JPWO2017029995A1 - Optical film and image display device - Google Patents

Abstract

An optical film in which an alkaline earth metal carbonate fine powder is dispersed in a resin, and the alkaline earth metal carbonate fine powder has an average major axis in the range of 10 to 100 nm and a content of 0.1 to the entire optical film. The optical film is characterized by being in the range of 1 to 50% by mass and having a surfactant attached to the surface. Moreover, it is an image display apparatus provided with said optical film.

Description

  The present invention relates to an optical film and an image display device, and more particularly to an optical film and an image display device containing an alkaline earth metal carbonate fine powder.

  Strontium carbonate fine powder is used in various fields such as multilayer ceramic capacitors. In recent years, an optical film such as a protective film used in a liquid crystal display device has been found to be used as a filler for suppressing or expressing birefringence.

  In general, there are a solution casting film forming method and a melt extrusion method for forming an optical film. The solution casting film forming method is a method in which a solvent in a solution state is cast on a substrate to volatilize the solvent. In this method, since a force in a certain direction is not applied to the resin, birefringence hardly occurs in the optical film after film formation, which is suitable for non-birefringent optical film applications. However, in this method, since the solvent is volatilized, the manufacturing cost increases, and there is a concern that the solvent may adversely affect the human body.

  On the other hand, the melt extrusion method is a method of forming a film by extruding a molten resin with a die or the like. This method does not require the solvent to be volatilized unlike the solution casting film forming method described above, and therefore has low manufacturing cost and high safety. However, since a force is applied in one direction when extruding the molten resin, the bond chain (main axis) of the resin is stretched and oriented in the extrusion direction, and birefringence may appear in the optical film after film formation. .

  Therefore, conventionally, fine strontium carbonate powder has been proposed as a filler (resin filler) for controlling the birefringence of the resin. Strontium carbonate is a biaxial birefringent crystal and has the property of exhibiting negative birefringence. For this reason, in the case of a resin material having a positive intrinsic birefringence, the major axis of the strontium carbonate fine particles is in the extrusion direction along the resin extrusion direction by performing melt extrusion by mixing as a filler in the molten resin in the melt extrusion method. Oriented to As a result, the intrinsic birefringence of the resin is offset and the birefringence of the optical film is lowered. The optical film in this case is suitable for applications such as a protective film.

  Further, by adding a large amount of strontium carbonate, the birefringence can be enhanced and the birefringence of the optical film can be enhanced. Furthermore, birefringence can be expressed more by further stretching the obtained film in a uniaxial or biaxial direction. The optical film in this case is suitable for applications such as a retardation film.

  As such a retardation film, for example, in the example of Patent Document 1, strontium carbonate, which is a needle-like crystal having a major axis of 200 nm and a width of 20 nm, is converted to methylene chloride at a ratio of 15% by weight to the alicyclic polyolefin resin. It is described that a dope solution is prepared by dissolution, and a film obtained from the dope solution is stretched uniaxially at 129 ° C. and 1.5 times to obtain a retardation film.

JP 2006-251644 A (paragraph 0055, etc.)

  In order to control the birefringence of the resin, it is necessary to highly disperse and blend strontium carbonate particles in the resin. However, as in Patent Document 1, strontium carbonate particles having a large average major axis reduce the transparency of the optical film compared to small strontium carbonate particles, and as a result, when such an optical film is used in an image display device or the like. There is an inconvenience of poor visibility.

  On the other hand, if the strontium carbonate particles are made fine in order to improve the transparency of the optical film, the surface area increases and the fine particles tend to aggregate. Since the aggregated particles cause light scattering, the transparency of the optical film is impaired.

  An object of the present invention is to provide an optical film and an image display device that have high transparency and birefringence is arbitrarily controlled.

  As a result of intensive investigations to achieve the above object, the present inventors have determined that the average major axis and content of the alkaline earth metal salt fine powder, and further, the surface treatment allows the resin to be a fine powder having a small average major axis. It has been found that the dispersibility can be improved. As a result, it was confirmed that both transparency improvement and refractive index control of the optical film could be realized, and the present invention was completed.

  That is, the present invention is an optical film in which alkaline earth metal carbonate fine powder is dispersed in a resin, wherein the alkaline earth metal carbonate fine powder has an average major axis in the range of 10 to 100 nm, The optical film is characterized in that the content with respect to the entire film is in the range of 0.1 to 50% by mass, and a surfactant is attached to the surface.

  In this case, the alkali metal carbonate is preferably strontium carbonate. The average major axis is preferably in the range of 20 to 50 nm, and the haze is preferably 1% or less. Furthermore, the content is preferably in the range of 1 to 35% by mass.

  The resin is polycarbonate, polymethyl methacrylate, cellulose ester, polystyrene, styrene acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyether sulfone, polyolefin, maleimide copolymer, polyethylene terephthalate, polyethylene naphthalate, polyimide, One or more types selected from the group consisting of polyamide and polyurethane are preferred.

  In particular, it is preferable that the resin is polycarbonate, and in this case, it further includes a surface modifier.

  Furthermore, in this case, it is preferable that the content is in the range of 8 to 16% by mass, the haze is 1% or less, and has a positive in-plane birefringence. Alternatively, the content is preferably in the range of 8 to 16% by mass, the haze is 1% or less, and the in-plane birefringence is preferably zero.

  The resin is preferably polymethyl methacrylate. In this case, it is preferable that the content is in the range of 8 to 32% by mass, the haze is 1% or less, and has a negative in-plane birefringence. The film thickness is preferably in the range of 20 to 150 μm. Furthermore, the optical film is preferably a stretched film. Furthermore, it is preferable that the arithmetic average surface roughness (Ra) is 20 nm or less, and the image clarity (based on JIS K 7374) at a comb width of 0.125 mm is 75% or more.

  Moreover, this invention is provided with the optical film in any one of said, The image display apparatus characterized by the above-mentioned.

  According to the present invention, an optical film having high transparency and birefringence being arbitrarily controlled can be provided. Moreover, according to this invention, the image display apparatus provided with such an optical film can be provided.

