JP2018012056A - Manufacturing method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an optical film, which can suppress variation in optical characteristics of an obtained optical film, the variation being caused by unevenness in thickness of the manufactured optical film in a width direction resulting from unevenness of a coating thickness of a coating liquid in the width direction when coating the coating liquid widely (for example 3000 mm or more in width) by using a coating device to manufacture a wide optical film.SOLUTION: The manufacturing method of an optical film includes a coating process of continuously supplying a coating liquid containing a resin for forming a polarization film to a die 12 and coating a base material 1 with the coating liquid through the die 12. The coating process starts supply of the coating liquid to the die 12 in a state where a difference between the temperature of the die 12 and the temperature of the coating liquid is less than 1°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an optical film.

  As a method for producing an optical film (for example, a polarizing film or a retardation film), a method for producing an optical film by coating a substrate with a coating solution containing an optical film-forming resin and then drying the coating solution. Are known. In such a manufacturing method, a coating apparatus (for example, a die coater or the like) is used in the step of applying a coating liquid to a substrate (Patent Document 1).

JP 2012-75978 A

  However, in order to produce a wide optical film, when a coating liquid is applied with a wide width (for example, a width of 3000 mm or more) using a coating apparatus, the coating thickness of the coating liquid becomes uneven in the width direction, The thickness of the manufactured optical film may be non-uniform in the width direction. As a result, the optical properties of the obtained optical film may vary.

  The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a production method for producing an optical film having a uniform thickness.

The method for producing an optical film of the present invention is a coating process in which a coating liquid containing a resin for forming an optical film is continuously supplied to a die, and the coating liquid is applied to a substrate through the die. A method for producing an optical film, wherein the coating step is performed by supplying the coating liquid to the die in a state where the difference between the temperature of the die and the temperature of the coating liquid is less than 1 ° C. Including starting.
In one embodiment, the coating process starts supplying the coating liquid to the die in a state where the difference between the temperature of the die and the temperature of the coating liquid is 0.3 ° C. or less. Including that.
In one embodiment, the coating step is the die attached to a stage provided at a predetermined interval between the substrate and the dimension in the longitudinal direction of the discharge port of the die. Coating using the die attached so that the position of the end portion is movable relative to the stage in accordance with the change.
In one embodiment, the application process includes applying the application liquid with an application width of 2500 mm or more.
In one embodiment, the thickness of the optical film is 10 μm or less.
In one embodiment, a drying step of obtaining a long resin layer having a width corresponding to the longitudinal direction of the discharge port by drying the coating liquid applied to the base material, A treatment step of treating the resin layer as the optical film by performing a treatment, and in the coating step, a ratio of a difference between an end thickness and a central thickness with respect to an average thickness in a width direction Coating the coating liquid so that the amount of the liquid becomes 6% or less.
In one embodiment, the optical film is a polarizing film.

  According to the present invention, an optical film having a uniform thickness in the width direction can be produced.

It is a perspective view which shows the positional relationship of the die | dye and a base material in a coating process. (A)-(c) is sectional drawing for demonstrating the manufacturing method of the polarizing film of one Embodiment of this invention to process order. It is the schematic which shows the structure of the coating apparatus which can be used in embodiment of this invention. It is a figure which shows the shape change of die | dye when the temperature of die | dye rises. It is a figure which shows the displacement of the discharge outlet to the discharge direction after the coating process start. It is a perspective view which shows the positional relationship of a die | dye and a base material when a die | dye deform | transforms. The thickness distribution along the width direction of the PVA-type resin layer in the laminated body obtained at the coating process of the Example is shown. The thickness distribution along the width direction of the PVA-type resin layer in the laminated body obtained at the coating process of the comparative example is shown.

  An embodiment of the present invention will be described in detail with reference to FIGS. Below, the manufacturing method of the optical film of this invention is demonstrated taking the example of the polarizing film used for a liquid crystal display panel etc. as an optical film.

  The polarizing film is typically composed of a PVA resin film containing a dichroic substance such as iodine. Examples of the PVA resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. The thickness of the polarizing film is 25 μm or less, preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, and particularly preferably 5 μm or less. On the other hand, the thickness of the polarizing film is preferably 0.5 μm or more, more preferably 1.5 μm or more. Below, the manufacturing method of the polarizing film comprised with a PVA-type resin film is demonstrated.

