WO2012091145A1 - Optical film manufacturing method, polarizing plate, and image display device. - Google Patents

Abstract

Provided is an optical film manufacturing method which includes: a coating process wherein a coating layer (12) is formed by coating a coating liquid containing an active energy ray-curable resin on a substrate film (11) which is being continuously conveyed; a first curing process wherein active energy rays are irradiated, from the coating layer (12) side, on a fore-region (A) of the coating layer (12); and a second curing process wherein, with the surface of a mold pushed against the surface of the coating layer (12), active energy rays are irradiated on the coating layer (12), from the substrate film (11) side. In the first curing process, it is preferable to also irradiate active energy rays onto a rear region (B) of the coating layer (12). Thus, the present invention provides a method which enables the continual efficient manufacture of an optical film, whilst being able to prevent the generation of resin remains on the mold, and without generating flaws such as defects.

Description

Optical film manufacturing method, polarizing plate, and image display device

The present invention relates to a method for producing an optical film in which a coating liquid containing an active energy ray-curable resin is applied on a base film and cured. The present invention also relates to a polarizing plate and an image display device using the optical film.

An optical film formed by coating a resin layer having a predetermined optical function on a base film is used in various image display devices such as a liquid crystal display device as an antiglare film, a light diffusion film, a hard coat film, etc. ing.

In general, the resin layer provided in the optical film is formed by applying a coating liquid containing an active energy ray-curable resin onto a substrate film, and irradiating the obtained coating layer with an active energy ray to be cured. It is formed by. Depending on the optical properties required for the optical film, in order to give a desired shape to the resin layer surface, a mold having a predetermined surface shape may be pressed against the coating layer surface and cured in this state.

For example, in JP2007-76089-A, an ultraviolet curable resin is applied to a base film, and an ultraviolet ray is applied in a state where the resin-coated surface is in close contact with an uneven roller (embossing roll) that rotates in synchronization with the base film. Has been disclosed to cure the resin, and then peel the laminate of the cured resin and the base film from the concavo-convex roller.

When an optical film is produced by curing a coating layer while pressing a mold such as an emboss roll on the surface of the coating layer as in the method described in JP2007-76089-A, the obtained optical film is used as a mold. When peeling from the mold, a “resin residue” may occur in which the cured resin remains on the mold surface. Resin residue is a continuous defect in the optical film obtained in the continuous production of an optical film in which a resin layer is continuously formed on a long base film (resin adhesion to the optical film surface or the surface of the optical film). Such as defects in shape or optical properties). Also, removing and cleaning the resin residue every time it occurs will greatly reduce the production efficiency.

On the other hand, as a method for preventing the resin residue, it is conceivable to add a release agent to the coating solution for forming the coating layer or to apply a release agent to the mold surface in advance. Addition may impair the mechanical strength and optical properties of the optical film.

The present invention has been made in view of the above, and provides a method capable of preventing the occurrence of resin residue and continuously and efficiently producing an optical film without causing defects such as defects. is there.

As a result of diligent study, the present inventor has found that the resin layer peeling causing the resin residue when the optical film is peeled from the mold is a region where the coating layer thickness increases rapidly, that is, the film in the coating layer. It has been found that it is concentrated in the leading region (front end region of the coating layer) and the trailing region (rear end region of the coating layer) in the transport direction. Furthermore, as a means for preventing the resin residue, it is extremely effective to harden a region where the resin layer is easily peeled in advance before the step of curing the coating layer while pressing the mold. I found. In particular, precuring the leading region of the coating layer is extremely advantageous in preventing continuous defects when an optical film is produced by continuously forming a resin layer on a long base film. is there. On the other hand, precuring the tail region of the coating layer in advance is extremely advantageous in preventing continuous defects in the production of the optical film of the next lot (using the next base film).

That is, the present invention includes the following.
[1] A coating process for forming a coating layer by coating a coating film containing an active energy ray-curable resin on a substrate film that is continuously conveyed, and a leading region of the coating layer In the first curing step of irradiating active energy rays from the coating layer side and the surface of the mold pressed against the surface of the coating layer, the active energy rays are irradiated from the substrate film side to the coating layer And a second curing step.

[2] In the adjacent region of the head region that is in contact with the head region irradiated with the active energy ray, the active energy line is continuously reduced at the end of the head adjacent region. The method according to [1], wherein irradiation is performed so as to be zero.

[3] is an active energy ray is ultraviolet, the irradiation amount of the active energy ray to the top region in the first curing step, an accumulated amount of light at UVA ultraviolet is 70 mJ / cm ² or more 400 mJ / cm ² or less [ [1] or [2].

[4] The method according to [2] or [3], wherein the active energy ray is ultraviolet light, and the reduction rate of the integrated light amount in UVA of ultraviolet light is 1500 mJ / cm ² · sec or less.

[5] The method according to any one of [1] to [4], wherein, in the tail region, the active energy ray is irradiated from the coating layer side to the tail region prior to the second curing step.

[6] In the tail adjacent region that is in contact with the tail region, the active energy ray is changed to the tail adjacent region prior to the irradiation of the active energy ray to the tail region, and the accumulated light amount gradually increases from 0 at the start point of the tail adjacent region. The method according to [5], wherein the irradiation is performed so that the irradiation dose to the region is obtained.

[7] is an active energy ray is ultraviolet ray irradiation amount of the active energy ray to the tail region, in at 400 mJ / cm ² or less 70 mJ / cm ² or more in accumulated light amount of UVA ultraviolet [5] or [6] The method described.

[8] The method according to [6] or [7], wherein the active energy ray is ultraviolet rays, and the rate of increase of the integrated light amount in UVA of ultraviolet rays is 1500 mJ / cm ² · sec or less.

[9] A polarizing film and an optical film produced by the method according to any one of [1] to [6], which is laminated on the polarizing film so that the base film side faces the polarizing film. A polarizing plate provided.

