JP2008304658A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which has a wide viewing angle, improved contrast and reduced uneven brightness even for a display for a high speed moving picture. <P>SOLUTION: In the liquid crystal display device comprising a liquid crystal cell 70 interposed between two polarizers 64 arranged with crossed Nicol, the liquid crystal display device is characterized in that an optical film 62 containing birefringent particles with 2-100 aspect ratio and 50-500 nm Ro is disposed between the two polarizers 64 in such a way that a transmission axis 74 of the polarizer 64 on the backlight side and a slow axis 63 of the optical film 62 is vertical to each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device with improved front contrast and uneven brightness.

  As the market for TV liquid crystal display devices expands, development of liquid crystal display devices that are particularly excellent in moving image display quality is desired.

  In general, a display method called a VA mode is adopted, but a liquid crystal display device using a horizontal electric field switching mode (hereinafter sometimes referred to as an IPS mode) which is a display device having excellent viewing angle characteristics is also available. Proposed.

  However, since these methods alone have problems such as a decrease in contrast and uneven brightness, various optical films are usually used together as retardation films to compensate for the retardation, and display devices are designed.

  For example, Patent Documents 1 and 2 disclose a retardation film produced using a heat-shrinkable film, and the refractive index in three directions of the film is preferably nz> nx ≧ ny. It is embodied as a physical property.

  However, the film made by this method is difficult to ensure the uniformity of retardation, and also has poor curl characteristics, and the display quality is uniform in a large display device using a polarizing plate made using the film. There was a problem that it was difficult to get.

  Patent Document 3 describes that a retardation film including a region of nx> nz> ny is provided by orienting particles having birefringence. With this retardation film, a relatively good image was obtained even with a large display device.

However, when the liquid crystal display device is required to support moving images with a further high-speed response, and the cell gap of the liquid crystal cell becomes small, the effect of the retardation film may not be sufficiently exhibited.
JP 2001-174632 A JP 2002-207123 A JP 2006-317733 A

  Accordingly, an object of the present invention is to provide a liquid crystal display device having a wide viewing angle and improved contrast and luminance unevenness even for high-speed moving images.

The above object of the present invention is achieved by the following configurations.
1. In a liquid crystal display device in which a liquid crystal cell and two polarizers sandwiching the liquid crystal cell are arranged in crossed Nicols, birefringent particles having an aspect ratio of 2 to 100 are contained between the two polarizers and Ro is 50 to 50. A liquid crystal display device, wherein an optical film having a thickness of 500 nm is arranged so that a transmission axis of a polarizer on a backlight side is perpendicular to a slow axis of the optical film.
2. 2. The liquid crystal display device according to 1, wherein the rubbing axis of the liquid crystal cell and the transmission axis of the polarizer on the viewing side are parallel.
3. 3. The liquid crystal display device as described in 1 or 2 above, wherein a cell gap dc of the liquid crystal cell is 2 to 5 μm.

  According to the present invention, a liquid crystal display device with a wide viewing angle and improved luminance unevenness can be provided.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The retardation film used in the liquid crystal display device of the present invention has been conventionally used on the backlight side of the liquid crystal cell. The reason for this is that compensation for polarized light before entering the liquid crystal cell is necessary to obtain a more optically compensated image.

  However, in the liquid crystal display device corresponding to the high-speed response of the image, there is a case where the concept cannot always be applied.

  The present inventor found that the cause of the fluctuation in the birefringence of the liquid crystal cell itself, such as the electrodes provided in the liquid crystal cell and the protrusions for aligning the liquid crystal, is that the cell gap is reduced due to high-speed response. It is estimated that it has become relatively large.

  When the liquid crystal cell gap is small, it is effective that the retardation film for optical compensation is closer to the viewing side than the liquid crystal cell. When the transmission axis of the polarizer on the light side and the slow axis of the optical film are required to be perpendicular, and when the rubbing axis of the liquid crystal cell is simultaneously parallel to the slow axis of the optical film, We found that the effect was the greatest.

The present inventor has paid attention to the scattering cross section and found that the above effect is appropriately evaluated by the scattering cross section. In other words, when Sx is the scattering cross section when polarized light is incident perpendicular to the long axis direction of the particle, and Sy is the scattering cross section when polarized light is incident parallel to the long axis direction of the particle, Sx <Sy. When the direction of the incident polarization plane at the time of black display is perpendicular to the film orientation axis and Sx> Sy, it is preferably parallel.
<Optical film>
The optical film used for the liquid crystal display device of the present invention comprises a transparent resin and birefringent particles contained therein as a basic structure.

<Transparent resin>
The transparent resin constituting the optical film of the present invention is preferably optically uniform and transparent.

  Any of these may be used, for example, cellulose ester resins, polyester resins, polycarbonate resins, polyarylate resins, polysulfone (including polyethersulfone) resins, polyethylene resins, norbornene resins. , Cycloolefin-based resins, acrylic resins, and the like, but are not limited thereto.

  Of these, cellulose ester resins, polycarbonate resin films, and cycloolefin resins are preferable from the viewpoint of birefringence, and cellulose ester resins are particularly preferable.

(Cellulose ester resin)
Although there is no limitation in particular as a cellulose of the cellulose ester-type resin raw material used for this invention, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be used individually or in mixture in arbitrary ratios, respectively.

  When the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), the cellulose ester resin according to the present invention is 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 COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), 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 resin that can be used for the cellulose ester film preferably has a total acyl group substitution degree of 2.4 to 2.8.

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

  The cellulose ester-based resin used in the present invention preferably has a weight average molecular weight (Mw) to number average molecular weight (Mn) ratio, Mw / Mn of 1.4 to 3.0 as described above. Preferably it is the range of 1.7-2.2.

  The average molecular weight and molecular weight distribution of the cellulose ester resin 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 measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. The 13 samples are preferably used at approximately equal intervals.

  The cellulose ester resin 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) 2.4 ≦ X + Y ≦ 2.9
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.

  The cellulose ester resin is also affected by a trace metal component in the cellulose ester. 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, etc., and it becomes hard water, and it is unsuitable as drinking water. It easily forms a coordination compound, that is, a complex with a ligand, and forms scum (insoluble starch, turbidity) derived from many insoluble calcium.

  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).

<Birefringent particles>
The birefringent particles constituting the optical film of the present invention are not particularly limited as long as they are acicular and birefringent particles (hereinafter also referred to as birefringent particles).

  As the birefringent particles, birefringent particles described in WO01 / 0253643 or JP-A-2004-109355 and JP-A-2006-317733 can be used.

For example, various carbonates such as calcium carbonate, strontium carbonate, magnesium carbonate, manganese carbonate, cobalt carbonate, zinc carbonate, barium carbonate, various oxides represented by titanium oxide, MgSO ₄ .5Mg (OH) ₂ .3H _{2 O, 6CaO · 6SiO 2 ·} H 2 O, 9Al 2 O 3 · 2B 2 O 3 birefringent whiskers of the like.

  For example, tetragonal, hexagonal and rhombohedral crystals are preferably uniaxial birefringent crystals, orthorhombic, monoclinic and triclinic crystals. These may be single crystals or polycrystals.

  Further, rod or short fiber particles of polystyrene or acrylic resin are also preferably used. For example, it may be a short fiber particle having a polystyrene resin or an acrylic resin and manufactured by finely cutting ultrafine fibers.

  These fibers are preferably stretched during the production process because they easily develop birefringence. The resin contained in these particles is preferably crosslinked.

  However, the present invention is not limited to these, and various types can be used as long as the above-described requirements such as size, shape, and aspect ratio are satisfied.

  These birefringent particles preferably have a major axis diameter (absolute maximum length) of 10 to 500 nm and an aspect ratio of 2 or more, particularly preferably an aspect ratio of 2 to 100 and 3 to 30. Further preferred.

  The aspect ratio is obtained from the absolute maximum length and the diagonal width of the particle by the following formula. This can be obtained from image data obtained by electron microscope observation of particles contained in the film.

Aspect Ratio = Absolute Maximum Length / Diagonal Width Here, the diagonal width is the shortest distance between two straight lines when the image of a particle projected by two straight lines parallel to the absolute maximum length is sandwiched.

  The birefringent particles may be surface-treated with a silane coupling agent, a titanate coupling agent, or the like.

  The birefringence of the birefringent particle is defined as follows. The refractive index for light polarized in the major axis radial direction, which is the absolute maximum length of the birefringent particles, is npr, and the average refractive index for light polarized in the direction orthogonal to the major axis radial direction is nvt. The birefringence Δn of the birefringent particle is defined by the following equation.

Δn = npr−nvt
That is, if the refractive index in the major axis diameter direction of the birefringent particles is larger than the average refractive index in the direction perpendicular to the birefringent particles, positive birefringence occurs, and vice versa.

