JP2017140725A - Production method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a long optical film in which the direction of an optical axis in a width direction is controlled while preventing stretching failure.SOLUTION: A tenter stretching apparatus is used, in which a gripping zone A, a preheating zone B, a stretching zone C and a cooling zone D are sequentially arranged from a conveyance inlet side to a conveyance outlet side. A production method of an optical film is provided, which includes: a preheating step of preheating in the preheating zone a long resin film held by gripping tools 20 in the gripping zone; a stretching step of stretching the long resin film in a longitudinal direction by enlarging an interval between the gripping tools in a conveyance direction of the long resin film in the stretching zone; and a cooling step of cooling the stretched long resin film in the cooling zone. The direction of an optical axis in a width direction of the obtained optical film is controlled by starting the stretching step at a halfway point of the stretching zone.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an optical film. More specifically, the present invention relates to a method for producing a long optical film including controlling the direction of the optical axis in the width direction by starting stretching from the midpoint of the stretching zone of the stretching apparatus.

  In an image display device such as a liquid crystal display device or an organic electroluminescence (EL) display device, an optical film (for example, a polarizing film or a retardation film) is used. Such an optical film is typically obtained by a production method including stretching. However, the optical film obtained by stretching has a problem that variation occurs in the direction of the optical axis in the width direction.

JP 2010-286619 A

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to produce a long optical film in which the orientation of the optical axis in the width direction is controlled without causing poor stretching. It is to provide a possible method.

According to the embodiment of the present invention, a method for producing a long optical film is provided. This manufacturing method uses a tenter stretching apparatus in which a gripping zone, a preheating zone, a stretching zone, and a cooling zone are sequentially provided from the carry-in side to the carry-out side. The manufacturing method includes a preheating step of heating the long resin film gripped by the gripping tool in the gripping zone in the preheating zone; and the stretching resin in the transporting direction of the long resin film in the stretching zone. A stretching step of extending the lengthy resin film in the longitudinal direction by enlarging the gap between the gripping tools; and a cooling step of cooling the stretched long resin film in the cooling zone. The direction of the optical axis in the width direction of the obtained optical film is controlled by starting the stretching process from the midpoint of the stretching zone.
In one embodiment, the manufacturing method described above, so that the temperature T _SS at the start the drawing process is 80 ° C. or more, to adjust the starting point of the drawing process in the stretching zone.
In one embodiment, the optical film is a polarizing film, and the optical axis is an absorption axis. In one embodiment, the variation of the absorption axis in the width direction of the long polarizing film obtained by the above manufacturing method is within ± 0.3 ° with respect to the longitudinal direction.
In one embodiment, the optical film is a retardation film, and the optical axis is a slow axis. In one embodiment, the dispersion | variation in the slow axis in the width direction of the elongate phase difference film obtained by the said manufacturing method is less than +/- 2.0 degrees with respect to a longitudinal direction.

  According to the present invention, in the method for producing a long optical film, the stretching process is started from the middle of the stretching zone of the tenter stretching apparatus, thereby causing poor stretching (for example, film tearing, film deflection and / or The direction of the optical axis in the width direction of the obtained optical film can be controlled without causing wrinkles.

It is a schematic plan view explaining the whole structure of an example of the extending | stretching apparatus which can be used for the manufacturing method of this invention. It is the schematic explaining an example of each process of preheating, extending | stretching, and cooling. (A) And (b) is the schematic explaining the guideline of temperature adjustment for controlling control of the direction of the optical axis in the manufacturing method of this invention, respectively. It is the schematic explaining the temperature profile in the manufacturing method of this invention. It is a graph which shows the dispersion | variation in the absorption-axis direction in the width direction of the polarizing film obtained in Example 1, the comparative example 1, and the comparative example 3. FIG.

A. 2. Manufacturing method of optical film The manufacturing method of the elongate optical film by embodiment of this invention is the preheating process which heats the elongate resin film hold | gripped with the holding tool, and the conveyance direction of elongate resin film A stretching step of extending the length of the long resin film in the longitudinal direction by enlarging the gap between the gripping tools, and a cooling step of cooling the stretched long resin film. This manufacturing method is performed using a tenter stretching device that includes a plurality of clips as gripping tools and is provided with a gripping zone, a preheating zone, a stretching zone, and a cooling zone in this order from the carry-in side to the carry-out side. In this manufacturing method, the direction of the optical axis in the width direction of the obtained optical film is controlled by starting the stretching process from the midpoint of the stretching zone. The long resin film forming the optical film may be a single-layer resin film or a laminate of two or more layers. Hereinafter, as an example, an embodiment in which a polarizing film is manufactured using a laminate of a resin base material and a polyvinyl alcohol (PVA) resin layer will be described, but the manufacturing method of the present invention is not limited to the embodiment. For example, the present invention is equally applicable to a method for producing a polarizing film or retardation film using a single-layer resin film or a method for producing a polarizing film or retardation film using a laminate of resin films. It is clear to the contractor.

