JP7238326B2 - Depolarizing film and image display device using the same - Google Patents

Description

The present invention relates to a depolarizing film and an image display device using the same.

It has been known that when a birefringent film such as a polyester film is used under the environment of a fluorescent lamp or a cold cathode tube light source, iridescence caused by retardation occurs. Therefore, optically isotropic cellulose-based films have been used as protective films for polarizers used in liquid crystal displays and the like.

Recently, a technique has been proposed to eliminate iridescence by combining a film with high retardation with a white light source with a continuous emission spectrum (for example, Patent Document 1, etc.). It has been put to practical use in liquid crystal displays and the like as a depolarizing film that does not cause blackout or iridescence even in the case of polarizing. However, this technology is improved when using a light source with a sharp emission peak in the red region of the emission spectrum, such as a cold cathode tube light source or a KSF phosphor (a phosphor in which Mn is added to K ₂ SiF ₆ crystal). There was room for In addition, the film needs to be thick in order to ensure a high retardation, and there is a fear that it will not be able to sufficiently cope with the thinning of image display devices in recent years.

As a depolarizing film for a liquid crystal display using a light source with a steep emission peak, by providing unevenness on the surface of the film having birefringence, it is possible to locally reduce the wavelength to λ/4 or more within a region smaller than the level visible to the naked eye. A film in which retardation is generated has been proposed (for example, Patent Document 2). However, such prior art has problems that the contrast of the image is low, and that the screen becomes white and the image is difficult to see in an environment of strong external light.

JP 2011-215646 A JP 2017-161599 A

The present invention has been made against the background of such problems of the prior art. That is, the object of the present invention is to suppress iridescence that occurs when an image is viewed through a polarizing filter such as polarized sunglasses when used in an environment of a light source having a steep emission peak, and to achieve high transparency, Another object of the present invention is to provide a depolarizing film capable of ensuring vivid image display and an image display device using the same.

The present inventor has completed the present invention as a result of intensive studies to achieve this object.
That is, the present invention includes the following aspects.
Section 1.
A depolarizing film comprising a laminated film having a substrate film and an optically isotropic layer, wherein the laminated film has all of the following characteristics.
(a) At least one surface of the substrate film is uneven, and the arithmetic mean roughness (Ra) of the uneven surface is 0.2 to 10 μm.
(b) The refractive index anisotropy (Bfnx-Bfny) of the base film is from 0.04 to 0.2.
(c) An optically isotropic layer is provided on the uneven surface of the base film, and the refractive index of the optically isotropic layer is from Bfny−0.15 to Bfnx+0.15.
(However, the refractive index in the slow axis direction of the base film is Bfnx, and the refractive index in the fast axis direction is Bfny.)
Section 2.
An image display device comprising an image display cell, a polarizer arranged on the viewer side of the image display cell, and the depolarizing film according to item 1 arranged on the viewer side of the polarizer.
Item 3.
Item 3. The image display device according to Item 2, wherein the angle formed by the transmission axis of the polarizer and the slow axis of the base film is 20 to 70 degrees.

The depolarizing film of the present invention suppresses iridescence that occurs when an image is viewed through a polarizing filter such as polarized sunglasses when used in an environment with a light source having a sharp emission peak, and has high transparency and high transparency. And vivid image displayability can be ensured.

The depolarizing film of the present invention preferably has an optically isotropic layer on the uneven surface of the substrate film having the uneven surface (roughened surface). In addition, the term "laminate film" or "depolarizing film" simply means this.
(Base film)
First, the base film will be explained.

At least the base film is not particularly limited as long as it can have refractive index anisotropy, and examples thereof include polyester, polyamide, polystyrene, syndiotactic polystyrene, polyamide, and polycarbonate. Among them, polyester is preferable because a film having high refractive index anisotropy can be easily obtained. Examples of polyester include polyethylene terephthalate, polyethylene naphthalate, polytetramethylene terephthalate, polytrimethylene terephthalate, etc. Among them, polyethylene terephthalate and polyethylene naphthalate are preferred. These polyesters include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, and ethylene glycol, as long as they do not impair the mechanical properties, heat resistance, and dimensional stability of the film (for example, 10 mol % or less). . For example, in the case of a polyethylene terephthalate polymer, 1 to 2 mol of diethylene glycol, which is a by-product, is usually copolymerized during polymerization, and such a by-product may be contained.

The base film has birefringence. The lower limit of the slow axis refractive index (Bfnx) of the base film is preferably 1.65, more preferably 1.66, still more preferably 1.67, and particularly preferably 1.68. The upper limit of the slow axis direction refractive index (Bfnx) of the base film is preferably 1.73, more preferably 1.72, still more preferably 1.71, and particularly preferably 1.7.

The lower limit of the fast axis refractive index (Bfny) of the base film is preferably 1.53, more preferably 1.55, still more preferably 1.56, and particularly preferably 1.57. The upper limit of the fast axis direction refractive index (Bfny) of the base film is preferably 1.62, more preferably 1.61, still more preferably 1.6.

The lower limit of the refractive index anisotropy (ΔBfNxy=Bfnx−Bfny) of the substrate film is preferably 0.04, more preferably 0.05, still more preferably 0.06, and particularly preferably 0.07. When the lower limit is 0.04 or more, iridescence can be eliminated more effectively. The upper limit of the refractive index anisotropy of the substrate film is preferably 0.2, more preferably 0.18, still more preferably 0.17, and particularly preferably 0.16. When the upper limit is 0.2 or less, the mechanical strength in the fast axis direction can be adjusted within a practical range, and production is facilitated. The refractive index of the base film is a value measured under the condition of a wavelength of 589 nm.

The lower limit of the thickness of the base film before providing the uneven surface (before roughening) is preferably 15 μm, more preferably 20 μm, and still more preferably 25 μm. If the lower limit is 15 μm or more, excellent mechanical strength is obtained even if the thickness is reduced when the unevenness is imparted. The upper limit of the thickness of the base film before the uneven surface is provided is preferably 200 μm, more preferably 150 μm, still more preferably 100 μm, particularly preferably 90 μm, and most preferably 80 μm. If the upper limit is 200 μm or less, it is excellent in handleability and suitable for thinning (eg, for use in thin image display devices).

The lower limit of the in-plane retardation (Re) of the substrate film before imparting the uneven surface is preferably 2000 nm, more preferably 2500 nm, even more preferably 3000 nm, particularly preferably 3500 nm, most preferably 4000 nm. is. When the lower limit is 2000 nm or more, iridescence can be eliminated more effectively. The upper limit of the in-plane retardation (Re) of the substrate film before imparting the uneven surface is preferably 30000 nm, more preferably 20000 nm, even more preferably 15000 nm, still more preferably 12000 nm, and particularly preferably 10000 nm, more preferably 9000 nm, most preferably 8000 nm, most preferably 7500 nm. When the upper limit is 30000 nm or less, it is suitable for thinning.

