JP5682760B2 - Optical film manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to an optical film manufacturing method and manufacturing apparatus, an optical film manufactured by the manufacturing method or manufacturing apparatus, a polarizing plate having the optical film as a protective film, and a liquid crystal using the optical film or the polarizing plate. The present invention relates to a display device.

  Conventionally, as a method for producing an optical film, for example, a solution casting method or a melt casting method is known. In the solution casting method, a resin solution in which a raw material resin is dissolved in a solvent is discharged from a casting die, and cast on a support such as an endless belt or a drum to form a casting film on the support. This is a method for producing an optical film by drying a cast film formed to some extent and then peeling it from the support, and carrying out the peeled film in the longitudinal direction and performing stretching, heat treatment, etc. as necessary. On the other hand, the melt film-forming method was formed by extruding a resin melt obtained by heating and melting a resin as a raw material from a casting die and casting it on a support such as a roll to form a casting film on the support. This is a method for producing an optical film by cooling and solidifying a cast film to some extent, then peeling it from the support, and carrying out the peeled film in the longitudinal direction and performing stretching, heat treatment or the like as necessary.

  Here, as described in Patent Document 1, inter-roll stretching may be performed as the stretching step. Stretching between rolls is performed by increasing the peripheral speed of the stretching roll in the stretching section between the heating roll upstream in the transport direction and the stretching roll downstream in the transport direction while transporting the film. The film is stretched in the transport direction. Such roll-to-roll stretching is intended to improve the optical performance of the optical film, thereby contributing to an increase in screen size and quality of the liquid crystal display device.

  By the way, in roll-to-roll stretching, when the temperature of the heating roll is made lower than the glass transition temperature of the resin, the torque of the stretching roll increases, and it may be difficult to stretch the film in the stretching section. On the other hand, if the temperature of the heating roll is made higher than the glass transition temperature of the resin, the film adheres to the heating roll, and stepped surface defects (step unevenness) may occur in the film.

  Therefore, a heating device such as an infrared heater is arranged in the stretching section to prevent the film from adhering to the heating roll by making the temperature of the heating roll lower than the glass transition temperature of the resin. It is known that the film is heated to a temperature higher than the glass transition temperature of the resin to facilitate the stretching of the film.

JP 2010-275434 A (paragraphs 0006, 0086, FIGS. 1 to 3)

  By the way, when arrange | positioning a heating apparatus in an extending | stretching area, in order to heat a film efficiently and uniformly, it is desirable to arrange | position a heating apparatus as close to a film as possible. However, in this case, when the film being transported on the transport path is broken, the following problem may occur. That is, when the film breaks, the tension of the film is loosened, and the possibility that the film in the stretching section meanders and contacts the heating device increases. Alternatively, when the film breaks, the conveyance of the film is stopped or slowed down, and the film in the stretching section is exposed to the heat of the heating device for a long time, and is likely to expand toward the heating device side and contact the heating device. Become.

  When the film comes into contact with the heating device, the contacted film remains attached to the heating device, and the remaining film deposits are heated and melted by the heating device after resuming production, and fall within the stretching section onto the film being conveyed. . Such a fall of the film melt causes troubles such as foreign matter failure of the optical film and poor image display (image distortion, etc.), lowers the optical performance of the optical film, increases the screen size of the liquid crystal display device, Impairs quality.

  Therefore, the object of the present invention is to prevent the film in the stretching section from coming into contact with the heating device disposed in the stretching section when the film breaks, thereby suppressing the decrease in the optical performance of the optical film, This contributes to an increase in the screen size and quality of the liquid crystal display device.

  The method for producing an optical film of the present invention is a method for producing an optical film having a step of stretching between rolls with a heating roll and a stretching roll while conveying the film, and detecting a breakage of the film on the conveyance path And a step of preventing the film in the stretching section between the heating roll and the stretching roll from coming into contact with the heating device disposed in the stretching section when the breakage of the film is detected. And

  According to this configuration, when the breakage of the film on the conveyance path is detected, the film in the stretching section is prevented from coming into contact with the heating device disposed in the stretching section. Problems such as failures and video display defects are eliminated, and the optical performance of the optical film is prevented from lowering, which can contribute to an increase in screen size and quality of the liquid crystal display device.

