Polarizing film, laminated polarizing film, image display panel, and image display device

Abstract

The invention relates to a polarizing film, a laminated polarizing film, an image display panel, and an image display device. A polarizer formed from a polyvinyl alcohol-based film, the polarizer containing boron and potassium, the content of the boron being 4-6 wt% inclusive in the polarizer, and the value obtained by multiplying the content (wt%) of the boron by the content (wt%) of the potassium being 1.2 or more. The polarizer has an excellent effect of suppressing a decrease in optical characteristics in a high-temperature environment.

Description

[0001] This application is a divisional application of application number 201980022317.6, filed on March 22, 2019, entitled "Polarizing element, polarizing film, laminated polarizing film, image display panel and image display device", and application number 202310236094.1, entitled "Polarizing element, polarizing film, laminated polarizing film, image display panel and image display device". Technical Field

[0002] This invention relates to polarizing elements, polarizing films, laminated polarizing films, image display panels, and image display devices. Background Technology

[0003] Traditionally, polarizing elements used in various image display devices such as liquid crystal displays and organic EL displays utilize dyed polyvinyl alcohol (PVA) films containing dichroic substances, which offer both high transmittance and high polarization. These polarizing elements are manufactured by subjecting the PVA film to various treatments in a bath, such as swelling, dyeing, cross-linking, and stretching, followed by cleaning and drying. Furthermore, these polarizing elements are typically used in the form of polarizing films (polarizing plates) with a protective film such as cellulose triacetate bonded to one or both sides using an adhesive.

[0004] The aforementioned polarizing film can be used as a stacked polarizing film (optical stack) by stacking other optical layers as needed. The aforementioned polarizing film or the aforementioned stacked polarizing film (optical stack) is bonded between an image display unit such as a liquid crystal cell or an organic EL element and a transparent plate such as a front panel or a touch panel on the visual recognition side by means of an adhesive layer, and is used as the aforementioned various image display devices.

[0005] In recent years, such image display devices have been widely used not only in mobile devices such as mobile phones and tablets, but also in in-vehicle image display devices such as car navigation devices and rearview monitors. Consequently, compared with previous requirements, the aforementioned polarizing films and the aforementioned stacked polarizing films are required to have higher durability under more severe environments (e.g., high temperature environments), and polarizing films for the purpose of ensuring such durability have been proposed (Patent Document 1).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2012-516468 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The conventional polarizing films and laminated polarizing films described above have the following problems: when exposed to high temperatures, polyvinyl alcohol undergoes polyolefination, resulting in coloration of the polarizing element and a decrease in its optical properties. In particular, image display devices constructed by bonding the aforementioned polarizing films and laminated polarizing films between the image display unit and the transparent plate using an adhesive layer suffer from significant coloration of the polarizing element and a significant decrease in its optical properties.

[0011] In view of the above, the object of the present invention is to provide a polarizing element with excellent suppression effect on the reduction of optical properties under high temperature environment.

[0012] Furthermore, an object of the present invention is to provide a polarizing film, a stacked polarizing film, an image display panel, and an image display device that utilize the aforementioned optical characteristics to achieve excellent suppression of light reduction.

[0013] Solution for solving the problem

[0014] That is, the present invention relates to a polarizing element formed of a polyvinyl alcohol-based film, wherein the polarizing element contains boron and potassium, wherein the boron content is 4% by weight or more and 6% by weight or less, and the value obtained by multiplying the boron content (by weight) by the potassium content (by weight) is 1.2 or more.

[0015] In addition, the present invention relates to a polarizing film having a transparent protective film attached to at least one side of the aforementioned polarizing element.

[0016] In addition, the present invention relates to a stacked polarizing film, wherein the aforementioned polarizing film is bonded to an optical layer.

[0017] In addition, the present invention relates to an image display panel, wherein the aforementioned polarizing film or the aforementioned stacked polarizing film is bonded to the image display unit.

[0018] In addition, the present invention relates to an image display device having a transparent plate on the side of the aforementioned image display panel with a polarizing film or a stacked polarizing film.

[0019] The effects of the invention

[0020] The exact mechanism of action of the polarizing element, the polarizing film having the polarizing element, the stacked polarizing film, the image display panel, and the image display device of the present invention is unclear in some aspects, and speculations are made as follows. However, the present invention is not limited to the interpretation of this mechanism of action.

[0021] The polarizing element of the present invention is formed from a polyvinyl alcohol-based film and contains boron and potassium. In the aforementioned polarizing element, the boron content is 4% by weight or more and 6% by weight or less, and the value obtained by multiplying the boron content (by weight) by the potassium content (by weight) is 1.2 or more. It is known that conventional polarizing elements contain boron and potassium, but the polarizing element of the present invention, by containing the aforementioned specific amounts of boron and potassium, can further improve heat resistance compared to conventional polarizing elements. In particular, as with the polarizing element of the present invention, polarizing elements with a boron content (by weight) multiplied by the potassium content (by weight) of 1.2 or more exhibit superior heat resistance compared to polarizing elements with values ​​lower than the aforementioned values, which is not previously known.

