JP2012016845A - Optical film forming method, optical film, polarizing plate, and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film which contains an acrylic resin and a cellulose ester resin and is improved in adhesion to a polarizer.SOLUTION: A forming method of an optical film 5 includes a casting process for casting a resin solution 2 on a support 101a, a peeling process for peeling a web 3 formed on the support 101a from the support 101a, and a stretching process for stretching the peeled web 3. As the resin of the resin solution 2, an acrylic resin and a cellulose ester resin are contained. As the stretching process, a first stretching process and a second stretching process which is carried out after the first stretching process are included. When the total of the draw ratio in the longitudinal direction and the draw ratio in the width direction of the web 3 in the first stretching process is A, and the total of the draw ratio in the longitudinal direction and the draw ratio in the width direction of the web 3 in the second stretching process is B, A≤B.

Description

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

  Conventionally, the demand for liquid crystal display devices has been expanded in applications such as liquid crystal televisions and personal computer liquid crystal displays. In recent years, as liquid crystal display devices have become larger, they can be used as large displays installed in streets and stores, and as displays for advertising in public places using display devices called digital signage. Is becoming more diverse.

  The liquid crystal display device includes a liquid crystal cell having a configuration in which a transparent electrode, a liquid crystal layer, a color filter, and the like are sandwiched between glass plates, and two polarizing plates disposed on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell. Yes. The polarizing plate includes a polarizer (also referred to as a polarizing film or a polarizing film) and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer. As the transparent protective film, an optical film, usually an optical film made of a cellulose ester resin film such as cellulose triacetate is used.

  A solution casting film forming method is known as a method for producing an optical film. The solution casting film forming method includes a casting process in which a resin solution called a dope is cast on a support such as an endless belt or a drum, and a dope casting called a web formed on the support. A peeling process for peeling the film from the support, a stretching process for stretching the peeled web in the longitudinal direction and / or the width direction, a heat treatment process for drying the stretched web, a winding process for winding the dried web as an optical film, etc. Prepare.

  Patent Document 1 describes a method for producing an acrylic film by a solution casting film forming method, and Patent Document 2 describes a method for producing a cellulose acylate film by a solution casting film forming method. .

  The film described in Patent Document 1 does not include a cellulose ester resin, and the film described in Patent Document 2 does not include an acrylic resin. However, Patent Document 3 includes an optical including both an acrylic resin and a cellulose ester resin. A film is described. The optical film described in Patent Document 3 is an optical film having low hygroscopicity, high transparency, excellent weather resistance, and improved brittleness.

  However, the optical film containing the acrylic resin and the cellulose ester resin has a problem that the adhesiveness to the polarizer is insufficient as compared with the optical film containing only the cellulose ester resin. This is because the polarizer is made of a polyvinyl alcohol-based film, and an optical film is bonded to the polarizer using a completely saponified polyvinyl alcohol aqueous solution as an adhesive, so that the acrylic resin has a lower saponification suitability than the cellulose ester resin. It is considered that the optical film containing the adhesive strength decreases with the polarizer.

JP 2007-118266 A (paragraph 0143) JP2009-126081 (paragraph 0069) International Publication No. WO2009 / 047924 (paragraph 0044)

  An object of the present invention is to provide an optical film containing an acrylic resin and a cellulose ester resin, and having improved adhesiveness to a polarizer.

  One aspect of the present invention includes a casting process for casting a resin solution on a support, a peeling process for peeling the web formed on the support from the support, and a stretching process for stretching the peeled web. A method for producing an optical film comprising: an acrylic resin and a cellulose ester resin as a resin of a resin solution, and a first stretching step and a second stretching step performed after the first stretching step as a stretching step The total value of the stretch ratio in the longitudinal direction and the stretch ratio in the width direction of the web in the first stretching process is A, and the stretch ratio in the longitudinal direction and the stretch ratio in the width direction of the web in the second stretching process. When the total value of B and B is B, A ≦ B.

  According to this method for producing an optical film, an optical film containing an acrylic resin and a cellulose ester resin is produced. Such an optical film is an optical film having low hygroscopicity, high transparency, excellent weather resistance, and improved brittleness. And when manufacturing such an optical film, a 1st extending | stretching process is performed and a 2nd extending process is performed after that, In that case, the draw ratio and the width direction of the longitudinal direction of the web in a 1st extending | stretching process are performed. The total value with the stretching ratio (hereinafter, this may be abbreviated as “total stretching ratio in the first stretching process”, “first total stretching ratio”, etc.) is A, and the longitudinal direction of the web in the second stretching process When the total value of the stretching ratio and the stretching ratio in the width direction (hereinafter, this may be abbreviated as “total stretching ratio in the second stretching step”, “second total stretching ratio”, etc.) is B, Since A ≦ B, an optical film with improved adhesion to a polarizer can be obtained even if it is an optical film containing an acrylic resin having a lower saponification suitability than a cellulose ester resin.

  This is probably due to the following reasons. That is, in addition to the first stretching step, by adding a second stretching step having a larger total longitudinal and lateral stretching ratio, the cellulose ester resin is surface-oriented on the surface of the optical film, and the saponification suitability of the optical film is improved. To do. As a result, when this optical film is bonded to a polarizer made of a polyvinyl alcohol film using a completely saponified polyvinyl alcohol aqueous solution, it is assumed that the adhesive force between the optical film and the polarizer is improved. The In addition to performing the second stretching step in addition to the first stretching step, the surface roughness (arithmetic average roughness (Ra) and maximum height (Rz)) of the optical film also increases. It is considered that.

  In the manufacturing method, the total stretching ratio A in the first stretching step is ensured from the viewpoints of ensuring good dryness, flatness and film thickness uniformity without voids of the manufactured optical film, and securing the elastic modulus and optical characteristics. Is preferably 1 to 30%, and the total stretching ratio B in the second stretching step is preferably 1 to 100%. Here, since it is a premise that A ≦ B, for example, when the first total stretch ratio A is 1%, the second total stretch ratio B is 1 to 100%, and the first total stretch ratio A Needless to say, when the ratio is 30%, the second total stretching ratio B is 30 to 100%.

  In the said manufacturing method, it is preferable to extend | stretch a web with a clip tenter or a pin tenter in an extending | stretching process from a viewpoint of versatility and the ease of operation.

  In the above production method, it is possible to achieve easy stretching, and from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids in the produced optical film, and securing elastic modulus and optical characteristics. 1 stretching step is performed at 30 ° C. or higher, at a temperature α + 30 ° C. or lower, which is 30 ° C. higher than the higher glass transition temperature α of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin, for 1 to 30 seconds, In the second stretching step, the glass transition temperature of the acrylic resin and the cellulose ester are 30 ° C. or more lower than the glass transition temperature β of the lower glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. It is preferable to carry out for 1 to 30 seconds at a temperature α + 50 ° C. or less which is 50 ° C. higher than the glass transition temperature α, which is the higher of the glass transition temperatures of the resin.

  In the said manufacturing method, it is preferable to manufacture an optical film with a film thickness of 20-100 micrometers from a viewpoint which prevents the curl, wrinkles, etc. of the manufactured optical film in consideration of the use of the manufactured optical film.

  In the production method, from the viewpoint of ensuring good thermal decomposition resistance and fluidity, the acrylic resin contains methyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate and 2 -It is preferable to copolymerize at least one selected from the group consisting of ethylhexyl acrylate.

  In the production method, from the viewpoint of ensuring good compatibility with the acrylic resin and ensuring high transparency of the produced optical film, the cellulose ester resin is cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, It is preferably at least one selected from the group consisting of cellulose acetate benzoate, cellulose propionate and cellulose butyrate.

  Another aspect of the present invention is an optical film manufactured by the above-described manufacturing method. This optical film is an optical film having low hygroscopicity, high transparency, excellent weather resistance, and improved brittleness. And the adhesiveness with respect to the polarizer of an optical film is improved.

  Yet another aspect of the present invention is a polarizing plate comprising a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer, and the two transparent protection films At least one of the films is a polarizing plate characterized by being the optical film described above. This polarizing plate can satisfactorily meet the demand for larger liquid crystal display devices. And the adhesiveness with respect to the polarizer of a transparent protective film is improved.

  Still another aspect of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell, the two polarizing plates At least one of the liquid crystal display devices is the polarizing plate described above. This liquid crystal display device can satisfactorily meet the demand for larger size. And in the polarizing plate, the adhesiveness with respect to the polarizer of the transparent protective film is improved.

  ADVANTAGE OF THE INVENTION According to this invention, it is an optical film containing an acrylic resin and a cellulose-ester resin, Comprising: The optical film with improved adhesiveness with respect to a polarizer is provided.

It is a schematic diagram which shows the structure of the manufacturing apparatus of the optical film which can be used for implementation of the manufacturing method of the optical film of this invention.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not limited to these.

<Optical film manufacturing equipment>
First, an optical film manufacturing apparatus that can be used to carry out the optical film manufacturing method of the present invention will be described.

  As shown in FIG. 1, the optical film manufacturing apparatus 1 according to this embodiment includes a casting apparatus 101, a first stretching apparatus 102, a second stretching apparatus 103, a drying apparatus 104, and a winding apparatus 105. The web 3 formed by the casting apparatus 101 is stretched in the longitudinal direction (conveying direction) and the width direction (direction orthogonal to the conveying direction) by the first stretching apparatus 102 while being transported, and the second stretching apparatus In 103, the film is additionally stretched in the longitudinal and width directions, dried (heat treated) by a drying device 104, and wound up as an optical film by a winding device 105. The web 3 may be dried by disposing a drying device between the first stretching device 102 and the second stretching device 103.

[Casting device]
The casting apparatus 101 is a metal endless belt having a mirror-finished surface (a metal cylindrical drum having a mirror-finished surface instead of an endless belt) 101a as a support, and a resin solution. The die 101b for casting the (dope) 2 on the endless belt 101a, the heating device 101c for removing the solvent from the dope 2 cast on the endless belt 101a, and the endless belt 101a were formed. And a peeling roller 4 for peeling the web 3 from the endless belt 101a. The endless belt 101a is wound around a driving roller 101a1 and a driven roller 101a2, and can travel in the direction of an arrow in the figure. The peeling roller 4 is disposed at an end portion on the side where the dope 2 is cast on the endless belt 101a. The casting apparatus 101 includes a casting process in which the resin solution (dope) 2 is cast on the endless belt 101a, and a casting film (web) 3 of the dope 2 formed on the endless belt 101a is peeled from the endless belt 101a. The peeling process to perform is performed.

  When the dope 2 is cast on the endless belt 101a from the die 101b, the dope 2 gels on the endless belt 101a to form a cast film (web) 3. The web 3 formed on the endless belt 101a is peeled from the endless belt 101a by the peeling roller 4. Here, the thickness of the web 3 on the endless belt 101a can be changed to various values so that the thickness of the optical film wound up by the winding device 105 becomes a predetermined thickness. The thickness of the web 3 on the endless belt 101a is adjusted according to the casting amount of the dope 2, the traveling speed of the endless belt 101a, and the like.

