JP2023003918A - Retardation film, polarizing plate and image display device - Google Patents

Abstract

To provide a retardation film which prevents occurrence of a crack in a solvent resistance test.SOLUTION: A retardation film is a stretched film of a cyclic polyolefin-based resin. A glass transition temperature of the retardation film is preferably 145°C or higher. An interaction radius Ro in a Hansen solubility parameter (HSP) of the retardation film, and a distance Ra between a coordinate of the HSP of the retardation film in the HSP space and a coordinate of the HSP of hexane preferably satisfies 1<Ra/Ro<2.SELECTED DRAWING: None

Description

The present invention relates to a retardation film, a polarizing plate and an image display device.

2. Description of the Related Art 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 shielding (antireflection) external light reflected by metal electrodes. A retardation film using a non-liquid crystal polymer is imparted with optical anisotropy by stretching the polymer film in at least one direction. Many polymers have positive intrinsic birefringence, increasing the refractive index in the stretch direction.

The retardation film has a positive A plate (nx>ny=nz ), negative A plate (nz=nx>ny), positive C plate (nx=ny<nz), negative C plate (nx=ny>nz) and other uniaxial films, and positive B plate (nz>nx>ny ), negative B plate (nx>ny>nz), and Z plate (nx>nz>ny).

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

When a heat-shrinkable film is attached to at least one surface of a polymer film and stretched in the longitudinal direction, due to the shrinkage force of the heat-shrinkable film, the length in the width direction is lower than in the case of normal free-end uniaxial stretching. shrinkage amount increases. Therefore, in the case of a polymer having a 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. A tropic retardation film is obtained (see, for example, Patent Document 1).

A retardation film is generally used by laminating a polarizer and a retardation film, and an image display panel is formed by laminating a polarizing plate in which a polarizer and a retardation film are laminated to an image display cell such as a liquid crystal cell or an organic EL cell. be done. An image display device is formed by connecting an image display panel to a drive circuit, combining a cover glass, a backlight, and the like, if necessary, and housing them in a housing.

Japanese Patent Application Laid-Open No. 2006-72309

In assembling an image display device, an adhesive is used when a cover glass is attached to the surface of a polarizing plate, and the end surface of the film may be exposed to the solvent contained in the adhesive. Further, when assembling the image display device, cleaning with a solvent may be carried out. Therefore, the retardation film is required to have solvent resistance.

Cyclic polyolefins are excellent in transparency and heat resistance as well as in chemical resistance, and are suitable as optical film materials for displays. However, when a solvent resistance test is conducted with the stretched retardation film of cyclic polyolefin incorporated in an image display panel, fine cracks may occur on the end face of the film when a hydrocarbon solvent such as hexane is used. . In particular, in a stretched film having refractive index anisotropy of nx>nz>ny, cracks are conspicuous in a solvent resistance test.

In view of the above, an object of the present invention is to provide a stretched retardation film in which edge cracks are less likely to occur even in a solvent resistance test using a hydrocarbon solvent such as hexane.

A retardation film of one embodiment of the present invention is a stretched film of a cyclic polyolefin resin. The glass transition temperature of the retardation film is preferably 145°C or higher. The retardation film may have a heating dimensional change rate of 0.40% or less at a temperature of 95°C.

The interaction radius Ro in the Hansen solubility parameter (HSP) space of the retardation film and the distance Ra between the coordinates of the retardation film and the coordinates of hexane in the HSP space preferably satisfy 1<Ra/Ro<2.

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

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.

A polarizing plate having a retardation film can be obtained by laminating and integrating the above retardation film with a polarizer. This polarizing plate is suitably used for forming an image display device such as a liquid crystal display device or an organic EL display device.

In the above retardation film, the generation of cracks is suppressed even when the film comes into contact with a solvent due to heating, washing, or the like in the manufacturing process of the image display device.