  In the manufacturing method, it is preferable that the film breakage is detected based on at least one of the presence / absence of an object on the conveyance path, the temperature of the space occupied by the conveyance path, and the film winding torque. This is because the film breakage can be detected with high responsiveness and accuracy.

  In the manufacturing method, it is preferable to prevent the film from coming into contact with the heating device by retracting the heating device to a position away from the conveyance path. This is because, when the film is broken, the contact of the film with the heating device can be well prevented by keeping the heating device away from the film.

  In the said manufacturing method, it is preferable to prevent the contact to the heating apparatus of a film by inserting a shield between a heating apparatus and a conveyance path | route. This is because, when the film is broken, it is possible to satisfactorily prevent the film from contacting the heating device by bringing the film into contact with the shield.

  In the manufacturing method, the film is prevented from coming into contact with the heating device by blowing air from the heating device side toward the conveyance path side and / or sucking air from the conveyance route side toward the counter heating device side. Is preferred. This is because, when the film is broken, the film can be prevented from coming into contact with the heating device by moving the film away from the heating device by wind pressure or suction.

  In the said manufacturing method, it is preferable to prevent the contact to the heating apparatus of a film by increasing the distance between a heating roll and a extending | stretching roll, and suppressing the fall of the tension | tensile_strength of the film in an extending | stretching area. This is because, when the film is broken, the contact of the film with the heating device can be satisfactorily prevented by suppressing the meandering of the film in the stretching section.

  In the said manufacturing method, it is preferable to prevent the contact to the heating apparatus of a film by making a tension | tensile_strength act on the film outside a extending | stretching area, and suppressing the fall of the tension | tensile_strength of the film in an extending | stretching area. This is because, when the film is broken, the contact of the film with the heating device can be satisfactorily prevented by suppressing the meandering of the film in the stretching section.

  The optical film manufacturing apparatus of the present invention is an optical film manufacturing apparatus having an apparatus that stretches between rolls with a heating roll and a stretching roll while transporting the film, and is an apparatus that detects the breakage of the film on the transport path. And a device that prevents the film in the stretching section between the heating roll and the stretching roll from coming into contact with the heating device disposed in the stretching section when the film breakage is detected. And

  According to this configuration, when the breakage of the film on the conveyance path is detected, the film in the stretching section is prevented from coming into contact with the heating device disposed in the stretching section. Problems such as failures and video display defects are eliminated, and the optical performance of the optical film is prevented from lowering, which can contribute to an increase in screen size and quality of the liquid crystal display device.

  The optical film of the present invention is manufactured by the manufacturing method or the manufacturing apparatus. This optical film is a high-quality film that is free from defects such as foreign matter failure and image display failure and has excellent optical performance.

  The polarizing plate of this invention has the said optical film as a protective film, It is characterized by the above-mentioned. This polarizing plate is a high-quality one that is free from defects such as foreign matter failures and image display defects and has excellent optical performance.

  The liquid crystal display device of the present invention is characterized by using the optical film or the polarizing plate. This liquid crystal display device is of a high quality that is free from defects such as foreign matter failure and image display failure and has excellent optical performance.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of an optical film in which the contact prevention measure to the heating apparatus of the film at the time of a film fracture | rupture was taken are provided. As a result, defects such as foreign matter failure and image display failure are eliminated, and a high-quality optical film, polarizing plate and liquid crystal display device with excellent optical performance are obtained, which contributes to an increase in screen size and quality of the liquid crystal display device. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram of the manufacturing apparatus of the optical film which concerns on embodiment of this invention, Comprising: (A) is based on the solution casting method using an endless belt, (B) is based on the solution casting method using a drum (C) is based on a melt film forming method using a cooling roll. It is a block diagram of the extending apparatus between rolls of the manufacturing apparatus of the optical film of FIG. It is an enlarged view of the extending | stretching area of the extending | stretching apparatus between rolls of FIG. 2, Comprising: It is explanatory drawing of 1st Embodiment. Similarly, it is explanatory drawing of 2nd Embodiment. Similarly, it is explanatory drawing of 3rd Embodiment. Similarly, it is explanatory drawing of 4th Embodiment. Similarly, it is explanatory drawing of 5th Embodiment.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

<Optical film manufacturing equipment>
In the present embodiment, the optical film is manufactured by a solution casting method or a melt casting method. With reference to FIG. 1 (A), the manufacturing apparatus 1 of the optical film by the solution casting method using the endless belt 12 as a support body is demonstrated.

