JP4651054B2 - Manufacturing method of polarizer and wet stretching apparatus used therefor - Google Patents

Description

  The present invention relates to a method for manufacturing a polarizer. The obtained polarizer is used for a polarizing plate and an optical film, and further, the polarizing plate and the optical film are used for an image display device such as a liquid crystal display device, an organic EL display device, and a PDP. Furthermore, it is related with the wet extending | stretching apparatus which has a processing bath used for the wet extending | stretching process in the manufacturing method of a polarizer.

  Liquid crystal display devices (LCD) are used in personal computers, TVs, monitors, mobile phones, PDAs, and the like, and in recent years, colorization, reflection colorization, high definition, and high brightness are rapidly progressing. In order to improve the display quality such as the expansion of LCD applications, high definition, and high brightness, the optical properties of polarizing plates used in LCDs are improved (improvement of transmittance and polarization degree). It is necessary.

  Conventionally, as a polarizer used for a liquid crystal display device or the like, a dyed polyvinyl alcohol film has been used because it has both high transmittance and degree of polarization. Moreover, the said polarizer is normally used as a polarizing plate by which the protective film was bonded on the single side | surface or both surfaces. In recent years, liquid crystal display devices are required to have high performance, and polarizers are required to have higher transmittance and degree of polarization, and various methods for manufacturing polarizers that meet these requirements have been proposed. .

  As a method for improving the optical characteristics of a polarizer, there is a method of stretching a polyvinyl alcohol film at a high magnification in the manufacturing process of the polarizer. However, when a polyvinyl alcohol film is stretched at a high magnification, there is a high possibility that a so-called “stretch break” occurs in the film during stretching, which is not preferable in terms of productivity. Moreover, there is a method of stretching a polyvinyl alcohol film in two or more stages. However, if the stretch ratio in the second stage and thereafter is increased, “stretch break” is likely to occur, and a polarizer having a high degree of polarization cannot be obtained stably.

  An object of this invention is to provide the method which can manufacture stably the polarizer which consists of a polyvinyl-alcohol-type film of a high draw ratio. Furthermore, this invention relates to the wet extending | stretching apparatus which has a processing bath used for the wet extending | stretching process in the manufacturing method of a polarizer.

  As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by a method for producing a polarizer shown below, and have completed the present invention.

That is, the present invention provides a method for producing a polarizer in which a polyvinyl alcohol film is subjected to at least a stretching treatment step, a dyeing treatment step, and a boron compound treatment step.
The stretching process is performed at least twice so that the total stretching ratio is 5.5 times or more, and in the second and subsequent stretching processes, stretching with a stretching ratio of 1.2 times or more is performed between the first pinch roll and the second pinch roll. Performed by wet stretching using the difference in peripheral speed of pinch rolls,
In the wet stretching process, the film conveyed from the first pinch roll is the first guide roll that comes into contact with the first guide roll before and after the film conveyed from the first guide roll passes through the first guide roll. When the holding angle (A) is an angle formed through the first guide roll, the first guide roll is passed so as to form a holding angle (A) of 140 to 175 °. Method.

  In the said invention, the extending | stretching process whose total draw ratio is 5.5 times or more is performed in at least two steps. As a result, a high draw ratio is ensured and high performance of the optical characteristics can be achieved. The total draw ratio is preferably 5.7 times or more, and more preferably 6.1 times or more. If the total draw ratio becomes too large, it becomes easy to cause stretch breakage. Therefore, the total draw ratio is preferably 7 times or less. In the second and subsequent stretching, the stretching is performed by wet treatment so that the total stretching ratio is 5.5 times or more and the stretching ratio is 1.2 times or more. The wet stretch ratio after the second time is preferably 1.5 times or more, and more preferably 2.1 times or more. If the wet stretching ratio for the second and subsequent times becomes too large, the stretch is likely to be broken. Therefore, the wet stretching ratio for the second and subsequent times is preferably 3.5 times or less. In addition, the draw ratio in the 1st draw process is 1.2 to 4.5 times, Preferably it is 1.7 to 3.5 times.

