JP5069433B2 - Method for producing cellulose ester film, and polarizing plate and liquid crystal display device using the cellulose ester film - Google Patents

Description

  The present invention relates to a method for producing an optical film used for a screen configuration of a liquid crystal display device, a polarizing plate using the optical film, and a liquid crystal display device. In particular, the present invention relates to an optical film manufacturing technique capable of obtaining birefringence suitable for a liquid crystal display device.

  In recent years, TN (Twisted Nematic), STN (Super Twisted Nematic), IPS (In-plane Switching), VA (Vertical Alignment), OCB (Opt Bd) A liquid crystal display system has been proposed. In these liquid crystal display devices, since the liquid crystal cell has birefringence, a phase difference of light occurs and the contrast is reduced. Therefore, the need for a retardation film is increasing in order to remove or reduce the birefringence in the liquid crystal display device. Therefore, as a means for imparting birefringence to the film, a method of stretching a polycarbonate, an olefin-based film, or a cellulose ester-based resin film has been proposed. When using a polycarbonate or olefin-based film, it is necessary to attach a retardation film to the polarizing plate. Especially in the case of a cellulose acetate film, an optical film in which the protective film of the polarizing plate and the retardation film are integrated. Therefore, it is known that it is suitable as an optical film used in a liquid crystal display device in terms of reduction of members, simplification of manufacturing process, cost reduction, and the like.

  Conventionally, a resin solution in which a polymer resin such as cellulose acetate is dissolved in a solvent (hereinafter referred to as “dope”) is placed on a belt-like or drum-like endless metal support from a die slit. After casting, a dope film (hereinafter referred to as “cast film”) is prepared, the cast film is dried, and then peeled to form an optical film. A molten resin obtained by heating and melting a thermoplastic polymer resin such as acetate is extruded from a slit of a die onto an endless metal support that transitions infinitely in the form of a belt or drum, and the film is cooled and then peeled off. So far, it has been manufactured by a method of forming an optical film (see Patent Document 1 and Patent Document 2).

  However, in the case of a cellulose acetate resin, the range of phase difference that can be expressed is limited, and it is difficult to cope with various liquid crystal display methods.

  Therefore, by introducing birefringent particles (hereinafter sometimes simply referred to as “particles”) into the cellulose acetate film, the effect of the birefringence of the particles is added to the birefringence of the resin. Can be controlled, and an optical film compatible with various liquid crystal display methods can be manufactured. In particular, if the particles are needle-shaped particles, and the orientation of the needle-shaped particles is well aligned in a certain direction, it becomes possible to expand the control range of the phase difference in the optical film, and the optical in the manufacturing process. The difficulty of breaking when the film is cut (hereinafter referred to as “slitting property”) is improved, and the generation of chips during cutting can be reduced. Here, the orientation means that the particles are arranged in one direction. In this regard, as a method for adjusting the birefringence, inclusion of acicular particles in a polymer resin has been conventionally performed (see Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6). .

  Here, as a method of orienting the added particles, conventionally, the optical film is formed by MD (Machine Direction, the flow direction of the metal support) or TD (Traverse Direction, a direction orthogonal to the MD) at the time of forming the optical film. Or the linear velocity of the metal support relative to the speed at which the resin solution or molten resin is cast from the die slit (hereinafter referred to as the “linear velocity of the cast film”). A method of applying a shear stress by stretching the cast film immediately after film formation by increasing the draft ratio, which is the ratio of the speed), or a resin solution in which the resin containing the particles is dissolved in a solvent or a molten resin in which the resin is dissolved by heat The particle is oriented by applying shearing stress to the particles along the flow, or by applying an electric or magnetic field. There have been ways to promote it.

JP 2002-322314 A JP 2004-66545 A JP 2004-35347 A Japanese Patent No. 3648201 JP 2005-156863 A JP 2005-227427 A

  However, in order to accurately remove or reduce the birefringence in the liquid crystal cell, it is necessary to accurately adjust the birefringence in the optical film according to the birefringence of the liquid crystal cell. In this respect, in the inventions described in Patent Document 3 and Patent Document 4, even though the birefringence of the optical film itself can be eliminated, it is difficult to adjust the birefringence of the optical film from the relationship with the liquid crystal cell. Here, “adjusting the birefringence” means an adjustment performed in order to obtain a desired birefringence in the manufacturing process (hereinafter the same).

  Further, in the invention of Patent Document 5, only the relationship of the three-dimensional refractive index is adjusted, and it is difficult to accurately adjust the birefringence of the optical film itself. In the invention of Patent Document 6, cellulose ester or the like is used. The invention has various birefringence properties by containing particles such as strontium carbonate as a resin, but it is suitable for the size of particles suitable for accurately adjusting the birefringence of an optical film, The length of the land length that is the length of the dope flow direction of the slit for extruding the dope and the draft ratio that is the ratio of the linear velocity of the metal support to the linear velocity of the cast film are not specified, so the optical film is accurate. It is difficult to adjust the birefringence of. In this regard, if the absolute maximum length of the particles is too long, light is scattered and haze occurs, and if it is too short, it is difficult to align. Further, the absolute maximum length is divided by the diagonal width which is the shortest distance between the two straight lines when the image of the particle projected by two straight lines parallel to the absolute maximum length of the particle is sandwiched between them. If the aspect ratio is too small, it is difficult to align, and if it is too large, it becomes difficult to produce particles. Furthermore, if the draft ratio is too large, the optical film will have horizontal steps, and if it is small, there is a problem that it is difficult to align, and if the land length is too long, vertical stripes will appear in the optical film, and if it is short There is a problem that the particles are difficult to orient.

  The present invention has been made in view of such circumstances, and provides an optical film manufacturing method capable of adjusting the direction of particles well in a certain direction and adjusting birefringence over a wide range. It aims at providing the optical film which improved and suppressed generation | occurrence | production of the chip at the time of a cutting | disconnection, and its manufacturing method. Furthermore, it aims at enabling reduction of a member, simplification of a manufacturing process, and cost reduction in manufacture of a liquid crystal display device by using the optical film of this invention as a protective film of a polarizing plate.

In order to achieve the above object, the method for producing a cellulose ester film according to claim 1 includes a resin solution containing predetermined particles and mainly composed of an organic solvent, or a molten resin heated and melted by thermoplasticity. A liquid resin using cellulose ester as a resin is continuously cast from a slit of a die onto a moving metal support, and the predetermined particles include a metal carbonate. 90% or more of all particles are the shortest distance between two straight lines when an image of particles projected by two straight lines parallel to the absolute maximum length is sandwiched between 90% and 50% of the absolute maximum length. A value obtained by dividing the absolute maximum length by a diagonal width which is a distance is larger than a value obtained by dividing the square of the absolute maximum length (unit: nm) by 20000, and the absolute maximum length (unit: nm). ) It is a particle included in a particle size range larger than a value obtained by multiplying 0.5 to the power of 20 and smaller than 20, and is a negative birefringent needle-like particle. The ratio of the linear velocity of the metal support to the velocity at which the liquid resin is poured is 2.1 to 6.0 when the liquid resin solution is used, and 10 when the liquid resin is a molten resin. A method for producing a cellulose ester film, which satisfies the condition that the time for the resin solution to pass through the slit of the die is in the range of 0.1 to 2.0 seconds,
The cellulose ester film is 160 ≦ in-plane retardation Ro ≦ 300 nm,
−10 ≦ thickness retardation Rth ≦ 10 nm,
The haze satisfies each condition of 1% or less.
The invention described in claim 2 includes a step of obtaining the predetermined particles in which 90% or more of all particles fall within the particle size range by performing particle size classification using a centrifuge.
The invention described in claim 3 includes the step of obtaining the predetermined particles in which 90% or more of all the particles fall within the particle size range by performing particle size classification using a filter.
The invention according to claim 4 is characterized in that the cellulose ester as the resin has an iron component of 1 ppm or less, calcium of 30 ppm or less, and magnesium of 20 ppm or less.
The invention according to claim 5 is characterized in that the resin is cellulose acetate propionate.
Invention of Claim 6 is a polarizing plate which consists of a polarizing film and the transparent protective film arrange | positioned at the both sides, Comprising: At least 1 of the transparent protective films of the said both sides WHEREIN: The cellulose ester of Claim 5 A film is used.
The invention according to claim 7 is a liquid crystal display device comprising 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. The polarizing plate is the polarizing plate according to claim 6.

According to the invention of claim 1, when using particles having a particle size range in which the direction of the particles is well oriented in a certain direction, and further using a resin solution, the draft ratio is 2.1 to 6.0, When using a molten resin, the optical film is manufactured with a draft ratio of 10 to 30. As a result, the casting membrane is stretched at a speed of 2.1 to 6 times when a resin solution is used, and at a speed of 10 to 30 times when a molten resin is used, and a strong shear is applied in the stretched direction. Since stress is applied, the direction of the particles can be oriented in a certain direction. In addition, when the film is formed, the slit passing time by the resin solution or molten resin to which the particles are added is increased, so that the time for applying the shear stress is increased and the direction of the particles is well oriented in a certain direction.
In addition, during film formation, by increasing the slit passage time with resin solution or molten resin to which particles are added, in addition to increasing the draft ratio, the optical film can be manufactured in a more uniform direction. Orient. Thereby, a larger phase difference can be obtained as compared with the prior art. Therefore, in the manufacturing process, by changing the conditions in the claims (hereinafter referred to as “phase difference control”), the phase difference can be changed to any one of a wide range (hereinafter referred to as “phase difference control range”). Refractiveness can be adjusted. Furthermore, when the direction of the particles is well oriented in a certain direction, the slitting property of the optical film can be improved, and the generation of chips during cutting can be reduced.
Moreover, since it manufactures using a cellulose ester, the protective film and retardation film of the polarizing plate of a liquid crystal display device are integrated.
In addition, since the particles have negative birefringence, the effect of both birefringences can be added and the phase difference can be accurately controlled by including the particles in a resin having birefringence.
In addition, it has a large phase difference, a wide phase difference control range, high slitting performance, and few deformation failures due to entanglement of chips during cutting.

  According to invention of Claim 2, it becomes possible by using a centrifuge to make sure that the content rate of the particles whose absolute maximum length and aspect ratio are within a desired range is 90% or more. As a result, the direction of the particles is better aligned in a certain direction, a large phase difference can be obtained, the control range of the phase difference of the optical film can be broadened, and the accuracy of birefringence adjustment can be increased. Can do. Moreover, the slitting property can be further improved, and the generation of chips during cutting can be further reduced.

  According to the invention of claim 3, by using a filter, it is possible to reliably make the content ratio of particles whose absolute maximum length and aspect ratio fall within a desired range to 90% or more. As a result, the orientation of the particles is better aligned in a certain direction, a large retardation can be obtained, the retardation control range of the optical film can be broadened, and the accuracy of birefringence adjustment can be increased. it can. Moreover, the slitting property can be further improved, and the generation of chips during cutting can be further reduced.

The invention of the polarizing plate of claim 6 is a polarizing plate comprising a polarizing film and a transparent protective layer disposed on both sides thereof, and the cellulose ester film according to the present invention is used for at least one of the two transparent protective layers. Therefore, the polarizing plate of the present invention has an effect that it is excellent in terms of simplification of the manufacturing process and cost as well as reduction of members.

The invention of a liquid crystal display device according to claim 7 is the polarizing plate according to claim 6 , wherein at least one of the two polarizing plates sandwiching the liquid crystal cell is the polarizing plate according to the present invention. An image display device capable of realizing an easy-to-view display with a high contrast ratio, particularly a liquid crystal display device operating in an IPS mode can be provided.

  An outline of a method for producing an optical film according to the present invention will be described with reference to FIG. Here, FIG. 1 is a process diagram of the method for producing an optical film according to the present invention. First, as shown in FIG. 1, the optical film manufacturing method of the present invention includes a fine particle creation step 001 for creating fine particles that are particles having a desired particle size range. This step includes a classification step 001 (A) for increasing the volume ratio of particles having a desired particle size range, and a fine particle dispersion preparation step 001 (B) for creating a fine particle dispersion for efficiently and uniformly dispersing fine particles. ) Etc. are included. Therefore, the desired particle size range in the present invention will be described in detail.

The fine particles constituting the optical film of the present invention need to belong to the category of fine particles having birefringence. In particular, the relationship of the three-dimensional refractive index is nx>nz> by a general orientation operation such as stretching. Since an optical film satisfying ny can be easily obtained, it is preferably in an elongated shape (hereinafter sometimes referred to as “needle shape”) such as a rod shape, a needle shape, or a spindle shape. Here, when it describes in the state contained in the optical film, nx indicates the refractive index in the slow axis (x axis) direction (orientation direction) in the optical film plane, and ny indicates the direction perpendicular to it (y axis). The refractive index of a direction is shown and nz shows the refractive index of the thickness (z-axis) direction of an optical film. Furthermore, since the fine particles are well oriented in a certain direction and the optical film is highly transparent with little haze, the absolute maximum length is X (nm) and the aspect ratio (two straight lines parallel to the absolute maximum length). (Equation 1), [Equation 2], where Y is a value obtained by dividing the absolute maximum length by the diagonal width that is the shortest distance between two straight lines when the image of the microparticles projected by Fine particles having a particle size range satisfying [Formula 3] and [Formula 4] are preferable.
[Formula 1] Y> (X ^ 2) / 20000
[Formula 2] Y> 20 × (X ^ (− 0.5))
[Formula 3] Y <20
[Formula 4] 50 <X <500

  Here, the calculation method of [Formula 1] will be described. First, actual haze in an optical film containing fine particles having various particle size ranges is measured. Here, the particle size range was measured with a transmission electron microscope. Next, the haze value that can be calculated from the particle size range using the Rayleigh scattering formula is compared with the actual measurement value, the coefficient of the Rayleigh scattering formula is adjusted, and the actual haze can be estimated from the particle size range. Created an expression. Then, a desirable particle size range was calculated using this formula, and [Formula 1] was calculated therefrom.

  Next, the calculation method of [Formula 2] will be described. The relationship between the size and aspect ratio of each particle and the direction of the particle when a variety of slit passage times or draft ratios are applied to resin solutions containing fine particles having various particle size ranges is examined. Then, [Equation 2] was calculated by analyzing how easily the particles are oriented for each particle size and aspect ratio.

  The particle size range of the fine particles is represented by a graph as shown in FIG. Here, FIG. 6 is a graph in which the vertical axis represents the aspect ratio and the horizontal axis represents the absolute maximum length (nm). The curve (a) represents [Expression 1], and the curve (b) represents [Expression 2]. The area on the left side of the curve (a) is an area representing fine particles to be used for haze reduction, and the area on the right side is an area representing fine particles to be removed for haze reduction. In addition, the upper region of the curve (b) is a region representing fine particles that are well oriented in a certain direction, and the lower region is a region representing fine particles to be removed because the orientation of the fine particles deteriorates. Therefore, the most preferable region containing fine particles is represented by a region (c) surrounded by a dotted line.

  Here, since it is difficult to produce fine particles having an aspect ratio of 10 or more as compared with fine particles having an aspect ratio of less than 10, those having an aspect ratio of less than 10 are particularly preferable. Therefore, the graph of FIG. 6 represents a region having an aspect ratio of less than 10 which is a particularly preferable range. However, since [Equation 1] is a monotonically increasing graph and [Equation 2] is a monotonically decreasing graph, the graph is enlarged as it is even in a region where the aspect ratio is larger than 10.

In the present invention, acicular fine particles having negative birefringence can be preferably used. The birefringence of the birefringent fine particles is defined as follows. The refractive index for light polarized in the absolute maximum length direction of the birefringent fine particles is npr, and the average refractive index for light polarized in the direction orthogonal to the absolute maximum length direction is nvt. The birefringence Δn of the birefringent fine particles is defined by the following formula (2).
Expression (2) Δn = npr−nvt
That is, if the refractive index in the absolute maximum length direction of the birefringent fine particles is larger than the average refractive index in the direction orthogonal to the birefringent fine particles, positive birefringence occurs, and vice versa. The absolute value of the birefringence of the birefringent fine particles used in the present invention is not particularly limited, but is preferably 0.01 to 0.3, more preferably 0.05 to 0.3. preferable. Examples of the birefringent crystal exhibiting negative birefringence include calcium carbonate, strontium carbonate, magnesium carbonate, cobalt carbonate, manganese carbonate, and barium carbonate. In the case of acicular crystals, it means a material in which the refractive index in the long direction of the crystal is smaller than the refractive index in the direction perpendicular thereto. The carbonate fine particles can be produced by a uniform precipitation method or a carbon dioxide gas compounding method. For example, it can be produced by the methods described in JP-A-3-88714, JP-B-55-51852, JP-A-59-223225, and the like. The fine particles used in the present invention may have a surface hydrophobized, and the degree of hydrophobicity is preferably 20% or less in terms of methanol wettability. The degree of hydrophobicity of the fine particles is preferably quantified using a solvent containing alcohol or pure water. As a method for quantifying the degree of hydrophobicity, the methanol wettability method (hereinafter referred to as MW method) is preferable, and the degree of hydrophobicity is represented by the methanol wettability value (hereinafter referred to as MW value) determined by this method. It is preferable. In the above MW method, in order to quantify the degree of hydrophobicity of the fine particles, a first solution and a second solution in which methanol and pure water are mixed are used. At this time, the mixing ratio of methanol and pure water is preferably 4: 6 for the first solution, and 6: 4 for the second solution. Then, the same amount of the fine particles is added to each solution and stirred and mixed, and each mixed solution is centrifuged to determine the volume of the fine particle sediment, and the volume of the fine particle sediment in the first solution is determined. The MW value is obtained from MW = (t / s) × 100 [%], where tml is the volume of the sediment of fine particles in the second solution.

