JP2011093106A - Method and apparatus for manufacturing optical film, optical film, polarizing plate, and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film which, when a solidification preventing liquid is made to flow down to both ends of a dope outlet, suppresses the scattering of the solidification preventing liquid into a pressure-reducing chamber, does not adhere to a cast film, suppresses skin spreading to both ends of the dope outlet, and has a surface good in plane properties, the optical film manufactured by using the method, a polarizing plate using the optical film, and a display. <P>SOLUTION: The method for manufacturing the optical film has a supply process for supplying a resin dissolving liquid to both ends in the longitudinal direction of the dope outlet. In the supply process, the liquid is made to flow down from a plurality of openings of a supply member having the plurality of openings. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical film manufacturing method, an optical film manufacturing apparatus, an optical film, a polarizing plate, and a display device.

  In recent years, the demand for liquid crystal display devices has increased due to the widespread use of liquid crystal displays mounted on automobiles, large liquid crystal television displays, mobile phones, notebook computers, and the like. A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, an optical film is used, and its demand is rapidly increasing.

  By the way, as an optical film used for a liquid crystal display device, for example, a polarizing film of a polarizing plate has a cellulose ester film laminated as a protective film on one or both sides of a polarizer made of a stretched polyvinyl alcohol film.

  Such an optical film is required to have a smooth surface without optical defects. In particular, as the size of monitors and TVs increases and the definition becomes higher, these required qualities are becoming stricter.

  There is a solution casting film forming method as an optical film manufacturing method. In this method, a resin is dissolved in a solvent, the solution (dope) is cast on a support from a dope outlet of a casting die, a predetermined amount of solvent is evaporated on the support, In this method, the film is peeled and stretched as necessary. In this method, if the moving speed of the support is increased in order to increase productivity, the adhesion between the support film and the dope film (also referred to as a casting film) cast on the support from the dope outlet is improved. In order to cope with the problem that the dope film flutters until it reaches the support, and a film with poor flatness is formed, a decompression chamber is provided on the upstream side in the movement direction of the support surface of the dope outlet, and the dope film is In general, a method of closely contacting the support is used.

  However, in this solution casting film forming method, as soon as the resin solution flows out from the dope outlet, the solvent starts to evaporate, and particularly at both ends of the dope outlet, the resin solution evaporates well due to the flow of wind through the decompression chamber, There is a problem that “skinning” occurs near both ends of the dope outlet. This skinning is the one in which the resin component in the dope grows in a spiral shape at both ends of the dope outlet, disturbs the flow of the dope from the dope outlet and inhibits the formation of a film with good flatness. When this skinning occurred, the casting speed had to be reduced and the skinning had to be removed, which caused a significant reduction in productivity.

  In order to solve such a problem, a liquid that dissolves the raw material resin (also referred to as anti-caking liquid) is dropped on both ends of the dope outlet, thereby preventing the occurrence of skinning near both ends of the dope outlet. A method for preventing this is known (see Patent Document 1).

  However, a decompression chamber is provided on the upstream side of the dope outlet in the direction of movement of the support so that the casting film flowing out from the dope outlet is in close contact with the support surface. The liquid is sucked in, and the sucked anti-solidification liquid is scattered in the decompression chamber, and the scattered anti-solidification liquid falls on the support at a position other than both ends of the decompression chamber and is mixed into the casting film. Due to this mixing, the surface of the cast film was deformed, and there was a problem that a round or elliptical deformed pattern was generated on the surface of the produced film.

  With respect to such a problem, in Patent Document 1, a scattering prevention member for preventing the anti-caking liquid from splashing is provided in the decompression chamber, the anti-caking liquid adhering to the anti-scattering member is stored in a basket, and the accumulated liquid is piped. The method of collecting by is proposed.

JP 2007-276458 A

  However, in the method of Patent Document 1, the anti-caking liquid cannot be sufficiently prevented by the scattering preventing member, and the deformation pattern on the film surface cannot be eliminated to a level where there is no problem. Moreover, when the amount of dripping of the anti-solidification liquid was reduced to suppress scattering to the decompression chamber, skinning occurred at both ends of the dope outlet, which became a problem.

  Therefore, in the present invention, when the anti-solidification liquid flows down to both ends of the dope outflow port, the anti-solidification liquid is prevented from scattering into the decompression chamber, there is no adhesion to the casting film, and the dope outflow port to both ends. The present invention provides a method and apparatus for producing an optical film having a surface with good flatness that suppresses the skinning of the film, an optical film produced using the production method, a polarizing plate using the optical film, and a display device. It is aimed.

  In order to solve the above problems, the present invention has the following features.

1. A casting step of casting a dope containing a resin and a solvent from a dope outlet of a casting die onto a support, and a casting film to cast the dope from the dope outlet onto the support, A pressure reducing step for maintaining the pressure on the upstream side in the movement direction of the surface of the support at the dope outlet in a state lower than atmospheric pressure so that the dope outlet is in close contact with the support; and a liquid for dissolving the resin is added to the dope outlet. In the manufacturing method of the optical film having a supply step of supplying to both ends of the
In the supplying step, the liquid is caused to flow down and supplied from the plurality of openings of a supply member having a plurality of openings arranged corresponding to both ends of the dope outlet. A method for producing a film.

2. The supply step includes
The tip of the nozzle in which the supply member having the plurality of openings is arranged at the tip thereof is arranged in the vicinity of both longitudinal ends of the dope outlet,
2. The method for producing an optical film as described in 1 above, wherein the liquid is supplied by flowing down from the plurality of openings.

3. A part of the casting die is a supply member having the plurality of openings,
The supply step includes
2. The method for producing an optical film as described in 1 above, wherein the liquid flows down from the plurality of openings of the supply member and is supplied to an end of the dope outlet.

