Method for manufacturing polarizing film, and method for manufacturing polarizing film

Abstract

Provided is a method for producing a polarizing film, the method including: a process (I-1) for producing a polarizing film containing water by transporting a polyvinyl alcohol-based film in a length direction while applying at least a dyeing process, a cross-linking process, and a stretching process to the polyvinyl alcohol-based film; a process (I-2) for producing a polarizing film containing components impregnated in a liquid by applying a coating liquid to the obtained polarizing film containing water in a state where the water content of the polarizing film is X% by mass or more; and a process (I-3) for producing a dried polarizing film by applying a drying process to the obtained polarizing film containing components impregnated in a liquid. The method for producing a polarizing film satisfies the condition of formula (1): X (% by mass) / thickness of the dried polarizing film (μm) > 1 (in formula (1), X is 10 or more and 70 or less). The method for producing a polarizing film of the present invention can allow a polarizing film to contain any components simply and sufficiently.

Description

Technical Field

[0001] This invention relates to a method for manufacturing polarizing films and a method for manufacturing polarizing films. Background Technology

[0002] Conventionally, polarizing films (polarizers) 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, such as dyeing, crosslinking, and stretching, in a bath followed by 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.

[0003] As a method for manufacturing polarizing films, Patent Documents 1 and 2 disclose methods for improving the durability of polarizing films by adding metal salts containing zinc, copper, aluminum, etc., to a processing bath. Patent Documents 3 and 4 disclose methods for manufacturing polarizing films by adding organotitanium compounds, etc., to a processing bath.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2016 / 117659

[0007] Patent Document 2: Japanese Patent Application Publication No. 2006-047978

[0008] Patent Document 3: Japanese Patent Application Publication No. 2008-46257

[0009] Patent Document 4: Japanese Patent Application Publication No. 6-172554 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, in the manufacturing method of polarizing film, when the above-mentioned components are added to the treatment bath, there are problems such as the large amount of components required and the need for waste liquid treatment.

[0012] In view of the above, the object of the present invention is to provide a method for manufacturing a polarizing film that can easily and sufficiently contain any components and has good polarization degree.

[0013] Furthermore, an object of the present invention is to provide a method for manufacturing a polarizing film using a polarizing film obtained by the above-described polarizing film manufacturing method.

[0014] Problem Solving Methods

[0015] That is, the present invention relates to a method for manufacturing a polarizing film, the method comprising: conveying a polyvinyl alcohol film along its length while performing at least a dyeing process, a crosslinking process and a stretching process on the polyvinyl alcohol film to manufacture a polarizing film containing water (I-1); coating the obtained polarizing film containing water with a moisture content of X wt% or more to manufacture a polarizing film impregnated with components in the liquid (I-2); and drying the obtained polarizing film impregnated with components in the liquid to manufacture a dried polarizing film (I-3), the method satisfying the condition of formula (1): X (wt%) / thickness (μm) of the dried polarizing film > 1 (in formula (1), X is 10 or more and 70 or less).

[0016] Furthermore, the present invention relates to a method for manufacturing a polarizing film, the method comprising: a step (II-0) of preparing a laminate by forming a polyvinyl alcohol resin layer comprising a polyvinyl alcohol resin on one side of a strip-shaped thermoplastic resin substrate; a step (II-1) of manufacturing a laminate having a water-containing polarizing film by transporting the obtained laminate along its length and performing at least an assisted stretching treatment in a gas atmosphere, a dyeing treatment, and a stretching treatment in an aqueous solution on the laminate; wherein the moisture content of the polarizing film is Y% by weight or more. In the state, a process of coating a obtained laminate containing a water-containing polarizing film with a liquid is performed to manufacture a laminate containing a polarizing film impregnated with the liquid (II-2); and a process of drying the obtained laminate containing a polarizing film impregnated with the liquid is performed to manufacture a dried polarizing film (II-3). The method satisfies the condition of formula (3): the above-mentioned Y (weight%) / the thickness (μm) of the above-mentioned dried polarizing film > 1 (in formula (3), Y is 10 or more and 70 or less).

[0017] In addition, the present invention relates to a method for manufacturing a polarizing film, the method comprising: a step of laminating a transparent protective film onto at least one side of a polarizing film obtained by the above-described polarizing film manufacturing method via an adhesive layer.

[0018] The effects of the invention

[0019] The exact mechanism of action of the polarizing film manufacturing method 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.

[0020] The method for manufacturing a polarizing film of the present invention includes: a step (I-1) in which a polyvinyl alcohol film is transported along its length and at least a dyeing step, a crosslinking step, and a stretching step are performed on the polyvinyl alcohol film to manufacture a polarizing film containing water; a step (I-2) in which the water content of the polarizing film is X wt% or more, the resulting polarizing film containing water is coated with a liquid to manufacture a polarizing film containing components in the liquid; and a step (I-3) in which the resulting polarizing film containing components in the liquid is dried to manufacture a dried polarizing film. The method satisfies the condition of formula (1): X (wt%) / thickness (μm) of the dried polarizing film > 1 (in formula (1), X is 10 or more and 70 or less). Alternatively, the method for manufacturing the polarizing film of the present invention includes: a step (II-0) of preparing a laminate by forming a polyvinyl alcohol resin layer containing a polyvinyl alcohol resin on one side of a strip-shaped thermoplastic resin substrate; a step (II-1) of manufacturing a laminate having a water-containing polarizing film by transporting the obtained laminate along the length direction and performing at least an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, and a stretching treatment in an aqueous solution on the obtained laminate having a water-containing polarizing film; a step (II-2) of coating the obtained laminate having a water-containing polarizing film with a moisture content of Y wt% or more; and a step (II-3) of drying the obtained laminate having a polarizing film containing a component in the liquid. The method satisfies the condition of formula (3): the above-mentioned Y (wt%) / the thickness (μm) of the above-mentioned dried polarizing film > 1 (in formula (3), Y is 10 or more and 70 or less). In existing methods for manufacturing polarizing films, a dyeing process, a crosslinking process, and a stretching process are performed on a polyvinyl alcohol film, followed by a drying process. Alternatively, in existing methods for manufacturing polarizing films, a process of preparing a laminate by forming a polyvinyl alcohol resin layer containing polyvinyl alcohol resin on one side of a strip-shaped thermoplastic resin substrate, and a process of performing at least an assisted stretching process in a gas atmosphere, a dyeing process, and a stretching process in an aqueous solution on the obtained laminate, are followed by a drying process. On the other hand, in the method for manufacturing polarizing films of the present invention, a polarizing film containing water or a laminate having a polarizing film containing water is manufactured as described above. Moreover, the method for manufacturing polarizing films of the present invention satisfies the conditions of formula (1) or (3) above. Therefore, in the above-described liquid coating process, the polarizing film containing water can be easily and sufficiently impregnated with any component contained in the liquid, and a polarizing film with good polarization can be manufactured. Detailed Implementation

