Patent Application
20150043070
The present invention relates to a polarizing film, an optically functional film laminate including the polarizing film, a production method for an optical film laminate including the polarizing film, and an organic EL display device having the polarizing film. In particular, the present invention relates to a thinned and high-transmittance polarizing film comprised of a polyvinyl alcohol-based resin containing molecularly-oriented iodine, an optically functional film laminate including the polarizing film, a production method for an optical film laminate including the polarizing film, and an organic EL display device having the polarizing film.
Generally, an organic EL display device has a light emitter (organic EL light-emitter) comprising a transparent electrode, an organic light-emitting layer and a metal electrode which are laminated on a transparent substrate in this order. In this regard, it is desirable to form the organic light-emitting layer as an extremely thin film having a thickness, for example, of about 10 nm. This is intended to allow light to be almost completely transmitted through the organic light-emitting layer, as with the transparent electrode. In this case, outside light entering through a surface of the transparent electrode is transmitted through the transparent electrode and the organic light-emitting layer, and reflected by the metal electrode, whereafter the reflected light exits to the outside through the surface of the transparent electrode. Thus, particularly in a black state, i.e., a non-luminous state, a display surface of the organic EL device looks like a minor surface when viewed from the outside.
Therefore, as means to prevent reflection on the metal electrode, there has been proposed a technique of using a polarizing film in combination with a retardation plate such as a ¼ wavelength retardation plate. Specifically, when light enters from the outside, a linearly-polarized component of the entering light perpendicular to a transmission axis direction of the polarizing film is absorbed by the polarizing film, whereas a linearly-polarized component of the entering light parallel to the transmission axis direction of the polarizing film is transmitted through the polarizing film. An angle between the transmission axis direction of the polarizing film and a slow axis direction of a ¼ wavelength retardation plate is set to 45 degrees, so that the ¼ wavelength retardation plate functions to convert the linearly-polarized light transmitted through the polarizing film into circularly-polarized light. Then, the resulting circularly-polarized light is reflected by the metal electrode, and the reflected light re-enters the polarizing film through the ¼ wavelength retardation plate. The light is controlled to re-enter the polarizing film at an angle perpendicular to the transmission axis direction of the polarizing film, for example, by adjusting a distance between the metal electrode and the ¼ wavelength retardation plate, and/or a thickness of the ¼ wavelength retardation plate. Thus, the linearly-polarized component of the entering light parallel to the transmission axis direction of the polarizing film is also absorbed by the polarizing film, so that it becomes possible to almost fully eliminate surface reflection in the organic EL display device.
As the polarizing film, it is common to use a polarizing film which comprises a polyvinyl alcohol-based resin (hereinafter referred to as “PVA-based resin”) layer obtained by subjecting a single layer body, i.e., non-laminate, made of a PVA-based resin and formed in a film shape, to dyeing and stretching to thereby cause a dichroic material to be adsorbed to the PVA-based resin in a molecularly-oriented state. The polarizing film obtainable by the above conventional method using a film-shaped PVA-based resin non-laminate has a thickness in the range of about 15 to 35 μm. This conventional method is capable of obtaining a polarizing film having optical properties including a single transmittance of 42% or more and a polarization degree of 99.95% or more. Currently, polarizing films produced by the conventional method are used in optical display devices for televisions, mobile phones, PDAs and others.
In this connection, a PVA-based resin is hydrophilic and highly hygroscopic, so that a polarizing film produced using the PVA-based resin is sensitive to changes in temperature and humidity, and more likely to expand and contract due to changes in surrounding environments and thus undergo crack formation. Moreover, the expansion and contraction caused by environmental changes during use will produce stress in an adjacent member to which the polarizing film is bonded, thereby leading to deformation, such as warp, in the adjacent member.
Thus, in order to suppress such expansion and contraction of a polarizing film to thereby reduce influences of changes in temperature and humidity, a polarizing film for use in optical display devices for televisions, mobile phones, PDAs and others has been typically used in the form of a laminate in which a 40 to 80 μm-thick TAC (triacetylcellulose-based) film is laminated onto each of opposite surfaces of the polarizing film to serve as a protection film. However, even in such a structure, expansion and contraction forces of the polarizing film are still at a non-ignorable level, i.e., it is difficult to completely suppress influences on expansion and contraction of the polarizing film, and a certain level of expansion and contraction will inescapably occur in the optically functional film laminate including the polarizing film. When expansion or contraction occurs in such a polarizing film-including optically functional film laminate, stress arising from the expansion or contraction thereof will cause deformation, such as warp, in an adjacent member. This deformation, even if it is small, leads to the occurrence of display unevenness in a display device. Thus, as means to suppress the occurrence of display unevenness, it is necessary to make design considerations, for example, to carefully select a material for each member to be used in the polarizing film-including optically functional film laminate. Further, contraction stress of the polarizing film can cause peel-off of the optically functional film laminate from a display panel. Thus, a pressure sensitive-adhesive having high adhesion force is required to bond the optically functional film laminate to the display panel. However, the use of such a pressure sensitive-adhesive with high adhesion force gives rise to a problem that it becomes difficult to perform reworking which is an operation of, when the presence of an optical defect is found in a polarizing film of an optically functional film laminate laminated to a display panel by a subsequent inspection, peeling the optically functional film laminate from the display panel and laminating another optically functional film laminate to the display panel. In a liquid crystal display device where a polarizing film-including optically functional film laminate disposed on each of opposite surfaces of a liquid crystal display panel, contraction stresses of two polarizing films of the optically functional film laminates on the opposite surfaces of the liquid crystal display panel cancel out each other to thereby somewhat ease the problem of causing deformation, such as warp, in an adjacent member. On the other hand, in an organic EL display device using an organic EL display panel, the problem becomes particularly prominent, because a polarizing film-including optically functional film laminate is disposed on only one of opposite surfaces of the display panel. In addition to display unevenness and difficulty in reworking, the organic EL display device further involves a problem that a sealing material for the display panel is destroyed due to the warp of the display panel, and an organic light-emitting layer is degraded due to humidity. These are technical problems in a polarizing film produced by the conventional method using a film-shaped PVA-based resin non-laminate.
In view of the above problems, there is a need for a polarizing film reduced in thickness and thus expansion and contraction forces. However, the conventional polarizing film production method using a film-shaped PVA-based resin non-laminate is incapable of achieving a satisfactory level of thickness reduction. That is, the conventional method using a film-shaped PVA-based resin non-laminate is incapable of producing a polarizing film having a thickness of 10 μm or less. The reason is that, in the polarizing film production method using a film-shaped PVA-based resin non-laminate, when a thickness of the PVA-based resin non-laminate is excessively reduced, the PVA-based resin non-laminate is likely to undergo dissolution and/or breaking in a dyeing step and/or a stretching step, resulting in failing to stably form a polarizing film with a uniform thickness.
In order to cope with this problem, there has been proposed a method of producing a significantly thin polarizing film as compared to a polarizing film obtainable by the conventional method, wherein the production method comprises: applying and forming a PVA-based resin layer onto a thermoplastic resin substrate; and subjecting the PVA-based resin layer formed on the resin substrate to stretching and dyeing, together with the resin substrate. This polarizing film production method using a thermoplastic resin substrate is noteworthy in that it makes it possible to produce a polarizing film more uniformly than the polarizing film production method using a film-shaped PVA-based resin non-laminate.