  The heating device 101c includes a drying box 101c1, a first heating air supply device 101d disposed in the drying box 101c1, a second heating air supply device 101e, and an exhaust port 101f. The first heating air supply device 101d and the second heating air supply device 101e include heating air supply pipes 101d1 and 101e1 and headers 101d2 and 101e2, respectively.

  The temperature of the web 3 on the endless belt 101a on the first heating air supply device 101d side and the temperature of the web 3 on the endless belt 101a on the second heating air supply device 101e side are based on the time required for evaporation of the solvent, respectively. Considering the travel speed of the endless belt 101a to be determined, the degree of dispersion of fine particles in the dope 2, productivity, and the like, for example, a range of −5 ° C. to 70 ° C. is preferable, and a range of 0 ° C. to 60 ° C. is more preferable. .

  The wind pressure of the heating air supplied from the first heating air supply device 101d and the second heating air supply device 101e is, for example, from 50 Pa to 50 Pa in consideration of the uniformity of solvent evaporation, the degree of dispersion of fine particles in the dope 2, and the like. A range of 5000 Pa is preferred.

  The first heating air supply device 101d and the second heating air supply device 101e may supply only the heating air having a constant temperature, or stepwise the heating air having a plurality of temperatures along the traveling direction of the endless belt 101a. You may supply.

  The heating device 101c shown in FIG. 1 removes the solvent by heating the web 3 with heated air, but is not limited thereto, for example, the one that heats the web 3 with an infrared heater, the back surface of the endless belt 101a It is also possible to heat the web 3 from the back side by spraying heated air.

  The time from casting the dope 2 on the endless belt 101a to peeling the web 3 from the endless belt 101a varies depending on the thickness of the manufactured optical film, the type of solvent, etc., but the endless belt 101a For example, the range of 0.5 minute to 5 minutes is preferable in view of good peelability from the surface.

  The endless belt 101a preferably has a mirror-finished surface. For example, a metal endless belt whose surface is plated with a casting is preferably used. The width of the endless belt 101a varies depending on the size of the optical film to be manufactured, but is preferably in the range of 1700 mm to 2700 mm, for example. And the width | variety which casts dope 2 has the preferable range of 80%-99% among the width | variety of endless belt 101a, for example.

  When the web 3 formed on the endless belt 101a is peeled from the endless belt 101a, the residual solvent ratio of the web 3 (residual solvent ratio of the web 3 at the time of peeling) is the peelability of the web 3 from the endless belt 101a. Considering the transportability of the subsequent web 3, the retention by the tenter during stretching, the appearance and optical properties of the produced optical film, and the like, for example, a range of 20% by mass to 100% by mass is preferable, and 35% by mass to The range of 90% by mass is more preferable, and the range of 45% by mass to 80% by mass is further preferable.

  In addition, after peeling, the residual solvent rate of the web 3 when the web 3 starts to be stretched by the first stretching device 102 (residual solvent rate of the web 3 at the start of stretching by the first stretching device 102) depends on the tenter at the time of stretching. Considering the retention, the appearance and optical properties of the produced optical film, for example, the range of 20% by mass to 100% by mass is preferable, the range of 35% by mass to 90% by mass is more preferable, and the range of 45% by mass to The range of 80% by mass is more preferable.

  Due to the tension (peeling tension) acting on the web 3 when the web 3 is peeled from the endless belt 101a and the tension acting on the web 3 (conveying tension) when the web 3 is transported after peeling, the web 3 Is stretched in the conveyance direction (Machine Direction: MD direction) of the web 3. Considering this, the peeling tension and the transport tension are preferably in the range of 50 N / m to 400 N / m, for example.

[First stretching device]
The 1st extending | stretching apparatus 102 is provided with the outer box 102a which has the dry wind intake port 102b and the discharge port 102c, and the tenter extending | stretching apparatus 102d put in the outer box 102a. The 1st extending | stretching apparatus 102 is the 1st extending | stretching the web 3 peeled from the endless belt 101a to a longitudinal direction (conveyance direction: MD direction) and / or the width direction (direction orthogonal to a conveyance direction: Transverse Direction: TD direction). The stretching step is performed. The tenter used in the tenter stretching apparatus 102d is not particularly limited, and examples thereof include a clip tenter and a pin tenter from the viewpoint of versatility and ease of operation, and can be selected and used as necessary. . However, in this embodiment, a pin tenter is used particularly in the first stretching step. The reason is that even when the web 3 has a residual solvent ratio of 20% by mass to 100% by mass at the time of peeling or at the start of stretching by the first stretching device 102, the web 3 remains soft. Since it is stretched using a pin tenter of a method of piercing and holding, compared to the case of stretching using a clip tenter of a method of gripping and holding the web 3, it is possible to firmly hold the side portion in the width direction of the web 3, This is because the web 3 can be stretched uniformly.

  As a result, stretching can be performed in a state where the residual solvent is relatively high, and as a result of improving the drying property, productivity can be improved and optical quality such as appearance and flatness can be improved.

  The tenter stretching apparatus 102d can stretch the web 3 in the MD direction and the TD direction as necessary. The dry air intake port 102b and the discharge port 102c may be reversed. Although the case where heated air is used as the solvent removal means in the first stretching apparatus 102 is shown, the solvent removal means is not particularly limited, and other examples include means for heating with an infrared heater, for example.

  The drying conditions in the first stretching apparatus 102 vary depending on the residual solvent ratio of the web 3 at the time of peeling or at the start of stretching by the first stretching apparatus 102, but drying time, shrinkage unevenness, stability of stretch amount, etc. In view of the above, it is possible to achieve a reasonable stretching, and from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids in the manufactured optical film, and ensuring the elastic modulus and optical characteristics. More than ℃, glass transition temperature of acrylic resin and glass transition temperature of cellulose ester resin higher temperature of glass transition temperature α 30 ℃ higher than α + 30 ℃ or less, 1-30 seconds, more preferably 10-20 seconds, It is preferable to perform drying. Moreover, it may be dried at a constant temperature, or may be divided into three to four stages of temperature and may be divided into several stages of temperature.

  In the first stretching apparatus 102, the MD direction of the web 3 (conveyance) from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids of the manufactured optical film, and securing the elastic modulus and optical characteristics. Direction A or the longitudinal direction) and the total value A of the TD direction of the web 3 in the TD direction (the direction perpendicular to the conveying direction or the width direction) is 1 to 30%, more preferably 10 to 20%. Is preferred. In that case, in the first stretching step, the ratio of the stretching ratio in the MD direction (transport direction or longitudinal direction) and the ratio of the stretching ratio in the TD direction (direction perpendicular to the transport direction or the width direction) are not particularly limited. . For example, the stretching ratio in the MD direction may be 1 to 30% and the stretching ratio in the TD direction may be zero (except for minus). Conversely, the stretching ratio in the TD direction may be 1 to 30% and the stretching ratio in the MD direction may be zero (except for minus). The ratio of the stretching ratio in the MD direction and the ratio of the stretching ratio in the TD direction is preferably 50:50. However, it may be appropriately changed in the range of 0: 100 to 98: 2. However, in general, it is desirable that the ratio of the stretching ratio in the TD direction is larger than the ratio of the stretching ratio in the MD direction from the viewpoint of improvement in productivity due to improvement in dryness and optical quality such as appearance and flatness.

  Here, the stretching ratio in the TD direction in the first stretching process is expressed by the formula “stretching ratio in the TD direction in the first stretching process (%) = {(web width after the first stretching process−first stretching. Web width before process) / web width before first stretching step} × 100 ”. The width of the web is a value measured with a C-type JIS grade 1 steel scale.

  In addition, the MD-direction stretching ratio in the first stretching step is expressed by the formula “MD-direction stretching ratio (%) in the first stretching process = {(web conveyance speed after the first stretching process−first stretching). Web transport speed before the process) / web transport speed before the first stretching step} × 100 ”.

  The value obtained by adding the TD-direction stretching rate in the first stretching step and the MD-direction stretching rate in the first stretching step is the “total stretching ratio A in the first stretching step”.

  The residual solvent ratio of the web 3 after the first stretching step is preferably 20% by mass or less, and more preferably 15% by mass or less.

[Second stretching device]
The second stretching device 103 has basically the same structure as the first stretching device 102. That is, the 2nd extending | stretching apparatus 103 is provided with the outer box 103a which has the dry wind inlet 103b and the discharge port 103c, and the tenter extending | stretching apparatus 103d put in the outer box 103a. The second stretching device 103 performs a second stretching step of additionally stretching the web 3 stretched by the first stretching device 102 in the longitudinal direction and / or the width direction. The tenter used in the tenter stretching apparatus 103d is not particularly limited, and examples thereof include a clip tenter and a pin tenter from the viewpoint of versatility and ease of operation, and can be selected and used as necessary. . However, in this embodiment, in particular, in the second stretching step, a clip tenter is used to grip and stretch the side portion of the web 3 that has been dried to some extent.

  In the tenter stretching apparatus 103d, the web 3 can be stretched in the MD direction and the TD direction as necessary. Note that the dry air intake port 103b and the discharge port 103c may be reversed. Although the case where heated air is used is shown as the solvent removal means in the second stretching apparatus 103, the solvent removal means is not particularly limited, and other examples include means for heating with an infrared heater, for example.

  The drying conditions in the second stretching apparatus 103 vary depending on the residual solvent ratio of the web 3 at the start of stretching by the second stretching apparatus 103, but considering drying time, shrinkage unevenness, stability of expansion and contraction, and the like. In addition, it achieves reasonable stretching, and from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids in the manufactured optical film, and securing elastic modulus and optical properties, 30 ° C. lower than the lower glass transition temperature β of the glass transition temperature and the glass transition temperature of the cellulose ester resin, β-30 ° C. or higher, higher of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. It is preferable to perform drying for 1 to 30 seconds, more preferably 10 to 20 seconds, at a temperature α + 50 ° C. or less which is 50 ° C. higher than the glass transition temperature α. Moreover, it may be dried at a constant temperature, or may be divided into three to four stages of temperature and may be divided into several stages of temperature.