[0021] <Manufacturing Method of Polarizing Film>

[0022] The method for manufacturing the polarizing film of the present invention includes: a step (I-1) in which a polyvinyl alcohol film is transported along the length direction and at least a dyeing step, a crosslinking step, and a stretching step are performed on the polyvinyl alcohol film to manufacture a polarizing film containing water; a step (I-2) in which the water content of the polarizing film is X wt% or more, the resulting polarizing film containing water is coated with a liquid to manufacture a polarizing film containing components in the liquid; and a step (I-3) in which the resulting polarizing film containing components in the liquid is dried to manufacture a dried polarizing film. The method satisfies the condition of formula (1): X (wt%) / thickness (μm) of the dried polarizing film > 1 (in formula (1), X is 10 or more and 70 or less).

[0023] <Process for manufacturing a water-containing polarizing film (I-1)>

[0024] The method for manufacturing the polarizing film of the present invention includes a step (I-1) of transporting a polyvinyl alcohol film along its length direction while performing at least a dyeing step, a crosslinking step, and a stretching step on the polyvinyl alcohol film.

[0025] 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 dichroic substances such as iodine and dichroic dyes. 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.

[0026] 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.

[0027] Plasticizers, surfactants, and other additives can be included in the aforementioned polyvinyl alcohol (PVA) films. Examples of plasticizers include 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, approximately 20% by weight or less is suitable in PVA films.

[0028] <Dyeing Process>

[0029] The above-described dyeing process involves immersing a polyvinyl alcohol (PVA) film in a dyeing bath, which allows dichroic substances such as iodine or dichroic dyes to be adsorbed onto the PVA film and oriented. The dyeing 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.

[0030] 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 10% by weight, more preferably about 0.05 to 5% by weight.

[0031] The temperature of the dyeing bath is preferably around 10–50°C, more preferably around 15–45°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.

[0032] <Cross-linking process>

[0033] The crosslinking process described above involves immersing a polyvinyl alcohol (PVA) film, which has been dyed in the dyeing process described above, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA film, allowing iodine molecules 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 miscible with water and water. Furthermore, the crosslinking bath may contain iodides such as potassium iodide.

[0034] 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 an iodide such as potassium iodide is used in the aforementioned crosslinking bath, the concentration of the iodide is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight.

[0035] 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.

[0036] <Stretching Process>

[0037] 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.

[0038] The treatment bath (stretching bath) in the above-described wet stretching method can typically be water, or a mixture of an organic solvent and water that is miscible with water. The stretching bath may contain iodides such as potassium iodide. When using iodides such as potassium iodide in the stretching bath, the concentration of the iodide is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight. Furthermore, to improve the degree of crosslinking, 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.

[0039] The temperature of the stretching bath is preferably around 25–80°C, more preferably around 40–75°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 uniformly determined; preferably around 10–800 seconds, more preferably around 30–500 seconds. It should be noted that the stretching treatment in the wet stretching method described above can be performed together with any one or more of the following processes: the dyeing process, the crosslinking process, the swelling process described later, and the cleaning process described later.

[0040] 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 implemented together with the drying process described later.

[0041] 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.

[0042] In the process of manufacturing the above-mentioned water-containing polarizing film, in addition to performing the above-mentioned dyeing process, cross-linking process and stretching process on the above-mentioned polyvinyl alcohol film, a swelling process and a cleaning process may also be performed.

[0043] <Swelling Process>

[0044] 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.

[0045] The temperature of the swelling bath is preferably around 10–60°C, more preferably around 15–45°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. The swelling process can be performed only once, or multiple times as needed.

[0046] <Cleaning Process>

[0047] The above-described cleaning process involves immersing the polyvinyl alcohol (PVA) membrane in a cleaning bath, which removes foreign matter remaining on the surface of the PVA membrane. The cleaning bath typically uses a water-based medium, such as water, distilled water, or pure water. Alternatively, the cleaning bath may contain iodides such as potassium iodide. In this case, the concentration of the iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 2 to 4% by weight, and even more preferably about 1.6 to 3.8% by weight.

[0048] 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 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.

[0049] 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.

[0050] <Process for manufacturing a polarizing film containing components impregnated in a liquid (I-2)>

[0051] The method for manufacturing the polarizing film of the present invention includes: a step of coating a water-containing polarizing film obtained above with a liquid while the water content of the polarizing film is X% by weight or more, thereby manufacturing a polarizing film impregnated with components in the liquid (I-2). Here, the components in the liquid are generally solutes contained in a solution. In addition, the solute can be any substance that can dissolve and disperse in a solvent, and as a single compound, it can be any substance among gaseous substances, liquid substances, and solid substances. It should be noted that when the solute is a liquid substance (for example, under conditions of 25°C and 1 atmosphere), the liquid substance itself (the liquid substance itself) can be a liquid and components in the liquid.

[0052] In the above-described process (I-2), from the viewpoint that it is easier to impregnate the components contained in the liquid and to more easily penetrate the polarizing film in the thickness direction, it is preferable that the moisture content (X wt%) of the polarizing film is 20 wt% or more, more preferably 22 wt% or more, and even more preferably 25 wt% or more. Moreover, from the viewpoint of preventing wrinkles during transportation, it is preferable that the moisture content of the polarizing film is 65 wt% or less, and more preferably 60 wt% or less.

[0053] The coating method used in the above-mentioned liquid coating process can be any existing coating method, such as: roller coating, spin coating, wire rod coating, dip coating, mold coating, curtain coating, spray coating, and blade coating (comma coating, etc.). It should be noted that the polarizing film can be coated on one or both sides.

