JP6453766B2 - Image display device - Google Patents

Description

The present invention relates to an image display device such as a liquid crystal display device or an organic EL display device, and particularly has good visibility regardless of the orientation of the screen when a viewer visually recognizes the screen while wearing polarized sunglasses or the like. The present invention relates to an image display device .

  The liquid crystal display device uses a liquid crystal panel in which a polarizer is disposed at least on the viewing side of the liquid crystal cell to adjust the transmission amount of the light emitted from the light source and the reflected light of the light incident on the liquid crystal cell from the outside light. Display is possible. Therefore, a polarizer is indispensable in the liquid crystal display device, and the emitted light (= image) from the liquid crystal display device reaches the viewer as linearly polarized light.

  The organic EL display device enables display by adjusting the light emission amount of an organic EL cell including an organic light emitting layer, and it is not necessary to use a polarizer in terms of display principle. However, since the thickness of the organic light emitting layer is as thin as about 10 nm, external light is reflected by the metal electrode (back electrode) and emitted to the viewing side, and when viewed from the outside, the screen looks like a mirror surface. In order to shield such specular reflection of external light, a configuration is adopted in which a circularly polarizing plate in which a polarizer and a quarter wavelength plate are laminated is disposed on the viewing side of the organic light emitting layer. In this configuration, since the quarter-wave plate of the circularly polarizing plate is arranged on the cell side and the polarizer is arranged on the viewing side, the emitted light (= image) from the organic EL display device reaches the viewer as linearly polarized light. .

  When the emitted light from the liquid crystal display device or the organic EL display device is visually recognized with the polarized sunglasses attached, the direction of the polarization axis (absorption axis) of the polarized sunglasses and the image display device The angle formed by the vibration direction of the emitted light changes. For this reason, the brightness of the screen changes depending on the arrangement angle, and there arises a problem (blackout) that the screen becomes completely dark when the polarization axis of the polarized sunglasses and the vibration direction of the emitted light are parallel.

  In order to suppress blackout when wearing polarized sunglasses, it has been proposed to arrange optical elements such as a phase difference plate and a depolarization layer further on the viewing side than the viewing side polarizer of the image display device. For example, in Patent Document 1, a quarter wavelength plate is arranged on the viewing side with respect to the viewing side polarizer, and the change in visibility is suppressed by converting the emitted light from the image display device into circularly polarized light. Has been proposed. Moreover, in patent document 2, it is proposed to use cyclic polyolefin as a material of the quarter wavelength plate arrange | positioned at the visual recognition side.

  As described in Patent Document 2, a stretched film of a cyclic polyolefin has low chemical resistance and is liable to cause a solvent crack due to contact with a human sebum component or a solvent. In recent years, an “interlayer filling structure” in which a front transparent member such as a transparent plate (window layer) or a touch panel is disposed on the viewing side of an image display panel, and a gap between the image display panel and the front transparent member is filled with an adhesive. Has been widely adopted. When a touch panel, a transparent plate, etc. are arranged by an interlayer filling structure on an image display panel in which a quarter-wave plate made of a stretched film of cyclic polyolefin is arranged on the viewing side surface, a quarter-wavelength made of cyclic polyolefin Solvent cracks can be a more prominent problem because the interlayer filling adhesive is placed adjacent to the plate.

  In Patent Document 3 and Patent Document 4, it is proposed that a stretched polyester film having a high retardation is disposed on the viewing side to cancel polarized light and suppress blackout. Polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are excellent in mechanical strength, heat resistance, and chemical resistance because the polymer is crystallized by being highly stretched and oriented. Moreover, since a polyester film can be manufactured at low cost, if a stretched polyester film is used as a retardation film arranged on the viewing side of a polarizer, it can contribute to cost reduction of an image display device.

  Patent Document 3 proposes to provide a biaxially stretched polyester film having a front retardation of about 1000 nm on the viewing side of the polarizer. However, the biaxially stretched film has a large change in the apparent retardation when viewed from an oblique direction, and when the screen is viewed from an oblique direction through polarized sunglasses, the screen may be affected by visible light interference. The problem of coloring in the iris color (current color polarization) occurs.

  Patent Document 4 proposes that the front retardation of the polyester film is further increased to suppress visible light interference and to suppress coloring of the screen due to the current color polarization when the screen is viewed through polarized sunglasses. Has been. In addition, referring to the examples of Patent Document 4, it is considered that front retardation of about 7000 nm is necessary to suppress the current color polarization. In order to give a front retardation of 7000 nm or more by biaxial stretching, a thickness of about 80 μm is required, and the cost merit of the polyester film is lost and the thickness of the device is increased.

  Patent Document 5 discloses a method of suppressing coloration due to the current color polarization by disposing a polyester film having a front retardation of about 500 nm on the viewing side of the viewing side polarizer of the image display cell. . However, suppression of the current color polarization in Patent Document 5 suppresses coloring when the image display device is viewed with the naked eye, and suppresses blackout and screen coloring when the screen is viewed through polarized sunglasses. Is not intended. The biaxially stretched polyester film used in Patent Document 5 has a Nz represented by a ratio Rth / Re of the front retardation Re and the thickness direction retardation Rth of 7 or more, and the retardation when viewed from an oblique direction. The change is large. Therefore, as in the case of Patent Document 3, when the screen is viewed from an oblique direction through polarized sunglasses, coloring of the iris pattern due to the current color polarization is observed.

