KR20230059745A - Method for manufacturing polarizer - Google Patents

Abstract

This invention provides the method which can manufacture the polarizer which can fully improve a single transmittance even if it reduces humidification time when it uses in a humidification process.
A method for manufacturing a polarizer according to an embodiment of the present invention includes: a first dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic substance; An extending step of extending the polyvinyl alcohol-based resin film after the first dyeing step in an aqueous solution of boric acid; A second dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic substance while eluting boric acid from the polyvinyl alcohol-based resin film after the stretching step is included.

Description

Manufacturing method of polarizer {METHOD FOR MANUFACTURING POLARIZER}

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

A polarizer is typically used for the image display device. Such a polarizer is manufactured by, for example, dyeing a polyvinyl alcohol-based resin film with a dichroic substance and then stretching the polyvinyl alcohol-based resin film in an aqueous solution of boric acid.

In recent years, improvement in the optical properties of polarizers has been increasingly demanded. Accordingly, a technique for humidifying the polarizer to improve the degree of polarization of the polarizer has been proposed (for example, Patent Document 1). However, with the technique described in Patent Literature 1, room for improvement remains in the improvement of the single transmittance of the polarizer.

Japanese Unexamined Patent Publication No. 2012-78780

The present invention has been made to solve the above conventional problems, and its main object is to provide a method for manufacturing a polarizer capable of sufficiently improving single transmittance even if the humidification time is reduced when applied to the humidification process. is to provide

In the method for manufacturing a polarizer according to an embodiment of the present invention, a first dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic substance; an extending step of stretching the polyvinyl alcohol-based resin film after the first dyeing step in an aqueous solution of boric acid; While eluting boric acid from the polyvinyl alcohol-type resin film after the said extending|stretching process, the 2nd dyeing process of dyeing the said polyvinyl alcohol-type resin film with a dichroic substance is included.

In one embodiment, in the polyvinyl alcohol-type resin film after the said 2nd dyeing process, a boric acid content rate is 10 mass % or less, and single transmittance is 35 % or less.

In one embodiment, the method for manufacturing the polarizer further includes a humidification step of humidifying the polyvinyl alcohol-based resin film after the second dyeing step under an atmosphere of a temperature of 40 ° C. to 100 ° C. and a humidity of 50% RH or higher. .

In one embodiment, the humidification time in the humidification process is 60 minutes or less.

In one embodiment, the manufacturing method of the said polarizer applies the coating liquid containing a polyvinyl alcohol-type resin and a halide on a long thermoplastic resin base material, and the polyvinyl alcohol-type resin layer as a polyvinyl alcohol-type resin film and a laminate manufacturing step of manufacturing a laminate provided with the thermoplastic resin substrate; an auxiliary stretching step of air-stretching the layered product; the first dyeing step; the stretching step; the second dyeing process; A drying shrinkage step of shrinking the polyvinyl alcohol-based resin film after the second dyeing step in the width direction orthogonal to the long direction is included in this order while conveying the polyvinyl alcohol-based resin film in the long direction.

In one embodiment, the humidifying process is performed after the heat shrinking process.

In one embodiment, in the said 2nd dyeing process, the polyvinyl alcohol-type resin film after the said extending|stretching process is immersed in the 2nd dyeing liquid containing a dichroic substance. The concentration of the dichroic substance in the second dyeing solution is 0.8% by mass or less, and the immersion time in the second dyeing step is 5 minutes or less.

ADVANTAGE OF THE INVENTION According to embodiment of this invention, when it uses for a humidification process, even if it reduces humidification time, the polarizer which can fully improve single transmittance can be manufactured.

1 is a schematic diagram for explaining a method for manufacturing a polarizer according to one embodiment of the present invention.
Fig.2 (a) is a schematic cross-sectional view of one embodiment of the polyvinyl alcohol-type resin film shown in FIG. Fig. 2(b) is a schematic cross-sectional view of another embodiment of the polyvinyl alcohol-based resin film shown in Fig. 1 .
3 is a graph showing the relationship between single transmittance and polarization degree in Examples and Comparative Examples.
4 is a graph showing the relationship between humidification time and single transmittance in Examples and Comparative Examples.

Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Outline of manufacturing method of polarizer

A method for manufacturing a polarizer according to one embodiment of the present invention includes: a first dyeing step of dyeing a polyvinyl alcohol-based resin film (hereinafter referred to as a PVA-based resin film) with a dichroic substance; Extending process of extending|stretching the PVA system resin film after a 1st dyeing process in boric acid aqueous solution; While eluting boric acid from the PVA-based resin film after the stretching step, a second dyeing step of dyeing the PVA-based resin film with a dichroic substance is included.

The present inventors discovered that the single transmittance could be sufficiently improved by sufficiently humidifying the PVA-based resin film after the stretching step. However, the problem that a remarkably long humidification time is required for sufficient improvement of single transmittance, and the manufacturing efficiency of a polarizer falls has arisen.

From this point, the present inventors perform a second dyeing step with respect to the PVA-based resin film after the stretching step, sufficiently reduce the content of boric acid in the PVA-based resin film after the second dyeing step, and sufficiently increase the single transmittance. When reduced, it was discovered that the single transmittance of the polarizer could be sufficiently improved with a remarkably short humidification time, and the present invention was completed.

More specifically, in the second dyeing step, the content ratio of boric acid in the PVA-based resin film after the second dyeing step (specifically, the PVA-based resin film after the second dyeing step and immediately before the humidification step) and the single transmittance, respectively It can be adjusted so that it becomes below the upper limit below.

