TW202219562A - Retardation film, polarizing plate with retardation layer, and image display device - Google Patents

Abstract

Provided is a retardation film which is formed from an inexpensive resin film and is extremely thin, and in which the Nz coefficient is controlled to within a prescribed range. The retardation film according to an embodiment of the present invention is constituted from a polyester resin stretched film, and the Nz coefficient thereof is smaller than 1.8. Here, Nz = (nx - nz)/(nx - ny), where nx is the refractive index in the direction in which the in-plane refractive index is maximized, ny is the refractive index in the direction orthogonal to the direction in which the in-plane refractive index is maximized, and nz is the refractive index in the thickness direction.

Description

Retardation film, polarizing plate with retardation layer, and image display device

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

In recent years, with the spread of thin displays, an image display device (organic EL display device) mounted with an organic EL (Electroluminescence) panel has been proposed. The organic EL panel has a highly reflective metal layer, which is prone to problems such as reflection of external light or reflection into the background. Therefore, it is known to prevent such problems by providing a retardation film on the viewing side. As a material of retardation film, a liquid crystal material is mentioned, for example. However, the liquid crystal material is expensive and disadvantageous in terms of cost. As a material for a retardation film in place of an expensive liquid crystal material, a polyester-based resin film has been used. However, in the retardation film using a polyester-based resin film, the retardation in the thickness direction (as a result, the Nz coefficient) becomes too large, and the desired optical properties may not be obtained. prior art literature Patent Literature

Patent Document 1: Japanese Patent No. 3325560

[Problems to be Solved by Invention]

The present invention has been accomplished in order to solve the above-mentioned problems, and an object of the present invention is to provide a retardation film formed of an inexpensive resin film, having an extremely thin thickness and having the Nz coefficient controlled within a specific range. [Technical means to solve problems]

The retardation film of the embodiment of the present invention is composed of a stretched resin film of polyester resin, and has an Nz coefficient of less than 1.8. Here, Nz=(nx-nz)/(nx-ny), nx is the refractive index in the direction of the maximum refractive index in the plane, ny is the refractive index in the direction perpendicular to the direction of the maximum refractive index in the plane, nz is the refractive index in the thickness direction. In one Embodiment, the thickness of the said retardation film is 20 micrometers or less. In one embodiment, in the X-ray diffraction measurement using CuKα rays of the retardation film, the integrated intensity α of the crystalline peak derived from polyester existing in the range of the diffraction angle 2θ=25.5°±1.5° and the presence of The ratio (α/β) of the integrated intensity β of the crystallization peak derived from the polyester in the range of 2θ=17.0°±1.0° is 1.0 or more. In one embodiment, the in-plane retardation value Re(550) of the retardation film is 50 nm to 400 nm. In this case, the in-plane retardation value Re(550) may be 220 nm to 320 nm, or 100 nm to 200 nm. According to another aspect of the present invention, a polarizing plate with a retardation layer is provided. The polarizing plate with a retardation layer includes a polarizing element and the above-mentioned retardation film. In one embodiment, the above-mentioned polarizing plate with a retardation layer includes a polarizing element and a retardation film whose in-plane retardation value Re(550) is 100 nm to 200 nm, and the absorption axis of the polarizing element is related to the phase difference. The angle formed by the retardation axis of the differential film is 35° to 55°. In one embodiment, the above-mentioned polarizing plate with retardation layer sequentially includes a polarizing element, the above-mentioned retardation film whose in-plane retardation value Re(550) is 220 nm to 320 nm, and the above-mentioned in-plane retardation value Re (550) is a retardation film of 100 nm to 200 nm. The angle formed between the absorption axis of the polarizing element and the retardation axis of the retardation film whose in-plane retardation value Re(550) is 220 nm to 320 nm is 5° to 20°. The angle formed by the retardation axis of the retardation film whose in-plane retardation value Re(550) is 100 nm to 200 nm is 70° to 85°. According to yet another aspect of the present invention, an image display device is provided. The image display device includes the above-mentioned polarizing plate with a retardation layer. [Effect of invention]

According to the embodiment of the present invention, by extending a specific polyester-based resin film under specific stretching conditions (especially, stretching temperature), a retardation film with extremely thin thickness and controlled Nz coefficient within a specific range can be realized.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

(Definition of Terms and Symbols) Definitions of terms and symbols in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is the largest (ie, the direction of the slow axis), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the direction of the advance axis), " nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d when the thickness of the layer (film) is d (nm). (3) Phase difference in thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is obtained by the formula: Rth(λ)=(nx−nz)×d when the thickness of the layer (film) is d (nm). (4) Nz coefficient The Nz coefficient is obtained by Nz=Rth/Re. That is, the Nz coefficient is obtained by (nx-nz)/(nx-ny).

