JP2013064814A - Optical film, and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film which has a sea-island structure, and both of excellent light diffusion property and light transmission property, and in which brittleness is improved; and a manufacturing method of the optical film.SOLUTION: The optical film contains acryl resin and cellulose acylate resin, and has the sea-island structure. The content mass ratio of the acryl resin and cellulose acylate resin is within a range of 51:49 to 90:10. The cellulose acylate resin includes at least two kinds of cellulose acylate resins of a cellulose acylate resin with average total number of carbon atoms in the acyl group being less than 6.0 per a glucose unit, and a cellulose acylate resin with average total number of carbon atoms being 6.0 or more.

Description

  The present invention relates to an optical film having excellent light diffusibility and light transmittance and improved brittleness, and a method for producing the same.

  A liquid crystal display device (hereinafter also referred to as “LCD”) is generally composed of a backlight unit, a liquid crystal cell, and a polarizing plate. The polarizing plate usually comprises a protective film for a polarizing plate and a polarizer (also referred to as “polarizing film”). As the polarizer, a polyvinyl alcohol film dyed with iodine and stretched is often used, and both surfaces thereof are covered with a protective film for a polarizing plate. As a protective film for a polarizing plate, a cellulose triacetate (TAC) film having excellent moisture permeability and excellent adhesion to a polarizer is often used.

  In recent years, thinning and cost reduction have been advanced in the field of LCD. Since the liquid crystal display device is not a self-luminous display device, a light source such as a cold cathode tube (CCFL) or LED is provided on the back side of the liquid crystal cell (backlight type) or on the edge portion (edge light type) of the light guide plate. Is always placed. Since these light sources are generally line light sources or point light sources, a light diffusion sheet or a light diffusion film (also referred to as a “diffusion sheet” or “diffusion film”) is used in order to form a uniform surface light source. ing. The light diffusion sheet is produced by interference between a light collecting sheet (prism sheet) often used as a member for imparting directivity to light and incident light, or by interference between pixels in a liquid crystal cell and incident light. Interference fringes such as moire can be suppressed.

  However, in recent years, with the trend toward thinning and cost reduction, the number of liquid crystal display device members has been reduced, and LCDs that do not use a light diffusion sheet have come out. Even when a light diffusing sheet is used, the distance between the light source and the light diffusing sheet is reduced due to the thinning of the LCD. Therefore, it is difficult to eliminate interference fringes such as moire only with the conventional light diffusing sheet. It is becoming. Therefore, an optical film having diffusibility on the surface of the backlight side polarizing plate has been used as an alternative to the light diffusion sheet.

  For example, Patent Document 1 proposes a surface light source device including a light-transmitting substrate having a recess in the order of a light source, a light collecting sheet, and a light-transmitting substrate. Since a resin solution containing water is formed into a film, there is a problem that the drying load is large and the manufacturing cost is very high. In addition, due to the recesses in which the holes are formed, the size of the recesses changes due to dimensional changes due to high humidity heat, and the light distribution characteristics change during use as a surface light source device.

  Patent Document 2 proposes a light diffusing polarizing plate having a light diffusing layer having a predetermined characteristic, which contains porous amorphous particles and spherical particles in a dispersed manner, and discloses that a light diffusing sheet can be omitted thereby. . According to this method, it is possible to eliminate moiré fringes, but when forming a polarizing plate, there is a problem that fine particles fall off and cause process contamination, and the front luminance decreases when a display device is used. There was a problem.

  Patent Documents 3 and 4 propose that a light diffusion film containing translucent fine particles and crosslinkable fine particles is used as a protective film for a polarizing plate. However, even with this method, there are problems such as the dropout of fine particles when forming a polarizing plate as described above, and the problem that it cannot be produced at low cost.

  For this reason, there has been a demand for a new optical film that does not drop fine particles and has both light diffusibility sufficient to eliminate moire fringes and suitability for a protective film for a polarizing plate.

  In Patent Documents 5 and 6, a light diffusion film having a sea-island structure in which a dope composed of a plurality of resins is cast on a support and phase-separated, or a mixed solution of a plurality of resins is applied on the support film. The produced light diffusion film is disclosed. According to this method, an optical film having light diffusibility can be produced, and since the fine particles are not used, the problem of fine particle dropping off can be solved. However, it has been found that there is a new problem in that when the film is used as a protective film for a polarizing plate while maintaining light diffusibility, the transmittance is lowered and the luminance when the display device is formed is lowered. It was also found that there was a problem that the film became brittle due to peeling at the interface between the sea part and the island part.

  In addition, a method for producing a light diffusable optical film by applying a mixed solution of a plurality of resins on a support film must be applied after film formation, and therefore the market is currently undergoing cost reduction. There is a fundamental problem that does not meet the requirements.

JP 2011-76954 A JP 2000-75134 A JP 2010-277080 A JP 2010-164931 A JP 2000-239535 A JP 2002-250806 A

  The present invention has been made in view of the above-described problems and circumstances, and the solution to the problem is an optical film having a sea-island structure, which has excellent light diffusibility and light transmittance, and is improved in brittleness. An optical film is provided. Moreover, it is providing the manufacturing method of the said optical film.

  In order to solve the above-mentioned problems, the present inventor has a specific film having a sea-island structure composed of an acrylic resin and at least two kinds of cellulose acylate resins in the process of examining the cause of the above-mentioned problem, and the like. The present invention has been found out that it has both light transmittance and high mechanical strength.