  The optical film manufacturing apparatus 1 includes a casting apparatus 10, a drying apparatus 20, an inter-roll stretching apparatus 30, and a winding apparatus 40.

  The casting apparatus 10 includes a casting die 11, an endless belt 12, and a peeling roll 13.

  The casting die 11 forms a casting film (web) 52 on the endless belt 12 by discharging a resin solution (dope) 51 in which a raw material resin is dissolved in a solvent and casting it on the running endless belt 12. Let

  The raw material resin is preferably a cellulose ester resin such as cellulose triacetate from the viewpoint of the transparency of the obtained optical film. The solvent is preferably a mixed solvent containing a good solvent (such as methylene chloride) and a poor solvent (such as alcohols) of the raw material resin. The resin content in the resin solution 51 is preferably, for example, 15 to 30% by mass. If necessary, the resin solution 51 may contain additives such as a plasticizer, a matting agent, an ultraviolet absorber, an antioxidant, and a retardation adjusting agent.

  The casting die 11 is preferably one whose discharge port shape is adjustable. Further, a pressure die that can easily make the film thickness of the casting film 52 uniform is preferable. In order to increase the film forming speed, two or more pressure dies may be arranged side by side, and the resin solution 51 may be divided and discharged.

  The discharge speed of the resin solution 51 by the casting die 11 is preferably about 30 to 200 L / min, for example, considering the transport speed and productivity of the casting film 52 by the endless belt 12.

  The endless belt 12 is wound around a pair of rollers and travels in the direction of the arrow in the drawing, thereby conveying the casting film 52 formed on the endless belt 12. The cast film 52 is dried to some extent on the endless belt 12 by hot air, a heater, or the like during conveyance by the endless belt 12.

  The endless belt 12 is preferably made of, for example, stainless steel (SUS316, SUS304, or the like) having a mirror-finished surface from the viewpoint of peelability of the cast film 52. The width of the endless belt 12 is preferably about 1700 to 2500 mm, for example. The width of the casting film 52 on the endless belt 12 is preferably 80 to 99% of the width of the endless belt 12, and is preferably about 1300 to 2400 mm, for example, from the viewpoint of increasing the screen size of the liquid crystal display device.

  The temperature of the casting film 52 on the endless belt 12 is preferably, for example, −5 to 70 ° C., more preferably 0 to 60 ° C. in consideration of the time required for evaporation of the solvent, the conveyance speed and productivity of the endless belt 12. preferable.

  The transport speed of the casting film 52 by the endless belt 12 is preferably about 30 to 200 m / min, for example, from the viewpoint of high-speed production of the optical film.

  The peeling roll 13 is in contact with the surface of the endless belt 12 in a pressurized state, and peels off the casting film 52 dried on the endless belt 12 to some extent from the endless belt 12. The peeled cast film 52 is transported in the longitudinal direction as a film F and passes through the drying device 20 and the inter-roll stretching device 30. The peeling tension at the time of peeling by the peeling roll 13 is preferably 50 to 400 N / m width, for example. The amount of residual solvent in the cast film 52 at the time of peeling is preferably, for example, 30 to 200% by mass in consideration of peelability from the endless belt 12, transportability after peeling, physical properties of the optical film, and the like.

Here, the residual solvent amount is a value defined by the following equation. The “heat treatment” in the formula is a heat treatment at 115 ° C. for 1 hour.
Residual solvent amount (%) = {(mass before heat treatment of cast film−mass after heat treatment of cast film) / mass after heat treatment of cast film} × 100
The drying device 20 includes a plurality of conveyance rolls, and dries the film F with warm air or a heater while conveying the film F in a meandering manner between these rolls. The drying temperature depends on the residual solvent amount of the film F, but is preferably 30 to 180 ° C., for example, in consideration of the drying time, shrinkage unevenness, stability of the stretch amount, and the like.

