Retardation film, polarizing plate, and image display device

Abstract

To provide a retardation film in which cracks are less likely to occur in a solvent resistance test.SOLUTION: The retardation film is a stretched film of a cycloolefin-based resin. The glass transition temperature of the retardation film is preferably 145°C or higher. An interaction radius Ro in a Hansen solubility parameter (HSP) space of the retardation film and the distance Ra between HSP coordinates of the retardation film and HSP coordinates of hexane in the HSP space preferably satisfy 1.38≤Ra / Ro<2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a retardation film, a polarizing plate, and an image display device. [Background technology]

[0002] Retardation films are used in displays such as liquid crystal display devices for optical compensation such as improving contrast and widening the viewing angle, and for blocking external light reflected by metal electrodes (anti-reflection). Retardation films made of non-liquid crystal polymers are given optical anisotropy by stretching the polymer film in at least one direction. Many polymers have positive intrinsic birefringence, and the refractive index increases in the stretching direction.

[0003] Retardation films are classified into positive A plates (nx>ny=nz), negative A plates (nz=nx>ny), and positive C plates (nx=ny) depending on the relationship between the refractive index nx in the slow axis direction in the plane, the refractive index ny in the fast axis direction in the plane, and the refractive index nz in the thickness direction.<nz)、ネガティブCプレート(nx=ny> They are classified into uniaxial films such as nz), positive B plates (nz>nx>ny), negative B plates (nx>ny>nz), and biaxial films such as Z plates (nx>nz>ny).

[0004] When a polymer film is stretched longitudinally (uniaxially stretched at the free end), the molecular chains of the polymer are oriented in the longitudinal direction (stretching direction) as a result of the stretching, and contraction occurs in the width and thickness directions. When a polymer film with a positive intrinsic refractive index is stretched longitudinally, the refractive index in the longitudinal direction (nx) increases, and the refractive index in the width direction (ny) and the refractive index in the thickness direction (nz) decrease, resulting in a positive A plate with a refractive index anisotropy of nx > ny = nz.

[0005] When a polymer film is stretched in the longitudinal direction with a heat-shrinkable film attached to at least one side thereof, the shrinkage force of the heat-shrinkable film causes a larger shrinkage in the width direction than in the case of normal free-end uniaxial stretching. Therefore, in the case of a polymer having positive intrinsic birefringence, the refractive index ny in the fast axis direction becomes smaller and the refractive index nz in the thickness direction becomes relatively larger, resulting in a retardation film having a refractive index anisotropy of nx>nz>ny (see, for example, Patent Document 1).

[0006] A retardation film is generally used by being stuck to a polarizer, and an image display panel is formed by sticking a polarizing plate, in which a polarizer and a retardation film are stacked, to an image display cell such as a liquid crystal cell or an organic EL cell. The image display panel is connected to a drive circuit, and if necessary, combined with a cover glass, a backlight, etc., and housed in a housing to form an image display device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-72309 Summary of the Invention [Problem to be solved by the invention]

[0008] In assembling an image display device, a pressure-sensitive adhesive is used to bond a cover glass to the surface of a polarizing plate, and the edge surface of the film may be exposed to a solvent contained in the pressure-sensitive adhesive. Furthermore, cleaning with a solvent may be performed during the assembly of the image display device. Therefore, the retardation film is required to have solvent resistance.

[0009] Cyclic polyolefins have excellent transparency, heat resistance, and chemical resistance, making them suitable as optical film materials for displays. However, when a stretched cyclic polyolefin retardation film is incorporated into an image display panel and subjected to a solvent resistance test, fine cracks may occur on the edge of the film if a hydrocarbon solvent such as hexane is used. The occurrence of cracks during the solvent resistance test is particularly pronounced in stretched films with a refractive index anisotropy of nx > nz > ny.

[0010] In view of the above, an object of the present invention is to provide a stretched retardation film that is less likely to develop edge cracks even in a solvent resistance test using a hydrocarbon solvent such as hexane. [Means for solving the problem]

[0011] The retardation film according to one embodiment of the present invention is a stretched film of a cyclic polyolefin resin. The retardation film preferably has a glass transition temperature of 145°C or higher. The retardation film may have a thermal dimensional change rate of 0.40% or less at a temperature of 95°C.

