JP2009263658A - Optical film, its method for manufacturing, polarizing plate having the film, and image display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film contributing to uniformizing of the display performance and thinning of an image display, such as a liquid crystal display; a polarizing plate using it; and a method for simply manufacturing the optical film. <P>SOLUTION: This optical film is made of a uniform composition and includes recesses on the film surface, wherein the depth of the recesses is 5 μm or less, the average long diameter of the recesses is 0.5 to 100 μm, and the number of the recesses on the film surface is 25 to 1,000,000/mm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film, a manufacturing method thereof, a polarizing plate having the optical film, and an image display device.

  Conventionally, diffusion sheets are used in various image display devices. For example, in a liquid crystal display device (LCD), a diffusion sheet is generally disposed between a backlight light source and a backlight side polarizing plate. By arranging the diffusion sheet, uniform display characteristics can be achieved, and it can be suppressed that incident light interferes with the pixels in the liquid crystal cell to generate interference fringes such as moire. In recent years, attempts have been made to reduce the number of members of a liquid crystal display device or to reduce the number of fluorescent lamps used as a light source in order to reduce power consumption for the purpose of reducing manufacturing costs. Further, since the LCD is made thinner, the distance between the backlight light source and the diffusion sheet becomes closer, so that it has become difficult to achieve uniform light diffusion with the conventional diffusion film.

  For example, Patent Document 1 proposes a light diffusing polarizing plate having a light diffusing layer having predetermined characteristics, which contains porous amorphous particles and spherical particles in a dispersed manner, and discloses that a light diffusing sheet can be omitted by this. ing. Patent Document 2 proposes a method for producing a light diffusing film including casting a dope containing fine particles on a support. According to this method, a light diffusing film excellent in optical isotropy and the like is provided. It is disclosed that it can be made. Patent Document 3 proposes a manufacturing method for transferring an uneven shape to a film, and according to this method, a light diffusion film with a controlled surface shape can be easily manufactured. Furthermore, Patent Document 4 discloses a film in which bubbles are generated inside, but the film surface shape is not described. Patent Document 5 discloses a film for a reflecting member having fine bubbles and a light-proofing agent, but only the glossiness is examined for the film surface shape, and the detailed structure is not described.

JP 2000-75134 A JP 2001-172403 A JP 2005-84113 A JP-A-9-155981 JP 2001-226501 A

  However, since the light diffusing film described in the above document has a low total light transmittance, when used in an image display device, it may contribute to a decrease in front white luminance. In addition, in order to ensure sufficient diffusibility, it is necessary to contain particles that do not dissolve in a large amount of solvent, so that the brittleness of the film deteriorates, or the quality of the film deteriorates due to aggregation of fine particles with the aging of the dope. It may get worse. The films described in Patent Documents 4 and 5 in which bubbles are generated also have problems from the viewpoint of uniform display performance and improvement of front white luminance.

It is an object of the present invention to provide a novel optical film and polarizing plate that contribute to uniform and thin display performance of an image display device such as a liquid crystal display device, and a method capable of easily manufacturing the optical film. And
It is another object of the present invention to provide an image display device that has high front luminance when displaying white, is uniform in the screen, and can cope with thinning.

  Means for solving the above problems are as follows. In particular, a cellulose acylate polymer is preferable from the viewpoint of thinning, and such a film can be produced by a method described later.

[1] An optical film comprising a uniform composition, having an independent dent on the film surface, the depth of the dent is 5 μm or less, and the average major axis length of the dent is 0.5 to 100 μm An optical film in which the number of depressions on the film surface is 25 to 1000000 / m ² .
[2] The optical film according to [1], wherein an average interval between the two recesses is 0.5 to 100 μm.
[3] The optical film as described in [1] or [2], wherein the standard deviation of the number distribution of the depressions on the film surface is ± 20% with respect to the average number.
[4] The optical film according to any one of [1] to [3], wherein a standard deviation of the depth of the depression is ± 20% with respect to an average depth.
[5] The depression on the surface of the film has a bottom portion that is convex downward and substantially parallel to the film surface, and a side portion that connects the bottom portion and the depression opening. [1] to [4] ] The optical film as described in any one of.
[6] The optical film according to any one of [1] to [5], wherein a dimensional change rate of the indentation before and after the glass transition temperature is 5% or less.
[7] The optical film according to any one of [1] to [6], wherein the haze is 15% or more.
[8] The optical film according to any one of [1] to [7], wherein the total light transmittance is 50% or more.
[9] The optical film as described in any one of [1] to [8], wherein the polymer composition contains a cellulose acylate polymer as a main component.
[10] A step of preparing a polymer solution by dissolving a polymer composition in a solvent containing at least two kinds of solvents incompatible with each other containing a solvent having a dielectric constant of 35 or more, and forming a polymer solution The manufacturing method of the optical film characterized by including.
[11] The method for producing an optical film as described in [10], wherein the solvent is a solvent containing 0.3 to 30% by mass of a solvent having a dielectric constant of 35 or more.
[12] The method for producing an optical film of [10] or [11], wherein the polymer is cellulose acylate.
[13] The optical film production according to any one of [10] to [12], wherein the solvent includes a solvent having a dielectric constant of 4 to 10 and a solvent having a dielectric constant of 10 to 35. Method.
[14] The method according to any one of [10] to [13], wherein the solvent having a dielectric constant of 35 or more is water.
[15] A step of preparing a polymer solution by dissolving a polymer composition in a solvent containing at least two kinds of solvents that are incompatible with each other, including a solvent having a dielectric constant of 35 or more, and forming a polymer solution A method in which a polymer solution is cast on a support to form a film, and thereafter the film is peeled off from the support, and further during film formation, after film formation, or both The manufacturing method of the optical film as described in any one of [10]-[14] including the process of evaporating a solvent.
[16] An optical film produced by the production method according to any one of [10] to [15].
[17] A polarizing plate comprising a polarizing film and at least one optical film according to any one of [1] to [9] and [16].
[18] An image display device comprising at least one optical film according to any one of [1] to [9] and [16] or a polarizing plate according to [17].
[19] A liquid crystal cell and a backlight are provided, and the optical film according to any one of [1] to [9] and [16] is provided on the backlight side between the liquid crystal cell and the backlight. The image display device according to [18], wherein the image display device is arranged as described above.

ADVANTAGE OF THE INVENTION According to this invention, the novel optical film which contributes to the uniformization and thickness reduction of display performance of image display apparatuses, such as a liquid crystal display device, and a polarizing plate having the same can be provided. Since the optical film of the present invention exhibits diffusibility based on its characteristic surface properties, it contributes to uniform display performance such as luminance of the image display device. By using the optical film of the present invention, the diffusion film can be omitted without generating interference fringes such as moire, which contributes to the thinning of the image display device. That is, according to the present invention, it is possible to provide an image display apparatus that has high and uniform front (normal direction) luminance at the time of white display and that can cope with a reduction in thickness.
Moreover, according to the manufacturing method of this invention, the optical film of this invention can be manufactured simply.

  Hereinafter, the present invention will be described in detail. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. In the present invention, the terms “polarizing film” and “polarizing plate” are used separately in this specification, but “polarizing plate” is a transparent protective film that protects the polarizing film on at least one side of the “polarizing film”. It shall mean a laminate having Further, an error allowed in the technical field to which the present invention belongs, such as a technical field of a polymer film, a polarizing plate, and an image display device, will also be allowed for a numerical range described in this specification.

[Optical film]
The optical film of the present invention is an optical film composed of a uniform composition, having a dent on the film surface, the depth of the dent is 5 μm or less, and the average major axis length of the dent is 0.5 to 100 μm. The number of the depressions on the film surface is 25 to 1,000,000 pieces / mm ² .
The optical film of the present invention exhibits light diffusibility based on the predetermined surface shape. Therefore, by using the polarizing plate having the optical film of the present invention for an image display device, the light diffusion film can be omitted without generating interference fringes such as moire.

