JP2019124920A - Depolarizing film and image display device using the same - Google Patents

Abstract

To provide a depolarizing film which suppresses rainbow spots that appear when viewing an image through a polarizing filter, such as polarized sunglasses, in an environment with a light source having a steep emission peak, and secures high transparency and capability to present clear images.SOLUTION: A depolarizing film is provided, which comprises a laminated film comprising a base material film and an optically isotropic film and having all of the following features. (a) The base material film has a rugged surface having an arithmetic mean roughness (Ra) in a range of 0.2-10 μm provided on at least one side thereof. (b) The base material film has a refractive index anisotropy (Bfnx-Bfny) in a range of 0.04-0.2. (c) An optically isotropic layer having a refractive index in a range of Bfny-0.15 to Bfnx+0.15 is provided on top of the rugged surface of the base material film, where Bfnx represents a refractive index of the base material film in a slow axis direction and Bfny represents a refractive index in a fast axis direction.SELECTED DRAWING: None

Description

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

  It has been known that when a film having birefringence, such as a polyester film, is used in the environment of a fluorescent lamp or a cold cathode tube light source, rainbow marks due to retardation occur. Therefore, a cellulose-based film having optical isotropy has been used as a protective film of a polarizer used for a liquid crystal display or the like.

Recently, a technique has been proposed to eliminate rainbow marks by combining a film having high retardation with a white light source having a continuous emission spectrum (for example, Patent Document 1 etc.), and an image was viewed through polarized sunglasses Even in this case, it has been put to practical use in liquid crystal displays and the like as a depolarizing film which does not cause blackout or rainbow marks. However, this technique is improved when using a light source having a sharp emission peak in the red region of the emission spectrum such as a cold cathode tube light source or a KSF phosphor (phosphor obtained by adding Mn to K ₂ SiF ₆ crystal). There was room for In addition, in order to ensure high retardation, the film needs to have a thickness, and there is a possibility that it can not sufficiently cope with the recent thinning of the image display apparatus.

  As a depolarizing film of a liquid crystal display using a light source having a sharp emission peak, unevenness is provided on the surface of the film having birefringence, so that λ / 4 or more is locally within a region smaller than the level visible to the naked eye. A film in which a phase difference is generated has been proposed (for example, Patent Document 2). However, such conventional techniques have a problem that the screen becomes white and the image is difficult to see in a strong external light environment where the image contrast is low.

JP, 2011-215646, A JP, 2017-161599, A

  The present invention has been made on the background of the problems of the prior art. That is, the object of the present invention is to suppress rainbow marks that occur when viewing an image through a polarizing filter such as polarized sunglasses when used under an environment of a light source having a sharp emission peak, etc. Another object of the present invention is to provide a depolarizing film capable of securing bright image displayability and an image display apparatus using the same.

As a result of intensive investigations to achieve such an object, the present inventor has completed the present invention.
That is, the present invention includes the following aspects.
Item 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 features.
(A) At least one surface of the base film is an uneven surface, and the arithmetic average roughness (Ra) of the uneven surface is 0.2 to 10 μm.
(B) The refractive index anisotropy (Bfnx-Bfny) of a base film is 0.04-0.2.
(C) The 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.
(However, let the refractive index in the slow axis direction of the base film be Bfnx and the refractive index in the fast axis direction be Bfny)
Item 2.
An image display device comprising an image display cell, a polarizer disposed on the viewing side with respect to the image display cell, and the depolarizing film according to item 1 disposed on the viewing side with respect to the polarizer.
Item 3.
Item 3. The image display device according to item 2, wherein an 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 rainbow marks that occur when viewing an image through a polarizing filter such as polarized sunglasses when used in an environment of a light source having a sharp emission peak, etc., and has 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 the following, the term "laminated film" or "depolarizing film" simply means this.
(Base film)
First, the substrate film will be described.

  There is no particular limitation on at least the base film as long as it can give refractive index anisotropy, and polyester, polyamide, polystyrene, syndiotactic polystyrene, polyamide, polycarbonate and the like can be mentioned. Above all, polyester is preferable in that a film having a high refractive index anisotropy can be easily obtained. Examples of the polyester include polyethylene terephthalate, polyethylene naphthalate, polytetramethylene terephthalate, polytrimethylene terephthalate, etc. Among them, polyethylene terephthalate and polyethylene naphthalate are preferable. These polyesters are terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, ethylene glycol as long as mechanical properties, heat resistance and dimensional stability as a film are not impaired (for example, 10 mol% or less). Diethylene glycol, trimethylene glycol, tetramethylene glycol, and ethylene oxide (EO) 1-2 mole adduct of cyclohexanedimethanol bisphenol A may be copolymerized. For example, in the case of a polymer of polyethylene terephthalate, 1 to 2 moles of a by-product diethylene glycol is usually copolymerized during polymerization, but such a by-product may be contained.

  The base film has birefringence. The lower limit of the slow axis direction 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 axial direction 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 axial direction refractive index (Bfny) of the base film is preferably 1.62, more preferably 1.61, and still more preferably 1.6.

  The lower limit of the refractive index anisotropy (ΔBfNxy = Bfnx−Bfny) of the base 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, rainbow spots 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. If the upper limit is 0.2 or less, the mechanical strength in the fast axis direction can be adjusted to the practical range, and the manufacture is also facilitated. In addition, the refractive index of a base film is a value measured on the conditions of wavelength 589 nm.

