JP2006215333A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film excellent in production efficiency, having uniform film thickness of each layer and favorable handling property during film formation, excellent in mechanical strength, durability and transparency, and giving a large effect on viewing angle compensation for various kinds of display devices, compared to a conventional film. <P>SOLUTION: The retardation film comprises polynorbornene resin films (B layers) layered on both surfaces of a polystyrene resin film (A layer), wherein the glass transition temperatures Tg(A) (°C) and Tg(B) (°C) of the polystyrene resin and the polynorbornene resin, respectively, satisfy the relation of Tg(A)>Tg(B)+20°C and 80°C≤Tg(B)≤120°C, and the melt flow rate of the polynorbornene resin is 5 to 50 g/10 minutes (measured according to JISK7210 under conditions (conditions S) of at 280°C and 21.18 N load). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a retardation film containing a polystyrene-based resin that has good handling properties during film formation, a uniform film thickness of each layer, and excellent mechanical strength and transparency.

A retardation film plays an important role as a member for improving the display performance of a liquid crystal display (LCD). Various types of retardation films are known, such as a film in which liquid crystal is oriented, but since the production efficiency is particularly excellent, stretched films obtained by orienting resin films by stretching have been widely used.
As the retardation film made of the stretched film, various materials such as a polycarbonate resin film have been used. Among them, polystyrene is excellent in transparency and has a large effect in viewing angle compensation for LCDs such as STN type. System resin films are attracting attention (Cited document 1).
However, since the polystyrene-based resin film is inferior in mechanical strength, it has been pointed out that it is easily broken when subjected to stretching treatment, resulting in inferior production efficiency.
In order to solve this problem, a laminated film obtained by laminating a layer made of a material having a negative intrinsic birefringence value such as a polystyrene resin and a layer made of a material having a positive intrinsic birefringence value such as a polynorbornene resin is shared. Techniques for obtaining a retardation film by stretching have been proposed (Cited documents 2, 3).

JP-A-2-256603 JP 2002-040258 A JP 2004-133313 A

  However, in the retardation films described in Patent Document 2 and Patent Document 3, when there is a difference in the glass transition temperature (Tg) of the resin of each layer, the resin layer having a higher Tg is oriented during film formation. Then, since the resin layer having a lower Tg would stick to the stretching equipment, the production efficiency was inferior and improvement was required.

  Therefore, the object of the present invention is that the thickness of each layer is uniform, the handling property at the time of film formation is good, the mechanical strength, the durability and the transparency are excellent, and the effect on the viewing angle compensation for various display devices is great. It is to provide a retardation film.

  As a result of intensive studies to solve the above problems, the present inventors have laminated a film made of a polynorbornene resin having a melt flow rate value in a specific range on both surfaces of a film made of a polystyrene resin having a Tg in a specific range. As a result, it has been found that the above object can be achieved, and the present invention has been completed.

Thus, according to the present invention,
(1) A retardation film in which a film (B layer) made of a polynorbornene resin is laminated on both surfaces of a film (A layer) made of polystyrene resin,
When the glass transition temperatures of the polystyrene resin and the polynorbornene resin are Tg (A) (° C.) and Tg (B) (° C.), respectively, Tg (A)> Tg (B) + 20 ° C. and 80 ° C. ≦ Tg (B) ≦ 120 ° C.
Retardation film characterized in that the melt flow rate of polynorbornene resin (measured according to JIS K7210 at a temperature of 280 ° C. and a load of 21.18 N (condition S)) is 5 to 50 g / 10 minutes,
(2) When Re (A) and Re (B) represent the retardation in the front direction of the A layer and the retardation in the front direction of the B layer, respectively, measured with light having a wavelength of 400 to 700 nm, | Re (A) | > | Re (B) | and | Re (B) | is 40 nm or less, The retardation film according to (1),
Is to provide.

  The retardation film of the present invention has excellent production efficiency, good handling properties during film formation, uniform film thickness of each layer, excellent viewing angle compensation performance, excellent mechanical strength and transparency, and long-term use. As a retardation film that maintains good optical characteristics, it can be widely applied to liquid crystal display devices and organic EL display devices.

  The retardation film of the present invention has a configuration in which a film (B layer) made of a polynorbornene resin is laminated on both surfaces of a film (A layer) made of a polystyrene resin.

