JP6236991B2 - Coating method and coating apparatus - Google Patents

Description

  The present invention relates to a coating method having excellent smoothness of a coating film and little change in coating thickness over time, and a coating apparatus for realizing the coating method.

  In general, coating is performed by applying a coating liquid to the surface of a web such as a resin film to provide functions such as easy adhesion and slipperiness. In recent years, a method capable of coating a thin film at high speed has been demanded due to the demand for cost reduction.

  A gravure roll type coating method is generally known as such a coating method. This method is a method in which a coating liquid is measured using a gravure roll having fine irregularities on the surface and applied to the web surface, and can be applied at a high speed. Moreover, since there are few components of an apparatus, equipment cost is low, handling is easy, and it is used in the wide field | area.

  However, in recent years, as the functionality of coating films has increased, it has been required to improve the smoothness of the coating film in order to maintain the uniformity of the function, and it is very important to manage the coating thickness stably in the coating process. It has become.

  Under such circumstances, the gravure can be measured while keeping the liquid level constant, and to maintain the constant coating amount in order to solve the decrease in the coating amount due to clogging of the gravure cell. A coating method has been proposed (Patent Document 1).

  In addition, when coating various coating liquids with a coating roll, particularly a gravure roll, ultrasonic cleaning is applied to the coating liquid instead of cleaning the roll after clogging of the recess (cell part) occurs. Thus, there has been proposed a coating method in which clogging of a concave portion (cell portion) of a coating roll during coating, particularly a gravure roll, is prevented in advance and a stable coating amount is obtained (Patent Document 2).

JP 2010-264398 A Japanese Patent Laid-Open No. 7-907

  The gravure coating method described in Patent Document 1 can maintain a stable coating liquid consumption per hour by controlling the gravure roll speed so that the weight of the coating liquid in the apparatus becomes constant. However, it is not sufficient for maintaining a stable coating thickness of the web surface over time, and no consideration is given to preventing clogging of the gravure cell itself.

  The coating method described in Patent Document 2 can prevent the coating liquid from being hardened by applying ultrasonic vibration to the coating liquid, and can suppress clogging of the concave portion (cell part) of the gravure roll. However, no consideration is given to preventing clogging of the gravure cell itself.

  An object of the present invention is to provide a coating method that is excellent in smoothness of a coating film and has little change with time in coating thickness, and a coating apparatus that realizes the coating method.

  In the coating method of the present invention, at least one surface of a continuously running web is contact-transferred from a gravure roll cell rotating with a speed difference relative to the speed of the web to contact the web. A gravure roll to be used is surrounded by a high bank and a low bank to form a cell. The height a from the bottom of the cell to the high bank and the bottom of the cell are low. The ratio b / a to the height b up to the bank is 0.10 or more and 0.60 or less.

  The coating apparatus of the present invention is an apparatus for forming a continuous coating film by bringing a coating liquid into contact with a web from a rotating gravure roll cell on the surface of a continuously running web. A cell is formed by being surrounded by a high bank and a low bank, and a ratio b / a of a height a from the bottom of the cell to the high bank and a height b from the bottom of the cell to the low bank is 0.10. It is above 0.60.

  INDUSTRIAL APPLICABILITY According to the present invention, there are provided a coating method excellent in smoothness of a coating film and little change in coating thickness with time, and a coating apparatus for realizing the coating method.

  More specifically, in a gravure roll type coating method capable of high-speed coating, the gravure cell has a wide allowable range of coating liquid viscosity, excellent smoothness of the coating film, and excellent transferability of the coating liquid to the web. Because it can reduce the cleaning work due to clogging, and there is little change in coating thickness over time, it can be used suitably for various coatings that apply various coating liquids to the surface of webs such as resin films to provide high functionality with coating films. Can do.

