JP5260165B2 - Optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having which excels in heat resistance and toughness, maintains transparency, and has a small photoelasticity coefficient. <P>SOLUTION: The optical film comprises (a) 100 pts.mass heat-resistant acrylic resin comprising 40-90 mass% methacrylic ester and/or acrylic ester unit, 5-40 mass% aromatic vinyl compound unit, and 5-30 mass% compound unit represented by formula (1) (wherein X is O or N-R; O is oxygen; N is nitrogen; R is hydrogen, an alkyl group, an aryl group or a cycloalkyl group) and (b) 0.1-50 pts.mass rubbery copolymer particles having a multilayered structure, a difference in refractive index from the above heat-resistant acrylic resin (a) of not greater than 0.015, and an average particle diameter of 0.04-0.13 &mu;m. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an optical film excellent in heat resistance, transparency, toughness, and optical properties.

Recently, with the expansion of the display market, there is an increasing demand for clearer images, and there is a demand for optical materials with higher optical properties than simple transparent materials.
The polymer has birefringence because the refractive index is different between the molecular main chain direction and the vertical direction. Depending on the application, it is required to strictly control this birefringence. In the case of a protective film used for a polarizing plate of a liquid crystal, a polymer material having a smaller birefringence even if the total light transmittance is the same. A molded body is required. In this application, an example in which a film of cellulose triacetate and polylactic acid is studied as a polarizing plate protective film is known (Patent Document 1), and cellulose triacetate is a representative material. On the other hand, in a liquid crystal display, a retardation film such as a quarter-wave plate having a function of converting light polarized by a polarizing plate into circularly polarized light consciously generates birefringence in a polymer material molded body. A typical material is polycarbonate and the like.
In recent years, with the increase in size of liquid crystal displays, the required size of polymer optical material moldings has increased. In order to reduce the distribution of birefringence caused by bias of external force, the change in birefringence due to external force, that is, photoelasticity A material with a small coefficient is required. However, cellulose acetate and polycarbonate generally used as an optical film at present have a large photoelastic coefficient and are not satisfactory for these requirements.
An acrylic resin is known as a material having a small photoelastic coefficient and a negative birefringence. However, a problem with acrylic resins is that they are inferior in toughness (trimming properties and folding strength) and are brittle and easily cracked, and cracks occur when the film breaks, resulting in poor productivity. As a method for improving the brittleness, there is generally a method of adding a toughening agent or the like, but with this method, although toughness is improved, transparency and heat resistance tend to be lowered.
Patent Document 2 discloses a polarizing film protective film in which an acrylic resin contains an impact-resistant acrylic rubber-methyl methacrylate graft copolymer.
Patent Document 3 discloses a polarizer protective film in which an acrylic resin contains a styrene elastomer, a styrene-butadiene rubber, or the like for the purpose of improving mechanical strength.
Furthermore, Patent Document 4 discloses a technique in which a cross-linked elastic body having a multilayer structure is contained in an acrylic resin containing a glutaric anhydride unit as an acrylic resin film imparted with heat resistance and toughness.

JP 2002-82223 A Japanese Patent Laid-Open No. 5-119217 JP 2006-284881 A JP 2000-178399 A

However, the film disclosed in Patent Document 2 cannot be said to be a sufficient value in transparency (haze value) and heat resistance (softening temperature), and details of acrylic rubber are not described.
The film disclosed in Patent Document 3 has a problem that a relatively small amount of styrenic elastomer is used and the haze value exceeds 1.0% despite the raw film.
The film disclosed in Patent Document 4 needs to contain a large amount of a cross-linked elastic body in order to improve the folding resistance, and there is a concern that the heat resistance decreases and the haze value increases accordingly.
Therefore, the above-described optical film of the prior art is still insufficient from the viewpoint of the balance of heat resistance, transparency and toughness.

  In view of the above circumstances, the problem to be solved by the present invention is to provide an optical film having excellent heat resistance and toughness and having a small photoelastic coefficient while maintaining transparency, and particularly a thin film. Is to provide a film.

  As a result of intensive studies on the above problems, the present inventors have found that the heat-resistant acrylic resin (a) having a specific composition ratio has a rubbery-containing copolymer having a multilayer structure in which the refractive index and the average particle diameter are controlled. It has been found that the above problems can be solved by blending the coalesced particles (b) at a specific ratio, and the present invention has been completed.

That is, the present invention is as follows.
[1]
Methacrylic acid ester and / or acrylic acid ester unit 40 mass% or more and 90 mass% or less, aromatic vinyl compound unit 5 mass% or more and 40 mass% or less, and compound unit 5 mass% represented by the following general formula (1) With respect to 100 parts by mass of the heat-resistant acrylic resin (a) including 30% by mass or less,

(Wherein, X represents a O, O represents an oxygen atom.)
The rubber-containing copolymer particles (b) having a multilayer structure having a difference in refractive index from the heat-resistant acrylic resin (a) of 0.015 or less and an average particle size of 0.04 μm or more and 0.13 μm or less are set to 0.0. An optical film containing 1 part by mass or more and 50 parts by mass or less.
[2]
The said rubber-containing copolymer particle (b) is an optical film of the said [1] description which is a particle | grains which have a multilayer structure more than a three-layer structure.
[3]
The said rubber-containing copolymer particle (b) is an optical film of the said [1] or [2] description which is a particle | grain which has a three-layer structure formed in order of the hard layer-soft layer-hard layer from the inner side.
[4]
The optical film according to any one of [1] to [3], wherein the film thickness is 100 μm or less and the haze value in a 23 ° C. environment is 1.2% or less.
[5]
The optical film according to any one of the above [1] to [4], wherein the haze value in a 70 ° C environment is 2.0% or less.
[6]
The optical film according to any one of [1] to [5], wherein Tg (glass transition temperature) is 120 ° C. or higher.
[7]
The optical film according to any one of the above [1] to [6], wherein the absolute value of the photoelastic coefficient in a 23 ° C. environment is 5.0 × 10 ⁻¹² / Pa or less.
[8]
The optical film according to any one of [1] to [7], wherein the bending strength in the direction perpendicular to MD is 1.0 or more.
[9]
The polarizing plate protective film which consists of an optical film in any one of said [1]-[8].
[10]
A retardation film comprising the optical film according to any one of [1] to [8].

