JP2006251644A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film which generates the smaller retardation with the shorter measurement wavelength in one sheet of the film. <P>SOLUTION: The retardation film is a single layer polymer oriented film which contains a synthetic polymer and an inorganic compound having ≤400 nm major axial length and ≤3/4 ratio of the minor diameter to the major diameter and having optical anisotropy. The retardation film exhibits retardation satisfying formula (1): R(λ1)/R(λ2)<1 at a wavelength λand ≤3% haze. In formula (1), R(λ1) and R(λ2) represent in-plane retardations of the polymer oriented film at wavelengths λ1 (nm), λ2 (nm) (wherein 400 nm<λ1 and λ2<700 nm), respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a retardation film. In particular, the present invention is used in an optical element such as a liquid crystal display device, a light emitting element, an antiglare film, an optical recording device, and a polarizing beam splitter, and a retardation film having a smaller retardation value at a measurement wavelength of 400 to 700 nm, And an optical apparatus using the same.

  The retardation film is used for STN (super twisted nematic system) of a liquid crystal display device and the like, and is used for solving problems such as color compensation and widening of the viewing angle. In general, polycarbonate, polyvinyl alcohol, polysulfone, polyethersulfone, amorphous polyolefin, and the like are used as a material for a retardation film for color compensation. A liquid crystal, an alignment-cured discotic liquid crystal, or the like is used.

  A quarter-wave plate, which is a kind of retardation film, can convert circularly polarized light into linearly polarized light and linearly polarized light into circularly polarized light. This is because a liquid crystal display device, particularly a reflective liquid crystal display device having a single polarizing film with the electrode on the back side as viewed from the observer side as a reflective electrode, or a combination of a polarizing film and a quarter-wave plate. And a reflective polarizing film that reflects only one of the clockwise and counterclockwise circularly polarized light composed of cholesteric liquid crystal or the like.

  The retardation film used in the reflective liquid crystal display device of the above-mentioned single polarizing film type and the reflective polarizing film is a circularly polarized light with linearly polarized light at a measurement wavelength of 400 to 700 nm, preferably 400 to 780 nm in the visible light region. It is necessary to have an action of converting polarized light into linearly polarized light. If this is to be realized with one retardation film, it is ideal that the retardation film has a retardation of λ / 4 (nm) at a measurement wavelength λ = 400 to 700 nm, preferably 400 to 780 nm.

  In general, as the quarter-wave plate, the above-described retardation film material for color compensation is used, and these materials have wavelength dispersion in birefringence. In general, the birefringence of a polymer film is larger as the measurement wavelength is shorter and smaller as the wavelength is longer. Therefore, it is difficult to obtain a material having a smaller birefringence as the measurement wavelength is shorter as in the ideal quarter-wave plate described above at the measurement wavelength λ = 400 to 700 nm with only one polymer. .

  In order to obtain a film in which the birefringence becomes smaller as the measurement wavelength is shorter, such as an ideal quarter-wave plate, Patent Document 1 describes that a quarter-wave plate and a half-wave plate are at appropriate angles. The technique of being used by bonding together is described. Patent Document 2 discloses that a cellulose ester film has at least two aromatic rings to achieve a quarter-wave plate using a single polymer film, and the conformation of two aromatic rings. Techniques involving compounds having molecular structures that do not sterically hinder are described. However, in the cellulose ester film, hydrolysis, dimensional deformation, orientation relaxation, etc. occur due to its water absorption, and the retardation and the retardation wavelength dispersion cannot be maintained at a practical level for a long time. It is a member whose durability is problematic as a phase difference film. Furthermore, Patent Document 3 discloses a technique relating to an optical compensation film containing an optically anisotropic material and excellent in scratch resistance. However, this technology relates to an optical compensation film that can obtain a wide viewing angle by controlling the optically anisotropic material so that it is hybrid-aligned in the film thickness direction. The wavelength dispersion of the retardation film is not controlled at all. Regarding the technique of adding liquid crystal to a polymer, Patent Documents 4 and 5 show optical anisotropic films having a temperature compensation effect in which retardation changes with temperature following the change in temperature of the birefringence of a liquid crystal cell. Has been. However, even in this system, the temperature compensation effect of the phase difference is the main point, and it is not a technique related to control of chromatic dispersion by adding liquid crystal. In addition, when the liquid crystal is added to the polymer, the glass transition temperature of the polymer may be drastically decreased, so that the amount of liquid crystal to be added is limited and the glass transition temperature of the polymer itself to be added is high. There is a case where it is necessary to select from the above, and when trying to obtain a retardation film having weather resistance that can be practically used, there is a possibility that it becomes a limited polymer having a very high glass transition temperature (200 degrees or more). Can be considered. Furthermore, in terms of the price of the liquid crystal itself, the liquid crystal is generally expensive relative to the polymer that is the raw material of the retardation film. In the retardation film using the liquid crystal, most of the cost contributes to the price of the liquid crystal. There is no advantage over the two-phase retardation film in terms of price obtained with the retardation film.

