JP2023030325A - Method for producing optical film - Google Patents

Abstract

Kind Code: A1 An optical method for suppressing discoloration of an easy-adhesion layer caused by a phenolic compound when forming an easy-adhesion layer containing a phenolic compound by coating and drying an easy-adhesion composition containing a phenolic compound on a resin film. It aims at providing the manufacturing method of a film. A coating step of applying a thermosetting easily adhesive composition containing a binder resin and a phenolic compound to the surface of a resin film to form a coating film on the surface of the resin film, and heating and drying the coating film. A method for producing an optical film, comprising, in this order, a curing step of forming an easy-adhesion layer on a resin film surface, and an irradiation step of irradiating the easy-adhesion layer with an active energy ray. [Selection diagram] Fig. 2

Description

TECHNICAL FIELD 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.

In recent years, applications such as organic electroluminescence display devices and touch panels are expanding. In such devices, various resin films are used for optical films such as protective films, retardation films, and front plates. Since optical films are required to have high transparency, polyester films, cycloolefin films, acrylic films and the like are used as resin films.

Optical films are usually used in a state of being laminated with other functional films, and it is necessary to have good adhesion with other functional films. It is known to provide an easy-adhesion layer mainly composed of a co-adhesive resin (binder resin) such as a base resin, acrylic resin, urethane-based resin, siloxane-based resin, etc., to impart easy-adhesion to an optical film. there is

WO15/098539 WO16/088633

On the other hand, the easy-adhesion layer may contain a phenolic antioxidant for the purpose of improving durability. Such an easy-adhesion layer is formed by applying an easy-adhesion 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 a coating on the resin film. An easy-adhesion layer is formed. However, in the easy-adhesion composition containing a phenol-based antioxidant, the easy-adhesion layer may be discolored and reddish due to heating during drying or curing of the coating film. In addition, an optical film having an easy-adhesion layer containing a phenol-based antioxidant may cause the easy-adhesion layer to become dry during drying when another coating layer is provided, or during drying after lamination with another functional film. When heated, the easy-adhesion layer may change color and become reddish. If the easy-adhesion layer becomes reddish, the transparency of the optical film is impaired, and various problems arise such that the optical film cannot be used in devices such as organic electroluminescence display devices and touch panels.

The present invention has been made in view of such problems, and when applying and drying an easy-adhesion composition containing a phenolic compound on a resin film to form an easy-adhesion layer containing a phenolic compound, the phenolic compound An object of the present invention is to provide a method for producing an optical film that suppresses discoloration (redness) of an easily adhesive layer caused by

The present inventors have investigated a method for producing an optical film that suppresses discoloration of the easy-adhesion layer caused by the phenolic compound when forming the easy-adhesion layer on a resin film using an easy-adhesion composition containing a phenolic compound. As a result of intensive studies, it was found that by irradiating the easy-adhesion layer with active energy rays such as ultraviolet rays after forming the easy-adhesion layer, discoloration of the easy-adhesion layer is suppressed and an optical film with excellent transparency can be obtained. The inventors have found that and completed the present invention.

According to the invention,
(1) A coating step of applying a thermosetting easily adhesive composition containing a binder resin and a phenolic compound to the surface of a resin film to form a coating film on the surface of the resin film, and heating and drying the coating film. a curing step of forming 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 in this order.
(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 ray is an ultraviolet ray,
(4) The method for producing an optical film according to any one of (1) to (3), wherein the irradiation step is performed so that the integrated light quantity is 550 mJ/cm ² or more;
(5) The method for producing an optical film according to any one of (1) to (4), wherein the irradiation step is performed in the presence of oxygen;
(6) The method for producing an optical film according to any one of (1) to (5), characterized in that in the curing step, the coating film is heated to a drying temperature of 90° C. or higher.
(7) An optical film having an easy-adhesion layer made of a thermosetting easy-adhesion composition containing a binder resin and a phenolic compound on the surface of a resin film, wherein the optical film has a temperature of 100°C or higher and 140°C or lower. Provided is an optical film characterized in that the change in a ^* value of transmitted light in the CIE 1976 color space before and after being heated for 5 minutes at a temperature of , satisfies the following formula (I):
(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (I)
(8) The optical film described in (7) is provided, wherein the optical film satisfies the following formula (II).
−0.15<(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (II)

