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

Abstract

The present application provides a polarizing film, which is formed by adsorbing iodine to a polyvinyl alcohol-based film and orienting it, has an iodine concentration of 6% by weight or more, and in a produced gas analysis method, the peak temperature of the maximum intensity of water detected in the presence of an inert gas at a temperature increase rate of 10°C / min and a temperature increase range of 40°C to 350°C is 200°C or more. The initial polarization degree of the polarizing film is good, and the effect of suppressing the decrease in monomer transmittance caused by the coloring of the polarizing film in a high-temperature environment is also excellent.

Description

[0001] This application is a divisional application of the application filed on November 12, 2019, with application number 201980063377.2 and entitled "Polarizing film, polarizing film, stacked polarizing film, image display panel, and image display device". Technical Field

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

[0003] Conventionally, polarizing films used in various image display devices such as liquid crystal displays and organic EL displays have employed dyed polyvinyl alcohol (PVA) films (containing dichroic substances such as iodine and dichroic dyes) to achieve both high transmittance and high polarization. These polarizing films are manufactured by subjecting the PVA film to various treatments in a bath, such as swelling, dyeing, crosslinking, and stretching, followed by cleaning and drying. Furthermore, these polarizing films are typically used in the form of polarizing films (polarizers) with a protective film such as cellulose triacetate bonded to one or both sides using an adhesive.

[0004] The aforementioned polarizing film is used in the form of 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 front surface transparent member such as a front surface transparent plate (window layer) or a touch panel on the visible side through an adhesive layer or a bonding agent layer, thereby making the aforementioned various image display devices for use (Patent Document 1).

[0005] In recent years, in addition to mobile devices such as mobile phones and tablets, such image display devices have also been used as in-vehicle image display devices such as car navigation devices and rearview monitors, and their applications are expanding. Along with this, compared with previous requirements, the above-mentioned image display devices are now required to have high durability in more severe environments (such as high-temperature environments), and image display devices that aim to ensure such durability have been proposed (Patent Document 2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-102353

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-101117 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] When polarizing films and laminated polarizing films using iodine-based polarizing films are exposed to high-temperature environments, the polyvinyl alcohol constituting the polarizing film undergoes a dehydration reaction and polyolefination, resulting in coloration of the polarizing film and a decrease in its monomer transmittance.

[0012] The inventors conducted in-depth research and found that iodine in iodine-based polarizing films promotes polyene formation in high-temperature environments. Therefore, reducing the iodine concentration (content) in the polarizing film is effective in suppressing the decrease in monomer transmittance caused by coloration of the polarizing film in high-temperature environments. On the other hand, it is difficult to obtain polarizing films with both good polarization and high iodine concentration.

[0013] In view of the above, the object of the present invention is to provide a polarizing film with high iodine concentration, which has good initial polarization degree and excellent effect in suppressing the reduction of monomer transmittance caused by coloration of the polarizing film in high temperature environment.

[0014] Furthermore, the present invention aims to provide a polarizing film, a stacked polarizing film, an image display panel, and an image display device using the aforementioned polarizing film.

[0015] Problem Solving Methods

[0016] That is, the present invention relates to a polarizing film formed by adsorbing iodine onto a polyvinyl alcohol film and orienting it, wherein the iodine concentration is 6% by weight or more, and in a gas generation analysis method, the polarizing film, in the presence of an inert gas, under the conditions of a heating rate of 10°C / min and a heating range of 40°C to 350°C, detects a peak temperature of water with the maximum intensity of water at 200°C or more.

[0017] 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 film.

[0018] In addition, the present invention relates to a laminated polarizing film, wherein the polarizing film is attached to an optical layer.

[0019] In addition, the present invention relates to an image display panel, wherein the aforementioned polarizing film or the aforementioned stacked polarizing film is attached to the image display unit.

[0020] In addition, the present invention relates to an image display device having a front surface transparent member on the side of the polarizing film or stacked polarizing film of the image display panel.

[0021] The effects of the invention

[0022] The exact mechanism of action of the polarizing film of the present invention is not fully understood, but it is presumed to be so. However, the present invention may be interpreted in a way that is not limited to this mechanism.

[0023] The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing iodine onto a polyvinyl alcohol film and orienting it. The iodine concentration is 6% by weight or more. Furthermore, in a gas generation analysis method, the peak temperature of the maximum intensity of water detected by the polarizing film in the presence of an inert gas, at a heating rate of 10°C / min and a heating range of 40°C to 350°C, is 200°C or more. As described above, iodine-based polarizing films undergo polyene formation due to the dehydration reaction of polyvinyl alcohol in high-temperature environments. However, for the polarizing film of the present invention, by setting the temperature at which this dehydration reaction occurs to a high-temperature side, that is, by setting the peak temperature of the maximum intensity of water detected (observed) by the gas generation analysis method to 200°C or more, the decrease in monomer transmittance caused by the coloration of the polarizing film in high-temperature environments can be suppressed. Furthermore, for the polarizing film of the present invention, by setting the iodine concentration in the polarizing film to a certain range or higher, the peak temperature of the maximum intensity of water detected (observed) by the gas generation analysis method can be controlled to be 200°C or more, and the initial polarization degree is improved.

[0024] On the other hand, the inventors exposed a polarizing film formed by adsorbing iodine onto an iodine-containing polyvinyl alcohol film and orienting it to a high-temperature environment for a certain period of time, and observed the generation of free radicals from the polarizing film. The time for the polarizing film to become colored through polyene formation was very similar to the time for the generation of these free radicals, thus suggesting that the phenomenon of free radical generation occurred due to the polyene formation of the polarizing film. Therefore, in order to set the temperature at which the above-mentioned dehydration reaction occurs in the polarizing film to a high-temperature side, that is, to set the peak temperature of the maximum intensity of water detected (observed) by the gas generation analysis method to 200°C or higher, it is preferable that the polarizing film contains a compound with free radical scavenging function.

[0025] Furthermore, with the trend towards thinner panels in image display devices, the polarizing film of the present invention is useful as a thin polarizing film from the viewpoint of preventing panel warping when heating polarizing films or stacked polarizing films. Attached Figure Description

[0026] Figure 1 This is an example of a graph showing the peak of water detected in a gas generation analysis method using an iodine-based polarizing film as the sample. Detailed Implementation

[0027] <Polarizing film>

[0028] The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing iodine onto a polyvinyl alcohol film and orienting it, wherein the iodine concentration is 6% by weight or more, and in the gas generation analysis method, the peak temperature of the maximum intensity of water detected by this polarizing film in the presence of an inert gas, under the conditions of a heating rate of 10°C / min and a heating range of 40°C to 350°C, is 200°C or more.

[0029] The aforementioned polyvinyl alcohol (PVA) films can be used without particular limitation. These films are transparent in the visible light region and are obtained by dispersing and adsorbing iodine. Furthermore, the thickness of PVA films typically used in rolls is approximately 1–100 μm, more preferably 1–50 μm, and the width is preferably approximately 100–5000 mm.

[0030] Polyvinyl alcohol (PVA) or its derivatives can be used as materials for the aforementioned polyvinyl alcohol films. Examples of PVA derivatives include: polyvinyl alcohol formaldehyde, polyvinyl alcohol acetal; olefins such as ethylene and propylene; and derivatives obtained by modification with 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 degree of saponification can be determined based on JIS K 6726.

[0031] Plasticizers, surfactants, and other additives can be included in the aforementioned polyvinyl alcohol films. Examples of plasticizers include, for instance, glycerol, diglycerol, triglyceride, ethylene glycol, propylene glycol, polyethylene glycol, and other polyols and their condensates. There are no particular limitations on the amount of these additives used; for example, 20% by weight or less is suitable in polyvinyl alcohol films.

[0032] From the viewpoint of ensuring good initial polarization of the polarizing film, the iodine concentration (content) of the aforementioned polarizing film is 6% by weight or more. From the viewpoint of improving the initial polarization of the polarizing film, the iodine concentration (content) of the aforementioned polarizing film is preferably 7% by weight or more, more preferably 8% by weight or more, and from the viewpoint of controlling the peak temperature of the maximum intensity of water detected by the gas generation analysis method to be 200°C or more, it is preferably 12% by weight or less, more preferably 10% by weight or less.

