WO2023153186A1

WO2023153186A1 - Method for manufacturing polarizer

Info

Publication number: WO2023153186A1
Application number: PCT/JP2023/001861
Authority: WO
Inventors: 佳司南澤
Original assignee: 住友化学株式会社
Priority date: 2022-02-14
Filing date: 2023-01-23
Publication date: 2023-08-17
Also published as: JP2023117673A

Abstract

The purpose of the present invention is to produce a polarizer having reduced wrinkles.　Provided is a method for manufacturing a polarizer composed of a polyvinyl alcohol-based resin film, the method including a treatment step for bringing the polyvinyl alcohol-based resin film into contact with a treatment solution and a drying step in this order, in which the drying step includes bringing at least one widening roll into contact with the polyvinyl alcohol-based resin film.

Description

Method for manufacturing polarizer

The present invention relates to a method for manufacturing a polarizer made of a polyvinyl alcohol resin film.

Polarizers obtained by uniaxially stretching polyvinyl alcohol resin films are widely used in liquid crystal display devices. Japanese Patent Application Laid-Open No. 2012-173544 (Patent Document 1) describes a method for producing a polarizer, wherein in at least one of the steps of subjecting a polyvinyl alcohol film to swelling treatment, dyeing treatment and crosslinking treatment, A method of stretching a film using widening rolls as guide rolls is disclosed.

JP 2012-173544 A

A polarizer made of a polyvinyl alcohol-based resin film may have vertical wrinkles along the transport direction of the film. An object of the present invention is to obtain a polarizer with reduced wrinkles.

The present invention relates to items exemplified below.
[1] A method for producing a polarizer made of a polyvinyl alcohol-based resin film,
A treatment step of contacting the polyvinyl alcohol resin film with a treatment liquid, and a drying step in this order,
The manufacturing method, wherein the drying step includes contacting at least one widening roll 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 drying step includes bringing the width-enlarging roll and the polyvinyl alcohol resin film into contact upstream of the center of the entire length of the conveying path of the polyvinyl alcohol resin film in the drying furnace, [1] or The production method according to [2].
[4] The production method according to any one of [1] to [3], wherein the treatment step includes at least one selected from the group consisting of a swelling step, a dyeing step and a cross-linking step.
[5] The manufacturing method according to any one of [1] to [4], wherein the widening roll is a curved widening roll.
[6] A manufacturing apparatus for a polarizer made of a polyvinyl alcohol-based resin film,
A processing unit and a drying furnace for contacting the polyvinyl alcohol-based resin film with a processing liquid,
An apparatus comprising at least one widening roll on a conveying path of the polyvinyl alcohol resin film in the drying oven.

According to the present invention, a polarizer with reduced wrinkles can be obtained.

It is a schematic diagram explaining the vertical wrinkle which arises in a polarizer. 1 is a schematic diagram showing a drying furnace used in a polarizer manufacturing method according to an embodiment of the present invention; FIG. For explaining the widening roll used in the method for manufacturing a polarizer according to one embodiment of the present invention, (a) a schematic top view of the widening roll, (b) a schematic cross-sectional view of the widening roll, and (c) by the widening roll It is a schematic diagram which shows the action of the force applied to a film. It is the schematic which shows the manufacturing method of the polarizer which concerns on one Embodiment of this invention.

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 drawings below, the scale of each component is adjusted appropriately to facilitate understanding, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

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

A method for manufacturing a polarizer according to the present invention includes:
Including a treatment step of contacting the polyvinyl alcohol resin film with the treatment liquid and a drying step in this order,
The drying step includes contacting at least one widening roll with the polyvinyl alcohol-based resin film.

As shown in FIG. 1, a polarizer made of a polyvinyl alcohol-based resin film may have vertical wrinkles along the transport direction of the film. Vertical wrinkles can be reduced by bringing the widening roll and the film into contact in the drying process.

As one embodiment of the method for manufacturing a polarizer according to the present invention, in the drying step, a plurality of widening rolls may be brought into contact with the polyvinyl alcohol resin film in a drying oven. In the first half of the drying oven, the amount of water contained in the polyvinyl alcohol-based resin film is rapidly reduced, so wrinkles are likely to occur. From the viewpoint of further suppressing the occurrence of wrinkles, in the drying process, the widening roll and the polyvinyl alcohol resin film are brought into contact with each other at least upstream from the center of the entire length of the conveying path of the polyvinyl alcohol resin film in the drying furnace. is preferred. The upstream side from the center of the entire length of the film transport path in the drying oven may be the upstream one-third area or the upstream one-fourth area of the entire length of the film transport path. FIG. 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. A transport path in the drying oven 123 may be provided with both the guide roll 11 and the widening roll 12 .