For example, JP 4279944B (Patent Document 1) discloses a polarizing plate production method which comprises: forming a PVA-based resin layer having a thickness of 6 to 30 μm on one of opposite surfaces of a thermoplastic resin film by a coating process; stretching the PVA-based resin layer at a stretching ratio of 2 to 5 times in such a manner as to allow the PVA-based resin layer to become a transparent coating element layer to thereby form a composite film consisting of the thermoplastic resin film and the transparent coating element layer; then laminating an optical transparent resin film layer to one surface of the two-layered composite film on the side of the transparent coating element layer, through an adhesive; then peeling and removing the thermoplastic resin film; and subjecting the transparent coating element layer to dyeing and dye fixing to form a polarizing element layer. A polarizing plate obtainable by this method has a two-layer structure consisting of the optically transparent resin film layer and the polarizing element layer. According to the description of the Patent Document 1, the polarizing element has a thickness of 2 to 4 μm.
The method disclosed in the Patent Document 1 is configured to perform stretching under elevating temperature by a uniaxial stretching process, wherein the stretching ratio is restricted to the range of 2.0 to 5.0 times. As for the reason why the stretching ratio is restricted to 5.0 times or less in the method disclosed in the Patent Document 1, the Patent Document 1 explains that it is because stretching at a high stretching ratio of greater than 5.0 times makes it extremely difficult to maintain stable production. Thus, when the stretching ratio is 5.0 times or less but close to 4.0 to 5.0 times, it would be difficult to ensure stable production. Further, regarding an ambient temperature during stretching, the Patent Document 1 makes mention that it is specifically set to: 55° C. for the case where ethylene-vinyl acetate copolymer is used as the thermoplastic resin film; 60° C. for the case where non-stretched polypropylene is used as the thermoplastic resin film; and 70° C. for the case where non-stretched nylon is used as the thermoplastic resin film. The method disclosed in the Patent Document 1 employs a uniaxial in-air stretching process at an elevated temperature. Further, as described in the Patent Document 1, the stretching ratio is restricted to 5.0 times or less.
Thus, this method has difficulty in stably producing a polarizing film which has an extremely small thickness of 2 to 4 μm and satisfies desired optical properties for allowing it to become usable for organic EL display devices. In other words, a polarizing film obtainable by this method with an extremely small thickness of 2 to 4 μm cannot satisfy desired optical properties of a polarizing film usable for organic EL display devices.
The method comprising forming a PVA-based resin layer on a thermoplastic resin substrate by a coating process and subjecting the PVA-based resin layer to stretching, together with the substrate to form a polarizing film is also disclosed in JP 2001-343521A (Patent Document 2) and JP 2003-043257A (Patent Document 3). The methods disclosed in the Patent Documents 2 and 3 are configured to subject a laminate comprising a thermoplastic resin substrate and a PVA-based resin layer applied on the substrate to uniaxial stretching at a temperature of 70 to 120° C. for the case where the substrate is made of a non-crystallizable polyester resin. Then, the PVA-based resin layer molecularly oriented by the stretching is subjected to dyeing to adsorb a dichroic material thereto. The Patent Document 2 makes mention that the uniaxial stretching may be longitudinal uniaxial stretching or may be transverse uniaxial stretching. On the other hand the Patent Document 3 describes a technique of performing transverse uniaxial stretching, and, during or after the transverse uniaxial stretching, causing a length in a direction perpendicular to a stretching direction to contract by a specific amount. In both of the Patent Documents 2 and 3, as for stretching ratio, they make mention that it is typically set to about 4.0 to 8.0 times. Further, as for a thickness of an obtainable polarizing film, they make mention of a value of 1 to 1.6 μm.
The Patent Documents 2 and 3 make mention that the stretching ratio is typically in the range of 4.0 to 8.0 times. However, a stretching process employed in the Patent Documents 2 and 3 is elevated-temperature in-air stretching. Thus, for example, when the stretching ratio is increased beyond 5.0 times, this stretching process makes it extremely difficult to maintain stable production, as described in the Patent Document 1. None of the Patent Documents 2 and 3 describes a particular technique for achieving a stretching ratio of greater than 5.0 times by the elevated-temperature in-air stretching process. In fact, when reviewing Examples described in the Patent Documents 2 and 3, only a stretching ratio of 5.0 times is described in the Patent Document 2, and a stretching ratio of 4.5 times is described in the Patent Document 3.
Through check experiments on the methods disclosed in the Patent Documents 2 and 3, the inventors of the present invention have ascertained that the methods disclosed therein are incapable of performing stretching at a stretching ratio of greater than 5.0 times, and stably performing stretching at a stretching ratio of 4 to 5 times. Therefore, it should be understood that each of the Patent Documents 2 and 3 describes only stretching to be performed at a stretching ratio of 5.0 times or less, and, when the stretching ratio is 5.0 or less but in the range of 4.0 to 5.0, the method has difficulty in maintaining stable production. Thus, as with the Patent Document 1, in the methods disclosed in the Patent Documents 2 and 3, the stretching ratio is restricted to 5.0 times or less. Thus, an obtainable extremely thin polarizing film is not enough to satisfy desired optical properties of a polarizing film usable for organic EL display devices, or it is difficult to stably produce an extremely thin polarizing film satisfying desired optical characteristics for allowing it to become usable for organic EL display devices.
U.S. Pat. No. 4,659,523B (Patent Document 4) discloses a polarizing film production method which comprises subjecting a PVA-based resin layer coated on a polyester film to uniaxial stretching, together with the polyester film. This method disclosed in the Patent Document 4 is intended to form the polyester film serving as a substrate of the PVA-based resin layer in such a manner as to have optical properties allowing the polyester film to be used together with a polarizing film, but it is not intended to produce a polarizing film comprising a PVA-based resin layer and having a small thickness and excellent optical properties. That is, the method disclosed in the Patent Document 4 is no more than a technique of improving optical properties of a polyester resin film to be stretched together with a PVA-based resin layer to be formed as a polarizing film. A polarizer material production method having the same object is also disclosed in JP 08-012296B (Patent Document 5).
However, the method which comprises: forming a PVA-based resin layer on a thermoplastic resin substrate by a coating process; and subjecting the PVA-based resin layer to stretching, together with the thermoplastic resin substrate to produce a polarizing film, as disclosed in the Patent Documents 1 to 5, is incapable of stably producing a polarizing film which has an extremely small thickness of 10 μm or less, and exhibiting a high single transmittance and a high polarization degree.
JP 4691205B (Patent Document 6) discloses a polarizing film improved in view of the above problems to have a thickness of 10 μm or less and exhibit an enhanced single transmittance and polarization degree. A polarizing film production method disclosed in the Patent Document 6 is configured to subject a non-crystallizable thermoplastic resin substrate and a PVA-based resin layer applied on the substrate to first-stage in-air stretching and second-stage in-boric-acid-solution stretching, together, thereby making it possible to stably form a thinned polarizing film having a thickness of 10 μm or less.
Patent Document 1: JP 4279944B
Patent Document 2: JP 2001-343521A
Patent Document 3: JP 2003-043257A
Patent Document 4: U.S. Pat. No. 4,659,523A
Patent Document 5: JP 08-012296B
Patent Document 6: JP 4691205B
Non-Patent Document 1: K. Matsuhiro, “Xpol and its Application to 3D-TV”, “EKISHO”, Vol. 14, No. 4, 2010, pp 219-232
Recently, there has been an increasing need for an organic EL display device to further reduce electrical consumption to save electricity, and extend a continuously usable time period of the device. In order to reduce electrical consumption, it is necessary to reduce an organic EL emission intensity. Further, in order to maintain sufficient viewability at lower emission intensity, it is necessary to improve a transmittance of a polarizing film used as a display surface of an organic EL display device. However, in a thinned polarizing film prepared by a conventional technique, an increase in single transmittance undesirably causes deterioration in durability. For example, when a thinned and high-transmittance polarizing film prepared by a conventional technique is subjected to a durability test, an appearance defect, such as color unevenness, occurs.
The problem of deterioration in durability first became prominent when a thinned and high-single transmittance polarizing film had been prepared. A causal factor of the problem clarified by inventors' speculations will be described below.
