Method for evaluating droplet removability

Abstract

A method for evaluating the droplet removability of a water repellent material (22) includes: acquiring a plurality of sliding angle measurement values obtained by performing sliding angle measurement of droplets on the water repellent material (22) a plurality of times within a given period; creating a graph with elapsed time on a horizontal axis and the plurality of sliding angle measurement values on a vertical axis; calculating an integrated value of the sliding angle measurement values based on the graph over a certain period; and evaluating the droplet removability to be higher when the integrated value is smaller.

Description

Droplet removal evaluation method

[0001] The present disclosure relates to a method for evaluating droplet removal properties.

[0002] Water-repellent materials are used in umbrellas, raincoats, waterproof shoes, etc. Non-Patent Document 1 discloses a method for measuring the sliding angle to evaluate the droplet removal properties of water-repellent materials.

[0003] In Non-Patent Document 1, a water-repellent material is applied to the surface of a horizontally placed substrate, and a droplet is dropped onto the water-repellent material. The substrate is gradually tilted from a horizontal position, and the angle of inclination at which the droplet falls (called the "falling angle") is measured. The smaller the falling angle, the higher the droplet removal ability of the water-repellent material is evaluated to be.

[0004] "Method for evaluating droplet removal performance using sliding angle; Kyowa Interface Science Co., Ltd." https: / / www.face-kyowa.co.jp / science / theory / what_sliding_angle.html

[0005] However, the method disclosed in the above-mentioned Non-Patent Document 1 does not take into account changes in droplet removability over the long term. That is, even if a water-repellent material has a small sliding angle and excellent droplet removability at the beginning of use, the droplet removability may deteriorate over time when exposed to an outdoor environment. Therefore, in order to evaluate the droplet removability of a water-repellent material, it is necessary to use not only data on the initial sliding angle but also data on sliding angles measured multiple times within a certain period of time.

[0006] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a method for evaluating droplet removability that can evaluate droplet removability within any period of time.

[0007] A method for evaluating droplet removability according to one embodiment of the present disclosure is a method for evaluating the droplet removability of a water-repellent material, which involves measuring the droplet sliding angle of the water-repellent material multiple times within an arbitrary period of time to obtain multiple measured sliding angle values, creating a graph with the passage of time as the first axis and the multiple measured sliding angle values ​​as the second axis, calculating an integrated value of the measured sliding angle values ​​based on the graph over a certain period of time, and evaluating the droplet removability to be higher the smaller the integrated value.

[0008] According to the present disclosure, it is possible to evaluate the droplet removal property within any desired period of time.

[0009] FIG. 1 is a block diagram showing the configuration of an evaluation device for evaluating the droplet removability of water-repellent materials. FIG. 2 is an explanatory diagram showing the configuration of a test specimen for evaluating droplet removability. FIG. 3A is an explanatory diagram showing a state in which a droplet is dropped on the surface of a test specimen placed on a horizontal surface. FIG. 3B is an explanatory diagram showing the state in which the test specimen is gradually tilted and the droplet sliding angle is measured. FIG. 4 is a graph showing the measured sliding angles of a first test specimen coated with a first water-repellent material and a second test specimen coated with a second water-repellent material when placed outdoors for 50 days. FIG. 5 is a graph showing data obtained by plotting sliding angles measured every 10 days, with outdoor exposure days ranging from 0 to 50 days, on a coordinate system. FIG. 6 is a diagram showing data obtained by plotting sliding angles measured multiple times at irregular intervals, with outdoor exposure days ranging from 0 to 50 days, on a coordinate system, and a region showing the area obtained by multiplying this data by the interval between the previous and current measurements. Figure 7 shows data on a coordinate system in which the sliding angles measured multiple times at irregular intervals over a period of 0 to 50 days of outdoor exposure are plotted, and a region showing the area obtained by multiplying the data by the interval between the current and next measurements. Figure 8 shows data on a coordinate system in which the sliding angles measured multiple times at irregular intervals over a period of 0 to 50 days of outdoor exposure are plotted, and a region showing the area obtained by multiplying the average value of the current and previous data by the interval between the current and previous measurements. Figure 9 shows a graph showing measurement data from a contact angle measurement test conducted on specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing the sliding angle, and a comparison with the first lower limit value Th1. Figure 10 shows a graph showing measurement data from a contact angle measurement test conducted on specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing the sliding angle, and a comparison with the second lower limit value Th2. Fig. 11 is a graph showing the measurement data when a measurement test of the fall angle was conducted on specimens M1 and M2, and the area after exceeding the first lower limit Th1, with the horizontal axis representing elapsed time and the vertical axis representing the fall angle. Fig. 12 is a graph showing the measurement data when a measurement test of the fall angle was conducted on specimens M1 and M2, and the slope of the graph when the first lower limit Th1 was exceeded, with the horizontal axis representing elapsed time and the vertical axis representing the fall angle. Fig. 13A is a graph showing the fall angle data for 50 days for three types of specimens.Fig. 13B is a graph showing predicted values ​​of the fall angle for a period thereafter based on the fall angle data for 50 days shown in Fig. 13A. Fig. 14 is a block diagram showing a hardware configuration of the embodiment.

