JP2022056553A - Retardation film, retardation layer-attached polarizing plate, and image display device - Google Patents

Abstract

To provide a retardation film formed of an inexpensive resin film, extremely thin, and controlled in Nz coefficient in a predetermined range.SOLUTION: A retardation film of the present invention is composed of a stretched resin film of a polyester resin, and has an Nz coefficient of less than 1.8. Here, Nz=(nx - nz)/(nx - ny) is satisfied. nx is a refractive index in a direction in which the refractive index in-plane becomes maximum, ny is the refractive index in the direction orthogonal to the direction in which the refractive index becomes maximum in-plane. nz is the refractive index in the thickness direction.SELECTED DRAWING: None

Description

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

In recent years, with the spread of thin displays, an image display device (organic EL display device) equipped with an organic EL panel has been proposed. The organic EL panel has a highly reflective metal layer, and tends to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a retardation film on the visual recognition side. Examples of the material of the retardation film include a liquid crystal material. However, the liquid crystal material is expensive and has a problem of being disadvantageous in terms of cost. A polyester resin film is used as a material for a retardation film that replaces an expensive liquid crystal material. However, in the retardation film using the polyester resin film, the retardation in the thickness direction (as a result, the Nz coefficient) becomes too large, and the desired optical characteristics may not be obtained.

Japanese Patent No. 3325560

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to be formed from an inexpensive resin film, have an extremely thin wall, and have an Nz coefficient controlled within a predetermined range. The purpose is to provide a retardation film.

The retardation film according to the embodiment of the present invention is composed of a stretched resin film of a 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 in which the in-plane refractive index is maximized, and ny is the direction in which the in-plane refractive index is maximized. Is the refractive index in the direction orthogonal to, and nz is the refractive index in the thickness direction.
In one embodiment, the retardation film has a thickness of 20 μm or less.
In one embodiment, the retardation film is the integrated intensity of the polyester-derived crystal peak existing in the range of the diffraction angle 2θ = 25.5 ° ± 1.5 ° in the X-ray diffraction measurement using CuKα ray. The ratio (α / β) of α to the integrated intensity β of the polyester-derived crystal peak existing in the range of 2θ = 17.0 ° ± 1.0 ° is 1.0 or more.
In one embodiment, the retardation film has an in-plane retardation value Re (550) of 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 polarizing plate with a retardation layer includes a polarizing element and a retardation film having an in-plane retardation value Re (550) of 100 nm to 200 nm, and the absorption axis of the polarizing element and the same. The angle formed by the retardation film with the slow axis is 35 ° to 55 °.
In one embodiment, the polarizing plate with a retardation layer includes a polarizing element, a retardation film having an in-plane retardation value Re (550) of 220 nm to 320 nm, and an in-plane retardation value Re (550). ) Is 100 nm to 200 nm, and the retardation film is included in this order. The angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film having the in-plane retardation value Re (550) of 220 nm to 320 nm is 5 ° to 20 °, and the angle is 5 ° to 20 °. The angle formed by the retardation axis of the retardation film having the in-plane retardation value Re (550) of 100 nm to 200 nm is 70 ° to 85 °.
According to yet another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned polarizing plate with a retardation layer.

According to the embodiment of the present invention, by stretching a specific polyester resin film under specific stretching conditions (particularly, stretching temperature), the thickness is extremely thin and the Nz coefficient is controlled within a predetermined range. A phase difference film 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 herein are as follows.
(1) Refractive index (nx, ny, nz)
"Nx" is the refractive index in the direction in which the refractive index in the plane is maximized (that is, the direction of the slow phase axis), and "ny" is the direction orthogonal to the slow phase axis in the plane (that is, the direction of the phase advance axis). Is the refractive index of, and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
“Re (λ)” is an in-plane phase difference measured with light having a wavelength of λ nm at 23 ° C. For example, "Re (550)" is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C. Re (λ) is obtained by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the layer (film).
(3) Phase difference in the thickness direction (Rth)
“Rth (λ)” is a phase difference in the thickness direction measured with light having a wavelength of λ nm at 23 ° C. For example, "Rth (550)" is a phase difference 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, where d (nm) is the thickness of the layer (film).
(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. Phase difference film The retardation film according to the embodiment of the present invention is composed of a stretched resin film made of a polyester resin. By using the polyester 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 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 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 smaller than 1.8, preferably smaller than 1.2, and more preferably smaller than 1.0. The Nz coefficient is more preferably 0.2 to 0.9, and particularly preferably 0.4 to 0.9. Therefore, the retardation film preferably has a refractive index characteristic of nx> ny ≧ nz or nx> nz> ny, and more preferably has a relationship of nx> nz> ny. According to the embodiment of the present invention, it is possible to realize a retardation film having a small Nz coefficient, which was difficult in the past, by using a polyester resin, and in particular, to realize a so-called Z film (nx> nz> ny). can do. Such a retardation film can be realized by controlling the stretching conditions (particularly, the stretching temperature) as described later.