  The optical film of the present invention is an optical film in which alkaline earth metal carbonate fine powder is dispersed in a resin, and the alkaline earth metal carbonate fine powder has an average major axis in the range of 10 to 100 nm, and the entire optical film. Is in the range of 0.1 to 50% by mass, and the surfactant adheres to the surface. The optical film of the present invention can be produced by forming a film of a resin composition in which alkaline earth metal carbonate fine powder is dispersed in a resin. Hereinafter, each component constituting the resin composition will be described.

1. Alkaline earth metal carbonate fine powder Alkaline earth metal carbonate fine powder is mainly composed of alkaline earth metal carbonate, has an average major axis of 10 to 100 nm, and has a surfactant attached to its surface. As described above, even alkaline earth metal carbonate fine particles having an average major axis smaller than the conventional one have high dispersibility when dispersed in a resin because the surfactant is attached to the surface.

(1) Alkaline earth metal carbonate fine particles (before surface treatment)
The alkaline earth metal carbonate fine particles before the surface treatment with the surfactant have an average major axis in the range of 10 to 100 nm, preferably in the range of 15 to 75 nm, and more preferably in the range of 20 to 50 nm. If the average major axis is less than 10 nm, the particles are too small to easily aggregate and the dispersibility tends to deteriorate. On the other hand, if the average major axis exceeds 100 nm, the particles are too large and the transparency tends to deteriorate when mixed with the resin.

  Here, the average major axis can be measured by visually or automatically image-processing a scanning electron microscope (SEM) photograph of alkaline earth metal carbonate fine particles. The major axis of the alkaline earth metal carbonate fine particles can be measured as the length in the longitudinal direction (long side length) when the alkaline earth metal carbonate particles such as strontium carbonate particles are regarded as a rectangle. Specifically, the rectangle circumscribing the alkaline earth metal carbonate particles in the image and having the smallest area is calculated, and the major axis is obtained from the length of the long side. Furthermore, the “average” means an average value obtained by measuring a statistically reliable number (N number) of alkaline earth metal carbonate, and the number is usually 300 or more. , Preferably 500 or more, more preferably 1000 or more. The minor axis of the alkaline earth metal carbonate particles can be measured as the length in the short direction (the length of the short side) when the alkaline earth metal carbonate particles are regarded as a rectangle.

  The average aspect ratio of the alkaline earth metal carbonate fine particles is not particularly limited, but is usually in the range of 1.0 to 5.0, preferably in the range of 2.0 to 4.5, 2.5 to A range of 4.0 is particularly preferred. When the average aspect ratio exceeds 5.0, the fine particles are too long and easily broken, and the particle size distribution is likely to deteriorate. If the aspect ratio is too small, it may be difficult to exert an effect on birefringence control.

  Here, the aspect ratio means “major axis / minor axis” of the particle. The average aspect ratio means an average value of the aspect ratio, and the average value of a plurality of particles is calculated by measuring the aspect ratio of one particle.

  Examples of the alkaline earth metal constituting the alkaline earth metal carbonate fine particles include calcium, strontium, barium, and radium. Examples of the alkaline earth metal carbonate fine particles include calcium carbonate fine particles, strontium carbonate fine particles, and barium carbonate fine particles. Of these, strontium carbonate fine particles are preferred from the viewpoint of controlling birefringence in applications such as optical resin fillers.

(2) Surfactant The surfactant has a function of improving the dispersibility in the resin or solvent by adhering to the surface of the alkaline earth metal carbonate fine particles. Although it does not specifically limit as a kind of surfactant, A nonionic surfactant and an anionic surfactant can be mentioned. Of these surfactants, anionic surfactants are preferable to nonionic surfactants such as stearic acid monoglyceride from the viewpoint of transparency of the optical film. Among these, a compound containing a hydrophilic group and a hydrophobic group and further having a group that forms an anion in water is preferable. The hydrophilic group is preferably a polyoxyalkylene group containing an oxyalkylene group having 1 to 8 carbon atoms. The hydrophobic group is preferably an alkyl group or an aryl group. The alkyl group and aryl group may have a substituent. The alkyl group generally has 3 to 30 carbon atoms, preferably 10 to 18 carbon atoms. An aryl group generally has 6 to 30 carbon atoms. The group that forms an anion in water is selected from the group consisting of a carboxylic acid group (—COOH), a sulfuric acid group (—OSO ₃ H), and a phosphoric acid group (—OPO (OH) ₂ , —OPO (OH) O—). It is preferably an acid group. The hydrogen atom of these acid groups may be substituted with an alkali metal ion such as sodium or potassium or an ammonium ion.

  Of these, polycarboxylic acid anionic surfactants or polyphosphoric acid anionic surfactants are preferred because the alkaline earth metal carbonate fine particles have good dispersibility in resins and solvents. .

  Examples of the polycarboxylic acid-based anionic surfactant include compounds represented by the following formula (I).

（ここで、Ｒ^１は置換若しくは無置換のアルキル基又は置換若しくは無置換のアリール基を意味し、Ｅ^１は炭素原子数が１〜８の範囲内にあるアルキレン基を意味し、ａは１〜２０の範囲内、好ましくは２〜６の範囲内の数を意味する。なお、Ｒ^１は炭素原子数が１０以上、好ましくは１０〜１８の範囲内にあるアルキル基であることが好ましい。）

(Wherein R ¹ represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, E ¹ represents an alkylene group having 1 to 8 carbon atoms, and a represents 1 It means a number in the range of ˜20, preferably in the range of 2 to 6. In addition, R ¹ is preferably an alkyl group having 10 or more carbon atoms, preferably in the range of 10 to 18. )

  Examples of the polyphosphate anionic surfactant include a compound (mono-form) represented by the following formula (II), a compound (di-form) represented by the following formula (III), or a formula (II) And mixtures of formula (III).