The retardation film of the present invention is a stretched retardation film obtained by stretching a cyclic polyolefin film. Cyclic polyolefins are polymers containing alicyclic structures in the repeating units of the main chain.

Examples of cyclic polyolefin resins include resins described in JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Specific examples include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers), and graft polymers and hydrides obtained by modifying these with unsaturated carboxylic acids or derivatives thereof. Commercially available cyclic polyolefin resins include "Zeonor" and "Zeonex" manufactured by Nippon Zeon, "Arton" manufactured by JSR, "Appel" manufactured by Mitsui Chemicals, and "Topas" manufactured by TOPAS ADVANCED POLYMERS.

As will be described in detail later, the cyclic polyolefin resin constituting the retardation film preferably has a large distance Ra between hexane and the HSP in the coordinate space of the Hansen solubility parameters (HSP).

The cyclic polyolefin film preferably contains 50% by weight or more of the cyclic polyolefin resin. The content of the cyclic polyolefin resin in the cyclic polyolefin film is more preferably 70% by weight or more, more preferably 80% by weight or more, and may be 90% by weight or more or 95% by weight or more.

Known methods such as a solution casting method and a melt extrusion method can be employed as the method for producing the cyclic polyolefin film. Although the thickness of the film is not particularly limited, it is generally about 5 μm to 300 μm. Additives such as UV absorbers, stabilizers, lubricants, and plasticizers may be contained in the film.

A retardation film can be obtained by stretching a polymer film to increase the molecular orientation in a specific direction. Examples of the stretching method include a vertical uniaxial stretching method, a horizontal uniaxial stretching method, a vertical and horizontal successive biaxial stretching method, a vertical and horizontal simultaneous biaxial stretching method, and the like. Any suitable stretching machine such as a roll stretching machine, a tenter stretching machine, a pantograph type or linear motor type biaxial stretching machine can be used as the stretching means.

In a state in which a heat-shrinkable film is laminated on at least one surface of a polymer film, the film is shrunk in a direction perpendicular to the stretching direction by utilizing the shrinkage force of the heat-shrinkable film while stretching in one direction. The refractive index in the thickness direction increases with respect to the shrinkage direction (fast axis direction), and a stretched retardation film having refractive index anisotropy of nx>nz>ny can be obtained. 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.

For example, if a laminate obtained by laminating a heat-shrinkable film on one or both sides of a polymer film is uniaxially stretched at the free end, the action of the heat-shrinkable film causes a large shrinkage in the direction perpendicular to the stretching direction (width direction). Thus, a stretched retardation film having refractive index anisotropy of nx>nz>ny is obtained. A simultaneous biaxial stretching machine may be used to stretch the film 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. In addition, while stretching in the width direction, the film is shrunk in the longitudinal direction using the shrinkage force of the heat shrinkable film, so that the width direction is the slow axis direction and the refractive index anisotropy of nx>nz>ny is achieved. It is also possible to produce a retardation film having

The heat-shrinkable film is not particularly limited as long as it heat-shrinks in a direction perpendicular to the stretching direction when the film is attached to the polymer film and stretched. The heat-shrinkable film may have anisotropic shrinkage. For example, when a laminate of a polymer film and a heat-shrinkable film is stretched in the width direction and shrunk in the longitudinal direction during stretching, a heat-shrinkable film having a greater amount of shrinkage in the longitudinal direction than in the width direction is used. good too. As an example, when a heat-shrinkable film is produced (stretched), both ends of the film are gripped with tenter clips or the like so that the distance between the clips in the width direction is increased while the distance between the clips in the width direction is increased. By moving the clip, a heat-shrinkable film that easily shrinks in the longitudinal direction can be obtained.

The material constituting the heat-shrinkable film is not particularly limited, but a material that heat-shrinks near the stretching temperature of the cyclic polyolefin film is preferable. Polyolefins such as polyethylene and polypropylene, and polyesters are preferably used as materials for heat-shrinkable films because of their excellent versatility and low cost.