[0010] Hereinafter, embodiments will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of an evaluation device 1 for evaluating the droplet removability of a water-repellent material. Fig. 2 is an explanatory diagram showing the configuration of a test specimen 20 for evaluating droplet removability. Fig. 3A is an explanatory diagram showing a state in which a droplet is dropped on the surface of the test specimen 20 placed on a horizontal surface, and Fig. 3B is an explanatory diagram showing how the test specimen 20 is gradually tilted to measure the droplet sliding angle.

[0011] [Explanation of First Example] As shown in Figure 2, test specimen 20 has a rectangular shape measuring approximately 15 cm x 6.5 cm. Test specimen 20 is formed by applying a water-repellent material 21 to the surface of a flat substrate 22. In this example, as shown in Figure 3A, a droplet (e.g., a water droplet) is dropped onto test specimen 20 placed on a horizontal surface, forming a hemispherical droplet 23 on the surface of water-repellent material 21. Furthermore, as shown in Figure 3B, the tilt angle θ of test specimen 20 is gradually increased, and the tilt angle θ (hereinafter referred to as the "falling angle") at which droplet 23 falls is measured. Hereinafter, the above test will be referred to as the "falling angle measurement test."

[0012] In this example, after the first sliding angle measurement test is started on the test specimen 20, multiple sliding angle measurement tests are performed within a certain period of time to obtain multiple sliding angles over time. For example, the test specimen 20 is placed in an outdoor environment, and the sliding angle is measured every certain period of time. The outdoor environment refers to, for example, an environment exposed to the open air, wind, rain, and sunlight. The certain period of time is, for example, one day. The obtained multiple sliding angles are input into the evaluation device 1 shown in Figure 1 to evaluate the droplet removability of the water-repellent material 21. This will be described in detail below.

[0013] As shown in FIG. 1 , the evaluation device 1 includes an acquisition unit 11 , a calculation unit 12 , and an evaluation unit 13 .

[0014] The acquisition unit 11 acquires a plurality of rolling angles measured in a plurality of rolling angle measurement tests. The acquisition unit 11 acquires a plurality of rolling angle measurement values ​​obtained by measuring the rolling angle of the droplet 23 on the water-repellent material 21 a plurality of times within an arbitrary period of time.

[0015] Based on the data on the plurality of fall angles, the calculation unit 12 creates a graph with time on the horizontal axis (first axis) and the measured values ​​of the fall angles on the vertical axis (second axis). Based on the created graph, the calculation unit 12 calculates an integral value for a predetermined period based on the measurement start time. The integral value is an example of an accumulated value.

[0016] The following describes the measurement results when the droplet removability was evaluated for the first water-repellent material 21A and the second water-repellent material 21B. Fig. 4 is a graph showing the measured values ​​of the sliding angle when a first test piece 20A coated with the first water-repellent material 21A and a second test piece 20B coated with the second water-repellent material 21B were left outdoors for 50 days.

