KR20230059744A - Method for manufacturing polarizer - Google Patents

Abstract

The present invention provides a method for manufacturing a polarizer which can sufficiently improve the single transmittance and suppress a decrease in polarization degree even if the humidification time is reduced when used in a humidification process. The method for manufacturing a polarizer according to an embodiment of the present invention includes: a dyeing process for dyeing a polyvinyl alcohol-based resin film with a dichroic material; and a stretching step in which the polyvinyl alcohol-based resin film after the dyeing step is stretched in a stretching bath which does not substantially contain boric acid.

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, improvements in optical properties (particularly single transmittance and polarization degree) of polarizers have 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 sufficiently improve the single transmittance even if the humidification time is reduced when applied to the humidification step, and suppress the decrease in polarization degree It is to provide a method capable of manufacturing a polarizer capable of

In the manufacturing method of the polarizer according to the embodiment of the present invention, a dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic substance; The stretching process of extending|stretching the polyvinyl alcohol-type resin film after the said dyeing process in the stretching bath which does not contain boric acid substantially is included.

In one embodiment, the content rate of boric acid in the polyvinyl alcohol-type resin film after the said extending process is 7.0 mass % or less.

In one embodiment, the manufacturing method of the said light polarizer further includes the bridge|crosslinking process which makes the polyvinyl alcohol-type resin film after the said dyeing process contact boric acid aqueous solution before the said extending process.

In one embodiment, the manufacturing method of the said polarizer further includes the humidification process of humidifying the polyvinyl alcohol-type resin film after the said extending process in the atmosphere of temperature 40 degreeC - 100 degreeC, and humidity 50%RH or more.

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 dyeing step; the stretching step; A drying shrinkage step of shrinking the laminate after the stretching step in the width direction orthogonal to the elongate direction while conveying it in the elongate direction is included in this order.

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

In one embodiment, the draw ratio of the said layered product in the said auxiliary drawing process is 2.1 times or more.

ADVANTAGE OF THE INVENTION According to embodiment of this invention, when it uses for a humidification process, even if it reduces the humidification time, the single transmittance can fully be improved, and the polarizer which can suppress the fall of polarization degree 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.
5 is a graph showing the amount of change in single transmittance in the humidification step 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 dyeing step of dyeing a polyvinyl alcohol-based resin film (hereinafter, referred to as a PVA-based resin film) with a dichroic material; The stretching process of extending|stretching the PVA-type resin film after a dyeing process in the drawing bath which does not contain boric acid substantially is included. In this specification, "substantially not containing boric acid" means that boric acid is not intentionally introduced into the stretching bath, and more specifically, it means that the concentration of boric acid in the stretching bath is less than 0.5% by mass. . In addition, the concentration of boric acid in the stretching bath is preferably 0.3% by mass or less, more preferably 0.1% by mass or less.

The inventors of the present invention found that, when sufficiently humidifying the PVA-based resin film after the stretching step, the single transmittance could be sufficiently improved and the decrease in polarization degree could be suppressed. 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, arose.

In this respect, the inventors of the present invention stretched the PVA-based resin film after the dyeing step in a drawing bath that does not substantially contain boric acid, and reduced the content of boric acid in the PVA-based resin film after the stretching step. With a remarkably short humidification time It was discovered that the single transmittance could be sufficiently improved, and the present invention was completed.

More specifically, when the PVA-based resin film after the dyeing step is stretched in a drawing bath that does not substantially contain boric acid, the PVA-based resin film after the stretching step (specifically, the PVA-based resin film after the stretching step and immediately before the humidification step) The content ratio of boric acid in a resin film) can be adjusted as follows.

The content of boric acid in the PVA-based resin film after the stretching step is, for example, 7.0% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less. If the content of boric acid is below the upper limit above, when the stretched PVA-based resin film is subjected to a humidifying step, moisture can be smoothly penetrated into the PVA-based resin film, and the dichroic substance can be obtained from the PVA-based resin film. can be smoothly eluted. 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, and the decrease in polarization degree of the polarizer can be suppressed. The content ratio of boric acid in the PVA-based resin film after the stretching step is typically 0.1% by mass or more.

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 dyeing process contact boric acid aqueous solution before an extending process. When the PVA-based resin film after the dyeing step is brought into contact with an aqueous solution of boric acid, it is possible to suppress the melting of the PVA-based resin film in the stretching bath in the stretching step. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution and forms crosslinks by hydrogen bonding with PVA-based resins, or crosslinking by dehydration condensation with hydroxyl groups of PVA-based resins to form boric acid esters. can 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 stretching step in an atmosphere of a temperature of 40°C to 100°C and a humidity of 50% RH or higher. 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. The humidification humidity is preferably 70% RH or higher, more preferably 80% RH or higher, and is typically 100% RH or lower, preferably 95% RH or lower.