  In the second stretching apparatus 103, the MD direction of the web 3 (conveyance) from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids of the manufactured optical film, and ensuring the elastic modulus and optical characteristics. Direction or longitudinal direction) and the total value B of the stretching ratio of the web 3 in the TD direction (direction perpendicular to the conveying direction or width direction) is 1 to 100%, more preferably 20 to 60%. Is preferred. That is, “the total value of the stretching ratio in the MD direction of the web 3 in the first stretching process and the stretching ratio in the TD direction (total stretching ratio in the first stretching process) A ≦ MD direction of the web 3 in the second stretching process. The web 3 is stretched by the two stretching devices 102 and 103 so as to satisfy the condition of “the total value of the stretching ratio and the stretching ratio in the TD direction (total stretching ratio in the second stretching step) B”. Here, for example, when the total stretching ratio A in the first stretching process is 1%, the total stretching ratio B in the second stretching process is 1 to 100%, and the total stretching ratio A in the first stretching process is 30%. In this case, it goes without saying that the total stretching ratio B in the second stretching step is 30 to 100%. In that case, in the second stretching step, the ratio of the stretching ratio in the MD direction (transport direction or longitudinal direction) and the ratio of the stretching ratio in the TD direction (direction perpendicular to the transport direction or the width direction) are not particularly limited. . For example, the stretching ratio in the MD direction may be 1 to 100% and the stretching ratio in the TD direction may be zero (except for minus). Conversely, the stretching ratio in the TD direction may be 1 to 100% and the stretching ratio in the MD direction may be zero (except for minus). The ratio of the stretching ratio in the MD direction and the ratio of the stretching ratio in the TD direction is preferably 50:50. However, it may be appropriately changed in the range of 0: 100 to 98: 2. However, in general, it is desirable that the ratio of the stretching ratio in the TD direction is larger than the ratio of the stretching ratio in the MD direction from the viewpoint of improvement in productivity due to improvement in dryness and optical quality such as appearance and flatness.

  Here, the stretching ratio in the TD direction in the second stretching process is expressed by the formula “stretching ratio in the TD direction in the second stretching process (%) = {(web width after the second stretching process−second stretching. Web width before process) / web width before second stretching step} × 100 ”. The width of the web is a value measured with a C-type JIS grade 1 steel scale.

  In addition, the MD direction stretching rate in the second stretching step is expressed by the formula “MD direction stretching rate in the second stretching step (%) = {(web transport speed after the second stretching step−second stretching Web transport speed before the process) / web transport speed before the second stretching step} × 100 ”.

  The value obtained by adding the TD-direction stretching rate in the second stretching step and the MD-direction stretching rate in the second stretching step is the “total stretching rate B in the second stretching step”.

  The residual solvent ratio of the web 3 after the second stretching process is preferably 20% by mass or less, for example, in consideration of the load of the drying process by the subsequent drying apparatus 104, the dimensional stability during storage and the expansion / contraction ratio, and the like. The mass% or less is more preferable. For example, 0.05 mass% or more is preferable and 1 mass% or more is more preferable. If it exceeds 20% by mass, the heat treatment step for drying the web after the stretching step may be too long. Moreover, the generation of voids when the solvent evaporates in the heat treatment step becomes significant, and the possibility that the appearance and physical properties such as flatness and transparency of the manufactured optical film are impaired is increased. If it is less than 0.05% by mass, the film is forcibly stretched in the stretching process, and the film thickness uniformity of the manufactured optical film is likely to be impaired.

[Drying equipment]
The drying device 104 includes a drying box 104a having a drying air intake port 104b and a discharge port 104c, an upper conveyance roller 104d that conveys the web 3, and a lower conveyance roller 104e. The drying device 104 performs a heat treatment step of drying the web 3 stretched in the longitudinal direction and / or the width direction in the first stretching step and the second stretching step. The upper conveyance roller 104d and the lower conveyance roller 104e are a pair of upper and lower, and are composed of a plurality of sets. The number of transport rollers disposed in the second drying device 104 varies depending on the drying conditions, the drying method, the length of the optical film 5 to be manufactured, and the like, and is appropriately set. The upper conveyance roller 104d and the lower conveyance roller 104e are free rotation rollers that are not rotated by a driving source. Further, not all of the transport rollers that freely rotate are used between the drying device 104 and the winding device 105, but usually one to several transport drive rollers (rollers that are rotationally driven by a drive source). Requires installation. Basically, the purpose of the conveyance drive roller is to convey the web 3 by its drive, so the conveyance of the web 3 and the rotation of the drive roller are synchronized by nip, suction (air suction) or the like. With the mechanism.

  In the drying device 104, drying may be performed using heated air, infrared rays, or the like alone, or drying may be performed using heated air and infrared rays in combination. It is preferable to use heated air from the viewpoint of simplicity. FIG. 1 shows a case where heated air is used. The drying temperature varies depending on the residual solvent ratio of the web when entering the drying step, but the drying temperature, for example, remains in the range of 30 ° C. to 180 ° C. in consideration of drying time, shrinkage unevenness, stability of the amount of expansion and contraction, etc. What is necessary is just to select and decide suitably by a solvent rate. Moreover, it may be dried at a constant temperature, or may be divided into three to four stages of temperature and may be divided into several stages of temperature.

  The residual solvent ratio of the web 3 after the drying process in the drying apparatus 104 is 0.01% by mass to 0.05% in consideration of the load of the drying process (heat treatment process), the dimensional stability during storage and the expansion / contraction rate. Mass% is preferred. In the present embodiment, the web 3 formed by the casting apparatus 101 is gradually removed by the drying apparatus 104, and the web 3 having a total residual solvent ratio of, for example, 2% by mass or less is referred to as an optical film. is there.

[Winding device]
The winding device 105 is a drying device 104 that winds the optical film 5 having a predetermined residual solvent ratio in a roll shape on a winding core to a required length. The temperature at the time of winding is preferably cooled to room temperature in order to prevent scratches and loosening due to shrinkage after winding. The winder to be used can be used without any particular limitation, and may be a commonly used one, such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. Can be wound up.

  In the present embodiment, it is preferable to manufacture an optical film having a film thickness of 20 to 100 μm from the viewpoint of preventing curling, wrinkles and the like of the manufactured optical film 5 in consideration of the application of the manufactured optical film 5. .

<Method for producing optical film>
According to the optical film manufacturing apparatus 1 as shown in FIG. 1, the casting step of casting the resin solution 2 on the metal support 101a and the web 3 formed on the support 101a are removed from the support 101a. A peeling process for peeling, a first stretching process for stretching the peeled web 3 in the longitudinal direction and / or the width direction, and a second stretching process for additionally stretching the web 3 in the longitudinal direction and / or the width direction after the first stretching process. And a heat treatment step for drying the stretched web 3 and a winding step for winding the dried web 3 as an optical film. The method for producing an optical film by such a solution casting film forming method is a preferred method for producing an optical film from the viewpoints of suppression of coloring, suppression of foreign matter defects, suppression of optical defects such as die lines, and the like. In addition, you may make it dry the web 3 by performing a drying process between a 1st extending | stretching process and a 2nd extending | stretching process. Hereinafter, in addition to the contents described above, further description will be given.

[Dissolution process]
In the dissolution step, a dope is prepared by dissolving the acrylic resin, cellulose ester resin, and in some cases acrylic particles and other additives in an organic solvent mainly composed of a good solvent for acrylic resin and cellulose ester resin while stirring. The step of forming, or the step of forming a dope which is a main solution by mixing the acrylic resin or cellulose ester resin solution with an acrylic particle solution or other additive solution as the case may be.

  For dissolution of acrylic resin and cellulose ester resin, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9- Various dissolution methods can be used such as a method performed by a cooling dissolution method as described in JP-A-95557 or JP-A-9-95538, a method performed at high pressure as described in JP-A No. 11-21379, In particular, a method of pressurizing at a temperature equal to or higher than the boiling point of the main solvent is preferable.

  The total amount of the acrylic resin and the cellulose ester resin in the dope is preferably 15 to 45% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  In this method, the aggregate remaining at the time of particle dispersion and the aggregate generated when the main dope is added are aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can only be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

  If necessary, remove large agglomerates from the acrylic particle charging kettle with a filter and feed it to the stock kettle. Thereafter, the acrylic particle additive liquid is added from the stock kettle to the main dope dissolving kettle.

  Thereafter, the main dope solution is filtered by a main filter, and an ultraviolet absorbent additive solution or the like may be further added in-line thereto.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. The return material may contain acrylic particles. In that case, it is preferable to control the addition amount of the acrylic particle addition liquid in accordance with the addition amount of the return material.

  The additive solution containing acrylic particles preferably contains 0.5 to 10% by mass of acrylic particles, more preferably 1 to 10% by mass, and 1 to 5% by mass. Most preferably.

  If it is in the said range, since an addition liquid is low-viscosity, it is easy to handle and it is easy to add to the main dope, it is preferable.

  A return material is a product obtained by finely pulverizing a protective film for a liquid crystal polarizing plate, which is generated when a protective film for a liquid crystal polarizing plate is formed, and is specified out by a material obtained by cutting off both sides of the film or by scratches. A protective film raw material for a liquid crystal polarizing plate is used.

  In addition, an acrylic resin, a cellulose ester resin, and, in some cases, acrylic particles kneaded into pellets can be preferably used.

(Solvent for resin solution (dope))
A solvent useful for forming a dope when the optical film according to the present invention is produced by the solution casting method is, for example, an organic solvent. As such an organic solvent, any organic solvent can be used without limitation as long as it can simultaneously dissolve an acrylic resin, a cellulose ester resin, and other additives.

  For example, as a chlorinated organic solvent, methylene chloride (methylene chloride), and as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone , Ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3 -Hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Methylene chloride, methyl acetate, ethyl acetate, and acetone can be preferably used.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the web gels and peeling from the metal support becomes easy, and when the proportion of alcohol is small, the acrylic resin and cellulose ester resin dissolve in a non-chlorine organic solvent system. There is also a role to promote.

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, at least 15 types of acrylic resin, cellulose ester resin, and acrylic particles are used. A dope composition in which 45% by mass is dissolved is preferable.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

[Casting process]
A description will be given with reference to FIG. 1 again. In the casting process, the dope is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump), and is supported by an endless metal belt such as a stainless steel belt or a rotating metal drum. This is a step of casting a dope from a pressure die slit to a casting position on the body.

  A pressure die that can adjust the slit shape of the die base and facilitates uniform film thickness is preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

(Solvent evaporation process during casting process)
This is a step of heating the web on the support and evaporating the solvent.

  To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of -5 to 70 ° C.

  From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 0.5 to 5 minutes.

[Peeling process]
A peeling process is a process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

  The temperature at the peeling position on the metal support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C.

  In addition, the residual solvent rate at the time of peeling of the web on the metal support at the time of peeling is in the range of 20 to 100% by mass depending on the strength of the drying conditions, the length of the metal support, etc. in addition to the above-described reason. However, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes due to the peeling tension are likely to occur. The residual solvent ratio at the time of peeling is determined in view of the above.

  The residual solvent ratio of the web is defined by the following formula.

Residual solvent ratio (%) = {(mass before heat treatment of web−mass after heat treatment of web) / (mass after heat treatment of web)} × 100
Note that the heat treatment when measuring the residual solvent ratio represents performing heat treatment at 115 ° C. for 1 hour.

  The peeling tension when peeling the metal support and the film is usually 196 to 245 N / m in addition to the above-mentioned values. However, if wrinkles easily occur during peeling, the peeling tension is 190 N / m or less. Further, it is preferable to peel at a minimum tension of ˜166.6 N / m that can be peeled, and then peel off at a minimum tension of ˜137.2 N / m, and particularly preferably peel at a minimum tension of ˜100 N / m. It is.