[0012] The interaction radius Ro of the retardation film in the Hansen solubility parameter (HSP) space and the distance Ra between the coordinate of the retardation film and the coordinate of hexane in the HSP space preferably satisfy 1.38≦Ra / Ro<2.

[0013] The retardation film may have an in-plane retardation of 200 nm or more. The retardation film may have a thickness of 10 to 300 μm. The in-plane birefringence Δn=nx−ny of the retardation film may be 1.0×10 -3 The retardation film may have a refractive index anisotropy of nx>nz>ny.

[0014] nx is the refractive index in the slow axis direction in the plane of the retardation film, ny is the refractive index in the fast axis direction in the plane of the retardation film, and nz is the refractive index in the thickness direction of the retardation film.

[0015] The retardation film can be laminated integrally with a polarizer to obtain a polarizing plate having the retardation film. This polarizing plate is suitable for use in forming image display devices such as liquid crystal display devices and organic EL display devices. [Effects of the Invention]

[0016] The retardation film is prevented from cracking even when it comes into contact with a solvent due to heating or cleaning during the manufacturing process of the image display device. DETAILED DESCRIPTION OF THE INVENTION

[0017] The retardation film of the present invention is a stretched retardation film obtained by stretching a cyclic polyolefin film. Cyclic polyolefins are polymers containing an alicyclic structure in the repeating unit of the main chain.

[0018] Examples of cyclic polyolefin resins include those described in JP-A-1-240517, JP-A-3-14882, and JP-A-3-122137. Specific examples include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers (typically random copolymers) of cyclic olefins with α-olefins such as ethylene and propylene, and graft polymers and hydrogenated products of these modified with unsaturated carboxylic acids or their derivatives. Commercially available cyclic polyolefin resins include "ZEONOR" and "ZEONEX" manufactured by Zeon Corporation, "ARTON" manufactured by JSR Corporation, "APEL" manufactured by Mitsui Chemicals, and "TOPAS" manufactured by TOPAS ADVANCED POLYMERS.

[0019] As will be described in detail later, it is preferable that the cyclic polyolefin resin constituting the retardation film has a large distance Ra from the HSP of hexane in the coordinate space of the Hansen solubility parameter (HSP).

[0020] The cyclic polyolefin film preferably contains 50% by weight or more of a cyclic polyolefin resin, more preferably 70% by weight or more, even more preferably 80% by weight or more, and may even be 90% by weight or more or 95% by weight or more.

[0021] The cyclic polyolefin film can be produced by known methods such as solution casting and melt extrusion. The thickness of the film is not particularly limited, but is generally about 5 μm to 300 μm. The film may contain additives such as ultraviolet absorbers, stabilizers, lubricants, and plasticizers.

[0022] A retardation film can be obtained by stretching a polymer film to enhance molecular orientation in a specific direction. Stretching methods include longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse sequential biaxial stretching, and longitudinal and transverse simultaneous biaxial stretching. Any appropriate stretching machine can be used as the stretching means, such as a roll stretching machine, a tenter stretching machine, or a pantograph or linear motor biaxial stretching machine.

[0023] A polymer film is laminated with a heat-shrinkable film on at least one side and stretched in one direction while shrinking the film in a direction perpendicular to the stretching direction using the shrinking force of the heat-shrinkable film, resulting in a stretched retardation film with a refractive index anisotropy of nx>nz>ny, where nx is the refractive index in the in-plane slow axis direction (stretching direction), ny is the refractive index in the in-plane fast axis direction, and nz is the refractive index in the thickness direction.

[0024] For example, if a laminate in which a heat-shrinkable film is attached to one or both sides of a polymer film is subjected to free-end uniaxial stretching, the action of the heat-shrinkable film increases shrinkage in the direction perpendicular to the stretching direction (width direction), resulting in a stretched retardation film with a refractive index anisotropy of nx>nz>ny. Using a simultaneous biaxial stretching machine, the film may be stretched in the longitudinal direction while controlling the amount of shrinkage in the width direction, while holding both ends of the film in the width direction with clips or the like. Alternatively, a retardation film in which the width direction is the slow axis direction and has a refractive index anisotropy of nx>nz>ny can be produced by shrinking the film in the longitudinal direction while stretching it in the width direction using the shrinkage force of the heat-shrinkable film.

