JP4646236B2 - Method for producing polarizer and method for producing polarizing plate - Google Patents

Description

The present invention relates to a polarizer having a high transmittance and a high degree of polarization, and a method for producing a polarizing plate .

  An image display device such as a liquid crystal display device is widely used as a display used in various applications such as a mobile phone, a television, and a personal computer. With the widespread use of such liquid crystal display devices, the demand for polarizing plates for visualizing changes in the orientation of liquid crystals is increasing rapidly. The polarizing plate has a great influence on the display characteristics of the liquid crystal display device.

  Generally as a polarizing plate, what stuck the protective film through the adhesive layer on the both surfaces or single side | surface of the polarizer which has polarization ability is used. As the polarizer, generally used is a uniaxially stretched polyvinyl alcohol film or the like obtained by adsorbing and orienting a dichroic substance such as iodine or an organic dye. As the protective film, a triacetyl cellulose (TAC) film is suitably used because it is optically transparent and has a small birefringence.

  In recent years, liquid crystal display devices using this polarizing plate have been improved in performance, and in order to obtain high visibility, it is required to improve the contrast of the liquid crystal panel constituting the liquid crystal display device. That is, it is desired that black is displayed in black and white is displayed in white and bright, and accordingly, further improvement in optical characteristics is required for the polarizing plate. In other words, it is very important to have a high transmittance and a high degree of polarization as the optical performance of the polarizing plate.

Many methods have been proposed to obtain the polarizing plate as described above. For example, a polarizer obtained by uniaxially stretching a film using polyvinyl alcohol having a high degree of polymerization has been proposed (see Patent Document 1 and Patent Document 2). Moreover, a polarizer formed by uniaxially stretching a film using polyvinyl alcohol having a syndiotacticity of 45 mol% or more and less than 50 mol% and a polymerization degree of 1000 to 30000 has been proposed (see Patent Document 3). Moreover, the method of performing two-stage extending | stretching during the process process in the boron compound of a polyvinyl alcohol-type film is proposed (refer patent document 4). In addition, a method has been proposed in which two-stage stretching is performed so that the draw ratio in the dyeing process of the polyvinyl alcohol film or in the previous process and the draw ratio in the boron compound treatment process have a specific relationship (patent) Reference 5). Furthermore, in addition to the proposal of two-stage stretching, a method of making the bath temperature of the first bath higher than the bath temperature of the second bath has been proposed (see Patent Document 6).
Japanese Patent No. 2543748 Japanese Patent No. 2631403 Japanese Patent No. 3317494 Japanese Patent No. 2512408 Japanese Patent No. 3392196 JP 2003-240945 A

  Among the above methods, a method using polyvinyl alcohol having a high degree of polymerization is most effective for improving optical properties, but in a method using polyvinyl alcohol having a high degree of polymerization and polyvinyl alcohol having tacticity, Since the solution before film formation is unstable when left at room temperature or uniform film formation is difficult, it is not practical. Although a method of performing two-stage stretching in a boron compound is also effective, there is a limit in improving optical characteristics as compared with a commonly used polarizer.

  The present invention has been made to solve such problems of the prior art, and it is an object of the present invention to provide a practical production method of a polarizer and a polarizing plate having high transmittance and high degree of polarization. To do.

  As a result of intensive studies, the inventors of the present invention have found that the above problems can be solved by irradiating the polyvinyl alcohol film after the dyeing treatment step and the uniaxial stretching treatment step with an electron beam. It came to be completed.

That is, the present invention is to provide a polyvinyl alcohol film, a dyeing process, and the manufacturing method of the polarizer is subjected at least uniaxial stretching process steps performed by immersion in an iodine solution, the dyeing process and the An object of the present invention is to provide a method for producing a polarizer, further comprising an electron beam irradiation step of irradiating an electron beam to the polyvinyl alcohol film after the uniaxial stretching treatment step.

  According to such an invention, by irradiating the polyvinyl alcohol film after the dyeing treatment step and the uniaxial stretching treatment step with an electron beam, the stress of the uniaxially oriented polyvinyl alcohol film is alleviated and the orientation is disturbed. Therefore, the polarizer manufactured thereby can satisfy both high transmittance and high degree of polarization.