  As will be described in detail later, the inter-roll stretching device 30 stretches the film F in the transport direction, that is, the longitudinal direction (MD direction) in the stretching section between the heating roll and the stretching roll while transporting the film F.

  In addition to the inter-roll stretching by the inter-roll stretching device 30, the film F may be stretched in the width direction (TD direction) using, for example, a tenter.

  The winding device 40 winds the film F that has been dried and stretched between rolls into a roll shape as an optical film. As the winding device 40, for example, a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress can be used without any particular limitation.

  From the viewpoint of dimensional stability, the amount of residual solvent in the optical film when wound by the winding device 40 is preferably, for example, 0.5% by mass or less, and more preferably 0.1% by mass or less. When the amount of residual solvent is 0.5 mass% or less, the width of the optical film is preferably about 1200 to 2400 mm, for example, and the thickness is preferably about 20 to 150 μm, for example. The transmittance of the optical film is preferably 90% or more, more preferably 92% or more, and further preferably 93% or more.

  The optical film according to this embodiment is suitable as a functional film for various displays such as a liquid crystal display, a plasma display, and an organic EL display, as well as a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, and a visual field. It is also suitable as an optical compensation film for increasing the angle.

  In the present embodiment, the transport tension of the film F on the transport path from being peeled off by the peeling roll 13 until being wound up by the winding device 40 depends on the residual solvent amount of the film F, etc. 300 N / m width is preferable and 20 to 270 N / m width is more preferable.

  In the present embodiment, a film breakage detection device 80 that detects breakage of the film F on the transport path is disposed in the vicinity of the transport path immediately before the winding device 40. As the detection device 80, for example, an optical detection device or a contact detection device that detects the breakage of the film F based on the presence or absence of an object on the conveyance route, or a space occupied by the conveyance route such as a temperature measurement type detection device. Those that detect the breakage of the film F depending on the temperature of the film can be used without particular limitation. Furthermore, what detects the fracture | rupture of the film F by the winding torque of the film F at the time of winding with the winding device 40, such as an electric signal type detector, may be used. These detection devices 80 can detect the breakage of the film F with high responsiveness and accuracy. These detection devices 80 may be used alone or in combination. Further, the detection device 80 may be disposed at any position on the conveyance path from the peeling roll 13 to the winding device 40 as long as it can detect the breakage of the film F on the conveyance path. In that case, in order to improve detection accuracy and detection responsiveness, it is preferable to arrange at a plurality of positions.

  Next, with reference to FIG. 1 (B), the manufacturing apparatus 1 of the optical film by the solution casting method using the drum 14 as a support body is demonstrated. Note that the same reference numerals are used for components that are the same as or similar to those in FIG. 1A, and only the characteristic portions in FIG.

  The optical film manufacturing apparatus 1 shown in FIG. 1B is different from FIG. 1A in that a drum 14 is used as a support. The drum 14 is preferably made of, for example, stainless steel (SUS316, SUS304, or the like) whose surface is hard chrome plated from the viewpoint of peelability of the cast film 52. The casting die 11 discharges a resin solution 51 in which a raw material resin is dissolved in a solvent and casts the resin solution 51 on the rotating drum 14 to form a casting film 52 on the drum 14.

  Next, with reference to FIG.1 (C), the manufacturing apparatus 1 of the optical film by the melt film-forming method using the cooling roll 63 as a support body is demonstrated. Note that the same reference numerals are used for components that are the same as or similar to those in FIGS. 1A and 1B, and only the characteristic portions in FIG. 1C are described.

  In the optical film manufacturing apparatus 1 shown in FIG. 1C, the casting die 61 extrudes a resin melt 71 obtained by heating and melting a raw material resin into a film shape and casts it on a rotating cooling roll 63. As a result, the casting film 72 is formed on the cooling roll 63.

  The raw material resin is a thermoplastic resin, and a cellulose ester resin such as cellulose triacetate is preferable from the viewpoint of the transparency of the obtained optical film. If necessary, the resin melt 71 may contain additives such as a plasticizer, a matting agent, an ultraviolet absorber, an antioxidant, a retardation adjusting agent, an acid scavenger, and a viscosity reducing agent.