The optical film obtained by the production method of the present invention suppresses discoloration (redness) of the easy-adhesive layer due to heating during drying or curing of the coating film, even if the easy-adhesive layer contains a phenolic compound. It has excellent transparency that can be used as In addition, the easy-adhesion layer that has been irradiated with active energy rays such as ultraviolet rays can be reactivated when drying when another coating layer is provided, or when drying after lamination with another functional film. It becomes possible to maintain transparency without discoloration even when heated.

It is a cross-sectional schematic diagram of the optical film which concerns on one Embodiment of this invention. 1 is a schematic diagram of a production line for an optical film according to one embodiment of the present invention; FIG.

Hereinafter, an optical film and a method for producing the same according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an optical film. As shown in FIG. 1 , the optical film 10 includes a resin film 11 and an easy-adhesion layer 12 positioned on the resin film 11 . The easy-adhesion layer 12 is formed by coating a resin film with a thermosetting easy-adhesion composition containing a binder resin diluted with a solvent and a phenolic compound, and then curing the composition by drying. be. Each component will be described in order.

[Resin film]
The resin film is made of a material that transmits visible light, such as a plastic material. Examples of plastic materials include, but are not limited to, cellulose resins, polyester resins, polyimide resins, polyamideimide resins, polyamide resins, polyolefin resins such as polyethylene and polypropylene, cycloolefin polymers, cyclo Examples include cycloolefin resins such as olefin copolymers, (meth)acrylic resins, polyvinyl chloride, polycarbonate resins, urethane resins, polyvinyl alcohol resins, and polyarylate resins. These can be used singly or in combination of two or more. The (meth)acrylic resin referred to here means an acrylic resin or a methacrylic resin.

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

The resin film may or may not be stretched. The stretching treatment may be either uniaxial stretching or biaxial stretching. For example, the stretching ratio in area ratio is preferably 1.5 times or more, more preferably 2.5 times or more, and still more preferably 4.5 times. That's it.

The resin film may be a single layer or multiple layers. In addition, each of these layers can contain various additives, if necessary, as long as the effect of the present invention is achieved. Examples of additives include coloring agents such as pigments and dyes; plasticizers; fluorescent brighteners; dispersants; heat stabilizers; light stabilizers; agent etc. can be mentioned. These can be used singly or in combination of two or more.

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

[Thermosetting easily adhesive composition]
The thermosetting easy-adhesion composition forms an easy-adhesion layer on the optical film by thermosetting, and contains a binder resin and a phenol compound. The thermosetting easily adhesive composition may be diluted with a solvent as necessary from the viewpoint of forming a coating film in the coating step described later. Ethers, hydrocarbons, aromatic solvents (benzene, toluene, xylene, etc.) can be mentioned, and these can be used alone or in combination of two or more.

[Binder resin]
The binder resin is a co-adhesive resin that imparts easy adhesion to the resin film, and conventionally known resins can be used without particular limitations. 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 singly or in combination of two or more. The binder resin may be a resin containing a thermosetting catalyst or a resin containing a thermosetting cross-linking agent.

[Phenolic compound]
The phenolic compound imparts durability to the easy-adhesion layer, and examples thereof include resol-type phenolic resins, novolac-type phenolic resins, and phenolic antioxidants. Among these, phenolic antioxidants are preferable from the viewpoint of durability.

Phenolic antioxidants include, for example, 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], 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], 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)butyric 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[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-hydroxy benzyl)sulfide, 4,4'-thiobis(6-t-butyl-2-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, 2,4-bis ((Octylthio)methyl)-5-methylphenol and the like. These can be used singly or in combination of two or more.