[0033] In the gas generation analysis method, the peak temperature of the maximum intensity of water detected by the aforementioned polarizing film in the presence of an inert gas, under conditions of a heating rate of 10°C / min and a heating range of 40°C to 350°C, is above 200°C. For the aforementioned polarizing film, by setting the temperature at which the dehydration reaction of polyvinyl alcohol occurs to the high-temperature side, that is, setting the peak temperature of the maximum intensity of water detected by the gas generation analysis method to above 200°C, the decrease in monomer transmittance caused by the coloration of the polarizing film in a high-temperature environment can be suppressed. On the other hand, when the peak temperature of the maximum intensity of water is below 200°C, it is difficult to control the change in monomer transmittance of the polarizing film before and after the heat durability test (95°C × 750 hours), which is considered an indicator of high-temperature durability and is required in high-end automotive displays, to be between 0% and 5%.

[0034] Figure 1 This is an example of a graph showing the peak of water detected by the above-described gas generation analysis method, where the peak temperature of the detected water with the maximum intensity is above 200°C.

[0035] In addition, the above-mentioned gas generation analysis method is an analytical method that directly connects the gas chromatography device and the mass spectrometry device with an inert metal capillary tube or the like and monitors in real time the gas generated when the sample is heated. It is generally called EGA / MS method, EGA / TOFMS method, etc.

[0036] Preferably, the aforementioned polarizing film contains a compound with free radical scavenging function. It is presumed that this compound with free radical scavenging function can capture free radicals generated by heating the polyvinyl alcohol in the polarizing film, thus setting the temperature of the polyene-reducing dehydration reaction to a high-temperature side. Examples of compounds with free radical scavenging function include, for example, hindered phenols, hindered amines, phosphorus compounds, sulfur compounds, benzotriazoles, benzophenones, hydroxylamines, salicylates, triazine compounds, and other compounds with free radical scavenging function (e.g., antioxidants). From the viewpoint that the temperature of the polyene-reducing dehydration reaction can be easily set to a high-temperature side, compounds containing, for example, nitroacyl radicals or nitroacyl groups are preferred.

[0037] As for the compounds containing nitryl radicals or nitryl groups mentioned above, from the viewpoint of having relatively stable free radicals at room temperature and in air, N-hydroxyl radical compounds (containing CN(-C)-O) can be listed as examples. · Compounds with functional groups (O) · (This refers to oxygen free radicals), and well-known compounds can also be used. Examples of N-hydroxyl radical compounds include compounds with organic groups having the following structures.

[0038] [Chemical Formula 1]

[0039]

[0040] (In general formula (1), R) 1 R represents oxygen free radicals. 2 ~R 5 The number of hydrogen atoms or alkyl groups with 1 to 10 carbon atoms can be independently represented (n represents 0 or 1). It should be noted that the left side of the dashed part in general formula (1) represents any organic group.

[0041] Examples of compounds having the above-mentioned organic groups include compounds represented by the following general formulas (2) to (5).

[0042] [Chemical Formula 2]

[0043]

[0044] (In general formula (2), R) 1 ~R 5 And n has the same meaning as above, R 6 (This indicates a hydrogen atom, an alkyl group, an acyl group, or an aryl group with 1 to 10 carbon atoms; n represents 0 or 1.)

[0045] [Chemical Formula 3]

[0046]

[0047] (In general formula (3), R) 1 ~R 5 And n has the same meaning as above, R 7 and R 8 (Independently representing a hydrogen atom, an alkyl group, an acyl group, or an aryl group having 1 to 10 carbon atoms.)

[0048] [Chemical Formula 4]

[0049]

[0050] (In general formula (4), R) 1 ~R 5 And n has the same meaning as above, R 9 ~R 11 Independently representing a hydrogen atom, an alkyl group, acyl group, amino group, alkoxy group, hydroxyl group, or aryl group having 1 to 10 carbon atoms.

[0051] [Chemical Formula 5]

[0052]

[0053] (In general formula (5), R) 1 ~R 5 And n has the same meaning as above, R 12(This refers to a hydrogen atom, or an alkyl, amino, alkoxy, hydroxyl, or aryl group having 1 to 10 carbon atoms.)

[0054] In the above general formulas (1) to (5), from the perspective of ease of acquisition, R 2 ~R 5 Preferably, it is an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. Furthermore, in the above general formula (2), from the viewpoint of ease of acquisition, R... 6 Preferably, it is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. Furthermore, from the viewpoint of ease of acquisition, R is preferred in the above general formula (3). 7 and R 8 Independently, it is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. Furthermore, in the above general formula (4), from the viewpoint of ease of acquisition, R... 9 ~R 11 Preferably, it is an alkyl group having 1 to 10 hydrogen atoms. Furthermore, in the above general formula (5), from the viewpoint of ease of acquisition, R... 12 Preferably, it is hydroxyl, amino, or alkoxy. In the above general formulas (1) to (5), from the viewpoint of ease of acquisition, n is preferably 1.

[0055] In addition, examples of the aforementioned N-hydroxyl compounds include those described in Japanese Patent Application Publication No. 2003-64022, Japanese Patent Application Publication No. 11-222462, Japanese Patent Application Publication No. 2002-284737, and International Publication No. 2016 / 047655.

[0056] Furthermore, from the viewpoint of being able to efficiently capture free radicals generated in the polyolefination reaction, the molecular weight of the above-mentioned compound with free radical capturing function is preferably 1000 or less, more preferably 500 or less, and even more preferably 300 or less.

[0057] From the viewpoint that the polarizing film can be efficiently infiltrated with water during the manufacturing process, that it can be impregnated with a high concentration in the polarizing film, and that even when using a thick polyvinyl alcohol film, it can be impregnated in a short time to improve the productivity of the polarizing film, the above-mentioned compound with free radical scavenging function is preferably soluble in 1 part by weight or more in 100 parts by weight of water at 25°C, more preferably soluble in 2 parts by weight or more in 100 parts by weight of water at 25°C, and even more preferably soluble in 5 parts by weight or more in 100 parts by weight of water at 25°C.

[0058] In addition, the following compounds can be listed as examples of compounds having nitrocellulose radicals or nitrocellulose groups.

[0059] [Chemical Formula 6]

[0060]

[0061] (In general formula (6), R represents a hydrogen atom, an alkyl group, an acyl group, or an aryl group with 1 to 10 carbon atoms.)

[0062] [Chemical Formula 7]

[0063]

[0064] [Chemical Formula 8]

[0065]

[0066] When the polarizing film contains the compound with the free radical scavenging function, from the viewpoint of suppressing the decrease in monomer transmittance caused by the coloring of the polarizing film in a high-temperature environment, the content of the compound with the free radical scavenging function in the polarizing film is preferably 0.005% by weight or more, more preferably 0.01% by weight or more, and even more preferably 0.02% by weight or more. In addition, from the viewpoint of appearance, it is preferably 15% by weight or less, more preferably 12% by weight or less, and even more preferably 10% by weight or less.

[0067] <Manufacturing Method of Polarizing Film>

[0068] The method for manufacturing the aforementioned polarizing film includes: performing an optional swelling and cleaning process on the aforementioned polyvinyl alcohol film, and performing at least a dyeing process, a crosslinking process, and a stretching process to obtain the aforementioned polarizing film. The iodine content contained in the aforementioned polarizing film can be controlled by the concentration of the aforementioned iodine and iodides such as potassium iodide in any of the processing baths in the swelling, dyeing, crosslinking, stretching, and cleaning processes, as well as the processing temperature and processing time in each of the aforementioned processing baths.

[0069] Furthermore, when manufacturing a polarizing film containing the aforementioned compound with free radical scavenging function, the compound with free radical scavenging function may be contained in any one or more of the processing baths in the swelling step, the cleaning step, the dyeing step, the crosslinking step, and the stretching step. The concentration of the compound with free radical scavenging function contained in any of the aforementioned processing baths is affected by the number of processing steps, processing time, processing temperature, etc., and therefore cannot be determined in a fixed manner. From the viewpoint of efficiently controlling the content of the compound with free radical scavenging function in the polarizing film, it is generally preferred to be 0.01% by weight or more, more preferably 0.05% by weight or more, further preferably 0.1% by weight or more, and preferably 30% by weight or less, more preferably 25% by weight or less, and further preferably 20% by weight or less.

