JP2023091923A - Method for manufacturing polarizer - Google Patents

Abstract

To provide a method for manufacturing a polarizer having an excellent visual sensitivity correction polarization degree and a neutral color phase (an orthogonal color phase is nearly 0).SOLUTION: The method for manufacturing a polarizer includes a processing step of immersing a polyvinyl alcohol-based resin film in a processing liquid and performing processing on the film. In the processing method, the polyvinyl alcohol-based resin film is subjected to humidifying processing immediately before the polyvinyl alcohol-based resin film is immersed in the processing liquid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a polarizer.

In Patent Document 1, the boron content in the polarizer and the shrinkage force during heating are controlled in order to improve the durability of the polarizing plate to the heat cycle test and to make the orthogonal hue neutral gray. A method for making a polarizer is disclosed.

JP 2013-148806 A

An object of the present invention is to provide a method for producing a polarizer that has a good luminosity-correcting degree of polarization (hereinafter also simply referred to as a degree of polarization) and a neutral hue (an orthogonal hue b value is close to 0). It is to be.

The present invention provides the following method for manufacturing a polarizer.
[1] A method for manufacturing a polarizer, comprising:
Including a treatment step of immersing the polyvinyl alcohol-based resin film in a treatment liquid to treat it,
A method for producing a polarizer, wherein in the treatment step, the polyvinyl alcohol resin film is subjected to a humidification treatment before being immersed in the treatment liquid.
[2] The method for producing a polarizer according to [1], wherein the treatment step is at least one selected from the group consisting of a dyeing step, a cross-linking step and a complementary color step.
[3] The method for producing a polarizer according to [1], wherein the treatment step is at least one selected from the group consisting of a dyeing step and a cross-linking step.
[4] Manufacture of the polarizer according to any one of [1] to [3], wherein the humidifying treatment is performed by spraying air at a temperature of 25° C. and a humidity of 90% RH or higher on the polyvinyl alcohol resin film. Method.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polarizer which has favorable polarization degree and has a neutral hue can be provided.

It is a cross-sectional schematic diagram which shows the example of arrangement|positioning of the apparatus in the manufacturing method of a polarizer. 1 is a schematic cross-sectional view of a polarizing plate including a polarizer; FIG.

Hereinafter, embodiments of the present invention will be described 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.

<Method for producing polarizer>
A method for producing a polarizer according to an aspect of the present invention includes a treatment step of immersing a polyvinyl alcohol-based resin film in a treatment liquid for treatment, and in the treatment step, before immersing the polyvinyl alcohol-based resin film in the treatment liquid. is a method for producing a polarizer in which a polyvinyl alcohol-based resin film is subjected to a humidifying treatment.

The polarizer can be a polyvinyl alcohol-based resin film in which a dichroic dye such as iodine is adsorbed and oriented. A polarizer is formed by, for example, a swelling step in which a polyvinyl alcohol resin film is immersed in a treatment liquid containing water to swell the polyvinyl alcohol resin film, and a treatment liquid containing a dichroic dye is applied to the polyvinyl alcohol resin film. A dyeing step in which the polyvinyl alcohol resin film is immersed to adsorb a dichroic dye, and the polyvinyl alcohol resin film is immersed in a treatment liquid containing a cross-linking agent, and the adsorbed dichroic dye is treated with polyvinyl alcohol. A cross-linking step of fixing the polyvinyl alcohol-based resin in the film and cross-linking the polyvinyl alcohol-based resin, and immersing the polyvinyl alcohol-based resin film in a treatment liquid containing water to remove chemicals and foreign substances adhering to the polyvinyl alcohol-based resin film A washing step for washing and removing, a drying step for drying the polyvinyl alcohol resin film, a stretching step for uniaxial stretching in the cross-linking step or a step prior to that, and a polyvinyl alcohol-based resin film between the cross-linking step and the washing step. It can be produced by a method of performing a primary drying step of drying. Each step will be described later.

FIG. 1 shows a schematic cross-sectional view of an arrangement example of an apparatus in the method for producing a polarizer of the present invention. In the apparatus shown in FIG. 1, a raw film 10 made of a polyvinyl alcohol-based resin is unwound from a delivery roll 11, and a swelling tank 13 for swelling treatment, a dyeing tank 15 for dyeing treatment, and a cross-linking treatment. It is configured to sequentially pass through a bridging tank 17 for performing After passing through the cross-linking bath 17, the film passes through the primary drying furnace 21 for performing the above-described primary drying and is primarily dried, and then passes through the washing bath 19 to wash away unreacted dichroic dyes such as iodine and boric acid. and finally dried through a final drying oven 23 to obtain the polarizer 30 . Although not shown, uniaxial stretching is applied in the cross-linking tank 17 or before it. Although the obtained polarizer 30 is shown to be wound around the winding roll 27, it may be subjected to the next step of applying a protective film without being wound up. FIG. 1 shows an example in which one swelling tank 13, one dyeing tank 15, one cross-linking tank 17, and one cleaning tank 19 are provided, but a plurality of tanks may be provided for one treatment. The arrows in FIG. 1 indicate the transport direction of the film.