That is, the said subject which concerns on this invention is solved by the following means.
1. An optical film containing an acrylic resin and a cellulose acylate resin and having a sea-island structure, wherein the mass ratio of the acrylic resin and the cellulose acylate resin is in the range of 51:49 to 90:10, and The cellulose acylate resin has at least two types of cellulose acylate, that is, a cellulose acylate resin having an average total carbon atom number of acyl groups of less than 6.0 and a cellulose acylate resin of 6.0 or more per glucose unit. An optical film containing a rate resin.
2. The cellulose acylate resin has at least an acetyl group or a propionyl group as the acyl group, and the average total number of carbon atoms of the acyl group is less than 6.0 per glucose unit. 2. The optical film as described in 1 above, wherein the degree of group substitution is 1.0 or less.
3. The total haze value of the optical film is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the average surface roughness (Ra) of the two surfaces of the optical film is The total value is in the range of 0.3 to 2 μm, The optical film as described in the above item 1 or 2,
4). In the first to third items, the image clarity of the optical film is within a range of 0.8 to 5.0% in measurement using an optical comb having a width of 0.25 mm. The optical film as described in any one.
5. The total haze value is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the total value of the average surface roughness (Ra) of the two surfaces of the optical film is 0. A method for producing an optical film having a sea-island structure in a range of 3 to 2 μm, wherein an acrylic resin and a cellulose acylate resin are mixed at a mass ratio in a range of 51:49 to 90:10, and The cellulose acylate resin has at least two kinds of cellulose acylates, ie, a cellulose acylate resin having an average total carbon atom number of acyl group of less than 6.0 and a cellulose acylate resin having a number of 6.0 or more per glucose unit. A method for producing an optical film, comprising mixing a resin to prepare a dope.

  By the above means of the present invention, it is possible to provide an optical film having a sea-island structure, which has both excellent light diffusibility and light transmittance and improved brittleness. Moreover, the manufacturing method of the said optical film can be provided.

  The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

  When the solvent of a uniform polymer solution in which two or more kinds of resins are mixed is evaporated to be concentrated and saturated, fine phase separation (microphase separation) occurs. Thereafter, by stretching the formed resin film, a resin component having a high glass transition temperature rises, and an uneven structure (sea-island structure) is formed. Thereby, it is estimated that the film which is light transmittance and the diffusion function was provided is formed.

The figure which showed typically an example of the dope preparation process, casting process, and drying process of a solution casting film forming method The figure which showed the example of the structure of the conventional liquid crystal display device typically The figure which showed typically the structural example of the liquid crystal display device using the optical film of this invention.

  The optical film of the present invention is an optical film containing an acrylic resin and a cellulose acylate resin and having a sea-island structure, and the content mass ratio of the acrylic resin to the cellulose acylate resin is 51:49 to 90:10. And the cellulose acylate resin has an acyl group having an average total carbon atom number of less than 6.0 per glucose unit and a cellulose acylate resin of 6.0 or more. It contains at least two kinds of cellulose acylate resins.

  This feature is a technical feature common to the inventions according to claims 1 to 5.

  As an embodiment of the present invention, from the viewpoint of the effect of the present invention, the cellulose acylate resin has at least an acetyl group or a propionyl group as the acyl group, and the average total number of carbon atoms of the acyl group is The cellulose acylate resin having a propionyl group substitution degree of less than 6.0 per glucose unit is preferably 1.0 or less. The total haze value of the optical film is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the average surface roughness (Ra ) Is preferably in the range of 0.3 to 2 [mu] m from the viewpoint of controlling the light transmittance and diffusibility within an appropriate range.

  Furthermore, in this invention, it is preferable that the image definition of the said optical film exists in the range of 0.8 to 5.0% in the measurement using the optical comb of 0.25 mm width. Thereby, the effect of light diffusibility is obtained.

  As a manufacturing method of the optical film of the present invention, the total haze value is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the average of the two surfaces of the optical film. A method for producing an optical film having a sea-island structure in which a total value of surface roughness (Ra) is within a range of 0.3 to 2 μm, wherein an acrylic resin and a cellulose acylate resin are mixed at 51:49 to 90:10. The cellulose acylate resin is mixed at a mass ratio within the range, and the cellulose acylate resin has a cellulose acylate resin having an average total carbon atom number of acyl group of less than 6.0 and a cellulose acylate of 6.0 or more per glucose unit. From the viewpoint of increasing the effects of the present invention, it is preferable that the production method is an embodiment in which a dope is prepared by mixing at least two kinds of cellulose acylate resins with a rate resin.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

(Outline of optical film of the present invention)
The optical film of the present invention is a resin film having a sea-island structure composed of a continuous phase corresponding to the sea and a dispersed phase corresponding to the island.

  In the present application, the “sea-island structure” means that when a plurality of (for example, two) resin components that are incompatible with each other are mixed, the higher-order structure of the mixture is a phase in which one of the resin components is continuous. The other is a structure in which islands or particles are dispersed. That is, it means a structure formed by one resin being a continuous phase (matrix) corresponding to the sea and the other being a dispersed phase corresponding to the island.

  In the present invention, it is necessary that the mass ratio of the acrylic resin and the cellulose acylate resin be in the range of 51:49 to 90:10, but the resin that is the main component constituting the continuous phase corresponding to the sea Is an acrylic resin, and a resin as a main component constituting a dispersed phase corresponding to an island is a cellulose acylate resin.