Generally, a polarizing film is prepared by subjecting a PVA resin to a dyeing step to cause a dichroic material to be adsorbed to the PVA resin, and subjecting the PVA resin with the adsorbed dichroic material to a stretching step to cause the dichroic material to be molecularly oriented. In recent years, iodine has been commonly used as the dichroic material. In the dyeing step, the PVA resin is immersed in an aqueous iodine solution. In this regard, however, iodine molecules (I2) are not soluble in water by themselves. Therefore, iodine is dissolved in water together with potassium iodide (KI) to prepare an aqueous iodine-potassium iodide solution. In the aqueous iodine-potassium iodide solution, in addition to potassium ions (K+) and iodine ions (I−), there are polyiodide ions (I3− and I5−) each formed by coupling between iodine ions and an iodine molecule. In the dyeing step, iodine ions and polyiodide ions are adsorbed to and impregnated into the PVA resin. Then, in the subsequent stretching step, the PVA resin is stretched and molecularly oriented, and the polyiodide ions are also oriented in a stretching direction. Depending on an angle of a polarization direction of entering light with respect to an orientation direction of the oriented polyiodide ions, the oriented polyiodide ions provide different transmittances, so that the dyed and stretched PVA resin functions as a polarizing film.
It is believed that iodine exists in a PVA resin in accordance with the following two chemical equilibrium equations:
As represented by Formula 1, a pentaiodide ion is subjected to thermal reaction with an iodine ion, and decomposed into two triiodide ions. Further, as can be seen from Formula 2, a triiodide ion is thermally decomposed into an iodine ion and an iodine molecule. On the other hand, in the presence of water such as a high-humidity environment, a reverse reaction with respect to the above thermal decomposition reaction occurs. However, except for usage in aqueous solution and a humidified environment, for example, in a normal usage state in an organic EL display device, the thermal decomposition reaction would be dominant, because of a small amount of water in the PVA resin. Thus, a polyiodide ion is decomposed by the thermal decomposition reaction, thereby causing degradation of the polarizing film.
In order to obtain sufficient polarization performance even when a thickness of a polarizing film is reduced (e.g., to 7 μm or less), it is necessary to maintain an amount of iodine in PVA, so that it becomes necessary to increase an iodine density in the PVA resin. The increased iodine density leads to an increase in speed of the reactions presented by Formulas 1 and 2, i.e., an acceleration of the polyiodide decomposition reaction, causing deterioration in durability. Therefore, along with a reduction in thickness of the polarizing film, durability of the polarizing film would become more deteriorated.
On the other hand, in order to increase the transmittance, it is necessary to reduce an amount of complex of the polyiodide ion and PVA (polyiodide ion complex) (the number of cross-linking nodes), under a condition that a thickness of a polarizing film is kept constant. It is assumed that, when the number of cross-linking nodes is reduced, a stability of the polyiodide ion is undesirably deteriorated, and therefore durability of the polyiodide ion against thermal decomposition is deteriorated.
That is, both smaller thickness and higher transmittance becomes a factor causing deterioration in durability, so that a thinned and high-transmittance polarizing film obtained by a conventional technique would have poor durability.
It is an object of the present invention to provide a polarizing film having a small thickness but exhibiting a high transmittance and a high durability. It is also an object of the present invention to provide an optically functional film laminate including the polarizing film, a production method for an optical film laminate including the polarizing film, and an organic EL display device having the polarizing film.
As a result of researches based on recognition of the above problems and clarification of causal factors, the inventors found that durability is improved by increasing a mole ratio (I/K) of elemental iodine to elemental potassium contained in a polarizing film, and have reached the present invention.
The reason why durability is improved by increasing a mole ratio (I/K) of iodine (I) to potassium (K), assumed by the inventors, will be described below.
As can be seen from Formulas 1 and 2, the thermal decomposition reaction proceeds in such a manner that a pentaiodide ion is subjected to collision with an iodine ion and thereby decomposed into two triiodide ions, and then the triiodide ion is decomposed into an iodine ion and an iodine molecule. Thus, thermal decomposition of a pentaiodide ion can be suppressed by reducing an amount of iodine ions to make the iodine ion less likely to collide with the pentaiodide ion. Further, the suppression of the thermal decomposition of the pentaiodide ion leads to a reduction in amount of triiodide ions, so that the decomposition of the triiodide ion represented by Formula 2 is also suppressed. Thus, it is expected that a reduction in iodine ion concentration makes it possible to suppress thermal decomposition of polyiodide ion to thereby improve durability.
In order to reduce the iodine ion concentration, it is necessary to reduce a potassium iodide concentration. This is because an amount of iodine ions becomes smaller along with a reduction in amount of potassium ions. Further, a reduction in amount of potassium iodide under a condition that an amount of elemental iodine is kept constant means that an amount of iodine ions is relatively small, and, on the other hand, an amount of iodine molecules is relatively large, so that it may be said that the iodine ions are bound to the iodine molecules, and thus there are a larger number of polyiodide ions. In other words, under the condition that an amount of elemental iodine is kept constant, along with a reduction in potassium ions, an amount of polyiodide ions becomes larger, and an amount of iodine ions becomes smaller, to allow positive and negative charges to balance out. Thus, it may be said that the thermal decomposition of polyiodide ion can be suppressed by relatively increasing an amount of elemental iodine contained in the PVA resin with respect to an amount of elemental potassium.
Based on the above speculations, the inventors propose a polarizing film which is in the form of a continuous web and capable of solving the durability problem. The polarizing film is comprised of a polyvinyl alcohol-based resin containing potassium and molecularly-oriented iodine, wherein the polarizing film has a thickness of 7 μm or less, and exhibits a single transmittance of 44.0% or more, and wherein a mole ratio (I/K) of elemental iodine (I) to elemental potassium (K) contained in the polarizing film is 1.8 or more.
Preferably, in the polarizing film of the present invention, an elemental iodine concentration in the polarizing film is 6 weight % or less.
Preferably, in the polarizing film of the present invention, the mole ratio (I/K) of elemental iodine (I) to elemental potassium (K) contained in the polarizing film is 3.0 or less.
In the polarizing film of the present invention, the single transmittance of the polarizing film may be 44.3% or more, and the thickness of the polarizing film may be 5 μm or less.
Further, according to another aspect of the present invention, there is provided an optically functional film laminate which comprises the above polarizing film; an optically functional film provided on the side of one of opposite surfaces of the polarizing film; and a peeling film releasably provided on the side of the other surface through a pressure-sensitive adhesive layer. In this case, the optically functional film is preferably composed of a transparent optically functional film, such as a TAC (triacetyl cellulose-based) film or an acrylic-based film. As a material for bonding or adhesively bonding a layer, it is possible to appropriately select and use a material comprising, as a base polymer, a polymer, such as acrylic-based polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine or rubber-based polymer, isocyanate-based polymer, polyvinyl alcohol-based polymer, gelatin-based polymer, vinyl or latex-based polymer, or waterborne polyester.
According to yet another aspect of the present invention, there is provided an optically functional film laminate which comprises: the above polarizing film; a first optically functional film provided on the side of one of opposite surfaces of the polarizing film; and a second optically functional film provided on the side of the other surface, wherein the optically functional film laminate further comprises a peeling film releasably provided on one of opposite surface thereof through a pressure-sensitive adhesive layer.
According to still another aspect of the present invention, there is provided an optically functional film laminate which comprises: the above polarizing film; a protective layer provided on the side of one of opposite surfaces of the polarizing film; and a retardation layer provided on the side of the other surface and configured to generate circularly-polarized light in cooperation with the polarizing film, wherein the optically functional film laminate further comprises a peeling film releasably provided on one surface thereof through a pressure-sensitive adhesive layer. In this case, it is preferable that the protective layer is composed of a TAC (triacetyl cellulose-based) film, and the retardation layer is composed of a biaxial retardation film having a three-dimensional refraction index satisfying the following relationship: nx>nz>ny.