An apparatus in the polarizer manufacturing method can be constructed by arranging the nip rolls 12, the guide rolls 14, and the like at appropriate positions on the film transport path. For example, the guide rolls 14 can be arranged before, after, or in the processing bath containing the processing liquid, thereby allowing the film to be introduced into, immersed in, and pulled out of the processing bath. More specifically, the nip rolls 12 are arranged at the entrance and exit of the processing tank, and the film can be conveyed while being tensioned. Also, by providing two or more guide rolls 14 in the treatment tank and transporting the film along these guide rolls 14, the film can be immersed in the treatment tank.

At least one selected from the group consisting of a dyeing process, a cross-linking process and a complementary color process can be mentioned as the treatment process in which the moisturizing process can be performed. In the apparatus shown in FIG. 1, a device 16 for performing a humidification treatment, which will be described later, is arranged between the nip roll 12 on the inlet side (upstream side) of the cross-linking tank 17 and the liquid surface 18 of the treatment liquid contained in the cross-linking tank 17. It is

A raw film 10 made of a polyvinyl alcohol-based resin, which is a raw material of a polarizer, is usually wound around a delivery roll 11 in a roll shape as shown in the figure, and is unwound from the delivery roll 11 in a long form. . The raw film 10 made of a polyvinyl alcohol-based resin has a thickness usually within the range of 20 to 100 μm, preferably within the range of 30 to 80 μm, and its industrially practical width is within the range of 1500 to 6000 mm. is.

(Polyvinyl alcohol resin film)
A polyvinyl alcohol-based resin film is a resin film that serves as a base material for a polarizer, and specifically is a film made of a resin obtained by saponifying a 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. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The degree of saponification of the polyvinyl alcohol resin is usually about 85 to 100 mol %, preferably 98 mol % or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1000-10000, preferably about 1500-5000.

A material obtained by forming a polyvinyl alcohol-based resin into a film is used as the original fabric of the polarizer. A method for forming a film from the polyvinyl alcohol-based resin is not particularly limited, and the film can be formed by a known method. The thickness of the polyvinyl alcohol-based raw film is not particularly limited, but may be appropriately selected from a range of, for example, about 20 to 150 μm.

A polarizer is obtained by adsorbing and aligning a dichroic dye on the polyvinyl alcohol-based resin film.

(Humidification treatment)
In the method for producing a polarizer, in the treatment step, the polyvinyl alcohol resin film is subjected to a moistening treatment before being immersed in the treatment liquid. The processing steps will be described later. The moisturizing treatment can be a treatment for imparting moisture to the polyvinyl alcohol-based resin film. Due to the humidification treatment, the degree of polarization of the polarizer tends to be improved, and a neutral hue tends to be exhibited. This is because the moisture content in the polyvinyl alcohol resin film increases by carrying out the humidification treatment, further swelling progresses, and the treatment liquid containing iodine and a cross-linking agent, which will be described later, penetrates the polyvinyl alcohol resin film. easier to penetrate. As a result, the stress relaxation of the polyvinyl alcohol-based resin film progresses further, and it is assumed that the film is easily stretched by the later-described stretching treatment.

As a method of applying moisture to the polyvinyl alcohol resin film, for example, a method of spraying humidity-controlled air onto the polyvinyl alcohol resin film, or a method of passing the polyvinyl alcohol resin film through an atmosphere whose humidity is controlled. and the like. Among them, a method of spraying humidity-controlled air onto the polyvinyl alcohol-based resin film is preferable. The air sprayed onto the polyvinyl alcohol resin film may have a temperature of, for example, 25° C. and a humidity of 90% RH or more, and may have a spray amount of, for example, 0.1 L/h or more and 10 L/h or less, preferably 1 L/h. It is more than 5 L/h or less. A humidifier, a high-humidity oven, and the like can be cited as examples of the apparatus for performing the humidification process.

The humidification treatment is performed before the polyvinyl alcohol resin film is immersed in the treatment liquid, so that the polyvinyl alcohol resin film can be immersed in the treatment liquid without reducing the water content in the polyvinyl alcohol resin film, which has increased due to the humidification treatment. can be immersed in The position where the humidification treatment is performed may be, for example, between the nip roll attached to the inlet of the processing tank containing the processing liquid and the liquid surface of the processing liquid contained in the processing tank, preferably 10 cm to 1 m above the liquid surface. Upstream side. The moistening treatment can be performed, for example, 0.5 to 4 seconds before immersing the film in the treatment liquid, more preferably 1 to 2 seconds before.

When humidification is performed by a method of spraying humidity-controlled air onto the polyvinyl alcohol-based resin film described above, a nip roll attached to the inlet side (upstream side) of a processing tank containing a processing liquid, and a processing tank A humidifier is installed between the liquid surface of the processing liquid contained in the chamber, and the polyvinyl alcohol-based resin film is immersed in the processing liquid by spraying humidity-controlled air on one or both sides of the polyvinyl alcohol-based resin film. A moisturizing treatment can be performed before the drying process.