  Patent Document 6 discloses a technique relating to a low birefringence optical resin material in which molecular orientation suppressing particles having a size smaller than the wavelength of light are mixed. In this technique, the added molecular orientation-suppressing granule is a granule made of a substance having isotropic property with respect to polarization, or a granule having isotropic property with respect to the shape. The effect added to the material is to suppress the expression of birefringence, and the effect of controlling the wavelength dispersion characteristic of the phase difference caused by the birefringence of the optical resin material is not obtained.

JP-A-10-68816 JP 2001-91743 A JP 2001-89964 A JP-A-8-278410 JP-A-8-190034 JP 2001-208901 A

  As described above, it is known that λ / 4 or λ / 2 can be achieved in a region where the phase difference is wide by laminating two or more polymer films. However, in this case, it is necessary to laminate the film while strictly adjusting the angle and retardation of two or more films. In contrast, the present inventors have previously proposed a λ / 4 plate or a λ / 2 plate made of one polymer film. However, there are almost no films in practical use that are excellent in weather resistance and hardly cause retardation change in films in which λ / 4 or λ / 2 is achieved in a wavelength region having a wide retardation.

  An object of the present invention is to achieve a retardation film having a broad band property such as λ / 4 or λ / 2 in a wavelength region having excellent weather resistance and wider retardation by using one polymer film. (There is no need to limit to λ / 4, λ / 2, and 3 / 4λ, 2 / 5λ, etc.).

  Another object of the present invention is to provide a retardation film capable of easily controlling the broadband property.

  In order to solve the above-mentioned problems, the present inventor diligently studied a polymer material for a retardation film. From the polymer oriented film obtained by adding an inorganic compound having optical anisotropy having a size smaller than the wavelength of light to the synthetic polymer, and orienting the composite material by a technique such as stretching. By using a single-layer retardation film as described above, it is possible to obtain a retardation film that has excellent transparency and excellent broadband properties such as a λ / 4 plate in a single-layer (one sheet) wavelength region with a wide retardation. As a result, the present invention has been completed.

That is, the present invention can be achieved from the following [1] to [7].
[1] A polymer oriented film containing a synthetic polymer and an inorganic compound having a major axis length of 400 nm or less, a ratio of a minor axis to a major axis of 3/4 or less, and optical anisotropy A retardation film having a retardation at a wavelength λ satisfying the following formula (1) and a haze of 3% or less.
R (λ1) / R (λ2) <1 (1)
[Wherein R (λ1) and R (λ2) are the surfaces of the polymer oriented film at respective wavelengths λ1 (nm) and λ2 (nm) (400 nm <λ1, λ2 <700 nm, λ1 <λ2) This is the internal phase difference. ]
[2] The above retardation film, wherein the content of the inorganic compound having optical anisotropy is 0.01% by weight or more and 20% by weight or less with respect to 100 parts by weight of the synthetic polymer.
[3] The retardation film as described above, wherein the synthetic polymer is an alicyclic polyolefin.
[4] The above retardation film, wherein the synthetic polymer is polycarbonate.
[5] A laminated polarizing film comprising a polarizing film and the retardation films of the above [1] to [4].
[6] A liquid crystal display element using the retardation film of the above [1] to [5].
[7] An optical device using the retardation film of [1] to [5].

  As a result of intensive studies, the present inventors have succeeded in producing a retardation film having a broadband property such as λ / 4 or λ / 2 in a wide wavelength region by searching for a composite material to be added to a polymer film. . The wavelength dispersion of a retardation film composed of a single polymer film is due to the optical anisotropy of the monomers that make up the polymer, so it can take the ideal λ / 4 in the short or long wavelength region. I couldn't do it and the color was lost. However, by adding an inorganic compound having optical anisotropy to the synthetic polymer, the wavelength dispersion in the retardation can be controlled, and a single retardation film having wider bandwidth can be obtained. Thereby, in a liquid crystal display device, it becomes possible to use one retardation film with respect to what used two or more retardation films conventionally, and two or more sheets with one retardation film can be used. Color display equivalent to that of a retardation film can be performed. Thereby, the exact adjustment of the angle at the time of using two or more polymer films and the bonding process became unnecessary. In addition, it is possible to control the wavelength dispersion in the retardation film that can reduce the color change due to the influence of the retardation of the liquid crystal with respect to the retardation wavelength dispersion of the liquid crystal. The retardation film of the present invention can achieve a broadband property such as λ / 4 or λ / 2 in a wide wavelength region.