The in-plane retardation Re of the retardation film is, for example, about 15 nm to 400 nm, may be 100 nm or more, or may be 150 nm or more. The retardation film may have a NZ coefficient of about 0 to 3, which is defined by NZ=(nx-nz)/(nx-ny). The NZ factor 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 according to the use of the retardation film, the optical design of the image display device, and the like. Applications of a retardation film having an NZ coefficient of less than 1 include optical compensation for liquid crystal display devices and circularly polarizing plates for shielding reflected light from organic EL display devices.

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

In the organic EL display device, a circularly polarizing plate is arranged on the viewing side of the organic EL cell in order to prevent light from being reflected by the metal electrode and the reflected light from the outside to be viewed as a specular surface. The circularly polarizing plate has a structure in which a λ/4 plate having a front retardation of 1/4 of the wavelength λ is arranged on one surface of the polarizer (the surface facing the organic EL cell). A retardation film having a refractive index anisotropy of nx>nz>ny has a small change in retardation depending on the viewing angle, so it can be used as a λ / 4 plate of a circularly polarizing plate with a refractive index anisotropy of nx>nz>ny. By using a retardation film having , it is possible to improve not only the front (normal direction) of the display device but also the oblique direction of light shielding.

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 handleability. In order to increase the in-plane 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.

The in-plane birefringence Δn of the retardation film may be 1.0×10 ⁻³ or more. The in-plane birefringence Δn=nx−ny is the difference between the in-plane slow axis refractive index nx and the in-plane fast axis refractive index ny, and is obtained by dividing the in-plane retardation Re by the thickness. be. In the stretched retardation film, Δn tends to increase as the stretch ratio increases, and as Δn increases, a large in-plane retardation can be achieved with a small thickness. Δn of the retardation film may be 1.3×10 ⁻³ or more, or 1.5×10 ⁻³ or more.

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 more difficult it is for the retardation to change due to heating. The dimensional change rate of the retardation film at 95° C. is preferably 0.40% or less. The dimensional change rate at 95°C is a value measured by thermomechanical analysis (TMA). There is a tendency that the higher the Tg, the smaller the dimensional change rate at 95°C.

In the manufacturing process of the image display device, heating may be performed for the purpose of adjusting the moisture content of the polarizer after the polarizing plate is attached to the surface of the image display cell. Moreover, the temperature of the panel may rise to about 80 to 100° C. during the lighting test. The higher the Tg of the retardation film and the smaller the rate of dimensional change at 95°C, the more likely the occurrence of cracks in the retardation film when the solvent resistance test is performed after the image display panel is heated.

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 between the HSP of hexane and the HSP in the coordinate space of the Hansen solubility parameter (HSP).

The Hansen Solubility Parameter (HSP) divides the Hildebrand solubility parameter δ into three components, the dispersion term δ _d , the polar term δ _p , and the hydrogen bonding term δ _h , and expresses them in a three-dimensional coordinate space. , and the relationship δ ² =δ _d ² +δ _p ² +δ _h ² holds. The dispersion term _δd indicates the effect of the dispersion force, the polar term _δp indicates the effect of the dipole force, and the hydrogen bond term _δh indicates the effect of the hydrogen bond force. The distance Ra between the HSPs of the two substances is Ra = {4Δδ _d ² + Δδ _p ² + Δδ _h from the difference Δδ _d in the dispersion term, the difference Δδ _p in the polar term, and the difference Δδ _h in the hydrogen bonding term between the two substances. ² } ^1/2 , the smaller the Ra, the higher the compatibility, and the larger the Ra, the lower the compatibility.