  In the present invention, the temperature at the peeling position on the metal support is preferably -5 to 70 ° C, more preferably 0 to 60 ° C, and most preferably 15 to 60 ° C.

[Stretching process (first stretching process, second stretching process)]
The stretching step (the first stretching step and the second stretching step performed after the first stretching step) uses a tenter stretching device that holds and transports the side portion in the width direction of the web with a pin tenter or clip tenter after peeling. The web is stretched in the MD direction and / or the TD direction (first stretching and second stretching).

  In the first and second stretching steps, when a tenter stretching apparatus is used, it is preferable to use an apparatus that can independently control the holding position of the film by the tenter on the left and right. It is also preferable to create compartments with intentionally different temperatures to improve planarity. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In the first and second stretching steps, the stretching operation may be performed in multiple stages, or biaxial stretching may be performed in the longitudinal direction (MD direction) and the width direction (TD direction). preferable. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, in each of the first and second stretching steps, for example, the following stretching steps are possible.
(A) Stretch only in MD direction (b) Stretch only in TD direction (c) Simultaneous stretching in MD direction and TD direction (d) Stretch in MD direction-then stretch in TD direction (e) Stretch in TD direction-Then Stretch in TD direction-Stretch in MD direction-Then stretch in MD direction

  Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferred draw ratio of simultaneous biaxial stretching can be set in the range of, for example, x1.01 times (stretching ratio: 1%) to x1.5 times (stretching ratio: 50%) in both the width direction and the longitudinal direction. .

  When the tenter is used, the residual solvent ratio of the web is preferably 20 to 100% by mass at the start of the first stretching, preferably 20% by mass or less after the first stretching, and the residual solvent ratio of the web after the second stretching is 10%. It is preferable to perform drying while applying a tenter until the content becomes less than or equal to 5% by mass, and more preferably 5% by mass or less.

  As described above, the specific temperature when performing the stretching step is 30 ° C. or higher for the first stretching step, which is the higher glass transition temperature of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. A temperature α + 30 ° C. higher than α by 30 ° C. is preferable, and in the second stretching step, a temperature β− lower by 30 ° C. than the lower glass transition temperature β of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. 30 ° C. or higher, preferably a temperature α + 50 ° C. that is 50 ° C. higher than the glass transition temperature α of the higher glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. About the 1st extending process, it is 30-175 ° C, 50-150 ° C, 70-140 ° C, etc. Te is, 70~200 ℃, 90~185 ℃, is 110~175 ℃ and the like. For example, when the glass transition temperature of the acrylic resin is 112 ° C. and the glass transition temperature of the cellulose ester resin is 158 ° C., the first stretching step is 30 to 188 ° C., and the second stretching step is 82 to It becomes 208 degreeC.

  In the stretching step, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film, and the temperature distribution in the width direction in the stretching step is preferably within ± 5 ° C, more preferably within ± 2 ° C. Preferably, it is within ± 1 ° C.

  And as above-mentioned, the 1st extending process and the 2nd extending process performed after the 1st extending process are included as an extending process, and the draw ratio and width of the longitudinal direction of the web in the 1st extending process A ≦ B, where A is the total value of the stretching ratio in the direction, and B is the total value of the stretching ratio in the longitudinal direction and the stretching ratio in the width direction of the web in the second stretching step.

  Thereby, even if it is the optical film 5 containing the acrylic resin whose saponification ability is lower than a cellulose ester resin, the optical film 5 with which the adhesiveness with respect to a polarizer was improved will be obtained.

  Specifically, for example, from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids of the manufactured optical film 5, and securing the elastic modulus and optical characteristics, the total stretching in the first stretching step The rate A is 1 to 30%, and the total stretch rate B in the second stretching step is 1 to 100%.

  Thereby, the favorable dryness without the void of the manufactured optical film 5, flatness, film thickness uniformity, an elastic modulus, and an optical characteristic are ensured.

  Therefore, in the first stretching step, for example, a temperature α + 30 ° C. or lower of 30 ° C. or higher to 30 ° C. higher than the glass transition temperature α of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. Stretching is performed for 1 to 30 seconds at a temperature within the range. As a result, reasonable stretching is realized, and good dryness, flatness, film thickness uniformity, elastic modulus and optical characteristics without voids of the manufactured optical film 5 are ensured.

  Therefore, in the second stretching step, for example, a temperature β-30 ° C. or more lower than the lower glass transition temperature β of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin β-30 ° C. or higher to the acrylic resin Stretching is performed for 1 to 30 seconds at a temperature within a range of a temperature α + 50 ° C. or less that is 50 ° C. higher than the glass transition temperature α of the glass transition temperature of the cellulose ester resin and the glass transition temperature of the cellulose ester resin. As a result, reasonable stretching is realized, and good dryness, flatness, film thickness uniformity, elastic modulus and optical characteristics without voids of the manufactured optical film 5 are ensured.

[Heat treatment process]
The heat treatment step is a step of drying (heat treatment) while the stretched web is alternately conveyed through rollers arranged in a drying apparatus.

  Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from a residual solvent ratio of about 8% by mass or less. Throughout the drying is generally carried out at 40-250 ° C. It is particularly preferable to dry at 40 to 160 ° C.

[Winding process]
The winding process is a process in which the residual solvent ratio in the web becomes 2% by mass or less and is wound as an optical film by a winder, and the dimensional stability is achieved by setting the residual solvent ratio to 0.05% by mass or less. Thus, an optical film according to the present invention can be obtained. It is particularly preferable to wind up at 0.00 to 0.05 mass%.

  As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  The optical film according to the present invention is preferably a long film. Specifically, the optical film has a thickness of about 100 m to 5000 m, and is usually provided in a roll shape. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-2.5m.

  Although there is no restriction | limiting in particular in the film thickness of the optical film which concerns on this invention, When using for the protective film for liquid crystal polarizing plates, it is preferable that it is 20-100 micrometers, It is more preferable that it is 25-90 micrometers, It is 30-80 micrometers. More preferably it is.

  The optical film manufactured by the method as described above is an optical film having low hygroscopicity, high transparency, excellent weather resistance, and improved brittleness. And the adhesiveness with respect to the polarizer of an optical film is improved.

<Optical film>
[acrylic resin]
The acrylic resin used in the present invention includes a methacrylic resin. Although it does not restrict | limit especially as resin, What consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer units copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Unsaturated group-containing divalent carboxylic acids such as saturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, Maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride and the like can be mentioned, and these can be used alone or in combination of two or more monomers.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of ensuring good thermal decomposition resistance and fluidity of the copolymer. Methyl acrylate and n-butyl acrylate are particularly preferably used.

  The acrylic resin used in the optical film according to the present invention has a weight average molecular weight (Mw) particularly from the viewpoint of improving brittleness as a protective film for a liquid crystal polarizing plate and improving transparency when compatible with a cellulose ester resin. 80,000 or more. When the weight average molecular weight (Mw) of the acrylic resin is less than 80,000, sufficient brittleness improvement cannot be obtained, and compatibility with the cellulose ester resin is deteriorated. The weight average molecular weight (Mw) of the acrylic resin is more preferably in the range of 80,000 to 1,000,000, particularly preferably in the range of 100,000 to 600,000, and 150,000. Most preferably in the range of ~ 400,000. Although the upper limit of the weight average molecular weight (Mw) of an acrylic resin is not specifically limited, It is a preferable form that it shall be 1,000,000 or less from a viewpoint on manufacture.

  The weight average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin in this invention, You may use any well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. The polymerization temperature may be 30 to 100 ° C. for suspension or emulsion polymerization, and 80 to 160 ° C. for bulk or solution polymerization. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dianal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Denki Kagaku Kogyo Co., Ltd.) and the like can be mentioned. . Two or more acrylic resins can be used in combination.

[Cellulose ester resin]
The cellulose ester resin of the present invention has a total acyl group substitution degree (T) of 2.0 to 3.0 and a carbon number of 3, particularly from the viewpoint of transparency when improved in brittleness or compatible with an acrylic resin. The degree of substitution of the acyl group of ˜7 is 1.2 to 3.0, and the degree of substitution of the acyl group of 3 to 7 carbon atoms is preferably 2.0 to 3.0. That is, the cellulose ester resin of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, but a propionyl group is particularly preferably used. .

  When the total substitution degree of the acyl group of the cellulose ester resin is less than 2.0, that is, when the residual degree of the hydroxyl groups at the 2,3,6-positions of the cellulose ester molecule exceeds 1.0, the acrylic resin and the cellulose When the ester resin is not sufficiently compatible and used as a protective film for a liquid crystal polarizing plate, haze becomes a problem. Moreover, even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility is not obtained, Brittleness will decrease. For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased. Moreover, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

  The acyl substitution degree of the cellulose ester resin of the present invention is that the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. If there is no problem, it is preferable that the total substitution degree of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms is 1.3 or less.

  The total substitution degree (T) of the acyl group of the cellulose ester resin is more preferably in the range of 2.5 to 3.0.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin has an aromatic acyl group as a substituent, it is preferable that the number of the substituents X substituted to an aromatic ring is 0-5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0. For example, since the benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzoyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the cellulose ester resin as described above, having a structure having at least one kind of an aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used for the cellulose ester resin of the present invention.

  The substitution degree of the cellulose ester resin according to the present invention is such that the total substitution degree (T) of the acyl group is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. It is.

  Moreover, it is a preferable structure that the sum total of the substitution degree of other than an acyl group having 3 to 7 carbon atoms, that is, an acetyl group and an acyl group having 8 or more carbon atoms is 1.3 or less.

  As the cellulose ester resin according to the present invention, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate are particularly preferable from the viewpoint of ensuring good compatibility with the acrylic resin and ensuring high transparency of the produced optical film. , Cellulose acetate benzoate, cellulose propionate, and cellulose butyrate are preferred, that is, those having an acyl group having 3 or 4 carbon atoms as a substituent.

  Among these, particularly preferred cellulose ester resins are cellulose triacetate, cellulose acetate propionate and cellulose propionate.

  The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is 75,000 or more, particularly from the viewpoint of improving compatibility with acrylic resin and brittleness, and may be in the range of 75,000 to 300,000. Preferably, it is in the range of 100,000 to 240,000, more preferably 160,000 to 240,000. When the weight average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the heat resistance and brittleness improvement effects are not sufficient, and the effects of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose ester resins can be mixed and used.

  In the optical film according to the present invention, the acrylic resin and the cellulose ester resin are contained in a mass ratio of 30:70 to 95: 5 and in a compatible state, preferably 50:50 to 95: 5, and more preferably. Is 60: 40-90: 10.

  When the acrylic resin and the cellulose ester resin have a mass ratio greater than 95: 5, the effect of the cellulose ester resin cannot be sufficiently obtained. When the mass ratio is less than 30:70, the moisture resistance The property becomes insufficient.

