Doctor device and gravure coating device

Abstract

To provide a doctor device and a coating device that can equalize the coating amount distribution of coating liquid in the width direction during gravure coating and reduce coating irregularities of the coating liquid.SOLUTION: A doctor device comprises: a doctor blade; a doctor holder that holds the doctor blade; and a backup blade interposed between at least one surface of the doctor blade and the doctor holder, wherein the backup blade includes a plurality of divided blades that are smaller in width than the doctor blade and arranged side by side in the width direction of the doctor blade, and a protruding length of the divided blades from the doctor holder is longer at a central portion in the width direction of the doctor blade than at both end portions.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a doctor device and a gravure coating device. [Background technology]

[0002] Gravure coating is a widely used method for applying a coating liquid to a web. In gravure coating, the coating liquid is supplied to the surface of a rotating gravure roll (gravure plate). A doctor blade is pressed against the surface of the gravure roll to scrape off excess coating liquid from the surface of the gravure roll. The coating liquid held in the cells of the gravure roll is then transferred onto the web, forming a web-like coating film of the coating liquid. The doctor blade is pressed against the surface of the gravure roll between the position where the coating liquid is supplied onto the gravure roll and the position where the gravure roll contacts the web.

[0003] The doctor blade is held in a jig called a doctor holder. A backup blade (backing plate) is sandwiched between the doctor blade and the doctor holder to improve the straightness of the doctor blade.

[0004] The straightness of the doctor blade is important for uniformly distributing the amount of coating liquid applied across the width (axial direction of the gravure roll). In particular, when forming a thin film such as an anti-reflection coating for an optical film, the amount of coating liquid applied is small, so uniforming the distribution of the amount of coating liquid applied across the width is extremely important, and various measures to achieve this have been investigated.

[0005] For example, Patent Documents 1 and 2 describe gravure coating devices that solve the problem of uneven scraping by a doctor blade due to deflection of the gravure roll. In the gravure coating devices described in Patent Documents 1 and 2, the doctor blade is deflected in accordance with the deflection of the gravure roll, thereby making the contact angle and contact pressure of the doctor blade with the gravure roll uniform in the width direction and improving the uniformity of scraping. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-260393 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-73926 Summary of the Invention [Problem to be solved by the invention]

[0007] The distribution of the coating amount of the coating liquid in gravure coating varies due to factors other than the deflection of the gravure roll. For example, when the gravure roll is used for a long time, the cell volume of the gravure roll fluctuates, and the fluctuation in cell volume causes the distribution of the coating amount of the coating liquid to be non-uniform across the width of the gravure roll. The non-uniform distribution of the coating amount of the coating liquid causes band-like coating unevenness in the coating film, but it is difficult to eliminate this band-like coating unevenness using the method of deflecting the doctor blade as described in Patent Document 1.

[0008] Therefore, an object of the present invention is to provide a doctor device and a coating device that can make the distribution of the coating amount of the coating liquid uniform in the width direction in gravure coating and reduce uneven coating of the coating liquid. [Means for solving the problem]

[0009] The doctor device according to the present invention comprises a doctor blade and a doctor holder for holding the doctor blade. The backup blade has a width smaller than that of the doctor blade and includes a plurality of split blades arranged in the width direction of the doctor blade, and the split blades protrude from the doctor holder by a greater distance at the center than at both ends in the width direction of the doctor blade.