  Next, as shown in FIG. 1, it has the liquefied resin production process 002 which makes liquid resin by melt | dissolving resin. The liquefied resin production step 002 includes a molten resin obtained by heating and melting a thermoplastic resin and a resin solution (hereinafter referred to as “dope”) obtained by dissolving a thermoplastic resin in a solvent. Details will be described in a first embodiment [0047] and a second embodiment [0194] which will be described later. Here, when the dope is formed, a cellulose ester solution preparation step 002 (A) and the like are included.

  Next, as shown in FIG. 1, there is a mixing step 003 in which the fine particles produced in the fine particle production step 001 and the liquid resin produced in the liquefied resin production step 002 are mixed and stirred. This mixing method includes a method in which a fine particle dispersion is prepared and mixed in the dissolution vessel 1 (see FIG. 2) or mixed by an in-line addition step 003 (A). Details will be described in a first embodiment described later. As another mixing method, when adding fine particles to the molten resin, by directly adding the particles to the molten resin without creating a fine particle dispersion, kneading with a twin screw extruder or kneader, There is also a mixing method for obtaining a molten resin in which fine particles are uniformly dispersed.

  Next, as shown in FIG. 1, an endless metal such as a rotationally driven metallic endless belt or a rotationally driven metallic drum is transferred from the slit of the die to the molten resin or resin solution containing fine particles by mixing step 003. A casting process 004 for casting a film on a support is provided.

  In the present invention, in the casting step 004, the land length of the die is increased so that the time required for the thermoplastic resin dope or molten resin to pass through the slit in the die manifold is increased. The draft ratio Vb / Vrm (see FIG. 5), which is the ratio of the linear velocity Vb of the metal support to the linear velocity Vrm (the velocity at which the dope or molten resin is cast from the slit of the die), is increased. It is characterized by. Here, the land length is the length in the dope flow direction of the slit for extruding the dope in the die (see FIG. 4A).

  If the draft ratio is large, the shear stress applied to the fine particles becomes strong, so that the fine particles are well oriented in a certain direction. Therefore, when the draft ratio is sufficiently large, the direction of the fine particles is well aligned in a certain direction. However, if the draft ratio is too large, a horizontal stage will appear on the optical film. Therefore, the draft ratio is preferably 2.1 to 6.0 in the case of dope and 10 to 30 in the case of molten resin.

  Furthermore, if the time for the dope or the molten resin to pass through the slit is long, the time for which the shear stress is applied to the fine particles can be lengthened, and the direction of the fine particles is well aligned in a certain direction. Therefore, when the slit passage time has a sufficient time, the direction of the fine particles is well aligned in a certain direction. However, if the slit passage time is too long, vertical stripes appear on the optical film. Therefore, it is preferable that the time required for the thermoplastic resin dope or molten resin to pass through the slit in the die manifold is 0.1 sec to 2.0 sec.

  Next, as shown in FIG. 1, the cast film created in the casting process 004 is subjected to the solvent evaporation process 005 (A), the peeling process 005 (B), the drying process 005 (C), and the winding process 005 (D Etc.) to complete the optical film.

  As described above, it is possible to produce an optical film in which fine particles are well oriented in a certain direction through the respective steps in the method of producing an optical film of the present invention shown in FIG.

  Furthermore, as an optical film produced by the method of the present invention, it is preferable that the production is easy, the adhesiveness with the actinic radiation curable resin layer is good, and the optical film is optically transparent. It is done.

  Here, the transparency of the optical film means that the transmittance of visible light is 60% or more, preferably the transmittance of visible light is 80% or more, and particularly preferably 90% or more.

  Further, examples of the thermoplastic resin preferably used in the present invention include cellulose ester resins having a substitution degree of acyl groups such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate of 2.3 to 2.8 or more. Can be mentioned.

[First Embodiment]
The case where the manufacturing method of the optical film of this invention is performed by the solution casting film forming method is demonstrated.

<Material for preparing dope>
Hereinafter, the present invention will be described by taking cellulose ester as an example of the thermoplastic resin.

  In the present invention, a cellulose ester solution containing a cellulose ester and an organic solvent for dissolving the cellulose ester is referred to as a dope, and this is used to cast a solution to form a cellulose ester film.

(Cellulose ester)
The cellulose used as a raw material for the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be used individually or in mixture in arbitrary ratios, respectively.

In the present invention, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), the cellulose ester uses an organic solvent such as acetic acid or an organic solvent such as methylene chloride. The reaction is carried out using a protic catalyst such as sulfuric acid. When the acylating agent is acid chloride (CH ₃ COCI, C ₂ H ₅ COCI, C ₃ H ₇ COCI), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized by the method described in JP-A-10-45804.

  In the cellulose ester, the acyl group reacts with the hydroxyl group of the cellulose molecule. Cellulose molecules are composed of many glucose units linked, and there are three hydroxyl groups per glucose unit. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution. For example, cellulose triacetate has an acetyl group bonded to all three hydroxyl groups of the glucose unit.

  The cellulose ester that can be used in the cellulose ester film preferably has a total acyl group substitution degree of 2.3 to 2.8 or more. This is because even if a resin having a substitution degree close to 3.0 is stretched, the birefringence of the resin itself hardly changes.

  The molecular weight of the cellulose ester used in the present invention is a number average molecular weight (Mn) of 50,000 to 200,000. Those having 60,000 to 200,000 are more preferable, and those having 80,000 to 200,000 are particularly preferable.

  In the cellulose ester used in the present invention, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw / Mn is preferably 1.4 to 3.0 as described above, more preferably It is in the range of 1.7 to 2.2.

  The average molecular weight and molecular weight distribution of the cellulose ester can be measured by a known method using high performance liquid chromatography. Using this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

  The cellulose ester used in the present invention is a carboxylic acid ester having about 2 to 22 carbon atoms, and is particularly preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate phthalate, etc., JP-A-10-45804, Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate as described in US Pat. No. 8,231,761, US Pat. No. 2,319,052 can be used. Alternatively, an ester of an aromatic carboxylic acid and cellulose and cellulose acylate described in JP-A Nos. 2002-179701, 2002-265639, and 2002-265638 are also preferably used. Among the above descriptions, the lower fatty acid esters of cellulose particularly preferably used are cellulose triacetate and cellulose acetate propionate. These cellulose esters can also be mixed and used.

  A preferred cellulose ester other than cellulose triacetate has an acyl group having 2 to 4 carbon atoms as a substituent, the substitution degree of acetyl group is x, and the substitution degree of propionyl group or butyryl group is y. It is a cellulose ester that simultaneously satisfies (a) and (b).

Formula (a) 2.3 ≦ x + y ≦ 2.8
Formula (b) 0 ≦ x ≦ 2.5
The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  These acyl group substitution degrees can be measured according to the method prescribed in ASTM-D817-96.

  In the case of acetylcellulose, it is necessary to extend the time of the oxidation reaction in order to increase the oxidation rate. However, if the reaction time is too long, the decomposition proceeds at the same time, and the polymer chain is broken or the acetyl group is decomposed, resulting in undesirable results. Therefore, in order to increase the degree of oxidation and suppress decomposition to some extent, it is necessary to set the reaction time within a certain range. It is not appropriate to define the reaction time because the reaction conditions vary and greatly vary depending on the reaction equipment, equipment and other conditions. As the decomposition of the polymer progresses, the molecular weight distribution becomes wider. Therefore, in the case of cellulose ester, the degree of decomposition can be defined by the value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is usually used. That is, in the process of oxidation of cellulose triacetate, the decomposition is not too long and the decomposition does not proceed too much, and the weight average molecular weight (Mw) / number is one index of the degree of reaction for allowing the oxidation reaction to take place for a sufficient period of time. Average molecular weight (Mn) values can be used.

  An example of a method for producing a cellulose ester is shown below. 100 parts by weight of cotton linter was crushed as a cellulose raw material, 40 parts by weight of acetic acid was added, and pretreatment activation was performed at 36 ° C. for 20 minutes. Thereafter, 8 parts by weight of sulfuric acid, 260 parts by weight of acetic anhydride and 350 parts by weight of acetic acid were added, and esterification was performed at 36 ° C. for 120 minutes. After neutralizing with 11 parts by weight of a 24 mass% magnesium acetate aqueous solution, saponification aging was performed at 63 ° C for 35 minutes to obtain acetylcellulose. This was stirred for 160 minutes at room temperature using a 10-fold acetic acid aqueous solution (acetic acid: water = 1: 1 (mass ratio)), then filtered and dried to obtain acetyl cellulose having a degree of acetyl substitution of 2.75. . This acetylcellulose had Mn of 92,000, Mw of 156,000, and Mw / Mn of 1.7. Similarly, cellulose esters having different degrees of substitution and Mw / Mn ratios can be synthesized by adjusting the esterification conditions (temperature, time, stirring) and hydrolysis conditions of the cellulose ester.

  The synthesized cellulose ester is preferably purified to remove low molecular weight components or to remove unoxidized components by filtration.

  In the case of mixed acid cellulose ester, it can be obtained by the method described in JP-A-10-45804. The measuring method of the substitution degree of an acyl group can be measured according to the rule of ASTM-D817-96.

  Cellulose esters are also affected by trace metal components in cellulose esters. These are considered to be related to water used in the production process, but it is preferable that there are few components that can become insoluble nuclei, and metal ions such as iron, calcium, and magnesium contain organic acidic groups. Insoluble matter may be formed by salt formation with a polymer degradation product or the like that may be present, and it is preferable that the amount is small. The iron (Fe) component is preferably 1 ppm or less. About calcium (Ca) component, it is contained in a lot of ground water and river water, and if it is too much, it becomes hard water and is unsuitable as drinking water. However, it has many acidic components such as carboxylic acid and sulfonic acid. Coordination compounds with ligands, that is, complexes are easily formed, and scum (insoluble starch, turbidity) derived from many insoluble calcium is formed.

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After performing, it can obtain | require by performing an analysis using ICP-AES (inductively coupled plasma optical emission spectrometry).

(Organic solvent)
Organic solvents useful for forming a dope by dissolving cellulose ester include chlorinated organic solvents and non-chlorinated organic solvents. Methylene chloride (methylene chloride) can be mentioned as a chlorinated organic solvent, and it is suitable for dissolving cellulose esters, particularly cellulose triacetate.

  Due to recent environmental problems, the use of non-chlorine organic solvents has been studied. Examples of the non-chlorine organic solvent include 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-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1, Examples include 1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like.

  When these organic solvents are used for cellulose triacetate, a dissolution method at room temperature can be used, but an insoluble material can be obtained by using a dissolution method such as a high-temperature dissolution method, a cooling dissolution method, or a high-pressure dissolution method. Can be reduced, which is preferable. Methylene chloride can be used for cellulose esters other than cellulose triacetate, but methyl acetate, ethyl acetate, and acetone are preferably used. Particularly preferred is methyl acetate. In the present invention, an organic solvent having good solubility with respect to the cellulose ester is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is a main (organic) solvent or a main ( Organic) solvent.

  In the present invention, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. After casting the dope on the metal support, the solvent starts to evaporate and the alcohol ratio increases. Then, the cast film (hereinafter, the cast film after casting the dope on the metal support is called “web”. Is used as a gelling solvent that gels and makes the web strong and easy to peel off from the metal support, or when these ratios are low, dissolve the cellulose esters of non-chlorine organic solvents. There is also a role to promote. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, and has good drying properties. These organic solvents are called poor solvents because they are not soluble in cellulose esters alone.

  It is preferable that the concentration of cellulose ester in the dope is adjusted to 15 to 30% by weight and the viscosity of the dope is adjusted to a range of 100 to 500 Pa · s in order to obtain good optical film surface quality.

  Additives added to the dope include fine particles such as a plasticizer, an ultraviolet absorber, an antioxidant, a dye, and a matting agent. In the present invention, these additives may be added when preparing a cellulose ester solution, or may be added when preparing a fine particle dispersion such as a matting agent. It is preferable to add a plasticizer, an antioxidant, an ultraviolet absorber, or the like that imparts heat resistance and moisture resistance to the polarizing plate used in the liquid crystal image display device. The additive will be described below.

(Plasticizer)
In the present invention, a compound known as a so-called plasticizer is added to the cellulose ester solution or dope for the purpose of improving mechanical properties, imparting flexibility, imparting water absorption resistance, reducing water vapor permeability, and adjusting retardation. For example, phosphoric acid esters and carboxylic acid esters are preferably used.

  Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like.

  Examples of the carboxylic acid ester include phthalic acid ester and citric acid ester. Examples of the phthalic acid ester include dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethyl hexyl phthalate. Mention may be made of tributyl. Other examples include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and triacetin. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferably used. These alkyl phthalyl alkyl glycolates may be used in combination of two or more.

  A polyhydric alcohol ester is also preferably used as a plasticizer.

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

(1) R1- (OH) n
In the formula, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic and / or phenolic hydroxyl group.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

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

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

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

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

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

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

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

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

  These compounds are contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, based on the cellulose ester. In order to suppress bleeding out during stretching and drying, a compound having a vapor pressure at 200 ° C. of 1400 Pa or less is preferable.

  These compounds may be added together with the cellulose ester or the solvent during the preparation of the cellulose ester solution, or may be added during or after the solution preparation.

  As other additives, polyesters and polyester ethers described in JP-A No. 2002-22956, urethane resins described in JP-A No. 2003-171499, rosins and rosin derivatives described in JP-A No. 2002-146044, Epoxy resin, ketone resin, toluenesulfonamide resin, ester of polyhydric alcohol and carboxylic acid described in JP-A-2003-96236, compound represented by general formula (1) described in JP-A-2003-165868 And polyester polymers or polyurethane polymers described in JP-A No. 2004-292696. These additives can be contained in the dope or the fine particle dispersion.

(UV absorber)
In the present invention, the cellulose ester solution or dope may contain an ultraviolet absorber in order to cut harmful ultraviolet rays.

  Examples of ultraviolet absorbers that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, triazine compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621, JP-A-8-337574, JP-A-2001-72782, JP-A-6-148430, JP-A-2002-31715, JP-A Polymer ultraviolet absorbers described in JP 2002-169020 A, JP 2002-47357 A, JP 2002-363420 A, and JP 2003-113317 A are also preferably used. As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred.

  Specific examples of UV absorbers useful in the present invention include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) Benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy-3'- ert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5 -Chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used. An example of the polymeric ultraviolet absorber is a reactive ultraviolet absorber RUVA-93 manufactured by Otsuka Chemical Co., Ltd.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The ultraviolet absorber described above preferably used in the present invention is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber, which has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and unnecessary coloring. A benzotriazole-based ultraviolet absorber with a lower content is particularly preferably used.

  The UV absorber can be added to the dope without limitation as long as the UV absorber is dissolved in the dope, but in the present invention, the UV absorber is cellulose such as methylene chloride, methyl acetate, dioxolane. A good solvent for esters, or a mixture of a good solvent and a poor solvent such as lower aliphatic alcohol (methanol, ethanol, propanol, butanol, etc.) dissolved in an organic solvent and added to the cellulose ester solution as an ultraviolet absorber solution or directly You may add during dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and the polymer to be dispersed and then added to the dope.

  The content of the ultraviolet absorber is 0.01 to 5% by weight, particularly 0.5 to 3% by weight.

  In the present invention, these ultraviolet absorbers may be used alone or in a mixture of two or more different types.

(Antioxidant)
As the antioxidant, hindered phenol compounds are preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t- Butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3 , 5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3 , 5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanate Examples include nurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1000 ppm, based on the cellulose ester.

(Matting agent)
Fine particles such as a matting agent can be added to the cellulose ester solution or dope of the present invention in order to improve the slipperiness of the optical film or to improve the physical properties. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound, and the shape may be spherical, flat, rod, needle, layer, or indefinite. Examples of fine particles of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium oxide, kaolin, talc, clay, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and Mention may be made of metal oxides such as calcium phosphate, hydroxides, silicates, phosphates and carbonates.

  Examples of the fine particles of the organic compound include fine particles such as a silicone resin, a fluororesin, and an acrylic resin. A silicone resin is preferable, and a three-dimensional network structure is particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120 and 240 (manufactured by Toshiba Silicone Co., Ltd.) can be mentioned.

  Among these, silicon dioxide is preferable because it can reduce the haze of the optical film. Fine particles such as silicon dioxide are often surface-treated with an organic material, but such a material is preferable because it can reduce haze of an optical film. Preferred materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like.