  In the optical film which concerns on this invention, an acrylic resin and a cellulose-ester resin need to contain in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

  Whether the acrylic resin and the cellulose ester resin are in a compatible state can be determined, for example, based on the glass transition temperature Tg.

  For example, when the two resins have different glass transition temperatures, when the two resins are mixed, there are two or more glass transition temperatures for each resin because there is a glass transition temperature for each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which is the glass transition temperature of the compatible resin.

  The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. The point glass transition temperature (Tmg).

  The acrylic resin and the cellulose ester resin are each preferably an amorphous resin, and either one may be a crystalline polymer or a partially crystalline polymer. It is preferable that the non-crystalline resin is formed by the compatibility between the cellulose ester resin and the cellulose ester resin.

  In the optical film according to the present invention, the weight average molecular weight (Mw) of the acrylic resin, the weight average molecular weight (Mw) of the cellulose ester resin, and the degree of substitution were classified using the difference in solubility in the solvents of both resins. Later, it is obtained by measuring each. When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that dissolves in only one of the resins. At this time, heating and refluxing are performed. May be. A combination of these solvents may be combined in two or more steps to separate the resin. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying. These fractionated resins can be identified by general structural analysis of polymers. When the optical film according to the present invention contains a resin other than an acrylic resin or a cellulose ester resin, it can be separated by the same method.

  If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

  In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin. By measuring the molecular weight distribution of each of the resins separated in advance based on the difference in solubility in a solvent by GPC, it is possible to detect each of the compatible resins.

  Further, in the present invention, “containing acrylic resin and cellulose ester resin in a compatible state” means that each resin (polymer) is mixed to result in a compatible state. In addition, a state in which a mixed resin is obtained by polymerizing a precursor of an acrylic resin such as a monomer, dimer, or oligomer with a cellulose ester resin is not included.

  For example, the step of obtaining a mixed resin by mixing a precursor of an acrylic resin such as a monomer, dimer, or oligomer with a cellulose ester resin and then polymerizing it involves a complicated polymerization reaction. It is difficult to control the reaction and it is difficult to adjust the molecular weight. In addition, when a resin is synthesized by such a method, graft polymerization, a crosslinking reaction or a cyclization reaction often occurs, and it is difficult to dissolve in a solvent or often cannot be melted by heating. It is difficult to measure the weight average molecular weight (Mw) by eluting the acrylic resin, so that it is difficult to control the physical properties and it cannot be used as a resin for stably producing an optical film.

  Unless the function as an optical film is impaired, the optical film which concerns on this invention may contain resin and additives other than an acrylic resin and a cellulose-ester resin, and may be comprised.

  When the resin other than the acrylic resin and the cellulose ester resin is contained, the resin to be added may be mixed without being dissolved even if it is in a compatible state.

  The total mass of the acrylic resin and the cellulose ester resin in the optical film of the present invention is preferably 55% by mass or more of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. .

  When using a resin or additive other than the acrylic resin and the cellulose ester resin, it is preferable to adjust the addition amount within a range not impairing the function of the optical film according to the present invention.

(Ionic surfactant)
Examples of the ionic surfactant that can be used in the present invention include a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. Examples of the cationic surfactant include aliphatic groups. Examples thereof include amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, and the like.

Examples of the anionic surfactant include higher alcohol (C ₈ -C ₂₂ ) sulfate esters (for example, sodium salt of lauryl alcohol sulfate, sodium salt of octyl alcohol sulfate, ammonium salt of lauryl alcohol sulfate, “Tepol-81” ( Trade name, manufactured by Shell Chemical Co., Ltd.), secondary sodium alkyl sulfate, etc.), aliphatic alcohol phosphate salts (eg, sodium salt of cetyl alcohol phosphate), alkylaryl sulfonates (eg, dodecylbenzenesulfonic acid) Sodium salt, isopropyl naphthalene sulfonic acid sodium salt, dinaphthalenedisulfonic acid sodium salt, metanitrobenzene sulfonic acid sodium salt), alkylamide sulfonates (eg Examples thereof include C ₁₇ H ₃₃ CON (CH ₃ ) CH ₂ SO ₃ Na) and sulfonates of dibasic fatty acid esters (for example, sodium sulfosuccinic acid dioctyl ester, sodium sulfosuccinic acid dihexyl ester, etc.). Of these, sulfates and sulfonates are particularly preferably used. Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine and the like.

  In the present invention, an anionic surfactant is preferred. The above surfactant is 0.01% by mass or more and 5% by mass or less, preferably 0.05% by mass or more and 3% by mass or less, more preferably 0.2% by mass with respect to the total amount of the resin constituting the film. % To 2% by mass is preferable. When the addition amount is larger than this range, the surfactant is precipitated from the film, or the hygroscopicity of the film is increased, and a quality undesirable for the quality of the optical film is exhibited. If the addition amount is less than this range, the effect of the present invention using a surfactant may not be obtained.

(Acrylic particles)
The optical film according to the present invention preferably contains acrylic particles.

  The acrylic particle according to the present invention represents an acrylic component that exists in a state of particles (also referred to as an incompatible state) in an optical film containing the acrylic resin and cellulose ester resin in a compatible state. In other words, the particles are mainly composed of acrylic resin.

  The acrylic particles may be obtained by, for example, collecting a predetermined amount of the produced optical film, dissolving it in a solvent, stirring, and sufficiently dissolving and dispersing the PTFE membrane filter having a pore diameter less than the average particle diameter of the acrylic particles. It is preferable that the weight of the insoluble matter filtered and collected is 90% by mass or more of the acrylic particles added to the optical film.

  The acrylic particles used in the present invention are not particularly limited, but are preferably acrylic particles having a layer structure of two or more layers, and particularly preferably the following multilayer structure acrylic granular composite.

  The multilayer structure acrylic granular composite is formed by laminating an innermost hard layer polymer, a cross-linked soft layer polymer exhibiting rubber elasticity, and an outermost hard layer polymer from the center to the outer periphery. It refers to a particulate acrylic polymer having a structure.

  That is, the multilayer structure acrylic granular composite is a multilayer structure acrylic granular composite comprising an innermost hard layer, a crosslinked soft layer, and an outermost hard layer from the central portion toward the outer peripheral portion. This three-layer core-shell multilayer acrylic granular composite is preferably used.

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following. (A) Monomer composed of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of polyfunctional grafting agent An innermost hard layer polymer obtained by polymerizing a mixture of the body, (b) in the presence of the innermost hard layer polymer, an alkyl acrylate having an alkyl group of 4 to 8 carbon atoms of 75 to 98.5% by mass. A crosslinked soft layer polymer obtained by polymerizing a mixture of monomers comprising 0.01 to 5% by mass of a polyfunctional crosslinking agent and 0.5 to 5% by mass of a multifunctional grafting agent, (c) In the presence of a polymer comprising an inner hard layer and a crosslinked soft layer, a mixture of monomers comprising 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Outermost obtained by polymerizing The three-layer structure polymer having a three-layer structure consisting of a soft layer polymer and the obtained three-layer structure polymer is 5 to 40% by mass of the innermost hard layer polymer (a), and 30 to 60% by mass of the soft layer polymer (b). And an outermost hard layer polymer (c) of 20 to 50% by mass, which has an insoluble part when fractionated with acetone, and the degree of swelling of methyl ethyl ketone in the insoluble part is 1.5 to 4.0 Granular composites.

  As disclosed in Japanese Patent Publication No. 60-17406 or Japanese Patent Publication No. 3-39095, not only the composition and particle size of each layer of the multilayer structure acrylic granular composite are defined, but also the multilayer structure acrylic granular composite. By setting the tensile modulus of the body and the degree of swelling of methyl ethyl ketone in the acetone-insoluble part within a specific range, it is possible to realize a further sufficient balance between impact resistance and stress whitening resistance.

  Here, the innermost hard layer polymer (a) constituting the multi-layer structure acrylic granular composite is 80 to 98.9% by mass of methyl methacrylate and 1 to 20% of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. % And a mixture of monomers consisting of 0.01 to 0.3% by mass of a polyfunctional grafting agent is preferred.

  Here, examples of the alkyl acrylate having 1 to 8 carbon atoms in the alkyl group include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like. And n-butyl acrylate are preferably used.

  The proportion of the alkyl acrylate unit in the innermost hard layer polymer (a) is 1 to 20% by mass. When the unit is less than 1% by mass, the thermal decomposability of the polymer is increased, while the unit is 20% by mass. If it exceeds 50%, the glass transition temperature of the innermost hard layer polymer (a) is lowered, and the impact resistance imparting effect of the three-layer structure acrylic granular composite is lowered.

  Examples of the polyfunctional grafting agent include polyfunctional monomers having different polymerizable functional groups, such as allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and allyl methacrylate is preferably used. . The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the ratio used during the innermost hard layer polymerization is 0.01 to 0.3% by mass. .

  The crosslinked soft layer polymer (b) constituting the acrylic granular composite is an alkyl acrylate 75 to 98.5 having 4 to 8 carbon atoms in the presence of the innermost hard layer polymer (a). What is obtained by polymerizing a monomer mixture consisting of mass%, polyfunctional crosslinking agent 0.01 to 5 mass% and polyfunctional grafting agent 0.5 to 5 mass% is preferred.

  Here, as the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, n-butyl acrylate or 2-ethylhexyl acrylate is preferably used.

  In addition to these polymerizable monomers, it is possible to copolymerize 25% by mass or less of other monofunctional monomers capable of copolymerization.

  Other monofunctional monomers that can be copolymerized include styrene and substituted styrene derivatives. As for the ratio of the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group and styrene, the glass transition temperature of the polymer (b) decreases as the former increases, that is, the ratio can be softened.

  On the other hand, from the viewpoint of the transparency of the resin composition, the refractive index of the soft layer polymer (b) at room temperature is set to the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard heat. It is more advantageous to make it closer to the plastic acrylic resin, and the ratio between them is selected in consideration of these.

  As the polyfunctional grafting agent, those mentioned in the item of the innermost hard layer polymer (a) can be used. The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c), and the proportion used during the soft layer polymerization is imparting impact resistance. 0.5-5 mass% is preferable from a viewpoint of an effect.

  As the polyfunctional crosslinking agent, generally known crosslinking agents such as divinyl compounds, diallyl compounds, diacrylic compounds, and dimethacrylic compounds can be used, but polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used.

  The polyfunctional cross-linking agent used here is used to generate a cross-linked structure at the time of polymerization of the soft layer (b) and develop an effect of imparting impact resistance. However, if the above-mentioned polyfunctional grafting agent is used during the polymerization of the soft layer, the polyfunctional crosslinking agent is not an essential component because the crosslinked structure of the soft layer (b) is generated to some extent. Is preferably 0.01 to 5% by mass from the viewpoint of imparting impact resistance.

  In the presence of the innermost hard layer polymer (a) and the soft layer polymer (b), the outermost hard layer polymer (c) constituting the multilayer structure acrylic granular composite is 80 to 99 masses of methyl methacrylate. % And a mixture of monomers consisting of 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferred.

