TWI545375B - An image display device, a retardation film for use, and a polarizing plate - Google Patents

Description

Image display device, phase difference film and polarizing plate therefor

The present invention relates to an image display device such as a liquid crystal display device or an organic EL (Electroluminescence) display device, and more particularly to a case where a screen is visually recognized while a viewer wears polarized sunglasses or the like. An image display device having good visibility regardless of the orientation of the screen. Further, the present invention relates to a retardation film and a polarizing plate for forming the liquid crystal display device.

The liquid crystal display device can display by the liquid crystal panel in which the polarizing element is disposed on at least the viewing side of the liquid crystal cell to adjust the amount of light emitted from the light source or the amount of light reflected from the light from the external light. Therefore, in the liquid crystal display device, a polarizing element is necessary, and the emitted light (=image) from the liquid crystal display device reaches the viewer in the form of linearly polarized light.

The organic EL display device can display by adjusting the amount of light emitted from the organic EL unit having the organic light-emitting layer, and the display principle does not require the use of a polarizing element. However, since the thickness of the organic light-emitting layer is extremely thin to about 10 nm, external light is reflected by the metal electrode (back surface electrode) and emitted to the viewing side, and when viewed from the outside, the screen looks like a mirror surface. In order to block the specular reflection of such external light, a circular polarizing plate in which a polarizing element and a quarter-wave 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 disposed on the unit side and the polarizing element is disposed on the viewing side, the emitted light (=image) from the organic EL display device reaches the viewer in the form of linearly polarized light.

If the emitted light from the liquid crystal display device or the organic EL display device is viewed in a state in which the polarized sunglasses are worn, the direction of the polarizing axis (absorption axis) of the polarized sunglasses and the image display are changed as the arrangement angle of the screen changes. The angle formed by the direction of vibration of the outgoing light of the device changes. Therefore, there arises a problem that the brightness of the screen changes depending on the arrangement angle, and the screen is black (black out) when the polarization axis of the polarized sunglasses is parallel to the vibration direction of the outgoing light.

In order to suppress blackout when the polarized sunglasses are worn, it is proposed to arrange optical elements such as a phase difference plate or a polarization canceling layer on the viewing side of the viewing side polarizing element of the image display device. For example, Patent Document 1 proposes to convert a light emitted from an image display device into a circularly polarized light by arranging a quarter-wave plate on the viewing side of the viewing-side polarizing element, thereby suppressing a change in visibility. Further, Patent Document 2 proposes the use of a cyclic polyolefin as a material for a quarter-wave plate disposed on the viewing side.

As described in Patent Document 2, the stretched film of the cyclic polyolefin has low chemical resistance and is liable to cause solvent cracking due to contact with a human sebum component or a solvent. In recent years, a front transparent member such as a transparent plate (window layer) or a touch panel is disposed on the viewing side of the image display panel, and an interlayer filling is used to fill the gap between the image display panel and the front transparent member. structure". When a touch panel or a transparent plate is disposed on an image display panel in which a quarter-wave plate including a stretched film of a cyclic polyolefin is disposed on the viewing side surface, a ring-shaped poly is included in the case where a touch panel or a transparent plate is disposed. The 1/4 wavelength plate on the olefin is adjacent to the interlayer filling agent, so solvent cracking may become a more significant problem.

Patent Document 3 and Patent Document 4 propose to eliminate the polarized light by disposing the polyester film having a high phase retardation on the viewing side, thereby suppressing blackout. Mechanical strength, heat resistance, and chemical resistance by crystallizing a polymer by highly extending a polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) Excellent. Further, since the polyester film can be produced at low cost, if the stretched polyester film is used as the retardation film disposed on the viewing side of the polarizing element, the cost of the image display device can be reduced.

Patent Document 3 proposes that a biaxially stretched polyester film having a front phase retard of about 1000 nm is provided on the viewing side of the polarizing element. However, when the biaxially stretched film is viewed from an oblique direction, the apparent phase retardation changes greatly, and when the screen is viewed from the oblique direction through the polarized sunglasses, a screen is generated due to interference of visible light. Coloring is a problem of rainbow color (color shifting).

Patent Document 4 proposes to suppress interference of visible light by further increasing the front phase retardation of the polyester film, thereby suppressing coloring of the screen due to color shifting light when the screen is viewed through the polarized sunglasses. Further, referring to the examples of Patent Document 4 and the like, it is considered that a front phase retardation of about 7000 nm is required in order to suppress color shifting light. In order to impart a frontal phase retardation of 7000 nm or more by biaxial stretching, a thickness of about 80 μm is required, and the cost advantage of the polyester film is lost, and the thickness of the device is increased.