[0010] The gravure coating device according to the present invention comprises a gravure roll, a coating liquid supply unit that supplies a coating liquid to the gravure roll, a doctor blade, a doctor holder that holds the doctor blade, and a backup blade that is sandwiched between at least one surface of the doctor blade and the doctor holder. The backup blade has a width smaller than that of the doctor blade and includes a plurality of split blades arranged in the width direction of the doctor blade, and the split blades protrude from the doctor holder by a greater distance at the center than at both ends in the width direction of the doctor blade. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a doctor device and a coating device that can make the distribution of the coating amount of the coating liquid uniform in the width direction in gravure coating and reduce uneven coating of the coating liquid. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagram showing a gravure coating device according to an embodiment. [Figure 2] FIG. 1 is a plan view of a doctor device according to a first embodiment; [Figure 3] Enlarged cross-sectional view taken along line III-III in Figure 2 [Figure 4] FIG. 10 is a plan view of a doctor device according to a second embodiment; [Figure 5] FIG. 1 is a diagram showing definitions of values used in the description of the embodiment. [Figure 6] Schematic diagram for explaining a method for measuring the thickness of a coating film coated using a conventional backup blade. [Figure 7] Scatter plot of the film thickness ratio t / tave at each measurement point measured using the backup blade shown in Figure 6(a). [Figure 8] Schematic diagram showing the method for measuring the contact pressure of the doctor blade against the gravure roll [Figure 9] Scatter plot of the contact pressure ratio T / Tave at each measurement point measured using the backup blade shown in Figure 8(a) and Figure 8(b). [Figure 10] Scatter plot of α value and measured contact pressure ratio T / Tave [Figure 11] Scatter plot of film thickness ratio t / tave and contact pressure ratio T / Tave for each measurement position [Figure 12] Scatter plot of the film thickness ratio t / tave and the contact pressure ratio T / Tave for each measurement position shown in Figure 11. [Figure 13] Scatter plot of α at each measurement position shown in FIG. 8(b) and the membrane pressure ratio t / tave corresponding to each measurement position shown in FIG. 11. [Figure 14] Scatter plot of the α value at each measurement point of the prototype backup blade and the (t / tave-tref / trefave) value at the same measurement point. [Figure 15] A scatter plot in which the vertical and horizontal axes of Figure 14 are swapped and the curve expressed by Equation (5) is also shown as a dashed line. [Figure 16] FIG. 10 is a diagram showing the ratio of lengths of the divided blades that make up the backup blade according to the embodiment. [Figure 17] Scatter diagram showing the film thickness ratio of low refractive index layers formed by applying a coating liquid for forming a low refractive index layer using a backup blade according to the embodiment and a conventional backup blade. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 1 is a schematic diagram showing a gravure coating device according to an embodiment.

[0014] The gravure coating device 1 includes a gravure roll 2, a coating liquid supply unit 5 that supplies a coating liquid to the gravure roll 2, and a doctor unit 6. The gravure roll 2 is rotationally driven by a mechanism (not shown), and the coating liquid is supplied to its surface from the coating liquid supply unit 5. Excess coating liquid on the gravure roll 2 is scraped off by the doctor unit 6. The coating liquid held in the cells of the gravure roll 2 is transferred to the surface of the web 10, which is being transported while being guided by guide rolls 3 and 4. In this specification, the term "width direction" refers to the direction corresponding to the width direction (TD direction) of the web being transported. The width of the doctor blade and the width of the backup blade refer to the dimension corresponding to the width direction of the web, and the length of the backup blade refers to the dimension in the direction perpendicular to the width direction of the backup blade.

[0015] (First embodiment) FIG. 2 is a plan view of the doctor device according to the first embodiment, and FIG. 3 is an enlarged cross-sectional view taken along the line III-III shown in FIG.

[0016] The doctor unit 6a includes a doctor blade 11, an upper holder 12, a lower holder 13, an upper backup blade 15, and a lower backup blade 16. The upper holder 12 and the lower holder 13 form a doctor holder that holds the doctor blade. The upper backup blade 15 is sandwiched and held between the upper holder 12 and the side of the doctor blade 11 that does not face the gravure roll 2 (the upper side in FIG. 1 ). The lower backup blade 16 is sandwiched and held between the lower holder 13 and the side of the doctor blade 11 that faces the gravure roll 2 (the lower side in FIG. 1 ). The upper holders 12 and 13 are fastened to each other with bolts 17, with the upper backup blade 15, doctor blade 11, and lower backup blade 16 sandwiched between them, and the doctor blade 11 is fixed to the upper holder 12 and lower holder 13.

[0017] The upper backup blade 15 has multiple split blades 14a to 14l. Each of the split blades 14a to 14l has a width smaller than that of the doctor blade and is arranged side by side with no gaps in the width direction of the doctor blade. The length l of each of the split blades 14a to 14l is not constant. Here, the length l of the split blades 14a to 14l refers to the length of protrusion from the upper holder 12. While a typical backup blade has a constant length, the length of the upper backup blade 15 according to this embodiment varies depending on the position in the width direction.

