JP4737629B2 - Elliptical polarizing plate and image display device using the same - Google Patents

Description

  The present invention relates to an elliptically polarizing plate and an image display device using the elliptically polarizing plate. More specifically, the present invention relates to an elliptically polarizing plate having a wide bandwidth and a wide viewing angle, and an image display device using the same, having uniform display characteristics when viewed from any direction of 360 ° when viewed from an oblique direction.

  Various image display devices such as liquid crystal display devices and electroluminescence (EL) displays generally use various optical films in which a polarizing film and a retardation plate are combined in order to perform optical compensation.

  A circularly polarizing plate which is a kind of the optical film can be usually produced by combining a polarizing film and a λ / 4 plate. However, the λ / 4 plate generally exhibits a characteristic that the phase difference value increases as the wavelength becomes shorter, that is, a so-called “positive wavelength dispersion characteristic”, and generally has a large wavelength dispersion characteristic. Therefore, there is a problem that desired optical characteristics (for example, a function as a λ / 4 plate) cannot be exhibited over a wide wavelength range. In order to avoid such problems, in recent years, as a phase difference plate exhibiting a wavelength dispersion characteristic in which a retardation value increases as the wavelength becomes longer, that is, a so-called “reverse dispersion characteristic”, for example, a modified cellulose film and Modified polycarbonate films have been proposed. However, these films have a problem in terms of cost.

  Therefore, at present, for a λ / 4 plate having positive wavelength dispersion characteristics, for example, by combining a retardation plate whose retardation value increases as it becomes longer wavelength side, or a λ / 2 plate, the above-mentioned λ / 4 plate is used. A method of correcting the wavelength dispersion characteristics of the plate is employed (see, for example, Patent Document 1).

  As described above, when the polarizing film, the λ / 4 plate, and the λ / 2 plate are combined, it is necessary to adjust the respective optical axes, that is, the angles between the absorption axis of the polarizing film and the slow axis of each retardation plate. However, since both the polarizing film and the retardation film made of a stretched film generally have an optical axis that depends on the stretching direction, in order to laminate them so that the absorption axis and the slow axis are at a desired angle, It is necessary to laminate the film after cutting it out according to the direction of the optical axis. Specifically, the absorption axis of the polarizing film is usually parallel to the stretching direction, and the slow axis of the retardation film is also parallel to the stretching direction. For this reason, in order to laminate | stack a polarizing film and a phase difference plate, for example so that the angle of an absorption axis and a slow axis may be 45 degrees, either one film is with respect to a longitudinal direction (stretching direction). It is necessary to cut in the direction of 45 °. When pasting after cutting out the film in this way, for example, there is a possibility that the angle of the optical axis varies in each cut out film, and as a result, there is a problem that the quality varies among products. . There is also a problem of cost and time. Furthermore, there is a problem that the waste increases due to the cutting and it is difficult to produce a large film.

  For such problems, for example, a method of adjusting the stretching direction such as stretching a polarizing film or a retardation plate in an oblique direction has been reported (for example, see Patent Document 2), but the adjustment is difficult. There is a problem with it.

Further, along with higher definition of the image display device, further improvement is required for the characteristics of the elliptically polarizing plate in the oblique direction and the viewing angle.
Japanese Patent No. 3174367 JP 2003-195037 A

  The present invention has been made to solve the above-described conventional problems. The object of the present invention is to provide a wide-band and wide-ranging display that has uniform display characteristics when viewed from an oblique direction at any angle of 360 °. An object is to provide an elliptically polarizing plate having a viewing angle and an image display device using the same.

  As a result of intensive studies on the characteristics of the elliptically polarizing plate, the present inventors have further laminated a birefringent layer having specific optical characteristics in a specific positional relationship in addition to the λ / 4 plate and the λ / 2 plate. The inventors have found that the above object can be achieved and have completed the present invention.

  The elliptically polarizing plate of the present invention includes: a polarizer; a protective layer; a first birefringent layer that functions as a λ / 2 plate; a second birefringent layer having a refractive index distribution of nz> nx = ny; A third birefringent layer functioning as a λ / 4 plate is provided in this order.

In a preferred embodiment, the elliptically polarizing plate has a ratio Rth ₂ / ratio between the absolute value Rthp of the retardation in the thickness direction of the protective layer and the absolute value Rth ₂ of the retardation in the thickness direction of the second birefringent layer. Rthp is in the range of 1.1-4.

  In a preferred embodiment, in the elliptically polarizing plate, the absorption axis of the polarizer and the slow axis of the third birefringent layer are substantially orthogonal.

  In a preferred embodiment, the slow axis of the first birefringent layer defines an angle of + 8 ° to + 38 ° or −8 ° to −38 ° with respect to the absorption axis of the polarizer.

  In preferable embodiment, the said protective layer consists of a film which contains a triacetyl cellulose as a main component.

  According to another aspect of the present invention, an image display device is provided. The image display device includes the elliptically polarizing plate. In a preferred embodiment, the elliptically polarizing plate is disposed on the viewing side.

As described above, according to the present invention, the polarizer, the protective layer, the first birefringent layer functioning as a λ / 2 plate, and the second birefringence having a refractive index distribution of nz> nx = ny. Layer and a third birefringent layer functioning as a λ / 4 plate in this order, thereby having a wide band and wide viewing angle elliptically polarizing plate having excellent characteristics in an oblique direction, and an image display using the same A device can be obtained. Preferably, a λ / 2 plate (first birefringent layer) having a refractive index distribution of nx> ny = nz and a λ / 4 plate (third birefringent layer) having a refractive index distribution of nx>ny> nz. By arranging the second birefringent layer having a refractive index distribution of nz> nx = ny between the two, it has a uniform display characteristic when viewed from any direction of 360 ° when viewed from an oblique direction, In addition, an elliptically polarizing plate having an appropriate contrast in an oblique direction can be obtained. Such an effect is not apparent in theory, and is an knowledge obtained only after actually manufacturing an elliptically polarizing plate and an image display device using the elliptically polarizing plate, and is an unexpectedly excellent effect. Light that has passed through the polarizer (ie, polarized light) is a first birefringent layer (λ / 2 plate), a second birefringent layer (so-called positive C plate), and a third birefringent layer (λ / 4 plate). By passing in this order, the optical axis deviation of each layer and the deviation of the polarization state due to the phase difference of the protective layer are compensated well, and as a result, the decrease in contrast not only in the front but also in the oblique direction is suppressed, In addition, it is presumed that the viewing angle characteristics are improved (that is, uniform display characteristics can be obtained from any 360 ° orientation). Furthermore, the ratio Rth ₂ / Rthp between the absolute value Rthp of the retardation in the thickness direction of the protective layer and the absolute value Rth ₂ of the retardation in the thickness direction of the second birefringent layer is in the range of 1.1 to 4. In some cases, the effect is significant.

A. Elliptical polarizing plate A-1. Overall configuration of elliptically polarizing plate The elliptically polarizing plate of the present invention includes a polarizer, a protective layer, a first birefringent layer functioning as a λ / 2 plate, and a second refractive index distribution of nz> nx = ny. And a third birefringent layer functioning as a λ / 4 plate in this order. For example, as shown in FIG. 1, the elliptically polarizing plate 10 includes a polarizer 11, a protective layer 12, a first birefringent layer 13, a second birefringent layer 14, and a third birefringent layer 15. According to such a configuration, it is possible to satisfactorily compensate for the deviation of the polarization state caused by the optical axis deviation of each layer and the phase difference of the protective layer when viewed from an oblique direction, so that it functions as a polarizing plate at a wide viewing angle. Can be ensured. Further, by canceling out the retardation of the protective layer with the second birefringent layer, the linear polarization property of the light emitted from the polarizing plate can be recovered, and the function as a polarizing plate with a wide viewing angle can be ensured. Practically, the elliptically polarizing plate of the present invention may have the second protective layer 16 on the side where the protective layer 12 of the polarizer is not laminated.

The first birefringent layer 13 functions as a so-called λ / 2 plate. In this specification, the λ / 2 plate refers to converting linearly polarized light having a specific vibration direction into linearly polarized light having a vibration direction orthogonal to the vibration direction of the linearly polarized light, or converting right circularly polarized light to the left circle. It has a function of converting into polarized light (or converting left circularly polarized light into right circularly polarized light). The second birefringent layer 14 has a refractive index profile of nz> nx = ny and can function as a so-called positive C plate. The third birefringent layer 15 functions as a so-called λ / 4 plate. In this specification, the λ / 4 plate refers to a plate having a function of converting linearly polarized light having a specific wavelength into circularly polarized light (or circularly polarized light into linearly polarized light). Further, the ratio Rth ₂ / Rthp between the absolute value Rthp of the retardation in the thickness direction of the protective layer 12 and the absolute value Rth ₂ of the retardation in the thickness direction of the second birefringent layer 14 is preferably 1.1 to 4. 0.0, more preferably 1.5 to 3.0. Since the retardation in the thickness direction of the protective layer 12 and the second birefringent layer 14 has such a relationship, the retardation of the protective layer can be satisfactorily compensated, and as a result, an extremely excellent oblique direction An elliptically polarizing plate having the following characteristics can be obtained. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), ny is the refractive index in the direction perpendicular to the slow axis, and nz is the thickness. The refractive index in the direction. The thickness direction retardation Rth is a thickness direction retardation value measured with light having a wavelength of 590 nm at 23 ° C. The thickness direction retardation Rth is determined by the formula: Rth = (nx−nz) × d, where d (nm) is the thickness of the film (layer). nx and nz are as described above. Rth is usually measured at a wavelength of 590 nm. “Nx = ny” includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. In the present specification, “substantially equal” is intended to include the case where nx and ny are different within a range that does not practically affect the overall polarization characteristics of the elliptically polarizing plate.

  FIG. 2 is an exploded perspective view for explaining the optical axis of each layer constituting the elliptically polarizing plate according to a preferred embodiment of the present invention. (In FIG. 2, the second protective layer 16 is omitted for the sake of clarity.) The first birefringent layer 13 has a slow axis B with respect to the absorption axis A of the polarizer 11. Are stacked so as to define a predetermined angle α. The angle α is preferably + 8 ° to + 38 ° or −8 ° to −38 °, more preferably + 13 ° to + 33 ° or −13 ° to −33 °, and particularly preferably + 19 ° to + 29 °. It is −19 ° to −29 °, particularly preferably + 21 ° to + 27 ° or −21 ° to −27 °, and most preferably + 23 ° to + 24 ° or −23 ° to −24 °. By laminating the first birefringent layer and the polarizer so as to form such an angle α, a polarizing plate having very excellent circular polarization characteristics can be obtained. Further, as shown in FIG. 2, the third birefringent layer 15 is laminated so that the slow axis C thereof is substantially perpendicular to the absorption axis A of the polarizer 11. In the present specification, “substantially orthogonal” includes a case of 90 ° ± 2.0 °, preferably 90 ° ± 1.0 °, more preferably 90 ° ± 0.5 °. It is.