Patent Document 5 discloses that coloring due to color shifting is suppressed by disposing a polyester film having a front surface retardation of about 500 nm on the viewing side of the polarizing element on the viewing side of the image display unit. However, the suppression of the color polarization in Patent Document 5 suppresses the coloring when the image display device is visually recognized, and does not intend to suppress the blackout or the color of the screen when the screen is viewed through the polarized sunglasses. The biaxially stretched polyester film used in Patent Document 5 has a Nz represented by a ratio Rth/Re of the front phase retardation Re and a thickness direction phase retardation Rth of 7 or more, and a phase retardation when viewed from an oblique direction. The change is larger. Therefore, similarly to the case of Patent Document 3 described above, if the screen is viewed from the oblique direction via the polarized sunglasses, the color of the iridescent pattern due to the color shifting light is observed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 10-010523

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2011-113018

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2013-194107

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2011-107198

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2011-112928

As described above, in order to impart mechanical strength, solvent resistance, and the like to the polyester film, biaxial stretching is necessary. Further, the birefringence of the polyester is large, and it is difficult to adjust the front phase retardation to about 1/4 wavelength. Therefore, in the prior art, as disclosed in Patent Documents 3 and 4, there has been proposed a method of suppressing blackout when wearing polarized sunglasses by eliminating polarized light by a high phase retarded stretched polyester film. However, in the case of using a polyester film having a high phase retardation, there is a problem that the coloring is conspicuous or the thickness of the retardation film has to be increased when the screen is viewed obliquely from the oblique direction of the polarized sunglasses.

In view of such circumstances, it is an object of the present invention to provide a case where a retardation film using a high birefringent material such as polyester is disposed on a viewing side of an image display unit and is suppressed from being viewed by a polarized sunglasses. An image display device that reduces visibility due to blackout or iridescence.

As a result of intensive studies, the inventors of the present invention have found that by providing a retardation film having a small thickness and having specific optical characteristics on the viewing side of the viewing-side polarizing element, it is suppressed from viewing the screen through the polarized sunglasses. In the case of blackening, it is also difficult to cause coloring when viewing the screen from the oblique direction, thereby completing the present invention.

The present invention relates to a retardation film which is disposed on the viewing side of the viewing side polarizing element of the image display unit. The retardation film of the present invention has a thickness d ₁ of 7 μm or less and satisfies the optical characteristics of the following (i) and (ii).

(i) 100 nm ≦ Re ₁ ≦ 200 nm

(ii) Nz ₁ ≦ 6

In Re ₁ and Nz ₁ , the thickness of the retardation film is d ₁ , the refractive index in the slow axis direction in the film plane is nx ₁ , and the refractive index in the in-plane axial direction is set to ny. _1. When the refractive index in the thickness direction is set to nz ₁ , they are each 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

When the retardation film of the present invention is used in the viewing side of the image display unit, it is preferable that the three-dimensional center plane average roughness SRa ₁ of the viewing side surface is 10 nm or less, and the three-dimensional surface of the image display unit side surface. The center plane average roughness SRa _{2 is} greater than 10 nm. The film having a small thickness is liable to cause scratches due to sliding when the film is conveyed or adhesion when the film is taken up. On the other hand, by making the three-dimensional center plane average roughness of one surface larger than 10 nm, the film is provided with slidability, thereby suppressing scratches or adhesion due to sliding during transportation. Further, by setting the three-dimensional center plane average roughness of the surface on the viewing side of the retardation film, that is, the exposed surface of the image display device to 10 nm or less, the particles are prevented from falling off from the surface of the film or the particles are buried in the film. Can maintain good visibility.

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

Moreover, the present invention relates to a polarizing plate comprising the retardation film on one side of a polarizing element.

Furthermore, the present invention relates to an image display device including the above retardation film. The image display device of the present invention includes the retardation film on the viewing side of the polarizing element disposed on the viewing side of the image display unit.

When the apparatus since the viewer side polarizer than closer to the visible side, a front retardation Re ₁ of 100nm ~ 200nm of the retardation film, and therefore even to wear polarized sunglasses visibility scenario screen, the result of a screen image of the present invention show The change in visibility (the brightness of the picture) caused by the angle is also small. Further, since the Nz of the retardation film is 6 or less, even when the polarized sunglasses are viewed from the oblique direction, it is difficult to produce the color of the screen.

Since the retardation film of the present invention has a thickness d ₁ of 7 μm or less, the production cost of the film can be reduced, and the thickness of the image display device can be reduced. In particular, when an aromatic polyester such as PET or PEN is used as the material of the retardation film, since the film is inexpensive and excellent in mechanical strength or solvent resistance, although the thickness of the retardation film is small, it may be high. Durability.

5‧‧‧Image display unit

10‧‧‧Polar plate

11‧‧‧Polarized components

12‧‧‧Transparent protective film

13‧‧‧Transparent protective film

20‧‧‧Polar plate

21‧‧‧Polarized components

30‧‧‧ phase difference film

31‧‧‧ core layer

32‧‧‧Microparticle-containing layer

33‧‧‧Microparticle-containing layer

36‧‧‧Microparticles

37‧‧‧Microparticles

39‧‧‧ Coating layer

50‧‧‧Image display panel

61‧‧‧Next layer (adhesive layer)

62‧‧‧Next layer (adhesive layer)

65‧‧‧Next layer (interlayer filler)

70‧‧‧ front transparent member

80‧‧‧Light source

100‧‧‧Image display device

101‧‧‧Image display device

102‧‧‧Image display device

103‧‧‧Image display device

311‧‧‧ core layer

321‧‧‧Microparticle-containing layer

331‧‧‧Microparticle-containing layer

341‧‧‧Binder resin

351‧‧‧Binder resin

361‧‧‧Microparticles

371‧‧‧Microparticles

Fig. 1 is a schematic cross-sectional view showing an image display device (liquid crystal display device or organic EL display device) according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing the configuration of an image display device (transmissive liquid crystal display device) according to an embodiment of the present invention.

