KR20230087391A - Method for manufacturing polarizer - Google Patents

Abstract

An object of the present invention is to provide a method for producing a polarizer having a good color (orthogonal color b value) of the polarizer and an improved degree of crosslinking.
As a method for producing a polarizer, a dyeing treatment step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, a crosslinking treatment step of crosslinking the polyvinyl alcohol-based resin film after the dyeing treatment step with a crosslinking agent, and after the crosslinking treatment step A complementary color treatment step of performing a complementary color treatment on a polyvinyl alcohol-based resin film using a complementary treatment liquid, and a washing treatment step of performing a cleaning treatment on the polyvinyl alcohol-based resin film after the complementary color treatment using a cleaning treatment liquid. Including, after performing at least one of the complementary color treatment and the washing treatment, and before removing the treatment liquid for complementary color or the treatment liquid for cleaning attached to the polyvinyl alcohol-based resin film, the polyvinyl alcohol-based resin film is kept at a temperature of 20 ° C. or less. The manufacturing method of the polarizer which performs the cooling process exposed in the atmosphere of.

Description

Manufacturing method of polarizer {METHOD FOR MANUFACTURING POLARIZER}

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

Patent Literature 1 discloses a method of manufacturing a polarizer by performing a washing treatment and a drying treatment after performing a dyeing treatment, a crosslinking treatment and an stretching treatment on a long polyvinyl alcohol-based resin film.

[Patent Document 1] Japanese Unexamined Patent Publication No. 2012-477999

An object of the present invention is to provide a method for producing a polarizer having a neutral color (orthogonal color b value close to 0).

The present invention provides a method for manufacturing the following polarizer.

[1] As a method for producing a polarizer,

A dyeing treatment step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye;

A crosslinking treatment step of crosslinking the polyvinyl alcohol-based resin after the dyeing treatment step with a crosslinking agent;

A complementary color treatment step of performing a complementary color treatment on the polyvinyl alcohol-based resin film after the crosslinking treatment step using a treatment liquid for a complementary color;

A cleaning treatment step of performing a cleaning treatment on the polyvinyl alcohol-based resin film after the complementary color treatment using a treatment liquid for cleaning.

including,

After performing at least one of the complementary color treatment and the washing treatment, and before removing the treatment liquid for complementary color or the treatment liquid for cleaning adhering to the polyvinyl alcohol-based resin film, the polyvinyl alcohol-based resin film is heated at a temperature. The manufacturing method of light polarizer which performs the cooling process to expose in 20 degreeC or less atmosphere.

[2] The method for producing a polarizer according to [1], in which the cooling treatment is performed after performing the complementary color treatment and before removing the treatment liquid for complementary colors.

[3] The manufacturing method of the polarizer according to [1] or [2], in which the cooling treatment is performed after performing the washing treatment and before removing the treatment liquid for cleaning.

[4] The method for producing a polarizer according to any one of [1] to [3], in which the treatment liquid for complementary colors or the treatment liquid for washing is removed by passing the polyvinyl alcohol-based resin film through a nip roll.

According to the present invention, a method for manufacturing a polarizer having a neutral color can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows the arrangement example of the apparatus in the manufacturing method of a polarizer.
2 is a schematic cross-sectional view of a polarizing plate including a polarizer.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described referring drawings, this invention is not limited to the following embodiment. In all of the following drawings, each component is shown with appropriately adjusted scales for easy understanding, and the scale of each component shown in the drawings and the scale of the actual component do not necessarily match.

<Method for manufacturing polarizer>

A method for producing a polarizer includes a dyeing treatment step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, a crosslinking treatment step of crosslinking the polyvinyl alcohol-based resin after the dyeing treatment step with a crosslinking agent, and a polyvinyl alcohol-based resin film after the crosslinking treatment step. A complementary color treatment step of performing a complementary color treatment on a vinyl alcohol-based resin film using a complementary treatment liquid, and a washing treatment step of performing a cleaning treatment on the polyvinyl alcohol-based resin film after the complementary color treatment process using a cleaning treatment liquid. Including, after performing at least one of the complementary color treatment and the washing treatment, and before removing the treatment liquid for complementary color or the treatment liquid for cleaning attached to the polyvinyl alcohol-based resin film, the polyvinyl alcohol-based resin film is 20 ° C. or less A cooling treatment is performed to expose it to an atmosphere at a temperature of .