The larger the average particle size of the fine particles, the greater the sliding effect. On the contrary, the smaller the average particle size, the better the transparency. The average particle size of the fine particles is in the range of 0.005 to 1.0 μm. These primary particles may be secondary particles formed by aggregation. The content of fine particles is preferably 0.01 to ²⁰ g per m ^{2 with} respect to the resin.

  Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., preferably Aerosil 200V, R972. , R972V, R974, R202, R812. Two or more kinds of these fine particles may be used in combination. When using 2 or more types together, it can mix and use in arbitrary ratios. In this case, fine particles having different average particle sizes and materials, for example, Aerosil 200V and R972V can be used in a mass ratio of 0.1: 99.9 to 99.9: 0.1.

  The presence of fine particles in the optical film used as the matting agent can be used for another purpose to improve the strength of the optical film.

(Fine particles for birefringence adjustment)
To the optical film of the present invention, fine particles having birefringence are added in order to ensure a large retardation control range or to improve physical properties. Thereby, the optical film of this invention turns into an optical film with which the relationship of a three-dimensional refractive index satisfy | fills nx>nz> ny. Here, nx represents the refractive index in the slow axis (x-axis) direction (orientation direction) in the optical film plane, ny represents the refractive index in the direction perpendicular to it (y-axis), and nz is optical. The refractive index in the film thickness (z-axis) direction is shown.

The fine particles having birefringence constituting the optical film of the present invention must belong to the category of fine particles having birefringence. In particular, the relationship of the three-dimensional refractive index by a general orientation operation such as stretching. Since it is easy to obtain an optical film satisfying nx>nz> ny, it is preferable to have an elongated shape such as a rod shape, a needle shape, or a spindle shape. Furthermore, since the fine particles are well oriented in a certain direction and the optical film has a low haze value and high transparency, the absolute maximum length is X (nm) and the aspect ratio (two parallel to the absolute maximum length). [Equation 1], [Equation 2] where Y is a value obtained by dividing the absolute maximum length by the diagonal width that is the shortest distance between two straight lines when the image of the fine particles projected by the straight line is ], [Formula 3], and fine particles having a particle size range satisfying [Formula 4] are preferable. (Hereinafter, when [Formula 1], [Formula 2], [Formula 3], and [Formula 4] are collectively described, they are referred to as [particle size range formula].)
[Formula 1] Y> (X ^ 2) / 20000
[Formula 2] Y> 20 × (X ^ (− 0.5))
[Formula 3] Y <20
[Formula 4] 50 <X <500

  The particle size range of the fine particles is represented by a graph as shown in FIG. Here, FIG. 6 is a graph in which the vertical axis represents the aspect ratio and the horizontal axis represents the absolute maximum length (nm). The curve (a) represents [Expression 1], and the curve (b) represents [Expression 2]. The area on the left side of the curve (a) is an area representing fine particles to be used for haze reduction, and the area on the right side is an area representing fine particles to be removed for haze reduction. In addition, the upper region of the curve (b) is a region representing fine particles that are well oriented in a certain direction, and the lower region is a region representing fine particles to be removed because the orientation of the fine particles deteriorates. Therefore, the most preferable region containing fine particles is represented by a region (c) surrounded by a dotted line.

  Here, since it is difficult to produce fine particles having an aspect ratio of 10 or more as compared with fine particles having an aspect ratio of less than 10, those having an aspect ratio of less than 10 are particularly preferable. Therefore, the graph of FIG. 6 represents a region having an aspect ratio of less than 10 which is a particularly preferable range. However, since [Equation 1] is a monotonically increasing graph and [Equation 2] is a monotonically decreasing graph, the graph is enlarged as it is even in a region where the aspect ratio is larger than 10.

  Furthermore, the fine particles in the present invention are preferably fine particles having negative birefringence, and particularly preferably fine particles having negative birefringence having a large Δn.

  Examples of the fine particles include strontium carbonate, calcium carbonate, magnesium carbonate, cobalt carbonate, barium carbonate, and manganese carbonate.

(Surfactant)
The dope or fine particle dispersion used in the present invention preferably contains a surfactant, and is not particularly limited to phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic-based, cationic-based and the like. These are described in, for example, JP-A-61-243837. The addition amount of the surfactant is preferably 0.002 to 2% by weight, more preferably 0.01 to 1% by weight with respect to the cellulose acylate. If the addition amount is less than 0.001% by weight, the effect of addition cannot be sufficiently exerted, and if the addition amount exceeds 2% by weight, precipitation or insoluble matter may occur.

  Furthermore, the strontium carbonate fine particles used in the present invention are preferably surface-treated before making a dope, and more preferably surface-treated with a nonionic surfactant. This is because the fine particles adhere to each other as they are, and thus the birefringence in the optical film is biased. Therefore, surface treatment is performed in order to prevent the fine particles from adhering to each other.

  Nonionic surfactants include surfactants having nonionic hydrophilic groups such as polyoxyethylene, polyoxypropylene, polyoxybutylene, polyglycidyl and sorbitan, and specifically include polyoxyethylene alkyl ethers, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl ethers. Oxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyhydric alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, fatty acid diethanolamide, triethanolamine Mention may be made of fatty acid partial esters.

  Examples of the anionic surfactant include carboxylate, sulfate, sulfonate, and phosphate ester salt. Representative examples include fatty acid salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfonate, α-olefin sulfonate, dialkylsulfosuccinate, α-sulfonated fatty acid salt, N-methyl-N oleyl taurine, petroleum sulfonate, alkyl sulfate, sulfated oil, polyoxyethylene alkyl ether sulfate, Examples thereof include polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate, and naphthalene sulfonate formaldehyde condensate.

  Examples of the cationic surfactant include amine salts, quaternary ammonium salts, pyridinium salts, etc., and primary to tertiary fatty amine salts, quaternary ammonium salts (tetraalkyl ammonium salts, trialkylbenzyl ammonium salts, Alkyl pyridium salt, alkyl imidazolium salt, etc.). Examples of amphoteric surfactants include carboxybetaine and sulfobetaine, such as N-trialkyl-N-carboxymethylammonium betaine and N-trialkyl-N-sulfoalkyleneammonium betaine.

The fluorosurfactant is a surfactant having a fluorocarbon chain as a hydrophobic group. Examples of the fluorine-containing _{surfactant, C 8 F 17 CH 2 CH} 2 O- (CH 2 CH 2 O) 10 -OSO 3 Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O _{) 16 -H, C 8 F 17} SO 2 N (C 3 H 7) CH 2 COOK, C 7 F 15 COONH 4, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O) 4 _{- (CH 2) 4 -SO 3} Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2) 3 -N + (CH 3) 3 · I -, C 8 F 17 SO 2 N (C _{3 H 7) CH 2 CH 2} CH 2 N + (CH 3) 2 -CH 2 COO -, C 8 F 17 CH 2 CH 2 O (CH 2 CH 2 O) 16 -H, C 8 F 17 CH 2 CH _{2 O (CH 2) 3 -N} + (CH 3) 3 · I -, H (CF 2) _{-CH 2 CH 2 OCOCH 2 CH (} SO 3) COOCH 2 CH 2 CH 2 CH 2 (CF 2) 8 -H, H (CF 2) 6 CH 2 CH 2 O (CH 2 CH 2 O) 16 -H, _{H (CF 2) 8 CH 2} CH 2 O (CH 2) 3 -N + (CH 3) 3 · I -, H (CF 2) 8 CH 2 CH 2 OCOCH 2 CH (SO 3) COOCH 2 H 2 CH _{2 CH 2 C 8 F 17,} C 9 F 17 -C 6 H 4 -SO 2 N (C 3 H 7) (CH 2 CH 2 O) 16 -H, C 9 F 17 -C 6 H 4 -CSO 2 N (C ₃ H ₇ ) (CH ₂ ) ₃ —N ⁺ (CH ₃ ) ₃ · I ^{− and the} like may be mentioned, but are not limited thereto.

(Peeling accelerator)
Furthermore, a peeling accelerator for reducing the load during peeling may be added to the dope. Of these, surfactants are effective, and there are phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic, cationic, and the like, but are not particularly limited thereto. These peeling accelerators are described in, for example, JP-A-61-243837. Japanese Patent Application Laid-Open No. 57-500833 discloses polyethoxylated phosphate ester as a release accelerator. JP-A-61-69845 discloses that the monoester or diphosphate alkyl ester in which the non-esterified hydroxy group is in the form of a free acid can be rapidly peeled off by adding to the cellulose ester. JP-A-1-299847 discloses that the peeling load can be reduced by adding a phosphoric ester compound containing a non-esterified hydroxyl group and a propylene oxide chain and inorganic particles.

  Moreover, it is preferable that the compound represented by following formula (2) or (3) is contained.

(2) (R ₁ -B ₁ -O) _n1 -P (= O)-(OM ₁ ) _n2
(3) R ₂ -B ₂ -X
In the formula, R ₁ and R ₂ are each a substituted or unsubstituted alkyl group, alkenyl group, aralkyl group, or aryl group having 4 to 40 carbon atoms, and M ₁ is an alkali metal, ammonia, or lower alkylamine. Each of B ₁ and B ₂ is a divalent linking group, X is a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, or a sulfate ester or a salt thereof; n1 is 1 or 2; Yes, and n2 is 3-n1.

  It is preferable to contain at least one release agent represented by the above formula (2) or (3) in the cellulose acylate film.

Hereinafter, these release agents will be described. Preferred examples of R ₁ and R ₂ include substituted and unsubstituted alkyl groups having 4 to 40 carbon atoms (eg, butyl, hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, eicosanyl, docosanyl, myrisyl). , Etc.), substituted with 4 to 40 carbon atoms, unsubstituted alkenyl groups (for example, 2-hexenyl, 9-decenyl, oleyl, etc.), substituted with 4 to 40 carbon atoms, unsubstituted aryl groups (for example, phenyl, Naphthyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, propylphenyl, diisopropylphenyl, triisopropylphenyl, t-butylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isopentylphenyl, octylphenyl, Isooctylphenyl, isononyl Eniru, diisononyl phenyl, dodecyl phenyl, iso-pentadecyl phenyl).

  Of these, more preferred are alkyl as hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, docosanyl, alkenyl as alkenyl, phenyl, naphthyl, trimethylphenyl, diisopropylphenyl, tripropyl as aryl groups. Isopropylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isooctylphenyl, isononylphenyl, diisononylphenyl, dodecylisopentadecylphenyl.

Next, the divalent linking group of B ₁ and B ₂ will be described. C1-10 alkylene, poly (degree of polymerization 1-50) oxyethylene, poly (degree of polymerization 1-50) oxypropylene, poly (degree of polymerization 1-50) oxyglycerin, and a mixture thereof. . Preferred linking groups among these are methylene, ethylene, propylene, butylene, poly (degree of polymerization 1-25) oxyethylene, poly (degree of polymerization 1-25) oxypropylene, and poly (degree of polymerization 1-15) oxyglycerin.

  X is carboxylic acid (or salt), sulfonic acid (or salt), sulfate ester (or salt), and particularly preferably sulfonic acid (or salt) or sulfate ester (or salt). Preferred salts are Na, K, ammonium, trimethylamine and triethanolamine. Specific examples of preferred compounds of the present invention are described below.

RZ-1 C ₈ H ₁₇ O—P (═O) — (OH) ₂
RZ-2 C ₁₂ H ₂₅ O—P (═O) — (OK) ₂
RZ-3 C ₁₂ H ₂₅ OCH ₂ CH ₂ O—P (═O) — (OK) _{2
RZ-4 C 15 H 31 (} OCH 2 CH 2) 5 O-P (= O) - (OK) 2
_{RZ-5 {C 12 H 25} O (CH 2 CH 2 O) 5} 2 -P (= O) -OH
_{RZ-6 {C 18 H 35} (OCH 2 CH 2) 8 O} 2 -P (= O) -ONH 4
_{RZ-7 (t-C 4} H 9) 3 -C 6 H 2 -OCH 2 CH 2 O-P (= O) - (OK) 2
_{RZ-8 (iso-C 9} H 19 -C 6 H 4 -O- (CH 2 CH 2 O) 5 -P (= O) - (OK) (OH)
RZ-9 C ₁₂ H ₂₅ SO ₃ Na
RZ-10 C ₁₂ H ₂₅ OS ₃ Na
RZ-11 C ₁₇ H ₃₃ COOH
RZ-12 C ₁₇ H ₃₃ COOH · N (CH ₂ CH ₂ OH) _{3
RZ-13 iso-C 8 H} 17 -C 6 H 4 -O- (CH 2 CH 2 O) 3 - (CH 2) 2 SO 3 Na
_{RZ-14 (iso-C 9} H 19) 2 -C 6 H 3 -O- (CH 2 CH 2 O) 3 - (CH 2) 4 SO 3 Na
RZ-15 sodium triisopropyl naphthalene sulfonate RZ-16 sodium tri-t-butyl naphthalene sulfonate RZ-17 C ₁₇ H ₃₃ CON (CH ₃ ) CH ₂ CH ₂ SO ₃ Na
_{RZ-18 C 12 H 25 -C} 6 H 4 SO 3 · NH 4
The amount of these compounds used is preferably 0.002 to 2% by weight in the dope. More preferably, it is 0.005-1 weight%, More preferably, it is 0.01-0.5 weight%. The addition method is not particularly limited, but it may be liquid or solid as it is and added together with other materials before dissolving, or may be added later to a cellulose acylate solution prepared in advance.

(Other additives)
In addition, thermal stabilizers such as inorganic fine particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, and alumina, and alkaline earth metal salts such as calcium and magnesium may be added. Furthermore, an antistatic agent, a flame retardant, a lubricant, an oil agent, etc. may be added.

<Solution casting film forming method>
The manufacturing method of the optical film of this embodiment is implemented by the solution casting film forming method.

  FIG. 2 shows a fine particle dispersion preparation step 001 (A), a cellulose ester solution preparation step 002 (A), an in-line addition step 003 (A), a casting step 004, and a finishing step 005 of the solution casting method for optical films. It is the schematic which showed typically. Here, the fine particle dispersion preparation step 001 (A), the cellulose ester solution preparation step 002 (A), and the in-line addition step 003 (A) are steps for preparing the dope.

(1) Fine particle dispersion preparation step 001 (A)
The method for preparing the fine particle dispersion is not particularly limited, but is preferably performed by the following method a) or b).

  a) An organic solvent and a fine particle-dispersing resin are introduced into the dissolution vessel 10 and dissolved by stirring to obtain a resin solution (see FIG. 2). Separately from this, the liquid mixture of the organic solvent and the fine particles is transferred to a disperser (not shown) such as a Manton gorey or a sand mill by the liquid feed pump 2 and pre-dispersed. The fine particle pre-dispersion is added to the resin solution, stirred, and sent to the filter 12 by the liquid feed pump 11 to remove the aggregates. As a fine particle dispersion, the stock is stored in the stock tank (stationary kettle) 13. To do. The prepared fine particle dispersion may be repeatedly dispersed and filtered several times.

  b) An organic solvent and, for example, a cellulose ester resin are added to the dissolution vessel 10 and dissolved by stirring to obtain a resin solution. Fine particles are added to the resin solution and dispersed by a disperser (not shown) such as Manton Gorin or a sand mill. Then, it is sent to the filter 12 by the liquid feeding pump 11 to remove the aggregates to obtain a fine particle dispersion (the same operation may be repeated several times). Then, the fine particle dispersion is transferred from the switching valve 17 to the stock tank 13, statically defoamed, transferred by a liquid feed pump (for example, a pressurized metering gear pump) 14, filtered by a filter 15, and transferred by a conduit 16.

  A plasticizer, a purple ray absorbent, a dispersant and the like may be further added to the fine particle dispersion.

  In the present invention, the dispersers used when preparing the fine particle dispersion as described above are roughly divided into a medialess disperser and a media disperser, and both can be used.

Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type. In the present invention, a high pressure disperser is preferably used. A high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. It is preferable that the maximum pressure condition inside the apparatus is 9.8 × 10 ⁶ Pa or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, it is 19.6 × 10 ⁶ Pa or more. At that time, it is preferable that the maximum reaching speed reaches 100 m / sec or more and the heat transfer speed reaches 100 kcal / hr or more. Examples of the high-pressure dispersing apparatus as described above include an ultrahigh-pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a nanomizer manufactured by Nanomizer, or Ultra Turrax, and other Manton Gorin type high-pressure dispersing apparatuses such as Izumi. Examples thereof include a food machinery homogenizer and UHN-01 manufactured by Sanwa Machinery Co., Ltd.

  Examples of the media disperser include a ball mill, a sand mill, and a dyno mill that disperse using a collision force of media such as glass beads and ceramic beads. In the present invention, a media disperser is particularly preferably used.

  Aggregates and foreign substances are removed from the fine particle dispersion prepared in this manner by filtration. A dope is prepared using the obtained fine particle dispersion.