The retardation film preferably has an integrated intensity α and 2θ = of the crystal peak derived from the polyester existing in the range of the diffraction angle 2θ = 25.5 ° ± 1.5 ° in the X-ray diffraction measurement using CuKα ray. The ratio (α / β) of the polyester-derived crystal peak existing in the range of 17.0 ° ± 1.0 ° to the integrated intensity β 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, and particularly preferably 2.2 to 4.2. When the ratio (α / β) is in such a range, it may be easy to realize a retardation film having the desired Nz coefficient. This is estimated as follows. However, the embodiments of the present invention are not bound by the estimation. The integrated strength α means the integrated strength of the (100) plane derived from polyester, and the integrated strength β means the integrated strength of the (010) plane derived from polyester. Therefore, the fact that the ratio (α / β) is large means that the ring structure (typically, aromatic ring and aliphatic ring) contained in the polyester resin constituting the retardation film is the main film. It shows that it has an angle (stands up) with respect to the surface. 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 resin according to the embodiment of the present invention, it is presumed that the polyester molecules constituting the film have an orientation state different from the conventional one.

The thickness of the retardation film is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. The lower limit of the thickness of the retardation film can be 0.5 μm. When the thickness of the retardation film is within such a range, the crystallinity of the retardation film is sufficient and excellent heat resistance can be obtained. Further, the retardation film is excellent in that it satisfies the Nz coefficient even though it is a thin retardation film.

The number of MITs of the retardation film is preferably 1000 times or more, more preferably 1500 times or more, and further preferably 2000 times or more. The upper limit of the number of MITs of the retardation film can be 20000. According to the embodiment of the present invention, it is possible to obtain a retardation film capable of achieving both the above 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 further preferably 400 g to 1800 g. According to the embodiment of the present invention, it is possible to obtain a retardation film capable of achieving both the above Nz coefficient and such crack resistance.

The retardation film may be single-wafer-shaped or long-shaped. A long retardation film having a slow axis in a predetermined direction according to a purpose with respect to the long direction can be laminated with another optical film (for example, a polarizing plate) by roll-to-roll, and thus laminated. The production efficiency of an optical film (for example, a polarizing plate with a retardation layer) can be significantly improved. Such a long retardation film can be obtained by diagonal stretching. A long retardation film having a slow axis in a direction substantially orthogonal or parallel to the long direction is easy to manufacture the film itself, and is a single-wafered film having a slow axis in a desired direction by cutting. A retardation film can be obtained. As used herein, the term "long" means an elongated shape having a length sufficiently long with respect to the width, and for example, the length is preferably 10 times or more, more preferably 20 times or more with respect to the width. Including elongated shape.

B. As described above, the polyester-based resin retardation film is composed of a stretched resin film of the polyester-based resin. The polyester resin can be obtained by condensation polymerization of a carboxylic acid component and a polyol component.

Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalic acid, diphenic acid, 4,4'-oxybenzoic acid, and 2,5-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, zebacic acid and fumaric acid. Examples thereof include maleic acid, itaconic acid, thiodipropionic acid and diglycolic acid. Examples of the alicyclic dicarboxylic acid include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornandicarboxylic acid and adamantandicarboxylic acid. The carboxylic acid component may be a derivative such as an ester, chloride or acid anhydride, for example, dimethyl 1,4-cyclohexanedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylic acid, dimethyl isophthalate, dimethyl terephthalate. And contains diphenyl terephthalate. The carboxylic acid component may be used alone or in combination of two or more.