The lower limit of the ratio (Re/Rth) between the in-plane retardation (Re) and the thickness direction retardation (Rth) of the base film before the uneven surface is imparted is preferably 0.2, more preferably 0.5, and even more preferably. is 0.6. When the lower limit is 0.2 or more, iridescence can be eliminated more effectively. The upper limit of Re/Rth of the base film before the rough surface is provided is preferably 2, more preferably 1.5, still more preferably 1.2, and particularly preferably 1 from the viewpoint of mechanical strength.

The lower limit of the Nz coefficient of the base film is preferably 1.3, more preferably 1.4, still more preferably 1.45. When the lower limit is 1.3 or more, the mechanical strength in the fast axis direction is also excellent. The upper limit of the Nz coefficient of the base film is preferably 2.5, more preferably 2.2, even more preferably 2, particularly preferably 1.8, most preferably 1.7. When the upper limit is 2.5 or less, iridescence can be more effectively eliminated.

The lower limit of the plane orientation degree ΔP of the substrate film is preferably 0.08, more preferably 0.09, and still more preferably 0.1. When the lower limit is 0.08 or more, not only can iridescence be effectively eliminated, but also thickness unevenness of the film can be reduced. The upper limit of the plane orientation degree ΔP of the substrate film is preferably 0.15, more preferably 0.14, and still more preferably 0.13. When the upper limit is 0.15 or less, the refractive index anisotropy can be kept higher.

The substrate film is preferably uniaxially oriented in order to have refractive index anisotropy. Orientation can be carried out by a normal method suitable for each resin. For example, if the melted resin is extruded on a cooling roll to form a sheet, the cooling roll is set to a speed higher than the speed of the extruded resin, and the unstretched film that has been melted and extruded is heated. Examples include a method of stretching and orienting the film in the longitudinal direction with a group of rolled rolls, and a method of stretching and orienting the unstretched film melted and extruded in the transverse direction or oblique direction by heating in a tenter.

Among these, the method of orienting the base film includes a method of stretching and orienting a melted and extruded unstretched film in the longitudinal direction with a group of heated rolls, and a method of stretching the melted and extruded unstretched film. A method of orientation by heating in a tenter and stretching in a horizontal direction or an oblique direction is preferred. The draw ratio in the longitudinal direction is preferably 2.5 to 10 times, more preferably 3 to 8 times, and particularly preferably 3.3 to 7 times. The draw ratio in the transverse direction or oblique direction is preferably 2.5 to 10 times, more preferably 3 to 8 times, and particularly preferably 3.3 to 7 times.

In addition, even in the case of orientation in the machine direction, it is weak (about 2.2 times or less) before stretching in the machine direction in order to increase the mechanical strength in the direction perpendicular to the orientation direction and to adjust the shrinkage characteristics. 2) transverse stretching may be added, or weak transverse stretching (about 1.5 times or less) may be added after longitudinal stretching. Similarly, even in the case of orientation in the transverse direction, a weak (about 2.2 times (less than 1.5 times) or weaker (less than about 1.5 times) stretching in the machine direction may be added after the stretching in the transverse direction. Further, in order to further increase the orientation in the orientation direction, the film may be slightly shrunk in the machine direction during or after stretching in the transverse direction. The width after shrinkage is preferably from 0.7 to 0.995 times, more preferably from 0.8 to 0.99 times, particularly preferably from 0.9 to 0.98 times the width during stretching. The stretching in the longitudinal direction and the stretching in the transverse direction may be performed by a tenter-type simultaneous biaxial stretching machine.

The stretching temperature (and preheating temperature) is preferably 80 to 150° C. both in the machine direction and in the transverse direction. Moreover, after stretching, in order to ensure the heat resistance of the base film, it is preferable to heat set at a temperature higher than the heating temperature during stretching. The heat setting temperature is preferably 150 to 250°C, more preferably 170 to 245°C.

The base film preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at a wavelength of 380 nm is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. The light transmittance at a wavelength of 380 nm is measured in the direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500).

In order to keep the light transmittance of the base film at a wavelength of 380 nm to 20% or less, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber to be blended in the base film, and the thickness of the base film. The ultraviolet absorbent used in the present invention includes organic ultraviolet absorbents and inorganic ultraviolet absorbents. From the viewpoint of transparency, organic UV absorbers are preferred. Examples of organic UV absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as the light transmittance is within the range described above. From the viewpoint of durability, benzotriazole-based and cyclic iminoester-based are particularly preferable. When two or more ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be absorbed at the same time, so that the ultraviolet absorption effect can be further improved.

In addition to the ultraviolet absorber, it is also preferable to incorporate various additives into the substrate film within a range that does not impair the effects of the present invention. Examples of additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, and anti-gelling agents. , surfactants, and the like. These additives can be used alone or in combination of two or more.
Moreover, in order to achieve high transparency, it is also preferred that the base film does not substantially contain particles. The term "substantially contains no particles" means, for example, in the case of inorganic particles, when the inorganic elements in the base film are quantified by fluorescent X-ray analysis, 50 ppm or less, preferably 10 ppm or less, particularly preferably less than the detection limit. means a content of

(Improvement of surface unevenness)
In the present invention, at least one surface of the substrate film has an uneven surface. The uneven surface may be provided only on one side of the base film, or may be provided on both sides. A substrate film having an uneven surface may be referred to as a roughened substrate film.

The lower limit of the arithmetic mean roughness (Ra) of the uneven surface of the roughened substrate film is preferably 0.2 μm, more preferably 0.4 μm, even more preferably 0.6 μm, and particularly preferably 0.7 μm. and most preferably 0.8 μm. The upper limit of Ra is preferably 10 μm, more preferably 7 μm, even more preferably 5 μm, particularly preferably 4 μm, most preferably 3 μm.

The lower limit of the root-mean-square roughness (Rq) of the uneven surface of the roughened substrate film is preferably 0.3 μm, more preferably 0.5 μm, still more preferably 0.7 μm, and particularly preferably 0.9. μm, most preferably 1 μm. The upper limit of Rq is preferably 13 μm, more preferably 10 μm, even more preferably 7 μm, particularly preferably 5 μm, most preferably 4 μm.

The lower limit of the ten-point average roughness (Rz) of the uneven surface of the roughened substrate film is preferably 1.0 μm, more preferably 2.0 μm, still more preferably 3.0 μm, and particularly preferably 3.5. μm, most preferably 4.0 μm. The upper limit of Rz is preferably 15 μm, more preferably 12 μm, even more preferably 10 μm, and particularly preferably 8 μm.