（ここで、Ｒ^２は置換若しくは無置換のアルキル基又は置換若しくは無置換のアリール基を意味し、Ｅ^２は炭素原子数が１〜８の範囲内にあるアルキレン基を意味し、ｂは１〜２０の範囲内、好ましくは２〜６の範囲内の数を意味する。なお、Ｒ^２は炭素原子数が１０以上、好ましくは１０〜１８の範囲内にあるアルキル基であることが好ましい。）

(Wherein R ² represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, E ² represents an alkylene group having 1 to 8 carbon atoms, and b represents 1 It means a number in the range of -20, preferably in the range of 2-6, wherein R ² is an alkyl group having 10 or more carbon atoms, preferably in the range of 10-18. )

（ここで、Ｒ^３とＲ^４は同一又は異なっていてもよく、置換若しくは無置換のアルキル基又は置換若しくは無置換のアリール基を意味し、Ｅ^３とＥ^４は同一又は異なっていてもよく、炭素原子数が１〜８の範囲内にあるアルキレン基を意味し、ｃとｄはそれぞれ１〜２０の範囲内、好ましくは２〜６の範囲内の数を意味する。なお、Ｒ^３とＲ^４は、いずれも炭素原子数が１０以上、好ましくは１０〜１８の範囲内にあるアルキル基であることが好ましい。）

(Here, R ³ and R ⁴ may be the same or different, meaning a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, and E ³ and E ⁴ may be the same or different. Represents an alkylene group having 1 to 8 carbon atoms, and c and d each represent a number within the range of 1 to 20, and preferably within the range of 2 to 6. R ³ and R ⁴ is preferably an alkyl group having 10 or more carbon atoms, preferably 10 to 18 carbon atoms.)

  The surfactant may be used alone or in combination of two or more with respect to the alkaline earth metal carbonate fine powder. Further, the surfactant may be attached only to one layer on the surface of the alkaline earth metal carbonate fine powder, or two or more layers may be attached. When two or more layers are attached, the same surfactant may be used for each layer, or different surfactants may be used for each layer. Whether the surfactant is attached to the surface of the alkaline earth metal carbonate fine powder is determined by measuring the infrared absorption spectrum of the particle surface using a Fourier transform infrared spectrometer (FT-IR). This can be confirmed.

(3) Manufacturing method of alkaline-earth metal carbonate fine powder Next, the manufacturing method of alkaline-earth metal carbonate fine powder is demonstrated. The method for producing the alkaline earth metal carbonate fine powder is not particularly limited as long as the alkaline earth metal carbonate fine particles as a raw material are prepared and surface-treated with a surfactant. Hereinafter, a method for producing fine strontium carbonate powder as an example of alkaline earth metal carbonate fine powder will be specifically described.

(A) Reaction step While stirring an aqueous solution or aqueous suspension (hereinafter referred to as an aqueous slurry) of strontium hydroxide as a raw material, carbon dioxide gas is introduced in the presence of a crystal growth inhibitor to carbonate strontium hydroxide. To produce spherical strontium carbonate fine particles having a low aspect ratio. The concentration of strontium hydroxide contained in the aqueous slurry is not particularly limited, but is usually in the range of 1 to 20% by mass, preferably in the range of 2 to 18% by mass, more preferably in the range of 3 to 15% by mass. It is.

  The crystal growth inhibitor is preferably an organic acid having 2 carboxyl groups and 3 to 6 hydroxyl groups in total. Preferable examples of the crystal growth inhibitor include tartaric acid, malic acid and tartronic acid. As the crystal growth inhibitor, an organic acid having two carboxyl groups and a hydroxyl group, and a total of at least three, can be used. From the viewpoint of improving dispersibility while being fine, dicarboxylic acid having one or more hydroxyl groups in the molecule or an anhydride thereof is more preferable, and DL-tartaric acid is particularly preferable. The amount of the crystal growth inhibitor used is generally in the range of 0.1 to 20 parts by mass, preferably in the range of 1 to 10 parts by mass with respect to 100 parts by mass of strontium hydroxide.

  The flow rate of carbon dioxide gas is usually in the range of 0.5 to 200 mL / min, preferably in the range of 0.5 to 100 mL / min, with respect to 1 g of strontium hydroxide. By the reaction step, for example, fine spherical strontium carbonate fine particles having an average aspect ratio lower than 1.5 and nearly spherical can be obtained. In addition, the manufacturing method of spherical strontium carbonate fine particles is described in international publication 2011/052680.

(B) Aging process The aging process is a process in which the aqueous slurry containing the spherical strontium carbonate fine particles obtained in the reaction process is aged at a predetermined temperature and time to grow into acicular strontium carbonate fine particles. The aging step can be performed in warm water. The aging temperature is in the range of 75 to 115 ° C, preferably in the range of 80 to 110 ° C, and particularly preferably in the range of 85 to 105 ° C. When the aging temperature is below 75 ° C., the crystal growth of the spherical strontium carbonate fine particles is insufficient and the average aspect ratio tends to be too low, and when it exceeds 115 ° C., the short-diameter crystal growth of the spherical strontium carbonate fine particles is promoted. Aspect ratio tends to be low. The aging time is not particularly limited, but is usually in the range of 1 to 100 hours, preferably in the range of 5 to 50 hours, and particularly preferably in the range of 10 to 30 hours.

  The reaction step and the aging step are steps for obtaining acicular strontium carbonate fine particles from strontium hydroxide as a raw material.

(C) Surface treatment step In the surface treatment step, primary particles are dispersed by applying shearing force to a dispersion in which strontium carbonate fine particles having an average major axis in the range of 10 to 100 nm are dispersed in an aqueous solvent. In this step, a highly dispersible strontium carbonate is obtained by contacting with a surfactant. As the surfactant, those described above can be used.

  As the dispersion used in the surface treatment step, an aqueous slurry after the aging step can be used when the aging step is performed. The surface treatment step can be performed by adding a surfactant to the dispersion while applying a shearing force. The content of strontium carbonate particles in the aqueous slurry is preferably in the range of 1 to 30% by mass. The total amount of surfactant added to the aqueous slurry is generally in the range of 1 to 60% by mass, preferably in the range of 10 to 50% by mass, and in the range of 20 to 40% by mass. Is more preferable. The application of the shearing force can be performed using a known stirring device such as a stirring blade mixer, a homomixer, a magnetic stirrer, an air stirrer, an ultrasonic homogenizer, a clear mix, a fill mix, and a wet jet mill.

  When surface treatment is performed using two or more kinds of surfactants, the amount of each surfactant added to the aqueous slurry is generally 1 to 40 parts by mass with respect to 100 parts by mass of the strontium carbonate particles in the aqueous slurry. The range is preferably 3 to 30 parts by mass. Surfactants can be added simultaneously or sequentially.