[0022] Conventional image display devices constructed by bonding polarizing films or stacked polarizing films between an image display unit and a transparent plate using an adhesive layer have the following problems: when exposed to high-temperature environments, moisture and other substances contained in the polarizing element, adhesive layer, etc., are trapped inside the image display device, thereby promoting the deterioration (polyene formation) of polyvinyl alcohol in the polarizing element, resulting in a significant reduction in its optical properties. However, when using the polarizing element of the present invention, compared with the previous polarizing element, the boron content is higher and the potassium content is lower. Therefore, through boric acid crosslinking, the hydroxyl ends of polyvinyl alcohol in the polarizing element are protected (stabilized). In addition, by using an appropriate potassium content, iodine ions, which act as counterions in the polarizing element, are stabilized, and it is speculated that the polyene formation described above can be suppressed.

[0023] Furthermore, in image display devices exposed to high-temperature environments as described above, in addition to the deterioration of the polarizer due to polyolefin formation, there is also the problem of cracking in the polarizer. Regarding this cracking, since the ends of the polarizing film are usually covered by a bezel, poor appearance at the ends is acceptable. However, from a design perspective, bezels are becoming thinner in recent image display devices, and some are even being manufactured as bezel-less. Therefore, even slight end defects in the polarizing film can impair the appearance; thus, preventing this cracking is crucial for the manufacturing of image display devices. On the other hand, the polarizer of the present invention, by adjusting the upper limit of the boron content in the aforementioned polarizer to 5.2% by weight or less, can effectively prevent the formation of the cracks described above.

[0024] Furthermore, in the aforementioned image display device, a material with low moisture permeability (e.g., moisture permeability of 200 g / (m²)) is bonded together. 2 In the case of polarizers with a transparent protective film (24h or less), since moisture in the polarizer is difficult to pass through the transparent protective film, the moisture is trapped in the polarizer, which presumably further promotes the polyene formation as described above. Therefore, the polarizer of the present invention is particularly useful for polarizers in which a transparent protective film with low moisture permeability is adhered to at least one side. Detailed Implementation

[0025] <Polarizer>

[0026] The polarizing element of the present invention is formed from a polyvinyl alcohol-based film and contains boron and potassium. In the aforementioned polarizing element, the boron content is 4% by weight or more and 6% by weight or less, and the value obtained by multiplying the boron content (by weight) by the potassium content (by weight) is 1.2 or more.

[0027] The aforementioned polyvinyl alcohol (PVA) based films can be used without particular limitation as films that are transparent in the visible light region and dispersed and adsorbed with dichroic substances such as iodine and dichroic dyes. In addition, the thickness of the PVA based film used as a preform is preferably about 10 to 100 μm, more preferably about 20 to 75 μm, and the width is preferably about 100 to 5000 mm.

[0028] Polyvinyl alcohol (PVA) or its derivatives can be listed as materials for the aforementioned polyvinyl alcohol-based films. Examples of PVA derivatives include, for instance, polyvinyl alcohol formaldehyde, polyvinyl alcohol acetal, and substances modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, their alkyl esters, and acrylamide. The average degree of polymerization of the aforementioned PVA is preferably about 100 to 10,000, more preferably about 1,000 to 10,000, and even more preferably about 1,500 to 4,500. Furthermore, the degree of saponification of the aforementioned PVA is preferably about 80 to 100 mol%, more preferably about 95 mol% to 99.95 mol%. It should be noted that the aforementioned average degree of polymerization and the aforementioned degree of saponification can be determined according to JIS K6726.

[0029] The aforementioned polyvinyl alcohol (PVA) films may contain additives such as plasticizers and surfactants. Examples of plasticizers include, for instance, polyols such as glycerol, diglycerol, triglyceride, ethylene glycol, propylene glycol, and polyethylene glycol, as well as their condensates. There are no particular limitations on the amount of these additives used; for example, approximately 20% by weight or less is appropriate in PVA films.

[0030] The aforementioned polarizing element contains boron and potassium. In the aforementioned polarizing element, the boron content is 4% by weight or more and 6% by weight or less, and the value obtained by multiplying the boron content (by weight) by the potassium content (by weight) is 1.2 or more. It should be noted that when the boron content (by weight) is defined as "B" and the potassium content (by weight) is defined as "K", the value obtained by multiplying the boron content (by weight) by the potassium content (by weight) is 1.2 or more can also be defined as "B×K≥1.2".

[0031] In the aforementioned polarizing element, from the viewpoint of suppressing the reduction of optical properties of the polarizing element under high temperature environment, the boron content is preferably 4.0% by weight or more, more preferably 4.2% by weight or more, and from the viewpoint of suppressing the generation of cracks in the polarizing element under high temperature environment, it is preferably 5.2% by weight or less, more preferably 5.0% by weight or less.

[0032] In the aforementioned polarizing element, from the viewpoint of suppressing the decrease in the optical properties of the polarizing element under high temperature conditions, the potassium content is preferably 0.28% by weight or more, more preferably 0.32% by weight or more, and even more preferably 0.34% by weight or more. Moreover, from the viewpoint of suppressing hue changes under high temperature conditions, it is preferably 0.60% by weight or less, more preferably 0.55% by weight or less, and even more preferably 0.50% by weight or less.

[0033] In the aforementioned polarizing element, the value obtained by multiplying the aforementioned boron content (weight%) by the aforementioned potassium content (weight%) (boron content (weight%) × potassium content (weight%)) is preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more, from the viewpoint of suppressing the reduction of the optical properties of the polarizing element under high temperature conditions. Moreover, from the viewpoint of suppressing hue changes under high temperature conditions, it is preferably 3.5 or less, more preferably 3.0 or less, and even more preferably 2.5 or less.