In the polarizer, a dichroic dye (iodine or dichroic dye) is adsorbed and oriented on a polyvinyl alcohol-based resin film uniaxially stretched. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying polyvinyl acetate-based resin. The saponification degree is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and other monomers copolymerizable therewith other than polyvinyl acetate which is a homopolymer of vinyl acetate. As another monomer which can be copolymerized, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids etc. are mentioned, for example. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1000 to 10000, preferably 1500 to 5000.

These polyvinyl alcohol-based resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes can also be used.

In the present invention, an unstretched polyvinyl alcohol-based resin film (original film) having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less is used as a starting material for polarizer production. Thereby, it is possible to obtain a thin film polarizer for which the market demand is gradually increasing. The raw film may be a polyvinyl alcohol-based resin film previously subjected to a stretching treatment in a gas phase.

The width of the raw film is not particularly limited, and may be, for example, 300 to 6000 mm, but the larger the film width, the easier it is to break the film during the stretching process.

In the present invention, the raw film is prepared as a roll (original roll) of a long unstretched polyvinyl alcohol-based resin film.

The manufacturing method of the polarizer continuously conveys a long unstretched polyvinyl alcohol-based resin film along the film conveyance path of the polarizer manufacturing device, and performs a dyeing treatment step, a crosslinking treatment step, a complementary color treatment step, and a washing treatment step described later. By doing, it can manufacture continuously as a long polarizer. The manufacturing method of the polarizer further includes the unwinding step of unwinding the above-described elongated raw film from the original roll, the swelling treatment step of taking out the raw film after immersing it in a swelling bath, and drying the polarizer after the washing treatment. can do. In addition, between each process (namely, before any one or more processes, after any one or more processes, and/or during any one or more processes), a wet or dry uniaxial stretching treatment can be performed.

Referring to FIG. 1, a method for manufacturing a polarizer will be described in more detail. 1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizer and a polarizer manufacturing apparatus used therein. The polarizer manufacturing apparatus shown in FIG. 1 conveys the original (unstretched) film 10 made of polyvinyl alcohol-based resin along the film conveyance route while continuously unwinding it from the original roll 11, thereby conveying the film conveyance path. It is configured to pass through a swelling bath 13, a dyeing bath 15, a crosslinking bath 17, a complementary color bath 19, a washing bath 21, and a drying furnace 23 installed thereon. Arrows in Fig. 1 indicate the transport direction of the film.

In the polarizer manufacturing apparatus shown in FIG. 1, between the liquid level 18 of the treatment liquid for the complementary color contained in the complementary color bath 19 and the nip roll 12 installed on the outlet side (downstream side) of the complementary color bath 19, An apparatus 16 for performing a cooling process is disposed. Although not shown, an apparatus for performing a cooling process is combined with or instead of the apparatus 16 for performing a cooling process shown in FIG. Between the nip rolls 12 installed on the exit side (downstream side) of the bath 21, a device for performing a cooling treatment may be disposed. The cooling treatment will be described later.

In FIG. 1, the obtained polarizer 30 can be conveyed as it is, for example to the next polarizing plate manufacturing process (process of bonding a protective film on one side or both surfaces of the polarizer 30).

1 shows an example in which one set of each of a swelling bath 13, a dyeing bath 15, a crosslinking bath 17, a complementary color bath 19, a washing bath 21, and a drying furnace 23 is installed. , If necessary, any one or more treatment baths (swelling bath 13, dyeing bath 15, crosslinking bath 17, complementary color bath 19, and cleaning bath 21) installed on the film transport path A bath containing a treatment liquid for processing a polyvinyl alcohol-based resin film is collectively referred to as a "treatment bath") and two or more drying furnaces may be provided. In this specification, the liquid accommodated in the treatment bath is also referred to as a treatment liquid.

The treatment bath may be equipped with a liquid removal means for removing the treatment liquid from the polyvinyl alcohol-based resin film treated with the treatment liquid so as not to carry the treatment liquid to the next step. As a liquid removal means, a nip roll etc. are mentioned, for example. When the liquid removal means is a nip roll, for example, a nip roll is installed on the outlet side (downstream side) of the treatment bath, and the polyvinyl alcohol-based resin film drawn out from the treatment liquid is pressed and clamped with the nip roll, so that the polyvinyl alcohol-based resin The treatment liquid adhering to the film can be removed.

In addition to the treatment bath and the drying furnace, the film transport path of the polarizer manufacturing device supports the film transported or presses and clamps the guide roll 14 that can change the film transport direction and the transported film, It can be constructed by arranging at an appropriate position a nip roll 12 capable of imparting a driving force by rotation to the film or changing the film transport direction. Guide rolls and nip rolls can be placed before and after each treatment bath and each drying furnace or in the treatment bath, whereby the film can be introduced into and immersed in the treatment bath and taken out of the treatment bath. For example, the film can be immersed in each treatment bath by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls.