The content of boric acid in the PVA-based resin film after the second dyeing step is, for example, 10% by mass or less, preferably 9.0% by mass or less, more preferably 7.0% by mass or less, still more preferably 4.0% by mass or less, particularly Preferably it is 1.0 mass % or less. The content ratio of boric acid in the PVA system resin film after a 2nd dyeing process is 0.1 mass % or more typically.

The single transmittance of the PVA-based resin film after the second dyeing step is, for example, 35% or less, preferably 25% or less, and more preferably 20% or less. The single transmittance of the PVA-based resin film after the second dyeing step is typically 1% or more.

In the PVA-based resin film after the second dyeing step, if the content of boric acid is less than the upper limit above and the single transmittance is less than or equal to the upper limit above, when the PVA-based resin film after the second dyeing step is subjected to the humidification step, moisture is added to the PVA It can penetrate smoothly into the system resin film and also can smoothly elute the dichroic substance from the PVA system resin film. Therefore, even if the humidification time is reduced, the single transmittance of the PVA-based resin film (ie, polarizer) after humidification can be efficiently improved.

In one embodiment, the manufacturing method of a light polarizer further includes the bridge|crosslinking process which makes the PVA system resin film after a 1st dyeing process contact boric acid aqueous solution before an extending process. When the PVA-type resin film after the 1st dyeing process is brought into contact with boric-acid aqueous solution, it can stably suppress that a PVA-type resin film melt|dissolves in boric-acid aqueous solution in an extending process. Specifically, boric acid generates tetrahydroxyboric acid anion in aqueous solution and crosslinks by hydrogen bonding with PVA-based resin, or cross-linking by dehydrating and condensing with hydroxyl groups of PVA-based resin to form boric acid esters. can do. As a result, water resistance can be imparted to the PVA-based resin film.

In one embodiment, the manufacturing method of the polarizer further includes a humidifying step of humidifying the PVA-based resin film after the second dyeing step under an atmosphere of a temperature of 40°C to 100°C and a humidity of 50% RH or more. The humidification temperature is, for example, 50°C or higher, preferably 60°C or higher, more preferably 70°C or higher, still more preferably 80°C or higher, and, for example, 90°C or lower. Preferably it is 50 degreeC - 90 degreeC. The humidification humidity is preferably 70%RH or more, more preferably 80%RH or more, and is typically 100%RH or less, preferably 95%RH or less.

When the PVA-type resin film after the 2nd dyeing|staining process is humidified in said atmosphere and a polarizer is manufactured, the fall of the polarization degree of a polarizer can be suppressed, being able to aim at the improvement of the single transmittance of a polarizer.

In one embodiment, the humidification time in the humidification step is, for example, 120 minutes or less, preferably 80 minutes or less, more preferably 60 minutes or less, still more preferably 40 minutes or less, even more particularly preferably 20 minutes or less, Especially preferably, it is 10 minutes or less, and most preferably 5 minutes or less. If the humidification time is less than or equal to such an upper limit, it is possible to stably improve the manufacturing efficiency of the polarizer.

Further, the humidification time in the humidification step is typically 30 seconds or longer, preferably 1 minute or longer. If the humidification time is more than this lower limit, it is possible to stably improve the single transmittance and polarization degree of the polarizer.

In one embodiment, a manufacturing method of a polarizer includes a layered product manufacturing process; an auxiliary stretching step; The first dyeing step described above; the stretching step described above; The second dyeing process described above; The drying shrinkage process is included in this order. In the laminate production step, a coating liquid containing a PVA-based resin and a halide is applied onto a long thermoplastic resin substrate to produce a laminate comprising a PVA-based resin layer as a PVA-based resin film and a thermoplastic resin substrate. In the auxiliary stretching step, the laminate is stretched in the air. In the drying shrinkage step, the PVA-based resin film after the second dyeing step is shrunk in the transverse direction orthogonal to the elongate direction while being conveyed in the elongate direction.

According to this method, it is possible to provide a polarizer having excellent optical properties as a polarizer having a reduced thickness. That is, by introducing the auxiliary drawing step, even when the PVA-based resin is applied on the thermoplastic resin, it becomes possible to increase the crystallinity of the PVA-based resin and achieve high optical properties. In addition, by simultaneously increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration in the orientation of the PVA-based resin and dissolution when immersed in water in a subsequent dyeing step or drawing step, thereby achieving high optical properties. it becomes possible to do Further, in the case where the PVA-based resin layer is immersed in a liquid, disorder of the orientation of PVA-based resin molecules and decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristics of the polarizer obtained through the processing process performed by immersing a layered product in liquid, such as a dyeing process and an extending process, can be improved. In addition, the optical properties of the polarizer can be improved by shrinking the PVA-based resin film in the width direction according to the drying shrinkage step.

The manufacturing method of said light polarizer may include a swelling process and/or a hue adjustment process.

In the swelling process, typically, the PVA-based resin film before the first dyeing process is immersed in a swelling bath (swelling liquid). Thereby, foreign matter on the surface of the PVA-based resin film can be removed, and the plasticizer in the PVA-based resin film can be removed. Further, the swelling liquid is preferably a boric acid aqueous solution containing boric acid. When the swelling liquid is a boric acid aqueous solution, water resistance can be imparted to the PVA-based resin film. In this case, the swelling process is called an insolubilization process.