  According to the present invention, it is possible to easily obtain a retardation film having a smaller retardation as the wavelength is shorter. By selecting the optical anisotropy and shape of the inorganic compound present in the synthetic polymer, the wavelength dispersion characteristic of the retardation can be easily controlled. A retardation film having such retardation wavelength dispersion and a retardation of a quarter wavelength can be combined with a polarizing film to provide a circularly polarizing film having excellent antireflection properties. Further, it has an effect that it can contribute to an improvement in image quality when used in a reflective liquid crystal display device, an anti-transmission reflective liquid crystal display device, a transmissive liquid crystal display device, or the like.

  In the process of seeking to obtain an ideal λ / 4 plate and λ / 2 plate that does not depend on the wavelength in the visible region in a single polymer oriented film, the present invention provides a single sheet having a smaller phase difference as the wavelength is shorter. The present invention has succeeded in providing a polymer oriented film, and has achieved the above-mentioned object and has also provided a retardation film having unprecedented characteristics.

  In addition, as a result of previous studies, the present inventors have found a retardation film that satisfies the above formula (1) with a single oriented polymer film, but according to the present invention, By containing an inorganic compound having optical anisotropy, the retardation wavelength dispersion can be easily controlled according to the target value, and an ideal retardation wavelength dispersion could be found. is there.

  The retardation (retardation) of the polymer oriented film in this specification refers to a retardation value in retardation measurement, and is perpendicular to the orientation direction of the film when light is transmitted through the film of thickness d. This is the phase difference based on the difference in the traveling speed (refractive index) of the light in the direction, expressed by the product Δn · d of the difference Δn in the refractive index between the orientation direction and the direction perpendicular thereto, and the thickness d of the film. Is known. In addition, since the retardation Δn · d is proportional to the birefringence Δn if the polymer oriented films are the same, the chromatic dispersion (wavelength dependence) of the retardation is expressed by the chromatic dispersion (wavelength dependence) of the birefringence Δn. I can do it. Here, the orientation of the polymer oriented film in the present invention indicates a state in which polymer chains are mainly arranged in a specific direction. The orientation of the polymer film is usually caused by stretching the film.

  Transparency is important for the retardation film, and it is necessary that the haze representing the light scattering property of the film be 3% or less, preferably 2% or less, more preferably 1% or less. Here, the measurement of haze is performed in accordance with Japanese Industrial Standard JIS K7105 “Optical characteristics test method for plastics”.

  In the present invention, the orientation of the polymer oriented film refers to a state in which polymer chains are mainly arranged in a specific direction. The orientation of the polymer film is usually caused by stretching the film. In the present invention, when the polymer chain is oriented, the inorganic compound having optical anisotropy contained in the film is also oriented. The orientation of the inorganic compound mainly depends on the orientation direction of the main chain of the polymer, and is oriented substantially parallel to or substantially perpendicular to the polymer main chain, or otherwise. In the present invention, the orientation of the inorganic compound in the film is mainly controlled by the molecular skeleton of the polymer main chain, and the orientation direction of the inorganic compound is random when simply added to the synthetic polymer material. However, by stretching, the main chain of the polymer and the inorganic compound can be affected by mutual steric hindrance, and the orientation direction of the inorganic compound can be controlled.

  By using the inorganic compound in this way, surprisingly, an inorganic compound having an optical anisotropy capable of controlling the optical anisotropy, particularly the retardation wavelength dispersibility of the retardation film, is obtained from the polymer film. Light scattering by the inorganic compound in the visible light region can be eliminated by setting the size to a specific direction together with the orientation and smaller than the wavelength of light.

The definition of the inorganic compound having optical anisotropy in the present invention is shown below.
[Inorganic compound having optical anisotropy]
According to the Asakura Shoten Polymer Dictionary First Edition p219, the optical anisotropy means that the optical quantity such as refractive index and optical absorption has direction dependency, but in the present invention, the material having large direction dependency of the refractive index. Is particularly preferred. For example, a material having a difference in refractive index between a certain direction and a direction orthogonal to this direction is preferably 0.01 or more, more preferably 0.05 or more, and most preferably 0.10 or more. Good. As for the inorganic compound having optical anisotropy, it is a compound having crystallinity and is used in a state mixed with a polymer. The particle diameter is less than the wavelength of light (particle diameter at which optical scattering does not occur, particularly 400 nm). (Size smaller than the wavelength region) is preferably used in a state dispersed in a polymer film.

  As the inorganic compound, for example, powders of metal oxide, metal nitride, metal carbide, metal halide, ferrite, metal hydroxide, metal salts (metal carbonate, metal sulfate, metal silicate, etc.) are used. In particular, it is preferably an inorganic compound that is colorless and transparent and has optical anisotropy, and the shape of the inorganic compound is preferably such that the ratio of the minor axis to the major axis is at least 3/4 or less.

