JP2009269225A - Optical film, its method for manufacturing, polarization plate using optical film and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film produced as a wide optical film excellent in flatness without producing the cramps and wrinkles caused by an air involving phenomenon in the film while reducing the involution of air and can meet the request of widening and the enhancement of quality, in a method for manufacturing of the optical film used as a protective film or the like for the polarization plate of a liquid crystal display (LCD), its method for manufacturing, the polarization plate using the optical film and a display. <P>SOLUTION: In the method for manufacturing of the optical film by a solution casting film forming method, air is blown on the contact point of a feed roll and a web from the surface side of the web in the state that the residual amount of the solvent in the web in a drying process is 50-150 wt.% to press the web to the surface of the roll in a close contact state. Air is preferably blown on the web over 0.7-1.0 times in the width direction of the web and the pressing force of the web by blown air is preferably 0.3-5 kPa. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention can be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used for a plasma display. The present invention relates to a film, a manufacturing method thereof, a polarizing plate using an optical film, and a display device.

  In recent years, liquid crystal display devices have come to be used in televisions and large monitors due to improvements in image quality and high definition technology. In particular, these liquid crystal display devices are costly due to their large size and efficient production. The demand for down and the like has become stronger in materials for liquid crystal display devices, and a wider optical film is required.

  In recent years, the demand for optical films has been increasing rapidly in response to the rapid growth of liquid crystal TVs, and there is a strong demand for improved productivity. In order to cope with an increase in the screen size of a liquid crystal TV, it is necessary to make a wide film that is wider than a conventional film.

  The optical film is generally manufactured by a solution casting film forming method. In the solution casting film forming method, a thermoplastic resin such as cellulose ester, which is a film raw material, is dissolved in a solvent, and it is necessary to dry the film (web) in order to evaporate the solvent during film formation. It becomes.

  Here, in the method for producing an optical film by the solution casting film forming method, immediately after the film (web) is peeled from the metal support, the drying rate of the residual solvent is high, so the film shrinkage is large, Is likely to occur.

  In particular, when the air entrainment amount between the roll and the film is large, the floating amount of the film is increased, and the regulating force in the width direction of the film by the roll is reduced, so that the occurrence of creases and wrinkles is promoted.

  The occurrence of creases and wrinkles in a region where the amount of residual solvent is large has a problem that the flatness of the film product is deteriorated because these marks remain on the film.

  Therefore, conventionally, by increasing the conveyance tension after peeling of the film (web), the roll and the film are brought into close contact with each other to suppress air entrainment.

  On the other hand, in Patent Document 1 below, for example, an optical film that dries while holding both ends of a film by a film width regulating device such as a tenter device and regulating the width shrinkage of the film or stretching in the width direction. A manufacturing method is disclosed.

Patent Document 2 below discloses an optical film manufacturing method that prevents the film from being creased or wrinkled by sandwiching both end portions of the polymer film between a transport roller and a nip roller.
JP-A-62-115035 JP 2005-161619 A

  However, according to the conventional method in which the conveyance tension after peeling of the film (web) is increased, there is a problem in that the physical properties of the film change because the film extends in the conveyance direction. Moreover, at the time of producing a wide film, it is difficult to suppress the entrainment of air only by increasing the conveyance tension.

  In addition, the method described in Patent Document 1 has a problem in that clip marks remain at both ends of the film and cannot be used as a product. Furthermore, the method described in Patent Document 2 has a problem that immediately after the film (web) is peeled off, the amount of residual solvent is high, and a nip mark remains on the film, thereby impairing the flatness.

  The object of the present invention is to solve the above-mentioned problems of the prior art, and in the optical film manufacturing method by the solution casting film forming method, it is possible to reduce air entrainment and generate creases and wrinkles due to the air entrainment phenomenon. Without making it, it is possible to produce a wide optical film with excellent flatness, whereby an optical film that can meet the demand for widening and high quality such as a protective film for a polarizing plate, its production method, An object of the present invention is to provide a polarizing plate using an optical film and a display device.

  As a result of intensive studies in view of the above points, the present inventor, as a result of an optical film manufacturing method using a solution casting film forming method, an air ejection device (air nozzle) near a transport roll in a film (web) drying process. , And by blowing air over the width direction of the web at the contact point between the transport roll and the web, the contact area between the web and the transport roll is increased, and the regulation force in the web width direction is increased. It has been found that occurrence of creases and wrinkles can be suppressed, and the present invention has been completed.

  In order to achieve the above object, the invention of claim 1 is characterized in that a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive is cast from a casting die onto a metal support. Solution casting comprising a casting process for forming a film (web) and peeling the web from the support, a drying process for drying the web while being transported by a transport roll, and a stretching process for stretching the web with a tenter In the method for producing an optical film by a film forming method, air is blown from the surface side of the web to the contact point between the transport roll and the web in a state where the residual solvent amount of the web in the drying step is 50 to 150% by weight. The web is pressed against the roll surface to be brought into close contact therewith.

  Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: Air is web width | variety from the air blowing opening part of a slit-shaped opening part or punch plate hole-shaped opening part with respect to a web. It is characterized by being sprayed over 0.7 to 1.0 times of the hand direction.

  Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: The web pressing force by blowing air is 0.3-5 kPa, It is characterized by the above-mentioned.

  Invention of Claim 4 is a manufacturing method of the optical film as described in any one of Claims 1-3, Comprising: Surface roughness (Ra1) of the both ends of a conveyance roll, and the center part of a conveyance roll The difference (Ra1-Ra2) from the surface roughness (Ra2) is 0 to 1.0 [mu] m.