In the hue adjustment step, typically, the PVA-based resin film after the second dyeing step is immersed in a hue adjustment bath (color adjustment liquid) before the humidification step. Accordingly, the PVA-based resin film can be washed, and the polarizer can be adjusted to have a desired color.

B. Details of the manufacturing method of the polarizer

1 is a schematic diagram for explaining a method for manufacturing a polarizer according to one embodiment of the present invention. In the manufacturing method of the polarizer of an illustration, said swelling process (insolubilization process), a 1st dyeing process, a crosslinking process, an extending process, a 2nd dyeing process, a hue adjustment process, and a drying shrinkage process are performed continuously.

More specifically, the elongated PVA-based resin film 1 is conveyed from the original roll 21 toward the take-up roll 22, and between the original roll 21 and the take-up roll 22 , a swelling process (insolubilization process), a 1st dyeing process, a crosslinking process, an extending process, a 2nd dyeing process, a hue adjustment process, and a drying shrinkage process are performed with respect to the PVA-type resin film 1 in order. In one embodiment, the PVA-based resin film 1 is a swelling bath 2A (swelling liquid), a first dyeing bath 2B' (first dyeing liquid), crosslinking by a plurality of rollers 24 Immersed in bath 2C (crosslinking liquid), drawing bath 2D (stretching liquid), second dye bath 2B'' (second dyeing liquid), and color adjustment bath 2E (color adjustment liquid) in this order After that, it is conveyed so as to pass through the heating and drying unit 23. Further, although described later in detail, when a PVA-based resin film is included in the laminate, the laminate containing the PVA-based resin film is immersed in each of the above baths (each liquid) to bring the PVA-based resin film into contact with each liquid .

After that, the humidification process described above is performed after the drying shrinkage process.

B-1. PVA-based resin film

In the original roll 21, the PVA-based resin film 1 (hereinafter referred to as the raw film 11) before each of the above steps is performed is wound into a roll shape.

The crystallization index of the PVA-based resin in the raw film 11 is, for example, 1.4 or higher, preferably 1.6 or higher, and more preferably 1.8 or higher. The crystallization index of the PVA-based resin is typically 3.0 or less. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer.

The raw film 11 may be a single layer resin film as shown in FIG. 2(a), or a thermoplastic resin substrate 12 (hereinafter referred to as the resin substrate 12) as shown in FIG. 2(b). .) may be laminated.

Specific examples of the single-layer resin film include hydrophilic polymer films such as PVA-based films, partially formalized PVA-based films, ethylene-vinyl acetate copolymer-based partially saponified films, dehydrated products of PVA and dehydrochlorinated products of polyvinyl chloride, etc. A polyene type orientation film is mentioned.

When the raw film 11 is a single-layer resin film, its thickness is, for example, 20 μm or more, preferably 30 μm or more, and, for example, 65 μm or less, preferably 60 μm or less.

When the raw film 11 is laminated on the thermoplastic resin substrate 12, the raw film 11 may be a PVA-based resin film supported on the resin substrate 12, or a PVA-based resin film applied to the resin substrate 12. The resin layer 13 may be sufficient.

In the case where the original film 11 is the PVA-based resin layer 13 coated and formed on the resin substrate 12, the PVA-based resin layer 13 is formed on the resin substrate 12 by the above-described laminate production process.

More specifically, a PVA-based resin layer (13) by applying a coating liquid containing a PVA-based resin and a halide onto the elongated resin substrate 12 by any suitable method and drying it at, for example, 50° C. or higher as necessary. ) and the resin base material 12, the laminate 10 is produced.

Any suitable material can be employed as the constituent material of the resin substrate 12 . As a constituent material of the resin base material, typically, an amorphous (non-crystallized) polyethylene terephthalate-based resin is exemplified, and preferably an amorphous (hardly crystallized) polyethylene terephthalate-based resin is exemplified. Specific examples of the amorphous polyethylene terephthalate-based resin include a copolymer further containing isophthalic acid as dicarboxylic acid and a copolymer further containing cyclohexanedimethanol as glycol.

The glass transition temperature (Tg) of the resin substrate is, for example, 170°C or lower, preferably 120°C or lower. The ductility of a laminated body can fully be ensured, being able to suppress crystallization of a PVA system resin layer as Tg of a resin base material is below the said upper limit. In addition, the glass transition temperature (Tg) of the resin substrate is typically 60°C or higher. Accordingly, problems such as deformation of the resin substrate (for example, unevenness, sagging, and wrinkles) during application and drying of the coating liquid to the resin substrate can be suppressed. In addition, the glass transition temperature (Tg) is measured according to JIS K 7121.

The thickness of the resin substrate before stretching is, for example, 20 μm or more, preferably 50 μm or more, and, for example, 300 μm or less, preferably 200 μm or less.

The surface of the resin substrate may be subjected to any suitable surface treatment (for example, corona treatment) or may have an easily bonding layer formed thereon. Thereby, the adhesiveness of a resin base material and a PVA system resin layer can be improved.

The coating liquid is typically a solution in which a PVA-based resin and a halide are dissolved in a solvent.

Arbitrary appropriate resins can be employed as the PVA-based resin. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%, still more preferably 99.0 mol% to 99.5 mol%. is mol%. The degree of saponification can be measured according to JIS K 6726-1994. A thin polarizing film with excellent durability can be obtained by using a PVA-based resin having such a degree of saponification. When the degree of saponification is too high, there is a possibility of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average polymerization degree is, for example, 1000 or more, preferably 1500 or more, more preferably 2000 or more, still more preferably 3000 or more, and is, for example, 10000 or less, preferably 6000 or less, still more preferably 4300 or less. In addition, the average degree of polymerization can be measured according to JIS K 6726-1994.