(Processing process)
The treatment step includes a dyeing step of immersing the polyvinyl alcohol resin film in a treatment liquid containing a dichroic dye, a cross-linking step of immersing the polyvinyl alcohol resin film in a treatment liquid containing a cross-linking agent, and a polyvinyl alcohol resin film. It may be at least one selected from the group consisting of a complementary color process of immersing the alcohol-based resin film in a treatment liquid containing a complementary color agent. The treatment step is preferably at least one selected from the group consisting of a dyeing step and a cross-linking step.

In the treatment process, when a plurality of treatment tanks containing treatment solutions are used for treatment, a humidification device may be provided for each treatment tank, or a humidification device may be provided only for the first treatment tank. may be placed.

(Swelling process)
The swelling step of performing the swelling treatment can be a step of bringing the raw film made of the polyvinyl alcohol-based resin into contact with a treatment liquid containing water to swell it (swelling treatment). This swelling treatment is performed for the purpose of removing foreign matter adhering to the surface of the film, removing plasticizers such as glycerin contained in the film, imparting easy dyeability in subsequent processes, and plasticizing the film. Conditions for the swelling treatment are determined within a range in which these objectives can be achieved and in which problems such as extreme dissolution and devitrification of the polyvinyl alcohol resin film do not occur. Specifically, a raw film made of a polyvinyl alcohol-based resin is immersed in a treatment liquid containing water at a temperature of, for example, 10 to 50°C, preferably 20 to 50°C, for swelling treatment. The swelling treatment time is usually 5 to 300 seconds, preferably 20 to 240 seconds.

Usually, in the swelling process, as shown in the figure, a plurality of guide rollers are arranged in a swelling bath 13 containing a water-containing treatment liquid to convey the polyvinyl alcohol resin film. In addition, since the film tends to swell in the width direction and cause wrinkles in the film, wrinkles in the film are removed by known widening devices such as expander rolls, spiral rolls, crown rolls, cross guiders, tenter clips, and bend bars. It is preferable to convey the film while removing it. Furthermore, for the purpose of stabilizing the film transport during immersion, the water flow in the swelling tank 13 is controlled by an underwater shower, and an EPC device (Edge Position Control device: detects the edge of the film to prevent the meandering of the film. It is also useful to use a device such as

The water-containing treatment liquid used in the swelling tank 13 includes pure water, boric acid, chlorides, other inorganic salts, water-soluble organic solvents, alcohols, etc. in the range of 0.01 to 10% by mass. It may be an aqueous solution. However, pure water containing substantially no dissolved components is preferably used for the purpose described above. Pure water free of dissolved components can be obtained by a method of subjecting ordinary water to reverse osmosis membrane treatment.

In the swelling process, only one swelling tank may be provided as shown in FIG. 1, or two or more tanks may be provided. When the swelling tank is composed of two tanks, they are referred to as the first swelling tank and the second swelling tank from the upstream side. The same applies to the case where the swelling tanks are composed of three or more tanks.

A device for performing humidification treatment can be arranged on the inlet side (upstream side) of the swelling tank 13 to perform the humidification treatment. When the swelling tanks are composed of two or more tanks, each tank may be provided with a humidifying device, or only the first swelling tank may be provided with a humidifying device.

In the swelling process, the film swells in both the width direction and the transport direction. In the swelling process, the film swells and expands also in the transport direction of the film. Therefore, in order to eliminate the slack of the film in the transport direction, measures such as controlling the speed of the transport rolls before and after the swelling tank 13 should be taken. is preferred. Specifically, it is preferable that the ratio of the peripheral speed of the outlet-side transport roll to the peripheral speed of the inlet-side transport roll of the swelling tank 13 is about 1.2 to 2 times depending on the temperature of the treatment bath. Uniaxial stretching can also be applied in this step, if desired.

(Dyeing process)
In the dyeing process, the polyvinyl alcohol-based resin film is immersed in a treatment liquid containing a dichroic dye (hereinafter also referred to as a dyeing liquid) to dye the polyvinyl alcohol-based resin film, and the dichroic dye is applied to the polyvinyl alcohol-based resin film. This is done for adsorption (dyeing). In this dyeing process, the polyvinyl alcohol-based resin film after undergoing a swelling process and, in some cases, a water immersion process, is immersed in a dyeing bath 15 containing a dyeing solution, as shown in the figure. usually done. The conditions for the dyeing treatment can be determined within a range in which the dichroic dye can be adsorbed on the polyvinyl alcohol-based resin film and in a range in which problems such as extreme dissolution and devitrification of the film do not occur. Dichroic dyes include, for example, iodine.

When the dichroic dye is iodine, the dyeing solution used in the dyeing process contains 0.003 to 0.2 parts by weight of iodine and 0.1 to 10 parts by weight of potassium iodide with respect to 100 parts by weight of water. It can be an aqueous solution containing Further, other iodides such as zinc iodide may be used instead of potassium iodide, and other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodides such as boric acid, zinc chloride, and cobalt chloride may coexist. In the present invention, an aqueous solution containing 0.003 parts by mass or more of iodine per 100 parts by mass of water can be regarded as a dyeing bath even if it contains components other than iodine. The temperature of the dyeing bath (dyeing temperature) is usually 10 to 50°C, preferably 20 to 40°C, and the time for dyeing (dyeing time) is usually 10 to 600 seconds, preferably 30 to 200 seconds. .