[0025] The heat-shrinkable film is not particularly limited as long as it is heat-shrunk in a direction perpendicular to the stretching direction when attached to the polymer film and stretched. The heat-shrinkable film may have anisotropic shrinkage. For example, when stretching a laminate of a polymer film and a heat-shrinkable film, stretching the laminate in the width direction and shrinking in the longitudinal direction, a heat-shrinkable film whose shrinkage in the longitudinal direction is greater than that in the width direction may be used. As an example, when producing (stretching) the heat-shrinkable film, both ends of the film are held with tenter clips or the like, and the clips are moved so that the tenter clip spacing in the longitudinal direction increases while maintaining the clip-to-clip distance in the width direction, thereby obtaining a heat-shrinkable film that easily shrinks in the longitudinal direction.

[0026] The material for the heat-shrinkable film is not particularly limited, but is preferably one that heat-shrinks at a temperature close to the stretching temperature of the cyclic polyolefin film. Polyolefins such as polyethylene and polypropylene, and polyesters are preferably used as the material for the heat-shrinkable film because they are versatile and inexpensive.

[0027] The front retardation Re of the retardation film is, for example, about 15 nm to 400 nm, and may be 100 nm or more, or 150 nm or more. The retardation film may have an NZ coefficient defined by NZ=(nx-nz) / (nx-ny) of about 0 to 3. The NZ coefficient may be 1.5 or less, 1.0 or less, 0.1 to 0.9, 0.2 to 0.8, or 0.3 to 0.7. The front retardation and NZ coefficient of the retardation film are appropriately set depending on the application of the retardation film, the optical design of the image display device, and the like. Applications of retardation films with an NZ coefficient of less than 1 include optical compensation in liquid crystal display devices and circular polarizers for blocking reflected light in organic EL display devices.

[0028] For example, when an IPS-mode liquid crystal display device is viewed obliquely at an angle of 45 degrees to the absorption axis of the polarizer (azimuth angles of 45 degrees, 135 degrees, 225 degrees, and 315 degrees), light leakage in the black display is large, and contrast reduction and color shift are likely to occur. By placing a retardation film with a front retardation of 1 / 2 the wavelength λ and an NZ coefficient of 0.5 between the liquid crystal cell and the polarizer, black brightness in the oblique direction can be reduced and contrast can be improved.

[0029] In organic EL display devices, a circular polarizer is placed on the viewing side of the organic EL cell to prevent light from being reflected by the metal electrodes and perceived as a mirror from the outside. A circular polarizer has a configuration in which a λ / 4 plate with a front retardation of ¼ the wavelength λ is placed on one side of a polarizer (the side facing the organic EL cell). A retardation film with a refractive index anisotropy of nx>nz>ny exhibits little change in retardation with respect to the viewing angle. Therefore, using a retardation film with a refractive index anisotropy of nx>nz>ny as the λ / 4 plate of a circular polarizer can improve the blocking of light not only from the front (normal direction) of the display device but also from oblique directions.

[0030] The thickness of the retardation film is not particularly limited, but is preferably 5 to 300 μm from the viewpoint of workability such as strength and handling. To increase the front retardation, the thickness of the retardation film is preferably 10 μm or more, more preferably 20 μm or more, and may be 30 μm or more, 40 μm or more, or 50 μm or more. The thickness of the retardation film may be 250 μm or less, or 200 μm or less.

[0031] The in-plane birefringence Δn of the retardation film is 1.0 × 10 -3 or more. The in-plane birefringence Δn=nx-ny is the difference between the refractive index nx in the in-plane slow axis direction and the refractive index ny in the in-plane fast axis direction, and is the value obtained by dividing the in-plane retardation Re by the thickness. In a stretched retardation film, the Δn tends to increase as the stretching ratio increases, and the larger the Δn, the greater the in-plane retardation can be achieved with a smaller thickness. The Δn of a retardation film is 1.3×10 -3 or more, or 1.5 x 10 -3 It may be more than that.