A-1. Preparation of laminated body A laminated body is produced by forming a PVA-type resin layer on a resin base material. The resin base material has any appropriate configuration as long as the PVA resin layer (the obtained polarizing film) can be supported from one side.

  Examples of the resin base material are ester resins such as polyethylene terephthalate resins, cycloolefin resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. It is done. Among these, cycloolefin resins (for example, norbornene resins) and amorphous polyethylene terephthalate resins are preferable. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol as a glycol.

  A surface modification treatment (for example, corona treatment or the like) may be performed on the resin base material in advance, or an easy adhesion layer may be formed on the resin base material. By performing such a treatment, the adhesion between the resin substrate and the PVA resin layer can be improved. The surface modification treatment and / or the formation of the easy adhesion layer may be performed before the stretching or after the stretching.

  Arbitrary appropriate methods can be employ | adopted for the formation method of the said PVA-type resin layer. Preferably, a PVA-based resin layer is formed by applying a coating liquid containing a PVA-based resin on a resin base material that has been subjected to a stretching treatment, and drying.

  Any appropriate resin can be used as the PVA-based resin. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The saponification degree can be determined according to JIS K 6726-1994. By using a PVA resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the saponification degree is too high, the coating solution is likely to gel, and it may be difficult to form a uniform coating film.

  The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

  The coating solution is typically a solution obtained by dissolving the PVA resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Among these, water is preferable. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the resin substrate can be formed.

  You may mix | blend an additive with a coating liquid. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the resulting PVA resin layer.

  Any appropriate method can be adopted as a coating method of the coating solution. Examples thereof include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method, etc.).

  It is preferable that the said drying temperature is below the glass transition temperature (Tg) of a resin base material, More preferably, it is below Tg-20 degreeC. By drying at such a temperature, it is possible to prevent the resin base material from being deformed before forming the PVA-based resin layer, and to prevent the orientation of the resulting PVA-based resin layer from deteriorating. . Thus, the resin base material can be deformed well together with the PVA-based resin layer, and stretching and shrinking of the laminate described later can be performed satisfactorily. As a result, good orientation can be imparted to the PVA-based resin layer, and a polarizing film having excellent optical properties can be obtained. Here, “orientation” means the orientation of molecular chains of the PVA resin layer.

A-2. Stretching device As described above, the manufacturing method according to the embodiment of the present invention includes a plurality of clips as gripping means for the laminate, and the gripping zone, the preheating zone, the stretching zone, and the cooling zone are sequentially arranged from the carry-in side to the carry-out side. It is carried out using a tenter stretching apparatus provided. As a tenter stretching device, for example, a pair of rails having a straight line portion where the distance between the rails is constant and a taper portion where the distance between the rails continuously decreases, and traveling on each rail while changing the clip interval are possible. A stretching device comprising a plurality of clips can be used. According to such a stretching apparatus, the clip interval in the transport direction (distance between clips on the same rail) and the clip interval in the width direction (between clips on different rails) with both side edges of the laminate held by clips. By changing the distance), the laminate can be stretched and contracted.

  FIG. 1 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the production method of the present invention. A stretching apparatus that can be used in the production method of the present invention will be described with reference to FIG. The extending | stretching apparatus 100 has the endless rail 10L and the endless rail 10R in the left-right both sides symmetrically by planar view. In the present specification, the left endless rail as viewed from the entrance side of the laminate is referred to as the left endless rail 10L, and the right endless rail is referred to as the right endless rail 10R. On each of the left and right endless rails 10L and 10R, a large number of clips 20 for gripping the stacked body are arranged. The clip 20 is guided by each rail and moves in a loop. The clip 20 on the left endless rail 10L rotates in a counterclockwise direction, and the clip 20 on the right endless rail 10R rotates in a clockwise direction. In the drawing apparatus of the illustrated example, a gripping zone A, a preheating zone B, a drawing zone C, and a cooling zone D are sequentially provided from the carry-in side to the carry-out side of the laminate. It should also be noted that the ratio of the lengths of the respective zones in the stretching apparatus of FIG. 1 is different from the actual ratio of lengths.

  In the gripping zone A and the preheating zone B, the left and right endless rails 10R and 10L are straight portions having a constant rail distance. Typically, the left and right endless rails 10R and 10L are configured to be substantially parallel to each other at a distance between the rails corresponding to the initial width of the laminate to be processed. In the extension zone C, the left and right endless rails 10R and 10L are tapered portions in which the distance between the rails continuously decreases. Typically, the left and right endless rails 10R and 10L are configured to gradually decrease until the distance between the rails corresponds to the desired width of the laminate as it goes from the preheating zone B side to the cooling zone D side. . In the cooling zone D, the left and right endless rails 10R and 10L are straight portions having a constant rail distance, and are typically substantially equal to each other at the rail distance corresponding to the final width of the laminate. It is comprised so that it may become parallel.