[0017] The horizontal axis in Figure 4 represents the number of outdoor exposure days, and the vertical axis represents the sliding angle. Curve s1 represents the measurement results for the first test specimen 20A, and curve s2 represents the test results for the second test specimen 20B. The sliding angle shown on the vertical axis represents the average value when the sliding angle measurement test is performed multiple times (e.g., 10 times). In the sliding angle measurement test, the inclination angle of the test specimen 20 is gradually increased as shown in Figure 3B, and the angle at which the droplet 23 slides off the water-repellent material 21 is measured as the sliding angle. Note that although the vertical axis in Figure 4 represents the average value of multiple tests, the result of only one test may also be used. Other representative values, such as the median, maximum, or minimum value of the multiple test results, may also be used.

[0018] As shown by curve s1 in FIG. 4 , the sliding angle of the first specimen 20A at "0 days" of outdoor exposure is a low value of about 2°. As the number of days of outdoor exposure increases, the sliding angle increases, reaching about 10° after 50 days. On the other hand, as shown by curve s2, the sliding angle of the second specimen 20B at "0 days" of outdoor exposure is 3° to 4°. As the number of days of outdoor exposure increases, the sliding angle increases slightly, but remains almost flat. In this example, droplet removability is not evaluated solely based on the sliding angle at "0 days" of outdoor exposure, but rather the sliding angle is measured multiple times over a certain period, such as 50 days, and the droplet removability is evaluated based on the data from the multiple sliding angles.

[0019] The calculation unit 12 shown in Fig. 1 calculates approximate curves of the curves s1 and s2, and calculates the integral values ​​of each of the curves s1 and s2 based on the approximate curves. In this embodiment, each of the curves s1 and s2 is approximated by a cubic function. Specifically, the curves s1 and s2 can be expressed by the following equations (1) and (2).

[0020] s1 = -0.0002x ３ +0.011x ２ -0.0019x+1.8681...(1) s2=8E-5x ３ -0.0041x ２ -0.0665x+3.2763 ... (2) In the above function approximation, the coefficient of determination R ２ to "R ２ = 0.9767", and in equation (2), the coefficient of determination R ２ "R ２ = 0.9825".

[0021] The calculation unit 12 integrates the curves s1 and s2 over a period of 0 to 50 days based on the approximation formulas (1) and (2) above. For example, the integral value obtained by integrating the formula (1) above is "237" according to the following formula (3). The integral value obtained by integrating the formula (2) above is "37" according to the following formula (4).

[0022]

[0023]

[0024] In this embodiment, an example of creating an approximate curve using a cubic function is shown, but the present invention is not limited to this, and each of the curves s1 and s2 may be approximated by a quadratic function or a quartic or higher order function.

[0025] 1 , the evaluation unit 13 evaluates the droplet removability of the first test piece 20A coated with the first water-repellent material 21A and the second test piece 20B coated with the second water-repellent material 21B, using the integral value calculated by the calculation unit 12 as an evaluation index for droplet removability. Specifically, the first test piece 20A is evaluated as having low droplet removability because of its large integral value, and the second test piece 20B is evaluated as having high droplet removability because of its small integral value. The evaluation unit 13 calculates the integral value (accumulated value) of the measured values ​​of the sliding angle based on the graph over a certain period of time, and evaluates that the smaller the integrated value, the higher the droplet removability.

[0026] That is, in the conventional evaluation method, the droplet removability is evaluated using the sliding angle at the start of use, and therefore the first test piece 20A is evaluated as having higher droplet removability than the second test piece 20B. In contrast, in the evaluation method according to the first embodiment, the droplet removability is evaluated using the integrated value of the graph showing the change in the sliding angle over 50 days as the evaluation index, and therefore it is possible to evaluate the droplet removability taking into account the change over time over a certain period of time.

[0027] Thus, the first embodiment is an evaluation method for evaluating the droplet removability of a water-repellent material, in which droplet sliding angle measurements are performed multiple times on the water-repellent material within an arbitrary period of time to obtain multiple sliding angle measurements, a graph is created with the passage of time on the horizontal axis (first axis) and the multiple sliding angle measurements on the vertical axis (second axis), and an accumulated value (e.g., integral value) of the sliding angle measurements based on the graph over a certain period of time is calculated, and the smaller the accumulated value, the higher the droplet removability is evaluated to be.