<Production method of polarizing film>
FIG. 2A to FIG. 2C are cross-sectional views for explaining the manufacturing method of the polarizing film of this embodiment in the order of steps. As shown in FIGS. 2A to 2C, the manufacturing process of the polarizing film is performed by applying a coating liquid containing a PVA-based resin on one surface of the long substrate 1. Polarizing the PVA-based resin layer 2 ′ by applying a predetermined process to the PVA-based resin layer 2 ′ by drying the coating liquid after the coating process And a processing step for forming the film 2. Through the above process, the polarizing film 2 is manufactured as a part of the optical film laminate 10 including the polarizing film 2 and the substrate 1. Thereafter, the base material 1 may be peeled off from the polarizing film 2 or the base material 1 may be left as a protective film without peeling off the base material 1. The details of the method for producing such a polarizing film are described in, for example, JP-A-2012-73580. This publication is incorporated herein by reference in its entirety.

  The substrate 1 is typically formed of a thermoplastic resin such as a (meth) acrylic resin, an olefin resin, a norbornene resin, or a polyester resin. The thickness of the base material 1 is preferably 20 μm to 300 μm, more preferably 30 μm to 200 μm.

  The coating solution containing the PVA resin is typically an aqueous solution of a PVA resin in which the PVA resin is dissolved in a solvent (typically water). After the coating liquid is applied to the substrate 1, the PVA-based resin layer 2 'can be formed by drying the coating liquid under appropriate drying conditions.

  Examples of the predetermined treatment for forming the PVA-based resin layer 2 ′ into the polarizing film 2 include dyeing treatment, stretching treatment, insolubilization treatment, crosslinking treatment, washing treatment, and drying treatment. These processes can be appropriately selected depending on the purpose. Further, the processing order, the processing timing, the number of processings, and the like can be set as appropriate. In addition, as long as the PVA-type resin layer formed at the coating process can be used as a polarizing film, the process for obtaining the polarizing film may be omitted.

  Further, as shown in FIGS. 2A to 2C, the antistatic layer 3 is formed on the other surface of the substrate 1 (the surface opposite to the coating surface) before the coating process. May be. Thereby, blocking of the base material 1 in the process after a coating process can be suppressed. The antistatic layer 3 typically includes a conductive material such as a conductive polymer, and a binder resin such as a polyurethane resin. Examples of the conductive polymer include a polythiophene polymer, a polyacetylene polymer, a polydiacetylene polymer, and the like. The thickness of the antistatic layer 3 is preferably 0.1 μm to 10 μm, more preferably 0.2 μm to 2 μm. However, as described above, it is not always necessary to form the antistatic layer 3 on the substrate 1.

<Coating process>
In the coating process, a PVA-based resin layer having a uniform film thickness can be formed by applying a coating solution under the coating conditions described later using a coating apparatus.

  FIG. 1 is a perspective view showing a positional relationship between a die and a substrate in a coating process. As shown in FIG. 1, the coating apparatus 20 includes a die 12 having a discharge port 14 for discharging a coating liquid and a coating liquid supply pipe 13, and is a so-called die coating type coating apparatus. . The die 12 is disposed so that the discharge port 14 and the substrate 1 face each other. For example, in order to enable coating with a coating width of 2500 mm or more, preferably 3000 mm or more, the discharge port 14 of the coating apparatus 20 has the same width as the coating width.

  The coating liquid is continuously supplied to the die 12 via the coating liquid supply pipe 13, discharged from the discharge port 14, and applied to the surface of the substrate 1. In the coating process of the present embodiment, the coating liquid is supplied to the die 12 in a state where the difference between the temperature of the die 12 and the temperature of the coating liquid is less than 1 ° C. (more preferably, 0.3 ° C. or less). Coating is performed under the coating condition of starting. Thereby, the temperature change of the die | dye 12 by supplying a coating liquid to the die | dye 12 can be suppressed, and the shape change of the die | dye 12 after a coating process start can be suppressed. As a result, the coating amount can be stabilized along the width direction of the discharge port 14, and fluctuations in the coating thickness of the coating liquid along the width direction can be suppressed.