FIG. 1 is a schematic three-dimensional view of a gravure cell in the present invention. FIG. 2 is a schematic plan view of FIG. FIG. 3 shows a schematic cross-sectional view when sectioned along the cross section A (dotted line portion) and the cross section B (dotted line portion) in FIGS. 1 and 2. FIG. 4 is a schematic diagram showing a line angle formed by the rotation direction of the gravure roll and the engraving direction of the cell. FIG. 5 is a schematic cross-sectional view of the coating apparatus of the present invention as seen from the direction orthogonal to the roll rotation axis. FIG. 6 is a schematic diagram for illustrating and explaining the gravure cell in the present invention and the cell type used in the comparative example.

  Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the drawings.

  The coating apparatus of the present invention is an apparatus for forming a continuous coating film by transferring a coating liquid from a rotating gravure roll cell to the web on the surface of a continuously running web. As the gravure roll, a gravure roll having a special surface shape described later is adopted.

  Then, the coating method of the present invention is a gravure roll cell that rotates on at least one surface of a continuously running web with a speed difference relative to the speed of the web using the coating apparatus of the present invention. Then, the coating solution is transferred to the web to form a continuous coating film.

  FIG. 5 shows a reverse coat method as an example of the gravure roll method used in the present invention. The coating liquid 15 discharged from the coating liquid supply means 13 is applied excessively on the surface of the gravure roll 12, scraped off by the doctor blade 14 and measured. The measured coating liquid 15a is applied to the web 11 by the gravure roll 12 to form a coating film 15b having a predetermined film thickness.

  Moreover, as the shape (type) of the gravure cell engraved on the gravure roll for the purpose of measuring a certain amount of coating liquid, as shown in FIG. 6, a hybrid 16, a honeycomb 17, a helical 18 and the like can be mentioned. . Among these, in the present invention, a hybrid type is used in order to achieve both excellent smoothness of the coating film and stabilization of the coating thickness.

  The hybrid type cell shape used in the present invention is shown in FIGS. The hybrid type has a high bank 5 and a low bank 6 unlike the individual cell types, and the cell bottom 4 is formed so as to be surrounded by them, and an open cell shape with continuous peaks and valleys. It is.

  Here, the “bank” in the present invention refers to a convex portion surrounding the periphery of the concave portion for picking up the coating liquid in the gravure cell engraved with the concave and convex shapes for picking up the coating liquid on the surface of the gravure roll. Point to. That is, the concave portion of the gravure cell is a “dent” that stores the coating liquid, and the convex portion is a “bank” that surrounds the “dent” so that the coating liquid does not flow out.

  A cell of a general honeycomb type or a helical type is engraved in a concave shape, and ink is held in the concave portion. On the other hand, the hybrid type cell used in the present invention is engraved so as to leave a bank which is a convex portion, and retains ink between the bottom 4 of the cell and the lower bank 6. Therefore, the hybrid type cell is superior in the transferability of the coating liquid compared to the honeycomb type or helical type cell.

  In the present invention, as shown in FIG. 3, the height a from the cell bottom 4 to the high bank 5 (hereinafter referred to as the bank height a) and the height b from the cell bottom 4 to the low bank 6 (hereinafter referred to as the bank). A gravure roll having a ratio b / a to a height b) of 0.10 to 0.60 is used.

  When the bank height ratio b / a is less than 0.10, the inner wall height (bank height b) for storing the coating liquid is low, so the volume of the part for storing the coating liquid per cell unit is small. As a result, during the rotation of the gravure roll, the coating liquid may flow out of the cell before being applied to the web, and the smoothness of the coating film due to coating unevenness may be impaired. When the bank height ratio b / a exceeds 0.60, the inner wall height (bank height b) for storing the coating liquid increases, so that the surface tension generated at the cell inner wall also increases at the same time. As a result, the transferability of the coating liquid to the web decreases, the amount of coating liquid remaining in the cell recesses increases, clogging occurs, and the amount of coating liquid retained decreases over time, resulting in stable coating thickness. It may be damaged.

