JP2006323349A - Manufacturing method of optical film, the optical film and image display device using the optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method, capable of manufacturing an optical film which is small in change with lapse of time for phase difference value, has superior characteristics also in oblique directions and has a broad band and a wide-viewing field angle, with very high manufacturing efficiency, to provide an optical film obtained according to such a method, and to provide an image display device that uses the optical film. <P>SOLUTION: The manufacturing method of optical film comprises a process of subjecting the surface of a substrate to alignment; a process of applying a liquid crystal composition to the surface subjected to the alignment of the substrate; a process of forming a first birefringence layer, by aligning liquid crystal material in the liquid crystal composition according to the alignment directions of the substrate; a process of aging the first birefringence layer, at a temperature ≥(liquid crystal transition temperature of the liquid crystal material + 20°C) and for ≥0.5 hr; and a process of transferring the first birefringence layer, formed on the surface of the substrate to the surface of a transparent protective film (T). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical film manufacturing method, an optical film, and an image display device using the optical film. More specifically, the present invention relates to a method for producing a broadband and wide viewing angle optical film with very high production efficiency, which has a small change in the retardation value with time and has excellent characteristics in an oblique direction, and The present invention relates to an optical film obtained by such a method, and an image display device using the optical film.

  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, 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 in order to solve the above-described conventional problems. The object of the present invention is to provide a wideband and wide viewing angle with a small change in retardation value over time and excellent characteristics in an oblique direction. It is an object of the present invention to provide a method capable of producing an optical film with very high production efficiency, an optical film obtained by such a method, and an image display device using the optical film.

  If the present inventors perform an aging process under a specific condition after forming the first birefringent layer, preferably, the absorption axis of the polarizer and the λ / 4 plate and the λ / 2 plate If the angle formed by the slow axis has a specific relationship, the change over time in the phase difference value can be reduced, and excellent characteristics can be exhibited even in the oblique direction. The inventors have found that angular characteristics can be obtained, and have completed the present invention.

  The method for producing an optical film of the present invention includes a step of performing an alignment treatment on the surface of a substrate, a step of applying a liquid crystal composition to the surface of the substrate that has been subjected to the alignment treatment, and the liquid crystal composition The liquid crystal material is aligned in accordance with the alignment direction of the base material to form a first birefringent layer, and the first birefringent layer formed on the surface of the base material is formed into a transparent protective film (T And aging the first birefringent layer at a temperature of (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) or higher for 0.5 hour or longer. The method further includes a step.

In a preferred embodiment, the step of laminating a polarizer on the surface of the transparent protective film (T), and laminating a polymer film on the surface of the transferred first birefringent layer, the second birefringence Forming the layer, and the polarizer and the first birefringent layer are disposed on opposite sides of each other through the transparent protective film (T), and the absorption axis of the polarizer and the first birefringent layer are arranged. When the angle formed by the orientation direction of the refractive layer is α, and the angle formed by the absorption axis of the polarizer and the slow axis of the second birefringent layer is β, the angles α and β are expressed by the following formula (1). Having:
2α + 40 ° <β <2α + 50 ° (1).

In a preferred embodiment, the polarizer and the transparent protective film (T) are both long films, and the long sides of the polarizer and the transparent protective film (T) are continuous in the step of laminating the polarizer. Pasted together.
In a 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 first birefringent layer and the polymer are formed. The long sides of the film are continuously bonded together.
In a preferred embodiment, the direction of the alignment treatment is + 8 ° to + 38 ° or −8 ° to −38 ° with respect to the absorption axis of the polarizer.
In a preferred embodiment, the alignment process is at least one selected from the group consisting of a rubbing process, an oblique deposition method, a stretching process, a photo alignment process, a magnetic field alignment process, and an electric field alignment process.
In a preferred embodiment, the liquid crystal composition includes at least one of a liquid crystal monomer and a liquid crystal polymer.
In a preferred embodiment, the liquid crystal composition includes a polymerizable monomer and / or a crosslinkable monomer, and the liquid crystal alignment step further includes performing a polymerization treatment and / or a crosslinking treatment.
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 optical film is provided. This optical film 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 optical film.