(D) Drying step The drying step is a step in which the aqueous slurry obtained in the surface treatment step is dried by heating at a temperature in the range of 100 to 300 ° C. to obtain a dried product of highly dispersible strontium carbonate fine powder. . When the drying temperature is lower than 100 ° C., the drying tends to be insufficient, and when the drying temperature is higher than 300 ° C., the surface treatment agent is likely to be thermally deteriorated. The drying temperature is preferably in the range of 110 to 180 ° C, and more preferably in the range of 120 to 160 ° C. The drying step can be performed by a known drying method using a thermal dryer such as a spray dryer, a drum dryer, or a disk dryer.

2. Resin composition The resin composition used in the present invention is a resin composition in which alkaline earth metal carbonate fine powder is dispersed in a resin, and the alkaline earth metal carbonate fine powder has an average major axis of 10 to 100 nm. Within the range, the content with respect to the entire resin composition is in the range of 1 to 50% by mass, and the surfactant adheres to the surface. Since the above alkaline earth metal carbonate fine powder is surface-treated, it has high dispersibility in the resin even though the average major axis is small. Therefore, the transparency of the film formed with the resin composition is increased. can do. Further, since the alkaline earth metal carbonate fine powder itself is a birefringent powder, the birefringence of the optical film obtained by forming the resin composition can be controlled. That is, the resin composition of the present invention can be suitably used as a raw material for optical films that are highly transparent and require birefringence to be arbitrarily controlled.

  As resin contained in a resin composition, if it is resin used for a normal optical film, it will not specifically limit, Various resin can be selected according to the objective. Examples of such resins include cellulose esters such as polycarbonate, polymethyl methacrylate, and triacetyl cellulose, polystyrene, styrene acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyether sulfone, polyolefins such as polycyclic olefin, and maleimide copolymers. One or more types selected from the group consisting of a polymer, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, and polyurethane can be mentioned.

  Content with respect to the whole resin composition of alkaline-earth metal carbonate fine powder exists in the range of 0.1-50 mass%. When the content of the alkaline earth metal carbonate fine powder is less than 0.1% by mass, the birefringence control effect by the alkaline earth metal carbonate fine powder becomes too small. On the contrary, when the content of the alkaline earth metal carbonate fine powder exceeds 50% by mass, the ratio of the alkaline earth metal carbonate fine powder to the resin becomes too large, so that the transparency of the film formed is increased. Becomes worse. The content of the alkaline earth metal carbonate fine powder with respect to the entire resin composition is preferably within a range of 0.5 to 40% by mass, and particularly preferably within a range of 1 to 35% by mass.

  A resin composition can be obtained by mixing the above resin and alkaline earth metal carbonate fine powder. For mixing alkaline earth metal carbonate fine powder and resin, the resin is dissolved in the alkaline earth metal carbonate dispersion (solution method), and the resin is uniformly dissolved in the alkaline earth metal carbonate dispersion. Then, a method of removing the solvent and pelletizing or pulverizing, a method of melting and kneading the alkaline earth metal carbonate and the resin with an extruder or the like (melting method), and the like can be mentioned. Alternatively, a master batch may be prepared in advance and kneaded with a kneader. The master batch can be prepared by the above-described solution method, melting method, or the like.

  Further, an optical film may be formed by adjusting a dope solution in which a resin composition and an appropriate solvent are mixed. The type of such solvent is not particularly limited, and can be appropriately selected and used depending on the properties of the resin. As an example of the solvent, an organic solvent is preferable, and examples of the organic solvent include alcohols (eg, ethanol, 1-propanol, 2-propanol, 1-butanol, ethylene glycol), methylene chloride, NMP, tetrahydrofuran, MEK, Examples thereof include ethyl acetate, butyl acetate, PGME, PGMEA, cyclohexane, and toluene. It is possible to use not only the above one type but also a plurality of combinations.

  The ratio of the resin to the solvent is preferably in the range of 1:10 to 10: 1 by mass ratio. The dope solution may be obtained by mixing a resin and a solvent to form a resin mixed solution, and adding and mixing the alkaline earth metal carbonate fine powder, or mixing the alkaline earth metal carbonate fine powder and the solvent. Then, a powder mixed solution may be prepared, and a resin may be added and mixed therewith. Furthermore, the resin mixed solution and the powder mixed solution described above may be prepared and mixed to form a dope solution. The alkaline earth metal carbonate fine powder, the resin and the solvent can be mixed by a known method such as a method using an ultrasonic homogenizer, a stirring blade, or a liquid jet mill.

  The resin composition and dope solution can be formed into an optical film by a known method. Examples of the film forming method include known film forming methods such as the above-described melt extrusion film forming method and solution casting film forming method. The melt extrusion film forming method is a method in which a resin composition is heated and melted to form a melt, which is cast into a film on a support and cooled and solidified. The solution casting film forming method is a method of casting a dope solution on a support and evaporating the solvent to form a film.

  Depending on the type of resin, convection may occur in the resin solution during film formation, and a Benard cell structure may be formed. During the formation of the Benard cell structure, the alkaline earth metal carbonate fine powder aggregates to deteriorate the transparency of the optical film. Further, this aggregation reduces the birefringence adjusting action by the alkaline earth metal carbonate fine powder. Therefore, it is preferable to add a surface modifier to the resin composition or the dope solution for the purpose of improving the wettability with the support and suppressing the formation of Benard cells. When polycarbonate is used as a resin, Benard cells are easily formed, and thus the effect of improving transparency by adding a surface modifier is great. Examples of the surface modifier include vinyl surfactants, fluorine surfactants, and silicone oil.

  The film after film formation can be appropriately stretched according to the application. Examples of the stretching method include uniaxial stretching and biaxial stretching. Biaxial stretching can be sequential or simultaneous stretching. Stretching can be performed using a known stretching apparatus such as a tenter.

3. Optical Film The optical film thus obtained contains fine and highly dispersed alkaline earth metal carbonate fine powder, and thus has excellent transparency, and the alkaline earth metal carbonate for the entire optical film. By adjusting the content of the salt fine powder, the birefringence of the optical film itself can be adjusted. Since the alkaline earth metal carbonate fine powder itself exhibits negative birefringence, the birefringence of the optical film can be adjusted according to the intended use of the optical film.

