Optical film manufacturing method

Abstract

To provide a method for producing an optical film which coats and dries an easily adhesive composition containing a phenolic compound onto a resin film, and suppresses discoloration of an easily adhesive layer containing the phenolic compound caused by the phenolic compound when the easily adhesive layer is formed.SOLUTION: A method for producing an optical film includes, in this order: a coating step of coating a thermosetting easily adhesive composition containing a binder resin and a phenolic compound onto the surface of a resin film, and forming a coated film on the surface of the resin film; a curing step of heating and drying the coated film, and forming an easily adhesive layer on the surface of the resin film; and an irradiation step of irradiating the easily adhesive layer with active energy rays.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing an optical film in which an easy-adhesion layer is formed on the surface of a resin film. [Background technology]

[0002] In recent years, applications of organic electroluminescence display devices, touch panels, etc. have expanded. In such devices, various resin films are used as optical films such as protective films, retardation films, and front panels. Since optical films are required to have high transparency, polyester-based films, cycloolefin-based films, acrylic-based films, etc. are used as the resin films.

[0003] Optical films are usually used in a laminated state with other functional films, and therefore, good adhesion to the other functional films is required. Therefore, it is known to provide an easy-adhesion layer, the main component of which is an adhesive-promoting resin (binder resin) such as a polyester resin, an acrylic resin, a urethane resin, or a siloxane resin, on the surface of the optical film to impart easy adhesion to the optical film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO15 / 098539 [Patent Document 2] WO16 / 088633 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, a phenolic antioxidant may be blended into the adhesive layer for the purpose of improving durability, etc. Such an adhesive layer is formed by applying an adhesive composition containing a phenolic antioxidant to the surface of a resin film to form a coating film, and then drying and curing the coating film to form an adhesive layer on the resin film. However, the adhesive layer of an adhesive composition containing a phenolic antioxidant may discolor and assume a reddish tinge when heated during drying or curing of the coating film. Furthermore, an optical film having an adhesive layer containing a phenolic antioxidant may discolor and assume a reddish tinge when the adhesive layer is heated, for example, during drying when providing another coating layer or during drying after lamination with another functional film. When the adhesive layer assumes a reddish tinge, the transparency of the optical film is impaired, causing various problems, such as making it unusable for devices such as organic electroluminescence displays and touch panels.

[0006] The present invention has been made in consideration of such problems, and aims to provide a method for producing an optical film that suppresses discoloration (redness) of an easy-adhesion layer caused by a phenolic compound when an easy-adhesion composition containing a phenolic compound is applied to a resin film and dried to form an easy-adhesion layer containing a phenolic compound. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into a method for producing an optical film that suppresses discoloration of an easy-adhesion layer caused by a phenolic compound when the easy-adhesion layer is formed on a resin film using an easy-adhesion composition containing a phenolic compound. As a result, they have found that by irradiating the easy-adhesion layer with active energy rays such as ultraviolet rays after the easy-adhesion layer is formed, discoloration of the easy-adhesion layer is suppressed and an optical film with excellent transparency can be obtained, and have completed the present invention.

[0008] According to the present invention, (1) There is provided a method for producing an optical film, which comprises, in this order: a coating step of coating a surface of a resin film with a thermosetting easy-adhesion composition containing a binder resin and a phenolic compound to form a coating film on the surface of the resin film; a curing step of heating and drying the coating film to form an easy-adhesion layer on the surface of the resin film; and an irradiation step of irradiating the easy-adhesion layer with active energy rays, (2) The method for producing an optical film according to (1), wherein the phenolic compound is a phenolic antioxidant, (3) The method for producing an optical film according to (1) or (2) is provided, wherein the active energy rays are ultraviolet rays; (4) The irradiation step is carried out with an integrated light dose of 550 mJ / cm 2 The method for producing an optical film according to any one of (1) to (3) is provided, characterized in that the irradiation is performed so that the above-mentioned (5) The method for producing an optical film according to any one of (1) to (4), wherein the irradiation step is carried out in the presence of oxygen, (6) There is provided the method for producing an optical film according to any one of (1) to (5), characterized in that the curing step involves heating the coating film so that the drying temperature is 90°C or higher; (7) An optical film having an adhesive layer on the surface of a resin film, the adhesive layer being made of a thermosetting adhesive composition containing a binder resin and a phenolic compound, wherein the optical film has a transmittance of a CIE 1976 color space before and after being heated at a temperature of 100°C or higher and 140°C or lower for 5 minutes. * An optical film is provided, characterized in that the change in value satisfies the following formula (I): (a of the optical film after heating) * value)-(a value of the optical film before heating * value)<0.02··Formula (I) (8) The optical film according to (7) is provided, which satisfies the following formula (II): -0.15<(a of optical film after heating * value)-(a value of the optical film before heating *value)<0.02··Formula (II) [Effects of the Invention]