  In the coating process, as shown in FIG. 1, the coating liquid may be applied to the surface of the substrate 1 being conveyed while the substrate 1 is being conveyed. In the coating apparatus 20, one of the plurality of rolls (coating roll, not shown) for transporting the substrate 1 and the discharge port 14 of the die 12 face each other with a predetermined interval. Placed in. Thereby, a coating gap is prescribed | regulated along the direction in which a coating liquid is discharged, and a coating liquid is applied with the thickness according to a coating gap. In the following description, the longitudinal direction of the discharge port 14 (longitudinal direction of the die 12) is the X direction, and the direction perpendicular to the X direction and in which the coating liquid is discharged (discharge direction) is the Y direction. .

<Attaching the die to the stage>
FIG. 3 is a schematic diagram showing a configuration of a coating apparatus that can be used in the present embodiment. The die 12 is attached to the stage 11 via a bolt fixing portion 15 on the side opposite to the side having the discharge port 14. The bolt fixing portion 15 fixes the die 12 to the stage 11 so that the die 12 does not move. The stage 11 is provided with a predetermined gap between the stage 11 and the coating roll. Thereby, the coating gap can be kept uniform along the X direction, and the coating liquid can be applied with a uniform thickness along the X direction. In the example shown in FIG. 3, the die 12 is attached to the stage 11 via five bolt fixing portions 15 arranged in a line along the X direction.

  Although not shown, the die 12 may be attached to the stage 11 by one bolt fixing portion 15 and four slide fixing portions. Specifically, using the bolt fixing portion 15 and the slide fixing portion arranged in a line along the X direction around the bolt fixing portion 15, the die 12 is a central portion in the X direction, and the stage 11 is moved by the bolt fixing portion 15. It may be attached to the stage 11 by the slide fixing part at both ends in the X direction.

  The slide fixing unit attaches the die 12 to the stage 11 so that the die 12 is stationary in the Y direction and the die 12 is movable in the X direction. In other words, the slide fixing unit attaches the die 12 to the stage 11 so that the die 12 can slide in the X direction.

  By attaching the die 12 to the stage 11 using the bolt fixing portion 15 and the slide fixing portion, when the die 12 expands along the X direction, the die 12 changes according to the dimensional change of the die 12 along the X direction. The end of the die 12 is moved relative to the stage 11 by sliding. Therefore, in the coating process, when the temperature of the die 12 rises due to the supply of the coating liquid to the die 12 and the die 12 thermally expands, the position of the end of the die 12 is relative to the stage 11. The thermal stress in the X direction can be released.

  The configuration of the slide fixing portion is not particularly limited as long as the die 12 can be attached to the stage 11 so that the die 12 can slide along the X direction. For example, a rail shape that slides the die 12 in the X direction is available. You may be comprised with the member of. In addition, a clamp bolt that applies a force in the Y direction to the die 12 to apply a frictional force between the die 12 and the rail-shaped member, and a frictional force in the X direction between the die 12 and the slide fixing portion. Reduced grease may be used. Furthermore, the number of slide fixing portions is not limited to four, and the die 12 may be fixed to the stage 11 using at least one slide fixing portion. As described above, in the coating apparatus 20, it is not essential to use the slide fixing portion, and the die 12 may be attached to the stage 11 only by the bolt fixing portion 15.

<Coating gap>
FIG. 4 is a diagram illustrating a change in the shape of the die when the temperature of the die increases. FIG. 4 shows that the surface temperature of the die increases by 1 ° C. when a 4000 mm wide die is attached to the stage using only the bolt fixing portion and when it is attached to the stage using the bolt fixing portion and the slide fixing portion. 3 shows the results of the shape change obtained by using the finite element method (FEM), the horizontal axis is the distance (mm) from the end of the die in the X direction, and the vertical axis is the Y direction with increasing temperature. Is the displacement (mm) of the discharge port.

  FIG. 5 is a diagram showing the displacement of the discharge port in the discharge direction after the start of the coating process. FIG. 5 shows the elapsed time from the start of the coating process when a 4000 mm wide die is attached to the stage using only the bolt fixing part and when it is attached to the stage using the bolt fixing part and the slide fixing part. Shows the value of the displacement of the discharge port actually measured using a displacement meter and the value obtained using the FEM, the horizontal axis is the elapsed time (minutes) from the start of the coating process, and the vertical axis is This is the amount of displacement (μm) in the Y direction at the midpoint in the X direction of the die.