[0034] In the aforementioned polarizing element, the value obtained by dividing the aforementioned boron content (weight%) by the aforementioned potassium content (weight%) (boron content (weight%) ÷ potassium content (weight%)) is preferably 5 or more, more preferably 8 or more, and even more preferably 10 or more, from the viewpoint of suppressing the reduction of the optical properties of the polarizing element under high temperature conditions. Moreover, from the viewpoint of ensuring good initial hue of the polarizing element, it is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less.

[0035] <Manufacturing Method of Polarizing Components>

[0036] The aforementioned polarizing element is obtained by performing at least one of the following processing steps on the aforementioned polyvinyl alcohol (PVA) film: dyeing, crosslinking, and stretching; and additionally, swelling, cleaning, and drying. The boron and potassium content in the aforementioned polarizing element can be controlled by adjusting the concentrations of boron-producing substances (such as boric acid, borates, and borax compounds) and potassium-producing substances (such as potassium halides) in any of the treatment baths in the swelling, dyeing, crosslinking, stretching, and cleaning processes, as well as the treatment temperature and time of each treatment bath. In particular, the crosslinking and stretching processes allow for easy adjustment of the boron content to a desired range by adjusting the concentration of the boron-producing substances. Furthermore, the cleaning process, considering the amounts of boron and potassium-producing substances used in the dyeing, crosslinking, or stretching processes, allows for easy adjustment of the boron and potassium content to a desired range, enabling the leaching or adsorption of boron and potassium from or onto the PVA film.

[0037] The aforementioned swelling process involves immersing a polyvinyl alcohol (PVA) film in a swelling bath. This process removes stains and adhesives from the surface of the PVA film. Furthermore, by swelling the PVA film, uneven dyeing can be suppressed. The swelling bath typically uses a medium with water, distilled water, or pure water as its main component. Surfactants and alcohols can be appropriately added to the swelling bath using conventional methods. Additionally, from the viewpoint of controlling the potassium content in the aforementioned polarizing element, potassium iodide can be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by weight or less, more preferably 1.0% by weight or less, and even more preferably 0.5% by weight or less.

[0038] The temperature of the aforementioned swelling bath is preferably around 10-60°C, more preferably around 15-45°C, and even more preferably around 18-30°C. Furthermore, the immersion time in the aforementioned swelling bath cannot be fixed because the degree of swelling of the polyvinyl alcohol film is affected by the temperature of the swelling bath; it is preferably around 5-300 seconds, more preferably around 10-200 seconds, and even more preferably around 20-100 seconds. The aforementioned swelling process can be performed only once or multiple times as needed.

[0039] The aforementioned dyeing process involves immersing a polyvinyl alcohol (PVA) film in a dyeing bath (iodine solution), which allows dichroic substances such as iodine or dichroic dyes to be adsorbed and oriented within the PVA film. The aforementioned iodine solution is typically an aqueous iodine solution containing iodine and iodides as a dissolving agent. It should be noted that examples of the aforementioned iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is suitable from the viewpoint of controlling the potassium content in the aforementioned polarizing element.

[0040] In the aforementioned staining bath, the concentration of iodine is preferably about 0.01 to 1% by weight, more preferably about 0.02 to 0.5% by weight. In the aforementioned staining bath, the concentration of the aforementioned iodide is preferably about 0.01 to 10% by weight, more preferably about 0.05 to 5% by weight, and even more preferably about 0.1 to 3% by weight.

[0041] The temperature of the aforementioned dyeing bath is preferably around 10-50°C, more preferably around 15-45°C, and even more preferably around 18-30°C. Furthermore, the immersion time in the aforementioned dyeing bath cannot be fixed because the degree of dyeing of the polyvinyl alcohol film is affected by the temperature of the dyeing bath; it is preferably around 10-300 seconds, more preferably around 20-240 seconds. The aforementioned dyeing process can be performed only once, or it can be performed multiple times as needed.

[0042] The aforementioned crosslinking process involves immersing the polyvinyl alcohol (PVA) film dyed in the aforementioned dyeing process in a treatment bath (crosslinking bath) containing a boron compound. Through the boron compound, the PVA film undergoes crosslinking, allowing iodine molecules or dye molecules to adsorb onto the crosslinked structure. Examples of the aforementioned boron compound include boric acid, borates, and borax. The aforementioned crosslinking bath is typically an aqueous solution, but it can also be, for example, a mixture of an organic solvent miscible with water and water. Furthermore, from the viewpoint of controlling the potassium content in the aforementioned polarizing element, the aforementioned crosslinking bath preferably contains potassium iodide.

[0043] In the aforementioned crosslinking bath, the concentration of the aforementioned boron compound is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight. Furthermore, when potassium iodide is used in the aforementioned crosslinking bath, the concentration of potassium iodide in the aforementioned crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight.

[0044] The temperature of the aforementioned crosslinking bath is preferably around 20-70°C, more preferably around 30-60°C. Furthermore, the immersion time in the aforementioned crosslinking bath cannot be fixed because the degree of crosslinking of the polyvinyl alcohol film is affected by the temperature of the crosslinking bath; it is preferably around 5-300 seconds, more preferably around 10-200 seconds. The aforementioned crosslinking process can be performed only once, or it can be performed multiple times as needed.

