Method for manufacturing polarizers

Abstract

To enable production of polarizers with less wrinkles.SOLUTION: A method of manufacturing a polarizer consisting of a polyvinyl alcohol resin film is provided, the method comprising a treatment step of bringing the polyvinyl alcohol resin film into contact with a treatment liquid and a drying step performed in the described order, where the drying step comprises bringing at least one width expansion rollers into contact with the polyvinyl alcohol resin film.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing a polarizer made of a polyvinyl alcohol-based resin film.

Background Art

[0002] In liquid crystal display devices, polarizers obtained by uniaxially stretching polyvinyl alcohol-based resin films are widely used. Japanese Patent Application Laid-Open No. 2012-173544 (Patent Document 1) discloses a method for producing a polarizer, in which a film is stretched using a width expansion roll as a guide roll in the treatment bath in at least any one of the steps of performing a swelling treatment, a dyeing treatment, and a crosslinking treatment on a polyvinyl alcohol-based film.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Polarizers made of polyvinyl alcohol-based resin films may generate longitudinal wrinkles along the film conveyance direction. An object of the present invention is to obtain a polarizer with reduced wrinkles.

Means for Solving the Problems

[0005] The present invention relates to the following items. [1] A method for producing a polarizer made of a polyvinyl alcohol-based resin film, including a treatment step of bringing the polyvinyl alcohol-based resin film into contact with a treatment liquid and a drying step in this order, wherein the drying step includes bringing at least one width expansion roll into contact with the polyvinyl alcohol-based resin film. [2] The manufacturing method according to [1], wherein the drying step includes bringing a plurality of widening rolls into contact with the polyvinyl alcohol-based resin film in a drying oven. [3] The manufacturing method according to [1] or [2], wherein the drying step includes bringing a widening roll into contact with the polyvinyl alcohol resin film upstream of the center of the entire length of the transport path for the polyvinyl alcohol resin film in the drying oven. [4] The manufacturing method according to any one of [1] to [3], wherein the processing step comprises at least one selected from the group consisting of a swelling step, a dyeing step, and a crosslinking step. [5] The widening roll is a curved widening roll, the manufacturing method according to any one of [1] to [4]. [6] A polarizer manufacturing apparatus made of a polyvinyl alcohol-based resin film, The system includes a processing unit for bringing the polyvinyl alcohol-based resin film into contact with a processing liquid and a drying oven, An apparatus comprising at least one widening roll in the transport path for the polyvinyl alcohol-based resin film within the drying oven. [Effects of the Invention]

[0006] According to the present invention, a polarizer with reduced wrinkles can be obtained. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram illustrating the vertical wrinkles that occur in polarizers. [Figure 2] This is a schematic diagram showing a drying oven used in a method for manufacturing a polarizer according to one embodiment of the present invention. [Figure 3] (a) A schematic top view of a widening roll used in a method for manufacturing a polarizer according to one embodiment of the present invention, (b) A schematic cross-sectional view of a widening roll, and (c) A schematic diagram showing the force acting on a film by the widening roll. [Figure 4] This is a schematic diagram showing a method for manufacturing a polarizer according to one embodiment of the present invention. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments. In all the following drawings, the scale has been adjusted as appropriate to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

[0009] [polarizer] A polarizer has the property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). The polarizer may be, for example, a uniaxially stretched polyvinyl alcohol-based resin film on which a dichroic dye such as iodine is adsorbed and oriented.

[0010] The method for manufacturing a polarizer according to the present invention is: The process includes, in this order, a processing step of bringing a polyvinyl alcohol-based resin film into contact with a processing solution, and a drying step. The drying process includes bringing at least one widening roll into contact with a polyvinyl alcohol-based resin film.

[0011] As shown in Figure 1, polarizers made of polyvinyl alcohol-based resin film may develop vertical wrinkles along the film's transport direction. These vertical wrinkles can be reduced by bringing the film into contact with a widening roll during the drying process.

[0012] As one embodiment of the polarizer manufacturing method according to the present invention, in the drying process, a plurality of widening rolls and a polyvinyl alcohol-based resin film may be brought into contact in a drying oven. In the first half of the drying oven, the amount of moisture contained in the polyvinyl alcohol-based resin film decreases rapidly, making it prone to wrinkles. From the viewpoint of further suppressing the occurrence of wrinkles, in the drying process, it is preferable to bring the widening rolls and the polyvinyl alcohol-based resin film into contact at least upstream of the center of the total length of the transport path for the polyvinyl alcohol-based resin film in the drying oven. The area upstream of the center of the total length of the transport path for the film in the drying oven may be the upstream one-third or upstream one-quarter of the total length of the transport path for the film. Figure 2 shows an example of a drying oven. A plurality of widening rolls 12 are installed in the drying oven 123 so as to be in contact with the film. Guide rolls 11 and widening rolls 12 may both be provided in the transport path in the drying oven 123.