Among these, as an inorganic compound having transparency and optical anisotropy, a metal oxide powder is preferable, and examples thereof include SiO, SiO ₂ , Bi ₂ O ₅ , ZnO, TiO ₂ , Nb ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , MnO ₂ , Al ₂ O ₃ , Sb ₂ O ₃ , Ta ₂ O ₅ , WO ₃ , SrCO _{3 and the} like are mainly exemplified, but not limited thereto.

  The inorganic compound may be a naturally occurring mineral, and examples of clay minerals include kaolinite, dickite, nacrite, halloysite, antigolite, chrysotile, pyroferrite, montmorillonite, hectorite, sodium 4 There are silicon mica, sodium deonilite, muscovite, margarite, talc, vermiculite, phlogopite, xanthosoferrite, chlorite. Among these, sodium tetrasilicon mica and smectite group are preferable because of their excellent transparency. Examples of those belonging to the smectite group include montmorillonite, beidellite, nontrolite, saponite, hectorite, sauconite, and chemistry having similar crystal structures. Examples include synthetic products.

  The content of the inorganic compound having optical anisotropy is preferably in the range of 0.01 to 30% by weight, based on the synthetic polymer forming the film, and in the range of 0.05 to 25% by weight. Are more preferred, and amounts in the range of 0.1 to 20% by weight are most preferred.

  As the shape of the inorganic compound having optical anisotropy, if the maximum particle size is not smaller than the wavelength of light, optical scattering occurs, so that it is sandwiched between polarizing plates arranged in crossed Nicols as a retardation film Thus, the desired characteristics cannot be expressed. For this reason, a size smaller than the wavelength region of 400 to 700, preferably 780 nm, which is visible light, is necessary, preferably 400 nm or less, more preferably in the range of 1 to 400 nm, and in the range of 5 to 400 nm. Even more preferably, it is even more preferably in the range of 5 to 350 nm, and most preferably in the range of 5 to 300 nm.

  Regarding the shape of the inorganic compound having optical anisotropy, since the particles must have optical anisotropy, those having an anisotropic shape as an ellipsoid or columnar shape are preferred, and the degree is The ratio of the minor axis to the major axis is 3/4 or less, preferably 2/3 or less, and more preferably 1/2 or less. As for the shape, since the inorganic compound needs to have an effect of being regularly oriented with respect to the orientation of the synthetic polymer, in the case of particles having isotropic properties such as a spherical shape or a regular polygon, Since the orientation regularity of the inorganic compound particles with respect to the orientation is not controlled, it cannot be used in the present invention.

  In the present invention, two or more kinds of inorganic compounds having optical anisotropy may be used in combination. Further, the film may contain a polymer modifier such as a heat stabilizer, an antioxidant, an ultraviolet absorber, a light stabilizer, a transparent nucleating agent, a permanent antistatic agent, and a fluorescent brightening agent at the same time.

(Synthetic polymer)
The synthetic polymer in the retardation film of the present invention may be any polymer as long as it can form an oriented film with excellent transparency. Specific examples include polyolefins such as polyethylene and polypropylene, aromatic vinyl polymers such as polystyrene, Poly (meth) acrylates such as polymethyl methacrylate, polyphenylene oxide, polycarbonates, polyvinyl chloride, polyethylene terephthalate, polyarylate, polyethersulfone, polyethylene naphthalate, polymethylpentene-1, alicyclic polyolefins (for example, Ring-opening (co) polymers of cyclic olefins such as dicyclopentadiene-based polyolefins and norbornene-based polyolefins, hydrogenated (co) polymers thereof, cyclic olefins and unsaturated double bond-containing compounds Saturated copolymers), for example, copolymers of alicyclic (meth) acrylates such as tricyclodecanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate and (meth) acrylic esters such as methyl methacrylate, polysulfone, poly There may be mentioned thermoplastic polymers such as etherimides, amorphous polyamides, polyphenylene ethers, and hydrogenated polymers of cyclic olefins, cyclopentadiene, and cationic (co) polymers of aromatic vinyl compounds. Among these, examples of preferable optical characteristics include polycarbonate and alicyclic polyolefin polymers. These may be either a blend polymer, a copolymer, or a mixture of a copolymer and a blend polymer.

  More specifically, the synthetic polymer in the present invention is a synthetic polymer compound such as synthetic resin, synthetic fiber, and synthetic rubber obtained by synthesis by addition polymerization or polycondensation of monomers, and can form a film. Any polymer that can orient a polymer can be used. For example, polysaccharides such as cellulose and starch obtained from natural products, proteins such as gelatin and keratin, mineral derived materials such as asbestos and mica, natural polymer compounds such as enzymes and nucleic acids, and derivatives from natural polymer compounds Is not included.

