KR20230082572A - Method for manufacturing polarizer and method for manufacturing polarizing plate - Google Patents

Abstract

The present invention provides a method for manufacturing a polarizer and a polarizing plate, which can suppress display unevenness of an image display device. A method for manufacturing a polarizer according to an embodiment of the present invention comprises: a dying step of dying a polyvinyl alcohol-based resin film with a dichroic substance; a cross-linking step of bringing the dyed polyvinyl alcohol-based resin film into contact with a boric acid aqueous solution; and a stretching step of stretching the cross-linked polyvinyl alcohol-based resin film in a stretch bath. The absolute value of the difference between the containing ratio of boric acid in the polyvinyl alcohol-based resin film before the dyeing step and the containing ratio of boric acid in the polyvinyl alcohol-based resin film after the dyeing step and before the crosslinking step is equal to or less than 5.0 mass%.

Description

Manufacturing method of polarizer and manufacturing method of polarizing plate {METHOD FOR MANUFACTURING POLARIZER AND METHOD FOR MANUFACTURING POLARIZING PLATE}

The present invention relates to a manufacturing method of a polarizer and a manufacturing method of a polarizing plate.

A polarizer is typically used for the image display device. Such a polarizer, for example, after immersing a polyvinyl alcohol-based resin film in an aqueous solution of boric acid to insolubilize it, dyeing the polyvinyl alcohol-based resin film with a dichroic substance, and then using polyvinyl alcohol It is manufactured by extending|stretching a system resin film in boric acid aqueous solution (for example, patent document 1).

In recent years, high precision of an image display device using a polarizer is required, and further reduction of display unevenness of the image display device is desired. However, in the image display apparatus provided with the polarizer of patent document 1, room for improvement remains for reduction of display nonuniformity.

International Publication No. 2010/100917

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 and a polarizing plate capable of suppressing display non-uniformity in an image display device.

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; a crosslinking step of bringing the polyvinyl alcohol-based resin film after the dyeing step into contact with an aqueous solution of boric acid; and a stretching step of stretching the polyvinyl alcohol-based resin film after the crosslinking step in a stretching bath. The absolute value of the difference between the content of boric acid in the polyvinyl alcohol-based resin film before the dyeing step and the content of boric acid in the polyvinyl alcohol-based resin film after the dyeing step and before the crosslinking step is 5.0% by mass or less.

In one embodiment, a polarizer having a single transmittance of 42% or more and 45% or less is manufactured.

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 the said polyvinyl alcohol-type resin film and a laminate manufacturing step of manufacturing a laminate comprising the thermoplastic resin substrate; an auxiliary stretching step of air-stretching the laminate; the dyeing step; the cross-linking step; the stretching step; A drying shrinkage step of shrinking the polyvinyl alcohol-based resin layer 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 thermoplastic resin substrate is a polyethylene terephthalate film.

In one embodiment, a polarizer having a thickness of 12 μm or less is manufactured.

In one embodiment, the stretching bath is an aqueous solution of boric acid.

The manufacturing method of the polarizing plate concerning another situation of this invention includes bonding a protective film to the polarizer manufactured by the manufacturing method of the said polarizer.

ADVANTAGE OF THE INVENTION According to embodiment of this invention, the polarizer and polarizing plate which can suppress display nonuniformity in an image display apparatus 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 .

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; a crosslinking step of bringing the PVA-based resin film after the dyeing step into contact with an aqueous solution of boric acid; A stretching step of stretching the PVA-based resin film after the crosslinking step in a stretching bath is included. The absolute value of the difference between the content of boric acid in the PVA-based resin film before the dyeing step and the content of boric acid in the PVA-based resin film after the dyeing step and before the crosslinking step is 5.0% by mass or less, preferably 4.0% by mass. or less, more preferably 3.0% by mass or less.

In an image display device using a polarizer dyed with a dichroic material, non-uniformity of dyeing in the polarizer may cause display non-uniformity of the image display device. Therefore, the present inventors studied closely the improvement of the uniformity of dyeing in the polarizer, and when the difference in the content ratio of boric acid in the PVA-based resin film before and after the dyeing process was adjusted to a specific range, the stripe-like dyeing unevenness that may occur in the polarizer can be suppressed, and it is discovered that the uniformity of dyeing in the polarizer can be improved, and the present invention has been completed. More specifically, if the absolute value of the difference in content ratio of boric acid in the PVA-based resin film before and after the dyeing process described above is below the above upper limit, uneven dyeing in the polarizer can be remarkably suppressed.