[0013] The widening roll allows an external force to be applied to the film in the width direction. In this invention, the external force applied to the film in the width direction is an inward-outward stretching force in the width direction of the film. The direction of widening can be adjusted by the arrangement angle of the widening roll 12, etc. The amount of widening can be adjusted by the arrangement angle of the widening roll 12, the contact angle between the widening roll 12 and the polyvinyl alcohol-based resin film 100, the degree of curvature (arc height) of the widening roll 12 used, etc.

[0014] Examples of widening rolls include curved widening rolls (expander rolls), pinch rolls, crown rolls, and reverse crown rolls. These may be used in combination.

[0015] An example of the arrangement of the expanding roll 12 when an arcuate curved expanding roll is used as the expanding roll is shown in Fig. 3. As shown in Fig. 3(a), the arcuate curved expanding roll has a plurality of spools with built-in ball bearings on a curved shaft 120. An expanding roll with a rubber cylinder coated on the spool is called a rubber expander roll, and an expanding roll without a rubber cylinder coated is called a metal expander roll. In the present invention, the expanding roll 12 may be a rubber expander roll or a metal expander roll. Usually, the perpendicular cross-section of the expanding roll 12 with respect to the shaft 120 is circular, and its area is equal in any perpendicular cross-section. The perpendicular cross-section of the expanding roll 12 with respect to the shaft 120 is, for example, 50 mm to 400 mm in diameter and may be about 100 mm.

[0016] The orthogonal cross-section (section a-a in Fig. 3(a)) of the expanding roll 12 at the central portion with respect to the shaft 120 is shown as section 122 in Fig. 3(b), and its center is designated as C'. The orthogonal cross-section of the expanding roll 12 at the portion where it contacts the end of the polyvinyl alcohol-based resin film 100 with respect to the shaft 120 is shown as section 121 in Fig. 3(b), and its center is designated as C. When the center C' of the cross-section 122 at the central portion is arranged on the downstream side in the conveying direction from the center C of the cross-section 121, that is, when the central portion in the width direction of the polyvinyl alcohol-based resin film 100 contacts the expanding roll 12 later than the end portions, an outward stretching force in the width direction can be applied to the polyvinyl alcohol-based resin film 100. Fig. 3(c) shows the action of the force applied to the film by the expanding roll. When the expanding roll 12 is arranged such that the end portions in the width direction of the polyvinyl alcohol-based resin film 100 contact the expanding roll 12 earlier than the central portion (shown in the region A2) and then the central portion contacts the expanding roll 12, an outward stretching force (shown by the arrow b2) can be applied to the film, and the generation of wrinkles can be suppressed.

[0017] In FIG. 3(b), when the incident direction of the end of the polyvinyl alcohol-based resin film 100 incident on the width expansion roll 12 is indicated by an arrow x, and the direction from the center C to the center C' in the width expansion roll 12 is indicated by an arrow y, from the viewpoint of appropriately expanding the polyvinyl alcohol-based resin film 100, the angle θ of the arrow y with respect to the arrow x is preferably in the range of -120° to 120°, and may be -90° to 90°. The arc height of the width expansion roll 12 is, for example, 1 mm to 20 mm, and may be about 10 mm. As used in this specification, the "arc height of the width expansion roll" means the distance between the center C and the center C', and the "arrangement angle of the width expansion roll" means the angle θ of the arrow y with respect to the arrow x.

[0018] The magnitude of the external force applied to the film can also be adjusted by the contact angle α of the polyvinyl alcohol-based resin film 100 on the width expansion roll 12. The contact angle α can be adjusted by moving the positions of the guide roll 11 and / or the width expansion roll 12 up and down. Since it is easy to adjust the magnitude of the stretching force applied by the width expansion roll 12, the contact angle α is preferably 0° to 30°, and may be about 10°.

[0019] The width of the polyvinyl alcohol-based resin film 100 in contact with the width expansion roll 12 is not particularly limited, but it is preferable that the film is within the existing width of the width expansion roll 12. When the film is within the existing width of the width expansion roll 12, it is easier to reduce wrinkles in the entire film. In addition, since the film does not contact the ends of the width expansion roll 12, the occurrence of appearance abnormalities such as scratches and wrinkles can be suppressed. The length in the longitudinal direction of the width expansion roll 12 is, for example, 500 mm to 3000 mm, and may be about 2000 mm.

