JP2006243653A - Manufacturing method of elliptically polarizing plate and image display device using elliptically polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an elliptically polarizing plate which has an excellent characteristic even in an oblique direction and has a wide band region and a wide viewing angle, and to provide an image display device using the elliptically polarizing plate which is obtained by such a manufacturing method. <P>SOLUTION: The manufacturing method of elliptically polarizing plate comprises a process of performing photoalignment to the surface of a transparent protective film, a process of forming a first birefringent layer by applying liquid crystal material on the surface of the transparent protective film to which the photoalignment is performed, a process of laminating a polarizer on the surface of the side opposite to the surface of the transparent protective film to which the photoalignment is performed and a process of forming a second birefringent layer by laminating a polymer film on the surface of the first birefringent layer. When the angle between the absorption axis of the polarizer and the orientation direction of the transparent protective film is α and the angle between the absorption axis of the polarizer and the slow axis of the second birefringent layer is β, the angles α, β satisfy the following relation; 2α+40°<β<2α+50° (1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an elliptically polarizing plate and an image display device using the elliptically polarizing plate. More specifically, the present invention relates to a method for producing a wide-band and wide-viewing-angle elliptical polarizing plate having excellent characteristics in an oblique direction with very high production efficiency, and the elliptically polarized light obtained by such a method. The present invention relates to a plate and an image display device using the elliptically polarizing plate.

  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, for example, a norbornene-based film and a modified film as a retardation 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”. 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, the angle between the absorption axis of the polarizing film and the slow axis of each retardation plate is currently adjusted for each product, and no comprehensive optimization means has been found.
Japanese Patent No. 3174367 JP 2003-195037 A

  The present invention has been made to solve the above-described conventional problems, and the object of the present invention is to produce an elliptically polarizing plate having a wide bandwidth and a wide viewing angle, which has excellent characteristics even in an oblique direction. And an elliptically polarizing plate obtained by such a method, and an image display device using the elliptically polarizing plate.

  As a result of intensive studies on the relationship between the absorption axis of the polarizer and the slow axis of the λ / 4 plate and the λ / 2 plate, the present inventors have found that the angle formed by the absorption axis and the slow axis has a specific relationship. In addition, it has been found that the optical alignment treatment is extremely useful as a means for obtaining a slow axis having a specific angle with respect to the absorption axis of the polarizer. The invention has been completed.

The method for producing an elliptically polarizing plate of the present invention includes a step of performing photo-alignment treatment on the surface of the transparent protective film, a step of applying a liquid crystal material to the surface of the transparent protective film that has been subjected to the photo-alignment treatment, The liquid crystal material is oriented according to the orientation direction of the transparent protective film to form a first birefringent layer, and the transparent protective film is polarized on the surface opposite to the surface subjected to the photo-alignment treatment. Laminating a polarizer and laminating a polymer film on the surface of the first birefringent layer to form a second birefringent layer, the absorption axis of the polarizer and the transparent protective film Where α is the angle between the orientation direction and β is the angle between the absorption axis of the polarizer and the slow axis of the second birefringent layer, the angles α and β satisfy the relationship of the following formula (1): Have:
2α + 40 ° <β <2α + 50 ° (1).

In a preferred embodiment, the polarizer and the transparent protective film on which the first birefringent layer is formed are both long films. In the step of laminating the polarizer, the length of the polarizer and the protective film is long. Sides are stuck together continuously. In a more preferred embodiment, the polymer film forming the second birefringent layer is a long film, and in the step of forming the second birefringent layer, the polarizer and the first birefringent layer are formed. The transparent protective film having the layer formed thereon and the long sides of the polymer film are continuously bonded to each other.
In a preferred embodiment, the direction of the photo-alignment treatment is + 8 ° to + 38 ° or −8 ° to −38 ° with respect to the absorption axis of the polarizer.
In a preferred embodiment, the photo-alignment treatment includes a step of forming a photo-alignment film on the surface of the transparent protective film and a step of irradiating the photo-alignment film with light. In a more preferred embodiment, the photo-alignment film comprises a cinnamate group, a chalcone group, an azobenzene group, a stilbene group, an α-hydrazono-β-ketoester group, a benzylidenephthalimidine group, a retinoyl group, a coumarin group, a styrylpyridine group, and It is formed from a composition containing an aligning agent having at least one photoreactive functional group selected from anthracene groups. In a further preferred embodiment, the light is polarized light generated by a wire grid polarizer having a polarization separation function at a predetermined wavelength.
In a preferred embodiment, the liquid crystal material includes at least one of a liquid crystal monomer and a liquid crystal polymer.
In a preferred embodiment, the first birefringent layer is a λ / 2 plate. In a preferred embodiment, the second birefringent layer is a λ / 4 plate.
In a preferred embodiment, the polymer film is a stretched film.