In the dyeing process, only one dyeing tank may be provided as shown in FIG. 1, or two or more dyeing tanks may be provided. When the dyeing tank is composed of two tanks, the first dyeing tank and the second dyeing tank are referred to from the upstream side. The same is true when the number of dyeing tanks is three or more.

A humidifying device can be arranged on the entrance side (upstream side) of the dyeing tank 15 to perform the humidifying process. When the dyeing tank is composed of two or more tanks, a humidifying device may be arranged for each tank, or a humidifying device may be arranged only for the first cross-linking tank. By performing a humidification treatment in the dyeing process, a space for impregnating the dyeing solution is secured between the molecules in the swollen polyvinyl alcohol resin film, the amount of adsorption of the dichroic dye increases, and the dyeability is improved. The hue (single hue b value and orthogonal hue b value) of the polarizer tends to be easily improved.

In the dyeing process, as in the swelling process, the polyvinyl alcohol-based resin film is conveyed while removing wrinkles from the film, so a widening device such as an expander roll, spiral roll, crown roll, cross guider, bend bar, etc. can be appropriately arranged. When these devices are used, they may be installed inside the dyeing tank 15 or at one or more of its inlet and outlet.

(Crosslinking step)
In the cross-linking step, the dyed polyvinyl alcohol-based resin film is treated with a treatment liquid containing a cross-linking agent to cross-link the polyvinyl alcohol-based resin and fix the adsorbed dichroic dye such as iodine in the resin ( cross-linking process). This step is usually performed by immersing the polyvinyl alcohol-based resin film after the dyeing step in a cross-linking tank 17 containing a treatment liquid containing a cross-linking agent.

The cross-linking agent can be, for example, boric acid. The treatment liquid containing the cross-linking agent can be an aqueous solution containing boric acid (boric acid treatment liquid). The boric acid treatment liquid can be an aqueous solution containing 0.5 to 15 parts by mass of boric acid with respect to 100 parts by mass of water. If the content of boric acid in the boric acid treatment solution is too low, it tends to be difficult to obtain a sufficient cross-linking effect, and dichroic dyes such as iodine are eluted from the polyvinyl alcohol resin film in the water washing process described later. As a result, the orthogonal hue of the polarizer tends to shift to blue. On the other hand, if the content of boric acid is too high, the contraction force in the direction of the absorption axis tends to increase under heating conditions, and the durability of the polarizing plate, especially in the heat cycle test, may decrease. . In the present invention, the content of boric acid in the boric acid treatment solution is preferably in the range of 1 to 3.5 parts by mass, particularly 2 to 3.5 parts by mass, per 100 parts by mass of water.

When the dichroic dye is iodine, the boric acid treatment liquid preferably contains iodide in addition to boric acid, and the amount thereof is usually 5 to 20 parts by mass, preferably 100 parts by mass of water. is 8 to 15 parts by mass. When the iodide content in the boration solution is low, the orthogonal hue of the polarizer tends to shift to blue. On the other hand, when the content of iodide increases, the cross-linking reaction by boric acid may be inhibited, and the orthogonal hue of the polarizer tends to shift to blue.

The iodide that can be contained in the boration solution can be potassium iodide, zinc iodide, or the like. Compounds other than iodide may coexist in the boric acid treatment solution, examples of which include zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, and the like. can be mentioned. Additionally, if desired, cross-linking agents other than boric acid, such as glyoxal, glutaraldehyde, etc., may be used with boric acid.

The cross-linking treatment is usually carried out at a temperature of 50-70°C, preferably 53-65°C. If the temperature is too low, the cross-linking reaction tends to proceed insufficiently. On the other hand, if the temperature is too high, the film tends to be cut during the cross-linking treatment, and the processing stability tends to decrease significantly. The time for the cross-linking treatment is usually 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 100 seconds.

In the cross-linking step, only one cross-linking tank may be provided as shown in FIG. 1, or two or more cross-linking tanks may be provided. When the cross-linking tank is composed of two tanks, they are referred to as the first cross-linking tank and the second cross-linking tank from the upstream side. The same is true when the cross-linking tanks are composed of three or more tanks. When the cross-linking tank is composed of two or more tanks, it is preferable that the concentration of boric acid in the upstream cross-linking tank is higher than that in the cross-linking tank installed thereafter.

A humidifying device can be arranged on the inlet side (upstream side) of the cross-linking tank 17 to perform the humidifying treatment. When the cross-linking baths are composed of two or more baths, each bath may be provided with a humidifying device, or only the first cross-linking bath may be provided with a humidifying device. By performing a moistening treatment in the cross-linking process, stress relaxation proceeds due to swelling before cross-linking, further stretching becomes possible, the degree of orientation is easily improved, and cross-linking occurs between molecules in the swollen polyvinyl alcohol-based resin film. A space for impregnating the agent is secured, and the degree of cross-linking tends to be easily improved.