  FIG. 6 is a perspective view showing the positional relationship between the die and the substrate when the die is deformed.

  As the temperature of the die 12 increases by 1 ° C. as shown in FIG. 4, the position of the discharge port 14 is displaced in the Y direction as the distance from the end portion increases. Further, the position of the discharge port 14 is lowered at the end portion and the position of the discharge port is raised at the center portion as compared to the initial position before the temperature rise. Further, as shown in FIG. 5, the position of the midpoint in the X direction of the die after a lapse of a predetermined time from the start of the coating process is displaced in the Y direction from the position at the start of the coating process.

  That is, when the coating liquid is supplied to the die 12 in the coating process, the die 12 is deformed by heat, and as shown in FIG. 6, the die 12 does not face the stage 11 (on the discharge port 14 side). Becomes an upwardly convex curved shape. This reduces the coating gap at the midpoint of the die 12 and consequently impairs thickness uniformity along the X direction.

  Therefore, in the manufacturing process of the polarizing film 2, it is preferable to control the difference between the temperature of the die 12 at the start of the coating process and the temperature of the coating liquid as small as possible, as in the manufacturing method of the present embodiment, It is preferable to start supplying the coating liquid to the die 12 in a state where the temperature difference is less than 1 ° C.

  Thereby, the temperature change of the die | dye 12 by supplying a coating liquid to the die | dye 12 can be suppressed, and the shape change of the die | dye 12 after a coating process start can be suppressed. As a result, fluctuations in the coating gap after the start of the coating process can be suppressed, and fluctuations in the coating thickness of the coating liquid along the X direction can be suppressed. Therefore, the thickness of the PVA resin layer can be kept uniform, and the polarizing film 2 having a uniform thickness can be manufactured.

  Furthermore, by starting the supply of the coating liquid to the die 12 with the temperature difference being 0.3 ° C. or less, the thickness of the PVA-based resin layer can be kept even more uniform. A polarizing film 2 with a sufficient thickness can be manufactured.

  As shown in FIG. 1, the temperature of the coating solution may be measured using a thermocouple T. Any appropriate means can be used as a means for reducing the difference between the temperature of the die 12 at the start of the coating process and the temperature of the coating liquid. For example, the heating device for heating the die 12 may be provided in the coating apparatus 20 and the die 12 may be heated to bring the temperature of the die 12 close to the temperature of the coating liquid. Further, the temperature of the die 12 may be brought close to the temperature of the coating liquid by controlling the room temperature to be equal to the temperature of the coating liquid.

  In addition, as shown in FIG. 4, compared to the case where the die 12 is attached to the stage 11 using only the bolt fixing portion, the case where the die 12 is attached to the stage 11 using the bolt fixing portion and the slide fixing portion. However, the displacement of the discharge port accompanying the temperature rise of the die is small. Further, as shown in FIG. 5, even in the actual measurement value using a displacement meter, the die using the bolt fixing portion and the slide fixing portion is compared with the case where the die 12 is attached to the stage 11 using only the bolt fixing portion. When 12 is attached to the stage 11, the amount of displacement at the midpoint of the die corresponding to the elapsed time from the start of the coating process is smaller.

  This is because the heat of the coating liquid supplied to the die 12 causes the temperature of the die 12 to rise with the elapsed time from the start of the coating process, causing a change in shape of the die 12. When the bolts are fixed, thermal stress is generated by limiting the thermal expansion in the longitudinal direction of the die 12, and as a result, the upper surface side (the discharge port 14 side) not facing the stage 11 is bent so as to protrude in the Y direction. This is probably because of this.

  On the other hand, by attaching the die 12 to the stage using the slide fixing portion, the position of the end portion moves relative to the stage 11 along the X direction according to the dimensional change of the die 12 in the X direction. . Thereby, it is considered that the thermal stress in the X direction can be released, and as a result, the displacement of the die 12 in the Y direction can be suppressed.

  In this way, by attaching the die 12 to the stage using the slide fixing portion, it is possible to suppress the variation in the coating gap accompanying the temperature rise of the die 12 after the start of the coating process, and as a result, along the X direction. The reduction in thickness uniformity can be further suppressed. Thereby, the thickness of a PVA-type resin layer can be kept still more uniform, and the polarizing film 2 of a much more uniform thickness can be manufactured.