  The lower limit of the thickness of the base film before the provision of the uneven surface (before the roughening) is preferably 15 μm, more preferably 20 μm, and still more preferably 25 μm. If the said minimum is 15 micrometers or more, even if thickness reduces at the time of uneven | corrugated provision, it has the outstanding mechanical strength. The upper limit of the thickness of the substrate film prior to the application of the uneven surface is preferably 200 μm, more preferably 150 μm, still more preferably 100 μm, particularly preferably 90 μm, and most preferably 80 μm. If the said upper limit is 200 micrometers or less, it is excellent in the handling property and suitable for making it thin (example: it uses for a thin image display apparatus).

  The lower limit of the in-plane retardation (Re) of the substrate film before the application of the uneven surface is preferably 2000 nm, more preferably 2500 nm, still more preferably 3000 nm, particularly preferably 3500 nm, most preferably 4000 nm. It is. Rainbow spots can be eliminated more effectively if the lower limit is 2000 nm or more. The upper limit of the in-plane retardation (Re) of the substrate film before the application of the uneven surface is preferably 30000 nm, more preferably 20000 nm, still more preferably 15000 nm, still more preferably 12000 nm, particularly preferably It is 10000 nm, more particularly preferably 9000 nm, most preferably 8000 nm and most particularly 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) of the in-plane retardation (Re) to the retardation (Rth) in the thickness direction of the substrate film prior to the application of the uneven surface is preferably 0.2, more preferably 0.5, and still more preferably Is 0.6. When the lower limit is 0.2 or more, rainbow marks can be eliminated more effectively. The upper limit of Re / Rth of the substrate film before the provision of the uneven surface is preferably 2 in view of mechanical strength, more preferably 1.5, still more preferably 1.2, and particularly preferably 1.

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

  The lower limit of the plane orientation degree ΔP of the base film is preferably 0.08, more preferably 0.09, and still more preferably 0.1. If the lower limit is 0.08 or more, it is possible not only to eliminate rainbow marks more effectively, but also to reduce thickness unevenness of the film. The upper limit of the plane orientation degree ΔP of the base film is preferably 0.15, more preferably 0.14, and still more preferably 0.13. Refractive index anisotropy can be kept higher as the upper limit is 0.15 or less.

  The substrate film is preferably uniaxially oriented in order to impart refractive index anisotropy. As an orientation method, it can carry out by the usual method according to each resin. For example, in the case of extruding a molten resin in the form of a sheet on a cooling roll, a method of orienting the cooling roll by setting it at a speed equal to or higher than the speed of the extruded resin, heating an unstretched film melted and extruded. The method of stretching and orienting in the longitudinal direction with the group of rolls, and the method of heating and stretching the molten and extruded unstretched film in the tenter and stretching and orienting in the transverse direction or in the oblique direction may be mentioned.

  Among these, as a method for orienting the base film, there is a method of stretching and orienting the unstretched film which has been melted and extruded in the longitudinal direction with a heated roll group, and the unstretched film which has been melted and extruded. Preferred is a method of heating in a tenter and stretching in a lateral direction or an oblique direction for orientation. 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 lateral 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 orienting in the longitudinal direction, it is weak before stretching in the longitudinal direction (about 2.2 times or less to increase mechanical strength in the direction perpendicular to the orientation direction or adjust shrinkage characteristics. ) After stretching in the longitudinal direction, or after stretching in the longitudinal direction, weak (about 1.5 times or less) transverse stretching may be added. Similarly, even in the case of transverse orientation, it is weak before stretching in the transverse direction (about 2.2 times) in order to increase the mechanical strength in the direction perpendicular to the orientation direction or to adjust the shrinkage characteristics. The following longitudinal stretching may be added, or a weak (about 1.5 times or less) longitudinal stretching may be added after the transverse stretching. In order to further increase the orientation in the orientation direction, the film may be slightly shrunk in the longitudinal direction during or after the transverse stretching. The width after contraction is preferably 0.7 to 0.995 times, more preferably 0.8 to 0.99 times, and particularly preferably 0.9 to 0.98 times the width at the time of drawing. 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 temperature at the time of stretching (and the temperature of the preheating) is preferably 80 to 150 ° C. in both the longitudinal direction and the transverse direction. Moreover, after extending | stretching, in order to ensure the heat resistance of a base film, it is preferable to heat-set at high temperature from the heating temperature at the time of extending | stretching. As a heat setting temperature, 150-250 degreeC is preferable, More preferably, it is 170-245 degreeC.

  The base film desirably 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, further 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 make the light transmittance at a wavelength of 380 nm of the base film 20% or less, it is desirable to appropriately adjust the type, concentration, and thickness of the base film of the ultraviolet absorber blended in the base film. As a ultraviolet absorber used by this invention, an organic type ultraviolet absorber and an inorganic type ultraviolet absorber are mentioned. From the viewpoint of transparency, organic UV absorbers are preferred. Examples of the organic ultraviolet absorber include benzotriazole type, benzophenone type, cyclic imino ester type and the like, and combinations thereof, but there is no particular limitation as long as it is within the above-mentioned range of light transmittance. From the viewpoint of durability, benzotriazoles and cyclic imino esters are particularly preferred. When two or more types of ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

It is also preferable to add various additives to the base film, as long as the effects of the present invention are not impaired, in addition to the ultraviolet light absorber. Additives include, for example, inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, thermal stabilizers, antioxidants, antigelling agents And surfactants. These additives can be used alone or in combination of two or more.
Moreover, in order to exhibit high transparency, it is also preferable not to contain particle | grains in a base film substantially. The phrase "does not substantially contain particles" means, for example, in the case of inorganic particles, 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less, when the inorganic element in the substrate film is quantified by fluorescent X-ray analysis. Mean the content of

(Surface irregularities)
In the present invention, an uneven surface is provided on at least one side of the substrate film. The uneven surface may be provided on only one side of the substrate film, or may be provided on both sides. In addition, the base film which has an uneven surface may be called the roughened base film.