According to the widening roll, an external force can be applied to the film in the width direction. In the present invention, the external force applied in the width direction of the film is the stretching force from the inside to the outside in the width direction of the film. The widening direction can be adjusted by the arrangement angle of the widening roll 12 or the like. The size of the 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 resin film 100, the degree of curvature (arc height) of the widening roll 12 to be employed, and the like.

Widening rolls include, for example, arcuate curved widening rolls (expander rolls), pinch rolls, crown rolls, and reverse crown rolls. These may be used in combination.

FIG. 3 shows an example of the arrangement of the widening rolls 12 when arch-curved widening rolls are used as the widening rolls. As shown in FIG. 3( a ), the arcuate curved widening roll has a plurality of spools with ball bearings arranged on a curved shaft 120 . A widening roll whose spool is covered with a rubber tube is called a rubber expander roll, and a widening roll whose rubber tube is not covered is called a metal expander roll. In the present invention, the widening roll 12 may be a rubber expander roll or a metal expander roll. Generally, the cross section of the widening roll 12 perpendicular to the axis 120 is circular, and the area is equal at any perpendicular cross section. The cross section of the widening roll 12 perpendicular to the axis 120 has a diameter of, for example, 50 mm to 400 mm, and may be about 100 mm.

A cross section perpendicular to the axis 120 (cross section aa in FIG. 3(a)) at the central portion of the widening roll 12 is indicated by a cross section 122 in FIG. In FIG. 3(b), a section 121 perpendicular to the axis 120 is shown at a portion where the widening roll 12 and the end of the polyvinyl alcohol resin film 100 are in contact with each other. When the center C′ of the cross section 122 of the central portion is arranged so as to be located downstream of the center C of the cross section 121 in the conveying direction, that is, the center in the width direction of the polyvinyl alcohol resin film 100 is the edge. When it is arranged so as to come into contact with the widening roll 12 afterward, the polyvinyl alcohol-based resin film 100 can be applied with stretching force from the inside to the outside in the width direction. FIG. 3(c) shows the action of the force applied to the film by the widening roll. The widening roll 12 is arranged so that the widthwise end of the polyvinyl alcohol-based resin film 100 contacts the widening roll 12 (indicated by area A2) before the center portion contacts the widening roll 12, and then the center portion contacts the widening roll 12. In this case, an outward stretching force (indicated by arrow b2) can be applied to the film to suppress the occurrence of wrinkles.

In FIG. 3B, the arrow x indicates the incident direction of the edge of the polyvinyl alcohol resin film 100 incident on the widening roll 12, and the arrow y indicates the direction from the center C to the center C′ of the widening roll 12. In this case, from the viewpoint of appropriately widening 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°, more preferably −90° to 90°. good too. The arc height of the widening roll 12 is, for example, 1 mm to 20 mm, and may be about 10 mm. As used herein, "widening roll arc height" means the distance between center C and center C', and "widening roll placement angle" means the angle θ of arrow y relative to arrow x.

The magnitude of the external force applied to the film can also be adjusted by the contact angle α of the polyvinyl alcohol resin film 100 on the widening roll 12 . The contact angle α can be adjusted by raising or lowering the position of the guide roll 11 and/or the widening roll 12 . The contact angle α is preferably 0° to 30°, and may be about 10°, since the magnitude of the stretching force applied by the widening roll 12 can be easily adjusted.

The width of the polyvinyl alcohol-based resin film 100 in contact with the widening roll 12 is not particularly limited, but the film is preferably present within the existence width of the widening roll 12 .
Since the film exists within the existence width of the widening roll 12, wrinkles of the entire film can be easily reduced. In addition, since the film does not come into contact with the ends of the widening roll 12, it is possible to suppress appearance defects such as scratches and wrinkles. The length of the widening roll 12 in the longitudinal direction is, for example, 500 mm to 3000 mm, and may be approximately 2000 mm.