[0009] The optical film obtained by the production method of the present invention has an easy-adhesion layer containing a phenolic compound, but discoloration (redness) of the easy-adhesion layer due to heating during drying or curing of the coating film is suppressed, and the easy-adhesion layer has excellent transparency suitable for use as an optical film. Furthermore, the easy-adhesion layer irradiated with active energy rays such as ultraviolet rays can maintain its transparency without discoloration even when the easy-adhesion layer is heated again, for example, during drying when providing another coating layer or during drying after lamination with another functional film. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an optical film according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a production line for an optical film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An optical film according to one embodiment of the present invention and a method for producing the same will now be described with reference to the drawings. FIG. 1 is a cross-sectional schematic diagram of an optical film. As shown in FIG. 1, an optical film 10 includes a resin film 11 and an easy-adhesion layer 12 located on the resin film 11. The easy-adhesion layer 12 is formed by applying a thermosetting easy-adhesion composition containing a binder resin and a phenolic compound, diluted with a solvent as necessary, onto the resin film, and then drying and curing the composition. Each component will be described in turn.

[0012] [Resin film] The resin film is made of a material that is translucent to visible light, such as a plastic material. The plastic material is not particularly limited, but examples include cellulose-based resins, polyester-based resins, polyimide-based resins, polyamideimide-based resins, polyamide-based resins, polyolefin-based resins such as polyethylene and polypropylene, cycloolefin-based resins such as cycloolefin polymers and cycloolefin copolymers, (meth)acrylic resins, polyvinyl chloride, polycarbonate-based resins, urethane-based resins, polyvinyl alcohol-based resins, and polyarylate-based resins. These can be used alone or in combination of two or more. The term "(meth)acrylic resin" as used herein refers to an acrylic resin or a methacrylic resin.

[0013] From the viewpoint of productivity, the resin film is preferably a long film. The thickness of the resin film is not particularly limited, but in consideration of strength and flexibility, it is preferably 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 10 to 100 μm. If the thickness is less than 5 μm, sufficient strength may not be obtained. If the thickness exceeds 300 μm, flexibility may decrease and the film may not be suitable for use as an optical film.

[0014] The resin film may or may not be stretched. The stretching may be uniaxial or biaxial, and the stretching ratio is preferably 1.5 times or more, more preferably 2.5 times or more, and even more preferably 4.5 times or more, in terms of area ratio.

[0015] The resin film may be a single layer or multiple layers. Furthermore, as long as the effects of the present invention are achieved, various additives may be incorporated into each of these layers as needed. Examples of additives include colorants such as pigments and dyes; plasticizers; fluorescent brighteners; dispersants; heat stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; antioxidants; fine particles; and surfactants. These may be used alone or in combination of two or more.

[0016] The total light transmittance of the resin film, calculated as a thickness of 1 mm, is preferably 85% or more, and more preferably 90% or more. The total light transmittance can be measured in accordance with JIS K0115 using a spectrophotometer (V-570 ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation).

[0017] [Thermosetting easily adhesive composition] The thermosetting adhesive composition forms an adhesive layer on an optical film by thermal curing, and contains a binder resin and a phenol compound. From the viewpoint of forming a coating film in the coating step described below, the thermosetting adhesive composition may be diluted with a solvent as needed. Examples of the solvent include water, alcohol (ethanol, etc.), ketone, ether, hydrocarbon, and aromatic solvent (benzene, toluene, xylene, etc.), which can be used alone or in combination of two or more.