  In the present invention, the variation in the bank height ratio b / a is preferably less than 0.30. When the variation in the bank height ratio b / a exceeds 0.30, coating unevenness may occur in the coating film of the web.

  In the present invention, the bank height a of the gravure cell is preferably 5 μm or more and 150 μm or less. When the bank height a is less than 5 μm, the processing accuracy may deteriorate when performing cell processing. When the bank height a exceeds 150 μm, the amount of the coating liquid remaining in the cell recess increases, which may cause clogging or a decrease in the amount of the coating liquid retained over time, which may impair the stability of the coating thickness. .

  In the present invention, the variation in the bank height a is preferably less than 0.30. If the variation in the bank height a exceeds 0.30, coating unevenness may occur in the coating film of the web.

  In the present invention, as shown in FIG. 4, the line angle (acute angle) between the line 2 (a row) from the center of the high bank 5 of the gravure cell to the adjacent low bank 6 and the rotation direction 1 of the gravure roll, and the same It is preferable that each of the line angles (acute angles) between the line 2 ′ (line b) from the center of the high bank to the adjacent low bank in another direction and the rotation direction 1 of the gravure roll is less than 85 °. When the line angle is 85 ° or more, the low bank 6 with respect to the bottom 4 of the cell is positioned in the rotation direction 1 of the gravure roll. The smoothness of the coating film may be impaired. In FIG. 6, the rotation direction 1 of the gravure roll is drawn substantially parallel to the line connecting “high bank−cell bottom−high bank−cell bottom...”. Is not necessarily limited to this direction.

  In this invention, it is preferable that the area ratio of the opening part with respect to the whole surface of a gravure cell is 60% or more and 96% or less. When the area ratio of the opening is less than 60%, the distance between the concave portions of the gravure cell is increased, and uneven coating may occur in the coating film of the web. Moreover, there is no upper limit in particular about the area ratio of an opening part, However, Since an uneven | corrugated area | region will disappear physically, it is preferable that it is 96% or less practically.

  In the present invention, the gravure roll 12 rotates while approaching the web 11. Preferably, it rotates relatively. The term “relatively” means that the gravure roll 12 itself also rotates, but the traveling speed of the web 11 and the rotational speed of the gravure roll 12 do not coincide with each other so as not to leave a gravure pattern (that is, a trace of a recess) on the coating surface. It means that. The rotation direction can be selected from the same direction or the reverse direction as the conveyance direction of the web 11. However, in the present invention, from the viewpoint of realizing the smoothness of the coating film, as shown in FIG. 5, the reverse direction (also referred to as the reverse direction). Is preferred.

  As the material of the gravure roll 12, steel can be preferably used, and the surface is hard chrome, copper, nickel plated, or a composite plating of these, preferably ceramic is sprayed on the surface. Things are good. Accordingly, it is possible to prevent the gravure roll from being worn by the doctor blade 14 or the web 11 and to prevent the surface of the upper surface of the convex portion from being roughened. As a method for forming grooves or holes on the surface of the gravure roll, there are cutting, rolling, laser engraving and the like. In the present invention, laser engraving is a preferable method from the viewpoint of forming a highly accurate dimensional shape.

  In the present invention, the web 11 can be preferably used for other films such as a plastic film such as a thermoplastic resin film, paper, leather, and metal strip. Among these, a plastic film can be particularly preferably used.

  Examples of plastic films include polyolefin films (eg, polyethylene film, polypropylene film, etc.), polyester films (eg, polyethylene terephthalate film, polyethylene-2,6-naphthalate film, etc.), polyamide films (eg, nylon 6 film, nylon 66 film, etc.) A polycarbonate film, an acrylic film, etc. can be illustrated. Among these, it is more preferable to use a polyester film, especially a polyethylene terephthalate film. This is because the polyethylene terephthalate film has a low raw material cost and is excellent in mechanical properties, electrical properties, chemical resistance, and the like.