The pinch rolls pinch the widthwise ends of the polyvinyl alcohol resin film. The pinch rolls are preferably installed at both side ends of the conveying path of the polyvinyl alcohol-based resin film. The pinch rolls can be metal rolls, plastic rolls or rubber rolls. The roll diameter of the pinch roll is, for example, about 10 mm to 50 mm. The length over which one pinch roll pinches the side edge of the film may be about 2% to 10% of the total width of the film. The pinch rolls may be inclined at an angle β in the film transport direction when the film is viewed from above. That is, in the plane of the film, the angle β formed by the axes of the pinch rolls with respect to the width direction perpendicular to the transport direction may be 0 to ±45°, 0 to ±30°, or 0 to ±15°. The pinch rolls may be inclined in the vertical direction with respect to the transport direction of the film. The tilt 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 with respect to the outside of the film.

In the drying process, when a plurality of widening rolls and the polyvinyl alcohol resin film are brought into contact with each other in the drying oven, the plurality of widening rolls may be the same or different.

The treatment step of bringing the polyvinyl alcohol-based resin film into contact with the treatment liquid may include at least one selected from the group consisting of a swelling step, a dyeing step and a cross-linking step.

Various treatment steps that can be included in the manufacturing method according to the present invention can be continuously performed by continuously transporting the polyvinyl alcohol resin film, which is the original film, along the film transport path of the polarizer manufacturing apparatus. . The film transport path is provided with facilities (processing tanks, furnaces, etc.) for carrying out the various processing steps described above in order of implementation.

In addition to the above equipment, the film transport path can be constructed by arranging guide rolls, nip rolls, etc. at appropriate positions. Guide rolls can be arranged, for example, before, after, and in each treatment tank, allowing the film to be introduced into, immersed in, and withdrawn from the treatment tank. More specifically, two or more guide rolls are provided in each treatment tank, and the film can be immersed in each treatment tank by transporting the film along these guide rolls.

An example of a polarizer manufacturing method will be described with reference to FIG. The polyvinyl alcohol-based resin film 110, which is the original film unwound from the delivery roll 111, is immersed in a swelling bath 113 using water as a swelling bath, and subjected to swelling treatment (swelling step). The film subjected to the swelling treatment is immersed in a dyeing tank 115 having an aqueous solution containing a dichroic dye as a dyeing bath, and the dye is adsorbed (dyeing step). After that, it is immersed in a cross-linking tank 117 using an aqueous solution containing a cross-linking agent as a treatment bath, and is cross-linked to fix the dye (cross-linking step). Next, the film is washed in washing tank 119 (washing process) and dried in drying oven 123 (drying process), and polarizer 130 is obtained. Polarizer 130 is wound on take-up roll 127 . The polyvinyl alcohol-based resin film is uniaxially stretched at one or more stages from before the swelling process to the cross-linking process (stretching process).

Examples of the polyvinyl alcohol-based resin that constitutes the polyvinyl alcohol-based resin film include those obtained by saponifying polyvinyl acetate-based resin. 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 therewith. 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. be done. The degree of saponification of the polyvinyl alcohol resin is generally about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. As used herein, "(meth)acryl" means at least one selected from acryl and methacryl. The same applies to "(meth)acryloyl".

The polyvinyl alcohol-based resin may be modified, for example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, etc. may be used.

The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 or more and 10000 or less, more preferably 1500 or more and 8000 or less, and still more preferably 2000 or more and 5000 or less. The average degree of polymerization of the polyvinyl alcohol-based resin can be determined according to JIS K 6726 (1994). When the average degree of polymerization is within the above range, the polarizing performance and film processability tend to be excellent.

The thickness of the polyvinyl alcohol resin film, which is the original film, may be, for example, 10 μm or more and 150 μm or less, preferably 15 μm or more and 100 μm or less, more preferably 20 μm or more and 80 μm or less. The length in the width direction of the polyvinyl alcohol resin film, which is the original film, may be, for example, 600 mm or more and 5000 mm or less.

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 still more preferably 15 μm or more. The thickness of the polarizer can be controlled, for example, by selecting a polyvinyl alcohol resin film, adjusting the draw ratio, and the like.

A polyvinyl alcohol resin film, which is a raw film, can be prepared, for example, as a roll (wound product) of a long unstretched or stretched polyvinyl alcohol resin film. In this case, the polarizer is also obtained as an elongated object. Each step will be described in detail below.