Solubility of a particular polymer in a solvent can be predicted from the HSP (δ _d , δ _p , δ _h ) and interaction radius Ro of the polymer and the HSP of the solvent. The interaction radius Ro is also referred to as the "melting sphere radius" and the ratio Ra/Ro of the HSP distance Ra to the interaction radius Ro is referred to as the relative energy difference (RED). Assuming a sphere (dissolving sphere) of radius Ro centered on the HSP coordinates of the polymer, if the coordinates of the HSP of the solvent are inside the dissolving sphere of the polymer (i.e., if Ra/Ro<1), The polymer is soluble in the solvent and is expected to be insoluble in the solvent if the HSP coordinates of the solvent are outside the solubility sphere of the polymer (ie Ra/Ro>1). If the HSP coordinates of the solvent lie on the surface of the polymer's dissolution sphere (ie Ra/Ro=1), the polymer is expected to be partially soluble in the solvent.

Details of the Hansen Solubility Parameters can be found in Charles M. Hansen, Hansen Solubility Parameters: A Users Handbook (CRC Press, 2007). HSPs for various organic solvents are known. The HSP and Ra of a polymer can be calculated by the Sphere program of the computer software Hansen Solubility Parameters in Practice (HSPiP) based on the results of solubility tests in solvents.

Cyclic polyolefin HSP and Ro can be used as solvents in toluene, hexane, methanol, trichlorobenzene, and γ-butyllactone, mixed solvents of toluene and hexane, mixed solvents of toluene and methanol, mixed solvents of toluene and trichlorobenzene, and A dissolution test is performed using a mixed solvent of toluene and γ-butyl lactone, and the result is calculated by inputting the results into the above program, assigning "1" for dissolution and "0" for non-dissolution. When the retardation film contains a plurality of polymers, a dissolution test may be performed on the retardation film, and HSP and Ro may be calculated using the above program.

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. 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 between the coordinates in the HSP space Ra={4Δδ _d ² +Δδ _p ² +Δδ _h ² } ^1/2 can be calculated.

As described above, in addition to the high glass transition temperature of the retardation film, Ra / Ro is greater than 1 (i.e., the HSP coordinates of hexane are outside the polymer dissolution sphere), so that the solvent resistance test The occurrence of cracks at the edges of the retardation film 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 cyclic polyolefin resins, Ra/Ro is generally less than 2, and Ra/Ro may be 1.8 or less, 1.6 or less, or 1.5 or less.

The generation of cracks at the edges of the retardation film in the solvent resistance test is considered to be due to the distortion of the stretched retardation film and the effects of local dissolution in the organic solvent. In a stretched retardation film, polymer chains are oriented in the stretching direction, and cracks along the stretching direction are generally likely to occur. In particular, since the cyclic polyolefin has a small intrinsic birefringence, it is necessary to increase the draw ratio in order to obtain a retardation film having a large in-plane birefringence Δn and a large in-plane retardation. Further, a stretched film having refractive index anisotropy of nx>nz>ny is stretched in the stretching direction (slow axis direction) and at the same time is highly shrunk in the direction perpendicular to the stretching direction (fast axis direction). Therefore, the degree of orientation of the polymer chains in the stretching direction is high, and cracks are likely to occur.

In the image display panel, the retardation film is attached and fixed to other members such as a polarizing plate (polarizer) and an image display cell. In this state, when heating and lighting tests are performed for adjusting the moisture content of the polarizer, the temperature of the image display panel rises to about 80 to 100.degree. Even if the image display cell is heated to about 100.degree.

In the state where the retardation film is attached to the image display cell or the like, the acting force of expansion of the film due to heating accumulates in the film as stress. When the edge of the film comes into contact with the solvent while a large amount of stress is accumulated, the stress is locally relieved at the solvent-contacted portion, but the stress concentrates in the vicinity of the solvent-contacted portion, which is thought to cause cracks. A film with a low glass transition temperature and a large dimensional change upon heating is considered to be susceptible to cracks due to contact with a solvent because of the large amount of stress that accumulates inside the film when it is attached to an image display cell or the like. In particular, a film with high molecular chain orientation, such as a stretched retardation film having a refractive index anisotropy of nx>nz>ny, is prone to cracks due to the high molecular orientation, and the stress generated by heating It is considered that the large size is also a factor in the tendency of cracks to occur.