  According to the present invention, it is possible to provide an optical film having excellent heat resistance and toughness and having a small photoelastic coefficient while maintaining transparency. Since the optical film of the present invention has excellent folding strength, it is possible to reduce the occurrence of cracks during the production process of the film and incorporation into the member, and the occurrence of microcracks and cracks in the trimming process. As a result, the productivity of the optical film can be remarkably improved.

Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.
In the present embodiment, the monomer component before polymerization is referred to as “˜monomer” (however, “monomer” may be omitted and only the compound name may be described), and a copolymer. The structural unit that constitutes is referred to as “unit”.

  The optical film of the present embodiment has a methacrylic acid ester and / or acrylic ester unit unit of 40% by mass to 90% by mass, an aromatic vinyl compound unit of 5% by mass to 40% by mass, and the following general formula (1) With respect to 100 parts by mass of the heat-resistant acrylic resin (a) containing 5% by mass to 30% by mass of the compound unit represented by

(Wherein, X represents a O, O represents an oxygen atom.)

  The rubber-containing copolymer particles (b) having a multilayer structure having a difference in refractive index from the heat-resistant acrylic resin (a) of 0.015 or less and an average particle size of 0.04 μm or more and 0.13 μm or less are set to 0.0. It is an optical film obtained by molding a resin composition containing 1 part by mass or more and 50 parts by mass or less.

  Specific examples of the methacrylic acid ester and / or acrylic acid ester that are the first monomer component of the heat-resistant acrylic resin (a) include, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and n-methacrylic acid. Methacrylic acid esters such as butyl, n-hexyl methacrylate, cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, 2-ethylhexyl acrylate Is mentioned. Among these, methyl methacrylate is preferable from the viewpoint of transparency and ease of polymerization.

  Specific examples of the aromatic vinyl compound that is the second monomer component of the heat-resistant acrylic resin (a) include, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4- Examples thereof include nuclear alkyl-substituted styrenes such as dimethylstyrene, ethylstyrene, and p-tert-butylstyrene; α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-p-methylstyrene. Among these, styrene is preferable from the viewpoints of thermal decomposition resistance and ease of polymerization.

  Among the compound units represented by the general formula (1) which is the third monomer component of the heat-resistant acrylic resin (a), those in which X is O include, for example, maleic anhydride, itaconic acid, ethyl Examples thereof include unsaturated dicarboxylic acid anhydride monomer units which are anhydrides such as maleic acid, methyl itaconic acid and chloromaleic acid. Among the above, a maleic anhydride monomer unit is preferable from the viewpoint of heat decomposition resistance and heat resistance improvement.

The copolymerization ratio of the monomer units constituting the heat-resistant acrylic resin (a) is 40% by mass or more and 90% by mass or less of methacrylic acid ester and / or acrylic acid ester unit from the viewpoint of heat resistance and photoelastic coefficient. The aromatic vinyl compound unit is 5% by mass or more and 40% by mass or less, and the compound unit represented by the general formula (1) is 5% by mass or more and 30% by mass or less.

When the copolymerization ratio of methacrylic acid ester and / or acrylic acid ester unit is 40% by mass or more, optical properties and polymerization stability tend to be good, and when it is 90% by mass or less, heat resistance is maintained. It tends to be. Further, when the copolymerization ratio of the aromatic vinyl compound unit is 5% by mass or more, the optical characteristics tend to be good, and when it is 40% by mass or less, the weather resistance tends to be maintained. Furthermore, when the compound unit represented by the general formula (1) is 5% by mass or more, the heat resistance tends to be good, and when it is 30% by mass or less, the colorability and the polymerization stability are maintained. It tends to be.

  More preferably, the methacrylic acid ester and / or acrylic acid ester unit is 42% by mass to 83% by mass, the aromatic vinyl compound unit is 12% by mass to 40% by mass, and the compound represented by the above general formula (1). A unit is 5 mass% or more and 18 mass% or less.

  More preferably, the methacrylic acid ester and / or acrylic acid ester unit is 45% by mass to 78% by mass, the aromatic vinyl compound unit is 16% by mass to 40% by mass, and the compound represented by the general formula (1). A unit is 6 mass% or more and 15 mass% or less.

  Moreover, it is preferable that the copolymerization ratio of the aromatic vinyl compound unit with respect to the copolymerization ratio of the compound unit represented by the general formula (1) is 1 to 3 times. If this ratio is smaller than the above range, it is difficult to obtain the effect of adding the aromatic vinyl compound, and the yield of the polymer tends to decrease, and if it is larger than the above range, it is difficult to dissolve in the monomer compounding phase. Therefore, the strength of the resin tends to be low.

  The heat-resistant acrylic resin (a) includes a heat-resistant acrylic resin obtained by copolymerizing other monomers that can be copolymerized as necessary in addition to the above-described essential constituent monomer components. . Examples of other copolymerizable monomers used here include unsaturated carboxylic acid monomers such as methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid and cinnamic acid; acrylonitrile, methacrylonitrile Unsaturated nitrile monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3- Conjugated diene monomers such as hexadiene can be used, and two or more of these can be copolymerized.

  As a method for producing the heat-resistant acrylic resin (a), bulk polymerization using a radical initiator is a suitable method, but solution polymerization and emulsion polymerization can also be used. Aqueous suspension polymerization is not recommended when maleic anhydride is used as the monomer component, because its water solubility is high, and it tends to be difficult to maintain a stable suspension system throughout.

  As the radical initiator, those generally used can be used. Among them, the peroxide initiators lauroyl peroxide, decanoyl peroxide, and t-butylperoxy 2-ethylhexanoate are used. The coloring of the heat-resistant acrylic resin (a) tends to be suppressed. Therefore, it is preferable to apply a diacyl peroxide such as lauroyl peroxide as a radical initiator when polymerizing the heat-resistant acrylic resin (a).

  As a preferable polymerization method of the heat-resistant acrylic resin (a), for example, a method described in JP-B-63-1964 can be mentioned.