[10] An image display device comprising the polarizing plate according to [9] and an image display element, wherein the polarizing plate is disposed on the image display element such that the polarizing film is on the image display element side.

According to the method of the present invention, it is possible to effectively prevent the occurrence of resin residue when the optical film is peeled from the mold. This causes continuous defects (resin adhesion to the surface, defects in surface shape or optical characteristics, etc.) in the continuous production of optical films in which a resin layer is continuously formed on a long base film. The optical film can be produced continuously and efficiently without any trouble. Moreover, since it is not necessary to remove and clean the resin residue, the production efficiency can be greatly improved. The optical film obtained by the present invention can be suitably applied to image display devices such as polarizing plates and liquid crystal display devices.

It is a figure which shows typically a preferable example of the manufacturing method of the optical film of this invention, and the manufacturing apparatus used for this. It is sectional drawing which shows a 1st hardening process typically.

<Method for producing optical film>
The method for producing an optical film of the present invention includes the following steps:
[1] A coating process in which a coating liquid containing an active energy ray-curable resin is coated on a continuously transported base film to form a coating layer;
[2] A first curing step of irradiating active energy rays from the coating layer side to the head region of the coating layer,
[3] A second curing step of irradiating the coating layer with active energy rays from the base film side to cure the coating layer in a state where the surface of the mold is pressed against the surface of the coating layer.
including.

Hereinafter, each process will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing a preferred example of the method for producing an optical film of the present invention and a production apparatus used therefor. FIG. 2 is a cross-sectional view schematically showing the first curing step. The arrows in the figure indicate the film transport direction or roll rotation direction.

[1] Coating step In this step, a coating layer containing an active energy ray-curable resin is coated on a continuously transported substrate film to form a coating layer. For example, as shown in FIG. 1, the coating process continuously unwinds the base film 11 from an original fabric (a long base film wound product) attached to the film unwinding device 31, It can be performed by applying a coating solution onto the substrate film 11 using the coating device 32.

Application of the coating liquid onto the base film 11 can be performed, for example, by a gravure coating method, a micro gravure coating method, a rod coating method, a knife coating method, an air knife coating method, a kiss coating method, a die coating method, or the like. .

(Base film)
The base film 11 only needs to be translucent, and for example, glass or plastic film can be used. The plastic film only needs to have appropriate transparency and mechanical strength. Specific examples include cellulose acetate resins such as TAC (triacetylcellulose), acrylic resins, polycarbonate resins, polyester resins such as polyethylene terephthalate, and polyolefin resins such as polyethylene and polypropylene. The thickness of the base film 11 is, for example, 10 to 500 μm, and is preferably 10 to 300 μm, more preferably 20 to 300 μm from the viewpoint of thinning the optical film.

Various surface treatments may be performed on the surface of the base film 11 (surface on the coating layer side) for the purpose of improving the coating property of the coating liquid or improving the adhesion with the coating layer. Examples of the surface treatment include corona discharge treatment, glow discharge treatment, acid surface treatment, alkali surface treatment, and ultraviolet irradiation treatment. Moreover, other layers, such as a primer layer, may be formed on the base film 11, and a coating liquid may be applied on this other layer.

When the optical film is used after being bonded to a polarizing film described later, the surface of the base film (on the side opposite to the coating layer) is used in order to improve the adhesion between the base film and the polarizing film. The surface) is preferably hydrophilized by various surface treatments. You may perform this surface treatment after manufacture of an optical film.

(Coating fluid)
The coating liquid contains an active energy ray-curable resin and usually further contains a photopolymerization initiator (radical polymerization initiator). If necessary, other components such as translucent fine particles, solvents such as organic solvents, leveling agents, dispersants, antistatic agents, antifouling agents, and surfactants may be contained.

(1) Active energy ray-curable resin The active energy ray-curable resin can be an ultraviolet curable resin, an electron beam curable resin, or the like, and for example, one containing a polyfunctional (meth) acrylate compound is preferably used. be able to. The polyfunctional (meth) acrylate compound is a compound having at least two (meth) acryloyloxy groups in the molecule. Specific examples of the polyfunctional (meth) acrylate compound include, for example, ester compounds of polyhydric alcohol and (meth) acrylic acid, urethane (meth) acrylate compounds, polyester (meth) acrylate compounds, epoxy (meth) acrylate compounds, and the like. And a polyfunctional polymerizable compound containing two or more (meth) acryloyl groups.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, propanediol, butanediol, and pentanediol. , Hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, 2,2'-thiodiethanol, divalent alcohols such as 1,4-cyclohexanedimethanol; trimethylolpropane, glycerol, pentaerythritol , Trihydric or higher alcohols such as diglycerol, dipentaerythritol and ditrimethylolpropane.

Specific examples of esterified products of polyhydric alcohol and (meth) acrylic acid include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and neopentyl glycol. Di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, tetramethylolmethanetetra ( (Meth) acrylate, pentaglycerol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerin tri (meth) acrylate, Pentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate.

Examples of the urethane (meth) acrylate compound include urethanization reaction products of an isocyanate having a plurality of isocyanate groups in one molecule and a (meth) acrylic acid derivative having a hydroxyl group. Examples of organic isocyanates having a plurality of isocyanate groups in one molecule include two isocyanates in one molecule such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and dicyclohexylmethane diisocyanate. Organic isocyanate having a group, organic isocyanate having three isocyanate groups in one molecule obtained by subjecting these organic isocyanates to isocyanurate modification, adduct modification, biuret modification, and the like. Examples of the (meth) acrylic acid derivative having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- Examples thereof include hydroxy-3-phenoxypropyl (meth) acrylate and pentaerythritol triacrylate.