For example, by adding alkaline earth metal carbonate fine powder to a resin exhibiting positive intrinsic birefringence such as polycarbonate or polycyclic olefin, an optical film whose birefringence is close to zero by offsetting the intrinsic birefringence of the resin It can be. An example of such an optical film is a protective film. Examples of the protective film include a normal protective film laminated on the surface of the polarizing plate, and a polarizer protective film that is directly laminated on the surface of the polarizer to protect the polarizer.

  Alternatively, an optical film having positive birefringence may be obtained by adding a small amount of alkaline earth metal carbonate fine powder to a resin exhibiting positive birefringence such as polycarbonate or polycyclic olefin. Furthermore, an optical film having negative birefringence may be obtained by adding a large amount of alkaline earth metal carbonate fine powder to the resin exhibiting positive birefringence. Here, “birefringence” means the value of the in-plane birefringence (ΔNxy) described above. Examples of the optical film exhibiting such positive or negative in-plane birefringence include a retardation film. Examples of the retardation film include a quarter wavelength plate and a half wavelength plate.

  On the other hand, by using a resin that exhibits negative birefringence such as polymethyl methacrylate or polystyrene, or a resin that has low birefringence, an optical film that exhibits negative birefringence can be obtained. An example of such an optical film is a retardation film. Examples of the retardation film include a quarter wavelength plate and a half wavelength plate.

  As an optical film of the present invention, a C plate can be mentioned as a suitable example among retardation films. In general, an A plate (positive: nx> ny = nz, negative: nx <ny = nz), a C plate (positive: nx = ny <nz, negative: nx = ny> nz) is used for the image display device. Thus, methods for improving optical characteristics such as viewing angle characteristics and color have been proposed. Currently, a positive C plate is produced by applying a coating liquid made of a liquid crystal material on a substrate and drying and solidifying it to form a vertical alignment film.

  Acicular strontium carbonate has a smaller refractive index in the longitudinal direction of the particles than in the lateral direction. When oriented by stretching, nx <ny≈nz. This acicular strontium carbonate is randomly oriented in the in-plane direction, so that nx = ny <nz. Since the longitudinal direction of the particles is random in the plane, the refractive indexes in the x and y directions are averaged, and nx = ny. However, since it is oriented in the thickness direction (particles are lying on the film surface), nz is larger than nx and ny.

  Examples of the optical film of the present invention include an antireflection film, an antiglare film, a brightness enhancement film, a prism film, and a viewing angle improvement film in addition to the retardation film and the protective film.

  The haze of the optical film can be 10% or less, preferably 5% or less, and more preferably 1% or less. Note that the haze can be intentionally deteriorated depending on the use of the optical film. For example, by adding light-scattering fine particles such as glass beads in the resin composition, the haze may be deteriorated to form an antiglare film. Moreover, the light transmittance of an optical film can be 85% or more, Preferably it is 88% or more, More preferably, it can be 90% or more. The film thickness of the optical film is preferably in the range of 20 to 150 μm, and more preferably in the range of 25 to 100 μm.

Since the alkaline earth metal carbonate fine powder of the present invention has a short average major axis and high dispersibility, it is difficult for the particles to interact with each other and to form particles due to Benard cell formation. For this reason, when the alkaline earth metal carbonate fine powder of the present invention is contained in the optical film, the number of aggregated particles protruding from the surface is reduced, and as a result, the optical film is excellent in surface smoothness. Become. Specifically, the optical film of the present invention can have an arithmetic average surface roughness (Ra) value of 20 nm or less, more preferably 15 nm or less. When the arithmetic average surface roughness (Ra) is a relatively high value, the smoothness of the surface becomes poor, and the visibility is likely to be lowered due to surface irregularities. The lower limit of the value of the arithmetic average surface roughness (Ra) is not particularly limited, but is 0 nm or more.

  As described above, the alkaline earth metal carbonate fine powder of the present invention is less likely to cause agglomeration of particles, so that there is little decrease in the visibility of the optical film due to light scattering by the agglomerated particles, and excellent transmission image clarity. It will be. Specifically, in the optical film of the present invention, for example, the image clarity at a comb width of 0.125 mm (based on JIS K 7374) can be 75% or more, preferably 80% or more. Preferably, it can be 85% or more. If the image clarity is relatively low, the clarity of the transmitted image tends to be low. The upper limit of the image clarity is not particularly limited, but is 100% or less in each comb width unit including the above comb width.

4). Optical Laminate The optical film of the present invention can be laminated with other optical films to form an optical laminate. Examples of other optical films include a polarizing film (also referred to as a polarizer), a substrate film, and the like. As an optical laminate, a polarizing plate in which a protective film and a polarizing film as an optical film of the present invention are laminated, an elliptical polarizing plate in which a retardation film and a polarizing film as an optical film of the present invention are laminated, Examples of the optical film of the invention include a retardation plate in which a retardation film and a base film are laminated.

5. Image display device The image display device of the present invention is provided with the optical film of the present invention. Examples of the image display device include a liquid crystal display device (LCD) and an organic electroluminescence display device. Examples of the use of the image display device include a portable information terminal such as a television, a computer monitor, a mobile phone, a smartphone, and a PDA.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, these do not limit the objective of this invention.

<Polycarbonate (PC) film>
(1) Example 1
(Surface treatment of nanoparticles)
A water slurry having a concentration of 5% of strontium carbonate nanoparticles (average major axis 35 nm, aspect ratio 2.1) is placed in a 300 mL beaker, and 5.25 g of polycarboxylic acid anionic surfactant (A) is added thereto, and a 5-minute stirrer is added. Stir with. The slurry solution was stirred for 20 minutes at 20000 rpm (corresponding to 30 m / s) at a chiller set temperature of 4 ° C. using CLEARMIX (manufactured by M Technique). Thereafter, the apparatus was stopped and the slurry was collected and sprayed onto an iron plate heated to 130 ° C., and the powder adhering to the surface was immediately scraped off to obtain surface-treated powder 1.

(SrCO ₃ addition dope preparation method)
6 g of polycarbonate (hereinafter referred to as “PC”) was added to 25 g of methylene chloride and stirred for 6 hours to prepare a PC-methylene chloride solution. Next, 0.48 g of the surface-treated powder 1 was added to 10 g of methylene chloride, placed in an ultrasonic bath for 30 seconds, and filtered as it was without applying pressure with a membrane filter having a pore diameter of 1 μm to prepare a dispersion 1. PC- mixed with methylene chloride dispersion of the dispersion 1, was dispersed in an ultrasonic homogenizer to obtain a SrCO ₃ added dope solution A-1.