[0032] The glass transition temperature (Tg) of the retardation film is preferably 145°C or higher, and may be 147°C or higher. The higher the Tg of the retardation film, the less likely the retardation change due to heating. The dimensional change rate of the retardation film at 95°C is preferably 0.40% or lower. The dimensional change rate at 95°C is a value measured by thermomechanical analysis (TMA). The higher the Tg, the smaller the dimensional change rate at 95°C tends to be.

[0033] In the manufacturing process of an image display device, after a polarizing plate is attached to the surface of an image display cell, heating may be performed to adjust the moisture content of the polarizer. Furthermore, during a lighting test, the temperature of the panel may rise to approximately 80 to 100°C. The higher the Tg of a retardation film and the smaller its dimensional change rate at 95°C, the more likely it is that cracks will be suppressed in the retardation film when a solvent resistance test is performed after heating the image display panel.

[0034] From the viewpoint of suppressing the occurrence of cracks in a solvent resistance test, the cyclic polyolefin resin constituting the retardation film preferably has a large distance Ra from the Hansen solubility parameter (HSP) of hexane in the coordinate space of HSP.

[0035] The Hansen solubility parameter (HSP) is calculated by multiplying the Hildebrand solubility parameter δ by the dispersion term δ d , polarity term δ p , and the hydrogen bond term δ h and expressed in three-dimensional coordinate space, and δ 2 =δ d 2 +δ p 2 +δ h 2 The following relationship holds: Dispersion term δ d is the effect of dispersion forces, and the polar term δ p is the effect of dipole-dipole forces, and the hydrogen bond term δ h indicates the effect of hydrogen bonding. The HSP distance Ra of two substances is the difference in dispersion terms between the two substances, Δδ d , the difference in polar terms Δδ p , and the difference in hydrogen bond terms Δδ h From this, Ra={4Δδ d 2 +Δδ p 2 +Δδ h 2} 1 / 2 The smaller the Ra, the higher the compatibility, and the larger the Ra, the lower the compatibility.

[0036] The solubility of a particular polymer in a solvent is determined by the HSP (δ d ,δ p ,δ h) and the interaction radius Ro, and the HSP of the solvent. The interaction radius Ro is also called the "solubility sphere radius," and the ratio Ra of the HSP distance to the interaction radius Ro, Ra / Ro, is called the relative energy difference (RED). Assuming a sphere of radius Ro (solubility sphere) centered on the coordinates of the polymer's HSP, if the coordinates of the solvent's HSP are inside the polymer's solution sphere (i.e., Ra / Ro<1), the polymer is predicted to be soluble in the solvent, and if the coordinates of the solvent's HSP are outside the polymer's solution sphere (i.e., Ra / Ro>1), the polymer is predicted to be insoluble in the solvent. If the coordinates of the solvent's HSP are on the surface of the polymer's solution sphere (i.e., Ra / Ro=1), the polymer is predicted to be partially soluble in the solvent.

[0037] Details of Hansen solubility parameters are described in "Hansen Solubility Parameters: A Users Handbook" by Charles M. Hansen (CRC Press, 2007). The HSP of various organic solvents is known. The HSP and Ra of a polymer can be calculated using the Sphere program in the computer software Hansen Solubility Parameters in Practice (HSPiP) based on the results of solubility tests in the solvent.

[0038] The HSP and Ro of cyclic polyolefins are calculated by conducting a solubility test using toluene, hexane, methanol, trichlorobenzene, and γ-butyllactone as solvents, as well as a mixed solvent of toluene and hexane, a mixed solvent of toluene and methanol, a mixed solvent of toluene and trichlorobenzene, and a mixed solvent of toluene and γ-butyllactone, and inputting the results into the above program, assigning "1" to dissolved samples and "0" to undissolved samples. When a retardation film contains multiple polymers, a solubility test is conducted on the retardation film, and the HSP and Ro can be calculated using the above program.