Fig. 3 is a schematic cross-sectional view schematically showing a film having a fine particle-containing layer on the surface of a core layer.

4(A) to 4(C) are schematic cross-sectional views schematically showing one embodiment of the retardation film of the present invention.

Fig. 5 is a schematic cross-sectional view schematically showing one embodiment of a polarizing plate including the retardation film of the present invention.

Fig. 6 is a schematic cross-sectional view schematically showing one embodiment of a polarizing plate including the retardation film of the present invention.

Fig. 7 is a schematic cross-sectional view showing an embodiment of an image display device of the present invention which is constructed by interlayer filling.

Figure 8 is a view schematically showing an image display device of the present invention which is constructed by interlayer filling; A schematic cross-sectional view of an embodiment.

[Summary structure of image display device]

Fig. 1 is a schematic cross-sectional view showing an image display apparatus according to an embodiment of the present invention. The image display device 100 includes an image display panel 50 including a polarizing element 11 and a retardation film 30 on the viewing side of the image display unit 5. As the image display unit 5, a liquid crystal cell or an organic EL unit is used.

As the liquid crystal cell, a transflective liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, and a transflective liquid crystal cell using both external light and light from the light source may be used. Any of them. Further, as a driving method of the liquid crystal cell, for example, a VA (Vertical Aligned) mode, an IPS (In plane switching) mode, a TN (Twisted Nematic) mode, and an STN (Super Twisted Nematic) can be used. Any type of super twisted nematic) mode or curved alignment (π type). In the case where a transmissive liquid crystal cell or a transflective liquid crystal cell is used as the liquid crystal cell, as shown in FIG. 2, the liquid crystal panel 50 includes the second polarizing element 21 on the side opposite to the viewing side of the liquid crystal cell 5, Further, the liquid crystal display device 101 includes a light source 80.

As the organic EL unit, for example, a laminate having a transparent electrode, an organic light-emitting layer, and a metal electrode can be sequentially provided on a transparent substrate. 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.

[Polarizing element]

The polarizing element 11 is disposed on the viewing side of the image display unit 5. The polarizing element 11 is a linear polarizing element that absorbs the vibration light in the absorption axis direction and emits the vibration light in the transmission axis direction as linearly polarized light. As such a polarizing element, for example, polyvinyl alcohol is used. a hydrophilic polymer film such as a film, a partially formalized polyvinyl alcohol film, or a vinyl acetyl acetate copolymer-based partial saponified film, which adsorbs a dichroic substance such as iodine or a dichroic dye, and is uniaxially stretched; and polyethylene A polyene-based alignment film such as a dehydrated product of an alcohol or a dehydrochlorinated product of polyvinyl chloride. Further, a guest-host type O-type polarizing element in which a liquid crystalline composition containing a dichroic substance and a liquid crystalline compound is aligned in a fixed direction, which is disclosed in U.S. Patent No. 6,049,428, etc., may be used as disclosed in U.S. Patent No. 5,523,863. An E-type polarizing element in which a liquid crystal is aligned in a fixed direction.

[Relativity film] (Optical characteristics of retardation film)

The image display device of the present invention includes a retardation film 30 on the viewing side of the polarizing element 11. The thickness d ₁ of the retardation film 30 is 7 μm or less. The thickness d _{1 of the} retardation film 30 is more preferably 6 μm or less. The retardation film 30 satisfies the optical characteristics of the following (i) and (ii).

(i) 100 nm ≦ Re ₁ ≦ 200 nm

(ii) Nz ₁ ≦ 6

The thickness of the retardation film is d ₁ , the refractive index in the direction of the slow axis in the film plane is nx ₁ , the refractive index in the direction of the in-plane axis is ny ₁ , and the refractive index is in the thickness direction. When the rate is set to nz ₁ , the front phase retardation Re ₁ and the thickness direction phase delays Rth ₁ and Nz ₁ are respectively defined by the following equations. Further, in the present specification, the refractive index, the phase 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 the above (i), the front surface retardation Re ₁ of the retardation film 30 is from 100 nm to 200 nm. When Re ₁ is in the above range, the linearly polarized light emitted from the image display unit 5 via the polarizing element 11 is converted into circular polarized light by the retardation film 30.

If the linear polarized light is observed while wearing polarized sunglasses, the straight line is biased. The brightness of the image changes when the angle between the direction of vibration of the light (the direction of the transmission axis of the polarizing element) and the direction of the polarization axis (absorption axis) of the polarized sunglasses changes (ie, when the angle of the picture changes). On the other hand, when the emitted light from the image display device is circularly polarized, since the azimuth angle is not dependent, even if the screen is viewed in a state in which the polarized sunglasses are worn, the angle of the screen changes. The resulting change in brightness is also suppressed.

If the front phase retardation of the retardation film 30 is 1/4 of the wavelength, and the angle between the absorption axis direction of the polarizing element 11 and the slow axis direction of the retardation film 30 is 45°, an ideal circular polarization can be obtained. . In the present invention, the light emitted from the image display device does not necessarily need to be an ideal circular polarized light, and may be elliptically polarized light. The front surface retardation Re _{1 of the} retardation film 30 is preferably from 100 nm to 200 nm, more preferably from 120 nm to 180 nm, even more preferably from 125 nm to 175 nm, as described above. Further, the angle between the absorption axis direction of the polarizing element 11 and the slow axis direction of the retardation film 30 is preferably 30 to 60, more preferably 40 to 50, and further preferably 42 to 48. . Furthermore, circular polarization and elliptically polarized light are either clockwise or counterclockwise. The polarized state does not necessarily need to be completely polarized, and may be partial polarized light including a part of the unpolarized state.