(1) Swelling step The swelling treatment in this step is carried out as necessary for the purpose of removing foreign matter from the polyvinyl alcohol-based resin film, which is the original film, removing the plasticizer, imparting easy dyeability, plasticizing the film, and the like. It is a process that Specifically, the swelling treatment can be a treatment of immersing the polyvinyl alcohol-based resin film 110 in a swelling bath containing a treatment liquid containing water. The film may be immersed in one swelling bath, or may be immersed in two or more swelling baths sequentially. Before the swelling treatment, during the swelling treatment, or before and during the swelling treatment, the film may be uniaxially stretched.

The treatment liquid contained in the swelling tank may be water (for example, pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added. As noted above, the treatment liquid contained in the swelling bath may contain zinc salts.

The temperature of the treatment liquid contained in the swelling tank when the film is immersed is usually 10°C or higher and 70°C or lower, preferably 15°C or higher and 50°C or lower. The immersion time of the film is usually 10 seconds or more and 600 seconds or less, preferably 20 seconds or more and 300 seconds or less.

(2) Dyeing process The dyeing process in this process is a process performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film. Specifically, the dyeing treatment can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a dyeing tank containing a treatment liquid containing a dichroic dye. The film may be immersed in one dyeing bath or sequentially immersed in two or more dyeing baths. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing process may be uniaxially stretched to at least some extent. Instead of the uniaxial stretching treatment before the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment may be performed during the dyeing treatment.

The dichroic dye can be iodine or a dichroic organic dye. 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 Includes Sky Blue, Direct First Orange S, and First Black. A dichroic dye may be used individually by 1 type, and may use 2 or more types together.

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used as the treatment liquid contained in the dyeing tank. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist in the treatment liquid. The addition of boric acid is distinguished from the cross-linking treatment described later in that it contains iodine. The content of iodine in the aqueous solution is usually 0.01 parts by mass or more and 1 part by mass or less per 100 parts by mass of water. Also, the content of iodides such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of water.

The temperature of the treatment liquid contained in the dyeing bath when the film is immersed is usually 10°C or higher and 45°C or lower, preferably 10°C or higher and 40°C or lower, and more preferably 20°C or higher and 35°C or lower. The immersion time of the film may be, for example, 20 seconds or more and 600 seconds or less, preferably 20 seconds or more and 300 seconds or less.

When a dichroic organic dye is used as the dichroic dye, an aqueous solution containing the dichroic organic dye can be used as the treatment liquid contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1 × 10 ^-4 parts by weight or more and 10 parts by weight or less, preferably 1 × 10 ^-3 parts by weight or more and 1 part by weight or less per 100 parts by weight of water. . A dyeing assistant or the like may coexist in the dyeing bath, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. A dichroic organic dye may be used individually by 1 type, and may use 2 or more types together. The temperature of the treatment liquid contained in the dye bath when the film is immersed is, for example, 20°C or higher and 80°C or lower, preferably 25°C or higher and 50°C or lower. The immersion time of the film is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

(3) Cross-linking step The cross-linking treatment of treating the polyvinyl alcohol-based resin film after the dyeing step with a cross-linking agent is a treatment performed for the purpose of water resistance by cross-linking, hue adjustment, and the like. Specifically, the cross-linking treatment can be a treatment in which the film after the dyeing step is immersed in a cross-linking tank containing a treatment liquid containing a cross-linking agent. The film may be immersed in one cross-linking bath, or may be immersed in two or more cross-linking baths sequentially. A uniaxial stretching treatment may be performed during the cross-linking treatment.

Examples of cross-linking agents include boric acid, glyoxal, glutaraldehyde, etc. Boric acid is preferably used. Two or more cross-linking agents can be used in combination. The content of boric acid in the treatment liquid contained in the cross-linking bath is usually 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the cross-linking tank preferably contains iodide in addition to boric acid. The content of iodide in the treatment liquid contained in the cross-linking bath is usually 0.1 to 15 parts by mass, preferably 5 to 12 parts by mass per 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist in the cross-linking tank.

The temperature of the treatment liquid contained in the cross-linking bath when the film is immersed may be, for example, 30°C or higher and 85°C or lower, preferably 30°C or higher and 60°C or lower. The immersion time of the film may be, for example, 2 seconds or more and 600 seconds or less, preferably 2 seconds or more and 300 seconds or less.