[0039] The interaction radius Ro in the HSP space of the retardation film (cyclic polyolefin resin) and the distance Ra between the HSP coordinates of the retardation film and the HSP coordinates of hexane in the HSP space preferably satisfy 1 < Ra / Ro. Note that the HSP of hexane is known, and (δ d ,δ p ,δ h ) = (14.9, 0, 0). Therefore, if the HSP of the retardation film (cyclic polyolefin resin) is obtained, the distance Ra between the coordinates in the HSP space can be calculated as Ra = {4Δδ d 2 + Δδ p 2 + Δδ h 2} 1 / 2 .

[0040] As described above, in addition to the high glass transition temperature of the retardation film, when Ra / Ro is greater than 1 (i.e., the HSP coordinates of hexane are outside the polymer dissolution sphere), the occurrence of cracks at the ends of the retardation film in the solvent resistance test tends to be suppressed. Ra / Ro is preferably 1.03 or more, and may be 1.05 or more or 1.07 or more. In the case of cyclic polyolefin resins, generally Ra / Ro is less than 2, and Ra / Ro may be 1.8 or less, 1.6 or less, or 1.5 or less.

[0041] The occurrence of cracks at the ends of the retardation film in the solvent resistance test is considered to be due to the strain of the stretched retardation film and the influence of local dissolution in the organic solvent. In the stretched retardation film, the polymer chains are oriented in the stretching direction, and generally, cracks are likely to occur along the stretching direction. In particular, since cyclic polyolefin has a small intrinsic birefringence, in order to obtain a retardation film with a large in-plane birefringence Δn and a large front retardation, it is necessary to increase the stretching ratio. In addition, a stretched film having a refractive index anisotropy of nx > nz > ny highly contracts in the direction perpendicular to the stretching direction (fast axis direction) simultaneously with the stretching in the stretching direction (slow axis direction). Therefore, the degree of orientation of the polymer chains in the stretching direction is high, and cracks are likely to occur.

[0042] In an image display panel, the retardation film is bonded and fixed to other components such as a polarizing plate (polarizer) and an image display cell. When heating or lighting tests are performed in this state to adjust the moisture content of the polarizer, the temperature of the image display panel rises to approximately 80 to 100°C. While the image display cell undergoes very little dimensional change even when heated to approximately 100°C, resin materials such as the retardation film expand when heated.

[0043] When a retardation film is bonded to an image display cell or the like, the force of the film's expansion due to heating accumulates as stress within the film. When the edge of the film comes into contact with a solvent while a large amount of accumulated stress is present, the stress is locally relieved at the solvent contact point, but conversely, the stress concentrates in the surrounding area, which is thought to be the cause of cracking. Films with low glass transition temperatures and large dimensional changes due to heat are likely to develop cracks due to contact with the solvent because of the large internal stress that accumulates when bonded to an image display cell or the like. In particular, films with high molecular chain orientation, such as stretched retardation films with a refractive index anisotropy of nx>nz>ny, are prone to cracking due to their high molecular orientation, and the large stress generated by heating is also thought to be a factor in the susceptibility to cracking.

[0044] In the present invention, the high glass transition temperature of the film reduces dimensional change upon heating, thereby reducing stress buildup within the film in image display devices. Furthermore, the Ra / Ro ratio is greater than 1, making the film less soluble in hexane. This reduces local stress relaxation and stress concentration in the surrounding area due to contact with the solvent, and is thought to prevent cracking even in cases where the molecular chains are highly oriented, such as in stretched films exhibiting a refractive index anisotropy of nx>nz>ny.

[0045] The retardation film of the present invention may be laminated integrally with a polarizer to form a polarizing plate. A polarizing plate can be obtained by laminating the retardation film to one main surface of the polarizer via an appropriate adhesive layer or pressure-sensitive adhesive layer. Another film may be laminated between the polarizer and the retardation film.

[0046] Examples of polarizers include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films, which are uniaxially stretched after adsorbing dichroic substances such as iodine or dichroic dyes, and polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride.

[0047] Among these, polyvinyl alcohol (PVA) polarizers are preferred because of their high polarization degree. For example, a PVA polarizer can be obtained by dyeing a polyvinyl alcohol film with iodine and stretching it, and then aligning the film in a predetermined direction.