[0020] Pinch rolls grip the widthwise edges of the polyvinyl alcohol resin film. It is preferable that pinch rolls be installed at both ends of the transport path for the polyvinyl alcohol resin film. Pinch rolls may be metal rolls, plastic rolls, or rubber rolls. The roll diameter of the pinch rolls is, for example, about 10 mm to 50 mm. The length over which a single pinch roll grips the side edge of the film may be about 2% to 10% of the total width of the film. When viewed from above, the pinch rolls may be inclined at an angle β in the film transport direction. That is, in the film plane, the angle β between the axis of the pinch roll and the width direction perpendicular to the transport direction may be 0 to ±45°, 0 to ±30°, or 0 to ±15°. The pinch rolls may also be inclined perpendicular to the film transport direction. The inclination angle γ of the pinch rolls may be 0 to ±45°, 0 to ±30°, or 0 to ±15° on the central side of the film relative to the outer side of the film.

[0021] In the drying process, when multiple widening rolls and a polyvinyl alcohol-based resin film are brought into contact in a drying oven, the multiple widening rolls may be identical to each other or may be different from each other.

[0022] The processing step of bringing a polyvinyl alcohol-based resin film into contact with a processing solution may include at least one selected from the group consisting of a swelling step, a dyeing step, and a crosslinking step.

[0023] The various processing steps that may be included in the manufacturing method according to the present invention can be carried out continuously by continuously transporting the polyvinyl alcohol-based resin film, which is the raw film, along the film transport path of the polarizer manufacturing apparatus. The film transport path is equipped with facilities (such as processing tanks and furnaces) for carrying out the above-mentioned various processing steps, in the order in which they are carried out.

[0024] In addition to the equipment described above, the film transport path can be constructed by placing guide rolls, nip rolls, etc., at appropriate positions. Guide rolls can be placed, for example, before, after, and inside each processing tank, thereby enabling the introduction, immersion, and withdrawal of film from the processing tank. More specifically, by providing two or more guide rolls inside each processing tank and transporting the film along these guide rolls, the film can be immersed in each processing tank.

[0025] An example of a polarizer manufacturing method will be explained with reference to Figure 4. The polyvinyl alcohol-based resin film 110, which is the raw film unwound from the feed roll 111, is immersed in a swelling tank 113 with water as the swelling bath and subjected to a swelling treatment (swelling step). The swollen film is immersed in a dyeing tank 115 with an aqueous solution containing a dichroic dye as the dye bath and the dye is adsorbed (dyeing step). Subsequently, it is immersed in a crosslinking tank 117 with an aqueous solution containing a crosslinking agent as the treatment bath and crosslinked to fix the dye (crosslinking step). Next, the film is washed in a washing tank 119 (washing step) and dried in a drying oven 123 (drying step) to obtain a polarizer 130. The polarizer 130 is wound onto a winding roll 127. The polyvinyl alcohol-based resin film is uniaxially stretched at one or more stages from before the swelling step to the crosslinking step (stretching step).

[0026] Examples of polyvinyl alcohol-based resins that constitute polyvinyl alcohol-based resin films include saponified polyvinyl acetate resins. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable thereto. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acid compounds, olefin compounds, vinyl ether compounds, unsaturated sulfonic acid compounds, and (meth)acrylamide compounds having an ammonium group. The degree of saponification of the polyvinyl alcohol-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, "(meth)acrylic" means at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl".

[0027] The polyvinyl alcohol-based resin may be modified; for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc., modified with aldehydes can also be used.

[0028] The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and even more preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol-based resin can be determined in accordance with JIS K 6726 (1994). When the average degree of polymerization is within the above range, the resin tends to have excellent polarization performance and film processability.

[0029] The thickness of the polyvinyl alcohol-based resin film used as the base film may be, for example, 10 μm to 150 μm, preferably 15 μm to 100 μm, and more preferably 20 μm to 80 μm. The length in the width direction of the polyvinyl alcohol-based resin film used as the base film may be, for example, 600 mm to 5000 mm.

[0030] The thickness of the polarizer is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less. The thickness of the polarizer is usually 2 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The thickness of the polarizer can be controlled, for example, by selecting a polyvinyl alcohol-based resin film or adjusting the stretching ratio.

[0031] The raw material, a polyvinyl alcohol-based resin film, can be prepared, for example, as a long roll (winding) of unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained as a long product. The following describes each process in detail.

[0032] (1) Swelling process The swelling treatment in this process is performed as needed for purposes such as removing foreign matter, removing plasticizers, imparting dyeability, and plasticizing the polyvinyl alcohol-based resin film, which is the raw film. Specifically, the swelling treatment can be a process in which the polyvinyl alcohol-based resin film 110 is immersed in a swelling tank containing a treatment solution containing water. The film may be immersed in one swelling tank, or it may be immersed sequentially in two or more swelling tanks. Uniaxial stretching may be performed on the film before the swelling treatment, during the swelling treatment, or before and during the swelling treatment.

[0033] The treatment liquid contained in the swelling tank may be water (e.g., pure water), or it may be an aqueous solution to which a water-soluble organic solvent such as alcohol has been added. As described above, the treatment liquid contained in the swelling tank may contain zinc salts.