In one embodiment, the lower limit of the absolute value of the difference in content of boric acid in the PVA-based resin film before and after the above dyeing step is typically 0% by mass or more, preferably 1.0% by mass or more, more preferably It is 1.50 mass % or more. If the absolute value of the difference in content ratio of boric acid in the PVA-based resin film before and after the above-mentioned dyeing step is more than the above lower limit, the uneven dyeing in the polarizer can be suppressed even more remarkably.

In one embodiment, the PVA-based resin film is brought into contact with a dyeing bath (dyeing solution) in a dyeing process without contacting with an aqueous solution of boric acid before a dyeing process. When the PVA-based resin film is brought into contact with an aqueous solution of boric acid, boric acid forms cross-links to impart water resistance to the PVA-based resin film. Therefore, in the manufacturing method of a light polarizer, a PVA-type resin film is generally made to contact with boric-acid aqueous solution before a dyeing process, and dissolution of the PVA-type resin film with respect to a staining solution is suppressed.

However, when the PVA-based resin film is brought into contact with an aqueous solution of boric acid in advance, boric acid is desorbed from the PVA-based resin film and eluted into the dyeing solution in the dyeing process. is likely to affect Therefore, it is guessed that it gives a bad influence to the uniformity of dyeing in a polarizer.

On the other hand, if the PVA-based resin film is brought into contact with the dyeing solution without contacting the aqueous solution of boric acid before the dyeing step, the complex of the dichroic substance and the PVA-based resin can be uniformly distributed, and the dyeing unevenness in the polarizer can be stably can be suppressed

In one embodiment, a manufacturing method of a polarizer includes a layered product manufacturing process; an auxiliary stretching step; The dyeing process described above; The crosslinking step 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 layer after the stretching step is shrunk in the width direction orthogonal to the direction of a long picture while being conveyed in the direction of a long picture.

According to such a method, a polarizer having a reduced thickness and excellent optical properties can be provided. 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 a decrease in the orientation of the PVA-based resin or dissolution when immersed in a liquid in a subsequent dyeing step, and to achieve high optical properties. It becomes possible. In addition, since the PVA-based resin layer is brought into contact with an aqueous solution of boric acid in the crosslinking step, water resistance can be imparted to the PVA-based resin layer, and dissolution of the PVA-based resin layer in the stretching bath can be suppressed in the next stretching step. Further, when 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 in the drying shrinkage step.

The manufacturing method of said light polarizer may include the hue adjustment process.

In the color adjustment step, typically, the PVA-based resin film after the stretching step (preferably, the PVA-based resin film after the stretching step and before the drying shrinkage step) is immersed in a color adjustment bath. In this way, 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 dyeing process, crosslinking process, extending|stretching process, hue adjustment process, and drying shrinkage process are performed continuously.

More specifically, the long PVA-based resin film 1 is conveyed from the original roll 21 toward the winding roll 22, and between the original roll 21 and the winding roll 22 , the dyeing process, the crosslinking process, the stretching process, the color adjustment process, and the drying shrinkage process are sequentially performed on the PVA-based resin film 1. In one embodiment, the PVA-based resin film 1 is provided with a dyeing bath 2B (dyeing liquid), a crosslinking bath 2C (crosslinking liquid), and a stretching bath 2D ( stretching liquid), and the color adjusting bath 2E (color adjusting liquid) in this order, and then conveyed so as to pass through the heating and drying unit 23. Further, as described later in detail, when the PVA-based resin film is a PVA-based resin layer included in the laminate, the laminate containing the PVA-based resin layer is immersed in each of the above baths (each liquid) to obtain a PVA-based resin layer is brought into contact with each bath (each liquid).

B-1. PVA-based resin film

In the raw roll 21, the PVA-based resin film 1 (hereinafter referred to as 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 at least this lower limit, for example, even if the PVA-based resin film is immersed in a dyeing bath without contact with an aqueous boric acid solution, the PVA-based resin film can be suppressed from dissolving in the dyeing solution. 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), and as shown in FIG. 2(b), the thermoplastic resin substrate 12 (hereinafter referred to as the resin substrate 12) ) 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 applied and formed on the resin substrate 12, the PVA-based resin layer 13 is formed on the resin substrate 12.