The polyvinyl alcohol-based resin film may be uniaxially stretched during the cross-linking process. The stretching treatment, which will be described in detail below, is usually applied along the mechanical flow direction (conveyance direction). When the film is uniaxially stretched in the cross-linking step, the stretching ratio is preferably in the range of, for example, 1.2 to 3 times. The uniaxial stretching at this time may be performed in multiple stages using a plurality of sets of rolls arranged at intervals.

(Complementary color process)
Although not shown, complementary color processing for hue adjustment (complementary color) may be performed. The complementary color process of performing complementary color treatment can usually be performed after the cross-linking process. The complementary color treatment can be performed by immersing the polyvinyl alcohol resin film in a complementary color tank containing a treatment liquid containing a complementary color agent. The temperature of the treatment liquid contained in the complementary color bath is, for example, 10°C or higher and 65°C or lower, preferably 20°C or higher and lower than 60°C. When the dichroic dye is iodine, iodide can be used as a complementary colorant. The content of the cross-linking agent in the treatment liquid containing the complementary color agent is, for example, 1 to 5 parts by mass per 100 parts by mass of water. The content of iodide in the treatment liquid containing the complementary colorant is, for example, 3 to 30 parts by weight per 100 parts by weight of water. The temperature of the complementary color liquid in the complementary color process is preferably lower than the temperature of the cross-linking liquid in the cross-linking process.

In the complementary color process, only one complementary color tank may be provided, or two or more tanks may be provided. When the complementary color tank is composed of two tanks, the first complementary color tank and the second complementary color tank are referred to from the upstream side. The same is true when the complementary color baths are composed of three or more baths.

A humidifying device can be arranged on the inlet side (upstream side) of the complementary color tank 17 to perform the humidifying process. When the complementary color tank is composed of two or more tanks, a humidifying device may be arranged for each tank, or a humidifying device may be arranged only for the first complementary color tank.

(Washing process)
The washing step is performed to wash the polyvinyl alcohol-based resin film (washing treatment). Specifically, excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film are removed by this cleaning treatment.

The cleaning treatment is performed by immersing the polyvinyl alcohol-based resin film in a treatment liquid containing water contained in the cleaning tank 19 . Alternatively, the treatment liquid containing water may be sprayed onto the polyvinyl alcohol-based resin film as a shower in the washing tank. Pure water containing substantially no dissolved component is preferably used as the treatment liquid containing water. As for the conditions of the cleaning treatment, the temperature of the treatment solution is usually 2 to 40° C., and the treatment time is usually 2 to 120 seconds.

The washing process may be carried out in one step by arranging one washing tank as shown in FIG. 1, or may be carried out in a plurality of steps by arranging several washing tanks in series. If the washing process is performed in multiple steps, an aqueous solution of an inorganic salt may be used as one of the upstream treatment liquids. This inorganic salt can be selected from, for example, potassium iodide, sodium iodide, zinc iodide, zinc chloride, sodium sulfate, sodium sulfite, and the like. In addition, one type of these inorganic salts may be used alone, or a plurality of types may be used in combination.

A humidifying device can be arranged on the inlet side (upstream side) of the cleaning tank 19 to perform the humidifying process. When the cleaning tanks are composed of two or more tanks, each tank may be provided with a humidifying device, or only the first cleaning tank may be provided with a humidifying device.

In the washing step, it is preferable to apply tension to the polyvinyl alcohol-based resin film along its mechanical flow direction in order to transport the polyvinyl alcohol-based resin film while removing wrinkles from the film in the same manner as in the swelling step. The tension at that time is preferably 300 to 1000 N/m, for example.

As for the conveying speed of the polyvinyl alcohol-based resin film in the washing step, an optimum speed can be appropriately selected, and for example, the running speed can be 5 to 30 m/min. If the conveying speed of the polyvinyl alcohol-based resin film is higher than 30 m/min, the film tends to slip easily on the rolls, and problems such as difficulty in stable stretching tend to occur.

Moreover, you may perform a uniaxial stretching process during a washing process. In the case of stretching here, the stretching ratio can be, for example, 1.05 to 1.2 times.

(Other processes)
The method for producing a polarizer can further include, for example, a stretching step, a primary drying step, a final drying step, etc., in addition to the treatment steps described above.

(Stretching process)
The stretching step is for uniaxially stretching and orienting the polyvinyl alcohol-based resin film, and orienting iodine along the orientation direction, and is performed in the cross-linking step described above or at a stage earlier than that. . Specifically, the stretching step is performed during at least one of the swelling step, dyeing step and cross-linking step, or before any one of these steps. Uniaxial stretching in any one of the swelling step, the dyeing step and the cross-linking step can be carried out, for example, by a method of creating a peripheral speed difference between the transport roll on the inlet side of the tank and the transport roll on the outlet side of the tank. On the other hand, when uniaxial stretching is performed in a stage prior to the swelling process, dyeing process, or cross-linking process, wet stretching in which a stretching bath is provided before each process may be employed, or a method of stretching in air or a heated roll may be employed. Dry stretching, such as a method of stretching while being in contact with the film, may be employed.