In the cross-linking step, there may be two or more cross-linking tanks. In this case, the composition and temperature of the treatment liquid contained in each cross-linking tank may be the same or different. The treatment liquid contained in the cross-linking tank may have the concentration and temperature of the cross-linking agent and iodide according to the purpose of immersing the polyvinyl alcohol-based resin film. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment (complementary color) may each be performed in a plurality of steps (for example, a plurality of tanks).
In general, when both the cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment (complementary color) are performed, the tank (complementary color tank) that performs the cross-linking treatment for hue adjustment (complementary color) is placed in the latter stage. placed. The temperature of the treatment liquid contained in the complementary color tank is, for example, 10° C. or higher and 55° C. or lower, preferably 20° C. or higher and 50° C. or lower. The content of the cross-linking agent in the treatment liquid contained in the complementary color bath is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the complementary color bath is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water.

As described above, in the production of the polarizer, the polyvinyl alcohol resin film is uniaxially stretched at one or more stages from before the swelling process to the cross-linking process (stretching process). From the viewpoint of enhancing the dyeability of the dichroic dye, the film to be subjected to the dyeing process is preferably a film that has been uniaxially stretched to at least some degree, or instead of the uniaxial stretching process before the dyeing process, or In addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

The uniaxial stretching treatment may be either dry stretching in which the film is stretched in the air or wet stretching in which the film is stretched in a tank, or both of them may be carried out. The uniaxial stretching treatment can be inter-roll stretching, hot roll stretching, tenter stretching, etc., in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between two nip rolls, but preferably includes roll-to-roll stretching. The draw ratio based on the original film (when the drawing treatment is performed in two or more stages, the cumulative draw ratio of those) is about 3 times or more and 8 times or less. In order to impart good polarizing properties, the draw ratio is preferably 4 times or more, more preferably 5 times or more.

(4) Washing process The washing process in this process is carried out as necessary for the purpose of removing chemicals such as excess cross-linking agents and dichroic dyes adhering to the polyvinyl alcohol resin film. This is a treatment for washing the polyvinyl alcohol-based resin film after the cross-linking step using the contained washing liquid. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film after the cross-linking step is immersed in a treatment liquid (washing liquid) contained in a washing tank. The film may be immersed in one washing tank, or may be immersed in two or more washing tanks sequentially. Alternatively, the washing treatment may be a treatment of spraying the polyvinyl alcohol-based resin film after the cross-linking step with the washing solution as a shower, or a combination of the immersion treatment and the spraying treatment.

The cleaning liquid may be water (for example, pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added.

When the polyvinyl alcohol-based resin film after the cross-linking step is immersed in the washing tank, the temperature of the washing solution in the washing tank is, for example, 2°C or higher and 40°C or lower, preferably 2°C or higher and 22°C or lower, more preferably 2°C. above 10°C. The immersion time in the cleaning tank may be, for example, 10 seconds or more and 100 seconds or less, preferably 20 seconds or more and 80 seconds or less.

When the cleaning solution is sprayed as a shower onto the polyvinyl alcohol-based resin film after the cross-linking step, the temperature of the cleaning solution may be the same at the center and at both ends in the width direction of the polyvinyl alcohol-based resin film, or may be different. Although the temperatures may be different, they are preferably different temperatures, more preferably the temperature at the center is lower than the temperature at the ends. The temperature of the washing liquid is preferably 2° C. to 10° C. at the central portion and 10° C. to 22° C. at both ends, more preferably 3° C. to 7° C. at the central portion and 15° C. to 22° C. at both ends. It is below.

(5) Drying step In the drying step, the polyvinyl alcohol resin film after the treatment step is dried. While the polyvinyl alcohol resin film after the washing step is continuously transported, the film can be subjected to a drying treatment by introducing the film into the drying step, thereby obtaining a polarizer.

The drying process is performed using film drying means (heating means). A preferred example of drying means is a drying oven. The drying oven is preferably one capable of controlling the temperature inside the oven. The drying oven is, for example, a hot air oven capable of increasing the temperature inside the oven by supplying hot air or the like. The drying treatment by the drying means may be a treatment of adhering the polyvinyl alcohol-based resin film after the washing step to one or more heating bodies having convex curved surfaces, or a treatment of heating the film using a heater. .

Examples of the heating body include a roll (for example, a guide roll that also serves as a heat roll) that has a heat source (for example, a heat medium such as hot water or an infrared heater) inside and can increase the surface temperature. Examples of heaters include infrared heaters, halogen heaters, and panel heaters.