  Preferably, the electron beam irradiation amount in the electron beam irradiation step is 10 to 500 kGy, more preferably 20 to 100 kGy, and further preferably 40 to 80 kGy. This is because when the electron beam irradiation amount is less than 10 kGy, the electron beam is attenuated when passing through the polyvinyl alcohol film and the optical properties (transmittance / polarization degree) of the polarizer are poorly improved, while 500 kGy is reduced. This is because if it exceeds, the film may collapse or the hue may change.

  Preferably, the moisture content of the polyvinyl alcohol film when irradiating the electron beam in the electron beam irradiation step is 5 to 50% by weight, more preferably 10 to 40% by weight. If the moisture content is less than 5% by weight, the physical strength of the film is weakened, making it difficult to transport, or the film is cut when irradiated with an electron beam, or polarized light obtained by laminating a transparent protective film. This is because the appearance characteristics of the plate may be deteriorated. On the other hand, if the moisture content exceeds 50% by weight, moisture remains on the polarizing plate obtained by laminating the transparent protective film, which may lead to deterioration of the optical properties of the polarizing plate.

  Moreover, this invention is provided also as a manufacturing method of the polarizing plate characterized by including the process of providing a transparent protective layer in the at least single side | surface of the polarizer manufactured by the said manufacturing method. In other words, in this production method, the polyvinyl alcohol film is irradiated with an electron beam after the dyeing treatment step and the uniaxial stretching treatment step and before the step of providing the transparent protective layer.

  According to the present invention, a polarizer and a polarizing plate having a high transmittance and a high degree of polarization can be produced. By using this polarizer or polarizing plate in an image display device, an optical film in which a retardation plate, a reflecting plate, a transflective plate, a visual compensation film, a brightness enhancement film, etc. is further laminated on this polarizing plate, etc. By using the image display device, the optical characteristics of the image display device can be improved. In particular, when applied to a liquid crystal display device, the contrast of the liquid crystal panel is improved, and the luminance with the same amount of power is greatly improved because of the high transmittance. Alternatively, if the luminance is set to the same level as before, power consumption can be suppressed.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing each step in a method for producing a polarizing plate according to an embodiment of the present invention.
As shown in FIG. 1, a polyvinyl alcohol film is used in the method for manufacturing a polarizing plate according to this embodiment. Polyvinyl alcohol or a derivative thereof is used as the material for the polyvinyl alcohol film. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal, etc., olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, alkyl esters thereof, acrylamide, etc. Is mentioned. Polyvinyl alcohol having a polymerization degree of about 1000 to 10000 and a saponification degree of about 80 to 100 mol% is generally used.

  The polyvinyl alcohol film may contain an additive such as a plasticizer. Examples of the plasticizer include polyols and condensates thereof, and examples include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the polyvinyl alcohol film.

  The polyvinyl alcohol film (unstretched film) is subjected to at least a dyeing process step (S2 in FIG. 1) and a uniaxial stretching process step (S3 in FIG. 1) according to a conventional method. An electron beam irradiation step (FIG. 1) for irradiating the polyvinyl alcohol film after the treatment step and the uniaxial stretching treatment step (preferably before the transparent protective layer formation step (S8 in FIG. 1)). 1 S7).

  Hereinafter, each process S1-S8 shown in FIG. 1 is demonstrated sequentially.

  As shown in FIG. 1, first, the polyvinyl alcohol film is subjected to a swelling treatment step (S1 in FIG. 1) as necessary. The swelling treatment is performed by immersing the polyvinyl alcohol-based film in a bath solution, and the film is swollen so that an effect of preventing unevenness such as uneven coloring can be obtained. In addition, as a bath liquid used for the swelling treatment, water such as pure water is generally used, but a solution containing an additive such as an iodide or a crosslinking agent may be used.

  Next, the dyeing process (S2 in FIG. 1) is performed on the polyvinyl alcohol film. The dyeing treatment is generally performed by immersing the film in an iodine solution. In the iodine aqueous solution used as the iodine solution, in addition to iodine, an aqueous solution containing iodine ions with, for example, potassium iodide or the like is used as a dissolution aid.