  And in this invention, a 1st guide roll is formed so that the film conveyed from a 1st pinch roll in the said wet extending | stretching process may form the holding angle (A) of 140-175 degrees in the 1st guide roll which contact | connects first. Let it pass. By allowing the film to pass through the first guide roll so as to be within the range of the holding angle (A), the film is not stretched rapidly, so that it is possible to prevent stretching. The holding angle (A) is preferably 150 to 170 °.

  In the manufacturing method of the said polarizer, it is preferable to pass the film conveyed from a 1st pinch roll under the 1st guide roll.

  In the method for producing a polarizer, the wet stretching treatment is preferably performed in a boron compound bath. When the boron compound treatment is performed together with the wet stretching treatment, the effect of preventing the stretching breakage is great.

  In addition, as a method for preventing stretching during film stretching, stretching is performed in a state where the concentration of the crosslinking treatment bath (boron compound treatment bath) is lowered, or stretching is performed by increasing the temperature during stretching to 50 ° C. or higher. Although the effect is achieved by slowing the stretching speed and stretching, etc., the effect of preventing stretching breakage is further recognized by arranging the guide rolls in the wet stretching bath as in the present invention.

  The present invention also relates to a wet stretching apparatus having a treatment bath used in a wet stretching process in a method for producing a polarizer, comprising a first pinch roll and a second pinch roll on both sides of the treatment bath. Each of the roll and the second pinch roll has an opposing guide roll, and the film conveyed from the first pinch roll is the first guide roll that comes into contact first, and the film conveyed from the first guide roll is the first guide roll. When the holding angle (A) is an angle formed through the first guide roll before and after passing through the roll, the first guide roll is installed so as to form a holding angle (A) of 140 to 175 °. The present invention relates to a wet stretching apparatus.

  The wet stretching apparatus is preferably installed so that the film conveyed from the first pinch roll passes through the lower side of the first guide roll.

  The wet stretching apparatus includes a first pinch roll and a contact roll (x) between the guide rolls provided to face the first pinch roll, and a guide roll on the first pinch roll side in the bath for performing the wet stretching process. The distance (C) between the rolls to the center point (y) of the guide roll closest to the bath bottom and closest to the first pinch roll is preferably 1 m or more.

  These wet stretching apparatuses are used for wet stretching in the method for producing a polarizer of the present invention.

  Polyvinyl alcohol or a derivative thereof is used as a material for the polyvinyl alcohol film applied to the polarizer of the present invention. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, alkyl esters thereof, acrylamide and the like. can give. 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 thereof 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. Usually, a film having a thickness of about 30 to 150 μm is used.

  The polyvinyl alcohol film is subjected to a stretching and stretching treatment process, a dyeing treatment process, and a boric acid treatment process.

  In the stretching process, the uniaxial stretching process is performed at least twice. The second and subsequent stretching processes are performed by a wet stretching process described later. In addition, the uniaxial stretching treatment method by dry stretching is not particularly limited. For example, while applying a tensile force between the method described in Patent No. 1524033, Patent No. 2731813, or between rolls installed in or outside the drying oven Any method such as a stretching method, a stretching method using a heating roll, a stretching method using a tenter stretching machine or the like can be adopted. In the dry stretching means, the unstretched film is usually heated to about 70 to 150 ° C.