[0054] From the viewpoint that the components can easily be impregnated in the aforementioned water-containing polarizing film, the components in the liquid can be water-soluble compounds. It should be noted that the aforementioned water-soluble compounds refer to compounds that have a solubility of 1g or more in 100g of water at 25°C.

[0055] Examples of components in the aforementioned liquids include: zinc salts (zinc halides such as zinc chloride and zinc iodide; inorganic zinc salts such as zinc sulfate and zinc acetate); organotitanium compounds (alkoxytitanium, titanium chelates, ammonium salts of titanium chelates, titanium chelates, etc.); organozirconium (alkoxyzirconium, zirconium chelates, ammonium salts of zirconium chelates, zirconium acylates); alkali metal salts; alkaline earth metal salts; and metal halides.

[0056] In addition, compounds with free radical scavenging function (also called free radical scavengers) can be included as components in the above-mentioned liquid. These compounds with free radical scavenging function can capture free radicals generated by heating in the polyvinyl alcohol of the polarizing film, inhibiting polyene formation, and thus improving the heat resistance of the polarizing film. From the viewpoint of easily inhibiting polyene formation, compounds having nitroacin radicals or nitroacin groups are preferred, for example.

[0057] Examples of compounds having nitryl radicals or nitryl groups include compounds having organic groups with the following structures.

[0058] [Chemical Formula 1]

[0059]

[0060] (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.

[0061] Examples of compounds having the above-mentioned organic groups include compounds represented by the following general formulas (2) to (5).

[0062] [Chemical Formula 2]

[0063]

[0064] (In general formula (2), R) 1 ~R 5 And n has the same meaning as above, R 6 (This refers to a hydrogen atom, or an alkyl, acyl, or aryl group having 1 to 10 carbon atoms.)

[0065] [Chemical Formula 3]

[0066]

[0067] (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.)

[0068] [Chemical Formula 4]

[0069]

[0070] (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.

[0071] [Chemical Formula 5]

[0072]

[0073] (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.)

[0074] 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.

[0075] In addition, the following compounds can be listed as examples of compounds having nitrocellulose radicals or nitrocellulose groups.

[0076] [Chemical Formula 6]

[0077]

[0078] (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.)

[0079] [Chemical Formula 7]

[0080]

[0081] [Chemical Formula 8]

[0082]

[0083] In addition, compounds with cross-linking functions (also called cross-linking agents) can be listed as components in the aforementioned liquid. These compounds with cross-linking functions react with the hydroxyl groups of the polyvinyl alcohol in the polarizing film to form a cross-linked structure, thereby improving the durability of the polarizing film to humidification. From the viewpoint of improving humidification durability, compounds with cross-linking functions, in addition to those having isocyanate groups, isocyanate-derived functional groups, epoxy groups, carbonyl groups, aziridine rings, vinyl ether groups, vinyl sulfonyl groups, etc., are also considered. Besides zoline-based organic compounds, other examples include organotitanium compounds (alkoxytitanium, titanium chelates, titanium chelate ammonium salts, titanium chelate acylates, etc.).

[0084] In addition, compounds with plasticizing functions (also known as plasticizers) can be included as components in the aforementioned liquid. These compounds, by imparting plasticity to the polarizing film, can mitigate quality defects such as scratches caused by the pressure applied. Examples of such compounds with plasticizing functions include ethylene glycol, polyethylene glycol, ethylene glycol derivatives, and glycerin.

[0085] In addition, dye compounds (also called dyes) can be listed as components of the aforementioned liquid. These dye compounds can impart properties such as hue adjustment and pattern printing to the polarizing film. Examples of such dye compounds include azo compounds, anthraquinones, and quinoline ketones.

[0086] The above-mentioned liquid is affected by the above-mentioned coating (application) method, so it cannot be determined in general. From the viewpoint of being able to make the components in the liquid penetrate with good efficiency, the concentration of the components in the liquid is preferably 0.1% by weight or more, more preferably 1.0% by weight or more. Moreover, from the viewpoint of preventing poor quality caused by the precipitation of the components in the liquid, the concentration of the components in the liquid is preferably 30% by weight or less, more preferably 20% by weight or less.

[0087] Examples of solvents mentioned above include: water; methanol, ethanol, ethylene glycol, polyethylene glycol and ethylene glycol derivatives, glycerol, dimethyl sulfoxide and other water-soluble solvents.

[0088] Regarding the time from the start of the above-mentioned process (I-1) until the start of the above-mentioned process (I-2) (the transport time of the polarizing film in actual equipment manufacturing), from the viewpoint of maintaining the moisture contained in the water-containing polarizing film, or from the viewpoint of productivity, it is preferably 300 seconds or less, more preferably 180 seconds or less, further preferably 60 seconds or less, and more preferably 10 seconds or less, when the temperature is around 15°C to 35°C, preferably around 20°C to 30°C.

[0089] Additionally, as needed, in the above-mentioned process (I-2), after the process of coating the water-containing polarizing film with liquid, a process of impregnating a portion of the liquid and removing the remaining liquid can be performed. Examples of liquid removal methods include wiping with cotton yarn, sponge rolls, suction removal, air removal, and scraping removal with rods or gravure rollers.

[0090] Furthermore, in the above-described process (I-2), it is preferable that the water-containing polarizing film satisfies the condition of the following formula (a). By setting the boron content in the water-containing polarizing film according to the thickness of the dried polarizing film as described in this condition, the components in the liquid can be permeated with good efficiency.

[0091] Equation (a): A (wt%) < 0.08 × B (μm) + 3.3

[0092] (In formula (a), A is the boron content (wt%) in the water-containing polarizing film, and B is the thickness (μm) of the dried polarizing film.)

[0093] <Process for manufacturing the dried polarizing film (I-3)>

[0094] The method for manufacturing the polarizing film of the present invention includes a step (I-3) of performing a drying process on the polarizing film impregnated with components in a liquid obtained above.

[0095] The above-described drying process involves drying a polarizing film impregnated with the components of the liquid obtained above to obtain a polarizing film. Drying yields a polarizing film with a desired moisture content. This drying can be performed by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0096] 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.