  The absolute value of the birefringence of the birefringent 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. .

The birefringent crystal having positive _{birefringence, MgSO 4 · 5Mg (OH)} 2 · 3H 2 O, 6CaO · 6SiO 2 · H 2 O, 9Al 2 O 3 · 2B 2 O 3, TiO 2 ( rutile Type crystal). Examples of the birefringent crystal exhibiting negative birefringence include carbonate particles such as calcium carbonate and strontium 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.

  In the present invention, carbonate particles are preferable.

《Carbonate particles》
The carbonate particles can be produced by a uniform precipitation method or a carbon dioxide 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 strontium carbonate crystal can be obtained by bringing strontium ions dissolved in water into contact with carbonate ions. Carbonate ions can be obtained by adding carbon dioxide gas into a solution containing a strontium compound by a method such as bubbling carbon dioxide, or by adding a substance that generates carbonate ions to react or decompose.

  For example, strontium carbonate crystal particles can be produced by the method described in JP-A-2004-35347, and strontium carbonate particles obtained by this method can be preferably used as birefringent particles.

  Examples of the substance that generates carbon dioxide include urea, and strontium carbonate particles can be obtained by reacting carbon dioxide ions and strontium ions generated in combination with a hydrolase of urea.

  In order to obtain fine crystals, it is preferable to lower the temperature as much as possible. Cooling below the freezing point is preferable because fine crystal particles can be obtained. For example, it is also preferable to add an organic solvent such as ethylene glycol as a freezing point depressing substance, and it is preferable to add so that the freezing point is below 5 ° C below freezing point.

  Thereby, particles of strontium carbonate having an average particle size in the major axis direction of 500 nm or less can be obtained.

  Strontium carbonate is a biaxial birefringent crystal, and according to Japanese Patent Laid-Open No. 2004-35347, the refractive index in each optical axis direction is n (na, nb, nc) = (1.520, 1.666). , 1.669), and it is reported that the major axis direction of the needle-like crystal substantially coincides with the optical axis direction having a refractive index of 1.520.

  Therefore, it has a negative birefringence effect with respect to the orientation direction of the acicular crystal. Since the strontium carbonate crystal particles have a needle-like shape, they can be statistically oriented in a predetermined direction by applying a stress in a state of being dispersed in a viscous medium.

<Orientation of birefringent particles in optical film>
The birefringent particles of the present invention are contained in an amount of 1 to 30% by mass with respect to the optical film, and the average azimuth angle of the particles in the film is perpendicular or parallel to the film-forming direction of the optical film, and the average azimuth It is manufactured such that the average value H of the absolute value of the angle formed by the direction of the angle and each birefringent particle is within 30 °.

  The slow axis of the optical film of the present invention usually coincides with the axis in the direction perpendicular to the average azimuth angle of the birefringent particles. Here, the vertical or parallel direction includes a case where the direction is within ± 5 ° which is substantially perpendicular or parallel to the reference axis.

  The evaluation of the orientation state and the dispersion state of the birefringent particles in the film can be obtained using image data obtained by observing the particles in the film with an electron microscope.

  From the image data, the azimuth angle and the aspect ratio are determined for each birefringent particle. Particles having an aspect ratio of less than 2 such as foreign particles or broken particles are noises and are excluded from the calculation of the average azimuth, and are obtained for each particle having an aspect ratio of 2 or more.

  The angle with the reference axis when taking the absolute maximum length of the birefringent particles is taken as the azimuth angle. The reference axis can be set arbitrarily, but can be set, for example, in the width direction of the film. The azimuth angle of each birefringent particle was determined, and the average value was taken as the average azimuth angle.

  Next, the direction of the obtained average azimuth angle is set as a new reference axis, and for each birefringent particle, the angle difference between the azimuth angle of the particle and the average azimuth angle direction is obtained, and the average of the absolute value of the angle difference is obtained. Asked.

  This is the [average value H of the absolute value of the angle formed by the direction of the average azimuth and the azimuth of each birefringent particle]. H is within 30 degrees.

  A specific evaluation method will be described. The produced film was photographed at a magnification of 20,000 with a transmission electron microscope, and the image was read with a scanner Canon Scan FB 636U by Canon Inc. in 300 dpi monochrome 256 gradation.

  The read image was taken into the image processing software WinROOF ver 3.60 (manufactured by Mitani Corp.) installed in Endeavor Pro 720L (CPU: Athlon-1 GHz, memory: 512 MB), which is a personal computer manufactured by Epson Direct.

  As a pre-processing of the captured image, a 2 × 2 μm visual field range was extracted (automatic binarization of the image) to extract particles. Confirm that 90% or more of the particles are extracted on the screen after extracting the image of the particles, and if the extraction is not enough, manually adjust the detection level so that 90% or more of the particles are detected and extracted. Make adjustments.

  When the number of birefringent particles in the observation range was less than 1000, the same operation was performed for another 2 × 2 μm field of view until the total number of particles reached 1000 or more.

  The azimuth angle was measured for each birefringent particle in the image data extracted in this way. The azimuth angle of the birefringent particles will be described with reference to FIG.

  FIG. 1 shows an example of an image obtained by photographing a film containing birefringent particles at a magnification of 20,000 with a microscope and reading with a scanner. For each particle, the azimuth of the absolute maximum length (long axis direction) of the particle with respect to the reference axis is calculated. a1, a2 ... an.

  The average value A = ave (a1 to an) of these azimuths is calculated and set as the average azimuth. As the number of particles (n), 1000 or more are measured, and an average value is calculated.

  When this average azimuth is within ± 5 ° with respect to the film forming direction of the film, it is said to be parallel to the film forming direction (longitudinal direction). Similarly, when it is within ± 5 ° with respect to the direction (width direction) perpendicular to the film forming direction of the film, it is said to be in the direction orthogonal to the film forming direction of the film.

  Preferably, the average azimuth angle is preferably in the direction of ± 3 °, more preferably in the direction of ± 1 °, particularly preferably ± 0, with respect to the film forming direction or the width direction of the film. It is in the direction of 5 °.

  Further, [the average value H of the absolute value of the angle formed by the direction of the average azimuth angle and the azimuth angle of each birefringent particle] is within 30 °.

FIG. 2 illustrates H. In the figure, b1, b2, b3,..., Bn are angles formed by the average maximum azimuth direction of the absolute maximum length direction (major axis direction) of each birefringent particle,
H = ave (| b1 | ˜ | bn |)
Thus, an average value H of the absolute values is obtained. This is also measured for 1000 or more particles in the same manner as the calculation of A above.

  H is within 30 °, more preferably 2 to 26 °, more preferably 2 to 19 °, and most preferably 2 to 11 °.

(Measurement of scattering cross section)
From the absolute maximum length and diagonal width, the refractive index of the major axis of the particle, the average refractive index of the minor axis, and the refractive index of the resin, using the FDTD calculation software Lumeric Solutions, Inc. FDTD Solutions TM Release 4.0, by the FDTD method The scattering cross sections Sx and Sy of the selected particles were calculated. In the case of SrCO ₃ needle-like particles, the scattering cross section calculated under the condition that the polarized light is incident perpendicular to the long axis direction is Sx, and the random cross section area under the condition where the polarized light is incident parallel to the long axis direction is Sy.
<Method for producing optical film>
As a method for orienting birefringent particles in an optical film, a method of stretching the film to TD or MD at the time of film production (casting), or a dope flow at the time of casting, and orienting the particles along this flow. It is possible to take a method. Further, the orientation of particles can be promoted by an electric field or a magnetic field.

  As a method for producing an optical film containing these birefringent particles, a particle dispersion liquid containing at least the needle-like birefringence particles and a resin for dispersing the particles is prepared in advance, and then the particle dispersion liquid is used. The optical film can be obtained by a method for producing an optical film that is cast using a dope prepared by mixing a resin constituting the optical film with a solvent.

<Resin for dispersing birefringent particles>
When the birefringent particles of the present invention are dispersed in a resin, a dispersing resin may be used separately from the resin constituting the optical film.

  The dispersing resin preferably has a weight average molecular weight of 3,000 to 200,000, and more preferably a weight average molecular weight of 3,000 to 90,000.

  Specifically, homopolymers or copolymers having ethylenically unsaturated monomer units, acrylic acid or methacrylic acid ester homopolymers or copolymers, methacrylic acid methyl ester homopolymers or copolymers, cellulose It is preferably at least one selected from esters, cellulose ether polyurethane resins, polycarbonate resins, polyester resins, epoxy resins and ketone resins. The cellulose ester preferably has a total acyl group substitution degree of 2.0 to 2.8.

  Even if these resins are contained in a dope (resin concentration 15 to 30% by mass) which is a high concentration resin solution used for solution casting, a uniform film can be formed with little increase in haze. Resin.