[0018] [Binder resin] The binder resin is an adhesive-promoting resin that imparts easy adhesion to the resin film, and conventionally known resins can be used without any particular limitation. Examples of binder resins include polyester-based resins, polycarbonate-based resins, (meth)acrylic-based resins, urethane-based resins, urethane acrylate-based resins, polyolefin-based resins, and siloxane-based resins. These can be used alone or in combination of two or more. The binder resin may also be a resin containing a thermosetting catalyst or a resin containing a thermosetting crosslinking agent.

[0019] [Phenol compounds] The phenol-based compound imparts durability to the easy-adhesion layer, and examples thereof include resol-type phenolic resins, novolac-type phenolic resins, phenol-based antioxidants, etc. Among these, phenol-based antioxidants are preferred from the viewpoint of durability.

[0020] Examples of phenolic antioxidants include pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]. pionate], 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2,6-diphenyl-4-octadecyloxyphenol, stearyl (3,5-di-t-butyl-4-hydroxyphenyl)propionate, distearyl (3,5-di-t-butyl-4-hydroxybenzyl)phosphonate, thiodiethylene glycol bis[(3,5-di-t-butyl-4-hydroxyphenyl)propionate] nate), 4,4'-thiobis(6-t-butyl-m-cresol), 2-octylthio-4,6-di(3,5-di-t-butyl-4-hydroxyphenoxy)-s-triazine, 2,2'-methylenebis(4-methyl-6-t-butyl-6-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), bis[3,3-bis(4-hydroxy-3-t-butylphenyl)butylic acid]glycol ester, 4,4'-butylidenebis(6-t-butyl-m-cresol), 2,2'-ethylidenebis(4,6-di -t-butylphenol), 2,2'-ethylidenebis(4-s-butyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, bis[2-t-butyl-4-methyl-6-(2-hydroxy-3-t-butyl-5-methylbenzyl)phenyl]terephthalate, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-t-butylbenzyl)isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, 1,3,5-Tris[(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 2-t-butyl-4-methyl-6-(2-acryloyloxy-3-t-butyl-5-methylbenzyl)phenol, 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4-8,10-tetraoxaspiro[5,5]undecane-bis Bis[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], triethylene glycol bis[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 1,1'-bis(4-hydroxyphenyl)cyclohexane, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,2'-methylenebis(6-(1-methylcyclohexyl)-4 -methylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 3,9-bis(2-(3-t-butyl-4-hydroxy-5-methylphenylpropionyloxy)1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro(5,5)undecane, 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-bis(3,5-di-t-butyl-4-hydroxybenzyl)sulfide, 4,4'-thiobis(6-t-butyl) Examples of suitable methyl esters include 2,4-dimethyl-6-(1-methylcyclohexyl)-5-methylphenol, 2,5-di-t-butylhydroquinone, 2,5-di-t-amylhydroquinone, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-dimethyl-6-(1-methylcyclohexyl)styreneated phenol, and 2,4-bis((octylthio)methyl)-5-methylphenol. These may be used alone or in combination of two or more.

[0021] The content of the phenolic compound is preferably 0.01 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and even more preferably 0.05 to 1 part by weight, calculated as solid content, relative to 100 parts by weight of the total binder resin. When resin components other than the binder resin are contained, the phenolic compound may be blended relative to 100 parts by weight of the solid content including the other resin components.

[0022] The thermosetting adhesive composition may contain a crosslinking agent to improve the moist heat resistance under high temperature and high humidity conditions. Any appropriate crosslinking agent can be used, and examples thereof include urea compounds, epoxy compounds, melamine compounds, isocyanate compounds, oxazoline compounds, silanol compounds, and carbodiimide compounds. These can be used alone or in combination of two or more.

[0023] The content of the crosslinking agent is preferably 0.1 to 15 parts by weight, calculated as solid content, per 100 parts by weight of the total binder resin. It is more preferably 0.3 to 5 parts by weight, and even more preferably 0.5 to 3 parts by weight. When resin components other than the binder resin are contained, the crosslinking agent may be blended per 100 parts by weight of the solid content including the other resin components.