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

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

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

  The lower limit of the maximum height (Ry) of the rough surface of the roughened base film is preferably 2.0 μm, more preferably 3.0 μm, still more preferably 4.0 μm, and particularly preferably 4.5 μm. And most preferably 5.0 μm. The upper limit of the Ry is preferably 20 μm, more preferably 17 μm, still 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. is there. The upper limit of the Rp is preferably 15 μm, more preferably 12 μm, still more preferably 10 μm, and particularly preferably 8 μm.

  The lower limit of the maximum valley depth (Rv) 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. It is. The upper limit of the Rv is preferably 15 μm, more preferably 12 μm, still 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 limit, rainbow marks can be eliminated more effectively.
When the values of Ra, Rq, Rz, Ry, Rp, and Rv are the upper limit or more, the productivity is excellent.
Ra, Rq, Rz, Ry, Rp, and Rv are calculated from the roughness curve measured using a contact-type roughness meter in accordance with JIS B0601-1994 or JIS B0601-2001.

  By providing unevenness (roughening) on the surface of the substrate film, a retardation difference is provided in a very small area, and although coloring (rainbow spots) due to retardation in each area is made, the coloring is visually obscured be able to. The retardation difference ΔRe can be expressed 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, and most preferably 100 nm. Rainbow spots can be eliminated more effectively if the lower limit is 30 nm or more. The upper limit of ΔRe is preferably 1500 nm, more preferably 1000 nm, still more preferably 800 nm, particularly preferably 500 nm, and most preferably 300 nm. When the upper limit is 1,500 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. It 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, and most preferably 300 μm. It is. When the upper limit is 500 μm or less, it is possible to prevent the coloring or flickering due to the retardation of each of the minute regions.
Sm is calculated from a roughness curve measured using a contact-type roughness meter in accordance with JIS B0601-1994.

The base film may be thinner than the original thickness by providing the unevenness and roughening. The lower limit of the thickness of the roughened substrate film is preferably 10 μm, more preferably 15 μm, still more preferably 20 μm, particularly preferably 25 μm, and most preferably 30 μm. The intensity | strength as a protective film can fully be ensured as the said minimum is 10 micrometers or more. The upper limit of the thickness of the roughened substrate film is preferably 150 μm, more preferably 120 μm, still more preferably 100 μm, particularly preferably 90 μm, and most preferably 80 μm. The upper limit of 150 μm or less is suitable for thinning.
The roughened base film is embedded by embedding the roughened base film in an epoxy resin, and cutting a section of the cross section for microscopic observation, and the uneven surface is based on the center of the convex portion and the concave portion of the field of view The thickness of 10 points is measured at equal intervals, and it is calculated as the average value.

  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, and most preferably 4000 nm. is there. Rainbow spots can be eliminated more effectively if the lower limit is 2000 nm or more. The upper limit of the in-plane retardation (Re) of the roughened base film is preferably 30000 nm, more preferably 20000 nm, still more preferably 15000 nm, still more preferably 12000 nm, particularly preferably 10000 nm. More preferably, it is 9000 nm, most preferably 8000 nm, and most preferably 7500 nm. When the upper limit is 30000 nm or less, it is suitable for thinning.

There are no particular limitations on the method for providing the surface asperity, and there may be mentioned conventionally known methods of surface roughening. For example, sand blasting treatment, sand paper or file, treatment with grindstone etc., treatment with sander (orbital sander, random sander, delta sander, belt sander, disc sander, roll sander etc), treatment with metal brush etc, chemical etching, mold And molding by pressing at Among these, sand blast treatment, treatment with a sander, and chemical etching are preferable.
The sandblasting process may be, for example, a method of supplying a roll-like base film to a centrifugal blast machine and projecting an abrasive 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 rotary blade, and the like. Moreover, a sandblasting process may be the method of affixing a base film to a glass plate, setting to air blast, and spraying an abrasives on a base film surface. In this case, the roughness can be adjusted by the type of abrasive, the size of the abrasive, the blowing pressure, the processing time, and the like.
The processing by the sander is, for example, a method of guiding a roll-like base film to a conveyance device having a roll of sanding paper attached to the roll surface of a part of the film conveyance roll (roll sander). Good. In this case, the roughness can be adjusted by the type of sanding paper, the number of revolutions of the roll sander, the transport speed of the film, and the like. Also, the processing direction can be adjusted by the holding angle between the roll sander and the film, the number of rotations of the roll sander, the transport speed of the film, and the like.
In the sander processing, a urethane foam is attached to a glass plate, and a base film is further attached thereon, and the base film surface is vertically, horizontally, and diagonally (45 degrees, 135 degrees) in a total of four directions using a sander. It may be a method of processing from. The roughness can be adjusted depending on the type of sanding disc, processing time, etc.
In the sander treatment and sandblast treatment, the treated surface may be further polished with sand paper or the like in order to remove local protrusions.
The chemical etching may be a method in which the film is dipped in an acid or alkaline solution and washed with water, and then the masking film is peeled off and dried. The roughness can be adjusted by the immersion time or the like. Although chemical etching is basically double-sided processing, in the case of processing only one side, for example, a masking film is attached to one side of the base film.