The PVA-based resin may contain acetoacetyl-modified PVA in one embodiment. The content of acetoacetyl-modified PVA in the PVA-based resin is, for example, 5% by mass or more, preferably 8% by mass or more, and, for example, 20% by mass or less, preferably 12% by mass or less. When the PVA-based resin contains acetoacetyl-modified PVA, the mechanical strength of the polarizer can be improved.

The content ratio of the PVA-based resin in the coating liquid is, for example, 3 parts by mass to 20 parts by mass with respect to 100 parts by mass of the solvent. With such a resin concentration, a uniform coating film in close contact with the resin substrate can be formed.

As the halide, any suitable halide can be employed. Representative examples of the halide include iodide and sodium chloride. As iodide, potassium iodide, sodium iodide, and lithium iodide are mentioned, for example, Potassium iodide is mentioned preferably.

The content of the halide in the coating liquid is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, and, for example, 20 parts by mass or less, preferably 15 parts by mass or less, based on 100 parts by mass of the PVA-based resin. When the content ratio of the halide is in such a range, it can suppress that the light polarizer finally obtained is clouded.

Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. . These may be used alone or in combination. Among the solvents, water is preferably used.

You may mix|blend additives with a coating liquid. As an additive, a plasticizer and surfactant are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants.

The thickness of the PVA-based resin layer formed from such a coating liquid before stretching is, for example, 3 μm or more, preferably 5 μm or more, and, for example, 40 μm or less, preferably 30 μm or less.

In addition, the laminate 10 provided with the PVA-based resin layer 13 and the resin substrate 12 is preferably subjected to the above-described auxiliary stretching step in advance, and is air-stretched at the above-described stretching ratio in the elongated direction. . That is, the auxiliary stretching process is performed after the laminate production process and before the first dyeing process, and in the illustrated example, it is performed after the laminate production process and before the swelling process.

The stretching temperature in the auxiliary stretching step is typically higher than the glass transition temperature (Tg) of the PVA-based resin, such as 95°C or higher, preferably 120°C or higher. The stretching temperature in the auxiliary stretching step is typically 150°C or lower.

The stretch ratio of the layered product in the auxiliary stretching step is 2.1 times or more, preferably 2.3 times or more. If the draw ratio of the laminate is at least this lower limit, the orientation of the PVA-based resin layer included in the laminate can be improved, and the melting of the PVA-based resin layer in the stretching bath can be stably suppressed in the stretching step. In addition, the upper limit of the draw ratio of the layered product in the auxiliary stretching step is typically 4 times or less.

The aerial stretching method in the auxiliary stretching step may be fixed-end stretching (eg, stretching using a tenter stretching machine), or free-end stretching (eg, a method of uniaxially stretching a laminate by passing it between rolls having different circumferential speeds) ) may be

B-2. Swelling process (insolubilization process)

The above-described raw film 11 (raw film alone or included in a laminate) is subjected to the above-described swelling step (insolubilization step) before the first dyeing step as needed. Below, the PVA-based resin film subjected to the swelling process (insolubilization process) is used as the swelling-treated film 1a.

In the swelling step, typically, the raw film 11 is immersed in a swelling liquid (swelling bath). The swelling liquid may be pure water or a boric acid aqueous solution. When the swelling liquid is an aqueous solution of boric acid (ie, insolubilization liquid), the content of boric acid in the insolubilization liquid is, for example, 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of water.

The temperature of the swelling bath is, for example, 10°C or higher, preferably 20°C or higher, and, for example, 60°C or lower, preferably 50°C or lower. The immersion time in the swelling step is, for example, 10 seconds or more, preferably 20 seconds or more, and, for example, 200 seconds or less, preferably 60 seconds or less.

B-3. 1st dyeing process

In the first dyeing step, the PVA-based resin film 1 (preferably the swelling treated film 1a) is dyed with a dichroic substance. Specifically, the first dye solution is brought into contact with the PVA-based resin film 1 (preferably the swelling treated film 1a) to adsorb the dichroic substance. Below, the PVA-type resin film after a 1st dyeing process and before an extending process is made into 1st dyeing film 1b'.

Examples of the dichroic substance include iodine and organic dyes. The dichroic substances may be used alone or in combination. Among the dichroic substances, iodine is preferably used.

The first staining solution is typically an iodine aqueous solution. The content of iodine in the first dye solution is, for example, 0.05 parts by mass or more, preferably 0.5 parts by mass or more, and, for example, 3 parts by mass or less, based on 100 parts by mass of water.

The first dye solution preferably further contains an iodine compound. When the first dye solution contains an iodine compound, the solubility of iodine in water can be improved.

Examples of the iodine compound include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. An iodine compound can be used individually or in combination. Among the iodine compounds, potassium iodide is preferably used.

The mass ratio (iodine:iodine compound) of iodine and the iodine compound in the first dye solution is, for example, 1:5 to 1:20, preferably 1:5 to 1:10. Accordingly, excellent optical properties can be imparted to the polarizer.

In the 1st dyeing process of an illustration, the PVA system resin film 1 (swelling treatment film 1a) is immersed in the said 1st dyeing bath.