  According to another aspect of the present invention, an elliptically polarizing plate is provided. This elliptically polarizing plate is manufactured by the above manufacturing method.

  According to another aspect of the present invention, an image display device is provided. The image display device includes the elliptically polarizing plate.

  As described above, according to the present invention, in the orientation treatment of the transparent protective film, the slow axis of the first birefringent layer can be set in an arbitrary direction, so that it is stretched in the longitudinal direction (that is, in the longitudinal direction). A long polarizing film (polarizer) having an absorption axis 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 aligned in the longitudinal direction (so-called roll-to-roll). In) can be pasted together. 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. In addition, by using a polymer film that is stretched in the width direction and has a slow axis in the width direction as the polymer film that forms the second birefringent layer, the long sides of the polarizer and the polymer film are continuously connected to each other. And an elliptically polarizing plate can be obtained with extremely excellent production efficiency.

  Furthermore, according to the present invention, the influence of static electricity, dust, dust, etc. can be eliminated very satisfactorily by using a photo-alignment process as the alignment process of the transparent protective film. As a result, an elliptically polarizing plate having extremely excellent quality stability and optical characteristics can be obtained. Such an effect is remarkably superior to the case where a rubbing process is used as the alignment process. The rubbing treatment may deteriorate the optical properties of the elliptically polarizing plate obtained by rubbing after the film surface is rubbed. However, according to the photo-alignment treatment of the present invention, such an adverse effect can be eliminated. is there.

  The elliptically polarizing plate thus obtained has an angle α formed by the absorption axis of the polarizer and the slow axis of the first birefringent layer (λ / 2 plate), and the absorption axis of the polarizer and the second axis. Since the angle β formed by the slow axis of the birefringent layer (λ / 4 plate) is optimized in the relationship of 2α + 40 ° <β <2α + 50 °, a broadband and wide viewing angle image display device can be obtained. it can. Moreover, since this relationship is comprehensive, it is not necessary to examine the stacking direction by trial and error for each product. That is, in most combinations of a polarizer, a λ / 2 plate, and a λ / 4 plate, a very excellent circular polarization characteristic can be realized by using this relationship. As a result, the optimization of the circular polarization characteristic can be performed very generally and easily.

A. Elliptical polarizing plate A-1. 1 is a schematic sectional view of an elliptically polarizing plate according to a preferred embodiment of the present invention. The elliptically polarizing plate 10 is formed by laminating a polarizer 11, a first birefringent layer 12, and a second birefringent layer 13. If necessary, a first protective layer 14 is provided between the polarizer 11 and the first birefringent layer 12, and a second protective layer 15 is provided on the opposite side of the polarizer 11 from the first protective layer 14. Is provided.

  The first birefringent layer 12 can function 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 13 can function 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).

  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 15 is omitted for the sake of clarity). ing). The first birefringent layer 12 is laminated such that the slow axis B defines a predetermined angle α with respect to the absorption axis A of the polarizer 11. The second birefringent layer 13 is laminated so that the slow axis C defines a predetermined angle β with respect to the absorption axis A of the polarizer 11. The slow axis refers to the direction in which the in-plane refractive index is maximized.

In the present invention, the angle α and the angle β have the relationship of the following formula (1):
2α + 40 ° <β <2α + 50 ° (1).
The relationship between the angle α and the angle β is more preferably 2α + 42 ° <β <2α + 48 °, particularly preferably 2α + 43 ° <β <2α + 47 °, and most preferably β = 2α + 45 °. When the angle α and the angle β have such a relationship, a polarizing plate having very excellent circular polarization characteristics can be obtained. Moreover, since this relationship is comprehensive, it is not necessary to examine the stacking direction by trial and error for each product. That is, in most combinations of a polarizer, a λ / 2 plate, and a λ / 4 plate, a very excellent circular polarization characteristic can be realized by using this relationship. The finding of such a relationship is one of the major features of the present invention, and this is a very useful result in the technical field related to the optimization of circular polarization characteristics.