According to yet still another aspect of the present invention, there is provided an organic EL display device which comprises an optically functional film laminate which includes: the above polarizing film; a first retardation layer on the side of one of opposite surfaces of the polarizing film; and a protective layer of a transparent resin material on the side of the other surface, wherein the optically functional film laminate is provided on one surface of an organic EL display panel through a pressure-sensitive adhesive layer lying on the side of the first retardation layer, and wherein the optically functional film laminate is operable to generate circularly-polarized light so as to prevent light entering from a viewing side of the polarizing film from exiting toward the viewing side after internal reflection.
According to another further aspect of the present invention, there is provided a method of producing an optical film laminate in which a polarizing film comprised of a polyvinyl alcohol-based resin having molecularly-oriented iodine is formed on a non-crystallizable ester-based thermoplastic resin substrate in the form of a continuous web, wherein the polarizing film has a thickness of 7 μm or less, and exhibits a single transmittance of 44.0% or more. The method comprises: a first stretching step of subjecting a laminate including the non-crystallizable ester-based thermoplastic resin substrate and a polyvinyl alcohol-based resin layer formed on the non-crystallizable ester-based thermoplastic resin substrate, to in-air stretching to form a stretched laminate comprising a stretched intermediate product consisting of a molecularly-oriented polyvinyl alcohol-based resin layer; a first insolubilization step of subjecting the stretched intermediate product comprised in the stretched laminate to insolubilization to form an insolubilized stretched laminate; a dyeing step of adsorbing iodine to the insolubilized stretched laminate to form a dyed laminate; a second insolubilization step of subjecting the stretched intermediate product comprised in the dyed laminate to insolubilization to form an insolubilized dyed laminate;
a second stretching step of subjecting the insolubilized dyed laminate to stretching in an aqueous boric acid solution to form an optical film laminate including a polarizing film comprised of a polyvinyl alcohol-based resin having molecularly-oriented iodine; and a cleaning step of cleaning the optical film laminate by an aqueous potassium iodide solution to allow a mole ratio (I/K) of elemental iodine (I) to elemental potassium (K) contained in the polarizing film to be 1.8 or more.
Preferably, in the method of the present invention, the first insolubilization step consists of a step of immersing the stretched laminate in an aqueous boric acid solution, and the second insolubilization step consists of a step of immersing the dyed laminate in an aqueous boric acid solution.
Preferably, in the method of the present invention, the second stretching step consists of a step of stretching the insolubilized dyed laminate in an aqueous boric acid solution containing boric acid in an amount of 6.5 weight parts or more and potassium iodide in an amount of 5 weight parts, with respect to 100 weight parts of water, to form an optical film laminate including a polarizing film comprised of a polyvinyl alcohol-based resin having molecularly-oriented iodine, and the cleaning step consists of a step of cleaning the optical film laminate by an aqueous potassium iodide solution containing potassium iodide in an amount of 0.5 to 2 weight parts with respect to 100 weight parts of water.
In the method of the present invention, the non-crystallizable thermoplastic resin substrate may be a non-crystallizable ester-based thermoplastic resin substrate. In this case, the non-crystallizable ester-based thermoplastic resin preferably consists of non-crystallizable polyethylene terephthalate including polyethylene terephthalate copolymerized with isophthalic acid, polyethylene terephthalate copolymerized with cyclohexanedimethanol or other copolymerized polyethylene terephthalate, wherein the non-crystallizable polyethylene terephthalate is set to have an orientation function of 0.10 or less, and subjected to elevated-temperature in-air stretching in-air stretching. Further, the non-crystallizable thermoplastic resin substrate is preferably made of a transparent resin.
As one embodiment, the method of the present invention may further comprise a step of applying a polyvinyl alcohol-based resin onto the non-crystallizable thermoplastic resin substrate and drying the applied polyvinyl alcohol-based resin to form a polyvinyl alcohol-based resin layer on the non-crystallizable thermoplastic resin substrate.
Preferably, the method of the present invention, the first stretching step is performed at a stretching ratio of 3.5 times or less. Further, the first stretching step is preferably performed at a stretching temperature equal to or greater than a glass transition temperature of the polyvinyl alcohol-based resin. A total stretching ratio for the stretched laminate and the dyed laminate in the first and second stretching steps is preferably set in the range of 5.0 to 6.5 times.
The present invention can provide a polarizing film having a high durability while achieving a small thickness and a high transmittance.
a is a sectional view illustrating one example of an organic EL display device according to a first embodiment of the present invention.
b is a sectional view illustrating another example of the organic EL display device according to the first embodiment of the present invention.
c is a sectional view illustrating yet another example of the organic EL display device according to the first embodiment of the present invention.
d is a sectional view illustrating still another example of the organic EL display device according to the first embodiment of the present invention.
e is a sectional view illustrating yet still another example of the organic EL display device according to the first embodiment of the present invention.
f is a sectional view illustrating another further example of the organic EL display device according to the first embodiment of the present invention.
g is a sectional view illustrating still a further example of the organic EL display device according to the first embodiment of the present invention.
h is a sectional view illustrating an additional example of the organic EL display device according to the first embodiment of the present invention.
a is a sectional view illustrating one example of an optical display device according to a third embodiment of the present invention.
b is a sectional view illustrating another example of an optical display device according to the third embodiment of the present invention.
Explanations about Inventive Examples 1 to 3 will be described below. For comparison and reference, Comparative Example and Reference Examples 1 and 2 will also be described.
Methods for determining respective properties of each polarizing film will be described below. Measurement items concerning properties of each polarizing film consist of thickness, transmittance, iodine concentration and content ratio of elemental iodine to elemental potassium. The following measurement method for each of the properties is one example, and any other suitable measurement method may be employed.
A thickness of each polarizing film was measured using a digital micrometer (KC-351C produced by Anritsu Corporation).
The measurements of optical properties of each polarizing film were performed in a state in which a protective layer (acrylic-based film) was laminated to the polarizing film in order to facilitate handling of the polarizing film. The polarizing film with the protective layer laminated thereto was subjected to measurement of single transmittance, using a UV-visible spectrophotometer (V7100 produced by JASCO Corporation), and the measured single transmittance was determined as a transmittance of the polarizing film. As used here, the term “transmittance” is a Y value measured by the 2-degree visual field (C light source) of JIS Z8701 and corrected for spectral luminous efficacy. Absorption of the protective layer is negligibly small as compared to absorption of the polarizing film. Thus, a transmittance of the laminate was determined as a transmittance of the polarizing film.
The polarizing film with the protective layer laminated thereto was subjected to quantitative measurement of elemental iodine concentration, using a calibration curve method for fluorescent X-ray analysis. An X-ray fluorescence spectrometer (ZSX produced by Rigaku Corporation) was used as an analyzer. Neither elemental iodine nor elemental potassium is contained in the protective layer, so that there is no influence of the protective layer on the measurement result.
A value directly obtained by the X-ray fluorescence spectrometer is not a concentration of each element but an absorption intensity at a wavelength corresponding to each element. Thus, in order to obtain a concentration of elemental iodine or elemental potassium contained in each polarizing film, it is necessary to convert the measured absorption intensity value into an element concentration. As used in this specification, the terms “elemental iodine concentration” and “elemental potassium concentration” in each polarizing film mean, respectively, an elemental iodine concentration (weight %) and an elemental potassium concentration (weight %) on the basis of a weight of the polarizing film.
The calibration curve was prepared as follows.