  In addition, since the synthetic polymer must have mechanical properties that can be sufficiently endured in order to be processed as a retardation film and handled as a film, the weight average molecular weight is preferably 8000 to 500,000, and preferably 10,000 to 400,000. Is more preferable, and 12000 to 300,000 is most preferable. In addition, since the retardation film made of a synthetic polymer must have a certain degree of environmental resistance, the glass transition temperature of the synthetic polymer is preferably 100 ° C. or higher and 300 ° C. or lower, more preferably 110 ° C. or higher and 280 ° C. or lower. Preferably, the temperature is 120 ° C. or higher and 260 ° C. or lower.

  Since the synthetic polymer is used as a retardation film, it should be excellent in optical transparency, and when processed into a 100 μm film, its optical properties are such that the total light transmittance is 75% or more and haze is 3% or less. Preferably, the total light transmittance is 80% or more and haze 2% or less, and the total light transmittance 85% or more and haze 1% or less is most preferable.

[Production method of polymer film]
The manufacturing method of the retardation film of this invention is demonstrated. Manufacture of a phase difference film consists of the process of obtaining a polymer orientation film by the preparation process of the synthetic polymer film containing an inorganic compound, and the extending process which orientates this inorganic compound and a polymer film in a surface direction. Any existing production method may be used for the production method of the polymer film. For example, a solvent casting method for dissolving and casting in a solvent, an extrusion molding method for kneading in a solid state to make an extruded film from a die, a calendering method for kneading in a solid state and then making a film with a calendar roll, a press for making a film with a press Examples include molding methods. Among these, in order to uniformly disperse the optically anisotropic compound in the polymer oriented film, it is essential to uniformly mix the polymer and the compound. The solvent casting method or the extrusion molding method of mixing in (1) is preferred. Among these, the solvent casting method which is excellent in film thickness accuracy is more preferable.

  As a solvent in the solvent casting method, any solvent can be used without limitation as long as the synthetic polymer and the inorganic compound can be sufficiently dissolved and formed into a film. For example, polycarbonate, alicyclic polyolefin-based polymer can be used as the polymer. When using a combination, methylene chloride, dioxolane and the like are preferably used as the solvent. Although there is no restriction | limiting in the thickness of the film after film-forming, 20-300 micrometers is preferable from the handling surface and cost surface of a film, More preferably, it is 30-200 micrometers. When manufacturing using a solution casting method, it is preferable to add an inorganic compound at the time of preparation of the dope solution for film forming from a viewpoint of uniform mixing.

  The polymer oriented film in which the optically anisotropic compound is dispersed is then oriented by stretching or the like to orient the polymer main chain and the inorganic compound to obtain a polymer oriented film. As the stretching method, any known method may be used. For example, methods such as a tenter stretching method and an inter-roll compression stretching method are exemplified. In view of the controllability of the refractive index in the thickness direction and the uniformity of the in-plane retardation of the film, a method of uniaxial stretching by an inter-roll stretching method or a tenter stretching method is preferable.

The thickness of the retardation film of the present invention composed of the polymer oriented film is 10 to 200 μm.
In such a film, for the purpose of improving stretchability, phthalate esters such as dimethyl phthalate and dibutyl phthalate which are known plasticizers, phosphate esters such as tributyl phosphate, aliphatic dibasic esters, glycerin derivatives, It may contain a glycol derivative or the like, but is not limited thereto. The organic solvent used at the time of film formation may remain in the film and stretched. The content of the residual organic solvent in this film is preferably 1 to 20% by weight relative to the polymer solid content.

[Retardation film, circularly polarizing film, elliptically polarizing film, and liquid crystal display element or optical device using them]
The retardation film of the present invention satisfies the above formula (1) in the entire wavelength region of 400 to 700 nm. As a typical example, when λ1 is 450 nm and λ2 is 650 nm, the above formula (1 Is satisfied. In particular, a good quarter-wave plate (λ / 4 plate) or a half-wave plate (λ / 2 plate) having a small wavelength dependency can be configured with a single polymer alignment film. However, it is preferable that 100 nm ≦ R (550) ≦ 180 nm for use as a λ / 4 plate, and 220 nm ≦ R (550) ≦ 330 nm for use as a λ / 2 plate. Here, R (550) is a retardation value at a wavelength of 550 nm. This is because when the retardation value at each wavelength of the retardation film is measured, R (λ1) / R (λ2) <1 where R (λ1) and R (λ2) are respectively It is an in-plane retardation of the polymer oriented film at wavelengths λ1 (nm) and λ2 (nm) (400 nm <λ1, λ2 <780 nm, λ1 <λ2). ] Is satisfied. In particular, when the wavelength of 550 (nm) showing the strongest green color in the visible light region is used as a reference value and compared with the retardation value of the wavelength 450 (nm) showing blue, the retardation film of the present invention is described. Can be used as a wideband λ / 4 plate, the phase difference chromatic dispersion is 0.60 <R (450) / R (550) <0.97, more preferably 0.65. <R (450) / R (550) <0.92, more preferably 0.70 <R (450) / R (550) <0.87.