  4). 4. The method for producing an optical film according to any one of 1 to 3, wherein an opening diameter of the plurality of openings is in a range of 0.001 to 0.5 mm.

5. 5. The method for producing an optical film according to claim 1, wherein an area occupied by the plurality of openings is 1 to 100 mm ² .

  6). The said supply member consists of a porous material, The said liquid flows down from the hole of this porous material, and supplies it to the edge part of the said dope outflow port, The said any one of 1-5 characterized by the above-mentioned. Manufacturing method of the optical film.

7). Means for casting a dope containing a resin and a solvent from a dope outlet of a casting die onto a support, and a casting film for casting the dope from the dope outlet onto the support. A pressure reducing chamber for maintaining the pressure on the upstream side in the movement direction of the surface of the support of the dope outlet at a state lower than atmospheric pressure so that the dope outlet is in close contact with the liquid, and the liquid dissolving the resin is at both ends of the dope outlet In an optical film manufacturing apparatus having a supply means for supplying to a section,
The supply means is a supply member that is arranged corresponding to each of both ends of the dope outlet, has a plurality of openings, and supplies the liquid by flowing down from the plurality of openings. An optical film manufacturing apparatus.

  8). 7. An optical film produced by the method for producing an optical film according to any one of 1 to 6 above.

  9. 9. A polarizing plate comprising the optical film according to 8 on at least one surface.

  10. 10. A display device using the polarizing plate as described in 9 above.

  According to the method for producing an optical film of the present invention, the both ends of the dope outlet in the longitudinal direction have a supply step of supplying a liquid for dissolving the resin, and the supply step of the supply member having a plurality of openings The liquid is supplied by flowing down from a plurality of openings. By doing so, when supplying the solidification preventing liquid to both ends of the dope outlet, the scattering of the solidification preventing liquid to the decompression chamber is suppressed, there is no adhesion to the casting film, and both ends of the dope outlet A method and apparatus for manufacturing an optical film having a surface with good flatness, which can suppress skinning to a part, an optical film manufactured using the manufacturing method, a polarizing plate using the optical film, and a display device are provided. be able to.

It is the schematic which shows the manufacturing method of the optical film of this invention. It is the schematic which shows the dope casting process in the manufacturing method of the optical film of this invention. The arrangement | positioning condition of the casting die seen from the support body side in the manufacturing method of the optical film of this invention, the decompression chamber, and the supply nozzle of anti-caking liquid is shown. It is the schematic which shows the side view of the casting die which concerns on this invention, and the cross section of a side plate. It is the schematic which shows arrangement | positioning of the supply nozzle and casting die which were used in the Example of this invention. It is the schematic which shows the position of the side plate which has arrange | positioned the supply member used in the Example of this invention, and a casting film.

  Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

  FIG. 1 is a schematic diagram illustrating an example of a flow from a casting process to a winding process in the method for producing an optical film of the present invention. A dope (resin solution) in which a resin raw material is dissolved in a solvent is cast from a casting die 1 onto a support 2 (casting process), and the cast film 3 cast onto the support 2 is formed as a support 2. After being dried to a predetermined concentration above, it is peeled off from the support 2 by the peeling roll 4 (peeling step). Then, after drying by the initial drying device 13 (initial drying step), the film is stretched by the stretching device 14, further dried by the post-drying device 15 (post-drying step), and wound by the winding device 18 (winding step). .

  FIG. 2A is an enlarged view of a casting process in which the dope is cast on the support 2 by the casting die 1.

  In the casting method of the optical film of the present invention, in the casting step, a dope containing a resin and a solvent is cast from the dope outlet 1a of the casting die 1 onto the moving support 2 and cast. In the step of forming the film 3, in order to prevent the dope from solidifying at both ends of the dope outlet 1a and causing skinning, a liquid that dissolves the resin stored in the liquid storage tank 32 (anti-solidification prevention) Liquid) 33 is supplied to both ends of the dope outlet 1a, and the casting film 3 is adhered to the support 2 so that the casting film 3 does not flutter on the support 2 For this purpose, the dope outlet 1a includes a decompression step 10 for reducing the pressure by providing a decompression chamber 10 that keeps the upstream side in the moving direction of the support 2 in a decompressed state. And the supply nozzle 30 at the tip of the supply nozzle 30 And location, and supplying the plurality of openings of the supply member 34 having a plurality of openings at both ends of the liquid flow down to dope outlet 1a.

  FIG. 2B is a schematic view of the supply member 34 as seen from the outlet side. On the outlet side of the supply member 34, there are a plurality of openings 341. A liquid that dissolves the resin contained in the dope flows out from each opening 341 and supplies the liquid to the end of the dope outlet. The supply member 34 may have a shape in which a large number of thin nozzles are combined.

  The anti-caking liquid 33 may be any liquid that dissolves the resin, but preferably the same as that used for the dope, because mixing with the dope occurs easily and more uniformly.

  FIG. 3 is a schematic view showing the arrangement of the casting die 1, the decompression chamber 10, and the anti-caking liquid supply nozzle 30 as viewed from the support 2 side. The anti-caking liquid 33 flowing down from the plurality of openings of the supply member 34 having a plurality of openings arranged at the tip of the supply nozzle 30 is supplied to both ends in the width direction of the dope outlet 1 a of the casting die 1. Is done. The decompression chamber 10 is arranged on the upstream side in the movement direction of the surface of the support body of the dope outlet 1a. The air pressure in the decompression chamber 10 is reduced by connecting the decompression pump 102 and the pipe 103 to the suction port 101 and performing suction. By this decompression, the casting film 3 is brought into close contact with the surface of the support 2 to form a film.