[0070] Especially when a cleaning process is performed after the dyeing, cross-linking, and stretching processes, the cleaning process can be adjusted to the desired range by taking into account the processing conditions in the dyeing, cross-linking, and stretching processes, from the viewpoint that iodine and the aforementioned compounds with free radical scavenging functions can be dissolved from or adsorbed onto the polyvinyl alcohol film.

[0071] Furthermore, additives such as zinc salts, pH adjusters, pH buffers, and other salts may be included in the treatment baths of the aforementioned swelling, dyeing, cross-linking, stretching, and cleaning processes. Examples of zinc salts include zinc halides such as zinc chloride and zinc iodide; and inorganic zinc salts such as zinc sulfate and zinc acetate. Examples of pH adjusters include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid; and strong bases such as sodium hydroxide and potassium hydroxide. Examples of pH buffers include carboxylic acids such as acetic acid, oxalic acid, and citric acid, and their salts; and inorganic weak acids such as phosphoric acid and carbonic acid, and their salts. Examples of other salts include chlorides such as sodium chloride, potassium chloride, and barium chloride; nitrates such as sodium nitrate and potassium nitrate; sulfates such as sodium sulfate and potassium sulfate; and salts of alkali metals and alkaline earth metals.

[0072] The swelling process described above involves immersing a polyvinyl alcohol (PVA) film in a swelling bath. This process removes dirt and anti-blocking agents from the surface of the PVA film. Furthermore, it inhibits uneven dyeing by causing the PVA film to swell. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants and alcohols can be appropriately added to the swelling bath using conventional methods.

[0073] The temperature of the 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 swelling bath cannot be uniformly determined 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 swelling process can be performed only once, or multiple times as needed.

[0074] The dyeing process described above involves immersing a polyvinyl alcohol (PVA) film in a dyeing bath (iodine solution), which allows iodine to be adsorbed onto the PVA film and oriented. The iodine solution is typically an aqueous iodine solution, more preferably containing iodine and an iodide as a dissolving agent. It should be noted that examples of the 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 preferred from the viewpoint of controlling the potassium content in the polarizing film.

[0075] In the above-mentioned 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 above-mentioned staining bath, the concentration of the above-mentioned iodide is preferably about 0.01 to 20% by weight, more preferably about 0.05 to 10% by weight, and even more preferably about 0.1 to 5% by weight.

[0076] The temperature of the 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 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 dyeing process can be performed only once, or multiple times as needed.

[0077] The aforementioned crosslinking process involves immersing a polyvinyl alcohol (PVA) film in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA film, allowing iodine or dye molecules to adsorb onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution, but can also be a mixture of an organic solvent and water that is miscible with water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing film, the crosslinking bath may contain potassium iodide.

[0078] In the aforementioned crosslinking bath, the concentration of the 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 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.

[0079] The temperature of the crosslinking bath is preferably around 20–70°C, more preferably around 30–60°C. Furthermore, the immersion time in the crosslinking bath affects the degree of crosslinking of the polyvinyl alcohol film, and therefore cannot be uniformly determined; it is preferably around 5–300 seconds, more preferably around 10–200 seconds. The crosslinking process can be performed only once, or multiple times as needed.

[0080] The stretching process described above is a process of stretching a polyvinyl alcohol (PVA) film at a given ratio along at least one direction. Generally, the PVA film is stretched unidirectionally in the transport direction (length direction). There are no particular limitations on the stretching method; either wet stretching or dry stretching can be used. The stretching process can be performed only once or multiple times as needed. The stretching process can be performed at any stage of the polarizing film manufacturing process.

[0081] The treatment bath (stretching bath) in the above-described 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 polarizing film, the stretching bath may contain potassium iodide. When potassium iodide is used in the stretching bath, its concentration 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. Furthermore, from the viewpoint of suppressing film breakage during stretching, the above-described treatment bath (stretching bath) may contain the above-described boron compound. In this case, the concentration of the 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.

[0082] The temperature of the stretching bath is preferably around 25–80°C, more preferably around 40–75°C, and even more preferably around 50–70°C. Furthermore, the degree of stretching of the polyvinyl alcohol film in the stretching bath is affected by the temperature of the bath and therefore cannot be determined uniformly; preferably, it is around 10–800 seconds, more preferably around 30–500 seconds. It should be noted that the stretching treatment in the wet stretching method can be performed together with any one or more of the following processes: the swelling process, the dyeing process, the crosslinking process, and the cleaning process.

[0083] Examples of the aforementioned dry stretching methods include: 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.

[0084] The total stretch ratio (cumulative stretch ratio) applied to the above-mentioned 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.

[0085] The above-described cleaning process involves immersing the 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 water-based medium, such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing film, potassium iodide can be included 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.

[0086] The temperature of the aforementioned cleaning bath is preferably around 5–50°C, more preferably around 10–40°C, and even more preferably around 15–35°C. Furthermore, the immersion time in the aforementioned cleaning bath affects the degree of cleaning of the polyvinyl alcohol film, and therefore cannot be uniformly determined; 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.

[0087] The method for manufacturing the polarizing film of the present invention may include a drying step. The drying step is a process of drying a polyvinyl alcohol film cleaned in the above-described cleaning step to obtain a polarizing film. Drying yields a polarizing film with a desired moisture content. The drying can be performed by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0088] The drying temperature is preferably around 20–150°C, more preferably around 25–100°C. Furthermore, the drying time varies depending on the drying temperature, and therefore cannot be fixed; preferably around 10–600 seconds, more preferably around 30–300 seconds. The drying process can be performed only once, or multiple times as needed.

[0089] From the viewpoint of improving the initial polarization degree of the polarizing film, the thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more, and from the viewpoint of preventing panel warping, it is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. In particular, in order to obtain a polarizing film with a thickness of about 8 μm or less, the following method for manufacturing a thin polarizing film can be applied, in which a laminate comprising a thermoplastic resin substrate and a polyvinyl alcohol resin layer formed on the thermoplastic resin substrate is used as the polyvinyl alcohol film.

[0090] <Manufacturing Method of Thin Polarizing Film>

[0091] A method for manufacturing a thin polarizing film includes: forming a polyvinyl alcohol (PVA) resin layer on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to assisted stretching in a gas atmosphere, dyeing, stretching in an aqueous solution, and drying shrinkage. Specifically, to obtain a polarizing film with high optical properties, a two-stage stretching method combining assisted stretching in a gas atmosphere (dry stretching) and stretching in an aqueous solution of boric acid is selected.

[0092] As a method for manufacturing the above-described laminate, any suitable method can be used, such as coating the surface of the above-described thermoplastic resin substrate with a coating liquid containing the above-described PVA-based resin and then drying it. The thickness of the above-described thermoplastic resin substrate is preferably about 20 to 300 μm, more preferably about 50 to 200 μm. The thickness of the above-described PVA-based resin layer is preferably about 3 to 40 μm, more preferably about 3 to 20 μm.

[0093] The aforementioned thermoplastic resin substrate absorbs water, resulting in a significant reduction in tensile stress. From the viewpoint of enabling high-ratio stretching, the water absorption rate is preferably about 0.2% or more, more preferably about 0.3% or more. On the other hand, from the viewpoint of preventing a significant decrease in the dimensional stability of the thermoplastic resin substrate, which could lead to deterioration of the appearance of the resulting polarizing film, the water absorption rate is preferably about 3% or less, more preferably about 1% or less. It should be noted that the aforementioned water absorption rate can be adjusted, for example, by introducing modifying groups into the constituent materials of the aforementioned thermoplastic resin substrate. The aforementioned water absorption rate is a value determined based on JIS K 7209.

[0094] For the aforementioned thermoplastic resin substrate, from the viewpoint of suppressing the crystallization of the PVA-type resin layer and sufficiently ensuring the tensile strength of the laminate, its glass transition temperature (Tg) is preferably around 120°C or less. Furthermore, considering the plasticization of the thermoplastic resin substrate using water and good stretching in aqueous solution, the aforementioned glass transition temperature (Tg) is preferably around 100°C or less, and more preferably around 90°C or less. On the other hand, from the viewpoint of preventing deformation of the thermoplastic resin substrate and producing a good laminate during coating / drying of the coating solution, the glass transition temperature of the thermoplastic resin substrate is preferably around 60°C or more. It should be noted that the aforementioned glass transition temperature can be adjusted, for example, by introducing modifying groups into the constituent materials of the aforementioned thermoplastic resin substrate or by heating with a crystallizing material. The aforementioned glass transition temperature (Tg) is a value obtained based on JIS K 7121.