  The iodine concentration of the iodine solution is preferably about 0.01 to 1% by weight, more preferably 0.02 to 0.5% by weight. The potassium iodide concentration is preferably about 0.01 to 10% by weight, more preferably 0.02 to 8% by weight. Moreover, the temperature of an iodine solution shall be about 20-50 degreeC normally, Preferably it shall be 25-40 degreeC. The immersion time of the film is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  Next, a uniaxial stretching treatment step (S3 in FIG. 1) is performed on the polyvinyl alcohol film subjected to the dyeing treatment. The stretching method in the uniaxial stretching process is not particularly limited, and either a wet stretching method or a dry stretching method can be employed. Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In the dry stretching method, the unstretched film is usually heated. Examples of the wet stretching method include an inter-roll stretching method in an aqueous solution after stretching a film. Stretching can be performed in multiple stages. As an unstretched film, a film with a thickness of about 30 to 150 μm is usually used. The stretch ratio of the stretched film can be appropriately set according to the purpose, but the total stretch ratio is preferably about 2 to 7 times, more preferably 3 to 6.5 times, and still more preferably 3.5 to 6 times. It is said. The thickness of the stretched film is preferably about 5 to 40 μm.

  In addition, although this embodiment demonstrated the aspect which performs a uniaxial extending | stretching process after a dyeing | staining process, this invention is not limited to this, A uniaxial extending | stretching process is before a dyeing process, during a dyeing process, after a dyeing process. It may be carried out at any stage. In addition, the uniaxial stretching treatment can be performed in a plurality of steps, and for example, it can be performed in a two-stage or three-stage process before the dyeing process, during the dyeing process, and after the dyeing process.

  Next, an immobilization (crosslinking) treatment step (S3 in FIG. 1) is performed on the polyvinyl alcohol film subjected to the uniaxial stretching treatment. The immobilization treatment is performed by immersing the film in an aqueous boric acid solution. The boric acid concentration in the boric acid aqueous solution is preferably about 2 to 15% by weight, more preferably 3 to 10% by weight. The boric acid aqueous solution may contain potassium ions and iodine ions with potassium iodide. The potassium iodide concentration in the boric acid aqueous solution is preferably about 0.5 to 10% by weight, more preferably 1 to 8% by weight. If a boric acid aqueous solution containing potassium iodide is used, a lightly colored polarizer, that is, a so-called neutral gray polarizer having a substantially constant absorbance over almost the entire wavelength range of visible light can be obtained.

  The temperature of the boric acid aqueous solution is preferably 30 ° C or higher, more preferably 40 to 85 ° C. The immersion time of the film is usually 1 to 1200 seconds, preferably 10 to 600 seconds, more preferably about 20 to 500 seconds. In addition, although this embodiment demonstrated the aspect which performs an immobilization process process after a uniaxial stretching process process, this invention is not restricted to this, If it is after a dyeing process, it will fix | immobilize during a uniaxial stretching process. Processing may be performed. Further, the immobilization process may be performed a plurality of times.

  Next, the washing process (S5 in FIG. 1) is performed on the polyvinyl alcohol film subjected to the immobilization treatment. The washing step can be performed using water, for example. This water washing step is usually performed by immersing a polyvinyl alcohol film in pure water. The water washing temperature is usually 5 to 50 ° C, preferably 10 to 45 ° C, and more preferably 15 to 40 ° C. The immersion time of the film is usually 10 to 300 seconds, preferably about 20 to 240 seconds.

  In the cleaning process, iodine ion treatment with potassium iodide or the like can be performed. For the iodine ion treatment, for example, an aqueous solution containing iodine ions with potassium iodide or the like is used. The potassium iodide concentration is preferably about 0.5 to 10% by weight, more preferably 1 to 8% by weight. The temperature of the aqueous solution is usually about 15 to 60 ° C, preferably 25 to 40 ° C. The immersion time of the film is usually about 1 to 120 seconds, preferably 3 to 90 seconds. In addition, there is no restriction | limiting in particular if the stage of an iodine ion process is before the drying process mentioned later. The iodine ion treatment can be performed in combination with water washing, and can be performed before or after water washing. In the washing step, a solution containing a metal salt such as boric acid or zinc salt in addition to the potassium iodide can be used.

  Next, a drying process (S6 in FIG. 1) is performed on the polyvinyl alcohol film subjected to the cleaning process. A drying process is 20-75 degreeC normally, Preferably it is 25-70 degreeC, and is performed by making it dry about 1 to 5 minutes. This drying step can be carried out under conditions where film deformation does not occur and the hue does not change significantly. Further, as will be described later, it also serves to adjust the moisture content of the film in the electron beam irradiation step.