  The dyeing process is performed by adsorbing and orienting iodine or a dichroic dye on the unstretched film or stretched film. Further, a dyeing treatment can be applied during stretching. In the dyeing treatment, a swelling step can be provided. In the present invention, it is preferable to subject the stretched film subjected to the first stretching treatment to a dyeing treatment step. The dyeing treatment is generally performed by immersing the film in a dyeing solution. As the staining solution, an iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions with, for example, potassium iodide or the like as iodine and a dissolution aid is used. The iodine concentration is about 0.01 to 0.5% by weight, preferably 0.02 to 0.4% by weight, and the potassium iodide concentration is about 0.01 to 10% by weight, and further 0.02 to 8% by weight. % Is preferably used. In the iodine dyeing treatment, the temperature of the iodine solution is usually about 20 to 50 ° C, preferably 25 to 40 ° C. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  The boron compound treatment step is performed in the boron compound. The order of the boron compound treatment step is not particularly limited. The boron compound treatment step can be performed together with the stretching step. The boron compound treatment step can be performed a plurality of times. In the present invention, it is preferable to perform the boron compound treatment step after the first stretching treatment and dyeing treatment and before the second wet stretching treatment. Furthermore, it is preferable to perform the boron compound treatment step together with the second wet drawing treatment. Examples of the boron compound include boric acid and borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution. The boric acid concentration of the boric acid aqueous solution or the like is about 2 to 20% by weight, preferably 3 to 15% by weight. An aqueous boric acid solution or the like can contain potassium iodide. The boron compound treatment is generally performed by immersing the stretched film in a boric acid aqueous solution or the like. In addition, the boron compound treatment can be performed by a coating method, a spraying method, or the like. The treatment temperature by the boron compound treatment is usually 30 ° C. or higher, preferably 50 to 85 ° C. The treatment time with the boron compound is usually about 10 to 800 seconds, preferably about 30 to 500 seconds.

  The second and subsequent wet stretching processes of the present invention will be described with reference to the drawings. It is preferable that a dyeing process and a boron compound process are performed before the wet stretching process. The said wet extending | stretching process is performed using the peripheral speed difference of the 1st pinch roll 21 and the 2nd pinch roll 22 about the film a which the said process is given and conveyed as shown in FIGS. . A guide roll 10 is provided opposite to the first pinch roll 21, and a guide roll 30 is provided opposite to the second pinch roll 22. A guide roll 31 is provided in front of the guide roll 30. Moreover, it is preferable that the treatment bath b for performing the wet stretching treatment contains a boron compound and simultaneously performs the boron compound treatment.

  The film a conveyed from the first pinch roll 21 is passed through the first guide roll 11 that comes into contact first so as to form a holding angle (A) of 140 to 175 °. The holding angle (A) is an angle formed via the first guide roll 11 before and after the film a conveyed by the first guide roll 11 passes through the first guide roll 11 as shown in the figure. .

  1 and 3, the film a passes below the first guide roll 11. As shown in FIG. 3, the first guide roll 11 can be subsequently provided with guide rolls 41, 42 and 43. In FIG. 2, the film a passes through the upper side of the first guide roll 11. When the upper side of the first guide roll 11 is passed through the film a, the lower side is passed through the guide roll 12 that first passes through the lower side. The guide roll 12 is a guide roll that first allows the film a conveyed from the first pinch roll 21 to pass through the lower side, and is preferably installed so that the holding angle (B) forms 120 to 175 °. The film conveyed from the first pinch roll has a holding angle of 120 to 175 ° in the guide roll that is first passed downward, thereby suppressing rapid stretching of the film and preventing occurrence of stretching breakage. Is preferable. Therefore, when the film conveyed from the first pinch roll is passed through the upper side of the first guide roll, the holding angle (B) in the guide roll that first passed through the lower side is 120 to 175 °. It is preferable to do so. The holding angle (B) is preferably 150 to 170 °.