(2) Cellulose ester solution preparation step 002 (A)
In the present invention, a dope is prepared by mixing a fine particle dispersion prepared in advance by the above method, a solvent, and a cellulose ester. Specifically, it is preferable to add and mix a part of the solvent and the fine particle dispersion into the dissolution vessel 1 and then add and dissolve the remaining solvent and cellulose ester with stirring. Additives such as plasticizers can be added later to the dissolution vessel 1 or later.

  Alternatively, an additive such as cellulose ester or a plasticizer may be added to the solvent in the dissolution vessel 1 while stirring, and the fine particle dispersion may be further added during dissolution of the cellulose ester. Alternatively, a solvent can be mixed with an additive such as cellulose ester and a plasticizer to obtain a cellulose ester solution, and the fine particle dispersion can be added thereto with stirring.

  The method for preparing the cellulose ester solution will be described in more detail.

  In the dissolution vessel 1, additives such as cellulose ester and plasticizer are dissolved in an organic solvent mainly composed of the above-mentioned good solvent for cellulose ester while stirring. For dissolution, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a high-temperature dissolution method performed by pressurization above the boiling point of the main solvent, a cooling dissolution method performed by cooling and a high-pressure dissolution method performed at a considerably high pressure However, in the present invention, the high temperature dissolution method is preferably used.

  The cellulose ester solution obtained by mixing the fine particle dispersion, the cellulose ester, and the solvent in the dissolution vessel 1 is sent to the filter 3 by the pump 2 and filtered after the cellulose ester is dissolved.

  Filtration is preferably carried out using this cellulose ester solution with an appropriate filter medium such as filter paper for filter press. In the present invention, as the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters, etc., but if the absolute filtration accuracy is too small, there is a problem that clogging of the filter medium is likely to occur, A filter medium having an absolute filtration accuracy of 8 μm or less is preferable, a filter medium in the range of 1 to 8 μm is more preferable, and a filter medium in the range of 3 to 6 μm is more preferable. As the filter paper, for example, No. of Azumi Filter Paper Co., Ltd., a commercially available product. 244 and No. 277 filter paper can be mentioned and is preferably used.

  There are no particular restrictions on the material of the filter medium for filtration, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark) and metal filter media such as stainless steel do not drop off fibers. preferable. Filtration can be performed by a normal method, but the method of filtering while heating or holding at a temperature in a range not lower than the boiling point of the organic solvent used at normal pressure and in a range where the organic solvent does not boil is a filter medium. The increase in differential pressure before and after (hereinafter sometimes referred to as filtration pressure) is small and preferable. Although a preferable temperature range depends on the organic solvent used, it is 45 to 120 ° C, more preferably 45 to 70 ° C, and further preferably 45 to 55 ° C.

  The filtration pressure is preferably as small as possible, preferably 0.3 to 1.6 MPa, more preferably 0.3 to 1.2 MPa, and still more preferably 0.3 to 1.0 MPa.

  The dope thus obtained is stored in the stock tank 4, defoamed, and then used for casting.

  As described above, it is preferable to prepare the dope by mixing the fine particle dispersion and the cellulose ester solution in the dope kettle. However, a part or all of the cellulose ester solution and the fine particle dispersion may be mixed in-line. You can also.

  For example, FIG. 2 shows an example of the step of adding the fine particle dispersion in-line. The fine particle dispersion is merged with the cellulose ester solution (or may be referred to as a dope stock solution) in the merging pipe 20. Filters 6 and 15 are disposed immediately before the merge pipe 20, and for example, large foreign matters generated from the path due to filter medium replacement or the like can be removed from the fine particle dispersion or dope stock solution being fed.

  Here, metal filters 6 and 15 having solvent resistance are preferably used. The filter medium is preferably a metal, particularly stainless steel, from the viewpoint of durability. From the viewpoint of clogging, it is preferable to have a porosity of 60 to 80%. Most preferably, the filtration is performed with a metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80%, so that coarse foreign substances can be reliably removed over a long period of time. preferable. Examples of the metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80% include NF-10, NF-12, and NF-13 of Finepore NF series manufactured by Nippon Seisen Co., Ltd. Can be mentioned.

  The porosity of the filter medium is preferably 60 to 80%, and more preferably 65 to 75%. A higher porosity is preferable from the viewpoint of reducing pressure loss, and a lower porosity is preferable because pressure resistance is excellent. To determine the porosity, first immerse the filter medium in a solvent with low double-sided tension, remove the air in the filter medium, determine the amount of pores in the filter medium from the increased amount of solvent, and divide by the volume of the filter medium. be able to.

(3) In-line addition process 003 (A)
When the dope is prepared by previously mixing the fine particle dispersion, the cellulose ester and the solvent in the dissolution vessel 1 shown in FIG. 2, it is usually unnecessary to add the fine particle dispersion in-line. However, if necessary, all or part of the fine particles can be mixed in-line.

  The in-line addition process will be described with reference to FIG. 2. A cellulose ester solution (sometimes referred to as a dope stock solution) is transferred by a liquid feed pump 5, filtered by a filter 6, and transferred by a conduit 8. On the other hand, each of the fine particle dispersions is transferred by the liquid feed pump 14, filtered by the filter 15, and transferred by the conduit 16. Then, both liquids are merged by the merge pipe 20. Since the two combined liquids are transported in layers in the conduit, they are difficult to mix as they are. Therefore, the two liquids are merged and then transferred to the next step while being sufficiently mixed by the mixer 21 such as an in-line mixer.

  As the in-line mixer as the mixer 21 that can be used in the present invention, for example, a static mixer SWJ (Toray static type in-pipe mixer Hi-Mixer, manufactured by Toray Engineering) is preferable.

  The dope prepared by the above (2) cellulose ester solution preparation step, or (2) cellulose ester solution preparation step and (3) in-line addition step, the solid content concentration in the dope is preferably adjusted to 15% by weight or more. In particular, 18 to 30% by weight is preferable. If the solid content concentration in the dope is too high, the viscosity of the dope becomes too high, and a sharkskin or the like may occur during casting to deteriorate the optical film flatness. Therefore, it is preferably 30% by weight or less.

(4) Casting process 004
An endless metal support 31 that feeds the dope prepared up to the previous step to the die 30 through the conduit 22 shown in FIG. 2 and transfers it infinitely, that is, for example, a rotationally driven stainless steel endless belt or a rotationally driven stainless steel. This is a step of casting the dope from the die 30 to the casting position on the drum (metal support) 31. The surface of the metal support 31 is a mirror surface. A die 30 (for example, a pressure die) is preferable because the slit shape of the die portion can be adjusted and the film thickness can be easily made uniform. The die 30 includes a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more dies 30 may be provided on the metal support 31, and the dope amount may be divided to be stacked.

  FIG. 3 is an enlarged perspective view showing a connection state between the die 30 and the dope supply pipe 23 of the solution casting film forming apparatus for carrying out the optical film manufacturing method of the present invention. 4A and 4B are enlarged cross-sectional views of the same die 30 having different land lengths. Here, W in FIG. 3 indicates the width of the slit. 4 indicates the slit of the die 30, H indicates the gap of the slit S, and L indicates the length of the slit S in the dope flow direction (hereinafter referred to as land length L). Yes.

  If the gap H of the slit of the die 30 is too narrow, the liquid feeding pressure becomes too high, and when a minute foreign matter is mixed in the dope, it is caught in the slit S, and the portion becomes a streak with the optical film. Also, the film thickness control becomes very severe. Moreover, since it becomes difficult to perform precise film thickness control even if the gap H is too wide, the range of 0.2 to 0.3 mm is preferable.

  Furthermore, if the slit passage time when the dope flows through the slit S of the die 30 becomes long, the time for applying the shear stress to the fine particles becomes long, so the fine particles contained in the thermoplastic resin dope are well oriented in a certain direction. It will be. That is, in order to align fine particles well in a certain direction, it is necessary to obtain a long slit passage time in film formation. However, if the land length L is made too long in order to lengthen the slit passing time, vertical stripes are formed on the optical film. Therefore, the dope slit passing time of the slit S is preferably in the range of 0.1 to 2.0 [sec].

  The surface temperature of the metal support 31 for casting is 10 to 55 ° C., the temperature of the dope is 25 to 60 ° C., and the temperature of the solution is preferably equal to or higher than the temperature of the support. It is more preferable to set the above temperature.

  The higher the solution temperature and the support temperature, the faster the solvent can be dried. However, if the temperature is too high, foaming or flatness may be deteriorated.

  Further, when the draft ratio Vb / Vrm, which is the ratio of the linear velocity Vb of the metal support to the linear velocity Vrm of the cast film, is increased, the shear stress applied to the fine particles increases, so the fine particles contained in the thermoplastic resin dope Are well oriented in a certain direction. Here, the linear velocity of the cast film is the velocity immediately after the dope comes out of the die 30, and the dope flow rate is divided by the product of the width S of the slit S and the gap H of the slit S (that is, the cross-sectional area). Desired. That is, in order to finely orient the fine particles in a certain direction, it is necessary to increase this draft ratio. However, if the draft ratio is too large, the optical film will have horizontal steps. Therefore, the draft ratio is preferably in the range of 2.1 to 6.0.

  Here, in this embodiment, the die 30 having a constant gap H between the slits S is used. This is because the gap H between the slits S is wide at the top so that the flow rate of the dope increases toward the lower end. A die (see Japanese Patent Application No. 2005-288042) that narrows toward the bottom may be used.

(5) Solvent evaporation step 005 (A)
In this step, the web 32 (the cast film after casting the dope on the metal support) 32 is heated on the metal support 31 to evaporate the solvent until the web 32 can be peeled from the metal support 31. In order to evaporate the solvent, there are a method of blowing air from the web 32 side and / or a method of transferring heat from the back surface of the metal support 31 by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. This method is preferable because of good drying efficiency. A method of combining them is also preferable. In the case of backside liquid heat transfer, it is preferable to heat at or below the boiling point of the main solvent of the organic solvent used in the dope or the organic solvent having the lowest boiling point.

(6) Peeling step 005 (B)
In this step, the web 32 having the solvent evaporated on the metal support 31 is peeled off at the peeling position 33. The peeled web 32 is sent to the next process. If the residual solvent amount of the web 32 (explained later) at the time of peeling is too large, it is difficult to peel off, or conversely, if it is peeled off after sufficiently drying on the metal support 31, a part of the web 32 is halfway May come off. In the present invention, when peeling the thin web from the metal support, it is preferable to peel the thin web with a force within 170 N / m from the minimum tension that can be peeled as the peeling tension in order to prevent the flatness from being deteriorated and hung. A force within 140 N / m is more preferred.

  There is a gel casting method (gel casting) as a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible). For example, a poor solvent for the cellulose ester is added to the dope, and the dope is cast and then gelled, and the temperature of the metal support is lowered to gel. By gelling on the metal support 31 and increasing the strength of the film at the time of peeling, the peeling can be accelerated and the film forming speed can be increased. The web 32 on the metal support 31 can be peeled in the range of 5 to 150% by mass depending on the strength of the condition, the length of the metal support 31, etc., but peels off when the amount of residual solvent is larger. In this case, if the web 32 is too soft, the flatness at the time of peeling is impaired, or slippage and vertical stripes due to peeling tension are likely to occur. Therefore, the residual solvent amount at the time of peeling can be determined in consideration of the economic speed and quality. . Therefore, in the present invention, the temperature at the peeling position on the metal support 31 is 10 to 40 ° C., preferably 15 to 30 ° C., and the residual solvent amount of the web 32 at the peeling position is 10 to 120% by mass. It is preferable to do.

  In order to maintain good flatness of the cellulose ester film during production, the amount of residual solvent when peeling from the metal support is preferably 10 to 150% by mass, more preferably 70 to 150% by mass. More preferably, it is 100-130 mass%. The proportion of the good solvent contained in the residual solvent is preferably 50 to 90%, more preferably 60 to 90%, and particularly preferably 70 to 80%.

  In the present invention, the residual solvent amount can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is a mass at an arbitrary time point of the web, and is a mass measured by the following gas chromatography. N is a mass when the M is dried at 110 ° C. for 3 hours.

(7) Drying step 005 (C)
After peeling, generally, as shown in FIG. 2, the web 32 is used by using a roll drying device 35 that alternately conveys the web 32 through a plurality of conveying rolls 36 and a tenter device 34 that grips and conveys both ends of the web 32. 32 is dried. In FIG. 2, the roll drying device 35 including the transport roll 36 is disposed after the tenter device 34, but is not limited to this configuration.

  As a drying means, hot air is generally blown on both surfaces of the web 32, but there is also a means of heating by applying a microwave instead of the wind. Excessive drying tends to impair the flatness of the finished optical film. Throughout, the drying temperature is usually in the range of 40 to 250 ° C. The drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used. 37 is winding of the completed cellulose ester film. In the step of drying the cellulose ester film, the amount of residual solvent is preferably 0.5% by mass or less, and more preferably 0.1% by mass or less.

  The stretching process by the tenter device 34 will be described in more detail. The draw ratio at the time of producing the cellulose ester film according to the present invention is 1.01 to 3 times, preferably 1.5 to 3 times, with respect to the film forming direction or the width direction. When stretching in the biaxial direction, the side to be stretched at a high magnification is 1.01 to 3 times, preferably 1.5 to 3 times, and the stretching ratio in the other direction is 0.8 to 1.5. The film can be stretched by a factor of preferably 0.9 to 1.2.

  Thereby, the cellulose ester film having the retardation value of the present invention can be preferably obtained, and a cellulose ester film having good flatness can be obtained. These width maintenance or lateral stretching in the film forming step is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  An example of a stretching process (also referred to as a tenter process) for producing the optical film according to the present invention will be described.

  In the tenter device 34, first, the first step is a step of gripping the optical film transported from the film transport step (not shown). In the next second step, the optical film is in the width direction (the optical film In the third step, the stretching is completed and the optical film is conveyed while being held.

  It is preferable to provide a slitter that cuts off the end portion in the optical film width direction after the optical film is peeled off and before the start of the second width direction stretching step and / or immediately after the third gripping step. In particular, it is preferable to provide a slitter that cuts off the film edge immediately before the start of the first gripping step. When the same stretching in the width direction is performed, particularly when the optical film end is cut off before the start of the second width direction stretching step and the condition in which the optical film end is not cut out, the former is more The effect of improving the optical slow axis distribution (hereinafter referred to as orientation angle distribution) in the width direction of the optical film can be obtained.

  This is considered to be an effect of suppressing unintended stretching in the longitudinal direction from the peeling with a relatively large amount of residual solvent to the second step of width stretching.

  In the tenter process, it is also preferable to intentionally create compartments with different temperatures in order to improve the orientation angle distribution. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is preferable to implement biaxial stretching in a casting direction and a width direction. Also, 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. Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  In addition, the stretching direction in the present invention is usually used in the sense of directly applying a stretching stress when performing a stretching operation, but when it is biaxially stretched in multiple stages, It is used to mean the one with a higher draw ratio.

  It is well known that the orientation angle distribution deteriorates when the cellulose ester film is stretched in the width direction. The first gripping step and the second width in the tenter step described above are performed in order to make the width direction retardation (Rth) and the in-plane direction retardation (Ro) a constant ratio and to perform widthwise stretching with a good orientation angle distribution. There is a preferable film temperature relative relationship in the hand drawing process and the third gripping process. When the film temperatures at the first gripping step, the second width direction stretching step, and the third gripping step end point are Ta ° C, Tb ° C, and Tc ° C, respectively, it is preferable that Ta ≦ Tb-10. Moreover, it is preferable that Tc ≦ Tb. More preferably, Ta ≦ Tb−10 and Tc ≦ Tb.

  The film heating rate in the second width direction stretching step is preferably in the range of 0.5 to 10 ° C./s in order to improve the orientation angle distribution.

  The stretching time in the second width direction stretching step is preferably a short time in order to reduce the dimensional change rate under conditions of a temperature of 80 ° C. and a humidity of 90% RH. However, from the viewpoint of the uniformity of the optical film, a minimum required stretching time range is defined. Specifically, the range is preferably 1 to 10 seconds, and more preferably 4 to 10 seconds. Moreover, the temperature of a 2nd width direction extending process is 40-180 degreeC, Preferably it is 100-160 degreeC.

In the tenter process, the heat transfer coefficient may be constant or changed. The heat transfer coefficient preferably has a heat transfer coefficient in the range of 41.9 to 419 × 10 ³ J / m ² hr. More preferably, in the range of ^{41.9~209.5 × 10 3 J / m 2} hr, and most preferably a range of ^{41.9~126 × 10 3 J / m 2} hr.

  In order to improve the dimensional stability under conditions of a temperature of 80 ° C. and a humidity of 90% RH, the stretching speed in the width direction in the second width direction stretching step may be constant or changed. May be. The stretching speed is preferably 50 to 500% / min, more preferably 100 to 400% / min, and most preferably 200 to 300% / min.

  In the tenter process, 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 optical film, and the temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C., ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable. By reducing the temperature distribution, it can be expected that the temperature distribution in the width of the optical film is also reduced.