JP-A-10-010523 JP 2011-1113018 A JP 2013-194107 A JP2011-107198A JP 2011-1112928 A

  As described above, biaxial stretching is essential for imparting mechanical strength and solvent resistance to the polyester film. In addition, polyester has a high birefringence and it is difficult to adjust the front retardation to about ¼ wavelength. Therefore, in the prior art, as disclosed in Patent Documents 3 and 4, a method for suppressing blackout at the time of wearing polarized sunglasses is proposed using depolarization by a stretched polyester film having a high retardation. . However, when a high retardation polyester film is used, there is a problem that the color when the screen is viewed from an oblique direction through polarized sunglasses is remarkable and the thickness of the retardation film must be increased. is there.

  In view of such a current situation, the present invention provides a blackout when a screen is viewed through polarized sunglasses by disposing a retardation film using a high birefringence material such as polyester on the viewing side of the image display cell. An object of the present invention is to provide an image display device in which a decrease in visibility due to an iris phenomenon is suppressed.

  As a result of intensive studies by the present inventors, a retardation film having a small thickness and having predetermined optical characteristics is disposed on the viewing side of the viewing side polarizer, thereby allowing the screen to be viewed through polarized sunglasses. It has been found that coloring is difficult to occur when blackout is suppressed and the screen is viewed from an oblique direction, and the present invention has been achieved.

The present invention relates to a retardation film that is used by being arranged further on the viewing side than the viewing side polarizer of an image display cell. The retardation film of the present invention has a thickness d ₁ of 7 μm or less and satisfies the following optical properties (i) and (ii).
(I) 100 nm ≦ Re ₁ ≦ 200 nm
(Ii) Nz ₁ ≦ 6

Re ₁ and Nz ₁ are the thickness of the retardation film d ₁ , the in-plane slow axis direction refractive index nx ₁ , the in-plane fast axis direction refractive index ny ₁ , and the thickness direction refraction. When the rate is nz ₁ , each is a value defined by the following formula.
Re ₁ = (nx ₁ −ny ₁ ) × d ₁
Rth ₁ = (nx ₁ −nz ₁ ) × d ₁
Nz ₁ = Rth ₁ / Re ₁

The retardation film of the present invention, when used in placed on the viewer side of the image display cell, three-dimensional center plane average roughness SRa ₁ on the viewing side surface is at 10nm or less, a three-dimensional center of the image display cell side surface it is preferable average surface roughness SRa ₂ is greater than 10 nm. A film having a small thickness tends to cause scratches due to slip during film conveyance, blocking during film winding, and the like. On the other hand, by making the average roughness of the three-dimensional center plane of one surface larger than 10 nm, the film is provided with slipperiness, and the occurrence of scratches due to slip during conveyance and the occurrence of blocking are suppressed. . Further, by setting the three-dimensional center plane average roughness of the viewing-side surface of the retardation film, that is, the exposed surface of the image display device surface, to 10 nm or less, the particles fall off from the film surface or the particles are buried inside the film. Suppressed and good visibility can be maintained.

The retardation film of the present invention is preferably one having an aromatic polyester as a main component, and particularly preferably one having polyethylene terephthalate or polyethylene naphthalate as a main component. Aromatic polyesters have high birefringence and are crystallized by stretching, and mechanical strength, solvent resistance and the like are greatly improved. Therefore, even when the thickness d ₁ is 7 μm or less, the front retardation Re ₁ can be adjusted within the range of the above formula (i), and high durability can be obtained.

  Moreover, this invention relates to the polarizing plate provided with the said retardation film on one surface of a polarizer.

  Furthermore, this invention relates to an image display apparatus provided with the said retardation film. The image display device of the present invention includes the retardation film further on the viewing side than the polarizer disposed on the viewing side of the image display cell.

In the image display device of the present invention, since the retardation film having a front retardation Re ₁ of 100 nm to 200 nm is arranged on the viewing side further than the viewing side polarizer, even when the screen is viewed with polarized sunglasses attached. The change in visibility (screen brightness) due to the screen angle is small. Further, since the Nz of the retardation film is 6 or less, even when the polarizing sunglasses are worn and the screen is viewed from an oblique direction, the screen is hardly colored.

Since the thickness d ₁ of the retardation film of the present invention is 7 μm or less, the film production cost can be reduced and the image display device can be made thinner. In particular, when an aromatic polyester such as PET or PEN is used as a material for the retardation film, the film is inexpensive and excellent in mechanical strength and solvent resistance, so that the retardation film is small in thickness. It can have high durability.

1 is a schematic cross-sectional view of an image display device (a liquid crystal display device or an organic EL display device) according to an embodiment of the present invention. It is a schematic sectional drawing which represents typically the structure of the image display apparatus (transmission type liquid crystal display device) by one Embodiment of this invention. It is a schematic sectional drawing which represents typically the film provided with a fine particle content layer on the surface of a core layer. Each of (A) to (C) is a schematic cross-sectional view schematically showing an embodiment of the retardation film of the present invention. It is a schematic sectional drawing which represents typically one form of a polarizing plate provided with the retardation film of this invention. It is a schematic sectional drawing which represents typically one form of a polarizing plate provided with the retardation film of this invention. It is a schematic sectional drawing which represents typically one Embodiment of the image display apparatus of this invention which employ | adopts an interlayer filling structure. It is a schematic sectional drawing which represents typically one Embodiment of the image display apparatus of this invention which employ | adopts an interlayer filling structure.