  In the particle dispersion containing birefringent particles, the concentration of the dispersing resin is preferably 0.1 to 10% by mass. Moreover, it is preferable that the density | concentration of particle | grains in this dispersion liquid is 0.2-10 mass%.

  In the present invention, the viscosity of the particle dispersion is preferably controlled in the range of 10 to 500 mPa · s.

  Examples of the resin preferably used in the particle dispersion according to the present invention include a homopolymer or copolymer having an ethylenically unsaturated monomer unit, and more preferably polymethyl acrylate, polyethyl acrylate. Of acrylic acid or methacrylic acid ester such as polypropyl acrylate, polycyclohexyl acrylate, alkyl acrylate copolymer, polymethyl methacrylate, polyethyl methacrylate, polycyclohexyl methacrylate, alkyl methacrylate ester copolymer, etc. Homopolymers or copolymers, and acrylic or methacrylic acid esters are excellent in transparency and compatibility, and are homopolymers or copolymers having acrylic acid ester or methacrylic acid ester units, in particular acrylic acid or Methyl methacrylate unit Homopolymer or copolymer having preferred.

  Specifically, polymethyl methacrylate is preferable. An alicyclic alkyl ester of acrylic acid or methacrylic acid such as polyacrylic acid or polymethacrylic acid cyclohexane is preferred because of its advantages such as high heat resistance, low hygroscopicity and low birefringence.

  Examples of other resins include cellulose ester resins having a substitution degree of acyl groups of 1.8 to 2.80 such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate; cellulose methyl ether, cellulose ethyl ether, Cellulose ether resins having an alkyl group substitution degree of 2.0 to 2.80, such as cellulose propyl ether; Polyamide resins of polymers of alkylene dicarboxylic acids and diamines; Polymers of alkylene dicarboxylic acids and diols, alkylene diols and dicarboxylic acids Polyester resin such as polymer of cyclohexanedicarboxylic acid and diol, polymer of cyclohexanediol and dicarboxylic acid, polymer of aromatic dicarboxylic acid and diol; polyvinyl acetate, vinyl acetate copolymer, etc. vinegar Polyvinyl acetal resins such as polyvinyl acetal and polyvinyl butyral; epoxy resins as shown below, ketone resins as shown below, polyurethanes as shown below such as linear polymers of alkylene diisocyanate and alkylene diol Resins and the like can be mentioned, and it is preferable to contain at least one selected from these.

  As an epoxy resin, a compound having two or more epoxy groups in one molecule is a resin formed by a ring-opening reaction. The following epoxy resins can be listed as typical commercial products. There is Araldide EPN1179 and Araldide AER260 (manufactured by Asahi Ciba Co., Ltd.). Araldide EPN1179 has a weight average molecular weight of about 405. n represents the degree of polymerization.

  Further, the ketone resin is obtained by polymerizing vinyl ketones, and examples thereof include the following ketone resins. As typical commercial products, Hilac 110 and Hilac 110H (Hitachi Chemical Co., Ltd.) ) Made). n represents the degree of polymerization.

  For the above resins, the present inventors have further devised a dispersion method as will be described later, and even if they are outside the above weight average molecular weight range (less than 3,000, more than 90,000). It has been found that the particle dispersibility can be improved and a particle dispersion with little cohesion can be formed.

  The above resin can be used without limitation on the weight average molecular weight, but the one having a smaller weight average molecular weight is easier to use, and the weight average molecular weight is preferably in the range of about 300 to 40,000, more preferably 500 to 20,000. Preferably, 5,000 to 20,000 is more preferable.

  The smaller the weight average molecular weight, the better the compatibility with the dope resin and the dispersibility of the particles, and the larger the weight average molecular weight, the more the viscosity of the particle dispersion can be adjusted with a small amount of resin.

<Other dispersants>
The particle dispersion or dope used in the present invention preferably contains a dispersant. The amount of the dispersant added is preferably 0.002 to 2% by mass, more preferably 0.01 to 1% by mass with respect to the resin constituting the optical film. As the dispersant, a polymer dispersant is particularly preferably used, and a nonionic polymer dispersant, an anionic polymer dispersant, and a cationic polymer dispersant are appropriately selected.

  In order to uniformly disperse solid particles in a solvent or a polymer composition solution, it is known that a polymer dispersant that adsorbs to the solid particles is used. The polymer dispersant forms an adsorbing layer on the surface of the solid particles, and the adsorbing layer causes repulsion between the solid particles, thereby preventing aggregation of the solid particles.

  Examples of the polymer used as the polymer dispersing agent for dispersing the particles include a homopolymer composed of a single monomer, a random copolymer composed of a plurality of monomers, etc. A complex that includes both a part that interacts and adsorbs with particles and a part that solvates and dissolves into the liquid from the surface of a solid particle in one molecule, and the functions of these two functions are shared within one molecule. A polymer dispersant having a structure has been devised, and specifically, a comb polymer in which the functions of these two functions are shared is known as a good polymer dispersant.

  In the present invention, these polymer dispersants are preferably contained in the dope or particle dispersion.

  Examples of the polymer dispersant include a polymer dispersant described in general formula (I) or general formula (II) in JP-A No. 2001-162934, a polymer dispersant described in JP-A No. 2004-97955, and JP-A-2001-2001. 260265, an anionic polymer dispersant described in paragraphs [0024] to [0027], a mixture of polyoxypropylene fatty acid alkanolamide compounds described in JP-A-8-337560, and JP-A-9-20740 Polyoxypropylene fatty acid isopropanolamide mixture, dispersants described in JP-A-9-192470 and JP-A-9-313917, dispersants described in JP-A-11-197485, dispersants described in JP-A-2004-89787, etc. However, it is not limited to only these.

  For example, there are F-1000, KF-1525, Hinoact T6000, 7000, 8000, 8000E, KM-1300M (manufactured by Kawaken Fine Chemical Co., Ltd.). In addition, polyethylene glycol, polypropylene glycol, polyvinyl methyl ether, polyvinyl acetate, polyvinyl alcohol, poly N-vinyl pyrrolidone, poly (2-methyl-2-oxazoline), poly (2-ethyl-2-oxazoline) and these Examples include macromers containing a polymer component.

  The content of the dispersant is preferably 0.0001 to 1% by mass in the dope or particle dispersion.

<Organic solvent>
Organic solvents useful for forming a resin solution or dope by dissolving the resin constituting the optical film of the present invention 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, 1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol and the like can be mentioned.

  When these organic solvents are used for the resin, a dissolution method at room temperature can be used, but insoluble materials can be removed by using a dissolution method such as a high-temperature dissolution method, a cooling dissolution method, or a high-pressure dissolution method. Since it can reduce, it 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.

  The dope of the cellulose ester resin according to the present invention preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent.

  These are gelling solvents that make dope film (web) gel when the dope is cast on a metal support and the solvent starts to evaporate and the ratio of alcohol increases, making the web strong and easy to peel off from the metal support. When these ratios are small, there is also a role of promoting the dissolution of the cellulose ester of the non-chlorine organic solvent.

  Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, 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 ester resins alone.

  The resin concentration in the dope is preferably adjusted in the range of 15 to 30% by mass and the dope viscosity in the range of 100 to 500 Pa · s in order to obtain good film surface quality.

  Additives added to the dope include plasticizers, ultraviolet absorbers, antioxidants, dyes, particles and the like.

<Other additives>
In the present invention, additives other than particles may be added when preparing the resin solution, or may be added when preparing the particle dispersion.

  It is preferable to add a plasticizer, an antioxidant, an ultraviolet absorber, or the like that imparts heat and moisture resistance to the polarizing plate used in the liquid crystal image display device. The additive will be described below.

《Plasticizer》
To the resin solution or dope according to the present invention, a compound known as a so-called plasticizer is added 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 as the cellulose ester resin.

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

  Examples of carboxylic acid esters include phthalic acid esters and citric acid esters; phthalic acid esters such as dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethyl hexyl phthalate; and citrate esters such as acetyl triethyl citrate and acetyl citrate. 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.

  In the case of a cellulose ester resin, a polyhydric alcohol ester is also preferably used.

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

Formula (1) R _1- (OH) n
However, R ₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the 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.

  It is preferable that these compounds are contained so that it may become 1-30 mass% with respect to a cellulose ester, Preferably it is 1-20 mass%. 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 resins, and ketone resins , Toluenesulfonamide resin, ester of polyhydric alcohol and carboxylic acid described in JP-A-2003-96236, compound described in general formula (1) of JP-A-2003-165868, polyester weight described in JP-A-2004-292696 Examples thereof include a coalescence or a polyurethane polymer. These additives can be contained in the dope or particle dispersion.