  The clip (left clip) 20 on the left endless rail 10L and the clip (right clip) 20 on the right endless rail 10R can each independently move around. For example, the driving sprockets 30a and 30b of the left endless rail 10L are driven to rotate counterclockwise by the electric motors 40a and 40b, and the driving sprockets 30a and 30b of the right endless rail 10R are rotated by the electric motors 40a and 40b. It is driven to rotate around. As a result, traveling force is applied to a clip carrying member (not shown) of a drive roller (not shown) engaged with the drive sprockets 30a and 30b. As a result, the left clip 20 moves in a counterclockwise direction, and the right clip 20 moves in a clockwise direction. By driving the left electric motor and the right electric motor independently, the left clip 20 and the right clip 20 can be moved independently.

  Further, the left clip 20 and the right clip 20 are each of a variable pitch type. That is, the left and right clips 20 and 20 can independently change the clip interval (clip pitch) in the transport direction (MD) with movement. The variable pitch clip can be realized by any appropriate configuration such as the configuration described in Japanese Patent Application Laid-Open No. 2008-23775.

  Hereinafter, the steps of gripping, preheating, stretching, and cooling will be described in more detail with reference to FIGS. 1 and 2. FIG. 2 is a schematic diagram illustrating an example of each process of preheating, stretching, and cooling.

A-3. Gripping process First, in the gripping process (gripping zone A), the left and right clips 20 are used to grip both side edges of the laminate 50 taken into the stretching apparatus at a constant gripping interval (clip interval), and to the left and right endless rails. The laminated body 50 is conveyed to the preheating zone B by the movement of each guided clip 20. The grip interval (clip interval) between both side edges in the grip zone A is typically set to an equal interval L1.

A-4. Preheating Step Next, in the preheating step (preheating zone B), the laminated body 50 held by the left and right clips 20 is preheated while being conveyed toward the stretching zone C. In the preheating zone B, the clip interval in the transport direction is maintained at L1, and the distance between the left and right endless rails 10R, 10L is maintained constant. The area temperature of the preheating process (that is, the average temperature in the entire preheating zone: preheating temperature) T1 and the area temperature of the stretching process that will be described later (that is, the average temperature in the entire stretching zone: stretching temperature) T3 are as follows. It can be set so that the relationship with the temperature T _{SS of the} laminate is appropriate. The preheating temperature T1 is typically 50 ° C to 150 ° C. The preheating time is typically 5 seconds to 120 seconds. The preheating time can be adjusted by changing the length of the preheating zone and the moving speed of the clip. When the temperature in the preheating process changes, the preheating temperature T1 means an average temperature in the entire preheating process.

A-5. Stretching Step Next, in the stretching step (stretching zone C), the laminate 50 held by the left and right clips 20 is transported and stretched in the longitudinal direction (MD stretching). MD stretching of the laminated body 50 is performed by gradually increasing the moving speed of the clip 20 in the transport direction and expanding the clip interval in the transport direction from L1 to L2. Controlling the draw ratio (L2 / L1) by adjusting the clip interval L1 in the transport direction at the entrance of the stretching zone C (the grip interval in the gripping process) L1 and the clip interval L2 in the transport direction at the exit of the stretch zone C Can do.

In the embodiment of the present invention, the stretching of the laminate may be started not from the entrance of the stretching zone C but from the midpoint of the stretching zone. The starting point of stretching can be appropriately set so that the temperature T _SS at the start of the stretching process becomes a desired temperature. By starting stretching from the midpoint of the stretching zone, the following advantages can be obtained: If _TSS is too low, the variation in the optical axis in the width direction of the resulting optical film often increases. Moreover, since the film is not sufficiently softened, the film may be torn and cannot be stretched. On the other hand, the higher the preheating temperature to the T _SS and the desired temperature, will sag is laminate, in that many if sputum shaped wrinkles the film, if a high drawing temperature, the film is crystallized In some cases, the film properties obtained may change, such as a decrease in orientation. By starting stretching from midway point of the drawing zone, since the T _SS without changing the preheating temperature and the stretching temperature can be set to a desired temperature without causing such a problem, an optical film obtained The direction of the optical axis in the width direction can be controlled well.

  The draw ratio (L2 / L1) in the drawing step is, for example, 1.1 times to 6.0 times, preferably 1.2 times to 5.0 times, and more preferably 1.3 times to 3.0 times. If the draw ratio is less than 1.1 times, desired optical properties may not be obtained. On the other hand, if the draw ratio exceeds 6.0 times, the laminate may break.