[Schematic configuration of image display device]
FIG. 1 is a schematic cross-sectional view of an image display device according to an embodiment of the present invention. The image display device 100 includes an image display panel 50, and the image display panel 50 includes the polarizer 11 and the retardation film 30 on the viewing side of the image display cell 5. As the image display cell 5, a liquid crystal cell or an organic EL cell is used.

  Liquid crystal cells include reflective liquid crystal cells that use external light, transmissive liquid crystal cells that use light from a light source such as a backlight, and semi-transmissive and semi-reflective types that use both external light and light from the light source. Any liquid crystal cell may be used. Further, as a driving method of the liquid crystal cell, for example, any type such as VA mode, IPS mode, TN mode, STN mode, bend alignment (π type), or the like is used. When a transmissive liquid crystal cell or a semi-transmissive / semi-reflective liquid crystal cell is employed as the liquid crystal cell, the liquid crystal panel 50 has a second polarization on the side opposite to the viewing side of the liquid crystal cell 5 as shown in FIG. The liquid crystal display device 101 includes a light source 80.

  As the organic EL cell, for example, a laminate including a transparent electrode, an organic light emitting layer, and a metal electrode in this order on a transparent substrate is used. The organic light emitting layer is a laminate of various organic thin films, and includes, for example, a hole injection layer, a light emitting layer, and an electron injection layer. The organic light emitting layer may further include a hole transport layer, an electron blocking layer, a hole blocking layer, an electron transport layer, and the like.

[Polarizer]
A polarizer 11 is disposed on the viewing side of the image display cell 5. The polarizer 11 is a linear polarizer that absorbs vibration light in the absorption axis direction and emits vibration light in the transmission axis direction as linearly polarized light. Examples of such polarizers include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, ethylene / vinyl acetate copolymer partially saponified films, iodine and dichroic dyes, etc. And uniaxially stretched by adsorbing the dichroic material, and polyene-based oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Further, a guest / host type O-type polarizer in which a liquid crystalline composition containing a dichroic substance and a liquid crystalline compound disclosed in US Pat. No. 5,523,863 is aligned in a certain direction, US Pat. An E-type polarizer or the like in which lyotropic liquid crystals disclosed in US Pat. No. 6,049,428 are aligned in a certain direction can also be used.

[Phase difference film]
(Optical characteristics of retardation film)
The image display device of the present invention includes a retardation film 30 on the further viewing side of the polarizer 11. The retardation film 30 has a thickness _{d 1} is 7μm or less. The thickness d ₁ of the retardation film 30 is more preferably 6 μm or less. The retardation film 30 satisfies the following optical properties (i) and (ii).
(I) 100 nm ≦ Re ₁ ≦ 200 nm
(Ii) Nz ₁ ≦ 6

When the thickness of the retardation film is d ₁ , the refractive index in the slow axis direction in the film plane is nx ₁ , the refractive index in the fast axis direction in the plane is ny ₁ , and the refractive index in the thickness direction is nz ₁ , Front retardation Re ₁ , thickness direction retardation Rth ₁ , and Nz ₁ are respectively defined by the following formulae. In the present specification, the refractive index, retardation, and the like are all values at a wavelength of 590 nm.
Re ₁ = (nx ₁ −ny ₁ ) × d ₁
Rth ₁ = (nx ₁ −nz ₁ ) × d _{1
Nz 1 = Rth 1 / Re 1} = (nx 1 -nz 1) / (nx 1 -ny 1)

As shown in (i) above, the front retardation Re ₁ of the retardation film 30 is 100 nm to 200 nm. If Re ₁ is within the above range, the linearly polarized light emitted from the image display cell 5 through the polarizer 11 is converted into circularly polarized light by the retardation film 30.

  When observing linearly polarized light while wearing polarized sunglasses, the angle between the direction of vibration of linearly polarized light (the transmission axis direction of the polarizer) and the direction of the polarization axis (absorption axis) of the polarized sunglasses changes (that is, the angle of the screen). The brightness of the image changes. On the other hand, if the light emitted from the image display device is circularly polarized light, there is no dependency on the azimuth angle of the polarized light.Therefore, even when the screen is viewed while wearing polarized sunglasses, Change is suppressed.

If the front retardation of the retardation film 30 is ¼ of the wavelength and the angle between the absorption axis direction of the polarizer 11 and the slow axis direction of the retardation film 30 is 45 °, an ideal circle Polarized light is obtained. In the present invention, the light emitted from the image display device is not necessarily ideal circularly polarized light, and may be elliptically polarized light. As described above, the front retardation Re ₁ of the retardation film 30 is preferably 100 nm to 200 nm, more preferably 120 nm to 180 nm, and further preferably 125 nm to 175 nm. The angle formed by the absorption axis direction of the polarizer 11 and the slow axis direction of the retardation film 30 is preferably 30 ° to 60 °, more preferably 40 ° to 50 °, and still more preferably 42 ° to 48 °. . It does not matter whether circularly polarized light and elliptically polarized light are clockwise or counterclockwise. The polarization state does not necessarily need to be completely polarized, and may be partially polarized including a state where a part of the polarization is not polarized.