  The total thickness of the elliptically polarizing plate of the present invention is preferably 80 to 250 μm, more preferably 110 to 220 μm, and most preferably 140 to 190 μm. According to the method for producing an elliptically polarizing plate of the present invention (described later), the first birefringent layer (and the second birefringent layer in some cases) can be laminated without using an adhesive. Compared with the elliptically polarizing plate, the total thickness can be reduced to about 1/4. As a result, the elliptically polarizing plate of the present invention can greatly contribute to thinning of the image display device. Hereinafter, details of each layer constituting the elliptically polarizing plate of the present invention will be described.

A-2. First Birefringent Layer As described above, the first birefringent layer 13 functions as a so-called λ / 2 plate. With the first birefringent layer functioning as a λ / 2 plate, the wavelength dispersion characteristics of the third birefringent layer functioning as a λ / 4 plate (particularly, the wavelength range where the phase difference deviates from λ / 4), The phase difference can be adjusted appropriately. The in-plane retardation (Δnd) of the first birefringent layer is preferably 180 to 300 nm, more preferably 210 to 280 nm, and most preferably 230 to 240 nm at a wavelength of 590 nm. The in-plane phase difference (Δnd) is obtained from the equation Δnd = (nx−ny) × d. Here, nx and ny are as described above, and d is the thickness of the first birefringent layer. Further, the first birefringent layer 13 preferably has a refractive index distribution of nx> ny = nz. In the present specification, “ny = nz” includes not only the case where ny and nz are exactly equal, but also the case where ny and nz are substantially equal.

  The thickness of the first birefringent layer can be set so as to function most appropriately as a λ / 2 plate. In other words, the thickness can be set so as to obtain a desired in-plane retardation. Specifically, the thickness is preferably 0.5 to 5 μm, more preferably 1 to 4 μm, and most preferably 1.5 to 3 μm.

  As a material for forming the first birefringent layer, any appropriate material can be adopted as long as the above characteristics are obtained. A liquid crystal material is preferable, and a liquid crystal material (nematic liquid crystal) in which the liquid crystal phase is a nematic phase is more preferable. By using a liquid crystal material, the difference between nx and ny of the obtained birefringent layer can be significantly increased compared to a non-liquid crystal material. As a result, the thickness of the birefringent layer for obtaining a desired in-plane retardation can be significantly reduced. As such a liquid crystal material, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystal material may exhibit a liquid crystallinity mechanism either lyotropic or thermotropic. The alignment state of the liquid crystal is preferably homogeneous alignment. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

  When the liquid crystal material is a liquid crystal monomer, for example, a polymerizable monomer and a crosslinkable monomer are preferable. This is because the alignment state of the liquid crystalline monomer can be fixed by polymerizing or crosslinking the liquid crystalline monomer, as will be described later. After aligning the liquid crystalline monomers, for example, if the liquid crystalline monomers are polymerized or crosslinked, the alignment state can be fixed thereby. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, in the formed first birefringent layer, for example, a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change specific to the liquid crystal compound does not occur. As a result, the first birefringent layer is a birefringent layer that is not affected by temperature changes and has extremely high stability.

  Any appropriate liquid crystal monomer can be adopted as the liquid crystal monomer. For example, polymerizable mesogenic compounds described in JP-T-2002-533742 (WO00 / 37585), EP358208 (US52111877), EP66137 (US4388453), WO93 / 22397, EP02661712, DE195504224, DE44081171, and GB2280445 can be used. Specific examples of such a polymerizable mesogenic compound include, for example, the trade name LC242 from BASF, the trade name E7 from Merck, and the trade name LC-Silicon-CC3767 from Wacker-Chem.

  As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable, and specific examples include a monomer represented by the following formula (1). These liquid crystal monomers can be used alone or in combination of two or more.

In the above formula (1), A ¹ and A ² each represent a polymerizable group and may be the same or different. One of A ¹ and A ² may be hydrogen. X is each independently a single bond, —O—, —S—, —C═N—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NR—. , —NR—CO—, —NR—, —O—CO—NR—, —NR—CO—O—, —CH ₂ —O— or —NR—CO—NR, wherein R is H or C _1. -C ₄ alkyl, M represents a mesogen group.

  In the above formula (1), X may be the same or different, but is preferably the same.

Among the monomers of the above formula (1), each A ² is preferably located in the ortho position with respect to A ¹ .

Furthermore, A ¹ and A ² are each independently represented by the following formula ZX- (Sp) _n (2)
And A ¹ and A ² are preferably the same group.

In the above formula (2), Z represents a crosslinkable group, X is as defined in the above formula (1), and Sp is a linear or branched substituent having 1 to 30 carbon atoms or It represents a spacer composed of an unsubstituted alkyl group, and n represents 0 or 1. A carbon chain in Sp may be, for example, oxygen in ether functional group, sulfur in a thioether functional group, it may be interrupted by such alkylimino group nonadjacent imino or C ₁ -C _4.

  In the above formula (2), Z is preferably any one of the atomic groups represented by the following formula. In the following formula, examples of R include groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, and t-butyl.

  In the above formula (2), Sp is preferably any one of the atomic groups represented by the following formula. In the following formula, m is preferably 1 to 3 and p is preferably 1 to 12.

In the above formula (1), M is preferably represented by the following formula (3). In the following formula (3), X is the same as defined in the above formula (1). Q represents, for example, a substituted or unsubstituted linear or branched alkylene or aromatic hydrocarbon group. Q may be, for example, a substituted or unsubstituted linear or branched C ₁ -C ₁₂ alkylene.

  When Q is an aromatic hydrocarbon atomic group, for example, an atomic group represented by the following formula or a substituted analog thereof is preferable.

The substituted analog of the aromatic hydrocarbon group represented by the above formula may have, for example, 1 to 4 substituents per aromatic ring, and may include one aromatic ring or one group. Each may have 1 or 2 substituents. The above substituents may be the same or different. As the substituent, for example, C ₁ -C ₄ alkyl, nitro, F, Cl, Br, a halogen such as I, phenyl, C ₁ -C ₄ alkoxy, and the like.

  Specific examples of the liquid crystal monomer include monomers represented by the following formulas (4) to (19).

  The temperature range in which the liquid crystal monomer exhibits liquid crystal properties varies depending on the type. Specifically, the temperature range is preferably 40 to 120 ° C, more preferably 50 to 100 ° C, and most preferably 60 to 90 ° C.

A-3. Second Birefringent Layer As described above, the second birefringent layer 14 has a refractive index profile of nz> nx = ny and can function as a so-called positive C plate. Further, as described above, the absolute value Rth ₂ retardation in the thickness direction of the second birefringent layer has a specific ratio with respect to the absolute value Rthp of retardation in the thickness direction of the protective layer. By providing the second birefringent layer having such optical characteristics, the retardation in the thickness direction of the protective layer can be favorably compensated. As a result, an elliptically polarizing plate having very excellent characteristics in the oblique direction can be obtained.

As described above, the absolute value Rth ₂ retardation in the thickness direction of the second birefringent layer may be optimized in accordance with the absolute value Rthp of retardation in the thickness direction of the protective layer. For example, the absolute value Rth ₂ of the retardation in the thickness direction of the second birefringent layer is preferably 50 to 200 nm, more preferably 75 to 150 nm, and most preferably 90 to 120 nm. The thickness of the second birefringent layer from which such an absolute value can be obtained can vary depending on the material used. For example, the thickness of the second birefringent layer is preferably 0.5 to 10 μm, more preferably 0.5 to 8 μm, and most preferably 0.5 to 5 μm.

  The second birefringent layer is preferably made of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Examples of typical liquid crystal compounds include nematic liquid crystal compounds. An outline of such a liquid crystal compound alignment technique is described in, for example, Chemical Review 44 (Surface Modification, Edited by Chemical Society of Japan, pages 156 to 163).

  Examples of the liquid crystal material capable of forming homeotropic alignment include, for example, a side chain containing a monomer unit (a) containing a liquid crystalline fragment side chain and a monomer unit (b) containing a non-liquid crystalline fragment side chain. Type liquid crystal polymer. Such a side-chain liquid crystal polymer can realize homeotropic alignment without using a vertical alignment agent or a vertical alignment film. The side chain type liquid crystal polymer is a monomer unit containing a non-liquid crystalline fragment side chain having an alkyl chain in addition to the monomer unit (a) containing a liquid crystalline fragment side chain of a normal side chain type liquid crystal polymer. (B) Due to the action of the monomer unit (b) containing the non-liquid crystalline fragment side chain, a liquid crystal state (for example, a nematic liquid crystal phase) can be expressed by, for example, heat treatment without using a vertical alignment agent or a vertical alignment film. It is speculated that homeotropic alignment can be realized.

  The monomer unit (a) has a side chain having nematic liquid crystallinity, and examples thereof include a monomer unit represented by the general formula (a).

In the formula (a), R ¹ is a hydrogen atom or a methyl group, a is a positive integer of 1 to 6, X ¹ is a —CO ₂ — group or a —OCO— group, and R ² is a cyano group. A group, an alkoxy group having 1 to 6 carbon atoms, a fluoro group, or an alkyl group having 1 to 6 carbon atoms, and b and c each represent an integer of 1 or 2.

  Moreover, a monomer unit (b) has a linear side chain, for example, the monomer unit represented by General formula (b) is mentioned.

In the above formula (b), R ³ is a hydrogen atom or a methyl group, and R ⁴ is represented by an alkyl group having 1 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or the general formula (b1). It is a group.

In the above formula (b1), d is a positive integer from 1 to 6, R ⁵ is an alkyl group having 1 to 6 carbon atoms.

  Further, the ratio of the monomer unit (a) to the monomer unit (b) can be appropriately set according to the purpose and the type of the monomer unit. (B) / {(a) + (b)} is preferably 0.01 to 0.8 (molar ratio), more preferably 0.1 to 0.5 (molar ratio). This is because when the proportion of the monomer unit (b) increases, the side chain type liquid crystal polymer often does not exhibit liquid crystal monodomain alignment.