  In the third gripping step of the tenter device 34, it is preferable to relax in the width direction in order to suppress a dimensional change. Specifically, it is preferable to adjust the film width so that it is in the range of 95 to 99.5% with respect to the film width of the previous step.

  It is preferable to provide a post-drying step after the treatment in the tenter step. It is preferable to carry out at 50-160 degreeC. More preferably, it is the range of 80-150 degreeC, Most preferably, it is the range of 110-150 degreeC.

  In the post-drying step, it is preferable from the viewpoint of improving the uniformity of the optical film that the atmospheric temperature distribution in the width direction of the optical film is small. Within ± 5 ° C is preferable, within ± 2 ° C is more preferable, and within ± 1 ° C is most preferable.

(8) Winding process 005 (D)
This is a step of winding the web 32 that has been dried as an optical film to obtain the original roll 37 of the optical film shown in FIG. An optical film with good dimensional stability can be obtained by setting the residual solvent amount of the optical film to be dried to 0.5% by weight or less, preferably 0.1% by weight or less.

  The winding method of the optical film may be a commonly used winder, and there are methods such as constant torque method, constant tension method, taper tension method, program tension control method with constant internal stress, etc. Should be used properly.

  The film thickness of the cellulose ester film varies depending on the purpose of use, but from the viewpoint of thinning the liquid crystal display device, the finished film is preferably in the range of 10 to 150 μm, more preferably in the range of 30 to 100 μm, and particularly preferably in the range of 40 to 80 μm. A range is preferred. If it is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If it is too thick, the advantage of thinning the conventional cellulose ester film is lost. In adjusting the film thickness, the dope concentration, the pumping amount, the slit gap of the die 30 die, the extrusion pressure of the die 30, the speed of the metal support 31 and the like are controlled so as to obtain a desired thickness. Is good. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

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

[Second Embodiment]
Next, the case where the manufacturing method of the optical film of the present invention is performed by a melt extrusion film forming method will be described.

<Melt extrusion film forming method>
As the melt extrusion film forming method, although not shown, there are a melt extrusion method such as a method using a T die and an inflation method, a calendar method, a hot press method, an injection molding method and the like. Among them, the melt extrusion method using a T die that has a small thickness unevenness, can be easily processed to a thickness of about 30 to 200 μm, and can reduce the absolute value of retardation and its variation is preferable.

  The conditions of the melt extrusion film forming method can be molded in the same manner as the conditions used for other thermoplastic resins. For example, the dried cellulose ester resin (and norbornene resin) is melted at an extrusion temperature of about 200 to 300 ° C. using a uniaxial or biaxial extruder, and filtered through a leaf disk type filter. After removing the foreign matter, it is cast into a sheet from a T die and solidified on the above-described rotationally driven metallic drum [0038].

  In the method of this embodiment, when introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition and the like under reduced pressure or in an inert gas atmosphere. The temperature of the cooling drum is preferably equal to or lower than the glass transition temperature (Tg) of the cellulose ester resin. In order to bring the resin into close contact with the cooling drum, it is preferable to use a method in which the resin is brought into contact by applying electrostatic force, a method in which the resin is brought into contact with wind pressure, a method in which the full width or the end is attached in a nip, a method in which the resin is brought into contact with reduced pressure. Further, in order to reduce surface defects such as die lines, it is preferable that the piping from the extruder to the die has a structure in which the staying portion is minimized. It is preferable to use a die that has as few scratches as possible inside the lip. Since the volatile component may be deposited from the resin around the die and cause a die line, it is preferable to suck the atmosphere containing the volatile component. Moreover, since it may precipitate also in apparatuses, such as an electrostatic application, it is preferable to apply alternating current or to prevent precipitation with another heating means.

  Additives such as antioxidants and plasticizers may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  Unlike the cellulose ester film formed by the solution casting film forming method, the cellulose ester film formed by the melt extrusion film forming method has a feature that the thickness direction retardation (Rth) is small. Such a cellulose ester film By stretching the film, it is easy to express in-plane retardation (Ro), and it is not necessary to increase the stretch ratio. Therefore, it is possible to obtain a cellulose ester film having no transparency and excellent transparency.

  Next, the obtained optical film is stretched in a uniaxial direction. The molecules are oriented by stretching. The stretching method is not particularly limited, but a known pin tenter or clip type tenter can be preferably used. The stretching direction can be the length direction, the width direction, or any direction (diagonal direction). However, in the present invention, the stretching direction is set to the width direction, which is preferable because lamination with an optical film can be performed in a roll form. By stretching in the width direction, the slow axis of the cellulose ester film becomes the width direction. On the other hand, the transmission axis of the optical film is also usually in the width direction. A good viewing angle can be obtained by incorporating a polarizing plate laminated so that the transmission axis of the optical film and the slow axis of the cellulose ester film are parallel to each other in the liquid crystal display device.

  As the stretching conditions, the temperature and magnification can be selected so that desired retardation characteristics can be obtained. Usually, the draw ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually Tg to Tg + 50 ° C. of the resin constituting the optical film, preferably Tg to Tg + 40. It is carried out in the temperature range of ° C. If the draw ratio is too small, the desired retardation may not be obtained, and if it is too large, it may break. If the stretching temperature is too low, it will break, and if it is too high, the desired retardation may not be obtained.

  When correcting the retardation of the optical film produced by the above method to a desired value, the optical film may be stretched or shrunk in the length direction or the width direction. In order to shrink in the length direction, for example, a method of contracting the optical film by temporarily clipping out the width stretching and relaxing in the length direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine. There is. The latter method can be performed by using a general simultaneous biaxial stretching machine and by using a pantograph method or a linear drive method to drive the clip portion in a smooth and gradually narrowing interval between adjacent clips in the longitudinal direction. it can. In addition, since the optical film is deform | transforming and cannot use as a product normally, the holding part of the clip of both ends of an optical film is excised and reused as a raw material.

  The film thickness of the optical film varies depending on the purpose of use, but as a finished optical film, the film thickness range used in the present invention is 30 to 200 μm, and the range of 30 to 100 μm is preferable for the recent thin tendency, especially 40 A range of ˜80 μm is preferred. The film thickness can be adjusted by controlling the extrusion flow rate, the slit gap of the die base, the speed of the cooling drum, etc. so as to obtain a desired thickness. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

[Physical properties of optical film]
The cellulose ester film according to the present invention is preferably used for a liquid crystal display member, specifically, a protective film for a polarizing plate, from the viewpoint of good moisture permeability and dimensional stability. The cellulose ester film according to the present invention is preferably used particularly in a protective film for polarizing plate that has strict requirements for both moisture permeability and dimensional stability.

  Hereinafter, the cellulose ester film according to the present invention and the physical properties of the optical film are collectively described below.

(Transmissivity of cellulose ester film)
High transmittance is required as a member of a liquid crystal display device, and the 500 nm transmittance of the produced cellulose ester film is preferably 85 to 100%, and 90 to 100% when added in combination with the above-mentioned additives. More preferably, 92 to 100% is most preferable. The 400 nm transmittance is preferably 40 to 100%, more preferably 50 to 100%, and most preferably 60 to 100%. Moreover, ultraviolet absorption performance may be calculated | required, In that case, 0 to 10% is preferable, as for 380 nm transmittance | permeability, 0 to 5% is more preferable, and 0 to 3% is the most preferable.

(Thickness distribution in the width direction of cellulose ester film)
The cellulose ester film of the present invention preferably has a film thickness distribution R (%) in the width direction of 0 ≦ R (%) ≦ 5%, more preferably 0 ≦ R (%) ≦ 3. %, Particularly preferably 0 ≦ R (%) ≦ 1%.

(Haze value of cellulose ester film)
The cellulose ester film of the present invention preferably has a haze value of 2% or less, more preferably 1.5% or less, and most preferably 1% or less.

(Elastic modulus of cellulose ester film)
The elastic modulus is preferably in the range of 1.5-5 GPa, more preferably 1.8-4 GPa, and particularly preferably 1.9-3 GPa.

  Further, the stress at break is preferably in the range of 50 to 200 MPa, more preferably in the range of 70 to 150 MPa, and most preferably in the range of 80 to 100 MPa.

  The elongation at break at 23 ° C. and 55% RH is preferably in the range of 20 to 80%, more preferably in the range of 30 to 60%, and most preferably in the range of 40 to 50%. .

  Further, the hygroscopic expansion coefficient is preferably in the range of −1 to 1%, more preferably in the range of −0.5 to 0.5%, and most preferably 0 to 0.2% or less.

Further, the bright spot foreign matter is preferably 0 to 80 pieces / cm ² , more preferably 0 to 60 pieces / cm ² , and most preferably 0 to 30 pieces / cm ^2. .

  In general, when a cellulose ester film is used as a polarizing plate protective film, an alkali saponification treatment is performed in order to improve the adhesion to the polarizer. Since the optical film after the alkali saponification treatment and the polarizer are bonded using a polyvinyl alcohol aqueous solution as an adhesive, if the contact angle of the cellulose ester film with the water after the alkali saponification treatment is high, it cannot be bonded with polyvinyl alcohol. It becomes a problem as a polarizing plate protective film.

  For this reason, the contact angle of the cellulose ester film after the alkali saponification treatment is preferably 0 to 60 °, more preferably 5 to 55 °, and most preferably 10 to 30 °.

(Center line average roughness of cellulose ester film (Ra))
When a cellulose ester film is used as a member for LCD, high flatness is required to reduce light leakage of the optical film. The center line average roughness (Ra) is a numerical value defined in JIS B 0601, and examples of the measuring method include a stylus method or an optical method.

  The centerline average roughness (Ra) of the cellulose ester film of the present invention is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 4 nm or less.

(Retardation value)
The optical film of the present invention comprises a component having positive birefringence and a component having negative birefringence, and the optical film has the highest refractive index in the stretching direction (nx> nz). The difference in refractive index between the normal light refractive index and the extraordinary light refractive index (hereinafter referred to as Δn) of the component having negative birefringence is much larger than the substantial Δn of the component having positive birefringence. The relationship of the three-dimensional refractive index satisfies nx>nz> ny.

Here, Ro represents an in-plane retardation value in the optical film, and Rth represents a retardation value in the thickness direction in the optical film. Ro and Rth are represented by the following equations.
Ro = (nx−ny) × d (nm)
Rth = {(nx + ny) / 2−nz} × d (nm)
Here, d is the thickness (nm) of the optical film, the refractive index nx (also referred to as the maximum refractive index in the plane of the film, the refractive index in the slow axis direction), and the refractive index ny (with the slow axis in the film plane). The refractive index in the direction perpendicular to the surface), and the refractive index nz (the refractive index of the film in the thickness direction).

  By setting Ro and Rth to 160 nm ≦ Ro ≦ 300 nm and −50 nm ≦ Rth ≦ 50 nm, the viewing angle of a liquid crystal display device using this optical film can be greatly widened. Therefore, Ro and Rth preferably satisfy 160 nm ≦ Ro ≦ 300 nm and −50 nm ≦ Rth ≦ 50 nm.

  Further, the variation of Rth and the width of distribution are preferably less than ± 10 nm, preferably less than ± 8 nm, and preferably less than ± 5 nm. Further, it is preferably less than ± 3 nm, more preferably less than ± 1 nm. Most preferably, there is no fluctuation of Rth.

  The retardation values (Ro) and (Rth) can be measured using an automatic birefringence meter. For example, using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), it can be obtained at a wavelength of 590 nm in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

  The slow axis is preferably in the width direction ± 1 ° of the long film or in the longitudinal direction ± 1 °. More preferably, ± 0.7 ° with respect to the width direction or longitudinal direction of the optical film, still more preferably ± 0.5 ° with respect to the width direction or longitudinal direction of the optical film, and particularly preferably ± 0.1 °.

[Polarizing plate and liquid crystal display]
The polarizing plate of the present invention and the liquid crystal display device of the present invention using the polarizing plate will be described.

<Polarizer>
The polarizing plate can be produced by a general method. The cellulose ester film of the present invention subjected to alkali saponification treatment is bonded to at least one surface of a polarizer prepared by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Is preferred. The cellulose ester film of the present invention may be used on the other surface, or another polarizing plate protective film may be used. With respect to the cellulose ester film of the present invention, a commercially available cellulose ester film can be used as the polarizing plate protective film used on the other surface. 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.) and the like are preferably used. Or you may use films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate, as a polarizing plate protective film of the other surface. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

  The polarizing plate of the present invention uses the cellulose ester film of the present invention as a polarizing plate protective film on at least one side of a polarizer. At that time, the cellulose ester film is preferably disposed so that the slow axis of the cellulose ester film is substantially parallel or perpendicular to the absorption axis of the polarizer.

  As one polarizing plate disposed across a liquid crystal cell that is a transverse electric field switching mode type, the cellulose ester film of the present invention (particularly preferably, the cellulose ester film A described above) is disposed on the liquid crystal display cell side. It is preferred that

  Examples of the polarizer preferably used for the polarizing plate of the present invention include a polyvinyl alcohol polarizing film, which includes a polyvinyl alcohol film dyed with iodine and a dichroic dye dyed. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. One side of the cellulose ester film of the present invention is bonded to the surface of the polarizer to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Moreover, in the case of resin films other than a cellulose ester film, it can be bonded to the polarizing plate via an appropriate adhesive layer.

  Since the polarizer is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction orthogonal to the stretching (usually normal) Extends in the width direction). As the thickness of the polarizing plate protective film decreases, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizer increases. Usually, the stretching direction of the polarizer is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when the polarizing plate protective film is thinned, it is particularly important to suppress the stretching rate in the casting direction. . Since the cellulose ester film of the present invention is excellent in dimensional stability, it is suitably used as such a polarizing plate protective film.

  The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection.

<Liquid crystal display device>
The liquid crystal display device according to the present invention comprises a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. A liquid crystal display device having two polarizing plates, and one of the two polarizing plates, for example, one polarizing plate has an in-plane retardation (Ro) value close to 0, and the film An optical film having a retardation (Rth) value in the thickness direction close to 0 is provided, and another polarizing plate is provided with the optical film according to the present invention.

  According to the liquid crystal display device of the present invention, an easy-to-view display having a high contrast ratio over a wide range can be realized, and in particular, a liquid crystal display device that operates in an IPS mode is provided. A stable display performance can be maintained over a long period of time.

  Examples of the optical film according to the present invention will be described below with reference to FIGS. 8, 9, 13, 14, 15, and 16 together with comparative examples. The present invention is not limited to these examples. Here, FIG. 8, FIG. 9, FIG. 13, FIG. 14, FIG. 15 and FIG. 16 are tables showing the results of the respective examples and comparative examples. Example numbers and comparative example numbers in the following description are those shown in FIGS. 8, 9, 13, 14, 15, and 16. FIG.

[Production of optical film by solution casting method]
<When changing the draft ratio>
In the example and comparative example of FIG. 8, the draft ratio is changed, and the volume fraction of fine particles and the particle distribution range are adjusted. Here, as shown in FIG. 11, the particle distribution range refers to the shape of fine particles in the case where a large number of fine particles having a certain particle size range are contained in the whole fine particles. For example, the particle distribution range in FIG. 11 is expressed as an absolute maximum length of 50 to 100 nm and an aspect ratio of 2 to 4. Examples 1 to 9 are the dope containing strontium carbonate having the same range within the preferable particle distribution range in substantially the same preferable volume ratio, and the draft ratio was changed within a preferable range of 2.1 to 6.0. In Examples 17 to 19 and Examples 20 to 22, the draft ratio was set in a range other than 2.1 to 6.0 under the same conditions. In Examples 10 to 14, the conditions of the draft ratio were made equal, and the particle distribution range was changed within a preferable range. Here, Example 10 is located in the center of the region (c) showing the preferred particle size range in FIG. 6, Example 11 is in the lower right of the region (c), and Example 12 is in the lower left of the region (c). Example 13 is located in the upper right of the area (c), and Example 14 is located in the upper left of the area (c). Comparative Examples 1 to 3 were prepared under the same conditions as in Examples 1 to 9 without adjusting the volume ratio of the fine particles. Further, Example 15 and Example 16 were obtained by classifying particles of the strontium carbonate dispersion used in Comparative Example 3 using a centrifuge or a filter to improve the volume ratio of fine particles. Comparative Example No. 4 uses the lower half obtained by centrifuging the strontium carbonate separation liquid used in Comparative Example 3, and the volume ratio is lowered. Further, Comparative Examples 8 to 10 have draft ratios in a range other than 2.1 to 6.0 under the conditions of Comparative Examples 1 to 3. (Hereinafter, Comparative Examples 1 to 4 and Comparative Examples 8 to 10 are collectively referred to as Comparative Examples 1 to 10.)