(Recess)
The indentation of the optical film of the present invention will be described. In this specification, a dent means that whose average major axis length is 0.5-100 micrometers.
The average major axis length of the recess of the optical film of the present invention is 0.5 to 100 μm, preferably 1 to 50 μm, and more preferably 1 to 30 μm. In addition, in this specification, the long diameter of a dent means the longest diameter among the diameters which connect the dent opening part (end part of a dent) formed in the film surface. The diameter of the dent was measured by recognizing each dent in the surface direction of the film using an image processing software (for example, Image Pro Plus) and measuring the longest part of each dent. The average major axis length of the indentation refers to the average value of the major axis of the indentation that is arbitrarily selected from one 1 mm ² film surface.
The depth of the recess of the optical film of the present invention is 5 μm or less, and from the viewpoint of high diffusion performance, it is more preferably 1 to 3 μm. The depth of the indentation refers to the average value of the indentation depth at an average major axis length of 0.5 to 100 μm on the surface of a sample film having a specific size.
The average distance between the two recesses of the recess is preferably 1 to 100 μm, more preferably 1 to 50 μm from the viewpoint of adjusting the diffusion performance. In this specification, the average distance between two indentations means the value obtained by measuring the distance between the centers of all indentations and the nearest indentation and dividing the total by the number of indentations. .

  In the present specification, the depth of the dent, the average major axis length, and the average interval of the film mean values calculated from the surface shape measured by the surface shape measuring device. As the surface shape measuring device, a light interference type measuring device can be used, and a stylus type measuring device can also be used. A three-dimensional non-contact surface shape measurement system (Micromap MM5000 series; manufactured by Ryoka System Co., Ltd.) or the like can be used as an optical interference method device. As a stylus device, a stylus type surface shape can be used. A measuring instrument (Dektak 6M; ULVAC-ES Co., Ltd.) etc. can be used. In addition, such a surface shape measuring apparatus can automatically measure and calculate the distance from the film surface to the deepest part of the dent in each dent, and the depth of the dent can be obtained by performing such a measurement on the dent completely. (That is, the average value of the depth of the dents) can be calculated.

In the optical film of the present invention, the number of the depressions on the film surface is 25 to 1000000 / mm ² . The number of said recesses in the film surface to be 100 to 100,000 pieces / mm ^2, a high diffusibility and, more preferably in view of the high total light transmittance, and particularly preferably 500 to 7000 pieces / mm ^2.

In the optical film of the present invention, the standard deviation of the number distribution of the depressions on the film surface is preferably ± 20% with respect to the average number from the viewpoint of in-plane uniform diffusion performance and total light transmittance. The standard deviation of the number distribution of the depressions on the film surface is more preferably ± 10% with respect to the average number, and particularly preferably ± 5% with respect to the average number.
Here, the average number means an average value of the number of indentations existing in each of 100 areas of 1 mm ² from the film surface. Thus, it has the light-scattering effect of this application by distributing uniformly.

In the optical film of the present invention, the standard deviation of the depth of the dent is preferably ± 20% with respect to the average depth, from the viewpoint of in-plane uniform diffusion performance and total light transmittance. The standard deviation of the number distribution of the depressions on the film surface is more preferably ± 10% with respect to the average depth, and particularly preferably ± 5% with respect to the average depth. The number average distribution of the depressions is preferably a monodisperse film in which the depressions are uniformly distributed.
Here, the average depth means an average value of 100 depths selected arbitrarily.

The shape of the dent opening when the dent is observed from a direction perpendicular to the film surface is a circle, a polygon, an ellipse, or a figure surrounded by other curves. However, a shape close to a circle is preferable from the viewpoint of high total light transmittance. The equivalent circle diameter (projected area equivalent circle diameter) when the recess is circular is preferably 0.5 to 100 μm from the viewpoint of adjusting the diffusion performance, more preferably 1 to 50 μm. It is particularly preferable that the thickness is ˜30 μm. Similarly, the shape of the flat portion that may be formed at the bottom of the recess when the recess is observed from a direction perpendicular to the film surface is circular, polygonal, or elliptical. However, a shape close to a circle is preferable from the viewpoint of high total light transmittance. The equivalent circle diameter (projected area equivalent circle diameter) when the planar portion that may be formed at the bottom of the depression is circular is preferably 0.12 to 85 μm from the viewpoint of high total light transmittance. More preferably, it is 35-40 micrometers, and it is especially preferable that it is 0.45-25 micrometers.
The ratio of the average major axis length to the average minor axis length (aspect ratio) of the depression is preferably 0.8 to 1.2 from the viewpoint of high total light transmittance, and is 0.85 to 1.15. Is more preferable, and 0.9 to 1.1 is particularly preferable.

(Cross sectional shape)
A preferable shape of the sectional shape of the recess will be described. In addition, the cross-sectional shape here represents the shape in the cross-sectional view cut perpendicularly to the thickness direction when the film is placed on the surface.
The cross-sectional shape of the recess is not particularly limited except that the depth of the deepest part is 5 μm or less and the average major axis length of the opening is 0.5 to 100 μm, but it is preferably convex downward, and the film surface It is more preferable that the bottom portion is substantially parallel to the bottom portion, and the side portion connects the bottom portion and the recessed opening. As a representative example of such a shape, a cup-like shape is preferable. The cup shape, like a coffee cup or a tea cup, has at least 25% of the lateral width of the indentation to be indented at the bottom of the indentation, approximately parallel to the film surface, and gently curving from the bottom to the indentation opening. The opening at the end means a shape having concave side portions (both side portions) that are substantially perpendicular to the film surface. In that sense, a crater shape or a cycloid curve shape is also included in the cup shape.
The cross-sectional shape of the indentation can be spherical or rectangular, but the spherical shape has a high curvature, so the haze can be increased, but since there is a lot of bending light, the forward transmission is slightly lower, resulting in a total light The transmittance is lowered. On the other hand, the rectangular shape has many planes parallel to the surface, so that the total light transmittance is high, but the haze is slightly lowered because there are few surfaces that bend light.
Considering these, if the cross-sectional shape of the recess is cup-shaped, there is a surface that bends light (for example, the side of the recess) and a plane parallel to the surface (for example, the bottom of the recess). In addition, an optical film having a high total light transmittance can be produced.
Although there is no restriction | limiting in particular in the confirmation method of the cross-sectional shape of the said hollow, For example, it can confirm with SEM.

  From the viewpoint of adjusting the diffusion performance, it is preferable that the length of the opening in any cross section of the recess (that is, both the average minor axis length and the average major axis length of the recess) be 0.5 to 100 μm. More preferably, it is -50 micrometers, and it is especially preferable that it is 1-30 micrometers.

  The bottom of the recess is preferably substantially parallel to the film surface from the viewpoint of high total light transmittance, and the inclination of the surface of the bottom of the recess with respect to the film surface is more preferably within ± 10 °, and within ± 5 °. It is particularly preferable that it is within ± 2.5 °.

From the viewpoint of high total light transmittance, the length of the bottom of the recess in any film cross section (that is, both the minor axis and the major axis of the recess bottom) is preferably 0.12 to 85 μm, and is 0.35 to 40 μm. Is more preferable, and it is especially preferable that it is 0.45-25 micrometers.
The bottom of the recess is preferably formed to have a width of at least 25 to 85% and a width of 35 to 80%, assuming that the lateral width of the recess is 100% in the film cross section at an arbitrary location. It is more preferable that the width is 45 to 75%.

  The preferable shape of the said side part of a hollow is the same as the preferable shape in description of the side part of the hollow which is the above-mentioned cup shape. From the bottom of the dent, draw a gentle curve from the bottom to the dent opening, and the dent opening has a dent side that is almost perpendicular to the surface of the film for high diffusion performance and high total light transmittance. To preferred. Furthermore, it is more preferable from the viewpoint of high diffusion performance and high total light transmittance that the radius of curvature gradually decreases from the bottom of the recess toward the recess opening.