  The cellulose acylate resin has at least two types of cellulose acylate, that is, a cellulose acylate resin having an average total carbon atom number of acyl groups of less than 6.0 and a cellulose acylate resin of 6.0 or more per glucose unit. It needs to contain a rate resin.

  Of these two types of cellulose acylate resins, cellulose acylate having an acyl group having an average total carbon number of less than 6.0 is a resin that is a main component constituting a dispersed phase corresponding to an island. On the other hand, the cellulose acylate having an acyl group having an average total carbon number of 6.0 or more is more compatible with the acrylic resin than the cellulose acylate having an acyl group having an average total carbon number of less than 6.0. It is added in order to moderate some discontinuity in the boundary region between the continuous phase and the dispersed phase and to prevent peeling at the interface.

  In addition, in this application, the average total carbon atom number of the acyl group which cellulose acylate has is the number of carbon atoms of each substituent (for example, acetyl group) in the acyl group substitution degree such as propionyl group substitution degree and butyryl group substitution degree. The total number of carbon atoms obtained by multiplying by 2), the number of carbon atoms of the propionyl group is 3, and the number of butyryl groups is 4).

  In the present invention, the image clarity of the optical film is in the range of 0.8 to 5.0% in the measurement using an optical comb having a width of 0.25 mm, and the total light transmittance is 91.0% or more. It is preferable that Further, the image definition is preferably in the range of 0.9 to 2.5%.

  In the present application, the image clarity (also referred to as “image clarity”) of the optical film is a value obtained by measurement by a transmission method in accordance with JIS K7374: 2007. Moreover, the total light transmittance made the average value of the light transmittance in the 450-650 nm light wavelength range the total light transmittance.

  Examples of means for controlling the image definition within a predetermined range include adjustment according to stretching conditions such as a stretching ratio and a stretching temperature. Further, as a means for controlling the total light transmittance to a predetermined value or higher, selection of a resin having a resin refractive index difference of 0.08 or less can be cited.

  In the present invention, the glass transition temperature of cellulose acylate as a main component constituting the dispersed phase (island) of the sea-island structure, and the glass transition temperature of acrylic resin as the main component constituting the continuous phase (sea) Is more than 10 ° C., and the difference in refractive index between the acrylic resin and the cellulose acylate resin is preferably 0.08 or less.

<acrylic resin>
The optical film of the present invention is an optical film containing an acrylic resin and a cellulose acylate resin.

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

  Examples of other copolymerizable monomers include alkyl methacrylates having 2 to 18 carbon atoms in the alkyl number, alkyl acrylates having 1 to 18 carbon atoms in the alkyl number, acrylic acid, and methacrylic acid. -Unsaturated group-containing divalent carboxylic acids such as unsaturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated such as acrylonitrile and methacrylonitrile Examples thereof include nitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like. These can be used alone or as a copolymer in combination of two or more monomers.

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

  The acrylic resin used in the optical film according to the present invention has a weight average molecular weight (Mw) of 80000 or more, particularly from the viewpoint of improving brittleness as an optical film and improving transparency when used in combination with a cellulose acylate resin. . When the weight average molecular weight (Mw) of the acrylic resin is less than 80000, sufficient brittleness improvement cannot be obtained, and compatibility with the cellulose acylate resin deteriorates. The weight average molecular weight (Mw) of the acrylic resin is more preferably in the range of 80,000 to 1,000,000, particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000. Although the upper limit of the weight average molecular weight (Mw) of an acrylic resin is not specifically limited, It is a preferable form that it shall be 1 million or less from a viewpoint on manufacture.

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

<Cellulose acylate resin>
The cellulose acylate resin according to the present invention is a resin in which a large number of β-glucose molecules are linearly polymerized by β-1,4-glycoside bonds. The glucose unit constituting cellulose with the β-1,4-glycosidic bond has free hydroxy groups (hydroxyl groups) at the 2nd, 3rd and 6th positions. Therefore, the cellulose acylate resin according to the present invention is a polymer (resin) obtained by esterifying part or all of these hydroxy groups (hydroxyl groups) with acyl groups.

  The cellulose acylate resin according to the present invention has at least two types of cellulose acylate resin having an average total carbon atom number of acyl group of less than 6.0 and a cellulose acylate resin of 6.0 or more per glucose unit. The cellulose acylate resin is contained.

  Of these two types of cellulose acylate resins, cellulose acylate having an acyl group having an average total carbon number of less than 6.0 is a resin that is a main component constituting a dispersed phase corresponding to an island.

  In the present invention, from the viewpoint of reducing compatibility with the acrylic resin and forming a dispersed phase, the cellulose acylate resin having an average total number of carbon atoms of the acyl group of less than 6.0 per glucose unit. The degree of propionyl group substitution is preferably 1.0 or less. The degree of acetyl group substitution is preferably in the range of 1.5 to 3.0.

  On the other hand, the cellulose acylate having an acyl group having an average total carbon number of 6.0 or more is more compatible with the acrylic resin than the cellulose acylate having an acyl group having an average total carbon number of less than 6.0. It is added in order to moderate some discontinuity in the boundary region between the continuous phase and the dispersed phase and to prevent peeling at the interface.

  In addition, it is preferable that the substitution degree of propionyl group of the cellulose acylate having an acyl group having an average total carbon number of 6.0 or more is in the range of 1.0 to 2.7. The degree of acetyl group substitution is preferably in the range of 0.1 to 2.0.