The temperature of the first dyeing bath is, for example, 10°C or higher, preferably 20°C or higher, and, for example, 50°C or lower, preferably 40°C or lower. The immersion time (first dyeing time) in the first dyeing step is, for example, 5 seconds or more, preferably 30 seconds or more, and, for example, 300 seconds or less, preferably 90 seconds or less.

Moreover, when the 1st dyeing process is performed continuously after the said insolubilization process, there exists a possibility that boric acid may mix from an insolubilization bath to a 1st dyeing bath. When boric acid is mixed in the 1st dyeing bath, the boric acid concentration of the 1st dyeing bath changes with time, and it may affect the content ratio of boric acid in a polarizer. Therefore, the content of boric acid in the first dyeing bath is preferably adjusted to be 4 parts by mass or less with respect to 100 parts by mass of water.

In addition, the adsorption method of the dichroic substance in the 1st dyeing process is not limited to the above-mentioned immersion. For example, the first dye solution may be applied to a raw film, or the first dye solution may be sprayed onto a raw film.

B-4. cross-linking process

In a bridge|crosslinking process, the 1st dyeing film 1b' is made to contact boric acid aqueous solution as a bridge|crosslinking liquid before an extending|stretching process. Typically, the first dyed film 1b' is immersed in boric acid aqueous solution (crosslinking bath). Below, what was given the bridge|crosslinking process among the 1st dyeing films 1b' is set as the crosslinked film 1c.

The content of boric acid in the crosslinking liquid is, for example, 1 part by mass or more, preferably 3 parts by mass or more, and, for example, 10 parts by mass or less, preferably 8 parts by mass or less, with respect to 100 parts by mass of water.

The crosslinking liquid preferably further contains the above iodine compound. When the crosslinking liquid contains an iodine compound, it can suppress elution of iodine adsorbed to the first dyeing film.

The content of the iodine compound in the crosslinking liquid is, for example, 0.1 parts by mass or more, preferably 1 part by mass or more, and, for example, 8 parts by mass or less, preferably 5 parts by mass or less, based on 100 parts by mass of water. The mass ratio of boric acid to iodine compound (boric acid:iodine compound) in the crosslinking liquid is, for example, 1:1 to 1:3, preferably 1:1.5 to 1:2.

The temperature of the crosslinking bath is, for example, 20°C or higher, preferably 30°C or higher, and, for example, 60°C or lower, preferably 50°C or lower. The immersion time in the crosslinking step is, for example, 5 seconds or more, preferably 10 seconds or more, and, for example, 200 seconds or less, preferably 60 seconds or less.

B-5. stretching process

In the stretching step, the first dyed film 1b' (preferably the crosslinked film 1c) is stretched in a boric acid aqueous solution as a stretching bath in a long direction. When the 1st dyeing film is extended|stretched in boric acid aqueous solution, it can suppress that a 1st dyeing film dissolves in boric acid aqueous solution. Below, the PVA-based resin film after the stretching process and before the second dyeing process is used as the stretched film 1d.

The draw ratio in the stretching process differs depending on whether or not the auxiliary stretching process is performed on the raw film. When the raw film is not subjected to the auxiliary stretching step (that is, when the raw film is a single-layer resin film or a resin film supported by a resin substrate), the draw ratio in the stretching step is, for example, 4.5 times or more and 7 times. or less, preferably 5 times or more and 6.5 times or less.

When the auxiliary stretching step is performed on the raw film (ie, when the raw film is a PVA-based resin layer applied and formed on a resin substrate), the stretching ratio in the stretching step is, for example, 1.5 times or more and 4 times or less, preferably. It is more than 1.5 times and less than 3 times. Further, the product of the draw ratio in the auxiliary stretching step and the draw ratio in the stretching step is, for example, 4.5 times or more and 7 times or less, and preferably 5 times or more and 6.5 times or less.

Extremely excellent optical properties can be imparted to the polarizer by stretching at the above stretching ratio.

The content of boric acid in the stretching solution (boric acid aqueous solution) is, for example, 0.5 parts by mass or more, preferably 0.7 parts by mass or more, and, for example, 5 parts by mass or less, preferably 3 parts by mass or less, based on 100 parts by mass of water. .

The concentration of boric acid in the stretching liquid (boric acid aqueous solution) is, for example, 5% by mass or less, preferably 3% by mass or less, and more preferably 1.5% by mass or less. If the concentration of boric acid in the stretching liquid is below the upper limit above, the content of boric acid in the polarizer before the humidification step can be stably reduced even if the second dyeing time is reduced as described later. Therefore, the improvement of the manufacturing efficiency of a polarizer can be aimed at. In addition, the concentration of boric acid in the stretching liquid is typically 0.1% by mass or more, preferably 3% by mass or less.

The stretching liquid preferably further contains the above-described iodine compound. When the stretching liquid contains an iodine compound, elution of iodine adsorbed to the first dyed film can be suppressed.

The content of the iodine compound in the stretching liquid is, for example, 0.1 parts by mass or more, preferably 1 part by mass or more, and, for example, 10 parts by mass or less, preferably 6 parts by mass or less, based on 100 parts by mass of water. The mass ratio (boric acid:iodine compound) of boric acid and iodine compound in the stretching liquid is, for example, 1:0.5 to 1:1.2, preferably 1:0.6 to 1:1.

The temperature of the stretching bath is, for example, 40°C or higher, preferably 60°C or higher, and, for example, 85°C or lower, preferably 80°C or lower, and more preferably 65°C or lower. If the temperature of the stretching bath is equal to or less than the above upper limit, even if the concentration of boric acid in the stretching bath is equal to or less than the above upper limit, it is possible to stably suppress the melting of the PVA-based resin layer in the stretching bath. The immersion time in the stretching step is, for example, 15 seconds or more and 300 seconds or less.