[0028] The method for evaluating the sliding angle according to the first embodiment allows for evaluation that takes into account changes in the sliding angle over the period of use of the water-repellent material. The range of the elapsed period to be integrated can be set according to the actual period of use of the water-repellent material. For example, if the water-repellent paint is used for approximately three years, the integrated value can be calculated assuming an elapsed period of three years.

[0029] [Explanation of Second Example] Next, a second example will be described. In the first example described above, curves s1 and s2 were created from a graph plotting the sliding angles measured every 10 days, as shown in Fig. 4. In the second example, a numerical value obtained by simply adding up the sliding angles plotted on the coordinate system is used as an evaluation index for droplet removability.

[0030] Figure 5 is a graph showing data plotting the sliding angle measured every 10 days, from 0 to 50 days of outdoor exposure. The sliding angle can be the average value of multiple measurements taken at the same time. As with Figure 4, the sliding angle shown on the vertical axis of Figure 5 may be the result of a single test, or other representative values ​​such as the median, maximum, or minimum of multiple test results. In the second example, the sliding angles measured at desired times are added together, and the sum (integrated value) is used as an evaluation index for droplet removability. That is, if the measurement interval and measurement time are the same for each test specimen 20, the sum of the respective values ​​can be used to compare the droplet removability of each test specimen 20. The smaller the sliding angle sum, the higher the droplet removability can be evaluated. The sum is the sum of the sliding angle measurements taken at multiple predetermined times within a given period. The sum is an example of an integrated value.

[0031] In the second embodiment, since there is no need for complex calculations such as calculation of an approximate curve and integration calculations as in the first embodiment, it is possible to reduce the calculation load.

[0032] [Description of the Third Example] Next, a description will be given of the third example, in which, instead of the integral value described in the first example, a total value of the sliding angles weighted by the measurement interval is calculated, and this total value is used as an evaluation index for the droplet removal performance.

[0033] FIG. 6 shows data plotting the average values ​​of the sliding angles (mean values) measured multiple times at irregular intervals over outdoor exposure days of 0 to 50 days. As shown in FIG. 6, the sliding angles were measured at times p0 to p5, and the respective measurement results are plotted on the coordinate system. As with FIG. 4, the sliding angle shown on the vertical axis of FIG. 6 may be a single test result or other representative values, such as the median, maximum, or minimum values ​​of multiple test results. In the third example, the sliding angle measured at the current measurement time (e.g., time p1) is multiplied by the elapsed time from the previous measurement time p0 to the current measurement time p1, i.e., the time "p0 to p1," to calculate the area of ​​region S1 shown in FIG. 6.

[0034] Similarly, the sliding angle measured at time p2 is multiplied by the elapsed time from the previous measurement time p1 to the current measurement time p2, i.e., the time "p1 to p2," to calculate a value (the area of ​​region S2). Then, the same process as above is performed to calculate the areas of regions S3, S4, and S5, and 50 days' worth of data is integrated. Specifically, the total area of ​​regions S1 to S5 is calculated, and this value is used as the evaluation index for droplet removability. That is, the sliding angle measurement value at any time during the measurement period is multiplied by the time indicating the interval between sliding angle measurements, and the integrated value is used as the evaluation index for droplet removability. The smaller the total area, the higher the droplet removability can be evaluated. The integrated value of the multiplied values ​​is an example of an integrated value.

[0035] In the third embodiment, even if the measurement interval of the sliding angle is not constant, it can be used as an evaluation index of droplet removal performance. Furthermore, in the third embodiment, since it does not require complex calculations such as calculation of an approximation curve and integral calculations as shown in the first embodiment, it is possible to reduce the calculation load.

[0036] [Description of the Fourth Example] Next, a fourth example will be described. In the fourth example, as in the third example described above, the sum of the sliding angles weighted by the measurement interval is calculated, and this sum is used as an evaluation index for droplet removability. In the third example, when the current sliding angle is measured, the sliding angle is multiplied by the elapsed time from the previous measurement to the current measurement to calculate the area. In contrast, in the fourth example, when the current sliding angle is measured, the sliding angle is multiplied by the elapsed time from the current measurement to the next measurement to calculate the area.