As shown in (ii) above, the ratio of the thickness direction retardation Rth _{1 to} Nz _{1 of} the retardation film 30, that is, the front retardation Re ₁ is 6 or less. In the retardation film, the difference between the retardation Re in the front direction and the apparent retardation from the oblique direction tends to increase as Nz increases. Therefore, if Nz ₁ is large, the change in the apparent retardation of the retardation film when the image display device is viewed from an oblique direction becomes large, and the deviation from the quarter wavelength, that is, from the circularly polarized light of the emitted light The divergence increases. Therefore, there is a tendency that coloring occurs when the screen is viewed from an oblique direction while wearing polarized sunglasses.

As described above, Nz _{1 of the} retardation film 30 is preferably 6 or less, more preferably 5.5 or less, and even more preferably 5.3 or less. In order to improve the visibility of the oblique screen, Nz ₁ is preferably as small as possible. On the other hand, in the biaxially stretched film, Nz is always larger than 1. Moreover, when Nz is small (when biaxiality is small), the mechanical strength and solvent resistance of the film tend to be low, and this tendency is particularly strong in crystalline polymer films such as polyester. Therefore, Nz ₁ is preferably 2 or more, more preferably 3 or more, and still more preferably 4 or more.

That is, Nz _{1 of the} retardation film 30 is preferably 2 to 6, more preferably 3 to 5.5, and still more preferably 4 to 5.3. If Nz ₁ is within the above range, the retardation film 30 made of polyester or the like has high mechanical strength and solvent resistance, and a screen when the image display device is viewed from an oblique direction with polarized sunglasses attached. The coloring of is suppressed.

The retardation Rth _{1 in} the thickness direction of the retardation film 30 is preferably 1200 nm or less, more preferably 1100 nm or less, and even more preferably 1000 nm or less. In the present invention, since a biaxially stretched film is used as the retardation film 30, Rth ₁ is larger than Re ₁ . In order to set Re ₁ and Nz ₁ within the above-mentioned range, Rth ₁ is preferably 400 nm or more, more preferably 500 nm or more, and further preferably 550 nm or more.

As described above, by setting the front retardation Re ₁ of the retardation film 30 to about ¼ of the wavelength, the light emitted from the image display device is circularly polarized, and the brightness depending on the screen angle when the polarized sunglasses are worn. Change (blackout) can be suppressed. On the other hand, in order to adjust the front retardation of a film using a material having a large birefringence such as an aromatic polyester to about ¼ wavelength, it is necessary to keep the draw ratio low. If the draw ratio is small, it is difficult to control the retardation. Aromatic polyesters and the like are crystallized by biaxially stretching at a high draw ratio, which tends to improve mechanical strength, heat resistance, and solvent resistance. If the draw ratio is reduced in order to adjust the retardation to about 1/4 wavelength, the retardation film tends to be inferior in mechanical strength, heat resistance, solvent resistance and the like.

On the other hand, in the present invention, by setting the thickness d _{1 of the} retardation film to 7 μm or less, the front retardation Re ₁ is set to 1 / wavelength with the same high draw ratio as that of a general biaxially stretched polyester film. It can be adjusted to about 4. Further, by appropriately adjusting the longitudinal and lateral stretch ratios, etc., the value of Nz ₁ can be adjusted to the above-mentioned range, and the visibility of the image display device from an oblique direction can be maintained while maintaining the strength and durability of the retardation film. And the difference in visibility from the front can be reduced.

As described above, the retardation Rth _{1 in} the thickness direction of the retardation film 30 is the difference between the refractive index nx ₁ in the slow axis direction and the refractive index nz _{1 in the} film thickness direction, that is, in the thickness direction birefringence ( nx ₁ −nz ₁ ) and the thickness d ₁ . The thickness direction birefringence (nx ₁ -nz ₁ ) correlates with the degree of orientation of the molecules in the film plane. That is, as (nx ₁ −nz ₁ ) increases, the degree of in-plane orientation of the molecule increases and crystallization is also promoted, so that the film strength tends to increase, and conversely (nx ₁ −nz ₁ ) decreases. And there exists a tendency for film strength to become small.

While adjusting the front retardation Re ₁ of the retardation film 30 to a value in the vicinity of a quarter wavelength, mechanical strength and solvent resistance are imparted so as not to cause deterioration such as solvent cracks, and the film thickness is further reduced. From the viewpoint of suppressing an increase in cost and thickness of the image display device, (nx ₁ -nz ₁ ) is preferably large. (Nx ₁ -nz ₁ ) is preferably 0.06 or more, more preferably 0.1 or more, further preferably 0.13 or more, and particularly preferably 0.15 or more. Since (nx ₁ -nz ₁ ) cannot exceed the value of intrinsic birefringence, the upper limit is naturally determined. For example, when the retardation film 30 is made of polyethylene terephthalate, (nx ₁ -nz ₁ ) is generally 0.3 or less, preferably 0.25 or less. If (nx 1 _{-nz 1)} is within the above range, without lowering the uniformity of the optical properties, it is possible to increase the mechanical strength and solvent resistance of the biaxially oriented film.