Preferred as the polyester (meth) acrylate compound is a polyester (meth) acrylate obtained by reacting a hydroxyl group-containing polyester with (meth) acrylic acid. The hydroxyl group-containing polyester preferably used is a hydroxyl group-containing polyester obtained by an esterification reaction of a polyhydric alcohol, a carboxylic acid, a compound having a plurality of carboxyl groups, and / or an anhydride thereof. Examples of the polyhydric alcohol include the same compounds as those described above. Moreover, bisphenol A etc. are mentioned as phenols other than a polyhydric alcohol. Examples of the carboxylic acid include formic acid, acetic acid, butyl carboxylic acid, benzoic acid and the like. The compounds having a plurality of carboxyl groups and / or their anhydrides include maleic acid, phthalic acid, fumaric acid, itaconic acid, adipic acid, terephthalic acid, maleic anhydride, phthalic anhydride, trimellitic acid, cyclohexanedicarboxylic anhydride Thing etc. are mentioned.

Among the polyfunctional (meth) acrylate compounds as described above, hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, diethylene glycol di (meth) from the viewpoint of improving the strength of the cured product and availability. Ester compounds such as acrylate, tripropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate; hexamethylene diisocyanate and 2-hydroxyethyl ( Addition product of (meth) acrylate; addition product of isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate; attachment of tolylene diisocyanate and 2-hydroxyethyl (meth) acrylate Body; adduct adduct modified isophorone diisocyanate with 2-hydroxyethyl (meth) acrylate; and adducts of biuret of isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate. Furthermore, each of these polyfunctional (meth) acrylate compounds can be used alone or in combination with one or more other compounds.

The active energy ray curable resin may contain a monofunctional (meth) acrylate compound in addition to the polyfunctional (meth) acrylate compound. Examples of the monofunctional (meth) acrylate compound include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, and 2-hydroxyethyl (meth) ) Acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, glycidyl (meth) acrylate, acryloylmorpholine N-vinylpyrrolidone, tetrahydrofurfuryl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, aceto (Meth) acrylate, benzyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, ethyl carbitol (meth) acrylate, phenoxy (meth) acrylate, ethylene oxide modified phenoxy (meta ) Acrylate, propylene oxide (meth) acrylate, nonylphenol (meth) acrylate, ethylene oxide modified (meth) acrylate, propylene oxide modified nonylphenol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, 2- (meth) acryloyloxyethyl-2 -Hydroxypropyl phthalate, dimethylaminoethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, etc. Meth) acrylate can be given. Each of these compounds can be used alone or in combination with one or more other compounds.

Moreover, the active energy ray curable resin may contain a polymerizable oligomer. By including the polymerizable oligomer, the hardness of the cured product can be adjusted. The polymerizable oligomer is, for example, the polyfunctional (meth) acrylate compound, that is, an ester compound of a polyhydric alcohol and (meth) acrylic acid, a urethane (meth) acrylate compound, a polyester (meth) acrylate compound, or an epoxy (meth). It can be an oligomer such as a dimer, trimer or the like such as an acrylate.

Other polymerizable oligomers include urethane (meth) acrylate oligomers obtained by reacting polyisocyanates having at least two isocyanate groups in the molecule with polyhydric alcohols having at least one (meth) acryloyloxy group. Can be mentioned. Examples of the polyisocyanate include hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, a polymer of xylylene diisocyanate, and the like. Hydroxyl group-containing (meth) acrylic acid ester obtained by esterification reaction of alcohol and (meth) acrylic acid, and as polyhydric alcohol, for example, 1,3-butanediol, 1,4-butanediol, 1,6 -Hexanediol, diethylene glycol, triethylene glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, glycerin, pentaerythritol What is dipentaerythritol and the like. In this polyhydric alcohol having at least one (meth) acryloyloxy group, a part of the alcoholic hydroxyl group of the polyhydric alcohol is esterified with (meth) acrylic acid, and the alcoholic hydroxyl group is present in the molecule. It remains.

Furthermore, as another example of the polymerizable oligomer, a polyester (meta) obtained by reacting a compound having a plurality of carboxyl groups and / or an anhydride thereof with a polyhydric alcohol having at least one (meth) acryloyloxy group. ) Acrylate oligomers. Examples of the compound having a plurality of carboxyl groups and / or anhydrides thereof are the same as those described for the polyester (meth) acrylate of the polyfunctional (meth) acrylate compound. Examples of the polyhydric alcohol having at least one (meth) acryloyloxy group include those described for the urethane (meth) acrylate oligomer.

In addition to the polymerizable oligomers as described above, examples of urethane (meth) acrylate oligomers are obtained by reacting isocyanates with hydroxyl groups of a hydroxyl group-containing polyester, a hydroxyl group-containing polyether or a hydroxyl group-containing (meth) acrylic acid ester. Compounds. The hydroxyl group-containing polyester preferably used is a hydroxyl group-containing polyester obtained by an esterification reaction of a polyhydric alcohol, a carboxylic acid, a compound having a plurality of carboxyl groups, and / or an anhydride thereof. Examples of the polyhydric alcohol, the compound having a plurality of carboxyl groups, and / or the anhydride thereof are the same as those described for the polyester (meth) acrylate compound of the polyfunctional (meth) acrylate compound. The hydroxyl group-containing polyether preferably used is a hydroxyl group-containing polyether obtained by adding one or more alkylene oxides and / or ε-caprolactone to a polyhydric alcohol. The polyhydric alcohol may be the same as that which can be used for the hydroxyl group-containing polyester. Examples of the hydroxyl group-containing (meth) acrylic acid ester preferably used include the same as those described for the polymerizable oligomeric urethane (meth) acrylate oligomer. As the isocyanates, compounds having one or more isocyanate groups in the molecule are preferable, and divalent isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate are particularly preferable.