  In the present invention, the thickness of the web is preferably 1 to 2000 μm from the viewpoints of transportability and coatability. More preferably, it is 5-1000 micrometers. The speed of the web is preferably 5 to 1000 m / min from the viewpoints of transportability and coatability. More preferably, it is 10-400 m / min. The web tension is preferably 10 to 10,000 N / m. More preferably, it is 100-3000 N / m. When the tension of the web is less than 10 N / m, there may be an obstacle to stable running such as wrinkling of the web or meandering of the web. When the web tension exceeds 10,000 N / m, the web surface is easily damaged. The tension of the web can be controlled by, for example, a dancer roll or a system that drives the transport roll with a servo motor based on a signal from a tension meter.

  In the present invention, the coating liquid 15 has functional properties on the web surface, such as adhesiveness (easy adhesion, heat sealability), easy slipperiness (runnability), antistatic properties, conductivity, wear resistance, weather resistance, Coating liquid for surface treatment that provides releasability, chemical resistance (water resistance, solvent resistance), easy printability, flowability, antifouling properties, writing properties, light shielding properties, waterproof properties, gas barrier properties, etc. Anything can be used. As these coating solutions, known ones can be used.

  In this invention, it is preferable that the viscosity of the coating liquid applied is 0.6 mPa * s or more and 1000 mPa * s or less. More preferably, it is 10 mPa · s or more and 500 mPa · s or less. When the viscosity of the coating liquid is less than 0.6 mPa · s, the coating liquid may flow out of the cell before being applied to the web when the gravure roll rotates, and the smoothness of the coating film due to coating unevenness may be impaired. . When the viscosity of the coating liquid is larger than 1000 mPa · s, the coating liquid filled in the concave portion of the gravure cell is difficult to be transferred to the web, and the coating liquid remains in the concave portion of the cell and easily causes clogging.

  It is preferable to use this invention for application | coating in the manufacturing process of a plastic film especially. By using the in-line coating process in the manufacturing process, the manufacturing cost can be significantly reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated along an Example, this invention is not restrict | limited by these Examples. Various characteristics were measured by the following methods.

(1) Bank height A high bank height a was determined by measuring 7 in FIGS. 1 and 3 using a dot checker α600Z manufactured by YOMOTA KOKI Co., Ltd. Moreover, the low bank height b was determined by measuring 8 of FIG. 1, FIG.

(2) Unevenness of the bank height Using the dot checker α600Z manufactured by YOMOTA KOKI Co., Ltd., the high bank height a is measured at five locations at intervals of about 20 cm in the width direction of the gravure roll. The variation of a was calculated by the following formula.
・ Variation of bank height = (q max−q min) / q average
q max... Maximum value of bank height measured at 5 locations. q min... Minimum value of bank height measured at 5 locations. q average... Average value of bank height measured at 5 locations.

(3) Dispersion of bank height ratio b / a Using a dot checker α600Z manufactured by YOMOTA KIKOH Co., Ltd., a high bank height a and adjacent to it at five locations about 20 cm apart in the width direction of the gravure roll. A low bank height b was measured. Next, the bank height ratio b / a between the adjacent high bank height a and the low bank height b was calculated, and the variation of the bank height ratio b / a was calculated by the following formula.
・ Variation of bank height ratio b / a = x max−x min
x max... Maximum value of the bank height ratio b / a calculated at five locations. x min... Minimum value of the bank height ratio b / a calculated at five locations.

(4) Linear Density of Gravure Cell The number of lines per inch (2.54 cm) was calculated with the line 2 in FIG. 4 as one line, and the linear density of the gravure cell was determined.

(5) Line angle of gravure cell The line angle of the gravure cell was determined by measuring 3, 3 ′ in FIG. 4 using a dot checker α600Z manufactured by YOMOTA OPTICAL CO., LTD.