  Also, for example, as a liquid crystal material capable of forming homeotropic alignment, the monomer unit (a) containing the liquid crystalline fragment side chain and the monomer unit (c) containing a liquid crystalline fragment side chain having an alicyclic ring structure are used. And a side chain type liquid crystal polymer. Such a side-chain liquid crystal polymer can also realize homeotropic alignment without using a vertical alignment agent or a vertical alignment film. The side chain type liquid crystal polymer is a monomer containing a liquid crystalline fragment side chain having an alicyclic ring structure in addition to the monomer unit (a) containing a liquid crystalline fragment side chain of a normal side chain type liquid crystal polymer. It has a unit (c). By the action of this monomer unit (c), it is presumed that a liquid crystal state (for example, nematic liquid crystal phase) can be expressed by heat treatment, for example, without using a vertical alignment film, and homeotropic alignment can be realized. The

  The monomer unit (c) has a side chain having nematic liquid crystallinity, and examples thereof include a monomer unit represented by the general formula (c).

In the above formula (c), R ⁶ is a hydrogen atom or a methyl group, h is a positive integer of 1 to 6, X ² is a —CO ₂ — group or a —OCO— group, and e and g are , Each is an integer of 1 or 2, f is an integer of 0 to 2, and R ⁷ is a cyano group or an alkyl group having 1 to 12 carbon atoms.

  Further, the ratio of the monomer unit (a) to the monomer unit (c) can be appropriately set according to the purpose and the type of the monomer unit. (C) / {(a) + (c)} is preferably 0.01 to 0.8 (molar ratio), more preferably 0.1 to 0.6 (molar ratio). This is because when the proportion of the monomer unit (b) increases, the side chain type liquid crystal polymer often does not exhibit liquid crystal monodomain alignment.

  The above monomer units are merely examples, and it goes without saying that the liquid crystal polymer capable of forming homeotropic alignment is not limited to those having the above monomer units. Moreover, the said exemplary monomer unit can be combined suitably.

  The weight average molecular weight of the side chain type liquid crystal polymer is preferably 2,000 to 100,000. By adjusting the weight average molecular weight to such a range, the performance as a liquid crystal polymer can be satisfactorily exhibited. The weight average molecular weight is more preferably 2,500 to 50,000. Within such a range, the alignment layer is excellent in film formability and a uniform alignment state can be formed.

  The exemplified side chain type liquid crystal polymer can be prepared by copolymerizing an acrylic monomer or a methacrylic monomer corresponding to the monomer unit (a), the monomer unit (b) or the monomer unit (c). The monomer corresponding to the monomer unit (a), the monomer unit (b) or the monomer unit (c) can be synthesized by any appropriate method. The copolymer can be prepared according to any appropriate polymerization method such as an acrylic monomer (for example, radical polymerization method, cationic polymerization method, anion polymerization method). In addition, when applying radical polymerization system, various polymerization initiators can be used. Preferred polymerization initiators include azobisisobutyronitrile or benzoyl peroxide. This is because the polymerization can be started with an appropriate mechanism and speed because it can be decomposed at an appropriate temperature (not high or low).

The homeotropic alignment can also be formed from a liquid crystalline composition containing the side chain liquid crystal polymer. Such a liquid crystal composition may contain a photopolymerizable liquid crystal compound in addition to the polymer. The photopolymerizable liquid crystal compound is a liquid crystal compound having at least one photopolymerizable functional group (for example, an unsaturated double bond such as an acryloyl group or a methacryloyl group). Those exhibiting nematic liquid crystallinity are preferred. Specific examples of such a photopolymerizable liquid crystal compound include acrylates and methacrylates that can also be used as the monomer unit (a). Further preferred photopolymerizable liquid crystal compounds have two or more photopolymerizable functional groups. This is because the durability of the resulting film (second birefringent layer) can be improved. Examples of such a photopolymerizable liquid crystal compound include a crosslinked nematic liquid crystal monomer represented by the following formula. Examples of the photopolymerizable liquid crystal compound include compounds in which the terminal “H ₂ C═CR—CO ₂ —” in the following formula is substituted with a vinyl ether group or an epoxy group, “— (CH ₂ ) _m —” and / or Alternatively, “— (CH ₂ ) _n —” is replaced with “— (CH ₂ ) ₃ —C ^* H (CH ₃ ) — (CH ₂ ) ₂ —” or “— (CH ₂ ) ₂ —C ^* H (CH ₃ )”. A compound substituted with “— (CH ₂ ) ₃ —” can be exemplified.

In the above formula, R ⁸ is a hydrogen atom or a methyl group, A and D are each independently a 1,4-phenylene group or a 1,4-cyclohexylene group, and Y is each independently —COO— group, —OCO— group or —O— group, and B is 1,4-phenylene group, 1,4-cyclohexylene group, 4,4′-biphenylene group or 4,4′-bicyclohexylene. And m and n each independently represents an integer of 2 to 6.

  The photopolymerizable liquid crystal compound can be brought into a liquid crystal state by heat treatment, for example, to exhibit a nematic liquid crystal phase and to be homeotropically aligned with the side chain liquid crystal polymer. Next, the durability of the homeotropic alignment liquid crystal film can be further improved by polymerizing or crosslinking the photopolymerizable liquid crystal compound to fix the homeotropic alignment.

  The ratio of the photopolymerizable liquid crystal compound to the side chain type liquid crystal polymer in the liquid crystal composition is the purpose, the type of the side chain type liquid crystal polymer and the photopolymerizable liquid crystal compound used, and the durability of the resulting homeotropic alignment liquid crystal film. It can be set as appropriate in consideration of the properties and the like. Specifically, the photopolymerizable liquid crystal compound: side chain type liquid crystal polymer (weight ratio) is preferably about 0.1: 1 to 30: 1, more preferably 0.5: 1 to 20: 1. Yes, most preferably 1: 1 to 10: 1.

  The liquid crystalline composition may further contain a photopolymerization initiator. Any appropriate photopolymerization initiator can be adopted as the photopolymerization initiator. Specific examples include Irgacure 907, 184, 651, and 369 manufactured by Ciba Specialty Chemicals. The content of the photopolymerization initiator can be adjusted to such an extent that the homeotropic orientation of the liquid crystalline composition is not disturbed in consideration of the kind of the photopolymerizable liquid crystal compound, the blending ratio of the liquid crystalline composition, and the like. Typically, the content of the photopolymerization initiator is preferably about 0.5 to 30 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the photopolymerizable liquid crystal compound. is there.

A-4. Third Birefringent Layer As described above, the third birefringent layer 15 functions as a so-called λ / 4 plate. According to the present invention, the wavelength dispersion characteristic of the third birefringent layer functioning as a λ / 4 plate is corrected by the optical characteristics of the first birefringent layer functioning as the λ / 2 plate, thereby obtaining a wide wavelength range. The circular polarization function in a range can be exhibited. The in-plane retardation (Δnd) of the third birefringent layer is preferably 90 to 180 nm, more preferably 90 to 150 nm, and most preferably 105 to 135 nm at a wavelength of 550 nm. The Nz coefficient (= (nx−nz) / (nx−ny)) of the third birefringent layer is preferably 1.0 to 2.2, more preferably 1.2 to 2.0, Most preferably, it is 1.4-1.8. Further, the third birefringent layer 15 preferably has a refractive index distribution of nx>ny> nz.

  The thickness of the third birefringent layer can be set so as to function most appropriately as a λ / 4 plate. In other words, the thickness can be set so as to obtain a desired in-plane retardation. Specifically, the thickness is preferably 10 to 100 μm, more preferably 20 to 80 μm, and most preferably 40 to 70 μm.

  The third birefringent layer can be typically formed by stretching a polymer film. For example, by appropriately selecting the type of polymer, stretching conditions (for example, stretching temperature, stretching ratio, stretching direction), stretching method, etc., desired optical properties (for example, refractive index distribution, in-plane retardation, thickness direction) A third birefringent layer having a retardation, Nz coefficient) can be obtained. More specifically, the stretching temperature is preferably 120 to 180 ° C, more preferably 140 to 170 ° C. The draw ratio is preferably 1.05 to 2.0 times, more preferably 1.3 to 1.6 times. Examples of the stretching method include lateral uniaxial stretching. The stretching direction is preferably a direction substantially perpendicular to the absorption axis of the polarizer (the width direction of the polymer film, ie, the direction perpendicular to the longitudinal direction).

  Any appropriate polymer can be adopted as the polymer constituting the polymer film. Specific examples include positive birefringent films such as polycarbonate polymers, norbornene polymers, cellulose polymers, polyvinyl alcohol polymers, and polysulfone polymers. Polycarbonate polymers and norbornene polymers are preferred.

A-5. Polarizer Any appropriate polarizer may be employed as the polarizer 11 depending on the purpose. For example, a dichroic substance such as iodine or a dichroic dye is adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film or an ethylene / vinyl acetate copolymer partially saponified film. Examples include uniaxially stretched films, polyene-based oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio. The thickness of these polarizers is not particularly limited, but is generally about 1 to 80 μm.

  A polarizer uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film can be produced by, for example, dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. . If necessary, it may contain boric acid, zinc sulfate, zinc chloride, or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

  By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but also the effect of preventing unevenness such as uneven dyeing can be obtained by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

A-6. Protective layer The protective layer 12 and the 2nd protective layer 16 consist of arbitrary appropriate films which can be used as a protective film of a polarizing plate. A transparent protective film is preferred. Specific examples of the material that is the main component of such a film include cellulose resins such as triacetylcellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, Examples thereof include transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, acrylic, and acetate. In addition, thermosetting resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone, or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material for 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 nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film may be an extruded product of the resin composition, for example. TAC, polyimide resin, polyvinyl alcohol resin, and glassy polymer are preferable, and TAC is more preferable. This is because the circularly polarized light property in the oblique direction is remarkably improved by using in combination with the second birefringent layer.

  The protective layer is preferably transparent and has no color. Specifically, the thickness direction retardation value is preferably −90 nm to +90 nm, more preferably −80 nm to +80 nm, and most preferably −70 nm to +70 nm.

  As the thickness of the protective layer, any appropriate thickness can be adopted as long as the preferable thickness direction retardation is obtained. Specifically, the thickness of the protective layer is preferably 1 to 100 μm, more preferably 5 to 80 μm, and most preferably 10 to 50 μm.