[0048] The PVA-based polarizer may be a thin polarizer having a thickness of 10 μm or less. Examples of thin polarizers include thin polarizing films described in JP-A-51-069644, JP-A-2000-338329, WO2010 / 100917, Japanese Patent No. 4691205, and Japanese Patent No. 4751481. Such thin polarizers can be obtained, for example, by stretching a PVA-based resin layer and a resin substrate for stretching in a laminate state, and then dyeing the laminate with iodine.

[0049] The arrangement angle between the polarizer and the retardation film is not particularly limited. For example, when a retardation film is used for the purpose of optical compensation to suppress light leakage when a liquid crystal display device is viewed from an oblique direction, it is preferable to arrange both of them so that the absorption axis direction of the polarizer and the slow axis direction of the retardation film are parallel or perpendicular to each other. When a polarizer and a retardation film are laminated to form a circular polarizing plate, it is preferable to arrange both of them so that the angle between the absorption axis direction of the polarizer and the slow axis direction of the retardation film is 45°. Note that the arrangement angle does not need to be strictly within the above range and may include an error of about ±2°.

[0050] A transparent film as a polarizer protective film may be attached to the other surface of the polarizer via an appropriate adhesive layer or pressure-sensitive adhesive layer. An optical film other than the above-mentioned retardation film and polarizer protective film may be laminated on the polarizing plate. An adhesive layer or pressure-sensitive adhesive layer for laminating the polarizing plate to an image display cell or the like may be laminated on the polarizing plate.

[0051] The retardation film and the polarizing plate can be used as an optical film for an image display device. For example, an image display panel can be obtained by bonding a polarizing plate having a retardation film to the surface of an image display cell via an appropriate adhesive. When the image display cell is a liquid crystal cell, a liquid crystal display device can be formed by further combining it with a backlight as a light source.

[0052] After laminating a polarizing plate to the surface of the image display cell, heating may be performed for the purpose of adjusting the moisture content of the polarizer, etc. Furthermore, during a lighting test, the panel reaches a high temperature of approximately 80 to 100°C. In the present invention, since the glass transition temperature of the retardation film is high, even if the temperature rises due to heating or a lighting test, stress accumulated inside or at the interface of the retardation film is small. Furthermore, since the resin material constituting the retardation film has low solubility in hydrocarbon solvents such as hexane (large Ra / Ro), even if the end surface of the retardation film comes into contact with an organic solvent after heating, the occurrence of cracks at the end surface of the retardation film is suppressed. [Example]

[0053] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0054] [Synthesis Example 1] Into a reaction vessel purged with nitrogen, 21 parts by weight of dicyclopentadiene and 8-methyl-8-carboxymethyltetracyclo[4.4.0.1 2,5 .1 7,1078 parts by weight of ]-3-dodecene, 1 part by weight of 2-norbornene, 14.7 parts by weight of 1-hexene as a molecular weight modifier, and 150 parts by weight of toluene as a solvent were added and heated to 107 °C. 0.4 parts by weight of a toluene solution of ethylaluminum (0.6 mol / L) and 1.8 parts by weight of a toluene solution of methanol-modified tungsten hexachloride (0.025 mol / L) were added to this solution, and the reaction was carried out for 1 hour at 107 °C to obtain a ring-opened polymer. 0.04 parts by weight of Ru[4-CH3(CH2)4C6H4CO2]H(CO)[P(C6H5)3] was added as a hydrogenation catalyst to 360 parts by weight of the resulting ring-opened polymer solution, and the reaction was carried out for 3 hours at a hydrogen gas pressure of 9 to 10 MPa and a temperature of 160 to 165 °C. After the reaction was completed, the resulting product (hydrogenated product) was precipitated in methanol and vacuum dried to obtain a cyclic polyolefin resin (weight average molecular weight: 46,000, glass transition temperature: 148°C). The resulting resin was melt-kneaded using a twin-screw extruder, extruded into strands, cooled with water, and passed through a feeder rudder to obtain pellets.

[0055] [Comparative Example 1] A cyclic polyolefin resin pellet ("ARTON R5000" manufactured by JSR) was melt-extruded to produce an unstretched film with a thickness of 135 μm. This film was then uniaxially stretched (longitudinal stretching) at a temperature of 150°C and a stretching ratio of 1.5 to obtain a stretched retardation film.