  Such a quarter-wave plate is used in a reflective liquid crystal display device that uses a liquid crystal display element, for example, a polarizing film that uses only one polarizing film and the back electrode also serves as a reflective electrode. It is possible to obtain a reflection type display device excellent in the above. It is also possible to use this retardation film on the back side with respect to the observer of the guest-host type liquid crystal layer. In these cases, the role of the retardation film is to convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light in the visible light region, but the retardation film of the present invention satisfies such a purpose. Can do.

Thus, as one of preferred embodiments of the present invention, a reflective liquid crystal display device including a liquid crystal cell including a liquid crystal layer between two substrates having a polarizing film, a λ / 4 plate, and a transparent electrode in this order. As such a λ / 4 plate, the phase difference is expressed by the following formula (1 ′).
R (450) / R (550) <1 (1 ′)
[Wherein, R (450) and R (550) are in-plane retardations of the polymer oriented film at wavelengths of 450 nm and 550 nm, respectively. ]
And a reflection type liquid crystal display device using the retardation film of the present invention in which R (550) is 100 to 180 nm.

  Moreover, it can use similarly as an element which converts the circularly polarized light of the reflective polarizing film comprised from the cholesteric liquid crystal etc. which reflect only either one of right and left circularly polarized light into linearly polarized light.

  In addition, the retardation film of the present invention is laminated with a polarizing film through an adhesive layer or an adhesive layer to form a laminated polarizing film such as a circular polarizing film or an elliptical polarizing film, or any material is coated on the retardation film. Then, wet heat durability may be improved, or solvent resistance may be improved.

  The retardation film of the present invention was specifically developed to make it possible to construct an ideal λ / 4 plate or λ / 2 plate having a smaller birefringence as the wavelength is shorter, from a single polymer oriented film. However, since a polymer oriented film having a smaller birefringence is newly provided as the wavelength is shorter, two or more retardation films of the present invention are laminated, or the retardation film of the present invention and another optical film. By laminating (transparent film, transparent conductive film, retardation film, polarizing film, optical compensation plate, etc.), for example, ideal λ / 4 plates and λ / 2 plates are produced in a wider wavelength range. Thus, it is possible to obtain a retardation film or an optical film suitable for various uses.

  The K value is an index of the three-dimensional refractive index anisotropy of the retardation film, but varies depending on the R value and the film thickness, and the optimum value varies depending on the application. Here, when a preferable range is described by Nz = (nx−nz) / (nx−ny), which is another index of three-dimensional refractive index anisotropy, instead of the K value, a λ / 4 plate or a λ / 2 plate If the retardation film has been subjected to a single orientation such as uniaxial stretching as described above, it is preferably between 0.3 and 1.5. In particular, when Nz = 0.5, the retardation hardly changes even if the angle of incidence on the retardation film changes from the front incidence. At this time, the K value is preferably −100 to 100. The three-dimensional refractive indexes nx, ny and nz of Nz are the same as those used in the calculation of the K value. On the other hand, when creating the retardation film of the present invention, it is also possible to perform a stretching process such as sequential biaxial stretching and simultaneous biaxial stretching to create a controlled Nz value, The R value has a phase difference necessary for a λ / 4 plate or a λ / 2 plate, but Nz can have a value of 1.5 to 10, or a value between 0.1 and 0.3. is there.

  In addition, by using such a retardation film in a liquid crystal display device, particularly a polarizing film single reflection type liquid crystal display device, a display device having excellent image quality can be obtained. This reflective liquid crystal display device is composed of a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer (liquid crystal cell), a substrate with a scattering reflecting electrode, a polarizing film, a scattering plate, and a retardation film. , A substrate with a transparent electrode, a liquid crystal layer, a substrate with a specular reflective electrode, a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer, a substrate with a transparent electrode, and a reflective layer. Things. Further, the quarter-wave plate can be used as a retardation film in a liquid crystal display device having both a transmission type and a reflection type. Examples of the configuration of the liquid crystal display device include a polarizing film, a retardation film, a substrate with a transparent electrode, a liquid crystal layer, a substrate with a reflection / transmission electrode, a retardation film, a polarizing film, and a backlight system. Furthermore, for example, in a reflective polarizing film made of cholesteric liquid crystal that reflects only the left or right circularly polarized light, if the circularly polarized light is converted into linearly polarized light, good linearly polarized light can be obtained in a wide band.

  Furthermore, the retardation film of the present invention can also be used as a quarter-wave plate used in an optical head of an optical recording apparatus. In particular, since such a retardation film can give a phase difference of a quarter wavelength with respect to multiple wavelengths, it contributes to reducing the number of retardation plates in an optical head using a plurality of laser light sources. be able to.