  The dimensional change rate of the optical film of the present invention was determined by the following measuring method. Each polymer was allowed to stand for 24 hours at a glass transition temperature of + 10 ° C. The dimension of the average major axis length of the recess before and after that was measured to determine the rate of change. The dimensional change rate is preferably 5% or less from the viewpoints of the diffusion performance against the change with time and the stability of the total light transmittance. The dimensional change rate of the recess before and after the glass transition temperature is more preferably 3% or less, and particularly preferably 1.5% or less. The optical film of the present invention is estimated to have a small dimensional change rate because the density of the film composition is substantially uniform throughout the film.

  The surface property having such characteristics is formed by producing a film by the production method of the present invention to be described later, and cannot be achieved by ordinary embossing or dispersion containing fine particles. In addition, it is possible to make a dent on the surface, for example, by scraping the surface with a paper file or applying fine particles (sand, silica particles, etc.) to the surface, but in these cases, the shape is almost random. Since the range of the shape of the depression of the film of the present invention is out of the above range, the total light transmittance is low although the haze is high. Further, in addition to the step of roughening the surface, the number of steps for recovering surface debris and the like increase, which increases the cost.

  In addition, the optical film of the present invention can reduce unevenness when incorporated in a liquid crystal display device, compared to the case where a surface shape is changed by a method using heat or pressure such as embossing to form a depression on the film surface. . Since the surface shape of the film of the present invention is due to spontaneous structure formation, it has a feature that the residual stress near the surface of the film is small. Therefore, it has the feature that the dimensional change rate such as the thermal expansion coefficient and the humidity expansion coefficient of the surface irregularities is small, which appears remarkably in the state of being heated, especially the relatively hydrophilic cellulose polymer. In the film used as, it appears particularly remarkably. That is, in recent liquid crystal display devices, the amount of heat generated by the backlight unit increases as the brightness increases, and at the same time, the distance between the backlight unit and the optical film decreases as the thickness decreases. Compared with the case where a film with a changed surface shape is incorporated, a change in surface shape caused by a temperature difference depending on a place can be suppressed, and as a result, uneven brightness in the liquid crystal display device can be reduced.

(Other characteristics)
The haze of the optical film of the present invention is preferably 15% or more, more preferably 30% or more, particularly preferably 50% or more, and further preferably 70% or more. The higher the haze, the higher the light diffusing performance. On the other hand, when used in an image display device due to a decrease in the total light transmittance, it contributes to a decrease in front white luminance. From this viewpoint, the haze of the optical film of the present invention is preferably 50 to 95%, and more preferably 60 to 90%.
The haze can be measured with a haze meter (NDH2000; manufactured by Nippon Denshoku Industries Co., Ltd.). When measuring the polymer solution, the dope was injected between a pair of glass plates whose interval was adjusted to 1 mm, and the measurement was performed.

  The total light transmittance of the optical film of the present invention is preferably 50% or more, more preferably 60 to 95%, and particularly preferably 65 to 90%. Furthermore, the parallel transmittance of the optical film of the present invention is preferably 5 to 35%, more preferably 10 to 30%, and particularly preferably 15 to 25%. In the present specification, the total light transmittance represents the transmittance of light including linear light and diffused light, and the parallel transmittance represents the transmittance of light including only linear light.

(composition)
The optical film of the present invention comprises a uniform composition. That is, if the composition is uniform, it is possible to reduce the backscattering generated inside the film, so that both the height of haze and the total light transmittance can be achieved. For example, even if film scraps generated in the manufacturing process are collected and mixed with the raw material, the quality does not deteriorate, so that the cost can be reduced. Here, the uniform composition means that it does not substantially contain a substance such as a particle having a size that causes light scattering, and if it does not substantially contain, it means a foreign substance having a size that causes light scattering. The resulting haze represents a contribution of less than 5% of the total haze.
Similarly, in the optical film of the present invention, since the indentation is also formed of a uniform composition, the total light transmittance can be increased and the cost can be reduced.

  The optical film of the present invention comprises a polymer composition. Although there is no restriction | limiting about the polymer to utilize, It is preferable to select from the polymer with a high light transmittance with respect to visible light. Moreover, when manufacturing by the method of this invention mentioned later, it is preferable to select from the polymer material which can be film-formed by solution. Examples of polymer materials that can be used include cellulose acylate, polycarbonate, polyvinyl alcohol, polyimide, polyolefin, polyarylate, polyester, polystyrene, styrene copolymer, polymethyl methacrylate, methyl methacrylate copolymer, and polyvinylidene chloride. Etc. are included. However, it is not limited to these. In consideration of the fact that the polarizing film to be bonded is usually a polyvinyl alcohol film, it is preferable to contain cellulose acylate and polyvinyl alcohol as a main component polymer having affinity and good adhesion. Cellulose acylate is preferred from the viewpoint of stability. Here, the “polymer as the main component” means a polymer when the film is composed of a single polymer, and when the film is composed of a plurality of polymers, the most mass fraction of the constituting polymers. This indicates a high polymer.

The cellulose acylate that can be used will be further described.
The cellulose acylate film raw material cellulose includes cotton linter, kenaf, wood pulp (hardwood pulp, softwood pulp), etc., and any cellulose ester obtained from any raw material cellulose can be used. Also good.

Cellulose acylate is an ester of cellulose and carboxylic acid. In the cellulose acylate, all or part of the hydrogen atoms of the hydroxyl groups present at the 2-position, 3-position and 6-position of the glucose unit constituting the cellulose are substituted with acyl groups. The number of carbon atoms in the acyl group is preferably 2 to 22, and more preferably 2 to 4. Examples of the acyl group include, for example, acetyl group, propionyl group, butyryl group, isobutyryl group, pivaloyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, and hexadecanoyl group. Examples include a noyl group, an octadecanoyl group, a cyclohexanecarbonyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group. As the acyl group, acetyl group, propionyl group, butyryl group, dodecanoyl group, octadecanoyl group, pivaloyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group are preferable, acetyl group, propionyl group, butyryl group Is most preferred.
The cellulose acylate may be an ester of cellulose and a plurality of carboxylic acids. That is, the cellulose acylate may be substituted with a plurality of acyl groups.

When the substitution degree of the acetyl group (carbon number 2) substituted on the hydroxyl group of cellulose of cellulose acylate is SA and the substitution degree of the acyl group of 3 or more carbon atoms substituted on the hydroxyl group of cellulose is SB, By adjusting SA and SB, the haze of the cellulose acylate film produced by the production method of the present invention can be adjusted.
SA + SB is appropriately adjusted depending on the haze required for the cellulose acylate film produced by the production method of the present invention, which is the optical film of the present invention, but preferably 2.70 <SA + SB ≦ 3.00. Preferably 2.80 ≦ SA + SB ≦ 3.00, more preferably 2.85 ≦ SA + SB ≦ 2.98. There is a tendency that haze is easily increased by increasing SA + SB.
Moreover, the haze of the cellulose acylate film produced by the production method of the present invention can also be adjusted by adjusting SB. By increasing the SB, the haze tends to be increased, and at the same time, the elastic modulus and melting point of the film are lowered. Considering the balance between the haze of the film and other physical properties, the SB range is preferably 0 ≦ SB ≦ 2.9, more preferably 0.5 ≦ SB ≦ 2.5, and further preferably 1 ≦ SB. ≦ 2.0. In addition, when all the hydroxyl groups of cellulose are substituted, said substitution degree will be 3.

  A method for synthesizing cellulose acylate is disclosed in JIII Journal of Technical Disclosure No. 2001-1745 (Japan Society for Invention and Invention Issued on March 15, 2001) p. Reference is made to 7 to 12 in detail.