  Furthermore, the electron beam irradiation process (S7 of FIG. 1) is performed to the polyvinyl alcohol-type film which performed the drying process. Electron beam irradiation is performed by arranging an electron beam irradiation device in the film conveyance path and directly irradiating the film with an electron beam. The electron beam irradiation amount is preferably 10 to 500 kGy, more preferably 20 to 100 kGy, and still more preferably 40 to 80 kGy. This is because when the electron beam irradiation amount is less than 10 kGy, the electron beam is attenuated when passing through the polyvinyl alcohol film and the optical properties (transmittance / polarization degree) of the polarizer are poorly improved, while 500 kGy is reduced. This is because if it exceeds, the film may collapse or the hue may change.

  Moreover, the moisture content of the polyvinyl alcohol-type film at the time of irradiating an electron beam in an electron beam irradiation process becomes like this. Preferably it is 5 to 50 weight%, More preferably, it is 10 to 40 weight%. If the moisture content is less than 5% by weight, the physical strength of the film is weakened, making it difficult to transport, or the film is cut when irradiated with an electron beam, or polarized light obtained by laminating a transparent protective film. This is because the appearance characteristics of the plate may be deteriorated. On the other hand, if the moisture content exceeds 50% by weight, moisture remains on the polarizing plate obtained by laminating the transparent protective film, which may lead to deterioration of the optical properties of the polarizing plate.

  A polarizer is manufactured by performing each process S1-S7 demonstrated above.

  Next, a polarizing plate is manufactured by performing the transparent protective layer formation process (S8 of FIG. 1) to the polarizer manufactured as mentioned above. In the transparent protective layer forming step, a transparent protective layer is provided on at least one surface of the polarizer. The transparent protective layer can be provided as a coating layer made of a polymer or as a laminate layer with a film attached thereto. As the polymer or film material forming the transparent protective layer, an appropriate transparent material can be used, but those having excellent transparency, mechanical strength, thermal stability, moisture barrier property, and the like are preferably used. Hereinafter, the transparent protective film provided as a laminate layer will be mainly described.

  Examples of the material for forming the transparent protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as cellulose diacetate and cellulose triacetate (triacetyl cellulose), and acrylic polymers such as polymethyl methacrylate. And styrene polymers such as polystyrene and acrylonitrile / styrene copolymer (AS resin), polycarbonate polymers, and the like.

  In addition, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like can also be mentioned as examples of the polymer forming the transparent protective film.

  The transparent protective film can also be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylic urethane, epoxy, or silicone.

  Further, a polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a substitution in the side chain And / or a resin composition containing unsubstituted phenyl and a thermoplastic resin having a nitrile group. Specific examples include a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. And the film which consists of mixed extrusion products etc. of these resin compositions can be used as a transparent protective film. Since these films have a small phase difference and a small photoelastic coefficient, problems such as unevenness due to distortion of the polarizing plate can be solved. Moreover, since moisture permeability is small, it is excellent in humidification durability.

  The thickness of the transparent protective film may be appropriately determined, but is generally about 1 to 500 μm from the viewpoints of workability such as strength and handleability, and thin layer properties. More preferably, it is 1-300 micrometers, More preferably, it is 5-200 micrometers.

  Moreover, it is preferable that a transparent protective film has as little color as possible. Therefore, Rth = (nx−nz) · d (where nx is the refractive index in the slow axis direction in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a direction retardation value of −90 nm to +75 nm is preferably used. By using a film having such a thickness direction retardation value Rth of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and further preferably −70 nm to +45 nm.

  As the transparent protective film, a cellulose-based polymer such as triacetyl cellulose is preferably used from the viewpoints of polarization characteristics and durability. In particular, a triacetyl cellulose film is suitable. On the other hand, the transparent protective film such as triacetylcellulose has a large retardation value Rth in the thickness direction and is slightly problematic in coloring. However, an alternating copolymer composed of isoprene and N-methylmaleimide and an acrylonitrile / styrene copolymer As the resin composition containing, those having a thickness direction retardation value Rth of 30 nm or less can be used, and coloring can be almost eliminated.

  In addition, when providing a transparent protective film on both surfaces of a polarizer, the film which consists of the same polymer material may be used as each transparent protective film, and the film which consists of a different polymer material may be used.

  It is also possible to provide a hard coat layer, an antireflection layer, an antisticking layer, or a diffusion or antiglare layer on the surface of the transparent protective film where the polarizer is not adhered.

  The hard coat layer is provided for the purpose of preventing scratches on the surface of the polarizing plate. For example, the hard coat layer is transparent with a cured film excellent in hardness, sliding properties, etc., by an appropriate ultraviolet curable resin such as acrylic or silicone. It can be formed by a method of adding to the surface of the protective film.