<Ultraviolet absorber>
The optical film of the present invention can contain an ultraviolet absorber. 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-2002-169020, 2002-2002. Polymer ultraviolet absorbers described in 47357, 2002-363420, and 2003-113317 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 ultraviolet absorber can be added to the dope without limitation as long as the ultraviolet absorber dissolves in the dope. In the present invention, the ultraviolet absorber is cellulose such as methylene chloride, methyl acetate, dioxolane. A dope by adding a good solvent for an ester or a mixed solvent of a good solvent and a poor solvent such as a lower aliphatic alcohol (methanol, ethanol, propanol, butanol, etc.) and adding it to a cellulose ester solution as an ultraviolet absorber solution. Is preferred.

  In this case, it is preferable to make the dope solvent composition and the solvent composition of the ultraviolet absorber solution as close as possible to each other. The content of the ultraviolet absorber is 0.01 to 5% by mass, particularly 0.5 to 3% by mass.

"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%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the resin constituting the optical film.

《Matting agent》
In the present invention, in addition to the birefringent particles, particles can be further contained in the optical film as a matting agent. Thereby, conveyance and winding can be facilitated.

  The particle size of the matting agent is preferably primary particles or secondary particles of 10 nm to 0.1 μm. A substantially spherical matting agent having a primary particle aspect ratio of 1.1 or less is preferably used.

  As the particles, those containing silicon are preferable, and silicon dioxide is particularly preferable. Examples of the silicon dioxide particles preferable for the present invention include, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.) manufactured by Nippon Aerosil Co., Ltd. What is marketed by a brand name can be mentioned, Aerosil 200V, R972, R972V, R974, R202, R812 can be used preferably.

  Examples of polymer particles include silicone resin, fluorine resin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. Examples include Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.). Can do.

  The silicon dioxide particles preferably have a primary average particle diameter of 20 nm or less and an apparent specific gravity of 70 g / L or more. The average diameter of primary particles is more preferably 5 to 16 nm, further preferably 5 to 12 nm. A smaller primary particle average diameter is preferred because haze is low. The apparent specific gravity is preferably 90 to 200 g / L or more, and more preferably 100 to 200 g / L or more. Higher apparent specific gravity makes it possible to produce a high-concentration particle dispersion, which is preferable because no haze or aggregates are generated.

The addition amount of the matting agent in the present invention is preferably 0.01 to 1.0 g, more preferably 0.03 to 0.3 g, and further preferably 0.08 to 0.16 g per 1 m ² of the optical film.

<Surfactant>
The dope or particle dispersion used in the present invention preferably contains a surfactant, and is not particularly limited to phosphoric acid, sulfonic acid, carboxylic acid, nonionic, cationic 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 mass, and more preferably 0.01 to 1% by mass with respect to the resin constituting the optical film. If the addition amount is less than 0.001% by mass, the effect of addition cannot be sufficiently exerted, and if the addition amount exceeds 2% by mass, precipitation or insoluble matter may occur.

  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 ) ₈ —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 ^−, etc. Absent.

<Peeling accelerator>
Furthermore, a peeling accelerator for reducing the load during peeling may be added to the dope. Of these, surfactants are effective, and phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic-based, cationic-based and the like 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 a polyethoxylated phosphate ester as a peeling accelerator.

  JP-A-61-69845 discloses that a mono- or di-phosphoric acid alkyl ester in which a non-esterified hydroxy group is in the form of a free acid can be rapidly removed 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; M ₁ is an alkali metal, ammonia, or a lower alkyl amine. Yes; B ₁ and B ₂ are each 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.

  The cellulose acylate film contains at least one release agent represented by the formula (2) or (3).

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 (for example, butyl, hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, eicosanyl, docosanyl, myricyl). , 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 phen Nyl, diisononylphenyl, dodecylphenyl, isopentadecylphenyl).

  Among 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 mass in the dope. More preferably, it is 0.005-1 mass%, More preferably, it is 0.01-0.5 mass%.

  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. By containing these, it becomes easy to align the orientation of the particles.

《Other general additives》
In addition, thermal stabilizers such as inorganic particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, and alumina, and salts of alkaline earth metals 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 production of a cellulose ester resin, which is preferable among the optical films of the present invention, by a solution casting method will be described as a representative example of the optical film of the present invention. Here, the solution casting film forming method will be described with reference to FIG.

  FIG. 4 is a diagram showing an example of a process schematically showing a dope preparation process, a casting process, and a drying process of the solution casting film forming method according to the present invention.

(1) Particle Dispersion Preparation Step The method for preparing the particle dispersion of the present invention is not particularly limited, but is preferably performed by the following method a) or b).

  a) An organic solvent and a particle-dispersing resin are introduced into a dissolving kettle and dissolved by stirring to obtain a resin solution. Separately, a mixed liquid of an organic solvent and particles is transferred to a disperser such as a Menton gorey or a sand mill by a liquid feed pump and pre-dispersed.

  This is added to the resin solution, stirred and agglomerated with a filter, and stocked as a particle dispersion (slightly different from FIG. 4). The prepared particle dispersion may be further repeatedly dispersed and filtered several times.

  b) Add an organic solvent and a resin in a dissolution vessel, dissolve with stirring to obtain a resin solution, add particles to the resin solution, and disperse it with a disperser (not shown) such as a manton gorin or a sand mill. It is sent to a filter by a liquid feed pump to remove aggregates to obtain a particle dispersion (the same operation may be repeated several times).

  Then, the particle dispersion is transferred from the switching valve to the stock tank. After static deaeration, the particle dispersion is transferred by a liquid feed pump (for example, a pressurized metering gear pump), filtered by a filter and transferred by a conduit.

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

  Dispersers used in preparing the particle dispersion as described above of the present invention 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 particles and a solvent are mixed at high speed through a narrow tube.

For example, the maximum pressure condition inside the apparatus is preferably 9.8 × 10 ⁶ Pa or more in a thin tube having a tube diameter of 1 to 2000 μm 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 dispersion apparatus include an ultrahigh-pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a nanomizer manufactured by Nanomizer, or UltraTurrax, and other Manton Gorin type high-pressure dispersion apparatuses such as Izumi Food. Examples thereof include a homogenizer manufactured by Machinery, UHN-01 manufactured by Sanwa Machinery Co., Ltd., and the like.

  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 thus prepared particle dispersion by filtration. A dope is prepared using the obtained particle dispersion.

(2) Cellulose ester solution preparation process In this invention, dope is prepared by mixing the particle dispersion liquid previously prepared by said method, a solvent, and cellulose ester. Specifically, it is preferable to add and mix a part of the solvent and the particle dispersion into the dissolution vessel, and then add and dissolve the remaining solvent and cellulose ester with stirring. Additives such as plasticizers can be added later to the melting pot or later.

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

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

  An additive such as cellulose ester and plasticizer is dissolved in an organic solvent mainly composed of a good solvent for the cellulose ester with 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 particle dispersion, the cellulose ester and the solvent in the dissolution vessel is dissolved in the cellulose ester and then sent to a filter by a pump and filtered.

  Filtration is preferably carried out using the cellulose ester solution with an appropriate filter medium such as filter paper for filter press.

  As the filter medium in the present invention, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matter, etc., but if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged, and absolute filtration A filter medium with an 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.

  Examples of filter paper include No. of Azumi Filter Paper Co., Ltd., a commercially available product. 244, 277, etc. can be mentioned and used preferably.

  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 a stock tank, defoamed and then used for casting.

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

  For example, FIG. 4 shows an example of the step of adding the particle dispersion in-line. The particle dispersion is merged with the cellulose ester solution (or may be referred to as a dope stock solution) in the merge tube 20. A filter is disposed immediately before the merging pipe 20. For example, a lump containing birefringent particles or a large foreign matter generated from a path due to exchange of the filter medium or the like is removed from the particle dispersion or dope stock solution being fed. Can be removed.

  Here, a metal filter having solvent resistance is 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 metal filter media having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80% include, for example, NF-10, NF-12, and NF-13 of Fine pore NF series manufactured by Nippon Seisen Co., Ltd. Can be mentioned.

  In the present invention, the absolute filtration accuracy is defined as follows. Glass beads and pure water of test powders having different particle diameters specified in JIS Z 8901 are put into a beaker, and suction filtration is performed with an apparatus as shown in FIG. 5 while stirring with a stirrer.

  FIG. 5 is a diagram schematically showing an apparatus for measuring the absolute filtration accuracy. Here, A represents a filter medium sample to be measured, B represents a liquid to be filtered, and C represents a filtrate.

  The to-be-filtrated liquid B is stirred by the stirrer S, and is filtered by the low pressure vacuum pump P while maintaining the pressure from atmospheric pressure to −4 kPa. V is a valve that can be opened and closed, and M is a manometer.

  At this time, the number of glass beads in the liquid to be filtered B and the filtrate C is observed with a microscope, and the particle collection rate is determined by the following equation. The particle diameter when the particle collection rate was 95% was defined as absolute filtration accuracy.