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 still more preferably 100 parts by weight of the binder resin in terms of solid content. is 0.05 to 1 part by weight. When resin components other than the binder resin are included, a phenolic compound may be blended with respect to 100 parts by weight of the solid content including the other resin components.

The thermosetting easily adhesive composition may contain a cross-linking agent in order to improve resistance to heat and humidity under high temperature and high humidity conditions. Any appropriate cross-linking agent can be employed as the cross-linking agent, and examples thereof include urea compounds, epoxy compounds, melamine compounds, isocyanate compounds, oxazoline compounds, silanol compounds, carbodiimide compounds, and the like. These can be used singly or in combination of two or more.

The content of the cross-linking agent is preferably 0.1 to 15 parts by weight in terms of solid content with respect to the total 100 parts by weight of the binder resin. More preferably 0.3 to 5 parts by weight, still more preferably 0.5 to 3 parts by weight. When resin components other than the binder resin are contained, a cross-linking agent may be blended with respect to 100 parts by weight of the solid content including the other resin components.

The heat-curable, easy-adhesion composition may contain any suitable fine particles to suit its function. Examples of 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, Calcium phosphate etc. are mentioned.

Although the average particle diameter of the fine particles is not particularly limited, it is preferably 1 to 500 nm, more preferably 50 to 350 nm, and still more preferably 100 to 300 nm from the viewpoint of maintaining the transparency of the easy-adhesion layer. By using fine particles having such a particle size, unevenness is appropriately formed on the surface of the easy-adhesion layer, and the frictional force at the contact surface between the resin film and the easy-adhesion layer and/or between the easy-adhesion layers is effectively reduced. blocking can be suppressed.

The content of fine particles is preferably 0.1 to 15 parts by weight in terms of solid content with respect to a total of 100 parts by weight of the binder resin. More preferably 0.3 to 5 parts by weight, still more preferably 0.5 to 3 parts by weight. When resin components other than the binder resin are contained, fine particles may be blended with respect to 100 parts by weight of the solid content including the other resin components.

The thermosetting easy-adhesion composition can further contain any appropriate additive. Additives include, for example, dispersion stabilizers, thixotropic agents, ultraviolet absorbers, antifoaming agents, thickeners, dispersants, surfactants, catalysts, lubricants, antistatic agents, and the like.

Next, a method for manufacturing 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 type optical film production line 20. As shown in FIG. As shown in FIG. 2, the method of manufacturing an optical film comprises a feeding step of feeding a long resin film 11 in the longitudinal direction by a feeding device 21, and a thermosetting easy-adhesive composition applied on one side of the resin film by a coating device 22. A coating step of applying an object to form a coating film on the resin film 11, and a curing step of heating and drying the coating film in a drying oven 23 to cure the coating film and form an easy-adhesion layer on the resin film 11. In a state in which the resin film is supported by the back roll 25 from the other side of the resin film, the easily adhesive layer is irradiated with an active energy ray such as ultraviolet rays from the one side of the resin film 11 by an active energy ray irradiation device 24. and a winding step of winding the optical film by the winding device 26 . The resin film is guided and transported by a plurality of transport rolls 27 from the feeding process to the winding process.

[Feeding process]
The feeding step is a step of rotating the roll-wound long resin film by a feeding device and feeding the resin film in the longitudinal direction. A known device can be used as the feeding device.

[Coating process]
The coating step is a step of continuously coating the thermosetting easily adhesive composition on one surface of the resin film with 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. Among these, slot die coating is preferable because the coating can be applied uniformly.

The amount of the thermosetting easy-adhesive composition to be applied in the coating step may be appropriately designed in consideration of the thickness of the easy-adhesive layer after drying, and is not ^particularly limited. / ^m2 . The thickness of the easily adhesive 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 1 μm or less. It is 05 μm or more and 0.5 μm or less.