  The antireflection layer is provided for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be formed of an antireflection film or the like according to the related art. The anti-sticking layer is provided for the purpose of preventing adhesion with an adjacent layer.

  The anti-glare layer is provided for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering viewing of the light transmitted through the polarizing plate. The antiglare layer can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a roughening method by a sandblasting method or an embossing method, or a blending method of transparent fine particles. Examples of the fine particles to be included for forming the surface fine concavo-convex structure include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be electrically conductive and organic fine particles made of a crosslinked or uncrosslinked polymer are used. In the case of forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, with respect to 100 parts by weight of the transparent resin forming the surface fine uneven structure. Is done. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle.

  The antireflection layer, antisticking layer, diffusion layer, and antiglare layer can be provided on the transparent protective film itself, or can be provided as an optical layer separate from the transparent protective film.

  An adhesive is used for the adhesion treatment when the polarizer and the transparent protective film are bonded together. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl adhesives, latex adhesives, and water-based polyesters. The said adhesive agent is normally used as an adhesive agent which consists of aqueous solution, and contains 0.5 to 60 weight% of solid content normally. The adhesive can contain a crosslinking agent. Moreover, it is also possible to mix | blend another additive and catalysts, such as an acid. As the adhesive, a polyvinyl alcohol-based adhesive having good adhesiveness with a polyvinyl alcohol-based film is suitable. As a crosslinking agent suitable for the polyvinyl alcohol-based adhesive, boric acid, borax, glutaraldehyde, melamine, oxalic acid and the like can be used.

  The adhesive may be applied to either the transparent protective film or the polarizer, or to both. After bonding a polarizer and a transparent protective film, a drying process is given and the contact bonding layer which consists of an application | coating drying layer is formed. Bonding of a polarizer and a transparent protective film can be performed with a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is usually about 1 to 500 nm, preferably 10 to 300 nm, and more preferably 20 to 100 nm.

  The polarizing plate or the polarizer produced as described above can be used as an optical film laminated with another optical layer in practical use. The optical layer to be laminated is not particularly limited. For example, formation of a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including a half-wave plate and a quarter-wave plate), a viewing angle compensation film, and the like. One optical layer or two or more optical layers may be used. In particular, a reflective polarizing plate (or transflective polarizing plate) in which a reflective plate (or semi-transmissive reflective plate) is laminated on a polarizing plate according to this embodiment, and a retardation plate is laminated on the polarizing plate according to this embodiment. An elliptically polarizing plate or circularly polarizing plate, a wide viewing angle polarizing plate in which a viewing angle compensation film is laminated on the polarizing plate according to this embodiment, or a polarizing plate in which a brightness enhancement film is laminated on the polarizing plate according to this embodiment. It is suitably used as an optical film.

  The reflective polarizing plate is a polarizing plate provided with a reflective plate (reflective layer) for forming a liquid crystal display device or the like of a type that reflects incident light from the viewing side (display side). In addition, there is an advantage that a built-in light source such as a backlight can be omitted and the liquid crystal display device can be easily thinned. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing plate via a transparent protective layer or the like, if necessary.

  The transflective polarizing plate can be formed by using the above reflective layer as a transflective reflective layer such as a half mirror that reflects and transmits light. The transflective polarizing plate is usually provided on the back side of the liquid crystal cell. When a liquid crystal display device is used in a relatively bright environment, the incident light from the viewing side (display side) is reflected to display an image. On the other hand, when used in a relatively dark environment, it is possible to form a liquid crystal display device that displays an image using a light source such as a backlight built in the back side of the transflective polarizing plate. is there. In other words, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright environment, and can be used with a built-in light source in a relatively dark environment. Useful for formation.

  The retardation plate is used when changing linearly polarized light into elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light into linearly polarized light, or changing the plane of polarization of linearly polarized light. In particular, a so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light to circularly polarized light or changes circularly polarized light to linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is usually used when changing the polarization plane of linearly polarized light.

  The elliptical polarizing plate is effective when compensating for (preventing) coloring (blue or yellow) caused by birefringence in the liquid crystal layer of a super twist nematic (STN) type liquid crystal display device, and displaying black and white without the color. Used for. Further, the one having a controlled three-dimensional refractive index is preferable in that it can compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. The circularly polarizing plate is used effectively, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which the image is displayed in color, and also has an antireflection function.