  Examples of the polystyrene resin used in the present invention include polystyrene, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, and p-carboxy. Styrene monomers such as styrene and p-phenylstyrene, ethylene, propylene, butadiene, isoprene, (meth) acrylonitrile, α-chloroacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) Examples thereof include copolymers with other monomers such as acrylic acid, maleic anhydride and vinyl acetate. Among these, polystyrene or a copolymer of styrene and maleic anhydride can be suitably used.

  The molecular weight of the polystyrene resin used in the present invention is appropriately selected depending on the purpose of use, but polyisoprene measured by gel permeation chromatography using cyclohexane (toluene when the polymer resin is not dissolved) as a solvent. Or it is a weight average molecular weight (Mw) of polystyrene conversion, and is 10,000-300,000 normally, Preferably it is 15,000-250,000, More preferably, it is 20,000-200,000. The polystyrene resin used in the present invention preferably has a glass transition temperature Tg (A) not exceeding 200 ° C. When Tg (A) exceeds 200 ° C., when the retardation film of the present invention is produced, the B layer may be burned, or the polynorbornene resin of the B layer may adhere to the stretching equipment. Moreover, there exists a possibility that the extending | stretching for manufacturing retardation film cannot be performed.

  In the present invention, the polystyrene-based resin may contain an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, an antistatic agent, a dispersant, a chlorine scavenger, a flame retardant, a crystallization nucleating agent, if necessary. Antiblocking agent, antifogging agent, release agent, pigment, organic or inorganic filler, neutralizing agent, lubricant, decomposition agent, metal deactivator, antifouling agent, antibacterial agent and other resins, thermoplastic elastomer Known additives such as these can be added as long as the effects of the invention are not impaired.

  Examples of the polynorbornene resin used in the present invention include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening polymer of a monomer having a norbornene structure and another monomer, or a hydride thereof. And an addition polymer of a monomer having a norbornene structure, an addition polymer of a monomer having a norbornene structure and another monomer, or a hydride thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,8. -Diene (common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . 1 ^7,10 ] dodec-3-ene (common name: tetracyclododecene), 8-ethylidene-tetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -dodec-3-ene (common name: ethylidenetetracyclododecene) and derivatives of these compounds (having substituents in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, an alkoxycarbonyl group, and a carboxyl group. Moreover, these substituents may be the same or different and a plurality may be bonded to the ring. Norbornene monomers can be used singly or in combination of two or more.

  Other monomers capable of ring-opening copolymerization with a monomer having a norbornene structure include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; and cyclic conjugates such as cyclohexadiene and cycloheptadiene. Dienes and derivatives thereof; and the like.

  Ring-opening polymers of norbornene monomers and ring-opening copolymers of norbornene monomers and other monomers capable of ring-opening copolymerization are used in the presence of a ring-opening polymerization catalyst. Can be obtained by polymerization.

  As the ring-opening polymerization catalyst to be used, for example, a catalyst comprising a metal halide such as ruthenium or osmium and a sulfate or acetylacetone compound and a reducing agent; or a metal halide such as titanium, zirconium, tungsten or molybdenum Or a catalyst comprising an acetylacetone compound and an organoaluminum compound;

An addition polymer of a monomer having a norbornene structure and an addition copolymer of a monomer having a norbornene structure and another monomer capable of addition copolymerization in the presence of an addition polymerization catalyst. Can be obtained by polymerization.
As the addition polymerization catalyst, for example, a catalyst composed of a metal compound such as titanium, zirconium, vanadium and an organoaluminum compound can be used.

  Other monomers that can be copolymerized with a monomer having a norbornene structure include, for example, ethylene, propylene, 1-butene, 1-pentene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene. , 1-hexadecene, 1-octadecene, 1-eicosene and the like α-olefins having 2 to 20 carbon atoms and derivatives thereof; cyclobutene, cyclopentene, cyclohexene, cyclooctene, 3a, 5,6,7a-tetrahydro-4,7 -Cycloolefins such as methano-1H-indene and derivatives thereof; non-conjugated such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 1,7-octadiene Examples include dienes. These monomers can be used alone or in combination of two or more. Among these, α-olefin is preferable and ethylene is more preferable.