A. retardation film The retardation film which concerns on embodiment of this invention consists of the stretched resin film of polyester-type resin. By using a polyester-based resin, a retardation film can be obtained at low cost.

The in-plane retardation value Re(550) of the retardation film is typically 50 nm to 400 nm, preferably 100 nm to 320 nm. In one embodiment, the above retardation film can function as a λ/4 plate. In this case, the in-plane retardation value Re(550) of the retardation film is preferably 100 nm to 200 nm, more preferably 120 nm to 180 nm. In another embodiment, the above retardation film can function as a λ/2 plate. In this case, the in-plane retardation value Re(550) of the retardation film is preferably 220 nm to 320 nm, more preferably 240 nm to 300 nm.

In the embodiment of the present invention, the Nz coefficient of the retardation film is less than 1.8, preferably less than 1.2, more preferably less than 1.0. The Nz coefficient is further preferably 0.2 to 0.9, particularly preferably 0.4 to 0.9. Therefore, it is preferable that the refractive index characteristic of the said retardation film shows the relationship of nx>ny≧nz or nx>nz>ny, and it is more preferable that it shows the relationship of nx>nz>ny. According to the embodiment of the present invention, a retardation film with a small Nz coefficient, which has been difficult to achieve in the past, can be realized by using a polyester-based resin, and especially a so-called Z film (nx>nz>ny) can be realized. Such a retardation film can be realized by controlling the stretching conditions (especially the stretching temperature) as described below.

The above retardation film preferably has the integrated intensity α of the crystalline peak derived from polyester existing in the range of the diffraction angle 2θ=25.5°±1.5° and the integral intensity α existing in 2θ= The ratio (α/β) of the integrated intensity β of the crystallization peak derived from the polyester in the range of 17.0°±1.0° is 1.0 or more. The ratio (α/β) is more preferably 1.5 to 5.0, still more preferably 2.0 to 4.5, still more preferably 2.2 to 4.2. If the ratio (α/β) is in such a range, it becomes possible to easily realize a retardation film having the desired Nz coefficient described above. The reason for this is presumed as follows. However, the embodiments of the present invention are not bound by this presumption. The integrated intensity α means the integrated intensity derived from the (100) plane of the polyester, and the integrated intensity β means the integrated intensity derived from the (010) plane of the polyester. Therefore, the ratio (α/β) is relatively large, which typically means that the ring structure (typically, an aromatic ring and an aliphatic ring) contained in the polyester resin constituting the retardation film is relative to the main surface of the film. Has an angle (erect). As a result, the refractive index nz in the thickness direction becomes large, and the Nz coefficient becomes small. That is, in the retardation film of the polyester-based resin according to the embodiment of the present invention, it is estimated that the polyester molecules constituting the film are in a different alignment state from the previous one.

The thickness of the said retardation film becomes like this. Preferably it is 20 micrometers or less, More preferably, it is 15 micrometers or less, More preferably, it is 10 micrometers or less. The lower limit of the thickness of the retardation film may be 0.5 μm. When the thickness of the retardation film is within such a range, the crystallinity of the retardation film becomes sufficient, and excellent heat resistance can be obtained. Furthermore, the above-mentioned retardation film is excellent in that it is a thin retardation film as described above and satisfies the above-mentioned Nz coefficient.

The MIT (bending resistance) number of the retardation film is preferably 1000 times or more, more preferably 1500 times or more, and still more preferably 2000 times or more. The upper limit of the MIT times of the retardation film may be 20,000 times. According to the embodiment of the present invention, it is possible to obtain a retardation film that can achieve both the above-mentioned Nz coefficient and such flexibility.