The stretching treatment is preferably performed at least in the cross-linking step, more preferably in both the dyeing step and the cross-linking step, and more preferably in each of the swelling step, the dyeing step and the cross-linking step. When the stretching treatment is performed during these steps, the polyvinyl alcohol resin film is uniaxially stretched while being immersed in the treatment liquid in the tank. Referring to FIG. 1, when uniaxially stretching in the crosslinking step, it is carried out in the treatment liquid in the crosslinking tank 17. Similarly, in the dyeing step, when uniaxially stretching, it is in the treatment liquid in the dyeing tank 15. When the film is uniaxially stretched in the swelling step, it is carried out in the treatment liquid in the swelling tank 13 .

The polyvinyl alcohol resin film that has undergone all the stretching steps preferably has a final cumulative stretch ratio (total cumulative stretch ratio) of 4.5 to 8 times, preferably 5 to 7 times. is more preferable. Here, the integrated draw ratio means how long the reference length in the drawing axis direction of the raw film 10 wound around the delivery roll 11 has become in the film after all the drawing steps have been completed. . In addition to stretching in the boric acid treatment process, if the film is stretched in the swelling process or the dyeing process, the value also includes these stretches. For example, if the original film had a length of 1 m in the direction of the stretching axis and became 5 m after all the stretching processes were completed, the cumulative stretching ratio at this time would be 5 times.

(Primary drying process)
A primary drying step may be performed between the cross-linking step and the washing step as shown in FIG. This primary drying step is performed for the purpose of adjusting the proportion of water contained in the crosslinked polyvinyl alcohol-based resin film, that is, the moisture content.

As shown in FIG. 1, the film exiting the cross-linking tank 17 is led to a primary drying oven 21 where it is heated and subjected to primary drying. The heating at this time can be performed, for example, by blowing hot air onto the polyvinyl alcohol resin film, by directly contacting the polyvinyl alcohol resin film with a heat-generating member, or by irradiating the polyvinyl alcohol resin film with radiant energy. can.

In the case of blowing hot air, for example, a hot air nozzle for injecting hot air serves as a heating means, and the hot air may be directly injected from there to the polyvinyl alcohol resin film. According to this method, it is possible to dry the surface of the polyvinyl alcohol-based resin film while removing water from the surface with hot air, so that the surface of the film can be dried efficiently.

When the polyvinyl alcohol-based resin film is brought into direct contact with the heat-generating member, for example, a heated roll (heat roll) serves as a heating means, and the polyvinyl alcohol-based resin film is wound thereon to heat the film. According to this method, since the heat-generating member is brought into direct contact with the polyvinyl alcohol-based resin film, the heating temperature of the film can be made uniform, and uneven drying and the like are less likely to occur.

In the case of irradiation with radiant energy, for example, an infrared heater serves as a heating means, and by irradiating the polyvinyl alcohol resin film with radiant energy therefrom, the film itself may be heated and dried. According to this method, the polyvinyl alcohol-based resin film itself is heated and dried, so that the entire film including the inside thereof can be uniformly heated.

The above methods may be implemented singly or in combination of multiple different methods. Moreover, it is preferable to arrange the above heating means on both sides of the film so that both sides of the polyvinyl alcohol resin film can be dried.

Primary drying can be carried out in an ambient atmosphere (outside air), for example, by applying heat from a heater to the moving film, but in that case, the heating efficiency may be reduced by the outside air, or the turbulence of the outside air may occur. Due to uneven drying, etc. are likely to occur. In order to prevent such a problem, it is preferable to carry out the drying inside the primary drying furnace 21, as shown in FIG. In particular, the method using hot air or radiant energy is likely to be greatly affected by outside air, so it is preferable to perform the drying treatment in a closed system. However, when the influence of outside air is small, such as a method in which the film is brought into direct contact with a hot roll, etc., it is also possible to dry in an open system without closing the inside of the drying oven or providing the drying oven itself.

The drying temperature in the primary drying step is preferably 40 to 300°C, more preferably 50 to 100°C. The drying temperature can be defined as the temperature measured in the drying oven in a closed system as described above. In the case of an open system, it can be defined as the temperature of the heating means (heat roll, etc.) itself.

The drying time in the primary drying step is about 1 to 100 seconds, preferably 3 to 30 seconds. This drying time is the time from when the polyvinyl alcohol resin film enters the drying oven until it leaves the drying oven in the case of a closed system. It can be defined as the time from coming into contact with the heating means to leaving a position less susceptible to the heat of the heating means or coming out of contact with the heating means.

The primary drying process may be carried out in one step using one heating means, or may be carried out in a plurality of steps by continuously providing several heating means. When drying is performed in a plurality of stages, the drying temperature in each stage may be the same or different, but it is preferable to provide a temperature gradient so that the drying temperature increases in later drying stages.

(Final drying process)
The final drying step is performed to heat and dry the polyvinyl alcohol-based resin film after the water washing step in the drying oven 23 . As a result, the target polarizer 30 is obtained. As a drying treatment method performed in the final drying treatment, the methods mentioned in the primary drying step can be used.