(PC film deposition method)
SrCO ₃ -added dope solution A-1 was applied to a polyethylene terephthalate (hereinafter “PET”) film with a wet film thickness of 11 mil using a Baker type applicator. This was dried at 40 ° C. for 2 minutes, 80 ° C. for 4 minutes, and 120 ° C. for 30 minutes. The PC film was peeled from the PET film to obtain PC film A-1. The PC film A-1 was subjected to free end uniaxial stretching 2.0 times at 160 ° C. with a film stretching apparatus (manufactured by Imoto Seisakusho, IMC-1A8D type) to obtain a PC stretched film A-1.

(Transmittance and haze measurement)
Using a spectrophotometer (manufactured by JASCO Corporation), the visible light transmittance and haze measurement of the PC stretched film A-1 were performed.

(Evaluation of retardation of film)
The film thickness of PC stretched film A-1 was measured with a micrometer. Then, the phase difference (ΔNxy) of the stretched film was measured using a phase measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR). The results are shown in Table 1.

(2) Example 2
The same method as in Example 1 was used except that 0.026 g of a vinyl-based surface modifier was added to a mixed solution obtained by mixing the PC-methylene chloride dispersion and the dispersion 1. This obtained PC stretched film B-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(3) Example 3
The same method as in Example 2 was used, except that the amount of SrCO ₃ added was 0.96 g. This obtained PC stretched film C-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(4) Example 4
The same method as in Example 2 was used except that the amount of SrCO ₃ added was 1.92 g. This obtained PC stretched film D-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(5) Comparative Example 1
The same method as in Example 1 was used except that SrCO ₃ was not added. This obtained PC stretched film E-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(6) Comparative Example 2
The same method as in Example 1 was used except that SrCO ₃ having an average major axis of 200 nm was used. This obtained PC stretched film F-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(7) Comparative Example 3
The same method as in Comparative Example 2 was used except that the amount of SrCO ₃ added was 15 wt%. This obtained PC stretched film G-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

(8) Comparative Example 4
The same method as in Example 2 was used, except that SrCO ₃ not subjected to surface treatment was used. This obtained PC stretched film H-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 1.

Comparing Example 1 and Comparative Example 2, it can be seen that Example 1 having a smaller average major axis has lower haze and lower birefringence (ΔNxy × 10 ⁻³ ) than Comparative Example 2 having a larger average major axis. . Further, when Example 1 and Comparative Example 4 are compared, it can be seen that the surface-treated Example 1 has a lower haze and lower birefringence than Comparative Example 4 that has not been surface-treated. Therefore, it was found that fine strontium carbonate fine particles having a small average major axis and surface-treated are preferable from the viewpoint of transparency and birefringence.
Further, comparing Example 1 and Example 2, it can be seen that Example 2 with the addition of the surface modifier has a smaller haze than Example 1 without the addition of the surface modifier. Therefore, it was found that it is preferable to add a surface modifier from the viewpoint of increasing transparency.
In particular, in Example 3, the haze was as low as less than 1%, and the birefringence was almost zero. Therefore, it was found that the film is particularly suitable for a film that is required to have high transparency and little birefringence, such as a protective film for a polarizing plate.

(Evaluation of reverse wavelength dispersion)
About the film of Example 2, Example 3, and the comparative example 1, reverse wavelength dispersion was evaluated. In the evaluation, the retardation value of each film was measured at seven single wavelengths described in Table 2 below. The phase difference value was measured by the same method as “((film retardation evaluation))” described above. _Then, based on the value of _{R 589.3,} and calculates the ratio _{(R / R 589.3)} of the retardation value of each wavelength. The results are shown in Table 2.

From this result, the comparative example 1 which does not contain strontium carbonate shows “normal wavelength dispersion” in which the phase difference value decreases as the wavelength increases. Similarly, Example 2 to which 8% by mass of strontium carbonate was added also shows normal wavelength dispersion. On the other hand, in Example 3 to which 16% by mass of strontium carbonate was added, it is understood that “reverse wavelength dispersion” in which the retardation value increases as the wavelength increases.

  The reverse wavelength dispersion is due to the difference in wavelength dispersion between polycarbonate and strontium carbonate. For polycarbonate and strontium carbonate, the sign of the intrinsic birefringence is reversed. Therefore, the difference between the intrinsic birefringence of polycarbonate and the intrinsic birefringence of strontium carbonate becomes the retardation value of the film. Further, polycarbonate has a large wavelength dependency in which the retardation value decreases as the wavelength increases. On the other hand, strontium carbonate has a small wavelength dependency. For this reason, when the amount of strontium carbonate added is small (for example, 8% by mass or less in this embodiment), the retardation development property of the polycarbonate is larger than the retardation development property of strontium carbonate. The difference in birefringence between strontium carbonate and strontium carbonate becomes smaller, and the film exhibits “normal wavelength dispersion” with a smaller retardation value toward the longer wavelength side. On the other hand, when the addition amount (16% by mass or more in the present example) that the retardation of strontium carbonate is larger than that of polycarbonate is increased, the difference in birefringence between the polycarbonate and strontium carbonate is increased, and the film has “reverse wavelength dispersion”. Indicates.

Also, ideal wavelength dispersion is that the same proportion of phase difference appears for each wavelength. For example, in the case of a retardation film having a quarter wavelength retardation, the wavelength dispersion is such that the retardation value is 100 nm at a wavelength of 400 nm, the retardation value is 150 nm at a wavelength of 600 nm, the retardation value is 200 nm at a wavelength of 800 nm, and the ideal wavelength. Distributed. If the deviation from the ideal chromatic dispersion is large, the display cannot produce a pure black display and has a bluish-purple color, resulting in poor display quality. In Example 3, since the phase difference value increases as the wavelength becomes longer, it can be said that it has characteristics close to ideal chromatic dispersion. The retardation film having such wavelength dispersion is useful for an antireflection film such as an organic EL display, a brightness enhancement film, and the like as well as a reflective liquid crystal display.