The puncture strength of the retardation film is preferably 40 g to 1800 g, more preferably 200 g to 1800 g, and still more preferably 400 g to 1800 g. According to the embodiment of the present invention, a retardation film which can achieve both the above-mentioned Nz coefficient and such crack resistance can be obtained.

The above-mentioned retardation film may be a single sheet or an elongated shape. The elongated retardation film having a slow phase axis in a specific direction with respect to the elongated direction can be laminated with other optical films (eg polarizers) by roll-to-roll, thus significantly improving the lamination optics. Manufacturing efficiency of films (eg, polarizers with retardation layers). Such an elongated retardation film can be obtained by extending obliquely. Regarding the elongated retardation film having a retardation axis in a direction substantially orthogonal or parallel to the elongated direction, the film itself is relatively easy to manufacture, and a retardation film in a desired direction can be obtained by cutting A monolithic retardation film for the shaft. In the present specification, "stripe" means an elongated shape with a sufficiently long length relative to the width, and includes, for example, an elongated shape whose length is preferably 10 times or more, and more preferably 20 times or more, relative to the width.

B. Polyester resin The retardation film is composed of a stretched resin film of polyester-based resin as described above. The polyester-based resin can be obtained by polycondensation of a carboxylic acid component and a polyol component.

As a carboxylic acid component, an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and an alicyclic dicarboxylic acid are mentioned. As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalenedicarboxylic acid, diphenic acid, 4,4'- Hydroxybenzoic acid, 2,5-naphthalenedicarboxylic acid. As aliphatic dicarboxylic acid, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2- Dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, methylenesuccinic acid, thiodipropionic acid, diglycolic acid. As alicyclic dicarboxylic acid, for example, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-cyclohexanedicarboxylic acid, Nor alkane dicarboxylic acid, adamantane dicarboxylic acid. The carboxylic acid component can be derivatives such as esters, chlorides, acid anhydrides, etc., such as dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 2,6-naphthalene dicarboxylate, dimethyl isophthalate esters, dimethyl terephthalate and diphenyl terephthalate. The carboxylic acid component may be used alone or in combination of two or more.

As a polyhydric alcohol component, dihydric alcohol is mentioned typically. As diols, aliphatic diols, alicyclic diols, and aromatic diols may, for example, be mentioned. Examples of aliphatic diols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propylene glycol, and 2,4-dimethyl-2-ethylhexane -1,3-diol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2 -Isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1, 5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol. Examples of alicyclic diols include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, and tricyclodecane. Dimethanol, adamantanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol. As the aromatic diol, for example, 4,4'-thiobiphenol, 4,4'-methylenediphenol, 4,4'-(2-norarylene)diphenol, 4,4'- 4'-dihydroxybiphenol, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, 4,4'-isopropylidene phenol, 4,4'-isopropylidene bis(2,6-dihydroxybenzene) chlorophenol) 2,5-naphthalenediol and p-Xylene-diol. The polyol component may be used alone or in combination of two or more.

As the polyester-based resin, polyethylene terephthalate (PET) or modified polyethylene terephthalate is preferably used. Polyethylene terephthalate and modified polyethylene terephthalate can also be used in blends.

As the modified polyethylene terephthalate, for example, a modified polyethylene terephthalate including a structural unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol, or isophthalic acid can be mentioned. Ethylene phthalate. The ratio of diethylene glycol in the polyol component is preferably more than 0 mol % and 10 mol % or less, more preferably more than 0 mol % and 3 mol % or less. The ratio of 1,4-butanediol in the polyol component is preferably more than 0 mol % and 10 mol % or less, more preferably more than 0 mol % and 3 mol % or less. The ratio of 1,3-propanediol in the polyol component is preferably more than 0 mol % and 10 mol % or less, more preferably more than 0 mol % and 3 mol % or less. The ratio of the isophthalic acid in the carboxylic acid component is preferably more than 0 mol % and 10 mol % or less, more preferably more than 0 mol % and 8 mol % or less. Within such a range, a polyester film having good crystallinity can be obtained. In addition, the molar % described above is the molar % with respect to the sum total of all repeating units of a polymer.

C. Manufacturing method of retardation film The manufacturing method of the retardation film which concerns on embodiment of this invention includes extending|stretching a polyester-type resin film.