The conditions for the final drying treatment are preferably a drying oven maintained at a temperature of 40 to 100° C., preferably 50 to 100° C., and a treatment time of about 30 to 600 seconds. The drying treatment may be performed using a plurality of drying ovens. In this case, the temperatures of the respective drying ovens may be the same or different, but it is preferable to provide a temperature gradient so that the temperature inside the ovens rises as the drying ovens progress toward the subsequent stages.

After the final drying process, the polarizer 30 is wound up on the winding roll 27 shown in FIG. and a polarizing plate in which a protective layer is formed on the surface of the polarizer 30 is manufactured.

(Polarizer)
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.

The degree of polarization of the polarizer may be, for example, 99.9800% or more, preferably 99.9900% or more, more preferably 99.9910% or more, still more preferably 99.9915% or more. The degree of polarization of the polarizer is usually 100% or less, practically less than 100%, and may be 99.9950% or less. The degree of polarization of the polarizer can be measured by the measurement method described in the Examples section below.

The luminous efficiency correction single transmittance of the polarizer (hereinafter also referred to as transmittance for simplicity) may be, for example, 43.0% or more, preferably 43.5% or more, and more preferably 43.9% or more. be. The transmittance is typically 50.0% or less, and may be, for example, less than 50.0% or 49.0% or less. The transmittance of the polarizer can be measured by the measurement method described in the Examples section below.

The single hue b value of the polarizer may range, for example, from 2.50 to 4.0, preferably from 2.55 to 3.0 or less. The crossed hue b value of the polarizer may be, for example, in the range -3 to 3, preferably in the range -2 to 2, more preferably in the range -1.5 to 1.5. Using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation), L*a*b* (CIE) colorimetry is performed using the color matching function of the C light source for the obtained transmittance. By calculating the chromaticity in the system, the single hue b value of the polarizer alone and the orthogonal hue b value of the polarizers arranged orthogonally can be obtained. The single hue b value and the orthogonal hue b value of the polarizer can be measured by the measurement method described in the Examples section below.

The degree of orientation of the polarizer may range, for example, from 0.100 to 0.300, preferably from 0.150 to 0.250, and more preferably from 0.200 to 0.220. The degree of orientation of the polarizer can be measured by the measurement method described in the Examples section below.

The degree of cross-linking of the polarizer may range, for example, from 5.00 to 6.00, preferably from 5.05 to 5.5. The degree of cross-linking of the polarizer can be measured by the measuring method described in the Examples section below.

A polarizing plate can be obtained by bonding a protective film to at least one surface of a polarizer with an adhesive layer interposed therebetween. Protective films include, for example, films made of acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose; films made of polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate-based resin films, cyclo Olefin-based resin films; acrylic-based resin films; and films made of linear olefin-based resins such as polypropylene-based resins.

In order to improve the adhesion between the polarizer and the protective film, the bonding surface of the polarizer and/or the protective film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. may be treated. The pressure-sensitive adhesive layer can be composed of an adhesive or pressure-sensitive adhesive.

A polarizing plate 60 shown in FIG. 2 has a polarizer 30, an adhesive layer 40, and a protective film 50 in this order. The polarizing plate may be a linear polarizing plate or a circular polarizing plate used in display devices. Any display device such as a liquid crystal display device or an organic EL display device may be used. The display device may be a display device used for mobile devices such as televisions, personal computers, mobile phones and tablet terminals.

The present invention will be described in more detail below with reference to examples. Unless otherwise specified, "%" and "parts" in the examples are mass % and mass parts.

<Evaluation test>
(1) Measurement of Polarization Degree After cutting the polarizers prepared in Examples and Comparative Examples into a size of 4 cm × 4 cm, the degree of polarization was evaluated with an ultraviolet-visible spectrometer (V-7100, manufactured by JASCO Corporation). . The degree of polarization (P) was determined by the following formula.
Degree of polarization (P)=[(T ₁ −T ₂ )/(T ₁ +T ₂ )] ^1/2 ×100
In the formula, _T1 is the parallel transmittance obtained when a pair of polarizers are arranged with their absorption axes parallel, and _T2 is the parallel transmittance obtained when a pair of polarizers are arranged with their absorption axes perpendicular to each other. is the orthogonal transmittance

(2) Measurement of Transmittance After cutting the polarizers produced in Examples and Comparative Examples into a size of 4 cm × 4 cm, the transmittance was evaluated with an ultraviolet-visible spectrometer (V-7100, manufactured by JASCO Corporation). .

(3) Measurement of hue (single b value and orthogonal hue b value) After cutting the polarizers prepared in Examples and Comparative Examples into a size of 4 cm × 4 cm, an ultraviolet-visible spectrometer (V-7100, JASCO Corporation) A single b value and an orthogonal hue b value were measured by a company).