  The molecular weight of the polynorbornene-based resin used in the present invention is appropriately selected depending on the purpose of use, but it is determined by gel permeation chromatography using cyclohexane (toluene when the polymer resin does not dissolve) as a solvent. The weight average molecular weight (Mw) in terms of isoprene or polystyrene is usually 5,000 to 500,000, preferably 10,000 to 100,000, more preferably 35,000 to 80,000. The polynorbornene-based resin used in the present invention has a glass transition temperature Tg (B) of 80 to 120 ° C, preferably 95 to 115 ° C, and more preferably 102 to 108 ° C. When Tg (B) is less than 80 ° C., thermal durability is deteriorated, and when Tg (B) is more than 120 ° C., stretch workability is deteriorated.

  The polynorbornene-based resin used in the present invention has a melt flow rate of 5 to 50 g / 10 minutes, preferably 10 to 35 g when measured at a temperature of 280 ° C. and a load of 21.18 N (conditions S) according to JIS K7210. / 10 minutes. When the melt flow rate of the copolymer is less than 5 g / 10 min, retardation in the front direction of the B layer is likely to be exhibited, and uneven thickness of the A layer is likely to occur. When the melt flow rate of the copolymer exceeds 50 g / 10 min, when the retardation film of the present invention is produced, polynorbornene with respect to a heating oven inner wall of a stretching machine, a clip or nip roll of a tenter stretching machine, etc. The layer made of a resin is adhered, and the film is broken or continuous production becomes difficult.

  In the present invention, to the polynorbornene resin, additives described in the description of the polystyrene resin can be added to the polynorbornene resin as necessary as long as the effects of the invention are not impaired.

  Tg (A) and Tg (B) preferably satisfy the relationship of Tg (A)> Tg (B) + 20 ° C., and more preferably satisfy Tg (A)> Tg (B) + 24 ° C. . When stretching a laminated film of a layer (a layer) composed of a polystyrene resin before stretching and a layer (b layer) composed of a polynorbornene resin before stretching, when stretching near the temperature Tg (A) (° C.), The birefringence characteristics of the A layer can be expressed sufficiently and uniformly. In general, a film made of a polystyrene-based resin is difficult to be stretched alone, and stretching unevenness or breakage may occur. However, in the present invention, by laminating the b layer having a low glass transition temperature on both surfaces of the a layer, it becomes possible to stably perform co-stretching and to reduce the thickness unevenness of the A layer. If the thickness unevenness occurs in the A layer, the retardation in the thickness direction of the retardation film of the present invention may increase, and when the retardation film is applied to a display device, display performance (viewing angle) Performance) may be significantly reduced.

  When the retardation in the front direction of the A layer and the retardation in the front direction of the B layer measured with light having a wavelength of 400 to 700 nm are Re (A) and Re (B), respectively, It is preferable that Re (A) |> | Re (B) | and | Re (B) | is 40 nm or less, and | Re (A) |> | Re (B) | and | Re (B) | is more preferably 30 nm or less, and | Re (A) |> | Re (B) |, and | Re (B) | is more preferably 20 nm or less. When | Re (A) |> | Re (B) | and | Re (B) | are 40 nm or less, the optical characteristics of the optically adjusted A layer can be effectively used. it can. In addition, the coefficient NZ described below can be efficiently reduced to 0.4 or less. If | Re (A) | ≦ | Re (B) |, the optical compensation function of the retardation film may not be sufficiently exhibited. If | Re (B) | exceeds 40 nm, the optical compensation function of the retardation film may not be sufficiently exhibited. Note that | Re (B) | is the sum of absolute values of the retardation in the front direction of each B layer.

The retardation film of the present invention has a variation in retardation (Re) in the front direction within 10 nm, preferably within 5 nm, and more preferably within 2 nm. By setting the variation of Re within the above range, it is possible to improve the display quality when used in various display devices. Here, the variation in Re is a difference between the maximum value and the minimum value of Re when the retardation in the front direction is measured in the width direction of the film. Note that Re in the present invention is the refractive index nx in the slow axis direction of the film, the refractive index ny in the direction perpendicular to the slow axis in the plane, the refractive index nz in the thickness direction, and the average thickness Tw of the film. to a value defined by _{(nx-ny) × T w} .

The retardation film of the present invention has a variation in retardation (Rth) in the thickness direction within 10 nm, preferably within 5 nm, and more preferably within 2 nm. By setting the variation in Rth within the above range, it is possible to improve display quality (viewing angle performance) when used as a retardation film for a liquid crystal display device. Here, the variation in Rth is the difference between the maximum value and the minimum value of Rth when the retardation in the thickness direction is measured in the width direction of the film. Incidentally, Rth in the present invention is a value defined by ((nx + ny) / 2 -nz) × T w.