The resin film can be obtained, for example, by film-forming resins such as the polyester resin described in the item B. As a method of forming a film, any appropriate molding processing method can be adopted. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP (fiberglass reinforced plastics) molding, casting A coating method (eg, a casting method), a calendering method, a hot pressing method, and the like. Among them, the extrusion molding method or the casting coating method which can improve the smoothness of the obtained film and obtain good optical uniformity is preferable. In the case of the casting coating method, there is a concern that the residual solvent may cause a problem. Therefore, the extrusion molding method is particularly preferred, and among them, from the viewpoints of the productivity of the film and the easiness of the subsequent stretching treatment, the preferred Melt extrusion molding method using T-die. The molding conditions can be appropriately set according to the composition and type of the resin to be used, properties desired as a retardation film, and the like.

By extending the polyester-based resin film obtained above in the conveyance direction (MD direction (Machine Direction, machine direction)), a stretched resin film having molecular alignment in the MD direction can be obtained. That is, a retardation film having a slow axis in a direction substantially parallel to the MD direction (longitudinal direction) can be obtained. As the stretching method, any appropriate method can be adopted as long as the stretched resin film can have molecular alignment in the MD direction. For example, uniaxial extension or biaxial extension can be exemplified. The stretching ratio of the uniaxial stretching is preferably more than 1.0 times and 4.0 times or less, more preferably 2.0 times to 3.5 times. The biaxial extension can be simultaneous biaxial extension or successive biaxial extension. The stretching ratio in the longitudinal direction is preferably more than 1.0 times and 4.0 times or less, more preferably 2.0 times to 3.5 times. The stretching ratio in the width direction is preferably 1.0 times to 4.0 times, more preferably 2.0 times to 3.5 times.

The polyester-based resin film obtained above can be used for diagonal stretching, and the stretched resin film obtained above can be further used for diagonal stretching or TD direction (Transverse Direction) (width direction). extend. Thereby, the retardation film which has a retardation axis in the direction which has a specific angle with respect to the MD direction (longitudinal direction) can be obtained. The specific angle can be changed according to the in-plane retardation of the retardation film. In one embodiment, the specific angle is preferably 5° to 20°, more preferably 10° to 15°, and more preferably about 12.5°; in another embodiment, preferably 35° to 55°, More preferably, it is 40° to 50°, still more preferably 42° to 48°, and particularly preferably about 45°. The oblique stretching can be performed by, for example, using a tenter stretching machine and changing the feed speed of the left and right clips holding the ends in the width direction of the film. By adjusting the feed speed difference between the left and right clamps, the direction of the slow axis (alignment angle) can be controlled. The magnification of the oblique stretching is preferably 1.1 times to 3.0 times, more preferably 1.3 times to 2.8 times, and still more preferably 1.5 times to 2.5 times.

The stretching temperature of the resin film is preferably Tg-20°C to Tg+20°C, more preferably Tg-15°C to Tg+15°C, still more preferably Tg-10°C to Tg+10°C. Furthermore, the glass transition temperature of the constituent material of the Tg-based film. The specific extension temperature may be, for example, 82°C to 89°C, or, for example, 84°C to 89°C, or, for example, 85°C to 88°C.

D. Polarizing plate with retardation layer The retardation film described in the above-mentioned items A to C can be provided in the form of a laminate with other optical films and/or optical members. In one embodiment, the retardation film can be provided in the form of a laminate (typically, a polarizing plate with a retardation layer) and a polarizing element (substantially, a polarizing plate). Therefore, an embodiment of the present invention includes a polarizing plate with a retardation layer including the above retardation film. The polarizing plate with retardation layer which concerns on embodiment of this invention is equipped with a polarizing element and the said retardation film. In the polarizing plate with the retardation layer, the angle formed by the absorption axis of the polarizing element and the retardation axis of the retardation film can be appropriately set according to the application and purpose. In one embodiment, the above-mentioned angles are substantially orthogonal. In another embodiment, the above-mentioned angles are substantially parallel. Furthermore, in another embodiment, the above-mentioned angle is preferably 35° to 55°, more preferably 40° to 50°, further preferably 42° to 48°, and particularly preferably about 45°.