The lower limit of the maximum height (Ry) of the uneven surface of the roughened substrate film is preferably 2.0 μm, more preferably 3.0 μm, still more preferably 4.0 μm, and particularly preferably 4.5 μm. Yes, most preferably 5.0 μm. The upper limit of Ry is preferably 20 μm, more preferably 17 μm, even more preferably 15 μm, and particularly preferably 13 μm.

The lower limit of the maximum peak height (Rp) of the uneven surface of the roughened base film is preferably 1.0 μm, more preferably 1.5 μm, still more preferably 2.0 μm, and particularly preferably 2.5 μm. be. The upper limit of Rp is preferably 15 μm, more preferably 12 μm, even more preferably 10 μm, particularly preferably 8 μm.

The lower limit of the maximum valley depth (Rv) of the uneven surface of the roughened substrate film is preferably 1.0 μm, more preferably 1.5 μm, even more preferably 2.0 μm, and particularly preferably 2.5 μm. is. The upper limit of Rv is preferably 15 μm, more preferably 12 μm, even more preferably 10 μm, and particularly preferably 8 μm.

When the values of Ra, Rq, Rz, Ry, Rp, and Rv are at least the lower limits, iris spots can be eliminated more effectively.
Productivity is excellent when the values of Ra, Rq, Rz, Ry, Rp, and Rv are at least the upper limits.
Ra, Rq, Rz, Ry, Rp, and Rv are calculated from roughness curves measured using a contact roughness meter in accordance with JIS B0601-1994 or JIS B0601-2001.

By providing unevenness (roughening) on the surface of the base film, a retardation difference is provided in a minute area, and although there is coloring (rainbow spots) due to retardation in each area, the coloring is visually invisible. be able to. This retardation difference ΔRe can be represented by ΔRe=Ra×ΔBfNxy. The lower limit of ΔRe is preferably 30 nm, more preferably 50 nm, still more preferably 70 nm, particularly preferably 90 nm, most preferably 100 nm. When the lower limit is 30 nm or more, iridescence can be eliminated more effectively. The upper limit of ΔRe is preferably 1500 nm, more preferably 1000 nm, still more preferably 800 nm, particularly preferably 500 nm, most preferably 300 nm. When the upper limit is 1500 nm or less, productivity is also excellent.

The lower limit of the average spacing (Sm) of the unevenness of the roughened substrate film is preferably 5 µm, more preferably 10 µm, still more preferably 15 µm, particularly preferably 20 µm, and most preferably 25 µm. is. When the lower limit is 5 μm or more, the slope of the unevenness becomes gentle, and the image becomes clearer. The upper limit of the average spacing (Sm) of the unevenness of the roughened substrate film is preferably 500 μm, more preferably 450 μm, still more preferably 400 μm, particularly preferably 350 μm, most preferably 300 μm. is. When the upper limit is 500 μm or less, it is possible to prevent a feeling of coloring or a feeling of flickering due to the retardation of each minute region.
Sm is calculated from a roughness curve measured using a contact roughness meter in accordance with JIS B0601-1994.

The base film may become thinner than the original thickness by providing unevenness and roughening the surface. The lower limit of the thickness of the roughened substrate film is preferably 10 μm, more preferably 15 μm, even more preferably 20 μm, particularly preferably 25 μm, and most preferably 30 μm. When the lower limit is 10 μm or more, sufficient strength as a protective film can be ensured. The upper limit of the thickness of the roughened substrate film is preferably 150 μm, more preferably 120 μm, even more preferably 100 μm, particularly preferably 90 μm, and most preferably 80 μm. When the upper limit is 150 μm or less, it is suitable for thinning.
The thickness of the roughened base film is determined by embedding the roughened base film in epoxy resin, cutting out a section of the cross section, and observing it under a microscope. , the thickness is measured at 10 points at equal intervals, and the average value is calculated.

The lower limit of the in-plane retardation (Re) of the roughened substrate film is preferably 2000 nm, more preferably 2500 nm, still more preferably 3000 nm, particularly preferably 3500 nm, most preferably 4000 nm. be. When the lower limit is 2000 nm or more, iridescence can be eliminated more effectively. The upper limit of the in-plane retardation (Re) of the roughened substrate film is preferably 30000 nm, more preferably 20000 nm, still more preferably 15000 nm, even more preferably 12000 nm, and particularly preferably 10000 nm. is more preferably 9000 nm, most preferably 8000 nm, most preferably 7500 nm. When the upper limit is 30000 nm or less, it is suitable for thinning.

The method for providing unevenness is not particularly limited, and conventionally known methods for surface roughening treatment can be used. For example, sandblasting, sandpaper or file, treatment with a whetstone, etc., treatment with a sander (orbital sander, random sander, delta sander, belt sander, disc sander, roll sander, etc.), treatment with a metal brush, etc., chemical etching, mold Examples include shaping by pressing with. Of these, sandblasting, sanding, and chemical etching are preferred.
Sandblasting may be, for example, a method in which a roll-shaped base film is supplied to a centrifugal blast machine and an abrasive is projected onto the base film surface. In this case, the roughness can be adjusted by the type of abrasive, the size of the abrasive, the processing time, the speed of the rotor blades, and the like. Further, the sandblasting treatment may be a method in which a substrate film is attached to a glass plate, set in air blasting, and an abrasive is blown onto the surface of the substrate film. In this case, the roughness can be adjusted by the type of abrasive, the size of the abrasive, the spraying pressure, the treatment time, and the like.
The treatment with a sander is, for example, a method in which a roll-shaped base film is guided to a conveying device having a roll sander attached to a part of the roll surface of the film conveying roll (roll sander). good. In this case, the roughness can be adjusted by the type of sanding paper, the rotation speed of the roll sander, the transport speed of the film, and the like. Also, the processing direction can be adjusted by the angle between the roll sander and the film, the rotation speed of the roll sander, the transport speed of the film, and the like.
In addition, sanding is performed by attaching urethane foam to a glass plate, then attaching a base film on top of it, and sanding the surface of the base film in four directions: vertical, horizontal, and diagonal (45 degrees, 135 degrees). It may be a method of processing from. Roughness can be adjusted by the type of sanding disk of the sander, processing time, and the like.
In addition, after sanding and sandblasting, the treated surface may be further polished with sandpaper or the like in order to remove local projections.
Chemical etching may be a method of immersing in an acid or alkaline solution, washing with water, peeling off the masking film, and drying. Roughness can be adjusted by immersion time or the like. Chemical etching is basically a double-sided treatment, but in the case of single-sided treatment, for example, a masking film is adhered to one side of the substrate film.