B. Manufacturing method of elliptically polarizing plate The manufacturing method of the elliptically polarizing plate in one embodiment of the present invention includes a step of performing an alignment treatment on the surface of the transparent protective film (which finally becomes the protective layer 12); A step of forming a first birefringent layer on the surface of the transparent protective film, a step of laminating a polarizer on the surface of the transparent protective film that has not been subjected to an orientation treatment, and a second step on the surface of the first birefringent layer. Forming a birefringent layer; and forming a third birefringent layer on the surface of the second birefringent layer. According to such a manufacturing method, for example, an elliptically polarizing plate as shown in FIG. 1 is obtained.

  The order of the above steps and / or the film subjected to the orientation treatment can be appropriately changed according to the target laminated structure of the elliptically polarizing plate. For example, the polarizer lamination step may be performed after any birefringent layer forming step or lamination step. Further, for example, the orientation treatment may be applied to the transparent protective film or may be applied to any appropriate base material. When the substrate is subjected to orientation treatment, the film (specifically, the first birefringent layer) formed on the substrate is in an appropriate order according to the desired laminated structure of the elliptically polarizing plate. It can be transferred (laminated). Details of each step will be described below. As an example, a manufacturing procedure of an elliptically polarizing plate as shown in FIG. 1 will be described.

B-1. Alignment treatment of transparent protective film The surface of the transparent protective film (which finally becomes the protective layer 12) is subjected to an alignment treatment, and a coating liquid containing a predetermined liquid crystal material is applied to the surface, as shown in FIG. Thus, the first birefringent layer 13 having a slow axis that forms an angle α with respect to the absorption axis of the polarizer 11 can be formed (the step of forming the first birefringent layer will be described later). .

  Arbitrary appropriate orientation processing may be employ | adopted as orientation processing to the said transparent protective film. Specifically, a mechanical alignment process, a physical alignment process, and a chemical alignment process are mentioned. Specific examples of the mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of the physical alignment process include a magnetic field alignment process and an electric field alignment process. Specific examples of the chemical alignment treatment include oblique vapor deposition and photo-alignment treatment. A rubbing process is preferred. In addition, arbitrary appropriate conditions may be employ | adopted for the process conditions of various orientation processes according to the objective.

  The orientation direction of the orientation treatment is a direction that forms a predetermined angle with the absorption axis of the polarizer when the transparent protective film and the polarizer are laminated. As will be described later, this orientation direction is substantially the same as the direction of the slow axis of the formed first birefringent layer 13. Therefore, the predetermined angle is preferably + 8 ° to + 38 ° or −8 ° to −38 °, more preferably + 13 ° to + 33 ° or −13 ° to −33 °, and particularly preferably + 19 °. ~ + 29 ° or -19 ° to -29 °, particularly preferably + 21 ° to + 27 ° or -21 ° to -27 °, most preferably + 23 ° to + 24 ° or -23 ° to -24 °. is there.

  As the orientation treatment that can define the predetermined angle as described above for the long transparent protective film, the longitudinal direction of the long transparent protective film or its vertical direction (width direction), and For example, the treatment may be performed in an oblique direction (specifically, a direction defining a predetermined angle as described above) with respect to the longitudinal direction of the long transparent protective film or the vertical direction (width direction) thereof. The polarizer is manufactured by stretching a polymer film dyed with the above-described dichroic material, and has an absorption axis in the stretching direction. And when mass-producing a polarizer, the elongate polymer film is prepared and the extending | stretching is performed continuously in the longitudinal direction. Therefore, when bonding a long polarizer and a long transparent protective film, the longitudinal direction of both becomes the absorption axis of the polarizer. For this reason, in order to align in a direction which makes a predetermined angle with respect to the absorption axis of the polarizer, it is desirable to perform an alignment process in an oblique direction. Since the direction of the absorption axis of the polarizer and the longitudinal direction of the long film (polarizer and transparent protective film) substantially coincide with each other, the direction of the orientation treatment is performed in a direction that forms the predetermined angle with respect to the longitudinal direction. Just do it. On the other hand, when processing in the longitudinal direction or the width direction of a transparent protective film, it is necessary to laminate | stack, after cutting out a transparent protective film in the diagonal direction. As a result, there may be variations in the angle of the optical axis in each cut out film, resulting in variations in quality between products, cost and time, increasing waste, making it difficult to manufacture large films It becomes.

  The alignment treatment may be performed directly on the surface of the transparent protective film, and any appropriate alignment film (typically, a silane coupling agent layer, a polyvinyl alcohol layer or a polyimide layer) is formed and applied to the alignment film. Also good. For example, the rubbing treatment is preferably performed directly on the surface of the transparent protective film. This is because when the alignment film is rubbed, there are the following disadvantages when forming the alignment film: When the alignment film is a polyimide layer, (1) it is necessary to select a solvent that does not erode the transparent protective film Therefore, it is difficult to select a solvent for the alignment film-forming composition; (2) Since curing at a high temperature (for example, 150 to 300 ° C.) is required, the resulting elliptically polarizing plate has poor appearance. There is a case. Further, when the alignment film is a polyvinyl alcohol layer, the heat resistance and moisture resistance of the alignment film are insufficient, so that the transparent protective film and the alignment film may be peeled off under high temperature and high humidity. , White blur may occur. Furthermore, when the alignment film is a silane coupling agent layer, the liquid crystal layer (first birefringent layer) to be formed is likely to be inclined, and it may be difficult to achieve desired positive uniaxiality. is there.

B-2. Step of applying liquid crystal material to form first birefringent layer Next, a coating liquid containing the liquid crystal material as described in the above section A-2 is applied to the surface of the transparent protective film subjected to the alignment treatment. Then, the liquid crystal material is aligned to form a first birefringent layer. Specifically, a coating solution in which a liquid crystal material is dissolved or dispersed in an appropriate solvent is prepared, and this coating solution may be applied to the surface of the transparent protective film that has been subjected to the alignment treatment. The alignment process of the liquid crystal material will be described in the section B-3 below.

  As the solvent, any suitable solvent that can dissolve or disperse the liquid crystal material can be adopted. The type of solvent used can be appropriately selected according to the type of liquid crystal material and the like. Specific examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, methylene chloride, trichloroethylene, tetrachloroethylene, chlorobenzene, and orthodichlorobenzene, phenol, p-chlorophenol, and o-chlorophenol. , M-cresol, o-cresol, p-cresol and other phenols, benzene, toluene, xylene, mesitylene, methoxybenzene, 1,2-dimethoxybenzene and other aromatic hydrocarbons, acetone, methyl ethyl ketone (MEK), methyl Ketone solvents such as isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone and N-methyl-2-pyrrolidone, ester solvents such as ethyl acetate, butyl acetate and propyl acetate Alcohol solvents such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol, dimethylformamide, dimethyl Amide solvents such as acetamide, nitrile solvents such as acetonitrile and butyronitrile, ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran and dioxane, or carbon disulfide, ethyl cellosolve, butyl cellosolve, ethyl cellosolve acetate, etc. It is done. Preferred are toluene, xylene, mesitylene, MEK, methyl isobutyl ketone, cyclohexanone, ethyl cellosolve, butyl cellosolve, ethyl acetate, butyl acetate, propyl acetate, and ethyl cellosolve. These solvents may be used alone or in combination of two or more.

  The content of the liquid crystal material in the coating liquid can be appropriately set according to the type of the liquid crystal material, the target layer thickness, and the like. Specifically, the content of the liquid crystal material is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and most preferably 15 to 30% by weight.

  The said coating liquid can further contain arbitrary appropriate additives as needed. Specific examples of the additive include a polymerization initiator and a crosslinking agent. These are particularly preferably used when a liquid crystal monomer is used as the liquid crystal material. Specific examples of the polymerization initiator include benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN). Specific examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, metal chelate crosslinking agents, and the like. These may be used alone or in combination of two or more. Specific examples of other additives include anti-aging agents, modifiers, surfactants, dyes, pigments, anti-discoloring agents, and ultraviolet absorbers. These can also be used alone or in combination of two or more. Examples of the anti-aging agent include phenol compounds, amine compounds, organic sulfur compounds, and phosphine compounds. Examples of the modifier include glycols, silicones, and alcohols. The surfactant is used, for example, to smooth the surface of the optical film, and specific examples include silicone-based, acrylic-based, and fluorine-based surfactants.

The coating amount of the coating solution can be appropriately set according to the concentration of the coating solution, the target layer thickness, and the like. For example, when the concentration of the liquid crystal material in the coating solution is 20% by weight, the coating amount is preferably 0.03 to 0.17 ml, more preferably 0.05 per area (100 cm ² ) of the transparent protective film. ˜0.15 ml, most preferably 0.08 to 0.12 ml.

  Any appropriate method can be adopted as the coating method. Specific examples include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, an extrusion method, a curtain coating method, and a spray coating method.

B-3. Step of Aligning Liquid Crystal Material Forming First Birefringent Layer Next, the liquid crystal material forming the first birefringent layer is aligned according to the alignment direction of the surface of the transparent protective film. The alignment of the liquid crystal material is performed by processing at a temperature showing a liquid crystal phase according to the type of the liquid crystal material used. By performing such temperature treatment, the liquid crystal material takes a liquid crystal state, and the liquid crystal material is aligned according to the alignment direction of the surface of the transparent protective film. Thereby, birefringence is generated in the layer formed by coating, and the first birefringent layer is formed.

  As described above, the treatment temperature can be appropriately determined according to the type of the liquid crystal material. Specifically, processing temperature becomes like this. Preferably it is 40-120 degreeC, More preferably, it is 50-100 degreeC, Most preferably, it is 60-90 degreeC. The treatment time is preferably 30 seconds or longer, more preferably 1 minute or longer, particularly preferably 2 minutes or longer, and most preferably 4 minutes or longer. When the treatment time is less than 30 seconds, the liquid crystal material may not take a sufficient liquid crystal state. On the other hand, the treatment time is preferably 10 minutes or less, more preferably 8 minutes or less, and most preferably 7 minutes or less. When processing time exceeds 10 minutes, there exists a possibility that an additive may sublime.

  Moreover, when using the liquid crystal monomer as described in the above section A-2 as the liquid crystal material, it is preferable to further subject the layer formed by the coating to a polymerization treatment or a crosslinking treatment. By performing the polymerization treatment, the liquid crystal monomer is polymerized, and the liquid crystal monomer is fixed as a repeating unit of the polymer molecule. Further, by performing the crosslinking treatment, the liquid crystal monomer forms a three-dimensional network structure, and the liquid crystal monomer is fixed as a part of the crosslinked structure. As a result, the alignment state of the liquid crystal material is fixed. The polymer or three-dimensional network structure formed by polymerizing or cross-linking the liquid crystal monomer is “non-liquid crystalline”. Therefore, the formed first birefringent layer has, for example, a temperature change peculiar to liquid crystal molecules. No transition to liquid crystal phase, glass phase, or crystal phase occurs due to.