More specifically, 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 as necessary, for example, at 50° C. or higher, the PVA coefficient is reduced. A layered product 10 including a ground layer 13 and a resin substrate 12 is produced.

Arbitrary appropriate materials can be employed as the constituent material of the resin substrate 12 . The resin substrate is typically a polyethylene terephthalate film. As a constituent material thereof, for example, 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 crystallization of the PVA-based resin layer. In addition, the glass transition temperature (Tg) of the resin substrate is typically 60°C or higher. This can suppress problems such as deformation of the resin substrate (for example, occurrence of unevenness, sagging, and wrinkles) when the coating liquid is applied to and dried on the resin substrate. 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 is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is 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 99.0 mol%. 99.5 mol%. The degree of saponification can be measured according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a thin polarizing film with excellent durability can be obtained. 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. 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, dimethylsulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. there is. 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 air-stretched in advance at a predetermined stretch ratio in the elongated direction. That is, the auxiliary stretching process is performed after the laminate production process and before the dyeing 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 laminate in the auxiliary stretching step is 2.1 times or more, preferably 2.3 times or more. When the draw ratio of the layered product is equal to or greater than this lower limit, the orientation property of the PVA-based resin layer included in the layered product can be improved, and the melting of the PVA-based resin layer in the dye solution can be stably suppressed. 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, uniaxial stretching by passing the laminate between rolls having different circumferential speeds) method) may be

The content of boric acid in the raw film 11 (PVA-based resin film 1 immediately before the dyeing step) is, for example, 10.0% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and further It is preferably 2.0% by mass or less, typically 0% by mass or more, and preferably 0.1% by mass or more. In addition, the content rate of boric acid can be measured by FT-IR, for example.

B-2. dyeing process

In the dyeing step, the PVA-based resin film 1 (original film 11) is dyed with a dichroic substance. Specifically, the dye solution is brought into contact with the PVA-based resin film 1 to adsorb the dichroic substance. The dichroic material forms a complex with the PVA-based resin. In the dyeing step of the illustrated example, the PVA-based resin film 1 is immersed in a dyeing bath (staining solution). Below, let the PVA-type resin film before a bridge|crosslinking process be dyed film 1b while it is after a dyeing process.

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. Iodine compounds can be used alone 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. In this way, excellent optical properties can be imparted to the polarizer.

Also, the dye solution may contain boric acid. The concentration of boric acid in the dye solution is, for example, 1.0% by mass or less, preferably 0.5% by mass or less, more preferably 0.45% by mass or less, particularly preferably 0.30% by mass or less, such as 0% by mass or more, preferably is 0.1% by mass or more. If the concentration of boric acid in the staining solution is within the above range, uneven dyeing in the polarizer can be more stably suppressed.

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 step is, for example, 5 seconds or more, preferably 30 seconds or more, and is, for example, 300 seconds or less, preferably 90 seconds or less, and more preferably 60 seconds or less.

In addition, the adsorption method of a dichroic substance in a 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.

In the case where the raw film is a single-layer resin film or a resin film supported by a resin substrate, the PVA-based resin film may be stretched in the dyeing step.

The content of boric acid in the dyed film 1b obtained in this way is, for example, 15.0% by mass or less, preferably 10.0% by mass or less, more preferably 6.0% by mass or less, still more preferably 5.0% by mass or less, Typically, it is 0% by mass or more, preferably 0.1% by mass or more. In addition, boric acid contained in a dyeing film is derived from boric acid contained in a raw film, and boric acid contained in a dyeing solution, for example. The absolute value of the difference between the content of boric acid in the original film and the content of boric acid in the dyed film is below the upper limit described in the above section A.

B-3. cross-linking process

In the crosslinking step, the dyed film 1b is brought into contact with an aqueous solution of boric acid as a crosslinking liquid. Typically, the dyed film 1b is immersed in boric acid aqueous solution (crosslinking bath). Hereinafter, the PVA-based resin film after the crosslinking step and before the stretching step is used as the crosslinked film 1c.