  As described above, according to the present invention, since the slow axis of the first birefringent layer can be set in an arbitrary direction, it is elongated in the longitudinal direction (that is, has an absorption axis in the longitudinal direction). A polarizing film (polarizer) can be used. That is, a long first birefringent layer that has been subjected to an orientation treatment to form a predetermined angle with respect to the longitudinal direction, a long transparent protective film (T), and a long polarizing film (polarizer) Can be continuously laminated with their respective longitudinal directions aligned (so-called roll-to-roll). Therefore, an optical film 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 optical film having no quality variation among products can be obtained. Furthermore, since no waste is generated by cutting, an optical film 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. The optical film can be obtained with very excellent production efficiency. The optical film 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 doublet. Since the angle β formed by the slow axis of the refractive layer (λ / 4 plate) is optimized in the relationship of 2α + 40 ° <β <2α + 50 °, an image display device with a wide bandwidth and a wide viewing angle 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. As a result, the optimization of the circular polarization characteristic can be performed very generally and easily. Further, by performing the aging process under a specific condition after forming the first birefringent layer, it is possible to reduce the phase difference value change of the first birefringent layer when mounted on the image display device. Become. As a result, good viewing angle characteristics can be maintained for a long time.

A. Optical film A-1. 1 is a schematic cross-sectional view of an optical film according to a preferred embodiment of the present invention. The optical film 10 includes a polarizer 11, a first birefringent layer 12, and a second birefringent layer 13 in this order. If necessary, a first protective layer (transparent protective film) 14 is provided between the polarizer 11 and the first birefringent layer 12, and the first protective layer (transparent protective film) 14 of the polarizer 11. A second protective layer (transparent protective film) 15 is provided on the opposite side.

  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 optical film according to a preferred embodiment of the present invention (in FIG. 2, a second protective layer (transparent protective film) is shown for the sake of clarity). 15 is omitted). 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 preferably 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, an optical film 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 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 °. In consideration of the optical film manufacturing procedure (described later), it is highly 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 optical film 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 optical film of the present invention (described later), since the first birefringent layer can be laminated without using an adhesive, the total thickness is a minimum of 4 minutes compared to the conventional optical film. The thickness can be reduced to about 1. As a result, the optical film of the present invention can greatly contribute to thinning of the liquid crystal display device. Hereinafter, the detail of each layer which comprises the optical film of this invention is demonstrated.

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 is the refractive index in the direction of the slow axis, ny is the refractive index in the direction of the fast axis (the direction perpendicular to the slow axis in the plane), and d is the first birefringent layer. Is the thickness. Furthermore, the first birefringent layer 12 preferably has a refractive index distribution of nx> ny = nz. nz is the refractive index in the thickness direction. 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 / or a crosslinkable monomer is 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, 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 second 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, that is, the direction perpendicular to the longitudinal direction).

  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. Polycarbonate and norbornene polymers are preferred.

  Or a 2nd birefringent layer is comprised from the film formed from the resin composition containing a polymeric liquid crystal and a chiral agent. The polymerizable liquid crystal and the chiral agent are described in JP-A No. 2003-287623, the disclosure of which is incorporated herein by reference. For example, when the resin composition is applied to any appropriate substrate and heated to a temperature at which the polymerizable liquid crystal exhibits a liquid crystal state, the polymerizable liquid crystal is twisted by a chiral agent (more specifically, Orient (form a cholesteric structure). When the polymerizable liquid crystal is polymerized in this state, a film in which the cholesteric structure is fixed and oriented is obtained. By adjusting the content of the chiral agent in the composition, it becomes possible to change the twist degree of the cholesteric structure, and as a result, to control the direction of the slow axis of the formed second birefringent layer Can do. Such a film is very preferable because the direction of the slow axis can be set to an angle other than parallel or orthogonal to the absorption axis of the polarizer.

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 transparent protective films which can be used as a protective film of a polarizing plate. A transparent protective film is preferred. Specific examples of the material as the main component of such a transparent protective film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, and polyethersulfone. And transparent resins such as polysulfone, 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 Rth is preferably −90 nm to +90 nm, more preferably −80 nm to +80 nm, and most preferably −70 nm to +70 nm. The thickness direction retardation Rth is obtained by the formula: Rth = (nx−nz) × d, where d (nm) is the thickness of the film (layer).