1. Potassium iodide and iodine were dissolved in an aqueous PVA solution in respective known amounts to prepare a plurality of types of aqueous PVA solutions each containing iodine and potassium iodide in respective known concentrations. The aqueous PVA solutions were applied and dried to prepare a plurality of types of PVA film samples each containing potassium and iodine in respective element concentrations. An elemental iodine concentration, an elemental potassium concentration and an element ratio of iodine to potassium are presented in
2. Each of the prepared PVA films was subjected to X-ray fluorescent spectrometric analysis using the X-ray fluorescence spectrometer to detect absorption intensities corresponding to elemental iodine and elemental potassium. A result of the detection is presented in
3. The absorption intensity was divided by a thickness (μm) of the PVA film to obtain an absorption intensity per unit film thickness (kcps/μm).
4. Then, based on the detection result presented in
(Elemental iodine concentration [weight %]=18.2×(detected intensity per unit film thickness) [kcps/μm] (Formula 3)
Elemental potassium concentration [weight %]=2.99×(detected intensity per unit film thickness) [kcps/μm] (Formula 4)
5: A ratio of the detected intensity of iodine to the detected intensity of potassium was calculated. The elemental iodine concentration and the elemental potassium concentration are known, so that a mole ratio of elemental iodine to elemental potassium in each prepared PVA film can be computationally obtained. Thus, a formula for converting a ratio of an iodine absorption intensity to a potassium absorption intensity detected by measurement of each polarizing film, into a mole ratio of elemental iodine to elemental potassium contained in the polarizing film, can be obtained by calculating a conversion factor between the detected intensity ratio and the known mole ratio with respect to each of the plurality of samples, and averaging the calculated conversion factors. The average of the intensity ratio-to-mole ratio conversion factors in the plurality of samples is 1.91, and the conversion formula is expressed as Formula 5.
I/K (mole ratio)=I/K (intensity ratio)×1.91 (Formula 5)
As with Inventive Examples 1 to 3, Comparative Example for comparison to Inventive Examples has a thickness of 5 μm and exhibits a transmittance of 45.0%. On the other hand, an element content ratio of iodine to potassium is 1.6. A polarizing film of Reference Example 1 is a thin type having a thickness of 5 μm but a low-transmittance type having a transmittance of 42.8%. A polarizing film of Reference Example 2 can be deemed as a high-transmittance type having a transmittance of 45.0% but is a thick type having a thickness of 23 μm.
Inventive Examples 1 to 3, Comparative Example and Reference Examples 1 and 2 were subjected to evaluation of durability in the following manner. The evaluation of durability was performed using a circularly-polarizing film formed by laminating a target polarizing film to be evaluated, and a ¼ wavelength retardation film. The ¼ wavelength retardation film was prepared by synthesizing a film material and subjecting the film material to film formation and stretching, in the following manner.
In order to synthesize a film material, 397.3 weight parts of isosorbide (produced by Roquette Freres, trade name: POLYSORB, hereinafter referred to as “ISB”), 960.1 weight parts of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (produced by Osaka Gas Chemicals Co., Ltd., hereinafter referred to as “BHEPF”), 14.6 weight parts of polyethylene glycol having a number average molecular weight of 1000 (produced by Sanyo Chemical Industries, Ltd., hereinafter referred to as “PEG #1000”), 1065.1 weight parts of diphenyl carbonate (produced by Mitsubishi Chemical Corporation, hereinafter referred to as “DPC”), and 8.45×10−3 weight parts of magnesium acetate tetrahydrate serving as a catalyst, were put into a reactor container, and, as a first-stage reaction step, a temperature of a heating medium of the reactor container was set to 150° C. to melt the raw materials in a nitrogen atmosphere, while stirring them as needed, by taking about 15 minutes. Then, an internal temperature of the reactor container was increased up to 220° C., and, immediately after reaching 220° C., an internal pressure of the reactor container was reduced from normal pressure to 13.3 kPa by taking 90 minutes. During the pressure reduction, the internal temperature was maintained at 220° C. Generated phenol was extracted and released to an outside of the reaction container. As a second-stage reaction step, after reaching 13.3 kPa, the internal temperature was increased up to 240° C. by taking 15 minutes. During the temperature rise, the internal pressure was maintained at 13.3 kPa. After the internal temperature reaches 240° C., the internal pressure was reduced from 13.3 kPa to 200 Pa or less by taking 15 minutes. After reaching a given stirring torque, the reaction is terminated. Then, a resulting reaction product was pushed out into water, and subjected to pelletization to obtain a polycarbonate resin in which BHEPF/IBS/PEG #1000=44.5 mol %/55.2 mol %/0.3 mol %.
Then, as a film formation and stretching step, the obtained polycarbonate resin was subjected to vacuum-drying at 80° C. for 5 hours, and a 95 μm-thick polycarbonate film was prepared using a film-forming apparatus equipped with a single-screw extruder (produced by Isuzu Kakoki Co, Ltd., screw diameter: 25 mm, cylinder preset temperature: 220° C.), a T-die (width: 200 mm, preset temperature: 220° C.), a chill roll (preset temperature: 120 to 130° C.) and a winder. The prepared polycarbonate film was subjected to vacuum-drying at 100° C. for 3 days to remove volatile components contained in the film, such as phenol. The film treated in this manner was subjected to uniaxial stretching at a stretching ratio of 1×2.0 times by using a batch-type biaxial stretching apparatus (produced by Bruckner Maschinenbau GmbH), at a stretching speed of 360 mm/min (stain rate: 300%/min), while adjusting a stretching temperature to allow R1 (550) to fall within 130±20 nm, to thereby obtaining a ¼ wavelength retardation film. In this step, the stretching was performed without holding the film in a direction perpendicular to a stretching direction.
A circularly-polarizing film was prepared by arranging a surface of the target polarizing film and the ¼ wavelength retardation film in such a manner that an angle between an absorption axis of the polarizing film and a slow axis of the ¼ wavelength retardation film becomes 45 degrees. Regarding Reference Example 2, a laminate was prepared by laminating a saponified triacetylcellulose film (40 μm) to each of opposite sides of a polarizing film, and a circularly-polarizing film was prepared by laminating the ¼ wavelength retardation film to the laminate. A PVA-based adhesive was used for the lamination between the polarizing film and the triacetylcellulose film.
Then, each of the circularly-polarizing films was cut into A4 size and laminated to a 0.7 μm-thick glass plate through an acrylic-based pressure-sensitive adhesive (20 μm) lying on the side of the ¼ wavelength retardation film of the circularly-polarizing film. In advance of a durability test, no presence of an appearance defect in the circularly-polarizing film laminated to the glass plate was ascertained. After ascertaining no presence of an appearance defect, the circularly-polarizing film was stored in an oven at 85° C. for 100 hours, and then a visual quality on reflected light at a surface of the circularly-polarizing film was checked. Specifically, the circularly-polarizing film laminated to the glass plate was placed on a reflective plate having a reflectance of 80% or more, while orienting the glass plate downwardly, and a visual quality was evaluated in this state.
A result of the evaluation is presented in
As for durability, any polarizing film having no appearance defect such as color unevenness or line-like pattern during visual inspection after the above durability test was evaluated as “Good”.
As for thinness, any polarizing film having a thickness of 7 μm or less, usable as a polarizing film for an organic EL display device, was evaluated as “Good”.
As for brightness, any polarizing film having a transmittance of 44.0% or more was evaluated as “Good”.
All of the polarizing films of Inventive Examples 1 to 3 have a small thickness of 5 μm, and exhibit a high transmittance of 45%. In addition, when they were subjected to the durability test after ascertaining no presence of an appearance defect, no appearance defect occurred in Inventive Examples 1 to 3 even after the durability test. Therefore, it can be said that each of the polarizing films of Inventive Examples 1 to 3 is a thinned and high-transmittance type with a high durability, and suitable as a polarizing film for use in, but not limited to, an organic EL display device.