In the polarizer manufacturing apparatus shown in FIG. 1, nip rolls are disposed at the inlet (upstream side) and outlet (downstream side) of each treatment bath (nip rolls 12), and thereby the film taken out from the treatment bath Adhering treatment liquid can be removed. In addition, in one or more treatment baths, it is possible to perform roll-to-roll stretching in which vertical uniaxial stretching is performed with a difference in circumferential speed between the nip rolls disposed before and after the treatment bath. Hereinafter, each process is demonstrated.

(Swelling treatment process)

The swelling treatment step is performed for purposes such as removal of foreign matter on the surface of the raw film 10, removal of plasticizers in the raw film 10, provision of dyeability, plasticization of the raw film 10, and the like. The treatment conditions are determined within a range in which the above object can be achieved and in a range in which problems such as extreme dissolution or devitrification of the raw film 10 do not occur.

Referring to FIG. 1 , in the swelling treatment step, the raw film 10 is continuously unwound from the raw roll 11, conveyed along the film transport path, and the raw film 10 is accommodated in the swelling bath 13 It can be carried out by immersing in the treatment liquid for swelling for a predetermined period of time and then taking it out. In the example of FIG. 1 , from unwinding the raw film 10 to immersion in the swelling bath 13, the raw film 10 is constructed by the guide rolls 14 and the nip rolls 12 It is conveyed along the film conveyance route. In the swelling process, it is conveyed along the film conveyance route built by the guide roll 14.

As the treatment liquid for swelling, in addition to pure water, boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, It is also possible to use an aqueous solution in which alcohols or the like are added in the range of 0.01 to 10% by mass.

The temperature of the treatment liquid for swelling is, for example, 10 to 50°C, preferably 10 to 40°C, and more preferably 15 to 30°C. The immersion time of the raw film 10 is preferably 10 to 300 seconds, more preferably 20 to 200 seconds. In the case where the raw film 10 is a polyvinyl alcohol-based resin film previously stretched in a substrate, the temperature of the treatment liquid for swelling is, for example, 20 to 70°C, preferably 30 to 60°C. The immersion time of the raw film 10 is preferably 30 to 300 seconds, more preferably 60 to 240 seconds.

In the swelling treatment, the problem that the raw film 10 swells in the width direction and wrinkles are formed in the film tends to occur. As one means for conveying the film while removing these wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as a guide roll, or a cloth guider, bend bar, tenter clip and It is possible to use or use other widening devices such as Another means for suppressing the occurrence of wrinkles is to perform stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 using the difference in circumferential speed of two nip rolls.

In the swelling treatment, since the film swells and expands also in the conveying direction of the film, when the film is not actively stretched, in order to eliminate the sagging of the film in the conveying direction, for example, a nip disposed before and after the swelling bath 13 It is preferable to devise means, such as controlling the speed of a roll. In addition, for the purpose of stabilizing the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, or EPC device (Edge Position Control device: detects the end of the film, It is also useful to use a device that prevents meandering) or the like.

In the example shown in FIG. 1 , the film taken out from the swelling bath 13 passes through the nip rolls of the swelling bath 13 and is introduced into the dyeing bath 15 .

(Dyeing treatment process)

The dyeing treatment step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol-based resin film after the swelling treatment. Dyeing treatment conditions are determined within a range capable of achieving the above object and within a range in which problems such as extreme dissolution or devitrification of the film do not occur. Referring to FIG. 1, in the dyeing treatment step, the film after the swelling treatment is conveyed along the film conveyance path constructed by the guide roll and the nip roll, and the dyeing treatment liquid containing the dichroic dye contained in the dyeing bath 15 It can be carried out by immersing in for a predetermined time and then pulling it out. In order to enhance the dyeability of the dichroic dye, it is preferable that the film subjected to the dyeing treatment step is a film subjected to at least a certain degree of uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or the uniaxial stretching treatment before the dyeing treatment. In addition, it is preferable to perform uniaxial stretching treatment at the time of dyeing treatment.

In the case of using iodine as the dichroic dye, for example, an aqueous solution having a concentration of iodine/potassium iodide/water = 0.003 to 0.3/0.1 to 10/100 in mass ratio can be used as the treatment liquid for dyeing. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described later in that iodine is included, and if the aqueous solution contains 0.003 parts by mass or more of iodine with respect to 100 parts by mass of water, it can be regarded as a dyeing bath 15. there is. The temperature of the dyeing bath 15 when the film is immersed is usually 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the immersion time of the film is usually 30 to 600°C. seconds, preferably 60 to 300 seconds.