  In addition, in this application, the average total carbon atom number of the acyl group which cellulose acylate has is the acetyl group substitution degree such as propionyl group substitution degree and butyryl group substitution degree. The total number of carbon atoms obtained by multiplying by 2), the number of carbon atoms of the propionyl group is 3, and the number of butyryl groups is 4).

  For example, when the average total carbon atom number of the acyl group is A, the acetyl group substitution degree is X, the propionyl group substitution degree is Y, and the butyryl group substitution degree is Z, the average total carbon atom number A is represented by the following formula. .

A = 2 × X + 3 × Y + 4 × Z
The “acyl group substitution degree” represents the total of the ratios of esterified hydroxy groups (hydroxyl groups) at the 2nd, 3rd and 6th positions of glucose as a repeating unit. Specifically, the substitution degree is 1 when the hydroxy groups (hydroxyl groups) at the 2-position, 3-position and 6-position of cellulose are esterified 100%. Therefore, when all of the 2nd, 3rd and 6th positions of cellulose are 100% esterified, the degree of substitution is 3 at the maximum.

  In the present application, “acyl group substitution degree” refers to an acyl group substitution degree in which the acyl group substitution degree of a plurality of glucose units constituting cellulose acylate is expressed as an average value per unit. In the present application, the average value of the degree of substitution of a specific acyl group, for example, acetyl group, propionyl group, etc., is expressed as “average” as “acetyl group substitution degree”, “propionyl group substitution degree”, respectively. It will be expressed for short.

  The measuring method of acyl group substitution degree can be measured according to ASTM-D817-96.

  Examples of the acyl group include acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, and isobutanoyl. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like.

  Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms), more preferably an acetyl group.

  In the case of an aliphatic acyl group, the number of carbon atoms is preferably 2 to 6, and more preferably 2 to 4, from the viewpoints of cellulose synthesis productivity and cost. Moreover, it is preferable that the part which is not substituted by the acyl group exists normally as a hydroxyl group (hydroxyl group).

  Cellulose as a raw material for cellulose acylate is not particularly limited, and examples thereof include cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like. Moreover, the cellulose acylate obtained from them can be mixed and used at an arbitrary ratio.

  The cellulose acylate according to the present invention can be produced by a known method.

  Generally, cellulose is esterified by mixing cellulose as a raw material, a predetermined organic acid (such as acetic acid or propionic acid), an acid anhydride (such as acetic anhydride or propionic anhydride), and a catalyst (such as sulfuric acid). The reaction proceeds until the triester is formed. In the triester, the three hydroxy groups (hydroxyl groups) of the glucose unit are substituted with an acyl acid of an organic acid. When two kinds of organic acids are used at the same time, a mixed ester type cellulose acylate such as cellulose acetate propionate or cellulose acetate butyrate can be produced. Next, a cellulose acylate resin having a desired degree of acyl group substitution is synthesized by hydrolyzing the cellulose triester. Thereafter, a cellulose acylate resin is completed through steps such as filtration, precipitation, washing with water, dehydration, and drying.

  Specifically, it can be synthesized with reference to the methods described in JP-A Nos. 10-45804 and 2009-161701.

  The cellulose acylate used in the optical film of the present invention is not particularly limited as long as the above conditions are satisfied. The ester group may be a linear or branched carboxylic acid ester having about 2 to 22 carbon atoms. Preferably, these carboxylic acids may form a ring or may be an ester of an aromatic carboxylic acid. In addition, these carboxylic acids may have a substituent. The cellulose acylate is particularly preferably a lower fatty acid ester having 6 or less carbon atoms.

  As a preferred cellulose acylate, specifically, in addition to cellulose acetate, a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate. And a mixed fatty acid ester of cellulose. Of these, cellulose acetate propionate is particularly preferred.

  The cellulose acylate having an acyl group having an average total number of carbon atoms of 6.0 or more used in the optical film of the present invention is particularly suitable for improvement in brittleness and transparency when it is compatible with an acrylic resin. Total substitution degree (T) is 2.0 to 3.0, substitution degree of acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and substitution of acyl group having 3 to 7 carbon atoms The degree is preferably 2.0 to 3.0. That is, the cellulose acylate resin according to the present invention is a cellulose acylate resin substituted with an acyl group having 3 to 7 carbon atoms, and specifically, propionyl, butyryl and the like are preferably used. Is preferably used.

  When the total substitution degree of the acyl group of the cellulose acylate resin is in the range of 2.0 to 3.0, that is, the residual degree of the hydroxy groups at the 2, 3, and 6 positions of the cellulose acylate molecule is less than 1.0. In such a case, the compatibility between the cellulose acylate resin and the acrylic resin is increased, and when used as an optical film, the transparency is increased.

  Even when the total substitution degree of the acyl group is less than 2.0, if the substitution degree of the acyl group having 3 to 7 carbon atoms is more than 1.2, compatibility is improved and brittleness is also increased. preferable. For example, even when the total substitution degree of the acyl group is less than 2.0, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is low, and the substitution degree of the acyl group having 3 to 7 carbon atoms is low. When exceeding 1.2, compatibility becomes high and transparency improves.

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

  When the cellulose acylate resin has an aromatic acyl group as a substituent, the number of substituents X substituted on the aromatic ring is preferably 0 to 5. Also in this case, it is preferable that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0.

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

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

  The cellulose acylate resin used in the optical film according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate. That is, those having an acyl group having 3 or 4 carbon atoms as a substituent are preferred.