[0034] The temperature of the treatment solution contained in the swelling tank when immersing the film is usually between 10°C and 70°C, preferably between 15°C and 50°C. The immersion time of the film is usually between 10 seconds and 600 seconds, preferably between 20 seconds and 300 seconds.

[0035] (2) Dyeing process The dyeing process in this step is performed for the purpose of adsorbing and oriented a dichroic dye onto a polyvinyl alcohol-based resin film. Specifically, the dyeing process can be performed by immersing the polyvinyl alcohol-based resin film in a dyeing tank containing a treatment solution that contains a dichroic dye. The film may be immersed in one dyeing tank, or it may be immersed sequentially in two or more dyeing tanks. In order to enhance the dyeability of the dichroic dye, the film used in the dyeing process may be subjected to at least some degree of uniaxial stretching. Uniaxial stretching may be performed during the dyeing process, either as an alternative to or in addition to uniaxial stretching before the dyeing process.

[0036] Dichroic dyes can be iodine or dichroic organic dyes. Specific examples of dichroic organic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct First Orange S, and First Black. Dichroic dyes may be used individually or in combination of two or more.

[0037] When iodine is used as a dichroic dye, the treatment solution contained in the staining tank may be an aqueous solution containing iodine and potassium iodide. Other iodides, such as zinc iodide, may be used instead of potassium iodide, or potassium iodide may be used in combination with other iodides. Compounds other than iodides, such as boric acid, zinc chloride, and cobalt chloride, may also be present in the treatment solution. The addition of boric acid distinguishes this from the cross-linking treatment described later, as it contains iodine. The iodine content in the above aqueous solution is typically 0.01 parts by mass to 1 part by mass per 100 parts by mass of water. The iodide content, such as potassium iodide, is typically 0.5 parts by mass to 20 parts by mass per 100 parts by mass of water.

[0038] The temperature of the processing solution contained in the dyeing tank when immersing the film is usually 10°C to 45°C, preferably 10°C to 40°C, and more preferably 20°C to 35°C. The immersion time of the film may be, for example, 20 seconds to 600 seconds, and preferably 20 seconds to 300 seconds.

[0039] When using a dichroic organic dye as the dichroic pigment, an aqueous solution containing the dichroic organic dye can be used as the processing solution contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1 × 10⁶ per 100 parts by mass of water. -4 The amount is between parts by mass and 10 parts by mass, preferably 1 × 10 -3 The amount is between parts by mass and 1 part by mass. Dyeing aids may be present in the dyeing tank, for example, inorganic salts such as sodium sulfate or surfactants may be included. Only one type of dichroic organic dye may be used alone, or two or more types may be used in combination. The temperature of the treatment solution contained in the dyeing tank when immersing the film is, for example, 20°C to 80°C, preferably 25°C to 50°C. The immersion time of the film is usually 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds.

[0040] (3) Crosslinking process Crosslinking treatment, which involves treating a polyvinyl alcohol-based resin film after the dyeing process with a crosslinking agent, is performed for purposes such as improving water resistance and adjusting hue through crosslinking. Specifically, the crosslinking treatment can be performed by immersing the film after the dyeing process in a crosslinking tank containing a treatment solution that includes a crosslinking agent. The film may be immersed in one crosslinking tank or sequentially in two or more crosslinking tanks. Uniaxial stretching may also be performed during the crosslinking treatment.

[0041] Examples of crosslinking agents include boric acid, glyoxal, and glutaraldehyde, with boric acid being preferred. Two or more crosslinking agents can also be used in combination. The boric acid content in the processing solution contained in the crosslinking tank is usually 0.1 parts by mass to 15 parts by mass per 100 parts by mass of water, preferably 1 part by mass to 10 parts by mass. When the dichroic dye is iodine, it is preferable that the processing solution contained in the crosslinking tank contains iodide in addition to boric acid. The iodide content in the processing solution contained in the crosslinking tank is usually 0.1 parts by mass to 15 parts by mass per 100 parts by mass of water, preferably 5 parts by mass to 12 parts by mass. Examples of iodides include potassium iodide and zinc iodide. In addition, compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may also be present in the crosslinking tank.

[0042] The temperature of the processing liquid contained in the crosslinking tank when immersing the film may be, for example, 30°C to 85°C, and preferably 30°C to 60°C. The immersion time of the film may be, for example, 2 seconds to 600 seconds, and preferably 2 seconds to 300 seconds.