  Here, the both ends of the transport roll refer to portions corresponding to 10 to 20% of the entire width of the transport roll inside the both ends of the transport roll, and the central portion of the transport roll is the width of the transport roll. The remainder shall be said. Therefore, the central portion of the transport roll is a portion corresponding to 80 to 60% of the entire width of the transport roll.

  The invention of an optical film of claim 5 is characterized by being manufactured by the method for manufacturing an optical film according to any one of claims 1 to 4.

  The invention of the polarizing plate of claim 6 has the optical film of claim 5 on at least one surface.

  The invention of a display device according to claim 7 is characterized in that the polarizing plate according to claim 6 is used.

  The invention of claim 1 is a method for producing an optical film by a solution casting film forming method, wherein the residual solvent amount of the web in the drying step is 50 to 150% by weight with respect to the contact point between the transport roll and the web. The air is blown from the surface side of the web, and the web is pressed against the roll surface to be brought into close contact. According to the invention of claim 1, the entrainment of air can be reduced, and the slippage due to the air entrainment phenomenon. -It is possible to produce a wide optical film with excellent flatness without generating wrinkles, and this makes it possible to meet demands for widening and high quality of protective films for polarizing plates, etc. Play.

  Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: Air with respect to a web, for example from the air blowing opening part of a slit-like opening part or a punch board hole-like opening part, According to the invention of claim 2, a film having high flatness can be obtained without blowing air between the web and the roll. There is an effect that it can be provided.

  According to a third aspect of the present invention, there is provided a method for producing an optical film according to the first or second aspect, wherein the web pressing force by the blowing air is 0.3 to 5 kPa. For example, a pressing force can be applied without deformation of the film in a non-contact manner, so that it is possible to provide a film with high flatness.

  Invention of Claim 4 is a manufacturing method of the optical film as described in any one of Claims 1-3, Comprising: Surface roughness (Ra1) of the both ends of a conveyance roll, and the center part of a conveyance roll The difference (Ra1-Ra2) from the surface roughness (Ra2) of the film is 0 to 1.0 [mu] m. According to the invention of claim 4, since the amount of contraction of the width can be controlled, The film physical properties can be made uniform, and an effect of providing a highly transparent film can be achieved.

  Here, the both ends of the transport roll refer to portions corresponding to 10 to 20% of the entire width of the transport roll inside the both ends of the transport roll, and the central portion of the transport roll is the width of the transport roll. The remainder shall be said. Therefore, the central portion of the transport roll is a portion corresponding to 80 to 60% of the entire width of the transport roll.

  The invention of the optical film of claim 5 is manufactured by the method of manufacturing an optical film according to any one of claims 1 to 4, and according to the invention of claim 5. , No wrinkles or wrinkles due to air entrainment phenomenon, excellent flatness, wide width, very low haze of film, excellent optical properties with transparency and flatness There is an effect that it is a thing.

  Since the invention of the polarizing plate of claim 6 has the optical film of claim 5 on at least one surface, according to the invention of the polarizing plate of claim 6, this is incorporated into a display device. Even in this case, there is an effect that the visibility of the display device is excellent without causing color unevenness that looks whitish when viewed from the front and oblique directions.

  The invention of the display device of claim 7 uses the polarizing plate of claim 6, and according to the display device of claim 7, there is no occurrence of color unevenness that looks whitish when viewed from the front and obliquely. There is an effect that the visibility of the display device is excellent.

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

  FIG. 1 is a flow sheet showing an embodiment of an apparatus for carrying out the method for producing an optical film by the solution casting film forming method of the present invention.

  In the figure, the method for producing an optical film of the present invention involves casting a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive from a casting die (2) onto a metal support (1). Then, a casting process for forming a casting film (web) (10) and peeling the web (10) from the support (1), and drying while transporting the web (10) by the transporting roll (7) are performed. A step and a stretching step of stretching the web (10) with a tenter (4).

  And in the manufacturing method of the optical film of this invention, as shown in detail in FIG.2 and FIG.3, near the conveyance roll (7) in the initial stage drying apparatus (3) of the drying process of a web (10), an air ejection apparatus ( Air nozzle) (15) is installed, and in a state where the residual solvent amount of the web (10) in the drying process is 50 to 150% by weight, the air is applied to the contact point between the transport roll (7) and the web (10). Is sprayed from the surface side of the web (10) over the width direction of the web (10), and the web (10) is pressed against and closely adhered to the roll surface.

  As a result, the contact area between the web (10) and the transport roll (7) is increased, and the regulating force in the width direction of the web is increased, so that a wide width having excellent flatness without causing creases or wrinkles due to an air entrainment phenomenon. The film can be manufactured.

  Moreover, in the manufacturing method of the optical film of this invention, air is the air blowing opening part of the slit-like opening part or punch plate hole-like opening part of an air ejection apparatus (air nozzle) (15) with respect to a web (10). From 0.7 to 1.0 times in the width direction of the web.

  Furthermore, in the manufacturing method of the optical film of this invention, it is preferable that the web (10) pressing force by blowing air is 0.3-5 kPa.

  Moreover, in the manufacturing method of the optical film of this invention, the difference (Ra1) of the surface roughness (Ra1) of the both ends of a conveyance roll (7) and the surface roughness (Ra2) of the center part of a conveyance roll (7). -Ra2) is preferably from 0 to 1.0 [mu] m.

  Here, the both ends of the transport roll (7) refer to portions corresponding to 10 to 20% of the entire width of the transport roll (7) on the inner side from both ends of the transport roll (7). ) Center portion means the remainder of the width of the transport roll (7). Accordingly, the central portion of the transport roll (7) is a portion corresponding to 80 to 60% of the entire width of the transport roll (7).

  A detailed method for increasing the contact force between the web (10) and the transport roll (7) and increasing the regulating force in the web width direction by air blowing according to the present invention will be described later.