<Polymethylmethacrylate (PMMA) film>
(9) Example 5
(SrCO ₃ addition dope preparation method)
To 25 g of methylene chloride, 6 g of polymethyl methacrylate (hereinafter, “PMMA”) was added and stirred for 3 hours to prepare a PMMA-methylene chloride solution. Next, 0.48 g of the surface-treated powder 1 was added to 10 g of methylene chloride, placed in an ultrasonic bath for 30 seconds, and filtered as it was without applying pressure with a membrane filter having a pore diameter of 1 μm to prepare a dispersion 1. PMMA- mixed dispersion 1 methylene chloride dispersion was dispersed in an ultrasonic homogenizer to obtain a SrCO ₃ added dope solution I-1.

(PMMA film deposition method)
The SrCO ₃ added dope solution I-1, using a Baker-type applicator, was applied wet film thickness 11mil on the PET film. This was dried at 40 ° C. for 2 minutes, 80 ° C. for 15 minutes, and 85 ° C. for 30 minutes. The PMMA film was peeled from the PET film to obtain a PMMA film I-1. The PMMA film I-1 was subjected to free end uniaxial stretching 2.0 times at 90 ° C. with a film stretching apparatus (manufactured by Imoto Seisakusho, IMC-1A8D type) to obtain a PMMA stretched film I-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3.

(10) Example 6
The same method as in Example 5 was used, except that the amount of SrCO ₃ added was 0.96 g. This obtained PMMA stretched film J-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3.

(11) Example 7
The same method as in Example 5 was used, except that the amount of SrCO ₃ added was 1.92 g. This obtained PMMA stretched film K-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3.

(12) Comparative Example 5
The same method as in Example 5 was used, except that SrCO ₃ was not added. This obtained PMMA stretched film L-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3.

(13) Comparative Example 6
The same method as in Example 5 was used except that SrCO ₃ having an average major axis of 200 nm was used. This obtained PMMA stretched film M-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3. Note that ΔNxy × 10 ⁻³ and ΔP × 10 ⁻³ could not be measured because the film became cloudy (ΔP is an index representing the out-of-plane retardation).

(14) Comparative Example 7
The same method as in Example 5 was used, except that SrCO ₃ not subjected to surface treatment was used. This obtained PMMA stretched film N-1. The characteristics of the film obtained in the same manner as in Example 1 were evaluated. The results are shown in Table 3.

When Example 7 and Comparative Example 6 are compared, Example 7 with a smaller average major axis has a lower haze than Comparative Example 6 with a larger average major axis. Moreover, when Example 5 and Comparative Example 7 are compared, it can be seen that the surface-treated Example 5 has a lower haze and lower birefringence than Comparative Example 7 that has not been surface-treated. Therefore, it was found that fine strontium carbonate fine particles having a small average major axis and surface-treated are preferable from the viewpoint of transparency and birefringence.
In particular, in Example 7, the haze was as low as less than 1%, and the birefringence was significantly negative. Therefore, it was found that the film is particularly suitable for an optical film that requires high transparency and high birefringence, such as a retardation film of a polarizing plate.

(Evaluation of retardation of unstretched film)
(15) Example 8 PMMA unstretched film A PMMA film before stretching was prepared by the same blending amount, dope solution preparation method and film formation method as in Example 6, and in-plane retardation expression (ΔNxy = nx−ny) and out-of-plane retardation (ΔP = nx + ny / 2−nz) were measured. The results are shown in Table 4.

(16) Comparative Example 8
A PMMA film before stretching was prepared by the same blending amount, dope solution preparing method, and film forming method as in Comparative Example 5, and in-plane retardation and out-of-plane retardation measurement were performed in an unstretched state. The results are shown in Table 4.

  In both Example 8 and Comparative Example 8, the in-plane phase difference is zero and the out-of-plane phase difference is a negative value, which indicates that it is a + C plate. Moreover, since the in-plane phase difference was zero, it was confirmed that there was no disturbance in the polarization state by the orthogonal Nicol method. However, when ΔP indicating the out-of-plane phase difference was compared, it was found that the out-of-plane phase difference of Example 8 was high. This is because, as described above, the needle-shaped strontium carbonate is randomly oriented in the film plane, so that nz is increased. From this result, the retardation development can be enhanced by adding acicular strontium carbonate to the film used for the + C plate. This effect is useful for thinning the film when a desired retardation is obtained.

  Further, an isotropic film (nx = ny = nz) can be produced by adding acicular strontium carbonate to a film to be a -C plate, such as a PC unstretched film. These can replace glass substrates and are useful for flexible display substrates.

<Measurement of surface roughness and image clarity>
About the stretched PC film prepared in Example 3 and Comparative Examples 1 to 4, the surface roughness and the image clarity were evaluated as follows. The results are shown in Table 5. Moreover, about the PMMA stretched film created in Examples 5-7 and Comparative Examples 5-7, surface roughness and image clarity were similarly evaluated. The results are shown in Table 6.

(Evaluation of surface roughness)
The surface roughness of the film was evaluated by using a stylus profiling system Dektak XT manufactured by Bruker, Inc., scanning 10,000 μm under the following conditions, removing coarse waviness due to waviness of the film by Gaussian function approximation, and calculating the arithmetic average surface. Roughness (Ra) was calculated and evaluated. The measurement was performed on the surface on the atmosphere side (the side opposite to the substrate surface) during casting.
Scan Type: standard scan
Range: 65.5 μm
Profile: Hills & Valleys
Stylus: 2 μm
Stylus Force: 15mg
Duration: 120 sec
Cutoff value when removing waviness: 80 μm

(Evaluation of image clarity)
The evaluation of the image clarity of the film was measured according to JIS K 7374 using the image clarity measuring device ICM-1T manufactured by Suga Test Instruments Co., Ltd., and the value when the comb width was 0.125 mm was used as an index of image clarity. . In addition, the measurement was performed in a form in which the air side surface at the time of cast film formation was arranged on the light source side.

（※ＰＣフィルム）

(* PC film)

（※ＰＭＭＡフィルム）

(* PMMA film)

As described above, in any of the examples, it can be seen that the value of the arithmetic average surface roughness Ra is as low as 15 nm or less, and the surface smoothness is good. In any of the examples, the value of image clarity (total) is as high as 400% or more, and is comparable to Comparative Examples 1 and 5 to which SrCO ₃ is not added. It can be seen that the transmitted image is excellent in clarity of the transmitted image. In particular, in any of the examples, the image clarity value at a narrow comb width of 0.125 mm is as high as 80% or more, so that it is understood that the sharpness of a fine image is particularly excellent.