[0037] FIG. 7 shows data plotting the average values ​​of the fall angles (measured multiple times) measured at irregular intervals over outdoor exposure days of 0 to 50 days. As shown in FIG. 7, the fall angles are plotted at times p10 to p15. As with FIG. 4, the fall angle shown on the vertical axis of FIG. 7 may be a single test result or a representative value such as the median, maximum, or minimum value of multiple test results. In the fourth example, the fall angle measured at the current measurement time (e.g., time p10) is multiplied by the elapsed time "p10 to p11" from the current measurement time p10 to the next measurement time p11 to calculate the area of ​​region S11 shown in FIG. 7.

[0038] Similarly, the sliding angle measured at time p11 is multiplied by the elapsed time "p11 to p12" from the current measurement time p11 to the next measurement time p12 to calculate the value, i.e., the area of ​​region S12. Then, the same process as above is performed to calculate the areas of regions S13, S14, and S15, and 50 days' worth of data is integrated. Specifically, the areas of regions S11 to S15 are totaled and used as an evaluation index for droplet removability. The smaller the total area, the higher the droplet removability can be evaluated. In other words, the evaluation index for droplet removability is the value obtained by multiplying the sliding angle measurement value at any time during the measurement period by the time indicating the interval between sliding angle measurements. The value obtained by integrating the multiplied values ​​is an example of an integrated value.

[0039] In the fourth embodiment, similar to the third embodiment, the sliding angle can be used as an evaluation index for droplet removal even if the measurement intervals are not constant. Furthermore, the fourth embodiment does not require complex calculations such as approximation curve calculations and integral calculations, as shown in the first embodiment, and therefore the calculation load can be reduced.

[0040] [Explanation of Fifth Example] Next, a fifth example will be described. In the fifth example, as in the third and fourth examples described above, the sum of the sliding angles weighted by the measurement interval is calculated, and this sum is used as an evaluation index for droplet removability. In the fifth example, when the current sliding angle is measured, the average value between the sliding angle measured last time is calculated. Furthermore, the area is calculated by multiplying this average value by the elapsed time from the previous measurement time to the current measurement time.

[0041] FIG. 8 shows data plotting the average values ​​of the fall angles measured multiple times at irregular intervals over outdoor exposure days ranging from 0 to 50 days. As shown in FIG. 8, the fall angles are plotted at times p20 to p25. As with FIG. 4, the fall angles shown on the vertical axis of FIG. 8 may be the result of a single test, or other representative values, such as the median, maximum, or minimum values ​​of multiple test results. In the fifth example, the average value q2 of the fall angle measured at the current measurement time (e.g., time p22) and the fall angle measured at the previous measurement time p21 is calculated. This average value q2 is multiplied by the elapsed time "p21 to p22" from the previous measurement time p21 to the current measurement time p22 to calculate the area of ​​region S22 shown in FIG. 8.

[0042] Similarly, the area of ​​region S21 is calculated using the average value q1 of the fall angles measured at times p20 and p21, the area of ​​region S23 is calculated using the average value q3 of the fall angles measured at times p22 and p23, the area of ​​region S24 is calculated using the average value q4 of the fall angles measured at times p23 and p24, and the area of ​​region S25 is calculated using the average value q5 of the fall angles measured at times p24 and p25, and these 50 days' worth of data are used. Specifically, the areas of regions S21 to S25 are summed up and used as an evaluation index for droplet removability. The smaller the sum of the areas, the higher the droplet removability can be evaluated. In other words, the evaluation index for droplet removability is the value obtained by multiplying the fall angle measurement value at any time during the measurement period by the time indicating the measurement interval between fall angles. The value obtained by integrating the multiplied values ​​is an example of an integrated value.

[0043] In the fifth embodiment, even if the measurement interval of the sliding angle is not constant, it can be used as an evaluation index of the droplet removal performance. Furthermore, in the fifth embodiment, as shown in the first embodiment, since it does not require complex calculations such as calculation of an approximation curve and integral calculations, it is possible to reduce the calculation load.

