value of the droplet changes rapidly along the direction of the straight line;
Performing curve fitting using the X and Y coordinates of the point; And
Obtaining the contact angle of the droplet using the slope of the straight line obtained by the curve fitting;
Contact angle measurement method comprising a.
The method of claim 1,
Discharging the droplets,
And discharging the droplets using an inkjet head, and controlling the size or the number of droplets by adjusting a voltage applied to the inkjet head.
The method of claim 1,
Discharging the droplets,
Contact angle measuring method characterized in that for discharging the droplets using a syringe, dispenser or pipette.
The method of claim 2,
The setting of the ROI may include:
And setting the region of interest to surround all the images of the droplet.
The method of claim 4, wherein
Forming the plurality of straight lines,
And forming the plurality of straight lines in the same manner for edge detection of the droplet image.
The method of claim 5,
The method of measuring the contact angle, characterized in that the point where the image value of the droplet suddenly changes in the step of obtaining the X coordinate and the Y coordinate is the point where the surface or boundary surface of the droplet and the straight line intersect.
The method according to claim 6,
The step of obtaining the X coordinate and the Y coordinate is a contact angle measurement method, characterized in that to obtain the X coordinate and the Y coordinate to obtain the profile (profile) of the droplet after storing over time.
The method of claim 7, wherein
The step of performing the curve fitting, the contact angle measurement method, characterized in that to reduce the influence of the image noise by using the X coordinate and the Y coordinate of a plurality of points.
9. The method of claim 8,
Obtaining the contact angle of the droplets,
And measuring a profile change of the droplet from the inclination of the curve-fitted straight line over time.
10. The method of claim 9,
Obtaining the contact angle of the droplets,
And measuring the amount of change in the profile of the droplet over time by differentiating the Y coordinate of the point at which the image value of the droplet rapidly changes with respect to the X axis.

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