Particle collection rate (%) = (number of filtrates−number of filtrates) / (number of filtrates) × 100
The porosity of the filter medium is preferably 60 to 80%, 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 low surface tension solvent, remove the air in the filter medium, calculate the amount of pores in the filter medium from the increased amount of solvent, and divide by the volume of the filter medium. can do.

(3) In-line addition process When preparing a dope by mixing a particle dispersion, a cellulose ester, and a solvent in advance in a dissolution vessel, it is usually not necessary to add the particle dispersion in-line.

  However, if desired, all or part of the particles can be mixed in-line. The in-line addition process will be described with reference to FIG. 4. A cellulose ester solution (sometimes referred to as a dope stock solution) and a particle dispersion are respectively transferred by liquid feed pumps 5 and 14, filtered by filters 6 and 15, and conduit 8 And 16 are transported and the two liquids are joined together by the joining pipe 20.

  Since the 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 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.

  In the present invention, the film is stretched in any of the drying steps described later, and the birefringence of the stretched film is measured. The content of particles having needle-like birefringence contained in the dope according to the measurement result of the birefringence. Is preferably adjusted.

  In other words, when it is confirmed that the measurement result of birefringence deviates from the desired birefringence value, it is considered that the cause is that the content of particles is low. It is preferable to further add particles to the dope stock solution in order to compensate for this.

  An in-line addition process is preferably used as a method of adding the particles at this time to the dope stock solution. Specifically, a method of adjusting the content of acicular and birefringent particles in the dope by adding an acicular and birefringent particle dispersion to the dope in-line.

  Specifically, it can be added by a method using the in-line mixer. As the particle dispersion added in-line (sometimes referred to as an in-line additive), the particle dispersion prepared by the above-described method can be used as it is.

  Or the liquid which adjusted the particle | grain density | concentration and the cellulose-ester density | concentration by adding a solvent, a cellulose-ester solution, another additive etc. further can be used as an in-line additive liquid.

  The in-line additive liquid preferably contains particles at a concentration of 1.1 to 50 times the particle concentration in the dope used for casting.

  The birefringence of the film after stretching is measured, and the particle content in the dope is adjusted by increasing or decreasing the amount of the particle additive liquid according to the measurement result of the birefringence. It is preferable to control the birefringence value to a desired value.

  The particle content in the dope can be increased or decreased by changing the mixing ratio of the particle additive solution and the dope stock solution. In order to change the mixing ratio, the ratio of the amount of the particle additive solution and the amount of the dope stock solution may be changed.

  In the dope prepared by the step (2) or the steps (2) and (3), the solid content concentration in the dope is preferably adjusted to 15% by mass or more, and particularly preferably 18 to 30% by mass. If the solid content concentration in the dope is too high, the viscosity of the dope becomes too high, and sharkskin or the like may occur during casting to deteriorate the film flatness. Therefore, it is preferably 30% by mass or less.

(4) Casting process On the metal support 31 such as an endless metal support 31, for example, a stainless steel belt or a rotating metal drum, the dope prepared up to the previous process is fed to the die 30 and transferred infinitely. This is a step of casting the dope from the die 30 at the casting position.

  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 may be provided on the metal support 31, and the dope amount may be divided and stacked.

  In adjusting the film thickness, it is preferable to control the dope concentration, the pumping amount, the slit gap of the die base, the extrusion pressure of the die, the speed of the metal support and the like 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.

  The surface temperature of the metal support 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. More preferably, the temperature is set to a temperature of

  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.

  Although the more preferable range of the temperature of a support body is dependent on the organic solvent to be used, it is 20-55 degreeC, and the more preferable range of solution temperature is 35-45 degreeC.

(5) Solvent evaporation step The web 32 can be peeled from the metal support 31 by heating the web (referred to as the dope film after casting the dope on the metal support) 32 on the metal support 31. This is a step of evaporating the solvent until.

  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 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, 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 tends to be lost, or a slip or vertical stripe due to the peeling tension is likely to occur, and the residual solvent amount at the time of peeling is 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.

  The measurement is performed by gas chromatography connected to a headspace sampler. In the present invention, gas chromatography 5890 type SERISII and headspace sampler HP7694 type manufactured by Hewlett-Packard Company were used and the measurement was performed under the following measurement conditions.

Headspace sampler heating conditions: 120 ° C, 20 minutes GC introduction temperature: 150 ° C
Temperature rise: 40 ° C, hold for 5 minutes → 100 ° C (8 ° C / min)
Column: J-W DB-WAX (inner diameter 0.32 mm, length 30 m).

(7) Drying step After peeling, generally, the web 32 is dried using a roll drying device 35 that alternately conveys the web 32 through a plurality of rolls and a tenter device 34 that grips and conveys both ends of the web 32. . In FIG. 4, the roll drying device 35 is arranged after the tenter device 34, but is not limited to this arrangement.

  As a drying means, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. Too rapid drying tends to impair the flatness of the finished 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 cellulose ester film according to the present invention is formed into a film by a casting process after preparing a dope to which birefringent particles are added. As a method for orienting the added birefringent particles, the film is formed by TD or MD at the time of film production. A method of stretching in the direction or a method of making a dope flow during casting and orienting birefringent particles along this flow can be employed. Further, the orientation of particles can be promoted by an electric field or a magnetic field.

  Hereinafter, a specific method for orienting birefringent particles will be described as a representative example in which a cellulose ester resin is used.

  In this invention, MD represents the film forming direction of a cellulose-ester film, and TD represents the direction orthogonal to the film-forming direction within the surface of a cellulose-ester film. Therefore, in the case of a roll-like cellulose ester film, MD is the film longitudinal direction and TD represents the film width direction.

<Method of arranging birefringent particles in TD direction>
The present invention can be created by the following manufacturing method.

  (A) A method for producing a needle-like cellulose ester film containing birefringent particles by a solution casting method, wherein needle-like particles having birefringence, cellulose ester, and a dope containing a solvent are introduced from a nozzle. A cellulose ester film characterized in that, when extruding onto a casting support, the dope is cast onto the casting support while moving the nozzle in a direction not parallel to the moving direction of the casting support. Production method.

In this case, it is preferable that the plurality of nozzles are arranged in the width direction (FIG. 6A).
Therefore, the dope is pushed out to the casting support while reciprocating or vibrating the coater in which the nozzle is arranged in a direction perpendicular to the moving direction of the casting support (FIG. 6B). Orient the refractive particles.

  Using a coater provided with the nozzle or a normal die, the dope is cast by overlapping the casting by casting the cover layer by successive casting to smooth the dope film on the casting support. preferable.

  (B) A method for producing a needle-like cellulose ester film containing birefringent particles by a solution casting method, wherein the needle-like birefringent particles, cellulose ester, and a dope containing a solvent are obtained from a die. A method for producing a cellulose ester film, wherein a die used for extrusion onto a casting support has a structure in which a dope flows in a direction not parallel to the direction of movement of the casting support in the die .

  For example, a die in which a dope supply unit and a dope discharge unit are arranged in a direction not parallel to the moving direction of the casting support is used (FIG. 7).

  Preferably, the dope supply unit and the dope discharge unit are arranged in a direction substantially orthogonal to the moving direction of the casting support in the die.

  Thus, the dope flows in a direction that is not parallel to the moving direction of the casting support, and a part of the flow is discharged from the die onto the casting support. Preferably, the dope once discharged from the dope discharging unit is circulated and returned to the dope supplying unit again.

  Thereby, the birefringent particles in the dope discharged onto the casting support can be oriented.

  This can also be smoothed by casting another dope by using another coater (cover layer). In this case, it is desirable that the structure of the coater for casting the cover layer is symmetrical with respect to the MD direction with respect to the coater that has been cast previously. Thereby, the alignment can be made uniform.

  Moreover, you may provide a groove | channel in the direction which is not parallel with the moving direction of a casting support body inside the slit of die | dye (FIG. 8 (a)). As a result, the dope in the state where the birefringent particles are oriented in the TD direction is cast by allowing the flow along the grooves during casting inside the die. Also in this case, it is preferable that the dope is cast by successive casting (cover layer) by using another die having grooves in the slit in the opposite direction to make the orientation uniform and smooth (FIG. 8). (B)).

  (C) A method for producing a cellulose ester film containing needle-like particles having birefringence by a solution casting method, wherein needle-like particles having birefringence, cellulose ester, and a dope containing a solvent are cast. A method for producing a cellulose ester film comprising rubbing on a support for use in a direction that is not parallel to the moving direction of the casting support (that is, pressing a member that determines the direction of the layer).

  The member to be rubbed is not limited, but includes, for example, a gravure roll having a hatched line described later, an orientation belt provided separately, and the like. This imparts a shearing force to the dope, thereby orienting the birefringent particles.

