Gravure roll evaluation method

Abstract

To control accurately a film thickness in a gravure roll; and to provide an evaluation method thereof.SOLUTION: In an evaluation method of a roll 1 having recesses and protrusions 4 formed alternately on the surface and coating coating liquid by approaching or contacting, while rotating, the surface of a traveling coated matter W, a surface contour line on a cross section of a protrusion part 41 at a constant height or higher from the bottom of the recesses and protrusions 4 is compared with a quadratic function most closely approximated thereto, and the roll 1 is evaluated based on the determined coefficients.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This technology relates to a method for evaluating rolls in gravure coater-type coating devices. [Background technology]

[0002] This type of coating device uses a roll with a surface that is unevenly formed by engraving, etc. The uneven shape can be of various shapes, such as oblique, trapezoidal, pyramidal, and tortoiseshell shapes, and oblique rolls are said to be suitable for thin film coating.

[0003] During coating, a roll containing coating liquid in the concave portions of the uneven surface is rotated close to or in contact with the surface of the object to be coated, such as a web. This applies the coating liquid to the surface of the object. Note that the shape of the uneven surface is not directly transferred to the object; rather, the coating liquid on the object is leveled due to factors such as the speed difference between the object and the roll during coating and the spreading of the coating liquid until it dries, resulting in the formation of a uniform coating film.

[0004] The coating film thus formed on the surface of the substrate must be uniform in thickness. If the coating film thickness is not uniform, defects in appearance will occur, such as rainbow coloring when exposed to light. The allowable film thickness difference to suppress rainbow coloring is within 5 to 10 nm.

[0005] Conventionally, in order to achieve this allowable film thickness difference, various controls have been implemented, such as suppressing roll deflection and rotational runout, controlling the precision of the gap between the roll and the workpiece, and improving the uniformity of the roll's unevenness, as well as adjusting the coating liquid formulation, drying conditions, and liquid supply device. [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-249186 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] However, even with the above-mentioned control, there are cases where the uniformity of the coating thickness is not improved, and the cause of this is desired to be elucidated.

[0007] As a result of extensive research, the present inventors have found that one of the causes of this is the uneven shape of the roll surface, and have completed a roll that can accurately control the film thickness and a method for evaluating the same. [Means for solving the problem]

[0008] That is, the present invention provides a method for evaluating a roll having alternating concave and convex surfaces which applies a coating liquid to the surface of a traveling workpiece while rotating in contact with or in close proximity to the surface, and which is characterized in that the surface contour line in the cross section of the convex portion located at a certain height or more from the bottom of the valley of the convex and concave portions is compared with a quadratic function which most closely approximates this, and the roll is evaluated based on the coefficient of determination.

[0009] The unique feature of the present invention is that it focuses on quadratic functions. By controlling the roll using this simple evaluation method, it is possible to effectively suppress unevenness in the coating film caused by surface irregularities.

[0010] To eliminate the above-mentioned defects in appearance, that is, to make the allowable film thickness difference within 5 to 10 nm, a roll with the coefficient of determination of 0.985 or more, more preferably 0.995 or more, should be considered suitable. [Effects of the Invention]

[0011] As described above, according to the present invention, it is possible to effectively suppress unevenness in the coating thickness caused by unevenness on the roll surface. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a partial schematic view of a coating device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a side view of the roll of the embodiment. [Figure 3] FIG. 4 is a diagram showing the concave and convex shape of the same embodiment. [Figure 4] 5A to 5C are explanatory diagrams showing a method for calculating the shape of a convex portion from the measurement results obtained by a surface roughness meter in the embodiment. [Figure 5] 1 is a photographed image showing the difference between a coating film produced by the roll of the present embodiment and a coating film produced by a conventional roll. [Figure 6] 10 is another photographed image showing the difference between the coating film produced by the roll of the present embodiment and the coating film produced by the conventional roll. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] The coating device according to this embodiment is of the so-called reverse coater type, and as shown in FIG. 1, it comprises a roll 1 that rotates while being close to or in contact with a continuously running web W, and a liquid supply mechanism 2 that supplies a coating liquid to the surface of this roll 1, and applies the coating liquid on the roll surface to the web W to form a coating film.

[0015] The web W is a silicone film in this example, but may be any sheet-like material such as a resin film, paper, metal strip, etc. Reference numerals 31 and 32 in the figure are support rollers that guide the web W along.

[0016] As shown in FIG. 2, the roll 1 has an oblique line shape in which concave and convex portions 4 are formed alternately at a constant pitch by milling on the entire side peripheral surface (except for both ends). In this embodiment, the angle of inclination of the oblique lines of the irregularities 4 relative to the central axis of the roll 1 is 60°, but it is not limited to this and may be, for example, in the range of 45° to 75°. Here, the irregularities 4 have a mesh of #180 (pitch of 0.141 mm) and the height of the convex portions 41 (depth of the concave portions 42) is 0.035 mm. However, the mesh and depth of the irregularities 4 are not limited to these. For example, meshes of #120 to #250 are also available.

[0017] The liquid supply mechanism 2 here includes a doctor chamber 21 which is a liquid storage structure provided so as to be in contact with the roll 1, and a pump 22 which supplies the coating liquid to the doctor chamber 21.