  Among these, cellulose acylate resins that are particularly preferable are cellulose acetate propionate and cellulose propionate.

  The weight average molecular weight (Mw) of the cellulose acylate resin used in the optical film according to the present invention is 75000 or more, particularly from the viewpoint of improving compatibility with acrylic resin and brittleness, and is in the range of 75,000 to 300,000. Preferably, it is more preferably in the range of 100,000 to 240,000, particularly preferably 160000 to 240000. When the important average molecular weight (Mw) of the cellulose acylate resin is less than 75000, the effect of improving the heat resistance and brittleness is not sufficient, and the effect of the present invention cannot be obtained.

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

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

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

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

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

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

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

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

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

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

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

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

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

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

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

(Outline of optical film manufacturing method)
The method for producing an optical film of the present invention is a method for producing an optical film having a sea-island structure composed of a continuous phase corresponding to the sea and a dispersed phase corresponding to an island, and is a resin that is a main component constituting the island ( The difference between the glass transition temperature Tg (B) of the cellulose acylate resin B) and the glass transition temperature Tg (A) of the acrylic resin that is the main component resin constituting the sea (A) (Tg (B) -Tg (A)) is more than 10 ° C, the difference in refractive index between the resin A and the resin B is 0.08 or less, and the production method of the embodiment having the following steps (a) to (d) Preferably there is.
Step (a): Step of forming a dope containing the resin A and the resin B (b): Step of casting the dope on a casting support to form a web (c): The web Drying step evaporating the organic solvent from (d): at a temperature at which the stretching temperature T satisfies Tg (A) <T <Tg (B),
Stretching step of stretching the web at a magnification within a range of 1.03 to 1.20 times. Specifically, the glass transition temperature Tg (B) of the resin B as a main component constituting the island constitutes the sea. It is preferably higher than the glass transition temperature of the resin A as the main component, and the difference between them (Tg (B) −Tg (A)) is more than 10 ° C. Moreover, it is preferable that it is a manufacturing method of the optical film whose refractive index difference of resin A and resin B is 0.08 or less. Furthermore, it is preferable that it is a manufacturing method which has the said process (a)-(d).

  According to the production method of the present invention, it is possible to provide an optical film having a light diffusing ability that overcomes the brittleness problem that has been a problem with conventional scattering films made of resin blends. In particular, when used as a protective film for a backlight side polarizing plate, it is possible to provide an image display device with excellent image quality in which moire fringes are eliminated without reducing the front luminance.

<Glass transition temperature of resins A and B and stretching temperature in stretching process>
In the present invention, the difference (Tg (B) −) between the glass transition temperature Tg (B) of the resin B as the main component constituting the island and the glass transition temperature Tg (A) of the resin A as the main component composing the sea. Tg (A)) is preferably more than 10 ° C. Furthermore, it is preferable to extend | stretch so that the temperature T in an extending process may satisfy | fill Tg (A) <T <Tg (B).

  As a result, by extending the resin that constitutes the sea while the island structure is not oval in shape but in a round shape, the protruding state of the island structure can be controlled, and sufficient moire can be achieved without causing a decrease in transmittance. A resolution ability can be imparted.

  From the viewpoint of preventing failure such as peeling at the interface between the sea structure and the island structure, and preventing reduction in transmittance and front luminance, a more preferable range is the difference in glass transition temperature between resin B and resin A (Tg (B) −Tg ( A)) is 15 ° C. or higher, that is, (Tg (B) −Tg (A)) ≧ 15 (° C.).

  In addition, in this application, a glass transition temperature is the meaning also including apparent Tg in case resin contains a solvent. Further, as the glass transition temperature of the resin, a midpoint glass transition temperature (Tmg) obtained by measuring at a temperature rising rate of 20 ° C./min using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer) is used. be able to.

  Moreover, the film made by the manufacturing method according to the present invention has a sea-island structure due to phase separation of the resin, and has a concavo-convex shape derived from the sea-island structure. In order to observe the shape of the island portion, a 3D laser microscope LEXT OLS4000 manufactured by Olympus Corporation can be used.

<Refractive index difference between resins A and B>
In the present invention, the difference between the refractive index (A) of the resin A as the main component constituting the sea and the refractive index (B) of the resin B as the main component constituting the island is 0.08 or less. That is, it is preferable that | refractive index (A) −refractive index (B) | ≦ 0.08.

  More preferably, | refractive index (A) −refractive index (B) | ≦ 0.03. By making both refractive index into this range, it can suppress that the internal haze of an optical film increases, and when it is set as a display apparatus, it can suppress that front luminance falls.

  In the present invention, the refractive index means an average refractive index, and the refractive index of the resin A and the refractive index of the resin B are measured using Abbe's refractometer or the like by producing a film made of each resin. be able to.

<Stretch ratio in stretching process>
In the present invention, the draw ratio in the drawing step is preferably 1.03 to 1.20 times at a temperature at which the drawing temperature T satisfies Tg (A) <T <Tg (B).

  If the draw ratio is 1.03 times or more, the effect of the present invention is exhibited. If it is 1.20 times or less, it can suppress that front brightness falls, when a haze value raises and it is set as a display apparatus.