  The casting film 72 formed on the cooling roll 63 is clamped by the touch roll 62 and then circumscribed to the cooling roll 63, and further circumscribed to the second cooling roll 64 and the third cooling roll 65 in this order. It is cooled and solidified to some extent. And after peeling from the 3rd cooling roll 65 with the peeling roll 66, it is conveyed in the longitudinal direction as the film F, and passes the extending | stretching apparatus 30 between rolls.

  The cooling rolls 63, 64, 65 are preferably made of, for example, stainless steel (SUS316, SUS304, etc.) whose surface is subjected to hard chrome plating from the viewpoint of peelability of the casting film 72.

  Next, with reference to FIG. 2, the inter-roll stretching apparatus 30 common to FIGS. 1 (A), 1 (B), and 1 (C) will be described.

  The inter-roll stretching device 30 includes preheating rolls 31 and 31, a heating roll 32, a stretching roll 33, and cooling rolls 34 and 34 in order from the upstream side in the transport direction of the film F. The film F is circumscribed by the preheating rolls 31 and 31 and the heating roll 32, and then heated, and then the film F is in a stretching section between the heating roll 32 and the stretching roll 33 rather than the peripheral speed of the heating roll 32. By increasing the peripheral speed, the film is stretched in the transport direction (MD direction). The heated and stretched film F is cooled by being circumscribed by the cooling rolls 34 and 34. Nip rolls 35 and 36 for holding the film F at the end of the stretching section are pressed against the heating roll 32 and the stretching roll 33. The stretching ratio in the MD direction by the inter-roll stretching apparatus 30 is not particularly limited, but is preferably in the range of, for example, about 1 to 300% depending on the situation.

Here, the stretching ratio (MD direction) is a value defined by the following equation.
MD direction stretching rate (%) = {(peripheral speed of stretching roll 33−peripheral speed of heating roll 32) / peripheral speed of heating roll 32} × 100

  A heating device 37 is disposed in the stretching section. In the present embodiment, the heating device 37 is disposed above the film F in the stretching section. As the heating device 37, for example, an infrared heater, a halogen heater, a carbon heater, a ceramic heater, a heating wire heater, a hot air heater (hot air blowing), or the like is used.

  In the present embodiment, the temperature of the heating roll 32 is set lower than the glass transition temperature of the resin of the film F. Thereby, the problem that the film F adheres to the heating roll 32 and a stepped surface defect occurs in the film F is prevented. On the other hand, in this embodiment, the film F in the stretching section is heated by the heating device 37 to a temperature higher than the glass transition temperature of the resin of the film F. Thereby, smoothing of the extending | stretching of the film F by the extending | stretching roll 33 is achieved. For example, the temperature of the heating roll 32 is preferably not less than the glass transition temperature Tg-30 ° C. of the resin of the film F and lower than the glass transition temperature Tg of the resin of the film F. The heating temperature of the film F by the heating device 37 is preferably not less than the glass transition temperature Tg of the resin of the film F and not more than the glass transition temperature Tg of the resin of the film F + 30 ° C.

  The heating device 37 is disposed close to the film F in order to efficiently and evenly heat the film F (for example, an interval between the film F and the heating device 37: 3 cm). On the other hand, as described above, the film F on the transport path from the peeling roll 13 to the winding device 40 is pulled with a force of, for example, 10 to 300 N / m width. Then, when the film F breaks, the tension of the film F is loosened, and the film F in the stretching section is likely to meander and come into contact with the heating device 37 as illustrated by the chain line X in FIG. . Alternatively, when the film F is broken, the conveyance of the film F is stopped or slowed down, and the film F in the stretching section is exposed to the heat of the heating device 37 for a long time as illustrated by a chain line X in FIG. There is a high possibility that the heating device 37 expands in a biased manner and contacts the heating device 37. The film F that has come into contact with the heating device 37 remains attached to the heating device 37, and this film F deposit is heated and melted by the heating device 37 after the production is resumed, and falls into the film F being conveyed in the stretching section. The fall of the film F melt causes the foreign matter failure of the optical film and the video display failure (distortion of the image, etc.), and decreases the optical performance of the optical film, thereby increasing the screen size and quality of the liquid crystal display device. Inhibit.