(4) Measurement of degree of cross-linking After cutting the central part of the polarizer produced in Examples and Comparative Examples into a size of 10 cm × 10 cm, Fourier transform infrared spectrophotometer (FT-IR) (Nicolet 5700, Thermo Fisher Scientific company) was used to measure the degree of cross-linking. The measurement was performed using VeeMAX III (ATR) manufactured by Pike technologies as an FT-IR chip with 16 scans and a wave number resolution of 4 cm ⁻¹ . The sum of the areas (a) when the regions at wave numbers of 1200 to 1360 cm ⁻¹ in the measured IR data are combined on the basis of 3.2, and the sum of the areas when the regions at wave numbers of 2850 to 3000 cm ⁻¹ are combined on the same basis The average value of three values divided by (b) was taken as the degree of cross-linking. The region at wave numbers of 1200 to 1360 cm ⁻¹ represents the absorption derived from the stretching vibration of the B—O—C bond formed by bonding the polyvinyl alcohol resin and boric acid, and the region at wave numbers of 2850 to 3000 cm ⁻¹ is polyvinyl alcohol. It represents the absorption originating from the stretching vibration of the C—H bond contained in the resin. A higher degree of cross-linking indicates that the boron contained in the polarizer is cross-linked more efficiently.

(5) Measurement of Orientation Degree After cutting the central portion of the polarizer produced in Examples and Comparative Examples into a size of 10 cm × 10 cm, Fourier transform infrared spectrophotometer (FT-IR) (Nicolet 5700, Thermo Fisher Scientific (manufactured by Co., Ltd.) was used to measure the degree of orientation. The degree of orientation (S) was determined by the following formula.
Orientation (S) = (A _// -A _⊥ )/(A _// +2A _⊥ )
In the formula, A _// represents the absorbance at a wave number of 1290 cm ⁻¹ obtained when a pair of polarizers are arranged with their absorption axes parallel, and A _⊥ is a pair of polarizers arranged with their absorption axes orthogonal. It represents the absorbance at the wave number of 1290 cm ⁻¹ obtained when

<Example 1>
A transparent unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) having a thickness of 45 μm and a degree of saponification of 99.9% or more was immersed in water (deionized water) at 25° C. for 1 minute and 20 seconds to swell it. After (swelling step), it was dyed by immersing it in an aqueous solution for dyeing at 30°C containing 1.25 mM/L iodine, 1.25% by mass of potassium iodide, and 0.3% by mass of boric acid for 2 minutes and 30 seconds (dyeing process). process). At this time, stretching was performed at a draw ratio of 1.56 times and 1.96 times in the swelling step and the dyeing step, respectively, and drawing was performed so that the cumulative draw ratio up to the dyeing tank was 3.05 times.

Next, the film was immersed in a cross-linking aqueous solution containing 9% by mass of potassium iodide and 3% by mass of boric acid at 63° C. for 26 seconds for cross-linking (first cross-linking step), and was stretched at a draw ratio of 1.46 times. Furthermore, in the first cross-linking step, a humidifier (JINBANG industrial humidifier JB-620A) was installed at the entrance of the first cross-linking tank and moisture at a temperature of 25 ° C. and humidity of 90% RH or more was given at a spray rate of 3 L / h. .

After that, the film was immersed in a cross-linking aqueous solution containing 9% by mass of potassium iodide and 3% by mass of boric acid at 63° C. for 20 seconds to be cross-linked (second cross-linking step), while being stretched at a draw ratio of 1.34 times. .

Next, in the complementary color process, the film was stretched 1.00 times while being immersed in a complementary color aqueous solution containing 9% by mass of potassium iodide and 3% by mass of boric acid at 57° C. for 10 seconds. At this time, the total area draw ratio in the swelling process, the dyeing process, the cross-linking process and the complementary color process was set to 6.0 times. Thereafter, the film was washed with an aqueous solution at 13°C for 2 seconds to remove foreign matter adhering to the film surface, and dried at 92°C for 110 seconds to obtain a polarizer. An evaluation test was performed on the obtained polarizer. Table 1 shows the results.

<Example 2 and Comparative Example 1>
A polarizer was produced in the same manner as in Example 1 except that the humidifier used in Example 1 was installed at the position shown in Table 1. An evaluation test was performed on the obtained polarizer. Table 1 shows the results.

10 raw film of polyvinyl alcohol-based resin, 11 feeding roll, 12 nip roll, 13 swelling tank, 14 guide roll, 15 dyeing tank, 16 humidifying device, 17 cross-linking tank, 18 liquid surface, 19 cleaning tank, 21 primary Drying oven, 23 Final drying oven, 27 Winding roll, 30 Polarizer, 40 Adhesive layer, 50 Protective film, 60 Polarizing plate.

Claims (4)

A method for manufacturing a polarizer,
Including a treatment step of immersing the polyvinyl alcohol-based resin film in a treatment liquid to treat it,
A method for producing a polarizer, wherein in the treatment step, the polyvinyl alcohol resin film is subjected to a humidification treatment before being immersed in the treatment liquid. 2. The method of manufacturing a polarizer according to claim 1, wherein said treatment step is at least one selected from the group consisting of a dyeing step, a cross-linking step and a complementary color step. 2. The method of manufacturing a polarizer according to claim 1, wherein said treatment step is at least one selected from the group consisting of a dyeing step and a cross-linking step. The method for producing a polarizer according to any one of claims 1 to 3, wherein the humidifying treatment is performed by spraying air at a temperature of 25°C and a humidity of 90% RH or higher to the polyvinyl alcohol resin film.

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