B-6. 2nd dyeing process

In the second dyeing step, boric acid is eluted from the stretched film 1d, and the stretched film 1d is dyed with the dichroic substance described above. Specifically, while bringing the second dye solution into contact with the stretched film 1d to elute boric acid from the stretched film 1d, the stretched film 1d is adsorbed with a dichroic substance. Below, the PVA system resin film after a 2nd dyeing|staining process is made into 2nd dyeing|staining film 1b''.

The second staining solution is explained similarly to the first staining solution described in section B-3. The concentration of the dichroic substance (iodine) in the second staining solution is, for example, 5% by mass or less, preferably 2% by mass or less, and more preferably 0.8% by mass or less. If the concentration of the dichroic substance in the second dyeing solution is equal to or less than the above upper limit, the humidification time can be shortened even if the immersion time (second dyeing time) in the second dyeing step is equal to or less than the upper limit described later. In addition, the concentration of the dichroic substance (iodine) in the second staining solution is typically 0.1% by mass or more, preferably 0.2% by mass or more.

In the second dyeing step of the illustrated example, the stretched film 1d is immersed in the second dyeing bath.

The temperature of the second dye bath is, for example, 10°C or higher, preferably 20°C or higher, and, for example, 50°C or lower, preferably 40°C or lower.

The immersion time (second dyeing time) in the second dyeing step is, for example, 30 seconds or more, preferably 1 minute or more, and, for example, 300 minutes or less, preferably 200 minutes or less, more preferably 60 minutes or less, still more preferably It is preferably 30 minutes or less, particularly preferably 5 minutes or less. If the immersion time in the second dyeing step is more than this lower limit, boric acid can be stably eluted from the stretched film, and the stretched film can be sufficiently dyed. If the immersion time in a 2nd dyeing|staining process is below such an upper limit, the improvement of the manufacturing efficiency of a light polarizer can be aimed at stably.

B-7. color adjustment process

In the hue adjustment process, the 2nd dyeing film 1b'' is typically immersed in a hue adjustment bath (color adjustment liquid). Below, what to which the color adjustment process was performed among the 2nd dyeing films is made into the color adjustment film 1e.

The color adjusting liquid is typically an iodine compound aqueous solution. The iodine compound aqueous solution is a solution in which the above iodine compound is dissolved in water.

The content of the iodine compound in the color adjusting liquid is, for example, 0.5 parts by mass or more, preferably 2 parts by mass or more, and, for example, 10 parts by mass or less, preferably 6 parts by mass or less, with respect to 100 parts by mass of water.

The color adjusting solution is substantially free of boric acid. In this specification, "substantially not containing boric acid" means that boric acid is not intentionally introduced into the color adjusting bath, and more specifically means that the concentration of boric acid in the color adjusting solution is 0.1% by mass or less.

The temperature of the color adjusting bath is, for example, 0°C or higher, preferably 10°C or higher, and, for example, 40°C or lower, preferably 30°C or lower. The immersion time in the color adjustment step is, for example, 5 seconds or more, preferably 10 seconds or more, and is, for example, 200 seconds or less, preferably 60 seconds or less.

B-8. drying shrinkage process

In the drying shrinkage step, typically, the second dyed film 1b'' (preferably the color adjustment film 1e) is heated while being conveyed in the elongate direction. Hereinafter, among the second dyed films, those subjected to the drying shrinkage step are referred to as the drying shrinkage film 1f. In one embodiment, the range of boric acid content and single transmittance in the dry shrink film 1f is the range of boric acid content and single transmittance of the PVA-based resin film after the second dyeing step described above. Same with

In the illustrated example, the drying shrinkage process is performed by the heat drying unit 23 . The heating and drying unit may be a zone heating system in which the entire inside of the heating and drying unit is heated, or a heating roll drying system in which a conveying roll is heated. The heat drying unit preferably uses both of them.

The internal temperature of the heating and drying unit is, for example, 70°C or higher, preferably 80°C or higher, and, for example, 120°C or lower, preferably 100°C or lower.

The surface temperature of the heating roll is, for example, 60°C or higher, preferably 70°C or higher, and, for example, 100°C or lower, preferably 80°C or lower.

By drying using a heating roll, the heating curl of the PVA system resin film (laminate) can be effectively suppressed, and a light polarizer excellent in appearance can be efficiently manufactured. Further, in the drying shrinkage step, the PVA-based resin film shrinks in the width direction orthogonal to the elongate direction.

The shrinkage rate in the width direction of the PVA-based resin film in the drying shrinkage step is, for example, 2% or more, preferably 4% or more. If the shrinkage rate in the width direction is at least this lower limit, the orientation properties of PVA and PVA/dichroic substance complexes (iodine complexes) can be improved, and the optical properties of the polarizer can be improved.

The shrinkage rate of the PVA-based resin film in the width direction is typically 10% or less, preferably 8% or less, and more preferably 6% or less. If the shrinkage rate in the width direction is less than or equal to such an upper limit, occurrence of appearance defects such as wrinkles in the polarizer can be suppressed.

After that, the second dyed film 1b'' (preferably the dry shrinkage film 1f) is rolled up as needed to constitute the winding roll 22.