[0095] As a constituent material of the aforementioned thermoplastic resin substrate, any suitable thermoplastic resin can be used. Examples of such thermoplastic resins include: ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymers thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferred. Furthermore, from the viewpoint that the thermoplastic resin substrate has excellent tensile properties and can suppress crystallization during stretching, amorphous polyethylene terephthalate resins are preferred. Examples of amorphous polyethylene terephthalate resins include copolymers containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers containing cyclohexanediol and diethylene glycol as diols.

[0096] Before forming the PVA-type resin layer, the thermoplastic resin substrate can be surface-treated (e.g., corona treatment), or an easy-to-adhere layer can be formed on the thermoplastic resin substrate. Such treatments improve the adhesion between the thermoplastic resin substrate and the PVA-type resin layer. Alternatively, the thermoplastic resin substrate can be stretched before forming the PVA-type resin layer.

[0097] The coating solution described above is a solution obtained by dissolving PVA-based resin in a solvent. Examples of such solvents include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, amines such as ethylenediamine and diethylenetriamine, with water being preferred. These solvents can be used alone or in combination of two or more. From the viewpoint of forming a uniform coating film that adheres closely to the thermoplastic resin substrate, the concentration of PVA-based resin in the coating solution is preferably about 3 to 20 parts by weight relative to 100 parts by weight of the solvent.

[0098] From the viewpoint of improving the orientation of polyvinyl alcohol molecules based on stretching, it is preferable to incorporate a halide into the coating solution. Any suitable halide can be used as the halide, such as iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide, with potassium iodide being preferred. The concentration of the halide in the coating solution is preferably about 5 to 20 parts by weight, more preferably about 10 to 15 parts by weight, relative to 100 parts by weight of PVA resin.

[0099] In addition, additives can be incorporated into the coating solution. Examples of such additives include plasticizers such as ethylene glycol and glycerin, and surfactants such as nonionic surfactants.

[0100] As for the coating method of the above-mentioned coating liquid, any suitable method can be used, such as: roller coating, spin coating, wire rod coating, dip coating, mold coating, curtain coating, spraying, and blade coating (comma coating, etc.). In addition, the drying temperature of the above-mentioned coating liquid is preferably about 50°C or higher.

[0101] In the above-mentioned assisted stretching process in a gas atmosphere, in order to suppress the crystallization of the thermoplastic resin substrate while stretching, the laminate can be stretched at a high ratio. The stretching method of the above-mentioned assisted stretching process in a gas atmosphere can be fixed-end stretching (e.g., stretching using a tenter frame) or free-end stretching (e.g., unidirectional stretching by passing the laminate through rollers with different circumferential speeds). From the viewpoint of obtaining high optical properties, free-end stretching is preferred.

[0102] The preferred stretching ratio in the assisted stretching under the aforementioned gas atmosphere is approximately 2 to 3.5 times. The assisted stretching under the aforementioned gas atmosphere can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio is the product of the stretching ratios of each stage.

[0103] The stretching temperature in the aforementioned gas atmosphere can be set to any suitable value based on the forming material of the thermoplastic resin substrate, the stretching method, etc. For example, it is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above the glass transition temperature (Tg) + 10°C, and even more preferably above the glass transition temperature (Tg) + 15°C. On the other hand, from the viewpoint of suppressing the rapid crystallization of PVA resin and suppressing adverse conditions caused by crystallization (such as hindering the orientation of the stretch-based PVA resin layer), the upper limit of the stretching temperature is preferably around 170°C.

[0104] As needed, an insoluble treatment can be performed after the assisted stretching treatment in the aforementioned gas atmosphere and before the dyeing treatment and the stretching treatment in the aqueous solution. The aforementioned insoluble treatment is typically performed by impregnating the PVA resin layer in an aqueous boric acid solution. By performing the insoluble treatment, the PVA resin layer can be given water resistance, preventing a decrease in the orientation of the PVA when impregnated in water. The concentration of this aqueous boric acid solution relative to 100 parts by weight of water is preferably about 1 to 5 parts by weight. The liquid temperature of the insoluble treatment bath is preferably about 20 to 50°C.

[0105] The above-described staining treatment is performed by staining the PVA resin layer with iodine. Examples of this adsorption method include: impregnating the PVA resin layer (laminated structure) in an iodine-containing staining solution; applying the staining solution onto the PVA resin layer; spraying the staining solution onto the PVA resin layer, etc., with the method of impregnating the PVA resin layer (laminated structure) in an iodine-containing staining solution being preferred.

[0106] The amount of iodine in the dyeing bath relative to 100 parts by weight of water is preferably about 0.05 to 0.5 parts by weight. To improve the solubility of iodine in water, it is preferable to incorporate the iodide in the iodine aqueous solution. The amount of the iodide relative to 100 parts by weight of water is preferably about 0.1 to 10 parts by weight, more preferably about 0.3 to 5 parts by weight. To suppress the dissolution of PVA resin, the temperature of the dyeing bath is preferably about 20 to 50°C. Furthermore, from the viewpoint of ensuring the transmittance of the PVA resin layer, the immersion time is preferably about 5 seconds to 5 minutes, more preferably about 30 seconds to 90 seconds. From the viewpoint of obtaining a polarizing film with good optical properties, the ratio of iodine to iodide content in the iodine aqueous solution is preferably about 1:5 to 1:20, more preferably about 1:5 to 1:10.

[0107] As needed, a crosslinking treatment can be performed after dyeing and before stretching in aqueous solution. This crosslinking treatment is typically performed by immersing the PVA resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, the PVA resin layer can be given water resistance, preventing a decrease in PVA orientation when immersed in hot water during subsequent stretching in aqueous solution. The boric acid concentration in this aqueous boric acid solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. Furthermore, when performing the crosslinking treatment, it is preferable to further incorporate the aforementioned iodide into the crosslinking bath during the crosslinking treatment. Incorporating the aforementioned iodide can suppress the dissolution of iodine adsorbed in the PVA resin layer. The amount of the aforementioned iodide incorporated is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. The temperature of the crosslinking bath (aqueous boric acid solution) is preferably about 20 to 50°C.

[0108] The above-described aqueous solution stretching treatment is performed by immersing the laminate in a stretching bath. According to the aqueous solution stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically around 80°C) of the aforementioned thermoplastic resin substrate and PVA-type resin layer, allowing for high-ratio stretching while suppressing crystallization of the PVA-type resin layer. The stretching method for the above-described aqueous solution stretching treatment can be fixed-end stretching (e.g., stretching using a tenter frame) or free-end stretching (e.g., unidirectional stretching by passing the laminate through rollers with different circumferential speeds). From the viewpoint of obtaining high optical properties, free-end stretching is preferred.

[0109] The stretching treatment in the above-mentioned aqueous solution is preferably performed by immersing the laminate in a boric acid aqueous solution (stretching in boric acid aqueous solution). By using a boric acid aqueous solution as the stretching bath, the PVA resin layer can be endowed with rigidity capable of withstanding the tension applied during stretching, as well as water resistance by insolubility in water. The boric acid concentration in the boric acid aqueous solution is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, relative to 100 parts by weight of water. Additionally, an iodide can be added to the above-mentioned stretching bath (boric acid aqueous solution). The temperature of the stretching bath is preferably around 40 to 85°C, more preferably around 60 to 75°C. The immersion time of the laminate in the stretching bath is preferably around 15 seconds to 5 minutes.

[0110] The stretching ratio in the above-mentioned aqueous solution is preferably about 1.5 times or more, and more preferably about 3 times or more.

[0111] It should be noted that the total stretch ratio of the laminate is preferably about 5 times or more, and more preferably about 5.5 times or more, relative to the original length of the laminate.

[0112] The aforementioned drying shrinkage process can be performed by regional heating of the entire area or by heating the transport rollers (using so-called heated rollers), with both methods being preferred. By using heated rollers for drying, heating curling of the laminate can be effectively suppressed, thereby producing a polarizing film with excellent appearance. Furthermore, the laminate can be dried while remaining flat, thus suppressing not only curling but also wrinkle formation. Additionally, from the viewpoint that shrinking the laminate in the width direction during the drying shrinkage process can improve the optical properties of the resulting polarizing film, the width-direction shrinkage rate of the laminate treated with the drying shrinkage process is preferably about 1 to 10%, more preferably about 2 to 8%.