  Therefore, in this embodiment, when the detection device 80 detects the breakage of the film F on the transport path, the film F in the stretching section contacts the heating device 37 disposed in the stretching section. Measures are taken to prevent this. Thereby, problems such as foreign matter failure and image display failure of the optical film are eliminated, and the optical performance of the optical film is suppressed from being lowered, which can contribute to an increase in screen size and quality of the liquid crystal display device.

  Specifically, as shown in FIG. 3, as shown in FIG. 3, when the film F is broken, the heating device 37 is positioned away from the conveyance path (for example, the distance between the film F and the heating device 37: 10 cm). By retracting to the above, contact of the film F with the heating device 37 is prevented. Thus, by keeping the heating device 37 away from the film F, the contact of the film F with the heating device 37 is well prevented. The retracting direction of the heating device 37 is not particularly limited, such as a vertical direction, a horizontal direction, and an oblique direction. The mechanism for retracting the heating device 37 is not particularly limited, such as a mechanical type, a hydraulic type, and an electric type.

  Alternatively, as a second embodiment, as shown in FIG. 4, when the film F is broken, a shield 81 is inserted between the heating device 37 and the transport path to contact the film F with the heating device 37. May be prevented. In this way, by bringing the film F into contact with the shield 81, the contact of the film F with the heating device 37 can be satisfactorily prevented. The shield 81 is preferably a flat thin plate. The mechanism for inserting the shield 81 is not particularly limited, such as a mechanical type, a hydraulic type, and an electric type.

  Alternatively, as shown in FIG. 5, as shown in FIG. 5, a blowing nozzle 82 is provided on the heating device 37 side in the stretching section, and when the film F is broken, air is blown from the heating device 37 side toward the conveyance path side. You may prevent the film F from contacting the heating device 37 by spraying. Alternatively, even if the suction nozzle 83 is provided on the counter heating device 37 side in the stretching section and the wind is sucked from the transport path side to the counter heating device 37 side, the film F can be prevented from contacting the heating device 37. Good. Alternatively, both the wind blowing and the wind suction may be performed. In this way, by moving the film F away from the heating device 37 by wind pressure or suction, the contact of the film F with the heating device 37 is well prevented. In FIG. 5, two blowing nozzles 82 and one suction nozzle 83 are described, but the number of these nozzles 82 and 83 is not particularly limited.

  Alternatively, as a fourth embodiment, as shown in FIG. 6, when the film F is broken, the distance between the heating roll 32 and the stretching roll 33 is increased to reduce the tension of the film F in the stretching section. By suppressing, the contact of the film F with the heating device 37 may be prevented. In this manner, by suppressing the meandering of the film F in the stretching section, the contact of the film F with the heating device 37 is well prevented. Although FIG. 6 describes that both the heating roll 32 and the stretching roll 33 are separated from each other, only one of them may be separated from the other.

  Alternatively, as a fifth embodiment, as shown in FIG. 7, guide roll pairs 84 and 84 are provided to guide the film F outside the stretched section, and when the film F is broken, the guide roll pairs 84 and 84 are conveyed. The film F is prevented from contacting the heating device 37 by moving in the direction in which the path extends and applying tension to the film F outside the stretching section to suppress a decrease in the tension of the film F inside the stretching section. May be. In this manner, by suppressing the meandering of the film F in the stretching section, the contact of the film F with the heating device 37 is well prevented. In FIG. 7, it is described that the guide roll pairs 84 and 84 are provided on the upstream side and the downstream side of the inter-roll stretching apparatus 30, but only one of them may be provided.

<Method for producing optical film>
By using the optical film manufacturing apparatus 1 having the above-described configuration, an optical film manufacturing method including a step of stretching between rolls with a heating roll 32 and a stretching roll 33 while transporting the film F, and a transport path The process of detecting the breakage of the film F above, and the heating in which the film F in the stretching section between the heating roll 32 and the stretching roll 33 is disposed in the stretching section when the breakage of the film F is detected. The manufacturing method of an optical film which has the process of preventing contacting with the apparatus 37 may be implemented. Thereby, problems such as foreign matter failure and image display failure of the optical film are eliminated, and the optical performance of the optical film is suppressed from being lowered, which can contribute to an increase in screen size and quality of the liquid crystal display device.