[0044] [Description of the Sixth Example] Next, the sixth example will be described. In the first to fifth examples described above, the smaller the sliding angle, the higher the droplet removability is determined to be. However, if the sliding angle is less than a certain allowable value, there is no significant difference in droplet removability. For example, if the sliding angle is less than 5°, whether it is 1° or 4° does not pose a significant problem in evaluating droplet removability.

[0045] In the sixth example, a lower limit value for the allowable sliding angle is set, and the time until the sliding angle reaches this lower limit value is used as an evaluation index for droplet removability. A detailed description will be given below with reference to FIG. 9. FIG. 9 is a graph showing measurement data obtained when a contact angle measurement test was conducted on test specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing sliding angle. In FIG. 9, the horizontal axis represents elapsed time and the vertical axis represents sliding angle. Furthermore, Th1 shown in FIG. 9 represents the first lower limit value of the sliding angle (a predetermined lower limit value; the lower limit value of the sliding angle that is considered to be allowable).

[0046] As shown in FIG. 9, the sliding angle of the test specimen M1 exceeds the first lower limit Th1 when the elapsed time from the start of use reaches T1. The sliding angle of the test specimen M2 exceeds the first lower limit Th1 when the elapsed time reaches T2 (<T1). In the sixth example, the elapsed times T1 and T2 until the sliding angle reaches the first lower limit Th1 are used as the evaluation index for droplet removability. The longer the elapsed time, the higher the droplet removability can be evaluated. In the example shown in FIG. 9, the test specimen M1 is evaluated as having higher droplet removability than the test specimen M2.

[0047] In the sixth example, the droplet removability can be evaluated for the test specimens M1 and M2 by the simple task of measuring the elapsed time from the start of the test. In the sixth example, since complex calculations such as calculation of an approximation curve and integral calculations are not required, the calculation load can be reduced.

[0048] [Explanation of Seventh Example] Next, a seventh example will be described. In the sixth example described above, an example was described in which the first lower limit Th1 of the allowable fall angle was set to a constant value. In the seventh example, the change in the fall angle over time for a reference test specimen is measured in advance. This measurement result is set as the second lower limit Th2 (predetermined lower limit). For example, as shown in FIG. 10, the second lower limit Th2 is set to increase monotonically and linearly over time. The second lower limit Th2 is an example of a predetermined lower limit.

[0049] Fig. 10 is a graph showing measurement data when a contact angle measurement test was conducted on specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing the fall angle. In Fig. 10, the horizontal axis represents elapsed time and the vertical axis represents the fall angle.

[0050] As shown in FIG. 10, the sliding angle of specimen M1 exceeds the second lower limit Th2 when the elapsed time reaches T3. The sliding angle of specimen M2 exceeds the second lower limit Th2 when the elapsed time reaches T4 (T4<T3). In the seventh example, the elapsed time until the sliding angle reaches the second lower limit Th2 is used as the evaluation index for droplet removability. The longer the elapsed time, the higher the droplet removability can be evaluated. In the example shown in FIG. 10, specimen M1 is evaluated as having higher droplet removability than specimen M2.

[0051] In the seventh embodiment, it is possible to evaluate the droplet removability of the test specimens M1 and M2 by the simple task of measuring the elapsed time from the start of the test. In the seventh embodiment, it is possible to reduce the computational load because complex calculations such as calculation of an approximation curve and integral calculations are not required.

[0052] [Explanation of Eighth Example] Next, an eighth example will be described. In the eighth example, a first lower limit Th1 of the allowable sliding angle is set, as in the sixth example described above. Furthermore, after the sliding angle measured by attaching a droplet to a test specimen exceeds this first lower limit Th1, the area measured during a predetermined period is calculated, and this area is used as an evaluation index for droplet removability.

[0053] Hereinafter, a detailed description will be given with reference to Fig. 11. Fig. 11 is a graph showing measurement data when a measurement test of the fall angle was conducted on specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing the fall angle. In Fig. 11, the horizontal axis represents elapsed time and the vertical axis represents the fall angle. Furthermore, Th1 represents a first lower limit value of the fall angle (the lower limit value of the fall angle that is considered to be acceptable).