(optical isotropic layer)
An optically isotropic layer is preferably provided on the uneven surface of the base film. The optically isotropic layer is preferably provided in contact with the uneven surface. "Provided in contact with" means that it is provided in direct contact with the uneven surface without interposing another layer. However, an easy-adhesion layer may be provided to improve the adhesion between the uneven surface and the optically isotropic layer. The thickness of the easy-adhesion layer is preferably a thickness that is not optically detectable, preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 20 nm or less. If the easy-adhesion layer satisfies the refractive index range of the optical isotropic layer described below, the easy-adhesion layer and the optically isotropic layer provided thereon together are regarded as one optically isotropic layer. be able to. Moreover, if the easy-adhesion layer has a sufficient thickness as an optically isotropic layer, the easy-adhesion layer may be regarded as an optically isotropic layer. By providing the optically isotropic layer, it is possible to reduce diffused reflection due to unevenness on the surface of the base film and ensure transparency. The preferable refractive index of the easy-adhesion layer is the same as the preferable refractive index range of the optically isotropic layer described below, and the method of adjusting the refractive index is also the same.

The lower limit of the refractive index of the optically isotropic layer is preferably Bfny-0.15, more preferably Bfny-0.12, even more preferably Bfny-0.1, even more preferably Bfny-0.08, and particularly preferably Bfny, most preferably Bfny+0.02.
The upper limit of the refractive index of the optically isotropic layer is preferably Bfnx+0.15, more preferably Bfnx+0.12, even more preferably Bfnx+0.1, even more preferably Bfnx+0.08, and particularly preferably Bfnx, most preferably Bfnx-0.02.
Within the above range, the contrast or sharpness of the image can be maintained, and the phenomenon that the screen becomes whitish when exposed to strong external light can be suppressed.

The lower limit of the refractive index of the optically isotropic layer is preferably 1.44, more preferably 1.47, even more preferably 1.49, even more preferably 1.51, and particularly preferably 1.53, more particularly preferably 1.55, most preferably 1.57, most particularly preferably 1.59. The upper limit of the refractive index of the optically isotropic layer is preferably 1.85, more preferably 1.83, even more preferably 1.80, still more preferably 1.78, and particularly preferably 1.76, more particularly preferably 1.74, most preferably 1.72, still most preferably 1.70, most particularly preferably 1.68. By setting the ratio within the above range, the contrast or the sharpness of the image can be maintained, and the phenomenon that the screen becomes whitish when exposed to strong external light can be suppressed. The refractive index of the optically isotropic layer is also a value measured under the condition of a wavelength of 589 nm.

Although the composition of the optically isotropic layer is not particularly limited, acrylic, polystyrene, polyester, polycarbonate, polyurethane, epoxy resin, thioepoxy resin and the like are preferable. By appropriately adjusting the composition, it is possible to set the refractive index within the above range. For example, PMMA (polymethyl methacrylate) generally has a refractive index of about 1.49. In acrylic pressure-sensitive adhesives, a long-chain or branched alkyl group is often introduced, further lowering the refractive index. In order to increase the refractive index, it is effective to copolymerize an acrylic monomer having an aromatic group or copolymerize styrene.
Introducing a sulfur, bromine, fluorene group or the like into a polymer or resin is also a preferred method for increasing the refractive index. A thioepoxy resin or the like is preferable as the high refractive index resin.

Adding highly refractive fine particles to a polymer or resin is also a suitable method for adjusting the refractive index.
The refractive index of the high refractive fine particles is preferably 1.60 to 2.74. Fine particles of TiO ₂ , ZrO ₂ , CeO ₂ , Al ₂ O ₃ , BaTiO ₃ , Nb ₂ O ₅ , SnO ₂ and the like can be used as high refractive particles. The high-refractive fine particles preferably have an average primary particle size of 3 nm to 100 nm as observed by TEM (transmission electron microscope). These high refractive fine particles may be used singly or in combination of two or more.
In the specification, "average primary particle size" or "average particle size of primary particles" refers to a 50% volume cumulative particle size. More specifically, 200 primary particles of the particles are observed under a microscope at an appropriate magnification, the diameter of each is measured, the volume is calculated, and the 50% particle size of the cumulative volume is taken as the average primary particle size. do.

The optically isotropic layer is preferably crosslinked and cured. The curing method is not particularly limited, and radiation curing such as heat curing, ultraviolet rays, and electron beams is preferred. Cross-linking agents for curing include isocyanate compounds, epoxy compounds, carbodiimides, oxazoline compounds, amino resins such as melamine, polyfunctional acrylates, and the like.

The optical isotropic layer is produced by applying a coating agent comprising the above components to the uneven surface of the base film, applying the release film to the uneven surface of the base film, and transferring the optical isotropic layer to the uneven surface of the base film. The optically isotropic layer provided on the film can be laminated by a method such as bonding to the uneven surface of the substrate film. In this case, the coating agent is preferably dissolved or diluted with a solvent so as to have a viscosity that facilitates coating. Moreover, the coating agent may be solventless as long as it is a radiation curing type coating agent such as acrylic.

For example, a radiation-curing type coating agent such as acrylic usually contains a photopolymerizable compound.

Photopolymerizable compounds include photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers, and these can be appropriately adjusted and used. The photopolymerizable compound is preferably a combination of a photopolymerizable monomer and a photopolymerizable oligomer or photopolymerizable polymer.

Photopolymerizable Monomer Photopolymerizable monomers are those having a weight average molecular weight of less than 1000. As the photopolymerizable monomer, a polyfunctional monomer having two (that is, bifunctional) or more photopolymerizable functional groups is preferable. As used herein, "weight average molecular weight" is a value obtained by dissolving in a solvent such as THF and converting to polystyrene by a conventionally known gel permeation chromatography (GPC) method.

Examples of polyfunctional monomers include tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, di Pentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol Penta(meth)acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, isocyanurate tri(meth)acrylate, isocyanurate di(meth)acrylate, polyester tri(meth)acrylate, polyester di( meth)acrylate, bisphenol di(meth)acrylate, diglycerin tetra(meth)acrylate, adamantyl di(meth)acrylate, isobornyl di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, Those modified with PO, EO or the like can be mentioned.

Among these, pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA) and the like are preferable from the viewpoint of obtaining a functional layer with high hardness.

Photopolymerizable Oligomer The photopolymerizable oligomer has a weight average molecular weight of 1,000 or more and less than 10,000. As the photopolymerizable oligomer, a bifunctional or higher polyfunctional oligomer is preferable. Polyfunctional oligomers include polyester (meth)acrylate, urethane (meth)acrylate, polyester-urethane (meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine (meth)acrylate, and isocyanurate (meth)acrylate. Acrylate, epoxy (meth)acrylate, and the like.

Photopolymerizable Polymer The photopolymerizable polymer has a weight average molecular weight of 10,000 or more, preferably 10,000 or more and 80,000 or less, more preferably 10,000 or more and 40,000 or less. If the weight-average molecular weight exceeds 80,000, the resulting laminated film may have poor appearance due to poor coating suitability due to its high viscosity. As the photopolymerizable polymer, a polyfunctional polymer having two or more functionalities is preferable. Polyfunctional polymers include urethane (meth)acrylate, isocyanurate (meth)acrylate, polyester-urethane (meth)acrylate, epoxy (meth)acrylate and the like.