In the present invention, since the glass transition temperature of the film is high, the dimensional change during heating is small, and the stress accumulated in the film in the image display device is reduced. In addition, since Ra / Ro is greater than 1 and the solubility in hexane is low, local stress relaxation due to contact with a solvent and concentration of stress in the surroundings are difficult to occur, and refractive index anisotropy of nx>nz>ny Even in the case where the molecular chains are highly oriented as in a stretched film exhibiting flexibility, the occurrence of cracks is thought to be suppressed.

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

As a polarizer, dichroic substances such as iodine and dichroic dyes are added to hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films. and a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride.

Among them, since it has a high degree of polarization, a polyvinyl alcohol-based film such as polyvinyl alcohol or partially formalized polyvinyl alcohol is oriented in a predetermined direction by adsorbing a dichroic substance such as iodine or a dichroic dye. Alcohol (PVA) based polarizers are preferred. For example, a PVA-based polarizer can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching.

A thin polarizer having a thickness of 10 μm or less can also be used as the PVA-based polarizer. Thin polarizers are described, for example, in JP-A-51-069644, JP-A-2000-338329, WO2010/100917, JP 4691205, JP 4751481, etc. A thin polarizing film can be mentioned. Such a thin polarizer can be obtained, for example, by stretching a PVA-based resin layer and a stretching resin substrate in a laminate state and dyeing the laminate with iodine.

The arrangement angle of the polarizer and the retardation film is not particularly limited. For example, when using a retardation film for the purpose of optical compensation to suppress light leakage when viewing the liquid crystal display device from an oblique direction, the absorption axis direction of the polarizer and the slow axis direction of the retardation film are parallel. Alternatively, it is preferable to arrange both so that they are orthogonal to each other. When a circularly polarizing plate is formed by laminating a polarizer and a retardation film, both are arranged so that the angle formed by the absorption axis direction of the polarizer and the slow axis direction of the retardation film is 45°. is preferred. Note that the arrangement angle does not have to be strictly within the above range, and may include an error of about ±2°.

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

A retardation film and a polarizing plate can be used as an optical film for an image display device. For example, an image display panel can be obtained by attaching a polarizing plate having a retardation film to the surface of an image display cell via an appropriate pressure-sensitive adhesive. When the image display cell is a liquid crystal cell, a liquid crystal display device is formed by further combining a backlight as a light source.

After the polarizing plate is attached to the surface of the image display cell, heating may be performed for the purpose of adjusting the moisture content of the polarizer. Further, during the lighting test, the panel reaches a high temperature of about 80 to 100.degree. In the present invention, since the glass transition temperature of the retardation film is high, even when the temperature rises due to heating, lighting test, etc., the stress accumulated inside or at the interface of the retardation film is small. In addition, 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 retardation The occurrence of cracks on the end face of the film is suppressed.

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.

[Synthesis Example 1]
Dicyclopentadiene: 21 parts by weight and 8-methyl-8-carboxymethyltetracyclo[4.4.0.1 ^2,5 . 1 ^7,10 ]-3-dodecene: 78 parts by weight, 2-norbornene: 1 part by weight, 1-hexene: 14.7 parts by weight as a molecular weight modifier, and toluene: 150 parts by weight as a solvent were added, and 107 °C. To this solution, a toluene solution of ethylaluminum (0.6 mol/l): 0.4 parts by weight and a toluene solution of methanol-modified tungsten hexachloride (0.025 mol/l): 1.8 parts by weight were added. C. for 1 hour to obtain a ring-opening polymer. Ru[4-CH ₃ (CH ₂ ) ₄ C ₆ H ₄ CO ₂ ]H(CO)[P(C ₆ H ₅ ) ₃ as a hydrogenation reaction catalyst was added to 360 parts by weight of the obtained ring-opening polymer solution. ]: 0.04 part by weight was added, the hydrogen gas pressure was adjusted to 9 to 10 MPa, and the reaction was carried out at a temperature of 160 to 165° C. for 3 hours. After completion of the reaction, the resulting product (hydrogenated product) was precipitated in methanol and vacuum dried to obtain a cyclic polyolefin resin (weight average molecular weight: 46000, glass transition temperature: 148°C). Using a twin-screw extruder, the resulting resin was melt-kneaded, extruded in a strand shape, cooled with water, and passed through a feeder ruder to obtain pellets.