Then, as this one aspect,
(D) A method for producing a cellulose ester film containing needle-like and birefringent particles by a solution casting method, in which needle-like particles having birefringence and cellulose ester and a dope containing a solvent are cast. A cellulose ester film characterized by using a gravure roll to cast on a support for use so that the dope is rubbed (pressed) in a direction not parallel to the moving direction of the cast support. Manufacturing method.

  In this method, gravure rolls with diagonal lines are used. In FIG. 9, the dotted line indicates the hatched groove on the gravure roll.

  The dope cast on the support is cast so that a gravure is formed in a lateral direction or an oblique direction by a gravure roll. Specifically, the rotational speed of the casting support and the gravure roll is controlled by using a slanted gravure roll as shown in the figure so that the gravure is noticed in the lateral direction or in the oblique direction.

  If it is 1: 1 with the web (rotational speed of gravure roll and web conveyance speed are in a state where there is no difference in peripheral speed), the gravure roll will be a diagonal line, but the peripheral speed difference should be given. Since the angle of the slanted line changes, the rotation speed of the casting support and the gravure roll can be adjusted so that the gravure can be seen sideways.

  The gravure roll may be provided in a direction orthogonal to the film forming direction or may be provided at an angle.

  (E) A method for producing a needle-like cellulose ester film containing birefringent particles by a solution casting method, wherein the needle-like particles having birefringence, a cellulose ester and a dope containing a solvent are added to a die. A cellulose ester characterized by pressing a dope on a casting support by a member that moves in a direction not parallel to the moving direction of the casting support when casting on the casting support. A method for producing a film.

  The member that moves in a direction that is not parallel to the moving direction of the casting support is an orientation belt.

  As shown in FIG. 10, the surface of the cast web is rubbed with an alignment belt as an example of the member.

  It is preferable that the surface of the alignment belt has a structure that promotes alignment by forming grooves like the gravure roll. The groove of the alignment belt is cut obliquely with respect to the moving direction of the alignment belt (FIG. 10A). In this case, as in the case of the gravure roll, the orientation can be adjusted horizontally by adjusting the moving speed of the alignment belt and the casting speed of the dope (that is, the moving speed of the casting support).

  Further, the grooves of the alignment belt may be cut along the belt rotation direction. In this case, the alignment belt should be arranged at an angle so that the rotation direction of the alignment belt is not parallel to the web conveyance direction. Thus, the same effect can be obtained (FIG. 10B).

  The grooves cut in the gravure rolls are spaced in the range of 25 to 250 lines / inch (2.54 mm), preferably 50 to 150 lines / inch, and the engraving depth is 30 to 500 μm for effective orientation. The engraving angle is preferably in the range of 45 ° ± 15 °.

  The same applies to a groove cut in the slit of the die or a groove cut on the orientation belt.

  (F) A method for producing a cellulose ester film, wherein a cellulose ester solution containing needle-like particles having birefringence is cast on a support, the web is stretched in a state containing a solvent, and then dried. .

  After peeling off the web containing the solvent, a film in which needle-like particles are oriented can be obtained by transverse stretching. Further, for example, a resin casting support may be used, and the web containing the solvent may be stretched together with the support.

  However, this method is preferably used in combination with the above method because the orientation may not be sufficient only by stretching.

  By orienting the birefringent particles in the TD direction by the method as described above, a cellulose ester film particularly preferably used for a liquid crystal display device in a transverse electric field switching mode can be produced.

  Next, a method for arranging birefringent particles in the MD direction will be described.

<Method of arranging birefringent particles in MD direction>
(G) A method for producing a cellulose ester film containing needle-like and birefringent particles by a solution casting method, wherein needle-like particles having birefringence, cellulose ester, and a dope containing a solvent are formed from a die. Production of a cellulose ester film characterized by casting a dope extruded in a laminar flow in a direction parallel to the direction of movement of the casting support when it is extruded onto the casting support. Method.

Laminar flow and turbulent flow are defined by Reynolds (Re) number. The Reynolds number is the typical length of an object in the flow, D, velocity U, density ρ, viscosity η,
Re = DUρ / η
Is defined by a dimensionless number.

  Generally, when Re <2300, it is called laminar flow, 2300 <Re <3000 is called a transition region, and when Re> 3000, it is called turbulent flow. In the present invention, the particle size, casting speed, dope density and the like are adjusted so that the Reynolds number is 2300 or less.

  For example, FIG. 11 shows a cross-sectional view of a die used for casting. For example, by slightly narrowing the slit interval (usually 400 to 1000 μm), for example, 350 μm or less, and making the slit length longer than usual (10 to 30 mm), For example, when the slit width is set to 35 mm or more, the birefringent particles in the dope can be oriented by utilizing a laminar flow inside the die.

  Although not shown in the figure, it is preferable to apply shear force to the dope by aligning the slit interval in multiple stages inside the die, thereby aligning the birefringent particles.

  (H) A method for producing a needle-like cellulose ester film containing birefringent particles by a solution casting method, wherein needle-like particles having birefringence, cellulose ester, and a dope containing a solvent are obtained from a die. When extruding onto a casting support, the dope ribbon extruded in a laminar flow in a direction parallel to the moving direction of the casting support is cast so as to be pulled by the casting support. A method for producing a cellulose ester film.

  This is shown in FIG. In the figure, the ribbon is stretched by pulling the ribbon in the MD direction based on the difference between the dope discharge speed and the conveyance speed of the support (belt).

  Similarly to (F), the orientation can be obtained in the same manner by stretching the web in the MD direction while containing a solvent.

  However, in this method, since sufficient alignment may not be obtained, it is preferable to use in combination with other methods. Further, this method cannot be oriented in the TD direction.

  Next, the stretching process in the present invention will be described.

(8) Stretching process (also called tenter process)
The cellulose ester film of the present invention can exhibit birefringence by stretching. A film containing a solvent can be stretched during the production of the solution casting method, or a film in a state where the solvent is dried can be stretched.

  The stretching temperature is preferably performed at a glass transition temperature of the film of −20 ° C. to a temperature at which the film flows. Here, the glass transition temperature of the film can be measured by a known method. Stretching can be performed in the film forming direction or the width direction, but in the present invention, it is preferable to stretch at least in the width direction.

  By stretching, the cellulose ester resin exhibits birefringence, and the ratio of birefringent particles oriented in the stretching direction increases. The birefringence value of the cellulose ester film is considered to be a value obtained by combining the birefringence due to the cellulose ester resin and the birefringence due to the orientation of needle-like particles having birefringence.

  As a result, it has become possible to stably produce a cellulose ester film having characteristics that were conventionally difficult to produce.

  The cellulose ester film of the present invention uses needle-like particles having negative birefringence, so that it is slow in the direction perpendicular to the width direction, that is, in the film forming direction, although it is stretched in the width direction. It can be set as the film which has an axis | shaft.

  The stretching process will be described in more detail. The draw ratio at the time of producing the cellulose ester film of 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, while being able to obtain the cellulose-ester film which has the retardation value of this invention preferably, a cellulose ester film with favorable planarity 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 compensation film according to the present invention will be described with reference to FIG.

  In FIG. 13, step A is a step of gripping the film that has been conveyed from the film conveyance step D0 (not shown). In the next step B, as shown in FIG. In step C, stretching is completed, and the film is conveyed while being gripped.

  It is preferable to provide a slitter for cutting off the end in the film width direction after the film is peeled off and before the start of the process B and / or immediately after the process C. In particular, it is preferable to provide a slitter that cuts off the film edge immediately before the start of the step A.

  When the same stretching is performed in the width direction, particularly when the film edge is cut off before the start of step B and the condition in which the film edge is not cut is compared, the former is more optically retarded in the width direction of the film. The effect of improving the axial distribution (hereinafter referred to as orientation angle distribution) 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 width stretching step B.

  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 a direction in which stretching stress is directly applied when performing a stretching operation. 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. Since width stretching is performed with the Rth and Ro values at a constant ratio and with a good orientation angle distribution, there is a preferred film temperature relative relationship in steps A, B, and C. When the film temperatures at the end points of Steps A, B, and C 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 step B is preferably in the range of 0.5 to 10 ° C./s in order to improve the orientation angle distribution.

  The stretching time in step B is preferably a short time in order to reduce the dimensional change rate under the conditions of 80 ° C. and 90% RH. However, the minimum required stretching time range is defined from the viewpoint of film uniformity.

  Specifically, the range is preferably 1 to 10 seconds, and more preferably 4 to 10 seconds. Moreover, the temperature of the process B 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 the conditions of 80 ° C. and 90% RH, the stretching speed in the width direction in the step B may be constant or may be changed. 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 film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 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 film is also reduced.

  In step C, it is preferable to relax in the width direction in order to suppress dimensional changes. 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.