[Curing process]
In the curing step, the resin film is transported into the drying furnace by a drying furnace 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. It is a process. A well-known thing can be used as a drying oven.

The drying temperature of the coating film in the curing step is preferably 90° C. or higher, more preferably 100° C. or higher, and still more preferably 120° C. or higher. The upper limit of the drying temperature may be appropriately adjusted according to the type of the resin film or thermosetting easy-adhesive composition, and is not particularly limited. It is more preferable to have If the drying temperature is 90° C. or higher, the coating film can be dried and the thermosetting easily adhesive composition can be cured. On the other hand, with a thermosetting easily adhesive composition containing a phenolic compound, when the coating film is heated to 90° C. or higher for thermal curing, the easily adhesive layer after curing may change color and appear reddish. Although the reason for this is not clear, it is presumed that the phenolic compound is oxidized to become a colored quinone compound.

[Irradiation process]
In the irradiation step, while the resin film is supported by a back roll from the other side of the resin film, the surface of the easily adhesive layer is irradiated with active energy rays such as ultraviolet rays from one side of the resin film using an active energy ray irradiation device. It is a process to do. In the present invention, this irradiation step can suppress discoloration (redness) of the easy-adhesion layer that occurs in the curing step. Specifically, by irradiating the easy-adhesion layer discolored by the curing step with an active energy ray such as ultraviolet rays, the reddishness of the easy-adhesion layer is eliminated and the easy-adhesion layer becomes transparent. Although the reason for this is not clear, it is presumed that the carbonyl group or the like of the quinone compound is activated by an active energy ray such as ultraviolet rays to form a radical, which undergoes an addition reaction to form a hydroquinone compound or the like. In the irradiation step, the active energy ray irradiation surface such as ultraviolet rays of the easy adhesion layer may be in a nitrogen purged state, but from the viewpoint of suppressing discoloration of the easy adhesion layer, a state that is not nitrogen purged (under an atmospheric atmosphere ) or in the presence of oxygen. The oxygen concentration on the surface of the easy-adhesion layer irradiated with active energy rays such as ultraviolet rays is preferably 100 ppm or more, more preferably 1000 ppm or more.

Examples of active energy rays include ultraviolet rays, electron beams, and the like, and known devices for irradiating active energy rays can be used. In the present invention, ultraviolet rays are preferably used as active energy rays, and examples of ultraviolet irradiation devices include ultraviolet LEDs, low-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, and electrodeless ultraviolet lamps.

The ultraviolet rays preferably have a main peak at a wavelength around 365 nm in the emission spectrum (here, the wavelength around 365 nm refers to a wavelength of 360 nm to 370 nm, and the main peak is a wavelength of 100 to 400 nm, which is the most It means strong luminous intensity).

In the irradiation step, the integrated amount of UV light on the surface of the easy-adhesion layer is preferably 300 mJ/cm ² or more, more preferably 550 mJ/cm ² or more, and further preferably 700 mJ/cm ² or more. 900 mJ/cm ² or more is particularly preferable. If the integrated amount of UV light on the surface of the easy-adhesion layer is within the above range, discoloration (redness) of the easy-adhesion layer can be sufficiently reduced.

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. If the set temperature of the back roll is within the above range, it is possible to effectively suppress temperature rise due to ultraviolet irradiation, and to effectively suppress discoloration of the easy-adhesion layer.

[Winding process]
The winding process is a process of winding the optical film produced by the winding device into a roll. A known winding device can be used.

The transport roll guides and transports the long resin film at a predetermined tension from the feeding device to the coating device, the drying furnace, the active energy ray irradiation device, (back roll), and the winding device in order. , a driving roll, a guide roll, a dancer roll, and the like. The conveying speed of the resin film is not particularly limited, but is, for example, 1 to 50 m/min.