In the drying process, the temperature of the drying process (for example, the temperature in the drying furnace, the surface temperature of the heat roll, etc.) is usually 30°C or higher and 100°C or lower, preferably 50°C or higher and 90°C or lower. Although the drying time is not particularly limited, it is, for example, 30 seconds or more and 600 seconds or less, preferably 30 seconds or more and 60 seconds or less.

The drying process may be one stage or divided into multiple stages, preferably divided into two stages or more and four stages or less. When the drying process is divided into multiple stages, it is preferable to set the temperature of the drying process 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 or more and 300 seconds or less, preferably 10 seconds or more and 20 seconds or less.

In the polarizer manufacturing process, at least one of the treatment liquids for treating the polyvinyl alcohol-based resin film may contain a zinc salt. Examples of the treatment tank containing the treatment liquid include a swelling tank, a dyeing tank, a cross-linking tank, a washing tank, a complementary color tank, and the like. The treatment tank containing the zinc salt-containing treatment solution is preferably a treatment tank located after the dyeing tank and before the washing tank, more preferably at least one tank selected from a bridging tank and a complementary color tank, and still more preferably. When there are two or more cross-linking baths, it is at least one selected from the last cross-linking bath and complementary color bath.
By immersing the polyvinyl alcohol-based resin film in a zinc salt-containing treatment liquid, the obtained polarizer can contain zinc element. The content of the zinc element in the polarizer can be adjusted by adjusting the concentration of the zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like. The content of zinc element can be in the range of

Examples of zinc salts contained in the treatment solution include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among them, zinc nitrate is preferred because it causes little change in tension. The zinc salt can be added to the processing liquid as a zinc salt solution.

The concentration of the zinc salt in the treatment liquid may be different for each treatment tank, but may be, for example, 1 part by mass or more and 10 parts by weight or less with respect to 100 parts by weight of the treatment liquid contained in the treatment tank. It is preferably at least 7 parts by mass and no more than 7 parts by mass.

A polarizer made of a polyvinyl alcohol resin film can be obtained through the above steps. In this polarizer, a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film.

[Manufacturing equipment]
The manufacturing apparatus according to the present invention includes:
A manufacturing apparatus for a polarizer made of a polyvinyl alcohol-based resin film,
A processing unit and a drying furnace for contacting the polyvinyl alcohol-based resin film with a processing liquid,
At least one widening roll is provided on the transport path of the polyvinyl alcohol-based resin film in the drying oven.
The treatment section may be a section that performs the above-described swelling treatment, dyeing treatment, cross-linking treatment, or washing treatment. The above-described polarizer can be obtained using the manufacturing apparatus according to the present invention.

A manufacturing apparatus according to one embodiment includes at least one of a swelling tank, a dyeing tank, a cross-linking tank and a washing tank, and a drying oven. A drying oven may be equipped with a plurality of widening rolls. It is preferable that the drying oven is equipped with a widening roll on the inlet side of the center of the entire length of the film conveying path.

[Polarizer]
The obtained polarizer can be transported as it is to the polarizing plate manufacturing process. In the polarizing plate manufacturing process, for example, a thermoplastic resin film is laminated on one side or both sides of the polarizer. A method for manufacturing a polarizing plate can include the above-described steps for manufacturing a polarizer.

A polarizing plate according to one embodiment is a laminate having a thermoplastic resin film on one side or both sides of a polarizer via an adhesive. The polarizing plate can 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 elliptically polarizing plate, or the like. A circular polarizer includes a linear polarizer and a retardation layer.

The thickness of the polarizing plate is usually 5 μm or more, may be 20 μm or more, may be 25 μm or more, or may be 30 μm or more. The thickness of the polarizing plate is preferably 80 μm or less, more preferably 60 μm or less.

[Thermoplastic resin film]
Examples of thermoplastic resin films include polyolefin resins such as linear polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose esters such as triacetyl cellulose and diacetyl cellulose; Resins; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resins; (meth)acrylic resins such as polymethyl methacrylate resins; It can be a resin film having translucency. The thermoplastic resin film may have a single-layer structure consisting of one resin layer made of one or more thermoplastic resins, or may have a single layer structure made of one or more thermoplastic resins. It may be a laminated multilayer structure.
The first thermoplastic resin film and the second thermoplastic resin film can be the same or different types of thermoplastic resin films.