Each of these polymerizable oligomer compounds can be used alone or in combination with one or more other compounds.

(2) Photopolymerization initiator Examples of the photopolymerization initiator include acetophenone photopolymerization initiators, benzoin photopolymerization initiators, benzophenone photopolymerization initiators, thioxanthone photopolymerization initiators, and triazine photopolymerization initiators. An oxadiazole-based photopolymerization initiator is used. Examples of the photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,2′-bis (o-chlorophenyl) -4,4 ′, 5,5′-tetraphenyl-1,2 '-Biimidazole, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, benzyl, 9,10-phenanthrenequinone, camphorquinone, methyl phenylglyoxylate, titanocene compound and the like can also be used. The amount of the photopolymerization initiator used is usually 0.5 to 20 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the active energy ray-curable resin.

(3) Translucent fine particles The translucent fine particles are not particularly limited. For example, organic fine particles made of acrylic resin, melamine resin, polyethylene, polystyrene, organic silicone resin, acrylic-styrene copolymer, and the like. Alternatively, inorganic fine particles made of calcium carbonate, silica, aluminum oxide, barium carbonate, barium sulfate, titanium oxide, glass, or the like can be used. An organic polymer balloon or hollow beads can also be used. These translucent fine particles may be used individually by 1 type, and 2 or more types may be mixed and used for them. The shape of the translucent fine particles may be any of a spherical shape, a flat shape, a plate shape, a needle shape, an indefinite shape, and the like.

The particle diameter and refractive index of the light-transmitting fine particles are not particularly limited, but when the optical film is a light diffusion film or an antiglare film, the particle diameter is 0 from the viewpoint of effectively developing internal haze. It is preferably in the range of 5 μm to 20 μm. For the same reason, the difference between the refractive index of the cured active energy ray-curable resin and the refractive index of the translucent fine particles is preferably in the range of 0.04 to 0.15. The content of the light-transmitting fine particles is usually 3 to 60 parts by weight, preferably 5 to 50 parts by weight with respect to 100 parts by weight of the active energy ray-curable resin. When the content of the translucent fine particles is less than 3 parts by weight with respect to 100 parts by weight of the active energy ray-curable resin, the light diffusibility or the antiglare property may not be sufficiently provided. On the other hand, if it exceeds 60 parts by weight, the transparency of the optical film may be impaired, and the antiglare property and the light diffusibility become too high and the contrast tends to be lowered.

In addition, when using translucent fine particles, in order to make the optical characteristic and surface shape of an optical film uniform, it is preferable that dispersion | distribution of the translucent fine particles in a coating liquid is isotropic dispersion | distribution.

The coating liquid can contain a solvent such as an organic solvent. Examples of organic solvents include aliphatic hydrocarbons such as hexane, cyclohexane, and octane; aromatic hydrocarbons such as toluene and xylene; alcohols such as ethanol, 1-propanol, isopropanol, 1-butanol, and cyclohexanol; methyl ethyl ketone and methyl isobutyl. Ketones such as ketone and cyclohexanone; esters such as ethyl acetate, butyl acetate and isobutyl acetate; glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether Ethers; ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, etc. Stealted glycol ethers; Cellsolves such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol; 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, 2- (2- It can be selected from carbitols such as butoxyethoxy) ethanol in consideration of viscosity and the like. These solvents may be used alone or as a mixture of several kinds as required. After coating, it is necessary to evaporate the organic solvent. Therefore, the boiling point is desirably in the range of 60 ° C to 160 ° C. The saturated vapor pressure at 20 ° C. is preferably in the range of 0.1 kPa to 20 kPa.

When the coating liquid contains a solvent, it is preferable to provide a drying step of evaporating the solvent and drying after the coating step and before the first curing step. Drying can be performed by allowing the substrate film 11 provided with a coating layer to pass through the drying furnace 33, for example, as in the example shown in FIG. The drying temperature is appropriately selected depending on the solvent used and the type of substrate film. Generally, it is in the range of 20 ° C. to 120 ° C., but is not limited thereto. When there are a plurality of drying furnaces, the temperature may be changed for each drying furnace.

[2] First curing step In this step, the head region (front end region) of the coating layer is irradiated with active energy rays from the coating layer side, and this head region is pressed against the mold surface. This is a step of curing in advance prior to the second curing step of curing the coating layer. The leading region of the coating layer is a portion where the thickness of the coating layer is remarkably increased, and is a portion where the resin peeling is concentrated. By pre-curing this part before pressing against the mold, the resin residue on the mold can be effectively prevented. In particular, preventing the resin residue due to the coating layer head region is extremely advantageous in preventing the occurrence of continuous defects in the obtained optical film. That is, when an optical film is produced by continuously forming a resin layer on a long base film, if a resin residue occurs from the production start stage, the resin residue The entire optical film produced using the film is adversely affected.
The head region and the tail region described later can be identified by continuously measuring the film thickness. In the case of a coating layer obtained by a general coating method, unless the film thickness is intentionally changed, almost all of the region where the film thickness rapidly increases is from a part considerably smaller than 1 cm from the tip part, or from the rear end part. Since it is formed only in a portion considerably smaller than 1 cm, in practice, the above-described film thickness measurement or the like is not performed, and for example, 1 cm from the front end can be regarded as the head region and 1 cm from the rear end as the rear region.

With reference to FIG. 1 and FIG. 2, the irradiation of the active energy ray to the coating layer head region is performed, for example, on the coating layer 12 that has passed through the coating device 32 (drying furnace 33 when drying). It can carry out by irradiating an active energy ray with respect to the base film 11 which has it using active energy ray irradiation apparatuses 10, such as an ultraviolet irradiation device installed in the coating layer 12 side.
Specifically, the active energy ray irradiation device 10 is turned on (a state where the active energy rays are irradiated) before the head region A of the coating layer 12 passes immediately below the active energy ray irradiation device 10. After passing through the head region A, the active energy ray irradiating apparatus 10 is turned off (the active energy ray irradiation is stopped).