  Hereinafter, although the manufacturing method of the polarizing film of this invention is demonstrated concretely based on an Example, this invention is not limited by these Examples.

[Example 1]
(1) Preparation of base material Amorphous polyethylene terephthalate resin (A-PET) was formed into a long film having a thickness of 200 μm to obtain an A-PET base material.

  Water-based urethane resin (Daiichi Kogyo Seiyaku Co., Ltd., trade name “Superflex 210R”, solid content: 35%) and oxazoline-based cross-linking agent (product of Nippon Shokubai Co., Ltd., trade name “Epocross WS700”, solid content: 25 %), Conductive material (trade name “Orgacon LBS”, manufactured by Agfa Gevaert Co., Ltd., solid content: 1.2%), ammonia water having a concentration of 1%, and water in a weight ratio of 9.03: 1. The antistatic layer was formed by apply | coating to the one side of A-PET base material, and drying the liquid mixture obtained by mixing by 0.000: 18.1: 0.060: 39.5. The thickness of the antistatic layer was 1 μm.

  Next, the A-PET film was stretched 2.3 times in the width direction (short direction) at 115 ° C. while being conveyed in the longitudinal direction. By slitting and removing both end portions of the stretched A-PET film, a substrate having a width of about 3500 mm was obtained.

(2) Coating condition of coating solution Polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol%) was dissolved in water using a coating apparatus as shown in FIG. 1 and FIG. A coating solution (concentration: 7%) at 1 ° C. was supplied to a die at 23 ° C. and coated on the other surface of the substrate with a coating width of 3500 mm while conveying the substrate in the longitudinal direction. After coating, the coating liquid was dried at 60 ° C. to obtain a laminate composed of a substrate, an antistatic layer, and a PVA resin layer having a thickness of about 10 μm.

(3) Other treatments Next, as an aerial stretching treatment, the laminate was stretched in air at 130 ° C. by 2.4 times (air stretching step).

  Next, as the insolubilization treatment, the stretched laminate was immersed in a 3% by weight boric acid aqueous solution (insolubilization bath) having a liquid temperature of 30 ° C. for 30 seconds (insolubilization step).

  Next, as a dyeing treatment, the insolubilized laminate is finally put in a dyeing bath (iodine aqueous solution obtained by mixing iodine and potassium iodide in water at a weight ratio of 1: 7) at a liquid temperature of 30 ° C. The polarizing film obtained was soaked so that the single transmittance (Ts) was 40 to 44% (dyeing step).

  Next, as a crosslinking treatment, the dyed laminate was immersed in an aqueous solution (crosslinking bath) having a liquid temperature of 30 ° C. containing 3 wt% boric acid and 3 wt% potassium iodide (crosslinking step).

  Next, a plurality of sets of rolls having different peripheral speeds in an aqueous solution having a temperature of 70 ° C. containing 4% by weight of boric acid and 5% by weight of potassium iodide as a stretched treatment in boric acid in water. In the meantime, the film was uniaxially stretched 2.3 times in the longitudinal direction (stretching process in boric acid solution). The total draw ratio was 5.5 times.

  Next, as a washing / drying treatment, the laminate subjected to the boric acid water stretching treatment was immersed in a 4 wt% potassium iodide aqueous solution (washing bath) having a liquid temperature of 30 ° C. and then dried with hot air at 60 ° C. (washing) -Drying process).

  Through the above steps, an optical film laminate including a polarizing film having a thickness of 4.3 μm, a base material, and an antistatic layer was produced.

[Example 2]
An optical film laminate was produced in the same manner as in Example 1 except that the temperature of the coating solution supplied to the die was 23.3 ° C.

Example 3
An optical film laminate was produced in the same manner as in Example 2 except that the width of the substrate was about 3000 mm and the coating width was 3000 mm.

Example 4
An optical film laminate was produced in the same manner as in Example 2 except that a coating apparatus in which the die was fixed to the stage by the bolt fixing part and the slide fixing part was used.

[Comparative Example 1]
An optical film laminate was produced in the same manner as in Example 3 except that the temperature of the coating solution supplied to the die was 24 ° C.

[Comparative Example 2]
An optical film laminate was produced in the same manner as in Comparative Example 1 except that the width of the substrate was about 3500 mm and the coating width was 3500 mm.

[Reference Example 1]
An optical film laminate was produced in the same manner as in Comparative Example 1 except that the width of the substrate was about 1500 mm and the coating width was 1500 mm.