[0054] As shown in FIG. 11 , the fall angle of the test specimen M1 exceeds the first lower limit Th1 at time p32. The calculation unit 12 shown in FIG. 1 calculates the area of ​​a region S32 where the fall angle exceeds the first lower limit Th1 during the period from time p32 to the measurement end time pm. Similarly, the fall angle of the test specimen M2 exceeds the first lower limit Th1 when time p31 is reached. The calculation unit 12 calculates the area of ​​a region S31 where the fall angle exceeds the first lower limit Th1 during the period from time p31 to the measurement end time pm.

[0055] In the eighth embodiment, the areas of regions S31 and S32 are used as evaluation indices for the droplet removability of test specimens M1 and M2, respectively. The smaller the areas, the higher the droplet removability can be evaluated. In the eighth embodiment, calculations are performed only on data after the sliding angle exceeds the first lower limit Th1, making it possible to evaluate the droplet removability of the test specimens with a small amount of calculation.

[0056] [Description of the Ninth Example] Next, a ninth example will be described. In the eighth example described above, a first lower limit Th1 of the allowable sliding angle is set, and when the sliding angle of the test specimens M1 and M2 exceeds the first lower limit Th1, the droplet removability is evaluated based on the area of ​​the region where the sliding angle exceeds the first lower limit Th1. In the ninth example, the slope of the curve is calculated when the sliding angle measured by attaching a droplet to the test specimen exceeds the first lower limit Th1, and the magnitude of this slope is used as an evaluation index for the droplet removability.

[0057] A detailed description will be given below with reference to Fig. 12. Fig. 12 is a graph showing measurement data obtained when a measurement test of the fall angle was conducted on specimens M1 and M2, with the horizontal axis representing elapsed time and the vertical axis representing the fall angle. In Fig. 12, the horizontal axis represents elapsed time and the vertical axis represents the fall angle. Furthermore, Th1 represents the first lower limit of the fall angle (the lower limit of the allowable fall angle).

[0058] As shown in Figure 12, the fall angle of the test specimen M1 exceeds the first lower limit value Th1 at time p42. The calculation unit 12 shown in Figure 1 calculates the slope φ1 of the graph for the test specimen M1 at time p42. Similarly, the fall angle of the test specimen M2 exceeds the first lower limit value Th1 at time p41. The calculation unit 12 calculates the slope φ2 of the graph for the test specimen M2 at time p41.

[0059] In the ninth embodiment, the slopes φ1 and φ2 are used as evaluation indexes for the droplet removability of test specimens M1 and M2, respectively. The smaller the slope, the higher the droplet removability can be evaluated. In the ninth embodiment, as in the eighth embodiment, calculations are performed only on data after the sliding angle exceeds the first lower limit Th1, making it possible to evaluate the droplet removability of the test specimens with a small amount of calculation.

[0060] [Explanation of the combination of Examples 6 to 9] It is also possible to use the evaluation index calculated in Example 6 or Example 7 described above as the first index, the evaluation index shown in Example 8 or Example 9 described above as the second index, and use the first index and the second index to evaluate droplet removal performance.

[0061] Specifically, the first index is the time elapsed until the sliding angle of the test specimen shown in Example 6 (FIG. 9) exceeds the first lower limit Th1, and the second index is the area of ​​regions S31 and S32 after the sliding angle exceeds the first lower limit Th1 shown in Example 8 (FIG. 11). The larger the first index and the smaller the second index, the higher the droplet removal ability can be evaluated.

[0062] In another combination, the first index is the time elapsed until the sliding angle of the test specimen shown in Example 7 (FIG. 10) exceeds the second lower limit Th2, and the second index is the slope of the curve showing the change in sliding angle when the sliding angle exceeds the first lower limit Th1, as shown in Example 9 (FIG. 12). The larger the first index and the smaller the second index, the higher the droplet removal ability can be evaluated.