  The optical film of the present invention may contain an additive together with one or two or more polymers as main raw materials. Examples of the additive include a plasticizer (preferably added amount is 0.01 to 10% by mass, the same applies hereinafter), an ultraviolet absorber (0.001 to 1% by mass), a fluorine-based surfactant (0 0.001 to 1% by mass), release agent (0.0001 to 1% by mass), deterioration inhibitor (0.0001 to 1% by mass), optical anisotropy control agent (0.01 to 10% by mass), infrared An absorbent (0.001 to 1% by mass) and the like are included. Moreover, the particle | grains which consist of a trace amount organic material, an inorganic material, and mixtures thereof may be dispersedly included in the range which does not impair the effect of this invention. These particles are added for the purpose of improving the transportability of the film during film formation. In order to achieve this object and not impair the effects of the present invention, the particle size of the particles is preferably 5 to 3000 nm, and the refractive index is different from the refractive index of the polymer film of the present invention from 0 to 0.00. 5 is preferable, and the addition amount is preferably 1% by mass or less. For example, particles of inorganic material include particles of silicon oxide, aluminum oxide, barium sulfate, and the like. Examples of organic material particles include acrylic resins, divinylbenzene resins, benzoguanamine resins, styrene resins, melamine resins, acrylic-styrene resins, polycarbonate resins, polyethylene resins, polyvinyl chloride resins, etc. Is included.

[Method for producing optical film]
An example of the manufacturing method of the optical film of the present invention is as follows. According to the following method, complicated operations and special devices are not required, and the optical film of the present invention can be easily produced.
First, a solution of the polymer composition is prepared. The concentration of the polymer in the solution is preferably 5 to 40% by mass, more preferably 10 to 25% by mass, and further preferably 10 to 15% by mass. When the concentration is in a preferable range, it is preferable from the viewpoint of improving the film forming property and reducing the streak-like failure that occurs in the film along with the long run.
In the present invention, when preparing the polymer solution, a solvent containing a solvent having a dielectric constant of 35 or more and containing at least two kinds of solvents that are incompatible with each other is used. Films with appropriately controlled shapes can be produced. Usually, since the polymer solution is made of solvents that are compatible with each other, the film often has no dents on the surface, and even if dents are formed on the surface by adjusting the solvent composition, voids within the film are also formed at the same time. It becomes a certain film. And in such a film, since a total light transmittance will also fall with a haze raise, a haze value and a total light transmittance cannot be made compatible. In the present invention, a step of preparing a polymer solution by dissolving a polymer composition in a solvent containing at least two kinds of solvents that have a dielectric constant of 35 or more and incompatible with each other, and forming a polymer solution Thus, it is possible to obtain a film having on the surface a fine depression having a shape defined in the present invention. The film of the present invention also has a feature that the internal porosity of the film is low. Specifically, the internal porosity of the film is preferably 10% or less (volume ratio), and preferably 5% or less. More preferably, it is more preferably 3% or less.

  In the present invention, specifically, a solvent containing 0.3% by mass or more of a solvent having a dielectric constant of 35 or more (hereinafter referred to as “high dielectric constant solvent”) is preferably used, and the surface shape of the film is more appropriate. Can be controlled. It is more preferable to use a solvent containing 1.0% by mass or more of a high dielectric constant solvent, and it is more preferable to use a solvent containing 1.5% by mass or more of a high dielectric constant solvent. On the other hand, if the ratio of the high dielectric constant solvent is too high, it becomes difficult to dissolve the polymer, and it becomes difficult to prepare the polymer solution, or even if the polymer solution can be prepared, the dope has a high haze, and the dope is stable over time. May deteriorate, or foreign matter in the film may increase. In this respect, the high dielectric constant solvent is preferably 30% by mass or less, and more preferably 10% by mass or less. By forming a polymer solution prepared using a solvent containing a high dielectric constant solvent in a predetermined range, when the solvent evaporates during film formation or after film formation, the polymer and the high dielectric constant solvent are contained in the solution. It is thought that phase separation occurs. As a result, it becomes easier to obtain fine dents on the surface as the optical film of the present invention has. Furthermore, from the viewpoint of effectively forming fine pits on the surface, the boiling point of the high dielectric constant solvent is preferably higher than the boiling point of the below-described low boiling point solvent, more preferably 5 ° C or higher, more preferably 10 ° C or higher. It is more preferable that it is high, and it is preferable that both do not azeotrope.

In the method of the present invention, it is preferable that the haze (τ0) of the dope and the haze (τ1) of the film after drying satisfy the following formula (I). In particular, the haze of the polymer solution increases the solubility of the dope. It is a correlated parameter, and if it is within the following range, sufficient dope stability over time can be secured, or foreign substances present in the film after film formation can be reduced.
(I) τ0 <τ1
The haze τ0 of the polymer solution is preferably about 0.2 to 50%, more preferably 0.2 to 30%, and still more preferably 0.3 to 10%.

  Here, the dielectric constant of the solvent is described. The dielectric constant refers to ε giving a relationship D = εE between the electric flux density D and the electric field E, and is a parameter having a correlation with the ease of polarization of solvent molecules. The value of the dielectric constant of the solvent is listed as “relative dielectric constant” on page I-770 of “Chemical Handbook Basic Edition I (5th revised edition)” edited by the Chemical Society of Japan.

  Examples of high dielectric constant solvents include water (dielectric constant 78), glycerin (dielectric constant 43), ethylene glycol (dielectric constant 37), dimethylformamide (dielectric constant 37), acetonitrile (dielectric constant 38), dimethyl sulfoxide (dielectric) 49), formic acid (dielectric constant 58), formamide (dielectric constant 110). Among these, water is preferable from the viewpoint of handling properties such as drying property and safety in the film forming process. The boiling point of the high dielectric constant solvent is preferably 70 to 300 ° C., more preferably 80 to 250 ° C., and most preferably 90 to 210 ° C. from the viewpoint of controlling the surface shape during film formation.

  An organic solvent which is a good solvent for at least one polymer is preferably used as a main solvent together with a high dielectric constant solvent. The type of main solvent is not particularly limited, but is preferably incompatible with the high dielectric constant solvent. When no solvent other than the high dielectric constant solvent and the main polymer solvent is used, the main solvent for the polymer is used. The solvent must be incompatible with the high dielectric constant solvent. The main solvent is more preferably an organic solvent having a boiling point of 80 ° C. or less from the viewpoint of reducing the drying load. The boiling point of the main solvent is more preferably 10 to 80 ° C, and particularly preferably 20 to 60 ° C. Moreover, the organic solvent whose boiling point is 30-45 degreeC depending on the case can also be used suitably as said main solvent. As such a main solvent, halogenated hydrocarbons can be particularly preferably mentioned, and in some cases, esters, ketones, ethers, alcohols and hydrocarbons can also be mentioned, and these have a branched structure or a cyclic structure. It may be. The main solvent may have two or more functional groups of esters, ketones, ethers and alcohols (that is, —O—, —CO—, —COO—, —OH). Furthermore, the hydrogen atom in the hydrocarbon portion of the ester, ketone, ether and alcohol may be substituted with a halogen atom (particularly a fluorine atom). In addition, the main solvent of the polymer solution used in the production method of the present invention means that solvent when it consists of a single solvent, and when it consists of a plurality of solvents, among the constituent solvents, It means the solvent with the highest mass fraction.

  In addition to the high dielectric constant solvent, examples of the organic solvent used in combination with these main solvents include halogenated hydrocarbons, esters, ketones, ethers, alcohols, and hydrocarbons. You may have a cyclic structure. The organic solvent may have any two or more of ester, ketone, ether and alcohol functional groups (that is, —O—, —CO—, —COO—, —OH). Furthermore, the hydrogen atom in the hydrocarbon portion of the ester, ketone, ether and alcohol may be substituted with a halogen atom (particularly a fluorine atom). When the main solvent of the polymer is a solvent compatible with the high dielectric constant solvent, in the present invention, the organic solvent used in combination with the main solvent needs to be a solvent incompatible with the high dielectric constant solvent. There is.