When the PVA-based resin film after the stretching step is humidified in the above atmosphere to produce a polarizer, the decrease in polarization degree of the polarizer can be suppressed while being able to improve the single transmittance of the 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, and among them 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, the improvement in the manufacturing efficiency of the polarizer can be stably achieved.

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 laminate manufacturing process; an auxiliary stretching step; The dyeing process described above; the stretching step 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 stretching step is shrunk in the width direction orthogonal to the elongate direction while being conveyed in the elongate direction.

According to this method, a polarizer having excellent optical characteristics as a polarizer having a reduced thickness can be provided. That is, by introducing the auxiliary stretching 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, at the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration in orientation or dissolution of the PVA-based resin when immersed in water in a subsequent dyeing step or stretching step, thereby achieving high optical properties. it becomes possible Further, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the PVA-based resin molecules and the 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.

In one embodiment, the stretch ratio of the laminate 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 manufacturing method of said light polarizer may include a swelling process and/or a hue adjustment process.

In the swelling step, typically, the PVA-based resin film before the dyeing step 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 color adjustment step, typically, the PVA-based resin film after the stretching step is immersed in a color adjustment bath 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, the said swelling process (insolubilization process), a dyeing process, a bridge|crosslinking process, an extending 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 film roll 21 toward the winding roll 22, and between the film roll 21 and the winding roll 22, a swelling step (insolubilization process), dyeing process, crosslinking process, stretching process, color adjustment process and drying shrinkage process are sequentially performed on the PVA-based resin film 1. In one embodiment, the PVA-based resin film 1 is a swelling bath 2A (swelling liquid), a dyeing bath 2B (dyeing liquid), and a crosslinking bath 2C (crosslinking liquid) by a plurality of rollers 24 ), the drawing bath 2D (stretching liquid), and the color adjustment bath 2E (color adjustment liquid) in this order, and then 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 PVA-based resin film is immersed in each bath (each liquid) described above by immersing the laminate containing the PVA-based resin film in each bath (each liquid) come into contact with

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, 1.6 or more, preferably 1.8 or more. If the crystallization index of the PVA-based resin is equal to or greater than this lower limit, even if the PVA-based resin film is stretched in a stretching bath that does not substantially contain boric acid, dissolution of the PVA-based resin film in the stretching bath can be more stably suppressed. can 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 raw film 11 is the PVA-based resin layer 13 applied 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 step. .

More specifically, the PVA-based resin layer 13 is formed by applying a coating liquid containing a PVA-based resin and a halide onto the elongated resin substrate 12 by any appropriate method, and drying it at, for example, 50° C. or higher as necessary. and a laminate 10 provided with a resin substrate 12 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 less, preferably 120°C or less. When the Tg of the resin substrate is equal to or less than the above upper limit, the stretchability of the layered product can be sufficiently secured while being able to suppress the crystallization of the PVA-based resin layer. 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.

Arbitrary suitable surface treatment (for example, corona treatment) may be given to the surface of a resin base material, and an easily bonding layer may be formed. 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 degree of polymerization is, for example, 1000 or more, preferably 1500 or more, more preferably 2000 or more, still more preferably 3000 or more, and, 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. As the halide, iodide and sodium chloride are typically exemplified. 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. can 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. As surfactant, a nonionic surfactant is mentioned, for example.

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 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 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, uniaxial stretching by passing the laminate between rolls having different circumferential speeds) method) 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 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 solution is an aqueous solution of boric acid (ie, insolubilization solution), the content of boric acid in the insolubilization solution 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. dyeing process

In the dyeing step, the PVA-based resin film 1 (preferably the swelling treated film 1a) is dyed with a dichroic substance. Specifically, the dye solution is brought into contact with the PVA-based resin film 1 (preferably the swelling treated film 1a) to adsorb the dichroic substance. Hereinafter, the PVA-based resin film after the dyeing process and before the stretching process is used as the dyed 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 staining solution is typically an iodine aqueous solution. The content of iodine in the 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 dye solution preferably further contains an iodine compound. When the 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 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 dyeing step of the illustrated example, the PVA-based resin film 1 (swelling treated film 1a) is immersed in the dyeing bath.

The temperature of the 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 in the dyeing process is, for example, 5 seconds or more, preferably 30 seconds or more, and, for example, 300 seconds or less, preferably 90 seconds or less.