[0024] The thermosetting adhesive composition may contain any suitable fine particles depending on the function. Examples of the fine particles include inorganic fine particles such as inorganic oxides such as silica, titania, alumina, and zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate.

[0025] The average particle size of the fine particles is not particularly limited, but from the viewpoint of maintaining the transparency of the adhesion layer, it is preferably 1 to 500 nm, more preferably 50 to 350 nm, and even more preferably 100 to 300 nm. By using fine particles with such a particle size, appropriate irregularities can be formed on the surface of the adhesion layer, which can effectively reduce the frictional force at the contact surface between the resin film and the adhesion layer and / or between the adhesion layers, thereby suppressing blocking.

[0026] The content of the fine particles is preferably 0.1 to 15 parts by weight, calculated as solid content, per 100 parts by weight of the total binder resin. It is more preferably 0.3 to 5 parts by weight, and even more preferably 0.5 to 3 parts by weight. When resin components other than the binder resin are contained, the fine particles may be blended with 100 parts by weight of the solid content including the other resin components.

[0027] The thermosetting adhesive composition may further contain any suitable additives, such as a dispersion stabilizer, a thixotropic agent, an ultraviolet absorber, an antifoaming agent, a thickener, a dispersant, a surfactant, a catalyst, a lubricant, and an antistatic agent.

[0028] Next, a method for producing an optical film according to one embodiment of the present invention will be described. FIG. 2 is a schematic diagram of a roll-to-roll optical film production line 20. As shown in FIG. 2, the method for producing an optical film includes a payout step in which a long resin film 11 is paid out in the longitudinal direction using a payout device 21; a coating step in which a thermosetting adhesive composition is applied to one side of the resin film using an applicator 22 to form a coating film on the resin film 11; a curing step in which the coating film is heated and dried in a drying oven 23 and cured to form an adhesive layer on the resin film 11; an irradiation step in which, while the resin film is supported from the other side by a back roll 25, an active energy ray irradiation device 24 irradiates the adhesive layer with active energy rays, such as ultraviolet rays, from one side of the resin film 11; and a winding step in which the optical film is wound up by a winding device 26. The resin film is guided and transported from the payout step to the winding step by multiple transport rolls 27.

[0029] [Feeding process] The unwinding step is a step in which the rolled long resin film is rotated by a unwinding device to unwind the resin film in the longitudinal direction. Any known unwinding device can be used.

[0030] [Coating process] The coating step is a step of continuously coating one side of a resin film with a thermosetting adhesive composition using a coating device to form a coating film. Examples of coating devices include spin coating, dip coating, bar coating, spray coating, blade coating, gravure coating, reverse coating, slot die coating, screen printing, and inkjet coating. Among these, slot die coating is preferred because it can apply the coating material uniformly.

[0031] The amount of the thermosetting adhesive composition to be applied in the application step may be appropriately determined in consideration of the thickness of the adhesive layer after drying, and is not particularly limited. For example, 2 ~40g / m 2 The thickness of the easy-adhesion layer after drying is, for example, 0.01 μm or more and 5 μm or less, preferably 0.03 μm or more and 3 μm or less, more preferably 0.05 μm or more and 1 μm or less, and particularly preferably 0.05 μm or more and 0.5 μm or less.

[0032] [Curing process] The curing step is a step in which the resin film is transported into a drying oven or the like, the coating film on the resin film is heated and dried, and the coating film is thermally cured to form an easy-adhesion layer on the resin film. Any known drying oven can be used.

[0033] The drying temperature of the coating film in the curing step is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. The upper limit of the drying temperature can be adjusted appropriately depending on the type of resin film and thermosetting adhesive composition, and is not particularly limited. For example, it is preferably 200°C or lower, more preferably 150°C or lower. If the drying temperature is 90°C or higher, the coating film can be dried and the thermosetting adhesive composition can be cured. On the other hand, when a thermosetting adhesive composition containing a phenolic compound is heated to 90°C or higher for thermal curing, the adhesive layer after curing may discolor and take on a reddish tinge. The reason for this is unclear, but it is presumed to be due to the phenolic compound being oxidized to a colored quinone compound.