As said halogenated hydrocarbon, a chlorinated hydrocarbon is more preferable, for example, a dichloromethane, chloroform, etc. are mentioned, A dichloromethane is further more preferable.
Examples of the ester include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate.
Examples of the ketone include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone.
Examples of the ether include diethyl ether, methyl tert-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, and phenetole. Etc.
Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, cyclohexanol, and 2-fluoro. Examples include ethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol.
Examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, benzene, and toluene.

  When the polymer as the main component is cellulose acylate, among the above solvents, a solvent having a dielectric constant of about 10 to 35 together with the high dielectric constant solvent (referred to as “medium dielectric constant solvent” in this specification) And a low-dielectric constant solvent having a dielectric constant of about 4 to 10 (sometimes referred to as “low-dielectric constant solvent” in this specification), a highly transparent polymer solution is obtained. It is preferable because it can be stably prepared. That is, from the viewpoint of surface shape control, it is preferable to use the high dielectric constant solvent, and from the viewpoint of improving the solubility of the polymer, it is preferable to use a low dielectric constant solvent, but these solvents have poor compatibility. Since the stability of the dope is inferior, the compatibility can be improved by using a medium dielectric constant solvent in combination, the range of compatibility between the film surface shape control and the dope stability is expanded, and the production suitability is improved. It can be done. The medium dielectric constant solvent is preferably contained in the solvent in an amount of 0.3 to 30% by mass, more preferably 1 to 15% by mass, and further preferably 2 to 10% by mass.

  Examples of the medium dielectric constant solvent include the alcohols, ketones, and ethers. Specifically, acetone (dielectric constant 21), methyl ethyl ketone (dielectric constant 19), diethyl ketone (dielectric constant 14), Diisobutyl ketone (dielectric constant 15), cyclopentanone (dielectric constant 19), cyclohexanone (dielectric constant 18), methylcyclohexanone (dielectric constant 18), ethyl 2-ethoxyacetate (dielectric constant 11), 2-methoxyethanol (dielectric constant) 30), 1,2-diacetoxyacetone (dielectric constant 16), acetylacetone (dielectric constant 17), ethyl acetoacetate (dielectric constant 16), methanol (dielectric constant 33), ethanol (dielectric constant 24), 1-propanol ( Dielectric constant 22), 2-propanol (dielectric constant 22), 1-butanol (dielectric constant 17), 2-butanol (dielectric constant 16) , Tert- butanol (dielectric constant 11), 1-pentanol (dielectric constant 14), 2-methyl-2-butanol (dielectric constant 13), include such cyclohexanol (dielectric constant 15).

  Examples of the low dielectric constant solvent include the above-mentioned halogenated hydrocarbons and esters. Specifically, dichloromethane (dielectric constant dielectric constant 9), dimethoxyethane (dielectric constant 6), 1,4-dioxane. (Dielectric constant 2), 1,3-dioxolane (dielectric constant 3), 1,3,5-trioxane (dielectric constant 3), tetrahydrofuran (dielectric constant 8), anisole (dielectric constant 4) and phenetole (dielectric constant 4) Ethyl formate (dielectric constant 9), n-propyl formate (dielectric constant 6), n-pentyl formate (dielectric constant 6), methyl acetate (dielectric constant 7), ethyl acetate (dielectric constant 6), n-pentyl acetate ( Dielectric constant 5), 2-butoxyethanol (dielectric constant 9) and the like are included.

  Among these solvents, a mixed solvent of water, at least one kind of alcohol and at least one kind of halogenated hydrocarbon is preferable, and 0.3 to 30% by mass of water and at least one kind of alcohol are 1 to 30. A mixed solvent containing 60% to 99% by mass of at least one of mass% and halogenated hydrocarbons is more preferable. Among these, a mixed solvent of water (dielectric constant 78), methanol (dielectric constant 33), and dichloromethane (dielectric constant 9) is preferable. The water content is preferably larger from the viewpoint of increasing the haze of the film, but considering film forming properties such as polymer solubility and polymer solution viscoelastic properties, 0.5 to 10% by mass is more preferable. 5 mass% is more preferable. Further, the content of alcohols is preferably smaller from the viewpoint of increasing the haze of the film, but considering the solubility of the polymer and the film-forming properties such as the reduction of streak-like failure that occurs in the film with a long run, 3 -20 mass% is more preferable, and 5-10 mass% is further more preferable. And as for the preferable range of the total ratio of solvents other than the main solvent, it is preferable that it is 0.8-40 mass% as these combinations, and it is more preferable that it is 2-35 mass%.

The polymer solution can be prepared by using a dope preparation method and apparatus in a normal solvent cast method. As an example, once the polymer and the additive added as desired are swelled in a solvent at low temperature, the dissolution is allowed to proceed (swelling step), and then the polymer is completely removed under heating and pressure. And a step of dissolving (dissolution step).
In the swelling step, the temperature of the solvent is maintained at a low temperature of about −10 to 39 ° C. In the swelling step, it is preferable to carry out agitation so that part or all of the polymer or the like is dissolved in the solvent. In general, the swelling step is preferably performed for about 0.1 to 6 hours.
Next, in the dissolving step, it is preferable to heat the solvent to a temperature of about 40 to 240 ° C. and pressurize it to about 0.2 to 30 MPa. However, it is not limited to this range, and is determined according to the type of solute and solvent. It is preferable to perform a melt | dissolution process for about 0.1 to 6 hours.

Next, the obtained polymer solution is formed into a film. Film formation can be performed according to a general solvent casting method. Specifically, the prepared polymer solution is cast on a drum or band, and the solvent is evaporated to form a film. The surface of the drum or band is preferably finished in a mirror state. The dope based on the production method of the present invention may be cast in a single layer or may be co-cast in multiple layers. When co-casting with multiple layers, a method generally used in multilayer sheet / film production can be used. For example, a feed block method in which the number of layers can be easily adjusted, and a multi-layer excellent in thickness accuracy of each layer can be used. The manifold method can be used, and the feed block method can be more preferably used in the present invention. In addition, when the film forming method is co-casting in which a plurality of layers are cast simultaneously or sequentially, particularly in the case of three or more layers, in terms of haze increase, the dope based on the manufacturing method of the present invention is It is preferably used for the surface layer or the layer following the surface layer. When the dope based on the production method of the present invention is used for the next layer, the thickness of the surface layer is preferably 10 μm, or the smaller one of 10% or less of the total film thickness, or 5 μm or 5 % Or less, more preferably 3 μm or 3% or less. In such a case, Gieser contamination with time may be reduced, which is preferable. In addition, from the viewpoint of releasability from the drum or band surface, the dope based on the production method of the present invention is preferably used for a layer that is not in direct contact with the support.
As for the casting and drying method in the solvent cast method, for example, JP-A-58-127737, JP-A-61-106628, JP-A-2-276830, JP-A-4-259511, and JP-A-5-163301. Publication No. 9-95544 Publication No. 10-45950 Publication No. 10-95854 Publication No. 11-71463 Publication No. 11-302388 Publication No. 11-322946 Publication No. 11-322947 Publication No. 11-322947 Publication No. 11-322947 11-323017, JP 2000-53784, 2000-273184, 2000-273239, U.S. Pat. No. 2,336,310, U.S. Pat. No. 2,367,603, U.S. Pat. No., U.S. Pat. No. 2492977, U.S. Pat. No. 2978, U.S. Pat. No. 2,607,704, U.S. Pat. No. 2,390,069, U.S. Pat. No. 2,739,070, British Patent No. 640731, British Patent No. 736892, Japanese Patent Publication No. 45-4554. No. 49, Japanese Patent Publication No. 49-5614, Japanese Patent Application Laid-Open No. 60-176834, Japanese Patent Application Laid-Open No. 60-203430, and Japanese Patent Application Laid-Open No. 62-115035 can be employed.
The dope is preferably cast on a support such as a drum or a band having a surface temperature of 10 ° C. or less.