In one embodiment, the retardation film included in the above-mentioned polarizing plate with a retardation layer can function as a λ/2 plate. The in-plane retardation value Re(550) of the retardation film is preferably 220 nm to 320 nm, more preferably 240 nm to 300 nm. In this case, the angle formed by the absorption axis of the polarizing element and the retardation axis of the laminated retardation film is preferably substantially orthogonal or substantially parallel.

In one embodiment, the retardation film included in the above-mentioned polarizing plate with a retardation layer can function as a λ/4 plate. The in-plane retardation value Re(550) of the retardation film is preferably 100 nm to 200 nm, more preferably 120 nm to 180 nm. In this case, the angle formed by the absorption axis of the polarizing element and the retardation axis of the laminated retardation film is preferably 35° to 55°, more preferably 40° to 50°, and more preferably 42° to 48° , preferably about 45°.

In one embodiment, the polarizing plate with a retardation layer includes a polarizing element, the retardation film functioning as a λ/2 retardation plate, and the retardation film functioning as a λ/4 retardation plate in this order. The angle formed between the absorption axis of the polarizing element and the retardation axis of the retardation film functioning as a λ/4 plate is preferably 5° to 20°, more preferably 10° to 15°, and more preferably about 12.5° . Furthermore, the angle formed between the absorption axis of the polarizing element and the retardation axis of the retardation film functioning as a λ/2 plate is preferably 70° to 85°, more preferably 75° to 80°, and more preferably about 77.5°.

In the above-mentioned polarizing plate with retardation layer, a protective layer may be disposed on at least one side of the polarizing element.

As the polarizing element, any appropriate polarizing element can be used. For example, the resin film forming the polarizing element may be a single-layer resin film, or may be a laminate of two or more layers.

As a specific example of the polarizing element which consists of a single-layer resin film, hydrophilicity for polyvinyl alcohol (PVA) type film, partially formalized PVA type film, ethylene-vinyl acetate copolymer type partially saponified film, etc. can be mentioned. Polymer film, which is obtained by dyeing and stretching treatment with dichroic substances such as iodine or dichroic dyes; polyolefin-based alignment films such as dehydration treated products of PVA or dehydrochlorination products of polyvinyl chloride, etc. From the viewpoint of being excellent in optical properties, it is preferable to use a polarizing element obtained by dyeing a PVA-based film with iodine and uniaxially extending it.

The above-mentioned dyeing with iodine can be performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 times to 7 times. The extension can be carried out after the dyeing treatment or simultaneously with the dyeing. Moreover, you may dye it after extending|stretching. The PVA-based film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, and the like as necessary. For example, by immersing the PVA film in water and washing it before dyeing, not only the stains and anti-blocking agents on the surface of the PVA film can be removed, but also the PVA film can be swelled to prevent uneven dyeing.

As a specific example of the polarizing element obtained by using the laminate, a laminate using a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a resin substrate and coating A polarizing element obtained by a laminate of PVA-based resin layers formed on the resin substrate. A polarizing element obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate can be produced, for example, by the following steps: coating a PVA-based resin solution on the resin substrate, This is dried to form a PVA-based resin layer on a resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and the laminate is stretched and dyed to make the PVA-based resin layer a polarizer. In this embodiment, it is preferable to form the polyvinyl-alcohol-type resin layer containing a halide and a polyvinyl-alcohol-type resin on one side of a resin base material. The stretching is typically performed by immersing the layered body in a boric acid aqueous solution. Further, the stretching may further include a step of stretching the laminate in air at a high temperature (eg, 95° C. or higher) before stretching in a boric acid aqueous solution, if necessary. Moreover, in this embodiment, it is preferable to subject a laminated body to the drying shrinkage process which shrinks 2% or more in the width direction by heating while conveying in the longitudinal direction. Typically, the manufacturing method of the present embodiment includes the steps of sequentially performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment on the laminate. By introducing the auxiliary extension, when the PVA is coated on the thermoplastic resin, the crystallinity of the PVA can also be improved, and higher optical properties can be achieved. In addition, by simultaneously improving the orientation of PVA in advance, when immersed in water in the subsequent dyeing step or stretching step, problems such as decrease in the orientation of PVA or dissolution can be prevented, and higher optical properties can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the alignment disorder of the polyvinyl alcohol molecules and the decrease in the alignment property can be suppressed. Thereby, the optical characteristics of the polarizing element obtained by the process step of immersing a laminated body in liquid, such as dyeing process and an underwater extension process, can be improved. Furthermore, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. The obtained laminate of resin substrate/polarizing element can be used as it is (that is, the resin substrate can be used as a protective layer of the polarizing element), or the resin substrate can be peeled off from the laminate of resin substrate/polarizing element, and placed in the This peeling surface can be used by laminating any appropriate protective layer as needed. Details of the manufacturing method of such a polarizing element are described in, for example, Japanese Patent Laid-Open No. 2012-73580 and Japanese Patent No. 6470455 . All the descriptions of these publications are incorporated herein by reference.