(Phase difference film material)
Although the material which comprises the phase difference film 30 is not specifically limited, As mentioned above, the material which is excellent in mechanical strength and solvent resistance is used preferably, for example, what has a (semi) crystalline material as a main component is suitable. . A typical example is a polyester-based material. The degree of crystallization of polyester increases by advancing crystallization by heating or the like, and mechanical strength, dimensional stability, heat resistance, and solvent resistance can be improved. Therefore, it is preferable to use a biaxially stretched film mainly composed of polyester as the retardation film 30. Polyester has higher gas barrier properties than triacetyl cellulose (TAC) widely used as a polarizer protective film, and particularly has a low water vapor transmission rate. Therefore, the humidification durability of the polarizing plate 10 can be enhanced by using the retardation film 30 as a protective film for the polarizer 11.

  Examples of the polyester include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and diphenylcarboxylic acid. Acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalate Acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, Die -Dicarboxylic acids such as acid, sebacic acid, suberic acid, dodecadicarboxylic acid, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene Glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) A homopolymer obtained by polycondensing one kind of diol such as sulfone, a copolymer obtained by polycondensing one kind or more of dicarboxylic acid and two or more kinds of diol, or two or more kinds of dicarboxylic acid and one or more kinds Copolymers obtained by polycondensation of diols, and homopolymers thereof Blend resins of the or copolymer obtained by blending two or more. Among these, from the viewpoint of the crystallinity of the polyester, an aromatic polyester using an aromatic dicarboxylic acid as the dicarboxylic acid component is preferable, and among these, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) is particularly preferably used.

  The polyester film can be obtained by, for example, a method in which the above-described polyester resin is extruded and melted from a T-die or the like, and cooled and solidified with a casting drum to form a film (film formation). From the viewpoint of imparting crystallinity to the polyester film and achieving the above characteristics, the film after film formation is preferably biaxially stretched. In addition, the retardation film which has an aromatic polyester as a main component may contain resin other than aromatic polyester, an additive, etc. “Aromatic polyester is the main component” means that the aromatic polyester is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably 80% by weight or more based on the total weight of the film. It means to contain.

  When stretching after forming a polyester film or the like, the stretching method is not particularly limited, and a longitudinal and lateral sequential biaxial stretching method, a longitudinal and lateral simultaneous biaxial stretching method, etc. can be employed. Any appropriate stretching machine such as a machine, a pantograph type or a linear motor type biaxial stretching machine may be used.

(Surface roughness of retardation film)
In the present invention, the retardation film 30 has a three-dimensional center plane average roughness SRa ₁ on the viewing side surface of 10 nm or less and a three-dimensional center plane average roughness SRa ₂ on the image display cell side surface of greater than 10 nm. Is preferred.

  A film having a small thickness tends to cause scratches due to slip during film conveyance, blocking during film winding, and the like. Therefore, it is preferable to form minute protrusions on the film surface to impart slipperiness to the film. Generally, in a film having a large thickness, a catalyst component at the time of polymer polymerization and additives such as inert silica fine particles are present in the film as a filler, and a slip of about several tens nm to 1 μm is formed on the surface. To improve the transportability of the film. These fillers have an average particle size of about several tens of nm to several μm. When a filler with such a large particle size is present in a very thin film with a thickness of 7 μm or less, the exposure of the filler on the film surface increases, and the uniformity of the surface shape is lost, or the filler falls off the film surface. It is easy to cause troubles such as. Also, when the thickness of the film is small, in order to maintain the protrusion density on the surface and to provide good transportability, it is necessary to increase the relative addition amount of fine particles, and the transparency of the film tends to decrease. There is.

  Therefore, in a film having a small thickness, as shown in FIG. 3, by forming the fine particle-containing layers 321 and 331 on the surface of the core layer 311 that does not contain a filler, protrusions of an appropriate size are appropriately formed on the film surface. It is preferable to improve the transportability by forming with a density. In the fine particle-containing layers 321, 331, fine particles 361, 371 made of inert silica or the like are dispersed in the binder resins 341, 351.

In order to impart an appropriate slippage to the film and improve the transportability, it is preferable that the three-dimensional center plane average roughness SRa of at least one surface is larger than 10 nm. In the embodiment in which the fine particle-containing layer is provided on the surface of the core layer, the surface roughness of the film can be appropriately adjusted by adjusting the average particle size and content of the fine particles in the binder resin. On the other hand, when the particle size of the filler is large or the filler content is large, when the surface of the filler-containing layer is wiped with a non-woven fabric or the like, the fine particles fall off from the fine-particle-containing layer or into the film In some cases, the fine particles are buried, resulting in a local visibility change on the film surface and a decrease in mechanical strength. Therefore, in the retardation film of the present invention, the surface exposed to the viewing-side surface when forming the image display device has no projections due to the fine particles, or has fine projections that do not cause the fine particles to fall off or be buried. It is preferable to have. From this point of view, the three-dimensional center plane average roughness SRa ₁ on the viewing side surface of the phase difference film 30 is preferably 10nm or less, more preferably 8 nm, more preferably 7nm or less.