Further, when the dyeing step is continuously performed after the insolubilization step described above, there is a possibility that boric acid may be mixed in the dyeing bath from the insolubilization bath. When boric acid is mixed in the dyeing bath, the concentration of boric acid in the dyeing solution changes over time, which may affect the content of boric acid in the polarizer. Therefore, the content of boric acid in the dye solution 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 dyeing process is not limited to the above-mentioned immersion. For example, the dye solution may be applied to a raw film, or the dye solution may be sprayed onto a raw film.

B-4. cross-linking process

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

The content of boric acid in the crosslinking solution is appropriately adjusted in order to make the content of boric acid in the stretched film fall within the above range. The content of boric acid in the crosslinking solution 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 solution contains an iodine compound, elution of iodine adsorbed onto the dyed film can be suppressed.

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 (boric acid:iodine compound) of boric acid and 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 dyed film 1b (preferably the crosslinked film 1c) is stretched in a long direction in a stretching bath (stretching liquid) that does not substantially contain boric acid. Hereinafter, the PVA-based resin film after the stretching step and before the humidifying step is referred to 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.

By stretching at the above stretching ratio, extremely excellent optical properties can be provided to the polarizer.

The stretching 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. As described above, the iodine compound aqueous solution contains substantially no boric acid. The content of the iodine compound in the stretching 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, based on 100 parts by mass of water.

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. The immersion time in the stretching step is, for example, 15 seconds or more and 300 seconds or less.

B-6. color adjustment process

In the color adjustment step, the stretched film 1d is typically immersed in a color adjustment bath (color adjustment liquid). Hereinafter, what was subjected to the color adjustment step among stretched films is referred to as the color adjustment film 1e.

A 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 aqueous solution of the iodine compound is substantially free of boric acid. 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 temperature of the color adjustment 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 process 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-7. drying shrinkage process

In the drying shrinkage step, typically, the stretched film 1d (preferably the color adjustment film 1e) is heated while being conveyed in the elongate direction. Hereinafter, the stretched film subjected to the drying shrinkage step is referred to as the dry shrinkage film 1f. In one embodiment, the range of the boric acid content in the dry shrink film 1f is the same as the range of the boric acid content in the stretched film described above.

In the illustrated example, the drying shrinkage step is performed by the heat drying unit 23 . The heating and drying unit may be a zone heating system in which the entire interior 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, heating curl of a stretched film (laminate) can be suppressed efficiently and a light polarizer excellent in appearance can be efficiently manufactured. Further, in the drying shrinkage step, the stretched film is shrunk in the width direction orthogonal to the elongate direction.

The shrinkage rate of the stretched film in the width direction in the drying shrinkage step is, for example, 2% or more, preferably 4% or more. If the shrinkage rate in the width direction is equal to or greater than this lower limit, the orientation properties of PVA and PVA/dichroic substance complex (iodine complex) can be improved, and the optical properties of the polarizer can be improved.

The shrinkage ratio in the width direction of the stretched film is typically 10% or less, preferably 8% or less, and more preferably 6% or less. It can suppress that appearance defects, such as wrinkles, arise in a polarizer as the shrinkage rate of the width direction is below this upper limit.

Thereafter, the stretched film 1d (preferably the dried shrink film 1f) is wound up in a roll shape as needed to constitute the winding roll 22 .

B-8. Humidification process

In the humidifying step, typically, the stretched film (layered product including the stretched film) once wound up is left still in the above-mentioned atmosphere for the above-mentioned humidification period.

In addition, the range of the content rate of boric acid in the stretched film immediately before the humidification process is the same as the range of the content rate of boric acid in the PVA-based resin film after the above-mentioned stretching process. In addition, the single transmittance of the stretched film immediately before the humidification step is, for example, 37.0% to 43.0%, preferably 39.0% to 41.0%. The polarization degree of the stretched film immediately before the humidification step is, for example, 98.0% or more, preferably 99.5% or more, and more preferably 99.8% or more. The stretched film immediately before the humidification step may be a stretched film not subjected to the color adjustment step and the drying shrinkage step, or a stretched film (color adjustment film or drying shrinkage film) subjected to the color adjustment step and/or the drying shrinkage step. . The stretched film immediately before the humidification step is preferably a dry shrink film subjected to a color adjustment step and a dry shrinkage step.

C. Polarizer

By the above, the humidified polarizer 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 polarization degree

The resin substrate of the laminate (test piece) obtained in each Example and each Comparative Example was peeled from the polarizer. Then, 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, 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

In addition, in order to simply measure the boric acid content rate, the boric acid amount index may be measured using FT-IR, and the boric acid content rate in the polarizer may be measured.