  The manufacturing method by embodiment of this invention includes extending | stretching a laminated body to a longitudinal direction (MD extending | stretching), and shrinking a laminated body to the width direction as needed (TD shrinkage | contraction). When performing TD shrinkage | contraction, TD shrinkage | contraction may be performed simultaneously with MD extending | stretching, may be performed before MD extending | stretching, and may be performed after MD extending | stretching. In the illustrated example, in the stretching zone C, MD stretching is started after starting TD shrinkage, and then MD stretching and TD shrinkage are performed simultaneously. Specifically, in the extending zone C, the left and right endless rails 10R and 10L are tapered portions in which the distance between the rails continuously decreases. Shrinkage is performed. The TD contraction rate can be controlled by adjusting the amount of change in the distance between rails. Specifically, the smaller the ratio of the distance between the rails at the exit of the stretching zone C (end on the cooling zone D) to the distance between the rails at the entrance (end of the preheating zone B) of the stretching zone C, the larger the shrinkage rate Is obtained.

  The TD shrinkage ratio ((width of the laminate at the exit of the stretching zone C: W2) / (width of the laminate at the entrance of the stretching zone C: W1)) can be set to any appropriate value. The TD shrinkage rate is preferably 0.9 or less, more preferably 0.8 to 0.5. By setting such a shrinkage rate, more excellent optical characteristics can be obtained.

Stretching temperature of the laminate, as long as it is set to T _SS is drawn starting point so that an appropriate temperature is properly positioned as described above, may be set to any suitable temperature profile in the stretching zone. In one embodiment, T1, T3, and a cooling temperature T2, which will be described later, have a relationship of T1 <T3 and T3> T2. The difference between T1 and T3 is preferably 0 ° C to 60 ° C. The difference between T3 and T2 is preferably 10 ° C to 70 ° C.

T _SS is preferably 65 ° C. or higher, and more preferably 80 ° C. to 120 ° C. In one embodiment, the temperature of the stretching zone can change continuously or stepwise.

A-6. Cooling Step and Release Step Next, in the cooling step (cooling zone D), the laminated body is cooled and cooled. In one embodiment of the present invention, when adjusting the temperature gradient of the laminate after the end of the stretching step, due to a synergistic effect with the adjustment of the stretching start position, the optical axis in the width direction of the obtained optical film The direction can be controlled even better. The adjustment of the temperature gradient can be performed by any appropriate means. Typical examples of the adjusting means include (1) controlling the temperatures T3 and T2 and (2) shifting the end point of the stretching step. As the means (1), typically, the stretching temperature (average temperature in the entire stretching zone) T3 and the cooling temperature (that is, the average temperature in the entire cooling zone) T2 are set to desired values. As the means (2), typically, the stretching is terminated at any appropriate position in the stretching zone C of the stretching apparatus, or the stretching is terminated at any appropriate position in the cooling zone D. Can be mentioned.

  The cooling time can be adjusted by changing the length of the cooling zone and the moving speed of the clip. When the temperature in the cooling process changes, the cooling temperature T2 means the average temperature in the entire cooling process as described above.

  Finally, the clip 20 that holds the stacked body 50 is released. In the cooling process (and the releasing process), typically, the distance between clips and the clip interval are both constant.