  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 optical film The manufacturing method of the optical film of the present invention includes a step of performing an alignment treatment on the surface of the substrate, a step of applying a liquid crystal composition to the surface of the substrate that has been subjected to the alignment treatment, Aligning the liquid crystal material in the liquid crystal composition according to the alignment direction of the base material to form a first birefringent layer; and forming the first birefringent layer formed on the surface of the base material. A step of transferring to the surface of the transparent protective film (T), and before or after the transfer step, the first birefringent layer is set to a temperature of not less than (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) at a temperature of 0.degree. It further includes a step of aging for 5 hours or more.
In a preferred embodiment, the step of laminating a polarizer on the surface of the transparent protective film (T), and laminating a polymer film on the surface of the transferred first birefringent layer, the second birefringence Forming the layer, and the polarizer and the first birefringent layer are disposed on opposite sides of each other through the transparent protective film (T), and the absorption axis of the polarizer and the first birefringent layer are arranged. When the angle formed by the orientation direction of the refractive layer is α, and the angle formed by the absorption axis of the polarizer and the slow axis of the second birefringent layer is β, the angles α and β are expressed by the following formula (1). Having:
2α + 40 ° <β <2α + 50 ° (1).
According to such a manufacturing method, for example, an optical film 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 laminated structure of the target optical film. For example, the polarizer lamination step may be performed after any birefringent layer forming step or lamination step. Details of each step will be described below.

B-1. Step of forming first birefringent layer The first birefringent layer is formed on the surface of the transparent protective film. The detailed procedure of the process of forming the first birefringent layer is as follows.

First, a liquid crystal composition (liquid crystal material-containing coating solution) is applied to a substrate whose surface has been subjected to orientation treatment.

  Any appropriate base material is used as the base material as long as the appropriate first birefringent layer in the present invention is obtained. Any appropriate base material can be adopted as the base material. Specific examples include a glass substrate, a metal foil, a plastic sheet, or a plastic film. An alignment film may be provided on the base material, but it may not be provided. Any appropriate film can be adopted as the plastic film. 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, a polyethylene terephthalate (PET) film is preferable.

  The thickness of a base material becomes like this. Preferably it is 20-100 micrometers, More preferably, it is 30-90 micrometers, Most preferably, it is 30-80 micrometers. By having a thickness in such a range, the strength to favorably support the very thin first birefringent layer in the laminating process is given, and the operability such as slipping property and roll running property is appropriately maintained. Is done.

  As the alignment treatment of the surface of the substrate, any appropriate alignment treatment is used as long as the appropriate first birefringent layer in the present invention is obtained. Examples include rubbing treatment, oblique vapor deposition method, stretching treatment, photo-alignment treatment, magnetic field orientation treatment, and electric field orientation treatment, and rubbing treatment is preferable.

  The orientation direction of the orientation treatment is a direction that forms a predetermined angle with the absorption axis of the polarizer when the polarizers are stacked. 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.

  The liquid crystal composition that forms the first birefringent layer is applied to the surface of the substrate that has been subjected to the alignment treatment, and the liquid crystal material is aligned on the substrate. 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 a 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 substrate surface. Thereby, birefringence is generated in the layer formed by coating, and the first birefringent layer is formed.

  The liquid crystal composition is prepared by dissolving or dispersing a liquid crystal material in an appropriate solvent.

  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 liquid crystal material concentration of the coating liquid is 20% by weight, the coating amount is preferably 0.03 to 0.17 ml, more preferably 0.05 to 0.17 per area (100 cm ² ) of the base material. 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.

  Next, the liquid crystal material forming the first birefringent layer is aligned according to the alignment direction of the substrate surface. 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 a 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 substrate surface. Thereby, birefringence is generated in the layer formed by coating, and the first birefringent layer is formed.

  The processing temperature can be appropriately determined according to the type of 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 said liquid-crystal monomer as a liquid-crystal material, it is preferable to give a polymerization process or a crosslinking process further to the layer formed by the said coating. 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 set according to the type of liquid crystal material, the type of base material and the type of alignment treatment, the properties desired for the first birefringent layer, etc. obtain.

  Next, the first birefringent layer formed on the substrate is transferred to the surface of the transparent protective film (T). The transfer method is not particularly limited. For example, the transfer is performed by attaching the first birefringent layer supported by the base material to the transparent protective film via an adhesive. By adopting the method of transfer, an optical film having excellent production efficiency and excellent adhesion between films (layers) can be obtained.