[0045] The aforementioned stretching process is a treatment process that stretches a polyvinyl alcohol (PVA) film to a specified ratio in at least one direction. Typically, the PVA film is stretched along the conveying direction (length direction) in one axis. There are no particular limitations on the stretching method; either wet stretching or dry stretching can be used. The aforementioned stretching process can be performed only once or multiple times as needed. The aforementioned stretching process can be performed at any stage of the manufacturing process of the polarizing element.

[0046] The treatment bath (stretching bath) in the aforementioned wet stretching method can typically be water, or a mixture of water and an organic solvent that is miscible with water. From the viewpoint of controlling the potassium content in the aforementioned polarizing element, the aforementioned stretching bath preferably contains potassium iodide. When potassium iodide is used in the aforementioned stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight, and even more preferably about 3 to 6% by weight. In addition, from the viewpoint of suppressing film breakage during stretching, the aforementioned treatment bath (stretching bath) may contain the aforementioned boron compound. In this case, the concentration of the aforementioned boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight.

[0047] The temperature of the aforementioned stretching bath is preferably around 25-80°C, more preferably around 40-75°C, and even more preferably around 50-70°C. Furthermore, the immersion time in the aforementioned stretching bath cannot be fixed because the degree of stretching of the polyvinyl alcohol film is affected by the temperature of the stretching bath; it is preferably around 10-800 seconds, more preferably around 30-500 seconds. It should be noted that the stretching treatment in the aforementioned wet stretching method can be performed together with any one or more of the aforementioned swelling process, dyeing process, crosslinking process, and cleaning process.

[0048] Examples of the aforementioned dry stretching methods include, for instance, inter-roll stretching, heated roll stretching, and compression stretching. It should be noted that the aforementioned dry stretching method can be performed concurrently with the aforementioned drying process.

[0049] The total stretch ratio (cumulative stretch ratio) applied to the aforementioned polyvinyl alcohol film can be appropriately set according to the purpose, preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and even more preferably about 3.5 to 6.5 times.

[0050] The aforementioned cleaning process involves immersing a polyvinyl alcohol (PVA) film in a cleaning bath, which removes foreign matter remaining on the surface of the PVA film. The cleaning bath typically uses a medium with water, distilled water, or pure water as its main component. Furthermore, from the viewpoint of controlling the potassium content in the aforementioned polarizing element, potassium iodide is preferably used in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 1.5 to 4% by weight, and even more preferably about 1.8 to 3.8% by weight.

[0051] The temperature of the aforementioned cleaning bath is preferably around 5-50°C, more preferably around 10-40°C, and even more preferably around 15-30°C. Furthermore, the immersion time in the aforementioned cleaning bath cannot be fixed because the degree of cleaning of the polyvinyl alcohol film is affected by the temperature of the cleaning bath; it is preferably around 1-100 seconds, more preferably around 2-50 seconds, and even more preferably around 3-20 seconds. The aforementioned swelling process can be performed only once or multiple times as needed.

[0052] The aforementioned drying process involves drying the polyvinyl alcohol-based film cleaned in the aforementioned cleaning process to obtain a polarizing element. Through drying, a polarizing element with a desired moisture content can be obtained. The aforementioned drying can be carried out by any suitable method, such as natural drying, forced-air drying, and heat drying. The moisture content of the aforementioned polarizing element is preferably about 8-25% by weight, more preferably about 12-20% by weight. It should be noted that the moisture content of the polarizing element is calculated using the following formula, based on the initial weight of a sample cut into 100mm square dimensions and the dried weight after drying at 120°C for 2 hours.

[0053] Moisture content (wt%) = {(Initial weight - Dry weight) / Initial weight} × 100

[0054] The aforementioned drying temperature is preferably around 20~150℃, more preferably around 25~100℃. Furthermore, the aforementioned drying time cannot be fixed because the degree of drying of the polarizing element is affected by the drying temperature; it is preferably around 30~600 seconds, more preferably around 60~300 seconds. The aforementioned drying process can be performed only once, or multiple times as needed.

[0055] The thickness of the aforementioned polarizing element is preferably about 10~30μm, more preferably about 12~20μm.

[0056] <Polarizing film>

[0057] The polarizing film of the present invention has a transparent protective film attached to at least one side of the aforementioned polarizing element.

[0058] There are no particular limitations on the aforementioned transparent protective film, and various transparent protective films previously used in polarizing films can be used. For example, thermoplastic resins with excellent transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy can be used as the materials constituting the aforementioned transparent protective film. Examples of such thermoplastic resins include cellulose ester resins such as cellulose triacetate, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamides, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic and / or cyclic polyolefin resins with a norbornene structure (norbornene resins), polyaryl ester resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. In addition, the aforementioned transparent protective film can be a cured layer formed from thermosetting resins or UV-curable resins such as (meth)acrylic, urethane, acrylic urethane, epoxy, and silicone resins. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are suitable.

[0059] The thickness of the aforementioned transparent protective film can be suitably determined. Generally, from the viewpoints of strength, operability (such as processability), and thinness, it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and even more preferably about 5 to 100 μm. Furthermore, from the viewpoint of reducing the moisture permeability of the aforementioned transparent protective film, the thickness is preferably about 10 to 100 μm, more preferably about 20 to 100 μm, and even more preferably about 30 to 100 μm.