The active energy ray can be appropriately selected from ultraviolet rays, electron rays, near ultraviolet rays, visible light, near infrared rays, infrared rays, X-rays and the like according to the type of the active energy ray curable resin contained in the coating liquid. Of these, ultraviolet rays and electron beams are preferred, and ultraviolet rays are particularly preferred because they are easy to handle and provide high energy.

As the ultraviolet light source, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, or the like can be used. An ArF excimer laser, a KrF excimer laser, an excimer lamp, synchrotron radiation, or the like can also be used. Among these, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a xenon arc, and a metal halide lamp are preferably used.

As the electron beam, 50 to 1000 keV emitted from various electron beam accelerators such as Cockloft Walton type, Bande graph type, resonance transformation type, insulation core transformation type, linear type, dynamitron type, and high frequency type, preferably 100 An electron beam having an energy of ~ 300 keV can be mentioned.

Irradiation amount to the head area in the first curing step, when the active energy ray is ultraviolet, an accumulated amount of light at UVA ultraviolet, is preferably 70 mJ / cm ² or more 400 mJ / cm ² or less, more preferably 100mJ / Cm ² or more and 250 mJ / cm ² or less. If the integrated light quantity is less than 70 mJ / cm ² , the degree of cure of the leading region A is too low, and there is a possibility that resin peeling (and hence resin residue) may occur. Further, if it exceeds 400 mJ / cm ² , the curing reaction proceeds excessively, and as a result, the resin peels off at the boundary between the cured portion (leading region A) and the uncured portion due to a difference in film thickness or distortion of internal stress. May occur.

After the irradiation of the active energy ray to the head region A in the first curing step, in the head adjacent region in contact with the head region, the active energy ray continues to the head adjacent region, and the integrated light amount is determined from the irradiation amount to the head region. It is preferable to irradiate so that it may decrease gradually along the conveyance direction of a film to 0 at the end point. Thereby, since the degree of curing in the leading region A gradually decreases to an uncured state along the film conveyance direction, the film at the boundary between the cured portion (leading region A) and the uncured portion of the coating layer Resin peeling that may occur due to thickness difference or distortion of internal stress can be prevented. Here, the head adjacent region refers to a region adjacent to the head region and until the irradiation dose becomes zero by irradiating the active energy ray while gradually decreasing the irradiation amount to the head region. The irradiation amount may start to decrease immediately from the start point of the head adjacent region that is in contact with the head region, and the irradiation amount to the head region may continue from the start point to the head region, and then start to decrease. As described above, when the exact range of the head region is not specified and specified by looking, the start point of the head adjacent region is also specified by looking.

When the integrated light amount is gradually decreased from the irradiation amount to the head region to 0, the reduction rate of the integrated light amount per second in UVA of ultraviolet rays is preferably 1500 mJ / cm ² · sec or less, and 1000 mJ / cm ^2. -More preferably, it is less than a second. If the reduction rate of the integrated light amount is too high, even if the integrated light amount is gradually decreased, the effect cannot be sufficiently obtained, and at the boundary between the cured portion (leading region A) and the uncured portion, Resin peeling may occur due to a difference in film thickness or distortion of internal stress. The width of the head adjacent area can be appropriately determined by adjusting the irradiation amount to the head area and the decreasing rate of the integrated light amount, but is usually about 0.3 to 500 cm.

In the first curing step, it is preferable to irradiate an active energy ray to the tail region in addition to the leading region A of the coating layer to cure it. This is because the film thickness of the coating layer is also remarkably thick in the tail region, and the resin peeling is concentrated. By curing the tail region in advance, the resin residue on the mold can be effectively prevented. In particular, preventing the resin residue caused by the tail region of the coating layer is extremely advantageous in preventing continuous defects in manufacturing the optical film of the next lot (using the next base film). is there.

Specifically, the irradiation of the active energy ray to the tail region of the coating layer is specifically performed with reference to FIG. 2 when the tail region B of the coating layer 12 approaches or directly below the active energy ray irradiation device 10. The active energy beam irradiation device 10 is turned on (a state where the active energy beam has been irradiated) immediately before passing through, and this state is maintained until the tail region B has passed.

For the same reason as in the case of the first region A, the irradiation amount to the tail region, when the active energy ray is ultraviolet, an accumulated amount of light at UVA ultraviolet, preferably be 70 mJ / cm ² or more 400 mJ / cm ² or less , more preferably 100 mJ / cm ² or more 250 mJ / cm ² or less.
Prior to irradiation of the active energy ray to the coating layer tail region B, for the same reason as in the case of the head region A, the active energy ray is placed in the tail adjacent region, and the integrated light quantity is from 0 at the start point of the tail adjacent region. It is preferable to irradiate so that it may increase gradually along the conveyance direction of a film until it becomes the irradiation amount in a tail area | region. Here, the tail adjacent region refers to a region that is adjacent to the tail region and is irradiated with the active energy ray so as to gradually increase from the above-described irradiation amount of 0 to reach the irradiation amount in the trailing region. The irradiation dose may be increased so as to reach the irradiation dose to the tail region at the end point of the tail adjacent region in contact with the tail region, and the irradiation amount to the tail region is reached at an appropriate point before the end point. The irradiation amount to the tail area may be continued until the end point. As described above, when the tail area is not specified accurately and specified by looking, the end point of the tail adjacent area is also specified by looking.
When the integrated light amount is gradually increased from 0 to the irradiation amount in the tail region, the increase rate of the integrated light amount per second in UVA of ultraviolet rays is 1500 mJ / cm ^{2 for} the same reason as in the head region A. -It is preferable that it is ² seconds or less, and it is more preferable that it is 1000 mJ / cm ² · second or less. The rear adjacent region width can be appropriately determined by adjusting the irradiation amount in the rear region and the increasing rate of the integrated light quantity, but is usually about 0.3 to 500 cm.