A-7. Temperature Adjustment A guideline for temperature adjustment (relationship between T1, T3, and T2) in the present invention will be briefly described. For example, as shown in FIG. 3 (a), when the optical axis of the optical film obtained faces inward in the width direction of the optical film with respect to the conveying direction is adjusted to T _SS is relatively low The For example, when the optical axis of the obtained optical film by prototype is facing inward in the width direction of the optical film with respect to the conveying direction, by a lower temperature setting value T _SS, the optical axis on the inside It can be adjusted to weaken the tendency to turn. In this case, the starting point of the stretching process is closer to the entrance in the stretching zone. The same effect can be obtained by reducing the temperature gradient of the laminate after the end of the stretching process. As a result, the direction of the optical axis can be substantially parallel to the longitudinal direction over the entire width direction. On the other hand, as shown in FIG. 3 (b), when the optical axis of the optical film obtained faces outwardly width direction of the optical film with respect to the conveying direction is adjusted to T _SS becomes relatively high temperature The In this case, the starting point of the stretching process is closer to the outlet than in the stretching zone. The same effect can be obtained by increasing the temperature gradient of the laminate after the end of the stretching process. As a result, similarly to the above, the direction of the optical axis can be substantially parallel to the longitudinal direction over the entire width direction. That is, the present inventors have found that if the temperature T _SS at the start stretching step is relatively low and is a temperature gradient in the case and stretching step at the end after the laminate is small, the optical axis optical optical film obtained it weakens the tendency toward the inner side of the width direction of the film; and, if the stretching step at the start of the temperature T _SS is relatively elevated temperatures are temperature ramp and when stretching step at the end after the laminate is large, is obtained We found that the optical axis of the optical film weakens the tendency to face outside in the width direction of the optical film, and using this knowledge, we realized the control of the direction of the optical axis by adjusting the stretching start point in the stretching zone. . By adjusting the stretching start point, the variation in the direction of the optical axis in the width direction of the obtained optical film can be remarkably suppressed. Furthermore, by using such adjustment of the stretching start point, not only the variation in the direction of the optical axis can be suppressed, but also the direction of the optical axis can be controlled in a desired direction according to the purpose. As a mechanism for obtaining such an effect, the following may be presumed: The manufacturing method of the present invention grips both ends of a film (laminated body in the present embodiment) with a tenter in the transport direction. Since it extends | stretches, the extending | stretching stress concerning a film generate | occur | produces in both ends. If the temperature T _SS of the laminate at the start of the stretching process is lowered, the film becomes hard and the stress at both ends increases (therefore, only both ends of the laminate are pulled in the transport direction), and the optical axis is in the transport direction. The tendency to turn outward in the width direction of the film becomes stronger. When _TSS is increased, the film becomes soft, stress at both ends is relaxed, and the tendency that the optical axis is directed outward in the width direction of the film with respect to the transport direction is weakened. When the temperature gradient of the laminated body after the end of the stretching process is increased, the laminated body is cooled and tends to shrink after stretching, so that it is pulled in the cooling direction. Since both ends of the laminate are gripped by the tenter, the center of the film is pulled, and the optical axis tends to be directed inward in the width direction of the film with respect to the transport direction. If the temperature gradient is reduced, this tendency is weakened because it is slowly cooled, and the tendency that the optical axis is directed inward in the width direction of the film with respect to the transport direction is weakened.

In the embodiment of the present invention, it is sufficient to adjust the starting point of the stretching process so that T _{SS is set} to a desired temperature, but from the viewpoint of more precise control of the optical axis direction, in the preheating, stretching, and cooling processes. A preferred temperature profile will be briefly described. FIG. 4 is a schematic diagram illustrating an example of a preferable temperature profile in the preheating, stretching, and cooling steps. In the drawing, the horizontal axis section is not a zone section of the stretching apparatus but a section according to the manufacturing process. From the viewpoint of suppressing variations in the direction of the optical axis in the width direction of the obtained optical film, temperature adjustment like profile A shown in FIG. According to temperature adjustment like the profile B shown by the dotted line in FIG. 4, the optical axis of the optical film obtained as shown in FIG. 3B may be directed outward in the width direction of the optical film with respect to the transport direction. is there. According to the temperature adjustment like the profile C indicated by the broken line in FIG. 4, the optical axis of the optical film obtained as shown in FIG. 3A may be directed inward in the width direction of the optical film with respect to the transport direction. is there. In FIG. 4, portions of profiles B and C that are not shown overlap profile A.

A-8. Other steps The manufacturing method of the polarizing film of the present embodiment may include other steps in addition to the above. Other processes include, for example, an insolubilization process, a dyeing process, a crosslinking process, a stretching process different from the stretching process, a cleaning process, a drying process (adjustment of moisture content), and the like, and a process using a PVA resin layer as a polarizing film. Can be mentioned. The other steps can be performed at any appropriate timing. In addition, the dispersion | variation in the optical axis in the width direction of the PVA-type resin layer before the process which uses a PVA-type resin layer as a polarizing film (typically immediately after a releasing process) is set direction (typically longitudinal). Direction) is preferably within a range of ± 2.0 °, more preferably within a range of ± 1.5 °. By performing the temperature control as described above, the variation in the optical axis in the width direction of the PVA-based resin layer at this time can be controlled within a desired range. As a result, the dispersion of the absorption axis in the width direction of the finally obtained polarizing film can be controlled within a desired range.

  The dyeing step is typically a step of dyeing the PVA resin layer with a dichroic substance. Preferably, it is performed by adsorbing a dichroic substance to the PVA resin layer. As the adsorption method, for example, a method of immersing a PVA resin layer (laminate) in a dye solution containing a dichroic substance, a method of applying a dye solution to the PVA resin layer, and a dye solution on a PVA resin layer The method of spraying etc. are mentioned. Preferably, the laminate is immersed in a staining solution containing a dichroic substance. It is because a dichroic substance can adsorb | suck favorably. In addition, both surfaces of the laminate may be immersed in the dyeing solution, or only one surface may be immersed.