[0097] From the viewpoint of preventing quality defects such as scratches caused by loss of plasticity, the moisture content of the dried polarizing film is preferably 10% by weight or more, more preferably 12% by weight or more. Furthermore, from the viewpoint of improving optical properties such as polarization degree, the moisture content is preferably 20% by weight or less, more preferably 16% by weight or less. It should be noted that, in the case of a dried polarizing film with a thickness of approximately 8 μm or less, as described later, from the viewpoint of preventing quality defects such as scratches caused by loss of plasticity, the moisture content of the dried polarizing film is preferably 2% by weight or more, more preferably 3% by weight or more. Furthermore, from the viewpoint of improving optical properties such as polarization degree, the moisture content is preferably 20% by weight or less, more preferably 10% by weight or less.

[0098] The thickness of the dried polarizing film is preferably about 1 to 30 μm, more preferably about 5 to 25 μm, and even more preferably 5 to 20 μm. In particular, in order to obtain a dried polarizing film with a thickness of about 8 μm or less, the following method for manufacturing a thin polarizing film can be used, in which a laminate comprising a thermoplastic resin substrate and a polyvinyl alcohol resin layer thereon is used as the polyvinyl alcohol film.

[0099] The method for manufacturing the polarizing film of the present invention satisfies the condition of formula (1): the above-mentioned X (wt%) / the thickness (μm) of the above-mentioned dried polarizing film > 1, preferably formula (1) > 1.2, more preferably formula (1) > 1.5.

[0100] Furthermore, from the viewpoint of improving the polarization degree when the polarizing film is manufactured, the method for manufacturing the polarizing film of the present invention preferably satisfies the condition of X (wt%) - the moisture content (wt%) of the polarizing film after drying > 0 (wt%), more preferably formula (2) > 2 (wt%), and even more preferably formula (2) > 5 (wt%).

[0101] <Manufacturing Method of Polarizing Film (Thin Polarizing Film)>

[0102] A method for manufacturing a polarizing film (thin polarizing film) includes: a step (II-0) of preparing a laminate by forming a polyvinyl alcohol resin layer containing a polyvinyl alcohol resin on one side of a strip-shaped thermoplastic resin substrate; a step (II-1) of manufacturing a laminate having a water-containing polarizing film; and a step of manufacturing a laminate having a water-containing polarizing film by subjecting the laminate to at least an assisted stretching treatment in a gas atmosphere, a dyeing treatment, and a stretching treatment in an aqueous solution while conveying the laminate along its length. The process involves applying a liquid coating to the obtained laminate containing a water-containing polarizing film to manufacture a laminate containing a polarizing film impregnated with the liquid (II-2); and performing a drying process on the obtained laminate containing a polarizing film impregnated with the liquid to manufacture a dried polarizing film (II-3). This method satisfies the condition of Equation (3): the above-mentioned Y (weight%) / the thickness (μm) of the above-mentioned dried polarizing film > 1 (in Equation (3), Y is 10 or more and 70 or less).

[0103] <Preparation process for laminated bodies (II-0)>

[0104] The method for manufacturing the polarizing film (thin polarizing film) of the present invention includes a step (II-0) of forming a polyvinyl alcohol resin layer (PVA resin layer) containing polyvinyl alcohol resin (PVA resin) on one side of a strip-shaped thermoplastic resin substrate.

[0105] 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.

[0106] 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.

[0107] 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 liquid, 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.

[0108] 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 (non-crystalline) 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 (non-crystalline) polyethylene terephthalate resins are preferred. Examples of amorphous (non-crystalline) polyethylene terephthalate resins include copolymers containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers containing cyclohexanediol and diethylene glycol as diols.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] <Process for manufacturing a laminate containing a water-containing polarizing film (II-1)>

[0115] The method for manufacturing the polarizing film (thin polarizing film) of the present invention includes a step (II-1) of transporting the obtained laminate along the length direction while performing at least an auxiliary stretching process in a gas atmosphere, a dyeing process, and a stretching process in an aqueous solution on the laminate to manufacture a laminate having a polarizing film containing water.

[0116] In the above-mentioned gas atmosphere-assisted stretching process, 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 in the above-mentioned gas atmosphere-assisted stretching process 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.

[0117] The preferred stretching ratio in the assisted stretching process within the aforementioned gas atmosphere is approximately 2 to 3.5 times. This assisted stretching process in 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.

[0118] The stretching temperature in the assisted stretching process 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.

[0119] As needed, an insoluble treatment process can be performed after the assisted stretching process in the aforementioned gas atmosphere and before the dyeing process or the stretching process in the aqueous solution. This insoluble treatment process is typically performed by impregnating the PVA resin layer in a boric acid aqueous solution. By performing the insoluble treatment process, 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 boric acid aqueous solution relative to 100 parts by weight of water is preferably about 1 to 5 parts by weight. The temperature of the insoluble treatment bath is preferably about 20 to 50°C.

[0120] The above-described dyeing process is performed by dyeing the PVA resin layer with iodine. Examples of this adsorption method include: impregnating the PVA resin layer (laminated structure) in an iodine-containing dyeing solution; applying the dyeing solution onto the PVA resin layer; spraying the dyeing solution onto the PVA resin layer, etc., with the method of impregnating the PVA resin layer (laminated structure) in an iodine-containing dyeing solution being preferred.

[0121] 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.

[0122] As needed, a crosslinking treatment step can be performed after the above-mentioned dyeing treatment step and before the stretching treatment step in aqueous solution. The crosslinking treatment step is typically performed by immersing the PVA resin layer in a boric acid aqueous solution. By performing the crosslinking treatment step, the PVA resin layer can be given water resistance, and during subsequent stretching in aqueous solution, the orientation of the PVA when immersed in high-temperature water can be prevented from decreasing. The boric acid concentration of this boric acid aqueous solution is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. Furthermore, when performing the crosslinking treatment step, it is preferable to further incorporate the above-mentioned iodide into the crosslinking bath. By incorporating the above-mentioned iodide, the dissolution of iodine adsorbed on the PVA resin layer can be suppressed. The amount of the above-mentioned iodide incorporated is preferably about 1 to 5 parts by weight relative to 100 parts by weight of water. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably about 20 to 50°C.

[0123] The above-described aqueous solution stretching process is performed by immersing the laminate in a stretching bath. According to this aqueous solution stretching process, stretching can be performed at a temperature lower than the glass transition temperature (typically around 80°C) of the 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 in the above-described aqueous solution stretching process 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.

[0124] The stretching process 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.

[0125] The stretching ratio in the stretching process in the above-mentioned aqueous solution is preferably about 1.5 times or more, and more preferably about 3 times or more.