(Optical isotropic layer)
It is preferable that the optically isotropic layer is 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 which can not be detected optically, preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 20 nm or less. If the easily bonding layer satisfies the range of the refractive index of the following optically isotropic layer, the easily bonding layer and the optically isotropic layer provided thereon are regarded as one optically isotropic layer. be able to. In addition, if the easily bonding layer has a sufficient thickness as an optically isotropic layer, the easily bonding layer may be regarded as an optically isotropic layer. By providing the optically isotropic layer, irregular reflection due to the unevenness of the surface of the base film can be reduced, and transparency can be ensured. In addition, the preferable refractive index of the easily bonding layer is the same as the range of the preferable refractive index of the following optical isotropic layer, and the adjustment method of 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, still more preferably Bfny-0.1, still more preferably Bfny-0.08, 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, still more preferably Bfnx + 0.1, still more preferably Bfnx + 0.08, particularly preferably It is Bfnx, most preferably Bfnx-0.02.
By setting the above-mentioned range, it is possible to maintain the contrast or the sharpness of the image and to suppress the phenomenon that the screen becomes whitish when strong external light is received.

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

The composition of the optically isotropic layer is not particularly limited, but 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, in the case of PMMA (polymethyl methacrylate), the refractive index is generally about 1.49. Acrylic pressure sensitive adhesives often introduce long chain or branched alkyl groups, and the refractive index is further lowered. In order to increase the refractive index, it is effective to copolymerize an acrylic monomer having an aromatic group or to copolymerize styrene.
Introduction of sulfur, bromine, fluorene group or the like into a polymer or resin is also a preferable method for raising the refractive index, and an acrylic copolymerized with a monomer containing these, a fluorene group-containing polyester, a fluorene group-containing polycarbonate, A thioepoxy resin is preferable as the high refractive index resin.

Further, addition of high refractive fine particles in a polymer or resin is also a suitable method of adjusting the refractive index.
The refractive index of the high refractive fine particles is preferably 1.60 to 2.74. Examples of the high refractive particles include fine particles of TiO ₂ , ZrO ₂ , CeO ₂ , Al ₂ O ₃ , BaTiO ₃ , Nb ₂ O ₅ , and SnO ₂ . The high refractive fine particles preferably have an average primary particle diameter of 3 nm to 100 nm as measured by TEM (transmission electron microscopy). These high refractive particles may be used alone or in combination of two or more.
In the specification, “average primary particle size” or “average particle size of primary particles” refers to 50% particle size of volume accumulation. More specifically, 200 primary particles are observed with an appropriate magnification by microscopic observation, each diameter is measured to calculate its volume, and 50% particle diameter of its volume accumulation is taken as the average primary particle diameter. Do.

  The optically isotropic layer is preferably crosslinked and cured. The curing method is not particularly limited, and thermal curing, radiation curing such as ultraviolet light, electron beam and the like are preferable. Examples of the crosslinking agent for curing include isocyanate compounds, epoxy compounds, carbodiimides, oxazoline compounds, amino resins such as melamine, polyfunctional acrylates, and the like.

  The optically isotropic layer is formed by applying a coating agent comprising the above components to the irregular surface of the substrate film, transferring an optically isotropic layer prepared by applying to a release film to the irregular surface of the substrate film, or the like The optically isotropic layer provided on the film of (1) can be laminated by a method such as bonding to the uneven surface of the base film. In this case, the coating agent is preferably dissolved or diluted with a solvent to have a viscosity that facilitates coating. The coating agent may be a non-solvent as long as it is a radiation curing type coating agent such as acrylic.

  For example, acrylic or other radiation curing type coating agents usually contain a photopolymerizable compound.

  As a photopolymerizable compound, a photopolymerizable monomer, a photopolymerizable oligomer, and a photopolymerizable polymer are mentioned, These can be adjusted suitably and can be used. As the photopolymerizable compound, a combination of a photopolymerizable monomer and a photopolymerizable oligomer or a photopolymerizable polymer is preferable.

Photopolymerizable Monomer The photopolymerizable monomer is one having a weight average molecular weight of less than 1000. As the photopolymerizable monomer, a polyfunctional monomer having two or more (that is, bifunctional) photopolymerizable functional groups is preferable. In the present specification, the "weight average molecular weight" is a value obtained by dissolving in a solvent such as THF and the like, and converting to polystyrene by a gel permeation chromatography (GPC) method known to date.

  Examples of the polyfunctional monomer include tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and 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, iso Anuric acid tri (meth) acrylate, isocyanuric acid di (meth) acrylate, polyester tri (meth) acrylate, polyester di (meth) acrylate, bisphenol di (meth) acrylate, diglycerin tetra (meth) acrylate, adamantyl di (meth) Acrylate, isoboronyl di (meth) acrylate, dicyclopentadi (meth) acrylate, tricyclodecane di (meth) acrylate, and those obtained by modifying these with PO, EO or the like.