  Examples of the dichroic substance include iodine and organic dyes. These may be used alone or in combination of two or more. The dichroic material is preferably iodine. When iodine is used as the dichroic substance, the staining solution is preferably an iodine aqueous solution. The blending amount of iodine is preferably 0.1 part by weight to 1.0 part by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide salt to the aqueous iodine solution. Examples of the iodide salt include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples include titanium. Among these, potassium iodide and sodium iodide are preferable. The compounding amount of the iodide salt is preferably 0.3 to 15 parts by weight with respect to 100 parts by weight of water.

  The liquid temperature during staining of the staining liquid is preferably 20 ° C to 40 ° C. When the PVA resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 300 seconds. Under such conditions, the dichroic substance can be sufficiently adsorbed to the PVA resin layer.

  The insolubilization step and the crosslinking step are typically performed by immersing the PVA resin layer in an aqueous boric acid solution. The cleaning step is typically performed by immersing the PVA resin layer in an aqueous potassium iodide solution. The drying temperature in the drying step is preferably 30 ° C to 100 ° C.

B. Polarizing Film The polarizing film produced by the above production method is substantially a PVA resin film in which a dichroic substance is adsorbed and oriented. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance (Ts) of the polarizing film is preferably 39% or more, more preferably 39.5% or more, still more preferably 40% or more, and particularly preferably 40.5% or more. The theoretical upper limit of the single transmittance is 50%, and the practical upper limit is 46%. Further, the single transmittance (Ts) is a Y value measured with a 2 degree visual field (C light source) of JIS Z8701 and corrected for visibility, for example, using a microspectroscopic system (Lambda Vision, LVmicro). Can be measured. The polarization degree of the polarizing film is preferably 99.9% or more, more preferably 99.93% or more, and further preferably 99.95% or more.

  In the polarizing film, the dispersion of the absorption axis in the width direction is preferably within a range of ± 0.3 °, more preferably ± 0, with respect to the set absorption axis direction (typically, the longitudinal direction). Within the range of 2 °. Thus, the polarizing film obtained by the manufacturing method of the present invention is very excellent in the axial accuracy in the width direction. As a result, since the polarizing film is excellent in in-plane uniformity of optical characteristics, the variation in quality of each polarizing film as a final product after cutting is small, and it is excellent when used in an image display device. Display characteristics can be realized. Further, the polarizing film obtained by the production method of the present invention can be practically used up to the end in the width direction, so that the yield is high and the cost is advantageous. When producing a retardation film by the production method of the present invention, the variation of the slow axis in the width direction of the retardation film is in the set slow axis direction (typically, the longitudinal direction). On the other hand, it is preferably within a range of ± 2.0 °, more preferably ± 1.5 °.

  Arbitrary appropriate methods can be employ | adopted for the usage method of a polarizing film. Specifically, it may be used as a single-layer PVA resin film, may be used as a laminate of a resin base material and a PVA resin film, and at least one of a PVA resin film or a PVA resin film You may use as a laminated body (namely, polarizing plate) which has arrange | positioned the protective film.

C. Polarizing plate The polarizing plate has a polarizing film and a protective film disposed on at least one side of the polarizer. Examples of the material for forming the protective film include cellulose resins such as diacetyl cellulose and triacetyl cellulose, (meth) acrylic resins, cycloolefin resins, olefin resins such as polypropylene, and ester resins such as polyethylene terephthalate resins. , Polyamide resins, polycarbonate resins, and copolymer resins thereof.

  The thickness of the protective film is preferably 20 μm to 100 μm. The protective film is typically laminated on the polarizer via an adhesive layer (specifically, an adhesive layer or an adhesive layer). The adhesive layer is typically formed of a PVA adhesive or an active energy ray curable adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. When using the laminated body of a resin base material / PVA-type resin film (polarizing film), Preferably, a resin base material can be peeled, after laminating | stacking a protective film on the surface on the opposite side to the resin base material of a polarizer. If necessary, another protective film can be laminated on the release surface. By peeling the resin base material, curling can be more reliably suppressed.

  Practically, the polarizing plate has an adhesive layer as the outermost layer. The pressure-sensitive adhesive layer is typically the outermost layer on the image display device side. A separator is temporarily attached to the pressure-sensitive adhesive layer so as to be peeled off, and the pressure-sensitive adhesive layer is protected until actual use, and roll formation is possible.