B-9. Humidification process

In a humidification process, typically, the 2nd dyeing|staining film (layered product containing a 2nd dyeing|staining film) once rolled up is left still in said atmosphere for said humidification time.

In addition, the range of the content rate of boric acid in the 2nd dyeing|dying film immediately before a humidification process is the same as the range of the content rate of boric acid in the PVA system resin film after the said 2nd dyeing process. In addition, the range of the single transmittance (initial single transmittance) of the stretched film immediately before the humidification step is the same as the range of the single transmittance of the PVA-based resin film after the above-described second dyeing step. The polarization degree (initial polarization degree) of the stretched film immediately before the humidification step is, for example, 98.0% or more, preferably 99.5% or more, more preferably 99.8% or more. The 2nd dyeing film immediately before the humidification process may be the 2nd dyeing film which is not given the color adjustment process and the drying shrinkage process, and the 2nd dyeing film to which the color adjustment process and / or the drying shrinkage process was given (color adjustment film or dry shrinkage film). The second dyed film immediately before the humidification process is preferably a drying shrinkage film subjected to a color adjustment process and a drying shrinkage process.

C. Polarizer

The polarizer humidified by the above is manufactured. More specifically, when the raw film is a single-layer resin film, a single-layer polarizer is produced, and when the raw film is laminated on a resin substrate, a polarizing plate having a configuration of polarizer/resin substrate is produced.

The thickness of the polarizer is, for example, 80 μm or less, preferably 15 μm or less, more preferably 12 μm or less, still more preferably 8 μm or less. In the case where the raw film is a PVA-based resin layer formed by coating on a resin substrate, the thickness of the polarizer can be 8 µm or less. In addition, the thickness of the polarizer is typically 1 μm or more, preferably 3 μm or more.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. Such a polarizer has excellent single transmittance and polarization degree. The single transmittance of the polarizer is, for example, 40.0% to 46.0%, preferably 41.0% to 46.0%, and more preferably 42.0% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, still more preferably 99.5% or more.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. The measurement method of each characteristic is as follows.

(1) Measurement of single transmittance and degree of polarization

The resin substrate of the laminate (test piece) obtained in each Example and each Comparative Example was peeled from the polarizer. Subsequently, single transmittance (Ts), parallel transmittance (Tp), and cross transmittance (Tc) of the polarizer single film were measured using an ultraviolet/visible spectrophotometer (manufactured by Nippon Spectroscopy Co., Ltd., product name 'V7100'). In addition, the degree of polarization (P) of the polarizer was calculated by the following formula (1).

Polarization degree (P) (%) = {(Tp-Tc)/(Tp+Tc)} 1/2 × 100... (1)

In addition, the said Ts, Tp, and Tc are Y-values measured by the 2-degree field of view (C light source) of JIS Z8701 and corrected for visibility.

(2) Measurement of crystallization index

In each Example and each Comparative Example, the crystallization index of the PVA-based resin layer was measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement was performed using polarized light as measurement light, and the crystallization index was determined according to the following formula (2) using the intensity (IC) of 1141 cm ^-1 and the intensity (IR) of 1440 cm ^-1 of the obtained spectrum. was calculated.

Crystallization index = (IC/IR)... (2)

(3) Measurement of boric acid content ratio in polarizer before humidification process

In each Example and each comparative example, the boric acid content ratio in the polarizer before a humidification process is computable as the amount of boric acid contained in the polarizer per unit mass using the following formula from the neutralization method, for example.

[Measurement method of boric acid content ratio (mass %) in polarizer]

A polarizer (about 0.2 g) dried at 120 ° C. for 2 hours was dissolved in water, and a 0.1 mol / L NaOH aqueous solution was neutralized and titrated using a burette to an aqueous solution to which a small amount of mannitol and BTB solution was added dropwise, and the boric acid content ratio of the polarizer was calculated based on the following formula.

Boric acid content ratio of polarizer (mass %) = C×V×Mw/M×100

C: concentration of NaOH aqueous solution (mol/L)

V: dropping amount of NaOH aqueous solution (L)

Mw: molecular weight of boric acid (g/mol)

M: 120 ° C., polarizer mass (g) after drying for 2 hours

<<Examples 1 to 5>>

As the thermoplastic resin substrate, a long amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and corona treatment was performed on one side of the resin substrate.

Polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer”) were mixed at a ratio of 9:1 to 100 parts by mass of a PVA-based resin 13 parts by mass of potassium iodide What was added was dissolved in water to prepare a PVA aqueous solution (coating liquid).

A PVA-based resin layer having a thickness of 13 μm was formed by applying the PVA aqueous solution to the corona-treated surface of the resin substrate and drying at 60° C. to prepare a laminate.

The obtained layered product was uniaxially stretched in a longitudinal direction (longitudinal direction) at a secondary stretching ratio of 2.4 times in a 130°C oven (auxiliary stretching step). In addition, the PVA-based resin layer included in the laminate after the auxiliary stretching and before the swelling step was subjected to the measurement of the crystallization index described above. The crystallization index of the PVA-based resin layer was 1.82.

Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution obtained by blending 4 parts by mass of boric acid with respect to 100 parts by mass of water) at a liquid temperature of 40°C for 30 seconds (swelling step, insolubilization step).

Next, the laminate was immersed in a first dyeing bath (an iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by mass of water) at a liquid temperature of 30°C for 60 seconds (first dyeing step). .

Next, the layered product was immersed in a crosslinking bath (boric acid aqueous solution obtained by blending 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with respect to 100 parts by mass of water) at a liquid temperature of 40°C for 30 seconds (crosslinking step).