[0113] The drying conditions can be controlled by adjusting the heating temperature of the conveyor rollers (temperature of the heating rollers), the number of heating rollers, and the contact time with the heating rollers. The temperature of the heating rollers is preferably around 60–120°C, more preferably around 65–100°C, and even more preferably 70–80°C. From the viewpoint of effectively increasing the crystallinity of the thermoplastic resin and effectively suppressing curling, the number of conveyor rollers is typically around 2 to 40, preferably around 4 to 30. The contact time (total contact time) between the laminate and the heating rollers is preferably around 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0114] The heating rollers can be installed in a heating furnace or in a typical manufacturing line (at room temperature), but are preferably installed in a heating furnace equipped with an air supply mechanism. By combining drying using heating rollers and hot air drying, rapid temperature changes between the heating rollers can be suppressed, thereby easily controlling shrinkage in the width direction. The hot air drying temperature is preferably around 30–100°C. Furthermore, the hot air drying time is preferably around 1–300 seconds.

[0115] The cleaning process is preferably performed after the stretching treatment in the aqueous solution and before the drying and shrinkage treatment. This cleaning process is typically carried out by immersing the PVA resin layer in an aqueous potassium iodide solution.

[0116] Furthermore, when manufacturing a thin polarizing film containing the aforementioned compound with free radical scavenging function, the compound with free radical scavenging function can be included in any one or more of the following treatment baths: dyeing treatment, stretching treatment in aqueous solution, insoluble treatment, crosslinking treatment, and cleaning treatment. The concentration of the compound with free radical scavenging function contained in any of the above-mentioned treatment baths is affected by the number of treatments, treatment time, treatment temperature, etc., and therefore cannot be determined in a fixed manner. From the viewpoint of efficiently controlling the content of the compound with free radical scavenging function in the polarizing film, it is generally preferred to be 0.01% by weight or more, more preferably 0.05% by weight or more, further preferably 0.1% by weight or more, and preferably 30% by weight or less, more preferably 25% by weight or less, and further preferably 20% by weight or less.

[0117] Especially when performing a cleaning process, considering the processing conditions such as dyeing and stretching in aqueous solution, from the viewpoint that iodine and the aforementioned compounds with free radical scavenging function can be dissolved from or adsorbed onto the polyvinyl alcohol membrane, the content of the aforementioned iodine and the aforementioned compounds with free radical scavenging function can be easily adjusted to the desired range.

[0118] <Polarizing film>

[0119] The polarizing film of the present invention is formed by attaching a transparent protective film to at least one side of the polarizing film.

[0120] There are no particular limitations on the aforementioned transparent protective film, and various transparent protective films used in polarizing films can be used. As materials constituting the aforementioned transparent protective film, thermoplastic resins with excellent transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy can be used. 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, nylon, aromatic polyamide resins, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic or cyclic polyolefin resins with a norbornene structure (norbornene resins), polyacrylic resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Furthermore, the aforementioned transparent protective film can be a cured layer formed from thermosetting resins such as (meth)acrylic acid, urethane, acrylate urethane, epoxy, and silicone resins, or ultraviolet-curable resins. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

[0121] The thickness of the aforementioned transparent protective film can be appropriately determined. Generally speaking, from the perspectives of strength, processability, operability, 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.

[0122] When the above-mentioned transparent protective film is attached to both sides of the above-mentioned polarizing film, the transparent protective film on both sides may be the same or different.

[0123] The aforementioned transparent protective film can use a phase retardation plate having a frontal phase difference of 40 nm or more and / or a thickness direction phase difference of 80 nm or more. Typically, the frontal phase difference is controlled within the range of 40–200 nm, and the thickness direction phase difference is typically controlled within the range of 80–300 nm. When a phase retardation plate is used as the aforementioned transparent protective film, the phase retardation plate also functions as a transparent protective film, thus enabling thinner designs.

[0124] Examples of phase retardation plates include: birefringent films formed by unidirectional or bidirectional stretching of polymer raw materials, alignment films of liquid crystal polymers, and phase retardation plates formed by supporting an alignment layer of liquid crystal polymers with a 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 plates can be bonded to a transparent protective film that does not possess phase retardation properties.

[0125] The aforementioned transparent protective film may contain any suitable additives such as UV absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, antistatic agents, pigments, and colorants. In particular, the inclusion of UV absorbers in the aforementioned transparent protective film can improve the lightfastness of the polarizing film.

[0126] Functional layers such as a hard coating layer, an anti-reflective layer, an anti-adhesion layer, a diffusion layer, and an anti-glare layer can be provided on the side of the aforementioned transparent protective film that is not bonded to the polarizing film. It should be noted that the aforementioned functional layers such as the hard coating layer, anti-reflective layer, anti-adhesion layer, diffusion layer, and anti-glare layer can be either the protective film itself or layers different from the protective film.

[0127] The polarizing film and the transparent protective film, or the polarizing film and the functional layer, are usually bonded together with an adhesive layer or bonding agent layer in between.

[0128] As the adhesive for forming the adhesive layer described above, various adhesives used in polarizing films can be applied, including, for example, rubber-based adhesives, acrylic adhesives, silicone adhesives, urethane adhesives, vinyl alkyl ether adhesives, polyvinyl alcohol adhesives, polyvinylpyrrolidone adhesives, polyacrylamide adhesives, cellulose adhesives, etc. Among these, acrylic adhesives are preferred.

[0129] Examples of methods for forming the adhesive layer include: applying the adhesive to a diaphragm or similar material that has undergone a peeling treatment and drying it to form an adhesive layer, and then transferring it to a polarizing film or similar material; or applying the adhesive to a polarizing film or similar material and drying it to form an adhesive layer. The thickness of the adhesive layer is not particularly limited, but is, for example, about 1 to 100 μm, preferably about 2 to 50 μm.

[0130] As the adhesive used to form the adhesive layer described above, various adhesives applicable to polarizing films can be used, such as isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, and waterborne polyester adhesives. These adhesives are typically used in the form of adhesives formed from aqueous solutions (waterborne adhesives) and contain 0.5 to 60% by weight of solid components.

[0131] The aforementioned water-based adhesive may include a crosslinking agent. As the crosslinking agent, a compound typically used is one having at least two functional groups in one molecule that are reactive with the polymer or other components constituting the adhesive. Examples include: alkylene diamines; isocyanates; epoxy compounds; aldehydes; amino-formaldehydes such as hydroxymethylurea and hydroxymethyl melamine. The amount of crosslinking agent in the adhesive is typically about 10 to 60 parts by weight relative to 100 parts by weight of the polymer or other components constituting the adhesive.

[0132] In addition to the above, examples of adhesives that can be cured by active energy rays, such as ultraviolet-cured adhesives and electron beam-cured adhesives, can be cited as examples of active energy ray-cured adhesives. Examples of (meth)acrylate adhesives can be cited as curing components in the above-mentioned (meth)acrylate adhesives, such as compounds having (meth)acryloyl groups and compounds having vinyl groups. Examples of compounds having (meth)acryloyl groups include, for example, alkyl esters of (meth)acrylate with 1 to 20 carbon atoms, alicyclic alkyl esters of (meth)acrylate, polycyclic alkyl esters of (meth)acrylate, and other alkyl esters of (meth)acrylate; hydroxyl-containing (meth)acrylates; glycidyl esters of (meth)acrylate, and epoxy-containing (meth)acrylates, etc. (Meth)acrylate adhesives may contain nitrogen-containing monomers such as hydroxyethyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, and (meth)acryloylmorpholine. (Meth)acrylate adhesives may also contain tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanediethanol diacrylate, cyclic trimethylolpropane methyl acetal acrylate, and di... Multifunctional monomers such as alkyl glycol diacrylate and EO-modified diglycerol tetraacrylate are used as crosslinking components. Additionally, compounds with epoxy groups or oxocyclic butyl groups can also be used as cationic polymerization curing adhesives. There are no particular limitations on compounds with epoxy groups, as long as they have at least two epoxy groups within the molecule; various commonly known curing epoxy compounds can be used.