  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 having high hardness.

Photopolymerizable Oligomer The photopolymerizable oligomer is one having a weight average molecular weight of 1,000 or more and less than 10,000. As a photopolymerizable oligomer, a bifunctional or higher polyfunctional oligomer is preferable. As a polyfunctional oligomer, polyester (meth) acrylate, urethane (meth) acrylate, polyester-urethane (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, isocyanurate (meth) Acrylate, epoxy (meth) acrylate, etc. are mentioned.

Photopolymerizable Polymer The photopolymerizable polymer has a weight average molecular weight of 10000 or more, and the weight average molecular weight is preferably 10000 or more and 80000 or less, and more preferably 10000 or more and 40000 or less. When the weight average molecular weight exceeds 80000, the coating suitability is lowered because the viscosity is high, and the appearance of the obtained laminated film may be deteriorated. As the photopolymerizable polymer, a bifunctional or higher polyfunctional polymer is preferable. As a polyfunctional polymer, urethane (meth) acrylate, isocyanurate (meth) acrylate, polyester-urethane (meth) acrylate, epoxy (meth) acrylate etc. are mentioned.

  The coating agent may contain, in addition to the components described above, a polymerization initiator, a catalyst for a crosslinking agent, a polymerization inhibitor, an antioxidant, an ultraviolet light absorber, a leveling agent, a surfactant, and the like.

  In addition, the optical isotropic layer composition is extruded and laminated on the irregular surface of the substrate film, and the optical isotropic layer composition is melted and extruded between the irregular surface of the substrate film and another film. And laminating are also preferable.

  The optically isotropic layer has the function of reducing irregular reflection of the uneven surface by being provided on the uneven surface, but may have other functions as well. The optically isotropic layer may have, for example, functions of a hard coat layer, an antireflective layer, an antiglare layer, an antistatic layer, and the like. The optically isotropic layer may be another film or sheet, a pressure-sensitive adhesive layer for bonding to a component of the apparatus, or an adhesive layer.

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, and most preferably 4 μm. The unevenness | corrugation of a base film can be planarized, a haze can be reduced as the said thickness is 0.5 micrometer or more, and 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, and most preferably 10 μm. It is suitable for thickness reduction that the said thickness is 30 micrometers or less.
The thickness of the optically isotropic layer is a 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, still more preferably 10 nm, particularly preferably 5 nm, from the viewpoint of suppressing the occurrence of rainbow marks.

  The upper limit of the refractive index difference between the refractive index in the direction of the highest refractive index of the optically isotropic layer and the refractive index in the direction of the lowest refractive index is preferably 0.01 from the viewpoint of suppressing the occurrence of rainbow marks Preferably it is 0.007, more preferably 0.005, particularly preferably 0.003 and most preferably 0.002.

(Laminated film)
The lower limit of the thickness of the laminated film is preferably 12 μm, more preferably 15 μm, still 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 the handling of production or subsequent processing becomes easy.
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 under a microscope, measuring the thickness of 10 points at regular intervals, and calculating the average value thereof.

  In the laminated film, only one side of the base film may be an uneven surface, but when ΔRe of the base film is relatively low, the rainbow pattern is effectively suppressed by the case where the roughness of the uneven surface is relatively small. For this purpose, it is preferable to make both sides of the substrate film uneven and to provide an optical isotropic layer on both sides.

  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 the reduction in contrast and the whitening of the screen when strong external light is received.

The laminated film may have two or more base films having an uneven surface (roughened surface), may have two or more optically isotropic layers, and the uneven surface (roughened surface) And a film or layer other than the optically isotropic layer.
Examples of lamination include the following types 1 to 4 and the like.
(Type 1) base film (concave / convex surface) / optical isotropic layer (adhesive or pressure sensitive adhesive) / other film (type 2) base film (concave / convex surface) / optical isotropic layer (adhesive or pressure sensitive adhesive) / (Concave surface) base film (type 3) base film (concave surface) / optical isotropic layer (adhesive or pressure sensitive adhesive) / other film / optical isotropic layer (adhesive or pressure sensitive adhesive) / (concave or convex surface Surface) Base film (Type 4) Other film / Optical isotropic layer (adhesive or pressure sensitive adhesive) / (concave / convex surface) Base film (concave / convex surface) / Optical isotropic layer (adhesive or pressure sensitive adhesive) / others When the ΔBfNxy of the substrate film of 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” also includes the configurations of types 1 to 4 above. In the case of type 2 to type 3, the slow axes of the two base films are preferably parallel or perpendicular to each other, and preferably parallel for ease of production. Here, “parallel or perpendicular” is acceptable from 0 degrees or 90 degrees to preferably ± 10 degrees, further ± 7 degrees, particularly ± 5 degrees.

  In the specification, when the term "pressure-sensitive adhesive" or "pressure-sensitive adhesive layer" is used, a target is coated with a coating agent for pressure-sensitive adhesive and crosslinked or dried, or a substrateless optical pressure-sensitive adhesive is transferred. Means

  The laminated film may further have various functional layers in accordance with each application. As various functional layers, a hard coat layer, an antiglare layer, an antireflective layer, a low reflective layer, a conductive layer, an antistatic layer, a colored layer, an ultraviolet absorbing layer, an antifouling layer, an adhesive layer and the like can be mentioned.