As shown in the above (ii), the ratio of Nz _{1 of the} retardation film 30, that is, the thickness direction phase retardation Rth ₁ to the front surface retardation Re ₁ is 6 or less. The retardation film has a tendency that the larger the Nz is, the larger the difference between the phase retardation Re in the front direction and the apparent phase retardation in the oblique direction is. Therefore, if Nz _{1 is} large, the change in the phase retardation of the phase difference film in the case of viewing the image display device from the oblique direction is increased, and the deviation from the 1/4 wavelength, that is, the outgoing light and the circle The deviation between the polarized lights increases. Therefore, there is a tendency to cause coloring when the polarized sunglasses are viewed from the oblique direction.

As described above, the Nz _{1 of the} retardation film 30 is preferably 6 or less, more preferably 5.5 or less, still more preferably 5.3 or less. In terms of improving the visibility of the oblique direction picture, Nz _{1 is} preferably as small as possible. On the other hand, in the biaxially stretched film, Nz must be greater than 1. Further, in the case where Nz is small (in the case where the biaxiality is small), the mechanical strength or solvent resistance of the film tends to be low, and in particular, the tendency of the crystalline polymer film such as polyester is strong. Therefore, Nz _{1 is} preferably 2 or more, more preferably 3 or more, still more preferably 4 or more.

That is, the Nz _{1 of the} retardation film 30 is preferably 2 to 6, more preferably 3 to 5.5, still more preferably 4 to 5.3. When Nz ₁ is in the above range, the retardation film 30 containing polyester or the like has high mechanical strength or solvent resistance, and is prevented from viewing the image display device from the oblique direction in a state in which polarized sunglasses are worn. The color of the picture in the situation.

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

As described above, by setting the front phase retardation Re _{1 of the} retardation film 30 to about 1/4 of the wavelength, the emitted light from the image display device can be circularly polarized, thereby suppressing the wearing of the polarized sunglasses. The change in brightness due to the angle of the screen (blackout). On the other hand, in order to adjust the front phase retardation of a film using a material having a large birefringence such as an aromatic polyester to about 1/4 wavelength, it is necessary to control the stretching ratio to be low. If the stretching ratio is small, the control of the phase delay becomes difficult. Further, aromatic polyester or the like tends to be crystallized by biaxial stretching at a high stretching ratio, whereby mechanical strength, heat resistance, and solvent resistance tend to be improved. When the stretching ratio is adjusted to adjust the phase retardation to about 1/4 wavelength, the mechanical strength, heat resistance, solvent resistance, and the like of the retardation film tend to be deteriorated.

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 phase retardation Re _{1 can be} adjusted to the wavelength 1 with the same high stretching ratio as that of the general biaxially stretched polyester film. /4 or so. Further, by appropriately adjusting the stretching ratio of the aspect ratio and the like, the value of Nz ₁ can be adjusted to the above range, and the strength or durability of the retardation film can be ensured, and the visibility of the image display device from the oblique direction can be reduced. The difference in visibility from the front.

As aforesaid, the retardation film 30 of the thickness direction phase retardation Rth of line ₁ the refractive index of the slow axis direction within the film plane and the refractive index NX ₁ in the thickness direction of the film nz i.e. _a difference between the thickness direction birefringence (nx ₁ - Nz ₁ ) is expressed by the product of the thickness d ₁ . The birefringence in the thickness direction (nx _{1 -} nz ₁ ) is related to the degree of alignment in the film plane of the molecule. That is, the larger (nx _{1 -} nz ₁ ) is, the higher the in-plane orientation of the molecule is, and the more the crystallization is promoted, the film strength tends to increase, and if (nx _{1 -} nz ₁ ) is small, There is a tendency for the film strength to shrink.

The front surface retardation Re _{1 of the} retardation film 30 is adjusted to a value near the 1/4 wavelength, and mechanical strength or solvent resistance is imparted to make it difficult to cause deterioration such as solvent cracking, thereby reducing the film thickness and suppressing cost or image display. From the viewpoint of an increase in the thickness of the device, (nx _{1 -} nz ₁ ) is preferably large. (nx _{1 -} nz ₁ ) is preferably 0.06 or more, more preferably 0.1 or more, still more preferably 0.13 or more, and still more preferably 0.15 or more. Since (nx _{1 -} nz ₁ ) cannot exceed the value of the intrinsic birefringence, the upper limit is self-defined. For example, when the retardation film 30 contains polyethylene terephthalate, (nx _{1 -} nz ₁ ) is usually 0.3 or less, preferably 0.25 or less. When (nx _{1 -} nz ₁ ) is in the above range, the mechanical strength or solvent resistance of the biaxially stretched film can be improved without lowering the uniformity of optical characteristics.