  Specific examples of the retardation plate to be laminated include a birefringent film obtained by stretching a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, and polyamide. , A liquid crystal polymer alignment film, a liquid crystal polymer alignment layer supported by a film, and the like. The retardation plate may have an appropriate retardation according to the purpose of use, for example, for the purpose of compensating for various wavelength plates or birefringence of liquid crystal layers, compensation for viewing angle, and the like. These retardation plates may be stacked to control optical characteristics such as retardation.

  The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction rather than perpendicular to the screen. Examples of such viewing angle compensation films include alignment films such as retardation films and liquid crystal polymers, and films in which an alignment layer such as a liquid crystal polymer is supported on a transparent substrate. A normal retardation film uses a birefringent polymer film uniaxially stretched in the plane direction, whereas a retardation film used as a viewing angle compensation film stretches biaxially in the plane direction. Birefringence films such as polymer films having a birefringence, biaxially stretched films such as a polymer film having a birefringence with a controlled refractive index in the thickness direction and uniaxially stretched in the plane direction and also in the thickness direction Etc. are used. Examples of the inclined alignment film include a film obtained by bonding a heat-shrink film to a polymer film and stretching or / and contracting the polymer film under the action of the contraction force by heating, or a film obtained by obliquely aligning a liquid crystal polymer. Is mentioned. The raw material polymer of the retardation plate used as the viewing angle compensation film is the same as the polymer described for the conventional retardation plate, and prevents coloring and the like due to a change in viewing angle based on the retardation by the liquid crystal cell. In addition, an appropriate one for the purpose of, for example, widening the viewing angle for good visual recognition can be used.

  In addition, from the viewpoint of achieving a wide viewing angle with good visibility, an optically compensated phase difference plate in which an alignment layer of a liquid crystal polymer, particularly an optically anisotropic layer composed of a tilted alignment layer of a discotic liquid crystal polymer, is supported by a triacetyl cellulose film. Can be preferably used.

  The polarizing plate obtained by bonding the polarizing plate according to this embodiment and the brightness enhancement film is usually provided on the back side of the liquid crystal cell. The brightness enhancement film has a characteristic of reflecting linearly polarized light with a predetermined polarization axis or circularly polarized light in a predetermined direction and transmitting other light when natural light is incident on the backlight of a liquid crystal display device or the like or reflected from the back side. It is. A polarizing plate obtained by laminating such a brightness enhancement film with the polarizing plate according to the present embodiment obtains transmitted light in a predetermined polarization state when light from a light source such as a backlight is incident, and light other than the predetermined polarization state. Is reflected without transmitting. If the light reflected on the surface of the brightness enhancement film is further inverted through a reflective layer or the like provided on the back side of the light and re-incident on the surface of the brightness enhancement film, a part or all of the light is converted into light having a predetermined polarization state. In order to transmit light, the amount of light transmitted through the polarizing plate can be increased, and the amount of light that can be used for liquid crystal display image display and the like can be increased by supplying polarized light that is not easily absorbed by the polarizer, thereby improving the luminance. Is possible.

  The optical film in which the various optical layers described above are laminated on the polarizing plate can be formed by a method of sequentially laminating them separately in the manufacturing process of a liquid crystal display device or the like. In addition, since it is excellent in quality stability and assembly work, there is an advantage that it is possible to improve the manufacturing efficiency of a liquid crystal display device or the like. In addition, suitable adhesion | attachment means, such as an adhesion layer, can be used for lamination | stacking. When adhering a polarizing plate and other optical layers, their optical axes may be arranged at an appropriate angle in accordance with the target phase difference characteristics.

  An adhesive layer for adhering to other members such as a liquid crystal cell can also be provided on the polarizing plate according to this embodiment or an optical film in which at least one polarizing plate is laminated. Although it does not restrict | limit especially as an adhesive which forms an adhesion layer, For example, what uses polymers, such as an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, a fluorine type, and a rubber type, as a base polymer suitably Can be selected and used. In particular, like acrylic pressure-sensitive adhesives, those excellent in optical transparency, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties and excellent in weather resistance, heat resistance and the like are preferably used.

  In addition to the above, prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion differences, prevention of warpage of liquid crystal cells, and formation of a liquid crystal display device with high quality and excellent durability. It is more preferable to use an adhesive layer having a low moisture absorption rate and excellent heat resistance.