[0060] From the perspective of suppressing the decrease in polarization performance under high temperature and high humidity environments, the aforementioned transparent protective film preferably has a moisture permeability of 800 g / (m²). 2 • 24h or less, more preferably 400g / (m 2 • 24h or less, more preferably 200g / (m 2 • 24h or less, more preferably 150g / (m 2 • 24h or less. The moisture permeability of the single-sided transparent protective film of the aforementioned polarizing element is preferably 200 g / (m²). 2 • 24h or less, more preferably 150g / (m 2• 24h or less. It should be noted that the moisture permeability can be calculated as follows: According to the moisture permeability test (cup method) of JIS Z 0208, a sample cut into 60mm diameter pieces is placed in a moisture permeability cup containing about 15g of calcium chloride and placed in a constant temperature machine at 40℃ and 90%RH. The weight increase of calcium chloride before and after 24 hours is measured and calculated from this.

[0061] When the aforementioned transparent protective film is attached to both sides of the aforementioned polarizer, the transparent protective films on both sides may be the same or different.

[0062] The aforementioned transparent protective film can use a retardation plate having a phase difference of 40 nm or more in the front direction and / or 80 nm or more in the thickness direction. The front phase difference is typically controlled in the range of 40 to 200 nm, and the phase difference in the thickness direction is typically controlled in the range of 80 to 300 nm. When using a retardation plate as the aforementioned transparent protective film, since the retardation plate also functions as a transparent protective film, a thinner profile can be achieved.

[0063] Examples of phase retardation plates include, for instance, birefringent films formed by uniaxial or biaxial stretching of polymer raw materials, oriented films of liquid crystal polymers, and films formed by supporting an oriented layer of liquid crystal polymers with a thin film. The thickness of the phase retardation plate is not particularly limited, typically ranging from 20 to 150 μm. It should be noted that the aforementioned phase retardation plate can be used by bonding it to a transparent protective film that does not possess phase retardation properties.

[0064] The aforementioned transparent protective film can undergo surface modification treatment. Examples of such surface modification treatments include corona treatment, plasma treatment, primer treatment, and saponification treatment.

[0065] Hard coating, anti-reflective treatment, and treatments for anti-sticking, diffusion, and / or anti-glare purposes can be applied to the surface of the aforementioned transparent protective film that is not attached to the polarizing element. It should be noted that hard coating, anti-reflective layer, anti-sticking layer, diffusion layer, and / or anti-glare treatment can be applied to the transparent protective film itself, or they can be applied separately as optical layers to an object different from the transparent protective film.

[0066] The aforementioned transparent protective film may contain any appropriate additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, antistatic agents, pigments, and colorants.

[0067] For bonding the aforementioned polarizing element to the aforementioned transparent protective film, an adhesive is typically used. Examples of such adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex-based adhesives, and water-based polyester adhesives. These adhesives are typically used in the form of adhesives containing an aqueous solution and generally contain 0.5 to 60% by weight of solid components. In addition to the above, examples of such adhesives include UV-curable adhesives and electron beam-curable adhesives. Furthermore, these adhesives may contain metal compound fillers.

[0068] The adhesive coating can be applied to either the aforementioned transparent protective film or the aforementioned polarizing element, or both. After bonding, a drying process is performed to form an adhesive layer containing the coated and dried layer. The bonding of the aforementioned polarizing element and the aforementioned transparent protective film can be performed using a roller laminator or the like. After the aforementioned drying process, ultraviolet light or an electron beam can be applied as needed. The thickness of the aforementioned adhesive layer is not particularly limited, but is preferably around 30 to 5000 nm, more preferably around 100 to 1000 nm.

[0069] <Layered polarizing film>

[0070] The stacked polarizing film (optical stack) of the present invention has the aforementioned polarizing film bonded to an optical layer. The aforementioned optical layer is not particularly limited; for example, optical layers sometimes used in the formation of liquid crystal display devices, such as one or more layers of reflective plates, semi-transparent plates, retardation plates (including wavelength plates of 1 / 2, 1 / 4, etc.), and viewing angle compensation films, can be used. Examples of the aforementioned stacked polarizing film include, in particular: a reflective polarizing film or a semi-transparent polarizing film formed by further stacking a reflective plate or a semi-transparent reflective plate on the aforementioned polarizing film; an elliptical polarizing film or a circular polarizing film formed by further stacking a retardation plate on the aforementioned polarizing film; a wide-viewing-angle polarizing film formed by further stacking a viewing angle compensation film on the aforementioned polarizing film; or a polarizing film formed by further stacking a brightness enhancement film on the aforementioned polarizing film.

[0071] An adhesive layer for bonding image display units such as liquid crystal cells and organic EL elements to other components such as transparent panels on the visual recognition side, such as front transparent panels and touch panels, can be attached to one or both sides of the aforementioned polarizing film or the aforementioned stacked polarizing film. An adhesive layer is suitable as this adhesive layer. There are no particular limitations on the adhesive forming the aforementioned adhesive layer; for example, adhesives with acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorinated polymers, rubber-based polymers, etc., as the base polymer can be appropriately selected. In particular, adhesives containing acrylic polymers, exhibiting excellent optical transparency, moderate wetting, aggregation and adhesion, weather resistance, and heat resistance, are preferred.

[0072] The aforementioned adhesive layer preferably has a low content of organic acid monomers such as acrylic acid. By reducing the content of organic acid monomers in the adhesive layer, the decrease in transmittance caused by the polyolefination of polyvinyl alcohol can be suppressed even when the image display device is exposed to a high-temperature environment.