[Reference Example 2]
An optical film laminate was produced in the same manner as in Comparative Example 1 except that the width of the substrate was about 2000 mm and the coating width was 2000 mm.

<Evaluation method>
In addition, the temperature of die | dye and a coating liquid and the thickness of the PVA-type resin layer were measured as follows. Moreover, the optical characteristic of the polarizing film of the optical film laminated body manufactured by each Example, each comparative example, and each reference example was measured as follows.

(Die and coating solution temperature)
As the die temperature, the temperature of the die surface before the start of the coating process and before the coating solution was supplied was measured using a thermocouple. Further, as the liquid temperature, the temperature of the coating liquid before being supplied to the die was measured using a thermocouple. Further, the liquid temperature-die temperature difference was calculated by subtracting the die temperature from the liquid temperature.

(PVA resin layer thickness)
After the start of the coating process, the temperature of the die rises, and the thickness of the PVA resin layer obtained by drying the coating liquid applied in a state equal to the temperature of the coating liquid The film thickness was measured using visible light. As the thickness of the PVA-based resin layer, the film thickness at the end and the center was measured. As the thickness of the central portion of the PVA-based resin layer, the thickness of the central portion in the width direction of the laminate is measured, and as the thickness of the end portion of the PVA-based resin layer, the coating width x 3% from the long side of the laminate The thickness at the inner position was measured. Moreover, the ratio (percentage) of the difference of the film thickness of an edge part and the film thickness of a center part with respect to the average value of the film thickness in the width direction was computed as a fluctuation width of the film thickness of the PVA-type resin layer in the width direction.

  Furthermore, when the thickness of the central portion and the thickness of the end portion are in the range of 9.7 μm to 10.3 μm and the variation width of the film thickness of the PVA resin layer in the width direction is 6% or less, the thickness determination result When the thickness of the central portion and the thickness of the end portion are out of the above ranges, the thickness determination result was determined to be defective (x).

(Optical characteristics of polarizing film)
After bonding a triacetyl cellulose (TAC) film (made by Fuji Film Co., Ltd., trade name “TD80UL”) to the surface of the polarizing film using an adhesive to the obtained optical film laminate, the base material and antistatic The layers were peeled off to create a polarizing plate. The transmittance of the polarizing plate was measured using an ultraviolet-visible spectrophotometer “V7100” manufactured by JASCO Corporation. When the variation in the transmittance of the polarizing plate is small enough to be used for a liquid crystal display panel, the determination result of the variation in the transmittance is good (◯), and when the variation in the transmittance of the polarizing plate is large, The determination result of the variation in transmittance was defined as defective (x).

  Each example, each comparative example, the thickness measurement result and thickness determination result of the PVA resin layer obtained under the coating conditions of each reference example, and each example, each comparative example, and the optical film manufactured by each reference example Table 1 shows the measurement results of the optical characteristics of the polarizing film of the laminate. Table 2 shows the thickness fluctuation width of the PVA resin layer with respect to the liquid temperature-die temperature difference and the coating width.

  As is clear from the comparison between Reference Example 1 and Reference Example 2 and Comparative Example 1 and Comparative Example 2, even if the liquid temperature-die temperature difference is 1 ° C., the thickness is determined if the coating width is 2000 mm or less. Although the result and the transmittance variation determination result were good, when the coating width was 3000 mm or more, the thickness determination result and the transmittance variation determination result were poor. Moreover, as shown in Table 2, when the liquid temperature-die temperature difference is 1 ° C., the thickness variation width of the PVA resin layer increases as the coating width increases.

  Further, as apparent from the comparison between Example 1 and Example 2 and Comparative Example 2, even if the coating width is 3500 mm, the thickness determination is performed if the liquid temperature-die temperature difference is 0.3 ° C. or less. Although the result and the transmittance variation determination result were good, when the liquid temperature-die temperature difference was 1 ° C., the thickness determination result and the transmittance variation determination result were poor. Therefore, it is preferable to start supplying the coating liquid to the die in a state where the liquid temperature-die temperature difference is less than 1 ° C.