  The specific procedure of the above-mentioned polymerization treatment or crosslinking treatment can be appropriately selected depending on the kind of polymerization initiator and crosslinking agent used. For example, light irradiation may be performed when a photopolymerization initiator or a photocrosslinking agent is used, and ultraviolet irradiation may be performed when an ultraviolet polymerization initiator or an ultraviolet crosslinking agent is used. Light or ultraviolet irradiation time, irradiation intensity, total irradiation amount, etc. are appropriately set according to the type of liquid crystal material, the type of transparent protective film, the type of alignment treatment, the characteristics desired for the first birefringent layer, etc. Can be done.

  By performing the alignment treatment as described above, the liquid crystal material is aligned according to the alignment direction of the transparent protective film. Therefore, the slow axis of the formed first birefringent layer is the alignment direction of the transparent protective film. And substantially the same. Therefore, the direction of the slow axis of the first birefringent layer is preferably + 8 ° to + 38 ° or −8 ° to −38 °, more preferably + 13 ° to + 33 ° with respect to the longitudinal direction of the transparent protective film. Or −13 ° to −33 °, particularly preferably + 19 ° to + 29 ° or −19 ° to −29 °, particularly preferably + 21 ° to + 27 ° or −21 ° to −27 °, most preferably + 23 ° to +24. ° or -23 ° to -24 °.

B-4. Laminator Step of Polarizer The polarizer is laminated on the surface of the transparent protective film. As described above, the lamination of the polarizer can be performed at any appropriate point in the production method of the present invention. For example, a polarizer may be previously laminated on a transparent protective film, may be laminated after forming the first birefringent layer, or may be laminated after forming the second birefringent layer.

  Any appropriate laminating method (for example, adhesion) can be adopted as a laminating method of the transparent protective film and the polarizer. Adhesion can be performed using any suitable adhesive or adhesive. The type of adhesive or pressure-sensitive adhesive can be appropriately selected depending on the type of adherend (that is, the transparent protective film and the polarizer). Specific examples of the adhesive include polymer adhesives such as acrylic, vinyl alcohol, silicone, polyester, polyurethane, and polyether, isocyanate adhesives, rubber adhesives, and the like. Specific examples of the pressure sensitive adhesive include acrylic, vinyl alcohol, silicone, polyester, polyurethane, polyether, isocyanate, and rubber pressure sensitive adhesives.

  The thickness of the adhesive or pressure-sensitive adhesive is not particularly limited, but is preferably 10 to 200 nm, more preferably 30 to 180 nm, and most preferably 50 to 150 nm.

  According to the manufacturing method as described above, since the slow axis of the first birefringent layer can be set in the alignment treatment of the transparent protective film, it is stretched in the longitudinal direction (that is, has an absorption axis in the longitudinal direction). ) A long polarizing film (polarizer) can be used. That is, a long transparent protective film that has been subjected to an orientation treatment so as to form a predetermined angle with respect to the longitudinal direction and a long polarizing film (polarizer) are continuously bonded together with their respective longitudinal directions aligned. be able to. Therefore, an elliptically polarizing plate can be obtained with very excellent production efficiency. Furthermore, according to this method, it is not necessary to cut and laminate the film obliquely with respect to the longitudinal direction (stretching direction). As a result, there is no variation in the angle of the optical axis in each cut out film, and as a result, an elliptically polarizing plate with no quality variation among products is obtained. Furthermore, no waste due to clipping is generated, so that an elliptically polarizing plate can be obtained at low cost. In addition, a large polarizing plate can be easily manufactured.

  The direction of the absorption axis of the polarizer is substantially parallel to the longitudinal direction of the long film. In the present specification, “substantially parallel” means that the angle between the longitudinal direction and the absorption axis direction includes 0 ° ± 10 °, preferably 0 ° ± 5 °, more preferably 0 °. ± 3 °.

B-5. Step of forming second birefringent layer Further, a second birefringent layer is formed on the surface of the first birefringent layer. Typically, the second birefringent layer is formed by laminating a film containing a liquid crystal material solidified in the homeotropic alignment described in the above section A-3 on the surface of the first birefringent layer. . A film containing a liquid crystal material solidified in homeotropic alignment is obtained by applying the liquid crystal material (liquid crystal monomer or liquid crystal polymer) and / or liquid crystal composition described in the above section A-3 on a substrate, and these are formed into a liquid crystal phase. The film is formed by homeotropic orientation in a state exhibiting the above, and immobilization while maintaining the orientation. Hereinafter, a detailed production procedure of the film will be described.

  Any appropriate substrate can be adopted as the substrate. Specific examples include a glass substrate, a metal foil, a plastic sheet, or a plastic film. The thickness of the substrate is usually about 10 to 1000 μm. Note that the vertical alignment film may not be provided on the substrate.

  As the plastic film, any appropriate film can be adopted as long as it does not change at the temperature at which the liquid crystal material is oriented. Specific examples include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. It is done. Also, styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides. Examples thereof include a film made of a transparent polymer such as an amide polymer. Furthermore, imide polymer, sulfone polymer, polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene Examples thereof include films made of transparent polymers such as epoxy polymers, epoxy polymers and blends thereof. Among these, plastic films such as triacetyl cellulose, polycarbonate, norbornene-based polyolefin, which have high hydrogen bonding properties and are used as an optical film, are preferably used. As said metal foil, aluminum foil is mentioned, for example.

  The substrate may be provided with any appropriate binder layer and anchor coat layer in order from the substrate side. Specific examples of the material constituting the binder layer include a coupling agent (for example, a silane coupling agent, a titanium coupling agent, and a zirconium coupling agent) and an organic primer. Metal alkoxide is mentioned as a material which comprises an anchor coat layer. The binder layer and the anchor coat layer can be formed by any appropriate method.

  As a method for coating the liquid crystal material (liquid crystal monomer or liquid crystal polymer) or the liquid crystalline composition on the substrate, a solution coating method using a solution obtained by dissolving the liquid crystal material or the liquid crystalline composition in a solvent, or the liquid crystal Examples thereof include a method in which a material or a liquid crystal composition is melted and melt-coated. A solution coating method is preferred. This is because homeotropic alignment can be realized precisely and easily.

  As a solvent used when preparing the solution coating solution, any appropriate solvent capable of dissolving the liquid crystal material or the liquid crystalline composition may be employed. Specific examples include halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, phenols such as phenol and parachlorophenol, benzene, toluene, xylene, methoxybenzene, 1,2- Aromatic hydrocarbons such as dimethobenzene, acetone, ethyl acetate, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene bricol monomethyl ether, diethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2 -Pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetate Amides, dimethyl sulfoxide, acetonitrile, butyronitrile, carbon disulfide, and cyclohexanone. The concentration of the solution can vary depending on the type (solubility) of the liquid crystal material used, the target thickness, and the like. Specifically, the concentration of the solution is preferably 3 to 50% by weight, more preferably 7 to 30% by weight.

  Examples of the method for applying the above solution to the substrate (anchor coat layer) include a roll coat method, a gravure coat method, a spin coat method, and a bar coat method. A gravure coating method and a bar coating method are preferred. This is because it is easy to coat a large area uniformly. After coating, the solvent is removed, and a liquid crystal material layer or a liquid crystal composition layer is formed on the substrate. The conditions for removing the solvent are not particularly limited, as long as the solvent can be substantially removed and the liquid crystal material layer or the liquid crystal composition layer does not flow or even flows down. Usually, the solvent is removed by drying at room temperature, drying in a drying furnace, heating on a hot plate, or the like.

  Next, the liquid crystal material layer or the liquid crystalline composition layer formed on the substrate is brought into a liquid crystal state and homeotropically aligned. For example, heat treatment is performed so that the liquid crystal polymer or the liquid crystalline composition has a liquid crystal state, and homeotropic alignment is performed in the liquid crystal state. The heat treatment can be performed by the same method as the above drying method. The heat treatment temperature can vary depending on the liquid crystal material or liquid crystalline composition used and the type of substrate. Specifically, the heat treatment temperature is preferably 60 to 300 ° C, more preferably 70 to 200 ° C, and most preferably 80 to 150 ° C. The heat treatment time can also vary depending on the liquid crystal material or liquid crystalline composition used and the type of substrate. Specifically, the heat treatment time is preferably 10 seconds to 2 hours, more preferably 20 seconds to 30 minutes, and most preferably 30 seconds to 10 minutes. When the heat treatment time is shorter than 10 seconds, homeotropic alignment formation may not sufficiently proceed. Even if the heat treatment time is longer than 2 hours, homeotropic alignment formation often does not proceed any more, which is not preferable in terms of workability and mass productivity.

  After the heat treatment is completed, a cooling operation is performed. As the cooling operation, the homeotropic alignment liquid crystal film after the heat treatment can be performed by taking it out from the heating atmosphere in the heat treatment operation to room temperature. Moreover, you may perform forced cooling, such as air cooling and water cooling. The orientation of the homeotropic alignment liquid crystal film is fixed by being cooled below the glass transition temperature of the liquid crystal material.

When using a liquid crystalline composition, the homeotropic liquid crystal alignment film fixed as described above is irradiated with light or ultraviolet rays to polymerize or crosslink the photopolymerizable liquid crystal compound, thereby making it photopolymerizable. The durability can be further improved by fixing the liquid crystal compound. For example, the ultraviolet irradiation conditions are preferably in an inert gas atmosphere in order to sufficiently accelerate the polymerization or crosslinking reaction. As the ultraviolet irradiation means, a high-pressure mercury ultraviolet lamp having an illuminance of about 80 to 160 mW / cm ² is typically used. In addition, other types of lamps such as metal halide UV lamps and incandescent tubes can be used. In addition, it is preferable to adjust the temperature so that the surface temperature of the liquid crystal layer during ultraviolet irradiation is in a temperature range that exhibits a liquid crystal state. Examples of temperature control methods include cold mirrors, water cooling and other cooling processes, or increasing the line speed.

  In this way, a thin film of a liquid crystal material or a liquid crystalline composition is formed and fixed while maintaining its homeotropic alignment, whereby a homeotropic aligned liquid crystal film is obtained. This film (which becomes the second birefringent layer) is laminated on the surface of the first birefringent layer via an adhesive or a pressure-sensitive adhesive. By peeling the substrate from the laminate (substrate / second birefringent layer / first birefringent layer), the second birefringent layer is disposed on the surface of the first birefringent layer.