[0133] The adhesives described above may also contain suitable additives as needed. Examples of such additives include: silane coupling agents, titanium coupling agents, and other coupling agents; ethylene oxide adhesive accelerators; ultraviolet absorbers; deterioration inhibitors; dyes; processing aids; ion trapping agents; antioxidants; tackifiers; fillers; plasticizers; leveling agents; foaming inhibitors; antistatic agents; heat stabilizers; and hydrolysis stabilizers.

[0134] The adhesive coating can be applied to either the transparent protective film side (or the functional layer side) or the polarizing film side, or to both sides. After bonding, a drying process is performed to form an adhesive layer made of the coated and dried layer. After the drying process, ultraviolet light or an electron beam can be applied as needed. The thickness of the adhesive layer is not particularly limited. When using water-based adhesives, it is preferably about 30 to 5000 nm, more preferably about 100 to 1000 nm. When using ultraviolet-curing adhesives or electron beam-curing adhesives, it is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm.

[0135] The aforementioned transparent protective film and the aforementioned polarizing film, or the aforementioned polarizing film and the aforementioned functional layer, can be stacked together with interlayers such as surface modification treatment layer, easy-to-adhere layer, blocking layer, and refractive index adjustment layer.

[0136] Examples of surface modification treatments for forming the above-mentioned surface modified layer include: corona treatment, plasma treatment, primer treatment, saponification treatment, etc.

[0137] Examples of easy-adhesive agents used to form the aforementioned easy-adhesive layer include: resins comprising various resins having a polyester backbone, polyether backbone, polycarbonate backbone, polyurethane backbone, silicone backbone, polyamide backbone, polyimide backbone, polyvinyl alcohol backbone, etc. The aforementioned easy-adhesive layer can typically be pre-formed onto a protective film, and the easy-adhesive layer side of this protective film is laminated to the polarizing film via the aforementioned adhesive layer or adhesive layer.

[0138] The aforementioned barrier layer is a layer that functions to prevent impurities such as oligomers and ions dissolved from a transparent protective film from migrating (invading) into the polarizing film. The barrier layer can be any layer that is transparent and can prevent impurities dissolved from a transparent protective film, etc. Examples of materials forming the barrier layer include: urethane prepolymer forming materials, cyanoacrylate forming materials, epoxy forming materials, etc.

[0139] The aforementioned refractive index adjustment layer is provided to suppress the decrease in transmittance caused by reflections between layers with different refractive indices, such as the transparent protective film and the polarizing film. Examples of refractive index adjustment materials forming this layer include, for instance, resins and additives comprising silica, acrylic, acrylic-styrene, melamine, and other similar resins.

[0140] The polarization degree of the above-mentioned polarizing film is preferably 99.98% or higher, and more preferably 99.99% or higher.

[0141] <Layered Polarizing Film>

[0142] In the stacked polarizing film (optical laminate) of the present invention, the aforementioned polarizing film is bonded to an optical layer. The optical layer is not particularly limited; for example, one or more layers of reflective plates, semi-transparent plates, retardation plates (including 1 / 2 and 1 / 4 wave plates), and vision compensation films, which are sometimes used in the formation of liquid crystal display devices, can be used. Examples of the aforementioned stacked polarizing film include reflective polarizing films or semi-transparent polarizing films formed by further stacking reflective plates or semi-transparent reflective plates on the aforementioned polarizing film; elliptical polarizing films or circular polarizing films formed by further stacking retardation plates on the aforementioned polarizing film; wide-viewing-angle polarizing films formed by further stacking viewing angle compensation films on the aforementioned polarizing film; and polarizing films formed by further stacking brightness-enhancing films on the aforementioned polarizing film.

[0143] An adhesive layer for bonding image display units such as liquid crystal cells and organic EL elements, as well as other components such as front-surface transparent panels and touch panels, to one or both sides of the aforementioned polarizing film or laminated polarizing film can be provided. An adhesive layer is preferred as this adhesive layer. There are no particular limitations on the adhesive forming the adhesive layer; adhesives using polymers such as acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorinated polymers, and rubber polymers as the base polymer can be suitably selected. Adhesives containing acrylic polymers, exhibiting excellent optical transparency, moderate wetting, cohesiveness, adhesion, weather resistance, and heat resistance, are particularly preferred.

[0144] The adhesive layer can be applied to one or both sides of the polarizing film or the laminated polarizing film in a suitable manner. Examples of applying the adhesive layer include: preparing an adhesive solution and directly applying it to the polarizing film or the laminated polarizing film using a suitable spreading method such as casting or coating; or forming an adhesive layer on a diaphragm and transferring it to the polarizing film or the laminated polarizing film. The thickness of the adhesive layer can be appropriately determined according to the intended use, adhesion, etc., and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. A material in which an adhesive layer is thus applied to at least one side of the polarizing film or the laminated polarizing film is called a polarizing film with an adhesive layer, or a laminated polarizing film with an adhesive layer.

[0145] For the purpose of preventing contamination, the exposed surface of the adhesive layer is preferably temporarily covered by an adhesive diaphragm until it is put into actual use. This prevents contamination of the adhesive layer under normal handling conditions. As the diaphragm, a suitable thin film such as plastic film, rubber sheet, paper, cloth, nonwoven fabric, mesh, foam sheet, metal foil, and their laminates can be used as needed, coated with suitable release agents such as silicone, long-chain alkyl, fluorine, or molybdenum sulfide.

[0146] <Image display panel and image display device>

[0147] The image display panel of the present invention is formed by bonding the aforementioned polarizing film or the aforementioned stacked polarizing film to the image display unit. Furthermore, the image display device of the present invention provides a front surface transparent member on the polarizing film or stacked polarizing film side (viewable side) of the aforementioned image display panel.

[0148] Examples of image display units include liquid crystal units (LCDs) and organic EL units (OLEDs). The liquid crystal unit can be any of the following: a reflective liquid crystal unit utilizing external light, a transmissive liquid crystal unit utilizing light from a backlight or other light source, or a semi-transmissive / semi-reflective liquid crystal unit utilizing both external light and light from a light source. In the case where the liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) also provides a polarizing film and a light source on the side of the image display unit (liquid crystal unit) opposite to the viewable side. The polarizing film on the light source side is preferably bonded to the liquid crystal unit with a suitable adhesive layer between them. Examples of driving methods for the liquid crystal unit include VA mode, IPS mode, TN mode, STN mode, bent alignment (π-type), and any other type.

[0149] As the aforementioned organic EL unit, 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 used. The aforementioned organic light-emitting layer is a stack of various organic thin films and can adopt various layer structures, including, for example: a stack of a hole injection layer made of a triphenylamine derivative and the like and a light-emitting layer made of a fluorescent organic solid such as anthracene; a stack of these light-emitting layers and an electron injection layer made of a dinaphthalene derivative and the like; or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0150] Examples of front-surface transparent members disposed on the viewable side of the aforementioned image display unit include: a front-surface transparent plate (window layer), a touch panel, etc. The front-surface transparent plate can be a transparent plate with suitable mechanical strength and thickness. Such a transparent plate can be, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate. The touch panel can be, for example, various touch panels of resistive film type, electrostatic capacitive type, optical type, ultrasonic type, etc., a glass plate with touch sensor function, a transparent resin plate, etc. When using an electrostatic capacitive touch panel as the front-surface transparent member, it is preferable to provide a front-surface transparent plate made of glass or a transparent resin plate on the side closer to the viewable side than the touch panel.

[0151] The polarizing film of the present invention has good initial polarization degree and excellent effect in suppressing the reduction of monomer transmittance caused by the coloring of the polarizing film in high temperature environment. Therefore, the polarizing film of the present invention, as well as the polarizing film using the polarizing film, the stacked polarizing film, the image display panel, and the image display device are suitable for use in vehicle image display devices such as car navigation devices and rearview monitors.