When the dyed film is brought into contact with an aqueous solution of boric acid, boric acid generates tetrahydroxyboric acid anions in the aqueous solution and crosslinks by hydrogen bonding with the PVA-based resin or dehydration condensation with the hydroxyl group of the PVA-based resin to form a boric acid ester. crosslinks can be formed by Thereby, elution of the PVA-based resin and the dichroic substance (preferably iodine) can be suppressed.

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 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 (iodine compound:boric acid) of the iodine compound and boric acid 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.

In the case where the raw film is a single-layer resin film or a resin film supported by a resin substrate, the PVA-based resin film may be stretched in the crosslinking step.

B-4. stretching process

In the stretching step, the crosslinked film 1c is stretched in a long direction in a stretching bath (stretching liquid). In the following, the PVA-based resin film after the stretching step 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. Further, when the PVA-based resin film is stretched in the dyeing step and/or the crosslinking step, the draw ratio in the stretching step is adjusted so that the product of the draw ratio in those steps falls within the above range.

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. In addition, the product of the draw ratio in the auxiliary drawing step and the draw ratio in the drawing 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.

By extending|stretching at the above draw ratios, extremely excellent optical characteristics can be provided to a polarizer.

The stretching liquid is typically a boric acid aqueous solution. The content of boric acid in the stretching liquid (boric acid aqueous solution) is, for example, 1 part by mass or more, preferably 3 parts by mass or more, for example 10 parts by mass or less, preferably 8 parts by mass or less, based on 100 parts by mass of water. .

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

B-5. 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 the 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-6. 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 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 interior of the heating and drying unit is heated, or a heating roll drying system in which a conveying roll is heated. As for the heat drying part, Preferably, both of them are used.

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 by contacting with the heating roll.

The shrinkage ratio 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 of the stretched 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, it can suppress appearance defects such as wrinkles in the polarizer.

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 .

C. Polarizer

By the above, a 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 polarizer/resin substrate structure is produced (ie, a resin substrate). is used as a protective layer of the polarizer).

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 (ie, the PVA-based resin layer) can be 12 μm or less, preferably 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, 41.0% or more and 46.0% or less, and preferably 42.0% or more and 45.0% or less. 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. According to the manufacturing method of the above-mentioned polarizer, dyeing unevenness can be suppressed remarkably in the polarizer in which each of single transmittance and polarization degree is the said range.

Moreover, arbitrary suitable protective films according to the objective may be bonded together to the light polarizer manufactured as mentioned above, and a light polarizer may be manufactured. In addition, when the polarizer is laminated on the resin substrate, the resin substrate may be peeled off from the polarizer and a protective film may be bonded to the peeling surface.

Specific examples of the material used as the main component of the protective film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate resins. Further, thermosetting resins such as (meth)acrylic, urethane-based, (meth)acrylurethane-based, epoxy-based, and silicone-based resins or ultraviolet curable resins may be used. In addition, "(meth)acrylic resin" refers to an acrylic resin and/or a methacrylic resin. In addition, glassy type polymers, such as a siloxane type polymer, are also mentioned, for example. Moreover, the polymer film of Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material for this film, a resin composition containing, for example, a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. For example, isobutene and N- and a resin composition containing an alternating copolymer containing methyl maleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

[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 boric acid content in PVA-based resin film

In each Example and each Comparative Example, the content ratio of boric acid in the PVA-based resin film before the dyeing process and after the dyeing process and before the crosslinking process, for example, using the following formula from the neutralization method, included in the polarizer per unit mass It can be calculated as the amount of boric acid.

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

Each of the PVA-based resin film before the dyeing process and the PVA-based resin film after the dyeing process and before the crosslinking process (about 0.2 g) was dried at 120° C. for 2 hours, then dissolved in water, and a small amount of mannitol and BTB solution added dropwise into an aqueous solution. , 0.1 mol/L NaOH aqueous solution was subjected to neutralization titration using a burette, and the boric acid content ratio of the PVA-based resin film was calculated based on the following formula.