The thermoplastic resin film may contain additives as necessary. Examples of additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, light stabilizers, impact modifiers, surfactants, and the like. Examples of ultraviolet absorbers include salicylate compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, and the like.

Either one or both of the thermoplastic resin films can be a protective film having optical functions such as a retardation film and a brightness enhancement film. For example, a retardation film provided with an arbitrary retardation value by stretching (uniaxially or biaxially stretching, etc.) a transparent resin film made of the above materials, or by forming a liquid crystal layer or the like on the film. can be

A surface treatment layer (coating layer) such as a hard coat layer, antiglare layer, antireflection layer, antistatic layer, and antifouling layer can 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 may be formed on both sides. The surface treatment layer may be formed on the surface of the thermoplastic resin film opposite to the polarizer side.

The thickness of the thermoplastic resin film is preferably thin from the viewpoint of thinning the polarizing plate. It is 5 μm or more and 100 μm or less, more preferably 10 μm or more and 60 μm or less.

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

Examples of resin components contained in the water-based composition include polyvinyl alcohol-based resins and urethane resins. Water-based compositions containing polyvinyl alcohol resins contain curable components such as polyhydric aldehydes, melamine compounds, zirconia compounds, zinc compounds, glyoxal, glyoxal derivatives, and water-soluble epoxy resins in order to improve adhesion and adhesiveness. or a cross-linking agent. Water-based compositions containing a urethane resin include water-based compositions containing a polyester-based ionomer-type urethane resin and a compound having a glycidyloxy group.

An active energy ray-curable composition is a composition that cures when exposed to active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. The UV-curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, a mixture of a cationic polymerizable epoxy compound and a photocationic polymerization initiator, or the like. Moreover, a cationic polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound can be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator can also be used together as initiators.

The thickness of the adhesive layer may be, for example, 1 μm or more and 25 μm or less. The thickness of the adhesive layer is preferably 2 µm or more, preferably 15 µm or less, and more preferably 5 µm or less. If the thickness of the adhesive layer is small, the impact resistance tends to decrease, and if the thickness of the adhesive layer is large, the bending repulsive force tends to increase.

In order to improve the adhesiveness between the polarizer and the resin film, prior to bonding the polarizer and the resin film, the bonding surface of the polarizer and/or the resin film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet ray Surface treatments such as irradiation treatment, primer coating treatment, and saponification treatment may be applied.

[Adhesive layer]
The polarizing plate may have a pressure-sensitive adhesive layer for laminating each layer constituting the polarizing plate or for laminating the polarizing plate and the translucent member or the image display element. The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition whose main component is a (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether resin. A pressure-sensitive adhesive composition containing a (meth)acrylic resin as a base polymer is suitable because of its excellent transparency, weather resistance, heat resistance, and the like. The adhesive composition may be active energy ray-curable or heat-curable.

The (meth)acrylic resin (base polymer) used in the adhesive composition includes butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. Polymers or copolymers containing one or more of the (meth)acrylic acid esters as monomers are preferably used. Preferably, the base polymer is copolymerized with a polar monomer. Polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, and N,N-dimethylaminoethyl (meth)acrylate compounds. , glycidyl (meth)acrylate compounds, and other monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like.

The adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. Cross-linking agents include divalent or higher metal ions that form carboxylic acid metal salts with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; and ester bonds with carboxyl groups. Polyepoxy compounds or polyols; and polyisocyanate compounds that form amide bonds with carboxyl groups are exemplified. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by being irradiated with an active energy ray such as an ultraviolet ray or an electron beam. It is a pressure-sensitive adhesive composition that can be adhered to an adherend such as the adhesive agent, and that can be cured by irradiation with an active energy ray to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably UV-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Furthermore, if necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

The adhesive composition contains fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders). etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

The pressure-sensitive adhesive layer is formed by dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a pressure-sensitive adhesive liquid, which is directly applied to the target surface of the laminated film to form the pressure-sensitive adhesive layer. Alternatively, a method of forming a sheet-like pressure-sensitive adhesive layer on a release-treated separate film and transferring it to the target surface of the polarizing plate can be used. When an active energy ray-curable pressure-sensitive adhesive composition is used, a cured product having a desired degree of curing can be obtained by irradiating the formed pressure-sensitive adhesive layer with an active energy ray.