  Moreover, as shown in FIGS. 1-3, the 1st pinch roll 21 and the contact (x) of the guide roll 10 provided facing the said 1st pinch roll, and the 1st pinch in the bath which performs a wet extending | stretching process. The guide roll on the roll side is installed so that the distance (C) between the rolls to the center point (y) of the guide roll closest to the bath bottom and closest to the first pinch roll is 1 m or more. Is preferred. By setting the distance between rolls (C) to 1 m or more, the film is not stretched rapidly, so that the occurrence of stretch breakage can be prevented. The distance between rolls (C) is preferably 1.5 m or more. The distance between rolls (C) is usually preferably in the range of 1 to 5 m. The film conveyed from the first pinch roll is stretched in the bath liquid by shortening the distance until the transport film enters the bath so that the film is immediately put in the wet bath liquid. This has a great effect of preventing stretching. If it becomes the reference | standard of center point (y), a guide roll is a guide roll in the 1st pinch roll 21 side in the bath b. That is, when the bath b is divided into left and right, it is a guide roll on the left side. Further, the guide roll is the guide roll closest to the bath bottom of the bath b and closest to the first pinch roll 21 as a reference for the center point (y). In other words, when several guide rolls are provided, the guide roll closest to the first pinch roll 21 is the guide roll that serves as the reference for the center point (y). Therefore, the guide roll serving as a reference for the center point (y) in FIG. 1 is the first guide roll 11. The guide roll becomes the guide roll 12 as a reference for the center point (y) in FIG. The guide roll becomes the guide roll 43 as a reference for the center point (y) in FIG.

  In addition, the polyvinyl alcohol film (stretched film) subjected to each treatment is subjected to a washing treatment and a drying treatment according to a conventional method to become a polarizer. In addition, the method for producing a polarizer of the present invention can be arbitrarily subjected to iodine ion impregnation treatment with a potassium iodide solution or the like.

  The obtained polarizer can be made into a polarizing plate provided with a transparent protective layer on at least one surface thereof according to a conventional method. The transparent protective layer can be provided as a polymer-coated layer or a film laminate layer. As the transparent polymer or film material for forming the transparent protective layer, an appropriate transparent material can be used, but a material excellent in transparency, mechanical strength, thermal stability, moisture barrier property and the like is preferably used. Examples of the material for forming the transparent protective layer include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as cellulose diacetate and cellulose triacetate, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile, Examples thereof include styrene polymers such as styrene copolymers (AS resins), 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 are also examples of the polymer that forms the transparent protective layer.

  The surface of the transparent protective film to which the polarizer is not adhered (the surface on which the coating layer is not provided) has been subjected to a hard coat layer, antireflection treatment, antisticking, or treatment for diffusion or antiglare. Also good.

  The hard coat treatment is applied for the purpose of preventing scratches on the surface of the polarizing plate. For example, a transparent protective film with a cured film excellent in hardness, sliding properties, etc. by an appropriate ultraviolet curable resin such as acrylic or silicone is used. It can be formed by a method of adding to the surface of the film. The antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  The anti-glare treatment is applied for the purpose of preventing the outside light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, the surface is roughened by a sandblasting method or an embossing method. It 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 blending method of transparent fine particles. The fine particles to be included in the formation of the surface fine concavo-convex structure are, for example, conductive materials made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide or the like having an average particle size of 0.5 to 50 μm. In some cases, transparent fine particles such as inorganic fine particles, organic fine particles composed of a crosslinked or uncrosslinked polymer, and the like are used. When 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, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. 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, diffusing layer, antiglare layer and the like can be provided on the transparent protective film itself, or can be provided separately from the transparent protective layer as an optical layer.

  An adhesive is used for the adhesion treatment between the polarizer and the transparent protective film. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, 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 polarizing plate of the present invention is produced by bonding the transparent protective film and the polarizer using the adhesive. The adhesive may be applied to either the transparent protective film or the polarizer, or to both. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. 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 0.1 to 5 μm.

  The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

  A reflective polarizing plate is a polarizing plate provided with a reflective layer, and is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side). Such a light source 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 as necessary.

  Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or a vapor deposition film made of a reflective metal such as aluminum on one side of a transparent protective film matted as necessary. Moreover, the transparent protective film contains fine particles so as to have a surface fine concavo-convex structure and a reflective layer having a fine concavo-convex structure thereon. The reflective layer having the fine concavo-convex structure has an advantage that incident light is diffused by irregular reflection to prevent directivity and glaring appearance and to suppress unevenness in brightness and darkness. The transparent protective film containing fine particles also has an advantage that incident light and its reflected light are diffused when passing through it, and light and dark unevenness can be further suppressed. The reflective layer of the fine concavo-convex structure reflecting the surface fine concavo-convex structure of the transparent protective film is formed by transparent the metal by an appropriate method such as a vapor deposition method such as a vacuum vapor deposition method, an ion plating method, a sputtering method, or a plating method. It can be performed by a method of directly attaching to the surface of the protective layer.