[0043] In the crosslinking process, there may be two or more crosslinking tanks. In this case, the composition and temperature of the processing liquid contained in each crosslinking tank may be the same or different. The processing liquid contained in the crosslinking tank may have concentrations of crosslinking agents and iodide, etc., and temperatures appropriate for the purpose of immersing the polyvinyl alcohol-based resin film. Crosslinking treatment for water resistance and crosslinking treatment for hue adjustment (complementary color) may each be carried out in multiple steps (for example, multiple tanks). Generally, when both crosslinking treatment for water resistance and crosslinking treatment for hue adjustment (complementary color) are performed, a tank for crosslinking treatment for hue adjustment (complementary color) is placed at the end. The temperature of the treatment solution contained in the complementary color tank is, for example, 10°C to 55°C, preferably 20°C to 50°C. The content of the crosslinking agent in the treatment solution contained in the complementary color tank is, for example, 1 to 5 parts by mass per 100 parts by mass of water. The content of the iodide in the treatment solution contained in the complementary color tank is, for example, 3 to 30 parts by mass per 100 parts by mass of water.

[0044] As described above, in the manufacture of polarizers, the polyvinyl alcohol-based resin film is subjected to uniaxial stretching in one or more stages from before the swelling process to the crosslinking process (stretching process). From the viewpoint of improving the dyeability of dichroic dyes, it is preferable that the film used in the dyeing process is a film that has undergone at least some degree of uniaxial stretching, or, instead of, or in addition to, uniaxial stretching before dyeing, uniaxial stretching is performed during the dyeing process.

[0045] The uniaxial stretching process may be either dry stretching performed in the air, wet stretching performed in a tank, or both. The uniaxial stretching process can be roll-to-roll stretching, hot roll stretching, tenter stretching, etc., where longitudinal uniaxial stretching is performed with a peripheral speed difference between two nip rolls, but roll-to-roll stretching is preferred. The stretching ratio based on the original film (or the cumulative stretching ratio if the stretching process is performed in two or more stages) is approximately 3 to 8 times. To impart good polarization characteristics, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

[0046] (4) Washing process The cleaning process in this step is performed as needed to remove excess crosslinking agents, dichroic dyes, and other chemicals adhering to the polyvinyl alcohol-based resin film, and involves cleaning the polyvinyl alcohol-based resin film after the crosslinking process using a cleaning solution containing water. Specifically, this can involve immersing the polyvinyl alcohol-based resin film after the crosslinking process in a treatment solution (cleaning solution) contained in a cleaning tank. The film may be immersed in one cleaning tank, or sequentially immersed in two or more cleaning tanks. Alternatively, the cleaning process may involve spraying the cleaning solution onto the polyvinyl alcohol-based resin film after the crosslinking process, and the immersion and spraying processes may be combined.

[0047] The cleaning solution may be water (e.g., pure water), or it may be an aqueous solution to which a water-soluble organic solvent such as alcohols has been added.

[0048] When the polyvinyl alcohol-based resin film after the crosslinking process is immersed in a washing tank, the temperature of the washing solution in the washing tank is, for example, 2°C to 40°C, preferably 2°C to 22°C, and more preferably 2°C to 10°C. The immersion time in the washing tank may be, for example, 10 seconds to 100 seconds, and preferably 20 seconds to 80 seconds.

[0049] When a cleaning solution is sprayed as a shower onto a polyvinyl alcohol-based resin film after the crosslinking process, the temperature of the cleaning solution may be the same or different in the center and both ends of the polyvinyl alcohol-based resin film in the width direction, but preferably they are different, and more preferably the temperature in the center is lower than the temperature at both ends. The temperature of the cleaning solution is preferably 2°C to 10°C in the center and 10°C to 22°C at both ends, and more preferably 3°C to 7°C in the center and 15°C to 22°C at both ends.

[0050] (5) Drying process The drying process dries the polyvinyl alcohol-based resin film after the processing process. By continuing to transport the polyvinyl alcohol-based resin film after the washing process and introducing it into the drying process, the drying treatment can be performed, thereby obtaining a polarizer.

[0051] The drying process is carried out using a drying means (heating means) for the film. A preferred example of a drying means is a drying oven. Preferably, the drying oven is one in which the internal temperature can be controlled. The drying oven is a hot air oven that can raise the internal temperature by, for example, supplying hot air. Alternatively, the drying process using a drying means may involve adhering the polyvinyl alcohol-based resin film after the washing process to one or more heating bodies having a convex curved surface, or heating the film using a heater.

[0052] Examples of heating elements include rolls (for example, guide rolls that also function as heating rolls) that have a heat source (for example, a heat transfer medium such as hot water or an infrared heater) inside and can raise the surface temperature. Examples of heaters include infrared heaters, halogen heaters, and panel heaters.

[0053] In the drying process, the drying temperature (e.g., the temperature inside the drying oven, the surface temperature of the heat roll, etc.) is usually between 30°C and 100°C, and preferably between 50°C and 90°C. The drying time is not particularly limited, but is for example between 30 seconds and 600 seconds, and preferably between 30 seconds and 60 seconds.