  In the retardation film of the present invention, the coefficient NZ expressing the relationship between the retardation in the front direction and the retardation in the thickness direction is 0.4 or less, preferably 0.2 or less, more preferably 0 or less, particularly preferably −0. .2 or less. When NZ is 0.4 or less, when used as a retardation film for various display devices, the effect on viewing angle compensation is particularly great. If NZ exceeds 0.4, the optical compensation function of the laminated film may not be sufficiently exhibited. NZ is a value represented by (nx−nz) / (nx−ny).

  As for the retardation film of this invention, the surface (B layer) can be roughened as needed. The means for roughening is not particularly limited, and examples thereof include corona discharge treatment, embossing, sand blasting, etching, and adhesion of fine particles. By roughening the surface, adhesion to a film such as a polarizing plate can be improved.

  In the retardation film of the present invention, an adhesive layer may be provided between the A layer and the B layer. An adhesive bond layer can be formed from what has affinity with respect to both A layer and B layer which comprise an optical laminated body. For example, ethylene- (meth) acrylate copolymer such as ethylene- (meth) acrylate methyl copolymer, ethylene- (meth) ethyl acrylate copolymer; ethylene-vinyl acetate copolymer, ethylene-styrene Examples thereof include ethylene copolymers such as copolymers, other olefin polymers, styrene-butadiene copolymers, styrene-isoprene copolymers, and hydrides thereof. In addition, modified products obtained by modifying these (co) polymers by oxidation, saponification, chlorination, chlorosulfonation, or the like can also be used. The thickness of the adhesive layer is preferably 1 to 50 μm, more preferably 2 to 30 μm.

  The retardation film of the present invention is preferably produced by co-stretching a laminated film in which the b layer is laminated on both sides of the a layer. There is no restriction | limiting in particular in the extending | stretching method, A conventionally well-known method can be applied. Specifically, a uniaxial stretching method such as a method of uniaxially stretching in the longitudinal direction using a difference in peripheral speed on the roll side, a method of uniaxially stretching in the lateral direction using a tenter; Tenter by holding both ends of the clip after stretching in the longitudinal direction using the simultaneous biaxial stretching method that stretches in the transverse direction according to the spread angle of the guide rail at the same time as stretching in the longitudinal direction or the difference in peripheral speed between the rolls. A biaxial stretching method such as a sequential biaxial stretching method in which the film is stretched in the transverse direction by using a tenter stretching machine that can add a feed force, a pulling force, or a take-up force at different speeds in the lateral or longitudinal direction; Alternatively, a tenter extension in which the feeding distance, the pulling force, or the pulling force at the same speed in the left-right direction can be added in the longitudinal direction so that the moving distance is the same and the stretching angle θ can be fixed or the moving distance is different. How to obliquely stretched with the machine: and the like.

  The laminated film in which the b layer is laminated on both sides of the a layer is preferably formed by a coextrusion method. The coextrusion molding method includes a flat die coextrusion molding method using a flat die and a coinflation molding method using a cylindrical die, and the flat die coextrusion molding method is preferable. The flat die co-extrusion molding method is a method in which a resin is heated and melted with an extruder and then co-extruded from a flat die to continuously obtain a film-shaped molded product. The extruder heats and kneads the resin and extrudes the melt in the form of a film from the die with a constant extrusion amount. Usually, it is preferable to remove a gel or a foreign substance by inserting a screen or a filter between the extruder and the die. The resin used is preferably dried before being introduced into the extruder, and the content of water and volatile solvents is reduced in order to prevent the generation of fish eyes and bubbles.

  The co-extrusion temperature is preferably 80 to 180 ° C. higher than the glass transition temperature of the polystyrene resin, and more preferably 100 to 150 ° C. higher than the glass transition temperature of the polystyrene resin. If the melting temperature in the extruder is excessively low, the fluidity of the resin may be insufficient. Conversely, if the melting temperature is excessively high, the resin may be deteriorated.

  The laminated film of the present invention can be formed by laminating a cured resin layer or a liquid crystal polymer layer by applying an ultraviolet curable resin, a liquid crystal polymer (including a liquid crystal monomer before curing), an antireflection agent, or the like.