  Instead of the method of directly applying the reflecting plate to the transparent protective film of the polarizing plate, the reflecting plate can be used as a reflecting sheet provided with a reflecting layer on an appropriate film according to the transparent film. Since the reflective layer is usually made of metal, the usage form in which the reflective surface is covered with a transparent protective film, a polarizing plate or the like is used to prevent the reflectance from being lowered due to oxidation, and thus to maintain the initial reflectance for a long time. In addition, it is more preferable to avoid a separate attachment of the protective layer.

  The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell, and displays an image by reflecting incident light from the viewing side (display side) when a liquid crystal display device is used in a relatively bright atmosphere. In a relatively dark atmosphere, a liquid crystal display device or the like that displays an image using a built-in light source such as a backlight built in the back side of the transflective polarizing plate can be formed. In other words, the transflective polarizing plate is useful for forming a liquid crystal display device of a type that can save energy of using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source even in a relatively dark atmosphere. It is.

  An elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on a polarizing plate will be described. A phase difference plate or the like is used when changing linearly polarized light to elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light to linearly polarized light, or changing the polarization direction 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 into circularly polarized light or changes circularly polarized light into linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is usually used when changing the polarization direction of linearly polarized light.

  The elliptically polarizing plate is effectively used for black and white display without the above color by compensating (preventing) the coloration (blue or yellow) generated by the birefringence of the liquid crystal layer of the super twist nematic (STN) type liquid crystal display device. It is done. Further, the one in which the three-dimensional refractive index is controlled is preferable because 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 effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which an image is displayed in color, and also has an antireflection function. Specific examples of the retardation plate 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. And an alignment film of a liquid crystal polymer, and a liquid crystal polymer alignment layer supported by a film. The retardation plate may have an appropriate retardation according to the purpose of use, such as those for the purpose of compensating for various wavelength plates or birefringence of the liquid crystal layer, viewing angle, and the like. What laminated | stacked the phase difference plate and controlled optical characteristics, such as phase difference, etc. may be used.

  The elliptical polarizing plate and the reflective elliptical polarizing plate are obtained by laminating a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination. Such an elliptically polarizing plate or the like can also be formed by sequentially laminating them sequentially in the manufacturing process of the liquid crystal display device so as to be a combination of a (reflective) polarizing plate and a retardation plate. An optical film such as a polarizing plate has an advantage that it can improve the production efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.

  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. As such a viewing angle compensation phase difference plate, for example, a retardation film, an alignment film such as a liquid crystal polymer, or an alignment layer such as a liquid crystal polymer supported on a transparent substrate is used. A normal retardation plate uses a birefringent polymer film uniaxially stretched in the plane direction, whereas a retardation plate used as a viewing angle compensation film stretches biaxially in the plane direction. Birefringent polymer film, biaxially stretched film such as polymer with birefringence with a controlled refractive index in the thickness direction that is uniaxially stretched in the plane direction and stretched in the thickness direction, etc. 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 shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. The raw material polymer for the phase difference plate is the same as the polymer described in the previous phase difference plate, preventing coloration due to a change in the viewing angle based on the phase difference by the liquid crystal cell and expanding the viewing angle for good visual recognition. An appropriate one for the purpose can be used.

  Also, from the viewpoint of achieving a wide viewing angle with good visibility, an optically compensated phase difference in which a liquid crystal polymer alignment layer, in particular an optically anisotropic layer composed of a discotic liquid crystal polymer gradient alignment layer, is supported by a triacetylcellulose film. A plate can be preferably used.