Typical examples of the polyol component include dihydric alcohols. Examples of the dihydric alcohol include aliphatic diols, alicyclic diols, and aromatic diols. Examples of the aliphatic diol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, and 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 Can be mentioned. Examples of the alicyclic diol include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecanedimethanol, adamantandiol, 2,2,4. , 4-Tetramethyl-1,3-Cyclobutanediol. Examples of the aromatic diol include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-(2-norbornylidene) diphenol, 4,4'-dihydroxybiphenol, o-, Included are m- and p-dihydroxybenzene, 4,4'-isopropyridenephenol, 4,4'-isopropyridenebis (2,6-dichlorophenol) 2,5-naphthalenediol and p-xylenediol. The polyol component may be used alone or in combination of two or more.

As the polyester resin, polyethylene terephthalate (PET) or modified polyethylene terephthalate is preferably used. Polyethylene terephthalate and modified polyethylene terephthalate may be blended and used.

Examples of the modified polyethylene terephthalate include modified polyethylene terephthalate containing a structural unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid. The proportion 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 proportion 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 proportion 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 proportion of 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. The mol% described above is mol% with respect to the total of all polymer repeating units.

C. Method for producing a retardation film The method for producing a retardation film according to the embodiment of the present invention includes stretching a polyester resin film.

The resin film can be obtained, for example, by forming a resin such as the polyester resin according to Item B into a film. As a method for forming the film, any suitable molding processing method can be adopted. Specific examples include a compression molding method, a transfer molding method, an injection molding method, an extrusion molding method, a blow molding method, a powder molding method, an FRP molding method, a cast coating method (for example, a casting method), a calendar molding method, and a hot press. The law etc. can be mentioned. Of these, an extrusion molding method or a cast coating method that can improve the smoothness of the obtained film and obtain good optical uniformity is preferable. Since the cast coating method may cause problems due to the residual solvent, the extrusion molding method, particularly the melt extrusion molding method using a T-die, is particularly preferable from the viewpoint of film productivity and ease of subsequent stretching treatment. preferable. The molding conditions can be appropriately set according to the composition and type of the resin used, the properties desired for the retardation film, and the like.

By stretching the polyester-based resin film obtained above in the transport direction (MD direction), a stretched resin film having a molecular orientation in the MD direction can be obtained. That is, a retardation film having a slow phase axis in a direction substantially parallel to the MD direction (long direction) can be obtained. As the stretching method, any suitable method can be adopted as long as the stretched resin film can have a molecular orientation in the MD direction. For example, uniaxial stretching or biaxial stretching can be mentioned. The draw ratio of uniaxial stretching is preferably more than 1.0 times and 4.0 times or less, and more preferably 2.0 times to 3.5 times. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. The stretching ratio in the longitudinal direction is preferably more than 1.0 times and 4.0 times or less, and more preferably 2.0 times to 3.5 times. The draw ratio in the width direction is preferably 1.0 to 4.0 times, more preferably 2.0 to 3.5 times.

The polyester-based resin film obtained above may be subjected to diagonal stretching, or the stretched resin film obtained above may be further subjected to diagonal stretching or stretching in the TD direction (width direction). Thereby, a retardation film having a slow phase axis in a direction having a predetermined angle with respect to the MD direction (long direction) can be obtained. The predetermined angle may change depending on the in-plane retardation of the retardation film. The predetermined angle is preferably 5 ° to 20 °, more preferably 10 ° to 15 °, still more preferably about 12.5 ° in one embodiment; in another embodiment. Is preferably 35 ° to 55 °, more preferably 40 ° to 50 °, still more preferably 42 ° to 48 °, and particularly preferably about 45 °. Diagonal stretching can be performed, for example, by using a tenter stretching machine to change the feed rate of the left and right clips that grip the widthwise ends of the film. By adjusting the difference in feed rate between the left and right clips, the direction of the slow axis (orientation angle) can be controlled. The magnification of the diagonal stretching is preferably 1.1 times to 3.0 times, more preferably 1.3 times to 2.8 times, and further 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, and even more preferably Tg-10 ° C to Tg + 10 ° C. Tg is the glass transition temperature of the constituent material of the film. The specific stretching temperature can be, for example, 82 ° C to 89 ° C, for example 84 ° C to 89 ° C, and for example 85 ° C to 88 ° C.