  The retardation film of the present invention can be widely applied to liquid crystal display devices, organic EL display devices, plasma display devices, FED (field emission) display devices, SED (surface electric field) display devices, and the like. Examples of the liquid crystal display device include an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, a continuous spin wheel alignment (CPA) mode, a hybrid alignment nematic (HAN) mode, Examples include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, and an optically compensated bend (OCB) mode. Among these, the viewing angle compensation effect is particularly large for an IPS mode liquid crystal display device.

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. Parts and% are based on weight unless otherwise specified.
In Examples and Comparative Examples, measurement and evaluation were performed by the following methods.
(1) Melt flow rate Based on JIS K7210 (temperature 280 ° C., load 21.18 N (condition S)), it is measured with a melt indexer F-B01 manufactured by Toyo Seiki Seisakusho.
(2) Glass transition temperature Measured by differential scanning calorimetry (DSC) based on JIS K7121.
(3) Frontal retardation Re
Measurement is performed using an automatic birefringence meter [manufactured by Oji Scientific Instruments, KOBRA-21ADH]. The Re of the A layer and the Re of the B layer are measured by separating the A layer and the B layer from the film.
(4) Thickness direction retardation Rth
In the same manner as in the above (3), measurement is performed using an automatic birefringence meter [manufactured by Oji Scientific Instruments, KOBRA-21ADH].
(5) NZ coefficient It is measured using an automatic birefringence meter [manufactured by Oji Scientific Instruments, KOBRA-21ADH].
(6) Viewing angle characteristics of the liquid crystal display device After the film is incorporated into the in-plane switching (IPS) mode liquid crystal display device, the screen when black is displayed from the top and bottom diagonal directions within 60 ° polar angle from the front direction. Observe the display characteristics visually. The polar angle means an angle when tilted from the front direction when observing the liquid crystal display screen.

Example 1
A B layer composed of a hydride of norbornene ring-opening polymer [glass transition temperature 100 ° C., melt flow rate 10 g / 10 min], an A layer composed of a styrene-maleic anhydride copolymer [glass transition temperature 130 ° C.], b A laminated film C1 having a layer (50 μm) -a layer (50 μm) -b layer (50 μm) was obtained by coextrusion molding.
The laminated film C1 was tenter transversely stretched at a stretching temperature of 136 ° C., a stretching speed of 7.5 m / min, and a stretching ratio of 2.4 times to obtain a retardation film D1 having a thickness of 75 μm.
A test piece is cut out from the center of the obtained retardation film D1 and laminated so that the slow axis of the retardation film (test piece) and the absorption axis of the polarizing plate [HLC2-5618, manufactured by Sanritz Corporation] are perpendicular to each other. The evaluated optical element E1 was replaced with a polarizing plate on the viewing side of a commercially available in-plane switching (IPS) mode liquid crystal display device for evaluation. At this time, the optical element E1 was incorporated so that the retardation axis of the retardation film and the absorption axis of the backlight side polarizing plate were parallel to each other and the retardation film was disposed on the liquid crystal cell side. The evaluation results are shown in Tables 1 and 2.

Example 2
B layer (50 μm) -a layer (50 μm) in the same manner as in Example 1 except that a hydride of norbornene ring-opening polymer [glass transition temperature 100 ° C., melt flow rate 30 g / 10 min] is used as the B layer. A laminated film C2 having a -b layer (50 μm) was obtained by coextrusion molding. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film D2. In addition, in the same manner as in Example 1, a retardation film D2 and a polarizing plate were laminated to produce an optical element E2. Further, the optical element E2 was incorporated into an IPS mode liquid crystal display device for evaluation. The evaluation results are shown in Tables 1 and 2.

Comparative Example 1
B layer (50 μm) -a layer (50 μm) in the same manner as in Example 1 except that a hydride of norbornene ring-opening polymer [glass transition temperature 100 ° C., melt flow rate 70 g / 10 min] is used as the B layer. A laminated film C3 having a -b layer (50 μm) was obtained by coextrusion molding. Furthermore, in the same manner as in Example 1, an attempt was made to perform lateral stretching. However, the resin of the b layer of the laminated film C3 adhered to the stretching equipment and could not be formed.