  A typical example of the adhesive is a curable adhesive. Typical examples of the curable adhesive include a photocurable adhesive such as an ultraviolet curable adhesive, a moisture curable adhesive, and a thermosetting adhesive. Specific examples of the thermosetting adhesive include thermosetting resin adhesives such as epoxy resins, isocyanate resins, and polyimide resins. Specific examples of the moisture curable adhesive include isocyanate resin-based moisture curable adhesive. A moisture curable adhesive (especially an isocyanate resin-based moisture curable adhesive) is preferred. Moisture curable adhesives cure by reacting with moisture in the air, adsorbed water on the surface of the adherend, active hydrogen groups such as hydroxyl groups and carboxyl groups, and so on. It can be cured and has excellent operability. Furthermore, since it is not necessary to heat for curing, the first birefringent layer and the transparent protective film (T) are not heated at the time of bonding (adhesion). As a result, since there is no fear of heat shrinkage, even when the first birefringent layer and the transparent protective film (T) are very thin as in the present invention, cracks during lamination can be remarkably prevented. The isocyanate resin adhesive is a general term for polyisocyanate adhesives and polyurethane resin adhesives.

  As the curable adhesive, for example, a commercially available adhesive may be used, or the above various curable resins may be dissolved or dispersed in a solvent to prepare a curable resin adhesive solution (or dispersion). Good. When preparing a solution (or dispersion liquid), the content of the curable resin in the solution is preferably 10 to 80% by weight, more preferably 20 to 65% by weight, and particularly preferably the solid content weight. It is 25 to 65% by weight, and most preferably 30 to 50% by weight. As a solvent to be used, any appropriate solvent can be adopted depending on the type of curable resin. Specific examples include ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene and the like. These may be used alone or in combination of two or more.

The coating amount of the adhesive can be appropriately set according to the purpose. For example, the coating amount is preferably 0.3 to 3 ml, more preferably 0.5 to ² ml, most preferably per area (cm ² ) of the first birefringent layer or the transparent protective film (T). Is 1 to 2 ml. After coating, if necessary, the solvent contained in the adhesive is volatilized by natural drying or heat drying. The thickness of the adhesive layer thus obtained is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, and most preferably 1 μm to 10 μm. The indentation hardness (Microhardness) of the adhesive layer is preferably 0.1 to 0.5 GPa, more preferably 0.2 to 0.5 GPa, and most preferably 0.3 to 0.4 GPa. . In addition, since the indentation hardness has a known correlation with Vickers hardness, it can also be converted into Vickers hardness. The indentation hardness can be calculated from the indentation depth and the indentation load using, for example, a thin film hardness meter (for example, trade name MH4000, trade name MHA-400) manufactured by NEC Corporation.

  Finally, if the base material is peeled from the first birefringent layer, the lamination of the first birefringent layer and the transparent protective film (T) is completed.

B-2. First Birefringent Layer Aging Step Before or after the transfer step, the first birefringent layer is aged at a temperature equal to or higher than (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) for 0.5 hour or longer. By performing the aging process under a specific condition after forming the first birefringent layer, it is possible to reduce the change in the retardation value of the first birefringent layer when mounted on an image display device. As a result, good viewing angle characteristics can be maintained for a long time. In order to simplify the entire production process in the present invention, the aging is preferably performed before the transfer process.

  The lower limit of the aging temperature is preferably (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) or more, more preferably (liquid crystal transition temperature of the liquid crystal material + 30 ° C.) or more, and further preferably (liquid crystal transition temperature of the liquid crystal material + 40 ° C.). ) Or more, particularly preferably (liquid crystal transition temperature of the liquid crystal material + 50 ° C.) or more. More specifically, the lower limit of the aging temperature is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, still more preferably 100 ° C. or higher, and particularly preferably 110 ° C. or higher. As the upper limit of the aging temperature, any appropriate temperature can be selected as long as the effects of the present invention are not impaired, but the melting point of the transparent protective film is preferably not more than 500 ° C, more preferably not more than 500 ° C, still more preferably not more than 300 ° C, particularly Preferably it is 250 degrees C or less, Most preferably, it is 200 degrees C or less. When the aging temperature is less than (liquid crystal transition temperature of the liquid crystal material + 20 ° C.), it may be difficult to sufficiently exert the aging effect.

  The aging time is preferably 0.5 hours or more, more preferably 0.5 to 72 hours, further preferably 1 to 48 hours, and particularly preferably 1 to 24 hours. If the aging time is less than 0.5 hours, it may be difficult to sufficiently exert the aging effect.

B-3. Lamination process of a polarizer A polarizer is laminated | stacked on the surface of the said transparent protective film (T). The lamination of the polarizer can be performed at any appropriate time in the production method of the present invention. For example, the polarizer may be laminated in advance on the transparent protective film (T), may be laminated after forming the first birefringent layer, or may be laminated after forming the second birefringent layer. Also good.