The coating agent may contain a polymerization initiator, a cross-linking agent catalyst, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a leveling agent, a surfactant, and the like, in addition to the above components.

Alternatively, the melted optically isotropic layer composition is extruded and laminated on the uneven surface of the base film, or the melted optically isotropic layer composition is extruded between the uneven surface of the base film and another film. A method such as lamination is also preferred.

The optically isotropic layer has a function of reducing irregular reflection on the uneven surface by being provided on the uneven surface, but may also have other functions. The optically isotropic layer may have functions such as a hard coat layer, an antireflection layer, an antiglare layer, and an antistatic layer. Also, the optically isotropic layer may be another film or sheet, a pressure-sensitive adhesive layer or an adhesive layer for bonding to a constituent member of a device.

The lower limit of the thickness of the optically isotropic layer is preferably 0.5 μm, more preferably 1.0 μm, still more preferably 2 μm, particularly preferably 3 μm, most preferably 4 μm. When the thickness is 0.5 μm or more, the unevenness of the substrate film can be flattened, the haze can be reduced, and the sharpness can be improved.
The upper limit of the thickness of the optically isotropic layer is preferably 30 μm, more preferably 25 μm, still more preferably 20 μm, particularly preferably 15 μm, most preferably 10 μm. When the thickness is 30 μm or less, it is suitable for thinning.
The thickness of the optically isotropic layer is the value obtained by subtracting the thickness of the roughened base film from the thickness of the laminated film described later.

The upper limit of the in-plane retardation of the optically isotropic layer is preferably 50 nm, more preferably 30 nm, even more preferably 10 nm, and particularly preferably 5 nm, from the viewpoint of suppressing the occurrence of iridescence.

The upper limit of the refractive index difference between the refractive index in the direction of the highest refractive index and the refractive index in the direction of the lowest refractive index of the optically isotropic layer is preferably 0.01, and more It is preferably 0.007, more preferably 0.005, particularly preferably 0.003, most preferably 0.002.

(Laminated film)
The lower limit of the thickness of the laminated film is preferably 12 µm, more preferably 15 µm, even more preferably 18 µm, and particularly preferably 20 µm. When the lower limit is 12 μm or more, the strength of the laminated film is excellent, and handling in production or subsequent processing is facilitated.
The upper limit of the thickness of the laminated film is preferably 180 µm, more preferably 150 µm, still more preferably 120 µm, particularly preferably 100 µm, and most preferably 90 µm. When the upper limit is 180 µm or less, it is suitable for thinning in various applications.
The thickness of the laminated film is calculated by embedding the laminated film in an epoxy resin, cutting out a section of the cross section, observing the section with a microscope, measuring the thickness at 10 points at equal intervals, and calculating the average value.

In the laminated film, only one side of the base film may be an uneven surface, but if the ΔRe of the base film is relatively low, or if the roughness of the uneven surface is relatively small, iridescence can be effectively suppressed. Therefore, it is preferable to make both surfaces of the base film uneven and to provide the optically isotropic layers on both surfaces.

The upper limit of the haze of the laminated film is preferably 10%, more preferably 7%, still more preferably 5%, particularly preferably 4%, most preferably 3%, and most preferably is 2.5%, most preferably 2%. When the upper limit is 5% or less, it is possible to more effectively suppress a decrease in contrast and a screen from becoming whitish when exposed to strong external light.

The laminated film may have two or more substrate films having an uneven surface (roughened surface), may have two or more optically isotropic layers, and may have an uneven surface (roughened surface). ) and a film or layer other than the optically isotropic layer.
Examples of lamination include types 1 to 4 below.
(Type 1) Base film (uneven surface)/optical isotropic layer (adhesive or adhesive)/Other film (Type 2) Base film (uneven surface)/optical isotropic layer (adhesive or adhesive) / (Uneven surface) Base film (type 3) Base film (uneven surface) / Optical isotropic layer (adhesive or adhesive) / Other film / Optical isotropic layer (adhesive or adhesive) / (Uneven Surface) Base film (Type 4) Other film/Optical isotropic layer (adhesive or adhesive)/(Uneven surface) Base film (uneven surface)/Optical isotropic layer (adhesive or adhesive)/Other Film When the ΔBfNxy of the base film with refractive index anisotropy is relatively small or the roughness of the unevenness is relatively small, it is preferable to adopt the configuration of type 2 to type 4. In the following description, the term "laminated film" includes the configurations of types 1 to 4 described above. In the case of Types 2 and 3, the slow axes of the two substrate films are preferably parallel or perpendicular to each other, preferably parallel from the viewpoint of ease of production. Here, "parallel or perpendicular" is allowed from 0 degree or 90 degrees, preferably ±10 degrees, further ±7 degrees, particularly ±5 degrees.

In addition, when referring to an adhesive or an adhesive layer in the specification, a coating agent for an adhesive is applied to an object and crosslinked or dried, or a substrate-less optical adhesive is transferred. means

The laminated film may further have various functional layers according to each application. Examples of various functional layers include a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a conductive layer, an antistatic layer, a colored layer, an ultraviolet absorption layer, an antifouling layer, and an adhesive layer.

(depolarizing film)
The depolarizing film of the present invention is preferably made of the laminated film described above. The depolarizing film can be suitably used as a depolarizing film in an image display device [eg, a liquid crystal display device, an EL display device (eg, an EL display device provided with an antireflection circularly polarizing plate, etc.)].
In order to depolarize, it is preferable to provide a depolarizing film on the viewing side of the image display cell of the image display device. Further, the depolarizing film is preferably provided on the visual recognition side of the polarizing plate or the circularly polarizing plate which is disposed on the visual recognition side of the image display cell of the image display device.
The angle formed by the transmission axis of the polarizer and the slow axis of the substrate film is preferably 20 to 70 degrees, more preferably 25 to 65 degrees, still more preferably 30 to 60 degrees, and particularly preferably 35 to 55 degrees. Within this range, it is possible to reduce the change in brightness due to tilting the head.

As a method for providing the depolarizing film, there are a method of simply placing it on the viewer side of the image display cell of the image display device, a method of laminating it to the viewer side of the viewer side polarizing plate of the image display device, and a method of attaching it to the viewer side of the image display cell of the image display device. and a method of bonding with a protective cover when there is a protective cover on the viewing side of the image display cell of the image display device.
When the depolarizing film is attached to a base material such as a touch panel, the position of the depolarizing film may be on the viewing side of the base material such as the touch panel or on the image display cell side.
When the depolarizing film is attached to the protective cover, the position of the depolarizing film may be on the viewing side of the protective cover or on the image display cell side.