[0034] [Irradiation process] The irradiation step involves irradiating the surface of the adhesive layer with active energy rays, such as ultraviolet rays, from one side of the resin film while the resin film is supported by a back roll from the other side. In the present invention, this irradiation step can suppress discoloration (redness) of the adhesive layer that occurs during the curing step. Specifically, by irradiating the adhesive layer discolored during the curing step with active energy rays, such as ultraviolet rays, the redness of the adhesive layer disappears and the adhesive layer becomes transparent. While the reason for this is unclear, it is presumed that the carbonyl group of the quinone compound is activated by active energy rays, such as ultraviolet rays, to form a radical, which then undergoes an addition reaction to form a hydroquinone compound, etc. During the irradiation step, the surface of the adhesive layer irradiated with active energy rays, such as ultraviolet rays, may be nitrogen-purged. However, from the viewpoint of suppressing discoloration of the adhesive layer, it is preferable to perform the irradiation step without nitrogen purging (in the atmosphere) or in the presence of oxygen. The oxygen concentration on the surface of the adhesive layer irradiated with active energy rays, such as ultraviolet rays, is preferably 100 ppm or higher, and more preferably 1000 ppm or higher.

[0035] Examples of the active energy ray include ultraviolet rays and electron beams, and known active energy ray irradiators can be used. In the present invention, ultraviolet rays are preferably used as the active energy ray, and examples of the ultraviolet irradiator include ultraviolet LEDs, low-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, and electrodeless ultraviolet lamps.

[0036] The ultraviolet light preferably has a main peak at a wavelength around 365 nm in its emission spectrum (here, the wavelength around 365 nm refers to a wavelength of 360 nm to 370 nm, and the main peak refers to the strongest emission intensity at a wavelength of 100 to 400 nm).

[0037] In the irradiation process, the cumulative amount of ultraviolet light on the surface of the easy-adhesion layer is 300 mJ / cm 2 Preferably, it is 550 mJ / cm or more. 2 More preferably, it is 700 mJ / cm or more. 2 More preferably, it is 900 mJ / cm or more. 2 If the integrated amount of ultraviolet light on the surface of the adhesive layer is within the above range, discoloration (redness) of the adhesive layer can be sufficiently improved.

[0038] A known back roll can be used. The set temperature of the back roll is, for example, preferably 25°C or higher and 75°C or lower, and more preferably 30°C or higher and 60°C or lower. When the set temperature of the back roll is within the above range, it is possible to effectively suppress the temperature rise due to ultraviolet irradiation and also to effectively suppress discoloration of the easy-adhesion layer.

[0039] [Winding process] The winding step is a step of winding the produced optical film into a roll using a winding device. Any known winding device can be used.

[0040] The transport rolls guide and transport the long resin film under a predetermined tension from the unwinding device to the coating device, drying oven, active energy ray irradiation device (back roll), and winding device in that order, and are composed of, for example, a drive roll, a guide roll, a dancer roll, etc. The transport speed of the resin film is not particularly limited, but is, for example, 1 to 50 m / min.

[0041] The optical film obtained by the manufacturing method of the present invention can maintain its transparency without discoloration even when the easy-adhesion layer is heated, for example, during drying when providing another coating layer or during drying after laminating with another functional film. Specifically, the optical film obtained by the manufacturing method of the present invention has a feature that the easy-adhesion layer does not discolor (become reddish) even when heated again after ultraviolet irradiation, and the a color of the CIE1976 color space before and after heating the optical film at any temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes, can be obtained by the following method. * It is preferable that the change in value satisfies the following formula (I) or the following formula (II): * The value is measured using a spectrophotometer (measurement conditions: transmitted light, measurement diameter φ15 mm, observation field 2°, light source C) * a * b * This refers to the average value when measuring a color system at three points. (a of the optical film after heating) * value)-(a value of the optical film before heating * value)<0.02··Formula (I) -0.15<(a of optical film after heating * value)-(a value of the optical film before heating * value)<0.02··Formula (II) The optical film is heated at a temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes, and the a in the CIE1976 color space is measured before and after the heating. * The lower limit of the change in value is preferably greater than -0.10, and more preferably greater than -0.05.