[0054] The drying process may be a single stage or divided into multiple stages, preferably two to four stages. When the drying process is divided into multiple stages, it is preferable to set the drying temperature so that the temperature in the later stages is higher than that in the first stage. When the drying process is divided into multiple stages, the drying time in each stage may be, for example, 10 seconds to 300 seconds, preferably 10 seconds to 20 seconds.

[0055] In the polarizer manufacturing process, at least one of the treatment solutions used to treat the polyvinyl alcohol-based resin film may contain a zinc salt. Examples of treatment tanks that contain the treatment solution include a swelling tank, a dyeing tank, a crosslinking tank, a washing tank, and a color-correcting tank. The treatment tank containing the zinc salt is preferably a treatment tank located after the dyeing tank and before the washing tank, more preferably at least one selected from the crosslinking tank and the color-correcting tank, and even more preferably at least one selected from the last crosslinking tank and the color-correcting tank if there are two or more crosslinking tanks. By immersing the polyvinyl alcohol-based resin film in a treatment solution containing a zinc salt, the resulting polarizer can be made to contain the element of zinc. The amount of element of zinc in the polarizer can be adjusted to the above-mentioned range by controlling the concentration of the zinc salt in the treatment solution, the immersion time of the polyvinyl alcohol-based resin film in the zinc salt-containing treatment solution, the temperature of the treatment solution, etc.

[0056] Examples of zinc salts included in the treatment solution include zinc halides such as zinc chloride and zinc iodide, as well as zinc sulfate, zinc acetate, and zinc nitrate. Among these, zinc nitrate is preferred because it causes a small change in tension. The zinc salt can be added to the treatment solution as a zinc salt solution.

[0057] The concentration of zinc salt in the processing solution may differ for each processing tank, but it may be, for example, 1 to 10 parts by mass, and preferably 2 to 7 parts by mass, per 100 parts by mass of processing solution contained in the processing tank.

[0058] Through the above process, a polarizer made of a polyvinyl alcohol-based resin film can be obtained. In this polarizer, a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film.

[0059] [Manufacturing equipment] The manufacturing apparatus according to the present invention is A polarizer manufacturing apparatus made of a polyvinyl alcohol-based resin film, The system includes a processing unit for bringing the polyvinyl alcohol-based resin film into contact with a processing liquid and a drying oven, The transport path for the polyvinyl alcohol-based resin film inside the drying oven is provided with at least one widening roll. The processing unit may be a unit that performs the swelling treatment, dyeing treatment, crosslinking treatment, or washing treatment described above. The polarizer described above can be obtained using the manufacturing apparatus according to the present invention.

[0060] A manufacturing apparatus according to one embodiment comprises at least one of a swelling tank, a dyeing tank, a crosslinking tank, and a washing tank, and a drying oven. The drying oven may be equipped with a plurality of widening rolls. Preferably, the widening rolls in the drying oven are located on the inlet side of the center of the entire length of the film transport path.

[0061] [Polarizing plate] The obtained polarizer can be directly transported to the polarizer manufacturing process. In the polarizer manufacturing process, for example, a thermoplastic resin film is laminated to one or both sides of the polarizer. The method for manufacturing a polarizer may include the polarizer manufacturing process described above.

[0062] A polarizing plate according to one embodiment is a laminate having a thermoplastic resin film on one or both sides of a polarizer via an adhesive. The polarizing plate may further comprise an adhesive layer, an optical functional layer, and a protective film. The polarizing plate may be, for example, a linear polarizing plate, a circular polarizing plate, an elliptical polarizing plate, etc. A circular polarizing plate comprises a linear polarizing plate and a phase difference layer.

[0063] The thickness of the polarizing plate is usually 5 μm or more, but may be 20 μm or more, 25 μm or more, or 30 μm or more. Preferably, the thickness of the polarizing plate is 80 μm or less, and more preferably 60 μm or less.

[0064] [Thermoplastic resin film] The thermoplastic resin film can be, for example, a translucent resin film made of polyolefin resins such as chain-like polyolefin resins (polypropylene resins, etc.) or cyclic polyolefin resins (norbornene resins, etc.); cellulose ester resins such as triacetylcellulose and diacetylcellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resins; (meth)acrylic resins such as polymethyl methacrylate resins; or mixtures or copolymers thereof. The thermoplastic resin film may have a single-layer structure consisting of one resin layer made of one or more types of thermoplastic resins, or a multilayer structure in which multiple resin layers made of one or more types of thermoplastic resins are laminated. The first thermoplastic resin film and the second thermoplastic resin film may be the same or different types of thermoplastic resin films.

[0065] Thermoplastic resin films may contain additives as needed. Examples of additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, UV absorbers, antistatic agents, lightfastness agents, impact resistance modifiers, and surfactants. Examples of UV absorbers include salicylate ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex salt compounds.