  In this way, by supplying the liquid (solidification preventing liquid) 33 for dissolving the resin contained in the dope from the plurality of openings of the supply member 34 having the plurality of openings, and supplying the liquid to both ends of the dope outlet 1a. Further, it is possible to suppress skinning at both ends of the dope outlet and to prevent the anti-caking liquid from scattering into the decompression chamber. This is because the tip of the supply nozzle has one opening as in the prior art, and in the method of discharging the solidification preventing liquid from the opening to the surface of the casting die near the dope outlet, The anti-caking liquid was in the form of droplets and did not flow smoothly, and was easily scattered into the decompression chamber on the upstream side. Moreover, if the amount of the dropping liquid was reduced so as not to scatter, it was not possible to suppress the skinning on both ends of the dope outlet. On the other hand, the anti-caking liquid flowing down from the supply member 34 having a plurality of openings according to the present invention is applied to the surface of the casting die immediately after flowing down in order to flow the required amount of liquid from the plurality of openings. By adhering, it is possible to form a liquid film that does not become droplets but conforms to the surface of the casting die. Thus, since the solidification preventing liquid can flow down in the form of a liquid film and be supplied to the end portion of the dope outlet, scattering to the decompression chamber 10 can be prevented and skinning can be sufficiently suppressed.

  Further, a part of the casting die 1 is a supply member having a plurality of openings, and the solidification preventing liquid flows out from the plurality of openings of the supply member and is supplied to both longitudinal ends of the dope outlet 1a. Anyway.

  FIG. 4A shows a side view of the casting die 1. The casting die 1 includes a die central portion 12 that constitutes upstream and downstream walls in the moving direction of the support surface of the dope outlet 1a, and a side plate 11 that constitutes a longitudinal wall of the dope outlet 1a. Have. FIG. 4B is a cross-sectional view of the side plate 11 cut along the AA cross section of FIG. The side plate 11 uses a supply member 34 for a part thereof. The solidification prevention liquid is supplied to the supply member 34 through the solidification prevention liquid supply port 35, and the supply member 34 flows down the solidification prevention liquid from a plurality of openings and supplies the solidification prevention liquid to both ends in the width direction of the casting film 3.

  In this way, a part of the casting die 1 is constituted by the supply member 34, and the anti-solidification liquid oozes out by supplying the anti-solidification liquid to both ends of the dope outlet 1 a from the plurality of openings of the supply member 34. In this state, it can be supplied to the surface of the casting die 1 and can flow down into a film shape on the surface of the casting die 1 to be supplied to the end of the dope outlet 1a. It can prevent more and can also suppress skinning sufficiently. Moreover, since the solidification preventing liquid can be accurately supplied in the vicinity of the dope outlet by arranging the supply member in a part of the casting die 1, the evaporation of the solidification preventing liquid is suppressed and a prescribed amount of solvent is supplied. In addition to this, cooling of the die surface due to evaporation can be suppressed, and inhibition of the flow of the solidification preventing liquid due to moisture condensation can be prevented.

  Moreover, it is preferable that the opening diameter from which the solidification preventing liquid of the supply member 34 having a plurality of openings is discharged is in the range of 0.001 to 0.5 mm. By making the opening diameter within this range, it is not necessary to excessively increase the pressure for discharging, and the discharged anti-solidification liquid can easily flow down the surface of the casting die 1 in the form of a liquid film, It becomes easy to suppress scattering of droplets. The opening diameter is a value obtained by calculating a diameter corresponding to a circle from the opening area of each opening of the supply member 34.

Further, the area occupied by the plurality of openings of the supply member 34 disposed at the tip of the supply nozzle 30 (also referred to as supply area) is preferably 1 to 100 mm ² . By setting it within this range, it is possible to suppress skinning at both ends of the dope outlet and to effectively prevent the anti-solidification liquid from being mixed into the decompression chamber. If it is less than 1 mm ² , the supply amount of the anti-caking liquid is small, and increasing the flow rate is not preferable because it becomes droplets and scatters. Undesirable because the liquid discharged to exceed 100 mm ² condensation moisture will evaporate occurs.

  The supply member 34 having a plurality of openings disposed at the tip of the supply nozzle 30 is preferably a porous material that is not dissolved in the anti-caking liquid, and more preferably metal or ceramic.

  As the shape of the porous material, a mesh filter, a laminate of mesh filters, a filter having a spongy communication port, or the like can be used.

  For example, as a porous body having a communication port made of metal, stainless steel (SUS316L, SUS630, SUS310Mo, SUS410L, SUS630, SUS420J2, SUS440C), titanium and a titanium alloy (Ti-6A1-4V), copper and a copper alloy, nickel A pore forming material is added to a raw material composed of a metal powder such as low alloy steel (SCM415) or aluminum and a binder, and molding, degreasing (removing the pore forming material into a porous body), and sintering. The metal porous material which has the created communicating port can be used.

  Next, the optical film manufacturing method of the present invention will be described in more detail with reference to FIG.

  An embodiment of the optical film manufacturing method using the solution casting film forming method of the present invention includes a dope preparation step, a casting step, a peeling step, a drying step, and a winding step.

  That is, in the method for producing an optical film by the solution casting film forming method of this embodiment, a dope (resin solution) obtained by dissolving a resin film raw material in a solvent is supplied from a casting die, for example, a rotationally driven metal having a width of 1.8 m or more In this method, the cast film (film) cast on an endless belt (belt support) and then peeled off from the belt support is dried, and then wound up to produce an optical film. Each step will be described.

[Dope preparation process]
In the present invention, cellulose ester is preferably used as the resin film raw material. When cellulose ester is used as the resin film raw material, a mixed solvent of methylene chloride and alcohol is preferably used as the solvent.

  Other additives added to the dope include a plasticizer, an ultraviolet absorber, an antioxidant, a dye, and a matting agent. In the present invention, these additives may be added when preparing a cellulose ester solution, or may be added when preparing a dispersion such as a matting agent.