  The melt index (ASTM D1238: I condition) of the heat-resistant acrylic resin (a) is preferably 10 g / 10 min or less, more preferably 6 g / 10 min or less, and further preferably 3 g / 10 from the viewpoint of the strength of the optical film. Is less than a minute.

  The Tg (glass transition temperature) of the heat-resistant acrylic resin (a) is preferably 120 ° C. or higher, more preferably 125 ° C. or higher, and further preferably 130 ° C. or higher for practical use. When Tg is 120 ° C. or higher, thermal deformation at a practical temperature tends to be reduced.

  The heat-resistant acrylic resin (a) may be a block polymer or a random polymer, but is preferably a statistical random polymer from the viewpoint of heat resistance, rigidity, and recyclability.

  The molecular weight distribution range of the heat-resistant acrylic resin (a) is preferably such that the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is in the range of 1.6 to 4.0. More preferably, it is 1.7-3.7, More preferably, it is the range of 1.8-3.5. When Mw / Mn is 1.6 or more, the balance between resin film processability and mechanical properties tends to be good. Moreover, when Mw / Mn is 4.0 or less, the melt fluidity is improved and the processability tends to be good.

  The ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) in the present embodiment refers to a value determined by polystyrene conversion using gel permeation chromatography (GPC).

  The weight average molecular weight (Mw) measured by GPC of the heat-resistant acrylic resin (a) is preferably 100,000 to 500,000, more preferably 120 to 300,000, and further preferably 140 to 200,000. When the weight average molecular weight of the heat-resistant acrylic resin (a) is 500,000 or less, sufficient fluidity can be obtained at the time of extrusion stretching, so that melt extrusion and stretched film formation tend to be performed without significant trouble. Moreover, when the weight average molecular weight of the heat-resistant acrylic resin (a) is 100,000 or more, good stretch stability and a sufficient degree of orientation tend to be imparted to the film.

  The optical film of the present embodiment contains a rubbery material having a multilayer structure with a refractive index difference of 0.015 or less and an average particle size of 0.04 μm or more and 0.13 μm or less from the above-described heat-resistant acrylic resin (a). Containing copolymer particles (b).

  The rubber-containing copolymer particles (b) are not particularly limited as long as they satisfy the above characteristics, and are multilayer structures such as general butadiene-based ABS rubber, acrylic-based, polyolefin-based, silicone-based, and fluororubber. Rubber particles having can be used. Among these, particles having a multilayer structure of three or more layers are preferable, and acrylic rubber particles having a multilayer structure of three or more layers are more preferable. By using rubber particles having a multilayer structure of three or more layers as the rubber-containing copolymer particles (b), deformation of the rubber-containing copolymer particles (b) due to heating is suppressed, and the optical film Glass transition temperature (Tg) and transparency tend to be maintained.

  The rubber-containing copolymer particles (b) having a multilayer structure of three or more layers are rubber particles having a multilayer structure in which a soft layer made of a rubbery polymer and a hard layer made of a glassy polymer are laminated, Preferably, the particles have a three-layer structure formed in the order of hard layer-soft layer-hard layer from the inside. By having a hard layer in the innermost layer and outermost layer, deformation of the rubber-containing copolymer particles (b) tends to be suppressed, and by having a soft component in the central layer, good toughness tends to be imparted. It is in.

  The copolymer forming the innermost layer (bi) of the rubber-containing copolymer particles (b) having a three-layer structure is preferably 65 to 90% by mass of methyl methacrylate and copolymerizable therewith. And 10 to 35% by mass of other copolymerizable monomers. From the viewpoint of appropriately controlling the refractive index, the other copolymerizable monomers are preferably 0.1 to 5% by mass of an acrylate monomer and 5 to 35% by mass of an aromatic vinyl compound monomer. % And 0.01 to 5% by mass of a copolymerizable polyfunctional monomer.

  The acrylate monomer in the copolymer forming the innermost layer (bi) of the rubber-containing copolymer particles (b) having a three-layer structure is not particularly limited, but preferably acrylic acid n-butyl, 2-hexyl acrylate. As the aromatic vinyl compound monomer, the same monomers as those used for the heat-resistant acrylic resin (a) can be used, but preferably the refractive index of the innermost layer (bi) is adjusted. From the viewpoint of improving the transparency of the optical film, styrene or a derivative thereof is used. Although it does not specifically limit as a copolymerizable polyfunctional monomer, Preferably, ethylene glycol di (meth) acrylate, polyethyleneglycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4 -One or more of butanediol di (meth) acrylate, allyl (meth) acrylate, triallyl isocyanurate, diallyl maleate, divinylbenzene and the like are used in combination. Of these compounds, allyl (meth) acrylate is particularly preferred.

  The copolymer forming the central layer (b-ii) of the rubber-containing copolymer particles (b) having a three-layer structure is preferably 55 to 75% by mass of an acrylate ester and copolymerizable therewith. And 25 to 45% by mass of other copolymerizable monomers. As said other copolymerizable monomer, Preferably, an aromatic vinyl compound monomer and 0.1-5 mass% of copolymerizable polyfunctional monomers are included.

  The copolymer forming the central layer (b-ii) of the rubber-containing copolymer particles (b) having a three-layer structure is a copolymer exhibiting soft rubber elasticity from the viewpoint of imparting excellent toughness to the optical film. A polymer is preferred. Although it does not specifically limit as an acrylate ester which comprises a center layer (b-ii), Preferably, 1 type from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, etc. or Two or more types are used in combination. Of these, n-butyl acrylate and 2-hexyl acrylate are more preferable. Moreover, as an aromatic vinyl compound monomer copolymerized with acrylic ester, the thing similar to the monomer used for heat-resistant acrylic resin (a) can be used, However, Preferably a center layer ( From the viewpoint of adjusting the refractive index of b-ii) to improve the transparency of the optical film, styrene or a derivative thereof is used. Moreover, as a copolymerizable polyfunctional monomer, the same thing as the copolymerizable polyfunctional monomer used by the innermost layer (bi) can be used, As the content, 0.1% When the content is not less than 5% by mass and not more than 5% by mass, it has a favorable cross-linking effect, is moderate in cross-linking, and has a large rubber elasticity effect, which is preferable because the toughness of the optical film tends to be improved.