In the case of using a water-soluble dichroic dye as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye/water = 0.001 to 0.1/100 in mass ratio can be used as the treatment liquid for dyeing. The dyeing bath 15 may coexist with a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surface active agent. As for the dichroic dye, only 1 type may be used independently, and two or more types of dichroic dye may be used together. The temperature of the treatment liquid for dyeing when the film is immersed is, for example, 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually 30 to 600 seconds, preferably 60 to 300 seconds.

As described above, in the dyeing treatment step, the film can be uniaxially stretched in the dyeing bath 15. Uniaxial stretching of the film can be performed by a method such as providing a difference in circumferential speed between nip rolls disposed before and after the dyeing bath 15.

Also in the dyeing treatment step, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles of the film similarly to the swelling treatment step, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as a guide roll, Other widening devices such as cloth guiders, bend bars and tenter clips may or may not be used. Another means for suppressing the occurrence of wrinkles is to perform the stretching treatment similarly to the swelling treatment.

In the example shown in FIG. 1 , the film drawn out from the dyeing bath 15 passes through the nip rolls 12 and is introduced into the crosslinking bath 17 .

(Crosslinking process)

The crosslinking treatment step is a treatment performed for the purpose of water resistance by crosslinking or the like. Referring to Fig. 1, the crosslinking treatment is carried out along a film conveyance path constructed by guide rolls and nip rolls, and the film after dyeing treatment is placed in a crosslinking treatment solution containing a crosslinking agent contained in a crosslinking bath 17. It can be implemented by immersing for a period of time and drawing it out continuously. As a crosslinking agent, boric acid etc. are mentioned, for example.

The treatment liquid for crosslinking may be an aqueous solution containing, for example, 1 to 10 parts by mass of boric acid per 100 parts by mass of water. When the dichroic dye used in the dyeing treatment is iodine, the treatment liquid for crosslinking preferably contains iodide in addition to boric acid, and the amount can be, for example, 1 to 30 parts by mass with respect to 100 parts by mass of water. As iodide, potassium iodide, zinc iodide, etc. are mentioned. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the crosslinking treatment, depending on the purpose, the concentrations of boric acid and iodide and the temperature of the treatment liquid for crosslinking can be appropriately changed. For example, when the purpose of the crosslinking treatment is water resistance by crosslinking, and the polyvinyl alcohol-based resin film is subjected to swelling treatment, dyeing treatment, and crosslinking treatment in this order, the concentration of the crosslinking agent-containing liquid in the crosslinking bath is the mass ratio It may be an aqueous solution of boric acid/iodide/water = 3 to 10/1 to 20/100. If necessary, instead of boric acid, other crosslinking agents such as glyoxal or glutaraldehyde may be used, or boric acid and other crosslinking agents may be used in combination. The temperature of the crosslinking bath when immersing the film is usually 50 to 70°C, preferably 53 to 65°C, and the immersion time of the film is usually 10 to 600 seconds, preferably 20 to 300 seconds, more preferably is 20 to 200 seconds. In the case where the dyeing treatment and the crosslinking treatment are performed in this order on the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment, the temperature of the crosslinking bath 17 is usually 50 to 85° C., preferably 55 to 80° C. is °C.

The crosslinking treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinking bath to be used may be the same or different as long as they are within the above ranges. Crosslinking treatment may be performed in a plurality of steps, respectively.

The uniaxial stretching treatment can also be performed in the crosslinking bath 17 using the difference in circumferential speed of the two nip rolls.

Also in the crosslinking treatment step, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles of the film similarly to the swelling treatment step, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as a guide roll, Other widening devices such as cloth guiders, bend bars and tenter clips may or may not be used. Another means for suppressing the occurrence of wrinkles is to perform the stretching treatment similarly to the swelling treatment step.

In the example shown in FIG. 1 , the film drawn out from the crosslinking bath 17 passes through the nip rolls 12 and is introduced into the complementary color bath 19 .

(Complementary color treatment process)

The complementary color processing step is a step of performing processing for color adjustment (complementary color). The complementary color treatment can be performed by immersing the polyvinyl alcohol-based resin film in the treatment liquid for complementary colors contained in the complementary color bath 19 . Iodide and boric acid can be used as a color complement.

For example, when iodine is used as a dichroic dye, a treatment liquid for complementary colors having a mass ratio of boric acid/iodide/water = 1 to 5/3 to 30/100 in concentration can be used. The temperature of the complementary color treatment liquid at the time of immersing the film is usually 10 to 45°C, and the immersion time of the film is usually 1 to 300 seconds, preferably 2 to 100 seconds. The temperature of the complementary color treatment liquid is preferably lower than the temperature of the crosslinking treatment liquid.