  After the treatment in the tenter process, it is preferable to further provide a post-drying process (hereinafter referred to as process D1). 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 step D1, it is preferable that the atmospheric temperature distribution in the width direction of the film is small from the viewpoint of improving the uniformity of the film. Within ± 5 ° C is preferable, within ± 2 ° C is more preferable, and within ± 1 ° C is most preferable.

  The film transport tension in the step D1 is affected by the physical properties of the dope, the peeling and the residual solvent amount in the step D0, the temperature in the step D1, etc., but is preferably 120 to 200 N / m, and 140 to 200 N / m. Further preferred. 140 to 160 N / m is most preferable.

  In order to prevent the film from stretching in the transport direction in step D1, it is preferable to provide a tension cut roll. After drying, it is preferable to provide a slitter and cut off the end portion before winding to obtain a good winding shape.

  In this invention, when a cellulose-ester film is elongate, it is preferable that the slow axis of a cellulose-ester film is orthogonal to a conveyance direction. This can form a slow axis in the width direction by continuously stretching a cellulose ester film containing needle-like negative birefringent particles in the width direction.

  A long polyvinyl alcohol (hereinafter abbreviated as PVA) polarizer has an absorption axis in the longitudinal direction, and the slow axis of a cellulose ester film applied as a polarizing plate protective film is in the longitudinal direction. It becomes the arrangement which can be pasted directly. This is a preferable configuration from the viewpoint of productivity of the polarizing plate.

(9) Winding step This is a step of winding the web after drying as a film. By setting the amount of residual solvent to finish drying to 0.5% by mass or less, preferably 0.1% by mass or less, a film having good dimensional stability can be obtained.

  The winding method may be a commonly used winder, and there are methods for controlling the tension such as the constant torque method, constant tension method, taper tension method, and program tension control method with constant internal stress. That's fine.

  The amount of residual solvent can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point, and N is the mass when M is dried at 110 ° C. for 3 hours.
<Physical properties of optical film>
The film thickness of the optical film of the present invention 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, particularly 40 to 40 μm. A range of 80 μm is preferred.

<Retardation>
The optical film of the present invention is characterized in that the retardation value Ro represented by the following formula (i) satisfies the optical value of 50 nm ≦ Ro ≦ 500 nm. Preferably, 100 nm ≦ Ro ≦ 300 nm. Rth is not defined with respect to the effect of the present invention, but −150 nm ≦ Rth ≦ 100 nm.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = {(nx + ny) / 2−nz} × d
Here, nx, ny, and nz are in-plane refractive indices at 590 nm. Said Ro can be calculated | required by performing retardation measurement of wavelength 590nm in 23 degreeC and 55% RH environment using automatic birefringence meter KOBRA-21ADH (made by Oji Scientific Instruments).

  Moreover, since nx, ny, and nz can be known, the accurate slow axis and fast axis of the optical film can be obtained simultaneously.

<Transmissivity>
The optical film of the present invention has a transmittance of 500 nm of preferably 85 to 100%, more preferably 90 to 100%, and most preferably 92 to 100%.

  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.

<Film thickness distribution in the width direction>
The optical film of the present invention preferably has a thickness distribution R (%) in the width direction of 0 ≦ R (%) ≦ 5%, more preferably 0 ≦ R (%) ≦ 3%. Particularly preferably, 0 ≦ R (%) ≦ 1%. The width is 1000 to 4000 mm.

<Haze value>
The optical film of the present invention preferably has a haze value of 2% or less, more preferably 1.5%, and most preferably 1% or less.

<Elastic modulus>
The optical film of the present invention preferably has an elastic modulus of 1.5 to 5 GPa, more preferably 1.8 to 4 GPa, and particularly preferably 1.9 to 3 GPa.

<Center line average roughness of cellulose ester film (Ra)>
In the optical film of the present invention, 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 center line average roughness (Ra) is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 4 nm or less.

<Other physical properties>
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. .
<Polarizing plate using optical film of the present invention>
The optical film of the present invention can be used as a polarizing plate protective film. In that case, it is preferable that the polarizing plate is on the viewing side with respect to the liquid crystal cell, and is disposed at a position between the polarizer and the liquid crystal cell.

  A polarizing plate using the optical film of the present invention can be produced by a general method.

  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.

  On the surface of the polarizer, one surface of the optical film of the present invention is bonded 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 optical 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. .

  The optical film of the present invention may be used on the other surface, or another polarizing plate protective film may be used. As another polarizing plate protective film used for the other surface, a commercially available cellulose ester film can be used.

  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.
<Liquid crystal display device>
The polarizing plate of the present invention is disposed on both the viewing side and the backlight side of the liquid crystal display device, and the optical film of the present invention is used as a polarizing plate protective film on at least the liquid crystal cell side of the polarizer. It is. In that case, the slow axis of the optical film on the liquid crystal cell side is arranged perpendicular to the transmission axis of the polarizer on the backlight side.
Here, the term “perpendicular or parallel” includes a case where the angle is within ± 5 ° which is a direction substantially perpendicular or parallel to the reference axis.

  The polarizing plate of the present invention can be incorporated into a commercially available VA liquid crystal display device or a lateral electric field switching mode liquid crystal display device, and the IPS mode is particularly preferable.

  The IPS mode of the present invention includes a fringe-field switching (FFS) mode in the present invention, and the polarizing plate of the present invention can be incorporated in the same manner as the IPS mode. A liquid crystal display device can be manufactured.

  In the liquid crystal display device of the present invention, the rubbing axis of the liquid crystal cell is preferably parallel to the transmission axis of the polarizer on the viewing side and the slow axis of the polarizing plate protective film which is the optical film of the present invention.

  The polarizing plate B disposed on the backlight side across the liquid crystal cell is an optical film that satisfies the optical values of −15 nm ≦ Ro ≦ 15 nm and −15 nm ≦ Rth ≦ 100 nm as the polarizing plate protective film on the liquid crystal cell side. A commercially available polarizing plate can be used.

  Examples thereof include polarizing plates NPF-F1205DU, NPF-SEG1425DU, NPF-TEG1465DU (manufactured by Nitto Denko Corporation), Sumikaran SQ-1852AP (manufactured by Sumitomo Chemical Co., Ltd.), and the like.

  Moreover, when optical compensation is insufficient, a retardation film can be used in combination.

  The liquid crystal cell gap dc of the present invention is 2 to 5 μm, preferably 2.2 to 4.5 μm. Since the liquid crystal cell gap dc varies depending on the location of the liquid crystal cell due to irregularities such as electrodes and spacers, the liquid crystal cell gap dc is defined as the average value in an area corresponding to a glass substrate of 500 mm × 500 mm.

  The liquid crystal cell gap can be adjusted by a usual method using a spacer, a substrate protrusion, or the like.

  The liquid crystal cell gap dc can be measured with a wavelength of 590 nm in a room at 25 ° C. and 55% RH by, for example, a cell gap inspection apparatus RETS-1200 (Otsuka Electronics Co., Ltd.).

  The liquid crystal display device of the present invention can be applied to all devices that support moving images, and can be used for, for example, liquid crystal display devices of 2 to 100 types.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

<Preparation of Dope 1>
(Preparation of particle dispersion 1)
A particle dispersion of SrCO ₃ was prepared by the following method.

  To 375 g of water, 81.75 g of urea (21.8% by mass with respect to water) and 30.75 g of strontium nitrate (8.2% by mass with respect to water) were added. Further, 75 g of ethylene glycol (20% by mass with respect to water) as an organic solvent was added to the reaction solution in order to carry out the reaction at below freezing point. This solution was put into a reaction vessel, stirred and cooled while being irradiated with ultrasonic waves.

  Shinto Kagaku Co., Ltd., Three-One Motor BLh600 as an agitator motor, Honda Electronics Co., Ltd. as an ultrasonic irradiation water bath, ultrasonic cleaner W-113MK-II, Cooler manufactured by Thomas Scientific Instruments Co., Ltd., sealed A tank type handy cooler TRL-C13 was used.

  The temperature of the reaction solution was lowered to −5 ° C. and kept at −5 ° C. by circulating an ethylene glycol antifreeze solution (Thomas Scientific Instruments Co., Ltd., Nybrine; registered trademark) in a water bath with a cooler.

  Subsequently, 1.50 g of digestive enzyme Urease was added to the reaction solution. After the digestive enzyme was added, crystals started to precipitate in the reaction solution and became cloudy. The reaction was carried out for 12 hours while maintaining the temperature of the reaction solution at −5 ° C.