In laminating the depolarizing film to the object, the base film side may be laminated or the optical isotropic layer side may be laminated. It may be on the cell side.

An adhesive or pressure-sensitive adhesive is preferably used to attach the depolarizing film to the object. Further, the uneven surface of the base film and the object to be bonded may be bonded together with an adhesive or pressure-sensitive adhesive that corresponds to the optically isotropic layer of the present invention. In this case, the base film and the adhesive or pressure-sensitive adhesive constitute the laminate film referred to in the present invention.

The depolarizing film of the present invention may also be used as a substrate for providing a transparent conductive layer of a touch panel or the like, or as a shatterproof film for a glass substrate of a touch panel or a surface protection cover. Furthermore, the depolarizing film may be printed with a design to give it design, or it may be used as a shatterproof film for window glass or the like, or as a decorative film.

(Image display device)
The image display device of the present invention preferably has an image display cell, a polarizer arranged on the viewer side of the image display cell, and a depolarizing film arranged on the viewer side of the polarizer. The base film side of the depolarizing film may be the polarizer side, or the optically isotropic layer side may be the polarizer side, but the base film side is preferably the polarizer side. The angle formed by the transmission axis of the polarizer and the slow axis of the base film can be selected from the range described for the depolarizing film, for example.

The image display device is, for example, a liquid crystal display device.
The light sources (backlights) for liquid crystal display devices include blue light emitting diodes and yellow phosphor light sources, blue, green and red light emitting diode light sources, blue light emitting diodes, green phosphors, and red phosphor light sources, and wavelength conversion using quantum dots. A light source, a semiconductor laser light source, a cold cathode tube, or the like can be used without particular limitation.

As the light source, a light source having a narrow half width of the emission peak of each color is more preferable. As for the half-value width of the light source, the half-value width of the emission peak with the narrowest half-value width is preferably 25 nm or less, more preferably 20 nm or less, still more preferably 15 nm or less, and particularly preferably 10 nm or less. The lower limit of the half-value width is 0.5 nm in terms of a realistic value or the resolution of the measuring instrument. Specific preferred light sources include a QD (quantum dot) light source and a light source using a KSF phosphor for the red region, and the most preferred light source uses a KSF phosphor.

The thickness of the depolarizing film of the present invention is preferably 12 to 60 μm, more preferably 15 to 50 μm, in line with recent thinning. In the case of such a thin image display device, the light source is preferably a blue light emitting diode and a yellow phosphor light source, a light source using a KSF phosphor, a QD light source, or the like.

Also, the image display device may be an organic EL display device. The organic EL display device preferably has a circularly polarizing plate on the viewing side of the image display cell. The depolarizing film of the present invention is preferably arranged on the viewing side of the circularly polarizing plate.

Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples, and it is possible to carry out the present invention with appropriate modifications within the scope of the gist of the present invention. All of them are included in the technical scope of the present invention.
Methods for evaluating physical properties in Examples are as follows.

(1) Slow axis refractive index (Bfnx), fast axis refractive index (Bfny), and refractive index anisotropy (ΔBfNxy) of the base film
Using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd.), the orientation axis direction of the base film before roughening is determined, and the orientation axis direction is 4 cm so that the long side becomes. A 2 cm x 2 cm rectangle was cut out and used as a measurement sample. The biaxial refractive index (Bfnx, Bfny) and the refractive index (Bfnz) in the thickness direction of this sample were measured using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). , and the absolute value of the biaxial refractive index difference (|Bfny−Bfnx|) was defined as the refractive index anisotropy (ΔBfNxy). The refractive index of the roughened substrate film can be measured by polishing the roughened surface with water-resistant emery paper or the like to flatten the roughened surface.

(2) Thickness d of raw film
Using an electric micrometer (Millitron 1245D manufactured by Fineruff Co.), the thickness was measured at five points, and the average value was obtained.

(3) In-plane retardation (Re)
The in-plane retardation (Re) was obtained from the product (ΔBfNxy×d) of the refractive index anisotropy (ΔBfNxy) and the film thickness d (nm).

(4) Nz Coefficient A value obtained by |Bfnx−Bfnz|/|Bfnx−Bfny| was used as the Nz coefficient.

(5) Degree of plane orientation (ΔP)
A value obtained by (Bfnx+Bfny)/2-Bfnz was defined as the degree of planar orientation (ΔP).

(6) Retardation in thickness direction (Rth)
The retardation in the thickness direction is obtained by multiplying the two birefringences ΔBfNxz (=|Bfnx−Bfnz|) and ΔBfNyz (=|Bfny−Bfnz|) when viewed from the cross section in the thickness direction of the film by the film thickness d. is a parameter that indicates the average retardation obtained by Bfnx, Bfny, Bfnz and the film thickness d (nm) are obtained in the same manner as described above, and the average value of (ΔBfNxz×d) and (ΔBfNyz×d) is calculated to calculate the thickness direction retardation (Rth). Calculated: Rth=(ΔBfNxz×d+ΔBfNyz×d)/2.

(7) Surface roughness (Ra, Rq, Rz, Ry, Rp, Rv, Sm)
Each parameter of the surface roughness is obtained from a roughness curve measured using a contact roughness meter (Mitutoyo, SJ-410, detector: 178-396-2, stylus: standard stylus 122AC731 (2 μm)). asked. The settings are as follows.
Curve: R
Filter: GAUSS
λc: 0.8mm
λs: 2.5 μm
Measuring length: 5mm
Measurement speed: 0.5mm/s
Rq was determined according to JIS B0601-2001, and others were determined according to JIS B0601-1994.

(8) Thickness of optically isotropic layer The thickness of the roughened base film and laminated film was determined by embedding each film in epoxy resin, cutting out a section of the cross section, and observing it under a microscope. The thickness was measured and taken as the average value. A polarizing microscope was used when the interface was difficult to see. In addition, the uneven surface of the roughened base film was based on the center of the convex portion and the concave portion in the field of view. The thickness of the optically isotropic layer was determined by subtracting the thickness of the roughened base film from the thickness of the laminated film.

(9) Refractive index of optically isotropic layer Under the same conditions as in the case of providing an optically anisotropic layer on a release film on an uneven surface, the refractive index of a sample peeled off from the release film was measured so as to have a thickness of about 20 μm. It was measured in the same manner as the base film. It was confirmed that nx, ny, and nz are the same value.