As shown in FIG. 1, a device for performing a cooling treatment is disposed between the liquid level 18 of the complementary color processing liquid and the nip roll 12 on the exit side (downstream side) of the complementary color bath 19, so that the liquid level ( 18) and the nip roll 12, the cooling process can be performed with respect to the polyvinyl alcohol-type resin film. When the number of complementary baths is composed of two or more, the cooling process may be performed for each complementary color bath, the cooling process may be performed only in the first complementary color bath, or the cooling process may be performed only in the last complementary color bath. After performing the complementary color treatment, by performing the cooling treatment before removing the treatment liquid for complementary color, the orthogonal color b value tends to be good. Moreover, there exists a tendency for the polarizer with improved degree of crosslinking to become easy to obtain. After performing the complementary color treatment, it is preferable to perform the cooling treatment before removing the treatment liquid for complementary color.

The complementary color treatment may be performed plural times, for example, 2 to 5 times. In this case, the composition and temperature of each complementary color treatment liquid to be used may be the same or different as long as they are within the above ranges.

The uniaxial stretching process can also be performed in the complementary color bath 19 using the difference in circumferential speed of the two nip rolls.

Also in the complementary color treatment step, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles of the film similarly to the swelling treatment step, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as a guide roll, Other widening devices such as cloth guiders, bend bars and tenter clips may or may not be used. Another means for suppressing the occurrence of wrinkles is to perform the stretching treatment similarly to the swelling treatment step.

In the example shown in FIG. 1 , the film taken out from the complementary color bath 19 passes through the nip rolls 12 and is introduced into the cleaning bath 21 .

(cleaning treatment process)

The manufacturing method of the polarizer may include a cleaning treatment step after the complementary color treatment step. Washing treatment is performed for the purpose of removing chemicals such as excess boric acid and iodine adhering to the polyvinyl alcohol-based resin film. In the cleaning treatment, for example, the polyvinyl alcohol-based resin film after the complementary color treatment is immersed in the cleaning treatment liquid contained in the cleaning bath 21, or the cleaning treatment liquid is sprayed on the film in the cleaning bath 21 as a shower. , or by using them in combination.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 21 to perform cleaning treatment. The temperature of the cleaning treatment liquid in the washing treatment is usually 2 to 40°C, and the time for performing the washing treatment is usually 2 to 120 seconds.

Although not shown, a device for performing a cooling treatment is disposed between the liquid level of the cleaning treatment liquid and the nip rolls 12 on the exit side (downstream side) of the cleaning bath 21, so that between the liquid level and the nip rolls 12 In this, a cooling treatment can be performed on the polyvinyl alcohol-based resin film. When there are two or more washing baths, the cooling treatment may be performed for each washing bath, the cooling treatment may be performed only for the first washing bath, or the cooling treatment may be performed only for the last washing bath.

In addition, in the washing treatment step, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as a guide roll, or a cloth guider or bend Other widening devices, such as bars and tenter clips, may be used or may be used. Further, in the washing treatment step, stretching treatment may be performed in order to suppress generation of wrinkles.

(cooling treatment process)

In the manufacturing method of the polarizer, after performing at least either one of a complementary color treatment and a washing treatment, before removing the treatment liquid for complementary colors or the treatment liquid for washing adhering to the polyvinyl alcohol-based resin film, the polyvinyl alcohol-based resin film is 20 A cooling treatment is performed by exposure to an atmosphere at a temperature of °C or lower. By performing such a cooling process, the color of the obtained polarizer (orthogonal color b value) tends to be neutral. Moreover, there exists a tendency for the crosslinking degree of the polarizer obtained to improve easily.

Conventionally, in the manufacturing method of a polarizer, the degree of crosslinking in a polyvinyl alcohol-type resin film increases by heat-drying performed in the drying process after washing process, and polyvinyl alcohol and polyiodine ion ( _I3- ^, _I5- ⁾ A complex of was formed, and the color of the polarizer (orthogonal color b value) tended to become neutral. By the present inventors, after performing at least either one of a complementary color treatment and a washing treatment, by performing the cooling treatment before removing the treatment liquid for complementary colors or the treatment liquid for washing adhering to the polyvinyl alcohol-based resin film, the light polarizer It was found that the degree of crosslinking increased and the color of the polarizer (orthogonal color b value) tended to become neutral.