  The copolymer that forms the outermost layer (b-iii) of the rubber-containing copolymer particles (b) having a three-layer structure is preferably 70 to 100% by mass of methyl methacrylate and copolymerizable therewith. 0-30 mass% of other copolymerizable monomers are included.

  The other copolymerizable monomer copolymerizable with methyl methacrylate in the outermost layer (b-iii) of the rubber-containing copolymer particles (b) having a three-layer structure is not particularly limited, but preferably Are n-butyl acrylate and 2-hexyl acrylate.

  The production method of the rubber-containing copolymer particles (b) is not particularly limited, and can be obtained by known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, and particularly by emulsion polymerization. It is preferable to obtain. In this case, in the presence of an emulsifier and an initiator, the monomer mixture of the innermost layer (bi) is first added to complete the polymerization, and then the monomer mixture of the central layer (b-ii) is added. By completing the polymerization and then adding the monomer mixture of the outermost layer (b-iii) to complete the polymerization, the multilayer structure particles can be easily obtained as a latex. The rubber-containing copolymer particles (b) can be recovered from the latex as a powder by a known method such as salting out, spray drying, freeze drying and the like.

  The rubber-containing copolymer particles (b) have a refractive index difference of 0.015 or less from the heat-resistant acrylic resin (a), more preferably 0.012 or less, and still more preferably 0.01 or less. . When the refractive index difference between the rubber-containing copolymer particles (b) and the heat-resistant acrylic resin (a) is 0.015 or less, an optical film excellent in transparency can be obtained.

  As a method for satisfying the refractive index condition, a method of adjusting the unit composition ratio of each monomer of the heat-resistant acrylic resin (a) and / or the rubber-containing copolymer particles (b) is used. And a method of adjusting the composition ratio of the polymer or monomer in each layer.

  As a method for measuring the refractive index difference, first, in the rubber-containing copolymer particles (b), media having refractive indexes of 1.59 and 1.49, respectively, are mixed and mixed with (b) while changing the ratio. The point at which the cloudiness disappears is defined as the refractive index (23 ° C., 550 nm) of the rubber-containing copolymer particles (b). And it can obtain | require by calculating the difference with the refractive index of the heat-resistant acrylic resin (a) press-molded separately measured with the laser refractometer.

  The rubber-containing copolymer particles (b) have an average particle size of 0.04 μm or more and 0.13 μm or less, preferably 0.05 μm or more and 0.1 μm or less, more preferably 0.055 μm or more and 0.08 μm. More preferably, it is 0.06 μm or more and 0.075 μm. When the average particle diameter of the rubber-containing copolymer particles (b) is 0.04 μm or more, the toughness of the optical film can be maintained, and when it is 0.13 μm or less, the transparency of the optical film can be maintained. In particular, in the case of an optical film having a film thickness of 100 μm or less, the average particle diameter is preferably 0.1 μm or less in order to maintain transparency, and 0.08 μm at high temperature haze (under 70 ° C.). The following is preferable.

  The rubber-containing copolymer particles (b) in the optical film of the present embodiment are 0.1 mass with respect to 100 mass parts of the acrylic resin (a) from the viewpoints of trimming properties, bending strength and transparency. Part to 50 parts by weight, more preferably 5 parts to 45 parts by weight, more preferably 10 parts to 40 parts by weight, and particularly preferably 15 parts to 35 parts by weight. When the content of the rubber-containing copolymer particles (b) is 0.1 parts by mass or more, the optical film is excellent in trimming properties and bending strength, and microcracks and cracks can be suppressed in the trimming process, and 50 masses. The heat resistance and transparency of an optical film can be maintained as it is below a part.

  In addition, a trimming process means the process of cutting off both ends, in order to make the width | variety of a film uniform, when manufacturing an optical film. At this time, if the film is inferior in trimming properties, microcracks or cracking phenomena occur during the process, and the productivity of the optical film is significantly reduced.

  In the optical film of the present embodiment, the haze value (turbidity) in a 23 ° C. environment, which is one of the indices representing transparency, is preferably 1.2% or less, more preferably 1.0% or less, and further Preferably it is 0.6% or less. When the haze value in a 23 ° C. environment is 1.2% or less, high transparency tends to be imparted to the optical film.

  Furthermore, the optical film of the present embodiment has a haze value in a 70 ° C. environment of preferably 2.0% or less, more preferably 1.5% or less, and further preferably 1.2% or less. When the haze value in a 70 ° C. environment is 2.0% or less, for example, when used in a liquid crystal display or the like, a decrease in transparency due to an increase in temperature tends to be suppressed.

In the optical film of the present embodiment, the absolute value of the photoelastic coefficient under a 23 ° C. environment is preferably 5.0 × 10 ⁻¹² / Pa or less, and preferably 4.0 × 10 ⁻¹² / Pa or less. Is more preferable, and it is further more preferable that it is 3.0 * 10 < ^-12 > / Pa or less. When the photoelastic coefficient is within the above range, the change in birefringence due to stress is small, and therefore, when used in a liquid crystal display device or the like, it tends to be excellent in contrast and screen uniformity.

The “photoelastic coefficient” in the present embodiment is a coefficient representing the ease with which birefringence changes due to external force, and is defined by the following equation.
C _R [/ Pa] = Δn / σ _R
Here, σ _R is extensional stress [Pa], Δn is birefringence when stress is applied, and Δn is defined by the following equation.
Δn = n ₁ −n ₂
(Where n ₁ is the refractive index in the direction parallel to the stretching direction, and n ₂ is the refractive index in the direction perpendicular to the stretching direction.)

  Here, the closer the value of the photoelastic coefficient is to zero, the smaller the change in birefringence due to external force.

  The photoelastic coefficient of the optical film can be controlled by changing the copolymerization ratio of the heat-resistant acrylic resin (a).

  The Tg (glass transition temperature) of the optical film of the present embodiment is preferably 120 ° C. or higher, more preferably 125 ° C. or higher, and further preferably 130 ° C. or higher for practical use. When Tg is 120 ° C. or higher, thermal deformation of the optical film in a processing step or the like tends to be suppressed.