  Here, as the alkyl acrylate, those described above are used, and methyl acrylate and ethyl acrylate are preferably used. The ratio of the alkyl acrylate unit in the outermost hard layer (c) is preferably 1 to 20% by mass.

  Further, for the purpose of improving the compatibility with the acrylic resin during the polymerization of the outermost hard layer (c), an alkyl mercaptan or the like can be used as a chain transfer agent to adjust the molecular weight.

  In particular, it is preferable to provide the outermost hard layer with a gradient such that the molecular weight gradually decreases from the inside toward the outside in order to improve the balance between elongation and impact resistance. Specifically, the outermost hard layer is divided into two or more monomer mixtures for forming the outermost hard layer, and the amount of chain transfer agent to be added each time is increased sequentially. It is possible to decrease the molecular weight of the polymer forming the layer from the inside to the outside of the multilayer structure acrylic granular composite.

  The molecular weight formed at this time can also be examined by polymerizing a mixture of monomers used each time under the same conditions and measuring the molecular weight of the resulting polymer.

  The particle diameter of the acrylic particles preferably used in the present invention is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, more preferably 20 nm or more and 500 nm or less, and particularly 50 nm. As mentioned above, it is most preferable that it is 400 nm or less.

  In the acrylic granular composite that is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core and the shell is not particularly limited, but when the entire multilayer structure polymer is 100 parts by mass, The core layer is preferably 50 parts by mass or more and 90 parts by mass or less, and more preferably 60 parts by mass or more and 80 parts by mass or less. In addition, the core layer here is an innermost hard layer.

  Examples of such commercially available multilayered acrylic granular composites include, for example, “Metablene” manufactured by Mitsubishi Rayon Co., “Kane Ace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Rohm and Haas "Acryloid" manufactured by KK, "Staffyroid" manufactured by Gantz Kasei Kogyo Co., Ltd., "Parapet SA" manufactured by Kuraray Co., Ltd., and the like can be used.

  Further, specific examples of the acrylic particles (C1) which are graft copolymers preferably used as the acrylic particles preferably used in the present invention include unsaturated carboxylic acid ester-based monomers in the presence of a rubbery polymer. Grafts obtained by copolymerizing a mixture of a monomer, an unsaturated carboxylic acid monomer, an aromatic vinyl monomer, and, if necessary, other vinyl monomers copolymerizable therewith A copolymer is mentioned.

  The rubbery polymer used for the acrylic particles (C1) that are the graft copolymer is not particularly limited, but diene rubber, acrylic rubber, ethylene rubber, and the like can be used. Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned. These rubbery polymers can be used alone or in a mixture of two or more.

  In addition, when adding acrylic particles to the optical film according to the present invention, it is preferable in terms of obtaining a highly transparent film that the refractive index of the mixture of the acrylic resin and the cellulose ester resin is close to the refractive index of the acrylic particles. . Specifically, the refractive index difference between the acrylic particles and the acrylic resin is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

  In order to satisfy such a refractive index condition, a method of adjusting the monomer unit composition ratio of the acrylic resin and / or a composition ratio of the rubbery polymer or monomer used in the acrylic particles is prepared. By the method or the like, the refractive index difference can be reduced, and an optical film excellent in transparency can be obtained.

  The difference in refractive index referred to here means that the optical film according to the present invention is sufficiently dissolved under a suitable condition in a solvent in which an acrylic resin is soluble to form a cloudy solution, which can be dissolved by an operation such as centrifugation. After separating into a soluble part and an insoluble part and purifying the soluble part (acrylic resin) and the insoluble part (acrylic particles), the difference in the measured refractive index (23 ° C., measurement wavelength: 550 nm) is shown.

  In the present invention, the method of blending the acrylic particles with the acrylic resin is not particularly limited, and the solution in which the acrylic particles are dispersed in advance is added to the solution (dope solution) in which the acrylic resin and the cellulose ester resin are dissolved and mixed. And a method of in-line addition of a solution obtained by dissolving and mixing acrylic particles and other optional additives is preferably used. Moreover, after blending an acrylic resin and other arbitrary components beforehand, the method of melt-kneading uniformly with a single screw or a twin screw extruder can be used normally at 200-350 degreeC, adding an acrylic particle.

  A commercially available thing can also be used as an acrylic particle concerning this invention. For example, metabrene W-341 (C2) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C3), MS-300X (C4) (manufactured by Soken Chemical Co., Ltd.) and the like can be mentioned.

  In the optical film according to the present invention, it is preferable to contain 0.5 to 30% by mass of acrylic particles with respect to the total mass of the resin constituting the film, and it is contained in the range of 1.0 to 15% by mass. More preferably.

(Other additives)
In the optical film according to the present invention, a plasticizer can be used in combination in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid, or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, preferably in the range of 600 to 3,000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the optical film according to the present invention. When the addition amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

  The optical film according to the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole, 2-hydroxybenzophenone, and salicylic acid phenyl ester. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine A hybrid system having both structures can be mentioned, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

  Furthermore, various antioxidants can also be added to the optical film of the present invention in order to improve the thermal decomposability and thermal coloring during molding. It is also possible to add an antistatic agent to give the optical film antistatic performance.

  For the optical film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphates, halogen-containing condensed phosphonates, halogen-containing phosphites, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

  According to the optical film of the present invention, it is possible to simultaneously achieve improvements in low hygroscopicity, transparency, high weather resistance, and brittleness that could not be achieved with conventional resin films. And the adhesiveness with respect to a polarizer is improved.

  In the present invention, the brittleness index is determined based on the criterion of whether or not it is “an optical film in which ductile fracture does not occur”. By obtaining an optical film with improved brittleness that does not cause ductile fracture, when creating a polarizing plate for a large-sized liquid crystal display device, breakage and cracking during production do not occur, and handling is excellent. It can be set as the protective film for liquid crystal polarizing plates. Here, the ductile fracture is a fracture caused by applying a stress larger than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material until the final fracture. The fracture surface is characterized by numerous indentations called dimples.

  In the present invention, whether or not it is “an optical film that does not cause ductile fracture” is evaluated based on the fact that no breakage or the like is observed even when a large stress is applied such that the film is folded in two. . Even if it is an optical film that does not cause ductile fracture even when such a large stress is applied, even when it is used as a protective film for a polarizing plate of an enlarged liquid crystal display device, problems such as breakage during production In addition, when the protective film for a liquid crystal polarizing plate is used after being peeled off after being pasted once, no breakage occurs, and the liquid crystal polarizing plate protective film is reduced in thickness. Is also fully compatible.

  In the present invention, the tension softening point is used as an index of heat resistance. In addition to the increase in the size of liquid crystal display devices and the increasing brightness of backlight light sources, there is a need for higher brightness for use in outdoor applications such as digital signage. Although it is calculated | required that a film can endure use in a higher temperature environment, if a tension softening point is 105 to 145 degreeC, it can be judged that it shows sufficient heat resistance. In particular, it is more preferable to control to 110 ° C to 130 ° C.

  As a specific method for measuring the temperature indicating the tension softening point of the protective film for a liquid crystal polarizing plate, for example, using a Tensilon tester (ORIENTEC, RTC-1225A), the protective film for the liquid crystal polarizing plate is 120 mm (vertical). ) × 10 mm (width) cut out, while continuing to raise the temperature at a rate of temperature increase of 30 ° C / min while pulling with a tension of 10 N, the temperature at the time of 9 N is measured three times, the average value can be obtained it can.

  From the viewpoint of heat resistance, the protective film for a liquid crystal polarizing plate preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. Point glass transition temperature (Tmg).

  As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used. In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  According to the optical film according to the present invention containing an acrylic resin and a cellulose ester resin, high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property, By reducing the difference in refractive index between the resin and the cellulose ester resin) and the acrylic particles, an increase in haze value can be prevented.

  In addition, since the surface roughness also affects the haze value as surface haze, it is also effective to reduce the particle diameter and addition amount of acrylic particles within the above range, and to reduce the surface roughness of the film contact portion during film formation. It is.

  In addition, the hygroscopicity of the optical film in the present invention is evaluated by dimensional change with respect to humidity change.

  The following method is used as an evaluation method of dimensional change with respect to humidity change.

  In the casting direction (longitudinal direction: MD direction) of the produced optical film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the marks (crosses) before and after the treatment. Is measured with an optical microscope to determine the dimensional change rate (%). The dimensional change rate (%) is expressed by the following formula.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
a1: Distance before processing a2: Distance after processing

  When an optical film is used as a protective film for a polarizing plate of a liquid crystal display device, the dimensional change due to moisture absorption causes unevenness or a change in retardation value in the protective film for liquid crystal polarizing plate, resulting in a decrease in contrast or uneven color. Cause a problem. In particular, the above-mentioned problem becomes remarkable if it is a protective film for a polarizing plate used for a liquid crystal display device used outdoors. However, if the dimensional change rate (%) under the above conditions is less than 0.5%, it can be evaluated as a protective film for a liquid crystal polarizing plate exhibiting sufficiently low hygroscopicity. Furthermore, it is preferable that it is less than 0.3%.

  In addition, the optical film according to the present invention preferably has a defect of 5 μm or more in diameter in the film plane of 1 piece / 10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as a transfer of a roll scratch or a scratch, the size of the defect is confirmed by observing the defect with reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

  If the number of defects is greater than 1/10 cm square, for example, when the film is tensioned during processing in a later step, the film may be broken with the defect as a starting point and productivity may be reduced. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

  Even when it cannot be visually confirmed, when a hard coat layer or the like is formed on the film, the coating agent may not be formed uniformly, resulting in a defect (missing coating). Here, the defect is a void in the film (foaming defect) generated due to the rapid evaporation of the solvent in the drying process of the solution casting, a foreign matter in the film forming stock solution, or a foreign matter mixed in the film forming. This refers to foreign matter (foreign matter defect) in the film.

  Further, the optical film according to the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more in the measurement based on JIS-K7127-1999.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  The optical film according to the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact portion (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roller, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the acrylic resin.

  The optical film according to the present invention can be particularly preferably used as a protective film for a polarizing plate for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

  Such physical properties include an optical film containing an acrylic resin and a cellulose ester resin in a mass ratio of 50:50 to 95: 5, and the acrylic resin has a weight average molecular weight (Mw) of 80,000 or more, The total substitution degree (T) of the acyl group of the cellulose ester resin is 2.00 to 3.00, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the weight average molecular weight (Mw ) Is 75,000 or more.

<Polarizing plate>
When using the optical film which concerns on this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film according to the present invention, and is bonded to at least one surface of a polarizer produced by immersing and stretching in an iodine solution.

  On the other side, the optical film according to the present invention may be used, or another protective film for polarizing plate may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  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.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

  The polarizing plate which concerns on this embodiment is equipped with a polarizer and the transparent protective film arrange | positioned on the surface of the said polarizer, and the said transparent protective film is the said optical film. The polarizer is an optical element that emits incident light by converting it into polarized light.