Boric acid content ratio (mass %) of PVA-based resin film = 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: Mass of PVA-based resin after drying at 120°C for 2 hours (g)

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 each of the PVA-based resin film before the dyeing process and the PVA-based resin film after the dyeing process and before the crosslinking process, using a Fourier Transform Infrared Spectrophotometer (FTIR) (manufactured by Perkin Elmer, trade name 'frontire'), polarization was measured. The intensity of the boric acid peak (665 cm ⁻¹ ) and the intensity of the reference peak (2941 cm ⁻¹ ) were measured by total reflection attenuation spectroscopy (ATR) measurement using measurement light. From the obtained boric acid peak intensity and the reference peak intensity, the boric acid amount index is calculated by the following formula, and further, using the calculated boric acid amount index, a calibration curve is prepared with the boric acid content ratio (% by mass) determined by the titration 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 )

(2) Measurement of single transmittance

The single transmittance (Ts) of the polarizer single film obtained in each Example and each Comparative Example was measured using an ultraviolet/visible ray spectrophotometer (manufactured by Nippon Spectroscopy Co., Ltd., product name 'V7100'). The results are shown in Table 1. In addition, when a polarizer is contained in a polarizing plate, the resin base material of a polarizing plate (test piece) was previously peeled from the polarizer.

(3) Measurement of crystallization index

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

Crystallization index = (IC/IR)...(1)

(4) Evaluation of dye staining

The state of dyeing unevenness (stripe unevenness) of the polarizer obtained in each Example and each Comparative Example was observed with the naked eye from a state 50 mm away from the repair line direction, and evaluated according to the following criteria. The results are shown in Table 1.

A: The stain is not visible.

B: A stain is slightly visible.

C: Stains are visible.

<<Examples 1 to 12>>

Corona treatment was performed on one side of the resin substrate using an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape and a Tg of about 75° C. as the thermoplastic 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 "Gosephamer") were mixed at a ratio of 9:1 to 100 parts by mass of a PVA-based resin, 13 potassium iodide What was added by mass 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 dyeing process was subjected to the measurement of the crystallization index. The crystallization index of the PVA-based resin layer was 1.82.

Next, the layered product was immersed in a dyeing bath (aqueous iodine 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 the dyeing time shown in Table 1 (dyeing step ). Table 1 shows the concentration of boric acid in the dyeing bath (dyeing solution).

In addition, the PVA-type resin layer contained in the laminate was subjected to measurement of the above-mentioned boric acid content ratio in each of after the auxiliary stretching step and before the dyeing step, and after the dyeing step and before the crosslinking step.

Next, the laminate 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 having a liquid temperature of 70 ° C. (boric acid aqueous solution obtained by blending 5 parts by mass of potassium iodide and blending 4 parts by mass of boric acid with respect to 100 parts by mass of water), while circumferential speeds are different Uniaxial stretching was performed between rolls so that the total draw ratio in the machine direction (longitudinal direction) was 5.5 times (stretching step).

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. A polarizer included in the polarizing plate was used for the measurement of the single transmittance described above. The results are shown in Table 1.

<<Example 13>>

Except having adjusted the ratio of water so that single transmittance might be 44%, it carried out similarly to Example 1, and obtained the polarizing plate which has a structure of a polarizer/resin base material.

<<Example 14>>

As the raw film, a polyvinyl alcohol-based film (PVA-based resin film) having a thickness of 30 µm was used. Each of the following steps was performed on the PVA-based resin film in the following order.

(Dyeing step) As the treatment solution for the dyeing bath, an iodine dyeing solution having a concentration of 0.3% by mass of iodine:potassium iodide (mass ratio = 0.5:8) was used. The PVA-based resin film was conveyed to a dyeing bath and dyed while uniaxially stretching to a draw ratio of 2.4 times the original length while being immersed in an iodine dyeing solution adjusted to 30°C for 60 seconds.

In addition, the PVA-based resin film was used for measurement of the above-mentioned boric acid content ratio in each of before the dyeing step and after the dyeing step and before the crosslinking step.

(Crosslinking step) As the treatment liquid for the crosslinking bath, a boric acid aqueous solution containing 5% by mass of boric acid and 3% by mass of potassium iodide was used. The dyed PVA-based resin film was transported to a crosslinking bath and immersed in a boric acid aqueous solution adjusted to 40° C. for 45 seconds, and crosslinked with boric acid while uniaxially stretching to a total draw ratio of 3.3 times the original length.