As described above, in order to improve the transportability of the film, it is preferable that one surface of the retardation film has a predetermined surface roughness. Therefore, the retardation film 30 of the present invention, the three-dimensional center plane average roughness of the image display cell 5 side surface SRa ₂ is preferably larger than 10 nm, more preferably 15nm or more, is 20nm or more More preferably. As shown in FIG. 4A, by forming the fine particle-containing layer 32 only on one surface (viewing side surface) of the core layer 31, the retardation film 30 having different surface roughnesses on the front and back sides can be formed. Further, as shown in FIG. 4B, by changing the average particle size of the fine particles 36 and 37 and the content of fine particles in the fine particle-containing layers 32 and 33 on one surface and the other surface of the core layer 31. In addition, retardation films having different surface roughness can be formed on the front and back sides. As shown in FIG. 4C, a fine particle-containing layer 32 may be formed on one surface of the core layer 31, and a coating layer 39 containing no fine particles may be formed on the other surface. For example, when the polyester retardation film 30 includes the coating layer 39 on the surface of the core layer 31 made of polyester on the image display cell 5 side, the adhesion with the polarizer 11 and the like can be improved.

  The fine particle-containing layers 32 and 33 and the coating layer 39 may be formed on the surface of the core layer 31 at any stage of the retardation film 30 formation process. For example, at the time of melt film formation, the core layer, the fine particle-containing layer, and the coating layer can be simultaneously formed by multilayer coextrusion. When the fine particle-containing layer or the coating layer is formed after the core layer is formed, these layers may be formed either before or after stretching. When performing sequential biaxial stretching, the fine particle-containing layers 32 and 33 and the coating layer 39 can also be formed after longitudinal stretching (roll stretching) and before lateral stretching (tenter stretching). If the fine particle-containing layer or coating layer forming solution is applied to the film surface before transverse stretching, the solution can be dried by heating during transverse stretching, thus simplifying the process and increasing the productivity of the retardation film Can do.

[Formation of image display device]
As shown in FIG. 1, the image display panel 50 is formed by disposing the polarizer 11 and the retardation film 30 on the viewing side surface of the image display cell 5. Further, as necessary, as shown in FIG. 2, a second polarizer 21 is disposed on the side opposite to the viewing side of the image display cell 5. As the second polarizer, for example, a linear polarizer is used similarly to the polarizer 11. Various optical layers such as a polarizer protective film (transparent protective film) and an optical compensation film may be disposed between the image display cell 5 and the polarizers 11 and 21.

  As a method of disposing the polarizer 11 and the retardation film 30 on the image display cell 5, it is preferable to laminate and fix an appropriate adhesive layer between the layers. From the standpoint that each layer can be easily bonded, the viewing-side polarizing plate 10 in which the polarizer 11 and the retardation film 30 are laminated and fixed via an appropriate adhesive layer (not shown) is formed, and an appropriate adhesive layer is formed. The viewing-side polarizing plate 10 is preferably bonded to the image display cell 5 via 61.

  5 and 6 are cross-sectional views schematically showing a configuration example of the viewing side polarizing plate used in the image display device of the present invention. In the form shown in FIG. 5, the retardation film 30 is disposed on the viewing side of the polarizer 11, and the transparent protective film 12 is disposed on the image display cell side of the polarizer 11. An adhesive layer 61 for attaching the polarizing plate 10 and the image display cell 5 is attached to the surface of the transparent protective film 12. As shown in FIG. 6, another transparent protective film 13 or the like may be disposed between the polarizer 11 and the retardation film 30.

  In the configuration in which the viewing-side polarizing plate 10 includes the transparent protective film 12 on the surface of the polarizer 11 on the image display cell 5 side, both surfaces of the polarizer 11 are protected by the retardation film 30 and the transparent protective film 12. The durability of the plate 10 is improved. The material and optical characteristics of the transparent protective film 12 are not particularly limited. However, since the transparent protective film 12 is disposed between the polarizer 11 and the image display cell 5, it is optically isotropic having substantially no birefringence. Even if it has a birefringence, it is preferable to use one having excellent retardation value and in-plane uniformity in the optical axis direction. Moreover, a retardation film (optical compensation layer) can also be used as the transparent protective film 12.

  When the image display cell 5 is a liquid crystal cell, a retardation film having appropriate optical characteristics (birefringence) is used as the transparent protective film 12 according to the driving method (TN, VA, IPS, etc.) of the liquid crystal cell. Thus, optical compensation such as viewing angle improvement and contrast enhancement can be performed. When the image display cell 5 is an organic EL cell, by using a retardation film having a front retardation of ¼ wavelength (approximately 100 to 200 nm) as the transparent protective film 12, a mirror surface of external light by the organic EL cell is used. Reflection can be shielded. In addition, these retardation films may be arrange | positioned between the polarizing plate 10 and the image display cell 5 as a different body from the transparent protective film 12 of the polarizer 11. FIG.

  As a material for the transparent protective films 12 and 13, a transparent polymer having uniform optical properties is preferably used. In particular, from the viewpoint of transparency, cellulose resin, cyclic polyolefin resin (norbornene resin), polycarbonate resin, polyarylate resin, amorphous polyester resin, polyvinyl alcohol resin, polysulfone resin, polyimide resin, etc. Amorphous polymers are preferably used.

  As shown in FIG. 2, when the 2nd polarizer 21 is arrange | positioned on the opposite side to the visual recognition side of the image display cell 5, a transparent protective film or phase difference is provided on one or both surfaces of the 2nd polarizer 21. The light source side polarizing plate on which a film or the like is laminated may be bonded to the image display cell 5 through an appropriate adhesive layer.