  In the method of the present invention, the polymer solution is preferably formed on a support, then peeled off, and further dried. In this drying step, the residual solvent in the film is evaporated. Drying can be performed by blowing dry air. Drying may be performed in multiple stages by increasing the temperature of the drying air in stages. Details of the casting process and the drying process of the solution casting film-forming method are also described in pages 120 to 146 of JP-A-2005-104148, and can be applied to the present invention as appropriate.

The polymer film thus formed can be used as it is as the optical film of the present invention. In addition, if desired, the haze may be adjusted by performing a stretching treatment. There is no restriction | limiting in particular about extending | stretching conditions. It can be carried out under conditions usually performed, for example, a stretching temperature of about (Tg-20) to (Tg + 50) ° C. and a stretching ratio of about 20 to 40%.
Stretching can be performed using a roll stretching machine. A longitudinal or lateral uniaxial stretching process may be performed, or a biaxial stretching process may be performed. Generally, a longitudinal uniaxial stretching process for stretching a long film in the longitudinal direction will be performed.

  Although there is no restriction | limiting in particular about the thickness of the optical film of this invention, Generally, it is about 20-200 micrometers, and it is preferable that it is about 20-100 micrometers from a viewpoint of thickness reduction.

[Polarizing plate, liquid crystal display]
The optical film of the present invention is bonded to a polarizing film (hereinafter also referred to as a polarizer) and used for various applications such as an image display device. Before bonding with a polarizing film, you may surface-treat the bonding surface of the said polarizing plate protective film. The adhesion with the polarizing film is improved by the surface treatment. Examples of the surface treatment include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment (saponification treatment), and ultraviolet irradiation treatment. When the polarizing plate protective film contains cellulose acylate as a main component, it is particularly preferable to perform a saponification treatment.

There is no restriction | limiting in particular about the said polarizer. Various polarizers can be used. Optiva Inc. And a polarizer comprising a binder and iodine or a dichroic dye are preferable.
It is preferable that the protective film is bonded also to the surface of the polarizer opposite to the surface on which the optical film of the present invention is bonded. Examples of the polymer material of the protective film are the same as those of the polymer material used for producing the optical film of the present invention. Among these, a cellulose acylate film, a norbornene resin film, and a polycarbonate film are preferable.

  When laminating the optical film of the present invention and the polarizing film, an adhesive may be used. For example, a polyvinyl alcohol resin (acetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylene group-modified polyvinyl alcohol And a boron compound aqueous solution can be used as an adhesive. Among these, polyvinyl alcohol resin is preferable. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

  The optical film of the present invention or the polarizing plate having the optical film of the present invention can be used for various image display devices such as a liquid crystal display device, a projection display device, and an EL display device. Diffusion film conventionally required for improving display performance uniformity such as brightness and suppressing interference fringes such as moire by using the optical film of the present invention or the polarizing plate of the optical film of the present invention This contributes to a reduction in the thickness of the image display device.

  The polarizing plate having the optical film of the present invention is preferably used as a polarizing plate disposed near the light source of the image display device, and is preferably incorporated in an arrangement where the optical film of the present invention is closest to the light source. For example, when used in a transmissive liquid crystal display device, it is preferably used as a polarizing plate on the backlight side, and the optical film of the present invention is preferably arranged on the backlight side, not on the liquid crystal cell side.

  The polarizing plate having the optical film of the present invention may further have another functional layer. In an embodiment used for a liquid crystal display device, an optical compensation layer, an antireflection layer, an antiglare layer, a hard coat layer, and the like for compensating birefringence of the liquid crystal cell may be provided.

  The features of the present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

(Measurement method)
First, measurement methods and evaluation methods for various characteristics measured in the following examples are shown below.
1. Glass transition point (Tg)
Using a DSC measuring device (DSC8230: manufactured by Rigaku Corporation), 5-6 mg of a polymer film sample before heat treatment is placed in a DSC aluminum measuring pan (Cat. No. 8578: manufactured by Rigaku Corporation). This is heated from 25 ° C. to 120 ° C. at a rate of temperature increase of 20 ° C./min and held for 15 minutes in a nitrogen stream of 50 mL / min, and then cooled to 30 ° C. at −20 ° C./min. Thereafter, the temperature is increased again from 30 ° C. to 250 ° C. at a rate of temperature increase of 20 ° C./min, and the temperature at the intersection of the sample thermogram and the midline of the two baselines is measured on the film. The glass transition point of

2. Crystallization temperature (Tc)
Using a DSC measuring device (DSC8230: manufactured by Rigaku Corporation), 5-6 mg of a polymer film sample before heat treatment is placed in a DSC aluminum measuring pan (Cat. No. 8578: manufactured by Rigaku Corporation). This is heated in a nitrogen stream at 50 mL / min from 25 ° C. to 120 ° C. at a rate of temperature increase of 20 ° C./min, held for 15 minutes, and then cooled to 30 ° C. at −20 ° C./min. Furthermore, the temperature was raised again from 30 ° C. to 320 ° C. at a rate of 20 ° C./min, and the starting temperature of the exothermic peak that appeared at this time was taken as the crystallization temperature of the film.

3. Degree of substitution The degree of acyl substitution of cellulose acylate is determined according to Carbohydr. Res. Was determined by ¹³ C-NMR according to the method described in 273 (1995) 83-91 (Tezuka et al.).

4). Haze, total light transmittance and parallel transmittance: 5 points in the width direction of the film (the central part of the film, the end part (a position at 5% of the total width from both ends), and the middle part of the center part and the end part) Sampling is performed every 100 m in the longitudinal direction, and a sample having a size of 5 cm □ is taken out. The sample was conditioned at 25 ° C. and 60% relative humidity for 24 hours, and then the haze of each sample was measured using a haze meter (NDH 2000: manufactured by Nippon Denshoku Industries Co., Ltd.). Haze. In the case of a polymer solution, the measurement was performed according to the method described above.
The total light transmittance and the parallel transmittance were also sampled in the same manner, and each sample was measured according to the method described above, and the average values were taken as the total light transmittance and parallel transmittance of the film.

5. Indentation shape Five points in the film transport direction are sampled with reference to the center of the film, and a sample with a size of 5 cm □ is taken out. Of the dents included in this sample, about 1000 points, the depth of the dent, the standard deviation of the depth, the dent opening, using a three-dimensional non-contact surface shape measurement system (manufactured by Ryoka System Co., Ltd.) The average major axis length, the average minor axis length of the recess opening, the number of recesses per fixed area, the standard deviation of the number of recesses, and the average interval between the recesses (the center interval between the recesses and the recesses) were measured.