  Any appropriate laminating method (for example, adhesion) can be adopted as a laminating method of the transparent protective film (T) 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 orientation treatment of the base material, the length 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, each of the long transparent protective film to which the first birefringent layer has been transferred and the long polarizing film (polarizer) subjected to the orientation treatment so as to form a predetermined angle with respect to the longitudinal direction, Can be bonded together continuously in the same longitudinal direction. Therefore, an optical film 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 optical film having no quality variation among products can be obtained. Furthermore, since no waste is generated by cutting, an optical film 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-4. 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 above section A-3 on the surface of the first birefringent layer transferred to the surface of the transparent protective film (T). It is formed. 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-3. 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-3).

  Alternatively, as described in the above section A-3, a resin composition containing a polymerizable liquid crystal and a chiral agent is applied to any appropriate base material, and heated to a temperature at which the polymerizable liquid crystal exhibits a liquid crystal state, The polymerizable liquid crystal is aligned in a state twisted by a chiral agent (more specifically, a cholesteric structure is formed). By polymerizing the polymerizable liquid crystal in this state, a film in which the cholesteric structure is fixed and oriented is obtained. By transferring this film from the substrate to the surface of the first birefringent layer, the second birefringent layer 13 is formed.

B-5. Specific Manufacturing Procedure An example of a specific procedure of the manufacturing method of the present invention will be described with reference to FIGS. 3 to 8, reference numerals 111, 111 ′, 112, 112 ′, 113, 114, 115, 116, 117, 118, 118 ′, 119, 119 ′ are films and / or laminates forming each layer. A roll that rolls around the body.

  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. 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 base material 16 is prepared, and a rubbing process is performed on one surface thereof by a rubbing roll 120. At this time, the rubbing direction is a direction having a predetermined angle with respect to the longitudinal direction of the substrate 16, for example, a direction of + 22 ° to + 26 ° or −22 ° to −26 °. Next, as shown in the perspective view of FIG. 4B, the first birefringent layer 12 is formed on the base material 16 subjected to the rubbing treatment as described in the section B-1. In the first birefringent layer 12, the liquid crystal material is aligned along the rubbing direction, so that the slow axis direction is substantially the same direction as the rubbing direction of the substrate 16 (arrow B direction).

  Next, the first birefringent layer 12 formed on the substrate 16 is aged at a temperature of (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) or higher for 0.5 hour or longer.

  Next, as shown in the schematic diagram of FIG. 5A, a long transparent protective film (to be a second protective layer) 15, a polarizer 11, and a long transparent protective film (to be a protective layer). 14 and the laminated body 121 of the first birefringent layer 12 and the base material 16 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, and the laminated body 123 is laminated. 'Form. Further, as shown in FIG. 5B, the substrate 16 is peeled from the laminate 123 ′, and the laminate 123 (the protective layer 15, the polarizer 11, the protective layer 14, and the first birefringent layer 12) is removed. Form. In addition, in Fig.5 (a), 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 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. Thus, the optical film 10 of the present invention is obtained.

  When a resin composition containing a polymerizable liquid crystal and a chiral agent is used as the second birefringent layer 13, a procedure as shown in FIG. 7 can be adopted. That is, as shown in the schematic diagram of FIG. 7A, a long laminated body 125 (the one in which the second birefringent layer 13 is supported on the base material sheet 26) is prepared, and this and the laminated body 123 ( The second protective layer 15, the polarizer 11, the protective layer 14, and the first birefringent layer 12) are sent out in the directions of the arrows and pasted with an adhesive or the like (not shown) with their respective longitudinal directions aligned. Match. Finally, as shown in FIG.7 (b), the base material sheet 26 is peeled and the optical film 10 of this invention is obtained.

  According to the present invention, it is possible to bond the very thin first and second birefringent layers by so-called roll-to-roll, and the production efficiency can be remarkably improved.

  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.

  On the other hand, as shown in the perspective view of FIG. 4A, a long base material 16 is prepared, and a rubbing process is performed on one surface thereof by a rubbing roll 120. At this time, the rubbing direction is a direction having a predetermined angle with respect to the longitudinal direction of the substrate 16, for example, a direction of + 22 ° to + 26 ° or −22 ° to −26 °. Next, as shown in the perspective view of FIG. 4B, the first birefringent layer 12 is formed on the base material 16 subjected to the rubbing treatment as described in the section B-1. In the first birefringent layer 12, the liquid crystal material is aligned along the rubbing direction, so that the slow axis direction is substantially the same direction as the rubbing direction of the substrate 16 (arrow B direction).