<Strontium carbonate dispersion>
(Preparation of fine particles of strontium carbonate)
A suspension in which 60 g of methanol (20% with respect to water) and 80 g of strontium hydroxide octahydrate (26.7% with respect to water) were added to 300 g of water was prepared. This suspension was put into a stainless beaker, and the suspension was stirred with a stirring blade attached to a stirring motor (ASONE-made Three-One Motor TORNADO PM203). Next, high temperature / low temperature circulator FC-25MC (manufactured by Yurabo) is filled with bath liquid thermal H5S (manufactured by Yurabo), and a beaker containing the suspension is placed in the bath of this circulator, and the temperature of the suspension is It was kept at 10 ° C to 0 ° C. Next, CO2 gas was introduced into the suspension at a flow rate of 50 to 200 ml / min while stirring the suspension, and the introduction of CO2 gas was stopped when the pH became 12 or less. Next, the suspension was added to 500 g of a mixture of water and methanol maintained at -5 ° C to 0 ° C while stirring to prepare a suspension dilution. Next, the temperature of this suspension dilution was raised to 25 ° C. over 1 to 6 hours to ripen the fine particles. Furthermore, in order to remove unreacted components, the suspension diluted solution was suction filtered with a 0.05 μm pore size membrane filter VMWP09025 (manufactured by ASONE), washed with pure water on the filter, and then washed with ethanol. Was naturally dried to obtain fine particles.

  In the above fine particle preparation method, the absolute temperature of the fine particles can be adjusted by adjusting the temperature of the suspension, the flow rate of CO2 gas, the ratio of water / methanol of the mixed solution, the temperature of the mixed solution, and the time for raising the temperature of the suspension dilution. Fine particles A to K having maximum length and aspect ratio as shown in FIG. 7 were prepared.

  The fine particle K produced above was subjected to ethanol dispersion in an ultrasonic disperser UH-300 (manufactured by SMT Co., Ltd.) with an output scale 10 for 40 minutes, and a centrifugal separator (H-103N from Kokusan Co., Ltd.) The mixture was centrifuged at 500 rpm for 1 minute, and the upper half was collected. The liquid was suction filtered through a 0.05 μm pore size membrane filter VMWP09025 (manufactured by ASONE), and the fine particles taken out were naturally dried to produce fine particles K-1. Further, the lower half of the centrifuged liquid was taken out in the same manner to produce fine particles K-3.

  In addition, the fine particle K produced above is a 0.2 μm pore size membrane filter Omnipore membrane obtained by dispersing a fine particle dispersion in ethanol for 40 minutes continuously with an output scale 10 in an ultrasonic disperser UH-300 (manufactured by SMT Co., Ltd.). The filtrate was separated by suction filtration with JGWP09025 (manufactured by ASONE), and further filtered by suction filtration with a 0.05 μm pore size membrane filter VMW09025 (manufactured by ASONE). did.

(Particle shape measurement method)
In this example, in order to obtain a desired fine particle shape, the absolute maximum length and aspect ratio of the fine particles were measured by the following method using observation with a transmission electron microscope (TEM) and image analysis with computer software, and the volume ratio was determined. Calculated.

  First, as a treatment before observation, the fine particles are dispersed in ethanol, dropped onto the C film and dried, and the fine particles are observed with a TEM. Here, JEM-2000FX (manufactured by JEOL Ltd.) (acceleration voltage: 200 kV) was used as the TEM. The target images used here are two cross-sectional TEM images of each sample × 10000 (directly × 5000). For input, a negative is printed on photographic paper and digitized by a flat head scanner (input resolution: 300 dpi). Next, in order to perform analysis from the image read by the scanner, filter processing is performed so that the image software can recognize the fine particles by enhancing the contrast of the fine particle image. Furthermore, the contrast is optimized by changing the conditions of the filter. Here, the median 3 × 3, then flattened 20 pixels, then high pass 3 × 3, then median 3 × 3 was used for filtering. Next, fine particles are extracted from the image with optimized contrast, and the shape of each fine particle is measured with image analysis software to measure the absolute maximum length, aspect ratio, and the like. In addition, selection is performed to remove what is considered to be noise on the image. Furthermore, the data processing for calculating the distribution state of the fine particles was performed by taking the data of the fine particles such as the measured absolute maximum length and aspect ratio into the data processing software. Here, the flat head scanner used was Sitios 9231 (manufactured by Konica Minolta Co., Ltd.), the image analysis software was ImagePro Plus (manufactured by Media Cybernetics), and the data processing software was Excel (manufactured by Microsoft). Specifically, the absolute maximum length and aspect ratio of each fine particle were calculated by image analysis software, and the volume ratio of the fine particles within a desired particle size range was calculated using Excel. Here, the volume of each fine particle was calculated by calculating the square root of the calculated projected area of the fine particle with the image analysis software.

(Method for evaluating crystallinity of fine particles)
The crystallinity of the fine particles was evaluated using an X-ray diffractometer. It can be determined that the narrower the half width measured, the higher the purity of the crystal (close to a single crystal). Specifically, when the half width of the diffraction peak on the (111) plane was measured using an X-ray diffraction measurement apparatus (CN2013 manufactured by Rigaku Corporation), the crystals obtained in all the examples were certainly strontium carbonate. It was found to be crystalline. In addition to the commercially available product and the strontium carbonate crystals of all Examples, the half-width of the diffraction peak on the (111) plane was 0.2 °.

(Surface treatment of fine particles)
1.0 g of fine particles of strontium carbonate are dispersed in 20.0 g of ethanol, 0.05 g of glyceryl stearate (Kao / Excel T-95) is added, and the mixture is stirred for 10 hours at 50 ° C., and this solution is filtered. The microparticles were dried.

<Creation of dope>
The following compositions are dispersed for 40 minutes on an output scale 10 in an ultrasonic disperser UH-300 (manufactured by SMT Co., Ltd.), and fine particle dispersion in fine particles A to K, K-1, K-2, and K-3 is performed. A liquid was prepared.
Fine particles A to K, K-1, K-2, K-3 16 parts by weight Methylene chloride 92 parts by weight Ethanol 92 parts by weight

Next, each of the following compositions was put into a container and completely dissolved.
Cellulose acetate propionate 25 parts by weight (acetyl group substitution degree 1.90, propionyl group substitution degree 0.75, weight average molecular weight 190,000)
Triphenyl phosphate (TTP) 21 parts by weight Ethylphthalyl ethyl glycolate (EPEG) 5 parts by weight Tinuvin 326 (manufactured by Ciba Special Chemicals) 1 part by weight Tinuvin 109 (manufactured by Ciba Special Chemicals) 1 part by weight Tinuvin 171 (manufactured by Ciba Special Chemicals) ) 1 part by weight Methylene chloride 468 parts by weight Ethanol 34 parts by weight

Next, after slowly adding 200 parts of the fine particle dispersion in the fine particles A to K to the above solution, this mixed solution is placed around the container with an output scale 10 in an ultrasonic dispersing machine UH-300 (manufactured by SMT Co., Ltd.). Re-dispersion was performed continuously for 10 minutes while cooling with cold water. The following composition was slowly added while thoroughly stirring the redispersed liquid, and completely dissolved to prepare dope liquids for fine particles AK, K-1, K-2, and K-3.
147 parts by weight of cellulose acetate propionate (acetyl group substitution degree 1.90, propionyl group substitution degree 0.75, weight average molecular weight 190,000)
100 parts by weight of methylene chloride

<Creation of cellulose acetate film by solution casting method>
Each of the above-prepared dope solutions was kept at 40 ° C. and uniformly cast on a stainless steel belt, which is an endless metal support that was kept at 40 ° C. and moved infinitely. After the cast film was dried to a residual solvent amount of 80%, it was peeled off from the stainless steel belt. After the peeled cellulose ester film web was evaporated at 40 ° C. to a residual solvent amount of 20%, a tenter was used. The film was stretched 1.3 times in the width direction. Further, the film was dried at 120 ° C. while being conveyed by many rolls to obtain an optical film having a thickness of 80 μm and a width of 1.3 m.

(Draft ratio change)
In Examples 1-22 and Comparative Examples 1-10 in FIG. 8, the draft ratio was changed by adjusting the flow rate of the dope and the running speed of the stainless steel belt. FIG. 5 shows the relationship between the linear velocity Vb of the stainless steel belt (metal belt) for adjusting the draft ratio Dr and the linear velocity Vrm of the cast film. Here, the linear velocity Vrm of the cast film is a velocity immediately after coming out of the die.

  Therefore, the draft ratio Dr is obtained by the following equation.

Dr = Vb / Vrm
Vrm = L / (Q × 10 ^ 3 / (W · H))
here,
Dr: draft ratio Vb: linear velocity of stainless steel belt (metal belt) [mm / sec]
Vrm: linear velocity of cast film [ml / sec]
Q: Dope flow rate [ml / sec] (dope volume coming out per unit time from the slit S of the die having a width W)
W: Width of slit S [mm]
H: Slit S gap [mm]
L: Land length [mm] (length of slit S in the dope flow direction)

  About Examples 1-22 manufactured as mentioned above and Comparative Examples 1-10, phase difference (retardation), haze, slitting property, a horizontal stage, and contrast were evaluated and it has shown according to FIG. Here, the contrast was evaluated using a liquid crystal display device prepared by <preparation of polarizing plate>, <creation of polarizing plate β>, and <creation of liquid crystal display device> described later.

(Measurement method of retardation)
In this example, the average refractive index of the optical film was measured using an Abbe refractometer 1T (manufactured by Atago Co., Ltd.) and a spectral light source device. Moreover, the thickness of the optical film was measured using a commercially available micrometer. Furthermore, in an optical film that was allowed to stand for 24 hours in an environment of 23 ° C. and 55% RH using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), an optical film having a wavelength of 590 nm under the same environment was used. Retardation measurement was performed. The above average refractive index and film thickness were input to the following formulas to obtain values for the inner surface retardation Ro and the thickness direction retardation Rth.
Ro = (nx−ny) × d
Rth = {(nx + ny) / 2−nz} × d
In the formula, the refractive index in the slow axis direction in the plane is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, the refractive index in the thickness direction of the optical film is nz, and d is the thickness of the optical film. (Nm) respectively. As described above, in the present invention, nx, ny, and nz satisfying 160 ≦ Ro ≦ 300 and −50 ≦ Rth ≦ 50 are preferable. Among these, nx, ny, and nz satisfying Ro = 270 nm and Rth = 0 nm are particularly preferable.

(Measurement method of haze)
In this example, haze was measured using a haze meter NDH2000 (Nippon Denshoku Industries Co., Ltd.) according to JIS K-7136, and this was used as an index of transparency. Here, the haze is preferably 1% or less.

(Evaluation method of slitting)
In order to evaluate the slitting property indicating the ease of breaking of the optical film, it is necessary to perform a long and long test in the process, but the cost and time are enormous. Therefore, in this embodiment, evaluation can be performed in a short time by performing a test under the following strict and strict conditions. The slitter 38 cuts a 300 mm wide optical film to a length of 1000 m, the slit width is 50 mm, the slit speed is 10 m / min, the tension is 5 kg, and the slit method is the upper blade / lower blade method. The number of breaks of the optical film is measured. There is accumulation of empirical data regarding the rupture frequency when evaluated under the above conditions and the rupture frequency in the actual process, and FIG. 10 shows the evaluation of the practical level with respect to the above rupture frequency.

(Horizontal evaluation method)
In this example, the film thickness unevenness appearing perpendicular to the transport direction of the produced cellulose ester film was regarded as a horizontal stage and evaluated visually. Here, the symbols in the horizontal row of the table of FIG. 8 are: ◎ is no crossing, ○ is crossing faint, Δ is crossing but can be used as an optical film, × is not acceptable as an optical film Each level represents an evaluation.

(Vertical stripe evaluation method)
In this example, the film thickness unevenness appearing parallel to the transport direction of the produced cellulose ester film was regarded as vertical streaks and evaluated visually. Here, symbols in the vertical streaks in the table of FIG. 8 are: ◎ indicates no vertical streaks, ○ indicates faint vertical streaks, △ indicates vertical streaks that can be used as an optical film, and × indicates vertical streaks are optical Each represents an evaluation of an unacceptable level as a film.

(Contrast evaluation method)
<Contrast at the time of white display and black display of the liquid crystal panel prepared by <Creation of Polarizing Plate><Creation of Polarizing Plate β><Creation of Liquid Crystal Display Device> described below was measured using EZ-contrast manufactured by ELDIM It was. It can be said that the viewing angle is wider as the contrast between white display and black display of the liquid crystal panel at an inclination angle of 80 ° from the normal direction of the panel surface is larger. A value obtained by averaging the contrast at an inclination angle of 80 ° from the normal direction of the panel surface in all directions was evaluated as the contrast. Here, the contrast value is preferably 30 or more.

(Comprehensive evaluation)
The optical film in each Example and Comparative Example is evaluated by comprehensively evaluating the horizontal stage, vertical stripe, phase difference, haze, contrast, and slitting property. Here, symbols in the comprehensive evaluation in the table of FIG. 8 represent evaluations that “◎” is particularly preferable, “◯” is preferable, “Δ” is approximately preferable, and “×” is inappropriate.

  A draft ratio that is more preferable than the evaluation results shown in FIG. In Examples 17 to 19 in which the draft ratio was 1.4, Ro <160, 50 <Rth and the contrast was less than 30, but the slitting property was maintained in a good state, and Comparative Examples 8 to Compared to 9, the contrast is improved. Moreover, both the horizontal stage and the haze are within a suitable range. In Examples 20 to 22 in which the draft ratio is 7.5, both the Ro and Rth are within the preferable range although the lateral evaluation is poor. Further, in the case of Comparative Examples 1 to 4 in which the particle size distribution range is the same and the volume ratio of the particles is low, the haze is 1% or more, the slitting property is 30 or more, and the effect of increasing the draft ratio is not obtained. . In the case of Comparative Examples 8 to 10 in which the volume ratio of particles having a suitable particle size range is low and the draft ratio is 1.4, Ro <160, 50 <Rth, contrast is less than 30, haze is 1% or more, The slitting property is 30 or more, and the evaluation is very poor and unsuitable. In particular, the slitting property is very important when actually manufacturing a film. When this evaluation is 10 or more, particularly 30 or more, breakage frequently occurs in the actual process during film production. When the film breaks, it is necessary to pass the film again between a plurality of transport rolls installed in a drying zone or the like over a long distance, which takes a very long time. That is, the productivity is remarkably deteriorated and the manufacturing becomes substantially difficult. Even if it dares to manufacture, the cost increase is very large and it is not acceptable. In other words, as long as the slitting property can be maintained, it can be manufactured at a low cost. For example, it can be said that it is sufficiently valuable even if the contrast improvement width is slightly small. Further, in the case of Example 10 in which the particle size distribution range is located in the center of the region of FIG. 6C, Ro = 270, Rth = 0, haze 1% or less, and the crossing is only faint, the contrast is 30 or more, The slitting property is 2, the best result is obtained, and in Examples 11 to 14 where the particle size distribution range slightly deviates from the center of FIG. 6C, it can be seen that each evaluation is slightly lowered. . Further, in Examples 15 and 16, 160 ≦ Ro ≦ 300, −50 ≦ Rth ≦ 50, haze is 1% or less, and slitting property is 10 or less, whereas in Comparative Examples 3 and 4, Ro <160. , 50 <Rth, haze is 1% or more, and slitting property is 30 or more. Therefore, it can be seen that the effect of increasing the draft ratio appears more greatly when particle classification is performed.

From the above, the shape of the fine particles is, when the absolute maximum length is X (nm) and the aspect ratio is Y,
[Particle size range formula]
Y> (X ^ 2) / 20000
Y> 20 × (X ^ (− 0.5))
Y <20
50 <X <500
It is preferable that the volume ratio of the fine particles in the particle diameter range satisfying the above condition is large and the draft ratio satisfies 2.1 to 6.0. Furthermore, it is more preferable to increase the volume ratio of the particles satisfying the [Particle Size Range Formula] by performing particle classification using a centrifugal separator or a filter.

<When changing the dope slit passage time>
In the example and comparative example of FIG. 9, the time for the dope to pass through the slit of the die, the particle distribution range, and the volume ratio of the fine particles are adjusted. Here, in Examples 101 to 109, in a dope containing strontium carbonate having the same range within the preferable particle distribution range at substantially the same preferable volume ratio, the slit passing time is preferably 0.1 to 2.0 [sec]. In Examples 117 to 119 and 120 to 122, the slit passage interruption time is set in a range other than 0.1 to 2.0 [sec] under the same conditions. In Examples 110 to 114, the conditions of the slit passage time are made equal, and the particle distribution range is changed within a preferable range. Here, Example 110 is located in the center of the region (c) showing the preferred particle size range in FIG. 6, Example 111 is in the lower right of region (c), and Example 112 is in the lower left of region (c). Example 113 is located at the upper right of region (c), and Example 114 is located at the upper left of region (c). Further, Comparative Examples 101 to 103 were prepared under the same conditions as in Examples 101 to 109 without adjusting the volume ratio of the fine particles. Further, Example 115 and Example 116 were obtained by classifying particles of the strontium carbonate dispersion used in Comparative Example 103 using a centrifuge or a filter to improve the volume ratio of fine particles. Comparative Example 104 is a lower half obtained by centrifuging the strontium carbonate dispersion used in Comparative Example 103, and has a reduced volume ratio. Further, in Comparative Examples 108 to 110, the slit passage time is set to a range other than 0.1 to 2.0 [sec] under the conditions of Comparative Examples 101 to 103. Comparative Examples 11 to 14 use the fine particles of Example 10 to set the draft ratio to a range other than 2.1 to 6.0, and the slit passing time to a range other than 0.1 to 2.0 [sec]. It is taken from. (Hereinafter, the comparative examples 101 to 104 and the comparative examples 108 to 110 will be referred to as comparative examples 101 to 110.)