(Material of retardation film)

The material constituting the retardation film 30 is not particularly limited, and a material excellent in mechanical strength or solvent resistance as described above can be preferably used. For example, a material having a (semi)crystalline property is preferable as a main component. As a representative, it is preferable to use a polyester as a main component. The polyester is crystallized by heating or the like to increase the crystallinity, thereby improving mechanical strength, dimensional stability, heat resistance, and solvent resistance. Therefore, it is preferable to use a biaxially stretched film containing polyester as a main component as the retardation film 30. Further, the polyester has higher gas barrier properties than triethylenesulfonate (TAC) which is generally used as a protective film for a polarizing element, and particularly has a small water vapor transmission rate. Therefore, by using the retardation film 30 as a protective film of the polarizing element 11, the humidifying durability of the polarizing plate 10 can be improved.

Examples of the polyester include terephthalic acid, isophthalic acid, and ophthalmic acid. Phthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylate, diphenoxyethane dicarboxylic acid Acid, diphenyl hydrazine carboxylic acid, hydrazine dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydro-p-benzene Dicarboxylic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethyl succinic acid, glutaric acid, 2,2-dimethylglutaric acid , dicarboxylic acid such as adipic acid, 2-methyladipate, trimethyl adipate, pimelic acid, sebacic acid, dimer acid, sebacic acid, suberic acid, dodecane dicarboxylic acid With ethylene glycol, propylene glycol, hexanediol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decanediol, 1,3-propanediol, 1,4- One type of diol such as butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)anthracene a homopolymer formed by polycondensation; a copolymer obtained by polycondensing one or more kinds of dicarboxylic acids with two or more kinds of diols; or a diol having two or more kinds of dicarboxylic acids and one or more kinds thereof Polycondensation a polymer; and a mixed resin obtained by mixing two or more kinds of such homopolymers or copolymers. Among them, from the viewpoint of the crystallinity of the polyester, an aromatic dicarboxylic acid is preferably used as the aromatic polyester of the above dicarboxylic acid component, and among them, polyethylene terephthalate can be preferably used. PET), or polyethylene naphthalate (PEN).

The polyester film can be obtained, for example, by extrusion-melting the above-mentioned polyester resin from a T-die or the like, and cooling and solidifying it by a casting drum to form a film (film formation). From the viewpoint of imparting the above properties to the polyester film to impart crystallinity, it is preferred that the film after film formation be biaxially stretched. Further, the retardation film containing the aromatic polyester as a main component may contain a resin or an additive other than the aromatic polyester. The term "having an aromatic polyester as a main component" means that the aromatic polyester is contained in an amount of 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 based on the total weight of the film. More than weight%.

When the polyester film or the like is stretched after being formed into a film, the stretching method is not particularly limited, and a vertical and horizontal sequential biaxial stretching method, a vertical and horizontal simultaneous biaxial stretching method, or the like may be employed. As the stretching mechanism, a roll stretching machine may be used. Tenter extension machine or zoom or linear motor type double shaft Any suitable extension machine such as an extension machine.

(surface roughness of retardation film)

In the present invention, the retardation film 30 preferably has a three-dimensional center plane average roughness SRa ₁ of the viewing side surface of 10 nm or less, and a three-dimensional center plane average roughness SRa _{2 of the} image display unit side surface of more than 10 nm.

The film having a small thickness is liable to cause scratches due to sliding when the film is conveyed or adhesion when the film is taken up. Therefore, it is preferred to form minute protrusions on the surface of the film to impart slidability to the film. In general, for a film having a large thickness, an additive such as a catalyst component or an inert ceria microparticles during polymerization of the polymer is present as a filler in the film to form a protrusion of about several tens nm to 1 μm on the surface to impart a sliding property. Sex, thereby improving the transportability of the film. The average particle diameter of the fillers is about several tens of nanometers to several micrometers. When such a filler having a large particle diameter is present in a film having an extremely thin thickness of 7 μm or less, the exposure of the filler on the surface of the film is increased, and the uniformity of the loss of the surface shape or the loss of the filler from the surface of the film tends to occur. Further, in order to ensure good transportability when the thickness of the film is small, it is necessary to increase the relative transfer amount of the fine particles, and the transparency of the film tends to be lowered.

Therefore, as for the film having a small thickness, as shown in FIG. 3, by forming the microparticle-containing layer 321 and 331 on the surface of the core layer 311 containing no filler, an appropriate size protrusion is formed on the surface of the film at an appropriate density. Thereby improving the transportability. In the fine particle-containing layers 321 and 331, fine particles 361 and 371 containing inert cerium oxide or the like are dispersed in the binder resins 341 and 351.

In order to impart appropriate slidability to the film and improve the transportability, it is preferred that the three-dimensional center plane average roughness SRa of at least one surface is greater than 10 nm. In the form in which the fine particle 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 diameter or content of the fine particles in the binder resin. On the other hand, if the particle size of the filler is large or the content of the filler is large, the surface of the filler-containing layer is wiped by a non-woven fabric or the like, and the microparticles are detached from the microparticle-containing layer or the microparticles are buried. Inside the film, there is a case where the visibility of the film surface is locally changed or the mechanical strength is lowered. Therefore, the retardation film of the present invention preferably has no protrusions formed of fine particles on the surface exposed to the viewing side surface when the image display device is formed, or has minute protrusions which do not cause the particles to fall off or bury. From this point of view, the three-dimensional center plane average roughness SRa ₁ of the viewing side surface of the retardation film 30 is preferably 10 nm or less, more preferably 8 nm or less, still more preferably 7 nm or less.