  Next, the first birefringent layer 12 formed on the substrate 16 is aged at a temperature of (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) or higher for 0.5 hour or longer.

  As shown in the schematic diagram of FIG. 8A, a long transparent protective film (being a second protective layer) 15, a polarizer 11, and a long transparent protective film (being a protective layer) 14 Are sent in the direction of the arrows, and bonded together with an adhesive or the like (not shown) in a state in which the respective longitudinal directions are aligned to form a laminated body 124. Next, as shown in the schematic diagram of FIG. 8B, the laminated body 124, the first birefringent layer 12 and the laminated body 121 of the base material 16 are sent out in the direction of the arrows, and the respective longitudinal directions are aligned. A laminated body 123 ′ is formed by bonding with an adhesive or the like (not shown). Further, as shown in FIG. 5B, the substrate 16 is peeled from the laminate 123 ′, and the laminate 123 (the protective layer 15, the polarizer 11, the protective layer 14, and the first birefringent layer 12) is removed. Form.

  Next, as shown in the schematic diagram of FIG. 6, 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. Thus, the optical film 10 of the present invention is obtained.

  When a resin composition containing a polymerizable liquid crystal and a chiral agent is used as the second birefringent layer 13, a procedure as shown in FIG. 7 can be adopted. That is, as shown in the schematic diagram of FIG. 7A, a long laminated body 125 (the one in which the second birefringent layer 13 is supported on the base material sheet 26) is prepared, and this and the laminated body 123 ( The second protective layer 15, the polarizer 11, the protective layer 14, and the first birefringent layer 12) are sent out in the directions of the arrows and pasted with an adhesive or the like (not shown) with their respective longitudinal directions aligned. Match. Finally, as shown in FIG.7 (b), the base material sheet 26 is peeled and the optical film 10 of this invention is obtained.

B-6. Other components of optical film The optical film 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 optical film 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 other members (for example, liquid crystal cell) becomes easy, and peeling from other members of the optical film 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-3. 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 can be covered with any appropriate separator until the optical film is actually used to prevent contamination. 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 optical film of the present invention has been imparted with an ultraviolet absorbing ability by, for example, treatment with an ultraviolet absorbent such as a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may be a thing.

C. Use of optical film The optical film of the present invention can be suitably used for various image display devices (for example, liquid crystal display devices, self-luminous display devices). Specific examples of applicable image display devices include a liquid crystal display device, an EL display, a plasma display (PD), and a field emission display (FED). When the optical film of the present invention is used in a liquid crystal display device, it is useful for viewing angle compensation, for example. The optical film of the present invention is used in, for example, a circular polarization mode liquid crystal display device, and is used in a homogeneous alignment type TN liquid crystal display device, a horizontal electrode type (IPS) type liquid crystal display device, a vertical alignment (VA) type liquid crystal display device, and the like. It is particularly useful. Moreover, when using the optical film 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 optical film of the present invention described in the above items A and B. 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. 9, in the liquid crystal display device (liquid crystal panel) of the present invention, the optical film 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) Durability test The film (layer) to be tested was maintained at a temperature of 90 ° C. for 250 hours, and the durability was measured.

(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.

(5) Measurement of transmittance It measured by brand name "DOT-3" (made by Murakami Color Co., Ltd.).
Transmittance before the durability test: The elliptically polarizing plate before the durability test (configuration shown in FIG. 1) and the elliptically polarizing plate before the durability test (configuration shown in FIG. 1) are superposed so that the absorption axes of the polarizers are orthogonal to each other. The transmittance was measured.
Transmittance after durability test: The elliptically polarizing plate before the durability test (configuration shown in FIG. 1) and the elliptically polarizing plate after the durability test (configuration shown in FIG. 1) are overlapped so that the absorption axes of the polarizers are orthogonal to each other. The transmittance was measured.