B-6. Step of forming third birefringent layer Further, a third birefringent layer is formed on the surface of the second birefringent layer. Typically, the third birefringent layer is formed by laminating the polymer film described in the above section A-4 on the surface of the second birefringent layer. Preferably, the polymer film is a stretched film. More specifically, the polymer film is a film stretched in the width direction as described in the above section A-4. Since such a stretched film has a slow axis in the width direction, the slow axis is substantially perpendicular to the absorption axis (longitudinal direction) of the polarizer. The lamination method is not particularly limited, and is performed using any appropriate adhesive or pressure-sensitive adhesive (for example, the adhesive or pressure-sensitive adhesive described in the above section B-4). As described above, the elliptically polarizing plate of the present invention is obtained.

B-7. When the first birefringent layer is formed on a surface other than the transparent protective film For example, the first birefringent layer may be formed on the surface other than the transparent protective film (in the example of FIG. When formed on the surface of a birefringent layer). In such a case, the first birefringent layer can be formed by the following method, for example. As a first method, a polymer film having the same size as the transparent protective film (typically, a polyethylene terephthalate (PET) film) is separately prepared, and the alignment treatment described in the above section B-1 is performed on the film. . The liquid crystal material described in the above section B-2 is applied to the polymer film subjected to the alignment treatment and dried to form a liquid crystal material layer. The liquid crystal material layer is peeled off from the polymer film and bonded to any appropriate surface on the surface of the second birefringent layer (typically, the second birefringent layer in the substrate / second birefringent layer laminate). A first birefringent layer is formed by laminating via an agent. The first birefringent layer (opposite to the second birefringent layer) of this laminate and a polarizer (typically a protective layer in a polarizer / protective layer laminate) may be any suitable Laminate through various adhesives. Finally, the substrate is peeled from the obtained laminate (substrate / second birefringent layer / first birefringent layer / protective layer / polarizer). The following procedure is performed in the same manner as described above to obtain the elliptically polarizing plate of the present invention.

  As a second method, a polymer layer (typically, a polyimide layer or a polyvinyl alcohol layer) is formed on the surface of the second birefringent layer, and the alignment treatment described in the above section B-1 is applied to the polymer layer. Apply. The liquid crystal material described in the above section B-2 is applied to the surface of the polymer layer subjected to the alignment treatment and dried to form the first birefringent layer. The first birefringent layer (opposite to the second birefringent layer) of this laminate and a polarizer (typically a protective layer in a polarizer / protective layer laminate) may be any suitable Laminate through various adhesives. Finally, the substrate is peeled from the obtained laminate (substrate / second birefringent layer / first birefringent layer / protective layer / polarizer). The following procedure is performed in the same manner as described above to obtain the elliptically polarizing plate of the present invention.

B-8. Specific Manufacturing Procedure An example of a specific procedure of the manufacturing method of the present invention will be described with reference to FIGS. For simplicity, only the case where the first birefringent layer is formed on the surface of the transparent protective film will be described. 3 to 8, reference numerals 111, 111 ′, 112, 113, 114, 115, 116, 117, 118, and 118 ′ are rolls that roll the film and / or laminate that form each layer. .

  First, a long polymer film as a raw material for a polarizer is prepared, and dyeing, stretching, and the like are performed as described in the above section A-5. Stretching is continuously performed in the longitudinal direction of a long polymer film. Thus, as shown in the perspective view of FIG. 3, a long polarizer 11 having an absorption axis in the longitudinal direction (stretching direction: arrow A direction) is obtained.

  On the other hand, as shown in the perspective view of FIG. 4A, a long transparent protective film (finally a protective layer) 12 is prepared, and a rubbing process is performed on one surface thereof by a rubbing roll 120. At this time, the rubbing direction is different from the longitudinal direction of the transparent protective film 12, for example, a range of + 8 ° to + 38 ° or a range of −8 ° to −38 ° with respect to the longitudinal direction. Next, as shown in the perspective view of FIG. 4B, the first birefringent layer 13 is formed on the transparent protective film 12 subjected to the rubbing treatment as described in the paragraphs B-2 and B-3. Form. In the first birefringent layer 13, the liquid crystal material is aligned along the rubbing direction, so that the slow axis direction is substantially the same direction (arrow B direction) as the rubbing direction of the transparent protective film 12.

  Next, as shown in the schematic diagram of FIG. 5, a transparent protective film (being a second protective layer) 16, a polarizer 11, a transparent protective film (being a protective layer) 12 and a first birefringent layer 13. The laminated body 121 is sent out in the direction of the arrow, and bonded together with an adhesive or the like (not shown) in a state where the respective longitudinal directions are aligned. As a result, a laminate 123 (second protective layer 16, polarizer 11, protective layer 12, first birefringent layer 13) can be obtained. In addition, in FIG. 5, the code | symbol 122 shows the guide roll for bonding films together (it is the same also in FIGS. 6-8).

  Furthermore, as shown in the schematic diagram of FIG. 6 (a), a laminate 124 (with the second birefringent layer 14 applied to the base material 26) is prepared, and this and the laminate 123 (second The protective layer 16, the polarizer 11, the protective layer 12, and the first birefringent layer 13) are sent out in the directions of the arrows, and bonded together with an adhesive or the like (not shown) in a state where the respective longitudinal directions are aligned. Finally, the base material 26 is peeled from the laminated body bonded as shown in FIG. As a result, the laminated body 125 (the second protective layer 16, the polarizer 11, the protective layer 12, the first birefringent layer 13, and the second birefringent layer 14) can be obtained.

  Further, as shown in the schematic diagram of FIG. 7, a long third birefringent layer 15 is prepared, and the laminated body 125 (second protective layer 16, polarizer 11, protective layer 12, first layer The birefringent layer 13 and the second birefringent layer 14) are sent out in the direction of the arrows, and bonded together with an adhesive or the like (not shown) in a state where the respective longitudinal directions are aligned. The third birefringent layer includes a stretched polymer film as described above, and the slow axis thereof can be appropriately determined depending on the stretching method (stretching direction, etc.). In the present invention, as described above, the slow axis direction of the first birefringent layer can be freely set by the orientation treatment on the transparent protective film, so that the third birefringent layer is, for example, perpendicular to the longitudinal direction. It is possible to use a general stretched polymer film that is transversely stretched in a direction that is easy to process.

  As described above, the elliptically polarizing plate 10 of the present invention is obtained.

  Another example of the specific procedure of the production method of the present invention will be described.

  Similarly to the above, as shown in the perspective view of FIG. 3, a long polarizer 11 is manufactured.

  Next, as shown in the schematic diagram of FIG. 8, a long second transparent protective film (to be a second protective layer) 16, a polarizer 11, and a long transparent protective film (to be a protective layer) 12, Are sent in the direction of the arrow, and bonded together with an adhesive or the like (not shown) in a state where the respective longitudinal directions are aligned. As a result, the stacked body 126 (second protective layer 16, polarizer 11, protective layer 12) is obtained.

  Next, the surface of the protective layer 12 opposite to the polarizer 11 is subjected to a rubbing process using a rubbing roll 120 '. At this time, the rubbing direction is different from the longitudinal direction of the transparent protective film 12, for example, a range of + 8 ° to + 38 ° or a range of −8 ° to −38 ° with respect to the longitudinal direction (not shown). . Next, the first birefringent layer 13 is formed on the transparent protective film 12 subjected to the rubbing treatment as described in the paragraphs B-2 and B-3. As a result, a laminate 123 (second protective layer 16, polarizer 11, protective layer 12, first birefringent layer 13) can be obtained. In the first birefringent layer 13, the liquid crystal material is aligned along the rubbing direction, so that the slow axis direction is substantially the same direction (arrow B direction) as the rubbing direction of the transparent protective film 12.

  The following procedure is the same as the case described with reference to FIGS. 6A, 6B, and 7, and the elliptically polarizing plate 10 of the present invention is obtained.

B-9. Other components of the elliptically polarizing plate The elliptically polarizing plate of the present invention may further include other optical layers. As such another optical layer, any appropriate optical layer may be employed depending on the purpose and the type of the image display device. Specific examples include a birefringent layer (retardation film), a liquid crystal film, a light scattering film, and a diffraction film.

  Moreover, as described above, the elliptically polarizing plate of the present invention may have another protective layer 16 on the surface of the polarizer 11 where the protective layer 12 is not formed. Any appropriate protective layer (transparent protective film) can be adopted as the second protective layer. For example, the film described in the above section A-6 can be used. The second protective layer 16 and the protective layer 12 may be the same or different. The second protective layer 16 may be subjected to a hard coat process, an antireflection process, an antisticking process, an antiglare process, and the like as necessary.

  The elliptically polarizing plate of the present invention may further have an adhesive layer as an outermost layer on at least one side. Thus, by having the adhesion layer as the outermost layer, for example, lamination with another member (for example, a liquid crystal cell) becomes easy, and peeling from the other member of the elliptically polarizing plate can be prevented. Any appropriate material can be adopted as the material of the pressure-sensitive adhesive layer. Specific examples of the adhesive include those described in the above section B-4. Preferably, a material excellent in hygroscopicity and heat resistance is used. This is because foaming and peeling due to moisture absorption, deterioration of optical characteristics due to a difference in thermal expansion, and warpage of the liquid crystal cell can be prevented.

  Practically, the surface of the pressure-sensitive adhesive layer is covered with any appropriate separator until the elliptically polarizing plate is actually used, and contamination can be prevented. The separator can be formed by, for example, a method of providing a release coat with a release agent such as silicone-based, long-chain alkyl-based, fluorine-based, molybdenum sulfide, or the like on any appropriate film as necessary.

  Each layer in the elliptically polarizing plate of the present invention imparts ultraviolet absorbing ability by, for example, treatment with an ultraviolet absorber such as a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may be what you did.

C. Use of elliptically polarizing plate The elliptically polarizing plate of the present invention can be suitably used for various image display devices (for example, liquid crystal display devices and self-luminous display devices). Specific examples of the applicable image display device include a liquid crystal display device, an EL display, a plasma display (PD), and a field emission display (FED). When the elliptically polarizing plate of the present invention is used in a liquid crystal display device, it is useful for viewing angle compensation, for example. The elliptically polarizing plate of the present invention is used in, for example, a circular polarization mode liquid crystal display device, such as a homogeneous alignment type TN liquid crystal display device, a horizontal electrode type (IPS) type liquid crystal display device, and a vertical alignment (VA) type liquid crystal display device. Is particularly useful. Moreover, when using the elliptically polarizing plate of this invention for EL display, it is useful for electrode reflection prevention, for example.