[0018] The contact pressure of the doctor blade 11 against the gravure roll 2 varies depending on the distance from the tip of the upper backup blade 15 to the cutting edge of the doctor blade 11, with the contact pressure increasing as the distance becomes shorter. The upper backup blade 15 according to this embodiment comprises a plurality of split blades 14a to 14l that are split in the width direction. With this configuration, the length l of each of the split blades 14a to 14l can be set, and therefore the contact pressure of the doctor blade 11 against the gravure roll 2 can be finely adjusted for each of the sections corresponding to the split blades 14a to 14l.

[0019] As mentioned above, the distribution of the coating amount of the coating liquid in the width direction during gravure coating can become uneven due to the deflection of the gravure roll 2, changes in the cell capacity over time, etc. When the upper backup blade 15 according to this embodiment is used, the contact pressure of the doctor blade 11 can be increased by increasing the length of the split blade located in the center of the width direction (i.e., shortening the distance from the tip of the split blade to the cutting edge of the doctor blade 11). Therefore, the contact pressure of the doctor blade 11 against the gravure roll 2 can be made uniform in the width direction. This unifies the coating amount distribution of the coating liquid in the width direction, thereby achieving a uniform coating amount distribution. Furthermore, if the coating amount distribution of the coating liquid varies locally due to factors other than the deflection of the gravure roll 2, the contact pressure of the doctor blade 11 can be locally increased or decreased by adjusting the length of the segmented blade corresponding to the part where the coating amount distribution of the coating liquid varies. Therefore, if localized band-like coating unevenness is observed in the coating film on the web 10, it is possible to eliminate the band-like coating unevenness by locally adjusting the contact pressure of the doctor blade 11.

[0020] In this embodiment, the upper backup blade 15 is composed of 12 segmented blades 14a-14l. However, the number of segmented blades, i.e., the number of segments of the upper backup blade 15, is preferably set according to the width of band-like coating irregularities that occur in the coating film. Specifically, when the coating width of the gravure roll 2 is W1 and the width of band-like coating irregularities that occur in the coating film applied by the gravure roll 2 is W2, the number of segmented blades is preferably W1 / W2 or greater. If multiple band-like coating irregularities occur in the coating film, W2 is defined as the width of the narrowest band-like coating irregularity. For example, if the width W2 of the band-like coating irregularity is half the coating width W1, the number of segmented blades is preferably two or more. If the width W2 of the band-like coating irregularity is 1 / 20 of the coating width W1, the number of segmented blades is preferably 20 or more. By setting the number of segmented blades of the upper backup blade 15 according to the width of the band-like coating irregularities that occur, the contact pressure of the doctor blade 11 can be finely adjusted to correspond to the portion of the band-like coating irregularity that occurs.

[0021] The backup blade consisting of multiple split blades may be provided on one side or both sides of the doctor blade 11. However, since the bending of the doctor blade 11 starts from the tip of the upper backup blade 15, it is preferable to provide the backup blade on the side of both sides of the doctor blade 11 that does not face the gravure roll 2, as in the doctor device 6a according to this embodiment.

[0022] As described above, the upper backup blade 15 according to this embodiment includes a plurality of divided blades 14a to 14l. By setting the length 1 of each of the divided blades 14a to 14l in accordance with the condition of the coating surface (presence or absence of band-like coating unevenness), it is possible to make the distribution of the coating amount of the coating liquid uniform in the width direction and reduce coating unevenness.

[0023] (Second embodiment) 4 is a plan view of a doctor device according to the second embodiment. The following description will focus on the differences between this embodiment and the first embodiment.

[0024] The doctor device 6b according to this embodiment includes the same components as the doctor device 6a according to the first embodiment, but also includes a holding mechanism for holding the split blades 14a to 14l so that the tip positions of the split blades 14a to 14l can be adjusted. In this embodiment, the holding mechanism is comprised of an upper holder 12 and multiple adjustment screws 19. The upper holder 12 is provided with multiple elongated holes 18 corresponding to the split blades 14a to 14l and extending parallel to the split blades 14a to 14l. Each of the adjustment screws 19 passes through the elongated holes 18, allowing each of the split blades 14a to 14l to be fixed to the upper holder 12. The tip positions of the split blades 14a to 14l are adjusted by loosening the adjustment screws 19 and sliding the split blades along their length. After adjusting the tip positions of the split blades 14a to 14l, the adjustment screws 19 can be tightened to fix the split blades 14a to 14l to the upper holder 12.