  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 °. Or −19 ° to −29 °, particularly preferably + 21 ° to + 27 ° or −21 ° to −27 °, and most preferably + 23 ° to + 24 ° or −23 ° to −24 °. Accordingly, in the most preferred embodiment (β = 2α + 45 °), the angle β is preferably + 61 ° to + 121 ° or −31 ° to + 29 °, more preferably + 71 ° to + 111 ° or −21 ° to +19. °, particularly preferably + 83 ° to + 103 ° or −13 ° to + 7 °, particularly preferably + 87 ° to + 99 ° or −9 ° to + 3 °, most preferably + 91 ° to + 93 ° or − 3 ° to −1 °. Considering the manufacturing procedure (described later) of the elliptically polarizing plate, it is very preferable that the angle β is substantially parallel or orthogonal to the absorption axis of the polarizer. In this specification, “substantially parallel” includes the case of 0 ° ± 3.0 °, preferably 0 ° ± 1.0 °, and more preferably 0 ° ± 0. 5 °. “Substantially orthogonal” includes the case of 90 ° ± 3.0 °, preferably 90 ° ± 1.0 °, and more preferably 90 ° ± 0.5 °.

  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 can be laminated without using an adhesive, and the thickness of the photo-alignment film is very thin. Compared with the elliptically polarizing plate, the total thickness can be reduced to about a quarter. As a result, the elliptically polarizing plate of the present invention can greatly contribute to thinning of the liquid crystal 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 12 can function as a so-called λ / 2 plate. With the first birefringent layer functioning as a λ / 2 plate, the wavelength dispersion characteristics of the second 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. Furthermore, the first birefringent layer 12 preferably has a refractive index distribution of nx> ny = nz. In this 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 is extremely stable.

  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 13 can function as a so-called λ / 4 plate. According to the present invention, the wavelength dispersion characteristic of the second 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 second 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 second 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 second birefringent layer 13 preferably has a refractive index distribution of nx>ny> nz.

  The thickness of the second 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 10 to 100 μm, more preferably 20 to 80 μm, and most preferably 40 to 70 μm.

  The second birefringent layer can be typically formed by stretching a polymer film. For example, a second compound having desired optical characteristics (for example, refractive index distribution, in-plane retardation, thickness direction retardation, Nz coefficient) can be selected by appropriately selecting the type of polymer, stretching conditions, stretching method, and the like. A refractive layer can be obtained.

  Any appropriate polymer can be adopted as the polymer constituting the polymer film. Specific examples include polycarbonate, norbornene polymer, cellulose polymer, polyvinyl alcohol polymer, polysulfone polymer and the like.

A-4. Polarizer Any appropriate polarizer may be employed as the polarizer 11 depending on the purpose. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. 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-5. Protective layer The said 1st protective layer 14 and the 2nd protective layer 15 consist of arbitrary appropriate films which can be used as a protective film of a polarizing plate. 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 can be, for example, an extruded product of the resin composition. TAC, polyimide resin, polyvinyl alcohol resin, and glassy polymer are preferable.

  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 5 mm or less, more preferably 1 mm or less, particularly preferably 1 to 500 μm, and most preferably 5 to 150 μm.

  The surface of the second protective layer opposite to the polarizer (that is, the outermost part of the polarizing plate) may be subjected to a hard coat treatment, an antireflection treatment, an antisticking treatment, an antiglare treatment, or the like as necessary.

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 photo-alignment treatment on the surface of a transparent protective film (which finally becomes the protective layer 14); Applying a liquid crystal material to the surface subjected to the photo-alignment treatment; and orienting the liquid crystal material according to the orientation direction of the transparent protective film to form a first birefringent layer; A step of laminating a polarizer on the surface of the protective film not subjected to the orientation treatment; and a step of laminating a polymer film on the surface of the first birefringent layer to form a second birefringent layer. . Here, as described above, the angle formed by the absorption axis of the polarizer and the orientation direction of the transparent protective film (that is, the slow axis of the first birefringent layer) is α, the absorption axis of the polarizer and the first axis. When the angle formed by the slow axis of the birefringent layer 2 is β, the angles α and β have the relationship of the following formula (1):
2α + 40 ° <β <2α + 50 ° (1).
According to such a manufacturing method, for example, an elliptically polarizing plate as shown in FIGS. 1 and 2 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.

B-1. Photo-alignment treatment of the transparent protective film The surface of the transparent protective film (which finally becomes the protective layer 14) is subjected to a photo-alignment treatment, and a coating liquid containing a predetermined liquid crystal material is applied to the surface, whereby FIG. As shown in FIG. 1, the first birefringent layer 12 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). To do). By adopting the photo-alignment process as the alignment process, the influence of static electricity, dust, dust, etc. can be eliminated very well. As a result, an elliptically polarizing plate having extremely excellent quality stability and optical characteristics can be obtained. In other words, according to the photo-alignment process, it is possible to avoid a decrease in optical characteristics due to scraps after rubbing, which is a big problem in the alignment process by the conventional rubbing process.