D. Polarizer with retardation layer The retardation film according to the above items A to C can be provided as a laminate with another optical film and / or an optical member. In one embodiment, the retardation film can be provided as a laminate (typically, a polarizing plate with a retardation layer) with a splitter (substantially a polarizing plate). Therefore, an embodiment of the present invention includes a polarizing plate with a retardation layer including the retardation film. The polarizing plate with a retardation layer according to the embodiment of the present invention includes a polarizing element and the retardation film. In the polarizing plate with a retardation layer, the angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film can be appropriately set according to the application and purpose. In one embodiment, the angles are approximately orthogonal. In another embodiment, the angles are approximately parallel. In yet another embodiment, the angle is preferably 35 ° to 55 °, more preferably 40 ° to 50 °, still more preferably 42 ° to 48 °, and particularly preferably about 45 °. Is.

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

In one embodiment, the retardation film included in the polarizing plate with a retardation layer can function as a λ / 4 plate. The in-plane retardation value Re (550) of this 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 splitter and the slow axis of the laminated retardation film is preferably 35 ° to 55 °, more preferably 40 ° to 50 °, and even more preferably 42 ° to 42 °. It is 48 °, particularly preferably about 45 °.

In one embodiment, the polarizing plate with a retardation layer includes a polarizing element, a retardation film that functions as a λ / 2 retardation plate, and a retardation film that functions as a λ / 4 plate. Include in order. The angle formed by the absorption axis of the splitter and the slow axis of the retardation film functioning as a λ / 4 plate is preferably 5 ° to 20 °, more preferably 10 ° to 15 °, and even more preferably. It is about 12.5 °. Further, the angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film functioning as a λ / 2 plate is preferably 70 ° to 85 °, more preferably 75 ° to 80 °, and further. It is preferably about 77.5 °.

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

As the polarizing element, any suitable polarizing element may be adopted. For example, the resin film forming the polarizing element may be a single-layer resin film or a laminated body having two or more layers.

Specific examples of the polarizing element composed of a single-layer resin film include a hydrophilic polymer film such as a polyvinyl alcohol (PVA) -based film, a partially formalized PVA-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. Examples thereof include those which have been dyed and stretched with a bicolor substance such as iodine and a bicolor dye, and polyene-based oriented films such as a dehydrated product of PVA and a dehydrogenated product of polyvinyl chloride. Preferably, since the PVA-based film is excellent in optical properties, a polarizing element obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used.

The dyeing with iodine is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or may be performed while dyeing. Further, it may be dyed after being stretched. If necessary, the PVA-based film is subjected to a swelling treatment, a crosslinking treatment, a cleaning treatment, a drying treatment and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, it is possible not only to clean the dirt and blocking inhibitor on the surface of the PVA-based film, but also to swell the PVA-based film to prevent uneven dyeing. Can be prevented.

Specific examples of the polarizing element obtained by using the laminate include a laminate of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin. Examples thereof include a polarizing element obtained by using a laminate with a PVA-based resin layer coated and formed on a base material. The polarizing element obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying it. It is produced by forming a PVA-based resin layer on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer a stator. obtain. In the present embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin base material. Stretching typically involves immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further comprise, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. In addition, in the present embodiment, preferably, the laminate is subjected to a drying shrinkage treatment in which the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Typically, the production method of the present embodiment includes subjecting the laminate to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, even when PVA is applied on the thermoplastic resin, the crystallinity of PVA can be enhanced and high optical characteristics can be achieved. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of PVA orientation and dissolution when immersed in water in a subsequent dyeing step or stretching step, and high optical characteristics. Will be possible to achieve. Further, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecule and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing element obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water. Further, the optical characteristics can be improved by shrinking the laminated body in the width direction by the drying shrinkage treatment. The obtained resin base material / polarizing element laminate may be used as it is (that is, the resin base material may be used as a protective layer for the polarizing element), and the resin base material is peeled off from the resin base material / polarizing element laminate. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of the method for producing such a polarizing element are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. The entire description of these publications is incorporated herein by reference.