The cooling treatment may be a treatment of lowering the temperature of the polyvinyl alcohol-based resin film immediately after performing at least one of the complementary color treatment and the washing treatment, for example, immediately after being taken out of the treatment liquid. As a method of performing the cooling treatment, for example, a method of spraying temperature-controlled air to the polyvinyl alcohol-based resin film, a method of passing air through a temperature-controlled furnace, and the like are exemplified. As an apparatus which performs a cooling process, a blower, a cooling furnace, etc. are mentioned, for example. Among them, a blower is preferable from the viewpoints of ease of installation and handling. In the case of performing a cooling treatment in which the polyvinyl alcohol-based resin film is exposed to an atmosphere at a temperature of 20 ° C. or less, for example, compared to the case of cooling by spraying cold water on the polyvinyl alcohol-based resin film, iodine in the polyvinyl alcohol-based resin film Leakage can be easily prevented.

An apparatus for performing the cooling treatment may be disposed, for example, between the liquid level of the treatment liquid contained in the treatment bath and the means for removing the treatment liquid. As a means for removing the treatment liquid, the aforementioned nip roll may be used.

In the cooling treatment, the temperature of the atmosphere for exposing the polyvinyl alcohol-based resin film (hereinafter also referred to as exposure temperature) is lower than the temperature of the polyvinyl alcohol-based resin film immediately after performing at least either one of the complementary color treatment and the washing treatment. The temperature may be any temperature, preferably 19°C or lower, more preferably 10°C or lower, and may be, for example, 3°C or higher. The exposure temperature may be, for example, 0.5°C or more lower than the temperature of the polyvinyl alcohol-based resin film immediately after performing at least one of the complementary treatment and the washing treatment, preferably 1°C or more, and more preferably 2°C or more. It is a temperature lower than °C, more preferably a temperature lower than 5 °C.

When the device performing the cooling treatment is a blower, the air velocity of the air sprayed onto the polyvinyl alcohol-based resin film is preferably 0.1 m/s or more, more preferably 0.5 m/s or more, and still more preferably 1.5 m/s or more and, for example, 5 m/s or less. The angle between the air blown out from the blower and the transport direction of the polyvinyl alcohol-based resin film is preferably 0 ° or more and 90 ° or less, from the viewpoint of reducing damage caused by wind pressure to the polyvinyl alcohol-based resin film, It is more preferable that it is 0° or more and 60° or less.

When the device that performs the cooling treatment is a blower, the temperature of air ejected from the blower can be regarded as the exposure temperature.

The time for performing the cooling treatment is preferably 10 seconds or more, more preferably 30 seconds or more, for example, 100 seconds or less, and preferably 50 seconds or less.

(stretching treatment process)

As described above, the raw film 10 is wet or dry between the series of treatment steps (that is, before any one or more treatment steps, after any one or more treatment steps, and / or during any one or more treatment steps). It is treated with uniaxial stretching. A specific method of uniaxial stretching treatment is, for example, inter-roll stretching in which vertical uniaxial stretching is performed by setting a difference in circumferential speed between two nip rolls constituting the film transport path (eg, two nip rolls disposed before and after the treatment bath), Japan It may be hot roll stretching, tenter stretching, etc. as described in Patent No. 2731813, preferably inter-roll stretching. The uniaxial stretching treatment process can be performed over a plurality of times until obtaining the polarizer 30 from the raw film 10 . As described above, the stretching treatment is also advantageous for suppression of wrinkling of the film.

The final cumulative stretching ratio of the polarizer 30 based on the raw film 10 is usually 4.5 to 7.0 times, preferably 5.0 to 6.5 times.

The stretching treatment step may be performed in any of the above treatment steps as long as it is before the drying step, and even when the stretching treatment is performed in two or more treatment steps, the stretching treatment may be performed in any treatment step.

(Drying process)

In the drying treatment step, the polyvinyl alcohol-based resin film is dried in a drying furnace 23 after the washing treatment. The drying treatment temperature is, for example, 80°C or higher, preferably 85°C or higher, and more preferably 90°C or higher. The drying treatment temperature is, for example, 120°C or lower.

As a method of drying treatment, for example, a hot air dryer, an infrared heater, or a method of drying by using these in combination is exemplified. The drying treatment time is preferably 10 seconds or longer, more preferably 30 seconds or longer, for example, 200 seconds or shorter, and preferably 150 seconds or shorter.

The polarizer 30 that has undergone the drying treatment process is stored as it is wound around the winding roll 27 shown in FIG. 1 as needed, or is supplied as it is to the next step of attaching a protective film without being wound up here, and the polarizer ( 30) to a polarizing plate with a protective layer formed on the surface.