  The photo-alignment treatment includes a step of forming a photo-alignment film on the surface of the protective film and a step of irradiating the photo-alignment film with polarized light. The photo-alignment film is formed by applying a composition containing an aligning agent (hereinafter referred to as an alignment film-forming composition) onto the surface of the transparent protective film and drying it. Any appropriate compound having a photoreactive functional group may be employed as the alignment agent contained in the alignment film forming composition. For example, a compound having a photoreactive functional group that causes a photochemical reaction such as a photoisomerization reaction, a photo-opening / closing ring reaction, a photo-dimerization reaction, a photolysis reaction, or a photo-fleece transfer reaction can be used. A compound having a photoreactive functional group that causes a photoisomerization reaction and / or a photodimerization reaction is preferable. This is because a birefringent layer having high surface uniformity can be obtained. The alignment agent is a polymer having a molecular weight sufficient to form an alignment film. The photoreactive functional group may be present in the main chain of the polymer molecule, may be present in the side chain, or may be present at the terminal.

  Specific examples of the photoreactive functional group that causes a photoisomerization reaction include azobenzene group, stilbene group, α-hydrazono-β-ketoester group, cinnamate group, benzylidenephthalimidine group, and retinoic acid. Specific examples of the photoreactive functional group that causes a photodimerization reaction include a cinnamate group, a benzylidenephthalimidine group, a chalcone group, a coumarin group, a styrylpyridine group, and an anthracene group. These functional groups may be contained in combination of two or more kinds in the alignment agent molecule.

  Specific examples of the compound having a photoreactive functional group include trade names “Staralign series (2100, 2110)” manufactured by HUNTSMAN, Chem. Mater. 201, 13, p. 695, a compound having a coumarin group described in Table 1, JSR TECHNIC REVIEW No. 106 (1999) in FIG. 1, JSR TECHNIC REVIEW No. 107 (2000) and the compound having a chalcone group described in FIG.

  Particularly preferred aligning agents are compounds having at least one photoreactive functional group selected from a cinnamate group, a chalcone group and an azobenzene group. This is because the photochemical reaction efficiency is excellent and the liquid crystal material can be uniformly oriented, and as a result, a birefringent layer having excellent optical uniformity and high transparency can be obtained. In particular, the 4-chalcone group has good reactivity with respect to long-wavelength ultraviolet light which is unlikely to deteriorate due to a photolytic reaction, and is excellent in heat resistance. The cinnamate group has high photoreactivity and is excellent in the transparency of the resulting alignment film.

  The alignment film-forming composition further includes a solvent and any appropriate additive depending on the purpose. Any appropriate solvent capable of dissolving or finely dispersing the alignment agent can be adopted as the solvent. Specific examples of the additive include a photoreaction initiator, a storage stabilizer, a dispersant, and a dispersion stabilizer. The alignment agent concentration (solid content concentration) in the alignment film forming composition can be appropriately set according to the purpose, the type of the alignment agent, the desired thickness of the alignment film, and the like. The total solids concentration in the composition is typically 1-5% by weight.

  The alignment film forming composition is applied to the surface of the transparent protective film and dried to form a photoalignment film. 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. The coating amount of the alignment film-forming composition can be appropriately set according to the concentration of the alignment film-forming composition, the thickness of the target photo-alignment film, and the like.

  Any appropriate method (for example, natural drying, heat drying, air drying) may be employed as the drying method. The drying temperature can vary depending on the type of alignment agent, the type of solvent, the characteristics of the desired photo-alignment film, and the like. The drying temperature is preferably 40 to 200 ° C, more preferably 60 to 160 ° C, and most preferably 80 to 120 ° C. The drying time is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes, and most preferably 1 to 4 minutes. Drying may be performed at a constant temperature, or may be performed while changing the temperature continuously or stepwise. The thickness of the photo-alignment film thus obtained is preferably 10 nm to 2 μm, more preferably 100 nm to 1.5 μm, and most preferably 300 nm to 1 μm. When the thickness of the photo-alignment film is within such a range, the photo-alignment process has a strength capable of sufficiently maintaining the film shape and does not substantially affect the optical characteristics of the obtained elliptically polarizing plate.

  Next, light is irradiated to the obtained photo-alignment film to align the photo-alignment film. As a light irradiation method, any appropriate method can be adopted depending on the type of photochemical reaction of the aligning agent, the direction desired for the slow axis of the resulting birefringent layer, and the like. Typically, a method is employed in which light having an undesired wavelength is cut from a predetermined light source, and the light from the light source is converted into polarized light for irradiation.