  Hereinafter, embodiments of the method for producing an optical film according to the present invention will be described in detail. The optical film can be produced by a solution casting film forming method.

  In FIG. 1 showing an embodiment of a solution casting film forming apparatus, a dope is supplied from a casting die (2) onto a metal support (1) made of, for example, a stainless steel rotationally driven endless belt, which is transferred infinitely. Cast.

  The dope is cast by the casting die (2) by a doctor blade method in which the film thickness of the cast dope film (web) (10) is adjusted by a blade, or by a reverse roll coater that is adjusted by a reverse rotating roll. Although there is a method, etc., a method using a pressure die that can adjust the slit shape of the die part and easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The casting die (2) is usually provided with a decompression chamber (not shown).

  Here, the solid content concentration of the cellulose ester solution (dope) is preferably 15 to 30% by weight. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by weight, sufficient drying cannot be performed on the metal support (1), and a part of the dope film (web) (10) is metal during peeling. Since it remains on the support (1) and leads to belt contamination, it is not preferable. If the solid content concentration exceeds 30%, the dope viscosity increases, filter clogging becomes faster in the dope adjustment process, or the pressure increases during casting on the metal support (1), and cannot be extruded. It is not preferable.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the metal support (1), the metal support (1) is held by a pair of front and rear winding drums and a plurality of intermediate rolls (not shown). . The belt metal support (1) is provided with a driving device for applying tension (not shown) to one or both of the winding drums at both ends of the metal support (1) made of a rotationally driven endless belt. Thus, the metal support (1) is used in a tensioned state.

  The width of the metal support (1) is preferably 1600 to 2400 mm, the casting width of the cellulose ester solution is 1500 to 2300 mm, and the width of the film after winding is preferably 1500 to 2400 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  Moreover, it is preferable that the moving speed of a metal support body (1) is 40-200 m / min.

  When an endless belt is used as the metal support (1), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and the mixed solvent is lower than the boiling point of the lowest boiling solvent. It can be cast at a temperature, and more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  The dope cast on the surface of the metal support (1) as described above also increases the strength (film strength) of the gel film by accelerating drying until stripping.

  In the system using an endless belt as the metal support (1), until the web (10) has a film strength that can be peeled from the metal support (1) by the peeling roll (6) on the metal support (1). In order to dry and solidify, it is preferable to dry the residual solvent amount in the web (10) to 150% by weight or less, and more preferably 70 to 130% by weight. Moreover, as for the web temperature when peeling a web (10) from a metal support body (1), 0-30 degreeC is preferable. Further, immediately after the web (10) is peeled off from the metal support (1), the temperature rapidly decreases once due to the solvent evaporation from the metal support (1) adhesion surface side, and vapor such as water vapor or solvent vapor in the atmosphere is volatilized. Since the sex component tends to condense, the web temperature during peeling is more preferably 5 to 30 ° C.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M is the weight of the web at an arbitrary time point, and N is the weight when a weight M is dried at a temperature of 110 ° C. for 3 hours.

  The dope film (web) (10) formed by the dope cast on the metal support (1) is heated on the metal support (1), and the release roll (6) from the metal support (1). To evaporate the solvent until the web (10) is peelable.

  To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the metal support (1) by a liquid, a method of transferring heat from the front and back by radiant heat, etc. What is necessary is just to use in combination. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the drying air (11) blown from the hot air inlet at the front portion of the bottom of the initial drying device (3), and the initial drying device (3) It is dried by exhaust air being discharged from the exit of the rear part of the ceiling.

  In the system using an endless belt for the metal support (1), the peeling tension when the web (10) is peeled from the metal support (1) by the peeling roll (6) is measured by peeling force as in JIS Z 0237. Peeling with a larger tension than the peeling force obtained in, but this may cause the peeling position to be taken downstream if the peeling tension is equal to the peeling force obtained by the JIS measurement method during high-speed film formation. Therefore, it goes higher for stabilization. Even if the film is formed with the same peel tension in the process, it has been confirmed that the variation of the crossed Nicols transmittance (CNT) of the film is greatly reduced when the peel force by the JIS measurement method is lowered.

  As a peeling tension value in the process, when preparing a retardation film that requires a high retardation value, the web after peeling from the support is prevented from extending in the MD direction due to the conveyance tension (extends in the MD direction). When the film is stretched in the TD direction by a subsequent tenter, it is difficult to raise the desired retardation value), and in other applications, peeling is performed at a high tension of about 300 N / m from a low tension of about 50 N / m.

  In the method for producing an optical film of the present invention, as shown in FIGS. 1 to 3, an air ejection device (air nozzle) (15) is provided near the transport roll (7) in the initial drying device (3) of the web (10). In a state where the residual solvent amount of the web (10) in the drying process is 50 to 150% by weight, preferably 60 to 140% by weight, more preferably 70 to 130% by weight, Air is blown over the width direction of the web (10) from the surface side of the web (10) against the contact point with the web (10), and the web (10) is pressed and brought into close contact with the roll surface.

  As a result, the contact area between the web (10) and the transport roll (7) is increased, and the regulating force in the width direction of the web is increased, so that a wide width having excellent flatness without causing creases or wrinkles due to an air entrainment phenomenon. The film can be manufactured.

  Here, when air is blown onto the surface of the web (10), if the residual solvent amount of the web (10) is less than 50% by weight, the film becomes cloudy by stretching after the drying process, which is not preferable. On the other hand, if the amount of residual solvent exceeds 150% by weight, the end of the film is curled during drying, which is not preferable.

  Note that a plurality of air ejection devices (air nozzles) (15) may be installed for one transport roll (7).