(polarizer)

The thickness of the polarizer is usually 65 μm or less, preferably 50 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less. The thickness of the polarizer is usually 2 μm or more, preferably 5 μm or more, and more preferably 10 μm or more. The thickness of the polarizer can be controlled by, for example, selection of a polyvinyl alcohol-based resin film, adjustment of a draw ratio, and the like.

The orthogonal hue b value of the polarizing film may, for example, be in the range of -3.0 to 3.0, preferably -2.5 to 2.6 or less, more preferably -2.0 to 2.0, still more preferably -1.5 to 1.5, Especially preferably, it is the range of -1.2 to 1.2. Using a spectrophotometer having an integrating sphere (“V7100” manufactured by Nippon Bunko Co., Ltd.), the chromaticity in the L*a*b* (CIE) colorimetric system was calculated using the isochromatic function of the C light source for the obtained transmittance. By calculating, the orthogonal color b value which orthogonally arrange|positioned the polarizing film is obtained. The orthogonal color b value of the polarizer is obtained by a measuring method described in the section of Examples described later. When the b value of the orthogonal hue of the polarizer is within the above range, the orthogonal hue of the polarizer tends to be closer to neutral gray.

The boric acid content in the polarizer may be, for example, 3 to 4% by mass based on the mass of the polarizer, preferably 3.4 to 3.8% by mass, more preferably 3.5 to 3.75% by mass, still more preferably 3.55 to 3.7% by mass. . Boric acid content in a polarizer is measured by the method demonstrated in the section of the Example mentioned later.

The degree of crosslinking of the polarizer may be, for example, in the range of 5 to 6, preferably in the range of 5.05 to 5.5, and more preferably in the range of 5.1 to 5.3. The crosslinking degree of a polarizer is measured by the measuring method demonstrated in the column of the Example mentioned later.

A polarizing plate can be obtained by bonding a protective film to at least one surface of a polarizer through an adhesive layer. As the protective film, for example, a film containing an acetyl cellulose-based resin such as triacetyl cellulose or diacetyl cellulose; films containing polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate-based resin films, cycloolefin-based resin films; acrylic resin film; A film containing a chain-shaped olefin resin of a polypropylene resin is exemplified.

In order to improve the adhesiveness between the polarizer and the protective film, surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, and saponification treatment may be performed on the bonding surface of the polarizer and/or the protective film. The pressure-sensitive adhesive layer can be composed of an adhesive or a pressure-sensitive adhesive.

The 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 a display device. The display device may be anything such as a liquid crystal display device and an organic EL display device. The display device may be a display device used for mobile devices such as televisions, personal computers, mobile phones, and tablet terminals.

[Example]

Hereinafter, the present invention will be described in more detail by examples. "%" and "part" in the example are mass % and mass part unless otherwise specified.

<Evaluation test>

(1) Measurement of color (orthogonal color b value)

After cutting the polarizer produced in Examples and Comparative Examples to a size of 4 cm × 4 cm, the orthogonal color b value was measured with an ultraviolet and visible ray spectrometer (V-7100, manufactured by Nippon Bunko Co., Ltd.).

(2) Measurement of boron content in polarizer

0.2 g of polarizer was dissolved in 200 g of 1.9% by mass mannitol aqueous solution. The obtained aqueous solution was titrated with 1 mol/L NaOH aqueous solution, and the boron content (mass %) of the polarizer was calculated by comparing the amount of NaOH solution required for neutralization with a calibration curve. The results are shown in Table 1.

(3) Measurement of degree of crosslinking

After cutting the central part of the polarizer produced in Examples and Comparative Examples to a size of 10 cm × 10 cm, the crosslinking degree was measured using a Fourier Transform Infrared Spectrophotometer (FT-IR) (Nicolet 5700, manufactured by Thermo Fisher Scientific) measured. The measurement was performed using a VeeMAX III (ATR) manufactured by Pike technologies as an FT-IR tip at a frequency of 16 scans and a wavenumber resolution of 4 cm ^-1 . The sum (a) of the areas when the area at the wave number of 1200 to 1360 cm ^-1 in the measured IR data is set to the standard of 3.2, and the area at the wave number from 2850 to 3000 cm ^-1 is set to the same standard The average value of three times of the value divided by the sum (b) of the area at the time was taken as the degree of crosslinking. The region at the wave number of 1200 to 1360 cm ^-1 represents absorption derived from the stretching vibration of the BOC bond formed by bonding the polyvinyl alcohol resin and boric acid, and the region at the wave number 2850 to 3000 cm ^-1 represents the polyvinyl alcohol resin shows the absorption derived from the stretching vibration of the CH bond included in . The higher the value of the degree of crosslinking, the boron contained in the polarizer is used for crosslinking, and it can be considered that the crosslinking is progressing efficiently.