  In the optical film of the present embodiment, other polymers than the components (a) and (b) described above can be mixed within a range not impairing the effects of the present invention. Examples of such other polymers include polyolefin resins such as polystyrene, polyethylene, and polypropylene, polyamide resins, polyphenylene sulfide resins, polyether ether ketone resins, polyesters, polysulfones, polyphenylene oxides, polyimides, polyether imides, polyacetals, and the like. And thermosetting resins such as phenol resins, melamine resins, silicone resins, and epoxy resins.

  Moreover, arbitrary additives can be mix | blended with the optical film of this Embodiment in the range which does not impair the effect of this invention according to various objectives. The type of additive is not particularly limited as long as it is generally used for compounding resins, for example, inorganic fillers such as silicon dioxide, pigments such as iron oxide, stearic acid, behenic acid, zinc stearate, Lubricants such as calcium stearate, magnesium stearate, ethylene bisstearamide, mold release agents, paraffinic process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, mineral oil, etc. Agents, flame retardants, antistatic agents, organic fibers, glass fibers, carbon fibers, metal whiskers and other reinforcing agents, colorants, other additives or mixtures thereof.

  Furthermore, an ultraviolet absorber can be added to the optical film of the present embodiment as long as the effects of the present invention are not impaired. Examples of ultraviolet absorbers that can be mixed include benzotriazole compounds, benzotriazine compounds, benzoate compounds, benzophenone compounds, oxybenzophenone compounds, phenol compounds, oxazole compounds, malonic ester compounds, cyanoacrylates. Compounds, lactone compounds, salicylic acid ester compounds, benzoxazinone compounds, hindered amine compounds, triazine compounds, and the like. These ultraviolet absorbers may be used alone or in combination of two or more.

  The method for producing the optical film of the present embodiment is not particularly limited, and the heat-resistant acrylic resin (a), the rubber-containing copolymer particles (b), and, if necessary, other polymers, It can be obtained by a known method using an additive as a raw material. For example, a resin composition containing the components (a) and (b) is produced using a melt kneader such as a single screw extruder, a twin screw extruder, a Banbury mixer, a brabender, various kneaders, and then a T die, It can be manufactured by extruding an original film or sheet using an extruder equipped with a circular die or the like. When a molded product is obtained by extrusion molding, a material obtained by melting and kneading the components (a) and (b) in advance may be used, or molding may be performed through melt kneading at the time of extrusion molding. In addition, if it is a thin film molded product, it can be produced by molding by a known method such as blow molding, injection blow molding, inflation molding, foam molding, etc., and a secondary processing molding method such as pressure molding or vacuum molding is used. You can also.

  The film thickness of the optical film of the present embodiment is preferably 100 μm or less, more preferably 10 μm or more and 90 μm or less, further preferably 20 μm or more and 80 μm or less, and particularly preferably 30 μm or more and 60 μm or less. In particular, when used as an optical film around a liquid crystal display, a film thickness of 100 μm or less is required, and a thin film is preferable from the viewpoint of folding strength.

  The optical film in the present embodiment has a folding strength in a direction perpendicular to MD of preferably 1.0 or more, more preferably 1.5 or more, and further preferably 2.0 or more. Here, the folding strength refers to a value obtained by logging the number of folding times determined according to JIS P 8115 (International Organization for Standardization: ISO 5626). When the bending strength in the direction perpendicular to the MD is 1.0 or more, the risk of cracking even when the optical film is incorporated into a housing or is hit during handling tends to be reduced. Here, MD refers to the mechanical flow direction during film formation.

  The optical film of the present embodiment may be appropriately stretched to give a phase difference. The stretching method is not particularly limited, and a longitudinal uniaxial stretching in the mechanical flow direction (MD), a transverse uniaxial stretching in a direction orthogonal to the mechanical flow direction (TD), etc. can be used. Uniaxial or biaxial stretching It is preferable to stretch by. For example, industrially, uniaxial stretching method by roll stretching or tenter stretching, sequential biaxial stretching method by combination of roll stretching and tenter stretching, simultaneous biaxial stretching method by tenter stretching, biaxial stretching method by tubular stretching, etc. A stretched molded body can be produced.

  The draw ratio is preferably 0.1% or more and 200% or less. More preferably, they are 1% or more and 150% or less, More preferably, they are 10% or more and 130% or less. By adjusting the draw ratio to the above range, a stretched molded article preferable in terms of photoelastic coefficient and mechanical strength tends to be obtained.

  The draw ratio can be determined from the following relational expression by shrinking the obtained stretched compact at a temperature 20 ° C. higher than the glass transition temperature. Stretch ratio (%) = [(length before shrinkage / length after shrinkage) −1] × 100

  Moreover, as extending | stretching temperature, Preferably it is Tg (glass transition temperature) -5 degreeC-+40 degreeC, More preferably, it is the range of Tg + 0 degreeC-30 degreeC, More preferably, it is the range of Tg + 5 degreeC-20 degreeC. Here, the glass transition temperature can be determined by a DSC method or a viscoelastic method.

  The optical film of this Embodiment can be used suitably for the use of the polarizing plate protective film or retardation film to which toughness was provided.

  When the optical film of the present embodiment is used as a polarizing plate protective film, the absolute value of in-plane retardation (Re) is preferably 0 nm to 50 nm, more preferably 40 nm or less, still more preferably 20 nm or less, particularly preferably. Is 10 nm or less. By adjusting Re to the above range, it can be suitably used as a polarizing plate protective film. In particular, in the case of producing by melt extrusion, since the original film (unstretched) Re is small, it is preferable to use the original film as a polarizing plate protective film.

  When the optical film of the present embodiment is used as a retardation film, the absolute value of Re is preferably 100 nm to 180 nm, more preferably 120 nm to 160 nm. By adjusting Re to the above range, it can be suitably used as a quarter wavelength plate.

  The in-plane retardation (Re) of the optical film can be controlled by designing the copolymerization ratio, the draw ratio, and the film thickness of the heat-resistant acrylic resin (a) within a preferable range.

Here, the in-plane retardation (Re) is defined by the following formula.
Re = (nx−ny) × d
(Where nx, ny: in-plane main refractive index, d: thickness)

  The optical film of the present embodiment may be appropriately subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, and gas barrier treatment.