(Depolarization film)
It is preferable that the depolarizing film of this invention consists of the above-mentioned laminated | multilayer film. The depolarizing film can be suitably used as a depolarizing film in an image display device [for example, a liquid crystal display device, an EL display device (for example, an EL display device provided with a circularly polarizing plate for reflection prevention, 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. The depolarizing film is preferably provided on the viewing side of the polarizing plate or the circularly polarizing plate disposed on the viewing side of the image display cell of the image display device.
The angle between 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 It is 35-55 degrees. Within this range, it is possible to reduce the change in brightness due to the angle when looking at the neck or the like.

As a method of providing the depolarizing film, a method of simply placing the depolarizing film on the viewing side of the image display cell of the image display device, a method of bonding it on the viewing side of the viewing side polarizing plate of the image display device, the viewing side of the image display cell of the image display device And a method of bonding to a base such as a touch panel, and a method of bonding to a protective cover when the protective cover is on the viewing side of the image display cell of the image display device.
When the depolarizing film is bonded to a substrate such as a touch panel, the position of the depolarizing film may be on the viewing side of the substrate such as a 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 visible side of the protective cover or on the image display cell side.

  In bonding the depolarizing film to the target, the base film side may be bonded or the optical isotropic layer side may be bonded, and the base film or the optical isotropic layer may be displayed on the viewing side even if it is viewed from the target. It may be on the cell side.

  An adhesive or a pressure-sensitive adhesive is preferably used to bond the depolarizing film to the object. In addition, the uneven surface of the base film and the object to be bonded may be bonded with an adhesive or a pressure-sensitive adhesive corresponding to the optically isotropic layer in the present invention. In this case, the base film and the adhesive or pressure-sensitive adhesive are the laminated film as referred to in the present invention.

  Moreover, you may use the depolarizing film of this invention as a base material for providing transparent conductive layers, such as a touch panel, and a scattering prevention film of the glass base material of a touch panel or a surface protection cover. Furthermore, design such as design may be imparted to the depolarizing film by printing, or it may be a scattering prevention film such as window glass or a decoration film.

(Image display device)
The image display device of the present invention preferably includes an image display cell, a polarizer disposed on the viewing side with respect to the image display cell, and a depolarizing film disposed on the viewing side with respect to the polarizer. The substrate film side of the depolarizing film may be a polarizer side, and the optical isotropic layer side may be a polarizer side, but it is preferable that the substrate film side is a polarizer side. The angle between the transmission axis of the polarizer and the slow axis of the substrate film can be selected, for example, from the range described in the depolarizing film.

The image display device is, for example, a liquid crystal display device.
As a light source (backlight) of a liquid crystal display device, a light source of blue light emitting diode and yellow phosphor, light source of blue-green red light emitting diode, a light source of blue light emitting diode, green phosphor and red phosphor, wavelength conversion by quantum dots A light source, a semiconductor laser light source, a cold cathode tube, etc. can be used without particular limitation.

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

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

  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. It is preferable that the depolarizing film of this invention is arrange | positioned from the said circularly-polarizing plate to the visual recognition side.

Hereinafter, the present invention will be more specifically described with reference to examples. The present invention is not limited to the following examples, and can be implemented with appropriate modifications as long as they are compatible with the spirit of the present invention. These are all included in the technical scope of the present invention.
The evaluation method of the physical property in an Example is as follows.

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

(2) Thickness d of original film
The thickness at five points was measured using an electric micrometer (Filt Luff, Millitron 1245D), and the average value was determined.

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

(4) Nz coefficient The value obtained by | Bfnx-Bfnz | / | Bfnx-Bfny |

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

(6) Thickness direction retardation (Rth)
The thickness direction retardation is obtained by multiplying the film thickness d by two birefringence ΔBfNxz (= | Bfnx-Bfnz |) and ΔBfNyz (= | Bfny-Bfnz |) as viewed from the cross section in the film thickness direction. It is a parameter which shows the average of the retardation obtained. Find Bfnx, Bfny, Bfnz and film thickness d (nm) by the same method as above, calculate the average value of (ΔBfNxz × d) and (ΔBfNyz × d), and calculate the thickness direction retardation (Rth) Obtained: Rth = (ΔBfNxz × d + ΔBfNyz × d) / 2.

(7) Surface roughness (Ra, Rq, Rz, Ry, Rp, Rv, Sm)
Each parameter of surface roughness was measured from a roughness curve measured using a contact roughness meter (Mitutoyo SJ-410, detector: 178-396-2, stylus: standard stylus 122 AC 731 (2 μm)). I asked. The setting was as follows.
Curve: R
Filter: GAUSS
λc: 0.8 mm
λs: 2.5 μm
Measurement length: 5 mm
Measurement speed: 0.5 mm / s
In addition, Rq was calculated | required based on JISB0601-2001 and others based on JISB0601-1994.

(8) Thickness of Optically Isotropic Layer The thickness of the roughened base film and laminated film is as follows: embedded each film in an epoxy resin, cut out a section of the cross section, and observe with a microscope to obtain 10 points at equal intervals. The thickness was measured and taken as the average value. In addition, when the interface was hard to see, a polarization microscope was used. Moreover, 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 the optically anisotropic layer on the uneven surface of the mold release film, the thickness is about 20 μm, and the refractive index of the sample peeled from the mold release film It measured by carrying out similarly to the base film. It was confirmed that nx, ny and nz had the same value.