[0073] The adhesive layer can be attached to one or both sides of the aforementioned polarizing film or the aforementioned stacked polarizing film in a suitable manner. Examples of attaching the adhesive layer include: preparing an adhesive solution and directly attaching it to the aforementioned polarizing film or the aforementioned stacked polarizing film using a suitable spreading method such as casting or coating; or forming an adhesive layer on a separator and transferring it to the aforementioned polarizing film or the aforementioned stacked polarizing film. The thickness of the adhesive layer can be appropriately determined according to the intended use, adhesion, etc., and is typically 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm.

[0074] For the exposed surface of the aforementioned adhesive layer, it is preferable to temporarily protect it with a release agent for the purpose of preventing contamination during the period until actual use. This prevents contamination of the adhesive layer under normal handling conditions. As the aforementioned release agent, for example, a suitable thin layer such as plastic film, rubber sheet, paper, cloth, nonwoven fabric, mesh, foam sheet, metal foil, and their laminates can be used, which is obtained by coating suitable release agents such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide as needed.

[0075] <Image display panel and image display device>

[0076] The image display panel of the present invention has the aforementioned polarizing film or the aforementioned stacked polarizing film bonded to the image display unit. Furthermore, the image display device of the present invention has a transparent plate on the polarizing film or stacked polarizing film side (visual recognition side) of the aforementioned image display panel.

[0077] Examples of image display units include liquid crystal units and organic EL units. For example, a reflective liquid crystal unit utilizing external light, a transmissive liquid crystal unit utilizing light from a light source such as a backlight, or a semi-transmissive / semi-reflective liquid crystal unit utilizing both external light and light from a light source can be used. When the liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) further provides a polarizing film on the side of the image display unit (liquid crystal unit) opposite to the visual recognition side, and then provides a light source. The polarizing film on the light source side is preferably bonded to the liquid crystal unit using a suitable adhesive layer. As for the driving method of the liquid crystal unit, any type of mode can be used, such as VA mode, IPS mode, TN mode, STN mode, or π-type bending orientation.

[0078] As the aforementioned organic EL unit, for example, an organic EL unit in which a light emitter (organic electroluminescent emitter) is formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate can be appropriately used. The aforementioned organic light-emitting layer is a stack of various organic thin films. For example, it can be a stack of a hole injection layer containing a triphenylamine derivative or the like and a light-emitting layer containing a fluorescent organic solid such as anthracene, a stack of these light-emitting layers and an electron injection layer containing a perylene derivative or the like, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0079] As a transparent panel disposed on the visual recognition side of the aforementioned image display unit, examples include a front transparent panel (window layer) and a touch panel. The front transparent panel can be a transparent panel with suitable mechanical strength and thickness. For example, a transparent resin panel such as acrylic resin or polycarbonate resin, or a glass panel, can be used. As the aforementioned touch panel, various touch panels using resistive film, capacitive, optical, or ultrasonic methods, as well as glass panels with touch sensor functionality, or transparent resin panels, can be used. When using a capacitive touch panel as the aforementioned transparent panel, it is preferable to provide a front transparent panel made of glass or a transparent resin panel closer to the visual recognition side than the touch panel itself.

[0080] Example

[0081] The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0082] <Example 1>

[0083] <Making of Polarizing Components>

[0084] Prepare a polyvinyl alcohol (PVA) film with an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, and a thickness of 45 μm. The PVA film is immersed in a swelling bath (water bath) at 20°C for 30 seconds between rollers with different circumferential speeds to swell, and then stretched to 2.4 times its original length in the conveying direction (swelling process). Next, it is immersed in a dyeing bath (an aqueous solution of 0.03 wt% iodine and 0.3 wt% potassium iodide) at 20°C for 45 seconds to dye, and then stretched to 3.7 times its original length in the conveying direction (dyeing process) based on the original PVA film (completely unstretched in the conveying direction). Then, the dyed PVA film is immersed in a crosslinking bath (an aqueous solution of 3.0 wt% boric acid and 3.0 wt% potassium iodide) at 40°C for 20 seconds and stretched to 4.2 times its original length in the conveying direction (crosslinking process). The obtained polyvinyl alcohol film was then immersed in a stretching bath (aqueous solution of boric acid concentration of 4.0 wt% and potassium iodide concentration of 5.0 wt%) at 65°C for 50 seconds and stretched to 6.0 times its original size along the conveying direction (stretching process). Afterward, it was immersed in a cleaning bath (aqueous solution of potassium iodide concentration of 2.5 wt%) at 18°C ​​for 5 seconds (cleaning process). The cleaned polyvinyl alcohol film was dried at 30°C for 2 minutes to produce a polarizing element. The boron content in the polarizing element was determined to be 4.2 wt%, and the potassium content was 0.32 wt%, as determined by the following method. Furthermore, the thickness of the polarizing element was 18 μm, and the moisture content was 16 wt%.

[0085] [Method for determining the boron content (wt%) in polarizing components]

[0086] The polarizer (approximately 0.2 g) dried at 120°C for 2 hours was dissolved in water. In an aqueous solution with a small amount of mannitol and BTB solution added, the solution was neutralized and titrated with 0.1 mol / L NaOH aqueous solution using a burette. The boron content of the polarizer was calculated based on the following formula.

[0087] Boron content (wt%) of polarizer = C × V × Mw / M × 100

[0088] C: Concentration of NaOH aqueous solution (mol / L)

[0089] V: Volume of NaOH aqueous solution added (L)

[0090] Mw: Molecular weight of boron (g / mol)

[0091] M: Weight (g) of the polarizer after drying at 120℃ for 2 hours.