  As the polarizing plate, for example, a completely saponified polyvinyl alcohol aqueous solution is used on at least one surface of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution. The thing which bonded together is preferable. Moreover, the said optical film may be laminated | stacked also on the other surface of the said polarizer, and another transparent protective film for polarizing plates may be laminated | stacked. As this transparent protective film for another polarizing plate, for example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto Co., Ltd.) Etc. are preferably used. Or you may use resin films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate. 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.

  As described above, the polarizing plate uses the optical film as a protective film laminated on at least one surface side of a polarizer. In that case, when the said optical film functions as a phase difference film, it is preferable to arrange | position so that the slow axis of an optical film may be substantially parallel or orthogonal to the absorption axis of a polarizer.

  Moreover, as a specific example of the said polarizer, a polyvinyl alcohol-type polarizing film is mentioned, for example. Polyvinyl alcohol polarizing films include those obtained by dyeing iodine on polyvinyl alcohol films and those obtained by dyeing dichroic dyes. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used.

  The polarizer is obtained as follows, for example. First, a film is formed using a polyvinyl alcohol aqueous solution. The obtained polyvinyl alcohol film is uniaxially stretched and then dyed or dyed and then uniaxially stretched. And preferably, a durability treatment is performed with a boron compound.

  The thickness of the polarizer is preferably 5 to 40 μm, more preferably 5 to 30 μm, and more preferably 5 to 20 μm.

  When a cellulose ester resin film is bonded to the surface of the polarizer, it is preferable to bond the cellulose ester resin film 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-type resin film, it is preferable to carry out the adhesive process to a polarizing plate through a suitable adhesion layer.

  The polarizing plate as described above uses the optical film according to the present embodiment as a transparent protective film, so that the deformation of the optical film is sufficiently suppressed. For example, when applied to a liquid crystal display device It is possible to realize high image quality of the liquid crystal display device, such as improvement of contrast. Moreover, since the optical film applied as a transparent protective film of a polarizing plate also suppresses dimensional changes due to changes in humidity, for example, when applied to a liquid crystal display device, so-called corner unevenness can also be suppressed.

  Thus, the polarizing plate according to the present embodiment is a polarizing plate including a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer, and the two sheets At least one of the transparent protective films is a polarizing plate characterized in that it is the optical film described above. This polarizing plate can satisfactorily meet the demand for larger liquid crystal display devices. And the adhesiveness with respect to the polarizer of a transparent protective film is improved.

<Liquid crystal display device>
By incorporating a polarizing plate in which the optical film according to the present invention is bonded as a protective film for a liquid crystal polarizing plate into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. It is preferably used for liquid crystal display devices for outdoor use such as display devices and digital signage. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate according to the present invention includes a reflective type, a transmissive type, a transflective type LCD or a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), an IPS type (including an FFS type), and the like. It is preferably used in LCDs of various driving methods. In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

  The liquid crystal display device according to this embodiment includes a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates is the polarizing plate. . Note that the liquid crystal cell is a cell in which a liquid crystal substance is filled between a pair of electrodes, and by applying a voltage to the electrodes, the alignment state of the liquid crystal is changed and the amount of transmitted light is controlled. In such a liquid crystal display device, the use of the polarizing plate according to the present embodiment uses an optical film whose deformation is sufficiently suppressed as a transparent protective film for the polarizing plate, so that the contrast and the like are improved. Thus, a high-quality liquid crystal display device is obtained. Moreover, since what used the optical film in which the dimensional change by the humidity change was suppressed was used for the polarizing plate as a transparent protective film, what is called a corner irregularity can also be suppressed.

  Thus, the liquid crystal display device according to the present embodiment is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell. At least one of the polarizing plates is a liquid crystal display device characterized in that it is the polarizing plate described above. This liquid crystal display device can satisfactorily meet the demand for larger size. And in the polarizing plate, the adhesiveness with respect to the polarizer of the transparent protective film is improved.

  Hereinafter, the present invention will be described in more detail through examples, but the present invention is not limited to these examples.

<Optical film production test>
[Dope solution composition]
Acrylic resin: Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd., Tg: 112 ° C.) 94 parts by mass Cellulose ester resin: cellulose acetate propionate (acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl) Group substitution degree 2.56, Mw = 200,000, Tg: 158 ° C.) 5 parts by mass Acrylic particles: C1 (this process will be described later) 1 part by mass Ionic surfactant: sodium dodecylbenzenesulfonate (ELECUT S- 412-2 Takemoto Yushi Co., Ltd.) 0.75 parts by mass Methylene chloride: 300 parts by mass Ethanol: 40 parts by mass The above composition was sufficiently dissolved while heating to prepare a dope solution.

The acrylic particles (C1) are produced as follows. Each abbreviation indicates the following material.
APS: ammonium persulfate MMA: methyl methacrylate BA: n-butyl acrylate ALMA: allyl methacrylate PEGDA: polyethylene glycol diacrylate (molecular weight 200)
n-OM: n-octyl mercaptan MA: methyl acrylate

  A reactor with a reflux condenser with an internal volume of 60 liters was charged with 38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate, and the temperature was raised to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. The effect of oxygen was virtually eliminated. APS 0.36g was added, and after stirring for 5 minutes, a monomer mixture consisting of MMA 1657g, BA 21.6g, and ALMA 1.68g was added all at once, and after the exothermic peak was detected, held for another 20 minutes, Polymerization was completed.

  Next, 3.48 g of APS was added, and after stirring for 5 minutes, a mixture of monomers consisting of 8105 g of BA, 31.9 g of PEGDA, and 264.0 g of ALMA was continuously added over 120 minutes. Thus, the polymerization of the soft layer was completed.

  Next, 1.32 g of APS was added, and after stirring for 5 minutes, a mixture of monomers consisting of 2106 g of MMA and 201.6 g of BA was continuously added over 20 minutes. The polymerization of layer 1 was completed.

  Next, 1.32 g of APS was added, and after 5 minutes, a mixture of monomers consisting of 3148 g of MMA, 201.6 g of BA, and 10.1 g of n-OM was continuously added over 20 minutes, and held for another 20 minutes after the addition was completed. . Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost hard layer 2.

  The polymer latex thus obtained was poured into a 3% by weight aqueous sodium sulfate solution, salted out and coagulated, then dried after repeated dehydration and washing, and three-layer acrylic particles ( C1) was obtained. When the average particle size was determined by the absorbance method, it was 100 nm.

[Test 1]
The prepared dope solution was uniformly cast on a stainless steel band support at a temperature of 2 ° C. and a width of 2 m using a belt type casting apparatus having a structure similar to the optical film manufacturing apparatus 1 shown in FIG. With the stainless steel band support, the solvent was evaporated until the residual solvent ratio reached 20% by mass, and peeling was performed from the stainless steel band support with a peeling tension of 100 N / m.

  The peeled resin web was first stretched using a pin tenter. The stretching conditions were 1.0025 times (stretching rate: 0.25%) in the transport direction (MD direction) and 1.0025 times (stretching rate) in the width direction (TD direction) while drying at 70 ° C. for 10 seconds. : 0.25%) was stretched (total stretching ratio A in the first stretching step: 0.5%). The reason why the drying temperature in this first stretching step is 70 ° C. and the drying time is 10 seconds is that each is one of the numerical values that give the best results. Next, 2nd extending | stretching was performed using the clip tenter. Stretching conditions are as follows: 1.0025 times (stretching ratio: 0.25%) in the transport direction (MD direction) and 1.0025 times (stretching ratio) in the width direction (TD direction) while drying at 90 ° C. for 10 seconds. : 0.25%) was stretched (total stretching ratio B in the second stretching step: 0.5%). The reason why the drying temperature in this second stretching step is 90 ° C. and the drying time is 10 seconds is that each is one of the numerical values that give the best results.

  After stretching, relaxation was performed at 130 ° C. for 5 minutes, and then drying was completed while conveying the drying zone at 120 ° C. and 140 ° C. with a large number of rollers, slitting to a width of 1.5 m, and a width of 10 mm at both ends of the film. A roll of an optical film that can be used as, for example, a protective film for a liquid crystal polarizing plate was obtained by performing a 5 μm knurling process and winding it around an inner diameter of 15.24 cm with an initial tension of 220 N / m and a final tension of 110 N / m. .

  The manufactured optical film had a residual solvent ratio of 0.01%, a film thickness of 60 μm, and a winding length of 4000 m. By producing a film having a thickness of 20 to 100 μm, the use of the optical film (for example, the use as a protective film for a liquid crystal polarizing plate) is taken into consideration, and curling, wrinkles, etc. of the produced optical film are prevented. The

[Test 2]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching step is 0.5%, and the stretching ratio in the TD direction is 0.5% ( The first total stretching ratio A: 1%), the MD stretching ratio in the second stretching step is 0.5%, and the TD stretching ratio is 0.5% (second total stretching ratio B: 1%). The optical film was manufactured in the same manner as in Test 1.

[Test 3]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching process is 5%, and the stretching ratio in the TD direction is 5% (first total stretching). Rate A: 10%), the same as Test 1 except that the MD drawing rate in the second drawing step was 10% and the TD drawing rate was 10% (second total drawing rate B: 20%). Thus, an optical film was produced.

[Test 4]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching step is 10%, and the stretching ratio in the TD direction is 10% (first total stretching). Ratio A: 20%), the stretching ratio in the MD direction in the second stretching step was 20%, and the stretching ratio in the TD direction was 40% (second total stretching ratio B: 60%). Thus, an optical film was produced.

[Test 5]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification in Table 1, the MD stretching ratio in the first stretching process is 10%, and the stretching ratio in the TD direction is 20% (first total stretching). Ratio A: 30%), the stretching ratio in the MD direction in the second stretching step was 30%, and the stretching ratio in the TD direction was 70% (second total stretching ratio B: 100%). Thus, an optical film was produced.

[Test 6]
Using the same dope solution and the same apparatus as those used in Test 1, as shown in the manufacturing method specification in Table 1, the MD stretching ratio in the first stretching process is 10%, and the stretching ratio in the TD direction is 30% (first total stretching). Rate A: 40%), the same as in Test 1, except that the MD drawing rate in the second drawing step was 30% and the TD drawing rate was 80% (second total drawing rate B: 110%). Thus, an optical film was produced.

[Test 7]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching step is 0.5%, and the stretching ratio in the TD direction is 0.5% ( First stretching ratio A: 1%), MD stretching ratio in the second stretching step is 0.25%, TD stretching ratio is 0.25% (second total stretching ratio B: 0.5%) Other than the above, an optical film was produced in the same manner as in Test 1.

[Test 8]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching process is 5%, and the stretching ratio in the TD direction is 5% (first total stretching). Ratio A: 10%), the MD stretching ratio in the second stretching step is 2.5%, the stretching ratio in the TD direction is 2.5% (second total stretching ratio B: 5%), An optical film was produced in the same manner as in Test 1.