(Synthesis example: Synthesis of cellulose acetate propionate)
150 g of cellulose (hardwood pulp) and 75 g of acetic acid were placed in a 5 L separable flask equipped with a reflux apparatus as a reaction vessel and stirred vigorously for 2 hours while heating in an oil bath adjusted to 60 ° C. The cellulose subjected to such pretreatment was swollen and crushed to form a fluff shape. The reaction vessel was placed in an ice water bath at 2 ° C. for 30 minutes and cooled.
Separately, a mixture of 1545 g of propionic anhydride and 10.5 g of sulfuric acid was prepared as an acylating agent, cooled to −30 ° C., and then added to the reaction vessel containing the pretreated cellulose at once. After 30 minutes, the external temperature was gradually increased, and the internal temperature was adjusted to 25 ° C. after 2 hours from the addition of the acylating agent. The reaction vessel was cooled in an ice water bath at 5 ° C., the internal temperature was adjusted to 10 ° C. 0.5 hours after addition of the acylating agent, and the internal temperature was 23 ° C. after 2 hours, and the internal temperature was 23 ° C. The mixture was further stirred for 3 hours. The reaction vessel was cooled in an ice water bath at 5 ° C., and 120 g of 25% by mass hydrous acetic acid cooled to 5 ° C. was added over 1 hour. The internal temperature was raised to 40 ° C. and stirred for 1.5 hours. Next, a solution obtained by dissolving magnesium acetate tetrahydrate in 2-fold mol of sulfuric acid in 50% by mass aqueous acetic acid was added to the reaction vessel, and the mixture was stirred for 30 minutes. Cellulose acetate propionate was precipitated by adding 1 L of 25% by mass hydrous acetic acid, 500 mL of 33% by mass hydrous acetic acid, 1 L of 50% by mass hydrous acetic acid and 1 L of water in this order. The obtained cellulose acetate propionate precipitate was washed with warm water. By changing the washing conditions at this time, cellulose acetate propionate in which the amount of residual sulfate radicals is changed can be obtained. The sulfate radical content can be measured according to ASTM D-817-96. After washing, the mixture was stirred in a 0.005 mass% calcium hydroxide aqueous solution at 20 ° C. for 0.5 hour, further washed with water until the pH of the washing solution became 7, and then vacuum dried at 70 ° C.
^The degree of acetyl substitution, the degree of propionyl substitution, and the degree of polymerization of the obtained cellulose acylate were measured by ¹ H-NMR and GPC measurement.
Cellulose acylates A and B used in the following examples were produced with reference to the conventional method described above.

[Examples 1 to 22, Comparative Examples 1, 2, and 4]
(Manufacture and evaluation of optical films)
As shown in the following table, add any of the following cellulose acylates A or B in the proportions shown in the table, dissolve in any of the following solvents, and select any of additives A to E The cellulose acylate dopes were prepared. Details of the preparation method are also shown below.
Each cellulose acylate was heated to 120 ° C. and dried to adjust the water content to 0.5% by mass or less, and then the amount shown in Table 1 [parts by mass] was used.
1) <Cellulose acylate>
Cellulose acylate A (cellulose acetate):
A cellulose acetate powder having a substitution degree of 2.94 was used. Cellulose acylate A had a viscosity average degree of polymerization of 300 and a 6-position acetyl group substitution degree of 0.94.
Cellulose acylate B (cellulose acetate):
A cellulose acetate powder having a substitution degree of 2.86 was used. Cellulose acylate B has a viscosity average degree of polymerization of 300, a 6-position acetyl substitution degree of 0.89, an acetone extract of 7% by weight, a weight average molecular weight / number average molecular weight ratio of 2.3, and a water content of 0.2. Viscosity in a mass%, 6 mass% dichloromethane solution is 305 mPa · s, residual acetic acid content is 0.1 mass% or less, Ca content is 65 ppm, Mg content is 26 ppm, iron content is 0.8 ppm, sulfate ion content The amount was 18 ppm, the yellow index was 1.9, and the amount of free acetic acid was 47 ppm. The average particle size of the powder was 1.5 mm, and the standard deviation was 0.5 mm.

2) <Solvent>
As the solvent, one or two or more types are selected from dichloromethane (dielectric constant 9), methanol (dielectric constant 33), 1-butanol (dielectric constant 17), and water (dielectric constant 78), and the amounts shown in the following table [ Part by mass] was used as the solvent. The water content of these solvents was 0.2% by mass or less.

3) <Additives>
Those listed in Table 1 were selected from the following additives A to E, and the addition amount [% by mass] in parentheses below was used with respect to the cellulose acylate amount described in Table 1.
Additive A:
No additive / additive B:
Triphenyl phosphate (8.0% by mass)
Biphenyl diphenyl phosphate (4.0% by mass)
Additive C:
Condensate with ethanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1000) (12.0% by mass)
Additive D:
Silicon dioxide fine particles (particle size 20nm, Mohs hardness about 7) (0.4% by mass)
Additive E:
Silicon dioxide fine particles (particle size 200nm, Mohs hardness about 7) (30.0% by mass)

4) <Preparation of cellulose acylate solution>
Cellulose acylate was gradually added to the 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery, while stirring and dispersing the solvent and additives. After completion of the addition, the mixture was stirred at room temperature for 2 hours, swollen for 3 hours, and then stirred again to obtain a cellulose acylate solution.
For the stirring, a dissolver type eccentric stirring shaft that stirs at a peripheral speed of 15 m / sec (shear stress 5 × 10 ⁴ kgf / m / sec ² [4.9 × 10 ⁵ N / m / sec ² ]). In addition, an agitation shaft having an anchor blade on the central axis and stirring at a peripheral speed of 1 m / sec (shear stress 1 × 10 ⁴ kgf / m / sec ² [9.8 × 10 ⁴ N / m / sec ² ]) is used. It was. Swelling was carried out with the high speed stirring shaft stopped and the peripheral speed of the stirring shaft having anchor blades set at 0.5 m / sec.
The swollen solution was heated from a tank to 50 ° C. with a jacketed pipe, and further heated to 90 ° C. under a pressure of 2 MPa to be completely dissolved. The heating time was 15 minutes. At this time, filters, housings, and pipes that were exposed to high temperature were made of Hastelloy alloy and had excellent corrosion resistance, and those having a jacket for circulating a heat medium for heat retention and heating were used.
Next, the temperature was lowered to 36 ° C. to obtain a cellulose acylate solution.

5) <Filtration>
The obtained cellulose acylate solution is filtered through a filter paper (# 63, manufactured by Toyo Roshi Kaisha, Ltd.) with an absolute filtration accuracy of 10 μm, and further filtered onto a sintered metal filter (FH025, manufactured by Pall) with an absolute filtration accuracy of 2.5 μm. And filtered to obtain a polymer solution.

6-1) <Preparation of film (1)>
The cellulose acylate solution was heated to 30 ° C. and cast on a mirror surface stainless steel support having a band length of 60 m set at 15 ° C. through a casting Giesser (described in JP-A-11-314233). The casting speed was 50 m / min and the coating width was 200 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose acylate film cast and rotated 50 cm before the end point of the casting part was peeled off from the band, and 45 ° C. dry air was blown. Next, it was dried at 110 ° C. for 5 minutes and further at 140 ° C. for 10 minutes to obtain a cellulose acylate film having a thickness of 80 μm. In Examples 13 to 16, a cellulose acylate solution having the same composition as in Example 12 was used, and the film thickness of the obtained film was changed to obtain a cellulose acylate film.
6-2) <Production of film (2)> (Example 17)
Except for co-casting according to the feed block method so that the dope of Example 12 is on the air interface side and the dope of Comparative Example 4 is on the stainless steel support side, the same as <Film Production (1)> This was carried out to obtain a cellulose acylate film having a film thickness of 80 μm and an air interface side of 40 μm and a support side of 40 μm.
6-3) <Production of Film (3)> (Example 18)
In <Preparation of film (2)>, except for replacing the dope on the air interface side and the dope on the support side, the same procedure as in <Preparation of film (2)> is performed, and the air interface side is 40 μm and the support side is 40 μm. A cellulose acylate film having a thickness of 80 μm was obtained.

7) <Extension>
The obtained cellulose acylate was stretched as described below under the stretching conditions shown in Table 1. In addition, the draw ratio of the film was obtained from the following formula by placing marked lines at regular intervals in a direction orthogonal to the film transport direction, measuring the intervals before and after the stretching step.
Stretch ratio (%) of film = 100 × (interval between marked lines after stretching−interval between marked lines before stretching process) / interval between marked lines before stretching process Also, in each example, reduction in film width after stretching The rate was about 10-25%.

  The cellulose acylate film was subjected to longitudinal uniaxial stretching using a roll stretching machine. The roll of the roll drawing machine was an induction heating jacket roll having a mirror-finished surface, and the temperature of each roll could be adjusted individually. The stretching zone was covered with a casing, and the temperatures shown in Table 1 were used. The roll before the stretching part was set so that it could be gradually heated to the stretching temperature described in Table 1. The draw ratio was controlled by adjusting the peripheral speed of the nip roll. The aspect ratio (distance between nip rolls / base inlet width) was adjusted to 0.5, and the stretching speed was 10% / min with respect to the distance between stretching.