The optical film obtained by the production method of the present invention can be used when the easily adhesive layer is heated, such as when drying when providing another coating layer or when drying after bonding with another functional film. It becomes possible to maintain transparency without discoloration. Specifically, the optical film obtained by the production method of the present invention is characterized in that the easily adhesive layer does not discolor (reddish) even if it is heated again after ultraviolet irradiation, and the optical film is heated at 90° C. or higher and 140° C. The change in a ^* value in the CIE 1976 color space before and after heating at any temperature of 100° C. for 5 minutes, preferably at 100° C. for 5 minutes, preferably satisfies the following formula (I) or the following formula (II). The a ^* value in the CIE1976 color space is obtained by measuring three points in the L ^* a ^* b ^* color system using a spectrocolorimeter (measurement conditions: transmitted light, measurement diameter φ15 mm, observation field of view 2°, light source C). means the average value of
(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (I)
−0.15<(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (II)
The lower limit of the change in the a ^* value in the CIE 1976 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 should be greater than −0.10. is preferred, and more preferably greater than -0.05.

Since the easy-adhesion layer is a thin film, the change in hue of the easy-adhesion layer in the optical film may be difficult to quantitatively evaluate with a single optical film. may For example, when 5 optical films are stacked and the change in hue before and after heating is evaluated, the 5 stacked optical films are heated at any temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably 100°C. It is preferable that the change in a ^* value in the CIE1976 color space before and after heating for 5 minutes satisfies the following formula (III) or the following formula (IV).
(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.10 Formula (III)
−0.25<(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.10 Formula (IV)
The upper limit of the change in a ^* value in the CIE 1976 color space before and after heating the optical film laminated by five layers at any temperature of 90° C. or higher and 140° C. or lower for 5 minutes, preferably at 100° C. for 5 minutes is It is preferably less than 0.07, more preferably less than 0.05, and the lower limit is preferably more than -0.15, more preferably more than -0.10.

When 10 optical films are stacked and the change in hue before and after heating is evaluated, the 10 stacked optical films are heated at any temperature of 90°C or higher and 140°C or lower for 5 minutes, preferably 100°C. It is preferable that the change in a ^* value in the CIE1976 color space before and after heating for 5 minutes satisfies the following formula (V) or the following formula (VI).
(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.40 Formula (V)
−0.35<(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.40 Formula (VI)
The upper limit of the change in the a ^* value in the CIE 1976 color space before and after heating the optical film laminated by 10 sheets at any temperature of 90° C. or higher and 140° C. or lower for 5 minutes, preferably at 100° C. for 5 minutes is It is preferably less than 0.20, more preferably less than 0.10, and the lower limit is preferably more than -0.25, more preferably more than -0.15.

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 functions as an optical member. preferable. The total light transmittance can be measured using a haze meter (NDH 7000II manufactured by Nippon Denshoku Industries Co., Ltd.) or the like in accordance with JIS K7361-1.

The haze of the optical film obtained by the production method of the present invention is not particularly limited, but is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.5% or less. . Haze conforms to JIS K7361-1997 and can be measured using a haze meter (NDH 7000II manufactured by Nippon Denshoku Industries Co., Ltd.).

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, preferably 300 µm or less, more preferably 200 µm or less, and particularly preferably 100 µm. It is below. By making the total thickness of the optical film equal to or higher than the lower limit of the above range, the mechanical strength of the optical film can be increased. Moreover, the thickness of the whole optical film can be made thin by making it below an upper limit.

If necessary, various functional layers may be formed on the surface of the optical film obtained by the production method of the present invention opposite to the surface on which the easy-adhesion layer is formed. Functional layers include, for example, an antistatic layer, an adhesive layer, an adhesive layer, an adhesive layer, an easy adhesive layer, an antiglare (non-glare) layer, an antifouling layer such as a photocatalyst layer, an antireflection layer, and a hard coat layer. , an ultraviolet shielding layer, a heat ray shielding layer, an electromagnetic wave shielding layer, a gas barrier layer, and the like.