(Optical film manufacturing method)
The method for producing an optical film according to the present invention is a method for producing an optical film having a sea-island structure composed of a continuous phase corresponding to the sea and a dispersed phase corresponding to an island, and is a resin that is a main component constituting the island The difference between the glass transition temperature Tg (B) of B (cellulose acylate resin) and the glass transition temperature Tg (A) of the resin A (acrylic resin) as the main component constituting the sea (Tg (B) −Tg ( A)) is more than 10 ° C., the difference in refractive index between the resin A and the resin B is 0.08 or less, and the production method of the embodiment having the steps (a) to (d). preferable.

In this invention, it is preferable that the extending | stretching speed | rate in the said extending | stretching process calculated | required by following formula (I) exists in the range of 20-300% / min.
Formula (I): Stretching speed (% / min) = {(width dimension after stretching / width dimension before stretching) -1} × 100 (%) / time required for stretching (min)
By manufacturing by the said method, the optical film of this invention can be produced with an easy process without the process contamination by fine particle fall-off.

  Hereinafter, the method for producing an optical film of the present invention will be described in more detail, but the present invention is not limited thereto.

  As a film forming method of the optical film of the present invention, solution film forming by the following casting method is preferable.

  FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention.

1) Dissolution process In an organic solvent mainly composed of a good solvent for the resin to be used, the resin B constituting the island, the resin A constituting the sea, and other additives are dissolved in the dissolution vessel while stirring to form a dope. It is a process to do.

  For dissolution of the resin, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557, or Various dissolution methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using a high pressure as described in JP-A-11-21379 can be used. A method in which pressure is applied as described above is preferable.

(Organic solvent)
In the method for producing an optical film according to the present invention, an organic solvent useful for forming a dope in the case of producing by a solution casting method is one that can simultaneously dissolve a plurality of resins and other additives to be used. Can be used without limitation.

  For example, as a chlorine organic solvent, methylene chloride, as a non-chlorine organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

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

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, the resin A constituting the sea and the resin B constituting the island are at least 15 to 45 mass% in total. A dissolved dope composition is preferred.

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

  After the resin and additives are dissolved, it is filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump. It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

  Moreover, what knead | mixed and pelletized resin A which comprises the sea previously and resin B which comprises an island can also be used preferably.

2) Casting process An endless metal belt 31 such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting a dope from a pressure die slit to a casting position on a metal support.

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

3) Solvent evaporation step In the step of evaporating the solvent by heating the web (the dope is cast on the casting support and the formed dope film is called “web”) on the casting support. is there.

  To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used.

  In order to adjust the amount of residual solvent in the subsequent peeling step, the temperature of the liquid brought into contact with the back surface of the support in the solvent evaporation step, the contact time with the support, and the like may be appropriately adjusted.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

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

  The residual solvent amount at the time of peeling of the web on the metal support at the time of peeling is preferably peeled in the range of 5 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. .

  The amount of residual solvent used in the present invention 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.

5) Drying and stretching step After peeling, a drying device 35 that transports the web alternately through rolls arranged in the drying device and / or a tenter stretching device 34 that clips and transports both ends of the web with clips. And dry the web.

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

  When using a tenter stretching apparatus, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

  It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is also preferable to implement biaxial stretching in a casting direction and a width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

  In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  The preferable draw ratio of simultaneous biaxial stretching can be taken in the range of x1.01 times to x1.5 times in both the width direction and the longitudinal direction.

  When performing tenter stretching, the drying temperature is preferably within 30 to 200 ° C, and more preferably within 100 to 200 ° C.

  In the manufacturing method which concerns on this invention, it is preferable to extend | stretch so that the extending | stretching temperature T at this time may satisfy | fill Tg (A) <T <Tg (B). By stretching at a temperature in this range, it is possible to stretch the resin that constitutes the sea while the island structure grain is not elliptical but round, and the projecting state of the island structure can be controlled. Sufficient moire eliminating ability can be imparted without causing a decrease.

  Moreover, in the manufacturing method which concerns on this invention, the draw ratio in an extending process is 1.03-1.2 times, It is characterized by the above-mentioned. If the draw ratio is 1.03 times or more, the effect of the present invention is exhibited. If it is 1.2 times or less, it can suppress that front brightness falls, when a haze value raises and it is set as a display apparatus.

Moreover, in this invention, it is preferable that the extending | stretching speed represented by following formula (I) is within 20-300% / min.
Formula (I): Stretching speed (% / min) = {(width dimension after stretching / width dimension before stretching) -1} × 100 (%) / time required for stretching (min)
The stretching speed can be set from the viewpoint of productivity and quality, but if it is 20% / min or more, there is no problem in productivity, and if it is 300% / min or less, a failure such as a crack occurs during stretching. Since it becomes difficult to do, it is preferable.

  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.

6) Winding process This is a process in which the amount of residual solvent in the web becomes 2% by mass or less, and is taken up by the winder 37 as a film, and the dimensional stability is achieved by setting the residual solvent amount to 0.4% by mass or less. Can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

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

  The film produced by the method according to the present invention is preferably a long film. Specifically, the film is about 100 m to 5000 m, and is usually in the form of a roll. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-2m.

  Moreover, it is preferable that the film manufactured by the method according to the present invention has a thickness of 20 μm or more. More preferably, it is 30 μm or more. The upper limit of the thickness is not limited, but in the case of forming a film by a solution casting method, the upper limit is about 250 μm from the viewpoint of applicability, foaming, solvent drying, and the like. Preferably it is 125 micrometers or less, More preferably, it is 60 micrometers or less.