The method of gradually changing (decreasing or increasing) the integrated light quantity is not particularly limited, and for example, a method of gradually changing the voltage applied to the active energy ray irradiation device 10; A method of using a comb filter having a plurality of tapered comb teeth whose width gradually decreases in the shutter opening / closing direction as the shutter. (As a result, when the shutter is closed / opened, the integrated light amount gradually decreases / increases depending on the opening area between the comb teeth.) As the shutter, a neutral density filter having a different attenuation rate is gradually reduced. A method using an arrangement in which the rate changes (for example, an arrangement in which the light attenuation rate gradually increases from the end of the shutter) If the shutter is used, when the shutter is closed / opened, the integrated light quantity gradually decreases / increases depending on the light attenuation rate of the filter.); Or a combination of any two or more of the above Can do.

[3] Second curing step This step irradiates the coating layer with active energy rays from the substrate film side in a state where the surface of the mold having a predetermined surface shape is pressed against the surface of the coating layer. It is a step of forming a cured resin layer on the base film by curing the coating layer. Thereby, the coating layer is cured, and the surface shape of the mold is transferred to the coating layer surface.

For example, as shown in FIG. 1, this step uses a pressure bonding device such as a nip roll 13 on the surface of the coating layer 12 of the laminate of the base film 11 and the coating layer 12 that has undergone the first curing step. The roll-shaped mold 14 is pressed, and in this state, the active energy ray irradiation device 15 is used to irradiate the coating layer 12 with the active energy ray from the base film 11 side to cure the coating layer 12. . The use of a nip roll is effective in preventing air bubbles from being mixed between the coating layer and the mold. One or a plurality of active energy ray irradiation apparatuses can be used.

After irradiation with active energy rays, the laminate is peeled from the mold 14 with the nip roll 16 on the exit side as a fulcrum. The obtained optical film consisting of the base film and the cured resin layer is usually wound up by a film winding device 34. At this time, for the purpose of protecting the resin layer, it may be wound up while a protective film made of polyethylene terephthalate, polyethylene or the like is attached to the surface of the resin layer through a pressure-sensitive adhesive layer having removability. The shape of the mold used is not limited to a roll shape.

After the mold has been peeled off, additional active energy ray irradiation may be performed. Moreover, instead of performing active energy ray irradiation in a state of being pressed against the mold, the substrate film on which the uncured coating layer is formed may be peeled from the mold and then cured by irradiation with active energy rays.

About the kind and light source of the active energy ray used at this process, it is the same as that of a 1st hardening process. When the active energy ray is ultraviolet, the integrated amount of light at UVA ultraviolet is preferably at 40 mJ / cm ² or more 2000 mJ / cm ² or less, more preferably at 70 mJ / cm ² or more 1800 mJ / cm ² or less. When the integrated light quantity is less than 40 mJ / cm ² , the coating layer is insufficiently cured, the resulting resin layer has low hardness, or uncured resin adheres to the guide roll, etc. There is a tendency to become. Moreover, when the integrated light quantity exceeds 2000 mJ / cm ² , the base film may shrink due to heat radiated from the ultraviolet irradiation device, which may cause wrinkles.

The mold used in this step is for imparting a desired shape to the surface of the resin layer formed on the base film, and has a surface shape composed of a transfer structure of the desired shape. The surface shape of the mold can be transferred onto the surface of the resin layer by curing the coating layer while pressing the surface shape against the surface of the coating layer. Examples of the mold include a mold having a mirror surface (for example, a mirror roll) and a mold having an uneven surface (for example, an emboss roll).

In the case where the mold has an uneven surface, the uneven pattern may be a regular pattern, a random pattern, or a pseudo random pattern in which one or more random patterns of a specific size are spread. Although it is good, it is preferably a random pattern or a pseudo-random pattern from the viewpoint of preventing the reflected image from becoming iridescent due to interference of reflected light caused by the surface shape.

The outer shape of the mold is not particularly limited, and may be a flat plate shape or a cylindrical or cylindrical roll. From the viewpoint of continuous productivity, a mirror surface roll, an emboss roll, etc. A columnar or cylindrical mold is preferred. In this case, a predetermined surface shape is formed on the side surface of the columnar or cylindrical mold.

The material of the base material of the mold is not particularly limited, and can be appropriately selected from metal, glass, carbon, resin, or a composite thereof, but metal is preferable from the viewpoint of workability. Suitable metal materials include aluminum, iron, or an alloy mainly composed of aluminum or iron from the viewpoint of cost.

As a method for obtaining a mold, for example, a method of polishing a substrate, sandblasting, and then applying electroless nickel plating (JP2006-53371-A); after applying copper plating or nickel plating to the substrate, Polishing, sand blasting, and chromium plating (JP2007-188952-A); copper plating or nickel plating, polishing, sand blasting, etching process or copper plating process And then applying chromium plating (JP 2007-237541-A); applying copper plating or nickel plating to the surface of the substrate, polishing, applying a photosensitive resin film on the polished surface, The pattern is exposed on the photosensitive resin film, then developed, and etched using the developed photosensitive resin film as a mask. A method of performing treatment, peeling the photosensitive resin film, further etching, dulling the uneven surface, and then plating the formed uneven surface with chrome; and a cutting tool using a machine tool such as a lathe And a method of cutting a base material to be a mold (WO2007 / 077892-A) and the like.

The surface irregularity shape of the template comprising a random pattern or a pseudo-random pattern is, for example, an FM screen method, a DLDS (Dynamic Low-Discretion Sequence) method, a method using a microphase separation pattern of a block copolymer, or a bandpass filter method. The random pattern generated by the above can be formed by exposing and developing on the photosensitive resin film, and performing an etching process using the developed photosensitive resin film as a mask.