After that, the laminate is immersed in a stretching bath (boric acid aqueous solution obtained by blending 5 parts by mass of potassium iodide with respect to 100 parts by mass of water and blending boric acid to the concentration shown in Table 1) at the temperature shown in Table 1, Uniaxial stretching was performed between rolls having different circumferential speeds so that the total stretching ratio in the machine direction (longitudinal direction) was 5.5 times (stretching step).

Next, the layered product was immersed in a second dyeing bath (an iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by mass of water) at a liquid temperature of 30°C for an immersion time shown in Table 1. (Second dyeing process). The concentration of iodine in the second dyeing bath (second dyeing solution) is shown in Table 1.

After that, the layered product was immersed in a color adjusting bath (aqueous solution obtained by blending 4 parts by mass of potassium iodide with respect to 100 parts by mass of water) at a liquid temperature of 20°C (color adjustment step).

Thereafter, while drying the layered product in an oven maintained at about 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75°C (dry shrinkage step).

In this way, a polarizer having a thickness of about 5 μm was formed on the resin substrate to obtain a polarizing plate having a structure of polarizer/resin substrate. In addition, the polarizer included in the polarizing plate after the drying shrinkage process and before the humidification process was used for the measurement of the above-described boric acid content ratio. The results are shown in Table 1.

Then, the polarizing plate was subjected to the measurement of the above-described single transmittance and polarization, and the single transmittance and polarization (ie, initial single transmittance and initial polarization) at 0 minute humidification time were measured.

Next, in the state where the polarizing plate was attached to the conveying roll, it was placed in a high-temperature, high-humidity oven maintained at a temperature of 85° C. and a humidity of 85% RH to obtain a humidified polarizing plate (humidifying step).

More specifically, for each humidification time shown in Table 1, the polarizing plate was subjected to the measurement of the above-mentioned single transmittance and polarization degree. Accordingly, the single transmittance and polarization degree at each humidification time were measured. The results are shown in Table 1 and FIGS. 3 and 4 .

Further, the humidification time until the single transmittance reaches 43.5% is plotted with the humidification time on the horizontal axis and the single transmittance on the vertical axis as shown in FIG. It was calculated from the intersection with 43.5%, and evaluated according to the following criteria. The results are shown in Table 1.

○: Humidification time until single transmittance reaches 43.5% is 20 minutes or less

×: Humidification time until single transmittance reaches 43.5% exceeds 20 minutes

<<Comparative Example 1>>

A humidified polarizing plate was obtained in the same manner as in Example 1 except that the color adjustment step was performed on the layered product after the stretching step without performing the second dyeing step.

[Table 1]

[evaluation]

As is clear from Table 1 and FIG. 4, by performing the second dyeing step on the PVA-based resin film after the stretching step, the boron content in the PVA-based resin film after the second dyeing step can be reduced to 10% by mass or less. In addition, the single transmittance can be reduced to 35% or less. Then, in a humidification process, water|moisture content can penetrate smoothly into a polarizer, and also the deiodination property of a polarizer can be improved. As a result, even if the humidification time is reduced, the single transmittance of the polarizer can be efficiently improved, and manufacture of the polarizer capable of suppressing a decrease in polarization degree can be realized.

The manufacturing method according to the embodiment of the present invention can be suitably used for manufacturing a polarizer applied to an image display device.

1: PVA-based resin film
10: laminate
12: thermoplastic resin substrate

Claims (7)

A first dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic material;
A stretching step of stretching the polyvinyl alcohol-based resin film after the first dyeing step in an aqueous solution of boric acid;
A second dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic substance while eluting boric acid from the polyvinyl alcohol-based resin film after the stretching step
Including, the manufacturing method of the polarizer. According to claim 1,
In the polyvinyl alcohol-type resin film after the said 2nd dyeing process, the manufacturing method of the light polarizer whose boric acid content rate is 10 mass % or less, and single transmittance is 35 % or less. According to claim 1 or 2,
The manufacturing method of the polarizer which further includes the humidification process of humidifying the polyvinyl alcohol-type resin film after the said 2nd dyeing process under the atmosphere of temperature 40 degreeC - 100 degreeC, and humidity 50 %RH or more. According to claim 3,
The humidification time in the humidification process is 60 minutes or less, the manufacturing method of the polarizer. According to claim 3,
A coating liquid containing a polyvinyl alcohol-based resin and a halide is applied onto a long thermoplastic resin substrate to prepare a laminate comprising a polyvinyl alcohol-based resin layer as the polyvinyl alcohol-based resin film and the thermoplastic resin substrate. A laminate manufacturing process to do;
An auxiliary stretching step of air-stretching the laminate;
The first dyeing step;
The stretching step;
The second dyeing step;
The manufacturing method of light polarizer which includes the heating-shrinking process of shrinking in the width direction orthogonal to the said long direction, conveying the polyvinyl alcohol-type resin film dyed by the said 2nd dyeing process in the direction of a long picture in this order. According to claim 5,
The manufacturing method of the polarizer in which the said humidification process is performed after the said heat shrinkage process. According to claim 1 or 2,
In the second dyeing step, the polyvinyl alcohol-based resin film after the stretching step is immersed in a second dyeing solution containing a dichroic substance,
The concentration of the dichroic substance in the second staining solution is 0.8% by mass or less,
The manufacturing method of the light polarizer whose immersion time in the said 2nd dyeing process is 5 minutes or less.

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