<Optical film>
The optical film according to the present embodiment is an optical film manufactured by the manufacturing method or the manufacturing apparatus 1. This optical film is a high-quality film that is free from defects such as foreign matter failure and image display failure and has excellent optical performance.

<Polarizing plate>
The polarizing plate according to the present embodiment is a polarizing plate having the optical film as a protective film. This polarizing plate is a high-quality one that is free from defects such as foreign matter failures and image display defects and has excellent optical performance.

  Specifically, in the polarizing plate according to this embodiment, an optical film is used as a protective film on at least one surface of the polarizer. Such a polarizing plate can be produced, for example, by attaching an optical film to at least one surface of a polarizer using a completely saponified polyvinyl alcohol aqueous solution.

<Liquid crystal display device>
The liquid crystal display device according to this embodiment is a liquid crystal display device using the optical film or the polarizing plate. This liquid crystal display device is of a high quality that is free from defects such as foreign matter failure and image display failure and has excellent optical performance.

  Specifically, in the liquid crystal display device according to this embodiment, a polarizing plate is provided on at least one surface of the liquid crystal cell. Such a liquid crystal display device can be produced, for example, by attaching a polarizing plate to at least one surface of a liquid crystal cell via an adhesive layer.

  The liquid crystal display device according to the present embodiment is suitable as a display device for a large screen of, for example, 30 type or more.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples.

<Preparation of resin solution>
The following raw materials were put into a sealed container, heated and dissolved by stirring, and then the resulting solution was filtered to prepare a resin solution.

(Resin solution composition)
-100 parts by mass of cellulose triacetate (Mn = 148000, Mw = 310000, Mw / Mn = 2.1)-8 parts by mass of triphenyl phosphate (plasticizer)-2 parts by mass of ethylphthalylethyl glycolate (plasticizer) Parts · Methylene chloride (good solvent) 440 parts by mass · Ethanol (poor solvent) 40 parts by mass · Tinuvin 109 (UV absorber, BASF Japan) 0.5 parts by mass · Tinuvin 171 (UV absorber, BASF Japan) 0.5 parts by mass) Aerosil 972V (matting agent, Nippon Aerosil Co., Ltd.) 0.2 parts by mass

<Manufacture of optical film>
An optical film (cellulose triacetate film) was manufactured using the optical film manufacturing apparatus 1 shown in FIG. First, the resin solution 51 was discharged from the casting die 11 under the following conditions and cast onto the traveling endless belt 12.

(Casting conditions)
Casting die: Pressurizing die Discharge speed: 30 L / min Support: Stainless steel endless belt Conveying speed: 60 m / min Casting film width: 1800 mm

  The cast film 52 formed on the endless belt 12 is being conveyed by the endless belt 12 by blowing warm air of 45 ° C. from above the endless belt 12 and heating to 45 ° C. from the back surface of the endless belt 12 with a heater. After drying on the endless belt 12, it was peeled off from the endless belt 12 by the peeling roll 13. The peeling tension at the time of peeling with the peeling roll 13 was 300 N / m width. The residual solvent amount of the cast film 52 at the time of peeling was 80% by mass.

  While the peeled film F was transported in the longitudinal direction with a transport tension of 270 N / m width, the drying device 20 was passed in a meandering manner and dried at 80 ° C. for 1 minute by blowing warm air.

  Next, the film F was passed through the inter-roll stretching device 30 and stretched in the transport direction. The stretch ratio was 30%. The temperature of the heating roll 32 was set to the glass transition temperature Tg-10 ° C. of the resin of the film F (cellulose triacetate). The heating temperature of the film F by the heating device 37 was the glass transition temperature Tg + 10 ° C. of the resin of the film F. As the heating device 37, an infrared heater was used. The heating device 37 was disposed above the film F in the stretching section, and the distance between the film F and the heating device 37 was 3 cm.