[0042] In addition, since the change in hue of the easy-adhesion layer in the optical film is a thin film, it may be difficult to quantitatively evaluate it with a single optical film, so it may be evaluated by stacking multiple optical films. For example, when five optical films are stacked and the change in hue before and after heating is evaluated, the five optical films stacked and laminated are heated at any temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes, and the a in the CIE1976 color space is measured before and after heating. * It is preferable that the change in value satisfies the following formula (III) or the following formula (IV). (a of the optical film after heating) * value)-(a value of the optical film before heating * value)<0.10··Equation (III) -0.25<(a of optical film after heating * value)-(a value of the optical film before heating * value)<0.10··Equation (IV) The optical film laminated with five sheets is heated at a temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes, and the a of the CIE1976 color space is measured before and after heating. * The upper limit of the change in value is preferably less than 0.07, more preferably less than 0.05, and the lower limit is preferably greater than -0.15, more preferably greater than -0.10.

[0043] In addition, when evaluating the change in hue before and after heating by stacking 10 optical films, the optical films stacked with 10 films are heated at a temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes, and the a * It is preferable that the change in value satisfies the following formula (V) or the following formula (VI). (a of the optical film after heating) * value)-(a value of the optical film before heating * Value)<0.40··Equation (V) -0.35<(a of optical film after heating * value)-(a value of the optical film before heating * value)<0.40··Equation (VI) Ten optical films are stacked and heated at a temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably at 100°C for 5 minutes. The a of CIE1976 color space is measured before and after the heating. * The upper limit of the change in value is preferably less than 0.20, more preferably less than 0.10, and the lower limit is preferably greater than -0.25, more preferably greater than -0.15.

[0044] The optical film obtained by the production method of the present invention preferably has a total light transmittance of 85% or more, more preferably 90% or more, from the viewpoint of stably exhibiting its function as an optical member. The total light transmittance can be measured in accordance with JIS K7361-1 using a haze meter (NDH 7000II manufactured by Nippon Denshoku Industries Co., Ltd.) or the like.

[0045] The haze of the optical film obtained by the manufacturing method of the present invention is not particularly limited, but is preferably 1.0% or less, more preferably 0.8% or less, and even more preferably 0.5% or less. The haze can be measured in accordance with JIS K7361-1997 using a haze meter (NDH 7000II manufactured by Nippon Denshoku Industries Co., Ltd.) or the like.

[0046] The total thickness of the optical film obtained by the production method of the present invention is preferably 5 μm or more, more preferably 7 μm or more, particularly preferably 10 μm or more, and preferably 300 μm or less, more preferably 200 μm or less, particularly preferably 100 μm or less. By making the total thickness of the optical film equal to or greater than the lower limit of the above range, the mechanical strength of the optical film can be increased. On the other hand, by making the total thickness equal to or less than the upper limit, the overall thickness of the optical film can be reduced.

[0047] In the optical film obtained by the production method of the present invention, various functional layers may be formed, if necessary, on the surface opposite to the surface on which the easy-adhesion layer is formed. Examples of the functional layer include an antistatic layer, a pressure-sensitive adhesive layer, an adhesive layer, a pressure-sensitive adhesive layer, an easy-adhesion layer, an antiglare layer, an antifouling layer such as a photocatalyst layer, an antireflection layer, a hard coat layer, an ultraviolet shielding layer, a heat ray shielding layer, an electromagnetic wave shielding layer, and a gas barrier layer.

[0048] Optical films obtained by the production method of the present invention are, for example, polarizer protective films, retardation films, viewing angle compensation films, light diffusion films, reflective films, antireflection films, antiglare films, brightness enhancement films, front panels for touch panels, etc. The optical films obtained by the production method of the present invention may be optically isotropic films or optically anisotropic films (for example, films that exhibit birefringence such as retardation). [Example]