[0126] 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.

[0127] Preferably, the cleaning process is performed after the stretching treatment in the above-mentioned aqueous solution. The cleaning process is typically carried out by immersing the PVA resin layer in an aqueous potassium iodide solution.

[0128] Furthermore, additives such as zinc salts, pH adjusters, pH buffers, and other salts may be included in the treatment baths of the aforementioned dyeing process, the aforementioned stretching process in the aqueous solution, the aforementioned insoluble treatment process, the aforementioned crosslinking process, and the aforementioned cleaning process. 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.

[0129] <Process for manufacturing a laminate containing a polarizing film impregnated with components in a liquid (II-2)>

[0130] The method for manufacturing the polarizing film (thin polarizing film) of the present invention includes: a step of coating a laminate containing a water-containing polarizing film with a liquid, wherein the water content of the polarizing film is Y% by weight or more, thereby manufacturing a laminate containing a polarizing film impregnated with a component in the liquid (II-2). For this step (II-2), the step (I-2) of manufacturing a polarizing film impregnated with a component in the liquid can be entirely applied, wherein the liquid is coated (applied) to one side of the polarizing film.

[0131] In the above-described process (II-2), from the viewpoint that it is easier to impregnate the components contained in the liquid and to more easily penetrate the polarizing film in the thickness direction, it is preferable that the moisture content (Y wt%) of the polarizing film is 20 wt% or more, more preferably 22 wt% or more, and even more preferably 25 wt% or more. Moreover, from the viewpoint of preventing wrinkles during transportation, it is preferable that the moisture content of the polarizing film is 65 wt% or less, and more preferably 60 wt% or less.

[0132] Regarding the time from the start of the above-mentioned process (II-1) until the start of the above-mentioned process (II-2) (the transport time of the laminate with polarizing film in actual equipment manufacturing), from the viewpoint of maintaining the moisture contained in the water-containing polarizing film, or from the viewpoint of productivity, when the temperature is around 15°C to 35°C, preferably around 20°C to 30°C, it is preferably 300 seconds or less, more preferably 180 seconds or less, further preferably 60 seconds or less, and even more preferably 10 seconds or less.

[0133] Furthermore, in the above-described process (II-2), it is preferable that the laminate containing the water-containing polarizing film satisfies the following condition (b). By setting the boron content in the polarizing film of the laminate containing the water-containing polarizing film according to the thickness of the dried polarizing film as described in this condition, the components in the liquid can be permeated with good efficiency.

[0134] Equation (b): A (wt%) < 0.08 × B (μm) + 3.3

[0135] (In formula (b), A is the boron content (wt%) in the polarizing film of the laminate containing the water-containing polarizing film, and B is the thickness (μm) of the polarizing film after drying.)

[0136] <Process for manufacturing the dried polarizing film (II-3)>

[0137] The method for manufacturing the polarizing film (thin polarizing film) of the present invention includes a step (II-3) of performing a drying process on the laminate having a polarizing film impregnated with components in a liquid obtained above.

[0138] The aforementioned drying process can be performed by any suitable method, such as natural drying, air drying, or heat drying. Alternatively, the drying process can be performed by area heating of the entire area or by heating the transport rollers (using so-called heated rollers). By using heated rollers for drying, heat curling of the laminate can be effectively suppressed, resulting in a polarizing film with excellent appearance. Furthermore, the laminate can be dried while remaining flat, thus suppressing not only curling but also wrinkle formation. From the viewpoint that shrinking the laminate in the width direction during the drying process can improve the optical properties of the resulting polarizing film, the width shrinkage rate of the laminate during the drying process is preferably about 1 to 10%, more preferably about 2 to 8%.

[0139] 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.

[0140] The heating rollers can be placed inside a heating furnace or in a typical manufacturing line (at room temperature), but are preferably placed in a heating furnace equipped with an air supply mechanism. By combining drying using heating rollers and hot air drying, abrupt 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.

[0141] The method for manufacturing the polarizing film of the present invention satisfies the condition of formula (3): the above-mentioned Y (weight%) / the thickness (μm) of the above-mentioned dried polarizing film > 1, preferably formula (3) > 1.5, more preferably formula (3) > 2.0, and even more preferably formula (3) > 3.0.

[0142] Furthermore, from the viewpoint of improving the polarization degree when the polarizing film is manufactured, the method for manufacturing the polarizing film of the present invention preferably satisfies the condition of formula (4): the above-mentioned Y (weight%) - the moisture content (weight%) of the above-mentioned dried polarizing film > 0 (weight%), more preferably formula (4) > 2 (weight%), and even more preferably formula (4) > 5 (weight%).

[0143] <Methods for manufacturing polarizing films>

[0144] The method for manufacturing the polarizing film of the present invention includes a step of laminating a transparent protective film onto at least one side of the polarizing film obtained by the above-described polarizing film manufacturing method via an adhesive layer.

[0145] 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, for example. 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, polyamide resins such as aromatic polyamides, 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), polyaryl ester 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, or ultraviolet-curable resins. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] The aforementioned transparent protective film may contain any appropriate additives such as UV absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, antistatic agents, pigments, and colorants.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] As the adhesive that forms the adhesive layer described above, various adhesives used in polarizing films can be applied, such as isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, and waterborne polyester adhesives. These adhesives are usually used in the form of adhesives formed from aqueous solutions and contain 0.5 to 60% by weight of solid components.

[0156] In addition to the above, examples of adhesives that can be cured by active energy radiation, such as UV-curable adhesives and electron beam-curable adhesives, can be cited. Examples of active energy radiation-curable adhesives include (meth)acrylate adhesives. Examples of curing components in (meth)acrylate adhesives include compounds having (meth)acryloyl groups and compounds having vinyl groups. Furthermore, compounds having epoxy groups or oxobutyl groups can also be used as cationic polymerization curing adhesives. There are no particular limitations on the epoxy group content of the epoxy group, as long as the compound has at least two epoxy groups within its molecule; various commonly known curable epoxy compounds can be used.

[0157] 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.

[0158] 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.

[0159] Examples of surface modification treatments for forming the above-mentioned surface modified layer include: corona treatment, plasma treatment, primer treatment, saponification treatment, etc.

[0160] 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.

[0161] 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.