  Here, a mirror roll or a mat roll having a surface roughness of 0.08 to 2.0 μm is used as the transport roll (7) in the drying step. The mat roll may have a uniform surface roughness in the width direction, but the grip edges increase when both ends are rough within a range of 1.0 μm or less compared to the central portion, and there are creases and wrinkles. Since it can suppress, it is preferable.

  Moreover, in the manufacturing method of the optical film of this invention, air is the air blowing opening part of the slit-like opening part or punch plate hole-like opening part of an air ejection apparatus (air nozzle) (15) with respect to a web (10). To 0.7 to 1.0 times, preferably 0.75 to 0.95 times, more preferably 0.8 to 0.95 times in the width direction of the web.

  Here, if the blowing of air to the web (10) is less than 0.7 times the web width direction, the film edge shrinks in the drying process due to insufficient pressing of the film edge, resulting in non-uniform physical properties. Therefore, it is not preferable. On the other hand, if the air blowing to the web (10) exceeds 1.0 times in the width direction of the web, the blowing air is caught between the film and the roll and the flatness is impaired, which is not preferable.

  Furthermore, in the manufacturing method of the optical film of this invention, the web pressing force by spraying air is 0.3-5.0 kPa, Preferably it is 0.6-4.8 kPa, More preferably, it is 0.8-4.5 kPa. It is.

  Here, if the pressing force of the web (10) by the blowing air is less than 0.3 kPa, since there is almost no pressing effect, it shrinks in the drying process, and the physical properties become non-uniform, which is not preferable. Moreover, since the film will deform | transform with air when the pressing force of the web (10) by blowing air exceeds 5 kPa, it is unpreferable.

  Moreover, in the manufacturing method of the optical film of this invention, the difference (Ra1) of the surface roughness (Ra1) of the both ends of a conveyance roll (7) and the surface roughness (Ra2) of the center part of a conveyance roll (7). -Ra2) is 0 to 1.0 [mu] m, preferably 0 to 0.9 [mu] m, more preferably 0 to 0.8 [mu] m.

  Here, the both ends of the transport roll (7) refer to portions corresponding to 10 to 20% of the entire width of the transport roll (7) on the inner side from both ends of the transport roll (7). ) Center portion means the remainder of the width of the transport roll (7). Accordingly, the central portion of the transport roll (7) is a portion corresponding to 80 to 60% of the entire width of the transport roll (7).

  When the difference (Ra1-Ra2) between the surface roughness (Ra1) at both ends of the transport roll (7) and the surface roughness (Ra2) at the center of the transport roll (7) exceeds 1.0 [mu] m, Since the roll roughness is transferred to the film, the film becomes cloudy and loses transparency.

  In the embodiment shown in FIG. 1, an air ejection device (air nozzle) (15) is installed near the first transport roll (7a) in the initial drying device (3) in the web drying step, and the web ( In the state where the residual solvent amount of 10) is 50 to 150% by weight, air is passed from the surface side of the web (10) to the width direction with respect to the contact point between the transport roll (7) and the web (10). The web (10) is pressed against the roll surface to be brought into close contact therewith.

  However, not only the first transport roll (7a) but also the second transport roll (7b) to 6th (7f) after the first transport roll (7a) in the initial drying device (3), the air ejection device (Air nozzle) (15) may be installed, and air may be blown from the surface side of the web (10) over the width direction to the contact point between the transport roll (7) and the web (10). It is. In short, in a state where the residual solvent amount of the web (10) in the drying step is 50 to 150% by weight, air is supplied to the surface of the web (10) with respect to the contact point between the transport roll (7) and the web (10). Therefore, an air ejection device (air nozzle) (15) is provided near the first transport roll (7a) and the subsequent transport rolls in the initial drying device (3). It may be installed and sprayed with the above-mentioned air, or an air ejection device (air nozzle) (close to each transport roll (7) with respect to all the transport rolls (7) in the initial drying device (3) ( 15) may be installed and the above-mentioned air blowing may be performed. Of course, the number of transport rolls (7) used is not limited to that shown in the figure.

  Further, the air to be blown may have a constant velocity distribution in the width direction of the transport roll (7), but as indicated by the arrow (A) in FIG. 3, the width direction of the transport roll (7). If the distribution is such that the speed at the center is high and the speed decreases toward the edge in the same width direction, the air will flow to the left and right sides as shown by the arrows (b) in the figure. The expelled effect becomes stronger and preferable.

  Next, in the apparatus for carrying out the method for producing the optical film shown in FIG. 1, the stretching step is a tenter for stretching the film by fixing the both side edges of the web (10) with clips or the like when manufacturing the film for a liquid crystal display device. The method is preferable for improving the flatness and dimensional stability of the film.

  It is preferable that the residual solvent amount of the web (10) immediately before entering the tenter of the stretching process is 2 to 100% by weight.

  In the present embodiment, the stretch ratio of the web (10) in the tenter of the stretching step is 1.03 to 2 times, preferably 1.05 to 1.8 times, and more preferably 1.05 to 1.6. It is desirable to be double. Moreover, the temperature of the warm air (12) blown out from the hot air blowing slit port in the tenter in the stretching step is 20 to 200 ° C, preferably 40 to 190 ° C, and more preferably 60 to 180 ° C.

  In the latter drying apparatus (5) provided on the rear side of the tenter in the stretching step, the film (web) (20) is meandered by a plurality of conveying rolls (8) arranged in a staggered manner as viewed from the side, The film (20) is dried. The film transport tension in the drying process is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, and the like. It is 3 to 3N, and 0.4 to 2.7N is more preferable.