The polarizing film of Comparative Example has a small thickness of 5 μm and a high transmittance of 45%, as mentioned above. However, although no presence of an appearance defect in Comparative Example was ascertained in advance of the durability test, an appearance defect of line-like pattern extending obliquely from an upper side toward a lower right side of the polarizing film was ascertained after the durability test, as indicated in
The polarizing film of Reference Example 1 exhibits a high durability but a low transmittance of 42.8%. Thus, in order to allow light transmitted through the polarizing film to have a certain level of intensity, it is necessary to enter light having a higher intensity. Therefore, in the case where the polarizing film of Reference Example 1 is used, for example, in an organic EL display device, it is necessary to generate entering light having a higher intensity, resulting in consumption of larger electricity. The polarizing film of Reference Example 2 also exhibits a high durability but has a large thickness of 23 μm. Thus, when the polarizing film of Reference Example 2 is used as a polarizing film for use, for example, in an organic EL display device, expansion and contraction thereof are likely to cause deformation, such as warp, in an adjacent member. From the above measurement results, it can be understood that, differently from the prior-art polarizing films, each of the polarizing films of Inventive Examples 1 to 3 has an advantageous effect of having a small thickness but exhibiting a high transmittance and a high durability.
Production methods for Inventive Examples 1 to 3, Comparative Example and Reference Examples 1 and 2 will be described below. Before that, an outline of general material properties of a thermoplastic resin usable in producing a polarizing film for use in the present invention will be described.
Thermoplastic resins are roughly classified into two types: one which is in a state in which polymer molecules are orderly arranged; and the other which is in a state in which only a small portion of polymer molecules are orderly arranged. The former state is called “crystallized state”, and the latter state is called “amorphous or non-crystallized state. Correspondingly, one type of thermoplastic resin having a property capable of being transformed from a non-crystallized state into a crystallized state depending on conditions is called “crystallizable resin”, and the other type of thermoplastic resin which does not have such a property is called “non-crystallizable resin”. On the other hand, regardless of whether a crystallizable resin or a non-crystallizable resin, a resin which is not in a crystallized state or has not been transformed into a crystallized state, is called “amorphous or non-crystalline resin”. The term “amorphous or non-crystalline” will be used herein in distinction from the term “non-crystallizable” which means a property incapable of transformation into a crystallized state.
Examples of the crystallizable resin include olefin-based resins such as polyethylene (PE) and polypropylene (PP), and ester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). One feature of the crystallizable resin is that it has a property of being able to achieve orderly arrangement of polymer molecules, i.e., a progress in crystallization, by means of heating and/or stretching/molecular-orientation. Physical properties of a resin vary according to a degree of crystallization. On the other hand, even in crystallizable resins such as polypropylene (PP) and polyethylene terephthalate (PET), it is possible to suppress crystallization by inhibiting orderly arrangement of polymer molecules to be caused by heating or stretching/molecular-orientation. The crystallization-inhibited polypropylene (PP) and polyethylene terephthalate (PET) will hereinafter be referred to respectively as “non-crystallizable polypropylene” and “non-crystallizable polyethylene terephthalate”, and referred to respectively and generically as “non-crystallizable olefin-based resin” and “non-crystallizable ester-based resin”.
For example, as for polypropylene (PP), it is possible to produce a crystallization-inhibited non-crystallizable polypropylene (PP) by forming it into an atactic structure having no stereoscopic regularity. For example, as for polyethylene terephthalate (PET), it is possible to produce a crystallization-inhibited non-crystallizable polyethylene terephthalate (PET) by copolymerizing therewith isophthalic acid or a modifier group such as 1,4-cyclohexanedimethanol, as a polymerizing monomer, i.e., by copolymerizing therewith a molecule which inhibits crystallization of polyethylene terephthalate (PET).
A continuous web of 200 μm-thick substrate (produced by Mitsubishi Plastics, Inc., trade name: NOVACLEAR SH046, thickness: 200 μm) made of isophthalic acid-copolymerized polyethylene terephthalate (hereinafter referred to as “non-crystallizable PET”) copolymerized with 6 mole % of isophthalic acid was used as a thermoplastic resin substrate serving as a substrate to which the polarizing film is to be applied. This thermoplastic resin is a non-crystallizable type, so that crystallization is less likely to occur even by applying heat thereto, and a stretching ratio is less likely to be lowered. The continuous web of substrate made of polyethylene terephthalate has a glass transition temperature of 75° C. For comparison, a PVA layer has a glass transition temperature of 80° C.
An aqueous PVA solution obtained by dissolving, in water in a concentration of 4 to 5%, a PVA power (polymerization degree: 4200, saponification degree: 99.2%) added with 1 wt % of acetoacetyl-modified PVA (produced by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Gohsefimer Z200) (polymerization degree: 1200, saponification degree: 99 mol %, acetoacetyl-modification degree: 4.6%) was used. Then, in a laminate preparation apparatus 20 equipped with a coating device 21, a drying device 22 and a surface modifying unit 23, the aqueous PVA solution is applied to the non-crystallizable PET substrate 1 in such a manner as to allow a film thickness after drying to become 12 μm, and subjected to hot-air drying in an atmosphere at 60° C. for 10 minutes to prepare a laminate in which a PVA-based resin film is formed on the substrate. The laminate obtained in the above manner will hereinafter be referred to as “laminate in which a PVA layer is formed on a non-crystallizable PET substrate”, “laminate including a PVA layer (PVA layer-including laminate)” or “laminate 7”.
The laminate 7 including a PVA layer 2 will be finally produced as a 5 μm-thick polarizing film 3 through the following process comprising a two-stage stretching process consisting of preliminary in-air stretching and in-boric-acid-solution stretching. While the present invention is intended to use a polarizing film having a thickness of 7 μm or less, it is possible to prepare a polarizing film having an arbitrary thickness equal to or less than 7 μm (e.g., 6 μm, 4 μm or 3 μm), by appropriately changing a thickness of the PVA-based resin layer formed on the non-crystallizable PET substrate 1 and an aftermentioned stretching ratio.
[Preliminary in-Air Stretching Step (B)]
In a first-stage preliminary in-air stretching step (B), the laminate 7 including the 12 μm-thick PVA layer 2 was stretched integrally with the non-crystallizable PET substrate 1 to form a “stretched laminate 8” including the stretched PVA layer 2.
Specifically, in a preliminary in-air stretching apparatus 30 having a stretching device 31 provided within an oven 33, the laminate 7 including the PVA layer 2 was subjected to free-end uniaxial stretching through the stretching device 31 within the oven 33 having an internal atmosphere set at a stretching temperature of 130° C. which is greater than glass-transition temperatures of the PVA layer and the substrate, so as to attain a stretching ratio of 2.0, thereby forming a stretched laminate 8 including an 8 μm-thick PVA layer 2. At this stage, the stretched laminate 8 can be rolled up by a take-up unit 32 provided in side-by-side relation to the oven 33, to produce a roll 8′ of the stretched laminate 8. In this process for Inventive Example 1, the stretching ratio in the preliminary in-air stretching step is set to 2.0 times. Alternatively, the stretching ratio may be increased up to 3.5 times greater than that in this process.
In this connection, an outline of free-end stretching and fixed-end stretching will be described below. When an elongated film is stretched in a conveyance direction thereof, the film is contracted in a direction perpendicular to a stretching direction along which the film is stretched, i.e., a width direction. The free-end stretching means a technique of stretching a film without suppressing such a contraction. Further, longitudinal uniaxial stretching means a technique of stretching a film only in a longitudinal direction thereof. Free-end uniaxial stretching is a technique typically contrasted with fixed-end uniaxial stretching as a technique of stretching a film while suppressing contraction which would otherwise occur in a direction perpendicular to the stretching direction. As a result of the above free-end uniaxial stretching, the 12 μm-thick PVA layer 2 included in the laminate 7 is formed as an 8 μm-thick PVA layer 2 in which PVA molecules are oriented in the stretching direction.