[0025] In the doctor unit 6b according to this embodiment, the length l of each of the divided blades 14a to 14l can be easily adjusted. Therefore, the distribution of the coating amount of the coating liquid in the width direction can be appropriately adjusted depending on the condition of the coating surface. For example, the gravure roll 2 can be adjusted depending on the condition of the coating surface. The distribution of the amount of coating liquid applied across the width may vary depending on the type of coating, but when uneven coating occurs on the coating surface, the contact pressure of the doctor blade 11 against the gravure roll 2 can be partially changed by adjusting the positions of the tips of the divided blades 14a to 14l, thereby making it possible to uniformize the distribution of the amount of coating liquid applied. [Example]

[0026] Examples of specific implementations of the present invention will be described below.

[0027] FIG. 5 is a diagram showing definitions of values used in the description of the embodiment.

[0028] In the following description, the length of the backup blade protruding from the upper blade holder is l, the length of the doctor blade protruding from the blade holder is L, and the ratio α of the difference between the length of the doctor blade and the length of the backup blade to the length of the doctor blade is (Ll) / L. Also, the contact pressure of the tip of the backup blade against the gravure roll is T.

[0029] First, when a cured film was formed by applying a coating liquid to a transparent substrate using a backup blade with a constant protruding length from the doctor holder, it was confirmed that the film thickness tended to vary depending on the position in the longitudinal direction of the gravure roll (the width direction of the transparent substrate).

[0030] Figure 6 is a diagram illustrating a method for measuring the thickness of a coating film applied using a conventional backup blade. More specifically, Figure 6(a) is a schematic diagram showing the general configuration of a gravure coater equipped with a conventional backup blade, and Figure 6(b) is a diagram illustrating measurement points P1 to P30 for the thickness of a cured coating film.

[0031] The gravure roll used was a microgravure roll with a diameter of 50 mm and a length of 1500 mm, with a hard chrome-plated iron core. The doctor blade was a rectangular metal plate with a thickness of 70 μm and a Vickers hardness of 650 Hv. The backup blade was a rectangular metal plate with a thickness of 0.8 mm. Using a microgravure coater (see FIG. 6(a)) equipped with the microgravure roll, doctor blade, and backup blade, a low refractive index layer-forming coating liquid containing UV-curable acrylic resin, hollow silica microparticles, a photopolymerization initiator, and a solvent was applied to a film thickness of 100 nm after curing. The coating was then cured by UV irradiation to form a low refractive index layer.

[0032] After forming the low refractive index layer, the reflectance spectrum of the low refractive index layer (cured film) at 30 measurement points P1 to P30 (see Figure 6(b)) on the film was measured using a Filmetrics spectral film measurement system. The film thickness of the low refractive index layer at measurement points P1 to P30 was calculated from the refractive index of the cured film (known value) and the wavelength at which the reflectance of the reflection spectrum was minimized. Measurement points P1 to P30 were aligned at 50 mm intervals in the width direction (TD) of the film, and measurement point P1 was located 50 mm away in the width direction of the film from point P0, which corresponds to one end of the tip edge of the doctor blade during coating (origin O shown in Figure 6(a)).

[0033] Figure 7 shows the film thickness ratio t / t at each measurement point measured using the backup blade shown in Figure 6(a). ave In Fig. 7, the horizontal axis represents the distance from point P0, which corresponds to the origin O of the backup blade, to each measurement point, and the vertical axis represents the film thickness t at each measurement point relative to the average film thickness t of all measurement points. ave Film thickness ratio t / t ave Represents.

[0034] Because the gravure roll is bent downward, the contact pressure of the doctor blade against the gravure roll is smaller at the center of the gravure roll than at both ends of the gravure roll. As a result, the thickness of the cured film is thicker at the center of the gravure roll than at both ends of the gravure roll, as shown in Figure 7. It was confirmed that the thickness tends to be thicker at the center of the gravure roll.