  The means for drying the film (web) (20) is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, a microwave, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the drying air (13) blown from the warm air inlet at the front portion of the bottom of the late drying device (5), and the late drying device (5) It is dried by exhaust air being discharged from the exit of the rear part of the ceiling. The temperature of the drying air (13) is preferably 40 to 160 ° C., more preferably 50 to 150 ° 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.

  For example, before the cellulose ester film exits the latter drying device (5) and is wound up by the winding device (14), generally, the embossing device (not shown) forms an emboss on the film.

  Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . For example, when the film thickness is 40 μm, the embossing height h 1 + h 2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The film (20) that has been dried is taken up by the take-up device (14) to obtain the original roll of the optical film. The film (20) having good dimensional stability can be obtained by setting the residual solvent amount of the film (20) after drying to 0.5% by weight or less, preferably 0.1% by weight or less.

  The winding method of the film (20) 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, and a program tension control method with a constant internal stress. You can use them properly.

  The film (20) may be joined to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  In the optical film according to the present embodiment, the width of the film after winding is preferably, for example, 1500 to 2400 mm.

  In the present embodiment, the dope for producing the optical film includes a thermoplastic resin such as a cellulose ester resin as a main material, and includes a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and a low molecular weight substance. Among these, at least one kind of substance and a solvent are included.

  Hereinafter, these will be described.

  In the method for producing an optical film of the present embodiment, various resins can be used as the film material, and among them, cellulose ester is preferable.

  A cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present embodiment are not impaired.

  As an example of cellulose triacetate, the substitution degree of acetyl groups is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

  Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester used for this Embodiment, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  In the present embodiment, the number average molecular weight of the cellulose ester is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 70,000-200,000 are preferable.

  In the present embodiment, various additives can be added to the cellulose ester.

  In the method for producing an optical film according to the present embodiment, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and exhibits a main effect on dissolution, and an organic solvent used in a large amount among them is used. It is called the main (organic) solvent or the main (organic) solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. After the dope is cast on a metal support, the alcohol starts to evaporate and the ratio of the alcohol increases, thereby making the web gel, making the web strong and easy to peel off from the metal support. It is also used as a gelling solvent, and when these ratios are small, it also has a role of promoting the dissolution of the cellulose derivative of the non-chlorine organic solvent.

  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 most preferable solvent for dissolving a cellulose derivative, which is a preferable polymer compound satisfying such conditions, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethanol of 95: 5 to 80:20. Alternatively, a mixed solvent having a methyl acetate: ethanol ratio of 60:40 to 95: 5 is also preferably used.

  The film in the present embodiment includes a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles (matting agent) that impart slipperiness to the film, an ultraviolet absorber that imparts an ultraviolet absorbing function, You may contain the antioxidant etc. which prevent deterioration.

  The plasticizer used in the present embodiment is not particularly limited, but a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation so as not to generate haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the polycondensate of the above by a hydrogen bond or the like.

  Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol used in the present embodiment is represented by the following general formula (1).

R ^1- (OH) n (1)
In the formula, R ¹ represents an n-valent organic group, and n represents a positive integer of 2 or more.

Examples of preferred polyhydric alcohols include, but are not limited to, the following.

  Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this Embodiment, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but are not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose derivative is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and derivatives thereof, and benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1,500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, etc. can be used, but in this embodiment, it is preferable that substantially no phosphate ester plasticizer is contained. .

  Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by weight, preferably less than 0.1% by weight, particularly preferably not added. . These plasticizers can be used alone or in combination of two or more.

  The amount of the plasticizer used is preferably 1 to 20% by weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film Since the physical properties of the material deteriorate, it is not preferable.

  In order to impart slipperiness to the cellulose derivative in the present embodiment, it is preferable to add fine particles such as a matting agent. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

  Examples of the organic compound fine particles include fine particles such as acrylic resin, silicone resin, fluorine compound resin, and urethane resin.

  The primary particle size of the fine particles is not particularly limited, but the average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1-1.0 micrometer.

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for one film, and the number of particles in 100 μm ² whose major axis length is in the range of 0.05 to 5 μm is determined for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size after being added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film. And controlling the particle size formed by aggregation.

  Here, when the average particle diameter of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or a failure may occur in the wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 0.5% by weight to the cellulose ester. Preferably, 0.05 to 0.3% by weight, more preferably 0.05 to 0.25% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat a composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present embodiment is an apparatus that creates special conditions such as high shear and high-pressure conditions by passing a composition in which fine particles and a solvent are mixed at high speed through a thin tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. At that time, it is preferable that the maximum reaching speed reaches 100 m / sec or more, and the heat transfer speed reaches 4.1840 × 105 J / hr or more.

  Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing devices such as those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  In the present embodiment, the fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is mixed with a metal support. A cellulose ester film is obtained which is cast on and dried to form a film.

  Here, the content ratio of the lower alcohol is preferably 50 to 100% by weight, more preferably 75 to 100% by weight.

  Examples of lower alcohols preferably include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by weight. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by weight, more preferably 10 to 20% by weight.

  The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film, and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on a film made of the cellulose derivative.

  Examples of ultraviolet absorbers that can be used in the present embodiment include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloration is preferred. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  As the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of a polarizer or liquid crystal and those having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. preferable.

  Specific examples of ultraviolet absorbers useful in the present embodiment include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert). -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butyl Phenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2 -Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydro Cis-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy Examples include, but are not limited to, a mixture of -5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

  Further, as commercially available products of ultraviolet absorbers, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Further, as specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in this embodiment, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy- Examples thereof include, but are not limited to, 5-sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  In this Embodiment, the compounding quantity of these ultraviolet absorbers has the preferable range of 0.01 to 10 weight% with respect to a cellulose ester (cellulose derivative), and also 0.1 to 5 weight% is preferable. If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Moreover, the ultraviolet absorber which can be used for the optical film of this Embodiment is the polymer ultraviolet absorber (or ultraviolet-absorbing polymer) of Unexamined-Japanese-Patent No. 6-148430 and 2002-47357. It can be preferably used. In particular, in general formula (1) described in JP-A-6-148430, general formula (2), or general formulas (3), (6), and (7) described in JP-A-2002-47357. The polymeric ultraviolet absorber represented is preferably used.