Then, in a first insolubilization step (C), the stretched laminate 8 unrolled from a feeding unit 43 loaded with the roll 8′ was subjected to insolubilization to form an insolubilized stretched laminate 9. Obviously, the stretched laminate 9 insolubilized in this step includes an insolubilized PVA layer 2. This laminate will hereinafter be referred to as “insolubilized stretched laminate 9”.
Specifically, in a first insolubilization apparatus 40 holding a first insolubilizing aqueous boric acid solution 41, the stretched laminate 8 was immersed in the first insolubilizing aqueous boric acid solution 41 set at a solution temperature of 30° C., for 30 seconds. The first insolubilizing aqueous boric acid solution 41 used in this step contains 3 weight parts of boric acid with respect to 100 weight parts of water. This step is intended to subject the stretched laminate 8 to insolubilization for preventing dissolution of the PVA layer included in the stretched laminate 8 at least in a subsequent dyeing step (D).
Then, in a dyeing step (C), a dyed laminate 10 in which iodine as a dichroic material is adsorbed to the 8 μm-thick PVA layer 2 having molecularly-oriented PVA molecules was formed. Specifically, in a dyeing apparatus 50 which comprises a dyeing bath 52 of a dyeing solution 51 containing iodine and potassium iodide, the insolubilized stretched laminate 9 fed out from the first insolubilization apparatus 40 was immersed in the dyeing solution 51 set at a solution temperature of 30° C. to form a dyed laminate 10 in which iodine is adsorbed to the molecularly-oriented PVA layer 2 of the insolubilized stretched laminate 9.
In this step, in order to prevent dissolution of the PVA layer 2 included in the stretched laminate 8, an iodine concentration and a potassium iodide concentration were set, respectively, in the range of 0.08 to 0.25 weight % and the range of 0.56 to 1.75 weight %, and a concentration ratio of iodine to potassium iodide is set to 1:7. The iodine concentration, the potassium iodide concentration and an immersion time in this step exerts a large influence on a concentration of elemental iodine contained in the PVA layer. Therefore, a single transmittance of a final polarizing film can be adjusted by adjusting the iodine concentration, the potassium iodide concentration and the immersion time in this step. For example, in this process, it is possible to adjust the iodine concentration and the potassium iodide concentration within the above respective ranges of the iodine and potassium iodide concentrations, and further adjust the immersion time, to allow iodine to be adsorbed to the molecularly-oriented PVA layer 2 of the stretched laminate 8, in such a manner that a PVA layer included in a polarizing film 3 to be finally formed has a single transmittance of 45%. In Inventive Example 1, the single transmittance is adjusted to 45.0%. Alternatively, it may be adjusted to 44.0%, 44.3%. 44.5 or 45.5%.
A second insolubilization step (E) described below is performed for the following purposes. This step has a first purpose of insolubilization for preventing dissolution of the PVA layer 2 included in the dyed laminate 10, a second purpose of dye stabilization for preventing elution of iodine adsorbed to dye the PVA layer 2, and a third purpose of node formation for mutually cross-linking PVA molecules of the PVA layer 2 to form nodes. In particular, the second insolubilization step is intended to achieve the first and second purposes.
The second insolubilization step (E) is performed as a preceding step with respect to an aftermentioned in-boric-acid-solution stretching (F). The dyed laminate 10 formed in the dyeing step (D) was subjected to insolubilization to form an insolubilized dyed laminate 11. This laminate will hereinafter be referred to as “insolubilized dyed laminate 11”. The insolubilized dyed laminate 11 includes an insolubilized PVA layer 2. Specifically, in a second insolubilization apparatus 60 holding an aqueous solution comprising boric acid and potassium iodide (hereinafter referred to as “second insolubilizing aqueous boric acid solution”) 61, the dyed laminate 10 was immersed in the second insolubilizing aqueous boric acid solution 61 set at a solution temperature of 40° C., for 60 seconds, to cause PVA molecules of the PVA layer with iodine adsorbed thereto to be mutually cross-linked, thereby forming an insolubilized dyed laminate 11. The second insolubilizing aqueous boric acid solution 61 used in this step contains 3 weight parts of boric acid with respect to 100 weight parts of water, and further contains 3 weight parts of potassium iodide with respect to 100 weight parts of water.
In a second-stage in-boric-acid-solution stretching step, the insolubilized dyed laminate 11 including the PVA layer 2 having molecularly-oriented iodine was further stretched to form an optical film laminate 12 which includes a PVA layer having molecularly-oriented iodine and making up a 5 μm-thick polarizing film 3. Specifically, in an in-boric-acid-solution stretching apparatus 70 which comprises a boric acid bath 72 of an aqueous boric acid solution 71 containing boric acid and potassium iodide, and a stretching device 73, the insolubilized dyed laminate 11 continuously fed out from the second insolubilization apparatus 60 was immersed in the aqueous boric acid solution 71 set at a solution temperature of 70° C. degree, and then subjected to free-end uniaxial stretching through the stretching device 73 comprised in the in-boric-acid-solution stretching apparatus 70, so as to attain a stretching ratio of 2.7 times, thereby forming an optical film laminate 12. In this process, a total stretching ratio is 5.4 times. However, in the present invention, the total stretching ratio may be set in the range of 5.6 to 6.5 times, by adjusting respective stretching ratios in the preliminary in-air stretching step and the in-boric-acid-solution stretching step.
More specifically, the aqueous boric acid solution 71 was adjusted to contain 6.5 weight parts of boric acid with respect to 100 weight parts of water, and further contain 5 weight parts of potassium iodide with respect to 100 weight parts of water. In the polarizing film of the present invention, the transmittance is relatively high, i.e., the number of cross-liking nodes where polyiodide ions are adsorbed to PVA is relatively small, so that, in this step and a subsequent cleaning step, polyiodide ions and iodine ions are more likely to be eluted. Therefore, a boric acid concentration of the aqueous boric acid solution in this step is increased as compared to conventional techniques, to thereby reduce an amount of elution of polyiodide ions adsorbed to PVA (and iodine ions and potassium iodide ions). For example, in an aftermentioned process for preparing Comparative Example, the boric acid concentration of the aqueous boric acid solution used in the in-boric-acid-solution stretching step is set to 4 weight parts, whereas, in this process, it is set to 6.5 weight parts.
In this step, the insolubilized dyed laminate 11 subjected to the adjustment of an adsorbed iodine amount was immersed in the aqueous boric acid solution 71 for 5 to 10 seconds. Then, the insolubilized dyed laminate 11 in the immersed state was subjected to free-end uniaxial stretching through a plurality of roll sets each having a different circumferential velocity, as the stretching device 73 of the in-boric-acid-solution stretching apparatus 70, so as to attain a stretching ratio of 2.7 times by taking 30 to 90 seconds. As a result of this stretching, the PVA layer included in the cross-linked dyed laminate 11 was changed to a 5 μm-thick PVA layer in which polyiodide ions (I3− and I5−) are highly oriented in one direction in the form of a PVA-iodine complex. This PVA layer makes up a polarizing film 3 of the optical film laminate 12.