[0152] Example

[0153] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0154] <Example 1>

[0155] <Production of Polarizing Film>

[0156] As the thermoplastic resin substrate, an amorphous polyethylene terephthalate (PET) copolymer of isophthalic acid (100 μm) with a strip-shaped structure, a water absorption rate of 0.75%, and a Tg of approximately 75 °C was used. One side of the resin substrate was subjected to corona treatment. A PVA aqueous solution (coating solution) was prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") at a ratio of 9:1, and adding 13 parts by weight of potassium iodide to 100 parts by weight of the resulting PVA-based resin. The aforementioned PVA aqueous solution was coated onto the corona-treated surface of the resin substrate and dried at 60 °C to form a 13 μm thick PVA-based resin layer, thus creating a laminate. The resulting laminate was subjected to unidirectional stretching along the longitudinal direction (length direction) to 2.4 times its free end length in an oven at 130°C between rollers with different circumferential speeds (assisted stretching treatment in a gas atmosphere). Next, the laminate was immersed in an insoluble bath (aqueous solution of boric acid at 4.0 wt%) at 40°C for 30 seconds (insoluble treatment). Then, it was immersed in a dyeing bath (an aqueous solution of iodine and potassium iodide in a 1:7 weight ratio relative to 100 parts by weight of water) at 30°C for 60 seconds, adjusting the concentration to achieve an iodine concentration of 9.3% for the final polarizing film (dyeing treatment). Finally, it was immersed in a crosslinking bath (aqueous solution of potassium iodide at 3.0 wt% and boric acid at 5.0 wt%) at 40°C for 30 seconds (crosslinking treatment). Then, while immersing the laminate in a boric acid aqueous solution (4.0 wt%) at a liquid temperature of 70°C, it was uniaxially stretched between rollers with different circumferential speeds along the longitudinal direction (length direction) at a total stretch ratio of 5.5 times (stretching treatment in aqueous solution). Then, the laminate was immersed in a cleaning bath (3 wt% potassium iodide and 1.0 wt% aqueous solution of a compound represented by the following general formula (9) with free radical scavenging function) at a liquid temperature of 20°C (cleaning treatment). Then, while drying in an oven maintained at 90°C, it was contacted with a heated roller made of SUS with a surface temperature maintained at 75°C for about 2 seconds (drying shrinkage treatment). In this way, a polarizing film with a thickness of 5 μm was formed on the resin substrate. In addition, for the obtained polarizing film, the peak temperature of the maximum intensity of water detected by gas generation analysis was 204°C, and the content of the compound represented by the following general formula (9) in the polarizing film was 0.3 wt%.

[0157] [Chemical Formula 9]

[0158]

[0159] [Method for determining the iodine concentration (wt%) in polarizing film]

[0160] For the polarizing film, the iodine concentration (wt%) was determined using a fluorescence X-ray analysis device (manufactured by Rigaku Corporation, trade name "ZSX-PRIMUSIV", measurement diameter: φ20mm) and the following formula.

[0161] Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kcps / μm)

[0162] It should be noted that the coefficient used to calculate concentration varies depending on the measuring device, but this coefficient can be obtained using an appropriate calibration curve.

[0163] [Gas Generation Analysis Method]

[0164] The polarizing film was introduced into a furnace-type pyrolyzer (Frontier Lab, PY-2020iD), and the generated gas was directly introduced into a TOFMS (JEOL, JMS-T100GCV) for generated gas analysis (EGA / TOFMS).

[0165] [Measurement Conditions]

[0166] Heating conditions: 40℃ → +10℃ / min → 350℃

[0167] Interface: Deactivated fused silica tube, 2.5m × 0.15mm id

[0168] Carrier gas: He (1.0 mL / min)

[0169] Inlet temperature: 300℃

[0170] Note: Flow ratio 20:1

[0171] Interface temperature: 300℃

[0172] Mass spectrometer: TOFMS

[0173] Ionization method: EI method

[0174] Mass range: m / z = 18

[0175] [Method for determining the content (wt%) of compounds with free radical scavenging function in polarizing films]

[0176] Approximately 20 mg of polarizing membrane was used for quantification. After dissolving in 1 mL of water by heating, it was diluted with 4.5 mL of methanol. The resulting extract was filtered through a membrane filter, and the concentration of compounds with free radical scavenging function in the filtrate was determined using HPLC (Waters ACQUITYUPLC H-class Bio).

[0177] <Fabrication of Polarizing Film>

[0178] As an adhesive, an aqueous solution containing polyvinyl alcohol resin with acetylacetyl groups (average degree of polymerization 1200, 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 and a roller laminator, a 30 μm thick transparent protective film (made by Nippon Shokubai, with a moisture permeability of 125 g / (m²)) formed from (meth)acrylic resin (a modified acrylic polymer with a lactone ring structure) was laminated onto the surface opposite to the resin substrate (image display unit side) of the polarizing film obtained above. 2 • 24h). Next, the resin substrate is peeled off, and a transparent protective film with a thickness of 47μm and HC is formed on the peeled side (visible side) using a UV-curable adhesive and a roller laminator, with UV curing adhesive. The film has a moisture permeability of 380g / (m³). 2 A 24h transparent protective film was used as the adhesive, and then UV light was irradiated from the surface of the transparent protective film to cure the adhesive, thus creating a polarizing film.

[0179] [Evaluation of degree of polarization]

[0180] The degree of polarization of a polarizing film can be measured using a spectrophotometer (Japanese Spectrophotometer, product name "V7100"). Specifically, the degree of polarization can be measured by determining the parallel transmittance (H0) and orthogonal transmittance (H90) of the polarizing film and calculating using the formula: Degree of polarization (%) = {(H0-H90) / (H0+H90)}¹ / ² × 100. The parallel transmittance (H0) is the transmittance value of a parallel-type stacked polarizing film manufactured by stacking two identical polarizing films with their absorption axes parallel. Similarly, the orthogonal transmittance (H90) is the transmittance value of an orthogonal-type stacked polarizing film manufactured by stacking two identical polarizing films with their absorption axes orthogonal. It should be noted that these transmittance values ​​are Y values ​​obtained by visibility correction using a 2-degree field of view (C light source) according to JlS Z8701-1982. The results are shown in Table 1.

[0181] [Evaluation of monomer transmittance in high-temperature environments]

[0182] The polarizing film obtained above was cut into 5.0 × 4.5 cm pieces with the absorption axis of the polarizing film parallel to its long side. A glass plate (simulating the image display unit) was laminated to the protective film side of the polarizing film through a 20 μm thick acrylic adhesive layer. The laminate was then subjected to autoclaving at 50°C and 0.5 MPa for 15 minutes to fabricate a laminate. The resulting laminate was then placed in a hot air oven at 95°C for 750 hours, and the monomer transmittance (ΔTs) before and after heating was measured. The monomer transmittance was measured using a spectrophotometer (Japanese Spectrophotometer, product name "V7100") and evaluated based on the following criteria. It should be noted that the measurement wavelength was 380–700 nm (in 5 nm intervals). The results are shown in Table 1.

[0183] ΔTs(%)=Ts 700 -Ts0

[0184] Where Ts0 is the monomer transmittance of the laminate before heating, and Ts 700 The transmittance of the laminate after heating for 500 hours is the monomer transmittance. The above-mentioned ΔTs(%) is preferably 5 ≥ ΔTs(%) ≥ 0, more preferably 3 ≥ ΔTs(%) ≥ 0.

[0185] [Evaluation of panel warping]

[0186] The polarizing film was cut to a size of 145×105mm with the absorption axis parallel to its long side. A 0.4mm thick glass plate with dimensions of 155×115mm was bonded to the protective film side of the polarizing film, separated by a 20μm thick acrylic adhesive layer. The resulting glass (simulated panel) sample with polarizing film was placed in a hot air oven at 85℃ for 5 hours and then placed in a normal temperature and humidity environment for 1 hour. The warpage of the glass was then evaluated. Warpage refers to the amount of warpage by which the glass and the polarizer become convex downwards. The results are shown in Table 1.

[0187] ○: Warpage less than 1.0mm

[0188] ×: Warpage of 1.0mm or more

[0189] <Example 2>

[0190] <Fabrication of Polarizing Films>

[0191] In the fabrication of the polarizing film, the iodine concentration in the staining bath was adjusted so that the final polarizing film had an iodine concentration of 6.3% by weight. Otherwise, the polarizing film and the polarizing film were fabricated using the same procedure as in Example 1. For the obtained polarizing film, the peak temperature of the maximum intensity of water, as detected by gas generation analysis, was 207°C, the content of the compound represented by the above general formula (9) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 5 μm.