In one embodiment, the thickness of the stator is preferably 1 μm to 25 μm, more preferably 3 μm to 10 μm, and even more preferably 3 μm to 8 μm. When the thickness of the splitter is in such a range, curling during heating can be satisfactorily suppressed, and good appearance durability during heating can be obtained.

The protective layer is formed of any suitable protective film that can be used as a film to protect the polarizing element. Specific examples of the material that is the main component of the protective film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone. Examples thereof include transparent resins such as polyester-based, polystyrene-based, polycarbonate-based, polyolefin-based, (meth) acrylic-based, and acetate-based. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

The thickness of the protective layer is preferably 10 μm to 100 μm. The protective layer may be laminated on the polarizing element via an adhesive layer (specifically, an adhesive layer or an adhesive layer), or may be laminated in close contact with the polarizing element (without interposing an adhesive layer). good. If necessary, a surface treatment layer such as a hard coat layer, an antiglare layer and an antireflection layer may be formed on the protective layer arranged on the outermost surface of the polarizing plate with a retardation layer.

E. Image display device The retardation film according to items A to C and the polarizing plate with a retardation layer according to item D can be used in 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. The image display device according to the embodiment of the present invention includes the retardation film according to the above items A to C or the polarizing plate with the retardation layer according to the item D.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method and evaluation method for each characteristic are as follows.
(1) Thickness The thickness of 10 μm or less was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-9800”). Thicknesses exceeding 10 μm were measured using a digital micrometer (manufactured by Anritsu, product name “KC-351C”).
(2) Stretchability The stretchability of the polyester-based resin film at the time of producing the retardation film was evaluated according to the following criteria.
◯: A retardation film could be produced without breaking.
X: The retardation film could not be produced due to breakage.
(3) In-plane retardation and Nz coefficient The retardation films obtained in Examples and Comparative Examples were cut into lengths of 4 cm and widths of 4 cm and used as measurement samples. For the measurement sample, the in-plane phase difference Re (550) and the thickness direction phase difference Rth (550) were measured using the product name “Axoscan” manufactured by Axometrics. The Nz coefficient was calculated from Rth (550) / Re (550).
(4) Integrated intensity ratio (α / β)
The retardation films obtained in Examples and Comparative Examples were subjected to a transmission method of wide-angle X-ray diffraction (WAXD: Wide Angle X-ray Diffraction). Using the following X-ray diffractometer, X-rays were irradiated from a direction perpendicular to one surface of the measurement sample under the following X-ray output conditions, and a diffraction image was taken by the transmission method.
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: Φ0.1mm collimator X-ray detector: Multidimensional pixel detector "Hypix-3000"
Measurement time: 320 minutes Next, the obtained diffraction pattern was converted into a 2θ-I profile for the entire circumference of the β angle on the analysis software “SmartLab studio II” (manufactured by Rigaku). Peak separation was performed and collation with ICDD-PDF was performed, and amorphous and crystals derived from each polyester were confirmed. Furthermore, surface indexing was performed on the diffraction peaks on the diffraction pattern, and the integrated intensity derived from each diffraction peak was calculated. The integral strength of the polyester-derived (100) plane in the range of diffraction angle 2θ = 25.5 ° ± 1.5 ° is α, and the integral strength of the polyester-derived (010) plane in the range of 2θ = 17.0 ° ± 1.0 °. The integrated intensity ratio (α / β) was obtained, where β was taken as the integrated intensity of.

[Resin used]
Resin A: Polyethylene terephthalate (PET) resin (manufactured by Bell Polyester Products, trade name "EFG6C", IV 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% (mol number with respect to the total of all polymer repeating units))
Resin C: Modified polyethylene terephthalate (PET) resin (IV value 0.85 (dl / g), isophthalic acid modification amount 14.0 mol% (mol number with respect to the total of all polymer repeating units))