(Production of easy-adhesion layer component)
(Polymerization of polyester resin)
194.2 parts by weight of dimethyl terephthalate, 184.5 parts by weight of dimethyl isophthalate, and 14.8 parts by weight of dimethyl-5-sodium sulfoisophthalate were added to a stainless steel autoclave equipped with an agitator, thermometer, and partial reflux condenser. , 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and transesterification was carried out at a temperature of 160° C. to 220° C. over 4 hours. Then, the temperature was raised to 255° C., and the pressure in the reaction system was gradually reduced, followed by reaction under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolymerized polyester resin. The resulting copolymerized polyester resin was pale yellow and transparent. When the reduced viscosity of the copolymerized polyester resin was measured, it was 0.70 dl/g. The glass transition temperature by DSC was 40°C.

(Preparation of polyester aqueous dispersion)
A reactor equipped with a stirrer, a thermometer and a reflux device was charged with 30 parts by mass of a copolymer polyester resin and 15 parts by mass of ethylene glycol n-butyl ether, heated at 110° C. and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution with stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester water dispersion having a solid content of 30% by mass.

(Polymerization of block polyisocyanate-based cross-linking agent used in easy-adhesion layer)
A flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 100 parts by mass of a polyisocyanate compound having an isocyanurate structure made from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals) and 55 parts by mass of propylene glycol monomethyl ether acetate. , and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight: 750) were charged and held at 70° C. for 4 hours in a nitrogen atmosphere. After that, the temperature of the reaction solution was lowered to 50° C., and 47 parts by mass of methyl ethyl ketoxime was added dropwise. By measuring the infrared spectrum of the reaction solution, it was confirmed that the absorption of isocyanate groups had disappeared, and an aqueous blocked polyisocyanate dispersion having a solid content of 75% by mass was obtained.

(Adjustment of coating liquid for easy adhesion layer)
A P1 coating solution was prepared by mixing the following coating agents.
Water 50.00% by mass
Isopropanol 33.00% by mass
Polyester water dispersion 12.00% by mass
Block isocyanate-based cross-linking agent 0.80% by mass
Particles 1.40% by mass
(Silica sol with an average particle size of 100 nm, solid content concentration of 40% by mass)
Catalyst (organotin compound solid content concentration 14% by mass) 0.30% by mass
Surfactant 0.50% by mass
(Silicone type, solid content concentration 10% by mass)

(Manufacture of polyester resin for film)
(Production Example 1-Polyester X)
When the temperature of the esterification reactor reaches 200° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol are charged, and 0.017 parts by mass of antimony trioxide as a catalyst is added while stirring. , 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine were charged. Then, the pressure was increased and the temperature was increased, and the pressure esterification reaction was performed under the conditions of gauge pressure 0.34 MPa and 240° C., then the pressure in the esterification reactor was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. . Furthermore, the temperature was raised to 260° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, dispersion treatment was performed with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reactor, and polycondensation reaction was performed at 280°C under reduced pressure.

After the polycondensation reaction is completed, filtration is performed with a NASLON (registered trademark) filter having a 95% cut diameter of 5 μm, extruded from the nozzle in strand form, and cooling water that has been pre-filtered (pore size: 1 μm or less) is filtered. It was cooled, solidified and cut into pellets. The resulting polyethylene terephthalate resin (X) had an intrinsic viscosity of 0.62 dl/g and contained substantially no inert particles or internal precipitated particles. (Hereinafter abbreviated as PET (X).)

(Production of raw films A and B)
PET (X) resin pellets containing no particles as a raw material for film are supplied to an extruder, extruded in a sheet form from a nozzle, and then wound around a casting drum with a surface temperature of 30 ° C. using an electrostatic casting method. It was cooled and solidified to produce an unstretched film. Next, the P1 coating liquid was applied to both sides of this unstretched PET film by a reverse roll method so that the coating amount after drying was 0.12 g / m ² , and then led to a dryer and dried at 80 ° C. for 20 seconds. bottom.

The unstretched film with the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, was guided to a hot air zone at a temperature of 135° C. and stretched 3.8 times in the width direction. Next, while maintaining the width stretched in the width direction, it was treated at a temperature of 225 ° C. for 30 seconds, and then cut at both ends of the film cooled to 130 ° C. with a shear blade, and a tension of 0.5 kg / mm ² After cutting off the selvages, the film was wound up to obtain a raw film A having a film thickness of 80 μm.

A raw film B having a different film thickness was obtained in the same manner as the raw film A except that the thickness of the unstretched film was changed by increasing the line speed after casting.

(Manufacturing raw film C)
An unstretched film (coated with an easy-adhesion layer) produced by the same method as the raw film A is heated to 105 ° C. using a heated roll group and an infrared heater, and then a roll group with a peripheral speed difference. After being stretched 2.0 times in the running direction in the same manner as the raw film A, it was led to a hot air zone at a temperature of 135° C. and stretched 4.0 times in the width direction to obtain a raw film C.

(Original film D)
An unstretched film (coated with an easy-adhesion layer) produced by the same method as the raw film A is heated to 105 ° C. using a heated roll group and an infrared heater, and then a roll group with a peripheral speed difference. After the film was stretched 3.5 times in the running direction, it was led to a hot air zone at a temperature of 135° C. and stretched 3.5 times in the width direction by the same method as for raw film A, to obtain raw film D.

(Production of surface-roughened film)
Attach urethane foam to a glass plate, and then attach the periphery of the original film A with double-sided tape. 45 degrees and 135 degrees) to obtain a surface-roughened film A1.
The periphery of raw film A was attached to a glass plate with double-sided tape, set in a dry sandblaster, and treated by spraying an abrasive (sandblasting) to obtain surface-roughened film A2.
A masking film made of polypropylene film is attached to one side of the original film A, which is immersed in a 38% potassium hydroxide aqueous solution (95 ° C.) (chemical etching), washed with water, and then the masking film is peeled off and dried. A surface-roughened film A4 was obtained.
Various surface-roughened films shown in Table 2 were obtained from raw films A, B, C, and D by changing the belt sander conditions (sanding belt type, etc.) and sandblasting conditions (abrasive particle size, etc.). rice field.
A #320 sanding belt was used to manufacture B1 and C1, and a #180 sanding belt was used to manufacture A3 and D1. Abrasives of the sand blaster were used in the order of A5, A6, B2 and A2.
In addition, in order to eliminate the influence of local projections, the belt-sanded and sandblasted surfaces were lightly polished with #400 sandpaper.

(Production of laminated film (or depolarizing film))
(Preparation of coating agent for optically isotropic layer)
As a coating agent for the optically isotropic layer, those shown in Table 3 were prepared.

Example 1
On the uneven surface of the surface roughened film A1 of 20 cm × 30 cm, the above-mentioned easy adhesion layer diluted 4 times with a solution of water / isopropanol = 2/1 is applied and dried to obtain an easy adhesion of about 30 nm. layer was established. Further, the coating agent a for the optically isotropic layer was applied thereon with an applicator, and then cured from the coated surface with a high-pressure mercury lamp to obtain a laminated film F1.