  In this case, the same procedure as in the example measured by changing the draft ratio is performed except for (change of the draft ratio).

(Change of slit passage time)
In Examples 101 to 122 and Comparative Examples 101 to 110, the change of the dope slit passage time in the die slit S is performed by exchanging the dope flowing die with a die having a different land length L and changing the dope flow rate. It was done by changing. FIGS. 4A and 4B show examples of dies having different land lengths L. FIG. FIG. 3 shows an example of a perspective view of these dies. Here, the running speed of the stainless steel belt was adjusted so that the finished film became 80 μm with the change of the die and the dope flow rate.

  The time θ through which the dope passes through the slit S of the die is obtained by the following equation.

θ = L / (Q × 10 ^ 3 / (W · H))
here,
Q: Dope flow rate [ml / sec] (dope volume coming out per unit time from the slit S of the die having a width W)
W: Width of slit S [mm]
H: Slit S gap [mm]
L: Land length [mm] (length of slit S in the dope flow direction)
θ: slit passage time [sec]
It is.

  About Examples 101-122, Comparative Examples 101-110, and Comparative Examples 11-14 manufactured as described above, retardation, haze, slitting property, horizontal stage, vertical stripe, and evaluation of contrast, and Comprehensive evaluation is shown according to FIG. 9 and FIG.

  In this case, the same haze measurement method, horizontal stage evaluation, vertical streak evaluation, slitting evaluation, phase difference measurement method, contrast evaluation, and overall evaluation as in the case of changing the draft ratio were performed. Yes.

  A preferable slit passage time is considered from the results of the evaluations shown in FIGS. 9 and 15 thus obtained. In the case of Examples 117 to 119 with a passage time of 0.07, Ro <160, 50 <Rth and the contrast is less than 30, but the slitting property is maintained in a good state, and Comparative Examples 108 to Compared to 109, the contrast is improved. Further, both the horizontal stage and the haze are within a suitable range. In Examples 120 to 122 in which the passage time is 2.5, although evaluation of the vertical stripe is bad, both Ro and Rth are within the preferable range. In the case of Comparative Examples 101 to 104 in which the particle size distribution range is the same and the volume ratio of the particles is low, the haze is 1% or more, the slitting property is 30 or more, and the effect of increasing the passage time is not obtained, which is inappropriate. . In the case of Comparative Examples 108 to 110 in which the volume ratio of particles having a suitable particle size range is 0.07 and the passage time is 0.07, Ro <160, 50 <Rth, contrast is less than 30, haze is 1% or more, The slitting property is 30 or more, and the evaluation is very poor and unsuitable. In particular, the slitting property is very important when actually manufacturing a film. When this evaluation is 10 or more, particularly 30 or more, breakage frequently occurs in the actual process during film production. When the film breaks, it is necessary to pass the film again between a plurality of transport rolls installed in a drying zone or the like over a long distance, which takes a very long time. That is, the productivity is remarkably deteriorated and the manufacturing becomes substantially difficult. Even if it dares to manufacture, the cost increase is very large and it is not acceptable. In other words, as long as the slitting property can be maintained, it can be manufactured at a low cost. For example, it can be said that it is sufficiently valuable even if the contrast improvement width is slightly small. Further, in Example 110 in which the particle size distribution range is located at the center of the region of FIG. 6C, Ro = 270, Rth = 0, haze 1% or less, only the crossing is faint, the contrast is 30 or more, and the slip In the case of Examples 111 to 114 in which the particle size distribution range is slightly off from the center of FIG. 6 (c), each evaluation is slightly lowered. Further, in Examples 115 and 116, 160 ≦ Ro ≦ 300 and −50 ≦ Rth ≦ 50, haze is 1% or less, and slitting property is 10 or less, whereas in Comparative Examples 103 and 104, Ro <160. , 50 <Rth, haze is 1% or more, and slitting property is 30 or more. Therefore, it can be seen that the effect of lengthening the passage time appears more greatly when particle classification is performed. In addition, horizontal rows and vertical stripes are also important items, and if these are present, unevenness may appear in the liquid crystal display when incorporated in an actual liquid crystal display device. This is not preferable because the commercial value is lowered even if the contrast is good. In Comparative Examples 11 to 13, the slitting property is poor and the productivity is deteriorated, and further, since horizontal rows or vertical stripes are generated, the cost is high and the commercial value is low, which is very undesirable. Further, as in Comparative Example 14, in particular, when a film in which horizontal rows and vertical stripes are generated at the same time is incorporated in a liquid crystal display device, unevenness occurs in a cross shape in the liquid crystal display. Becomes very unsightly and has little commercial value. Further, in Comparative Examples 11 to 14, the draft ratio and the slit passing time were outside the scope of the present invention despite the use of the particles with favorable results obtained in Example 10. Or the evaluation of the horizontal and vertical stripes is bad, and favorable results cannot be obtained.

  From the above, the shape of the fine particles is such that when the absolute maximum length is X and the aspect ratio is Y, the volume ratio of the fine particles in the particle size range satisfying the [particle size range formula] is large, and the time of the slit S is 0.1. It is preferable to satisfy -2.0 [sec]. Furthermore, it is more preferable to increase the volume ratio of the particles satisfying the [Particle Size Range Formula] by performing particle classification using a centrifugal separator or a filter.

[Production of optical film by melt extrusion film formation method]
<When changing the draft ratio>
In the example and comparative example of FIG. 13, the draft ratio was changed, and the volume ratio of fine particles and the particle distribution range were adjusted. Examples 201 to 209 are obtained by changing the draft ratio in a preferable range of 10 to 30 in a melt containing strontium carbonate having the same range within the preferable particle distribution range in almost the same preferable volume ratio. -219 and Comparative Examples 220-222 have the draft ratio in a range other than 10-30 under the same conditions. In Examples 210 to 214, the conditions of the draft ratio were made equal, and the particle distribution range was changed within a preferable range. Here, Example 210 is located in the center of region (c) showing the preferred particle size range of FIG. 6, Example 211 is in the lower right of region (c), and Example 212 is in the lower left of region (c). Example 213 is located at the upper right of region (c), and Example 214 is located at the upper left of region (c). Further, Comparative Examples 201 to 203 are prepared under the same conditions as in Examples 201 to 209 without adjusting the volume ratio of the fine particles. Further, in Examples 215 and 216, the strontium carbonate dispersion used in Comparative Example 203 was classified using a centrifuge or a filter to improve the volume ratio of the fine particles. Comparative Example Reference numeral 204 denotes a lower half obtained by centrifuging the strontium carbonate separation liquid used in Comparative Example 203, and has a reduced volume ratio. Further, Comparative Examples 208 to 210 have draft ratios in a range other than 10 to 30 under the conditions of Comparative Examples 201 to 203. (Hereinafter, the comparative examples 201 to 204 and the comparative examples 208 to 210 are referred to as comparative examples 201 to 210.)

  Also in the melt extrusion film forming method, steps other than <preparation of dope solution> and <preparation of cellulose acetate film by solution casting film forming method> are the same as those of the solution casting film forming method. Hereinafter, different steps will be described.

<Creation of melt>
Each of the following compositions is melt-mixed at 250 ° C. using a twin-screw extruder KZW-TW (manufactured by Technobel) and pelletized, whereby particle-containing resin pellets a to k, k-1, k-2, k-3 was created.
Fine particles A to K, K-1, K-2, K-3 8 parts by weight Cellulose acetate propionate 72 parts by weight (vacuum dried at 60 ° C. for 24 hours, acetyl substitution degree 1.90, propionyl substitution degree 0.75 , Weight average molecular weight 190,000)
Trimethylolpropane benzoate 10 parts by weight 2,6-di-t-butyl-p-cresol pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.01 weight Part The pellets prepared above were melted at 250 ° C. to obtain melts of fine particles A to K, K-1, K-2, and K-3.

<Creation of cellulose acetate film by melt extrusion film forming method>
The melt prepared above was melt extruded from a die into a film shape on a cooling drum at 30 ° C. and cooled and solidified to obtain a cellulose ester film.

(Draft ratio change)
In Examples 201-222 and Comparative Examples 201-210 in FIG. 13, the draft ratio was changed by adjusting the flow rate of the melt and the rotation speed of the cooling drum. Here, the rotational speed of the cooling drum is the linear speed of the outer peripheral portion, which is the same as the linear speed of the metal belt. Therefore, the draft ratio is obtained by the following equation.

Dr (Y) = Vb (Y) / Vrm (Y)
Vrm (Y) = Q × 10 ^ 3 / (W · H)
here,
Dr (Y): draft ratio Vb (Y): rotational speed of cooling drum (linear speed of metal belt) [mm / sec]
Vrm: linear velocity of cast film [ml / sec]
Q: Melt flow rate [ml / sec] (volume of melt coming out per unit time from the slit S of the die having a width W)
W: Width of slit S [mm]
H: Slit S gap [mm]
L: Land length [mm] (length of slit S in melt flow direction)

  For Examples 201 to 222 and Comparative Examples 201 to 210 manufactured as described above, the evaluation of haze, slitting property, phase difference, horizontal stage, vertical stripe, and contrast, and overall evaluation are matched with FIG. Show.

  Also in this case, the same haze measurement method, slitting evaluation, phase difference measurement method, horizontal stage evaluation, vertical streak evaluation, contrast evaluation, and overall evaluation as in the case of the solution casting film forming method are performed. Is doing.

  A preferable draft ratio is considered from the results of evaluation shown in FIG. In the case of Examples 205 to 207 in which the draft ratio was set to 5, Ro <160, 50 <Rth, and the contrast was less than 30, but the slitting property was maintained in a good state, while the comparative examples 208 to 209 were maintained. The contrast is improved. Further, both vertical stripes and haze are within a suitable range. In Examples 220 to 222 in which the draft ratio was set to 35, the evaluation of the horizontal stage was bad, but both Ro and Rth were within suitable ranges. In the case of Comparative Examples 201 to 204 in which the particle size distribution range is the same but the volume ratio of the particles is low, the haze is 1% or more, the slitting property is 30 or more, and the effect of increasing the draft ratio is not obtained, which is inappropriate. . In Comparative Examples 208 to 210 in which the volume ratio of particles having a suitable particle size range is low and the draft ratio is 5, Ro <160, 50 <Rth, contrast is less than 30, haze is 1% or more, and slitting The property is 30 or more, and the evaluation is very poor and unsuitable. In particular, the slitting property is very important when actually manufacturing a film. When this evaluation is 10 or more, particularly 30 or more, breakage frequently occurs in the actual process during film production. When the film breaks, it is necessary to pass the film again between a plurality of transport rolls installed in a drying zone or the like over a long distance, which takes a very long time. That is, the productivity is remarkably deteriorated and the manufacturing becomes substantially difficult. Even if it dares to manufacture, the cost increase is very large and it is not acceptable. In other words, as long as the slitting property can be maintained, it can be manufactured at a low cost. For example, it can be said that it is sufficiently valuable even if the contrast improvement width is slightly small. Furthermore, in the case of Example 210 in which the particle size distribution range is located in the center of the region of FIG. 6C, Ro = 270, Rth = 0, haze 1% or less, and the crossing is only faint, the contrast is 30 or more, The slitting property is 2, the best result is obtained, and in Examples 211 to 214 in which the particle size distribution range is slightly off the center of FIG. 6 (c), it can be seen that each evaluation is slightly lowered. . Further, in Examples 215 and 216, 160 ≦ Ro ≦ 300 and −50 ≦ Rth ≦ 50, haze is 1% or less, and slitting property is 10 or less, whereas in Comparative Examples 203 and 204, Ro <160. , 50 <Rth, haze is 1% or more, and slitting property is 30 or more. Therefore, it can be seen that the effect of increasing the draft ratio appears more greatly by performing particle classification.

  As for the shape of the fine particles, when the absolute maximum length is X and the aspect ratio is Y, it is preferable that the volume ratio of the fine particles in the particle size range satisfying [Particle Size Range Formula] is large and the draft ratio satisfies 10 to 30. . Furthermore, it is more preferable to increase the volume ratio of the particles satisfying the [Particle Size Range Formula] by performing particle classification using a centrifugal separator or a filter.

<When changing the melt passage time>
In the example and comparative example of FIG. 14, the time for the melt to pass through the slit of the die, the particle distribution range, and the volume ratio of the fine particles are adjusted. Here, in Examples 301 to 309, in a melt containing strontium carbonate having the same range within a preferable particle distribution range at approximately the same preferable volume ratio, the slit passage time is preferably 0.1 to 2.0 [sec]. In Examples 317 to 319 and Examples 320 to 322, the slit passage interruption time is set to a range other than 0.1 to 2.0 [sec] under the same conditions. In Examples 310 to 314, the conditions for slit passage time are made equal, and the particle distribution range is changed within a preferable range. Here, Example 310 is located in the center of region (c) showing the preferred particle size range in FIG. 6, Example 311 is in the lower right of region (c), and Example 312 is in the lower left of region (c). Example 313 is located at the upper right of region (c), and Example 314 is located at the upper left of region (c). Further, Comparative Examples 301 to 303 were prepared under the same conditions as in Examples 301 to 309 without adjusting the volume ratio of the fine particles. Further, in Example 315 and Example 316, the strontium carbonate dispersion used in Comparative Example 303 was classified using a centrifuge or a filter to improve the volume ratio of the fine particles. Comparative Example 304 is the one using the lower half obtained by centrifuging the strontium carbonate dispersion used in Comparative Example 303, and the volume ratio is lowered. Further, in Comparative Examples 308 to 310, the slit passage time is set to a range other than 0.1 to 2.0 [sec] under the conditions of Comparative Examples 301 to 303. In Comparative Examples 211 to 214, using the fine particles of Example 210, the draft ratio was set to a range other than 10 to 30, and the slit passage time was set to a range other than 0.1 to 2.0 [sec]. Is. (Hereinafter, the comparative examples 301 to 304 and the comparative examples 308 to 310 are collectively referred to as comparative examples 301 to 310.)

  In this case, the same procedure as in the example measured by changing the draft ratio is performed except for (change of the draft ratio).

(Change of slit passage time)
In Examples 301-322 and Comparative Examples 301-310, the change of the slit passage time of the melt flowing in the slit S of the die is performed by exchanging the die for flowing the melt with a die having a different land length L. This was done by changing the flow rate. FIGS. 4A and 4B show examples of dies having different land lengths L. FIG. FIG. 3 shows an example of a perspective view of these dies. Here, the rotation speed of the cooling drum was adjusted so that the finished film would be 80 μm in accordance with the change of the die and the melt flow rate.

  The time θ (Y) for the molten liquid to pass through the slit S of the die is obtained by the following equation.

θ (Y) = L / (Q × 10 ^ 3 / (W · H))
here,
Q (Y): Melt flow rate [ml / sec] (volume of melt coming out per unit time from slit S of die with width W)
W: Width of slit S [mm]
H: Slit S gap [mm]
L: Land length [mm] (length of slit S in melt flow direction)
θ: slit passage time [sec]
It is.

    About Example 301-322, Comparative Example 301-310, and Comparative Example 211-214 manufactured as mentioned above, evaluation of haze, slitting property, phase difference, horizontal stage, vertical stripe and contrast, and comprehensive evaluation are performed. 14 and 16 are also shown.

  Also in this case, the same haze measurement method, slitting evaluation, phase difference measurement method, horizontal stage evaluation, vertical streak evaluation, contrast evaluation, and overall evaluation as in the case of the solution casting film forming method are performed. Is doing.