Hereinafter, the present embodiment will be described in more detail with reference to examples. However, the present embodiment is not limited to the examples described below.
[Measuring method]
The measurement and evaluation methods for physical properties and the like in the examples are as follows.
(1) Photoelastic coefficient tensile path measurement measuring light (C _R) device arranged (Imoto Seisakusho Co., Ltd.), the birefringence RETS-RFI while applying a tensile stress to the test piece (Otsuka Electronics Co., Ltd. ). The strain rate during stretching was 0.3% / min (between chucks: 30 mm, chuck moving speed 0.1 mm / min), and the specimen width was 10 mm. The absolute value of birefringence (| Δn |) in the strain range of 0 to 0.5% of the test piece at 23 ° C. is plotted as the y-axis and the tensile stress (σ _R ) as the x-axis. The slope of the straight line was determined, and the absolute value (| C _R |) of the photoelastic coefficient was calculated.

(2) Measurement of planar retardation (Re) The planar retardation (Re) of each film at 23 ° C was measured by a rotating analyzer method using a birefringence measuring apparatus RETS-100 manufactured by Otsuka Electronics Co., Ltd.

(3) Measurement of glass transition temperature (Tg) In DSC-7 type (manufactured by Perkin Elmer), in a temperature increase measurement from room temperature to 200 ° C., the raw film sample mass 8 at a temperature increase rate of 20 ° C./min. 0.0 to 10 mg of Tg was measured.

(4) Measurement of average particle diameter of rubber-containing copolymer particles (b) The emulsion of the rubber-containing copolymer particles having a three-layer structure is sampled and diluted with water to a solid content of 500 ppm. Absorbance at a wavelength of 550 nm was measured using a UV1200V spectrophotometer (manufactured by Shimadzu Corporation). From this value, the average particle size was determined using a calibration curve prepared by measuring the absorbance in the same manner for the sample whose particle size was measured from a transmission electron micrograph.

(5) Measurement of bending strength (evaluation of toughness)
The toughness of the optical film was evaluated by measuring the following bending strength.
Samples cut to a length of 110 mm and a width of 15 mm were measured in accordance with JIS P 8115 (International Organization for Standardization: ISO 5626), and the number of foldings in the direction perpendicular to the MD direction was measured. The test conditions are described below.
Test conditions Test machine: MIT weather resistance tester (Toyo Seiki Seisakusho Co., Ltd.)
Load: 2.45N (= 250g)
Bending angle: ± 135 °
Bending speed: 175 cpm
Specimen gripper
Tip radius: R = 0.38mm
Opening: 0.25mm
The result of the folding test is displayed with the folding strength.
Folding strength is calculated by the following formula.
Folding strength = Log n
(In the formula, n indicates the number of times the test piece reaches the damage (breaking fracture).)

(6) Measurement of film thickness The center part of each original film was measured using a micrometer (manufactured by Mitutoyo Corporation).

(7) Measurement of refractive index The average refractive index at 23 ° C. and 550 nm of the heat-resistant acrylic resin (a) film was measured using a laser refractometer Model 2010 manufactured by Metricon.

(8) Measurement of haze The haze value of each raw film was measured according to JIS-K7136.

The manufacturing method of each resin in an Example is as follows.
[Resin manufacturing method]
・ Heat-resistant acrylic resin (a)
(1-1) Heat-resistant acrylic resin (a-1)
A heat-resistant acrylic resin (a-1) which is a methyl methacrylate-styrene-maleic anhydride copolymer was obtained by the method described in JP-B-63-1964. The composition of the obtained copolymer was 72% by weight of methyl methacrylate, 16% by weight of styrene, and 12% by weight of maleic anhydride, and the copolymer melt flow rate value (ASTM-D1238; 230 ° C., 3.8 kg load). ) Was 1.6 g / 10 min.
(1-2) Acrylic resin (a-2)
By the same method as described above, an acrylic resin (a-2) having a copolymer composition of 51% by mass of methyl methacrylate, 45% by mass of styrene, and 4% by mass of maleic anhydride was obtained. The acrylic resin (a-2) was used in Comparative Example 2 described later.

(2) Rubber-containing copolymer particles (b)
The abbreviations used in the method for producing rubber-containing copolymer particles indicate the following compounds.
MMA; methyl methacrylate BA; n-butyl acrylate St; styrene MA; methyl acrylate ALMA; allyl methacrylate PEGDA; polyethylene glycol diacrylate (molecular weight 200)
DPBHP; diisopropylbenzene hydroperoxide n-OM; n-octyl mercaptan HMBT; 2- (2′-hydroxy-5′-methylphenyl) benzotriazole

(2-1) Rubber-containing copolymer particles having a three-layer structure (b-1)
A reactor with an internal volume of 10 L equipped with a reflux condenser was charged with 4600 mL of ion-exchanged water and 24 g of sodium dioctylsulfosuccinate as an emulsifier, and the temperature was raised to 80 ° C. in a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. There was virtually no state. Next, Rongalite l. 2 g was added and dissolved uniformly.
As a first layer, a monomer mixture of MMA 150 g, BA 2.5 g, St 40 g, ALMA 0.2 g, and DPBHP 0.2 g was added and polymerized at 80 ° C. The reaction was complete in about 15 minutes.
Next, as a second layer, a monomer mixture of BA 1110 g, St 572 g, PDEGA 40 g, ALMA 7.0 g, DPBHP 3.5 g and Rongalite 2.0 g was added dropwise over 90 minutes. The reaction was completed 60 minutes after the completion of the dropwise addition.
Next, a monomer mixture of 190 g of MMA, 2.0 g of BA, 0.2 g of DPBHP, and 0.1 g of n-OM was dropped over 5 minutes as the third layer, and after completion of the dropping, the reaction at this stage was completed in about 15 minutes. .
Finally, a monomer mixture of MMA 380 g, BA 2.5 g, DPBHP 0.4 g, and n-OM 1.2 g was added as the third layer two steps over 10 minutes. This step was complete in about 15 minutes.
The temperature is raised to 95 ° C. and held for 1 hour, and the resulting emulsion is poured into a 0.5% aluminum chloride aqueous solution to agglomerate the polymer, washed 5 times with warm water, dried and dried in a white floc form. Obtained material. The rubber-containing copolymer particles (b-1) obtained had an average particle size of 0.1 μm. Moreover, the refractive index difference with heat-resistant acrylic resin (a) was 0.004.