The optical film obtained by the production method of the present invention includes, for example, a polarizer protective film, a retardation film, a viewing angle compensation film, a light diffusion film, a reflective film, an antireflection film, an antiglare film, a brightness enhancement film, and a touch panel. Front panel and the like. The optical film obtained by the production method of the present invention may be an optically isotropic film, or an optically anisotropic film (for example, exhibiting birefringence such as retardation). It can be.

The present invention will be described in more detail below with reference to examples. In addition, the present invention is not limited to the following examples.

(Example 1)
An optical film was produced by the production method according to the above embodiment. A polyethylene terephthalate film (manufactured by Toray Industries, Inc., product name: U48) having a thickness of 50 μm was prepared as a resin film. Prepare a thermosetting adhesive composition containing 100 parts by weight of an alkoxysilane hydrolyzed polycondensate and 1 part by weight of a phenolic antioxidant, and add a solvent (IPA :BtOH=3:1 mixture). The conveying speed of the resin film was set to 2.5 m/min, a slot die coater was used as the coating device, the coating amount was set to 9.1 g/ ^m2 , and the thickness of the easily adhesive layer after drying was set to 0.08 µm. was made to be In the drying oven, the drying temperature was set at 100° C. and the drying time was 2 minutes. An electrodeless UV lamp (H bulb, manufactured by Heraeus Co., Ltd.) is used as the UV irradiation device, and the integrated amount of UV light having a main peak at a wavelength of 365 nm in the emission spectrum on the surface of the easy-adhesion layer is 500 mJ/cm ² . Irradiated like this. The integrated amount of light was estimated by an ultraviolet measuring device (Microcure manufactured by Heraeus Co., Ltd.).

(Example 2)
An optical film was produced under the same conditions as in Example 1, except that the UV irradiation conditions were changed so that the integrated amount of light on the surface of the easily adhesive layer was 670 mJ/cm ² .

(Example 3)
An optical film was produced under the same conditions as in Example 1, except that the ultraviolet irradiation conditions were changed so that the integrated amount of light on the surface of the easy-adhesion layer was 1070 mJ/cm ² .

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

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

(Example 6)
An optical film was produced under the same conditions as in Example 2, except that the UV irradiation surface of the easy-adhesion layer was purged with nitrogen (under nitrogen atmosphere, oxygen concentration: 90 ppm).

(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 changed so as not to be irradiated with ultraviolet rays.

(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 oven was changed to 140°C.

The optical films prepared in Examples and Comparative Examples were evaluated as follows. Table 1 shows the evaluation results.

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

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

<a ^* value in CIE1976 color space>
Using a spectral color difference meter manufactured by Nippon Denshoku Industries Co., Ltd. (model number: SE7700, measurement conditions: transmitted light, measurement diameter φ 15 mm, observation field of view 2 °, light source C) L ^* a ^* b ^* color system was measured at three points, The average was taken as the a ^* value.

<Color>
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 end of the optical film was wrapped with an adhesive tape to prevent the optical film roll from unraveling. fixed with . Next, the color of the optical film roll was visually evaluated. Evaluation criteria are as follows.
○: colorless △: slightly reddish ×: reddish ××: deep reddish

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 the formation of the easy-adhesion layer, active energy such as ultraviolet light is applied to the easy-adhesion layer. The optical films of Examples 1 to 6, which were irradiated with rays, exhibited excellent results in which discoloration of the easy-adhesion layer was suppressed and transparency was excellent. On the other hand, when forming an easy-adhesion layer on a resin film using a thermosetting easy-adhesion composition containing a phenolic compound, the easy-adhesion layer was not irradiated with active energy rays such as ultraviolet rays after the formation of the easy-adhesion layer. In the optical films of Comparative Examples 1 and 2, the easy-adhesion layer was discolored and reddish.