(6) Area ratio of the opening to the entire surface of the gravure cell Using the dot checker α600Z manufactured by YOMOTA OPTICAL CO., LTD., 5 in FIG. 1 and FIG. Bank area (unit: μm ² ), that is, the area of the plane portion located at the top of the high bank was measured. In addition, the linear density (line / inch) was measured at five locations at intervals of about 20 cm in the width direction of the gravure roll. Next, the average area of the five banks was y (μm ² ), the average line density of the five areas was z (line / inch), and the area ratio of the opening was calculated by the following formula.
-Area ratio (%) of opening part = {1- (y * z < ² >) / (2.54 * 10 < ⁴ >) < ² >} * 100.

(7) Cell volume of gravure cell Using a simple cell volume measurement system capaccha made by STEINHART, the cell volume is measured at five locations at intervals of about 20 cm in the width direction of the gravure roll, and the average value of the five locations is taken. This was the cell volume of the gravure cell.

(8) Viscosity of coating liquid The viscosity was measured according to JIS Z8803-1996 using a rheometer (manufactured by Rheotech Co., Ltd., RC20).

(9) Smoothness of coating film The coating is started at an initial coating thickness of 10 μm, and after 10 minutes from the start of coating, the width of the gravure roll using a fiber-type water film thickness meter RF-60-P manufactured by Kurashiki Boseki Co., Ltd. The coating thickness was measured at five locations at intervals of about 20 cm toward the direction, and the smoothness of the coating film was evaluated by the following formula and reference.
・ Coating thickness variation = (r max−r min) / r average
r max... Maximum value of coating thickness measured at 5 locations. r min... Minimum value of coating thickness measured at 5 locations. r average... Average value of coating thickness measured at 5 locations. Less than Δ: 0.15 or more and less than 0.20 x: More than 0.20.

(10) Stability of coating thickness The coating was started at an initial coating thickness of 10 μm, and 12 hours after the start of coating, the width of the gravure roll was measured using a fiber-type water film thickness meter RF-60-P manufactured by Kurashiki Boseki Co., Ltd. The coating thickness at the center position with respect to the direction was measured, and the stability of the coating thickness was evaluated according to the following criteria.
○: 9.0 μm or more (90% or more of the initial coating thickness)
X: Less than 9.0 μm (less than 90% of initial coating thickness).

Example 1
Using the coating method shown in FIG. 5, the web 11 made of a polyethylene terephthalate film having a width of 1000 mm and a thickness of 500 μm is rotated in the reverse direction with respect to the web while running at a tension of 1000 N / m in the direction of the arrow at 33 m / min. Application was performed using a gravure roll 12. The gravure roll 12 was provided with a coating liquid supply means 13 and a doctor blade 14.

  At the time of coating, the gravure roll was rotated so that its surface moved at 30 m / min in the reverse direction with respect to the web running direction. The speed difference between the web and the gravure roll was 63 m / min.

The gravure roll 12 is made of a roll whose base material is stainless steel having a diameter of 270 mm, and has a continuous groove (line angle (3) in FIG. Cell a row / rotary direction of gravure roll) 45 °, line angle 3 ′ in FIG. 4 (gravure cell b row / rotary direction of gravure roll) 45 °) is 250 per 2.54 cm in the rotation axis direction ( (Line density: 250 lines / inch), high bank height a is 70 μm, variation of high bank height a is 0.10, low bank height b is 35 μm, bank height ratio b / a is 0.50, bank A hybrid gravure cell having a height ratio b / a variation of 0.20, an area ratio of the opening to the entire surface of the gravure cell of 85%, and a cell volume of 20 cm ³ / m ² was obtained.

  For the coating solution, an aqueous polyester resin solution containing 20 wt% of an organic sulfonate group-containing polyester resin and having a viscosity of 50.0 mPa · s is adjusted to 10 μm on one side of the web 11 with a coating thickness immediately after coating and before drying. Application was started. The coating thickness immediately after coating and before drying was measured with a fiber type water film thickness meter RF-60-P manufactured by Kurashiki Boseki Co., Ltd.