  Although the example in case resin of an optical film is a cellulose ester below is shown, this invention is not necessarily limited to this.

  First, cellulose ester is usually dissolved by a method such as a stirring dissolution method, a heating dissolution method, or an ultrasonic dissolution method in a dissolution vessel, and the solvent boils above the boiling point at normal pressure of the solvent under pressure. A method of heating at a temperature within a range not to dissolve and dissolving while stirring is more preferable in order to prevent generation of massive undissolved material called gel or mamako. Further, a cooling dissolution method described in JP-A-9-95538 or a method of dissolving under high pressure described in JP-A-11-21379 may be used.

  A method in which cellulose ester is mixed with a poor solvent and wetted or swollen, and then mixed with a good solvent and dissolved is also preferably used. At this time, an apparatus for mixing or dissolving cellulose ester with a poor solvent and an apparatus for mixing and dissolving with a good solvent may be separately provided.

  The type of the pressure vessel used for dissolving the cellulose ester is not particularly limited as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. In addition, instruments such as a pressure gauge and a thermometer are appropriately disposed in the pressurized container. The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature when the solvent is added is equal to or higher than the boiling point of the solvent to be used. In the case of two or more mixed solvents, the heating temperature is higher than the boiling point of the lower boiling solvent and the solvent does not boil. Is preferred. If the heating temperature is too high, the required pressure increases and productivity decreases. The range of preferable heating temperature is 20-120 degreeC, 30-100 degreeC is more preferable, The range of 40-80 degreeC is further more preferable. The pressure is adjusted so that the solvent does not boil at the set temperature.

  After dissolving the cellulose ester, take it out from the container while cooling, or take it out from the container with a pump and cool it with a heat exchanger, etc., and use the resulting resin dope for film formation. May be cooled to room temperature.

  The mixture of the raw material cellulose ester and the solvent is dissolved by a dissolving device having a stirrer, and at this time, the peripheral speed of the stirring blade is preferably at least 0.5 m / second and is dissolved by stirring for 30 minutes or more.

  In the present invention, the cellulose ester dope is filtered to remove foreign matter, particularly foreign matter that is mistakenly recognized as an image in a liquid crystal image display device.

  Filter media used for filtration preferably have a low absolute filtration accuracy, but if the absolute filtration accuracy is too low, the filter media is likely to be clogged, and the filter media must be frequently replaced. There is a problem of lowering.

  For this reason, the filter medium used for the cellulose ester dope preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and more preferably in the range of 0.003 to 0.006 mm. Further preferred.

  There are no particular restrictions on the material of the filter medium, and normal filter media can be used. However, plastic fiber filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel fibers are used to remove fibers. This is preferable.

  Filtration of the cellulose ester dope can be performed by a normal method, but the method of filtering while heating under pressure at a temperature not lower than the boiling point of the solvent at a normal pressure and in which the solvent does not boil is a differential pressure before and after the filter medium. (Hereinafter, it may be referred to as filtration pressure) The rise of a small is preferable.

  A preferred temperature range is 45 to 120 ° C, more preferably 45 to 70 ° C, and even more preferably 45 to 55 ° C.

  The filtration pressure is preferably 3500 kPa or less, more preferably 3000 kPa or less, and even more preferably 2500 kPa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

[Casting process]
First, in the casting process, the dope adjusted in the melting pot is fed to the casting die 1 by a conduit and is transported infinitely, for example, at a casting position on the support 2 made of a rotationally driven stainless steel endless belt. In this step, the dope is cast from the casting die 1.

  The casting die 1 is preferably a pressure die that can adjust the slit shape of the dope outlet 1a and easily make the film thickness uniform.

  The gap between the dope outlet 1a of the casting die 1 and the surface of the support 2 is preferably set with a gap of 0.2 to 10 mm, more preferably 0.5 to 5 mm.

  The slit gap of the casting die 1 is preferably 0.05 to 1.5 mm, more preferably 0.15 to 1.0 mm.

  Next, the support 2 will be described.

  The surface roughness Ra of the support 2 is 0.0001 to 1 μm, more preferably 0.0003 to 0.1 μm, and still more preferably 0.0005 to 0.05 μm.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the support body 2, the belt support body 2 is disposed between a pair of drums 19 and an intermediate portion thereof, and an upper transition portion and a lower transition portion of the endless belt support body 2 are respectively provided. It consists of a plurality of rolls (not shown) supported from the back side. The plurality of rolls are called support rolls, and the distance between adjacent support rolls is greater than 0 m and within a range of 5 m or less, preferably 1 to 5 m, more preferably 2 to 5 m.

  In addition, one or both of the drums 19 at both ends of the rotary drive endless belt support 2 are provided with a drive device that applies tension to the belt support 2, whereby the belt support 2 is tensioned. Used in a stretched state.