D. Image Display Device A liquid crystal display device will be described as an example of the image display device of the present invention. Here, a liquid crystal panel used in a liquid crystal display device will be described. As for other configurations of the liquid crystal display device, any appropriate configuration may be adopted depending on the purpose. FIG. 9 is a schematic cross-sectional view of a liquid crystal panel according to a preferred embodiment of the present invention. The liquid crystal panel 100 includes a liquid crystal cell 20, retardation plates 30 and 30 ′ disposed on both sides of the liquid crystal cell 20, and polarizing plates 10 and 10 ′ disposed on the outer sides of the respective retardation plates. As the retardation plates 30 and 30 ′, any appropriate retardation plate can be adopted depending on the purpose and the alignment mode of the liquid crystal cell. Depending on the purpose and the alignment mode of the liquid crystal cell, one or both of the retardation plates 30 and 30 ′ may be omitted. The polarizing plate 10 is the elliptically polarizing plate of the present invention described in the A and B terms. The polarizing plate 10 ′ is any appropriate polarizing plate. The polarizing plates 10, 10 ′ are typically arranged so that their absorption axes are orthogonal to each other. As shown in FIG. 9, in the liquid crystal display device (liquid crystal panel) of the present invention, the elliptically polarizing plate 10 of the present invention is preferably arranged on the viewing side (upper side). The liquid crystal cell 20 includes a pair of glass substrates 21 and 21 'and a liquid crystal layer 22 as a display medium disposed between the substrates. One substrate (active matrix substrate) 21 ′ includes a switching element (typically a TFT) for controlling the electro-optical characteristics of the liquid crystal, a scanning line for supplying a gate signal to the switching element, and a signal line for supplying a source signal. Are provided (both not shown). The other glass substrate (color filter substrate) 21 is provided with a color filter (not shown). The color filter may be provided on the active matrix substrate 21 ′. The distance (cell gap) between the substrates 21 and 21 'is controlled by a spacer (not shown). An alignment film (not shown) made of polyimide, for example, is provided on the side of the substrates 21, 21 ′ in contact with the liquid crystal layer 22.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited by these Examples. The measuring method of each characteristic in an Example is as follows.

(1) Retardation measurement Refractive indexes nx, ny and nz of a sample film are measured by an automatic birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., automatic birefringence meter KOBRA31PR), and in-plane retardation Δnd and thickness direction The phase difference Rth was calculated. The measurement temperature was 23 ° C. and the measurement wavelength was 590 nm.
(2) Measurement of thickness The thickness of the first and second birefringent layers was measured by an interference film thickness measurement method using MCPD2000 manufactured by Otsuka Electronics. The thicknesses of other various films were measured using a dial gauge.
(3) Measurement of transmittance About the elliptically polarizing plates A01 to A19 obtained in the examples, the same elliptically polarizing plates were bonded together using an adhesive. The elliptically polarizing plate A series was bonded so that the respective third birefringent layers faced each other. At the time of bonding, the slow axes of the third birefringent layers (ie, λ / 4 plates) are 90 ° (as a result, the absorption axes of the polarizers are 90 °). Arranged). The transmittance of the bonded sample was measured by a trade name DOT-3 (Murakami Color Co., Ltd.). In addition, the laminated structure of an elliptically polarizing plate is shown below.
Ellipsoidal polarizing plates A01 to A19: Polarizer / protective layer / first birefringent layer / second birefringent layer / third birefringent layer (4) Measurement of contrast ratio Backlight by overlapping the same elliptical polarizing plates And display a white image (absorption axis of the polarizer is parallel) and a black image (absorption axis of the polarizer are orthogonal), and the ELDIM product name “EZ Contrast 160D” makes the absorption axis of the polarizer on the viewer side visible. On the other hand, scanning was performed in the direction of 45 ° to 135 ° and from −60 ° to 60 ° with respect to the normal line. Then, the contrast ratio “YW / YB” in the oblique direction was calculated from the Y value (YW) in the white image and the Y value (YB) in the black image.
(5) Moisture resistance test The obtained elliptically polarizing plate was allowed to stand for 500 hours under conditions of 60 ° C and 95% (RH), and then the appearance was visually observed. The case where the elliptically polarizing plate was transparent was designated as “good”, and the case where the elliptically polarizing plate was clouded was designated as “normal”.

I. Preparation of elliptically polarizing plate Ia. Alignment treatment of transparent protective film (production of alignment substrate)
The transparent protective film was subjected to an alignment treatment to produce an alignment substrate (which eventually becomes a protective layer).
Substrates (1) to (8): After forming a PVA film (thickness 0.1 μm) on the surface of the TAC film (thickness 40 μm), the rubbing cloth is used to apply the rubbing angle shown in the table below to the PVA film surface. By rubbing, an alignment substrate was prepared.
Base materials (9) to (10): A TAC film (thickness: 40 μm) was rubbed at a rubbing angle shown in the following table using a rubbing cloth to prepare an alignment base material.
Substrates (11) to (12): After applying a silane coupling agent (trade name KBM-503: manufactured by Shin-Etsu Silicone Co., Ltd.) to the surface of the TAC film (thickness 40 μm), the surface is subjected to the following using a rubbing cloth. Rubbing was carried out at the rubbing angle shown in the table to prepare an alignment substrate.
Substrates (13) to (14): After forming a PVA film (thickness 0.1 μm) on the surface of the TAC film (thickness 40 μm), the rubbing cloth is used to apply the rubbing angle shown in the following table to the PVA film surface. By rubbing, an alignment substrate was prepared. The retardation in the thickness direction of the protective layer is also shown in Table 1 below.

Ib. Preparation of first birefringent layer First, 10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name Paliocolor LC242) and a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by Ciba Specialty Chemicals: trade name) 3 g of Irgacure 907) was dissolved in 40 g of toluene to prepare a liquid crystal coating solution. And after apply | coating the said liquid-crystal coating liquid with the bar coater on the orientation base material produced as mentioned above, the liquid crystal was orientated by heat-drying for 2 minutes at 90 degreeC. The liquid crystal layer was irradiated with light of 1 mJ / cm ² using a metal halide lamp to cure the liquid crystal layer, thereby forming first birefringent layers (1) to (5). Table 2 below shows the thickness and in-plane retardation value (nm) of the formed first birefringent layer.

Ic. Production of Second Birefringent Layer Side-chain type liquid crystal represented by the following chemical formula (numbers 65 and 35 in the formula represent mol% of the monomer unit and are represented by block polymer for convenience: weight average molecular weight 5000) 20 parts by weight of a polymer, 80 parts by weight of a polymerizable liquid crystal showing a nematic liquid crystal phase (manufactured by BASF: trade name Paliocolor LC242) and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals: trade name Irgacure 907) A liquid crystal coating solution was prepared by dissolving in 200 parts by weight. And after apply | coating the said coating liquid to a base film (norbornene-type resin film: Nippon Zeon Co., Ltd. make, brand name ZEONOR) with a bar coater, the liquid crystal was orientated by heating and drying at 100 degreeC for 10 minutes. The liquid crystal layer was irradiated with ultraviolet rays to cure the liquid crystal layer, thereby forming second birefringent layer films C1 to C4 on the substrate. The in-plane retardation of the second birefringent layer film was substantially zero. The thickness direction retardation of this second birefringent layer film was as shown in Table 3 below.

Id. Production of Third Birefringent Layer A third birefringent layer film is produced by uniaxially stretching a polycarbonate film (thickness: 60 μm) or a norbornene-based film (manufactured by JSR: trade name: Arton: thickness: 60 μm) at a predetermined temperature. did. Table 4 shows the types of films used (PC for polycarbonate film and NB for norbornene film), stretching conditions (stretching direction), orientation angle, and retardation value obtained. The orientation angle means the angle of the slow axis with respect to the longitudinal direction of the film. The following third birefringent layers all had optical characteristics of nx>ny> nz. Furthermore, a norbornene-based film (manufactured by Nippon Zeon Co., Ltd., trade name ZEONOR: thickness 60 μm) was uniaxially stretched 1.5 times at 138 ° C. to obtain a third birefringent layer (b3) having a thickness of 50 μm. This birefringent layer had a refractive index distribution of nx>ny> nz, an in-plane retardation of 120 μm, and an Nz coefficient of 1.6.

Ie. Preparation of Elliptical Polarizing Plate A polyvinyl alcohol film was dyed in an aqueous solution containing iodine, and then uniaxially stretched 6 times between rolls having different speed ratios in an aqueous solution containing boric acid to obtain a polarizer. A protective layer, a first birefringent layer, a second birefringent layer, and a third birefringent layer were used in combinations as shown in Table 5 below. The polarizer, the protective layer, the first birefringent layer, and the second birefringent layer are laminated by the manufacturing procedure shown in FIGS. 3 to 7 to obtain elliptically polarizing plates A01 to A19 as shown in FIG. It was.

Example 1
The contrast ratio was measured by superimposing the elliptical polarizing plates A01. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 1.1. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 10 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions. Further, since the minimum and maximum difference is as small as 10 degrees, the visual characteristics are well balanced, which is also a practically preferable level.

(Example 2)
The contrast ratio was measured by overlapping the elliptically polarizing plates A02. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 1.1. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 10 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions. Further, since the minimum and maximum difference is as small as 10 degrees, the visual characteristics are well balanced, which is also a practically preferable level.

(Example 3)
The contrast ratio was measured by overlapping the elliptically polarizing plates A03. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 1.8. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 60 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

Example 4
The contrast ratio was measured by overlapping the elliptically polarizing plates A04. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 1.8. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 60 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

(Example 5)
The contrast ratio was measured by overlapping the elliptically polarizing plates A05. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 2.5. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 70 degrees maximum in all directions, and the maximum minimum difference was 30 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

(Example 6)
The contrast ratio was measured by superimposing the elliptically polarizing plates A06. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 2.5. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 70 degrees maximum in all directions, and the maximum minimum difference was 30 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

(Example 7)
The contrast ratio was measured by overlapping the elliptically polarizing plates A07. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 3. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 90 degrees maximum in all directions, and the maximum minimum difference was 50 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

(Example 8)
The contrast ratio was measured by superposing the elliptically polarizing plates A08. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 3. According to this elliptically polarizing plate, the angle of contrast 10 or more was 40 degrees minimum, 90 degrees maximum in all directions, and the maximum minimum difference was 50 degrees. It was a practically preferable level that the angle of 10 or more contrast was a minimum of 40 degrees in all directions.