Comparative Example 2
B layer (50 μm) -a layer (50 μm) is the same as Example 1 except that norbornene ring-opening polymer hydride [glass transition temperature 140 ° C., melt flow rate 30 g / 10 min] is used as B layer. A laminated film C4 having a -b layer (50 μm) was obtained by coextrusion molding. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film D4. In addition, in the same manner as in Example 1, a retardation film D4 and a polarizing plate were laminated to produce an optical element E4. Further, the optical element E4 was incorporated into an IPS mode liquid crystal display device for evaluation. The evaluation results are shown in Tables 1 and 2.

Comparative Example 3
B layer (50 μm) -a layer (50 μm) in the same manner as in Example 1 except that a hydride of norbornene ring-opening polymer [glass transition temperature 100 ° C., melt flow rate 2 g / 10 min] is used as the B layer. A laminated film C5 having a -b layer (50 μm) was obtained by coextrusion molding. Further, in the same manner as in Example 1, transverse stretching was performed to obtain a retardation film D5. In addition, in the same manner as in Example 1, a retardation film D5 and a polarizing plate were laminated to produce an optical element E5. Further, the optical element E5 was incorporated into an IPS mode liquid crystal display device for evaluation. The evaluation results are shown in Tables 1 and 2.

Comparative Example 4
B layer (50 μm) -a layer (50 μm) in the same manner as in Example 1 except that a hydride of norbornene ring-opening polymer [glass transition temperature 140 ° C., melt flow rate 70 g / 10 min] is used as the B layer. A -b layer (50 μm) laminated film C6 was obtained by coextrusion molding. Furthermore, in the same manner as in Example 1, an attempt was made to perform transverse stretching, but the b-layer resin of the laminated film C6 was stuck to the stretching equipment and could not be formed.

From the results shown in Tables 1 and 2, the following can be understood.
From Example 1 and Example 2, it can be seen that the retardation film of the present invention is stably formed without causing breakage or burning in the film, and the variation in Re and Rth of the film are small. Furthermore, when the retardation film of the present invention is used in a liquid crystal display device to confirm the display performance, a partial hue change on the screen is not seen at all, and a good display is obtained even when observed obliquely. It can be confirmed that the display characteristics are good.

  On the other hand, when the film of Comparative Example 1 and Comparative Example 4 in which the melt flow rate value of the polynorbornene resin is larger than 50 g / 10 minutes is to be formed, the polynorbornene resin adheres to the stretching equipment. As a result, film formation cannot be performed.

  Further, in the retardation film of Comparative Example 2 in which the Tg of the polynorbornene resin is greater than 120 ° C., no rupture or burning is observed during film formation, but the variation in Re and the variation in Rth increase. When the retardation film of Comparative Example 2 was used for a liquid crystal display device to confirm the display performance, many band-like hue changes were observed over the entire screen, resulting in poor display. In addition, when the screen is observed obliquely, the band-like hue change is observed more conspicuously, and the display quality is further deteriorated.

Furthermore, although the retardation film of Comparative Example 3 having a melt flow rate value of polynorbornene-based resin smaller than 5 g / 10 minutes does not show breakage or burn at the time of film formation, the film has variations in Re and Rth. growing. In addition, when the retardation film of Comparative Example 3 was used in a liquid crystal display device to confirm the display performance, many band-like hue changes were observed over the entire screen, resulting in poor display. In addition, when the screen is observed obliquely, the band-like hue change is observed more conspicuously, and the display quality is further deteriorated.

Claims (2)

A retardation film in which a film (B layer) made of a polynorbornene resin is laminated on both surfaces of a film (A layer) made of a polystyrene resin,
When the glass transition temperatures of the polystyrene resin and the polynorbornene resin are Tg (A) (° C.) and Tg (B) (° C.), respectively, Tg (A)> Tg (B) + 20 ° C. and 80 ° C. ≦ Tg (B) ≦ 120 ° C.
A phase difference film having a melt flow rate (measured at 280 ° C. under a load of 21.18 N (condition S) according to JIS K7210) of 5 to 50 g / 10 minutes of a polynorbornene resin. When the retardation in the front direction of the A layer and the retardation in the front direction of the B layer measured with light having a wavelength of 400 to 700 nm are Re (A) and Re (B), respectively, | Re (A) |> | Re The retardation film according to claim 1, wherein (B) | and | Re (B) | are 40 nm or less.