[Comparative Example 1]
Using cyclic polyolefin resin pellets ("ARTON R5000" manufactured by JSR), an unstretched film having a thickness of 135 µm was produced by a melt extrusion method. This film was uniaxially stretched (longitudinal stretching) at a temperature of 150° C. at a magnification of 1.5 to obtain a stretched retardation film.

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

[Comparative Example 2]
Using cyclic polyolefin resin pellets ("ARTON R5000" manufactured by JSR), an unstretched film having a thickness of 135 µm was produced by a melt extrusion method. On both sides of this film, a heat-shrinkable biaxially stretched propylene film ("Torayfan" manufactured by Toray Industries, Inc.) was adhered via an adhesive to obtain a laminate. This laminate was longitudinally stretched at a temperature of 150 ° C. and a magnification of 1.3 times, and then the heat-shrinkable films laminated on both sides were peeled off to obtain a stretched retardation film (hereinafter, this stretching method is described as "Z stretching").

[Comparative Examples 3 and 4, Example 2]
Unstretched films were produced by changing the type of cyclic polyolefin resin and the thickness of the film as shown in Table 1, and Z-stretching was performed under the conditions shown in Table 1. Other than that was carried out in the same manner as in Comparative Example 2 to obtain a stretched retardation film.

[Comparative Example 5]
A commercially available cyclic polyolefin film (“Zeonor Film ZF16” manufactured by Zeon Corporation) was subjected to Z-stretching under the conditions shown in Table 1 to obtain a stretched retardation film.

[Comparative Example 6]
A commercially available cyclic polyolefin film (“Zeonor Film ZF14” manufactured by Zeon Corporation) was subjected to Z-stretching under the conditions shown in Table 1 to obtain a stretched retardation film.

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

[evaluation]
<Retardation characteristics>
The retardation film was cut into a size of 50 mm × 50 mm, and the front retardation at a measurement wavelength of 550 nm and the slow axis direction were tilted at 40 ° with a polarization and phase difference measurement system ("AxoScan" manufactured by Axometrics) as the center of rotation. The retardation in the state was measured. From these measured values, the in-plane retardation at a wavelength of 550 nm: Re=(nx−ny)×d and the NZ coefficient: NZ=(nx−nz)/(nx−ny) were calculated. nx is the refractive index in the in-plane slow axis direction, ny is the in-plane refractive index in the fast axis direction, nz is the refractive index in the thickness direction, and d is the thickness. In calculating the NZ coefficient, the average refractive index of the film measured with an Abbe refractometer manufactured by Atago Co., Ltd. was used.

<Hansen Solubility Parameter (HSP)>
About 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 it was visually confirmed whether or not the solution was dissolved. Solvents used in the dissolution test include toluene, hexane, methanol, trichlorobenzene, γ-butyllactone, mixed solvents of toluene and hexane, mixed solvents of toluene and methanol, mixed solvents of toluene and trichlorobenzene, and toluene and γ-butyllactone. A mixed solvent of The mixed solvent was varied in five or more stages in the mixing ratio in the range of 10:90 to 90:10, and the dissolution test was carried out for each mixed solvent.

Enter the sphere program of the computer software Hansen Solubility Parameters in Practice (HSPiP) as "1" for dissolved substances and "0" for those that are not dissolved, and obtain the Hansen Solubility Parameters (HSP) _δd of the resin pellet (polymer). , δ _p , and δ _h , and the radius Ro of the lysing sphere were calculated.