[Test 9]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specification of Table 1, the MD stretching ratio in the first stretching step is 10%, and the stretching ratio in the TD direction is 10% (first total stretching). Ratio A: 20%), the same as in Test 1, except that the MD stretching ratio in the second stretching step was 5% and the stretching ratio in the TD direction was 5% (second total stretching ratio B: 10%). Thus, an optical film was produced.

[Test 10]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification in Table 1, the MD stretching ratio in the first stretching process is 10%, and the stretching ratio in the TD direction is 20% (first total stretching). Rate A: 30%), the same as Test 1 except that the MD drawing rate in the second drawing step was 10% and the TD drawing rate was 10% (second total drawing rate B: 20%). Thus, an optical film was produced.

[Test 11]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specifications in Table 3, the drying temperature in the first stretching step was 25 ° C., and the drying temperature in the second stretching step was 78 ° C. An optical film was produced in the same manner as in Test 4.

[Test 12]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 3, the drying temperature in the first stretching step was 30 ° C., and the drying temperature in the second stretching step was 82 ° C. An optical film was produced in the same manner as in Test 4.

[Test 13]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 3, except that the drying temperature of the first stretching step was 188 ° C and the drying temperature of the second stretching step was 208 ° C, An optical film was produced in the same manner as in Test 4.

[Test 14]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 3, except that the drying temperature of the first stretching step was 192 ° C. and the drying temperature of the second stretching step was 212 ° C., An optical film was produced in the same manner as in Test 4.

[Test 15]
Using the same dope solution and the same apparatus as those in Test 1, as shown in the manufacturing method specification of Table 4, the drying time of the first stretching step is 0.5 seconds, and the drying time of the second stretching step is 0.5 seconds. An optical film was produced in the same manner as in Test 4.

[Test 16]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 4, except that the drying time of the first stretching step was 1 second and the drying time of the second stretching step was 1 second, An optical film was produced in the same manner as in Test 4.

[Test 17]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 4, except that the drying time of the first stretching step was 30 seconds and the drying time of the second stretching step was 30 seconds, An optical film was produced in the same manner as in Test 4.

[Test 18]
Using the same dope solution and the same apparatus as in Test 1, as shown in the manufacturing method specification of Table 4, except that the drying time of the first stretching step was 33 seconds and the drying time of the second stretching step was 33 seconds, An optical film was produced in the same manner as in Test 4.

<Evaluation method>
The following evaluation (main evaluation) was implemented about Tests 1-10. The results are shown in Table 1.

(Adhesiveness with polarizer)
A polyvinyl alcohol film is uniaxially stretched and then dyed, and a surface of a polarizer having a thickness of 20 μm prepared by applying a durability treatment with a boron compound, using a water-based adhesive mainly composed of completely saponified polyvinyl alcohol, The optical film obtained by each test 1-10 was bonded together. The situation when trying to peel off the bonded polarizer and optical film by hand was visually observed and evaluated according to the following criteria.
○: Does not peel even when the polarizer and the optical film are peeled off. Δ: Partially peels when the polarizer and the optical film are peeled off. ×: All peels when the polarizer and the optical film are peeled off. Do

  The following evaluation was implemented about test 1-6, 11-18. The results are shown in Tables 2-4.

(Drying)
The inside of the obtained optical film was visually observed and evaluated according to the following criteria.
○: No void is seen inside the film Δ: A little void is seen inside the film ×: There is a void inside the film and it looks like a bright spot

(Thickness uniformity)
The thickness of the obtained optical film was measured with a film thickness meter and evaluated according to the following criteria.
○: The film thickness distribution (variation) in the width direction is less than ± 5% of the film thickness (60 μm). Δ: The film thickness distribution (variation) in the width direction is less than ± 7% of the film thickness (60 μm). Film thickness distribution (variation) of ± 7% or more of film thickness (60 μm)

<Consideration of results>
[Table 1]
As is apparent from Table 1, the first stretching step is performed, and then the second stretching step is performed. In this case, “total stretching ratio A of the first stretching step ≦ total stretching ratio B of the second stretching step. The optical films of Tests 1 to 6 that were manufactured to be stretched so as to satisfy the conditions of “ It was improved and the adhesiveness with the polarizer which is the main evaluation was excellent. In addition to the first stretching step, the cellulose ester resin is oriented on the surface of the optical film by adding a second stretching step having a larger total longitudinal and lateral stretching ratio, so that the saponification suitability of the optical film is improved. As a result, when this optical film is bonded to a polarizer made of a polyvinyl alcohol film using a completely saponified polyvinyl alcohol aqueous solution, the adhesion between the optical film and the polarizer is improved. It is considered that it was. In addition to performing the second stretching step in addition to the first stretching step, the surface roughness (arithmetic average roughness (Ra) and maximum height (Rz)) of the optical film also increased. It is considered from.

  On the other hand, the first stretching process is performed, and then the second stretching process is performed, so that “the total stretching ratio A of the first stretching process> the total stretching ratio B of the second stretching process”. The optical films of Tests 7 to 10 produced by being stretched were inferior in adhesion to the polarizer.

[Table 2]
As is clear from Table 2, tests 2 to 5 were dried because the total stretching ratio A in the first stretching process was 1 to 30% and the total stretching ratio B in the second stretching process was 1 to 100%. And excellent in film thickness uniformity. This is considered to be because good dryness, flatness, and film thickness uniformity without voids of the manufactured optical film were secured. In tests 2 to 5, the elastic modulus and optical characteristics were also ensured.

  On the other hand, in Test 1, since the total stretching ratio A in the first stretching process was less than 1% and the total stretching ratio B in the second stretching process was less than 1%, the drying property and the film thickness uniformity were somewhat. Declined. In Test 6, since the total stretching ratio A in the first stretching process exceeded 30% and the total stretching ratio B in the second stretching process exceeded 100%, the film thickness uniformity slightly decreased.

[Table 3]
As is clear from Table 3, tests 4, 12, and 13 have a drying temperature of 30 ° C. to 188 ° C. in the first stretching step and a drying temperature of 82 ° C. to 208 ° C. in the second stretching step. Excellent film thickness uniformity. This is considered to be because the stretching without difficulty was realized, and good dryness, flatness, and film thickness uniformity without voids of the manufactured optical film were secured. In tests 4, 12, and 13, the elastic modulus and optical characteristics were also ensured. The preferable upper limit of the drying temperature in the first stretching step is 188 ° C., which is the higher of the glass transition temperature (112 ° C.) of the acrylic resin and the glass transition temperature (158 ° C.) of the cellulose ester resin. This is because the transition temperature is 158 ° C. (158 ° C. + 30 ° C. = 188 ° C.). The preferable lower limit of the drying temperature in the second stretching step is 82 ° C., which is the lower glass of the glass transition temperature (112 ° C.) of the acrylic resin and the glass transition temperature (158 ° C.) of the cellulose ester resin. This is because the transition temperature is 112 ° C. (112 ° C.-30 ° C. = 82 ° C.). Moreover, the preferable upper limit of the drying temperature in the second stretching step is set to 208 ° C., which is the higher of the glass transition temperature (112 ° C.) of the acrylic resin and the glass transition temperature (158 ° C.) of the cellulose ester resin. This is because the transition temperature is 158 ° C. (158 ° C. + 50 ° C. = 208 ° C.).

  On the other hand, in Test 11, the drying temperature in the first stretching step was less than 30 ° C., and the drying temperature in the second stretching step was less than 82 ° C., so the drying property was slightly lowered. In Test 14, since the drying temperature in the first stretching step exceeded 188 ° C. and the drying temperature in the second stretching step exceeded 208 ° C., the film thickness uniformity slightly decreased.

[Table 4]
As is apparent from Table 4, in tests 4, 16, and 17, the drying time of the first stretching process was 1 to 30 seconds, and the drying time of the second stretching process was 1 to 30 seconds. Excellent uniformity. This is considered to be because the stretching without difficulty was realized, and good dryness, flatness, and film thickness uniformity without voids of the manufactured optical film were secured. In tests 4, 16, and 17, the elastic modulus and optical characteristics were also ensured.

  On the other hand, in Test 15, the drying time in the first stretching step was less than 1 second, and the drying time in the second stretching step was less than 1 second. In Test 18, since the drying time of the first stretching process exceeded 30 seconds and the drying time of the second stretching process exceeded 30 seconds, the film thickness uniformity slightly decreased.

1 Optical film production equipment 2 Dope (resin solution)
3 Web (casting membrane)
4 peeling roller 5 optical film 101 casting apparatus 101a metal support (endless belt)
101b Die 102 First stretching device 102d Tenter stretching device 103 Second stretching device 103d Tenter stretching device 104 Drying device 105 Winding device 105a Rolled optical film wound up

Claims (10)

A method for producing an optical film, comprising: a casting process for casting a resin solution on a support; a peeling process for peeling the web formed on the support from the support; and a stretching process for stretching the peeled web. Because
An acrylic resin and a cellulose ester resin are included as a resin of the resin solution,
Including a first stretching step and a second stretching step performed after the first stretching step as a stretching step;
The total value of the stretch ratio in the longitudinal direction and the stretch ratio in the width direction of the web in the first stretching process is A, and the total value of the stretch ratio in the longitudinal direction and the stretch ratio in the width direction of the web in the second stretching process. A method for producing an optical film, wherein A ≦ B, where B is B.   The method for producing an optical film according to claim 1, wherein A is 1 to 30% and B is 1 to 100%.   The method for producing an optical film according to claim 1, wherein the web is stretched by a clip tenter or a pin tenter in the stretching step. The first stretching step is 30 ° C. or higher, a temperature 30 ° C. higher than the glass transition temperature α of the higher glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin α + 30 ° C. Done
In the second stretching step, the glass transition temperature of the acrylic resin and the cellulose are 30 ° C. or more lower than the lower glass transition temperature β of the glass transition temperature of the acrylic resin and the glass transition temperature of the cellulose ester resin. It carries out for 1 to 30 seconds at the temperature (alpha) +50 degrees C or less 50 degreeC higher than the higher glass transition temperature (alpha) among the glass transition temperature of ester resin, The any one of Claims 1-3 characterized by the above-mentioned. Manufacturing method of optical film.   The method for producing an optical film according to any one of claims 1 to 4, wherein an optical film having a film thickness of 20 to 100 µm is produced.   The acrylic resin is obtained by copolymerizing methyl methacrylate and at least one selected from the group consisting of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, and 2-ethylhexyl acrylate. The manufacturing method of the optical film of any one of Claims 1-5 characterized by the above-mentioned.   The cellulose ester resin is at least one selected from the group consisting of cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate. The manufacturing method of the optical film of any one of -6.   The optical film manufactured by the manufacturing method of any one of Claims 1-7. A polarizing plate comprising a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer,
A polarizing plate, wherein at least one of the two transparent protective films is the optical film according to claim 8. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell,
The liquid crystal display device, wherein at least one of the two polarizing plates is the polarizing plate according to claim 9.