As described above, in order to improve the transportability of the film, it is preferred that one surface of the retardation film has a specific surface roughness. Therefore, the retardation film 30 of the present invention preferably has a three-dimensional center plane average roughness SRa _{2 of the} side surface of the image display unit 5 of more than 10 nm, more preferably 15 nm or more, still more preferably 20 nm or more. As shown in FIG. 4(A), 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 front and back surface roughnesses can be formed. Further, as shown in Fig. 4(B), the front and back sides may be formed by changing the average particle diameter or the content of the fine particles 36, 37 in the fine particle-containing layers 32, 33 on one side and the other side of the core layer 31. A phase difference film having a different surface roughness. As shown in FIG. 4(C), the fine particle-containing layer 32 may be formed on one surface of the core layer 31, and the fine particle-free coating layer 39 may be formed on the other surface. For example, by providing the polyester retardation film 30 with the coating layer 39 on the surface of the image display unit 5 including the core layer 31 of the polyester, adhesion to the polarizing element 11 and the like can be improved.

The formation of the microparticle-containing layer 32, 33 or the coating layer 39 on the surface of the core layer 31 can be performed at any stage of the step of forming the retardation film 30. For example, the core layer and the microparticle-containing layer or the coating layer may be simultaneously formed by multilayer co-extrusion at the time of melt film formation. In the case where a microparticle-containing layer or a coating layer is formed after film formation in the core layer, the layer formation may be performed before or after stretching. Further, in the case of performing the secondary biaxial stretching, the microparticle-containing layer 32, 33 or the coating layer 39 may be formed after the longitudinal stretching (roll stretching) and the lateral stretching (later stretching). If a solution containing a fine particle layer or a coating layer is applied to the surface of the film before the lateral stretching, the solution can be dried by heating in the lateral extension, so that the step can be simplified and the phase can be improved. Poor film production.

[Formation of Image Display Device]

As shown in FIG. 1, the image display panel 50 is formed by disposing the polarizing element 11 and the retardation film 30 on the viewing side surface of the image display unit 5. Moreover, as shown in FIG. 2, the second polarizing element 21 is disposed on the side opposite to the viewing side of the image display unit 5 as needed. As the second polarizing element, for example, a linear polarizing element can be used similarly to the above-described polarizing element 11. Various optical layers such as a polarizing element protective film (transparent protective film) or an optical compensation film may be disposed between the image display unit 5 and the polarizing elements 11 and 21.

As a method of disposing the polarizing element 11 and the retardation film 30 on the image display unit 5, it is preferable to form an appropriate bonding layer between the layers to laminate the layers. From the viewpoint of facilitating the bonding of the respective layers, it is preferable to form the viewing-side polarizing plate 10 in which the polarizing element 11 and the retardation film 30 are laminated and fixed via a suitable adhesive layer (not shown), and then appropriately The layer 61 attaches the viewing side polarizing plate 10 to the image display unit 5.

FIG. 5 and FIG. 6 are schematic cross-sectional views showing a configuration example of a viewing-side polarizing plate used in the image display device of the present invention. In the embodiment shown in FIG. 5, the retardation film 30 is disposed on the viewing side of the polarizing element 11, and the transparent protective film 12 is disposed on the image display unit side of the polarizing element 11. An adhesive layer 61 for bonding the polarizing plate 10 and the image display unit 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 polarizing element 11 and the retardation film 30.

In the configuration in which the transparent polarizing film 12 is provided on the surface of the polarizing element 11 on the image display unit 5 side, since both surfaces of the polarizing element 11 are protected by the retardation film 30 and the transparent protective film 12, the polarizing plate is improved. 10 durability. The material or optical characteristics of the transparent protective film 12 are not particularly limited, and in terms of being disposed between the polarizing element 11 and the image display unit 5, it is preferable to use an optically isotropic person having substantially no birefringence. Or, even in the case of having birefringence, the phase retardation value or the in-plane uniformity of the optical axis direction is excellent. Further, a retardation film (optical compensation layer) may be used as the transparent protective film 12.

In the case where the image display unit 5 is a liquid crystal cell, a retardation film having appropriate optical characteristics (birefringence) may be used as the transparent protective film 12 depending on the driving mode (TN, VA, IPS, etc.) of the liquid crystal cell. Optical compensation such as improvement in viewing angle or improvement in contrast is performed. In the case where the image display unit 5 is an organic EL unit, the phase difference film having a front side retardation of 1/4 wavelength (approximately 100 to 200 nm) can be used as the transparent protective film 12 to block the generation of the organic EL unit. Specular reflection of external light. Further, the retardation film may be disposed between the polarizing plate 10 and the image display unit 5 as an individual different from the transparent protective film 12 of the polarizing element 11.

As the material of the transparent protective films 12, 13, a transparent polymer having uniform optical characteristics can be preferably used. In particular, from the viewpoint of transparency, a cellulose resin or a cyclic polyolefin resin can be preferably used. An amorphous polymer such as an olefin resin, a polycarbonate resin, a polyarylate resin, an amorphous polyester resin, a polyvinyl alcohol resin, a polyfluorene resin, or a polyimide resin.

When the second polarizing element 21 is disposed on the side opposite to the viewing side of the image display unit 5 as shown in FIG. 2, it may be provided on one or both of the second polarizing elements 21 via an appropriate bonding layer. A light source side polarizing plate such as a transparent protective film or a retardation film is bonded to the image display unit 5.