[0092] [Method for determining potassium content (wt%) in polarizing components]

[0093] For the polarizing element, the fluorescence X-ray intensity (kcps) of potassium was measured using a fluorescence X-ray analyzer (Rigaku Corporation, trade name "ZSX100E", measuring diameter: φ10mm). Conversely, the thickness (μm) of the polarizing element was measured using a spectrophotometer (PEACOCK Corporation, trade name "DG-205"). The potassium content (wt%) was calculated from the obtained fluorescence X-ray intensity and thickness using the following formula. It should be noted that "2.99" below refers to the coefficient of the standard curve derived from measuring the fluorescence X-ray intensity (kcps) of a sample with known thickness (μm) and potassium concentration (wt%) (e.g., a PVA-based resin film with a certain amount of KI added).

[0094] Potassium content (wt%) in the polarizing element = 2.99 × (X-ray fluorescence intensity of potassium) / (thickness of polarizing element)

[0095] <Fabrication of Polarizing Film>

[0096] As an adhesive, an aqueous solution containing polyvinyl alcohol resin with acetylacetyl groups (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetylacetylation 5 mol%) and hydroxymethyl melamine in a weight ratio of 3:1 was used. Using this adhesive, a 30 μm thick transparent protective film (saturated water absorption 0.2 g / m²) formed of (meth)acrylic resin (a modified acrylic polymer with a lactone ring structure) was laminated onto one side (image display unit side surface) of the polarizer obtained above using a roller laminator. 2 The moisture permeability is 125g / (m²). 2 • 24h) (hereinafter referred to as "transparent film A") as the second transparent protective film, and additionally, a 40μm thick cellulose triacetate film with a hard coating (with a moisture permeability of 342g / (m)) is laminated on the other side (visual identification side). 2 Using KONICA MINOLTA, INC. (manufactured under the trade name "KC4UYW") (hereinafter referred to as "Transparent Film B") as the first transparent protective film, the polarizing film is then heated and dried in an oven (at a temperature of 88°C for 10 minutes) to produce a polarizing film with the transparent protective film attached to both sides of the polarizing element.

[0097] <Fabrication of Analog Image Display Device>

[0098] The polarizing film obtained above is cut into 150×50cm dimensions with the absorption axis of the polarizing element as the long side. A glass plate (analog image display unit) is bonded to one side of the polarizing film (the side of transparent film A) using an acrylic adhesive layer with a thickness of 20μm. Another glass plate is bonded to the other side of the polarizing film (the side of transparent film B) using an acrylic monomer-free adhesive (manufactured by Nitto Denko Corporation, trade name "LUCIACS CS9868") with a thickness of 200μm to create an analog image display device.

[0099] [Evaluation of optical properties under high temperature conditions]

[0100] The simulated image display device obtained above was placed in a hot air oven at 95°C for 500 hours, and the single-cell transmittance (ΔTs) and polarization (ΔP) before and after heating were measured. The single-cell transmittance and polarization were measured using a spectrophotometer (manufactured by Murakami Color Technology Research Institute Co., Ltd., product name "DOT-3"). The single-cell transmittance is the Y value after visual sensitivity correction according to JlS Z8701-1982, which has a 2-degree field of view (C light source). It should be noted that the measurement wavelength was 380~700nm (per 10nm).

[0101] ΔTs (%) = Ts 500 -Ts0

[0102] ΔP (%) = P 500 -P0

[0103] Here, Ts0 and P0 represent the monomer transmittance and polarization before heating, respectively. 500 and P 500 The transmittance and polarization of the monomers are shown in Table 1 after heating for 500 hours.

[0104] The polarization described above is defined by the following formula: parallel transmittance (Tp) obtained when the analog image display device and the reference polarizing film (manufactured by Nichido Denko Co., Ltd., trade name "CWQ1463CU") are arranged parallel to each other with their absorption axes parallel, and orthogonal transmittance (Tc) obtained when they are orthogonal to each other with their absorption axes at 90°.

[0105] P(%)=[(Tp-Tc) / (Tp+Tc)] 1 / 2 ×100

[0106] The aforementioned ΔTs (%) is preferably -1.0 to 1.0, more preferably -0.5 to 0.5. In addition, the aforementioned ΔP (%) is preferably -0.010 to 0.000, more preferably -0.005 to 0.000.

[0107] [Evaluation of appearance under high temperature conditions]

[0108] The simulated image display device obtained above was placed in a hot air oven at 95°C for 500 hours, and its appearance after heating was evaluated visually according to the following criteria. The results are shown in Table 1.

[0109] ○: No abnormalities in appearance, or cracks smaller than 100μm appear at the end of the polarizing film.

[0110] ×: Abnormal appearance (polyolefination), or cracks larger than 100μm at the end of the polarizing film.