(Example 2)
The web surface was coated in the same manner as in Example 1 except that the viscosity of the coating liquid was increased to 500.0 mPa · s with a thickener.

(Example 3)
5 except that the surface of the gravure roll 12 was rotated at 300 m / min in the reverse direction with respect to the film running direction while running the web 11 at a tension of 1000 N / m in the arrow direction of FIG. 5 at 330 m / min. In the same manner as in Example 1, the web surface was coated.

Example 4
The web surface was coated in the same manner as in Example 1 except that the gravure roll 12 cell had a bank height ratio b / a variation of 0.40.

(Comparative Example 1)
The web surface was coated in the same manner as in Example 3 except that the gravure roll 12 cell bank height ratio b / a was 0.06.

(Comparative Example 2)
The web surface was coated in the same manner as in Example 2 except that the gravure roll 12 cell bank height ratio b / a was 0.90.

(Comparative Example 3)
The web surface was coated in the same manner as in Example 3 except that the gravure roll 12 was of a helical type as indicated by 18 in FIG.

(Comparative Example 4)
The cell surface of the gravure roll 12 was coated on the web surface in the same manner as in Example 2 except that the cell type of the gravure roll 12 was a honeycomb type as shown in FIG.

  According to the present invention, in a gravure roll type coating method capable of high-speed coating, the tolerance of the coating liquid is wide, the coating film has excellent smoothness, and the coating liquid has excellent transferability to the web. Since it can reduce cleaning work due to clogging and there is little change in coating thickness over time, it can be used suitably for various coatings that apply various coating liquids to the surface of a web such as a resin film to provide high functionality with a coating film. .

1: Rotation direction of gravure roll 2, 2 ′: Cell engraving direction 3, 3 ′: Line angle 4: Cell bottom 5: High bank 6: Low bank 7: High bank height a
8: Low bank height b
11: Web 12: Gravure roll 13: Coating liquid supply means 14: Doctor blade 15: Coating liquid 16: Gravure cell type / hybrid 17: Gravure cell type / honeycomb 18: Gravure cell type / helical

Claims (9)

On at least one surface of the continuously running web, the coating liquid is contacted and transferred from the cell of the gravure roll rotating with a speed difference relative to the web speed to form a continuous coating film. In the coating method,
The gravure roll to be used has a plurality of cells surrounded by high and low banks on the surface of the roll, and each cell is formed.
The ratio b / a of the height b from the bottom of the cell to the lower bank from the bottom of the cell and the height a of up to the high bank is 0.10 to 0.60,
Coating method.   The coating method according to claim 1, wherein the variation in the ratio b / a is less than 0.30. The coating method according to claim 1 or 2, wherein a height a from the bottom of the cell to the high bank is 5 µm or more and 150 µm or less. The coating method according to claim 1, wherein a variation in height a from the bottom of the cell to the high bank is less than 0.30.   Line angle (acute angle) between the line from the center of the high bank to the adjacent low bank and the rotation direction of the gravure roll, and rotation of the line and gravure roll from the center of the same high bank to the adjacent low bank in another direction The coating method according to claim 1, wherein each of the line angles (acute angles) with the direction is less than 85 °.   The coating method according to any one of claims 1 to 5, wherein the area ratio of the opening to the entire surface of the gravure cell is 60% or more and 96% or less.   The coating method according to any one of claims 1 to 6, wherein the viscosity of the coating liquid to be applied is 0.6 mPa · s or more and 1000 mPa · s or less.   Coating method in any one of Claims 1-7 apply | coated within the manufacturing process of a plastic film. A coating apparatus for continuously transferring a coating liquid from a rotating gravure roll cell onto the surface of a continuously running web, thereby forming a continuous coating film,
The gravure roll has a plurality of cells surrounded by a high bank and a low bank on the surface of the roll to form each cell,
The ratio b / a of the height b from the bottom of the cell to the lower bank from the bottom of the cell and the height a of up to the high bank is 0.10 to 0.60,
Coating equipment.

Images