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

The polarizing plate may contain a separate film. The separate film can be a film made of a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate, or the like, and is preferably a stretched polyethylene terephthalate film.

[Optical function layer]
The optical functional layer may be an optical functional film other than the polarizer for imparting desired optical functions. A suitable example of the optical functional film is a retardation film. Examples of the retardation film include a film giving a retardation of λ/2 (λ/2 wavelength plate), a film giving a retardation of λ/4 (λ/4 wavelength plate) and a positive C plate. The optical functional film may contain an alignment layer and a substrate, or may have two or more liquid crystal layers, two or more alignment layers, and two or more substrates. The thermoplastic resin film can also serve as a retardation film, but a retardation film can be laminated separately from these films.

As a retardation film, a birefringent film composed of a stretched film of a thermoplastic resin having translucency; a film in which a discotic liquid crystal or nematic liquid crystal is oriented and fixed; and the above liquid crystal layer formed on a substrate film. and the like. The base film is usually a film made of a thermoplastic resin, and an example of the thermoplastic resin is a cellulose ester resin such as triacetyl cellulose.

Examples of other optically functional films (optical members) that can be included in the polarizing plate include light collectors, brightness enhancement films, reflective layers (reflective films), semi-transmissive reflective layers (semi-transmissive reflective films), light diffusion layers (light diffusion film), etc. These are generally provided when the polarizing plate is arranged on the back side (backlight side) of the liquid crystal cell.

[Protection film]
The polarizing plate can contain a protective film for protecting its surface (typically, the surface of the thermoplastic resin film of the polarizing plate). After the polarizing plate is attached to, for example, an image display element or other optical member, the protective film is peeled off together with the pressure-sensitive adhesive layer of the protective film.

A protective film can be composed of a base film and an adhesive layer laminated thereon. As for the pressure-sensitive adhesive layer, the above description is cited. The resin constituting the base film may be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, or a thermoplastic resin such as a polycarbonate resin. can. Polyester-based resins such as polyethylene terephthalate are preferred.

Although the thickness of the protective film is not particularly limited, it is preferably in the range of 20 μm or more and 200 μm or less. When the thickness of the base film is 20 μm or more, strength tends to be easily imparted to the polarizing plate.

A polarizing plate can be used as a component of an image display device. The image display device is not particularly limited, and examples thereof include organic electroluminescence (organic EL) display devices, inorganic electroluminescence (inorganic EL) display devices, liquid crystal display devices, and electroluminescence display devices. When incorporated into a display device, the polarizing plate is preferably arranged in front of the image display element (visible side). Since the circularly polarizing plate can absorb external light reflected in the image display device, it can function as an antireflection film.

100 polyvinyl alcohol-based resin film, 11 guide roll, 12 widening roll, 110 raw film of polyvinyl alcohol-based resin, 111 delivery roll, 113 swelling tank, 115 dyeing tank, 117 cross-linking tank, 119 washing tank, 123 drying furnace, 127 Winding roll, 130 Polarizer.

Claims

A method for producing a polarizer made of a polyvinyl alcohol-based resin film, comprising:
A treatment step of contacting the polyvinyl alcohol resin film with a treatment liquid, and a drying step in this order,
The manufacturing method, wherein the drying step includes contacting at least one widening roll with the polyvinyl alcohol-based resin film.
The manufacturing method according to claim 1, wherein the drying step includes bringing a plurality of widening rolls into contact with the polyvinyl alcohol resin film in a drying oven.
3. The drying process according to claim 1 or 2, wherein the drying step includes bringing a widening roll and the polyvinyl alcohol resin film into contact upstream from the center of the entire length of the conveying path of the polyvinyl alcohol resin film in a drying furnace. manufacturing method.
The manufacturing method according to any one of claims 1 to 3, wherein the treatment step includes at least one selected from the group consisting of a swelling step, a dyeing step and a cross-linking step.
The manufacturing method according to any one of claims 1 to 4, wherein the widening roll is an arcuate curved widening roll.
A manufacturing apparatus for a polarizer made of a polyvinyl alcohol-based resin film,
A processing unit and a drying furnace for contacting the polyvinyl alcohol-based resin film with a processing liquid,
An apparatus comprising at least one widening roll on a conveying path of the polyvinyl alcohol-based resin film in the drying oven.