  Further, as is clear from the comparison between Example 3 and Comparative Example 1, even if the coating width is 3000 mm, if the liquid temperature-die temperature difference is 0.3 ° C., the thickness determination result and the transmittance The variation determination result was good, but when the liquid temperature-die temperature difference was 1 ° C., the thickness determination result and the transmittance variation determination result were poor. Therefore, it is preferable to start supplying the coating liquid to the die in a state where the liquid temperature-die temperature difference is less than 1 ° C.

  Further, as is clear from the comparison between Example 2 and Example 4, the PVA resin obtained by coating using a coating apparatus in which the die is fixed to the stage by the bolt fixing part and the slide fixing part. The thickness variation width of the layer is smaller than the thickness variation width of the PVA-based resin layer obtained by coating using a coating apparatus in which the die is fixed to the stage only by the bolt fixing portion.

  FIG. 7 shows the thickness distribution along the width direction of the PVA-based resin layer in the laminate obtained in the coating process of Example 2. FIG. 8 shows the thickness distribution along the width direction of the PVA-based resin layer in the laminate obtained in the coating process of Comparative Example 2. 7 and 8 show the thickness of the PVA-based resin layer applied immediately after the start of the coating process and the thickness of the PVA-based resin layer applied after the die temperature is saturated. In FIG. 8, the horizontal axis represents the distance (mm) from the end in the width direction of the laminate, and the vertical axis represents the coating thickness (μm) of the PVA resin layer.

  As shown in FIG. 8, in the laminate obtained in the coating process of Comparative Example 2, the thickness of the PVA resin layer applied after the die temperature was saturated was applied immediately after the start of the coating process. Compared to the thickness of the processed PVA-based resin layer, the thickness was smaller at the central portion in the width direction of the laminate and larger at the end. In particular, at the end in the width direction of the laminate, the thickness of the PVA-based resin layer applied after the die temperature is saturated is significantly larger than the set value of 10 μm, which is a standard value of 9.7 μm. The value greatly exceeded ˜10.3 μm.

  On the other hand, as shown in FIG. 7, the laminated body obtained in the coating process of Example 2 was saturated in die temperature as compared with the laminated body obtained in the coating process of Comparative Example 2. The difference between the thickness of the PVA-based resin layer applied later and the thickness of the PVA-based resin layer applied immediately after the start of the coating process was small.

  The optical film of the present invention is suitably used for liquid crystal display panels such as liquid crystal displays, mobile phones, personal digital assistants, digital cameras, video cameras, portable game machines, car navigation systems, copy machines, printers, fax machines, watches, and microwave ovens. It is done.

DESCRIPTION OF SYMBOLS 1 Base material 2 Polarizing film 3 Antistatic layer 10 Optical film laminated body 11 Stage 12 Die 13 Coating liquid supply pipe 14 Discharge port 15 Bolt fixing | fixed part 20 Coating apparatus

Claims (7)

An optical film manufacturing method comprising a coating step of continuously supplying a coating liquid containing a resin for forming an optical film to a die and coating the coating liquid on a substrate through the die. And
The method for producing an optical film, wherein the coating step includes starting the supply of the coating liquid to the die in a state where the difference between the temperature of the die and the temperature of the coating liquid is less than 1 ° C. .   The said coating process includes starting supply of the said coating liquid to the said die in the state whose difference between the temperature of the said die and the temperature of the said coating liquid is 0.3 degrees C or less. The manufacturing method of the optical film of description.   The coating step is the die attached to a stage provided with a predetermined interval between the substrate and the end of the die according to a dimensional change in the longitudinal direction of the discharge port of the die. The method for producing an optical film according to claim 1, comprising coating using the die attached so that the position thereof can be moved relative to the stage.   The manufacturing method of the optical film of any one of Claims 1-3 in which the said coating process includes applying the said coating liquid with the coating width of 2500 mm or more.   The manufacturing method of the optical film of any one of Claims 1-4 whose thickness of the said optical film is 10 micrometers or less. A drying step of obtaining a long resin layer having a width corresponding to the longitudinal direction of the discharge port by drying the coating liquid applied to the substrate;
And a processing step of making the resin layer the optical film by performing a predetermined treatment,
The coating step includes coating the coating liquid so that the ratio of the difference between the thickness of the end portion and the thickness of the center portion is 6% or less with respect to the average thickness value in the width direction. 5. A method for producing an optical film according to 5.   The method for producing an optical film according to claim 1, wherein the optical film is a polarizing film.

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