(Production of Comparative Example 3 Film)
A cellulose acylate film was produced in the same manner as Example 1 and Film 3 of JP-A No. 2001-172403, and used as an optical film of Comparative Example 3. In Table 1 below, the details of the production method of Comparative Example 3 are described as “* 1”.

8) <Evaluation of cellulose acylate film>
Each obtained cellulose acylate film was evaluated. The results are shown in Table 1 below. In each of the obtained examples, the shape of the recessed opening when observed from the direction perpendicular to the film surface is close to a circular shape, and the equivalent circle diameter (projected area equivalent circle diameter) is about 5 to 15 μm. Range. Similarly, the shape of the bottom of the dent when observed from the direction perpendicular to the film surface of the dent was close to a circle, and the equivalent circle diameter (projected area equivalent circle diameter) was in the range of about 3 to 10 μm. Moreover, the details of the cross section in the thickness direction of the film other than those described in Table 1 in each Example are such that the bottom of the dent is formed with a width of 60 to 70% when the lateral width of the entire dent is 100%, The slope of the surface of the bottom of the recess was within ± 2.5 °, and the curvature radius gradually decreased from the bottom of the recess toward the end of the recess. Moreover, the internal porosity of the obtained film was 3% (volume ratio) or less in any case. The dimensional change rate of the indentation was 0.5% or less.

(Preparation of polarizing plate)
The back surface of the produced film was alkali saponified. It was immersed in a 1.5 N aqueous sodium hydroxide solution at 55 ° C. for 2 minutes, washed in a water bath at room temperature, and neutralized with 0.1 N sulfuric acid at 30 ° C. Again, it was washed in a water bath at room temperature and further dried with hot air at 100 ° C. Subsequently, a roll-shaped polyvinyl alcohol film having a thickness of 80 μm was continuously stretched 5 times in an iodine aqueous solution and dried to obtain a polarizing film having a thickness of 20 μm. Using the 3% aqueous solution of polyvinyl alcohol (Kuraray PVA-117H) as an adhesive, the above alkali saponified films and the same alkali saponified Fujitac TD80UL (manufactured by FUJIFILM) were prepared. The polarizing films were bonded to each other with the polarizing film sandwiched therebetween to produce polarizing plates in which each film and TD80UL was a protective film for the polarizing film.

(Production and evaluation of liquid crystal display devices)
A liquid crystal display device was produced using each of the produced polarizing plates. Specifically, a VA mode liquid crystal cell is used as the liquid crystal cell, the polarizing plate on the backlight side is peeled off, and the prepared polarizing plate is pasted with an adhesive so that the surface of the diffusive protective film is on the backlight side. In combination, a liquid crystal display device was produced.

The display performance of each produced liquid crystal display device was confirmed. Specifically, the diffusion sheet used was removed, and the luminance distribution change rate (brightness uniformity) and the front white luminance during white display were confirmed by the following method. BM-5 (manufactured by Topcon) was used for luminance measurement.
For the luminance distribution change rate (uniformity), the BM-5 was scanned in the horizontal direction (CCFL and vertical direction), and the luminance profile in the horizontal direction (CCFL and vertical direction) was measured. Values obtained by dividing these values by each background luminance, that is, the rate of change were obtained. The rate of change corresponds to the discrimination threshold (JND) for the brightness of the human eye. Generally, when it exceeds 10%, it is recognized that the brightness has changed. The evaluation criteria were not exceeding.
Since the front white luminance of the VA mode liquid crystal TVs that have been sold so far is 350 to 600 [cd / m ² ], the front white luminance was set to exceed 350 [cd / m ² ].

Of these two evaluation criteria of luminance distribution change rate and frontal white luminance, “◯” indicates that both of them are satisfied, and “X” indicates that the two are not satisfied. Of the “◯”, those close to the critical value were described as “Δ”.
The results are shown in Table 1 below.

  As shown in Table 1, in Examples using the polarizing plate protective film of the present invention, the uniformity of luminance was high, and all were evaluated as “◯”. On the other hand, in Comparative Example 1 using an optical film having a surface property outside the range of the present invention, the luminance was non-uniform and the evaluation was “x”. In Comparative Example 2, the front white brightness was poor and the evaluation was “x”. In Comparative Example 3, the haze was high, but the total light transmittance was too low, the front white luminance was poor, and the evaluation was “x”. In Comparative Example 4, the total light transmittance was high, but the haze was too low, the luminance was uneven, and the evaluation was “x”. From this, it can be understood that the present invention shows an excellent effect as compared with the conventional example. In Example 19 where the polymer concentration was high and Example 20 where the amount of alcohol was very small, some streak marks were visually confirmed on the film surface.

Claims (19)

An optical film comprising a uniform composition, having an independent depression on the film surface, the depth of the depression is 5 μm or less, the average major axis length of the depression is 0.5 to 100 μm, and the film surface An optical film in which the number of depressions in the film is 25 to 1,000,000 pieces / m ² .   2. The optical film according to claim 1, wherein an average interval between the two recesses is 0.5 to 100 μm.   3. The optical film according to claim 1, wherein a standard deviation of the number distribution of the depressions on the film surface is ± 20% with respect to the average number.   The optical film according to any one of claims 1 to 3, wherein a standard deviation of the depth of the dent is ± 20% with respect to an average depth.   The said depression | indentation in the surface of a film has a bottom part which protrudes below and is substantially parallel to a film surface, and a side part which connects the said bottom part and a depression | indentation opening part. An optical film according to item.   6. The optical film according to claim 1, wherein a dimensional change rate of the dent before and after the glass transition temperature is 5% or less.   Haze is 15% or more, The optical film as described in any one of Claims 1-6 characterized by the above-mentioned.   The optical film according to claim 1, wherein the total light transmittance is 50% or more.   The optical film according to any one of claims 1 to 8, wherein the polymer composition contains a cellulose acylate polymer as a main component. A step of dissolving a polymer composition in a solvent containing at least two kinds of solvents incompatible with each other containing a solvent having a dielectric constant of 35 or more and preparing a polymer solution, and forming the polymer solution into a film A method for producing an optical film.   The method for producing an optical film according to claim 10, wherein the solvent is a solvent containing 0.3 to 30% by mass of a solvent having a dielectric constant of 35 or more.   The method for producing an optical film according to claim 10 or 11, wherein the polymer is cellulose acylate.   The said solvent contains the solvent whose dielectric constant is 4-10, and the solvent whose dielectric constant is 10-35, The manufacturing method of the optical film as described in any one of Claims 10-12 characterized by the above-mentioned.   The method according to claim 10, wherein the solvent having a dielectric constant of 35 or more is water. A step of preparing a polymer solution by dissolving a polymer composition in a solvent containing a solvent having a dielectric constant of 35 or more and containing at least two kinds of solvents that are not compatible with each other; and an optical method comprising forming a film of the polymer solution In the film manufacturing method,
A process comprising casting a polymer solution onto a support to form a film, and thereafter peeling the film from the support, and further comprising a step of evaporating the solvent during film formation, after film formation, or both Item 15. The method for producing an optical film according to any one of Items 10 to 14.   The optical film manufactured by the manufacturing method as described in any one of Claims 10-15.   A polarizing plate comprising a polarizing film and at least one optical film according to any one of claims 1 to 9 and 16.   An image display device comprising at least one optical film according to any one of claims 1 to 9 and 16, or a polarizing plate according to claim 17.   It has a liquid crystal cell and a backlight, The said polarizing plate is arrange | positioned with the optical film as described in any one of Claims 1-9 and 16 on the backlight side between a liquid crystal cell and a backlight. The image display device according to claim 18.