(Production of easy adhesion layer components)
(Polymerization of polyester resin)
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate Then, 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 performed at a temperature of 160 ° C. to 220 ° C. for 4 hours. Then, the temperature was raised to 255 ° C., and the reaction system was gradually depressurized, and then reacted under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolyester resin. The resulting copolyester resin was pale yellow and transparent. The reduced viscosity of the copolyester resin was measured and found to be 0.70 dl / g. The glass transition temperature by DSC was 40.degree.

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

(Polymerization of block polyisocyanate type crosslinking agent used in easy adhesion layer)
100 parts by mass of polyisocyanate compound having isocyanurate structure (Duranate TPA, manufactured by Asahi Kasei Chemicals Corp.) having hexamethylene diisocyanate as a raw material in a flask equipped with a stirrer, thermometer, and reflux condenser, 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 maintained at 70 ° C. for 4 hours under a nitrogen atmosphere. Thereafter, the reaction solution temperature was lowered to 50 ° C., and 47 parts by mass of methyl ethyl ketoxime was dropped. The infrared spectrum of the reaction solution was measured to confirm that the absorption of the isocyanate group disappeared, and a block polyisocyanate water dispersion having a solid content of 75% by mass was obtained.

(Preparation of coating solution for easy adhesion layer)
The following coating agents were mixed to prepare a P1 coating solution.
Water 50.00 mass%
Isopropanol 33.00 mass%
Polyester water dispersion 12.00 mass%
Blocked isocyanate type crosslinking agent 0.80 mass%
Particles 1.40% by mass
(Silica sol with an average particle size of 100 nm, solid concentration 40% by mass)
Catalyst (Organotin-based compound solid concentration 14% by mass) 0.30% by mass
0.50 mass% of surfactant
(Silicone, solid content 10% by mass)

(Production of polyester resin for film)
(Production Example 1-Polyester X)
The temperature of the esterification reactor was raised, and when it reached 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged, and 0.017 parts by mass of antimony trioxide as a catalyst while stirring Then, 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the temperature was raised under pressure, and a pressure esterification reaction was carried out under conditions of a gauge pressure of 0.34 MPa and 240 ° C. Then, the esterification reaction vessel 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. Then, after 15 minutes, dispersion treatment was carried out with a high pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and a polycondensation reaction was performed at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, filtration treatment is carried out with a Naslon (registered trademark) filter with a 95% cut diameter of 5 μm, extruded in a strand form from a nozzle, and cooling water subjected to filtration treatment (pore diameter: 1 μm or less) It was cooled, solidified, and cut into pellets. The intrinsic viscosity of the obtained polyethylene terephthalate resin (X) was 0.62 dl / g, and substantially no inert particles and internally precipitated particles were contained. (Hereafter, it is abbreviated as PET (X).)

(Production of original film A, B)
The PET (X) resin pellet containing no particles is supplied to an extruder as a raw material for a film, sheeted and extruded from a die, and then wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method. It solidified by cooling and produced the unstretched film. Next, the P1 coating solution is applied to both sides of this unstretched PET film so that the coating amount after drying is 0.12 g / m ² by reverse roll method, and then it is directed to a dryer and dried at 80 ° C. for 20 seconds did.

The unstretched film on which this coated layer was formed was guided to a tenter stretching machine, and while holding the end of the film with a clip, it 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, the film is treated at a temperature of 225 ° C. for 30 seconds, and then both ends of the film cooled to 130 ° C. are cut with a shear blade and a tension of 0.5 kg / mm ² The ear portion was cut off with the above, and wound up to obtain an original film A having a film thickness of 80 μm.

  A film was produced in the same manner as in the raw film A except that the line speed after casting was increased to change the thickness of the unstretched film, and a raw film B having a different film thickness was obtained.

(Production of original film C)
An unstretched film (coated with an easily adhesive layer) prepared 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 having a peripheral speed difference The film was drawn by 2.0 times in the running direction, and then introduced into a hot air zone at a temperature of 135 ° C. by a method similar to that for the raw film A, and then stretched by 4.0 times in the width direction to obtain a raw film C.

(Raw film D)
An unstretched film (coated with an easily adhesive layer) prepared 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 having a peripheral speed difference After stretching 3.5 times in the running direction, the film was introduced into a hot air zone at a temperature of 135 ° C. in the same manner as in the raw film A and stretched 3.5 times in the width direction to obtain a raw film D.

(Production of surface roughened film)
Affix polyurethane foam to a glass plate and affix the periphery of the original film A with a double-sided tape on top of that, and use this hand-held belt sander (sanding belt # 320) to hold the original film surface vertically, horizontally or diagonally The surface roughened film A1 was obtained by processing from a total of 4 directions of 45 degrees and 135 degrees.
The periphery of the raw film A was attached to a glass plate with a double-sided tape, set in a dry sand blaster, and treated by blowing an abrasive (sand blast treatment) to obtain a surface roughened film A2.
A masking film made of polypropylene film is laminated on one side of the raw film A, dipped in a 38% aqueous potassium hydroxide solution (95 ° C.) (chemical etching), washed with water, peeled off and dried. The surface roughened film A4 was obtained.
The surface roughened films shown in Table 2 are obtained from the raw films A, B, C, and D by changing the conditions of the belt sander (type of the sanding belt, etc.) and the conditions of the sand blast (particle diameter of the abrasive). The
The # 320 sanding belt was used for the production of B1 and C1, and the # 180 sanding belt was used for the production of A3 and D1. Moreover, the abrasives of the sand blaster used a large thing in order of A5, A6, B2, and A2.
In the belt sander treatment and sand blast treatment, the treated surface was lightly polished with # 400 sandpaper to remove the influence of local protrusions.