[0066] Either or both of the thermoplastic resin films can be protective films that also possess optical functions, such as phase difference films or brightness-enhancing films. For example, a transparent resin film made of the above materials can be stretched (uniaxially or biaxially, etc.) or a liquid crystal layer or the like can be formed on the film to create a phase difference film to which any desired phase difference value is assigned.

[0067] Surface treatment layers (coating layers) such as hard coat layers, anti-glare layers, anti-reflective layers, anti-static layers, and anti-fouling layers can also be formed on the surface of the thermoplastic resin film. The surface treatment layer may be formed on one side of the thermoplastic resin film or on both sides. The surface treatment layer may also be formed on the surface of the thermoplastic resin film opposite to the polarizer side.

[0068] While a thin polarizing plate is preferable for the thermoplastic resin film, if it is too thin, its strength tends to decrease and its processability deteriorates. Therefore, it is preferably 5 μm to 150 μm, more preferably 5 μm to 100 μm, and even more preferably 10 μm to 60 μm.

[0069] [glue] An adhesive can be used to bond the polarizer and the thermoplastic resin film. Examples of adhesives include water-based adhesives containing a water-based composition and active energy ray-curable adhesives containing an active energy ray-curable composition.

[0070] Examples of resin components contained in aqueous compositions include polyvinyl alcohol-based resins and urethane resins. Aqueous compositions containing polyvinyl alcohol-based resins may further contain curing components and crosslinking agents such as polyhydric aldehydes, melamine compounds, zirconia compounds, zinc compounds, glyoxal, glyoxal derivatives, and water-soluble epoxy resins to improve adhesion and bonding properties. Examples of aqueous compositions containing urethane resins include those containing polyester-based ionomer-type urethane resins and compounds having glycidyloxy groups.

[0071] Active energy ray curable compositions are compositions that harden upon irradiation with active energy rays such as ultraviolet light, visible light, electron beams, and X-rays. UV-curable adhesives can be mixtures of radically polymerizable (meth)acrylic compounds and photo-radical polymerization initiators, or mixtures of cationic polymerizable epoxy compounds and photo-cationic polymerization initiators. Furthermore, cationic polymerizable epoxy compounds and radically polymerizable (meth)acrylic compounds can be used in combination, with both photo-cationic polymerization initiators and photo-radical polymerization initiators acting as initiators.

[0072] The thickness of the adhesive layer may be, for example, 1 μm or more and 25 μm or less. Preferably, the thickness of the adhesive layer is 2 μm or more, preferably 15 μm or less, and more preferably 5 μm or less. A smaller adhesive layer thickness tends to reduce impact resistance, while a larger adhesive layer thickness tends to increase bending rebound force.

[0073] To improve the adhesion between the polarizer and the resin film, prior to bonding the polarizer and the resin film, surface treatments such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer application treatment, and saponification treatment may be applied to the bonding surface of the polarizer and / or resin film.

[0074] [Adhesive layer] A polarizing plate may have an adhesive layer for bonding the layers constituting the polarizing plate together, or for bonding the polarizing plate to a light-transmitting member or image display element. The adhesive layer can be composed of an adhesive composition mainly composed of a resin such as (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether. An adhesive composition using a (meth)acrylic resin as the base polymer is preferred because it has excellent transparency, weather resistance, heat resistance, etc. The adhesive composition may be of the active energy ray curing type or thermosetting type.

[0075] As the (meth)acrylic resin (base polymer) used in the adhesive composition, polymers or copolymers using one or more (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate as monomers are preferably used. It is preferable to copolymerize polar monomers into the base polymer. Examples of polar monomers include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds.

[0076] The adhesive composition may contain only the above-mentioned base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form carboxylate metal salts with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; polyepoxy compounds or polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

[0077] An active energy ray curable adhesive composition is an adhesive composition that has the property of curing when irradiated with active energy rays such as ultraviolet rays or electron beams. It can adhere to a substrate such as a film even before irradiation with active energy rays, and the adhesion strength can be adjusted by curing with irradiation with active energy rays. The active energy ray curable adhesive composition is preferably ultraviolet curable. In addition to a base polymer and a crosslinking agent, the active energy ray curable adhesive composition further contains an active energy ray polymerizable compound. Furthermore, it may also contain a photopolymerization initiator and a photosensitizer as needed.

[0078] The adhesive composition may contain additives such as fine particles for light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0079] The adhesive layer can be formed by preparing an adhesive solution by dissolving or dispersing an adhesive composition in an organic solvent such as toluene or ethyl acetate, and then directly coating this solution onto the target surface of the laminated film; or by forming the adhesive layer in a sheet on a release-treated separator film and then transferring it to the target surface of the polarizing plate. When an active energy ray-curable adhesive composition is used, the formed adhesive layer can be irradiated with active energy rays to produce a cured product with a desired degree of curing.