The insolubilized dyed laminate 11 was subjected to stretching in the in-boric-acid-solution stretching step (F), and then extracted from the aqueous boric acid solution 71. The extracted optical film laminate 12 including the polarizing film 3 was fed to a cleaning step (G). The cleaning step (G) is intended to wash out unnecessary residues adhering on a surface of the thinned and high-performance polarizing film 3. Specifically, the optical film laminate 12 was fed into a cleaning apparatus 80, and immersed in a cleaning solution 81 containing potassium iodide and set at a solution temperature of 30° C., for 1 to 10 seconds, in such a manner as to avoid dissolution of PVA of the thinned and high-performance polarizing film 3. A concentration of iodine in the cleaning solution 81 is 2.0 weight parts with respect to 100 weight parts of water.
In the present invention, it is necessary that an amount of elemental potassium contained in a polarizing film is set to be less than an amount of elemental iodine contained in the polarizing film. In this situation, an amount of potassium ions contained in the polarizing film is largely influenced by a potassium ion concentration of the cleaning solution in the cleaning step. That is, the amount of potassium ions contained in the polarizing film can be reduced by reducing the potassium ion concentration of the cleaning solution. A potassium iodide concentration of the cleaning solution used for preparation of Inventive Example 1 is 2.0 weight parts, which is less than a potassium iodide concentration (4.0 weight parts) of a cleaning solution used in the aftermentioned process for preparation of Comparative Example, as a conventional technique. The mole ratio of elemental iodine to elemental potassium contained in the polarizing film can be increased by reducing the potassium iodide concentration in the cleaning solution in this step to reduce the amount of elemental potassium contained in the polarizing film.
The cleaned optical film laminate 12 was fed to a drying step (H) and dried therein. Then, the dried optical film laminate 12 was wound on a take-up unit 91 provided in side-by-side relation to a drying apparatus 90, as a continuous web of the optical film laminate 12, to form a roll of the optical film laminate 12 including the thinned and high-performance polarizing film 3. In the drying step (H), any suitable technique, such as natural drying, blow drying and thermal drying, may be employed. In this process, the drying was performed by warm air at 60° C. for 240 seconds in the oven type drying apparatus 90.
Based on a thickness reduction by stretching, the polarizing film 3 produced in this process has a thickness of only 5 μm. Thus, it is difficult to handle such a thin polarizing film 3 as a single layer body, non-laminate. For this reason, it is common to handle the polarizing film 3, for example, in the form of the optical film laminate 12, i.e., in a state in which it is left on the non-crystallizable PET substrate 1, or, in the form of an optically functional film laminate 13 prepared by laminating the optical film laminate 12 to an additional optically functional film 4 through an adhesive and peeling off the non-crystallizable PET substrate 1 to thereby transfer the polarizing film 3 from to the non-crystallizable PET substrate 1 to the optically functional film 4. In this process, a 40 μm-thick protective layer (acrylic-based film) was laminated to one surface of the polarizing film on an opposite of the other surface in contact with the non-crystallizable PET substrate, by using an adhesive, to prepare an optically functional film laminate 13, and the optically functional film laminate 13 was subjected to measurement of optical properties as Inventive Example.
Further, a peeling film for protection may be releasably provided on one of opposite surfaces of the optically functional film laminate 13 on an opposite side of the other surface defined by the optically functional film (protective layer) laminated thereto, through a pressure-sensitive layer. Alternatively, a second optically functional film, such as a retardation layer for generating circularly-polarized light in cooperation with the polarizing film, may be provided on one of opposite surfaces of the optically functional film laminate 13 on an opposite side of the other surface defined by the first optically functional film (protective layer) laminated thereto, and further a peeling film for protection may be releasably provided on a surface of the optically functional film laminate 13 defined by the second optically functional film laminated thereto, through a pressure-sensitive layer. In the above alternative, the protective layer and the retardation film were used, respectively, as a first optically functional film and a second optically functional film. Further, according to need, an optically functional film having a different function may be additionally laminated, and a peeling film to be attached through a pressure sensitive adhesive may be attached to either one or each of opposite surfaces of the optically functional film laminate, depending on intended purposes.
Except that the content of potassium iodide in the cleaning solution in the cleaning step is set to 1 weight part with respect to 100 weight parts of water, Inventive Example 2 was prepared in the same manner as that for Inventive Example 1. Further, except that the content of potassium iodide in the cleaning solution is set to 0.5 weight parts with respect to 100 weight parts of water, Inventive Example 3 was prepared in the same manner as that for Inventive Example 1.
Except that the boric acid concentration of the aqueous boric acid solution in the in-boric-acid-solution stretching step is set to 4 weight parts with respect to 100 weight parts of water (the potassium iodide concentration is the same), the potassium iodide concentration in the cleaning solution in the cleaning step is set to 4 weight parts with respect to 100 weight parts of water, Comparative Example was prepared in the same manner as that for Inventive Example 1.
Except that the insolubilized stretched laminate is immersed in the dyeing solution in the dyeing step while adjusting the iodine concentration in the dyeing solution and the dying (immersion) time to allow a single transmittance of a finally obtained PVA layer to be 42.8%, Reference Example 1 was prepared in the same manner as that for Inventive Example 1.
A 60 μm-thick polyvinyl alcohol film (produced by Kuraray Co., Ltd, trade name: PE6000) was subjected to longitudinal uniaxially stretching by using a roller stretching machine, and simultaneously subjected to swelling, dyeing, cross-linking and cleaning. Then, the cleaned film was finally subjected to drying to prepare a 23 μm-thick polarizing film of Reference Example 2.
a to 12b illustrate organic EL display devices each using the above polarizing film, according to some embodiments of the present invention.
a is a sectional view illustrating the most basic example of an organic EL display device according to a first embodiment of the present invention. This organic EL display device 200 comprises an organic EL display panel 201, and a laminate 205 including a polarizing film 203 and a first retardation layer 204. The laminate 205 is bonded to one of opposite surfaces of the organic EL display panel 201 through an optically transparent pressure-sensitive adhesive layer 202. The polarizing film 203 and the first retardation layer 204 are configured to produce circularly-polarized light so as to prevent light entering from a viewing side of the polarizing film 203 from exiting toward the viewing side after internally reflection. A protective layer 206 made of an optically transparent resin material is adhesively bonded to an outer surface of the polarizing film 203.
As illustrated in
Optionally, a transparent window 207 as indicated by the dotted line in
The polarizing film 203 is formed to have a thickness of 7 μm or less, and exhibit a high durability. This polarizing film 203 is extremely thin, so that stress arising from expansion/contraction occurring depending on conditions of temperature or humidity becomes significantly small. Thus, it becomes possible to considerably reduce a risk that stress arising from expansion/contraction of the polarizing film causes deformation, such as warp, in the organic EL display panel 201 adjacent thereto, and drastically suppress deterioration in quality of display due to the deformation and destruction of a panel sealing material. As compared to polarizing films used in this type of conventional optical display device, the polarizing film 203 has a small thickness and exhibits a high transmittance and excellent durability, and can withstand the above durability test. This means that it can maintain performance necessary for an organic EL display device over a practically required period of use.
In this structure, as the pressure-sensitive adhesive layer 202, a material having a diffusing function may be used, or a two-layer structure of a pressure-sensitive adhesive layer and a diffusion layer may be employed.
An optical display device illustrated in
An optical display device illustrated in
An optical display device illustrated in
In an optical display device 200 illustrated in
In an organic EL display device 300 illustrated in
a illustrates an organic EL display device 400 according to another embodiment of the present invention, wherein the organic EL display device 400 has a touch input sensor function. A structure of a device body of the optical display device 400 is substantially the same as that illustrated in
b illustrates an organic EL display device 500 according to still another embodiment of the present invention, wherein the organic EL display device 500 has a touch input sensor function. A structure of a device body of the optical display device 500 is substantially the same as that illustrated in
Although the present invention has been described in term of specific exemplary embodiments, it is to be understood that the present invention is not limited to details of the embodiments, but only by the appended claims and their legal equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-167728 | Aug 2013 | JP | national |