  When an endless belt is used as the support 2, the belt temperature during film formation can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, and further from 5 ° C. to the boiling point of the solvent− A range of 5 ° C. is more preferred. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  In the present invention, the resin used in the dope is dissolved in order to prevent the resin in the dope from adhering to both ends in the width direction of the dope outlet 1a of the casting die 1 to cause skinning. A supplying step of supplying the liquid (anti-solidification liquid) to be supplied to both ends of the dope outlet 1a. In this supply step, the anti-caking liquid is supplied by flowing down from the plurality of openings of the supply member having the plurality of openings. In FIG. 1, the supply nozzle 3 is used to dispose a supply member at the tip of the supply nozzle 3 and supply the solidification preventing liquid from a plurality of openings of the supply member. The member used from the storage tank of the anti-caking liquid shown in FIG. 1 to the supply port is preferably free from components eluted by the solvent. For example, a member made of an inorganic substance such as glass, stainless steel, or ceramic is preferably used. Further, a filter may be provided in the middle in order to suppress the outflow of foreign substances. The filter medium used at this time is also preferably made of metal in order to suppress elution. By suppressing the eluted components and foreign substances, the solidification preventing liquid can be smoothly flowed down. In order to obtain a stable flow, it is preferable that the anti-caking liquid supplied in this way does not contain a non-volatile component. In order to supply the solidification preventing liquid at a constant flow rate, a flow rate adjusting mechanism is provided between the storage tank and the supply port. The flow rate adjustment mechanism includes valve opening + free fall, flow rate control by a pump, and the like. In the case of free fall, a function to keep the liquid level of the storage tank constant is necessary. When using a pump, a pump capable of controlling a small flow rate with high accuracy is preferable. For example, a precision gear pump, a diaphragm pump, a plunger pump, a magnet pump, etc. are used. Since the supply member at the tip has already been described in detail, a description thereof is omitted here.

  In addition, a decompression chamber 10 is provided for maintaining the upstream side in the movement direction of the surface of the support 2 at the dope outlet 1a in a decompressed state. In the decompression chamber 10, when the conveying speed of the support 2 is 10 m / min or more, the casting film 3 coming out from the dope outlet 1 a of the casting die 1 is depressurized to be mixed with air or horizontally in the film width direction. Although provided in order to suppress fluttering of the casting ribbon that causes stepped streaks, since the decompression chamber 10 is provided, a liquid (anti-solidification solution) for dissolving the resin used for the dope is provided in the decompression chamber 10. It becomes easy to scatter.

  When the anti-caking liquid splashes into the decompression chamber, it falls directly on the support or adheres to the inner wall of the decompression chamber, and a part of it falls on the support surface and the pattern is transferred to the film, resulting in quality failure. However, in the present invention, since the solidification preventing liquid is supplied to the end portion of the dope outflow port from the plurality of openings of the supply member 34 having a plurality of openings, the excess solidification prevention liquid is supplied. It is possible to suppress the scattering to the decompression chamber 10 and to prevent the anti-caking liquid adhering to the decompression chamber wall from adhering to the support and generating a round or elliptical deformation pattern on the created film surface. Can do.

  The anti-caking liquid is not particularly limited as long as it dissolves the resin used for the dope, but it is preferable to use the solvent used for the dope, and more preferably, the same solvent composition as the dope. It is good to use. By using a solvent having the same composition as that of the dope, the solvent evaporation rate on the film surface becomes uniform even when it flows down to the casting film 3, and a more uniform casting film can be formed.

  Examples of organic solvents having good solubility for cellulose derivatives include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1 , Ethers such as 2-dimethoxyethane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, and other esters, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, Examples include dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride, and methyl acetoacetate, and 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate, and methylene chloride are preferable. In addition to the organic solvent, it is preferable to contain 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms. After the above-mentioned alcohol is cast on the casting membrane, the solvent starts to evaporate and the ratio of the alcohol increases, thereby causing the web to gel, making the web strong, and casting from the metal support. It can be used as a gelling solvent that facilitates peeling. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

  The pressure in the decompression chamber is preferably 10 to 1500 Pa reduced from the atmospheric pressure.

  The gap between the lower end surface of the decompression chamber and the surface of the support 2 is in the range of 0.1 to 5 mm, the suction air volume does not become too large, so that the dope dry film ( This is desirable because the occurrence of skinning is further suppressed.

  When casting the dope onto the support 2, it is preferable to control the temperature below the boiling point of the solvent used for dissolving the raw resin, and below the boiling point of the solvent having the lowest boiling point in the mixed solvent.

  In the system using an endless belt as the support 2, since the cast film 3 is dried and solidified on the support 2 until the film strength becomes detachable from the support 2, the residual solvent amount in the cast film 3 is reduced. It is preferable to dry to 100% by mass or less with respect to 100% by mass of the solid content, and more preferably 80 to 120% by mass. Moreover, as for the casting membrane temperature when peeling the casting membrane 3 from the support body 2, 0-30 degreeC is preferable. Further, immediately after peeling from the support 2, the temperature of the cast film 3 rapidly decreases due to solvent evaporation from the support 2 contact surface side, and volatile components such as water vapor and solvent vapor in the atmosphere tend to condense. Therefore, the casting film temperature during peeling is more preferably 5 to 30 ° C.

  The dope film (cast film) formed by the dope cast on the endless belt support 2 is heated on the support 2 to evaporate the solvent until the cast film can be peeled from the support 2. . In order to evaporate the solvent, there are a method of blowing air from the casting film side, a method of transferring heat from the back surface of the support 2 by liquid, a method of transferring heat from the front and back by radiant heat, and the like.

[Peeling process]
In the system using an endless belt for the support 2, the peeling tension when peeling the support 2 and the casting film 3 is the tension per 1 m of the casting film width, and the casting film 3 is wrinkled during peeling. Since it is easy to enter, it is preferable to peel at a minimum tension that can be peeled to 200 N, and more preferably to peel at a minimum tension to 150 N.

[Drying process]
In the system using an endless belt for the support 2, the cast film 3 after peeling is introduced into the initial drying device 13. In the initial drying apparatus 13, the casting film 3 is conveyed by a plurality of conveying rolls 17 arranged in a staggered manner as viewed from the side, and the casting film 3 is blown from the front portion of the bottom of the initial drying apparatus 13 in the meantime. Rarely, it is dried by the warm air 26 discharged from the rear portion of the ceiling of the initial drying device 13.

  The diameter of the roll used is preferably 50 to 300 mm, more preferably 100 to 200 mm.