(2-2) Rubber-containing copolymer particles having a three-layer structure (b-2)
Ion exchange water 4600mL and sodium dioctylsulfosuccinate 33g are put into a reactor with a reflux condenser with an internal volume of 10L, and the temperature is raised to 80 ° C under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. It was in a state that was not above. Five minutes after adding 1.0 g of sodium formaldehyde sulfoxylate, 30% by mass of a monomer mixture consisting of MMA 220 g, BA 3.5 g, St 48 g, ALMA 0.27 g and DPBHP 0.27 g was added all at once. The remaining 70% by mass was continuously added over 20 minutes, and after completion of the addition, the mixture was further maintained for 60 minutes to complete the polymerization of the innermost layer.

  Next, 5 minutes after adding 0.8 g of sodium formaldehyde sulfoxylate, a monomer mixture consisting of BA620 g, St325 g, ALMA 14 g, tetraethylene glycol diacrylate 4.8 g and DPBHP 2.0 g was continuously added over 60 minutes. After completion of the addition, the mixture was held for another 80 minutes to complete the polymerization of the soft layer (intermediate layer).

  Next, a monomer mixture composed of MMA 760 g, BA 50 g, DPBHP 1.6 g and n-OM 1.0 g was continuously added over 70 minutes, and the mixture was held for 60 minutes after the addition was completed. Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost layer. A small amount of the polymer emulsion thus obtained was collected and the average particle size was determined by the absorbance method and found to be 0.09 μm. The remaining emulsified liquid is poured into a 3% by mass sodium sulfate warm aqueous solution, salted out and coagulated, then dried after repeated dehydration and washing, and the rubber-containing copolymer particles (b-2) are powdered. -Obtained as Moreover, the refractive index difference with heat-resistant acrylic resin (a) was 0.008.

(2-3) Rubber-containing copolymer particles having a three-layer structure (b-3)
Ion exchange water 5600mL and sodium dioctylsulfosuccinate 40g were put into a reactor with a reflux condenser with an internal volume of 10L, and the temperature was raised to 80 ° C under a nitrogen atmosphere while stirring at 250 rpm. It was in a state that was not above. 5 minutes after adding 1.2 g of sodium formaldehyde sulfoxylate, 30% by mass of a monomer mixture consisting of MMA 260 g, BA 4.2 g, St64 g, ALMA 0.33 g and DPBHP 0.33 g was added at once. Immediately thereafter, the remaining 70% by mass was continuously added over 20 minutes, and after completion of the addition, the mixture was further maintained for 60 minutes to complete the polymerization of the innermost layer.
Next, 5 minutes after adding 1.0 g of sodium formaldehyde sulfoxylate, a monomer mixture consisting of 917 g of BA, St 480 g of St, ALMA 21 g, 7.0 g of tetraethylene glycol diacrylate and 2.9 g of DPBHP was added over 90 minutes. The mixture was continuously added and maintained for 80 minutes after the addition was completed to complete the polymerization of the soft layer (intermediate layer).
Next, a monomer mixture composed of MMA 695 g, BA 45 g, DPBHP 1.47 g and n-OM 0.9 g was continuously added over 60 minutes, and the mixture was held for 60 minutes after the addition was completed. Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost layer. A small amount of the polymer emulsion thus obtained was collected and the average particle size was determined by the absorbance method and found to be 0.08 μm. The remaining emulsified liquid is poured into a 3% by weight sodium sulfate warm aqueous solution, salted out and coagulated, then dried after repeated dehydration and washing, and the rubber-containing copolymer (b-3) is used as a powder. Obtained. Moreover, the refractive index difference with heat-resistant acrylic resin (a) was 0.008.

(2-4) Rubber-containing copolymer particles having a three-layer structure (c-1)
A reactor with an internal volume of 10 L equipped with a reflux condenser was charged with 4600 mL of ion-exchanged water and 24 g of sodium dioctylsulfosuccinate as an emulsifier, and the temperature was raised to 80 ° C. in a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. There was virtually no state. Next, 1.3 g of Rongalite was added as a reducing agent and dissolved uniformly. As a first layer, a monomer mixture of MMA 190 g, BA 2.5 g, ALMA 0.2 g and DPBHP 0.2 g was added and polymerized at 80 ° C. The reaction was complete in about 15 minutes.
Next, as a second layer, a monomer mixture of BA 1360 g, St 320 g, PDEGA 40 g, ALMA 7.0 g, DPBHP 1.6 g and Rongalite 1.0 g was added dropwise over 90 minutes. The reaction was completed 40 minutes after the completion of the dropwise addition.
Next, a monomer mixture of MMA 190 g, BA 2.3 g, and DPBHP 0.2 g was dropped over 5 minutes as the third layer, and after completion of the dropping, the reaction at this stage was completed in about 15 minutes.
Finally, MMA 380 g, BA 4.6 g, DPBHP 0.4 g, and n-OM 1.2 g monomer mixture was added over 10 minutes as the second layer of the third layer. This step was complete in about 15 minutes.
The temperature is raised to 95 ° C. and held for 1 hour, and the resulting emulsion is poured into a 0.5% aluminum chloride aqueous solution to agglomerate the polymer, washed 5 times with warm water, dried and dried in a white floc form. Obtained material. The rubber-containing copolymer particles (c-1) obtained had an average particle size of 0.1 μm. Moreover, the refractive index difference with heat-resistant acrylic resin (a) was 0.019.