[0080] The thickness of the adhesive layer may be, for example, 1 μm or more and 100 μm or less. Preferably, the thickness of the adhesive layer is 3 μm or more, preferably 50 μm or less, and more preferably 30 μm or less.

[0081] The polarizing plate may include a separator film. The separator film can be a film made of polyethylene resin such as polyethylene, polypropylene resin such as polypropylene, polyester resin such as polyethylene terephthalate, and preferably a stretched film of polyethylene terephthalate.

[0082] [Optical functional layer] The optical functional layer may be an optically functional film other than a polarizer, for imparting a desired optical function. A preferred example of an optically functional film is a phase difference film. Examples of phase difference films include a film that provides a λ / 2 phase difference (λ / 2 wave plate), a film that provides a λ / 4 phase difference (λ / 4 wave plate), and a positive C plate. The optically functional film may include an alignment layer and a substrate, or it may have two or more liquid crystal layers, alignment layers, and substrates. A thermoplastic resin film can also serve as a phase difference film, but a phase difference film can be laminated separately from these films.

[0083] Examples of phase difference films include birefringent films composed of stretched films of translucent thermoplastic resins; films in which discotic or nematic liquid crystals are oriented and fixed; and films in which the above-mentioned liquid crystal layer is formed on a base film. The base film is usually a film made of thermoplastic resin, and an example of a thermoplastic resin is a cellulose ester resin such as triacetylcellulose.

[0084] Other optically functional films (optical components) that may be included in a polarizing plate include light-gathering plates, brightness-enhancing films, reflective layers (reflective films), semi-transparent reflective layers (semi-transparent reflective films), and light-diffusing layers (light-diffusing films). These are generally provided when the polarizing plate is placed on the back side (backlight side) of the liquid crystal cell.

[0085] [Protective film] A polarizing plate may include a protective film to protect its surface (typically the surface of the thermoplastic resin film of the polarizing plate). The protective film, along with its adhesive layer, is removed after the polarizing plate is bonded to, for example, an image display element or other optical component.

[0086] The protective film may consist of a base film and an adhesive layer laminated thereon. The adhesive layer is described above. The resin constituting the base film can be, for example, a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate, or a thermoplastic resin such as polycarbonate. Preferably, it is a polyester-based resin such as polyethylene terephthalate.

[0087] The thickness of the protective film is not particularly limited, but it is preferably in the range of 20 μm to 200 μm. When the thickness of the base film is 20 μm or more, the polarizing plate tends to gain strength more easily.

[0088] Polarizing plates can be used as components of image display devices. The image display device is not particularly limited and examples include organic electroluminescent (OLED) displays, inorganic electroluminescent (OLED) displays, liquid crystal displays, and electroluminescent displays. When incorporated into a display device, it is preferable to place the polarizing plate in front of the image display element (on the viewing side). Circular polarizing plates can absorb ambient light reflected within the image display device, thus providing them with the function of an anti-reflective film. [Explanation of Symbols]

[0089] 100 Polyvinyl alcohol resin film, 11 Guide roll, 12 Widening roll, 110 Polyvinyl alcohol resin raw film, 111 Feed roll, 113 Swelling tank, 115 Dyeing tank, 117 Crosslinking tank, 119 Washing tank, 123 Drying oven, 127 Winding roll, 130 Polarizer.

Claims

1. A method for manufacturing a polarizer made of a polyvinyl alcohol-based resin film, The process includes, in this order, a processing step of bringing the polyvinyl alcohol-based resin film into contact with a processing liquid, and a drying step. The drying process includes bringing at least one widening roll into contact with the polyvinyl alcohol-based resin film upstream of the center of the entire length of the transport path for the polyvinyl alcohol-based resin film in the drying oven, A manufacturing method wherein the drying oven is a furnace capable of controlling the internal temperature.

2. The manufacturing method according to claim 1, wherein the drying step includes bringing a plurality of widening rolls into contact with the polyvinyl alcohol-based resin film in a drying oven.

3. The manufacturing method according to claim 1 or 2, wherein the contact angle α of the polyvinyl alcohol-based resin film in the widening roll is 0° to 30°.

4. The manufacturing method according to any one of claims 1 to 3, wherein the processing step includes at least one selected from the group consisting of a swelling step, a dyeing step, and a crosslinking step.

5. The manufacturing method according to any one of claims 1 to 4, wherein the widening roll is a curved widening roll.

6. A polarizer manufacturing apparatus made of a polyvinyl alcohol-based resin film, The system includes a processing unit for bringing the polyvinyl alcohol-based resin film into contact with a processing liquid and a drying oven, The conveying path for the polyvinyl alcohol-based resin film inside the drying oven is provided with at least one widening roll on the inlet side from the center of the overall length, The drying oven is a device in which the internal temperature of the oven can be controlled.

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