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0050] Example 1 An optical film was produced by the manufacturing method according to the embodiment described above. A 50 μm-thick polyethylene terephthalate film (manufactured by Toray Industries, Inc., product name: U48) was prepared as the resin film. A thermosetting adhesive composition containing 100 parts by weight of an alkoxysilane hydrolysis polycondensate and 1 part by weight of a phenolic antioxidant was prepared, and diluted with a solvent (a mixture of IPA and BtOH = 3:1) to a solids concentration of 1.0%. The conveying speed of the resin film was set to 2.5 m / min, and a slot die coater was used as the coating device, with a coating amount of 9.1 g / m 2The drying temperature in the drying oven was set to 100°C, and the drying time was 2 minutes. An electrodeless ultraviolet lamp (Heraeus, H bulb) was used as the ultraviolet irradiation device, and ultraviolet light having a main peak at a wavelength of 365 nm in the emission spectrum was irradiated at an integrated light intensity of 500 mJ / cm on the surface of the adhesive layer. 2 The cumulative light intensity was estimated using an ultraviolet meter (Microcure, manufactured by Heraeus K.K.).

[0051] Example 2 The cumulative light intensity on the surface of the adhesive layer is 670 mJ / cm 2 An optical film was produced under the same conditions as in Example 1, except that the ultraviolet irradiation conditions were changed so that:

[0052] Example 3 The cumulative light intensity on the surface of the adhesive layer is 1070 mJ / cm 2 An optical film was produced under the same conditions as in Example 1, except that the ultraviolet irradiation conditions were changed so that:

[0053] Example 4 An optical film was produced under the same conditions as in Example 2, except that the drying temperature in the drying oven was changed to 140°C.

[0054] Example 5 An optical film was produced under the same conditions as in Example 3, except that the drying temperature in the drying oven was changed to 140°C.

[0055] Example 6 An optical film was produced under the same conditions as in Example 2, except that the surface of the adhesive layer to be irradiated with ultraviolet light was purged with nitrogen (under a nitrogen atmosphere, oxygen concentration 90 ppm).

[0056] (Comparative Example 1) An optical film was produced under the same conditions as in Example 1, except that the surface of the easy-adhesion layer was not irradiated with ultraviolet light.

[0057] (Comparative Example 2) An optical film was produced under the same conditions as in Comparative Example 1, except that the drying temperature of the drying furnace was changed to 140°C.

[0058] The optical films produced in the Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Table 1.

[0059] <Haze> Referring to JIS K7136, the haze was measured using a haze meter (product name: NDH 7000II, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0060] <Light transmittance> Referring to JIS K7361-1, the light transmittance was measured using a haze meter (product name: NDH 7000II, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0061] <a value in the CIE1976 color space * value> Using a spectrocolorimeter (model number: SE7700, manufactured by Nippon Denshoku Industries Co., Ltd.) with the following measurement conditions: transmitted light, measurement diameter φ15mm, observation field of view 2°, light source C, the L * a * b * The color system was measured at three points, and the average was taken as the a * value.

[0062] <Taste> A sample of the produced optical film (320 mm (TD direction) × 50 mm (MD direction)) was wound in the TD direction to form an optical film roll (diameter 10 mm), and the ends of the optical film were fixed with adhesive tape so that the optical film roll would not unwind. Next, the taste of the optical film roll was visually evaluated. The evaluation criteria are as follows. ○: Colorless △: Slightly reddish ×: Reddish ××: Strongly reddish

[0063]

Table 1

[0064] As shown in Table 1, when forming an easy - adhesion layer on a resin film using a thermosetting easy - adhesion composition containing a phenolic compound, after forming the easy - adhesion layer, the optical films of Examples 1 to 6 irradiated with active energy rays such as ultraviolet rays on the easy - adhesion layer showed that the discoloration of the easy - adhesion layer was suppressed and excellent transparency was achieved. On the other hand, when forming an easy - adhesion layer on a resin film using a thermosetting easy - adhesion composition containing a phenolic compound, after forming the easy - adhesion layer, the optical films of Comparative Examples 1 and 2 that were not irradiated with active energy rays such as ultraviolet rays on the easy - adhesion layer showed that the easy - adhesion layer was discolored and showed a reddish color.

[0065] Next, the following evaluations were performed on the optical films of Example 2 and Comparative Example 1. The evaluation results are shown in Table 2.