(2-5) Rubber-containing copolymer particles having a three-layer structure (c-2)
Ion-exchanged water 6868 mL and sodium dihexyl sulfosuccinate 13.7 g were put into a reactor with a reflux condenser with an internal volume of 10 L, and the temperature was raised to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. There was virtually no state. Of the mixture (1-1) consisting of MMA 907 g, BA 33 g, HMBT 0.28 g and ALMA 0.93 g, 222 g was added all at once, and after 5 minutes, 0.22 g of ammonium persulfate was added. Forty minutes later, the remaining 719 g of (I-1) was continuously added over 20 minutes, and held for another 60 minutes after the addition was completed.
Next, after adding 1.01 g of ammonium persulfate, a mixture (I-2) comprising 1067 g of BA, St219 g, 0.39 g of HMBT, and 27.3 g of ALMA was continuously added over 140 minutes, and the mixture was further maintained for 180 minutes. did.
Next, after adding 0.30 g of ammonium persulfate, a mixture (I-3) composed of MMA 730 g, BA 26.5 g, HMBT 0.22 g, and n-OM 0.76 g was continuously added over 40 minutes. The temperature was raised to 95 ° C. and held for 30 minutes.
The remaining latex was put into a 3% by mass sodium sulfate warm aqueous solution, salted and coagulated, and then dried after repeated dehydration and washing to obtain rubber-containing copolymer particles (c-2). The rubber-containing copolymer particles (c-2) obtained had an average particle size of 0.23 μm. Moreover, the refractive index difference with heat-resistant acrylic resin (a) was 0.02.

(2-6) Rubber-containing copolymer particles having a three-layer structure (c-3)
Polymerization was carried out in the same formulation as (b-1) except that 15 g of sodium dioctyl sulfosuccinate was added as an emulsifier. The average particle diameter of the obtained rubber-containing copolymer particles (c-3) was 0.15 μm, and the difference in refractive index from the heat-resistant acrylic resin (a) was 0.004.

[Examples 1-5 and Comparative Examples 1-5]
Using a T-die mounting extruder (BT-30-C-36-L type / width 400 mm, T-die mounting / lip thickness 0.8 mm) manufactured by the Institute of Plastics Engineering, screw rotation speed, resin temperature in the cylinder of the extruder, T A raw film was obtained by adjusting the temperature of the die and performing extrusion molding. The flow (extrusion direction) of the film was MD direction, and the direction perpendicular to the MD direction was TD direction.
In Examples 1 to 3 and Comparative Examples 3 to 5, the heat-resistant acrylic resin and various rubber-containing copolymer particles were compounded by a twin screw extruder, and the pellets were T-die extruded. In Comparative Examples 1 and 2, extrusion molding was performed without blending the rubber-containing copolymer particles.
Table 1 shows the copolymer composition ratio of the heat-resistant acrylic resin, the blending ratio of the rubber-containing copolymer particles, the film molding conditions, the property evaluation results, and the film optical property results.

In Examples 1 to 3, by blending rubber-containing copolymer particles (b-1 to b-3) having a specific three-layer structure with a heat-resistant acrylic resin having a specific copolymer composition ratio, An optical film having a small absolute value of photoelastic coefficient excellent in toughness and maintaining heat resistance and transparency was obtained. Moreover, since the drawing process was not performed, the plane retardation was very small, and a film suitable for a polarizing plate protective film was obtained.
In Comparative Example 1, the toughness was insufficient because the rubber-containing copolymer particles were not mixed. In Comparative Example 2, since the copolymer composition ratio of the heat-resistant acrylic resin was not appropriate, the heat resistance was insufficient, and the rubber-containing copolymer particles were not mixed, so the toughness was also insufficient.
Moreover, in the comparative example 3, since the refractive index difference with a heat resistant acrylic resin and rubber-containing copolymer particle (c-1) was large, the raise of the haze value was seen. Furthermore, in Comparative Example 4, by using the rubber-containing copolymer particles (c-2) having a large average particle diameter, surface irregularities (external haze) occurred when the film was formed into a thin film, and the haze of the film The value rose.
In Comparative Example 5, the difference in refractive index from the heat-resistant acrylic resin was appropriate by using the rubber-containing copolymer particles (c-3), but the haze value of the film was large because the average particle diameter was large. Rose.

  The optical film of the present invention includes a light guide plate, a diffusion plate, a polarizing plate protective film, a quarter-wave plate, a half-wave plate used in a display such as a liquid crystal display, a plasma display, an organic EL display, a field emission display, and a rear projection television. It has industrial applicability to retardation films such as wave plates, viewing angle control films, liquid crystal optical compensation films, display front plates, display substrates, lenses, touch panels, and transparent substrates used for solar cells. In addition, in the fields of optical communication systems, optical switching systems, and optical measurement systems, the present invention can also be used for waveguides, lenses, optical fibers, optical fiber coating materials, and the like. The optical film of the present invention can be subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, and gas barrier treatment.

Claims (10)

Methacrylic acid ester and / or acrylic acid ester unit 40 mass% or more and 90 mass% or less, aromatic vinyl compound unit 5 mass% or more and 40 mass% or less, and compound unit 5 mass% represented by the following general formula (1) With respect to 100 parts by mass of the heat-resistant acrylic resin (a) including 30% by mass or less,

(Wherein, X represents a O, O represents an oxygen atom.)
The rubber-containing copolymer particles (b) having a multilayer structure having a difference in refractive index from the heat-resistant acrylic resin (a) of 0.015 or less and an average particle size of 0.04 μm or more and 0.13 μm or less are set to 0.0. An optical film containing 1 part by mass or more and 50 parts by mass or less.   The optical film according to claim 1, wherein the rubber-containing copolymer particles (b) are particles having a multilayer structure of three layers or more.   The optical film according to claim 1 or 2, wherein the rubber-containing copolymer particles (b) are particles having a three-layer structure formed in the order of hard layer-soft layer-hard layer from the inside.   The optical film of any one of Claims 1-3 whose film thickness is 100 micrometers or less and whose haze value in 23 degreeC environment is 1.2% or less.   The optical film of any one of Claims 1-4 whose haze value in a 70 degreeC environment is 2.0% or less.   The optical film of any one of Claims 1-5 whose Tg (glass transition temperature) is 120 degreeC or more. The optical film according to any one of claims 1 to 6, wherein an absolute value of a photoelastic coefficient in a 23 ° C environment is 5.0 × 10 ^-12 / Pa or less.   The optical film according to any one of claims 1 to 7, wherein a bending strength in a direction perpendicular to MD is 1.0 or more.   The polarizing plate protective film which consists of an optical film of any one of Claims 1-8.   A retardation film comprising the optical film according to claim 1.