[0035] Next, the relationship between the contact pressure against the gravure roll, the film thickness, and the protrusion amount (ratio α) of the divided blade was investigated using a conventional backup blade and a backup blade according to the present invention.

[0036] Figure 8 is a schematic diagram showing a method for measuring the contact pressure of a doctor blade against a gravure roll. More specifically, Figure 8(a) shows the method for measuring the contact pressure using a conventional backup blade, and Figure 8(b) shows the method for measuring the contact pressure using a prototype backup blade consisting of multiple split blades.

[0037] In both measurements shown in Figures 8(a) and 8(b), a microgravure roll with a diameter of 50 mm and a length of 1500 mm and a hard chrome-plated iron core was used as the gravure roll. A rectangular metal plate (1500 mm wide) with a thickness of 70 μm and a Vickers hardness of 650 Hv was used as the doctor blade. The contact pressure of the doctor blade tip against the gravure roll was measured using a pressure sensor (a squeegee balance measuring device manufactured by NewLuon Instrument Precision Industry Co., Ltd.).

[0038] The backup blade shown in Figure 8(a) is a single rectangular metal plate with a thickness of 0.8 mm, and the length of the backup blade protruding from the doctor holder is constant. A pressure sensor was placed between the gravure roll and the doctor blade, and the cutting edge of the doctor blade was pressed against the pressure sensor with a predetermined pressure. The contact pressure was measured at 30 measurement points Q1 to Q30 on the pressure sensor. Measurement points Q1 to Q30 were aligned at 50 mm intervals along the cutting edge of the doctor blade, and measurement point Q1 was located 50 mm away from one end of the cutting edge of the doctor blade (origin O shown in Figure 8(a)) toward the other end of the cutting edge of the doctor blade.

[0039] The prototype backup blade shown in Figure 8(b) is composed of 10 split blades (150 mm wide) obtained by dividing the conventional backup blade shown in Figure 8(a) equally across the width. The position of the cutting edge of each split blade was adjusted so that the protruding length l of the 10 split blades from the doctor holder increased from both ends of the gravure roll toward the center, and the α (= (Ll) / L) of each split blade was set to the value shown in Figure 8(b). As in the measurements using the conventional backup blade, a pressure sensor was placed between the gravure roll and the doctor blade, and the cutting edge of the doctor blade was pressed against the pressure sensor with the same pressure as in the measurements using the conventional backup blade. The contact pressure was measured at 30 measurement points Q1 to Q30 on the pressure sensor.

[0040] Figure 9 is a scatter plot of the contact pressure ratio T / Tave at each measurement point measured using the backup blade shown in Figures 8(a) and 8(b). In Figure 8, the horizontal axis represents the distance from the origin O of the backup blade to each measurement point, and the vertical axis represents the contact pressure T at each measurement point relative to the average contact pressure T of all measurement points. ave This represents the contact pressure ratio, calculated by dividing the contact pressure by the doctor blade by the gravure roll. When a conventional backup blade was used, the contact pressure of the doctor blade against the gravure roll (white circles) was smaller at the center of the gravure roll than at both ends of the gravure roll. However, when the prototype backup blade shown in Figure 8(b) was used, the contact pressure of the doctor blade against the gravure roll (black circles) could be made larger at the center of the gravure roll than at both ends of the gravure roll.

[0041] Next, using the prototype backup blade shown in Figure 8(b), the doctor blade contact pressure T was measured multiple times at measurement points Q1 to Q30 using the method described above. Figure 10 shows the relationship between the value of α and the contact pressure ratio T / T ave The scatter plot of the measured values is shown below. The following equation (1) was obtained from the data in the figure using power approximation. T / T ave =0.0911α -1.446 ···(1)

[0042] Next, the relationship between the doctor blade contact pressure and the thickness of the cured film was investigated using the prototype backup blade shown in Figure 8(b).

[0043] Using the prototype backup blade shown in Figure 8(b), a pressure sensor was placed between the gravure roll and the doctor blade, and the backup blade was pressed against the gravure roll with a predetermined pressure to measure the contact pressure of the doctor blade at measurement points Q1 to Q30. The pressure sensor was then removed, and the doctor blade was pressed against the gravure roll with the same pressure to coat the transparent substrate with the above-described low-refractive-index layer-forming coating liquid, and the coating was cured to form a low-refractive-index layer. The film thickness of the low-refractive-index layer was measured at measurement points P1 to P30 using the method described above.