  Next, after the film F is cooled to 20 ° C., both ends in the width direction of the film are cut with a slitter (for example, a rotary blade type) and wound into a roll with the winding device 40 using a constant torque method. Thus, an optical film (cellulose triacetate film) having a thickness of 40 μm and a width of 1500 mm was produced.

<Evaluation>
(Example)
The film breakage detection device 80 is disposed in the vicinity of the conveyance path immediately before the winding device 40. The detection device 80 is an optical detection device. When the detection device 80 detects the breakage of the film F, the detection device 80 receives the detection signal and retracts the heating device 37 to a position on the side away from the transport direction. The retraction direction was the vertical direction, and the retraction mechanism was mechanical. The distance between the retracted film F and the heating device 37 was 10 cm.

  Then, during the production of the optical film as described above, a cut was made in the side edge portion of the film F between the inter-roll stretching device 30 and the winding device 40 to break the film F. After the production of the optical film was temporarily suspended and the roll taken up by the winding device 40 was exchanged, the production of the optical film was resumed. When the optical film after the resumption of production was evaluated, no foreign matter failure or defective image display of the optical film was observed.

(Comparative example)
On the other hand, when the film breakage detection device 80 was not arranged and the retracting mechanism of the heating device 37 was not provided, foreign matter failure, image display failure, etc. were observed in the optical film after the resumption of production. This is because when the film F breaks, the film F in the stretching section comes into contact with the heating device 37, and the film F deposits remaining in the heating device 37 are heated and melted by the heating device 37 after the production is resumed. It is considered that the melt has fallen on the film F being conveyed in the stretching section.

DESCRIPTION OF SYMBOLS 1 Optical film manufacturing apparatus 10 Casting apparatus 11 Casting die 12 Endless belt (support)
13 Peeling roll 14 Drum (support)
20 Drying device 30 Inter-roll stretching device 40 Winding device 51 Resin solution 52 Casting film 61 Casting die 62 Touch roll 63 Cooling roll (support)
64 Second cooling roll (support)
65 Third cooling roll (support)
66 Peeling roll 71 Resin melt 72 Casting film 80 Film breakage detector F Film

Claims (3)

It is a method for producing an optical film having a step of stretching between rolls with a heating roll and a stretching roll while conveying the film,
Detecting the breakage of the film on the transport path;
A step of preventing the film in the stretching section between the heating roll and the stretching roll from coming into contact with the heating device disposed in the stretching section when the film breakage is detected, and the film The step of preventing the film in the stretching section between the heating roll and the stretching roll from coming into contact with the heating device disposed in the stretching section when detecting the breakage of:
Preventing the film from contacting the heating device by blowing air from the heating device side toward the conveyance path and / or sucking air from the conveyance route side toward the anti-heating device;
Preventing the film from coming into contact with the heating device by increasing the distance between the heating roll and the stretching roll to suppress the decrease in the tension of the film in the stretching section, or for the film outside the stretching section An optical film characterized in that it is at least one selected from preventing contact of a film with a heating device by applying a tension to suppress a decrease in tension of the film in the stretching section. Production method.   The optical film manufacturing method according to claim 1, wherein the breakage of the film is detected based on at least one of presence / absence of an object on the conveyance path, temperature of a space occupied by the conveyance path, and film winding torque. Method. An apparatus for producing an optical film having an apparatus for stretching between rolls with a heating roll and a stretching roll while conveying the film,
A device for detecting the breakage of the film on the transport path;
A device that prevents a film in a stretching section between a heating roll and a stretching roll from coming into contact with a heating device disposed in the stretching section when the film breakage is detected; and the film A device that prevents a film in a stretching section between a heating roll and a stretching roll from contacting a heating device disposed in the stretching section when detecting a break in
A device that prevents the film from contacting the heating device by blowing wind from the heating device side toward the conveyance path side and / or sucking air from the conveyance path side toward the counter heating device side,
By increasing the distance between the heating roll and the stretching roll to suppress the decrease in the tension of the film in the stretching section, the device that prevents the film from contacting the heating device, or the film outside the stretching section An optical film characterized in that it is at least one device selected from a device that prevents a film from coming into contact with a heating device by applying a tension to suppress a decrease in the tension of the film in the stretching section. Manufacturing equipment.

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