  A polarizing plate obtained by bonding a polarizing plate and a brightness enhancement film is usually provided on the back side of a liquid crystal cell. The brightness enhancement film reflects a linearly polarized light with a predetermined polarization axis or a circularly polarized light in a predetermined direction when natural light is incident due to a backlight such as a liquid crystal display device or reflection from the back side, and transmits other light. In addition, a polarizing plate in which a brightness enhancement film is laminated with a polarizing plate allows light from a light source such as a backlight to enter to obtain transmitted light in a predetermined polarization state, and reflects light without transmitting the light other than the predetermined polarization state. The The light reflected on the surface of the brightness enhancement film is further inverted through a reflective layer or the like provided behind the brightness enhancement film and re-incident on the brightness enhancement film, and part or all of the light is transmitted as light having a predetermined polarization state. Luminance can be improved by increasing the amount of light transmitted through the enhancement film and increasing the amount of light that can be used for liquid crystal display image display or the like by supplying polarized light that is difficult to be absorbed by the polarizer. That is, when light is incident through the polarizer from the back side of the liquid crystal cell without using a brightness enhancement film, light having a polarization direction that does not coincide with the polarization axis of the polarizer is almost polarized. It is absorbed by the polarizer and does not pass through the polarizer. That is, although depending on the characteristics of the polarizer used, approximately 50% of the light is absorbed by the polarizer, and the amount of light that can be used for liquid crystal image display or the like is reduced accordingly, resulting in a dark image. The brightness enhancement film allows light having a polarization direction that is absorbed by the polarizer to be reflected once by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflective layer provided on the rear side thereof. Repeatedly re-enter the brightness enhancement film, and the brightness enhancement film transmits only polarized light whose polarization direction is such that the polarization direction of light reflected and inverted between the two can pass through the polarizer. Therefore, light such as a backlight can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.

  A diffusion plate may be provided between the brightness enhancement film and the reflective layer. The polarized light reflected by the brightness enhancement film is directed to the reflective layer or the like, but the installed diffuser plate uniformly diffuses the light passing therethrough and simultaneously cancels the polarized state and becomes a non-polarized state. That is, the diffuser plate returns the polarized light to the original natural light state. The light in the non-polarized state, that is, the natural light state is directed toward the reflection layer and the like, reflected through the reflection layer and the like, and again passes through the diffusion plate and reenters the brightness enhancement film. Thus, while maintaining the brightness of the display screen by providing a diffuser plate that returns polarized light to the original natural light state between the brightness enhancement film and the reflective layer, etc., the brightness unevenness of the display screen is reduced at the same time, A uniform and bright screen can be provided. By providing such a diffuser plate, it is considered that the first incident light has a moderate increase in the number of repetitions of reflection, and in combination with the diffusion function of the diffuser plate, a uniform bright display screen can be provided.

  The brightness enhancement film has a characteristic of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of dielectric material or a multilayer laminate of thin film films having different refractive index anisotropies. Such as an alignment film of a cholesteric liquid crystal polymer or an alignment liquid crystal layer supported on a film substrate, which reflects either left-handed or right-handed circularly polarized light and transmits other light. Appropriate things, such as a thing, can be used.

  Therefore, in the brightness enhancement film of the type that transmits linearly polarized light having the predetermined polarization axis as described above, the transmitted light is incident on the polarizing plate with the polarization axis aligned as it is, thereby efficiently transmitting while suppressing absorption loss due to the polarizing plate. Can be made. On the other hand, in a brightness enhancement film of a type that emits circularly polarized light such as a cholesteric liquid crystal layer, it can be incident on a polarizer as it is, but from the viewpoint of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable to make it enter into a polarizing plate. Note that circularly polarized light can be converted to linearly polarized light by using a quarter wave plate as the retardation plate.

  A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a quarter-wave plate for light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superposing a retardation layer, for example, a retardation layer functioning as a half-wave plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.

  In addition, the cholesteric liquid crystal layer can also be obtained by reflecting circularly polarized light in a wide wavelength range such as a visible light region by combining two or more layers having different reflection wavelengths and having an overlapping structure. Based on this, transmitted circularly polarized light in a wide wavelength range can be obtained.

  Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers like the above-described polarization separation type polarizing plate. Therefore, a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above-mentioned reflective polarizing plate or transflective polarizing plate and a retardation plate are combined may be used.

  An optical film in which the optical layer is laminated on a polarizing plate can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. There is an advantage that the manufacturing process of the liquid crystal display device and the like can be improved. For the lamination, an appropriate adhesive means such as an adhesive layer can be used. When adhering the polarizing plate and other optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.

  An adhesive layer for adhering to other members such as a liquid crystal cell may be provided on the polarizing plate described above or an optical film in which at least one polarizing plate is laminated. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.

  In addition to the above, in terms of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical properties and liquid crystal cell warpage due to differences in thermal expansion, etc., as well as formability of liquid crystal display devices with high quality and excellent durability An adhesive layer having a low moisture absorption rate and excellent heat resistance is preferred.

  The adhesive layer is, for example, natural or synthetic resins, in particular, tackifier resins, fillers or pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, etc. It may contain an additive to be added to the adhesive layer. 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 pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method in which it is directly attached on a polarizing plate or an optical film by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on a separator according to the above, and this is applied to a polarizing plate or an optical film. The method of moving up 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 different compositions or types. Moreover, when providing in both surfaces, it can also be set as the adhesion layers of a different composition, a kind, thickness, etc. in 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, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered 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, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate ones according to the prior art, such as those coated with an appropriate release agent such as a long mirror alkyl type, fluorine type or molybdenum sulfide, can be used.

  In the present invention, the polarizer, transparent protective film, optical film, and the like that form the polarizing plate described above, and each layer such as an adhesive layer include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylates. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.

  The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. In other words, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the polarizing plate or optical film by this invention can be installed in the one side or both sides of a liquid crystal cell. When providing a polarizing plate or an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable 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, a backlight, Two or more layers can be arranged.

  Next, an organic electroluminescence device (organic EL display device) will be described. 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 and the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Alternatively, a structure having various combinations such as a laminate of such a light-emitting layer and an electron injection layer composed of a perylene derivative or the like, or a laminate of these hole injection layer, light-emitting layer, and electron injection layer is known. It has been.

  In organic EL display devices, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by recombination of these holes and electrons excites the phosphor material. Then, light is emitted on the principle that the excited fluorescent material emits light when returning to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.

  In an organic EL display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes must be transparent, and a transparent electrode usually formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is used as. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.

  In the organic EL display device having such a configuration, 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, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted 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 comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode While providing a polarizing plate on the side, 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, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization action. 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. .

  That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light becomes generally elliptically polarized light by the phase difference plate, but becomes circularly polarized light particularly when the phase difference plate is a quarter wavelength plate and the angle formed by the polarization direction of the polarizing plate and the phase difference plate is π / 4. .

  This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again on the retardation plate. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.

  The present invention will be specifically described below with reference to examples and comparative examples. In addition,% in each example is weight%.

Example 1
Using a 75 μm-thick polyvinyl alcohol film (average polymerization degree 2400, saponification degree 99.9%: vinylon film manufactured by Kuraray Co., Ltd.), it was washed and swelled in a 35 ° C. water bath to obtain potassium iodide. The film was uniaxially stretched 3.7 times while being dyed in an aqueous iodine solution having a concentration of 0.3% and an iodine concentration of 0.05% at 30 ° C. for 60 seconds. Further, crosslinking treatment (non-stretching) was performed in a boric acid aqueous solution having a boric acid concentration of 8% at 34 ° C.

  Next, the stretched film (film a in FIG. 1) is transported to a bath b in which the guide roll shown in FIG. 1 is arranged, and a second stretch is performed at a stretch ratio of 1.7 times by a wet stretching process. The total draw ratio was set to 6.3 times. As the bath b, a boric acid aqueous solution having a boric acid concentration of 7% at 60 ° C. was used and subjected to a crosslinking treatment along with stretching. In FIG. 1, the guide rolls were arranged so that the holding angle (A) was 160 ° and the distance between rolls (C) was 2 m. Then, the water washing process was performed for 10 second with 25 degreeC pure water, and it dried for 4 minutes at 60 degreeC, and produced the polarizer.