[0063] Although detailed explanation will be omitted, it is also possible to combine Example 6 with Example 9, or to combine Example 7 with Example 8. In this way, by setting the first index and the second index and combining them, it becomes possible to evaluate the droplet removability with higher accuracy.

[0064] That is, a graph is created with the passage of time as the horizontal axis (first axis) and the measured values ​​of the fall angle from multiple times as the vertical axis (second axis), and based on this graph, the elapsed time from the start of the fall angle measurement until the fall angle exceeds a predetermined lower limit value (first lower limit value Th1 or second lower limit value Th2) is used as the first index, and based on the graph, the area enclosed by the graph and the predetermined lower limit value after the fall angle exceeds the predetermined lower limit value, or the slope of the graph when the fall angle exceeds the predetermined lower limit value, is used as the second index, and the larger the first index and the smaller the second index, the higher the droplet removal ability is evaluated to be.

[0065] Next, a tenth embodiment will be described. For example, if the measurement period of the sliding angle is 50 days, measurement data of multiple sliding angles over the 50 days is acquired. In the tenth embodiment, the sliding angle after 50 days is predicted from a curve estimated from the sliding angles over the 50 days, and this is used to estimate the evaluation value of the droplet removability.

[0066] For example, as shown in FIG. 13A, when 50-day sliding angle data is obtained for three test specimens, the sliding angle after 50 days is predicted by approximating the data for each test specimen with a curve. Specifically, as shown in FIG. 13B, curves s11, s12, and s13 (FIG. 13B shows an example of linear approximation) are calculated based on the data plotted in FIG. 13A. Based on these curves, the sliding angle after 50 days (the period indicated by symbol R1) is predicted, and the predicted sliding angle is used as an evaluation index for droplet removability. As a result, it is possible to evaluate droplet removability over a long period of time based on the sliding angle measured within a certain period of time.

[0067] The evaluation device 1 of the present embodiment described above can be, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906, as shown in Fig. 14. The memory 902 and the storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded on the memory 902, thereby realizing each function of the evaluation device 1.

[0068] The evaluation device 1 may be implemented by one computer or by multiple computers, or may be a virtual machine implemented on a computer.

[0069] The program for the evaluation device 1 can be stored in a computer-readable recording medium such as a HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0070] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0071] REFERENCE SIGNS LIST 1 Evaluation device 11 Acquisition unit 12 Calculation unit 13 Evaluation unit 20 Test piece 20A First test piece 20B Second test piece 21 Water-repellent material 21A First water-repellent material 21B Second water-repellent material 22 Substrate 23 Liquid droplet M1, M2 Test piece Th1 First lower limit value Th2 Second lower limit value

Claims

1. A method for evaluating the droplet removability of a water-repellent material, comprising: measuring the sliding angle of a droplet on the water-repellent material multiple times within a given period of time to obtain multiple measured values ​​of the sliding angle; creating a graph with the passage of time as the first axis and the multiple measured values ​​of the sliding angle as the second axis; calculating an integrated value of the measured values ​​of the sliding angle based on the graph over a certain period of time; and evaluating that the smaller the integrated value, the higher the droplet removability.

2. The method for evaluating droplet removability according to claim 1, wherein the integrated value includes the sum of measured values ​​of the sliding angle measured at a plurality of preset times within the given period.

3. The method for evaluating droplet removability according to claim 1, wherein the integrated value includes a numerical value obtained by multiplying the measured value of the fall angle at any time by the time indicating the measurement interval of the fall angle.

4. A method for evaluating the droplet removability of a water-repellent material, comprising: measuring the sliding angle of a droplet on the water-repellent material multiple times within an arbitrary period of time to obtain multiple measured values ​​of the sliding angle; creating a graph with the passage of time as the first axis and the multiple measured values ​​of the sliding angle as the second axis; using, based on the graph, the time elapsed from the start of the sliding angle measurement until the sliding angle exceeds a predetermined lower limit as a first index; and using, based on the graph, the area enclosed by the graph and the predetermined lower limit after the sliding angle has exceeded the predetermined lower limit, or the slope of the graph when the sliding angle exceeds the predetermined lower limit as a second index; and evaluating the droplet removability to be higher as the first index and the second index are smaller.

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