Next, the optical films of Example 2 and Comparative Example 1 were evaluated as follows. Table 2 shows the evaluation results.

<Change in a ^* value in CIE1976 color space (comparison before and after heating)>
The optical films of Example 2 and Comparative Example 1 were cured in a constant temperature and humidity environment (23° C., 50% RH) for one month, and the optical films after curing were each measured by the above-described measurement method to measure a ^* in the CIE 1976 color space. values were measured. Next, the cured optical film was heated in a hot air dryer at 100° C. for 5 minutes, and the a ^* value of the CIE 1976 color space was measured for each of the optical films after heating by the above measuring method. Then, the difference between the a ^* value of the optical film after heating and the a ^* value of the optical film after curing was calculated. The a ^* values of the optical films of Example 2 and Comparative Example 1 were measured by the following methods for the single layer optical films as well as the 5-ply and 10-ply laminated optical films.
(Method for measuring laminated optical film)
A sample obtained by laminating a predetermined number of optical films cut to 50 mm × 50 mm is sandwiched between two fixing jigs (fixing jig/laminate Film/fixing jig), and the a ^* value was measured by setting it in a measuring instrument so that the measurement light of the spectrocolorimeter was applied to the holed portion.

As shown in Table 2, the optical film of Comparative Example 1 cured for one month in a constant temperature and humidity environment (23° C., 50% RH) showed the result that the discoloration (reddish) of the easy adhesion layer became lighter. The optical film of Example 2 showed almost no change in discoloration of the easily adhesive layer. However, when these optical films were heated at 100° C. for 5 minutes in a hot air dryer, the optical film of Comparative Example 1 exhibited a reddish color due to discoloration of the easily adhesive layer. As can be seen from this result, the easy-adhesion layer made of a thermosetting easy-adhesion composition containing a phenol-based compound reversibly changes color when heated, but the easy-adhesion layer after curing is exposed to active energy such as ultraviolet rays. By irradiating with rays, discoloration of the easy-adhesion layer can be irreversibly suppressed. Therefore, the optical film of the present invention does not discolor even when the easy-adhesion layer is heated, such as when drying when another coating layer is provided or when drying after lamination with another functional film. transparency can be maintained.

10: Optical film 11: Resin film 12: Easy adhesion layer 20: Production line 21: Feeding device 22: Coating device 23: Drying furnace 24: Active energy ray irradiation device 25: Back roll 26: Winding device 27: Conveying roll

Claims (8)

A coating step of applying a thermosetting easily adhesive composition containing a binder resin and a phenolic compound to the surface of a resin film 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 easy-adhesion layer with an active energy ray;
A method for producing an optical film, comprising: 2. The method of manufacturing an optical film according to claim 1, wherein the phenolic compound is a phenolic antioxidant. 3. The method for producing an optical film according to claim 1, wherein the active energy rays are ultraviolet rays. 4. The method for producing an optical film according to any one of claims 1 to 3, wherein in the irradiation step, irradiation is performed so that the integrated light quantity is 550 mJ/ ^cm2 or more. 5. The method for producing an optical film according to claim 1, wherein the irradiation step is performed in the presence of oxygen. 6. The method for producing an optical film according to any one of claims 1 to 5, wherein in the curing step, heating is performed so that the coating film is dried at a temperature of 90[deg.] C. or higher. An optical film having an easy-adhesion layer made of a thermosetting easy-adhesion composition containing a binder resin and a phenolic compound on the surface of a resin film, wherein the optical film is heated to any temperature of 100°C or higher and 140°C or lower. An optical film, wherein a change in a ^* value of transmitted light in CIE1976 color space before and after being heated for 5 minutes satisfies the following formula (I).
(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (I) 8. The optical film according to claim 7, wherein the optical film satisfies the following formula (II).
−0.15<(a ^* value of optical film after heating)−(a ^* value of optical film before heating)<0.02 Formula (II)

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