  Further, as an optical member in a liquid crystal projector or the like, for example, the retardation film of the present invention may be used for a polarization conversion element, a polarization beam splitter, or the like as a quarter wavelength plate or a quarter wavelength plate.

  In addition, organic or inorganic electroluminescent elements, which are light emitting elements, use a metal electrode on the back side of the light emitting layer. However, since this metal electrode reflects light, the contrast is significantly reduced in the presence of external light. Sex is reduced. In order to prevent this, the retardation film of the present invention and a polarizing film may be combined to form a circularly polarizing film, which may be used as an antireflection film. Since this circularly polarizing film uses the retardation film of the present invention capable of setting the phase difference to a quarter wavelength in a wide wavelength range of visible light, reflection can be prevented at a wide wavelength range. It is possible to provide an element with less coloration and excellent visibility. Moreover, you may use as a touch panel and may be used for CRT and PDP.

  Furthermore, the retardation film of the present invention can be used as an image quality improving film for improving the color tone and widening the viewing angle of a transmissive liquid crystal display device. Examples of the liquid crystal display device include a twisted nematic mode, a vertical alignment mode, an OCB (Optically Compensated Bend) alignment mode, an in-plane switching mode, and the like.

  The retardation film of the present invention may be used simultaneously with an optical compensation film such as another retardation film or a viewing angle widening film (for example, a discotic liquid crystal layer or a polymer liquid crystal layer is oriented in the film thickness direction of the film). Viewing angle expansion film, etc.). Further, the retardation film of the present invention may be used for a liquid crystal display device using a ferroelectric liquid crystal or an antiferroelectric liquid crystal.

  Examples of the present invention will be described below, but the present invention is not limited thereto. Moreover, the material characteristic value etc. which are described in this specification were obtained by the following evaluation methods.

(1) Measurement of R value The phase difference R value, which is the product of birefringence Δn and film thickness d, is measured by a product name “JASCO M-150 Polarized Modulated Spectroscopic Ellipsometer” manufactured by JASCO Corporation, a spectroscopic ellipsometer. It is a thing. The R value is measured in a state where the incident light beam is perpendicular to the surface of the film, and R = Δn · d = (nx−ny) · d. The unit of R value is nm. Here, nx, ny, and nz are defined as follows.
nx: Refractive index in the main stretching direction in the film plane ny: Refractive index in the direction orthogonal to the main stretching direction in the film plane nz: Refractive index in the normal direction of the film surface (the main stretching direction is the case of uniaxial stretching) (In the case of biaxial stretching, it means the direction of stretching so that the degree of orientation increases, and in terms of chemical structure, it refers to the orientation direction of the polymer main chain.)

(2) Measurement of total light transmittance and haze The total light transmittance and haze were measured by an integrating sphere light transmittance measuring device according to Japanese Industrial Standard JIS K 7105 “Testing method for optical properties of plastic”. As an evaluation apparatus, a color difference / turbidity measuring instrument manufactured by Nippon Denshoku Industries Co., Ltd .: trade name “CHD-300A” was used.

(3) Film thickness measurement It measured with the electronic micro made from Anritsu.

[Example 1]
Polyplastic Co., Ltd. alicyclic polyolefin resin (trade name TOPAS5013, glass transition temperature 134 ° C.) is used as a synthetic polymer, and needle-like strontium carbonate (IDW'04 Proceedings) is used as an inorganic compound having optical anisotropy. , pp. 643), SrCO ₃ , length (major axis) 200 nm, width (minor axis) 20 nm, particle minor axis / major axis = 20/200 = 1/10 (≦ 3/4) ), Nz (: refractive index in the length direction) 1.5230, refractive index in the width direction nx = 1.6662, ny = 1.6680), respectively, in a ratio of 85:15 (wt%) to methylene chloride. It was dissolved to prepare a dope solution of 18% by weight in terms of resin concentration. A cast film was prepared from this dope solution, and then the obtained film was stretched uniaxially with a width of 1.5 times at a temperature of 129 ° C. to obtain a 76 μm retardation film.

  It was confirmed that the retardation of the film becomes smaller as the wavelength becomes shorter at the measurement wavelength. R (450) / R (550) = 0.87, total light transmittance was 91%, and haze was 0.3%.

[Example 2]
Teijin Bayer Plastics Co., Ltd. polycarbonate resin (trade name ST-3000, glass transition temperature 150 ° C.) is used as a synthetic polymer, and as an inorganic compound having optical anisotropy, strontium carbonate (SrCO 3, long) as an acicular crystal 200 nm in width, 20 nm in width, minor axis / major axis of particles = 20/200 = 1/10 (≦ 3/4), nz (: refractive index in the length direction) 1.5230, refractive index nx in the width direction = 1. 6662, ny = 1.6680) and dissolved in methylene chloride at a ratio of 85:15 (% by weight) to prepare a dope solution of 18% by weight in terms of resin concentration. A cast film was prepared from this dope solution, and then the obtained film was stretched uniaxially with a width of 1.5 times at a temperature of 155 ° C. to obtain an 80 μm retardation film.