Thereafter, the temperature of the reaction solution was raised to 20 ° C., and the crystals were aged for 12 hours while maintaining the temperature at 20 ° C. The obtained crystal was taken out by filtration and dried. When the dried crystal was observed with a scanning electron microscope (SEM), it was confirmed that the crystal was a strontium carbonate needle crystal particle having an aspect ratio of 8.8 having a major axis diameter of 350 nm and a minor axis diameter of 40 nm. The scattering cross sections were Sx = 3 nm ⁻² and Sy = 35 nm ⁻² .
32 g of SrCO ₃ particle dispersion prepared above
184 g of methylene chloride
Ethanol 184g
The composition was dispersed with an ultrasonic disperser UH-300 (manufactured by SMT Co., Ltd.) on an output scale 10 for 5 minutes continuously, and then dispersed with an Ultra Apex Mill UAM015 (Koto Kogyo) under the following conditions.
Dispersion amount 400g
Dispersion media 50μm zirconia beads 400g
Circulation was performed at a peripheral speed of 10 m / sec and a dispersion circulation flow rate of 60 ml / min for 5 hours, and the mill jacket was cooled with cooling water.
(Particle liquid 1)
8.7 parts by mass of cellulose toacetate propionate (acetyl substitution degree 1.90, propionyl substitution degree 0.75 weight average molecular weight 190,000)
Triphenyl phosphate 16 parts by weight ethylphthalyl ethyl glycolate 4 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 0.60 parts by weight Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 1.02 parts by weight Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 1.02 parts by mass Methylene chloride 149.6 parts by mass Ethanol 15.0 parts by mass The above composition was put into a container and completely dissolved.

  While stirring this solution, 152.2 parts by mass of the particle liquid 1 was slowly added, and 350 g of this mixed liquid was cooled around the container with an output scale 10 using an ultrasonic disperser UH-300 (manufactured by SMT Co., Ltd.). Re-dispersion was carried out for 10 minutes continuously while cooling.

(Preparation of dope stock solution)
166 parts by mass of cellulose toacetate propionate (acetyl substitution degree 1.90, propionyl substitution degree 0.75)
Methylene chloride 449.9 parts by mass Ethanol 42.6 parts by mass The above composition was charged into a container and completely dissolved. While this solution was stirred, 341.7 parts by mass of the particle dispersion 1 was mixed to obtain a dope 1.

<< Production of film >>
Example 1 Stretched TD Orientation The dope 1 was uniformly cast on a stainless steel belt kept at 40 ° C.

  The slit length of the die used for casting was 20 mm, and the slit interval was 500 μm. After the residual solvent amount was dried to 80%, it was peeled off from the stainless steel belt, and then stretched 1.4 times in the width direction with a tenter. Furthermore, it dried at 120 degreeC, making it convey with many rolls, and obtained the cellulose-ester film 1 of thickness 80micrometer and width 1.3m. Ro was 120 nm.

  Furthermore, the particle liquid and the film thickness in which the major axis diameter and minor axis diameter of the birefringent particles were adjusted were adjusted to obtain Ro80, 240, and 360 nm films.

(Measurement of slow axis of optical film and retardation Ro)
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 film was measured using a commercially available micrometer.

  Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the retardation of the film at a wavelength of 590 nm in the same environment was measured for a film left for 24 hours in an environment of 23 ° C. and 55% RH . The above-mentioned average refractive index and film thickness were inputted into the following formula, and the value of in-plane retardation Ro was obtained.

Ro = (nx−ny) × 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, and d represents the thickness (nm) of the film.

<Preparation of polarizing plate>
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 a ratio 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 1. Subsequently, the polarizing plate 1 was produced according to the steps 1-5. Hereinafter, the polarizing plate was produced so that it might become about 70 mm x 70 mm.

This polarizing plate is the polarizing plate A in the configuration-1 of FIG. 15, that is, as the polarizing plate protective film 1a, a commercially available cellulose ester film KC8UX2M (manufactured by Konica Minolta Opto Co., Ltd.) is used as the polarizing plate protective film 2a. 1 is a polarizing plate A using the cellulose ester film 1 of the present invention produced in Example 1.
Process 1
As a polarizing plate protective film, the cellulose ester film 1 of the present invention produced in Example 1 was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water, dried and bonded to a polarizer. The side was saponified.

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 1 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 1 in Step 2 was gently wiped off, and this was placed on the saponified surface of the cellulose ester film 1 of the present invention prepared in Example 1 treated in Step 1 and further on the opposite side. The polarizing plate protective film was laminated so that the saponified surface of the commercially available cellulose ester film KC8UX2M treated in Step 1 was in contact with the polarizer 1.

In addition, when bonding the polarizing plate protective film 2a to the polarizer 1, the transmission axis of the polarizer 1 and the slow axis of the polarizing plate protective film 2a were made parallel.
Process 4
In Step 3, the polarizing plate obtained by laminating the cellulose ester film and the polarizer 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 produced in step 4 was dried for 2 minutes in a dryer at 80 ° C. to produce polarizing plate 1.

Similarly, in Step 2, a polarizing plate 11 was prepared in which the transmission axis of the polarizer 1 and the slow axis of the polarizing plate protective film 2a were perpendicular.
<Visibility evaluation of liquid crystal display device>
The relationship between the cell gap of the 17-type IPS mode liquid crystal cell, the rubbing axis of the cell, and the transmission axis of the polarizer 1 is prepared as shown in Table 1, and the polarization as shown in FIG. The plate was attached to a liquid crystal cell, and front contrast and luminance unevenness were evaluated (Test Nos. 1 to 15).

  The same evaluation was performed using a VA mode liquid crystal cell. The results are shown in Table 1 (Test Nos. 16 to 24).

<Front contrast>
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance from the normal direction of the display screen of white display and black display with a liquid crystal display device, and the ratio was defined as the front contrast.

Front contrast = (brightness of white display measured from the normal direction of the display device)
/ (Luminance of black display measured from normal direction of display device)
<Luminance unevenness>
The front contrast at any five points of the liquid crystal display device was measured and evaluated according to the following criteria.

  A: The front contrast varies from 0 to less than 3%.

  ○: The front contrast has a variation of less than 3 to 5%.

  Δ: Front contrast varies from 5 to less than 7%.

  X: The front contrast has a variation of less than 7 to 10%.

  XX: The front contrast varies by 10% or more.

It is a figure which shows the azimuth angle of a birefringent particle. It is a figure which shows the angle which each birefringent particle | grain makes with respect to the direction of an average azimuth. It is a figure which shows the distance between the gravity centers of each birefringent particle. It is the figure which showed typically the dope preparation process, casting process, and drying process of the solution casting film forming method concerning this invention. It is the figure which showed typically the apparatus which measures absolute filtration accuracy. It is a figure which shows the example of the dice | dies with which the some nozzle is arrange | positioned in the width direction. It is a figure which shows an example of the die | dye by which the liquid supply part and the liquid discharge part are arrange | positioned in the direction which is not parallel with respect to the moving direction of a casting support body within a die | dye. It is a figure which shows an example of the die | dye which provided the groove | channel in the direction which is not parallel with respect to the moving direction of a casting support body inside die | dye. It is a figure which shows an example of the method using a diagonal gravure roll. It is a figure which shows an example of the method using an orientation belt. An example of a die having a long slit length for laminar flow is shown. It is a figure which shows an example of the method of pulling dope by conveyance of a belt and performing substantial extending | stretching during casting. It is the schematic which shows an example of the tenter process used for this invention. It is a figure explaining the extending | stretching angle in an extending | stretching process. It is the schematic which shows the structure of the liquid crystal display device in the Example of this invention. It is a schematic diagram which shows the direction of the absorption axis / transmission axis | shaft of the optical film, polarizer, and liquid crystal cell of a liquid crystal display device preferable for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 Melting pot 3,6,12,15 Filter 4,13 Stock tank 5,14 Liquid feed pump 8,16 Conduit 20 Junction pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer A Filter medium sample B Filtrate C Filtrate M Manometer P Low pressure vacuum pump S Stirrer V valve 60 Polarizing plate A using the optical film of the present invention
61 Normal polarizing plate B
62 Polarizing plate protective film 2a using optical film of the present invention
63 Slow axis of the optical film of the present invention 64 Polarizer 66 Normal polarizing plate protective film 68 Normal polarizing plate protective film 1a
70 Liquid crystal cell 71 Rubbing axis of liquid crystal cell 72, 74 Transmission axis of polarizer 73, 75 Absorption axis of polarizer

Claims (3)

  In a liquid crystal display device in which a liquid crystal cell and two polarizers sandwiching the liquid crystal cell are arranged in crossed Nicols, birefringent particles having an aspect ratio of 2 to 100 are contained between the two polarizers and Ro is 50 to 50. A liquid crystal display device, wherein an optical film having a thickness of 500 nm is arranged so that a transmission axis of a polarizer on a backlight side is perpendicular to a slow axis of the optical film.   The liquid crystal display device according to claim 1, wherein the rubbing axis of the liquid crystal cell and the transmission axis of the polarizer on the viewing side are parallel.   The liquid crystal display device according to claim 1, wherein a cell gap dc of the liquid crystal cell is 2 to 5 μm.

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