Furthermore, from 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 Ra = {4Δδ _d ² + Δδ _p ² + Δδ _h ² } ^1/2 was calculated to obtain the ratio Ra/Ro of the HSP distance Ra to the radius Ro of the dissolving sphere.

<Glass transition temperature>
Differential thermal analysis of the stretched retardation film was performed 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
Reference: Aluminum pan Introduced gas: Nitrogen Temperature range: Room temperature to 230°C
Heating rate: 10°C/min

<Heat dimensional change rate>
The stretched retardation film is cut into strips of 16 mm × 4 mm with the stretching direction as the long side direction, and a thermomechanical analysis device ("TMA7100" manufactured by Hitachi High-Tech Science) is used to perform thermomechanical analysis of the stretched retardation film under the following conditions. was carried out, and from the obtained TMA curve, the dimensional change rate (%) at 95 ° C. based on the sample length L ₀ at room temperature and the sample length L at 95 ° C. = 100 × (L−L ₀ ) / L ₀ was calculated.
Introduced gas: Nitrogen Load: 0.0196N
Temperature range: Room temperature to 100°C
Heating rate: 10°C/min

<Solvent resistance test>
The retardation film was cut into a size of 50 mm×50 mm and attached to a glass plate with an adhesive. This sample was heated at 95° C. for 3 hours, allowed to cool at room temperature for 20 minutes, and then hexane was added dropwise to the edges (all four sides) of the film for visual confirmation. A film in which cracks occurred at the edges of the film was evaluated as NG, and a film in which no cracks were observed was evaluated as OK.

Table 1 shows the production conditions and evaluation results of the stretched retardation films of Examples and Comparative Examples.

The uniaxially stretched retardation film of Example 1 using a cyclic polyolefin with Ra/Ro greater than 1 did not show cracks even after the solvent resistance test using hexane. The same was true for Example 2 in which Z-stretching was performed, and the same was true for Example 3 in which a cyclic polyolefin different from Examples 1 and 2 was used.

The Z-stretched films of Comparative Examples 5 and 6, in which Ra/Ro was less than 1, had cracks after the solvent resistance test. In Comparative Examples 1 to 4, although Ra/Ro was greater than 1 and the solubility in hexane was low, cracks occurred after the solvent resistance test. In Comparative Examples 1 to 4, compared to Examples 1 and 2, the glass transition temperature is lower and the dimensional change during heating is large, which is presumed to be the cause of crack generation.

From the above results, it can be seen that a retardation film having a high glass transition temperature and a high Ra/Ro ratio is less prone to cracks on the end face even when contacted with an organic solvent such as hexane after heating.

Claims (8)

A retardation film made of a stretched film of a cyclic polyolefin resin,
A glass transition temperature of 145° C. or higher,
The interaction radius Ro in the Hansen solubility parameter space of the retardation film, and the distance Ra between the coordinates in the Hansen solubility parameter space of the retardation film and the coordinates in the Hansen solubility parameter space of hexane satisfy 1 < Ra / Ro < 2,
retardation film. 2. The retardation film according to claim 1, which has an in-plane retardation of 200 nm or more. 3. The retardation film according to claim 1, which has a thickness of 10 to 300 μm. Claims 1 to 1, wherein the in-plane birefringence Δn, which is the difference between the in-plane refractive index nx in the slow axis direction and the in-plane fast axis direction refractive index ny, is 1.0×10 ⁻³ or more. 4. The retardation film according to any one of 3. Any one of claims 1 to 4, wherein the in-plane refractive index nx in the slow axis direction, the in-plane refractive index ny in the fast axis direction, and the refractive index nz in the thickness direction satisfy nx>nz>ny. The retardation film according to the item. The retardation film according to any one of claims 1 to 5, which has a dimensional change rate upon heating of 0.40% or less at a temperature of 95°C. 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. An image display device comprising an image display cell and the polarizing plate according to claim 7 .