[0056] [Example 1] An unstretched film having a thickness of 60 μm was produced by melt extrusion using the pellets of the cyclic polyolefin resin obtained in Synthesis Example 1. This film was stretched longitudinally under the conditions shown in Table 1 to obtain a stretched retardation film.

[0057] Comparative Example 2 A 135 μm thick unstretched film was prepared by melt extrusion using pellets of cyclic polyolefin resin ("ARTON R5000" manufactured by JSR). Heat-shrinkable biaxially oriented propylene films ("TORAYFAN" manufactured by Toray) were attached to both sides of this film via an adhesive to obtain a laminate. This laminate was stretched longitudinally at a temperature of 150°C and a stretching ratio of 1.3, and then the heat-shrinkable films attached to both sides were peeled off to obtain a stretched retardation film (hereinafter, this stretching method will be referred to as "Z-stretching").

[0058] [Comparative Examples 3 and 4, Example 2] Unstretched films were prepared by changing the type of cyclic polyolefin resin and the film thickness as shown in Table 1, and Z-stretching was performed under the conditions shown in Table 1. Otherwise, a stretched retardation film was obtained in the same manner as in Comparative Example 2.

[0059] Comparative Example 5 A commercially available cyclic polyolefin film ("ZEONORFILM ZF16" manufactured by ZEON Corporation) was subjected to Z-stretching under the conditions shown in Table 1 to obtain a stretched retardation film.

[0060] Comparative Example 6 A commercially available cyclic polyolefin film ("ZEONORFILM ZF14" manufactured by ZEON Corporation) was subjected to Z-stretching under the conditions shown in Table 1 to obtain a stretched retardation film.

[0061] [Reference example 3] Cyclic olefin polymer (COP) resin pellets ("ARTON R5000" manufactured by JSR) were dissolved in methylene chloride, and an unstretched film with a thickness of 100 μm was produced by the solution film formation method. Z-stretching was performed under the conditions shown in Table 1 to obtain a stretched retardation film.

[0062] [evaluation] <Phase difference characteristics> The retardation film was cut into a 50mm x 50mm piece and measured using a polarization / retardation measurement system (Axometrics "AxoScan") at a wavelength of 550nm. The in-plane retardation (Re) and the retardation (NZ) were measured with the sample tilted 40° around the slow axis. From these measurements, the in-plane retardation (Re) at a wavelength of 550nm was calculated as Re = (nx - ny) x d, and the NZ coefficient (NZ) was calculated as NZ = (nx - nz) / (nx - ny). nx is the in-plane refractive index along the slow axis, ny is the in-plane refractive index along the fast axis, nz is the refractive index in the thickness direction, and d is the thickness. The average refractive index of the film measured with an Abbe refractometer (Atago Co., Ltd.) was used to calculate the NZ coefficient.

[0063] <Hansen Solubility Parameter (HSP)> Approximately 10 g of resin pellets (film pieces in Comparative Examples 5 and 6) were dissolved in 50 mL of solvent in an environment of 25°C, and whether or not they dissolved was confirmed visually. The solvents used in the dissolution test were toluene, hexane, methanol, trichlorobenzene, γ-butyllactone, a mixed solvent of toluene and hexane, a mixed solvent of toluene and methanol, a mixed solvent of toluene and trichlorobenzene, and a mixed solvent of toluene and γ-butyllactone. The mixed solvents were varied in mixing ratios of 10:90 to 90:10 in five or more steps, and dissolution tests were carried out for each mixed solvent.

[0064] The dissolved particles were assigned a value of "1" and the undissolved particles were assigned a value of "0." These values ​​were then entered into the Sphere program of the computer software Hansen Solubility Parameters in Practice (HSPiP) to calculate the Hansen solubility parameter (HSP) δ of the resin pellets (polymer). d , δ p , and δ h , as well as the radius of the molten sphere, Ro, were calculated.