[0044] Figure 11 shows the film thickness ratio t / t ave and contact pressure ratio T / T ave As shown in Figure 11, the contact pressure ratio T / T ave When the thickness ratio of the cured film decreases, the thickness ratio of the cured film decreases. ave The contact pressure ratio T / T ave As the thickness ratio of the cured film increases, ave There was a tendency for this to decrease.

[0045] Figure 12 shows the film thickness ratio t / t ave and contact pressure ratio T / T ave As shown in Figure 12, the film thickness ratio t / t ave and contact pressure ratio T / T ave There is a negative correlation between the two, and the following equation (2) was obtained by linear approximation. T / T ave =-0.1103(T / T ave )+1.1113 (2)

[0046] From the above formulas (1) and (2), the film thickness ratio t / t ave The relationship between the ratio α and the temperature is expressed by the following equation (3). T / T ave=-0.010048α -1.446 +1.1113 (3)

[0047] FIG. 13 shows the relationship between α at each measurement position shown in FIG. 8(b) and the membrane pressure ratio t / t corresponding to each measurement position shown in FIG. 11. ave 13 shows a scatter diagram in which α and t / t are plotted. In addition, the curve expressed by the above formula (3) is also shown by a dashed line in Fig. 13. From Fig. 13, it can be seen that formula (3) is a function of α and the membrane pressure ratio t / t ave It can be seen that this is an approximate expression of the relationship between

[0048] From the above, it was confirmed that the film thickness of the prototype backup blade can be adjusted by adjusting the value of α, i.e., the protruding length l of the divided blade.

[0049] Next, we investigated the relationship between the difference in thickness of the coating film formed using the prototype backup blade (Fig. 8(b)) and the coating film formed under the same conditions using the conventional backup blade (Fig. 8(a)), and the value of α for the segmented blade.

[0050] A low refractive index layer was applied to the film under the same conditions using the prototype backup blade (Fig. 8(b)) and the conventional backup blade (Fig. 8(a)). The coating was cured by UV irradiation, and the thickness of the cured film was measured at each measurement point Q1 to Q30. From the measurements, the thickness ratio t / t when the prototype backup blade was used was ave and the film thickness ratio tref / tref when using a conventional backup blade. ave difference (T / T ave -tref / tref ave ) was calculated.

[0051] Figure 14 shows the values of α at each measurement point of the prototype backup blade and the (t / t ave -tref / tref ave The following equation (4) was obtained from the data of the scatter diagram by polynomial approximation (3rd order): Ta. t / ave -tref / tref ave =-25.584α 3 +24.474α 2 -8.0398α+0.8319 (4)

[0052] The real solution α of equation (4) is expressed by the following equation (5) using the formula for solving a cubic equation. α=e+[f / g+(3h) 1 / 2 / i)] 1 / 3 +[f / g-(3h) 1 / 2 / i)] 1 / 3 ···(5) When the coefficients of each term in equation (4) are a=-25.584, b=24.474, c=-8.0398, and d=0.8319, e to i in equation (5) above are expressed by the following equations. e=-b / 3a f=-2b 3 +9abc-27a 2 ×[d-(t / t ave -tref / tref ave )] g=54a 3 h=27a 2 d 2 -18abcd+4b 3 ×[d-(t / t ave -tref / tref ave )]+4ac 3 -b 2 c 2 i=18a 2

[0053] FIG. 15 shows a scatter diagram in which the vertical and horizontal axes of FIG. 14 are interchanged, and the curve expressed by equation (5) is also shown by a dashed line.

[0054] The derived equation (5) represents the value of α corresponding to the difference between the film thickness ratio when the prototype backup blade shown in Figure 8(b) is used and the film thickness ratio when the conventional backup blade shown in Figure 8(a) is used. Therefore, we will explain how to calculate the optimal ratio α (the ratio of the difference between the doctor blade L and the segment blade length l to the doctor blade length L) using the derived equation (5). When calculating the value of the ratio α using equation (5), t / t ave The ideal film thickness (design film thickness) is substituted into . In addition, the coating liquid is applied and cured using one backup blade as shown in Figure 8(a), and the film thickness of the cured film at each measurement point is measured. The film thickness of the cured film at each measurement point is calculated as tref / tref ave By substituting the above, the ideal value of α at each measurement point can be calculated from equation (5).