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  The amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1,000 ppm, by weight with respect to the cellulose derivative.

  In this Embodiment, the film thickness after drying of a cellulose-ester film has the preferable range of 20-150 micrometers as a finished film from a viewpoint of thickness reduction of a liquid crystal display device. Here, “after drying” refers to a film dried to a state where the amount of residual solvent in the film is 0.5% by weight or less.

  Here, when the film thickness of the cellulose ester film after winding is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If the film thickness is too thick, the advantage of thinning the film becomes less than the conventional cellulose ester film. To adjust the film thickness, control the dope concentration, pump feed volume, slit gap of the die of the casting die, extrusion pressure of the casting die, and the moving speed of the metal support to achieve the desired thickness. It is good to do. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

  In the present embodiment, the cellulose ester film has a moisture content of preferably 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

  In the present embodiment, the cellulose ester film desirably has a transmittance of 90% or more, more preferably 92% or more, and further preferably 93% or more.

  In addition, the optical film manufactured by the method of the present embodiment has a haze of 0.3 to 2.0 when three sheets are stacked, and according to the optical film of the present embodiment, It has very low haze and has optical properties excellent in transparency and flatness.

  Here, the haze of the optical film may be measured using, for example, a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to a method defined in JIS K 6714.

  Moreover, the tensile elasticity modulus of MD direction (conveyance direction) of the cellulose-ester film manufactured with the manufacturing method of the optical film by this Embodiment is 1500 MPa-3,500 MPa, and the tensile elasticity of TD direction (width direction). The rate is preferably 3,000 MPa to 4,500 MPa, and the ratio of the TD direction elastic modulus / MD direction elastic modulus of the film is preferably 1.40 to 1.90.

  Here, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the optical film is less than 1.40, the sag of the central portion becomes large when winding a film having a width exceeding 1,650 mm, and the winding core Since sticking of a film increases, it is not preferable. Further, when the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage occurs after heating on the deflecting plate, or the backlight is heated by the heat of the backlight when incorporated in the liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

  As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JIS K 7217 can be mentioned.

  That is, using a tensile tester (TG-2KN, manufactured by Minebea Co., Ltd.), a sample was set at a chucking pressure: 0.25 MPa, a distance between marked lines: 100 ± 10 mm, and a pulling speed: 100 ± 10 mm / min. Pull on. As a result, from the obtained tensile stress-strain curve, the elastic modulus calculation start point is 10N, the end point is 30N, and the tangent line drawn between them is extrapolated to calculate the elastic modulus.

  The optical film produced by the method of the present embodiment is preferably used for a liquid crystal display member, specifically, a protective film for a polarizing plate. In particular, an optical film produced by the method of the present embodiment is preferably used in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability.

  By using the protective film for polarizing plates made of the optical film of the present embodiment, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film.

  By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

  The polarizing plate may be prepared by laminating the optical film produced by the method of the present embodiment as a retardation film, or the optical film produced by the method of the present embodiment may be prepared as a retardation film. Alternatively, the protective film may be used as a direct attachment to the polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. As this water-soluble polymer adhesive, a completely saponified polyvinyl alcohol aqueous solution is preferably used. Furthermore, a long polarizing plate is obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of the present embodiment. Can do. A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer). It can be easily attached to a cell or the like.

  The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. It is preferable to use for.

  By the way, a polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is immersed and stretched in an iodine solution and bonded to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. is there. The alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness.

  The optical film produced by the method of this embodiment includes a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optical anisotropic layer, a liquid crystal layer, an alignment layer, and an adhesive layer. Various functional layers such as a layer, an adhesive layer, and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

  Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and a liquid crystal display device is obtained using this.

  In the present embodiment, the liquid crystal display device includes a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. It has two polarizing plates.

  By using a protective film for a polarizing plate made of an optical film produced by the method of the present embodiment, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. it can. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

  The optical film produced by the method of the present embodiment can also be used as a base material for an antireflection film or an optical compensation film.

  Hereinafter, the present embodiment will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example 1
(Preparation of dope)
Cellulose triacetate 100 parts by weight Triphenyl phosphate 5.5 parts by weight Ethylphthalyl ethyl glycolate 5.5 parts by weight Methylene chloride 400 parts by weight Ethanol 45 parts by weight The above cellulose ester blend was placed in an airtight container and mixed. After the temperature was raised to 80 ° C., the mixture was stirred for 3 hours and completely dissolved. Thereafter, stirring was stopped, the liquid temperature was lowered to 43 ° C., and filtration was performed using a filter paper having a filtration accuracy of 0.005 mm. By allowing this to stand overnight, the bubbles in the dope were degassed.

(Production of cellulose triacetate film)
Using the above-mentioned dope, the dope temperature was adjusted to 35 ° C. and the support temperature was 25 ° C., and flowed onto the support (1) made of a stainless steel endless belt having a width of 2000 mm and mirror-finished from the casting die (2). Extended.

  The web (10) was peeled from the support (1) with a peeling roll (6) at a peeling residual solvent amount of 110% by weight, and introduced into the next drying device (3) with a transport tension of 100N.