(6) Measurement of liquid crystal transition temperature The liquid crystal transition temperature was measured using a heating device (manufactured by Japan Tech Co., Ltd., model name: LK-600PM) and a polarizing microscope (manufactured by NIKON Corp., model name: EC LIPSE E600POL).
[Examples 1 to 10]

a. Alignment treatment of substrate (preparation of alignment substrate)
An orientation substrate was produced by subjecting the substrate to an orientation treatment.
Substrates (1) to (6): On the surface of a polyethylene terephthalate (PET) film (thickness 50 μm), using a rubbing cloth, the surface of the PET film is rubbed at a rubbing angle shown in Table 1 below. Created.

b. Production of first birefringent layer Polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name Paliocolor LC242, liquid crystal transition temperature = 60 ° C.) 10 g, and photopolymerization initiator (Ciba Specialty Chemicals) for the polymerizable liquid crystal compound Company: 0.5 g of trade name Irgacure 907) was dissolved in 40 g of toluene to prepare a liquid crystal composition (liquid crystal coating solution). On the alignment base material (4) produced as described above, the liquid crystal coating liquid was applied with a bar coater, and then the liquid crystal was aligned by heating and drying at 90 ° C. for 2 minutes. The liquid crystal layer was irradiated with 300 mJ / cm ² of light using a high-pressure mercury lamp to cure the liquid crystal layer, thereby forming a first birefringent layer (0) on the substrate. The thickness and retardation of the first birefringent layer (0) were adjusted by changing the coating amount of the liquid crystal coating solution. The formed first birefringent layer (0) had a thickness of 2 μm and an in-plane retardation value Δnd of 247.7 nm.
Next, an aging treatment was performed on the first birefringent layer (0) under the aging treatment conditions shown in Table 2.
The first birefringent layers (1) to (10) after the aging treatment were subjected to a durability test at 90 ° C. × 250 hours. As shown in Table 2, (in-plane retardation value Δnd after durability test) − (in-plane retardation value Δnd before durability test) was calculated. The results are shown in Table 2.

〔実施例１１〜２０〕

[Examples 11 to 20]

c. Production of Second Birefringent Layer A polycarbonate film (thickness 60 μm) was uniaxially stretched 1.45 times in the lateral direction at 150 ° C. to produce a second birefringent layer film (a3). The obtained second birefringent layer film (a3) had an angle β (angle of slow axis with respect to the longitudinal direction of the film) of 90 °, a thickness of 50 μm, and a retardation value of 120 nm.

d. Production of Optical Film 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. Protective layer (triacetyl cellulose film (hereinafter sometimes referred to as TAC), thickness = 40 μm), first birefringent layers (1) to (10) and second birefringent layers after aging treatment (before durability test) The refractive layer (a3) was used. These polarizer, protective layer, first birefringent layer and second birefringent layer are laminated by the manufacturing procedure shown in FIGS. 3 to 7, and an optical film (elliptic polarizing plate) A01 as shown in FIG. -A10 was obtained. With respect to the optical films (elliptical polarizing plates) A01 to A10, the transmittance (%) before the durability test and the transmittance (%) after the durability test were measured. The results are shown in Table 3.

[Comparative Examples 1-5]
In Example 1, the first birefringent layer (C1) after the aging treatment was performed in the same manner as in Example 1 except that the aging treatment conditions for the first birefringent layer (0) were changed as shown in Table 4. To (C5).
With respect to the first birefringent layers (C1) to (C5) after the aging treatment, a durability test at 90 ° C. × 250 hours was performed. As shown in Table 4, (in-plane retardation value Δnd after durability test) − (in-plane retardation value Δnd before durability test) was calculated. The results are shown in Table 4.

[Comparative Examples 6 to 10]
As in Example 1, the protective layer (TAC, thickness = 40 μm), the first birefringent layers (C1) to (C5) and the second birefringent layer (a3) after the aging treatment (before the durability test) Using. These polarizer, protective layer, first birefringent layer and second birefringent layer are laminated by the manufacturing procedure shown in FIGS. 3 to 7, and an optical film (elliptical polarizing plate) B01 as shown in FIG. ~ B05 was obtained. For the optical films (elliptical polarizing plates) B01 to B05, the transmittance (%) before the durability test and the transmittance (%) after the durability test were measured. The results are shown in Table 5.

〔実施例２１〕

Example 21

  The contrast ratio was measured by overlaying the optical film A01. This optical film A01 had a relationship of β = 2α + 44 °. According to this optical film A01, the angle of contrast 10 was a minimum of 40 degrees, a maximum of 50 degrees, and a maximum and minimum difference of 10 degrees in all directions. 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.

  According to the manufacturing method of the present invention, when the first birefringent layer is formed, an aging process is performed under a specific condition, so that the phase difference value of the first birefringent layer is changed when mounted on an image display device. Can be reduced. As a result, good viewing angle characteristics can be maintained for a long time.

  According to the production method of the present invention, a long transparent protective film in which a first birefringent layer having a slow axis in an oblique direction is formed and a long polarizer are rolled to roll with the long sides thereof aligned. Thus, an optical film can be obtained with very high production efficiency.