  Adhesives that make up the adhesive layer for bonding each layer include acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxy polymers, and fluorine-based adhesives. What uses polymers, such as a polymer and a rubber-type polymer, as a base polymer can be selected suitably, and can be used. A water-based adhesive is preferably used for laminating the polarizer and the retardation film, and laminating the polarizer and the transparent protective film, and among them, those mainly composed of a polyvinyl alcohol-based resin are preferably used.

  As the adhesive layer 61 used for bonding the image display cell 5 and the viewing-side polarizing plate 10, a pressure-sensitive adhesive (adhesive) layer is preferably used. An adhesive layer is also preferably used for bonding the image display cell 5 and the light source side polarizing plate 20 together. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layers 61 and 62 is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is used as a base polymer. Can be appropriately selected and used. In particular, an acrylic pressure-sensitive adhesive that is excellent in transparency, exhibits appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and is excellent in weather resistance, heat resistance, and the like can be preferably used.

  The exposed surface of the pressure-sensitive adhesive layer 61 attached to the surface of the polarizing plate 10 may be temporarily covered with a release film (separator) for the purpose of preventing contamination until it is put to practical use. preferable. Thereby, it can prevent contacting an adhesive layer in the usual handling state. As a release film, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foamed sheet or metal foil, laminate thereof, if necessary, silicone-based or long-chain alkyl-based, Appropriate ones according to the prior art such as those coated with an appropriate release agent such as fluorine-based or molybdenum sulfide can be used.

  An image display device can be obtained by further incorporating a light source 80 and a drive circuit into the image display panel 50 as necessary. In addition to these, various members necessary for forming the image display device can be combined.

  FIG. 7 is a cross-sectional view schematically showing a configuration example of the image display device 102 including the front transparent member 70 on the viewing side of the image display panel (transmission type liquid crystal panel) 50. Examples of the front transparent member 70 include a front transparent plate (window layer) and a touch panel. As the front transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate is used. As the touch panel, a touch panel of an arbitrary system such as a resistive film system, a capacitance system, an optical system, and an ultrasonic system is used.

  When a front transparent member such as a window layer or a touch panel is disposed on the viewing side surface of the image display panel, if there is an air layer (gap) between the image display panel 50 and the front transparent member 70, the air interface is refracted. Since the reflectance due to the rate difference is large, the visibility of the image display device tends to be reduced. Therefore, an “interlayer filling structure” in which the space between the image display panel 50 and the front transparent member 70 is filled with the adhesive layer 65 to reduce the difference in refractive index at the interface is preferably employed.

  FIG. 8 is a cross-sectional view schematically showing another configuration example of the image display device 103 including the front transparent member 70 on the viewing side of the image display panel (transmission type liquid crystal panel) 50. In the embodiment shown in FIG. 8, on the viewing side of the image display cell 5, the viewing-side polarizing plate 10 including the transparent protective films 12 and 13 on both sides of the polarizer 11 is disposed, and an adhesive layer (interlayer filler) is disposed thereon. ) 65 is disposed through the front transparent member 70, and the retardation film 30 is disposed on the front transparent member 70. As shown in FIG. 8, the retardation film 30 of the present invention does not need to be disposed adjacent to the polarizer 11, and may be disposed on the viewer side of the polarizer 11 via another optical member. Good. 8 illustrates an example in which the retardation film 30 is provided on the viewing side of the front transparent member 70, the retardation film may be disposed on the front transparent member 70 on the image display panel 50 side.

  The image display device of the present invention includes, for example, monitors for OA devices such as personal computers, mobile monitors such as mobile phones, smartphones, digital cameras, portable information terminals, portable game machines, video cameras, televisions, car navigation systems, and commercial facilities. It can be used for various purposes such as exhibition equipment such as an information display for monitoring, and a monitor for monitoring. In particular, the image display device of the present invention suppresses a change in visibility (brightness of the screen) due to the angle of the screen when wearing polarized sunglasses, so that mobile devices that are often used outdoors It is suitably used as a display for in-vehicle devices.

  Hereinafter, the present invention will be described by way of examples in which a retardation film is disposed on the surface of a transmissive liquid crystal display device, but the present invention is not limited to these examples.

[Measurement and evaluation methods]
(Retardation)
Using a polarization / phase difference measurement system (Axometrics product name “AxoScan”), in a 23 ° C. environment, the front wavelength is measured at a measurement wavelength of 590 nm, and the film is tilted by 40 ° with the slow axis direction as the center of rotation. The retardation in the obtained state was measured, and front retardation Re ₁ , thickness direction retardation Rth ₁ , and Nz ₁ were calculated from these measured values. In the calculation, the average refractive index of polyethylene terephthalate was set to 1.60.

(Three-dimensional center plane average roughness)
Using a surface roughness measuring instrument (manufactured by Kosaka Laboratory, model number: SE3500K), a three-dimensional roughness curved surface is measured in the range of 500 μm × 500 μm (scanning speed: 0.1 mm / second, cutoff: 0.25 mm). The original center plane average roughness SRa was calculated.

(Wiping test)
A nonwoven fabric was placed on the surface of the polyester film on the liquid crystal display device, and was wiped 10 times at a speed of 100 mm / sec while applying a pressing force of 0.98 N / 25 mm. The surface after wiping was observed visually, and the presence or absence of a change in the turbidity of the surface before and after wiping was confirmed.