  And in the present Example, the air nozzle (15) was provided over the width direction of the conveyance roll (7) in the location where the web residual solvent amount of a drying apparatus (3) exceeds 70 weight%. Specifically, in a state where the residual solvent amount of the web (10) is 100% by weight, the air nozzle (15) with respect to the contact point between the first conveying roll (7a) of the drying device (3) and the web (10). ) Was blown from the surface side of the web (10), and the web (10) was pressed and brought into close contact with the roll surface, thereby reducing entrained air and preventing occurrence of creases and wrinkles.

  The air was sprayed onto the web (10) from the slit-like opening (not shown) of the air nozzle (15) over 0.9 times the web width direction. The web pressing force by the blowing air at this time was 2.0 kPa on average.

  Here, a mirror roll or a mat roll having a surface roughness of 0.08 to 2.0 μm is used as the transport roll (7). The mat roll may have a uniform surface roughness in the width direction, but when both ends are rougher in a range of 1.0 μm or less than the center, so-called grip force increases, This is preferable because creases and wrinkles can be suppressed.

  In this example, the difference (Ra1-Ra2) between the surface roughness (Ra1) at both ends of the transport roll (7) and the surface roughness (Ra2) at the center of the transport roll (7) is 0 [mu] m. It was.

  Further, the air to be blown may have a constant speed distribution in the width direction of the transport roll (7), but the speed of the central portion in the width direction of the transport roll (7) is fast, If the distribution is such that the speed decreases toward the end, the effect of air expulsion becomes stronger and preferable, so that is done.

  Table 1 below shows the air blowing width in the web width direction (times) by the air nozzle (15), the web pressing force by air (kPa), the surface roughness (Ra1) at both ends of the transport roll (7), and transport. The surface roughness (Ra2) at the center of the roll (7) and the difference (Ra1-Ra2) are collectively described.

  Next, in the stretching step of the web (10) after the drying step, the web (10) was stretched in the width direction while holding both ends of the web (10) with clips using the tenter (4). At this time, the stretch ratio of the web by the tenter (4) was set to 30%, and a drying air (12) of 140 ° C. was introduced into the tenter (4) to set the stretching temperature to 140 ° C.

  The stretched cellulose triacetate film is introduced into the latter drying apparatus (5) and dried with 120 ° C. drying air (13) to finally produce a cellulose triacetate film having a film thickness of 40 μm and a product width of 2300 mm, and wound up. It was wound up by a machine (14).

Examples 2-5
A cellulose triacetate film is produced in the same manner as in Example 1 above. In Examples 2 to 5, web pressing force by air (kPa), surface roughness (Ra1) at both ends of the transport roll (7). The surface roughness (Ra2) at the center of the transport roll (7) and the difference (Ra1-Ra2) between them are constant, and the air blowing width (times) in the width direction of the web by the air nozzle (15) is as described above. Various changes were made to be different from the case of the first embodiment. The second embodiment was 0.6 (times), the third embodiment was 0.7 (times), the fourth embodiment was 1.0 (times), and the fifth embodiment. Then, it carried out as 1.1 (times).

Examples 6-10
Cellulose triacetate films are produced in the same manner as in Example 1 above, but in Examples 6 to 10, the air blowing width (times) in the web width direction by the air nozzle (15), the conveyance roll (7) The surface roughness (Ra1) at both ends, the surface roughness (Ra2) at the center of the transport roll (7), and the difference (Ra1-Ra2) between them are constant, and the web pressing force (kPa) by air is the above. In Example 6, the web pressing force by air was 0.2 kPa, in Example 7, 0.3 kPa, in Example 8, 3.1 kPa, and in Example 9, 5 in various ways, different from the case of Example 1. It was carried out at 0.0 kPa and 5.5 kPa in Example 10.

Examples 11-14
Cellulose triacetate films are produced in the same manner as in Example 1 above. In Examples 11 to 14, the air blowing width (times) in the web width direction by the air nozzle (15), and the web pressing force by air. (KPa) is constant, the surface roughness (Ra1) at both ends of the transport roll (7), the surface roughness (Ra2) at the center of the transport roll (7), and the difference (Ra1-Ra2), respectively. In Example 11, the surface roughness (Ra1) at both ends of the transport roll (7) was 0.8 μm, and the surface of the central portion of the transport roll (7) was changed variously so as to be different from the case of Example 1 above. The roughness (Ra2) is 0.8 μm, and the difference (Ra1−Ra2) is 0 μm. In Example 12, the surface roughness (Ra1) at both ends of the transport roll (7) is 0.8 μm, and the transport roll ( 7) Surface roughness at the center ( a2) is 1.0 μm, and the difference between them (Ra1−Ra2) is −0.2 μm. In Example 13, the surface roughness (Ra1) at both ends of the transport roll (7) is 2.0 μm, and the transport roll ( 7) The surface roughness (Ra2) of the central portion is 1.1 μm, and the difference between these (Ra1−Ra2) is 0.9 μm. In Example 14, the surface roughness (Ra1) at both ends of the transport roll (7) ) Was 1.3 μm, the surface roughness (Ra 2) of the central portion of the transport roll (7) was 0.2 μm, and the difference (Ra 1 −Ra 2) was 1.1 μm.

Comparative Example 1
For comparison, it is carried out in the same manner as in the case of the first embodiment, but the point different from the case of the first embodiment is that it is carried out without air blowing in the web width direction by the air nozzle.

(Evaluation of film flatness)
Next, the planarity of the cellulose triacetate films prepared in Examples 1 to 14 and Comparative Example 1 was evaluated as follows.

  Film samples prepared by cutting the cellulose triacetate films prepared in Examples 1 to 14 and Comparative Example 1 into a size of 100 cm in length and 40 cm in width were prepared, and each film sample was pasted on a flat desk. Three fluorescent lamps placed on the surface of the paper and arranged obliquely above were projected on each film, and the flatness of each film sample was evaluated by the degree of bending of the fluorescent lamp. And it ranked according to the following reference | standard and the result obtained was shown according to Table 1.