[0162] 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, various resins and additives comprising silica, acrylic, acrylic-styrene, melamine, etc.

[0163] The polarization degree of the above-mentioned polarizing film is preferably 99.98% or higher, and more preferably 99.99% or higher.

[0164] Example

[0165] 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.

[0166] <Example 1>

[0167] <Manufacturing of Polarizing Film>

[0168] <Manufacturing of Water-Containing Polarizing Film (I-1)>

[0169] Polyvinyl alcohol (PVA) films with an average degree of polymerization of 2400, a saponification degree of 99.9 mol%, and a thickness of 45 μm were prepared. The PVA films were 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 them 2.2 times in the transport direction (swelling process). Next, the films were immersed in a dyeing bath (an aqueous solution of 0.03 wt% iodine and 0.3 wt% potassium iodide) at 30°C for 30 seconds, while simultaneously stretching the original PVA film (completely unstretched in the transport direction) 3.3 times in the transport direction as a reference (dyeing process). Finally, the dyed PVA films were immersed in a crosslinking bath (an aqueous solution of 3.0 wt% boric acid and 3.0 wt% potassium iodide) at 40°C for 28 seconds, while stretching the original PVA film 3.6 times in the transport direction as a reference (crosslinking process). Furthermore, the obtained polyvinyl alcohol film was immersed in a stretching bath (an aqueous solution of boric acid concentration of 4.0 wt% and potassium iodide concentration of 5.0 wt%) at 61°C for 60 seconds, and the original polyvinyl alcohol film was stretched to 6.0 times in the transport direction as a reference (stretching process). Then, it was immersed in a cleaning bath (an aqueous solution of potassium iodide concentration of 2.0 wt%) at 20°C for 5 seconds (cleaning process) to produce a polarizing film containing water.

[0170] <Manufacturing of polarizing film containing components in liquid (I-2)>

[0171] Using a wire rod (manufactured by Daiichi Rikaku Co., Ltd., No. 3), liquid A (a 10% by weight aqueous solution of the compound represented by chemical formula (9) below) was coated onto the above-obtained water-containing polarizing film. After standing at 25°C for 3 seconds, the remaining liquid A on the surface was wiped off to produce a polarizing film impregnated with the components in the liquid. Here, the water content of the water-containing polarizing film was determined to be 33.0% by weight by the following measurement method.

[0172] [Chemical Formula 9]

[0173]

[0174] [Method for determining the moisture content (wt%) in polarizing film]

[0175] Measure about 0.2g of polarizing film, dry it at 120℃ for 2 hours, and measure the weight after drying. Calculate the moisture content (W) in the polarizing film based on the following formula.

[0176] The moisture content W (wt%) of the polarizing film = {(M0 - M1) / M0} × 100

[0177] M0: Weight of the polarizing film measured (g)

[0178] M1: Weight (g) of polarizing film after drying at 120℃ for 2 hours.

[0179] [Method for determining the boron content (wt%) in water-containing polarizing films]

[0180] The above-mentioned water-containing polarizing film (0.2-0.3 g) was dried at 120°C for 2 hours, then dissolved in water. The solution was neutralized and titrated with a burette and 0.1 mol / L NaOH aqueous solution in an aqueous solution with a small amount of mannitol and BTB solution added. The boron content of the polarizing film was calculated based on the following formula.

[0181] Boron content (wt%) of water-containing polarizing film = C × V × Mw / M × 100

[0182] C: Concentration of NaOH aqueous solution (mol / L)

[0183] V: Volume of NaOH aqueous solution added (L)

[0184] Mw: Atomic weight of boron (g / mol)

[0185] M: Weight (g) of the polarizing film after drying at 120°C for 2 hours.

[0186] <Manufacturing of the dried polarizing film (I-3)>

[0187] The polarizing film impregnated with the liquid components obtained above was dried at 60°C for 4 minutes to produce a dried polarizing film (hereinafter referred to as polarizing film). The moisture content of the dried polarizing film, determined by the above method, was 11.3% by weight. The content (M) of the compound represented by chemical formula (9) in the polarizing film was determined by the following method. H The content of the compound represented by chemical formula (9) per unit area is 0.27% by weight (m). H The concentration was 5.4 μg / cm³. 2 In addition, the thickness (T) of the polarizing film is 18 μm.

[0188] [Method for determining the content (wt%) of the compound represented by chemical formula (9) in the polarizing film]

[0189] Approximately 20 mg of polarizing membrane was used for quantification. After dissolving it 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 the compound represented by chemical formula (9) in the filtrate was determined by HPLC (Waters ACQUITY UPLC H-class Bio).

[0190] [The content of the compound represented by chemical formula (9) per unit area of ​​polarizing film (μg / cm³)] 2[Determination method]

[0191] The content (m) of the compound represented by chemical formula (9) per unit area is calculated based on the following formula. H ).

[0192] m H =1.2×T×M H (μg / cm 2 )

[0193] T: Thickness of the polarizing film (μm)

[0194] M H Content (wt%) of the compound represented by chemical formula (9) in the polarizing film.

[0195] <Fabrication of Polarizing Films>

[0196] 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, a 40 μm thick cellulose triacetate membrane with a hard coating (humidity permeability 342 g / (m²)) was laminated onto both sides of the obtained polarizing film using a roller laminator. 2 After drying the polarizing film (24h), manufactured by Konica Minolta under the trade name "KC4UYW"), it was then heated and dried in an oven (at a temperature of 60°C for 4 minutes) to produce a polarizing film with a transparent protective film bonded to both sides of the polarizing film.

[0197] [Methods for measuring the degree of polarization]

[0198] 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 then 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.

[0199] [Heating Durability Evaluation (A)]

[0200] 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 produce a laminate. The resulting laminate was then placed in a hot air oven at 110°C, and the time until coloring was observed with the naked eye was determined according to the following criteria.

[0201] ○: No coloring occurred after more than 500 hours.

[0202] △: Coloration occurred between 300 hours and 500 hours.

[0203] ×: Coloring occurred in less than 300 hours.

[0204] [Heating Durability Evaluation (B)]

[0205] 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 produce a laminate. The resulting laminate was then left to stand in a hot air oven at 105°C, and the time until coloring was observed with the naked eye was determined based on the following criteria.

[0206] ○: No coloring occurred after 750 hours.