(Production of laminated film (or depolarizing film))
(Preparation of coating agent for optically isotropic layer)
What was shown in Table 3 as a coating agent for optical isotropic layers was prepared.

Example 1
A surface of the surface roughening film A1 of 20 cm × 30 cm is coated with a four-fold diluted solution of the above-mentioned easy adhesion layer with a solution of water / isopropanol = 2/1 and dried, and the adhesion is about 30 nm A layer was provided. Furthermore, after coating agent a for optical isotropic layers with an applicator with an applicator, it was made to harden | cure from a coated surface with a high pressure mercury lamp, and laminated film F1 was obtained.

Examples 2 to 7 and 9 to 14 and Comparative Examples 1 to 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 the surface roughened film and / or the coating agent was changed. In addition, the laminated film F15 provided the optically isotropic layer on both surfaces.

Example 8
A surface of the surface roughening film A1 of 20 cm × 30 cm is coated with a four-fold diluted solution of the above-mentioned easy adhesion layer with a solution of water / isopropanol = 2/1 and dried, and the adhesion is about 30 nm A layer was provided. Furthermore, a coating agent a for an optical isotropic layer is coated thereon with an applicator, and then a surface nickel-plated metal plate mold provided with a concavo-convex structure to overlap the coated surface to give anti-glare properties is overlaid. From the surface, it was cured with a high pressure mercury lamp to obtain a laminated film F9 having an antiglare property to the optically isotropic layer.

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

(Evaluation of laminated film)
(Observation of depolarization state)
The transmission axis of the viewing side polarizing plate and the slow axis of the base film are 45 degrees on the viewing side of the obtained laminated film on the viewing side of a liquid crystal display (regza Z20X manufactured by Toshiba Corporation) using a KSF light source, and the viewing side is optically isotropic I used cellophane tape to make a layer. While wearing polarized sunglasses, they tilted their faces and viewed the display diagonally to observe the presence or absence of rainbow marks. In addition, the display displayed full white.
○: Rainbow spots were not observed in any case Δ: Rainbow spots were slightly observed ×: Rainbow spots were observed

(Observation of contrast)
The display on the display was a landscape image, and the fluorescent light from the tabletop was illuminated from above to observe the contrast from the front.
◎: vivid contrast remained.
○: A slight decrease in contrast was observed due to scattered light.
Δ: A decrease in contrast was observed, but observation of the image was possible.
X: The image became difficult to see due to scattered light.

  Physical properties and evaluation results of the laminated films of Examples 1 to 15 and Comparative Examples 1 to 3 are shown in Table 4.

(Manufacture of display with laminated film adhered with adhesive)
(Preparation of coating agent for pressure-sensitive adhesive used as optically isotropic layer, and optical pressure-sensitive adhesive sheet)
What was shown in Table 5 as an adhesive and an optical adhesive sheet was 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 An ethyl acetate solution (solid content concentration: 30% by mass) of a copolymer (Mw = 400,000) was obtained by reacting 0.25 parts by mass of bisisobutyronitrile in ethyl acetate.

Example 16
After coating the coating agent i for adhesive as an optical isotropic layer with an applicator on the uneven surface of the surface roughened film A1 of 20 cm × 30 cm, the coated surface was cured by a high pressure mercury lamp to obtain a laminated film P1. On the adhesive layer side of the obtained laminated film P1, the transmission axis of the visual recognition side polarizing plate and the slow axis of the base film are 45 degrees on the visual recognition side of the liquid crystal display (regza Z20X manufactured by Toshiba Corporation) using a KSF light source I paste it to

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

Example 17
A coating agent k for pressure-sensitive adhesive is applied as an optically isotropic layer to a rough surface of a surface roughened film A1 of 20 cm × 30 cm with an applicator, and then dried at 100 ° C. to obtain a laminated film P2, using a KSF light source It stuck on the liquid crystal display (Regusa Z20X made by Toshiba Corporation).

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

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

  The depolarizing film of the present invention suppresses rainbow marks that occur when viewing an image through a polarizing filter such as polarizing sunglasses when used under an environment of a light source having a sharp peak, etc., and has high transparency, Vivid image displayability can be secured.

Claims (3)

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 features.
(A) At least one surface of the base film is an uneven surface, and the arithmetic average roughness (Ra) of the uneven surface is 0.2 to 10 μm.
(B) The refractive index anisotropy (Bfnx-Bfny) of a base film is 0.04-0.2.
(C) The 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.
(However, let the refractive index in the slow axis direction of the base film be Bfnx and the refractive index in the fast axis direction be Bfny) The image display apparatus which has an image display cell, the polarizer arrange | positioned on the visual recognition side rather than the said image display cell, and the depolarizing film of Claim 1 arrange | positioned on the visual recognition side rather than the said polarizer. The image display device according to claim 2, wherein an angle formed by the transmission axis of the polarizer and the slow axis of the base film is 20 to 70 degrees.