  The polarizing plate may further have any appropriate optical functional layer depending on the purpose. Representative examples of the optical functional layer include a retardation film (optical compensation film) and a surface treatment layer. For example, a retardation film may be disposed between the protective film and the pressure-sensitive adhesive layer (not shown). The optical characteristics (for example, refractive index ellipsoid, in-plane retardation, thickness direction retardation) of the retardation film can be appropriately set according to the purpose, characteristics of the image display device, and the like. For example, when the image display device is an IPS mode liquid crystal display device, there are a retardation film in which the refractive index ellipsoid is nx> ny> nz and a retardation film in which the refractive index ellipsoid is nz> nx> ny. Can be placed. The retardation film may also serve as a protective film. In this case, the protective film arranged on the image display device side can be omitted. Conversely, the protective film may have an optical compensation function (that is, may have an appropriate refractive index ellipsoid, an in-plane retardation and a thickness direction retardation depending on the purpose). “Nx” is the refractive index in the direction in which the refractive index in the film plane is maximum (ie, the slow axis direction), and “ny” is the refractive index in the direction perpendicular to the slow axis in the film plane. “Nz” is the refractive index in the thickness direction.

  The surface treatment layer may be disposed on the outer side of the outer protective film (not shown). Typical examples of the surface treatment layer include a hard coat layer, an antireflection layer, and an antiglare layer. For example, the surface treatment layer is preferably a layer having a low moisture permeability for the purpose of improving the humidification durability of the polarizer. The hard coat layer is provided for the purpose of preventing scratches on the surface of the polarizing plate. The hard coat layer can be formed by, for example, a method of adding a cured film excellent in hardness, slipping properties, etc., to an appropriate ultraviolet curable resin such as acrylic or silicone. The hard coat layer preferably has a pencil hardness of 2H or more. The antireflection layer is a low reflection layer provided for the purpose of preventing reflection of external light on the surface of the polarizing plate. As the antireflection layer, for example, a thin layer type for preventing reflection by using a canceling effect of reflected light by the interference action of light as disclosed in JP-A-2005-248173, JP-A-2011-2759 The surface structure type which expresses a low reflectance by giving a fine structure to the surface as disclosed in (1). The antiglare layer is provided for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the viewing of the light transmitted through the polarizing plate. The antiglare layer is formed, for example, by imparting a fine concavo-convex structure to the surface by an appropriate method such as a roughening method by a sandblasting method or an embossing method, or a blending method of transparent fine particles. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle. Instead of providing the surface treatment layer, the same surface treatment may be applied to the surface of the outer protective film.

  So far, as an example of the method for producing an optical film of the present invention, an embodiment for producing a polarizing film using a laminate of a resin base material and a PVA-based resin layer has been described. It will be apparent to those skilled in the art that the invention is applicable to a method for producing a polarizer or retardation film using a single layer resin film or a method for producing a polarizing film or retardation film using a laminate of resin films. It is. That is, in the present invention, even if the laminate of the resin base material / PVA resin layer is replaced with a single-layer resin film or a laminate of resin films, the same procedure can be applied and the same effect can be obtained. . For example, by applying the present invention to a single-layer film of PVA-based resin, it is possible to obtain a polarizer with excellent axial accuracy in the width direction; by applying the present invention to a single-layer film of cycloolefin-based resin A retardation film having excellent axial accuracy in the width direction can be obtained; by applying the present invention to a resin film / resin film laminate, a polarizer or retardation film having excellent axial accuracy in the width direction can be obtained. Can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Example 1]
<Laminated body production process>
An amorphous PET substrate (100 μm thick) was prepared as a resin substrate, and an aqueous PVA solution was applied to the amorphous PET substrate and dried at a temperature of 50 ° C. to 60 ° C. As a result, a PVA layer having a thickness of 15 μm was formed on the amorphous PET base material to produce a laminate (width: 1000 mm).

<Preheating, stretching and cooling process>
The obtained laminate was subjected to each step of preheating, stretching (MD stretching and TD shrinkage), and thermal process using a tenter stretching apparatus as shown in FIG. Specifically, in the gripping zone A, the both side edges of the laminate were gripped at a clip interval L1: 35 mm and conveyed in the longitudinal direction, and the laminate was heated from the preheating zone B inlet to the midpoint of the stretching zone C. The preheating temperature T1 was set to 80 ° C., the stretching temperature T3 was set to 140 ° C., the temperature T _SS at the start of the stretching process was 90 ° C., and the temperature T _ES of the laminate at the end of stretching was 110 ° C. In the stretching zone C, the rail bending point (starting point of the tapered portion) is located at the midway point. That is, the bending point is positioned on the drawing zone side of the partition between the preheating zone and the drawing zone. Using the bending point as a starting point for stretching in the longitudinal direction (and contraction in the width direction), the heated laminate was contracted by 30% in the width direction and simultaneously stretched in the longitudinal direction three times in the longitudinal direction (in the stretching zone C). Clip interval L2 at the outlet: 105 mm, width of the laminate: 650 mm). Thereafter, the cooling zone D temperature (cooling process area temperature) T2 was set to 70 ° C., and cooling was performed.

<Dyeing process>
Next, the laminate was immersed in an aqueous iodine solution at 25 ° C. (iodine concentration: 0.5 wt%, potassium iodide concentration: 10 wt%) for 30 seconds.