[0192] <Example 3>

[0193] <Fabrication of Polarizing Films>

[0194] A polyvinyl alcohol (PVA) film with an average degree of polymerization of 2400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. The PVA film was immersed in a swelling bath (water bath) at 20°C for 30 seconds between rollers with different circumferential speeds to induce swelling, while simultaneously stretching it 2.2 times in the transport direction (swelling process). Next, it was immersed for 30 seconds in a dyeing bath at 30°C (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a 1:7 weight ratio relative to 100 parts by weight of water), adjusting the iodine concentration to 6.1 wt% for the final polarizing film, while simultaneously dyeing. The original PVA film (completely unstretched in the transport direction) was then stretched 3.3 times in the transport direction as a reference (dyeing process). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath at 40°C (an aqueous solution of 3.5 wt% boric acid, 3.0 wt% potassium iodide, and 3.6 wt% zinc sulfate) for 28 seconds, and the original polyvinyl alcohol film was stretched to 3.6 times its original length in the transport direction (crosslinking process). Further, the obtained polyvinyl alcohol film was immersed in a stretching bath at 64°C (an aqueous solution of 4.5 wt% boric acid, 5.0 wt% potassium iodide, and 5.0 wt% zinc sulfate) for 60 seconds, and the original polyvinyl alcohol film was stretched to 6.0 times its original length in the transport direction (stretching process). Then, it was immersed in a cleaning bath at 27°C (an aqueous solution of 2.3 wt% potassium iodide and 1.0 wt% of a compound represented by the following general formula (6) having free radical scavenging function) for 10 seconds (cleaning process). The cleaned polyvinyl alcohol film was dried at 40°C for 30 seconds to produce a polarizing film. For the obtained polarizing film, the peak temperature of the maximum intensity of water detected by the gas generation analysis method is 209°C, the content of the compound represented by the above general formula (9) in the polarizing film is 0.2% by weight, and the thickness of the polarizing film is 12 μm.

[0195] Next, as an adhesive, an aqueous solution containing polyvinyl alcohol resin (average degree of polymerization of 1200, degree of saponification of 98.5 mol%, degree of acetylation of 5 mol%) and trimethylol melamine in a weight ratio of 3:1 was used. Using this adhesive and a roller laminator, a 30 μm thick transparent protective film (made by Nippon Shokubai, moisture permeability of 125 g / (m²)) formed from (meth)acrylic resin (a modified acrylic polymer with a lactone ring structure) was laminated onto one side (image display unit side) of the polarizing film obtained above. 2 • 24h)), and on the other side (visible side), a transparent protective film with a thickness of 47μm and HC is formed on a cellulose triacetate membrane (Fuji Film Manufacturing, trade name "TJ40UL") (humidity permeability is 380g / (m²)). 2 After 24 hours, the film was dried in an oven (at 90°C for 10 minutes) to produce a polarizing film with a transparent protective film bonded to both sides of the polarizing film.

[0196] <Example 4>

[0197] <Fabrication of Polarizing Films>

[0198] In the fabrication of the polarizing film, the iodine concentration in the dyeing bath was adjusted to achieve an iodine concentration of 7.9% by weight in the final polarizing film. Furthermore, a compound represented by the aforementioned general formula (8) at a concentration of 1.0% by weight was added to the bath during the cleaning process to replace the compound represented by general formula (9) as a compound with free radical scavenging function. Otherwise, the polarizing film and polarizing film were fabricated using the same procedures as in Example 1. For the obtained polarizing film, the peak temperature of the maximum water intensity, as detected by gas analysis, was 206°C. The content of the compound represented by the aforementioned general formula (8) in the polarizing film was 0.3% by weight, and the thickness of the polarizing film was 5 μm.

[0199] <Comparative Example 1>

[0200] <Fabrication of Polarizing Films>

[0201] In the fabrication of the polarizing film, the iodine concentration in the staining bath was adjusted to 8.5% by weight so that the final polarizing film had an iodine concentration of 8.5% by weight. No compound represented by the above general formula (9), which has a free radical scavenging function, was added to the washing bath. Otherwise, the polarizing film and the polarizing film were fabricated using the same procedure as in Example 1. For the obtained polarizing film, the peak temperature of the maximum water intensity detected by gas generation analysis was 193°C, the content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 5 μm.

[0202] <Comparative Example 2>

[0203] <Fabrication of Polarizing Films>

[0204] In the fabrication of the polarizing film, the iodine concentration in the staining bath was adjusted to achieve an iodine concentration of 5.6% by weight in the final polarizing film. No compound represented by the above general formula (9), which has free radical scavenging function, was added to the washing bath. Otherwise, the polarizing film and polarizing film were fabricated using the same procedures as in Example 1. For the obtained polarizing film, the peak temperature of the maximum water intensity, as detected by gas generation analysis, was 203°C. The content of the compound represented by the above general formula (9) in the polarizing film was 0% by weight, and the thickness of the polarizing film was 5 μm.

[0205] Using the polarizing films of the above-obtained embodiments and comparative examples, the above-described evaluations of polarization degree, single-cell transmittance in high-temperature environments, and panel warpage were performed. The results are shown in Table 1.

[0206] [Table 1]

[0207]

Claims

1. A method for manufacturing a polarizing film, comprising: adsorbing iodine onto a polyvinyl alcohol film and orienting it to form the polarizing film; the method comprising: The process involves performing optional swelling and cleaning steps on the polyvinyl alcohol film, and at least performing dyeing, crosslinking, and stretching steps to obtain a polarizing film containing a compound with free radical scavenging function and an iodine concentration of 6% by weight or more and 12% by weight or less. The processing bath in any one or more of the above-mentioned swelling, cleaning, dyeing, crosslinking, and stretching steps contains a compound with free radical scavenging function, and the compound with free radical scavenging function can dissolve at least 1 part by weight in 100 parts by weight of water at 25°C. A laminate is prepared by forming a polyvinyl alcohol resin layer containing a polyvinyl alcohol resin on one side of a strip-shaped thermoplastic resin substrate. The laminate is then subjected to optional insolubility treatment, crosslinking treatment, and cleaning treatment, and at least the following processes are performed: assisted stretching treatment in a gas atmosphere, dyeing treatment, stretching treatment in an aqueous solution, and drying shrinkage treatment. This process yields a polarizing film containing a compound with free radical scavenging function and an iodine concentration of 6% to 12% by weight. The compound with free radical scavenging function is contained in any one or more of the following treatment baths: dyeing treatment, stretching treatment in an aqueous solution, insolubility treatment, crosslinking treatment, and cleaning treatment. The compound with free radical scavenging function is soluble in at least 1 part by weight of water at 25°C out of 100 parts by weight. It also includes a process of designing a polarizing film in such a way that the peak temperature of the maximum intensity of water detected by the obtained polarizing film containing a compound with free radical scavenging function is confirmed to be above 200°C in the presence of an inert gas, under the conditions of a heating rate of 10°C / min and a heating range of 40°C to 350°C, and the difference in monomer transmittance ΔTs(%) before and after a heat resistance test of 95°C × 750 hours is 5 ≥ ΔTs(%) ≥ 0.

2. The method for manufacturing the polarizing film according to claim 1, wherein, The thickness of the polarizing film is less than 15 μm.

3. The method for manufacturing the polarizing film according to claim 1 or 2, wherein, The compound with free radical scavenging function is a compound containing nitryl radicals or nitryl groups.

4. A method for manufacturing a polarizing film, the method comprising: The step of laminating a transparent protective film onto at least one side of a polarizing film obtained by the manufacturing method of any one of claims 1 to 3.

5. The method for manufacturing a polarizing film according to claim 4, wherein, The polarization degree of the polarization film is above 99.98%.

6. A method for manufacturing a stacked polarizing film, the method comprising: The process of attaching an optical layer to a polarizing film obtained by the manufacturing method of a polarizing film according to claim 4 or 5.

7. A method for manufacturing an image display panel, the method comprising: The process of attaching a polarizing film obtained by the manufacturing method of the polarizing film according to claim 4 or 5, or a stacked polarizing film obtained by the manufacturing method of the stacked polarizing film according to claim 6, to an image display unit.

8. A method for manufacturing an image display device, the method comprising: The process of setting a front surface transparent member on the polarizing film or laminated polarizing film side of an image display panel obtained by the manufacturing method of the image display panel according to claim 7.

9. The method for manufacturing an image display device according to claim 8, wherein, The image display device is a vehicle-mounted image display device.

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