As the adhesive constituting the adhesive layer for bonding the respective layers, an acrylic polymer, a polyoxymethylene polymer, a polyester, a polyurethane, a polyamide, a polyvinyl ether, or the like can be suitably used. A polymer such as a vinyl acetate/vinyl chloride copolymer, a modified polyolefin, an epoxy polymer, a fluorine polymer, or a rubber polymer is used as the base polymer. When a laminate of a polarizing element and a retardation film or a layer of a polarizing element and a transparent protective film is used, an aqueous adhesive can be preferably used. Among them, a polyvinyl alcohol-based resin as a main component can be preferably used.

As the adhesive layer 61 for bonding the image display unit 5 to the viewing-side polarizing plate 10, a pressure-sensitive adhesive (adhesive) layer can be preferably used. Moreover, the image display unit 5 and the light source side It is also preferable to use an adhesive layer for the bonding of the polarizing plate 20. The adhesive constituting the adhesive layers 61 and 62 is not particularly limited, and for example, an acrylic polymer, a polyoxymethylene polymer, a polyester, a polyurethane, a polyamide, a polyether can be appropriately selected and used. A polymer such as a fluorine-based or rubber-based polymer is used as a base polymer. In particular, it is excellent in transparency such as an acrylic pressure-sensitive adhesive, and exhibits excellent wettability, cohesiveness, and adhesion properties, and is excellent in weather resistance and heat resistance.

It is preferable that the exposed surface of the adhesive layer 61 attached to the surface of the polarizing plate 10 is temporarily covered with a release film (spacer) in order to prevent contamination or the like before being used for actual use. Thereby, it is possible to prevent contact with the adhesive layer in a normal operation state. As the release film, for example, a suitable sheet such as a plastic film, a rubber sheet, a paper, a cloth, a non-woven fabric, a mesh, a foamed sheet, a metal foil, or the like can be used, and a suitable sheet is used as needed. Or a suitable release agent such as a long-chain alkyl group, a fluorine-based or a molybdenum sulfide, or the like, which has been suitably coated according to the prior art.

Further, a light source 80, a drive circuit, or the like is incorporated into the image display panel 50 as needed, thereby obtaining an image display device. Further, in addition to these, various members required for forming an image display device may 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 (transmissive liquid crystal panel) 50. Examples of the front transparent member 70 include a front transparent plate (window layer), a touch panel, and the like. As the front transparent plate, a transparent plate having an appropriate mechanical strength and thickness can be 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 or the like is used. As the touch panel, a touch panel of any method such as a resistive film method, a capacitive method, an optical method, or an ultrasonic method can be 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 an air layer (void) exists between the image display panel 50 and the front transparent member 70, the air interface is present. The difference in refractive index causes a large reflectance, so there is a map The tendency for visibility of a display device to decrease. Therefore, it is preferable to use an "interlayer filling structure" in which the space between the image display panel 50 and the front transparent member 70 is filled by the adhesive layer 65 to lower the refractive index difference of the interface.

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 (transmissive liquid crystal panel) 50. In the embodiment shown in FIG. 8, the viewing side polarizing plate 10 including the transparent protective films 12 and 13 on both surfaces of the polarizing element 11 is disposed on the viewing side of the image display unit 5, and the interlayer is filled thereon. The front surface transparent member 70 is disposed on 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 polarizing element 11, and may be disposed closer to the viewing side than the polarizing element 11 via another optical member. In the example shown in FIG. 8, the retardation film 30 is provided on the viewing side of the front transparent member 70. However, the retardation film may be disposed on the image display panel 50 side of the front transparent member 70.

The image display device of the present invention can be used, for example, as a monitor for an OA (Office Automation) machine such as a computer or a mobile phone, a smart phone, a digital camera, a portable information terminal, a portable game machine, a video camera. Various applications such as display monitors for vehicles such as televisions and car navigation systems, information displays for commercial facilities, and monitoring monitors. In particular, the image display device of the present invention can be preferably used as a movement that is mostly used outdoors because it suppresses changes in visibility (brightness of the screen) due to the screen angle in a state in which polarized sunglasses are worn. A display for a machine or vehicle device.

[Examples]

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

[Measurement, evaluation method] (phase delay)

Using a polarization-phase difference measurement system (product name "AxoScan" manufactured by Axometrics), the phase retardation in the front direction was measured at a measurement wavelength of 590 nm in an environment of 23 ° C, and the film was tilted by 40 ° in the direction of the slow axis. The phase of the state is delayed, and the front phase retardation Re ₁ , the thickness direction phase delays Rth ₁ , and Nz _{1 are} calculated based on the measured values. Further, in the calculation, the average refractive index of polyethylene terephthalate was set to 1.60.

(three-dimensional center plane average roughness)

The surface roughness measuring device (manufactured by Kosaka Research Institute, model: SE3500K) was used to measure the three-dimensional roughness surface in the range of 500 μm × 500 μm (scanning speed: 0.1 mm/sec, cutoff: 0.25 mm), and the average roughness of the three-dimensional center plane was calculated. Degree SRa.