The optical film of the present invention obtained as described above is suitably applied to an image display device such as a liquid crystal display device. For example, the resin layer on the base film is damaged due to various external forces. Hard coat film (which may contain translucent fine particles); a light diffusion layer for improving the viewing angle by diffusing light emitted from the liquid crystal cell ( Viewing-side light diffusing film that contains translucent fine particles as a light diffusing agent; Antiglare layer (containing translucent fine particles) with resin surface unevenness to prevent reflection of external light and glare A light diffusing layer (translucent fine particles as a light diffusing agent) for diffusing light incident on the liquid crystal cell and preventing moire caused by the backlight unit. The Back-side light-diffusing film is a) (can be diffusion plate) is like. The hard coat film, the viewing-side light diffusion film and the antiglare film are usually used by being bonded to a polarizing film as a viewing-side protective film for the viewing-side polarizing plate (that is, disposed on the surface of the image display device). . The back side light diffusion film is usually bonded to the polarizing film as a backlight side protective film of the backlight side polarizing plate.

The optical film of the present invention may further include an antireflection layer laminated on the resin layer (surface opposite to the base film). The antireflection layer is provided to reduce the reflectance as much as possible, and reflection on the display screen can be prevented by forming the antireflection layer. As the antireflection layer, a low refractive index layer composed of a material lower than the refractive index of the resin layer; a high refractive index layer composed of a material higher than the refractive index of the resin layer, and the refractive index of the high refractive index layer A laminated structure with a low refractive index layer composed of a lower material can be exemplified. There is no particular limitation on the method of laminating the antireflection layer, and the antireflection layer may be laminated directly on the resin layer, or separately prepared by previously laminating the antireflection layer on the base film, and using a pressure sensitive adhesive or the like. You may paste on the layer.

<Polarizing plate>
The polarizing plate of this invention is equipped with a polarizing film and the optical film obtained by the above-mentioned manufacturing method laminated | stacked on this polarizing film so that a base film side may oppose this polarizing film. A polarizing film has a function which takes out linearly polarized light from incident light, The kind is not specifically limited. As an example of a suitable polarizing film, there can be mentioned a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin. Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol, which is a saponified product of vinyl acetate, partially formalized polyvinyl alcohol, and a saponified product of an ethylene / vinyl acetate copolymer. As the dichroic dye, iodine or a dichroic organic dye is used. In addition, a polyene-oriented film of a polyvinyl alcohol dehydrated product or a polyvinyl chloride dehydrochlorinated product can also be a polarizing film. The thickness of the polarizing film is usually about 5 to 80 μm.

The polarizing plate of the present invention may be one in which the optical film according to the present invention is laminated on one side or both sides (usually one side) of the polarizing film, and a transparent protective layer is provided on one side of the polarizing film. The optical film according to the present invention may be laminated on the other surface.
At this time, the optical film also has a function as a transparent protective layer (protective film) of the polarizing film. The transparent protective layer can be formed on the polarizing film by a method of laminating a transparent resin film using an adhesive or the like, a method of applying a transparent resin-containing coating solution, or the like. Similarly, the optical film according to the present invention can be bonded to a polarizing film using an adhesive or the like.

The transparent resin film serving as the transparent protective layer is preferably excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, etc., and examples thereof include triacetyl cellulose, diacetyl cellulose, cellulose acetate propio Cellulose resins such as cellulose acetate such as nates; Polycarbonate resins; (Meth) acrylic resins such as polyacrylate and polymethyl methacrylate; Polyester resins such as polyethylene terephthalate and polyethylene naphthalate; Chains such as polyethylene and polypropylene Examples thereof include films made of polyolefin resin; cyclic polyolefin resin; styrene resin; polysulfone; polyether sulfone; polyvinyl chloride resin. These transparent resin films may be optically isotropic, or have optical anisotropy for the purpose of compensating the viewing angle when incorporated in an image display device. Also good.

<Image display device>
The image display device of the present invention is a combination of the polarizing plate of the present invention and an image display element that displays various information on a screen. The type of the image display device of the present invention is not particularly limited. In addition to a liquid crystal display (LCD) using a liquid crystal panel, a cathode ray tube (CRT) display, a plasma display (PDP), a field emission display (FED), a surface Examples thereof include a conduction electron-emitting device display (SED), an organic EL display, a laser display, and a projector television screen.

For example, when a liquid crystal panel is manufactured by arranging the polarizing plate of the present invention on a liquid crystal cell, the polarizing plate is placed on the liquid crystal cell so that the polarizing film is on the liquid crystal cell side (with the resin layer on the outside). Be placed. The same applies to other image display apparatuses. The optical film may be disposed on the viewing side of the image display element, on the backlight side, or on both. When the optical film is arranged on the viewing side, the optical film can function as a hard coat film, a light diffusion film, an antiglare film, an antireflection film, or the like. On the other hand, when the optical film is disposed on the backlight side, the optical film can function as a light diffusion film (diffusion plate) that diffuses light incident on the liquid crystal cell and prevents moiré or the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>
The following components were mixed to prepare an ultraviolet curable coating solution.
UV curable resin: 60 parts by weight of pentaerythritol triacrylate and 40 parts by weight of polyfunctional urethanized acrylate (reaction product of hexamethylene diisocyanate and pentaerythritol triacrylate)
Photopolymerization initiator: “Lucillin TPO” (manufactured by BASF, chemical name: 2,4,6-trimethylbenzoyldiphenylphosphine oxide) 5 parts by weight,
-Diluting solvent: 100 parts by weight of ethyl acetate.