  Specific examples of light sources used for light irradiation include ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, dielectric excimer discharge lamps, flash UV lamps, deep UV lamps, xenon lamps, xenon flash lamps, and metal halide lamps. It is done. Any appropriate wavelength can be adopted as the wavelength of the irradiated light depending on the wavelength region in which the photoreactive functional group of the alignment agent has optical absorption. The wavelength of the irradiated light is preferably 210 to 380 nm, more preferably 230 to 380 nm, and most preferably 250 to 380 nm. By irradiating light having a wavelength in such a range, an undesired photodecomposition reaction in the photo-alignment film can be suppressed. As a result, a birefringent layer having a uniform homogeneous orientation can be obtained. The light having such a wavelength is obtained by passing light from the light source through a predetermined filter or the like and cutting light having an undesired wavelength (typically 100 to 200 nm).

The amount of light irradiation is preferably 5 to 500 mJ / cm ² , more preferably 7 to 400 mJ / cm ² , and most preferably 10 to 300 mJ / cm ² at a wavelength of 310 nm. By employing an irradiation amount in such a range, a birefringent layer having a uniform homogeneous orientation can be obtained.

  The temperature at the time of light irradiation is preferably 15 to 90 ° C, more preferably 15 to 60 ° C. Within such a temperature range, a highly uniform birefringent layer can be obtained. Arbitrary appropriate heating means and / or temperature control means can be adopted as means for keeping the temperature at the time of irradiation constant. Specific examples include an air circulation type thermostatic oven in which hot air or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature adjustment, a heat pipe roll, and a metal belt.

  Preferably, the irradiation light is polarized light. By irradiating polarized light having a predetermined polarization direction, the photo-alignment film can be aligned in a direction corresponding to the polarization direction. Therefore, the photo-alignment film can be oriented in a desired direction by controlling the polarization direction. As a result, a birefringent layer having a slow axis in a desired direction can be obtained.

  Any appropriate polarizing plate can be adopted as means for generating polarized light. Preferably, it is a wire grid polarizer. This is because it has a filter function for cutting an undesired wavelength (that is, a polarization separation function at a predetermined wavelength) and is excellent in heat resistance, so that it is less likely to deteriorate during irradiation. FIG. 3 is a schematic diagram for explaining a wire grid polarizer used in the present invention. As shown in FIG. 3, the wire grid polarizer is configured by arranging wires in a lattice pattern. The wire is made of metal (for example, tungsten). The diameter d of the wire can be appropriately set according to the purpose. The space | interval p of a wire can be suitably set according to the wavelength to cut. In this invention, the space | interval p of a wire is shorter than UV wavelength, and is specifically 100-200 nm. By adopting such a wire interval, a polarization separation function is imparted at a wavelength of 210 to 380 nm. Here, for example, “having a polarization separation function at 210 to 380 nm” means substantially transmitting only light having a wavelength of 210 to 380 nm and substantially absorbing light having other wavelengths. . As shown in FIG. 3, when light passes through a wire grid polarizer, only a component having a predetermined wavelength and a direction perpendicular to the grating is transmitted. This phenomenon has not been explained theoretically.

  Here, a mechanism capable of aligning the photo-alignment film in a direction corresponding to the polarization direction by irradiating polarized light having a predetermined polarization direction will be described. FIG. 4 is a schematic diagram for explaining a mechanism in which the photo-alignment film is oriented by irradiation with polarized light. As an example, a case where the photoreactive functional group is a cinnamate group and the photochemical reaction is a photodimerization reaction will be described. As shown in FIG. 4A, before the light irradiation, the aligner molecules in the photo-alignment film are present in a statistically random direction. As shown in FIG. 4B, in the dimerization reaction, the double bond of the cinnamate group of each molecule is cleaved to form a radical, and the radicals react to form a four-membered ring. As shown in FIG. 4C, a dimer is formed. Here, in order for two molecules to form a dimer, the two molecules are typically arranged in a state as shown in FIGS. 4A and 4B (ie, substantially in parallel). It is necessary to be out. Otherwise, the dimer is not formed due to the steric hindrance of the molecule. Furthermore, although not theoretically clear, the probability that a dimer is formed is greatest when molecular chains are aligned in the polarization direction (see FIG. 4C). As a result, the entire alignment film has an alignment axis (slow axis) in the polarization direction.

  The orientation direction of the photo-alignment 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 first birefringent layer 12 to be formed. 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. In effect, the orientation direction is, for example, the lattice direction of the wire grid polarizer so that the polarization direction of light that has passed through the wire grid polarizer (ie, the direction perpendicular to the lattice direction) is at the above angle. Can be controlled by arranging so as to define a predetermined angle with respect to the longitudinal direction (roll conveyance direction) of the transparent protective film.