<Crosslinking treatment>
The layered product after dyeing was immersed in a 60 ° C. boric acid aqueous solution (boric acid concentration: 5% by weight, potassium iodide concentration: 5% by weight) for 60 seconds, and further 1.8 times in the longitudinal direction in the boric acid aqueous solution. Stretched.

<Cleaning process>
After the crosslinking treatment, the laminate was immersed in a 25 ° C. aqueous potassium iodide solution (potassium iodide concentration: 5% by weight) for 5 seconds.
In this way, a polarizing film having a thickness of 6.0 μm was produced on the resin base material.

<Evaluation>
Variation in the direction of the optical axis (absorption axis) in the width direction of the PVA resin layer immediately after tenter stretching and the obtained polarizing film was measured. Specifically, AXOSCAN manufactured by AXOMETRICS was used as a measuring device, and the direction of the optical axis of the PVA resin layer or the absorption axis of the polarizing film was measured every 20 mm across the width direction. The results are shown in FIG. The case where the deviation in the absorption axis direction from the longitudinal direction was within 0.4 ° was regarded as “good”, and the case where it exceeded 0.4 ° was regarded as “bad”. In addition, the obtained polarizing film was visually observed for wrinkles. The case where no wrinkles were observed was determined as “good”, and the case where wrinkles were observed was determined as “bad”. Furthermore, the chucking state of the clip during stretching was observed. These results are shown in Table 1.

[Comparative Example 1]
Example 1 except that the bending point of the rail is located at the partition between the preheating zone and the stretching zone (that is, stretching of the laminate starts from the entrance of the stretching zone C), and _TSS is 77 ° C. A polarizing film was produced in the same manner as described above. The obtained polarizing film was subjected to the same evaluation as in Example 1. The results are shown in FIG.

[Comparative Example 2]
Implemented except that the rail bending point is positioned on the preheating zone side of the partition between the preheating zone and the stretching zone (that is, starting the stretching of the laminate from the preheating zone B), and _TSS was set to 70 ° C. In the same manner as in Example 1, an attempt was made to produce a polarizing film. However, the laminate was torn and could not be stretched, and a polarizing film could not be obtained.

[Comparative Example 3]
A polarizing film was produced in the same manner as in Comparative Example 2 except that the preheating temperature T1 was 100 ° C. and _TSS was 90 ° C. The obtained polarizing film was subjected to the same evaluation as in Example 1. The results are shown in FIG.

As is apparent from Table 1, according to the embodiment of the present invention, by starting stretching from the midpoint of the stretching zone of the stretching apparatus, a long optical film ( The direction of the optical axis in the width direction of the polarizing film can be controlled well. Comparative Example began stretching from stretching zone inlet 1 T _SS is low, as a result, variations in the width direction of the optical axis is larger. Comparative Example began stretching from the preheating zone 2 is T _SS is very low, as a result, can not be stretched by tearing the laminate, it was not possible to obtain a polarizing film. In Comparative Example 3 in which the preheating temperature was set high and stretching was started from the preheating zone, the film softened and slackened quickly, and as a result, wrinkles of the film were remarkable.

  The manufacturing method of this invention is used suitably for manufacture of optical films, such as a polarizing film and an optical compensation film.

10 rails 20 clips 50 laminate (resin film)
100 Stretching device

Claims (6)

A method for producing a long optical film using a tenter stretching device in which a gripping zone, a preheating zone, a stretching zone, and a cooling zone are provided in this order from the carry-in side to the carry-out side,
A preheating step of heating the long resin film gripped by the gripping tool in the gripping zone in the preheating zone;
In the stretching zone, the stretching step of stretching the long resin film in the longitudinal direction by enlarging the interval of the gripping tool in the conveying direction of the long resin film;
A cooling step for cooling the stretched long resin film in the cooling zone,
By controlling the direction of the optical axis in the width direction of the resulting optical film by starting the stretching step from the midpoint of the stretching zone;
Method. So that the said temperature T _SS during the stretching step starts 80 ° C. or more, to adjust the starting point of the drawing process in the stretching zone, The method according to claim 1.   The manufacturing method according to claim 1, wherein the optical film is a polarizing film, and the optical axis is an absorption axis.   The manufacturing method according to claim 1, wherein the optical film is a retardation film and the optical axis is a slow axis.   The manufacturing method according to claim 3, wherein the dispersion of the absorption axis in the width direction of the obtained long polarizing film is within ± 0.3 ° with respect to the longitudinal direction. The manufacturing method of Claim 4 whose dispersion | variation in the slow axis in the width direction of the obtained elongate phase difference film is less than +/- 2.0 degrees with respect to a longitudinal direction.