[0055] FIG. 16 is a diagram showing the ratio of the lengths of the divided blades constituting the backup blade according to the embodiment, and FIG. 17 is a scatter plot showing the film thickness ratio of the low refractive index layers formed by applying the coating liquid for forming the low refractive index layer using the backup blade according to the embodiment and a conventional backup blade.

[0056] As shown in Fig. 15, the backup blade according to the example was composed of 30 divided blades, each 50 mm wide. First, a coating liquid for forming a low refractive index layer was applied to a transparent substrate using the backup blade shown in Fig. 8(a), and the coating was cured to form a low refractive index layer. The film thickness of the low refractive index layer was then measured at measurement points Q1 to Q30. Using the obtained measured values and the designed film thickness of the low refractive index layer, the value of α for each divided blade (corresponding to measurement points Q1 to Q30) was calculated from equation (5). The calculated value of α for each divided blade was as shown in Fig. 15 (vertical axis).

[0057] Based on the calculated α value, each divided blade was fixed to a doctor holder, a low refractive index forming coating liquid was applied to a transparent substrate, the coating film was cured, and the film thickness of the low refractive index layer was measured at measurement points Q1 to Q30. Also, a conventional backup blade was used to apply a low refractive index forming coating liquid to a transparent substrate under the same conditions, and after curing the coating film, the film thickness of the low refractive index layer was measured at measurement points Q1 to Q30.

[0058] When coating was performed using one backup blade, the thickness of the cured film was thicker at the center of the gravure roll than at both ends of the gravure roll, as shown by the white circles in Figure 17. In contrast, when coating was performed using the backup blade according to the embodiment (Fig. 16), the film thickness ratio t / t ave became almost constant, the distribution of the coating amount of the coating liquid in the width direction was made uniform, and coating unevenness of the coating liquid was reduced. [Industrial Applicability]

[0059] The present invention can be used in a doctor device used for gravure coating and a gravure coating device equipped with the doctor device. [Explanation of symbols]

[0060] 1 Gravure coating device 2 Gravure Roll 5 Coating fluid supply section 6(6a, 6b) Doctor device 11 Doctor Blade 12 Upper holder 13 Lower holder 14 split blades 15 Upper backup blade 18 long hole 19 Adjustment screw

Claims

1. Doctor blade and a doctor holder for holding the doctor blade; a backup blade sandwiched between at least one surface of the doctor blade and the doctor holder, The backup blade is a plurality of divided blades each having a width smaller than that of the doctor blade and arranged side by side in the width direction of the doctor blade; A doctor device characterized in that the length of the split blades projecting from the doctor holder is longer at the center than at both ends in the width direction of the doctor blade.

2. The doctor blade is used to scrape off excess coating liquid from the surface of the gravure roll, 2. The doctor device according to claim 1, wherein the number of the divided blades is equal to or greater than W1 / W2, where W1 is the coating width of the gravure roll and W2 is the width of band-like coating irregularities occurring in the coating film applied by the gravure roll.

3. 3. The doctor device according to claim 1, wherein the backup blade is provided on one of both surfaces of the doctor blade that does not face the gravure roll.

4. 4. The doctor device according to claim 1, further comprising a holding mechanism for holding each of the plurality of divided blades so that the distance from the tip of each of the plurality of divided blades to the cutting edge of the doctor blade is variable.

5. Gravure roll and a coating liquid supply unit that supplies a coating liquid to the gravure roll; Doctor blade and a doctor holder for holding the doctor blade; a backup blade sandwiched between at least one surface of the doctor blade and the doctor holder, The backup blade is a plurality of divided blades each having a width smaller than that of the doctor blade and arranged side by side in the width direction of the doctor blade; 10. A gravure coating device, wherein the length of the split blades projecting from the doctor holder is longer at a central portion than at both end portions in the width direction of the doctor blade.

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