[0066] <Change in the a value in the CIE1976 color space (comparison before and after heating)> * The optical films of Example 2 and Comparative Example 1 were cured for 1 month in a constant - temperature and constant - humidity environment (23°C, 50%RH). For the cured optical films, the a value in the CIE1976 color space was measured by the above - mentioned measurement method respectively. Then, the cured optical films were heated at 100°C for 5 minutes in a hot - air dryer, and for the heated optical films, the a value in the CIE1976 color space was measured by the above - mentioned measurement method respectively. And the difference between the a value of the heated optical film and the a value of the cured optical film was calculated. The a values of the optical films of Example 2 and Comparative Example 1 were also measured by the following method for the single - layer optical film, the laminated optical film with 5 layers stacked, and the laminated optical film with 10 layers stacked. * * * * * (Measurement method for laminated optical film) ​​​​​​A sample made by laminating a predetermined number of optical films cut to 50 mm x 50 mm was sandwiched between two fixtures (fixing fixture / laminated film / fixing fixture) with a hole cut out in the center (outer dimensions: 60 mm x 60 mm, hole cutout: 35 mm x 35 mm), and set in the measuring device so that the measurement light of the spectrophotometer hits the hole cutout. * The values were measured.

[0067] [Table 2]

[0068] As shown in Table 2, the optical film of Comparative Example 1 aged for one month in a constant temperature and humidity environment (23°C, 50% RH) showed a decrease in discoloration (redness) of the adhesive layer, while the optical film of Example 2 showed almost no change in discoloration of the adhesive layer. However, when these optical films were heated in a hot air dryer at 100°C for 5 minutes, the adhesive layer of the optical film of Comparative Example 1 discolored and became reddish. As can be seen from these results, the adhesive layer made of a thermosetting adhesive composition containing a phenolic compound reversibly discolors upon heating. However, by irradiating the cured adhesive layer with active energy rays such as ultraviolet light, discoloration of the adhesive layer can be irreversibly suppressed. Therefore, the optical film of the present invention can maintain its transparency without discoloration even when the adhesive layer is heated, such as during drying when providing another coating layer or during drying after lamination with another functional film. [Explanation of symbols]

[0069] 10: Optical film 11: Resin film 12: Easy adhesive layer 20: Production line 21: Feeding device 22: Coating device 23:Drying oven 24: Active energy ray irradiation device 25: Back roll 26: Winding device 27: Transport roll

Claims

1. a coating step of coating a surface of a resin film with a thermosetting adhesive composition containing a binder resin and a phenolic compound (excluding cases where the thermosetting adhesive composition contains a photopolymerization initiator that generates radicals when irradiated with ultraviolet light), to form a coating film on the surface of the resin film; a curing step of heating and drying the coating film to form an easy-adhesion layer on the surface of the resin film; an irradiation step of irradiating the adhesive layer with ultraviolet light; In this order, The method for producing an optical film, wherein the irradiation step comprises irradiating in the presence of oxygen at an oxygen concentration of 100 ppm or more so that the cumulative light amount is 550 mJ / cm 2 or more.

2. The method for producing an optical film according to claim 1 , wherein the phenolic compound is a phenolic antioxidant.

3. 3. The method for producing an optical film according to claim 1, wherein the curing step comprises heating the coating film so that the drying temperature of the coating film reaches 90° C. or higher.

4. A method for manufacturing an optical film described in any one of claims 1 to 3, characterized in that the ultraviolet light has a main peak at 360 to 370 nm in its emission spectrum.

5. A method for manufacturing an optical film described in any one of claims 1 to 4, characterized in that the easy-adhesion layer has a thickness of 0.01 μm or more and 5 μm or less.

6. The optical film is measured using a CIE 1976 color space after being heated at a temperature of 100° C. or higher and 140° C. or lower for 5 minutes. ＊ The method for producing an optical film according to any one of claims 1 to 5, wherein the change in value satisfies the following formula (I): (a of the optical film after heating) ＊ value) - (a value of the optical film before heating ＊ Value) <0.02 Formula (I)

7. The method for producing an optical film according to claim 6, wherein the optical film satisfies the following formula (II): -0.15<(a of optical film after heating ＊ value) - (a value of the optical film before heating ＊ Value) <0.02 Formula (II)

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