[0207] △: Coloration occurred between 500 hours and 750 hours.

[0208] ×: Coloring occurred in less than 500 hours.

[0209] <Example 2>

[0210] <Manufacturing of Polarizing Films>

[0211] After the cleaning process, the polarizing film was left to stand at 25°C for 30 seconds to obtain a polarizing film containing water. Liquid A was then coated onto the film. Otherwise, the polarizing film and polarizing film were manufactured using the same procedures as in Example 1, and the above measurements were performed. The results are shown in Table 1.

[0212] <Example 3>

[0213] <Manufacturing of Polarizing Films>

[0214] After the cleaning process, the polarizing film was left to stand at 25°C for 1 minute to obtain a polarizing film containing water. Then, liquid A was coated on it. Otherwise, the polarizing film and polarizing film were manufactured using the same operation as in Example 1, and the above measurements were performed. The results are shown in Table 1.

[0215] <Comparative Example 1>

[0216] <Manufacturing of Polarizing Films>

[0217] After the cleaning process, the polarizing film was left to stand at 25°C for 3 minutes to obtain a polarizing film containing water. Liquid A was then coated onto the film. Otherwise, the polarizing film and polarizing film were manufactured using the same procedures as in Example 1, and the above measurements were performed. The results are shown in Table 1.

[0218] <Comparative Example 2>

[0219] <Manufacturing of Polarizing Films>

[0220] After the cleaning process, the polarizing film was left to stand at 60°C for 1 minute, and then coated with liquid A. Otherwise, the polarizing film and polarizing film were manufactured using the same procedure as in Example 1, and the above measurements were performed. The results are shown in Table 1.

[0221] <Comparative Example 3>

[0222] <Manufacturing of Polarizing Films>

[0223] In step (I-3) of manufacturing the dried polarizing film, the heating and drying at 60°C for 4 minutes was not performed. Otherwise, the polarizing film and polarizing film were manufactured using the same operation as in Example 1, and the above measurements were performed. The results are shown in Table 1.

[0224] <Example 4>

[0225] <Manufacturing of Polarizing Films>

[0226] Using a 30 μm thick polyvinyl alcohol film, the iodine concentration in the dyeing bath was adjusted to achieve the same monomer transmittance as the final polarizing film. Otherwise, the polarizing film and polarizing film were manufactured using the same procedures as in Example 1, and the above measurements were performed. The results are shown in Table 1. It should be noted that the thickness (T) of the polarizing film was 12 μm.

[0227] <Comparative Example 4>

[0228] <Manufacturing of Polarizing Films>

[0229] After the cleaning process, the polarizing film was dried at 60°C for 1 minute and then coated with liquid A. Otherwise, the polarizing film and polarizing film were manufactured using the same procedure as in Example 4, and the above measurements were performed. The results are shown in Table 1.

[0230] <Example 5>

[0231] <Manufacturing of Polarizing Film>

[0232] <Preparation for the fabrication of laminates (II-0)>

[0233] As the thermoplastic resin substrate, an amorphous polyethylene terephthalate copolymer (100 μm thickness) 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 adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-like resin obtained 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. The aforementioned PVA aqueous solution was coated onto the corona-treated side of the resin substrate and dried at 60°C to form a PVA-like resin layer with a thickness of 13 μm, thus manufacturing (preparing) a laminate.

[0234] <Process for manufacturing a laminate containing a water-containing polarizing film (II-1)>

[0235] 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 process in a gas atmosphere). Next, the laminate was immersed in an insoluble bath (a boric acid aqueous solution containing 4 parts by weight of boric acid relative to 100 parts by weight of water) at 40°C for 30 seconds (insoluble treatment process). Then, it was immersed in a dyeing bath (an iodine aqueous solution containing 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 so that the monomer transmittance (Ts) of the final polarizing film was 42% (dyeing process). Finally, it was immersed in a crosslinking bath (a boric acid aqueous solution containing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) at 40°C for 30 seconds (crosslinking process). Then, the laminate was immersed in a boric acid aqueous solution (4.0 wt% boric acid concentration) at 70°C, and simultaneously subjected to unidirectional stretching along the longitudinal direction (length direction) between rollers with different circumferential speeds to achieve a total stretch ratio of 5.5 times (stretching process in aqueous solution). Next, the laminate was immersed in a cleaning bath at 20°C (an aqueous solution containing 4 wt% potassium iodide relative to 100 wt% water) to produce a laminate with an aqueous polarizing film (cleaning process).

[0236] <Manufacturing of a laminate containing a polarizing film impregnated with components in a liquid (II-2)>

[0237] Using a wire rod (manufactured by Daiichi Rikaku Co., Ltd., No. 3), liquid A (a 10% by weight aqueous solution of the compound represented by chemical formula (9)) was coated onto the polarizing film surface of the above-obtained laminate containing an aqueous polarizing film. After standing at 25°C for 3 seconds, the liquid A remaining on the surface was wiped off, thus producing a laminate containing a polarizing film impregnated with the components in the liquid. Here, the water content of the aqueous polarizing film determined by the above-described method is 35.5% by weight.

[0238] <Preparation of the dried polarizing film (II-3)>

[0239] The film was dried in an oven at 95°C for 10 minutes (drying process). This resulted in a 5 μm thick polarizing film on the resin substrate. The moisture content of the dried polarizing film, determined by the above method, was 9.9% by weight. The content of the compound represented by chemical formula (9) in the polarizing film (M...) H The content of the compound represented by chemical formula (9) per unit area is 0.41% by weight (m). H The concentration was 2.5 μg / cm³. 2 .

[0240] <Fabrication of Polarizing Films>

[0241] As an adhesive, an aqueous solution containing polyvinyl alcohol resin (average degree of polymerization 1200, degree of saponification 98.5 mol%, degree of acetylation 5 mol%) and hydroxymethyl melamine in a weight ratio of 3:1 was used. Using this adhesive, a 40 μm thick cellulose triacetate film with a hard coating (humidity permeability 342 g / (m²)) was laminated onto the opposite side of the obtained polarizing film using a roller laminator. 2 After drying the polarizing film (using Konica Minolta's product "KC4UYW") for 24 hours, the film was then heated and dried in an oven (at 60°C for 4 minutes) to produce a polarizing film with a transparent protective film laminated on one side. Next, the resin substrate was peeled off, and the aforementioned cellulose triacetate film was laminated onto the peeled surface using the aforementioned adhesive and a roller laminator. This was then dried in an oven (at 60°C for 4 minutes) to produce a polarizing film with transparent protective films laminated on both sides of the polarizing film.