<Example 1>

A transparent unstretched polyvinyl alcohol-based film (VF-TS#4500, manufactured by Kuraray Co., Ltd.) having a thickness of 45 μm and a degree of saponification of 99.9% or more was immersed in pure water (deionized water) at 25 ° C. for 1 minute and 20 seconds to swell ( swelling treatment process). Then, it dyed by immersing for 2 minutes and 30 seconds in the 30 degreeC aqueous solution for dyeing containing 1.25 mM/L of iodine, 1.25 mass % of potassium iodide, and 0.3 mass % of boric acid (dyeing process). At this time, stretching was performed at a stretch ratio of 1.56 times and 1.96 times in the swelling treatment step and the dyeing treatment step, respectively, and stretching was performed so that the cumulative draw ratio to the dyeing bath was 3.05 times.

Subsequently, it is immersed in an aqueous solution for crosslinking at 63 ° C. containing 9% by mass of potassium iodide and 3% by mass of boric acid for 26 seconds and crosslinked (first crosslinking treatment step), and then stretched at a draw ratio of 1.46, and then potassium iodide 9 Stretching was performed at a draw ratio of 1.34 times while being immersed for 20 seconds in an aqueous solution for crosslinking at 63°C containing 3% by mass and 3% by mass of boric acid for crosslinking (second crosslinking treatment step).

Subsequently, in the complementary color treatment step, it was stretched 1.00 times while being immersed for 10 seconds in a 43°C aqueous solution for a complementary color containing 9% by mass of potassium iodide and 4% by mass of boric acid. At this time, the total cumulative stretching ratio in the swelling treatment, dyeing treatment, crosslinking treatment, and complementary color treatment was set to 6.0 times. After the film is immersed in the complementary aqueous solution, and the film whose temperature has reached a temperature close to that of the complementary aqueous solution is taken out of the complementary aqueous solution, before removing the complementary aqueous solution from the film using a nip roll, a blower is used to blow the film. Air at a temperature of 5°C was sprayed. Thereafter, water washing was performed for 2 seconds with pure water at 13°C to remove foreign matter adhering to the film surface (washing treatment step). Then, it was made to dry at 92 degreeC for 110 second, the film was dried, and the polarizer was obtained. An evaluation test was done about the obtained polarizer. The results are shown in Table 1.

<Examples 2 to 7 and Comparative Examples 1 to 4>

Except having changed the position and temperature of the cooling process performed in Example 1 to the position and temperature shown in Table 1, it carried out similarly to Example 1, and produced the polarizer. An evaluation test was done about the obtained polarizer. The results are shown in Table 1.

10: Raw film of polyvinyl alcohol-based resin 11: Feeding roll
12: nip roll 13: swelling tank
14: guide roll 15: dyeing tank
16: Cooling treatment device 17: Crosslinking tank
18: face value 19: complementary tone
21: washing tank 23: drying furnace
27: winding roll 30: polarizer
40: adhesive layer 50: protective film
60: polarizer

Claims (4)

As a method for producing a polarizer,
A dyeing treatment step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye;
A crosslinking treatment step of crosslinking the polyvinyl alcohol-based resin film after the dyeing treatment step with a crosslinking agent;
A complementary color treatment step of performing a complementary color treatment on the polyvinyl alcohol-based resin film after the crosslinking treatment step using a treatment liquid for a complementary color;
A cleaning treatment step of performing a cleaning treatment on the polyvinyl alcohol-based resin film after the complementary color treatment using a treatment liquid for cleaning.
including,
After performing at least one of the complementary color treatment and the washing treatment, and before removing the treatment liquid for complementary color or the treatment liquid for cleaning adhering to the polyvinyl alcohol-based resin film, the polyvinyl alcohol-based resin film is heated at a temperature. The manufacturing method of the polarizer which performs the cooling process to expose in 20 degreeC or less atmosphere. The method for manufacturing a polarizer according to claim 1, wherein the cooling treatment is performed after performing the complementary color treatment and before removing the treatment liquid for complementary colors. The manufacturing method of the light polarizer of Claim 1 or 2 which the said cooling process is performed after performing the said washing process, and before removing the said process liquid for cleaning. The manufacturing method of the polarizer according to any one of claims 1 to 3, wherein the treatment liquid for complementary color or the treatment liquid for cleaning is removed by passing the polyvinyl alcohol-based resin film through a nip roll.

Images