In one embodiment, the thickness of the polarizing element is preferably 1 μm˜25 μm, more preferably 3 μm˜10 μm, and more preferably 3 μm˜8 μm. When the thickness of the polarizing element is within such a range, curling during heating can be suppressed favorably, and favorable appearance durability during heating can be obtained.

The protective layer is formed of any appropriate protective film that can be used as a film for protecting the polarizing element. Specific examples of the material used as the main component of the protective film include cellulose-based resins such as triacetate cellulose (TAC), polyester-based, polyvinyl-alcohol-based, polycarbonate-based, and polyamide-based resins. transparent resins such as polyimide series, polyetherimide series, polyether series, polystyrene series, polynorene series, polyolefin series, (meth)acrylic series, acetate series, etc. Moreover, thermosetting resins, such as (meth)acrylic type, urethane type, (meth)acrylate urethane type, epoxy type, polysiloxane type, etc., or ultraviolet curing type can also be mentioned. resin, etc. In addition, glass-type polymers, such as a siloxane-type polymer, can also be mentioned, for example. Moreover, the polymer film described in Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imino group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. For example, the resin composition which has an alternating copolymer which consists of isobutylene and N-methylmaleimide, and an acrylonitrile-styrene copolymer is mentioned. The polymer film may be, for example, an extruded product of the above-mentioned resin composition.

The thickness of the protective layer is preferably 10 μm˜100 μm. The protective layer may be laminated on the polarizing element via an adhesive layer (specifically, an adhesive layer and an adhesive layer), or may be laminated on the polarizing element in close contact (without an adhesive layer). Surface treatment layers such as a hard coat layer, an anti-glare layer, and an anti-reflection layer can be formed on the protective layer disposed on the outermost surface of the polarizing plate with the retardation layer as needed.

E. Image Display Device The retardation film described in the above items A to C and the polarizing plate with the retardation layer described in the item D can be used for an image display device. Therefore, in the embodiment of the present invention, an image display device using such a polarizing plate with a retardation layer is also included. Typical examples of the image display device include a liquid crystal display device and an organic EL display device. An image display device according to an embodiment of the present invention includes the retardation film described in the above-mentioned items A to C or the polarizing plate with a retardation layer described in the item D. [Example]

0.1 mm準直器 X射線檢測器：多維像素檢測器「Hypix-3000」 測定時間：320分鐘 繼而，對所獲得之繞射圖案，於解析軟體“SmartLab studio II”(Rigaku公司製造)上轉換成全周之β角之2θ-I分佈。進行峰分離，與ICDD-PDF(International Centre for Diffraction Data-Powder Diffraction File，國際繞射資料中心-粉末繞射檔案)進行對照，確認源自各聚酯之非晶及結晶。進而，對繞射圖案上之繞射峰標註平面指數，計算源自各繞射峰之積分強度。將繞射角2θ＝25.5°±1.5°之範圍之源自聚酯之(100)面之積分強度設為α，將2θ＝17.0°±1.0°之範圍之源自聚酯之(010)面之積分強度設為β，求出積分強度比(α/β)。 Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples. In addition, the measurement method and evaluation method of each characteristic are as follows. (1) The thickness of 10 μm or less was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd. named “MCPD-9800”). Thicknesses exceeding 10 μm were measured using a digital micrometer (a product named “KC-351C” manufactured by Amway Corporation). (2) Extensibility The extensibility of the polyester-based resin film at the time of producing a retardation film was evaluated by the following criteria. ○: A retardation film can be produced without breaking. ×: A retardation film could not be produced due to breakage. (3) In-plane retardation and Nz coefficient The retardation films obtained in the examples and comparative examples were cut out with a length of 4 cm and a width of 4 cm to prepare measurement samples. About this measurement sample, the in-plane retardation Re (550) and the thickness direction retardation Rth (550) were measured using the product called "Axoscan" manufactured by Axometrics. The Nz coefficient is calculated according to Rth(550)/Re(550). (4) Integrated Intensity Ratio (α/β) The retardation films obtained in Examples and Comparative Examples were used in the transmission method of Wide Angle X-ray Diffraction (WAXD: Wide Angle X-ray Diffraction). Using the following X-ray diffraction apparatus, X-rays were irradiated from a direction perpendicular to one surface of the sample for measurement under the following X-ray output conditions, and a diffraction image obtained by the transmission method was photographed. X-ray diffractometer: "SmartLab X-ray diffractometer" manufactured by Rigaku Co., Ltd. X-ray output conditions: Cu target, tube voltage: 45 kV, tube current: 200 mA Measurement mode: WAXD method Incident optical system:

0.1 mm collimator X-ray detector: Multi-dimensional pixel detector "Hypix-3000" Measurement time: 320 minutes Then, the obtained diffraction pattern was converted into full-scale images using analysis software "SmartLab studio II" (manufactured by Rigaku Corporation). 2θ-I distribution of the beta angle of the week. The peaks were separated and compared with ICDD-PDF (International Centre for Diffraction Data-Powder Diffraction File, International Centre for Diffraction Data-Powder Diffraction File) to confirm the amorphous and crystalline origin of each polyester. Furthermore, the plane index is marked on the diffraction peaks on the diffraction pattern, and the integrated intensity derived from each diffraction peak is calculated. Let the integrated intensity of the (100) plane derived from polyester in the range of the diffraction angle 2θ=25.5°±1.5° be α, and the (010) plane derived from polyester in the range of 2θ=17.0°±1.0° The integrated intensity is set to β, and the integrated intensity ratio (α/β) is obtained.

[Resin used] Resin A: polyethylene terephthalate (PET) resin (a commodity named "EFG6C" manufactured by Bell Polyester Products, IV (Intrinsic Viscosity, intrinsic viscosity) value 0.71 (dl/g)) Resin B: modified polyethylene terephthalate (PET) resin (IV value 0.77 (dl/g), isophthalic acid modification amount 5.0 mol% (relative to the total mol of all repeating units of the polymer) number)) Resin C: modified polyethylene terephthalate (PET) resin (IV value 0.85 (dl/g), isophthalic acid modification amount 14.0 mol% (relative to the total mol of all repeating units of the polymer) number))

[Example 1] The resin A was subjected to melt extrusion molding to obtain a resin film (thickness 30 μm). A stretched resin film having molecular alignment in the MD direction is obtained by uniaxially extending the obtained resin film in the longitudinal direction. The stretching ratio of the resin film was 2.5 times in the MD direction, and the stretching temperature of the resin film was 88°C. Next, the obtained stretched resin film is subjected to oblique stretching. The magnification of oblique stretching was 2.0 times, and the stretching temperature was 88°C. In this way, a retardation film is obtained. The thickness of the obtained retardation film was 4 μm, and the angle formed by the MD direction (longitudinal direction) and the retardation axis was 12.5°. The obtained retardation film was used for the evaluation of the above-mentioned (3) and (4). The Re(550) is 152 nm, the Nz coefficient is 0.5, and the integrated intensity ratio (α/β) is 4.01. The results are shown in Table 1.

[Example 2] A retardation film was obtained in the same manner as in Example 1, except that the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 87°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Example 3] A retardation film was obtained in the same manner as in Example 1, except that the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 85°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Comparative Example 1] A retardation film was obtained in the same manner as in Example 1, except that the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 90°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Comparative Example 2] Except having made the temperature of longitudinal uniaxial stretching into 80 degreeC, it carried out similarly to Example 1 and tried to produce a retardation film, but a fracture|rupture occurred and a retardation film was not obtained.

[Example 4] A retardation film was obtained in the same manner as in Example 1, except that the resin B was used instead of the resin A. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Example 5] A retardation film was obtained in the same manner as in Example 4, except that the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 85°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Comparative Example 3] A retardation film was obtained in the same manner as in Example 3, except that the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 90°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Comparative Example 4] Except having made the temperature of longitudinal uniaxial stretching into 80 degreeC, it carried out similarly to Example 3 and tried to produce a retardation film, but fracture|rupture occurred and a retardation film could not be obtained.