Film flatness evaluation rank A: All three fluorescent lamps look straight, no problem as a product B: There are places where the fluorescent lamps appear to be slightly bent,
There is no problem as a product. C: There is a place where the fluorescent lamp looks slightly bent, but there is no problem as a product. D: The fluorescent lamp appears to crawl and cannot be used as a product (production of polarizing plate)
Next, using the cellulose triacetate films prepared in Examples 1 to 14 and Comparative Example 1 as protective films for polarizing plates, various polarizing plates were prepared by the following methods and evaluated.

(Preparation of polarizing film)
A long polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a long polarizing film.

  Subsequently, this polarizing film and the cellulose triacetate film produced in Examples 1-14 and Comparative Example 1 were bonded together according to the following processes 1-5, and the polarizing plate was produced.

  Step 1: The cellulose triacetate films prepared in Examples 1 to 14 and Comparative Example 1 were dipped in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, and then washed with water. Dried.

  On the other hand, a commercially available long cellulose ester film was immersed in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, then washed with water and dried.

  Step 2: The long polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by weight for 1 to 2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and the long cellulose triacetate films of Examples 1 to 14 and Comparative Example 1 that were alkali-treated in Step 1 and a commercially available long length Laminated and placed between cellulose ester films.

Process 4: These films were laminated together at a speed of about 2 m / min at a pressure of ^{20 to} 30 N / cm ² with two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The film sample produced in Step 4 was dried for 2 minutes in a dryer at 80 ° C. to produce a polarizing plate.

(Production of liquid crystal display panel)
Carefully peel off the polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD1525J, model name LA-1529HM), and paste the various polarizing plates prepared above in accordance with the polarization direction. A liquid crystal display panel was produced.

  The color unevenness of the polarizing plate using the cellulose triacetate films prepared in Examples 1 to 14 and Comparative Example 1 as a protective film was visually observed. The obtained results are shown in Table 1 below.

(Visual evaluation of polarizing plate)
About each liquid crystal display panel produced as mentioned above, the color unevenness which looks whitish when it sees from the front and diagonally by several evaluators was observed, and it was set as evaluation of a polarizing plate.

A: None of the evaluators can see color unevenness at all. ○: The evaluator hardly sees color unevenness. Δ: The evaluator may slightly see color unevenness.
Level that can be used as a product ×: Level that can be confirmed as color unevenness by many evaluators and cannot be used as a product. Table 1 below shows the atmospheric temperature and stretching in the casting process in Examples 1 to 48 and Comparative Example 1. The temperature difference from the process ambient temperature is also shown.

  As is clear from the results of Table 1 above, according to the cellulose triacetate films prepared in Examples 1 to 14 of the present invention, the entrainment of air can be reduced, and the occurrence of slippage and wrinkles due to the entrainment phenomenon of air can be generated. In addition, the flatness was excellent, and a wide cellulose triacetate film could be produced. As a result, it was possible to meet the demand for widening and high quality of protective films for polarizing plates. Moreover, even after processing the cellulose triacetate film produced in Examples 1-14 of the present invention into a polarizing plate, whitish color unevenness was not confirmed.

  On the other hand, in the cellulose triacetate film of Comparative Example 1, creases and wrinkles due to the air entrainment phenomenon occur and the flatness is inferior, and responds to the demand for high quality optical films such as polarizing plate protective films. It was something that could not be done. Moreover, after processing into the polarizing plate, the cellulose triacetate film produced in Comparative Example 1 was found to be whitish color unevenness and could not be used as a protective film product for polarizing plates.

It is a flow sheet which shows embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method of this invention. It is a principal part expanded side view of FIG. 1, and shows the conveyance roll of an initial stage drying apparatus, and the air ejection apparatus (air nozzle) installed near this. It is the expansion perspective view which looked at the conveyance roll and the air ejection apparatus (air nozzle) from the bottom.

Explanation of symbols

1: Stainless steel rotationally driven endless belt (metal support)
2: casting die 3: initial drying device 4: tenter 5: late drying device 6: peeling roll 7: transport rolls 7a to 7f: transport roll 8: transport roll 10: web 11: drying air 12: drying air 13: drying Wind 14: Winding device 15: Air ejection device (air nozzle)
20: Film i: Spraying aero: Expulsion air

Claims (7)

  A flow in which a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive is cast from a casting die onto a metal support to form a cast film (web) and to peel the web from the support. In a method for producing an optical film by a solution casting film forming method, comprising: a stretching process; a drying process for transporting the web while being transported by a transport roll; and a stretching process for stretching the web with a tenter. In a state where the amount of residual solvent is 50 to 150% by weight, air is blown from the surface side of the web against the contact point between the transport roll and the web, and the web is pressed against the roll surface to be brought into close contact with the web. A method for producing an optical film.   The method for producing an optical film according to claim 1, wherein air is blown against the web over 0.7 to 1.0 times in the width direction of the web.   The method for producing an optical film according to claim 1, wherein the web pressing force by the blowing air is 0.3 to 5 kPa. The difference (Ra1-Ra2) between the surface roughness (Ra1) at both ends of the transport roll and the surface roughness (Ra2) at the center of the transport roll is 0 to 1.0 [mu] m, Item 4. The method for producing an optical film according to any one of Items 1 to 3.
Here, the both ends of the transport roll refer to portions corresponding to 10 to 20% of the entire width of the transport roll inside the both ends of the transport roll, and the central portion of the transport roll is the width of the transport roll. The remainder shall be said.   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 5 on at least one surface.   A display device comprising the polarizing plate according to claim 6.

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