B-2. Step of coating liquid crystal material for forming 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 photo-alignment treatment. And then aligning the liquid crystal material 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, 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 agent 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 to be 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 determined according to the type of liquid crystal material, the type of transparent protective film, the type of photo-alignment treatment, the desired characteristics of the first birefringent layer, etc. Can be set. In addition, it is preferable that light and an ultraviolet-ray are non-polarized light. This is so as not to affect the alignment direction of the photo-alignment film remaining on the transparent protective film.

  By performing the photo-alignment treatment as described above, the liquid crystal material is aligned according to the alignment direction of the transparent protective film, so that the slow axis of the formed first birefringent layer is the alignment of the transparent protective film. It is substantially the same as the direction. 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. Polarizer Laminating Step Further, the polarizer is laminated on the surface of the transparent protective film opposite to the surface subjected to the photo-alignment treatment. 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 production method of the present invention, since the slow axis of the first birefringent layer can be set in the photo-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 a photo-alignment treatment so as to form a predetermined angle with respect to the longitudinal direction and a long polarizing film (polarizer) are continuously pasted with their respective longitudinal directions aligned. Can be combined. 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.

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 the polymer film described in the section A-3 on the surface of the first birefringent layer. Preferably, the polymer film is a stretched film. 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).

B-6. Specific Manufacturing Procedure An example of a specific procedure of the manufacturing method of the present invention will be described with reference to FIGS. 5 to 9, reference numerals 111, 111 ′, 112, 113, 114, 115, and 116 are rolls for winding the film and / or the laminated body forming 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-4. Stretching is continuously performed in the longitudinal direction of a long polymer film. As a result, as shown in the perspective view of FIG. 5, 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 schematic diagram of FIG. 6, a long transparent protective film (which eventually becomes the first protective layer) 14 is prepared, and an alignment film forming composition is applied on one surface thereof. And drying to form the alignment film 14 '. The alignment film is aligned by irradiating the alignment film with light. At this time, as shown in FIG. 7A, the orientation direction is a direction different from the longitudinal direction of the transparent protective film 14, for example, a direction of + 23 ° to + 24 ° or −23 ° to −24 °. Furthermore, as shown in the above-mentioned paragraphs B-2 and B-3, on the transparent protective film 14 subjected to the photo-alignment treatment (the photo-alignment film 14 ′ is aligned in a predetermined direction) as shown in FIG. Thus, the first birefringent layer 12 is formed. In the first birefringent layer 12, since the liquid crystal material is aligned along the alignment direction of the alignment film, the slow axis direction is substantially the same as the direction of the optical alignment treatment as shown in FIG. The same direction (arrow B direction). In addition, as shown in FIG. 6, the wire grid polarizer of a light irradiation part is supported rotatably, and it fixes so that it may have a predetermined angle with respect to the longitudinal direction (conveyance direction) of a transparent protective film according to the objective. By performing light irradiation, the alignment direction of the photo-alignment treatment can be controlled. Although the photo-alignment film 14 ′ remains on the transparent protective film 14, it is very thin and its optical characteristics are neutral, so that it does not substantially affect the optical characteristics of the entire elliptically polarizing plate.

  Next, as shown in the schematic diagram of FIG. 8, the transparent protective film (being a second protective layer) 15, the polarizer 11, the transparent protective film (being a protective layer) 14 and the first birefringent layer 12. 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. In addition, in FIG. 8, the code | symbol 122 shows the guide roll for bonding films together (same also in FIG. 9). 8 and 9, the alignment film 14 'is omitted.

  Furthermore, as shown in the schematic diagram of FIG. 9, a long second birefringent layer 13 is prepared, and this is laminated with a laminate 123 (second protective layer 15, polarizer 11, protective layer 14, and first layer). The birefringent layer 12) is sent out in the direction of the arrow, and bonded with an adhesive or the like (not shown) in a state where the respective longitudinal directions are aligned. As described above, the slow axis direction (angle α) of the first birefringent layer 12 is + 23 ° to + 24 ° or −23 ° to −24 with respect to the longitudinal direction of the film (absorption axis of the polarizer 11). If it is set to ° and the relationship of β = 2α + 45 ° is used, the angle β is 91 ° to 93 °. That is, the slow axis of the second birefringent layer 13 may be substantially orthogonal to the longitudinal direction of the film (absorption axis of the polarizer 11). As a result, a general stretched polymer film transversely stretched in a direction perpendicular to the longitudinal direction can be used, and the production efficiency can be significantly improved.

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

B-7. 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.