An angle α formed between the absorption axis of the polarizer and the slow axis of the first birefringent layer, and an angle β formed between the absorption axis of the polarizer and the slow axis of the second birefringent layer are expressed as 2α + 40 ° <β. By optimizing in a relationship such as <2α + 50 °, the angle of contrast 10 can be set to a minimum of 40 degrees in all directions, and a practically preferable level can be secured. When the angles α and β did not satisfy the above relationship, the angle of contrast 10 was a minimum of 30 degrees in all directions.

  The optical film of the present invention is very thin. Therefore, it turns out that the optical film of this invention can contribute to thickness reduction of an image display apparatus.

  The optical film of the present invention has a significantly low light transmittance and little light leakage.

  In manufacturing the optical film of the present invention, the moisture resistance (high temperature durability) is remarkably improved by directly rubbing the surface of the transparent protective film.

  The optical film of the present invention can be suitably used for various image display devices (for example, liquid crystal display devices, self-luminous display devices).

It is a schematic sectional drawing of the optical film by preferable embodiment of this invention. 1 is an exploded perspective view of an optical film 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 optical film of this invention. It is a perspective view which shows the outline of another process in an example of the manufacturing method of the optical film of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the optical film of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the optical film of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the optical film of this invention. It is a schematic diagram which shows the outline of another process in an example of the manufacturing method of the optical film 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 Optical film 11 Polarizer 12 1st birefringent layer 13 2nd birefringent layer 14 1st protective layer 15 2nd protective layer 16 Base material 20 Liquid crystal cell 100 Liquid crystal panel

Claims (13)

A step of performing an orientation treatment on the surface of the substrate;
Applying a liquid crystal composition to the surface of the substrate that has undergone the alignment treatment;
Aligning the liquid crystal material in the liquid crystal composition according to the alignment direction of the substrate to form a first birefringent layer;
Transferring the first birefringent layer formed on the surface of the base material to the surface of the transparent protective film (T),
A method for producing an optical film, further comprising the step of aging the first birefringent layer at a temperature of (liquid crystal transition temperature of the liquid crystal material + 20 ° C.) or higher for 0.5 hour or longer before or after the transfer step. Laminating a polarizer on the surface of the transparent protective film (T);
Laminating a polymer film on the surface of the transferred first birefringent layer to form a second birefringent layer,
The polarizer and the first birefringent layer are disposed on opposite sides of each other via a transparent protective film (T),
When the angle between the absorption axis of the polarizer and the orientation direction of the first birefringent layer is α, and the angle between the absorption axis of the polarizer and the slow axis of the second birefringent layer is β, The manufacturing method of the optical film of Claim 1 with which angle (alpha) and (beta) have the relationship of following formula (1):
2α + 40 ° <β <2α + 50 ° (1).   The polarizer and the transparent protective film (T) are both long films, and in the lamination process of the polarizer, the long sides of the polarizer and the transparent protective film (T) are continuously bonded together. The manufacturing method according to claim 2.   The polymer film forming the second birefringent layer is a long film, and in the step of forming the second birefringent layer, the long sides of the first birefringent layer and the polymer film are The manufacturing method of Claim 2 or 3 bonded together continuously.   The manufacturing method according to any one of claims 2 to 4, wherein a direction of the alignment treatment is + 8 ° to + 38 ° or -8 ° to -38 ° with respect to an absorption axis of the polarizer.   The alignment process according to any one of claims 1 to 5, wherein the alignment process is at least one selected from the group consisting of a rubbing process, an oblique vapor deposition method, a stretching process, a photo alignment process, a magnetic field alignment process, and an electric field alignment process. The manufacturing method as described.   The production method according to claim 1, wherein the liquid crystal composition contains at least one of a liquid crystal monomer and a liquid crystal polymer.   8. The liquid crystal composition according to claim 1, wherein the liquid crystal composition includes a polymerizable monomer and / or a crosslinkable monomer, and the alignment step of the liquid crystal further includes performing a polymerization treatment and / or a crosslinking treatment. Production method.   The manufacturing method according to claim 1, wherein the first birefringent layer is a λ / 2 plate.   The manufacturing method according to claim 2, wherein the second birefringent layer is a λ / 4 plate.   The manufacturing method according to any one of claims 2 to 10, wherein the polymer film is a stretched film.   The optical film manufactured by the manufacturing method in any one of Claim 1-11. An image display device comprising the optical film according to claim 12.

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