[0242] [Heating Durability Evaluation (C)]

[0243] 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 produce a laminate. The resulting laminate was then placed in a hot air oven at 95°C, and the time until coloring was observed with the naked eye was determined according to the following criteria.

[0244] ○: No coloring occurred after 750 hours.

[0245] △: Coloration occurred between 500 hours and 750 hours.

[0246] ×: Coloring occurred in less than 500 hours.

[0247] <Comparative Example 5>

[0248] <Manufacturing of Polarizing Films>

[0249] After the cleaning process, the polarizing film was dried at 95°C for 10 minutes and then coated with liquid A. Otherwise, the polarizing film and polarizing film were manufactured using the same procedure as in Example 5, and the above measurements were performed. The results are shown in Table 2.

[0250] <Example 6>

[0251] <Manufacturing of Polarizing Films>

[0252] In the manufacture of the polarizing film, the potassium iodide concentration in the cleaning bath was set to 4.0% by weight, and liquid B (an aqueous solution containing 10% by weight zinc sulfate hydrate and 0.2% by weight Olfine EXP.4200 (manufactured by Nissin Chemical Industry Co., Ltd.)) was used instead of liquid A. Otherwise, the polarizing film and polarizing film were manufactured using the same procedures as in Example 1, and the above and following measurements were performed. The results are shown in Table 3.

[0253] [Determination of zinc content (wt%) in polarizing film]

[0254] Approximately 25 mg of polarizing film was weighed into a Teflon (registered trademark) container, acid was added, and the container was sealed tightly. Microwave irradiation was then performed for pressurized acid decomposition at a maximum temperature of 200°C. After complete decomposition, ultrapure water was added to bring the volume to 50 mL, and the zinc concentration was determined using ICP-MS (Agilent Technologies Agilent 8800). The decomposition apparatus used was a CEM MARS5.

[0255] [Heating Durability Evaluation (D)]

[0256] 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 autoclave treatment at 50°C and 0.5 MPa for 15 minutes to fabricate a laminate. The resulting laminate was placed in a hot air oven at 105°C for 500 hours. The tested samples were arranged in an orthogonal Nicol configuration, and the orthogonal transmittance (%) at a wavelength of 700 nm was measured using the aforementioned spectrophotometer (V7100). The results were judged based on the following criteria.

[0257] ○: No red color after heating (the difference in orthogonal transmittance at 700nm wavelength before and after the heating test at 105℃ for 500 hours is less than 1%).

[0258] ×: There is red coloration upon heating (the difference in orthogonal transmittance at 700nm wavelength before and after a heating test at 105℃ for 500 hours is more than 1%).

[0259] <Comparative Example 6>

[0260] <Manufacturing of Polarizing Films>

[0261] After the cleaning process, the polarizing film was dried at 60°C for 1 minute and then coated with liquid B. Otherwise, the polarizing film and polarizing film were manufactured using the same procedure as in Example 6, and the above measurements were performed. The results are shown in Table 3.

[0262]

[0263]

[0264]

[0265] The above-mentioned heat durability test is affected by the film thickness of the polarizing film. Therefore, polarizing films with the same film thickness can be compared with each other. It can be seen that the polarizing film of the embodiment contains more components in the liquid than the polarizing film of the comparative example, and therefore has better heat durability.

Claims

1. A method for manufacturing a polarizing film, the method comprising: Process (I-1): While transporting the polyvinyl alcohol film along its length, at least a dyeing process, a crosslinking process, and a stretching process are performed on the polyvinyl alcohol film to produce a water-containing polarizing film. Process (I-2): With the water content of the polarizing film at or above X% by weight, a process of coating the obtained water-containing polarizing film with liquid is performed to manufacture a polarizing film impregnated with the components in the liquid. Step (I-3): The obtained polarizing film containing the components in the liquid is subjected to a drying process to produce a dried polarizing film; as well as An adhesive is applied to the liquid coating surface of the dried polarizing film, and a transparent protective film is then bonded to it via the adhesive layer. The liquid contains water-soluble compounds, including free radical scavengers or zinc salts. This method satisfies the condition of equation (1) below. Formula (1): X (weight %) / thickness (μm) of the dried polarizing film > 1.5 In formula (1), X is 10 or more and 70 or less. Alternatively, the method may include: Process (II-0): A polyvinyl alcohol resin layer containing polyvinyl alcohol resin is formed on one side of a strip-shaped thermoplastic resin substrate to prepare a laminate; Process (II-1): While transporting the obtained laminate along the length direction, at least an assisted stretching process in a gas atmosphere, a dyeing process, and a stretching process in an aqueous solution are performed on the laminate to produce a laminate having a polarizing film containing water. Process (II-2): With the moisture content of the polarizing film being Y% by weight or more, a process of coating the obtained laminate containing the water-containing polarizing film is performed to manufacture a laminate containing the components impregnated in the liquid. Step (II-3): A drying process is performed on the obtained laminate containing the components impregnated in the liquid to manufacture a dried polarizing film; and An adhesive is applied to the liquid coating surface of the dried polarizing film, and a transparent protective film is then bonded to it via the adhesive layer. The liquid contains water-soluble compounds, including free radical scavengers or zinc salts. This method satisfies the condition of the following equation (3). Formula (3): The ratio of Y (weight %) to the thickness (μm) of the dried polarizing film is greater than 1.

5. In equation (3), Y is 10 or more and 70 or less. The moisture content of the dried polarizing film obtained above is less than 20% by weight.

2. The method for manufacturing a polarizing film according to claim 1, wherein the method satisfies the condition of the following formula (2), Formula (2): X (weight %) - the moisture content (weight %) of the dried polarizing film > 0 (weight %). In equation (2), X is greater than 10 and less than 70. Or the method satisfies the condition of the following equation (4), Formula (4): Y (weight%) - the moisture content (weight%) of the dried polarizing film > 0 (weight%). In equation (4), Y is 10 or more and 70 or less.

3. The method for manufacturing a polarizing film according to claim 1 or 2, wherein, The liquid is a solution, and the components in the liquid are solutes.

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