  Thereafter, post-drying is performed by the post-drying device 15. In the post-drying device 15, the casting film 3 is transported by a plurality of transporting rolls 17 arranged in a staggered manner as viewed from the side, and the casting film 3 is dried in the meantime. Moreover, although the film conveyance tension | tensile_strength in the post-drying apparatus 15 is influenced by the physical property of dope, the amount of residual solvents at the time of peeling and a film conveyance process, the temperature in the post-drying apparatus 15, etc., per 1 m of casting film width | variety The tension is preferably 30 to 250N, and more preferably 50 to 150N. 80 to 120N is most preferable.

  The means for drying the cast film 3 (or film) is not particularly limited and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, the air is blown from the front portion of the bottom of the post-drying device 15 and dried by the warm air 25 discharged from the rear portion of the ceiling of the post-drying device 15. The drying temperature is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve the flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  Next, an embossing process and a static elimination process can be provided.

  The embossing provided in the both-sides edge part of the cast film 3 after a post-drying process is demonstrated. For the resin film that has finished the post-drying process, embossing is performed on the film by the embossing apparatus 60 in the previous stage of introduction into the winding process.

  Here, the height of the emboss is set in a range of 0.05 to 0.3 times the film thickness T, and the width is set in a range of 0.005 to 0.02 times the film width L. For example, when the film thickness is 40 μm and the film width is 100 cm, the height of the emboss 31 is set to 2 to 12 μm and the width is set to 5 to 30 mm. Embossing may be formed on both sides of the film.

  It is preferable that a static eliminator is installed before winding and immediately after the winding unit to neutralize the film.

  The static eliminator can be configured to apply a reverse potential by a static eliminator or a forced charging device at the time of winding so that the charging potential when the original winding is re-drawn is ± 2 kV or less. It can also be set as the structure which static-eliminates with the static elimination device converted into positive / negative alternately at 1-150Hz.

  Moreover, it can replace with said static elimination device and can utilize the ionizer and static elimination bar which generate | occur | produce ion wind. Here, the ionizer static elimination is performed by blowing an ion wind toward the film wound up from the embossing device via the transport roll. The ion wind is generated by a static eliminator. Any known static eliminator can be used without limitation.

  The static elimination at the time of film forming winding is to induce coating unevenness when the charged potential is ± 2kV or more when the original film is redrawn and the functional film is applied, especially when pursuing thin film and high speed. Since film peeling electrification at the time of re-feeding becomes high, static elimination during film formation is essential.

[Winding process]
The cast film 3 that has been dried is wound up as a film by the winding device 18. This is a step of obtaining the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film 20 to be dried to 0.5% by mass or less, preferably 0.1% by mass or less.

  The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. Use it properly.

  The film may be bonded to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  The film thickness of the optical film produced by the production method of the present invention varies depending on the purpose of use, but from the viewpoint of thinning the liquid crystal display device and film strength, it is preferable to adjust the finished film to a range of 10 to 150 μm, Furthermore, it is more preferable to adjust to the range of 20-100 micrometers, and it is especially preferable to adjust to the range of 25-80 micrometers.

  Next, the cellulose ester film produced by the production method of the present invention can be used for polarizing plates and display devices.

  The polarizing plate in this invention has the protective film for polarizing plates which consists of an optical film manufactured by this invention in at least one surface.

  And in this invention, a liquid crystal display device has said polarizing plate in the at least one surface of a liquid crystal cell.

  Next, these polarizing plates and a liquid crystal display device using the polarizing plates will be described.

  The polarizing plate can be produced by a general method. The cellulose ester film according to the present invention subjected to alkali saponification treatment is preferably bonded to at least one surface of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. . The cellulose ester film according to the present invention may be used on the other surface, or another protective film for polarizing plate may be used. With respect to the cellulose ester film according to the present invention, a commercially available cellulose ester film can be used as the protective film for polarizing plate used on the other surface. For example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA, KC8UX-RHA-N (manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used. Or you may use films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate, as a protective film for polarizing plates of the other surface. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

  The polarizing plate of the present invention is obtained by using the cellulose ester film according to the present invention as a protective film for a polarizing plate on at least one side of a polarizer. In that case, it is preferable to arrange | position so that the slow axis of this cellulose-ester film may be substantially parallel or orthogonal to the absorption axis of a polarizer.

  It is preferable that the cellulose ester film by this invention is arrange | positioned at the liquid crystal display cell side as one polarizing plate arrange | positioned on both sides of the liquid crystal cell which is a horizontal electric field switching mode type | mold.

  Examples of the polarizer preferably used for the polarizing plate include a polyvinyl alcohol polarizing film, which includes a polyvinyl alcohol film dyed with iodine and a dichroic dye dyed. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

  The film thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. One side of the cellulose ester film according to the present invention is bonded to the surface of the polarizer to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Moreover, in the case of resin films other than a cellulose ester film, it can be bonded to the polarizing plate via an appropriate adhesive layer.

  Since the polarizer is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction orthogonal to the stretching ( Usually stretches in the width direction). As the film thickness of the protective film for polarizing plate decreases, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizer increases. Usually, the stretching direction of the polarizer is bonded to the casting direction (MD direction) of the protective film for polarizing plate. Therefore, when thinning the protective film for polarizing plate, it is important to suppress the stretch rate in the casting direction. It is. Since the cellulose ester film according to the present invention has no unevenness on the surface and is excellent in smoothness, it is preferably used as such a protective film for a polarizing plate.

The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection.
(Liquid crystal display device)
By incorporating a polarizing plate using an optical film produced according to the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced.

  Here, the liquid crystal display device generally absorbs light by a polarizing plate protective film / dichroic material having polarizing scattering anisotropy adjacent to a light reflection plate, a backlight, a light guide plate, and a light diffusion plate. It is preferable that the structure of the dichroic polarizing film / polarizing plate protective film using the action, and the liquid crystal display panel and the viewing side polarizing plate are stacked in this order.