[0111] <Example 2>

[0112] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0113] In the fabrication of the polarizing element, a crosslinking bath (an aqueous solution of boric acid at a concentration of 3.5 wt% and potassium iodide at a concentration of 2.5 wt%) was used in the crosslinking process; a stretching bath (an aqueous solution of boric acid at a concentration of 4.5 wt% and potassium iodide at a concentration of 5.0 wt%) was used in the stretching process; and a cleaning bath (an aqueous solution of potassium iodide at a concentration of 1.8 wt%) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 5.2 wt% boron and 0.28 wt% potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0114] <Example 3>

[0115] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0116] In the fabrication of the polarizing element, a stretching bath (an aqueous solution of boric acid at a concentration of 3.5% by weight and potassium iodide at a concentration of 5.0% by weight) was used in the stretching process, and a cleaning bath (an aqueous solution of potassium iodide at a concentration of 3.0% by weight) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 4.0% by weight of boron and 0.34% by weight of potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0117] <Example 4>

[0118] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0119] As a polarizing element, the polarizing element obtained in Example 3 was prepared. In the fabrication of the polarizing film, as a second transparent protective film, a cellulose triacetate film with a thickness of 80 μm (with a moisture permeability of 560 g / (m²)) was used on one side of the polarizing element (the image display unit side surface). 2 •24h), KONICA MINOLTA, INC., trade name "KC8UYW" (hereinafter referred to as "transparent film C"), except that, a polarizing film and an analog image display device are manufactured by the same operation as in Example 1.

[0120] <Example 5>

[0121] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0122] In the fabrication of the polarizing element, a crosslinking bath (an aqueous solution of boric acid at 3.5 wt% and potassium iodide at 2.5 wt%) was used in the crosslinking process, a stretching bath (an aqueous solution of boric acid at 5.0 wt% and potassium iodide at 5.0 wt%) was used in the stretching process, and a cleaning bath (an aqueous solution of potassium iodide at 1.8 wt%) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 5.3 wt% boron and 0.28 wt% potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0123] <Comparative Example 1>

[0124] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0125] In the fabrication of the polarizing element, a crosslinking bath (an aqueous solution of boric acid at a concentration of 2.5 wt% and potassium iodide at a concentration of 2.5 wt%) was used in the crosslinking process; a stretching bath (an aqueous solution of boric acid at a concentration of 3.0 wt% and potassium iodide at a concentration of 5.0 wt%) was used in the stretching process; and a cleaning bath (an aqueous solution of potassium iodide at a concentration of 4.0 wt%) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 3.9 wt% boron and 0.36 wt% potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0126] <Comparative Example 2>

[0127] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0128] In the fabrication of the polarizing element, a cleaning bath (an aqueous solution of potassium iodide at a concentration of 1.3% by weight) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 4.1% by weight of boron and 0.27% by weight of potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0129] <Comparative Example 3>

[0130] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0131] In the fabrication of the polarizing element, a stretching bath (an aqueous solution of boric acid at a concentration of 3.5% by weight and potassium iodide at a concentration of 5.0% by weight) was used in the stretching process, and a cleaning bath (an aqueous solution of potassium iodide at a concentration of 1.5% by weight) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 4.0% by weight of boron and 0.28% by weight of potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0132] <Comparative Example 4>

[0133] <Fabrication of polarizing components, polarizing films, and analog image display devices>

[0134] In the fabrication of the polarizing element, a crosslinking bath (an aqueous solution of boric acid at a concentration of 1.5 wt% and potassium iodide at a concentration of 2.5 wt%) was used in the crosslinking process; a stretching bath (an aqueous solution of boric acid at a concentration of 1.5 wt% and potassium iodide at a concentration of 5.0 wt%) was used in the stretching process; and a cleaning bath (an aqueous solution of potassium iodide at a concentration of 10.0 wt%) was used in the cleaning process. Otherwise, the polarizing element was fabricated in the same manner as in Example 1. The resulting polarizing element contained 2.4 wt% boron and 0.65 wt% potassium. Furthermore, using the obtained polarizing element, a polarizing film and an analog image display device were fabricated using the same procedures as in Example 1.

[0135] Using the analog image display devices of Examples 2-5 and Comparative Examples 1-4 obtained above, the evaluations in [Optical properties under high temperature environment] and [Appearance under high temperature environment] were performed. The results are shown in Table 1.

[0136] [Table 1]

[0137]

Claims

1. A polarizing film, wherein a transparent protective film is laminated to at least one side of a polarizing element, characterized in that, The polarizing element is formed of a polyvinyl alcohol-based film. The polarizing element contains boron and potassium. In the polarizing element, the boron content is 4% by weight or more and 6% by weight or less, and the value obtained by multiplying the boron content (by weight%) by the potassium content (by weight%) is 1.2 or more. A laminate formed by bonding a glass plate to both sides of the polarizing film using an adhesive layer satisfies the condition that ΔP (%) is -0.010 to 0.000, where ΔP (%) = P 500 -P0, P 500 P0 is the polarization after heating at 95°C for 500 hours, and P0 is the polarization before heating.

2. The polarizing film according to claim 1, characterized in that, The potassium content in the polarizing element is 0.28% by weight or more.

3. The polarizing film according to claim 1 or 2, characterized in that, The boron content in the polarizing element is less than 5.2% by weight.

4. The polarizing film according to claim 1 or 2, characterized in that, The transparent protective film has a moisture permeability of 200 g / (m²). 2 (24 hours or less) 5. A layered polarizing thin film, characterized in that, The optical layer is laminated with the polarizing film as described in any one of claims 1 to 4.

6. An image display panel, characterized in that, The image display unit is bonded with any one of claims 1 to 4, or with the laminated polarizing film of claim 5.

7. An image display device, characterized in that, The image display panel of claim 6 has a transparent plate on the side of the polarizing film or the stacked polarizing film.

Images