  The optical film produced by the method according to the present invention preferably has an arithmetic surface roughness Ra based on JIS B0601-2001 on at least one surface in the range of 0.08 to 2.0 μm. When the value of Ra is 0.08 μm or more, a sufficient scattering effect can be obtained, and moire fringes can be eliminated. If Ra is 2.0 micrometers or less, it can suppress effectively that front luminance falls when it is set as a display apparatus.

  Arithmetic surface roughness Ra is measured using a measuring instrument according to JIS B0601-2001, such as Olympus 3D Laser Microscope LEXT OLS4000, Kosaka Laboratory Ltd., Surfcoder MODEL SE-3500, etc. Can be measured.

  The optical film manufactured by the method according to the present invention has a total haze value of 20 to 80% in one film, and an internal haze value obtained by (total haze value) − (surface haze value) Is preferably in the range of 0.15 to 30%.

  When the total haze value is 20% or more, moire fringes can be eliminated, and when the total haze value is 80% or less, it is preferable in that it is possible to suppress a decrease in front luminance. A more preferable range of the total haze value is within 35 to 50%. The internal haze value is preferably in the range of 0.15 to 30% from the viewpoint of suppressing moire fringes and preventing reduction in front luminance. A more preferable range of the internal haze value is 0.5 to 20%.

  As these haze values, values measured according to JIS K7136 using a Nippon Denshoku Co., Ltd. haze meter NDH2000 in an atmosphere of 23 ° C. and 55% RH can be used.

  The total haze value is a haze value of one film according to the present invention, and the internal haze value is a value obtained by subtracting the external haze value from the total haze value. As the internal haze value, a measurement value obtained by covering both surfaces of the film with glycerin having a refractive index of 1.47 and sandwiching the film between two glass plates and measuring it in the same manner as the total haze can be used. By doing in this way, the influence of the haze value (namely, external haze value) by the uneven | corrugated shape of a surface can be disregarded, and only the haze value inside a film can be measured.

(Polarizer)
The optical film of the present invention can be used for a polarizing plate.

  The polarizing plate is mainly composed of two optical films that protect both the front side and the back side of the polarizer. The optical film of the present invention is used for at least one of two optical films sandwiching a polarizer from both sides. Since the optical film of the present invention has not only a moire eliminating ability but also a protective film property, the manufacturing cost of the polarizing plate can be reduced. The polarizing plate according to the present invention can be used as a polarizing plate on the backlight side of the image display device or a polarizing plate on the viewing side. When used for the backlight unit side polarizing plate, it is preferable that the optical film of the present invention is disposed so as to be the most on the backlight side.

(Liquid crystal display device)
As an example of the configuration of a conventional liquid crystal display device, in the backlight type (direct type), as shown in FIG. 2A, from the light source side, [light source 1a / diffusion plate 3a / light collecting sheet 4a (prism sheet) Etc.) / Upper diffusion sheet 5a / liquid crystal panel 12a (polarizer 10a / protective film (retardation film etc.) 9a / substrate 8a / liquid crystal cell 7a / protective film 11a)] It is the structure used.

  On the other hand, as shown in FIG. 2B, in the side light type configuration, the light source 1a is composed of a light emitting light source 2a and a light guide plate 13a, and is mainly used for small LCDs for monitors and mobile applications. .

  The lower diffusion sheet is an optical sheet having strong light diffusibility mainly for reducing in-plane luminance unevenness of the backlight unit (BLU) 6a, and the condensing sheet transmits diffused light in the front direction of the liquid crystal display device (display device plane). The upper diffusion sheet is used to reduce the moire generated by a periodic structure such as a prism sheet that is a light condensing sheet or a pixel in a liquid crystal cell, and the lower diffusion sheet. This optical sheet is used to further reduce in-plane luminance unevenness that cannot be removed by the sheet.

  In the liquid crystal display device according to the present invention, in the surface light source device shown in FIGS. 2A and 2B, the optical film of the present invention can be used at least in place of the upper diffusion sheet.

  When using the optical film of the present invention, as shown in FIGS. 3 (a) and 3 (b), the polarizing plate protective film for the polarizing plate (lower polarizing plate) on the backlight unit side is removed. You may make it the structure formed by affixing the optical film of this invention on a polarizing plate. Even with such a configuration, moire fringes can be suppressed without reducing the front luminance. Furthermore, the cost reduction of the whole liquid crystal display device is realizable by setting it as the structure which removed the protective film for upper polarizing plates in this way.

  Liquid crystal cell display methods include twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS), and optically compensated bend cells (OCB). It can be preferably used for a transmissive, reflective, or transflective liquid crystal display device.

  As a light-emitting light source (light emitter) used for the light source, CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp, hot cathode tube), LED (Light Emitting Diode, Light-Emitting Diode), OLED Organic light-emitting diode, organic light emitting diode [organic EL]), inorganic EL, and the like can be preferably used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

[Production of optical film]
<Preparation of optical film 1>
(Dope solution composition 1)
Polymethyl methacrylate (VB-7103, manufactured by Mitsubishi Rayon Co., Ltd., weight average molecular weight 300,000, glass transition temperature 105 ° C., refractive index 1.490) 55 parts by mass Cellulose acylate (cellulose acetate propionate acyl group total substitution degree 2 .75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, weight average molecular weight 200,000, glass transition temperature 140 ° C., refractive index 1.487) 25 parts by mass Cellulose acylate (cellulose acetate propionate acyl) Total group substitution degree 2.46, acetyl group substitution degree 1.58, propionyl group substitution degree 0.88, weight average molecular weight 190,000, glass transition temperature 170 ° C., refractive index 1.489) 20 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass Dissolve the above composition while heating to make a dope solution. It was.