(wiping test)

The non-woven fabric was placed on the surface of the polyester film on the liquid crystal display device, and while applying a pressing force of 0.98 N/25 mm, it was rubbed back and forth 10 times at a speed of 100 mm/sec. The surface after wiping was visually observed, and it was confirmed whether or not the blurring of the surface before and after wiping was changed.

(Viewability evaluation of image display device)

The liquid crystal display device displays a white image in a bright environment, and observes from the front in a state in which polarized sunglasses are worn to confirm the presence or absence of iridescence. In this state, the screen is rotated by 360°, and it is confirmed whether or not the brightness of the screen due to the angle changes (blackout). In addition, it is confirmed whether there is a difference in visibility between the case where the front view image display device is worn and the case where the self-oblique direction (polar angle 20° direction) is viewed in the state in which the polarized sunglasses are worn.

[Example 1] (Polyester retardation film)

A biaxially stretched polyester film having a thickness of 4.5 μm, a front surface retardation Re ₁ =170 nm, a thickness direction phase retardation Rth ₁ =935 nm, and Nz ₁ =935 nm was prepared. The three-dimensional center plane average roughness SRa ₁ of one surface of the polyester film was 5.2 nm, and the three-dimensional center plane average roughness SRa ₂ of the other surface was 10.5 nm.

(Production of liquid crystal display device for evaluation)

A liquid crystal display device provided with a polarizing plate on the viewing side surface of the liquid crystal display unit. The viewing-side polarizing plate of the liquid crystal display device is provided with an optically isotropic transparent protective film on the viewing side of the polarizing element. The retardation film is bonded to the polarizing plate via an adhesive so that the angle between the absorption axis direction of the polarizing element and the retardation axis direction (MD direction) of the retardation film is 45°. At the time of bonding, the polyester retardation film was disposed such that the surface of SRa=10.5 nm became the polarizing plate side and the surface of SRa=5.2 nm became 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 a polyester retardation film having the thickness, surface roughness and optical characteristics shown in Table 1 was used.

[Reference Example 1]

When the polarizing plate and the polyester retardation film are bonded together, the surface on which the surface of SRa = 5.2 nm is on the side of the polarizing plate, and the surface on which SRa = 10.5 nm is placed on the viewing side. A liquid crystal display device for evaluation was produced in the same manner as in Example 1 except for the above.

[Evaluation results]

The visibility of the liquid crystal display device of each of the above examples, comparative examples, and reference examples, and the results of the wiping test, and the optical characteristics of the polyester retardation film used for each liquid crystal display device and the three-dimensional center plane average roughness (SRa) And shown in Table 1. In addition, in Table 1, the three-dimensional center plane average roughness of the viewing side surface of the polyester retardation film was set to SRa ₁ , and the three-dimensional center plane average roughness of the liquid crystal cell side surface was set to SRa ₂ .

As shown in Table 1, when the image display device of the first to fourth embodiments having the retardation film of the present invention is used to view the screen of the polarized sunglasses, the color of the rainbow color caused by blackout or color shifting is not observed. Show good visibility. Moreover, the visibility in the case of visually recognizing the screen from the oblique direction is also good as in the front view.

In Comparative Examples 1 and 2, since the front phase retardation greatly deviated from the 1/4 wavelength, when the polarized sunglasses were viewed from the screen, the brightness greatly changed depending on the angle of the screen. In Comparative Examples 3 and 4, the visibility of the front view was good as in the first to fourth embodiments. However, since the Nz _{1 of the} retardation film was large, the field of change from the front view was large when viewed from the oblique direction.

The liquid crystal display device of Reference Example 1 showed good visibility similarly to Example 1. However, since the SRa of the viewing side surface was large, the blurring property of the wiping portion was lowered after the wiping test. Therefore, the difference between the visibility of the local part and the surrounding area after the wiping test was remarkable, and the visibility was locally lowered. According to the result, it is considered that, particularly in the case where the retardation film of the present invention is disposed on the viewing side surface of the image display device, it is preferable to reduce the SRa of the viewing side surface.

5‧‧‧Image display unit

10‧‧‧Polar plate

11‧‧‧Polarized components

30‧‧‧ phase difference film

50‧‧‧Image display panel

100‧‧‧Image display device

Claims (5)

A retardation film which is disposed on a viewing side of a polarizing element disposed on a viewing side of an image display unit in an image display device, and has a thickness d ₁ of 7 μm or less and a three-dimensional viewing surface The center plane average roughness SRa ₁ is 10 nm or less, and the three-dimensional center plane average roughness SRa _{2 of the} image display unit side surface is larger than 10 nm, and satisfies the optical characteristics of the following (i) and (ii): (i) 100 nm ≦Re ₁ ≦ 200 nm (ii) Nz ₁ ≦6 Here, Re ₁ and Nz ₁ are obtained by setting the thickness of the retardation film to d ₁ and setting the refractive index in the direction of the slow axis in the film plane to nx ₁ . When the refractive index in the direction of the in-phase axis is ny ₁ and the refractive index in the thickness direction is nz ₁ , respectively, the 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 claim 1 which has an aromatic polyester as a main component. The retardation film of claim 2, wherein the aromatic polyester is polyethylene terephthalate or polyethylene naphthalate. An image display device comprising an image display unit, a polarizing element sequentially disposed on a viewing side of the image display unit, and a retardation film according to any one of claims 1 to 3. A polarizing plate comprising a retardation film according to any one of claims 1 to 3 on one side of a polarizing element.