<Triacetylcellulose (TAC) film>
(17) Example 9
(SrCO ₃ addition dope preparation method)
To 25 g of methylene chloride, 6 g of triacetylcellulose (hereinafter “TAC”) was added and stirred for 3 hours to prepare a TAC-methylene chloride solution. Next, 0.6 g of the surface-treated powder 1 was added to 10 g of methylene chloride, placed in an ultrasonic bath for 30 seconds, and filtered as it was without applying pressure with a membrane filter having a pore diameter of 1 μm to prepare a dispersion 1. TAC- mixed dispersion 1 methylene chloride dispersion was dispersed in an ultrasonic homogenizer to obtain a SrCO ₃ added dope solution I-1.

(TAC film formation method)
The SrCO ₃ -added dope liquid I-1 was applied on a PET film with a wet film thickness of 200 μm using a Baker type applicator. This was dried at 40 ° C. for 2 minutes, 80 ° C. for 15 minutes, and 85 ° C. for 30 minutes. The TAC film was peeled from the PET film to obtain TAC film O-1. The characteristics of the film obtained in the same manner as in Example 8 were evaluated. The results are shown in Table 7.

(18) Example 10
The same method as in Example 9 was used except that the polycarboxylic acid anionic surfactant (B) was used as the surface treating agent. This obtained TAC film P-1. The characteristics of the film obtained in the same manner as in Example 8 were evaluated. The results are shown in Table 7.

(19) Comparative Example 9
The same method as in Example 9 was used, except that SrCO ₃ not subjected to surface treatment was used. This obtained TAC film Q-1. The characteristics of the film obtained in the same manner as in Example 8 were evaluated. The results are shown in Table 7.

  When Examples 9 and 10 were compared with Comparative Example 9, the values of ΔP were negative in Examples 9 and 10 to which strontium carbonate was added, indicating that a negative phase difference was developed. That is, from the above results, it can be seen that by applying an optimal surface treatment to the fine needle-like particles of strontium carbonate, it has high transparency and can reduce the out-of-plane retardation of the film.

<Polyethylene terephthalate (PET) film>
(20) Example 11
The surface-treated powder 1 used in Example 1 was kneaded into a PET resin by a melt kneading method. For the kneading, a lab plast mill 4C150 (manufactured by Toyo Seiki) was used, and kneading was performed at 275 ° C. and a kneading speed of 60 rpm for 5 minutes. The kneaded PET was formed into a sheet at 280 ° C. and 40 MPa with a hot press, and the out-of-plane retardation was measured. The results are shown in Table 8.

(21) Comparative Example 11
The same method as in Example 10 was used except that SrCO ₃ was not kneaded. The results are shown in Table 8.

From the above results, it was found that the out-of-plane retardation of the PET film added with SrCO ₃ can be reduced by the melt-kneading method.

<Resin molecule orientation suppression effect>
The in-plane orientation of PC molecules in the PC films used in Examples 2 and 3 and Comparative Example 1 was evaluated by transmission X-ray φ scan and Raman spectroscopy.

<Transmission X-ray φ scan>
Using a Bruker D8 ADVANCE X-ray diffractometer, the angle of the diffraction intensity can be reduced by measuring while rotating the sample 360 ° while fixing 2θ to 16.4 ° using a transmitted X-ray φ scan. It measured and evaluated by the half value width of the periodic pattern obtained. The obtained measurement results were normalized with the result of Comparative Example 1 as 100. The results are shown in Table 9.

<Raman spectroscopy>
The orientation of PC molecules was evaluated using a laser Raman spectrometer NRS-3300 manufactured by JASCO Corporation. The measurement was performed while rotating the sample at an excitation solid laser wavelength of 532 nm, a grating of 600 L / mm, and 225 points per measurement part, and an exposure time of 1 second. The orientation of the PC molecules was evaluated from the obtained periodic pattern. The obtained measurement results were normalized with the result of Comparative Example 1 as 100. The results are shown in Table 9.

From the above results, it can be seen that the addition of fine acicular SrCO ₃ suppresses the orientation of PC molecules. By adding fine SrCO ₃ to a film with large intrinsic birefringence, such as PC and PET, and high orientation of resin molecules, the orientation of resin molecules, which are retardation factors, can be suppressed, and the retardation can be greatly reduced. Become.

Claims (15)

An optical film in which alkaline earth metal carbonate fine powder is dispersed in a resin,
The alkaline earth metal carbonate fine powder has an average major axis in the range of 10 to 100 nm, a content of 0.1 to 50% by mass with respect to the entire optical film, and a surfactant on the surface. An optical film characterized by adhering.   The optical film according to claim 1, wherein the alkali metal carbonate is strontium carbonate.   2. The optical film according to claim 1, wherein the average major axis is in the range of 20 to 50 nm and the haze is 1% or less.   The optical film according to claim 1, wherein the content is in the range of 1 to 35 mass%.   The resin is polycarbonate, polymethyl methacrylate, cellulose ester, polystyrene, styrene acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyether sulfone, polyolefin, maleimide copolymer, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, The optical film according to claim 1, wherein the optical film is at least one selected from the group consisting of polyurethane.   The optical film according to claim 5, wherein the resin is polycarbonate.   The optical film according to claim 6, further comprising a surface modifier.   The optical film according to claim 6, wherein the content is in the range of 8 to 16% by mass, the haze is 1% or less, and has a positive in-plane birefringence.   The optical film according to claim 6, wherein the content is in the range of 8 to 16% by mass, the haze is 1% or less, and the in-plane birefringence is zero.   The optical film according to claim 5, wherein the resin is polymethyl methacrylate.   The optical film according to claim 10, wherein the content is in the range of 8 to 32 mass%, the haze is 1% or less, and has a negative in-plane birefringence.   The optical film according to any one of claims 1 to 11, wherein the film thickness is in the range of 20 to 150 µm.   It is a stretched film, The optical film of any one of Claims 1-12 characterized by the above-mentioned.   The arithmetic average surface roughness (Ra) is 20 nm or less, and the image clarity (based on JIS K 7374) at a comb width of 0.125 mm is 75% or more. 2. An optical film according to item 1. An image display device comprising the optical film according to claim 1.