<Measurement of boric acid content in polarizer using FT-IR>

For the polarizers obtained in Examples and Comparative Examples, total reflection attenuation spectroscopy (ATR) using polarized light as measurement light using a Fourier transform infrared spectrophotometer (FTIR) (manufactured by Perkin Elmer, trade name 'frontire') The intensity of the boric acid peak (665 cm ^-1 ) and the intensity of the reference peak (2941 cm ^-1 ) were measured by the measurement. From the obtained boric acid peak intensity and the reference peak intensity, the boric acid amount index was calculated by the following formula, and further, using the calculated boric acid amount index, a calibration curve was prepared with the boric acid content ratio (% by mass) determined by the measurement method, and FT- The boric acid content ratio can be calculated using IR.

(boric acid amount index) = (intensity of boric acid peak 665 cm ^-1 ) / (intensity of reference peak 2941 cm ^-1 )

<<Examples 1 and 2>>

As the thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 µm) having a long 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 the machine direction (longitudinal direction) at the auxiliary stretch ratio shown in Table 1 in a 130°C oven (subsidiary 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 results are shown in Table 1.

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 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 (dyeing step).

Next, the laminate was immersed in a crosslinking bath (a 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, while immersing the layered product in a stretching bath containing substantially no boric acid at a liquid temperature of 70°C (an aqueous solution obtained by blending 5 parts by mass of potassium iodide with 100 parts by mass of water; boric acid concentration: 0% by mass), the circumferential speed is Uniaxial stretching was performed between different rolls so that the total stretching ratio in the machine direction (longitudinal direction) was 5.5 times (stretching step).

Then, 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) having 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 boric acid content ratio described above. The results are shown in Table 1.

Next, the polarizing plate was subjected to the measurement of the above-described single transmittance and polarization degree, and the single transmittance and polarization degree at 0 minute humidification time were measured.

Then, in a 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 60° C. and a humidity of 90% 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. Those results are shown in Table 1, FIGS. 3 and 4.

In addition, the change amount (ΔTs) of the single transmittance in the humidification step was calculated and evaluated according to the following criteria. The results are shown in Table 1 and FIG. 5 .

Humidification time from 0 to 20 minutes;

○: change in single transmittance (ΔTs) is 1.2% or more

×: Change in single transmittance (ΔTs) is less than 1.2%

humidification time from 0 to 40 minutes;

○: change in single transmittance (ΔTs) is 1.5% or more

×: Change in single transmittance (ΔTs) is less than 1.5%

Humidification time from 0 to 60 minutes;

○: change in single transmittance (ΔTs) is 2.0% or more

×: Change in single transmittance (ΔTs) is less than 2.0%

<<Comparative Examples 1 to 3>>

A polarizing plate having a configuration of a polarizer/resin base material was obtained in the same manner as in Example 2, except that boric acid was dissolved in the stretching bath so that the boric acid concentration became the value shown in Table 1.

[Table 1]

[evaluation]

As is clear from Table 1, FIG. 4 and FIG. 5, the boron content ratio in the polarizer manufactured can be reduced to 7.0 mass % or less by extending|stretching a PVA system resin film in the drawing bath which does not contain boric acid substantially. 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 (8)

A 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 dyeing step in a stretching bath substantially containing no boric acid.
Including, the manufacturing method of the polarizer. According to claim 1,
The manufacturing method of the light polarizer whose content rate of boric acid in the polyvinyl alcohol-type resin film after the said extending process is 7.0 mass % or less. According to claim 1 or 2,
The manufacturing method of light polarizer which further includes the bridge|crosslinking process of making the polyvinyl alcohol-type resin film after the said dyeing process contact boric acid aqueous solution before the said extending process. According to claim 1 or 2,
The manufacturing method of the light polarizer which further includes the humidification process of humidifying the polyvinyl alcohol-type resin film after the said extending process under the atmosphere of temperature 40 degreeC - 100 degreeC, and humidity 50%RH or more. According to claim 4,
The humidification time in the humidification process is 60 minutes or less, the manufacturing method of the polarizer. According to claim 4,
A coating liquid containing a polyvinyl alcohol-based resin and a halide is applied onto a long thermoplastic resin substrate to produce 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;
An auxiliary stretching step of air-stretching the laminate;
The dyeing process;
The stretching step;
Dry shrink step of shrinking the polyvinyl alcohol-based resin film after the stretching step in the width direction orthogonal to the long direction while conveying it in the long direction
A method for manufacturing a polarizer including in this order. According to claim 6,
The method of manufacturing a polarizer in which the humidification step is performed after the drying shrinkage step. According to claim 6,
A method for manufacturing a light polarizer in which the draw ratio of the layered product in the auxiliary stretching step is 2.1 times or more.

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