[Example 1]
The resin A was subjected to melt extrusion molding to obtain a resin film (thickness 30 μm). By stretching the obtained resin film vertically and uniaxially, a stretched resin film having a molecular orientation in the MD direction was obtained. The draw ratio of the resin film was 2.5 times in the MD direction, and the draw temperature of the resin film was 88 ° C. Then, the obtained stretched resin film was subjected to diagonal stretching. The magnification of diagonal stretching was 2.0 times, and the stretching temperature was 88 ° C. In this way, a retardation film was obtained. The thickness of the obtained retardation film was 4 μm, and the angle between the MD direction (long direction) and the slow axis was 12.5 °. The obtained retardation film was subjected to the evaluations of (3) and (4) above. Re (550) was 152 nm, the Nz coefficient was 0.5, and the integrated intensity ratio (α / β) was 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 temperatures for longitudinal uniaxial stretching and diagonal stretching were 87 ° C. The obtained retardation film was subjected to the same evaluation as in 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 temperatures for longitudinal uniaxial stretching and diagonal stretching were set to 85 ° C. The obtained retardation film was subjected to the same evaluation as in 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 temperatures for longitudinal uniaxial stretching and diagonal stretching were set to 90 ° C. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
An attempt was made to produce a retardation film in the same manner as in Example 1 except that the temperature of the longitudinal uniaxial stretching was set to 80 ° C., but the retardation film was not obtained due to breakage.

[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 subjected to the same evaluation as in 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 temperatures for longitudinal uniaxial stretching and diagonal stretching were set to 85 ° C. The obtained retardation film was subjected to the same evaluation as in 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 temperatures for longitudinal uniaxial stretching and diagonal stretching were set to 90 ° C. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 4]
An attempt was made to produce a retardation film in the same manner as in Example 3 except that the temperature of the longitudinal uniaxial stretching was set to 80 ° C., but the retardation film was not obtained due to breakage.

[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 temperatures of the longitudinal uniaxial stretching and the diagonal stretching were set to 90 ° C. The obtained retardation film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 6]
An attempt was made to produce a retardation film in the same manner as in Comparative Example 5 except that the temperature of the longitudinal uniaxial stretching was set to 85 ° C., but the retardation film was not obtained due to breakage.

As is clear from Table 1, according to the embodiment of the present invention, a retardation film having a small Nz can be obtained by using a polyester resin. In particular, as is clear when comparing Example 1 and Comparative Example 1 and Example 3 and Comparative Example 3, the Nz coefficient is drastically reduced by lowering the stretching temperature by several ° C. (specifically, negative B). It changes from a plate to a Z film). That is, it can be seen that when a retardation film is manufactured using a polyester resin, there is a critical stretching temperature that drastically changes the characteristics. This is a finding obtained only by trial and error for producing a retardation film using a polyester resin, and is an unexpectedly excellent effect.

The retardation film and the polarizing plate with a retardation layer according to the embodiment of the present invention are suitably used for an image display device.

Claims (10)

A retardation film composed of a stretched resin film made of polyester resin and having an Nz coefficient smaller than 1.8:
Here, Nz = (nx-nz) / (nx-ny), nx is the refractive index in the direction in which the in-plane refractive index is maximized, and ny is the direction in which the in-plane refractive index is maximized. Is the refractive index in the direction orthogonal to, and nz is the refractive index in the thickness direction. The retardation film according to claim 1, wherein the thickness is 20 μm or less. In the X-ray diffraction measurement using CuKα ray, the integrated intensity α of the crystal peak derived from polyester existing in the diffraction angle 2θ = 25.5 ° ± 1.5 ° and 2θ = 17.0 ° ± 1.0 ° The retardation film according to claim 1 or 2, wherein the ratio (α / β) of the polyester-derived crystal peak existing in the range to the integrated intensity β 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. The retardation film according to claim 4, wherein the in-plane retardation value Re (550) is 220 nm to 320 nm. The retardation film according to claim 4, wherein 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. The stator and the retardation film according to claim 6 are included.
The angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film is 35 ° to 55 °.
Polarizing plate with retardation layer. The extruder, the retardation film according to claim 5, and the retardation film according to claim 6 are included in this order.
The angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film according to claim 5 is 5 ° to 20 °.
The angle formed by the absorption axis of the polarizing element and the slow axis of the retardation film according to claim 6 is 70 ° to 85 °.
Polarizing plate with retardation layer. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 7 to 9.