(Stretching process) As the treatment liquid of the stretching bath, a boric acid aqueous solution containing 4% by mass of boric acid and 5% by mass of potassium iodide was used. The crosslinked PVA-based resin film was transferred to a stretching bath and uniaxially stretched to a total draw ratio of 6 times the original length while being immersed in an aqueous solution of boric acid adjusted to 60°C for 30 seconds.

(Hue adjustment step) As the treatment liquid for the hue adjustment bath, an aqueous solution containing 3% by mass of potassium iodide was used. The stretched PVA-based resin film was conveyed to a color adjusting bath and immersed in the aqueous solution adjusted to 27°C for 10 seconds.

(Drying shrinkage step) Subsequently, the PVA-based resin film subjected to the color adjustment treatment was dried in an oven at 60°C for 4 minutes to obtain a polarizer.

In this way, a polarizer made of a PVA-based resin film was obtained. The polarizer was used for the measurement of the single transmittance described above. In addition, staining unevenness (striped unevenness) of the polarizer was evaluated as described above.

<<Comparative Example 1>>

After the auxiliary stretching but before the dyeing step, 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 60 seconds (that is, the insolubilization step was performed) Except for that, it carried out similarly to Example 1, and obtained the polarizing plate which has the structure of a polarizer/resin base material. In addition, the content rate of boric acid in the PVA system resin layer before a dyeing process was measured after the insolubilization process and before a dyeing process.

<<Comparative Example 2>>

After auxiliary stretching and before the dyeing step, 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 (that is, the insolubilization step was performed) Except for that, it carried out similarly to Example 7, and obtained the polarizing plate which has a structure of a polarizer/resin base material. In addition, the content rate of boric acid in the PVA system resin layer before a dyeing process was measured after the insolubilization process and before a dyeing process.

<<Comparative Example 3>>

After the auxiliary stretching but before the dyeing step, 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 60 seconds (that is, the insolubilization step was performed) Except for that, it carried out similarly to Example 13, and obtained the polarizing plate which has a structure of a polarizer/resin base material. In addition, the content rate of boric acid in the PVA system resin layer before a dyeing process was measured after the insolubilization process and before a dyeing process.

<<Comparative Example 4>>

After auxiliary stretching and before the dyeing step, 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 (that is, the insolubilization step was performed) A polarizing plate having a structure of a polarizer/resin substrate was obtained in the same manner as in Example 7, except that the ratio of the water in the dyeing bath was adjusted so that the thing and the single transmittance were 44%. In addition, the content rate of boric acid in the PVA system resin layer before a dyeing process was measured after the insolubilization process and before a dyeing process.

[Table 1]

[evaluation]

As is clear from Table 1, if the absolute value of the difference between the content of boric acid in the PVA-based resin film before the dyeing step and the content of boric acid in the PVA-based resin film after the dyeing step and before the crosslinking step is 5.0% by mass or less, uneven dyeing occurs. Manufacture of suppressed polarizers can be realized.

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

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

Claims (7)

A dyeing step of dyeing a polyvinyl alcohol-based resin film with a dichroic material;
A crosslinking step of contacting the polyvinyl alcohol-based resin film after the dyeing step with an aqueous solution of boric acid;
A stretching step of stretching the polyvinyl alcohol-based resin film after the crosslinking step in a stretching bath,
Polarizer whose absolute value of the difference between the content of boric acid in the polyvinyl alcohol-based resin film before the dyeing step and the content of boric acid in the polyvinyl alcohol-based resin film after the dyeing step and before the crosslinking step is 5.0% by mass or less manufacturing method. According to claim 1,
The manufacturing method of the polarizer which manufactures the polarizer whose single transmittance is 42 % or more and 45 % or less. According to claim 1,
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 crosslinking step;
The stretching step;
Dry shrinkage step of shrinking the polyvinyl alcohol-based resin layer after the stretching step in the width direction orthogonal to the elongate direction while conveying it in the elongate direction
A method for manufacturing a polarizer including in this order. According to claim 3,
The thermoplastic resin substrate is a polyethylene terephthalate film, a method for producing a polarizer. According to claim 3,
A method for producing a polarizer having a thickness of 12 µm or less. According to claim 1,
The manufacturing method of the light polarizer whose said stretching bath is a boric acid aqueous solution. The manufacturing method of the polarizing plate which includes bonding a protective film to the light polarizer manufactured by the manufacturing method of the light polarizer in any one of Claims 1-6.

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