Examples 2-7, 9-14, and Comparative Examples 1-3
Laminated films F2 to F8 and F10 to F17 were obtained in the same manner as in Example 1, except that the type of surface-roughened film and/or coating agent was changed. Note that the laminated film F15 was provided with an optical isotropic layer on both sides.

Example 8
On the uneven surface of the surface roughened film A1 of 20 cm × 30 cm, the above-mentioned easy adhesion layer diluted 4 times with a solution of water / isopropanol = 2/1 is applied and dried to obtain an easy adhesion of about 30 nm. layer was established. Furthermore, after applying the coating agent a for the optically isotropic layer on it with an applicator, a surface nickel-plated metal plate mold having a concave-convex structure provided on the coated surface to provide anti-glare properties is superimposed, and the substrate film is coated. A laminated film F9 having an antiglare property in the optically isotropic layer was obtained by curing from the surface with a high-pressure mercury lamp.

Example 15
A solution of Vylon (registered trademark) 200 (RV200) (manufactured by Toyobo Co., Ltd.) in a 20% toluene/methyl ethyl ketone mixed solvent is applied to the uneven surface of the 20 cm × 30 cm roughened film B2, and then dried to form an optically isotropic layer. was established. The optically isotropic layers of the obtained two laminate films were superimposed and passed between rolls heated to 100° C., and the two laminate films were bonded together so that the slow axes were parallel to each other. Byron 200 has a refractive index of 1.55.

(Evaluation of laminated film)
(Observation of depolarized state)
The resulting laminated film is placed on the viewing side of a liquid crystal display (REGZA Z20X manufactured by Toshiba Corporation) using a KSF light source, and the transmission axis of the viewing side polarizing plate and the slow axis of the base film are at 45 degrees, and the viewing side is optically isotropic. The layers were fixed with cellophane tape. The presence or absence of rainbow spots was observed by tilting the face or looking at the display from an angle while wearing polarized sunglasses. In addition, the display displayed only white.
○: No iridescence was observed in any case △: Slight iridescence was observed ×: Iridescence was observed

(observation of contrast)
The image of the scenery was displayed on the display, and the contrast from the front was observed by illuminating the light from the fluorescent lamp on the table from above.
⊚: Vivid contrast remained.
◯: Slight decrease in contrast was observed due to scattered light.
Δ: A decrease in contrast was observed, but the image could be observed.
x: The image became difficult to see due to scattered light.

Table 4 shows the physical properties and evaluation results of the laminated films of Examples 1 to 15 and Comparative Examples 1 to 3.

(Manufacturing of a display in which a laminated film is attached with an adhesive)
(Preparation of coating agent for adhesive used as optical isotropic layer and optical adhesive sheet)
The adhesives and optical adhesive sheets shown in Table 5 were used.

Preparation of high refractive index adhesive k 30 parts by mass of 2-ethylhexyl acrylate, 70 parts by mass of ethoxylated o-phenylphenol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: A-LEN-10), and azo as a polymerization initiator 0.25 parts by mass of bisisobutyronitrile was reacted in ethyl acetate to obtain an ethyl acetate solution (solid concentration: 30% by mass) of a copolymer (Mw=400,000).

Example 16
After coating the uneven surface of the 20 cm × 30 cm surface-roughened film A1 with a coating agent i for adhesive as an optically isotropic layer with an applicator, the coated surface was cured with a high-pressure mercury lamp to obtain a laminated film P1. The adhesive layer surface of the obtained laminate film P1 is placed on the viewing side of a liquid crystal display (Regza Z20X manufactured by Toshiba Corporation) using a KSF light source so that the transmission axis of the viewing side polarizing plate and the slow axis of the base film are at 45 degrees. pasted on.

Comparative example 4
A laminate film P3 was obtained and attached to a liquid crystal display in the same manner as in Example 16, except that the optical adhesive sheet j was attached as an optically isotropic layer to the uneven surface of the surface-roughened film A1.

Example 17
After coating the uneven surface of the surface-roughened film A1 of 20 cm × 30 cm with a coating agent k for adhesive as an optical isotropic layer with an applicator, it is dried at 100 ° C. to obtain a laminated film P2, and a KSF light source is used. It was attached to a liquid crystal display (Regza Z20X manufactured by Toshiba Corporation).

Example 18
The laminated film P1 was attached to a polycarbonate plate of 20 cm×30 cm×2 mm to form a front protective cover sheet. This cover sheet was attached to a liquid crystal display (Regza Z20X manufactured by Toshiba Corporation) using a KSF light source with cellophane tape so that the polycarbonate plate of the cover sheet was on the viewing side.

The results of Examples 16-18 and Comparative Example 4 are shown in Table 6.

The depolarizing film of the present invention suppresses iridescence that occurs when an image is viewed through a polarizing filter such as polarized sunglasses when used in an environment with a light source having a sharp peak, and has high transparency and high transparency. Vivid image displayability can be ensured.

Claims (6)

A depolarizing film comprising a laminated film having a substrate film and an optically isotropic layer, wherein the laminated film has all of the following characteristics.
(a) At least one surface of the substrate film is uneven, and the arithmetic mean roughness (Ra) of the uneven surface is 0.4 to 4 μm.
(b) The refractive index anisotropy (ΔBfNxy) of the base film is 0.07 to 0.2.
(c) An optically isotropic layer is provided on the uneven surface of the base film, and the refractive index of the optically isotropic layer is Bfny−0.15 to Bfnx+0.15 and is 1.57 or more. .
(However, the refractive index in the slow axis direction of the base film is Bfnx, the refractive index in the fast axis direction is Bfny , and ΔBfNxy=Bfnx−Bfny )
(d) The substrate film has a retardation difference (ΔRe) of 90 to 800 nm.
(However, ΔRe=Ra×ΔBfNxy)
(e) The in-plane retardation of the substrate film is 3000 to 30000 nm.
(f) Bfnx of the base film is 1.67 to 1.73.
(g) The base film is a polyester film.
(h) The optically isotropic layer is provided in direct contact with the uneven surface without any other layer interposed therebetween, or is provided only via the easy-adhesion layer. 2. The depolarizing film according to claim 1, wherein the base film has a plane orientation degree (ΔP) of 0.09 to 0.15. 3. The depolarizing film according to claim 1, wherein the optically isotropic layer has a refractive index of Bfny to Bfnx. 4. The depolarizing film according to claim 1, wherein the optically isotropic layer has a refractive index of Bfny+0.02 to Bfnx. An image display device comprising an image display cell, a polarizer arranged on the viewer side of the image display cell, and the depolarizing film according to any one of claims 1 to 4 arranged on the viewer side of the polarizer. . 6. The image display device according to claim 5, wherein the angle formed by the transmission axis of the polarizer and the slow axis of the base film is 20 to 70 degrees.