  The polarizer was continuously manufactured for 5 hours, and the number of occurrences of film breakage (stretching breakage) that occurred in the second stretching process was confirmed. The results are shown in Table 1.

Examples 2-5 and Comparative Examples 1-4
In Example 1, the layout, the degree of hugging (A), the degree of hugging (B), and the distance between rolls (C) applied to the second stretching process performed in the bath b were changed as shown in Table 1. A polarizer was produced in the same manner as in Example 1 except for the above. Table 1 shows the number of stretch cuts.

It is a layout drawing of the guide roll of the bath used for the wet stretching process of the 2nd time or later of the manufacturing method of the polarizer of the present invention. It is another arrangement | positioning drawing of the guide roll of the bath used for the wet extending process after the 2nd time of the manufacturing method of the polarizer of this invention. It is another arrangement | positioning drawing of the guide roll of the bath used for the wet extending process after the 2nd time of the manufacturing method of the polarizer of this invention.

Explanation of symbols

11 First Guide Roll 21 First Pinch Roll 22 Second Pinch Roll a Film b Treatment Bath (Crosslinking Bath)
A Holding angle B Holding angle C Distance between rolls

Claims (10)

In the method for producing a polarizer, the polyvinyl alcohol film is subjected to at least a stretching treatment step, a dyeing treatment step, and a boron compound treatment step.
The stretching process is performed at least twice so that the total stretching ratio is 5.5 times or more, and in the second and subsequent stretching processes, stretching with a stretching ratio of 1.2 times or more is performed between the first pinch roll and the second pinch roll. Performed by wet stretching using the difference in peripheral speed of pinch rolls,
In the wet stretching process, the film conveyed from the first pinch roll is the first guide roll that comes into contact with the first guide roll before and after the film conveyed from the first guide roll passes through the first guide roll. When the holding angle (A) is an angle formed through the first guide roll, the first guide roll is passed so as to form a holding angle (A) of 140 to 175 °. Method.   The method for producing a polarizer according to claim 1, wherein the film conveyed from the first pinch roll is passed under the first guide roll.   The method for producing a polarizer according to claim 1 or 2, wherein the wet stretching is performed in a boron compound bath.   The method for producing a polarizer according to claim 3, wherein the boron compound bath is an aqueous boric acid solution having a boric acid concentration of 2 to 20% by weight.   The method for producing a polarizer according to claim 3 or 4, wherein the treatment temperature with the boron compound is in the range of 30 to 85 ° C.   The method for producing a polarizer according to claim 1, wherein the first stretching process is performed by a wet stretching process.   The method for producing a polarizer according to claim 6, wherein the first stretching treatment is performed together with the dyeing treatment step.   A wet stretching apparatus having a treatment bath used for a wet stretching process in a method for producing a polarizer, comprising a first pinch roll and a second pinch roll on both sides of the treatment bath, the first pinch roll and the second pinch roll Each of the rolls has an opposing guide roll, and the film conveyed from the first pinch roll is the first guide roll that comes into contact with the film before and after the film conveyed from the first guide roll passes through the first guide roll. The first guide roll is installed so as to form a holding angle (A) of 140 to 175 ° when the angle formed via the first guide roll is the holding angle (A). A wet stretching apparatus.   9. The wet stretching apparatus according to claim 8, wherein the film conveyed from the first pinch roll is installed so as to pass under the first guide roll. A contact (x) of the first pinch roll and the guide roll provided to face the first pinch roll;
The distance between the rolls (C) to the center point (y) of the guide roll which is on the first pinch roll side in the bath for performing the wet stretching process and which is closest to the bath bottom and closest to the first pinch roll ) Is 1 m or more, The wet stretching apparatus according to claim 8 or 9.