  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. 10 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. This polarizing plate (elliptical polarizing plate) 10 is disposed so that the birefringent layers 12 and 13 are between the polarizer 11 and the liquid crystal cell 20. The polarizing plate 10 ′ is any appropriate polarizing plate. The polarizing plates 10, 10 ′ are typically arranged so that the absorption axes of the polarizers are orthogonal to each other. As shown in FIG. 10, in the liquid crystal display device (liquid crystal panel) of the present invention, the elliptically polarizing plate 10 of the present invention is preferably disposed 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 active 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 and 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 are measured. 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 birefringent layer 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 The same elliptically polarizing plates obtained in Example 1 were bonded together. 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.
(4) Measurement of contrast ratio The same elliptical polarizing plates are overlapped and illuminated with a backlight to display a white image (absorption axes of polarizers are parallel) and a black image (absorption axes of polarizers are orthogonal), manufactured by ELDIM The product name “EZ Contrast 160D” was scanned in the direction of 45 ° to 135 ° with respect to the absorption axis of the polarizer on the viewing side and from −60 ° to 60 ° with respect to the normal. 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.

I. Preparation of elliptical polarizing plate as shown in FIG. Photo-alignment treatment of transparent protective film (production of alignment substrate)
The transparent protective film was subjected to a photo-alignment treatment to produce an alignment substrate (which eventually becomes a protective layer). The specific procedure is as follows. On the surface of the TAC film (thickness 40 μm), a composition containing an aligning agent having a cinnamate group (manufactured by HUNTSMAN, trade name “Staralign 2100”, total solid content concentration: 2% by weight) was applied using a gravure coater. The film was dried in an air circulation type constant temperature oven at 90 ° C. ± 1 ° C. for 2 minutes to form a photo-alignment film having a thickness of 0.3 μm. Next, using a high-pressure mercury lamp as a light source and an ultraviolet irradiation device equipped with a wire grid polarizer (having a polarization separation function at a wavelength of 210 to 380 nm), the surface of the photo-alignment film is formed in an air atmosphere of 30 ° Polarized ultraviolet light was irradiated at an irradiation amount of 100 mJ / cm ² (measured at a wavelength of 310 nm). Upon irradiation, the polarization vector of the transmitted light has a film longitudinal direction and an angle α (8 °, −8 °, 13 °, −13 °, 23 °, −23 °, 33 °, −33 °, 38 °, -38 °). In this way, alignment substrates (1) to (10) were obtained. The retardation in the thickness direction of the protective layer is also shown in the table 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). The thickness and retardation of the first birefringent layer were adjusted by changing the coating amount of the liquid crystal coating liquid. Table 2 below shows the thickness and in-plane retardation value (nm) of the formed first birefringent layer.

Ic. Production of second birefringent layer A polycarbonate film (thickness 60 μm) or a norbornene-based film (manufactured by JSR: trade name Arton: thickness 60 μm) is uniaxially stretched at a predetermined temperature to produce a second birefringent layer film. did. Table 3 below shows the type of film used (PC for polycarbonate film, NB for norbornene film), stretching conditions (stretching direction), angle β (angle of slow axis with respect to the longitudinal direction of the film), and retardation obtained. Indicates the value.

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, and a second birefringent layer were used in combinations as shown in Table 4 below. The polarizer, the protective layer, the first birefringent layer, and the second birefringent layer are laminated by the manufacturing procedure shown in FIGS. 5 to 9 to obtain elliptically polarizing plates A01 to A21 as shown in FIG. It was.

  The contrast ratio was measured by superimposing the elliptical polarizing plates A01. As apparent from Table 4, this elliptically polarizing plate had a relationship of β = 2α + 44 °. According to this elliptically polarizing plate, the angle of contrast 10 is 40 degrees minimum, 50 degrees maximum in all directions, and the maximum minimum difference is 10 degrees. It was a practically preferable level that the angle of the contrast 10 was a minimum of 40 degrees in all directions. Furthermore, since the difference between the maximum and minimum is as small as 10 degrees, the visual characteristics are well balanced, which is also a very favorable level for practical use.

  The contrast ratio was measured by overlapping the elliptically polarizing plates A21. As is apparent from Table 4, this elliptically polarizing plate had a relationship of β = 2α + 49 °. According to this elliptically polarizing plate, the angle of contrast 10 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 the contrast 10 was a minimum of 40 degrees in all directions.

(Comparative Example 1)
The contrast ratio was measured by overlapping the elliptically polarizing plates A11. As apparent from Table 4, this elliptically polarizing plate had a relationship of β = 2α + 64 °. According to this elliptically polarizing plate, the angle of contrast 10 was 30 degrees minimum and 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. According to this elliptically polarizing plate, the angle of the contrast 10 is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

(Comparative Example 2)
The contrast ratio was measured by overlapping the elliptically polarizing plates A13. As apparent from Table 4, this elliptically polarizing plate had a relationship of β = 2α + 24 °. According to this elliptically polarizing plate, the angle of contrast 10 was 30 degrees minimum and 50 degrees maximum in all directions, and the maximum minimum difference was 20 degrees. According to this elliptically polarizing plate, the angle of the contrast 10 is a minimum of 30 degrees in all directions, which is a level that cannot be put to practical use.