[Comparative Example 5] A retardation film was obtained in the same manner as in Example 1, except that the resin C was used instead of the resin A, and the temperature of the longitudinal uniaxial stretching and the oblique stretching was set to 90°C. The obtained retardation film was used for the same evaluation as Example 1. The results are shown in Table 1.

[Comparative Example 6] A retardation film was attempted in the same manner as in Comparative Example 5 except that the temperature of the longitudinal uniaxial stretching was set to 85° C., but cracks occurred and a retardation film could not be obtained.

[Table 1] resin Extension temperature (℃) Extensibility Thickness (μm) Re(550) Nz coefficient Integrated intensity ratio (α/β) Example 1 A 88 〇 4 152.48 0.46 4.01 Example 2 A 87 〇 5 133.37 0.47 Not implemented Example 3 A 85 〇 5 65.75 0.87 4.04 Comparative Example 1 A 90 〇 4 139.32 4.7 0.99 Comparative Example 2 A 80 × - - - - Example 4 B 88 〇 4 81.87 0.56 2.23 Example 5 B 85 〇 5 76.87 1.1 2.04 Comparative Example 3 B 90 〇 4 124.66 4.59 0.14 Comparative Example 4 B 80 × - - - - Comparative Example 5 C 90 〇 4 224.33 1.94 0.55 Comparative Example 6 C 85 × - - - -

As can be seen from Table 1, according to the examples of the present invention, a retardation film with a small Nz can be obtained by using a polyester-based resin. In particular, comparing Example 1 with Comparative Example 1, and Example 3 with Comparative Example 3, it is clear that by lowering the stretching temperature by several degrees, the Nz coefficient sharply decreases (specifically, from the negative B plate to the negative B plate). for the Z film). That is, when a retardation film is produced using a polyester-based resin, it was found that there is a critical elongation temperature that drastically changes the characteristics. This is the first knowledge obtained by trial and error in order to manufacture a retardation film using a polyester-based resin, and the effect is surprisingly excellent. [Industrial Availability]

The retardation film and the polarizing plate with the retardation layer according to the embodiment of the present invention can be preferably used in an image display device.

Claims (10)

A retardation film, which is composed of a stretched resin film of polyester resin, and whose Nz coefficient is less than 1.8; Here, Nz=(nx-nz)/(nx-ny), nx is the refractive index in the direction of the maximum refractive index in the plane, ny is the refractive index in the direction perpendicular to the direction of the maximum refractive index in the plane, nz is the refractive index in the thickness direction. The retardation film according to claim 1 has a thickness of 20 μm or less. The retardation film according to claim 1 or 2, wherein in the X-ray diffraction measurement using CuKα rays, the integrated intensity α of the crystalline peak derived from polyester existing in the range of the diffraction angle 2θ=25.5°±1.5° The ratio (α/β) to the integrated intensity β of the crystallization peak derived from polyester existing in the range of 2θ=17.0°±1.0° is 1.0 or more. The retardation film according to any one of claims 1 to 3, wherein the in-plane retardation value Re(550) is 50 nm to 400 nm. As in the retardation film of claim 4, the in-plane retardation value Re(550) is 220 nm to 320 nm. As in the retardation film of claim 4, the in-plane retardation value Re(550) is 100 nm to 200 nm. A polarizing plate with a retardation layer, comprising a polarizing element and the retardation film according to any one of claims 1 to 6. A polarizing plate with a retardation layer, comprising a polarizing element and the retardation film as claimed in item 6, and The angle formed by the absorption axis of the polarizer and the retardation axis of the retardation film is 35°˜55°. A polarizing plate with a retardation layer, which sequentially comprises a polarizing element, a retardation film as claimed in item 5, and a retardation film as in claim 6, and The angle formed by the absorption axis of the polarizing element and the retardation axis of the retardation film as claimed in claim 5 is 5° to 20°, The angle formed by the absorption axis of the polarizing element and the retardation axis of the retardation film as claimed in claim 6 is 70° to 85°. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 7 to 9.