  The optical film produced by the present invention can be used in various drive systems such as reflective, transmissive, transflective LCD or TN, STN, OCB, HAN, VA (PVA, MVA) and IPS. It is preferably used in LCDs, and has the effect that there is little color unevenness, glare and wavy unevenness, and eyes are not tired even during long-time viewing.

  As described above, a liquid crystal display device having a polarizing plate using an optical film produced according to the present invention on at least one surface of a liquid crystal cell has very excellent display quality.

Hereinafter, although the example implemented with the manufacturing method of the optical film using this invention is shown, this invention is not limited by this.
(Examples 1 to 19)
(Dope preparation for solution casting film formation)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate 100 parts by mass (Mn = 148000, Mw = 310000, Mw / Mn = 2.1)
Triphenyl phosphate 8 parts by mass Ethylphthalyl ethyl glycolate 2 parts by mass Methylene chloride 440 parts by mass Ethanol 40 parts by mass Tinuvin 109 (manufactured by Ciba Japan) 0.5 part by mass Tinuvin 171 (manufactured by Ciba Japan) ) 0.5 part by mass Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.2 part by mass The material of the above dope composition 1 was put into a sealed container, heated, stirred and completely dissolved, and filtered. The filtration was performed through a sintered metal filter (capture particle size = 10 microns) after filtration by a filter press.

(Production of optical film)
Using the above dope, an optical film was produced as follows. Film formation was performed with the manufacturing apparatus shown in FIG. First, the filtered dope was cast in the form of a film from a casting die made of a coat hanger die onto a metal support made of an endless belt made of SUS316 and polished to a super mirror surface.

  As a solidification preventing liquid, methylene chloride was allowed to flow down from the both ends of the dope outlet to the cast film. The liquid temperature of the anti-caking liquid was 25 ° C.

As the supply member 34, SUS316L powder is kneaded with a binder and a pore-forming material, and the communication obtained through a molding step, a degreasing step (removing the pore-forming material into a porous body), and a sintering step. A metal porous material having a mouth was used. FIG. 5 shows an enlarged view of the arrangement of the casting die 1, the supply nozzle 30 and the supply member 34 when the supply nozzle 30 is used. 6 is an enlarged view of the arrangement of the casting die 1 and the feeding member 34 arranged on the side plate 11 of the casting die 1 when the feeding member 34 arranged at the end of the side plate 11 of the casting die 1 is used. Show. When the supply nozzle 30 of FIG. 5 is used, the tip portion has a circular opening (inner diameter d), and the supply member 34 is disposed in the opening. The outlet side of the supply member 34 is disposed in the vicinity of the dope outlet 1a of the casting die 1, and a liquid film is formed on the surface of the casting die 1 as soon as the anti-caking liquid is discharged from the plurality of openings of the supply member 34. Then, they are arranged close to each other so as to flow down and to be supplied to the end of the dope outlet 1a. The supply distance between the supply member 34 and the dope outlet 1a of the casting die 1 is L, the supply area of the supply member 34 (area occupied by a plurality of openings on the outlet side = (d / 2) ² × π × aperture ratio) , S, and the opening diameter of the porous material (the diameter corresponding to the circle of the area obtained by dividing the supply area S by the number of openings) is d1. When the supply member 34 is used as a part of the side plate in FIG. 6, the shape of the outlet discharged from the supply member 34 is a regular square having one side h. In this case, the supply area S was calculated as h × h × opening ratio. The supply flow rate supplied from the supply member 34 to the end portion of the dope outflow port was set to W. Each value was changed to obtain the production conditions for producing the optical films of Examples 1 to 19 shown in Table 1.

  The decompression chamber on the upstream side in the movement direction of the surface of the support 2 at the dope outlet was decompressed to a value lower by 500 Pa than the atmospheric pressure. Note that the decompression was controlled by connecting the decompression pump 102 and the pipe 103 to control the degree of decompression.

As a support, a metal belt is used, and the cast film cast on the support is peeled off by a peeling roll, and then dried in an initial drying zone of 90 ° C. while being transported by a roll. Drying was terminated in the drying zone, and the film was continuously formed for 48 hours at a film thickness of 40 μm and a film width of 2000 mm, and wound up to produce the cellulose triacetate film of each Example.
(Comparative Example 1)
As Comparative Example 1, it was produced in the same manner as in Example 3 except that the opening at the tip of the supply nozzle 30 was used as it was without using the supply member 34 in Example 3.
(Comparative Example 2)
As Comparative Example 2, it was produced in the same manner as in Example 15 except that the supply member 34 in Example 15 was not used and the portion where the supply member 34 was used was used as the opening.

Evaluation of the optical films of Examples 1 to 19 and Comparative Examples 1 and 2 obtained as described above was performed as follows.
(Evaluation of skinning at both ends of dope outlet)
During the production of the optical film, the skin is visually observed. If the skin occurs, the device is stopped, the skin is removed, and the production is continued again. The number of skinning occurrences was evaluated. If the number of occurrences of skinning is less than 5 times, 3 times or less is more preferable at a level where there is no problem in productivity. If it exceeds 5 times, productivity will fall and it will be a level which cannot be adopted as manufacturing conditions.
(Evaluation of deformation pattern on film surface)
The deformation pattern on the surface of the film immediately before winding was optically detected by a detection device, and the number of deformation patterns with a diameter of 1000 μm or more was compared with the number per 24 hours during the 48 hours when the product was actually manufactured. If it is less than 10, there is no problem as a product, and 5 or less is more preferable. When the number is 10 or more, there is a problem level as a product.

  The evaluation results are shown in Table 1.