  As is clear from Example 1, according to the manufacturing method of the present invention, a long transparent protective film having a first birefringent layer having a slow axis in an oblique direction and a long polarizer are provided. Since the long sides can be aligned and bonded continuously by roll-to-roll, an elliptically polarizing plate can be obtained with very high production efficiency. Further, as is apparent from the results of Examples 2-3 and Comparative Examples 1-2, according to the present invention, the angle α formed by the absorption axis of the polarizer and the slow axis of the first birefringent layer, and By optimizing the angle β formed by the absorption axis of the polarizer and the slow axis of the second birefringent layer in a relationship of 2α + 40 ° <β <2α + 50 °, the angle of contrast 10 is minimized in all directions. It could be 40 degrees, and a practically preferable level could be secured. In particular, according to Example 2, the maximum / minimum difference could be reduced to 10 degrees. This value was very well balanced in terms of visual characteristics and was a very favorable level for practical use. On the other hand, according to the comparative example in which the angle α and the angle β do not satisfy the above relationship, the angle of the contrast 10 is a minimum of 30 degrees in all directions, which is not practical.

  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).

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 schematic diagram for demonstrating the wire grid polarizer used for this invention. It is a schematic diagram explaining the mechanism which a photo-alignment film orientates by the polarized light irradiation in the photo-alignment process of this 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 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 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 sectional drawing of the liquid crystal panel used for the liquid crystal display device by preferable embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Elliptical polarizing plate 11 Polarizer 12 1st birefringent layer 13 2nd birefringent layer 14 1st protective layer 14 'Photo-alignment film | membrane 15 2nd protective layer 20 Liquid crystal cell 100 Liquid crystal panel

Claims (13)

A step of performing photo-alignment treatment on the surface of the transparent protective film;
Applying a liquid crystal material to the surface of the transparent protective film that has been subjected to the photo-alignment treatment;
Orienting the liquid crystal material according to the orientation direction of the transparent protective film to form a first birefringent layer;
Laminating a polarizer on the surface of the transparent protective film opposite to the surface subjected to the photo-alignment treatment;
Laminating a polymer film on the surface of the first birefringent layer to form a second birefringent layer,
When the angle between the absorption axis of the polarizer and the orientation direction of the transparent protective film is α, and the angle between the absorption axis of the polarizer and the slow axis of the second birefringent layer is β, the angle α And β have the relationship of the following formula (1):
2α + 40 ° <β <2α + 50 ° (1).   Both the polarizer and the transparent protective film on which the first birefringent layer is formed are long films. In the step of laminating the polarizer, the long sides of the polarizer and the protective film are continuous with each other. The manufacturing method of Claim 1 bonded together.   The polymer film forming the second birefringent layer is a long film, and in the step of forming the second birefringent layer, the transparent film on which the polarizer and the first birefringent layer are formed. The manufacturing method of Claim 1 or 2 with which the long sides of a protective film and this polymer film are bonded together continuously.   The manufacturing method according to claim 1, wherein the direction of the photo-alignment treatment is + 8 ° to + 38 ° or −8 ° to −38 ° with respect to the absorption axis of the polarizer.   The manufacturing method according to claim 1, wherein the photo-alignment treatment includes a step of forming a photo-alignment film on the surface of the transparent protective film and a step of irradiating the photo-alignment film with light.   The photo-alignment film is at least selected from a cinnamate group, a chalcone group, an azobenzene group, a stilbene group, an α-hydrazono-β-ketoester group, a benzylidenephthalimidine group, a retinoyl group, a coumarin group, a styrylpyridine group, and an anthracene group. The manufacturing method of Claim 5 formed from the composition containing the orientation agent which has a kind of photoreactive functional group.   The manufacturing method according to claim 5 or 6, wherein the light is polarized light generated by a wire grid polarizer having a polarization separation function at a predetermined wavelength.   The manufacturing method according to claim 1, wherein the liquid crystal material contains at least one of a liquid crystal monomer and a liquid crystal polymer.   The manufacturing method according to claim 1, wherein the first birefringent layer is a λ / 2 plate.   The manufacturing method according to claim 1, wherein the second birefringent layer is a λ / 4 plate.   The manufacturing method according to any one of claims 1 to 10, wherein the polymer film is a stretched film.   An elliptically polarizing plate manufactured by the manufacturing method according to claim 1. An image display device comprising the elliptically polarizing plate according to claim 12.

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