[0065] Furthermore, the HSP of the polymer and the HSP of hexane (δ d ,δ p ,δ h) = (14.9,0,0), the HSP distance between the polymer and hexane is Ra = {4Δδ d 2 +Δδ p 2 +Δδ h 2} 1 / 2 was calculated, and the ratio Ra / Ro of the HSP distance Ra to the radius Ro of the melting sphere was determined.

[0066] <Glass transition temperature> The stretched retardation film was subjected to differential thermal analysis under the following conditions using a differential scanning calorimeter (DSC6200 manufactured by SII), and the inflection point of the obtained DSC curve was taken as the glass transition temperature. Sample amount: 7-9 mg See: Aluminum pan Inlet gas: Nitrogen Temperature range: Room temperature to 230°C Heating rate: 10°C / min

[0067] <Dimensional change rate due to heating> The stretched retardation film was cut into a 16 mm x 4 mm strip with the stretching direction as the long side direction, and a thermomechanical analysis of the stretched retardation film was performed under the following conditions using a thermomechanical analyzer ("TMA7100" manufactured by Hitachi High-Tech Science). From the obtained TMA curve, the dimensional change rate at 95°C (%) = 100 × (L - L) / L was calculated based on the sample length L0 at room temperature and the sample length L at 95°C. Inlet gas: Nitrogen Load: 0.0196N Temperature range: Room temperature to 100°C Heating rate: 10°C / min

[0068] <Solvent resistance test> The retardation film was cut into a size of 50 mm x 50 mm and attached to a glass plate with adhesive. This sample was heated at 95 ° C for 3 hours and allowed to cool at room temperature for 20 minutes. After that, hexane was dropped onto the edge (all four sides) of the film and visually inspected. Films with cracks at the edge were rated as NG, and films with no cracks were rated as OK.

[0069] Table 1 shows the production conditions and evaluation results of the stretched retardation films of the Examples, Reference Examples, and Comparative Examples.

[0070] [Table 1]

[0071] The uniaxially stretched retardation film of Example 1, which used a cyclic polyolefin with an Ra / Ro ratio of more than 1, showed no cracks even after a solvent resistance test using hexane. The same was true for Example 2, which was subjected to Z-stretching.

[0072] The Z-stretched films of Comparative Examples 5 and 6, in which the Ra / Ro ratio was less than 1, developed cracks after the solvent resistance test. In Comparative Examples 1 to 4, cracks developed after the solvent resistance test, even though the Ra / Ro ratio was greater than 1 and the solubility in hexane was low. It is presumed that the glass transition temperature of Comparative Examples 1 to 4 was lower than that of Examples 1 and 2, and the dimensional change upon heating was greater, which was the cause of the cracks.

[0073] From the above results, it can be seen that a retardation film having a high glass transition temperature and a large Ra / Ro is less likely to develop cracks on the edge surface even when it comes into contact with an organic solvent such as hexane after heating.

Claims

1. A retardation film made of a stretched film of a cyclic polyolefin resin, The glass transition temperature is 145°C or higher, The interaction radius Ro of the retardation film in the Hansen solubility parameter space and the distance Ra between the coordinate of the retardation film in the Hansen solubility parameter space and the coordinate of hexane in the Hansen solubility parameter space satisfy 1.38≦Ra / Ro<2; Phase contrast film.

2. The retardation film according to claim 1 , wherein the in-plane retardation is 200 nm or more.

3. 3. The retardation film according to claim 1, having a thickness of 10 to 300 μm.

4. The in-plane birefringence Δn, which is the difference between the refractive index nx in the in-plane slow axis direction and the refractive index ny in the in-plane fast axis direction, is 1.0×10 －３ The retardation film according to any one of claims 1 to 3.

5. The retardation film according to any one of claims 1 to 4, wherein the refractive index nx in the in-plane slow axis direction, the refractive index ny in the in-plane fast axis direction, and the refractive index nz in the thickness direction satisfy nx>nz>ny.

6. The retardation film according to any one of claims 1 to 5, wherein a thermal dimensional change rate at a temperature of 95°C is 0.40% or less.

7. A polarizing plate comprising a polarizer and the retardation film according to any one of claims 1 to 6 laminated on one surface of the polarizer.

8. An image display device comprising an image display cell and the polarizing plate according to claim 7.

Images