A coating layer is formed by applying the coating liquid on a triacetyl cellulose (TAC) film (base film) having a thickness of 80 μm with a gravure coater, and a laminate of the base film and the coating layer is formed. Obtained [Coating process]. After the obtained laminate is dried in a drying furnace, an accumulated light amount in UVA is a first predetermined amount using an ultraviolet irradiation device provided with a comb filter having a plurality of tapered comb teeth whose width gradually decreases in the opening and closing direction. The ultraviolet ray is irradiated from the coating layer side to the leading region of the coating layer so that the value (irradiation amount to the leading region) gradually decreases to 0, and the accumulated light amount in UVA is changed from 0 to a second predetermined value ( The ultraviolet rays were irradiated from the coating layer side to the rear region of the coating layer so as to gradually increase the irradiation amount to the rear region) [first curing step]. In this embodiment, the first and second predetermined values are set to 100 mJ / cm ^2, and the decrease rate (irradiation to the head region) and increase rate (irradiation to the tail region) per second in UVA of ultraviolet rays. [In the following, the rate of decrease and the rate of increase are collectively referred to as the rate of change] were both 700 mJ / cm ² · sec.

Next, a chromium plating roll that had been polished so that the surface became a mirror surface was pressed and adhered to the coating layer surface of the laminate that had undergone the first curing step using a nip roll. In this state, the coating layer was cured by irradiating with ultraviolet rays so that the maximum illuminance in UVA was 700 mW / cm ² and the integrated light amount in UVA was 300 mJ / cm ² from the substrate film side [second curing step]. . Then, the optical film whose average film thickness of the resin layer which consists of hardened | cured material of an ultraviolet curable resin was 10 micrometers was obtained by peeling a laminated body from a chromium plating roll.

<Examples 2 to 5>
An optical film was produced in the same manner as in Example 1, except that the first and second predetermined values and the rate of change of the integrated light quantity per second in UVA of ultraviolet rays were changed as shown in Table 1. In Example 4, no comb filter was used.

<Comparative Example 1>
An optical film was produced in the same manner as in Example 1 except that the first curing step was not performed.

(Residual resin evaluation)
The surface of the chromium plating roll after producing each example and comparative example was observed, 1) the coating layer end (leading end and tail end), and 2) the cured portion (first) in the first curing step. Area and tail area) and the boundary between the uncured portion and the presence of resin residue at the position corresponding to the boundary, and the degree of resin residue was evaluated according to the following criteria.
○: Resin residue is not observed in the entire width direction at the positions 1) and 2).
Δ: Resin residue is observed at the position 1) or 2), but the range is 1/3 or less of the full width.
X: Resin residue is recognized at the position 1) or 2), and the range exceeds 1/3 of the entire width.

The resin residue slightly generated in Example 3 and the resin residue in Comparative Example 1 were generated at the position 1) above. Further, the resin residue generated in Examples 4 and 5 was generated at the position 2).

As shown in Table 1, it can be seen that the resin residue can be reduced by performing the first curing step in which the end region of the coating layer is cured in advance. Moreover, it turns out that the resin remainder can be prevented effectively by making the integrated light quantity and its change rate of the ultraviolet-ray in a 1st hardening process into the predetermined range.

DESCRIPTION OF SYMBOLS 10,15 Active energy ray irradiation apparatus 11 Base film 12 Coating layer 13, 16 Nip roll 14 Mold 31 Film unwinding apparatus 32 Coating apparatus 33 Drying furnace 34 Film winding apparatus

Claims (10)

1. A coating process that forms a coating layer by coating a coating liquid containing an active energy ray-curable resin on a substrate film that is continuously conveyed;
   A first curing step of irradiating an active energy ray from the coating layer side to the top region of the coating layer;
   A second curing step of irradiating the coating layer with active energy rays from the base film side in a state where the surface of the mold is pressed against the surface of the coating layer;
   The manufacturing method of the optical film containing this.
2. In the head adjacent region that is in contact with the head region that has been irradiated with the active energy ray, the active energy line continues to be reduced to zero at the end point of the head adjacent region. The method according to claim 1, wherein the irradiation is performed as follows.
3. The active energy rays are ultraviolet rays;
   The irradiation amount of the active energy ray to the head area in the first curing step, the method according to the range 1 or 2 according to an accumulated amount of light at UVA of the ultraviolet 70 mJ / cm ² or more 400 mJ / cm ² or less.
4. The active energy rays are ultraviolet rays;
   The method according to claim 2 or 3, wherein a reduction rate of the integrated light quantity in UVA of the ultraviolet ray is 1500 mJ / cm ² · sec or less.
5. The method according to any one of claims 1 to 4, wherein in the tail region, the active energy ray is irradiated from the coating layer side to the tail region prior to the second curing step.
6. In the tail adjacent region that is in contact with the tail region, the active energy ray is increased to the tail adjacent region prior to the irradiation of the active energy ray to the tail region, and the accumulated light amount gradually increases from 0 at the starting point of the tail adjacent region. The method of Claim 5 which irradiates so that it may become the irradiation amount to.
7. The active energy rays are ultraviolet rays;
   The irradiation amount of the active energy ray to the tail region, the method according to 70 mJ / cm ² or more 400 mJ / cm ² range 5 or 6 according to or less is an accumulated amount of light at UVA of the ultraviolet.
8. The active energy rays are ultraviolet rays;
   The method according to claim 6 or 7, wherein an increase rate of the integrated light quantity in UVA of the ultraviolet ray is 1500 mJ / cm ² · sec or less.
9. A polarizing film;
   The optical film produced by the method according to any one of claims 1 to 6, which is laminated on the polarizing film so that the base film side faces the polarizing film;
   A polarizing plate comprising:
10. The polarizing plate according to claim 9 and an image display element,
    The said polarizing plate is an image display apparatus arrange | positioned on the said image display element so that the polarizing film may become the said image display element side.

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