From the results of Table 1, when Examples 1 to 19 and Comparative Examples 1 and 2 are compared, a solidification preventing liquid is supplied to the casting film flowing out from both ends of the dope outlet using a supply member having a plurality of openings. By doing so, the skinning at both ends of the dope outlet is suppressed, and the generation of deformation patterns caused by the anti-caking liquid splashing into the decompression chamber and falling from the inside of the decompression chamber to the support is also suppressed. It turns out that a film can be manufactured. Moreover, when Examples 1-19 are compared, it is preferable that the opening diameter of the opening part of a supply member is 0.001-0.5 mm, and, as a supply area of a supply member, 1-100 mm < ² > is preferable. I understand.
(Preparation of polarizing plate)
In accordance with the method described below, the optical films of Examples 1 to 19 and Comparative Examples 1 and 2 were subjected to alkali saponification treatment, and then polarizing plates were produced.
<Alkali saponification treatment>
Saponification step: 2 mol / L NaOH 50 ° C. 90 seconds water washing step: Water 30 ° C. 45 seconds neutralization step: 10% by mass HCl 30 ° C. 45 seconds water washing step: water 30 ° C. 45 seconds Each sample was saponified under the above conditions. , Water washing, neutralization and water washing in this order, followed by drying at 80 ° C.

A 120 μm thick polyvinyl alcohol film was immersed in 100 kg of an aqueous solution containing 1 kg of iodine and 4 kg of boric acid, and stretched 6 times at 50 ° C. to prepare a polarizing film. The optical films of Examples 1 to 19 and Comparative Examples 1 and 2 were applied to one side of this polarizing film, and Konica Minolta Tack KC8UCR (manufactured by Konica Minolta Opto) was subjected to the alkali saponification treatment on the opposite side, and then completely A polarizing plate was prepared by bonding saponified polyvinyl alcohol 5% by mass aqueous solution as an adhesive.
(Characteristic evaluation as a liquid crystal display device)
Strip the polarizing plate on the viewing side of the Sony 40-type display KLV-40V1000, and make each polarizing plate perpendicular to each other so that the polarizing axis of the polarizing plate does not change according to the size of the liquid crystal cell. A 40-inch TFT color liquid crystal display was prepared, and the properties of the optical film as a polarizing plate were evaluated.

  The liquid crystal display device mounted with the polarizing plate using the optical film of Examples 1 to 19 of the present invention is different from the liquid crystal display device mounted with the polarizing plate using the optical film of Comparative Examples 1 and 2 in terms of color unevenness. There was no display unevenness such as unevenness in the wave, and the display was excellent. Thereby, it was confirmed that the polarizing plate of this invention is excellent as a polarizing plate for image display apparatuses, such as a liquid crystal display.

DESCRIPTION OF SYMBOLS 1 Casting die 1a Dope outflow port 2 Support body 3 Casting film 4 Peeling roll 17 Conveyance roll 10 Depressurization chamber 11 Side plate 12 Die center part 13 Initial drying apparatus 15 Post-drying apparatus 18 Winding apparatus 30 Supply nozzle 31 Flow control mechanism 32 Liquid storage tank 33 Anti-caking liquid 34 Supply member 341 Opening 35 Anti-caking liquid supply port 70 Shield plate 101 Suction port 20 Film 60 Embossing device

Claims (10)

A casting step of casting a dope containing a resin and a solvent from a dope outlet of a casting die onto a support, and a casting film to cast the dope from the dope outlet onto the support, A pressure reducing step for maintaining the pressure on the upstream side in the movement direction of the surface of the support at the dope outlet in a state lower than atmospheric pressure so that the dope outlet is in close contact with the support; and a liquid for dissolving the resin is added to the dope outlet. In the manufacturing method of the optical film having a supply step of supplying to both ends of the
In the supplying step, the liquid is caused to flow down and supplied from the plurality of openings of a supply member having a plurality of openings arranged corresponding to both ends of the dope outlet. A method for producing a film. The supply step includes
The tip of the nozzle in which the supply member having the plurality of openings is arranged at the tip thereof is arranged in the vicinity of both longitudinal ends of the dope outlet,
The method for producing an optical film according to claim 1, wherein the liquid is supplied by flowing down from the plurality of openings. A part of the casting die is a supply member having the plurality of openings,
The supply step includes
The method for producing an optical film according to claim 1, wherein the liquid flows down from the plurality of openings of the supply member and is supplied to an end of the dope outlet. The method for producing an optical film according to any one of claims 1 to 3, wherein an opening diameter of the plurality of openings is in a range of 0.001 to 0.5 mm. 5. The method for producing an optical film according to claim 1, wherein an area occupied by the plurality of openings is 1 to 100 mm ² . The said supply member consists of porous materials, The said liquid is flowed down from the hole of this porous material, and it supplies to the edge part of the said dope outflow port, Any one of Claim 1 to 5 characterized by the above-mentioned. The manufacturing method of the optical film of description. Means for casting a dope containing a resin and a solvent from a dope outlet of a casting die onto a support, and a casting film for casting the dope from the dope outlet onto the support. A pressure reducing chamber for maintaining the pressure on the upstream side in the movement direction of the surface of the support of the dope outlet at a state lower than atmospheric pressure so that the dope outlet is in close contact with the liquid, and the liquid dissolving the resin is at both ends of the dope outlet In an optical film manufacturing apparatus having a supply means for supplying to a section,
The supply means is a supply member that is arranged corresponding to each of both ends of the dope outlet, has a plurality of openings, and supplies the liquid by flowing down from the plurality of openings. An optical film manufacturing apparatus. An optical film manufactured by the method for manufacturing an optical film according to claim 1. A polarizing plate comprising the optical film according to claim 8 on at least one surface. A display device comprising the polarizing plate according to claim 9.

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