  The adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, a filler or pigment made of glass fiber, glass beads, metal powder, other inorganic powders, a colorant, an antioxidant, and the like. The additive added to the adhesion layer, such as, may be contained. Moreover, the adhesion layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.

  Attachment of the adhesive layer to one or both sides of the polarizing plate or the optical film can be performed by an appropriate method. For example, a 10 to 40% by weight mild pressure-sensitive adhesive solution in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of an appropriate solvent alone or a mixture such as toluene and ethyl acetate is prepared and run. An adhesive layer is formed on a separator according to the above-described method of directly attaching on a polarizing plate or an optical film by an appropriate development method such as a drawing method or a coating method, and this is formed on a polarizing plate or an optical film. The method of transfer is mentioned.

  The pressure-sensitive adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as a superimposed layer of pressure-sensitive adhesive layers having different compositions, types and thicknesses. Moreover, when providing in both surfaces, it can also be set as the adhesion layer of a different composition, a kind, and thickness by the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm.

  A separator may be temporarily attached to the exposed surface of the adhesive layer for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, for example, an appropriate thin leaf body such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foamed sheet, metal foil, and a laminate thereof, if necessary, silicone-based, long mirror alkyl-based, Appropriate materials according to the prior art, such as those coated with an appropriate release agent such as fluorine-based and molybdenum sulfide, can be used.

  In addition, each layer such as a polarizer, a transparent protective film, an optical film, and an adhesive layer forming a polarizing plate is, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. Ultraviolet absorbing ability may be provided by a method of treating with an ultraviolet absorber such as.

  The polarizer, polarizing plate or optical film described above can be preferably used for forming various image display devices such as a liquid crystal display device. The liquid crystal display device can be formed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling a liquid crystal cell, a polarizer, a polarizing plate or an optical film, and components such as an illumination system as necessary, and incorporating a drive circuit. However, there is no particular limitation except that the polarizer, the polarizing plate or the optical film according to this embodiment is used, and the film may be formed by a method according to a conventional method. As the liquid crystal cell, for example, any type of liquid crystal cell such as a TN type, an STN type, or a π type can be used.

  Appropriate liquid crystal display devices such as a liquid crystal display device in which the polarizer, polarizing plate or optical film according to the present embodiment is arranged on one side or both sides of the liquid crystal cell, and a backlight or reflector as an illumination system. Can be formed. When providing a polarizer, a polarizing plate or an optical film on both sides of a liquid crystal cell, these may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer of an appropriate part such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight at an appropriate position. Alternatively, two or more layers can be arranged.

  In addition, the polarizer, the polarizing plate, or the optical film according to the present embodiment can be used for an organic electroluminescence device (organic EL display device) as an image display device. In general, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Alternatively, there are known configurations having various combinations such as a laminate of such a light-emitting layer and an electron injection layer made of a perylene derivative, and further a laminate of these hole injection layer, light-emitting layer, and electron injection layer. It has been.

  In the organic EL display device configured as described above, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely, like the transparent electrode. As a result, the light that is incident from the surface of the transparent substrate when not emitting light, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is emitted again to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.

  In an organic EL display device including an organic electroluminescent light emitter having a transparent electrode on the surface side of an organic light emitting layer that emits light by applying a voltage and a metal electrode on the back surface side of the organic light emitting layer, the surface side of the transparent electrode In addition to providing the polarizing plate according to the present embodiment, a retardation plate can be provided between the transparent electrode and the polarizing plate.

  Since the retardation plate and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, an effect of preventing the mirror surface of the metal electrode from being visually recognized by this polarization action is obtained. In particular, the mirror surface of the metal electrode can be completely shielded by configuring the retardation plate with a quarter-wave plate and adjusting the angle formed by the polarization direction of the polarizing plate and the retardation plate to π / 4. .

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

<Example>
A 75 μm thick polyvinyl alcohol (PVA) film (average polymerization degree 2400, saponification degree 99.7 mol%) was dyed and stretched between rolls having different speed ratios. Specifically, the PVA film is immersed and dyed in an aqueous iodine solution at 30 ° C. and stretched three times in the film conveying direction, and then the boric acid concentration at 60 ° C. is 4% by weight and the potassium iodide concentration is 5% by weight. While dipping and fixing the PVA film in an aqueous boric acid solution, the film was stretched to a total draw ratio of 6 times, and finally the PVA film was immersed in an aqueous potassium iodide solution having a potassium iodide concentration of 2% by weight at 30 ° C. for several seconds. Washed.