<Formation of optical film 1>
The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the amount of residual solvent reached 100%, and peeling was performed from the stainless steel band support with a peeling tension of 154 N / m.

  The solvent of the peeled resin web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while being stretched 1.1 times in the width direction by a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%.

  After stretching with a tenter, relaxation was performed at 130 ° C., and then drying was completed while transporting a drying zone at 120 ° C. and 140 ° C. with many rolls, slitting to a width of 1.5 m, and a width of 10 mm at both ends of the film. A knurling process of 5 μm was performed, and the film was wound around a core having an initial tension of 220 N / m and a final tension of 110 N / m and an inner diameter of 15.24 cm, thereby obtaining an optical film 1 which is a resin film having a sea-island structure.

  The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.1 times.

  The residual solvent amount of the optical film 1 was 0.1%, the film thickness was 60 μm, and the winding length was 4000 m.

(Preparation of optical films 2-9)
Dopes were produced with the resin compositions shown in Table 1, and various optical films were produced in the same manner as described above.

［光学フィルムの評価］
上記で作製した光学フィルム１〜９について下記の測定・評価を行った。

[Evaluation of optical film]
The optical film 1-9 produced above was subjected to the following measurement / evaluation.

<Haze value>
The total haze of each film was measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

<Measurement of total light transmittance>
Measured every 1 nm in the haze calculation mode using an extra-UV visible / near infrared spectrophotometer (V-670, manufactured by JASCO Corporation), and the average value of the transmittance within the range of 450 to 650 nm was measured as the total light transmittance. Calculated as

<Surface shape observation and measurement of surface roughness Ra>
The film produced above was observed and analyzed using a 3D measurement laser microscope LEXT OLS4000 manufactured by Olympus Corporation, and it was confirmed that the optical film of the present invention formed irregularities due to the sea-island structure, and JIS B0601- The arithmetic surface roughness Ra in accordance with 2001 was determined.

<Measurement of image clarity>
The image sharpness of the film is determined by the transmission method according to JIS K7374: 2007, using the image clarity tester ICM-1T manufactured by Suga Test Instruments Co., Ltd. It measured in the range of 0.125-2.0 mm.

<Brittleness evaluation>
The various films produced above were cut out at 100 mm (length) × 10 mm (width), bent at the center in the vertical direction, and then folded once into two, one into the valley and one into two. It was evaluated with. In addition, breaking of evaluation here represents having broken into two or more pieces.
◯: Not broken at all four times Δ: One diffracted out of four times ×: Folded two or more out of four times The measurement / evaluation results are shown in Table 2.

表２に示したヘイズ値、全光線透過率及び像鮮明度の測定結果から明らかなように、本発明の光学フィルムは、高い光透過率を維持し、かつ防眩性を有していることが分かる。

As is apparent from the measurement results of haze value, total light transmittance and image definition shown in Table 2, the optical film of the present invention maintains high light transmittance and has antiglare properties. I understand.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Pipe | tube 10 Ultraviolet absorber preparation pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter 1a Light source 2a Light emission source 3a Lower diffusion sheet (or diffusion plate)
4a Light collecting sheet (prism sheet, lens sheet)
5a Upper diffusion sheet 6a Surface light source device (backlight unit)
7a Liquid crystal cell 8a Transparent substrate (glass, plastic)
9a Protective film (or retardation film)
10a Polarizer 11a Protective film 12a Liquid crystal panel 13a Light guide plate 14a Optical film of the present invention

Claims (5)

  An optical film containing an acrylic resin and a cellulose acylate resin and having a sea-island structure, wherein the mass ratio of the acrylic resin and the cellulose acylate resin is in the range of 51:49 to 90:10, and The cellulose acylate resin has at least two types of cellulose acylate, that is, a cellulose acylate resin having an average total carbon atom number of acyl groups of less than 6.0 and a cellulose acylate resin of 6.0 or more per glucose unit. An optical film containing a rate resin.   The cellulose acylate resin has at least an acetyl group or a propionyl group as the acyl group, and the average total number of carbon atoms of the acyl group is less than 6.0 per glucose unit. The optical film according to claim 1, wherein the degree of group substitution is 1.0 or less.   The total haze value of the optical film is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the average surface roughness (Ra) of the two surfaces of the optical film is 3. The optical film according to claim 1, wherein the total value is in a range of 0.3 to 2 μm.   The image clarity of the optical film is within a range of 0.8 to 5.0% in measurement using an optical comb having a width of 0.25 mm. An optical film according to claim 1.   The total haze value is in the range of 20 to 90%, the total light transmittance is in the range of 86 to 99%, and the total value of the average surface roughness (Ra) of the two surfaces of the optical film is 0. A method for producing an optical film having a sea-island structure in a range of 3 to 2 μm, wherein an acrylic resin and a cellulose acylate resin are mixed at a mass ratio in a range of 51:49 to 90:10, and The cellulose acylate resin has at least two kinds of cellulose acylates, ie, a cellulose acylate resin having an average total carbon atom number of acyl group of less than 6.0 and a cellulose acylate resin having a number of 6.0 or more per glucose unit. A method for producing an optical film, comprising mixing a resin to prepare a dope.

Images