Example 9
The contrast ratio was measured by overlapping the elliptically polarizing plates A19. As is apparent from Table 5, Rth ₂ / Rthp in this elliptically polarizing plate was 1.1. According to this elliptically polarizing plate, the angle of contrast 10 or more was 37 degrees minimum, 40 degrees maximum in all directions, and the maximum minimum difference was 3 degrees. It is a practically preferable level that the angle of 10 or more contrast is a minimum of 37 degrees in all directions. Furthermore, the maximum / minimum difference of 3 degrees (that is, the variation due to the azimuth angle is within 3 degrees) is a very excellent viewing angle characteristic with very little change in display characteristics depending on the azimuth angle. More specifically, the elliptically polarizing plate has uniform display characteristics when viewed from any direction at an angle of 360 ° when viewed from an oblique direction, and is used for viewing still images and / or moving images by rotating up and down and left and right. It has been confirmed that it has extremely favorable characteristics (typically, applications such as mobile phones, digital cameras, and mobile phones).

  On the other hand, the liquid crystal panel was taken out from the liquid crystal display device (product name: PlayStation Portable, manufactured by Sony Corporation), and all the optical films such as polarizing plates arranged above and below the liquid crystal cell were removed. The surfaces of both glass substrates of the obtained liquid crystal cell were washed to obtain a liquid crystal cell. The elliptically polarizing plate A19 was bonded to both sides of the liquid crystal cell via an acrylic adhesive. At that time, the third birefringent layer was laminated so as to be disposed on the liquid crystal cell side. Moreover, it bonded together so that the absorption axis of the viewing side polarizer might be orthogonal to the longitudinal direction of a liquid crystal cell. Note that the absorption axes of the polarizers of the respective elliptically polarizing plates A19 are arranged so as to be orthogonal to each other. The liquid crystal panel thus obtained was combined with a PlayStation Portable backlight unit to produce a liquid crystal display device. FIG. 10 shows a contrast contour map of this liquid crystal display device.

(Comparative Example 1)
Except that the second birefringent layer was not formed, an elliptically polarizing plate having the same configuration as that of the elliptically polarizing plate A01 was bonded, and the contrast ratio was measured. According to this elliptically polarizing plate, the angle of contrast 10 or more was 30 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. An angle with a contrast of 10 or more is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

(Comparative Example 2)
Except that the second birefringent layer was not formed, an elliptically polarizing plate having the same configuration as that of the elliptically polarizing plate A02 was bonded, and the contrast ratio was measured. According to this elliptically polarizing plate, the angle of contrast 10 or more was 30 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. An angle with a contrast of 10 or more is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

(Comparative Example 3)
The elliptically polarized light having the order of (polarizer / protective layer / third birefringent layer / second birefringent layer / first birefringent layer) is rearranged in the stacking order of the elliptically polarizing plates A01 produced in the examples. I got a plate. The obtained elliptical polarizing plate was bonded and the contrast ratio was measured. In addition, it bonded together so that a 1st birefringent layer might face each other. According to this elliptically polarizing plate, the angle of contrast 10 or more was 30 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. An angle with a contrast of 10 or more is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

(Comparative Example 4)
An elliptically polarizing plate (polarized light) having the same configuration as the elliptically polarizing plate A01 except that a λ / 2 plate similar to the first birefringent layer is used instead of the second birefringent layer (positive C plate). Substrate / protective layer / first birefringent layer / (λ / 2 plate) / third birefringent layer) were bonded together to measure the contrast ratio. According to this elliptically polarizing plate, the angle of contrast 10 or more was 30 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. An angle with a contrast of 10 or more is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

(Comparative Example 5)
Except that the second birefringent layer was not formed, an elliptically polarizing plate having the same configuration as that of the elliptically polarizing plate A19 was bonded, and the contrast ratio was measured. According to this elliptically polarizing plate, the angle of the contrast 10 or more was 40 degrees at the minimum and 80 degrees at the maximum in all directions, and the difference between the maximum and the minimum was 40 degrees. According to this elliptically polarizing plate, the maximum and minimum difference was 40 degrees, and the change in display characteristics depending on the azimuth angle was very large. Such an elliptically polarizing plate has a remarkable change in display characteristics such as contrast depending on the azimuth angle, which is very uncomfortable for the viewer. A liquid crystal display device was produced in the same manner as in Example 9 except that this elliptically polarizing plate was used. A contrast contour map of this liquid crystal display device is shown in FIG.

(Comparative Example 6)
The elliptically polarized light having the order of (polarizer / protective layer / second birefringent layer / first birefringent layer / third birefringent layer) is rearranged in the order of lamination of the elliptically polarizing plates A19 produced in the examples. I got a plate. The obtained elliptical polarizing plate was bonded and the contrast ratio was measured. In addition, it bonded together so that a 3rd birefringent layer might face each other. According to this elliptically polarizing plate, the angle of the contrast 10 or more was 40 degrees at the minimum and 80 degrees at the maximum in all directions, and the difference between the maximum and the minimum was 40 degrees. Such an elliptically polarizing plate has a remarkable change in display characteristics such as contrast depending on the azimuth angle, which is very uncomfortable for the viewer. A liquid crystal display device was produced in the same manner as in Example 9 except that this elliptically polarizing plate was used. FIG. 12 shows a contrast contour map of this liquid crystal display device.

(Comparative Example 7)
The elliptically polarized light having the order of (polarizer / protective layer / first birefringent layer / third birefringent layer / second birefringent layer) is rearranged in the stacking order of the elliptically polarizing plates A19 produced in the examples. I got a plate. The obtained elliptical polarizing plate was bonded and the contrast ratio was measured. In addition, it bonded together so that a 2nd birefringent layer might face each other. According to this elliptically polarizing plate, the angle of contrast 10 or more was 30 degrees minimum and 40 degrees maximum in all directions, and the difference between the maximum and minimum was 10 degrees. This elliptical polarizing plate had a contrast of 10 or more at a minimum of 30 degrees in all directions, and was at a level that could not be put to practical use. FIG. 13 shows a contrast contour map of this liquid crystal display device.

  As is clear from the results of the above examples and comparative examples, according to the example of the present invention, the first birefringent layer (λ / 2 plate) and the third birefringent layer (λ / 4 plate) By arranging the second birefringent layer (positive C plate) between them, the change in contrast depending on the azimuth angle can be reduced, and an elliptical shape having uniform display characteristics from any azimuth 360 ° A polarizing plate could be obtained. In particular, in Example 9, the maximum and minimum difference could be made extremely small, 3 degrees. Furthermore, according to the embodiment of the present invention, an angle with a contrast of 10 or more can be set to a minimum of 40 degrees in all directions, and a practically preferable level can be secured. That is, according to the embodiment of the present invention, the viewing angle dependency of the display characteristics and the contrast ratio in the oblique direction can both be ensured at a preferable level. On the other hand, according to the comparative example, the viewing angle dependency of the display characteristics and the contrast ratio in the oblique direction could not be ensured at a preferable level. Such an effect of the embodiment of the present invention is remarkable when FIG. 10 is compared with FIGS. More specifically, in Example 9 (FIG. 10), a usable contrast can be obtained at any 360 ° azimuth, and the contrast is substantially constant regardless of the azimuth angle. In Comparative Example 5 (FIG. 11) and Comparative Example 6 (FIG. 12), the contrast itself is high, but the variation due to the azimuth is very large, and the high-contrast region is shifted from the vertical and horizontal directions. The display characteristics are very uncomfortable. In Comparative Example 7 (FIG. 13), the contrast is almost constant regardless of the azimuth angle, but the contrast is very small and is not practically usable.

  Furthermore, as is apparent from comparing the moisture resistance of the elliptically polarizing plates A15, A16 and A19 with the moisture resistance of the other elliptically polarizing plates, moisture resistance (high It can be seen that the wet durability is significantly improved.

  The elliptically polarizing plate of the present invention can be suitably used for various image display devices (for example, liquid crystal display devices, self-luminous display devices). In particular, the elliptically polarizing plate of the present invention can be suitably used for so-called mobile applications (for example, applications such as mobile phones, digital cameras, and mobile phones).

1 is a schematic cross-sectional view of an elliptically polarizing plate according to a preferred embodiment of the present invention. 1 is an exploded perspective view of an elliptically polarizing plate according to a preferred embodiment of the present invention. It is a perspective view which shows the outline of one process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a perspective view which shows the outline of another process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the elliptically polarizing plate of this invention. It is a schematic sectional drawing of the liquid crystal panel used for the liquid crystal display device by preferable embodiment of this invention. It is a contrast contour map of the liquid crystal display device using the elliptically polarizing plate of the Example of this invention. It is a contrast contour map of the liquid crystal display device using the elliptically polarizing plate of the comparative example. It is a contrast contour map of the liquid crystal display device using the elliptically polarizing plate of another comparative example. It is a contrast contour map of the liquid crystal display device using the elliptically polarizing plate of another comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Elliptical polarizing plate 11 Polarizer 12 Protective layer 13 1st birefringent layer 14 2nd birefringent layer 15 3rd birefringent layer 20 Liquid crystal cell 100 Liquid crystal panel

Claims (7)

A polarizer; a protective layer; a first birefringent layer functioning as a λ / 2 plate; a second birefringent layer having a refractive index profile of nz> nx = ny; a refractive index of nx>ny> nz An elliptically polarizing plate having a third birefringent layer having a distribution and functioning as a λ / 4 plate in this order. The ratio Rth ₂ / Rthp between the absolute value Rthp of the retardation in the thickness direction of the protective layer and the absolute value Rth ₂ of the retardation in the thickness direction of the second birefringent layer is in the range of 1.1 to 4. The elliptically polarizing plate according to claim 1.   The elliptically polarizing plate according to claim 1 or 2, wherein an absorption axis of the polarizer and a slow axis of the third birefringent layer are substantially orthogonal to each other.   The slow axis of the first birefringent layer defines an angle of + 8 ° to + 38 ° or -8 ° to -38 ° with respect to the absorption axis of the polarizer. The elliptically polarizing plate described in 1.   The elliptically polarizing plate according to claim 1, wherein the protective layer is made of a film containing triacetyl cellulose as a main component.   An image display device comprising the elliptically polarizing plate according to claim 1. The image display device according to claim 6, wherein the elliptically polarizing plate is disposed on a viewing side.