  It was confirmed that the retardation of the film becomes smaller as the wavelength becomes shorter at the measurement wavelength. R (450) / R (550) = 0.85, total light transmittance was 90%, and haze was 0.6%.

[Comparative Example 1]
Using only Teijin Bayer Plastics Co., Ltd. polycarbonate resin (trade name ST-3000, glass transition temperature 150 ° C.) as a synthetic polymer, it was dissolved in methylene chloride to prepare a 18% by weight dope solution in terms of resin concentration. A cast film was prepared from this dope solution, and then the obtained film was uniaxially stretched with a width of 1.5 times at a temperature of 155 ° C. to obtain an 81 μm retardation film.

  It was confirmed that the shorter the wavelength of the film, the larger the phase difference of this film, the in-plane refractive index of the stretching direction was the largest, and the refractive index anisotropy was positive. R (450) / R (550) = 1.05, total light transmittance was 91%, and haze was 0.2%.

[Comparative Example 2]
Silica (Nippon Aerosil Co., Ltd.), which is a spherical particle, is used as an inorganic compound having optical anisotropy using Teijin Bayer Plastics Co., Ltd. polycarbonate resin (trade name ST-3000, glass transition temperature 150 ° C.) as a synthetic polymer. “Aerosil OX50”, SiO ₂ , major axis 40 nm, minor axis 32 nm, minor axis / major axis of particles = 4/5 (> 3/4), nz (: refractive index in the length direction) 1.47, refraction in the width direction The ratios nx = 1.490 and ny = 1.492) were used and dissolved in methylene chloride at a ratio of 85:15 (wt%), respectively, to prepare a dope solution of 18 wt% in terms of resin concentration. A cast film was prepared from this dope solution, and then the obtained film was stretched uniaxially with a width of 1.5 times at a temperature of 155 ° C. to obtain a 83 μm retardation film.

  It was confirmed that the retardation of the film increases as the wavelength becomes shorter at the measurement wavelength. R (450) / R (550) = 1.04, total light transmittance was 90%, and haze was 0.6%.

[Comparative Example 3]
Teijin Bayer Plastics Co., Ltd. polycarbonate resin (trade name ST-3000, glass transition temperature 150 ° C.) is used as a synthetic polymer, and silica (spherical particles) (Sekisui Chemical Co., Ltd.) is used as an inorganic compound having optical anisotropy. ) “Micropearl SI”, SiO ₂ , diameter 500 nm, particle minor axis / major axis = 1 (> 3/4), nz (: refractive index in length direction) 1.493, refractive index nx = 1 in width direction 490, ny = 1.492) and dissolved in methylene chloride at a ratio of 95: 5 (% by weight), respectively, to prepare a 18% by weight dope solution in terms of resin concentration. A cast film was prepared from this dope solution, and then the obtained film was stretched uniaxially with a width of 1.5 times at a temperature of 155 ° C. to obtain a 83 μm retardation film.

  This film was confirmed to have a larger phase difference as the wavelength was shorter at the measurement wavelength, and did not have the characteristic of λ / 4 at a broad wavelength range. R (450) / R (550) = 1.04, total light transmittance was 73%, and haze was 8.6%.

  The retardation film of the present invention contributes to improvement of image quality in combination with a display element using liquid crystal or the like, for example, a reflective liquid crystal display device, an anti-transmission reflective liquid crystal display device, or a transmissive liquid crystal display device. I can do it.

Claims (7)

A single polymer comprising a synthetic polymer and an oriented polymer film containing an inorganic compound having a major axis length of 400 nm or less, a ratio of a minor axis to a major axis of 3/4 or less, and optical anisotropy. A retardation film of a layer, wherein the retardation film has a retardation at wavelength λ satisfying the following formula (1) and a haze of 3% or less.
R (λ1) / R (λ2) <1 (1)
[Wherein R (λ1) and R (λ2) are the surfaces of the polymer oriented film at respective wavelengths λ1 (nm) and λ2 (nm) (400 nm <λ1, λ2 <700 nm, λ1 <λ2) This is the internal phase difference. ]   The retardation film according to claim 1, wherein the content of the inorganic compound having optical anisotropy is 0.01 wt% or more and 30 wt% or less with respect to 100 parts by weight of the synthetic polymer.   The retardation film according to claim 1, wherein the synthetic polymer is an alicyclic polyolefin.   The retardation film according to claim 1, wherein the synthetic polymer is polycarbonate.   A laminated polarizing film comprising a polarizing film and the retardation film according to claim 1.   A liquid crystal display element using the retardation film according to claim 1.   An optical device using the retardation film according to claim 1.