  The stretched film obtained as described above was dried at 60 ° C. for 2 minutes, and then the stretched film was irradiated with an electron beam at an irradiation amount of 80 kGy by an electron beam irradiation apparatus. As the electron beam irradiation device, an electron beam irradiation device (Electrobeam CEC110 / 30/20 mA) manufactured by Iwasaki Electric Co., Ltd. was used. The moisture content of the stretched film when irradiated with an electron beam was adjusted to 25% by weight.

  Next, a transparent protective film was bonded to both surfaces of the stretched film using a polyvinyl alcohol-based adhesive, and dried at 60 ° C. for 4 minutes to prepare a polarizing plate.

  Here, the initial value of the iodine concentration in the aqueous iodine solution used for the dyeing treatment is adjusted to 0.02% by weight (corresponding to the single transmittance of the polarizing plate of 44 to 45%), while a certain amount of iodine is added every one minute. Was added stepwise to increase the iodine concentration to 0.05% by weight, and the dyeing treatment was performed at different iodine concentrations for each predetermined portion in the transport direction of the PVA film. As a result, polarizing plates having different single transmittances for each of the predetermined portions are produced.

<Comparative example>
A polarizing plate was produced by the same method as in the example except that the electron beam irradiation was not performed.

<Evaluation>
The polarizing plate produced by the Example and the comparative example was cut out for every said predetermined site | part, and the optical characteristic (single transmittance | permeability, polarization degree) of each cut-out polarizing plate was measured with the following method.

(Single transmittance)
This is a Y value measured using a spectrophotometer (DOT-3, manufactured by Murakami Color Research Laboratory) and corrected for visibility by a 2 degree viewing angle (C light source) of JIS Z 8701.

(Degree of polarization)
The transmittance H ₀ when two polarizing plates cut out from the same part are superposed so that their polarization axes are parallel to each other, and the transmittance H ₉₀ when superposed so as to be orthogonal to each other are described above. The degree of polarization (crossed Nicol polarization degree) was determined by the following equation (1). The transmittance H ₀ when superimposed so as to be parallel to each other and the transmittance H ₉₀ when superimposed so as to be orthogonal to each other are Y values obtained by performing visibility correction.
Polarization degree (%) = {(H ₀ −H ₉₀ ) / (H ₀ + H ₉₀ )} ^1/2 × 100 (1)

  FIG. 2 is a graph showing the measurement results of the polarizing plates produced according to the examples and comparative examples. In FIG. 2, the horizontal axis indicates the single transmittance, and the vertical axis indicates the degree of polarization. With respect to the polarizing plate at the site subjected to the dyeing treatment with the same iodine concentration, the optical characteristics changed as indicated by arrows in FIG. 2 by irradiation with the electron beam. And especially about the polarizing plate with a single transmittance of 43.50 to 44.00 (%), the result that the degree of polarization increased by 0.03% or more by electron beam irradiation was obtained.

FIG. 1 is a block diagram schematically showing each step in a method for producing a polarizing plate according to an embodiment of the present invention. FIG. 2 is a graph showing an example of the results of evaluating the optical characteristics of polarizing plates prepared according to examples and comparative examples of the present invention.

Explanation of symbols

S1 ... Swelling treatment step S2 ... Dyeing treatment step S3 ... Uniaxial stretching treatment step S4 ... Immobilization treatment step S5 ... Washing step S6 ... Drying step S7 ... Electron beam irradiation step S8 ... Transparent protective layer forming step 20 ... Supporting part

Claims (4)

A polyvinyl alcohol film, a dyeing process performed by immersing in an iodine solution , and a method for producing a polarizer that performs at least a uniaxial stretching process,
A method for producing a polarizer, further comprising an electron beam irradiation step of irradiating an electron beam to the polyvinyl alcohol film after the dyeing treatment step and the uniaxial stretching treatment step.   The method for producing a polarizer according to claim 1, wherein an electron beam irradiation amount in the electron beam irradiation step is 10 to 500 kGy.   3. The method for producing a polarizer according to claim 1, wherein the polyvinyl alcohol film has a moisture content of 5 to 50% by weight when the electron beam is irradiated in the electron beam irradiation step.   A method for producing a polarizing plate, comprising a step of providing a transparent protective layer on at least one surface of a polarizer produced by the production method according to claim 1.

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