[0018] In this embodiment, as shown in Figure 3, when the irregularities 4 of the roll 1 are viewed in a cross section cut perpendicular to the diagonal direction (extension direction of the grooves), the surface contour of the convex parts 41 (diagonal parts in the figure) that are at a certain height or more from the bottom of the valleys of the irregularities 4 has a coefficient of determination of 0.985 or more for the quadratic function that most closely approximates this.

[0019] To explain the specific evaluation procedure, first, the irregularities 4 of the manufactured roll 1 are measured using a surface roughness meter. Here, the irregularities 4 are measured along the central axis of the roll 1, and in this primary measurement, the shape of the convex portions 41 is not bilaterally symmetrical, but is biased to either the left or right, as shown in Figure 4.

[0020] On the other hand, since the positions of the valley bottoms can be measured correctly, the convex portion shape obtained by the primary measurement and the inverted convex portion shape obtained by flipping it left and right are superimposed so that the valley bottoms match, and the average shape is calculated to determine the surface contour of the convex portion 41.

[0021] The surface contour of the upper 30% of the height of the convex portion identified in this way (the shaded area in Figure 3) is determined to be a suitable roll if the coefficient of determination for the quadratic function that most closely approximates this is 0.985 or greater.

[0022] An example of the difference in coating between such a roll 1 and a conventional roll is shown in Figs. 5 and 6.

[0023] 5 and 6, (a) shows an image of the coating film captured by the roll 1 of this embodiment, and (b) shows an image of the coating film captured by a conventional roll.

[0024] The coating liquid in Figure 5 is based on silicone and contains at least toluene and methyl ethyl ketone as additives. The coating liquid in Figure 6 is based on silicone and contains at least toluene, methyl ethyl ketone, and heptane as additives. Both result in transparent coating films.

[0025] The coefficient of determination for the roll 1 of this embodiment in this comparative example is 0.9987. On the other hand, the conventional roll has an oblique line shape with the same pitch and oblique line angle as the roll of this embodiment, except that the cross-sectional shape of the concave and convex portions is approximately trapezoidal. Incidentally, the coefficient of determination for the quadratic function of the convex portion of this conventional roll is 0.9658.

[0026] Naturally, all coating conditions such as web running speed and roll rotation speed were kept the same for the comparison.

[0027] If the coating film has uneven thickness and develops rainbow colors when irradiated with light, a band-like rainbow pattern (5 mm to 50 mm wide) will appear in the captured image.

[0028] Although it is somewhat difficult to see because the images are close to monotone, comparing (a) and (b) makes it clear that the image of the roll 1 of this embodiment does not contain thin vertical streaks that represent a rainbow pattern, whereas the image of the conventional roll does contain thin vertical streaks that represent a rainbow pattern. This clearly shows that the roll 1 of this embodiment improves the uniformity of the coating thickness.

[0029] Furthermore, when other oblique rolls with different pitches (mesh) were evaluated, it was found that film thickness uniformity could be ensured even with coefficients of determination of 0.9957 and 0.989.

[0030] Therefore, as mentioned above, a roll is deemed suitable if the surface contour of the convex portion in the upper 30% of the height has a coefficient of determination of 0.985 or more for the quadratic function that most closely approximates this.

[0031] The present invention is not limited to the above-described embodiment.

[0032] For example, the coefficient of determination is more preferably 0.995 or higher. The convex portion for calculating the coefficient of determination for a quadratic function is not limited to the upper 30%. It may be 15% to 50%. More preferably, it may be 20% to 40%, and even more preferably, it may be 25% to 35%.

[0033] The method for measuring the unevenness during evaluation may be to move the surface roughness meter in a direction perpendicular to the oblique line. The surface roughness meter may be of any type, such as a non-contact type or a stylus type.

[0034] In the above embodiment, the present invention is applied to a reverse coater as a coating device, but it may also be applied to a forward-direction type coating device in which the roll rotation direction is the same as the traveling direction of the object to be coated.

[0035] The present invention is not limited to the above-described embodiment, and various modifications are possible. [Explanation of symbols]

[0036] W···Coated object (web) 1 roll 4...Unevenness 41...Convex part

Claims

1. A method for evaluating a roll having alternating concave and convex surfaces that applies a coating liquid to a traveling surface of a workpiece while rotating in close proximity to or in contact with the surface, comprising the steps of: A method for evaluating a roll, characterized in that the surface contour line in the cross section of the convex portion located at a certain height or more from the bottom of the valley of the unevenness is compared with the quadratic function that most closely approximates the surface contour line, and the roll is evaluated based on the coefficient of determination.

2. The roll evaluation method according to claim 1, wherein a roll having a coefficient of determination of 0.985 or more is deemed to be suitable.

3. A roll with alternating concave and convex surfaces that applies a coating liquid to a moving object while rotating and in close proximity to or in contact with the object. A roll characterized in that the surface contour line in a cross section of a convex portion located at a certain height or more from the bottom of the valley of the unevenness has a coefficient of determination of 0.985 or more for a quadratic function that most closely approximates the surface contour line.

4. A coating device comprising the roll according to claim 3.

Images