(Visibility evaluation of image display device)
In a bright environment, a white image was displayed on the liquid crystal display device, and was observed from the front with polarized sunglasses attached, and the presence or absence of iridescent coloring was confirmed. The screen was rotated 360 ° as it was, and the presence or absence of a change in screen brightness (blackout) due to the angle was confirmed. Moreover, the presence or absence of a difference in visibility between the case where the image display device was viewed from the front and the case where the image display device was viewed from an oblique direction (polar angle 20 ° direction) was confirmed.

[Example 1]
(Polyester retardation film)
A biaxially stretched polyester film having a thickness of 4.5 μm, a front retardation Re ₁ = 170 nm, a thickness direction retardation Rth ₁ = 935 nm, and Nz ₁ = 935 nm was prepared. This polyester film had a three-dimensional center plane average roughness SRa ₁ on _one side of 5.2 nm and a three-dimensional center plane average roughness SRa ₂ on the other side of 10.5 nm.

(Production of liquid crystal display device for evaluation)
A liquid crystal display device having a polarizing plate on the viewing side surface of the liquid crystal display cell was prepared. The viewing side polarizing plate of this liquid crystal display device was provided with an optically isotropic transparent protective film on the viewing side of the polarizer. On the polarizing plate, the above retardation film is bonded via an adhesive so that the angle formed by the absorption axis direction of the polarizer and the slow axis direction (MD direction) of the retardation film is 45 °. Combined. At the time of bonding, the polyester retardation film was arranged so that the surface of SRa = 10.5 nm was on the polarizing plate side and the surface of SRa = 5.2 nm was on the viewing side.

[Examples 2 to 4 and Comparative Examples 1 to 5]
A liquid crystal display device for evaluation was produced in the same manner as in Example 1 except that the polyester retardation film having the thickness, surface roughness and optical properties shown in Table 1 was used.

[Reference Example 1]
In laminating the polarizing plate and the polyester retardation film, the surface of SRa = 5.2 nm was disposed on the polarizing plate side, and the surface of SRa = 10.5 nm was on the viewing side. Otherwise, an evaluation liquid crystal display device was produced in the same manner as in Example 1.

[Evaluation results]
The results of the visibility and the wiping test of the liquid crystal display devices of each of the above Examples, Comparative Examples and Reference Examples, the optical characteristics of the polyester retardation film used for each liquid crystal display device and the three-dimensional center plane average roughness (SRa) The results are shown in Table 1. In Table 1, the three-dimensional center plane average roughness of the viewing side surface of the polyester retardation film is SRa ₁ , and the three-dimensional center plane average roughness of the liquid crystal cell side surface is SRa ₂ .

  As shown in Table 1, in the image display devices of Examples 1 to 4 provided with the retardation film of the present invention, when the screen is viewed while wearing polarized sunglasses, the coloring of iris colors by blackout or current color polarization is performed. No visibility was observed. Further, the visibility when the screen was viewed from an oblique direction was also good as in the front view.

In Comparative Examples 1 and 2, since the front retardation is greatly deviated from the ¼ wavelength, when the screen is viewed while wearing polarized sunglasses, the brightness varies greatly depending on the angle of the screen. In Comparative Examples 3 and 4, the front view visibility was as good as in Examples 1 to 4, but because the Nz _{1 of the} retardation film is large, the change field from the front view when viewed from an oblique direction. It was big.

  The liquid crystal display device of Reference Example 1 showed good visibility as in Example 1. However, the turbidity of the wiping portion was reduced after the wiping test because SRa on the viewing side surface was large. For this reason, the difference in visibility from the surroundings is remarkable in the portion where the wiping test was performed, and local visibility was lowered. From this result, it can be said that it is preferable to reduce SRa on the surface on the viewing side, particularly when the retardation film of the present invention is disposed on the surface on the viewing side of the image display device.

5: Image display cell 10, 20: Polarizing plate 11, 21: Polarizer 12, 13: Transparent protective film 30: Retardation film 31: Core layer 32, 33: Fine particle containing layer 39: Coating layer 50: Image display panel 61 62: Adhesive layer (adhesive layer)
65: Adhesive layer (interlayer filler)
70: Front transparent member 80: Light source 100, 101, 102, 103: Image display device

Claims (3)

An image display cell, and a polarizer and a retardation film sequentially disposed on the viewing side of the image display cell,
The retardation film has a thickness d ₁ is at 7μm or less, a three-dimensional center plane average roughness SRa ₁ on the viewing side surface 10nm or less, a three-dimensional center plane average roughness of the image display cell side surface SRa ₂ is An image display device that is larger than 10 nm and satisfies the following optical properties (i) and (ii).
(I) 100 nm ≦ Re ₁ ≦ 200 nm
(Ii) Nz ₁ ≦ 6
Here, Re ₁ and Nz ₁ are d ₁ as the thickness of the retardation film, nx _{1 as} the refractive index in the slow axis direction in the film plane, ny _{1 as} the refractive index in the fast axis direction in the plane, and the thickness. When the refractive index in the direction is nz ₁ , each is a value defined by the following formula.
Re ₁ = (nx ₁ −ny ₁ ) × d ₁
Rth ₁ = (nx ₁ −nz ₁ ) × d ₁
Nz ₁ = Rth ₁ / Re ₁ The image display device according to claim 1, wherein the retardation film is mainly composed of aromatic polyester. Aromatic polyester is polyethylene terephthalate or polyethylene naphthalate, the image display apparatus according to claim 2.

Images