  A preferable slit passage time is considered from the results of the evaluations shown in FIGS. 14 and 16 thus obtained. In the case of Comparative Examples 317 to 319 with a passage time of 0.07, Ro <160, 50 <Rth and the contrast is less than 30, but the slitting property is maintained in a good state, and Comparative Examples 308 to 308 are maintained. Compared to 309, the contrast is improved. Further, both vertical stripes and haze are within a suitable range. In Examples 320 to 322 in which the passage time is 2.5, the evaluation of the vertical stripe is bad, but both Ro and Rth are within the preferable range. In the case of Comparative Examples 301 to 304 in which the particle size distribution range is the same but the volume ratio of the particles is low, the haze is 1% or more, the slitting property is 30 or more, and the effect of increasing the passage time is not obtained, which is inappropriate. . In the case of Comparative Examples 308 to 310 in which the volume ratio of particles having a suitable particle size range is low and the passage time is 0.07, Ro <160, 50 <Rth, contrast is less than 30, haze is 1% or more, The slitting property is 30 or more, and the evaluation is very poor and unsuitable. In particular, the slitting property is very important when actually manufacturing a film. When this evaluation is 10 or more, particularly 30 or more, breakage frequently occurs in the actual process during film production. When the film breaks, it is necessary to pass the film again between a plurality of transport rolls installed in a drying zone or the like over a long distance, which takes a very long time. That is, the productivity is remarkably deteriorated and the manufacturing becomes substantially difficult. Even if it dares to manufacture, the cost increase is very large and it is not acceptable. In other words, as long as the slitting property can be maintained, it can be manufactured at a low cost. For example, it can be said that it is sufficiently valuable even if the contrast improvement width is slightly small. Further, in Example 310 in which the particle size distribution range is located in the center of the region of FIG. 6C, Ro = 270, Rth = 0, haze 1% or less, only the crossing is faint, the contrast is 30 or more, and the slip In the case of Examples 311 to 314 in which the particle size distribution range is slightly off from the center of FIG. 6 (c), each evaluation is slightly lowered. Further, in Examples 315 and 316, 160 ≦ Ro ≦ 300, −50 ≦ Rth ≦ 50, haze is 1% or less, and slitting property is 10 or less, whereas in Comparative Examples 303 and 304, Ro <160. , 50 <Rth, haze is 1% or more, and slitting property is 30 or more. Therefore, it can be seen that the effect of lengthening the passage time appears more greatly when particle classification is performed. In addition, horizontal rows and vertical stripes are also important items, and if these are present, unevenness may appear in the liquid crystal display when incorporated in an actual liquid crystal display device. This is not preferable because the commercial value is lowered even if the contrast is good. In Comparative Examples 211 to 213, the slitting property is poor and the productivity is deteriorated, and furthermore, since horizontal rows or vertical stripes are generated, the cost is high and the commercial value is low, which is very undesirable. Further, as in Comparative Example 214, when a film in which horizontal and vertical stripes are generated at the same time is incorporated in a liquid crystal display device, unevenness occurs in a cross shape in the liquid crystal display, so even if the contrast is very good, the actual liquid crystal display Becomes very unsightly and has little value. In addition, although Comparative Examples 211 to 214 use particles with favorable results obtained in Example 210, the draft ratio and the slit passage time are outside the scope of the present invention, so the contrast is evaluated. A favorable result cannot be obtained because the evaluation of the horizontal stage or the vertical stripe is bad.

  From the above, the shape of the fine particles is such that when the absolute maximum length is X and the aspect ratio is Y, the volume ratio of the fine particles in the particle size range satisfying the [particle size range formula] is large, and the time of the slit S is 0.1. It is preferable to satisfy -2.0 [sec]. Furthermore, it is more preferable to increase the volume ratio of the particles satisfying the [Particle Size Range Formula] by performing particle classification using a centrifugal separator or a filter.

<Creation of polarizing plate>
In this example, as shown in FIG. 12, the polarizing plate 61 prepared using the cellulose ester film prepared according to the present invention was bonded to the backlight side with the transverse electric field switching mode type liquid crystal cell 70 interposed therebetween, The polarizing plate β60 is bonded to the opposite side across the transverse electric field switching mode type liquid crystal cell 70. Here, the polarizing plate protective film 62 on the liquid crystal cell side of the polarizing plate β uses a film in which both Ro and Rth are nearly 0, and thus the contrast is very high when combined with the polarizing plate 61 of the present invention. Get better. Here, FIG. 12 is a diagram for explaining the configuration of the liquid crystal display device.

  A 50 μm thick polyvinyl alcohol film was uniaxially stretched (temperature 110 ° C., stretch ratio 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 6 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. Then, it was immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer. Next, polarizing plates J1 to J22, J101 to J122, J201 to J222, J301 to J322, H1 to H14, H101 to H110, H201 to H214, and H301 to H310 were prepared according to Steps 1 to 5. (The J number and the H number are simply matched to the example number and the comparative example number, respectively.)

(Process 1)
As a polarizing plate protective film, the cellulose ester film prepared in Example 1 was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to saponify the side to be bonded to the polarizer. . Similarly, saponification of a commercially available cellulose ester film KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.) was also performed as the polarizing plate protective film on the opposite side.

(Process 2)
The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

(Process 3)
The excess adhesive adhering to the polarizer in (Step 2) was gently wiped off, and this was placed on the saponified surface of the cellulose ester film of the present invention prepared in Example 1 treated in (Step 1), and the opposite As the polarizing plate protective film on the side, the commercially available cellulose ester film KC8UX2M treated in (Step 1) was laminated so that the saponified surface was in contact with the polarizer, and the polarizing plate J1 was obtained.

(Process 4)
The polarizing plate obtained by laminating the cellulose ester film and the polarizer in (Step 3) was bonded at a pressure of 20 to 30 N / cm 2 and a conveyance speed of about 2 m / min.

(Process 5)
The polarizing plate prepared in (Step 4) was dried for 2 minutes in a dryer at 80 ° C.

  Similarly, polarizing plates J2 to J22, J101 to J122, J201 to J222, J301 to J312 using the cellulose ester films of the present invention prepared in Examples 2 to 22, 101 to 122, 201 to 222, 301 to 312. It was created. Similarly, polarizing plates H1 to H14, H101 to H110, H201 to H214, and H301 to H310 are formed using the cellulose ester films prepared in Comparative Examples 1 to 14, 101 to 110, 201 to 214, 301 to 310. Created.

<Creation of polarizing plate β>
Cellulose ester film-β used for polarizing plate β was prepared as follows.

(Preparation of polymer)
Bulk polymerization was performed by the polymerization method described in JP-A No. 2000-344823. That is, the contents were heated to 70 ° C. while introducing the following methyl methacrylate and ruthenocene into a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, an inlet, and a reflux condenser. Next, half of the following β-mercaptopropionic acid which had been sufficiently purged with nitrogen gas was added to the flask under stirring. After the addition of β-mercaptopropionic acid, the contents in the stirring flask were maintained at 70 ° C. and polymerization was carried out for 2 hours. Further, after adding the other half of β-mercaptopropionic acid substituted with nitrogen gas, the temperature of the content being stirred was maintained at 70 ° C., and polymerization was carried out for 4 hours. The temperature of the reaction product was returned to room temperature, and 20 parts by weight of a 5 mass% benzoquinone tetrahydrofuran solution was added to the reaction product to terminate the polymerization. While gradually heating the polymer to 80 ° C. under reduced pressure with an evaporator, tetrahydrofuran, residual monomer and residual thiol compound were removed to obtain polymer 7. The weight average molecular weight was 3,400. The hydroxyl value (according to the measurement method described below) was 50.
Methyl methacrylate 100 parts by weight Ruthenocene (metal catalyst) 0.05 parts by weight β-mercaptopropionic acid 12 parts by weight

(Measurement method of hydroxyl value)
This measurement conforms to JIS K 0070 (1992). This hydroxyl value is defined as the number of mg of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when 1 g of a sample is acetylated. Specifically, sample Xg (about 1 g) is precisely weighed in a flask, and 20 ml of an acetylating reagent (a solution obtained by adding pyridine to 20 ml of acetic anhydride to 400 ml) is accurately added thereto. An air cooling tube is attached to the mouth of the flask and heated in a glycerin bath at 95-100 ° C. After 1 hour and 30 minutes, the mixture is cooled, 1 ml of purified water is added from an air condenser, and acetic anhydride is decomposed into acetic acid. Next, titration is performed with a 0.5 mol / L potassium hydroxide ethanol solution using a potentiometric titrator, and the inflection point of the obtained titration curve is set as the end point. Further, as a blank test, titration is performed without a sample, and an inflection point of the titration curve is obtained. The hydroxyl value is calculated by the following formula.
Hydroxyl value = {(BC) × f × 28.05 / X} + D
In the formula, B is the amount (ml) of 0.5 mol / L potassium hydroxide ethanol solution used for the blank test, C is the amount (ml) of 0.5 mol / L potassium hydroxide ethanol solution used for titration, f is a factor of 0.5 mol / L potassium hydroxide ethanol solution, D is an acid value, and 28.05 is 1/2 of 1 mol amount of potassium hydroxide 56.11.

(Production of cellulose ester film-β used for polarizing plate β)
(Silicon dioxide dispersion β)
Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) 12 parts by weight (average primary particle diameter 16 nm, apparent specific gravity 90 g / liter)
More than 88 parts by weight of ethanol was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. The liquid turbidity after dispersion was 200 ppm. 88 parts by weight of methylene chloride was added to the silicon dioxide dispersion with stirring, and the mixture was stirred and mixed for 30 minutes with a dissolver to prepare a silicon dioxide dispersion dilution β.

(Preparation of inline additive solution β)
Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 11 parts by weight Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 5 parts by weight 100 parts by weight of methylene chloride Dissolved and filtered.

  To this was added 36 parts by weight of silicon dioxide dispersion diluted solution β with stirring, and the mixture was further stirred for 30 minutes, followed by cellulose acetate propionate (acetyl group substitution degree 1.9, propionyl group substitution degree 0.8) 6 weights The components were added with stirring, and further stirred for 60 minutes, and then filtered through a polypropylene wind cartridge filter TCW-PPS-1N manufactured by Advantech Toyo Co., Ltd. to prepare an in-line additive solution β.

(Preparation of dope solution β)
Cellulose acetate 100 parts by weight (acetyl substitution degree 2.92, molecular weight Mn = 148000, molecular weight Mw = 310000, Mw / Mn = 2.1)
Polymer prepared above 12 parts by weight Methylene chloride 440 parts by weight Ethanol 40 parts by weight The above is put into a sealed container, heated and stirred, completely dissolved, and manufactured by Azumi Filter Paper No. 24 was used to prepare a dope solution β.

  The dope solution β was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. in the film production line. In-line additive solution β was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. in the in-line additive solution line. Add 100 parts by weight of the filtered dope solution β to 2 parts by weight of the filtered in-line additive solution β, mix thoroughly with an in-line mixer (Toray static in-tube mixer Hi-Mixer, SWJ), and then add the dope solution β to 40 parts by weight. It was kept at ℃ and cast uniformly on a stainless steel belt kept at 40 ℃. After the residual solvent amount was dried to 80%, it was peeled off from the stainless steel belt, and the peeled cellulose ester film web was evaporated at 40 ° C. to a residual solvent amount of 20%. Three-fold stretching was performed. Furthermore, it dried at 120 degreeC, making it convey with many rolls, and obtained the cellulose-ester film- (beta) of 80 micrometers and width 1.3m.

  The dope flowing through the slit of the die has a slit passage time of 0.07 sec, a draft ratio of 1.5, and is replaced with a die having a different land length so that the film thickness of the finished film is 80 μm. The travel speed was adjusted.

  When the retardation value of this cellulose ester film-β was measured, Ro = 0.1 nm and Rth = 0 nm. The measurement of Ro and Rth was performed in the same manner as the measurement of Ro and Rth described above.

  In the production of the polarizing plate, a polarizing plate β was produced in the same manner except that the cellulose ester film-β was used instead of the cellulose ester film of Example 1 according to the present invention.

<Creation of liquid crystal display device>
A liquid crystal panel for contrast evaluation was produced as follows.

The polarizing plates prepared above were peeled off using the Hitachi liquid crystal television Wooo W17-LC50 manufactured by Hitachi, which is an IPS mode type liquid crystal display device, and the polarizing plates prepared above were each bonded to the glass surface of the liquid crystal cell. At that time, the slow axis of the cellulose ester film, the absorption axis of the polarizer, the direction of the slow axis of the liquid crystal cell, and the configuration of the liquid crystal display device are bonded together when creating the polarizing plate as shown in FIG. The liquid crystal panel was bonded.
Here, as shown in FIG. 12, in the liquid crystal display device according to the present invention, the polarizing plate β60 is composed of a polarizing plate protective film 68, a polarizer 64, and a cellulose ester film-β62. Here, the polarizer 64 in the polarizing plate β60 has a transmission axis 72 of the polarizer and an absorption axis 73 of the polarizer. The polarizing plate 61 is composed of the cellulose ester film 66, the polarizer 64, and the polarizing plate protective film 68 of the examples and comparative examples. Further, the polarizer 64 in the polarizing plate 61 has a transmission axis 74 of the polarizer and an absorption axis 75 of the polarizer. The transverse electric field switching mode type liquid crystal cell 70 has a liquid crystal rubbing axis 71.

Process drawing of the manufacturing method of the optical film of this invention Schematic of a solution casting film forming apparatus for carrying out the method for producing an optical film of the present invention Enlarged perspective view of a die for carrying out the optical film manufacturing method of the present invention Expanded cross-sectional view of the die Diagram explaining how to adjust draft ratio Graph showing the desired particle size range of particle size / aspect ratio Table showing absolute maximum length and aspect ratio of fine particles prepared in this example Table showing the results of Examples and Comparative Examples in which the draft ratio was adjusted in the solution casting method Table showing results of Examples and Comparative Examples in which slit passage time was adjusted in the solution casting film forming method Table showing evaluation of breaking frequency in examples and comparative examples Graph for explaining the particle size distribution of fine particles The figure for demonstrating the structure of the liquid crystal display device in a present Example. Table showing results of examples and comparative examples in which draft ratio was adjusted in melt extrusion film formation method Table showing the results of Examples and Comparative Examples in which the slit passage time was adjusted in the melt extrusion film forming method A table showing the results of a comparative example in which the draft ratio and slit passage time were adjusted to values outside the preferred ranges in the solution casting method. A table showing the results of Comparative Examples in which the draft ratio and slit passage time were adjusted to values outside the preferred ranges in the melt extrusion film formation method.

Explanation of symbols

1: Dissolution pot 2: Liquid feed pump 3: Filter 4: Stock tank 5: Liquid feed pump 6: Filter 8: Conduit 10: Dissolution pot 11: Liquid feed pump 12: Filter 13: Stock tank 14: Liquid feed Pump 15: Filter 16: Conduit 17: Switching valve 20: Merge pipe 21: Mixer 22: Conduit 23: Supply pipe 30: Die 31: Metal support 32: Web 33: Peeling position 34: Tenter device 35: Roll drying Device 36: Conveying roll 37: Original winding 60: Polarizing plate β
61: Polarizing plates J1 to J22, J101 to J122, J201 to J222, J301
J322, H1-H14, H101-H110, H201-H214, H301-
H310
62: Cellulose ester film-β (polarizing plate protective film)
64: Polarizer 66: Cellulose ester film (polarizing plate protective film) of Examples and Comparative Examples
68: Polarizing plate protective film 70: Horizontal electric field switching mode type liquid crystal cell 71: Liquid crystal rubbing axis 72, 74: Polarizer transmission axis 73, 75: Polarizer absorption axis 76: Cellulose of Examples and Comparative Examples Slow axis of ester film S: Slit W: Slit width L: Length of slit in dope flow direction (land length)
H: Slit gap

Claims (7)

Either a resin solution containing a predetermined particle and containing an organic solvent as a main component, or a molten resin heated and melted by thermoplasticity, and a liquid resin using cellulose ester as the resin is transferred from the slit of the die. Continuously casting on a metal support,
The predetermined particle includes a metal carbonate, and 90% or more of the total particle is larger than 50 nm in absolute maximum length and smaller than 500 nm, and is further projected by two straight lines parallel to the absolute maximum length. The value obtained by dividing the absolute maximum length by the diagonal width that is the shortest distance between two straight lines when an image is sandwiched is larger than the value obtained by dividing the square of the absolute maximum length (unit: nm) by 20000. In addition, the absolute maximum length (unit: nm) is larger than the value obtained by multiplying the power of −0.5 by 20 and is smaller than 20, and is a negative particle. Birefringent needle-like particles,
When the ratio of the linear velocity of the metal support to the velocity at which the liquid resin is poured from the slit is the liquid resin solution, the ratio is 2.1 to 6.0, and the liquid resin is a molten resin. The method is for producing a cellulose ester film, wherein the condition is 10 to 30 and the time for the resin solution to pass through the slit of the die is in the range of 0.1 to 2.0 seconds,
The cellulose ester film is 160 ≦ in-plane retardation Ro ≦ 300 nm,
−10 ≦ thickness retardation Rth ≦ 10 nm,
A method for producing a cellulose ester film, wherein the haze satisfies each condition of 1% or less.   The method for producing a cellulose ester film according to claim 1, further comprising the step of obtaining the predetermined particles in which 90% or more of all particles fall within the particle size range by performing particle size classification using a centrifuge. Method.   The method for producing a cellulose ester film according to claim 1, further comprising a step of obtaining the predetermined particles in which 90% or more of all the particles fall within the particle size range by performing particle size classification using a filter. . The cellulose ester as the resin has an iron component of 1 ppm or less, calcium of 30 ppm or less, and magnesium of 20 ppm or less. The production of a cellulose ester film according to any one of claims 1 to 3 Method.   The method for producing a cellulose ester film according to claim 1, wherein the resin is cellulose acetate propionate.   A polarizing plate comprising a polarizing film and transparent protective films disposed on both sides thereof, wherein the cellulose ester film according to claim 5 is used in at least one of the transparent protective films on both sides. A polarizing plate.   7. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, wherein at least one polarizing plate of the two polarizing plates is according to claim 6. A liquid crystal display device characterized by being a polarizing plate.

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